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Ethanol: Sugar, Starch or CelluloseSee also:
Ethanol or ethyl alcohol is the second member of the alcohols family. Even when used as synonym of fuel alcohol, from a chemical point of view, fuel alcohol is actually a blend of several members of the family (methanol, ethanol, propanol, butanol, etc.) and other chemical compounds such as esters, aldehydes and a minimal amount of water (less than 0.1%). In general, alcohol can be obtained from petrol as well as from biomass, this being called bioethanol mostly. When biomass is the feedstock, ethanol results from the conversion of glucose into alcohol by yeast metabolism through fermentation.
Cellulose and starch, in the other hand are polymers of glucose units coupled into chains of 2,000-4,000 units. In order to ferment cellulose or starch has to be subject to hydrolysis, in other words, the polymeric chains have to be broken into individual glucose units. This is the case of grains, vegetable waste and starch-rich roots. Fermentation process results in 7 to 10% alcohol mashes. The alcohol content varies according to feedstock type. It as been reported that 18% alcohol content can be achieved, 23% in Lab (Kelsall y Lyons). To obtain concentrated alcohol, mash is heated up using thermal energy in special equipments through distillation. This process can yield up to 96% alcohol. But in order to use it as fuel in blends with gasoline, it is necessary to remove more water. Currently this is achieved in most production plants using molecular sieve technology. In the early days of ethanol industry though, azeotropic distillation was the dehydration process. Today it is almost out of use. Alcohol has been produced by man for centuries from grains and fruits in the form of alcoholic beverages. When internal combustion engines and the first vehicles appeared, ethanol was one of the fuel choices. But petrol soon displaced it as a real alternative. It was until middle 70's, with the world oil crisis, that USA and Brazil started programs for developing new alternative fuels to diminish their economies' dependency on foreign oil. With succes, but after struggling with several obstacles, Brazil, with its program PROALCOOL, became at last a world leader in production and consumption of ethanol as a fuel.
It is appropriate to point out here, that renewable not necesarily means sustainable, and even when biofuels are considered renewable, it is possible that some feedstock sources or production processes make them not sustainable. The concept of sustainable development according to the UN Comission on Sustainable Development (CSD), is "development that meet the needs of the present without compromising the ability of future generations to meet their own needs." Ethanol as well as biodiesel are facing great controversy around sustainability and both have advocates and detractors. It is important to remain open-minded and keep looking for objective information.
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In plants, glucose is available in the form of cellulose, starch and sugars. Sugars are mainly mono and disaccharides which are directly fermentable, that means they can be converted into alcohol without previous treatment. This is the case of sugarcane molasses rich in sucrose.
Currently, fuel alcohol faces harsh controversy due to the relationship with world high food prices that some attribute to its production. But it is important to keep objectivity while analyzing this topic, because of the crucial role of really sustainable biofuels search and development. It is a priority for human kind.
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