Catalyst for synthesizing dimethyl isophthalate as well as preparation method and application of catalyst

Abstract

The invention discloses a catalyst for synthesizing dimethyl isophthalate as well as a preparation method and application of the catalyst, and belongs to the technical field of preparation of dimethyl isophthalate. The preparation method disclosed by the invention comprises the following steps: S1, adding a carbohydrate compound and a pore-forming agent into water, and carrying out rotary evaporation to obtain a mixed solid; s2, carbonizing the mixed solid to obtain a porous carbon-based carrier; s3, putting the porous carbon-based carrier, a sulfonating agent and water into a reaction kettle, and sulfonating to obtain the catalyst. When the catalyst obtained through the method is used for preparing dimethyl isophthalate, generation of by-products can be reduced, emission of waste water, waste gas and waste residues can be reduced, meanwhile, the strong acid corrosion risk is avoided, the green chemistry principle is met, and an environment-friendly solution is provided for production of aromatic acid ester compounds.

Description

Technical Field

[0001] This invention belongs to the field of dimethyl isophthalate preparation technology, specifically relating to a catalyst for synthesizing dimethyl isophthalate, its preparation method, and its application. Background Technology

[0002] Dimethyl isophthalate (DMI), as an important chemical intermediate, plays a crucial role in multiple industrial sectors. It is not only a core monomer in the synthesis of high-performance heat-resistant polymers (such as polyarylates and liquid crystal polymers), but also widely used as a plasticizer in nylon resins to improve the material's flexibility and processing properties. Furthermore, in analytical chemistry, DMI is a major component of gas chromatography stationary phases, enabling the efficient separation of complex mixtures through selective adsorption. With the rapid development of high-temperature resistant materials, high-end engineering plastics, and precision analytical technologies, the market demands increasing purity, production efficiency, and environmental friendliness for this compound, driving continuous optimization of its preparation process.

[0003] Despite the promising applications of dimethyl isophthalate, traditional production processes present numerous challenges. Currently, industrially, inert solvents (such as toluene or cyclohexane) are commonly used as dehydrating agents, with concentrated sulfuric acid as a catalyst, to prepare the target product via esterification. This method reveals a series of drawbacks in practical operation: First, the crude product requires multiple alkaline washes after the reaction to remove residual acids, followed by activated carbon decolorization, resulting in a lengthy and complex process. Second, the high-temperature reaction and subsequent purification steps lead to high energy consumption, while also generating large amounts of wastewater and waste residue, significantly impacting the environment. Furthermore, the strong corrosiveness of concentrated sulfuric acid not only imposes stringent requirements on equipment materials, increasing maintenance costs, but also introduces leakage risks, affecting production safety. These problems collectively result in low resource utilization and high overall costs, making it difficult to meet the development trends of green chemistry.

[0004] To alleviate these problems, existing technologies attempt to improve both catalysts and process design. On one hand, researchers have developed solid acid catalysts (such as heteropoly acids, ion exchange resins, or modified molecular sieves) to replace concentrated sulfuric acid. These catalysts can be recovered through simple filtration, partially enabling reuse and reducing waste acid emissions. On the other hand, some approaches aim to reduce energy consumption in the separation process by optimizing the selection of water-carrying agents (such as using azeotropic distillation) or introducing continuous reaction units. These improvements have, to some extent, simplified post-processing steps, reduced equipment corrosion, and improved the local efficiency of the reaction.

[0005] However, existing improvement schemes still have significant limitations. Solid acid catalysts are costly to prepare and prone to instability due to carbon buildup or loss of active components during long-term operation. Process optimization often focuses on single steps, failing to systematically address the issues of lengthy overall processes and the interconnectedness of energy consumption and pollution. Furthermore, some alternative solvents are toxic or difficult to recycle, potentially causing secondary pollution. Overall, current technologies have not yet achieved an ideal balance between reaction efficiency, environmental impact, and economic efficiency, necessitating the development of a highly integrated, mild, and entirely green preparation method. Summary of the Invention

[0006] The purpose of this invention is to provide a catalyst for the synthesis of dimethyl isophthalate, its preparation method, and its application, so as to solve the environmental pollution problems existing in the current production process of dimethyl isophthalate.

[0007] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing a catalyst for the synthesis of dimethyl isophthalate, comprising the following steps: S1: Add sugar compounds and pore-forming agents to water, and obtain a mixed solid by rotary evaporation; S2: After carbonizing the mixed solid, a porous carbon-based support is obtained; S3: The porous carbon-based support, sulfonating agent and water are placed in a reactor for sulfonation to obtain the catalyst.

[0008] Further, the carbohydrate compound is one or more selected from starch, sucrose, cellulose, and glucose; the pore-forming agent is an inorganic base; the inorganic base is one or more selected from NaOH, Na2CO3, and NaHCO3; The sulfonating agent is one or more of methanesulfonic acid, p-toluenesulfonic acid, hydroxyethylsulfonic acid, dodecylbenzenesulfonic acid, and p-aminobenzenesulfonic acid.

[0009] Further, in S1, the mass ratio of the carbohydrate compound to the pore-forming agent is 1:(0.1~2). The mass ratio of water to carbohydrates is (20~100):1.

[0010] Furthermore, in S2, the carbonization is carried out under nitrogen protection; the carbonization temperature is 300~600℃, and the carbonization time is 2~6h.

[0011] Further, in S3, the mass ratio of the porous carbon-based support to the sulfonating agent is 1:(0.5~5); the mass ratio of the porous carbon-based support to water is 1:(5~30).

[0012] Furthermore, in S3, the sulfonation temperature is 120~180℃, and the sulfonation time is 1~5h.

[0013] The present invention also discloses a catalyst for the synthesis of dimethyl isophthalate prepared by the above preparation method. This invention also discloses the application of the above-mentioned catalyst in the synthesis of dimethyl isophthalate. The esterification and recrystallization using the catalyst to obtain solid dimethyl isophthalate specifically includes the following steps: Dimethyl isophthalate, methanol, and the above catalyst were mixed in a reactor and esterified to obtain a crude product. Then, methanol and water were added to the crude product for recrystallization and filtration to obtain solid dimethyl isophthalate.

[0014] Further, the mass ratio of methanol to isophthalic acid is 1 to 10; the amount of catalyst used is 0.1 wt.% to 10 wt.% of the mass of isophthalic acid. The esterification reaction temperature is 150~220℃, and the reaction time is 1~10h.

[0015] Further, the mass ratio of dimethyl isophthalate to the total mass of methanol and water is 1:(0.5~5); the mass ratio of methanol to water is 1:(0.5~5). The recrystallization temperature is -10~0℃, and the recrystallization time is 0.5~5h.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing a catalyst for the synthesis of dimethyl isophthalate. The method uses a carbohydrate compound as a carbon source, an inorganic base as a pore-forming agent, and an organic sulfonic acid as a sulfonating agent. Through carbonization and sulfonation, a porous carbon-based solid acid is obtained. The porous structure increases the specific surface area, and sulfonation introduces more sulfonic acid groups onto the carbon support, increasing the acid active sites on the catalyst surface. This results in a catalyst with excellent catalytic activity and stability, easy separation from the product, and repeated reuse. In the preparation of dimethyl isophthalate, this method reduces the generation of byproducts, lowers wastewater, waste gas, and waste residue emissions, and avoids the risk of strong acid corrosion, conforming to green chemistry principles and providing an environmentally friendly solution for the production of aromatic ester compounds.

[0017] This invention also discloses the application of the above-mentioned catalyst in the synthesis of dimethyl isophthalate. The catalyst can be used to synthesize dimethyl isophthalate from dimethyl isophthalate and methanol. It has excellent catalytic performance, good reusability, and effectively solves the corrosion and high pollution problems in the current industrial synthesis route of dimethyl isophthalate. Detailed Implementation

[0018] 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.

[0019] 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.

[0020] 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.

[0021] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0022] 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.

[0023] This invention provides a method for preparing a catalyst for the synthesis of dimethyl isophthalate, comprising the following steps: Step 1: Dissolve the carbohydrate compound and pore-forming agent in water, remove the water by rotary evaporation, and form a homogeneous mixed solid; Step 2: The mixed solid is placed in a quartz tube furnace and calcined (carbonized) at a certain temperature under nitrogen protection to obtain a porous carbon-based support; Step 3: Mix the obtained solid powder with sulfonating agent and water and put it into a reaction vessel. Sulfonate at a certain temperature to obtain a porous carbon-based solid acid (catalyst) for the synthesis of dimethyl isophthalate.

[0024] Preferably, the carbon source is a carbohydrate compound such as starch, sucrose, cellulose, or glucose.

[0025] Preferably, a porous carbon-based support is obtained by high-temperature carbonization in a tube furnace under a nitrogen atmosphere. The inorganic base is one of NaOH, Na2CO3 and NaHCO3. The mass ratio of the carbohydrate compound to the pore-forming agent is 1:0.1~2. The carbonization temperature is 300~600℃ and the carbonization time is 2~6h.

[0026] Preferably, the catalyst is obtained by hydrothermal sulfonation using an organic sulfonic acid as the sulfonating agent; the sulfonating agent used is one of methanesulfonic acid, p-toluenesulfonic acid, hydroxyethylsulfonic acid, dodecylbenzenesulfonic acid, or p-aminobenzenesulfonic acid; the mass ratio of porous carbon-based support to sulfonating agent is 1:0.5~5; the ratio of porous carbon-based support to water is 1:5~30; the sulfonation temperature is 120~180℃; and the sulfonation time is 1~5h.

[0027] This invention also discloses the application of the above-mentioned catalyst in the synthesis of dimethyl isophthalate. The esterification and recrystallization using the catalyst to obtain solid dimethyl isophthalate specifically includes the following steps: Dimethyl isophthalate, methanol, and the porous carbon-based solid acid catalyst are mixed in a reactor, a certain temperature is set, and after a period of time, esterification is carried out to obtain a crude product. Then, methanol and water are added, and after recrystallization and filtration, solid dimethyl isophthalate is obtained.

[0028] Preferably, the mass ratio of methanol to isophthalic acid is 1 to 10, and the amount of catalyst used is 0.1 wt.% to 10 wt.% of isophthalic acid.

[0029] Preferably, the esterification reaction temperature is 150℃~220℃, and the reaction time is 1~10h.

[0030] Preferably, the mass ratio of dimethyl isophthalate to the crystallization solution is 1:0.5~5, the crystallization solution is methanol and water with a mass ratio of 1:0.5~5, the recrystallization temperature is -10~0℃, and the recrystallization time is 0.5~5h.

[0031] 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. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0032] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0033] This invention utilizes a porous carbon-based solid acid catalyst for the synthesis of dimethyl isophthalate from isophthalic acid and methanol. The carbon source includes a carbohydrate compound such as starch, sucrose, cellulose, or glucose; the inorganic base is one of NaOH, Na₂CO₃, and NaHCO₃; and the organic sulfonic acid is one of methanesulfonic acid, p-toluenesulfonic acid, hydroxyethylsulfonic acid, dodecylbenzenesulfonic acid, or p-aminobenzenesulfonic acid. The catalyst uses a carbohydrate compound as the carbon source, an inorganic base as a pore-forming agent, and an organic sulfonic acid as a sulfonating agent, undergoing carbonization-sulfonation to obtain the porous carbon-based solid acid.

[0034] This invention provides the industrial application of the above-mentioned solid acid catalyst for the synthesis of dimethyl isophthalate. The catalyst is used to synthesize dimethyl isophthalate from isophthalic acid and methanol. Isophthalic acid and methanol are mixed in a mass ratio of 1:0.5~5, and the catalyst is added at 0.1wt.%~10wt.% of the isophthalic acid. The reaction is carried out at a temperature of 150~220℃ for 1~10 hours. After recrystallization and filtration, the dimethyl isophthalate product is obtained.

[0035] Example 1 A method for preparing a catalyst for the synthesis of dimethyl isophthalate includes the following steps: Add 2g starch and 2g NaOH to 50g water, remove the water by rotary evaporation, and form a uniform mixed solid. The mixed solid was placed in a quartz tube furnace and calcined at 400°C for 4 hours under nitrogen protection. After cooling to room temperature, a solid black powder was obtained. Then, it was treated with 1 mol·L⁻¹... -1 After soaking in HCl for 2 hours, the solid black powder was obtained by filtration and separation. It was washed with distilled water until neutral and dried at 100°C to obtain the black powder, which is the porous carbon-based support. Take 3g of the above porous carbon-based support and place it in a hydrothermal reactor. Add p-toluenesulfonic acid (mass ratio of 1:1.5 to the porous carbon-based support) and water (mass ratio of 1:20 to the porous carbon-based support). After sulfonation at 150℃ for 2h, allow it to cool naturally to room temperature. Filter to obtain a black solid. Wash repeatedly with water until the filtrate is neutral. Finally, vacuum dry at 80℃ to obtain a porous carbon-based solid acid catalyst.

[0036] Application Example 1 The catalyst prepared in Example 1, isophthalic acid, and methanol were added to the reactor in a mass ratio of 0.03:1:3.0. After purging with N2 to remove air, the mixture was stirred at 500 r / min for 5 h at 180 °C. After the reaction, a crystallization solution with a mass ratio of 1:1.5 (methanol to water in the crystallization solution was 1:1) was added according to the theoretical yield. The solution was heated to dissolve, and the catalyst was removed by hot filtration. The solution was then placed in a cold trap and cooled to -5 °C for 2 h to crystallize. After filtration, the solution was dried in an oven at 100 °C to obtain the product dimethyl isophthalate. The results of liquid chromatography analysis showed that the conversion rate of isophthalic acid was 90.7%, the selectivity of dimethyl isophthalate was 97.5%, and the product yield was 80.7%.

[0037] Application Example 2 The catalyst prepared in Example 1, isophthalic acid, and methanol were added to the reactor in a mass ratio of 0.05:1:3.0. After purging with N2 to remove air, the mixture was stirred at 500 r / min for 5 h at 180 °C. After the reaction, a crystallization solution with a mass ratio of 1:1.5 (methanol to water in the crystallization solution was 1:1) was added according to the theoretical yield. The solution was heated to dissolve, and the catalyst was removed by hot filtration. The solution was then placed in a cold trap and cooled to -5 °C for 2 h to crystallize. After filtration, the solution was dried in an oven at 100 °C to obtain the product dimethyl isophthalate. The results of liquid chromatography analysis showed that the conversion rate of isophthalic acid was 92.8%, the selectivity of dimethyl isophthalate was 96.8%, and the product yield was 81.3%.

[0038] Application Example 3 The catalyst prepared in Example 1, isophthalic acid, and methanol were added to the reactor in a mass ratio of 0.03:1:3.0. After purging with N2 to remove air, the mixture was stirred at 210°C and 500 r / min for 5 h. After the reaction, a crystallization solution with a mass ratio of 1:1.5 (methanol to water in the crystallization solution was 1:1) was added according to the theoretical yield. The solution was heated to dissolve, and the catalyst was removed by hot filtration. The solution was then placed in a cold trap and cooled to -5°C for 2 h to crystallize. After filtration, the solution was dried in an oven at 100°C to obtain the product dimethyl isophthalate. The results of liquid chromatography analysis showed that the conversion rate of isophthalic acid was 96.6%, the selectivity of dimethyl isophthalate was 92.8%, and the product yield was 82.8%.

[0039] Application Example 4 The catalyst prepared in Example 1, isophthalic acid, and methanol were added to the reactor in a mass ratio of 0.03:1:5.0. After purging with N2 to remove air, the mixture was stirred at 210°C and 500 r / min for 5 h. After the reaction, a crystallization solution with a mass ratio of 1:1.5 (methanol to water in the crystallization solution was 1:1) was added according to the theoretical yield. The solution was heated to dissolve, and the catalyst was removed by hot filtration. The solution was then placed in a cold trap and cooled to -5°C for 2 h to crystallize. After filtration, the solution was dried in an oven at 100°C to obtain the product dimethyl isophthalate. The results of liquid chromatography analysis showed that the conversion rate of isophthalic acid was 98.7%, the selectivity of dimethyl isophthalate was 95.7%, and the product yield was 86.9%.

[0040] Application Example 5 The catalyst prepared in Example 1, isophthalic acid, and methanol were added to the reactor in a mass ratio of 0.03:1:3.0. After purging with N2 to remove air, the mixture was stirred at 500 r / min for 5 h at 180 °C. After the reaction, a crystallization solution with a mass ratio of 1:2 (methanol to water in the crystallization solution was 1:1) was added according to the theoretical yield. The solution was heated to dissolve, and the catalyst was removed by hot filtration. The solution was then placed in a cold trap and cooled to -10 °C for 2 h to crystallize. After filtration, the solution was dried in an oven at 100 °C to obtain the product dimethyl isophthalate. The results of liquid chromatography analysis showed that the conversion rate of isophthalic acid was 90.3%, the selectivity of dimethyl isophthalate was 96.9%, and the product yield was 88.1%.

[0041] Example 2 A method for preparing a catalyst for the synthesis of dimethyl isophthalate includes the following steps: Add 2g of glucose and 2g of NaOH to 50g of water, remove the water by rotary evaporation, and form a homogeneous solid mixture. The mixed solid was placed in a quartz tube furnace and calcined at 400°C for 2 hours under nitrogen protection. After cooling to room temperature, a solid black powder was obtained. Then, 1 mol·L⁻¹ was used... -1 After soaking in HCl for 2 hours, the solid black powder was obtained by filtration. It was washed with distilled water until neutral and dried at 100°C to obtain the black powder, which is the porous carbon-based support. Take 3g of the above porous carbon-based support and place it in a hydrothermal reactor. Add p-toluenesulfonic acid (mass ratio of 1:1.5 to the porous carbon-based support) and water (mass ratio of 1:20 to the porous carbon-based support). After sulfonation at 150℃ for 2h, allow it to cool naturally to room temperature. Filter to obtain a black solid. Wash repeatedly with water until the filtrate is neutral. Finally, vacuum dry at 80℃ to obtain a porous carbon-based solid acid catalyst.

[0042] Application Example 6 The catalyst prepared in Example 2, isophthalic acid, and methanol were added to the reactor in a mass ratio of 0.03:1:3.0. After purging with N2 to remove air, the mixture was stirred at 500 r / min for 5 h at 180 °C. After the reaction, a crystallization solution with a mass ratio of 1:1.5 (methanol to water in the crystallization solution was 1:1) was added according to the theoretical yield. The solution was heated to dissolve, and the catalyst was removed by hot filtration. The solution was then placed in a cold trap and cooled to -5 °C for 2 h to crystallize. After filtration, the solution was dried in an oven at 100 °C to obtain the product dimethyl isophthalate. The results of liquid chromatography analysis showed that the conversion rate of isophthalic acid was 86.7%, the selectivity of dimethyl isophthalate was 97.9%, and the product yield was 76.9%.

[0043] Example 3 A method for preparing a catalyst for the synthesis of dimethyl isophthalate includes the following steps: Add 2g starch and 2g NaHCO3 to 80g water, remove the water by rotary evaporation, and form a homogeneous mixed solid. The mixed solid was placed in a quartz tube furnace and calcined at 500°C for 4 hours under nitrogen protection. After cooling to room temperature, a solid black powder was obtained. Then, 1 mol·L⁻¹ was used... -1 After soaking in HCl for 2 hours, the solid black powder was obtained by filtration. It was washed with distilled water until neutral and dried at 100°C to obtain the black powder, which is the porous carbon-based support. Take 3g of the above porous carbon-based support and place it in a hydrothermal reactor. Add p-toluenesulfonic acid (mass ratio of 1:1.5 to the porous carbon-based support) and water (mass ratio of 1:20 to the porous carbon-based support). After sulfonation at 150℃ for 2h, allow it to cool naturally to room temperature. Filter to obtain a black solid. Wash repeatedly with water until the filtrate is neutral. Finally, vacuum dry at 80℃ to obtain a porous carbon-based solid acid catalyst.

[0044] Application Example 7 The catalyst prepared in Example 3, isophthalic acid, and methanol were added to the reactor in a mass ratio of 0.03:1:3.0. After purging with N2 to remove air, the mixture was stirred at 500 r / min for 5 h at 180 °C. After the reaction, a crystallization solution with a mass ratio of 1:1.5 (methanol to water in the crystallization solution was 1:1) was added according to the theoretical yield. The solution was heated to dissolve, and the catalyst was removed by hot filtration. The solution was then placed in a cold trap and cooled to -5 °C for 2 h to crystallize. After filtration, the solution was dried in an oven at 100 °C to obtain the product dimethyl isophthalate. The results of liquid chromatography analysis showed that the conversion rate of isophthalic acid was 92.6%, the selectivity of dimethyl isophthalate was 98.2%, and the product yield was 82.3%.

[0045] Example 4 A method for preparing a catalyst for the synthesis of dimethyl isophthalate includes the following steps: Add 2g of starch and 4g of NaHCO3 to 100g of water, remove the water by rotary evaporation, and form a uniform mixed solid. The mixed solid was placed in a quartz tube furnace and calcined at 500°C for 4 hours under nitrogen protection. After cooling to room temperature, a solid black powder was obtained. Then, 1 mol·L⁻¹ was used... -1 After soaking in HCl for 2 hours, the solid black powder was obtained by filtration. It was washed with distilled water until neutral and dried at 100°C to obtain the black powder, which is the porous carbon-based support. Take 3g of the above porous carbon-based support and place it in a hydrothermal reactor. Add p-toluenesulfonic acid (mass ratio of 1:2 to the porous carbon-based support) and water (mass ratio of 1:25 to the porous carbon-based support). After sulfonation at 150℃ for 2h, allow it to cool naturally to room temperature. Filter to obtain a black solid. Wash repeatedly with water until the filtrate is neutral. Finally, vacuum dry at 80℃ to obtain a porous carbon-based solid acid catalyst.

[0046] Application Example 8 The catalyst prepared in Example 4, isophthalic acid, and methanol were added to the reactor in a mass ratio of 0.03:1:3.0. After purging with N2 to remove air, the mixture was stirred at 500 r / min for 5 h at 180 °C. After the reaction, a crystallization solution with a mass ratio of 1:1.5 (methanol to water in the crystallization solution was 1:1) was added according to the theoretical yield. The solution was heated to dissolve, and the catalyst was removed by hot filtration. The solution was then placed in a cold trap and cooled to -5 °C for 2 h to crystallize. After filtration, the solution was dried in an oven at 100 °C to obtain the product dimethyl isophthalate. The results of liquid chromatography analysis showed that the conversion rate of isophthalic acid was 94.8%, the selectivity of dimethyl isophthalate was 96.7%, and the product yield was 83.1%.

[0047] Comparative Example 1 Compared to Example 1, this comparative example uses a carbon-based solid acid catalyst without a pore-forming agent to carry out the esterification reaction: 2g of starch was placed in a quartz tube furnace and calcined at 400℃ for 4 hours under nitrogen protection. After cooling to room temperature, a solid black powder was obtained. Then, 1mol·L⁻¹ starch was used to calcine the powder. -1 After soaking in HCl for 2 hours, the solid black powder was obtained by filtration. It was washed with distilled water until neutral and dried at 100°C to obtain the black powder, which is the porous carbon support. Take 3g of the above porous carbon support and place it in a hydrothermal reactor. Add p-toluenesulfonic acid (mass ratio of 1:1.5 to the porous carbon support) and water (mass ratio of 1:20 to the porous carbon support). After sulfonation at 150℃ for 2h, naturally cool to room temperature, filter to obtain a black solid, wash repeatedly with water until the filtrate is neutral, and finally vacuum dry at 80℃ to obtain a porous carbon-based solid acid catalyst. The catalyst, isophthalic acid, and methanol prepared in this comparative example were added to a reaction vessel at a mass ratio of 0.03:1:3.0. After purging with N2 to remove air, the reaction was carried out at 180℃ and stirred at 500 r / min for 5 h. After the reaction, a crystallization solution with a mass ratio of 1:1.5 (methanol to water in the crystallization solution was 1:1) was added according to the theoretical yield. The solution was heated to dissolve, and the catalyst was removed by hot filtration. The solution was then placed in a cold trap and cooled to -5℃ for 2 h to crystallize. Finally, the solution was filtered and dried in an oven at 100℃ to obtain the product dimethyl isophthalate. Liquid chromatography analysis showed that the conversion rate of isophthalic acid was 78.9%, the selectivity of dimethyl isophthalate was 96.4%, and the product yield was 57.9%.

[0048] Comparative Example 2 Compared to Example 1, this comparative example uses porous carbon that has not been sulfonated with organic sulfonates as a catalyst for esterification: Add 2g starch and 2g NaOH to 50g water, remove the water by rotary evaporation to form a homogeneous solid mixture; place the solid mixture in a quartz tube furnace, calcine at 400℃ for 4h under nitrogen protection, then cool to room temperature to obtain a solid black powder, and then use 1mol·L⁻¹... -1 After soaking in HCl for 2 hours, the solid black powder was obtained by filtration. It was washed with distilled water until neutral and dried at 100°C to obtain the black powder, which is porous carbon. The catalyst, isophthalic acid, and methanol prepared in this comparative example were added to a reaction vessel at a mass ratio of 0.03:1:3.0. After purging with N2 to remove air, the reaction was carried out at 180℃ and stirred at 500 r / min for 5 h. After the reaction, a crystallization solution with a mass ratio of 1:1.5 (methanol to water in the crystallization solution was 1:1) was added according to the theoretical yield. The solution was heated to dissolve, and the catalyst was removed by hot filtration. The solution was then placed in a cold trap and cooled to -5℃ for 2 h to crystallize. Finally, the solution was filtered and dried in an oven at 100℃ to obtain the product dimethyl isophthalate. Liquid chromatography analysis showed that the conversion rate of isophthalic acid was 38.5%, the selectivity of dimethyl isophthalate was 95.7%, and the product yield was 31.3%.

[0049] As can be seen from the above examples and comparative examples, the catalytic activity of carbon-based solid acids without porous structures and porous carbon catalysts not sulfonated with organic sulfonates is lower than that of the catalysts in the examples. This is because porous carbon-based solid acid catalysts have a larger specific surface area and more acid active sites, which can improve the mass transfer and conversion rate of reactants.

[0050] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a catalyst for the synthesis of dimethyl isophthalate, characterized in that, Includes the following steps: S1: Add sugar compounds and pore-forming agents to water, and obtain a mixed solid by rotary evaporation; S2: After carbonizing the mixed solid, a porous carbon-based support is obtained; S3: The porous carbon-based support, sulfonating agent and water are placed in a reactor for sulfonation to obtain the catalyst.

2. The method for preparing a catalyst for synthesizing dimethyl isophthalate according to claim 1, characterized in that, The carbohydrate compound is one or more of starch, sucrose, cellulose, and glucose; the pore-forming agent is an inorganic base; the inorganic base is one or more of NaOH, Na2CO3, and NaHCO3; The sulfonating agent is one or more of methanesulfonic acid, p-toluenesulfonic acid, hydroxyethylsulfonic acid, dodecylbenzenesulfonic acid, and p-aminobenzenesulfonic acid.

3. The method for preparing a catalyst for synthesizing dimethyl isophthalate according to claim 1, characterized in that, In S1, the mass ratio of the carbohydrate compound to the pore-forming agent is 1:(0.1~2). The mass ratio of water to carbohydrates is (20~100):

1.

4. The method for preparing a catalyst for synthesizing dimethyl isophthalate according to claim 1, characterized in that, In S2, the carbonization is carried out under nitrogen protection; the carbonization temperature is 300~600℃, and the carbonization time is 2~6h.

5. The method for preparing a catalyst for synthesizing dimethyl isophthalate according to claim 1, characterized in that, In S3, the mass ratio of the porous carbon-based support to the sulfonating agent is 1:(0.5~5); the mass ratio of the porous carbon-based support to water is 1:(5~30).

6. The method for preparing a catalyst for synthesizing dimethyl isophthalate according to claim 1, characterized in that, In S3, the sulfonation temperature is 120~180℃ and the sulfonation time is 1~5h.

7. A catalyst for synthesizing dimethyl isophthalate, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. The application of the catalyst according to claim 7 in the synthesis of dimethyl isophthalate, characterized in that, Esterification and recrystallization using the catalyst to obtain solid dimethyl isophthalate specifically includes the following steps: Dimethyl isophthalate, methanol, and the above catalyst were mixed in a reactor and esterified to obtain a crude product. Then, methanol and water were added to the crude product for recrystallization and filtration to obtain solid dimethyl isophthalate.

9. The application of the catalyst according to claim 8 in the synthesis of dimethyl isophthalate, characterized in that, The mass ratio of methanol to isophthalic acid is 1 to 10; the amount of catalyst used is 0.1 wt.% to 10 wt.% of the mass of isophthalic acid. The esterification reaction temperature is 150~220℃, and the reaction time is 1~10h.

10. The application of the catalyst according to claim 8 in the synthesis of dimethyl isophthalate, characterized in that, The mass ratio of dimethyl isophthalate to the total mass of methanol and water is 1:(0.5~5); the mass ratio of methanol to water is 1:(0.5~5). The recrystallization temperature is -10~0℃, and the recrystallization time is 0.5~5h.