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.
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 D6751-07b specifications.
Do not use raw vegetable oil in a diesel engine. Fats and oils (triglycerides) are much more viscous than biodiesel, and low-level vegetable oil blends can cause long-term engine deposits, ring sticking, lube oil gelling, and other maintenance problems that can reduce engine life.
The U.S. biodiesel industry is small but growing rapidly. Production tripled from 2004 to 2005 and again from 2005 to 2006. Much of the original biodiesel production capacity comes from companies already making products from vegetable oil or animal fat in the detergent industry among others. More than half the biodiesel industry can use any fat or oil feedstock, including recycled cooking grease. The other half of the industry is limited to vegetable oils; soy oil is the most common source in the United States today. The soy industry has been the driving force behind biodiesel commercialization because of excess production capacity, product surpluses, and declining prices. Similar issues apply to the recycled grease and animal fats industry, even though these feedstocks are less expensive than soy oils. A possibly limiting factor for biodiesel industry growth is potential saturation of the market for glycerin.
Enough virgin soy oil, recycled restaurant grease, and other feedstocks are readily available in the United States to provide feedstock for about 1.7 billion gallons of biodiesel per year (under policies designed to encourage biodiesel use). This represents roughly 5% of on-road diesel used in the United States.
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