Biofuel
Biofuels are non-fossil fuels. They are energy carriers that store the energy derived from organic materials (biomass), including plant materials and animal waste[1]. they may be solid, such as fuelwood, charcoal and wood pellets; liquid such as ethanol, biodiesel and pyrolysis oils; or gaseous such as biogas[1].
Overview
Biofuels are fuels produced directly or indirectly from organic material - biomass, including plant materials and animal waste. Biofuels can be solid, gaseous or liquid, even though the term often refers only to liquid biofuels for transport[1].
Biofuels may be derived from agricultural crops, including conventional food plants or from special energy crops. Biofuels may also be derived from forestry, agricultural or fishery products or municipal wastes, as well as from agro-industry, food industry and food service by-products and wastes[1].
Biofuels can be spilt into primary and secondary biofuels. Primary biofuels include fuelwood, wood chips and pellets, organic materials are used in an unprocessed form, primarily for heating, cooking or electricity production. Secondary biofuels result from processing of biomass and include liquid biofuels such as ethanol and biodiesel that can be used in vehicles and industrial processes[1].
Biofuels for transport[1]
The most widely used liquid biofuels are ethanol and biodiesel.
Ethanol is a type of alcohol that can be produced using any feedstock containing significant amounts of sugar, such as sugar cane or sugar beet, or starch, such as maize and wheat. Sugar can be directly fermented to alcohol, while starch first needs to be converted to sugar. The fermentation process is similar to that used to make wine or beer, and pure ethanol is obtained by distillation. The main producers are Brazil and the USA.
Ethanol can be blended with petrol or burned in nearly pure form in slightly modified spark-ignition engines. A litre of ethanol contains approximately two thirds of the energy provided by a litre of petrol. However, when mixed with petrol, it improves the combustion performance and lowers the emissions of carbon monoxide and sulphur oxide.
Biodiesel is produced, mainly in the European Union, by combining vegetable oil or animal fat with an alcohol. Biodiesel can be blended with traditional diesel fuel or burned in its pure form in compression ignition engines. Its energy content is somewhat less than that of diesel (88 to 95%). biodiesel can be derived from a wide range of oils, including rapeseed, soybean, palm, coconut or jatropha oils and therefore the resulting fuels can display a greater variety of physical properties, such as viscosity and combustibility than ethanol.
Second-generation Biofuels[1]
Currently used liquid biofuels, which include ethanol produced from crops containing sugar and starch and biodiesel from oilseeds, are referred to as first-generation biofuels. These fuels only use a portion of the energy potentially available in the biomass.
Most plant matter is composed of cellulose, hemicellulose and lignin, and “second-generation biofuel” technologies refer to processes able to convert these components to liquid fuels. Once commercially viable, these could significantly expand the volume and variety of sources that could be used for biofuel production.
Potential cellulosic sources include municipal waste and waste products from agriculture, forestry, processing industry as well as new energy crops such as fast growing trees and grasses. As a result second generation biofuel production could present major advantages in terms of environmental sustainability and reduced competition for land with food and feed production. It could also offer advantages in terms of greenhouse gas emissions.