Preparation method of a filtration membrane for purifying aminoacetic acid, filtration membrane for purifying aminoacetic acid and application thereof

Abstract

The application provides a preparation method of a filtering membrane for aminoacetic acid purification, the filtering membrane for aminoacetic acid purification and application thereof, and the preparation method of the filtering membrane for aminoacetic acid purification comprises the following steps: step S1, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol, an amide solvent and a hydroxyl-containing solvent are mixed, and vacuum defoaming is performed to prepare a casting solution; step S2, a polypropylene membrane is pretreated; step S3, the casting solution is controlled by a doctor blade to be cast on both sides of the polypropylene membrane in a film casting machine, and the polypropylene membrane coated with the casting solution is placed, solidified, cleaned, dried to prepare the filtering membrane for aminoacetic acid purification. The filtering membrane prepared in the application has high content and purity of separated aminoacetic acid under the condition that the filtering speed and filtering time are the same, and the filtering membrane still has high separation efficiency after being placed for a long time.

Description

Technical Field

[0001] This invention belongs to the field of aminoacetic acid separation and purification, specifically relating to a method for preparing a filter membrane for aminoacetic acid purification, the filter membrane for aminoacetic acid purification, and its application. Background Technology

[0002] Glycine, also known as aminoacetic acid or glucoside, has both acidic and basic functional groups in its molecule. It is ionizable in water, exhibits strong hydrophilicity, and possesses high boiling and melting points. It is a non-essential amino acid. Because aminoacetic acid is used not only in the synthesis of the herbicide glyphosate and the plant growth regulator glyphosate, but also has a certain inhibitory effect on the growth of Bacillus subtilis and Escherichia coli, and is used as an antioxidant in food, it has found wide application in the food, pharmaceutical, agricultural, and chemical industries.

[0003] In China, the main industrial synthesis methods for glycine are the Strecker process and the ammonolysis of chloroacetic acid. The Strecker process uses sodium cyanide, formaldehyde, ammonium chloride, and glacial acetic acid as raw materials, and has the advantages of easy product purification and low production cost, but it has the disadvantages of harsh production conditions and a long process route. On the other hand, the ammonolysis of chloroacetic acid uses monochloroacetic acid and ammonia as raw materials to synthesize glycine, and has the advantages of simple synthesis process, low equipment requirements, and less environmental pollution, and is therefore widely used.

[0004] However, since ammonium chloride is generated during the synthesis of glycine, existing technologies use glycol solvents and aqueous solutions as media to separate ammonium chloride and glycine, as described in patent CN104193634B. This improves the purity of glycine. However, during the separation of ammonium chloride and glycine, crystalline glycine not only passes through the separation membrane into the liquid ammonium chloride, but also easily clogs the filter membrane. This results in a relatively low purity and content of glycine. Furthermore, prolonged storage of the separation membrane further reduces the filtration effect of glycine, leading to even lower purity and content and wasting glycine.

[0005] In view of the problems existing in the prior art, how to provide a filter membrane that not only improves the purity and content of ammonium chloride when separating ammonium chloride and glycine, but also maintains good filtration effect when the filter membrane is left to stand for a long time is the problem that this invention urgently needs to solve. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a filter membrane for purifying glycine, the filter membrane for purifying glycine, and its application, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In one aspect, the present invention provides a method for preparing a filter membrane for purifying aminoacetic acid, comprising the following steps:

[0008] Step S1: After mixing polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol, amide solvent, and hydroxyl-containing solvent, vacuum degassing is performed to obtain the casting solution.

[0009] Step S2: Pre-treat the polypropylene film;

[0010] Step S3: In a film casting machine, the casting solution is controlled by a doctor blade to flow onto both sides of the polypropylene membrane. The polypropylene membrane coated with the casting solution is then allowed to stand, solidify, be cleaned, and dried to obtain a filter membrane for the purification of glycine.

[0011] As a further improvement, in step S1, the mass ratio of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol is 2-4:1.

[0012] As a further improvement, the preparation method of the polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol includes the following steps: dissolving aminated polyvinylidene fluoride-hexafluoropropylene and monoepoxide-terminated polyethylene glycol in dimethyl sulfoxide under stirring, heating in a water bath to 50-70°C while stirring, adding deionized water to the reaction solution after the reaction is completed, and washing, filtering and vacuum drying the precipitate to obtain the polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol copolymer.

[0013] As a further improvement, the pore size of the polypropylene membrane is 15-30 μm and the thickness is 150-250 μm.

[0014] As a further improvement, in step S1, the amide solvent is at least one of dimethylformamide, hexamethylphosphoramide, N,N-dimethylformamide, and dimethylacetamide.

[0015] As a further improvement, in step S1, the hydroxyl-containing solvent is at least one of 3-methoxy-1-butanol, 3-methoxy-2-butanol, and 1-methoxy-2-propanol.

[0016] As a further improvement, in step S2, the polypropylene film is cleaned in a mixture of ethanol and acetone to remove surface impurities.

[0017] As a further improvement, in step S2, the volume ratio of ethanol to acetone is 2-4:1.

[0018] As a further improvement, coagulation is carried out in step S3 using a coagulation bath, which is ultrapure water, and the coagulation temperature is 25-35℃.

[0019] On the other hand, the present invention provides a method for preparing a filter membrane for purifying glycine, which yields a filter membrane for purifying glycine.

[0020] On the other hand, the present invention also provides the application of the method for preparing a filter membrane for purifying glycine in the purification of glycine.

[0021] Compared with the prior art, the beneficial effects of the present invention are: the filter membrane prepared by the method of preparing the filter membrane for purifying glycine provided in this application can effectively remove ammonium chloride contained in glycine under the same filtration speed and filtration time, and the glycine content and purity obtained are high. Moreover, the filter membrane still has a high separation efficiency after being placed for a long time. Detailed Implementation

[0022] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0023] In the following examples, except for the monoepoxy-terminated polyethylene glycol, the aminated polyvinylidene fluoride-hexafluoropropylene, and the polyvinylidene fluoride-hexafluoropropylene-grafted polyethylene glycol, all other compounds and related reagents used were commercially available. Among them, the polyvinylidene fluoride-hexafluoropropylene was purchased from Wuhan Lanabai Pharmaceutical Chemical Co., Ltd., the polyethylene glycol monomethyl ether was purchased from Shandong Li'ang New Material Technology Co., Ltd., and the polypropylene film was purchased from Hebei Songbu New Building Materials Co., Ltd.

[0024] A method for preparing polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol includes the following steps:

[0025] (1) Add 0.3 mol NaOH, 0.5 mol epichlorohydrin and 0.03 mol water to a three-necked flask, heat in a water bath to 45°C, weigh 0.01 mol polyethylene glycol monomethyl ether and add it to the mixed solution, stir and react for 3 h, filter the mixture obtained from the reaction, add UBK530 ion exchange resin (purchased from Mitsubishi Japan) to the filtrate, let stand for 18 h, filter, add anhydrous magnesium sulfate to the filtered solution, let stand for 26 h, and perform vacuum distillation (temperature is 85°C) on the filtered solution to remove residual epichlorohydrin and obtain monoepoxy-terminated polyethylene glycol;

[0026] (2) Polyvinylidene fluoride-hexafluoropropylene was vacuum dried at 70℃ for 20h. Polyvinylidene fluoride-hexafluoropropylene powder was soaked in 2.5mol / L NaOH aqueous solution and stirred to completely wet the powder. The mixture was heated in a water bath to 55℃ for 25min. The mixture after reaction was filtered. The filtrate was repeatedly washed with deionized water and filtered again. It was then vacuum dried at 45℃ for 24h to obtain polyvinylidene fluoride-hexafluoropropylene containing double bonds.

[0027] (3) Polyvinylidene fluoride-hexafluoropropylene containing double bonds was immersed in a carbon tetrachloride solution of 8 mol / L Br2, and argon gas was blown in to remove the air in the solution. Then it was sealed and reacted magnetically at 0°C for 13 h under light-proof conditions. The bromine solution was removed, and the product was washed with carbon tetrachloride and dichloromethane in turn. After washing four times, it was dried under vacuum at 35°C for 20 h to obtain bromine-grafted polyvinylidene fluoride-hexafluoropropylene.

[0028] (4) The bromine-grafted polyvinylidene fluoride-hexafluoropropylene was placed in a flask, ammonia was introduced into the flask for 15 min, sealed, and placed at room temperature for 48 h under light protection. The product was purged with argon for 15 min, and then washed with methanol and dichloromethane in turn. After washing three times, it was dried under vacuum at 40 °C for 24 h to obtain aminated polyvinylidene fluoride-hexafluoropropylene.

[0029] (5) Dissolve 4g of aminated polyvinylidene fluoride-hexafluoropropylene and 24g of the monoepoxy-terminated polyethylene glycol obtained in step (1) in dimethyl sulfoxide. While stirring, heat in a water bath to 60°C and continue the reaction for 5 hours. Add deionized water to the reaction solution. Wash the precipitate repeatedly with pure water, filter, and vacuum dry (at 35°C for 24 hours) to obtain polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol copolymer.

[0030] The filter membranes of Examples 1-5 and Comparative Examples 1-2 were prepared using the following steps:

[0031] Step S1: After mixing the reagents, heat to 40°C and stir for 36 hours. Then transfer the mixture into a degassing tank and strictly control the vacuum level of the degassing tank. After degassing for 40 hours, the casting solution is obtained.

[0032] Step S2: The polypropylene membrane is placed in a mixture of ethanol and acetone (the amount of the mixture is enough to completely cover the polypropylene membrane, and the volume ratio of ethanol to acetone is 2:1) to clean it and remove surface impurities.

[0033] Step S3: In a film casting machine, the casting solution is controlled by a doctor blade to cast on both sides of a polypropylene membrane (the pore size of the polypropylene membrane is 20 μm and the thickness is 100 μm) (wherein, the gap between the doctor blade and the support membrane is 20 μm). After the polypropylene membrane coated with the casting solution is left to stand in the air for 5 minutes, it is then placed in pure water at 30°C to solidify for 30 minutes. Through the phase inversion method, the casting solution undergoes phase separation, resulting in membrane pore coagulation, interphase flow, and polymer-rich phase solidification to form a film. After rinsing the membrane with purified water, it is dried in a drying oven at 35°C for 10 hours.

[0034] In Examples 1-5 and Comparative Examples 1-2, the components and contents of the mixed reagents in step S1 are shown in Tables 1 and 2, where polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol is represented by compound A:

[0035] Table 1

[0036]

[0037] Table 2

[0038]

[0039] When the filter membranes prepared in Examples 1-5 and Comparative Examples 1-2 are used to separate ammonium chloride and aminoacetic acid, the specific operating procedures are as follows:

[0040] 15 kg of a mixed crystal containing 56 wt% glycine, 43 wt% ammonium chloride, and 1 wt% water was placed in a crystallization vessel. 40 L of ethylene glycol was added, and the stirrer was turned on while maintaining the crystallization vessel temperature at 75°C. After crystallization for 3 hours, the crystal slurry was removed. The resulting slurry was filtered using the filter membranes prepared in Examples 1-5 and Comparative Examples 1-2, respectively. The filter membranes had been stored for 1 month and 12 months, respectively. The filtration rate was 30 L / h. After filtration for 1 hour, the crystals obtained on the filter membrane were dried, and the quality of the crystals and the purity of the glycine were tested.

[0041] Standard for determination of glycine content: HG / T2029-2004;

[0042] Standard for determination of ammonium chloride content: GB / T 2946-2018;

[0043] The measured data are shown in Table 3:

[0044] Table 3

[0045]

[0046] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, when the filter membrane made of polyvinylidene fluoride-hexafluoropropylene grafted with polyethylene glycol is used for the separation of ammonium chloride and glycine, under the same filtration speed and filtration time, the content of glycine obtained is high and the content of ammonium chloride in glycine is low. Moreover, the filter membrane still has a high separation efficiency after being placed for a long time (the content and purity of the separated glycine are still high).

[0047] A comparison of Examples 1, 4, and 5 shows that when the mass ratio of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol is 2-4:1, the filter membrane prepared is used to separate ammonium chloride and glycine. Under the same filtration speed and filtration time, the content of glycine obtained is higher and the content of ammonium chloride in glycine is lower. Moreover, the filter membrane prepared still has a high separation efficiency when stored for a long time.

[0048] In summary, the filter membrane prepared using the method for preparing the filtration membrane for purifying glycine provided in this application has a higher content and purity of glycine (ammonium chloride content in glycine) under the same filtration speed and filtration time, and the filter membrane still has a high separation efficiency after being stored for a long time.

[0049] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a filter membrane for purifying glycine, characterized in that: Includes the following steps: Step S1: After mixing polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol, amide solvent, and hydroxyl-containing solvent, vacuum degassing is performed to obtain the casting solution. Step S2: Pre-treat the polypropylene film; Step S3: In the film casting machine, the casting solution is controlled by a doctor blade to flow on both sides of the polypropylene membrane. The polypropylene membrane coated with the casting solution is allowed to stand, solidify, be cleaned and dried to obtain a filter membrane for the purification of glycine. The preparation method of polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol includes the following steps: aminated polyvinylidene fluoride-hexafluoropropylene and monoepoxide-terminated polyethylene glycol are dissolved in dimethyl sulfoxide under stirring, and heated to 50-70°C in a water bath while stirring. After the reaction is completed, deionized water is added to the reaction solution, and the precipitate is washed, filtered, and vacuum dried to obtain polyvinylidene fluoride-hexafluoropropylene grafted polyethylene glycol copolymer.

2. The method for preparing a filter membrane for purifying glycine according to claim 1, characterized in that: In step S1, the mass ratio of polyvinylidene fluoride (PVDF) to PVDF-hexafluoropropylene-grafted polyethylene glycol (PEG) is 2-4:

1.

3. The method for preparing a filter membrane for purifying glycine according to claim 1, characterized in that: In step S2, the pore size of the polypropylene membrane is 15-30 μm.

4. The method for preparing a filter membrane for purifying aminoacetic acid according to claim 3, characterized in that: In step S1, the amide solvent is at least one of dimethylformamide, hexamethylphosphoramide, N,N-dimethylformamide, and dimethylacetamide.

5. A method for preparing a filter membrane for purifying glycine according to claim 3 or 4, characterized in that: In step S1, the hydroxyl-containing solvent is at least one of 3-methoxy-1-butanol, 3-methoxy-2-butanol, and 1-methoxy-2-propanol.

6. The method for preparing a filter membrane for purifying glycine according to claim 1, characterized in that: In step S2, the polypropylene film is cleaned in a mixture of ethanol and acetone to remove surface impurities.

7. The method for preparing a filter membrane for purifying glycine according to claim 1, characterized in that: In step S3, coagulation is performed using a coagulation bath. The coagulation bath is ultrapure water, and the coagulation temperature is 25-35℃.

8. The filter membrane for purifying glycine obtained by the method for preparing the filter membrane for purifying glycine according to any one of claims 1-7.

9. The application of the method for preparing the filter membrane for purifying glycine according to any one of claims 1-7 in the purification of glycine.

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