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.

Future of bio-ethanol

The energy yield of bio-ethanol is about one third lower than petrol. One liter of bio-ethanol substitute only about 0.65 liters of petrol. This is due to different caloric values of petrol & ethanol. The energy content of petrol is 32.5MJ/L & 21.2MJ/L of bio-ethanol. In Brazil, all brands of automotive gasoline contain anhydrous ethanol in the range of 20-25% (E20-E25).

For using fuels that are highly blended with bio-ethanol (E20-E100) conventional engines have to be refitted with more efforts. This is due to the characteristic of bio-ethanol to dissolve some rubber and plastic. Recently an increasing number of vehicles are manufactured, which support petrol as well as bio-ethanol. Sensors of these flexible fuel vehicles can automatically detect the types of fuel and adapt engine running.

Fuel cells- although the use of bio-ethanol in fuel is not commercially viable, technical applications of ethanol are possible.

Table 1a - consumption of petrol in India

10000000	Kiloliters
500000	Kiloliters  of 5% ethanol
500000000	Liters of ethanol

Table 1b - Ethanol in India

Ethanol	Lakh Liter
Demand all over country	5000
Existing production	1840
Total demand	2460
Demand in Maharashtra	700

Table 2 - Worldwide production cost of gasoline & bio-ethanol from other sources

FUEL	BIOMASS SOURCES	PRODUCTION COST [€/liter]
Fossil fuel	Gasoline	0.24-0.27
Bio-ethanol	Corn	0.43-0.48
	Sugar cane molasses	0.22-0.29
	Wheat straw	0.43-0.55
	Sweet sorghum	0.21-0.26
	Sugar beet	0.42-0.46
	Lignocelluloses	0.22

Figure 3: CO2 emission from fuels

Manufacturing of bio-ethanol from sugarcane molasses

Manufacturing of bio-ethanol from sugarcane molasses:

Molasses (Black strap) are considered as the mother liquor left after the removal of sugar crystals. Hence, it is a by-product of the sugar industry. It contains about 55% sugar (2/3 sucrose and 1/3 inert sugar).

From the selected strains of yeast the inoculum is prepared. The starter containing yeast is in its log phase. The yeast developed in a seed tank should be pure and free from contaminating and mutation. The molasses is diluted with water to 10 to 18%. These molasses can be used directly as fermentation medium. Nutrients such as ammonium sulphate or ammonium phosphate may be added to improve the quality of fermentation. The pH value of medium adjusts 4 or 5 by adding sulphuric acid or lactic acid.

figure: 1 process flow sheet of bio-ethanol from sugarcane molasses

Alcoholic fermentation is an example of anaerobic fermentation. Fermentation has therefore to be carried out in the absence of oxygen. The carbon dioxide produces pushes out air automatically creates an anaerobic atmosphere. The fermentation is carried out for 40-50 hours at 30 to 40°C in a fermenter, after mixing then yeast starter and medium. The fermented mash (beer) is diluted to obtain pure ethyl alcohol. The fractions containing 60% alcohol are known as high wine. These fractions are the distilled to get 95% alcohol. After successive distillation only 95% alcohol is obtained. Modern ethanol plants used a molecular sieve system to produce the absolute 100% of ethanol.

High boiling fuse oil is obtained during distillation and finds commercial use as a lacquer solvent. The carbon dioxide is also obtained and is converted to dry ice for commercial grade use.