CS236998B1 - Process for producing methyl methacrylate - Google Patents

Abstract

The invention describes a method for the production of methyl methacrylate, in which the starting material is acetone cyanohydrin. The methacrylamide sulfate prepared from it is esterified in the first stage with 1.5 to 2 moles of methanol, calculated on acetone cyanohydrin, in the second stage it is esterified with 0.05 to 1 mole of methanol with continuous distillation of methyl methacrylate. Next, the esterification mixture is diluted with water in a weight ratio of 5:1 to 1:1 with distillation of methyl methacrylate and methanol, the distillation residue is neutralized with gaseous ammonia, left to mature for 16 to 24 h, while the precipitated polymers are removed and the solution is fed to the crystallization of ammonium sulfate.

Description

The present invention relates to a process for the preparation of methyl methacrylate by the acetone cyanohydrin process.

Conventional production of methyl methacrylate by acetone cyanohydrin technology has its major problems in the xzolation stage of production and in the subsequent treatment of waste sulphate liquors. However, these problems depend on the way in which the methyl methacrylate synthesis is employed, i.e. the amidation and especially esterification modes.

In the synthesis of methyl methacrylate under commonly used conditions / mole ratios of raw materials * acetone cyanohydrin: HgSO4:

: methanol: water »1 from 1.6 to 1.3 from 1.6 t 4.0, mixing temperature 80 to 90 ° C, amidation temperature 130 to 135 ° C with a residence time of 20 to 30 minutes, esterification temperature 85 to 135 ° C in individual reactors / 1 to 5% by weight of methacrylic acid as by-product is formed in addition to methyl tetraacetate. Methacrylic acid as the active monomer (after neutralization of sodium methacrylate) is a source of difficulties in the formation of polymers and oligomers (with methacrylate and unreacted methacrylamide), which clog the process equipment, contaminate waste sulphate lyes and recover the produced ammonium sulphate. leaches acquires »

Conventional technology removes methacrylic acid by vigorous routes, e.g. by neutralization with sodium hydroxide solution and subsequent extraction of salt and methanol, by extraction azeotropic de-distillation in which the methacrylic acid exits at the bottom of the rectification column, differently combined rectification processes after previous methanol extraction are used. However, all these processes do not prevent the formation of methacrylic acid and the

236 998 only eliminate it, and the demands for inhibition of these isolation processes are high.

By suppressing the formation of methacrylic acid with a higher excess of methanol, the excess of methanol is undesirably bound to the free sulfuric acid by reducing the excess of water. The resulting methyl hydrogen sulphate leaves with sulphate liquors, increasing the loss of methanol, acting as a good solvent for undesirable organic polymers, and subsequent neutralization with ammonia gas releases methanol into the atmosphere, while polymers fall out of solution and clog the process equipment.

The above disadvantages are overcome by the process for the production of methyl methacrylate according to the invention, which is carried out by an acetone cyanohydrin process in the presence of an inhibitor, such that methacrylamide sulphate is estrified in a first step with 1.5 to 2 moles of methanol. mole of methanol, with the continuous distillation of crude matylmethacrylate, then the esterification mixture is controlled with water at a weight ratio of aetherification mixture to water of from 3: 1 to 1: 1 with de-distillation of the matylmethacrylate and methanol, neutralized with ammonia gas; h to remove the precipitated polymers and to settle for ammonium sulfate crystallization.

An advantage of the present invention is the production of methyl macrylate to produce a minimum amount of methacrylic acid and thus a reduced amount of undesirable polymers, with the concomitant use of methanol, which is used in excess in the process. A saler advantage is the fact that the difficulty in processing the sulphate liquors into ammonium sulfate suitable for breast farming purposes is eliminated.

The present invention solves a process for the production of methyl methacrylate from acatone cyanohydrin, wherein the estsrification is carried out in a mode in which only very little methacrylic acid is produced. Neutralization with sodium hydroxide solution can be omitted and the sulphate liquors are also free of organic matter to such an extent that the device is free of clogging and ammonium sulphate

236 998 cattle for agricultural purposes · Esterification is carried out in two stages when 1.5 to 2.5 moles of excess methanol are used under other unchanged reaction conditions relative to the acetone cyanohydrin feed. After a two-hour reflux for the discontinuous process and after a holding time of 120 to 150 minutes for continuous processes, ee retains the lips up to a temperature of 88 to 97 ° C. The condensate, which is crude methyl methacrylate, contains only 0.2 to 0.7 wt. · The reaction mixture is esterified in the second step with 0.05 to 1 mol of methanol to the acetone cyanohydrin feed. After a holding time of 30 minutes, the lips are collected at a temperature of 75 to 80 ° C. This proportion of the raw product is also fed to the insulation part,

In esterification, the excess methanol is controlled by the methacrylic acid content of the crude methyl methacrylate. The isolation portion need not include neutralization of the crude methyl methacrylate, but only the extraction of methanol with process water and rectification. The extraction waters partially return to synthesis / in an amount corresponding to the molar ratio of acetone: 4 / and the remainder of the extraction vdd is fed * to a methanol column where methanol is recovered · The reaction mixture from the second esterification stage is diluted with water and fed either to a stripping column (organic substances are fed to the column with water vapor) or to another reactor where the residue of methyl methacrylate and the liberated methanol are distilled off. Depending on the methyl methacrylate content, this stream is either fed to the isolation portion as crude methyl methacrylate or, at low methyl methacrylate content, to a methanol column where methanol is recovered. From the bottom of the stripper column (from the reactor), the sulphate liquors are passed to neutralize with ammonia gas. The neutralized liquors are aged in large-volume containers so that the residence time of the sulphate liquors is 16-24 hours. The latter residues of organic matter fall out of solution and are removed mechanically. The solution goes further to filtration, to evaporators and to crystallization of ammonium sulphate ·

4Example 3

236 998

440 kg / h of acetone cyanohydrin and 828 kg / h of 100% H 2 SO 4 are metered into the mixing reactor continuously for the methyl methacrylate production line. The temperature of the reaction mixture is kept at 85 ° C through the cooling circuit through a cooling exchanger. a powdered mixed inhibitor, e.g. CuSO ^ · 5 H ₂ 0-phenothiazine in the mass ratio 1: 3 mixture through four coils korobónovými / amidation reactor /, where the temperature is gradually increased to l30 ° C JO conceived, min and V Nals výmenníkusa cooled to 90 DEG C. and passed into a three-membered esterification cascade (each 2.5 m 2) where 331 kg / h (2.0 mole) of excess methanol was metered into acetone cyanohydrin (540 kg / h) in v8d works containing 16-20% by weight · from the second cascade member, the vapors are taken at a temperature of 75 * 85 ° C, taken after condensation., treated as raw methyl methacrylate · At the same time, 83 kg / h / 0 are fed into the second cascade member. 5 molar excess to acetone cyanohydrin / methanol feed. From the third cascade member, the vapors are removed at a temperature of 80-85 ^p CL, which after condensation. they form another proportion of crude methyl methacrylate with a content of 0,2-0,7% by weight of methacrylic acid. The methacrylic acid content is controlled by excess methanol by metering into the first and second cascade members. The reaction mixture from the third cascade member is added in addition to the fourth reactor (at 2.5 m @ 2) and is added while boiling the mixture * 500 kg / h process water · Q coming in vapors containing azeotrope methyl methacrylate - water, methanol and other organic substances *

With a methyl methacrylate content above 5 wt. the fraction is fed to the lzolation step together with crude methyl methacrylate.

At a lower methyl methacrylate content, the fraction is fed together with the extraction waters onto a methanol column ·

236 998

The reaction mixture from the fourth reactor is led to neutralization with ammonia gas and further processing to sulfate.

, * ammonium. There is at least a number of undesirable polymers in the cartridges after neutralization of the sulphate xuh. The yield of methyl methacrylate after extraction! methanol; and rectification is 80-83% by weight, to acetone cyanohydrin.

Example 2

95 g of AKH and 165 g of sulfuric acid are charged successively into a 1-L three-necked flask at temperature; shall not exceed '85 ° Art. After mixing the above amounts, <

g inhibitor of CuSO4 → 5HgQ + phenothiazine 1: 3.

The reaction mixture was then heated to 135 ° C for 35 minutes. After this; At this time, the reaction mixture was cooled to 90 ° C. When this temperature is reached, 77 g of water and 90 g of methanol are added successively. The reaction mixture was refluxed for about 2 hours until the vapor temperature reached 79 ° C. After; reaching this temperature, the heating is stopped and the reflux condenser is exchanged for the descending one, and heating is continued, distilling the crude methyl methacrylate to a vapor temperature of 80 ° C. After reaching this; 10 g of methanol are added at reflux temperature and refluxed. The crude methyl methacrylate is then distilled off; 85 ° C. The distillate is collected together with the first distillate. Extract twice with water; in a ratio of 1 L to the crude ester. Rafinátz obidvoch'extrakci! will connect. The extract is rectified. Methyl methacrylate yield calculated on acetone cyanohydrin is 83% ·

The reaction mixture is passed through steam until the temperature reaches 99 ° C and falls out of the reaction mixture; solid, good filterable polymer. The steam distillate is combined with the raffinate after extraction! and is rectified so as to result in 60% methanol, which is used to sleep for esterification.

238 988

The reaction mixture, after distilling off the methyl methacrylate and methanol, is neutralized with ammonia and concentrated by treatment. to crystalline ammonium sulphate * When the saturated solution is thickened, no asphalt-like substances * fall out of it.

Claims (1)

SUBJECT OF THE INVENTION 236 998 A process for the production of methyl methacrylate by acetone cyanohydrin in the presence of a polymerization inhibitor, characterized in that the methacrylamide sulfate is esterified in a first stage with 1.5 to 2 moles of methanol, calculated on the input of acatocyanohydrin, and esterified with 0.05 to 1 mol of methanol in the second stage. the continuous esterification of the crude methyl methacrylate, then the esterification mixture is diluted with water in an esterification mixture to water ratio of 3: 1 to 1: 1 by distillation of the methyl methacrylate and methanol, the distillation residue is neutralized with ammonia gas and vortexed for 16 to 24 hours while removing the precipitated polymers. and the solution is next to the ammonium sulfate crystallization