Production method for high-purity polymerization-grade succinic anhydride

Abstract

The present invention provides a production method for high-purity polymerization-grade succinic anhydride, comprising the steps of: (1) mixing hydrogen and maleic anhydride, heating the mixture, introducing the mixture into a gas-liquid separator for flash vaporization and gasification, separating heavy component impurities from the maleic anhydride, and introducing the hydrogen and maleic anhydride into a reactor from the top of the reactor; (2) in the presence of a nickel-based catalyst, allowing the hydrogen and maleic anhydride to react in a gas phase form in the reactor to generate crude succinic anhydride; (3) subjecting the crude succinic anhydride to two-stage vacuum evaporation to remove heavy components, thereby obtaining a first purified succinic anhydride; (4) subjecting the first purified succinic anhydride to two-stage rectification to remove light components, thereby obtaining a second purified succinic anhydride; and (5) subjecting the second purified succinic anhydride to two-stage low-temperature crystallization to improve the purity of succinic anhydride, thereby obtaining a succinic anhydride product. The present invention adopts a gas-phase hydrogenation reaction of maleic anhydride, which improves the reaction efficiency and reduces by-products, enabling the purity of the succinic anhydride product to be improved to 99.9 wt% or above.

Description

A method for producing high-purity polymer-grade succinic anhydride Technical Field

[0001] This invention belongs to the field of organic chemical synthesis, and specifically relates to a method for producing high-purity polymeric succinic anhydride. Background Technology

[0002] Polybutylene succinate (PBS) is a novel biodegradable plastic with excellent biodegradability, mechanical and processing properties comparable to polypropylene (PP), heat resistance exceeding 100°C, and good light stability. It has wide applications in food, surfactants, coatings, pharmaceuticals, and agriculture. The polymerization process of PBS generally uses succinic acid or succinic anhydride as raw materials. Succinic anhydride, due to its non-corrosive nature and lower wastewater production during polymerization, is more valuable. However, the purity of succinic anhydride significantly affects the performance of the polymerized PBS; high-purity succinic anhydride can improve the performance of PBS and meet the requirements of PBS polymerization.

[0003] Currently, succinic anhydride is mainly produced through liquid-phase catalytic hydrogenation of maleic anhydride. According to published reports, such liquid-phase catalytic reaction systems typically require the addition of large amounts of solvent and high-flow-rate external circulation to prevent maleic anhydride solidification and achieve heat removal from the reaction. For example, invention patent ZL201110235411.5 controls the hydrogenation reaction temperature by installing a cooler in the middle of the catalyst bed in a trickle-bed reactor, thereby achieving highly selective synthesis of succinic anhydride. This method can effectively control the catalyst bed temperature. However, when the concentration of maleic anhydride in the feed solution increases to improve the capacity of a single reactor, extremely high temperatures can easily form at the hydrogenation sites on the catalyst surface, causing sintering of the active catalyst components or polymerization and coking of organic matter. CN103566837B, on the other hand, dissolves maleic anhydride in a suitable solvent and typically uses external circulation for heat removal to control the reaction temperature. CN117486842A uses a copper-based catalytic system, which has relatively harsh operating conditions. From the perspective of reaction mechanism, the metallic properties of Cu-based catalysts can lead to violent reactions and are prone to excessive hydrogenation to generate γ-butyrolactone (GBL). GBL is the main impurity affecting the purity of succinic anhydride and is difficult to separate. Therefore, the key to controlling the hydrogenation reaction is whether the generation of GBL can be controlled.

[0004] The existing methods for producing succinic anhydride have the following main problems: (1) The maleic anhydride liquid-phase hydrogenation reaction system needs to be carried out in a solvent (such as the commonly used GBL), which is inefficient. The solvent needs to be completely separated and purified. Once mixed into the succinic anhydride, it is difficult to separate. This is one of the reasons why the purity of succinic anhydride is difficult to improve by traditional production methods. (2) The maleic anhydride hydrogenation reaction has a large heat of reaction. If the heat is not removed in time, excessive hydrogenation will occur, resulting in many by-products, GBL and other impurities, which are difficult to separate. The purity of the product is poor, generally between 99.0% and 99.5%, which leads to poor performance of PBS made from succinic anhydride and affects its application in the field of PBS synthesis. Liquid-phase hydrogenation requires heat removal through a large flow rate of external circulation, which has the limitations of high consumption and difficulty in scale-up. (3) Separation is difficult, and the product quality is hard to meet the requirements of the polymerization grade. The product contains byproducts such as GBL, succinic acid, acrylic acid, and fumaric acid. Since the boiling points of these byproducts are very high and close to those of succinic anhydride, they are difficult to separate using traditional distillation methods. Larger reflux flow rates and higher evaporation rates are required, leading to higher energy consumption. High-temperature heating will also cause the color number to increase, and side reactions at high temperatures will generate more polymer impurities, leading to coking, scaling, and blockage of the heat exchanger. Therefore, how to improve the reaction, overcome the limitations of distillation methods, improve the purity of succinic anhydride, reduce energy consumption, and avoid coking, scaling, and blockage of the heat exchanger are important problems currently facing succinic anhydride production technology. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing high-purity polymeric grade succinic anhydride.

[0006] A first aspect of the present invention provides a method for producing succinic anhydride, comprising the steps of:

[0007] (1) Mix hydrogen and maleic anhydride and heat to 160-180°C. Then, enter the gas-liquid separator for flash vaporization to separate the heavy component impurities in maleic anhydride. Then, introduce hydrogen and maleic anhydride into the reactor from the top of the reactor.

[0008] (2) In the presence of a nickel-based catalyst, hydrogen and maleic anhydride are reacted in the reactor in the gas phase, wherein the molar ratio of hydrogen to maleic anhydride is 20-500:1, the reaction pressure is 5.0-8.0 MPaG, the reaction temperature is 160-180℃, and crude succinic anhydride is produced.

[0009] (3) The crude succinic anhydride is subjected to two-stage vacuum evaporation to remove heavy components. The vacuum pressure is 0.1-50 kPaA and the temperature is 130-170℃ to obtain the first purified succinic anhydride.

[0010] (4) The first purified succinic anhydride is subjected to two-stage distillation to remove light components. The vacuum pressure is 0.1-50 kPaA and the temperature is 120-160℃ to obtain the second purified succinic anhydride.

[0011] (5) The purity of the second purified succinic anhydride is improved by two-stage low-temperature crystallization. The evaporation temperature is 110-135℃ and the crystallization pressure is 0.01-30kPaA to obtain the succinic anhydride product.

[0012] In one or more embodiments, in step (5), the first stage of low-temperature crystallization involves cooling and crystallizing in a first crystallizer, followed by heating to induce sweating and remove impurities; the second stage of low-temperature crystallization involves cooling and crystallizing in a second crystallizer, followed by heating to induce sweating and remove impurities, to obtain the succinic anhydride product; and / or, in step (5), the sweating temperature is 120-130°C.

[0013] In one or more embodiments, in step (3), the vacuum pressure is 0.1-30 kPaA.

[0014] In one or more embodiments, the method has one or more of the following features:

[0015] In step (3), the first-stage vacuum evaporation is carried out first in a rising film evaporator and then in a falling film evaporator;

[0016] In step (3), the second-stage vacuum evaporation is carried out in a thin-film evaporator;

[0017] In step (3), the first-stage vacuum evaporation is carried out at 1-20 kPaA;

[0018] In step (3), the second-stage vacuum evaporation is carried out at 0.1-1 kPaA;

[0019] In step (3), the first-stage vacuum evaporation is carried out at 130-150℃;

[0020] In step (3), the second-stage vacuum evaporation is carried out at 150-170℃.

[0021] In one or more embodiments, the method has one or more of the following features:

[0022] In step (4), the first-stage distillation is carried out in the first-stage distillation column, the first light component is collected from the top of the first-stage distillation column, and succinic anhydride is collected from the bottom of the first-stage distillation column for the second-stage distillation.

[0023] In step (4), the second-stage distillation is carried out in the second-stage distillation column, the second light component is collected from the bottom of the second-stage distillation column, and the second purified succinic anhydride is collected from the top of the second-stage distillation column;

[0024] In step (4), the first-stage distillation is carried out at 1-20 kPa A;

[0025] In step (4), the first-stage distillation is carried out at 130-150℃;

[0026] In step (4), the second-stage distillation is carried out at 0.1-1 kPa A;

[0027] In step (4), the second-stage distillation is carried out at 140-150℃.

[0028] In one or more embodiments, the first light component comprises one or more selected from γ-butyrolactone, 1,4-butanediol, tetrahydrofuran, and maleic anhydride; and / or, the second light component comprises one or two selected from succinic acid and succinic acid.

[0029] In one or more embodiments, in step (2), the unreacted hydrogen in the reactor is recycled after removing entrained organic matter by absorption washing; and / or, the crude succinic anhydride obtained in step (2) is first separated into hydrogen by a washing tower and then subjected to vacuum evaporation in step (3).

[0030] In one or more embodiments, in step (1), the reactor is a fixed-bed reactor, preferably a tubular fixed-bed reactor.

[0031] In one or more embodiments, the nickel-based catalyst is a Ni-supported catalyst on an Al2O3 support.

[0032] In one or more embodiments, the nickel-based catalyst contains 5-40 wt% Ni.

[0033] In one or more embodiments, the nickel-based catalyst is prepared by an equal-volume impregnation method.

[0034] In one or more embodiments, the Ni source is Ni(NO3)2.6H2O.

[0035] In one or more embodiments, the diameter of the Al2O3 support is 1-5 mm.

[0036] In one or more embodiments, the specific surface area of ​​the Al2O3 support is ≥200 m². 2 / g.

[0037] In one or more embodiments, the pore volume of the Al2O3 support is 0.30-0.80 cm³. 3 / g.

[0038] In one or more embodiments, the purity of the succinic anhydride product obtained in step (5) is ≥99.9 wt%. Attached Figure Description

[0039] Figure 1 is a flowchart of the succinic anhydride production process in some embodiments of the present invention.

[0040] Figure 2 shows the chromatographic results of the succinic anhydride prepared in Example 1.

[0041] Figure 3 shows the chromatographic results of the succinic anhydride prepared in Example 2.

[0042] Explanation of reference numerals in the attached drawings: 1-Preheater; 2-Gas-liquid separator; 3-Reactor; 4-Compressor; 5-Scrubbing tower; 6-Heat exchanger; 7-Detergent recovery tower; 8-Rising film evaporator; 9-Falling film evaporator; 10-Thin film evaporator; 11-First-stage distillation column; 12-Second-stage distillation column; 13-First crystallizer; 14-Second crystallizer; 15-Vacuum pack. Detailed Implementation

[0043] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0044] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0045] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0046] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0047] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0048] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0049] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0050] This invention employs an impregnation method to prepare Ni-Al2O3 catalysts, controlling the formation of byproducts during the reaction stage. The invention utilizes a gas-phase hydrogenation reaction of maleic anhydride, avoiding hot spots and coking issues caused by excessively high local temperatures in the reaction system, thus suppressing side reactions and preventing over-hydrogenation. The gas-phase hydrogenation reaction of maleic anhydride does not require a solvent, improving efficiency and reducing the load on distillation. Polymer-grade succinic anhydride is produced through distillation coupled with low-temperature crystallization, meeting the technical requirements of PBS synthesis.

[0051] This invention provides a method for producing succinic anhydride, comprising the following steps:

[0052] (1) Mix hydrogen and maleic anhydride and heat to 160-180°C. Then, enter the gas-liquid separator for flash vaporization to separate the heavy component impurities in maleic anhydride. Then, introduce hydrogen and maleic anhydride into the reactor from the top of the reactor.

[0053] (2) Under the action of a nickel-based catalyst, hydrogen and maleic anhydride are reacted in the reactor in the gas phase, wherein the molar ratio of hydrogen to maleic anhydride is 20-500:1, the reaction pressure is 5.0-8.0 MPaG, the reaction temperature is 160-180℃, and crude succinic anhydride is produced.

[0054] (3) The crude succinic anhydride is subjected to two-stage vacuum evaporation to remove heavy components. The vacuum pressure is 0.1-50 kPaA and the temperature is 130-170℃ to obtain the first purified succinic anhydride.

[0055] (4) The first purified succinic anhydride is subjected to two-stage distillation to remove light components. The vacuum pressure is 0.1-50 kPaA and the temperature is 120-160℃ to obtain the second purified succinic anhydride.

[0056] (5) The purity of the second purified succinic anhydride is improved by two-stage low-temperature crystallization. The evaporation temperature is 110-135℃ and the crystallization pressure is 0.01-30kPaA to obtain the succinic anhydride product.

[0057] In step (1), hydrogen and maleic anhydride can be mixed and heated to 160-180°C, for example, 160°C, 170°C, or 180°C. For instance, hydrogen and maleic anhydride can be heated to 160-180°C using preheater 1. After hydrogen and maleic anhydride are introduced into gas-liquid separator 2, the saturated vapor pressure of maleic anhydride decreases. Through flash evaporation, the boiling point of maleic anhydride decreases accordingly, allowing it to vaporize at a temperature above 160°C but below the atmospheric boiling point (200°C). After the raw material maleic anhydride vaporizes, the heavy component impurities entrained in the maleic anhydride cannot vaporize and are separated from the reaction raw materials from the bottom of gas-liquid separator 2. Hydrogen and maleic anhydride enter the reactor from the top of reactor 3.

[0058] In step (2), the molar ratio of hydrogen to maleic anhydride can be 20-500:1, for example 50:1, 80:1, 100:1, 130:1, 150:1, 180:1, 200:1, 230:1, 250:1, 280:1, 300:1, 330:1, 350:1, 380:1, 400:1, 450:1, or 500:1. Preferably, the molar ratio of hydrogen to maleic anhydride can be 200-400:1.

[0059] In step (2), the reaction pressure can be 5.0-8.0 MPaG, for example 5.2 MPaG, 5.5 MPaG, 5.8 MPaG, 6.0 MPaG, 6.2 MPaG, 6.5 MPaG, 6.8 MPaG, 7.0 MPaG, 7.2 MPaG, 7.5 MPaG, 7.8 MPaG, or 8.0 MPaG. Preferably, the reaction pressure is 5.0-7.0 MPaG or 5.5-6.5 MPaG. Using the reaction pressure defined herein allows for the production of crude succinic anhydride with high purity. Using the reaction pressure defined herein, the purity of the crude succinic anhydride can reach 97% or higher, 98% or higher, or 99% or higher, for example 99.1% or higher, 99.2% or higher, or 99.3% or higher. Furthermore, by using the reaction pressure defined in this paper, the succinic anhydride product purified by steps (3), (4), and (5) can have a high purity. For example, the purity of the succinic anhydride product purified by steps (3), (4), and (5) can reach more than 98%, more than 99%, more than 99.1%, more than 99.2%, more than 99.3%, more than 99.5%, more than 99.8%, or more than 99.9%, such as more than 99.91%, more than 99.92%, more than 99.93%, more than 99.94%, more than 99.95%, and more than 99.96%.

[0060] In step (2), the reaction temperature can be 160-180℃, for example, 160℃, 165℃, 170℃, 175℃, or 180℃. Preferably, the reaction temperature is 160-170℃ or 170-180℃. Using the temperature defined herein allows hydrogen and maleic anhydride to react in the gaseous phase in the reactor. At lower reaction temperatures, hydrogen and maleic anhydride react in the liquid phase, resulting in a higher content of impurities in the crude succinic anhydride obtained in step (2). By controlling the reaction temperature in step (2) within the range defined herein, the purity of the crude succinic anhydride obtained in step (2) can reach 97% or higher, 98% or higher, or 99% or higher, for example, 99.1% or higher, 99.2% or higher, or 99.3% or higher. Furthermore, by using the temperature defined herein for the reaction in step (2), the succinic anhydride product purified by steps (3), (4), and (5) can have a high purity. For example, the purity of the succinic anhydride product purified by steps (3), (4), and (5) can reach 98% or more, 99% or more, 99.1% or more, 99.2% or more, 99.3% or more, 99.5% or more, 99.8% or more, or 99.9% or more, such as 99.91% or more, 99.92% or more, 99.93% or more, 99.94% or more, 99.95% or more, or 99.96% or more.

[0061] Reactor 3 can be a fixed-bed reactor. Preferably, the reactor is a tubular fixed-bed reactor. The mixture flowing out of reactor 3 enters washing tower 5 for washing. Unreacted hydrogen in reactor 3 is washed to remove entrained organic matter by absorption washing and then recycled. Unreacted hydrogen first removes entrained organic matter in washing tower 5, then is pressurized by compressor 4 and sent out. It exchanges heat with the mixture flowing out of reactor 3 in heat exchanger 6. The hydrogen after heat exchange is returned to the feed inlet and mixed with maleic anhydride feedstock. The mixture flows out of washing tower 5 and enters detergent recovery tower 7. After the detergent is recovered in detergent recovery tower 7, the detergent is returned to washing tower 5 for reuse, while the crude succinic anhydride enters the vacuum evaporation process. Gas chromatography analysis shows that the maleic anhydride conversion rate can reach 99.9%.

[0062] In step (3), the vacuum pressure can be 0.1-50 kPaA, for example, 0.1 kPaA, 0.3 kPaA, 0.5 kPaA, 0.8 kPaA, 1 kPaA, 3 kPaA, 5 kPaA, 8 kPaA, 10 kPaA, 15 kPaA, 20 kPaA, 25 kPaA, 30 kPaA, 35 kPaA, 40 kPaA, 45 kPaA, or 50 kPaA. Preferably, the vacuum pressure is 0.1-30 kPaA. The vacuum evaporation temperature can be 130-170℃, for example, 140℃, 150℃, 160℃, or 170℃. Preferably, the vacuum evaporation temperature is 130-140℃ or 160-170℃. The first stage of vacuum evaporation is carried out at 1-20 kPaA, for example, 2 kPaA, 4 kPaA, 6 kPaA, 8 kPaA, 10 kPaA, 12 kPaA, 14 kPaA, 16 kPaA, or 18 kPaA, preferably at 9-11 kPaA. The first stage of vacuum evaporation is carried out at 130-150°C, for example, 135°C. The second stage of vacuum evaporation is carried out at 0.1-1 kPaA, for example, 0.2 kPaA, 0.3 kPaA, 0.4 kPaA, 0.5 kPaA, 0.6 kPaA, 0.7 kPaA, 0.8 kPaA, or 0.9 kPaA. The second stage of vacuum evaporation is carried out at 150-170°C, for example, 155°C or 165°C. Vacuum evaporation is carried out in an evaporator. The evaporator used in step (3) can be one or more of a rising film evaporator, a falling film evaporator, and a thin-film evaporator. Preferably, the evaporator may be a combination of a rising film evaporator, a falling film evaporator, and a thin-film evaporator. In some embodiments, the first-stage vacuum evaporation is performed in a rising film evaporator and / or a falling film evaporator. In other embodiments, the second-stage vacuum evaporation is performed in a thin-film evaporator. Preferably, the first-stage vacuum evaporation is performed once or more, for example, once, twice, three times, four times, or five times. In some embodiments, the first-stage vacuum evaporation is performed twice. Preferably, the first-stage vacuum evaporation is performed sequentially in a rising film evaporator 8 and a falling film evaporator 9. In some embodiments, crude succinic anhydride is vacuum-evaporated sequentially in a rising film evaporator 8, a falling film evaporator 9, and a thin-film evaporator 10 to obtain first purified succinic anhydride.

[0063] In step (4), the vacuum pressure for distillation can be 0.1-50 kPaA, for example, 0.1 kPaA, 0.3 kPaA, 0.5 kPaA, 0.8 kPaA, 1 kPaA, 3 kPaA, 5 kPaA, 8 kPaA, 10 kPaA, 15 kPaA, 20 kPaA, 25 kPaA, 30 kPaA, 35 kPaA, 40 kPaA, 45 kPaA, or 50 kPaA. Preferably, the vacuum pressure is 0.1-30 kPaA. The temperature for distillation can be 120-160℃, for example, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, or 160℃. Preferably, the temperature for distillation is 130-140℃ or 140-150℃. The first-stage distillation is carried out at 1-20 kPaA, for example, 2 kPaA, 4 kPaA, 6 kPaA, 8 kPaA, 10 kPaA, 12 kPaA, 14 kPaA, 16 kPaA, or 18 kPaA, preferably at 9-11 kPaA. The first-stage distillation is carried out at 130-150°C, for example, 135°C or 145°C. The second-stage distillation is carried out at 0.1-1 kPaA, for example, 0.2 kPaA, 0.3 kPaA, 0.4 kPaA, 0.5 kPaA, 0.6 kPaA, 0.7 kPaA, 0.8 kPaA, or 0.9 kPaA. The second-stage distillation is carried out at 140-150°C, for example, 140°C, 145°C, or 150°C. The first-stage distillation is carried out in the first-stage distillation column 11. In some embodiments, the first-stage distillation column 11 is a light component removal column. The first light component is distilled off from the top of the column, and the succinic anhydride from the bottom of the column enters the second-stage distillation. The second-stage distillation is carried out in a second-stage distillation column 12. In some embodiments, the second-stage distillation column 12 is a product purification column. Low-purity succinic anhydride is collected from the bottom of the second-stage distillation column, and second-purified succinic anhydride is collected from the top of the second-stage distillation column. The first light component contains one or more selected from γ-butyrolactone, 1,4-butanediol, tetrahydrofuran, and maleic anhydride. The low-purity succinic anhydride component from the bottom of the column contains a second light component, which contains one or two selected from succinic acid and succinic acid, and the purity of the low-purity succinic anhydride from the bottom of the column is ≤95 wt%.

[0064] In step (5), the second purified succinic anhydride distilled from the top of the second-stage distillation column is fed into a low-temperature crystallization unit. Through two stages of low-temperature crystallization, the purity of the succinic anhydride is increased from 99 wt% to over 99.9 wt%. The first stage of low-temperature crystallization involves cooling and crystallizing in the first crystallizer 13, followed by heating to induce sweating and remove impurities. The second stage of low-temperature crystallization involves cooling and crystallizing in the second crystallizer 14, followed by heating to induce sweating and remove impurities, yielding the succinic anhydride product. In this document, the succinic anhydride product refers to succinic anhydride with a purity of 99.9 wt% or higher. In some embodiments, the succinic anhydride product refers to succinic anhydride with a purity of 99.91 wt% or higher. In some embodiments, the succinic anhydride product refers to succinic anhydride with a purity of 99.96 wt% or higher. The sweating temperature can be 110-135℃, for example, 115℃, 120℃, 125℃, 130℃, and 135℃. Preferably, the sweating temperature is 120-130°C. In some embodiments, the sweating temperature is 120-125°C. The crystallization pressure can be 0.01-30 kPaA, for example 0.02 kPaA, 0.05 kPaA, 0.08 kPaA, 0.1 kPaA, 0.2 kPaA, 0.5 kPaA, 0.8 kPaA, 1 kPaA, 2 kPaA, 3 kPaA, 5 kPaA, 8 kPaA, 10 kPaA, 15 kPaA, 20 kPaA, 25 kPaA, 28 kPaA, or 30 kPaA. Preferably, the crystallization pressure is 0.4-0.6 kPaA. In some embodiments, the sweating temperature of the first stage of low-temperature crystallization is the same as that of the second stage of low-temperature crystallization. In other embodiments, the sweating temperature of the first stage of low-temperature crystallization is different from that of the second stage of low-temperature crystallization. In some embodiments, the crystallization pressure of the first stage of low-temperature crystallization is the same as that of the second stage. In other embodiments, the crystallization pressure of the first stage of low-temperature crystallization is different from that of the second stage.

[0065] In this invention, the nickel-based catalyst used for the catalytic hydrogenation of maleic anhydride is a Ni-supported Al2O3 catalyst, which can be represented as a Ni-Al2O3 catalyst. The Ni content in the nickel-based catalyst can be 5-40 wt%, for example, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%. Preferably, the Ni content in the nickel-based catalyst can be 10-30 wt%. The nickel-based catalyst can be prepared by an equal-volume impregnation method, for example, by impregnating the Al2O3 support in a solution containing Ni ions, filtering, and then calcining. Calcination can be carried out at 500-600°C for 3-7 hours. Preferably, the Al2O3 support is calcined before impregnation. Calcination can be carried out at 450-550°C for 2-4 hours. The Ni source can be Ni(NO3)2·6H2O. The Al2O3 support can be commercially available alumina spheres. The diameter of the Al2O3 support can be 1-5 mm, such as 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, preferably 2-4 mm. The length of the Al2O3 support can be 1-15 mm, such as 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, preferably 2-8 mm. The specific surface area of ​​the Al2O3 support can be ≥200 m². 2 / g, for example 250m 2 / g、300m 2 / g, 350m 2 / g. The specific surface area of ​​the prepared nickel-based catalyst can be 190-210 m². 2 / g, for example, 191m 2 / g、193m 2 / g、195m 2 / g、197m 2 / g、199m 2 / g、201m 2 / g、203m 2 / g、205m 2 / g、207m 2 / g、209m 2 / g, preferably 195-205m 2 / g. The pore volume of the prepared nickel-based catalyst can be 0.30-0.80 cm³. 3 / g, for example 0.35cm 3 / g, 0.40cm 3 / g, 0.43cm 3 / g, 0.48cm 3 / g, 0.50cm 3 / g, 0.55cm 3 / g, 0.60cm 3 / g, 0.65cm 3 / g, 0.70cm3 / g, 0.75cm 3 / g, preferably 0.40-0.70cm 3 / g.

[0066] In this invention, the vacuum pack 15 is used to regulate the pressure in the first-stage distillation column 11, the second-stage distillation column 12, the first crystallizer 13, and the second crystallizer 14.

[0067] This invention has wide applications in organic chemical synthesis, chemical engineering and processes, and environmental engineering and technology. Particularly in the production of biodegradable PBS, high-purity succinic anhydride is a key raw material. This invention provides an efficient and low-energy-consumption method for producing succinic anhydride, which can significantly improve the purity of succinic anhydride, meeting the requirements of PBS polymerization, thereby improving the performance of PBS and satisfying the market demand for high-performance, environmentally friendly biodegradable plastics. Simultaneously, this method can also be applied to other fields requiring high-purity succinic anhydride, such as coatings, pharmaceuticals, and agriculture, and has broad market prospects.

[0068] Using the catalyst prepared in this paper, the flash vaporization conditions defined in this paper, and the reaction conditions (especially the reaction temperature and reaction pressure) of hydrogen and maleic anhydride defined in this paper to produce succinic anhydride, the purity of the crude succinic anhydride can reach more than 97%, more than 98%, or more than 99%, for example, more than 99.1%, more than 99.2%, or more than 99.3%. Furthermore, the crude succinic anhydride obtained by the method described herein can be purified by two-stage evaporation, two-stage distillation, and two-stage crystallization as defined herein. This can result in a purified succinic anhydride product with a purity of ≥98%, ≥99%, ≥99.1%, ≥99.2%, ≥99.3%, ≥99.5%, ≥99.8%, or ≥99.9%, for example, ≥99.91%, ≥99.92%, ≥99.93%, ≥99.94%, ≥99.95%, or ≥99.96%.

[0069] In some embodiments, the crude succinic anhydride obtained in steps (1) and (2) of the method of the present invention has a purity of 99.0-99.5%, for example 99.1-99.4%, 99.2-99.4%, or 99.23-99.31%.

[0070] In some embodiments, the succinic anhydride obtained in steps (1) to (5) of the method of the present invention has a purity of 99.90-99.99%, preferably 99.91-99.96%.

[0071] The present invention also provides a method for preparing polybutylene succinate, the method comprising the steps of:

[0072] (1) Butanediol is esterified with succinic anhydride to obtain the esterified product;

[0073] (2) The esterified reactants are subjected to a pre-condensation reaction to obtain a pre-condensation product;

[0074] (3) The prepolymerization product is subjected to a final polymerization reaction to obtain the final polymerization product.

[0075] First, butanediol is mixed with the second anhydride, and then the esterification reaction in step (1) is carried out. The mixing can be carried out under heating conditions, preferably at 130-150°C (e.g., 140°C), and preferably for 0.5-1.5 h (e.g., 1 h).

[0076] In step (1), the molar ratio of butanediol to succinic anhydride is 1:(0.8-1.5), for example 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, preferably 1:(1.1-1.5) or 1:(0.8-1.1).

[0077] In step (1), the reaction pressure of the esterification reaction is 0.5-2 kPaA, for example 0.8 kPaA, 1 kPaA, 1.2 kPaA, 1.5 kPaA, 1.8 kPaA, preferably 0.8-1 kPaA or 1-1.2 kPaA.

[0078] In step (1), the reaction temperature of the esterification reaction is 150-170℃, for example 155℃, 160℃, 165℃, 170℃, preferably 155-165℃, 158-162℃.

[0079] In step (1), the actual water output reaches more than 95% of the theoretical water output, and the esterification reaction is completed.

[0080] In step (2), the prepolymerization reaction is carried out under the catalysis of a catalyst. In some embodiments, the catalyst is tetraisopropyl titanate.

[0081] In step (2), the molar ratio of the catalyst to succinic anhydride is 1:(300-500), for example 1:350, 1:380, 1:400, 1:420, 1:450, 1:480, preferably 1:(300-400), 1:(400-500), or 1:(350-450).

[0082] In step (2), the reaction temperature of the pre-condensation reaction is 150-250℃, for example 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, preferably 190-210℃, 210-230℃.

[0083] In step (2), the reaction pressure of the pre-condensation reaction is 0.5-2 kPaA, for example 0.8 kPaA, 1 kPaA, 1.2 kPaA, 1.5 kPaA, 1.8 kPaA, preferably 0.8-1 kPaA or 1-1.2 kPaA.

[0084] In step (2), the reaction time of the pre-condensation reaction is 2-8 hours, for example 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, preferably 2-3 hours or 3-5 hours.

[0085] In step (3), the reaction pressure of the final polycondensation reaction is 30-100 PaA, for example 40 PaA, 50 PaA, 60 PaA, 65 PaA, 70 PaA, 80 PaA, 90 PaA, preferably 50-65 PaA, 40-70 PaA, or 45-70 PaA.

[0086] In step (3), the reaction time of the final polycondensation reaction is 2-8 hours, for example 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, preferably 2-3 hours or 3-5 hours.

[0087] In step (3), the reaction temperature of the final polycondensation reaction is 200-250℃, for example 210℃, 220℃, 230℃, 240℃, 250℃, preferably 220-230℃, 210-240℃, 215-235℃.

[0088] In step (3), the stirring speed of the final polycondensation reaction is 150-250 rpm, for example 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm, 210 rpm, 220 rpm, 230 rpm, preferably 210-230 rpm, 190-210 rpm, 200-220 rpm.

[0089] In step (3), the Weissenberg effect occurs in the reaction system, and the final polycondensation reaction is completed.

[0090] In some embodiments, the final polycondensation product is dried to obtain polybutylene succinate.

[0091] In some embodiments, the melt index of polybutylene succinate prepared by the method of the present invention is 5-6.5 g / min, preferably 5.5-6 g / min or 5.6-5.8 g / min.

[0092] In some embodiments, the intrinsic viscosity of polybutylene succinate prepared by the method of the present invention is 1.9-2 dL / g, preferably 1.91-1.96 dL / g.

[0093] In some embodiments, the polybutylene succinate prepared by the method of the present invention has a color value B of 1-5, preferably 2-3 or 2.3-2.8.

[0094] In some embodiments, the color value L of the polybutylene succinate prepared by the method of the present invention is 80-110, preferably 85-105, 90-100, or 92-98.

[0095] In some embodiments, the tensile strength of polybutylene succinate prepared by the method of the present invention is 36-40 MPa, preferably 37-38 MPa.

[0096] In some embodiments, the flexural strength of the polybutylene succinate prepared by the method of the present invention is 31-35 MPa, preferably 32-33 MPa.

[0097] In some embodiments, the flexural modulus of polybutylene succinate prepared by the method of the present invention is 590-620 MPa, preferably 600-610 MPa.

[0098] The present invention has the following beneficial effects:

[0099] 1. This invention uses maleic anhydride gas-phase hydrogenation reaction, which has a low vaporization temperature, does not require solvent, improves reaction efficiency, and reduces by-products.

[0100] 2. The method of the present invention improves the purity of succinic anhydride: by using a method of distillation and evaporation coupled with low-temperature crystallization, the purity of succinic anhydride can be increased to more than 99.9 wt%, or even more than 99.95 wt%, which meets the requirements of PBS polymerization and improves the quality and performance of the product.

[0101] 3. The method of the present invention reduces energy consumption: Compared with traditional distillation methods, the present invention effectively removes heavy and light components from crude succinic anhydride through three vacuum evaporations and two-stage distillation, reducing the evaporation amount and operating temperature, thereby reducing energy consumption and achieving energy conservation and emission reduction.

[0102] 4. The method of the present invention avoids coking, scaling and clogging of heat exchangers: Since the present invention uses a low-temperature crystallization method, it avoids the side reaction of succinic anhydride at high temperatures to generate more polymer impurities, thereby preventing the problem of coking, scaling and clogging of heat exchangers, and improving the operating efficiency and service life of the equipment.

[0103] In summary, compared with the prior art, this invention not only improves the purity of succinic anhydride to meet the requirements of PBS polymerization, but also reduces energy consumption and avoids the problems of coking, scaling and clogging of heat exchangers, thus having significant advantages.

[0104] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Percentages and parts are by weight unless otherwise stated.

[0105] In this article, purity expressed as a percentage is a mass fraction.

[0106] The catalyst was tested using the BET method with a Bayer BELSORP-mini micropore analyzer from Japan. The static volumetric method was used to measure the specific surface area and pore size distribution of the catalyst, and the pore volume was calculated using the BJH method.

[0107] The conversion rate of maleic anhydride and the purity of succinic anhydride and succinic acid were determined using an Agilent 7890 chromatograph.

[0108] Example 1

[0109] High-purity polymeric grade succinic anhydride is produced according to the process shown in Figure 1:

[0110] Step 1: Preparation of Ni-Al2O3 catalyst (Ni content 15wt%). Commercially available Al2O3 support (KNT Group Grade T cloverleaf activated alumina support, diameter 1.8-2.2 mm, length 2-8 mm; specific surface area 210 m²) was used. 2 5 kg of the prepared Al2O3 support was calcined in air at 500°C for 3 hours. 4.1 kg of nickel source Ni(NO3)2·6H2O was dissolved in 15 L of deionized water. Assuming a 10% loss of active metal, the calcined Al2O3 support was immersed in a nickel-containing aqueous solution for 24 hours, filtered, washed, and calcined at 550°C for 5 hours. The specific surface area of ​​the prepared catalyst was measured to be 201 m². 2 / g, pore volume 0.65cm 3 / g, add it to the reactor.

[0111] Step Two: Purchase maleic anhydride raw material (Zibo Qixiang, national standard industrial grade, purity ≥99.5wt%), feed amount 2.0kg, maleic anhydride raw material and hydrogen are fed at a molar ratio of 1:300. After mixing hydrogen and maleic anhydride, heat to 160℃ and enter the gas-liquid separator for instantaneous flash vaporization. At the same time, a small amount of heavy component impurities in the raw material are separated and discharged. The vaporized maleic anhydride and hydrogen mixture is added to the reactor from the top of the reactor. The reaction pressure is 6MPaG, the reaction temperature is 160℃, and the reactor is a tubular fixed-bed reactor. The maleic anhydride conversion rate reaches 99%, yielding crude succinic anhydride. Unreacted hydrogen is removed by absorption and washing to remove entrained organic matter and then recycled.

[0112] Step 3: The molten crude succinic anhydride is passed through a washing tower to separate hydrogen, and then pumped through a two-stage vacuum evaporation process. The first stage of vacuum evaporation is carried out under a vacuum of 10 kPaA and a temperature of 135°C. This first stage is performed twice: the first time in a rising film evaporator, and the second time under the same conditions in a falling film evaporator. The second stage of vacuum evaporation is carried out under a vacuum of 0.1 kPaA and a temperature of 165°C using a thin-film evaporator. Through these two stages of vacuum evaporation, heavy components are removed from the crude succinic anhydride, yielding the first purified succinic anhydride.

[0113] Step 4: The first purified succinic anhydride, from which heavy components have been removed, is then subjected to a two-stage distillation. The first stage distillation is carried out under a vacuum of 10 kPaA and a temperature of 135°C to remove trace amounts of γ-butyrolactone, 1,4-butanediol, tetrahydrofuran, maleic anhydride, and other light components. The second stage distillation is carried out under a vacuum of 0.1 kPaA and a temperature of 150°C to remove succinic acid, succinic acid, and unidentified light components. The succinic anhydride is collected from the top of the column, with a purity of 99.5 wt%, yielding the second purified succinic anhydride.

[0114] Step 5: The purified succinic anhydride obtained from the second-stage distillation is subjected to two-stage low-temperature dissolution and crystallization to improve its purity. The first stage of low-temperature crystallization occurs in a pre-crystallizer (serving as the first crystallizer), where the temperature is lowered for crystallization, followed by heating to induce sweating and remove impurities. The sweating temperature is 120-125℃, and the crystallization pressure is 0.5 kPaA. The second stage of low-temperature crystallization occurs in a refining crystallizer (serving as the second crystallizer), where the temperature is lowered for crystallization, followed by heating to induce sweating and remove impurities. The sweating temperature is 120-130℃, and the crystallization pressure is 0.5 kPaA. The purified high-purity polymer-grade succinic anhydride has a purity of 99.96 wt%, and the chromatographic results are shown in Figure 2.

[0115] Example 2

[0116] High-purity polymeric grade succinic anhydride is generated according to the process shown in Figure 1:

[0117] Step 1: Preparation of Ni-Al2O3 catalyst (Ni content 30wt%). Commercially available Al2O3 support (KNT Group Grade T cloverleaf activated alumina support, diameter 1.8-2.2 mm, length 2-8 mm; specific surface area 210 m²) was used. 2 5.0 kg (g) was calcined in air at 500°C for 3 hours.

[0118] 8.2 kg of nickel source Ni(NO3)2·6H2O was dissolved in 15 L of deionized water. Assuming a 10% loss of active metal, the calcined Al2O3 support was immersed in the nickel-containing aqueous solution for 24 hours, filtered, washed, and calcined at 550 °C for 5 hours. The specific surface area of ​​the prepared catalyst was measured to be 197 m².2 / g, pore volume 0.43cm 3 / g, add it to the reactor.

[0119] Step Two: Purchase maleic anhydride raw material (Zibo Qixiang, national standard industrial grade, purity ≥99.5wt%), feed amount 2.0kg, maleic anhydride raw material and hydrogen are fed at a molar ratio of 1:300. After mixing hydrogen and maleic anhydride, heat to 160℃ and enter the gas-liquid separator for instantaneous flash vaporization. At the same time, a small amount of heavy component impurities in the raw material are separated and discharged. The vaporized maleic anhydride and hydrogen mixture is added to the reactor from the top of the reactor. The reaction pressure is 6MPaG, the reaction temperature is 160℃, and the reactor is a tubular fixed-bed reactor. The maleic anhydride conversion rate reaches 99%, yielding crude succinic anhydride. Unreacted hydrogen is removed by absorption and washing to remove entrained organic matter and then recycled.

[0120] Step 3: The molten crude succinic anhydride is passed through a washing tower to separate hydrogen, and then pumped through a two-stage vacuum evaporation process. The first stage of vacuum evaporation is carried out under a vacuum of 10 kPaA and a temperature of 135°C. This first stage is performed twice: the first time in a rising film evaporator, and the second time under the same conditions in a falling film evaporator. The second stage of vacuum evaporation is carried out under a vacuum of 0.1 kPaA and a temperature of 165°C using a thin-film evaporator. Through these two stages of vacuum evaporation, heavy components are removed from the crude succinic anhydride, yielding the first purified succinic anhydride.

[0121] Step 4: The first purified succinic anhydride, from which heavy components have been removed, is then subjected to a two-stage distillation. The first stage distillation is carried out under a vacuum of 10 kPaA and a temperature of 135°C to remove trace amounts of γ-butyrolactone, 1,4-butanediol, tetrahydrofuran, maleic anhydride, and other light components. The second stage distillation is carried out under a vacuum of 0.1 kPaA and a temperature of 150°C to remove succinic acid, succinic acid, and unidentified light components. The succinic anhydride is collected from the top of the column, with a purity of 99.5 wt%, yielding the second purified succinic anhydride.

[0122] Step 5: The purified succinic anhydride obtained from the second-stage distillation is subjected to two-stage low-temperature dissolution and crystallization to improve its purity. The first stage of low-temperature crystallization occurs in a pre-crystallizer (serving as the first crystallizer), where the temperature is lowered for crystallization, followed by heating to induce sweating and remove impurities. The sweating temperature is 120-122℃, and the crystallization pressure is 0.5 kPaA. The second stage of low-temperature crystallization occurs in a refining crystallizer (serving as the second crystallizer), where the temperature is lowered for crystallization, followed by heating to induce sweating and remove impurities. The sweating temperature is 120-125℃, and the crystallization pressure is 0.5 kPaA. The purified high-purity polymer-grade succinic anhydride has a purity of 99.91 wt%, and the chromatographic results are shown in Figure 3.

[0123] Example 3

[0124] The production method of Example 1 is repeated, except that in step two, maleic anhydride raw material and hydrogen are fed in a molar ratio of 1:100.

[0125] The purified high-purity polymer-grade succinic anhydride has a purity of 99.92 wt%.

[0126] Example 4

[0127] The production method of Example 1 is repeated, except that in step two, maleic anhydride raw material and hydrogen are fed in a molar ratio of 1:450.

[0128] The purified high-purity polymer-grade succinic anhydride has a purity of 99.95 wt%.

[0129] Example 5

[0130] The production method of Example 1 is repeated, except that in step two, hydrogen and maleic anhydride are mixed and heated to 180°C.

[0131] The purified high-purity polymer-grade succinic anhydride has a purity of 99.91 wt%.

[0132] Example 6

[0133] The production method of Example 1 is repeated, except that in step three, the first-stage vacuum evaporation is carried out under vacuum conditions of 15 kPaA and temperature of 145°C.

[0134] The purified high-purity polymer-grade succinic anhydride has a purity of 99.94 wt%.

[0135] Example 7

[0136] The production method of Example 1 is repeated, except that in step three, the second-stage vacuum evaporation is carried out under vacuum conditions of 0.7 kPaA and temperature of 150°C.

[0137] The purified high-purity polymer-grade succinic anhydride has a purity of 99.92 wt%.

[0138] Example 8

[0139] The production method of Example 1 is repeated, except that in step four, the first-stage distillation is carried out under vacuum of 5 kPaA and temperature of 150°C.

[0140] The purified high-purity polymer-grade succinic anhydride has a purity of 99.93 wt%.

[0141] Example 9

[0142] The production method of Example 1 is repeated, except that in step four, the second-stage distillation is carried out under vacuum of 0.8 kPaA and temperature of 140°C.

[0143] The purified high-purity polymer-grade succinic anhydride has a purity of 99.92 wt%.

[0144] Example 10

[0145] The production method of Example 1 is repeated, except that in step five, the crystallization pressure of the first stage of low-temperature crystallization and the second stage of low-temperature crystallization is 25 kPaA.

[0146] The purified high-purity polymer-grade succinic anhydride has a purity of 99.91 wt%.

[0147] Table 1 below lists the purity of the succinic anhydride obtained in Examples 1-10.

[0148] Table 1

[0149] The analytical results of Examples 1-10 show that the purity of the succinic anhydride synthesized by this method is greater than 99.9 wt%, which is high.

[0150] Comparative Example 1

[0151] Succinic acid produced by the biological method from purchased goods (bio-based succinic acid purchased from Shandong Landian Biotechnology Co., Ltd.) was subjected to PBS polymerization test, and the succinic acid met the requirements of GB34686-2017 superior grade.

[0152] Comparative Example 2

[0153] Succinic anhydride produced by liquid-phase hydrogenation of industrial-grade maleic anhydride (purchased from Henan Coal Chemical Hebi Coal Chemical Co., Ltd., superior grade) was subjected to PBS polymerization test. The succinic anhydride met the enterprise standard requirements for superior grade (purity of succinic anhydride ≥ 99.5 wt%).

[0154] Comparative Example 3

[0155] The method of Example 1 of this application is repeated, except that in step two, maleic anhydride is vaporized at atmospheric pressure and 200°C, and the reaction conditions in the reactor are atmospheric pressure and 270°C. Due to the high vaporization temperature, hot oil (Sonol T-55, supply temperature 300°C) is used for heating, with a feed rate of 2.0 kg. This reaction product is then sent to steps three to five as described in Example 1 for purification.

[0156] Comparative Example 4

[0157] The method of Example 1 of this application is repeated, except that in step two, the reaction conditions in the reactor are a reaction pressure of 6 MPaG, a reaction temperature of 110°C, and a feed rate of 2.0 kg. Due to the low temperature, the reactants react in the liquid phase, and the reactants are then sent to steps three to five of Example 1 for purification.

[0158] The crude succinic anhydride obtained in step two of Examples 1-2 and Comparative Examples 3-4, and the succinic anhydride products refined in steps three to five, were subjected to component analysis, and the results are shown in Table 2.

[0159] Table 2

[0160] Test case

[0161] The purified succinic anhydride produced in Examples 1-2, the succinic acid purchased in Comparative Example 1, the succinic anhydride purchased in Comparative Example 2, and the purified succinic anhydride produced in Comparative Examples 3-4 were selected for 200L batch PBS polymerization tests.

[0162] The PBS polymerization method is as follows:

[0163] (1) Add butanediol and succinic anhydride or succinic acid to the reactor at a molar ratio of 1:1.1. After stirring and mixing, the succinic anhydride or succinic acid is completely dissolved in butanediol (if the dissolution is not good, it can be heated at 140°C for 1 hour). Then add the mixed slurry to the reactor for esterification reaction.

[0164] (2) The esterification reaction is carried out under negative pressure (1 kPaA) and the temperature is 160±2℃. When the actual water output reaches 95% of the theoretical water output (actual water received / theoretical value) or more, the esterification reaction is stopped and the esterified reactants are sent to the pre-condensation reactor.

[0165] (3) The esterification reactants from the previous process are subjected to pre-condensation reaction in a pre-condensation reactor. Tetraisopropyl titanate (TTiPO, CAS: 546-68-9) is used as a catalyst. The molar ratio of the catalyst to succinic anhydride (or succinic acid) is 1:400. The reaction system is heated to 210°C and kept under vacuum of 1 kPaA for 3 hours to obtain the pre-condensation product. The pre-condensation product is then sent to the final condensation reactor.

[0166] (4) The polycondensation reaction is carried out at 50-65 PaA for 3 hours, the reaction system temperature is 220-230℃, and the stirring speed is 210 rpm. The final polycondensation is marked when the viscosity of the system increases significantly and the rod climbing phenomenon (Weisenberg effect) occurs. The final polycondensation product is extracted by the discharge pump through the gas phase pipeline.

[0167] (5) The final polycondensation product is dried to obtain the finished PBS.

[0168] The performance of succinic anhydride, succinic acid, and finished PBS was tested using the following methods. The test results are shown in Table 3.

[0169] The purity of succinic anhydride and succinic acid was determined using an Agilent 7890 chromatograph.

[0170] Melt flow index was measured according to ASTM-D1238 using Ray-Ran MFR300.

[0171] The intrinsic viscosity was measured according to GB14190-2017 using a Ubbelohde capillary viscometer, part number 4-0.8.

[0172] The color value test method follows GB14190-2017, using an automatic colorimeter, D65 light source, 10° viewing angle, and HunterLabL*a*b* color system.

[0173] Tensile strength was tested according to GB / T 1040.2-2006 using a tensile testing machine. The gauge length of the specimen was 25 mm, and the tensile rate was 50 mm / min.

[0174] Bending strength and bending modulus were tested according to GB / T 9341-2008 using a bending testing machine at a test speed of 2 mm / min.

[0175] As can be seen from Table 3, the PBS plastics prepared using succinic anhydride obtained in Examples 1-2 as raw materials have better performance than the PBS synthesized using succinic acid or succinic anhydride as raw materials in Comparative Examples 1-4.

[0176] Table 3

[0177] The PBS polymerization test results showed that, compared with PBS obtained by polymerization using succinic acid purchased from Comparative Example 1, succinic anhydride purchased from Comparative Example 2, and succinic anhydride produced from Comparative Examples 3-4 as raw materials, PBS obtained by polymerization using succinic anhydride purified by the method of Examples 1-10 of this application as raw material had better color value and mechanical properties, and met the requirements of PBS polymerization.

Claims

1. A method for producing succinic anhydride, characterized in that, Including the following steps: (1) Mix hydrogen and maleic anhydride and heat to 160-180°C. Then, enter the gas-liquid separator for flash vaporization to separate the heavy component impurities in maleic anhydride. Then, introduce hydrogen and maleic anhydride into the reactor from the top of the reactor. (2) In the presence of a nickel-based catalyst, hydrogen and maleic anhydride are reacted in the reactor in the gas phase, wherein the molar ratio of hydrogen to maleic anhydride is 20-500:1, the reaction pressure is 5.0-8.0 MPaG, the reaction temperature is 160-180℃, and crude succinic anhydride is produced. (3) The crude succinic anhydride is subjected to two-stage vacuum evaporation to remove heavy components. The vacuum pressure is 0.1-50 kPaA and the temperature is 130-170℃ to obtain the first purified succinic anhydride. (4) The first purified succinic anhydride is subjected to two-stage distillation to remove light components. The vacuum pressure is 0.1-50 kPaA and the temperature is 120-160℃ to obtain the second purified succinic anhydride. (5) The purity of the second purified succinic anhydride is improved by two-stage low-temperature crystallization. The evaporation temperature is 110-135℃ and the crystallization pressure is 0.01-30kPaA to obtain the succinic anhydride product.

2. The method as described in claim 1, characterized in that, In step (5), the first stage of low-temperature crystallization involves cooling and crystallizing in the first crystallizer, then heating up to induce sweating and remove impurities; the second stage of low-temperature crystallization involves cooling and crystallizing in the second crystallizer, then heating up to induce sweating and remove impurities, to obtain the succinic anhydride product; and / or, in step (5), the sweating temperature is 120-130℃.

3. The method as described in claim 1, characterized in that, In step (3), the vacuum pressure is 0.1-30 kPaA.

4. The method as described in claim 1 or 3, characterized in that, The method has one or more of the following characteristics: In step (3), the first-stage vacuum evaporation is carried out first in a rising film evaporator and then in a falling film evaporator; In step (3), the second-stage vacuum evaporation is carried out in a thin-film evaporator; In step (3), the first-stage vacuum evaporation is carried out at 1-20 kPaA; In step (3), the second-stage vacuum evaporation is carried out at 0.1-1 kPaA; In step (3), the first-stage vacuum evaporation is carried out at 130-150℃; In step (3), the second-stage vacuum evaporation is carried out at 150-170℃.

5. The method as described in claim 1, characterized in that, The method has one or more of the following characteristics: In step (4), the first-stage distillation is carried out in the first-stage distillation column, the first light component is collected from the top of the first-stage distillation column, and succinic anhydride is collected from the bottom of the first-stage distillation column; In step (4), the second-stage distillation is carried out in the second-stage distillation column, the second light component is collected from the bottom of the second-stage distillation column, and the second purified succinic anhydride is collected from the top of the second-stage distillation column; In step (4), the first-stage distillation is carried out at 1-20 kPa A; In step (4), the first-stage distillation is carried out at 130-150℃; In step (4), the second-stage distillation is carried out at 0.1-1 kPa A; In step (4), the second-stage distillation is carried out at 140-150℃.

6. The method as described in claim 5, characterized in that, The first light component comprises one or more selected from γ-butyrolactone, 1,4-butanediol, tetrahydrofuran, and maleic anhydride; and / or, the second light component comprises one or two selected from succinic acid and succinic acid.

7. The method as described in claim 1, characterized in that, In step (2), the unreacted hydrogen in the reactor is removed by absorption and washing to remove entrained organic matter and then recycled; and / or, the crude succinic anhydride obtained in step (2) is first separated by a washing tower to remove hydrogen, and then vacuum evaporated in step (3).

8. The method as described in claim 1, characterized in that, In step (1), the reactor is a fixed-bed reactor, preferably a tubular fixed-bed reactor.

9. The method as described in claim 1, characterized in that, The nickel-based catalyst is a Ni-supported catalyst on an Al2O3 support. The Ni content in the nickel-based catalyst is 5-40 wt%. The nickel-based catalyst is preferably prepared by an equal-volume impregnation method. The Ni source is preferably Ni(NO3)2·6H2O. The diameter of the Al2O3 support is preferably 1-5 mm, and the specific surface area of ​​the Al2O3 support is preferably ≥200 m². 2 The preferred pore volume of the Al2O3 support is 0.30-0.80 cm³ / g. 3 / g.

10. The method as described in claim 1, characterized in that, The purity of the succinic anhydride product obtained in step (5) is ≥99.9 wt%.

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