GB803047A - A process for rectifying ethanol by distillation under elevated pressure - Google Patents

Abstract

<PICT:0803047/III/1> Ethanol is separated from the crude liquors obtained by the fermentation of vegetable carbohydrate material by distilling the crude liquor to obtain a distillate with an ethanol content of 5-50 per cent by weight, then stripping the distillate, preferably after dilution with water, to remove acetaldehyde, esters, amines and higher alcohols, and finally rectifying the purified ethanol-water mixture under superatmospheric pressure, the pH at the bottom of the rectifying column being maintained above 6.5 by addition of alkali to the column. The pH at the bottom of the stripping column should be below 7; but usually it is not necessary to take special steps to achieve this owing to the presence of acid in the original fermentation liquor. Fermented liquor containing approximately 6 per cent by weight ethanol is introduced, after preheating to 70 DEG C. in condenser 2, into the head of column 1, at the rate of about 9000 litres/hour. Impure ethanol-water vapours are led from the top of column 1 to condenser 2, and a condensate containing 30 per cent by weight ethanol is obtained. This condensate is conducted to the head of column 3; and aqueous ethanol from column 5 is also introduced into the head of column 3. Volatile as well as less volatile impurities are stripped out of the aqueous ethanol in column 3; the vaporized impurities also contain a small quantity of ethanol. The vapours are condensed in condenser 4 and the condensate is introduced into column 5. Approximately 500-1000 litres of water per hour are fed into the head of column 5, and this water washes out the ethanol from the impurities. The latter are condensed in condenser 6. Purified ethanol-water mixture, containing approximately 13 per cent by weight ethanol, leaves the base of column 3 and is introduced into rectifying column 7, which is equipped with 60 plates and is operated at a gauge-pressure of at least 4 atmospheres. A 5-10 per cent aqueous sodium hydroxide solution is introduced into column 7 through pipe 11 in quantities sufficient to keep the pH in the bottoms above 6.5. Concentrated ethanol vapours leave the top of column 7 and are condensed in the heat-exchanger 8 of a steam-generator 9. The resulting steam can be used as heating medium in the other columns. The bottoms from column 7 may be partly used as feed-water in steam-generator 9; the other part may be fed into the top of column 5 as diluent.