Preparation method of fiber-based oil-water emulsion separation membrane material with adjustable surface charge

Abstract

The application belongs to the field of oily wastewater treatment, and specifically discloses a preparation method of a fiber-based oil-water emulsion separation membrane material with adjustable surface charge. The preparation method comprises the following steps: performing amino grafting modification on the surface of the fiber, and then performing polyethylene imine grafting on the surface of the fiber through a sulfur-based coupling reaction; in order to realize zwitterionization of the surface of the fiber, an anion group is introduced to the surface of the fiber, so that the surface of the fiber contains both anion and cation groups; and then the modified fiber is formed into a fiber membrane through a wet forming process, and is used for oil-water emulsion separation. The obtained fiber membrane can be pre-wetted by different pH solutions to adjust the surface charge, so as to realize selective separation of stable oil-in-water emulsions of different types of surfactants, and the two-step wetting can be used to separate stable water-in-oil emulsions of surfactants, and the fiber membrane has a good application prospect in the fields of oily wastewater treatment and oil purification.

Description

Technical Field

[0001] This invention belongs to the field of oily wastewater treatment, specifically relating to a method for preparing a fiber-based oil-water emulsion separation membrane material with adjustable surface charge. The fiber surface of this separation membrane material is amphoteric ionized, and through surface charge regulation, it can be used for demulsification and separation of oil-water emulsions stabilized by various surfactants. Background Technology

[0002] Because polymers, surfactants and other additives are used in the extraction process, oily wastewater has a high degree of emulsification and is difficult to treat. Effective treatment of emulsified oily wastewater is a major challenge for the petrochemical industry.

[0003] Currently, commonly used demulsification methods mainly include physical methods such as ultrasonic microwave mechanical shearing and heating-pressurized demulsification, as well as chemical methods such as adding demulsifiers. Physical methods require large equipment footprints and consume high energy during operation, while chemical demulsification methods pose secondary pollution problems. Membrane separation, as a physical method, has received widespread attention due to its simple operation and high separation efficiency. Traditional membrane separation methods can separate oil-water emulsions through membrane pore size and membrane surface, but most only target emulsions stabilized by a single surfactant. Chinese patent application CN111330462A discloses a method for obtaining superhydrophobic oil-water separation membrane materials by hydrophobically modifying fibers with polydimethylsiloxane, but hydrophobic separation membranes are prone to membrane fouling during use, which can significantly affect flux. Chinese patent application CN110079358A discloses a method for manufacturing fiber felt with demulsification function by needle punching. Because needle punching can generate many burr structures on the surface of the prepared material, it has a good demulsification function for emulsions, but this material can only rely on the rough structure for demulsification, its function is relatively limited, and it does not have selective separation capability. Chinese patent application CN112642304B discloses a superhydrophilic separation membrane material obtained by surface modification of fibers through the reaction of elemental sulfur, polyethyleneimine and amino groups on silane coupling agent KH-550. This material can selectively separate oil-in-water emulsions prepared by anionic emulsifiers and amphoteric emulsifiers, but its application is relatively narrow. Summary of the Invention

[0004] This invention provides a method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge. The method includes the following steps: first, the fiber surface is modified by amylation grafting; then, polyethyleneimine (PEI) is grafted onto its surface via a sulfonyl coupling reaction. To achieve amphoteric ionization of the fiber surface, anionic groups are further introduced, resulting in the fiber surface containing both anionic and cationic groups. The modified fibers are then processed using a wet forming process to obtain a fiber membrane for oil-water emulsion separation. The resulting fiber membrane can have its surface charge controlled by pre-wetting with solutions of different pH values, achieving selective separation of oil-in-water emulsions stabilized by different types of surfactants. Simultaneously, two-step wetting can be used to separate surfactant-stabilized water-in-oil emulsions, showing promising application prospects in oily wastewater treatment and oil purification.

[0005] To achieve the above objectives, the present invention employs the following technical solution: a method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge, the preparation method comprising:

[0006] 1) After cleaning the fiber, its surface is modified by amylation grafting using an amino-containing silane coupling agent;

[0007] 2) Grafting polyethyleneimine onto surface-aminated fibers via a sulfur-based coupling reaction;

[0008] 3) Further zwitterionic modification of the surface of the grafted polyethyleneimine fiber is carried out, and zwitterionic groups are introduced by the reaction between the tertiary amine groups in polyethyleneimine and different small molecule compounds.

[0009] 4) A fiber-based oil-water emulsion separation membrane material with adjustable surface charge was prepared by wet film formation process after the amphoteric ionization modified fiber.

[0010] Preferably, the fibers used in step 1) are glass fiber, basalt fiber, or carbon fiber.

[0011] In step 1), the amylation grafting modification of the fiber surface is achieved by immersing the fiber in an ethanol solution of an amino-containing silane coupling agent, followed by curing. After curing, the fiber is cleaned with anhydrous ethanol and dried (preferably at a drying temperature of 60°C). The silane coupling agent used is γ-aminopropyltriethoxysilane (KH-550), γ-aminopropyltrimethoxysilane (HD-540), or N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (HD-792), etc. The concentration of the ethanol solution of the silane coupling agent is 5-30 wt%, the immersion conditions are 20-25°C for 1-2 hours, and the curing conditions are 80-120°C for 1-3 hours.

[0012] Step 2) involves grafting polyethyleneimine onto the fiber surface via a sulfur-coupled reaction. The specific procedure is as follows: Aminated fibers are dispersed in a sulfur / pyridine solution. Then, a polyethyleneimine / pyridine solution is added to the mixture to initiate the reaction. After the reaction, the sample is thoroughly washed with hot pyridine and deionized water, and then dried (preferably at 60°C). The concentration of the sulfur / pyridine solution is 25-35 g / L, the concentration of the polyethyleneimine / pyridine solution is 10-30 wt%, and the reaction conditions are 80-100°C for 12-16 hours.

[0013] The specific operation of amphoteric ionization of the fiber surface in step 3) is as follows: the fiber grafted with polyethyleneimine is dispersed in the amphoteric ionization treatment agent and reacted at 40-90℃ for 24-72 hours. After the reaction, the sample is washed with anhydrous ethanol and deionized water respectively and dried (preferably at 60℃).

[0014] Preferably, the zwitterionic treatment agent used in step 3) is 1,4-sulfonate butyrolactone; or, a methanol solution of 1,3-propanesulfonate, 2-alkoxy-2-oxo-1,3,2-dioxophosphazenecyclopentane or α,β-unsaturated carboxylic acid with a concentration of 5-30 wt%.

[0015] The specific operation of preparing the fiber membrane by wet film formation process in step 4) is as follows: the amphoteric ionized modified fiber is cut to about 0.5-1cm and uniformly dispersed in 200-250mL of deionized water at a speed of 1000-1500rpm using a high-speed stirrer. The fiber dispersion is then poured into a filter device and dehydrated by an oil pump to obtain a fiber membrane for oil-water emulsion separation.

[0016] The fiber-based oil-water emulsion separation membrane material with adjustable surface charge obtained by the preparation method of the present invention can be used for efficient separation of various types of surfactant-stabilized emulsions after pre-wetting with solutions of different pH values.

[0017] A method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge, the synthesis mechanism of which is shown in the following equation:

[0018]

[0019] Specifically, the present invention also provides a method for separating surfactant-stabilized oil-water emulsions, the separation method comprising:

[0020] The fiber membrane prepared by the above-mentioned method for preparing fiber-based oil-water emulsion separation membrane material with adjustable surface charge is pre-wetted with an aqueous solution of a certain pH, and then the pre-wetted fiber membrane is used to perform efficient selective separation of surfactant-stabilized oil-in-water emulsions.

[0021] Alternatively, a fiber-based oil-water emulsion separation membrane with adjustable surface charge can be pre-wetted with a certain amount of oil phase, and then the pre-wetted fiber membrane can be used to demulsify the surfactant-stabilized water-in-oil emulsion; then, the fiber membrane can be pre-wetted with a certain amount of aqueous solution to separate the oil and water in the demulsified water-in-oil emulsion.

[0022] The emulsions prepared using the different surfactants mentioned above are anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants, specifically such as sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), dodecyl betaine (BS-12), and Tween-80. The oil-water emulsions treated by this invention are oil-in-water emulsions or water-in-oil emulsions prepared using the above-mentioned surfactants.

[0023] The surface charge properties of membrane materials significantly influence emulsion separation efficiency during emulsion separation, and electrostatic attraction can further enhance the demulsification ability of membrane materials. Amphoteric polymers are compounds possessing both cations and anions, and their electrical properties can be adjusted by the pH value of the environment. Therefore, by modifying fiber membranes with zwitterionic grafting, the surface charge properties of the membrane can be utilized for efficient demulsification and separation of oil-water emulsions. On the other hand, various inorganic fibers exhibit good chemical stability, are not easily reacted with chemicals in complex oily wastewater, and after wet processing, the fibers overlap to form abundant channels and pores, which facilitates the collision and interception of emulsion droplets within them.

[0024] This invention discloses a method for demulsifying and separating oil-water emulsions stabilized by various surfactants by amphoteric ionization of fiber surfaces and the subsequent surface charge regulation. By adjusting the charge on the fiber surface with different pH solutions, the amphoteric ionization separation membrane can achieve efficient separation of various surfactant-stabilized emulsions.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. This invention introduces zwitterionic groups through the reaction between tertiary amine groups and different small molecule compounds, thereby achieving zwitterionicization of the fiber surface and making the fiber surface contain both anionic and cationic groups.

[0027] 2. This invention uses a wet film-forming process to form modified fibers into zwitterionic fiber membranes for oil-water emulsion separation, which exhibit stable superhydrophilic properties in different pH environments.

[0028] 3. The fiber membrane material prepared by this invention has different separation effects on oil-in-water emulsions prepared by surfactants with different charges, and has the characteristic of selective separation. Its surface charge properties can be adjusted by pre-wetting with different pH solutions to achieve efficient separation of all kinds of surfactants (anionic, cationic, nonionic and amphoteric surfactants).

[0029] 4. The fiber membrane material prepared by the present invention can achieve the effects of demulsification and separation of water-in-oil emulsions prepared by surfactants by pre-wetting with oil and water twice, and has universal applicability to the separation of emulsions prepared by various surfactants.

[0030] 5. The preparation method used in this invention has the potential for wide application, and can be used not only on inorganic fiber substrates but also on polymer fiber substrates. Attached Figure Description

[0031] Figure 1 The present invention relates to a fiber-based oil-water emulsion separation membrane material with adjustable surface charge, which demonstrates the separation performance of emulsions stabilized by different surfactants under acidic aqueous solution pre-wetting conditions.

[0032] Figure 2 The present invention relates to a fiber-based oil-water emulsion separation membrane material with adjustable surface charge, which demonstrates separation performance of emulsions stabilized by different surfactants under pre-wetting conditions in a neutral aqueous solution.

[0033] Figure 3 The present invention relates to a fiber-based oil-water emulsion separation membrane material with adjustable surface charge, which demonstrates the separation performance of emulsions stabilized by different surfactants under alkaline aqueous solution pre-wetting conditions.

[0034] Figure 4 This is an electron microscope image magnified 1000 times of the fiber-based oil-water emulsion separation membrane material with tunable surface charge according to the present invention.

[0035] Figure 5 This is an electron microscope image magnified 8000 times of the fiber-based oil-water emulsion separation membrane material with adjustable surface charge according to the present invention.

[0036] Figure 6 The water contact angle (WCA) in air for the fiber-based membrane material with adjustable surface charge obtained in Example 1.

[0037] Figure 7 The oil contact angle (OCA) in air for the fiber-based film material with adjustable surface charge obtained in Example 1.

[0038] Figure 8 The underwater oil contact angle (UOCA) is the surface charge adjustable fiber-based membrane material obtained in Example 1. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to specific embodiments, but is not limited to the following embodiments.

[0040] Example 1

[0041] A method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge, the method comprising the following steps:

[0042] 1. Aminoation of glass fiber surface: The glass fiber was ultrasonically cleaned in ethanol for 20 min. The cleaned glass fiber was then immersed in an ethanol solution with a concentration of 5 wt% KH-550 and reacted at 20°C for 1 h. After curing, it was cleaned with anhydrous ethanol and dried at 60°C.

[0043] 2. Grafting PEI onto glass fiber surface: Aminated glass fibers were dispersed in a 25 g / L sulfur / pyridine solution, followed by the addition of a 10 wt% PEI / pyridine solution. The mixture was reacted at 80 °C for 12 h. After the reaction, the sample was thoroughly washed with hot pyridine and deionized water and dried at 60 °C.

[0044] 3. Amphoteric ionization of glass fiber surface: Glass fibers grafted with polyethyleneimine were dispersed in a methanol solution of 1,3-propane sulfonyl lactone at a concentration of 5 wt%, and reacted at 40 °C for 24 h. After the reaction, the samples were washed with anhydrous ethanol and deionized water, respectively, and dried at 60 °C.

[0045] 4. Wet-process glass fiber membrane: The amphoteric ionized modified glass fiber is cut to about 0.5 cm and uniformly dispersed in 200 mL of deionized water at 1000 rpm using a high-speed stirrer. The glass fiber dispersion is then poured into a filtration device and dehydrated using an oil pump to obtain a glass fiber membrane for oil-water emulsion separation.

[0046] The surface charge-tunable fiber separation membrane obtained by the method achieved a separation efficiency of 96.3% for SDS surfactant-stabilized water-in-toluene emulsions after pre-wetting with an aqueous solution at pH=1; and higher separation efficiencies (94.4% and 92.5%, respectively) for BS-2 and Tween 80 surfactant-stabilized water-in-toluene emulsions after pre-wetting with an aqueous solution at pH=7; and a separation efficiency of 96.7% for CTAB surfactant-stabilized water-in-toluene emulsions after pre-wetting with an aqueous solution at pH=7. By pre-wetting twice with toluene and deionized water, the demulsification and separation of toluene-in-water emulsions prepared with the nonionic surfactant Span80 were achieved sequentially, with a separation efficiency of 99.0%.

[0047] The surface charge-tunable fiber-based membrane material obtained by the method of the present invention can have its surface charge properties tunable by pre-wetting with solutions of different pH values. It exhibits selective separation characteristics by showing different separation effects on oil-in-water emulsions prepared with surfactants of different charges. Figure 1-3 The separation efficiency of the fiber membrane material obtained in Example 1 for oil-in-water emulsions prepared by four different types of surfactants when wetted in acidic, neutral and alkaline solutions is shown.

[0048] Figure 4-5 The image shown is a scanning electron microscope image of the fiber-based film material with adjustable surface charge obtained in Example 1. It can be observed that the originally smooth glass fiber surface has a distinct coating after surface modification.

[0049] Figure 6-8 The surface charge adjustable fiber-based membrane material obtained in Example 1 has water contact angle, oil contact angle in air, and oil contact angle underwater. The fiber membrane material exhibits good superhydrophilicity and superoleophilicity in air. Its static contact angle with hexadecane oil droplets underwater is 147°, indicating that the fiber membrane material has superoleophobic properties underwater, providing a valid basis for the fiber membrane material to achieve the separation of oil-in-water emulsions.

[0050] Example 2

[0051] A method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge, the method comprising the following steps:

[0052] 1. Aminoation of basalt fiber surface: Basalt fiber was ultrasonically cleaned in ethanol for 30 min. The cleaned basalt fiber was then immersed in an ethanol solution of 30 wt% HD-540 and reacted at 25 °C for 2 h. After curing, it was cured at 100 °C for 2 h. After curing, it was cleaned with anhydrous ethanol and dried at 60 °C.

[0053] 2. Grafting PEI onto basalt fiber surface: Aminated basalt fibers were dispersed in a 35 g / L sulfur / pyridine solution, followed by the addition of a 30 wt% PEI / pyridine solution. The reaction was carried out at 100 °C for 16 h. After the reaction, the sample was thoroughly washed with hot pyridine and deionized water and dried at 60 °C.

[0054] 3. Amphoteric ionization of basalt fiber surface: Basalt fibers grafted with polyethyleneimine were dispersed in 1,4-sulfonate butyrolactone and reacted at 90°C under solvent-free conditions for 72 h. After the reaction, the samples were washed with anhydrous ethanol and deionized water, respectively, and dried at 60°C.

[0055] 4. Wet-process basalt fiber membrane: The amphoteric ionized modified fibers are cut to about 1 cm and uniformly dispersed in 250 mL of deionized water at 1500 rpm using a high-speed stirrer. The fiber dispersion is then poured into a filtration device and dehydrated using an oil pump to obtain a fiber membrane for oil-water emulsion separation.

[0056] The surface charge-tunable fiber separation membrane obtained by the method showed a separation efficiency of 96.9% for SDS surfactant-stabilized water-in-toluene emulsions after pre-wetting with an aqueous solution at pH=1. The same membrane also showed good separation effects for BS-12 and Tween 80 surfactant-stabilized water-in-toluene emulsions after pre-wetting with deionized water at pH=7, with separation efficiencies of 94.6% and 92.4%, respectively, and an efficiency of 97.2% for CTAB surfactant-stabilized water-in-toluene emulsions. Furthermore, by pre-wetting twice with toluene and deionized water, demulsification and separation were achieved sequentially for toluene-in-water emulsions prepared with the nonionic surfactant Span80, with a separation efficiency of 99.3%.

[0057] Example 3

[0058] A method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge, the method comprising the following steps:

[0059] 1. Aminoation of carbon fiber surface: The carbon fiber was ultrasonically cleaned in ethanol for 30 min. The cleaned carbon fiber was then immersed in an ethanol solution with a concentration of 5 wt% HD-792 and reacted at 20°C for 1 h. After curing, it was cured at 80°C for 3 h. After curing, it was cleaned with anhydrous ethanol and dried at 60°C.

[0060] 2. PEI grafting onto carbon fiber surface: Aminated carbon fibers were dispersed in a 25 g / L sulfur / pyridine solution, followed by the addition of a 10 wt% PEI / pyridine solution. The mixture was reacted at 80 °C for 12 h. After the reaction, the sample was thoroughly washed with hot pyridine and deionized water and dried at 60 °C.

[0061] 3. Amphoteric ionization of carbon fiber surface: The carbon fiber grafted with polyethyleneimine was dispersed in a methanol solution of 10wt% α,β-unsaturated carboxylic acid and reacted at 40℃ for 24h. After the reaction, the sample was washed with anhydrous ethanol and deionized water respectively and dried at 60℃.

[0062] 4. Wet-process carbon fiber membrane: The amphoteric ionized modified carbon fiber is cut to about 0.5 cm and uniformly dispersed in 200 mL of deionized water at 1000 rpm using a high-speed stirrer. The fiber dispersion is then poured into a filtration device and dehydrated using an oil pump to obtain a carbon fiber membrane for oil-water emulsion separation.

[0063] The surface charge-tunable fiber separation membrane obtained by the method showed a separation efficiency of 96.6% for SDS surfactant-stabilized water-in-toluene emulsions after pre-wetting with an aqueous solution at pH=1. The same membrane also showed good separation effects for BS-12 and Tween 80 surfactant-stabilized water-in-toluene emulsions after pre-wetting with deionized water at pH=7, with separation efficiencies of 94.1% and 93.0%, respectively, and an efficiency of 97.3% for CTAB surfactant-stabilized water-in-toluene emulsions. Furthermore, by pre-wetting twice with toluene and deionized water, demulsification and separation were achieved sequentially for toluene-in-water emulsions prepared with the nonionic surfactant Span80, with a separation efficiency of 99.2%.

[0064] Example 4

[0065] A method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge, the method comprising the following steps:

[0066] 1. Aminoation of glass fiber surface: The glass fiber was ultrasonically cleaned in ethanol for 20 min. The cleaned glass fiber was then immersed in an ethanol solution of 30 wt% HD-540 and reacted at 20 °C for 1 h. After curing, it was cleaned with anhydrous ethanol and dried at 60 °C.

[0067] 2. Grafting PEI onto glass fiber surface: Aminated glass fibers were dispersed in a 25 g / L sulfur / pyridine solution, followed by the addition of a 10 wt% PEI / pyridine solution. The mixture was reacted at 80 °C for 12 h. After the reaction, the sample was thoroughly washed with hot pyridine and deionized water and dried at 60 °C.

[0068] 3. Amphoteric ionization of glass fiber surface: Glass fibers grafted with polyethyleneimine were dispersed in a methanol solution of 10 wt% 2-alkoxy-2-oxo-1,3,2-dioxophosphazenecyclopentane and reacted at 40 °C for 24 h. After the reaction, the samples were washed with anhydrous ethanol and deionized water, respectively, and dried at 60 °C.

[0069] 4. Wet-process glass fiber membrane: The amphoteric ionized modified glass fiber is cut to about 0.5 cm and uniformly dispersed in 200 mL of deionized water at 1000 rpm using a high-speed stirrer. The fiber dispersion is then poured into a filtration device and dehydrated using an oil pump to obtain a glass fiber membrane for oil-water emulsion separation.

[0070] The surface charge-tunable fiber separation membrane obtained by the method showed a separation efficiency of 95.1% for SDS surfactant-stabilized water-in-toluene emulsions after pre-wetting with an aqueous solution at pH=1. The same membrane also showed good separation effects for BS-12 and Tween 80 surfactant-stabilized water-in-toluene emulsions after pre-wetting with deionized water at pH=7, with separation efficiencies of 94.8% and 92.0%, respectively, and an efficiency of 96.9% for CTAB surfactant-stabilized water-in-toluene emulsions. By pre-wetting twice with toluene and deionized water, the toluene-in-water emulsion prepared with the nonionic surfactant Span80 was demulsified and separated sequentially, achieving a separation efficiency of 99.0%.

[0071] Example 5

[0072] A method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge, the method comprising the following steps:

[0073] 1. Aminoation of glass fiber surface: The glass fiber was ultrasonically cleaned in ethanol for 20 min. The cleaned glass fiber was then immersed in an ethanol solution of 30 wt% HD-792 and reacted at 25 °C for 2 h. After curing, it was cured at 120 °C for 1.5 h. After curing, it was cleaned with anhydrous ethanol and dried at 60 °C.

[0074] 2. Grafting PEI onto glass fiber surface: Aminated glass fibers were dispersed in a 35 g / L sulfur / pyridine solution, followed by the addition of a 30 wt% PEI / pyridine solution. The mixture was reacted at 100 °C for 16 h. After the reaction, the sample was thoroughly washed with hot pyridine and deionized water and dried at 60 °C.

[0075] 3. Amphoteric ionization of glass fiber surface: Glass fibers grafted with polyethyleneimine were dispersed in a methanol solution of 1,3-propane sulfonyl lactone at a concentration of 25 wt%, and reacted at 50 °C for 24 h. After the reaction, the samples were washed with anhydrous ethanol and deionized water, respectively, and dried at 60 °C.

[0076] 4. Wet-process glass fiber membrane: The amphoteric ionized modified glass fiber is cut to about 1 cm and uniformly dispersed in 250 mL of deionized water at 1500 rpm using a high-speed stirrer. The fiber dispersion is then poured into a filtration device and dehydrated using an oil pump to obtain a glass fiber membrane for oil-water emulsion separation.

[0077] The surface charge-tunable fiber separation membrane obtained by the method showed a separation efficiency of 96.7% for SDS surfactant-stabilized water-in-toluene emulsions after pre-wetting with an aqueous solution at pH=1. The same membrane also showed good separation effects for BS-12 and Tween 80 surfactant-stabilized water-in-toluene emulsions after pre-wetting with deionized water at pH=7, with separation efficiencies of 94.1% and 92.2%, respectively, and an efficiency of 97.0% for CTAB surfactant-stabilized water-in-toluene emulsions. Furthermore, by pre-wetting twice with toluene and deionized water, demulsification and separation were achieved sequentially for toluene-in-water emulsions prepared with the nonionic surfactant Span80, with a separation efficiency of 99.1%.

[0078] Example 6

[0079] A method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge, the method comprising the following steps:

[0080] 1. Aminoation of basalt fiber surface: Basalt fiber was ultrasonically cleaned in ethanol for 30 min. The cleaned basalt fiber was then immersed in an ethanol solution with a concentration of 10 wt% KH-550 and reacted at 20 °C for 1 h. After curing, it was cleaned with anhydrous ethanol and dried at 60 °C.

[0081] 2. Grafting PEI onto basalt fiber surface: Aminated basalt fibers were dispersed in a 30 g / L sulfur / pyridine solution, followed by the addition of a 20 wt% PEI / pyridine solution. The reaction was carried out at 80 °C for 12 h. After the reaction, the sample was thoroughly washed with hot pyridine and deionized water and dried at 60 °C.

[0082] 3. Amphoteric ionization of basalt fiber surface: Basalt fibers grafted with polyethyleneimine were dispersed in a methanol solution of 20 wt% 2-alkoxy-2-oxo-1,3,2-dioxophosphazenecyclopentane and reacted at 40 °C for 24 h. After the reaction, the samples were washed with anhydrous ethanol and deionized water, respectively, and dried at 60 °C.

[0083] 4. Wet-process basalt fiber membrane: The amphoteric ionized basalt fibers are cut to about 0.5 cm and uniformly dispersed in 200 mL of deionized water at 1000 rpm using a high-speed stirrer. The fiber dispersion is then poured into a filtration device and dehydrated using an oil pump to obtain a basalt fiber membrane for oil-water emulsion separation.

[0084] The surface charge-tunable fiber separation membrane obtained by the method showed a separation efficiency of 96.4% for SDS surfactant-stabilized water-in-toluene emulsions after pre-wetting with an aqueous solution at pH=1. The same membrane also showed good separation performance for BS-12 and Tween 80 surfactant-stabilized water-in-toluene emulsions after pre-wetting with deionized water at pH=7, with separation efficiencies of 93.6% and 93.4%, respectively. The efficiency for CTAB surfactant-stabilized water-in-toluene emulsions was 96.9%. Furthermore, by pre-wetting twice with toluene and deionized water, demulsification and separation were achieved sequentially for toluene-in-water emulsions prepared with the nonionic surfactant Span80, with a separation efficiency of 98.9%.

[0085] Example 7

[0086] A method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge, the method comprising the following steps:

[0087] 1. Aminoation of carbon fiber surface: The carbon fiber was ultrasonically cleaned in ethanol for 30 min. The cleaned carbon fiber was then immersed in an ethanol solution of 15 wt% HD-792 and reacted at 25 °C for 2 h. After curing, it was cured at 120 °C for 1.5 h. After curing, it was cleaned with anhydrous ethanol and dried at 60 °C.

[0088] 2. PEI grafting onto carbon fiber surface: Aminated carbon fibers were dispersed in a 30 g / L sulfur / pyridine solution, followed by the addition of a 30 wt% PEI / pyridine solution. The mixture was reacted at 100 °C for 16 h. After the reaction, the sample was thoroughly washed with hot pyridine and deionized water and dried at 60 °C.

[0089] 3. Amphoteric ionization of carbon fiber surface: The carbon fiber grafted with polyethyleneimine was dispersed in a methanol solution of 1,3-propane sulfonyl lactone at a concentration of 25 wt%, and reacted at 50 °C for 24 h. After the reaction, the sample was washed with anhydrous ethanol and deionized water, respectively, and dried at 60 °C.

[0090] 4. Wet-process carbon fiber membrane: The amphoteric ionized modified carbon fiber is cut to about 1 cm and uniformly dispersed in 250 mL of deionized water at 1500 rpm using a high-speed stirrer. The fiber dispersion is then poured into a filter device and dehydrated using an oil pump to obtain a carbon fiber membrane for oil-water emulsion separation.

[0091] The surface charge-tunable fiber separation membrane obtained by the method showed a separation efficiency of 95.7% for SDS surfactant-stabilized water-in-toluene emulsions after pre-wetting with an aqueous solution at pH=1. The same membrane also showed good separation effects for BS-12 and Tween 80 surfactant-stabilized water-in-toluene emulsions after pre-wetting with deionized water at pH=7, with separation efficiencies of 94.8% and 93.1%, respectively, and an efficiency of 96.8% for CTAB surfactant-stabilized water-in-toluene emulsions. By pre-wetting twice with toluene and deionized water, the toluene-in-water emulsion prepared with the nonionic surfactant Span80 was demulsified and separated sequentially, achieving a separation efficiency of 99.0%.

[0092] Example 8

[0093] A method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge, the method comprising the following steps:

[0094] 1. Aminoation of glass fiber surface: The glass fiber was ultrasonically cleaned in ethanol for 20 min. The cleaned glass fiber was then immersed in an ethanol solution with a concentration of 20 wt% HD-792 and reacted at 20 °C for 1 h. After curing, it was cleaned with anhydrous ethanol and dried at 60 °C.

[0095] 2. Grafting PEI onto glass fiber surface: Aminated glass fibers were dispersed in a 30 g / L sulfur / pyridine solution, followed by the addition of a 30 wt% PEI / pyridine solution. The mixture was reacted at 80 °C for 12 h. After the reaction, the sample was thoroughly washed with hot pyridine and deionized water and dried at 60 °C.

[0096] 3. Amphoteric ionization of glass fiber surface: Glass fibers grafted with polyethyleneimine were dispersed in a methanol solution of 25wt% α,β-unsaturated carboxylic acid and reacted at 40℃ for 24h. After the reaction, the samples were washed with anhydrous ethanol and deionized water respectively and dried at 60℃.

[0097] 4. Wet-process glass fiber membrane: The amphoteric ionized modified glass fiber is cut to about 0.5 cm and uniformly dispersed in 200 mL of deionized water at 1000 rpm using a high-speed stirrer. The fiber dispersion is then poured into a filtration device and dehydrated using an oil pump to obtain a glass fiber membrane for oil-water emulsion separation.

[0098] The surface charge-tunable fiber separation membrane obtained by the method showed a separation efficiency of 97.9% for SDS surfactant-stabilized water-in-toluene emulsions after pre-wetting with an aqueous solution at pH=1. The same membrane also showed good separation effects for BS-12 and Tween 80 surfactant-stabilized water-in-toluene emulsions after pre-wetting with deionized water at pH=7, with separation efficiencies of 95.1% and 94.0%, respectively, and an efficiency of 95.3% for CTAB surfactant-stabilized water-in-toluene emulsions. Furthermore, by pre-wetting twice with toluene and deionized water, demulsification and separation were achieved sequentially for toluene-in-water emulsions prepared with the nonionic surfactant Span80, with a separation efficiency of 99.2%.

[0099] The upper and lower limits of the process parameters (such as temperature, time, etc.) and the range values ​​of the intervals can all achieve this method, and specific embodiments are not listed here. All aspects not described in detail in this invention can be achieved using conventional technical knowledge in the field.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge, the preparation method comprising: 1) After cleaning the fiber, its surface is modified by amylation grafting using an amino-containing silane coupling agent; 2) Grafting polyethyleneimine onto surface-aminated fibers via a sulfur-based coupling reaction; 3) The surface of the grafted polyethyleneimine fiber is modified by zwitterionization. The zwitterion groups are introduced by the reaction between the tertiary amine groups in polyethyleneimine and different small molecule compounds, and the zwitterionized fiber is obtained. 4) A fiber-based oil-water emulsion separation membrane material with adjustable surface charge was prepared by a zwitterionic modification of the fiber through a film-forming process. In step 2), the sulfur coupling reaction grafts polyethyleneimine onto the surface-aminated fibers, including: dispersing the surface-aminated fibers in a sulfur / pyridine solution, then adding a polyethyleneimine / pyridine solution to carry out the grafting reaction, and washing and drying the sample after the reaction is completed. The concentration of sulfur / pyridine solution was 25-35 g / L, the concentration of polyethyleneimine / pyridine solution was 10-30 wt%, and the grafting reaction conditions were 80-100℃ for 12-16 h. In step 3), the surface of the grafted polyethyleneimine fiber is modified by zwitterionic oxidation, including: The grafted polyethyleneimine fibers were dispersed in an amphoteric ionizing agent and reacted at 40-90℃ for 24-72 hours. After the reaction was completed, the fibers were washed and dried. The zwitterionic treatment agent is 1,4-sulfonate butyrolactone; or, a methanol solution of 1,3-propanesulfonate, 2-alkoxy-2-oxo-1,3,2-dioxophosphazenecyclopentane or α,β-unsaturated carboxylic acid at a concentration of 5-30 wt%. In step 4), a fiber-based oil-water emulsion separation membrane material with tunable surface charge is prepared through a film-forming process, including: The amphoteric ionized modified fibers were cut to 0.5-1 cm and uniformly dispersed in 200-250 mL of deionized water at a high speed of 1000-1500 rpm. The fiber dispersion was then poured into a filtration device and dehydrated to obtain a fiber-based oil-water emulsion separation membrane material with adjustable surface charge.

2. The method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge according to claim 1, characterized in that, In step 1), the fiber is glass fiber, basalt fiber or carbon fiber.

3. The method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge according to claim 1, characterized in that, In step 1), the amination grafting modification is performed by impregnating the fiber in an ethanol solution of an amino-containing silane coupling agent, followed by curing, and then cleaning and drying after curing. The concentration of the ethanol solution of the silane coupling agent is 5-30 wt%, the impregnation conditions are 20-25℃ for 1-2 h, and the curing conditions are 80-120℃ for 1-3 h.

4. The method for preparing a fiber-based oil-water emulsion separation membrane material with tunable surface charge according to claim 1, characterized in that, The silane coupling agent is γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, or N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane.

5. A method for separating surfactant-stabilized oil-water emulsions, the separation method comprising: The fiber membrane prepared by the preparation method of the fiber-based oil-water emulsion separation membrane material with adjustable surface charge according to any one of claims 1-4 is pre-wetted with an aqueous solution of a certain pH, and then the pre-wetted fiber membrane is used to selectively separate the surfactant-stabilized oil-in-water emulsion. or, The fiber membrane prepared by the preparation method of the fiber-based oil-water emulsion separation membrane material with adjustable surface charge according to any one of claims 1-4 is pre-wetted with a certain amount of oil phase, and then the pre-wetted fiber membrane is used to demulsify the surfactant-stabilized water-in-oil emulsion; then the fiber membrane is pre-wetted with a certain amount of aqueous solution to separate the oil and water in the demulsified water-in-oil emulsion.

6. The method for separating an oil-water emulsion stabilized by a surfactant according to claim 5, characterized in that, The surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants; the anionic surfactants include sodium dodecyl sulfate; the cationic surfactants include hexadecyltrimethylammonium bromide; the amphoteric surfactants include dodecyl betaine; and the nonionic surfactants include Tween-80.

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