Distillieries - Environmental Clearance

Distilleries3.5 EthanolEthanol is produced both as a petrochemical, through the hydration of ethylene, andbiologically, by fermenting sugars with yeast. Determining the most economical amongthe products depends upon the prevailing prices of petroleum and of grain feedstock.This EIA manual focuses on the fermentation process of alcohols production. Summaryof both the processes is given below.Ethylene Hydration: Ethanol for use as industrial feedstock is most often made frompetrochemical feedstock, typically by the acid-catalyzed hydration of ethylene,represented by the chemical equationC 2 H 4 (g) + H 2 O (g) CH 3 CH 2 OH (l)The catalyst is most commonly phosphoric acid, adsorbed onto a porous support such asdiatomaceous earth or charcoal. This catalyst was first used for large-scale ethanolproduction by the Shell Oil Company in 1947. The reaction is carried out with an excessof high pressure steam at 300°C.In an older process, first practiced on the industrial scale in 1930 by Union Carbide, butnow almost entirely obsolete, ethylene was hydrated indirectly by reacting it withconcentrated sulphuric acid to produce ethyl sulfate, which was then hydrolyzed to yieldethanol and regenerate the sulfuric acid:C 2 H 4 + H 2 SO 4 CH 3 CH 2 SO 4 HCH 3 CH 2 SO 4 H + H 2 O CH 3 CH 2 OH + H 2 SO 4Ethanol by Fermentation: Ethanol for use in alcoholic beverages, and the vast majorityof ethanol for use as fuel, is produced by fermentation. When certain species of yeast(e.g., Saccharomyces cerevisiae) metabolize sugar in the absence of oxygen, theyproduce ethanol and CO 2 . The chemical equation below summarizes the conversion:C 6 H 12 O 6 2CH 3 CH 2 OH + 2CO 2Ethanol's toxicity to yeast limits the ethanol concentration obtainable by brewing. Themost ethanol-tolerant strains of yeast can survive up to approximately 15% ethanol byvolume.The fermentation process must exclude oxygen. If oxygen is present, yeast undergoesaerobic respiration which produces CO 2 and water rather than ethanol.In order to produce ethanol from starchy materials such as cereal grains, the starch mustfirst be converted into sugars. In brewing beer, this has traditionally been accomplishedby allowing the grain to germinate, or malt, which produces the enzyme, amylase. Whenthe malted grain is mashed, the amylase converts the remaining starches into sugars. Forfuel ethanol, the hydrolysis of starch into glucose can be accomplished more rapidly bytreatment with dilute sulphuric acid, fungally produced amylase, or some combination ofthe two.TGM for Distillery Industry 3-16 August 2010