CS254236B1 - Specifying the polymerization of methyl methacrylate during its synthesis - Google Patents

Abstract

The solution relates to inhibiting the polymerization of . nféíkyaim^fitkiryiátp'ÍfMWAi) ipr.i 'its .synthesis from SbWftBtyfflttihyeifeu « sulfuric acid and ®i051eitó©j estefíkáOiii jmetemttOBi. The method of preparation of the mixture is based on the addition of phenothiazine and one component from the group of phenothiazine derivatives N4ίζ©ρΓ0ρ5ίΐ--Ν··/ΰυ6ηψΐ4ρ4ί;6η,5Λβΐϊ<3ίϊ®ηπιη, r4- -amíffiodphenytlBniin, and also the eKtiilnňných zhyíkbv obtained from the distillation of di-ianíxnadESenýWffiin in a mass ratio of 1: 0(5-®S 1::-2, .«with preference 1: 1. The effect is manifested in the "Reduction of other organic impurities in the aurous MMA as well as in waste sulfate solutions and final ammonium sulfate.

Description

The subject of the invention is a method of inhibiting the polymerization of a reaction mixture in the synthesis of methyl methacrylate from acetone, sulfuric acid and methanol.

CH3 gn \ / + H2SO4

C ---> CH2 / \ 135 °C

CH3 OH from which in the next stage, by hydrolysis in an aqueous environment, transient methacrylic acid is formed and subsequent esterification meCH2 = C — COOH + CH3OH--->

CH3

The substances formed in both stages are prone to polymerization and therefore it is necessary to inhibit this polymerization. In practice, various inorganic and organic substances, or their combinations, are used as inhibitors. These include inorganic ones, e.g. Cu salts, Cr2O7 ^_ or MnOá ^- salts, used mainly for inhibition in amidation.

Organic inhibitors include:

pyrocatechin, hydroquinone, phenothiazine, tannin, distillation residues from the production of phenol, fulvene, methylene blue, thiourea,

N,N-dinaphthyl-p-phenylenediamine, (S-naphthol, phenylhydrazine, o-aminophenol, etc.

They are mostly used in quantities that have an adverse effect either by contaminating the resulting product during its isolation by distillation (e.g. phenothiazine) or by remaining in the waste sulfate liquors. The ammonium sulfate crystal obtained from these liquors is contaminated with these inhibitors. In addition,

In the synthesis of methyl methacrylate from acetone cyanohydrin and sulfuric acid, the first step is dehydration with sulfuric acid to form sulfuric acid amide according to equation (1) = C — CO . NH2 . H2SO4

I

CH3 (1) ethanol produces methyl methacrylate according to equation (2)

CH2 = C — COOCH3 + H2O

CH3 (2) clogs crystallization apparatuses, especially evaporator tubes.

According to the process of the invention, the inhibition of the polymerization of the reaction mixture in the production of methyl methacrylate from acetone cyanohydrin in the presence of sulfuric acid and subsequent esterification with methanol is carried out by adding to the incoming acetone cyanohydrin 0.005 to 0.5 wt. % of the inhibitor, which is a mixture of phenothiazine and one component from the group of substances N-isopropyl-N'-diphenyl-p-phenylenediamine or distillation residues obtained from the distillation of 4-amino-diphenylamine in a mass ratio of 1:0.5 to 1:2, preferably 1:1, to the amidation of acetone cyanohydrin with sulfuric acid and/or to the esterification of the amidation mixture with methanol.

In contrast to known methods of inhibiting the reaction mixture, the process according to the invention is characterized by a higher, synergistic effect compared to the addition of phenothiazine alone or any of the described set of substances based on 4-amino-diphenylamine.

The effect of inhibition is felt, in addition to increasing the yield of methyl methacrylate, also on the quality of waste sulfate liquors and the crystalline ammonium sulfate prepared from them by neutralizing them with ammonia.

The effect of individual inhibitors can be seen from the following table.

With 8 Table 1 phenothiazine 4-aminodiphenylamine distillation residue a mixture of phenothiazine and the precipitate residue from 4-amino-diphenyl- of amine 1:1

1. Content of organic impurities in raw MMA wt. % 5.63 2. Content of organic impurities in sulfate liquors. % 9.51 3. Solid polymer content in sulphate liquors wt. % 0.314 4. The content of organic impurities in the crystal, ammonium sulfate mass. % 3.16 Example 1 Into the amidation mixture continuously prepare-

4.31 3.31

7.87 6.41

0.187 0.148 prepared from 95 wt. parts of acetone cyanohydrin and 165 wt. parts of sulfuric acid, 0.05 wt. parts of a mixture of phenothiazine and distillation residues from the desilylation of 4-amino-diphenylamine are added at 80 °C in a weight ratio of 1 : 1.5. The reaction mixture is heated to 135 °C with a hold time of 30 min. and in the next step esterified with 60 wt. parts of methanol. 100 wt. parts of crude methyl methacrylate are obtained with a content of 3.4 wt. % of organic impurities.

With the same procedure only with phenothiazine

2.43 2.26 is the content of organic impurities in the crude ester of 5.5% by mass.

Example 2

The amidation mixture is prepared from 490 wt. parts of acetone cyanohydrin and 442 wt. parts of sulfuric acid. After reaction at 135 °C with a 30 min. retention, esterification is carried out with 30 wt. parts of methanol and 320 wt. parts of water. 0.025 wt. % of phenothiazine and 0.025 wt. % of N-isopropyl-N'-diphenyl-p-phenylenediamine are added to the esterification as an inhibitor per batch of acetone cyanohydrin as a solution in the crude ester. 500 wt. parts of crude ester containing 3.5 wt. % of organic impurities are obtained.

Claims (3)

SUBJECT Method of inhibiting the polymerization of methyl methacrylate during its synthesis from acetone cyanohydrin in the presence of sulfuric acid and subsequent esterification with methanol, characterized in that 0.005 to 0.5% of γ n A is added to acetone cyanohydrin amidation and / or methanol amidation of the amidation mixture. wt. an inhibitor which is a mixture of phenothiazine and one of N-isopropyl-N‘-diphenyl-p-phenylenediamine, 4-amino-diphenylamine, or the distillation residues obtained from the distillation of 4-aminodiphenylamine in the mass of the mixture; ratio 1: 0.5 to 1: 2, preferably 1: 1.