Novel filtering membrane used in VB12 production process and preparation method thereof

Abstract

The invention provides a novel filtering membrane used in a VB12 production process and a preparation method thereof, and belongs to the technical field of vitamin B12 production.The preparation method comprises the following steps that firstly, graphene oxide is obtained after graphene powder is oxidized, a diphenyl substitute is grafted to the surface of the graphene oxide, and an intermediate is obtained; 2, carrying out mixed reaction on the modified chitosan and the intermediate to obtain modified graphene; and 3, mixing the modified graphene with the cellulose ester membrane casting solution, and preparing the novel filtering membrane used in the VB12 production process through a phase inversion method. Through collaborative design of a graphene-chitosan hybrid structure and a polyphenylsilane cross-linked network, high selectivity, strong pollution resistance and chemical corrosion resistance of the filtering membrane are realized, and the filtering membrane is worthy of popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of vitamin B12 production, and particularly relates to a novel filter membrane for VB12 production process and a preparation method thereof. Background Art

[0002] Vitamin B12 is an important water-soluble vitamin, which is widely used in the fields of medicine, food additives, feed industry, etc. At present, the main production method of VB12 is microbial fermentation method, and its production process involves complex separation and purification steps. Especially, the VB12 extraction link in the fermentation broth has extremely high requirements for filtration technology. Traditional filtration processes often adopt technologies such as centrifugation, plate and frame filtration, ceramic membrane or organic polymer membrane separation, etc., but there are the following technical bottlenecks in practical applications: The pore size distributions of traditional filter membranes such as polyethersulfone and polyvinylidene fluoride membranes are uneven, and it is difficult to effectively intercept tiny bacterial cell fragments, colloidal impurities and macromolecular proteins in the VB12 fermentation broth, resulting in an increase in the load of subsequent purification steps and a decrease in product yield. In addition, the molecular weight of VB12 is relatively small, and the existing ultrafiltration membranes have limited selective separation ability for it, which is likely to cause loss of target products.

[0003] High-concentration organic substances, polysaccharides and lipid substances in the fermentation broth are likely to cause membrane surface contamination and pore blockage, resulting in an increase in transmembrane pressure difference and a decrease in flux. Frequent chemical cleaning not only increases production costs, but also accelerates the aging of membrane materials and shortens the service life.

[0004] Existing organic membranes are prone to swelling, hydrolysis or structural collapse under extreme pH or high-temperature sterilization environments, resulting in irreversible decline in separation performance. Although inorganic ceramic membranes have strong corrosion resistance, their high brittleness and expensive processing costs limit large-scale industrial applications; traditional filtration processes require a large amount of water consumption for backwashing, and the contaminated membrane materials are difficult to degrade, causing an environmental burden. At the same time, the high-energy-consuming transmembrane pressure difference operation further increases the comprehensive cost of VB12 production. Summary of the Invention

[0005] The present invention provides a novel filter membrane for VB12 production process and a preparation method thereof, which are used to solve the technical problems of insufficient separation efficiency and accuracy, fast membrane fouling and flux decline rate, and low chemical resistance and stability in the existing vitamin B12 production process.

[0006] The preparation method of the novel filter membrane for VB12 production process provided by the present invention includes the following steps: In the first step, after oxidizing graphene powder, graphene oxide is obtained, and a diphenyl substituent is grafted on the surface of graphene oxide to obtain an intermediate; In the second step, modified chitosan and the intermediate are mixed and reacted to obtain modified graphene; Step 3: Mix the modified graphene with the cellulose acetate casting solution, and prepare a novel filter membrane for use in the VB12 production process through the phase inversion method.

[0007] Preferably, in the first step, the specific steps of the oxidation operation are as follows: Add graphene to concentrated sulfuric acid, stir evenly, then add potassium permanganate, stir at a temperature not higher than 10 °C for 2 h, raise the temperature to 35 °C, stir for 2 h, add 230 ml of water, raise the temperature to 98 °C, stir for 30 min, add 30% hydrogen peroxide, centrifuge, and repeatedly wash the obtained solid with dilute hydrochloric acid and deionized water until the pH is neutral to obtain graphene oxide.

[0008] Preferably, the mass-volume ratio of the graphene, concentrated sulfuric acid, potassium permanganate, and 30% hydrogen peroxide is 3 - 5 g: 110 - 130 ml: 10 - 15 g: 5 ml.

[0009] Preferably, in the operation of grafting a diphenyl substituent on the surface of graphene oxide in the first step, the mass ratio of graphene oxide to the diphenyl substituent is 1:2; the diphenyl substituent is one of diphenylphosphine and diphenylsilicon; the grafting reaction is carried out in an organic solvent, the organic solvent is anhydrous toluene, a catalyst needs to be added during the reaction, the catalyst is dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and the operating conditions are to raise the temperature to 80 °C and stir for 24 h under a nitrogen environment. After the reaction, the product needs to be filtered, washed, and dried.

[0010] It can be understood that in the embodiments of the present application, the diphenyl compound can be diphenylphosphine or diphenylsilicon, and the double bond on the surface of graphene oxide reacts and combines with the P-H bond or Si-H bond of the diphenyl compound, so that the surface of graphene oxide has a large steric hindrance group of a diphenyl ring, preventing the adsorption of proteins on the membrane.

[0011] Preferably, in the second step, the mass ratio of the modified chitosan to the intermediate is 2:3; the mixing reaction is carried out in an organic solvent, the organic solvent is N,N-dimethylformamide, a catalyst needs to be added during the reaction, the catalyst is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide, and the reaction operation is to stir at 20 - 37 °C for 48 h. After the reaction, the product needs to be dialyzed and dried.

[0012] It can be understood that in the embodiments of the present application, the amino group on the surface of the modified chitosan combines with the carboxyl group on the surface of the intermediate through an amidation reaction, and an amide bond is formed after the reaction, and the chemical properties are stable, enhancing the acid and alkali resistance of the filter membrane.

[0013] Preferably, in the second step, the preparation method of the modified chitosan is as follows: Weigh 5 parts of chitosan and dissolve it in 50 parts of 2% acetic acid solution. Add 1 part of phenyltrimethoxysilane, 1 part of diphenyldimethoxysilane, 1 part of methylvinyldiethoxysilane, 1 part of vinyltrimethoxysilane, 1 part of γ-methacryloxypropyltrimethoxysilane, and 1 part of phenylethylenemethoxysilane. Stir for 30 min, add 1 part of 98% hydrochloric acid, and stir and react at 50 °C for 48 h. After the reaction, pour the reaction solution into acetone for precipitation, filter, wash with acetone, and dry to obtain the modified chitosan.

[0014] It can be understood that in the embodiments of the present application, the hydroxyl groups on the surface of chitosan undergo a dehydration reaction with the siloxane bonds in the silane coupling agent, grafting the silane coupling agent onto the surface of chitosan, adding double bonds and benzene rings to the surface of chitosan, increasing the steric hindrance effect, and reducing the adsorption of proteins.

[0015] Preferably, in the third step, the mass ratio of the modified graphene to the cellulose ester casting solution is 1:50 - 70.

[0016] Preferably, in the third step, the cellulose ester casting solution contains cellulose ester and a solvent. The cellulose ester is one of cellulose acetate and cellulose nitrate, and the solvent is dimethyl sulfoxide.

[0017] The present invention also provides a novel filtration membrane prepared by the preparation method of a novel filtration membrane for use in the production process of VB12.

[0018] The present invention has at least the following beneficial effects: (1) By grafting diphenyl substituents on the surface of graphene oxide, the present invention forms modified graphene with regular nanopores. Combining with the phase inversion method of the cellulose ester casting solution, the membrane pore size is precisely regulated to 1 - 5 nm, realizing the highly selective separation of VB12 and small molecule proteins, and improving the rejection rate of small molecule proteins and the yield of VB12.

[0019] (2) By introducing phenylethylenemethoxysilane into the modified chitosan, the present invention endows the membrane surface with superhydrophobic properties. The graphene - chitosan composite cross - links to form an anti - adhesion layer, inhibiting the adsorption of organic substances. In the filtration of VB12 fermentation broth, the membrane flux decay rate is reduced, and the chemical cleaning cycle is extended.

[0020] (3) By using the graphene oxide framework to enhance the mechanical strength of the membrane and using various siloxanes to form a silane cross - link network to endow the membrane with acid - resistance and high - temperature resistance, the membrane swelling rate is <5% in the acidic environment of VB12 post - treatment, and the service life is greatly extended.

[0021] (4) The present invention uses cellulose acetate to replace traditional petroleum-based polymers, reducing the production cost of the membrane, and the membrane material is biodegradable, reducing industrial waste pollution.

[0022] (5) Through the synergistic design of the graphene-chitosan hybrid structure and the polyphenylsilane crosslinked network, the present invention achieves high selectivity, strong anti-fouling property and chemical corrosion resistance in a single membrane system, which is worthy of popularization. Detailed implementation manners

[0023] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] The cellulose acetate solutions used in the embodiments of the present invention are all prepared by the following method: Weigh 20 g of cellulose acetate and slowly add it to 80 g of DMSO. Under the conditions of 70 °C and a stirring speed of 500 r / min, continuously stir for 3.5 hours until the cellulose acetate is completely dissolved to obtain a homogeneous and transparent cellulose ester solution for standby.

[0025] Example 1 This example provides a preparation method of a novel filtration membrane for the production process of VB12.

[0026] S1. Weigh 5 g of chitosan, dissolve it in 50 mL of 2% acetic acid solution, stir until the chitosan is completely dissolved, and while continuously stirring, sequentially and slowly add 1 g of phenyltrimethoxysilane, 1 g of diphenyldimethoxysilane, 1 g of methylvinyldiethoxysilane, 1 g of vinyltrimethoxysilane, 1 g of γ-methacryloxypropyltrimethoxysilane, and 1 g of phenylethylenemethoxysilane. Continuously stir for 30 min. After the addition is completed, add 1 mL of hydrochloric acid as a catalyst, control the temperature of the reaction system at 50 °C, and stir and react for 48 h. After the reaction is completed, pour the reaction solution into acetone for precipitation, collect the precipitate by filtration, wash it with acetone multiple times to remove impurities, and finally place the washed product in a dry environment for drying to obtain modified chitosan.

[0027] S2. Measure 110 ml of concentrated sulfuric acid and place it in a reaction vessel. Slowly add 3 g of graphene powder under stirring, stir evenly, then add 10 g of potassium permanganate, control the reaction temperature not higher than 10 °C, continuously stir for 2 h, then raise the temperature to 35 °C, continue to stir for 2 h, add 230 ml of water, raise the temperature to 98 °C, stir for 30 min. Before the reaction ends, add 5 mL of 30% hydrogen peroxide, stir evenly and then centrifuge. Wash the centrifuged solid repeatedly with dilute hydrochloric acid and deionized water until the pH value of the washing solution is neutral to obtain graphene oxide.

[0028] S3. Add graphene oxide and diphenylphosphine to anhydrous toluene organic solvent according to a mass ratio of 1:2, and add dicyclohexylcarbodiimide and 4-dimethylaminopyridine as catalysts. Under the protection of a nitrogen environment, raise the temperature of the reaction system to 80 °C, stir and react for 24 h. After the reaction ends, filter, wash and dry the product in sequence to obtain intermediate 1.

[0029] S4. Add the prepared modified chitosan and intermediate 1 to N,N-dimethylformamide organic solvent according to a mass ratio of 2:3, and add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide as catalysts. Stir in the temperature range of 20 - 37 °C for 48 h. After the reaction ends, dialyze and dry the product to obtain modified graphene.

[0030] S5. According to the mass ratio of modified graphene to cellulose acetate casting solution of 1:50, add modified graphene to the cellulose acetate solution, stir and mix evenly. Coat the mixed casting solution evenly on a clean glass plate, control the coating thickness at 0.1 - 0.3 mm with a scraper. After coating, quickly immerse the glass plate in a deionized water coagulation bath. After soaking in the coagulation bath for 1.5 h, peel the membrane off the glass plate, then rinse it repeatedly with deionized water to remove residual solvents and impurities. Finally, air-dry the membrane at room temperature to obtain a new filter membrane for use in the VB12 production process.

[0031] Example 2 This example provides a preparation method for a new filter membrane for use in the VB12 production process.

[0032] S1. Weigh 5 g of chitosan and dissolve it in 50 mL of 2% acetic acid solution. Stir until the chitosan is completely dissolved to form a homogeneous solution. While continuously stirring, slowly add 1 g of phenyltrimethoxysilane, 1 g of diphenyldimethoxysilane, 1 g of methylvinyldiethoxysilane, 1 g of vinyltrimethoxysilane, 1 g of γ-methacryloxypropyltrimethoxysilane, and 1 g of phenylethylenemethoxysilane in sequence. The entire dropping process is continuously stirred for 30 min. After the dropping is completed, add 1 mL of hydrochloric acid as a catalyst, control the temperature of the reaction system at 50 °C, and stir and react for 48 h. After the reaction is completed, pour the reaction solution into a large amount of acetone for precipitation, collect the precipitate by filtration, wash it with acetone multiple times to remove impurities, and finally place the washed product in a dry environment for drying to obtain modified chitosan.

[0033] S2. Measure 110 ml of concentrated sulfuric acid and place it in a reaction vessel. Slowly add 3 g of graphene powder under stirring and stir evenly. Then add 10 g of potassium permanganate, control the reaction temperature not higher than 10 °C, and continuously stir for 2 h. Subsequently, raise the temperature to 35 °C and continue to stir for 2 h. Then add 230 ml of water, raise the temperature to 98 °C, and stir for 30 min. Before the reaction ends, add 5 mL of 30% hydrogen peroxide, stir evenly and then centrifuge. Wash the solid obtained by centrifugation with dilute hydrochloric acid and deionized water repeatedly until the pH value of the washing solution is neutral to obtain graphene oxide.

[0034] S3. Add graphene oxide and diphenylphosphine to anhydrous toluene organic solvent according to a mass ratio of 1:2, and add dicyclohexylcarbodiimide and 4-dimethylaminopyridine as catalysts. Under the protection of a nitrogen environment, raise the temperature of the reaction system to 80 °C and stir and react for 24 h. After the reaction is completed, filter, wash, and dry the product in sequence to obtain intermediate 1.

[0035] S4. Add the prepared modified chitosan and intermediate 1 to N,N-dimethylformamide organic solvent according to a mass ratio of 2:3, and add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide as catalysts. Stir in the temperature range of 20 - 37 °C for 48 h. After the reaction is completed, dialyze and dry the product to obtain modified graphene.

[0036] S5. According to the mass ratio of modified graphene to cellulose acetate casting solution of 1:60, add the modified graphene into the cellulose acetate solution, stir well and mix evenly. Coat the mixed casting solution evenly on a clean glass plate, and control the coating thickness at 0.1 - 0.3 mm with a scraper. After coating, quickly immerse the glass plate into a deionized water coagulation bath. After soaking in the coagulation bath for 1.5 hours, peel the membrane off the glass plate, then rinse it repeatedly with deionized water to remove the residual solvent and impurities. Finally, air-dry the membrane at room temperature to obtain a novel filter membrane for the production process of VB12.

[0037] Example 3 This example provides a preparation method of a novel filter membrane for the production process of VB12.

[0038] S1. Weigh 5 g of chitosan, dissolve it in 50 mL of 2% acetic acid solution, stir until the chitosan is completely dissolved to form a homogeneous solution. Under continuous stirring, slowly add 1 g of phenyltrimethoxysilane, 1 g of diphenyldimethoxysilane, 1 g of methylvinyldiethoxysilane, 1 g of vinyltrimethoxysilane, 1 g of γ-methacryloxypropyltrimethoxysilane, and 1 g of phenylethylenemethoxysilane in sequence. The whole dropping process is continuously stirred for 30 min. After dropping, add 1 mL of hydrochloric acid as a catalyst, control the temperature of the reaction system at 50 °C, and stir and react for 48 h. After the reaction is completed, pour the reaction solution into a large amount of acetone for precipitation, collect the precipitate by filtration, wash it with acetone multiple times to remove impurities, and finally place the washed product in a dry environment for drying to obtain modified chitosan.

[0039] S2. Measure 110 ml of concentrated sulfuric acid and place it in a reaction vessel. Slowly add 3 g of graphene powder under stirring and mix evenly. Then add 10 g of potassium permanganate, control the reaction temperature not higher than 10 °C, and continuously stir for 2 h. Subsequently, raise the temperature to 35 °C and continue stirring for 2 h. Add 230 ml of water, raise the temperature to 98 °C, and stir for 30 min. Before the reaction ends, add 5 mL of 30% hydrogen peroxide, stir evenly and then centrifuge. Wash the centrifuged solid repeatedly with dilute hydrochloric acid and deionized water until the pH value of the washing solution is neutral to obtain graphene oxide.

[0040] S3. Add graphene oxide and diphenylphosphine into anhydrous toluene organic solvent according to the mass ratio of 1:2, and add dicyclohexylcarbodiimide and 4-dimethylaminopyridine as catalysts. Under the protection of a nitrogen environment, raise the temperature of the reaction system to 80 °C and stir and react for 24 h. After the reaction is completed, filter, wash, and dry the product in sequence to obtain Intermediate 1.

[0041] S4. Add the prepared modified chitosan and intermediate 1 into the organic solvent of N,N-dimethylformamide according to the mass ratio of 2:3, and add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide as catalysts. Stir for 48 h in the temperature range of 20-37 °C. After the reaction is completed, the product is dialyzed and dried to obtain modified graphene.

[0042] S5. Take the prepared cellulose acetate solution in Example 1. According to the mass ratio of modified graphene to the cellulose acetate casting solution of 1:70, add the modified graphene into the cellulose acetate solution, stir well and mix evenly. Coat the mixed casting solution evenly on a clean glass plate, control the coating thickness to be 0.1-0.3 mm. After coating, quickly immerse the glass plate into a deionized water coagulation bath. After soaking in the coagulation bath for 1.5 hours, peel the membrane off the glass plate, and then rinse it repeatedly with deionized water to remove the residual solvent and impurities. Finally, dry the membrane at room temperature to obtain a novel filter membrane for the production process of VB12.

[0043] Comparative Example 1 This comparative example provides a preparation method of a novel filter membrane for the production process of VB12. The difference between this comparative example and Example 1 is that in S1, the chitosan is not modified with a silane coupling agent, and other steps are the same as those in Example 1.

[0044] Comparative Example 2 This comparative example provides a preparation method of a novel filter membrane for the production process of VB12. The difference between this comparative example and Example 1 is that in S2, the graphene oxide is not grafted with a diphenyl substituent, and other steps are the same as those in Example 1.

[0045] Comparative Example 3 Select a mixed cellulose filter membrane provided by Shanghai Weixi Biotechnology Co., Ltd., with the model number A045A293C.

[0046] Performance detection Perform protein rejection rate detection, VB12 purity detection, tensile strength and elongation at break, tear strength, filtration flux and flux decay rate tests on the novel filter membranes of the examples and comparative examples.

[0047] The protein rejection rate detection refers to ISO16558-1:2015 "Test Methods for Membrane Separation Performance"; The VB12 purity detection is carried out by HPLC detection; The detection of tensile strength and elongation at break refers to ASTM D882-18 "Standard Test Method for Tensile Properties of Plastic Films"; The tear strength was referred to ASTM D624-00 "Standard Test Method for Rubber Tear Strength". The test of filtration flux and flux decay rate was referred to GB / T32360-2015 "Test Methods for Performance of Membrane Separation Technology".

[0048] Table 1 Test Results of Performance

[0049] It can be seen from Table 1 that the performance of the filtration membrane in each aspect of the embodiment of the present invention is superior to that of Comparative Example 1 and Comparative Example 2, indicating that the modification treatment of chitosan with silane coupling agent and the grafting treatment of graphene oxide with diphenyl substituents can both improve the performance of the membrane, and there is a synergistic effect between the two in improving the performance of the membrane in each aspect; and compared with the commercially available mixed cellulose filter membrane of Comparative Example 3, the filtration membrane of the embodiment of the present invention shows obvious advantages in each aspect of performance.

[0050] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. All equivalent changes and improvements made within the scope of the application of the present invention shall still fall within the scope covered by the patent of the present invention.

Claims

1. A method for preparing a new type of filter membrane used in the production process of VB12, characterized in that: The following steps are involved: The first step is to oxidize the graphene powder to obtain graphene oxide, and graft a diphenyl substituent on the surface of the graphene oxide to obtain an intermediate; In the second step, the modified chitosan is mixed with the intermediate to react to obtain modified graphene; The third step is to mix the modified graphene with the cellulose ester casting solution and prepare a new filter membrane for use in the VB12 production process through a phase inversion method; The preparation method of modified chitosan is as follows: weigh 5 parts of chitosan, dissolve it in 50 parts of 2% acetic acid solution, add 1 part of phenyltrimethoxysilane, 1 part of diphenyldimethoxysilane, 1 part of methylvinyldiethoxysilane, 1 part of vinyltrimethoxysilane, 1 part of γ-methacryloxypropyltrimethoxysilane, and 1 part of phenylvinylmethoxysilane, stir for 30 minutes, add 1 part of 98% hydrochloric acid, stir and react at 50°C for 48 hours, after the reaction is completed, pour the reaction solution into acetone for precipitation, filter, wash with acetone, and dry to obtain modified chitosan.

2. The method for preparing a novel filter membrane used in the VB12 production process according to claim 1, characterized in that: In the first step, the specific steps of the oxidation operation are: adding graphene to concentrated sulfuric acid, stirring evenly, then adding potassium permanganate, stirring at a temperature not higher than 10°C for 2h, heating to 35°C, stirring for 2h, adding 230ml of water, heating to 98°C, stirring for 30min, adding 5mL of 30% hydrogen peroxide, centrifuging, and washing the obtained solid with dilute hydrochloric acid and deionized water until the pH is neutral to obtain graphene oxide; Among them, the mass volume ratio of graphene, concentrated sulfuric acid, potassium permanganate and 30% hydrogen peroxide is 3-5g:110-130ml:10-15g:5ml.

3. The method for preparing a novel filter membrane used in the VB12 production process according to claim 1, characterized in that: In the operation of grafting diphenyl substituents on the surface of graphene oxide in the first step, the mass ratio of graphene oxide to diphenyl substituents is 1:

2.

4. The method for preparing a novel filter membrane used in the VB12 production process according to claim 1, characterized in that: In the operation of grafting a diphenyl substituent on the surface of graphene oxide in the first step, the diphenyl substituent is one of diphenylphosphine and diphenylsilicon.

5. The method for preparing a novel filter membrane used in the VB12 production process according to claim 1, characterized in that: In the operation of grafting a diphenyl substituent on the surface of graphene oxide in the first step, the grafting reaction is carried out in an organic solvent, and the organic solvent is anhydrous toluene.

6. The method for preparing a novel filter membrane used in the VB12 production process according to claim 1, characterized in that: In the operation of grafting diphenyl substituents on the surface of graphene oxide in the first step, a catalyst needs to be added during the reaction process. The catalysts are dicyclohexylcarbodiimide and 4-dimethylaminopyridine. The operating conditions are heating to 80°C and stirring the reaction for 24 hours in a nitrogen environment. After the reaction is completed, the product needs to be filtered, washed, and dried.

7. The method for preparing a novel filter membrane used in the VB12 production process according to claim 1, characterized in that: In the second step, the mass ratio of modified chitosan to the intermediate is 2:3; the mixed reaction is carried out in an organic solvent, the organic solvent is N,N-dimethylformamide, a catalyst needs to be added during the reaction, the catalyst is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide, the reaction operation is stirring at 20-37°C for 48h, and the product needs to be dialyzed and dried after the reaction is completed.

8. The method for preparing a novel filter membrane used in the VB12 production process according to claim 1, characterized in that: In the third step, the mass ratio of modified graphene to cellulose ester casting liquid is 1:50-70.

9. The method for preparing a novel filter membrane used in the VB12 production process according to claim 1, characterized in that: In the third step, the cellulose ester casting solution contains cellulose ester and a solvent, wherein the cellulose ester is one of cellulose acetate and cellulose nitrate, and the solvent is dimethyl sulfoxide.

10. A novel filter membrane obtained by the method for preparing a novel filter membrane used in the VB12 production process according to claim 1.

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