Patent GB-796565-A (GB)
Title: Process for improving alcohol quality
Filed: 1956-08-17
Abstract: An improved distillation finishing process for crude alcohols formed by acid-catalysed hydration of a C2-C4 olefin is characterised by diluting the crude alcohol with water and distilling the diluted alcohol in a first distillation <PICT:0796565/IV (b)/1> zone to remove low and high boiling impurities, removing an intermediate fraction which is the alcohol-water azeotrope, extractively distilling the latter with more than 70 mol. per cent of water to remove remaining impurities, and purified azeotrope. After scrubbing the crude alcohol with aqueous caustic alkali, the alcohol, diluted to contain preferably above 25 per cent, and more preferably 50-75 per cent of water by volume, is passed into tower T-1 of Fig. 1, at about the mid-point.  Low boiling impurities are withdrawn through line 8, and a bottoms reject containing most of the water with most of the high boiling impurities is withdrawn through 14.  Part of the low boiling impurities may be recycled through condenser 9 and line 10.  An intermediate fraction of composition close to the azeotrope is withdrawn through 12 and passed into an intermediate point of the water extractive distillation tower T-2.  Enough water is supplied through 15 to maintain above 70 mol. per cent of water in the internal reflux, preferably about 90-95 mol. per cent; the pressure may be atmospheric or superatmospheric.  Water and impurities distil overhead through 16 to condenser 17, part of which may be recycled through 18.  Aqueous bottoms are withdrawn through 21 and pass into the rectifying column T-3, which may contain more plates or equivalent fractionating means than the preceding columns.  Low boiling impurities pass overhead through 22 to condenser 23, part of which may be refluxed via 24. Purified azeotrope is withdrawn from an upper plate through 26. Some high boiling oily impurities may be removed with water through 27, e.g. 4 or 5 plates below the feedplate.  Aqueous bottoms are withdrawn through 28, part may be recycled through 30 and 15 to T-2.  Fresh water may be added through 31.  In a preferred apparatus (Fig. 2, not shown), the removal of low-boiling impurities only is carried out in T-1, the bottoms passing to an additional tower from which aqueous bottoms are rejected, high-boiling impurities removed as a side stream and aqueous alcohol withdrawn overhead to be passed into T-2.  Further processing is as described above.  Alcohols mentioned are ethyl, isopropyl and sec.-butyl alcohols.ALSO:An improved distillation finishing process for crude alcohols formed by acid-catalysed hydration of a C2-C4 olefin is characterized by diluting the crude alcohol with water and distilling the diluted alcohol in a first distillation zone to remove low and high boiling impurities, removing an intermediate fraction which is the alcohol-water azeotrope, extractively distilling the latter with more than 70 mol. per cent of water to remove remaining impurities, and rectifying the purified azeotrope.  After scrubbing the crude alcohol with aqueous caustic <PICT:0796565/III/1> alkali, the alcohol, diluted to contain preferably above 25 per cent, and more preferably 50-75 per cent, of water by volume, is passed into tower T-1 of Fig. 1 at about the mid-point.  Low boiling impurities are withdrawn through line 8, and a bottoms reject containing most of the water with most of the high boiling impurities is withdrawn through 14.  Part of the low boiling impurities may be recycled through condenser 9 and line 10.  An intermediate fraction of composition close to the azeotrope is withdrawn through 12 and passed into an intermediate point of the water extractive distillation tower T-2.  Enough water is supplied through 15 to maintain above 70 mol. per cent of water in the internal reflux, preferably about 90-95 mol. per cent; the pressure may be atmospheric or superatmospheric.  Water and impurities distil overhead through 16 to condenser 17, part of which may be recycled through 18.  Aqueous bottoms are withdrawn through 21 and pass into the rectifying column T-3, which may contain more plates or equivalent fractionating means than the preceding columns.  Low boiling impurities pass overhead through 22 to condenser 23, part of which may be refluxed via 24. Purified azeotrope is withdrawn from an upper plate through 26. Some highboiling oily impurities may be removed with water through 27, e.g. 4 or 5 plates below the feed plate.  Aqueous bottoms are withdrawn through 28, part may be recycled through 30 and 15 to T-2.  Fresh water may be added through 31.  In a preferred apparatus (Fig. 2, not shown), the removal of low-boiling impurities only is carried out in T-1, the bottoms passing to an additional tower from which aqueous bottoms are rejected, high-boiling impurities removed as a side stream and aqueous alcohol withdrawn overhead to be passed into T-2.  Further processing is as described above.  Alcohols mentioned are ethyl, isopropyl and sec.-butyl alcohols.