Bio-ethanol

Bio-ethanol (alcohol, ethanol or ethyl alcohol) is derived by fermentation from plant materials, particularly carbohydrates. Chemically it is the same molecule as found in potable alcohol. Bio-ethanol is by far the biggest fermentation product to date. In the world as a whole, 26 million ton of ethanol was produced in 2002, 63 % of which was used as a bio-fuel. Europe made only about 1.6 million tons of ethanol in 2002, very little compared to the USA and Brazil, where respectively 5.7 and 8.7 million ton of ethanol were produced as a bio-fuel.

Ethanol is presently produced with the help of yeasts that convert easily fermentable carbohydrates obtained from sugar beet, sugar cane or cereals into ethanol. Currently, significant research efforts are directed towards producing alcohol from more difficult substrates such as agricultural residues (e.g. corn cobs, straw) or other organic waste (e.g. waste paper). Agricultural co-products or waste such as straw, bran, corn cobs, corn stover, etc., products that are either being poorly valorised or left to decay on the land, are attracting increasing attention as an abundantly available and cheap renewable feedstock. Estimations from the US Department of Energy have shown that up to 500 Million tonnes of such raw materials are available in the USA each year. As vast amounts of these raw materials are available at low prices, such a process would considerably improve the overall economics of ethanol as a biofuel and would seriously impact the energy sector. However because of their complex composition, these substrates are not easily converted to free sugars. On the one hand, by genetic modification, a number of micro-organisms have been modified such that they can convert more complex substrates like cellulose or lignocellulosic waste to alcohol. These "superbugs" are then used to convert more complex substrates like bagasse, straw and waste paper to ethanol. On the other hand, much effort has been put into biotechnological research for inexpensively producing and improving the required cellulase enzymes. These "supercellulases" must hydrolyse cellulose to glucose that can be easily fermented. Considerable difficulties are yet to be overcome to make this dream an industrial reality.

Besides ethanol, a number of co-products are being produced during production such as vinasses or protein fractions that are used as animal feed or as a fertilizer. The concomitant production of CO 2 is very significant, as there is as much production of CO 2 as ethanol during fermentation. This kind of CO 2 is very pure and is often recovered for use in the chemical industry and for the production of soft drinks. Bio-ethanol is also used in the chemical, cosmetic and pharmaceutical industry and a small part is used for human consumption. Potable alcohol is in a certain way also a bio-fuel: it provides our bodies with 6,5 kcal/g.

For use in motor fuels, the alcohol must be dewatered, mostly with the help of regenerable absorption agents. The dewatered alcohol (bio-ethanol) can be used under different forms in motor fuels, usually in mixtures with normal gasoline. Bio-ethanol can be added directly to gasoline, a procedure that is mostly used in Brasil. A practice more used in Europe and the US is to react the bio-ethanol with the petrochemical intermediate isobutylene, and then add the obtained ETBE (Ethyl Tertiary Butyl Ether) to normal gasoline. Whereas European practice adds ETBE in low percentages, higher percentages are being used in the US. A common blend in the US is E15, containing 15% ethanol.

The application of bio ethanol does not require an adaptation of the vehicle motor up to an addition percentage of 15 %. Quite to the contrary, the addition of bio ethanol or ETBE increases the oxygen value of the fuel, plays a role as an octane enhancer and leads to a better combustion of the fuel mixture. A fuel with 10 to 15 volume % ETBE leads - in comparison with normal fuel - to a reduction of 20 to 25 % of the carbon monoxide emission, 10 to 15 % reduction of volatile hydrocarbons , 30 % less soot, 20 to 30 % less benzene and a strong reduction of the ozone content (in function of the weather conditions). It is also remarkable that ETBE acts as a lead substitute in fuel, so that strong ecological progress is obtained through the use of bio-ethanol in fuel blends.

More information about bio-ethanol production via the Renewable Fuels Association

More information on biofuels in Europe via the Biofuels Technology Platform