Biofuels can be defined as liquid fuels produced from biomass for either transport or burning purposes. They can be produced from agricultural and forest products, and the biodegradable portion of industrial and municipal waste.

This paper concentrates on two types of transport biofuel: bioethanol and biodiesel, which account for more than 90 per cent of global biofuel usage.

Bioethanol is a distilled liquid produced by fermenting sugars from sugar plants and cereal crops (sugarcane, corn, beet, cassava, wheat, sorghum) and whose manufacturing process is presented in our website. A second generation of bioethanol–lignocellulosic – also includes a range of forestry products such as short rotation coppices and energy grasses. Bioethanol can be used in pure form in specially adapted vehicles or blended with gasoline. Bioethanol can be blended with gasoline in any proportion up to 10 per cent without the need for engine modification. Blends of 5 per cent or 10 per cent of bioethanol in gasoline are denominated B5 and B10, respectively.

Biodiesel or vegetable oil methyl ester (VOME) is produced from the reaction of vegetable oil with ethanol or bioethanol in the presence of a catalyst to yield monoalkyl esters and glycerine, which is then removed. Oil is produced from oily crops or trees such as rapeseed, sunflower, soya, palm, coconut or jatropha, but it can also be produced from animal fats, tallow and waste cooking oil. A second generation of biodiesel technologies – the Fischer-Tropsch process – synthesises diesel fuels from wood and straw to a gasification stage. Similar to bioethanol, biodiesel can be used in pure form in specially adapted vehicles or blended with automotive diesel. A blend of 5 per cent of biodiesel is denominated as B5.