Patent GB-770551-A (GB)
Title: Continuous esterification process
IPC: B01D3/06
Filed: 1954-08-26
Abstract: A process for the continuous production of an ester by the esterification of a carboxylic acid reactant with an alcohol reactant wherein the distillation temperature of at least one reactant is lower than the distillation temperaature of the water of reaction comprises continuously feeding the reactants to an esterification zone in which an esterification catalyst is present, continuously flashing off therefrom a vaporized mixture of the more volatile reactant, the ester and the water of reaction, by maintaining the esterification zone at a sufficiently high temperature, and separating said more volatile reactant from the ester and water of the vaporized mixture as an azeotrope with an auxiliary liquid, said azeotrope having a boiling point below that of the ester.  The process is particularly applicable to the continuous production of methyl acrylate from methyl alcohol and acrylic acid, the vaporized mixture flashed off from the esterification zone being a mixture of methyl acrylate, water and unreacted methyl alcohol from which the methyl alcohol is separated as an azeotrope with the auxiliary liquid.  In the latter process a polymerization inhibitor such as methylene blue or hydroquinone must also be present in the esterification zone and it is preferred to use an excess of methyl alcohol, e.g. from more than one up to 3 mol. of methyl alcohol for each mol. of acrylic acid.  The esterification temperature in this case is suitably from about 75 DEG  to 90 DEG  C. and the methyl alcohol may be separated from the vapours of methyl acrylate, water and unreacted methyl alcohol as an azeotrope with pentane.  This may be done by leading the vapours flashed off from the esterification zone into a distillation column at an intermediate point on the column while pentane is fed to the top portion of the column at a point above the point of introduction of the said vapours.  The low boiling methyl alcohol-pentane azeotrope distils from the top of the column and is then condensed forming two phases-a pentane phase which is returned to the top portion of the column and a methyl alcohol phase which is recycled to the reactor.  From the bottom of the column a liquid consisting of an azeotropic mixture of methyl acrylate and water is withdrawn and separates into two phases-a water phase and a methyl acrylate phase relatively free of water.  The latter phase may be purified by leading it continuously into a second distillation column at an intermediate point on the column and drawing off the purified methyl acrylate as a vapour at a lower intermediate point on the column.  The distillate from the upper part of the second column comprising methyl acrylate, water, and some methyl alcohol may be passed through a phase separator to remove part of the water and may then be combined with the feed to the first distillation column.  The residue from the bottom of the second column comprises methyl acrylate, acrylate polymers and the inhibitor and may be further distilled to recover the methyl acrylate therein. A diagrammatic flow sheet of an apparatus suitable for the production of methyl acrylate is given.  In an example for the production of methyl acrylate from methanol and acrylic acid the esterification reactor is initially charged with acrylic acid, methyl alcohol, sulphuric acid and methylene blue and the molar ratio of the alcohol to acid fed to the reactor is 2.5 : 1.  The reactor is maintained at 85 DEG  to 86 DEG  C. and the vapours leave the reactor at 70 DEG  C. and are fed to a distillation column where the methyl alcohol is stripped off in the form of its pentane azeotrope which boils at 30.5 DEG  C., whilst an azeotrope boiling at 71 DEG  C. and comprising methyl acrylate and water is withdrawn continuously in liquid form from the base of the column.ALSO:A process for the continuous production of an ester by the esterification of a carboxylic acid reactant with an alcohol reactant wherein the distillation temperature of at least one reactant is lower than the distillation temperature of the water of reaction comprises continuously feeding the reactants to an esterification zone in which an esterification catalyst is present, continuously flashing off therefrom a vaporized mixture of the more volatile reactant, the ester and the water of reaction, by maintaining the esterification zone at a sufficiently high temperature, and separating said more volatile reactant from the ester and water of the vaporized mixture as an azeotrope with an auxiliary liquid, said azeotrope having a boiling point below that of the ester.  The process is particularly applicable to the continuous production of methyl acrylate from methyl alcohol and acrylic acid, the vaporized mixture flashed off from the esterification zone being a mixture of methyl acrylate, water and unreacted methyl alcohol from which the methyl alcohol is separated as an azeotrope with the auxiliary liquid.  In the latter process for the production of methyl acrylate, a polymerization inhibitor such as methylene blue or hydroquinone must also be present in the esterification zone and it is preferred to use an excess of methyl alcohol, e.g. from more than one up to 3 moles of methyl alcohol for each mole of acrylic acid. The esterification temperature in this case is suitably from about 75 to 90 DEG C. and the methyl alcohol may be separated from the vapours of methyl acrylate, water and unreacted methyl alcohol as an azeotrope with pentane.  This may be done by leading the vapours flashed off from the esterification zone into a distillation column at an intermediate point on the column while pentane is fed to the top portion of the column at a point above the point of introduction of the said vapours.  The low boiling methyl alcohol-pentane azeotrope distils from the top of the column and is then condensed forming two phases-a pentane phase which is returned to the top portion of the column and a methyl alcohol phase which is recycled to the reactor.  From the bottom of the column a liquid consisting of an azeotropic mixture of methyl acrylate and water is withdrawn and separates into two phases-a water phase and a methyl acrylate phase relatively free of water.  The latter phase may be purified by leading it continuously into a second distillation column at an intermediate point on the column and drawing off the purified methyl acrylate as a vapour at a lower intermediate point on the column. The distillate from the upper part of the second column comprising methyl acrylate, water, and some methyl alcohol may be passed through a phase separator to remove part of the water and may then be combined with the feed to the first distillation column.  The residue from the bottom of the second column comprises methyl acrylate, acrylate polymers and the inhibitor and may be further distilled to recover the methyl acrylate therein.  A diagrammatic flow sheet of an apparatus suitable for the production of methyl acrylate is given. In an example for the production of methyl acrylate from methanol and acrylic acid the esterification reactor is initially charged with acrylic acid, methyl alcohol, sulphuric acid and methylene blue and the molar ratio of the alcohol to acid fed to the reactor is 2.5:1. The reactor is maintained at 85 to 86 DEG C. and the vapours leave the reactor at 70 DEG C. and are fed to a distillation column where the methyl alcohol is stripped off from the vapours in the form of its pentane azeotrope which boils at 30.50 DEG C., whilst an azeotrope boiling at 71 DEG C. and comprising methyl acrylate and water is withdrawn continuously in liquid form from the base of the column.