Fermentation of Ethyl Alcohol
Ethyl Alcohol is also called as ethanol. Ethanol is produced by biological process in which sugars such as glucose, fructose, sucrose are converted into alcohol and carbon dioxide. The fermentation carried out is anaerobic condition. Ethanol is volatile and flammable liquid.
Alcohol fermentation was the first fermentation that was carried out by human beings. Previously alcohol was used for consumption purpose only but later on the different application of alcohol such as universal solvent and chemical raw material, surface disinfectant, medicinal solvent, antiseptic were known. So the method of production of alcohol by fermentation in distilleries was started.
Substrates used in fermentation of ethyl alcohol are the waste products of fermentation industries like saccharides, starchy and cellulosic material. The bacteria as well as fungi can ferment sugar to alcohol. Generally alcohol is produced by fermentation or by petrochemical process.
Structure of Ethanol
2] Micro-organism used in fermentation
The microorganism used for fermentation depends upon the type of raw material used for fermentation.
- If Starch and sugar are used as substrate then the fermentation organism used is Saccharomyces cerevisiae or Saccharomyces ellipsoideus.
- Fermentation of alcohol from dairy waste Candida pseudotropicalis is used.
- If the Sulphite waste liquor is used from the paper industry then Candida utilis strain is used for fermentation.
The fermentation micro-organism is selected on the basis
- The strain used should give high yield of product.
- The strain should be fast growing and tolerate high concentration of sugar so it can give high yield of product.
- The microorganism should be genetically stable.
3] Inoculum preparation
Inoculum added in fermentation tank is of a yeast culture. A large amount of innoculum is required in the ethanol fermentation process. Inoculum added in fermentation process is generally 4 % but in sometimes 8 % to 10 % of innoculum may be added.
The composition of nutrient media used for innoculum preparation is similar to the composition of fermentation media. During the process of innoculum preparation the nutrient media is facilitated with high amount of aeration and agitation. It is important for fast growth of cells. The optimum temperature maintained is about 28° C to 30 ° C and optimum pH used is 4.8 to 5. The maintenance of optimum conditions in innoculum preparation media is important for growth and production of cell mass.
4] Raw material used for fermentation
A variety of industrial waste and agricultural waste is used as a raw material for fermentation of ethanol.
- Cellulosic material used contains sulphite waste liquor, straw.
- Starchy material like corn starch, potato starch and wheat flour.
- Saccharides like sugar cane molasses, beet molasses, hydrol, fruit juices are used.
5] Fermentation medium
Raw material used in fermentation should be economically cheap. It should be easily available mostly the agricultural waste is used as a raw material for ethanol fermentation. Generally molasses is used in India for fermentation. The agricultural waste used should be pre-treated for removal of unwanted, toxic products and the raw material is converted into sugar form. So this sugar can be easily utilized by innoculum and produce high amount of ethanol. The molasses used for fermentation is pre-treated and the sugar content of molasses is diluted and adjusted to 10 % to 18 %.
The beet molasses is also added in the medium as a source of biotin as it is one of the important growth factor. Nitrogen source is added in the form of ammonium sulphate or ammonium phosphate in a concentration of about 0.015 %. The optimum pH maintained of the fermentation media is about 4.8 to 5 and optimum temperature maintained is 28° C to 30 ° C. Here in this case of fermentation there is no need of sterilization of media only pasteurization of this media can be done.
The fermented broth is allowed to stand still for settling down of product and further it is distilled by fraction distillation process. The product is distilled by using analyser and rectifier column the distilled product obtained is ethyl alcohol and fusel oil. The product obtain is 95 % ethyl alcohol and 5 % water.
Laboratory Scale Distillation Plant
7] By products
The by products obtained after fermentation
- The distillery effluent – The distillery effluent is nothing but fusel oil. This fusel oil is used in perfume manufacture, used in paint industries, spent wash contain potassium salts used in manufacture of potassium fertilizers.
- The residual yeast cells are used in fodder preparation.
- The carbon dioxide produced is purified and used as dry ice or used in soft drinks.