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Biodiesel production under ultrasound and homogeneous catalysts
Thèse
Kiran Shinde
Doctorat en génie chimique
Philosophiae Doctor (Ph.D.)
Québec, Canada
© Kiran Shinde, 2017
ii
Résumé
Le biodiesel est obtenu par une réaction de transestérification de triglycérides d’huiles
végétales ou des graisses par un monoalcool comme le méthanol. Cette réaction est aussi connue
sous la désignation d’alcoholyse. La technique de production de biodiesel sous ultrasons est une
nouvelle technologie prometteuse pour cette alternative aux combustibles fossiles. La production
de biodiesel sous ultrasons est basée sur l’utilisation de sondes ultrasoniques. En utilisant cette
technique, le biodiesel peut être produit à grande échelle. Des techniques d’ultrasonification
continue peuvent causer une forte émulsion des phases de l’alcool et d’huile rapidement. Pour un
temps de résidence faible, de fortes conversions sont obtenues en présence de différents
catalyseurs homogènes. Par conséquent, il est nécessaire de régler les défis restants de la
production de biodiesel, en termes de conception de réacteur, de récupération des catalyseurs, de
coûts et d’enjeux environnementaux, pour que cette méthode de production de biodiesel
devienne une technologie industrielle viable.
Les technologies de production de biodiesel étudiées précédemment comportent encore
certains défis comme : le problème de récupération du méthanol, la séparation des catalyseurs, le
temps de réaction, la température de réaction et les impuretés dans les produits. Donc, il y a
toujours un besoin continu pour le développement et la modification des technologies de
production du biodiesel.
Ce travail abordera le sujet du développement de la production de biodiesel sous
ultrasons. L’aspect original des conclusions du travail est la vision par laquelle les ondes
ultrasonores affectent la vitesse des réactions de transestérification. Les ultrasons génèrent de
fines émulsions du système biphasique dans tout le volume du réacteur. Ceci va évidemment
affecter le transfert de masse interphase. Le volume catalytiquement actif est toutefois restreint a
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une petite zone de réaction située à proximité de la sonde sonotrode. Dans cette fraction du
volume, une vitesse de réaction extrêmement élevée est fort probablement associée à des effets
de cavitation.
Pour augmenter la production de biodiesel par l’éthanol sous ultrasons, nous
avons testé les effets possibles d’une addition de méthanol ou d’autres composantes à basse
tension de vapeur sur le phénomène accélérant dans les réactions de transestérification des
triglycérides, du aux ultrasons.
Dans la dernière partie de ce travail, nous avons étudié la réaction de transestérification
de l’huile de canola avec du méthanol sur différents types de catalyseurs utilisant à la fois une
agitation mécanique et les ultrasons. L’efficacité du transfert de masse dans le champ ultrasonore
a amélioré la conversion maximale de transestérification comparativement aux conditions
d’agitation mécanique. Dans le cas du propyl-2, 3 dicyclohexylguanidine et 1, 3- dicyclohexyl 2
n-octylguanidine (DCOG) utilisés comme catalyseurs sous ultrasons, les réactions de
transestérification que nous avons obtenues ont causé une augmentation notable de la vitesse de
conversion des triglycérides. Dams ce cas plus de 80% de récupération de la guanidine dans le
mélange réactionnel a été possible en utilisant une colonne d’échange cationique à base de silice.
Mots clés: ultrason, transestérification, huile de canola, FAME, méthoxyde de sodium,
hydroxyde de sodium, l'hydroxyde de potassium, tétraméthyle d’hydroxyde d’ammonium,
Guanidine, colonnes d'échange de cation de silice.
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Abstract
Biodiesel is obtained by transesterification reaction of triglycerides from vegetable oils or
fats and a mono alcohol like methanol. This reaction is also known as alcoholysis. Ultrasound
biodiesel production technique has recently emerged as a promising technology for synthesis of
this alternative for fossil fuels. Ultrasound biodiesel production is based on the use of ultrasonic
probes. By using this technique biodiesel production can be made on a large scale. Continuous
ultrasonication technique can induce strong emulsion of alcohol and oil phases in a short time.
Within very small residence time, high conversions are obtained in presence of different
homogeneous catalysts. Therefore, it is necessary to solve the remaining challenges of biodiesel
production, in terms of reactor design, catalyst recovery, cost and environment issues, in order to
address the biodiesel production as a viable industrial technology.
The previously studied biodiesel production technologies still show some challenges such
as: methanol recovery issue, catalyst separation, reaction time, reaction temperature and oxide
impurities in products. Therefore, there is still need to develop and modify the continuous
biodiesel production technology.
This work deals with the development of ultrasound biodiesel production. The original
aspect of the present work conclusions is a vision of how ultrasound waves affect the
transesterification reactions rates. Ultrasounds generate a fine emulsion of the biphasic system in
the entire reactor volume. This will obviously affect interphase mass transfer. The catalytically
active volume is however restricted to a small part of the reaction medium located in the
immediate vicinity of the sonotrode probe. Within this volume fraction the extremely high
reaction rate is very likely associated with the effects of cavitation.
v
To increase the biodiesel production in presence of ethanol under ultrasound we tested
the possible effects of minor methanol or other low vapor tension component additions on the
accelerating phenomenon in triglycerides transesterification reactions due to ultrasounds.
In the last part of the work we studied the transesterification reaction of canola oil with
methanol and different types of catalysts using both mechanical stirring and ultrasonication
reaction. The efficiency of mass transfer in the ultrasound field enhanced the higher rate of
transesterification reaction as compared to stirring conditions. In case of propyl-2, 3
dicyclohexylguanidine and 1, 3- dicyclohexyl 2 n-octylguanidine (DCOG) as catalysts under
ultrasound transesterification reaction we got noticeable TG conversion where as more than 80%
regeneration of guanidine is possible from the reaction mixture by using silica cation exchanger
columns.
Keywords: ultrasound, transesterification, canola oil, FAME, sodium methoxide, sodium
hydroxide, potassium hydroxide, Tetramethyl ammonium hydroxide, Guanidine, silica cation
exchanger columns.
vi
Table of contents
Résumé……………………………………………………………………………………...ii
Abstract……………………………………………………………………………………..iv
List of tables…………………………………………………………………………………x
List of figures……………………………………………………………………………….xi
Ackowledgements………………………………………………………………………….xv
Foreward………………………………………………………………………………….xvii
Chapter 1 Introduction ............................................................................................................ 1
1.1 Biodiesel ........................................................................................................ 2
1.2 Historical developments of biodiesel production .......................................... 5
1.3 Transesterification reaction ........................................................................... 6
1.4 Alcohols and catalysts commonly used in biodiesel production................... 7
1.5 Main feed stocks for biodiesel fuel ............................................................... 9
1.6 New technologies for biodiesel production ................................................. 14
1.7 International biodiesel regulations .............................................................. 16
1.8 Annual biodiesel production worldwide ..................................................... 20
1.9 Thesis structure ........................................................................................... 24
1.10 References ............................................................................................... 25
Chapter 2. .............................................................................................................................. 32
2.1 Biodiesel production under ultrasound ....................................................... 33
2.1.1 Homogeneous base catalyzed transesterification .................................. 38
2.1.2 Homogeneous acid catalyzed transesterification .................................. 41
2.2 Engineering of ultrasound reactors ............................................................. 45
2.2.1 Ultrasonication ...................................................................................... 45
vii
2.2.2 Cavitation .............................................................................................. 48
2.2.3 Acoustic streaming ................................................................................ 49
2.2.4 Tooling design ....................................................................................... 50
2.2.5 Transesterification reaction using ultrasounds ...................................... 53
2.2.6 Objectives .............................................................................................. 58
2.3 References ................................................................................................... 59
Chapter 3. .............................................................................................................................. 69
3.1 Introduction ................................................................................................. 72
3.2 Experimental ............................................................................................... 75
3.2.1 Materials ................................................................................................ 75
3.2.2 Catalyst preparation............................................................................... 75
3.2.3 Apparatus .............................................................................................. 76
3.2.4 Transesterification reaction tests ........................................................... 76
3.2.5 UHPLC analysis .................................................................................... 77
3.3 Results and discussion ................................................................................. 78
3.4 Conclusions ................................................................................................. 88
3.5 References ................................................................................................... 89
Chapter 4. .............................................................................................................................. 96
4.1 Introduction ................................................................................................. 99
4.2 Results ....................................................................................................... 100
4.2.1 Glycerolysis ......................................................................................... 100
4.2.2 FAME transesterification by glycerol ................................................. 101
4.2.3 FAME transesterification by ethanol .................................................. 102
4.2.4 FAME transesterification by butanol .................................................. 103
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4.3 Discussion and conclusion ........................................................................ 104
4.4 Supporting Information ............................................................................. 105
4.5 References ................................................................................................. 107
Chapter 5. ............................................................................................................................ 109
5.1 Introduction ............................................................................................... 112
5.2 Experimental ............................................................................................. 115
5.2.1 Materials .............................................................................................. 115
5.2.2 Catalyst preparation............................................................................. 116
5.2.3 Ultrasonic Irradiation Unit .................................................................. 116
5.2.4 Transesterification reaction ................................................................. 117
5.2.5 Methyl ester analysis ........................................................................... 118
5.3 Result and discussion ................................................................................ 118
5.3.1 Experimental data of biodiesel production.......................................... 118
5.3.2 Catalyst concentration and the effect of methanol to oil ratio ............ 119
5.3.3 Comparison between ultrasound and mechanical stirring in presence of
CH3ONa catalyst. ........................................................................................................ 120
5.3.4 Comparison between ultrasound and mechanical stirring in presence of KOH
catalyst…………………….. ...................................................................................... 122
5.3.5 Comparison between ultrasound and mechanical stirring in presence of
NaOH catalyst. ............................................................................................................ 124
5.3.6 Comparison between ultrasound and mechanical stirring in presence of
Tetramethyl ammonium hydroxide catalyst. .............................................................. 125
5.3.7 Comparison between ultrasound and mechanical stirring in presence of
catalyst Guanidines. .................................................................................................... 127
5.3.8 Guanidine separation by using strong cation exchanger. .................... 130
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5.4 Conclusions ............................................................................................... 135
5.5 References ................................................................................................. 136
Chapter 6. Conclusion and future work .............................................................................. 140
6.1 Conclusions ............................................................................................... 141
6.2 Future research .......................................................................................... 143
Chapter 7. Scientific Contributions..................................................................................... 144
x
List of tables
Table 1-1. Average density and heating value of diesel, biodiesel and blends………………....3
Table 1-2. Properties of B100 biodiesel and diesel……………………………………………...4
Table 1-3. Fatty acid composition of oils……………………………………………………….11
Table 1-4. World biodiesel projections in average for the period from 2013-2025………….…22
Table 2-1. A comparison among the various techniques used in the biodiesel production.
…………………………………………………………………………………………………...37
Table 2-2. Biodiesel production from various feedstocks under different conditions using
ultrasound irradiation…………………………………………………………………………….56
Table 5-1. Sequence of operations in the catch and release technique………….…………….135
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List of figures
Figure 1-1. Transesterification reaction…………………………………………………………..7
Figure 1-2. World biodiesel production and trade……………………………………………....23
Figure 1-3. (a)-(b) Regional distributions of world biodiesel production and use in 2025……..23
Figure 2-1. Classification of biodiesel production techniques…………………………..............35
Figure 2-2. Growth and collapse of cavitation bubble in a liquid medium when ultrasonic waves
are applied………………………………………………………………………………………..46
Figure 2-3. Streaming observed in a liquid after ultrasonication……………………………….49
Figure 2-4. Ultrasonic probe…………………………………………………………………….50
Figure 2-5. Different shapes of Converter………………………………………………............51
Figure 2-6. Titanium Ultrasonic Booster………………………………………………………..52
Figure 2-7. Different types of Ultrasonic Horn…………………………………………………52
Figure 3-1. Reaction setup……………………………………………………………………....77
Figure 3-2. UHPLC Chromatograms for A = Canola oil, B = Non-polar phase at 60 % TG
conversion, C= Non-polar phase at 100% TG conversion………………………………………80
Figure 3-3. Effect of reaction time on methyl ester production with 0.5 wt % catalyst (CH3ONa)
Methanol/Oil ratio 4:1, ultrasound amplitude 60%. Temperature 35°C………………………...80
Figure 3-4. Effect of catalyst concentration on methyl ester production. Catalyst (CH3ONa)
methanol/oil ratio 4:1, ultrasound amplitude 60 %, Residence time 20 s. Temperature 35
°C………………………………………………………………………………………………...81
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Figure 3-5. Mole fraction of TG, FAME, DG and MG, Reaction conditions 4:1 CH3ONa:Canola
oil, Amplitude 60 %, Residence time 20 s. CH3ONa 0.5 wt% with canola oil. Temperature 35
°C………………………………………………………………………………………………...82
Figure 3-6. Steady state mole fraction of TG, FAME, DG and MG with different wt % of
catalyst, Reaction conditions 4:1 CH3ONa:Canola oil, Amplitude 60%, Residence time 20 s,
CH3ONa 0.5 wt % with canola oil. Temperature 35°C………………………………………….83
Figure 3-7. Temperature and power change during reaction……………………………............83
Figure 3-8. Effect of amplitude on methyl ester production with 0.5 wt % catalyst (CH3ONa)
methanol/Oil ratio 4:1, residence time 20 second. Temperature 35°C…………………………..84
Figure 3-9. Effect of temperature on TG conversion: a= 35°C, b= 45°C, C=55°C. 0.5 wt %
catalyst (CH3ONa) Methanol/Oil ratio 4:1, ultrasound amplitude 60%........................................85
Figure 3-10. Effect of mole ratio on continuous methyl ester production with 0.5 wt % catalyst
(CH3ONa), ultrasound amplitude 60%, residence time 20 s. Temperature 35°C………………..85
Figure 4-1. Glycerolysis of Canola oil at 140 °C A-Stirring without US; B-US without solvent
addition; C-US with dropwise addition of THF; D- US with 0.33 wt % octane; E- US with 0.33
wt % nonane (with respect to oil)………………………………………………………………101
Figure 4-2. FAME conversion by reaction with glycerol at 140 °C A-US and F:G*= 1:1; B-US
and F:G=1:2; C- stirring no US, F:G=1:1; D- stirring no US, F:G=1:2; E- US with 0.33 wt %
octane; F:G=1:1, F- US with 0.33 wt % octane F:G=1:2. F:G*=FAME to glycerol molar
ratio……………………………………………………………………………………………..102
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Figure 4-3. Transesterification of triglycerides by ethanol. Catalyst KOH 0.5 wt %; ethanol/oil
molar ratio 4:1; residence time 75 s; Temperature 35°C; ultrasound amplitude
60%..............................................................................................................................................103
Figure 4-4. Transesterification of triglycerides by butanol. Catalyst KOH 0.5 wt %; butanol/oil
molar ratio 4:1; residence time 75 s; Temperature 35 ºC; ultrasound amplitude
60%..............................................................................................................................................104
Figure 5-1. Effect of catalyst concentration on triglyceride conversion. Catalyst (CH3ONa),
methanol:oil ratio ( 6:1, 4:1, 3:1 ) ultrasound amplitude 60%, temperature 35 ºC…………….121
Figure 5-2. Ultrasound biodiesel production batch reaction, catalyst (CH3ONa), methanol:oil
ratio ( 6:1, 4:1, 3:1 ) ultrasound amplitude 60%, 0.5 wt %, temperature 35
ºC……………………………………………………………………………………………….122
Figure 5-3. Mechanical stirring biodiesel production batch reaction, catalyst (CH3ONa),
methanol:oil ratio ( 6:1, 4:1, 3:1 ) 0.5 wt %, temperature 65 ºC……………………………….123
Figure 5-4. Ultrasound biodiesel production batch reaction, catalyst (KOH), methanol:oil ratio (
6:1, 4:1, 3:1 ) ultrasound amplitude 60%, 0.5 wt %, temperature 35 ºC………………………124
Figure 5-5. Mechanical stirring biodiesel production batch reaction, catalyst (KOH),
methanol:oil ratio ( 6:1, 4:1, 3:1) 0.5 wt %, temperature 65 ºC………………………………..124
Figure 5-6. Ultrasound biodiesel production batch reaction, catalyst (NaOH), methanol:oil ratio (
6:1, 4:1, 3:1 ) ultrasound amplitude 60%, 0.5 wt %, temperature 35 ºC………………………125
Figure 5-7. Mechanical stirring biodiesel production batch reaction, catalyst (NaOH),
methanol:oil ratio ( 6:1, 4:1, 3:1 ) 0.5 wt %, temperature 65 ºC……………………………..…126
xiv
Figure 5-8. Ultrasound biodiesel production batch reaction, catalyst (Tetramethyl ammonium
hydroxide) 3 wt %, methanol:oil ratio ( 6:1, 4:1) ultrasound amplitude 60%, temperature 35
ºC……………………………………………………………………………………………….127
Figure 5-9. Stirring biodiesel production batch reaction, catalyst (Tetramethyl ammonium
hydroxide) 3 wt %, methanol:oil ratio ( 6:1, 4:1), temperature 35 ºC…………………………127
Figure 5-10. Ultrasound biodiesel production batch reaction, catalyst (Guanidine A) 3 % mol,
4:1 and 3:1 (Methanol: Canola oil) 3 % catalyst 60% amplitude, 35 ºC………………………128
Figure 5-11. Ultrasound batch reaction 4:1 (Methanol : Canola oil ), Catalyst (Guanidine A) 3
and 5 % mol, 60% amplitude, temperature 35 ºC……………………………………………...129
Figure 5-12. Ultrasound batch reaction 4:1 (Methanol : Canola oil ) 3 % mol catalyst,
60% amplitude, temperature 35 ºC……………………………………………………………..130
Figure 5-13. Mechanical stirring batch reaction 4:1 (Methanol : Canola oil ) 3 % mol catalyst,
temperature 65 ºC………………………………………………………………………………130
Figure.5-14. Guanidine catch and release technique…………………………………………..134
xv
ACKNOWLEDGEMENTS
I want to begin by thanking my advisor (Guru), Professor Serge Kaliaguine. Without his
inputs, it wouldn’t have been possible to accomplish my doctoral degree. Every scientific
discussion with him enhanced my knowledge in the field of research and helped me to think and
act independently. I really value his guidance and support, and the independence that he gives us
in lab to explore our research interests. My time in his lab has been very educational and
enjoyable. I also deeply appreciate that he has been very supportive of my career goals and
choices, and has really done a lot to help me reach them. I have learnt lots of valuable spiritual
wealth, which is definitely priceless. I would also like to acknowledge my Co-supervisor:
François Béland for his motivation and for allowing me to use his Silicycle lab facilities. I would
be especially grateful to Madam Guoying Xu for the kindness and support since the first day.
Additionally, I want to acknowledge my doctoral general examination committee
members Prof. Frej Mighri, Prof. Trong-On Do, Dr. Bendaoud Nohair for their thoughtful
comments and suggestions. I want to thank chemical engineering program director Prof. Alain
Garnier for his valuable guidance. I am very thankful for all of their support over the years.
The Kaliaguine’s group has been a great group to work with, and I especially want to
thank our wonderful research assistants Dr. Bendaoud Nohair and Mr. Gilles Lemay for their
help in my experiments. Special thanks to my lab members Luc Charbonneau, Lin Chen, Zheng
Fang, Arsia Afshar Taromi, Thanh Binh Nguyen, Tien Binh Nguyen, Valerica Pandarus, Neyra
Mighri, Chi Cong Tran, Rouholamin Biriaei, Xavier Foster and Sara Madadi. I also wish to
thank my past lab members Dr. Vinh Thang Hoang, Dr. Zhen Kun Sun and Dr. Foroughazam
Afsahi.
xvi
I am also greatly indebted to many teachers in the past: Dr. B. D. Kulkarni, Dr. S.
Mayadevi, Dr. Venkat Panchagnula, Dr. A.G. Gaikwad and Dr. P.P. Wadgaonkar, at National
Chemical Laboratory, Pune, India, for the motivation and for getting me interested in research
and coming to Canada. Thanks to working group Dr. B. D Kulkarni and CEPD for making my stay
comfortable at NCL.
My sincere thanks and best wishes were also extended to my close Indian friends Dr.
Aniruddha Joshi, Dr. Tushar Borase and Dr. Sagar Mohan for their friendship, encouragement,
and support.
Finally, I want to thank my family for supporting me and being in my life. I always know
how important you are in my life. Thanks for making me feel loved and always being supportive
of me.
Dedicated to my Family.
I love you!
xvii
Forweword
This dissertation is composed of seven chapters. The first chapter is an introduction of the
field of biodiesel production. It contains sections on Biodiesel, Historical developments of
biodiesel, Transesterification reaction, Catalysts and Alcohols commonly used in biodiesel
production, Oilseed crops as raw materials, International biodiesel regulations, Annual biodiesel
production worldwide and New technologies for biodiesel production. The second chapter
introduces the biodiesel production under ultrasounds using homogeneous alkali catalyzed and
homogeneous acid catalyzed transesterification. In this chapter, Engineering of ultrasound
reactors, Ultrasonication, Cavitation, Acoustic streaming and tooling design are also discussed.
This second chapter constitutes a complete review of different ultrasound technologies for
biodiesel production.
Chapters three, four and five report the results of this dissertation in the form of three
scientific articles, two of which are already published whereas the third one is not yet submitted.
The list of articles relevant to each chapter is as follows. The first author for the three articles is
the author of this Ph D thesis.
Chapter 3
A Parametric Study of Biodiesel Production Under Ultrasounds
xviii
Published in Int. J. Chem. React. Eng., 15(1), 117–125, 2017.
Kiran Shinde, Bendaoud Nohair and Serge Kaliaguine
Department of Chemical Engineering Laval University, Quebec, G1 V 0 A6, Canada
In this chapter we showed a systematic experimental analysis of ultrasound assisted
continuous biodiesel production using canola oil in the presence of methanol and sodium
methoxide as catalysts. The effects of various reaction parameters such as residence time,
catalyst concentration, reaction temperature, ultrasounds amplitude and power, methanol/oil
molar ratio were established by the first author of the paper who is the principal author of the
paper.
Chapter 4
Triglycerides Transesterification Reactions under Ultrasounds
Published in ChemistrySelect, 1(18), 6008-6010, 2016.
Kiran Shinde and Serge Kaliaguine
Department of Chemical Engineering Laval University, Quebec, G1 V 0 A6, Canada
xix
In this chapter, we studied possible effects of minor methanol or other low vapor tension
component additions on the accelerating phenomenon in triglycerides transesterification
reactions with alcohols due to ultrasounds. The most important effect of ultrasound on the rate of
triglyceride transesterification is due to cavitation and the mass transfer enhancement in this
biphasic reaction due to high dispersion of the polar phase.
Chapter 5
Ultrasound biodiesel production using various homogeneous catalysts and their separation over
silica cation exchanger columns
Kiran Shinde1, François Béland2 and Serge Kaliaguine1
1Department of Chemical Engineering Laval University, Quebec, G1 V 0 A6, Canada
2SiliCycle Inc., 2500, Boul. du Parc-Technologique, Québec City, Québec G1P 4S6, Canada
In this chapter, NaOH, KOH, CH3ONa, tetramethyl ammonium hydroxide and two
guanidines are tested for transesterification reaction in a batch reactor both under ultrasound and
mechanical stirring. The synthesis of different guanidines and separation of guanidines from
reaction medium using silica cation exchanger columns are described. This manuscript will soon
be submitted for publication. The first author of the paper and principal investigator is the author
of this thesis.
Chapter 6, gives the general conclusions and some recommendations for future work.
Finally, in chapter 7, the scientific contributions complete the dissertation
Chapter 1. Introduction
2
1.1 Biodiesel
Biodiesel is a term designating fatty acid alkyl esters produced as a result of
transesterification reaction between triglycerides and any alkyl alcohol. It is widely recognized in
the alternative fuels industry as well as by the Department of Energy (DOE), the American
Society of Testing and Materials (ASTM) and the Environmental Protection Agency (EPA).
Biodiesel can be produced from virgin oil feedstock (such as rapeseed or soyabean), animal
oil/fats, tallow and waste cooking oil. The National Soy Diesel Development Board (presently
National Bio-diesel Board) is pioneer in the commercialization of bio-diesel in the USA since
1992 [1]. Biodiesel has properties similar to diesel fuel, but has many following advantages over
diesel fuel.
1) High oxygen content: The high oxygen content in biodiesel facilitates its complete
combustion that leads to the complete utilization of the fuel without producing any harmful by-
products.
2) Reduction of particulate matter emissions: Particulate matter is a mixture of complex
organic and inorganic compounds, such as carbon residues, lubricating oil components etc. The
suspension of these particulate matters in the environment leads to many adverse effects such as
pollution, intoxication of air, climate imbalance etc.
3) Reduction of carbon dioxide emissions: It is known that the carbon dioxide is a
greenhouse gas and a major contributor of global warming. The use of biodiesel significantly
reduces the carbon dioxide atmospheric balance since the carbon in vegetable materials is
borrowed from the atmosphere.
3
4) Reduction of carbon monoxide emissions: carbon monoxide causes serious health
hazards by blocking oxygen intake in humans and animals. It is reported that the use of 100%
biodiesel [B100] reduces carbon monoxide emissions by 35%.
5) Reduction of sulfur oxides emissions: Sulfur based compounds are also identified to be
among the potential harms for the environment. For example, the sulfur dioxide causes
respiratory tract irritation in humans. Biodiesel is generally sulfur-free, as long as sulfuric acid is
not used in the biodiesel production process.
6) High flash point: Flash point is the temperature at which a fuel becomes flammable.
As the biodiesel has higher flash point than diesel, it sufficiently avoids any sort of fire accidents.
The following table (Table 1-1) gives average heating and density values of
biodiesel in comparison with diesel.
Table 1-1. Average density and heating value of diesel, biodiesel and blends [2].
Fuel Net heating value Avg. (MJ/L) Density (g/cm3)
Diesel 36.09 0.85
Biodiesel (B 100) 32.97 0.88
B 20 Blend 35.04 0.85
B 2 Blend 36.03 0.85
4
Table 1-2 Comparison of the properties of biodiesel and diesel [3].
Fuel property Biodiesel (B 100) Diesel
Lower heating value Btu/gal 118,170 129,050
Fuel standard ASTM D6751 ASTM D975
Specific gravity kg/L@150C 0.88 0.85
Kinematic viscosity cSt@600C 4-6 1.3-4.1
Density Ib/gal @ 150C 7.32 7.07
Carbon, wt. % 77 87
Hydrogen, wt. % 12 13
Water and sediment, vol. % 0.05 max 0.05 max
Sulfur, wt. % 0.0 to 0.0024 15-50 ppm
Flash point, 0C 100 to 170 60 to 80
Boiling point, 0C 315 to 350 180 to 340
Pour point 0C -15 to 10 - 35 to -15
Cloud point, 0C -3 to 12 -15 to 5
Oxygen, by dif. wt.% 11 0
5
1.2 Historical developments of biodiesel production
In the historical development of biodiesel productions, the vegetable oils have been used
as fuel more than one hundred years ago as per the report by Knothe [4,5]. It is a noteworthy
historical event that Rudolf Diesel conducted engine tests using peanut oil at the Paris show 1900
under the French government. However, the interest in vegetable oils-based biodiesel production
diminished as the fossil fuels soon became available in much higher quantity and lower cost as
compared to the biodiesel productions. It was established that the high fuel viscosity in
compression ignition is one of the major problems associated in use of vegetable oils as a fuel. It
should be noted that the viscosity of vegetable oil is around 10-20 times higher than that of diesel
[6,7]. Therefore, the use of such oil directly in engines is limited because of high viscosity and
low volatility.
Alternatively, it was proposed to use the mixture of fossil fuel and vegetable oil as fuels.
However, it was found, according to the high end point of the distillation curve, coupled with
poor fuel atomization that this mixed use of fuels led to incomplete evaporation and mixing
processes and poor combustion (formation of small particles and carbonaceous deposits) [8,9].
Therefore, long-term operation on mixture of vegetable oil and fossil fuel resulted in engine
damage [10]. As a result the alternative approach proposed to overcome this problem was
preheating the oil [11] and using oil mixed in very low proportions with fossil fuel [12].
Since the use of mixtures of fossil fuel and vegetable oil in modern engines can present
similar difficulties as reported above, the “transformation” of the oil directly into fuels, is
recommended as the products are expected to exhibit properties similar to fossil fuels.
One of the major drawbacks of vegetable oils is their high viscosity. In order to
reduce/control the viscosity, there are four major techniques such as microemulsion, dilution,
6
pyrolysis and transesterification as well as direct dose of the oil, which were employed
essentially to reduce the viscosity of these vegetable oils.
It is found that microemulsions with different alcohols overcome the problem of high
viscosity of vegetable oils. Similarly, pyrolysis, which is defined as the cleavage to smaller
molecules by thermal energy, of vegetable oils over catalysts has been investigated [7,13]. The
transesterification process has also been shown to reduce the viscosity of triglycerides [14].
Biodiesel has been prepared as the mixture of monoalkyl esters of fatty acids derived
from vegetable oil or animal fat [8]. Therefore, biodiesel is biodegradable, lacks toxic aromatics,
lowers automobile emissions and is carbon neutral. Compared to fossil fuel, biodiesel produces
around 75-90% less particulate matters [15], unburned hydrocarbons, CO and sulphates.
Monoalkyl esters of fatty acids appeared as a fuel in Belgium in 1937 [16]. After the Belgium
patent two more patents are recorded in 1980 one from Germany and a second one from Brazil.
Today, biodiesel production is commercialized in many countries such as Austria, Italy,
Argentina, Spain, USA, Brazil, Indonesia, Germany and France [8]. Currently, there are number
of large scale biodiesel production plants under operation and they produce more than 5000
million gallons of biodiesel per year worldwide. Only in America, there are more than 90
biodiesel-production plants under operation [17].
1.3 Transesterification reaction
Transesterification reactions were first reported in 1852 [18] for high quality soap and
water free glycerol production. Transesterification is the process of modifying esters. There are
two transesterification biodiesel production methods: a) without catalyst b) with catalyst. In more
detail, one mole of triglyceride reacts with three moles of alcohols to form one mole of glycerol
7
and three moles of esters. This process includes three reversible reactions in which the
triglyceride molecule is converted step by step into diglycerides, monoglycerides and glycerol. In
every step, one mole of alcohol is consumed and one mole of ester is liberated. In order to shift
the equilibrium to the right, alcohol is added in excess in most of biodiesel production plants.
Fig.1-1. Transesterification reaction
1.4 Alcohols and catalysts commonly used in biodiesel production
The most commonly used primary alcohols in biodiesel production are methanol, ethanol,
straight chain high carbon alcohols, and other kinds of alcohols available to date [19]. Increasing
the length of alcohol chain can greatly increase the difficulty of separation after the reaction.
[20]. An important factor to choose the primary alcohol is the water content. Water interferes
with biodiesel production reactions when using alkaline catalysts which results in poor biodiesel
yield, with high level of soap, free fatty acid and triglycerides. Lower alcohols are hygroscopic
and may absorb water from the atmosphere. After transesterification, methanol is considerably
easier to recover than ethanol, as the latter forms an azeotrope with water so that it is expensive
to purify. If the water is not removed then it interferes with biodiesel production [8]. Methanol
can be recycled more easily because it does not form an azeotrope. For this reason, the use of
anhydrous alcohol is needed. Since chemical grade ethanol is typically denatured with poisonous
materials to prevent its intake, to find undenatured ethanol is difficult [19]. Nevertheless, ethanol
8
has a positive impact for biodiesel production as it can be considered as a more sustainable
reactant than methanol [19, 21]. Other advantage of methanolysis is that both products, FAME
and glycerol, are immiscible, thus producing separate phases. FAME yields can be increased by
minimizing the excess methanol and carrying out the reaction in two or three steps [19, 22].
In addition, the ultrasound-assisted biodiesel production exhibits a certain relationship at
different chain lengths of alcohols [23-25]. Hanh et al. [26] reported the effect of different
alcohols. In this study they showed that the reaction rate was the fastest with methanol and
ethanol which gave good yields among the different kinds of alcohols. However, the straight
chain of high carbon alcohols, such as 1-octanol, 1-hexanol and 1 decanol showed relatively
slow reaction rate on yielding the biodiesel.
Transesterification reactions can occur in the absence of catalysts [8] however, it requires
high temperature, long reaction time and pressure. There are different types of catalyst reported,
such as homogeneous or heterogeneous (including enzymes). The most commonly used
homogeneous catalysts in biodiesel production are potassium hydroxide and sodium hydroxide
[19]. Alkaline catalysts are highly hygroscopic and form chemical water. That absorbed chemical
water affects biodiesel production yield. Alkaline catalysts give good results when raw material
with high quality (FFA<1 % w/w and less moisture) are used [27]. Acid catalysts were also
reported for biodiesel production, but they are very slow for industrial process and commonly
used for the esterification of free fatty acid, only in the case of high free fatty acid oils [19, 28].
Heterogeneous catalysis involves the use of insoluble compounds in either ethanol or methanol
that reduce the problems arising from employment of homogeneous catalysts, such as
contamination and washing steps. This leads to a decrease of both economic and environmental
costs [29]. Heterogeneous catalysts consist of a large number of compounds of different
9
chemical nature such as transition metal oxides, mesoporous silica, alkaline earth oxides, alkali
doped materials, acidic polymers, heteropolyacids, waste carbon-derived solid acids and
miscellaneous solid acid [30]. Commercially used enzymes in the biodiesel production are
Pseudomonas cepacia, Rhizomucor miehei, Candida Antarctica, Pseudomonas fluorescens [31].
1.5 Main feed stocks for biodiesel fuel
The main feedstocks for biodiesel production are listed below:
(i) Waste vegetable oil:
This includes the use of spent frying oil that considerably reduces the cost of biodiesel.
The waste vegetable oil from food industries is getting popular as a possible source of feedstock.
However, the presence of free fatty acids or water in waste oil to be used as feedstock results in
changes in the reaction procedure, which is a limitation in use of waste vegetable oils.
(ii) Non-Edible oils:
Non-edible oils such as those of Jatropha, Pongamia, Madhuca and Azhadirachta are
used to produce biodiesel. The fatty acids composition of the Jatropha oil is similar to other oils.
The presence of some toxic material in kernel renders the oil inedible. Jatropha is being actively
investigated as a promising source of feed stocks for biodiesel production in development in
developing countries of Asia.
(iii) Animal fats:
Waste animal fat is a cheap source of for biodiesel production and its utilization
also serves environmental benefits.
(iv) Virgin oil feedstock:
10
Sunflower, Canola, Palmoils and Soybean are the most commonly used virgin oil based
raw materials for biodiesel fuel. Their production quantity governs their selection for biodiesel
production. The other commonly used feedstock vegetable oils are castor, peanut, cottonseed,
rapeseed oils, due to their content of triglycerides.
(v) Algaes:
Algaes offer many advantages in the search for their sustainable, renewable
bioenergy feedstocks. They have been recognized as a potentially good source for biodiesel
production for a long period of time because of their high lipid content and rapid biomass
production.
Composition of different vegetable oils
Vegetable oils are extracted from different plants and their combustion yields completely
recycled carbon, since the plants assimilate atmospheric carbon dioxide.
The fatty acid compositions of different origins are reported in Table 1-3[32].
Table 1-3. Fatty acid composition of oils [32]
(a) Vegetable Origin
11
12
(b) Animal Origin
13
It should be noted that the biodiesel has higher cloud and pour points compared to diesel fuels so
it is not convenient to use in winter [33, 34]. The cetane number of vegetable oils is very high
hence reducing the ignition delay [35]. Vegetable oil has high iodine value and therefore
increased oxidation rate. Therefore the long time storage is not possible or recommended for
these kinds of fuels [36].
Natural fat oils are esters of glycerol and fatty acids. There are two types of fatty acids, saturated
fatty acid and unsaturated fatty acids. Saturated fatty acids contain single carbon-carbon bonds,
while the unsaturated fatty acids contain one or more double bonds. The common fatty acids are
stearic (18:0), linoleic (18:2), oleic (18:1) and palmitic (16:0).
The schemes below show the chemical structures of triglycerides, diglycerides and
monoglycerides.
a) Triglycerides
b) Diglycerides
14
c) Monoglycerides
The chemical structures of fatty acids are described below:
Palmitic acid/Hexadecanoic acid R-(CH2)14CH3
Stearic acid/Octadecanoic acid R-(CH2)16CH3
Oleic acid/9(Z)-octadecenoic acid R-(CH2)7CH=CH-(CH2)7CH3
Linoleic acid/9(Z), 12(Z) -octadecadienoic acid R- (CH2)7CH=CH-CH2-CH=CH-(CH2)4CH3
Linolenic acid/ R-(CH2)7-(CH=CH-CH2)3-CH3
1.6 New technologies for biodiesel production
Human beings have always been dependant on the use of energy in every sphere of life
such as industry, agriculture, transportation, food, etc. [37,38]. With the increase in population,
the requirement of energy has also increased. Especially, the fuels play major role in the above
said fields. Therefore, producing energy from biodiesel is the best way to meet out the energy
requirements without affecting the ecological balance of the environment. In this context, there is
a rapid growing interest on the production of biodiesel. The growing biodiesel production has
made the scientific community and private sector to seek new efficient and economical
technology for the energy requirements. This is the reason why the biodiesel production has
15
undergone numerous technological developments. All of them are intended to make the reaction
rate faster by using lower quantity of raw materials and avoiding significant energy consumption.
In the context of biodiesel production, the vigorous mixing of the reactant is most important. For
instance, the conventional transesterification reaction requires a temperature of 40-65oC and
vigorous stirring of the reaction mixture as to establish a maximum contact between alcohol and
oil [39, 40]. Based on the above requirements, the new technologies in biodiesel production
involve the use of different kind of techniques in order to optimize different reaction parameters.
This kind of new technologies involves the use of auxiliary energy to mix the reactants by
replacing heating. In such strategies, the hydrodynamic cavitation, ultrasound, microwaves and
radio frequencies are employed [41-46]. Consequently, research and the use of these
technologies have been expanded significantly in the last couple of decades, which could be
evidenced by the number of papers published.
In order to improve the transesterification process, solvents are used to control the
physical properties especially the viscosity of the oil. These solvents include tetrahydrofuran,
hexane, diethyl ether, dibutyl ether, tert-butyl methyl ether, diisopropyl ether, etc [47-49]. It has
been shown that the use of solvents improves the process conversion. However, the use of new
substances can make the process even more complex and expensive. Another approach in the
transesterification process involves performing the reaction under supercritical and subcritical
conditions [50, 51]. In such cases, there are some advantages such as the enhancement of
reaction rate, enhanced yields and improved purity of the resulting products, etc. Nevertheless,
the production of biodiesel through supercritical and subcritical reactions has some
disadvantages such as high energy consumption and sophisticated equipment as high temperature
16
and pressure has to be developed in the system. These requirements are relatively not feasible for
the industrial scale applications [52-53].
1.7 International biodiesel regulations
The consistent global growth of biodiesel production required standardization in the
quality of biodiesel. It is known that the introduction of any new product for day-to-day
applications demands the recognition and surpassing of technical, economic, social and
legislative hurdles. It is vital to establish rules and standards in order to define the quality of the
product according to its usages in the everyday life. The postulation of quality rules must be the
outcome of the sharing of information, discussion and accordance among the people involved in
the production and distribution. Accordingly, the standards of biodiesel are of importance for
their producers, suppliers and consumers. Therefore, the authorities should require the approved
standards for the assessment of safety risks and other issues such as environmental pollution.
Similarly, standards are also necessary for the vehicles that are operated using biodiesel and
therefore, they are becoming the essential prerequisites for the introduction and
commercialization of biodiesel in the market. The quality of biodiesel requires the inclusion of
its physical and chemical properties into the requirements of the adequate standard for the
utilization of biodiesel. Accordingly the quality standards of biodiesel are also continuously
updated because of the evolution of the factors such as compression ignition engines, ever
stricter emission standards, re-evaluation of the eligibility of feed-stocks used for biodiesel
production, etc. The specifications of biodiesel technology are having a direct control over the
selection of raw materials and production strategies. Regulation of the biodiesel standards started
in the 1990s, as to mainly support the increasing use of alkyl esters-based biodiesel and its
mixtures as automotive fuels. In the development of quality standards for biodiesel, Austria was
17
found to be pioneer in all levels. Consequently, the Austrian Standards Institute published the
first quality standard for FAME from rapeseed oil (ONORM C1190) and its subsequent
amendment ONORM C1191 (1996) [54]. However, this standard was not allowed for either
diesel fuel-biodiesel blends or using sunflower oil as feedstock. In Germany, a pre-standard
norm was developed and revealed in 1992 (DIN V 51606 for FAME, animal fats and vegetable
oils). Despite this, it was only until 1997 that, the DIN E 51605 for rapeseed methyl esters and
vegetable oil methyl esters was set and also limits were established for the density, kinematic
viscosity and cold filter plugging point. A mandate was also given to CEN (European Committee
for Standardization) by the EC to develop standards and methods applied for biodiesel
production and utilization concerns [55]. In Europe, EN 14214 BD standard (based on former
DIN 51606) commenced in October 2003. Previously, in November 2001, the EC released a
draft proposal for a Directive of the European Parliament and of the Council on the promotion of
the use of biofuels for transport [56], with a specific objective to provide the Community with a
scope that would promote the use of biofuels exclusively for transport within the EU. Later, a
proposal has been put forth with a commitment on Member States in 2005 to make sure that
there should be a minimum of share of transport fuel sold on their territory which should be
biofuels, with permission for the Member States to decide how to meet this at their best. As a
result, a share of minimum 2% was proposed in 2005, which was increased by 0.75% per year up
to 5.75% in 2010. The ASTM International (formerly American Society for Testing and
Materials) followed a provisional specification PS121 for biodiesel in 1999 and the first ASTM
standard (ASTM D6751) was taken up in 2002.
Among the developed standards, the European and USA standards possessed
international recognition as they are conventionally the beginning point for biodiesel
18
specifications developed in other countries. In this context, there are two major specifications
established the quality requirements for alkyl ester-based biodiesel; they are the ASTM D6751 in
USA and the EN 14214 in Europe.
European biodiesel standards
The European standard EN 14214 is accepted and followed by all 31 member states
involved in CEN. These member states are Austria, Belgium, Greece, Bulgaria, Finland, Croatia,
Cyprus, Czech Republic, Denmark, Norway, Estonia, France, Germany, Hungary, Malta,
Iceland, Ireland, Italy, Latvia, Slovenia, Lithuania, Luxembourg, Netherlands, Poland, Spain,
Portugal, Romania, Slovakia, Sweden, Switzerland and Britain [8]. The European biodiesel
specification is even more restrictive and is implemented only to mono-alkyl esters made with
methanol (FAME) [57]. As per their standards, the addition of components that are not FAME
(excluding the additives) is not permitted. In Europe, EN 14214 developed the specifications for
FAME used as fuel for diesel engines. European standard could be used ‘unblends’ in a diesel
engine (if the engine has been adapted to operate on B100) or blended with diesel fuel to produce
a blend as per the EN 590, which is the European diesel fuel specification. Later, EN 14214:2012
introduced a number of modifications that includes an extension of the scope to cover heating oil
applications and to cover blends up to B10. Further, an auxiliary set of climatic classes that are
based on monoglycerides contents were also developed. Biodiesel/diesel fuel blends are
essentially covered by EN 590. The EN 590:2004 allowed the blends up to 5% of FAME in
diesel fuel, while EN 590:2009 increased the allowable FAME content up to 7%. The authentic
EN 590:2013 standard does not limit the blending ratio of the paraffinic bio-component in diesel
fuels. Eventually, these products obtained by the catalytic hydrogenation of vegetable oils can be
19
blended into gasoil by up to 10 % or even more as to satisfy the above EU requirements with
respect to the renewable fuels utilization.
American biodiesel standards
A Task Force was formed in June 1994 within the American Society for Testing and
Materials to initiate the development of “standards” for biodiesel. The first step adopted by the
Task Force was the resolution of the philosophy for the standard. As per the resolution, various
options were considered that included the addition of a section into the existing ASTM petro-
diesel standards (ASTM D975), development of a standard for a blend of biodiesel with petro-
diesel, and even a ‘stand-alone’ standard. As a result, the following was approved by Biodiesel
Task Force and subsequently by the membership of ASTM in the mid1990s.
1. To work closely and cooperatively with petroleum, engine manufacturing and
biodiesel interests.
2. To establish a ‘stand-alone’ specification for straight biodiesel, B100.
3. To start with existing D975 petro-diesel specifications and the removal of items that
are not applicable to biodiesel.
4. To focus the development of the standard on the end-products’ physical and chemical
attributes that are needed for satisfactory operation and not either on the source of biodiesel or
the manufacturing process. (This is the same philosophy adopted for the development of the
USA petro-diesel requirement, ASTM D 975.)
5. To broaden it to address the biodiesel specific properties that are needed for the
satisfactory engine operations.
6. To extend it to novel characteristics that are being considered for D975 updates.
20
Finally, ASTM D6751-03 standard specification for biodiesel fuel blend stock for
distillate fuels was approved. This norm defined the biodiesel as “mono-alkyl esters of long
chain fatty acids derived from vegetable oils and animal fats”. In this norm the type of alcohol
used was not specified and thereby mono-alkyl esters could be produced with any alcohol
(methanol, ethanol, etc.) as far as it meets the detailed needs that are outlined in the fuel
specifications. Then, the ASTM D6751 standard defines two grades of biodiesel since 2012.
They are (i) grade 2-B (identical to biodiesel defined by earlier versions of the standard) and (ii)
grade 1-B with tighter controls on monoglycerides and cold soak filterability. In addition to this,
there are two more automotive standards for biodiesel/diesel fuel blends also published by
ASTM: The ASTM standard specification for diesel oil ASTM D975, which was modified in
2008, is allowing up to 5% biodiesel to be blended with the fuel and the ASTM D7467 is a
specification for biodiesel blends in the range from 6% BD (B6) to 20% (B20).
1.8 Annual biodiesel production worldwide
Currently, worldwide there are number of large scale biodiesel production plants under
operation. Only in America there are more than 90 biodiesel production plants in operation [15].
“Pacific Biodiesel” is one of the first biodiesel production plants in the USA in 1996 by
recycling the used cooking oil in Hawaii. In 2005, worldwide biodiesel production reached
around 1 million gallons and the major contributor was the European Union, (EU). Biodiesel
production is increased because of two reasons (i) global warming and (ii) rising of crude oil
prices [58]. It is unfortunate that the reliable data on biodiesel production is not documented until
the early 90’s. However, in mid 2000s, a significant production of biodiesel was reported, where
the global biodiesel production is also increasing yearly. It should be noted that the biodiesel is
taking up a significant role in the modern renewable energy production and consumption. In
21
connection with the raw materials for the production of biodiesel, the rapeseed, soybean and
palm oils are the preferred raw materials. According to predictions of Oil World Information
Service (OWIS), which is about the increasing global production and consumption of biodiesel
in 2014, reported that one-third of around 30 million t of biodiesel production comes from palm
oil, followed by soybean and rapeseed oils [59].
The EU is reportedly the world topper in importing the palm oil for biodiesel production.
According to the report [59], for instance, in 2013, the EU attained a record of 6.9 million t of
palm oil of which 3.7 million were spent for energy production that includes biodiesel
production which is 2.5 million. The data according to the OWIS report, confirmed that the
major target of palm oil that enters into EU is for the energy needs. OWIS estimated nearly 9.6
million t of palm oil used for biodiesel consumption in 2014 globally [59].
In another recent report by OECD Agriculture [60], statistical data were given on the
yearly production of biodiesel from vegetable oil, waste based oil and biomasses as shown in
Table 1-4. Estimations of the production, consumption and price of biodiesel up to the year 2025
were also given.
22
Table 1-4. World biodiesel yearly incremental increases in average for the period from
2013-2025 [60].
Avera
ge
2013-
15
2016
2017
2018
2019
2020
2021
2022
2023
2
2024
2025
BD world
production
(bIn L)
31.1 33.2 34.5 35.3 36.7 37.9 38.8 39.6 40.2 40.8 41.4
Vegetable
oil based
(bIn L)
25.2
2
26.3
2
26.6
2
26.9
2
27.5
28.4
29.0
29.3
29.5
29.8
30.1
Waste oil
based
(bIn L)
2.4 2.9 3.4 3.7 4.2 4.4 4.7 5.1 5.4 5.8 6.0
Consumpti
on(bIn L) 30.3 33.5 34.7 35.5 36.9 38.1 39.0 39.8 40.4 41.0 41.6
Price1
(USD/t)
93.9 72.1 71.9 73.7 76.8 81.5 85.9 87.3 87.1 88.4 88.4
[Note: Average 2013-15est: Data for 2015 are estimated
1. Producer price Germany net of biodiesel tariff and energy tax.]
23
Further, Fig.1- 2 shows the world biodiesel production and international trade from 2008
to 2025, and Fig. 1-3(a)-(b) shows the prediction over the regional distributions of world
biodiesel production and use in 2025, respectively.
Fig. 1- 2 World biodiesel production and international trade [61].
Fig. 1-3(a)-(b) Regional distributions of world biodiesel production and use in 2025 [62].
24
1.9 Thesis structure
This PhD thesis is divided into six chapters:
Chapter 1 describes biodiesel, production mechanisms, historical developments, regulations,
worldwide production and finally thesis structure.
Chapter 2 is a literature review of ultrasound biodiesel production and objectives of the work.
Chapter 3 is a publication published in International Journal of Chemical Reactor Engineering,
entitled “A Parametric Study of Biodiesel Production Under Ultrasounds”.
Chapter 4 is a journal paper published in ChemistrySelect, entitled “Triglycerides
Transesterification Reactions under Ultrasounds”.
Chapter 5 is a journal paper, this manuscript is will soon be submitted for publication, entitled
“Ultrasound biodiesel production using various homogeneous catalysts and their
separation over silica cation exchanger columns”.
Chapter 6 gives some conclusions and recommandations for future work.
Chapter 7 is a list of scientific contributions by the author of this thesis.
25
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32
Chapter 2.
33
2.1 Biodiesel production under ultrasound
The most common method for biodiesel production is the transesterification process,
where the triglycerides (TG) are gradually converted through two intermediates i.e diglycerides
and monoglycerides, into three molecules of fatty acid methyl ester (FAME), which is known as
biodiesel, and one molecule of glycerol [1]. For FAME production proper mixing is very much
important to establish the sufficient contact between the two phases of oil or animal fat and
alcohol. For this, ultrasonication helps to increase the liquid–liquid interfacial area through
emulsification, which is important for the formation of vapor bubbles and cavitation bubbles in
viscous liquids, such as plant oils and animal fats. Vapor bubbles within the liquid, such as
methanol bubbles generated mechanically or ultrasonically in liquid oils or fats, oscillate and
move with the steady currents in the bulk liquid caused by the high frequency acoustic
oscillations or acoustic streaming. This phenomenon enhances the mass transfer across the
interfaces of the bubbles and, thus, accelerates the chemical reaction rates under diffusion limited
conditions such as the early stage of transesterification of oils and fats in biodiesel production.
Therefore, it is more crucial to explore this technique for large scale biodiesel production.
Consequently, there are several publications on FAME production available in the current
literature. Most of this works are focused on the laboratory scale [2]. However, few articles
describe the production of FAME in a large scale. Carlini et al. [3] in their pilot study
investigated the operating conditions for biodiesel production from waste cooking oils obtained
from households with an acid value of 2.12 mg KOH g-1. Their work was focused on the
comparison of catalyst type i.e H2SO4 and NaOH, at different concentrations. The best reaction
conditions with the highest FAME yield (94.3 %) were obtained using 0.5 % of NaOH and
excess methanol. Da Cunha et al [4] reported the biodiesel production from a pilot plant using
34
beef tallow and methanol (1:6), and potassium hydroxide (1.5 % w/w) as an alkali catalyst. From
their results, it is clear that they produced high quality biodiesel and the acid number of the
feedstock ranged from 1.2 to 1.8 mg KOH g-1. Alptekin et al. [5] reported, biodiesel production
from corn oil and low-cost animal fats with FFA content. In their first step, methanol and sulfuric
acid were used for the pretreatment of low-cost animal fats. They then used alkali-catalyzed
transesterification, using KOH and methanol that produced a satisfactory yield of FAME. Torres
et al. [6] compared the results obtained in the laboratory with the pilot scale. Their results
showed that the biodiesel quality produced from waste vegetable oil on the pilot scale, using
methanol and KOH and NaOH as catalysts, is almost same with the biodiesel produced from
laboratory and the total yield was found to be 90%. Chitra et al. [7] reported biodiesel production
from laboratory to pilot-scale, Jatropha curcas as a feedstock and NaOH (1% w/w) and methanol
(20% w/w), where the total biodiesel yield was found to be 96%.
It is predicted that in 2030 the world will need to produce 50% more energy than the
current consumption as reported by International Energy Agency report (IEA 2007) especially
due to increased demand by developing countries such as China and India. The main use of
FAME is biodiesel, many other industrial applications exist [8]. Indeed, FAME is nontoxic, has
good solvent properties with low volatility and is biodegradable. FAME have been used to wash
metal pieces [9], automobiles and planes parts [10], and different printing materials as well [11].
Other uses of biodiesel include lubricant phytosanitary products and pesticides [12].
Biodiesel has only a few drawbacks that include solvency effects, (especially for B100)
which may affect some polymeric components of the engine, cold flow properties [13], and
oxidative stability associated with unsaturation of the alkyl chains [14,52].
35
The techniques used to produce FAME can be broadly addressed into two categories, (i)
catalytic and (ii) non-catalytic mediated techniques [15], as shown in Fig. 1.
Fig. 2-1 Classification of biodiesel production techniques
A) Catalytic based biodiesel production techniques:
1. Homogenous catalytic reaction
2. Heterogeneous catalytic reaction
2.1. Solid base catalysts
2.1.1. Single and mixed alkali, alkaline oxides
2.1.2. Supported base catalysts
2.1.3. Zeolites
2.1.4. Clay minerals
2.1.5. Non-oxide bases
Biodiesel production
Catalytic Non-catalytic
Homogeneous Heterogeneous
Acid Acid Base Base Enzymatic
36
2.2. Solid acid catalysts
3. Enzyme catalysts reaction
B) Non-catalytic based biodiesel production techniques:
1. Synthesis via supercritical reaction
2. Enhancement in non-catalytic supercritical reaction
The following table (Table 1) shows a comparison among the most used techniques for
the biodiesel production [16].
Table 2-1. A comparison among the various techniques used in the biodiesel production
[16].
Parameters Homogeneous
Catalysis
Heterogeneous
Catalysis
Enzymatic
Catalysis
Non Catalytic
SMP
Sonochemical
Catalysis
Reaction
time 0.5-4 h 0.5-5.5 h 1-8 h 120-240 s 30-60s
Operation
conditions
0.1MPa
30-65°C
0.1-5MPa
30-200°C
0.1MPa
35-40°C
> 25MPa
> 240°C
0.1MPa
25°C
Catalyst Acid/base Metal oxides or
carbonates Lipase None Base
Free fatty
acid
Soap
formation Esters Esters Esters
Soap
formation
Water Interference Less Interference Less
interference
Act as catalyst
to the process Interference
Yield Normal Low to normal Low to High High
37
normal
Purification Difficult Easy Easy Very easy Easy
Glycerol
purity Low Low to normal Normal High
Low to
Normal
Process Complex Normal Simple Simple Simple
Capital cost Low Medium High Very high Low
Operation
cost High High Normal High Low
Among all the techniques developed as listed above, ultrasound is relatively best due to
its low cost, time saving, and other safety issues. For this process, different types of catalysts are
reported in literature such as heterogeneous catalyst [17,18], enzyme catalyst [19,20],
homogeneous catalysts. But using heterogeneous catalysts and enzyme for biodiesel production
under ultrasound may not be efficient because of the issues concerning biodiesel purity,
separation of catalyst from products and enzyme cost. Therefore, researchers largely focused on
homogeneous catalysts for biodiesel production.
In the context of biodiesel production, this chapter highlights the important
considerations involved in the biodiesel production under ultrasound using homogeneous alkali
and homogeneous acid catalyzed transesterification reaction. This chapter also provides an in-
depth discussion on the biodiesel production from fats/vegetable oil using different catalysts
under ultrasounds.
38
As discussed above, there are two types of homogeneous catalysts reported in literature;
(i) Homogeneous base catalyzed transesterification (ii) Homogeneous acid catalyzed
transesterification.
2.1.1 Homogeneous base catalyzed transesterification
In biodiesel production the most commonly used alkali catalysts are CH3ONa, KOH and
NaOH [21]. Base catalyzed transesterification of triglycerides proceeds faster than acid catalyzed
reactions. The base catalyzed mechanism of the triglycerides transesterification was discussed by
Dermiras et al. [22]
The majority of ultrasound based transesterification studies are focused on homogeneous
transesterification under probes, ultrasonic baths and sonochemical reactors. Stavarache et al.
[23] carried out different transesterification reactions with vegetable oil and methanol using
NaOH as catalyst. They used a batch ultrasonic bath at two different frequencies 28 and 40 kHz.
They compared this with conventional transesterification (stirring speed 1800 rpm) and the
results showed that for 10 min reaction, the sonicated samples reached conversions above 90%
using a catalyst concentration of 1-1.5 % w/w, where they also optimized the frequency for the
first time. Finally they concluded that, (i) the use of ultrasounds allows reducing the amount of
catalyst. For a catalyst concentration of 0.5 %w/w, they got 98% conversion, while non-
sonicated reaction only achieved a conversion of 80% w/w. (ii) Fatty acid methyl ester yield
increases when transesterification is aided by ultrasound. After 10 minutes of reaction time, fatty
acid methyl ester conversions were almost doubled in the reaction sonicated at 40 kHz and more
than doubled in the reaction sonicated at 28 kHz with respect to conventional transesterification.
39
Several reports showed similar results indicating that at a 40 kHz frequency, the
reduction of the reaction time was much more effective than at frequencies of 28 kHz [24-26].
Zhao et al [27] reported a study of the different ultrasound parameters, including ultrasonic
power, catalyst dosage, reaction temperature, frequency, alcohol/oil ratio, and alcohol types on
the yield of ultrasonic-assisted biodiesel production. Georgogiainni et al. [28] tested both ethanol
and methanol in sonicated transesterification. All those experiments were performed under low
frequency (20-40 kHz) and temperature below 40 oC, many of them conducted at room
temperature. These works were focused on the optimization of biodiesel reaction parameters, i.e.
amount of catalyst, molar ratio, reaction time and temperature, without optimizing any
ultrasound physical characteristic. Ji et al. [29] carried out the transesterification of coconut oil at
high energy input and different duty cycles, 6:1 molar ratio and 30 minutes of reaction time.
They showed that the higher the duty cycle and ultrasound power the higher the conversion.
Their first study indicated that an increase of such ultrasound physical characteristics as duty
cycle, amplitude and ultrasonic power implies an increase in fatty acid methyl ester yield. Singh
et al [30] observed huge decrease in reaction time in a batch reactor achieving conversions never
previously reached in such a short reaction time. Kumar et al. [31] carried out the
transesterification of coconut oil reaching a maximum yield of 98% using an amplitude of 60%
and 0.3 cycles per second. Under these conditions, reaction temperatures were considerably high
(72 and 89 oC) due to the high melting point of coconut oil that requires preheating before
transesterification. Temperature is a very complicated factor to control in experiments with
probes, especially if the reaction mixture is heated after being sonicated. Boffito et al. [32]
reported that ultrasonic-assisted mixing device they designed converts most of the triglycerides
with methanol within one minute of pulsed ultrasonic irradiation in presence of KOH catalyst
40
and she also showed the performance of continuous flow ultrasound (US) reactors, a Rosett US
cell reactor, and a batch US reactor are compared to a conventional mechanically stirred batch
reactor. The reaction with ethanol and isopropanol is faster than in classical batch reactors, she
also showed the benefit of using ultrasound to overcome the common mass transfer limitations in
biodiesel production, reaction rates 300 times faster than the conventional process. Martinez-
Guerra and Gude [33] reported the pulse sonication effects using ethanol, methanol and ethanol-
methanol mixtures to convert waste cooking oil into biodiesel in presence of sodium hydroxide
catalyst. A maximum biodiesel yield of 99% was obtained for pulse on-off combination of 7s -2s
at 150W power output, and reaction conditions of 9:1 alcohol to oil molar ratio, 1 w% of sodium
hydroxide, and 1.5 min reaction time. Reyman et al. [34] monitored the ultrasound-assisted
conversion of triglycerides to FAME by controlling the ratio of infrared peak intensities at 1437
and 1464 cm-1. The proposed infrared method turned out to be inexpensive and independent of
the type of oil, avoiding chromatographic analysis. Sajjadi et al. [35] reported the influence of
ultrasound-assisted transesterification on several biodiesel physicochemical properties and
results were compared to those of traditionally stirred reactors. Different combinations of
operational variables were used for alkali-catalyzed transesterification of palm oil. They showed
that ultrasound-assisted transesterification could improve some properties, like kinematic
viscosity and density. Cold flow properties and pour point were also improved, although cloud
point did not show any significant reduction. Flash point was slightly lower than that achieved by
conventional transesterification.
Ultrasonic probes show limitations to simulate large-scale conditions in both continuous
and batch modes that can be solved by using ultrasonic reactors. According to this strategy,
Stavarache et al. [36] designed an ultrasonic reactor for continuous transesterification of
41
vegetable oils. They found that the highest conversion was achieved when short residence time
was selected. This was the first time ultrasound-assisted biodiesel synthesis was performed under
continuous flow.
Hingu et al. [37] demonstrated through parametric investigations the effects of ultrasonic
power, pulse and horn position on the conversion of waste cooking oil catalysed by KOH. When
the ultrasonic power was increased from 150 to 200W, the conversion increased from 66% to
89%. This positive effect was attributed to enhanced mixing and emulsification of the two
immiscible reaction layers at higher levels of power dissipation. However, the conversion
suffered a reduction of approximately 30% when the power was further increased to 250 W.
Cushioning effect, which results in reduced energy transfer and decreased cavitational activity
was linked to this. They also showed that pulsed ultrasound could be optimised to reduce net
power consumption and sufficiently cool the transducers. For instance, they observed that for a
pulse duration of 1 min ON and 5s OFF, conversion of 89.5% was obtained due to better
emulsification of the two immiscible layers. A horn position in the methanol rich layer
reportedly resulted in maximum conversion of 89.5% while the lowest conversion (8.5%)
occurred when the horn was positioned in the oil phase. At the interface of the two phases, the
reported conversion was 58.5%. The observations were attributed to the extent of cavitational
intensity generated in oil or ethanol with varying physicochemical properties namely viscosity,
surface tension and density.
2.1.2 Homogeneous acid catalyzed transesterification
Acid-catalyzed transesterification is useful for fats with high free fatty acid contents. It
was used for transesterification [38] and ultrasound-assisted esterification of oleic acid with
short-chain alcohols (ethanol, propanol and butanol) as investigated by Hanh et al. [39] where,
42
95% of fatty acid ethyl ester conversion was achieved with the use of 5 wt% H2SO4 as catalyst.
The optimum esterification reaction conditions were an ethanol to oleic acid molar ratio of 3:1
with 5 wt% of H2SO4 at 60 °C and an irradiation time of 2 h. Ultrasonic irradiation time was
found to contribute to the high conversion and quality of esters. In the case of handling
feedstocks with high FFAs, the transesterification rate was slow when homogenous acid catalyst
was used. Conversely, when homogenous base catalyst was used, saponification reaction of free
fatty acids occurred. A combined acid-catalysed esterification and base-catalysed
transesterification has been proposed as a solution to this problem. Deng et al. [40] performed a
two-step biodiesel production process with ultrasonic irradiation from high FFAs Jatropha
curcas oil. Using the single-step process, 47.2% with saponification problem reaction stopped
before 4 h and 92.8% conversion was achieved in 4 h with sodium hydroxide (NaOH) and
H2SO4 catalysts respectively at 60 °C temperature. In the two-step process initially they
performed H2SO4 pre-treatment on oil for 1h during that time they reduced acid value of oil and
subsequently they used NaOH for transesterification reaction. In comparison, using the two step
process, a conversion of 96.4% was achieved in just 1.5 h. They concluded that the two-step
process with ultrasonic irradiation was an effective and time-saving method for biodiesel
production especially from high FFA oils. For large-scale industrial applications, continuous
processes are preferred over batch processes due to high efficiency and low production cost [41].
In 2012, only base-catalysed methanolysis had been carried out in continuous flow reactors [38].
Somnuk et al. [42] carried out the first continuous H2SO4 catalysed esterification for FFAs
reduction in mixed crude palm oil (MCPO) using a static mixer coupled with low-frequency high
intensity ultrasonic irradiation. The key parts of this continuous process were a designed static
mixer and an ultrasonic homogeniser. Each element of the static mixer was twisted by 180° with
43
a length to diameter ratio of 1.5 and was connected to the next element at 90°, designated as the
twisted ribbon. During the reaction, methanol and H2SO4 were continuously fed into the 3-m
long tube that housed the static mixer and through the ultrasonic reactor. The acid value was
reduced from 28 mg KOH/g to less than 2 mg KOH/g with 18 vol% of methanol, 2.7 vol% of
catalyst and 20 L/h of flow rate. The results obtained also demonstrated that the use of
ultrasound could shorten the settling time of the esterified oil. Ho et al. also reported systematic
study of ultrasound acid catalyzed transesterification reaction [43]. Deshmane et al. also showed
the H2SO4 catalyzed synthesis of isopropyl esters in presence of ultrasound irradiation at 25 kHz
frequency [44].
In another study, the biodiesel production from soybean oil with methanol in the presence
of a Brønsted acidic ionic liquid-based catalyst under ultrasonication process is reported. The
parametric studies on the transesterification reaction, including (i) the amount of catalyst, (ii) the
molar ratio of methanol to oil, (iii) the temperature, and (iv) the ultrasound power, were
investigated. The optimal conditions were found to be methanol/oil molar ratio of 9:1, 1.0 wt. %
catalyst in oil, ultrasound power of 200 W, at reaction temperature of 60 ºC. Under these
conditions, it was found that the conversion of triglycerides into fatty acid methyl esters was
about 93.2% within the reaction time of 1 h [45].
Interestingly, transesterification of low quality vegetable oils having high free fatty acid
content for biodiesel production was carried out using an effective catalyst based on an acidic
symmetrical acidic ionic liquid, [MMBIM] HSO4. It was observed that the low melting point
of [MMBIM] HSO4 made it easy to recover the catalyst simply by cooling the reaction system
[46].
44
A recent study reported the use of ionic liquid as a green solvent and catalyst [47]. A
new approach using dimethyl carbonate instead of methanol, with sulfonated imidazolium
ionic liquid (SIIL) as catalyst produced a glycerol-free biodiesel. Together with FAME two
other products, the fatty acid 1, 3 dimethoxypropyl ester and 1, 3 dimethoxypropan-2-ol were
also generated. They could be used as oxygenate additives without separating them from the
biodiesel. Further, this paper also reported the effect of the molar ratio of dimethyl
carbonate/rapeseed oil, catalyst dosage, reaction temperature and time. The highest yield of
FAME with the SIIL catalyst 1-propylsulfonate-3-methylimidazolium hydrogen sulfate
([PrSO3HMIM][HSO4]) was found to be 97.7% under optimum conditions.
45
2.2 Engineering of ultrasound reactors
2.2.1 Ultrasonication
Sonochemistry is defined as the use of sound to enhance chemical reaction rates and it
has recently received much attention in several chemical reactions [48]. Ultrasounds is the term
used for sound waves having frequencies higher than the normal human hearing range (>18 kHz)
[49]. Ultrasonic waves propagate in a medium as a series of alternate compression and
rarefaction regions of pressure as detailed in Fig. 2 [50]. The frequency of a sound wave is
defined as the number of waves that pass through a single point per unit time (s). Wavelength is
the peak to peak distance between two adjacent waves.
When a liquid is irradiated by a strong ultrasonic wave the pressure at some regions in the
liquid becomes negative because the acoustic amplitude of the wave is larger than the ambient
pressure. This is the reason why the pressure wave propagating through a liquid with enough
intensity, formation of vapor bubbles may occur because the gas dissolved in the liquid can no
longer be kept dissolved, since the gas solubility is proportional to pressure. This is known as the
cavitation phenomenon [51] as shown in Fig. 2-2. The bubbles formed in the cavitation
phenomenon grow from nuclei, over many acoustic cycle [52].
46
Fig. 2-2 Growth and collapse of cavitation bubble in a liquid medium when ultrasonic
waves are applied [52].
Ultrasounds are divided into two categories:
(i) High power ultrasound (frequency range of 20 kHz to 100 kHz): High-power
ultrasonic fields can be extremely difficult to characterize because of the cavitational activities
themselves. This kind of ultrasonic waves have high power and typically lower frequency. These
waves, have the potential of producing physical and chemical changes in the liquids. They are
used in industry for chemical reactions and welding purposes with different ultrasound power.
(ii) Low power ultrasound (frequency range of 100 kHz to 1 MHz): These kinds of
ultrasound waves have high frequency and low power. They do not cause any chemical physical
changes in the medium that they pass through. They are used to measure velocity and the
absorption coefficient of waves in a medium, and thus are used in treatments of stains, medical
scanning, imaging, dentistry, etc [53]. High frequency ultrasonic waves have small wavelengths
that enable detection and imaging of small areas with high resolution.
47
Ultrasound has been used in industry for many years. The first commercial application of
ultrasounds was an attempt to detect submarines by Paul Langevin in 1917. Ultrasounds can be
used in several fields that include.
(i) Medicine: Ultrasound technique is very useful in medicine. It has been used
by sonographers and radiologists. Ultrasound imaging (2-10 MHz) is used in drilling of teeth,
muscle strain treatments and cleaning (20-50 kHz) etc [53]. This technology is relatively
inexpensive and portable compared with other techniques, such as Computed Tomography (CT)
and Magnetic Resonance Imaging (MRI).
(ii) Industry: Ultrasound-welding and ultrasound-cleaning are the most common
applications of high power ultrasonics. It is also used for cutting, sonic weapon, drilling and
grinding. Low power applications include non-destructive testing and processing. Ultrasounds
were also used successfully in food industry to improve quality and process control [54].
(iii) Biology and biochemistry: By using ultrasound, a simple method for trace
elemental determination in biological tissue has been developed [55]. Ultrasound is used for
degassing of liquids, cell disruption, filtration, crystallization (by producing more uniform and
smaller crystals in supersaturated solutions), and dispersion of solids. Ultrasound also has
healing applications, which can be highly favourable when used with dosage precautions.
Ultrasounds do not directly react with liquids in a chemical reaction but it induces several
physical property in the liquid that help in rising the reaction rate, namely streaming and
cavitation, which are described in more detail in the following sections.
48
2.2.2 Cavitation
Cavitation is the phenomenon of production of large numbers of microbubbles in a liquid
when a negative pressure is applied. When sound waves spread through a liquid medium, they
generate compression and rarefaction regions in the liquid. The intermolecular distances between
the liquid molecules also expand and contract along these waves. At very low pressure in the
rarefaction region, the intermolecular spaces exceed the critical molecular distance and the liquid
tears apart to form void spaces or micro bubbles. These micro bubbles oscillate with the wave
motion and grow in size by taking in vapor from the surrounding liquid medium and by
aggregating with other micro bubbles [50]. Within a few cycles they grow to an unstable size and
collapse violently, releasing large amounts of energy and creating localized point temperatures of
up to 5000 K for extremely short periods of time [56]. The growth and subsequent collapse of
cavitation bubbles is shown in Fig. 2-2. The collapse of the bubble produces high shear forces
which mix the liquid vigorously and rupture nearby particles and when acoustic bubbles reach a
critical size range they undergo a violent collapse.
There are three theories to explain the chemical effects arising from the collapse of
cavitation bubbles:
1. Plasma discharge theory
2. Electrical theory
3. Super-critical theory
Another approach is the hot spot theory. This theory proposes that bubbles growth is
almost adiabatic up to the collapse. At this point, the gas in the bubble core is quickly
49
compressed hence, temperature of thousands of degrees and pressure of more than hundreds of
atmospheres can be locally created, and this is the hot spot condition.
2.2.3 Acoustic streaming
Acoustic streaming is a steady flow in a fluid driven by the absorption of high
amplitude acoustic oscillations. When ultrasounds are introduced into a liquid, a movement of
liquid opposite to the direction of ultrasonic waves is observed (Figure 2-3). The sound energy is
converted into kinetic energy and this effect is independent of the cavitation effect. Acoustic
streaming is very helpful for heat and mass transfer in the liquid. It helps spreading of ultrasonic
energy and dissipation of
Fig 2-3. Streaming observed in a liquid after ultrasonication
50
heat [57]. In addition to cavitation and acoustic streaming, heat is produced in the liquid by
shearing at interfaces such as the interface between a metal horn and liquid.
2.2.4 Tooling design
During direct ultrasonication of a reaction medium, different typs of ultrasonic probes are
used to produce and transfer ultrasonic waves to the liquid medium [58]. Figure 2-4 shows a
typical set-up of an ultrasonic assembly. The chimney is connected to a power supply which
converts line voltage to DC voltage which is then modulated at the desired high frequency. This
chimney consists of three parts. i) Converter, ii) Booster and iii) Horn.
Fig 2-4. Ultrasonic probe
1. Converter
The sandwich-style ultrasonic converter, was developed by Paul Langevin in 1917. Currently,
lots of manufacturers are producing converters as shown in Figure 2-5. This device converts
51
electrical energy to mechanical energy (vibrations). The transducer consists of a piezoelectric
element. Thin crystals of piezoceramic are loaded together and voltage is applied to their relative
interfaces. When a charge is applied to the two faces of a piezoelectric material, it expands and
contracts depending on the polarity of the applied charge. Thus, if a rapidly alternating voltage is
applied to such a material, its dimensions change depending on the frequency of the applied
voltage and the ultrasonic vibrations are created.
Fig. 2-5: Different shapes of converter
2. Booster
The booster and other stack components are generally made of titanium or aluminum alloy
(Fig.2-6). The ultrasonic booster is typically a tuned half wave component shaped so that it
increases or decreases amplitude passed between the converter and sonotrode (horn). These
boosters are amazingly durable in hard use.
52
Fig. 2-6: Titanium ultrasonic booster
3. Horn
The ultrasonic horn is commonly a solid metal rod made up of titanium or aluminum alloy.
Different types of ultrasonic horn are available in the market as shown in Fig. 2-7. Its function is
to pass the ultrasonic waves into the liquid mixture. For this reason, the horn should be
chemically inert, resistant to deterioration from cavitation, and should have maximum efficiency
in transferring ultrasonic waves. Ultrasonic horns are classified into three parts by the following
main features: i) Transverse cross-section shape, ii) Longitudinal cross-section shape and iii.)
Number of elements with different longitudinal cross- section profile – common and composite.
Fig 2-7: Different types of ultrasonic horn.
53
2.2.5 Transesterification reaction using ultrasounds
Transesterification reactions essentially integrate the reactions between alcohol and oil in the
vicinity of catalysts. Basically, methyl alcohol and oil are immiscible liquids and they together
form separate layers in the mixture. Normally, the traditional transesterification reactions require
a continuous mixing of the reactants for long periods importantly to promote the chemical
reactions between the oil and alcohol. This is because of the fact that the transesterification
reaction takes place only in the interfacial region of the two liquids. Under such circumstances,
when this solution mixture is sonicated, the ultrasonic waves produce cavitation at these
interfacial regions because of some dissolved gases in the reaction mixture. As a result, it leads
to the formation of an emulsion of oil and alcohol that provides large surface areas for the
reaction to take place. Therefore, it is generally observed that the reaction time is considerably
reduced.
It is proved that the ultrasound technique is an effective and useful process in improving
the reaction rates in a range of reacting systems. It also showed a significant improvement in the
conversion, yield and found to change the reaction pathways, and/or initiate the reactions in
chemical, biological, and electrochemical systems [59]. It is known that the ultrasounds are
sounds with a frequency beyond that to which the human ear can respond. Normally, the range of
hearing is from 16 Hz and 18 kHz and the ultrasound generally lies between 20 kHz to above
100 MHz [56]. Similar to any sound waves, ultrasound also alternately compresses and stretches
the molecular spacing of the medium through which it propagates and causes a sequence of
compression and rarefaction cycles. When a large negative pressure gradient is applied to the
liquid, the distance between the molecules stretches beyond the critical molecular distance,
which is necessary to hold the liquid intact, the liquid will be broken down and voids (cavities)
54
will be created, which is known as cavitation bubbles. A small cavity may also grow due to the
inertial effects at the higher ultrasonic intensities. Eventually, some bubbles may experience a
sudden expansion to an over and unstable size and collapse aggressively, which may generate
energy for some mechanical and chemical effects [60]. Further, these collapses of the cavitation
bubbles dislocate the phase boundary and cause emulsification process through the ultrasonic jets
that impinge upon one liquid to another [24]. It is found that a low frequency ultrasonic
irradiation is useful for the transesterification of triglyceride with alcohol. Notably,
ultrasonication provides mechanical energy for mixing as well as the required activation energy
to initiate the transesterification reaction [61]. It is also found that ultrasonication increases the
yield of the transesterification of animal fats and vegetable oils into bio-diesel and also increases
the speed of the chemical reaction [62]. Further, the ultrasonic mediated transesterification
process also provides advantages such as minimizing the reaction time and less energy
consumption as compared to the conventional mechanical stirring method [29], efficient molar
ratio of TG to methanol, and uncomplicatedness [63]. For instance, it is reported that for a
transesterification of 1 kg of soybean oil, the conventional mechanical stirring and ultrasonic
cavitation methods consume 500 and 250 W/kg of energy, respectively [29]. In another study,
[24,64] it is reported that the conversion of vegetable oil (the nature of the oil was unknown) to
methyl esters was found to be the highest for a 1.0% (w/w) NaOH concentration, which means
95% after 10 min at room temperature using ultrasonication process at 28 kHz. Similarly, it is
shown that the ultrasonic can also be used to enhance the rate of transesterification in grapeseed
oil, corn oil, palm oil, etc [24].
A study on the effects of molar ratio, catalyst concentration and temperature on
transesterification of triolein with ethanol under ultrasonic irradiation reported that the formation
55
of ethyl ester under ultrasonic irradiation at 25 ºC occurred in a reaction time of less than 20 min,
with optimum conditions of E/T (ethanol to triolein) molar ratio of 6:1, base catalyst (NaOH or
KOH) concentration of 1 wt% [65]. Similarly, the effect of ultrasonication versus mechanical
stirring was studied on the alkaline transesterification of rapeseed oil using NaOH at a
concentration of 0.5% w/w at 45 ºC [66], in which a conversion of 80–85% was obtained for
both ultrasonicated and mechanically stirred reactions after 30 min. In another report, an
ultrasonically driven continuous process was used for the palm oil transesterification and over
90% conversion was reported at 20 min residence time in reactor, with 6:1 methanol to oil molar
ratio [36]. For reference, Table 2 shows the bio-diesel production from various feedstocks under
different conditions using ultrasound irradiation.
56
Oil/Triolein Catalysts Alcohol
Oil to
alcohol
molar ratio
Catalyst
% of oil
Ester
yield
(%)
Ultrasound
Power (W)
Ultrasonic
Frequency
(kHz)
Reaction
time in
min
Ref.
Triolein NaOH Ethanol 1:6 1 88 132 40 20 20
Triolein KOH Methanol 1:6 1 98 1200 40 20 67
Waste
vegetable oil NaOH
MeOh-
EtOH
mixtures
9:1 1 98.5 1000 25 1-2 68
Waste
cooking oil
Alkaline
(KOH) Methanol 4.5:1 0.5 95.2 - 25-30 3-30 69
Waste
cooking oil
Alkaline
(KOH) Methanol 6:1 1 95 - 40 45 70
Rapeseed oil KOH Methanol 20:1 1 95.03 400 20 40 71
Table 2-2. Biodiesel production from various feedstocks under different conditions using ultrasound irradiation.
57
Soyabean oil Alkaline
KOH Methanol 10:1 1.8 96.1 600 20 50 72
Castor oil Alkaline
KOH Methanol 4.87:1 1.4 86.5 450 20 3.75 73
Canola oil Alkaline
KOH
Methanol
5:1, 4:1 0.7 99 - 20 50 74
Palm oil Alkaline
KOH
Methanol
3:1 1 93 - 28-40-70 15 75
58
2.2.6 Objectives
Based on the above analysis of literature the following objectives have been set for this
thesis. These encompass the synthesis of some homogeneous catalysts and a study of
biodiesel production under ultrasound. More detailed objectives may be listed as:
1. Parametric study of the transesterification of Canola oil under ultrasounds in a
continuous flow reactor using sodium methoxide as a homogeneous catalyst.
2. Synthesis of different guanidines.
3. Comparison between the total conversion using sodium methoxide and guanidine
homogeneous catalysts for the production of biodiesel from canola oil in the presence of
ultrasounds.
4. Separation of homogeneous catalysts after reaction by using cation exchanged silica
based columns.
.
59
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69
Chapter 3.
A Parametric Study of Biodiesel Production Under Ultrasounds
Published in Int. J. Chem. React. Eng., 15(1), 117–125, 2017.
Kiran Shinde, Bendaoud Nohair and Serge Kaliaguine*
Department of Chemical Engineering Laval University, Quebec, G1 V 0 A6, Canada
70
Résumé
Le biodiesel, un carburant dérivé de l’huile végétale, peut être utilisé partiellement
ou complètement comme substitut au carburant diesel. Le principal argument pour son
utilisation dans les moteurs à combustion interne est son bilan net de CO2 qui est
considérablement réduit comparativement aux combustibles diesel d’origine fossile. Une
étude systématique de la production continue du biodiesel sous ultrasons utilisant l’huile de
canola a été conduite en présence de méthanol et de méthylate de sodium comme
catalyseur. Les effets des différents paramètres de réaction comme le temps de résidence, la
concentration des catalyseurs, la température de réaction, l’amplitude et la puissance des
ultrasons, le rapport molaire méthanol/huile ont été analysés. Les esters méthyliques des
acides gras (FAME) ont été produits rapidement en utilisant la transestérification sous
ultrasons. Dans les conditions typiques (35 C), une conversion en FAME supérieure à 80%
a pu être atteinte pour un temps de résidence aussi bas que 20 secondes. Cette étude
paramétrique permet d’établir que les effets des ondes d’ultrasonores sur la vitesse de
transestérification sont localisés dans un très petit volume entourant la pointe du sonotrode.
Cette conclusion, sans précédent, a des conséquences très importantes pour la conception
d’un réacteur de production de biodiesel à alimentation continue à grande échelle.
71
Abstract
Biodiesel, a vegetable oil-derived fuel, can be used as a partial or complete
substitute to diesel oil. The main argument for its usage in internal combustion engines is
its net CO2 balance which is considerably reduced compared to diesel fuel of fossil origin.
A systematic study of ultrasound continuous biodiesel production using canola oil was
conducted in the presence of methanol and sodium methoxide as catalyst. Effects of various
reaction parameters such as residence time, catalyst concentration, reaction temperature,
ultrasounds amplitude and power, methanol/oil molar ratio were analyzed. Fatty acid
methyl esters were produced rapidly by using ultrasound assisted transesterification. In
typical conditions (35 °C) conversion to FAME higher than 80% could be reached at
residence time as low as 20 s. The parametric study allowed to establish that the effect of
ultrasound wave on transesterification reaction rate is localized in a very small volume
surrounding the sonotrode tip. This unprecedented conclusion has significant consequences
for the design of the large scale continuous flow biodiesel production reactor.
72
3.1 Introduction
Biofuels such as biodiesel from renewable energy sources are already prepared on a
rather large scale and in the future they may replace a significant fraction of fuels of fossil
origin (Canakci 2007; Sharma and Singh 2009; Talebian-Kiakalaieh, et al. 2013). Biodiesel
is derived from the transesterification of different vegetable or algal oils and animal fats
(Gerpen 2005; Chisti 2007; Dermirbas 2003; Zhang et al. 2003). It is produced on large
scale and may be used in any compression ignition engine without modification either as a
blend with diesel fuel or as a substitute. There are numerous advantages to the use of
biodiesel. Its cetane is in the range of 50–65 compared to 40 for petro diesel. It shows a
high lubricity and its oxygen content reduces particulates in the exhaust by about 50 %. It
meets the health effects requirements of the 1990 Clean Air Act Amendments. In particular
it reduces significantly total unburnt hydrocarbons, carbon monoxide, sulfates (due to quasi
absence of sulfur in oil) and such carcinogenics as polycyclic aromatics (PAH) and nitrated
PAHs. The main advantage however is the drastic reduction in CO2 emission by about 80%
compared to petro diesel on the same energy basis (Net Energy Balance up to 4 MJ/MJ)
(Antolin, Tinaut, and Briceno 2002; Lang, Dalai, and Bakhshi 2001; Srivastava and Prasad
2000; Dalai, Kulkarni, and Meher 2006; Joshi and Pegg 2007; Lapuerta, Fernandez, and de
Mora 2009; Knothe, Van Gerpen, and Krahl 2005).
Homogeneously base-catalyzed transesterification is suffering from mass transfer
limitations due to the biphasic nature of the reaction medium. Different intensification
methods such as microwave irradiation (Verma 2001; Refaat, et al. 2008; Barnard et al.
2007; Motasemi and Ani 2012; Saifuddin and Chua 2004; Yoni and Aharon 2008; Duz,
Saydut, and Ozturk 2011; Azcan and Danisman 2007; Majeshwski, Pollack, and Curtis-
73
palmer 2009; Patil et al. 2011; Yaakob et al. 2009; Mazzocchia et al. 2004;
Lertsathaponsuk et al. 2008; Chen et al. 2012), ultrasonic or hydrodynamic cavitation
(Kelkar, Gogate, and Pandit 2008; Stavarache et al. 2005; Deshmane, Gogate, and Pandit
2009; Santos, Rodrigues, and Fernades 2009; Stavarache et al. 2007; Salamatinia et al.
2010; Maghami, Sadrameli, and Ghobadian 2015; Yin et al. 2015; Maran and Priya 2015;
Pukale et al. 2015), addition of co-solvents and supercritical synthesis conditions (Huang et
al. 2010; Yoo et al. 2010) have been tested to minimize these mass transfer limitations. The
base-catalyzed production process requires high purity oils deprived of water and free fatty
acid contaminants.
There is a rather abundant literature dealing with the use of ultrasounds to accelerate
biodiesel production. The process is rather inexpensive even at industrial scale. When
ultrasonic waves pass through the mixture of immiscible liquids (oil and methanol) a
microemulsion is generated. The large surface area of this emulsionis a kinetic factor which
accelerates the transesterification process and allows to reduce the requirements for other
kinetic factors such as methanol to oil ratio, catalyst amount, reaction temperature and
reaction time (Hanh et al. 2008; Cintas et al. 2010; Mason 2000). It is also likely that the
cavitation process which generates locally very high pressures and temperatures for
microseconds, can accelerate the reaction (Mason 1999; Vivekanand and Wang 2011).
There are however some significant differences in the published results describing these
effects.
Nieves-Soto et al. (2012) discussed the different advantages of biodiesel production
from Jatropha oil and briefly described current technologies and the fundamentals and
benefits of sonochemistry. In 1 min of reaction time in a batch reactor these authors
74
obtained a 65% yield of FAME with a methanol to oil molar ratio of 6:1, alkaline catalyst
(KOH), power intensity 105W/cm2 and reaction temperature 25 °C. Thanh et al. (2010)
reported biodiesel production from canola oil with methanol performed in the presence of a
base (KOH) catalyst in a continuous flow process at room temperature. The
transesterification was accelerated by low frequency (20 kHz) ultrasonic irradiation, the
optimum conditions for the reaction being methanol to oil molar ratio 5:1 and 0.7 wt%
catalyst. A conversion higher than 99% was reached within 50 min of reaction time. Hanh
et al. (2008) reported the methanolysis of triolein at room temperature using 40 kHz
ultrasounds in a batch reactor and showed that the yield of methyl ester depends on KOH
concentration and the ratio of methanol to oil. After 30 min reaction time they reached high
conversion of methyl ester at 1 wt% KOH catalyst and methanol to oil ratio 6:1.
The above three examples of biodiesel production under ultrasounds are reported
here to illustrate the kind of differences in observed rate enhancement which may be found
in the relevant literature (Kelkar, Gogate, and Pandit 2008; Stavarache et al. 2005;
Deshmane, Gogate, and Pandit 2009; Santos, Rodrigues, and Fernades 2009; Stavarache et
al. 2007; Salamatinia et al. 2010; Maghami, Sadrameli, and Ghobadian 2015; Yin et al.
2015; Maran and Priya 2015; Pukale et al. 2015; Hanh et al. 2008; Nieves-Soto et al. 2012;
Thanh et al. 2010). Typically even though working with similar kinetic parameters (T,
catalyst/oil ratio, methanol/oil ratio) and triglycerides feedstocks of similar composition,
with strongly basic catalysts, the nominal time to reach 85–90% conversions ranges from
seconds to hours. The current study was therefore undertaken in order to investigate the
physico-chemical reasons for these significant differences in reaction rates. To this end a
systematic study of the kinetic parameters involved in the transesterification of Canola oil
75
by methanol in a continuous flow reactor, in the presence of the basic catalyst sodium
methoxide under ultrasound wave, was undertaken.
3.2 Experimental
3.2.1 Materials
The Canola oil used in the reaction was of a commercial edible oil with
characteristic fatty acid composition C16:0 (4 %), C18:0 (2 %), C18:1 (56 %), C18:2 (26
%), C18:3 (10 %), kinematic viscosity: 38.2mm2/s (at 40 °C), average molecular weight:
876.6 Da. Minor amounts of long chain (C20:0-C24:0) and saturated fatty acids occurred
mostly in the 1- and 3-positions, while the octadecanoic (C18) fatty acids, especially
linoleic and linolenic, are integrated in the 2-position (Przybylski et al. 2005). Metallic
sodium and dry methanol were purchased from Sigma-Aldrich. Analytical standards of
monoglycerides, diglycerides, triglycerides and fatty acid methyl esters were also
purchased from Sigma-Aldrich.
3.2.2 Catalyst preparation
CH3ONa was prepared by reacting dry methanol with sodium metal in ambient
conditions. The sodium methoxide content in methanol was adjusted depending on the
targeted catalyst/oil ratio.
76
3.2.3 Apparatus
An ultrasonic UP 200S from Hielscher ultrasonic was used to perform the
transesterification reaction. The ultrasound generator operates at 26 kHz. The amplitude for
the reaction was adjustable from 20% to 100% of maximum. The sonotrode acting as an
ultrasonic probe had a 7mm tip diameter. The system was completed by a Seepex dosing
pump (group D) and a temperature controller (Barnant Thermocouple Thermometer). The
continuous flow glass reactor had a volume of 67 ml. The sonotrode tip was located at 10 ±
1mm below the steady liquid level.
Figure 3-1: Reaction setup.
3.2.4 Transesterification reaction tests
77
The experiments were carried out in the continuous flow ultrasonicated glass reactor
illustrated in Figure 3-1. The Seepex feed inlet was fed using two peristaltic pumps
(Watson-Marlow 101 U/R) one for the canola oil and one for the methanol solution of the
catalyst. The relative flow rate of these two pumps was set in order to control the
methanol/oil ratio of the reactor feed. The sum of these flow rates was equal to the Seepex
pump flow rate and the feeder volume is kept very small (1–2 cm3) to avoid accumulation
and possible phase separation in the feed inlet. The ultrasound processor UP 200St was
used simultaneously with the temperature controller in order to control the reactor
temperature. The polar and non-polar phases of the mixture leaving the reactor were
separated by centrifugation (BECKMAN AvantiTM J-30I centrifuge machine). Samples of
the non-polar phase were analyzed by UHPLC.
3.2.5 UHPLC analysis
The polar phase samples were analyzed for monoglycerides (MG), diglycerides
(DG), triglycerides (TG) and methyl esters (FAME) using UHPLC (UltiMate 3000 Dionex)
equipped with column AcclaimTM 120, C18, 5 μm, 120, A 4.6 × 100 mm, and a UV
(Thermo SCIENTIFIC Dionex UltiMate 3000) variable wavelength detector. Acetonitrile,
hexane and isopropanol were used as solvents. The solvent flow rate was 0.5 ml/min. The
sample injection volume was 10 μL and the peak identification was made by comparing the
retention time between the sample and the standards. The analysis of each sample was
repeated three times. Since the saturated chains are not detected by UV, the conversions
measured using the UV detector were compared with those obtained using a Charge
78
Aerosol Detector (Dionex corona ultra). Differences were within 1% owing to the low
content of saturated fatty acids in Canola oil. The CAD detector could not be used for
FAME analysis as described in Robert (2009).
3.3 Results and discussion
Figure 3-2 shows typical examples of UHPLC chromatograms at various
conversions. These traces allow precise separation and quantification of tri-, di, and
monoglycerides as well as FAMEs. Using these traces, it is possible to calculate a global
value for TG conversion and the precision of these estimates is thought to be with ± 1 %.
Figure 3 shows the time volution of TG conversion at different residence times
ranging from 20 to 72 s. The other reaction conditions for these tests were a temperature of
35 °C, methanol/oil 4:1, CH3ONa catalyst content 0.5 wt% with respect to oil. Changing
the residence time was obtained by varying feed flowrate and/ or reactor volume by
introducing an inert polymer mass in the bottom of the reactor. After a 1–2 min start-up
period, the exit conversion reaches an essentially steady value of 80–82 %. This value is
practically unchanged with residence time. This absence of variation indicates that either
chemical equilibrium is reached after a residence time of 20 s or that the actual volume in
which reaction occurs is not commensurate with the reactor volume. The latter hypothesis
would correspond to a very intense energy dispersion at the sonotrode tip, yielding very
high reaction rates in a very small volume.
Whatever the explanation the increase in conversion rate due to ultrasonication is
spectacular. For comparison, in typical industrial base catalyzed processes with
79
temperatures of 65–70 °C, methanol:oil = 10:1, catalyst content 1 wt%, a conversion of
80% is only reached in 60–90 min. Note here that the initial conversion (obtained in
absence of ultrasounds) is not zero which indicates that some conversion is already
observed at the exhaust of the Seepex pump. These values may serve as the reference
values to show the effect of ultrasounds on conversion. They also suggest that some
conversion already happens within this pump likely due to some hydrodynamic cavitation
(Pal et al. 2010; Ghayal, Pandit, and Rathod 2013).
Fig. 3-2. UHPLC Chromatograms for A = Canola oil, B = Non-polar phase at 60 %
TG conversion, C= Non-polar phase at 100% TG conversion
D
e
t
e
c
t
o
r
R
e
s
p
o
n
s
e
80
Fig. 3-3. Effect of reaction time on methyl ester production with 0.5 wt % catalyst
(CH3ONa) Methanol/Oil ratio 4:1, ultrasound amplitude 60%. Temperature 35°C
This result is confirmed by the tests described in Figure 3-4 which shows data
obtained at various catalyst contents. The other conditions of these tests were same as those
in Figure 3-3 and a 20 s residence time. The experimental observations reported in Figure
3-4 confirm that ultrasounds have no effect in absence of catalyst (no conversion at 0%
catalyst content). A non-negligible conversion is also observed at time zero at varying
catalyst content, and almost no conversion variation is found after 1 min on stream. Note
that the steady state conversion is varying with catalyst content which indicates that
thermodynamic chemical equilibrium is not reached.
Figure 3-5 shows the evolution with time on stream of the various mole fractions of
TG, DG, MG and FAME.
0
20
40
60
80
100
0 2 4 6TG
co
nvv
ers
ion
. %Time on stream(min)
20
33
46
72
81
Figure 3-4: Effect of catalyst concentration on methyl ester production. Catalyst
(CH3ONa) methanol/oil ratio 4:1, ultrasound amplitude 60 %, Residence time 20 s.
Temperature 35 °C.
Figure 3-5: Mole fraction of TG, FAME, DG and MG, Reaction conditions 4:1
CH3ONa:Canola oil, Amplitude 60 %, Residence time 20 s. CH3ONa 0.5 wt% with canola
oil. Temperature 35 °C.
in the non-polar phase collected during reaction tests conducted in the conditions of
Figure 3 at 20 s residence time. The reactions involved are:
TG+CH3OH FAME+DG (1)
DG+CH3OH FAME+MG (2)
MG+CH3OH FAME+glycerol (3)
0
20
40
60
80
100
0 0.5 1 1.5T
G C
on
ver
sio
n i
n %
wt % catalyst
0
1
2
3
4
5
Time on stream (min)
0
20
40
60
80
100
0 1 2 3 4 5
Mo
le f
ract
ion
%
Time on stream (min)
FAME
TG
DG
MG
82
The quasi-constant values for DG and MG conversions even before the steady state
is reached (2 min > time) indicate that reactions (2) and (3) progress faster towards steady
state than reaction (1).
For the experiments reported in Figure 3-4, the mole fractions of TG, DG, MG and
FAME after 5 min on stream and 20 s residence time, are given in Figure 3-6 as unctions of
catalyst content. Raising the catalyst loading to 1 wt% allows to decrease TG and DG
partial onversions, yielding residual mole fractions of 10 and 4% respectively at 20 s
residence time. This result also reflects the relative enhancement in rates of reactions (2)
and (3) compared to reaction (1) under the combined action of the catalyst and ultrasounds.
Fig. 3-6. Steady state mole fraction of TG, FAME, DG and MG with different wt %
of catalyst, Reaction conditions 4:1 CH3ONa:Canola oil, Amplitude 60%, Residence time
20 s, CH3ONa 0.5 wt % with canola oil. Temperature 35°C
0
20
40
60
80
100
0 0.2 0.4 0.6 0.8 1 1.2
Mo
le f
ract
ion
%
wt% catalyst
TG
DG
MG
FAME
83
Figure 3-7: Temperature and power change during reaction.
Figure 3-7 shows how in absence of temperature control,varying the ultrasound
generator amplitude affects power dissipated at the tip of the sonotrode and therefore the
temperature of the reaction medium. As a consequence, the study of the effect of ultrasound
generator amplitude on transesterification rate has to be performed in strictly controlled
reaction temperature conditions. The data reported in Figure 8 were therefore recorded at
various amplitudes and a constant temperature of 35 °C. They show that amplitude
variation, which could affect temperature, has essentially no effect on TG conversion in the
conditions reported for Figure 3-4, at constant temperature.
The effect of temperature on TG conversion in conditions otherwise similar to those
in Figure 4 is shown in Figure 9. At zero reaction time a regular increase is found upon
raising temperature from 35 to 55 °C but when steady state is reached, no more increase is
observed above 45 °C.
It may be concluded from the data reported in Figures 3-8 and 3-9 that the average
temperature of the reaction medium is not a major factor governing the catalytic reaction
0
10
20
30
40
50
60
70
29
30
31
32
33
34
35
36
37
0 30 60 90
Temp.
Power
Amplitude
Po
wer
Wcm
-2
Tem
per
ature
oC
84
rate under ultrasounds. This is likely associated with the transient high temperatures
reached during cavitation, being the main parameter which determines the kinetic behavior.
These very local and very short temperature excursions have little effect on the actual
average temperature in the reactor.
Fig. 3-8. Effect of amplitude on methyl ester production with 0.5 wt % catalyst
(CH3ONa) Methanol/Oil ratio 4:1, residence time 20 second. Temperature 35°C
Fig. 3-9. Effect of temperature on TG conversion: a= 35°C, b= 45°C, C=55°C. 0.5
wt % catalyst (CH3ONa) Methanol/Oil ratio 4:1, ultrasound amplitude 60%
Methanol to oil molar ratio is another significant kinetic parameter. Figure 3-10 shows the
TG conversion as a function of time on stream in three experiments conducted at 35 °C, 20
s residence time, amplitude of 60 %, 0.5 wt% catalyst and three values of methanol to oil
0
20
40
60
80
100
0 2 4 6
TG
Co
nv
ersi
on
%
Time on stream (min)
40
50
60
70
80
Amplitude in %
0
20
40
60
80
100
0 1 2 3 4 5
TG
Co
nv
ersi
on
%
Time on stream (min)
b
c
85
molar ratio namely 3:1, 4:1 and 6:1. Here again very little difference is observed between
the three curves.
Fig. 3-10. Effect of mole ratio on continuous methyl ester production with 0.5 wt %
catalyst (CH3ONa), ultrasound amplitude 60%, residence time 20 s. Temperature 35°C
As discussed above, the absence of variation of the steady state TG conversion with
residence time (Figure 3) could have two explanations namely that chemical equilibrium is
reached at the reactor outlet or that the reactor volume value used in calculating residence
time is far larger than the actual volume in which reaction actually occurs. Since however
the steady state conversion varies with catalyst content (Figure 4) the system has not
reached chemical equilibrium in these conditions. Thus the only acceptable hypothesis is
that the reaction occurs in a small volume at the ultrasound generator tip and that this
volume is essentially not affected neither by flow rate nor by a change in the volume of the
remainder of the reactor.
To our knowledge this effect has never been discussed before in the biodiesel
related literature. It has several important consequences. First if the process is run in a batch
mode, the concentration fields will be non-homogeneous and the instantaneous average
concentrations of reactants and products will depend on the total volume of the reaction
0
20
40
60
80
100
0 2 4 6T
G C
on
ver
sio
n i
n %
Time on stream (min)
3:1
4:1
6:1
CH3OH / Oil
86
medium. The sample collection and phase separation protocols will therefore affect
drastically the concentration measurements. These effects provide an explanation for some
of the discrepancies among research laboratories underlined in the introduction section.
Secondly the spectacular increase in transesterification rate will be better utilized
industrially if the process is run in a continuous flow reactor, the volume of which will have
a value close to the one of the active volume around the ultrasound generator tip. This
means very low residence time even lower than the 20 s reached in this work.
Understanding and modelling the effects of ultrasounds is however not
straightforward: the reaction medium is biphasic and reactions (1), (2) and (3) occur in the
interfacial region. Initially methanol must be solubilised in the nonpolar phase. In every
immiscible liquid-liquid phase separation some mutual solubilization occurs in both phases.
In the biphasic reaction medium they diffuse toward the bulk and react. The methanol
concentration profile depends essentially on the relative rates of diffusion and reaction. The
large increase in transesterification rate upon ultrasonication suggests that increasing
interfacial surface area induces a large increase in methanol mass transfer. Interfacial mass
transfer would then be rate limiting and the reactant concentration gradients would be very
steep. The products of reaction (1) and (2) are kept in the nonpolar phase but glycerol will
obviously back diffuse to the polar phase. The situation is made more complex owing to the
fact that this polar phase is initially constituted of methanol, the density of which (0.79
g/cm3 at RT) is lower than that of oil (0.92 g/cm3 at RT). As glycerol (1.21 g/cm3 at RT)
enters the polar phase, the density of this phase increases and overcomes the oil density as
the glycerol mole fraction reaches a value on the order of 25 %. Thus whereas the low
conversion droplets of the polar phase tend to move upward, the high conversion ones tend
87
to move downward. At steady state there is therefore a spatial distribution of droplets of
varying compositions with the glycerol concentrated ones having a tendency to settle.
Moreover since reactions (1–3) are reversible this concentration depending settling effect
which tends to move glycerol from the active zone, should be beneficial for the FAME
production rate.
Enhanced mass transfer is however not the only possible effect of ultrasounds on
the overall transesterification rate. The cavitation process may also intervene. Owing to the
pressure fluctuations associated with the ultrasound wave some gas bubbles are formed and
compressed to explosion initiating extremely high temperatures (several thousands K) for
extremely short period of time (on the order of milliseconds). Such effects associated with
the intense energy dissipation at the ultrasound generator tip is likely to also affect the rates
of reactions (1), (2) and (3). It may even be hypothesized that the high curvature for small
size systems, (curvature is a parameter of the gas-liquid equilibrium of the methanol
droplets) and the low methanol vapor pressure facilitate the cavitation of methanol in this
system.
88
3.4 Conclusions
The combined effects of high dispersion of the polar phase and cavitation result in a
dramatic increase of the global rate of methanolysis of triglycerides under ultrasounds. The
original aspect of the present work conclusions is a vision of how ultrasound waves affect
the transesterification reactions rates. Ultrasounds generate a fine emulsion of the biphasic
system in the entire reactor volume. This will obviously affect interphase mass transfer.
The catalytically active volume is however restricted to a small part of the reaction medium
located in the immediate vicinity of the sonotrode probe. Within this volume fraction the
extremely high reaction rate is very likely associated with the effects of cavitation. Our
results indicate also that the design of the ultrasonic reactor for large scale production of
biodiesel will not follow the usual modelling procedure of catalytic reactors. The optimal
design will involve a series of very small volume continuous flow ultrasonic reactors with
intercalated settling tanks for continuous separation of the glycerol rich polar phase (Thanh
et al. 2010; Delavari, Halek, and Amini 2015). This separation will allow to push chemical
equilibrium represented by reactions (1), (2) and (3) toward complete conversion of TG to
FAMEs at initial methanol/oil molar ratio close to the stoichiometric value of 3.
Acknowledgments: The authors are grateful to NSERC for financial support.
89
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[35] Refaat, A. A., El Sheltawy, S. T., Sadek, K. U. Optimum reaction time, performance
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assisted heterogeneous biodiesel production from palm oil: A response surface
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[39] Santos, F. F. P., Rodrigues, S., Fernades, F. A. N. Optimization of the production of
biodiesel from soybean oil by ultrasound assisted methanolysis. Fuel Process Technology,
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process for vegetable oil transesterification. Ultrason. Sonochem, 2007, 14, 413–417.
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vegetable oil by means of ultrasound energy. Ultrason. Sonochem, 2005, 12, 367–372.
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biodiesel production from waste cooking oil. Applied Energy, 2013, 104, 683–710.
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step continuous ultrasound assisted production of biodiesel fuel from waste cooking oils: A
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96
Chapter 4.
Triglycerides Transesterification Reactions under Ultrasounds
Published in ChemistrySelect, 1(18), 6008-6010, 2016.
Kiran Shinde and Serge Kaliaguine a,*
Department of Chemical Engineering Laval University, Quebec, G1 V 0 A6, Canada
97
Résumé
Des exemples de réactions de transestérification des triglycérides par des alcools à
chaines courtes comme l’éthanol, le butanol ou le glycérol sont utilisés pour illustrer
l’importance de la cavitation dans les réactions assistées par les ultrasons. Il a été montré
que des additions mineures d’une substance à tension de vapeur basse dans les conditions
de réactions résultent dans des améliorations significatives des vitesses de réaction en
améliorant la cavitation.
98
Abstract
Examples of triglyceride transesterification reactions by small alcohols such as
ethanol, butanol and glycerol are used to illustrate the significance of cavitation in
ultrasound assisted reactions. It was shown that minor addition of a compound with low
vapor tension in the reaction conditions results in significant enhancements in reaction rate
by promoting cavitation.
99
4.1 Introduction
The most studied transesterification of triglycerides is the reaction of vegetable or
algae oil or animal fat with methanol yielding fatty acid methyl ester (FAME) blends
designated as biodiesel[1]. There are however other triglyceride transesterifications of
commercial significance- First glycerolysis which uses glycerol instead of methanol is
important for the production of monoglycerides which are commonly used as surfactants
and emulsifiers in the food, pharmaceutical, cosmetic and lubricant industries [2]. Other
reactions of interest would be making use of ethanol or butanol of agricultural origin to
replace methanol, which is mostly of fossile origin, in production of FAEE or FABE
yielding a biodiesel completely issued from green sources. Ultrasounds have been shown to
accelerate drastically the production of FAME in the presence of a homogeneous, usually
basic, catalyst [3–8]. The mechanism of this effect is thought to be associated to the high
dispersion of the biphasic system yielding high interphase surface area and therefore
enhanced interface mass transfer. In a recent work [9] conducted in a continuous ultrasound
reactor, we have also demonstrated that cavitation has another even more important effect.
Cavitation is the phenomenon associated with the high pressure fluctuations created by the
acoustic wave. Microbubbles are formed during the negative pressure excursions and these
are violently imploding creating high speed jets during the positive pressure excursions.
These effects result in extreme pressure and temperature peaks generated at the implosion
site for a few microseconds [10]. The microbubbles are obviously mainly constituted of the
more volatile component of the system, which in FAME production in methanol. The
present work was undertaken to investigate the possible effect of minor methanol or other
100
low vapor tension component additions on the accelerating phenomenon in triglycerides
transesterification reactions due to ultrasounds.
4.2 Results
4.2.1 Glycerolysis
Figure 4-1 reports the evolution of TG conversion as a function of reaction time in
five experiments. It shows that the initial
Figure 4-1. Glycerolysis of Canola oil at 140°C A-Stirring without US; B-US
without solvent addition; C-US with dropwise addition of THF; D- US with
0.33 wt % octane; E- US with 0.33 wt % nonane (with respect to oil).
conversion rate is about 50 times higher under ultrasounds (curves B, C and D) than in the
purely catalytic system (curve A) whether or not solvent was added. This low rate of
glycerol reaction in absence of ultrasound is translated into the high temperature of 230°C
needed to reach 58% conversion in 40 mL/min in the commercial process [11]. Performing
this reaction under ultrasounds will therefore have important consequences for future
developments of this industrial process. Dropwise addition of THF (boiling point 66 °C)
led to minor enhancement of reaction rate after 30 min reaction time (curve C) compared to
0
10
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30
40
50
60
70
80
90
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0 100 200 300
Co
nversi
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%
Reaction time (min)
A
B
CD
E
101
the experiment run under ultrasounds but in absence of any solvent (curve B). This limited
enhancement may be related to the high rate of evaporation of THF at this temperature. It
was therefore tried to add to the reaction medium a small amount of a higher boiling point
component. Curve C was obtained by adding 0.33 wt % (with respect to oil) octane (boiling
point 125.1-126°C). A still minor yet significant increase in reaction rate was also observed
after 30 min reaction. The addition of a less volatile compound (0.33 wt % nonane-boiling
point 150.4-151°C) had the opposite effect, (curve E) decreasing reaction rate compared to
curve B.
4.2.2 FAME transesterification by glycerol
In order to conduct this reaction, a FAME mixture was produced by complete
conversion of Canola oil by conventional transesterification by methanol in the presence of
0.5 wt % KOH as catalyst at 45 °C for 24 hours. This blend was then reacted with glycerol
in a biphasic reaction conducted at 140ºC. The results are reported in Figure 4-2. Cure A
shows the FAME conversion vs time at
Figure 4-2. FAME conversion by reaction with glycerol at 140 °C A-US and F:G*=
1:1; B-US and F:G=1:2; C- stirring no US, F:G=1:1; D- stirring no US, F:G=1:2; E- US
with 0.33 wt % octane; F:G=1:1, F- US with 0.33 wt % octane F:G=1:2. F:G*=FAME to
glycerol molar ratio.
0
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30
40
50
60
70
80
90
100
0 100 200 300
con
v. in
%
Time in min
F
A
BE
D
C
102
FAME:glycerol molar ratio 1:1 in the presence of ultrasounds. Raising the glycerol
concentration to a FAME:glycerol of 1:2 yielded a neat increase in reaction rate as shown
by curve B. The corresponding reference curves obtained in absence of ultrasounds are
reported as curves D and C. When 0.33 wt % octane was added to the same reaction media
as those in curves A and B, curves E and F were obtained respectively. A very significant
increase in reaction rate was observed in the conditions of curve A (F:G= 1:1) as indicated
by curve E. In the case of curve B the rate enhancement was only minor (curve F compared
to curve to curve B).
4.2.3 FAME transesterification by ethanol
Figure 4-3 shows a comparison of triglyceride conversion as a function of time on
stream using either ethanol (curve A) or a
Figure 4-3. Transesterification of triglycerides by ethanol. Catalyst KOH 0.5 wt %;
ethanol/oil molar ratio 4:1; residence time 75 s; Temperature 35°C; ultrasound amplitude
60%.
1% methanol solution in ethanol (curve B) as reactant. The reaction conditions were
a reaction temperature of 35ºC and an ethanol/oil molar ratio of 4:1. The residence time in
the continuous flow reactor was 75 s and the sonotrode amplitude 60% (35 W/cm2). The
0
10
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30
40
50
60
70
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90
100
0 1 2 3 4 5 6
TG
Co
nversi
on
%
Time on stream (min)
B
A
ethanol + 1% methanol
ethanol
103
catalyst was potassium hydroxide and its concentration was 0.5 wt % related to oil. In these
conditions introducing 1% methanol yields a spectacular increase in triglyceride
conversion, well above the minor increase which corresponds to reaction of TG with the
added methanol. Actually the HPLC analysis allowed to quantify the FAME formed during
this test to less than 1% of the increase in fatty acid ethyl ester (FAEE).
4.2.4 FAME transesterification by butanol
Figure 4-4 reports a comparison of triglyceride conversion as a function of time on
stream using either butanol (curve A) or a
Figure 4-4. Transesterification of triglycerides by butanol. Catalyst KOH 0.5 wt %;
butanol/oil molar ratio 4:1; residence time 75 s; Temperature 35oC; ultrasound amplitude
60%.
1% methanol solution in butanol (curve B). The reaction conditions were same as in
the test described in Figure 3. The butanol/oil molar ratio was also 4:1. It is also observed
that triglyceride conversion as well as fatty acid butyl esters (FABE) are significantly
enhanced by adding 1% methanol in the alcohol feedstock.
0
10
20
30
40
50
60
70
80
90
0 2 4 6
TG
Co
nversi
on
%
Time on stream (min)
B
A
butanol + 1% methanol
butanol
104
4.3 Discussion and conclusion
As hypothesized in our recent publication [9], the most important effect of
ultrasounds on the rate of triglyceride transesterification transesterification is due to
cavitation. This is in line with recent literature on the effect of mechanical cavitation on the
rate of biodiesel production [12]. This effect is in addition to the interphase mass transfer
enhancement in this biphasic reaction due to the high dispersion of the polar phase. Both
effects are not completely independent from each other as cavitation is associated with gas
bubbles formation which not only depends on the liquid vapor equilibrium of the more
volatile constituent but also on the curvature of liquid dispersion. The results of this work
show that it is possible to significantly increase the rates of ultrasound assisted reactions by
introducing traces of a volatile in the reaction conditions compound, which promotes the
beneficial effect of cavitation.
105
4.4 Supporting Information
Experimental: Materials: Potassium hydroxide (85+%) was purchased from Sigma-
Aldrich Chemicals and is dissolved in alcohol by means of stirring, 99.7 % glycerol was
bought from BDH, methanol ( HPLC grade) was from Fisher Scientific, ethanol and n-
butanol with more than 99% purity were purchased from Alfa Aesar, THF (HPLC grade)
was obtained from Fisher Scientific. Canola oil as a vegetable oil was purchased from
Messina Chemicals. Catalytic tests: Glycerolysis tests were performed in a batch reactor
whereas transesterification involving ethanol and butanol was conducted in a continuous
flow reactor. The ultrasonication batch experiments were carried out in a water jacketed 67
ml glass reactor using an ultrasound generator UP 200st (Hielscher Ultrasonic) with probe
diameter 7 mm, at 120W and 60% amplitude. For glycerolysis tests the reaction
temperature was controlled at 140±0.5°C, canola oil to glycerol molar ratio was 1: 3 and
potassium hydroxide catalyst 5 wt% of canola oil. The glycerolysis reaction was conducted
in three different conditions namely in absence of any additional solvent or by adding a
solvent dropwise (5 drops /min) for the whole duration of the test. In one case this solvent
was THF (boiling point 66°C). In the case of glycerol reaction with FAME the same batch
reactor was used at the same 140±0.5°C temperature with 5 wt % KOH with respect to
FAME as catalyst and FAME / glycerol molar ratio at either 1:1 or 1:2. Control batch
experiments were carried out in the 67 ml glass reactor, stirred at 200 rpm, at 140±0.5°C
temperature. Conditions similar to the ultrasonication experiments were adopted, with
mechanical stirring replacing ultrasounds. The continuous flow experiments were
performed in the set up described in our previous work [9]. This system uses the above
mentioned ultrasound generator (Hielscher Ultrasonic with 7 mm, sonotrode, 120 W, UP
106
200 st). The continuous flow temperature controlled glass reactor (67 ml) is fed by a
Seepex dosing pump (group D) provided with a small feed tank continuously refilled using
two peristatic pumps (Watson- Marlow 101 U/R). One of these was for the canola oil and
the other one for the alcohol catalyst solution. The relative flow rates of these liquids were
set in order to control alcohol/oil molar ratio, whereas the sum of these flow rates was equal
to the Seepex pump flow rate in order to avoid accumulation and phase separation in the
feed tank. Analysis: Before analysis the two phase products were centrifuged using a
Beckman Avanti: J. 301 centrifuge machine. The polar phase samples were analyzed for
monoglycerides (MG), diglycerides (DG), triglycerides (TG) and methyl esters (FAME)
using UHPLC (UltiMate 3000 Dionex) equipped with column AcclaimTM 120, C18 5μm
120 A, 4.6 x100 mm and a UV (Thermo SCIENTIFIC Dionex UltiMate 3000) variable
wavelength detector. Acetonitrile, hexane and isopropanol were used as HPLC solvents.
The solvent flow rate was 0.5ml/min. The sample injection volume was 10μL and the peak
identification was made by comparing the retention times of the sample components and
the standards. The analysis of each sample was repeated three times.
107
4.5 Reference
[1] A. Talebian-Kiakalaieh, N. A. S. Amin, H. A. Mazaheri. Appl. Energy. 2013, 104, 683–
710.
[2] N. Sonntag, J. Am. Oil Chem. Soc. 1982, 59, 795 A
[3] a) M. A. Kelkar, P. R. Gogate, A. B. Pandit. Ultrason. Sonochem., 2008, 15, 188–194
.b) C. Stavarache, M. Vinatoru, R. Nishimura, Y. Maeda. Ultrason. Sonochem., 2005, 12,
367– 372. c) V. G. Deshmane, P. R. Gogate, A. B. Pandit. Ind. Eng. Chem. Res., 2009, 48,
7923–7927. d) F. F. P. Santos, S.Rodrigues, F. A. N. Fernandes. Fuel Process. Technol.,
2009, 90, 312–316.
[4] M. Maghami, S. M. Sadrameli, B. Ghobadian. Appl. Therm. Eng., 2015, 75, 575–579.
[5] X. Yin, Q. You, H. Ma, C. Dai, H. Zhang, K. Lin, Y. Li. Ultrason. Sonochem., 2015,
23, 53–58.
[6] J. P. Maran, B. Priya. Ultrason. Sonochem., 2015, 23, 192–200.
[7] D. D. Pukale, G. L. Maddikeri, P. R. Gogate, A. B. Pandit, A. P. Pratap. Ultrason.
Sonochem., 2015, 22, 278–286.
[8] H. D. Hanh, N. T. Dong, C. Starvarache, K. Okitsu, Y. Maeda, R. Nishimura, Energy
Convers. Manage., 2008, 49, 276–280.
[9] K. Shinde, B. Nohair, S, Kaliaguine. Int. J. Chem. React. Eng., 2016, Doi:
10.1515/ijcre-2016-0070.
[10] T. J. Mason, Sonochemistry, NewYork: Oxford University Press, 1999, p. 2– 30.
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[11] H. Noureddini, D. W. Harkey, M. R. Gutsman. Chemical and Biomolecular
Engineering Research and Publications, 2004.
[12] R. Gordon, I. Gorodnitsky, V. Grichko. (Cavitation Technologies, Inc., Chatsworth,
CA, (US)), 8, 981, 135 B2, 2015.
109
Chapter 5.
Ultrasound biodiesel production using various homogeneous
catalysts and their separation over silica cation exchanger
columns
Kiran Shinde1, François Béland2 and Serge Kaliaguine1
1Department of Chemical Engineering Laval University, Quebec, G1 V 0 A6, Canada.
2SiliCycle Inc., 2500, Boul. du Parc-Technologique, Québec City, Québec G1P
4S6, Canada.
(This manuscript is will soon be submitted for publication)
110
Résumé
Le biodiesel (BD) est un carburant liquide constitué d’esters d’acides gras
monoakyle à longues chaines dérivés d’huiles végétales ou des graisses animales.
Récemment, le biodiesel a reçu une attention supplémentaire et d’intenses recherches ont
été effectuées dans ce domaine aux quatre coins du globe, dû à son impact environnemental
plus faible comparativement aux combustibles fossiles conventionnels. Dans ce travail, une
comparaison de la transestérification de l’huile de canola avec du méthanol sous ultrasons
ou sous agitation mécanique a été faite. Les aspects généraux du processus de
transestérification et l’étude comparative de différents types de catalyseurs (NaOH, KOH,
CH3ONa, tétraméthyle d’hydroxyde d’ammonium et de guanidines) sont décrits. Une
attention spéciale est portée sur la réaction de transestérification sous ultrasons en utilisant
une guanidine comme catalyseur et la récupération de cette guanidine à partir du mélange
réactionnel en utilisant des colonnes de séparation « SiliaPrep Propylsulfonic Acid ».
111
Abstract
Biodiesel (BD) is a liquid fuel that consists of mono alkyl esters of long chain fatty
acids derived from vegetable oil or fat. Recently, biodiesel has received additional attention
and intense research is performed in this field all over the world due to its lower
environmental impact compared to the conventional fossil fuels. In this work, a comparison
of transesterification of Canola oil with methanol under ultrasound or mechanical stirring is
reported. The general aspects of ultrasound transesterification process and comparative
study of different types of catalysts (NaOH, KOH, CH3ONa, tetramethyl ammonium
hydroxide and guanidines) are described. Special attention is given to ultrasound
transesterification reaction by using guanidine as a catalyst and regeneration of guanidine
from reaction mixture by using SiliaPrep Propylsulfonic Acid separation column.
112
5.1 Introduction
Fossil fuel is the world’s most primary source of energy. The demand for fossil fuel
is increasing day by day. A projection demand in 2030 will be 116 million barrels per day
[1]. Therefore, searching for alternative sources has become of primary importance in the
field of energy production. In this direction, the crop based oil energy sources, such as
biodiesel and other biofuels, can be one of the reliable sources. Biodiesel (BD) is a liquid
fuel that consists of mono alkyl esters of long chain fatty acids derived from vegetable oil
or fat. Most importantly, BD is free from sulfur and aromatic components, which makes it
environmentally benign. The production of BD is widely conducted through
transesterification reaction by using homogeneous and heterogeneous catalysts [2-3].
Generally, these catalysts are acidic [4], base [5, 6] or enzymatic [7] in nature and each has
its own pros and cons. The most notable catalysts used in the production of BD are the
homogeneous catalysts that include KOH, NaOH, CH3OK and CH3ONa. Ionic liquids may
also be good potential catalysts. Muhammad et al [8] reported an overview of the
possibility of applying ionic liquids in biodiesel production.
The homogenous catalysts can be split into two categories, which are acid and base
catalysts. The process of using homogenous catalysts causes difficulties in their separation
and cleaning from the products. In BD production, the produced methyl esters and glycerol
must be separated and purified to remove the catalyst, a process that is time consuming and
requires expensive separation steps [9]. Another main disadvantage of base catalysts is the
side reactions forming soaps, thus decreasing the BD yield [10]. Using homogeneous
amine-based catalysts, deals with most of the economical and environmental drawbacks of
the traditional transesterification process. This process makes the removal of the typical
113
catalytic species easier and the produced methyl ester and glycerol are also free of alkali
metals such as Na, K, Ca and Mg [11, 12]. The most important feature in selecting a
catalyst is its high activity or high reaction rate. The BD process faces various problems
related to insolubility of the oil and alcohol, which leads to poor mass transfer rate. This
requires higher methanol-oil molar ratio, long reaction time, higher catalyst content, high
temperature and high stirring.
It is found that the conversion efficiency of oil into FAME using ultrasonication
was higher than under mechanical stirring [13-15]. Biodiesel production by using ultrasonic
homogenization has developed as an expanding research area for the past two decades [16–
19]. The use of ultrasound is applied in BD production as the ultrasonic field is known to
produce chemical and physical effects that arise from the collapse of cavitation bubbles
[20]. Consequently, BD production from seed oils and waste oils has been improved with
the application of the ultrasound. Stavarache et al. [16] reported that with high frequency
ultrasound (40 kHz), the transesterification process increases quickly with an increased
biodiesel yield. Thereby, several new BD production plants use the ultrasonication
technique. Shinde et al. [21] also reported a detailed study of the continuous biodiesel
production by using ultrasounds. They showed a systematic experimental analysis of
ultrasound assisted continuous biodiesel production using canola oil in the presence of
methanol and sodium methoxide as catalyst. The effects of various reaction parameters
such as residence time, catalyst concentration, reaction temperature, ultrasounds amplitude
and power, methanol/oil molar ratio were established.
Singh et al [22] observed a high decrease in reaction time and achieved conversion
efficiencies that were never reached previously in such a short reaction time. They showed
114
that, by using ultrasonication, a biodiesel yield in excess of 99% can be achieved in a
remarkably short time duration of 5 min. Kumar et al. [23] carried out the
transesterification of coconut oil and reached a maximum yield of 98% using an amplitude
of 60% and 0.3 cycles per second. Under these conditions, reaction temperatures were
considerably high (72 and 89 oC) and preheating before transesterification due to the high
melting point of coconut oil was required. Temperature is a very complicated factor to
control in experiments with probes, especially if the reaction mixture is heated after being
sonicated. Boffito et al. [24] reported that ultrasonic-assisted mixing device they designed,
converts most of the triglycerides with methanol within one minute of pulsed ultrasonic
irradiation in presence of KOH catalyst and they showed the reaction with ethanol and
isopropanol is also faster than in classical batch reactors. Martinez-Guerra, and Gude [25]
reported pulse sonication (batch reaction) effects using ethanol, methanol and ethanol-
methanol mixtures in the conversion of waste cooking oil into biodiesel in presence of
sodium hydroxide catalyst. A maximum biodiesel yield of 99% was obtained for pulse on-
off combination of 7s -2s at 150W power output, and reaction conditions of 9:1 alcohol to
oil molar ratio, 1 wt % of sodium hydroxide, and 1.5 min reaction time. Different examples
of triglyceride transesterification reactions by using ethanol, butanol and glycerol were used
to illustrate the significance of cavitation in ultrasound assisted reactions [26]. Reyman et
al. [27] monitored the ultrasound-assisted conversion of triglycerides to fatty acid methyl
ester (FAME) by recording the ratio of infrared peak intensities at 1437 and 1464 cm-1. The
proposed infrared method turned out to be inexpensive and independent of the type of oil.
For the FAME production proper mixing is critically important to create sufficient
contact between oil and alcohol. In this context, ultrasonication helps increasing the liquid–
115
liquid interfacial area through emulsification, which is also important for the formation of
vapor bubbles and cavitation bubbles in viscous liquids. In this present work NaOH, KOH,
CH3ONa, tetramethyl ammonium hydroxide and two guanidines are tested for
transesterification reaction in a batch reactor both under ultrasound and mechanical stirring.
The increasing popularity of biodiesel has generated great demand for its commercial
production methods, which in turn calls for the development of new technologies. In the
case of the tested guanidine, catalyst recovery from the reaction mixture was performed by
using a commercial SiliaPrep propylsulfonic acid column.
5.2 Experimental
5.2.1 Materials
The Canola oil used in the transestrification reaction was a commercial edible oil
with characteristic fatty acid composition C16:0 (4 %), C18:0 (2 %), C18:1 (56 %), C18:2
(26 %), C18:3 (10 %) and average molecular weight 876.6 Da. Minor amounts of long
chain (C20:0-C24:0) saturated fatty acids occurred mostly in the 1- and 3-positions.
Metallic sodium, KOH pellets, NaOH pellets, tetramethyl ammonium hydroxide, 1, 1, 3, 3
Tetramethylguanidine, 1, 3 diphenyl guanidine, ammonia solution (2.0 M in methanol) and
dry methanol were purchased from Sigma-Aldrich. Analytical standards of
monoglycerides, diglycerides, triglycerides and fatty acid methyl esters were also
purchased from Sigma-Aldrich. Propylamine, dicyclohexylcarbodiimide and n-octylamine
were purchased from sigma Aldrich. Si-Propylsulfonic acid silica was graciously provided
by Silicycle Inc., Québec, Canada.
116
5.2.2 Catalyst preparation
KOH and NaOH solutions were prepared by using KOH and NaOH pellets, 0.5 wt
% with respect to oil dissolved in methanol. CH3ONa was prepared by reacting dry
methanol with sodium metal in ambient conditions. The sodium methoxide content in
methanol was adjusted depending on the targeted catalyst/oil ratio.
Synthesis of Propyl-2, 3 dicyclohexylguanidine (A) consists of mixing 5 g
propylamine and 6.5 g of dicyclohexylcarbodiimide with 15 g of tetrahydofuran solvent
and refluxing at 70 ºC for 24h. The final mixture, which is colorless, is concentrated at 60
ºC using a rotary evaporator. Proton NMR analysis then shows a conversion of more than
99.5% of the Propyl-2, 3 dicyclohexylcarbodiimide. NMR Data: 0.83-CH2CH2CH3, 1.94 -
4H, 1.98 – 4H, 2.11- 4H, 2.90 – Cyclohexane, 3.38 – 3H [28].
1, 3- dicyclohexyl 2 n-octylguanidine (DCOG) (B) was prepared by mixing of 20
ml dry tert-butanol, octylamine 2.58 g and 2.06 g of dicyclohexylcarbodiimide, stirred
under nitrogen in a 100 ml two necked flask at 100 ºC for 19 h. The solvent was evaporated
and the product was distilled. The final yield was 91%. Elemental analysis: Calc.: C 75.2%,
H 12.7%, N 12.3%; Found: C 75.0%, H 12.7%, N 12.3% [29].
Tetramethyl ammonium hydroxide, 1, 1, 3, 3 Tetramethylguanidine (TMG) (C) and
1, 3 diphenyl guanidine (DPG) (D) were purchased from sigma Aldrich.
5.2.3 Ultrasonic Irradiation Unit
Hielscher ultrasonic processor UP 200St was used for the transesterification
reaction. The ultrasound generator operates at 26 kHz (200W) using 60% amplitude. The
117
sonotrode is made of titanium alloy. The ultrasonic probe had a 7 mm tip diameter.
Temperature controller (Barnant Thermocouple Thermometer). The ultrasound batch glass
reactor had a volume of 67 ml. For mechanical stirring a 250 ml round bottom flask batch
reactor was used. A BECKMAN AvantiTM J-30I centrifuge machine was employed for
phase separation of the products.
5.2.4 Transesterification reaction
The transesterification reaction tests were carried out by using ultrasound processor
UP 200St. The sonotrode is attached with the transducer which produces ultrasonic
irradiation in the mixture. There is an integrated arrangement for supporting the glass batch
reactor (67 ml) so as the transducer sonotrode should be submerged at the separating
boundary of two immiscible liquids. The sonotrode of the transducer was submerged
approx. 2-3 cm in the reactive mixture of methanol and canola oil. The temperature (35 ºC)
of the reaction mixture was controlled using a thermostated water bath. The reaction started
when a mixture consisting of desired amount of catalyst was dissolved in methanol and this
mixture is mixed with vegetable oil. Cavitation is created by the irradiation of power
ultrasonic with sufficient energy in immiscible liquids. As a result micro fine bubbles are
formed. During reaction samples were collected for analysis at different time interval.
Mechanical stirring transesterification reaction tests were carried out by using 50g
of canola oil and 12g of methanol (6:1 molar ratio methanol to oil) in round bottom flask
(250ml). Media with some other methanol to oil ratios 4:1 and 3:1, were also prepared.
Different amounts of homogeneous catalyst (0.25, 0.5, 1.0, 1.5 2.0 % relative to oil) were
used. The reaction mixture is mechanically stirred at 65 ºC for different time durations.
118
Both polar and non-polar phases of the reacted mixture were separated by
centrifugation. Samples of the non-polar phase (FAME) were analyzed by UHPLC.
5.2.5 Methyl ester analysis
The polar phase samples contain monoglycerides (MG), diglycerides (DG),
triglycerides (TG) and methyl esters (FAME). These were analyzed by using UHPLC
(UltiMate 3000 Dionex) equipped with column AcclaimTM 120, C18, 5 μm, 120, A 4.6 ×
100 mm, and a UV (Thermo SCIENTIFIC Dionex UltiMate 3000) variable wavelength
detector. Hexane, acetonitrile, and isopropanol were used as HPLC solvents. The solvent
flow rate was 2.0 ml/min. The sample injection volume was 10 μL and the peak
identification was made by comparing the retention time between the sample and the
standards. The analysis of each sample was repeated three times.
5.3 Results and discussion
5.3.1 Experimental data of biodiesel production
Canola oil is taken for this experiment with a methanol/oil molar ratio (6:1,4:1,3:1).
Catalysts (NaOH, KOH, CH3ONa, Tetramethyl ammonium hydroxide and Guanidines)
were selected and used in (0.25, 0.5, and 1.0%) by weight of oil. Then the mixture of
methanol and catalyst was stirred until the catalyst dissolves completely. This mixture was
then contacted with canola oil. The mixture of oil, methanol and catalyst come in contact
with the ultrasonic processor (Hielscher ultrasonic UP 200St). During the reaction the
temperature was kept at 35 ºC. The product polar and non-polar phases were separated by
centrifugation for HPLC analysis of the non-polar phase.
119
In this study experiments have been performed to prepare biodiesel from canola oil
by using both ultrasonication and mechanical stirring. The main aim of all these
experiments is to compare the reaction time at specified molar ratio for the biodiesel
production with maximum yield between ultrasound assisted process and mechanical
stirring in batch reactors. Our interest in the work is to reduce the use of alcohol and
catalyst (NaOH, KOH, CH3ONa and Tetramethyl ammonium hydroxide) because these are
pollutants for the water. Biodiesel production on industrial scale uses large amounts of
catalyst, that will be discharged in rivers or open land, and lead to environmental problems.
Another important objective was to collect experimental data using some
guanidines as catalysts. These non-ionic organic bases gave promising results for industrial
scale, economical and environmentally friendly biodiesel production. In addition they
might be more easily separated from the products than ionic bases.
5.3.2 Catalyst concentration and the effect of methanol to oil ratio
Fig. 5-1 shows the effect of catalyst amount and methanol to oil ratio on
transesterification of the canola oil with sodium methoxide catalyst. The experimental
observations reported in Fig 1 confirm that ultrasounds have no effect in absence of
catalysts. Within one minute of time duration more than 80% conversion was reached in
presence of 0.5 wt % catalyst. Therefore, all remaining experiments were performed by this
concentration of catalyst. Another benefit of a lower concentration of catalyst is to limit
soap formation.
120
Fig. 5-1. Effect of catalyst concentration on triglyceride conversion Batch reactor.
Catalyst (CH3ONa), methanol:oil ratio ( 6:1, 4:1, 3:1 ) ultrasound amplitude 60%,
temperature 35 ºC, reaction time 1 min.
The transesterification reaction is a series of three successive and reversible
reactions transforming the triglyceride into a diglycerides, a monoglycerides and, finally,
into glycerine and the fatty acid methyl esters. If an excess of alcohol is used glycerine is
formed in substantial amount and the yield of methyl ester is improved. Transesterification
reaction can be complete if a large quantity of alcohol is used (such as alcohol:oil >30:1).
5.3.3 Comparison between ultrasound and mechanical stirring in
presence of CH3ONa catalyst.
The molar ratio of alcohol to oil is one of the important factors that affect the TG
conversion efficiency [30]. The comparison of ultrasound and mechanical stirring for molar
0
10
20
30
40
50
60
70
80
90
100
0 0.5 1 1.5 2 2.5
TG C
on
vers
ion
in %
Wt % Catalyst
6:1
4:1
3:1
121
ratio (6:1, 4:1, 3;1) shown in Figure 5-2 and Figure 5-3, illustrates the relationship between
the TG conversion when exposing reactants to ultrasound or mechanical stirring conditions
respectively. The reaction conditions were 0.5 wt % catalyst (CH3ONa), in presence of
different molar ratios of oil to methanol and a temperature of 35 ºC with US and 65 ºC in
the stirred reactor. It can be seen that using ultrasonic method reaction time is much less
compared to the conventional method using mechanical stirring.
Fig. 5-2. Ultrasound biodiesel production in batch reactor, catalyst (CH3ONa),
methanol:oil ratio ( 6:1, 4:1, 3:1 ) ultrasound amplitude 60%, 0.5 wt %, temperature 35 ºC.
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350
TG c
on
vers
ion
in %
Reaction time (sec)
6:1
4:1
3:1
122
Fig. 5-3. Mechanical stirring biodiesel production in batch reactor, catalyst
(CH3ONa), methanol:oil ratio ( 6:1, 4:1, 3:1 ) 0.5 wt %, temperature 65 ºC.
5.3.4 Comparison between ultrasound and mechanical stirring in
presence of KOH catalyst
Similar comparison has been done for the canola oil for different molar ratio (6:1,
4:1, 3:1) and 0.5 wt % KOH catalyst which is shown in Figure 5-4 and figure 5-5
respectively. A triglyceride conversion more than 80% was recorded in a very short period
of time by using ultrasound technique. This conversion is very high as compared to
mechanical stirring. Reaction time show similar pattern as above. Therefore, by using
ultrasound we can save lot of time and it is very safe because it works at 35 ºC temperature.
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150
TG c
on
vers
ion
in %
Reaction time in (min)
6:1
4:1
3:1
123
Fig. 5-4. Ultrasound biodiesel production in batch reactor, catalyst (KOH),
methanol:oil ratio ( 6:1, 4:1, 3:1 ) ultrasound amplitude 60%, 0.5 wt %, temperature 35 ºC.
Fig. 5-5. Mechanical stirring biodiesel production in batch reactor, catalyst (KOH),
methanol:oil ratio ( 6:1, 4:1, 3:1) 0.5 wt %, temperature 65 ºC.
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350
TG c
on
vers
ion
in %
Reaction time (sec)
6:1
4:1
3:1
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80 100 120 140
TG c
on
vers
ion
in %
Reaction time in (min)
6:1
4:1
3:1
124
5.3.5 Comparison between ultrasound and mechanical stirring in
presence of NaOH catalyst.
NaOH is also another catalyst reported for biodiesel production, Figure 5-6 and 5-7
shows the biodiesel production by using NaOH catalyst by using ultrasound and
mechanical stirring conditions respectively. The reaction conditions were kept constant
such as 0.5 wt % NaOH catalyst, in presence of different molar ratio of oil to methanol and
temperature is 35 ºC and 65 ºC. A triglyceride conversion more than 80% was recorded
under ultrasound which was higher than the value mechanical stirring method in a very
short period of reaction time.
Fig. 5-6. Ultrasound biodiesel production in batch reactor, catalyst (NaOH),
methanol:oil ratio ( 6:1, 4:1, 3:1 ) ultrasound amplitude 60%, 0.5 wt %, temperature 35 ºC.
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400
TG c
on
vers
ion
in %
Reaction time (sec)
6:1
4:1
3:1
125
Fig. 5-7. Mechanical stirring biodiesel production in batch reactor, catalyst (NaOH),
methanol:oil ratio ( 6:1, 4:1, 3:1 ) 0.5 wt %, temperature 65 ºC.
5.3.6 Comparison between ultrasound and mechanical stirring in
presence of Tetramethyl ammonium hydroxide catalyst.
Figure 5-8 and figure 5-9 shows the comparative study of biodiesel production by
using ultrasound and mechanical stirring conditions respectively. The catalyst amount was
3 wt % (Tetramethyl ammonium hydroxide), in presence of different molar ratio of oil to
methanol and temperature is 35 ºC and 65 ºC. A triglyceride conversion more than 80%
was recorded by using ultrasound technique in a short time. This reaction time is
comparatively very less as compared to mechanical stirring.
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80 100 120 140
TG c
on
vers
ion
in %
reaction time (min)
6:1
4:1
3:1
126
Fig. 5-8. Ultrasound biodiesel production in batch reactor, catalyst (Tetramethyl
ammonium hydroxide) 3 wt %, methanol:oil ratio ( 6:1, 4:1) ultrasound amplitude 60%,
temperature 35 ºC.
Fig. 5.9. Stirring biodiesel production in batch reactor, catalyst (Tetramethyl
ammonium hydroxide) 3 wt %, methanol:oil ratio ( 6:1, 4:1), temperature 35 ºC.
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350
TG c
on
vers
ion
in %
Reaction time (sec)
6:1
4:1
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120 140
TG c
on
v. In
%
Time in min
6:1
4:1
127
5.3.7 Comparison between ultrasound and mechanical stirring in
presence of guanidines as catalysts.
Amount of methanol is very important factor that affect the conversion of
triglyceride (TG) to FAME. Following Fig 5-10 shows the slight increase in TG conversion
in presence of 4:1 ratio and guanidine A. It is well know that excess of methanol bring the
reaction equilibrium towards the products and produce more FAME.
Fig. 5.10. Ultrasound biodiesel production in batch reactor, catalyst (Guanidine A) 3
% mol, 4:1 and 3:1 (Methanol: Canola oil) 3 % catalyst 60% amplitude, 35 ºC.
The effect of catalyst amount is also very important that affects the reaction. The
experiments were carried out by using catalyst (guanidine A) concentration between 3 and
5% mol while other parameters were fixed at 35 ºC. Fig 5-11 clearly show the increase of
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350
TG c
on
vers
ion
in %
Reaction time (sec)
4:1
3:1
128
the amount of catalyst (guanidine A) from 3 to 5% results in an increase in FAME yield,
from 89 to 95 % .
Fig. 5.11. Ultrasound in batch reactor 4:1 (Methanol : Canola oil ), Catalyst
(Guanidine A) 3 and 5 % mol, 60% amplitude, temperature 35 ºC.
Figure 5-12 and 5-13 shows the ultrasound reaction and mechanical stirring
reaction. In presence of ultrasound, guanidine (A) and guanidine (B) transesterification
reaction rate is higher in a small duration of time and in presence of guanidine (C) and
guanidine (D) very small triglyceride conversion observed. In case of mechanical stirring
reaction guanidine (A) and guanidine (B) showed very low conversion and guanidine (C)
and guanidine (D) showed no reaction.
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350
TG c
on
vers
ion
in %
Reaction time (sec)
3%
5%
129
Fig.5-12. Ultrasound batch reactor 4:1 (Methanol : Canola oil ) 3 % mol catalyst,
60% amplitude, temperature 35 ºC
Fig.5-13. Mechanical stirring in batch reactor 4:1 (Methanol : Canola oil ) 3 % mol
catalyst, temperature 65 ºC
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350
TG c
on
vers
ion
in %
Reaction time (sec)
A
B
C
D
0
5
10
15
20
25
30
35
40
45
50
0 50 100 150 200 250 300 350
TG C
on
vesi
on
in %
Reaction time (sec)
A
B
130
The TMG (C) and DPG (D) guanidines studied were less active than propyl 2-3
diclohexylguanidine, DCOG as shown in Fig. 12. This reduced activity is due to a lower
base strength which decreases when the guanidinium cation is less symmetric (e.g. TMG),
or has no substituents with a positive inductive effect (e.g. DPG). The activity order of the
catalysts was propyl 2-3 diclohexylguanidine> DCOG > DPG > TMG. DCOG and propyl
2-3 diclohexylguanidine are good, to the best of our knowledge, described here for the first
time under ultrasound batch reaction. So, ultrasound is good technique for future
development of continuous biodiesel production under ultrasound using A and B guanidine
as a catalysts.
To investigate the reaction time on biodiesel production, a series of above
experiments were performed with constant concentration of different catalysts. The
catalysts amount for BD production from canola oil was 0.5wt %, in presence of KOH,
NaOH, CH3ONa and Tetramethyl ammonium hydroxide 3 wt % and 3% mol in presence
of Propyl-2, 3 dicyclohexylguanidine, 1, 3- dicyclohexyl 2 n-octylguanidine (DCOG), 1, 3
diphenyl guanidine and 1, 1 3, 3 Tetramethylguanidine. As shown in above figs. the
changes in TG conversion with reaction time compared with mechanical stirring and
ultrasound BD production are particularly noticeable.
5.3.8 Guanidine separation by using strong cation exchanger.
Supported sulfonic acids are in a class of strong acids (pKa < 1) widely used in different
fields of synthetic organic chemistry [31]. Their applications are widely known and the
various forms of these products are used in a large number of drug discovery laboratories
131
and even up to the manufacturing process scale. Silica-functionalized sulfonic acid (SiO2-
Pr-SO3H) as a highly efficient heterogeneous solid acid catalyst, catalyzes various organic
reactions [32]. The most common application is probably their use as strong cation
exchanger (SCX) for the Catch and Release purification of amines in SPE cartridges or
glass columns. For catch and release experiments we selected Guanidines A and B, which
have been found active in the transesterification process (see section 3.7). Using these
guanidines we prepared two synthetic mixtures with glycerol. In this experiment we used 5
g of SiliaPrep Propylsulfonic Acid (SCX-2).
SiliaPrep Propylsulfonic Acid (SCX-2)
SiliaPrep Propylsulfonic Acid was loaded in the glass column using cotton in bottom of the
column. This has adsorption capacity 0.69 mmol/g and particle size 40-63 µm. Then 15 ml
of methanol was passed over the column, so silica became moist. On that moist silica we
injected a synthetic mixture mimicking polar phase which contained glycerol (1g),
guanidine (1g). This adsorbed polar phase was then washed with methanol (15 ml) glycerol
was desorbed from the column at this stage. The collected mixture of methanol and
glycerol was evaporated by using rotary evaporator (BUCHI Rotavapor R110) and glycerol
132
was analysed by GC. Guanidine was still adsorbed on silica at this stage. It was retrieved
upon washing with an ammonia solution in methanol (150 ml) and collected in the round
bottom flask. This process takes a little more time. The collected mixture of guanidine and
ammonia solution in methanol was evaporated by using rotary evaporator. The recovered
guanidine recovery shown in table 1 (80%) was determined by using proton NMR. The
same guanidine was used for another time in the ultrasound transesterification reaction in
the same concentrations as in the first step. In that case the time evolution for TG
conversion was found to exactly replicate the shown in Fig. 5-12. For both guanidine.
Therefore, this catch and release technique shown in Fig.5-14 is suitable for catalyst
(guanidine) recovery.
133
Figure.5-14. Guanidine catch and release technique
[1 – Column conditioning: 15 ml of methanol
2 – Sample application
3 – Wash with 15 ml of methanol (1 ml/min)
4 – Release: 150 ml of ammonia solution in methanol]
134
Table 5-1. Sequence of operations in the catch and release technique.
135
5.4 Conclusions
In this present work the transesterification reaction of canola oil with methanol and
different types of catalysts using both mechanical stirring and ultrasonication reaction was
investigated. Ultrasound homogenization proved suitable for large scale biodiesel
production by using canola oil in a good yield and higher conversion. The efficiency of
mass transfer in the ultrasound field enhanced the higher rate of transesterification reaction
as compared to stirring condition. Ultrasonic cavitation method is energy efficient and
industrially viable alternative for the biodiesel production. In case of Propyl-2, 3
dicyclohexylguanidine and 1, 3- dicyclohexyl 2 n-octylguanidine (DCOG) as a catalyst
under ultrasound transesterification reaction we got higher conversion and more than 80%
regeneration of guanidine is possible from the reaction mixture by using SiliaPrep
Propylsulfonic Acid separation column.
136
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Chapter 6. Conclusion and future work
141
6.1 Conclusions
The development of continuous biodiesel production by using ultrasound and
different homogeneous catalysts was the scope of this dissertation. Examples of triglyceride
transesterification reactions by small alcohols such as ethanol, butanol and glycerol were
used to illustrate the significance of cavitation in ultrasound assisted reactions. In this thesis
general aspects of ultrasound transesterification process and comparative study of different
types of catalysts (NaOH, KOH, CH3ONa, tetramethyl ammonium hydroxide and
guanidines) are described. This work also describes the preparation of different types of
homogeneous catalysts. Special attention is given to ultrasound transesterification reaction
by using guanidine as a catalyst and recovery of guanidine from reaction mixture by using
SiliaPrep Propylsulfonic Acid separation column (SCX-2).
The main conclusions of this study are as follows.
1. In agreement with the literature, the use of ultrasound helps biodiesel production
under milder reactions conditions than those requested by mechanical stirring. Therefore, it
has been possible to reduce all kinetic parameters including reaction temperature, alcohol to
oil molar ratio, catalyst loading and time.
2. Ultrasounds are beneficial in biphasic transesterification reactions of
triglycerides.
3. Both the enhancement in dispersion of the polar phase and cavitation increase
reaction rates.
142
4. There are numerous implications of these results for both experimental and large
scale reactor design.
5. It was found that a minor addition of a compound with low vapor tension
(methanol) in the reaction conditions results in significant enhancements in reaction rate by
promoting cavitation.
6. Guanidines synthesized as catalysts for transesterification reaction show
noticeable results for biodiesel production.
7. Ultrasonication transesterification process works at room temperature. Therefore,
significant energy saving is possible over mechanical stirring.
8. Finally, it was shown that for the ultrasound transesterification reaction using
guanidine as a catalyst, the separation of guanidine from reaction mixture by using silica
cation exchanger columns is possible.
143
6.2 Future research
This dissertation investigated the promising results of ultrasound biodiesel
production. By using this kind of technique large scale biodiesel production plant can be
developed. Some more research is however needed. Some suggestions for future work are:
1) To evaluate other ultrasonic devices for biodiesel production, i.e. sonochemical
reactors that can operate under both continuous and in batch modes in larger scale.
2) To conduct transesterification reactions at frequencies above 26 kHz and to
compare results with those provided by the frequencies evaluated in this PhD thesis,
including comparative studies in terms of FAME yield and energy consumption.
3) To develop an ultrasound-assisted biodiesel production process that may be
extrapolated to industrial scale.
4) To optimize both physical and chemical properties of canola oil biodiesel
according to American standard.
5) Deeper study of non-edible species for ultrasound-assisted biodiesel synthesis.
6) Use of biguanides as catalysts for biodiesel production. These are organic
compounds having formula HN(C(NH)NH2)2. They are colorless, soluble in water and form
strongly basic solutions.
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Chapter 7. Scientific Contributions
List of publications
1. A Parametric Study of Biodiesel Production Under Ultrasounds.
Kiran Shinde, Bendaoud Nohair, Serge Kaliaguine, Int. J. Chem. React. Eng., 2017, 15(1):
117–125.
2. Triglycerides Transesterification Reactions under Ultrasounds.
Kiran Shinde, Serge Kaliaguine, ChemistrySelect, 2016, 1, 6008-6010.
3. Ultrasound biodiesel production using various homogeneous catalysts and their
separation over silica cation exchanger columns.
Kiran Shinde1, François Béland2 and Serge Kaliaguine1. (This manuscript is will soon be
submitted for publication).
Oral presentation and posters
1. Biodiesel production by using ultrasounds and homogeneous catalysts.
Shinde K, Nohair B, Kaliaguine S. 64th Canadian Chemical Engineering Conference,
OCTOBER 19-22, 2014 NIAGARA FALLS, ON, Canada (poster).
2. Base Catalyzed Biodiesel Production Under Ultrasounds.
Shinde K, Nohair B, Kaliaguine S. NAM 24, JUNE 14-19, 2015, PITTSBURGH, PA USA
(poster).
3. Base Catalyzed Biodiesel Production Under Ultrasounds.
145
Shinde Kiran, Nohair Bendaoud, Kaliaguine Serge. PAEES conference, OCT 14-16, 2015,
QUÉBEC CITY, Canada ( poster).
4. A Parametric Study of Biodiesel Production Under Ultrasounds.
Shinde Kiran, Nohair Bendaoud, Kaliaguine Serge. 66th Canadian Chemical Engineering
Conference, OCTOBER 16-19, 2016, QUÉBEC CITY, Canada (oral).
5. A Parametric Study of Biodiesel Production Under Ultrasounds.
Shinde Kiran, Nohair Bendaoud, Kaliaguine Serge. AlChE, Annual Meeting, November
13-18, 2016, San Francisco, USA (poster).
6. Production of Biodiesel Under Ultrasounds.
Kiran Shinde and Serge Kaliaguine. CRIBIQ student symposium, 25- 26 Sep. 2017,
Pavillon Desjardins, Laval University, Quebec, Canada (poster).
