Butanol is a flammable liquid that is used as a fuel and as an industrial solvent. Like gasoline, it is a hydrocarbon, meaning that it is composed of the chemical elements hydrogen, oxygen, and carbon. Most internal combustion engines can burn butanol without experiencing problems, especially more modern engines. This fact has led to research into the use of it as a fuel additive and as an alternative fuel.
The interest in butanol as an alternative fuel stems in large part from the fact that it has certain significant advantages over ethanol. For instance, an engine which runs on this hydrocarbon will have an easier time starting in cold temperatures than one which uses ethanol. This is because of a chemical property called heat of vaporization. Fuel must be vaporized before it can be burned in an engine, and butanol can be vaporized more easily at low temperatures than ethanol. It is also much less evaporative than either gasoline or ethanol, and releases more energy than ethanol when burned.
These different chemical structures all have the same chemical formula and components, but have somewhat different properties. One of the isomers, known as tert-butanol, is actually a solid at room temperature, and therefore cannot be used as a fuel by itself. Because of the way it is structured on a molecular level, butanol is considered an alcohol. In practical terms, this means, among other things, that it is able to be dissolved in water, and that it is somewhat toxic, especially if its fumes are not properly contained or are not ventilated. It also exists in several slightly different forms, called isomers.
The production of butanol for fuel was traditionally accomplished by fermenting biomass, such as algae, corn, and other plant materials containing cellulose that could not be used for food and would otherwise go to waste. The fermentation process is facilitated mainly by a type of bacteria called Clostridium acetobutylicum. Oddly enough, these bacteria are rather closely related to those which cause botulism. Other microorganisms are also able to ferment these materials, and research into these types of production techniques is ongoing. More recently, most butanol has been produced industrially from fossil fuels.
Given the advantages of butanol over some other fuels, many wonder why it is not more widely used. The main reason is that the cost of producing and bringing it to the market results in a much higher cost to the consumer than the cost of gasoline, in many cases. Also, while it has a higher energy content than ethanol, it takes quite a bit more raw material to produce it. Some new developments, however, show some promise as being able to dramatically increase the yield of butanol through fermentation.