Hydrothermal Treatment of Algal Biomass: from Batch to Continuous Pilot Plant Operations

214 Pages·2014·6.8 MB·English

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SCHOOL OF CHEMICAL & BIOMOLECULAR ENGINEERING

HYDROTHERMAL TREATMENT OF ALGAL
BIOMASS: FROM BATCH TO CONTINUOUS PILOT
PLANT OPERATIONS

CHRISTOPHER JAZRAWI

A THESIS SUBMITTED IN FULFILMENT OF THE
REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

May 2014
S C D
TUDENT ONTRIBUTION ECLARATION

I hereby declare that the work presented in this thesis is solely my own work and that, to the
best of my knowledge, the work is original except where otherwise indicated by reference to
other authors. No part of this work has been submitted for any other degree or diploma.

______________________
Christopher Jazrawi
May, 2014

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CKNOWLEDGEMENTS

First and foremost I would like to thank my supervisor Professor Brian S. Haynes.
After 3-4 years of working under Brian, it has become apparent that his invaluable guidance,
support and advice have not only been instrumental in the realisation of this work, but have
tremendously improved my general approach to thinking about problems. His powerful way
of thinking will stick on me forever.

I am very grateful to Professor Thomas Maschmeyer from the School of Chemistry for his
involvement in the project. His wealth of knowledge in the field has been extremely helpful. I
also thank Thomas for giving me the opportunity to speak at the various symposia he has
organised over the past few years and for helping me make contacts for future employment.

This work was supported by the Science and Industry Endowment Fund and by the
Australian Government through the Australian Renewable Energy Agency. The construction
of the pilot plant was funded jointly by the Australian National Collaborative Research
Infrastructure Strategy (NCRIS), the NSW State Government Science Leveraging Fund
(SLF) and the University of Sydney. The financial support in the form of the Australian
Postgraduate Award (APA) is also gratefully acknowledged.

My team, Dr. Xiao Liang and Yaya He, were vital in helping me obtain experimental results
and have been exceedingly cooperative in all aspects of my work – it was through their
persistence, understanding and kindness that I completed my thesis.

I also owe thanks to Sergio Londono whom I spent a lot of time working with in the
beginning of my PhD. His initial construction of the plant and the training he provided me are
gratefully acknowledged. Dr. Alejandro Montoya is likewise thanked for his input to the
project and for allowing me to use his lab space.

One of the most rewarding experiences in my PhD was having the chance to work with Dr.
Patrick Biller and Dr. Andy Ross from Leeds University in the UK. My trip to Leeds was not
only extremely productive, but the memorable (and rainy) football matches after work made
the trip even more worthwhile. This collaboration has been very important to my work.
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I was also fortunate enough to be part of a collaboration with Professor Rocky de Nys and his
group from James Cook University in Queensland. Their kind and professional manner has
been a pleasure to work with. A significant amount of my results have been part of this
collaboration. Dr. Alex Yuen (Sydney University) and Dr. Helga Seyler (CSIRO) are
additionally acknowledged for their input into this partnership.

At the School of Chemical and Biomolecular Engineering, I wish to express my sincere
appreciation to Dr. Ali Abbas who initially advised me to approach Professor Haynes for a
PhD position in 2009; this has turned out to be one of the best decisions I have made.
Professor Tim Langrish, Dr. Jeffery Shi, Nancy Xie, Gary Towel, Alex Farago as well as the
administrative staff are all thanked for their continued support and assistance.

I am also thankful to all the members of the combustion group for making my experience at
the university both rewarding and enjoyable, especially Adjunct Professor David F. Fletcher,
Marta Kremky, Clara Spencer, Dr. Maximilian Warner, Jason Mann, Dr. Zhanying Zheng,
Dr. Sharon Leung, Zhenhui Dai, Dr. Christian Renk, Dr. Asanka Rahubadda, Mohammad
Zangouei, Juan David Gonzalez Calderon, and Dr. Ryan Zhou. My lunchtime breaks with
Maximilian Warner and Jason Mann have kick-started valuable friendships which I am sure
will last for many years.

Last but not least, I wish to express my upmost gratitude for the unconditional love and
support from my wonderful family. My loving father, whom back in 1990 at the University
of Baghdad had the misfortune of not completing a PhD thesis due to factors well outside his
jurisdiction including war and other political sagas, has been a constant source of inspiration
and motivation throughout my life – this thesis is dedicated to you.

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BSTRACT

In the search for large-scale production of renewable fuels and chemicals, hydrothermal
liquefaction (HTL) of biomass has emerged as one of the most promising routes – generating
a primary ‘renewable crude oil’ product (referred to as bio-crude oil) for refining. Whilst this
conversion route is suitable for various types of feedstocks, recently, there has been an
enormous increase in attention directed towards the utilisation of algal biomass – largely due
to their high productivities, and ability to grow in non-arable land.

Despite the vast wealth of research into this field, little progress has been made in addressing
much of the well-recognised bottlenecks of the process. Specifically, the majority of the
available literature makes use of small-scale batch reactor systems, with little development
being made with respect to process engineering and scaling. In addition, the bio-crude oils
derived from the HTL of algae have been reported to contain high levels of nitrogen, limiting
their downstream usability in conventional refineries. The work described in this thesis aims
to contribute to the knowledge development of these specific areas.

Firstly, a continuous flow HTL pilot plant, capable of processing biomass slurry with up to
10 wt.% solids at a feeding rate of 15-70 L/h, is introduced and described. The upper design
temperature and pressure of the system are 350 ºC and 250 bar respectively, which fall in the
sub-critical region of water. The successful operation of two commercially-available
microalgae, Chlorella and Spirulina, is initially demonstrated across a wide range of
operating conditions, including temperature (250-350 °C), residence time (3-5 minutes) and
biomass loading (1-10 wt.%) at constant pressure (150-200 bar). A maximum bio-crude yield
of ~42 wt.% on a dry ash-free (daf) basis was achieved for Chlorella while being processed
with a 10 wt.% solid concentration at 350 °C, 3 minutes residence time and 200 bar. The
results indicated that maximal product yields may be obtained in much shorter residence
times under continuous flow hydrothermal processing than batch studies have previously
suggested.

At the lower processing range (250 °C and 3 minutes) only the lipids present in the algae (3-
8%) are extracted, while at more severe processing conditions other components including
proteins and carbohydrates are also liquefied and become part of the bio-crude. Overall,
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higher temperatures and longer residence times increased the bio-crude yields and reduced
the oxygen content. However, due to the conversion of protein at higher temperatures, the
elemental analyses of the oils also showed an increase in the nitrogen levels. This is perhaps
the biggest drawback for the derived bio-crudes, reaching nitrogen concentrations of up to ~8
wt.%, compared to <1% in conventional crude oil.

A substantial fraction of the feedstock carbon was also found in the process water – this was
up to 60% but decreased to ~30% at the highest biomass loadings tested. The main
compounds identified in the HTL aqueous phase were typical of low molecular weight
oxygenates. Only a small fraction of the input carbon (<10%) was found in the gaseous
product stream, predominately as CO (93-99%, balance CO). The solid residue yields from
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HTL were also small and were observed to decrease with increasing temperatures and longer
residence times.

A novel feature of this work is that it has involved collaboration with algal cultivation
specialists and has been able to explore links between algal production and its subsequent
processing. Processing of microalgae polycultures (TPC), grown under i) a lab-controlled
environment and ii) waste streams (wastewater and CO ) from a coal-fired power station
2
were investigated. The biomass derived utilising waste streams at the power station (referred
to as ‘ash-dam TPC’) exhibited a similar biochemical composition but contained greater
amounts of ash, relative to the lab-grown algae.

The results showed that similar bio-crude quantities, and properties, were obtained from the
lab-grown and ash-dam TPC. The results were additionally comparable to those reported for
Chlorella and Spirulina, and were attributed to the similar biochemical compositions of the
biomass. This work set the foundation for the integration between producing biomass as part
of an industrial framework, incorporating CO mitigation and nutrients supply via wastewater
2
effluents, with subsequent conversion through both batch as well as continuous flow HTL.

The opportunity of tailoring the algal growth process to improve subsequent bio-crude
production was additionally explored. The approach investigated placed particular emphasis
on addressing the high nitrogen levels found in the bio-crude, as well as demonstrating the
suitability of utilising macroalgae as a resource for bio-fuels and chemicals – an untapped
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biomass source which has been largely neglected when viewed against the vast wealth of
research into other feedstocks.

Two Oedogonium macroalgae, cultivated under i) high-nutrient and ii) nutrient-starved
conditions, were studied in the continuous flow HTL plant. This approach intended to firstly
reduce the internal nitrogen content of the biomass, through nutrient starvation, and in turn
facilitate the production of low-nitrogen oil.

The bio-crudes obtained from starved Oedogonium were shown to contain considerably
lower nitrogen levels (1.6-1.9%) compared to those from the high-N feedstock (4.4-5.1%), as
well as those reported for microalgae (4-8%). The nitrogen reductions achieved in the present
work enhance the suitability of the derived oils for conventional refining and could reduce
costs associated with downstream upgrading. The overall process however requires
optimisation of any property enhancements with the reduced biomass growth rates that are
associated with the starvation procedure.

With respect to the development and scaling of the HTL process to a continuous flow pilot-
scale reactor, the present study revealed that greater residue yields and larger particles post-
HTL caused difficulties for the main pressure control valve of the system. Due to the more
complete liquefaction and reduced solids residues at the more severe reaction conditions, the
control valve provided more stable control under these conditions. Flow rate and temperature
control on the other hand were not affected with the varying operating conditions. Limitations
associated with processing high ash-containing algae, such as the ash-dam TPC, were also
highlighted – further development of the process hardware is required so that to enhance the
scalability of the high-ash biomass for continuous operations.

Finally, a two-step batch hydrothermal upgrading process was investigated. This approach
also aimed at producing low-nitrogen oil by firstly removing significant amounts of the cell
protein fraction (Stage I), prior to further conversion of the residual algae solids into bio-
crude (Stage II).

The microalga Chlorella was subjected to various Stage I treatments, where lower solid
residue yields were obtained with higher temperatures and longer holding times.
Correspondingly, the Stage I aqueous phase was found to retain almost 50% of the input
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nitrogen, and hence was not further processed in Stage II. Bio-crudes derived in Stage II of
the process (from Stage I solids) were shown to contain a reduced nitrogen content, relative
to oil from the direct HTL of Chlorella at 300 ºC and 10 minutes. Best results (3.4 wt.% N)
were obtained with water pre-treatment for 15 minutes at 200 °C, achieving a 55% reduction
in the nitrogen concentration of the bio-crude compared to that found from direct HTL.
However, since considerable amounts of the starting material was lost to the Stage I aqueous
phase, smaller masses of biomass passed onto the second stage which reduced the bio-crude
quantities being produced.

In summary, a number of key contributions are contained in this thesis which included
providing insights into scaling the HTL process for continuous operations, as well as
employing novel approaches which aimed at enhancing the quality of the derived products. A
series of suggestions are also proposed for future research, including: i) utilising catalysts and
co-solvents to target certain chemical pathways, aid in the separation of the bio-crude oil, and
determine the potential of further reducing the concentration of undesired heteroatoms in the
final product; and ii) perform more detailed chemical analysis of the aqueous dissolved
chemicals in order to establish potential applications.

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URRENT UBLICATIONS

JOURNALS
C. Jazrawi, P. Biller, A.B. Ross, A. Montoya, T. Maschmeyer, B.S. Haynes. Pilot plant
testing of continuous hydrothermal liquefaction of microalgae. Algal Research 2 (2013) 268-
277.

CONFERENCE/SYMPOSIUM PRESENTATIONS
C. Jazrawi, A.J. Cole, X. Liang, Y. He, A.K.L. Yuen, R. de Nys, T. Maschmeyer, B.S.
Haynes. Pilot plant testing: continuous HTU of macroalgae. Renewable Chemicals
Symposium. Sydney, Australia. May 2013.

C. Jazrawi, P. Biller, A.B. Ross, A. Montoya, T. Maschmeyer, B.S. Haynes. Hydrothermal
processing of microalgae in a continuous flow pilot-scale reactor. 2nd International
Conference on Algal Biomass, Biofuels & Bioproducts. San Diego, USA. June 2012. (Poster
presentation)

C. Jazrawi, P. Biller, A.B. Ross, A. Montoya, T. Maschmeyer, B.S. Haynes. Microalgae in
continuous flow HTU processing. Advanced Catalytic Processes for Renewable Chemicals
Manufacture & Biofuels from Algae Symposium. Sydney, Australia. March 2012.

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