Preparation method of pH response type oil-water separation membrane

Abstract

The invention provides a preparation method of a pH response type oil-water separation membrane. Specifically, the preparation method comprises the following steps: firstly, grafting polystyrene-maleic anhydride with a substance with primary amine and tertiary amine to prepare an amphiphilic copolymer; and then blending with a high-molecular polymer, and preparing the super-hydrophilic / underwater super-oleophobic film by adopting a phase inversion method. The surface of the blended membrane has rich hydrophilic functional groups including carboxyl and tertiary amine, so that the membrane shows good hydrophilicity and underwater super-oleophobic property, efficient oil-water separation is realized, and meanwhile, the tertiary amine and carboxyl on the surface of the membrane can be activated by acid or alkali and have certain pH responsiveness, so that the membrane has a self-cleaning function.

Description

Technical Field

[0001] The invention belongs to the technical field of functional polymer membrane separation, and in particular relates to a method for preparing a pH-responsive oil-water separation membrane. Background Art

[0002] With the rapid development of industries such as petrochemicals, pharmaceuticals, and food processing, the generation of large quantities of oily wastewater has become a significant environmental concern. This wastewater not only severely disrupts the natural ecological balance but also poses a potential threat to human health. When discharged into the ocean, it forms a dense oil film on the surface, hindering oxygen dissolution and suffocating marine life, leading to widespread marine environmental pollution. If oily wastewater seeps into the soil, it contaminates groundwater, endangering drinking water safety and reducing crop yields. More seriously, toxic substances in the wastewater can accumulate in plants and animals through the food chain, ultimately causing irreversible damage to human health.

[0003] Common methods for treating oily wastewater include gravity separation, filtration, adsorption, chemical demulsification, coagulation and flocculation, membrane separation and biological methods. Chemical demulsification is recognized as the most effective separation method for treating oil-in-water emulsions and has been widely used. The main mechanism of chemical demulsification is that the demulsifier is adsorbed on the oil-water interface of the emulsified droplets, reducing the interfacial membrane strength, making the emulsion membrane easy to break, and then promoting the aggregation of dispersed droplets, thereby phase separation and ultimately achieving oil-water separation. However, although this method has good demulsification and oil-water separation effects on oil-water emulsions, it has problems such as large dosage and residue in sewage that can easily cause secondary pollution. In addition, for low-concentration oily sewage, the demulsification effect of the demulsifier is poor, and the treated sewage often does not meet the discharge standards.

[0004] As a physical separation process, membrane technology has the advantages of high separation efficiency and low energy consumption. It can solve the problems existing in traditional oil-water separation methods and is a simple and efficient separation technology. Membrane separation uses the selective permeation function of the membrane to separate solvents and solutions. When certain mixtures pass through the membrane, they are driven by the forces generated by temperature differences, pressure differences, concentration differences, or potential differences to achieve the purpose of purification or concentration. Membrane separation can effectively separate solids in liquids and gases dissolved in solutions. However, for oily wastewater containing surfactants and polymers, conventional separation membranes are prone to membrane fouling and have no demulsification effect on emulsions, making it difficult to achieve effective oil-water separation.

[0005] In recent years, stimuli-responsive membranes have become a research hotspot for oil-water separation, aiming to cope with complex oily wastewaters and improve membrane lifespan. These stimuli include temperature, pH, light, electric fields, and magnetic fields. pH-responsive membranes have been widely studied in wastewater treatment due to their rapid response and low energy consumption. However, the preparation of the pH-responsive polymer poly (N,N-dimethylaminoethyl methacrylate) (PDMAEMA) is complex and expensive.

[0006] Building on the above research, the present invention, inspired by the pH-responsive polymer PDMAEMA, grafts polystyrene-maleic anhydride (SMA) with substances containing primary and tertiary amines to produce an amphiphilic copolymer. This copolymer is then blended with a polymer to prepare a superhydrophilic / underwater superoleophobic membrane using a phase inversion method. By using substances containing primary and tertiary amines, pH-responsive groups are generated in situ on the polymer surface to regulate the charge on the membrane surface. The chemical structure of the membrane surface is also explored, as is the effect of charge on the separation performance of oil-water emulsions using different types of surfactants. This provides a strategy for practical oil-water separation of crude oil produced fluids. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for preparing a pH-responsive oil-water separation membrane.

[0008] The present invention provides a method for preparing a pH-responsive oil-water separation membrane, comprising the following steps:

[0009] (1) A substance having both primary and tertiary amines and dried polystyrene-maleic anhydride (abbreviated as SMA) are dissolved in an organic solvent A, and reacted in a water bath at 30-80°C for 2-12 hours. After the reaction is completed, the solvent is evaporated to obtain an SMA-grafted amphiphilic copolymer; (2) The SMA-grafted amphiphilic copolymer is blended with a high molecular weight polymer, dissolved in an organic solvent B at 40-90°C, and prepared into a casting liquid. The casting liquid is poured onto a clean glass plate, and a 250 μm scraper is used to scrape out a liquid film on a scraping machine, and then the film is transferred to a coagulation bath and prepared by a non-solvent-induced phase inversion method to obtain a pH-responsive oil-water separation membrane. Among them, the substance with both primary and tertiary amines is one of N,N-dimethylethylenediamine (DMEDA), 3-dimethylamino-1-propylamine (DMPA), N,N-dimethyl-1,4-butanediamine (DMBDA) or N,N-dimethyl-1,6-hexanediamine (DMHDA); the molecular weight of SMA is between 3000 and 200000 Da, and the anhydride content is 3-30%; the high molecular polymer is polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polypropylene (PP), polysulfone (PS F) or polyethersulfone (PES); organic solvent A is one of tetrahydrofuran, dioxane, ethanol, propanol, butanol, dichloromethane, and chloroform; organic solvent B is one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, or dimethyl sulfoxide; the viscosity of the casting solution is controlled within a range of 500 to 3000 mPa·s; and the coagulation bath is one of water, ethanol, methanol, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone, or a combination thereof.

[0010] The pH-responsive oil-water separation membrane of the present invention has outstanding hydrophilicity and underwater superoleophobicity, with the pure water contact angle of the membrane being less than 30° and the underwater oil contact angle being greater than 150°.

[0011] The pH-responsive oil-water separation membrane of the present invention has excellent oil-water separation properties, and the oil removal rate of oil-produced wastewater is greater than 95%.

[0012] The pH-responsive oil-water separation membrane of the present invention has a certain pH responsiveness, and the tertiary amine and carboxyl groups on its surface can be activated by acid or alkali, so that it has a self-cleaning function. DETAILED DESCRIPTION

[0013] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0014] Example 1

[0015] (1) SMA (molecular weight 100,000, anhydride content 20%) was dissolved in tetrahydrofuran (THF) with a molar ratio of 1:1 to anhydride and 3-dimethylamino-1-propylamine (DMPA). The mixture was heated in a water bath at 60°C for 9 h. After the reaction was complete, the solvent was evaporated to obtain a DMPA-grafted SMA amphiphilic polymer, referred to as DMPA@SMA.

[0016] (2) 2.0 g DMPA@SMA and 3.2 g PVDF were dissolved in 30 g DMAc under heating at 70 °C in a water bath to prepare a casting solution. The casting solution was poured onto a non-woven fabric and a 250 μm scraper was used to scrape the liquid film. The film was then transferred to a coagulation bath (35 °C deionized water) for phase inversion to obtain a DMPA@SMA / PVDF blend membrane.

[0017] (3) The pure water contact angle of the DMPA@SMA / PVDF blend membrane is 18°, the underwater oil contact angle is greater than 150°, and the pure water flux reaches 782.0 L·m -2 ·h -1 The separation efficiency of water-in-oil emulsion (oil content 1.0wt%, sodium lauryl sulfate 0.2wt%) prepared with petroleum ether, toluene, kerosene and crude oil exceeded 96.5%.

[0018] (4) The DMPA@SMA / PVDF blend membrane was cyclically treated with a crude oil emulsion containing 1.0 wt% oil. The emulsion was filtered for 60 min, and the membrane was washed with pure water or an alkaline aqueous solution containing NaOH (pH = 10) for 30 min, and the pure water flux of the membrane was measured; then the emulsion was filtered for another 60 min, and the membrane was washed with pure water or an alkaline aqueous solution for 30 min, and the pure water flux of the membrane was measured; 10 cycles were repeated, and the flux retention rate of the membrane washed with pure water after the 10th cycle was 85.2%, while the flux retention rate of the membrane washed with alkaline solution after the 10th cycle was 92.3%.

[0019] Example 2

[0020] (1) The molar ratio of anhydride to N,N-dimethylethylenediamine (DMEDA) in SMA (molecular weight 120,000, anhydride content 15%) was controlled to be 1:1, dissolved in ethanol, and reacted in a water bath at 60°C for 9 h. After the reaction was completed, the solvent was evaporated to obtain a DMEDA-grafted SMA amphiphilic polymer, referred to as DMEDA@SMA.

[0021] (2) 2.0 g of DMEDA@SMA and 3.2 g of PVDF were dissolved in 30 g of dimethyl sulfoxide under heating at 70 °C in a water bath to prepare a casting solution. The casting solution was poured onto a non-woven fabric and a 250 μm scraper was used to scrape the liquid film. The film was then transferred to a coagulation bath (35 °C deionized water) for phase inversion to obtain a DMEDA@SMA / PVDF blend membrane.

[0022] (3) The pure water contact angle of the DMEDA@SMA / PVDF blend membrane is 22°, the underwater oil (kerosene) contact angle exceeds 150°, and the pure water flux is close to 680 L·m -2 ·h -1 The separation efficiency of water-in-oil emulsion (oil content 1.0wt%, dodecyltrimethylammonium bromide 0.2wt%) prepared with petroleum ether, toluene, kerosene and crude oil exceeds 95.6%.

[0023] (4) The DMEDA@SMA / PVDF blend membrane was cyclically treated with a crude oil emulsion containing 1.0 wt% oil. The emulsion was filtered for 60 min, the membrane was washed with pure water or a dilute hydrochloric acid solution (pH = 4) for 30 min, and the pure water flux of the membrane was measured. The emulsion was then filtered for another 60 min, the membrane was washed with pure water or a dilute hydrochloric acid solution for 30 min, and the pure water flux of the membrane was measured. This cycle was repeated 10 times. The flux retention rate of the membrane washed with pure water after the 10th cycle was 83.0%, while the flux retention rate of the membrane washed with a dilute hydrochloric acid solution after the 10th cycle was 91.8%.

[0024] Example 3

[0025] (1) SMA (molecular weight 100,000, anhydride content 25%) was dissolved in propanol (a solvent) at a molar ratio of 1:1 to anhydride and reacted in a water bath at 60°C for 9 h. After the reaction was complete, the solvent was evaporated to obtain a DMHDA-grafted SMA amphiphilic polymer, referred to as DMHDA@SMA.

[0026] (2) 2.0 g DMHDA@SMA and 3.2 g PSF were dissolved in 30 g N-methylpyrrolidone under heating at 70 °C in a water bath to prepare a casting solution. The casting solution was poured onto a non-woven fabric and a 250 μm scraper was used to scrape the liquid film. The film was then transferred to a coagulation bath (35 °C deionized water) for phase inversion to obtain a DMHDA@SMA / PSF blend film.

[0027] (3) The pure water contact angle of the DMHDA@SMA / PSF blend membrane is 15°, the underwater oil (kerosene) contact angle is 154°, and the pure water flux is close to 820.0 L·m -2 ·h -1The separation efficiency of water-in-oil emulsion (oil content 1.0wt%, sodium lauryl sulfate 0.2wt%) prepared with petroleum ether, toluene, kerosene and crude oil reached 98.4%.

[0028] (4) The DMHDA@SMA / PSF blend membrane was cyclically treated with a crude oil emulsion containing 1.0 wt% oil. The emulsion was filtered for 60 min, and the membrane was washed with pure water or an alkaline aqueous solution containing 1.0 wt% NaOH for 30 min, and the pure water flux of the membrane was measured. The emulsion was then filtered for another 60 min, and the membrane was washed with pure water or an alkaline aqueous solution containing NaOH (pH = 10) for 30 min, and the pure water flux of the membrane was measured. This cycle was repeated 10 times. The flux retention rate of the membrane washed with pure water after the 10th cycle was 86.4%, while the flux retention rate of the membrane washed with alkaline solution after the 10th cycle was 93.5%.

[0029] Comparative Example 1

[0030] (1) 2.0 g SMA (molecular weight 100,000, anhydride content 20%) and 3.2 g PVDF were dissolved in 30 g DMAc under heating at 70 °C in a water bath to prepare a casting solution. The casting solution was poured onto a non-woven fabric and a 250 μm scraper was used to scrape the liquid film. The film was then transferred to a coagulation bath (35 °C deionized water) for phase inversion to obtain an SMA@PVDF blend membrane.

[0031] (2) The pure water contact angle of the SMA@PVDF blend membrane is 88°, the underwater oil contact angle is greater than 123°, and the pure water flux is 75.5 L·m -2 ·h -1 The separation efficiency of water-in-oil emulsion (oil content 1.0wt%, sodium lauryl sulfate 0.2wt%) prepared with petroleum ether, toluene, kerosene and crude oil exceeded 64.2%.

[0032] (3) The SMA@PVDF blend membrane was circulated to treat a crude oil emulsion containing 1.0 wt% oil. The emulsion was filtered for 60 min, and the membrane was washed with pure water or an alkaline aqueous solution containing NaOH (pH = 10) for 30 min, and the pure water flux of the membrane was measured. The emulsion was then filtered for another 60 min, and the membrane was washed with pure water or an alkaline aqueous solution for 30 min, and the pure water flux of the membrane was measured. This cycle was repeated 10 times. The flux retention rate of the membrane washed with pure water after the 10th cycle was 15.4%, and the flux retention rate of the membrane washed with alkaline solution after the 10th cycle was 24.6%.

Claims

1. A method for preparing a pH-responsive oil-water separation membrane, characterized in that: The method comprises the following steps: (1) dissolving a substance having both primary and tertiary amines and dried polystyrene-maleic anhydride in an organic solvent A, and reacting them in a water bath at 30 to 80° C. for 2 to 12 hours. After the reaction is complete, the solvent is evaporated to obtain an SMA-grafted amphiphilic copolymer; (2) The SMA grafted amphiphilic copolymer is blended with a high molecular weight polymer and dissolved in an organic solvent B at 40-90°C to prepare a casting liquid. The casting liquid is poured onto a glass plate, and a liquid film is scraped out on a scraping machine using a scraper. The liquid film is then transferred to a coagulation bath and a pH-responsive oil-water separation membrane is prepared by a non-solvent-induced phase inversion method.

2. The method for preparing a pH-responsive oil-water separation membrane according to claim 1, wherein: The substance having both primary and tertiary amines is one of N,N-dimethylethylenediamine, 3-dimethylamino-1-propylamine, N,N-dimethyl-1,4-butanediamine or N,N-dimethyl-1,6-hexanediamine.

3. The method for preparing a pH-responsive oil-water separation membrane according to claim 1, wherein: The molecular weight of the SMA is between 3000 and 200000 Da, and the anhydride content is 3 to 30%.

4. The method for preparing a pH-responsive oil-water separation membrane according to claim 1, wherein: The high molecular polymer is one of polyvinylidene fluoride, polyacrylonitrile, polypropylene, polysulfone or polyethersulfone.

5. The method for preparing a pH-responsive oil-water separation membrane according to claim 1, wherein: The organic solvent A is one of tetrahydrofuran, dioxane, ethanol, propanol, butanol, dichloromethane and chloroform.

6. The method for preparing a pH-responsive oil-water separation membrane according to claim 1, wherein: The organic solvent B is one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide.

7. The method for preparing a pH-responsive oil-water separation membrane according to claim 1, wherein: The viscosity of the casting solution is controlled within a range of 500 to 3000 mPa·s.

8. The method for preparing a pH-responsive oil-water separation membrane according to claim 1, wherein: The coagulation bath is one or a combination of water, ethanol, methanol, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

9. A pH-responsive oil-water separation membrane prepared by the preparation method according to any one of claims 1 to 8.

10. A pH-responsive oil-water separation membrane according to claim 9, characterized in that: The pure water contact angle of the prepared pH-responsive oil-water separation membrane is less than 30°, and the underwater oil contact angle is greater than 150°.