Method for improving quality of ethylenediamine tetraacetic acid disodium salt

Abstract

The invention relates to the field of working standard reagents, and particularly discloses a method for improving the quality of disodium ethylene diamine tetraacetate, which comprises the following steps: dispersing a disodium ethylene diamine tetraacetate crude product in water, adjusting the pH value of a system, adding sodium carbonate, separating out salt, adding a negative electricity polymer, stirring, standing, adding activated carbon for adsorption, and filtering to obtain a filtrate, the negative electricity polymer comprises one or more of sodium polyacrylate, polyaspartic acid, sodium polystyrenesulfonate and sodium alginate, performing ultrafiltration on the filtrate obtained in the step I, adding absolute ethyl alcohol into the obtained liquid phase, controlling the volume ratio of the absolute ethyl alcohol to the filtrate to be 1.5: (2-4.5), filtering after stirring, and drying the obtained filter residue to obtain the negative electricity polymer. The ethylenediamine tetraacetic acid disodium salt is obtained. According to the method disclosed by the invention, a plurality of steps are linked with one another, so that a tight and smooth overall scheme is formed, and the purity of the ethylene diamine tetraacetic acid is improved to 99.5% or above.

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 Art

[0002] Disodium ethylenediaminetetraacetate is the disodium salt form of ethylenediaminetetraacetic acid (EDTA). It is easily soluble in alkaline solutions such as sodium hydroxide and sodium carbonate to form stable water-soluble complexes. It has strong chelating ability and can form stable complexes with metal ions such as calcium, magnesium, iron, and lead, thereby eliminating the catalytic oxidation effect of metal ions. Disodium ethylenediaminetetraacetate has great application significance in many fields. In the food industry, it can be used as a color fixative and antioxidant to prevent food discoloration and deterioration caused by metal ions (such as the oxidation loss of vitamin C); in the pharmaceutical field, it is used as a stabilizer for injections to inhibit blood coagulation (such as anticoagulation of blood samples), and can also be used to treat heavy metal poisoning (such as lead poisoning); in industry, it can be used as a detergent to enhance detergency, foaming power, and soften hard water; or in the rubber industry, it can be used as an activator for the redox initiation system to control the polymerization reaction rate, and can also be used as a light-sensitive material for bleaching and fixing solutions to prevent the precipitation of ferric ions.

[0003] Disodium ethylenediaminetetraacetate is divided into different purity grades, including the following grades: primary standard grade with a purity of 99.95 - 100.05%, used as a reference reagent for analytical chemistry, such as titration analysis; pharmaceutical grade meets the pharmacopoeia standard with a purity of ≥99.0%, and biological safety needs to be ensured; guaranteed reagent / analytical reagent, with purities of ≥99.5% and 99.0% respectively, used for routine laboratory tests (such as water quality analysis, environmental monitoring). Disodium ethylenediaminetetraacetate is generally purified by methods such as water recrystallization, acid-base adjustment crystallization of ethylenediaminetetraacetic acid and sodium hydroxide, and extraction with organic solvents and water. The total recovery rates of the products and mother liquors obtained by these purification methods are relatively low, generally less than 90%, and it is easy to introduce new impurities, resulting in the final pure product not meeting the quality standards of guaranteed reagent / primary standard grade. Summary of the Invention

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

[0005] A method for improving the quality of disodium ethylenediaminetetraacetate provided by this application includes the following steps: I. Disperse the crude disodium ethylenediaminetetraacetate in water, adjust the pH of the system to 9 - 11, add sodium carbonate to precipitate salts, then add a negatively charged polymer and stir at a temperature of 70 - 95 °C for 1 - 2 h, keep warm and stand for 1 - 2 h, add activated carbon for adsorption, stand for 1 - 2 h, and filter to obtain a filtrate. The weight ratio of the crude disodium ethylenediaminetetraacetate, sodium carbonate, and the 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; II. Ultrafilter the filtrate obtained in step I, and add absolute ethanol to the resulting liquid phase. Control the volume ratio of absolute ethanol to the filtrate to be 1.5:(2 - 4.5). After stirring, filter, and dry the obtained filter residue to obtain disodium ethylenediaminetetraacetate. The ultrafiltration membrane used in the ultrafiltration is a composite ultrafiltration membrane prepared by the following method: Mix and disperse cellulose acetate, a film-forming polymer, and a pore-forming agent with a weight ratio of 1:(10 - 30):(0.5 - 2) in an organic solvent. After defoaming treatment, scrape the film, cure it, and soak it to obtain a composite ultrafiltration membrane. The film-forming polymer includes polyvinylidene fluoride and bisphenol A polycarbonate with a weight ratio of (7 - 9):(1 - 3).

[0006] By adopting the above technical solution, in this application, first, sodium hydroxide is used to adjust the acidity and alkalinity, and sodium carbonate is added to precipitate positively charged metal salts in the system. Subsequently, a negatively charged polymer is added to combine with the metal salts to form a precipitate. After adsorption by activated carbon and filtration, a filtrate is obtained. Further ultrafiltration is carried out to remove the macromolecular polymers in the system. Subsequently, absolute ethanol is added to the liquid phase. Utilizing the property that the solubility of disodium ethylenediaminetetraacetate in water and absolute ethanol varies greatly, and strictly controlling the addition amount of absolute ethanol, disodium ethylenediaminetetraacetate is recrystallized in the system, and at the same time, disodium ethylenediaminetetraacetate is separated from small molecule impurities. Subsequently, the crystalline product of disodium ethylenediaminetetraacetate is dried to obtain reference-grade disodium ethylenediaminetetraacetate.

[0007] In this application, a composite ultrafiltration membrane is prepared using cellulose acetate, polyvinylidene fluoride, and bisphenol A polycarbonate. This composite ultrafiltration membrane has good mechanical strength, solvent resistance, a wide pH application range, good hydrophilicity, and high membrane flux. It can efficiently intercept the small molecule impurities and microparticles remaining in the filtrate, effectively improving the product recovery rate and product purity.

[0008] Generally speaking, the steps of the method in this application are closely linked to form a rigorous and smooth overall scheme. Compared with the methods of recrystallization with water, crystallization by adjusting the acidity and alkalinity with ethylenediaminetetraacetic acid and sodium hydroxide, and extraction with organic solvents and water, it has a more significant impurity removal effect and can successfully increase the purity of disodium ethylenediaminetetraacetate to 99.95% or above.

[0009] The specific embodiments of the present application only describe the purification process of the premium grade / reference reagent. However, the purification difficulty of other purity levels is lower than that of the premium grade / reference reagent. Therefore, those skilled in the art can make changes according to actual conditions, that is, by adjusting the parameters of the purification process, disodium EDTA of different purity levels can be produced.

[0010] When benchmark-grade disodium EDTA is finally obtained, a mother liquor is also obtained. This mother liquor is subjected to reduced-pressure distillation to remove ethanol to obtain a disodium EDTA product with a purity slightly lower than that of the benchmark grade. In industrial production, the mother liquor can be blended with the filtrate obtained in the next batch of step I and further subjected to the recrystallization step, thereby improving the raw material utilization rate and the overall industrial yield.

[0011] Preferably, in step I, the weight ratio of crude disodium edetate, sodium carbonate and negatively charged polymer is 300:2:(0.6-0.7).

[0012] By adopting the above technical solution, the present application optimizes the ratio between crude disodium ethylenediaminetetraacetic acid, sodium carbonate and negatively charged polymer, which not only enables the metal salt in the system to precipitate more fully and combine with the negatively charged polymer to form a precipitate, thereby improving the efficiency of impurity removal, but also reduces the cost increase and subsequent separation difficulty caused by excess reagents, thereby significantly improving the purity of the final product to the benchmark grade standard.

[0013] Preferably, in step I, the negatively charged polymer comprises polyaspartic acid and sodium polystyrene sulfonate.

[0014] Preferably, the weight ratio of the polyaspartic acid to sodium polystyrene sulfonate is 2:(2-3).

[0015] By adopting the above-mentioned technical solution, the present 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 polymer, avoiding the problems of slow sedimentation or incomplete wrapping caused by excess or insufficient amount. More importantly, activated carbon has a better adsorption and removal effect on the precipitate formed by polyaspartic acid, sodium polystyrene sulfonate and metal salts. Therefore, under the dual effect, the preferred polyaspartic acid and sodium polystyrene sulfonate in the present application can further remove the metal salts precipitated in the system, greatly improving the product purity.

[0016] Preferably, in the step I, the negatively charged polymer is added and stirred at a temperature of 85-90°C.

[0017] By adopting the above technical solution, the present application limits the stirring temperature within the range of 85 - 90 °C, 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.

[0018] Preferably, in the step II, the weight ratio of cellulose acetate, film-forming polymer, and pore-forming agent is 1:(15 - 18):1.

[0019] Preferably, in the step II, the weight ratio of polyvinylidene fluoride and bisphenol A polycarbonate is (7.5 - 8):(2 - 2.5).

[0020] By adopting the above technical solution, the present application optimizes the raw material ratio in the preparation process of the composite ultrafiltration membrane. While ensuring that the composite ultrafiltration membrane has good mechanical strength, it can significantly improve its membrane flux and solvent resistance, and also takes into account a wide pH application range and good hydrophilicity. This optimized ratio helps to more effectively intercept impurities in the filtrate. At this time, the internal morphology structure of the membrane becomes more orderly, and the connected pore structure increases, thereby reducing the occurrence of clogging phenomena, further improving the purity of disodium ethylenediaminetetraacetate, and ensuring that the final product meets the benchmark quality standard.

[0021] Preferably, in the step II, the volume ratio of absolute ethanol to the filtrate is 1.5:(3.75 - 4).

[0022] Preferably, in the step II, after stirring for 10 - 12 h, ultrafiltration is carried out, and the obtained filter residue is dried at a temperature of 55 - 60 °C to obtain disodium ethylenediaminetetraacetate.

[0023] By adopting the above technical solution, the present application strictly controls the volume ratio of absolute ethanol to the filtrate, making the recrystallization more complete. It also strictly controls the stirring time and drying temperature, which can not only effectively remove the residual liquid in the filter residue but also avoid damage to the product structure caused by high temperature. Finally, a benchmark-grade disodium ethylenediaminetetraacetate with high recovery rate, high purity, and stable quality is obtained.

[0024] In summary, the present application has the following beneficial technical effects: 1. By adjusting the system pH and adding sodium carbonate and negatively charged polymer, the present application can efficiently remove metal ions and other impurities. It also uses the solubility difference between absolute ethanol and the filtrate for recrystallization, and combines precisely controlled ultrafiltration and drying conditions to achieve the effective separation and purification of the target product, avoiding the problem of easily introducing new impurities in the traditional method, and significantly improving the purity of disodium ethylenediaminetetraacetate to more than 99.5%; 2. The composite ultrafiltration membrane used in this application takes into account mechanical strength, solvent resistance, hydrophilicity, high membrane flux, and broad pH adaptability, significantly improving the filtration efficiency and accuracy and ensuring a high recovery rate throughout the process. Detailed implementation mode

[0025] Material source Unless otherwise specified, all raw materials used in this application are commercially available products, specifically from the following suppliers: Cellulose acetate was purchased from Shanghai Macklin Biochemical Co., Ltd., with an acetyl substitution degree of 1.77; The pore-forming agent was purchased from Nantong Jingwei Biotechnology Co., Ltd., with the product number PVPK30, M w = 25000 - 40000; N-Methylpyrrolidone was purchased from Shanghai Macklin Biochemical Co., Ltd.; Polyvinylidene fluoride was purchased from Sinochem Lantian Fluorine Materials Co., Ltd.; Bisphenol A polycarbonate was purchased from Covestro Polymer (China) Co., Ltd., M w = 42100; Activated carbon was purchased from Henan Yujia Environmental Protection Materials Co., Ltd., first-class product, 10 - 24 mesh; Polyetheretherketone was purchased from Guangdong Yunxing Biotechnology Co., Ltd.; Sodium polyacrylate was purchased from Shandong Lingchuang Biotechnology Co., Ltd., with a density of 1.09 g / cm 3 ; Sodium alginate was purchased from Anhui Zhonghong Bioengineering Co., Ltd., with a density of 1.09 g / cm 3 ; Polyaspartic acid was purchased from Jining Yuanlian Chemical Technology Co., Ltd.; Sodium polystyrene sulfonate was purchased from Dow Chemical; Polyacrylamide was purchased from Zhengzhou Zhuohang Water Purification Materials Co., Ltd., with a density of 1.302 g / cm 3 .

[0026] The present application will be further described in detail below with reference to preparation examples, examples, and comparative examples.

[0027] In the following description of "ultrafiltration" in this application, only the ultrafiltration membrane is specifically described. The specific types of ultrafiltration machines used include, but are not limited to, cartridge ultrafiltration units, hollow fiber membrane module ultrafiltration machines, plate and frame ultrafiltration machines, spiral wound membrane module ultrafiltration machines, and tubular ultrafiltration machines. In this application, a tubular ultrafiltration machine is used for illustration, but the protection scope of this application cannot be limited accordingly.

[0028] Preparation Example 1.1 The preparation method of the composite ultrafiltration membrane includes the following steps: Disperse 10 g of cellulose acetate and 20 g of pore former in 800 mL of N-methylpyrrolidone, stir at a speed of 500 r / min until completely dissolved, then add 100 g of film-forming polymer (70 g of polyvinylidene fluoride and 30 g of bisphenol A polycarbonate), increase the stirring speed to 700 r / min, and stir until completely dissolved to form a homogeneous and stable casting solution. Let the casting solution stand for 12 h for degassing treatment, then perform ultrasonic treatment for 15 min under the condition of a power of 240 W. Pour out the casting solution, scrape the film, control the thickness of the liquid film to be 200 ± 5 μm, expose it to the air for 15 s, then immerse the plate with the liquid film in the pre-prepared ultrapure water. After the liquid film solidifies and gradually falls off from the plate, quickly transfer the solidified film to clean ultrapure water and soak it for 24 h to completely remove the residual solvent in the film. During this period, change the water every 12 h. Finally, obtain a composite ultrafiltration membrane and store it in a 30% glycerol aqueous solution for standby.

[0029] Preparation Example 1.2 A method for preparing a composite ultrafiltration membrane, comprising the following steps: Disperse 10 g of cellulose acetate and 5 g of pore former in 800 mL of N-methylpyrrolidone, stir at a speed of 500 r / min until completely dissolved, then add 300 g of film-forming polymer (270 g of polyvinylidene fluoride and 30 g of bisphenol A polycarbonate), increase the stirring speed to 700 r / min, and stir until completely dissolved to form a homogeneous and stable casting solution. Let the casting solution stand for 12 h for degassing treatment, then perform ultrasonic treatment for 15 min under the condition of a power of 240 W. Pour out the casting solution, scrape the film, control the thickness of the liquid film to be 200 ± 5 μm, expose it to the air for 15 s, then immerse the plate with the liquid film in the pre-prepared ultrapure water. After the liquid film solidifies and gradually falls off from the plate, quickly transfer the solidified film to clean ultrapure water and soak it for 24 h to completely remove the residual solvent in the film. During this period, change the water every 12 h. Finally, obtain a composite ultrafiltration membrane and store it in a 30% glycerol aqueous solution for standby.

[0030] Preparation Example 2.1 The method for preparing a composite ultrafiltration membrane is different from Preparation Example 1.1 in that: the amount of the film-forming polymer is 150 g, including 105 g of polyvinylidene fluoride and 45 g of bisphenol A polycarbonate, and the rest are the same as Preparation Example 1.1.

[0031] Preparation Example 2.2 The method for preparing a composite ultrafiltration membrane is different from Preparation Example 1.1 in that: the amount of the film-forming polymer is 180 g, including 126 g of polyvinylidene fluoride and 54 g of bisphenol A polycarbonate, and the rest are the same as Preparation Example 1.1.

[0032] Preparation Example 2.3 The preparation method of the composite ultrafiltration membrane is different from Preparation Example 1.1 in that the amount of the film-forming polymer is 200 g, including 140 g of polyvinylidene fluoride and 60 g of bisphenol A polycarbonate, and the rest are the same as Preparation Example 1.1.

[0033] Preparation Example 2.4 The preparation method of the composite ultrafiltration membrane is different from Preparation Example 1.1 in that the amount of the film-forming polymer is 250 g, including 175 g of polyvinylidene fluoride and 75 g of bisphenol A polycarbonate, and the rest are the same as Preparation Example 1.1.

[0034] Preparation Example 3.1 The preparation method of the composite ultrafiltration membrane is different from Preparation Example 2.1 in that the film-forming polymer includes 112.5 g of polyvinylidene fluoride and 37.5 g of bisphenol A polycarbonate, and the rest are the same as Preparation Example 2.1.

[0035] Preparation Example 3.2 The preparation method of the composite ultrafiltration membrane is different from Preparation Example 2.1 in that the film-forming polymer includes 120 g of polyvinylidene fluoride and 30 g of bisphenol A polycarbonate, and the rest are the same as Preparation Example 2.1.

[0036] Preparation Example 3.3 The preparation method of the composite ultrafiltration membrane is different from Preparation Example 2.1 in that the film-forming polymer includes 127.5 g of polyvinylidene fluoride and 22.5 g of bisphenol A polycarbonate, and the rest are the same as Preparation Example 2.1.

[0037] Preparation Example 3.4 The preparation method of the composite ultrafiltration membrane is different from Preparation Example 2.1 in that the film-forming polymer includes 135 g of polyvinylidene fluoride and 15 g of bisphenol A polycarbonate, and the rest are the same as Preparation Example 2.1.

[0038] Preparation Example 3.5 The preparation method of the composite ultrafiltration membrane is different from Preparation Example 2.1 in that the film-forming polymer includes 142.5 g of polyvinylidene fluoride and 7.5 g of bisphenol A polycarbonate, and the rest are the same as Preparation Example 2.1.

[0039] Comparative Preparation Example 1.1 It is different from Preparation Example 1.1 in that polyvinylidene fluoride is removed, and the amount of bisphenol A polycarbonate is adjusted to 100 g, and the rest are the same as Preparation Example 1.1.

[0040] Comparative Preparation Example 1.2 It is different from Preparation Example 1.1 in that bisphenol A polycarbonate is removed, and the amount of polyvinylidene fluoride is adjusted to 100 g, and the rest are the same as Preparation Example 1.1.

[0041] Comparative Preparation Example 2.1 The difference from Preparation Example 1.1 is that all polyvinylidene fluoride is replaced by polyetheretherketone, and the rest is the same as Preparation Example 1.1.

[0042] Comparative Preparation Example 2.2 The difference from Preparation Example 1.1 is that all bisphenol A polycarbonate is replaced by polyetheretherketone, and the rest is the same as Preparation Example 1.1.

[0043] Example 1.1 A method for improving the quality of disodium ethylenediaminetetraacetate, comprising the following steps: I. Disperse the crude disodium ethylenediaminetetraacetate in water, heat until completely dissolved, then let it stand for 1 h. After filtering out the solid matter, add sodium hydroxide to adjust the pH of the liquid phase system to 11, and then add sodium carbonate until the system pH reaches 12.5 for salting out. After 1 h, add a negatively charged polymer (sodium polyacrylate) and stir at 95 °C for 1 h. Keep warm and let it stand for 2 h, add activated carbon for adsorption, let it stand for 2 h, and then filter to obtain a filtrate. During the feeding process, control the weight ratio of the crude disodium ethylenediaminetetraacetate, sodium carbonate, and the negatively charged polymer to be 300:2:0.5; II. Ultrafilter the filtrate obtained in step I using the composite ultrafiltration membrane prepared in Preparation Example 1.1, and add absolute ethanol to the liquid phase obtained after ultrafiltration. Control the volume ratio of absolute ethanol to the filtrate to be 1.5:4.5, stir for 10 h and then filter to obtain a filter residue and a mother liquor. Dry the obtained filter residue at 60 °C to obtain disodium ethylenediaminetetraacetate, and keep the mother liquor.

[0044] Example 1.2 A method for improving the quality of disodium ethylenediaminetetraacetate, comprising the following steps: I. Disperse the crude disodium ethylenediaminetetraacetate in water, heat until completely dissolved, then let it stand for 1 h. After filtering out the solid matter, add sodium hydroxide to adjust the pH of the liquid phase system to 9, and then add sodium carbonate until the system pH reaches 12.5 for salting out. After 1 h, add a negatively charged polymer (sodium alginate) and stir at 70 °C for 2 h. Keep warm and let it stand for 1 h, add activated carbon for adsorption, let it stand for 1 h, and then filter to obtain a filtrate. During the feeding process, control the weight ratio of the crude disodium ethylenediaminetetraacetate, sodium carbonate, and the negatively charged polymer to be 300:2:0.8; II. Ultrafilter the filtrate obtained in step I using the composite ultrafiltration membrane prepared in Preparation Example 1.2, and add absolute ethanol to the obtained liquid phase. Control the volume ratio of absolute ethanol to the filtrate to be 1.5:2, stir for 8 h and then filter to obtain a filter residue and a mother liquor. Dry the obtained filter residue at 55 °C to obtain disodium ethylenediaminetetraacetate, and keep the mother liquor.

[0045] Example 1.3 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.1 in that: in Step I, the weight ratio of the crude disodium ethylenediaminetetraacetate, sodium carbonate, and negatively charged polymer is controlled to be 300:2:0.6, and the rest are the same as in Example 1.1.

[0046] Example 1.4 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.1 in that: in Step I, the weight ratio of the crude disodium ethylenediaminetetraacetate, sodium carbonate, and negatively charged polymer is controlled to be 300:2:0.7, and the rest are the same as in Example 1.1.

[0047] Example 2.1 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.3 in that: in Step I, sodium polyacrylate is replaced with polyaspartic acid, and the rest are the same as in Example 1.1.

[0048] Example 2.2 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.3 in that: in Step I, sodium polyacrylate is replaced with sodium polystyrene sulfonate, and the rest are the same as in Example 1.1.

[0049] Example 2.3 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.3 in that: in Step I, sodium polyacrylate is replaced with a 1:1 weight ratio of sodium polyacrylate and polyaspartic acid, and the rest are the same as in Example 1.1.

[0050] Example 2.4 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.3 in that: in Step I, sodium polyacrylate is replaced with a 1:1 weight ratio of sodium polyacrylate and sodium polystyrene sulfonate, and the rest are the same as in Example 1.1.

[0051] Example 2.5 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.3 in that: in Step I, sodium polyacrylate is replaced with a 1:1 weight ratio of polyaspartic acid and sodium polystyrene sulfonate, and the rest are the same as in Example 1.1.

[0052] Example 2.6 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.3 in that: in Step I, sodium polyacrylate is replaced with a 1:1 weight ratio of polyaspartic acid, sodium alginate, and sodium polystyrene sulfonate, and the rest are the same as in Example 1.1.

[0053] Example 3.1 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 2.5 in that: in Step I, the weight ratio of polyaspartic acid to sodium polystyrene sulfonate is 1:2, and the rest are the same as in Example 2.5.

[0054] Example 3.2 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different 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 are the same as in Example 2.5.

[0055] Example 3.3 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 2.5 in that: in Step I, the weight ratio of polyaspartic acid to sodium polystyrene sulfonate is 1:1.5, and the rest are the same as in Example 2.5.

[0056] Example 4.1 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.3 in that: in Step I, after adding the negatively charged polymer, stirring is carried out at a temperature of 85°C, and the rest are the same as in Example 1.3.

[0057] Example 4.2 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.3 in that: in Step I, after adding the negatively charged polymer, stirring is carried out at a temperature of 90°C, and the rest are the same as in Example 1.3.

[0058] Examples 5.1 - 5.4 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.3 in that: in Step II, the composite ultrafiltration membranes prepared in Preparation Example 1.1 are respectively replaced with the composite ultrafiltration membranes prepared in Preparation Examples 2.1 - 2.4, and the rest are the same as in Example 1.3.

[0059] Examples 6.1 - 6.5 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 5.1 in that: in Step II, the composite ultrafiltration membranes prepared in Preparation Example 2.1 are respectively replaced with the composite ultrafiltration membranes prepared in Preparation Examples 3.1 - 3.5, and the rest are the same as in Example 5.1.

[0060] Example 7.1 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.3 in that: in Step II, the volume ratio of absolute ethanol to the filtrate is controlled to be 1.5:3.75, and the rest are the same as in Example 1.3.

[0061] Example 7.2 A method for improving the quality of disodium ethylenediaminetetraacetate, which is different from Example 1.3 in that: in Step II, the volume ratio of absolute ethanol to the filtrate is controlled to be 1.5:4, and the rest are the same as in Example 1.3.

[0062] Comparative Example 1 It is different from Example 1.3 in that: in Step I, sodium polyacrylate is replaced with polyacrylamide, and the rest are the same as in Example 1.3.

[0063] Comparative Examples 2.1 - 2.4 It is different from Example 1.3 in that: in Step I, the composite ultrafiltration membrane prepared in Preparation Example 1.1 is respectively replaced with the composite ultrafiltration membranes prepared in Comparative Preparation Examples 1.1 - 2.2, and the rest are the same as in Example 1.3.

[0064] Comparative Example 3.1 It is different from Example 1.3 in that: in Step II, the volume ratio of absolute ethanol to the filtrate is controlled to be 1.5:1, and the rest are the same as in Example 1.3.

[0065] Comparative Example 3.2 It is different from Example 1.3 in that: in Step II, the volume ratio of absolute ethanol to the filtrate is controlled to be 1.5:10, and the rest are the same as in Example 1.3.

[0066] Product detection Referring to the records in "GB 12593 - 2007 Working Reference Reagent Disodium Ethylenediaminetetraacetate", the purity of the reference-grade disodium ethylenediaminetetraacetate (hereinafter referred to as the product) obtained by the methods of the examples and comparative examples was measured and recorded in Table 1; Weighing record: The total amount of the crude disodium ethylenediaminetetraacetate is M / g, the yield of the product is m1 / g. The mother liquor was subjected to vacuum distillation until a large amount of solid precipitated, and then cooled and filtered. The weight of the obtained solid was weighed and recorded as m2 / g, and the following were calculated: Total recovery rate % = [(m1 + m2) / M] × 100%; Product recovery rate % = (m1 / M) × 100%; The above calculation results were all recorded in Table 1.

[0067] Table 1 EDTA-2Na purity

[0068] Data analysis: As can be seen from Table 1, the product purity of Examples 1.1 - 1.4 can reach over 99.537%, proving that the various steps of the method of this application are closely linked, forming a rigorous and smooth overall solution. Compared with the methods of using water recrystallization, adjusting the crystallization by ethylenediaminetetraacetic acid and sodium hydroxide for acid-base, and extracting with organic solvents and water, it has a more significant impurity removal effect. Among them, the product purity of Examples 1.3 - 1.4 is higher than that of Example 1.1, proving that by optimizing the ratio among crude ethylenediaminetetraacetic acid disodium, sodium carbonate, and the negatively charged polymer in this application, not only can the metal salts in the system precipitate more fully and combine with the negatively charged polymer to form a precipitate, improving the impurity removal efficiency, but also the cost increase and subsequent separation difficulty caused by excessive reagents are reduced.

[0069] The difference between Examples 2.1 - 2.6 and Example 1.3 is that this application replaces the type of the negatively charged polymer. Among them, the product purity of Example 2.5 is higher than that of other examples, proving that this application uses polyaspartic acid and sodium polystyrene sulfonate as the negatively charged polymer, fully utilizing the high binding degree of polyaspartic acid with metal salts, good temperature resistance characteristics, and the acid and alkali resistance of sodium polystyrene sulfonate. The two can also exert a synergistic effect, enhancing the balance of the steric hindrance effect and electrostatic attraction of the negatively charged polymer, avoiding the problems of slow sedimentation or incomplete encapsulation caused by excess or deficiency, further removing the metal salts precipitated in the system, and improving the product purity.

[0070] 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. Among them, the product purity of Example 3.3 is higher than that of other examples, proving that by adjusting the dosage, this application further enhances the balance of the steric hindrance effect and electrostatic attraction of the negatively charged polymer, and the adsorption and removal effect of activated carbon on the precipitate formed by polyaspartic acid, sodium polystyrene sulfonate, and metal salts is better, greatly improving the product purity.

[0071] The difference between Examples 4.1 - 4.2 and Example 1.3 is that this application changes the stirring temperature after adding the negatively charged polymer in Step I, and it is found that the product purity has increased compared with Example 1.3, proving that by limiting the stirring temperature within the range of 85 - 90 °C in this application, the interaction between the negatively charged polymer and metal salts is accelerated, the residue of unreacted substances is reduced, and a more stable precipitate is formed, further improving the purity of the ethylenediaminetetraacetic acid disodium product.

[0072] Examples 5.1 - 5.4 are different from Example 1.3 in that the raw material composition of the composite ultrafiltration membrane is changed in this application. Among them, the product purity of Examples 5.1 - 5.2 is higher than that of other examples, proving that by optimizing the raw material ratio in the preparation process of the composite ultrafiltration membrane, this application can significantly improve its membrane flux and solvent resistance while ensuring that the composite ultrafiltration membrane has good mechanical strength, and also takes into account a wide pH application range and good hydrophilicity.

[0073] Based on Example 5.1, Examples 6.1 - 6.5 further controlled the dosage ratio of polyvinylidene fluoride and bisphenol A polycarbonate. The results showed that the product purity of Examples 6.1 - 6.2 was higher than that of 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 blockage phenomena, thereby further improving the purity of disodium ethylenediaminetetraacetate and ensuring that the final product meets the benchmark quality standard.

[0074] Examples 7.1 - 7.2 are different from Example 1.3 in the amount of anhydrous ethanol added. It was found that the product purity was improved compared to Example 1.3, proving that by strictly controlling the volume ratio of anhydrous ethanol to the filtrate, the recrystallization was more complete.

[0075] Comparative Example 1 is different from Example 1.3 in that the type of negatively charged polymer is changed in this application. The results showed that the product purity was greatly reduced, proving that the negatively charged polymer in this application can indeed form a tighter bond with metal salts, thereby improving the product purity.

[0076] Comparative Examples 2.1 - 2.4 are different from Example 1.3 in that the parameters and materials used in the preparation of the composite ultrafiltration membrane are changed in this application. The results showed that both the product purity and the recovery rate decreased, proving that the composite ultrafiltration membrane in this application has good mechanical strength, solvent resistance, a wide pH application range, good hydrophilicity, and high membrane flux, and can efficiently intercept residual small molecule impurities and microparticles in the filtrate, effectively improving the product recovery rate and product purity.

[0077] In Comparative Examples 3.1 - 3.2, the amount of anhydrous ethanol used was significantly different from that in Example 1.3. At the same time, the results showed that the product purity of Comparative Example 3.1 decreased, and the product yield and total recovery rate of Comparative Example 3.2 both decreased significantly, proving that by strictly controlling the amount of anhydrous ethanol added, the product yield and purity were improved at the same time.

[0078] The examples of this specific implementation manner are all preferred examples of this application, and do not limit the protection scope of this application accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. A method for improving the quality of disodium ethylenediaminetetraacetate, characterized in that, It includes the following steps: Disperse the crude product of disodium ethylenediaminetetraacetate in water, adjust the pH of the system to 9 - 11, add sodium carbonate, precipitate salts, then add a negatively charged polymer and stir at a temperature of 70 - 95 °C for 1 - 2 h, keep warm and stand for 1 - 2 h, add activated carbon for adsorption, stand for 1 - 2 h, filter to obtain a filtrate. The weight ratio of the crude product of disodium ethylenediaminetetraacetate, sodium carbonate and the negatively charged polymer is 300:2:(0.5 - 0.8), and the negatively charged polymer includes one or more of sodium polyacrylate, polyaspartic acid, sodium polystyrene sulfonate and sodium alginate; Ultrafilter the filtrate obtained in step I, and add absolute ethanol to the obtained liquid phase, control the volume ratio of absolute ethanol to the filtrate to be 1.5:(2 - 4.5), stir and then filter, dry the obtained filter residue to obtain disodium ethylenediaminetetraacetate, The ultrafiltration membrane used in the ultrafiltration is a composite ultrafiltration membrane prepared by the following method: Mix and disperse cellulose acetate, film-forming polymer and pore-forming agent with a weight ratio of 1:(10 - 30):(0.5 - 2) in an organic solvent, perform defoaming treatment, then scrape the film, cure and soak to obtain a composite ultrafiltration membrane. The film-forming polymer includes polyvinylidene fluoride and bisphenol A polycarbonate with a weight ratio of (7 - 9):(1 - 3).

2. The method for improving the quality of disodium ethylenediaminetetraacetate according to claim 1, wherein In the said step I, the weight ratio of the crude product of disodium ethylenediaminetetraacetate, sodium carbonate and the negatively charged polymer is 300:2:(0.6 - 0.7).

3. A method for improving the quality of disodium edetate according to claim 1, characterized in that, In the said step I, the negatively charged polymer includes polyaspartic acid and sodium polystyrene sulfonate.

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

5. A method for improving the quality of disodium ethylenediaminetetraacetate according to claim 1, characterized in that, In the said step I, stir at a temperature of 85 - 90 °C after adding the negatively charged polymer.

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

1.

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

8. A method for improving the quality of disodium ethylenediaminetetraacetate according to claim 1, characterized in that, In the said step II, the volume ratio of absolute ethanol to the filtrate is 1.5:(3.75 - 4).

9. A method for improving the quality of disodium ethylenediaminetetraacetate according to claim 1, characterized in that, In the said step II, ultrafilter after stirring for 10 - 12 h, and dry the obtained filter residue at a temperature of 55 - 60 °C to obtain disodium ethylenediaminetetraacetate.

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