Manufacturing of bio-ethanol from Corn:

Today, most Bio-ethanol is produced from corn by either the dry grind (67%) or the wet mill (33%) process.

Dry grind ethanol production:

The entire corn kernel is ground into coarse flour through a hammer mill, to pass through a 30 mesh screen, then slurried with water to form a “mash” Starch exists as insoluble, partially crystalline granules in the endosperm of the corn kernel. Starch cannot be metabolized directly by yeast, but must first be broken down into sample six carbon sugar prior to fermentation. To accomplish this conversion, the pH of the mash is adjusted to 6.0. The mash is heated above 100°C using a jet cooker, which provides the high temperature and mechanical shear necessary to cleave and rupture starch molecules.

figure 2:  process flow sheet of bio-ethanol from Corn

Enough glucoamylase is added such that the saccharification of the starch to glucose, which occurs continuously through the fermentation, does not limi8t the rate of ethanol production. After cooking, the mash is cooled to 32°C and transferred to fermenters where yeast is added. Often, ammonium sulfate or urea is added as nitrogen acids, which serve as an additional source of nitrogen for the yeast.

The fermentation requires 48-72 hr and has a final ethanol concentration of 10-12%. Either batch or continuous fermentation systems may be used, although batch processing is more common. There is the some few new fermentation systems has been designed so that can reduce the dilution of the water, and reduce the evaporation and thus that the energy required for the processing of feed after the fermentation process. Distillation is the process which is carried out to separate the pure ethanol from the slurry of the solids and water in the mash the vaporization point of the alcohol is 78°C and of water is 100°C. As there is a difference between the boiling of the alcohol and the water. The ethanol is separated from the water by using the distillation column. The methods used to produce 95% of pure ethanol are convectional distillation/rectification. At this point, the alcohol and the water form and azeotrope, modern ethanol plants used a molecular sieve system to produce the absolute 100% of ethanol.

The solid and liquid which is remained after the distillation process is known as “whole stillage” , this whole stillage contains the substances like fiber, oil, protein components of the grains, and the non-fermented starch. This substance which is produced during the manufacturing of the ethanol is a valuable feed ingredient like poultry, livestock, and fishes.