Preparation method of glycine

Abstract

The invention belongs to the technical field of glycine preparation, and particularly discloses a preparation method of glycine. The method comprises the following steps: controlling the reaction temperature, efficiently synthesizing ammonium chloroacetate from chloroacetic acid and liquid ammonia in a reactor, carrying out catalytic ammonolysis on the ammonium chloroacetate and ammonia gas in a reactor filled with a solid catalyst to realize continuity and reinforcement of the process, and carrying out alcohol precipitation crystallization, separation and purification to obtain glycine. The solid catalyst provided by the invention has the advantages of simple preparation, reproducibility, long service life, no metal pollution, easily available raw materials, controllable cost, long-acting cyclic utilization, high efficiency, simple recovery and the like; the method for preparing glycine by using the solid catalyst solves the problems of high consumption, high recovery cost, low production and purification efficiency and pollution caused by the traditional catalyst, and is a key technology for green and low-cost industrial production of glycine.

Description

Technical Field

[0001] This invention belongs to the field of glycine preparation, and specifically relates to a method for preparing glycine. Background Technology

[0002] Glycine, an important fine chemical intermediate widely used in pesticides, pharmaceuticals, and food, is still primarily produced in China through the ammonolysis of chloroacetic acid using hexamethylenetetramine as a catalyst. However, this traditional process suffers from several drawbacks, including high catalyst consumption that cannot be recycled, resulting in high production costs; numerous side reactions, making product separation and purification difficult; and large volumes of waste liquid that are difficult to treat.

[0003] In existing technologies, homogeneous synthesis using ionic liquids as catalysts improves catalyst recyclability, but the high cost and complex recovery process of ionic liquids limit their industrial application. Separating glycine and ammonium chloride via electrodialysis and recovering hexamethylenetetramine still faces problems such as mother liquor impurity enrichment, large equipment investment, and high energy consumption. Using high-boiling-point polar solvents to separate glycine and ammonium chloride mixed crystals reduces solvent evaporation loss, but still involves solvent recycling and recovery steps, and the high-boiling-point solvents themselves are expensive. The biological route of synthesizing glycine from CO2 via enzymatic catalysis has green and environmentally friendly potential, but currently, the enzyme activity and stability are insufficient, and it is still far from industrialization.

[0004] Therefore, designing a simple, recyclable solid heterogeneous catalyst to replace hexamethylenetetramine and solve the problems of high consumption, high recovery cost, low production and purification efficiency, and pollution caused by traditional catalysts has become a key technological bottleneck for the green and low-cost industrial production of glycine. Summary of the Invention

[0005] To address the shortcomings of traditional catalysts in the preparation of glycine, this invention provides a solid catalyst that is recyclable for a long period of time, highly efficient, easy to recover, and low in cost, and a method for preparing glycine using this solid catalyst.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a method for preparing glycine, comprising the following steps: In a low-chain alkanol solution, ammonium chloroacetate and ammonia are reacted under the catalysis of a solid catalyst to yield glycine.

[0007] The solid catalyst is at least one of a strong acid cation exchange resin or a strong base anion exchange resin.

[0008] The low-chain alkanol solution comprises C2-C3 low-chain alkanols and water in a volume ratio of 1:9 to 9:1.

[0009] This invention provides a novel glycine synthesis process based on strong acid or strong base solid resin catalysis. It uses a recyclable solid heterogeneous catalyst instead of hexamethylenetetramine, solving the problems of high catalyst consumption, difficult recovery, and resulting pollution. Compared to existing technologies, the solid catalyst mentioned in this invention is relatively simple and mature to prepare, highly regenerable, long-lasting, and free of metal pollution, making it more suitable for high-end applications. Raw materials are readily available and costs are controllable. This invention uses a strong acid cation exchange resin as a catalyst, which can precisely guide the reaction pathway to generate glycine. Using a strong base anion exchange resin as a catalyst ensures absolute safety. The C2-C3 low-chain alkanol solution and mixing volume ratio can maximally suppress potential esterification side reactions. The glycine preparation method protected by this invention has comprehensive advantages such as improved production efficiency, reduced catalyst costs, and environmental friendliness, providing a competitive new approach for the green and low-cost industrial production of glycine.

[0010] Preferably, the method for preparing the glycine includes the following steps: S1. Chloroacetic acid is reacted with liquid ammonia to obtain ammonium chloroacetate; S2. Dissolve ammonium chloroacetate in a low-chain alkanol solution and react it with ammonia gas in a reactor containing a solid catalyst to obtain a mixed solution of glycine. S3. The glycine mixture is concentrated and crystallized to remove ammonium chloride, and then subjected to alcohol precipitation crystallization to obtain glycine.

[0011] This invention utilizes chloroacetic acid and liquid ammonia to efficiently synthesize ammonium chloroacetate, which is then catalytically hydrolyzed with ammonia in a reactor containing a solid catalyst, thus achieving continuous and enhanced process. The product system after the reaction of this invention has a clear separation path, and ammonium chloride can be directly obtained by concentration, crystallization, and filtration. The filtrate can then be subjected to alcohol precipitation crystallization to obtain high-purity glycine, avoiding the complexity and high energy consumption of traditional mixed crystal separation.

[0012] Preferably, the strongly acidic cation exchange resin is a polystyrene sulfonic acid type ion exchange resin; and the strongly basic anion exchange resin is a strongly basic acrylic anion exchange resin.

[0013] This invention uses a strongly acidic cation exchange resin as a catalyst. From a catalytic performance perspective, the catalyst precisely guides the reaction pathway to glycine production by specifically protonating the carbonyl carbon. Its solid-state acid characteristics allow for a pre-neutralization-post-catalysis strategy, actively suppressing key side reactions at the source. Using a strongly basic anion exchange resin as a catalyst offers absolute safety; the alkaline environment reduces the risk of esterification side reactions, resulting in a more stable process, better reproducibility, easier control, and lower equipment corrosivity.

[0014] The reactor used in S1 is at least one of a falling film reactor, a static mixer reactor, a tubular reactor, or a continuous stirred tank reactor. The reactor in S2 is at least one of the following: tubular fixed bed reactor, multi-tube fixed bed reactor, adiabatic fixed bed reactor, slurry bed reactor, or trickle bed reactor.

[0015] Preferably, the reactor in S1 is a continuous stirred tank reactor.

[0016] Preferably, the reactor in S2 is a slurry bed reactor.

[0017] The continuous stirred tank reactor provided by this invention enables the efficient synthesis of ammonium chloroacetate from chloroacetic acid and liquid ammonia in the reactor. The strong stirring and large-area heat exchange ensure uniform temperature inside the reactor, sensitive thermal signal response, and precise and safe temperature control. The production volume can be flexibly adjusted by regulating the stirring rate and feed flow rate, and the pH and temperature are easy to detect and automatically control online.

[0018] The slurry bed reactor provided by this invention has good heat transfer performance, uniform temperature within the reaction system, and will not cause catalyst deactivation or aggravated side reactions due to local overheating. It has higher reaction selectivity, longer catalyst life, and safer operation. It has high mass transfer efficiency, and the gas, liquid, and solid phases are fully mixed and contacted under the agitation of the gas flow or stirring, which significantly improves the reaction rate and conversion rate. Old catalyst can be discharged and new catalyst can be added continuously or intermittently to maintain the stability of the average activity in the reactor. The bed is in a suspended state, and the gas flow resistance is less than that of a fixed bed, which reduces the requirements for the compressor and reduces energy consumption.

[0019] The reaction temperature in S1 is -10~30℃, and the reaction time is 10~20min.

[0020] The reaction temperature in S2 is 60~100℃, and the reaction time is 1~6h.

[0021] Preferably, the S2 reaction temperature is 80°C and the reaction time is 3 hours.

[0022] The inventors discovered that increasing the temperature significantly accelerates the hydrolysis step, propelling the reaction towards the target product (glycine), thereby greatly improving the selectivity and yield of the main product. However, higher temperatures also mean greater volatility of ammonia, which intensifies the volatilization of the solvent ethanol, leading to a decrease in glycine yield. Furthermore, shortening the reaction time reduces the glycine yield. From an industrial perspective, higher temperatures and longer reaction times mean higher energy consumption, and the increased volatility of ammonia also places higher demands on the sealing and pressure control of the reaction system. Therefore, 80℃ for 3 hours is currently the optimal reaction condition.

[0023] Preferably, the low-chain alkanol is at least one of anhydrous ethanol or propanol.

[0024] More preferably, the low-chain alkanol is anhydrous ethanol.

[0025] The low-chain alkanol solution and mixing volume ratio provided by this invention can suppress potential esterification side reactions to the greatest extent, improve the reaction efficiency of the main product, and at the same time, it does not affect the subsequent solubility of the main product in the solvent. Attached Figure Description

[0026] Figure 1 This is a process flow diagram for the preparation of glycine in this invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] The polystyrene sulfonic acid ion exchange resin and the strongly basic acrylic anion exchange resin used in the following examples were purchased from Kerry Environmental Protection Technology Co., Ltd.; the other compounds or related reagents used can be purchased from the market.

[0029] Example 1 This embodiment provides a method for preparing glycine, the process flow diagram of which is shown below. Figure 1 As shown, it includes the following steps: S1. Take 1 mol of chloroacetic acid and 1.05 mol of liquid ammonia to synthesize ammonium chloroacetate in a continuous stirred tank reactor at a reaction temperature of 20℃ for 15 min. S2. Prepare a 100 mL mixture of anhydrous ethanol and water in a ratio of 4:6. Dissolve 1 mol of ammonium chloroacetate in the 100 mL mixture to obtain a homogeneous solution. S3. A homogeneous solution (flow rate of 0.5 m / s) and ammonia (rate of 15 ml / min) are introduced into a slurry bed reactor filled with polystyrene sulfonic acid type ion exchange resin (the amount is half the volume of the homogeneous solution) and reacted. The reaction temperature is 80℃ and the reaction time is 3h. After the reaction is completed, a mixed mother liquor containing glycine is obtained. S4. Concentrate the mixed mother liquor at 60℃ for 2 hours, cool it to 10℃ and crystallize it for 1 hour. Filter to obtain solid ammonium chloride and recover the filtrate solution. S5. Add anhydrous ethanol (volume ratio of 1:1 to the filtered solution) to the filtered solution. Slowly add the anhydrous ethanol at 10℃ and stir. Allow the alcohol to crystallize for 2 hours. Filter to obtain crystalline solid. Repeat washing 3 times, recrystallize and dry to obtain glycine solid. The results showed that the yield of glycine was 91.51% and the purity was 99.08%, while the yield of ammonium chloride was 96.50%.

[0030] Example 2 This embodiment provides a method for preparing glycine, including the following steps: S1. Take 1 mol of chloroacetic acid and 1.05 mol of liquid ammonia to synthesize ammonium chloroacetate in a continuous stirred tank reactor at a reaction temperature of 20℃ and a reaction time of 15 min. S2. Prepare a mixed solvent of 100 mL anhydrous ethanol:water = 2:8, and dissolve 1 mol of ammonium chloroacetate in 100 mL of the mixed solution to obtain a homogeneous solution; S3. A homogeneous solution (flow rate of 0.5 m / s) and ammonia gas (rate of 15 ml / min) are introduced into a slurry bed reactor filled with a strong basic acrylic anion exchange resin (the amount of which is half the volume of the homogeneous solution). The reaction temperature is 80℃ and the reaction time is 3 h. After the reaction is completed, a mixed mother liquor containing glycine is obtained. S4. Concentrate the mixed mother liquor at 60℃ for 2 hours, cool it to 10℃ and crystallize it for 1 hour. Filter to obtain solid ammonium chloride and recover the filtrate solution. S5. Add anhydrous ethanol (volume ratio of 1:1 to the filtered solution) to the filtered solution. Slowly add the anhydrous ethanol at 10℃ and stir. Allow the alcohol to crystallize for 2 hours. Filter to obtain crystalline solid. Repeat washing 3 times, recrystallize and dry to obtain glycine solid. The results showed that the yield of glycine was 90.25% and the purity was 99.54%, while the yield of ammonium chloride was 96.05%.

[0031] Example 3 This embodiment provides a method for preparing glycine, including the following steps: S1. Take 1 mol of chloroacetic acid and 1.05 mol of liquid ammonia to synthesize ammonium chloroacetate in a continuous stirred tank reactor at a reaction temperature of 20℃ and a reaction time of 15 min. S2. Prepare a mixed solvent of 100 mL anhydrous ethanol:water = 1:9, and dissolve 1 mol of ammonium chloroacetate in 100 mL of the mixed solution to obtain a homogeneous solution; S3. A homogeneous solution (flow rate of 0.5 m / s) and ammonia (rate of 15 ml / min) are introduced into a slurry bed reactor filled with polystyrene sulfonic acid type ion exchange resin (the amount is half the volume of the homogeneous solution) and reacted. The reaction temperature is 80℃ and the reaction time is 3h. After the reaction is completed, a mixed mother liquor containing glycine is obtained. S4. Concentrate the mixed mother liquor at 60℃ for 2 hours, cool it to 10℃ and crystallize it for 1 hour. Filter to obtain solid ammonium chloride and recover the filtrate solution. S5. Add anhydrous ethanol (volume ratio of 1:1 to the filtered solution) to the filtered solution. Slowly add the anhydrous ethanol at 10℃ and stir. Allow the alcohol to crystallize for 2 hours. Filter to obtain crystalline solid. Repeat washing 3 times, recrystallize and dry to obtain glycine solid. The results showed that the yield of glycine was 94.30% and the purity was 99.6%, while the yield of ammonium chloride was 97.8%.

[0032] Example 4 This embodiment provides a method for preparing glycine, including the following steps: S1. Take 1 mol of chloroacetic acid and 1.05 mol of liquid ammonia to synthesize ammonium chloroacetate in a continuous stirred tank reactor at a reaction temperature of 30℃ for 10 min. S2. Prepare a mixed solvent of 100 mL anhydrous ethanol:water = 1:9, and dissolve 1 mol of ammonium chloroacetate in 100 mL of the mixed solution to obtain a homogeneous solution; S3. A homogeneous solution (flow rate of 0.5 m / s) and ammonia gas (rate of 15 ml / min) are introduced into a tubular fixed-bed reactor filled with polystyrene sulfonic acid type ion exchange resin (the amount is half the volume of the homogeneous solution) for reaction. The reaction temperature is 60℃ and the reaction time is 6h. After the reaction is completed, a mixed mother liquor containing glycine is obtained. S4. Concentrate the mixed mother liquor at 60℃ for 2 hours, cool it to 10℃ and crystallize it for 1 hour. Filter to obtain solid ammonium chloride and recover the filtrate solution. S5. Add anhydrous ethanol (volume ratio of 1:1 to the filtered solution) to the filtered solution. Slowly add the anhydrous ethanol at 10℃ and stir. Allow the alcohol to crystallize for 2 hours. Filter to obtain crystalline solid. Repeat washing 3 times, recrystallize and dry to obtain glycine solid. The results showed that the yield of glycine was 83.51% with a purity of 99.22%, and the yield of ammonium chloride was 94.05%.

[0033] Example 5 This embodiment provides a method for preparing glycine, including the following steps: S1. Take 1 mol of chloroacetic acid and 1.05 mol of liquid ammonia to synthesize ammonium chloroacetate in a continuous stirred tank reactor at a reaction temperature of -10℃ for 20 min. S2. Prepare a 100 mL mixture of anhydrous ethanol and water in a ratio of 9:1. Dissolve 1 mol of ammonium chloroacetate in the 100 mL mixture to obtain a homogeneous solution. S3. A homogeneous solution (flow rate of 0.5 m / s) and ammonia gas (rate of 15 ml / min) are introduced into a slurry bed reactor filled with polystyrene sulfonic acid type ion exchange resin (the amount is half the volume of the homogeneous solution) and reacted at a reaction temperature of 100℃ for 2 hours. After the reaction is completed, a mixed mother liquor containing glycine is obtained. S4. Concentrate the mixed mother liquor at 60℃ for 2 hours, cool it to 10℃ and crystallize it for 1 hour. Filter to obtain solid ammonium chloride and recover the filtrate solution. S5. Add anhydrous ethanol (volume ratio of 1:1 to the filtered solution) to the filtered solution. Slowly add the anhydrous ethanol at 10℃ and stir. Allow the alcohol to crystallize for 2 hours. Filter to obtain crystalline solid. Repeat washing 3 times, recrystallize and dry to obtain glycine solid. Calculations showed that the yield of glycine was 92.2% with a purity of 99.52%, and the yield of ammonium chloride was 92.27%.

[0034] Example 6 This embodiment provides a method for preparing glycine, including the following steps: S1. Take 1 mol of chloroacetic acid and 1.05 mol of liquid ammonia to synthesize ammonium chloroacetate in a continuous stirred tank reactor at a reaction temperature of 20℃ and a reaction time of 15 min. S2. Prepare a 100 mL mixture of propanol and water in a 1:9 ratio. Dissolve 1 mol of ammonium chloroacetate in the mixture to obtain a homogeneous solution. S3. A homogeneous solution (flow rate of 0.5 m / s) and ammonia gas (rate of 15 ml / min) are introduced into a slurry bed reactor filled with polystyrene sulfonic acid type ion exchange resin (the amount is half the volume of the homogeneous solution) and reacted. The reaction temperature is 90℃ and the reaction time is 3h. After the reaction is completed, a mixed mother liquor containing glycine is obtained. S4. Concentrate the mixed mother liquor at 60℃ for 3 hours, cool it to 10℃ and crystallize it for 1 hour. Filter to obtain solid ammonium chloride and recover the filtrate solution. S5. Add anhydrous ethanol (volume ratio of 1:1 to the filtered solution) to the filtered solution. Slowly add the anhydrous ethanol at 10℃ and stir. Allow the alcohol to crystallize for 2 hours. Filter to obtain crystalline solid. Repeat washing 3 times, recrystallize and dry to obtain glycine solid. The results showed that the yield of glycine was 91.33% and the purity was 99.23%, while the yield of ammonium chloride was 97.55%.

[0035] Example 7 The catalyst used in the preparation of glycine in this invention is the solid catalyst recovered in step (3) of Example 3 for the preparation of glycine. Other process conditions and operating steps are the same as in Example 3.

[0036] Recovery method: Wash 100g of used polystyrene sulfonic acid ion exchange resin with deionized water for 30 minutes, then soak it in 100g of 5% hydrochloric acid aqueous solution for 3 hours, filter it, and rinse it again with deionized water until neutral.

[0037] The recovered polystyrene sulfonic acid ion exchange resin was recycled six times, repeating the steps of Example 3. The yield of glycine prepared from the catalyst was 91.8%, the purity was 99.4%, and the yield of ammonium chloride was 97.0%.

[0038] Comparative Example 1 A method for preparing glycine, based on Example 3, is modified in that an equal amount of MgO / γ-Al2O3 supported solid catalyst is used instead of the strongly acidic cation exchange resin as the solid catalyst to be filled into the slurry bed reactor for reaction.

[0039] The specific steps for preparing the MgO / γ-Al2O3 supported solid catalyst are as follows: A 25% magnesium nitrate solution (converted to magnesium oxide) was mixed with γ-ray distillate. Al2O3 was mixed uniformly at a mass ratio of 1:5, calcined at 400℃ for 1.5h, cooled, and then impregnated in tripropylamine at room temperature (20℃) for 24h. After drying and grinding, MgO / γ-Al2O3 supported solid catalyst was obtained.

[0040] Comparative Example 2 A method for preparing glycine, based on Example 3 with modifications, the difference being that an equal amount of CeO2-MnO2 / SiO2 composite metal oxide is used instead of the strongly acidic cation exchange resin as a solid catalyst packed into a slurry bed reactor for reaction.

[0041] Comparative Example 3 A method for preparing glycine, based on Example 1 with modifications, the difference being that ammonium chloroacetate is dissolved in a mixed solvent of methanol:water = 1:9 to form a homogeneous solution.

[0042] Comparative Example 4 A method for preparing glycine, based on Example 3 with modifications, the difference being that ammonium chloroacetate is dissolved in a mixed solvent of butanol and water in a ratio of 1:9 to form a homogeneous solution.

[0043] Table 1

[0044] The glycine preparation method provided in this invention achieves a glycine yield of up to 94.3% and a purity of 99.6%. In contrast, comparative examples 1-4, regardless of whether the solid catalyst or the ammonium chloroacetate solvent was changed, failed to achieve the same glycine yield and purity as the present invention. Furthermore, the solid catalyst selected in this invention possesses advantages such as simple preparation and regeneration, long service life, no metal pollution, readily available and cost-controllable raw materials, long-term recyclability, high efficiency, and simple recovery—advantages not found in the other solid catalysts used in the comparative examples.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing glycine, characterized in that, Includes the following steps: In a low-chain alkanol solution, ammonium chloroacetate and ammonia are reacted under the catalysis of a solid catalyst to obtain glycine; wherein the solid catalyst is at least one of a strong acidic cation exchange resin or a strong basic anion exchange resin. The low-chain alkanol solution comprises C2-C3 low-chain alkanols and water in a volume ratio of 1:9 to 9:

1.

2. The method for preparing glycine as described in claim 1, characterized in that, Includes the following steps: S1. Chloroacetic acid is reacted with liquid ammonia to obtain ammonium chloroacetate; S2. Dissolve ammonium chloroacetate in a low-chain alkanol solution and react it with ammonia gas in a reactor containing a solid catalyst to obtain a mixed solution of glycine. S3. The glycine mixture is concentrated and crystallized to remove ammonium chloride, and then subjected to alcohol precipitation crystallization to obtain glycine.

3. The method for preparing glycine according to claim 1 or 2, characterized in that, The strongly acidic cation exchange resin is a polystyrene sulfonic acid type ion exchange resin; The strongly basic anion exchange resin is a strongly basic acrylic anion exchange resin.

4. The method for preparing glycine according to claim 2, characterized in that, In S2, the reactor is at least one of a tubular fixed-bed reactor, a multi-tube fixed-bed reactor, an adiabatic fixed-bed reactor, a slurry-bed reactor, or a trickle-bed reactor.

5. The method for preparing glycine according to claim 2, characterized in that, In S1, the reaction temperature is -10~30℃ and the reaction time is 10~20min.

6. The method for preparing glycine according to claim 2, characterized in that, In S2, the reaction temperature is 60~100℃ and the reaction time is 1~6h.

7. The method for preparing glycine according to claim 2, characterized in that, In S2, the low-chain alkanol is at least one of anhydrous ethanol or propanol.

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