Sugar industries produce molasses from the sugar cane processing. Molasses have 50 -55% concentration of sugar in the form of sucrose, with chemical formula C12H22O11. This source of compound is used for preparing ethyl alcohol. Ethanol in the form of absolute and rectified spirit can be made from molasses. Basis raw materials for an industry to produce 1 ton of ethyl alcohol requires, molasses up to 5.6 tons, sulfuric acid 27 kg and ammonium sulphate 2.5 kg.
The chemical reactions involved for ethanol production from molasses:
C12H22O11 + H2O → 2C6H12O6 ,with enzyme invertase.
C6H12O6 → 2C2H5OH + 2CO2 -31.2 KCal ,with enzyme zymase.
2C6H12O6 + H2O → ROH +RCHO (high molecular weight alcohols C2H5OH)
Description of the ethanol production process:
Large volume storage tanks of molasses provide continuous supply of molasses and store the fresh molasses from sugar processing section during the fermentation process. The molasses from the tanks are diluted with water to obtain the sugar concentration around 10-15%. The acidic nature of molasses supports the growth of yeast during breaks up of sucrose, for that purpose acids are added to maintain the pH between 4 and 5. Continuous diluter equipment takes up this task. A yeast culture tank, which is provided with nutrition supply of ammonium and magnesium phosphate or sulphate, is used as nutrient to the yeast. The acidic condition favours the yeast to produce catalytic enzymes, invertase and zymase.
Diluted and treated molasses and the yeast from storage are fed to the fermentation chamber. Modern fermentation tanks are made with stainless steel material provided with heating coils or jacket provision. The temperature 20-30 oC is maintained in the tanks by the heating and cooling system. The process of fermentation takes place around 30-70 hours based on the temperature and sugar concentration to yeast count. Final temperature 35 oC is attained at the end of the process. During the fermentation process, microorganism yeast produces carbon dioxide as by-product.
After the process cycle, the product liquid mixture is fed to beer still to perform distillation. Solid and slurry mass is separated leaving the solution of alcohol and water. The concentration of alcohol in the liquid mixture would around 8-10%. A series of beer still work out to produce different quality of beer products. The slurry form of material obtained from bottom of beer still is called as slops. It is used for cattle feed and fertilizer after some waste treatment operations.
However, the aldehydes are not allowed in consumable beer so aldehydes present in the solution are removed by aldehyde column. The streams coming out at different section of the column are aldehydes from top, fusel oil and ethanol mixture from middle and bottom stream with water. The middle stream is fed to rectification column to produce a product called rectified spirit having 95% ethanol. Rectified spirit further made to absolute alcohol by anhydrous still using benzene as third component. Absolute alcohol with 100% ethanol concentration is a standard product used as intermediate for producing other chemical products and blending agent in power fuels. The end use of the ethanol would be largely in solvent, acetaldehyde, acetic acid, polyethylene and synthetic rubber production.
Ethanol production can be increased by utilizing sugarcane juice also. Fermentation molasses is not disturbed if treated sugarcane juice is added at frequent intervals.
Other methods for ethanol production:
- Ethanol manufacturing by catalytic hydration of ethylene: Direct method
- Indirect method using sulfuric acid
Application of ethanol as fuel in IC engines:
Gasoline is blend with methanol or ethanol that was produced biologically. This type of fuel is used for cars and petrol engine vehicles that already run on roads. Scientists claim that using such fuels will reduce the greenhouse gas emission. Petrol engines used in automobiles used spark plug ignition technology and the fuel vapours are combusted in the cylinder. Gasoline itself is not the outstanding fuel in terms of octane number. The octane value of the fuel has increased by adding additives in recent times. The additives that were used in gasoline has harmful effect on environment for example tetraethyl lead is toxic compound, MTBE cause water pollution and when coming toluene and benzene they are best cancer causing compounds. Ethanol now used as additive that replaces all other harmful compounds. Due to oxygen content in its structure it improve combustion and decrease the emission of harmful unburnt hydrocarbons and carbon monoxide.