CN111517953A

CN111517953A - Production process method for synthesizing methyl methacrylate by methyl acetate and formaldehyde

Info

Publication number: CN111517953A
Application number: CN202010387352.2A
Authority: CN
Inventors: 向家勇; 向能; 李晓峰; 吴婷
Original assignee: Jiangsu Huda Chemical Technology Co ltd
Current assignee: Jiangsu Huda Chemical Technology Co ltd
Priority date: 2020-05-09
Filing date: 2020-05-09
Publication date: 2020-08-11

Abstract

The invention discloses a production process method for synthesizing methyl methacrylate by methyl acetate and formaldehyde, which adopts a gradual reaction and gradual separation mode, two sections of aldol condensation reactions are respectively carried out in two independent reactors, and a multistage high-efficiency rectification separation and purification method is adopted by combining the two sections of aldol condensation reactions, so that the separation of various intermediate products and products is realized, and the product yield is high. The rectification separation circulating material has high purity, reduces the amount of impurities brought into a reaction system, and effectively reduces the occurrence of side reactions. The method has the characteristics of low investment, low raw material cost, mild reaction conditions, high raw material conversion rate, high product yield and less wastewater.

Description

Production process method for synthesizing methyl methacrylate by methyl acetate and formaldehyde

Technical Field

The invention belongs to the technical field of chemical production, and particularly relates to a production process device and a production method of Methyl Methacrylate (MMA).

Background

Methyl methacrylate (MMA for short) is an important chemical raw material and is widely used for organic glass, paint and medical materials. As methods for synthesizing MMA, there are an acetone cyanohydrin method (ACH method), an isobutylene method and an ethylene method. The present propionach method and its improved method are the most important methods for synthesizing MMA, and have high conversion rate. Hydrocyanic acid which is a raw material of an ACH method is a highly toxic dangerous chemical, and the method has the problems of complex process, large investment, high energy consumption and large pollution. With the increasing environmental requirements, the development of this process is limited. The isobutene process uses isobutene in C4 fraction as raw material, firstly, isobutene is oxidized to generate methacrolein, and then methacrolein is oxidized and esterified to generate MMA. The isobutene method has simple process, and avoids the problems of waste acid generated by the ACH method and equipment corrosion. But has the problems of lower yield and higher isobutene cost. The ethylene method is that ethylene and synthetic gas are used as raw materials to generate propionaldehyde, propionaldehyde and formaldehyde are subjected to recondensation reaction to generate methacrylic acid, and the methacrylic acid and methanol are subjected to esterification reaction to generate MMA. At present, the ethylene method is mastered by only a few countries, and the investment cost is too high.

At present, methyl acetate and formaldehyde are used as raw materials, and MMA production through aldol condensation reaction is receiving more and more attention. The research on aldol condensation catalysts and the like by units such as the institute of process engineering of the Chinese academy of sciences, such as CN109999922A, CN109364908A, CN103506107B and the like, makes it possible to produce MMA by taking methyl acetate and formaldehyde as raw materials.

Patent CN104513163A describes a process for producing methyl methacrylate from methyl acetate and formaldehyde. In this patent, the first aldol condensation of methyl propionate and formaldehyde and the second aldol condensation of methyl propionate and formaldehyde are circulated in a fluidized bed. In the reaction process, unreacted methyl acetate and methanol, intermediate products of methyl acrylate and methyl propionate, a product MMA, byproducts of propionic acid, methacrolein and the like enter a rectification system for separation, and an azeotropic system can be formed among multiple components in the substances of the circulation return field reaction, such as the boiling point of methyl acrylate of 80 ℃ and the boiling point of methyl propionate of 79.7 ℃, so that the methyl acetate and the methanol, the intermediate products of methyl acrylate and methyl propionate are difficult to separate. The separated methyl acrylate contains a large amount of methyl propionate, so that the energy consumption in the methyl acrylate hydrogenation process is greatly increased, the equipment size in the hydrogenation process is greatly increased, the equipment investment is increased, the product yield is influenced, and the large-scale industrial production is not facilitated. Furthermore, it is not described how to separate the by-product water produced in the aldol condensation reaction, and the presence of the by-product water is extremely disadvantageous to the forward progress of the reaction and should be separated from the system in time. Therefore, the reaction method adopted by the patent technology is not beneficial to the adjustment of a fluidized bed, influences the conversion rate of raw materials and the yield of products, generates more byproducts and is difficult to obtain high-purity MMA products.

In the prior art, the whole reaction system adopts an internal circulation reaction mode, the types of system substances are various, an azeotropic system (such as methyl acetate and water, methyl acetate and methanol, methyl acrylate and water, methyl propionate and water, methyl acrylate and methanol, MMA and water, MMA and methanol and the like) is formed among various substances, unreacted methyl acetate needs to be separated and returned to the reaction system, and the yield needs to be improved as much as possible in order to reduce the consumption of raw materials. The intermediate products of methyl acrylate and methyl propionate need to be separated for the next reaction, and the purity is required to be higher in order to reduce the occurrence of side reactions. How to improve the reaction conversion efficiency and reduce the occurrence of side reactions to realize the separation of various substances is the key of industrialization of the technology.

Disclosure of Invention

The purpose of the invention is as follows: aiming at the existing problems and defects, the invention aims to provide a production process method for synthesizing methyl methacrylate from methyl acetate and formaldehyde.

The technical scheme is as follows: in order to solve the technical problems, the invention adopts the following technical scheme: a production process method for synthesizing methyl methacrylate by methyl acetate and formaldehyde comprises the following steps:

(1) preheating methyl acetate and formaldehyde serving as reaction raw materials, feeding the preheated methyl acetate and formaldehyde into a first reactor, and carrying out aldol condensation reaction under the action of a catalyst to obtain a reaction product containing methyl acrylate, acetic acid, methanol and acrylic acid;

(2) feeding a reaction product obtained by the reaction into a first rectifying tower for rectification separation, separating an azeotrope of methyl acetate and methanol from the tower top, returning the azeotrope to the first reactor for recycling, and feeding a main material containing methyl acrylate, methanol and formaldehyde obtained from the tower bottom into a second rectifying tower;

(3) performing secondary rectification separation on the material obtained at the bottom of the first rectifying tower in a second rectifying tower, and separating from the top of the tower to obtain an azeotrope containing methyl acrylate, water and methanol; obtaining materials containing methanol, water and formaldehyde at the bottom of the tower, and sending the materials into a third rectifying tower;

(4) performing tertiary rectification separation on the material obtained at the bottom of the second rectifying tower in a third rectifying tower, separating from the top of the tower to obtain 90-95% methanol solution, and obtaining dilute formaldehyde solution at the bottom of the tower;

(5) feeding azeotrope containing methyl acrylate, water and methanol and hydrogen obtained by separation at the top of the second rectifying tower into a second reactor, carrying out hydrogenation reaction under the action of a catalyst to obtain a reaction product containing methyl propionate, carrying out gas-liquid separation on the reaction product to obtain hydrogen and methyl propionate products, and circularly feeding the hydrogen back to the second reactor;

(6) preheating a methyl propionate product obtained by the hydrogenation reaction in the step (5), formaldehyde and methanol, and then sending the preheated methyl propionate product into a third reactor to perform aldol condensation reaction under the action of a catalyst to obtain methyl methacrylate and a byproduct;

(7) feeding methyl methacrylate and a byproduct obtained by aldol condensation reaction in the step (6) into a fourth rectifying tower for rectification separation, obtaining an azeotrope of methyl propionate and methanol at the tower top, and feeding the azeotrope back to a third reactor for cyclic reaction; separating the bottom product by a delayer to obtain a water phase and an organic phase containing MMA and methyl propionate;

(8) rectifying and separating the organic phase obtained in the step (7) in a fifth rectifying tower to obtain over 95% of methyl propionate at the tower top, sending the methyl propionate back to the third reactor through a pipeline, and obtaining crude MMA at the tower bottom;

(9) and (4) sending the crude MMA obtained at the tower bottom in the step (8) into a sixth rectifying tower for rectification again to obtain over 99 percent of MMA product from the tower top and obtain heavy components at the tower bottom.

Preferably, an extraction unit is further arranged between the outlet at the bottom of the fourth rectifying tower and the delayer in the step (7), and products at the bottom of the fourth rectifying tower are extracted by extractant water and then sent to the delayer for layering.

Preferably, in the first reactor in the step (1), the operating conditions of the aldol condensation reaction are as follows: the reaction temperature is 200-500 ℃, the pressure is normal pressure to-5.0 MPa, and the molar ratio of methyl acetate to formaldehyde is 1: 5-5: 1.

Preferably, in the first reactor in the step (1), paraformaldehyde, trioxymethylene or concentrated formaldehyde solution is used as formaldehyde raw material for aldol condensation reaction.

Preferably, the operating conditions in the first rectifying tower in the step (2): the operation pressure is 5-30 KPa, the tower top temperature is 40-60 ℃, and the tower bottom temperature is 60-80 ℃.

Preferably, the operating conditions in the second rectification column in the step (3): the operation pressure is-60 to-30 kPa, the tower top temperature is 50 to 60 ℃, and the tower bottom temperature is 60 to 80 ℃.

As a preferable mode, the hydrogenation reaction in the step (5) is carried out under the following operating conditions: the operating pressure is controlled to be-60 to-30 kPa, the temperature at the top of the tower is 50 to 60 ℃, and the temperature at the bottom of the tower is 60 to 80 ℃; the molar ratio of hydrogen to methyl acrylate is 1: 1-5: 1; the hydrogenation catalyst is SiO₂Or Al₂O₃A catalyst with one or more active components of Ni, Pb or Pt loaded on a carrier.

Preferably, the pore diameter of the catalyst used in the aldol condensation reaction in step (6) is larger than that of the catalyst used in the aldol condensation reaction in step (1).

The main components of the solid catalyst used in the reaction are the same as those of the first fluidized bed catalyst. However, the carbon content of the raw material and impurities is larger than that of the first fluidized bed, so that the catalyst is easier to deposit carbon. Therefore, the aperture of the catalyst is larger than that of the first fluidized bed catalyst, so that the carbon deposition resistance of the catalyst is improved, and the service life of the catalyst is prolonged.

The catalyst used for the aldol condensation reaction is a bifunctional catalyst with two active centers of acid and base. The basic active center Cs plays a major role, has a higher catalyst activity, but has a poorer selectivity. The acidic center P acts as a promoter and contributes to the increase in the selectivity of the aldol condensation reaction. The active component Cs is one of cesium acetate, cesium nitrate, cesium sulfate or cesium carbonate, the active center P is ammonium monohydrogen phosphate or ammonium monohydrogen phosphate, and the active center P is loaded on SiO₂、TiO₂、Al₂O₃And ZSM-5, and an auxiliary agent such as W, Zr, Fe, Cu or Ce.

Preferably, the first reactor and the third reactor are fluidized bed reactors or fixed bed reactors.

Preferably, the rectification separation in the steps (7) to (9) adopts the following operating conditions:

the fourth rectifying tower operating conditions are as follows: the operation pressure is 5-30 kPa, the tower top temperature is 50-70 ℃, and the tower bottom temperature is 60-80 ℃;

the fifth rectifying tower operating conditions are as follows: the operation pressure is-80 to-70 kPa, the tower top temperature is 40 to 50 ℃, and the tower bottom temperature is 65 to 75 ℃;

the sixth rectifying tower operating conditions are as follows: the operation pressure is-90 to-80 kPa, the tower top temperature is 40 to 50 ℃, and the tower bottom temperature is 65 to 75 ℃.

Has the advantages that: compared with the prior patent process flow, the method has the following characteristics:

firstly, the aldol condensation reaction of methyl acetate and formaldehyde and the aldol condensation reaction of methyl propionate and formaldehyde are respectively carried out in two fluidized beds or fixed bed reactors, which is different from the prior patents (CN104513163A and CN109232247A) that the two aldol condensation reactions are carried out in one reactor, so that the reaction process conditions can be adjusted according to different reaction conditions, which is more beneficial to improving the reaction conversion rate and reducing the occurrence of side reactions. More importantly, the two aldol reactions are respectively carried out in two independent reactors, thereby avoiding the recycling of byproducts of the two aldol reactions and reducing the difficulty of subsequent rectification and purification, and further obtaining the MMA product with higher purity.

In addition, the aldol condensation process of methyl acetate and methyl propionate uses an acid-base bifunctional catalyst, the basic active center plays a main role, and the acidic center plays a promoting role. Can inhibit the occurrence of side reaction and improve the selectivity of catalytic reaction. The methyl acrylate hydrogenation is carried out at a lower temperature and pressure, and unreacted hydrogen is recycled.

Aiming at the purification of high-purity MMA, the invention adopts a multi-stage high-efficiency rectification separation and purification method by combining two-stage aldol condensation reaction, realizes the separation of various intermediate products and products, and has high product yield. The rectification separation circulating material has high purity, reduces the amount of impurities brought into a reaction system, and effectively reduces the occurrence of side reactions.

Drawings

FIG. 1 is a schematic process flow diagram of the production process for synthesizing methyl methacrylate from methyl acetate and formaldehyde.

The system comprises a preheater 1, a first reactor 2, a first rectifying tower 3, a second rectifying tower 4, a third rectifying tower 5, a second reactor 6, a gas-liquid separator 7, a third reactor 8, a fourth rectifying tower 9, a delayer 10, a fifth rectifying tower 11, a sixth rectifying tower 12 and a circulating fan 13.

Detailed Description

The present invention is further illustrated by the following figures and specific examples, which are to be understood as illustrative only and not as limiting the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalent modifications thereof which may occur to those skilled in the art upon reading the present specification.

As shown in FIG. 1, the process flow is divided into three steps, the first step is a reaction of formaldehyde and methyl acetate to produce methyl acrylate, the second step is a hydrogenation of methyl acrylate to produce methyl propionate, and the third step is a reaction of methyl propionate and formaldehyde to produce MMA.

(1) First unit

Methyl acetate, formaldehyde and circulating materials enter a reactor after being preheated and vaporized, and are subjected to aldol condensation reaction under the action of a catalyst to generate methyl acrylate. The main reaction and side reaction of the process are as follows:

CH₃COOCH₃+HCHO→CH₂＝CHCOOCH₃+H₂O

CH₃COOCH₃+H₂O→CH₃COOH+CH₃OH

CH₂＝CHCOOCH₃+H₂O→CH₂＝CHCOOH+CH₃OH

reaction temperature range: 200 to 500 ℃. Reaction pressure range: normal pressure is-5.0 MPa. The molar ratio of methyl acetate to formaldehyde is 1: 5-5: 1.

The presence of water affects the activity of the catalyst, and side reactions such as methyl acetate hydrolysis and methyl acrylate hydrolysis occur, while increasing the cost of subsequent separation, thereby controlling the water content in the raw material. The molar ratio of methyl acetate to water is 1:1 to 10: 1. The raw material formaldehyde is paraformaldehyde, trioxymethylene or concentrated formaldehyde solution.

The raw materials are added with methanol, so that the hydrolysis side reaction can be inhibited, and the side reaction can be prevented, wherein the molar ratio of the methyl acetate to the methanol is 1: 5-5: 1.

The catalyst used for the aldol condensation reaction is a bifunctional catalyst with two active centers of acid and base. The basic active center Cs plays a major role, has a higher catalyst activity, but has a poorer selectivity. The acidic center P acts as a promoter and contributes to the increase in the selectivity of the aldol condensation reaction. Active component is loaded on SiO₂、TiO₂、Al₂O₃ZSM-5, etc. And (3) adding auxiliaries such as W, Zr, Fe, Cu, Ce and the like to increase the stability of the catalyst and prolong the service life of the catalyst.

The reactor is a fixed bed or a fluidized bed. After a period of reaction, the catalyst can deposit carbon, which affects the service life of the catalyst and needs to be regenerated. When the reactor is a fixed bed, a plurality of fixed beds are arranged, and after the catalyst in one reactor is deactivated, the catalyst is regenerated and switched to other reactors for reaction. The particle size of the fixed bed catalyst is 1mm-6 mm.

When the reactor is a fluidized bed, only one fluidized bed is needed, and the catalyst can be continuously regenerated. The feeding material enters from the bottom of the fluidized bed, starts to react after contacting with the catalyst, continuously flows upwards, enters the cyclone separator, the gas with the separated catalyst comes out from the top of the fluidized bed, the catalyst enters the regenerator from the regenerated catalyst pipe, and the catalyst returns to the reactor through the regenerated catalyst pipe after being regenerated in the regenerator. The particle size of the fluidized bed catalyst is 0.02mm-0.5 mm.

The carbon-deposition deactivated catalyst is regenerated in the regenerator, and the regenerated gas may be air or oxygen. The catalyst regeneration temperature is 500-650 ℃, and the catalyst regeneration time is 1-10 h.

And (3) the product after the reaction passes through a first rectifying tower, azeotrope of methyl acetate and methanol is separated from the tower top and returns to the first reactor for cyclic utilization, and the material at the tower bottom is sent to a second rectifying tower. The azeotrope of methyl acrylate and water and a small amount of methanol are obtained from the top of the second rectifying tower, and the product at the bottom of the second rectifying tower is sent to a third rectifying tower. And (3) recovering the methanol with the concentration of 90-95% at the top of the third rectifying tower, sending the methanol to a methanol storage tank, recovering the formaldehyde solution obtained at the bottom of the third rectifying tower, and sending the recovered wastewater to a wastewater treatment device. The first rectifying tower is operated under normal pressure, and the second rectifying tower and the third rectifying tower are operated under reduced pressure.

The first rectifying tower adopts a partial condenser or a side line with gas phase extraction, and the material returns to the reactor in a gas phase, so that the energy consumption in the process of tower top condensation or preheating is reduced. The rectifying tower adopts a plate tower or a packed tower.

(2) Second unit

Preheating 80-95% concentration methyl acrylate and hydrogen recovered by rectification, then feeding the preheated methyl acrylate and hydrogen into a hydrogenation reactor, hydrogenating the methyl acrylate to generate methyl propionate, cooling and carrying out gas-liquid separation on materials at the outlet of the hydrogenation reactor, and recycling the hydrogen. The reaction of the process is as follows:

CH₂＝CHCOOCH₃+H₂→CH₃CH₂COOCH₃

CH₂＝CHCOOH+H₂→CH₃CH₂COOH

reaction temperature range: 80-300 ℃. Reaction pressure range: normal pressure is-5.0 MPa. The hydrogenation catalyst active component is one of Ni, Pb and Pt, and the carrier is SiO₂Or Al₂O₃。

The molar ratio of hydrogen to methyl acrylate is 1:1 to 5: 1.

The reactor is a fixed bed. The feeding is gas-liquid two-phase, and a gas distributor and a liquid distributor are arranged in the reactor to ensure that the gas-liquid two-phase is uniformly distributed.

The reactor is provided with a jacket or a tube nest, and circulating water is introduced into the jacket and the tube nest for regulating the temperature of the reactor.

(3) Third unit

After hydrogenation, 80-95% of methyl propionate, formaldehyde and circulating material are obtained, preheated and then enter a reactor, and are subjected to aldol condensation reaction under the action of a catalyst to generate methyl acrylate. The main reactions of the process are:

CH₃CH₂COOCH₃+HCHO→CH₂＝C(CH₃)COOCH₃+H₂O

CH₃CH₂COOCH₃+H₂O→CH₃CH₂COOH+CH₃OH

the molar ratio of methyl propionate to formaldehyde is 1: 5-5: 1.

Reaction temperature range: 200 to 500 ℃. Reaction pressure range: normal pressure to 5.0 MPa.

The molar ratio of methyl propionate to water is 1:1 to 10: 1. The molar ratio of methyl propionate to methanol is 1: 5-5: 1.

The main component of the solid catalyst used in the reaction is the same as the composition of the first fluidized bed catalyst. However, the carbon content of the raw material and impurities is larger than that of the first fluidized bed, so that the catalyst is easier to deposit carbon. Therefore, the aperture of the catalyst is larger than that of the first fluidized bed catalyst, so that the carbon deposition resistance of the catalyst is improved, and the service life of the catalyst is prolonged. Preferably, when the third reactor adopts a fixed bed, the particle size of the catalyst is 5mm-15 mm; when the third reactor adopts a fluidized bed, the particle size of the catalyst is 0.5mm-1.5 mm.

And feeding the product after reaction into a fourth rectifying tower, separating an azeotrope of methyl propionate and methanol from the tower top, returning the azeotrope to the reactor for recycling, and feeding the material at the tower bottom into a delayer. Separating into oil phase and water phase, wherein the oil phase contains MMA and methyl propionate. The material phase balance is broken through the fourth rectifying tower, so that the residual organic phase and water can be separated by a layering method. And (3) feeding the oil phase into a fifth rectifying tower, obtaining over 95 percent of methyl propionate at the tower top, returning the methyl propionate to the reactor, and obtaining crude MMA at the tower bottom. And (3) feeding the crude MMA to a sixth rectifying tower, obtaining over 99 percent of MMA product at the tower top, and feeding heavy carbon components at the tower bottom to incineration treatment.

The fourth rectifying tower adopts normal pressure operation, the fifth rectifying tower and the sixth rectifying tower adopt reduced pressure operation, and the rectifying tower adopts a plate tower or a packed tower.

And (3) further improving the purity of the product, adding an extraction unit at the bottom outlet of the fourth rectifying tower, using an extracting agent as water to dissolve a small amount of ester and alcohol water-soluble substances in the material in water, further separating, and feeding the water-insoluble MMA into the fifth rectifying tower for further refining, wherein the ratio of the extracting agent to the material is preferably 1: 10-1: 2.

Specific example 1:

raw materials are as follows: formaldehyde: the methanol is prepared according to the molar ratio of 1:1:2, the raw material is preheated to 300 ℃ and then enters a first fluidized bed, and the first fluidized bed is filled with SiO₂A supported Cs catalyst. At the temperature of 350 ℃, the pressure of 0.12MPa and the space velocity of 2.0h^-1The reaction is carried out under the condition that the catalyst continuously flows from the fluidized bed to the regenerator, the regenerator is at the temperature of 550 ℃, the pressure is 0.12MPa, the regeneration gas is air, and the reaction time is 3.0h^-1Burning carbon to regenerate under the condition, and returning the regenerated catalyst to the first fluidized bed. And (3) cooling and separating the product at the outlet of the first fluidized bed to obtain methyl acrylate, and recycling unreacted raw materials to the first fluidized bed. The methyl acrylate obtained by reaction and separation and hydrogen enter a hydrogenation reactor according to the molar ratio of 1:3, the reaction temperature is 100-120 ℃, the pressure is 1.0MPa, and the propylene obtained by hydrogenationAcid methyl ester. According to the weight ratio of methyl propionate: formaldehyde: the methanol is prepared according to the molar ratio of 1:1:2, and is preheated and then sent into a third reactor, and the process conditions of the third reactor are the same as those of the first fluidized bed. Separating the product obtained from the third reactor to obtain MMA, and returning the unreacted material to the fluidized bed for secondary recycling.

The conversion of methyl acetate in the first fluidised bed was 33% and the selectivity to methyl acrylate 93%. The conversion of methyl propionate in the third reactor was 30% with 96% selectivity to MMA.

Specific example 2:

raw materials are as follows: formaldehyde: the methanol is prepared according to the molar ratio of 1:3:2, the raw material is preheated to 300 ℃ and then enters a first fluidized bed, and the first fluidized bed is filled with SiO₂A supported Cs catalyst. At the temperature of 350 ℃, the pressure of 0.12MPa and the space velocity of 2.0h^-1The reaction is carried out under the conditions. The catalyst continuously flows from the fluidized bed to the regenerator, the regenerator is at the temperature of 550 ℃, the pressure is 0.12MPa, the regeneration gas is air, and the reaction time is 3.0h^-1Burning carbon to regenerate under the condition, and returning the regenerated catalyst to the first fluidized bed. And (3) cooling and separating the product at the outlet of the first fluidized bed to obtain methyl acrylate, and recycling unreacted raw materials to the first fluidized bed. The methyl acrylate obtained by reaction and separation and hydrogen enter a hydrogenation reactor according to the molar ratio of 1:2, the reaction temperature is 80-110 ℃, the pressure is 1.0MPa, and the methyl propionate is obtained by hydrogenation. According to the weight ratio of methyl propionate: formaldehyde: the methanol is prepared according to the molar ratio of 1:1:2, and is preheated and then sent into a third reactor, and the process conditions of the third reactor are the same as those of the first fluidized bed. Separating the product obtained from the third reactor to obtain MMA, and returning the unreacted material to the fluidized bed for secondary recycling.

The conversion of methyl acetate in the first fluidised bed was 35% and the selectivity to methyl acrylate was 90%. The conversion of methyl propionate in the third reactor was 35% with a selectivity for MMA of 95%.

Specific example 3:

raw materials are as follows: formaldehyde: the methanol is prepared according to the molar ratio of 2:1:1.5, the raw material is preheated to 300 ℃ and then enters a first fluidized bed, and the first fluidized bed is filled with SiO₂A supported Cs catalyst. At the temperature of 350 ℃, the pressure of 0.12MPa and the space velocity2.0h^-1The reaction is carried out under the conditions. The catalyst continuously flows from the fluidized bed to the regenerator, the regenerator is at the temperature of 550 ℃, the pressure is 0.12MPa, the regeneration gas is air, and the reaction time is 3.0h^-1Burning carbon to regenerate under the condition, and returning the regenerated catalyst to the first fluidized bed. And (3) cooling and separating the product at the outlet of the first fluidized bed to obtain methyl acrylate, and recycling unreacted raw materials to the first fluidized bed. The methyl acrylate obtained by reaction and separation and hydrogen enter a hydrogenation reactor according to the molar ratio of 1:5, the reaction temperature is 120-150 ℃, the pressure is 1.0MPa, and the methyl propionate is obtained by hydrogenation. According to the weight ratio of methyl propionate: formaldehyde: the methanol is prepared according to the molar ratio of 1:1:2, and is preheated and then sent into a third reactor, and the process conditions of the third reactor are the same as those of the first fluidized bed. Separating the product obtained from the third reactor to obtain MMA, and returning the unreacted material to the fluidized bed for secondary recycling.

The conversion of methyl acetate in the first fluidised bed was 35% and the selectivity to methyl acrylate was 95%. The conversion of methyl propionate in the third reactor was 27% with a selectivity for MMA of 91%.

Specific example 4:

raw materials are as follows: formaldehyde: the methanol is prepared according to the molar ratio of 2:5:1, the raw material is preheated to 300 ℃ and then enters a first fluidized bed, and the first fluidized bed is filled with SiO₂A supported Cs catalyst. At the temperature of 350 ℃, the pressure of 0.12MPa and the space velocity of 2.0h^-1The reaction is carried out under the conditions. The catalyst continuously flows from the fluidized bed to the regenerator, the regenerator is at the temperature of 550 ℃, the pressure is 0.12MPa, the regeneration gas is air, and the reaction time is 3.0h^-1Burning carbon to regenerate under the condition, and returning the regenerated catalyst to the first fluidized bed. And (3) cooling and separating the product at the outlet of the first fluidized bed to obtain methyl acrylate, and recycling unreacted raw materials to the first fluidized bed. The methyl acrylate obtained by reaction and separation and hydrogen enter a hydrogenation reactor according to the molar ratio of 1:3, the reaction temperature is 160-180 ℃, and the methyl propionate is obtained by hydrogenation under the normal pressure condition. According to the weight ratio of methyl propionate: formaldehyde: the methanol is prepared according to the molar ratio of 1:1:2, and is preheated and then sent into a third reactor, and the process conditions of the third reactor are the same as those of the first fluidized bed. Separating the product obtained from the third reactor to obtain MMA, and returning the unreacted material to the fluidized bed for secondary recycling.

The conversion of methyl acetate in the first fluidised bed was 27% and the selectivity for methyl acrylate was 89%. The conversion of methyl propionate in the third reactor was 29% with a selectivity for MMA of 92%.

Claims

1. A production process method for synthesizing methyl methacrylate by methyl acetate and formaldehyde is characterized by comprising the following steps:

2. The production process of synthesizing methyl methacrylate from methyl acetate and formaldehyde according to claim 1, wherein: and (4) in the step (7), an extraction unit is also arranged between the outlet at the bottom of the fourth rectifying tower and the delayer, and products at the bottom of the fourth rectifying tower are extracted by extractant water and then are sent into the delayer for layering.

3. The production process of synthesizing methyl methacrylate from methyl acetate and formaldehyde according to claim 1, wherein: in the first reactor in the step (1), the operating conditions of the aldol condensation reaction are as follows: the reaction temperature is 200-500 ℃, the pressure is normal pressure to-5.0 MPa, and the molar ratio of methyl acetate to formaldehyde is 1: 5-5: 1.

4. The production process of synthesizing methyl methacrylate from methyl acetate and formaldehyde according to claim 1, wherein: in the first reactor in the step (1), formaldehyde raw materials for aldol condensation reaction adopt paraformaldehyde, trioxymethylene or concentrated formaldehyde solution.

5. The production process of synthesizing methyl methacrylate from methyl acetate and formaldehyde according to claim 1, wherein: operating conditions in the first rectifying tower in the step (2): the operation pressure is 5-30 KPa, the tower top temperature is 40-60 ℃, and the tower bottom temperature is 60-80 ℃.

6. The production process of synthesizing methyl methacrylate from methyl acetate and formaldehyde according to claim 1, wherein: operating conditions in the second rectifying tower in the step (3): the operation pressure is-60 to-30 kPa, the tower top temperature is 50 to 60 ℃, and the tower bottom temperature is 60 to 80 ℃.

7. The production process of synthesizing methyl methacrylate from methyl acetate and formaldehyde according to claim 1, wherein: the hydrogenation reaction in the step (5) is carried out under the following operating conditions: the operating pressure is controlled to be-60 to-30 kPa, the temperature at the top of the tower is 50 to 60 ℃, and the temperature at the bottom of the tower is 60 to 80 ℃; the molar ratio of hydrogen to methyl acrylate is 1: 1-5: 1; the hydrogenation catalyst is SiO₂Or Al₂O₃A catalyst with one or more active components of Ni, Pb or Pt loaded on a carrier.

8. The production process of synthesizing methyl methacrylate from methyl acetate and formaldehyde according to claim 1, wherein: the aperture of the catalyst adopted in the aldol condensation reaction in the step (6) is larger than that of the catalyst for the aldol condensation in the step (1).

9. The production process of synthesizing methyl methacrylate from methyl acetate and formaldehyde according to claim 1, wherein: the first reactor and the third reactor are fluidized bed reactors or fixed bed reactors.

10. The production process of synthesizing methyl methacrylate from methyl acetate and formaldehyde according to claim 1, wherein: the rectification separation in the steps (7) to (9) adopts the following operating conditions: