Method for continuously preparing succinic anhydride through maleic anhydride hydrogenation

Abstract

The invention provides a method for continuously preparing succinic anhydride through maleic anhydride hydrogenation, which comprises the following steps: inputting dissolved maleic anhydride and a solvent from the upper part of a reactor, and carrying out reverse contact reaction with hydrogen input from the lower part of the reactor; the reaction mixture sequentially passes through a trickle bed reaction section, a cooling section and a bubbling bed reaction section from top to bottom, and a succinic anhydride crude product is output from the bottom of the reactor; separating and purifying the succinic anhydride crude product to obtain a succinic anhydride product; wherein the cooling section is a falling film cooling section. According to the reactor, heat released by the trickle bed reaction section is timely removed through falling film cooling, meanwhile, the solubility of hydrogen is improved, a liquid phase is used as a continuous phase in the bubbling bed reaction section to promote maleic anhydride to fully react, and the reaction temperature is controlled within a proper range; the whole process is simple and convenient to operate, the raw material conversion rate and the product selectivity are improved, the process energy consumption is saved, and the service life of the catalyst is prolonged.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, specifically to a method for the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride. Background Technology

[0002] Succinic anhydride, also known as succinic anhydride, with the molecular formula C4H4O3, is an important intermediate in the synthesis of fine organic chemicals and is widely used in the synthesis of pesticides, pharmaceuticals, and other chemical products. Succinic anhydride can be directly used to synthesize the biodegradable plastic polybutylene succinate (PBS), greatly expanding its applications. In recent years, the rapid increase in demand for biodegradable plastics has placed new demands on the development of succinic anhydride synthesis technology and the expansion of production scale.

[0003] There are two main methods for producing succinic anhydride: the succinic acid dehydration method and the maleic anhydride hydrogenation method. The maleic anhydride hydrogenation method offers higher conversion rates and product purity. Maleic anhydride hydrogenation is further divided into direct hydrogenation and solvent hydrogenation. Since succinic anhydride is a solid at room temperature and has a high melting point, direct hydrogenation requires very high reaction temperatures to prevent the succinic anhydride product from crystallizing in the reaction system. Within a certain temperature range, the reaction rate increases with increasing temperature, but the selectivity decreases significantly with increasing temperature. Therefore, direct hydrogenation at high temperatures results in low selectivity for the succinic anhydride product. Solvent hydrogenation, on the other hand, allows the hydrogenation reaction to proceed at lower temperatures, reducing side reactions and improving selectivity. Therefore, solvent hydrogenation is currently the mainstream method for succinic anhydride synthesis.

[0004] It is worth noting that the hydrogenation of maleic anhydride to succinic anhydride is a strongly exothermic reaction, and the heat of reaction must be removed in a timely manner during the process. Otherwise, it will lead to a series of problems such as difficulty in controlling the reaction temperature, reduced product selectivity, and shortened catalyst life.

[0005] As early as 1941, US Patent US2245404 disclosed a method for the catalytic hydrogenation of maleic anhydride in a solvent to synthesize succinic anhydride. This method uses a built-in spiral heat exchange tube to remove the heat of reaction, and the equipment used is directly transplanted from experimental equipment, which is only suitable for small-scale industrial reaction devices.

[0006] The earliest domestic patent for the continuous production of succinic anhydride by hydrogenation of maleic anhydride is CN101891718A. In this patent, the reactor is an adiabatic trickle bed reactor with gas and liquid flowing downwards in parallel. No heat removal method is considered during the reaction process. The temperature rise of the catalyst bed is controlled by adjusting the concentration of maleic anhydride in the solvent.

[0007] Chinese patent CN101735182A also discloses a method for the continuous production of succinic anhydride from maleic anhydride by hydrogenation. The reactor is also a gas-liquid parallel downward trickling bed adiabatic reactor. This method uses partial reaction liquid cooling circulation to control the temperature rise of the catalyst bed. The disadvantage of this patent is that the circulating liquid contains impurities generated in the reaction. The repeated circulation of impurities through the catalyst bed will lead to catalyst deactivation and reduce the catalyst's lifespan over a long period of time. Later, the inventor of this patent applied for another patent, CN103566837A, for the continuous hydrogenation of maleic anhydride to produce succinic anhydride. This patent uses a two-stage hydrogenation reactor. The first-stage hydrogenation reactor is a bubbling bed reactor for liquid-phase hydrogenation, in which the feed liquid and hydrogen flow upwards in parallel. The heat of reaction is removed by external circulation cooling of the reaction liquid. After cooling, the gas-liquid material after the first-stage reactor enters the second-stage hydrogenation reactor. The second-stage reactor is an adiabatic trickling bed reactor. In the second-stage reactor, the reaction liquid and hydrogen flow downwards in parallel for further hydrogenation reaction, allowing the unconverted maleic anhydride to further complete the reaction. Because this patent uses a circulating reaction liquid for heat removal, there is also the problem of impurities accumulating in the catalyst bed; moreover, setting up a two-stage reactor makes the reaction system more complex, the reaction control is more difficult, and the equipment investment is also increased.

[0008] Patent CN102389751A discloses a fixed-bed reactor and method for preparing succinic anhydride by hydrogenation of maleic anhydride solution. In this method, maleic anhydride solution and hydrogen flow in parallel from top to bottom through the catalyst bed. The heat of reaction is removed by a tube cooler set between the catalyst beds. Fresh hydrogen is added between different beds to maintain the hydrogen pressure, thereby maintaining the reaction rate. The technical challenge of this patent is how to make the gas and liquid two-phase materials uniformly distributed on the bed through the tube cooler between the catalyst beds.

[0009] Patent CN105801536A discloses a method for preparing succinic anhydride by liquid-phase hydrogenation of maleic anhydride. It uses two reactors connected in series. Maleic anhydride is partially catalytically hydrogenated in the first reactor, and the incompletely converted reactants enter the second reactor for further catalytic hydrogenation. The reaction system is complex. This patent uses cold hydrogen gas circulation for heat removal. Since the heat capacity of hydrogen is very small, the heat removal effect of cold hydrogen gas is poor, and the compression and circulation of a large amount of hydrogen gas requires a large amount of compression work.

[0010] Patent CN107253938A discloses a method for preparing succinic anhydride by hydrogenation of maleic anhydride in a multi-stage trickle bed. The reaction liquid is added from the top of the reactor, and hydrogen is added between the beds, employing a dual circulation of liquid phase and hydrogen for heat removal. This patent also suffers from the problem of impurities accumulating in the catalyst bed during material circulation, as well as drawbacks such as poor hydrogen heat removal effect and the large amount of compression work consumed by hydrogen compression.

[0011] Patent CN113856569A discloses a reactor and its control method for the hydrogenation of maleic anhydride to succinic anhydride. The reactor adopts a tubular fixed-bed catalytic reactor configuration, with the catalyst loaded into the tubes. Circulating cooling water is used in the shell side to maintain the bed temperature of the catalyst. Theoretically, this type of reactor can solve the problem of heat removal during reaction. However, this type of reactor is often used for gas-solid two-phase catalytic reactions. For gas-liquid-solid three-phase reactions, the uniform distribution of liquid and gas within the tubes remains difficult.

[0012] Patent CN114452902A discloses a reactor and method for the liquid-phase hydrogenation of maleic anhydride to prepare succinic anhydride. This method employs a two-stage reactor system connected in series. The first stage reactor is a non-adiabatic tubular fixed-bed reactor, with the catalyst packed inside the tubes. A cooling medium is continuously introduced through the shell side to remove the heat of reaction. The effluent from the non-adiabatic reactor enters the second-stage adiabatic reactor, which is also a fixed-bed reactor. Liquid-phase hydrogenation is used, with the reaction liquid and hydrogen entering from the top and exiting from the bottom. This method employs a two-stage reactor, resulting in a complex reaction system. Furthermore, the use of a tubular fixed-bed reactor presents challenges in distributing hydrogen and the reaction liquid within the tubes.

[0013] CN216573024U discloses a method for hydrogenating maleic anhydride in an adiabatic trickle bed reactor. This method involves countercurrent gas-liquid contact during the reaction, with the heat released through a dual gas-liquid circulation system for heat dissipation. However, this method also suffers from the drawbacks of trickle bed reactors: the heat released during the reaction causes excessively high local temperatures at the hydrogenation sites on the catalyst surface, while the circulation of the reaction liquid leads to the accumulation of impurities in the reaction bed.

[0014] In summary, for the solvent hydrogenation process of maleic anhydride, whether it is liquid-phase bubbling bed catalytic hydrogenation or trickling bed gas-phase hydrogenation, in order to achieve good reaction results, it is necessary to solve the problems of sufficient mass transfer contact between the gas and liquid phases and the control of the reaction bed temperature, that is, the problem of heat removal. Summary of the Invention

[0015] To address the shortcomings of existing technologies, this invention discloses a method for the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride. This method organically combines the advantages of trickle bed reactors and liquid-phase bubble bed reactors, enabling uniform mass transfer between the gas and liquid phases at different reaction stages. Simultaneously, it allows for timely removal of reaction heat and avoids the accumulation of impurities during material circulation, thus achieving continuous production to obtain high-purity products.

[0016] To achieve the above technical objectives, this invention proposes a method for the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride. The dissolved maleic anhydride and solvent mixture are input from the top of the reactor and react counter-currently with hydrogen gas input from the bottom. The reaction mixture passes sequentially from top to bottom through a trickle bed reaction section, a cooling section, and a bubble bed reaction section, and crude succinic anhydride is output from the bottom of the reactor. The crude succinic anhydride is then separated and purified to obtain the final succinic anhydride product. The cooling section is a falling film cooling section.

[0017] In the above technical solution, gaseous hydrogen is the continuous phase in the trickle bed reaction section, and the mixture formed by dissolved maleic anhydride and solvent flows through the catalyst bed in the form of droplets. A cooling section is set at the bottom of the trickle bed reaction section to remove the heat of reaction generated in the trickle bed reaction section in a timely manner, so as to prevent the temperature of the reaction system from rising too high and reduce the occurrence of side reactions during the reaction process.

[0018] Furthermore, the cooling section is in the form of a falling film cooler. The material reacting in the trickle bed reaction section is evenly distributed as a film in the downcomer in the falling film cooling section, flowing downwards as a liquid film. During this downward flow, it exchanges heat with the refrigerant and is cooled. Through the forced falling film in the cooling section, the liquid phase material output from the trickle bed reaction section is more evenly distributed in the axial space of the reactor and input into the lower bubbling bed reaction section, thereby promoting the uniform distribution of the gas and liquid phases in the bubbling bed reaction section.

[0019] Furthermore, during the falling film cooling process, the solubility of hydrogen gas in the reactants increases as the temperature decreases, which increases the reaction rate of the bubbling bed reaction section and improves the overall raw material conversion rate of the process.

[0020] Within the bubbling bed reaction section, the catalyst is immersed in liquid, resulting in a high gas-liquid mass transfer coefficient and good heat transfer performance. The high thermal conductivity of the liquid and the mixing of reactants caused by gas bubbling lead to a more uniform radial temperature distribution within the reaction bed.

[0021] This reactor structure effectively achieves balanced control of the reactor reaction temperature, mitigating localized temperature rise at hydrogenation sites on the catalyst surface during hydrogenation. It effectively reduces the occurrence of side reactions, ensuring high selectivity in the hydrogenation reaction, thereby reducing impurity formation. The suitable reaction temperature inhibits the polymerization of organic matter on the catalyst surface, resulting in less carbon accumulation on the catalyst surface and extending its lifespan.

[0022] The method for the continuous preparation of succinic anhydride from maleic anhydride by hydrogenation of this invention achieves a maleic anhydride conversion rate of 99.8% and a succinic anhydride selectivity of 99.6%. In practical processes, the high maleic anhydride conversion rate reduces the amount of hydrogen circulating, thereby lowering the energy consumption for hydrogen circulation compression and saving process energy. Furthermore, compared to existing technologies that use cold hydrogen circulation or rely on the circulation of reactants to remove reaction heat, this invention eliminates the need for material circulation, avoiding the poisoning effect of impurities repeatedly circulating through the catalyst bed and further extending the catalyst's lifespan.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: The reactor of the present invention adopts a gas-liquid countercurrent contact reaction. The reaction mixture passes through the trickling bed reaction section, the cooling section and the bubbling bed reaction section from top to bottom. The exothermic reaction of the trickling bed reaction section is removed in time by falling film cooling, while the solubility of hydrogen in the reactants is improved. In the bubbling bed reaction section, the liquid phase is used as the continuous phase to promote the full reaction of maleic anhydride and control the reaction temperature within a suitable range. The overall process is simple to operate, improves the raw material conversion rate and product selectivity, saves process energy consumption and extends the service life of the catalyst. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0025] Figure 1 This diagram illustrates a structural representation of the reaction used in the method for the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride according to the present invention.

[0026] The above figures include the following reference numerals:

[0027] 1-Shell, 11-First feed inlet, 12-Second feed inlet, 13-Liquid phase outlet, 14-Gas phase outlet, 2-Trickling bed, 3-Falling film cooling section, 31-Downcomer, 32-Refrigerant inlet, 33-Refrigerant outlet, 4-Bubble bed, 51-First liquid distributor, 52-First liquid distributor, 53-Second liquid distributor, 54-Second liquid distributor, 55-Gas distributor. Detailed Implementation

[0028] To facilitate understanding of the present invention, a more comprehensive description will be provided below, along with preferred embodiments. However, it should be understood that these embodiments are merely for more detailed explanation and should not be construed as limiting the invention in any way, i.e., not intended to limit the scope of protection of the invention.

[0029] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0030] For ease of explanation, spatial relative terms such as "upper" and "lower" are used in the embodiments to describe the relationship of one element or feature shown in the figures relative to another element or feature. It should be understood that, in addition to the orientation shown in the figures, spatial terms are intended to include different orientations of the device during use or operation. For example, if the device in the figures is inverted, an element described as being "below" other elements or features would be positioned "upper" of those other elements or features. In this invention, the upper part of the reactor refers to the area from the middle of the reactor height to the top, and the lower part of the reactor refers to the area from the middle of the reactor height to the bottom.

[0031] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0032] Example 1

[0033] A method for the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride is disclosed. Dissolved maleic anhydride and solvent are introduced from the top of the reactor and react counter-currently with hydrogen introduced from the bottom. The reaction mixture passes sequentially from top to bottom through a trickle bed reaction section, a cooling section, and a bubbling bed reaction section, and crude succinic anhydride is output from the bottom of the reactor. The crude succinic anhydride is then separated and purified to obtain the final succinic anhydride product. The cooling section is a falling film cooling section.

[0034] Figure 1The diagram illustrates an optional reactor structure for the continuous hydrogenation of maleic anhydride to succinic anhydride according to the present invention. The reactor includes a shell 1, which, from top to bottom, comprises a trickling bed 2, a falling film cooling section 3, and a bubbling bed 4. Dissolved maleic anhydride and solvent are fed into the first inlet 11 at the top of the reactor and enter the trickling bed 2 to react with hydrogen gas introduced from the second inlet 12 at the bottom of the reactor. The reacted material then enters the falling film cooling section 3 under gravity. The reactor includes a downcomer 31 and a heat exchange shell surrounding the downcomer 31. The refrigerant is introduced through the refrigerant inlet 32 ​​and exchanges heat with the material in the downcomer 31 before being discharged from the refrigerant outlet 33. After the reaction, the material passes through the downcomer 31 and exchanges heat with the refrigerant in the shell to lower its temperature. It then flows into the bubbling bed 4 at the bottom of the reactor to continue the reaction. After the material has fully reacted in the bubbling bed 4, the crude succinic anhydride is discharged from the liquid phase outlet 13 of the reactor. Unreacted hydrogen is discharged from the gas phase outlet 14 at the top of the reactor.

[0035] It should be noted that the reactor may be equipped with upper and lower end flanges to facilitate the installation of devices and components within the shell, and may also be equipped with catalyst loading and unloading ports for use in different reaction sections. In actual process operation, a hydrogen circulation system may be established first, followed by the continuous hydrogenation reaction of maleic anhydride by introducing a mixture of dissolved maleic anhydride and solvent from the top of the reactor.

[0036] In some examples of the present invention, optionally, the operating pressure of the reactor is 2.0 to 8.0 MPa. Controlling the reaction pressure is beneficial to the regulation process and improves the temperature control effect of the process.

[0037] In some examples of the present invention, the molar ratio of maleic anhydride to solvent may be selected as 1:(3-6), thereby controlling the reaction rate by optimizing the concentration of maleic anhydride in the feed of the trickle bed 2, and making the temperature of the reaction system more stable and easier to control.

[0038] In some examples of the present invention, the molar ratio of hydrogen to maleic anhydride input to the lower part of the reactor can be selected as 1:(1.1 to 1.3), and excess hydrogen is input to promote the full reaction of maleic anhydride.

[0039] In some examples of the present invention, the temperature at which the dissolved maleic anhydride and solvent are input into the reactor can be selected as 50-55°C. Controlling the temperature of the inlet material enhances the regulation of the reaction rate and the stability of temperature control.

[0040] In some examples of the present invention, the outlet temperature may be selected as 70-90°C.

[0041] In some examples of the present invention, after cooling in the cooling section, the temperature of the reaction mixture can be selected as 50-65°C. This part of the material will be input under gravity to continue the maleic anhydride hydrogenation reaction. Optimizing the inlet temperature of the incoming reaction material to 50-65°C is beneficial to improving the solubility of hydrogen and promoting the full reaction of maleic anhydride in the subsequent process. This controls the temperature of the reaction system within a suitable temperature range, reduces the occurrence of side reactions, and improves the selectivity of succinic anhydride.

[0042] In some examples of the present invention, the volume hourly space velocity (VHSV) of the bubbling bed reaction section is 2.0–4.0 h⁻¹. -1 This facilitates the control of the reaction process in the bubbling bed reaction section during actual process, thereby further controlling the temperature of the bubbling bed reaction section.

[0043] In some examples of this invention, the temperature of the hydrogen gas input from the bottom of the reactor can be selected as 50–70°C. This portion of hydrogen gas is input from the bottom of the reactor and preferentially enters the bubbling bed reaction section to continue the maleic anhydride hydrogenation reaction with the reacted material. This invention optimizes the hydrogen inlet temperature of the newly input reactor to 50–70°C, which is beneficial for the efficient hydrogenation reaction and for controlling the temperature of the bubbling bed reaction section within a suitable range.

[0044] It should be noted that the present invention does not limit the specific operation of reducing the temperature of the hydrogen gas input to the reactor. It can be achieved by using a compressor in combination with a condenser. Those skilled in the art can select appropriate equipment and operation methods as needed.

[0045] In some examples of the present invention, the outlet temperature of the bubbling bed reaction section may be selected as 80-100°C.

[0046] In some examples of this invention, the method for the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride may optionally further include mixing the unreacted hydrogen output from the reactor and / or the hydrogen obtained from separation and purification with fresh hydrogen for recycling. In a specific process, unreacted hydrogen is collected from the upper outlet of the reactor; the separation and purification process may include gas-liquid separation of the reacted material, with the separated liquid phase undergoing subsequent purification to obtain a high-purity product, and the separated gaseous phase being unreacted hydrogen; both portions of hydrogen can be recycled as circulating gas. The fresh hydrogen mentioned in this invention is relative to the recycled hydrogen gas; fresh hydrogen refers to the non-recycled hydrogen input into the process system.

[0047] In some examples of the present invention, the molar ratio of newly input hydrogen to recycled hydrogen can be selected as 1:(500-1200), thereby improving the utilization rate of raw materials and saving process costs.

[0048] This invention does not limit the catalyst used for the hydrogenation of maleic anhydride to succinic anhydride. Those skilled in the art can select suitable catalysts based on this invention and as needed, without limiting the scope of protection of this invention. In a further example of this invention, the catalyst packed in the bubbling bed reaction section can be a granular nickel-based hydrogenation catalyst, and more particularly, at least one of Raney nickel, Ni / Al2O3-SiO2, or Ni / Al2O3.

[0049] This invention does not limit the type of solvent. Those skilled in the art can select a suitable solvent to dissolve maleic anhydride based on this invention and as needed, without limiting the scope of protection of this invention. In a further example of this invention, the solvent may include one or more of dimethyl succinate, diethyl succinate, ethyl acetate, butyl acetate, and γ-butyrolactone.

[0050] It should be noted that the cooling section is equipped with a downcomer 31 for film distribution and a shell side surrounding the downcomer 31. Refrigerant is introduced into the shell side to reduce the temperature of the reacted material through heat exchange. In a further example of the invention, the type of refrigerant is not limited; it can be cooling water or circulating water, and those skilled in the art can select according to actual needs. In a further example of the invention, the temperature of the refrigerant introduced into the cooling section can be selected as 40–60°C.

[0051] In some examples of the present invention, a first liquid distributor 51 is provided on the upper part of the drip bed 2. The dissolved maleic anhydride and solvent input into the reactor are distributed into the reaction bed through the liquid distributor for reaction. Furthermore, the pipeline for inputting the dissolved maleic anhydride and solvent is connected to a first liquid distributor 52.

[0052] In some examples of the present invention, the cooling section is provided with a second distributor 53 for uniformly distributing the material after reaction in the drip bed 2 to each downcomer 31.

[0053] In some examples of the present invention, optionally, the lower part of the downcomer 31 is connected to a second liquid distributor 54 for uniformly distributing liquid to the bubble bed 4.

[0054] In some examples of the present invention, a gas distributor 55 is provided at the lower part of the bubbling bed reaction section so that the hydrogen gas input into the reactor is uniformly distributed in the bed of the bubbling bed reaction section.

[0055] Based on the method for the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride shown in Example 1, Examples 2-5 illustrate the process of the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride under specific operating conditions according to the present invention. It should be noted that these examples are only preferred embodiments and do not limit the scope of protection of the present invention.

[0056] Example 2

[0057] A method for the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride involves dissolving the raw material maleic anhydride by mixing it with the solvent γ-butyrolactone at a molar ratio of 1:4 at 50°C, and then feeding the solution into the upper feed inlet of the reactor. Fresh hydrogen is mixed with circulating gas and fed into the reactor at a molar ratio of 1.2 times that of maleic anhydride at 50°C from the lower feed inlet. The molar ratio of fresh hydrogen to circulating gas is 1:1200.

[0058] The feed liquid flows from top to bottom, while hydrogen flows from bottom to top in a countercurrent contact reaction. The operating pressure of the reactor is controlled at 8.0 MPa by adjusting the valve opening of the exhaust gas system. The catalyst used in this embodiment is Raney nickel. The temperature at the end of the upper trickle bed reaction section is 80°C. After cooling through the falling film cooling section 3 between the beds, the reaction mixture is cooled to 60°C. The shell side of the cooling section uses 50°C circulating desalination cooling water for cooling. The reactants, after being cooled, continue to react in the lower bubbling bed. The volume hourly space velocity (VHSV) of the bubbling bed reaction section is 3.0 h⁻¹. -1 The liquid phase outlet temperature of the bubbling bed reaction section is 90℃.

[0059] Crude succinic anhydride is discharged from the bottom outlet of the reactor. This crude product is then separated and purified to obtain the final succinic anhydride product. In this embodiment, the conversion rate of maleic anhydride is 99.3%, and the selectivity of succinic anhydride is 99.2%.

[0060] The specific separation and purification process includes: the crude succinic anhydride flows into the gas-liquid separator by gravity; after gas-liquid separation, the gaseous hydrogen enters the cold hydrogen gas-liquid separator; unreacted hydrogen is discharged from the top outlet of the reactor, cooled by the cooler, and also enters the cold hydrogen gas-liquid separator; in the cold hydrogen gas-liquid separator, hydrogen and entrained liquid undergo gas-liquid separation; the circulating gas from the top of the tower is compressed and pressurized before entering the lower feed inlet of the reactor for circulating reaction; the liquid phase obtained from the cold hydrogen gas-liquid separator is input into the gas-liquid separator; the liquid phase output from the gas-liquid separator is purified to obtain the succinic anhydride product.

[0061] Example 3

[0062] A method for the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride involves dissolving the raw material maleic anhydride by mixing it with the solvent γ-butyrolactone at a molar ratio of 1:3 at 55°C, and then feeding the mixture into the upper feed inlet of the reactor. Fresh hydrogen gas is mixed with circulating gas and fed into the reactor at a molar ratio of 1.1 times that of maleic anhydride, with the temperature controlled at 70°C. The molar ratio of fresh hydrogen gas to circulating gas is 1:500.

[0063] The feed liquid flows from top to bottom, while hydrogen flows from bottom to top in a countercurrent contact reaction. The operating pressure of the reactor is controlled at 2.0 MPa by adjusting the valve opening of the exhaust gas system. The catalyst used in this embodiment is Raney nickel. The end temperature of the upper trickling bed reaction section is 70°C. After cooling through the falling film cooling section 3 between the beds, the reaction mixture is cooled to 50°C. The shell side of the cooling section uses circulating desalination cooling water at 45°C for cooling. The reactants, after being cooled, continue to react in the lower bubbling bed. The volume hourly space velocity (VHSV) of the bubbling bed reaction section is 2.0 h⁻¹. -1 The liquid phase outlet temperature of the bubbling bed reaction section is 100℃.

[0064] Crude succinic anhydride is discharged from the bottom outlet of the reactor. This crude product is then separated and purified to obtain the final succinic anhydride product. In this embodiment, the conversion rate of maleic anhydride is 96.5%, and the selectivity of succinic anhydride is 98.6%.

[0065] The method for separating and purifying crude succinic anhydride in this embodiment is the same as that in Example 2.

[0066] Example 4

[0067] A method for the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride involves dissolving the raw material maleic anhydride by mixing it with the solvent γ-butyrolactone at a molar ratio of 1:6 at 50°C, and then feeding the solution into the upper feed inlet of the reactor. Fresh hydrogen is mixed with circulating gas and fed into the reactor at a molar ratio of 1.3 times that of maleic anhydride, with the temperature controlled at 60°C, through the lower feed inlet. The molar ratio of fresh hydrogen to circulating gas is 1:800.

[0068] The feed liquid flows from top to bottom, while hydrogen flows from bottom to top in a countercurrent contact reaction. The operating pressure of the reactor is controlled at 6.0 MPa by adjusting the valve opening of the exhaust gas system. The catalyst used in this embodiment is Ni / Al2O3-SiO2. The end temperature of the upper trickling bed reaction section is 90°C. After cooling through the falling film cooling section 3 between the beds, the reaction mixture is cooled to 65°C. The shell side of the cooling section uses 55°C circulating desalination cooling water for cooling. The reactants, after being cooled, continue to react in the lower bubbling bed. The volume hourly space velocity (VHSV) of the bubbling bed reaction section is 4.0 h⁻¹. -1 The liquid phase outlet temperature of the bubbling bed reaction section is 85℃.

[0069] Crude succinic anhydride is discharged from the bottom outlet of the reactor. This crude product is then separated and purified to obtain the final succinic anhydride product. In this embodiment, the conversion rate of maleic anhydride is 99.5%, and the selectivity of succinic anhydride is 99.3%.

[0070] The method for separating and purifying crude succinic anhydride in this embodiment is the same as that in Example 2.

[0071] Example 5

[0072] A method for the continuous preparation of succinic anhydride by hydrogenation of maleic anhydride involves dissolving the raw material maleic anhydride by mixing it with the solvent γ-butyrolactone at a molar ratio of 1:5 at 52°C, and then feeding the mixture into the upper feed inlet of the reactor. Fresh hydrogen is mixed with circulating gas and fed into the reactor at a molar ratio of 1.3 times that of maleic anhydride, with the temperature controlled at 50°C, through the lower feed inlet. The molar ratio of fresh hydrogen to circulating gas is 1:1000.

[0073] The feed liquid reacts countercurrently from top to bottom, while hydrogen gas reacts from bottom to top. The operating pressure of the reactor is controlled at 7.0 MPa by adjusting the valve opening of the exhaust gas system. The catalyst used in this embodiment is Ni / Al2O3. The end temperature of the upper trickling bed reaction section is 85°C. After cooling in the falling film cooling section 3 between the beds, the reaction mixture is cooled to 55°C. The shell side of the cooling section uses 40°C circulating desalination cooling water for cooling. The reactants, after cooling, continue to react in the lower bubbling bed. The material space velocity (HSV) of the reaction mixture in the bubbling bed reaction section is 3.5 h⁻¹. -1 The liquid phase outlet temperature of the bubbling bed reaction section is 90℃.

[0074] Crude succinic anhydride is discharged from the bottom outlet of the reactor. This crude product is then separated and purified to obtain the final succinic anhydride product. In this embodiment, the conversion rate of maleic anhydride is 99.8%, and the selectivity of succinic anhydride is 99.6%.

[0075] The method for separating and purifying crude succinic anhydride in this embodiment is the same as that in Example 2.

[0076] It should be noted that the above description is a further detailed explanation of the present invention in conjunction with specific embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple improvements can be made without departing from the concept of the present invention, and all such improvements should be considered to fall within the scope of protection of the present invention.

Claims

1. A process for the continuous production of succinic anhydride by hydrogenation of maleic anhydride, characterized in that, The dissolved maleic anhydride and solvent are input from the upper part of the reactor and react reversely with hydrogen input from the lower part of the reactor; the reaction mixture passes through the trickle-bed reaction section, the cooling section and the bubbling-bed reaction section in turn from top to bottom, and the crude product of succinic anhydride is output from the bottom of the reactor; the crude product of succinic anhydride is separated and purified to obtain the product of succinic anhydride; wherein the cooling section is a falling-film cooling section.

2. The process for the continuous production of succinic anhydride by hydrogenation of succinic acid according to claim 1, characterized in that, The operating pressure of the reactor is 2.0-8.0 MPa.

3. The process for the continuous production of succinic anhydride by hydrogenation of succinic acid according to claim 1, characterized in that, The molar ratio of the maleic anhydride to the solvent is 1:(3-6).

4. The process for the continuous production of succinic anhydride by hydrogenation of succinic acid according to claim 1, characterized in that, The temperature of the dissolved maleic anhydride and solvent input into the reactor is 50-55℃.

5. The process for the continuous production of succinic anhydride by hydrogenation of succinic acid according to claim 1, characterized in that, After being cooled by the cooling section, the temperature of the reaction mixture is 50-65℃.

6. The process for the continuous production of succinic anhydride by hydrogenation of succinic acid according to claim 1, characterized in that, The volume space velocity of the bubbling bed reaction section is 2.0-4.0h -1 .

7. The process for the continuous production of succinic anhydride by hydrogenation of succinic acid according to claim 1, characterized in that, The temperature of the hydrogen input from the lower part of the reactor is 50-70℃.

8. The process for the continuous production of succinic anhydride by hydrogenation of succinic acid according to claim 1, characterized in that, The unreacted hydrogen output from the reactor and / or the hydrogen obtained by the separation and purification is recycled after being mixed with fresh hydrogen.

9. The process for the continuous production of succinic anhydride by hydrogenation of maleic anhydride according to claim 8, characterized in that, The molar ratio of the newly input hydrogen to the recycled hydrogen is 1:(500-1200).

10. The process for the continuous production of succinic anhydride by hydrogenation of succinic acid according to claim 1, characterized in that, The catalysts filled in the trickle-bed reaction section and the bubbling-bed reaction section are granular nickel-based hydrogenation catalysts.

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