How is Ethanol Made

Ethanol or ethyl alcohol is a clear, colorless alcohol-based alternative fuel produced by fermenting and concentrating starch crops that have been converted into simple sugars. It can be made not only from corn, barley, and wheat, but also from cellulose feedstock like corn stalks, rice straw, sugar cane bagasse, pulpwood, switchgrass, and municipal solid waste that have considerable amounts of sugar and other material that can be converted into starch or cellulose. Besides this, ethanol can also be produced from 'cellulosic biomass' which include trees and grasses, and so is called bioethanol.

The production of ethanol from starch or sugar-based feedstock is considered to be one of the man's earliest ventures into value-added processing. Although, the basic steps remain the same, the process has been significantly refined in recent years, hence leading to a highly efficient ethanol production process. There are two main ethanol production processes: wet milling and dry milling. The primary difference between these two processes is the initial treatment of the grain. However, in this article we will try to understand how is ethanol made from corn, which is rich in starch and is relatively easy to convert into sugar.

How is Ethanol Made
The modern ethanol production plants employ dry mill method, that involves use of yeast to convert sugar into alcohol, hence the same old fermentation process that has been used for centuries. In fact on an average a typical dry mill production plant produces up to 50 to 100 million gallons of ethanol per year. The major steps in this process are as follows:

Milling: The entire corn kernel or feedstock or other starchy grain is passed through a hammer mill which grinds it into a course flour called meal.

Liquefaction: The meal is mixed with water and alpha-amylase enzyme to form a 'mash' which is passed through cookers where the starch is liquefied. Cookers with high temperature stage (120 - 150º Celsius) and a lower temperature holding period (95º Celsius) are used for liquefaction. These high temperatures reduce the bacteria levels in the mash.

Saccharification: At this stage the mash from the cookers is cooled down and the secondary enzyme (gluco-amylase) is added to turn the liquefied starch into fermentable sugars (dextrose).

Fermentation: The mash is cooled and transferred to fermenters where yeast is added and fermentation of sugar to ethanol and carbon dioxide (CO2) begins. This fermenting mash is allowed to pass through several fermenters until is it completely fermented and leaves the final tank. The entire fermentation process usually takes about 40 to 50 hours, during which the mash is stirred up and kept cool to increase the activity of the yeast.

Distillation: The fermented mash, now referred to as beer, comprises nearly 15% alcohol with all the non-fermentable solids from the corn and yeast cells. The beer is pumped to the continuous flow, multi-column distillation system where the alcohol is separated from the solids and water with the help of heat. In the final distillation column, the alcohol at the top of the final column leaves behind a highly concentrated ethanol. The residue mash from the distillation process, called stillage, is then shifted from the base of the first column to the co-product processing area.

Dehydration: At this stage, the alcohol in the top of the last column is then passed through a dehydration system where the left over water is removed. Commonly a molecular sieve system is used, which is capable of capturing even the last bit of water in the ethanol. The alcohol product now called anhydrous ethanol (pure, without water), is nearly 200 proof.

Denaturing: In this stage, ethanol which is used as a fuel is denatured, or made unhealthy for human consumption, by adding a small amount (2-5%) of gasoline.

Co-Products: Distillers grains and carbon dioxide are the two main products formed during this process. Of which, distillers grains in either wet or dry form are used as a valuable animal feed, while carbon dioxide is collected, compressed and sold to be used in carbonated beverages, food processing and other industries.

I hope after going through these aforementioned steps of ethanol production you will get a fair idea about how it is made. Ethanol is a high-octane premium fuel, that enhances the engine performance and prevents any 'break down' conditions. Hence, in its very pure form, it can be used as a great substitute to gasoline in cars and vehicles.