In the original proposal from the European Commission for a directive on biofuels three principal categories of alternative fuels were identified:
- Biofuels i.e. fuels derived from biomass crops or by-products that are suitable for use in vehicle engines or heating systems;
- Natural gas, with future large-scale use likely to be based on purpose built cars;
- Hydrogen, with natural gas or electrolysis being the most likely initial large scale production methods.
Biofuels and natural gas were considered as having the potential to achieve market levels of between 5% and 10% by 2020 with hydrogen, which requires significant development before it is widely used as a transport fuel, attaining a 5% level by the same date.
Biofuels can be considered as potential replacements or extenders for mineral fuels such as diesel or petrol. They can be sub-divided into a number of categories, the principal two being:
- Vegetable oils / animal fats which can be used in unprocessed form or converted to biodiesel;
- Bio-ethanol produced from the fermentation of organic materials such as sugar beet, cereals, etc.
Vegetable oils include oil from purpose grown oil seed crops (oil seed rape, camelina sativa, etc.). They also include waste vegetable oil (or recovered vegetable oil – RVO) such as waste cooking oil from the catering industry. Animal fats include tallow produced by the rendering industry.
Other biofuels include the following:
- Biogas (principally composed of methane), which is collected at landfill sites or from anaerobic digestion systems, could be used in vehicles in compressed form.
- Bio-methanol and dimethylether (DME), which are produced from biomass derived methane, offer limited attraction compared to alternatives.
- Bio-oil produced from the pyrolysis of biomass materials continues to be the subject of extensive research, although commercial uptake is limited as yet.
Vegetable oil and bio-ethanol technologies are now well developed and have reached commercial acceptance in many countries. The use of vegetable oil or its derivative, biodiesel, as a transport fuel is established in Germany and Austria where production in 2001 was 350,000 tonnes and 31,400 tonnes respectively. Bio-ethanol is widely used as an oxygenate in petrol in the USA, where production levels have reached 1.4 billion gallons, or approximately 1.1% of US gasoline consumption. A derivative of bio-ethanol, ethyl tertiary butyl ether (ETBE), is similarly used in France, where 219,000 tonnes were produced in 2001.
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