Ethanol, sometimes known as grain alcohol, is made by fermenting plant materials. Traditionally, this has meant fermenting the consumable part of the crops, especially from corn or sugar cane.
A big downside of this is that it encroaches on the food supply of people and livestock. New research focuses instead on using cellulosic biomass, which consists of the non-food parts of plants like corn stalks]. The process involves turning the plant material into glucose, which can then be fermented like any other sugar, producing ethanol. Lignin, a byproduct of the process, is burned to provide energy to help complete the process.
While it can be used as a fuel in its pure form, biodiesel is usually combined with gasoline. All gasoline-powered vehicles can take readily available gasohol, a mixture of 90 percent gasoline and 10 percent ethanol. Flex-fuel vehicles can also use what's called E85 fuel, a mixture of 85 percent ethanol and 15 percent gasoline.
Unlike ethanol, biodiesel has only taken off in the United States since around 2005. The science behind it is also much newer and a bit more complex. Most methods of producing biodiesel in the U.S. start with soybean oil or used vegetable oil, though other oils and even algae can be used, too.
According to the National Sustainable Agricultural Information Service, the oil is combined with an alcohol, usually methanol or even ethanol. A catalyst like potassium hydroxide or sodium hydroxide (lye) is used to begin the process called transesterification, which produces the biodiesel, with glycerol created as a byproduct.
Like ethanol, biodiesel is usually combined with petroleum-based fuel, allowing use by all diesel vehicles. The most common mix is called B20, reflecting a 20 percent biodiesel and 80 percent petroleum diesel mix. Modified vehicles can use B100, or 100 percent biodiesel, to power them down the road.
Ethanol and biodiesel are two fuels that get a lot of the glory, but there's a lot more to the biofuels picture. In the next section, we'll explore some other biofuel options.