What is Biodiesel?

Biodiesel is a diesel replacement fuel for use in diesel engines. It is manufactured from plant oils (e.g., soybean oil, cottonseed oil, canola oil, corn oil); recycled cooking greases or oils (e.g., yellow grease); or animal fats (beef tallow, pork lard); and various combinations of these feedstocks. Used cooking oils are mostly plant based, but may also contain animal fats. Used cooking oils are both recycled and renewable.

As biodiesel production and use increase, new feedstocks are being developed and may soon be introduced into the market. Some examples include pennycress, camelina, cuphea, brown grease, and various strains of algae. Although there is little biodiesel from these feedstocks currently available, there is great potential for these feedstocks to supplement the current feedstock supply.

The biodiesel manufacturing process converts oils and fats into chemicals called long-chain mono alkyl esters, or biodiesel. These chemicals are also referred to as fatty acid methyl esters (FAME), and the process is referred to as esterification. Figure 1 provides a simplified diagram of the esterification process. Roughly speaking, 100 pounds of oil or fat are reacted with 10 pounds of a short-chain alcohol (usually methanol) in the presence of a catalyst (usually sodium hydroxide or potassium hydroxide) to form 100 pounds of biodiesel and 10 pounds of glycerin (or glycerol). Glycerin is a sugar and is a co-product of the biodiesel process.

Biodiesel is a legally registered fuel and fuel additive with the U.S. Environmental Protection Agency (EPA). The EPA registration is feedstock and process agnostic and includes all biodiesel that meets the ASTM biodiesel specification, ASTM D6751.