UNIVERSITI PUTRA MALAYSIA

EVALUATION OF MICROWAVE PYROLYSIS OF OIL PALM EMPTY FRUIT BUNCHES

ROZITA OMAR

FK 2010 94

© COPYRIG

HT UPM

EVALUATION OF MICROWAVE PYROLYSIS OF OIL PALM EMPTY

FRUIT BUNCHES

By

ROZITA OMAR

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia,

in Fullfilment of the Requirements for the Degree of Doctor of Philosophy

July 2010

© COPYRIG

HT UPM

ii

For my beloved Hafizul, Hanz and Dayana

© COPYRIG

HT UPM

iii

Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment

of the requirement for the degree of Doctor of Philosophy

EVALUATION OF MICROWAVE PYROLYSIS OF OIL PALM EMPTY

FRUIT BUNCHES

By

ROZITA OMAR

July 2010

Chair: Azni Idris, PhD

Faculty: Faculty of Engineering

Agriculture waste such as oil palm empty fruit bunch (EFB) is an environmental

concern to our country as one of the world’s biggest oil palm producers. Pyrolysis

has been used as a thermal process to treat biomass wastes due to its flexibility in

producing solid, liquid and gas products. This study evaluated the possibility to treat

EFB via microwave pyrolysis. In this study, the EFB taken from a local oil palm

mill was directly placed inside a fixed-bed quartz reactor which was placed in a

modified household microwave oven, where both drying and pyrolysis took place

simultaneously. Microwave absorbers were added to elevate the reaction temperature

so as to reach the required temperature for a pyrolysis reaction to take place.

Parameters, such as effects of residence time, addition of inorganic materials

(catalysts) and pre-treatment of the EFB, were studied. Meanwhile, a comparison

experiment with a conventionally heated reactor was also conducted.

Fuel, chemical and dielectric characterization of the EFB undertaken in this study

confirmed that it is a good candidate for a microwave pyrolysis process as it is

© COPYRIG

HT UPM

iv

comparable to other biomass. However, dielectric properties of the EFB indicated

that it is almost a transparent material to microwave, and for this reason, addition of

microwave absorber is required. Studying several microwave absorbers, namely

SiC, activated carbons (coconut and palm kernel shell) and char which were

produced from a previously conducted experiment, concluded that 5% coconut

activated carbon in a granular form was enough to maintain a reaction temperature

above 500oC within 15 minutes (60.8

oC/min) with highest productivity of 5.1 mol%

syngas per g EFB per g absorber.

Two types of common pre-treatment, namely cutting and drying, were also studied.

Reduction of the EFB size without drying seemed to favor gas production; however,

untreated sample was found to give the highest H2 composition but with a similar

CH4 concentration as in the other treatments. A slow release of volatile matters in

the untreated sample might have provided the opportunity for secondary reaction to

produce more H2. Nevertheless, the addition of inorganic materials for tar

minimization and syngas enhancement (NaCO3, HSZM5, CaO and CaCO3) did not

influence the product distribution. On the other hand, the composition of gas was

found to be greatly influenced by the addition of HSZM5, especially H2. Meanwhile,

increasing residence time (0.02 - 0.10 s) of volatiles within the reactor was shown to

have increased gas composition (increment of 68.4% for H2), particularly for the

production of CH4 which resulted in a higher calorific value of the gas.

Liquid product (bio-oil) and solid product (char) were also characterized for their

potential end use. The char produced in this study has high carbon content (68%),

giving it a moderate calorific value at 21.5 MJ/kg, which is similar to that of the

© COPYRIG

HT UPM

v

commercially produced EFB char, rendering it a good candidate for solid fuel

substitute. The EFB char is characterized as mesoporous with highest pore size

distribution around 4 nm. The BET surface area is modest at 14.2 m2g

-1 and has high

mesopore area of 28.3 m2g

-1. These characteristics present microwave pyrolysis of

EFB as a superior alternative for the carbonization step for activated carbon

preparation. Also, EFB char produced from this study is suitable for soil

amendment. Highly oxygenated, acidic and viscous bio-oil produced from pyrolysis

of EFB has high heating value (30.8 MJ/kg) which is higher than wood tar. Palmitic

acid is the most abundant chemical component (12.0-36.4%) in bio-oil.

A shorter time was needed in the microwave pyrolysis of EFB compared to the

conventional one, and this gives a higher gas production with four times better

calorific value (7.6 MJ/m3) but lower calorific value as compared to pyrolyzed coffee

hulls and rice straw. The energy cost to produce twelve times higher energy products

in the EFB microwave pyrolysis is lower, i.e. at 1.90 cent/MJ as compared to 49.90

cent/MJ in conventional heating. These findings reflect the potential of microwave

pyrolysis as an alternative method to both treat waste and produce energy.

In summary, EFB was successfully pyrolyzed using microwave as heating source.

The bio-oil product has better quality compared to wood oil therefore it has

potentially for fuel oil substitute. The char also has the potential for activated carbon

or solid fuel. EFB pyrolysis using microwave produced better syngas and cost

cheaper compared to conventional heating. Further study is needed to optimize the

parameters as to produce product of choice.

© COPYRIG

HT UPM

vi

Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai

memenuhi keperluan untuk ijazah Doktor Falsafah

PENILAIAN PIROLISIS GELOMBANG MIKRO TANDAN KELAPA

SAWIT KOSONG

Oleh

ROZITA OMAR

Julai 2010

Pengerusi: Azni Idris, PhD

Fakulti: Fakulti Kejuruteraan

Bahan buangan pertanian seperti tandan kelapa sawit kosong (TKSK) adalah

kerisauan alam sekitar kepada negara kita yang merupakan antara pengeluar minyak

kelapa sawit terbesar dunia. Pirolisis merupakan proses terma yang telah digunakan

untuk merawat bahan buangan biojisim kerana fleksibilitinya untuk menghasilkan

produk pepejal, cecair dan gas. Kajian ini menilai kemungkinan untuk merawat

TKSK menggunakan pirolisis gelombang mikro untuk menghasilkan gas sintesis

(singas) yang tinggi. Di dalam kajian ini, TKSK yang diperoleh dari sebuah kilang

pemprosesan minyak kelapa sawit tempatan telah diletakkan ke dalam reaktor

lapisan tetap yang diperbuat daripada kuarza yang ditempatkan di dalam ketuhar

gelombang mikro domestik, yang mana proses pengeringan dan pirolisis berlaku

secara serentak. Sementara itu, bahan penyerap gelombang mikro telah ditambah

untuk menaikkan suhu tindakbalas sehingga mencapai suhu yang diperlukan untuk

membolehkan tindakbalas pirolisis berlaku. Parameter-parameter seperti kesan masa

mastautin, penambahan bahan tak-organik (pemangkin) dan pra-rawatan TKSK telah

© COPYRIG

HT UPM

vii

dikaji. Ekperimen perbandingan dengan reaktor yang dipanaskan secara

konvensional juga dijalankan.

Ciri-ciri bahan api dan kimia TKSK telah memastikan bahawa ia ialah kandidat yang

sesuai untuk proses pirolisis gelombang mikro yang sebanding dengan biojisim lain.

Sifat dielektrik TKSK telah membuktikan bawa ia merupakan bahan yang telus

gelombang mikro, dan oleh itu penambahan bahan penyerap gelombang mikro

adalah diperlukan. Kajian beberapa bahan penyerap gelombang mikro seperti SiC,

karbon-karbon teraktif (tempurung kelapa dan kelompang kepala sawit) serta arang

yang dihasilkan dari eksperimen terdahulu menyimpulkan bahawa 5% karbon

teraktif dari tempurung kelapa berbentuk butiran adalah cukup untuk mengekalkan

suhu tindakbalas di atas 500oC didalam masa 15 minit (60.8

oC/min) dengan

produktiviti tertinggi iaitu 5.1 mol% singas per g EFB per g penyerap.

Dua jenis pra-rawatan am iaitu pemotongan dan pengeringan juga telah dikaji.

Pengurangan saiz TKSK tanpa dikeringkan didapati telah membantu produksi gas

tetapi sampel tanpa rawatan memberikan komposisi H2 yang tertinggi walaupun

kepekatan CH4 adalah sebanding dengan pra-rawatan lain. Pembebasan jirim

meruap oleh sampel tidak dirawat yang lambat mungkin telah memberi peluang

tindakbalas sekunder untuk menghasilkan lebih banyak H2. Bagaimanapun,

penambahan bahan tak-organik untuk mengurangkan penghasilan tar dan

penambahan singas (NaCO3, HSZM5, CaO dan CaCO3) tidak mempengaruhi taburan

produk. Walau bagaimanapun, komposisi gas adalah sangat dipengaruhi oleh

penambahan HSZM5, terutamanya H2. Kenaikan masa mastautin (0.02 - 0.10 s)

jirim di dalam reaktor telah membantu menaikkan komposisi gas (kenaikan 68.4%

© COPYRIG

HT UPM

viii

untuk H2), terutamanya penhasilan CH4 yang telah menyebabkan gas berkalori tinggi

dihasilkan.

Produk cecair (bio-minyak) dan produk pepejal (arang) juga dicirikan untuk menilai

potensi kegunaan bahan-bahan ini. Arang yang dihasilkan dari kajian ini didapati

mengandungi kandungan karbon yang tinggi yang telah memberikan nilai kalori

sebanyak 21.5 MJ/kg iaitu sebanding dengan arang TKSK yang dihasilkan secara

komersil, dan dapatan ini telah menjadikan ia kandidat yang baik untuk bahan api

pepejal gantian. Arang daripada TKSK telah dicirikan sebagai berliang-meso dengan

agihan liang tertinggi bersaiz 4 nm. Luas permukaan BET adalah sederhana pada

14.2 m2g

-1 dan keluasan berliang-meso yang tinggi pada 28.3 m

2g

-1. Ciri-ciri ini

membuatkan pirolisis gelombang mikro satu alternatif yang lebih baik untuk langkah

karbonisasi untuk penyediaan karbon teraktif. Arang daripada TKSK dari kajian ini

sesuai untuk pengubahsuaian tanah. Bio-minyak yang dihasilkan adalah beroksigen

tinggi, berasid dan likat yang mempunyai nilai pemanasan yang tinggi (30.8 MJ/kg),

lebih tinggi dari tar daripada kayu. Asid palmitik ialah bahan kimia yang terbanyak

(12.0-36.4%) di dalam bio-minyak yang mungkin diwarisi dari buah kelapa sawit.

Hanya masa yang singkat diperlukan dalam pirolisis gelombang mikro TKSK

berbanding dengan cara konvensional dengan memberikan hasil produk gas yang

tinggi dengan nilai kalori empat kali lebih tinggi (7.6 MJ/m3) sesuai untuk digunakan

sebagai bahan api pemanasan sederhana tetapi nilai kalorinya adalah kurang

berbanding gas pirolisis kulit kopi dan jerami padi. Kos tenaga untuk menghasilkan

dua belas kali lebih tinggi tenaga produk dalam pirolisis gelombang mikro TKSK

adalah kurang iaitu 1.90 sen/MJ berbanding 49.90 sen/MJ. Hasil penyelidikan ini

© COPYRIG

HT UPM

ix

menunjukkan bahawa pirolisis mikro gelombang adalah satu metod alternatif untuk

merawat bahan buangan dan juga penghasilan tenaga.

Kesimpulannya, TKSK telah berjaya dipirolisis menggunakan gelombang mikro

sebagai sumber pemanas. Produk bio-minyak adalah lebih berkualiti berbanding

minyak kayu oleh itu ia berpotensi untuk dijadikan bahan bakar gentian. Produk

arang juga berpontensi sebagai karbon teraktif atau bahan bakar pepejal. Pirolisis

EFB menggunakan gelombang mikro menghasilkan produk syngas yang lebih baik

dan lebih murah berbanding pemanasan konvensional. Walaubagaimana pun, kajian

mendalam diperlukan untuk mendapatkan parameter optimum untuk menghasilkan

produk yang dipilih.

© COPYRIG

HT UPM

x

ACKNOWLEDGEMENTS

Alhamdulillah to Almighty for giving me the patience and perseverance to finish this

thesis to the end. To my beloved husband, children and parents, I appreciate all the

love and support. I would like to dedicate my gratitude to my supervisors Prof. Dr.

Azni Idris, Prof. Dr. Kaida Khalid, Associate Prof. Dr. Robiah Yunus and Prof. Dr.

Gwendoline Ee Cheng Lian. My deepest thanks are for my examiners Prof. Jim

Swithenbank, Associate Prof. Dr. Norhafizah and Prof. Dr. Dzulkifly Kuang for their

constructive comments on my thesis. My special appreciation is extended to my

colleagues Dr. Tinia, Dr. Salmiaton, Dr. Dayang, Dr. Siti Mazlina, Dr. Wan Azlina,

Mdm. Faezah, Mr. Razif Harun and all Chemical Engineering Department lecturers

for helping me in any way throughout my study. My appreciation also goes to the

technicians, research officers and science officers at Department of Chemical

Engineering, Department of Mechanical Engineering, Departments of Physics and

Chemistry and Department of Soil Science who have helped me at the experimental

stage. My heartfelt gratitude to have helping hands of my fellow friends Aida Isma,

Dr. Chong, Brother Asri, Mohamed, Mohamad, Mr. Ali, Baiti, Mustika, Taha, Faiz,

Shanti, Pak Darmadi, Azahari, Mustafa, Fioni and others that I might have forgotten

to mention their names. Thank you also to Universiti Putra Malaysia for giving me

the scholarship to further my study and MOSTI for trusting me the grant to pursue

this project. Lastly to those I failed to remember, thank you very much.

© COPYRIG

HT UPM

xi

I certify that a Thesis Examination Committee has met on 2 July 2010 to conduct the

final examination of Rozita Omar on her thesis entitled “Evaluation of Microwave

Pyrolysis of Oil Palm Empty Fruit Bunch” in accordance with the Universities and

University Colleges Act 1971 and the Constitution of the Universiti Putra Malaysia

[P.U.(A) 106] 15 March 1998. The Committee recommends that the student be

awarded the Doctor of Philosophy.

Members of the Thesis Examination Committee were as follows:

Salmiaton Ali, PhD

Associate Professor

Faculty of Engineering

Universiti Putra Malaysia

(Chairman)

Norhafizah Abdullah, PhD

Associate Professor

Faculty of Engineering

Universiti Putra Malaysia

(Internal Examiner)

Dzulkifly Kuang Abdullah, PhD

Professor

Faculty of Science

Universiti Putra Malaysia

(Internal Examiner)

Jim Swithenbank, PhD

Professor

Chemical and Biological Engineering

Faculty of Engineering

University of Sheffield

United Kingdom

(External Examiner)

________________________________

SHAMSUDDIN SULAIMAN, PhD

Professor and Deputy Dean

School of Graduate Studies

Universiti Putra Malaysia

Date: 2 September 2010

© COPYRIG

HT UPM

xii

This thesis was submitted to the Senate of Universiti Putra Malaysia and has been

accepted as fulfilment of the requirement for the degree of Doctor of Philosophy.

The members of the Supervisory Committee were as follows:

Azni Idris, PhD

Professor

Faculty of Engineering

Universiti Putra Malaysia

(Chairman)

Kaida Khalid, PhD

Professor

Faculty of Science

Universiti Putra Malaysia

(Member)

Robiah Yunus, PhD

Associate Professor

Faculty of Engineering

Universiti Putra Malaysia

(Member)

Gwendoline Ee Chiang Lian, PhD

Professor

Faculty of Science

Universiti Putra Malaysia

(Member)

________________________________________

HASANAH MOHD GHAZALI, PhD

Professor and Dean

School of Graduate Studies

Universiti Putra Malaysia

Date: 6 September 2010

© COPYRIG

HT UPM

xiii

DECLARATION

I declare that the thesis is my original work except for quotations and citations which

have been duly acknowledged. I also declare that it has not been previously, and is

not concurrently, submitted for any other degree at Universiti Putra Malaysia or at

any other institution

___________________________

ROZITA OMAR

Date: 2 July 2010

© COPYRIG

HT UPM

xiv

TABLE OF CONTENTS

Page

DEDICATIONS ii

ABSTRACT iii

ABSTRAK vi

ACKNOWLEDGEMENTS x

APPROVAL SHEET xi

DECLARATION FORM xiii

LIST OF TABLES xvii

LIST OF FIGURES xix

LIST OF NOMENCLATURE xxii

LIST OF ABBREVIATION AND ACRONYMS xxiv

CHAPTER

1 INTRODUCTION 1.1

1.1 Background 1.1

1.2 Problem Statements 1.5

1.3 Research Objectives 1.10

1.4 Thesis Layout 1.11

2 LITERATURE REVIEW 2.1

2.1 Introduction 2.1

2.2 Properties of Oil palm Solid Waste 2.1

2.3 Thermal Conversion of Oil palm Waste 2.3

2.3.1 Combustion in Boiler 2.3

2.3.2 Combustion in Fluidized Bed 2.7

2.3.3 Gasification 2.9

2.3.4 Pyrolysis 2.11

2.4 Pyrolysis Process 2.13

2.4.1 Pyrolysis Mechanism 2.13

2.4.2 Conventional Pyrolysis 2.18

2.4.3 Fast Pyrolysis 2.19

2.5 Main Parameters Governing Pyrolysis 2.20

2.5.1 Effect of Temperature 2.20

2.5.2 Effect of Particle Size 2.26

2.5.3 Effect of Heating Rate 2.28

2.5.4 Effect of Residence Time 2.29

2.5.5 Effect of Initial Moisture 2.31

2.5.6 Effect of Catalyst Addition 2.32

2.6 Pyrolysis Products 2.35

2.6.1 Char 2.35

2.6.2 Bio-oil 2.41

2.6.3 Non-condensable Gas 2.46

2.6.4 Synthesis Gas 2.49

2.7 Microwave Fundamentals 2.51

2.7.1 The Interactions between Microwave and Materials 2.51

2.7.2 Conductive Losses 2.54

© COPYRIG

HT UPM

xv

2.7.3 Polarization 2.54

2.7.4 Variation of Dielectric Properties with Moisture

and Temperature

2.57

2.8 Microwave Volumetric Heating 2.57

2.9 Addition of Absorber in Microwave Pyrolysis 2.63

2.10 Benefits and Challenges of Microwave Heating 2.66

2.11 Microwave Treatment of Waste 2.69

2.11.1 Microwave Pyrolysis of Tyres 2.70

2.11.2 The Microwave Pyrolysis of Sludge 2.71

2.11.3 The Microwave Pyrolysis of Glycerol 2.73

2.11.4 The Microwave Pyrolysis of Agro-wastes 2.75

3 CHARACTERIZATION OF EMPTY FRUIT BUNCH AND

MICROWAVE PRELIMINARY

3.1

3.1 Introduction 3.1

3.2 Materials and Methods 3.1

3.2.1 Empty Fruit Bunch 3.1

3.2.2 Microwave Absorbers 3.2

3.2.3 Characterization of Empty Fruit Bunch 3.3

3.2.4 Microwave Electric Properties, Power Output and

Distribution

3.9

3.3 Results and Discussions 3.15

3.3.1 Proximate, Decomposition and Ultimate Analysis 3.15

3.3.2 Physical, Thermal and Inorganic Characteristics 3.22

3.3.3 Dielectric Properties of EFB 3.26

3.3.4 Microwave Heating Preliminary 3.32

3.4 Conclusions 3.40

4 MICROWAVE PYROLYSIS OF EMPTY FRUIT BUNCH 4.1

4.1 Introduction 4.1

4.2 Materials and Methods 4.1

4.2.1 Empty Fruit Bunch 4.1

4.2.2 Modification of House-hold Microwave Oven 4.3

4.2.3 Experimental Set-up 4.3

4.2.4 Experimental Procedure 4.8

4.2.5 Inorganic Materials Addition 4.9

4.2.6 Conventional Pyrolysis of EFB 4.10

4.2.7 Product Recovery 4.11

4.2.8 Product Gas Analysis 4.12

4.3 Results and Discussion 4.16

4.3.1 Effect of Microwave Absorbers Type and Concentration 4.16

4.3.2 Effect of Pre-treatment of Sample 4.25

4.3.3 Effects of Inorganic Materials Addition 4.30

4.3.4 Effect of Residence Time 4.33

4.3.5 Comparison between Conventional and Microwave

Pyrolysis

4.36

4.4 Conclusion 4.43

5 CHARACTERIZATION OF PYROLYSIS PRODUCTS 5.1

5.1 Introduction 5.1

© COPYRIG

HT UPM

xvi

5.2 Materials and Methods 5.1

5.2.1 Materials 5.1

5.2.2 Characterization of Bio-oil and Char 5.2

5.3 Results and Discussion 5.4

5.3.1 Characteristics of Char 5.4

5.3.2 Characteristics of Bio-oil 5.15

5.3.3 Quality of Produced Gas 5.24

5.3.4 Energy Comparison between Microwave and

Conventional

5.27

5.4 Conclusion 5.29

6 CONCLUSION AND RECOMMENDATIONS 6.1

6.1 Conclusions 6.1

6.2 Recommendations for Future Works 6.4

REFERENCES R.1

APPENDICES A.1

APPENDIX A – Lignocellulosic Content Determination A.1

APPENDIX B – Calculation of Residence Time A.3

APPENDIX C – Chromatogram for Gas Sample Analysis A.5

APPENDIX D – Conditions of Conventional Pyrolysis A.9

APPENDIX E – GC-MS Analysis of Bio-oil A.10

APPENDIX F – Scanning Electron Microscopy Images A.21

APPENDIX G – Waterloo-mechanism A.22

BIODATA OF STUDENT A.5

LIST OF RELATED PUBLICATIONS A.6