biodiesel

biodiesel fuel made from natural, renewable sources, such as new and used vegetable oils and animal fats, for use in a diesel engine . Biodiesel has physical properties very similar to petroleum-derived diesel fuel, but its emission properties are superior. Using biodiesel in a conventional diesel engine substantially reduces emissions of unburned hydrocarbons, carbon monoxide, sulfates, polycyclic aromatic hydrocarbons, nitrated polycyclic aromtic hydrocarbons, and particulate matter. Diesel blends containing up to 20% biodiesel can be used in nearly all diesel-powered equipment, and higher-level blends and pure biodiesel can be used in many engines with little or no modification. Lower-level blends are compatible with most storage and distribution equipment, but special handling is required for higher-level blends.

Biodiesel is made from oils or fats, which are hydrocarbons. Fresh soybean oil is most commonly used, although biodiesel can be made from mustard seed oil or waste vegetable oil (such as used oil from restaurant deep fryers). These hydrocarbons are filtered and mixed with an alcohol, such as methanol, and a catalyst (sodium hydroxide or potassium hydroxide), resulting in a chemical reaction whose major products are the biodiesel fuel and glycerol .

biofuel A gaseous, liquid, or solid fuel that contains an energy content derived from a biological source. The organic matter that makes up living organisms provides a potential source of trapped energy that is beginning to be exploited to supply the ever-increasing energy demand around the world. An example of a biofuel is rapeseed oil, which can be used in place of diesel fuel in modified engines. The methyl ester of this oil, rapeseed methyl ester (RME), can be used in unmodified diesel engines and is sometimes known as biodiesel. Other biofuels include biogas and gasohol.