Process for removing water from aqueous methanol

Abstract

A process for separating water from methanol in an aqueous methanol initial mixture, comprising subjecting said mixture to azeotropic distillation in the presence of sufficient added methyl acrylate to form an azeotrope with most of the methanol in said initial mixture such that a substantial proportion of methanol in the initial mixture is removed as an azeotrope of methanol and methyl acrylate in the overhead vapors resulting from said distillation and a major proportion of water in said initial mixture is removed in the liquid residue of said distillation.

We claim:  
     
         1 . A process for separating water from methanol in an aqueous methanol initial mixture, comprising subjecting said mixture to azeotropic distillation in the presence of sufficient added methyl acrylate to form an azeotrope with most of the methanol in said initial mixture such that a substantial proportion of methanol in the initial mixture is removed as an azeotrope of methanol and methyl acrylate in the overhead vapors resulting from said distillation and a major proportion of water in said initial mixture is removed in the liquid residue of said distillation.  
     
     
         2 . The process of  claim 1  wherein said initial mixture contains about 1 to about 99 wt. % of methanol, and about 99 to about 1 wt. % of water.  
     
     
         3 . The process of  claim 2  wherein the methanol is present in the initial mixture in the range of about 5 to about 10 wt. % and water is present in the range of about 85 to 95 wt. %.  
     
     
         4 . The process of  claim 1  wherein the amount of methyl acrylate added to the system ranges from about 95% of the amount necessary to form an azeotrope with all the methanol present to about a 20% excess over the latter amount.  
     
     
         5 . The process of  claim 4  wherein said amount of methyl acrylate ranges from about the approximate amount necessary to form an azeotrope with substantially all the methanol present, to about a 5% excess over the latter amount.  
     
     
         6 . The process of  claim 1  wherein said azeotropic distillation is carried out in a fractional distillation tower at an intermediate point of which is fed the sole or main stream of initial aqueous methanol feed mixture, the bottom of said tower where said residue is withdrawn being at a temperature of about 95 to about 100° C., the intermediate point of said tower where said sole or main stream of the initial aqueous methanol mixture enters the tower being at a temperature of about 90 to about 95° C. and the top of the tower where the overhead vapors are removed being at a temperature of about 60 to about 65° C.  
     
     
         7 . The process of  claim 1  wherein said overhead vapors are condensed with most of the condensate being recycled to the distillation as reflux at a reflux ratio of about 3 to about 10 and the remainder of the condensate being withdrawn as a product of the azeotropic distillation with reduced water content.  
     
     
         8 . The process of  claim 7  wherein said water content of the condensate is no greater than about 10 wt. %.  
     
     
         9 . The process of  claim 8  wherein said water content is no greater than about 3 wt. %.  
     
     
         10 . The process of  claim 1  wherein the amount of methanol in said residue is no greater than about 1 000 ppm.  
     
     
         11 . The process of  claim 10  wherein said amount of methanol is no greater than about 150 ppm.  
     
     
         12 . The process of  claim 7  wherein the portion of the condensate withdrawn as a product of said azeotropic distillation is fed to the reaction stage of a process for producing methyl acrylate by esterification of acrylic acid with excess methanol, and methanol in the reaction product is separated from methyl acrylate by extraction with water.  
     
     
         13 . The process of  claim 12  wherein at least a portion of said aqueous methanol initial mixture fed to said azeotropic distillation is an aqueous residue obtained from said extraction.  
     
     
         14 . The process of  claim 7  wherein a polymerization inhibitor is added to said condensate.  
     
     
         15 . The process of  claim 14  wherein said inhibitor is phenothiazine.  
     
     
         16 . The process of  claim 6  wherein energy is supplied to said azeotropic distillation by directly injecting live steam into said tower.