CS238426B1 - A method of reducing polymerization and decomposition of feedstocks and intermediates in the production of C 1 to C 4 esters of methacrylic acid - Google Patents

Abstract

The invention solves the problem of limiting the polymerization and decomposition of input raw materials and intermediates in the production of Cl and Ci esters of methacrylic acid from acetone cyanohydrin by a mixed inorganic-organic inhibitor system. In this method, copper sulfate and at least one substance from the group of pyrocatechin, hydroquinone, p-aminodiphenylamine, diphenylamine are added in the mixing phase of the input raw materials, while the amine inhibitors are used either in pure form or as by-products in the production of 4-aminodiphenylamine, benzothiazolyl-2-sulfenyl-N-morpholinamide or benzothiazolyl-2-sulfenyl-N-cyclohexylamide, in an amount of 0.05 to 0.8 % by weight per entering acetone cyanohydrin and with a weight ratio of the inorganic component to the organic component in the inhibitor system of 3:1 to 1:3,

Description

The invention relates to a method for reducing the polymerization and decomposition of feedstocks and intermediates in the production of C 1 -C 4 esters of methacrylic acid from acetone cyanohydrin by a mixed inorganic-organic inhibitor.

A variety of inhibitors have been described to inhibit polymerization in the manufacture of methacrylate esters, which reduces the yield of the final product. The main reason for the inhibition in this process is not only an increase in the overall economic effect of production, but also an improvement in the operability of the mainly continuous methyl methacrylate technology. Ineffective inhibition leads to clogging of pipes, deposition of polymers on the walls and stirrers in reaction vessels, resulting in plant downtime and ultimately reducing the overall production capacity of the plant.

Thus, two types of inhibitors are used in the production of methacrylic acid and acrylic acid, which can be divided into inorganic and organic. Organic inhibitors frequently used are, for example, hydroquinone, substituted phenols, phenothiazine and derivatives thereof, as well as other types, such as methylene blue.

In general, an inhibitor can be considered to be a substance that can bind, block a radical or complex that can potentially initiate the formation of a radical from an unsaturated bond molecule and further form an undesirable polymer by propagation and termination.

Among the inorganic type inhibitors, dichromates, potassium permanganate, copper sulfate, iron sulfate are described. These inhibitors are usually dissolved in the starting materials for synthesis. For example, in the synthesis of methyl methacrylate in the first phase, acetone cyanohydrin is reacted with concentrated sulfuric acid (98 to 100% by weight) in an optimal molar ratio of 1: 1.5. This reaction produces 2-hydroxyisobutyric acid amide sulfate at lower temperature (60-90 ° C) and methacrylamide sulfate at elevated temperature (up to 130 ° C).

The uninhibited first phase may also lead to losses, for example, by decomposition of acetone cyanohydrin. However, the dissolution of some salts in concentrated sulfuric acid in the cold is problematic. It is necessary to provide separately containers equipped with stirrers. In the winter months at low temperatures, due to the decrease in solubility, considerable problems can arise using this method of administration of the inhibitor. Pre-dissolution of inhibitors in cartridges containing acetone cyanohydrin also presents some safety concerns.

In the next stage of the process, methyl methacrylate is formed in the reaction of methacrylamide sulfate with methanol and water and the hydrophobic and hydrophilic charge is used for isolation. Here, inhibition of both the aqueous and organic phases is desirable. Most commonly, the orc phase is inhibited by inhibitors that are soluble therein.

In addition to the above inhibitors, the use of a mixed inorganic-organic CuSO4-phenothiazine inhibition system is also known.

According to the present invention, the method of limiting the polymerization and decomposition of feedstocks and intermediates in the production of C 1 -C 4 methacrylic acid esters from acetone cyanohydrin by a mixed inorganic-organic inhibitor system is accomplished by adding copper sulfate and at least one of pyrocatechin, hydroquinone, p-aminodiphenylamine, diphenylamine, the amine inhibitors being used either in pure form or as by-products in the production of 4-aminodiphenylamine, benzothiazolyl-2-sulfenyl-N-morpholinamide or benzothiazolyl-2-sulfenyl-N-cyclohexylamide 0.05 to 0.8% by wt., preferably 0.1 to 0.4 wt.%, the incoming and acetone cyanohydrin weight ratio of the inorganic components of the body ¹ ckej component of the inhibiting system of 3: 1 to 1: 3.

The inhibitory effects of the mixtures of inorganic inhibitor (CuSCU) and organic used are based on the exploitation of the synergistic effect. It is especially advantageous to dispense the mixture of inhibitors with a bulk material dispenser. Thus, it is not necessary to dissolve the organic inhibitors in methanol and dispense them to multiple sites in the production line. The effect of the mixture of organic inhibitors with CuSO4 applied in the sense of the present invention can also be explained by the formation of a complex of media, since their formation is mainly known from amines and phenols.

The organic substances used for the inhibition are either pure substances or mixtures, sometimes byproducts of the production, thereby further improving the economic parameters of the process.

Thus, residues from the manufacture of CD antioxidant include p-aminodiphenylamine (30 to 56% by weight), polymeric substances (66 to 40% by weight) and a small amount of sodium chloride (0.1 to 1% by weight). nitrogen (9.2 wt.%), sulfur (23.7 wt.%), sodium (7.5 wt.%), are products obtained as waste products by the condensation of mercaptobenzothiazole with cyclohexylamine and morpholine. Their viscosity at 90 ° C is 103 mPas and the density at 90 ° C is 1.23 kgm ³ .

EXAMPLE

440 kg / h of acetone cyanohydrin and 828 kg / h of 100% H2SO4 are metered into the mixing reactor of the continuous methyl methacrylate production line. Through the cooling circuit through the cooling exchanger, the temperature of the mixture is maintained at 85 ° C. 0.9 kg / h of powder mixer (CuSCk. 5 HaO and pyrocatechia in a weight ratio of 1: 1) are fed into the cooling circuit of the mixing reactor through a continuous feeder. The reaction mixture is passed through four heat exchangers where the temperature is gradually raised to 130 ° C over 30 min. In a further exchanger, it is cooled to 90 ° C and passed into a three-member esterification cascade (each member having a volume of 2.5 cubic meters), where 301 kg / h of methanol and 540 kg / h of wash water are added to the first member. % to 20 wt. methanol and about 80% water. In methanolic solution, 0.6 kg / h of pyrocatechin is metered into the esterification. From the second and third cascade members, vapors are removed which, after condensation, are crude methyl methacrylate. Acidic sulphate liquors, which are not contaminated with polymeric substances, leave the third boiler. Likewise, there are no problems with clogging apparatus. The yield of methyl methacrylate is in the range of 80-82% by weight. to acetone cyanohydrin.

Example 2

The procedure is as described in Example 1, except that 2.0 kg of a mixed powder inhibitor containing 25 wt. CUSO. 5 H2O and organic residue (1: 1 weight ratio), distillation residue from CD antioxidant production. The organic component of the mixed inhibitor must be dosed in methanol solution until esterified. Polymers are absent! neither in the sulphate liquors nor in the esterification reactors.

Example 3

The procedure of Example 1 is followed except that 1.5 kg / h of mixed powder inhibitor containing 30 wt. CuSOd.

. % H2O as inorganic constituents and 70 wt. hydroquinone as an organic component (weight ratio 1: 2). There is no need to add the organic component to the esterification in the form of a methanolic solution. In the off-gases the carbon monoxide (product of the decomposition of the feedstocks) and the undesirable polymers in the outgoing acidic sulphate liquors are not polluted.

Example 4

The procedure of Example 1 was followed, except that 2.0 kg / h of mixed powder inhibitor containing 25% by weight was charged to the mixing reactor. CuSCh. . % H2O and as an organic component 75 wt. diphenylamine. The organic component need not be dosed until esterified. The apparatus is incompatible with polymers and the outgoing sulphate liquors are free of polymers.

Example 5

The procedure is as described in Example 1, except that 2.0 kg / h of mixed powder inhibitor containing 25% by weight are fed into the mixing reactor. CUSO. . 5 H2O and 75% by weight of 4-aminodiphenylamine as an organic component. The organic component need not be dosed until esterified. The apparatus is not clogged with polymers and the outgoing sulphate liquors are free of polymers.

Example 6

500 g of 100% H 2 SO ⁴ are charged to a 100 cm ³ reaction vessel. 255 g of acetone cyanohydrin are added while stirring so that the temperature does not rise to 85 ° C. No inhibitor is added. The reaction mixture was heated with stirring at 130-135 ° C for 30 min. It is further cooled to 70 ° C. Then, while distilling off the product, 153.4 g of methanol and 216 g of water are added. The distillation is stopped only after reaching 130 ° C in the reaction mixture. An undesirable polymer appears on the inhaler in the flask, and in the off-gas during the amidation, 0.5 to 1% by volume of ulmfuate is determined.

Example 1 and d 7

The procedure of Example 6 was followed, with the addition of 0.5 g of mixed inhibitor containing 75% CuSO 6. And contains as residues of the production of Sulfenax CB as an organic component. After the crude ester was distilled off, no polymer was observed in the stirrer or flask.

Claims (7)

238426 5 of the reactor dosed 0.9 kg / h of powder mixture of the inhibitor (CuSCk.SH2O and pyrokatequin in a 1: 1 weight ratio). The reaction mixture passes through four heat exchangers, where its temperature gradually increases to 130 ° C for 30 min. In another heat exchanger, 90 ° C is cooled down and passed into a three-member esterification cascade (each member having a volume of 2.5 cubic meters), where 301 kg / h of methanol and 540 kg / boiling water of 16-20% are dispensed into the first member wt. methanol and about 80% water. In the methanolic solution, 0.6 kg / h of pyrocatechin is added to the esterification. Pairs are removed from the second and third members of the cascade, which are condensed as crude methyl meta-crystals. From the third boiler, acid sulphate liquors that are not contaminated with polymeric materials leave. Likewise, clogging of apparatus is not a problem. The yield of methyl methacrylate is in the range of 80 to 82%. to acetone cyanohydrin. Example The procedure of Example 1 is followed, except that 2.0 kg of a mixed powder inhibitor containing 25 wt. CuSOá. 5 H2Oa residue of organic component (1: 1 weight ratio), distillation residue from production of anti-oxidant CD. The organic component of the mixed blender must be dispensed in a solution of methanol to esterify. Polymers do not extrude! neither in sulphate mead nor in the esterification reactors. Example 3 The procedure of Example 1 is followed, with the difference that 1.5 kg / h of mixed powder inhaler containing 30 wt. CuSOi. . 5 H2O as inorganic components and 70% by weight of hydroquinone as organic component (1: 2 weight ratio). The organic component does not need to be added to the esterification of the methanolic solution. In degasses there is no carbon monoxide (the feedstock product) or undesirable polymers in the leaving acid sulphates. Example 4 Proceed as described in Example 1, except that 2.0 kg / h of mixed powder inhaler containing 25 wt. CuSOi .. 5 HeO and as an organic component 75% by weight of diphenylamine. It is not necessary to dispense the organic component in the esterification. The apparatus incorporates polymers and the outgoing sulphates are not contaminated with polymers. EXAMPLE 5 The procedure of Example 1 is followed, with the addition of 2.0 kg / h of mixed powder inhibitor containing 25% by weight into the mixing reactor. CuSO 4 · 5 H 2 O and 75% by weight of 4-aminodiphenyl amine as organic. The organic component does not need to be dosed for esterification. The apparatus is free of polymers and outgoing sulfur-free liquors are not contaminated with polymers. Example 6 Into a 100 cm 3 reaction vessel of sanarium 500 g of 100% H 2 SO 4. Next, 255 g of acetone cyanohydrin are added with stirring so that the temperature does not rise to 85 ° C. No inhibitor is added. The reaction mixture was heated with stirring for 30 min at 130-135 ° C. It is further cooled to 70 ° C. Thereafter, 153.4 g of methanol and 216 g of water are added with distillation of the product. The distillation is stopped after reaching 130 ° C in the reaction mixture. An undesirable polymer is found on the flask in the flask, 0.5 to 1% by volume, of oxibibenzate, is determined in the degassing during the agitation. 7 The procedure of Example 6 is followed, with the difference that 0.5 g of a mixed inhibitor containing 75% CuSO5.5H2O is added and the organic component contains sulfenax CB residues. After distilling off the crude ester, no polymer is observed on either the stirrer or the flask. PREFACE The process of limiting the polymerization and resolution of feedstocks and the intermediate in the production of C 1 to C 4 methacrylic acid esters of acetone cyanohydrin by a mixed inorganic-organic inhibitory system, characterized in that in the mixing phase of the feedstock, the reaction system at the copper sulphate and at least one pyrocatechin, hydroquinone, p-aminodiphenylamine moiety, wherein the amine inhibitors of the invention are used either in pure form, in other products in the production of 4-aminodiphenylamine, benzothiazolyl-2-sulphenyl-N- morpholinamide or benzothiazolyl-2-sulfenyl-N-cyclohexylamide, in an amount of 0.05 to 0.8% by weight, preferably 0.1 to 0.4% by weight, of the acetone cyanohydrin and the weight ratio of inorganic component to in the 3: 1 to 1: 3 inhibitory system.