RU2497802C1 - Method of obtaining dimethylaminoethylacrylate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to improved method of obtaining aminoacrylates (dimethylaminoethylacrylate and dimethylaminoethylmethacrylate) by transesterification of methylacrylate or methylmethacrylate by dimethylethanolamine at increased temperature in presence of Ti-containing liquid-phase catalyst. Synthesis is realised in two successive reactors: first, which works without methanol distillation, to conversion of DMAE 30-40% and second, from which distillation of methanol is carried out continuously to complete conversion of initial DMAE, with recycle of unreacted acrylate into first reactor and recycle of DMAE into second reactor.

EFFECT: method makes it possible to simplify reactor unit, increase specific productivity with preservation of high selectivity of process.

1 dwg, 2 tbl

Description

The invention relates to a method for producing dialkylaminoethyl esters of acrylic acid, and in particular to a method for producing dimethylaminoethyl acrylate (DMAEA).

DMAEA is used as a raw material component for the production of water-soluble polymers having a wide range of applications as flocculants, antistatic agents, extractants, etc.

DMAEA is known to be obtained by transesterification of methyl acrylate with dimethylethanolamine (DMEA) in the presence of a liquid phase transesterification catalyst (kt).

As a result, the target aminoacrylate and a reaction byproduct, methanol, are formed:

The reaction is reversible and in order to increase the degree of conversion of the starting reagents to the target product, the methanol formed is removed from the reaction mixture by distillation in the form of an azeotrope with the starting methyl (meth) acrylate [EP 0906902 B1, publ. 02/28/2002; US 6977310 B2, publ. December 20, 2005].

As a catalyst for transesterification, it is preferable to use neutral catalysts - alkoxy derivatives of titanium [US 4281175 publ. 07.28.1981, US 6977310 B2, publ. December 20, 2005] or tin [US 4301297, publ. 11/17/1981; US 7078560 B2, publ. 07/18/2006]. The authors of the method [US 2009/0253930 A1, publ. 8.10.2009] comparative tests of the activity and selectivity of a number of transesterification catalysts were carried out under the same conditions. The best results were obtained using the catalyst Ti (DMEA) ₄ - tetra-N, N-dimethylaminoethoxy titanate.

In addition to the target reaction, side processes occur: reversible transesterification reactions and irreversible double-bond acrylate and DMAEA reactions — in this case, products are formed that are referred to in the literature as “Michael reaction products”. The rate of the main and adverse reactions depends on both the catalyst used and the synthesis conditions. Therefore, the issue of hardware design of the reactor unit to a large extent determines the selectivity and speed of the target reaction, as well as the volume of investments in the organization of industrial production.

It is known that the transesterification reaction is carried out in an esterizer - a capacitive reactor with stirring, connected in the gas phase to a distillation column to remove side alcohol, at an elevated temperature (100-140 ° С), atmospheric or reduced pressure (400-800 mbar), in the presence of homogeneous catalyst and polymerization inhibitor. The starting methyl (meth) acrylate is fed in 1 ÷ 3-fold molar excess to dimethylethanolamine [EP 0906902 B1, publ. 08/28/2002; US 6977310 B2, publ. December 20, 2005, US 7078560 B2, publ. 07/18/2006].

It is possible to carry out the transesterification process in a reactor column [US 2009/0253930 A1, publ. 10/08/2009]. This hardware option is used if an auxiliary solvent, dibenzyl ether, diethylene glycol dibutyl ether, etc., is added to the reaction mixture. to prevent the formation of an azeotrope, methyl (meth) acrylate - methanol. The method allows to distill off methanol with a methyl (meth) acrylate content of 1-2%. The main disadvantage of this method is that. that the auxiliary solvent stream accounts for ~ 60% of the total reaction mixture stream.

The authors of the method [US 7294240 B2, publ. November 13, 2007] propose to transesterify lower alkyl (ethyl, butyl) (meth) acrylates with dimethylethanolamine in the presence of titanium alcoholate in one reactor or cascade of reactors connected to at least one distillation column at a temperature of 100-130 ° С, pressure 400-600 mbar. In the case of a cascade of reactors, the temperature in them may be the same or different, but should preferably increase from the previous reactor to the next within the specified range.

A preferred embodiment of the method is to conduct the process in at least one reactor connected to a column (reactor-ester), from which the reaction mixture enters a post-reactor connected in the gas phase to either the previous reactor or the column of the previous reactor-ester.

The temperature in the postreactor should be 1-10 ° C higher than in the main reactor.

The residence time in the reaction zone (reactor-postreactor) is 1.5-3 hours.

The distillation column connected to the reactor has 10-30 theoretical plates, the reflux number is 7 ÷ 15. The process is carried out in the presence of at least one polymerization inhibitor (phenothiazine, hydroquinone, p-methoxyphenol, etc.).

Known continuous method for producing DMAEA [US 7268251 B2, publ. 09/11/2007] - a prototype.

The method includes:

- the stage of preparation of the catalyst Ti (DMEA) _{4 by} transesterification of lower titanium alcoholate with dimethylethanolamine;

- the stage of transesterification of methyl (meth) acrylate with dimethylethanolamine;

- distillation stages of the selection of the target ether (distillation of methyl (meth) acrylate, separation of the catalyst, separation of DMAEA - raw, purification of the target ether, treatment of bottoms).

The transesterification of methyl (meth) acrylate with dimethylethanolamine was carried out by the authors in two successive forced or natural circulation reactors connected through a gas phase to distillation columns.

The synthesis is carried out at a temperature of 100-130 ° C, a pressure of 400-600 mbar, a molar ratio of methyl (meth) acrylate / DMEA 1 ÷ 4: 1 in the presence of a homogeneous catalyst obtained in the preliminary stage, and a polymerization inhibitor. The methanol content in the reaction mixture is 0.01-0.1% by weight. The total stay is 2-4 hours. Heating is carried out by external or built-in heat exchangers. The reaction zone is continuously purged with a stream of inert gas (nitrogen, nitrogen / air, air, etc.).

The columns used to remove methanol, connected to the reactors, can be packed or disk-shaped (10-30 tons), equipped with tubular or plate capacitors. The resulting methanol is removed through the top of the column with part of the starting methyl (meth) acrylate. Reflux number 5 ÷ 15.

From the second reactor, the reaction mixture enters an intermediate tank. The residence time of the reaction mixture in this tank is 0.5-1.5 hours, a temperature of 50-140 ° C. Part of the reaction mixture (10-75%) from this tank is sent to the next stage of the process - distillation of methyl (meth) acrylate. Another part of the reaction mixture (25-90%) is recycled to the reactors, preferably to the second reactor. The vessel is connected in the gas phase to the second reactor or its column, i.e. in fact, it is the third reactor (pre-heater). This allows you to increase the degree of conversion of DMEA and more completely remove from the reaction mixture the formed methanol.

The azeotrope driven over the top of the columns contains 20-40% methanol, 60-80% metal (meth) acrylate and not more than 0.3% DMEA. The resulting azeotrope can be sent to the production of methyl (meth) acrylate without further purification.

The main disadvantage of this method is that its industrial implementation is associated with the need to use large-volume ether-reactors (to achieve complete conversion, the volume of the mixing reactor tends to infinity). Therefore, they usually work on incomplete conversion, unreacted raw materials are separated from the reaction mixture and returned to the process. In addition, the reactor unit is organized in the form of two or more consecutive etherifiers (in the prototype there are three). This allows you to reduce the total volume of the reactor unit, however, it greatly increases the cost of equipment and complicates the control system of the reactor unit, including synthesis and rectification.

An alternative way of organizing the reactor assembly, which can significantly reduce the reactor volume — one displacement reactor — is not suitable for this reaction, since without the distillation of methanol, the proportion of adverse reactions leading to a decrease in selectivity increases.

The aim of the present invention is to reduce the volume of the reactor unit, simplifying its design while maintaining high selectivity of the synthesis.

The proposed solution includes a cascade of two types of reactors, which makes it possible to take advantage of both types of reactors and reduce the role of their inherent disadvantages.

This goal is achieved by the continuous catalytic liquid-phase synthesis of DMAEA from acrylate, which is present in excess, and DMEA in two successive reactors: in the first reactor of the displacement type, the synthesis is carried out without distillation of methanol to the conversion of DMEA 30-40%, in the second - a mixing reactor equipped with distillation a column for distillation of methanol, a complete conversion of DMEA from the 1st reactor is carried out.

The figure shows a schematic diagram of the implementation of the method.

The method is carried out as follows: the feed streams - methyl acrylate, dimethylethanolamine and a Ti-containing catalyst are fed into the displacement reactor (item 1) (for example, a partitioned column apparatus) at a rate that ensures DMEA conversion of 30-40% at a temperature in the reactor of 100-110 ° C, the molar ratio of the starting methyl acrylate and DMEA is 2-3, the content of the P-containing catalyst in the reaction mixture is 0.5-2%.

A study of the kinetic characteristics of the target and side reactions showed that the use of a displacement reactor in the first stage of synthesis, carried out far from equilibrium and at temperatures favoring the prevalence of the rate of the target reaction over side reactions, allows one to have a high selectivity of the process. Under these synthesis conditions, the selectivity is ≥98%.

The reaction mixture leaving the first reactor (pos. 1) is fed into the mixing reactor — an ester (pos. 2) —a capacitive apparatus with forced or natural mixing equipped with a distillation column (pos. 3). The temperature in the ester is 100-120 ° C. The methanol released during the reaction is continuously distilled off together with part of the acrylate. Due to this, the target reaction is accelerated and side reactions involving methanol are suppressed.

A combined reaction stream containing unreacted DMEA from the first reactor, plus a stream recycled from the separation system of the reaction mixture, is fed to the inlet of the second reactor. In the second reactor, the complete conversion of DMEA coming from the 1st reactor is achieved, but the conversion to the total DMEA flow, including DMEA recycling, is 50-70%.

The reaction mixture containing DMAEA, starting acrylate, DMEA and 1-2% by-products is fed to the separation. Unreacted raw materials are recycled to synthesis. A commercial product is isolated by highly efficient distillation. Methyl acrylate is recycled mainly to a displacement reactor; DMEA is recycled to a mixing reactor. This separation is associated with the characteristics of the reactions in two types of reactors - mixing and displacement. The return flow of DMEA always contains a certain amount of DMAEA - up to 20% by weight, because the column for separating a pair of components of DMEA - DMAEA always works in the mode of maximum exhaustion of DMEA from bottoms liquid. This is due to the increased demand for quality of the target product. In commercial DMAEA, the content of DMEA should not exceed 0.01% of the mass. Recycling of DMEA with an admixture of DMAEA into the 1st reactor operating without methanol distillation leads to a decrease in the selectivity of the process due to the occurrence of side reactions involving DMAEA. Therefore, recycling DMEA in the claimed method is carried out only in the mixing reactor.

In comparison with the prototype of the proposed method has the following distinctive features:

- the method is carried out in two serial devices: the first reactor of the displacement type without distillation of methanol and the second reactor of the mixing type, equipped with a distillation column for distillation of methanol (in the prototype, 2 (3) mixing reactors equipped with two distillation columns for distillation of methanol) ;

- DMEA conversion in the first apparatus is 30-40% (in the prototype in the first reactor, DMEA conversion is up to 55%);

- recycling of methyl acrylate is carried out in the first displacement apparatus, DMEA is recycled to the mixing apparatus (in the prototype, all recycled components are fed to the beginning of the process).

The proposed solution has the following advantages.

1. The decrease in the volume of the reactor node:

with the same production capacity having similar synthesis parameters, the volume of the reactor zone by the proposed method is ~ 20% less than by the prototype.

2. The first stage reactor according to the proposed method is a simple column apparatus without distillation column. The reactor unit, consisting of a column apparatus and one ester, requires significantly less investment, provides stability when using simple control systems.

The laboratory setup for the synthesis process is presented in the figure. The starting materials methyl acrylate, dimethylethanolamine and a tetra-N, N-dimethylaminoethoxy titanate catalyst are fed continuously to the first cascade reactor (item 1), an extrusion apparatus, which is a thermostatic glass tube with a diameter of 5 mm and a length of 70 cm, the temperature in the reactor is 100-110 ° С, pressure - equilibrium for a given composition and temperature. The reaction mixture from the reactor (item 1) enters the reactor-ester (item 2) with a cube volume of 7000 ml, the temperature in the reactor (item 2) is 100-115 ° C. Methanol is distilled off from the reactor (item 2) and, in a mixture with methyl acrylate distillate, is collected in the upper part of the over-reactor column (item 3). The reaction mixture from the 2nd reactor, containing MA, DMEA, DMAEA and a catalyst, enters the separation system, where, after separation of the recyclable raw materials: DMEA and MA, DMAEA and the catalyst are isolated, which can also be recycled to the beginning of the process. The MA recycling is carried out in the reactor (pos. 1), the DMEA recycling is carried out in the reactor (pos. 2).

Installation for implementing the prototype method consists of two successive mixing reactors with distillation columns, such as pos.2 and pos.3 in the figure. The volume of the first reactor according to the claimed method is 1.5 liters. With smaller volumes of this apparatus, it is impossible to provide a conversion of> 30% in the given synthesis parameters. The volume of the 2nd apparatus is 7 liters. Both recycles - MA and DMEA - are carried out in the 1st reactor.

Table 1 shows the results of laboratory experiments according to the claimed method and the prototype method, and their comparison with the calculated data to demonstrate the adequacy of the mathematical model by which both laboratory experiments and the calculation of equipment for industrial production of DMAEA were calculated according to the claimed method and method prototype.

The calculation of reactor 1 for the claimed method was carried out according to the model of the ideal displacement reactor (RIV), the calculation of reactor 2 and the prototype reactors was calculated according to the model of the ideal mixing reactor (RIS) combined with a distillation column to distill the methanol - methacrylate azeotrope. The kinetic characteristics of the main and adverse reactions are determined by special experiments. Experiments 1, 3, 4, 5 and 7 demonstrate an experiment according to the claimed method within the claimed parameters. Rows 1 ^a , 3 ^a , 4 ^a , 5 ^a and 7 ^a show the calculated data for these experiments.

Experiments 2, 6, 8 demonstrate the results of experiments by the prototype method, lines 2 ^a , 6 ^a , 8 ^a are the calculation results for these experiments. Comparison of experimental and calculated data confirms the adequacy of the model.

Table 2 shows the results of calculations of industrial reactor units according to the claimed method and the prototype method. The volume of the reactor unit by the prototype method is ~ 20% more than by the claimed method.

Equipment for industrial synthesis of DMAEA according to the claimed method is much simpler - the 1st reactor is a column, the 2nd reactor is a capacity in a distillation column. The prototype method: 2 capacitive apparatus with distillation columns, which requires both large investments in the apparatus and a more complex process control system.

Claims (1)

A method for the production of aminoacrylates (dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate) by transesterification of methyl acrylate or methyl methacrylate with dimethylethanolamine at an elevated temperature in the presence of a Ti-containing liquid phase catalyst, characterized in that the synthesis is carried out in two successive reactors: the first, which works without distillation of 30% methanol; the second, from which methanol is continuously distilled off, until the initial DMEA is completely converted, with unreacted acrylate recycled to the first reaction p DMEA and recycled into the second reactor.