A method for purifying pentaerythritol based on ion exchange membrane

Abstract

The application discloses a kind of based on ion exchange membrane's purification method of pentaerythritol, it is related to membrane material preparation technical field.In the application, modified metal organic framework containing pyridine ring and quaternary ammonium salt cation is prepared, and is loaded to the surface of ion exchange membrane, pyridine ring can be protonated and positive, can improve the selective permeability of anion, and have good acid and alkali resistance, can improve the chemical stability of ion exchange membrane in acid and alkali environment, prolong service life, metal framework itself has good hydrophilicity, rigidity and high temperature stability, the side chain methyl of introduced 2,6-dimethylpyridine-4-formaldehyde provides steric hindrance, both synergies, can effectively inhibit ion exchange membrane water absorption swelling, improve dimensional stability and mechanical strength;Quaternary ammonium salt can increase the cation sites on membrane surface, increase ion transport capacity, improve ion conductivity, reduce membrane resistance, improve the flux of ion exchange membrane, conducive to improving separation efficiency.

Description

Technical Field

[0001] This invention relates to the field of membrane material preparation technology, specifically a pentaerythritol purification method based on ion exchange membranes. Background Technology

[0002] Pentaerythritol is an important fine chemical intermediate used in many fields. In its production, formaldehyde and acetaldehyde are often condensed under alkaline conditions to produce a mixture containing pentaerythritol and sodium formate. Sodium formate is a byproduct, and how to efficiently separate it from pentaerythritol is a problem that needs to be solved to improve the purity of pentaerythritol.

[0003] In recent years, membrane separation technology has developed rapidly due to its advantages such as being environmentally friendly, having low energy consumption, and being simple to operate, gradually replacing traditional separation processes. Pentaerythritol is a non-electrolyte with low conductivity, while sodium formate exists in an ionic state and has good conductivity. The significant difference between the two provides a theoretical basis for separation. By utilizing the selective permeability of ion exchange membranes, efficient separation of sodium formate and pentaerythritol can be achieved. Patent CN202511267354.7 discloses the use of ion exchange membranes to separate pentaerythritol, but commercially available ion exchange membranes have the disadvantage of insufficient anti-fouling ability.

[0004] Therefore, this invention proposes a pentaerythritol purification method based on ion exchange membranes to solve the aforementioned problems. Summary of the Invention

[0005] The purpose of this invention is to provide a pentaerythritol purification method based on an ion exchange membrane, which solves the problems mentioned in the prior art by preparing an anti-fouling, high-flux ion exchange membrane.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a pentaerythritol purification method based on an ion exchange membrane, comprising the following steps: Step 1: Cool the pentaerythritol condensate to 25~35℃ and use an antifouling ion exchange membrane to perform electrodialysis separation to obtain pentaerythritol desalted solution, electrodialysis concentrate, sodium formate and low-boiling-point organic matter. Step 2: Evaporate and concentrate the pentaerythritol desalting solution to obtain pentaerythritol.

[0007] Furthermore, in step 1, the process conditions for electrodialysis separation are: temperature 20~25℃, voltage 10~15V.

[0008] Furthermore, in step 2, the evaporation process conditions are: temperature 60~90℃, vacuum degree 0.05~0.10MPa, and time 1~3h.

[0009] Furthermore, the preparation process of the antifouling ion exchange membrane is as follows: S1: Take dopamine hydrochloride, modified metal-organic framework and Tris-HCl buffer, mix and stir to obtain composite dopamine impregnation solution, place ion exchange membrane in composite dopamine impregnation solution, sonicate to form polydopamine intermediate layer, dry to obtain pretreated ion exchange membrane. S2: The pretreated ion exchange membrane is placed in a hydrogen peroxide solution for oxidation treatment. After removal, it is placed in an antifouling treatment solution, and the pH is adjusted to 6.5~7.0 with NaOH. The reaction is carried out at a constant temperature to form an antifouling layer, thus obtaining an antifouling ion exchange membrane.

[0010] Furthermore, in S1, the ratio of dopamine hydrochloride, modified metal-organic framework, and Tris-HCl buffer is (2~3) g: (0.1~0.3) g: 100 mL.

[0011] In S1, the bath ratio of the ion exchange membrane and the composite dopamine impregnation solution is 1:(30~50).

[0012] Furthermore, the Tris-HCl buffer solution has a pH of 8.5 and a concentration of 0.1 mol / L.

[0013] Furthermore, in S1, the ultrasonic treatment process conditions are: frequency 40~60kHz, temperature 25~30℃, and time 25~30min; The drying process conditions are: temperature 50~60℃, time 10~12h.

[0014] Furthermore, in S2, the bath ratio of the pretreated ion exchange membrane to the hydrogen peroxide solution is 1:(20~30). The mass concentration of the hydrogen peroxide solution is 0.5~1.0%.

[0015] Furthermore, in S2, the oxidation treatment process conditions are: temperature 25~30℃, time 25~30min; In S2, the process conditions for the isothermal reaction are: temperature 25~30℃, time 24~48h.

[0016] Furthermore, the modified metal-organic framework is prepared by the following process: S1.1: Under a nitrogen atmosphere, 2,5-diaminoterephthalic acid, TiCl4 (titanium tetrachloride) and anhydrous N,N-dimethylformamide were mixed, stirred and dissolved, then anhydrous methanol was added, stirred evenly, and heated to react. After the reaction was completed, the mixture was cooled, washed and dried to obtain an aminated metal framework. S1.2: Mix 2,6-dimethylpyridine-4-carboxaldehyde and ethanol, stir to dissolve, then add the aminated metal framework and glacial acetic acid, stir and sonicate to disperse, heat to react, cool, wash and dry after the reaction is complete to obtain a pyridine-containing metal framework; S1.3: Mix pyridine-containing metal framework, methanol, and 7-bromo-1-heptanol, stir the reaction, and centrifuge to obtain the modified metal-organic framework.

[0017] Furthermore, in S1.1, the ratio of 2,5-diaminoterephthalic acid, TiCl4, anhydrous N,N-dimethylformamide, and anhydrous methanol is 18g:(22~26)g:(70~80)mL:(1.6~1.8)mL.

[0018] Furthermore, in S1.1, the process conditions for the heating reaction are: temperature 145~155℃, time 40~48h; In S1.1, the drying process conditions are: temperature 60~80℃, time 20~24h.

[0019] Furthermore, in S1.2, the ratio of 2,6-dimethylpyridine-4-carboxaldehyde, ethanol, aminated metal framework, and glacial acetic acid is 1g:(120~150)mL:(0.9~1.1)g:(0.03~0.05)g.

[0020] Furthermore, in S1.2, the process conditions for ultrasonic dispersion by stirring are: frequency 40~60kHz, time 25~30min, and rotation speed 100~200r / min; In S1.2, the process conditions for the heating reaction are: temperature 75~85℃, time 4~5h; In S1.2, the drying process conditions are: temperature 60~80℃, time 10~15h.

[0021] Furthermore, in S1.3, the ratio of pyridine metal framework, methanol, and 7-bromo-1-heptanol is 1.2 g: (190~210) mL: (5.2~5.6) g.

[0022] Furthermore, in S1.3, the process conditions for the stirring reaction are: rotation speed 150~250 r / min, time 20~24 h; The centrifugation process conditions are: 5000~8000 r / min, time 8~10 min.

[0023] In the above technical solution, in S1.1, under high-temperature heating conditions, the carboxyl group of 2,5-diaminoterephthalic acid is deprotonated, and reacts with Ti... 4+ Coordination self-assembly occurs to form a metal framework while retaining the amino group, resulting in an aminated metal framework. In S1.2, the amino group on the aminated metal framework undergoes aldehyde-amine condensation with the aldehyde group of 2,6-dimethylpyridine-4-carboxaldehyde to generate an imine bond, grafting the pyridine ring onto the surface of the metal framework. The pyridine ring contains a tertiary amine structure, which reacts with the bromoalkyl group of 7-bromo-1-heptanol to obtain a modified metal-organic framework.

[0024] Furthermore, the antifouling treatment solution includes modified chitosan and deionized water; The mass concentration of the antifouling treatment solution is 4~6 g / L.

[0025] Furthermore, the preparation process of the modified chitosan is as follows: Chitosan and glacial acetic acid aqueous solution were mixed and stirred to dissolve. 2,4-Butanesulfonate lactone was added and heated to react. After the reaction was completed, the mixture was cooled, acetone was added to precipitate the precipitate, and the precipitate was dried to obtain modified chitosan.

[0026] Furthermore, the ratio of chitosan, glacial acetic acid aqueous solution, 2,4-butanesulfonate lactone, and acetone is (1~3) g : (80~100) mL : (1.0~1.5) g : (160~250) mL; The mass concentration of the glacial acetic acid aqueous solution is 2-3%.

[0027] Furthermore, the process conditions for the heating reaction are: temperature 35~40℃, time 5~6h; The drying process conditions are: temperature 45~50℃, time 12~24h.

[0028] In the above technical solution, the amino group of chitosan undergoes a ring-opening reaction with the sulfonate ring of 2,4-butanesulfonate lactone, introducing sulfonic acid groups into the chitosan molecular chain to obtain modified chitosan. The ion exchange membrane is immersed in a composite dopamine impregnation solution. Under alkaline conditions, dopamine self-polymerizes to form a polydopamine intermediate layer rich in reactive sites. Then, hydrogen peroxide is used for oxidation, which oxidizes the catechol structure of polydopamine to quinone groups, which react with the amino groups of modified chitosan. At the same time, the sulfonic acid groups can also form hydrogen bonds with the polar groups of polydopamine. This dual effect helps to improve the bonding force between the antifouling layer and the ion exchange membrane, thereby improving the antifouling effect.

[0029] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, the modified metal-organic framework contains a pyridine ring and a quaternary ammonium salt cation. The pyridine ring can be protonated to carry a positive charge, which can improve the selective permeability of anions and has good acid and alkali resistance, which can improve the chemical stability of the ion exchange membrane under acid and alkali environments and extend its service life. The metal framework itself has good hydrophilicity, rigidity and high temperature stability. The side chain methyl of the introduced 2,6-dimethylpyridine-4-carboxaldehyde provides steric hindrance. The two work together to effectively inhibit the water absorption and swelling of the ion exchange membrane and improve its dimensional stability and mechanical strength. By loading modified metal-organic frameworks onto the surface of ion exchange membranes, quaternary ammonium salts can increase the number of cation sites on the membrane surface, enhance ion transport capacity, improve ion conductivity, reduce membrane resistance, and increase the flux of ion exchange membranes, which is beneficial to improving separation efficiency. In addition, the introduced long-chain alkyl groups and quaternary ammonium salts form an amphiphilic interface, which can effectively reduce the adsorption of organic matter on the membrane surface and play an antifouling role.

[0030] 2. In this invention, the antifouling layer contains strong hydrophilic groups such as sulfonic acid groups, hydroxyl groups, and amino groups, which form a hydration layer on the surface of the ion exchange membrane, improve the wettability of the ion exchange membrane, weaken the adsorption of pollutants to the ion exchange membrane, and inhibit pollution from the source; in addition, the sulfonic acid group is an anionic group, which can increase the ion sites of the ion exchange membrane, further improve the ion conductivity, thereby improving the separation and purification efficiency of the ion exchange membrane. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] In the following examples, the relevant raw materials are: the ion exchange membrane is a perfluorosulfonic acid cation exchange membrane with a thickness of 0.12 mm, a burst strength ≥ 0.5 MPa, and a resistivity ≤ 3 Ω·cm. -2 The nanofiltration membrane was DK-1812; the chitosan had a degree of deacetylation ≥80% and a pH of 6.5~8.5; the remaining raw materials were commercially available.

[0033] Example 1: A pentaerythritol purification method based on an ion exchange membrane, comprising the following processes: (1) Preparation of antifouling treatment solution: Chitosan and glacial acetic acid aqueous solution were mixed and stirred to dissolve. 2,4-Butanesulfonate lactone was added, and the mixture was heated to 40°C and reacted for 6 hours. After the reaction was completed, the mixture was cooled, and acetone was added to precipitate the precipitate. The precipitate was dried at 50°C for 24 hours to obtain modified chitosan. The ratio of chitosan, glacial acetic acid aqueous solution, 2,4-butanesulfonate lactone, and acetone was 3 g: 100 mL: 1.5 g: 250 mL; the mass concentration of glacial acetic acid aqueous solution was 3%. An antifouling treatment solution with a mass concentration of 6 g / L was prepared by mixing modified chitosan and deionized water. (2) Preparation of modified metal-organic frameworks: S1.1: Under a nitrogen atmosphere, 2,5-diaminoterephthalic acid, TiCl4, and anhydrous N,N-dimethylformamide were mixed and stirred to dissolve. Anhydrous methanol was then added, and the mixture was stirred until homogeneous. The mixture was heated to 155°C and reacted for 48 hours. After the reaction was completed, the mixture was cooled, washed, and dried at 80°C for 24 hours to obtain an aminated metal framework. S1.2: 2,6-dimethylpyridine-4-carboxaldehyde and ethanol were mixed and stirred to dissolve. The aminated metal framework and glacial acetic acid were then added, and the mixture was stirred and ultrasonically dispersed. The mixture was heated to 85°C and reacted for 5 hours. After the reaction was completed, the mixture was cooled, washed, and dried at 80°C for 15 hours to obtain a pyridine-containing metal framework. S1.3: The pyridine-containing metal framework, methanol, and 7-bromo-1-heptanol were mixed in a 1:1 ratio. 2g:210mL:5.6 were mixed and stirred at 250r / min for 24h. The mixture was then centrifuged at 8000r / min for 10min to obtain the modified metal-organic framework. In S1.1, the ratio of 2,5-diaminoterephthalic acid, TiCl4, anhydrous N,N-dimethylformamide, and anhydrous methanol was 18g:26g:80mL:1.8mL. In S1.2, the ratio of 2,6-dimethylpyridine-4-carboxaldehyde, ethanol, aminated metal framework, and glacial acetic acid was 1g:150mL:1.1g:0.05g. The ultrasonic dispersion conditions in S1.2 were: frequency 60kHz, time 30min, and rotation speed 200r / min. (3) Preparation of antifouling ion exchange membrane: S1: Mix dopamine hydrochloride, modified metal-organic framework, and Tris-HCl buffer at a ratio of 3g:0.3g:100mL, stir, and obtain a composite dopamine impregnation solution. Place the ion exchange membrane in the composite dopamine impregnation solution, sonicate to form a polydopamine interlayer, and dry at 60℃ for 12h to obtain a pretreated ion exchange membrane. S2: Place the pretreated ion exchange membrane in hydrogen peroxide solution and oxidize at 30℃ for 30min. After removal, place it in an antifouling treatment solution, using N... The pH was adjusted to 7.0 with aOH, and the mixture was reacted at 30℃ for 48 hours to form an antifouling layer, thus obtaining an antifouling ion exchange membrane. In S1, the bath ratio of the ion exchange membrane to the composite dopamine impregnation solution was 1:50; the pH of the Tris-HCl buffer solution was 8.5. In S1, the ultrasonic treatment conditions were: frequency 60kHz, temperature 30℃, and time 30min. In S2, the bath ratio of the pretreated ion exchange membrane to the hydrogen peroxide solution was 1:30; the mass concentration of the hydrogen peroxide solution was 1.0%. (4) Purification method of pentaerythritol: Step 1: Cool the pentaerythritol condensate to 35°C and perform electrodialysis separation using an antifouling ion exchange membrane to obtain pentaerythritol desalted solution, electrodialysis concentrate, sodium formate, and low-boiling-point organic matter; Step 2: Evaporate and concentrate the pentaerythritol desalted solution to obtain pentaerythritol; In Step 1, the electrodialysis separation process conditions are: temperature 25°C, voltage 15V; In Step 2, the evaporation process conditions are: temperature 90°C, vacuum degree 0.10MPa, time 3h.

[0034] Example 2: A pentaerythritol purification method based on an ion exchange membrane, comprising the following processes: (1) Preparation of antifouling treatment solution: Chitosan and glacial acetic acid aqueous solution were mixed and stirred to dissolve. 2,4-Butanesulfonate lactone was added, and the mixture was heated to 38°C and reacted for 5.5 hours. After the reaction was completed, the mixture was cooled, and acetone was added to precipitate the mixture. The precipitate was then dried at 48°C for 18 hours to obtain modified chitosan. The ratio of chitosan, glacial acetic acid aqueous solution, 2,4-butanesulfonate lactone, and acetone was 2 g:90 mL:1.3 g:200 mL; the mass concentration of the glacial acetic acid aqueous solution was 2.5%. A 5 g / L antifouling treatment solution was prepared by mixing modified chitosan and deionized water. (2) Preparation of modified metal-organic frameworks: S1.1: Under a nitrogen atmosphere, 2,5-diaminoterephthalic acid, TiCl4, and anhydrous N,N-dimethylformamide were mixed and stirred to dissolve. Anhydrous methanol was then added, and the mixture was stirred until homogeneous. The mixture was heated to 150°C and reacted for 44 hours. After the reaction, the mixture was cooled, washed, and dried at 70°C for 22 hours to obtain an aminated metal framework. S1.2: 2,6-dimethylpyridine-4-carboxaldehyde and ethanol were mixed and stirred to dissolve. The aminated metal framework and glacial acetic acid were then added, and the mixture was stirred and ultrasonically dispersed. The mixture was heated to 80°C and reacted for 4.5 hours. After the reaction, the mixture was cooled, washed, and dried at 70°C for 13 hours to obtain a pyridine-containing metal framework. S1.3: The pyridine-containing metal framework, methanol, and 7-bromo-1-heptanol were mixed in a 1:1 ratio. 0.2g:200mL:5.4 were mixed and stirred at 200r / min for 22h. The mixture was then centrifuged at 6500r / min for 9min to obtain the modified metal-organic framework. In S1.1, the ratio of 2,5-diaminoterephthalic acid, TiCl4, anhydrous N,N-dimethylformamide, and anhydrous methanol was 18g:24g:75mL:1.7mL. In S1.2, the ratio of 2,6-dimethylpyridine-4-carboxaldehyde, ethanol, aminated metal framework, and glacial acetic acid was 1g:130mL:1.0g:0.04g. The ultrasonic dispersion conditions in S1.2 were: frequency 50kHz, time 28min, and rotation speed 150r / min. (3) Preparation of antifouling ion exchange membrane: S1: Dopamine hydrochloride, modified metal-organic framework, and Tris-HCl buffer were mixed at a ratio of 2.5g:0.2g:100mL and stirred to obtain a composite dopamine impregnation solution. The ion exchange membrane was placed in the composite dopamine impregnation solution and sonicated to form a polydopamine interlayer. It was then dried at 55℃ for 11 hours to obtain a pretreated ion exchange membrane. S2: The pretreated ion exchange membrane was placed in a hydrogen peroxide solution and oxidized at 28℃ for 28 minutes. After removal, it was placed in an antifouling treatment solution and subjected to further treatment. The pH was adjusted to 6.8 with NaOH, and the reaction was carried out at 28℃ for 35 hours to form an antifouling layer, thus obtaining an antifouling ion exchange membrane. In S1, the bath ratio of the ion exchange membrane to the composite dopamine impregnation solution was 1:40; the pH of the Tris-HCl buffer solution was 8.5. In S1, the ultrasonic treatment conditions were: frequency 50kHz, temperature 28℃, and time 28min. In S2, the bath ratio of the pretreated ion exchange membrane to the hydrogen peroxide solution was 1:25; the mass concentration of the hydrogen peroxide solution was 0.8%. (4) Purification method of pentaerythritol: Step 1: Cool the pentaerythritol condensate to 30℃ and perform electrodialysis separation using an antifouling ion exchange membrane to obtain pentaerythritol desalted solution, electrodialysis concentrate, sodium formate, and low-boiling-point organic matter; Step 2: Evaporate and concentrate the pentaerythritol desalted solution to obtain pentaerythritol; In Step 1, the electrodialysis separation process conditions are: temperature 23℃, voltage 13V; In Step 2, the evaporation process conditions are: temperature 75℃, vacuum degree 0.08MPa, time 2h.

[0035] Example 3: A pentaerythritol purification method based on an ion exchange membrane, comprising the following processes: (1) Preparation of antifouling treatment solution: Chitosan and glacial acetic acid aqueous solution were mixed and stirred to dissolve. 2,4-Butanesulfonate lactone was added, and the mixture was heated to 35°C and reacted for 5 hours. After the reaction was completed, the mixture was cooled, and acetone was added to precipitate the precipitate. The precipitate was dried at 45°C for 12 hours to obtain modified chitosan. The ratio of chitosan, glacial acetic acid aqueous solution, 2,4-butanesulfonate lactone, and acetone was 1 g: 80 mL: 1.0 g: 160 mL; the mass concentration of glacial acetic acid aqueous solution was 2%. An antifouling treatment solution with a mass concentration of 4 g / L was prepared by mixing modified chitosan and deionized water. (2) Preparation of modified metal-organic frameworks: S1.1: Under a nitrogen atmosphere, 2,5-diaminoterephthalic acid, TiCl4, and anhydrous N,N-dimethylformamide were mixed and stirred to dissolve. Anhydrous methanol was then added, and the mixture was stirred until homogeneous. The mixture was heated to 145°C and reacted for 40 hours. After the reaction, the mixture was cooled, washed, and dried at 60°C for 20 hours to obtain an aminated metal framework. S1.2: 2,6-dimethylpyridine-4-carboxaldehyde and ethanol were mixed and stirred to dissolve. The aminated metal framework and glacial acetic acid were then added, and the mixture was stirred and ultrasonically dispersed. The mixture was heated to 75°C and reacted for 4 hours. After the reaction, the mixture was cooled, washed, and dried at 60°C for 10 hours to obtain a pyridine-containing metal framework. S1.3: The pyridine-containing metal framework, methanol, and 7-bromo-1-heptanol were mixed in a 1:1 ratio. 2g:190mL:5.2 were mixed and stirred at 150r / min for 20h, then centrifuged at 5000r / min for 8min to obtain the modified metal-organic framework; in S1.1, the ratio of 2,5-diaminoterephthalic acid, TiCl4, anhydrous N,N-dimethylformamide, and anhydrous methanol was 18g:22g:70mL:1.6mL; in S1.2, the ratio of 2,6-dimethylpyridine-4-carboxaldehyde, ethanol, aminated metal framework, and glacial acetic acid was 1g:120mL:0.9g:0.03g; in S1.2, the stirring and ultrasonic dispersion conditions were: frequency 40kHz, time 25min, and rotation speed 100r / min; (3) Preparation of antifouling ion exchange membrane: S1: Mix dopamine hydrochloride, modified metal-organic framework, and Tris-HCl buffer at a ratio of 2g:0.1g:100mL, stir, and obtain a composite dopamine impregnation solution. Place the ion exchange membrane in the composite dopamine impregnation solution, sonicate to form a polydopamine interlayer, and dry at 50℃ for 10h to obtain a pretreated ion exchange membrane. S2: Place the pretreated ion exchange membrane in hydrogen peroxide solution and oxidize at 25℃ for 25min. After removal, place it in an antifouling treatment solution, using N... The pH was adjusted to 6.5 with aOH, and the reaction was carried out at 25℃ for 24 hours to form an antifouling layer, thus obtaining an antifouling ion exchange membrane. In S1, the bath ratio of the ion exchange membrane to the composite dopamine impregnation solution was 1:30; the pH of the Tris-HCl buffer solution was 8.5. In S1, the ultrasonic treatment conditions were: frequency 40kHz, temperature 25℃, and time 25min. In S2, the bath ratio of the pretreated ion exchange membrane to the hydrogen peroxide solution was 1:20; the mass concentration of the hydrogen peroxide solution was 0.5%. (4) Purification method of pentaerythritol: Step 1: Cool the pentaerythritol condensate to 25°C and perform electrodialysis separation using an antifouling ion exchange membrane to obtain pentaerythritol desalted solution, electrodialysis concentrate, sodium formate, and low-boiling-point organic matter; Step 2: Evaporate and concentrate the pentaerythritol desalted solution to obtain pentaerythritol; In Step 1, the electrodialysis separation process conditions are: temperature 20°C, voltage 10V; In Step 2, the evaporation process conditions are: temperature 60°C, vacuum degree 0.05MPa, time 1h.

[0036] Comparative Example 1: Unlike Example 1, only the ion exchange membrane was placed in a composite dopamine impregnation solution for treatment, without antifouling treatment. All other conditions remained unchanged, the same as in Example 1. Specifically: (1) Preparation of modified metal-organic frameworks: S1.1: Under a nitrogen atmosphere, 2,5-diaminoterephthalic acid, TiCl4, and anhydrous N,N-dimethylformamide were mixed and stirred to dissolve. Anhydrous methanol was then added, and the mixture was stirred until homogeneous. The mixture was heated to 155°C and reacted for 48 hours. After the reaction was completed, the mixture was cooled, washed, and dried at 80°C for 24 hours to obtain an aminated metal framework. S1.2: 2,6-dimethylpyridine-4-carboxaldehyde and ethanol were mixed and stirred to dissolve. The aminated metal framework and glacial acetic acid were then added, and the mixture was stirred and ultrasonically dispersed. The mixture was heated to 85°C and reacted for 5 hours. After the reaction was completed, the mixture was cooled, washed, and dried at 80°C for 15 hours to obtain a pyridine-containing metal framework. S1.3: The pyridine-containing metal framework, methanol, and 7-bromo-1-heptanol were mixed in a 1:1 ratio. 2g:210mL:5.6 were mixed and stirred at 250r / min for 24h. The mixture was then centrifuged at 8000r / min for 10min to obtain the modified metal-organic framework. In S1.1, the ratio of 2,5-diaminoterephthalic acid, TiCl4, anhydrous N,N-dimethylformamide, and anhydrous methanol was 18g:26g:80mL:1.8mL. In S1.2, the ratio of 2,6-dimethylpyridine-4-carboxaldehyde, ethanol, aminated metal framework, and glacial acetic acid was 1g:150mL:1.1g:0.05g. The ultrasonic dispersion conditions in S1.2 were: frequency 60kHz, time 30min, and rotation speed 200r / min. (2) Preparation of modified ion exchange membranes: Dopamine hydrochloride, modified metal-organic framework, and Tris-HCl buffer were mixed at a ratio of 3g:0.3g:100mL and stirred to obtain a composite dopamine impregnation solution. The ion exchange membrane was placed in the composite dopamine impregnation solution and sonicated to form a polydopamine intermediate layer. After drying at 60℃ for 12h, the modified ion exchange membrane was obtained. The bath ratio of the ion exchange membrane to the composite dopamine impregnation solution was 1:50. The pH of the Tris-HCl buffer was 8.5. In S1, the ultrasonic treatment conditions were: frequency 60kHz, temperature 30℃, and time 30min. (3) Purification method of pentaerythritol: Step 1: Cool the pentaerythritol condensate to 35°C and perform electrodialysis separation using an antifouling ion exchange membrane to obtain pentaerythritol desalted solution, electrodialysis concentrate, sodium formate, and low-boiling-point organic matter; Step 2: Evaporate and concentrate the pentaerythritol desalted solution to obtain pentaerythritol; In Step 1, the electrodialysis separation process conditions are: temperature 25°C, voltage 15V; In Step 2, the evaporation process conditions are: temperature 90°C, vacuum degree 0.10MPa, time 3h.

[0037] Comparative Example 2: Unlike Example 1, only the ion exchange membrane underwent antifouling treatment, while all other conditions remained unchanged, the same as in Example 1, specifically: (1) Preparation of antifouling treatment solution: Chitosan and glacial acetic acid aqueous solution were mixed and stirred to dissolve. 2,4-Butanesulfonate lactone was added, and the mixture was heated to 40°C and reacted for 6 hours. After the reaction was completed, the mixture was cooled, and acetone was added to precipitate the precipitate. The precipitate was dried at 50°C for 24 hours to obtain modified chitosan. The ratio of chitosan, glacial acetic acid aqueous solution, 2,4-butanesulfonate lactone, and acetone was 3 g: 100 mL: 1.5 g: 250 mL; the mass concentration of glacial acetic acid aqueous solution was 3%. An antifouling treatment solution with a mass concentration of 6 g / L was prepared by mixing modified chitosan and deionized water. (2) Preparation of antifouling ion exchange membrane: S1: Dopamine hydrochloride and Tris-HCl buffer were mixed at a ratio of 3g:100mL and stirred to obtain a dopamine impregnation solution. The ion exchange membrane was placed in the dopamine impregnation solution and sonicated to form a polydopamine intermediate layer. The membrane was then dried at 60℃ for 12h to obtain a pretreated ion exchange membrane. S2: The pretreated ion exchange membrane was placed in hydrogen peroxide solution and oxidized at 30℃ for 30min. After removal, it was placed in an antifouling treatment solution, and the pH was adjusted to 7.0 with NaOH. The membrane was reacted at 30℃ for 48h to form an antifouling layer, resulting in an antifouling ion exchange membrane. In S1, the bath ratio of the ion exchange membrane to the dopamine impregnation solution was 1:50; the pH of the Tris-HCl buffer solution was 8.5; the sonication conditions in S1 were: frequency 60kHz, temperature 30℃, and time 30min; in S2, the bath ratio of the pretreated ion exchange membrane to the hydrogen peroxide solution was 1:30; the mass concentration of the hydrogen peroxide solution was 1.0%. (3) Purification method of pentaerythritol: Step 1: Cool the pentaerythritol condensate to 35°C and perform electrodialysis separation using an antifouling ion exchange membrane to obtain pentaerythritol desalted solution, electrodialysis concentrate, sodium formate, and low-boiling-point organic matter; Step 2: Evaporate and concentrate the pentaerythritol desalted solution to obtain pentaerythritol; In Step 1, the electrodialysis separation process conditions are: temperature 25°C, voltage 15V; In Step 2, the evaporation process conditions are: temperature 90°C, vacuum degree 0.10MPa, time 3h.

[0038] Comparative Example 3: Unlike Example 1, the antifouling ion exchange membrane was replaced with a cation exchange membrane, while all other conditions remained the same as in Example 1. Specifically: Step 1: Cool the pentaerythritol condensate to 35°C and perform electrodialysis separation using an antifouling ion exchange membrane to obtain pentaerythritol desalted solution, electrodialysis concentrate, sodium formate, and low-boiling-point organic matter; Step 2: Evaporate and concentrate the pentaerythritol desalted solution to obtain pentaerythritol; In Step 1, the electrodialysis separation process conditions are: temperature 25°C, voltage 15V; In Step 2, the evaporation process conditions are: temperature 90°C, vacuum degree 0.10MPa, time 3h.

[0039] Experimental test: Separation performance test: A liquid chromatography analyzer was used to perform isocratic elution with 3% acetonitrile-water as the mobile phase to detect the purity and yield of pentaerythritol in order to characterize its throughput and separation performance. The flow rate was 0.7 mL / min and the column temperature was 40℃. Antifouling test: An electrodialysis fouling experiment was conducted. The membrane stack consisted of one anion exchange membrane and two antifouling ion exchange membranes. A 0.1M sodium sulfate solution was pumped to the electrode chamber of the membrane stack by a peristaltic pump. The feed solution for the desalination and concentration chambers was a 0.1M sodium chloride-SDS (sodium dodecyl sulfonate) mixed solution. The current density was 3 mA / cm². 2 The potential difference ΔE across the antifouling ion exchange membrane was monitored to characterize its antifouling performance.

[0040] Based on the data in the table above, the following conclusions can be drawn: Compared with Example 1, Comparative Example 1 only placed the ion exchange membrane in the composite dopamine impregnation solution for treatment without antifouling treatment. The potential difference across the antifouling ion exchange membrane was significantly increased, indicating that the antifouling effect was poor. Compared with Example 1, Comparative Example 2 only treated the ion exchange membrane with antifouling, and the purity and yield of pentaerythritol decreased. It can be seen that the flux of the obtained antifouling ion exchange membrane decreased, thereby reducing the separation performance. Compared with Example 1, Comparative Example 3 replaced the antifouling ion exchange membrane with a cation exchange membrane, resulting in a decrease in the purity and yield of pentaerythritol, while the potential difference across the cation exchange membrane was significantly increased. In summary, the antifouling ion exchange membrane prepared in this application can promote the comprehensive improvement of the separation performance and antifouling effect of the antifouling ion exchange membrane.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for purifying pentaerythritol based on an ion-exchange membrane, characterized in that: Includes the following steps: Step 1: Cool the pentaerythritol condensate to 25~35℃ and use an antifouling ion exchange membrane to perform electrodialysis separation to obtain pentaerythritol desalted solution, electrodialysis concentrate, sodium formate and low-boiling-point organic matter. Step 2: Evaporate and concentrate the pentaerythritol desalting solution to obtain pentaerythritol; The antifouling ion exchange membrane comprises, from bottom to top, an ion exchange membrane, a polydopamine intermediate layer, and an antifouling layer.

2. The pentaerythritol purification method based on an ion exchange membrane according to claim 1, characterized in that: The preparation process of the antifouling ion exchange membrane is as follows: S1: Take dopamine hydrochloride, modified metal-organic framework and Tris-HCl buffer, mix and stir to obtain composite dopamine impregnation solution, place ion exchange membrane in composite dopamine impregnation solution, sonicate to form polydopamine intermediate layer, dry to obtain pretreated ion exchange membrane. S2: The pretreated ion exchange membrane is placed in a hydrogen peroxide solution for oxidation treatment. After removal, it is placed in an antifouling treatment solution, and the pH is adjusted to 6.5~7.0 with NaOH. The reaction is carried out at a constant temperature to form an antifouling layer, thus obtaining an antifouling ion exchange membrane.

3. The pentaerythritol purification method based on an ion exchange membrane according to claim 2, characterized in that: The modified metal-organic framework is prepared by the following process: S1.1: Under a nitrogen atmosphere, 2,5-diaminoterephthalic acid, TiCl4, and anhydrous N,N-dimethylformamide were mixed, stirred and dissolved, then anhydrous methanol was added, stirred evenly, and heated to react. After the reaction was completed, the mixture was cooled, washed, and dried to obtain an aminated metal framework. S1.2: Mix 2,6-dimethylpyridine-4-carboxaldehyde and ethanol, stir to dissolve, then add the aminated metal framework and glacial acetic acid, stir and sonicate to disperse, heat to react, cool, wash and dry after the reaction is complete to obtain a pyridine-containing metal framework; S1.3: Mix pyridine-containing metal framework, methanol, and 7-bromo-1-heptanol, stir the reaction, and centrifuge to obtain the modified metal-organic framework.

4. The pentaerythritol purification method based on an ion exchange membrane according to claim 2, characterized in that: The antifouling treatment solution is prepared by mixing modified chitosan and deionized water; The preparation process of the modified chitosan is as follows: Chitosan and glacial acetic acid aqueous solution were mixed and stirred to dissolve. 2,4-Butanesulfonate lactone was added and heated to react. After the reaction was completed, the mixture was cooled, acetone was added to precipitate the precipitate, and the precipitate was dried to obtain modified chitosan.

5. The pentaerythritol purification method based on an ion exchange membrane according to claim 3, characterized in that: In S1.1, the ratio of 2,5-diaminoterephthalic acid, TiCl4, anhydrous N,N-dimethylformamide, and anhydrous methanol is 18g: (22~26)g: (70~80)mL: (1.6~1.8)mL.

6. The pentaerythritol purification method based on an ion exchange membrane according to claim 3, characterized in that: In S1.2, the ratio of 2,6-dimethylpyridine-4-carboxaldehyde, ethanol, aminated metal framework, and glacial acetic acid is 1g:(120~150)mL:(0.9~1.1)g:(0.03~0.05)g.

7. The pentaerythritol purification method based on an ion exchange membrane according to claim 4, characterized in that: The ratio of chitosan, glacial acetic acid aqueous solution, 2,4-butanesulfonate lactone, and acetone is (1~3) g : (80~100) mL : (1.0~1.5) g : (160~250) mL; The mass concentration of the glacial acetic acid aqueous solution is 2-3%.

8. The pentaerythritol purification method based on an ion exchange membrane according to claim 1, characterized in that: In step 1, the process conditions for electrodialysis separation are: temperature 20~25℃, voltage 10~15V.

9. The pentaerythritol purification method based on an ion exchange membrane according to claim 2, characterized in that: In S1, the ratio of dopamine hydrochloride, modified metal-organic framework, and Tris-HCl buffer is (2~3) g: (0.1~0.3) g: 100 mL.

10. The pentaerythritol purification method based on an ion exchange membrane according to claim 1, characterized in that: In step 2, the evaporation process conditions are: temperature 60~90℃, vacuum degree 0.05~0.10MPa, and time 1~3h.

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