Corn ethanol

Corn ethanol is ethanol produced from corn that is used as a biomass. Corn ethanol is produced by means of ethanol fermentation and distillation. Corn ethanol is mainly used as an oxygenate in gasoline to produce a low-level blend. To a lesser extent, it is used as fuel for E85 flex-fuel vehicles. Corn is the main used for producing ethanol fuel in the United States.

There are two main types of corn ethanol production: dry milling and wet milling. The products of each type are utilized in different ways.

In the dry milling process the entire corn kernel is ground into flour and referred to as "meal." The meal is then slurried by adding water. Enzymes are added to the mash that convert starch to dextrose, a simple sugar. Ammonia is added to control the pH and as a nutrient for the yeast, which is added later. The mixture is processed at high-temperatures to reduce the bacteria levels and transferred and cooled in fermenters. This is where the yeast is added and conversion from sugar to ethanol and carbon dioxide begins.

The entire process takes between 40 and 50 hours, during which time the mash is kept cool and agitated in order to facilitate yeast activity. After the process is complete, everything is transferred to distillation columns where the ethanol is removed from the "stillage". The ethanol is dehydrated to about 200 proof using a molecular sieve system and a denaturant such as gasoline is added to render the product undrinkable. With this last addition, the process is complete and the product is ready to ship to gasoline retailers or terminals. The remaining stillage then undergoes a different process to produce a highly nutritious livestock feed. The carbon dioxide released from the process is also utilized to carbonate beverages and to aid in the manufacturing of dry ice.

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