A method for separating glucaric acid using a bimodal pore amphoteric post-crosslinked resin

Abstract

The application discloses a method for separating glucaric acid by using a bimodal pore amphoteric post-crosslinked resin. 2 The bimodal pore amphoteric post-crosslinked resin mainly comprises a precursor resin with a mesoporous structure, and the pore diameter of the resin is cut to form micropores and mesopores through a Friedel-Crafts alkylation reaction. 2 The specific surface area of the bimodal pore amphoteric post-crosslinked resin is 300-800 m 2 / g; the specific surface area of the micropores is 150-500 m / g; and the specific surface area of the mesopores is 100-300 m / g. The bimodal pore amphoteric post-crosslinked resin prepared by the application has a bimodal pore distribution pore structure, a large adsorption capacity for glucaric acid, high selectivity, and is easy to elute after adsorption by using hot water, and can be used as a new type of adsorption medium for separating glucaric acid from a fermentation broth.

Description

Technical Field

[0001] This invention relates to the field of resin preparation technology, and in particular to a method for separating gluconic acid using a bimodal amphoteric post-crosslinking resin. Background Technology

[0002] Gluconic acid is a platform compound that can complex metal ions and is biodegradable, finding wide applications in pharmaceuticals, chemicals, and materials science. In the chemical industry, gluconic acid can be used as a raw material to produce household detergents, preservatives, and concrete admixtures. In the materials industry, gluconic acid can be used as a polymer synthesis unit to prepare biodegradable polymers such as polyamides and hydroxylated nylons.

[0003] To meet environmental protection requirements and the needs of green chemistry, microbial fermentation has become one of the main preparation methods. Microbial fermentation primarily uses glucose as a raw material, utilizing the metabolic processes of microorganisms such as Escherichia coli and yeast to produce gluconic acid. It has a short production cycle, a mild reaction, and reduces the generation of toxic substances such as nitrogen oxides (NOx), thus lowering production costs and environmental protection expenses. However, the fermentation broth contains substances such as gluconic acid, glucose, inositol, and glucuronic acid, which affect downstream processing. Therefore, separating high-purity gluconic acid from the fermentation broth is crucial for large-scale preparation.

[0004] Common methods for separating and purifying gluconic acid include extraction and membrane separation. While these methods can effectively separate and purify gluconic acid, they also have drawbacks such as low product purity, low yield, and numerous steps involved. Adsorption is a low-energy-consumption, high-efficiency separation method that can be used for the separation and purification of organic acids.

[0005] The adsorption method for separating gluconic acid is mainly based on the difference in interaction forces between the adsorption medium and gluconic acid and other components, and it features high product purity, low energy consumption, and excellent separation effect. Activated carbon can be used to adsorb and separate gluconic acid, but its adsorption is non-specific and often faces regeneration difficulties. Compared with activated carbon, adsorption resin, as a porous material, has the characteristics of large adsorption capacity, high adsorption selectivity, and good reusability, making it one of the better methods for adsorbing and separating gluconic acid. There are reports on the use of anion exchange resins for the adsorption and separation of gluconic acid, but this technology requires the consumption of acid or alkali solutions for elution and regeneration, which is difficult to meet the purpose of separating gluconic acid.

[0006] Post-crosslinked resins, as one of the resins with excellent adsorption performance, possess characteristics such as high specific surface area, tunable pore structure, and ease of functionalization, and are considered an ideal medium for separating gluconic acid. However, the key issue is how to improve the adsorption and separation performance of gluconic acid. Traditional post-crosslinked resins have strong hydrophobicity and low functional group loading, resulting in low adsorption capacity and poor selectivity for gluconic acid in solution. Furthermore, the adsorption performance of post-crosslinked resins is also related to their pore structure. Typical post-crosslinked resins have numerous micropores with a single pore size distribution, which is unfavorable for the diffusion and mass transfer of gluconic acid molecules within the resin's internal channels. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for separating gluconic acid using a bimodal amphoteric post-crosslinking resin. The bimodal amphoteric post-crosslinking resin prepared by this invention has a bimodal pore structure, exhibiting high adsorption capacity and selectivity for gluconic acid. It is easily eluted with hot water after adsorption and can serve as a novel adsorption medium for separating gluconic acid from fermentation broth.

[0008] One object of the present invention is to provide a bimodal amphoteric post-crosslinking resin, wherein the bimodal amphoteric post-crosslinking resin is mainly composed of a precursor resin having a mesoporous structure, which undergoes a Friedel-Crafts alkylation reaction to split the internal pore size of the resin into micro-mesopores; the bimodal amphoteric post-crosslinking resin includes mesopores and micropores; the specific surface area of ​​the bimodal amphoteric post-crosslinking resin is 300~800 m². 2 / g; Furthermore, the surface area occupied by the micropores is 150~500 m². 2 / g; the mesopores account for 100~300 m² of the total surface area. 2 / g.

[0009] Furthermore, the pore volume of the bimodal amphoteric post-crosslinking resin is 0.2~1 cm³. 3 / g; the micropores occupy a pore volume of 0.03~0.3 cm³. 3 / g; the mesopores occupy a pore volume of 0.3~0.9 cm³. 3 / g.

[0010] Furthermore, the average pore size of the bimodal amphoteric post-crosslinked resin ranges from 2 to 9 nm.

[0011] Furthermore, the backbone of the bimodal amphoteric post-crosslinking resin is connected with acidic and basic groups; preferably, the acidic group is a carboxyl group; and the basic group is an amine group.

[0012] Another object of the present invention is to provide a method for preparing a bimodal amphoteric post-crosslinking resin, the preparation method comprising the following steps: (1) After mixing the oil phase mixture with the aqueous phase solution, the precursor resin is obtained by suspension polymerization; (2) The precursor resin from step (1) was subjected to chloromethylation under the catalysis of tin tetrachloride to obtain chloromethylated precursor resin; (3) The chloromethylated precursor resin was subjected to Friedel-Crafts alkylation reaction under ferric chloride catalysis to obtain the post-crosslinked resin; (4) The post-crosslinking resin from step (3) is subjected to an amination reaction to obtain a bimodal amphoteric post-crosslinking resin.

[0013] Further, in step (1), the oil phase mixture includes monomers, crosslinking agents, porogens, and initiators, and the mass ratio of monomers, crosslinking agents, porogens, and initiators is (1~3):(0.1~0.4):(0.5~3):(0.01~0.05); the mass ratio of the oil phase mixture to the aqueous phase solution is 1:3~6; the suspension polymerization is carried out at 70~80 ℃ for 14~20 h at a constant temperature; and the average pore size of the precursor resin is 40~100 nm.

[0014] Further, in step (2), the chloromethylation reaction is carried out at 5~20℃ for 13~18 h; the average pore size of the chloromethylated precursor resin is 40~100 nm.

[0015] Further, in step (3), the Friedel-Crafts alkylation reaction is carried out at 70~90℃ for 1~9 h, and the average pore size of the post-crosslinking resin is 0.2~15 nm; in step (4), the amination reagent includes at least one of methylamine, dimethylamine, diethylenetriamine, and ethylenediamine; the amination reaction is carried out at 70~90℃ for 10~15 h.

[0016] The preparation method of the above-mentioned bimodal porous amphoteric post-crosslinking resin includes the following steps: (1) After mixing the oil phase mixture with the aqueous phase solution, the mixture is subjected to suspension polymerization, washed with water, the pore-forming agent is extracted, and dried to obtain the precursor resin; (2) Add chloromethyl methyl ether to the precursor resin prepared in step (1), swell overnight, add tin tetrachloride in an ice-water bath, stir, and wash with hot water after the reaction is complete to obtain chloromethylated precursor resin. (3) Add 1,2-dichloroethane to the chloromethylated precursor resin obtained in step (2), swell overnight, then add ferric chloride, stir, and after the reaction is complete, wash with ethanol and hydrochloric acid solution alternately to obtain the post-crosslinked resin; (4) Add an amination agent to the post-crosslinking resin prepared in step (3), stir and heat. After the reaction is complete, wash with water until neutral to obtain a bimodal amphoteric post-crosslinking resin.

[0017] Further, in step (1), the oil phase mixture is composed of monomer, crosslinking agent, pore-forming agent and initiator; the mass ratio of monomer, crosslinking agent, pore-forming agent and initiator is (1~3):(0.1~0.4):(0.5~3):(0.01~0.05).

[0018] Further, the monomer includes an ethylene monomer containing an acidic group and styrene, wherein the ethylene monomer containing the acidic group includes one of acrylic acid, pentenoic acid, and butenoic acid, and the mass ratio of pentenoic acid to styrene is 1:(5~2); the crosslinking agent is divinylbenzene; Furthermore, the pore-forming agent is composed of toluene and n-heptane, with a mass ratio of toluene to n-heptane of (5~0.1):1; Furthermore, the initiator is one or more of azobisisobutyronitrile and benzoyl peroxide.

[0019] Further, in step (1), the aqueous solution is composed of a gelatin solution and a NaCl solution, with a mass ratio of gelatin solution to NaCl solution of (5~1):1; the mass concentration of gelatin in the gelatin solution is 1~3%, and the mass concentration of NaCl in the NaCl solution is 3~5%. Furthermore, the mass ratio of the oil phase mixture to the aqueous phase solution is 1:(3~6). Furthermore, the specific method of suspension polymerization is as follows: the oil phase mixture is added to the aqueous phase solution according to the mass ratio, and while stirring at 180~250 r / min, the temperature is raised to 70~80 ℃ and then the reaction is carried out at a constant temperature for 14~20 h.

[0020] Further, the water washing is performed with water at 70-80 °C for 0.5-1 h; the extraction of the pore-forming agent is carried out in a Soxhlet extractor, and the reagents used include one or more of methanol, acetone, ethanol, and petroleum ether, with a volume of 50-300 mL; the drying temperature is 50-60 °C, and the time is 0.5-2 h.

[0021] Further, in step (2), the volume-to-mass ratio of the chloromethyl methyl ether to the precursor resin is 6-12 mL:1 g; the volume-to-mass ratio of the tin tetrachloride to the precursor resin is 1-2 mL:1 g; the tin tetrachloride is anhydrous tin tetrachloride; the stirring speed is 50-100 r / min, the temperature is raised to 5-20℃, and the reaction time is 13-18 h; the hot water is 70-80℃, and the washing time is 0.5-1 h.

[0022] Further, in step (3), the volume-to-mass ratio of 1,2-dichloroethane to the chloromethylated precursor resin is 6-12 mL:1 g; the ferric chloride is anhydrous ferric chloride, and the mass ratio of ferric chloride to the chloromethylated precursor resin is 0.2-0.3:1; the stirring speed is 50-100 r / min, the temperature is raised to 70-90℃, and the reaction time is 1-9 h; the ethanol is anhydrous ethanol; the mass concentration of the hydrochloric acid solution is 1-5%, and the washing time is 0.5-1 h.

[0023] Further, in step (4), the amination agent is one of methylamine, dimethylamine, diethylenetriamine, and ethylenediamine, and the volume-to-mass ratio of the amination agent to the post-crosslinking resin is 2~3 mL:1 g; the stirring speed is 50~100 r / min, the temperature is raised to 70~90℃, and the reaction time is 10~15 h.

[0024] Another object of the present invention is to use bimodal pore amphoteric post-crosslinked resin for the separation of gluconic acid.

[0025] Another objective of this invention is to provide a method for separating gluconic acid using a bimodal amphoteric post-crosslinking resin. The method involves passing a pretreated gluconic acid fermentation broth through an adsorption column packed with bimodal amphoteric post-crosslinking resin, followed by pretreatment, water washing, adsorption, and hot water desorption to obtain a gluconic acid solution.

[0026] Furthermore, the pretreatment involves removing solid particles and macromolecular impurities from the gluconic acid fermentation broth using ultrafiltration to obtain a pretreated gluconic acid fermentation broth. Furthermore, the bimodal amphoteric post-crosslinking resin is packed into the adsorption column at a height-to-diameter ratio of (5~15):1; Furthermore, the flow rate of the water wash is 3~8 BV / h; Further, the adsorption and desorption process is as follows: the pretreated glucose diacid fermentation broth is passed into the adsorption column at a flow rate of 3~8 BV / h. After the resin is saturated, the adsorption column is eluted with hot water at a flow rate of 10~20 BV / h. The eluted solution is collected, which is a glucose diacid solution with high purity. The adsorption saturation is determined by high performance liquid chromatography (HPLC) to determine the chromatographic peaks and plot the time versus the concentration of the fermentation broth eluted from the adsorption column. When the concentration of the eluted fermentation broth reaches its maximum and remains constant, the adsorption is considered saturated.

[0027] The beneficial technical effects of this invention are as follows: The bimodal post-crosslinked resin of this invention exhibits a bimodal pore structure, which facilitates the diffusion and mass transfer of gluconic acid within the resin's internal pores, resulting in a faster adsorption rate and a larger adsorption capacity. Furthermore, the resin backbone contains amine and carboxyl groups, which can form hydrogen bonds and hindrance interactions with gluconic acid molecules, thereby enhancing the resin's adsorption capacity and selectivity for gluconic acid.

[0028] Furthermore, the bimodal amphoteric post-crosslinking resin prepared by this invention can adjust the polarity of the resin by changing the type of amination agent, and regulate the resin pore structure by changing the ratio of monomer, crosslinking agent or pore-forming agent, thereby achieving better adsorption and separation of gluconic acid.

[0029] Furthermore, the bimodal amphoteric post-crosslinking resin prepared by this invention can be used for the separation of gluconic acid, and has good adsorption performance for gluconic acid, while also having high selectivity. The gluconic acid adsorbed by the resin can be desorbed using hot water, which solves the problems of limited adsorption capacity and poor selectivity of resins containing single pore types and / or single acid or basic groups for gluconic acid, as well as the need to consume acid and alkali for desorption. Attached Figure Description

[0030] Figure 1 This is a scanning electron microscope image of the bimodal amphoteric post-crosslinked resin prepared in Example 1 of the present invention.

[0031] Figure 2 The infrared spectrum is shown for the bimodal amphoteric post-crosslinked resin prepared in Example 2 of this invention. Figure 3 The pore size distribution diagrams are for the bimodal amphoteric post-crosslinked resins prepared in Examples 3-4 of this invention. Figure 4 The adsorption and desorption curves are those of the bimodal amphoteric post-crosslinked resin prepared in Example 5 of this invention. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] This invention provides a bimodal amphoteric post-crosslinking resin, which is mainly composed of a precursor resin with a mesoporous structure, which undergoes a Friedel-Crafts alkylation reaction to split the internal pore size of the resin into micropores.

[0034] The preparation method of the bimodal pore amphoteric post-crosslinking resin of the present invention includes the following steps: (1) After mixing the oil phase mixture with the aqueous phase solution, the mixture is subjected to suspension polymerization, washed with water, the pore-forming agent is extracted, and dried to obtain the precursor resin; (2) Add chloromethyl methyl ether to the precursor resin prepared in step (1), swell overnight, add tin tetrachloride in an ice-water bath, stir, and wash with hot water after the reaction is complete to obtain chloromethylated precursor resin. (3) Add 1,2-dichloroethane to the chloromethylated precursor resin obtained in step (2), swell overnight, then add ferric chloride, stir, and after the reaction is complete, wash with ethanol and hydrochloric acid solution alternately to obtain the post-crosslinked resin; (4) Add an amination agent to the post-crosslinking resin prepared in step (3), stir and heat. After the reaction is complete, wash with water until neutral to obtain a bimodal amphoteric post-crosslinking resin.

[0035] In one embodiment of the present invention, in step (1), the oil phase mixture is composed of monomer, crosslinking agent, porogen and initiator; the mass ratio of monomer, crosslinking agent, porogen and initiator is 3:0.4:3:0.05, 1:0.1:0.5:0.01, 2.5:0.3:2.5:0.04, 1.5:0.2:0.7:0.02 or 2:0.25:2:0.03.

[0036] In one embodiment of the present invention, the monomer comprises an ethylene monomer containing an acidic group and styrene, wherein the ethylene monomer containing the acidic group is acrylic acid, pentenoic acid or butenoic acid, and the mass ratio of pentenoic acid to styrene is 1:5, 1:4, 1:3 or 1:2; and the crosslinking agent is divinylbenzene.

[0037] In one embodiment of the present invention, the pore-forming agent is composed of toluene and n-heptane, wherein the mass ratio of toluene to n-heptane is 0.1:1, 0.5:1, 5:1, 1:1, 2:1, 0.2:1 or 4:1.

[0038] In one embodiment of the present invention, the initiator is azobisisobutyronitrile or benzoyl peroxide.

[0039] In one embodiment of the present invention, in step (1), the aqueous phase solution is composed of a gelatin solution and a NaCl solution, wherein the mass ratio of the gelatin solution to the NaCl solution is 1:1, 2:1, 3:1, 4:1 or 5:1; the mass concentration of gelatin in the gelatin solution is 1%, 2% or 3%, and the mass concentration of NaCl in the NaCl solution is 3%, 4% or 5%.

[0040] In one embodiment of the present invention, the mass ratio of the oil phase mixture to the aqueous phase solution is 1:3, 1:4, 1:4.5, 1:5 or 1:6.

[0041] In one embodiment of the present invention, the specific method of suspension polymerization is as follows: the oil phase mixture is added to the aqueous phase solution according to the mass ratio, and while stirring at 180 r / min, 200 r / min, 210 r / min, 220 r / min or 250 r / min, the temperature is raised to 70℃, 75℃ or 80℃, and then the reaction is carried out at a constant temperature for 14h, 16h, 18h, 15h or 20h.

[0042] In one embodiment of the present invention, the water washing is performed with water at 70°C, 75°C, 78°C, or 80°C for 0.5 h, 0.8 h, or 1 h; the extraction of the pore-forming agent is carried out in a Soxhlet extractor, and the reagents used include methanol, acetone, ethanol, or petroleum ether, with volumes of 50 mL, 80 mL, 100 mL, 200 mL, or 300 mL; the drying temperature is 50°C, 52°C, 55°C, or 60°C, and the time is 0.5 h, 1 h, 1.5 h, or 2 h.

[0043] In one embodiment of the present invention, in step (2), the volume-to-mass ratio of the chloromethyl methyl ether to the precursor resin is 6 mL:1 g, 7 mL:1 g, 8 mL:1 g, 10 mL:1 g, or 12 mL:1 g; the volume-to-mass ratio of the tin tetrachloride to the precursor resin is 1 mL:1 g, 1.5 mL:1 g, or 2 mL:1 g; the tin tetrachloride is anhydrous tin tetrachloride; the stirring speed is 50 r / min, 60 r / min, 80 r / min, or 100 r / min, the temperature is raised to 5°C, 10°C, 15°C, 18°C, or 20°C, and the reaction time is 13 h, 15 h, 16 h, 17 h, or 18 h; the hot water is 70°C, 75°C, or 80°C, and the washing time is 0.5 h, 0.6 h, 0.8 h, or 1 h.

[0044] In one embodiment of the present invention, in step (3), the volume-to-mass ratio of 1,2-dichloroethane to the chloromethylated precursor resin is 6 mL:1 g, 8 mL:1 g, 10 mL:1 g, or 12 mL:1 g; the ferric chloride is anhydrous ferric chloride, and the mass ratio of ferric chloride to the chloromethylated precursor resin is 0.2:1, 0.25:1, or 0.3:1; the stirring speed is 50 r / min, 80 r / min, 90 r / min, or 100 r / min, the temperature is raised to 70°C, 80°C, or 90°C, and the reaction time is 1 h, 2 h, 3 h, 5 h, 8 h, or 9 h; the ethanol is anhydrous ethanol; the mass concentration of the hydrochloric acid solution is 1%, 2%, 3%, 4%, or 5%, and the washing time is 0.5 h, 0.8 h, or 1 h.

[0045] In one embodiment of the present invention, in step (4), the amination agent is methylamine, dimethylamine, diethylenetriamine or ethylenediamine, and the volume-to-mass ratio of the amination agent to the post-crosslinking resin is 3 mL:1 g, 2 mL:1 g or 2.5 mL:1 g; the stirring speed is 50 r / min, 80 r / min or 100 r / min, the temperature is raised to 70°C, 80°C or 90°C, and the reaction time is 10 h, 11 h, 12 h, 13 h, 14 h or 15 h.

[0046] Another object of the present invention is to use bimodal pore amphoteric post-crosslinked resin for the separation of gluconic acid.

[0047] The present invention will be further described below with reference to the embodiments.

[0048] Example 1 A bimodal amphoteric post-crosslinking resin is prepared by the following steps: (1) Preparation of precursor resin First, prepare the oil phase mixture and the aqueous phase solution.

[0049] The oil phase mixture is composed of monomer, crosslinking agent, porogen and initiator in a mass ratio of 3:0.4:3:0.05. The monomer is obtained by mixing acrylic acid and styrene in a mass ratio of 1:5. The crosslinking agent is divinylbenzene. The porogen is toluene and n-heptane in a mass ratio of 5:1. The initiator is benzoyl peroxide.

[0050] The aqueous solution consists of a gelatin solution and a NaCl solution. A 3% gelatin solution and a 5% NaCl solution are prepared separately. The prepared gelatin solution and NaCl solution are mixed at a mass ratio of 5:1 to obtain the aqueous solution.

[0051] The prepared oil phase mixture and aqueous phase solution were mixed at a mass ratio of 1:6. The mixture was stirred at 250 rpm while the temperature was raised to 80°C and kept at a constant temperature for 20 h to complete the suspension polymerization reaction. The mixture was then washed with water at 80°C for 1 h. The porogen was extracted using a Soxhlet extractor with acetone in a volume of 300 mL. Finally, the mixture was dried at 60°C for 2 h to obtain the precursor resin.

[0052] (2) Chloromethylation of precursor resin The precursor resin prepared in step (1) was placed in a three-necked round-bottom flask. 120 mL of chloromethyl methyl ether was added at a volume mass ratio of 12 mL:1 g to the precursor resin. The resin was allowed to swell overnight. 20 mL of anhydrous tin tetrachloride (the volume mass ratio of anhydrous tin tetrachloride to the precursor resin was 2 mL:1 g) was added in an ice-water bath. The mixture was mechanically stirred at 100 rpm and heated to 20 °C. The reaction was allowed to proceed for 18 h. After the reaction was completed, the resin was washed with hot water at 80 °C for 1 h to obtain the chloromethylated precursor resin.

[0053] (3) Preparation of post-crosslinking resin The chloromethylated precursor resin prepared in step (2) was placed in a three-necked round-bottom flask. 120 mL of 1,2-dichloroethane was added at a volume-to-mass ratio of 12 mL:1 g of 1,2-dichloroethane to the chloromethylated precursor resin. The mixture was allowed to swell overnight. Then, 3 g of anhydrous ferric chloride (the mass ratio of ferric chloride to the chloromethylated precursor resin was 0.3:1) was added. The mixture was mechanically stirred at 100 rpm and heated to 90 °C. The reaction was allowed to proceed for 9 h. After the reaction was completed, the mixture was washed alternately with anhydrous ethanol and 5% hydrochloric acid solution for 1 h to obtain the post-crosslinked resin.

[0054] (4) Preparation of bimodal amphoteric post-crosslinking resin The post-crosslinking resin prepared in step (3) was placed in a three-necked round-bottom flask. 30 mL of methylamine was added at a volume mass ratio of 3 mL: 1 g of amination agent to post-crosslinking resin. The mixture was mechanically stirred at 100 rpm and heated to 90 °C for 15 h. After the reaction was completed, the mixture was washed with water until neutral to obtain a bimodal amphoteric post-crosslinking resin.

[0055] Example 2 A bimodal amphoteric post-crosslinking resin is prepared by the following steps: (1) Preparation of precursor resin First, prepare the oil phase mixture and the aqueous phase solution.

[0056] The oil phase mixture is composed of monomer, crosslinking agent, porogen and initiator in a mass ratio of 1:0.1:0.5:0.01. The monomer is obtained by mixing pentenoic acid and styrene in a mass ratio of 1:2. The crosslinking agent is divinylbenzene. The porogen is toluene and n-heptane in a mass ratio of 0.2:1. The initiator is benzoyl peroxide.

[0057] The aqueous solution consists of a gelatin solution and a NaCl solution. A 1% gelatin solution and a 3% NaCl solution are prepared separately. The prepared gelatin solution and NaCl solution are mixed at a mass ratio of 1:1 to obtain the aqueous solution.

[0058] The prepared oil phase mixture and aqueous phase solution were mixed at a mass ratio of 1:3. The mixture was stirred at 180 rpm while the temperature was raised to 70°C and kept at a constant temperature for 14 h to complete the suspension polymerization reaction. The mixture was then washed with water at 70°C for 0.5 h. The porogen was extracted using a Soxhlet extractor with 50 mL of ethanol. Finally, the mixture was dried at 50°C for 0.5 h to obtain the precursor resin.

[0059] (2) Chloromethylation of precursor resin The precursor resin prepared in step (1) was placed in a three-necked round-bottom flask. 60 mL of chloromethyl methyl ether was added at a volume mass ratio of 6 mL:1 g to chloromethyl methyl ether. The mixture was allowed to swell overnight. 10 mL of anhydrous tin tetrachloride (the volume mass ratio of anhydrous tin tetrachloride to precursor resin was 1 mL:1 g) was added in an ice-water bath. The mixture was mechanically stirred at 50 rpm and heated to 5 °C. The reaction was allowed to proceed for 13 h. After the reaction was completed, the mixture was washed with hot water at 70 °C for 0.5 h to obtain the chloromethylated precursor resin.

[0060] (3) Preparation of post-crosslinking resin The chloromethylated precursor resin prepared in step (2) was placed in a three-necked round-bottom flask. 60 mL of 1,2-dichloroethane was added at a volume-to-mass ratio of 6 mL:1 g of 1,2-dichloroethane to the chloromethylated precursor resin. The mixture was allowed to swell overnight. Then, 2 g of anhydrous ferric chloride (the mass ratio of ferric chloride to the chloromethylated precursor resin was 0.2:1) was added. The mixture was mechanically stirred at 50 rpm and heated to 70 °C. The reaction was allowed to proceed for 1 h. After the reaction was completed, the mixture was washed alternately with anhydrous ethanol and 1% hydrochloric acid solution for 0.5 h to obtain the post-crosslinked resin.

[0061] (4) Preparation of bimodal amphoteric post-crosslinking resin The post-crosslinking resin prepared in step (3) was placed in a three-necked round-bottom flask. 20 mL of dimethylamine was added at a volume mass ratio of 2 mL:1 g of amination agent to post-crosslinking resin. The mixture was mechanically stirred at 50 rpm and heated to 70 °C for 10 h. After the reaction was completed, the mixture was washed with water until neutral to obtain a bimodal amphoteric post-crosslinking resin.

[0062] Example 3 A bimodal amphoteric post-crosslinking resin is prepared by the following steps: (1) Preparation of precursor resin First, prepare the oil phase mixture and the aqueous phase solution.

[0063] The oil phase mixture is a mixture of monomer, crosslinking agent, porogen and initiator in a mass ratio of 2.5:0.3:2.5:0.04. The monomer is obtained by mixing butenoic acid and styrene in a mass ratio of 1:4. The crosslinking agent is divinylbenzene. The porogen is a mixture of toluene and n-heptane in a mass ratio of 2:1. The initiator is azobisisobutyronitrile.

[0064] The aqueous solution consists of a gelatin solution and a NaCl solution. A gelatin solution with a mass concentration of 2.5% and a NaCl solution with a mass concentration of 4.5% are prepared separately. The prepared gelatin solution and NaCl solution are mixed at a mass ratio of 4:1 to obtain the aqueous solution.

[0065] The prepared oil phase mixture and aqueous phase solution were mixed at a mass ratio of 1:5. The mixture was stirred at 220 rpm while the temperature was raised to 87°C and kept at a constant temperature for 18 h to complete the suspension polymerization reaction. The mixture was then washed with water at 77°C for 0.8 h. The porogen was extracted using a Soxhlet extractor with methanol in a volume of 250 mL. Finally, the mixture was dried at 57°C for 1.5 h to obtain the precursor resin.

[0066] (2) Chloromethylation of precursor resin The precursor resin prepared in step (1) was placed in a three-necked round-bottom flask. 110 mL of chloromethyl methyl ether was added at a volume mass ratio of 11 mL:1 g to the precursor resin. The resin was allowed to swell overnight. 17 mL of anhydrous tin tetrachloride (the volume mass ratio of anhydrous tin tetrachloride to the precursor resin was 1.7 mL:1 g) was added in an ice-water bath. The mixture was mechanically stirred at 80 rpm and heated to 15 °C. The reaction was allowed to proceed for 16 h. After the reaction was completed, the resin was washed with hot water at 77 °C for 0.8 h to obtain the chloromethylated precursor resin.

[0067] (3) Preparation of post-crosslinking resin The chloromethylated precursor resin prepared in step (2) was placed in a three-necked round-bottom flask. 110 mL of 1,2-dichloroethane was added at a volume-to-mass ratio of 11 mL:1 g of 1,2-dichloroethane. The mixture was allowed to swell overnight. Then, 2.8 g of anhydrous ferric chloride (the mass ratio of ferric chloride to chloromethylated precursor resin was 0.28:1) was added. The mixture was mechanically stirred at 80 rpm and heated to 85 °C. The reaction was allowed to proceed for 7 h. After the reaction was completed, the mixture was washed alternately with anhydrous ethanol and 4% hydrochloric acid solution for 0.8 h to obtain the post-crosslinked resin.

[0068] (4) Preparation of bimodal amphoteric post-crosslinking resin The post-crosslinking resin prepared in step (3) was placed in a three-necked round-bottom flask. 27 mL of diethylenetriamine was added at a volume mass ratio of 2.7 mL:1 g of amination agent to post-crosslinking resin. The mixture was mechanically stirred at 80 rpm and heated to 85 °C for 14 h. After the reaction was completed, the mixture was washed with water until neutral to obtain a bimodal amphoteric post-crosslinking resin.

[0069] Example 4 A bimodal amphoteric post-crosslinking resin is prepared by the following steps: (1) Preparation of precursor resin First, prepare the oil phase mixture and the aqueous phase solution.

[0070] The oil phase mixture is composed of monomer, crosslinking agent, porogen and initiator in a mass ratio of 1.5:0.2:0.7:0.02. The monomer is obtained by mixing butenoic acid and styrene in a mass ratio of 1:3. The crosslinking agent is divinylbenzene. The porogen is toluene and n-heptane in a mass ratio of 0.5:1. The initiator is azobisisobutyronitrile.

[0071] The aqueous solution consists of a gelatin solution and a NaCl solution. A gelatin solution with a mass concentration of 1.5% and a NaCl solution with a mass concentration of 3.5% are prepared separately. The prepared gelatin solution and NaCl solution are mixed at a mass ratio of 2:1 to obtain the aqueous solution.

[0072] The prepared oil phase mixture and aqueous phase solution were mixed at a mass ratio of 1:4. The mixture was stirred at 200 rpm while the temperature was raised to 73°C and kept at a constant temperature for 15 h to complete the suspension polymerization reaction. The mixture was then washed with water at 73°C for 0.6 h. The porogen was extracted using a Soxhlet extractor with methanol in a volume of 100 mL. Finally, the mixture was dried at 53°C for 1 h to obtain the precursor resin.

[0073] (2) Chloromethylation of precursor resin The precursor resin prepared in step (1) was placed in a three-necked round-bottom flask. 70 mL of chloromethyl methyl ether was added at a volume mass ratio of 7 mL:1 g to the precursor resin. The resin was allowed to swell overnight. 13 mL of anhydrous tin tetrachloride (the volume mass ratio of anhydrous tin tetrachloride to the precursor resin was 1.3 mL:1 g) was added in an ice-water bath. The mixture was mechanically stirred at 60 rpm and heated to 10 °C. The reaction was allowed to proceed for 14 h. After the reaction was completed, the resin was washed with hot water at 73 °C for 0.6 h to obtain the chloromethylated precursor resin.

[0074] (3) Preparation of post-crosslinking resin The chloromethylated precursor resin prepared in step (2) was placed in a three-necked round-bottom flask. 70 mL of 1,2-dichloroethane was added at a volume-to-mass ratio of 7 mL:1 g of 1,2-dichloroethane to the chloromethylated precursor resin. The mixture was allowed to swell overnight. Then, 2.3 g of anhydrous ferric chloride (the mass ratio of ferric chloride to the chloromethylated precursor resin was 0.23:1) was added. The mixture was mechanically stirred at 60 rpm and heated to 75 °C. The reaction was allowed to proceed for 3 h. After the reaction was completed, the mixture was washed alternately with anhydrous ethanol and 2% hydrochloric acid solution for 0.6 h to obtain the post-crosslinked resin.

[0075] (4) Preparation of bimodal amphoteric post-crosslinking resin The post-crosslinking resin prepared in step (3) was placed in a three-necked round-bottom flask. 23 mL of ethylenediamine was added at a volume mass ratio of amination agent to post-crosslinking resin of 2.3 mL:1 g. The mixture was mechanically stirred at 60 rpm and heated to 75 °C for 12 h. After the reaction was completed, the mixture was washed with water until neutral to obtain a bimodal amphoteric post-crosslinking resin.

[0076] Figure 3 The pore size distribution of the bimodal amphoteric post-crosslinked resins prepared in Examples 3-4 is shown. The results show that the pore size of the resin is concentrated below 10 nm and between 10 and 30 nm, exhibiting a clear bimodal pore distribution.

[0077] Example 5 A bimodal amphoteric post-crosslinking resin is prepared by the following steps: (1) Preparation of precursor resin First, prepare the oil phase mixture and the aqueous phase solution.

[0078] The oil phase mixture is a mixture of monomer, crosslinking agent, porogen and initiator in a mass ratio of 2:0.25:2:0.03. The monomer is obtained by mixing acrylic acid and styrene in a mass ratio of 1:3.5. The crosslinking agent is divinylbenzene. The porogen is a mixture of toluene and n-heptane in a mass ratio of 1:1. The initiator is azobisisobutyronitrile.

[0079] The aqueous solution consists of a gelatin solution and a NaCl solution. A gelatin solution with a mass concentration of 2.2% and a NaCl solution with a mass concentration of 4% are prepared separately. The prepared gelatin solution and NaCl solution are mixed at a mass ratio of 3:1 to obtain the aqueous solution.

[0080] The prepared oil phase mixture and aqueous phase solution were mixed at a mass ratio of 1:4.5, and the mixture was stirred at 210 rpm while the temperature was raised to 75°C. The reaction was carried out at a constant temperature for 16 h to complete the suspension polymerization reaction. The mixture was then washed with water at 75°C for 0.7 h. The porogen was extracted using a Soxhlet extractor with petroleum ether in a volume of 150 mL. Finally, the mixture was dried at 55°C for 1.2 h to obtain the precursor resin.

[0081] (2) Chloromethylation of precursor resin The precursor resin prepared in step (1) was placed in a three-necked round-bottom flask. 100 mL of chloromethyl methyl ether was added at a volume mass ratio of 10 mL:1 g to the precursor resin. The resin was allowed to swell overnight. 15 mL of anhydrous tin tetrachloride (the volume mass ratio of anhydrous tin tetrachloride to the precursor resin was 1.5 mL:1 g) was added in an ice-water bath. The mixture was mechanically stirred at 75 rpm and heated to 13 °C. The reaction was allowed to proceed for 15 h. After the reaction was completed, the resin was washed with hot water at 75 °C for 0.7 h to obtain the chloromethylated precursor resin.

[0082] (3) Preparation of post-crosslinking resin The chloromethylated precursor resin prepared in step (2) was placed in a three-necked round-bottom flask. 80 mL of 1,2-dichloroethane was added at a volume-to-mass ratio of 8 mL:1 g of 1,2-dichloroethane to the chloromethylated precursor resin. The mixture was allowed to swell overnight. Then, 2.5 g of anhydrous ferric chloride (the mass ratio of ferric chloride to the chloromethylated precursor resin was 0.25:1) was added. The mixture was mechanically stirred at 75 rpm and heated to 80 °C. The reaction was allowed to proceed for 5 h. After the reaction was completed, the mixture was washed alternately with anhydrous ethanol and 3% hydrochloric acid solution for 0.7 h to obtain the post-crosslinked resin.

[0083] (4) Preparation of bimodal amphoteric post-crosslinking resin The post-crosslinking resin prepared in step (3) was placed in a three-necked round-bottom flask. 25 mL of dimethylamine was added at a volume mass ratio of 2.5 mL:1 g of amination agent to post-crosslinking resin. The mixture was mechanically stirred at 70 rpm and heated to 80 °C for 13 h. After the reaction was completed, the mixture was washed with water until neutral to obtain a bimodal amphoteric post-crosslinking resin.

[0084] Application Examples 1-5 Application Examples 1-5 respectively used the bimodal amphoteric post-crosslinking resins prepared in Examples 1-5 and performed adsorption separation of gluconic acid solutions using the following methods, the specific steps of which are as follows: (1) Use ultrafiltration to remove solid particles and macromolecular impurities from the fermentation broth to obtain pretreated glucose dicarboxylic acid fermentation broth; (2) The amphoteric post-crosslinking resins prepared in Examples 1-5 were respectively loaded into adsorption columns at a height-to-diameter ratio of 15:1, and the resin bed was washed with deionized water at a flow rate of 8 BV / h. (3) At 35°C, the pretreated glucose diacid fermentation broth from step (1) is injected into the adsorption column at a flow rate of 8 BV / h. After the resin is saturated, it is eluted with deionized water at 80°C at a flow rate of 20 BV / h. The eluted solution is collected, which is a glucose diacid solution with high purity.

[0085] Application Example 6-10 Application Examples 6-10 used the bimodal amphoteric post-crosslinking resins prepared in Examples 1-5 respectively and performed adsorption separation of gluconic acid solutions using the following methods, the specific steps of which are as follows: (1) Use ultrafiltration to remove solid particles and macromolecular impurities from the fermentation broth to obtain pretreated glucose dicarboxylic acid fermentation broth; (2) The amphoteric post-crosslinking resins prepared in Examples 1-5 were respectively loaded into the adsorption column at a height-to-diameter ratio of 5:1, and the resin bed was washed with deionized water at a flow rate of 3 BV / h. (3) At 35°C, the pretreated glucose diacid fermentation broth from step (1) is injected into the adsorption column at a flow rate of 3 BV / h. After the resin is saturated, it is eluted with deionized water at 85°C at a flow rate of 10 BV / h. The eluted solution is collected, which is a glucose diacid solution with high purity.

[0086] Comparative Example 1 An amine-modified crosslinked resin, the preparation method of which includes the following steps: (1) Preparation of white balls First, prepare the oil phase mixture and the aqueous phase solution.

[0087] The oil phase mixture is composed of monomer, crosslinking agent, porogen and initiator mixed in a mass ratio of 3:0.4:3:0.05. The monomer is styrene, the crosslinking agent is divinylbenzene, the porogen is toluene and n-heptane mixed in a mass ratio of 5:1, and the initiator is benzoyl peroxide.

[0088] The aqueous solution consists of a gelatin solution and a NaCl solution. A 3% gelatin solution and a 5% NaCl solution are prepared separately. The prepared gelatin solution and NaCl solution are mixed at a mass ratio of 5:1 to obtain the aqueous solution.

[0089] The prepared oil phase mixture and aqueous phase solution were mixed at a mass ratio of 1:6. The mixture was stirred at 250 rpm while the temperature was raised to 80°C and kept at a constant temperature for 20 h to complete the suspension polymerization reaction. The mixture was then washed with water at 80°C for 1 h. The porogen was extracted using a Soxhlet extractor with acetone in a volume of 300 mL. Finally, the mixture was dried at 60°C for 2 h to obtain white spheres.

[0090] (2) Preparation of Chlorine Spheres Place the white spheres prepared in step (1) into a three-necked round-bottom flask, add 120 mL of chloromethyl methyl ether at a volume mass ratio of 12 mL: 1 g, allow to swell overnight, add 20 mL of anhydrous tin tetrachloride (anhydrous tin tetrachloride at a volume mass ratio of 2 mL: 1 g) in an ice-water bath, mechanically stir at 100 rpm, heat to 20 °C, react for 18 h, and after the reaction is complete, wash with 80 °C hot water for 1 h to obtain chloro spheres.

[0091] (3) Preparation of post-crosslinking resin The chlorine beads prepared in step (2) were placed in a three-necked round-bottom flask. 120 mL of 1,2-dichloroethane was added at a volume-to-mass ratio of 12 mL:1 g of chlorine beads. The mixture was allowed to swell overnight. Then, 3 g of anhydrous ferric chloride (the mass ratio of ferric chloride to chlorine beads was 0.3:1) was added. The mixture was mechanically stirred at 100 rpm and heated to 90 °C. The reaction was allowed to proceed for 9 h. After the reaction was completed, the mixture was washed alternately with anhydrous ethanol and 5% hydrochloric acid solution for 1 h to obtain the post-crosslinked resin.

[0092] (4) Amination of post-crosslinking resin The post-crosslinking resin prepared in step (3) was placed in a three-necked round-bottom flask. 30 mL of methylamine was added at a volume mass ratio of 3 mL: 1 g of amination agent to post-crosslinking resin. The mixture was mechanically stirred at 100 rpm and heated to 90 °C for 15 h. After the reaction was completed, the mixture was washed with water until neutral to obtain the amine-modified post-crosslinking resin.

[0093] Comparative Example 2 An amine-modified crosslinked resin, the preparation method of which includes the following steps: (1) Preparation of white balls First, prepare the oil phase mixture and the aqueous phase solution.

[0094] The oil phase mixture is composed of monomer, crosslinking agent, porogen and initiator mixed in a mass ratio of 1:0.1:0.5:0.01. The monomer is styrene, the crosslinking agent is divinylbenzene, the porogen is toluene and n-heptane mixed in a mass ratio of 0.2:1, and the initiator is benzoyl peroxide.

[0095] The aqueous solution consists of a gelatin solution and a NaCl solution. A 1% gelatin solution and a 3% NaCl solution are prepared separately. The prepared gelatin solution and NaCl solution are mixed at a mass ratio of 1:1 to obtain the aqueous solution.

[0096] The prepared oil phase mixture and aqueous phase solution were mixed at a mass ratio of 1:3. The mixture was stirred at 180 rpm while the temperature was raised to 70°C and kept at a constant temperature for 14 h to complete the suspension polymerization reaction. The mixture was then washed with water at 70°C for 0.5 h. The porogen was extracted using a Soxhlet extractor with 50 mL of ethanol. Finally, the mixture was dried at 50°C for 0.5 h to obtain white spheres.

[0097] (2) Preparation of Chlorine Spheres Place the white spheres prepared in step (1) into a three-necked round-bottom flask, add 60 mL of chloromethyl methyl ether at a volume mass ratio of 6 mL: 1 g, allow to swell overnight, add 10 mL of anhydrous tin tetrachloride (anhydrous tin tetrachloride at a volume mass ratio of 1 mL: 1 g) in an ice-water bath, mechanically stir at 50 rpm, heat to 5 °C, and react for 13 h. After the reaction is complete, wash with 70 °C hot water for 0.5 h to obtain chloro spheres.

[0098] (3) Preparation of post-crosslinking resin The chlorine beads prepared in step (2) were placed in a three-necked round-bottom flask. 60 mL of 1,2-dichloroethane was added at a volume-to-mass ratio of 6 mL:1 g of 1,2-dichloroethane. The mixture was allowed to swell overnight. Then, 2 g of anhydrous ferric chloride (the mass ratio of ferric chloride to chlorine beads was 0.2:1) was added. The mixture was mechanically stirred at 50 rpm and heated to 70 °C. The reaction was allowed to proceed for 1 h. After the reaction was completed, the mixture was washed alternately with anhydrous ethanol and 1% hydrochloric acid solution for 0.5 h to obtain the post-crosslinked resin.

[0099] (4) Amination of post-crosslinking resin The post-crosslinking resin prepared in step (3) was placed in a three-necked round-bottom flask. 20 mL of dimethylamine was added at a volume mass ratio of 2 mL:1 g of amination agent to post-crosslinking resin. The mixture was mechanically stirred at 50 rpm and heated to 70 °C for 10 h. After the reaction was completed, the mixture was washed with water until neutral to obtain the amine-modified post-crosslinking resin.

[0100] Comparative Example 3 A macroporous amphoteric resin, the preparation method of which includes the following steps: (1) Preparation of precursor resin First, prepare the oil phase mixture and the aqueous phase solution.

[0101] The oil phase mixture is a mixture of monomer, crosslinking agent, porogen and initiator in a mass ratio of 2.5:0.3:2.5:0.04. The monomer is obtained by mixing butenoic acid and styrene in a mass ratio of 1:4. The crosslinking agent is divinylbenzene. The porogen is a mixture of toluene and n-heptane in a mass ratio of 2:1. The initiator is azobisisobutyronitrile.

[0102] The aqueous solution consists of a gelatin solution and a NaCl solution. A gelatin solution with a mass concentration of 2.5% and a NaCl solution with a mass concentration of 4.5% are prepared separately. The prepared gelatin solution and NaCl solution are mixed at a mass ratio of 4:1 to obtain the aqueous solution.

[0103] The prepared oil phase mixture and aqueous phase solution were mixed at a mass ratio of 1:5. The mixture was stirred at 220 rpm while the temperature was raised to 87°C and kept at a constant temperature for 18 h to complete the suspension polymerization reaction. The mixture was then washed with water at 77°C for 0.8 h. The porogen was extracted using a Soxhlet extractor with methanol in a volume of 250 mL. Finally, the mixture was dried at 57°C for 1.5 h to obtain the precursor resin.

[0104] (2) Chloromethylation of precursor resin The precursor resin prepared in step (1) was placed in a three-necked round-bottom flask. 110 mL of chloromethyl methyl ether was added at a volume mass ratio of 11 mL:1 g to the precursor resin. The resin was allowed to swell overnight. 17 mL of anhydrous tin tetrachloride (the volume mass ratio of anhydrous tin tetrachloride to the precursor resin was 1.7 mL:1 g) was added in an ice-water bath. The mixture was mechanically stirred at 80 rpm and heated to 15 °C. The reaction was allowed to proceed for 16 h. After the reaction was completed, the resin was washed with hot water at 77 °C for 0.8 h to obtain the chloromethylated precursor resin.

[0105] (3) Preparation of macroporous amphoteric resins The chloromethylated precursor resin prepared in step (2) was placed in a three-necked round-bottom flask. 27 mL of diethylenetriamine was added at a volume-to-mass ratio of amination agent to chloromethylated precursor resin of 2.7 mL:1 g. The mixture was mechanically stirred at 80 rpm and heated to 85 °C for 14 h. After the reaction was completed, the mixture was washed with water until neutral to obtain a macroporous amphoteric resin.

[0106] Comparative Example 4 A macroporous amphoteric resin, the preparation method of which includes the following steps: (1) Preparation of precursor resin: First, prepare the oil phase mixture and the aqueous phase solution.

[0107] The oil phase mixture is composed of monomer, crosslinking agent, porogen and initiator in a mass ratio of 1.5:0.2:0.7:0.02. The monomer is obtained by mixing butenoic acid and styrene in a mass ratio of 1:3. The crosslinking agent is divinylbenzene. The porogen is toluene and n-heptane in a mass ratio of 0.5:1. The initiator is azobisisobutyronitrile.

[0108] The aqueous solution consists of a gelatin solution and a NaCl solution. A gelatin solution with a mass concentration of 1.5% and a NaCl solution with a mass concentration of 3.5% are prepared separately. The prepared gelatin solution and NaCl solution are mixed at a mass ratio of 2:1 to obtain the aqueous solution.

[0109] The prepared oil phase mixture and aqueous phase solution were mixed at a mass ratio of 1:4. The mixture was stirred at 200 rpm while the temperature was raised to 73°C and kept at a constant temperature for 15 h to complete the suspension polymerization reaction. The mixture was then washed with water at 73°C for 0.6 h. The porogen was extracted using a Soxhlet extractor with methanol in a volume of 100 mL. Finally, the mixture was dried at 53°C for 1 h to obtain the precursor resin.

[0110] (2) Chloromethylation of precursor resin The precursor resin prepared in step (1) was placed in a three-necked round-bottom flask. 70 mL of chloromethyl methyl ether was added at a volume mass ratio of 7 mL:1 g to the precursor resin. The resin was allowed to swell overnight. 13 mL of anhydrous tin tetrachloride (the volume mass ratio of anhydrous tin tetrachloride to the precursor resin was 1.3 mL:1 g) was added in an ice-water bath. The mixture was mechanically stirred at 60 rpm and heated to 10 °C. The reaction was allowed to proceed for 14 h. After the reaction was completed, the resin was washed with hot water at 73 °C for 0.6 h to obtain the chloromethylated precursor resin.

[0111] (3) Preparation of macroporous amphoteric resins The chloromethylated precursor resin prepared in step (2) was placed in a three-necked round-bottom flask. 23 mL of ethylenediamine was added at a volume-to-mass ratio of amination agent to chloromethylated precursor resin of 2.3 mL: 1 g. The mixture was mechanically stirred at 60 rpm and heated to 75 °C for 12 h. After the reaction was completed, the mixture was washed with water until neutral to obtain a macroporous amphoteric resin.

[0112] Comparative Example 5 A carboxyl-modified crosslinked resin, the preparation method of which includes the following steps: (1) Preparation of precursor resin First, prepare the oil phase mixture and the aqueous phase solution.

[0113] The oil phase mixture is a mixture of monomer, crosslinking agent, porogen and initiator in a mass ratio of 2:0.25:2:0.03. The monomer is obtained by mixing acrylic acid and styrene in a mass ratio of 1:3.5. The crosslinking agent is divinylbenzene. The porogen is a mixture of toluene and n-heptane in a mass ratio of 1:1. The initiator is azobisisobutyronitrile.

[0114] The aqueous solution consists of a gelatin solution and a NaCl solution. A gelatin solution with a mass concentration of 2.2% and a NaCl solution with a mass concentration of 4% are prepared separately. The prepared gelatin solution and NaCl solution are mixed at a mass ratio of 3:1 to obtain the aqueous solution.

[0115] The prepared oil phase mixture and aqueous phase solution were mixed at a mass ratio of 1:4.5, and the mixture was stirred at 210 rpm while the temperature was raised to 75°C. The reaction was carried out at a constant temperature for 16 h to complete the suspension polymerization reaction. The mixture was then washed with water at 75°C for 0.7 h. The porogen was extracted using a Soxhlet extractor with petroleum ether in a volume of 150 mL. Finally, the mixture was dried at 55°C for 1.2 h to obtain the precursor resin.

[0116] (2) Chloromethylation of precursor resin The precursor resin prepared in step (1) was placed in a three-necked round-bottom flask. 100 mL of chloromethyl methyl ether was added at a volume mass ratio of 10 mL:1 g to the precursor resin. The resin was allowed to swell overnight. 15 mL of anhydrous tin tetrachloride (the volume mass ratio of anhydrous tin tetrachloride to the precursor resin was 1.5 mL:1 g) was added in an ice-water bath. The mixture was mechanically stirred at 75 rpm and heated to 13 °C. The reaction was allowed to proceed for 15 h. After the reaction was completed, the resin was washed with hot water at 75 °C for 0.7 h to obtain the chloromethylated precursor resin. (3) Preparation of post-crosslinking resin The chloromethylated precursor resin prepared in step (2) was placed in a three-necked round-bottom flask. 80 mL of 1,2-dichloroethane was added at a volume-to-mass ratio of 8 mL:1 g of 1,2-dichloroethane to the chloromethylated precursor resin. The mixture was allowed to swell overnight. Then, 2.5 g of anhydrous ferric chloride (the mass ratio of ferric chloride to the chloromethylated precursor resin was 0.25:1) was added. The mixture was mechanically stirred at 75 rpm and heated to 80 °C. The reaction was allowed to proceed for 5 h. After the reaction was completed, the mixture was washed alternately with anhydrous ethanol and 3% hydrochloric acid solution for 0.7 h to obtain the post-crosslinked resin.

[0117] Comparative Example 6 Comparative Example 6 uses commercially available D315 resin.

[0118] Compare and contrast examples 1-5 Comparative Application Examples 1-5: The resins prepared in Comparative Examples 1-5 were used to perform adsorption and separation of gluconic acid solutions using the following methods, with the specific steps as follows: Fixed-bed resin column separation.

[0119] (1) Use ultrafiltration to remove solid particles and macromolecular impurities from the fermentation broth to obtain pretreated glucose dicarboxylic acid fermentation broth; (2) The resins prepared in Comparative Examples 1 to 5 were loaded into adsorption columns at a height-to-diameter ratio of 15:1, and the resin bed was washed with deionized water at a flow rate of 8 BV / h. (3) At 35°C, the pretreated glucose diacid fermentation broth from step (2) is injected into the adsorption column at a flow rate of 8 BV / h. After the resin is saturated, it is eluted with deionized water at 80°C at a flow rate of 20 BV / h for 8 h. The eluted solution is collected, which is a glucose diacid solution with high purity.

[0120] Compare and contrast with example 6-10 Comparative Application Examples 6-10 used the resins prepared in Comparative Examples 1-5 to perform adsorption and separation of gluconic acid solutions using the following methods, with specific steps as follows: (1) Use ultrafiltration to remove solid particles and macromolecular impurities from the fermentation broth to obtain pretreated glucose dicarboxylic acid fermentation broth; (2) The resins prepared in Comparative Examples 1 to 5 were respectively loaded into adsorption columns at a height-to-diameter ratio of 5:1, and the resin bed was washed with deionized water at a flow rate of 3 BV / h. (3) At 35°C, the pretreated glucose diacid fermentation broth from step (2) is injected into the adsorption column at a flow rate of 3 BV / h. After the resin is saturated, it is eluted with deionized water at 85°C at a flow rate of 10 BV / h for 3 h. The eluted solution is collected, which is a glucose diacid solution with high purity.

[0121] Comparative Application Example 11 Commercially available D315 resin from Comparative Example 6 was packed into an adsorption column at a height-to-diameter ratio of 15:1. Solid particles and macromolecular impurities in the gluconic acid fermentation broth were removed by ultrafiltration to obtain a pretreated gluconic acid fermentation broth (concentration of 7 g / L). The pretreated gluconic acid fermentation broth was injected into the adsorption column at a flow rate of 8 BV / h at 35°C. After the resin was saturated (the method for detecting adsorption saturation was the same as in Example 1), the column was eluted with deionized water at 80°C at a flow rate of 16 BV / h for 3 h, and the eluted gluconic acid solution was collected.

[0122] Test case The adsorption and desorption properties of the amphoteric post-crosslinking resins prepared in Examples 1-5 of this invention, the resins prepared in Comparative Examples 1-5, and the commercially available resin purchased in Comparative Example 6 were tested, and the test results are shown in Table 1.

[0123] Table 1. Performance comparison of resins prepared in the examples and comparative examples.

[0124] As shown in Table 1, the bimodal amphoteric post-crosslinking resins prepared in Examples 1-5 of the present invention have better adsorption performance for gluconic acid than the amino-modified post-crosslinking resins prepared in Comparative Examples 1-2, the macroporous amphoteric resins prepared in Comparative Examples 3-4, the carboxyl-modified post-crosslinking resins prepared in Comparative Example 5, and the commercially available resin in Comparative Example 6.

[0125] Figure 1 The image shows a SEM image of the bimodal amphoteric post-crosslinked resin prepared in Example 1. The results show that the resin surface is relatively smooth and the particle diameter is between 0.5 and 1 mm.

[0126] Figure 2 The image shows the infrared spectrum of the bimodal porous amphoteric post-crosslinked resin prepared in Example 2. In the image, 3434 cm⁻¹... -1 The absorption peak is that of an amine group, indicating that the bimodal porous amphoteric post-crosslinked resin prepared in the example contains amine groups; 2924 cm⁻¹ -1 The absorption peak at 1601 cm⁻¹ is due to the stretching vibration of the carboxyl group, indicating that the resin contains carboxyl groups. -1 The peak at this location is the skeletal absorption peak of the benzene ring, indicating that the resin contains a benzene ring.

[0127] Figure 3 The figure shows the pore size distribution of the bimodal amphoteric post-crosslinked resins prepared in Examples 3 and 4 of this invention. As can be seen from the figure, the resin pore size is mainly concentrated below 10 nm and between 15 and 30 nm, showing a clear bimodal pore distribution.

[0128] Figure 4 The figure shows the adsorption and desorption curves of the bimodal amphoteric post-crosslinked resin prepared in Example 5 of this invention. c v The concentration of the effluent. c 0 represents the initial feed concentration. As shown in the figure, hot water can be used to desorb the gluconic acid adsorbed by the resin.

[0129] From the Figure 1-4 Analysis shows that the embodiments of the present invention prepared a bimodal amphoteric post-crosslinking resin by adjusting the porogen ratio and the type of amination agent. The prepared resin can be used to adsorb gluconic acid, and hot water can be used to desorb the saturated resin, avoiding the use of acids, bases, and organic reagents. The resin prepared in Example 5 has a high adsorption capacity for gluconic acid and a good desorption effect because dimethylamine is basic, and the resin adsorbs gluconic acid through hydrogen bonding and acid-base interactions. In addition, according to the size matching mechanism, the average pore size of the resin is well matched with the molecular size of gluconic acid.

[0130] This invention, through analysis of the gluconic acid molecule structure, discovered that the molecule contains carboxyl groups at both ends. Therefore, by loading weakly basic amine groups onto the post-crosslinked resin backbone, the adsorption and separation of GA from the product solution can be achieved. However, according to relevant experimental studies, the desorption efficiency of the amine-modified post-crosslinked resin with adsorption saturation using hot water is relatively low (see Comparative Examples 1-2).

[0131] In addition, in order to improve the desorption efficiency of the post-crosslinked resin using hot water and at the same time weaken the interaction between the resin-supported groups and gluconic acid molecules, this invention overcomes the difficulty of directly introducing carboxyl and amine groups into the post-crosslinked resin skeleton. Instead, it introduces carboxyl-containing monomers, first introduces carboxyl groups into the resin skeleton through suspension polymerization, and then introduces amine groups through amination reaction after the post-crosslinking reaction, thus successfully introducing amine and carboxyl groups into the resin skeleton at the same time.

[0132] Furthermore, conventional bimodal pore resins typically have a pore size distribution concentrated in micropores and mesopores. While mesopores facilitate the entry of gluconic acid molecules into the resin interior, they also easily allow them to flow out, thus hindering the adsorption of gluconic acid molecules by the micropores. This invention utilizes a small-molecule porogen to prepare a bimodal pore post-crosslinked resin with a pore size concentrated in both micropores and mesopores. Compared to macropores, mesopores have smaller pore sizes, reducing the outflow of gluconic acid molecules from the resin interior and thereby improving the resin's adsorption efficiency.

[0133] The bimodal amphoteric post-crosslinking resin of the present invention has abundant mesoporous and microporous structures. The mesoporous structure is conducive to the diffusion, mass transfer and adsorption of gluconic acid in the internal pores of the resin; the microporous structure can improve the adsorption performance of the resin for gluconic acid; the carboxyl and amino groups on the resin skeleton can form hydrogen bonds and retardation effects with gluconic acid molecules, which can further improve the adsorption selectivity of the resin.

[0134] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that are directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A method for separating gluconic acid using a bimodal amphoteric post-crosslinking resin, characterized in that, The method is as follows: the pretreated glucose diacid fermentation broth is passed through an adsorption column packed with bimodal amphoteric post-crosslinking resin, and then pretreated, washed with water, adsorbed, and eluted with hot water to obtain a glucose diacid solution. The bimodal amphoteric post-crosslinking resin comprises mesopores and micropores; the specific surface area of ​​the bimodal amphoteric post-crosslinking resin is 300~800 m². 2 / g; The surface area occupied by the micropores is 150~500 m². 2 / g; the mesopores account for 100~300 m² of the total surface area. 2 / g; The pore volume of the bimodal amphoteric post-crosslinking resin is 0.2~1 cm³. 3 / g; the micropores occupy a pore volume of 0.03~0.3cm³. 3 / g; the mesopores occupy a pore volume of 0.3~0.9 cm³. 3 / g; The average pore size range of the bimodal amphoteric post-crosslinking resin is 2~9 nm. The backbone of the bimodal amphoteric post-crosslinking resin is connected with acidic and basic groups. The acidic group is a carboxyl group; the basic group is an amino group. The preparation method of the bimodal porous amphoteric post-crosslinking resin is as follows: (1) After mixing the oil phase mixture with the aqueous phase solution, the precursor resin is obtained by suspension polymerization; (2) The precursor resin from step (1) was subjected to chloromethylation under the catalysis of tin tetrachloride to obtain chloromethylated precursor resin; (3) The chloromethylated precursor resin was subjected to Friedel-Crafts alkylation reaction under ferric chloride catalysis to obtain the post-crosslinked resin; (4) The post-crosslinking resin from step (3) is subjected to an amination reaction to obtain a bimodal amphoteric post-crosslinking resin; In step (1), the mass ratio of the oil phase mixture to the aqueous phase solution is 1:(3~6); the oil phase mixture includes monomers, crosslinking agents, pore-forming agents, and initiators, and the mass ratio of the monomers, crosslinking agents, pore-forming agents, and initiators is (1~3):(0.1~0.4):(0.5~3):(0.01~0.05). The monomers include ethylene monomers containing acidic groups and styrene. The ethylene monomers containing acidic groups include one of acrylic acid, pentenoic acid, and butenoic acid. The mass ratio of the ethylene monomers containing acidic groups to styrene is 1:(5~2).

2. The method according to claim 1, characterized in that, In step (1), the suspension polymerization is carried out at 70~80 ℃ for 14~20 h at a constant temperature; the average pore size of the precursor resin is 40~100 nm.

3. The method according to claim 1, characterized in that, In step (2), the chloromethylation reaction is carried out at 5~20℃ for 13~18 h; the average pore size of the chloromethylation precursor resin is 40~100 nm.

4. The method according to claim 1, characterized in that, In step (3), the Friedel-Crafts alkylation reaction is carried out at 70-90°C for 1-9 h, and the average pore size of the post-crosslinking resin is 0.2-15 nm; in step (4), the amination reagent includes at least one of methylamine, dimethylamine, diethylenetriamine, and ethylenediamine; the amination reaction is carried out at 70-90°C for 10-15 h.

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