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Bioethanol Production Process
Bioethanol (usually called "ethanol" for short) is the most common biologically-derived automotive fuel in the world. Ethanol is one type of biologically-produced alcohols that can be used as fuel in combustion engines. Others including propanal and butanol.
Bioethanol is made from a variety of sources, most of which are food crops. In the U.S., it is most often made from sweet corn (maize) while in Brazil (the second-largest manufacturer), it is made from sugar cane. It can and is also made from wheat, sugar beets, and molasses.
Ethanol production is a mutli-step process starting with the base feedstock (corn, sugar cane, etc).
How the Enzyme Digestion method works
The feedstock is usually put under microbial fermentation to reduce sugars (the starch and cellulose of the feedstock) to ethanol. Starch is usually the only sugar converted as it is faster and cheaper, but strides are being made towards celluosic ethanol production.
Once the sugars are fermented, they are put through a distillation process to remove excess water. This leaves an ethanol with about 4.4% m/m water mixture. At this stage, the ethanol can be burnt in an engine made specifically to run on pure ethanol (E100). To run in gasoline engines as a gas:ethanol mix, however, more water must be removed.
This is done through dehydration. There are five processes used to accomplish this, with the most common modern method being the use of molecular sieves. This saves energy over the older azeotropic and extractive distillation processes. It works by passing the ethanol vapor through a bed of sieve beds which absorb the water and allow the ethanol to pass through.
How Ethanol is Used
The majority of bioethanol produced is used for automotive transportation. In Brazil and some other countries, many vehicles capable of using pure ethanol are common. In those countries, pure ethanol (E100) is offered at the pump at most fueling stations.
In other countries, such as the U.S., ethanol is offered commonly as a mixture with petroleum gasoline since most automotive engines are not made to run on ethanol alone. The common mixes for this are E10, E15, and E85 - the number denoting the percentage of ethanol in the fuel. E10 (10% ethanol, 90% petroleum gasoline) is the most common, but many "flex-fuel" vehicles capable of running on either pure gasoline or ethanol mixes up to 85% (E85) are also on the American market.
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