A review of recent laboratory research and commercial developments in fast pyrolysis and upgrading

TL;DR: In this paper, the authors provide an update on recent laboratory research and commercial developments in fast pyrolysis and upgrading techniques, which is a relatively mature technology and is on the verge of commercialisation.

Abstract: Robust alternative technology choices are required in the paradigm shift from the current crude oil-reliant transport fuel platform to a sustainable, more flexible transport infrastructure. In this vein, fast pyrolysis of biomass and upgrading of the product is deemed to have potential as a technology solution. The objective of this review is to provide an update on recent laboratory research and commercial developments in fast pyrolysis and upgrading techniques. Fast pyrolysis is a relatively mature technology and is on the verge of commercialisation. While upgrading of bio-oils is currently confined to laboratory and pilot scale, an increased understanding of upgrading processes has been achieved in recent times.

Summary

1. Introduction

• Concerns over global warming and finite fossil fuel reserves have led to the realisation that a more environmentally friendly, flexible transport infrastructure is required, that draws on multiple technologies.
• Global production of biofuels has increased rapidly to 83 billion litres in 2008, but still retains a small share of the transport fuel market [3].
• Such technologies can be classified as biochemical or thermochemical.
• Biomass fast pyrolysis is a component of thermochemical conversion technologies and has a more recent history of development (1980s) than gasification [7].
• It is widely accepted that the quality of bio-oil from thermal fast pyrolysis can not be considered a realistic candidate for large scale liquid transport fuel substitution unless it is upgraded.

2. Concepts for Liquid Transport Fuel Production via Pyrolysis

• Numerous discussions can be found in literature about the potential of substituting crude-oil feedstocks with biomass feedstocks [29-34].
• This is exacerbated by the large scales of production on which biomass-to-liquid will need to be produced to produce an economically viable fuel [35].
• Upgrading technology at centralised facilities might include gasification and synthesis, fluid catalytic cracking, hydroprocessing (hydrocracking and hydrotreatment), steam reforming etc. (See Fig. 1.).
• They were allocated 25 m$ by the DoE for development of a 1tpd demonstration unit at the Tesoro Corporation refinery in Kapolei, Hawaii with operations expected to begin in 2014 [36, 37].
• The IH 2 concept being developed by GTI (USA) proposes to reform a portion of the gases liberated from 1) the fast hydropyrolysis process and 2) hydropyrolysis vapour hydrodeoxygenation to provide the hydrogen required [45, 46].

3. Biomass Fast Pyrolysis

• The reactor is the core and most distinguishing piece of equipment for a pyrolysis process.
• Currently only Bubbling Fluidised Beds (BFBs) and Circulating Fluidised Beds (CFBs) can be applied for commercialscale production of biofuel [21].
• While several reactors have been investigated on a laboratory scale and pilot scale no single reactor has emerged as being vastly superior to the others.
• Detailed information on various fast pyrolysis reactors can be found in previous reviews [8-15, 21, 22, 51-53] and so will not be covered in this review.

3.1.1. Bubbling Fluidised Bed Technology

• Bubbling Fluidised Beds (BFBs) exhibit consistent performance and product quality, with high liquid yields ranging between 70-75 wt% [8].
• Biomass Engineering Ltd. (UK) are currently constructing 6 tpd modified version of a previous BFB design (by Wellman Engineering and Aston University UK) which aims to overcome scaling problems associated with the Dynamotive design by surrounding the reactor walls with a char combustor [15].
• Several BFB installations have been installed in China with throughputs ranging from 14-24 tpd [56-58].
• Agri-Therm offers a noveldesign mobile pyrolyser to convert agricultural residue to bio-oil.
• The annular fluidised bed is heated by a cylindrical fluidised bed combustor.

3.1.2. Circulating Fluidised Bed Conversion Technology

• While CFBs have similar features to BFBs a distinct difference is that the residence time of the char is almost the same for vapours (~ 1 second) [52].
• The hydrodynamics are more complicated, but they are already used at very high throughputs in the petroleum and petrochemical industries [8, 52].
• Ensyn are the leaders of CFB technology for biomass pyrolysis and have constructed a total of eight facilities to date based on their ‘Rapid Thermal Process’ [14].
• A Finnish Consortium involving Metso, Fortum, UPM and VTT are developing an integrated CHP/Bio-oil production concept, and tests are ongoing on a 7.2 tpd plant [50, 64].
• A fast pyrolysis reactor which appears to be a CFB is coupled with a fluidised-bed biomass boiler.

3.1.3. Rotary Cone Conversion Technology

• Rotary Cone Pyrolysis Technology is applied by the Biomass Technology Group .
• This is taking place under the EMPYRO European Project [67].
• Construction of two 5 tpd plants is underway, one in Holland and Belgium.
• The technology employed is similar to RCR technology by BTG, though the companies are no longer associated [15].
• Feedstocks processed are mixtures of industrial wastes, SRF, mixtures of plastic/organic and inorganic mixtures [Personal Communication].

3.1.4. Auger Conversion Technology

• The KIT Bioliq model comprises decentralised densification of biomass by pyrolysis (without solids separation), followed by centralised gasification and synthesis of methanol or DME [41, 69].
• Being a relatively old technology considerable experience has been gained over the past 50 years (coal degassing or heavy crude coking).
• A recently presented economic analysis of the process calculated that biosyncrude production from dry lignocellulosic material have manufacturing costs of about €140/tonne; about 2/3 rd of which are feedstock costs [69].
• The units range in scale from 1tpd to 50 tpd plants and it is expected that the first commercial 50tpd plant will be operational soon [12, 15, 60].
• The economics of the process are presented in [70].

3.1.5. Ablative Conversion Technology

• In the ablative pyrolysis process, wood is pressed against a rotating heated surface melting the wood and leaving behind an oil film which subsequently evaporates.
• No heat carrier is used and the process is limited by the rate of heat supply to the reactor rather than from the heat source to the biomass.
• PyTec have built 2 ablative units, the largest of which is 6 tpd and fits in a 40ft container.
• The company is targeting application of the bio-oils in a CHP unit running on a diesel engine [68].
• An LCA for the PyTec BTO process was recently presented [68].

3.1.6. Comments on Fast Pyrolysis Technology

• A summary of fast pyrolysis developments are presented in Table 1.
• FP technology is close to commercialisation, there still appears to be scope for improvement.
• Feedstock quality is a critical parameter for fast pyrolysis operations.
• The difficulties associated with processing high ash feedstocks at pilot scale are described by Venderbosch and Prins [15].
• This section aims to review some recent studies in this area.

3.2.1. Feedstocks for Fast Pyrolysis

• At research level, hundreds of biomass feedstocks have been screened [7, 8], though wood feedstocks are generally used for ease of comparison.
• Some feedstocks that have been experimented with on laboratory fluidised beds are summarised in Table 2.
• Properties of biomass feedstocks and the resulting bio-oil obtained from fluidised bed pyrolysis are presented in Table 3.
• While it is difficult to make generalisations, it can be seen that woody feedstocks generally produce the best quality oil in terms of C and H content and water content.
• The cultivar type of a particular biomass species [72], level of maturity [73], husbandry practices [74], seasonal variation [75] all influence the composition of the crop and consequently the physical and chemical quality of the bio-oil.

3.2.2. The Influence of Ash on Pyrolysis

• The ash content is one of the most influential parameters in the pyrolysis process.
• High ash contents in biomass pyrolysis feedstocks are not desirable because ash catalyses reactions which compete with biomass pyrolysis, leading to increased formation of water and gas at the expense of liquid organics [28, 50, 79-83].
• The most problematic metal is potassium which has a strong catalytic effect [28, 84].
• This process decreases the ash content and results in a better quality bio-oil .
• A recent study has shown that application of high levels of Nitrogen to a growing biomass crop is disadvantageous in terms of the quality of the resulting bio-oil produced because it results in a lower portion of cell wall components in the plant and higher levels of ash [74].

3.2.3. The Fate of Lignocellulosic Components in Pyrolysis

• The relative portions of cellulose, hemicellulose and lignin in biomass feedstocks have a significant influence on the quality of the bio-oil product.
• Agricultural residues generally contain less lignin and more hemicelluloses and ash/alkali metals than wood biomass, resulting in a higher O/C molar ratio than for woody biomass [50].
• Cellulose contributes mainly to bio-oil production (72 wt% at 580˚C) by decomposing into sugars and water.
• So biooils from agricultural feedstocks have lower heating values than those form woody biomass (with a comparatively higher lignin content).
• On the other hand lignin is cracked better in agricultural feedstocks possibly due to the catalysing effect of alkali metals present in significant quantities.

3.2.4. Recent research in Laboratory Fluidised Bed Pyrolysis

• References to recently commissioned fluidised beds can be found in literature: University of Maine (USA) [92], Pacific Northwest Laboratories (1kg/h, USA) [93], University of Western Ontario [94]; University of Monash [95]; and the University of Twente [96].
• It can generally be stated that conditions maximising liquid yields are a pyrolysis temperature in the range of 400-550˚C and a vapour residence time of <2s.
• This is thought to be due to increased conversion of lignin (since char yields decrease in this range).
• The configuration of the condensation system generally depends on the intended applications of the bio-oil product.
• Hot gas vapour filtration can reduce the concentration of metals in bio-oils, though problems with clogging of the filter and catalytic decomposition of pyrolysis vapours by accumulated chars still need to be addressed.

4. Upgrading of Pyrolysis Vapours/Bio-oils

• The use of heterogeneous catalysis in biofuel production processes increases selectivity to certain types of products.
• The main upgrading mechanism is the rejection of oxygen in biomass as coke or gas [26].
• The resulting liquid product is generally more viscous than bio-oils derived by non-catalytic processes, and contains more aromatics.
• This section summarises some recent studies in this area.

4.1.1. Recent Catalytic Pyrolysis Research

• 1.1.1.Micro-Catalytic Pyrolysis Studies/Catalyst Screening Carlson et al. [116] report catalytic pyrolysis of model biomass compounds with a ZSM-5 catalyst yielding 20-30% aromatics which are a valuable chemical feedstock.
• With pine wood catalytic fluidised bed pyrolysis with a ZSM-5 catalyst yielded 14% aromatics at a low space velocity and temperature of 600˚C.
• They compared 40 laboratory-synthesised and commercially available catalysts.
• Upgrading of bio-oil post pyrolysis is also being investigated.
• The upgraded bio-oil is more viscous and has a higher aromatic character.

4.1.2. Commercial Developments in Catalytic Cracking of Biomass

• The work group of George Huber at the University of Massachusetts have developed a process for the production of aromatics by catalytic pyrolysis of biomass.
• The technology is licensed by Anellotech, Inc (www.anellotech.com) [122].
• KiOR, a company based in Texas, offer direct biomass catalytic cracking technology.
• The product is a bio-crude which can be processed in conventional refineries (Liu and Czernik, 2008).
• They are currently producing 15 barrels of biocrude per day at a pilot facility [123] and were granted funds for construction of five plants based on their technology in Mississippi, USA [124].

4.1.3. Comments on Catalytic Upgrading

• The problem of coke formation and catalyst deactivation are significant barriers to commercial deployment of catalytic cracking of biomass-derived products.
• Fluid Catalytic Cracking (FCC) technology is frequently applied at large scales in oil refineries and possesses the ability to regenerate the cracking-catalyst.
• Positive results have emerged from exploration of the concept of hydrotreating bio-oil prior to fluid catalytic cracking.
• A summary of commercial developments catalytic pyrolysis developments plus other upgrading strategies are summarised in Table 6.

4.2.1. Recent Laboratory Research in Hydroprocessing

• Readers are referred to previous reviews for background information [23-25, 29, 34].
• Bio-oil was treated at 360˚C and 17 MPa in a two step (stabilisation and hydroprocessing) batch process yielding 36 % light product with 7% oxygen and 30% liquid residue.
• 36% of the carbon from the feed oil was captured in the light liquid product with additional 30% in the residual liquid product.
• 2.1.2.European Research in Hydroprocessing Insights into catalytic hydrotreatment at University of Twente/BTG/University of Gronigen were recently presented [128-130].
• Heeres [128] recently discussed the influence of the pyrolytic lignin fraction of bio-oil on hydrotreating reactions and products.

4.2.2. Fast Hydropyrolysis

• Concepts for hydropyrolysis have already been discussed.
• The process comprises three stages, 1) biomass hydropyrolysis under medium hydrogen pressure in the presence of a novel glass ceramic catalyst.
• The hydrocarbon liquid yield is 24-28 wt% which is comparable with fast pyrolysis coupled with FCC or HDO.
• GTI were recently allocated 3m$ to investigate this further [138].

4.3.1. UOP/PNNL/NREL

• Integrated processing strategies are likely to be required for producing liquid transport fuels from bio-oils.
• These include hydrotreating followed either by co-processing in a HDS or FCC unit with heavy crude-derivatives.
• For hydrotreating a UOP Ni-Mo and PNNL Pd/C catalyst were examined.
• Co-processing of bio-oil, the pyrolytic lignin fraction of bio-oil and a hydrotreated bio-oil with VGO were simulated on an ACE reactor.
• Bio-oil, pyrolytic lignin and hydrotreated- pyrolytic lignin all produce more coke than VGO.

4.3.2. Amherst-Massachusetts, USA

• The working group of Huber at Amherst-Massachusetts are investigating the coupling of fast pyrolysis, hydrotreating, and catalytic cracking for the production of commodity chemicals.
• In a significant development, the group found that coupling hydrotreating of bio-oil with catalytic cracking yields of aromatic hydrocarbons and light olefins in quantities up to three times greater than catalytic cracking of raw biooil [142].

4.3.3. CPERI, Greece

• Lappas et al. [143] summarise research into co-processing CPERI which goes back to a previous collaboration with Veba Oel [144].
• A combined HDO step and co-processing in an FCC unit produced on-spec transport grade fuel.
• The nozzle plugged under continuous operation, so the heavy fraction of fast pyrolysis liquid was diluted with light cycle oil (LCO) (15/75) and blended with vacuum gas oil (VGO) (at 15/75).
• FCC of VGO was the reference case for comparison.
• Coke production was higher, and liquid petroleum gas (LPG) yields were lower, and an increased selectivity towards gasoline and diesel were observed when bio-oil is in the feed.

4.3.4. The Biocoup Project, Europe

• Considerable research in the area of co-processing has been undertaken as part of the Biocoup Project (http://www.biocoup.com/).
• 2006-2011 and developments are discussed in the following paragraphs.
• They observed decreasing catalyst performance at low temperature and high contact time, though to be due to intermediate phenols competing with sulfur containing molecules on dehydrogenation sites.
• Since hydrogen is consumed in deoxygenation reactions from the VGO feedstock, the final product is poorer in hydrogen and contains more coke, aromatics and olefins.
• So further co-processing by HDO would be required before co-processing in a refinery.

4.3.5. Comments on Integrated Co-Processing

• Integrated co-processing would provide a relatively straightforward route to the production of liquid transport fuels via fast pyrolysis since oil refining infrastructure is already available.
• Combined hydrotreating and catalytic cracking appears to possess significant potential for the production of commodity chemicals.
• However this is a relatively new area of research and requires more investigation.
• Recent research has shown that pressurised fluidised-bed gasification of bio-oil followed by catalytic reforming can readily be used to convert bio-oil to syngas [155, 156].
• KIT, developers of the bioliq process, plan to finish construction of a demonstration bioslurry gasification, gas cleaning and synthesis plant in 2011 [42].

4.6.1. Developments in Bio-oil Filtration

• It is well known that char and ash particles in bio-oil contribute to instability.
• Javaid et al. [157] and Ford et al. [158] applied liquid-phase microfiltration processes to remove char particles from bio-oil to sub-micron levels.
• Results demonstrate the removal of the major quantity of char particles with a significant reduction in overall ash-content of the bio-oil.

4.6.2. Developments in Bio-oil Esterification

• The highly acidity and chemical instability of bio-oils impose severe limitations on the extent to which they might be processed in a refinery.
• The reactions are equilibrium driven, so the reaction products are unstable.
• A solution to this problem is to remove the reaction products as they are formed by azetropic water removal or reactive distillation [162, 164].
• Acid numbers of the bio-oil were decreased by 88.54 and 85.95% respectively, representing the conversion of organic acids to esters.

5. Application of Oils/Upgraded Oils as Transport Fuels

• Applications of bio-oils are already reviewed [27, 28].
• This section aims to summarise recent studies in this area.
• There was little difference in performance with the 20% blend, but for the 40% blend a higher in cylinder gas temperature and pressure was observed.
• The potential for bio-oil and bio-diesel blends has also been investigated [173, 174].
• There are other references to emulsification of bio-oil in recent literature [105-107].

6. Conclusions

• Fast pyrolysis of biomass is verging on commercial application.
• Demonstration of upgrading technologies is underway, though it may be some time before they are deployed on an industrial scale.
• Acid washing, water leaching, hot gas filtration, and post pyrolysis filtration can improve the quality of the resulting bio-oil, but more research in this area is required.
• It is also apparent that the chemical composition of biomass feedstocks for fast pyrolysis can vary significantly between and within different species.
• Coking of the catalyst in biomass or bio-oil catalytic cracking remains an issue, and research in this area is continuing.

Figures

Table 3 Summary of the properties of oil laboratory fast pyrolysis reactors. Where multiple references for one feedstock are available, values are averaged. For feedstocks with more than one phase, values are also averaged. Abbreviations: Moist. = Feedstock Moisture, PT= Pyrolysis Temperature, P = Number of Phases in the Liquid Product, LY = Liquid Yield (organics and water), Acid. = Acidity, E.Crops = Energy Crops, RCG = Reed Canary Grass, Tim. Grass = Timothy Grass, B. Straw = Barley Straw, FR = Forestry Residue, Oreg. Stalk = Oreganum Stalk, Bam. Sawd. = Bamboo Sawdust, EFB = Empty Fruit Bunches, Jatrop. Shell = Jatropha Nut Shell, Macroalg. = Macroalgae (seaweed).

Fig. 2. Commercial potential of various fast pyrolysis technologies (Adapted from [182]).

Fig. 1. The Pyrolysis Biorefinery (Adapted from [128]).

Fig. 3. The Mass and Carbon Efficiencies Associated with combined HDO and FCC (Adapted from [150]).

Table 1 Overview of Fast Pyrolysis Developments.

Table 2 Some Feedstocks Recently Characterised on Fluidised Bed Units

Table 6 Some Findings from Recent Hydroprocessing Studies

Table 5 Developments in Bio-oil Upgrading. Abbreviations: CP=Catalytic Pyrolysis, FP=Fast Pyrolysis, HP=Hydroprocessing, FCC=Fluid Catalytic Cracking, IH 2 =Catalytic hydropyrolysis and Vapour Hydrodeoxygenation, VU=Vapour Upgrading, G=Gasification, S=Synthesis, IP=Intermediate Pyrolysis, U=Upgrading, SR=Steam Reforming.

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Title A review of recent laboratory research and commercial developments in fast pyrolysis and
upgrading
Authors(s) Butler, Eoin; Devlin, Ger; Meier, Dietrich; McDonnell, Kevin
Publication date 2011-10
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1
A Review of Recent Laboratory Research and Commercial
Developments in Fast Pyrolysis and Upgrading
Eoin Butler
1
a
, Ger Devlin
a
, Kevin McDonnell
a
a
Charles Parsons Energy Research Programme, Bioresources Research Centre, School
of Agriculture, Food Science and Veterinary Medicine, University College Dublin,
Belfield, Dublin 4, Ireland.
ABSTRACT
Robust alternative technology choices are required in the paradigm shift from the
current crude oil-reliant transport fuel platform to a sustainable, more flexible
transport infrastructure. In this vein, fast pyrolysis of biomass and upgrading of the
product is deemed to have potential as a technology solution. The objective of this
review is to provide an update on recent laboratory research and commercial
developments in fast pyrolysis and upgrading techniques. Fast pyrolysis is a relatively
mature technology and is on the verge of commercialisation. While upgrading of bio-
oils is currently confined to laboratory and pilot scale, an increased understanding of
upgrading processes has been achieved in recent times.
Keywords
pyrolysis, biomass, biofuel, upgrading, bio-oil, conversion
Contents
_____________________________________________________________________
1. Introduction ................................................................................................................................. 2
2. Concepts for Liquid Transport Fuel Production via Pyrolysis ...................................................... 3
3. Biomass Fast Pyrolysis ................................................................................................................ 4
3.1. Commercialisation of Fast Pyrolysis Technology ............................................................... 4
3.1.1. Bubbling Fluidised Bed Technology .............................................................................. 4
3.1.2. Circulating Fluidised Bed Conversion Technology ........................................................ 5
3.1.3. Rotary Cone Conversion Technology ............................................................................ 6
3.1.4. Auger Conversion Technology ...................................................................................... 6
3.1.5. Ablative Conversion Technology................................................................................... 6
3.1.6. Comments on Fast Pyrolysis Technology ...................................................................... 6
3.2. Review of Recent Fast Pyrolysis Laboratory Research ....................................................... 7
3.2.1. Feedstocks for Fast Pyrolysis ......................................................................................... 7
3.2.2. The Influence of Ash on Pyrolysis ................................................................................. 7
3.2.3. The Fate of Lignocellulosic Components in Pyrolysis.................................................... 8
3.2.4. Recent research in Laboratory Fluidised Bed Pyrolysis .................................................. 8
4. Upgrading of Pyrolysis Vapours/Bio-oils .................................................................................... 9
4.1. Catalytic Cracking of Biomass/Bio-oils .............................................................................. 9
4.1.1. Recent Catalytic Pyrolysis Research .............................................................................. 9
4.1.2. Commercial Developments in Catalytic Cracking of Biomass ..................................... 10
1
Corresponding author. Tel: +353 1 716 7458; Fax: +353 1 716 7415;
E-mail: eoin.butler@ucd.ie.

2
4.1.3. Comments on Catalytic Upgrading .............................................................................. 10
4.2. Upgrading Techniques Involving Hydrogen ..................................................................... 11
4.2.1. Recent Laboratory Research in Hydroprocessing ......................................................... 11
4.2.2. Fast Hydropyrolysis..................................................................................................... 13
4.3. Integrated Upgrading Approaches and Co-processing ...................................................... 13
4.3.1. UOP/PNNL/NREL ...................................................................................................... 13
4.3.2. Amherst-Massachusetts, USA ..................................................................................... 14
4.3.3. CPERI, Greece ............................................................................................................ 14
4.3.4. The Biocoup Project, Europe ....................................................................................... 14
4.3.5. Comments on Integrated Co-Processing ...................................................................... 15
4.4. Developments in Upgrading Bio-oil by Steam Reforming ................................................ 15
4.5. Developments in Upgrading Bio-oil by Gasification and Synthesis .................................. 15
4.6. Mild Stabilisation Techniques for Bio-oil ......................................................................... 16
4.6.1. Developments in Bio-oil Filtration............................................................................... 16
5. Application of Oils/Upgraded Oils as Transport Fuels .......................................................... 17
5.1. Developments in Blending Bio-oil with Other Fuels .................................................... 17
5.2. Developments in Combustion of Bio-oils and Upgraded Bio-oils ................................ 18
6. Conclusions ............................................................................................................................... 18
Acknowledgements ............................................................................................................................ 19
References .......................................................................................................................................... 19
___________________________________________________________________________________
1. Introduction
Concerns over global warming and finite fossil fuel reserves have led to the
realisation that a more environmentally friendly, flexible transport infrastructure is
required, that draws on multiple technologies. While solutions with efficiencies that
surpass the current combustion engine are likely to be developed, this will take time,
and furthermore current consumer preferences favour liquid alkane fuels [1]. It is also
likely that liquid fuels will continue to dominate the market for heavy vehicles (ships,
aeroplanes, trucks) into the future [2]. Biofuels are seen as a possible solution. Global
production of biofuels has increased rapidly to 83 billion litres in 2008, but still
retains a small share of the transport fuel market [3]. Some first generation biofuels
have encountered significant criticisms over their ability to achieve meaningful
substitution, climate change mitigation and economic growth. While more advanced
second generation technologies do not completely overcome these problems, they are
none-the-less expected to become at least a part of the solution in the shift from fossil
resources in the short to medium term [4, 5]. It is expected that second generation
biofuels will be produced under commercially viable conditions between 2015 and
2020 [5]. Such technologies can be classified as biochemical or thermochemical.
While there are no significant advantages of one group of technologies over the other,
an added benefit of thermochemical approaches is the ability to yield longer chain
hydrocarbons suitable for aviation, marine, or heavy road freight applications [2]. It is
has been suggested that biochemical and thermochemical technologies could be
employed synergistically in integrated biorefineries with the added benefit of
increased flexibility and efficiency [6]. Biomass fast pyrolysis is a component of
thermochemical conversion technologies and has a more recent history of
development (1980s) than gasification [7]. Thermal decomposition of biomass
feedstocks at high heating rates in inert atmospheres yields char, liquid, and gas.
While the yield structure is highly dependent on the feedstock and the process
conditions employed, liquid (termed 'bio-oil') yields of up to 70 -75 wt% from wood
can be achieved [8]. One of the main advantages of fast pyrolysis lies in the fact that it
is an effective method for densification of voluminous biomass for decentralised

3
densification/centralised conversion platform models [5]. As a biorefinery feedstock
bio-oil is very versatile and can be put to other uses apart from the production of
biofuels. While bio-oil possesses undesirable fuel properties, it can, be directly
applied as a fuel for modified stationary engines. It is widely accepted that the quality
of bio-oil from thermal fast pyrolysis can not be considered a realistic candidate for
large scale liquid transport fuel substitution unless it is upgraded. Furthermore, if
traditional petroleum fuels like diesel and petrol are considered to be model liquid
fuels, biomass needs to undergo fundamental chemical changes before it is
acceptable, since it contains significant portions of oxygen. Fast pyrolysis is a
relatively technically mature process. Upgrading technologies are in the early stages
of demonstration, and it is likely to be some time before they are deployed on a
commercial scale.
The objective of this review is to present recent (2006 onwards) laboratory research
and commercial developments in fast biomass pyrolysis and upgrading. It is beyond
the scope of this review to cover theory behind processing operations and earlier
research. For this, readers are referred to previous review publications e.g. fast
pyrolysis [7-22], hydroprocessing [23-25], heterogeneous catalysts [1, 26],
applications of bio-oil [27, 28].
2. Concepts for Liquid Transport Fuel Production via Pyrolysis
Numerous discussions can be found in literature about the potential of substituting
crude-oil feedstocks with biomass feedstocks [29-34]. One of the main problems
associated with the use of biomass as a liquid fuel source is their delocalised
distribution and poor energy density. This is exacerbated by the large scales of
production on which biomass-to-liquid will need to be produced to produce an
economically viable fuel [35]. One proposed solution is decentralised densification of
biomass to bio-oil (and possibly stabilisation) followed by centralised upgrading. This
model is being pursued by several pyrolysis companies. Centralised upgrading
facilities might include existing crude oil refineries or dedicated ‘biorefineries’.
Upgrading technology at centralised facilities might include gasification and
synthesis, fluid catalytic cracking, hydroprocessing (hydrocracking and
hydrotreatment), steam reforming etc. (See Fig. 1.). Envergent
(www.envergenttech.com) is a joint venture pursuing a model of delocalised pyrolysis
based on Ensyn’s (Canada) Rapid Thermal Processing (RTP) Technology followed by
centralised upgrading based on UOP Hydroprocessing Technology. They were
allocated 25 m$ by the DoE for development of a 1tpd demonstration unit at the
Tesoro Corporation refinery in Kapolei, Hawaii with operations expected to begin in
2014 [36, 37]. The plant will be an integrated fast pyrolysis and hydroconversion
facility and aims to produce 4 barrels per day of gasoline, diesel and jet fuel. The
commercial model is based on 4 RTP plants and one central upgrading facility [36].
Plans for 9 new plants based on Ensyn and UOP technology in Malaysia have also
recently been announced [38]. Dynamotive (Canada, www.dynamotive.com), a well-
known fast pyrolysis company, are also pursuing hydrotreating of bio-oil and a co-
operation with IFP was recently announced [39, 40]. The KIT (Germany) Bioliq
concept is based on decentralised fast pyrolysis of biomass to bioslurry followed by
gasification and synthesis of transport fuels at a central facility [41]. A demonstration
plant is currently being developed. Tests have begun on the 12 tpd pyrolysis unit
which was commissioned in 2008, and construction of the gasification and synthesis

4
plants are expected to be completed by the end of 2011 [42]. PyTec (Germany,
www.pytec.de ) ablative technology would be particularly suited for decentralised
densification and centralised upgrading since no carrier gases are required and it is
likely to be feasible on a smaller scale. However the company appears to be pursuing
power generation in modified engines rather than upgrading. The BTG (Netherlands,
www.btgworld.com) biorefinery model is similar to that illustrated in Fig. 1.
Efforts are also being directed towards small-scale feasible solutions. The
Metso/Fortum/UPM/VTT consortium is developing a concept which produces CHP
and bio-oil [43, 44]. Another solution might be the production of high quality fuel in a
stand alone facility with upgrading technology. The IH
2
concept being developed by
GTI (USA) proposes to reform a portion of the gases liberated from 1) the fast
hydropyrolysis process and 2) hydropyrolysis vapour hydrodeoxygenation to provide
the hydrogen required [45, 46].
Another group of organisations are pursuing mobile fast pyrolysis solutions e.g. Agri-
Therm (Canada), ABRI-Tech, and Renewable Oil International. More information on
these organisations can be found in (Section 3.1).
Agrawal et al.[47] and Singh et al. [48] propose that increased conversion efficiencies
could be achieved by a natural gas reformer or coal-powered power plant to a fast
hydropyrolysis facility, with the former facilities providing H
2
/CO. This process was
termed (the H
2
Bio-oil process). Alternatively reliance on fossil-derived hydrogen
required for fast-hydropyrolysis could be supplied by 1) solar splitting of water to H
2
2) gasification of a portion of the biomass feedstock.
3. Biomass Fast Pyrolysis
3.1. Commercialisation of Fast Pyrolysis Technology
The reactor is the core and most distinguishing piece of equipment for a pyrolysis
process. Reactors are generally the most researched aspect of fast pyrolysis, though
control and improvement of liquid quality and improvement of liquid collection
systems are receiving increasing attention [12]. Currently only Bubbling Fluidised
Beds (BFBs) and Circulating Fluidised Beds (CFBs) can be applied for commercial-
scale production of biofuel [21]. While several reactors have been investigated on a
laboratory scale and pilot scale no single reactor has emerged as being vastly superior
to the others. That said certain reactors are more suitable for commercial application
than others (See Fig. 2.), and this has been reflected in commercialisation efforts.
Fluid beds, circulating fluid bed and transport reactors, and auger pyrolysis reactors
have a strong technology basis and high market attractiveness. The fast pyrolysis of
biomass is at an early stage of commercialisation [49] with companies like Ensyn
Technologies, Dynamotive, KIT and BTG leading developments [15, 50]. Detailed
information on various fast pyrolysis reactors can be found in previous reviews [8-15,
21, 22, 51-53] and so will not be covered in this review.
3.1.1. Bubbling Fluidised Bed Technology
Bubbling Fluidised Beds (BFBs) exhibit consistent performance and product quality,
with high liquid yields ranging between 70-75 wt% [8]. They are readily scaled up,

Frequently asked questions

Q1. What are the contributions mentioned in the paper "A review of recent laboratory research and commercial developments in fast pyrolysis and upgrading" ?

The objective of this review is to provide an update on recent laboratory research and commercial developments in fast pyrolysis and upgrading techniques. 

Q2. What are the future works mentioned in the paper "A review of recent laboratory research and commercial developments in fast pyrolysis and upgrading" ?

While work in this area is continuing, future research will need to address the search for cheap ( i. e. non precious metal ) catalysts. While milder intensity upgrading approaches may be applied in niche applications, it is unlikely that the quality of the resulting bio-oil will be acceptable for refiners or end-consumers alike. 

Q3. Why is an intermediate upgrading step required?

Because direct co-processing of bio-oil results in an FCC unit results in excessive char formation and unacceptably low yields of gasoline, an intermediate upgrading step is required. 

Q4. What are the main barriers to development of a market for bio-oil?

Handling and storage issues and the current lack of large scale applications are the main barriers to development of a market for bio-oil [39]. 

Q5. What are the main factors that influence the composition of the crop?

The cultivar type of a particular biomass species [72], level of maturity [73], husbandry practices [74], seasonal variation [75] all influence the composition of the crop and consequently the physical and chemical quality of the bio-oil. 

Q6. What is the main reason for the increase in the economic viability of pyrolysis?

The production of commodity chemicals via hydroprocessing and catalytic cracking routes within the biorefinery infrastructure may enhance the economic viability of pyrolysis and pyrolysis-related processes. 

Q7. What is the way to reduce the concentration of metals in bio-oils?

Hot gas vapour filtration can reduce the concentration of metals in bio-oils, though problems with clogging of the filter and catalytic decomposition of pyrolysis vapours by accumulated chars still need to be addressed. 

Q8. What are the main barriers to commercial deployment of catalytic cracking of biomass-derived products?

The problem of coke formation and catalyst deactivation are significant barriers to commercial deployment of catalytic cracking of biomass-derived products. 

Q9. What is the effect of the use of pyrolysis gas on the bio-oil?

Other observations are that while increasing the feed rate of the reactor above its design capacity increases the bio-oil yield, the homogeneity of the oil decreases [101], and the use of pyrolysis gas as a fluidising medium increases bio-oil yields [102-104]. 

Q10. What is the main reason why high ash content in biomass feedstocks is undesirable?

High ash contents in biomass pyrolysis feedstocks are not desirable because ash catalyses reactions which compete with biomass pyrolysis, leading to increased formation of water and gas at the expense of liquid organics [28, 50, 79-83]. 

Q11. What are the main problems associated with the use of biomass as a liquid fuel source?

One of the main problems associated with the use of biomass as a liquid fuel source is their delocalised distribution and poor energy density. 

Q12. How many wt% of bio-oil can be mixed with ethanol?

Developments in Blending Bio-oil with Other FuelsNguyen and Honnery [171] found that fast pyrolysis bio-oil can be mixed up to 20 wt% with ethanol and combusted at elevated pressures (2.5 MPa at 827˚C) without any significant drop in performance. 

Q13. What is the way to improve the quality of bio-oil?

While milder intensity upgrading approaches may beapplied in niche applications, it is unlikely that the quality of the resulting bio-oil will be acceptable for refiners or end-consumers alike. 

Q14. What is the way to overcome the problem of high ash content feedstocks?

One way to overcome the problem of high ash content feedstocks is by water or acid washing prior to pyrolysis [76, 78-80, 86-88]. 

Q15. What is the potential of combining hydrotreating and catalytic cracking?

Combined hydrotreating and catalytic cracking appears to possess significant potential for the production of commodity chemicals. 

Q16. What are the prospects for increasing the feasibility of smaller scale operations?

The integrated bio-oil/CHP concept by the Metso consortium and the IH 2 concept by GTI are particularly interesting prospects for increasing the feasibility of smaller scale operations. 

Q17. How long will it take to deploy bio-oil on a commercial scale?

Upgrading technologies are in the early stages of demonstration, and it is likely to be some time before they are deployed on a commercial scale. 

Q18. How do you address the problem of unstable reaction products in bio-oils?

One way to address this is by treating the bio-oil it with a low-cost alcohol (e.g. methanol, ethanol or butanol) in the presence of an acid catalyst (optional), converting the carboxyl and carbonyl groups to esters and acetals (or ketals) respectively [159-161]. 

Q19. How many TANs could Moens and Honnery achieve?

The minimum TAN that Moens et al. [162] could achieve from various approaches to catalysed esterification and removal of products was 20. 

Q20. What is the main problem associated with the use of biomass as a liquid fuel source?

This is exacerbated by the large scales of production on which biomass-to-liquid will need to be produced to produce an economically viable fuel [35].