Introduction
Properties
Application
Chemicals from bio-oil
Status of the technology
Projects
Reference
Links
Contact

Introduction
Bio-oil can be used as a substitute for fossil fuels to generate heat, power and / or chemicals. Short-term applications are boilers and furnaces (including power stations), whereas turbines and diesel engines may become available on the somewhat longer term. Upgrading of the bio-oil to a transportation fuel is technically feasible, but needs further development. Transportation fuels such as methanol and Fischer-Tropsch fuels can be derived from the bio-oil through synthesis gas processes. Furthermore, there is a wide range of chemicals that can be extracted or derived from the bio-oil.

Properties
Representative values for the pyrolysis oil properties are listed in the Table below. It is typically a liquid, almost black through dark red-brown, depending on its chemical composition and the presence of micro-carbon. The density of the liquid is about 1200 kg/m³, which is higher than of fuel oil, and significantly higher than of the original biomass The viscosity of the oil varies from as low as 25 cP up to 1000 cP depending on the water content, the amount of light ends, and the extent to which the oil has aged.

Due to large amounts of oxygenated components present, the oil has a polar nature and does not mix readily with hydrocarbons. It contains less nitrogen than petroleum products, and almost no metal and sulphur components

The degradation products from the biomass constituents include organic acids (like formic and acetic acid), giving the oil its low pH of about 2 to almost 4. The oil attacks mild steel, and storage of the oils should be in acid proof materials like stainless steel or poly-olefins. Neutralisation of the oil is not an interesting option as it can cause polymerisation.

Water is an integral part of the single-phase chemical solution. The (hydrophilic) bio-oils have water contents of typically 15 - 35 wt.%, which can not be removed by conventional methods like distillation. Phase separation may occur above certain water contents. It is reported that this phase separation does not occur until the moisture content increases above about 30 to 45 %.

Beneficial effects of the high water contents have also been reported, viz. in case of combustion. It causes a decrease in viscosity of the oil (facilitating transport, pumping and atomisation), it improves the stability, it lowers the combustion temperature and, as a consequence, it may cause a reduction of the NO_x emission.

The heating values: the higher heating value (HHV) is below 19 MJ/kg (compared to 42 - 44 MJ/kg for conventional fuel oils).

The range of the elemental composition and of the properties for a wood derived bio-oil.
	Physical property					pyrolysis conditions
water content (wt.%)			15-30			Temperature (K)			770
pH			2.8-3.8			Gas residence time (s)			0.46
Density (kg/m3)			1110-1250			particle size (µm)			590
Elemental analysis						moisture (wt.%)			3.3
(wt.% moisture free)						cellulose (wt.%)			49.1
	C		55.3-63.5			Ash (wt.%)			0.46
	H		5.2-7.0
	N		0.07-0.39			Yields (wt.%)
	S		0.00-0.05			Organic liquid			65.8
	O		Balance			Water			12.2
	Ash		0.03-0.30			Char			7.7
						Gas			10.8
HHV (MJ/kg)			16-19
Viscosity (315 K, cP)			25-1000
ASTM vacuum						Pour point (K)			250
distillation (wt.%)	430 K		10
	466 K		20			Solubility (wt.%)		Hexane		1
	492 K		40					Toluene		16
	distillate		50					Acetone		> 99
								acetic acid		> 99

Application

Many different applications have been developed or under developent for the use of bio-oil.

Heat Production
The heating value of bio-oil is lower than for fossil fuel, and a significant portion of the bio-oil consists of water. Nevertheless, flame combustion tests showed that fast pyrolysis oils can replace heavy and light fuel oils in industrial boiler applications. In its combustion characteristics, the oil is more similar to light fuel oil, although significant differences in ignition, viscosity, energy content, stability, pH and emission levels are observed. Problems identified in flame combustion of bio-oil are related to these deviating characteristics, but these can be overcome in practice. Bio-oil combustion in a boiler and / or furnace is shown to be the most straightforward approach for use of bio-oil. Meanwhile, bio-oil has been used commercially to co-fire a coal utility boiler for power generation.

Electricity production
Several hundreds of hours has been achieved in the last years on various diesel engines from laboratory test units to large size modified dual fuel engines. Test results mention positive results of engine performance in terms of smooth running. Nevertheless some problems still need to be resolved to use bio-oil to replace diesel, especially if the acidic nature of the oil (pH 3) and its tendency for soot formation and re-polymerisation is considered. The use of a bio-oil requires modification of various parts of the engine, amongst which the most important ones are the fuel pump, the linings and the injection system. Slight modifications of both the bio-oil and the diesel engine can render bio-oils a quite acceptable substitute for diesel fuel in stationary engines (CHP applications)

Experience with bio-oil combustion in gas turbines is limited. R&D projects known are those carried out by a Canadian company (Orenda), and Italian and German Research institutes. The potential is high, but there are technical limitations such as the fuel thermal stability, contaminants, and acidity. Non-conventional atomisers are required to account for the special properties of the oil. Ignition difficulties and significant carbonaceous deposits of unburned material inside the combustion chamber have been noticed. Nevertheless, commercially available gas turbines are said to be available within several years.

Synthesis gas
For the production of "green" hydrocarbons, only biomass can play a major role, because it is impossible to produce these from the other renewable sources. A comparison between the use of the solid biomass and the use of the liquid bio-oil as feedstock for synthesis gas production encourages considering gasification of bio-oil in large-scale syngas generation. In that case a conventional entrained flow gasifier can be used, which is proven technology. Apart from the scale-related considerations, another problem of solid biomass gasification is that the gasification conditions usually do not match properly with synthesis gas requirements:

• Direct biomass gasification is carried out at relatively low temperatures with air or with steam / oxygen mixtures, to avoid ash melting. The syngas produced therefore contains large amounts of nitrogen (when air is used), and high "tar" and methane concentrations. These "inert" compounds reduce the selectivity and reactivity of catalysts applied in further processing. Operation of a direct biomass gasification on pure oxygen requires steam to decrease the gasification temperature.
• Pressurization of biomass is expensive, and biomass gasifiers are yet developed for atmospheric conditions only. High-pressure syngas processing requires expensive syngas compression to 60 bar.
• The design of biomass gasifiers is different, due to the special requirements for the biomass-solids handling

Chemicals from bio-oil

Chemical components
More than 300 compounds have been identified as fragments of the basic compounds of biomass, viz. the lignin (amongst others phenols, eugenols and guaiacols), cellulose and hemi-cellulose derivatives (sugars, acetaldehyde and formic acids). Large fractions of acetic acid, acetol, and hydroxyacetaldehyde are reported in the analysis results. Until now, only 40 to 50 % of the oil identity (excluding the water) is revealed, but especially the large, less severely cracked molecules are not yet identified. All types of functional groups are present: acids, sugars, alcohols, ketones, aldehydes, phenols and their derivatives, furanes and other mixed oxygenates. Phenols are present in high concentrations (up to 50 wt.%).

The important chemicals identified in the oil are summarised in Table below. Pre-treatment of wood can result in an increase of one particular component at the expense of the other. In wood-derived pyrolysis oil, specific oxygenated compounds are present in relatively large amounts. Basically, the recovery of pure compounds from the complex bio-oil is technically feasible but probably economically unattractive because of the high costs for the recovery of the chemical and its low concentration in the oil.

A large fraction of the oil is the phenolic fraction, consisting of relatively small amounts of phenol, eugenol, cresols, and xylenols, and much larger quantities of alkylated (poly-) phenols (the so-called water insoluble pyrolytic lignin). It showed good performance as adhesive for waterproof plywood.

Levoglucosan is a sugar derivative. Existing and potential applications and markets for biomass-derived LG are due to the possible self-polymerisation of LG, giving low molecular weight oligo- or poly-saccharides. Another anhydrosugar identified in the oil is the doubly dehydrated anhydrosugar Levoglucosenone.. Yields of LGS from cellulose can amount up to 24 wt.%. Another sugar derivate, hydroxy-acetaldehyde can be present in relatively large amounts in the bio-oil. It represents the smallest sugar, and can be used for the browning of foods.

Components that can also be derived from bio-oil are carboxylic acids. In the aqueous fraction of the bio-oil these acids are present in small amounts. Finally, furfural and furfurylalcohol are present in amounts up to 30 wt.% and 12 to 30 wt.%, respectively were produced.

Unfractionated bio-oil
The only commercial application of bio-oil is that of wood flavour or liquid smoke. A number of companies produce these liquids by adding water to the bio-oil. A red coloured product is then obtained that can be used as such to brown and flavour sausages, bacon, fish, etc.

The use of bio-oil or its water-soluble aldehyde fraction is investigated for the replacement of formaldehyde in urea-formaldehyde resins for particleboards. Due to the higher cross-linking of the lignin derived compounds in the bio-oil, a polymer with an improved strength can be obtained when mixed with conventional urea-formaldehyde resins.

Pure bio-oil can be mixed with lime to form BioLime . Injection of the mixture into flue-gas tunnels results in almost complete removal of sulphur oxides and a significant reduction of nitrogen oxides.

Reaction of bio-oil with ammonia, urea or other amino compounds produces stable amides, amines, etc. They are non-toxic to plants and can be used as slow release organic fertilisers.

Important chemicals identified in bio-oil.
Chemical	concentration (wt.%)
Hydroxy-acetaldehyde	up to 17 (from cellulose)
Levoglucosan	up to 47 (from cellulose)
Levoglucosene	up to 24 (from cellulose)
Phenolic compounds	30-100
Wood Preservatives
MethylArylether
Calcium Carboxylate salts
Furfural, Furfuryl alcohol	up to 30 (from cellulose)
Steroids	detected in vacuum pyrolysis oil
Nicotine/taxol precurors
Heavy metal recovery
polymeric carbon adsorbents
BioLime™
Blended fuels
Slow release fertilizer

Status of technology
The current status of the processing of bio-oil is summarised in the Table below. Indicated in bold are the most promising options on a short time scale.

The status of primary, secondary and tertiary processing of bio-oil. Indices: 1=conceptual, 2=laboratory, 3=pilot, 4=demonstration and 5=commercial. Indicated in bold are the most promising options on a short time scale.
secondary processing	secondary product	tertiary processing	final product
transport5	fuel	combustion5	heat/steam/electricity
Boiler / furnace2	heat/steam	steam turbine5	electricity
engine/turbine1	electricity
Stabilisation1	stabilised oil	engine/turbine1	electricity
Upgrading2	hydrocarbons	Refining5	diesel/gasoline
extraction1,5	chemicals	refining1,5	chemicals
conversion5	chemicals	refining1,2	chemicals
conversion2,3	(syn)gas2	fuel cell1 gas engine1 processing5	electricity electricity5

Projects

• Diesel engine on bio-oil: a review
• Gasification of bio-oil for the production of green transportation fuels
• Toxicity and Health novem project

Reference

• Venderbosch R.H., van Helden, 2001, Diesel engine on bio-oil: a review, SDE
• Venderbosch R.H., Vos J., Prins, 2000, Flash Pyrolysis technologies for Biomass Usage in Small Decentralised Co-generation Units, in: Proceedings van het Symposium Biomassa, Verbranden, Vergassen, Vergisten, Pyrolyse (edited by W.L. Prins W.L. and J. van Ham), Utrecht
• Venderbosch R.H., Wagenaar B.M., Gansekoele E., Sotirchos S., Moss H.D.T. 2000, Co-firing of bio-oil with simultaneous SO_x and NO_x reduction. Paper presented at the Conference on Thermochemical Biomass Conversion Technologies, Tyrol, Austria, 17-22 September 2000
• Venderbosch R.H., Wagenaar B.M., Vos J., Prins W., 2001, Combined Heat and Power (CHP) Production on basis of bio-oil produced from agricultural waste streams, paper to be presented at Sustain 2001, May 2001
• Van de Beld B., Venderbosch R.H., 2001, Production of Transportation Fuels from Biomass, CTI-report (confidential)
• Prins W., Vos J., Venderbosch R.H., Wagenaar B.M., Van den Berg, Van Haren P., 1998, Market Study for Applications of Flash Pyrolysis Oil, EWAB Report 355297/6040
• >R.H. Venderbosch, B.M. Wagenaar, W. Prins, H.E.M. Stassen, 2002, Hout-olie in bestaande ketels, NDEC hellip;..

Links
Pyne EET-pagina

Contact
Dr. Ir. R.H. Venderbosch
Tel +31 53 486 2281

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