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> Bio-oil applications
> Introduction
> Introduction
> Properties 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 NOx emission. The heating values: the higher heating value (HHV) is below 19 MJ/kg (compared to 42 - 44 MJ/kg for conventional fuel oils).
> Application
Heat Production
Electricity production
Synthesis gas
> Chemicals from bio-oil 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.
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 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.
> Status of technology
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| © BTG Biomass Technology Group BV 2002-2003. Last modified on: 13 March 2003 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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.
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.
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.%).
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.