Biodiesel
Friday, March 7th, 2008Biodiesel, made from animal fat or vegetable oil, is a renewable pollution-reducing alternative to petroleum diesel. It is made by transforming animal fat or vegetable oil with alcohol, and can be directly substituted for diesel either as neat fuel (B100) or as an oxygenate additive (typically 20%—B20). B20 earns credits for alternative fuel use under the Energy Policy Act of 1992, the only fuel that does not require purchase of new vehicles. In Europe, the largest producer and user of biodiesel, the fuel is usually made from rapeseed (canola) oil. In the United States, the second largest producer and user of biodiesel, the fuel is usually made from soybean oil or recycled restaurant grease. The National Biodiesel Board, a trade association for biodiesel producers is a good source of additional information.
Soybean oil and recycled restaurant cooking oil are in surplus, and biodiesel production uses only a small portion of each, so there is no resource constraint.
Esters are compounds of alcohol and organic acids. Fatty acid methyl ester, commonly known as biodiesel, is made by bonding methanol to animal fat or vegetable oil. The process is relatively straightforward, but must consistently achieve prescribed standards to minimize the risk of damaging expensive diesel engines.
Because it is oxygenated, biodiesel dramatically reduces air toxins, carbon monoxide, soot, small particles, and hydrocarbon emissions by 50% or more, reducing the cancer-risk contribution of diesel up to 90% with pure biodiesel. Air quality benefits are roughly proportional for diesel/biodiesel mixtures. Biodiesel’s superior lubricity helps reduce engine wear, even as a small percentage additive.
The most common use of biodiesel is as B20: -20% biodiesel, 80% diesel. It requires no engine modifications. Because it gels at higher temperatures than petroleum diesel, however, pure biodiesel requires special management in cold climates. Biodiesel contains slightly less energy than petroleum diesel, but it is denser, so fuel economy tends to fall 7% for every 10% biodiesel in a fuel blend.