Biodiesel Education Logo

What is Biodiesel?

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.

Biodiesel is of interest because:

  • it is a renewable fuel which can help reduce our dependence on imported fossil fuels
  • it is a renewable fuel which can help reduce our dependence on imported fossil fuels
  • it has a lower carbon footprint than petro-diesel, and so can help reduce greenhouse gas emissions
  • it produces less air pollution than conventional diesel
  • it can provide an additional source of income to farmers who grow oilseed crops

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.

What Biodiesel is made of?

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:

  • mustard seed oil
  • rapeseed oil
  • canola oil
  • soybean oil
  • hydrogenated soybean oil
  • tallow/lard (animal fat), and
  • others

The basic ingredients of biodiesel are:

  • vegetable oil or animal fat
  • alcohol (typically ethanol or methanol)
  • a hydroxide catalyst (typically sodium hydroxide or potassium hydroxide)

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.