Process for the preparation of succinic anhydride by hydrogenation of maleic anhydride

Abstract

A process for preparing succinic anhydride by hydrogenation of maleic anhydride is disclosed. The process uses an organic solvent with a boiling point not exceeding 150℃ that can dissolve maleic anhydride and does not react with it as the reaction solvent. After dissolving the maleic anhydride, it reacts with hydrogen and a solid catalyst in a hydrogenation reactor. The reaction pressure is adjusted to maintain the reaction temperature between 30℃ and 150℃, and the solvent in the reaction system is kept boiling by adjusting the pressure. A gas outlet is provided on the hydrogenation reactor, from which the organic solvent and unreacted hydrogen are continuously discharged. After the reaction is completed, the reaction product is subjected to solid-liquid separation and / or crystallization separation to obtain succinic anhydride. This invention uses an organic solution containing dissolved maleic anhydride as a raw material and utilizes pressure adjustment to maintain the solution in the reaction system at a boiling state, thereby utilizing the phase change of the organic solvent to promptly remove the heat from the reaction system. This solves the temperature rise problem in the process of preparing succinic anhydride by hydrogenation of maleic anhydride. The method is simple and easy to operate, and is convenient for industrial application.

Description

Technical Field

[0001] This invention relates to a process for preparing succinic anhydride by hydrogenation of maleic anhydride, belonging to the field of catalytic process technology. Background Technology

[0002] As plastic pollution worsens, the demand for PBS (polybutylene succinate) series copolyester biodegradable materials continues to increase due to their superior performance. However, although the polymerization technology for PBS series copolyester biodegradable plastic products is already mature, the technology for large-scale, low-cost synthesis of succinic acid monomer materials is still incomplete, which restricts the promotion and application of high-quality biodegradable materials.

[0003] Currently, PBS materials are produced by polymerizing succinic acid with butanediol. However, the removal of water during the polymerization reaction affects the molecular weight and properties of the synthesized material. In contrast, the direct polymerization of succinic anhydride with butanediol requires half the water removal compared to succinic acid polymerization, resulting in a higher quality product. Therefore, succinic anhydride products have a promising future.

[0004] However, the catalytic hydrogenation of maleic anhydride to succinic anhydride is a double-bond saturation reaction, which proceeds relatively easily. Simultaneously, the reaction is strongly exothermic (ΔH = -128 kJ / mol), resulting in a significant temperature rise during the maleic anhydride hydrogenation reaction. Furthermore, the direct hydrogenation of maleic anhydride involves multiple unsaturated bonds such as C=C and C=O, making the reaction highly temperature-sensitive. If the temperature increases during the maleic anhydride hydrogenation reaction, C=O double bond saturation is highly likely to occur, generating byproducts such as butyrolactone, which negatively impacts the reaction efficiency.

[0005] Because the hydrogenation of maleic anhydride is highly exothermic, researchers are currently employing various methods to address this issue and ensure the smooth progress of the reaction. Patent CN103570650A utilizes a mixed solution of organic solvent and maleic anhydride as raw material, employs heterogeneous catalysts such as silicon and aluminum, and utilizes a two-stage reactor method. The first-stage reactor pre-hydrogenates the maleic anhydride to reduce heat generation, and the two-stage reactor method achieves high selectivity and high conversion rate in the hydrogenation of maleic anhydride. The resulting reaction products are then separated by distillation, the solvent is recycled, and the obtained succinic anhydride is hydrolyzed and crystallized to produce succinic acid.

[0006] Patent CN102311332A discloses a method for producing succinic acid, which uses butyrolactone as a solvent, employs a heterogeneous catalyst supported on alumina, and prepares a maleic anhydride / γ-butyrolactone solution. The latent heat of the γ-butyrolactone solution is utilized to achieve temperature control, thereby ensuring the smooth progress of the reaction. The generated succinic anhydride is then separated, hydrolyzed, and crystallized to obtain high-purity succinic acid.

[0007] Although the above research methods have achieved highly selective conversion of maleic anhydride, it can be seen that in order to reduce the impact of reaction heat, researchers usually use a large amount of solvent to dilute maleic anhydride, reduce the total heat of reaction in the same reaction volume, and use latent heat to reduce the temperature rise. The concentration of maleic anhydride that can be processed is low, and the addition of solvent circulation and product separation processes increases the investment in reaction equipment and the cost of materials and energy consumption. Summary of the Invention

[0008] In their research addressing the above-mentioned technical problems, the inventors conceived that by controlling the reaction conditions to induce a phase change in the solvent, since the enthalpy of the solvent phase change is much higher than the enthalpy change that causes the temperature rise, the solvent after the phase change can be removed in time and used as a heat transfer method to effectively control the temperature rise of the highly exothermic reaction and achieve precise control of the reaction temperature. This would also broaden the range of maleic anhydride concentrations that can be handled in the existing technology, and enable the direct hydrogenation of maleic anhydride solution to prepare succinic anhydride while ensuring the reaction conversion rate and selectivity.

[0009] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0010] A process for preparing succinic anhydride by hydrogenation of maleic anhydride involves using an organic solvent with a boiling point not exceeding 150°C, capable of dissolving maleic anhydride, and not reacting with it as the reaction solvent. The maleic anhydride is dissolved at a concentration of 10wt%-75wt%, and then reacted with hydrogen and a solid catalyst in a hydrogenation reactor. The reaction pressure is adjusted to maintain the reaction temperature between 30°C and 150°C, and the solvent in the reaction system is kept boiling by adjusting the pressure. A gas outlet is provided on the hydrogenation reactor, from which the organic solvent and unreacted hydrogen are continuously discharged. After the reaction is completed, the reaction product is subjected to solid-liquid separation and / or crystallization to obtain succinic anhydride.

[0011] Furthermore, the boiling point of the organic solvent is preferably not higher than 120°C, and more preferably not higher than 100°C.

[0012] Furthermore, the organic solvent is selected from at least one of tetrahydrofuran (boiling point 66°C at normal pressure), diethyl ether (boiling point 34.5°C at normal pressure), methyl formate (boiling point 31.5°C at normal pressure) and methyl acetate (boiling point 56.8°C at normal pressure), preferably tetrahydrofuran.

[0013] Furthermore, a stirring device is provided inside the hydrogenation reaction apparatus.

[0014] Furthermore, the solid catalyst is fixed outside the bottom of the hydrogenation reactor to minimize contact with the succinic anhydride that crystallizes after the reaction, thus preventing the succinic anhydride from adhering to the catalyst surface and affecting the catalytic effect. Preferably, the solid catalyst is fixed to the stirring device of the hydrogenation reactor. More specifically, the catalyst is encapsulated into several catalytic units and then fixed to the stirring paddle of the stirring device. Preferably, it is encapsulated in several porous mesh bags and dispersedly fixed to the stirring paddle. This not only achieves fixation but also allows the catalyst to rotate with the stirring paddle, enhancing contact with the reactants and reducing the adhesion of succinic anhydride during rotation due to the scouring effect of the materials.

[0015] Furthermore, the active component of the solid catalyst is selected from at least one of Pd, Pt, Ru, Ni, and Cu, and the support is an acid-resistant support. The acid-resistant support is selected from at least one of C, resin, and inorganic refractory oxides, and includes supports modified to acquire acid resistance.

[0016] Furthermore, the amount of the solid catalyst used is 1%-50% of the volume of the reaction liquid in the reactor, preferably 5%-20%.

[0017] Furthermore, the concentration of maleic anhydride is preferably 15wt%-70wt%, more preferably 25wt%-60wt%, and most preferably 30wt%-50wt%. The technical solution of this invention utilizes the phase change heat recovery of organic solvents to effectively solve the temperature rise problem. Therefore, from an economic perspective, within a controllable temperature rise range, the higher the raw material concentration, the higher the reaction efficiency, and more products can be obtained in a single reaction. Within the raw material concentration range of this invention, the temperature rise can be well controlled, and compared with existing technologies, the range of processable raw material concentrations is significantly improved.

[0018] Furthermore, the temperature of the hydrogenation reaction is 40℃-120℃, more preferably 50℃-120℃, and most preferably 60℃-100℃. The time of the hydrogenation reaction is 20min-5h, preferably 40min-2h.

[0019] Furthermore, the hydrogen gas is added at a hydrogen:maleic anhydride molar ratio of 0.1-1000:1, preferably 1-100:1, and most preferably 1-10:1.

[0020] Furthermore, the maleic anhydride feedstock and hydrogen are either pre-mixed or mixed within the hydrogenation reactor. When the maleic anhydride feedstock and hydrogen are pre-mixed, a gas-liquid mixer is preferably used to enhance hydrogen dissolution; when the maleic anhydride feedstock and hydrogen are mixed within the hydrogenation reactor, the hydrogen is preferably introduced into the hydrogenation reactor using a membrane disperser or a porous distribution method.

[0021] Furthermore, the hydrogen can be added in stages or continuously. The hydrogen is added from the bottom of the reactor or introduced through a conduit into a mesh bag containing the catalyst.

[0022] In the technical solution of this invention, maleic anhydride has a high solubility in the selected organic solvent, while succinic anhydride has a relatively low solubility. During the reaction, when the concentration of maleic anhydride is high, succinic anhydride crystals continuously precipitate as succinic anhydride is continuously generated. Simultaneously, the vapors formed by the boiling of the solvent are continuously discharged from the reaction system, further promoting the precipitation of succinic anhydride crystals. Maleic anhydride continues to react in the solution. After the reaction is complete, succinic anhydride precipitates through crystallization. Part of the succinic anhydride is separated by means of filtration or centrifugation, while the remainder is separated through crystallization, and the mother liquor is recycled.

[0023] Furthermore, the crystallization is a cooling crystallization at a temperature of 0°C-60°C, preferably 15-40°C.

[0024] Furthermore, after the reaction of the present invention is completed, the product can be cooled and crystallized directly in the reaction vessel without being removed, thus eliminating many equipment and processes.

[0025] Furthermore, the gas outlet is located at the top of the hydrogenation reaction unit.

[0026] Furthermore, the process method also includes a step of condensing the organic solvent and unreacted hydrogen at the gas outlet to recover hydrogen.

[0027] Furthermore, the maleic anhydride is a solid anhydride or a liquid anhydride, preferably a liquid anhydride.

[0028] The technical solution of this invention has the following advantages:

[0029] (1) In the process method of the present invention, an organic solution of maleic anhydride is used as raw material. The pressure is adjusted to keep the solution in the reaction system boiling. The heat of the reaction system can be removed in time by utilizing the phase change of the organic solvent. This solves the temperature rise problem of the hydrogenation of maleic anhydride to prepare succinic anhydride. No external heat removal method is required. The method is simple and easy to operate, and is convenient for industrial promotion and application.

[0030] (2) The process method of the present invention can broaden the range of maleic anhydride concentration in raw materials that can be processed. From an economic point of view, within the range where the temperature rise can be controlled, a higher concentration of raw materials can be used for the reaction, and more products can be obtained in one reaction, which greatly improves the reaction production efficiency. The upper limit of the raw material concentration that the present invention can process is unattainable by other technical solutions in the field.

[0031] (3) The process method of the present invention uses a solid catalyst. In the preferred embodiment, the solid catalyst is encapsulated and fixed to achieve full contact between the catalyst and the reactants and reduce the adhesion of succinic anhydride crystals, thereby ensuring the catalytic effect and extending the service life of the solid catalyst.

[0032] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0033] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0034] In the following embodiments, a hydrogenation reactor is used to complete the hydrogenation reaction. The hydrogenation reactor has the following structure: a gas outlet is provided at the top and a material outlet is provided at the bottom. During the reaction, the bottom outlet is closed. During the reaction, the pressure inside the hydrogenation reactor is controlled by a back pressure valve. A stirring device is provided inside the hydrogenation reactor to ensure that the reactants are mixed evenly. The solid catalyst is loaded in multiple porous mesh bags and dispersedly suspended on the stirring paddle.

[0035] Example 1

[0036] The solid catalyst is a resin palladium catalyst (the palladium loading on the catalyst is 1% by total catalyst weight), and the amount of resin palladium catalyst is 10% by total volume of maleic anhydride added to the hydrogenation reactor.

[0037] A 10wt% maleic anhydride was prepared using tetrahydrofuran. The solution and hydrogen were introduced into a hydrogenation reactor. The hydrogen was added using a membrane disperser. The molar ratio (hydrogen-to-anhydride ratio) of hydrogen to maleic anhydride in the reactants was 1:1. The absolute pressure in the reaction system was controlled at 1 bar using a vacuum pump and a back pressure valve to keep the reaction system boiling. At this time, the reaction temperature was 66℃. Tetrahydrofuran vapor and unreacted hydrogen were discharged from the gas outlet. The reaction lasted for 2 hours.

[0038] After the reaction is completed, the hydrogenation reactor is cooled to 20~40℃, the product is taken out and centrifuged. During the centrifugation process, the organic solvent is rinsed twice. The mother liquor after rinsing is transferred to the hydrogenation reaction unit. The separated succinic anhydride solid is dried at 150℃. The purity of succinic anhydride is tested to be ≥99.5%.

[0039] The results of maleic anhydride conversion and succinic anhydride selectivity in the hydrogenation reaction are shown in Table 1.

[0040] Example 2

[0041] The solid catalyst is a resin palladium catalyst (the palladium loading on the catalyst is 1% by total catalyst weight), and the amount of resin palladium catalyst is 10% by total volume of maleic anhydride added to the hydrogenation reactor.

[0042] A 30wt% maleic anhydride was prepared using tetrahydrofuran. The solution and hydrogen were introduced into a hydrogenation reactor. The hydrogen was added using a membrane disperser. The molar ratio (hydrogen-to-anhydride ratio) of hydrogen to maleic anhydride in the reactants was 2:1. The absolute pressure in the reaction system was controlled at 1.5 bar using a vacuum pump and a back pressure valve to keep the reaction system boiling. The reaction temperature was 80°C. Tetrahydrofuran vapor and unreacted hydrogen were discharged from the gas outlet. The reaction lasted for 2 hours.

[0043] After the reaction is completed, the hydrogenation reactor is cooled to 20~40℃, the product is taken out and centrifuged. During the centrifugation process, the organic solvent is rinsed twice. The mother liquor after rinsing is transferred to the hydrogenation reaction unit. The separated succinic anhydride solid is dried at 150℃. The purity of succinic anhydride is tested to be ≥99.5%.

[0044] The results of maleic anhydride conversion and succinic anhydride selectivity in the hydrogenation reaction are shown in Table 1.

[0045] Example 3

[0046] The solid catalyst is a Ni catalyst (Ni loading is 30% by total catalyst weight), and the amount of catalyst used is 10% by total volume of maleic anhydride added to the hydrogenation reactor.

[0047] A 40wt% maleic anhydride was prepared using tetrahydrofuran. The solution and hydrogen were introduced into a hydrogenation reactor. The hydrogen was added using a membrane disperser. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 3:1. The absolute pressure in the reaction system was controlled at 1.5 bar using a vacuum pump and a back pressure valve to keep the reaction system boiling. The reaction temperature was 80°C. Tetrahydrofuran vapor and unreacted hydrogen were discharged from the gas outlet. The reaction lasted for 3 hours.

[0048] After the reaction is completed, the hydrogenation reactor is cooled to 20~40℃, the product is taken out and centrifuged. During the centrifugation process, the organic solvent is rinsed twice. The mother liquor after rinsing is transferred to the hydrogenation reaction unit. The separated succinic anhydride solid is dried at 150℃. The purity of succinic anhydride is tested to be ≥99.5%.

[0049] Example 4

[0050] The solid catalyst is a Cu catalyst (Cu loading is 35% by total catalyst weight), and the amount of catalyst used is 10% by total volume of maleic anhydride added to the hydrogenation reactor.

[0051] A 40wt% maleic anhydride was prepared using tetrahydrofuran. The solution and hydrogen were introduced into a hydrogenation reactor. The hydrogen was added using a membrane disperser. The molar ratio (hydrogen-to-anhydride ratio) of hydrogen to maleic anhydride in the reactants was 3:1. The absolute pressure in the reaction system was controlled at 2 bar using a vacuum pump and a back pressure valve to keep the reaction system boiling. At this time, the reaction temperature was 90℃. Tetrahydrofuran vapor and unreacted hydrogen were discharged from the gas outlet. The reaction lasted for 3 hours.

[0052] After the reaction is completed, the hydrogenation reactor is cooled to 20~40℃, the product is taken out and centrifuged. During the centrifugation process, the organic solvent is rinsed twice. The mother liquor after rinsing is transferred to the hydrogenation reaction unit. The separated succinic anhydride solid is dried at 150℃. The purity of succinic anhydride is tested to be ≥99.5%.

[0053] Example 5

[0054] The solid catalyst is a Cu catalyst (Cu loading is 35% by total catalyst weight), and the amount of catalyst used is 10% by total volume of maleic anhydride added to the hydrogenation reactor.

[0055] A 30wt% maleic anhydride was prepared using methyl formate. The solution and hydrogen were introduced into a hydrogenation reactor. The hydrogen was added using a membrane disperser. The molar ratio (hydrogen-to-anhydride ratio) of hydrogen to maleic anhydride in the reactants was 4:1. The absolute pressure in the reaction system was controlled at 2 bar using a vacuum pump and a back pressure valve to keep the reaction system boiling. At this time, the reaction temperature was 51℃. Methyl formate vapor and unreacted hydrogen were discharged from the gas outlet. The reaction lasted for 4 hours.

[0056] After the reaction is completed, the hydrogenation reactor is cooled to 20~40℃, the product is taken out and centrifuged. During the centrifugation process, the organic solvent is rinsed twice. The mother liquor after rinsing is transferred to the hydrogenation reaction unit. The separated succinic anhydride solid is dried at 150℃. The purity of succinic anhydride is tested to be ≥99.5%.

[0057] Example 6

[0058] The solid catalyst is a Ni catalyst (Ni loading is 35% by total catalyst weight), and the amount of catalyst used is 10% by total volume of maleic anhydride added to the hydrogenation reactor.

[0059] A 50 wt% maleic anhydride was prepared using methyl formate. The solution and hydrogen were introduced into a hydrogenation reactor. The hydrogen was added using a membrane disperser. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 4:1. A vacuum pump and a back pressure valve were used to control the absolute pressure in the reaction system at 4.7 bar, keeping the reaction system boiling. The reaction temperature was 80°C. Methyl formate vapor and unreacted hydrogen were discharged from the gas outlet. The reaction lasted for 4 hours.

[0060] After the reaction is completed, the hydrogenation reactor is cooled to 20~40℃, the product is taken out and centrifuged. During the centrifugation process, the organic solvent is rinsed twice. The mother liquor after rinsing is transferred to the hydrogenation reaction unit. The separated succinic anhydride solid is dried at 150℃. The purity of succinic anhydride is tested to be ≥99.5%.

[0061] Example 7

[0062] The solid catalyst is a Ni catalyst (Ni loading is 35% by total catalyst weight), and the amount of catalyst used is 20% by total volume of maleic anhydride added to the hydrogenation reactor.

[0063] A 65wt% maleic anhydride was prepared using tetrahydrofuran. The solution and hydrogen were introduced into a hydrogenation reactor. The hydrogen was added using a membrane disperser. The molar ratio (hydrogen-to-anhydride ratio) of hydrogen to maleic anhydride in the reactants was 4:1. The absolute pressure in the reaction system was controlled at 2 bar using a vacuum pump and a back pressure valve to keep the reaction system boiling. At this time, the reaction temperature was 90℃. Tetrahydrofuran vapor and unreacted hydrogen were discharged from the gas outlet. The reaction lasted for 4 hours.

[0064] After the reaction is completed, the hydrogenation reactor is cooled to 20~40℃, the product is taken out and centrifuged. During the centrifugation process, the organic solvent is rinsed twice. The mother liquor after rinsing is transferred to the hydrogenation reaction unit. The separated succinic anhydride solid is dried at 150℃. The purity of succinic anhydride is tested to be ≥99.5%.

[0065] Table 1

[0066]

[0067] Comparative Example 1

[0068] A 10% (w / w) maleic anhydride solution was prepared using γ-butyrolactone as a solvent and reacted in a fixed-bed reactor at 80°C and 3 MPa. The catalyst was a Ni-based catalyst supported on a silica-alumina carrier, and heat was extracted via circulating heat transfer oil. The reaction products were sequentially separated using a light-weight removal tower, a heavy-weight removal tower, and a solvent purification tower to obtain succinic anhydride. The maleic anhydride conversion, succinic anhydride selectivity, and energy consumption are shown in Table 2.

[0069] In this comparative example, because the reaction is rapidly exothermic, the concentration of maleic anhydride can only be around 10%, and heat transfer oil circulation is required for heat extraction. Higher concentrations would make the reaction process uncontrollable.

[0070] Comparative Example 2

[0071] A 40 wt% maleic anhydride solution was prepared using γ-butyrolactone as the solvent. The solid catalyst was a Ni catalyst (Ni loading was 30% by total catalyst weight), and the catalyst dosage was 10% based on the total volume of maleic anhydride added to the hydrogenation reactor. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 3:1. The differences were: the absolute pressure within the reaction system was controlled at 1.5 bar using a vacuum pump and back pressure valve; the reaction temperature was 80°C; the system was not in a boiling state; external heat transfer oil was used for heat exchange in the reactor; unreacted hydrogen was discharged from the gas outlet; and the reaction time was 3 hours. During the reaction, it was observed that although there was external heat transfer oil, the internal temperature was rising.

[0072] After the reaction is complete, the hydrogenation reactor is cooled to 20-40°C, the product is removed and centrifuged. During the centrifugation process, the organic solvent is rinsed twice. The mother liquor after rinsing is transferred to the hydrogenation reaction unit, and the separated succinic anhydride solid is dried.

[0073] Comparative Example 3

[0074] Tetrahydrofuran was used as the solvent. The maleic anhydride concentration, catalyst, catalyst setting method, hydrogen introduction method, hydrogen-to-anhydride ratio and other conditions were the same as in Example 7. The difference was that a vacuum pump and back pressure valve were used to control the absolute pressure in the reaction system to 15 bar and the reaction temperature in the reactor to 100°C. Due to the high pressure, the system was not boiling. In order to keep the reaction temperature at around 100°C and prevent overheating, the reactor needed to use external circulating cooling water for heat extraction. Unreacted hydrogen was discharged from the gas outlet. The reaction lasted for 3 hours.

[0075] After the reaction is complete, the hydrogenation reactor is cooled to 20-40°C, the product is removed and centrifuged. During the centrifugation process, the organic solvent is rinsed twice. The mother liquor after rinsing is transferred to the hydrogenation reaction unit, and the separated succinic anhydride solid is dried.

[0076] Table 2 shows the maleic anhydride conversion rate, succinic anhydride selectivity, and energy consumption for succinic anhydride production in Examples 3, 7, and Comparative Examples 1-3.

[0077] Table 2

[0078]

[0079] Energy consumption includes the energy consumption of the hydrogenation reaction process and the purification of succinic anhydride.

Claims

1. A process for preparing succinic anhydride by hydrogenation of maleic anhydride, comprising using tetrahydrofuran or methyl formate as a reaction solvent to dissolve maleic anhydride at a concentration of 10wt%-75wt%, and then reacting it with hydrogen and a solid catalyst in a hydrogenation reactor. The reaction pressure is adjusted to maintain the reaction temperature at 80-90℃, and the solvent in the reaction system is kept in a boiling state by adjusting the pressure. A gas outlet is provided on the hydrogenation reactor, from which organic solvent and unreacted hydrogen are continuously discharged. After the reaction is completed, the reaction product is subjected to solid-liquid separation and / or crystallization separation to obtain succinic anhydride.

2. The process method according to claim 1, characterized in that, The hydrogenation reactor is equipped with a stirring device.

3. The process method according to claim 1, characterized in that, The solid catalyst is fixed outside the bottom of the hydrogenation reactor.

4. The process method according to claim 2, characterized in that, The solid catalyst is fixed on the stirring device.

5. The process method according to claim 4, characterized in that, The solid catalyst is encapsulated in several porous mesh bags and dispersedly fixed on the stirring paddle.

6. The process method according to claim 1, characterized in that, The active component of the solid catalyst is selected from at least one of Pd, Pt, Ru, Ni and Cu, and the support is an acid-resistant support.

7. The process method according to claim 1, characterized in that, The concentration of maleic anhydride is 20wt%-70wt%.

8. The process method according to claim 7, characterized in that, The concentration of maleic anhydride is 25wt%-60wt%.

9. The process method according to claim 8, characterized in that, The concentration of maleic anhydride is 30wt%-50wt%.

10. The process method according to claim 1, characterized in that, The hydrogenation reaction takes 20 minutes to 5 hours.

11. The process method according to claim 1, characterized in that, The hydrogen gas is introduced at a hydrogen:maleic anhydride molar ratio of 0.1-1000:

1.

12. The process method according to claim 7, characterized in that, Hydrogen gas is added from the bottom of the hydrogenation reactor or introduced into a mesh bag containing the catalyst through a conduit.

13. The process method according to claim 1, characterized in that, The process also includes the step of reusing the mother liquor after crystallization separation to the maleic anhydride hydrolysis unit.

14. The process method according to claim 1, characterized in that, The process also includes a step of condensing the water vapor and unreacted hydrogen at the gas outlet to recover hydrogen.

Images