Patent GB-802767-A (GB)
Title: Alcohol purification process
Filed: 1956-09-28
Abstract: A process for the purification of an aqueous aliphatic alcohol produced by hydration of mono-olefins, containing residual oils that thermally degrade to malodorous substances including such substances that are lower boiling than said residual oils but higher boiling than the product alcohol, comprises feeding said aqueous alcohol containing said residual oils into a rectification zone maintained at conditions to concentrate the aqueous alcohol to a product alcohol of substantially higher alcohol concentration (180-192 proof), withdrawing from the rectification zone a first stream containing residual oils accumulating in the vicinity of the feed zone, withdrawing from the rectification zone at a point whereat the aqueous alcohol undergoing concentration is at a substantially higher alcohol concentration (170-190 proof) than the aqueous alcohol fed to the rectification zone, a second stream containing malodorous residual oil degradation substances lower boiling than the residual oils fed to the rectification zone but higher boiling than the product alcohol, and withdrawing from the rectification zone, at a point whereat the alcohol concentration is higher than at the point of withdrawal of said second stream, a product alcohol substantially devoid of said malodorous degradation products higher boiling that the product alcohol but lower boiling than the residual oils fed to the rectification zone.  Preferably the rectification is carried out with the use of more fractionation, in a portion of the rectification zone, in between the point of withdrawal of product alcohol and said second stream withdrawal, than is normally required for rectifying the aqueous alcohol feed to the desired alcohol content of the product alcohol.  Preferably also, the product alcohol is further treated to remove residual oil degradation products more volatile than the product alcohol.  The preferred alcohol is ethanol, e.g. prepared by the sulphuric acid hydration of ethylene.  When using aqueous ethanol as the feed, it preferably contains about 3 to about 20 per cent ethanol, the product alcohol being at least 190 proof. The additional fractionation is then preferably carried out in a portion of the rectification zone whereat the aqueous ethanol is at a proof of more than about 180, the second side stream being preferably withdrawn in an amount of about 1 to about 10 per cent based on the ethanol fed to the rectification zone, preferably at a portion thereof whereat the ethanol proof is from about 175 to about 188, more preferably about 185.  The process of the invention is described in detail with reference to ethanol and two diagrams (not shown).  In the first description the crude ethanol is preheated and rectified to remove low-boiling impurities such as ether, and the aqueous ethanolic bottoms passed to an extractive distillation column fed with water or an aqueous stream from the main rectification column. The aqueous ethanolic bottoms are then passed to the main rectification column, operated as described above, and the pure product alcohol withdrawn as a side stream.  In the description referring to the second diagram, the product alcohol from the main rectification column is withdrawn overhead and passed to a rectifying column to remove residual degradation impurities lower boiling than the product alcohol.ALSO:A process for the purification of an aqueous aliphatic alcohol produced by hydration of mono-olefins, containing residual oils that thermally degrade to malodorous substances including such substances that are lower boiling than said residual oils but higher boiling than the product alcohol, comprises feeding said aqueous alcohol containing said residual oils into a rectification zone maintained at conditions to concentrate the aqueous alcohol to a product alcohol of substantially higher alcohol concentration (180-192 proof), withdrawing from the rectification zone a first stream containing residual oils accumulating in the vicinity of the feed zone, withdrawing from the rectification zone at a point whereat the aqueous alcohol undergoing concentration is at a substantially higher alcohol concentration (170-190 proof) than the aqueous alcohol fed to the rectification zone, a second stream containing malodorous residual oil degradation substances lower boiling than the residual oils fed to the rectification zone but higher boiling than the product alcohol, and withdrawing from the rectification zone, at a point whereat the alcohol concentration is higher than at the point of withdrawal of said second stream, a product alcohol substantially devoid of said malodorous degradation products higher boiling than the product alcohol but lower boiling than the residual oils fed to the rectification zone.  Preferably the rectification is carried out with the use of more fractionation, in a portion of the rectification zone in between the point of withdrawal of product alcohol and said second stream withdrawal, than is normally required for rectifying the aqueous alcohol feed to the desired alcohol content of the product alcohol.  Preferably also, the product alcohol is further treated to remove residual oil degradation products more volatile than the product alcohol.  The preferred alcohol is ethanol, e.g. prepared by the sulphuric acid hydration of ethylene.  When using aqueous ethanol as the feed, it preferably contains about 3 to about 20 per cent ethanol, the product alcohol being at least 190 proof.  The additional fractionation is then preferably carried out in a portion of the rectification zone whereat the aqueous ethanol is at a proof of more than about 180, the second side stream being preferably withdrawn in an amount of about 1 to about 10 per cent based on the ethanol fed to the rectification zone, preferably at a portion thereof whereat the ethanol proof is from about 175 to about 188, more preferably about 185.  The process of the invention is described in detail with reference to ethanol and two diagrams (not shown).  In the first description the crude ethanol is preheated and rectified to remove low-boiling impurities such as ether, and the aqueous ethanolic bottoms passed to an extractive distillation column fed with water or an aqueous stream from the main rectification column.  The aqueous ethanolic bottoms are then passed to the main rectification column, operated as described above, and the pure product alcohol withdrawn as a side stream.  In the description referring to the second diagram, the product alcohol from the main rectification column is withdrawn overhead and passed to a rectifying column to remove residual degradation impurities lower boiling than the product alcohol.