This second article by Absolute Futures will explain the commercial production of ethanol. Ethanol is a product of fermentation. Fermentation is a sequence of reactions which release energy from organic molecules in the absence of oxygen. In this application of fermentation, energy is obtained when sugar is changed to ethanol and carbon dioxide.
Changing corn to ethanol by fermentation takes many steps. Starch in corn must be broken down into simple sugars before fermentation can occur. In earlier times, this was done by chewing the corn. This allowed the salivary enzymes to naturally break down the start. Today, this is achieved by cooking the corn and adding the enzymes alpha amylase and gluco amylase.
Once a simple sugar is obtained, yeast is added. Yeast is a single-celled fungi which feeds on the sugar and causes the fermentation. As the fungi feeds on the sugar, it produces alcohol (ethanol) and carbon dioxide. In fermentation, the ethanol retains much of the energy that was originally in the sugar, and explains why ethanol is an excellent fuel.
Most ethanol production in the United States is made in 50 production facilities in 20 different states. Most of these plants are located in the Midwest.
Changing the starch in kernels of corn to sugar and changing sugar to ethanol is a complex process and requires a mix of technologies that include microbiology, chemistry and engineering.
Ethanol is produced from corn by using one of two standard processes: wet-milling or dry-milling. Dry-milling plants cost less to build and produce higher yields of ethanol, but the value of co-products is less. Most of the ethanol plants in the U.S. utilize a dry-milling process. The wet-milling operation is more elaborate because the grain must be separated into its components.
After fermentation, the ethanol is removed from the mix of ethanol, water, yeast, and residue. It is then purified through distillation. The distilling process takes advantage of the low boiling point (78C.) of ethanol. When the temperature of the mix is increased slightly higher than the boiling point, the ethanol evaporates. It is then captured as a gas vapor and condensed back to a liquid. Other chemicals are added and molecular sieves are used to purify the ethanol.
Advances in technology are being made to further reduce the large amounts of energy needed for distillation. These advances help to reduce the costs and make producing ethanol much more economical.