Biodiesel Production: Biodiesel can be made from new or used vegetable oils and animal fats, which are nontoxic, biodegradable, and renewable. Fats and oils are chemically reacted with an alcohol (methanol is most commonly used in the United States) to produce chemical compounds known as fatty acid methyl esters. Biodiesel is the name given to these esters when they are intended for use as fuel. Glycerin (used in pharmaceuticals and cosmetics, among other markets) is produced as a co-product.

Biodiesel can be produced using a variety of esterification technologies. The oils and fats are filtered and preprocessed to remove water and contaminants. If free fatty acids are present, they can be removed or transformed into biodiesel using special pretreatment technologies. The pretreated oils and fats are then mixed with an alcohol (usually methanol) and a catalyst (usually sodium hydroxide). The oil molecules (triglycerides) are broken apart and reformed into methyl esters and glycerin, which are then separated from each other and purified.

Diagram 1: Schematic of a biodiesel production path, which has several branching steps. Vegetable oils and recycled greases (the greases first undergo dilute acid esterification with sulfuric acid and methanol) undergo transesterification (with input of methanol and KOH) to form crude glycerin and crude biodiesel. The crude biodiesel is refined to produce biodiesel. The crude glycerin is refined to produce glycerin. Methanol is recovered from the crude biodiesel and crude glycerin refining steps for reuse in the transesterification process.

Although the process is relatively simple, homemade biodiesel is not recommended. Diesel engines are expensive, and it is not worth risking damage or even minor operational problems from fuel that does not meet rigorous ASTM D6751-07a specifications. Section 3.1 of the Biodiesel Handling and Use Guidelines (PDF 1.5 MB) provides a summary of this standard. Download Adobe Reader. The full standard can be purchased from ASTM International.