A method for improving the quality of disodium ethylenediaminetetraacetate

Abstract

This application relates to the field of working reference reagents, specifically disclosing a method for improving the quality of disodium ethylenediaminetetraacetate (EDTA), comprising the following steps: dispersing crude EDTA in water, adjusting the pH of the system, adding sodium carbonate to induce salt precipitation, adding a negatively charged polymer and stirring, allowing it to stand, adding activated carbon for adsorption, filtering to obtain a filtrate, wherein the negatively charged polymer includes one or more of sodium polyacrylate, polyaspartic acid, sodium polystyrene sulfonate, and sodium alginate; ultrafiltration of the filtrate obtained in step I, and adding anhydrous ethanol to the resulting liquid phase, controlling the volume ratio of anhydrous ethanol to filtrate to be 1.5:(2-4.5); stirring and filtering; drying the resulting filter residue to obtain disodium EDTA. The method of this application involves multiple interconnected steps, forming a rigorous and streamlined overall scheme, which improves the purity of disodium EDTA to 99.5% or higher.

Description

Technical Field

[0001] This application relates to the field of working reference reagents, and in particular to a method for improving the quality of disodium ethylenediaminetetraacetate. Background Technology

[0002] Disodium ethylenediaminetetraacetate (EDTA) is the disodium salt of EDTA. It is readily soluble in alkaline solutions such as sodium hydroxide and sodium carbonate, forming stable water-soluble complexes. It possesses strong chelating ability, forming stable complexes with metal ions such as calcium, magnesium, iron, and lead, thereby eliminating the catalytic oxidation of these metal ions. Disodium EDTA has significant applications in multiple fields. In the food industry, it serves as a color-protecting agent and antioxidant, preventing discoloration and spoilage caused by metal ions (such as vitamin C oxidation loss). In the pharmaceutical field, it acts as a stabilizer for injections, inhibiting blood clotting (e.g., blood sample anticoagulation) and treating heavy metal poisoning (e.g., lead poisoning). In industry, it is used as a detergent to enhance cleaning and foaming power and soften hard water. In the rubber industry, it acts as an activator in chlorination reduction initiation systems, controlling the polymerization rate. It can also be used in photosensitive materials, such as bleaching and fixing solutions, to prevent the precipitation of ferric ions.

[0003] Disodium EDTA is available in different purity grades, including: Primary standard grade (99.95-100.05%), used as a primary standard in analytical chemistry, such as in titration analysis; Pharmaceutical grade (compliant with pharmacopoeia standards, purity ≥99.0%, ensuring biocompatibility); and Superior grade / Analytical grade (purities ≥99.5% and 99.0%, respectively), used for routine laboratory testing (such as water quality analysis and environmental monitoring). Disodium EDTA is generally purified using methods such as water recrystallization, acid-base adjustment with EDTA and sodium hydroxide, organic solvent extraction, and water extraction. These purification methods result in low overall recovery rates for both the product and the mother liquor, typically below 90%, and easily introduce new impurities, preventing the final pure product from meeting the quality standards of superior grade / primary standard. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a method for improving the quality of disodium ethylenediaminetetraacetate.

[0005] This application provides a method for improving the quality of disodium ethylenediaminetetraacetate, comprising the following steps:

[0006] I. Disperse crude disodium ethylenediaminetetraacetate in water, adjust the pH of the system to 9-11, add sodium carbonate to precipitate salt, then add the negatively charged polymer and stir at 70-95℃ for 1-2 hours, keep warm and let stand for 1-2 hours, add activated carbon for adsorption, let stand for 1-2 hours, filter to obtain filtrate. The weight ratio of crude disodium ethylenediaminetetraacetate, sodium carbonate and negatively charged polymer is 300:2:(0.5-0.8). The negatively charged polymer includes one or more of sodium polyacrylate, polyaspartic acid, sodium polystyrene sulfonate and sodium alginate.

[0007] II. The filtrate obtained in step I is subjected to ultrafiltration, and anhydrous ethanol is added to the resulting liquid phase, controlling the volume ratio of anhydrous ethanol to filtrate to be 1.5:(2-4.5). After stirring, the mixture is filtered, and the resulting filter residue is dried to obtain disodium ethylenediaminetetraacetate.

[0008] The ultrafiltration membrane used in the ultrafiltration process is a composite ultrafiltration membrane prepared according to the following method:

[0009] Cellulose acetate, film-forming polymer, and pore-forming agent in a weight ratio of 1:(10-30):(0.5-2) are mixed and dispersed in an organic solvent. After degassing, the membrane is scraped, cured, and soaked to obtain a composite ultrafiltration membrane. The film-forming polymer includes polyvinylidene fluoride and bisphenol A type polycarbonate in a weight ratio of (7-9):(1-3).

[0010] By adopting the above technical solution, this application first uses sodium hydroxide to adjust the pH and adds sodium carbonate to precipitate a positively charged metal salt in the system. Then, a negatively charged polymer is added to combine with the metal salt to form a precipitate. After adsorption by activated carbon and filtration, the filtrate is obtained. Further ultrafiltration is performed to remove the large molecular polymers in the system. Then, anhydrous ethanol is added to the liquid phase. Taking advantage of the significant difference in solubility of disodium ethylenediaminetetraacetate in water and anhydrous ethanol, and by strictly controlling the amount of anhydrous ethanol added, disodium ethylenediaminetetraacetate is recrystallized in the system. At the same time, disodium ethylenediaminetetraacetate is separated from small molecule impurities. The crystalline product of disodium ethylenediaminetetraacetate is then dried to obtain standard grade disodium ethylenediaminetetraacetate.

[0011] This application utilizes cellulose acetate, polyvinylidene fluoride, and bisphenol A type polycarbonate to prepare a composite ultrafiltration membrane. This composite ultrafiltration membrane has good mechanical strength, solvent resistance, a wide pH range, good hydrophilicity, and high membrane flux. It can efficiently intercept small molecule impurities and particles remaining in the filtrate, effectively improving product recovery rate and product purity.

[0012] Overall, the method of this application has multiple interconnected steps, forming a rigorous and smooth overall scheme. Compared with the method of using water recrystallization, acid-base adjustment of crystallization with ethylenediaminetetraacetic acid and sodium hydroxide, organic solvent and water extraction, it has a more significant impurity removal effect and can successfully improve the purity of disodium ethylenediaminetetraacetate to 99.95% and above.

[0013] The specific embodiments of this application only describe the purification process of the superior grade / reference reagent. However, the purification difficulty of other purity levels is lower than that of the superior grade / reference reagent. Therefore, those skilled in the art can make changes according to the actual situation. That is, by adjusting the parameters in the purification process, disodium ethylenediaminetetraacetate of different purity levels can be produced.

[0014] While obtaining the standard grade disodium ethylenediaminetetraacetate, a mother liquor is also obtained. This mother liquor can be distilled under reduced pressure to remove ethanol, resulting in a product with a purity slightly lower than the standard grade disodium ethylenediaminetetraacetate. In industrial production, it can be blended with the filtrate obtained in the next batch of step I and further recrystallized to improve raw material utilization and overall industrial yield.

[0015] Preferably, in step I, the weight ratio of crude disodium ethylenediaminetetraacetate, sodium carbonate, and negatively charged polymer is 300:2:(0.6-0.7).

[0016] By adopting the above technical solution, this application optimizes the ratio between crude disodium ethylenediaminetetraacetate, sodium carbonate, and negatively charged polymer. This not only allows the metal salt in the system to precipitate more fully and combine with the negatively charged polymer to form a precipitate, thus improving the removal efficiency of impurities, but also reduces the cost increase and subsequent separation difficulty caused by excessive reagents, thereby significantly improving the purity of the final product to the benchmark standard.

[0017] Preferably, in step I, the negatively charged polymer comprises polyaspartic acid and sodium polystyrene sulfonate.

[0018] Preferably, the weight ratio of polyaspartic acid to sodium polystyrene sulfonate is 2:(2-3).

[0019] By adopting the above technical solution, this application utilizes polyaspartic acid and sodium polystyrene sulfonate as negatively charged polymers, making full use of the high binding degree of polyaspartic acid with metal salts, good temperature resistance, and acid and alkali resistance of sodium polystyrene sulfonate. The two can also play a synergistic role, enhancing the steric hindrance effect and electrostatic attraction balance of the negatively charged polymers, avoiding the problems of slow sedimentation or incomplete encapsulation caused by excessive or insufficient amounts. More importantly, activated carbon has a better adsorption and removal effect on the precipitates formed by polyaspartic acid and sodium polystyrene sulfonate with metal salts. Therefore, with the support of the dual effects, the preferred polyaspartic acid and sodium polystyrene sulfonate of this application can further remove the metal salts precipitated in the system, significantly improving the purity of the product.

[0020] Preferably, in step I, the negatively charged polymer is added and then stirred at a temperature of 85-90°C.

[0021] By adopting the above technical solution, this application limits the stirring temperature to the range of 85-90℃, which accelerates the interaction between the negatively charged polymer and the metal salt, reduces the residue of unreacted substances, forms a more stable precipitate, and further improves the purity of the disodium ethylenediaminetetraacetate product.

[0022] Preferably, in step II, the weight ratio of cellulose acetate, film-forming polymer, and pore-forming agent is 1:(15-18):1.

[0023] Preferably, in step II, the weight ratio of polyvinylidene fluoride to bisphenol A polycarbonate is (7.5-8):(2-2.5).

[0024] By adopting the above technical solution, this application optimizes the raw material ratio in the preparation process of the composite ultrafiltration membrane. This optimizes the membrane flux and solvent resistance while ensuring good mechanical strength, and also maintains a wide pH range and good hydrophilicity. This optimized ratio helps to more effectively intercept impurities in the filtrate. The membrane's internal morphology becomes more ordered, and the interconnected pore structure increases, thereby reducing clogging and further improving the purity of disodium ethylenediaminetetraacetate, ensuring that the final product meets benchmark quality standards.

[0025] Preferably, in step II, the volume ratio of anhydrous ethanol to filtrate is 1.5:(3.75-4).

[0026] Preferably, in step II, after stirring for 10-12 hours, ultrafiltration is performed, and the resulting filter residue is dried at a temperature of 55-60°C to obtain disodium ethylenediaminetetraacetate.

[0027] By adopting the above technical solution, this application strictly controls the volume ratio of anhydrous ethanol to filtrate, which makes recrystallization more complete. It also strictly controls the stirring time and drying temperature, which can effectively remove residual liquid in the filter residue and avoid damage to the product structure caused by high temperature. Finally, it obtains standard grade disodium ethylenediaminetetraacetate with high recovery rate, high purity and stable quality.

[0028] In summary, this application has the following beneficial technical effects:

[0029] 1. This application achieves efficient removal of metal ions and other impurities by adjusting the pH of the system and adding sodium carbonate and negatively charged polymers. It also utilizes the difference in solubility between anhydrous ethanol and filtrate for recrystallization, and combines precise control of ultrafiltration and drying conditions to achieve effective separation and purification of the target product. This avoids the problem of easily introducing new impurities in traditional methods and significantly improves the purity of disodium ethylenediaminetetraacetate to over 99.5%.

[0030] 2. The composite ultrafiltration membrane used in this application combines mechanical strength, solvent resistance, hydrophilicity, high membrane flux, and broad pH adaptability, which significantly improves filtration efficiency and accuracy and ensures a high recovery rate throughout the process. Detailed Implementation

[0031] Material source

[0032] Unless otherwise specified, all raw materials used in this application are commercially available products, specifically from the following suppliers:

[0033] Cellulose acetate was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with an acetyl substitution degree of 1.77.

[0034] The pore-forming agent was purchased from Nantong Jingwei Biotechnology Co., Ltd., brand name PVPK30, M w =25000-40000;

[0035] Methylpyrrolidone was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0036] Polyvinylidene fluoride was purchased from Sinochem Lantian Fluorine Materials Co., Ltd.

[0037] Bisphenol A polycarbonate was purchased from Covestro Polymers (China) Co., Ltd., M w =42100;

[0038] The activated carbon was purchased from Henan Yujia Environmental Protection Materials Co., Ltd., and was grade 1, 10-24 mesh.

[0039] Polyetheretherketone (PEEK) was purchased from Guangdong Yunxing Biotechnology Co., Ltd.

[0040] Sodium polyacrylate was purchased from Shandong Lingchuang Biotechnology Co., Ltd., with a density of 1.09 g / cm³.3 ;

[0041] Sodium alginate was purchased from Anhui Zhonghong Bioengineering Co., Ltd., with a density of 1.09 g / cm³. 3 ;

[0042] Polyaspartic acid was purchased from Jining Yuanlian Chemical Technology Co., Ltd.

[0043] Sodium polystyrene sulfonate was purchased from Dow Chemical.

[0044] The polyacrylamide was purchased from Zhengzhou Zhuohang Water Purification Materials Co., Ltd., with a density of 1.302 g / cm³. 3 .

[0045] The present application will be further described in detail below with reference to preparation examples, embodiments and comparative examples.

[0046] The term "ultrafiltration" used in this application refers only to ultrafiltration membranes. The specific types of ultrafiltration machines used include, but are not limited to, cartridge ultrafiltration units, hollow fiber membrane module ultrafiltration units, plate and frame ultrafiltration units, spiral wound membrane module ultrafiltration units, and tubular ultrafiltration units. This application uses tubular ultrafiltration units for description, but this should not be used to limit the scope of protection of this application.

[0047] Preparation Example 1.1

[0048] The method for preparing a composite ultrafiltration membrane includes the following steps:

[0049] 10g of cellulose acetate and 20g of pore-forming agent were dispersed in 800mL of N-methylpyrrolidone and stirred at 500r / min until completely dissolved. Then, 100g of film-forming polymer (70g of polyvinylidene fluoride and 30g of bisphenol A polycarbonate) was added, and the stirring speed was increased to 700r / min until completely dissolved, forming a homogeneous and stable casting solution. The casting solution was allowed to stand for 12h for degassing treatment, and then ultrasonically treated at 240W for 15min. The casting solution was poured out, and the membrane was scraped to control the thickness of the liquid membrane to 200±5um. It was exposed to air for 15s, and then the plate with the liquid membrane was immersed in pre-prepared ultrapure water. After the liquid membrane solidified and gradually detached from the plate, the solidified membrane was quickly transferred to clean ultrapure water and soaked for 24h to completely remove the residual solvent in the membrane. During this period, the water was changed once every 12h. Finally, the composite ultrafiltration membrane was obtained and stored in a 30% glycerol aqueous solution for later use.

[0050] Preparation Example 1.2

[0051] The method for preparing a composite ultrafiltration membrane includes the following steps:

[0052] 10g of cellulose acetate and 5g of pore-forming agent were dispersed in 800mL of N-methylpyrrolidone and stirred at 500r / min until completely dissolved. Then, 300g of film-forming polymer (270g of polyvinylidene fluoride and 30g of bisphenol A polycarbonate) was added, and the stirring speed was increased to 700r / min until completely dissolved, forming a homogeneous and stable casting solution. The casting solution was allowed to stand for 12h for degassing treatment, and then ultrasonically treated at 240W for 15min. The casting solution was poured out, and the membrane was scraped to control the thickness of the liquid membrane to 200±5um. It was exposed to air for 15s, and then the plate with the liquid membrane was immersed in pre-prepared ultrapure water. After the liquid membrane solidified and gradually detached from the plate, the solidified membrane was quickly transferred to clean ultrapure water and soaked for 24h to completely remove the residual solvent in the membrane. During this period, the water was changed once every 12h. Finally, the composite ultrafiltration membrane was obtained and stored in a 30% glycerol aqueous solution for later use.

[0053] Preparation Example 2.1

[0054] The method for preparing the composite ultrafiltration membrane differs from that in Preparation Example 1.1 in that the amount of the membrane-forming polymer used is 150g, including 105g of polyvinylidene fluoride and 45g of bisphenol A type polycarbonate, while the rest is the same as in Preparation Example 1.1.

[0055] Preparation Example 2.2

[0056] The method for preparing the composite ultrafiltration membrane differs from that in Preparation Example 1.1 in that the amount of the membrane-forming polymer used is 180g, including 126g of polyvinylidene fluoride and 54g of bisphenol A type polycarbonate, while the rest is the same as in Preparation Example 1.1.

[0057] Preparation Example 2.3

[0058] The method for preparing the composite ultrafiltration membrane differs from that in Preparation Example 1.1 in that the amount of the membrane-forming polymer used is 200g, including 140g of polyvinylidene fluoride and 60g of bisphenol A type polycarbonate, while the rest is the same as in Preparation Example 1.1.

[0059] Preparation Example 2.4

[0060] The method for preparing the composite ultrafiltration membrane differs from that in Preparation Example 1.1 in that the amount of the membrane-forming polymer used is 250g, including 175g of polyvinylidene fluoride and 75g of bisphenol A type polycarbonate, while the rest is the same as in Preparation Example 1.1.

[0061] Preparation Example 3.1

[0062] The preparation method of the composite ultrafiltration membrane differs from that of Preparation Example 2.1 in that the membrane-forming polymer includes 112.5g of polyvinylidene fluoride and 37.5g of bisphenol A type polycarbonate, while the rest are the same as those in Preparation Example 2.1.

[0063] Preparation Example 3.2

[0064] The method for preparing the composite ultrafiltration membrane differs from that in Preparation Example 2.1 in that the membrane-forming polymer includes 120g of polyvinylidene fluoride and 30g of bisphenol A type polycarbonate, while the rest are the same as in Preparation Example 2.1.

[0065] Preparation Example 3.3

[0066] The method for preparing the composite ultrafiltration membrane differs from that in Preparation Example 2.1 in that the membrane-forming polymer includes 127.5g of polyvinylidene fluoride and 22.5g of bisphenol A type polycarbonate, while the rest are the same as in Preparation Example 2.1.

[0067] Preparation Example 3.4

[0068] The method for preparing the composite ultrafiltration membrane differs from that in Preparation Example 2.1 in that the membrane-forming polymer includes 135g of polyvinylidene fluoride and 15g of bisphenol A type polycarbonate, while the rest are the same as in Preparation Example 2.1.

[0069] Preparation Example 3.5

[0070] The method for preparing the composite ultrafiltration membrane differs from that in Preparation Example 2.1 in that the membrane-forming polymer includes 142.5g of polyvinylidene fluoride and 7.5g of bisphenol A type polycarbonate, while the rest are the same as in Preparation Example 2.1.

[0071] Comparative preparation example 1.1

[0072] The difference from Preparation Example 1.1 is that polyvinylidene fluoride was removed, and the amount of bisphenol A polycarbonate was adjusted to 100g, while the rest were the same as Preparation Example 1.1.

[0073] Comparative preparation example 1.2

[0074] The difference from Preparation Example 1.1 is that bisphenol A type polycarbonate is removed, the amount of polyvinylidene fluoride is adjusted to 100g, and the rest are the same as Preparation Example 1.1.

[0075] Comparative preparation example 2.1

[0076] The difference from Preparation Example 1.1 is that all polyvinylidene fluoride is replaced with polyether ether ketone, while the rest is the same as Preparation Example 1.1.

[0077] Comparative preparation example 2.2

[0078] The difference from Preparation Example 1.1 is that all bisphenol A type polycarbonate is replaced with polyether ether ketone, while the rest is the same as Preparation Example 1.1.

[0079] Example 1.1

[0080] A method for improving the quality of disodium ethylenediaminetetraacetate includes the following steps:

[0081] I. Disperse crude disodium ethylenediaminetetraacetate in water, heat until completely dissolved, let stand for 1 hour, filter out the solid matter, add sodium hydroxide to adjust the pH of the liquid phase system to 11, then add sodium carbonate to the system pH to 12.5 to precipitate salt, add negatively charged polymer (sodium polyacrylate) after 1 hour, stir at 95℃ for 1 hour, keep warm and let stand for 2 hours, add activated carbon for adsorption, let stand for 2 hours, filter to obtain filtrate. During the feeding process, control the weight ratio of crude disodium ethylenediaminetetraacetate, sodium carbonate and negatively charged polymer to be 300:2:0.5;

[0082] II. The filtrate obtained in step I was subjected to ultrafiltration using the composite ultrafiltration membrane prepared in Preparation Example 1.1. Anhydrous ethanol was added to the liquid phase obtained after ultrafiltration, and the volume ratio of anhydrous ethanol to filtrate was controlled at 1.5:4.5. After stirring for 10 hours, the mixture was filtered to obtain filter residue and mother liquor. The obtained filter residue was dried at 60°C to obtain disodium ethylenediaminetetraacetate, and the mother liquor was stored.

[0083] Example 1.2

[0084] A method for improving the quality of disodium ethylenediaminetetraacetate includes the following steps:

[0085] I. Disperse crude disodium ethylenediaminetetraacetate in water, heat until completely dissolved, let stand for 1 hour, filter out the solid matter, add sodium hydroxide to adjust the pH of the liquid phase system to 9, then add sodium carbonate to the system pH to 12.5 to precipitate salt, add negatively charged polymer (sodium alginate) after 1 hour, stir at 70℃ for 2 hours, keep warm and let stand for 1 hour, add activated carbon for adsorption, let stand for 1 hour, filter to obtain filtrate. During the feeding process, control the weight ratio of crude disodium ethylenediaminetetraacetate, sodium carbonate and negatively charged polymer to be 300:2:0.8;

[0086] II. The filtrate obtained in step I was subjected to ultrafiltration using the composite ultrafiltration membrane prepared in Preparation Example 1.2. Anhydrous ethanol was added to the resulting liquid phase, and the volume ratio of anhydrous ethanol to filtrate was controlled at 1.5:2. After stirring for 8 hours, the mixture was filtered to obtain filter residue and mother liquor. The obtained filter residue was dried at 55°C to obtain disodium ethylenediaminetetraacetate, and the mother liquor was stored.

[0087] Example 1.3

[0088] A method for improving the quality of disodium ethylenediaminetetraacetate (EDTA) differs from Example 1.1 in that: in step I, the weight ratio of crude EDTA, sodium carbonate, and negatively charged polymer is controlled to be 300:2:0.6, while the rest is the same as in Example 1.1.

[0089] Example 1.4

[0090] A method for improving the quality of disodium ethylenediaminetetraacetate (EDTA) differs from Example 1.1 in that: in step I, the weight ratio of crude EDTA, sodium carbonate, and negatively charged polymer is controlled to be 300:2:0.7, while the rest is the same as in Example 1.1.

[0091] Example 2.1

[0092] A method for improving the quality of disodium ethylenediaminetetraacetate, which differs from Example 1.3 in that: in step I, sodium polyacrylate is replaced with polyaspartic acid, while the rest is the same as in Example 1.1.

[0093] Example 2.2

[0094] A method for improving the quality of disodium ethylenediaminetetraacetate, which differs from Example 1.3 in that: in step I, sodium polyacrylate is replaced with sodium polystyrene sulfonate, while the rest is the same as in Example 1.1.

[0095] Example 2.3

[0096] A method for improving the quality of disodium ethylenediaminetetraacetate (EDTA) differs from Example 1.3 in that, in step I, sodium polyacrylate is replaced with sodium polyacrylate and polyaspartic acid in a weight ratio of 1:1, while the rest is the same as in Example 1.1.

[0097] Example 2.4

[0098] A method for improving the quality of disodium ethylenediaminetetraacetate, which differs from Example 1.3 in that: in step I, sodium polyacrylate is replaced with sodium polyacrylate and sodium polystyrene sulfonate in a weight ratio of 1:1, while the rest is the same as in Example 1.1.

[0099] Example 2.5

[0100] A method for improving the quality of disodium ethylenediaminetetraacetate, which differs from Example 1.3 in that: in step I, sodium polyacrylate is replaced with polyaspartic acid and sodium polystyrene sulfonate in a weight ratio of 1:1, while the rest is the same as in Example 1.1.

[0101] Example 2.6

[0102] A method for improving the quality of disodium ethylenediaminetetraacetate, which differs from Example 1.3 in that: in step I, sodium polyacrylate is replaced with polyaspartic acid, sodium alginate and sodium polystyrene sulfonate in a weight ratio of 1:1, while the rest is the same as in Example 1.1.

[0103] Example 3.1

[0104] A method for improving the quality of disodium ethylenediaminetetraacetate, which differs from Example 2.5, is as follows: in step I, the weight ratio of polyaspartic acid to sodium polystyrene sulfonate is 1:2, while the rest is the same as in Example 2.5.

[0105] Example 3.2

[0106] A method for improving the quality of disodium ethylenediaminetetraacetate, which differs from Example 2.5 in that: in step I, the weight ratio of polyaspartic acid to sodium polystyrene sulfonate is 1:3, and the rest is the same as in Example 2.5.

[0107] Example 3.3

[0108] A method for improving the quality of disodium ethylenediaminetetraacetate, which differs from Example 2.5, is as follows: in step I, the weight ratio of polyaspartic acid to sodium polystyrene sulfonate is 1:1.5, while the rest is the same as in Example 2.5.

[0109] Example 4.1

[0110] A method for improving the quality of disodium ethylenediaminetetraacetate (EDTA) differs from Example 1.3 in that: in step I, the negatively charged polymer is added and then stirred at 85°C; otherwise, the method is the same as in Example 1.3.

[0111] Example 4.2

[0112] A method for improving the quality of disodium ethylenediaminetetraacetate (EDTA) differs from Example 1.3 in that: in step I, the negatively charged polymer is added and then stirred at a temperature of 90°C; the rest is the same as in Example 1.3.

[0113] Examples 5.1-5.4

[0114] A method for improving the quality of disodium ethylenediaminetetraacetate (EDTA) differs from Example 1.3 in that, in step II, the composite ultrafiltration membrane prepared in Preparation Example 1.1 is replaced with the composite ultrafiltration membrane prepared in Preparation Examples 2.1-2.4, while the rest is the same as in Example 1.3.

[0115] Examples 6.1-6.5

[0116] A method for improving the quality of disodium ethylenediaminetetraacetate (EDTA) differs from Example 5.1 in that, in step II, the composite ultrafiltration membrane prepared in Preparation Example 2.1 is replaced with the composite ultrafiltration membrane prepared in Preparation Examples 3.1-3.5, while the rest is the same as in Example 5.1.

[0117] Example 7.1

[0118] A method for improving the quality of disodium ethylenediaminetetraacetate (EDTA) differs from Example 1.3 in that, in step II, the volume ratio of anhydrous ethanol to filtrate is controlled at 1.5:3.75, while the rest is the same as in Example 1.3.

[0119] Example 7.2

[0120] A method for improving the quality of disodium ethylenediaminetetraacetate (EDTA) differs from Example 1.3 in that, in step II, the volume ratio of anhydrous ethanol to filtrate is controlled at 1.5:4, while the rest is the same as in Example 1.3.

[0121] Comparative Example 1

[0122] The difference from Example 1.3 is that in step I, sodium polyacrylate is replaced with polyacrylamide, while the rest is the same as in Example 1.3.

[0123] Comparative Examples 2.1-2.4

[0124] The difference from Example 1.3 is that in step I, the composite ultrafiltration membrane prepared in Preparation Example 1.1 is replaced with the composite ultrafiltration membrane prepared in Comparative Preparation Examples 1.1-2.2, and the rest is the same as in Example 1.3.

[0125] Comparative Example 3.1

[0126] The difference from Example 1.3 is that in step II, the volume ratio of anhydrous ethanol to filtrate is controlled to be 1.5:1, while the rest is the same as in Example 1.3.

[0127] Comparative Example 3.2

[0128] The difference from Example 1.3 is that in step II, the volume ratio of anhydrous ethanol to filtrate is controlled to be 1.5:10, while the rest is the same as in Example 1.3.

[0129] Product Testing

[0130] Referring to the description in GB 12593-2007 Working Standard Reagent Disodium Ethylenediaminetetraacetate, the purity of the standard grade disodium ethylenediaminetetraacetate (hereinafter referred to as the product) obtained by the methods of the examples and comparative examples was determined and recorded in Table 1;

[0131] Weighing record: The total amount of crude disodium ethylenediaminetetraacetate is M / g, and the product yield is m1 / g. The mother liquor is distilled under reduced pressure until a significant amount of solid precipitates, then cooled and filtered. The solid yield obtained is recorded as m2 / g. Calculate the following:

[0132] Total recovery rate % = [(m1 + m2) / M] × 100%;

[0133] Product recovery rate % = (m1 / M) × 100%;

[0134] The above calculation results are recorded in Table 1.

[0135] Table 1 Purity of EDTA-2Na

[0136]

[0137] Data Analysis:

[0138] As can be seen from Table 1, the purity of the products in Examples 1.1-1.4 can reach over 99.537%, proving that the multiple steps of the method in this application are interconnected, forming a rigorous and smooth overall scheme. Compared with the method using water recrystallization, acid-base adjustment of crystallization with ethylenediaminetetraacetic acid and sodium hydroxide, organic solvent and water extraction, it has a more significant impurity removal effect. The purity of the products in Examples 1.3-1.4 is higher than that in Example 1.1, proving that by optimizing the ratio between crude ethylenediaminetetraacetic acid disodium salt, sodium carbonate and negatively charged polymer, this application not only allows the metal salt in the system to precipitate more fully and combine with the negatively charged polymer to form a precipitate, improving the impurity removal efficiency, but also reduces the cost increase and subsequent separation difficulty caused by excessive reagents.

[0139] The difference between Examples 2.1-2.6 and Example 1.3 is that the type of negatively charged polymer was changed in this application. The product purity of Example 2.5 is higher than that of other examples, which proves that this application uses polyaspartic acid and sodium polystyrene sulfonate as negatively charged polymers. It makes full use of the high binding degree of polyaspartic acid with metal salts, good temperature resistance, and acid and alkali resistance of sodium polystyrene sulfonate. The two can also play a synergistic role, enhance the steric hindrance effect and electrostatic attraction balance of negatively charged polymers, avoid the problems of slow sedimentation or incomplete encapsulation caused by excessive or insufficient amounts, further remove the metal salts precipitated in the system, and improve the purity of the product.

[0140] The difference between Examples 3.1-3.3 and Example 2.5 is that this application further controls the weight ratio of polyaspartic acid and sodium polystyrene sulfonate. The product purity of Example 3.3 is higher than that of other examples, which proves that by adjusting the dosage, this application further enhances the balance between the steric hindrance effect and electrostatic attraction of the negatively charged polymer. Activated carbon has a better adsorption and removal effect on the precipitates formed by polyaspartic acid and sodium polystyrene sulfonate with metal salts, thus significantly improving the product purity.

[0141] The difference between Examples 4.1-4.2 and Example 1.3 is that this application changed the stirring temperature after adding the negatively charged polymer in step I. The purity of the product was found to be improved compared to Example 1.3. This proves that by limiting the stirring temperature to the range of 85-90°C, this application accelerated the interaction between the negatively charged polymer and the metal salt, reduced the residue of unreacted substances, formed a more stable precipitate, and further improved the purity of the disodium ethylenediaminetetraacetate product.

[0142] The difference between Examples 5.1-5.4 and Example 1.3 is that this application changes the raw material composition of the composite ultrafiltration membrane. The product purity of Examples 5.1-5.2 is higher than that of other examples, which proves that by optimizing the raw material ratio in the preparation process of the composite ultrafiltration membrane, this application can significantly improve the membrane flux and solvent resistance while ensuring that the composite ultrafiltration membrane has good mechanical strength, and also takes into account a wide pH range and good hydrophilicity.

[0143] Examples 6.1-6.5 further controlled the ratio of polyvinylidene fluoride and bisphenol A polycarbonate based on Example 5.1. The results showed that the purity of the product in Examples 6.1-6.2 was higher than that in other examples, proving that by optimizing the raw material ratio in the preparation process of the composite ultrafiltration membrane, this application helps to more effectively intercept impurities in the filtrate, reduce the occurrence of clogging, and thus further improve the purity of disodium ethylenediaminetetraacetate, ensuring that the final product meets the benchmark quality standard.

[0144] The difference between Examples 7.1-7.2 and Example 1.3 lies in the amount of anhydrous ethanol added. It was found that the purity of the product was improved compared to Example 1.3, proving that the present application has made recrystallization more complete by strictly controlling the volume ratio of anhydrous ethanol to filtrate.

[0145] The difference between Comparative Example 1 and Example 1.3 is that the type of negatively charged polymer was changed in this application. The results showed that the purity of the product was greatly reduced, proving that the negatively charged polymer of this application can indeed form a tighter bond with the metal salt, thereby improving the purity of the product.

[0146] The difference between Comparative Examples 2.1-2.4 and Example 1.3 is that the parameters and materials used in the preparation of the composite ultrafiltration membrane were changed in this application. The results showed that the product purity and recovery rate were reduced, which proves that the composite ultrafiltration membrane of this application has good mechanical strength, solvent resistance, wide pH range, good hydrophilicity and high membrane flux. It can efficiently intercept small molecule impurities and particles remaining in the filtrate, and effectively improve the product recovery rate and product purity.

[0147] The amount of anhydrous ethanol used in Comparative Examples 3.1-3.2 differed significantly from that in Example 1.3. The results also showed that the purity of the product in Comparative Example 3.1 was reduced, and the product yield and total recovery rate of Comparative Example 3.2 were significantly reduced. This demonstrates that by strictly controlling the amount of anhydrous ethanol added, this application has improved the product yield and purity.

[0148] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for improving the quality of disodium ethylenediaminetetraacetate, characterized by, The method comprises the following steps: I. dispersing the crude disodium ethylenediaminetetraacetate in water, adjusting the pH of the system to 9-11, adding sodium carbonate, salt separation, adding a negative polymer and stirring at a temperature of 70-95℃ for 1-2h, standing for 1-2h, adding activated carbon for adsorption, standing for 1-2h, filtering to obtain a filtrate, the weight ratio of the crude disodium ethylenediaminetetraacetate, sodium carbonate and negative polymer being 300:2:(0.5-0.8), the negative polymer comprising one or more of sodium polyacrylate, polyaspartic acid, sodium polystyrene sulfonate and sodium alginate; II. subjecting the filtrate obtained in step I to ultrafiltration, adding anhydrous ethanol to the obtained liquid phase, controlling the volume ratio of anhydrous ethanol to the filtrate to be 1.5:(2-4.5), filtering after stirring, and drying the obtained filter residue to obtain disodium ethylenediaminetetraacetate, The ultrafiltration membrane used in the ultrafiltration is a composite ultrafiltration membrane prepared according to the following method: mixing and dispersing cellulose acetate, a film-forming polymer and a pore-forming agent in an organic solvent at a weight ratio of 1:(10-30):(0.5-2), defoaming, coating, solidifying, and soaking to obtain a composite ultrafiltration membrane, the film-forming polymer comprising polyvinylidene fluoride and bisphenol A polycarbonate at a weight ratio of (7-9):(1-3).

2. The method for improving the quality of disodium ethylenediaminetetraacetate according to claim 1, characterized in that, In step I, the weight ratio of the crude disodium ethylenediaminetetraacetate, sodium carbonate and negative polymer is 300:2:(0.6-0.7).

3. The method for improving the quality of disodium ethylenediaminetetraacetate according to claim 1, characterized in that, In step I, the negative polymer comprises polyaspartic acid and sodium polystyrene sulfonate.

4. The method for improving the quality of disodium ethylenediaminetetraacetate according to claim 3, characterized in that, The weight ratio of the polyaspartic acid and sodium polystyrene sulfonate is 2:(2-3).

5. The method for improving the quality of disodium ethylenediaminetetraacetate according to claim 1, characterized in that, In step I, the stirring is performed at a temperature of 85-90℃ after adding the negative polymer.

6. The method for improving the quality of disodium ethylenediaminetetraacetate according to claim 1, characterized in that, In step II, the weight ratio of cellulose acetate, a film-forming polymer and a pore-forming agent is 1:(15-18):

1.

7. The method for improving the quality of disodium ethylenediaminetetraacetate according to claim 1, characterized by, In step II, the weight ratio of polyvinylidene fluoride and bisphenol A polycarbonate is (7.5-8):(2-2.5).

8. The method for improving the quality of disodium ethylenediaminetetraacetate according to claim 1, characterized by, In step II, the volume ratio of anhydrous ethanol to the filtrate is 1.5:(3.75-4).

9. The method for improving the quality of disodium ethylenediaminetetraacetate according to claim 1, characterized by, In step II, the stirring is performed for 10-12h, the obtained filter residue is dried at a temperature of 55-60℃, and disodium ethylenediaminetetraacetate is obtained.

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