GB823339A - Improvements in or relating to the distillation of ethanol - Google Patents

Abstract

<PICT:0823339/III/1> Ethanol is separated from aqueous solutions thereof by stripping the solution in a beer still or stripping column, condensing part of the vapours obtained in a steam generator to produce steam which is compressed and used as heating medium in the stripper, introducing part of the vapours from the stripper into a rectifying column into which ethanol with a water content below that of the azeotropic mixture is introduced as reflux, condensing the overhead vapours and withdrawing the condensate as product. The vapours are preferably dehydrated and condensed and part of this condensate is used as the reflux to the rectifying column. Aqueous ethanol, e.g. mash containing 7 or 8% by weight of ethanol is introduced by line 7, heated and introduced to a preliminary stripper 2 containing 15-20 plates where volatile impurities such as acetaldehyde and esters are removed. Purified mash passes by line 14 to stripping column 1 containing 10-20 plates fed with live steam from ejector 23. The vapours partly pass by line 18 to be used as heating medium for the stripper 2 and partly to steam generator 16. Steam produced in the generator by condensation of the vapours passes by line 22 is compressed in the ejector 23 and passed to the stripper. Water from the base of the stripper is pumped by line 19 to the steam generator from which excess is withdrawn by line 21. Vapours from the stripper are further condensed in condenser 17 to provide reflux for the stripper. The amount of condensation in the condenser 17 may be regulated according to the temperature in the following column 3, more vapours being passed to the column if the temperature falls. Remaining vapours pass to rectifying column 3 having 10-20 plates and fed with a reflux containing less water than the azeotropic mixture by line 38. Bottoms are passed by line 29 for use as reflux to the stripper. Overhead vapours pass by line 28 to the dehydrating column 4 fed with a water-absorbing substance such as glycerol, acetates or, more preferably, ethylene glycol by line 30. This column may contain 15-20 plates in the lower part and 5-10 in the upper part. Vapours pass to heat exchanger 8 and condenser 34 to give liquid which is withdrawn as product by line 39 and returned as reflux to columns 3 and 4 by lines 38 and 37. The product may be anhydrous. Bottoms from column 4 containing glycol, ethanol and water pass to column 5 where ethanol is stripped by added live steam and returned to column 4. Bottoms from column 5 are fractionated under reduced pressure in column 6 to give glycol as bottoms which are pumped back to column 4 and water overhead. Fused oil may be withdrawn by line 13 and also if desired from one or more plates of column 3. The pH on the lower plates of column 3 and of the reflux to stripper 1 is preferably maintained at at least 4 by adding an alkaline solution to a higher plate of column 3 and allowing this to flow countercurrent to the vapours.