Biofuels

The identification and development of new sources of energy is a major challenge for our future and will continue to appear in news reports on a regular basis. This entry provides some basic background on a particular type of alternative energy source that is beginning to receive more attention: biofuels. These are sources of energy (solid, liquid, or gas) derived from biomass, which is defined as any organic matter that is produced and available on a recurring basis. Biofuels, therefore, are considered to be renewable sources of energy. The energy is supplied by the sun through photosynthesis, which captures solar energy and combines it with atmospheric carbon dioxide to convert it to chemical energy in various plant compounds. After the plant material is harvested, converted to a usable fuel, and burned for its energy, carbon dioxide is released to the atmosphere to begin the cycle anew.

Biofuels are distinguished from fossil fuels, which are derived from plant matter that grew and was deposited millions of years ago. Coal and petroleum are sources of fossil fuel. When fossil fuels are burned, large amounts of carbon that had been immobilized for eons are released into the atmosphere, increasing levels of carbon dioxide beyond the capacity of living plants and other earth systems to absorb it. In 150 years of increasing fossil fuel use since the beginning of the Industrial Revolution, atmospheric carbon dioxide levels have increased from 150 parts per million to 330, causing the atmosphere to retain heat (the greenhouse effect) and resulting in global climate change.

Interest in biofuels is based not only on a need to reduce emissions of carbon dioxide but also on the growing awareness that the world is running out of oil. Liquid transportation fuels are vital to industrial economies; with escalating petroleum costs (a fourfold increase from 2004 to 2008) as well as the reality that global demand for oil is beginning to exceed supply, many countries are turning to biofuels for transportation. Currently, the chief biofuels are ethanol, made from plant carbohydrates, and biodiesel, made primarily from plant oils. In 2006, world total ethanol production was 10 billion gallons, and world biodiesel production was about 1.6 billion gallons. Approximately 90% of global biofuel production was concentrated in the United States, Brazil, and Europe. European nations have tended to favor biodiesel made from rapeseed, while the United States and Brazil have focused more on ethanol from corn and sugarcane.

First-generation biofuels refer to ethanol made from sugarcane or corn starch and biodiesel made from soybean oil, canola oil, or palm oil. Waste animal fats can also be made into biodiesel. For ethanol, the starch from corn kernels is broken down to sugars, which are then fermented by yeast to produce ethanol. With sugarcane, sugar is simply squeezed out of the sugarcane and fermented. This general process has been used for hundreds of years to produce a variety of alcoholic beverages and is a mature technology. Biodiesel is made by mixing the plant oil with methanol to produce a methyl ester (biodiesel) and a coproduct, glycerin, that has a number of uses, including its use in cosmetics. First-generation biofuels have caused controversy because of concerns that diverting crops and cropland from food to fuel will have negative consequences for the food system. For this reason, the U.S. Department of Energy and the U.S. Department of Agriculture agree that first-generation biofuels will only be able to meet about 15% of U.S. liquid transportation fuel demand, which was approximately 150 billion gallons per year in 2007. To reduce the U.S. reliance on petroleum, the U.S. Congress passed the 2007 Renewable Fuel Standard, a mandate for 36 billion gallons of biofuels to be produced annually by the year 2022.

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