GB920353A - Process for stabilizing acrylic acid alkyl esters - Google Patents

Abstract

In the preparation of esters of acrylic acid by the hydrolysis of acrylonitrile with sulphuric acid to give acrylamide sulphate which is then esterified with the appropriate alcohol, the products are stabilized during the esterification, and the purification by distillation, by blowing in air and/or oxygen. In an example acrylic acid methyl ester and methanol are extractively distilled in countercurrent with water in a column with the addition of air or oxygen at from 1 to 2 litres per hour. The resulting azeotrope of ester and water is condensed, separated, and the ester further distilled preferably under reduced pressure, with the passage of 1,5 litres of air or 0,3 to 0,5 litres of oxygen per hour. The passage of the air or oxygen prevents polymerization during the distillation stages.ALSO:<PICT:0920353/IV(a)/1> Methyl, ethyl, propyl and butyl esters of acrylic acid prepared by hydrolysing acrylonitrile with sulphuric acid to give acrylamide sulphate which is then esterified with the appropriate alcohol, are stabilized during the esterification and purification by blowing in air and/or oxygen. A proportion of from 0.1 to 10.0% by volume of air and/or oxygen calculated on the amount of vapour flowing, is preferred and other inhibitors such as methylene blue, phenothiazine or hydroquinone are used. In an example acrylamide sulphate prepared in a saponifying vessel 2, is esterified in a column 10, with the addition of air, 90, the resulting acrylic acid methyl ester and methanol are extractively distilled 20, with the addition of air or oxygen 91, and the ester and water separated, condensed 26, and separated 27, and the ester distilled 30, while air or oxygen passed in 92, separated from water 34 and condensed 86, to the final product. The introduction of the air or oxygen prevents polymerization during the various stages.