Continuous preparation of alkyl esters of (meth) acrylic acid

一种连续制备(甲基)丙烯酸烷基酯的方法，其中a)(甲基)丙烯酸和链烷醇以摩尔比1∶0.75至1∶2反应，b)部分在精馏单元(III)的顶部形成的水相返回到精馏单元中，c)从反应段卸出的反应混合物被送到另一精馏单元(I)，在此单元中将反应混合物分离成包含催化剂的产物(II)和包含目标酯和剩余原料的产物(I)，和d)产物(I)被送到另一个精馏单元(II)中，在此单元中，将目标酯和剩余原料分离，并将剩余原料送回到反应段。 In the continuous production of alkyl (meth)acrylates (AA) by reacting (meth)acrylic acid with 1-8 carbon (C) monohydric alkanols in homogeneous liquid phase, free from solvent, at elevated temperature and in the presence of an acid esterification catalyst; (a) (meth)acrylic acid, alkanol and catalyst are fed to a reaction zone; (b) during a residence time, the water formed is separated in a rectification unit (RU) III above the reaction zone; (c) the aqueous distillate is separated into an organic phase containing the alkanol and an aqueous phase; (d) the organic phase is recycled to RU III; and (e) the reaction mixture is discharged from the reaction zone and passed to another RU, where AA is separated by distillation. The novel features are that: (i) the molar ratio of (meth)acrylic acid and alkanol is 1:(0.75-2); (ii) the aqueous phase from RU III is partly recycled to RU III; (iii) the reaction mixture is passed to RU I, in which it is separated into a product (II) containing the catalyst and a product (I) containing AA, residual alkanol and residual (meth)acrylic acid; and (iv) (I) is passed to RU II, in which AA is separated from residual alkanol and residual (meth)acrylic acid and the alkanol and acid are recycled to the reaction zone. Preferably the alkanol is 2-ethylhexanol. The catalyst is para-toluenesulphonic acid (p-TSA) and/or other organic sulphonic acids, e.g. methane-, benzene- or dodecylbenzene-sulphonic acid, and/or sulphuric acid (H2SO4). The catalyst concentration in the reaction mixture is 0.1-10, especially 0.1-6 wt.% p-TSA in the reaction zone and 2.5-50 wt.% p-TSA in the sump or an equimolar amount of organic sulphonic acid and/or H2SO4. The reaction zone consists of a cascade of NOTLESS 2, especially 2-4 consecutive sections, especially reactors with circulating vapourisers. All rectification units are rectification columns.