GB670229A - Improvements in or relating to purification of ethanol by distillation - Google Patents

Abstract

<PICT:0670229/III/1> Crude ethanol containing n-propanol and other organic contaminants normally boiling between 20 DEG and 150 DEG C., is purified by feeding it into the side of a fractionating column and introducing water into the column above the feed-point of the crude alcohol, to produce an internal liquid reflux containing 95 to 99 mol per cent of water. The other operating conditions in the column are maintained so that the n-propanol and all the other contaminants, except methanol and organic acids (if present in the crude) pass overhead, while a dilute aqueous solution of purified ethanol is withdrawn as bottoms. The dilute aqueous solution of ethanol is concentrated, and if necessary freed from methanol and organic acids, by simple rectification. Crude ethanol (boiling-range 69-82 DEG C.) containing n-propanol (25 per cent), methanol (0.6 per cent) and other neutral contaminants is fed through line 2 into column 1 which contains sixty plates; and water is introduced into the column through line 4 so as to produce the internal reflux referred to above. The overhead vapours, which contain the n-propanol and the other contaminants (except methanol) are condensed. The reflux ratio is 20 : 1 so that 20 parts of the condensate is returned through line 8 to the column, and the remaining part is discharged through line 9. The aqueous bottoms withdrawn from the base of column 1 contain the methanol. These bottoms are passed to reboiler 13; and that portion not vaporized and returned to column 1 through line 14, is passed through line 15 to column 16. A side-stream is withdrawn through line 24 from column 16, and is passed to reboiler 25. Methanol is stripped from the side-stream in reboiler 25, and is returned to column 16 through line 26. Pure ethanol (96 per cent) is withdrawn from the base of reboiler 25; and is partly withdrawn from the system as product through line 29, and partly returned to column 16 through line 28. Part of the overhead condensate from column 16 is returned as reflux through line 22, and part is withdrawn from the system through line 23. Water is withdrawn from the base of column 16, and part thereof is recycled to column 1 via lines 35 and 4. The water supplied to the upper part of column 1 may contain various salts or acids which do not interfere with recovery of pure ethanol by azeotropic distillation. Specification 647,903 is referred to.