HISTORY OF ETHANOL PRODUCTION:
- Louis Pasteur demonstrated the fermentation of sugar by microbes and their regulations as well. He found that the yeast cells produce 20 times more cell materials under aerobic conditions than under unaerobic conditions. He explained that Oxygen inhibits fermentation process. Yeasts are aerobic microorganism, but glucose fermentation takes place under unaerobic condition. This is also known as” Pasteur effect “.
- In 1815, Gay- Lussac formulated the conversion of glucose to ethanol.
- During 1980, lactic acid was produced by fermentation as a substitute for tartaric acid used in baking powder which was not commercialized.
CHARACTERISTICS OF ETHANOL:
- Ethanol is a volatile, flammable, colourless liquid.
- Ethanol is a straight-chain alcohol, and its molecular formula is C2H5OH.
- Its empirical formula is C2H6O, making it a constitutional isomer of dimethyl ether .
- The fermentation of sugar into ethanol is one of the earliest organic reactions employed by humanity
The entire process of ethanol production is divided into two stages namely upstream process and downstream process.
Upstream processing encompasses any technology that leads to the synthesis of a product as well as the fundamental science and engineering needed to understand product formation. Upstream includes the exploration, development and production of crude oil, bitumen and natural gas etc.
TYPES OF ETHANOL PRODUCTION:
Ethanol is produced both as a petrochemical, through the hydration of ethylene, and biologically, by fermenting sugars with yeast .
Ethanol hydration is most often made from petrochemical feed stocks, typically by the acid-catalyzed hydration of ethylene. The catalyst is most commonly phosphoric acid absorbed on to a porous support such as diatomaceous earth or charcoal. This catalyst was first used for large scale production by shell Oil Company in 1947. The reaction is carried out with an excess of high pressure steam at 300°C.
Nowadays ethylene was hydrated indirectly by reacting it with concentrated sulphuric acid to produce ethyl sulphate, which was then hydrolysed to yield ethanol and regenerate the sulphuric acid.
MICROORGANISMS USED IN ETHANOL PRODUCTION:
Some of the microorganisms that are used in the fermentation process are mentioned below:
Clostridium acetobutylicum; Klebsiella pneumoniae; Leuconostoc mesenteroides etc.
Aspergillus oryza; Mucor sp; Neurospora crassa; Saccharomyces sp. (yeast); etc
SELECTIVE FEATURES FOR THE STRAINS:
- It should be an efficient strain. In otherwise it should produce a large quantity of alcohol.
- It should be fast growing.
- It should have a high tolerance to alcohol as well as to osmotic pressure.
- It should posses uniform and stable biochemical properties.
After selection of the desired organism and its isolation in pure form, the inoculum is prepared under aseptic conditions. For this purpose the organism are first cultured in flasks under aerobic conditions to increase the size of the inoculum which can be used for inoculation.
A variety of carbohydrates available as waste products of agricultural industries are used for the preparation of fermentation medium on the basis of their chemical nature. They are grouped as;
- Saccharide materials : molasses, whey, glucose, sucrose.
- Starchy materials : potato, wheat, rice, corn, starch.
- Cellulosic material : waste liquor, wood.
Most of the raw materials of alcohol fermentation require some degree of pre treatment. The actual process depends on the chemical composition of the raw materials. In general, the sugary raw materials require mild or no pretreatment, while the cellulosic materials need extensive pretreatment. This is because the cellulosic substances have to be subjected to acidic or enzyme hydrolysis to release monosaccharide units that are needed for alcohol production.
Sugar concentration in the range of 10 to 18 % is found satisfactory. Sugar concentration of 12 % is often used. For example, cane molasses contain sucrose as a carbon source. High concentration affects yeast adversely while low concentration makes the process uneconomical.
Many organic as well as inorganic nitrogenous compounds may be used. Ammonium sulphate is generally used. The level of nitrogen in the medium is limited.
It is not necessary to add the growth factors separately in the preparation of the fermentation medium. Since the raw materials used satisfy the requirements of the culture.
PH of the fermentation medium is 4.8 to 5. The higher PH increases the chances of contamination, whereas lower PH values inhibit the yield of ethyl alcohol.
Usually, the temperature range of 70 to 80°F is preferred. Temperature can be controlled by cold water spray around the fermentation tank. Higher temperature favours the growth of bacteria and also causes loss of alcohol due to evaporation.
Fermentation of ethanol is carried out in large fermentation tanks. The Inoculum of microorganisms is maintained in the fermenter at the optimum growth conditions. At the same time fermentation medium is formulated and transferred to the sterile fermenter. Liquid medium in fermenter is inoculated with a small amount of inoculum of yeast. Fermentation starts within a few hours after the addition of yeast. The process becomes rapid after 24 hours to complete. Duration of ethyl alcohol fermentation is usually 30 to 72 hours when the specific gravity of the fermented liquid becomes constant.
The extraction and purification of a biotechnological product from fermentation is referred to as downstream processing.
STAGES IN DOWNSTREAM PROCESS:
SOLID LIQUID SEPERATION:
The first step in product recovery is the separation of whole cells and other insoluble ingredients from the culture broth. Some of these methods are;
When a gas is introduced into the liquid broth, it forms bubbles. The cells and other solid particles get adsorbed on to these gas bubbles. These bubbles rise to form foam layer which can be collected and removed.
In this, the cells form large aggregates to settle down for easy removal. The process of flocculation depends on the nature of cells and ionic constituents of the medium.
The concentration of biological products can be achieved by transferring the desired product from one liquid phase to another liquid phase, which is referred to as liquid-liquid extraction.
The biological product of fermentation can be concentrated by using solid adsorbent particles.
The biological products of fermentation are very effectively purified by chromatograph techniques. One such is;
It involves the separation of molecules based on their surface charges. Ion exchangers are of two types- cation exchangers with negative charged groups and anion exchangers with positively charged groups. The most commonly used cation-exchangers are dowex HCR and amberlite IR, the anion- exchangers are dowex SAR and amberlite IRA.
In ion-exchange chromatography, the PH of the medium is very crucial, since the net charge varies with PH. In other words, the PH determines the effective charge on both the target molecules and the ion exchanger. The ionic bound molecules can be eluted from the matrix by changing the PH of the eluant or by increasing the concentration of salt solution. Ion-exchange chromatography is useful for the purification of antibiotics, besides the purification of proteins.
Ethanol is separated from the fermentation broth in continuous stilts resembling those utilized for the recovery of acetone, butanol, and ethanol of 95% concentration is obtained by successive distillations in these stilts. To obtain alcohol concentrations greater than 95%, however requires special distillation techniques because of the ability of alcohol to form an azeotropic mixture of benzene, water and ethanol, which is then distilled with increasing temperature increaments. This procedure removes first the azeotropic benzene-water-ethanol mixture, and then an ethanol-benzene azeotropic mixture so that absolute alcohol remains. The absolute alcohol as well as 95% ethanol is marketed with and without denaturation.
A high-boiling fusel oil fraction also is recovered during distillation of the fermentation broth and this fraction accounts for approximately 0.5% of the crude distillates. Other products of the fermentation, except for the carbon dioxide which is often collected for reuse are present in only small amounts. These trace amounts of succinic acid and slightly larger amounts of glycerol occur. Some acrolein also may be present in the distillate, have been formed by microbiological contaminants attacking the glycerol.
DISTILLERIES PRODUCING ALCOHOL:
There are over 127 distilleries in INDIA producing 732m lit. of alcohol per annum.some of the distelleries functioning in U.P. are given below,
- Narang distillery, Gonda.
- Cooperative sugar factory Ltd.,nainital.
- Hindustan sugar mills Ltd.,gola.
- Standard Refineries and distilleries,Unnao
- Saraya distillery, Gorakhpur.
- Modi industries Ltd. Ghaziabad. Etc.
ETHANOL PLANT IN TURNER COUNTRY, SOUTH DAKOTA
It is mainly an European drink produced from juice of fresh grapes. In ripen grapes concentration of sugar increases.it has an alcoholic content of 10-22%.
It is produced from the fermentation of mixture of barley malt and starchy solutions by Saccharomyces cerevisiae. It has an alcoholic content of 4-8%.
Rum is the distilled product of culture fluid. Saccharomyces cerevisiae or other yeast is used as the fermenting microorganism. Culture medium is prepared from the black strap molasses. The alcoholic content varies from 51-59%.
It is prepared thyrough the fermentation of grain mash by a top yeast. When fermentation is over, the culture fluid contains alcohols, traces of acids and esters. The alcoholic content varies from 51-59%.
Sake, the rice wine, is manufactured from the starch. The culture fluid contains about 20% alcohol; therefore before marketing the concentration of alcohol is adjusted to 16%.
Uses of alcohol:
- Ethanol is used as a solvent, extractant, and antifreeze.
- N-butanol is used in the manufacture of plasticizers, brake fluids, urea-formaldehyde, extractants and petrol additives.
- Glycerol is used in medicals. Mannitol is used in industry and research.
- Butanol plus acetone is used in the production of explosive materials.