What is corn ethanol used for?

Bioethanol can be produced from various vegetable raw materials. The production can be based on starchy (e.g. cereals, potatoes, maize) as well as on sugary (e.g. sugar beet, sugar cane) plants as well as cellulosic biomass. The process technology for bioethanol made from cellulosic raw materials is still in the development phase. German bioethanol producers mainly use grain and sugar beet.

Bioethanol is produced through alcoholic fermentation of the sugars contained in the plants. For raw materials containing starch and sugar, the production process differs at the beginning. A mill first crushes the starchy grain. The chemical conversion of starch into sugar is thus easier in the next step: The crushed raw materials are heated during mashing with the addition of water and saccharifying enzymes. The sugary mash can now be fermented in the fermenter of the bioethanol plant with the addition of yeast.

In the production of sugar, sugary juices are produced. For bioethanol production, these can be fermented directly in the fermenter of the bioethanol plant. During the fermentation process, the sugar is dissolved in ethanol (C.2H5OH), an alcohol. A bioethanol-water mixture and a residue that has been freed from alcohol are then separated from one another by distillation. In order to be able to use the bioethanol as fuel, a degree of purity of over 99 percent is required. The desired fuel quality can be achieved by separating the water. In a thermal separation process, the bioethanol, which turns into gas more quickly, is separated from the water by evaporation. Bioethanol evaporates well below 100 ° Celsius, while water remains in the drainage tank at this temperature level. The ethanol vapor then condenses. In a final chemical cleaning step, the bioethanol reaches a degree of purity of over 99 percent. Prepared in this way, bioethanol can then be offered as a five (E5) or ten percent (E10) admixture to gasoline. In suitable vehicles, however, it can also be used as an E85 fuel, i.e. the fuel mixture consists of 85 percent bioethanol and 15 percent fossil gasoline.

The residue left over from the distillation, also known as vinasse, is a nutrient-rich coproduct and can be used further. If stillage is dehydrated, dried and pelletized, it can be used as a high-quality animal feed. Alternatively, the stillage can also be fermented in the fermenter of a biogas plant. The resulting biogas can be converted into electricity and heat by burning in a block-type thermal power station or processed into biomethane, which is fed into the natural gas network.

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