Ethanol

Production

Ethanol (Isophopol) for use in alcoholic beverages is produced by fermentation: it is a product of sugar metabolism in certain species of yeast in the absence of oxygen. The process of culturing yeast under conditions to produce alcohol is referred to as brewing. Yeasts can grow in the presence of up to about 20% alcohol, but the concentration of alcohol in the final product can be increased by distillation.

Related Topics:
Fermentation - Sugar - Metabolism - Yeast - Oxygen - Brewing - Distillation

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For a mixture of ethanol and water, there is a maximum boiling azeotrope at 96% ethanol and 4% water. For this reason, fractional distillation of ethanol-water mixtures (of less than 96% ethanol) cannot yield ethanol purer than 96%. Therefore, 95% ethanol in water is a fairly common solvent.

Related Topics:
Azeotrope - Fractional distillation

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To produce absolute ethanol, a small amount of benzene is added, and the mixture is again fractionally distilled. Benzene forms a tertiary azeotrope with water and ethanol to remove the last of the water, and a binary azeotrope with ethanol removes most of the benzene. The resulting ethanol is water free, for processes that require it. However, several parts per million of benzene remains, so consumption by humans leads to distinctive liver damage.

Related Topics:
Benzene - Parts per million - Liver

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Ethanol for industrial use is often made from petroleum feedstocks, typically by the catalytic hydration of ethylene with sulfuric acid as catalyst. This process is cheaper than the production by fermentation.

Related Topics:
Petroleum - Ethylene - Sulfuric acid - Catalyst

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Ethanol for industrial use is normally made unfit for human consumption ("denatured") by the inclusion of small amounts of substances that are either toxic (such as methanol) or unpleasant (such as denatonium), thus avoiding the applicable taxes or inventory controls. Denatured ethanol has the UN number UN 1987 and toxic denatured ethanol has UN 1986.

Related Topics:
Toxic - Methanol - Denatonium - Tax - UN number

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