A kind of purification method of sodium citrate

Abstract

The invention discloses a method for purifying sodium citrate, which comprises the following steps: first, fermenting corn flour and Aspergillus niger to produce citric acid fermentation broth; then, separating citric acid from the fermentation broth by countercurrent extraction with a mixed extractant; then, reacting with a sodium hydroxide aqueous solution to generate sodium citrate, and obtaining a sodium citrate solution by oil-water separation, and then further improving the purity by using an adsorption material and anion exchange resin. Finally, a high-purity sodium citrate product is obtained by crystallization, centrifugation and drying steps. Compared with the prior art, the method has the advantages of improving the purity and yield of sodium citrate, while reducing production costs and environmental impacts.

Description

Technical Field

[0001] The invention relates to the technical field of sodium citrate purification, and in particular to a method for purifying sodium citrate. Background Art

[0002] As an important organic acid salt, sodium citrate is widely used in food, medicine, chemical and other industries. Traditional sodium citrate production methods have some limitations, for example: traditional methods usually rely on starchy raw materials and require a large amount of agricultural resources and land. In the process of extracting and purifying citric acid, a large amount of wastewater and waste residue will be generated, which will burden the environment. In traditional processes, the extraction and purification steps of citric acid have high energy consumption, which is not conducive to sustainable development.

[0003] In the prior art, the purification of sodium citrate usually involves extracting citric acid from the fermentation broth and then generating sodium citrate through a neutralization reaction. Citric acid is purified through a series of steps such as decolorization, ion exchange, concentration and crystallization. However, these methods have several defects: first, they have high quality requirements for the raw material citric acid and require complex pretreatment steps; second, a large amount of carbon dioxide and calcium sulfate waste residue are produced in the process, which not only burdens the environment, but also increases the cost of waste treatment; third, the yield of citric acid in the extraction and purification process of the traditional method is not high, resulting in low raw material utilization; finally, the process is cumbersome and costly, and in some cases, the impurity content in the sodium citrate product is difficult to reduce to the ideal level, affecting the product quality. Therefore, it is of great industrial value and practical significance to develop an efficient, environmentally friendly and economical method for purifying sodium citrate.

[0004] Chinese invention patent CN105315149B discloses a method for preparing sodium citrate, the method comprising: (1) fully contacting citric acid fermentation supernatant with an organic composite extraction phase, so that the citric acid in the citric acid fermentation supernatant is extracted into the organic composite extraction phase to obtain an oil phase and an aqueous phase; (2) fully contacting the oil phase obtained in step (1) with a sodium hydroxide solution, so that the citric acid in the oil phase is extracted into the sodium hydroxide solution and reacts with sodium hydroxide to generate sodium citrate; wherein the organic composite extraction phase contains an extractant, a phase regulator and a solvent, and the extractant is a tertiary amine compound represented by (CnH2n+1)3N, wherein n is 10-12. The method of the invention is used to prepare sodium citrate, which is environmentally friendly, low in cost, high in citric acid yield, and low in the carbon multiple of sodium citrate. However, the method of preparing sodium citrate in the invention still has the problem of low sodium citrate extraction rate and purity. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention aims to provide an improved method for purifying sodium citrate, which can not only improve the purity and yield of the product, but also has the characteristics of being environmentally friendly, easy to operate, and reducing production costs.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] A method for purifying sodium citrate is as follows:

[0008] Step 1, using corn flour as a raw material and Aspergillus niger as a strain for fermentation to obtain citric acid fermentation liquid, and taking the supernatant; extracting the supernatant at 30-50° C. using a mixed extractant by countercurrent extraction to transfer citric acid from the supernatant to an organic phase to form an oil phase and an aqueous phase;

[0009] Step 2, countercurrent extraction of the oil phase with a sodium hydroxide aqueous solution at 30-50° C. to react citric acid with sodium hydroxide to generate sodium citrate; oil-water separation, removal of the residual organic phase, to obtain a sodium citrate solution;

[0010] Step 3: further purify the sodium citrate solution using an adsorption material to remove metal ion impurities in the solution; use an anion exchange resin to remove anion impurities in the solution; concentrate and crystallize the purified sodium citrate solution, perform solid-liquid separation, collect sodium citrate crystals, and dry to obtain sodium citrate.

[0011] The mass ratio of the corn flour to Aspergillus niger is 80-120:1.

[0012] The mixed extractant is composed of trioctylamine, n-heptanol and n-hexane in a volume ratio of 0.8-1.2:0.4-0.6:2-4.

[0013] The volume ratio of the supernatant to the mixed extractant is 1:1-3.

[0014] The volume ratio of the oil phase to the sodium hydroxide aqueous solution is 0.8-1.2:0.2-0.4, and the concentration of the sodium hydroxide aqueous solution is 0.5-2 mol / L.

[0015] The amount of the adsorption material is 1-8% of the mass of the sodium citrate solution.

[0016] The amount of the anion exchange resin used is 0.5-5% of the mass of the solution.

[0017] The preparation method of the adsorbent material is as follows, in parts by weight:

[0018] S1, adding 4 to 6 parts of diatomaceous earth to 25 to 35 parts of 0.05 to 0.2 g / mL polylysine aqueous solution, adjusting the pH value to 9 to 11, and adding 30 to 50 parts of n-hexane to the polylysine aqueous solution under stirring to obtain a pretreated product;

[0019] S2, adding 7 to 9 parts of pentaerythritol glycidyl ether to the pre-treated product, continuing stirring for 1 to 5 minutes, standing to solidify, and forming a stable porous structure; performing Soxhlet extraction with anhydrous ethanol to remove unreacted raw materials and solvent, and vacuum drying to obtain a post-treated product;

[0020] S3, adding the post-treated product to 25-35 parts of 0.4-0.6 mol / L 5-chloromaleic acid aqueous solution, adjusting the pH value to 7.5-8.5 with 0.5-2 mol / L sodium hydroxide aqueous solution, heating for reaction, removing reaction by-products by centrifugation at 10000-15000 rpm and washing with water, to obtain an adsorbent material.

[0021] The static curing parameters are static curing at 0 to 30° C. for 10 to 30 hours.

[0022] The heating reaction condition is heating the reaction at 50-70° C. for 40-50 hours.

[0023] In the sodium citrate purification method of the present invention, the functions of each substance are as follows:

[0024] Corn flour is used as a raw material for fermentation and provides the carbon source required for citric acid production.

[0025] Aspergillus niger is used as a microbial strain in the fermentation process to convert the sugar in the corn flour into citric acid.

[0026] A mixed extractant (trioctylamine, n-heptanol and n-hexane) is used to extract citric acid from citric acid fermentation broth, and the extraction efficiency of citric acid is improved by countercurrent extraction.

[0027] The sodium hydroxide aqueous solution reacts with the extracted citric acid to generate sodium citrate.

[0028] The adsorption material is used to remove metal ion impurities in the sodium citrate solution and improve the purity of the product.

[0029] Diatomaceous earth is a porous natural material with a high specific surface area and unique pore structure, which can provide a stable support structure for adsorption materials.

[0030] Pentaerythritol glycidyl ether, as a cross-linking agent, reacts with the pretreated material to form a porous structure, thereby enhancing the stability and adsorption capacity of the adsorption material.

[0031] Anhydrous ethanol is used for Soxhlet extraction to remove unreacted raw materials and solvents during the preparation of adsorption materials.

[0032] 5-Chloromaleacetic acid reacts with amino groups in the adsorbent material during the post-treatment step of the adsorbent material, imparting better adsorption properties.

[0033] The sodium hydroxide aqueous solution is used to adjust the pH value during the preparation of the adsorption material to ensure the smooth progress of the reaction.

[0034] Anion exchange resin is used to remove anionic impurities such as sulfate and oxalate from the sodium citrate solution to further improve the purity.

[0035] The entire purification process involves multiple steps, and each substance plays a key role in its specific link, which together ensures the high purity and high yield of sodium citrate.

[0036] Compared with the prior art, it has the following beneficial effects:

[0037] 1) The present invention can effectively remove impurities in citric acid fermentation broth, improve the purity and yield of sodium citrate, and reduce the loss of raw materials and products by using specific adsorption materials, multi-stage countercurrent extraction technology, optimized process flow and condition control.

[0038] 2) The present invention adopts low-cost raw materials and simplified process steps, which reduces production costs and makes the production of sodium citrate more economical and efficient.

[0039] 3) The present invention adopts a specific adsorption material preparation method to obtain an adsorption material with better adsorption performance, which can more effectively remove metal ion impurities in the solution, realize the efficient, environmentally friendly and low-cost production of the sodium citrate purification process, and has significant industrial application value and market potential. DETAILED DESCRIPTION

[0040] Main sources of substances:

[0041] Corn flour: Hebei Tengying Technology Co., Ltd., item number: TY-0668.

[0042] Aspergillus niger: CGMCC: 3.15663, scientific name: Aspergillus niger.

[0043] Anion exchange resin: Hebei Yunxiang Chemical Co., Ltd., product number: 201.

[0044] Diatomaceous earth: Lingshou County Zhan Teng Mineral Products Processing Plant, item number: GZT-I7U6.

[0045] Poly-L-lysine: Guangzhou Ruichuang Biotechnology Co., Ltd., catalog number: 01.

[0046] 2-Chloroacrylic acid: CAS number: 598-79-8.

[0047] Pentaerythritol glycidyl ether: CAS number: 3126-63-4.

[0048] 5-Chloromaleacetic acid: CAS number: 114435-26-6.

[0049] 2-Chloro-3-methylbut-2-enoic acid: CAS number: 15052-93-4.

[0050] Chloroacetic acid: Merck, CAS No.: 79-11-8.

[0051] Glyceryl propoxy triglycidyl ether: CAS number: 37237-76-6.

[0052] Polyethylene glycol diglycidyl ether: Jinan Yunuo Chemical Co., Ltd., model: YN.

[0053] The design idea of ​​the present invention is to develop an efficient, environmentally friendly and cost-effective method for purifying sodium citrate, and ensure the high purity and high yield of the product through carefully designed steps. First, corn flour and Aspergillus niger are selected for fermentation to obtain citric acid fermentation broth, and then the citric acid is effectively separated and enriched by a specific mixed extractant through countercurrent extraction technology. Secondly, sodium hydroxide solution is used to react with citric acid in the oil phase to generate sodium citrate, and organic impurities are removed by oil-water separation technology. Then, a new adsorption material is innovatively prepared, which forms a porous structure under specific conditions by polylysine and pentaerythritol glycidyl ether, and then introduces functional groups through the chemical reaction of 5-chloromaleic acid to enhance its adsorption performance for removing metal ions in sodium citrate solution. Finally, high-purity sodium citrate crystals are obtained through concentration, crystallization, centrifugation and drying steps. The entire process takes into account the optimization of reaction conditions, the use of environmentally friendly materials, the treatment of by-products and the strict control of product quality, ensuring the efficiency and environmental friendliness of the purification process.

[0054] Example 1

[0055] A method for purifying sodium citrate is as follows:

[0056] Step 1, using corn flour as a raw material and using Aspergillus niger as a strain for fermentation, the mass ratio of corn flour to Aspergillus niger is 100:1, thereby obtaining citric acid fermentation liquid, and taking the supernatant; the supernatant is subjected to countercurrent extraction at 40° C. using a mixed extractant to transfer citric acid from the supernatant to an organic phase to form an oil phase and an aqueous phase, the mixed extractant is composed of trioctylamine, n-heptanol and n-hexane in a volume ratio of 1:0.5:3, and the volume ratio of the supernatant to the mixed extractant is 1:2;

[0057] Step 2, countercurrent extraction of the oil phase with a sodium hydroxide aqueous solution at 40° C. to react citric acid with sodium hydroxide to generate sodium citrate, wherein the volume ratio of the oil phase to the sodium hydroxide aqueous solution is 1:0.3, and the concentration of the sodium hydroxide aqueous solution is 1 mol / L; oil-water separation is performed, and the residual organic phase is removed to obtain a sodium citrate solution;

[0058] Step 3: further purify the sodium citrate solution by using an adsorption material to remove metal ion impurities in the solution, and the amount of the adsorption material is 5% of the mass of the sodium citrate solution; use an anion exchange resin to remove anion impurities in the solution, and the amount of the anion exchange resin is 2% of the mass of the solution, concentrate and crystallize the purified sodium citrate solution, perform solid-liquid separation, collect sodium citrate crystals, and dry to obtain sodium citrate.

[0059] The preparation method of the adsorbent material is as follows:

[0060] S1, adding 5 g of diatomaceous earth to 30 g of 0.1 g / mL polylysine aqueous solution, adjusting the pH value to 10, and adding 40 g of n-hexane to the polylysine aqueous solution under stirring to obtain a pretreated product;

[0061] S2, adding 8 g of pentaerythritol glycidyl ether to the pre-treated product, continuing stirring for 2 minutes, standing and curing at 10° C. for 20 hours to form a stable porous structure; performing Soxhlet extraction with anhydrous ethanol to remove unreacted raw materials and solvent, and vacuum drying to obtain a post-treated product;

[0062] S3, adding the post-treated product to 30 g of 0.5 mol / L 5-chloromaleic acid aqueous solution, adjusting the pH value to 8 with 1 mol / L sodium hydroxide aqueous solution, heating the reaction at 60° C. for 48 hours, removing the reaction by-products by centrifugation at 12000 rpm and washing with water, and obtaining an adsorbent material.

[0063] Example 2

[0064] A method for purifying sodium citrate is substantially the same as that of Example 1, the only difference being that the preparation method of the adsorption material is different.

[0065] The preparation method of the adsorbent material is as follows:

[0066] S1, adding 5 g of diatomaceous earth to 30 g of 0.1 g / mL polylysine aqueous solution, adjusting the pH value to 10, and adding 40 g of n-hexane to the polylysine aqueous solution under stirring to obtain a pretreated product;

[0067] S2, adding 8 g of glyceryl propoxy triglycidyl ether to the pre-treated product, continuing stirring for 2 minutes, standing and curing at 10° C. for 20 hours to form a stable porous structure; performing Soxhlet extraction with anhydrous ethanol to remove unreacted raw materials and solvent, and vacuum drying to obtain a post-treated product;

[0068] S3, adding the post-treated product to 30 g of 0.5 mol / L 5-chloromaleic acid aqueous solution, adjusting the pH value to 8 with 1 mol / L sodium hydroxide aqueous solution, heating the reaction at 60° C. for 48 hours, removing the reaction by-products by centrifugation at 12000 rpm and washing with water, and obtaining an adsorbent material.

[0069] Example 3

[0070] A method for purifying sodium citrate is substantially the same as that of Example 1, the only difference being that the preparation method of the adsorption material is different.

[0071] The preparation method of the adsorbent material is as follows:

[0072] S1, adding 5 g of diatomaceous earth to 30 g of 0.1 g / mL polylysine aqueous solution, adjusting the pH value to 10, and adding 40 g of n-hexane to the polylysine aqueous solution under stirring to obtain a pretreated product;

[0073] S2, adding 8 g of polyethylene glycol diglycidyl ether to the pre-treated product, continuing stirring for 2 minutes, standing and curing at 10° C. for 20 hours to form a stable porous structure; performing Soxhlet extraction with anhydrous ethanol to remove unreacted raw materials and solvent, and vacuum drying to obtain a post-treated product;

[0074] S3, adding the post-treated product to 30 g of 0.5 mol / L 5-chloromaleic acid aqueous solution, adjusting the pH value to 8 with 1 mol / L sodium hydroxide aqueous solution, heating the reaction at 60° C. for 48 hours, removing the reaction by-products by centrifugation at 12000 rpm and washing with water, and obtaining an adsorbent material.

[0075] Example 4

[0076] A method for purifying sodium citrate is substantially the same as that of Example 1, the only difference being that the preparation method of the adsorption material is different.

[0077] The preparation method of the adsorbent material is as follows:

[0078] S1, adding 5 g of diatomaceous earth to 30 g of 0.1 g / mL polylysine aqueous solution, adjusting the pH value to 10, and adding 40 g of n-hexane to the polylysine aqueous solution under stirring to obtain a pretreated product;

[0079] S2, adding 8 g of pentaerythritol glycidyl ether to the pre-treated product, continuing stirring for 2 minutes, standing and curing at 10° C. for 20 hours to form a stable porous structure; performing Soxhlet extraction with anhydrous ethanol to remove unreacted raw materials and solvent, and vacuum drying to obtain a post-treated product;

[0080] S3, adding the post-treated product to 30 g of 0.5 mol / L 2-chloroacrylic acid aqueous solution, adjusting the pH value to 8 with 1 mol / L sodium hydroxide aqueous solution, heating the reaction at 60° C. for 48 hours, removing the reaction by-products by centrifugation at 12000 rpm and washing with water, and obtaining an adsorption material.

[0081] Example 5

[0082] A method for purifying sodium citrate is substantially the same as that of Example 1, the only difference being that the preparation method of the adsorption material is different.

[0083] The preparation method of the adsorbent material is as follows:

[0084] S1, adding 5 g of diatomaceous earth to 30 g of 0.1 g / mL polylysine aqueous solution, adjusting the pH value to 10, and adding 40 g of n-hexane to the polylysine aqueous solution under stirring to obtain a pretreated product;

[0085] S2, adding 8 g of pentaerythritol glycidyl ether to the pre-treated product, continuing stirring for 2 minutes, standing and curing at 10° C. for 20 hours to form a stable porous structure; performing Soxhlet extraction with anhydrous ethanol to remove unreacted raw materials and solvent, and vacuum drying to obtain a post-treated product;

[0086] S3. The post-treated product was added to 30 g of a 0.5 mol / L 2-chloro-3-methylbut-2-enoic acid aqueous solution, the pH value was adjusted to 8 with a 1 mol / L sodium hydroxide aqueous solution, the mixture was heated at 60° C. for 48 hours, and the reaction by-products were removed by centrifugation at 12000 rpm and washing with water to obtain an adsorbent material.

[0087] Example 6

[0088] A method for purifying sodium citrate is substantially the same as that of Example 1, the only difference being that the preparation method of the adsorption material is different.

[0089] The preparation method of the adsorbent material is as follows:

[0090] S1, adding 5 g of diatomaceous earth to 30 g of 0.1 g / mL polylysine aqueous solution, adjusting the pH value to 10, and adding 40 g of n-hexane to the polylysine aqueous solution under stirring to obtain a pretreated product;

[0091] S2, adding 8 g of pentaerythritol glycidyl ether to the pre-treated product, continuing stirring for 2 minutes, standing and curing at 10° C. for 20 hours to form a stable porous structure; performing Soxhlet extraction with anhydrous ethanol to remove unreacted raw materials and solvent, and vacuum drying to obtain a post-treated product;

[0092] S3, adding the post-treated product to 30 g of 0.5 mol / L chloroacetic acid aqueous solution, adjusting the pH value to 8 with 1 mol / L sodium hydroxide aqueous solution, heating the reaction at 60° C. for 48 hours, removing the reaction by-products by centrifugation at 12000 rpm and washing with water, and obtaining an adsorbent material.

[0093] Comparative Example 1

[0094] A method for purifying sodium citrate is as follows:

[0095] Step 1, using corn flour as a raw material and using Aspergillus niger as a strain for fermentation, the mass ratio of corn flour to Aspergillus niger is 100:1, thereby obtaining citric acid fermentation liquid, and taking the supernatant; the supernatant is subjected to countercurrent extraction at 40° C. using a mixed extractant to transfer citric acid from the supernatant to an organic phase to form an oil phase and an aqueous phase, the mixed extractant is composed of trioctylamine, n-heptanol and n-hexane in a volume ratio of 1:0.5:3, and the volume ratio of the supernatant to the mixed extractant is 1:2;

[0096] Step 2, countercurrent extraction of the oil phase with a sodium hydroxide aqueous solution at 40° C. to react citric acid with sodium hydroxide to generate sodium citrate, wherein the volume ratio of the oil phase to the sodium hydroxide aqueous solution is 1:0.3, and the concentration of the sodium hydroxide aqueous solution is 1 mol / L; oil-water separation is performed, and the residual organic phase is removed to obtain a sodium citrate solution;

[0097] Step 3: further purify the sodium citrate solution using diatomaceous earth to remove metal ion impurities in the solution, wherein the amount of diatomaceous earth used is 5% of the mass of the sodium citrate solution; remove anion impurities in the solution using anion exchange resin, wherein the amount of anion exchange resin used is 2% of the mass of the solution; concentrate and crystallize the purified sodium citrate solution, perform solid-liquid separation, collect sodium citrate crystals, and dry to obtain sodium citrate.

[0098] Comparative Example 2

[0099] A method for purifying sodium citrate is as follows:

[0100] Step 1, using corn flour as a raw material and using Aspergillus niger as a strain for fermentation, the mass ratio of corn flour to Aspergillus niger is 100:1, thereby obtaining citric acid fermentation liquid, and taking the supernatant; the supernatant is subjected to countercurrent extraction at 40° C. using a mixed extractant to transfer citric acid from the supernatant to an organic phase to form an oil phase and an aqueous phase, the mixed extractant is composed of trioctylamine, n-heptanol and n-hexane in a volume ratio of 1:0.5:3, and the volume ratio of the supernatant to the mixed extractant is 1:2;

[0101] Step 2, countercurrent extraction of the oil phase with a sodium hydroxide aqueous solution at 40° C. to react citric acid with sodium hydroxide to generate sodium citrate, wherein the volume ratio of the oil phase to the sodium hydroxide aqueous solution is 1:0.3, and the concentration of the sodium hydroxide aqueous solution is 1 mol / L; oil-water separation is performed, and the residual organic phase is removed to obtain a sodium citrate solution;

[0102] Step 3: using anion exchange resin to remove anion impurities in the solution, the amount of anion exchange resin used is 2% of the mass of the solution, concentrating and crystallizing the purified sodium citrate solution, performing solid-liquid separation, collecting sodium citrate crystals, and drying to obtain sodium citrate.

[0103] Test Example 1

[0104] Sodium citrate crystallinity

[0105] The crystal purity of sodium citrate can be evaluated by its crystallinity, which reflects the proportion of sodium citrate crystals in the overall structure. High crystallinity means higher purity of sodium citrate. According to the national standard GB1886.25-2016, i.e. "National Food Safety Standard Food Additive Sodium Citrate", we can quantitatively analyze the crystallinity of sodium citrate crystals. See Table 1 for specific test data.

[0106] Table 1

[0107] Experimental protocol Crystallinity(%) Example 1 99.4 Example 2 99.1 Example 3 98.2 Example 4 98.6 Example 5 98.1 Example 6 98.4 Comparative Example 1 95.1 Comparative Example 2 93.5

[0108] Test Example 2

[0109] Yield test

[0110] Yield is a key parameter in chemical synthesis and industrial production, and is defined as the ratio between the actual amount of product produced and the theoretically available yield. The level of this indicator is directly related to the loss of raw materials during the production process. A high yield indicates that in the process of synthesizing sodium citrate crystals from citric acid fermentation broth, the utilization rate of raw materials is high and the loss is low. According to the provisions of GB1886.25-2016 "National Food Safety Standard Food Additive Sodium Citrate", the yield of sodium citrate crystals is accurately determined. Detailed measurement results are shown in Table 2.

[0111] Table 2

[0112] Experimental protocol Yield (%) Example 1 98.2 Example 2 96.8 Example 3 95.3 Example 4 96.4 Example 5 95.1 Example 6 95.5 Comparative Example 1 89.0 Comparative Example 2 84.1

[0113] It can be seen from Test Examples 1 to 2 that the sodium citrate obtained by the purification method of Example 1 of the present invention has good purity and yield.

[0114] In Example 1 of the present invention, pentaerythritol glycidyl ether is selected as a cross-linking agent, and its molecular structure contains multiple reactive epoxy groups, which can effectively undergo cross-linking reactions with the abundant amino groups in polylysine. The multifunctional characteristics of pentaerythritol glycidyl ether allow it to form multiple covalent bonds between the amino groups of polylysine, thereby constructing a more stable and uniform three-dimensional network structure. This structure not only improves the mechanical strength of the adsorption material, but also increases the specific surface area and porosity, providing more metal adsorption sites and more efficient metal ion impurity removal capabilities for the purification of sodium citrate.

[0115] In contrast, although the glycerol propoxy triglycidyl ether in Example 2 and the polyethylene glycol diglycidyl ether in Example 3 also contain epoxy groups, their molecular structures and functional group arrangements are different from those of pentaerythritol glycidyl ether and may not form the same stable and porous structure in the polylysine network. The propoxy group of glycerol propoxy triglycidyl ether may hinder the cross-linking efficiency with polylysine to a certain extent, and the longer polyethylene glycol chain of polyethylene glycol diglycidyl ether may lead to inconsistency in pore size in the network structure. These factors may affect the performance of the adsorbent material.

[0116] In Example 1 of the present invention, 5-chloromaleic acid is selected as a key reaction reagent, which is related to the two carboxyl groups contained in its molecular structure. The molecular structure of 5-chloromaleic acid is characterized by containing two carboxyl groups and a reactive chlorine atom. Under the condition of pH 8, this structure of 5-chloromaleic acid can form covalent bonds and generate stable functional groups when reacting with amino groups in porous materials. These functional groups not only enhance the adsorption performance of the material, but also increase the connection points with the material surface due to the dicarboxyl structure of 5-chloromaleic acid, thereby improving the mechanical strength and chemical stability of the adsorbent material.

[0117] In contrast, other chlorinated carboxylic acids such as 2-chloroacrylic acid, 2-chloro-3-methylbut-2-enoic acid and chloroacetic acid may not be able to form the same stable and multi-connection point functional groups on the surface of porous materials as 5-chloromaleic acid due to the different number or position of carboxyl groups in the molecular structure. 2-Chloroacrylic acid has only one carboxyl group and may not be able to form multiple adsorption sites; although 2-chloro-3-methylbut-2-enoic acid contains one carboxyl group, the methyl part in its molecule may produce a steric hindrance effect on the activity of the carboxyl group, reducing its reaction efficiency with the amino group. At the same time, this steric hindrance may also limit the distribution of functional groups on the surface of porous materials, thereby affecting the adsorption performance; although chloroacetic acid also contains one carboxyl group, it may be because the reactivity of the chlorine atom in its molecule is not as good as 5-chloromaleic acid, resulting in adsorption performance not as good as Example 1.

[0118] The above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for purifying sodium citrate, characterized in that: Here’s how: Step 1, using corn flour as a raw material and Aspergillus niger as a strain for fermentation to obtain citric acid fermentation liquid, and taking the supernatant; extracting the supernatant at 30-50° C. using a mixed extractant by countercurrent extraction to transfer citric acid from the supernatant to an organic phase to form an oil phase and an aqueous phase; Step 2, countercurrent extraction of the oil phase with a sodium hydroxide aqueous solution at 30-50° C. to react citric acid with sodium hydroxide to generate sodium citrate; oil-water separation, removal of the residual organic phase, to obtain a sodium citrate solution; Step 3: further purifying the sodium citrate solution using an adsorption material to remove metal ion impurities in the solution; Anion exchange resins are used to remove anionic impurities from the solution; The purified sodium citrate solution is concentrated and crystallized, solid-liquid separation is performed, sodium citrate crystals are collected, and dried to obtain sodium citrate; The amount of the adsorption material is 1-8% of the mass of the sodium citrate solution; The preparation method of the adsorbent material is as follows, in parts by weight: S1, adding 4 to 6 parts of diatomaceous earth to 25 to 35 parts of 0.05 to 0.2 g / mL polylysine aqueous solution, adjusting the pH value to 9 to 11, and adding 30 to 50 parts of n-hexane to the polylysine aqueous solution under stirring to obtain a pretreated product; S2, adding 7 to 9 parts of pentaerythritol glycidyl ether to the pre-treated product, continuing stirring for 1 to 5 minutes, standing to solidify, and forming a stable porous structure; performing Soxhlet extraction with anhydrous ethanol to remove unreacted raw materials and solvents, and vacuum drying to obtain a post-treated product; S3, adding the post-treated product to 25-35 parts of 0.4-0.6 mol / L 5-chloromaleic acid aqueous solution, adjusting the pH value to 7.5-8.5 with 0.5-2 mol / L sodium hydroxide aqueous solution, heating for reaction, removing reaction byproducts by centrifugation at 10000-15000 rpm and washing with water, to obtain an adsorption material; The static curing parameters are static curing at 0-30°C for 10-30 hours; The heating reaction conditions are heating the reaction at 50-70°C for 40-50 hours; The mixed extractant is composed of trioctylamine, n-heptanol and n-hexane in a volume ratio of 0.8-1.2:0.4-0.6:2-4.

2. The method for purifying sodium citrate according to claim 1, wherein The mass ratio of the corn flour to Aspergillus niger is 80-120:

1.

3. The method for purifying sodium citrate according to claim 1, wherein The volume ratio of the supernatant to the mixed extractant is 1:1-3.

4. The method for purifying sodium citrate according to claim 1, wherein The volume ratio of the oil phase to the sodium hydroxide aqueous solution is 0.8-1.2:0.2-0.4, and the concentration of the sodium hydroxide aqueous solution is 0.5-2 mol / L.

5. The method for purifying sodium citrate according to claim 1, wherein The amount of the anion exchange resin used is 0.5-5% of the solution mass.