Biodiesel is a biofuel produced from vegetable oils and animal fats (lipids) and is used as an alternative and/or an additive to petroleum derived diesel fuel. Biodiesel production in the U.S. has been increasing from an estimated 0.5 million gallons of production in 1999 to an estimated 250 million gallons in 2006. Pure (100%) biodiesel is designated B100. Currently, most fleets use blends consisting of 2 to 20% biodiesel and the remainder petroleum-derived diesel (B2 to B20 blends).
The primary resource used to produce biodiesel in the U.S. is soybean oil (about 2.6 billion pounds, 13 percent of domestic production in 2006), but other virgin vegetable oils (e.g., Canola, castor, peanut, palm, rapeseed, sunflower) and greases and recycled oils (e.g., tallow, yellow grease, trap grease) can also be potentially used depending on their availability and price.
Biodiesel is composed of mono-alkyl esters of long chain fatty acids. Through a process called transesterification, biodiesel is made by reacting triglycerides (vegetable oils or fats) with alcohol (methanol) in the presence of a catalyst to produce either fatty acid methyl esters (FAME) or fatty acid ethyl esters (FAEE) and glycerol. For biodiesel derived from soybean oil, one pound of oil yields approximately 1 pound (0.1 gallons) of biodiesel and 0.1 pounds of glycerol and consumes 0.1 pounds of alcohol in its production.