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University of Calgary PRISM: University of Calgary's Digital Repository Graduate Studies The Vault: Electronic Theses and Dissertations 2018-11-13 Assessment of Stage 1 in a Novel Bio-Oil Upgrading Process: Catalytic Hydrotreating Scheele Ferreira, Erika Maria Scheele Ferreira, E. M. (2018). Assessment of Stage 1 in a Novel Bio-Oil Upgrading Process: Catalytic Hydrotreating (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/34509 http://hdl.handle.net/1880/109182 master thesis University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. Downloaded from PRISM: https://prism.ucalgary.ca

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Assessment of Stage 1 in a Novel Bio-Oil Upgrading Process: Catalytic HydrotreatingGraduate Studies The Vault: Electronic Theses and Dissertations
2018-11-13
Process: Catalytic Hydrotreating
Scheele Ferreira, Erika Maria
Scheele Ferreira, E. M. (2018). Assessment of Stage 1 in a Novel Bio-Oil Upgrading Process:
Catalytic Hydrotreating (Unpublished master's thesis). University of Calgary, Calgary, AB.
doi:10.11575/PRISM/34509
http://hdl.handle.net/1880/109182
University of Calgary graduate students retain copyright ownership and moral rights for their
thesis. You may use this material in any way that is permitted by the Copyright Act or through
licensing that has been assigned to the document. For uses that are not allowable under
copyright legislation or licensing, you are required to seek permission.
Downloaded from PRISM: https://prism.ucalgary.ca
UNIVERSITY OF CALGARY
Assessment of Stage 1 in a Novel Bio-Oil Upgrading Process: Catalytic Hydrotreating
by
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF MASTER OF SCIENCE
GRADUATE PROGRAM IN CHEMICAL ENGINEERING
CALGARY, ALBERTA
NOVEMBER, 2018
ii
Abstract
The increasing awareness of global warming and depletion of conventional fossil fuel reserves
has motivated the study of alternative fuel sources to fulfill the increasing worldwide demand of
fuels. One promising alternative is the production of fuels using lignocellulose-derived bio-oils
that would not compete with the human food chain. However, this type of bio-oil remains a
challenge due to its high acidic oxygen content that results in corrosiveness and low energy density
compared with crude oils. Therefore, the present MSc. research focuses on the study of the first
stage of a novel catalytic upgrading approach that involves two different hydrogen-addition
processes. First, a mild hydrotreating process is carried out to reduce the oxygen content in the
bio-oil. Then, catalytic steam cracking (CSC), where hydrogen is produced by splitting water
molecules, is used to obtain lighter products from the hydro-treated oil. The main focus of this
research is to optimize the hydrotreating process.
The effect of the process variables such as operating pressure, temperature and space velocity,
on the product quality was evaluated, finding that the best quality hydrotreated product was
obtained at 345 °C, 0.2 h-1, 1400 psig, and increasing the temperature beyond 345 °C at these
conditions resulted in the appearance of fine solids dispersed in the synthetic product. Additionally,
a comparison of different catalyst formulations was done, finding that acidity is needed in the
catalyst to carry out hydrodeoxygenation reactions. It was also found that the two main compounds
contributing to the acidity of the bio-oil are carboxylic acids and phenols, the latest with a minor
contribution. By hydrotreating, it was possible to achieve a Total Acid Number (TAN) reduction
of 100 % and a maximum of 28 % reduction of the phenols content. A high quality hydrotreated
bio-oil with much reduced oxygen content, low viscosity and higher energy density was produced
in this work.
Hydrodeoxygenation
iii
Acknowledgments
First of all, I would like to give my most sincere appreciation to Dr. Pedro Pereira Almao for
the opportunity of being part of the Catalysis and Adsorption for Fuels and Energy (CAFE) group
at the University of Calgary. His guidance and advice during my years in Canada, especially, in
the development of this research work are greatly appreciated. I am very lucky to had him as my
supervisor during all these years.
I would like to thank Dr. Monica Bartolini, Mr. Lante Carbognani, Dr. Gerardo Vitale, Dr.
Carlos Scott, Dr. Josefina Scott and Dr. Azfar Hassan for all their insightful technical discussions
and helpful suggestions that guided this research work. Additionally, thanks to all the members of
CAFE group for their support, friendship and all those moments of joy that made this journey more
pleasant, especial thanks to Josune, Marianna, Eduardo, Victor, Christian and Jose Luis.
I would like to acknowledge the Department of Chemical and Petroleum Engineering at the
Schulich School of Engineering for offering me an outstanding formation. The financial support
provided by the Department and Steeper Energy Canada is also greatly appreciated.
I would also like to infinitely thank my parents for all the unconditional support they have
given me during my professional formation and life projects. Thanks for always believing in me,
for encouraging me, being the best examples and provide all the opportunities for me to grow as a
professional and as a person. In addition, I would like to thank my number one fans: my
grandparents Landys, Bertha and Maria. Thanks for the guidance and the advices and for always
cheering me up when I needed encouragement.
Finally, my infinite appreciation and love to my husband Fredy Cabrales. Thanks for being
the best company I could ever had during these past years. Thanks for your patience and
understanding during the hard times and for giving me the motivation and the extra push when I
needed it.
iv
Dedication
To my parents Sergio and Katiuska, my brother Stefan and my grandparents Pito, Tortu and
Nonnita, for all their support and motivation during this journey
To my thoughful and supporting hubby with all my love
v
List of Symbols, Abbreviations and Nomenclatures .................................................................... xii
Chapter 1: Introduction ....................................................................................................... 1
1.2. Novel Bio-oil Upgrading Approach............................................................................ 3
Chapter 2: Literature Review .............................................................................................. 6
2.1. Lignocellulosic biomass.............................................................................................. 6
2.2.1. Hydrothermal Liquefaction ....................................................................................... 11
2.2.1.1. Hydrofaction Process ........................................................................................ 12
2.3. Bio-oil from lignocellulose ....................................................................................... 13
2.3.1. Chemical composition of bio-oil derived from lignocellulose via HTL ................... 14
2.3.2. Important properties of bio-oil .................................................................................. 16
2.4. Bio-oil upgrading ...................................................................................................... 18
vi
3.2.1. Feed Section .............................................................................................................. 26
3.2.2. Reaction Section ....................................................................................................... 26
3.3. Experimental Procedure ............................................................................................ 28
3.3.1. Reactor Filling .......................................................................................................... 29
3.4.2. Water Content ........................................................................................................... 31
3.4.3. Product Distribution .................................................................................................. 32
3.4.8. Fourier-transform Infrared spectroscopy (FTIR) ...................................................... 35
3.4.9. Pre-asphaltenes stability............................................................................................ 37
4.1. Effect of the total operating pressure ........................................................................ 40
4.2. Temperature and space velocity screening ............................................................... 42
4.2.1. Temperature effect .................................................................................................... 43
4.2.2. Space velocity effect ................................................................................................. 51
4.2.3. Correlation between TAN and Infrared absorptivity at 1710-1750 cm-1 .................. 53
4.2.4. Catalyst Lifetime ....................................................................................................... 56
4.3.1. Product distribution of the HDT-bio-oils .................................................................. 62
4.4. Evaluation of a dual-catalyst bed reactor (Reaction #4) ........................................... 67
4.5. Catalyst performance comparison............................................................................. 69
References ......................................................................................................................... 81
Appendix II: Operational Data and Experimental Results ........................................................... 88
Appendix III. Hydrogen consumption calculation........................................................................ 96
List of Tables
Table 2.1. Typical biomass and waste compositions (wt. % dry mass) adapted from ENC25 ........ 7
Table 2.2. Thermochemical conversion technologies and products, adapted from Bridgewater32
....................................................................................................................................................... 10
Table 2.3. Typical properties of wood derived bio-oil and crude oil ........................................... 14
Table 2.4. Typical operating conditions for hydrotreating bio-oils12, 36, 53 ................................... 20
Table 3.1. Properties of the bio-oil provided by Steeper Energy.................................................. 24
Table 3.2. Relative error for gas chromatography ........................................................................ 38
Table 4.1. Characterization of HDT-bio-oil at 310 °C, 0.2 h-1 and different operating pressures 41
Table 4.2. Characterization of HDT-bio-oil at 1400 psig and 315 °C using CAT-M3. Cx describes
tested condition evaluated during R2 (See Figure 4.2) ................................................................. 52
Table 4.3. Characterization of HDT-bio-oil at 1400 psig and 320 °C using CAT-M3................. 53
Table 4.4. Relative error between the measured and calculated TAN for different samples of HDT-
bio-oil ............................................................................................................................................ 55
Table 4.5. Characterization of HDT-bio-oil at 325 °C, 1400 psig, 0.2 h-1 using CAT-M3 in different
reactions (R2 and R3) ................................................................................................................... 58
Table 4.6. Temperature range for the product cuts determined via SimDist or TGA .................. 64
Table 4.7. Characterization of HDT-bio-oil at different temperatures using CAT-M3+ ............. 69
Table 4.8. Characterization of HDT-bio-oil at different temperatures during different reactions 77
ix
List of Figures and Illustrations
Figure 1.1. Proposed novel bio-oil upgrading scheme combining HDT and CSC. ........................ 4
Figure 2.1. Structure of lignocellulosic biomass10 .......................................................................... 7
Figure 2.2. Chemical structure of cellulose14.................................................................................. 8
Figure 2.3. Main components of hemicellulose14 ........................................................................... 8
Figure 2.4. Partial structure of a hardwood lignin molecule from European beech14 .................... 9
Figure 2.5. Phase diagram of water for different operating regimes10.......................................... 12
Figure 2.6. Reaction scheme for the bio-oil formation proposed by Pedersen & Rosendahl42 .... 15
Figure 2.7. Chemical composition of bio-oils according to Milne et al.39 .................................... 16
Figure 2.8. Main reactions occurring in HDT process of bio-oil64, 65 ........................................... 21
Figure 2.9. Reactivity scale of oxygenated groups under hydrotreating conditions15 .................. 22
Figure 3.1. RTU-1 diagram, adapted from Cabrales Navarro69 .................................................... 25
Figure 3.2. Reactor and thermocouple profile probe schematic, adapted from Cabrales Navarro69
....................................................................................................................................................... 27
Figure 3.3. FTIR spectra for bio-oil with the most important bands ............................................ 36
Figure 4.1. H/C ratio and butane/butene ratio vs operating pressure for HDT-bio-oil. H/C ratios
determined over the liquid product; C4/C4= determined over the associated gas phase ............. 41
Figure 4.2. Temperature and space velocity changes during R2. In order to verify the stable
behavior of the catalyst the return of the initial condition was performed twice with the last one
being at the end of the whole test run. .......................................................................................... 43
Figure 4.3. Effect of the temperature on the TAN and viscosity reduction (1400 psig, 0.2 h-1).
Viscosities were determined at 40°C ............................................................................................ 44
Figure 4.4. FTIR spectra for the feedstock (bio-oil) and HDT-bio-oil at two temperatures. ....... 46
Figure 4.5. Carboxylic acids reduction vs DOD for HDT-bio-oil at different temperatures. Values
in parenthesis are set up experimental temperatures..................................................................... 47
Figure 4.6. H/C ratio and O/C ratio vs DOD for HDT-bio-oil at 1400 psig, 0.2 h-1 using CAT-M3
....................................................................................................................................................... 48
Figure 4.7. Microscope images at 40 X for the bio-oil feed (left) and HDT-bio-oil at 325 °C (right)
....................................................................................................................................................... 48
Figure 4.8. Hydrogen consumption and water yield vs DOD for HDT-bio-oil in R2 .................. 49
x
Figure 4.9. Gas yield distribution for different temperatures in R2.............................................. 50
Figure 4.10. TAN Reduction vs Time on Stream for CSC processing adapted from Trujillo.21 .. 51
Figure 4.11. Graphic given by the TAN equipment for bio-oil feed (left) and HDT-bio-oil 315 °C
(right) ............................................................................................................................................ 54
Figure 4.12. FTIR spectra of the bio-oil feed and HDT-bio-oil at 315 °C ................................... 54
Figure 4.13. Correlation between transmittance obtained by FTIR for the bands 1710 and 1740
cm-1 between 17 and ln (TAN) ..................................................................................................... 55
Figure 4.14. TAN Conversion of the HDT-bio-oil vs time on stream in R2 using CAT-M3 ...... 56
Figure 4.15. Carboxylic acids and phenols reduction for different temperatures in R3 ............... 58
Figure 4.16. Carboxylic acids and phenols reduction vs DOD in R3 ........................................... 59
Figure 4.17. Microscope images at 40 X for the HDT-bio-oil at different temperatures in R3 ... 60
Figure 4.18. Hydrogen consumption and water yield vs DOD for HDT-bio-oil in R3 ................ 61
Figure 4.19. Gas yield distribution for different temperatures in R3 ............................................ 62
Figure 4.20. Weight percentage of CS2 insoluble material at different temperatures in R2 & R3 63
Figure 4.21. TGA in N2 of the CS2 insoluble material from the HDT-bio-oil at 340 °C in R3 ... 65
Figure 4.22. Product distribution and conversion at 343 °C+ at different temperatures in R2 & R3
....................................................................................................................................................... 66
Figure 4.23. Product yields vs conversion at 343 °C+ for different conditions in R2 & R3 ........ 66
Figure 4.24. Carboxylic acids and phenols reduction for different temperatures using CAT-M3+
....................................................................................................................................................... 67
Figure 4.25. Microscopic images at 40 X for the HDT-bio-oil at different temperatures in R4 .. 68
Figure 4.26. Carboxylic acids and phenols reduction at different T and catalysts ....................... 70
Figure 4.27. Natural logarithm of viscosity vs conversion at 343 °C+ for R2, R3, R4 & R5 ...... 72
Figure 4.28. Natural logarithm of viscosity vs conversion at 343 °C+ for the same conditions tested
in R2 & R3 .................................................................................................................................... 72
Figure 4.29. MCR vs conversion at 343 °C+ for R2, R3, R4 & R5 ............................................. 73
Figure 4.30. Product distribution and conversion at 343 °C+ for different T and catalysts ......... 74
Figure 4.31. Comparison of CS2 insoluble material in the liquid product obtained using different
catalysts ......................................................................................................................................... 75
Figure 4.32. Microscope images for the HDT-bio-oil for different T and catalysts ..................... 76
xi
Figure 4.33. H2 consumption vs DOD for different catalysts ....................................................... 77
xii
Symbol Description Units
BPV Back Pressure Valve
CHN Carbon, Hydrogen and Nitrogen
CS2 Carbon disulfide
HDM Hydrodemetallization
HDN Hydrodenitrogenation
HDO Hydrodeoxygenation
HDS Hydrodesulphurization
HDT Hydrotreating
HTL Hydrothermal liquefaction
K-F Karl Fischer
KOH Potassium hydroxide
PTV Programmable Temperature Vaporizing
SimDist Simulated Distillation
TCD Thermal Conductivity Detector
VGO Vacuum Gas Oil
WGS Water Gas Shift
WGM Wet Gas Meter
XTAN TAN Conversion %
1.1. Background and motivation
In the mid-1800s, biomass supplied more than 90% of U.S. energy and fuel demands. But in
the late 1800s to early 1900s, fossil fuels became the preferred energy resource. The discovery of
crude oil helped to industrialize the world and improved living standards by creating an
inexpensive fuel source.1 In the past few years, transport has been almost totally dependent on
petroleum-based fuels such as gasoline, diesel, liquefied petroleum gas and compressed natural
gas; nevertheless, depletion of conventional fossil fuel reserves mainly used for transportation
purposes has motivated the exploration of alternative fuel sources to fulfill the increasing
worldwide demand.2 Additionally, the increasing awareness of global warming have led to strict
regulations for releasing greenhouse gases.3 Usage of biologically derived fuels, may play an
important role for blending with crude oil fractions to supply part of the global demand and to
meet the end-product specifications as they come from a cleaner, CO2 neutral, feedstock.
Investigations in this area are becoming more relevant, as these bio-oils have the advantage of
having reduced contents of contaminants such as sulphur and nitrogen.4 Therefore, they produce
lower amounts and less harmful gas emissions compared to conventional fossil fuels on a life cycle
basis.5
Traditional oil and chemical companies such as Shell, Conoco-Phillips, Dupont and BP are
already transitioning to the carbohydrate economy by developing the technology and infrastructure
for biofuels and biochemicals production.6 Government leaders are also recognizing the
importance of this growing industry by providing tax breaks, grants, incentives and mandates. For
example, in 2006 the U.S. government started giving $0.14/L for ethanol production as a subsidy;
a number of European Union (EU) countries give full tax exemption for biotransportation fuels;
and EU is promoting the growing of crops used for biodiesel and bioethanol production by
providing a carbon credit of $54/ha.6
However, there are some political, economic and technical disadvantages associated with
using biofuels. First, most of the natural material used for producing bio-oils like corn, wheat,
sugar beet and oil seeds, can interfere with the human food chain and can lead to exacerbate current
global food shortage issues.4, 7 Second, because the biofuels industry is starting to grow, some
2
current biomass technologies have low overall thermal conversion efficiencies, making the process
highly expensive and inefficient.6 Finally, bio-oils face some technical challenges regarding some
of their properties such as poor volatility, high viscosity and acidity, thermal instability (gum-
polymers formation) and high content of oxygenated compounds that reduce their miscibility with
petroleum-based fuels.7
The biofuels industry is in its early stage with many novel biomass conversion technologies
being developed to improve overall energy and economic efficiency.8 It is foreseeable that, as
petroleum reserves decline, the price of fossil fuel products will increase and biofuels will
eventually be cost-competitive with petroleum-derived fuels.6 One promising alternative is the
production of biofuels using low-value feedstock, such as waste wood from the pulp and paper
industry, which would not interfere with the human food chain. Additionally, the greatest
advantage of using biological-derived fuels is that, unlike fossil fuels, biomass takes carbon out of
the atmosphere while it is growing, and returns it as it is burned. This maintains a closed carbon
cycle with almost no net increase in atmospheric CO2 levels.9
Steeper Energy Ltd, a Danish-Canadian company, is in the process of commercializing a
hydrothermal liquefaction technology called Hydrofaction™ for production of added-value liquid
fuel from lignocellulosic biomass via water supercritical chemistry.7 This process has been proven
to yield between 45-50 wt.% of liquid product with a low oxygen content when compared with
regular lignocellulose processing technologies.10 The bio-oil produced by Hydrofraction™ still
presents a high acidity, viscosity and oxygen content compared with petroleum-derived fuels.
Hence, an upgrading process is required to convert the bio-oil in bio-fuels or a product miscible
with crude oil.
In the last two decades, literature related to the catalytic removal of oxygen from bio-oil
derived from lignocellulose has been rapidly growing. In a hydrotreating process,
hydrodeoxygenation (HDO) reactions are used to remove oxygen from bio-oils in the form of
water, CO and CO2 by adding H2 to the process.11 Catalytic HDO has been investigated as a
feasible route for the production of fuels from bio-oils. Hydrotreating processes address the
instability of the bio-oil and it is carried out in order to prevent catalyst deactivation in further
processing, minimize coke formation and improve the properties of the oil.6
3
In 2000, the literature of kinetics and reaction networks of HDO was reviewed by Furimsky.12
Four years later, Czernik and Bridgwater investigated developments in the applications of bio-oils
in the industry13 and in 2006 Mohan et al. discussed the process of converting wood into bio-oils
via pyrolysis.14 In 2007, Elliot summarized the historical perspective on developments in catalytic
hydroprocessing of bio-oils.15 Properties and applications of bio-oils produced via pyrolysis or
hydrothermal liquefaction (HTL) has been reviewed by several authors.16, 17 Additionally, different
standard hydrotreating catalysts have been tested for HDO of bio-oils derived from
lignocellulose.18, 19
The early work demonstrated that hydroprocessing of bio-oils was feasible, although not
economical yet due to the severe reaction conditions, hydrogen consumption and the necessity of
further upgrading the hydrotreated product to obtain the commercial products.11 A promising
approach proposed in the present research is to combine hydrotreating with a catalytic steam
cracking (CSC) process, which produces hydrogen, in order to reduce or eventually eliminate
external hydrogen production making the upgrading economically viable.
1.2. Novel Bio-oil Upgrading Approach
The novel bio-oil upgrading approach aims to combine a mild hydrotreating process to mainly
reduce the oxygen content of the feedstock with a catalytic steam cracking process to reach a
deeper conversion of the bio-oil into light fuels. Catalytic steam cracking (CSC) is a process that
uses water as a hydrogen supply by catalytically splitting water molecules while cracking large
and heavy molecules in the feedstock.2 This process is configured in a single catalyst bed and it
uses a dual-function catalyst. The catalyst has a rare earth metal that cleaves the water molecule to
form hydrogen radicals and a hydrogenating metal combined with an acid support to promote
hydrocracking.20 The produced hydrogen radicals are involved in the saturation of hydrocarbon
radicals generated by molecules cracking and act as scavengers to prevent condensation reactions,
thus coke formation.2
The proposed scheme has two main features that look promising for future of upgrading of
bio-oil. First, CSC produces its own hydrogen by cleaving water molecules; hence, there is no
need to feed hydrogen to the CSC process. Second, and most importantly, the unconsumed
hydrogen produced in CSC may be recovered and recycled back to the HDT unit, reducing the
4
fresh hydrogen make-up needed for this unit. According to a study of this process made by Trujillo
in her MSc. thesis,21 the recycle of the unconsumed hydrogen per se from the CSC stage would
meet 8.6% of the hydrogen requirement for the HDT stage. However, the theoretical hydrogen
available from the hydrocarbons gaseous stream from CSC to be recovered considering a catalytic
steam reforming step was calculated and the yield exceeded the hydrogen requirements for the
HDT stage. This means, that with proper treatment for the gas stream produced in CSC, there is
enough hydrogen produced in this process to guarantee all the hydrogen make-up for HDT.
Figure 1.1 shows the proposed bio-oil upgrading diagram via HDT and CSC. First, the HDT
process consists of an up-flow fixed bed reactor containing an in-house formulated catalyst. This
catalyst has been found to be active for hydrogenation reactions in bio-oils by Trujillo in her MSc.
thesis.21 Next, the hydrotreated oil is to be further upgraded via CSC in an up-flow fixed bed
reactor containing a catalyst also assessed by Trujillo. As seen in Figure 1.1, product gases from
both reactors are going to be submitted to catalytic steam reforming (CSR) to process hydrocarbon
gases and recover hydrogen. The hydrogen produced is to be recycled to the HDT process to
minimize or eliminate the make-up hydrogen needed.
Figure 1.1. Proposed novel bio-oil upgrading scheme combining HDT and CSC.
5
In order to optimize the conditions and catalysts for each stage, the processes were evaluated
separately as a first step of the general study. Screening of conditions and catalysts for HDT were
made by Trujillo in her MSc. thesis that produced the starting point for this research. Trujillo also
studied the CSC process including some operating conditions, catalyst types and their deactivation
as well as the hydrogen balance for the whole process.21 The present work in this thesis is going
to have its main focus in optimizing the HDT process in terms of finding the best pressure, catalyst
configuration, temperature and space velocity to produce a high-quality bio-oil that can be
processed by CSC without deactivating the catalyst used in this second processing step (CSC)
while allowing it to fulfill the highest yield of distillate and naphtha products for the integrated
process.
1.3. Scope of the Research
The general objective of this research is to study the novel proposed hydrogenation process
of bio-oil derived from lignocellulosic biomass material provided by Steeper Energy. In order to
accomplish the general goal, some specific objectives were established as follows:
1. Conduct a systematic study of the variables effect such as total operating pressure,
temperature and space velocity on the reactivity of bio-oil via HDT.
2. Evaluate the best conditions and catalysts to minimize the acidity and oxygen content
on the feedstock.
3. Understand the catalyst lifetime during long term evaluation runs.
4. Develop a correlation between two analytical characterization techniques: Total Acid
Number (TAN) and Fourier-transform Infrared (FTIR) to simplify the acid content
analysis.
5. Compare the effect of different catalyst formulations and reactor configurations on the
product quality.
6. Produce a high-quality hydrotreated product for further processing via CSC to prevent
rapid CSC catalyst deactivation due to coke formation.
6
2.1. Lignocellulosic biomass
Biomass is an abundant renewable source to produce energy efficient fuels such as bioethanol
and bio-diesel in an eco-friendly manner. These types of fuels mainly utilize plants rich in
carbohydrates like sugar cane, wheat, maize, potato, barley, corn or sugar beet as feedstock and
makes up the first generation of bio-fuels.22 The first generation of biofuels is based on well-known
and established technologies, whereas the production of bio-fuels from wood mass is still in the
early stages of research and development and is considered the second-generation bio-fuels.23
Nowadays, a large volume of wood and forest biomass is readily and commercially accessible.
The components of the biomass are obtained from wood harvest and processing residues and
include: tree branches, bark, leaves and limbs, non-merchantable wood, wood pulp wastes and
sawdust.24 Also, biomass from waste wood does not interfere with the human feed chain, which is
one of the main disadvantages of first-generation biofuels.4
Wood-based biomass is essentially a composite material constructed from oxygen-containing
organic polymers and is usually called lignocellulosic biomass. Figure 2.1 shows the main
structure of lignocellulosic biomass. Lignocellulose can be found in the cell walls of plants and
wood and is composed by three major components: cellulose, hemicellulose and lignin. Some
organic extractives such as proteins, resins and waxes and inorganic minerals can be found in
minor concentrations.10, 14 The weight percent of the components varies depending on the wood
species. Table 2.1 shows the typical composition of cellulose, hemicellulose and lignin for
different lignocellulosic materials. As a general trend, it can be observed that the major component
in all different lignocellulosic biomass is cellulose, followed by lignin that in some forest residues
represent the major component.
Figure 2.1. Structure of lignocellulosic biomass10
Table 2.1. Typical biomass and waste compositions (wt. % dry mass) adapted from ENC25
Lignocellulosic materials Cellulose Hemicellulose Lignin
Hard woods
Forest residues
8
Cellulose is a high molecular weight linear polymer that consists of D-glucose molecules
bound together by -1,4-glycoside linkages.14 Cellulose fibers comprise between 40-50 % of dry
wood providing the strength of the wood.22 A large portion of cellulose is crystalline and it has a
high tendency to form intermolecular and intramolecular hydrogen bonds.10 In Figure 2.2, the
structure of the cellulose can be observed. The crystalline structure of the cellulose makes it very
resistant to thermal or biological decomposition. However, when exposed at water at supercritical
conditions , cellulose transforms from a crystalline to an amorphous structure allowing cellulose
degradation.26 When cellulose is decomposed by a complete acid hydrolysis, it breaks down to
form glucose.6, 27
Hemicellulose is composed by amorphous and heterogeneous groups of branched
polysaccharides (copolymer of glucose, mannose, galactose, xylose and arabinose) shown in
Figure 2.3. Hemicellulose exhibits a lower average molecular weight than cellulose.14 Cellulose
fibers are surrounded by hemicellulose that acts as a linkage between cellulose and lignin as seen
in Figure 2.1.22 Hemicellulose contains short side-chain branches pending along the main
polymeric chain that makes its decomposition easier. It decomposes at lower temperature (200-
260 C) and forms less chars than cellulose.28 When hemicellulose is decomposed via hydrolysis,
it breaks down to form its 5 monomer sugars (glucose, galactose, mannose, xylose and arabinose).6
Figure 2.3. Main components of hemicellulose14
9
polymerization of different phenylpropane units bound together by ether and carbon-carbon
bonds.22 Figure 2.4 shows a partial structure of a lignin molecule.29 The phenyl propanoid units
that comprised lignin are not linked in a simple, repeating way due to electron delocalization in
the aromatic ring, the double bond-containing chain and the oxygen functionalities.6 Lignin is
markedly different in structure and composition from cellulose and hemicellulose because of its
high aromaticity.11 Thus, it is more difficult to dehydrate than cellulose or hemicellulose and its
maximum rate of decomposition occurs between 350 and 450 C.30 The main products from lignin
decomposition are phenols due to the cleavage of ether and carbon-carbon bonds.14
Figure 2.4. Partial structure of a hardwood lignin molecule from European beech14
10
As mentioned before, cellulose, hemicellulose and lignin interact at the plant cell wall
structural level. Cellulose and hemicellulose adhere to each other due to hydrogen bonding and
van der Waals forces. Additionally, lignin and hemicellulose form ether and ester bonds with each
other.31
In general, lignocellulosic biomass is comprised of carbon (50 wt.%), hydrogen (6 wt.%) and
oxygen (43 wt.%).10 Nitrogen and small traces of chloride account for the remaining 1%. Sulphur
is not present in this type of biomass. The high oxygen content present in this biomass is the main
disadvantage to produce transportation biofuels that are compatible and expectantly competitive
with fossil fuels. Therefore, processing lignocellulosic biomass is needed to decrease the oxygen-
to-carbon (O/C) ratio while increasing the hydrogen-to-carbon (H/C) ratio.
2.2. Thermochemical processing of lignocellulosic biomass
There are three methods of converting biomass into valuable products: gasification, pyrolysis
and liquefaction. Each one of the methods gives different range of products and employs different
equipment and operating conditions. As seen in Table 2.2, gasification is mainly used to produce
synthesis gas and fuel gas; pyrolysis is used to produce liquid fuels or chemicals, charcoal or solid
char and fuel gas; finally, the liquefaction process produces directly bio-oil or liquid fuels.32 Since
the purpose of this work is to upgrade converted biomass into liquid products that can be used as
biofuels, either pyrolysis or liquefaction must be employed.
Table 2.2. Thermochemical conversion technologies and products, adapted from Bridgewater32
Technology Primary Product Application
Pyrolysis
Carbonization Charcoal Solid fuel or slurry fuel
Slow pyrolysis Gas, liquid char, solid char Fuel gas, solid fuel, liquid fuel
Liquefaction Liquid Oil or liquid fuel substitution
Combustion Heat Heating
11
Pyrolysis is the process where organics are thermally decomposed to solid, liquid or gas by
heating in absence of oxygen.14 Depending on the operating conditions, solid, liquid or gas
products can be produced. For example, slow pyrolysis produces large amounts of coke that can
be used as solid fuel, whereas fast pyrolysis has proven to maximize the liquid products by using
temperatures of 500 C and very short residence time (less than 1 s).32 Fast pyrolysis has the
advantage of lower capital cost compared with liquefaction processes.6 However, this process
requires a dry biomass, high heating rates and high temperatures and produces a highly-oxygenated
bio-oil because the process does not reduce the oxygen content.14
On the other hand, liquefaction or Hydrothermal Liquefaction (HTL) is considered a
promising technology for bio-oil production because of its high biomass conversion, high bio-oil
yield and low O/C ratio products.33 Additionally, HTL has no limitation to input biomass with high
water content.34
The focus of this research is to upgrade a bio-oil produced with lignocellulosic biomass via
hydrothermal liquefaction. Thus, more details including the operating conditions and catalysts are
given in Section 2.2.1.
2.2.1. Hydrothermal Liquefaction
Hydrothermal liquefaction is a biomass to bio-oil conversion route carried out in water at
moderate temperature between 250 and 400 C and high pressures (up to 30 MPa) with or without
the presence of a catalyst.33 HTL is less developed than fast pyrolysis due to the high cost and
technical difficulties associated with high-pressure processing. Many complex reactions take place
during the transformation of biomass into bio-oil where macromolecular compounds are degraded
into unstable and reactive small molecules that can repolymerize into products with a wide range
of molecular weight distribution.35 The general objective of the process is to control the reaction
rate and reaction mechanisms to minimize the oxygen content of the liquid product and maximize
the yield of the liquid product.32
The presence of different catalysts have been studied by several authors,33, 35 finding that alkali
(alkaline oxides, carbonates and bicarbonates), metals (zinc, copper, iodine, cobalt sulphide, ferric
hydroxide) and Ni and Ru heterogeneous catalysts (which aid preferential hydrogenation) have
been used for liquefaction.
Hydrofaction™ is a hydrothermal liquefaction process developed by Steeper Energy that
combines super-critical water chemistry and homogenous catalysts to convert biomass residues to
a high-energy bio-oil.10 More details about this technology will be given in Section 2.2.1.1.
2.2.1.1. Hydrofaction Process
Steeper Energy is commercializing a hydrothermal liquefaction technology called
Hydrofaction™ as a promising path to convert lignocellulosic biomass to bio-oil. This technology
has been proven successfully in a continuous pilot facility.10 Hydrofaction™ includes the use of
supercritical water chemistry, higher pressure and temperatures than other HTL processes reported
in literature.10 The operating conditions are above the critical point of water at pressures between
300-350 bar and temperatures of 390-420 °C. Figure 2.5 shows a phase diagram of water to
visualize the different operating regimes.10 In Hydrofaction™, a homogenous catalyst is used in
the form of potassium carbonate (K2CO3) for desired catalytic effects; recirculation of the oil and
aqueous products is also used to improve feed characteristics, energy balance, oil yields and
desired kinetics.10
Figure 2.5. Phase diagram of water for different operating regimes10
The polarity and dielectric constant decrease significantly when water gets closer to its
supercritical state allowing water to dissolve biomass molecules that are hydrophobic at ambient
conditions including phenolics and polyaromatic hydrocarbons derived from lignin.36 Also, at
supercritical conditions, mass and heat transfer rates are enhanced and interphase mass and heat
transfer resistances are significantly diminished.10 Finally, it was proven that water at supercritical
conditions, sustains a high-density at a high-pressure range compared to most HTL processes
operating near the critical point of water.10
13
Jensen, et al. proposed a scheme for the major reactions taking place at Hydrofaction™
conditions that includes: water dissociation, solvolysis, hydrolysis, dehydration, decarboxylation,
steam and CO2 reforming, water gas shift (WGS), aldol condensation and retro aldol, among
others.10 The high-density, alkaline supercritical water promotes depolymerization of
macromolecules through hydrolysis and solvolysis reactions. Some radical reactions may occur as
well due to the high temperatures; however, radical scavengers are used to participate in chain-
terminating reactions.37
Organic solvents and alkaline conditions favor the degradation of the lignocellulose to its
major macromolecules: cellulose, hemicellulose and lignin. First, the cellulose and hemicellulose
depolymerize to oligomers and eventually monomers through hydrolysis and solvolysis. The
oligomers and monomers further dehydrate and isomerize to carboxylic acids, aldehydes and
enols. Depolymerization of lignin can take two different pathways: an ionic pathway where
hydrolysis and solvolysis reactions take place, which is favored because of the conditions of the
process; or a radical pathway through the thermolytical cleavage of both ether and C-C bonds.
From the ionic pathway, low molecular weight phenols are formed.10
The organic compounds contained in the bio-oil resulting from this technology along with
some reaction pathways for cellulose, hemicellulose and lignin are presented in Section 2.3.1.
2.3. Bio-oil from lignocellulose
Bio-oils are physically very similar to crude oil as they are dark brown flowing liquids;
however, they have a very distinctive smoky and acid odor that distinguish them from petroleum-
derived oils.38 Bio-oils are a complex mixture of compounds derived from the depolymerization
of cellulose, hemicellulose and lignin. This complex mixture include water, solid particles and
hundreds of organic compounds such as acids, alcohols, ketones, aldehydes, phenols and ethers,
among others.39 Some of these compounds are directly related to the undesired properties of bio-
oil like high acidity, oxygen content, viscosity, low heating value and instability.
When comparing the properties of bio-oil and crude oil a significant difference is noticed.
Table 2.3 presents the typical properties of a bio-oil and a crude oil.6, 16 It can be seen that the two
properties that differ the most between a bio-oil and crude oil are the moisture content and the
elemental composition, where it can be observed that bio-oils have higher oxygen content than
14
crude oils. However, a low content of contaminants such as nitrogen9 and sulphur has been found
in bio-oils derived from lignocellulose.6
Table 2.3. Typical properties of wood derived bio-oil and crude oil
Bio-oil6, 16 Alberta Bitumen40
Elemental Composition [wt. %]
C 65-75 82-83
H 5-8 10-11
O 10-40 <1
N <0.5 <1
S <0.05 4.5-6.0
2.3.1. Chemical composition of bio-oil derived from lignocellulose via HTL
The chemical composition of bio-oils may vary depending on different factors, such as
biomass type, feedstock composition, feedstock pretreatment, process for converting biomass and
operating conditions of the process.6 In general, bio-oils are a blend of more than 400 important
organic compounds at different compositions.41 Oxygenated aromatics, heterocyclic compounds
and long chain aliphatic backbones can be found on this renewable oil.42
Carrier et al. investigated the conversion of hemicellulose, cellulose and lignin at supercritical
water conditions and found that products can be grouped into two main pools: oxygenated and
substituted 5-membered ring structures, such as ketonic cyclopentanes and cyclopentanes; and
oxygenated and substituted aromatics.43, 44 Quitain et al. performed a qualitative evaluation on
hydrothermal treatment of a type of bark and identified furfural, benzenes, phenols and acids such
as stearic and palmitic as the main compounds found in the produced bio-oil.27
The reaction mechanism to produce bio-oil is complex and consists of multiple chemical
reactions. It was found that cellulose and hemicellulose (carbohydrates) present similarities in
15
terms of yield, composition and chemical mechanism,42 which reduces the complexity of the
mechanism. Figure 2.6 shows a proposed reaction scheme for the formation of bio-oil.42
Figure 2.6. Reaction scheme for the bio-oil formation proposed by Pedersen & Rosendahl42
Quitain et al.27 found that carbohydrates mainly yield oxygenated 5-membered ring structures
such as furfural and 5-hydroxymethyl furfural whereas lignin yields oxygenated aromatic
compounds such as catechol, phenols and cresols.42, 45 The composition of the different elements
was found to be directly related with the content of lignin, cellulose and hemicellulose in the
biomass. Feedstocks with higher content of lignin yielded more content of aromatics than those
with more cellulose or hemicellulose.42 Milne et al. summarized the chemical composition of bio-
oils derived from lignocellulosic biomass and it is presented in Figure 2.7. It can be observed that
bio-oil contains a numerous variety of compounds such as acids, esters, ketones, aldehydes, sugars,
miscellaneous oxygenates, furans, phenols, guaiacols and syringols.6, 39. In this Figure, the black
column corresponds to the minimum composition found in bio-oils of this compound while the
16
of the same compound.
Figure 2.7. Chemical composition of bio-oils according to Milne et al.39
2.3.2. Important properties of bio-oil
The main physicochemical properties resulting from the chemical composition of bio-oils will
be discussed in this section. By following the changes of these properties, it can be determined if
a bio-oil was successfully upgraded to be use as a petroleum-derived fuel.
Water in bio-oils result from the original moisture of the feedstock and from dehydration
reactions during biomass processing. Water content can vary from 15 to 30 % and although water
reduces the viscosity of the oil and enhances the fluidity, it is hard to remove from bio-oils. Its
presence lowers the heating value and flame temperature, reducing the combustion rates of the
oil.16, 46 Bio-oil produced via Hydrofaction™ has only 1-3 % of water which is another advantage
of this process.10
Due to its chemical composition, bio-oils usually have a pH of 2-4 and a total acid number of
50-100 mgKOH/g.38 As mentioned before, they comprise a substantial amount of carboxylic acids
in the form of acetic and formic acids that leads to a high level of acidity. For this reason, bio-oils
17
are corrosive to common construction materials such as carbon steel and aluminum.47 The
corrosiveness is extremely severe at high temperatures, which imposes more requirements on
construction materials and operating conditions for the upgrading process before using bio-oil as
transportation fuels.38
The oxygen content of bio-oils may vary between 10-40 %,46 distributed in more than 300
identified organic compounds. These oxygenated compounds make bio-oils polar, and therefore
immiscible with non-polar petroleum fuels. The presence of oxygen leads to a low heating value,
corrosiveness and instability.13, 16 Also, polymerization of oxygenated compounds in the form of
phenols has been reported.6 One of the primary reasons for differences in the properties and
behavior between hydrocarbon fuels and bio-oils is the high oxygen content. As seen in Table 2.3,
oxygen content for petroleum-derived hydrocarbons is between 10-40 times lower than for bio-
oils.
Viscosity plays an important role in the design and operation of the fuel injection because it
is a measure of the fluid resistance to shearing forces.16 The viscosity for bio-oils can vary between
6000-40000 cP at 40°C, depending on the feedstock and processing of the biomass. Also, the
chemical structure of the bio-oil may be related to this property. Studies have found that alcohols,
acid groups and intermolecular interactions have a strong effect on viscosity; hydrogenated
compounds are more viscous than aromatic compounds and branched hydrocarbons have lower
viscosities than straight chains.48, 49
The heating value is the amount of heat produced by a complete combustion of fuel and it is
measured as a unit of energy per unit mass or volume of substance.50 It is a quantitative
representation of the energy content of an oil because it dictates the amount of energy produced
for each volume of burned fuel. Usually bio-oils produced from plants have a higher heating value
than those produced from straw, wood or agricultural residues. The heating value of a bio-oil (20-
30 MJ/kg) is lower than the one of crude oil (40 MJ.kg). This could be related to the high amount
of oxygenated compounds found in bio-oils, since studies have found that the heating value is
proportional to the elemental composition of an oil being negatively affect by the oxygen content.9
These undesired properties have limited the range of bio-oil applications. They cannot be
directly used as transportation fuels due to bio-oils high viscosity, acidity, oxygen content and low
18
heating value. Therefore, upgrading of bio-oil is needed to improve its properties for liquid fuel,
starting with the removal of the oxygen content that will affect directly the other properties
mentioned above.
2.4. Bio-oil upgrading
In order to unlock the potential commercialization of bio-oils, upgrading of the converted
biomass is needed. Properties that negatively discern the quality of bio-oil from crude oil such as
high viscosity, acidity and high oxygen content can be improved by different upgrading routes.
The three different routes described for upgrading bio-oil to liquid transportation fuels are:
hydrotreating, hydrocracking and emulsification.6
Hydrotreating (HDT) is a simple hydrogenation process that is used to improve the product
quality without significantly altering the boiling range of an oil.16 This process is the most
commonly applied because it reduces the oxygen content of the bio-oil while increasing the H/C
ratio of heavy molecules.51 In general, depending on the targeted molecules, reactions can be
classified as hydrodesulphurization (HDS), hydrodenitrogenation (HDN), hydrodemetallization
(HDM) or hydrodeoxygenation (HDO).12 For bio-oil, the main reaction taking place is HDO
because, in contrast with crude oil, it does not have a significant amount of sulphur, nitrogen or
metals for the other reactions to take place. One of the advantages of HDO is that during the
process, oxygen in the feed is mainly converted to water, which is environmentally friendly.52
Hydrotreating involves processing bio-oil at moderate temperatures to avoid coke formation.53
It serves as a pre-treatment step to hydrogenate unsaturated hydrocarbons and remove oxygen from
the feedstock. Hence, further upgrading is needed to have a high-quality oil.
Hydrocracking (HDC) is a high-temperature process (>350 ºC) where hydrogenation
accompanies cracking to produce a large amount of light product while increasing the H/C ratio
of the feedstock.6 The products from this reaction include hydrocarbons, water-soluble organics,
oil-soluble organics, gases and coke. The wide range of products is the result of combining
catalytic cracking reactions with hydrogenation reactions.6 A dual-function catalyst containing a
cracking function (silica-alumina or zeolite) and a hydrogenating function (Pt, W and Ni) is used
for catalyzing the reactions.54 Although HDC combines hydrogenation with further upgrading of
19
the feedstock, the high costs due to the severe conditions required such as high temperature and
high hydrogen pressure to deal with acids makes this route not as common as hydrotreating.54
Finally, one of the simplest methods for using bio-oil as a transportation fuel is
emulsification. This process has been investigated by many researchers55-58 and consists of
blending bio-oils with diesel using surfactants.6 Overall, upgrading bio-oil through emulsification
provides a short-term approach to the use of this type of oil in diesel engines due to the promising
ignition characteristics showed by the emulsion. However, most fuels properties like heating value,
cetane number and acidity did not meet the requirements which is why other alternatives such as
HDT and HDC are being favored.6, 54
As mentioned before, a better alternative for upgrading the bio-oil is to combine
hydrogenation with cracking reactions in order to first pre-treat the feedstock by increasing the
H/C ratio and decreasing the O/C ratio; and then reach a deeper conversion with a cracking process.
The main disadvantage of this approach is the high amount of hydrogen needed for processing the
bio-oil in a regular hydrotreating-hydrocracking configuration. Nevertheless, the novel bio-oil
upgrading scheme proposed in this research that combines HDT with CSC, where hydrogen can
be produced and recycled, could be a promising upgrading approach.
2.4.1. Hydrotreating
A main goal of upgrading bio-oil is to convert the oxygen-rich, high-molecular-weight
compounds into hydrocarbons that are compatible with petroleum-derived fuels.11 A potentially
valuable process for pre-treating the feedstock is hydrotreating or hydrodeoxygenation, which has
been proven to significantly improve the quality of bio-oils in terms of oxygen content, viscosity,
acidity and stability.12 Without the HDO step, direct high-temperature catalytic processing, needed
to obtain the commercial products like gasoline and diesel, resulted in high levels of coke
production that plugged the catalyst bed.53
For HDT reactions to take place, the presence of hydrogen and a catalyst with a hydrogenating
function is needed. Conventional hydroprocessing catalysts, such as CoMo and NiMo supported
in alumina were useful for HDO in the sulphided form.59, 60 However, the alumina supports were
found to be instable in the presence of high levels of water. Also, a significant amount of coke was
observed when using alumina as the catalyst support.53 Other catalysts, containing Pt, Ni, Pd or
20
other metallic group, are currently being tested for this type of feed. These catalysts were assessed
to be more active at lower temperatures than the sulphided molybdenum-based ones. Metallic
phases can be easily supported on non-alumina supports like carbon or titania to avoid the water
instability of alumina. The main concern for the metallic catalysts is the high cost associated with
most hydrogenating metals like Pt or Pd.53
Regarding the operating conditions for hydrotreating bio-oils, Table 2.4 summarizes typical
conditions found in the literature. Generally, the temperature for HDT is in the low range to remove
oxygen primarily in the form of water, without severely reducing the chain length of the molecules
in the feed. Also, high-temperatures when treating bio-oils promote coke formation resulting from
the original oxygenated compounds.53 High pressure range, as seen in Table 2.4, is generally used
for HDT because hydroprocessing catalysts usually require high pressures to enable H2 and
reagents to reach all the active sites of the catalyst and perform the hydrogenation reactions.15, 61
Additionally, high pressures ensure a higher solubility of hydrogen in the oil, thus a higher
availability of hydrogen in the catalyst surrounding area. By favoring hydrogenation, the reaction
rate increases and the coke formation in the reactor decreases.62
Table 2.4. Typical operating conditions for hydrotreating bio-oils12, 36, 53
Parameter Common values
Temperature [°C] 250-400
Pressure [MPa] 3-18
H2 feed rate [L H2 STP/ L oil] 100-700
Some of the O-compounds in the feed tend to polymerize from undesirable reactions between
aldehydes and organic acids. This leads to an increase of the molecular weight and is the main
cause for bio-fuels instability.12 Nevertheless, studies have proven that HDT is an effective way to
convert aldehydes and unsaturated compounds into more stable molecules by removing oxygen
atoms.63 The main reactions expected to take place during the HDO of bio-oils are presented in
Figure 2.8. Additionally, undesired reactions such as reverse water gas shift, methanation and coke
formation are expected to occur.64 Hydro-decarboxylation and hydro-decarbonylation remove
21
oxygen in the form of carbon dioxide and carbon monoxide, respectively. Hydro-deoxygenation
removes oxygen in the form of water without cleaving the molecules chain length.65
Figure 2.8. Main reactions occurring in HDT process of bio-oil64, 65
As reported by Milne et al.,39 bio-oil comprise many functional groups that are expected to
react at different temperatures. Grange et al. studied the activation energies and the reactivity
temperatures of different compounds found in bio-oils, finding that molecules with a bound or
sterically hindered oxygen (furans or ortho substituted phenols) required a significantly high
temperature for the reaction of hydrodeoxygenation to take place.66 Furimsky12 summarized the
apparent reactivity for different compounds as:
alcohol > ketone > alkylether > carboxylic acid ≈ M-/p-phenol ≈ naphtol > phenol > diarylether ≈
O-phenol ≈ alkylfuran > benzofuran > dibenzofuran
A study made by Weisser et al. is in agreement with Furimsky’s reactivity proposal67. In
Figure 2.9 it can be observed that at low temperatures (<200 °C), olefins, aldehydes and ketones
are the components reduced by hydrogen. Removing these components have a positive impact on
the stability of the bio-oil.15 Alcohols are reacted at 250-300 °C by catalytic hydrogenation but
also by thermal dehydration to form olefins. Carboxylic and phenolic ethers are reacted at 300 °C
while phenols and dibenzofurans need temperatures higher than 350 °C to react with hydrogen.
3 +
22
Figure 2.9. Reactivity scale of oxygenated groups under hydrotreating conditions15
Finally, Elliot et al. studied the effect of temperature for HDO of wood-based oil using a Pd/C
catalyst in a fixed bed reactor. The operating pressure was 14 MPa and the temperature range was
between 310-340 °C. It was found that above 340 °C the degree of deoxygenation (DOD) did not
increase further, but instead extensive cracking took place accompanied by a decrease in the oil
yield.68
Although HDT is considered a very effective technology to process and improve the
properties of bio-oil, it is important to consider the amount of hydrogen needed to achieve high
HDO conditions and its impact on the profitability of the process. Venderbosch et al. investigated
the hydrogen consumption for bio-oil upgrading as a function of the DOD, finding that the
hydrogen consumption increases sharply when the DOD reaches more than 50%.61 This could be
related with the reactivity of different compounds, e.g. highly reactive oxygenates like ketones can
be easily converted with low hydrogen consumption because oxygen is available for reaction,
whereas complex molecules like furans, need to be hydrogenated/saturated first which increases
the hydrogen consumption notably.12
23
The product after HDT is usually a bio-oil with a reduced oxygen content, viscosity and
acidity. Nevertheless, it still comprises non-polar high-molecular-weight organic compounds51
that, in order to obtain commercial products, require further processing of the oil in a hydrogen
rich environment. To allow further processing without consuming more hydrogen in a
hydrocracking process, a new alternative is proposed. Catalytic Steam Cracking (CSC) is a
moderate-conversion process that produces hydrogen through steam dissociation and cracks heavy
molecules both thermally and catalytically.20 The unconsumed hydrogen in CSC can be recycle to
the HDT process in order to make bio-oil upgrading more economically viable.
24
3.1. Bio-oil feedstock
The experiments performed in this research project were done using a bio-oil feedstock
provided by Steeper Energy. This feedstock is produced using lignocellulosic biomass via a
patented process named Hydrofraction™, a supercritical hydrothermal liquefaction technology
explained in detail in Section 2.2.1.1. Properties of the feedstock used in this research are presented
in Table 3.1.
Table 3.1. Properties of the bio-oil provided by Steeper Energy
Property Value
TAN [mg KOH/g] 48.32
Jet Fuel (190 - 260 °C) 5.2
Diesel (260 - 343 °C) 10.5
VGO (343 - 545 °C) 26.5
Residue (545 °C +) 55.8
3.2. Experimental Set Up
The reactivity tests for upgrading the bio-oil in this research were carried out in a Reactivity
Test Unit (RTU-1) bench-scale pilot plant designed and constructed by Cabrales Navarro.69 RTU-
1 is equipped with an up-flow tubular reactor that can be used to emulate the performance of
industrial processes such as hydrotreating, thermal cracking or visbreaking. Catalytic Steam
25
Cracking (CSC) and thermal cracking reactions of De-Asphalted Oil (DAO) were performed in
this unit by Cabrales Navarro69 prior to the beginning of this research. Also, a detailed description
of the design, construction and operation of RTU-1 is reported.69
The unit can be divided in three main sections: Feed section, Reaction section and Separation
and Sampling section. For the purposes of this thesis, the Separation and Sampling section was
modified to accommodate the unit for the bio-oil feedstock and hydrotreating conditions. A
summary of the modifications is found in Appendix I.
A whole schematic of RTU-1 including the modifications done to the unit is presented in
Figure 3.1.
26
3.2.1. Feed Section
The feed section is equipped with two steel tanks to supply feedstock to the pump. The main
tank is a 10 L custom made stainless steel vessel of 6.7” and 15” height, built in the Engineering
Machine Shop at the University of Calgary. This tank is equipped with a spring-type relief valve
that opens at 100 psig in case the vessel over pressurizes. The main feed tank is heated between
80-100 °C to ensure mobility of the feedstock and it is pressurized up to 100 psig for
homogenization purposes and to provide head pressure to refill the pumps. The second feed tank
is an auxiliary 1 L Swagelok vessel operated at room temperature where vacuum gas oil (VGO) or
dichloromethane is stored for cleaning purposes. A Teledyne ISCO series 500D dual-pump
continuous flow system with dual pneumatic valves and controlled by a Series D Controller is used
to pump the feedstock to the system. The continuous flow mode allows refilling one pump while
the other one delivers fluid to the system. In case there is a reactor or lines plugging downstream,
a spring-type relief valve is placed in the pump outlet line that directs the feed flow to an auxiliary
500 mL Swagelok tank depending on the set pressure. The feed section is also equipped with a
heated water and gas outlet line (TC-201) for CSC processing. In this thesis, only hydrotreating
reactions were performed, thus only hydrogen was injected through this line. A Brooks Instrument
5850 EM hydrogen mass flow controller is installed for hydrogen injection. Lines made of ¼’’
O.D. 316 stainless steel tubing provided by Swagelok connect all the parts of the feedstock
pumping. Additionally, heating tapes are used for heating the lines at temperatures up to 140 °C
(TC-101 to TC-108) due to limitations in temperature of the pneumatic valves of the ISCO pumps.
Finally, every heated piece is insulated with Superwool insulation (Ref. 6# SW 607 supplied by
Improheat-Edmonton) to reduce heat losses.
3.2.2. Reaction Section
RTU-1 is equipped with a tubular reactor operated in up-flow mode. In this case, the reactor
was operated as a fixed-bed, filled with different types of supported catalyst for different test runs.
Volume of the reactor for most of the test runs was 29.1 mL. The reactor was assembled with 35.5
cm length 316 stainless steel Swagelok tubing, ½” O.D. and 0.049’’ wall thickness. An Omega
thermocouple with 7 sensing points is installed inside the reactor for temperature monitoring as
27
presented in Figure 3.2. As seen in Figure 3.2, 6 sensing points are distributed inside the reaction
zone and the other point indicates the temperature before the inlet of the reactor.
Figure 3.2. Reactor and thermocouple profile probe schematic, adapted from Cabrales Navarro69
To heat the reaction section, three individually controlled heating tapes (TC-204, TC-205 &
TC-206) are wrapped around the reactor to have versatility to adjust any of the sections output
independently to obtain a homogenous temperature profile. There is a ¼” O.D. pre-heating line
before the reactor entrance in order to increase the temperature of the feed and reduce the heat load
at the reactor entrance.
3.2.3. Separation and Sampling Section
The hot separation system is equipped with the following double ended 304L stainless tanks
supplied by Swagelok: one 1 gallon stability tank (not used in this research), two 1 L mass balance
vessels and one 40 mL intermediate tank.
The mixture of gases, water and liquid hydrocarbons exiting the reactor go to a collector tank
(MB Tank 1) operated at low temperature (90 °C) because of restrictions of the tank at high
28
pressure (1400 psig). In this collector tank, gases are separated from the liquid products and passed
through a back pressure valve (BPV) that maintains the operating pressure at the given set point.
Then, the gas stream is sent to the gas release and depressurization section. This section consists
of two KOH traps for gas sweeting in case of having hydrogen sulphide as a product of the reaction,
a Gas Chromatograph (GC) for gas analysis and a Shinagawa W-NK-0.5-18 Wet Gas Meter
(WGM) for gas flow measurements.
The first tank (MB Tank 1), as mentioned before, is used to separate the gases and collect the
liquid product. The second tank (MB Tank 2) works as a hot separator at 110 °C and atmospheric
pressure to ensure water separation. To collect mass balances and separate the water from the
liquid product, the last one must pass from MB Tank 1 to the hot separator (MB Tank 2) without
a high drop in the pressure of the system. For this purpose, an automated sampling system equipped
with two computer-controlled pneumatic valves are set to control the valve between MB Tank 1
and the 40 mL vessel (V-301) and the valve between the 40 mL vessel and MB Tank 2 (V-302).
The pneumatic valves are timed in such a way that V-301 opens and approximately 90% of the
small vessel is filled with liquid. This causes a small pressure drop in the unit, less than 3% of the
operating pressure. V-301 is left open for 300 s and then it closes automatically. After 10 s, V-302
opens 300 s and the product is released to the hot separator. After this point, the cycle set in the
computer starts again. To ensure water separation, a constant amount of nitrogen is injected at the
bottom of the hot separator and the residence time should not be less than one hour before
collecting the sample. Water and light products that distill at 110 °C are sent to a 304L Swagelok
stainless steel 75 mL mass balance tank (MB Tank 3) operated at room temperature and
atmospheric pressure. Nitrogen is used to flush the samples from MB Tank 2 and MB Tank 3.
3.3. Experimental Procedure
RTU-1 was used to test different catalysts and conditions through this thesis. Prior to the start-
up of the unit, it is necessary to fill the reactor with the catalyst and to treat the catalyst to activate
the metals on it. These two steps will be explained in section.3.3.1 and 3.3.2. Also, the operation
and start-up of RTU-1 for hydrotreating will be discussed in section 3.3.3.
29
3.3.1. Reactor Filling
Figure 3.2 shows a schematic of the packed bed reactor used on the experiments. First, the
reactor inlet fittings, containing the thermocouple, were closed and attached to the empty tubing
(reactor). Next, quartz wool was introduced through the tube exit end to reach the inlet of reactor.
Using a funnel, carborundum previously washed with hydrogen chloride was added until reaching
the isothermal zone (point #2 of the thermocouple). To separate the carborundum from the catalyst,
more quartz wool was incorporated to the tube. Then, catalyst was loaded until reaching point #7
applying vibration to ensure a well-packing. Afterward, more quartz wool, carborundum and
quartz wool again, were incorporated to the reactor until reaching the outlet.
The filled reactor was assembled into RTU-1 and leak test was performed at 1650 psig of
Nitrogen for at least 24 hours. Leaks were detected using Snoop Liquid Leak Detector from
Swagelok. The maximum acceptable pressure drop per hour was 0.5%.
The amount of catalyst loaded in the reactor and the Weight Hourly Space Velocity (WHSV)
selected for each experiment allowed the determination of the oil mass flowrate to be used. It can
be determined following Eq. 3.1.
[−1] = [

3.3.2. Catalyst Activation
The oxidation states of the metals added to the catalyst at the start of the test run are very
important to obtain maximum performance. In order to reach the desired oxidation state for the
catalysts tested in this research, a reduction under nitrogen and hydrogen was required for
activation of the catalyst. Previous studies done by Vitale, et. al70 showed that all the metals used
in the catalysts were reduced at 500 °C. To start the reduction, nitrogen was flowed through the
reactor filled with catalyst at a rate of 60 mL/min. The temperature was ramped to 500 °C at a rate
of 10 °C/min. After reaching the set point, external temperatures were adjusted to ensure a
homogenous profile. The temperature was maintained at 500 °C for 6 hours and the nitrogen flow
was set to zero after reaching room temperature. The same procedure was repeated using hydrogen
instead of nitrogen. However, after reaching the set point (500 °C), the temperature was maintained
30
for 8 hours instead of 6 hours. Hydrogen flow was set to 10 mL/min after reaching room
temperature to keep the unit under a hydrogen environment for the start-up. The catalyst activation
was done at atmospheric pressure.
3.3.3. Hydrotreating Operation
In order to bring all the process variables to reaction conditions in a smooth manner after the
catalyst treatment, there is a procedure that needs to be followed. First, the temperatures in the feed
and separation and sampling section were increased to the regular operation set-point (between
90 °C and 110 °C). Next, the pressure of the system was increased and hydrogen flow was set to
reaction conditions. The back pressure valve (BPV) was manually closed to constrain the gas flow
at the exit of the system until reaching the set-point value. Then, the reactor temperatures were
increased at a rate of 10 °C/min until reaching the set-point. External temperatures were adjusted
to obtain a homogeneous temperature profile. Afterward, oil was flowed through the system at a
rate of 2 mL/min for 60 minutes to fill the lines leading to the reactor, and the reactor as well.
Finally, oil mass flow rate was fixed to the set-point determined using Eq. 3.1 and the time to reach
stability for the reaction was started when the internal temperatures achieved the reaction set-point.
Each condition tested was considered stable after oil passed through the reactor three times its
volume at the corresponding set-points of temperature, pressure and oil and hydrogen flowrate.
As explained in Section 3.2.3, an automated sampling system was used to transfer the liquid
product to the separation tank. The valves cycle time (tv) in the automated system was calculated
from Eq. 3.2, where 40 mL is the volume of the vessel between MB Tank 1 and MB Tank 2.
[] = 40
Eq. 3.2
3.4. Characterization Techniques
The liquid and gas products obtained from hydrotreating the bio-oil were analyzed to
understand the effect of varying different operation conditions. Most of the techniques described
in this section were modified from the ASTM norms used for heavy oil for a feasible
implementation with the resources available at the CAFE group at the University of Calgary. Also,
some modifications due to the nature of the feedstock (bio-oil) were done.
31
3.4.1. Total Acid Number
Total Acid Number (TAN) is defined as the naphthenic acid content on a crude oil and it is
commonly expressed as the milligrams of potassium hydroxide (KOH) needed to neutralize a gram
of crude oil.71 TAN number or the acidity of the samples was measured following the ASTM D644
norm.72 Although this method is well-established and accepted, with the available Mettler T70
titrator this method has disadvantages. It does not differentiate strong acids from weak acids, thus
it does not distinguish the type of molecules in the sample such as naphthenic acids, phenols,
mercaptans or other acidic components present in the sample.71 From the preceding drawbacks,
this technique was coupled with other characterization methods in order to obtain more
information about the samples.
A Mettler Toledo T70 Titration Excellence was used for measuring the acidity of the samples
using a titrant solution of 0.05 M KOH in 2-propanol and water. In this method, between 0.5 and
0.7 g of sample is diluted with 60 ml of solvent composed by 50 % toluene, 49.5 % 2-propanol
and 0.5 % of water. The vessel with the solution was placed in the auto-sampler tray and the
electrode, titrant dispenser and mixer were placed inside the vessel. The neutralization reaction
was monitored by potentiometry until reaching completion. Total Acid Number was reported by
the equipment depending on the amount of titrant used, its respective concentration and the amount
of sample used. Finally, Eq. 3.3 was used to calculate TAN conversion (XTAN). The relative error
for the TAN measurement is 3% for TAN>50 mgKOH/g, 10% for TAN ranging between 1-
5 mgKOH/g and 20% for TAN<1 mgKOH/g.
[%] = (1 − [
]
3.4.2. Water Content
In order to corroborate the correct separation of the water from the hydrocarbon product and
to quantify the water content on the heavy product for further calculations, the water content in the
bio-oil sample was determined by coulometric Karl-Fischer (K-F) following the procedure
described by Carbognani, et. al.73 This procedure is a modification of the ASTM D4928 method
where tetrahydrofuran (THF) is used as a solvent for homogenization purposes.74
32
In this method, approximately 0.5 g of sample diluted in 10 mL of THF were agitated until
the bio-oil was completely dissolved. A known mass of this solution was injected into the Karl-
Fischer Mettler Toledo Model DL-32. Later on, the water content was determined from the current
generated by titration of the sample with the K-F reagent applying the calibration for the
equipment.
3.4.3. Product Distribution
Product Distribution for oils provides the quantity of the weight fractions that can be distilled
at different temperatures. This is directly related to the economic value of the oil because the
fractions that can be distilled at lower temperature are easier to process and transform into valuable
products. This property is very important when defining the upgrading scheme required to process
the feedstock.75
Simulated Distillation (SimDist) was used to obtain the liquid product distribution following
the ASTM D-7169-05 norm76 with an in-house modification by Carbognani et al.77 In this method,
1 μL of a solution prepared with 150 mg of sample diluted in 20 mL of CS2 and previously filtered
with a 0.45 μm membrane was injected in an Agilent 6890N chromatograph instead of 0.2 μL as
established in the ASTM norm. The chromatograph is equipped with an automatic injector, a PTV
injection port and a 5 m x 0.53 mm metallic capillary column with a 0.1 μm film methyl silicone
stationary phase (Ref. P/N SS 112-102-01 from Separation Systems Inc). The in-house norm
modification was made to reduce from 25% to 5% the volumetric error from the injection of the
sample. Also, to diminish the volumetric error due to the potential presence of nanoparticles. For
example, the presence of 100 nm particles can result in a 20% error when 0.2 μL of sample are
injected.77 Using SimDist, the liquid distribution of an oil can be determined. Also, the conversion
for a product at 343°C+ can be determined using Eq. 3.4 where VGO is the oil fraction that boils
above 343 °C and Residue is the oil fraction with boiling point above 550 °C. The error of this
characterization technique is 1% for the light fractions (<550 °C) and 4% for heavier fractions
(>550 °C).78
33
The feedstock and products obtained from lignocellulose biomass contain a great quantity of
polar molecules.14 These molecules are not completely soluble in nonpolar solvents such as CS2.
In this way, to account for the CS2-insolubles left out, samples were filtered and a quantification
of the insolubles was done. For that purpose, approximately 1 g of sample was diluted in 100 mL
of CS2. The solution was passed through a 0.45 μm membrane (previously weighted) using a
vacuum pump to accelerate filtration. When all the solution was filtrated, the membrane plus the
solids were dried in a VWR oven at 80 ºC. Finally, the membrane and solids were weighted and
the CS2-insolubles were calculated as a percentage of the initial sample following Eq. 3.5.
2 [%] = []
[] ∗ 100 Eq. 3.5
3.4.4. Viscosity
A Brookfield viscometer model DV-II+ Pro coupled with a water recirculation system model
TC-502 was used to determine dynamic viscosity. The temperature range for the equipment is
between 0 and 100 ºC. The measurement starts by setting up the temperature controller at 40 ºC.
Next, the spindle or the measuring device was screwed to the bottom of the motor and the
viscometer was closed with the sample cell. Once the temperature was reached, the gap between
the bottom of the sample cell and the spindle was adjusted to a value of 0.1 mm. Then, an amount
of sample enough to cover the surface of the spindle was placed in the sample cell. The viscometer
was closed and the rotation engine was started. The rotation speed was adjusted until reaching a
torque of 50-70%. The shear is generated by the cohesive forces between the fluid and the metal
plates. Rotation was continued until the spindle completed at least 5 full rotations to guarantee
proper formation of the fluid film. Finally, the dynamic viscosity (in cP) was reported by the
equipment. Viscosity reduction can be determined using Eq. 3.6. The relative error for the viscosity
measurement is ± 5%.
[] ) ∗ 100 Eq. 3.6
3.4.5. Thermogravimetric Analysis (TGA)
Thermogravimetric analysis consists on analyzing the heat and weight changes experienced
by a liquid or solid sample when submitted to an increase of temperature under the flow of a gas.
34
For this method, a DT Q 600 system from “Thermal Analysis Instruments Company” was used.
The oil sample (approx. 10 mg) is heated at 10 ºC/min up to 1000 ºC under a nitrogen flow of 100
Std. mL/min. The equipment produced data for weight loss, differential mass loss, heat flow and
differential heat flow for different temperatures.
3.4.6. CHN Elemental Analysis
A Perkin Elmer 2400 CHN Analyzer was used to determine the elemental composition of
carbon, hydrogen and nitrogen of the samples. The composition of these elements was used to
determine the H/C ratio and the percentage of oxygen removed of the samples, the later determined
by difference since sulphur contents are negligible. This characterization technique was conducted
in the Department of Chemistry Instrumentation Facility at the University of Calgary following
the ASTM D5291 norm.79 In this method, the combustion of the sample to form CO2, H2O and
NOx was reached at very high temperature (1000 °C) in a combustion tube loaded with an oxidation
catalyst. Next, NOx was reduced to N2 in a reduction tube and passed through a separation column
to be detected by a thermal conductivity detector (TCD). Finally, the composition of carbon,
hydrogen and nitrogen were determined using a standard chemical as reference and oxygen was
calculated by difference of the other elements. To evaluate the conversion of oxygen, the degree
of deoxygenation (DOD) was defined following Eq. 3.7. The relative error for each component is
different, for carbon is 0.5%, for hydrogen is 2% and for oxygen is 3%.
The high heating value (HHV) of a bio-oil is defined by the formula presented in Eq. 3.8.9
[%] = (1 − [. %]
[. %] ) ∗ 100 Eq. 3.7
[
3.4.7. Microcarbon residue (MCR)
Microcarbon residue (MCR) determines the carbon residue remaining after evaporation and
pyrolysis of an oil under given conditions. This property is an indicative of the coke forming
tendency of an oil under thermal degradation conditions.
35
MCR was determined using the muffle furnace method developed by Hassan, Carbognani and
Pereira-Almao.80 This method is an in-house modification of the ASTM norms (ASTM D-189, D-
524 and D-4530) which reduces the analysis time and increases the samples turnaround. For this
analysis, between 10 and 20 mg of sample were weighted in a 2 mL glass vial on a 5-digits Mettler
Toledo XS 205 balance. Each sample was weighted twice. Vials were placed on the sample
platform assembly inside the muffle furnace. The platform is equipped with 26 nitrogen injection
tubes (1 per sample) to create an oxygen free environment. Next, vials were covered with a glass
cover with a 1/8” orifice in the middle and the nitrogen flush was started with a flow of 900 mL/min
for 45 min to purge the air from the furnace. Then, the temperature was increased at a rate of 10
°C/min until reaching a temperature of 520 °C that was maintained for 20 min. Finally, the furnace
was let to cool down, vials were weighted and MCR weight percentage was calculated following
Eq. 3.9. The relative error for this analytical technique is 2%.
[%] = []
[] ∗ 100 Eq. 3.9
3.4.8. Fourier-transform Infrared spectroscopy (FTIR)
Infrared spectroscopy is one of the most sensitive techniques for studying the functional
groups in solid and liquid samples.81 It is used to study the chemical footprint and main functional
groups present in oils. In this research, FTIR was vital to determine the acid reduction of the bio-
oil, more specifically, the phenols and carboxylic acids present in the feedstock.
FTIR spectra were recorded using an IRAffinity-1S spectrometer from Shimadzu. Samples
for FTIR were prepared by weighting 150 mg of oil in 10 mL of carbon tetrachloride (CCl4). This
solvent was selected because it is transparent in the 1000 to 4000 cm-1 wavelength range to avoid
its interference with the peaks of interest. The background was measured before each analysis with
a CaF2 cell containing CCl4 (dichloromethane was used for cleaning). Next, each sample was
injected in the same CaF2 cell and immediately put inside the chamber to acquire the spectrum that
ranged between 1000 to 4000 cm-1. All spectra were baseline corrected in a systematic way to
avoid subjective influence. Also, spectra were normalized by bringing the strongest absorbing
spectra signal to 10 % of transmittance. In this way, spectra for all the samples can be compared
36
between them and their relative intensities can provide information concerning chemical changes
during hydroprocessing.
The most important bands taken into consideration in this work are shown in Figure 3.3. The
band assignment is based on Silverstein’s work and it will allow the understanding of the behavior
of compounds of interest during the processing of the bio-oil.82 Region #1 is assigned to the ethers
and they are specifically located between 1350 and 1150 cm-1. Following the ethers band, there is
region #2 that represents the C=O acids, more specifically, the carboxylic acids. In this region,
there is two bands, the one at 1710 cm-1 is assigned to intermolecular bonded carboxylic acids
while the one at 1740 cm-1 corresponds to the free C=O acids. Lastly, region #3 is allocated to
phenol OH groups. The first band near 3600 cm-1 depicts phenols with no intermolecular hydrogen
bonding and the second band near 3550 cm-1 corresponds to vibrations for phenol groups forming
intermolecular hydrogen bonds with other molecules.
Figure 3.3. FTI