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.