Manufacture of ethyl alcohol from molasses:
Let me explain to you today manufacture of ethyl alcohol from molasses. In India of the ethyl alcohol is prepared from molasses. Molasses is the mother liquor left after the crystallization of cane sugar from concentrated juice. It is dark coloured thick syrupy mass. Molasses contain about 60% fermentable sugars, mostly sucrose, glucose, and fructose. It forms a brilliant cheap source of industrial ethyl alcohol. Molasses is converted into ethyl alcohol by the following steps:
Molasses id first diluted with water. One volume of molasses is blended with 5 volumes of water.
Addition of Ammonium Sulphate.
Molasses usually contain enough nitrogenous matter to act as food for yeast during fermentation. If the nitrogen content of the molasses is poor, it may be fortified with ammonium sulphate or ammonium phosphate.
Addition of Sulphuric Acid.
The solution is then made acidic with a little amount of sulphuric acid. Acidity is favourable to the growth of yeast but unfavourable to most other bacteria. Care should be taken to avoid an excess of acid as the yeast may be killed.
Addition of Yeast (Fermentation).
The resulting solution is received in a large fermentation tank and yeast is added to it. The mixture is maintained at about 30ºC for 2 or 3 days. During this period the enzymes invertase and zymase present in yeast bring about the conversion of sugars into ethyl alcohol. During the process, the liquor froths owing to the evolution of carbon dioxide. The fermented liquid is known as WASH.
Fractional Distillation of wash.
The wash contains 15-18% ethyl alcohol. It is subjected to fractional distillation in a special column (Fig. 1.1) The column is divided into the number of compartments by means of plates. These plates are provided with valves and drop tubes. Wash is admitted near the top. As it travels down the column, it meets the up-coming current of steam. The steam converts ethyl alcohol into vapours. These vapours rise up and are fed into the condenser. The high boiling impurities travel down the column. The fractional refining of the wash yields 3 fractions:
The low boiling fraction is drawn from the head of the section. It consists of acetaldehyde.
The main fraction is drawn near the up of the section. It consists of 95% ethyl alcohol. It is sold under the name R field Spirit or Commercial Alcohol.
High boiling fraction (125-140ºC) drawn near the base of the column. It is called Fusel Oil. It consists mainly of amyl alcohol (C5H11OH).