GB660773A - Improvements in or relating to the separation and purification of methanol - Google Patents

Abstract

<PICT:0660773/IV (b)/1> Methanol is separated from a crude mixture containing neutral organic compounds normally boiling within the range of 10.8 DEG to 150 DEG C. by continuously introducing a feed mixture of the crude methanol into a fractional distillation zone, in which vapours of the neutral organic contaminants fractionally distilling from the mixture contact liquid reflux condensates of the vapours dissolved in at least 65 mole. per cent of water, continuously removing an aqueous vapour mixture of the neutral organic contaminants and continuously removing from the zone a residual portion of the liquid reflux which is a dilute aqueous solution of methanol. The crude mixture may contain methanol contaminated with aldehydes, ketones, other alcohols, carboxylic acids, ethers, esters, acetals, ketals and hydrocarbons in mixtures produced by various processes, as, for example, synthesis from carbon monoxide and hydrogen, oxidation of hydrocarbons, decomposition of alcohols, destructive distillation of wood &c. In the Figure, 1 is a fractional distillation column provided with means for obtaining efficient counter-current liquid-vapour phase contacting, e.g. by bubble plates or packing. The crude methanol feed is charged to column 1 at the bottom of the rectification zone 3. The water to be added continuously enters the column 1 at the upper part of the rectification zone 3. A portion of the condensate collected in receiver 7 is returned to the top part of column 1 as external reflux. A secondary rectifying zone 10 may be provided in the upper part of column 1. The internal liquid reflux flows downward from the feed-plate in column 1 through the stripping zone provided with means for obtaining liquid-vapour phase contacting. In this zone a sufficient number of contact stages is provided to strip the liquid reflux of neutral organic compounds which are rendered more volatile than the remaining methanol. The residual liquid reflux is withdrawn from the bottom part of the column and is passed through a reboiler 13. The heated and partially vaporized portion of the bottoms is recycled from the reboiler to the lower part of column 1. The remaining portion of the bottoms liquid is passed into the concentrating column 16 which is equipped with liquid-vapour phase contacting means and overhead line 17, for passing overhead purified methanol vapours. Some of the methanol distillate is passed as external reflux to the upper part of column 16 and a remaining portion of the purified methanol distillate is withdrawn to storage. Vapours from the dilute methanol feed to column 16 are rectified in the upper part of the column and the down-flowing internal reflux in column 16 is stripped of methanol. If the crude methanol feed contains carboxylic acid the acid will remain in the residual aqueous bottoms of the concentrator 16. In the example methanol is separated from a crude Fischer Synthesis water-layer product containing methanol, ethanol, isopropanol, methyl ethyl ketone, acetal, aldehyde and water. Specification 647,903 is referred to.ALSO:Methanol is separated from a crude mix<PICT:0660773/III/1> ture containing neutral organic compounds normally boiling with in the range of 108 DEG C. to 150 DEG C. by continuously introducing a feed mixture of the crude methanol into a fractional distillation zone, in which vapours of the neutral organic contaminants fractionally distilling from the mixture contact liquid reflux condensates of the vapours dissolved in at least 65 mol per cent of water, continuously removing an aqueous vapour mixture of the neutral organic contaminants and continuously removing from the zone a residual portion of the liquid reflux which is a dilute aqueous solution of methanol. The crude mixture may contain methanol contaminated with aldehydes, ketones, other alcohols, carboxylic acids, ethers, esters, acetals, ketals and hydrocarbons in mixtures produced by various processes, as, for example, synthesis from carbon monoxide and hydrogen, oxidation of hydrocarbons, decomposition of alcohols, destructive distillation of wood &c. In the Figure 1, is a fractional distillation column provided with means for obtaining efficient counter-current liquid-vapour phase contacting, e.g. by bubble plates or packing. The crude methanol feed is charged to column 1 at the bottom of the rectification zone 3. The water which is added continuously enters the column 1 at the upper part of the rectification zone 3. A portion of the condensate collected in receiver 7 is returned to the top part of column 1 as external reflux. A secondary rectifying zone 10 may be provided in the upper part of column 1. The internal liquid reflux flows downward from the feed plate in column 1 through the stripping zone provided with means for obtaining liquid-vapour phase contacting. In this zone a sufficient number of contact stages is provided to strip the liquid reflux of neutral organic compounds which are rendered more volatile than the remaining methanol. The residual liquid reflux is withdrawn from the bottom part of the column and is passed through a reboiler 13. The heated and partially vaporized portion of the bottoms is recycled from the reboiler to the lower part of column 1. The remaining portion of the bottoms liquid is passed into the concentrating column 16 which is equipped with liquid-vapour phase contacting means and overhead line 17 for passing overhead purified methanol vapours. Some of the methanol distillate is passed as external reflux to the upper part of column 16 and a remaining portion of the purified methanol distillate is withdrawn to storage. Vapours from the dilute methanol feed to column 16 are rectified in the upper part of the column and the downflowing internal reflux in column 16 is stripped of methanol. If the crude methanol feed contains carboxylic acid, the acid will remain in the residual aqueous bottoms of the concentator 16. In the example, methanol is separated from a crude Fischer synthesis water-layer product containing ethanol, isopropanol, methyl ethyl ketone, acetal, aldehyde and water. Specification 647,903 is referred to.