Process for preparing 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°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 homogeneous 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, through which the organic solvent and unreacted hydrogen are continuously discharged. After the reaction, the reaction product is subjected to solid-liquid separation and / or crystallization to obtain succinic anhydride. This process 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. This allows for timely removal of heat from the reaction system through the phase change of the organic solvent, effectively solving the temperature rise problem in the hydrogenation of maleic anhydride to prepare succinic anhydride. The method is simple to operate and easy to promote and apply industrially.

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 maleic anhydride as the reaction solvent. The maleic anhydride is dissolved at a concentration of 10wt%-75wt%, and then reacted with hydrogen and a homogeneous 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 in a boiling state 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, diethyl ether, methyl formate, and methyl acetate, preferably tetrahydrofuran.

[0013] 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.

[0014] 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.

[0015] Furthermore, the homogeneous catalyst is selected from at least one salt of Pd, Ti, Co, V, Fe, Ir, Rh, Au, Pt, Ni, Ag, Sn, Mo, Zn, Mn, Cu, and Ru. Preferably, it is selected from at least one salt of Co, Ni, Pd, Pt, and Ru.

[0016] Furthermore, the homogeneous catalyst is selected from at least one of RuCl3, PdCl2, CoCl2, NiCl2 and H2PtCl4.

[0017] Furthermore, the homogeneous catalyst also includes a corresponding ligand to maintain the dissolution stability of the metal salt in the organic solution, wherein the ligand is specifically selected from at least one of sodium triphenylphosphine sulfonate, diphenylphosphine diethylcarboxylic acid, polyhydroxyphosphine ligand, and quaternary phosphine ligand.

[0018] Furthermore, the concentration of the homogeneous catalyst in the reaction raw material formed by mixing the maleic anhydride solution and the homogeneous catalyst, based on metal element, is not less than 0.001 mmol / L, preferably not less than 1 mmol / L; more preferably 1-20 mmol / L, and most preferably 5-15 mmol / L.

[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 process method also includes the step of reusing the mother liquor containing the homogeneous catalyst obtained after separation.

[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, and the remainder is recovered through crystallization separation. The mother liquor containing the homogeneous catalyst is then recycled.

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

[0024] Furthermore, the hydrogenation reaction device is a reaction vessel. A stirring device is installed inside the reaction vessel to ensure thorough stirring and mixing of the materials during the reaction.

[0025] 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.

[0026] Furthermore, the gas outlet is located at the top of the hydrogenation reaction unit.

[0027] Furthermore, the hydrogenation reactor is equipped with a stirring device to fully disperse the hydrogen and promote the reaction.

[0028] Furthermore, the process method also includes a step of condensing the organic solvent and unreacted hydrogen at the gas outlet to recover hydrogen.

[0029] Furthermore, the maleic anhydride is a solid anhydride or a liquid anhydride, preferably a liquid anhydride.

[0030] The technical solution of this invention has the following advantages:

[0031] (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.

[0032] (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.

[0033] (3) The process method of the present invention uses a homogeneous catalyst. Some of the succinic anhydride products are separated by filtration or centrifugation, and some are separated by cooling crystallization. Compared with the prior art, the reaction and crystallization processes are coupled, reducing the number of crystallization operation steps and process energy consumption, and greatly simplifying the process.

[0034] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0035] 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.

[0036] The hydrogenation reactor used in the following embodiments has the following structure: a gas outlet is provided at the top of the hydrogenation reactor 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.

[0037] Example 1

[0038] A 10 wt% maleic anhydride was prepared using tetrahydrofuran. RuCl3 was added as an active catalyst at a concentration of 6 mmol / L, followed by triphenylphosphine ligand at a concentration of 8 mmol / L. The solution and hydrogen were introduced into a hydrogenation reactor using a membrane disperser. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 1:1. A vacuum pump and back pressure valve were used to control the absolute pressure in the reaction system at 1 bar, maintaining the reaction system at boiling point. The reaction temperature was 66 °C. Tetrahydrofuran vapor and unreacted hydrogen were discharged from the gas outlet. The reaction was carried out for 2 hours.

[0039] 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%.

[0040] The results of maleic anhydride conversion and succinic anhydride selectivity in the hydrogenation reaction are shown in Table 1.

[0041] Example 2

[0042] A 30 wt% maleic anhydride was prepared using tetrahydrofuran. H₂PtCl₄ was added as an active catalyst at a concentration of 8 mmol / L, followed by triphenylphosphine ligand at a concentration of 10 mmol / L. The solution and hydrogen were introduced into a hydrogenation reactor using a membrane disperser. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 3:1. A vacuum pump and back pressure valve were used to control the absolute pressure in the reaction system at 1.5 bar, maintaining the reaction system at boiling point. The reaction temperature was 80 °C. Tetrahydrofuran vapor and unreacted hydrogen were discharged from the gas outlet. The reaction was carried out 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] A 30 wt% maleic anhydride was prepared using tetrahydrofuran. RuCl3 was added as an active catalyst at a concentration of 9 mmol / L, followed by the addition of 10 mmol / L of biphenylphosphine ligand. The solution and hydrogen were introduced into a hydrogenation reactor using a membrane disperser. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 5:1. A vacuum pump and back pressure valve were used to control the absolute pressure in the reaction system at 2.7 bar, maintaining the reaction system at boiling point. The reaction temperature was 100°C. Tetrahydrofuran vapor and unreacted hydrogen were discharged from the gas outlet. The reaction was carried out for 3 hours.

[0047] 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%.

[0048] The results of maleic anhydride conversion and succinic anhydride selectivity in the hydrogenation reaction are shown in Table 1.

[0049] Example 4

[0050] A 40 wt% maleic anhydride was prepared using tetrahydrofuran. RuCl3 was added as an active catalyst at a concentration of 5 mmol / L, followed by trimethylphosphine ligand at a concentration of 6 mmol / L. The solution and hydrogen were introduced into a hydrogenation reactor using a membrane disperser. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 8:1. A vacuum pump and back pressure valve were used to control the absolute pressure in the reaction system at 5 bar, maintaining the reaction system at boiling point. The reaction temperature was 126 °C. Tetrahydrofuran vapor and unreacted hydrogen were discharged from the gas outlet. The reaction was carried out for 3 hours.

[0051] 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%.

[0052] The results of maleic anhydride conversion and succinic anhydride selectivity in the hydrogenation reaction are shown in Table 1.

[0053] Example 5

[0054] A 50 wt% maleic anhydride was prepared using tetrahydrofuran. NiCl2 was added as an active catalyst at a concentration of 12 mmol / L, followed by triphenylphosphine ligand at a concentration of 16 mmol / L. The solution and hydrogen were introduced into a hydrogenation reactor using a membrane disperser. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 8:1. A vacuum pump and back pressure valve were used to control the absolute pressure in the reaction system at 5 bar, maintaining the reaction system at boiling point. The reaction temperature was 126 °C. Tetrahydrofuran vapor and unreacted hydrogen were discharged from the gas outlet. The reaction was carried out for 4 hours.

[0055] 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%.

[0056] The results of maleic anhydride conversion and succinic anhydride selectivity in the hydrogenation reaction are shown in Table 1.

[0057] Example 6

[0058] A 30 wt% maleic anhydride was prepared using methyl formate. NiCl2 was added as an active catalyst at a concentration of 5 mmol / L, followed by triphenylphosphine ligand at a concentration of 6 mmol / L. The solution and hydrogen were introduced into a hydrogenation reactor 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 back pressure valve were used to control the absolute pressure in the reaction system at 3.5 bar, maintaining the reaction system at boiling point. The reaction temperature was 70°C. Methyl formate vapor and unreacted hydrogen were discharged from the gas outlet. The reaction was carried out for 4 hours.

[0059] 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%.

[0060] The results of maleic anhydride conversion and succinic anhydride selectivity in the hydrogenation reaction are shown in Table 1.

[0061] Example 7

[0062] A 40 wt% maleic anhydride was prepared using methyl formate. RuCl3 was added as an active catalyst at a concentration of 6 mmol / L, followed by the addition of 8 mmol / L of binaphthylphosphine ligand. The solution and hydrogen were introduced into a hydrogenation reactor using a membrane disperser. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 5:1. A vacuum pump and back pressure valve were used to control the absolute pressure in the reaction system at 7 bar, maintaining the reaction system at boiling point. The reaction temperature was 100°C. Methyl formate vapor and unreacted hydrogen were discharged from the gas outlet. The reaction was carried out for 5 hours.

[0063] 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%.

[0064] The results of maleic anhydride conversion and succinic anhydride selectivity in the hydrogenation reaction are shown in Table 1.

[0065] Example 8

[0066] A 70 wt% maleic anhydride was prepared using tetrahydrofuran. RuCl3 was added as an active catalyst at a concentration of 16 mmol / L, followed by triphenylphosphine ligand at a concentration of 20 mmol / L. The solution and hydrogen were introduced into a hydrogenation reactor using a membrane disperser. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 5:1. A vacuum pump and back pressure valve were used to control the absolute pressure in the reaction system at 2 bar, maintaining the reaction system at boiling point. The reaction temperature was 90 °C. Tetrahydrofuran vapor and unreacted hydrogen were discharged from the gas outlet. The reaction was carried out for 5 hours.

[0067] 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%.

[0068] The results of maleic anhydride conversion and succinic anhydride selectivity in the hydrogenation reaction are shown in Table 1.

[0069] Table 1

[0070]

[0071] Comparative Example 1

[0072] This technical solution is the most widely used existing method for producing γ-butyrolactone by hydrogenating maleic anhydride:

[0073] 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.

[0074] 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.

[0075] Comparative Example 2

[0076] Catalytic experiments using γ-butyrolactone as a solvent and a homogeneous catalyst:

[0077] A 30 wt% maleic anhydride solution was prepared using γ-butyrolactone, with RuCl3 added as an active catalyst at a concentration of 9 mmol / L. A 10 mmol / L phosphine ligand was then added. This solution, along with hydrogen gas, was introduced into a hydrogenation reactor via a membrane disperser. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 5:1. The absolute pressure within the reaction system was controlled at 10 bar using a vacuum pump and back pressure valve. The reaction temperature was 100 °C, and external heat transfer oil was used for heating. The system was not in a boiling state, and unreacted hydrogen was discharged from the gas outlet. The reaction lasted for 3 hours. During the reaction, it was observed that although external heat transfer oil was used for heat exchange, the internal temperature continued to rise.

[0078] 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.

[0079] Comparative Example 3

[0080] A 30 wt% maleic anhydride solution was prepared using tetrahydrofuran. RuCl3 was added as an active catalyst at a concentration of 9 mmol / L, followed by 10 mmol / L of binaphthylphosphine ligand. This solution, along with hydrogen gas, was introduced into a hydrogenation reactor via a membrane disperser. The molar ratio of hydrogen to maleic anhydride in the reactants (hydrogen-to-anhydride ratio) was 5:1. A vacuum pump and back pressure valve were used to control the absolute pressure within the reaction system at 15 bar, and the reaction temperature within the reactor was maintained at 100°C. The system was not boiling at this temperature, and the reactor required external circulating cooling water for heat extraction. Unreacted hydrogen gas was discharged from the gas outlet. The reaction was carried out for 3 hours. During the reaction, it was observed that although there was external heat exchange via heat transfer oil, the internal temperature continued to rise.

[0081] 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.

[0082] Table 2 shows the maleic anhydride conversion rate, succinic anhydride selectivity, and energy consumption for succinic anhydride production in Example 3 and Comparative Examples 1-3.

[0083] Table 2

[0084]

[0085] 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, characterized in that, Using tetrahydrofuran or methyl formate as the reaction solvent, maleic anhydride is dissolved at a concentration of 10wt%-70wt%. Then, it is reacted with hydrogen and a homogeneous catalyst in a hydrogenation reactor. The reaction pressure is adjusted to maintain the reaction temperature at 30℃-150℃, and the solvent in the reaction system is kept boiling by adjusting the pressure. A gas outlet is provided on the hydrogenation reactor, and the organic solvent and unreacted hydrogen are continuously discharged from the gas outlet. After the reaction is completed, the reaction product is subjected to solid-liquid separation and / or crystallization to obtain succinic anhydride. The homogeneous catalyst is selected from at least one salt of Pd, Ti, Co, V, Fe, Ir, Rh, Au, Pt, Ni, Ag, Sn, Mo, Zn, Mn, Cu, and Ru.

2. The process method according to claim 1, characterized in that, The concentration of maleic anhydride is 15wt%-70wt%.

3. The process method according to claim 2, characterized in that, The concentration of maleic anhydride is 25wt%-60wt%.

4. The process method according to claim 3, characterized in that, The concentration of maleic anhydride is 30wt%-50wt%.

5. The process method according to claim 1, characterized in that, The hydrogenation reaction is carried out at a temperature of 40℃-120℃.

6. The process method according to claim 5, characterized in that, The hydrogenation reaction is carried out at a temperature of 50℃-120℃.

7. The process method according to claim 6, characterized in that, The hydrogenation reaction is carried out at a temperature of 60℃-100℃.

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

9. The process method according to claim 8, characterized in that, The hydrogenation reaction takes 40 minutes to 2 hours.

10. The process method according to claim 1, characterized in that, The homogeneous catalyst is selected from at least one of RuCl3, PdCl2, CoCl2, NiCl2 and H2PtCl4.

11. The process method according to claim 1, characterized in that, The concentration of the homogeneous catalyst, calculated as a metal element, in the reaction feedstock formed after mixing the maleic anhydride solution and the homogeneous catalyst is not less than 0.001 mmol / L.

12. The process method according to claim 11, characterized in that, The concentration of the homogeneous catalyst, calculated as a metal element, in the reaction feedstock formed after mixing the maleic anhydride solution and the homogeneous catalyst is not less than 1 mmol / L.

13. 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.

14. The process method according to claim 1, characterized in that, It also includes the step of reusing the mother liquor containing the homogeneous catalyst obtained after separation.

15. The process method according to claim 1, characterized in that, The crystallization is a cooling crystallization process, with a temperature of 0℃-60℃.

16. The process method according to claim 1, characterized in that, It also includes the step of condensing the organic solvent and unreacted hydrogen at the gas outlet to recover the hydrogen.

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