Biodiesel is a diesel fuel replacement made from vegetable oil or animal fat. It is not the same as ethanol, which is made from sugar or starch, and which is used in engines that run on gasoline. Biodiesel is used in engines that run on diesel fuel.
According to the EPA’s Renewable Fuel Standards Program Regulatory Impact Analysis, released in February 2010, biodiesel from soy oil results, on average, in a 57% reduction in greenhouse gases compared to fossil diesel, and biodiesel produced from waste grease results in an 86% reduction. See chapter 2.6 of the EPA report for more detailed information.
Biodiesel and glycerinBiodiesel can be made from most any vegetable oil or animal fat. Research at the University of Idaho has involved the following types of oils:
Put very simply, the ingredients are mixed in a reactor and stirred. After the reaction (called transesterification) takes place, the heavier glycerol component settles to the bottom and the resulting ester is pumped off to be used as biodiesel. The image above shows a layer of biodiesel at the top, and a layer of glycerol (also called glycerin) at the bottom.