Oil-water separation membrane and preparation method thereof

Abstract

The invention relates to the technical field of membrane material preparation, and particularly discloses an oil-water separation membrane and a preparation method thereof.The oil-water separation membrane is characterized in that polyethyleneimine is grafted to zeolite powder under the action of a cross-linking agent epichlorohydrin, and a large number of amido groups on a polyethyleneimine chain can serve as effective chelating coordination sites of metal ions in subsequent steps; meanwhile, polyethyleneimine has excellent hydrophilic performance and is grafted on the zeolite powder, so that the hydrophilic performance of the zeolite powder is improved; then, three metal salts of magnesium, aluminum and cerium are compounded with urea on the surface of the PEI grafted zeolite through a hydrothermal reaction to generate a composite metal hydroxide structure, Mg and Al form a basic framework of a layered double-metal hydroxide structure, oxygen vacancy defects can be easily formed by doping Ce, and the defects can adsorb water molecules, so that a stable hydration layer is formed on the surface of the material, and the surface of the material is protected; the excellent super-hydrophilicity is shown.

Description

Technical Field

[0001] This invention relates to the field of membrane material preparation technology, specifically to an oil-water separation membrane and its preparation method. Background Technology

[0002] Oil-water separation membrane technology, as a highly efficient and energy-saving physical separation method, has demonstrated significant application value in fields such as oily wastewater treatment, crude oil extraction, food processing, and environmental protection. The core separation mechanism of this type of membrane typically relies on its unique surface wettability—that is, constructing a surface with superhydrophilic and underwater superoleophobic properties. This allows the aqueous phase to pass through rapidly while effectively blocking oil droplets, achieving efficient separation of oil-water mixtures. An ideal oil-water separation membrane needs to maintain high separation efficiency while also possessing high throughput, strong antifouling capabilities, and good mechanical and chemical stability to meet the long-term usage requirements under complex operating conditions.

[0003] Despite the significant advantages of membrane separation technology, many existing oil-water separation membranes still have obvious limitations in performance. Hydrophilic modification of the membrane surface often struggles to balance pore structure and surface energy, potentially sacrificing membrane flux or mechanical strength while increasing hydrophilicity. More critically, when dealing with emulsified oils or complex systems containing surfactants, most membrane materials are prone to the adsorption and accumulation of oil droplets and organic contaminants on the membrane surface and within the pores, causing irreversible blockage, severely shortening membrane lifespan, and increasing cleaning and replacement costs.

[0004] Therefore, developing an oil-water separation membrane with stable and durable hydrophilic properties and strong anti-fouling ability remains a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an oil-water separation membrane and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an oil-water separation membrane includes the following steps: S1. Preparation of pretreated zeolite powder Zeolite powder is added to an acid solution, heated and stirred, and then filtered, washed, dried, calcined and ground to obtain pretreated zeolite powder.

[0007] In this step, the acid solution used is sulfuric acid solution, nitric acid solution or hydrochloric acid solution.

[0008] In this step, the concentration of the acid solution used is 0.5-3 mol / L. For example, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, and 3 mol / L can be selected, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0009] In this step, the ratio of zeolite powder to acid solution is 1g:10-15mL. For example, you can choose 1g:10mL, 1g:11mL, 1g:12mL, 1g:13mL, 1g:14mL, or 1g:15mL, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0010] In this step, the heating and stirring temperature is 60-80℃, for example, 60℃, 65℃, 70℃, 75℃, or 80℃ can be selected; the heating and stirring time is 3-5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours can be selected, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0011] In this step, the calcination temperature is 400-450℃, for example, 400℃, 410℃, 420℃, 430℃, 440℃, or 450℃ can be selected; the calcination time is 1-3h, for example, 1h, 1.5h, 2h, 2.5h, or 3h can be selected, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0012] In this step, an acid solution is first used for heating and stirring to dissolve amorphous impurities, some metal cations and other soluble minerals on the surface of the zeolite powder, increasing its specific surface area and surface silanol (-Si-OH) density, thereby exposing more active sites. Calcination treatment makes the zeolite skeleton more stable, ensuring that it is not prone to structural collapse or performance degradation in subsequent chemical treatments and application environments.

[0013] S2. Preparation of polyethyleneimine-grafted zeolite powder Pretreated zeolite powder was dispersed in deionized water, and then polyethyleneimine and epichlorohydrin were added to it. The mixture was heated and stirred to react. After the reaction was completed, the powder was filtered, washed, and dried to obtain polyethyleneimine-grafted zeolite powder.

[0014] In this step, the mass ratio of pretreated zeolite powder, polyethyleneimine, and epichlorohydrin is 10-15:4-8:1-2.

[0015] In this step, the temperature for heating and stirring the reaction is 50-90℃, for example, 50℃, 60℃, 70℃, 80℃, or 90℃ can be selected; the heating and stirring reaction time is 2-4h, for example, 2h, 2.5h, 3h, 3.5h, or 4h can be selected; but it is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0016] In this step, polyethyleneimine is grafted onto zeolite powder through the action of the crosslinking agent epichlorohydrin. The numerous amine groups on the polyethyleneimine chain can serve as effective chelating coordination sites for metal ions in subsequent steps. At the same time, polyethyleneimine has excellent hydrophilic properties, and grafting it onto zeolite powder improves the hydrophilicity of the zeolite powder.

[0017] S3, Preparation of composite materials Polyethyleneimine-grafted zeolite powder was dispersed in deionized water, and then magnesium salt, aluminum salt, cerium salt and urea were added to it. After hydrothermal reaction, the composite material was obtained by filtration, washing, drying and grinding.

[0018] In this step, the mass ratio of polyethyleneimine-grafted zeolite powder, magnesium salt, aluminum salt, cerium salt, and urea is 10-15:4-8:4-8:1-2:10-20.

[0019] In this step, the magnesium salt is selected from magnesium nitrate, magnesium chloride, or magnesium sulfate.

[0020] In this step, the aluminum salt is selected from aluminum nitrate or aluminum chloride.

[0021] In this step, the cerium salt is selected from cerium nitrate or cerium acetate.

[0022] In this step, the temperature of the hydrothermal reaction is 120-150℃, for example, 120℃, 130℃, 140℃, or 150℃ can be selected; the time of the hydrothermal reaction is 4-8h, for example, 4h, 5h, 6h, 7h, or 8h can be selected; but it is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0023] In this step, the Mg in the solution 2+ Al 3+ Ce 3+ With OH -The reaction generates corresponding metal hydroxides. These hydroxide particles undergo heterogeneous nucleation at the amino groups of PEI-grafted zeolite and are firmly fixed by coordination bonds, effectively preventing the detachment and failure of functional materials during long-term water flow shearing, pressure fluctuations, or repeated cleaning, thus laying a solid structural foundation for the long-term recycling of the membrane. The composite metal hydroxide has strong hydrophilicity and works together with the amino groups of polyethyleneimine to construct a stable and robust superhydrophilic surface, thereby achieving efficient water flow and oil blocking effect. Mg and Al form the basic framework of the layered bimetallic hydroxide structure, and the incorporation of Ce easily forms oxygen vacancy defects. These defects can adsorb water molecules, thereby forming a stable hydration layer on the material surface, exhibiting excellent superhydrophilicity. In addition, in near-neutral or slightly alkaline water environments, the CeO2 surface is usually negatively charged, generating electrostatic repulsion between it and the similarly negatively charged oil droplets, which can further enhance the oil-water separation efficiency of the membrane.

[0024] S4. Preparation of oil-water separation membrane Prepare a polyacrylic acid solution, then add the composite material and disperse it evenly to obtain a membrane solution. Coat the membrane solution evenly on the surface of a PET base membrane, and after drying, you will get an oil-water separation membrane.

[0025] In this step, the mass fraction of the polyacrylic acid solution is 5-10%, for example, 5%, 6%, 7%, 8%, 9%, 10%, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] In this step, the mass ratio of polyacrylic acid solution to composite material is 100:5-10. For example, 100:5, 100:6, 100:7, 100:8, 100:9, and 100:10 can be selected, but are not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] The present invention also provides an oil-water separation membrane prepared by the above preparation method.

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention first uses acid solution heating and stirring treatment to dissolve amorphous impurities, some metal cations and other soluble minerals on the surface of zeolite powder, increase its specific surface area and surface silanol (-Si-OH) density, thereby exposing more active sites; calcination treatment makes the zeolite skeleton more stable, ensuring that it is not prone to structural collapse or performance degradation in subsequent chemical treatment and application environment.

[0029] (2) In this invention, polyethyleneimine is grafted onto zeolite powder by the action of the crosslinking agent epichlorohydrin. A large number of amino groups on the polyethyleneimine chain can serve as effective chelation sites for metal ions in subsequent steps. At the same time, polyethyleneimine has excellent hydrophilic properties, and grafting it onto zeolite powder improves the hydrophilic properties of zeolite powder.

[0030] (3) In this invention, magnesium, aluminum and cerium metal salts are combined with urea on the surface of PEI grafted zeolite through hydrothermal reaction to generate a composite metal hydroxide structure. Mg and Al form the basic framework of the layered bimetallic hydroxide structure. The incorporation of Ce easily forms oxygen vacancy defects. These defects can adsorb water molecules, thereby forming a stable hydration layer on the material surface, exhibiting excellent superhydrophilicity. In addition, in near-neutral or slightly alkaline water environments, the CeO2 surface is usually negatively charged, generating electrostatic repulsion between it and the similarly negatively charged oil droplets, which can further enhance the oil-water separation efficiency of the membrane. Attached Figure Description

[0031] Figure 1 This is an electron microscope image of the PET base film in Example 1 of the present invention; Figure 2 This is an electron microscope image of the hydrophilic film layer in Example 1 of the present invention; Figure 3 This is an electron microscope image of the interface bonding layer between the PET base film and the hydrophilic film layer in Example 1 of the present invention. Detailed Implementation

[0032] The present invention will be further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments.

[0033] It should be noted that, unless otherwise specified, all chemical reagents involved in this invention were purchased through commercial channels.

[0034] The relative molecular mass of the polyethyleneimine used in this embodiment of the invention is 600.

[0035] Example 1 A method for preparing an oil-water separation membrane includes the following steps: S1. Add 10g of zeolite powder to 100mL of 1mol / L nitric acid solution, heat and stir at 80℃ for 3h, then filter, wash and dry, calcine at 450℃ for 1h, grind through a 400-mesh sieve to obtain pretreated zeolite powder. S2. Disperse 10g of pretreated zeolite powder in 100mL of deionized water, then add 6g of polyethyleneimine and 1.5g of epichlorohydrin to it, heat and stir at 80℃ for 3h. After the reaction is completed, filter, wash and dry to obtain polyethyleneimine grafted zeolite powder. S3. Disperse 10g of polyethyleneimine-grafted zeolite powder in 100mL of deionized water, then add 4g of magnesium nitrate, 4g of aluminum nitrate, 1g of cerium nitrate and 10g of urea to it, and perform hydrothermal reaction at 120℃ for 8h. After filtration, washing, drying and grinding through a 400-mesh sieve, the composite material is obtained. S4. Prepare 100g of 8wt% polyacrylic acid solution, then add 8g of composite material and disperse evenly to obtain a membrane solution. Coat the membrane solution evenly onto the surface of a PET base film at a coating amount of 80g / m². 2 After drying, an oil-water separation membrane is obtained.

[0036] The oil-water separation membrane prepared in this embodiment consists of two layers, with the base layer being a PET substrate membrane. The electron micrograph is shown below. Figure 1 As shown; the surface layer is a hydrophilic film layer, and the electron micrograph is shown below. Figure 2 As shown; electron micrograph of the interface layer between the PET base film and the hydrophilic film layer is shown below. Figure 3 As shown.

[0037] Example 2 A method for preparing an oil-water separation membrane includes the following steps: S1. Add 10g of zeolite powder to 100mL of 1mol / L nitric acid solution, heat and stir at 80℃ for 3h, then filter, wash and dry, calcine at 450℃ for 1h, grind through a 400-mesh sieve to obtain pretreated zeolite powder. S2. Disperse 10g of pretreated zeolite powder in 100mL of deionized water, then add 4g of polyethyleneimine and 1g of epichlorohydrin to it, heat and stir at 80℃ for 3h, and after the reaction is completed, filter, wash and dry to obtain polyethyleneimine grafted zeolite powder. S3. Disperse 10g of polyethyleneimine-grafted zeolite powder in 150mL of deionized water, then add 8g of magnesium nitrate, 8g of aluminum nitrate, 2g of cerium nitrate and 20g of urea to it, and perform hydrothermal reaction at 120℃ for 8h. After filtration, washing, drying and grinding through a 400-mesh sieve, the composite material is obtained. S4. Prepare 100g of 8wt% polyacrylic acid solution, then add 5g of composite material and disperse evenly to obtain the membrane solution. Coat the membrane solution evenly onto the surface of the PET base film at a coating amount of 80g / m². 2 After drying, an oil-water separation membrane is obtained.

[0038] Example 3 A method for preparing an oil-water separation membrane includes the following steps: S1. Add 10g of zeolite powder to 100mL of 1mol / L nitric acid solution, heat and stir at 80℃ for 3h, then filter, wash and dry, calcine at 450℃ for 1h, grind through a 400-mesh sieve to obtain pretreated zeolite powder. S2. Disperse 15g of pretreated zeolite powder in 200mL of deionized water, then add 8g of polyethyleneimine and 2g of epichlorohydrin to it, heat and stir at 80℃ for 3h, and after the reaction is completed, filter, wash and dry to obtain polyethyleneimine grafted zeolite powder. S3. Disperse 15g of polyethyleneimine-grafted zeolite powder in 250mL of deionized water, then add 6g of magnesium nitrate, 6g of aluminum nitrate, 1.5g of cerium nitrate and 15g of urea to it, and perform hydrothermal reaction at 120℃ for 8h. After filtration, washing, drying and grinding through a 400-mesh sieve, the composite material is obtained. S4. Prepare 100g of 8wt% polyacrylic acid solution, then add 10g of composite material and disperse evenly to obtain a membrane solution. Coat the membrane solution evenly onto the surface of a PET base film at a coating amount of 80g / m². 2 After drying, an oil-water separation membrane is obtained.

[0039] Comparative Example 1 A method for preparing an oil-water separation membrane includes the following steps: S1. Add 10g of zeolite powder to 100mL of 1mol / L nitric acid solution, heat and stir at 80℃ for 3h, then filter, wash and dry, calcine at 450℃ for 1h, grind through a 400-mesh sieve to obtain pretreated zeolite powder. S2. Disperse 10g of pretreated zeolite powder in 100mL of deionized water, then add 4g of magnesium nitrate, 4g of aluminum nitrate, 1g of cerium nitrate and 10g of urea to it, and hydrothermally react at 120℃ for 8h. After filtration, washing, drying and grinding through a 400-mesh sieve, the composite material is obtained. S3. Prepare 100g of 8wt% polyacrylic acid solution, then add 8g of composite material and disperse evenly to obtain a membrane solution. Coat the membrane solution evenly onto the surface of a PET base film at a coating amount of 80g / m². 2 After drying, an oil-water separation membrane is obtained.

[0040] Compared to Comparative Example 1, the zeolite powder was not treated with polyethyleneimine grafting.

[0041] Comparative Example 2 A method for preparing an oil-water separation membrane includes the following steps: S1. Add 10g of zeolite powder to 100mL of 1mol / L nitric acid solution, heat and stir at 80℃ for 3h, then filter, wash and dry, calcine at 450℃ for 1h, grind through a 400-mesh sieve to obtain pretreated zeolite powder. S2. Disperse 10g of pretreated zeolite powder in 100mL of deionized water, then add 6g of polyethyleneimine and 1.5g of epichlorohydrin to it, heat and stir at 80℃ for 3h. After the reaction is completed, filter, wash and dry to obtain polyethyleneimine grafted zeolite powder. S3. Prepare 100g of 8wt% polyacrylic acid solution, then add 8g of polyethyleneimine-grafted zeolite powder and disperse evenly to obtain a membrane solution. Coat the membrane solution evenly onto the surface of a PET base film with a coating amount of 80g / m². 2 After drying, an oil-water separation membrane is obtained.

[0042] Compared to Comparative Example 2 and Example 1, the polyethyleneimine-grafted zeolite powder did not have metal hydroxide loaded on it.

[0043] Comparative Example 3 A method for preparing an oil-water separation membrane includes the following steps: S1. Add 10g of zeolite powder to 100mL of 1mol / L nitric acid solution, heat and stir at 80℃ for 3h, then filter, wash and dry, calcine at 450℃ for 1h, grind through a 400-mesh sieve to obtain pretreated zeolite powder. S2. Disperse 10g of pretreated zeolite powder in 100mL of deionized water, then add 6g of polyethyleneimine and 1.5g of epichlorohydrin to it, heat and stir at 80℃ for 3h. After the reaction is completed, filter, wash and dry to obtain polyethyleneimine grafted zeolite powder. S3. Disperse 10g of polyethyleneimine-grafted zeolite powder in 100mL of deionized water, then add 4g of magnesium nitrate, 4g of aluminum nitrate and 10g of urea to it, and perform a hydrothermal reaction at 120℃ for 8h. After filtration, washing, drying and grinding through a 400-mesh sieve, the composite material is obtained. S4. Prepare 100g of 8wt% polyacrylic acid solution, then add 8g of composite material and disperse evenly to obtain a membrane solution. Coat the membrane solution evenly onto the surface of a PET base film at a coating amount of 80g / m². 2 After drying, an oil-water separation membrane is obtained.

[0044] Compared to Comparative Example 3 and Example 1, no cerium was introduced into the composite material.

[0045] The oil-water separation membrane materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to contact angle tests. The contact angle of the membrane was detected using a contact angle measuring instrument. The test liquid was dropped onto the membrane surface, and the shape of the droplet was recorded using an optical imaging system. The contact angle of the liquid on the membrane surface was calculated using the circular arc fitting method. The test results are shown in Table 1.

[0046] Table 1. Contact angle test results for different groups

[0047] As can be seen from Table 1, compared with Comparative Examples 1-4, the oil-water separation membrane material prepared in the embodiments of the present invention has excellent hydrophilicity and underwater oleophobicity.

[0048] Oil-water separation test: The oil phase (n-hexane):water phase was mixed in a volume ratio of 1:9. Tween 80 was used as the surfactant, and Sudan I dyed oil phase was added. The mixture was stirred at 500 rpm for 2 hours, sonicated for 2 hours, and allowed to stand for 1 hour to prevent the emulsion from separating, thus obtaining an oil-in-water emulsion. The oil-water separation membrane materials prepared in Examples 1-3 and Comparative Examples 1-3 were clamped between a filter cup and a glass frit core and fixed with clamps. A triangular flask was connected to the glass frit core to carry the filtrate. A circulating water vacuum pump was connected to the glass frit core, and the oil-in-water emulsion was poured into the filter cup. The vacuum pump was turned on, and the emulsion was forced through the membrane into the suction flask below under pressure. The membrane material was subjected to 10 oil-water separation cycle tests according to the above steps. The water flux and separation efficiency of the 1st and 10th cycles were calculated, and the results are shown in Table 2.

[0049] Table 2. Test results of oil-water separation performance for different groups

[0050] As can be seen from Table 2, after 10 cycles of use, the water flux of the oil-water separation membrane prepared in this embodiment of the invention can still reach 35 L / (m²). 2 Even at around 1000 h, the separation efficiency can still reach 95%. Compared with comparative examples 1-3, the oil-water separation membrane prepared by this invention has a higher separation efficiency and better separation effect.

[0051] Finally, it should be noted that the above embodiments do not limit the present invention in any way. Those skilled in the art can make modifications and improvements based on the present invention. Therefore, any modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing an oil-water separation membrane, characterized in that, Includes the following steps: S1. Add zeolite powder to an acid solution, heat and stir, then filter, wash, dry, calcin, and grind to obtain pretreated zeolite powder; S2. Disperse the pretreated zeolite powder in deionized water, then add polyethyleneimine and epichlorohydrin to it, heat and stir to react. After the reaction is completed, filter, wash and dry to obtain polyethyleneimine grafted zeolite powder. S3. Disperse polyethyleneimine-grafted zeolite powder in deionized water, then add magnesium salt, aluminum salt, cerium salt and urea to it, perform hydrothermal reaction, and obtain composite material by filtration, washing, drying and grinding. S4. Prepare a polyacrylic acid solution, then add the composite material and disperse it evenly to obtain a membrane solution. Coat the membrane solution evenly on the surface of the PET base membrane and dry it to obtain an oil-water separation membrane.

2. The preparation method according to claim 1, characterized in that, In step S1, the heating and stirring treatment temperature is 60-80℃, and the heating and stirring treatment time is 3-5 hours.

3. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of pretreated zeolite powder, polyethyleneimine, and epichlorohydrin is 10-15:4-8:1-2.

4. The preparation method according to claim 1, characterized in that, In step S2, the temperature for heating and stirring the reaction is 50-90℃, and the reaction time is 2-4 hours.

5. The preparation method according to claim 1, characterized in that, In step S3, the mass ratio of polyethyleneimine-grafted zeolite powder, magnesium salt, aluminum salt, cerium salt and urea is 10-15:4-8:4-8:1-2:10-20.

6. The preparation method according to claim 1, characterized in that, In step S3, the hydrothermal reaction temperature is 120-150℃, and the hydrothermal reaction time is 4-8h.

7. The preparation method according to claim 1, characterized in that, In step S4, the mass fraction of the polyacrylic acid solution is 5-10%.

8. The preparation method according to claim 1, characterized in that, In step S4, the mass ratio of polyacrylic acid solution to composite material is 100:5-10.

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

Images