An imidazole-modified sulfonic acid resin, its preparation method and application

Abstract

This application relates to the field of organic synthesis technology, specifically to an imidazole-modified sulfonic acid resin, its preparation method, and its application. The imidazole-modified sulfonic acid resin provided in this application is prepared through suspension copolymerization and sulfonation, achieving a synergistic acid-base effect between the imidazole and sulfonic acid groups. It is used to catalyze the reactive distillation of acetic anhydride and n-butyric acid to prepare butyric anhydride, simultaneously achieving high catalytic activity and high stability. The sulfonic acid groups can activate acyl groups, significantly accelerating the rate-determining reaction and shortening the material residence time to 0.1-1 hours. The imidazole groups, acting as nucleophilic sites, specifically promote the conversion of acetic butyric anhydride to butyric anhydride and inhibit the reverse reaction, ensuring that the acetic butyric anhydride content in the bottom of the distillation column is ≤0.5%, and the product purity is ≥99.5%, eliminating the need for complex byproduct recovery. Simultaneously, the imidazole and sulfonic acid form a hydrogen bond network, significantly improving the resin's temperature resistance and hydrolysis resistance, resulting in a catalyst lifetime exceeding 1000 hours.

Description

Technical Field

[0001] This application relates to the field of organic synthesis technology, specifically to an imidazole-modified sulfonic acid resin, its preparation method, and its application in the catalytic preparation of butyric anhydride. Background Technology

[0002] Butyric anhydride is an important organic chemical raw material widely used in pharmaceuticals, fragrances, and food additives. Traditional methods for producing butyric anhydride mainly include butyric acid dehydration and the reaction of butyryl chloride with sodium butyrate, but these methods suffer from low conversion rates, high energy consumption, and severe equipment corrosion. Currently, the reactive distillation process using acetic anhydride and n-butyric acid is commonly employed, offering advantages such as high product purity and low waste volume.

[0003] The reaction process of butyric anhydride is divided into two steps: (1) Acetic anhydride + butyric acid → Acetic butyric anhydride + acetic acid; (2) Acetic butyric anhydride + butyric acid Butyric anhydride + acetic acid. Both of these reactions are acyl exchange reactions, with step (2) being a reversible slow reaction and the rate-determining step of the entire process. Catalytically inert distillation relies on the continuous removal of acetic acid from the top of the column to drive the reaction forward, but it suffers from drawbacks such as slow kinetics, long residence time, high residual butyric anhydride intermediates, and high energy consumption in subsequent separation. Existing technologies struggle to stably obtain butyric anhydride with a purity ≥99.5% under low feed excess ratios.

[0004] For example, Chinese patent CN104086405A discloses an apparatus and method for preparing butyric anhydride through continuous reactive distillation. Although this technology attempts to optimize the process, it still faces problems such as a high yield of the byproduct acetate butyric anhydride (approximately 20 wt%) and low purity of the butyric anhydride product (maximum only 96.7%). Chinese patent CN114805057B proposes a method for producing butyric anhydride using a partitioned reactive distillation column. This technology, through innovative equipment structure, achieves the recycling of acetate butyric anhydride and successfully increases the purity of butyric anhydride to over 99.5%. However, its process requires a high molar ratio of butyric acid to acetic anhydride, resulting in a large amount of excess butyric acid and recycled acetate butyric anhydride needing to be distilled off and reused as a light component, leading to significantly higher energy consumption.

[0005] Therefore, developing catalysts with high activity, high selectivity, and high stability, and matching them with low-energy reactive distillation processes, is of great significance for improving the production efficiency and economy of butyric anhydride. Summary of the Invention

[0006] This application provides an imidazole-modified sulfonic acid resin, its preparation method, and its application, to solve the problems of slow reaction rate, high intermediate content, and insufficient catalyst stability in the prior art.

[0007] In a first aspect, this application provides a method for preparing an imidazole-modified sulfonic acid resin, comprising the following steps: S1, styrene, divinylbenzene and 1-vinylimidazole were subjected to suspension copolymerization to obtain imidazole-based crosslinked polymer microspheres; S2, the imidazole-based crosslinked polymer microspheres are subjected to sulfonation treatment to obtain the imidazole-modified sulfonic acid resin.

[0008] In an optional embodiment, in S2, the sulfonation treatment includes the following steps: S21, the imidazole-based cross-linked polymer microspheres are swollen using a first organic solvent to obtain swollen microspheres; S22, the swollen microspheres are mixed with a sulfonating agent and subjected to a sulfonation reaction. The products are then separated to obtain the imidazole-modified sulfonic acid resin.

[0009] In an optional embodiment, in S21, the first organic solvent includes at least one of 1,2-dichloroethane, dichloromethane, chloroform, and tetrachloroethylene; In one alternative embodiment, the mass ratio of the imidazole-based crosslinked polymer microspheres to the first organic solvent is 1:6-8; as an example, the mass ratio of the imidazole-based crosslinked polymer microspheres to the first organic solvent can be 1:6, 1:6.5, 1:7, 1:7.5, 1:8, or within any of the above values.

[0010] In one alternative embodiment, the swelling time is 2-3 hours.

[0011] In an optional embodiment, in S22, the sulfonating agent includes at least one of sulfur trioxide, concentrated sulfuric acid, fuming sulfuric acid, and chlorosulfonic acid, and optionally sulfur trioxide; in this application, sulfur trioxide has moderate sulfonating activity and mild reaction conditions, and will not destroy the imidazole group, thus better ensuring the acid-base synergistic catalytic effect.

[0012] In one optional embodiment, the mass ratio of the sulfonating agent to the imidazole-based crosslinked polymer microspheres is 0.8-1.2:1; In one optional embodiment, the swollen microspheres are mixed with a sulfonating agent at 0-10°C under nitrogen protection; In one optional embodiment, the sulfonation reaction is carried out at a temperature of 25-35°C and with stirring for 6-10 hours.

[0013] In one optional embodiment, in S1, the suspension copolymerization includes the following steps: S11, styrene, divinylbenzene, 1-vinylimidazole, a second organic solvent, and an initiator are mixed to obtain an oil phase; S12, the dispersant is mixed with water to obtain the dispersed phase; S13, the oil phase is added to the dispersed phase, and the mixture is reacted at 60-65℃ for 4-5 hours with stirring, and then the temperature is raised to 75-80℃ for 6-8 hours. The imidazole-based crosslinked polymer microspheres are obtained by separation.

[0014] In an optional embodiment, in S11, the mass ratio of styrene, divinylbenzene, 1-vinylimidazole, the second organic solvent, and the initiator is 20-30:5-8:8-12:10-15:0.3-0.5; In one optional embodiment, the second organic solvent includes at least one of n-heptane, n-hexane, cyclohexane, and isooctane; In one optional embodiment, the initiator includes at least one of an azo initiator or a peroxide initiator; optionally, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, and tert-butyl peroxide. In one alternative embodiment, the dispersant includes at least one of polyvinyl alcohol, hydroxypropyl methylcellulose, and hydroxyethyl cellulose.

[0015] In one optional embodiment, in S12, the mass ratio of the dispersant to water is 0.5-1:150-200; In an optional embodiment, in S13, the mass ratio of styrene in the oil phase to the dispersant in the dispersed phase is 20-30:0.5-1; In an alternative embodiment, in S13, the stirring speed is 300-800 r / min.

[0016] Secondly, this application provides an imidazole-modified sulfonic acid resin, obtained by the above-described preparation method.

[0017] In one alternative embodiment, the imidazole-modified sulfonic acid resin has an acid value of 2.5-3.5 mmol / g.

[0018] Thirdly, this application provides a method for preparing butyric anhydride, which uses acetic anhydride and n-butyric acid as raw materials to carry out an acyl exchange reaction under the action of a catalyst, wherein the catalyst is the above-mentioned imidazole modified sulfonic acid resin.

[0019] In one alternative embodiment, the reaction is carried out in a reactive distillation column, with byproducts removed at the top and butyric anhydride collected at the bottom. In one optional embodiment, the feed molar ratio of butyric acid to acetic anhydride is 1.90-2.10, and the residence time of the material in the reaction section is 0.1-1.0 h; In one optional embodiment, the operating conditions of the reactive distillation column include: a top pressure of 5-15 kPaA, a reaction section temperature of 120-140°C, a top temperature of 65-85°C, a bottom temperature of 140-155°C, and a reflux ratio of 2.0-3.0.

[0020] In this application, the divinylbenzene is an industrial mixture of m-divinylbenzene and p-divinylbenzene with a purity of 50wt% to 100wt%, preferably 80wt%. The impurities, such as isomers of ethyl styrene, do not participate in the cross-linking reaction. The proportion of divinylbenzene in each formulation of this application is based on pure product, and the actual input is calculated based on the effective content of the raw materials.

[0021] In this application, the dispersant polyvinyl alcohol used has a weight-average molecular weight of 50,000-100,000 and a degree of alcoholysis of 85%-90%.

[0022] This application introduces imidazole and sulfonic acid groups into the resin framework simultaneously through suspension copolymerization, forming an acid-base synergistic catalytic system, and enhances structural stability through a hydrogen bond network. (1) The sulfonic acid group provides a strong acidic site, which activates the acyl group and significantly accelerates the rate-determining step reaction, shortening the residence time to 0.1-1h; (2) The imidazole group is a weakly basic nucleophilic site, which can selectively promote the conversion of acetic butyric anhydride to butyric anhydride and inhibit the reverse reaction, so that the intermediate content is ≤0.5%; (3) Imidazole forms strong hydrogen bonds with sulfonic acid, anchoring the sulfonic acid group, improving hydrolysis resistance and thermal stability, and the catalyst life is >1000h.

[0023] The reactive distillation process using the catalyst provided in this application can continuously and stably produce butyric anhydride with a purity of ≥99.5% under conditions where the butyric acid / acetic anhydride molar ratio is close to 2.0, without the need for by-product recovery and with a significant reduction in energy consumption.

[0024] Specifically, the preparation method of the imidazole-modified sulfonic acid resin described in this application includes the following steps: (a) Preparation of imidazole-based crosslinked polymer microspheres by suspension copolymerization: 20-30 parts by mass of styrene, 5-8 parts by divinylbenzene, 8-12 parts by mass of 1-vinylimidazolium, 10-15 parts by mass of a second organic solvent, and 0.3-0.5 parts by mass of initiator are mixed evenly to form an oil phase; 0.5-1.0 parts by mass of dispersant are dissolved in 150-200 parts by mass of deionized water to form a dispersed phase; the oil phase is added to the dispersed phase, and the mixture is reacted at a stirring speed of 300-800 r / min and 60-65℃ for 4-5 h, and then the temperature is raised to 75-80℃ for 6-8 h; the mixture is cooled and filtered, washed with water and ethanol, and vacuum dried at 80-85℃ for 12-16 h to obtain imidazole-based crosslinked polymer microspheres.

[0025] (b) Sulfonation to introduce sulfonic acid groups: Take 10 parts of the microspheres obtained in step (a) and swell them with 60-80 parts of the first organic solvent for 2-3 hours; add sulfonating agent dropwise at 0-10℃ under nitrogen protection, so that the mass ratio of sulfonating agent to microspheres is 0.8-1.2:1; heat to 25-35℃ and stir at 150-300 r / min for 6-10 hours; cool with ice water, filter, wash with water until pH=2-3, and vacuum dry at 70-75℃ for 8-12 hours to obtain imidazole modified sulfonic acid resin with an acid value of 2.5-3.5 mmol / g.

[0026] In the preparation method of this application, the swelling plays the following roles: 1. It expands the gaps between polymer chains, opens polymer channels, and allows the solvent to enter the interior of the microspheres, providing a pathway for the subsequent entry of sulfonating agents and the uniform introduction of sulfonic acid groups. 2. It avoids sulfonation only on the surface of the microspheres while the interior is insufficiently sulfonated. Sufficient internal sulfonation ensures a stable group structure, making the catalyst more resistant to hydrolysis and less prone to deactivation in high-temperature, aqueous systems. Without swelling: the sulfonating agent has difficulty entering the interior of the microspheres, the acid value is low and unevenly distributed, and the catalytic activity decreases; the internal and external stress of the microspheres is uneven, making them prone to cracking and breakage, resulting in poor catalyst stability and reduced lifespan.

[0027] In this application, the test method for the acid value of the imidazole-modified sulfonic acid resin is as follows: The imidazole-modified sulfonic acid resin sample was dried to constant weight. A certain amount of the sample was weighed and exchanged with NaCl solution, followed by titration with NaOH standard solution to obtain the acid value of the imidazole-modified sulfonic acid resin. In some optional embodiments, the specific testing method for the acid value may include the following steps: the imidazole-modified sulfonic acid resin sample was vacuum dried to constant weight at 100°C, 0.5 g was accurately weighed, and 50 mL of 0.5 mol / L NaCl solution was added. The sample was exchanged at room temperature for 4 h. Using phenolphthalein as an indicator, the sample was titrated to the endpoint with 0.1 mol / L NaOH standard solution, while simultaneously performing a blank test.

[0028] Acid value calculation formula: Acid value (mmol / g) = C × (V) V0) / m In the formula: C is the concentration of NaOH standard solution (mol / L); V is the sample titration volume (mL); V0 is the blank titration volume (mL); m is the sample mass (g).

[0029] The following is a detailed explanation of the butyric anhydride preparation process: In one optional embodiment, the reaction is carried out in a reactive distillation column with a total of 25-45 theoretical plates. The middle section of the column is the reaction section, which has 10-25 theoretical plates and is filled with a composite bed of catalyst and structured packing, with a catalyst-to-packing volume ratio of 1:2-1:10. Above the reaction section is the rectification section, which has 5-15 theoretical plates, and below the reaction section is the stripping section, which also has 5-15 theoretical plates and is filled with structured packing.

[0030] In one alternative embodiment, the structured packing is conventionally, typically, and non-limitingly, within the field. The structured packing is preferably a perforated metal plate corrugated packing or a wire mesh corrugated packing, and more preferably a 250Y, 350Y, 450Y, 252Y, 352Y, or 452Y type packing.

[0031] In one optional embodiment, the reactive distillation column is fed as follows: butyric acid is fed from the upper part of the reaction section, 2-5 theoretical plates above the catalyst packing layer; acetic anhydride is fed from the lower part of the reaction section, 2-5 theoretical plates below the catalyst packing layer; high-purity acetic acid is collected from the top of the column, and high-purity butyric anhydride is collected from the bottom of the column.

[0032] In one optional embodiment, the acetic acid collected from the top of the column has a purity of ≥99.0 wt%, and is partially refluxed after condensation; the butyric anhydride collected from the bottom of the column has a purity of ≥99.5 wt%, wherein the acetic acid butyric anhydride content is ≤0.5 wt%.

[0033] The technical solution of this application has the following advantages: The method for preparing imidazole-modified sulfonic acid resin provided in this application, obtained through suspension copolymerization and sulfonation, achieves the synergistic effect of imidazole and sulfonic acid groups. When used in the preparation of butyric anhydride, it balances high catalyst activity and high stability. The sulfonic acid group activates the acyl group, accelerating the reaction and significantly speeding up the rate-determining step, reducing the material residence time to 0.1-1 hours and solving the problem of slow kinetics. The imidazole group, acting as a nucleophilic site, specifically promotes the conversion of acetate butyric anhydride to butyric anhydride and inhibits the reverse reaction, ensuring that the acetate butyric anhydride content in the bottom of the column is ≤0.5%, and the product purity is ≥99.5%, eliminating the need for complex byproduct recovery.

[0034] In addition, the imidazole group forms a strong hydrogen bond network with the sulfonic acid group, anchoring the sulfonic acid group and significantly enhancing its thermal stability, resisting the damage caused by the exothermic hydrolysis reaction. The catalyst can operate without deactivation for a long time below 160°C, and the catalyst life exceeds 1000 hours, ensuring continuous production.

[0035] When used in the preparation of butyric anhydride, it can reduce the molar ratio of butyric acid to acetic anhydride to about 2.0, significantly reduce the excess proportion of butyric acid raw material, and achieve a butyric anhydride purity of over 99.5% in the bottom of the column. There is no need to add an additional butyric acid or acetic anhydride recovery device, and the energy consumption for recycling is significantly reduced.

[0036] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Detailed Implementation

[0037] The following embodiments are provided to better understand this application. However, the following embodiments do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining the features of this application with other prior art, falls within the scope of protection of this application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having” and any variations thereof in the text of this application are intended to cover non-exclusive inclusion.

[0039] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0040] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter can be, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0042] In the description of the embodiments of this application, the term "at least one" refers to one or more (including two).

[0043] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0044] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0045] The present application will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present application in any way.

[0046] The main raw material information in the following embodiments and comparative examples of this application is as follows: Butyric acid (Inokai, 99.5%), acetic anhydride (Inokai, 99.5%), styrene (Inokai, 99%), divinylbenzene (Inokai, 80%), 1-vinylimidazole (Inokai, 99%), azobisisobutyronitrile (Inokai, 98%), polyvinyl alcohol (Inokai, PVA-1788, weight average molecular weight 85,000, degree of alcoholysis 88%), n-heptane (Inokai, 99%), sulfur trioxide (Jianlong, 99%), 1,2-dichloroethane (Inokai, 99%). Other raw materials and reagents, unless otherwise specified, can be purchased commercially.

[0047] Example 1 This embodiment provides an imidazole-modified sulfonic acid resin, and also provides a method for preparing butyric anhydride using the imidazole-modified sulfonic acid resin. The specific preparation steps and operating conditions are as follows: (1) Preparation of imidazole modified sulfonic acid resin (a) Preparation of imidazole-based crosslinked polymer microspheres by suspension copolymerization: 20 parts by weight of styrene, 8.13 parts by weight of divinylbenzene (6.5 parts by weight of pure product), 11 parts by weight of 1-vinylimidazolium, 10 parts by weight of n-heptane, and 0.3 parts by weight of azobisisobutyronitrile were weighed and mixed evenly to obtain an oil phase; 0.6 parts by weight of polyvinyl alcohol and 150 parts by weight of deionized water were weighed and dissolved in deionized water by stirring to obtain a dispersed phase; the oil phase was slowly added to the dispersed phase and reacted at 300 r / min and 60℃ for 4 hours, and then the temperature was raised to 75℃ and reacted for 6 hours; the mixture was cooled and filtered, washed three times with water and ethanol, and dried under vacuum at 80℃ for 12 hours to obtain imidazole-based crosslinked polymer microspheres; (b) Sulfonation reaction to introduce sulfonic acid groups: 10 parts of dried imidazole-based crosslinked polymer microspheres were added to 60 parts of 1,2-dichloroethane for swelling for 3 hours; 11 parts of SO3 were slowly added to the microsphere dispersion at 3°C ​​under nitrogen protection; the mixture was heated to 25°C and sulfonated at a stirring speed of 150 r / min for 7 hours. The reaction solution was cooled in ice water, filtered, washed with water until pH=2, and dried under vacuum at 70°C for 8 hours to obtain an imidazole-modified sulfonic acid resin catalyst. The acid value of the catalyst was tested to be 2.5 mmol / g.

[0048] (2) Preparation of butyric anhydride by reactive distillation: The reactive distillation column has 25 theoretical plates. The middle section is the reaction section, which has 10 theoretical plates and is packed with catalyst and 452Y packing in a volume ratio of 1:2. Above the reaction section is the rectification section, which has 5 theoretical plates. Below the reaction section is the stripping section, which has 10 theoretical plates and is packed with 452Y structured packing. Butyric acid is continuously fed from the upper feed inlet of the reaction section (two theoretical plates above the catalyst packing layer); acetic anhydride is continuously fed from the lower feed inlet of the reaction section (two theoretical plates below the catalyst packing layer). The molar ratio of butyric acid to acetic anhydride is 1.90, and the residence time is 0.1 h. The pressure at the top of the column is 5 kPaA, the temperature of the reaction section is 120℃, the temperature at the top of the column is 65℃, the temperature at the bottom of the column is 140℃, and the reflux ratio is 2.0.

[0049] (c) The top product was acetic acid with a purity of 99.34 wt%; the bottom product was butyric anhydride with a purity of 99.53 wt%, of which the acetic acid butyric anhydride content was 0.41 wt%. After continuous operation for 1000 h, the catalyst activity did not decrease significantly, and the acid value remained at 2.4 mmol / g.

[0050] Example 2 This embodiment provides an imidazole-modified sulfonic acid resin, and also provides a method for preparing butyric anhydride using the imidazole-modified sulfonic acid resin. The specific preparation steps and operating conditions are as follows: (a) Preparation of imidazole-based crosslinked polymer microspheres by suspension copolymerization: 25 parts by weight of styrene, 6.25 parts by weight of divinylbenzene (5 parts by weight of pure product), 10 parts by weight of 1-vinylimidazolium, 12.5 parts by weight of n-hexane, and 0.4 parts by weight of azobisisobutyronitrile were weighed and mixed evenly to obtain an oil phase; 0.75 parts by weight of polyvinyl alcohol and 175 parts by weight of deionized water were weighed and dissolved in deionized water, and stirred to obtain a dispersed phase; the oil phase was slowly added to the dispersed phase, and the reaction was carried out at a stirring speed of 550 r / min and 62℃ for 4.5 hours, and then the temperature was raised to 77℃ and the reaction was carried out for 7 hours; the mixture was cooled and filtered, washed three times with water and ethanol, and dried under vacuum at 82℃ for 14 hours to obtain imidazole-based crosslinked polymer microspheres; (b) Sulfonation reaction to introduce sulfonic acid groups: 10 parts of dried imidazole-based crosslinked polymer microspheres were added to 70 parts of 1,2-dichloroethane for swelling for 2.5 h; 8 parts of 98wt% concentrated sulfuric acid were slowly added dropwise to the microsphere dispersion at 0 °C under nitrogen protection; the temperature was raised to 30 °C and the mixture was kept at a constant temperature of 225 r / min for 8 h. The reaction solution was cooled in ice water, filtered, washed with water until pH=2.5, and vacuum dried at 72 °C for 10 h to obtain an imidazole-modified sulfonic acid resin catalyst. The titration acid value of the catalyst reached 3.0 mmol / g.

[0051] (2) Preparation of butyric anhydride by reactive distillation (a) The reactive distillation column has 35 theoretical plates, of which the reaction section is located in the middle of the column and has 18 theoretical plates. The reaction section is packed with catalyst and 250Y packing in a volume ratio of 1:10. Above the reaction section is the rectification section, which has 8 theoretical plates. Below the reaction section is the stripping section, which has 9 theoretical plates, all of which are packed with 250Y structured packing. (b) Butyric acid is continuously fed from the upper feed inlet of the reaction section (three theoretical plates above the catalyst packing layer); acetic anhydride is continuously fed from the lower feed inlet of the reaction section (three theoretical plates below the catalyst packing layer); the molar ratio of butyric acid to acetic anhydride is controlled at 2.00, and the material residence time is 0.5 hours. The top pressure of the column is 10 kPaA, the temperature of the reaction section is 130℃, the temperature of the top of the column is 75℃, and the temperature of the bottom of the column is 148℃; the reflux ratio is 2.5. Results: The product from the top of the column was acetic acid with a purity of 99.64 wt%; the product from the bottom of the column was butyric anhydride with a purity of 99.65 wt%, of which the acetic acid butyric anhydride content was 0.22 wt%. After continuous operation for 1200 h, the catalyst activity did not decrease significantly, and the acid value remained at 2.9 mmol / g.

[0052] Example 3 This embodiment provides an imidazole-modified sulfonic acid resin, and also provides a method for preparing butyric anhydride using the imidazole-modified sulfonic acid resin. The specific preparation steps and operating conditions are as follows: (1) Preparation of imidazole modified sulfonic acid resin (a) Preparation of imidazole-based crosslinked polymer microspheres by suspension copolymerization: Weigh 30 parts styrene, 10 parts divinylbenzene (8 parts based on pure product), 12 parts 1-vinylimidazolium, 15 parts n-heptane, and 0.5 parts azobisisoheptanenitrile by mass, and mix them evenly to obtain an oil phase; weigh 1.0 part polyvinyl alcohol and 200 parts deionized water, dissolve the polyvinyl alcohol in the deionized water, and stir to obtain a dispersed phase; slowly add the oil phase to the dispersed phase, and react at 800 r / min and 65℃ for 5 hours, then raise the temperature to 80℃ and react for 8 hours; cool and filter, wash with water and ethanol 4 times, and vacuum dry at 85℃ for 16 hours to obtain imidazole-based crosslinked polymer microspheres; (b) Sulfonation reaction to introduce sulfonic acid groups: 10 parts of dried imidazole-based crosslinked polymer microspheres were added to 80 parts of dichloromethane for swelling for 2 hours; using chlorosulfonic acid as the sulfonating agent, 12 parts of chlorosulfonic acid were slowly added dropwise to the microsphere dispersion at 10°C under nitrogen protection; the temperature was raised to 35°C and the stirring speed was kept constant at 300 r / min for 10 hours. The reaction solution was poured into ice water for cooling, filtered, washed with water until pH=3, and vacuum dried at 75°C for 12 hours to obtain an imidazole-modified sulfonic acid resin catalyst. The titration acid value of the catalyst was tested to reach 3.5 mmol / g.

[0053] (2) Preparation of butyric anhydride by reactive distillation (a) The reactive distillation column has 45 theoretical plates, of which the reaction section is located in the middle of the column; the reaction section has 25 theoretical plates; the reaction section is packed with catalyst and 450Y packing in a volume ratio of 1:5; the upper part of the reaction section is the rectification section, which has 10 theoretical plates; the lower part of the reaction section is the stripping section, which has 10 theoretical plates, all packed with 450Y structured packing. (b) Butyric acid is continuously fed from the upper feed inlet of the reaction section (5 theoretical plates above the catalyst packing layer); acetic anhydride is continuously fed from the lower feed inlet of the reaction section (5 theoretical plates below the catalyst packing layer); the molar ratio of butyric acid to acetic anhydride is controlled at 2.10, and the material residence time is 1.0 hour. The top pressure of the column is 15 kPaA, the temperature of the reaction section is 140℃, the temperature of the top of the column is 85℃, and the temperature of the bottom of the column is 155℃; the reflux ratio is 3.0. Results: The product from the top of the column was acetic acid with a purity of 99.51 wt%; the product from the bottom of the column was butyric anhydride with a purity of 99.73 wt%, of which the acetic acid butyric anhydride content was 0.17 wt%. After continuous operation for 1500 h, the catalyst activity did not decrease significantly, and the acid value remained at 3.4 mmol / g.

[0054] Example 4 This embodiment provides an imidazole-modified sulfonic acid resin, and also provides a method for preparing butyric anhydride using the imidazole-modified sulfonic acid resin. The specific preparation steps and operating conditions are as follows: (1) Preparation of imidazole modified sulfonic acid resin (a) Preparation of imidazole-based crosslinked polymer microspheres by suspension copolymerization: 22 parts by weight of styrene, 8.75 parts by weight of divinylbenzene (7 parts by weight of pure product), 8 parts by weight of 1-vinylimidazolium, 13 parts by weight of cyclohexane, and 0.35 parts by weight of benzoyl peroxide were weighed and mixed evenly to obtain an oil phase; 0.5 parts by weight of hydroxypropyl methylcellulose and 160 parts by weight of deionized water were weighed and dissolved in deionized water, and stirred to obtain a dispersed phase; the oil phase was slowly added to the dispersed phase, and the reaction was carried out at a stirring speed of 400 r / min and 63℃ for 4.2 hours, and then the temperature was raised to 76℃ and the reaction was carried out for 6.5 hours; the mixture was cooled and filtered, washed three times with water and ethanol, and dried under vacuum at 81℃ for 13 hours to obtain imidazole-based crosslinked polymer microspheres; (b) Sulfonation reaction to introduce sulfonic acid groups: 10 parts of dried imidazole-based crosslinked polymer microspheres were added to 65 parts of chloroform and swollen for 2.2 h; 10 parts of concentrated sulfuric acid were slowly added dropwise to the microsphere dispersion at 3 °C under nitrogen protection using 98 wt% concentrated sulfuric acid as the sulfonating agent; the mixture was heated to 28 °C and sulfonated at a stirring speed of 180 r / min for 6 h. The reaction solution was cooled in ice water, filtered, washed with water until pH=2.2, and dried under vacuum at 71 °C for 9 h to obtain the imidazole-modified sulfonic acid resin catalyst. The titration acid value of the catalyst was tested to be 2.8 mmol / g.

[0055] (2) Preparation of butyric anhydride by reactive distillation (a) The reactive distillation column has 30 theoretical plates, of which the reaction section is located in the middle of the column; the reaction section has 15 theoretical plates; the reaction section is packed with catalyst and 350Y packing in a volume ratio of 1:7; the upper part of the reaction section is the rectification section, which has 8 theoretical plates; the lower part of the reaction section is the stripping section, which has 7 theoretical plates, all of which are packed with 350Y structured packing. (b) Butyric acid is continuously fed from the upper feed inlet of the reaction section (3 theoretical plates above the catalyst packing layer); acetic anhydride is continuously fed from the lower feed inlet of the reaction section (2 theoretical plates below the catalyst packing layer); the molar ratio of butyric acid to acetic anhydride is controlled at 1.95, and the material residence time is 0.3 hours. The top pressure of the column is 8 kPaA, the temperature of the reaction section is 135℃, the temperature of the top of the column is 72℃, and the temperature of the bottom of the column is 145℃; the reflux ratio is 2.2. Results: The product from the top of the column was acetic acid with a purity of 99.76 wt%; the product from the bottom of the column was butyric anhydride with a purity of 99.68 wt%, of which the acetic acid butyric anhydride content was 0.26 wt%. After continuous operation for 2000 h, the catalyst activity did not decrease significantly, and the acid value remained at 2.7 mmol / g.

[0056] Comparative Example 1 This comparative example provides a method for preparing butyric anhydride via continuous reactive distillation, using the same reactive distillation column as in Example 2. The reaction section is packed with only structured packing (without any catalyst), while the rectification and stripping sections are packed with the same structured packing as in Example 2. Operating parameters are consistent with those of Example 2. Product results: Acetic acid collected from the top of the column has a purity of 97.55 wt%; crude butyric anhydride collected from the bottom of the column has a purity of 92.36 wt%, of which the acetic acid butyric anhydride content is 5.28 wt%.

[0057] Comparative Example 2 This comparative example provides a method for preparing butyric anhydride via continuous reactive distillation. The difference from Example 2 is that 1-vinylimidazole is not used in the preparation of the polymer microspheres; all other operations remain consistent with Example 2. The titratable acid value of the obtained sulfonic acid resin catalyst is 3.6 mmol / g. Product results: The top product was acetic acid with a purity of 99.24 wt%; the bottom product was butyric anhydride with a purity of 97.65 wt%, of which the acetic acid butyric anhydride content was 2.02 wt%. The catalyst showed significant deactivation after 300 hours of continuous operation, with the acid value decreasing to 1.8 mmol / g.

[0058] Comparative Example 3 Commercially available D001 strong acid cation exchange resin (acid value 4.5 mmol / g) was used, and the process conditions were the same as in Example 2.

[0059] Results: The purity of acetic acid at the top of the column was 99.05 wt%; the purity of butyric anhydride at the bottom of the column was 96.44 wt%, and the content of acetic acid and butyric anhydride was 3.16 wt%. The catalyst was significantly deactivated after 200 h of operation, and the acid value dropped to 1.5 mmol / g.

[0060] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing an imidazole-modified sulfonic acid resin, characterized in that, Includes the following steps: S1, styrene, divinylbenzene and 1-vinylimidazole were subjected to suspension copolymerization to obtain imidazole-based crosslinked polymer microspheres; S2, the imidazole-based crosslinked polymer microspheres are subjected to sulfonation treatment to obtain the imidazole-modified sulfonic acid resin.

2. The method for preparing imidazole-modified sulfonic acid resin according to claim 1, characterized in that, In S2, the sulfonation treatment includes the following steps: S21, the imidazole-based cross-linked polymer microspheres are swollen using a first organic solvent to obtain swollen microspheres; S22, the swollen microspheres are mixed with a sulfonating agent and subjected to a sulfonation reaction. The products are then separated to obtain the imidazole-modified sulfonic acid resin.

3. The method for preparing imidazole-modified sulfonic acid resin according to claim 2, characterized in that, In S21, the first organic solvent includes at least one of 1,2-dichloroethane, dichloromethane, chloroform, and tetrachloroethylene; And / or, the mass ratio of the imidazole-based crosslinked polymer microspheres to the first organic solvent is 1:6-8; And / or, the swelling time is 2-3 hours.

4. The method for preparing imidazole-modified sulfonic acid resin according to claim 2, characterized in that, In S22, the sulfonating agent includes at least one of sulfur trioxide, concentrated sulfuric acid, fuming sulfuric acid, and chlorosulfonic acid, and optionally sulfur trioxide; And / or, the mass ratio of the sulfonating agent to the imidazole-based crosslinked polymer microspheres is 0.8-1.2:1; And / or, mix the swollen microspheres with the sulfonating agent at 0-10°C under nitrogen protection; And / or, the sulfonation reaction is carried out at a temperature of 25-35°C and with stirring for 6-10 hours.

5. The method for preparing imidazole-modified sulfonic acid resin according to claim 1, characterized in that, In S1, the suspension copolymerization includes the following steps: S11, styrene, divinylbenzene, 1-vinylimidazole, a second organic solvent, and an initiator are mixed to obtain an oil phase; S12, the dispersant is mixed with water to obtain the dispersed phase; S13, the oil phase is added to the dispersed phase, and the mixture is reacted at 60-65℃ for 4-5 hours with stirring, and then the temperature is raised to 75-80℃ for 6-8 hours. The imidazole-based crosslinked polymer microspheres are obtained by separation.

6. The method for preparing imidazole-modified sulfonic acid resin according to claim 5, characterized in that, In S11, the mass ratio of styrene, divinylbenzene, 1-vinylimidazole, the second organic solvent, and the initiator is 20-30:5-8:8-12:10-15:0.3-0.5; And / or, the second organic solvent includes at least one of n-heptane, n-hexane, cyclohexane, and isooctane; And / or, the initiator includes at least one of azo initiators or peroxide initiators; optionally, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, and tert-butyl peroxide. And / or, the dispersant includes at least one of polyvinyl alcohol, hydroxypropyl methylcellulose, and hydroxyethyl cellulose.

7. The method for preparing imidazole-modified sulfonic acid resin according to claim 5, characterized in that, In S12, the mass ratio of the dispersant to water is 0.5-1:150-200; And / or, in S13, the mass ratio of styrene in the oil phase to the dispersant in the dispersed phase is 20-30:0.5-1; And / or, in S13, the stirring speed is 300-800 r / min.

8. An imidazole-modified sulfonic acid resin, characterized in that, Obtained by the preparation method according to any one of claims 1-7; Optionally, the imidazole-modified sulfonic acid resin has an acid value of 2.5-3.5 mmol / g.

9. A method for preparing butyric anhydride, characterized in that, Acetic anhydride and butyric acid are used as raw materials to carry out an acyl exchange reaction under the action of a catalyst, wherein the catalyst is the imidazole modified sulfonic acid resin as described in claim 8.

10. The preparation method according to claim 9, characterized in that, The reaction is carried out in a reactive distillation column, where byproducts are removed from the top of the column and butyric anhydride is collected from the bottom of the column. And / or, the feed molar ratio of butyric acid to acetic anhydride is 1.90-2.10, and the residence time of the material in the reaction section is 0.1-1.0 h; And / or, the operating conditions of the reactive distillation column include: top pressure 5-15 kPaA, reaction section temperature 120-140℃, top temperature 65-85℃, bottom temperature 140-155℃, and reflux ratio 2.0-3.0.