Continuous production method of food-grade glycine

Abstract

The invention relates to the technical field of preparation of glycine, in particular to a continuous production method of food-grade glycine, which comprises the following steps: constructing a solvent reaction system and a solvent purification system by utilizing the synergistic effect of a solvent and an anti-solvent, and matching with the contents of glycine and ammonium chloride in an ammonification reaction system and the purification system to obtain the food-grade glycine. The addition proportion and dosage of the solvent and the anti-solvent in the reaction system and the purification system are determined, auxiliary conditions such as electrodialysis, membrane separation, low temperature and the like with high energy consumption and high investment are not used, repeated refining and purification of glycine are not facilitated, and by means of the constructed reaction system and purification system, the purity of glycine is improved. The food-grade glycine can be continuously produced from an initial raw material chloroacetic acid through four steps of ammonification reaction, ammonification reaction, purification and recrystallization. The problems of high alcohol consumption in alcohol precipitation, high energy consumption in cyclic utilization of a catalyst, high production cost caused by production of high-quality glycine through repeated refining and purification and the like in the current production technology are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of glycine preparation, and particularly relates to a continuous production method of food-grade glycine. Background Technique

[0002] Glycine, also known as aminoacetic acid, as one of the 20 amino acids that make up proteins, widely exists in animals. Glycine is an important chemical intermediate, and in various fields, according to the consumption ratio from high to low, they are pesticides, food, feed, medicine, etc.

[0003] At present, the industrialized and industrially promising glycine synthesis methods mainly include chloroacetic acid ammonolysis method, Strecker method, hydroxyacetonitrile method, direct hydantoin method, biosynthesis method, etc., and in China, the chloroacetic acid ammonolysis process technology is generally used to produce glycine. The chloroacetic acid ammonolysis method uses chloroacetic acid and ammonia water as starting materials, and synthesizes glycine under the action of the catalyst hexamethylenetetramine, and crystallizes out glycine by the method of alcohol precipitation. The advantages of this method are that the reaction raw materials are widely available, the synthesis process is simple, the reaction conditions are mild, the requirements for equipment materials are not high, and the operation is simple and easy for industrial production. The main problems in the production of high-quality glycine by the traditional aqueous phase method are as follows:

[0004] (1) The synthesis cycle is long, the by-product ammonium chloride is not easy to separate, the product quality is poor, and the product yield is low, generally 80%-85%;

[0005] (2) The consumption of hexamethylenetetramine catalyst is large, and it is difficult to recycle, resulting in higher production costs;

[0006] (3) It is difficult to refine glycine. Since it is difficult to separate glycine from ammonium chloride, there is still a certain amount of ammonium chloride in the separated glycine product; after multiple purifications and recrystallizations, pure glycine products of different grades are obtained, but the production cost is high and it lacks industry competitiveness;

[0007] In order to realize the recycling of the catalyst and the separation of glycine and ammonium chloride, and reduce the production cost, the prior art often separates ammonium chloride from the reaction solution and mixed crystals by high-energy-consuming and high-production-cost methods such as low-temperature cooling, membrane separation, and electrodialysis of the reaction solution, so as to realize the purification of the catalytic recycling and glycine:

[0008] Patent CN111187173A, a continuous glycine synthesis method, is divided into three parts: "ammonia dissolution", "salt formation reaction", and "amination reaction", and different reaction temperatures and reaction pH controls are adopted for the "salt formation reaction" and "amination reaction",

[0009] After adding the mixed solution containing hexamethylenetetramine and ammonia water into the solution in multiple parts and undergoing an ammoniation reaction, side reactions caused by excessive temperature and pH are avoided. However, this process requires treating the reaction solution at a low temperature of -5°C to 30°C and a crystallization time of 0.5 - 10 hours to achieve the separation of glycine and ammonium chloride mixed crystals and thus realize the catalytic cycle. However, there are still the following problems: This method using low-temperature crystallization treatment has problems such as high energy consumption and long time.

[0010] Patent CN107253916A synthesizes glycine by a two-step method. First, ammonium chloroacetate is synthesized. Under aqueous phase conditions, hexamethylenetetramine is used as a catalyst. After the reaction ends, it is cooled and centrifuged to separate the mixed crystals of aminoacetic acid and ammonium chloride. And by using the membrane separation method without using methanol alcohol precipitation, the aminoacetic acid and ammonium chloride are separated to achieve the purification of glycine, saving a large amount of energy consumption. However, there are still the following problems: This method requires using an EDI electro-deionizer with a heterogeneous ion exchange membrane, and the production cost is relatively high; as described in this patent, calculated based on 800 kg of desalination per ton of product, about 200 degrees of electricity is required (excluding power consumption), and the power consumption is relatively large, which will lead to a relatively high production cost.

[0011] Patent CN115124436A synthesizes aminoacetic acid by a one-step method. After dissolving chloroacetic acid and hexamethylenetetramine in water, an ammoniation reaction is carried out with ammonia to obtain a mixed solution of aminoacetic acid and ammonium chloride; the mixed solution is cooled and crystallized, and after centrifugation, the original solution and crystals are obtained. The original solution obtains a primary dialysis solution and an organic solution containing a catalyst and aminoacetic acid after primary electrodialysis, and the organic solution is recycled; the mixed crystals are centrifuged after being put into a saturated solution of aminoacetic acid to obtain an aminoacetic acid product and a saturated solution, and the saturated solution obtains a secondary dialysis solution and a saturated organic solution after secondary electrodialysis; the primary dialysis solution and the secondary dialysis solution are evaporated to obtain an ammonium chloride product. This method has a relatively high product yield and purity. However, there are still the following problems: This method needs to realize the recycling of the catalyst and the purification of aminoacetic acid through two-stage electrodialysis, with relatively high energy consumption and the process is not simple, increasing the production cost. Therefore, it is urgently needed to be solved. Summary of the Invention

[0012] The technical problem to be solved by the present invention is to provide a continuous production method for food-grade aminoacetic acid. This method adopts a mixed solvent crystallization method, utilizes the synergistic effect of the solvent and the anti-solvent, establishes a reaction solvent system and a purification solvent system, and adjusts the solubility of the reaction products aminoacetic acid and ammonium chloride in the system, so as to realize the separation of the mixed crystals of aminoacetic acid and ammonium chloride prepared by the ammoniation reaction from the reaction mother liquor, purify and refine the separation of aminoacetic acid and ammonium chloride in the mixed crystals, and further purify the aminoacetic acid crystals by recrystallization, and finally obtain a food-grade aminoacetic acid product.

[0013] To achieve the above object, the technical solution of the present invention is realized as follows. A continuous production method of food-grade glycine includes the following steps:

[0014] (1) Dissolve chloroacetic acid in a monohydric alcohol, and introduce ammonia gas at a set temperature to carry out an ammoniation and salification reaction to prepare ammonium chloroacetate. Ammonium chloroacetate precipitates directly in ethanol, and ammonium chloroacetate and filtrate 1 are obtained through centrifugal separation. The obtained filtrate 1 is recycled;

[0015] (2) Add the ammonium chloroacetate obtained in step (1) to the reaction system solvent, and add a certain amount of hexamethylenetetramine. At a certain temperature, introduce ammonia gas to carry out an ammoniation reaction. Glycine and ammonium chloride will precipitate in the reaction system solvent, and filtrate 2 and glycine mixed crystals are obtained through centrifugal separation. The obtained filtrate 2 is recycled;

[0016] (3) Put the glycine mixed crystals obtained in step (2) into a purification kettle equipped with a purification system solvent, and carry out refining and purification at a set temperature, and obtain purified glycine crystals and filtrate 3 through centrifugal separation;

[0017] (4) Put the purified glycine crystals obtained in step (3) into a recrystallization kettle equipped with a saturated glycine solution, carry out recrystallization at a set temperature, and obtain glycine crystals and filtrate 4 through centrifugal separation. The glycine crystals precipitated by crystallization are dried at 55 °C to obtain food-grade glycine;

[0018] (5) Carry out vacuum distillation on the filtrate 3 obtained in step (3) to recover the low-boiling solvent, and obtain ammonium chloride and the high-boiling solvent through centrifugal separation; the obtained low-boiling solvent and high-boiling solvent are used for refining and purification and recycled.

[0019] Preferably, in step (1), the monohydric alcohol is ethanol or propanol, preferably ethanol; the reaction temperature for preparing ammonium chloroacetate is 20 - 30 °C, the reaction duration is 0.5 - 1.5 h, the pH at the end of the reaction is 7.4 - 7.8, and the holding temperature is 30 - 40 °C.

[0020] Preferably, in step (1), the mass ratio of chloroacetic acid to the solvent is 0.25 - 0.40:1.

[0021] Preferably, in the reaction system solvent of step (2), the low-boiling mixed solvent is a mixed solvent of water and ethanol, and the mass ratio of water to ethanol is 1.5 - 2.0:1; the mass ratio of the low-boiling mixed solvent to the high-boiling solvent is 4 - 6:5; the mass ratio of ammonium chloroacetate, the reaction system solvent, and hexamethylenetetramine is 60 - 90:200 - 280:5 - 15.

[0022] Preferably, in step (2), in the reaction system solvent, the high-boiling solvent is glycine, ammonium chloride, or an aprotic polar organic solvent with extremely low solubility, and the boiling point of the aprotic polar organic solvent is more than 50 °C higher than that of the low-boiling mixed solvent; the aprotic polar organic solvent is any one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), and dimethyl sulfoxide (DMSO), preferably N,N-dimethylacetamide (DMAC).

[0023] Preferably, in step (2), the ammoniation reaction temperature is controlled at 53-58 °C, and by adjusting the ammonia flux, the pH of the reaction system is controlled between 7.0 and 7.5.

[0024] Preferably, in step (3), in the purification system solvent, the low-boiling solvent is water, and the high-boiling antisolvent is glycine, ammonium chloride, or an aprotic polar organic solvent with extremely low solubility, and the boiling point of the aprotic polar organic solvent is more than 50 °C higher than that of the low-boiling mixed solvent. The aprotic polar organic solvent is N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), etc., preferably N,N-dimethylacetamide (DMAC).

[0025] Preferably, in step (3), the mass ratio of the low-boiling solvent to the high-boiling antisolvent is 1.05-1.25:1; the mass ratio of the purification solvent to the glycine mixed crystal is 0.25-0.45:1; the purification temperature of the glycine mixed crystal is 45-55 °C.

[0026] Preferably, in step (4), the mass ratio of the glycine crystal to the saturated glycine solution is 0.15-0.40:1; the recrystallization temperature is 65 °C - 70 °C. After the crystal is completely dissolved, the temperature is decreased at a rate of 3 °C - 5 °C / min until it is decreased to 25 °C ± 2 °C.

[0027] Preferably, in step (5), the reduced pressure for vacuum distillation is 0.08-0.1 Mpa, and the temperature for vacuum distillation is 45 °C - 55 °C.

[0028] The beneficial effects of the present invention are reflected in:

[0029] (1) The method provided by the present invention constructs a reaction solvent system and a purification solvent system by utilizing the synergistic effect of a solvent and an anti-solvent. According to the different purposes of completely separating glycine and ammonium chloride from the reaction solution and completely separating glycine and ammonium chloride during purification, the addition ratios and dosages of the solvent and anti-solvent in the reaction system and purification system are determined. Without relying on high-energy-consuming and high-investment auxiliary conditions such as electrodialysis, membrane separation, and low temperature, relying on the constructed reaction system and purification system, food-grade glycine can be continuously produced from the initial raw material chloroacetic acid through ammoniation reaction, amination reaction, purification, and recrystallization.

[0030] (2) The method provided by the present invention realizes catalyst recycling. In the existing traditional process for producing glycine, the catalyst hexamine cannot be recycled or has a large consumption, while the method of the present invention realizes the complete separation of the product glycine, ammonium chloride, and the reaction mother liquor. The reaction mother liquor containing the catalyst can continue to be recycled and reused, realizing catalytic recycling and greatly reducing the production cost.

[0031] (3) The method provided by the present invention has low consumption of organic solvents: In the existing traditional process for producing glycine, alcohol precipitation requires 4-5 times the volume of methanol of the ammonolysis reaction solution, while the method of the present invention adopts a reaction crystallization method, without the need for alcohol precipitation, and the dosage of organic solvents is greatly reduced; moreover, the purification solvent adopts a combination of high- and low-boiling point solvents and an anti-solvent, and the solvent can be recovered and reused by vacuum distillation.

[0032] (4) The method for synthesizing glycine by the present invention has relatively low mixed crystal impurities, and the yield of glycine can reach 91%-94%, and it is easy to purify to obtain high-end quality glycine. Through one-time purification and one-time recrystallization, glycine with a content of 99.5%-99.8% can be obtained, and the chlorine content in the glycine product is lower than 0.01 wt.%, and all indicators are better than the existing process, meeting the standard requirements of food-grade glycine. Description of the Drawings

[0033] Figure 1 is the process flow chart of the present invention. Detailed Embodiments

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the specification. The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0035] Example 1

[0036] In a reactor equipped with a thermometer, stirrer, heater, and circulating water cooling device, 160 g of ammonium chloroacetate was added to the reaction system solvent composed of 180 g of DMAC, 132 g of water, and 68 g of ethanol. 10 g of hexamethylenetetramine was added as a catalyst. The reaction temperature was 53 °C. The ammoniation reaction was carried out between ammonium chloroacetate and ammonia. By adjusting the ammonia flux, the pH of the system was maintained at 7.0. During this period, when the concentration of ammonium chloroacetate in the system was monitored by HPLC and reached zero, the ammoniation reaction was stopped. Under this reaction system, after the reaction ended, glycine and ammonium chloride could directly crystallize out. The mixed crystal of glycine and ammonium chloride was obtained by centrifugal separation. The centrifugal filtrate 2 containing the catalyst entered the next ammoniation reaction for continuous recycling.

[0037] The obtained mixed crystal of glycine was put into a purification kettle equipped with a purification system solvent. The purification system solvent was composed of water and DMAC, and the mass ratio of water to DMAC was 1.05:1. The total mass ratio of the purification solvent to the mixed crystal of glycine was 0.25:1. The purification temperature was 45 °C. The purified glycine 1 crystal and filtrate 3 were obtained by centrifugal separation.

[0038] Under the condition of 25 °C ± 2 °C, a saturated glycine solution was prepared using pure water and heated to 65 °C. The obtained purified glycine crystal 1 was put into a recrystallization kettle filled with the saturated glycine solution, and the mass ratio of glycine crystal 1 to the saturated glycine solution was 0.15:1. Cooling was carried out at a rate of 3 °C / min until the temperature dropped to 25 °C ± 2 °C. Glycine would crystallize out, while a small amount of impurities such as ammonium chloride would dissolve in it. The glycine crystal and filtrate 4 were obtained by centrifugal separation. The crystallized glycine crystal was dried at 55 °C to obtain food-grade glycine.

[0039] In the ammoniation reaction, the centrifugal filtrate 2 containing the catalyst was recycled 10 times. The content of glycine in the obtained mixed crystal of glycine was 57.6 wt.%, the content of ammonium chloride was 41.1 wt.%, and the average yield of glycine was 93.9%.

[0040] After one purification and one recrystallization, the content of glycine in the obtained glycine product was 99.6 wt.%, and the chlorine content in the glycine product was 0.009 wt.%, meeting the standard requirements of food-grade glycine.

[0041] Example 2

[0042] In a reactor equipped with a thermometer, stirrer, heater, and circulating water cooling device, 165 g of ammonium chloroacetate was added to a reaction system solvent composed of 263 g of DMAC, 165 g of water, and 90 g of ethanol. 21 g of hexamethylenetetramine was added as a catalyst. The reaction temperature was 55 °C. The ammoniation reaction was carried out using ammonium chloroacetate and ammonia. By adjusting the ammonia flux, the pH of the system was maintained at 7.3. During this period, when the concentration of ammonium chloroacetate in the system was monitored by HPLC and reached zero, the ammoniation reaction was stopped. Under this reaction system, after the reaction ended, glycine and ammonium chloride could directly crystallize out. The mixed crystal of glycine and ammonium chloride was obtained by centrifugal separation. The centrifugal filtrate 2 containing the catalyst entered the next ammoniation reaction for continuous recycling.

[0043] The obtained mixed crystal of glycine was put into a purification kettle equipped with a purification system solvent. The purification system solvent was composed of water and DMAC, and the mass ratio of water to DMAC was 1.15:1. The total mass ratio of the purification solvent to the mixed crystal of glycine was 0.35:1. The purification temperature was 50 °C. The purified glycine 1 crystal and filtrate 3 were obtained by centrifugal separation.

[0044] Under the condition of 25 °C ± 2 °C, a saturated glycine solution was prepared using pure water and heated to 68 °C. The obtained purified glycine crystal 1 was put into a recrystallization kettle equipped with the saturated glycine solution. The mass ratio of glycine crystal 1 to the saturated glycine solution was 0.30:1. Cooling was carried out at a rate of 4 °C / min until the temperature dropped to 25 °C ± 2 °C. Glycine would crystallize out, while a small amount of impurities such as ammonium chloride would dissolve in it. The glycine crystal and filtrate 4 were obtained by centrifugal separation. The crystallized glycine crystal was dried at 55 °C to obtain food-grade glycine.

[0045] In the ammoniation reaction, the centrifugal filtrate 2 containing the catalyst was recycled 10 times. The content of glycine in the obtained mixed crystal of glycine was 58.3 wt.%, the content of ammonium chloride was 40.9 wt.%, and the average yield of glycine was 92.6%.

[0046] After one purification and one recrystallization, the content of glycine in the obtained glycine product was 99.7 wt.%, and the chlorine content in the glycine product was 0.006 wt.%, meeting the standard requirements of food-grade glycine.

[0047] Example 3

[0048] In a reactor equipped with a thermometer, stirrer, heater, and circulating water cooling device, 172 g of ammonium chloroacetate was added to the reaction system solvent composed of 400 g of DMAC, 210 g of water, and 110 g of ethanol. 36 g of hexamethylenetetramine was added as a catalyst. The reaction temperature was 58 °C. The ammoniation reaction was carried out between ammonium chloroacetate and ammonia. By adjusting the ammonia flux, the pH of the system was maintained at 7.5. During this period, when the concentration of ammonium chloroacetate in the system was monitored by HPLC and reached zero, the ammoniation reaction was stopped. Under this reaction system, after the reaction ended, glycine and ammonium chloride could directly crystallize out. The mixed crystals of glycine and ammonium chloride were obtained by centrifugal separation. The centrifugal filtrate 2 containing the catalyst entered the next ammoniation reaction for continuous recycling.

[0049] The obtained mixed crystals of glycine were put into a purification kettle filled with the purification system solvent. The purification system solvent was composed of water and DMAC, and the mass ratio of water to DMAC was 1.25:1. The total mass ratio of the purification solvent to the mass of the mixed crystals of glycine was 0.45:1. The purification temperature was 55 °C. The purified glycine 1 crystals and filtrate 3 were obtained by centrifugal separation.

[0050] Under the condition of 25 °C ± 2 °C, a saturated glycine solution was prepared using pure water and heated to 70 °C. The obtained purified glycine 1 crystals were put into a recrystallization kettle filled with the saturated glycine solution, and the mass ratio of the glycine 1 crystals to the saturated glycine solution was 0.45:1. Cooling was carried out at a rate of 5 °C / min until the temperature dropped to 25 °C ± 2 °C. Glycine would crystallize out, while a small amount of impurities such as ammonium chloride would dissolve in it. The glycine crystals and filtrate 4 were obtained by centrifugal separation. The crystallized glycine crystals were dried at 55 °C to obtain food-grade glycine.

[0051] In the ammoniation reaction, the centrifugal filtrate 2 containing the catalyst was recycled 10 times. The average content of glycine in the total mixed crystals of glycine obtained was 58.7 wt.%, the content of ammonium chloride was 40.3 wt.%, and the average yield of glycine was 91.3%.

[0052] After one purification and one recrystallization, the content of glycine in the obtained glycine product was 99.9 wt.%, and the chlorine content in the glycine product was 0.006 wt.%, meeting the standard requirements of food-grade glycine.

[0053] Comparative Example 1:

[0054] In a reactor equipped with a thermometer, stirrer, heater, and circulating water cooling device, 170 g of chloroacetic acid, 25 g of hexamethylenetetramine, and 500 mL of water were added and dissolved. At 60 °C, ammonia was introduced for the ammoniation reaction, and the reaction was stopped when the pH of the reaction system reached 7. 800 g of methanol was added to the reaction solution for alcohol precipitation, and the crude glycine crystals and the mother liquor containing ammonium chloride and the catalyst were obtained by centrifugal separation.

[0055] The mother liquor is subjected to primary electrodialysis treatment at a controlled temperature of 35°C to remove ammonium chloride from the mother liquor. The organic liquid containing the catalyst, a small amount of glycine, and ammonium chloride continues to circulate for the ammoniation reaction.

[0056] The obtained crude glycine crystals are dissolved in water and subjected to secondary electrodialysis treatment to obtain a glycine feed liquid and an aqueous solution containing a small amount of ammonium chloride. The glycine feed liquid is concentrated to dryness to obtain a glycine product.

[0057] In the obtained glycine product, the content of glycine is 99.2 wt.%, and the chloride ion content in the glycine product is 0.07 wt.%.

[0058] In summary, the method provided by the present invention has low consumption of organic solvents in practical applications: in the existing traditional process for producing glycine, alcohol precipitation requires 4 - 5 times the volume of methanol of the ammonolysis reaction solution, while the method of the present invention uses the reaction crystallization method, without alcohol precipitation, and the amount of organic solvent used is greatly reduced; and the purification solvent uses a combination of high and low boiling point solvents and an antisolvent, and the solvent can be recovered and reused by vacuum distillation. At the same time, the glycine mixed crystals synthesized by the method provided by the present invention have lower impurities, and the glycine yield can reach 91% - 94%, and it is easy to purify to obtain high-end quality glycine. Through one-time purification and one-time recrystallization, glycine with a content of 99.5% - 99.8% can be obtained, and the chlorine content in the glycine product is less than 0.01 wt.%. All indicators are better than the existing process, meeting the requirements of the food-grade glycine standard, and having the prospect of application and promotion.

[0059] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A continuous production method of food-grade glycine, characterized in that, It includes the following steps: (1) Dissolve chloroacetic acid in a monohydric alcohol, introduce ammonia gas at a set temperature to carry out an ammoniation and salification reaction to prepare ammonium chloroacetate. The ammonium chloroacetate precipitates directly in ethanol, and ammonium chloroacetate and filtrate 1 are obtained through centrifugal separation; the obtained filtrate 1 is recycled continuously; (2) Add the ammonium chloroacetate obtained in step (1) to the reaction system solvent, add hexamine, introduce ammonia gas to carry out an ammoniation reaction, and aminoacetic acid and ammonium chloride will crystallize out in the reaction system solvent, and filtrate 2 and aminoacetic acid mixed crystals are obtained through centrifugal separation; the obtained filtrate 2 is recycled continuously; (3) Put the aminoacetic acid mixed crystals obtained in step (2) into a purification kettle filled with a purification system solvent for refined purification, and purified aminoacetic acid crystals and filtrate 3 are obtained through centrifugal separation; (4) Put the purified aminoacetic acid crystals obtained in step (3) into a recrystallization kettle filled with a saturated aminoacetic acid solution for recrystallization, and aminoacetic acid crystals and filtrate 4 are obtained through centrifugal separation. The crystallized aminoacetic acid crystals are dried at 55 °C to obtain food-grade aminoacetic acid; (5) Carry out vacuum distillation on the filtrate 3 obtained in step (3) to recover the low-boiling solvent, and ammonium chloride and the high-boiling solvent are obtained through centrifugal separation; the obtained low-boiling solvent and high-boiling solvent are used for refined purification and recycled.

2. The continuous production method of food-grade glycine according to claim 1, characterized in that, In step (1), the monohydric alcohol is ethanol or propanol; the reaction temperature for preparing ammonium chloroacetate is 20 - 30 °C, the reaction duration is 0.5 - 1.5 h, the pH at the reaction end point is 7.4 - 7.8, and the holding temperature is 30 - 40 °C.

3. The continuous production method of food-grade glycine according to claim 1, characterized in that, In step (1), the mass ratio of the chloroacetic acid to the solvent is 0.25 - 0.40:

1.

4. A continuous production method of food-grade glycine according to claim 1, characterized in that, In step (2), the low-boiling mixed solvent is a mixed solvent of water and ethanol, and the mass ratio of water to ethanol is 1.5 - 2.0:1; the mass ratio of the low-boiling mixed solvent to the high-boiling solvent is 4 - 6:5; the mass ratio of the ammonium chloroacetate, the reaction system solvent, and hexamine is 60 - 90:200 - 280:5 - 15.

5. A continuous production method of food-grade glycine according to claim 1, characterized in that, In step (2), the high-boiling solvent is aminoacetic acid, ammonium chloride, or an aprotic polar organic solvent; the aprotic polar organic solvent is any one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), and dimethyl sulfoxide (DMSO).

6. The continuous production method of food-grade glycine according to claim 1, characterized in that, In step (2), the ammoniation reaction temperature is controlled at 53 - 58 °C, and by adjusting the ammonia gas flux, the pH of the reaction system is controlled between 7.0 - 7.

5.

7. A continuous production method of food-grade glycine according to claim 1, characterized in that, In step (3), the low-boiling solvent in the purification system solvent is water, the high-boiling anti-solvent is aminoacetic acid, ammonium chloride, or an aprotic polar organic solvent with extremely low solubility, and the boiling point of the aprotic polar organic solvent is more than 50 °C higher than that of the low-boiling mixed solvent. The aprotic polar organic solvent is any one of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC).

8. The continuous production method of food-grade glycine according to claim 1, characterized in that, In step (3), the mass ratio of the low-boiling solvent to the high-boiling anti-solvent is 1.05 - 1.25:1; the mass ratio of the purification solvent to the glycine mixed crystal is 0.25 - 0.45:1; the purification temperature of the glycine mixed crystal is 45 - 55 °C.

9. The continuous production method of food-grade glycine according to claim 1, characterized in that, In step (4), the mass ratio of the glycine crystal to the saturated glycine solution is 0.15 - 0.40:1; the temperature of recrystallization is 65 °C - 70 °C. After the crystal is completely dissolved, the temperature is decreased at a rate of 3 °C - 5 °C / min until it is decreased to 25 °C ± 2 °C.

10. The continuous production method of food-grade glycine according to claim 1, characterized in that, In step (5), the reduced pressure for vacuum distillation is 0.08 - 0.1 Mpa, and the temperature of vacuum distillation is 45 °C - 55 °C.

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