RU2476419C1 - Method of producing alkyl methacrylates - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical engineering and specifically to an improved method of producing alkyl methacrylates via transesterification of methyl methacrylate with alcohols of general formula C_nH_2n+1OH, where n≥4, in the presence of potassium or sodium carbonate and sodium borohydride, as well as a radical polymerisation inhibitor with distillation of the formed methanol in form of an azeotrope with methyl methacrylate, wherein the potassium or sodium carbonate in amount of 0.5-1.5 wt % of the total weight of the reactants used is used as a catalyst until achieving alcohol conversion of 40-80%, after which sodium borohydride is added to the reaction mass in amount of 0.005-0.05 wt % of the amount of alcohols used.

EFFECT: fewer steps, high efficiency of the process, high quality of the commercial-grade alkyl methacrylate.

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Description

The invention relates to chemical technology, in particular to a technology for the production of methacrylic acid esters of the general formula

where RC _n H _{2n + 1} , n≥4.

Esters of unsaturated carboxylic acids have recently gained great practical importance, they are monomers for the production of polyalkyl (meth) acrylates, which are used as plasticizers, viscous and depressant additives to oils and fuels, components of coatings, components of adhesive compositions and other useful products.

Alkyl methacrylates are obtained by esterification of methacrylic acid with alcohols, alkylation of methacrylic acid with olefins. Currently, widespread use has been made of a method for the production of alkyl methacrylates based on the transesterification of methyl methacrylate with alcohols; this method allows the use of acidic and basic type catalysts.

In the patents (US 2129722, C08F 20/10, 1938; US 6818791, C07C 67/08, 2004), inorganic acids, sulfuric and phosphoric, are proposed as catalysts. The use of acids has a number of significant drawbacks, which necessitates the neutralization and washing of the reaction mixture, resulting in the formation of a large amount of acidic wastewater, which poses a serious threat to the environment. Due to the high corrosivity of acids, it becomes necessary to select more expensive anticorrosive materials for the reaction equipment. In addition, acidic catalysts cause side reactions that lead to the formation of hard-to-remove high-boiling products that impair the quality of the commodity monomer.

Known methods for producing alkyl methacrylates by transesterification of methyl methacrylate with alcohols, catalyzed by non-acid compounds. Such catalysts include basic compounds such as alkoxides, hydroxides, carbonates, phosphates, oxides and complexes of alkali and alkaline earth metals, aluminum, magnesium, titanium, zinc, tin, zirconium compounds and others.

The method for producing alkyl methacrylates by transesterification of methyl methacrylate using titanium alkoxide as a catalyst is described in a number of patents (US 3887609, C07C 67/03, 1975; US 6977310, C07C 67/02, 2005). Effective transesterification catalysts are sodium alkoxides (CH 239750, C07C 67/03, 1945; JP 63-05055, C07C 67/03, 1963). The disadvantage of the methods based on the use of alkali and alkaline earth metals, titanium, zirconium and other alcoholates as transesterification catalysts is that their use is associated with the difficulty of separating the catalyst from the reaction mass.

Magnesium methoxide can be used as a transesterification catalyst (CS 262252, C07C 67/02, 1989; CS 259635, C07C 69/54, 1988). The yield of alkyl methacrylate is 97.5%. After completion of the process, the catalyst decomposes with dilute sulfuric acid, the excess methyl methacrylate (MMA) is distilled off with steam, which leads to the formation of a large amount of wastewater.

Organometallic complexes of titanium and tin are proposed as transesterification catalysts in patents (US 4020010 B01J 31/02, 1977; US 4018708, B01J 31/12, 1977). Zirconium acetylacetonate (DE 3725344, B01J 31/00, 1988; US 4202990, C07C 67/03, 1980), sulfocationionites (JP 77-39620, C07C 67/03, 1977), lithium compounds (FR 2584711, C07C are used as catalysts). 67/03, 1987), a mixture of lithium and calcium salts and oxides (US 4745213, C07C 67/02, 1988; DE 3423441, B01J 23/00, 1984) and others. These catalysts make it possible to achieve high yields of alkyl methacrylates, however, they require severe process conditions.

In the patent (RF 2280652, C08F 120/10, 2006), the transesterification of methyl methacrylate is carried out in the presence of potassium carbonate. The method allows to achieve a yield of not more than 92-93.5% for 15 hours of synthesis.

Thus, the known methods for producing alkyl methacrylates and the catalytic systems used have certain disadvantages: low yield of alkyl methacrylate, harsh synthesis conditions, and a complex catalyst purification system, which leads to the formation of a large amount of waste.

The closest in technical essence to the proposed invention is a method for producing alkyl methacrylate, proposed in the patent of the Russian Federation 2411231, C07C 67/03, 2011 - prototype. Alkyl methacrylates are obtained by transesterification of methyl methacrylate with alcohols of the general formula C _n H _{2n + 1} OH, where n≥4, in the presence of a radical polymerization inhibitor of diethyl hydroxylamine on basic catalysts - sodium borohydride, its alkyl esters or mixtures of sodium borohydride and its alkyl ethers. The resulting methanol is removed from the reaction zone by distillation in the form of an azeotrope with methyl methacrylate.

Before transesterification, the reaction mixture containing fatty alcohol and methyl methacrylate is dried in the presence of water-binding potassium carbonate or sodium, taken in non-catalytic amounts - not more than 0.07 wt.% Of the loaded methyl methacrylate.

The use of sodium borohydride and its alkyl esters in large quantities as transesterification catalysts has several disadvantages.

The use of sodium borohydride leads to partial hydrogenation of double bonds, ether groups and other side processes. The interaction of sodium borohydride with methanol leads to its decomposition. The high activity of sodium borohydride requires the process to be carried out at lower temperatures, which requires the creation of a deeper vacuum.

Sodium borohydride reacts with water, organic acids and alcohols with a loss of catalytic activity. Therefore, the use of sodium borohydride requires additional drying of the reagents from water. Drying is carried out to a residual moisture content of the initial mixture of not more than 0.03 wt.% (RF 2411231).

Partially sodium borohydride is dissolved in the reaction mass. The resulting mass is very difficult to separate from the suspension of the catalyst.

These shortcomings lead to a decrease in the quality of commodity alkyl methacrylate and a decrease in the productivity of the process.

This invention is aimed at improving the method for producing alkyl methacrylates by transesterification of methyl methacrylate with alcohols.

The technical result is a reduction in the number of stages, an increase in the productivity of the process, an increase in the quality of commercial alkyl methacrylate.

This technical result is achieved by the fact that alkyl methacrylates are obtained by transesterification of MMA with alcohols of the general formula C _n H _{2n + 1} OH, where n≥4, in the presence of potassium or sodium carbonate and sodium borohydride, as well as a radical polymerization inhibitor with distillation of the resulting methanol in the form of an azeotrope with methyl methacrylate, characterized in that the potassium or sodium carbonate in an amount of 0.5-1.5 wt.% of the total weight of the loaded reagents is used as a catalyst until the conversion of alcohols of 40-80% is reached, after which the Borghi are introduced into the reaction mass sodium dride in an amount of 0.005-0.05 wt.% from alcohol.

The use of potassium or sodium carbonate as a transesterification catalyst at the first stage allows, unlike the prototype, the process to be carried out without preliminary drying of the reaction mixture. The water contained in the starting materials does not affect the activity of potassium and sodium carbonates and will be removed from the reaction zone during the transesterification of methyl methacrylate. This eliminates the stage of preliminary drying of the starting materials and thereby reduce energy costs and increase the productivity of the process.

It is known that potassium and sodium carbonates are quite active transesterification catalysts. At the initial stage, their activity in the process of transesterification is practically not inferior to the activity of sodium borohydride and, unlike sodium borohydride, practically do not lose their catalytic activity when reused. Potassium and sodium carbonates do not dissolve in the reaction mass and are easily separated from it by simple filtration. The use of potassium carbonate and sodium allows the process to be carried out at higher temperatures, while maintaining high selectivity of the process and high quality of the obtained alkyl methacrylate.

Sodium borohydride is added in significantly smaller quantities, compared with the prototype, only at the last stage of the process (after reaching the alcohol conversion of 40-80%). This reduces the use of expensive, poorly stored sodium borohydride, simplify the stage of separation of the catalyst and increase the quality of the commercial product.

The alkyl methacrylate obtained after filtration can be used in polymerization processes without further purification.

The proposed method for the production of alkyl methacrylates can be illustrated by the following examples:

Example 1. Comparative (prototype)

94.6 g of molten fatty alcohols of the C12-C18 fraction (average molecular weight 214), 141.9 g of methyl methacrylate, 0.047 g of phenothiazine (0.02 wt.% Of the total amount of charged reagents) and 0.165 g of potassium carbonate (0.07 wt.%) Are loaded into the reactor with the stirrer operating. of the total number of loaded reagents). A vacuum of 0.6 atm is created in the system, the mixture is heated to boiling at a temperature of ~ 80 ° C and boiled. The reaction mass is dried to a residual moisture content of not more than 0.02 mass% for 1.5 hours. After the drying is completed, 0.057 g of sodium borohydride (0.06 wt.% Of alcohol) is added to the reactor and the reaction mixture is boiled without distillate selection for 30 minutes under a vacuum of 0.6 atm. Next, distillate begins to be selected. The vapor temperature in this case gradually decreases to ~ 40 ° C. To maintain the temperature in the reactor ~ 80 ° C, the vacuum is gradually deepened to a value of 0.85-0.9 atm. The end of the reaction is determined by the cessation of the formation of methanol. After completion of the reaction, the excess methyl methacrylate is first distilled off at 80 ° C, gradually deepening the vacuum to ~ 0.95 atm, while the temperature in the reactor rises to 90-100 ° C. Next, the reaction mass is cooled and filtered through a paper filter. The yield of alkyl methacrylates was 97.8%. The dependence of the yield of alkyl methacrylate on the time of the process is presented in the figure.

Example 2. Comparative

94.1 g of molten fatty alcohols of the C12-C18 fraction (average molecular weight 214), 142.2 g of methyl methacrylate, 0.045 g of phenothiazine (0.02% of the total amount of charged reagents) and 2.36 g of potassium carbonate (1% of the total number of charged reagents). A vacuum of 0.6 atm is created in the system, the mixture is heated to a boil and boiled without distillate selection for 30 minutes. Next, distillate begins to be selected. The temperature of the vapor gradually decreases to ~ 40-50 ° C. As the temperature in the reactor rises above 100 ° C, the vacuum is gradually increased to 0.85 atm. The end of the reaction is determined by the cessation of the formation of methanol. After completion of the reaction, excess methyl methacrylate is distilled off, gradually deepening the vacuum to ~ 0.95 atm, while the temperature in the reactor is ~ 100 ° C. Next, the reaction mass is cooled and filtered through a paper filter. The yield of alkyl methacrylates is 94.2%. The dependence of the yield of alkyl methacrylate on the time of the process is presented in the figure.

Example 3

93.8 g of molten fatty alcohols of the C12-C18 fraction (average molecular weight 214), 141.5 g of methyl methacrylate, 0.048 g of phenothiazine (0.02% of the total amount of charged reagents) and 2.37 g of potassium carbonate (1% of the total amount) are loaded into the reactor with the stirrer operating. loaded reagents). A vacuum of 0.6 atm is created in the system, the mixture is heated to a boil and boiled, without distillate being taken for 30 minutes. Next, distillate begins to be selected. The temperature of the vapor gradually decreases to ~ 40-50 ° C. As the temperature in the reactor rises above 100 ° C, the vacuum is gradually increased to 0.8 atm. When the alcohol conversion reaches 50%, the vacuum in the reactor is increased to 0.85-0.9 atm, while the temperature in the reactor decreases to ~ 80 ° C, then sodium borohydride in the amount of 0.012 g (0.013% of the loaded alcohol) is added to the reaction mass. The end of the reaction is determined by the cessation of the formation of methanol. After the completion of the reaction, excess methyl methacrylate is distilled off, gradually deepening the vacuum to ~ 0.95 atm, while the temperature in the reactor rises to 90-100 ° C. Next, the reaction mass is cooled and filtered through a paper filter. The yield of alkyl methacrylates is 98.3%. The dependence of the yield of alkyl methacrylate on the time of the process is presented in the figure.

Example 4

98.5 g of molten fatty alcohols of the C12-C18 fraction (average molecular weight 214), 147.8 g of methyl methacrylate, 0.049 g of phenothiazine (0.02% of the total amount of charged reagents) and 2.46 g of sodium carbonate (1% of the total amount) are loaded into the reactor with the stirrer operating. loaded reagents). A vacuum of 0.6 atm is created in the system, the mixture is heated to a boil and boiled without distillate selection for 30 minutes. Next, distillate begins to be selected. The temperature of the vapor gradually decreases to ~ 40-50 ° C. As the temperature in the reactor rises above 100 ° C, the vacuum is gradually increased to 0.8 atm. When the alcohol conversion reaches 50%, the vacuum in the reactor is increased to 0.85-0.9 atm, while the temperature in the reactor decreases to ~ 80 ° C, then sodium borohydride in the amount of 0.024 g (0.024% of the loaded alcohol) is added to the reaction mixture. The end of the reaction is determined by the cessation of the formation of methanol. After the completion of the reaction, excess methyl methacrylate is distilled off, gradually deepening the vacuum to ~ 0.95 atm, while the temperature in the reactor rises to 90-100 ° C. Next, the reaction mass is cooled and filtered through a paper filter. The yield of alkyl methacrylates is 97.9%.

Example 5

99.1 g of isooctyl alcohol, 148.7 g of methyl methacrylate, 0.05 g of phenothiazine (0.02% of the total amount of charged reagents) and 2.48 g of potassium carbonate (1% of the total number of charged reagents) are loaded into the reactor with the stirrer operating. A vacuum of 0.6 atm is created in the system, the mixture is heated to a boil and boiled without distillate selection for 30 minutes. Next, distillate begins to be selected. The temperature of the vapor gradually decreases to ~ 40-50 ° C. As the temperature in the reactor rises above 100 ° C, the vacuum is gradually increased to 0.8 atm. When the alcohol conversion reaches 40%, the vacuum in the reactor is increased to 0.85-0.9 atm, while the temperature in the reactor decreases to ~ 80 ° C, then sodium borohydride in the amount of 0.011 g (0.011% of the loaded alcohol) is added to the reaction mass. The end of the reaction is determined by the cessation of the formation of methanol. After the completion of the reaction, excess methyl methacrylate is distilled off, gradually deepening the vacuum to ~ 0.95 atm, while the temperature in the reactor rises to 90-100 ° C. Next, the reaction mass is cooled and filtered through a paper filter. The yield of 2-ethylhexylmethacrylate is 98.9%.

Example 6

95.6 g of decyl alcohol, 143.4 g of methyl methacrylate, 0.048 g of phenothiazine (0.02% of the total amount of charged reagents) and 2.39 g of potassium carbonate (1% of the total number of loaded reagents) are loaded into the reactor with the stirrer running. A vacuum of 0.6 atm is created in the system, the mixture is heated to a boil and boiled without distillate selection for 30 minutes. Next, distillate begins to be selected. The temperature of the vapor gradually decreases to ~ 40-50 ° C. As the temperature in the reactor rises above 100 ° C, the vacuum is gradually increased to 0.8 atm. When the alcohol conversion reaches 50%, the vacuum in the reactor is increased to 0.85-0.9 atm, while the temperature in the reactor decreases to ~ 80 ° C, then sodium borohydride in the amount of 0.014 g (0.015% of the loaded alcohol) is added to the reaction mass. The end of the reaction is determined by the cessation of the formation of methanol. After the completion of the reaction, excess methyl methacrylate is distilled off, gradually deepening the vacuum to ~ 0.95 atm, while the temperature in the reactor rises to 90-100 ° C. Next, the reaction mass is cooled and filtered through a paper filter. The yield of decyl methacrylate is 98.4%.

In other examples, the amount of potassium and sodium carbonates added and the alcohol conversion were changed, after which sodium borohydride was added.

A decrease in the amount of added potassium and sodium carbonates less than 0.5 wt.% Of the total amount of loaded reagents led to a decrease in the process speed at the initial stage. With an increase in the amount of potassium and sodium carbonates more than 1.5 wt.% Of the total amount of loaded reagents, the process speed does not change significantly and the filtration stage is complicated.

The introduction of sodium borohydride at an alcohol conversion of less than 40% led to an increase in the residence time of sodium borohydride in the reaction mass, as a result of which the yield of by-products increased and the quality of the alkyl methacrylate deteriorated. The introduction of sodium borohydride after reaching an alcohol conversion of more than 80% led to an increase in the process time and a decrease in its productivity.

In addition, in the examples, the amount of sodium borohydride added was changed. A decrease in the amount of sodium borohydride less than 0.005 wt.% Of the amount of charged alcohols led to a sharp decrease in the rate of transesterification and an increase in the time required to achieve a high yield of alkyl methacrylates. An increase in the number of borohydride more than 0.05 wt.% Of the number of loaded alcohols led to a decrease in the selectivity of the process and a deterioration in the quality of alkyl methacrylate.

As can be seen from the examples, our proposed method allows, in contrast to the prototype, to carry out the process without preliminary drying of the reaction mass, as a result, the process time is reduced and, accordingly, productivity is increased and energy costs are reduced.

Sodium borohydride is added only at the last stage of the process (after reaching the alcohol conversion of 40-80%) in significantly smaller quantities compared to the prototype. This reduces the use of sodium borohydride, simplifies the stage of separation of the catalyst and increases the quality of the commercial product.

Claims (1)

A method of producing alkyl methacrylates by transesterification of methyl methacrylate with alcohols of the general formula C _n H _{2n + 1} OH, where n≥4, in the presence of potassium or sodium carbonate and sodium borohydride, as well as a radical polymerization inhibitor with distillation of the resulting methanol in the form of an azeotrope with methyl methacrylate, characterized in that potassium or sodium carbonate in an amount of 0.5-1.5 wt.% of the total weight of the loaded reagents is used as a catalyst until the alcohol conversion of 40-80% is reached, after which sodium borohydride is introduced into the reaction mass in an amount of 0, 005-0.05 wt.% Of the number of loaded alcohols.

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