Dimethyl maleate reactive distillation production method and device based on structured catalytic filler and application

Abstract

The invention belongs to the technical field of chemical organic solvent production, and discloses a dimethyl maleate reactive distillation production method and device based on structured catalytic filler and application. The device comprises a reactive distillation tower, a distillation tower, a raw material tank, a first reboiler, a second reboiler, a first condenser, a second condenser, a first reflux tank, a second reflux tank, a first product tank, a second product tank, a third product tank, a feeding pump, a first extraction pump and a second extraction pump. According to the method and the device disclosed by the invention, the in-situ coupling of the separation filler and the catalyst is realized by filling the reaction rectifying tower with the in-situ coupling type structured catalytic filler based on the solid acid, the energy utilization efficiency is remarkably improved, and the equipment and operation cost can be reduced by the integrated device. The production process provided by the invention has the advantages of simple flow, high reactant conversion rate, high product quality and purity, small catalyst dosage, easiness in replacement of catalytic filler and the like.

Description

Technical Field

[0001] This invention belongs to the field of chemical organic solvent production technology, and in particular to a method, apparatus and application for the reactive distillation of dimethyl maleate based on structured catalytic packing. Background Technology

[0002] Dimethyl maleate is an important organic chemical raw material with wide applications in industry. It is a crucial intermediate in the synthesis of unsaturated polyester resins, coatings, plasticizers, surfactants, and other fine chemicals. In the environmental protection field, dimethyl maleate is also used as an adjuvant in water and waste gas treatment. Furthermore, dimethyl maleate has applications in the synthesis of pesticides and pharmaceuticals.

[0003] Traditional methods for producing dimethyl maleate primarily involve esterification, specifically the reaction of maleic anhydride with excess methanol. This method typically requires sulfuric acid or other strong acids as homogeneous catalysts, and the operation must be carried out under strictly controlled temperature and pressure conditions. After the reaction, the product often contains unreacted methanol, catalyst residue, water, and other byproducts, necessitating complex separation and purification steps such as neutralization, extraction, and distillation to obtain high-purity dimethyl maleate. This process presents challenges including high energy consumption, highly corrosive catalysts, high pollution, and low yield.

[0004] Furthermore, an azeotropic phenomenon exists in the esterification reaction system of maleic anhydride and methanol, making product separation difficult and resulting in low conversion rates in traditional pre-reaction and post-separation processes. Reactive distillation is a process that combines chemical reaction with material separation. Its basic principle is to simultaneously purify the product through a distillation column during the reaction. In this system, the target product, such as dimethyl maleate, generated in the reaction section is separated as the lighter components rise in the column; on the other hand, unreacted feedstock can be refluxed to the reaction section to continue the reaction, thereby improving the conversion rate and product selectivity.

[0005] To address the aforementioned problems and deficiencies, the purpose of this invention is to provide a reactive distillation process and apparatus for the production of dimethyl maleate. Unlike traditional processes that involve reaction followed by distillation, this invention couples the reaction and separation processes by incorporating a reaction section within the reactive distillation column. By removing the product to be separated, it promotes a forward shift in the reaction equilibrium, increases the conversion rate, and produces high-purity dimethyl maleate at the bottom of the column. Compared to traditional reactive distillation technologies based on a combination of particulate catalysts and distillation packing materials, this process utilizes a structured catalytic packing material based on solid acids, which enhances heat and mass transfer and reduces side reactions.

[0006] The search revealed the following patent documents related to this application, the specific contents of which are as follows: 1. Chinese patent publication CN107473966B discloses a method for producing dimethyl maleate. The method uses dimethyl maleate as a solvent to absorb a mixed gas containing maleic anhydride, generating a mixed liquid as a raw material. This liquid is then reacted with methanol in an esterification reaction to produce dimethyl maleate. This process is an absorption process, designed to recover residual maleic anhydride, and does not involve reactive distillation for the production of dimethyl maleate.

[0007] 2. Chinese patent publication CN102908955B discloses a macroporous sieve plate esterification reactor and a method for preparing dimethyl maleate. The reactor includes a tower-shaped reactor shell with at least one layer of trays installed inside the shell. Solid esterification catalyst is scattered on the trays, which are macroporous guide sieve plates. However, this device only involves a tower-type reactor and does not couple the reaction and separation unit operations. The method also does not involve the use of structured catalytic packing.

[0008] 3. Chinese patent publication CN103360253B discloses a method for producing dimethyl maleate. In this method, maleic anhydride and a first stream of methanol are fed into a monoesterification reactor, where they react to produce monomethyl maleate. A second stream of methanol then enters a diesterification fixed-bed reactor, where it contacts a catalyst to produce a mixture containing monomethyl maleate, dimethyl maleate, and a third stream of methanol, which then enters a diesterification catalytic distillation column. This system involves multiple components and a complex process, including two reactors and a catalytic distillation column, and does not include a methanol recovery or product separation system.

[0009] 4. Chinese patent publication CN114984866B discloses a system and method for preparing dimethyl maleate. The product is directly fed to a partitioned-wall reactive distillation column via an adiabatic fixed-bed reaction, methanol is recovered using the heat of reaction, and diesterization is performed using reactive distillation coupled with membrane separation technology. This system also involves a fixed-bed reactor, and the subsequent use of membrane equipment for separation raises questions for large-scale industrial application.

[0010] By comparison, the present invention patent application is fundamentally different from the aforementioned patent publications.

[0011] Therefore, this invention is a new reactive distillation technology for dimethyl maleate based on structured catalytic packing, which separates the corresponding products during the reaction, promotes the forward shift of equilibrium, and improves the conversion degree of the reaction. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method, apparatus and application for the reactive distillation production of dimethyl maleate based on structured catalytic packing.

[0013] The technical solution adopted by this invention to solve its technical problem is: A reactive distillation production apparatus for dimethyl maleate based on structured catalytic packing, the apparatus comprising a reactive distillation column, a distillation column, a feed tank, a first reboiler, a second reboiler, a first condenser, a second condenser, a first reflux tank, a second reflux tank, a first product tank, a second product tank, and a third product tank, a feed pump, a first product pump, and a second product pump, wherein the reactive distillation column and the distillation column are connected to each other and are all arranged in a vertical direction; The feed tank has an input end that can receive feed materials, and its output end is tightly connected to the input end of the reactive distillation column via a feed pump. The reactive distillation column has a first top outlet at the top and a first bottom outlet at the bottom. The first top outlet is connected to the input end of the distillation column via a first condenser, a first reflux tank, and a first product pump. The first top outlet is also connected to the upper part of the reactive distillation column via the first condenser and the first reflux tank. The first bottom outlet is connected to the first product tank via a first reboiler, and also connected to the lower part of the reactive distillation column via the first reboiler. The distillation column has a second top outlet at the top and a second bottom outlet at the bottom. The second top outlet is connected to a third product tank via a second condenser, a second reflux tank, a second product pump, and a second product tank. The second top outlet is also connected to the upper part of the distillation column via a second condenser and a second reflux tank. The second bottom outlet is connected to the second product tank via a second reboiler and to the lower part of the distillation column via a second reboiler.

[0014] Furthermore, the reactive distillation column is provided with a rectification section, a reaction section, and a stripping section in sequence from top to bottom; the distillation column is provided with a rectification section and a stripping section in sequence from top to bottom.

[0015] Furthermore, the internal components of the rectification section and the stripping section are packing materials or trays; the reaction section is filled with structured catalytic packing materials.

[0016] Furthermore, the carrier of the structured catalytic packing is silicon carbide foam packing, wire mesh packing, stainless steel wire mesh packing, copper packing, or honeycomb ceramic; the catalyst coating is molecular sieve, strong acid ion exchange resin catalyst, or solid acid catalyst such as heteropoly acid.

[0017] Furthermore, the reactive distillation column has 30-45 theoretical plates, 8-15 feed plates, a reflux ratio of 3-8, and a column diameter of 0.20-0.60 m; the rectification column has 22-31 theoretical plates, 10-20 feed plates, a reflux ratio of 0.5-3, and a column diameter of 0.20-0.60 m.

[0018] Furthermore, the top temperature of the reactive distillation column is 60~70℃ and the bottom temperature is 200~250℃; the top temperature of the distillation column is 60~70℃ and the bottom temperature is 100~105℃.

[0019] Furthermore, the pressure operating range of the reactive distillation column is 101.325~150.325 kPa, and the pressure operating range of the distillation column is 101.325~130.325 kPa.

[0020] The application of the reactive distillation production apparatus described above in the production of dimethyl maleate.

[0021] The method for producing dimethyl maleate using the reactive distillation apparatus described above includes the following steps: The raw materials, methanol and maleic anhydride, are fed into the reactive distillation column from the feed tank via a feed pump. From top to bottom, the column consists of a rectification section, a reaction section, and a stripping section. The material streams include the feed point, overhead vapor, overhead return, overhead product, bottom liquid, bottom product, and bottom return. The bottom liquid is connected to the inlet of the first reboiler, with part of its outlet being the bottom product sold to the first product tank, and part being the bottom product returned to the column and connected to the bottom of the reactive distillation column. The overhead vapor is connected to the inlet of the first condenser, the overhead return is connected to the top of the column, and the reflux return is connected to the inlet of the first reflux tank. The outlet stream of the first reflux tank is the overhead product, which is connected to the first product pump and goes to the rectification column. The rectification column, from top to bottom, consists of a rectification section and a stripping section. The material streams include the feed point, overhead vapor, overhead return, overhead product, bottom liquid, bottom product, and bottom return. The bottom liquid phase is connected to the inlet of the second reboiler. Part of the outlet is the bottom product collected and sent to the second product tank, and part of the outlet is the bottom product returned to the distillation column and connected to the bottom of the column. The top gas phase is connected to the inlet of the second condenser. The top product returned to the column and connected to the top of the column. The liquid phase guide is connected to the inlet of the second reflux tank. The outlet stream of the second reflux tank is the top product collected and connected to the second product pump to the third product tank.

[0022] Furthermore, the yield of the prepared dimethyl maleate product is greater than 99%, and the purity is greater than 99.9%.

[0023] The advantages and positive effects of this invention are as follows: 1. Due to the integration of the reaction and separation processes, the energy utilization efficiency of this invention is significantly improved, and the integrated device can reduce equipment and operating costs. The production process provided by this invention has the advantages of simple process, high reactant conversion rate, high product purity, low catalyst dosage, and easy replacement of catalytic packing.

[0024] 2. This invention is a new reactive distillation technology for dimethyl maleate based on structured catalytic packing, which separates the corresponding products during the reaction, promotes the forward shift of equilibrium, and improves the conversion rate of the reaction.

[0025] 3. The reaction section of this invention uses an in-situ coupled structured catalytic packing material based on solid acid, which can enhance heat and mass transfer, reduce side reactions, significantly reduce catalyst dosage, and achieve in-situ coupling of reaction and separation.

[0026] 4. This invention enhances the esterification reaction of maleic anhydride and methanol through reactive distillation technology, and continuously recovers methanol, while obtaining high-quality dimethyl maleate product. This invention opens up a new method for improving the reactive distillation conversion rate of various systems (reactions limited by equilibrium constraints).

[0027] 5. The method of this invention includes reacting and separating raw materials through a reactive distillation column, obtaining high-purity dimethyl maleate from the bottom of the column, and further separating methanol and water from the top of the column through another distillation column. The method and apparatus of this invention achieve in-situ coupling of the separation packing and catalyst by filling the reactive distillation column with an in-situ coupled structured catalytic packing based on a solid acid, thereby improving the reactive distillation efficiency, effectively simplifying the process flow, and enabling large-scale production of dimethyl maleate. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structural connection of the device in this invention; wherein: reactive distillation column T01, distillation column T02, raw material tank V01, first reboiler E01, second reboiler E03, first condenser E02, second condenser E04, first reflux tank V02, second reflux tank V04, first product tank V03, second product tank V06, third product tank V05, feed pump P01, first extraction pump P02, and second extraction pump P03. Detailed Implementation

[0029] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0030] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0031] A reactive distillation apparatus for producing dimethyl maleate based on structured catalytic packing, such as... Figure 1As shown, the apparatus includes a reactive distillation column T01, a distillation column T02, a feed tank V01, a first reboiler E01, a second reboiler E03, a first condenser E02, a second condenser E04, a first reflux tank V02, a second reflux tank V04, a first product tank V03, a second product tank V06, and a third product tank V05, a feed pump P01, a first product pump P02, and a second product pump P03. The reactive distillation column and the distillation column are connected to each other and are all arranged in a vertical direction. The feed tank has an input end that can receive feed materials, and its output end is tightly connected to the input end of the reactive distillation column via a feed pump. The reactive distillation column has a first top outlet (not labeled in the diagram) at its top and a first bottom outlet (not labeled in the diagram) at its bottom. The first top outlet is connected to the input end of the distillation column sequentially via a first condenser, a first reflux tank, and a first product pump. The first top outlet is also connected to the upper part of the reactive distillation column sequentially via a first condenser and a first reflux tank. The first bottom outlet is tightly connected to the first product tank via a first reboiler, and also tightly connected to the lower part of the reactive distillation column via a first reboiler. The distillation column has a second top outlet (not labeled in the figure) at the top and a second bottom outlet (not labeled in the figure) at the bottom. The second top outlet is connected to the third product tank in sequence via a second condenser, a second reflux tank, a second product pump, and a second product tank. The second top outlet is also connected to the upper part of the second distillation column in sequence via a second condenser and a second reflux tank. The second bottom outlet is connected to the second product tank in sequence via a second reboiler and is also connected to the lower part of the distillation column in sequence via a second reboiler.

[0032] Using the above-mentioned methods Figure 1 The method for producing dimethyl maleate using the reactive distillation apparatus shown includes the following steps: The raw materials, methanol and maleic anhydride, enter the reactive distillation column T01 from the raw material tank V01 via the feed pump P01. From top to bottom, the column consists of a rectification section, a reaction section, and a stripping section. The material streams include the feed point, overhead vapor, overhead return, overhead product, bottom liquid, bottom product, and bottom return. The bottom liquid is connected to the inlet of the first reboiler E01, with part of the outlet being the bottom product collected and sent to the first product tank V03, and part being the bottom product returned and connected to the bottom of the reactive distillation column T01. The overhead vapor is connected to the inlet of the first condenser E02, the overhead return is connected to the top of the column, and the reflux return is connected to the inlet of the first reflux tank V02. The outlet stream of the first reflux tank V02 is the overhead product, which is connected to the first product pump P02 and sent to the rectification column T02. Distillation column T02 consists of a rectification section and a stripping section from top to bottom. The material streams include the feed point, overhead vapor, overhead return stream, overhead product, bottom liquid, bottom product, and bottom return stream. The bottom liquid is connected to the inlet of the second reboiler E03, with part of its outlet being the bottom product that goes to the second product tank V06, and part being the bottom product that returns to the column and connects to the bottom of distillation column T02. The overhead vapor is connected to the inlet of the second condenser E04, and the overhead return stream is connected to the top of the column. The liquid stream is connected to the inlet of the second reflux tank V04, and the outlet stream of the second reflux tank V04 is the overhead product that connects to the second product pump P03 and goes to the third product tank V05.

[0033] Preferably, the reactive distillation column is provided with a rectification section, a reaction section, and a stripping section from top to bottom; The distillation column is arranged from top to bottom as a rectification section and a stripping section.

[0034] Preferably, the internal components of the rectification section and the stripping section are packing or trays; the reaction section is filled with structured catalytic packing.

[0035] Preferably, the carrier of the structured catalytic packing is silicon carbide foam packing, wire mesh packing, stainless steel wire mesh packing, copper packing, honeycomb ceramics, etc.; the catalyst coating is molecular sieve, strong acid ion exchange resin catalyst, heteropoly acid and other solid acid catalyst.

[0036] Preferably, the method yields a dimethyl maleate product with a yield greater than 99% and a purity greater than 99.9%.

[0037] Preferably, the reactive distillation column T01 has 30-45 theoretical plates, 8-15 plates for the mixture feed, a reflux ratio of 3-8, and a column diameter of 0.20-0.60 m; the distillation column T02 has 22-31 theoretical plates, 10-20 plates for the mixture feed, a reflux ratio of 0.5-3, and a column diameter of 0.20-0.60 m.

[0038] Preferably, the top temperature of the reactive distillation column T01 is 60~70℃ and the bottom temperature is 200~250℃, and the top temperature of the distillation column T02 is 60~70℃ and the bottom temperature is 100~105℃.

[0039] Preferably, the pressure operating range of the reactive distillation column T01 is 101.325~150.325 kPa, and the pressure operating range of the distillation column T02 is 101.325~130.325 kPa.

[0040] The specific preparation and testing methods are as follows: The apparatus used in the following related embodiments are all as follows: Figure 1 The dimethyl maleate reactive distillation production apparatus based on structured catalytic packing shown below, and the methods used in the related embodiments below, all employ the methods described above. Figure 1 The method for producing dimethyl maleate using the reactive distillation apparatus shown.

[0041] Example 1: The reaction section of reactive distillation column T01 is packed with structured catalytic packing. The feed flow rates of maleic anhydride and methanol in column T01 are 120 kg / h and 200 kg / h, respectively, with a feed temperature of 25°C and an operating pressure of 1 atm (absolute pressure). The number of theoretical plates is 41. Maleic anhydride and methanol are fed together from the 10th theoretical plate. The number of plates in the reaction section is 10-25. The structured catalytic packing carrier is silicon carbide wire mesh packing. The molecular sieve catalyst coating mass is 66 kg. The reflux ratio is 4.6, and the top product is 186.5 kg / h. The feed to distillation column T02 is the top product of the reactive distillation column. The operating pressure is 1 atm (absolute pressure), the number of theoretical plates is 25, the feed plate is the 18th theoretical plate, the reflux ratio is 0.90, and the top product is 170.4 kg / h. Under these process conditions, the purity of dimethyl maleate at the bottom of reactive distillation column T01 is 99%, the conversion rate of maleic anhydride is 99%, the purity of methanol at the top of distillation column T02 is 99.9%, and the purity of water at the bottom of the column is 99.9%.

[0042] Comparative Example 1: The reaction section of the reactive distillation column T01 was filled with conventional bundled catalytic packing, and all other operating conditions were the same as in Example 1. Under these process conditions, the purity of dimethyl maleate at the bottom of the reactive distillation column T01 was 94.6%, and the conversion rate of maleic anhydride was 91.2%. Compared with Example 1, the production energy consumption increased by 26%, and the mass of catalyst in the catalytic packing increased by 72%.

[0043] Example 2: The reaction section of reactive distillation column T01 is packed with structured catalytic packing. The feed flow rates of maleic anhydride and methanol in column T01 are 120 kg / h and 250 kg / h, respectively, with a feed temperature of 50°C and an operating pressure of 1 atm (absolute pressure). The number of theoretical plates is 35. Maleic anhydride and methanol are fed together from the 10th theoretical plate. The number of plates in the reaction section is 10-25. The structured catalytic packing carrier is silicon carbide wire mesh packing. The catalyst coating mass is 66 kg, the reflux ratio is 4.6, and the top product is 236.5 kg / h. The feed to distillation column T02 is the top product of the reactive distillation column. The operating pressure is 1 atm (absolute pressure), the number of theoretical plates is 30, the feed plate is the 20th theoretical plate, the reflux ratio is 0.83, and the top product is 220.4 kg / h. Under these process conditions, the purity of dimethyl maleate at the bottom of reactive distillation column T01 is 99%, the conversion rate of maleic anhydride is 99%, the purity of methanol at the top of distillation column T02 is 99.9%, and the purity of water at the bottom of the column is 99.9%.

[0044] Comparative Example 2: The reaction section of the reactive distillation column T01 was packed with conventional KATAPAK type catalytic packing, and all other operating conditions were the same as in Example 2. Under these process conditions, the purity of dimethyl maleate at the bottom of the reactive distillation column T01 was 93.2%, and the conversion rate of maleic anhydride was 92.5%. Compared with Example 2, the production energy consumption increased by 33%, and the mass of catalyst in the catalytic packing increased by 68%.

[0045] As can be seen from Examples 1, 2, Comparative Examples 1 and 2, the mass purity of dimethyl maleate and the conversion rate of maleic anhydride in the method of the present invention both reached 99%. Compared with Comparative Examples 1 and 2, the in-situ coupled structured catalytic packing based on solid acid achieves in-situ coupling between the packing and the catalyst, which greatly improves the conversion rate of maleic anhydride and the purity of dimethyl maleate in the reactive distillation column. Furthermore, the amount of catalyst used in the catalytic packing is reduced by more than 60%, and energy consumption is synergistically reduced by more than 20%.

[0046] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A reactive distillation apparatus for producing dimethyl maleate based on structured catalytic packing, characterized in that: The apparatus includes a reactive distillation column, a distillation column, a feed tank, a first reboiler, a second reboiler, a first condenser, a second condenser, a first reflux tank, a second reflux tank, a first product tank, a second product tank, and a third product tank, a feed pump, a first product pump, and a second product pump. The reactive distillation column and the distillation column are connected to each other and are all arranged in a vertical direction. The feed tank has an input end that can receive feed materials, and its output end is tightly connected to the input end of the reactive distillation column via a feed pump. The reactive distillation column has a first top outlet at the top and a first bottom outlet at the bottom. The first top outlet is connected to the input end of the distillation column via a first condenser, a first reflux tank, and a first product pump. The first top outlet is also connected to the upper part of the reactive distillation column via the first condenser and the first reflux tank. The first bottom outlet is connected to the first product tank via a first reboiler, and also connected to the lower part of the reactive distillation column via the first reboiler. The distillation column has a second top outlet at the top and a second bottom outlet at the bottom. The second top outlet is connected to a third product tank via a second condenser, a second reflux tank, a second product pump, and a second product tank. The second top outlet is also connected to the upper part of the distillation column via a second condenser and a second reflux tank. The second bottom outlet is connected to the second product tank via a second reboiler and to the lower part of the distillation column via a second reboiler.

2. The reactive distillation production apparatus according to claim 1, characterized in that: The reactive distillation column is provided with a rectification section, a reaction section, and a stripping section from top to bottom; the distillation column is provided with a rectification section and a stripping section from top to bottom.

3. The reactive distillation production apparatus according to claim 2, characterized in that: The internal components of the rectification and stripping sections are packing materials or trays; the reaction sections are all filled with structured catalytic packing materials.

4. The reactive distillation production apparatus according to claim 3, characterized in that: The carrier of the structured catalytic packing is silicon carbide foam packing, wire mesh packing, stainless steel wire mesh packing, copper packing, or honeycomb ceramic; the catalyst coating is molecular sieve, strong acid ion exchange resin catalyst, or solid acid catalyst such as heteropoly acid.

5. The reactive distillation production apparatus according to claim 1, characterized in that: The reactive distillation column has 30-45 theoretical plates, 8-15 plates for the mixture feed, a reflux ratio of 3-8, and a column diameter of 0.20-0.60 m; the rectification column has 22-31 theoretical plates, 10-20 plates for the mixture feed, a reflux ratio of 0.5-3, and a column diameter of 0.20-0.60 m.

6. The reactive distillation production apparatus according to claim 1, characterized in that: The temperature at the top of the reactive distillation column is 60-70℃, and the temperature at the bottom is 200-250℃; the temperature at the top of the distillation column is 60-70℃, and the temperature at the bottom is 100-105℃.

7. The reactive distillation production apparatus according to any one of claims 1 to 6, characterized in that: The pressure operating range of the reactive distillation column is 101.325~150.325 kPa, and the pressure operating range of the distillation column is 101.325~130.325 kPa.

8. The use of the reactive distillation apparatus as described in any one of claims 1 to 7 in the production of dimethyl maleate.

9. A method for producing dimethyl maleate using the reactive distillation apparatus as described in any one of claims 1 to 7, characterized in that: Includes the following steps: The raw materials methanol and maleic anhydride are fed into the reactive distillation column from the raw material tank via a feed pump. From top to bottom, there are a rectification section, a reaction section, and a stripping section. The material streams are respectively the feed point, the top vapor phase, the top return phase, the top product, the bottom liquid phase, the bottom product, and the bottom return phase. The bottom liquid phase is connected to the inlet of the first reboiler. Part of the outlet is the bottom product collected and sent to the first product tank, and part is the bottom return phase connected to the bottom of the first distillation column. The top vapor phase is connected to the inlet of the first condenser. The top return phase is connected to the top of the column. The reflux return phase is connected to the inlet of the first reflux tank. The outlet stream of the first reflux tank is the top product collected and connected to the first product pump to the distillation column. The distillation column has a rectification section and a stripping section from top to bottom. The material streams are the feed point, the top vapor phase, the top return phase, the top product collected, the bottom liquid phase, the bottom product collected, and the bottom return phase. The bottom liquid phase is connected to the inlet of the second reboiler. Part of the outlet is the bottom product collected and sent to the second product tank, and part of the outlet is the bottom product returned to the distillation column and connected to the bottom of the column. The top gas phase is connected to the inlet of the second condenser. The top product returned to the column and connected to the top of the column. The liquid phase guide is connected to the inlet of the second reflux tank. The outlet stream of the second reflux tank is the top product collected and connected to the second product pump to the third product tank.

10. The method according to claim 9, characterized in that: The yield of the prepared dimethyl maleate product is greater than 99%, and the purity is greater than 99.9%.

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