Patent ID: 9637574
Date: 2017-05-02
CPC Classifications: C07C,C08F,C09D,D21H

Claim:
1. A process for preparing an alkyl methacrylate, comprising the following steps a)-j) in order: a) subjecting a reaction mixture comprising methacrylamide, water, concentrated sulphuric acid and at least one alkanol to an esterification reaction in a series of two or more reaction chambers comprising at least a first reaction chamber and a second reaction chamber to obtain a crude reaction product, wherein the water, the methacrylamide and the concentrated sulphuric acid are charged to the first reaction chamber and the alkanol is charged to each of the reaction chambers in the series such that the amount of the alkanol charged decreases by at least 10% from the reaction chamber to the next reaction chamber based in each case on the amount charged in the preceding reaction chamber; b) heating the reaction chambers in the series with steam such that vapor phase of an esterification reaction product mixture comprising water, alkyl methacrylate, alkanol and compounds having a higher boiling point than the alkyl methacrylate and alkanol, is formed; c) transferring the vaporous esterification reaction product mixture from the first reaction chamber to the second reaction chamber and any further reaction chambers, and transferring the vapor phase from the at least the second reaction chamber to a rectification column using steam as a carrier; d) separating the high boiling compounds of the vapor phase from the water, the alkyl methacrylate and the alkanol in the rectification column, recycling the high boiling compounds to the first reaction chamber and drawing off a vapor mixture of the water, the alkyl methacrylate and the alkanol from the top of the rectification column; e) condensing and cooling the vapor mixture of the water, the alkyl methacrylate and the alkanol in one or more heat exchangers to provide a condensate having an aqueous phase comprising water and alkanol and an organic product phase comprising the alkyl methacrylate; f) separating the aqueous phase of the condensate from the product organic phase and recycling the separated aqueous phase to the first reaction chamber; g) washing the separated product organic phase with water to obtain a washed product organic phase comprising a crude alkyl methacrylate and an aqueous phase comprising the washing water and alkanol washed from the product organic phase; h) recycling the aqueous phase comprising the washing water and alkanol from the step g) back into the first reaction chamber; i) freeing the crude alkyl methacrylate of low-boiling impurities which have a lower boiling point than the alkyl methacrylate by distillation in a distillation column; and j) freeing the alkyl methacrylate obtained in i) of higher-boiling impurities which have a higher boiling point than the alkyl methacrylate prepared; wherein the low-boiling impurities from step i) are condensed in one or more heat exchangers, to obtain a condensate of the low boiling impurities; the condensate of the low boiling impurities is treated with water, followed by a phase separation, the aqueous phase of the condensate of the low boiling impurities is recycled into at least one reaction chamber in the series, and the organic phase removed by phase separation is used to spray the top of the distillation column in the step i); wherein the water present in the reaction mixture stems to an extent of at least 60% by weight from the following sources: optionally comprising the steps of obtaining a stream comprising a spent sulfuric acid from the esterification reaction chambers in the series, contacting the spent sulfuric acid with steam and subsequently condensing a mixture of a crude reaction product and the steam thus obtained, and recycling the condensate of the mixture of the crude reaction product and the steam to the first reaction chamber.