Biodiesel

Biodiesel refers to a diesel-equivalent, processed fuel derived from biological sources. Though derived from biological sources, it is a processed fuel that can be readily used in diesel-engined vehicles, which distinguishes biodiesel from the straight vegetable oils or waste vegetable oils used as fuels in some modified diesel vehicles.

Biodiesel is alkyl esters made from the trans-esterfication of both vegetable oils and/or animal fats. Biodiesel is biodegradable and non-toxic, and has significantly fewer emissions than petroleum-based diesel when burned. Biodiesel functions in current diesel engines. It can be distributed using today's infrastructure, and its use and production are increasing rapidly. European legislation gives an extra impulse to the production and use of biofuels too. Biodiesel is generally more expensive to purchase than petroleum diesel but this differential may diminish due to economies of scale, the rising cost of petroleum and government tax subsidies in several European countries.

Chemically, trans-esterfied biodiesel comprises a mix of mono-alkyl esters of long chain fatty acids. The most common form uses methanol to produce methyl esters as it is the cheapest alcohol available, though ethanol can be used to produce an ethyl ester biodiesel and higher alcohols such as isopropanol and butanol have also been used. Using alcohols of higher molecular weights improves the cold flow properties of the resulting ester, at the cost of a less efficient trans-esterfication reaction. A sideproduct of the trans-esterfication process is the production of glycerol. A lipid trans-esterfication production process is used to convert the base oil to the desired esters. Any Free Fatty Acids (FFAs) in the base oil are either converted to soap and removed from the process, or they are esterfied (yielding more biodiesel) using an acidic catalyst. After this processing, unlike straight vegetable oil, biodiesel has combustion properties very similar to those of petroleum diesel, and can replace it in most current uses.