Industrial Production of Ethanol

Ethanol is a renewable, alcohol biofuel, which can be used as an alternative to reduce dependence on oil, and toxic emissions from gas. The use of ethanol has many benefits; it lowers levels of toxic ozone-forming pollutants, reduces greenhouse gas emissions by 20 percent when compared to gasoline, and is an octane-enhancer. Ethanol production in the United States is approximately 14 billion gallons annually; however only 2 percent of ethanol is used for transportation fuel. There are approximately 200 industrial ethanol plants in the United States, primarily in the Corn Belt, Midwestern states.

During the industrial production of ethanol, the process called dry milling begins when processors grind organic matter, usually corn, into coarse flour or meal. This is added to water, which coverts starch to dextrose, creating a simple sugar. To control the pH, ammonia is added, and the mass is cooked at a high-temperature, reducing bacteria. Next, it is cooled, and placed in fermenters; the addition of yeast begins the sugar’s conversion to carbon dioxide (CO2) and ethanol, which occurs in approximately 40-50 hours. Afterwards, the ethanol that results from this process is separated from the remaining liquid and spent grains, which are either recycled to be used in the cooking system or used as livestock feed. Conventional distillation methods are used to concentrate the ethanol, first to 190 proof; then a dehydration molecular sieve system is used to concentrate it to 200 proof, making it undrinkable. The CO2 that is produced during the fermentation process is sold to be used in the carbonation of soft drinks and the production of dry ice.

In the wet milling process, the corn is first soaked in water and diluted with sulfurous acid, then grinded. The corn oil is extracted and the gluten, starch and fiber that remains is segregated further by centrifugal, hydroclonic separators. An evaporator is used to concentrate the liquid further, and then the fermentation and distillation processes are done in the same way as the dry mill process. It is then shipped to gasoline retailers.

Corn is not the only biomass that can produce ethanol. Technology can be used to produce it from other materials, such as trees, plant stalks and industrial waste, by breaking down the materials’ cellulose into fermentable sugars. However, the cellulose production of ethanol is more expensive than producing it from corn, and requires more processing steps, and thus not a feasible alternative.

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