supercritical water gasification of algae

245 Pages·2015·3.44 MB·English

by  Windows User

SUPERCRITICAL WATER GASIFICATION
OF ALGAE

Ramzi Cherad

Submitted in accordance with the requirements for the degree of
Doctor of Philosophy

The University of Leeds
Doctoral Training Centre in Low Carbon Technologies
Energy Research Institute
School of Chemical and Process Engineering

September 2015
The candidate confirms that the work submitted is his own, except where work
which has formed part of jointly-authored publications has been included. The
contribution of the candidate and the authors to this work has been explicitly
indicated below. The candidate confirms that appropriate credit has been given
within the thesis where reference has been made to the work of others.

The details of chapters 4, 5 and 6 of the thesis are based on the following published
papers respectively:

1. Cherad, R., Onwudili, J.A., Williams, P.T., Ross, A.B., 2014. A parametric
study on supercritical water gasification of Laminaria hyperborea:
a carbohydrate-rich macroalga. Bioresource Technology, 169, 573–80.
doi:10.1016/j.biortech.2014.07.046
2. Cherad, R., Onwudili, J.A., Ekpo, U., Williams, P.T., Lea-Langton, A.R.,
2013. Macroalgae Supercritical Water Gasification Combined with Nutrient
Recycling for Microalgae Cultivation. Environmental Progress and
Sustainable Energy, 32, 902–909. doi:10.1002/ep
3. Cherad, R., Onwudili, J.A., Biller, P., Williams, P.T., Ross, A.B., 2016.
Hydrogen production from the catalytic supercritical water gasification of
process water generated from hydrothermal liquefaction of microalgae. Fuel,
166, 24–28. doi:10.1016/j.fuel.2015.10.088
II
Details of contributions from the candidate and co-authors are listed below:
1. The candidate performed all the experiments, analysis and write up.
Ms. Ekpo performed the growth trials. Dr. Onwudili supported in the
experimental and analytical techniques and proof reading. Dr. Ross and
Professor Williams contributed with comments, guidance and proof reading.
2. The candidate performed all the experiments, analysis and write up.
Dr. Onwudili supported in the experimental and analytical techniques and
proof reading. Dr. Ross and Professor Williams contributed with comments,
guidance and proof reading.
3. The candidate performed all the experiments, analysis and write up.
Dr. Onwudili and Dr. Biller supported in the experimental and analytical
techniques and proof reading. Dr. Ross and Professor Williams contributed
with comments, guidance and proof reading.

This copy has been supplied on the understanding that it is copyright material and
that no quotation from the thesis may be published without proper
acknowledgement.

© 2015 The University of Leeds and Ramzi Cherad
The right of Ramzi Cherad to be identified as Author of this work has been asserted
by him in accordance with the Copyright, Designs and Patents Act 1988.

III
ACKNOWLEDGEMENTS
This work was carried out thanks to funding from the Engineering and Physical
Sciences Research Council (EPSRC) via the Doctoral Training Centre in
Low Carbon Technologies at the University of Leeds.
Thanks to my supervisors, Dr. Andrew Ross and Professor Paul Williams, for their
guidance and support. Andy, your passion for research and interest in using algae for
energy has been a source of inspiration during the course of this work; Paul, for your
encouragement and immeasurable support through the trying journey.
Thanks to Dr. Jude Onwudili for your support during the experiments, write-up, and
publications associated with the research. Your expertise helped overcome any
issues. Your support through exchanging of ideas, keeping an eye on the broader
picture and practical assistance has been invaluable.
Thanks to my colleagues – the 2010 cohort of the Doctoral Training Centre in
Low Carbon Technologies – Gemma Brady, Zarashpe Kapadia, Philippa Usher,
Jayne Windeatt and David Wyatt. Thanks to the Management Committee of the
Doctoral Training Centre, Professor Paul Williams, James McKay, Rachael Brown
and Emily Bryan-Kinns.
Thanks to Dr. Patrick Biller, Ugo Ekpo, Sara Dona, Eyup Yildir, and Edmund
Woodhouse for all the help and support.
Thanks to my father, brother and sister for all the love and support.
This thesis is dedicated to my late mother who saw me start the journey but never
got to read the final draft.
IV
ABSTRACT
Diversification of our energy supplies – especially in the transport and electricity
generation sectors – is required to meet decarbonisation targets. Algae have been
identified as suitable alternative feedstocks for third generation biofuels due to their
fast growth rates and non-competitiveness with land for food crops. Hydrothermal
processing of algae is an appropriate conversion route as it allows the processing of
wet feedstock thus removing the energy penalty of drying.
In this study, supercritical water gasification was used for (i) the hydrothermal
processing of macroalgae for the production of gaseous fuel – mainly hydrogen and
methane – and (ii) the upgrading of the process water from hydrothermal
liquefaction of microalgae for hydrogen production for biocrude hydrotreating.
The supercritical water gasification (SCWG) of the four macroalgae species
investigated (Saccharina latissima, Laminaria digitata, Laminaria hyperborea, and
Alaria esculenta) produced a gas that mainly consisted of hydrogen, methane and
carbon dioxide. Non-catalytic SCWG resulted in hydrogen yields of
3.3 - 4.2 mol kg-1 and methane yields of 1.6 - 3.3 mol kg-1 . Catalytic
macroalgae macroalgae
SCWG (using ruthenium) resulted in hydrogen yields of 7.8 - 10.2 mol kg-1
macroalgae
and methane yields of 4.7 - 6.4 mol kg-1 .
macroalgae
The yield of hydrogen was approximately three times higher when using sodium
hydroxide as catalyst (16.3 mol H kg-1 ) compared to non-catalysed SCWG
2 macroalgae
of L. hyperborea (5.18 mol H kg-1 ). The energy recovery (an expression of
2 macroalgae
how much chemical energy of the feedstock is recovered in the desired product
V
following hydrothermal processing) was 83% when sodium hydroxide was used as a
catalyst, compared to 52% for the non-catalytic SCWG of L. hyperborea.
The yield of methane was approximately 2.5 times higher (9.0 mol CH kg-1 )
4 macroalgae
when using ruthenium catalyst compared to the non-catalysed experiment
(3.36 mol CH kg-1 ) and the energy recovery increased by 22% to 74%.
4 macroalgae
The selectivity of methane or hydrogen production during the SCWG of macroalgae
can be controlled using ruthenium or sodium hydroxide respectively. Longer hold
times and increased reaction temperature favoured methane production when using
ruthenium. An increase in catalyst loading had no significant effect on the methane
yield. Higher hydrogen yields were obtained through using higher concentrations of
sodium hydroxide, lower algal feed concentration and shorter hold times (30 min).
Increasing reaction times (>30 min) with a base catalyst (sodium hydroxide)
decreased the hydrogen yield. Overall energy recovery was highest at the lowest
feed concentrations; 90.5% using ruthenium and 111% using sodium hydroxide.
The process waters from the hydrothermal liquefaction (HTL) of microalgae
(Chlorella, Pseudochoricystis, and Spirulina) were gasified under supercritical water
conditions to maximise hydrogen production. Hydrogen yields ranged from
0.18 - 0.29 g H g-1 from SCWG of the process water of HTL along with near
2 biocrude
complete gasification of the organics (~98%). Compared to the hydrogen
requirements for hydrotreating algal biocrude (~0.05 g H g-1 ), excess
2 biocrude
hydrogen can be produced from upgrading the process water through SCWG. The
results indicate that process waters following SCWG are still rich in nutrients that
can be recycled for algal cultivation.
VI
TABLE OF CONTENTS

Acknowledgements ………………….....................................................………….IV
Abstract…………...………..…………………...……...………………....................V
Table of Contents...……..….……………………………………………….……..VII
List of Tables…………………………………………………………....................XII
List of Figures…………….………………………………………….....................XV
Nomenclature……………..…………………………………………………..…XVII
Outline of Thesis………….……………………………………………………….XX
1 Introduction ....................................................................................................... 23
1.1 Climate change mitigation .......................................................................... 25
1.2 Biofuels ...................................................................................................... 27
1.3 First generation biofuels ............................................................................. 30
1.4 Second generation biofuels ........................................................................ 33
1.5 Third generation biofuels ........................................................................... 37
1.5.1 Processing algae for fuel ..................................................................... 38
1.5.2 Hydrothermal processing .................................................................... 39
1.6 Research Objectives ................................................................................... 48
2 Hydrothermal processing of algae for biofuels ................................................. 51
2.1 Macroalgae ................................................................................................. 51
2.1.1 Description .......................................................................................... 51
2.1.2 Classification ....................................................................................... 52
2.1.3 Cultivation ........................................................................................... 54
2.1.4 Brown algae - Kelps ............................................................................ 55
2.1.5 Species under investigation ................................................................. 59
2.2 Microalgae .................................................................................................. 62
2.2.1 Description .......................................................................................... 62
VII
2.2.2 Classification ....................................................................................... 62
2.2.3 Cultivation ........................................................................................... 63
2.2.4 Structure .............................................................................................. 65
2.3 Hydrothermal liquefaction of algae (HTL) ................................................ 67
2.3.1 Batch microalgal HTL......................................................................... 67
2.3.2 Batch macroalgal HTL ........................................................................ 75
2.3.3 Continuous microalgal HTL and biocrude upgrading ........................ 78
2.4 Hydrothermal gasification of algae ............................................................ 89
2.4.1 Microalgal HTG .................................................................................. 89
2.4.2 Macroalgal HTG ................................................................................. 92
2.5 Nutrient recycling ....................................................................................... 96
2.6 Energy recovery ......................................................................................... 99
2.7 Supercritical water gasification (SCWG) ................................................. 102
2.7.1 Physiochemical characteristics.......................................................... 102
2.7.2 Role of water in reaction ................................................................... 105
2.7.3 Advantages of supercritical water gasification ................................. 106
2.7.4 SCWG of biomass and the influence of main operating parameters 108
2.7.5 Catalytic SCWG of biomass ............................................................. 116
2.7.6 Status of technology and challenges ................................................. 130
3 Methodology ................................................................................................... 137
3.1 Introduction .............................................................................................. 137
3.2 Algal species ............................................................................................. 137
3.2.1 Macroalgal species ............................................................................ 137
3.2.2 Microalgal species ............................................................................. 140
3.2.3 Catalysts ............................................................................................ 140
3.3 Hydrothermal processing ......................................................................... 141
3.3.1 SCWG Reactor .................................................................................. 141
VIII
3.3.2 SCWG Experimental procedure ........................................................ 142
3.3.3 HTL Reactor...................................................................................... 143
3.3.4 HTL Experimental procedure ........................................................... 144
3.3.5 Product separation and analysis ........................................................ 145
3.3.6 Experiment reproducibility ............................................................... 151
4 SCWG of macroalgae combined with nutrient recycling for microalgae
cultivation ................................................................................................................ 154
4.1 Introduction .............................................................................................. 154
4.2 Methodology ............................................................................................ 155
4.2.1 SCWG experiments ........................................................................... 155
4.2.2 Cultivation trials ................................................................................ 155
4.3 SCWG of macroalgae ............................................................................... 156
4.4 Catalytic SCWG of macroalgae ............................................................... 160
4.5 Catalyst poisoning and spent catalyst re-use ............................................ 162
4.6 Hydrogen yields ....................................................................................... 165
4.7 Effect of seasonal variation on SCWG of Saccharina latissima .............. 165
4.8 Process water and cultivation trials of Chlorella vulgaris ....................... 167
4.9 Conclusions .............................................................................................. 172
5 Parametric study on SCWG of Laminaria hyperborea................................... 173
5.1 Introduction .............................................................................................. 173
5.2 Methodology ............................................................................................ 174
5.3 Catalytic SCWG of macroalgae: Laminaria hyperborea ......................... 175
5.4 Effect of catalyst loading .......................................................................... 177
5.5 Effect of feed concentration ..................................................................... 178
5.6 Effect of hold time .................................................................................... 180
5.7 Effect of temperature ................................................................................ 184
5.8 Conclusions .............................................................................................. 188
IX
6 Hydrogen production from the catalytic SCWG of microalgal HTL process
water ........................................................................................................................ 189
6.1 Introduction .............................................................................................. 189
6.2 Methodology ............................................................................................ 192
6.3 Hydrothermal liquefaction (HTL) of Chlorella at varying hold times .... 193
6.4 SCWG of the process water from HTL of Chlorella ............................... 196
6.5 Composition of the process water ............................................................ 198
6.6 Combined HTL and SCWG of Chlorella, Pseudochoricystis, and Spirulina
.................................................................................................................. 201
6.7 Conclusions .............................................................................................. 203
6.7.1 HTL of microalgae ............................................................................ 203
6.7.2 SCWG of the process water from microalgae HTL .......................... 203
7 Conclusions ..................................................................................................... 206
7.1 Introduction .............................................................................................. 206
7.2 Supercritical water gasification of macroalgae ........................................ 207
7.2.1 Non-catalytic SCWG of macroalgae ................................................. 207
7.2.2 Catalytic SCWG of macroalgae using ruthenium ............................. 207
7.2.3 Seasonal variation in macroalgae and influence on gas yields ......... 208
7.2.4 Nutrient recycling from macroalgae for microalgae cultivation ....... 208
7.2.5 Catalytic SCWG of macroalgae using ruthenium, nickel and sodium
hydroxide ........................................................................................................ 208
7.2.6 Influence of catalyst loading ............................................................. 209
7.2.7 Influence of algal concentration (feed concentration) ...................... 209
7.2.8 Effect of hold time ............................................................................ 210
7.2.9 Effect of temperature......................................................................... 210
7.3 SCWG of the process water from hydrothermal liquefaction of microalgae .
.................................................................................................................. 211
7.3.1 HTL of Chlorella and the separation of biocrude ............................. 211
X