GB791220A - Purifying synthetic ethanol by distillation - Google Patents

Abstract

<PICT:0791220/III/1> In the purification, by distillation, of aqueous ethanol produced by the catalytic hydration of ethylene, the crude aqueous ethanol is subjected to pre-rectification to eliminate some of the heavy polymer oils, and is then subjected to water-extractive distillation, followed by concentration by straight rectification. If desired, the pre-rectification step may be omitted, in which case the concentrated alcohol is finally subjected to stripping in order to remove the last traces of volatile impurities. Crude aqueous ethanol is preheated to about 200 DEG F. in preheater 1, and fed into column 3, which contains 40-60 trays and is heated by live steam introduced through line 11. Vapours from column 3 consisting of ethanol, ether and volatile oils are withdrawn overhead, and passed to condenser 5. Part of the condensate is returned to column 3 as reflux, and the remainder is introduced through line 8 into column 13. Heavy polymer oils are withdrawn from the side of column 3 via pipes 9, and water is withdrawn from the base of the column. Column 13, which contains about 40 trays, is heated by steam supplied through line 14, and is operated at a pressure of 5 to 30 p.s.i.g. The temperature at the top of column 13 is maintained at about 127 DEG F., and that at the base at 210 DEG F. Vapours containing ether, low-boiling polymer oils and water leave the head of column 13, and are condensed. A major portion of the condensate is refluxed to column 13, and the remainder is withdrawn from the system via line 18. Polymer oils are withdrawn from the side of column 13 via line 20. Aqueous ethanol is withdrawn from the base of column 13 and is pumped through line 23 into column 24, which contains about 45 plates and is heated by steam-line 32. Water is introduced into the top of column 24 through line 33 so as to reduce the concentration of ethanol in the internal reflux to about 15 to 30 weight per cent. The vapours from the head of column 24, which contain light oil impurities, are condensed; and the condensate is passed to decanter 28. Oil is withdrawn from the decanter through line 29; while the aqueous layer is returned to column 24 via line 31, although a portion may be withdrawn from the system through line 30. Dilute aqueous ethanol is withdrawn from the base of column 24, and is pumped to column 37, which contains 60 to 70 plates. Pure concentrated ethanol may be taken off from the head of column 37, in which case a portion is returned to the column as reflux while the remainder is removed as product via line 42. Alternatively the pure concentrated ethanol may be withdrawn from the side of column 37 via line 47. Any heavy oils which reach column 37 are withdrawn via pipe 44; and water is withdrawn from the base of the column. Specification 788,475 is referred to.