Method for producing glycine by one-step synthesis and step-by-step purification in a mixed solvent

Abstract

The present invention belongs to the technical field of glycine production and discloses a method for producing glycine by one-step synthesis and step-by-step refining in a mixed solvent. The method comprises the following steps: adding chloroacetic acid and hexamethylenetetramine to a methanol aqueous solution or a synthesis mother liquor, then introducing liquid ammonia, heating the mixture to 60-65°C while introducing the liquid ammonia, and reacting for 1 hour; cooling the reaction liquid to no less than 50°C, separating the mixture, and de-washing the mixture with methanol to obtain qualified glycine and a filtrate containing ammonium chloride; cooling the filtrate containing ammonium chloride to 5-15°C, and separating the synthesis mother liquor and crude ammonium chloride; dissolving the crude ammonium chloride in an ammonium chloride purification mother liquor at 30°C, discharging the mixture at 30°C, and separating the qualified ammonium chloride and a filtrate containing glycine; and cooling the glycine-containing filtrate to 10°C, separating the crude glycine and the ammonium chloride purification mother liquor. The present invention achieves a glycine yield of over 90% through step-by-step refining and recycling of the crude glycine. The synthesis mother liquor is also recycled, reducing solvent consumption.

Description

Technical Field

[0001] The invention belongs to the technical field of glycine production, and relates to a method for producing glycine by one-step synthesis and step-by-step purification in a mixed solvent. Background Art

[0002] Glycine is an important raw material for products such as glyphosate and glycine ethyl ester hydrochloride. It can also be refined into food-grade glycine for use. The traditional domestic aqueous chloroacetic acid ammonolysis process for glycine production is as follows: add an aqueous solution containing about 25% of the catalyst urotropine to a reactor with cooling water, and at the same time, add a chloroacetic acid aqueous solution containing about 80% and introduce ammonia, and carry out the ammonolysis reaction at a pH of about 7 and a reaction temperature of about 80°C. After the reaction is completed, the ammonolysis reaction liquid containing glycine and ammonium chloride is separated by methanol precipitation to obtain the glycine product. The production of one ton of glycine will produce 12~13m 3 The methanol-containing mother liquor contains approximately 5% ammonium chloride, about 1% hexamine, and a small amount of glycine. Producing one ton of glycine requires approximately 5 tons of steam to recover the methanol. Furthermore, producing one ton of glycine consumes approximately 150 kilograms of hexamine, which cannot be recycled. Producing one ton of glycine also consumes 60-100 kilograms of methanol. After methanol is recovered from the methanol-precipitated mother liquor through distillation, dealcoholization wastewater is obtained. Evaporation and concentration of this dealcoholization wastewater yields ammonium chloride as a byproduct, which is used in fertilizer production. However, the remaining black wastewater, containing large amounts of organic matter such as hexamine and glycine, is extremely difficult to treat, polluting the environment and wasting precious resources. Therefore, the traditional aqueous glycine production process, which uses urotropine as a catalyst, has the following major problems: 1) Hexamine has low catalytic activity and requires a high concentration in the aqueous solution of the synthesis reaction. The production of one ton of glycine requires approximately 150 kilograms of catalyst, which is single-use and cannot be recycled. 2) Hexamine is easily decomposed. At high temperatures or slightly acidic conditions, it decomposes into formaldehyde and ammonia. The formaldehyde reacts with organic matter in the reaction system, condensing and polymerizing into colored, viscous impurities. 3) Wastewater containing urotropine cannot be treated biochemically due to its high concentration of formaldehyde. It can only be treated through catalytic oxidation, which greatly increases the difficulty and cost of wastewater treatment.

[0003] Patent CN101982456A discloses an environmentally friendly method for producing glycine using the chloroacetic acid method. This method utilizes the principle of the common ion effect to directly separate glycine and ammonium chloride from a glycine ammonia solution. The remaining aqueous solution containing the catalyst hexamine is supplemented with 2-4 times the amount of aqueous solution. The remaining aqueous solution is then electrodialyzed to remove the ammonium chloride. After decolorization, the resulting aqueous solution containing the catalyst hexamine is obtained. This aqueous solution must be evaporated under reduced pressure and concentrated before reuse.

[0004] Patent CN102838497A discloses a clean production process for glycine: The glycine amination reaction solution is first cooled and crystallized, then filtered to produce a mixed crystal solid of glycine and ammonium chloride and a filtrate. The filtrate is diluted with an aqueous solution, and then the ammonium chloride in the solution is separated by electrodialysis. The separated ammonium chloride solution is first evaporated and concentrated to remove 30-50% of the water. The mixed crystal solid of glycine and ammonium chloride separated by cooling and crystallization is then added to the solution. Glycine is then crystallized again, and the aqueous solution is recycled. This solution has the following major problems: First, the glycine product cannot be directly obtained from the glycine amination reaction liquid. Only a mixed crystal solid of glycine and ammonium chloride can be obtained first, which requires subsequent treatment to obtain the glycine product. Second, the amination reaction liquid needs to be diluted with water before it can be used for electrodialysis treatment. The reaction liquid must be evaporated and concentrated before it can be reused. Another point, and the most important one, is that the amination reaction contains by-product impurities. As the amination reaction liquid is recycled more and more times, the impurities are enriched and the color becomes darker, which will seriously affect the quality of the glycine product.

[0005] Patent CN1176062C discloses a method for producing glycine by an alcohol phase process. Although the catalyst can be recycled, there is no good way to separate the mixed crystal solid of glycine and ammonium chloride obtained by the reaction. Separation can only be done by electrodialysis or alcohol precipitation, which consumes a lot of energy.

[0006] Patent CN111196768A discloses a method for preparing glycine using the common ion effect. However, since ammonium chloroacetate is produced separately during production, the resulting mother liquor turns red after several cycles and cannot be reused, requiring separate disposal, generating a significant amount of wastewater and solid waste. Furthermore, ammonium chloroacetate reacts slowly during the glycine synthesis process, requiring an excess of ammonia for complete reaction. This increases the production of harmful gases and heightens safety risks.

[0007] In summary, the improved glycine production method still has the problem that the separation method of the mixed crystal solid of glycine and ammonium chloride consumes a lot of energy, or the mother liquor cannot be recycled and the wastewater treatment is difficult. Summary of the Invention

[0008] The present invention addresses the technical problems of high energy consumption, inability to recycle mother liquor, and difficulty in wastewater treatment in the prior art of glycine production. The present invention provides a method for producing glycine through one-step synthesis and step-by-step refining in a mixed solvent. The method achieves a glycine yield of over 90% through step-by-step cooling and refining. The filtrate is recycled, reducing solvent consumption. The entire process generates no wastewater, significantly reducing sewage treatment costs.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for producing glycine by one-step synthesis and step-by-step purification in a mixed solvent, comprising the following steps:

[0011] 1) Add measured amounts of chloroacetic acid and hexamethylenetetramine to a methanol-water solution or synthetic mother liquor with a water content of 20-30%, then introduce measured amounts of liquid ammonia, while heating to 60-65°C and reacting for 1 hour;

[0012] 2) Cooling the reaction solution to no less than 50°C, separating, and de-eluting with methanol to obtain qualified glycine and a filtrate containing ammonium chloride;

[0013] 3) The filtrate containing ammonium chloride is cooled to 5-15°C to separate the synthesis mother liquor and crude ammonium chloride. The synthesis mother liquor is returned to step 1) for recycling;

[0014] 4) The crude ammonium chloride obtained in step 3) is dissolved in the ammonium chloride purification mother liquor at 30°C, and the mixture is discharged at 30°C to separate qualified ammonium chloride and a filtrate containing glycine. The filtrate containing glycine is cooled to 10°C to separate crude glycine and an ammonium chloride purification mother liquor. The ammonium chloride purification mother liquor is returned to dissolve the crude ammonium chloride, and the obtained crude glycine is returned to step 1).

[0015] In one technical solution, the mass ratio of the methanol aqueous solution or synthetic mother liquor to chloroacetic acid is 10:1.

[0016] In one technical solution, the mass ratio of chloroacetic acid to hexamethylenetetramine is 10:1.

[0017] In one technical solution, when the synthetic mother liquor obtained in step 3) is recycled for more than 10 times, activated carbon is added for adsorption treatment for 0.5 to 1 hour, and after removing the activated carbon, the mother liquor is returned to step 1) for continued recycling.

[0018] In one technical solution, the amount of activated carbon added is 1-2% of the total mass of the synthesis mother liquor.

[0019] The present invention recycles the synthesis mother liquor to replace the fresh methanol-water solution prepared in step 1). This replacement can be partial or complete. When using the synthesis mother liquor to replace the methanol-water solution, it is important to note the following: 1) Because the separation step removes a certain amount of water, reducing the moisture content of the synthesis mother liquor, the moisture content fluctuates with each recycling of the synthesis mother liquor. When the moisture content is high, the crystallization temperature of ammonium chloride should be low; when the moisture content is low, the crystallization temperature of ammonium chloride should be high. Therefore, when the first discharge is performed after the reaction, the moisture content of the reaction liquid should be measured to determine the initial discharge temperature. For example, when the moisture content of the reaction liquid is 29.5%, the initial discharge temperature is 50°C; when the moisture content of the reaction liquid is 23.3%, the initial discharge temperature is 57°C. 2) Pay attention to the hexamine catalyst content in the synthesis mother liquor. Determine whether to add more hexamine catalyst by testing the filtrate for hexamine catalyst content. Generally, synthesis mother liquors with a higher number of cycles contain more catalyst and do not require additional catalyst during the cycle. 3) After a certain number of reuses of the synthesis mother liquor, due to the decomposition of a small amount of hexamine and the presence of side reactions, certain macromolecular substances will be produced. These have a certain dispersing effect and can deteriorate the crystal quality. For filtrates that have been recycled more than 10 times, add 1-2% of the total weight of activated carbon for adsorption treatment at 50°C. After adsorption for 0.5-1 hour, remove the activated carbon, and the synthesis mother liquor can be further recycled.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention synthesizes glycine in a methanol-water mixed solvent in one step. The reaction conditions are mild, and the temperature is reduced from 80° C. to 60-65° C. The reaction speed is fast, the reaction is thorough, and excessive ammonia is not passed, thereby reducing ammonia consumption and reducing the generation of harmful gases during the production process. The yield of glycine is high and can reach over 90% through step-by-step refining and recycling of crude glycine.

[0022] The present invention recycles the synthesis mother liquor obtained in the step-by-step refining, which, on the one hand, greatly reduces the loss of methanol solvent, and on the other hand, omits the steam consumption for recovering methanol compared with the traditional process. Still further, the entire process does not generate wastewater, greatly reducing the cost of sewage treatment. In addition, the catalyst hexamethylenetetramine is also in the synthesis mother liquor and can be recycled, which greatly reduces the consumption of the catalyst to less than 50 kg / ton, thereby reducing the production cost.

[0023] The invention uses the ammonium chloride purification mother liquor obtained in the graded refining of crude ammonium chloride for the crude ammonium chloride, thereby realizing the recycling of the ammonium chloride purification mother liquor. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1The present invention is a flow chart of the method for producing glycine by one-step synthesis and step-by-step purification in a mixed solvent. DETAILED DESCRIPTION

[0025] The following examples are used to illustrate the present invention but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. The test methods in the following examples are all conventional methods unless otherwise specified.

[0026] Example 1

[0027] like Figure 1 As shown in the flow diagram, the steps of the method for producing glycine by one-step synthesis and step-by-step purification in a mixed solvent in this embodiment are as follows:

[0028] 1) In a 1000 ml four-necked round-bottom flask, add 600 g of the synthesis mother liquor, which had been recycled three times, followed by 60 g of solid chloroacetic acid and 3 g of hexamethylenetetramine. Ammonia gas was introduced at 30°C, with a pH of 4.54. The temperature was gradually raised, maintaining the temperature between 60 and 65°C. Ammonia flow was continued for 2 hours. When the pH reached 7, the flow was stopped and the temperature was maintained at 64°C for 1 hour. The water content of the reaction solution was sampled and determined to be 29.5%. The discharge temperature of the reaction solution was determined to be 50°C, and the pH at the time of discharge was 6.93.

[0029] 2) The reaction solution was cooled to 50°C, filtered, and then de-eluted with methanol to obtain 33.5 g of qualified glycine and a filtrate containing ammonium chloride. The first-stage yield of glycine reached 70.3%.

[0030] 3) Cool the filtrate containing ammonium chloride to 10°C and filter to obtain the synthetic mother liquor and 42 g of crude ammonium chloride (a mixture containing 70.9% ammonium chloride and 29.0% glycine).

[0031] 4) Dissolve 42 g of crude ammonium chloride in 200 g of ammonium chloride purification mother liquor at 30°C, discharge the material and filter at 30°C to obtain 24 g of qualified ammonium chloride (ammonium chloride content is 98%) and a filtrate containing glycine. The filtrate containing glycine is cooled to 10°C and filtered to obtain 17.2 g of crude glycine (containing 70% glycine and 30% ammonium chloride) and ammonium chloride purification mother liquor.

[0032] Example 2

[0033] like Figure 1 As shown in the flow diagram, the steps of the method for producing glycine by one-step synthesis and step-by-step purification in a mixed solvent in this embodiment are as follows:

[0034] 1) To a 1000 ml four-necked round-bottom flask, 600 g of a synthetic mother liquor that had been recycled four times was added, followed by 60 g of solid chloroacetic acid. No hexamine was added. 17.2 g of crude glycine (70% glycine and 30% ammonium chloride) obtained in Example 2 was added. Ammonia gas was introduced at 30°C, with a pH of 4.71. The temperature was gradually raised, controlling the temperature not to exceed 65°C. Ammonia was introduced for 2 hours, and when the pH reached 7.1, the ammonia flow was stopped. The reaction mixture was then incubated at 65°C for 1 hour. A sample was taken to determine the water content of the reaction solution, which was 29.4%. The discharge temperature was determined to be 51°C, and the pH during discharge was 6.97.

[0035] 2) The reaction solution was cooled to 51°C, filtered, and then de-eluted with methanol to obtain 44.5 g of qualified glycine and a filtrate containing ammonium chloride. The first-stage yield of glycine reached 93.4%.

[0036] 3) The filtrate containing ammonium chloride was cooled to 10°C and discharged into a centrifuge for centrifugation to obtain a synthetic mother liquor and 49.3 g of crude ammonium chloride (a mixture containing 70.5% ammonium chloride and 28.8% glycine).

[0037] 4) Dissolve 49.3 g of crude ammonium chloride in 220 g of ammonium chloride purification mother liquor at 30°C, and filter at 30°C to obtain 28.5 g of qualified ammonium chloride (ammonium chloride content is 98%) and a filtrate containing glycine. The filtrate containing glycine is cooled to 10°C and centrifuged to obtain 19.4 g of crude glycine (containing 69% glycine and 30.5% ammonium chloride) and ammonium chloride purification mother liquor.

[0038] Example 3

[0039] like Figure 1 As shown in the flow diagram, the steps of the method for producing glycine in a mixed solvent by one-step synthesis and step-by-step cooling are as follows:

[0040] 1) First, add 6g of activated carbon to 600g of the synthetic mother liquor, which had been recycled 10 times, at 50°C. After removing the activated carbon, add it to a 1000ml four-necked round-bottom flask. Then, add 60g of solid chloroacetic acid and 3g of methenamine. At 30°C and a pH of 4.55, introduce ammonia gas. Gradually increase the temperature, controlling it not to exceed 65°C. Ammonia flow is continued for 2 hours. When the pH reaches 7, the flow is stopped and the temperature is maintained at 65°C for 1 hour. Samples of the reaction solution are taken and the water content is 22%. The discharge temperature is determined to be 58°C, and the pH during discharge is 6.97.

[0041] 2) The reaction solution was cooled to 58°C, filtered, and then de-eluted with methanol to obtain 33.1 g of qualified glycine and a filtrate containing ammonium chloride. The first-stage yield of glycine reached 69.5%.

[0042] 3) Cool the filtrate containing ammonium chloride to 10°C and filter with suction to obtain the synthetic mother liquor and 40.3 g of crude ammonium chloride (a mixture containing 70.5% ammonium chloride and 28% glycine).

[0043] 4) Dissolve 40.3 g of crude ammonium chloride in 200 g of purified ammonium chloride mother liquor at 30°C, discharge the mixture at 30°C and filter to obtain 25.4 g of qualified ammonium chloride (ammonium chloride content: 98%) and a filtrate containing glycine. The filtrate containing glycine is cooled to 10°C and filtered to obtain 14.2 g of crude glycine (containing 70.8% glycine and 29.5% ammonium chloride) and purified ammonium chloride mother liquor.

[0044] Example 4

[0045] like Figure 1 As shown in the flow diagram, the steps of the method for producing glycine by one-step synthesis and step-by-step purification in a mixed solvent in this embodiment are as follows:

[0046] 1) At 12.5m 3 8000 kg of five-times recycled synthesis mother liquor was added to a reactor, along with 800 kg of solid chloroacetic acid and 25 kg of methenamine. At 30°C and a pH of 4.83, a total of 282 kg of ammonia was introduced over 3.5 hours. The temperature was controlled to not exceed 65°C, achieving a pH of 6.78. The reaction mixture was then held at 65°C for 1 hour. The water content of the reaction solution was sampled and determined to be 23.3%. The discharge temperature was then determined to be 57°C.

[0047] 2) The reaction solution was cooled to 57°C and discharged into a centrifuge. Methanol was used for decontamination during centrifugation to obtain 435 kg of qualified glycine and a filtrate containing ammonium chloride. The first-stage yield of glycine reached 68.5%.

[0048] 3) The filtrate containing ammonium chloride was cooled to 10°C and discharged into a centrifuge for centrifugation to obtain a synthetic mother liquor and 553 kg of crude ammonium chloride (a mixture containing 69% ammonium chloride and 30.8% glycine).

[0049] Example 5

[0050] like Figure 1 As shown in the flow diagram, the steps of the method for producing glycine by one-step synthesis and step-by-step purification in a mixed solvent in this embodiment are as follows:

[0051] 1) At 12.5m 3 To a reactor, 10,000 kg of seven-times recycled synthesis mother liquor was added, along with 800 kg of solid chloroacetic acid (no hexamine). 240 kg of crude glycine (69% glycine and 30.2% ammonium chloride) was then added. At 30°C and a pH of 4.41, a total of 282 kg of ammonia was introduced over 3.5 hours. The temperature was controlled to not exceed 65°C, achieving a pH of 6.75. The reaction mixture was held at 65°C for 1 hour. A sample was taken to determine the water content of the reaction solution, which was 23.1%. The discharge temperature was then determined to be 57°C.

[0052] 2) The reaction solution was cooled to 57°C and discharged into a centrifuge. Methanol was used for decontamination during centrifugation to obtain 584.4 kg of qualified glycine and a filtrate containing ammonium chloride. The primary yield of glycine reached 91.5%.

[0053] 3) The filtrate containing ammonium chloride was cooled to 10°C and discharged into a centrifuge for centrifugation to obtain a synthetic mother liquor and 590 kg of crude ammonium chloride (a mixture containing 68.5% ammonium chloride and 30.8% glycine).

[0054] Example 6

[0055] Add 10,000 kg of ammonium chloride purification mother liquor into the ammonium chloride purification kettle. When the temperature is above 30°C, add 2,500 kg (containing 30.3% glycine and 69% ammonium chloride) of crude ammonium chloride. Stir thoroughly to dissolve the glycine in the ammonium chloride purification mother liquor. Cool to 30°C and centrifuge to produce 1,320 kg of industrial-grade ammonium chloride (containing 98.0% ammonium chloride and 2.0% glycine). Then cool the filtrate to 10°C and centrifuge to produce 1,165 kg of crude glycine (containing 34.0% ammonium chloride and 65.0% glycine).

[0056] The embodiments described above are only preferred embodiments of the present invention and are only used to explain the present invention, not to limit the scope of implementation of the present invention. For those skilled in the art, it is of course possible to easily make other implementation methods by replacing or changing the technical content disclosed in this specification. Therefore, all changes and improvements made on the principles of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A method for producing glycine by one-step synthesis and step-by-step purification in a mixed solvent, characterized in that: The following steps are involved: 1) Add measured amounts of chloroacetic acid and hexamethylenetetramine to a methanol-water solution or synthetic mother liquor with a water content of 20-30%, then introduce measured amounts of liquid ammonia. While introducing the liquid ammonia, raise the temperature to 60-65°C and react for 1 hour. Detect the water content in the reaction solution to determine the temperature at the time of discharge. 2) Cooling the reaction solution to no less than 50°C, separating, and de-eluting with methanol to obtain qualified glycine and a filtrate containing ammonium chloride; 3) The filtrate containing ammonium chloride is cooled to 5-15°C to separate the synthesis mother liquor and crude ammonium chloride. The synthesis mother liquor is returned to step 1) for recycling; 4) The crude ammonium chloride obtained in step 3) is dissolved in the ammonium chloride purification mother liquor at 30°C, and the mixture is discharged at 30°C to separate qualified ammonium chloride and a filtrate containing glycine. The filtrate containing glycine is cooled to 10°C to separate crude glycine and an ammonium chloride purification mother liquor. The ammonium chloride purification mother liquor is returned to dissolve the crude ammonium chloride, and the obtained crude glycine is returned to step 1).

2. The method according to claim 1, characterized in that The mass ratio of the methanol aqueous solution or synthetic mother liquor to chloroacetic acid is 10:

1.

3. The method according to claim 1, characterized in that The mass ratio of the chloroacetic acid to the hexamine is 10:

1.

4. The method according to claim 1, wherein When the synthetic mother liquor obtained in step 3) is recycled for more than 10 times, activated carbon is added for adsorption treatment for 0.5 to 1 hour. After removing the activated carbon, return to step 1) and continue recycling.

5. The method according to claim 4, characterized in that The amount of activated carbon added is 1-2% of the total mass of the synthesis mother liquor.

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