Explain the manufacture of ethanol from molasses.
Explain the manufacture of ethanol from molasses.
Molasses is a dark coloured syrupy liquid left after the crystallization of sugar from the concentrated sugarcane juice. Molasses still contains about 30% of sucrose which cannot be separated by crystallization. It is converted into ethanol by the following steps:
(i) Dilution
Molasses is first diluted with water to bring down the concentration of sugar to about 8 to 10 percent.
(ii) Addition of Ammonium Salts
Molasses usually contains enough nitrogenous matter to act as food for yeast during fermentation. If the nitrogen content of the molasses is poor, it may be fortified by the addition of ammonium sulphate or ammonium phosphate.
(iii) Addition of Yeast
The solution from step (ii) is collected in large ‘fermentation tanks’ and yeast is added to it. The mixture is kept at about 303K for a few days. During this period, the enzymes invertase and zymase present in yeast, bring about the conversion of sucrose into ethanol. The fermented liquid is technically called wash.
C12H22O11+H2OSucroseinvertase−−−−−→C6H12O6Glucose+C6H12O6Fructose
C6H12O6Glucosezymase−−−−→2C2H5OHEthanol+2CO2↑
(iv) Distillation of Wash
The fermented liquid containing 15 to 18 percent alcohol and the rest of the water is now subjected to fractional distillation. The main fraction drawn is an aqueous solution of ethanol which contains 95.5% of ethanol and 4.5% of water. This is called rectified spirit. This mixture is then heated under reflux over quicklime for about 5 to 6 hours and then allowed to stand for 12 hours. On distillation of this mixture, pure alcohol (100%) is obtained. This is called absolute alcohol.
Molasses is a dark coloured syrupy liquid left after the crystallization of sugar from the concentrated sugarcane juice. Molasses still contains about 30% of sucrose which cannot be separated by crystallization. It is converted into ethanol by the following steps:
(i) Dilution
Molasses is first diluted with water to bring down the concentration of sugar to about 8 to 10 percent.
(ii) Addition of Ammonium Salts
Molasses usually contains enough nitrogenous matter to act as food for yeast during fermentation. If the nitrogen content of the molasses is poor, it may be fortified by the addition of ammonium sulphate or ammonium phosphate.
(iii) Addition of Yeast
The solution from step (ii) is collected in large ‘fermentation tanks’ and yeast is added to it. The mixture is kept at about 303K for a few days. During this period, the enzymes invertase and zymase present in yeast, bring about the conversion of sucrose into ethanol. The fermented liquid is technically called wash.
C12H22O11+H2OSucroseinvertase−−−−−→C6H12O6Glucose+C6H12O6Fructose
C6H12O6Glucosezymase−−−−→2C2H5OHEthanol+2CO2↑
(iv) Distillation of Wash
The fermented liquid containing 15 to 18 percent alcohol and the rest of the water is now subjected to fractional distillation. The main fraction drawn is an aqueous solution of ethanol which contains 95.5% of ethanol and 4.5% of water. This is called rectified spirit. This mixture is then heated under reflux over quicklime for about 5 to 6 hours and then allowed to stand for 12 hours. On distillation of this mixture, pure alcohol (100%) is obtained. This is called absolute alcohol.
