Anti-pollution high-efficiency red acid separation membrane and preparation method and use thereof

Abstract

This invention discloses an antifouling red acid separation membrane, comprising: a transparent or semi-transparent porous support layer, a light-transmitting PVDF-HFP porous separation layer, a polydopamine adhesion layer, and a photocatalytic antifouling layer loaded with an oxygen vacancy-modified pg-C3N4 / CdS / BiOCl catalyst, arranged sequentially from bottom to top. This invention further relates to a method for preparing the separation membrane. The separation membrane of this invention can be used as a photocatalytic antifouling pretreatment membrane and can be connected in series with a nanofiltration membrane to achieve efficient separation and resource recovery of red acid-related organic acid components and inorganic salts, solving the problem of vitamin B... 12 The membrane fouling and separation stability issues in the recovery process of red acid waste liquid components during production have significant economic and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically, it relates to a fouling-resistant, high-efficiency red acid separation membrane, and further relates to the preparation method and uses of the membrane, which is particularly suitable for vitamin B12. 12 Separation of red acid waste liquid generated during pharmaceutical manufacturing. Background Technology

[0002] Vitamin B 12 During the production process, the large amount of red acid waste liquid generated in the desorption or regeneration of anion exchange resin contains hydroxyglutaric acid-like organic acids and a small amount of vitamin B. 12 / Valuable byproduct streams of cobalamin-related components. Untreated red acid wastewater is high in salt, organic load, complex in composition, and has large pH fluctuations. It must be separated, purified, and quality controlled to achieve high-value utilization. For example, its valuable components can be a potential source of raw materials for feed additives, food fortifiers, or related functional additives.

[0003] Existing red acid wastewater treatment technologies primarily aim at pollution reduction, focusing on the treatment of valuable organic acids and vitamin B. 12 Insufficient attention has been paid to the resource attributes of relevant components, resulting in problems such as low recovery rates, unstable product purity, and poor compatibility between process parameters and key material properties. Furthermore, red acid wastewater can be subjected to acidic, neutral, or strongly alkaline conditions after adjustment through different process stages. The wastewater in the initial or regeneration stages can be strongly alkaline, with a pH of 12-14, and typically exhibits high COD, reaching 15,000-25,000 mg / L. Therefore, achieving selective enrichment and efficient recovery of valuable components while reducing pollution load is a key technical challenge for the resource-based treatment of red acid wastewater.

[0004] The commonly used process for recovering red acid is the "neutralization-membrane separation" method. This involves adjusting the pH to improve the form of organic acid components and the membrane's compatibility, followed by ultrafiltration or nanofiltration to remove suspended impurities, enrich valuable organic acids, and separate inorganic salts. However, red acid wastewater contains a large amount of proteins, bacterial fragments, extracellular polymers, and colloidal substances. These contaminants are easily adsorbed onto the membrane surface or clog the membrane pores during ultrafiltration or nanofiltration, leading to increased membrane fouling, rapid flux decline, and reduced separation stability. Traditional physical backwashing or chemical cleaning can restore membrane flux to some extent, but these methods are cumbersome, consume large amounts of cleaning agents, generate more secondary wastewater, and shorten membrane lifespan, making it difficult to meet the requirements for efficient resource recovery and green treatment of red acid wastewater.

[0005] CN118079680A discloses a coral-like Cu / TiO2 modified PVDF piezoelectric photocatalytic self-cleaning separation membrane. This membrane has poor stability in a strongly alkaline environment with pH>10 and is difficult to adapt to the extreme working conditions of red acid waste liquid.

[0006] The polytetrafluoroethylene hollow fiber nanofiltration membrane disclosed in CN120094415A has insufficient selective separation precision for inorganic salts and cannot achieve efficient separation of red acid from inorganic salts such as NaCl and K2SO4.

[0007] CN116850796A discloses a superhydrophilic photocatalytic antifouling ceramic composite membrane, which improves antifouling performance through TiO2 nanotube modification. However, the photocatalytic activity of the membrane decreases sharply under high salinity (>50 g / L) conditions, with a membrane flux attenuation rate as high as 40-60%.

[0008] CN121819935A discloses a K / FeS / g-C3N4 / TiO2@PVDF membrane, but its preparation process is complex and costly. Furthermore, the stability of the composite photocatalyst cannot be guaranteed in an extremely alkaline environment with pH 12-14.

[0009] To address the above problems, this invention provides a fouling-resistant, high-efficiency red acid separation membrane, suitable for red acid wastewater systems with high salt content and large pH fluctuations, especially suitable for membrane separation processes of red acid wastewater after pH adjustment. It exhibits strong antifouling capabilities and can be connected in series with a nanofiltration unit to achieve vitamin B1 separation. 12 Resource recovery of waste liquid from the production of red acid. Summary of the Invention

[0010] The present invention aims to provide a high-efficiency, anti-fouling red acid separation membrane, comprising a transparent or semi-transparent porous support layer, a light-transmitting polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) porous separation layer, a polydopamine adhesion layer, and a photocatalytic anti-fouling layer. It is a composite membrane with visible light response and in-situ anti-fouling function. This membrane is suitable for red acid wastewater systems with high salt content and large pH fluctuations, exhibiting strong anti-fouling capabilities. When used as a photocatalytic anti-fouling pretreatment membrane in series with a nanofiltration unit, it can achieve vitamin B12 separation. 12 Enrichment, desalination, and resource recovery of valuable components in red acid production wastewater.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: A high-efficiency red acid separation membrane with anti-fouling properties includes: a transparent or semi-transparent porous support layer, a light-transmitting polyvinylidene fluoride-hexafluoropropylene copolymer porous separation layer, a polydopamine adhesion layer, and a photocatalytic anti-fouling layer, wherein the layers are arranged sequentially from bottom to top.

[0012] The transparent or semi-transparent porous support layer is a polypropylene nonwoven fabric, polyester nonwoven fabric, or polyvinylidene fluoride microporous support membrane, used to provide mechanical support; the layer thickness is 30-200 μm, the pore size is 0.1-10 μm, and the porosity is 40-85%.

[0013] The light-transmitting polyvinylidene fluoride-hexafluoropropylene copolymer porous separation layer, with a thickness of 30-150 μm, preferably 50-120 μm, is located on the support layer. It provides visible light transmission channels, basic separation pores, and acid and alkali resistance, enabling initial retention of pollutants and ensuring that visible light can reach the photocatalyst on the membrane surface and in the near-surface pores. A layer that is too thin affects film integrity, pore size uniformity, and retention stability; a layer that is too thick increases mass transfer resistance and reduces visible light transmittance.

[0014] The transparent or semi-transparent porous support layer and the light-transmitting polyvinylidene fluoride-hexafluoropropylene copolymer porous separation layer constitute a porous composite base film. In a wetted state, the average transmittance of the porous composite base film in the visible light range of 420-780 nm is not less than 30%. The finished film, after polydopamine modification and photocatalyst immobilization, still has an average transmittance of not less than 15% in the visible light range of 420-780 nm in a wetted state. This indicates that after the polydopamine adhesive layer and photocatalyst loading, the interconnecting pores of the transparent or semi-transparent porous support layer and the PVDF-HFP porous separation layer are not completely covered or blocked. The finished film still retains the effective light-incident channels required for visible light response, allowing visible light to reach the photocatalyst on the film surface and in the near-surface pores.

[0015] The amount of the polydopamine adhesion layer is 0.05-0.50 mg / cm² of film area, preferably 0.10-0.30 mg / cm² of film area. This layer is used to fix the photocatalyst; too little will result in insufficient fixation, while too much will cause blockage of the near-surface pores or light blocking.

[0016] The photocatalytic antifouling layer is a layer supporting an oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst. The oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst is fixed to the light-incident surface and near-surface pores of the PVDF-HFP porous separation layer via a polydopamine adhesion layer. The loading amount of the oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst is 0.5-5.0 wt%, preferably 2.0-4.0 wt%, based on the mass of the transparent or semi-transparent porous support layer and the light-transmitting polyvinylidene fluoride-hexafluoropropylene copolymer porous separation layer.

[0017] The oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst is a ternary photocatalyst that modifies pg-C3N4 through oxygen vacancy defect engineering and forms a Z-type heterojunction with CdS / BiOCl, which can significantly enhance visible light absorption and carrier separation efficiency. Under visible light irradiation, the photocatalytic antifouling layer generates electron-hole pairs, thereby degrading proteins, colloids, and organic pollutants on the membrane surface in situ, achieving in-situ recovery of membrane flux.

[0018] The antifouling high-efficiency red acid separation membrane of this invention possesses excellent visible light transmittance, catalytic activity, acid and alkali resistance, and antifouling performance. It can be used as a photocatalytic antifouling pretreatment membrane before nanofiltration separation of red acid waste liquid. In the pretreatment application of red acid waste liquid, the membrane can reduce the membrane fouling rate by more than 60%, reduce the frequency of chemical cleaning by 80%, and effectively remove suspended solids, colloidal, proteinaceous pollutants, and some macromolecular organic pollutants. When used as a photocatalytic antifouling pretreatment membrane in series with a DK-type nanofiltration membrane or an acid-resistant nanofiltration membrane, the retention rate of red acid-related organic acid components can reach over 95%, the average transmittance of inorganic salts can reach over 90%, and the overall recovery rate of red acid-related organic acid components is approximately 75-80%.

[0019] The present invention further relates to a method for preparing the aforementioned antifouling, high-efficiency red acid separation membrane, comprising the following steps: (1) Preparation of light-transmitting PVDF-HFP casting solution: Mix PVDF-HFP, pore-forming agent and organic solvent, stir at 50-80℃ for 8-24 h to fully dissolve PVDF-HFP and pore-forming agent, let stand for 6-24 h to degas, and obtain a uniform casting solution. The preferred mass fraction of PVDF-HFP is 10-20 wt%, and the preferred mass fraction of the pore-forming agent is 2-8 wt%, based on the total mass of the casting solution. The pore-forming agent is polyvinylpyrrolidone or polyethylene glycol; the organic solvent is one of N,N-dimethylacetamide, N,N-dimethylformamide or N-methylpyrrolidone.

[0020] (2) Preparation of light-transmitting PVDF-HFP porous composite base film: The casting solution obtained in step (1) is scraped onto the surface of a transparent or semi-transparent porous support layer. The wet film thickness is 50-200 μm. After being left in the air for 5-30 s, it is immersed in a deionized water coagulation bath at 15-30℃ to undergo non-solvent-induced phase separation and form a light-transmitting PVDF-HFP porous composite base film. After the film is completely cured, it is taken out and soaked and washed with deionized water for 24-48 h. The water is changed every 6-8 h and the washing is repeated several times to remove residual solvent and pore-forming agent. The porous support layer is a transparent or semi-transparent polypropylene nonwoven fabric, polyester nonwoven fabric, or polyvinylidene fluoride microporous support membrane; the thickness of the porous support layer is 30-200 μm, the pore size is 0.1-10 μm, and the porosity is 40-85%.

[0021] (3) Surface activation of the composite base film: The light-transmitting PVDF-HFP porous composite membrane obtained in step (2) is immersed in a 1-3 g / L dopamine hydrochloride solution and shaken at room temperature for 2-12 h to allow dopamine to undergo oxidative self-polymerization and form a polydopamine adhesion layer on the membrane surface. After the reaction is completed, it is thoroughly rinsed with deionized water to remove unreacted dopamine monomers and unattached polydopamine particles, thus obtaining a surface-activated light-transmitting PVDF-HFP porous composite membrane. The dopamine hydrochloride solution was prepared with 10 mM Tris-HCl buffer and the pH was adjusted to 8.0-8.8.

[0022] The amount of dopamine hydrochloride solution used is 0.5-2.0 mL / cm² membrane area, preferably 0.8-1.2 mL / cm² membrane area, ensuring that the membrane is completely immersed and that the membrane surface is in full contact; the final amount of polydopamine adhesion layer deposited is 0.05-0.50 mg / cm² membrane area, preferably 0.10-0.30 mg / cm² membrane area, ensuring that the photocatalyst is fixed without clogging the near-surface pores of PVDF-HFP.

[0023] (4) Photocatalyst immobilization: The oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst was dispersed in deionized water or an ethanol / water (volume ratio 1:1) mixed solvent and ultrasonically dispersed for 20-60 min to obtain a uniform catalyst dispersion with a concentration of 0.5-5.0 g / L. The above-mentioned surface-activated light-transmitting PVDF-HFP porous composite membrane was immersed in the catalyst dispersion and adsorbed by shaking at room temperature for 2-12 h, so that the photocatalyst was fixed on the light-incident surface and near-surface pores of the PVDF-HFP porous separation layer of the composite membrane. After adsorption, it was gently rinsed with deionized water to remove unbonded particles, and then vacuum dried at 40-60℃ for 6-12 h to obtain a fouling-resistant and highly efficient red acid separation membrane.

[0024] This invention further relates to the use of the aforementioned anti-fouling, high-efficiency red acid separation membrane, which can be used to separate vitamin B. 12 The red acid waste liquid generated during the production process can be used to recover valuable components; it can also be used as a photocatalytic anti-fouling pretreatment membrane, and can be used in series with DK type nanofiltration membrane or other acid-resistant nanofiltration membrane for fine separation of red acid waste liquid to realize resource utilization.

[0025] The present invention further relates to a method for separating red acid waste liquid, characterized by using the anti-fouling and high-efficiency red acid separation membrane of the present invention, comprising the following steps: (1) Pretreatment of red acid waste liquid: vitamin B 12Wastewater containing red acid, high salt, suspended particles, colloids and organic impurities generated during the production process is treated by sedimentation, screening or coarse filtration to remove large suspended particles, and then the pH of the wastewater is adjusted to a range suitable for membrane separation with hydrochloric acid, sulfuric acid or alkaline solution, preferably pH 4.0-6.0. (2) Photocatalytic anti-fouling pretreatment: The pretreated red acid waste liquid is pumped into a cross-flow flat sheet membrane module or a transparent window spiral wound membrane module equipped with the anti-fouling red acid separation membrane, so that visible light is irradiated onto the light-incident surface of the membrane for membrane separation; during the separation process, proteins, colloids, bacterial fragments and macromolecular organic pollutants in the waste liquid are intercepted or reduced by the anti-fouling red acid separation membrane, and the permeate after photocatalytic anti-fouling pretreatment is obtained, thereby reducing the pollution load of subsequent steps; (3) Nanofiltration fine separation: The permeate after photocatalytic anti-pollution pretreatment is introduced into DK type nanofiltration membrane or other acid-resistant nanofiltration membrane unit; during the nanofiltration process, red acid and some organic acid components are mainly enriched on the concentrate side, while inorganic salt components mainly enter the permeate side, thereby realizing the separation, desalination and resource enrichment of red acid components and inorganic salts.

[0026] During step (2), the trapped proteins, colloids, bacterial fragments, and macromolecular organic pollutants are deposited on the membrane surface and in the near-surface pores to form a fouling layer, which leads to a decrease in membrane flux. When the membrane flux decreases to 70-80% of the initial flux, the flow of the red acid waste liquid to be treated into the membrane module is stopped, and the flow is switched to a circulation mode of deionized water or diluted red acid waste liquid (1000-2000 mg / L low-pollution load red acid waste liquid). Visible light irradiation is continued for 20-40 min to cause the fouling layer to undergo photocatalytic degradation and desorb from the membrane surface, thereby achieving in-situ recovery of membrane flux and completing the photocatalytic regeneration of the membrane fouling layer.

[0027] The separation membrane of this invention solves the vitamin B problem. 12 In the treatment of red acid wastewater, ultrafiltration membranes are susceptible to fouling by organic matter such as proteins and colloids, leading to rapid flux decline, frequent chemical cleaning, easy damage to membrane fibers, and poor visible light response. This solution is suitable for red acid wastewater systems with high salt content and large pH fluctuations. It can reduce membrane fouling rate by more than 60% and reduce chemical cleaning frequency by 80% through visible light response. When used in series with DK-type nanofiltration membranes or acid-resistant nanofiltration membranes, the retention rate of red acid-related organic acid components can reach over 95%, the average permeability of inorganic salts can reach over 90%, and the overall recovery rate of red acid-related organic acid components is approximately 75-80%, thereby achieving the goal of vitamin B12 recovery. 12 The precise separation and resource utilization of high-value components in pharmaceutical wastewater provides technical support for green manufacturing and clean production in the pharmaceutical industry.

[0028] Compared with the prior art, the anti-fouling high-efficiency red acid separation membrane of the present invention has the following advantages: 1. The base film layer is composed of a transparent or semi-transparent porous support layer and a light-transmitting separation layer, which allows visible light to penetrate effectively and excite the supported oxygen vacancy modified ternary heterojunction photocatalyst to generate photogenerated electrons and holes and active oxygen species, thereby achieving in-situ degradation of organic pollutants deposited on the membrane surface and significantly alleviating membrane fouling.

[0029] 2. By firmly fixing the photocatalyst through the polydopamine surface activation layer, catalyst loss can be reduced, and the membrane can still maintain the effective light-incident channel required for visible light response, thus controlling the impact on the light transmittance and separation performance of the base membrane.

[0030] 3. The oxygen vacancy modified pg-C3N4 / CdS / BiOCl photocatalyst has a ternary heterojunction structure and oxygen vacancy defects, which greatly improves the visible light absorption efficiency and photogenerated carrier separation efficiency, and enhances the photocatalytic oxidation ability.

[0031] 4. The membrane fouling layer can be rapidly regenerated by short-term visible light irradiation, which extends the membrane's service life and reduces cleaning costs and operating energy consumption.

[0032] 5. When combined with photocatalytic ultrafiltration and nanofiltration separation processes, it can effectively retain and enrich the red acid components in red acid waste liquid, while removing inorganic salts, which is conducive to the resource recovery of valuable components. Attached Figure Description

[0033] Appendix Figure 1 These are SEM images of the antifouling high-efficiency red acid separation membrane prepared in Example 2 of this invention. Figure A is an SEM image of the membrane surface, and Figure B is an SEM image of the membrane cross-section. It can be seen that the membrane surface and cross-section have a porous structure.

[0034] Figure 2A This is a graph showing the change of the relative concentration of pollutants C / C0 over time in the reaction of oxygen vacancy modified pg-C3N4 / CdS / BiOCl photocatalyst under visible light irradiation to degrade target organic pollutants.

[0035] Figure 2B This is a graph showing the change in pollutant degradation efficiency over time in the reaction of oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst under visible light irradiation.

[0036] Figure 2C It is a pseudo-first-order kinetic fitting curve of the photocatalytic degradation process of target organic pollutants in the reaction of oxygen vacancy modified pg-C3N4 / CdS / BiOCl photocatalyst under visible light irradiation.

[0037] Appendix Figure 3This is a graph showing the changes over time in the fine separation stage of the DK-type nanofiltration membrane in Application Example 2, specifically the retention rate of red acid-related organic acid components and the average permeability of inorganic salts.

[0038] Appendix Figure 4 This is a schematic diagram of the photocatalytic regeneration performance of the anti-fouling high-efficiency red acid separation membrane prepared in Example 2 of the present invention under cyclic operation conditions. The red curve shows the flux retention rate at the end of each operation cycle, and the blue curve shows the flux recovery rate after visible light catalytic regeneration for 30 min. It can be seen that the flux recovery rate after visible light regeneration is relatively high, indicating that the photocatalytic layer can still be effectively excited. Detailed Implementation

[0039] The present invention will be further described below with reference to specific embodiments. These embodiments are merely exemplary and do not constitute any limitation on the present invention. Within the technical concept of the present invention, those skilled in the art can make various modifications. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present invention.

[0040] Example 1: Preparation of a fouling-resistant, high-efficiency red acid separation membrane (1) Preparation of light-transmitting PVDF-HFP casting solution: 6.0 g of PVDF-HFP and 1.5 g of polyethylene glycol (PEG-4000) were weighed as pore-forming agents and added to 43.3 g of N-methylpyrrolidone (NMP, approximately 42.0 mL) to obtain a casting solution with a total mass of 50.8 g. The mass fraction of PVDF-HFP in the casting solution was 11.8 wt%, and the mass fraction of PEG-4000 was 3.0 wt%. The mixture was mechanically stirred in a 60°C water bath for 16 h to ensure complete dissolution of PVDF-HFP and PEG-4000. Subsequently, the mixture was allowed to stand at room temperature for 16 h to remove bubbles, resulting in a uniform and transparent PVDF-HFP casting solution. (2) Preparation of light-transmitting PVDF-HFP porous composite base film: A semi-transparent polypropylene (PP) porous nonwoven fabric was selected as the support layer, with a thickness of 80 μm, an average pore size of 2.0 μm, and a porosity of 65%. The PVDF-HFP casting solution obtained in step (1) was uniformly coated onto the surface of the support layer to form a film with a coating thickness of 90 μm. Then, it was left to stand in the air for 15 s, and then immediately immersed in a 20℃ deionized water coagulation bath to undergo non-solvent-induced phase separation, forming a composite base film composed of a semi-transparent porous support layer and a PVDF-HFP porous separation layer. After the film was completely cured, it was taken out and immersed in deionized water for 36 h, with the deionized water being replaced every 6 h to remove residual NMP solvent and PEG-4000 porogen, thus obtaining a light-transmitting PVDF-HFP porous composite base film. The results of UV-Vis spectrophotometer testing showed that the average transmittance of the PVDF-HFP porous composite base film in the wetted state in the visible light range of 420-780 nm was 31.6%. (3) Surface activation of the composite base film: Weigh 0.20 g of dopamine hydrochloride and add it to 100 mL of 10 mM Tris-HCl buffer. Adjust the pH of the solution to 8.2 to obtain a dopamine hydrochloride solution with a concentration of 2.0 g / L. Cut the PVDF-HFP porous composite membrane obtained in step (2) into 10 cm × 10 cm membrane pieces and immerse them completely in the dopamine hydrochloride solution. Shake and react at room temperature for 8 h. Dopamine undergoes oxidative self-polymerization on the membrane surface and in the near-surface pores to form a polydopamine adhesion layer. After the reaction is complete, rinse the membrane surface repeatedly with deionized water 3 times, 5 min each time, to remove unreacted dopamine monomers and poorly attached polydopamine particles, thus obtaining a surface-activated light-transmitting PVDF-HFP porous composite membrane.

[0041] (4) Photocatalyst immobilization: Weigh 0.10 g of oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst, add it to 100 mL of deionized water, and ultrasonically disperse for 30 min to obtain a photocatalyst dispersion with a concentration of 1.0 g / L. Completely immerse the surface-activated, light-transmitting PVDF-HFP porous composite membrane obtained in step (3) into the photocatalyst dispersion, and allow it to adsorb at room temperature for 8 h with shaking. This allows the oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst to be fixed to the light-incident surface and near-surface pores of the PVDF-HFP porous separation layer through a polydopamine adhesion layer. After adsorption, gently rinse the membrane surface three times with deionized water for 3 min each time to remove unbonded photocatalyst particles. Then, dry the membrane in a 50℃ vacuum drying oven for 8 h to obtain the anti-fouling, high-efficiency red acid separation membrane of this invention, denoted as M1.

[0042] According to the UV-Vis spectrophotometer, the average transmittance of the M1 finished film in the wetted state is 22.5% in the visible light range of 420-780 nm. Example 2: Preparation of a high-efficiency, anti-fouling red acid separation membrane

[0043] (1) Preparation of light-transmitting PVDF-HFP casting solution: 8.0 g of PVDF-HFP and 2.0 g of polyvinylpyrrolidone (PVP, K30) were weighed as pore-forming agents and added to 37.5 g of N,N-dimethylacetamide (DMAc, approximately 40.0 mL) to obtain a casting solution with a total mass of 47.5 g. The mass fraction of PVDF-HFP in the casting solution was 16.8 wt%, and the mass fraction of PVP was 4.2 wt%. The mixture was mechanically stirred in a 70°C water bath for 18 h to ensure complete dissolution of PVDF-HFP and PVP. Subsequently, it was allowed to stand at room temperature for 12 h to degas, resulting in a uniform and transparent PVDF-HFP casting solution. (2) Preparation of light-transmitting PVDF-HFP porous composite base film: Transparent polypropylene (PP) porous nonwoven fabric was selected as the support layer, with a thickness of 100 μm, an average pore size of 1.0 μm, and a porosity of 70%. The casting solution obtained in step (1) was uniformly coated onto the surface of the support layer to form a film with a coating thickness of 120 μm. Then, it was left to stand in the air for 10 s, and then immediately immersed in a 25°C deionized water coagulation bath to undergo non-solvent-induced phase separation, forming a composite base film composed of a transparent porous support layer and a PVDF-HFP porous separation layer. After the film was completely cured, it was taken out and immersed in deionized water for 48 h, with the deionized water being replaced every 6 h to fully remove residual DMAc solvent and PVP pore-forming agent, thus obtaining a light-transmitting PVDF-HFP porous composite base film. The UV-Vis spectrophotometer test results showed that the average transmittance of the light-transmitting PVDF-HFP porous composite base film in the wetted state was 34.8% in the visible light range of 420-780 nm. (3) Surface activation of the composite base film: Weigh 0.20 g of dopamine hydrochloride and add it to 100 mL of 10 mM Tris-HCl buffer. Adjust the pH of the solution to 8.5 to obtain a dopamine hydrochloride solution with a concentration of 2.0 g / L. Cut the PVDF-HFP porous composite membrane obtained in step (2) into 10 cm × 10 cm membrane pieces and immerse them completely in the dopamine hydrochloride solution. Shake and react at room temperature for 6 h. During the reaction, dopamine undergoes oxidative self-polymerization on the surface of the PVDF-HFP porous separation layer and in the near-surface pores to form a polydopamine adhesion layer. After the reaction, rinse the membrane surface with deionized water 3 times, each time for 5 min, to remove unreacted dopamine monomers and unattached polydopamine particles, and obtain a surface-activated light-transmitting PVDF-HFP porous composite membrane. (4) Photocatalyst immobilization: Weigh 0.20 g of oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst and add it to 100 mL of a 1:1 volume ratio ethanol / water mixed solvent. Disperse the mixture ultrasonically for 45 min to obtain a photocatalyst dispersion with a concentration of 2.0 g / L. Completely immerse the surface-activated PVDF-HFP composite membrane obtained in step (3) into the photocatalyst dispersion and allow it to adsorb at room temperature for 8 h. This allows the oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst to be fixed to the light-incident surface and near-surface pores of the PVDF-HFP porous separation layer via a polydopamine adhesion layer. After adsorption, gently rinse the membrane surface three times with deionized water for 3 min each time to remove unbonded photocatalyst particles. Then, dry the membrane in a 50℃ vacuum drying oven for 10 h to obtain the anti-fouling, high-efficiency red acid separation membrane of this invention, denoted as M2.

[0044] According to the UV-Vis spectrophotometer, the average transmittance of the M2 finished film in the wetted state is 22.6% in the visible light range of 420-780 nm.

[0045] Combination Figure 1 The PVDF-HFP separation layer and support layer connecting channel structure shown in section B and Figure 4 The flux recovery rate after regeneration under visible light indicates that the polydopamine adhesion layer and photocatalyst loading did not completely block the light path, and the finished membrane can still be effectively excited by visible light. Application Example 1: Antifouling high-efficiency red acid separation membrane for the separation and component recovery of red acid waste liquid.

[0046] This embodiment uses the antifouling, high-efficiency red acid separation membrane M2 prepared in Example 2, and the experimental raw water is vitamin B1. 12Red acid wastewater is generated during the anion exchange resin regeneration process in the production process. This red acid wastewater is dark reddish-brown, with an initial pH of 1.9, a COD of 15,480 mg / L, a conductivity of 57.8 mS / cm, a total dissolved solids content of 41.9 g / L, a suspended solids content of 312 mg / L, a turbidity of 148 NTU, a protein contaminant content of 126 mg / L, and a red acid-related organic acid component content of 8.2 g / L based on total organic acids.

[0047] (1) Take 6.0 L of the red acid waste liquid and let it stand for 2 h to remove some large particulate sedimentation impurities; filter it with a 100 μm nylon screen and then coarsely filter it with a 5 μm polypropylene filter to remove larger suspended particles and bacterial fragments; then, slowly add 4 wt% NaOH solution under magnetic stirring to adjust the pH of the waste liquid to 5.6 to obtain the red acid waste liquid to be treated; (2) The antifouling high-efficiency red acid separation membrane M2 was cut into membrane sheets with an effective membrane area of ​​50 cm² and assembled into a cross-flow flat sheet membrane module with a quartz transparent window, so that visible light could directly irradiate the light-incident surface of the membrane. The red acid waste liquid to be treated obtained in step (1) was pumped into the membrane module for membrane separation under the following conditions: operating pressure 0.3 MPa, temperature 25℃, cross-flow velocity 1.6 m / s, feed liquid pH 5.6, and volume concentration factor 2.5 times. During operation, suspended particles, bacterial fragments, colloidal substances, proteins and macromolecular organic pollutants in the red acid waste liquid were retained by the M2 membrane, while red acid-related organic acid components and inorganic salts entered the permeate side of the membrane. The permeate after treatment was a clearer reddish-brown color, and the suspended impurities were significantly reduced, indicating that the membrane has good clarification and antifouling operation capabilities under the condition of being used alone.

[0048] (3) The initial flux of the M2 membrane for treating red acid waste liquid was 116 L / (m²·h). After 8 hours of continuous operation, the membrane flux was 82.5 L / (m²·h), and the flux retention rate was 71.1%. This indicates that the supported oxygen vacancy modified pg-C3N4 / CdS / BiOCl photocatalyst was excited under visible light irradiation, causing the organic pollutants deposited on the membrane surface to degrade in situ, delaying membrane fouling and maintaining a high flux.

[0049] Testing showed that after treatment with the M2 membrane, the suspended solids content in the red acid wastewater decreased to 39 mg / L, with a suspended solids removal rate of 87.5%; the turbidity decreased to 12.6 NTU, with a turbidity removal rate of 91.5%; and the protein pollutant content decreased to 26.2 mg / L, with a removal rate of 79.2%. The COD of the permeate after treatment was 11,080 mg / L, with a COD reduction rate of 28.4%, indicating that the membrane can effectively reduce some macromolecular organic pollutants and colloidal pollutants.

[0050] The content of red acid-related organic acid components in the original red acid waste liquid, calculated as total organic acids, remained at 7.3 g / L in the permeate after treatment with the M2 membrane. The permeate rate of red acid-related organic acid components was 89.0%, indicating that the membrane, while removing suspended solids, colloidal and protein pollutants, allows most of the red acid-related organic acid components to pass through, avoiding significant loss of valuable components during the pretreatment stage. The conductivity of the permeate after treatment was 55.1 mS / cm, which was only slightly lower than the conductivity of the original water (57.8 mS / cm), indicating that inorganic salt components basically permeated through the membrane.

[0051] (4) After the M2 membrane had been running continuously for 8 hours, the flow of red acid waste liquid was stopped, and the residual concentrate in the membrane module was discharged. Then, 1.0 L of deionized water was introduced into the membrane module and circulated at a cross-flow velocity of 1.0 m / s, while simultaneously being irradiated with visible light for 30 minutes, maintaining the incident light intensity on the membrane surface at 100 mW / cm² for M2 regeneration. After regeneration, the red acid waste liquid to be treated was reintroduced for flux testing. The results showed that the red acid waste liquid flux of the M2 membrane recovered from 82.5 L / (m²·h) before regeneration to 106.8 L / (m²·h), with a flux recovery rate of 92.1%.

[0052] (5) Under the same feed, pressure, temperature, and crossflow velocity conditions, the M2 membrane was operated under no-light conditions for 8 hours. The results showed that under no-light conditions, the membrane flux decreased from the initial 114 L / (m²·h) to 58.4 L / (m²·h), with a flux retention rate of only 51.2%. After rinsing with deionized water for 30 min, the membrane flux recovered to 75.6 L / (m²·h), with a flux recovery rate of 66.3%. In contrast, under visible light-assisted operation, the flux retention rate of the M2 membrane after 8 hours of operation was 71.1%, and the flux recovery rate after visible light regeneration was 92.1%. This indicates that the M2 membrane loaded with oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst not only has the impurity removal function of conventional porous membranes, but also can achieve in-situ degradation of the fouling layer and flux recovery through visible light response, which is significantly better than simple physical filtration or operation under no-light conditions.

[0053] Application Example 2: The anti-fouling high-efficiency red acid separation membrane of the present invention is connected in series with a DK-type nanofiltration membrane for the resource recovery of red acid waste liquid. This embodiment uses the antifouling, high-efficiency red acid separation membrane M2 prepared in Example 2, and the experimental raw water is vitamin B1. 12The wastewater is red acid produced during the anion exchange resin regeneration process. The wastewater is dark reddish-brown and contains red acid, high concentrations of inorganic salts, proteins, bacterial fragments, colloids, and other organic impurities. Its initial pH was 1.8, COD was 15,600 mg / L, conductivity was 58.4 mS / cm, total dissolved solids were 42.7 g / L, suspended solids were 286 mg / L, and the content of red acid-related organic acid components (based on total organic acids) was 8.4 g / L.

[0054] (1) Pretreatment of red acid solution: Take 10.0 L of the described red acid waste liquid and let it stand for 2 h to remove large particulate sedimentation impurities. Then, filter it through a 100 μm nylon screen and then coarsely filter it through a 5 μm polypropylene filter to remove large particulate suspended solids, bacterial fragments, and some colloidal impurities. Afterward, slowly add 4 wt% NaOH solution under magnetic stirring to adjust the pH of the waste liquid to 5.6, obtaining the red acid waste liquid to be treated. (2) Photocatalytic anti-pollution pretreatment: The antifouling high-efficiency red acid separation membrane M2 was cut into membrane sheets with an effective membrane area of ​​50 cm² and assembled into a cross-flow flat sheet membrane module with a quartz transparent observation window, allowing visible light to directly illuminate the light-incident surface of the membrane. The red acid waste liquid to be treated was pumped into the membrane module for pretreatment separation. The pretreatment conditions were as follows: operating pressure 0.1 MPa, temperature 25℃, cross-flow velocity 1.5 m / s, feed volume 5.0 L, running time 6 h, visible light source 300 W xenon lamp with a 420 nm cutoff filter, and incident light intensity on the membrane surface 100 mW / cm². 2 During operation, proteins, bacterial fragments, colloidal particles, and macromolecular organic pollutants in the red acid waste liquid are retained by the M2 membrane. The M2 membrane was found to have a removal rate of 85% for suspended solids, 90% for turbidity, an 80% retention rate for protein pollutants, and a 75% reduction rate for macromolecular organic pollutants. The permeability of red acid-related organic acid components remained above 85%.

[0055] After 6 hours of continuous operation, the membrane flux was measured to be 89.0 L / (m²·h), and the flux retention rate was 75.4%. This indicates that the oxygen vacancy modified pg-C3N4 / CdS / BiOCl photocatalyst was excited under visible light irradiation, generating photogenerated electrons, holes and active oxygen species, which degraded organic pollutants deposited on the membrane surface in situ and delayed the formation of the membrane fouling layer. (3) Photocatalytic regeneration of the membrane fouling layer: The initial flux of red acid waste liquid into the M2 membrane was 118 L / (m²·h). When it dropped to 75.4% of the initial flux, the feeding of red acid waste liquid into the membrane module was stopped, and the residual concentrate in the membrane module was discharged. Subsequently, 1.0 L of deionized water was circulated into the membrane module at a cross-flow velocity of 1.0 m / s, and the light-incident surface of the membrane was irradiated with visible light for 30 min at an intensity of 100 mW / cm² for membrane regeneration. After photocatalytic regeneration, the circulating liquid in the membrane module was drained, and the red acid waste liquid to be treated was re-infused for flux testing. The results showed that the flux of red acid waste liquid after M2 membrane regeneration recovered to 109 L / (m²·h), with a flux recovery rate of 92.4%, indicating that visible light irradiation can promote the degradation, loosening, and desorption of the fouling layer on the membrane surface, achieving in-situ recovery of membrane flux. (4) DK type nanofiltration membrane fine separation: Approximately 3.0 L of the permeate after photocatalytic antifouling pretreatment via the M2 membrane in step (2) was collected and used as the nanofiltration feed liquid. This permeate was then introduced into a DK-type nanofiltration membrane unit for fine separation. The effective membrane area of ​​the DK-type nanofiltration membrane is 100 cm². ² The nanofiltration operating conditions are: operating pressure 0.6-1.2 MPa, temperature 25℃, crossflow velocity 1.0-2.0 m / s, feed solution pH 5.6, and volume concentration factor 2.5 times. During operation, red acid and some organic acid components are mainly retained and enriched on the concentrate side by the DK-type nanofiltration membrane, while inorganic salt components such as NaCl, KCl, and Na2SO4 mainly enter the permeate side, achieving separation, desalination, and resource enrichment of red acid components and inorganic salts. After the nanofiltration operation, the test results are as follows: the concentration of red acid-related organic acid components in the nanofiltration concentrate, calculated as total organic acids, increased from 7.6 g / L in the feed liquid to 18.5 g / L; the conductivity of the nanofiltration permeate was 43.2 mS / cm; the retention rate of red acid-related organic acid components was 96.4%; the average permeate rate of inorganic salts was 91.2%; and the overall recovery rate of the series system was 80.6% based on the total amount of red acid-related organic acids entering the M2 photocatalytic anti-fouling pretreatment unit. If only the mass of red acid-related organic acids in the DK-type nanofiltration feed liquid is considered, the recovery rate of the nanofiltration stage is approximately 97%. (5) Evaluation of the stability of the series system: Ten run-regeneration cycles were continuously performed according to the process conditions in steps (2) to (4). In each cycle, the M2 membrane was used for photocatalytic antifouling pretreatment of red acid waste liquid for 6 h; when the flux dropped to 70-80% of the initial flux, it was circulated with deionized water and regenerated under visible light for 30 min; then the next round of red acid waste liquid treatment experiment was continued. After each cycle, the DK nanofiltration membrane was rinsed with deionized water under a low pressure of 0.1 MPa for 15 min. After 10 cycles, the M2 membrane still maintained stable photocatalytic antifouling performance. In the 10th cycle, the initial flux of red acid waste liquid of the M2 membrane was 113 L / (m ² The flux after 6 hours of operation is 83 L / (m³). ² The flux retention rate was 73.5% (·h). After 30 minutes of visible light regeneration, the flux recovered to 10³ L / (m²). ² The flux recovery rate was 91.2%. The tandem DK nanofiltration membrane maintained good separation performance, with a rejection rate of 95.7% for red acid-related organic acid components and an average inorganic salt permeation rate of 90.5% in the 10th cycle. The overall recovery rate of red acid-related organic acid components was 79.8%.

Claims

1. A fouling-resistant, high-efficiency red acid separation membrane, comprising: The transparent or semi-transparent porous support layer, the light-transmitting polyvinylidene fluoride-hexafluoropropylene copolymer porous separation layer, the polydopamine adhesion layer, and the photocatalytic anti-fouling layer loaded with oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst are arranged sequentially from bottom to top.

2. The separation membrane according to claim 1, wherein the transparent or semi-transparent porous support layer has a thickness of 30-200 μm, a pore size of 0.1-10 μm, and a porosity of 40-85%.

3. The separation membrane according to claim 1, wherein the thickness of the light-transmitting polyvinylidene fluoride-hexafluoropropylene copolymer porous separation layer is 30-150 μm.

4. The separation membrane according to claim 1, wherein the amount of the polydopamine adhesive layer is 0.05-0.50 mg / cm² membrane area.

5. The separation membrane according to claim 1, wherein the loading of the oxygen vacancy modified pg-C3N4 / CdS / BiOCl photocatalyst is 0.5-5.0 wt%, based on the mass of the transparent or semi-transparent porous support layer and the light-transmitting polyvinylidene fluoride-hexafluoropropylene copolymer porous separation layer.

6. A method for preparing a separation membrane according to any one of claims 1-5, comprising the following steps: (1) Preparation of light-transmitting PVDF-HFP casting solution: Mix PVDF-HFP, pore-forming agent and organic solvent, stir at 50-80℃ for 8-24 h to fully dissolve PVDF-HFP and pore-forming agent, let stand for 6-24 h to degas, and obtain a uniform casting solution. (2) Preparation of light-transmitting PVDF-HFP porous composite base film: The casting solution obtained in step (1) is scraped onto the surface of a transparent or semi-transparent porous support layer. The thickness of the wet film is 50-200 μm. After being left in the air for 5-30 s, it is immersed in a deionized water coagulation bath at 15-30℃ to undergo non-solvent-induced phase separation and form a light-transmitting PVDF-HFP porous composite base membrane. After the membrane is completely cured, it is taken out and soaked and washed with deionized water for 24-48 h, with the water changed every 6-8 h to remove residual solvent and pore-forming agent. (3) Surface activation of the composite base film: The light-transmitting PVDF-HFP porous composite membrane obtained in step (2) is immersed in a 1-3 g / L dopamine hydrochloride solution and shaken at room temperature for 2-12 h to allow dopamine to undergo oxidative self-polymerization and form a polydopamine adhesion layer on the membrane surface. After the reaction is completed, it is thoroughly rinsed with deionized water to remove unreacted dopamine monomers and unattached polydopamine particles, thus obtaining a surface-activated light-transmitting PVDF-HFP porous composite membrane. (4) Photocatalyst immobilization: The oxygen vacancy-modified pg-C3N4 / CdS / BiOCl photocatalyst was dispersed in deionized water or ethanol / water with a volume ratio of 1:1 and ultrasonically dispersed for 20-60 min to obtain a uniform catalyst dispersion. The surface-activated PVDF-HFP porous base membrane was immersed in the catalyst dispersion and adsorbed by shaking at room temperature for 2-12 h to fix the photocatalyst on the light-incident surface and near-surface pores of the PVDF-HFP porous separation layer of the composite base membrane. After adsorption, the membrane was rinsed with deionized water to remove unbonded particles and then vacuum dried at 40-60℃ for 6-12 h to obtain a fouling-resistant, high-efficiency red acid separation membrane.

7. The method according to claim 6, wherein in step (1), the mass fraction of the PVDF-HFP is 10-20 wt%, the mass fraction of the pore-forming agent is 2-8 wt%, based on the total mass of the casting solution; the pore-forming agent is polyvinylpyrrolidone or polyethylene glycol; and the organic solvent is one of N,N-dimethylacetamide, N,N-dimethylformamide or N-methylpyrrolidone.

8. The method according to claim 6, wherein in step (3), the amount of dopamine hydrochloride solution used is 0.5-2.0 mL / cm² membrane area.

9. The method according to claim 6, wherein in step (4), the concentration of the catalyst dispersion is 0.5-5.0 g / L.

10. Use of the antifouling, high-efficiency red acid separation membrane according to any one of claims 1-5.

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