Process for the preparation of glutamic acid-n,n-diacetic acid

Abstract

This invention provides a method for preparing glutamic acid-N,N-diacetate, characterized by the following steps: a) reacting glutamic acid or its alkali metal salt or a mixture thereof with formaldehyde and hydrogen cyanide in water to prepare a dinitrile compound; b) optionally, adjusting the reaction solution with alkali once, and hydrolyzing the dinitrile compound from step a) in the presence of a catalyst to obtain a mixture of carboxylic acid and carboxylate; c) optionally, adjusting the reaction solution with alkali a second time to completely convert the carboxylic acid product into the carboxylate. The method of this invention for preparing glutamic acid-N,N-diacetate has a high reaction yield, and the obtained aqueous solution product has a low color number.

Description

Technical Field

[0001] This invention relates to the field of organic chemical engineering, and specifically to a method for preparing glutamic acid-N,N-diacetate. Background Technology

[0002] Tetrasodium glutamate-N,N-diacetic acid, abbreviated as GLDA.4Na, is a small-molecule green chelating agent capable of forming ligand compounds with common metal ions. It possesses both strong chelating ability and high efficiency, along with excellent toxicological safety and biodegradability. In recent years, it has attracted significant attention from the detergent industry, with industrially available products typically at a concentration of 47%. · 4Na aqueous solution.

[0003] About GLDA · Reported methods for preparing 4Na mainly employ routes involving the hydrolysis of the intermediate glutamate-N,N-diacetonitrile under acidic or alkaline conditions. For example, US2500019 describes the preparation of the corresponding α-amino acid-N,N-diacetic acid by reacting an α-amino acid with formaldehyde and sodium cyanide, preferably in a strongly alkaline aqueous solution, at a temperature of 30-100°C. When glutamate is used as the α-amino acid, a mixture of glutamate-N,N-diacetic acid salt and α-aminobutyric acid-N,N-diacetic acid salt is obtained because the terminal carboxyl group is partially decarboxylated under strongly alkaline conditions.

[0004] Patent DE4211713 discloses a method for preparing aminodicarboxylic acid-N,N-diacetic acid compounds by reacting aminodicarboxylic acid with formaldehyde and hydrogen cyanide, and then hydrolyzing the resulting amide and nitrile groups by adding an acid or base to the reaction mixture. It also discloses the preparation of aminodicarboxylic acid-N,N-diacetic acid salts by reacting with formaldehyde and alkali metal cyanides.

[0005] Patent CN101784514A discloses a method for preparing glutamic acid-N,N-diacetonitrile by reacting monosodium glutamate with formaldehyde and hydrogen cyanide, and then preparing high-purity GLD amide under mild acidic conditions instead of immediately hydrolyzing it under alkaline conditions to obtain diacetate, which facilitates storage and transportation. Finally, it is further hydrolyzed under alkaline conditions to obtain sodium salt of GLDA.

[0006] Patent CN101959847A discloses the preparation of aminodicarboxylic acid-N,N-diacetic acid or its salt by reacting aminodicarboxylic acid with formaldehyde and hydrogen cyanide, and by adding acid or base to the reaction mixture and hydrolyzing at 60-120°C.

[0007] However, the hydrolysis of the intermediate glutamate-N,N-diacetonitrile has certain drawbacks under both acidic and alkaline conditions. This is because the reaction of glutamate or its alkali metal salts with formaldehyde and hydrogen cyanide to form glutamate-N,N-diacetonitrile inevitably produces nitrile byproducts, such as hydroxyacetonitrile and aminoacetonitrile. Hydrolysis under acidic conditions enhances the thermal stability of glutamate-N,N-diacetonitrile and the nitrile byproducts, but it introduces difficult-to-remove byproducts; for example, hydrolysis in the presence of sulfuric acid produces inorganic impurities such as ammonium sulfate. Furthermore, most commercially available products exist in the form of alkali metal salts, increasing costs. Hydrolysis under alkaline conditions is faster, but glutamate-N,N-diacetonitrile and the nitrile byproducts are unstable under alkaline conditions and prone to polymerization, leading to problems such as increased color or decreased yield.

[0008] Therefore, there is a need to develop a method for preparing glutamic acid-N,N-diacetate with low raw material cost, few by-products, and high reaction stability. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing a tetraalkali metal salt of glutamic acid-N,N-diacetic acid, which has a high reaction yield and the obtained aqueous solution product has a low color number.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for preparing glutamic acid-N,N-diacetate includes the following steps:

[0012] a) A dinitrile compound is prepared by reacting glutamic acid or its alkali metal salt or a mixture thereof with formaldehyde and hydrogen cyanide in water;

[0013] b) Optionally, the reaction solution is alkali-adjusted once, and the dinitrile compound in step a) is hydrolyzed in the presence of a catalyst to obtain a mixture of carboxylic acid and carboxylate.

[0014] c) Optionally, the reaction solution is adjusted to a second alkali level to completely convert the carboxylic acid product into a carboxylate.

[0015] Preferably, in steps b) and c), sodium hydroxide or potassium hydroxide or a mixture thereof are used for pH adjustment.

[0016] Preferably, in the case of glutamic acid or its alkali metal salt, the alkali metal salt of glutamic acid is selected from potassium salt or sodium salt or a mixture thereof, preferably sodium salt. Preferably, the reaction product glutamic acid-N,N-diacetate is tetrapotassium glutamic acid-N,N-diacetate, tetrasodium glutamic acid-N,N-diacetate, or a mixture thereof, more preferably tetrasodium glutamic acid-N,N-diacetate.

[0017] In this invention, the molar ratio of glutamic acid or its alkali metal salt or a mixture thereof: hydrogen cyanide: formaldehyde is 1.0:(2.02-2.06):(2.01-2.05).

[0018] In some specific embodiments of the present invention, after glutamic acid or its alkali metal salt or a mixture thereof is mixed with water, it can be first mixed with 0.9-1.2 equivalents of formaldehyde, and then the remaining formaldehyde and hydrogen cyanide are added simultaneously. Alternatively, it can be first mixed with 0.9-1.2 equivalents of formaldehyde and 0.9-1.2 equivalents of hydrogen cyanide, and then the remaining formaldehyde and hydrogen cyanide are added separately or simultaneously. Regardless of the method, the pH must be maintained at acidic or neutral during the reaction. Preferably, the aqueous solution of glutamic acid or its alkali metal salt or a mixture thereof is first mixed with 0.9-1.2 equivalents of formaldehyde, and then the remaining formaldehyde and hydrogen cyanide are added simultaneously.

[0019] Since the above reaction process requires heat removal, the preferred reaction temperature is 20-50°C, and more preferably 30-40°C.

[0020] In this invention, in step b), the pH of the obtained dinitrile compound reaction solution is adjusted to 7.5-9.0, usually using hydroxides such as alkali metal hydroxides. If the pH of the dinitrile compound reaction solution is already within the required range, no further hydroxide is needed. Higher pH environments easily lead to the polymerization of dinitrile and nitrile byproducts, resulting in increased color and decreased yield. Conversely, lower pH environments result in slower hydrolysis rates, and the catalyst is relatively unstable in acidic environments. To accelerate the reaction, even lower pH environments are often required, such as pH < 3. In such cases, introduced impurities cannot be effectively separated, affecting product quality.

[0021] In this invention, step b) involves hydrolyzing the dinitrile compound reaction solution to prepare a mixture of the corresponding carboxylic acid and carboxylate. The reaction rate is slow under weakly alkaline conditions, requiring the addition of a catalyst to accelerate the reaction. The catalyst is a supported catalyst, comprising a first active component, a second active component, and a support. The first active component comprises manganese, iron, and nickel, wherein the atomic ratio of manganese, iron, and nickel is 1:0.5-2:0.1-0.5. The second active component is platinum, with a platinum loading of 0.1-1% of the catalyst mass. The support mass is 30-80% of the catalyst mass.

[0022] Preferably, the carrier is silicon dioxide.

[0023] Preferably, the amount of catalyst added accounts for 0.05-0.5% of the total weight of the reaction solution in step b), and more preferably 0.1-0.2%.

[0024] The catalyst can be loaded using impregnation or other methods known in the art. Preferably, the first active component is first loaded onto the support, and then the second active component is loaded. Preferably, the catalyst is prepared as follows:

[0025] 1) Immerse silica microspheres in an aqueous solution of manganese nitrate, ferric chloride, and nickel nitrate, and then dry them;

[0026] 2) The microspheres obtained in step 1) are mixed with tetrapropylammonium hydroxide solution, and then crystallized and calcined to obtain microspheres loaded with metal oxides;

[0027] 3) The microspheres obtained in step 2) are mixed with a chloroplatinic acid solution, and the chloroplatinic acid undergoes a photocatalytic reduction reaction under ultraviolet light. The reaction product is dried to obtain the catalyst. The reaction in step b) is carried out at a temperature of 80-105°C, preferably 90-100°C, for a reaction residence time of 3-6 hours. Under normal circumstances, a shorter residence time is combined with a higher temperature, such as 3 hours at 105°C or 6 hours at 80°C, etc.

[0028] After the reaction in step b) is completed, the catalyst needs to be separated from the reaction solution. Common separation methods include filtration, centrifugation, etc.

[0029] In this invention, the reaction solution of the carboxylic acid and carboxylate mixture obtained in step b) needs to be further reacted in an alkaline environment to obtain a product that is entirely composed of carboxylates. Preferably, the pH is adjusted to 13-14, at which point the carboxylic acid is almost absent from the reaction solution. The molar amount of hydroxide added is generally 1.0 to 1.03 times the molar amount of carboxylic acid groups in step b).

[0030] In step b), ammonia removal also occurs, that is, a certain amount of nitrogen gas is introduced during the reaction to separate the generated ammonia gas from the reaction liquid.

[0031] In this invention, step c) is carried out at a temperature of 0-50°C, preferably 20-30°C, and the reaction residence time is 0.5-3h. As mentioned above, a shorter residence time is combined with a higher temperature.

[0032] In this invention, the aqueous solution obtained after the reaction has a solid content of 30-50% by weight, and the solid mainly contains GLDA tetraalkali metal salt, preferably 38-50% by weight, more preferably 46-48% by weight.

[0033] In this invention, to obtain a product with accurate solid content, it can be concentrated by vacuum distillation or diluted by adding water.

[0034] The aqueous solution obtained in this invention can be used in oil well applications, in detergent compositions, descaling compositions, microbial compositions, micronutrient compositions, in gas desulfurization, pulp and paper bleaching, or in any of these compositions.

[0035] The technical solution provided by this invention has the following beneficial effects:

[0036] Our research revealed that the stability of the intermediate product, glutamic acid-N,N-diacetonitrile, and nitrile byproducts is closely related to the alkalinity of the hydrolysis process. Stronger alkalinity makes the nitrile groups more susceptible to the undesirable polymerization reaction. Therefore, this invention utilizes this characteristic by employing a two-stage alkalinity adjustment process. First, a weakly alkaline condition is established, and a high-temperature hydrolysis reaction is carried out in the presence of a catalyst, converting the intermediate into carboxylic acid and its carboxylate. Then, a second alkalinity adjustment is performed to completely convert the remaining carboxylic acid into its carboxylate. Furthermore, this invention found that modification of manganese, iron, and nickel oxides with the noble metal Pt results in catalysts exhibiting higher catalytic activity, leading to a more complete hydrolysis of the intermediate glutamic acid-N,N-diacetonitrile. The resulting GLDA tetraalkali metal salt exhibits a lower color number and higher reaction yield, and contains lower impurities, such as NTA impurities. Effective separation and recovery of the catalyst also results in relatively low production costs. Detailed Implementation

[0037] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the listed embodiments, and should also include any other known modifications within the scope of the claims of the present invention.

[0038] Raw material source:

[0039] Sulfuric acid, Beijing Inokai, 96%.

[0040] Manganese nitrate tetrahydrate, Aladdin, 99%

[0041] Nickel nitrate, Comio, 99%

[0042] Ferric chloride hexahydrate, Comio, 99%

[0043] Formaldehyde, Comio, 36.5%

[0044] Sodium hydroxide, Aladdin, 99%

[0045] Potassium hydroxide, Aladdin, 99%

[0046] TPAOH (Tetrapropylammonium Hydroxide), Matrix, 95%

[0047] TEOS (Tetraethyl Orthosilicate), Inokai, 99%

[0048] Chloroplatinic acid, acros, 99%

[0049] Sodium glutamate monohydrate, Inokai, 99%

[0050] Analysis method:

[0051] Glutamic acid-N,N-diacetonitrile: Liquid chromatography area normalization method, chromatographic column 5μm, 250×4.6mm (5μm porous spherical, silica-based, C18-bonded reversed-phase column), mobile phase: water: acetonitrile = 40:60, flow rate: 1mL / min, detection wavelength: 195nm, injection volume: 20μL, column temperature 30℃.

[0052] Method for detecting GLDA or its alkali metal salt content: Ferric chloride complexation potentiometric titration.

[0053] Hazen color codes: Liquid chemical product color determination method (platinum-cobalt color codes).

[0054] Free ammonia: The chemical titration method for detecting ammonia nitrogen according to national standards was used.

[0055] NTA·3Na content: quantitative analysis by liquid chromatography.

[0056] Determination of hydroxyacetonitrile content in glutamic acid-N,N-diacetonitrile: Gas chromatography was used with an Agilent 7890B instrument and a flame ionization detector (FID). The recommended column was an HP-VOC capillary column. The stationary phase was 6% cyanopropyl-phenyl-polymethylsiloxane with an inner diameter of 0.32 mm and a length of 60 m. The carrier gas N2 was 1.5 mL / min. The column temperature was initially 50 °C and held for 2 min, then increased to 80 °C at 5 °C / min, and then increased to 250 °C at 15 °C / min and held for 10 min. The vaporization chamber temperature was 150 °C, and the detector temperature was 260 °C. The injection volume was 1 μL, the split ratio was 10:1, the hydrogen flow rate was 30 mL / min, the air flow rate was 400 mL / min, and the make-up gas flow rate was 25 mL / min. The methanol content was determined by establishing a standard curve using the gas chromatography external standard method. The samples were pre-diluted 5-50 times with acetonitrile solution according to the concentration range. The determination of hydroxyacetonitrile could be done using industrial grade 40% or 50% hydroxyacetonitrile. A standard curve of 100-1000 mg / kg was established for the samples.

[0057] Example 1 (Catalyst 1)

[0058] Take 400g of water and place it in a beaker. Add 225g of TPAOH (tetrapropylammonium hydroxide) and stir. Then add 230g of TEOS (tetraethyl orthosilicate). Heat to 80℃ and stir under a sealed container for 65 minutes. Then open the container and remove the alcohol for 30 minutes. Add water to the original volume. Pour the mixture into a 1000mL crystallization vessel with a polytetrafluoroethylene liner and crystallize at 180℃ for 36 hours. After crystallization, wash the resulting turbid liquid until neutral, dry at 100℃ for 6 hours, and calcine at 540℃ for 4 hours to obtain solid S-1.

[0059] Take 200g of water, add 25.1g of manganese nitrate tetrahydrate, 13.5g of ferric chloride hexahydrate, and 9.1g of nickel nitrate. After stirring at 50℃ for 30min, take 59.2g of solid S-1 and add it to the metal solution. After adsorption for 60min, remove, filter, and dry.

[0060] Prepare 10g of 5% TPAOH solution and add 2g of S-1 loaded with metal. After stirring evenly, pour into a crystallization vessel and crystallize at 170℃ and 10r / min for 4h. After crystallization, calcine at 540℃ for 6h to obtain S-1 loaded with metal oxide.

[0061] The above-mentioned S-1, containing a metal oxide, was dispersed in a methanol solution [(V(water):V(methanol))=99:1] containing 0.042g of chloroplatinic acid, and sonicated for 15min, followed by stirring for 30min. Under N2 protection, the solution was directly irradiated with a 250W high-pressure mercury lamp for 10h, resulting in the photoreduction reaction of chloroplatinic acid and the formation of highly dispersed Pt particles, which deposited on the catalyst surface. The resulting precipitate was repeatedly washed with distilled water and dried to obtain catalyst 1.

[0062] Example 2 (Catalyst 2)

[0063] Take 200g of water, add 25.1g of manganese nitrate tetrahydrate, 27.0g of ferric chloride hexahydrate, and 3.6g of nickel nitrate. After stirring at 50℃ for 30min, add 16.6g of solid S-1 to the metal solution. After adsorption for 60min, remove, filter, and dry.

[0064] Prepare 10g of 5% TPAOH solution and add 2g of S-1 loaded with metal. After stirring evenly, pour into a crystallization vessel and crystallize at 170℃ and 10r / min for 4h. After crystallization, calcine at 540℃ for 6h to obtain S-1 loaded with metal oxide.

[0065] The above-mentioned supported metal oxide S-1 was dispersed in a methanol solution containing 0.021 g of chloroplatinic acid [(V(water):V(methanol))=99:1] and sonicated for 15 min, followed by stirring for 30 min. Under N2 protection, it was directly irradiated with a 250W high-pressure mercury lamp for 10 h, resulting in the photoreduction reaction of chloroplatinic acid, generating highly dispersed Pt particles, which were deposited on the catalyst surface. The resulting precipitate was repeatedly washed with distilled water and dried to obtain catalyst 2.

[0066] Example 3 (Catalyst 3)

[0067] Take 200g of water, add 17.9g of manganese nitrate tetrahydrate, 54.0g of ferric chloride hexahydrate, and 1.8g of nickel nitrate. Stir at 50℃ for 30min, then add 55.6g of solid S-1 to the metal solution. After adsorption for 60min, remove, filter, and dry. 23.8

[0068] Prepare 10g of 5% TPAOH solution and add 2g of S-1 loaded with metal. After stirring evenly, pour into a crystallization vessel and crystallize at 170℃ and 10r / min for 4h. After crystallization, calcine at 540℃ for 6h to obtain S-1 loaded with metal oxide.

[0069] The above-mentioned supported metal oxide S-1 was dispersed in a methanol solution containing 0.0042 g of chloroplatinic acid [(V(water):V(methanol))=99:1] and sonicated for 15 min, followed by stirring for 30 min. Under N2 protection, it was directly irradiated with a 250W high-pressure mercury lamp for 10 h, resulting in the photoreduction reaction of chloroplatinic acid, generating highly dispersed Pt particles, which were deposited on the catalyst surface. The resulting precipitate was repeatedly washed with distilled water and dried to obtain catalyst 3.

[0070] Example 4

[0071] 188.9 g of monosodium glutamate monohydrate (1.0 mol) was added to a four-necked flask equipped with a reflux condenser, dissolved in 374.4 g of water, and kept at 20 °C with stirring. 82.2 g (1.0 mol) of 36.5% formaldehyde solution was slowly added dropwise over 0.5 h, and the mixture was kept at this temperature for another 0.5 h. Separately, 83.0 g of formaldehyde solution (1.01 mol) and 54.5 g of HCN (2.02 mol) were simultaneously added dropwise to the above reaction solution, keeping the reaction temperature at 20-25 °C for 1 h. After the addition was complete, the reaction continued for 2 h, yielding 783.0 g of a pale yellow reaction solution (pH 4.3, hydroxyacetonitrile content 0.11%).

[0072] Add 50wt% sodium hydroxide solution to the reaction solution to adjust the pH to 7.5, then add 0.4g of catalyst 1, and heat to 80℃ to react. During the reaction, continuously add 50wt% sodium hydroxide solution to maintain the pH of the reaction system at 7.5. Nitrogen gas is purged throughout the process to remove ammonia. After 6 hours, no ammonia gas is detected, and the reaction is stopped. A total of 88.0g of 50% sodium hydroxide solution (1.1mol) was added. After the reaction is completed, cool to room temperature, filter, and obtain 815.0g of reaction solution.

[0073] Separately, 160.0 g (2.0 mol) of 50 wt% sodium hydroxide solution was slowly added to the above reaction solution at 0 °C. The addition was completed after 0.5 h, yielding 975 g of solution with a pH of 14.0. Based on the monosodium glutamate used, the yield was 93.6%, the GLDA·4Na content was approximately 33.8 wt%, and after vacuum concentration, the content was 38.1 wt%, the color number was 130 Hazen, and the NTA·3Na content was 0.01 wt%.

[0074] Example 5

[0075] 188.9 g of monosodium glutamate monohydrate (1.0 mol) was added to a four-necked flask equipped with a reflux condenser, dissolved in 233.6 g of water, and kept at 30 °C with stirring. 82.2 g (1.0 mol) of 36.5% formaldehyde solution was slowly added dropwise over 0.5 h, and the reaction was continued at this temperature for another 0.5 h. Separately, 83.8 g of formaldehyde solution (1.02 mol) and 54.8 g of HCN (2.03 mol) were simultaneously added dropwise to the above reaction solution, keeping the reaction temperature at 30-35 °C for 1 h. After the addition was complete, the reaction continued for 2 h, yielding 640.0 g of a pale yellow reaction solution (pH 4.2, hydroxyacetonitrile content 0.12%).

[0076] Add 50wt% sodium hydroxide solution to the reaction solution to adjust the pH to 8.0, then add 1.3g of catalyst 2, and heat to 90℃ to react. Continuously add 50wt% sodium hydroxide solution during the reaction to maintain the pH of the reaction system at 8.0. Nitrogen gas is purged throughout the process to remove ammonia. No ammonia gas is detected after 5 hours, and the reaction is stopped. A total of 96.0g of 50% sodium hydroxide solution (1.2mol) was added. After the reaction is completed, cool to room temperature, filter, and obtain 698.0g of reaction solution.

[0077] 152.0 g (1.9 mol) of 50% sodium hydroxide solution was slowly added to the above reaction solution at 10 °C. The addition was completed after 0.5 h, yielding 850 g of solution with a pH of 14.0. Based on the monosodium glutamate used, the yield was 93.9%, and the GLDA·4Na content was approximately 38.7 wt%. After concentration under reduced pressure, the content was 40.3 wt%, the color number was 168 Hazen, and the NTA·3Na content was 0.01 wt%.

[0078] Example 6

[0079] 188.9 g of monosodium glutamate monohydrate (1.0 mol) was added to a four-necked flask equipped with a reflux condenser. 149.1 g of water was added to partially dissolve it. The temperature was controlled at 45°C, and the mixture was cooled and stirred. 82.2 g (1.0 mol) of 36.5% formaldehyde solution was slowly added dropwise over 0.5 h, and the mixture was kept at this temperature for another 0.5 h. Separately, 84.7 g of formaldehyde solution (1.03 mol) and 54.8 g of HCN (2.03 mol) were simultaneously added dropwise to the above reaction solution. The reaction temperature was controlled at 45-50°C, and the addition time was 1 h. After the addition was completed, the reaction was continued for 2 h, yielding 558.0 g of a pale yellow reaction solution (pH 4.0, hydroxyacetonitrile content 0.15%).

[0080] Add 50wt% sodium hydroxide solution to the reaction solution to adjust the pH to 8.5, then add 2.9g of catalyst 3, and heat to 105℃ for reaction. During the reaction, continuously add 50wt% sodium hydroxide solution to maintain the pH of the reaction system at 8.5. Nitrogen gas is purged throughout the process to remove ammonia. After 3 hours, no ammonia gas is detected, and the reaction is stopped. A total of 100.0g of 50% sodium hydroxide solution (1.25mol) was added. After the reaction is completed, cool to room temperature, filter, and obtain 619.0g of reaction solution.

[0081] Separately, 140.0 g (1.75 mol) of 50 wt% sodium hydroxide solution was slowly added to the above reaction solution at 20 °C. The addition was completed after 0.5 h, yielding 759 g of solution with a pH of 13.0. Based on the monosodium glutamate used, the yield was 93.2%, and the GLDA·4Na content was approximately 43.1 wt%. After concentration under reduced pressure, the content was 46.0 wt%, the color number was 202 Hazen, and the NTA·3Na content was 0.01 wt%.

[0082] Example 7

[0083] 188.9 g of monosodium glutamate monohydrate (1.0 mol) was added to a four-necked flask equipped with a reflux condenser, dissolved in 233.6 g of water, and kept at 40 °C with stirring. 82.2 g (1.0 mol) of 36.5% formaldehyde solution was slowly added dropwise over 0.5 h, and the mixture was kept at this temperature for another 0.5 h. Separately, 86.3 g of formaldehyde solution (1.05 mol) and 55.4 g of HCN (2.05 mol) were simultaneously added dropwise to the above reaction solution, keeping the reaction temperature at 40-45 °C for 1 h. After the addition was complete, the reaction continued for 2 h, yielding 645.0 g of a pale yellow reaction solution (pH 4.2, hydroxyacetonitrile content 0.13%).

[0084] Add 50 wt% sodium hydroxide solution to the reaction solution to adjust the pH to 9.0, then add 0.7 g of catalyst 1, and heat to 100 °C for reaction. During the reaction, continuously add 50 wt% sodium hydroxide solution to maintain the pH of the reaction system at 9.0. Nitrogen gas is purged throughout the process to remove ammonia. After 4 hours, no ammonia gas is detected, and the reaction is stopped. A total of 104.0 g of 50 wt% sodium hydroxide solution (1.3 mol) was added. After the reaction is completed, cool to room temperature, filter, and obtain 709.2 g of reaction solution.

[0085] Separately, 140.8 g (1.76 mol) of 50 wt% sodium hydroxide solution was slowly added to the above reaction solution at 30 °C. The addition was completed after 0.5 h, yielding 850 g of solution with a pH of 13.5. Based on the monosodium glutamate used, the yield was 94.1%, the GLDA·4Na content was approximately 38.9%, and after vacuum concentration, the content was 48.0 wt%, the color number was 195 Hazen, and the NTA·3Na content was 0.01%.

[0086] Example 8

[0087] 188.9 g of monosodium glutamate monohydrate (1.0 mol) was added to a four-necked flask equipped with a reflux condenser, dissolved in 233.6 g of water, and kept at 30 °C with stirring. 82.2 g (1.0 mol) of 36.5% formaldehyde solution was slowly added dropwise over 0.5 h, and the mixture was kept at this temperature for another 0.5 h. Separately, 87.1 g of formaldehyde solution (1.06 mol) and 55.4 g of HCN (2.05 mol) were simultaneously added dropwise to the above reaction solution, keeping the reaction temperature at 30-35 °C for 1 h. After the addition was complete, the reaction continued for 2 h, yielding 646.0 g of a pale yellow reaction solution (pH 4.2, hydroxyacetonitrile content 0.15%).

[0088] Add 50wt% sodium hydroxide solution to the reaction solution to adjust the pH to 9.0, then add 1.3g of catalyst 1, and heat to 90℃ to react. During the reaction, continuously add 50wt% sodium hydroxide solution to maintain the pH of the reaction system at 9.0. Nitrogen gas is purged throughout the process to remove ammonia. After 5 hours, no ammonia gas is detected, and the reaction is stopped. A total of 104.0g of 50% sodium hydroxide solution (1.3mol) was added. After the reaction is completed, cool to room temperature, filter, and obtain 711.2g of reaction solution.

[0089] Separately, 140.8 g (1.76 mol) of 50 wt% sodium hydroxide solution was slowly added to the above reaction solution at 50 °C. The addition was completed after 0.5 h, yielding 852 g of solution with a pH of 13.5. Based on the monosodium glutamate used, the yield was 94.0%, the GLDA·4Na content was approximately 38.7%, and after vacuum concentration, the content was 47.5 wt%, color number 199 Hazen, and NTA·3Na content was 0.02%.

[0090] Comparative Example 1

[0091] 188.9 g of monosodium glutamate monohydrate (1.0 mol) was added to a four-necked flask equipped with a reflux condenser, dissolved in 233.6 g of water, and kept at 30 °C with stirring. 82.2 g (1.0 mol) of 36.5% formaldehyde solution was slowly added dropwise over 0.5 h, and the mixture was kept at this temperature for another 0.5 h. Separately, 87.1 g of formaldehyde solution (1.06 mol) and 55.4 g of HCN (2.05 mol) were simultaneously added dropwise to the above reaction solution, keeping the reaction temperature at 30-35 °C for 1 h. After the addition was complete, the reaction continued for 2 h, yielding 646.0 g of a pale yellow reaction solution (pH 4.2, hydroxyacetonitrile content 0.15%).

[0092] 104.0 g of 50% sodium hydroxide solution (1.3 mol) was added to the reaction solution, the pH was adjusted to 9.0, the temperature was raised to 90 °C, and nitrogen gas was introduced to remove ammonia during the reaction for a total of 5 h. After the reaction was completed, the solution was cooled to room temperature to obtain 713.2 g of reaction solution.

[0093] 140.8 g (1.76 mol) of 50% sodium hydroxide solution was slowly added to the above reaction solution at 50 °C. The addition was completed after 0.5 h, yielding 854 g of solution. Based on the monosodium glutamate used, the yield was 71.2%, and the content was about 38.1 wt%. After concentration under reduced pressure, the content was 47.1 wt%, the color number was 360 Hazen, and the NTA·3Na content was 0.56%.

[0094] Comparative Example 2

[0095] 188.9 g of monosodium glutamate monohydrate (1.0 mol) was added to a four-necked flask equipped with a reflux condenser, dissolved in 233.6 g of water, and kept at 30 °C with stirring. 82.2 g (1.0 mol) of 36.5% formaldehyde solution was slowly added dropwise over 0.5 h, and the mixture was kept at this temperature for another 0.5 h. Separately, 87.1 g of formaldehyde solution (1.06 mol) and 55.4 g of HCN (2.05 mol) were simultaneously added dropwise to the above reaction solution, keeping the reaction temperature at 30-35 °C for 1 h. After the addition was complete, the reaction continued for 2 h, yielding 646.0 g of a pale yellow reaction solution (pH 4.2, hydroxyacetonitrile content 0.15%).

[0096] 244.8 g (3.06 mol) of 50% sodium hydroxide solution was added to a four-necked flask. The above reaction solution was slowly added at room temperature, and the addition was completed after 0.5 h. The temperature was then raised to 90 °C. Nitrogen gas was introduced to remove ammonia during the reaction. No ammonia was detected after 4 h, and the reaction was stopped, yielding 853 g of solution. Based on the monosodium glutamate used, the yield was 90.8 wt%, and the content was about 37.4%. After concentration under reduced pressure, the content was 47.5 wt%, the color number was 346 Hazen, and the NTA·3Na content was 0.18 wt%.

[0097] Comparative Example 3

[0098] 188.9 g of monosodium glutamate monohydrate (1.0 mol) was added to a four-necked flask equipped with a reflux condenser, dissolved in 233.6 g of water, and kept at 30 °C with stirring. 82.2 g (1.0 mol) of 36.5% formaldehyde solution was slowly added dropwise over 0.5 h, and the mixture was kept at this temperature for another 0.5 h. Separately, 87.1 g of formaldehyde solution (1.06 mol) and 55.4 g of HCN (2.05 mol) were simultaneously added dropwise to the above reaction solution, keeping the reaction temperature at 30-35 °C for 1 h. After the addition was complete, the reaction continued for 2 h, yielding 646.0 g of a pale yellow reaction solution (pH 4.2, hydroxyacetonitrile content 0.15%).

[0099] Add 50% sodium hydroxide solution to the reaction solution to adjust the pH to 9.0, then add 1.3g of unloaded Pt catalyst S-1 (prepared in the same way as in Example 1, except that it is not loaded with Pt). Heat to 90°C and react. Continuously add 50% sodium hydroxide solution during the reaction to maintain the pH of the reaction system at 9.0. Nitrogen gas is purged throughout the process to remove ammonia. No ammonia gas is detected after 5 hours, and the reaction is stopped. A total of 104.0g of 50% sodium hydroxide solution (1.3mol) was added. After the reaction is completed, cool to room temperature and filter to obtain 715.1g of reaction solution.

[0100] Separately, 140.8 g (1.76 mol) of 50% sodium hydroxide solution was slowly added to the above reaction solution at 50 °C. The addition was completed after 0.5 h, yielding 855.9 g of solution with a pH of 13.5. Based on the monosodium glutamate used, the yield was 91.0%, and the GLDA·4Na content was approximately 37.3 wt%. After concentration under reduced pressure, the content was 47.5 wt%, the color number was 260 Hazen, and the NTA·3Na content was 0.09 wt%.

[0101] Although the present invention has been described in detail through the preferred embodiments described above, it should be understood that the above description should not be considered as a limitation of the present invention. Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing glutamic acid-N,N-diacetate, characterized in that, Includes the following steps: a) A dinitrile compound is prepared by reacting glutamic acid or its alkali metal salt or a mixture thereof with formaldehyde and hydrogen cyanide in water; b) Adjust the pH of the reaction solution to 7.5-9.0, and then hydrolyze the dinitrile compound from step a) in the presence of a catalyst to obtain a mixture of carboxylic acid and carboxylate. c) The reaction solution is alkali-adjusted a second time to adjust the pH to 13-14, so that the carboxylic acid product is completely converted into carboxylate. Step b) also includes the addition of a catalyst, which is a supported catalyst comprising a first active component, a second active component, and a support. The first active component comprises manganese, iron, and nickel, wherein the atomic ratio of manganese, iron, and nickel is 1:0.5-2:0.1-0.

5. The second active component is platinum, and the platinum loading is 0.1-1% of the catalyst mass. The mass of the support is 30-80% of the catalyst mass.

2. The preparation method according to claim 1, characterized in that, In steps b) and c), pH adjustment is performed using alkali metal hydroxides, respectively.

3. The preparation method according to claim 2, characterized in that, In steps b) and c), one or more of potassium hydroxide or sodium hydroxide are used, respectively.

4. The preparation method according to claim 1, characterized in that, In glutamic acid or its alkali metal salt, the alkali metal salt of glutamic acid is selected from the potassium salt or sodium salt of glutamic acid or a mixture thereof.

5. The preparation method according to claim 1, characterized in that, The glutamic acid-N,N-diacetate salt is tetrapotassium glutamic acid-N,N-diacetate, tetrasodium glutamic acid-N,N-diacetate, or a mixture thereof.

6. The preparation method according to claim 5, characterized in that, The glutamic acid-N,N-diacetate mentioned is tetrasodium glutamic acid-N,N-diacetate.

7. The preparation method according to claim 1, characterized in that, The molar ratio of the glutamic acid or its alkali metal salt or mixture thereof: hydrocyanic acid: formaldehyde is 1.0:(2.02-2.06):(2.01-2.05).

8. The preparation method according to claim 1, characterized in that, Glutamic acid, its alkali metal salt, or mixtures thereof are mixed with water, then first mixed with 0.9-1.2 equivalents of formaldehyde, and then the remaining formaldehyde and hydrogen cyanide are added. Alternatively, glutamic acid or its alkali metal salt or a mixture thereof is mixed with water, then first mixed with 0.9-1.2 equivalents of formaldehyde and 0.9-1.2 equivalents of hydrogen cyanide, and then the remaining formaldehyde and hydrogen cyanide are added.

9. The preparation method according to claim 1, characterized in that, In step a), the pH during the reaction is either acidic or neutral.

10. The preparation method according to claim 9, characterized in that, In step a), the reaction temperature is 20-50℃.

11. The preparation method according to claim 10, characterized in that, In step a), the reaction temperature is 30-40℃.

12. The preparation method according to claim 1, characterized in that, The carrier is silicon dioxide.

13. The preparation method according to claim 1, characterized in that, The amount of catalyst added is 0.05-0.5% of the total weight of the reaction solution in step b).

14. The preparation method according to claim 13, characterized in that, The amount of catalyst added accounts for 0.1-0.2% of the total weight of the reaction solution in step b).

15. The preparation method according to claim 1, characterized in that, In the preparation process of the catalyst, the first active component is first loaded onto the support, and then the second active component is loaded.

16. The preparation method according to claim 1, characterized in that, The catalyst is prepared by: 1) Immerse silica microspheres in an aqueous solution of manganese nitrate, ferric chloride, and nickel nitrate, and then dry them; 2) The microspheres obtained in step 1) are mixed with tetrapropylammonium hydroxide solution, and then crystallized and calcined to obtain microspheres loaded with metal oxides; 3) The microspheres obtained in step 2) are mixed with chloroplatinic acid solution, and the chloroplatinic acid undergoes a photocatalytic reduction reaction under ultraviolet light. The reaction product is dried to obtain the catalyst.

17. The preparation method according to claim 1, characterized in that, The reaction in step b) is carried out at a temperature of 80-105℃ for a residence time of 3-6 hours.

18. The preparation method according to claim 17, characterized in that, The reaction in step b) is carried out at a temperature of 90-100°C.

19. The preparation method according to claim 1, characterized in that, In step b), ammonia removal also occurs, where nitrogen gas is introduced to separate the generated ammonia gas from the reaction solution.

20. The preparation method according to claim 1, characterized in that, Step c) is carried out at a temperature of 0-50℃, and the reaction residence time is 0.5-3h.

21. The preparation method according to claim 20, characterized in that, Step c) is carried out at a temperature of 20-30℃.