Catalytic hydrodeoxygenation of guaiacol and its application in bio oil upgrading

In this study, Al-MCM-41 supported monometallic Ni, Co and Fe and bimetallic Pd-Co and Pd-Fe catalysts were prepared, characterized and evaluated for HDO of guaiacol at atmospheric press

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TRAN THI TO NGA

Prof Dr Yoshimitsu Uemura

22 Chau Hiep town, Nam Phuoc ward, Duy Xuyen

district, Quang Nam province,

Vietnam

UNIVERSITI TEKNOLOGI PETRONAS CATALYTIC HYDRODEOXYGENATION OF GUAIACOL AND

ITS APPLICATION IN BIO-OIL UPGRADING

by TRAN THI TO NGA

The undersigned certify that they have read, and recommend to the Postgraduate Studies Programme for acceptance this thesis for the fulfillment of the requirements for the degree stated

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Prof Dr Yoshimitsu Uemura

Assoc Prof Dr Anita Bt Ramli

Assoc Prof Dr Suriati Bt Sufian

CATALYTIC HYDRODEOXYGENATION OF GUAIACOL AND

ITS APPLICATION IN BIO-OIL UPGRADING

by

TRAN THI TO NGA

A Thesis Submitted to the Postgraduate Studies Programme

as a Requirement for the Degree of

DOCTOR OF PHILOSOPHY CHEMICAL ENGINEERING UNIVERSITI TEKNOLOGI PETRONAS BANDAR SERI ISKANDAR,

PERAK

OCTOBER 2018

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Date : _ Date :

TRAN THI TO NGA

22 Chau Hiep town, Nam Phuoc ward, Duy Xuyen

district, Quang Nam province,

Vietnam

Prof Dr Yoshimitsu Uemura

DEDICATION

To my family for their unconditional love, encouragement and support

To my supervisor who always be the inspiration for this thesis

vi

ACKNOWLEDGEMENTS

I would like to express my deepest gratitude and appreciation to my supervisor, Prof Yoshimitsu Uemura, for his excellent and constant guidance, patience, generous support, and encouragement I am also very thankful to my co-supervisors, AP Dr Anita Binti Ramli and Dr Sujan Chowdhury, for tremendous support and valuable discussion

Moreover, I would like to offer my most profound gratitude to Centre for Biofuel and Biochemical Research, and Chemical Engineering department, Universiti Teknologi PETRONAS, Malaysia for providing a congenial work environment and state-of-the-art research facilities I gratefully acknowledge Prof Masaharu Komiyama and Prof Taufiq Yap Yun Hin for their valuable supports, comments and suggestions

I would like to acknowledge the financial support from Mitsubishi Corporation Educational Trust Fund and Universiti Teknologi PETRONAS, Malaysia

Last but not least, I would like to thank to my parents for raising, loving and supporting me all my life; to my brother for his guideline in my childhood; to my husband, Trinh Hoai Thanh, for being on my side, supporting, inspiration and encouraging me to achieve my goals; and to my daughter for what she means to my life

ABSTRACT

Fast pyrolysis of lignocellulosic biomass is an attractive thermochemical conversion process to produce bio-oil as an alternative liquid fuel source Upgrading of

bio-oil via hydrodeoxygenation (HDO) is an important route to accomplish this

renewable energy production process However, there are still some challenges such as high hydrogen consumption, carbon loss, catalyst deactivation, complex reaction network, and limitation in upgrading of real bio-oil In this study, Al-MCM-41 supported monometallic (Ni, Co and Fe) and bimetallic (Pd-Co and Pd-Fe) catalysts were prepared, characterized and evaluated for HDO of guaiacol at atmospheric pressure in a fixed-bed continuous flow reactor A detail kinetic model has been established for HDO of guaiacol over Pd-Co and Pd-Fe catalysts Furthermore, Pd-Fe and Pd-Co catalysts were screened for successive pyrolysis and catalytic upgrading of lignin to produce bio-oil In vapor-phase HDO of guaiacol, Ni was found as an active metal for methanization activity while Co favored the deoxygenation activity The Co/Al-MCM-41 catalyzed not only HDO to remove oxygen but also transalkylation to

prevent the carbon loss via methanization Furthermore, increasing reaction

temperature improved the HDO and suppressed the hydrogenation but promoted the methanization activities In comparison with Co catalyst, Fe catalyst had higher HDO yield and lower gas-phase yield in HDO of guaiacol Moreover, bimetallic Pd-Co and Pd-Fe shown higher stability and HDO yield than monometallic Co and Fe The addition of Pd enhanced significantly the stability of both Co and Fe catalysts since it might prevent the coke formation during the HDO reaction Pd-Fe had higher stability, regeneration ability and lower gasification activity than Pd-Co catalyst From the kinetic model, guaiacol was converted to phenol through demethoxylation over Pd-Fe catalyst while it was transformed to catechol and further to phenol over Pd-Co catalyst The lignin-derived bio-oil mainly contained phenolic compounds which have one to three oxygen atoms The catalytic upgrading could eliminate significantly the oxygen

viii

in phenolic molecular to produce the lower oxygen content bio-oil In summary, Pd-Fe/Al-MCM-41 present as a suitable catalyst for upgrading of lignin-derived bio-oil since it produced not only more monooxygenated phenolic but also less dioxygenated, trioxygenated and gas-phase products than Pd-Co catalyst

ABSTRAK

Pirolisis pantas dengan menggunakan biomas lignoselulosa merupakan proses penukaran termokimia yang berkesan untuk menghasilkan bio-minyak yang memainkan peranan sebagai sumber alternatif bahan api cecair Penaikkan taraf bio-minyak melalui hidrodeoksigenasi (HDO) merupakan laluan proses yang penting untuk memastikan pengeluaran tenaga yang boleh diperbaharui lancar Walau bagaimanapun, masih terdapat banyak cabaran seperti penggunaan hidrogen yang tinggi, kehilangan karbon, penyahaktifan pemangkin, rangkaian reaksi yang kompleks, dan had dalam peningkatan bio-minyak tulen Dalam kajian ini, Al-MCM-41 menyokong mono-logam (Ni, Co dan Fe) dan bi-logam (Pd-Co dan Pd-Fe) pemangkin dikategorasikan dan dinilai untuk HDO guaikol yang beroperasi pada tekanan atmosfera dalam reaktor tetap Model kinetik yang terperinci iaitu HDO guaikol melalui pemangkin Pd-Co dan Pd-Fe telah dihasilkan Selain daripada itu, pemangkin Pd-Fe dan Pd-Co telah dikaji melalui pirolisis berturutan dan peningkatan lignin untuk menghasilkan bio-minyak Tambahan pula, bi-logam Pd-Fe dan Pd-Co pemangkin disaring untuk Dalam fasa wap HDO, Ni telah dijumpai sebagai logam aktif untuk aktiviti pembukaan cincin manakala Co lebih sesuai untuk aktiviti deoksigenasi Co/Al-MCM-41 pemangkin bukan sahaja HDO untuk mengeluarkan oksigen tetapi transaklisasi untuk mengelakkan kehilangan karbon melalui aktiviti metanisasi Selainitu, meringgikai suhu reaksi telah bertanbah baik HDO dan merirdas hidrogerasi, tetapi merggalakkar aktiviti metarisasi Dalam membandingkan dengan pemangkin Co, pemangkin Fe mempunyai HDO hasil yang lebih tinggi dan hasil fasa gas yang kurang dalam HDO guaikol Selain itu, bi-logam Pd-Co dan Pd-Fe menunjukkan kestabilan yang lebih tinggi dan hasil HDO daripada mono-logam Co dan Fe Penambahan Pd meningkatkan dengan ketara kestabilan pemangkin Co dan Fe sebab pemangkin yang dinyatakan mungkin dapat mengelakkan pembentukan kok semasa reaksi HDO Pd-Fe mempunyai kestabilan yang lebih tinggi, keupayaan penjanaan semula dan aktiviti gasifikasi yang lebih rendah daripada

x

pemangkin Pd-Co Daripada model kinetik, guaiacol telah ditukar kepada fenol melalui demethoxylation dengan pemangkin Pd-Fe manakala ia telah berubah kepada catechol dan seterusnya kepada fenol dengan pemangkin Pd-Co Lignin yang diperolehi daripada bio-minyak terutamanya mengandungi sebatian fenolik yang mempunyai satu hingga tiga atom oksigen Penaik taraf pemangkin dapat menghapuskan oksigen dalam molekul fenolik untuk menghasilkan bio-minyak dengan kandungan oksigen yang rendah Ringkasnya, Pd-Fe/Al-MCM-41 hadir sebagai pemangkin yang sesuai untuk menaik taraf bio-minyak lignin kerana ia menghasilkan bukan sahaja menghasillar lebih bayak mono-oksigen fenol, tetapi juga kurang diokseganisi, tri-oksigenasi dan fasa gas produk berbanding pemangkin Pd-Co

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© Tran Thi To Nga, 2018 Institute of Technology PETRONAS Sdn Bhd All rights reserved

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TABLE OF CONTENT

ABSTRACT vii

ABSTRAK ix

LIST OF FIGURES xv

LIST OF TABLES xx

LIST OF ABBREVIATION xxi

LIST OF SYMBOLS xxiii

CHAPTER 1 INTRODUCTION 1

1.1 Back ground of study 1

1.2 Problem statement 3

1.3 Objective 5

1.4 Scope of Research 5

1.5 Thesis outline 7

CHAPTER 2 LITERATURE REVIEW 9

2.1 Overview 9

2.2 Pyrolysis oil 10

2.2.1 Bio-oil production 10

2.2.2 Bio-oil properties 13

2.3 Upgrading of bio-oil 17

2.3.1 Zeolite cracking 18

2.3.2 Catalytic hydrodeoxygenation (HDO) 18

2.3.2.1 Catalyst in HDO 21

2.3.2.2 Reaction condition 22

2.3.2.3 HDO of actual oil in batch reactor 23

2.3.2.4 HDO of actual bio-oil in continuous flow reactor 24

2.3.2.5 HDO of guaiacol in continuous flow reactor 25

2.4 Catalyst deactivation and regeneration 29

2.5 HDO reactions pathway and mechanism 31

2.6 Research Gap 35

CHAPTER 3 METHODOLOGY 38

3.1 Overall Research Project’s Methodology 38

3.2 Materials 39

3.3 Catalyst preparation 41

3.3.1 Monometallic Ni and Co catalysts 41

3.3.2 Bimetallic Pd-Me catalysts (Me = Co or Fe) 42

3.4 Characterization of catalyst 42

3.5 Products analysis 45

3.6 Catalytic HDO of model compound 46

3.6.1 Fixed-bed reactor 47

3.6.2 Catalytic HDO on Al-MCM-41 supported Ni and Co catalysts 48

3.6.3 Catalytic HDO on Al-MCM-41 supported Pd, Fe and Co catalysts 49

3.7 Kinetic study 51

3.7.1 Reaction rate equations 51

3.7.2 MATLAB modeling and optimization 53

3.8 Catalytic upgrading of lignin-derived bio-oil 54

CHAPTER 4 RESULTS AND DISCUSSION 57

4.1 Catalyst characterization 57

4.1.1 Al-MCM-41 supported Ni and Co catalysts 57

4.1.2 Al-MCM-41 supported Pd-Co and Pd-Fe catalysts 64

4.2 Catalytic HDO of guaiacol 70

4.2.1 GC-FID calibration 70

4.2.2 Blank test for hydrotreatment of guaiacol 72

4.2.3 HDO of guaiacol over Ni and Co catalysts 73

4.2.3.1 Effect of metal sites 73

4.2.3.2 Effect of reaction conditions 74

4.2.3.3 Reaction pathway of HDO of guaiacol on Al-MCM-41 supported Ni and Co 80

4.2.3.4 Catalyst deactivation and regeneration 81

4.2.4 HDO of guaiacol over bimetallic Pd-Co and Pd-Fe catalysts 87

4.2.4.1 The synergistic effect of bimetallic in catalytic HDO 87

4.2.4.2 Catalyst regeneration 91

4.3 Kinetic and reaction pathway of catalytic HDO of guaiacol 99

4.3.1 Study on HDO of different feedstock 99

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4.3.2 Kinetic study of HDO of guaiacol 103

4.3.2.1 Reaction networks 103

4.3.2.2 Kinetic model for bimetallic catalysts 105

4.4 Catalytic upgrading of lignin-derived bio-oil 112

4.4.1 Successive of pyrolysis and upgrading process 112

4.4.2 Bio-oil composition 115

CHAPTER 5 CONCLUSION 119

5.1 Conclusions 119

5.2 Recommendations 121

APPENDIX A LIST OF SUPPORTING FIGURES AND TABLES 139

APPENDIX B SAMPLE CALCULATIONS 166

APPENDIX C OPTIMIZATION CODE FOR KINETIC USING MATLAB 168

LIST OF FIGURES

Figure 2.1: Products from thermal biomass conversion 9

Figure 2.2: Pyrolysis for biomass conversion [59] 11

Figure 2.3: Phase behavior of aged bio-oil LP-raw and LP-310T form gum phase at 9 or 12 months storage while LP-280T and LP-330T keep one phase after 12 months storage [21] (LP-T are pyrolysis oil from torrified biomass) 15

Figure 2.4: Relative peak area percentage distribution of major component of EFB (#75) and pine wood (#85) bio-oil samples [58] 16

Figure 2.5: Reaction pathways for pyrolysis of lignocellulosic biomass [83] 17

Figure 2.6: Number of HDO related publications according to Web of Science (Data retrieved on January 13, 2018 ) [51] 19

Figure 2.7: Reaction pathway of furfural on Cu catalyst at 1 atm H2 pressure, 290C [128] 31

Figure 2.8: Two reaction possibility of hydrogen with furfural on catalyst surface [128] 32

Figure 2.9: Proposed reaction pathway for the HDO of phenol at 40 bar initial H2 and 473K [129] 32

Figure 2.10: Proposed model for hydrotreating of pine pyrolysis oil [130] 34

Figure 3.1: Flow chart of overall research project 38

Figure 3.2: Flow chart of catalyst preparation of monometallic catalyst 41

Figure 3.3: Flow chart of catalyst preparation of bimetallic catalyst 42

Figure 3.4: A schematic diagram of continuous fixed-bed tubular reactor for catalytic HDO of model compound 47

Figure 3.5: Flow chart of catalytic HDO of guaiacol on Ni and Co catalysts 48

Figure 3.6: Flow chart of catalytic HDO of guaiacol on Pd, Fe and Co catalysts 50

Figure 3.7: A schematic diagram of continuous fixed-bed tubular reactor for catalytic upgrading of lignin-derived bio-oil 55

Figure 4.1: N2 adsorption (solid line)/desorption (dashdot line) isotherms (A) and BJH pore size distribution (from adsorption branch) (B) of fresh Al-MCM-41 supported Ni and Co catalysts 58

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Figure 4.2: TEM images of fresh catalysts (A) Ni/Al-MCM-41, (B) Co/Al-MCM-41, (C) Ni-Co/Al-MCM-41 59 Figure 4.3: SEM images combined with EDX spectra of fresh Al-MCM-41 supported

Ni and Co catalysts A) 10Co/Al-MCM-41, B) 10Ni/Al-MCM-41 60 Figure 4.4: XRD patterns of support and fresh metal modified catalysts A) Fresh and B) reduced catalysts 61 Figure 4.5 Temperature-programmed reduction (TPR-H2) profile of fresh metal modified Al-MCM-41 catalysts 63 Figure 4.6 NH3-TPD profiles of support and Co catalysts 63 Figure 4.7: N2 adsorption (solid line)/desorption (dashdot line) isotherms (A) and BJH pore size distribution (from adsorption branch) (B) of fresh Al-MCM-41

supported Pd-Me (Me = Co or Fe) catalysts 65 Figure 4.8 TEM images of fresh catalysts A) Co/Al-MCM-41, B) Fe/Al-MCM-41, C) Pd-Co/Al-MCM-41, D) Pd-Fe/Al-MCM-41 66 Figure 4.9 FESEM images of (A) Pd-Co/Al-MCM-41 and (B) Pd-Fe/Al-MCM-41, EDX spectra and elemental mapping images of (C) Pd-Co/Al-MCM-41 and (D) Pd-Fe/Al-MCM-41 67 Figure 4.10 Hydrogen temperature-programmed reduction (TPR-H2) of fresh Al-MCM-41 supported Pd-Co and Pd-Fe catalysts 68 Figure 4.11 XRD patterns of Al-MCM-41 supported Pd-Co and Pd-Fe catalysts A) Fresh and B) reduced catalyst 69 Figure 4.12 Conversion and product yields of guaiacol HDO on fresh Ni and Co supported Al-MCM-41 catalysts Reaction condition: T = 400 oC, P = 1 atm,

H2/guaiacol molar ratio = 25, W/F = 1.67 h, TOS = 30 min 73 Figure 4.13 Conversion and product yields of guaiacol HDO on fresh Co/Al-MCM-

41 catalyst (A) Guaiacol conversion, (B) Oxygenated products, (C) Oxygen-free products Reaction condition: T = 400 oC, P = 1 atm, H2/guaiacol molar ratio = 25, TOS = 30 min 75 Figure 4.14 Conversion and product yields of HDO of guaiacol (A) Co/Al-MCM-41; (B) Ni/Al-MCM-41 Reaction condition: T = 400 oC, P = 1 atm, H2/guaiacol molar ratio = 25, TOS = 30 min 76

Figure 4.15 Conversion and product yields of HDO of guaiacol on Co/Al-MCM-41 and Ni/Al-MCM-41 Reaction condition: P = 1 atm, H2/guaiacol molar ratio = 25, W/F = 1.67 h, TOS = 30 min 77 Figure 4.16 Chromatograms of liquid samples of HDO of guaiacol on Co/Al-MCM-

41 at various reaction temperatures Reaction condition: P = 1 atm, H2/guaiacol molar ratio = 25, W/F = 1.67 h, TOS = 30 min 79 Figure 4.17 Chromatograms of liquid samples of HDO of guaiacol on Ni/Al-MCM-

41 at various reaction temperatures Reaction condition: P = 1 atm, H2/guaiacol molar ratio = 25, W/F = 1.67 h, TOS = 30 min 79 Figure 4.18 Proposed reaction network for HDO of guaiacol on Ni and Co supported Al-MCM-41 catalysts HDO reactions catalyzed by metal function are presented by red solid arrows; transalkylation reactions catalyzed by acidic function are presented

by blue dash arrows 80 Figure 4.19 Conversion and product yields of guaiacol HDO on fresh Co/Al-MCM-

41 catalyst (A) Guaiacol conversion, (B) Oxygen products, (C) Oxygen-free

products Reaction condition: T = 400 oC, P = 1 atm, H2/guaiacol molar ratio = 25, W/F = 1.67 h 82 Figure 4.20: TEM images of the used Co/Al-MCM-41 82 Figure 4.21 Conversion and product yields of guaiacol HDO on regenerated Co/Al-MCM-41 (A) Conversion, (B) Oxygen products, (C) Oxygen-free products Reaction condition: T = 400 oC, P = 1 atm, H2/guaiacol molar ratio = 25, TOS = 30 min 83 Figure 4.22 TEM image of the regenerated Co/Al-MCM-41 catalyst 84 Figure 4.23 DTG curve of fresh Co/Al-MCM-41 and used catalysts after two HDO cycles under air atmosphere 85 Figure 4.24 Conversion and product yields of guaiacol HDO on regenerated Ni and

Co supported Al-MCM-41 catalysts Reaction condition: T = 400 oC, P = 1 atm,

H2/Gua molar ratio = 25, W/F = 1.67 h, TOS = 30 min 86 Figure 4.25 The mass loss of used catalysts in the range 200750 oC from TGA 86 Figure 4.26 HDO of guaiacol over mono and bimetallic catalysts Reaction

conditions: T = 400 ºC, P = 1 bar, W/F = 0.83 h, H2/Gua = 25, TOS = 30 min 88 Figure 4.27 HDO of guaiacol over mono and bimetallic catalysts Reaction

conditions: T = 400 ºC, P = 1 bar, H2/Gua = 25, TOS = 30 min 88

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Figure 4.28 Guaiacol conversion and HDO yield of HDO reactions over mono- and bi-metallic catalysts Reaction conditions: T = 400 ºC, P = 1 bar, W/F = 0.83 h, and

H2/Gua = 25 89 Figure 4.29 TG and DTG curves of used catalysts in air atmosphere 90 Figure 4.30 Mass loss of used and fresh catalysts from TGA result 90 Figure 4.31 Recycle of Co/Al-MCM-41 in HDO of guaiacol (Reduction – Reaction – Regeneration) Reaction condition: T = 400 ºC, P = 1 bar, H2/Gua = 25, W/F = 1.67 h 92 Figure 4.32 Recycle of Pd-Co/Al-MCM-41 in HDO of guaiacol (Reduction –

Reaction – Regeneration) Reaction condition: T = 400 ºC, P = 1 bar, H2/Gua = 25, W/F = 1.67 h 92 Figure 4.33 Recycle of Fe/Al-MCM-41 in HDO of guaiacol (Reduction – Reaction – Regeneration) Reaction condition: T = 400 ºC, P = 1 bar, H2/Gua = 25, W/F = 1.67 h 93 Figure 4.34 Recycle of Pd-Fe/Al-MCM-41 in HDO of guaiacol (Reduction –

Reaction – Regeneration) Reaction condition: T = 400 ºC, P = 1 bar, H2/Gua = 25, and W/F = 1.67 h 93 Figure 4.35 XPS survey spectra (A), de-convoluted O1s (B), C1s (C) and Co2p (D) spectra of fresh, reduced, used and regenerated Pd-Co/Al-MCM-41catalysts 95 Figure 4.36 XPS survey spectra (A), de-convoluted O1s (B), C1s (C) and Co2p (D) spectra of fresh, reduced, used and regenerated Pd-Fe/Al-MCM-41catalysts 96 Figure 4.37 Hydrotreatment of benzene reaction pathway (red arrow was catalyzed

by metal site; blue arrow was catalyzed by acid site) 101 Figure 4.38 Hydrotreatment of anisole reaction pathway (red arrow was catalyzed by metal site; blue arrow was catalyzed by acid site) 102 Figure 4.39 Hydrotreatment of phenol reaction pathway (red arrow was catalyzed by metal site; blue arrow was catalyzed by acid site) 102 Figure 4.40: Possible reaction pathways for vapor phase HDO process over Pd-Fe and Pd-Co catalysts based on the analyzed products 104 Figure 4.41 Experimental and kinetic model profiles of reactant and some

representative products versus catalyst weight Reaction conditions:

Pd-Fe/Al-MCM-41, T = 400 ºC, P = 1 bar, H2/GUI = 25, and TOS = 30 min 107

Figure 4.42 Diagram of differences C-O bonds in guaiacol [182] 108 Figure 4.43 Mechanism of demethoxylation pathway under the present of catalyst [183] 108 Figure 4.44 Experimental and kinetic model profiles of reactant and some

representative products versus catalyst weight Reaction conditions:

Pd-Co/Al-MCM-41, T = 400 ºC, P = 1 bar, H2/GUI = 25, and TOS = 30 min 109 Figure 4.45 Major reaction route for Pd-Fe catalyst based on kinetic results 111 Figure 4.46 Major reaction route for Pd-Co catalyst based on kinetic results 111 Figure 4.47 Product yield for the upgrading of lignin-derived bio-oil on Al-MCM-41 supported Pd-Fe and Pd-Co catalysts Pyrolysis conditions: T = 500 ºC and mLignin = 3.0 g Upgrading conditions: T = 400 ºC, P = 1 bar, mCatalyst = 1.5 g, and H2 flow = 90 mL/min 113 Figure 4.48 TG and DTG curves of lignin in nitrogen atmosphere 113 Figure 4.49 TG and DTG curve of used Pd-Co and Pd-Fe catalysts after upgrading process of lignin-derived bio-oil 114 Figure 4.50 The visual images of heavy oil samples for the upgrading of lignin-derived bio-oil without catalyst, with Pd-Co and Pd-Fe catalysts 115 Figure 4.51 Liquid-phase products yield for the upgrading of lignin-derived bio-oil

on Al-MCM-41 supported Pd-Fe and Pd-Co catalysts Pyrolysis condition: T = 500

ºC, mLignin = 3.0 g Upgrading conditions: T = 400 ºC, P = 1 bar, mCatalyst = 1.5 g, H2flow = 90 mL/min 116 Figure 4.52 Chromatography of heavy oil (A) and light oil (B) products in upgrading

of lignin-derived bio-oil on Al-MCM-41 supported Pd-Fe and Pd-Co catalysts 117

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LIST OF TABLES Table 2.1: Industrial fast pyrolysis system worldwide [60, 61] 12 Table 2.2: Characterization of bio-oil on the basis of different biomass sources and production method 14 Table 2.3: Summary of catalytic HDO for upgrading of bio-oil and its model

compounds 20 Table 2.4: Bond dissociation energy value of OC bond in aromatic compounds [119] 26 Table 2.5: HDO of guaiacol in the continuous flow reactor 28

Table 2.6: Kinetic and reactor parameters (A i are at 8,720 kPa) [130] 35

Table 2.7: Summary of the limitation of the HDO process in literature and expected achievements by the present research 36 Table 3.1: List of chemicals was used in the study 39 Table 4.1: The textural properties of fresh Al-MCM-41 supported Ni and Co catalysts 58 Table 4.2: The textural properties of fresh Al-MCM-41 supported mono- and bi- metallic Pd, Fe and Co catalysts 64 Table 4.3: List of components in guaiacol HDO sample calibrated with GC-FID 71 Table 4.4: Overview results of the hydrotreatment of guaiacol in blank (no catalyst) and support-packed reactors 72 Table 4.5: Surface chemical composition of Pd-Co and Pd-Fe catalysts from XPS 98 Table 4.6: Conversion and products yield of HDO over Co/Al-MCM-41 with different feedstock (Reaction condition: mCAT = 0.5 g, T = 400 C, P = 1 atm, feeding rate = 0.018 ml/min) 99 Table 4.7: Reactions and reaction constants of each individual step 106

LIST OF ABBREVIATION

BDE Bond dissociation energy

BET Brunauer – Emmet – Teller model

BJH Barret – Joyner – Halenda model

BTG Biomass Technology Group

B.P Boiling point

CAE Constant analyzer energy

CAr Carbon in Aromatic ring

xxii

HDS Hydrodesulfurification

HHV Higher Heating Value

ISTD Internal standard

NH3-TPD Temperature Programmed Desorption of Ammonia NRMSD Normalized root means square of deviation

ODE Ordinary differential equation

PKS Palm kernel shell

R.T Retention time

RMSD Root means square of deviation

SEM Scanning electron microscopy

TCD Thermal conductivity detector

TEM Transmission electron microscopy

TGA Thermogravimetric analysis

TPR Temperature programmed reduction

XPS X-ray photoelectron spectroscopy

XRD X-ray diffraction

LIST OF SYMBOLS

i The carbon number in product i, ()

Ai Frequency factor, (min-1)

 Line broadening at half the maximum intensity (FWHM) of XRD

peak, (rad)

i The oxygen number in product i, ()

i Oxygen number of component i in upgraded bio-oil (except

water), ()

j Oxygen number of component j in raw bio-oil, ()

c i Concentration of component i (mol m-3)

2 Bragg angle, (rad)

d i Size of particle i, (nm)

D i Product distribution, (MolCarbon%)

E i Activation energy, (kJ/mol)

F 0 Total molar in the inlet, (mol)

F GUA Molar of guaiacol in the outlet, (mol)

F i Molar of product i in the outlet, (mol)

K Dimensionless shape factor, ()

k i * Apparent rate constant, (s-1)

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k j Reaction rate constant, (mol gcat-1s-1bar-1)

k' j Reaction rate constant, (mol gcat-1s-1)

k j ” Reaction rate constant, (gcat-1)

 X-ray wavelength, (Å)

M biomass Weight of lignin, (g)

M i Weight of product i, (g)

M water Weight of water in bio-oil, (g)

n pi Number of particle i, ()

n i molar of component i in upgraded bio-oil, (mol)

n i * Mole fraction of product i, (mol%)

n j molar of component j in raw bio-oil, (mol)

P Total pressure, (kPa)

p 0 Total pressure of the inlet, (bar)

p i Partial pressure of product i, (bar)

r j Reaction rate, (mol%gcat-1s-1)

 The mean size of the crystalline domains, (Å)

t Reaction time, (s)

v j The sign represented the formation or consumption of F i , (v j = ±1)

W Mass of catalyst, (g)

W oxy Ratio of oxygen mass in the product to that in the raw bio-oil,

(g/g)

X Gua Guaiacol conversion, (MolCarbon%)

Y i Product yield in HDO of guaiacol, (MolCarbon%)

Y i lignin Product i yield in upgrading of lignin-derived bio-oil, (wt%)

Y water Water yield in upgrading of lignin-derived bio-oil, (wt%)

CHAPTER 1 INTRODUCTION

1.1 Back ground of study

Malaysia has tremendous biomass resources from agricultural sector such as oil palm, paddy, sugarcane and rubber trees [1, 2] Among them, biomass from oil palm plantation and mill has the main contribution, and this solid biomass is predicted to reach 85-110 million tons by 2020 [2] Nowadays, the biomass residues are utilized for steam and power generation at mills, fiber material, pellets and fertilizer [3, 4] However, a certain big portion of biomass residues is not fully utilized, raising waste treatment and environmental pollution issues [5, 6]

The lignocellulose biomass resource can be used not only as direct energy in combustion, but also as a more valuable fuel after conversion and upgrading process [7] Thermal conversion of biomass is one of the prominent technologies to produce bio-char, bio-oil and bio-gas [7] In comparison with torrefaction or gasification, pyrolysis is conducted at moderate temperature (400600 ºC) and in the absence of oxygen [8] The pyrolysis oil (bio-oil) product has significant advantages in storage, transport and ability to utilize as useful petrochemical and fuel [9] In Malaysia, pyrolysis oil can be produced from different biomass feedstock such as palm kernel shell (PKS) [10, 11], empty fruit bunch (EFB) [12, 13], rice husk [14, 15] and wood sawdust [16] Interestingly, BTG (the coordinator of the EMPYRO project) has already constructed a 2 t/h pyrolysis plan using EFB as the feedstock [17]

Bio-oil is considered a promising second-generation biofuel and has been used to generate heat and electricity, e.g in combustors or turbines or as a co-feed in heat and power production plants However, it is very difficult to directly utilize the pyrolysis

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oil because of its higher water (1634 wt%) and oxygen contents (3257 wt%) than heavy fuel oil (0.1 wt% and <1 wt%) [14, 18] The presence of oxygenated compounds (e.g acids, esters, alcohols, ketones, furans, phenols) makes the bio-oil low heating value, low thermal stability, high viscosity and corrosiveness [10, 19–21] Therefore, the upgrading step was required to make the bio-oil lower acidity, energy density, lower viscosity and higher chemical- thermo-stability There are some upgrading processes such as catalytic cracking, hydrodeoxygenation (HDO), supercritical fluids, esterification, emulsification, molecular distillation, and catalytic pyrolysis [22, 23] Bio-oil obtained from fast pyrolysis contains a large fraction of lignin-derived phenolic compounds [22, 24–26] These compounds such as guaiacol, phenol, anisole, cresol, etc can be upgraded to renewable fuel source such as aromatic or naphthenic hydrocarbon by hydrodeoxygenation [27] This is a prominent process because it not only removes oxygen, but also preserves the carbon number in the product [28, 29] The final products can be utilized as petrochemical feedstock or high-octane gasoline base materials For example, C6  8 aromatics are valuable petrochemicals for use as solvents or intermediate in polyester fiber and film manufacture [30], and C9-12aromatics are the major blending component (1220 % by volume) in gasoline engine fuels to obtain high octane number because there has been a limitation of low vapor pressure aromatics content (e g., benzene and toluene) [31]

Hydrodeoxygenation is the hydrogenolysis process for oxygen removing from oxygenated compounds in the presence of hydrogen and catalysts [32] The HDO of pyrolysis oil and model phenolic compounds was mostly conducted at high hydrogen pressure in a batch-wise autoclave (40200 bar) or in a continuous-flow fixed-bed reactor (1040 bar) [33–35] The high hydrogen pressure is required to give high deoxygenation degree but it leads to saturate the aromatic ring before oxygen elimination [33, 36, 37] Besides resulting a high hydrogen consumption, this condition also produced ring saturation products with lower octane number for co-feeding in existing oil refineries [38] In recent time, there have been some studies investigated the HDO with low hydrogen consumption (atmospheric pressure), resulting in high selectivity to the oxygen-free aromatics [28, 29, 38] However, the H2/feedstock molar ratio was varied from 60 to 100, and still higher than the stoichiometric ratio of HDO

reaction [27–29, 39–43] Meanwhile, Gao et al used a smaller H2/feedstock molar ratio (i.e 10), but they could not achieve the formation of oxygen-free aromatic products [44]

The stability and regeneration ability of catalyst are very important in the application of catalyst In HDO process, the deactivation of catalysts is mainly from coke deposits, sintering, poisoning and metal deposition [22, 45, 46] However, there are a few studies investigated the deactivation and regeneration ability of catalytic HDO [44, 47, 48] Coke deposit is the main cause of catalyst deactivation, follows by metal sintering [44] In catalyst HDO, the mesoporous supports exhibited a much higher stability than the microporous supports [37, 47]

Catalytic upgrading of real bio-oil were mostly conducted in the batch autoclave due to the complex composition and instability of bio-oil [22] The catalytic upgrading could not only enhance the H/C ratio and thermo-stability but also decrease the O/C ratio and molecular weight of bio-oil [33, 49] However, the upgraded bio-oil mostly contained acids, ketones and lignin-derived phenol [33] In addition, the thermally polymerization reactions occurred during the treatment, resulting in the formation of solid phase [49] There are a few researches which carried out the upgrading of bio-oil

in the continuous reactor at low pressure reaction Sanna [50] proposed the 2-stage reactor, in which the 1st step at low temperature could enhance the thermal stability of bio-oil before HDO process Meanwhile, Koike [19] conducted the successive fast pyrolysis and catalytic upgrading at ambient atmosphere for both reactors

1.2 Problem statement

The HDO reaction of model compounds or bio-oil has been widely studied over different catalysts in the literature These studies revealed that the metal and support played an important role on the HDO activity and stability However, there is not a systematic study about the Al-MCM-41 supported catalysts for HDO process This support has the mesoporous structure, high resistance and moderate acidity which could

be a promising support for catalytic HDO

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In HDO process, there are still some challenges such as higher hydrogen consumption than HDO stoichiometric ratio, catalyst deactivation and carbon loss The high pressure operation and high H2/feedstock ratio not only increase the cost but also produce less valuable ring saturation products Moreover, there are a few studies investigated the deactivation and regeneration ability of catalytic HDO [44, 47, 48] In

addition, carbon loss via methanization is unavoidable in catalytic HDO process [38]

Therefore, the improvement in catalyst type, reaction and regeneration conditions is required to achieve higher HDO efficiency

The catalytic HDO of bio-oil is a complex reaction network which including hydrodeoxygenation, decarbonylation/decarboxylation, direct deoxygenation, cracking, hydrogenolysis, hydrogenation, demothoxylation, demethylation, and methyl transfer [19, 51] However, the HDO reactions pathway and mechanism were established on 48 reactions [44, 52–54] Hence, the more detail kinetics of HDO should be investigated to better understand the mechanism of HDO process

In addition, there are few studies in upgrading of actual pyrolysis oil using the continuous flow reactor due to the low thermal stability of pyrolysis oil The HDO processes in continuous flow reactor are normally investigated with model phenolic compounds while the HDO of actual pyrolysis oil are mostly conducted in batch autoclave reactor Catalytic upgrading of bio-oil in the continuous reactors have the advance in operation cost and scale-up

Thus, this project will study the HDO of a model phenolic compound on

Al-MCM-41 supported monometallic (Ni, Co and Fe) and bimetallic (Pd-Co and Pd-Fe) catalysts

in order to find out suitable catalysts and the reaction conditions for high selectivity of HDO, low hydrogen consumption and high regeneration ability catalyst The mesoporous Al-MCM-41 was selected as the catalyst support since it has good internal mass-transport, high stability and transalkylation activity [38, 55] Guaiacol was chosen

as a model phenolic compound because it contains both major functional groups of lignin-derived phenolic such as hydroxyl (OH) and methoxy (OCH3) Moreover, guaiacol is found as the major product in lignin-derived bio-oil [56–58] Finally, the

upgrading of lignin-derived bio-oil was investigated with bimetallic Co and Fe/Al-MCM-41 catalysts

Pd-1.3 Objective

Based on the research problem statements, the objectives of this study are:

i) To prepare and characterize the mesoporous Al-MCM-41 supported monometallic (Ni, Co and Fe) and bimetallic (Pd-Co and Pd-Fe) catalysts for HDO process

ii) To evaluate the efficiency of catalysts and reaction conditions in HDO activity, stability and regeneration ability to catalytic HDO of model compound (guaiacol) iii) To develop the kinetic model and reaction pathway of catalytic HDO

iv) To evaluate the efficiency of selected catalysts on catalytic upgrading of derived bio-oil

lignin-1.4 Scope of Research

In view of this brief background and our research objectives, to get more details on hydrodeoxygenation process, this study investigated the HDO of a model compound and then catalytic upgrading of lignin-derived bio-oil in the continuous fixed-bed reactor In this dissertation, HDO of guaiacol was investigated as a model reaction to clarify how the reaction conditions effect to HDO yield and selectivity Moreover, the deactivation and regeneration of catalyst during HDO process were also studied In addition, the kinetic model of HDO of guaiacol was also developed Furthermore, bimetallic Pd-Fe and Pd-Co catalysts were screened for upgrading of lignin-derived bio-oil in hydrogen atmosphere

Commercial mesoporous Al-MCM-41 was selected as the support for Ni, Co, Fe and Pd catalysts since its mesoporous structure and acidity could enhance the internal

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mass-transport, stability and transalkylation activity The catalysts were prepared by wetness impregnation, and divided to two groups: 1) monometallic Ni and Co; 2) bimetallic Pd-Fe and Pd-Co These two groups have different calcined time (14 h or 4

h) and in situ reduction time (1 h or 2 h) The percentage of Co, Ni and Fe was kept at

10 wt% while the Pd was added with 2 wt% The fresh, reduced and regenerated catalysts were characterized with TEM, TPR, TPD, TGA, SEM, BET, XRD, XPS, etc The HDO of guaiacol over monometallic Ni and Co catalysts at atmospheric pressure was used to investigate the effects of reaction conditions to HDO yield and selectivity The activities of Ni and Co were compared at different W/F ratio (mass of catalyst to feed rate) and reaction temperatures The W/F ratio was varied from 0.21 to 1.67 h by changing the amount of catalyst, while the reaction temperature was increased from 300 to 400 ºC The H2/guaiacol ratio was kept at 25 for all experiments to reduce the H2 consumption In HDO of guaiacol, the liquid product was analyzed with GC-

FID using n-dodecane as the ISTD, while the gas product was analyzed with GC-TCD

The catalysts were screened on HDO, methanization and transalkylation activities The deactivation of Co/Al-MCM-41 catalyst was also studied by using TEM, TGA and TPD techniques The HDO of guaiacol over Pd-Fe at W/F=1.67 h, 400 ºC and 1 atm were repeated twice and the standard deviation of all results were less than 1 MolC% The other HDO experiments were run only once

From the HDO of guaiacol over monometallic results, the bimetallic Co and

Pd-Fe catalysts were further investigated in order to find the more suitable catalyst The HDO of guaiacol was compared between monometallic (Co, Fe and Pd) and bimetallic (Pd-Co and Pd-Fe) to find out the enhancement of Pd addition in HDO activity, stability and regeneration ability The catalytic HDO was run for two or three cycles of reduction, reaction and regeneration within the fixed-bed reactor The reaction conditions were maintained at 400 ºC, 1 atm, and H2/guaiacol ratio of 25 while the W/F ratio was changed from 0.83 to 1.67 h The regeneration of catalyst was conducted at

500 ºC for 4 h The increase in stability and regeneration ability of bimetallic catalyst were discussed by TGA and XPS characterization of catalyst

Since the HDO of guaiacol was very complex, the kinetic study was investigated to get more understanding in mechanism and reaction pathways There were more than 26

components that were detected in the liquid products of HDO of guaiacol This study proposed 21 possible pathways for catalytic HDO from only 13 components These components were chosen based on the primary intermediate products MATLAB ode45s subroutine was used to calculate the reaction profiles for each reaction The optimum kinetic parameters were determined using the nonlinear fitting subroutine fmincon The kinetic results were investigated for Pd-Co and Pd-Fe catalysts to get more understanding in different mechanism of each catalyst

Bimetallic Pd-Co and Pd-Fe were chosen to investigate the upgrading of of derived bio-oil in the fixed-bed tubular reactor at ambient pressure The catalytic upgrading was conducted in the 2-stage pyrolysis upgrading process The lignin feedstock of 3.0 g was the double of catalyst amount The pyrolysis temperature was at

lignin-500 ºC while the catalytic HDO temperature was at 400 ºC The lignin was sandwiched with glass wool at the top part of the reactor, while the catalysts were packed at the bottom part of reactor The hydrogen flow was used as the carrier gas and reactant gas for both pyrolysis and catalytic upgrading The volatile product of the pyrolysis process

at the top part was further upgraded by catalytic HDO at the bottom part The bio-oil products were analyzed with KF and GC-FID to determine the composition The gas products were sampling every 15 minutes and analyzed with GC-TCD The char residue and catalyst were collected after reaction and analyzed with TGA The activity of Pd-

Co and Pd-Fe catalysts in HDO and cracking reactions were compared and discussed based on visual observation, TGA, KF, GC-TCD and GC-FID results

1.5 Thesis outline

This thesis holds five chapters, namely, introduction, literature review, methodology, result & discussion, and conclusion The description of each chapter now follows

Chapter 1 provides a brief introduction and background about pyrolysis oil, catalytic HDO, and upgrading of bio-oil process, leading to the current research This includes the problem statements, research objectives and scope of research

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Chapter 2 presents the rigorous literature review that motivated this research It begins with the introduction about production and property of bio-oil, followed by a detail literature about HDO upgrading of bio-oil and model compounds The studies on catalyst deactivation and regeneration ability are also addressed Lastly, the development of HDO kinetic model is reviewed This chapter points out the research gap needed to be fulfilled by this study

Chapter 3 plays a major role as the direction of the research This chapter firstly presents the preparation and characterization of the catalysts In addition, the analysis methods for gas, liquid and solid products are also described The detail on the catalytic HDO experiment with a model compound, guaiacol, is declared The methodology for kinetic model is also mentioned in this chapter Lastly, the experimental for catalytic upgrading of lignin-derived pyrolysis oil is included

Chapter 4 is the most important as it contains the results from this study’s catalytic HDO of guaiacol and catalytic upgrading of bio-oil The first section presents the characterization of catalysts that used as the supporting information in the discussion

of HDO activities The HDO of guaiacol over monometallic Ni and Co catalysts are screened with different W/F ratio and reaction temperatures The catalyst deactivation and regeneration of Co catalyst also is demonstrated The comparison of monometallic (Co, Fe and Pd) with bimetallic (Pd-Co and Pd-Fe) in HDO of guaiacol is included in this chapter Moreover, the kinetic study provides the reaction networks of HDO of guaiacol over Pd-Co and Pd-Fe catalysts Lastly, there is the catalytic upgrading of lignin-derived bio-oil results

Finally, Chapter 5 concludes with a review of this project’s achievements and findings This chapter also presents a proposal for future works to enhance the catalytic HDO activity and expand to more type of bio-oil

CHAPTER 2 LITERATURE REVIEW

2.1 Overview

Lignocellulose biomass resource can be used as an energy by direct combustion or convert to more valuable fuel through thermal conversion and upgrading process [7] The product of these conversions can be in the form of gas (gasification), liquid (pyrolysis), or solid (torrefaction, carbonization) as summarized in Figure 2.1

Figure 2.1: Products from thermal biomass conversion

In gasification, solid biomass raw material is converted to gas fuel or syngas by partial combustion Most gasification furnaces use normal pressure and a direct gasification process To keep the reaction temperature at 750 − 900 °C for direct gasification, air, oxygen and steam (as appropriate) are required for the gasification agent The syngas produced from gasification process contains carbon monoxide, hydrogen, and methane along with carbon dioxide and nitrogen Syngas may be burned

directly in gas turbine, converted to methanol and hydrogen, or produced fuel via the

• Bio-oil, char, bio-gas

bio-• Bio-char

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Torrefaction is a thermal process at 200–350C to convert biomass into a coal-like material, which has better fuel characteristics than the original biomass The heating rate is less than 5 C/min During the process, the water contained in the biomass as well as superfluous volatiles are removed, and the biopolymers (cellulose, hemicellulose and lignin) partly decompose giving off various types of volatilesTorrefied biomass is more brittle, making grinding easier and less energy intensive [59]

Pyrolysis is thermal decomposition occurring in the absence of oxygen Pyrolysis

of biomass generated the gas, liquid, and char products [7] Similar to torrefaction, pyrolysis is also a thermal process but at very high heating rate to obtain a high liquid yield The pyrolysis oil (bio-oil) product has significant advantages in storage, transport and ability to utilize as useful petrochemical and fuel [9] The presence of oxygenated compounds (e.g acids, esters, alcohols, ketones, furans, phenols) makes the bio-oil low heating value, low thermal stability, high viscosity and corrosiveness [10, 19–21] Hydrodeoxygenation in the presence of catalyst is the hydrogenolysis process for oxygen removing [32] The HDO becomes more attractive together with the arising of interest in biofuel as they help removing O-containing compounds The requirement to reduce the oxygen content in biofuel emerges a variety of researches in the development catalysts, optimize reaction conditions, and also reaction kinetics These recent achievements will be summarized and discussed in this chapter

2.2 Pyrolysis oil

2.2.1 Bio-oil production

In the pyrolysis process, the quality of bio-oil is affected by different factors such as: feedstock, heating rate, moisture, pressure, temperature, type of reactor, catalyst, etc [7] Figure 2.2 shows the different energy products/forms that can be obtained from pyrolysis In which, the bio-oil can be used for turbine or boiler in factory or further upgraded to produce bio-chemical and bio-fuel [59]

Figure 2.2: Pyrolysis for biomass conversion [59]

Table 2.1 illustrates the industrial fast pyrolysis system worldwide with different technologies, involving fluidized bed (Dynamotive – 8,000 kg/h), circulating fluidized bed or transported bed (Ensyn – 4,000 kg/h, VTT – 20 kg/h), ablative pyrolyser (PYTEC – 250 kg/h, NREL, Aston University – 20 kg/h), rotating cone (BTG – 2,000 kg/h), in addition some currently developing reactors such as vacuum pyrolyser (Laval University/Pyrovac) and Entrained flow (Georgia Tech Research Institute) [60, 61] Fortum's pyrolysis oil from forest residues and other wood-based biomass is used produce electricity and district heat BTG Biomass Technology Group has facilitated the operation of more than 60 bio-energy systems and factories worldwide [62] The BTG commercial bio-oil was used as the feedstock for upgrading process which studied

by Wildschut [24, 63], Mercader [64], Tessatoro [58] and Bimbela [65]

In Malaysia, pyrolysis oil can be produced from different biomass feedstock such

as palm kernel shell (PKS) [10, 11], empty fruit bunch (EFB) [12, 13], rice husk [14, 15] and wood sawdust [16] Interestingly, BTG (the coordinator of the EMPYRO project) has already constructed a 2 t/h pyrolysis plan using EFB as the feedstock [17] The EFB is collected directly from a nearby palm mill, is pretreated and converted to pyrolysis oil This plan has produced over 1,000 tons of bio-oil, which can be applied

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as the co-fire or diesel-replacement a waste disposal system [17] The excess heat from the pyrolysis process is utilized for drying the wet EFB feedstock

Table 2.1: Industrial fast pyrolysis system worldwide [60, 61]

Technology Industrial organization Units Capacity (kg feed/h) Fluidized bed Agritherm, Canada 2 200

Fortum – VALMET, Finland 1 10000

Moving bed Anhui Yineng Bio-energy, China 3 600

Microwave Carbonscape, NZ and UK NA NA

Lignin is the second most important component of lignocellulosic biomass after cellulose, which is about 23–33% of the mass of softwoods and 16–25% of the mass of hardwoods [66, 67] The potential amount of lignin is very promising since the development of ethanol fuel, cellulose rich fiber production and paper industry which uses cellulose and leaves lignin as a residue [68–70] Lignin can be utilized as the renewable aromatic resources for chemical and biofuel [68, 70, 71] The lignin-derived phenolic compounds could be upgraded to valuable petrochemical feedstock [66, 72] However, these phenolic compounds remain a great challenge for upgrading process [38, 73, 74] Hence, lignin was utilized as the feedstock to produce the upgraded bio-oil in this research work

2.2.2 Bio-oil properties

Bio oil is a complex mixture of oxygenated hydrocarbons and water [7] It is very difficult to directly utilize the pyrolysis oil because of its higher water and oxygen contents than fossil oil as shown in Table 2.2 The heating value of bio-oil is varied from 13 to 22 MJ/kg which is lower than that of heavy fuel oil of 41 MJ/kg Meanwhile, the pH of bio-oil is around 3, which primarily is related to the present of acetic acid and formic acid [22] The presence of oxygenated compounds (e.g acids, esters, alcohols, ketones, furans, phenolics, guaiacols) makes the bio-oil low heating value, low chemical and thermal stability, high viscosity and corrosiveness [10, 19, 21]

Because the liquid product from pyrolysis contains large quantity of O-containing compounds which are very unstable; for example, they quickly form deposits on exposure to air, tending to polymerize rapidly [75] The chemical instability comes from condensation and polymerization reactions of oxygenated components to form polymers and sludge, which occurs especially at high temperature [33, 47, 49] During room temperature storage, bio-oil was separated and formed the sticky gum phase at the bottom (as in Figure 2.3) The bio-oil has high viscosity of 128 mm2.s-1 (at 20 C) and 82 mm2.s-1 (at 40 C) [76], yielding the difficulties in chemicals extraction and fuel production Existence of considerable percentage of acids causes the corrosive property [77, 78] All these disadvantages will be mitigated or solved if oxygen is removed partially or entirely, respectively

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Table 2.2: Characterization of bio-oil on the basis of different biomass sources and

production method Feedstock Palm

kernel shell

Rice husk Corncob Pine wood Heavy fuel

oil Reactor Fluidized

bed

Fluidized bed

Fluidized bed

Continuous auger