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Welcome to PyroWiki, where experts share their combined knowledge on all matters pertaining to the production, application and sustainability of FAST PYROLYSIS from BIOMASS.

Generally, pyrolysis is the thermochemical decomposition of organic material at elevated temperatures in absence of oxygen. It involves the simultaneous change of chemical composition and physical state, and is irreversible. The word is coined from the Greek-derived elements pyro "fire" and lysis "separating".

The focus of this Wiki is on fast pyrolysis using ligno-cellulosic biomass and residues as feedstock, primarily with the aim to maximize the liquid product yield. Fast refers to the fast/rapid heating of the biomass particles. The resulting liquid can be used as fuel, energy carrier or feedstock for further processing. PyroWiki aims to cover all aspects related to the technology and product use.



History of fast pyrolysis

The word “pyrolysis” is used for the degradation of a substance upon exposure to high temperatures. Exclusion of air of oxygen is essential in case ignition and combustion of the primary products is considered undesirable. Slow pyrolysis of wood at temperatures up to 400 degrees centigrade is a process that has exploited for thousands of years. Charcoal is a smokeless fuel that is still used widely for cooking and heating purposes. It has been used industrially as well, viz. in blast furnaces for the making of iron. A further description on pyrolysis can be found elsewhere

Before the eighties of the last century, 'fast' pyrolysis research was mostly dealing with the thermal decomposition of organic compounds, polymer, salts, etc. Quite a number of papers can be found regarding coal pyrolysis (production of metallurgic coke), and some on the pyrolysis of oil shale. In the field of biomass fast pyrolysis no more than 10 scientific publications can be found for the period 1955 to 1980. Cellulose, one of the main biomass constituents, was investigated quite frequently, but merely in relation to flame retardation purposes. Likewise, some lignin pyrolysis studies can be traced back, because wood chemistry scientists were interested in the analysis of lignitic vapors in particular. A single publication is found when using the keywords “biomass fast pyrolysis”; the hit refers to the abstracts of papers of the American Chemical Society made available to its members in 1980. A short historical review on biomass fast pyrolysis was published by Radlein & Quignard [1]

The research and development of biomass fast pyrolysis started around 1980, when the Solar Energy Research Institute (today NREL) organized a specialists’ workshop on fast pyrolysis of biomass in Copper Mountain, Colorado. [2] Founders of various fast pyrolysis technologies were part of research groups pioneering in the development of reactor technology during the eighties and nineties of the past century.

Why fast pyrolysis of biomass?

The production of pyrolysis oil is an efficient method to utilize biomass as a renewable energy resource for energy, chemicals and/or materials. Raw biomass is mostly collected from distant areas in relatively small quantities. Besides, the biomass is often difficult to handle due to unfavourable properties like:

  • a fluffy structure and low volumetric density
  • the presence of contaminants such as sand and ash
  • a high moisture content
  • a complex chemical structure, built up mainly from cellulose , hemicellulose and lignin.

In fast pyrolysis a uniform liquid is produced with improved properties. It enables the distributed production of pyrolysis liquids at a relatively small scale and in remote areas, for centralized utilization elsewhere at a much lager scale and any desirable time. In this way, the biomass usage is fully decoupled (time & place) from its production. The improved properties enable a more efficient transport and processing if compared to the original biomass.

Fast pyrolysis principle

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Pyrolysis is a process in which organic materials are heated in the absence of air/oxygen. Under these conditions the organic material decomposes, forming vapors, permanent gases and charcoal. The vapors can be condensed to form the main product: pyrolysis liquid. In order to maximize the liquid production, the biomass heating as well as the vapor condensing needs to be done quickly. Hence the name fast pyrolysis. Alternatively, the biomass conversion can be directed at producing charcoal. In this case heating is less rapid and the process is called slow pyrolysis or carbonisation. The latter is usually carried out at temperatures below 400 degrees centigrade.


Fast pyrolysis is meant to convert the biomass to a maximum quantity of liquid of around 60 to 70 wt.% of the feedstock. Beneficially, a more uniform, stable and cleaner-burning product is obtained, that could serve as an intermediate energy carrier and feedstock for subsequent processing. The essential conditions of fast pyrolysis for the production of pyrolysis liquids are:

  • a very fast heating of relatively small biomass particles (order of seconds)
  • controlling the pyrolysis reactor temperature at a level around 500 degrees centigrade
  • a short vapour residence time to avoid further cracking to permanent gases
  • rapid cooling of all the vapors to form the desired pyrolysis liquid.


By-products in the form of char and non-condensable gases are produced as well. In an industrial process, these two by-products (both 10 to 20 wt.%) would be used primarily as a fuel for the generation of the required process heat (including feedstock drying). But sometimes the char is also proposed to be applied as a (‘biochar soil improver’) or as a substitute for metallurgic coke in the steel industry. Alternatively, for specific purposes (and reasons), it can be recombined with the fast pyrolysis oil to form a char-oil slurry (for example the BioLiq process and formerly Dynamotive's Bio-oil Plus). The gaseous by-product essentially is a mixture of CO and CO2. Apart from possible flue gas emissions resulting from the char combustion, there are no waste streams. The biomass ash will be largely concentrated in the char by-product. It is separated when the char is combusted in the process, viz. to generate the heat for drying and heating of the biomass feedstock. Ash separation enables recycling of the minerals as a natural fertilizer to the soil on which the biomass was grown originally.

More details on the Main Principles of Fast Pyrolysis of biomass are given elsewhere.

Properties of fast pyrolysis liquid

Fast pyrolysis liquid is a mixture of many different components, and a unique definition is lacking. One definition of the desired pyrolysis liquid or Fast Pyrolysis Bio-Oil (FPBO) has been given by the IEA Bioenergy task 34 members.

Definition of Fast Pyrolysis Liquid by IEA Task 34
Liquid condensate recovered by thermal treatment of lignocellulosic biomass at short hot vapour residence time (typically less than about 5 seconds) typically at between 450 – 600 °C at near atmospheric pressure or below, in the absence of oxygen, using small (typically less than 5 mm) dry (typically less than 10% water) biomass particles. A number of engineered systems have been used to effect high heat transfer into the biomass particle and quick quenching of the vapor product, usually after removal of solid by-product ”char”, to recover a single phase liquid product. Bio-oil is a complex mixture of, for the most part; oxygenated hydrocarbon fragments derived from the biopolymer structures. It typically contains 15–30% water. Common organic components include acetic acid, methanol, aldehydes and ketones, cyclopentenones, furans, alkyl-phenols, alkyl-methoxy-phenols, anhydrosugars, and oligomeric sugars and water-insoluble lignin-derived compounds. Nitrogen- and sulfur-containing compounds are also sometimes found depending on the biomass source.


Pyrolysis liquid is a dark-brown, free flowing, oil-like substance with a pungent odor and several distinctive properties. While it is usually called pyrolysis oil, here the term pyrolysis liquid (PL) is used to avoid any confusion with fossil oils. Ligno-cellulosic biomass derived PL essentially contains 20 to 30 wt% water and fragments of the cellulose, hemicelluloses, lignin, and extractives. The organics in PL include hundreds of different compounds with various functionalities (e.g. ketones, aldehydes, sugars, acids, phenols, aromatics, extractives etc). The density of pyrolysis liquid is near 1.2 kg/l and its lower heating value is 15 to 17 MJ/kg. The corresponding crude oil values are 0.85 kg/l and 42 MJ/kg respectively. PL therefore contains 40% of the energy of crude oil on weight basis, and roughly 60% on a volumetric basis. Pyrolysis liquid is acidic with a pH of 2.5 to 3, due to the presence of organic acids. The analysis of the liquid is not straightforward as many of the analysis methods developed for fossil oil can not be applied directly. [3] [4] and analytical methods needs to be validated.

Fast pyrolysis technologies

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Various fast pyrolysis technologies have been developed over the last decades on basis of different reactor types [5]. The essential characteristics of a fast pyrolysis reactor for maximal oil production are the very rapid heating of the biomass, an operating temperature around 500°C, and a rapid quenching of the produced vapors. In small dedicated laboratory reactors high oil yields can be obtained when very small particles are used while imposing high heat (and mass) transfer rates, and low vapor residence times. In real scale installation however, the consequences of heat transfer limitations and excessive vapor residence times may be significant.

Indeed, high interparticle heat transfer rates are required (heat transfer coefficients of more than 500 W/m2K). Moreover, intra-particle biomass heat transfer limitations should be avoided, which would require particles sized to less than 3 mm for the effective heat penetration depth. Vapor phase residence times should be kept within a few seconds in order to maintain the oil yield. In case a pyrolysis plant is meant to produce a liquid fuel for combustion or gasification, the process could be designed in a way that maximizes the energy conversion to the liquid product. However, when the bio-oil product is meant to derive bio-fuels or chemicals from it (see one of the next paragraphs), other factors than just the vapor residence time should be considered as well. The composition of the oil obviously depends on the type of feedstock used, but can be steered further by process conditions, equipment dimensions and the application of catalysis.

Several fast pyrolysis technologies have been developed (on laboratory-, pilot, demo or commercial scale); One way to distinguish the different technology is on basis of the type of reactor or mixing employed:

Catalytic Fast Pyrolysis

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The pyrolysis liquid derived from fast pyrolysis by just a thermal treatment is a mixture of hundreds of different, highly oxygenated chemical compounds. A growing interest and activity is noticed on Catalytic Fast Pyrolysis (BIOBOOST,CASCATBEL). This catalytic pyrolysis is seen as a promising route to yield liquids of a higher quality, and catalysis could indeed be applied for a number of reasons, and at different positions in the process. Objectives are e.g. improved chemical and physical stability, high yields of target compounds, and improved miscibility with refinery streams. An appealing example from the recent past is the KIOR plant which was meant to commercially produce 40,00 ton drop-in transportation fuel annually, via catalytic fast pyrolysis. The company however never reached their production targets and eventually felt into bankruptcy; the IP was transferred to Inaeris Technologies. Literature data show that, when using a zeolite type of catalyst, the most reactive components are quickly converted to coke, gas, and water, while only a limited yield of liquid products (mostly phenols and aromatics) is obtained. The diagram shown here is adopted from [6]. It illustrates how for various biofuel production routes the final deoxygenation degree correlates with the overall carbon yield. For catalytic pyrolysis the results are quite poor: in case of a high degree of deoxygenation, the carbon yields are extremely low. Whether or not this can be improved by developing more efficient catalysts (for instance with an increased meso-porosity) or a better process control, is still obscure. Meanwhile it has been reported that the application of pressurized hydrogen, viz. in the IH2 process developed by IGT [1] and licensed to CRI catalyst company, leads to a significant improvement in product yield and quality when a close-coupled hydro-treating of the pyrolysis vapors is applied before condensation. A relatively new company called Annelotech [2] is focusing on the production of benzene, toluene and xylenes (BTX) as aromatic chemicals. Obviously the application of pressure and the consumption of hydrogen adds to the costs of catalytic pyrolysis. It complicates the pyrolysis process such that it would be bound to well-developed industrial sites and relatively large scales of operation. As an alternative one could also hydro-treat a crude bio-oil after its transportation to a central facility. Catalytic post-treatment of the liquid is discussed elsewhere in this PyroWiki, see Biofuels.

Processing pyrolysis liquids in refineries, specifically in the FCC unit, are interesting though: The proof of concept using such treated pyrolysis liquids in an FCC was first demonstrated in the FP6 project BIOCOUP, and further developed, detailed and demonstrated in a few others. Right now the FP7 project FASTCARD is aiming towards a more energetic efficient conversion of biomass into advanced biofuels through improvement of catalysts. The most important conclusion from this is that ‘co-FCC of treated pyrolysis liquid is technically possible, and no unexpected deviation in the product spectrum derived from standard vacuum gas oil is observed. Co-FCC results clearly depend on the severity the liquids have been processed in a prior hydrotreatment step, and three types of pyrolysis derived feedstocks can be distinguished, i.e. (1) fully deoxygenated liquids, (2) partially deoxygenated liquids, and (3) untreated pyrolysis liquids, set by the severity (pressure, temperature, space time) of a prior hydrotreating step. Fully deoxygenated liquids likely behave similar to usual feed for FCC (VGO) while untreated pyrolysis liquids yield higher coke and gas yields compared to VGO, while the dilution ratio of VGO with pyrolysis liquids might have a strong effect on the respective yields.[7][8]

Implementation

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During the 1980s and the early 1990s, research was focused on the development of special reactors such as the vortex reactor, rotating blades reactor, rotating cone reactor, cyclone reactor, transported bed reactor, vacuum reactor, and the fluid bed reactor. Since the late nineties the process realization emerged, resulting in the construction of pilot plants in Spain (Union Fenosa), Italy (Enel), UK (Wellman), Canada (Pyrovac, Dynamotive), Finland (Fortum) and The Netherlands (BTG). In the US and Canada, Ensyn’s entrained flow bed process is applied at a scale of around 1 ton/hr for commercial production of a food flavor called “liquid smoke”. Dynamotive built demonstration installations (West Lorne and Guelph) of 3 to 6 tons biomass throughput per hour for utilization of bio-oil in energy production primarily, but are dormant (West Lorne) or dismantled (Guelph). Meanwhile, many pilot-plant projects have stopped, soon or late after the initial testing. Due to many different reasons the plants of Union Fenosa, Enel, Wellman, Fortum and Pyrovac’s large-scale installation in Jonquiere, Canada, are not in operation any more. A recent update of ongoing activities have been given by IEA Task 34.[9] In the bullets below, a list with pyrolysis production units can be found.

Fate and role of minerals

An advantage of fast pyrolysis is the separation of inorganic compounds from the main liquid product. Typically, more than 95% of the minerals in the original biomass end up in the char. However, the presence of these minerals in the biomass do effect the performance of the pyrolysis process in a negative way (i.e reduced yield, increased water content). Certain minerals - in particular alkali based salts- can also cause operational problems like slag formation. To minimize the negative effect of these minerals on fast pyrolysis process biomass pretreatment like washing is considered.

For more information, see minerals in pyrolysis


Applications of fast pyrolysis liquid

Heat & Power

Fast Pyrolysis liquid can be used as a renewable fuel for the production of heat, power and cooling and different system are demonstrated or under development. Assuming a typical composition for a pyrolysis liquid (including 25wt% of water) the combustion can be written as:

           C10H15O8 (l) + 9.75 O2 (g) = 10 CO2 (g) + 7.5 H2O (g)      dH = 16.5 MJ/kg of pyrolysis liquid. 

For the stoichiometric combustion of 1 kg of pyrolysis liquid about 6 Nm3 of air is needed, and 1.7 kg of CO2 is produced.


The production of heat and power can be further subdivided into:

(co-) Combustion

Compression-Ignition Engines - diesel engines

Turbines

Biofuels

Biomass is the only alternative for fossil derived crude oil derivatives. However, main problems concerning the application of biomass for biofuels and bio-based chemicals are related to transport and handling,and the limited scale of the conversion process. To overcome these intrinsic problems of biomass, fast pyrolysis can be considered as a pretreatment technique to produce a liquid feedstock for further processing. Compared to fossil fuels, the properties of fast pyrolysis liquids are very different and further upgrading is required and/or desired to improve compatibility with existing applications and fuels. Different approaches are followed ranging from simple physical treatment to severe chemical treatment as indicated in the figure.

Biofuels.png

Physical treatment and/or mild chemical treatment of pyrolysis liquid is considered to improve specific properties like acidity, viscosity and stability. It should simplify the application of the pyrolyis liquid in for example stationary engines and turbines. Examples of such treatment is blending, emulsifying or esterification . However, this treatment is insufficient to enable automotive applications.

For the production of transportation fuels (diesel, kerosene, gasoline) more severe chemical treatment will be needed. An integral processing route for the conversion of biomass to transportation fuels is to consider the fast pyrolysis as a pretreatment technique to produce a (pyrolysis) liquid, followed by upgrading to produce a crude-oil like product. Finally co-refining in traditional crude oil refineries is possible (see above).

The upgrading processes include a thermal treatment step and subsequent hydroprocessing, or direct hydroprocessing. Substantial work is ongoing to understand the different aspect relevant in the upgrading processes. Likely, a lower operating temperature step of 200 to 250oC should be applied first, in which the (very) reactive components in the oil are ‘stabilized’, subsequently the stable product fraction can be deoxygenated in a hydrotreating step. Within this respect it is a process that involves carbohydrate chemistry at the low temperatures and lignin chemistry at the high temperatures, with only the latter more or less similar to petrochemical refining. Specifically the cellulose-derived fraction of the oil need to be transformed first, preferably into alcohols in a ‘mild hydrogenation’ step. This subsequently allows further dehydration and hydrogenation. A further deoxygenation step allows the transformation of the liquid into crude oil like component.

Upgraded liquids can be treated further, for example by FCC processing or by full deoxygenation to yield mixtures of transportation fuels. Full deoxygenation, if carried out using active and selective catalysts, hereby reducing charring, promoting hydrogenation and reducing methanation, allows an overall carbon yield (from pyrolysis liquid to a fully deoxygenated product) of over 50 wt.%. Direct co-feeding of crude pyrolysis oil is possible in low amounts as demonstrated by Petrobras (ref), but carbon yields will be lower.


An indirect route to fuels and chemicals is via pyrolysis oil gasification. In a first step, pyrolysis oil is gasified to a syngas (CO/H2) and subsequently the syngas is converted into the desired product. Some advantages exist compared to direct biomass gasification like i) much easier to pressurize, ii) decentral primary conversion of solid biomass and transport of liquid to central gasification plant, iii) application of a catalyst might be enabled (Autothermal Catalytic Reforming). In Sweden, Chemrec is considering the co-gasification of pyrolysis oil with black liquor.

Chemicals & Materials

Pyrolysis oil is a mixture of cracked components originating from the pyrolysis of the three main building blocks of biomass; cellulose, hemicellulose and lignine. Pyrolysis is a good pretreatment to facilitate the fractionation of biomass. After pyrolysis the (ash free) oil can easily be fractionated into three product streams namely; pyrolytic lignin (from lignin), pyrolytic sugars (from cellulose) and a watery phase containing smaller organic components e.g. acetic acid (mainly from hemicellulose). Pyrolysis oil as such or each of the fraction is considered to be a good renewable resource for renewable chemicals and materials.

PO Fractions.png


The three fraction obtained from pyrolysis oil:


Subsequently after fractionation of the pyrolysis oil, the obtained fractions can be further processed to produce chemicals and/or green products. A highly potential application for the pyrolytic lignin (looking at it's functionality) could be as a renewable substituent for fossil phenol in phenol/formaldehyde resins and derivatives. These types of resins are widely used in wood products like particle boards, plywood etc. recently it has already been demonstrated that the phenol in phenol/formaldehyde resins can be substituted up to 75 wt% by pyrolytic lignin standards for this type of (resin ).

Another interesting application of the pyrolytic lignin is in the replacement of fossil bitumen in various bitumen based materials e.g. in asphalt and roofing materials, the latter recently demonstrated in the Biotumen project. Also the pyrolytic lignin could be used in the production of green phenolic (mono-) derivatives, as a possible raw material for various coatings, composites and preservatives.


This sugar phase could be a renewable source for the production (via glucose) of e.g. bio-ethanol, levulinic acid, polyols etc. It has a high potential as a renewable sugar source due to the fact that it is not extracted from food sources like corn, sugarcane etc. Exploratory experiments by different researchers already indicated that a substantial amount of the pyrolytic sugars can be converted to fermentable sugar monomers (especially C6 sugars). Subsequently, fermentation of this phase by means of a yeast culture resulted in the production of ethanol.[10]

From the last fraction, the water phase, which contains smaller volatile organics like VFA's a mixture of organic acid salts can be produced f.i. by means of a reaction with hydroxides or carbonates.

Biomass feedstock

Almost all types of biomass are suitable for pyrolysis. Main requirements for the pyrolysis process is that the biomass is relatively dry (less than 10% moisture content) and a relatively small size (about 0.5 to 1 mm). Since few types of biomass meet these criteria when harvested commercial pyrolysis oil production plants require a biomass pretreatment section. This pretreatment section can be powered using the excess heat and power from the pyrolysis installation as long as the moisture content does not exceed a certain limit (55%.wt in the case of BTG-BTL's modified rotating cone technology).

Sustainability

Sustainability means that the needs of the present generation are met without compromising the ability of future generations to meet their own needs. The concept of sustainability is made tangible by definition of sustainability principles, criteria and measurable indicators. In case of biomass production and use the following themes are typically addressed: greenhouse gas savings, carbon stock change, land use change, biodiversity, emissions to soil, water and air, labour conditions, land use rights, and local economic impacts.

If bioliquids like pyrolysis liquid and biofuels like pyrolysis diesel are counted towards European renewable energy targets and/or receive renewable energy subsidies, they need to comply with a minimum set of sustainability criteria as defined in the Renewable Energy Directive (RED). Verification takes place by voluntary sustainability schemes that have been recognised by the European Commission, like NTA8080, ISCC, and RSB. These schemes have independent third party auditing procedures to verify that biomass is produced according to the sustainability criteria of these schemes and to trace the biomass troughout the supply chain. More information on certification of pyrolysis liquids can be found here.

The concept of biomass sustainability is still under development. For instance the issue of indirect land use change (ILUC) have been much debated on national and European level and resulted in a proposal of the European Commission to lower biofuels production from agricultural crops and to stimulate advanced biofuels.

Standards, Norms & Legislation

First standards on fast pyrolysis oil have been developed by ASTM . In 2014, the European standardization body CEN received a mandate to develop European standards and specifications for specific applications. Furthermore, to produce or import Fast Pyrolysis Liquid in the European Union a so-called REACH registration is required. REACH means Registration, Evaluation, Authorisation & restriction of Chemicals.

Transport of pyrolysis oil

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Transport of pyrolysis oil requires special attention due to its acidic nature and tendency to phase separation. Recently, requirements FPBO transport have been discussed by Mika Laihanen, Antti Karhunen, and Tapio Ranta of Lappeenranta University of Technology (Finland) [11]. Different transport modes can be considered like waterway, railway or tank container. Currently, commercial supply takes primarily place by tank container.

Acknowledgement

The development of this wiki or knowledge database was initiated as part of the Empyro project which is financially supported by the 7th Framework Programme of the European Commission (Grant number 239357). If you wish to contribute to this PyroWiki please send your credentials to the Administrator.


References

  1. A short historical review of fast pyrolysis of biomass, D. Radlein and A. Quignard, Oil & Gas Science and Technologies, vol. 68 (2013), No4, pp. 765-783
  2. Specialists' workshop on fast pyrolysis of biomass proceedings, 1980, Foxpine Inn, Copper Mountain, Colorado, SERI/CP - 622-1096
  3. Anja Oasmaa & Cordner Peacocke, Properties and fuel use of biomass derived fast pyrolysis liquids - A guide, VTT Publications 731, 2010
  4. Anja Oasmaa, Bert van de Beld, Pia Saari, Douglas C. Elliott, Yrjö Solantausta, Norms, Standards & Legislation for Fast Pyrolysis Bio-Oils, ref to be included, 2015
  5. RH Venderbosch, W. Prins, Fast Pyrolysis Technology Development, DOI: 10.1002/bbb.205; Biofuels,Bioprod. Bioref. 4:178-208 (2010)
  6. Venderbosch R.H., ChemSusChem. 2015 Apr 24;8(8):1306-16. doi: 10.1002/cssc.201500115. Epub 2015 Apr 14
  7. de Rezende Pinho, A.; de Almeida, M. B. B.; Mendes, F. L.; Ximenes, V. L.; Casavechia, L. C., Co-processing raw bio-oil and gasoil in an FCC Unit. Fuel Process Technol 2015, 131
  8. de Rezende Pinho, A.; de Almeida, M. B. B.; Mendes, F. L.; Ximenes, V. L., Production of lignocellulosic gasoline using fast pyrolysis of biomass and a conventional refining scheme. Pure and Applied Chemistry 2014, 86 (5)
  9. Dietrich Meier, Bert van de Beld, Anthony V.Bridgwater, Douglas C. Elliott, Anja Oasmaa, Fernando Preto; State-of-the-art of fast pyrolysis in IEA bioenergy member countries, Renewable and Sustainable Energy Reviews 20 (2013)619–641
  10. Jieni Lian, Shulin Chena, Shuai Zhoua, Zhouhong Wanga, James O’Fallon a, Chun-Zhu Li b, Manuel Garcia-Perez a, Bioresource Technology 101 (2010) 9688–9699
  11. Requirements for transportation of fast pyrolysis bio-oil, IEA Task 34 Newsletter — PyNe 35, Page 18

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