GB431398A - Improvements in the manufacture and production of unsaturated esters - Google Patents

Abstract

Esters of aliphatic unsaturated acids having a low boiling point are separated from the materials used in their preparation by distilling the respective mixtures, washing the vapours evolved with water, condensing the vaporous binary azeotropic mixture of ester and water so formed, and separating the ester therefrom. Suitable esters comprise methyl, ethyl, propyl, butyl, allyl, ethylene glycol and monoethyl glycol esters of acrylic acid; methyl, ethyl, allyl and butyl esters of angelic, tiglic and methylacrylic acids; and methyl and ethyl esters of crotonic acid. In an example, a vaporous mixture of acrylic acid methyl ester, excess methanol, acrylic acid and water flows from the top of an esterification column II, <PICT:0431398/IV/1> kept at a temperature of 125--150 DEG C., to the lower part of a washing column IV where it encounters a downward flow of hot water admitted through a pipe 7. The still is kept at a temperature of 96 DEG C., and the binary azeotropic mixture of boiling point 71 DEG C. leaves the column through a pipe 8, passes through a dephlegmator V kept at 60 DEG C., is condensed and flows through a cooler VI to a separating vessel VII. The upper layer of ester is removed and the lower layer returned continuously to the washing column. Impure methanol from the latter is re-distilled in a column XI for re-use in the process. The ester may be prepared continuously in the column II by reacting ethylene cyanhydrin with methanol in the presence of sulphuric acid. The columns may be constructed of iron, aluminium, copper or materials lined with zinc, tin, lead or copper.ALSO:<PICT:0431398/III/1> Esters of aliphatic unsaturated acids having a low boiling point are separated from the materials used in their preparation by distilling the respective mixtures, washing the vapours evolved with water, condensing the vaporous binary azeotropic mixture of ester and water so formed, and separating the ester therefrom. Suitable esters comprise methyl, ethyl, propyl, butyl, allyl, ethylene glycol and monoethyl glycol esters of acrylic acid; methyl, ethyl, allyl and butyl esters of angelic, tiglic, and methyl acrylic acids; and methyl and ethyl esters of crotonic acid. In an example, a vaporous mixture of acrylic acid methyl ester, excess methanol, acrylic acid and water flows from the top of an esterification column II, kept at a temperature of 125 DEG --150 DEG C., to the lower part of a washing column IV where it encounters a downward flow of hot water admitted through a pipe 7. The still is kept at a temperature of 96 DEG C., and the binary azeotropic mixture of boiling point 71 DEG C., leaves the column through a pipe 8, passes through a dephlegmator V kept at 60 DEG C., is condensed and flows through a cooler VI to a separating vessel VII. The upper layer of ester is removed and the lower layer returned continuously to the washing column. Impure methanol from the latter is re-distilled in a column XI for re-use in the process. The ester may be prepared continuously in the column II by reacting ethylene cyanhydrin with methanol in the presence of sulphuric acid. The columns may be constructed of iron, aluminium, copper or materials lined with zinc, tin, lead or copper.