Method for preparing glycine by aqueous phase method

Abstract

The invention belongs to the technical field of acyclic compounds, and particularly relates to a method for preparing glycine by an aqueous phase method. Mixing the ammonium salt aqueous solution, chloroacetic acid and a catalyst, adding ammonia gas, and carrying out ammonification reaction to obtain a reaction solution; cooling and crystallizing the reaction liquid, performing primary centrifugal separation to obtain a glycine crude product and a primary separation liquid, and drying the glycine crude product to obtain a glycine product; adding an ammonium source into the primary separation liquid for dissolving to obtain an ammonium dissolving liquid; cooling the ammonium dissolving solution, and performing secondary centrifugal separation to obtain an ammonium chloride crude product and a secondary separation solution; the ammonium chloride crude product is dried to obtain an ammonium chloride byproduct, and the secondary separation liquid continues to participate in the ammoniation reaction. According to the invention, steam consumption is reduced, the catalyst utilization rate is improved, and the product yield is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of acyclic compounds, and particularly relates to a method for preparing glycine by an aqueous phase method. Background Art

[0002] Glycine has a wide range of uses. For example, in the food field: it can be used as a biochemical reagent for medicine, feed, and food additives; as a nutritional supplement, it is mainly used for flavoring, etc.; it has a certain inhibitory effect on the reproduction of Bacillus subtilis and Escherichia coli, so it can be used as a preservative for surimi products, peanut butter, etc.; in the medical field: it is used as a drug for the study of medical microorganisms and biochemical amino acid metabolism; in the agricultural field: it is mainly used as an additive and attractant for the feed of poultry, livestock, etc.; it is used as a hydrolyzed protein additive and a synergist for hydrolyzed protein; in pesticide production, it is used to synthesize the intermediate glycine ethyl ester hydrochloride of pyrethroid insecticides, and can also synthesize the fungicide iprodione and the herbicide glyphosate solid.

[0003] The synthesis methods of glycine include the Strecker method, the phase transfer catalysis method, the chloroacetic acid ammonolysis method, etc. The commonly used synthesis method in China is the chloroacetic acid ammonolysis method. The chloroacetic acid ammonolysis method uses chloroacetic acid as the raw material, and under the catalysis of hexamine, it undergoes an ammonolysis reaction with ammonia to produce glycine and by-product ammonium chloride at the same time.

[0004] Chinese Patent CN 109836344 A discloses a method for producing glycine using organic solvents. Ethylene glycol, propylene glycol, and dimethylacetamide (DMAC) are used as organic solvents respectively, or methanol or ethanol is mixed with the above solvents as organic solvents. It can also be an organic solvent composed of several of ethylene glycol, propylene glycol, dimethylacetamide (DMAC) solvents and methanol or ethanol mixed together to synthesize glycine. Ammonium chloride can be co-produced while producing glycine. The method includes the following steps: (1) Add organic solvent and the catalyst hexamethylenetetramine to the reactor for producing glycine, add chloroacetic acid (or add solid ammonium chloroacetate), and then slowly introduce ammonia; (2) After the reaction is completed, cool down to a temperature of 35°C - 55°C and filter out the crude glycine crystals. After washing, filtering, and drying with methanol (or ethanol), the glycine product is obtained; (3) For the recycled reaction organic solvent filtered out, add chloroacetic acid or ammonium chloroacetate (the dosage of chloroacetic acid or ammonium chloroacetate is the same as that during glycine synthesis), cool down to 10°C - 35°C, and centrifuge to obtain crude ammonium chloride and the recycled reaction organic solvent containing chloroacetic acid (or ammonium chloroacetate); (4) After the crude ammonium chloride is washed with methanol (or ethanol), it is dried to obtain the ammonium chloride product; (5) For the recycled reaction organic solvent containing chloroacetic acid (or ammonium chloroacetate), introduce ammonia for glycine synthesis reaction, cool down, filter, and wash to obtain the glycine product; (6) For the recycled reaction organic solvent filtered out, add chloroacetic acid or ammonium chloroacetate again, cool down, crystallize, filter, wash, and dry to obtain the ammonium chloride product. This patent produces glycine in an organic solvent, with a large circulation volume of the organic solvent and high consumption of the organic solvent.

[0005] Chinese Patent CN 114105798 A discloses a method and equipment for continuously preparing high-purity glycine by circulating mother liquor, including the following steps: 1) The recycled mother liquor returned from the ammonium chloride reaction crystallization system is supplemented with water, methanol, and the hexamethylenetetramine catalyst; in the alcohol-water mixed solvent, ammonium chloroacetate reacts with liquid ammonia at a certain temperature and within a certain pH range to precipitate glycine crystals; 2) After the ammoniation reaction is completed, the reaction solution is slowly cooled down in multiple stages, and the crystals increase; the solid crude glycine is separated by centrifugation, and the by-produced ammonium chloride is dissolved in the mother liquor; 3) Most of the recycled mother liquor containing ammonium chloride described in step 2) enters the reaction crystallizer, and then molten chloroacetic acid and liquid ammonia are added simultaneously, and the temperature and pH are controlled within a certain range, and then centrifuged to obtain crude ammonium chloride, and the mother liquor is returned to the reaction system in step 1); 4) A small part of the recycled mother liquor containing ammonium chloride described in step 2) is successively processed by methods such as rectification, crystallization, and ammoniation to recover methanol, ammonium chloride, hexamethylenetetramine, etc. in the mother liquor respectively, and the residual liquid is sent to wastewater treatment. This patent produces glycine in an alcohol-water mixed solvent with a high methanol content, with a large circulation volume of the solvent and high treatment and recovery costs of the solvent. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing glycine by an aqueous phase method, which reduces steam consumption, improves the utilization rate of the catalyst, and has a high product yield.

[0007] The method for preparing glycine by the aqueous phase method described in the present invention comprises the following steps: (1) An ammonium salt aqueous solution, chloroacetic acid and a catalyst are mixed and then ammonia is added for ammoniation reaction to obtain a reaction solution; (2) After the reaction solution is cooled and crystallized, it is subjected to the first centrifugal separation to obtain crude glycine and a primary separation solution, and the crude glycine is dried to obtain a glycine product; (3) An ammonium source is added to the primary separation solution obtained in step (2) for dissolution to obtain an ammonium dissolution solution; (4) After the ammonium dissolution solution obtained in step (3) is cooled, it is subjected to the second centrifugal separation to obtain crude ammonium chloride and a secondary separation solution; the crude ammonium chloride is dried to obtain an ammonium chloride by-product, and the secondary separation solution is returned to step (1) to continue participating in the ammoniation reaction.

[0008] In step (1), the ammonium salt aqueous solution is an ammonium carbonate aqueous solution or an ammonium bicarbonate aqueous solution.

[0009] In step (1), the mass concentration of the ammonium salt aqueous solution is 5-15%.

[0010] In step (1), the catalyst is hexamethylenetetramine.

[0011] In step (1), the mass ratio of the ammonium salt aqueous solution, chloroacetic acid, the catalyst and ammonia is 1490-1500:396-403:4.8-5.1:70-130.

[0012] In step (1), the ammoniation reaction temperature is 60-80°C.

[0013] In step (2), the cooling crystallization temperature is 48-53°C.

[0014] In step (3), the ammonium source is ammonium carbonate or ammonium bicarbonate, and the ammonium source can also be a mixed gas of ammonia and carbon dioxide.

[0015] In step (3), the mass ratio of the ammonium source and the chloroacetic acid in step (1) is 110-115:396-403.

[0016] In step (4), it is cooled to 10-15°C.

[0017] The method for preparing glycine by the aqueous phase method described in the present invention comprises the following specific steps: (1) An ammonium salt aqueous solution, chloroacetic acid and a catalyst are mixed and then ammonia is added for ammoniation reaction to obtain a reaction solution; After the reaction solution is cooled and crystallized to precipitate glycine, the first centrifugal separation is carried out to obtain crude glycine and a primary separation liquid containing glycine, ammonium chloride and a catalyst. The crude glycine is dried to obtain a glycine product. (3)An ammonium source is added to the primary separation liquid obtained in step (2) for dissolution to obtain an ammonium-dissolved solution. (4)After the ammonium-dissolved solution obtained in step (3) is cooled, the second centrifugal separation is carried out to obtain crude ammonium chloride and a secondary separation liquid containing glycine, ammonium chloride, an ammonium source and a catalyst. The crude ammonium chloride is dried to obtain an ammonium chloride by-product, and the secondary separation liquid is returned to step (1) to continue participating in the ammoniation reaction instead of the ammonium salt aqueous solution.

[0018] The reaction mechanism of the ammoniation reaction in the present invention is as follows: Chloroacetic acid (ClCH2COOH) first reacts with an ammonium salt (ammonium carbonate or ammonium bicarbonate) to form ammonium chloroacetate (ClCH2COONH4), and then ammonium chloroacetate reacts with ammonia under the catalytic condition of hexamethylenetetramine to form glycine (NH2CH2COOH). The reaction equations are as follows: 2ClCH2COOH+(NH4)2CO3 2ClCH2COONH4+CO2+H2O ClCH2COOH+ NH4HCO3 ClCH2COONH4+CO2+H2O ClCH2COONH4+ NH3 NH2CH2COOH+ NH4Cl Chloroacetic acid can also directly react with ammonia under the catalytic condition of hexamethylenetetramine to form glycine (NH2CH2COOH). The reaction equation is as follows: ClCH2COOH+2NH3 NH2CH2COOH+ NH4Cl In the ammoniation reaction process of the present invention, part of the ammonium source required is introduced in the form of salt state NH4 + , and the other part is introduced in the form of gaseous NH3; while the existing traditional process is completely introduced in the form of gaseous NH3 or liquid NH3. During the ammoniation reaction process, the amount of NH3 used is large and difficult to control. NH4 + is more stable than NH3 and is easier to control the dosage to reduce the reaction consumption. In addition, the present invention pre-introduces an ammonium salt into the ammoniation reaction system, so that NH4 + already exists in the ammoniation reaction system before ammonia is introduced. After ammonia is introduced, the intermediate ammonium chloroacetate formed by the reaction of chloroacetic acid and the ammonium salt is more likely to directly react with ammonia, and the ammoniation reaction starts faster and the reaction efficiency is higher.

[0019] In the present invention, the solvent water continuously circulates in the production system. After obtaining the product glycine through cooling crystallization, an ammonium source is added to the solvent system to increase the ammonium ion concentration, so that the dissolution equilibrium shifts towards the direction of forming ammonium chloride crystals [NH4Cl(s)], and finally the by-product ammonium chloride is obtained.

[0020] NH4Cl(s) NH4 + +Cl - After the mixed gas of ammonia and carbon dioxide is introduced into the solvent water, it can react to form ammonium carbonate or ammonium bicarbonate. The reaction equations are as follows: 2NH3 + CO2 + H2O (NH4)2CO3 NH3 + CO2 + H2O NH4HCO3 The beneficial effects of the present invention are as follows: (1) The solvent used in the present invention is water, which reduces the consumption of organic solvents and the treatment and recovery costs; (2) The entire process system is a large circulation system, and the product yield is high; (3) There is no high-temperature section in the process, the catalyst can be kept stable and recycled, reducing consumption; (4) The products and by-products can be obtained without evaporation, thus greatly reducing the steam energy consumption; (5) Part of the ammonium source required in the process reaction is introduced in the form of salt NH4 + , and it is easy to control the dosage to reduce ammonia consumption. Brief Description of the Drawings

[0021] Figure 1 is the process flow chart of the present invention. Detailed Embodiments

[0022] The present invention will be further described below in conjunction with embodiments.

[0023] Example 1 (1) 1500 g of an ammonium carbonate aqueous solution with a mass concentration of 10%, 400 g of chloroacetic acid and 5 g of hexamine are mixed and heated to 60 °C, and ammonia gas is introduced. The reaction temperature is controlled at 65 °C and the pH is 6.8 for ammoniation reaction. When the pH reaches 7.5 and is stable, the introduction of ammonia gas is stopped. The amount of ammonia gas introduced is 93 g, and a reaction solution is obtained; (2) The reaction solution is slowly cooled to 51 °C for crystallization, and centrifuged for the first time to obtain crude glycine and a primary separation liquid. The crude glycine is dried to obtain 316.7 g of glycine product, with a glycine content of 98.9% and a calculated yield of 99.76%; (3) Add 110 g of ammonium carbonate to the primary separation liquid obtained in step (2) for dissolution to obtain an ammonium solution. (4) After cooling the ammonium solution obtained in step (3) to 10 °C, perform a second centrifugal separation to obtain crude ammonium chloride and a secondary separation liquid; the crude ammonium chloride is dried to obtain an ammonium chloride by-product, and the secondary separation liquid is returned to step (1) to continue participating in the ammoniation reaction.

[0024] Example 2 (1) Mix 1490 g of an aqueous ammonium bicarbonate solution with a mass concentration of 5%, 396 g of chloroacetic acid, and 4.8 g of hexamethylenetetramine, heat up to 60 °C, introduce ammonia gas, control the reaction temperature at 60 °C and pH 6.8, carry out the ammoniation reaction, stop introducing ammonia gas after the pH reaches 7.5 and stabilizes, with the ammonia gas introduction amount being 130 g, to obtain a reaction liquid. (2) Slowly cool the reaction liquid to 48 °C for crystallization, perform a first centrifugal separation to obtain crude glycine and a primary separation liquid, the crude glycine is dried to obtain 313.2 g of glycine product, with a glycine content of 98.6% and a calculated yield of 99.65%. (3) Add 115 g of ammonium bicarbonate to the primary separation liquid obtained in step (2) for dissolution to obtain an ammonium solution. (4) After cooling the ammonium solution obtained in step (3) to 12 °C, perform a second centrifugal separation to obtain crude ammonium chloride and a secondary separation liquid; the crude ammonium chloride is dried to obtain an ammonium chloride by-product, and the secondary separation liquid is returned to step (1) to continue participating in the ammoniation reaction.

[0025] Example 3 (1) Mix 1496 g of an aqueous ammonium carbonate solution with a mass concentration of 15%, 403 g of chloroacetic acid, and 5.1 g of hexamethylenetetramine, heat up to 60 °C, introduce ammonia gas, control the reaction temperature at 80 °C and pH 6.8, carry out the ammoniation reaction, stop introducing ammonia gas after the pH reaches 7.5 and stabilizes, with the ammonia gas introduction amount being 70 g, to obtain a reaction liquid. (2) Slowly cool the reaction liquid to 53 °C for crystallization, perform a first centrifugal separation to obtain crude glycine and a primary separation liquid, the crude glycine is dried to obtain 318.8 g of glycine product, with a glycine content of 98.8% and a calculated yield of 99.67%. (3) Add 113 g of ammonium carbonate to the primary separation liquid obtained in step (2) for dissolution to obtain an ammonium solution. (4) After cooling the ammonium solution obtained in step (3) to 15 °C, perform a second centrifugal separation to obtain crude ammonium chloride and a secondary separation liquid; the crude ammonium chloride is dried to obtain an ammonium chloride by-product, and the secondary separation liquid is returned to step (1) to continue participating in the ammoniation reaction.

[0026] The process flow chart of the present invention is shown in Figure 1 .

[0027] Comparative Example 1 Taking Example 1 in Chinese Patent CN 114105798 A as Comparative Example 1, the specific steps are as follows: Preparation of circulating mother liquor: Prepare a mixed solvent with 6.05 kg of methanol and 1.51 kg of water, introduce 1.27 kg of chloroacetic acid and 0.23 kg of liquid ammonia, and control the reaction temperature between 15 - 20 °C and the pH between 6.5 - 7.0 during the whole process.

[0028] Ammonification reaction: Dissolve 0.05 kg of hexamine in 0.03 kg of water in the reaction kettle of the hexamine batching tank, stir for 20 min and then enter the raw material tank of hexamine, and then enter the ammonification reactor through a pump; at the same time, supplement 0.12 kg of methanol from the methanol storage tank, and react with 7.56 kg of circulating mother liquor dissolved with 1.27 kg of chloroacetic acid and 0.23 kg of liquid ammonia in the ammonification reactor. In the alcohol - water mixed solvent for the ammonification reaction, the mass percentage of methanol is 80.0%; control the reaction temperature between 63 - 67 °C and the pH between 6.5 - 7.0. As the reaction proceeds, the white solid in the reactor gradually increases, and the reaction is completed after 1 h. After the reaction is completed, the reaction liquid is slowly cooled to between 15 - 20 °C in three stages, and the crystallization increases; the reaction product in the reactor is pumped into a centrifuge, the centrifugal speed is 10,000 rpm, and the centrifugal time is 3 min. Finally, 2.04 kg of glycine is obtained, the solid content is 50%, and the glycine yield is 98.9%. The purity of glycine after drying is 99.2%, and the chloride ion content is 0.30%.

[0029] Reaction crystallization: 7.56 kg of mother liquor is pumped into the reaction crystallizer, and 1.27 kg of chloroacetic acid and 0.23 kg of liquid ammonia are slowly added into the reaction crystallizer, and control the reaction temperature between 15 - 20 °C and the pH between 6.5 - 7.0 during the whole process. As the reaction proceeds, the white solid in the reactor gradually increases, and the reaction is completed after 1 h. The reaction product in the reactor is pumped into a centrifuge, the centrifugal speed is 10,000 rpm, and the centrifugal time is 3 min. Finally, 1.44 kg of crude ammonium chloride is obtained, and the solid content is 50%.

[0030] Recovery of circulating mother liquor: 0.15 kg of mother liquor is pumped into the circulating mother liquor recovery system, and 0.10 kg of methanol and 0.02 kg of water are obtained by distillation respectively, and 58.00 g of crude hexamine with a solid content of 50% is precipitated by introducing liquid ammonia, and the rest is sent to the waste liquid system.

[0031] In Comparative Example 1, an organic solvent methanol is used, and the recovery of methanol needs to be achieved by distillation, and the treatment and recovery cost of methanol is high.

[0032] Comparative Example 2 (1) 1500 g of water, 400 g of chloroacetic acid and 5 g of hexamethylenetetramine were mixed and heated to 60 °C. Ammonia gas was introduced while controlling the reaction temperature at 65 °C and the pH at 6.8 for the ammoniation reaction. The introduction of ammonia gas was stopped after the pH reached 7.5 and stabilized. The amount of ammonia gas introduced was 182 g, and a reaction solution was obtained; Other steps were the same as those in Example 1.

[0033] Comparative Example 3 (1) 1500 g of a mixed solution of methanol and water (the mass ratio of methanol to water was 4:1), 400 g of chloroacetic acid and 5 g of hexamethylenetetramine were mixed and heated to 60 °C. Ammonia gas was introduced while controlling the reaction temperature at 65 °C and the pH at 6.8 for the ammoniation reaction. The introduction of ammonia gas was stopped after the pH reached 7.5 and stabilized. The amount of ammonia gas introduced was 173 g, and a reaction solution was obtained; Other steps were the same as those in Example 1.

Claims

1. A method for preparing glycine by an aqueous phase process, characterized in that The steps include: (1) an aqueous ammonium salt solution, chloroacetic acid and a catalyst are mixed and then ammonia gas is added to carry out an amination reaction to obtain a reaction solution; (2) After the reaction solution is cooled and crystallized, it is centrifuged for the first time to obtain a crude glycine product and a primary separation liquid, and the crude glycine product is dried to obtain a glycine product; (3) adding an ammonium source to the primary separated liquid obtained in step (2) to dissolve the ammonium source to obtain an ammonium-dissolved liquid; (4) The ammonium solution obtained in step (3) is cooled and centrifuged for a second time to obtain a crude ammonium chloride product and a secondary separation liquid; the crude ammonium chloride product is dried to obtain an ammonium chloride by-product, and the secondary separation liquid is returned to step (1) to continue to participate in the amination reaction.

2. The method for preparing glycine by aqueous phase method according to claim 1, characterized in that The ammonium salt aqueous solution in step (1) is an ammonium carbonate aqueous solution or an ammonium bicarbonate aqueous solution.

3. The method for preparing glycine by aqueous phase method according to claim 1, characterized in that The mass concentration of the ammonium salt aqueous solution in step (1) is 5-15%.

4. The method for preparing glycine by aqueous phase method according to claim 1, characterized in that In step (1), the catalyst is urotropine.

5. The method for preparing glycine by aqueous phase method according to claim 1, characterized in that In step (1), the mass ratio of the ammonium salt aqueous solution, chloroacetic acid, catalyst and ammonia is 1490-1500:396-403:4.8-5.1:70-130.

6. The method for preparing glycine by aqueous phase method according to claim 1, characterized in that The amination reaction temperature in step (1) is 60-80°C.

7. The method for preparing glycine by aqueous phase method according to claim 1, characterized in that The cooling crystallization temperature in step (2) is 48-53°C.

8. The method for preparing glycine by aqueous phase method according to claim 1, characterized in that In step (3), the ammonium source is ammonium carbonate or ammonium bicarbonate.

9. The method for preparing glycine by aqueous phase method according to claim 1, characterized in that The mass ratio of the ammonium source in step (3) to the chloroacetic acid in step (1) is 110-115:396-403.

10. The method for preparing glycine by aqueous phase method according to claim 1, characterized in that In step (4), the temperature is lowered to 10-15°C.

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