Preparation method of terephthalic acid and 2-methylimidazole organic framework catalyst

Abstract

The invention relates to a preparation method of a terephthalic acid and 2-methylimidazole organic framework catalyst, and relates to a preparation method of a high polymer material catalyst, the preparation method comprises the following steps: weighing C6H4 (COOH) 2 and 2-methylimidazole, dissolving C6H4 (COOH) 2 and C4H6N2 in N, N-dimethylformamide (DMF), weighing zinc nitrate hexahydrate (Zn (NO3) 2.6 H2O), dissolving in DMF, and preparing into a solution; the preparation method comprises the following steps: mixing a C6H4 (COOH) 2 solution and a C4H6N2 solution in proportion, and uniformly stirring; slowly adding the mixed ligand solution into a mixed solution of zinc nitrate hexahydrate (Zn (NO). 6HO) dissolved in DMF (Dimethyl Formamide), and transferring into a high-pressure reaction kettle for reaction; after cooling, centrifugally separating to obtain a white solid product, washing with methanol, and drying to obtain the Zn-MOF catalyst. The Zn-MOF catalyst provided by the invention can be widely applied to polyester synthesis, esterification reaction and other organic catalytic reactions, and especially has significant advantages in PBAT synthesis.

Description

Technical Field

[0001] The present invention relates to a method for preparing a polymer material catalyst, in particular to a method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst. Background Art

[0002] Terephthalic acid (PTA) is an important organic compound with the chemical formula C8H6O4, belonging to the aromatic dicarboxylic acid family. C6H4(COOH)2 is a white crystalline solid that is slightly soluble in water but readily soluble in alkaline solutions and organic solvents such as N,N-dimethylformamide (DMF). Its melting point is approximately 300°C, and it can sublime at elevated temperatures. C6H4(COOH)2 exhibits typical carboxylic acid properties, capable of esterification with alcohols to form corresponding ester compounds. It can also form coordination complexes with metal ions, such as metal-organic frameworks (MOFs). In the preparation of MOFs, C6H4(COOH)2 acts as an organic ligand, capable of coordinating with metal ions (such as zinc and copper), forming porous materials with high surface area and tunable pore structures. These materials are widely used in catalysis, gas adsorption, and separation.

[0003] N,N-Dimethylformamide (DMF) is a common polar aprotic solvent with the chemical formula C3H7NO. It is a colorless, transparent liquid with a slight ammoniacal odor, a boiling point of 153°C, and a melting point of -61°C. DMF possesses extremely high polarity and excellent solubility, dissolving most organic compounds, inorganic salts, and polymers. Therefore, it is widely used as a solvent, reaction medium, and catalyst support. DMF's molecular structure contains a formamide group (-CONH-), in which the two hydrogen atoms on the nitrogen atom are replaced by methyl groups, forming an N,N-dimethyl structure. This gives DMF high stability and low volatility. DMF has a wide range of applications in chemical engineering and materials science. Firstly, as an excellent polar solvent, it is widely used in organic synthesis reactions, particularly in polymerization, condensation reactions, and the preparation of metal-organic frameworks (MOFs). Due to its excellent solubility and stability, DMF effectively promotes the dissolution of reactants and the progress of reactions. Secondly, DMF is also used as a solvent in the synthesis and processing of polymers such as polyurethane, polyacrylonitrile, and polyimide. In addition, DMF has certain applications in the pharmaceutical field, as a solvent and reaction medium for drug synthesis. In the electronics industry, DMF is used for cleaning and processing liquid crystal displays and semiconductor materials.

[0004] Zinc nitrate hexahydrate (chemical formula: Zn(NO₃)₂·6H₂O) is a common inorganic salt, a hydrate formed by the combination of zinc nitrate and water molecules. It is a colorless or white crystalline solid, easily soluble in water and ethanol, hygroscopic, and easily deliquescent in air. Zinc nitrate hexahydrate has a melting point of 36.4°C. When heated, it gradually loses its water of crystallization, ultimately decomposing into zinc oxide, nitrogen oxides, and oxygen. Because it contains zinc ions (Zn⁺) and nitrate ions (NO⁻), zinc nitrate hexahydrate exhibits oxidizing and coordination properties in chemical reactions and is often used to prepare other zinc compounds or as a catalyst precursor. Zinc nitrate hexahydrate has a wide range of applications in chemical engineering, materials science, and catalysis. Primarily, it is often used as a zinc source in the preparation of other zinc compounds, such as zinc oxide, zinc sulfide, and metal-organic frameworks (MOFs). In the synthesis of MOFs, zinc nitrate hexahydrate serves as a metal ion source, capable of coordinating with organic ligands (such as PTA and C₄H₆N₂) to form crystalline materials with porous structures. Furthermore, zinc nitrate hexahydrate is used as a catalyst or catalyst precursor, exhibiting excellent catalytic activity in organic synthesis reactions. Furthermore, it is used in the electroplating industry to prepare zinc coatings and in agriculture as a trace element fertilizer to supplement the zinc required by plants.

[0005] MOFs are a class of porous crystalline materials formed by the self-assembly of metal ions or metal clusters with organic ligands through coordination bonds. MOFs are characterized by highly ordered pores and cavities, whose pore size and structure can be regulated by the selection of different metal ions and organic ligands. MOFs typically have very high surface areas, reaching thousands of square meters per gram, and their tunable pore size and surface chemistry give them great potential for applications in gas adsorption, separation, catalysis, sensing, and drug delivery. MOFs have a wide range of applications. In gas adsorption and storage, MOFs are widely used for the adsorption and storage of hydrogen, methane, and carbon dioxide due to their high surface area and tunable pore structure. In catalysis, MOFs are used as highly efficient catalysts or catalyst supports due to their abundant active sites and tunable surface chemistry, and are widely used in organic synthesis, photocatalysis, and electrocatalysis. MOFs also exhibit potential applications in drug delivery, chemical sensing, and environmental protection.

[0006] Polybutylene adipate / terephthalate (PBAT) is an important biodegradable polyester widely used in packaging, agriculture, and biomedicine. However, existing catalysts for PBAT synthesis suffer from low catalytic efficiency, poor stability, and high cost, limiting their industrial application. Metal-organic frameworks (MOFs) have shown great potential in catalysis due to their high surface area, tunable structure, and abundant active sites. However, efficient Zn-MOF-based catalysts for PBAT synthesis have not yet been reported.

[0007] 2-Methylimidazole (C4H6N2) is a nitrogen-containing heterocyclic compound belonging to the class of imidazole derivatives. 2-Methylimidazole (C4H6N2) is a white to light yellow crystalline solid with a slight ammoniacal odor. It is soluble in water and various organic solvents, such as ethanol, methanol, and dimethylformamide (DMF). It has a melting point of 140-145°C and a boiling point of 267°C. It exhibits a certain degree of basicity and coordination capacity. C4H6N2 has a wide range of applications in chemical engineering and materials science. Firstly, it is often used as an organic ligand in the synthesis of metal-organic frameworks (MOFs). Because its nitrogen atom is present in the molecule, it can form stable coordination bonds with metal ions (such as zinc and copper), playing a key role in the preparation of MOFs. Secondly, C4H6N2 is used as a curing agent for epoxy resins, improving their mechanical properties and thermal stability. Furthermore, it has certain applications in the pharmaceutical field, serving as an intermediate in the synthesis of certain drugs and bioactive molecules. Summary of the Invention

[0008] The present invention aims to provide a method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst, which is synthesized by a solvent thermal method and has a high specific surface area, abundant active sites and excellent thermal stability; the application of this catalyst in PBAT synthesis significantly improves the reaction efficiency and product quality.

[0009] The purpose of the present invention is achieved through the following technical solutions: A method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst, the preparation steps of the method are as follows: (1) Weigh C6H4(COOH)2 and C4H6N2 separately and prepare a mixed solution; (2) Weigh zinc nitrate hexahydrate and prepare a solution; (3) Slowly adding the mixed ligand solution to the Zn(NO3)2 solution and stirring; transferring the mixed solution to a reactor for reaction; (4) After the reaction is completed, the precipitate is taken out and centrifuged to obtain a white solid product; (5) The product was washed with methanol and dried in vacuo to obtain a Zn-MOF catalyst.

[0010] 2. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 1, wherein the molar ratio of terephthalic acid to 2-methylimidazole in the Zn-MOF catalyst is 1:1 to 2:1.

[0011] 3. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 1, characterized in that the Zn-MOF catalyst has a solvothermal reaction temperature of 100-150° C., a reaction time of 12-24 hours, and a solvent of N,N-dimethylformamide.

[0012] 4. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 1, wherein the Zn-MOF catalyst has a specific surface area of 800-1200 m² / g, a pore size of 0.5-2.0 nm, and a thermal decomposition temperature higher than 350°C.

[0013] 5. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 1, wherein the Zn-MOF catalyst is used to synthesize PBAT and catalyze the copolymerization reaction of terephthalic acid, adipic acid and 1,4-butanediol.

[0014] 6. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 5, wherein the Zn-MOF catalyst is used to synthesize PBAT, the reaction temperature is 180-220°C, and the reaction time is 6-8 hours.

[0015] 7. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 5, wherein the Zn-MOF catalyst is used to synthesize PBAT, and the amount of the Zn-MOF catalyst is 1-5% of the total mass of the reactants.

[0016] The significant features and positive effects of the present invention are: 1. The present invention provides an efficient, stable and environmentally friendly Zn-MOF catalyst and a preparation method thereof, which solves the problems of low efficiency and poor stability of existing PBAT synthesis catalysts and has broad application prospects. In Example 2, the catalyst prepared when the ratio of terephthalic acid (C6H4(COOH)2) to 2-methylimidazole (C4H6N2) is 1:2 has the highest condensation conversion rate and has a catalytic effect on PBAT synthesis.

[0017] 2. The present invention recovers the catalyst by centrifugation or magnetic separation and can be reused after washing with N,N-dimethylformamide (DMF) and heat treatment without significant degradation of catalytic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a graph showing the conversion rate of PBAT polycondensation catalyzed by the Zn-MOF catalyst synthesized with different raw material ratios of the present invention. DETAILED DESCRIPTION

[0019] The metal organic catalyst particles of the present invention are: (1) Weigh terephthalic acid (C6H4(COOH)2) and 2-methylimidazole (C4H6N2) in mass ratios of 1:1, 1:2, 2:1, 2:3, and 3:2, respectively. Dissolve terephthalic acid (C6H4(COOH)2) and 2-methylimidazole (C4H6N2) in DMF to prepare a 0.1 M solution. Weigh zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and dissolve it in N,N-dimethylformamide (DMF) to prepare a 0.1 M solution (M represents 1 mole of solute per liter).

[0020] (2) Slowly add the mixed ligand solution to the Zn(NO3)2 solution and stir for 30 minutes. Transfer the mixed solution to a high-pressure reactor and react at 120°C for 24 hours.

[0021] (3) After the reaction is completed, the precipitate is removed and centrifuged to obtain a white solid product. The product is washed with methanol 6-8 times and vacuum dried to obtain the Zn-MOF catalyst.

[0022] The mass ratio of the raw materials used in the preparation of the metal organic particles of the present invention is: Zinc nitrate hexahydrate 0.1-0.5g Terephthalic acid 0.1-0.5g 2-Methylimidazole 0.1-0.3g N,N-dimethylformamide 5-30mL Preferably, the mass ratio of zinc nitrate hexahydrate, terephthalic acid, and 2-methylimidazole is 1:1:2.

[0023] Preferably, the mass of zinc nitrate hexahydrate is 0.165 g, and the mass of terephthalic acid is 0.165 g.

[0024] The present invention will be described in further detail below: This embodiment is implemented based on the technical solution of the present invention and provides a detailed implementation method, but the protection scope of the present invention is not limited to the following embodiments. Example 1

[0025] Step 1, metal organic catalyst particles: ① Evenly mix 0.274g of terephthalic acid (C6H4(COOH)2) and 0.274g of 2-methylimidazole (C4H6N2) in 50mL of N,N-dimethylformamide (DMF) solution and stir for 12min to obtain mixed solution A for later use. Meanwhile, dissolve 0.274g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) in 9.21mL of ② The obtained mixed solution was centrifuged at 8000 rpm for 10 min, and the precipitate was washed with N,N-dimethylformamide (DMF) 7 times, and finally the precipitate was vacuum dried at 80 ° C for 10 h; ③ The precipitate was placed in a tube furnace and filled with nitrogen for 30 min. Under the protection of nitrogen atmosphere, the heating rate was 4 ° C / min, and after heating to 500 ° C and holding for 4 h, the cooling rate was maintained at 10 ° C / min, and it was cooled to room temperature to obtain Zn-MOF powder.

[0026] Step 2: Synthesis and preparation of a metal organic catalyst for PBAT synthesis: ① Add 223g of adipic acid, 196g of terephthalic acid, 365g of 1,4-butanediol, and 2g of catalyst tetrabutyl titanate in a molar ratio into a reaction vessel, heat to 195°C for the esterification reaction of the alkyd. The esterification reaction is considered to be completed when the collected esterification water volume reaches 95% of the theoretical value; ② After the esterification reaction is completed, add 1.2g of catalyst Zn-MOF and continue to heat to 260°C. The polycondensation reaction is carried out in a vacuum system of less than 50Pa for 2h; ③ Stop the vacuum system, blow in nitrogen to cool down, and protect the discharge with nitrogen. Example 2

[0027] Step 1, metal organic catalyst particles: ① Evenly mix 0.165g of terephthalic acid (C6H4(COOH)2) and 0.330g of 2-methylimidazole (C4H6N2) in 50mL of N,N-dimethylformamide (DMF) solution and stir for 12min to obtain mixed solution A for later use. Meanwhile, dissolve 0.165g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) in 5.55mL of ② The obtained mixed solution was centrifuged at 8000 rpm for 10 min, and the precipitate was washed with N,N-dimethylformamide (DMF) 7 times, and finally the precipitate was vacuum dried at 80 ° C for 10 h; ③ The precipitate was placed in a tube furnace and filled with nitrogen for 30 min. Under the protection of nitrogen atmosphere, the heating rate was 4 ° C / min, and after heating to 500 ° C and holding for 4 h, the cooling rate was maintained at 10 ° C / min, and it was cooled to room temperature to obtain Zn-MOF powder.

[0028] Step 2: Synthesis and preparation of a metal organic catalyst for PBAT synthesis: ① Add 223g of adipic acid, 196g of terephthalic acid, 365g of 1,4-butanediol, and 2g of catalyst tetrabutyl titanate in a molar ratio into a reaction vessel, heat to 195°C for the esterification reaction of the alkyd. The esterification reaction is considered to be completed when the collected esterification water volume reaches 95% of the theoretical value; ② After the esterification reaction is completed, add 1.2g of catalyst Zn-MOF and continue to heat to 260°C. The polycondensation reaction is carried out in a vacuum system of less than 50Pa for 2h; ③ Stop the vacuum system, blow in nitrogen to cool down, and protect the discharge with nitrogen. Example 3

[0029] Step 1, metal organic catalyst particles: ① Evenly mix 0.412g of terephthalic acid (C6H4(COOH)2) and 0.206g of 2-methylimidazole (C4H6N2) in 50mL of N,N-dimethylformamide (DMF) solution and stir for 12min to obtain mixed solution A for later use. Meanwhile, dissolve 0.412g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) in 13.84mL of ② The obtained mixed solution was centrifuged at 8000 rpm for 10 min, and the precipitate was washed with N,N-dimethylformamide (DMF) 7 times, and finally the precipitate was vacuum dried at 80 ° C for 10 h; ③ The precipitate was placed in a tube furnace and filled with nitrogen for 30 min. Under the protection of nitrogen atmosphere, the heating rate was 4 ° C / min, and after heating to 500 ° C and holding for 4 h, the cooling rate was maintained at 10 ° C / min, and it was cooled to room temperature to obtain Zn-MOF powder.

[0030] Step 2: Synthesis and preparation of a metal organic catalyst for PBAT synthesis: ① Add 223g of adipic acid, 196g of terephthalic acid, 365g of 1,4-butanediol, and 2g of catalyst tetrabutyl titanate in a molar ratio into a reaction vessel, heat to 195°C for the esterification reaction of the alkyd. The esterification reaction is considered to be completed when the collected esterification water volume reaches 95% of the theoretical value; ② After the esterification reaction is completed, add 1.2g of catalyst Zn-MOF and continue to heat to 260°C. The polycondensation reaction is carried out in a vacuum system of less than 50Pa for 2h; ③ Stop the vacuum system, blow in nitrogen to cool down, and protect the discharge with nitrogen. Example 4

[0031] Step 1, metal organic catalyst particles: ① Evenly mix 0.206g of terephthalic acid (C6H4(COOH)2) and 0.309g of 2-methylimidazole (C4H6N2) in 50mL of N,N-dimethylformamide (DMF) solution and stir for 12min to obtain mixed solution A for later use. Meanwhile, dissolve 0.206g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) in 6.93mL of ② The obtained mixed solution was centrifuged at 8000 rpm for 10 min, and the precipitate was washed with N,N-dimethylformamide (DMF) 7 times, and finally the precipitate was vacuum dried at 80 ° C for 10 h; ③ The precipitate was placed in a tube furnace and filled with nitrogen for 30 min. Under the protection of nitrogen atmosphere, the heating rate was 4 ° C / min, and after heating to 500 ° C and holding for 4 h, the cooling rate was maintained at 10 ° C / min, and it was cooled to room temperature to obtain Zn-MOF powder.

[0032] Step 2: Synthesis and preparation of a metal organic catalyst for PBAT synthesis: ① Add 223g of adipic acid, 196g of terephthalic acid, 365g of 1,4-butanediol, and 2g of catalyst tetrabutyl titanate in a molar ratio into a reaction vessel, heat to 195°C for the esterification reaction of the alkyd. The esterification reaction is considered to be completed when the collected esterification water volume reaches 95% of the theoretical value; ② After the esterification reaction is completed, add 1.2g of catalyst Zn-MOF and continue to heat to 260°C. The polycondensation reaction is carried out in a vacuum system of less than 50Pa for 2h; ③ Stop the vacuum system, blow in nitrogen to cool down, and protect the discharge with nitrogen. Example 5

[0033] Step 1, metal organic catalyst particles: ① Evenly mix 0.354g of terephthalic acid (C6H4(COOH)2) and 0.236g of 2-methylimidazole (C4H6N2) in 50mL of N,N-dimethylformamide (DMF) solution and stir for 12min to obtain mixed solution A for later use. Meanwhile, dissolve 0.354g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) in 11.9mL of ② The obtained mixed solution was centrifuged at 8000 rpm for 10 min, and the precipitate was washed with N,N-dimethylformamide (DMF) 7 times, and finally the precipitate was vacuum dried at 80 ° C for 10 h; ③ The precipitate was placed in a tube furnace and filled with nitrogen for 30 min. Under the protection of nitrogen atmosphere, the heating rate was 4 ° C / min, and after heating to 500 ° C and holding for 4 h, the cooling rate was maintained at 10 ° C / min, and it was cooled to room temperature to obtain Zn-MOF powder.

[0034] Step 2: Synthesis and preparation of a metal organic catalyst for PBAT synthesis: ① Add 223g of adipic acid, 196g of terephthalic acid, 365g of 1,4-butanediol, and 2g of catalyst tetrabutyl titanate in a molar ratio into a reaction vessel, heat to 195°C for the esterification reaction of the alkyd. The esterification reaction is considered to be completed when the collected esterification water volume reaches 95% of the theoretical value; ② After the esterification reaction is completed, add 1.2g of catalyst Zn-MOF and continue to heat to 260°C. The polycondensation reaction is carried out in a vacuum system of less than 50Pa for 2h; ③ Stop the vacuum system, blow in nitrogen to cool down, and protect the discharge with nitrogen.

Claims

1. A method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst, characterized in that: The preparation steps of the method are as follows: (1) Weigh C6H4(COOH)2 and C4H6N2 separately and prepare a mixed solution; (2) Weigh zinc nitrate hexahydrate and prepare a solution; (3) Slowly add the mixed ligand solution into the Zn(NO3)2 solution and stir; Transferring the mixed solution to a reactor for reaction; (4) After the reaction is completed, the precipitate is taken out and centrifuged to obtain a white solid product; (5) The product was washed with methanol and dried in vacuo to obtain a Zn-MOF catalyst.

2. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 1, characterized in that: The molar ratio of terephthalic acid to 2-methylimidazole in the Zn-MOF catalyst is 1:1 to 2:

1.

3. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 1, characterized in that: The solvent thermal method of the Zn-MOF catalyst has a reaction temperature of 100-150° C., a reaction time of 12-24 hours, and a solvent of N,N-dimethylformamide.

4. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 1, characterized in that: The Zn-MOF catalyst has a specific surface area of 800-1200 m² / g, a pore diameter of 0.5-2.0 nm, and a thermal decomposition temperature higher than 350°C.

5. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 1, characterized in that: The Zn-MOF catalyst is used to synthesize PBAT and catalyze the copolymerization reaction of terephthalic acid, adipic acid and 1,4-butanediol.

6. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 5, characterized in that: The Zn-MOF catalyst is used to synthesize PBAT, and the reaction temperature is 180-220° C. and the reaction time is 6-8 hours.

7. The method for preparing a terephthalic acid and 2-methylimidazole organic framework catalyst according to claim 5, characterized in that: The Zn-MOF catalyst is used to synthesize PBAT, and the amount of the Zn-MOF catalyst used is 1-5% of the total mass of the reactants.

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