Optimized process for synthesizing alkyl methacrylate by reducing unwanted byproducts

2:

• The process according to claim 1, wherein the at least one stream comprising the methacrylonitrile and the acetone which is at least partly recycled into the third reaction stage is a water-containing heteroazeotrope comprising the methacrylonitrile and the acetone from at least one of the at least two distillation steps.

3:

• The process according to claim 1, wherein at least one aqueous phase which is obtained by condensation and phase separation of the water-containing heteroazeotrope from at least one of the at least two distillation steps is recycled fully or partly into the third reaction stage, where the at least one aqueous phase is contacted with the second reaction mixture comprising predominantly the methacrylamide and the sulfuric acid.

4:

• The process according to claim 1, wherein at least one aqueous phase which is obtained by condensation and phase separation of the water-containing heteroazeotrope from at least one of the at least two distillation steps is discharged fully or partly from the process, optionally after an extraction step.

5:

• The process according to claim 1, wherein the water-containing heteroazeotrope from at least one of the at least two distillation steps is discharged fully or partly from the process, at least partly in the form of a gaseous stream, optionally after a scrubbing step.

6:

• The process according to claim 1, wherein the separation of the alkyl methacrylate from the third reaction mixture comprises at least one phase separation step in which the water-containing heteroazeotrope from at least one of the at least two distillation steps is separated into an aqueous phase comprising the methacrylonitrile and the acetone, and an organic phase comprising predominantly the alkyl methacrylate,
• wherein the aqueous phase is partly discharged from the process and/or partly recycled into the third reaction stage, and
• wherein the organic phase comprising predominantly the alkyl methacrylate is recycled fully or partly into the at least one of the at least two distillation steps.

7:

• The process according to claim 1, wherein the third reaction mixture obtained in the third reaction stage is evaporated continuously, wherein a resultant vapour stream is fed to a first distillation step K1 in which a tops fraction comprising the alkyl methacrylate, water and the alcohol, and a bottoms fraction comprising higher-boiling components are obtained, and
• wherein the bottoms fraction is recycled fully or partly into the third reaction stage.

9:

• The process according to claim 8, wherein the aqueous phase WP-1 is recycled fully or partly into the third reaction stage and the organic phase OP-1 comprising the predominant portion of the alkyl methacrylate is subjected to an extraction using water as extractant,
• wherein an aqueous phase of the extraction is recycled into the third reaction stage and a organic phase of the extraction is guided into the second distillation step K2.

10:

• The process according to claim 8, wherein a portion of the aqueous phase WP-2 comprising the methacrylonitrile and the acetone is subjected to an extraction to obtain an aqueous phase WP-3 and an organic phase OP-3,
• wherein the aqueous phase WP-3 is discharged fully or partly from the process, and
• wherein the organic phase OP-3 is recycled fully or partly into the third reaction stage.

13:

• The process according to claim 1, wherein the second reaction mixture contains not more than 3% by weight of methacrylic acid, not more than 1.5% by weight of alpha-hydroxyisobutyramide and not more than 0.3% by weight of the methacrylonitrile, based in each case on the overall amount of the second reaction mixture.

14:

• The process according to claim 1, wherein the second reaction mixture contains 30% to 40% by weight of the methacrylamide, based on the overall amount of the second reaction mixture.

15:

• The process according to claim 1, wherein the conversion of the acetone cyanohydrin and the sulfuric acid in the first reaction stage is effected in at least two separate reaction zones or in at least two separate reactors.

16:

• The process according to claim 1, wherein, in the first reaction stage, the conversion of the acetone cyanohydrin (ACH) and the sulfuric acid is effected in at least two separate reactors,
• wherein the sulfuric acid and the acetone cyanohydrin are used in a first reactor in a molar ratio of the sulfuric acid to the ACH in the range from 1.6 to 3.0, and
• wherein the sulfuric acid and the acetone cyanohydrin are used in a second reactor in a molar ratio of the sulfuric acid to the ACH in the range from 1.2 to 2.0.

17:

• The process according to claim 1, wherein the reaction mixture of acetone cyanohydrin (ACH) and sulfuric acid in the first reaction mixture includes a total amount of water in the range from 0.1 mol % to 20 mol %, based on an entirety of the ACH supplied to the first reaction stage.

18:

• The process according to claim 8, wherein a crude alkyl methacrylate product is obtained as a bottoms fraction in the second distillation step K2,
• wherein the crude alkyl methacrylate product is purified in a further distillation step K3, to obtain a pure alkyl methacrylate product as a tops fraction, having a methacrylonitrile content in the range from 10 to 300 ppm, based on an amount of the pure alkyl methacrylate product.

19:

• The process according to claim 1, wherein the process comprises a regeneration of the sulfuric acid, wherein a portion of the third reaction mixture obtained in the third reaction stage and at least one aqueous or organic waste stream comprising sulfuric acid, ammonium hydrogensulfate and sulfonated acetone derivatives that results from discharge of the water-containing heteroazeotrope comprising the methacrylonitrile and the acetone is sent to a thermal regeneration step in which the sulfuric acid is obtained, which is recycled into the first reaction stage.

20:

• The process according to claim 1, wherein the process comprises obtaining ammonium sulfate, wherein a portion of the third reaction mixture obtained in the third reaction stage and at least one aqueous or organic waste stream comprising sulfuric acid, ammonium hydrogensulfate and sulfonated acetone derivatives that results from discharge of the water-containing heteroazeotrope comprising the methacrylonitrile and the acetone is sent to a thermal regeneration step in which the ammonium sulfate is obtained by crystallization, which is separated off as a by-product.