A superhydrophilic oleophobic film, its preparation method and application

Abstract

This invention provides a superhydrophilic oleophobic membrane, its preparation method, and its applications. Chitosan and acrylic acid are used as crosslinking layer materials. A crosslinking layer is constructed on the surface of porous materials through surface coating crosslinking technology. The preparation method is simple, environmentally friendly, highly applicable, and low-cost, and can be used for surface modification of various porous materials. Utilizing free radical polymerization technology, hydrophilic monomers are grafted onto the surface of the crosslinking layer, simultaneously constructing a hydrophilic functional layer on the surface and inside the pores of the porous material, improving the hydrophilicity and antifouling ability of the separation membrane. The superhydrophilic oleophobic membrane prepared by this invention exhibits good chemical stability, extremely strong hydrophilicity, high flux, high antifouling ability, and a large difference in wettability between oil and water, making it suitable for liquid separation applications such as oily wastewater treatment and material separation. It has achieved particularly good separation results in oily wastewater treatment and can be applied to the oil-water separation process of oily wastewater such as kitchen wastewater, cutting fluid wastewater, oilfield wastewater, and coal chemical wastewater.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, and in particular to a superhydrophilic oleophobic membrane, its preparation method, and its application. Background Technology

[0002] Oily wastewater is widely found in oil extraction, transportation, storage, refining, fine chemical industry, metal processing, and coal chemical industry. Every year, 5 to 10 million tons of oil flow into the ocean through various pathways. Due to the high chemical oxygen demand (COD) of oily wastewater, its difficulty in treatment, and the poor biodegradability of pollutants, high demands are placed on oil-water separation in terms of environmental governance, oil recovery, and water reuse.

[0003] Taking oily wastewater as an example, the oil in the water can be classified into four categories: floating oil, dispersed oil, emulsified oil, and dissolved oil. During the oil-water separation process, floating oil and dispersed oil can be separated by gravity separation, centrifugal separation, air flotation, or chemical demulsification. However, the removal of emulsified oil and dissolved oil is more difficult. After treatment, the oil content in the wastewater can usually reach 40-100 ppm, and it also contains a certain amount of suspended particles, making it difficult to meet discharge and reinjection standards. Furthermore, it requires the addition of chemicals and generates additional oily sludge that needs to be treated.

[0004] Membrane technology offers advantages such as high separation efficiency and ease of operation, making it a highly efficient oil-water separation technology. Traditional membrane separation technology primarily relies on pore size sieving as its separation mechanism. Materials smaller than the membrane pore size can permeate through the membrane, while materials larger than the pore size are retained on the membrane surface, thus completing the separation process. Based on the sieving principle, the separation membrane requires a very small pore size and low porosity, resulting in high filtration resistance and necessitating higher operating pressures. However, increasing the operating pressure can cause oil droplets to deform and permeate through the membrane, reducing the oil-water separation efficiency. Summary of the Invention

[0005] To address the problems in the background technology and the shortcomings of traditional membrane separation technology, this invention proposes a superhydrophilic oleophobic membrane, and provides its preparation method and application. The superhydrophilic oleophobic membrane provided by this invention separates oil and water by utilizing the difference in wettability of the membrane material rather than the membrane pore size. Since the surface tension between water and oil is generally very different, selecting surfaces with different wettability to water and oil can selectively adsorb one phase and repel the other. Enhancing the surface wettability can improve the separation efficiency. When oily wastewater comes into contact with the membrane surface, water can continuously permeate downwards, while the surface always maintains superoleophobicity, and oil is trapped on the surface, thus achieving the effect of oil-water separation. Furthermore, due to the membrane's potential oleophobicity, oil can never contaminate the membrane surface. It is suitable for situations with more water and less oil, and is a truly anti-fouling, low-energy-consumption, long-life, and high-efficiency separation membrane.

[0006] This invention provides the following technical solution:

[0007] A method for preparing a superhydrophilic oleophobic film includes the following steps:

[0008] S1: Chitosan, polyacrylic acid and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) are dissolved in deionized water and stirred to obtain a uniform modified solution;

[0009] S2: The modified solution is coated onto the surface and pores of the porous material. The coated porous material is placed in an oven to dry the deionized water and complete the crosslinking reaction.

[0010] S3: Dissolve the hydrophilic monomer and initiator in deionized water and stir to obtain a homogeneous grafting solution;

[0011] S4: Immerse the cross-linked porous material in a grafting solution, introduce nitrogen gas, and heat to carry out the grafting reaction to obtain a superhydrophilic and oleophobic film.

[0012] Furthermore, in S1, the molecular weight of chitosan is 2000-10000, and the molecular weight of polyacrylic acid is 2000-10000; the concentration of chitosan in the modified solution is 1-10 g / L, the concentration of polyacrylic acid is 1-10 g / L, and the concentration of EDC is 0.1-1 g / L.

[0013] Furthermore, the porous material in S2 includes a metal mesh, non-woven fabric, and microporous filter membrane, wherein the pore size of the porous material is 5-10 μm and the thickness of the porous material is 0.2-5 mm.

[0014] Furthermore, the coating process described in S2 involves immersing the porous material in a modified solution for 30–60 minutes, then removing it after coating. The crosslinking reaction conditions described in S2 are a temperature of 75–90°C and a reaction time of 1–8 hours.

[0015] Furthermore, the hydrophilic monomers described in S3 include acrylic acid, acrylamide, vinylpyrrolidone, and hydroxyethyl acrylate.

[0016] Furthermore, the initiator described in S3 includes cerium ammonium nitrate, potassium persulfate, and ammonium persulfate.

[0017] Furthermore, the concentration of the hydrophilic monomer in the grafting solution described in S3 is 1–10 g / L; the concentration of the initiator is 0.1–1 g / L.

[0018] Furthermore, the grafting reaction conditions described in S4 are: under nitrogen protection, the soaking temperature is 40–90°C, and the soaking time is 5–20 h.

[0019] The present invention also provides a superhydrophilic oleophobic film, which is prepared by the above-described method for preparing a superhydrophilic oleophobic film.

[0020] The present invention also provides an application of the superhydrophilic oleophobic membrane, which is applied to oil-water separation.

[0021] The beneficial effects of this invention are as follows:

[0022] Chitosan is a product of N-deacetylation of chitin, and its chemical structure is formed by replacing the C2 position of cellulose with a hydroxyl amino group. Chitosan possesses many unique properties, including biodegradability, cell affinity, and biological effects. In particular, chitosan containing free amino groups is the only basic polysaccharide among natural polysaccharides. As a product of the natural polysaccharide chitin with the removal of some acetyl groups, chitosan exhibits various physiological functions such as biodegradability, biocompatibility, non-toxicity, antibacterial activity, anticancer properties, lipid-lowering effects, and immune enhancement. It is widely used in food additives, textiles, agriculture, environmental protection, beauty and health care, cosmetics, antibacterial agents, medical fibers, medical dressings, artificial tissue materials, drug sustained-release materials, gene transduction vectors, biomedical applications, absorbable medical materials, tissue engineering carrier materials, medical treatment, drug development, and many other fields and daily chemical industries.

[0023] However, chitosan is a water-soluble polymer and is easily lost during oil-water separation. Chemical cross-linking technology can form cross-linked structures between chitosan molecules, significantly improving the hydrodynamic stability of chitosan on the membrane surface. Simultaneously, the residual hydroxyl groups on the chitosan surface can provide secondary grafting sites, allowing for the grafting of hydrophilic monomers onto the membrane surface, further enhancing the hydrophilicity and oleophobicity of the separation membrane, forming a superhydrophilic and oleophobic membrane.

[0024] This invention provides a superhydrophilic oleophobic film, its preparation method, and its application. Chitosan, polyacrylic acid, and EDC are dissolved in deionized water and stirred to obtain a uniform modified solution. The modified solution is coated onto the surface and pores of a porous material. The coated porous material is placed in an oven to dry the deionized water, completing the crosslinking reaction. A hydrophilic monomer and initiator are dissolved in deionized water and stirred to obtain a uniform grafting solution. The crosslinked porous material is immersed in the grafting solution, nitrogen gas is introduced, and heating is performed to carry out the grafting reaction, resulting in a superhydrophilic oleophobic film.

[0025] This invention uses chitosan and acrylic acid as crosslinking layer materials. A crosslinking layer is constructed on the surface of porous materials through surface coating crosslinking technology. The preparation method is simple, environmentally friendly, highly applicable, and low in cost. It can be used for surface modification of various porous materials. By using free radical polymerization technology, hydrophilic monomers are grafted onto the surface of the crosslinking layer, which can simultaneously construct a hydrophilic functional layer on the surface of the porous material and inside the pores, thereby improving the hydrophilicity and antifouling ability of the separation membrane.

[0026] The superhydrophilic oleophobic membrane prepared by this invention has good chemical stability, extremely strong hydrophilicity, high flux, high anti-fouling ability, and large difference in wettability between oil and water. It is suitable for liquid separation fields, such as oily wastewater treatment and material separation. In particular, it has achieved good separation effect in the treatment of oily wastewater and can be applied to the oil-water separation process of oily wastewater such as kitchen wastewater, cutting fluid wastewater, oilfield wastewater, and coal chemical wastewater. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] A method for preparing a superhydrophilic oleophobic film includes the following steps:

[0030] S1: Dissolve 10g of chitosan (molecular weight 2000), 10g of polyacrylic acid (molecular weight 10000) and 1g of EDC in 980g of deionized water and stir at 30℃ for 24h to obtain a uniform modified solution.

[0031] S2: Immerse a nonwoven fabric with a thickness of 5 mm and a pore size range of 5-10 μm in the modified solution. After immersion for 60 min to complete the coating, remove the nonwoven fabric and place it in an oven. Heat it at 90℃ for 5 h to dry the deionized water and complete the crosslinking reaction.

[0032] S3: Dissolve 10g of acrylic acid and 0.1g of cerium ammonium nitrate in 990g of deionized water and stir at 30℃ for 24h until completely dissolved to obtain a homogeneous grafting solution;

[0033] S4: The cross-linked nonwoven fabric is immersed in the grafting solution, nitrogen gas is introduced, and the temperature is heated to 40°C for 20 hours to carry out the grafting reaction and obtain a superhydrophilic oleophobic film.

[0034] The superhydrophilic oleophobic membrane prepared in Example 1 had a pure water flux of 2000 L·m⁻¹. -2 ·h -1 The superhydrophilic oleophobic film has a water contact angle of 0° and an underwater oil contact angle of 135°.

[0035] The superhydrophilic oleophobic membrane prepared in Example 1 was applied to oilfield wastewater for oil-water separation testing. Before the test, the oil content in the oilfield wastewater was 120 ppm, the suspended particle content was 80 ppm, and the median particle size was 10 μm. After filtration using the superhydrophilic oleophobic membrane prepared in Example 1, the oil content in the permeate was less than 20 ppm, the suspended particle content was 30 ppm, and the median particle size was less than 3 μm. The water flux of the superhydrophilic oleophobic membrane in oily wastewater was 200 L·m⁻¹. -2 ·h -1 After a simple rinse, the flow rate of the separation membrane recovered to 98% of its initial value.

[0036] Example 2

[0037] A method for preparing a superhydrophilic oleophobic film includes the following steps:

[0038] S1: Dissolve 8g of chitosan (molecular weight 5000), 8g of polyacrylic acid (molecular weight 8000) and 0.8g of EDC in 984g of deionized water and stir at 45℃ for 24h to obtain a uniform modified solution.

[0039] S2: Immerse a microporous filter membrane with a thickness of 0.5 mm and a pore size of 5 μm in the modified solution. After immersion for 30 min to complete the coating, remove the membrane and place it in an oven. Heat at 75 °C for 8 h to dry the deionized water and complete the crosslinking reaction.

[0040] S3: Dissolve 8g of vinylpyrrolidone and 0.2g of cerium ammonium nitrate in 992g of deionized water and stir at 30℃ for 24h until completely dissolved to obtain a homogeneous grafting solution;

[0041] S4: The cross-linked microporous filter membrane is immersed in the grafting solution, nitrogen gas is introduced, and the temperature is heated to 50°C for 15 hours to carry out the grafting reaction, thereby obtaining a superhydrophilic and oleophobic membrane.

[0042] The superhydrophilic oleophobic membrane prepared in Example 2 had a pure water flux of 800 L·m⁻¹. -2 ·h -1 The superhydrophilic oleophobic film has a water contact angle of 0° and an underwater oil contact angle of 135°.

[0043] The superhydrophilic oleophobic membrane prepared in Example 2 was applied to oilfield wastewater for oil-water separation testing. Before the test, the oil content in the oilfield wastewater was 120 ppm, the suspended particle content was 80 ppm, and the median particle size was 10 μm. After filtration using the superhydrophilic oleophobic membrane prepared in Example 1, the oil content in the permeate was less than 15 ppm, the suspended particle content was 20 ppm, and the median particle size was less than 2 μm. The water flux of the superhydrophilic oleophobic membrane in oily wastewater was 100 L·m⁻¹. -2 ·h -1After a simple rinse, the flow rate of the separation membrane recovered to 92% of its initial value.

[0044] Example 3

[0045] A method for preparing a superhydrophilic oleophobic film includes the following steps:

[0046] S1: Dissolve 4g of chitosan (molecular weight 7000), 4g of polyacrylic acid (molecular weight 4000) and 0.4g of EDC in 992g of deionized water and stir at 60℃ for 24h to obtain a uniform modified solution.

[0047] S2: Immerse a metal filter screen with a thickness of 0.2 mm and a pore size of 5 μm in the modified solution. After immersion for 60 min to complete the coating, remove the coated metal filter screen and place it in an oven. Heat it at 75 °C for 4 h to dry the deionized water and complete the crosslinking reaction.

[0048] S3: Dissolve 4g of acrylamide and 0.6g of ammonium persulfate in 996g of deionized water and stir at 30℃ for 24h until completely dissolved to obtain a homogeneous grafting solution;

[0049] S4: Immerse the cross-linked metal filter in the grafting solution, introduce nitrogen gas, heat to 70°C, and react for 8 hours to carry out the grafting reaction and obtain a superhydrophilic and oleophobic film.

[0050] The superhydrophilic oleophobic membrane prepared in Example 3 had a pure water flux of 2600 L·m⁻¹. -2 ·h -1 The superhydrophilic oleophobic film has a water contact angle of 0° and an underwater oil contact angle of 137°.

[0051] The superhydrophilic oleophobic membrane prepared in Example 3 was applied to oilfield wastewater for oil-water separation testing. Before the test, the oil content in the oilfield wastewater was 120 ppm, the suspended particle content was 80 ppm, and the median particle size was 10 μm. After filtration using the superhydrophilic oleophobic membrane prepared in Example 1, the oil content in the permeate was less than 35 ppm, the suspended particle content was 50 ppm, and the median particle size was less than 5 μm. The water flux of the superhydrophilic oleophobic membrane in oily wastewater was 500 L·m⁻¹. -2 ·h -1 After a simple rinse, the flow rate of the separation membrane recovered to 91% of its initial value.

[0052] Example 4

[0053] A method for preparing a superhydrophilic oleophobic film includes the following steps:

[0054] S1: Dissolve 1g of chitosan (molecular weight 10000), 1g of polyacrylic acid (molecular weight 2000) and 0.1g of EDC in 998g of deionized water and stir at 80℃ for 24h to obtain a uniform modified solution.

[0055] S2: Immerse a nonwoven fabric with a thickness of 1 mm and a pore size range of 5-10 μm in the modified solution. After immersion for 60 min to complete the coating, remove the nonwoven fabric and place it in an oven. Heat it at 90℃ for 1 h to dry the deionized water and complete the crosslinking reaction.

[0056] S3: Dissolve 1g of hydroxyethyl acrylate and 0.1g of potassium persulfate in 999g of deionized water, stir at 30℃ for 24h until completely dissolved, and obtain a homogeneous grafting solution;

[0057] S4: Immerse the cross-linked nonwoven fabric in the grafting solution, introduce nitrogen gas, heat to 90°C, and react for 5 hours to carry out the grafting reaction and obtain a superhydrophilic and oleophobic film.

[0058] The superhydrophilic oleophobic membrane prepared in Example 4 had a pure water flux of 1600 L·m⁻¹. -2 ·h -1 The superhydrophilic oleophobic film has a water contact angle of 0° and an underwater oil contact angle of 133°.

[0059] The superhydrophilic oleophobic membrane prepared in Example 4 was used for oil-water separation testing of oilfield wastewater. Before the test, the oil content in the oilfield wastewater was 120 ppm, the suspended particle content was 80 ppm, and the median particle size was 10 μm. After filtration using the superhydrophilic oleophobic membrane prepared in Example 1, the oil content in the permeate was less than 15 ppm, the suspended particle content was 10 ppm, and the median particle size was less than 3 μm. The water flux of the superhydrophilic oleophobic membrane in oily wastewater was 200 L·m⁻¹. -2 ·h -1 After a simple rinse, the flow rate of the separation membrane recovered to 88% of its initial value.

[0060] Comparative Example 1

[0061] A polyester nonwoven fabric with a thickness of 5 mm and a pore size range of 5–10 μm was used as the separation membrane, and the water flux of the separation membrane was 1800 L·m. -2 ·h -1 The water contact angle of the separation membrane is 78°, and the underwater oil contact angle is 25°.

[0062] Oil-water separation tests were conducted using oilfield wastewater. Before the test, the oil content in the oilfield wastewater was 120 ppm, the suspended particle content was 80 ppm, and the median particle size was 10 μm.

[0063] After filtration with polyester nonwoven fabric, the oil content in the permeate was 110 ppm, the suspended particulate content was 60 ppm, the median particle size was less than 5 μm, and the water flux of the separation membrane in oily wastewater was 50 L·m. -2 ·h -1 After a simple rinse, the flow rate of the separation membrane recovered to 20% of the initial value.

[0064] Comparative Example 2

[0065] A polypropylene microporous filter membrane with a thickness of 5 mm and a pore size range of 3–5 μm was used as the separation membrane, and the water flux of the separation membrane was 600 L·m. -2 ·h -1 The water contact angle of the separation membrane is 110°, and the underwater oil contact angle is 10°.

[0066] Oil-water separation tests were conducted using oilfield wastewater. Before the test, the oil content in the oilfield wastewater was 120 ppm, the suspended particle content was 80 ppm, and the median particle size was 10 μm.

[0067] After filtration using a polypropylene microporous membrane, the oil content in the permeate was 110 ppm, the suspended particulate content was 20 ppm, the median particle size was less than 5 μm, and the water flux of the separation membrane in oily wastewater was 30 L·m⁻¹. -2 ·h -1 After a simple rinse, the flow rate of the separation membrane recovered to 15% of the initial value.

[0068] As can be seen from Examples 1-4 and Comparative Examples 1 and 2, the superhydrophilic oleophobic membrane prepared by the superhydrophilic oleophobic membrane preparation method provided by the present invention has extremely strong hydrophilicity, high flux, and high anti-fouling ability when applied to the oil-water separation process.

[0069] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a superhydrophilic oleophobic film, characterized in that, Includes the following steps: S1: Chitosan, polyacrylic acid and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) are dissolved in deionized water and stirred to obtain a uniform modified solution; S2: The modified solution is coated onto the surface and pores of the porous material. The coated porous material is placed in an oven to dry the deionized water and complete the crosslinking reaction. S3: Dissolve the hydrophilic monomer and initiator in deionized water and stir to obtain a uniform grafting solution. The hydrophilic monomer includes acrylic acid, acrylamide, vinylpyrrolidone and hydroxyethyl acrylate. S4: Immerse the cross-linked porous material in a grafting solution, introduce nitrogen gas, and heat to carry out the grafting reaction to obtain a superhydrophilic and oleophobic film.

2. The method for preparing the superhydrophilic oleophobic film as described in claim 1, characterized in that, The molecular weight of chitosan in S1 is 2000~10000, and the molecular weight of polyacrylic acid is 2000~10000; the concentration of chitosan in the modified solution is 1~10g / L, the concentration of polyacrylic acid is 1~10g / L, and the concentration of EDC is 0.1~1g / L.

3. The method for preparing the superhydrophilic oleophobic film as described in claim 1, characterized in that, The porous material mentioned in S2 includes metal mesh, non-woven fabric, and microporous filter membrane. The pore size of the porous material is 5~10μm and the thickness of the porous material is 0.2~5mm.

4. The method for preparing the superhydrophilic oleophobic film as described in claim 1, characterized in that, The coating process described in S2 involves immersing the porous material in a modified solution for 30-60 minutes, then removing it after coating. The crosslinking reaction conditions described in S2 are a temperature of 75-90°C and a reaction time of 1-8 hours.

5. The method for preparing the superhydrophilic oleophobic film as described in claim 1, characterized in that, The initiators described in S3 include cerium ammonium nitrate, potassium persulfate, and ammonium persulfate.

6. The method for preparing the superhydrophilic oleophobic film as described in claim 1, characterized in that, The concentration of the hydrophilic monomer in the grafting solution described in S3 is 1~10 g / L; the concentration of the initiator is 0.1~1 g / L.

7. The method for preparing the superhydrophilic oleophobic film as described in claim 1, characterized in that, The grafting reaction conditions described in S4 are: under nitrogen protection, soaking temperature of 40~90℃, and soaking time of 5~20h.

8. A superhydrophilic oleophobic film, characterized in that, The superhydrophilic oleophobic film was prepared using the preparation method described in any one of claims 1 to 7.

9. An application of a superhydrophilic oleophobic film, characterized in that, The superhydrophilic oleophobic membrane as described in claim 8 is applied to oil-water separation.