A composite nanofiltration membrane based on an oil-immersed gel coating and its preparation method

Abstract

This invention provides a composite nanofiltration membrane based on an oil-impregnated gel coating and its preparation method. The composite nanofiltration membrane comprises a porous support membrane, an oil-impregnated gel coating, and an active separation layer. The oil-impregnated gel coating comprises a gelation product of a block copolymer, and the active separation layer comprises an interfacial polymer formed by an aqueous monomer and an organic monomer. The preparation method of the composite nanofiltration membrane comprises: (1) mixing an organic monomer solution and a block copolymer solution to form an oil-impregnated gel coating containing an organic monomer on the surface of the porous support membrane; (2) coating an aqueous monomer solution onto the surface of the porous support membrane and forming an active separation layer through an interfacial polymerization reaction to obtain the composite nanofiltration membrane based on the oil-impregnated gel coating. The composite nanofiltration membrane based on the oil-impregnated gel coating has high water flux and high rejection rate.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation, specifically relating to a composite nanofiltration membrane based on an oil-immersed gel coating and its preparation method. Background Technology

[0002] Nanofiltration membrane separation technology has shown broad application potential in the selective separation of small molecules and polyvalent salts due to its advantages of low energy consumption and high separation efficiency. Currently, nanofiltration membranes are mainly thin-layer composite membranes formed by the interfacial polymerization of aqueous polyamine monomers and organic polyacrylamide chloride monomers. However, the vigorous and unstable interfacial polymerization process often leads to inhomogeneous structure and high surface roughness of the composite membrane separation layer. Furthermore, for porous supported membranes with low porosity and poor uniformity, the disordered distribution of reactive monomers on their surface can also disrupt the stability of the phase interface and reduce separation efficiency.

[0003] The performance of composite nanofiltration membranes is determined by the structure of the separation layer. Preparing a uniform and defect-free separation layer is beneficial for improving the separation selectivity of the composite nanofiltration membrane. Therefore, to obtain an active separation layer with uniform structure and excellent permeation separation performance, it is necessary to optimize the diffusion and reaction behavior of monomers to improve the interfacial stability of the interfacial polymerization reaction. CN107837689A discloses a method for preparing a nanofiltration membrane with an ultrathin separation layer. By introducing polyol molecules into the aqueous reactant solution, the diffusion coefficient of the monomers is reduced, thereby improving the interfacial stability of the interfacial polymerization, resulting in a thinner separation layer and increased permeation flux. However, inhibited interfacial polymerization reactions usually reduce the crosslinking degree of the separation layer and lead to a large waste of reactive monomers. In addition, the unreacted charged monomers remaining on the surface of the separation layer can also exert a significant electrostatic adsorption effect on counterions, reducing the solute rejection rate. CN112808021A discloses a method for preparing a polyamide composite membrane using aqueous additives. The composite membrane utilizes surfactants to improve the dispersion uniformity of aqueous monomers and enhance their diffusion behavior at the phase interface. The prepared composite membrane exhibits increased flux and rejection rate. However, this method requires high levels of surfactant dispersion in solution and stability at the phase interface. CN112999898A discloses a method for preparing a high-flux nanofiltration membrane for selective separation of monovalent / divalent ions. By depositing hydroxyapatite nanowires as an intermediate layer on the surface of a supporting membrane, the distribution of aqueous monomers at the phase interface is improved, increasing the permeate flux of the composite membrane. However, the nanomaterial intermediate layer introduces an additional membrane-forming step, hindering its industrial application.

[0004] Therefore, how to balance the improvement of phase interface stability and separation layer crosslinking degree, and develop a composite nanofiltration membrane with high permeation flux, uniform separation layer structure, simple preparation method, and adjustable separation capacity is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a composite nanofiltration membrane based on an oil-impregnated gel coating and its preparation method. On one hand, the present invention improves the uniformity of monomer distribution on the membrane surface and restricts monomer diffusion behavior by forming an oil-impregnated gel coating on the porous support membrane surface, thereby reducing the thickness of the separation layer. On the other hand, during heat treatment, the sol-gelation of the oil-impregnated gel coating can release unreacted monomers for secondary reactions, modifying the internal structure of the separation layer and improving the utilization rate of reactant monomers. The resulting composite nanofiltration membrane exhibits high permeation flux and high rejection rate.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a composite nanofiltration membrane based on an oil-immersed gel coating, the composite nanofiltration membrane comprising a porous support membrane, an oil-immersed gel coating and an active separation layer, the oil-immersed gel coating comprising a gelation product of a block copolymer, and the active separation layer comprising an interfacial polymer formed by an aqueous phase monomer and an organic phase monomer.

[0008] This invention coats a porous support membrane with a mixed solution of polystyrene-polyisoprene-polystyrene and organic monomers. Utilizing the difference in compatibility of polymer segments with the organic solvent, a sol-gel phase separation process occurs, forming a smooth and stable oil-impregnated gel coating. This reduces surface roughness and improves the interfacial stability of the interfacial polymerization. Simultaneously, the gel coating formed by the organic solution restricts the diffusion behavior of the organic monomers, reducing the intensity of the interfacial polymerization reaction and creating a more uniform active separation layer. Furthermore, heat treatment resolubilizes the coating, releasing unreacted monomers for secondary polymerization, improving the crosslinking degree, interfacial stability, and monomer utilization of the separation layer. The more uniform the structure of the active separation layer, the higher the separation selectivity of the composite nanofiltration membrane.

[0009] Preferably, the porous support membrane comprises an inorganic porous support membrane and / or a polymer porous support membrane.

[0010] Preferably, the inorganic porous support membrane includes any one or a combination of at least two of the following: alumina ceramic porous support membrane, titanium dioxide ceramic porous support membrane, silicon dioxide ceramic porous support membrane, or zirconia ceramic porous support membrane.

[0011] Preferably, the polymer porous support membrane includes any one or a combination of at least two of the following: polysulfone porous support membrane, polyethersulfone porous support membrane, polyvinylidene fluoride porous support membrane, polytetrafluoroethylene porous support membrane, polyacrylonitrile porous support membrane, polyethylene porous support membrane, polyetherimide porous support membrane, polypropylene porous support membrane, polyimide porous support membrane, or polyamide porous support membrane.

[0012] Preferably, the thickness of the porous support membrane is, for example, 100-200 μm, such as 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, etc.

[0013] Preferably, the thickness of the oil-impregnated gel coating is 30–150 μm, for example, it can be 30 μm, 50 μm, 70 μm, 90 μm, 110 μm, 130 μm, 150 μm, etc.

[0014] Preferably, the thickness of the active separation layer is 30-100 nm, for example, it can be 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.

[0015] Preferably, the mass ratio of the aqueous phase monomer, the organic phase monomer, and the block copolymer is (2-1000):(1-500):(1-500), for example, it can be 2:1:1, 2:10:1, 2:100:1, 10:1:1, 100:10:1, 200:1:1, 200:50:3, 200:3:1, etc., preferably (10-200):(5-100):(1-100).

[0016] Preferably, the aqueous monomer comprises any one or a combination of at least two of polyethyleneimine, diethylenetriamine, piperazine, m-phenylenediamine, 3-aminobenzenesulfonamide, resorcinol, cyclohexanediamine, or triethylenetetramine.

[0017] Preferably, the organic phase monomer is an acyl chloride monomer.

[0018] Preferably, the acyl chloride monomer includes any one or a combination of at least two of pyromellitic trisulfonyl chloride, pyromellitic trisulfonyl chloride, isophenylene disulfonyl chloride, isophenylene disulfonyl chloride, o-phenylene disulfonyl chloride, o-phenylene disulfonyl chloride, terephthalene disulfonyl chloride, or terephthalene disulfonyl chloride.

[0019] Preferably, the block copolymer comprises polystyrene-polyisoprene-polystyrene.

[0020] In a second aspect, the present invention provides a method for preparing a composite nanofiltration membrane as described in the first aspect, the method comprising the following steps:

[0021] (1) Mix the organic phase monomer solution and the block copolymer solution and coat them onto the surface of the porous support membrane to form an oil-impregnated gel coating containing the organic phase monomer;

[0022] (2) The aqueous monomer solution is coated on the surface of the porous support membrane, and an active separation layer is formed by interfacial polymerization reaction to obtain the composite nanofiltration membrane.

[0023] Preferably, the solvent in the organic phase monomer solution includes any one or a combination of at least two of the following: n-hexane, heptane, isoparaffin solvents, petroleum ether, cyclohexane, and ethyl acetate.

[0024] Preferably, the mass percentage of organic phase monomers in the organic phase monomer solution is 0.01% to 5%, for example, it can be 0.01%, 0.02%, 0.03%, 0.1%, 1%, 2%, 3%, 5%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the solvent in the aqueous monomer solution includes water.

[0026] Preferably, the mass percentage of the aqueous monomer in the aqueous monomer solution is 0.01% to 5%, for example, it can be 0.01%, 0.02%, 0.03%, 0.1%, 1%, 2%, 5%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the solvent in the block copolymer solution includes any one or a combination of at least two of petroleum ether, n-hexane, cyclohexane, tetradecane, n-hexadecane, or 1-octadecene.

[0028] Preferably, the block copolymer solution contains 0.01% to 5% by mass, for example, 0.01%, 0.02%, 0.1%, 0.5%, 1%, 2%, 5%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, in step (1), the mixing process further includes temperature control.

[0030] Preferably, in step (1), the temperature of the temperature control treatment is 80 to 120°C, for example, 80°C, 85°C, 90°C, 95°C, 100°C, 120°C, etc., but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, in step (1), the temperature control process takes 1 to 10 minutes, for example, 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, etc.

[0032] Preferably, in step (2), the temperature of the interfacial polymerization reaction is 20 to 60°C, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, etc.

[0033] Preferably, in step (2), the time for the interfacial polymerization reaction is 1 to 15 min, for example, 1 min, 3 min, 6 min, 9 min, 12 min, 15 min, etc., but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, in step (2), the interfacial polymerization reaction is followed by heat treatment.

[0035] Preferably, in step (2), the temperature of the heat treatment is 60 to 100°C, for example, 60°C, 65°C, 75°C, 80°C, 90°C, 100°C, etc., but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, in step (2), the heat treatment time is 1 to 20 minutes, for example, it can be 1 minute, 3 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the preparation method includes the following steps:

[0038] (1) Mix the organic phase monomer solution with the block copolymer solution, and treat it at 80-120℃ for 1-10 min. Then coat it onto the surface of the porous support membrane to form an oil-impregnated gel coating containing organic phase monomers.

[0039] (2) Coat the surface of the porous support membrane with an aqueous monomer solution, perform interfacial polymerization reaction at 20-60°C for 1-15 min to form an active separation layer, and heat treat at 60-100°C for 1-20 min to obtain the composite nanofiltration membrane.

[0040] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] (1) The composite nanofiltration membrane based on oil-immersed gel coating prepared in this invention has high water flux and high rejection rate. The water flux of the composite nanofiltration membrane is 12.3-31.4 Lm. -2 h -1 bar -1 The rejection rate of magnesium chloride at a concentration of 1 g / L is 90-94.7%, which shows great application potential in the treatment of saline wastewater.

[0043] (2) The present invention improves the phase interface uniformity of the interfacial polymerization reaction by coating a reactant solution containing polystyrene-polyisoprene-polystyrene and organic phase monomers on the surface of a porous support membrane, and utilizes the thermal response characteristics of block copolymers to construct a smooth oil-immersed gel coating, without introducing an additional intermediate layer construction step.

[0044] (3) The oil-impregnated gel coating prepared by the present invention can restrict the diffusion of organic phase monomers, reduce the intensity of interfacial polymerization reaction, and improve the uniformity of the separation layer; at the same time, the low surface energy oil-impregnated gel coating can prevent the rapid volatilization of organic phase solution and ensure the integrity of phase interface; and, through heat treatment, the coating can be resolidified to release unreacted monomers for secondary polymerization reaction, further improving the crosslinking degree of the separation layer, and obtaining an active separation layer with low thickness and uniform structure, thereby improving the separation efficiency of composite nanofiltration membrane in water treatment process;

[0045] (4) The high-throughput composite nanofiltration membrane preparation method provided by the present invention is simple, has good reproducibility, can effectively improve the utilization rate of monomers, has a significant improvement effect on membrane preparation processes that require reverse interfacial polymerization, and can adjust the concentration of polystyrene-polyisoprene-polystyrene according to the treatment requirements of different feed solutions to obtain composite nanofiltration membranes with different properties. Detailed Implementation

[0046] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0047] The materials used in all embodiments and comparative examples of this invention are as follows:

[0048] Polyethyleneimine: weight average molecular weight 1800, purchased from Aladdin Biochemical Technology Co., Ltd.;

[0049] m-Phenylenediamine, pyromellitic acid trichloroethylene chloride, isophthaloyl chloride, isophenylene sulfonyl chloride, diethylenetriamine, n-hexane: analytical grade, purchased from Aladdin Biochemical Technology Co., Ltd.;

[0050] Polystyrene-polyisoprene-polystyrene: weight average molecular weight of 140,000, purchased from Aladdin Biochemical Technology Co., Ltd.

[0051] Polyethersulfone porous supported membrane: molecular weight cutoff of 50 kDa, purchased from Ande Membrane Separation Technology Engineering Co., Ltd.;

[0052] Polysulfone porous support membrane: molecular weight cutoff of 50 kDa, purchased from Ande Membrane Separation Technology Engineering Co., Ltd.

[0053] Alumina ceramic porous support membrane: average pore size 10nm, purchased from Yirun Fine Ceramics New Materials Co., Ltd.

[0054] Polyacrylonitrile porous support membrane: molecular weight cutoff of 50 kDa, purchased from Ande Membrane Separation Technology Engineering Co., Ltd.

[0055] Example 1

[0056] This embodiment provides a composite nanofiltration membrane based on an oil-impregnated gel coating and its preparation method. The composite nanofiltration membrane comprises, from bottom to top, a polyethersulfone porous support membrane, an oil-impregnated gel coating, and an active separation layer. The thickness of the oil-impregnated gel coating is 50 μm, and the thickness of the active separation layer is 50 nm. The oil-impregnated gel coating is a gelled product of a polystyrene-polyisoprene-polystyrene hexane solution. The active separation layer comprises an interfacial polymer of an aqueous solution of polyethyleneimine and a hexane solution of trimesoyl chloride. The mass ratio of polyethyleneimine, trimesoyl chloride, and polystyrene-polyisoprene-polystyrene is 2:1:1.

[0057] The method for preparing the composite nanofiltration membrane includes the following steps:

[0058] (1) Mix a hexane solution of 2.5% trimesoyl chloride and a hexane solution of 2.5% polystyrene-polyisoprene-polystyrene uniformly, heat to 100°C and control the temperature for 5 min, then impregnate the surface of the polyethersulfone porous support membrane for 1 min.

[0059] (2) The polyethersulfone porous support membrane was immersed in an aqueous solution of polyethyleneimine with a mass percentage of 2.5% and subjected to interfacial polymerization reaction at 40°C for 1 min. After heat treatment at 80°C for 15 min, the composite nanofiltration membrane was obtained.

[0060] Example 2

[0061] This embodiment provides a composite nanofiltration membrane based on an oil-impregnated gel coating and its preparation method. The composite nanofiltration membrane comprises, from bottom to top, a polyethersulfone porous support membrane, an oil-impregnated gel coating, and an active separation layer. The thickness of the oil-impregnated gel coating is 40 μm, and the thickness of the active separation layer is 100 nm. The oil-impregnated gel coating is a gelled product of a polystyrene-polyisoprene-polystyrene hexane solution. The active separation layer comprises an interfacial polymer of an aqueous solution of polyethyleneimine and a hexane solution of trimesoyl chloride. The mass ratio of polyethyleneimine, trimesoyl chloride, and polystyrene-polyisoprene-polystyrene is 2:1:1.

[0062] The method for preparing the composite nanofiltration membrane includes the following steps:

[0063] (1) Mix the n-hexane solution of 0.01% pyromellitic chloride and the n-hexane solution of 0.01% polystyrene-polyisoprene-polystyrene evenly, heat to 80°C and control the temperature for 1 min, and then impregnate the surface of the polyethersulfone porous support membrane for 1 min.

[0064] (2) The polyethersulfone porous support membrane was immersed in an aqueous solution of polyethyleneimine with a mass percentage of 0.1% and subjected to interfacial polymerization reaction at 20°C for 1 min. The membrane was then heat-treated at 60°C for 10 min to obtain the composite nanofiltration membrane.

[0065] Example 3

[0066] This embodiment provides a composite nanofiltration membrane based on an oil-impregnated gel coating and its preparation method. The composite nanofiltration membrane comprises, from bottom to top, a polyethersulfone porous support membrane, an oil-impregnated gel coating, and an active separation layer. The thickness of the oil-impregnated gel coating is 100 μm, and the thickness of the active separation layer is 70 nm. The oil-impregnated gel coating is a gelled product of a polystyrene-polyisoprene-polystyrene hexane solution. The active separation layer comprises an interfacial polymer of an aqueous solution of polyethyleneimine and a hexane solution of trimesoyl chloride, wherein the mass ratio of polyethyleneimine, trimesoyl chloride, and polystyrene-polyisoprene-polystyrene is 2:1:1.

[0067] The method for preparing the composite nanofiltration membrane includes the following steps:

[0068] (1) Mix a 5% hexane solution of pyromellitic chloride and a 5% hexane solution of polystyrene-polyisoprene-polystyrene evenly, heat to 120°C and control the temperature for 10 min, then impregnate the surface of the polyethersulfone porous support membrane for 1 min.

[0069] (2) The polyethersulfone porous support membrane was immersed in an aqueous solution of polyethyleneimine with a mass percentage of 5% and subjected to interfacial polymerization reaction at 60°C for 1 min. After heat treatment at 100°C for 20 min, the composite nanofiltration membrane was obtained.

[0070] Example 4

[0071] This embodiment provides a composite nanofiltration membrane based on an oil-impregnated gel coating and its preparation method. The composite nanofiltration membrane comprises, from bottom to top, a polyethersulfone porous support membrane, an oil-impregnated gel coating, and an active separation layer. The thickness of the oil-impregnated gel coating is 120 μm, and the thickness of the active separation layer is 30 nm. The oil-impregnated gel coating is a gelled product of a polystyrene-polyisoprene-polystyrene hexane solution. The active separation layer comprises an interfacial polymer of an aqueous solution of polyethyleneimine and a hexane solution of trimesoyl chloride, wherein the mass ratio of polyethyleneimine, trimesoyl chloride, and polystyrene-polyisoprene-polystyrene is 300:50:3.

[0072] The method for preparing the composite nanofiltration membrane includes the following steps:

[0073] (1) Mix a hexane solution of 0.5% pyromellitic chloride and a hexane solution of 0.03% polystyrene-polyisoprene-polystyrene uniformly, heat to 100°C and control the temperature for 5 min, and then impregnate the surface of the polyethersulfone porous support membrane for 1 min.

[0074] (2) The polyethersulfone porous support membrane was immersed in an aqueous solution of polyethyleneimine with a mass percentage of 1.5% and subjected to interfacial polymerization reaction at 25°C for 1 min. After heat treatment at 90°C for 10 min, the composite nanofiltration membrane was obtained.

[0075] Example 5

[0076] This embodiment provides a composite nanofiltration membrane based on an oil-impregnated gel coating and its preparation method. The composite nanofiltration membrane comprises, from bottom to top, a polysulfone porous support membrane, an oil-impregnated gel coating, and an active separation layer. The thickness of the oil-impregnated gel coating is 120 μm, and the thickness of the active separation layer is 80 nm. The oil-impregnated gel coating is a gelation product of a polystyrene-polyisoprene-polystyrene hexane solution; the active separation layer comprises an interfacial polymerization product of an aqueous solution of polyethyleneimine and a hexane solution of trimesoyl chloride, wherein the mass ratio of polyethyleneimine, trimesoyl chloride, and polystyrene-polyisoprene-polystyrene is 150:50:3.

[0077] The method for preparing the composite nanofiltration membrane includes the following steps:

[0078] (1) Mix the n-hexane solution of 0.5% pyromellitic chloride and the n-hexane solution of 0.03% polystyrene-polyisoprene-polystyrene evenly, heat to 100°C and control the temperature for 5 min, and then impregnate the surface of the polysulfone porous support membrane for 1 min.

[0079] (2) The polysulfone porous support membrane was immersed in an aqueous solution of polyethyleneimine with a mass percentage of 1.5% and subjected to interfacial polymerization reaction at 25°C for 1 min. After heat treatment at 90°C for 10 min, the composite nanofiltration membrane was obtained.

[0080] Example 6

[0081] This embodiment provides a composite nanofiltration membrane based on an oil-impregnated gel coating and its preparation method. The composite nanofiltration membrane comprises, from bottom to top, a polyethersulfone porous support membrane, an oil-impregnated gel coating, and an active separation layer. The thickness of the oil-impregnated gel coating is 40 μm, and the thickness of the active separation layer is 50 nm. The oil-impregnated gel coating is a gelled product of a polystyrene-polyisoprene-polystyrene hexane solution. The active separation layer comprises an interfacial polymer of an aqueous solution of m-phenylenediamine and a hexane solution of trimesoyl chloride, wherein the mass ratio of m-phenylenediamine, trimesoyl chloride, and polystyrene-polyisoprene-polystyrene is 30:10:1.

[0082] The method for preparing the composite nanofiltration membrane includes the following steps:

[0083] (1) Mix 0.5% by mass of a hexane solution of pyromellitic chloride and 0.03% by mass of a hexane solution of polystyrene-polyisoprene-polystyrene, heat to 100°C and control the temperature for 5 minutes, and then spray it onto the surface of the polyethersulfone porous support membrane.

[0084] (2) After 15 seconds, an aqueous solution of m-phenylenediamine with a mass percentage of 1.5% was sprayed onto the surface of the support membrane, and an interfacial polymerization reaction was carried out at 25°C. After heat treatment at 90°C for 10 minutes, the composite nanofiltration membrane was obtained.

[0085] Example 7

[0086] This embodiment provides a composite nanofiltration membrane based on an oil-impregnated gel coating and its preparation method. The composite nanofiltration membrane comprises, from bottom to top, an alumina ceramic porous support membrane, an oil-impregnated gel coating, and an active separation layer. The thickness of the oil-impregnated gel coating is 80 μm, and the thickness of the active separation layer is 70 nm. The oil-impregnated gel coating is a gelled product of a polystyrene-polyisoprene-polystyrene n-hexadecane solution. The active separation layer comprises an interfacial polymer of an aqueous solution of diethylenetriamine and a hexane solution of isophenylenesulfonyl chloride, wherein the mass ratio of diethylenetriamine, isophenylenesulfonyl chloride, and polystyrene-polyisoprene-polystyrene is 150:50:3.

[0087] The method for preparing the composite nanofiltration membrane includes the following steps:

[0088] (1) Mix 0.5% hexane solution of pyromellitic trisulfonyl chloride and 0.03% hexadecane solution of polystyrene-polyisoprene-polystyrene evenly, heat to 100°C and control the temperature for 5 min, then impregnate the surface of the porous alumina ceramic support membrane for 1 min.

[0089] (2) The alumina ceramic porous support membrane was placed in an aqueous solution of 1.5% by mass of diethylenetriamine and subjected to interfacial polymerization at 25°C. After heat treatment at 90°C for 10 min, the composite nanofiltration membrane was obtained.

[0090] Example 8

[0091] This embodiment provides a composite nanofiltration membrane based on an oil-impregnated gel coating and its preparation method. The composite nanofiltration membrane comprises, from bottom to top, a polyacrylonitrile porous support membrane, an oil-impregnated gel coating, and an active separation layer. The thickness of the oil-impregnated gel coating is 40 μm, and the thickness of the active separation layer is 90 nm. The oil-impregnated gel coating is a gelled product of a polystyrene-polyisoprene-polystyrene n-hexadecane solution. The active separation layer comprises an interfacial polymer of an aqueous solution of polyethyleneimine and a hexane solution of isophthaloyl chloride, wherein the mass ratio of polyethyleneimine, isophthaloyl chloride, and polystyrene-polyisoprene-polystyrene is 30:10:3.

[0092] The method for preparing the composite nanofiltration membrane includes the following steps:

[0093] (1) Mix 0.5% hexane solution of isophthaloyl chloride and 0.03% hexane solution of polystyrene-polyisoprene-polystyrene evenly, heat to 100°C and control the temperature for 5 min, then impregnate the surface of the polyacrylonitrile porous support membrane for 1 min.

[0094] (2) The polyacrylonitrile porous support membrane was immersed in an aqueous solution of polyethyleneimine with a mass percentage of 1.5% and subjected to interfacial polymerization reaction at 25°C for 1 min. After heat treatment at 90°C for 10 min, the composite nanofiltration membrane was obtained.

[0095] Example 9

[0096] This embodiment provides a composite nanofiltration membrane based on an oil-immersed gel coating and its preparation method. The only difference between this embodiment and Example 4 is that the mass percentage of polystyrene-polyisoprene-polystyrene in step (2) is 10%, while the other components, dosages, structures and preparation methods are the same as in Example 4.

[0097] Example 10

[0098] This embodiment provides a composite nanofiltration membrane based on an oil-immersed gel coating and its preparation method. The only difference between this embodiment and Example 4 is that the polystyrene-polyisoprene-polystyrene described in step (2) is replaced with an equal amount of polyisoprene. The other components, amounts, structures and preparation methods are the same as in Example 4.

[0099] Comparative Example 1

[0100] This comparative example provides a composite nanofiltration membrane based on an oil-immersed gel coating and its preparation method. The difference between this and Example 4 is that no block copolymer is added in step (1), while the rest is the same as Example 4.

[0101] Comparative Example 2

[0102] This comparative example provides a composite nanofiltration membrane based on an oil-immersed gel coating and its preparation method. The difference between this and Example 4 is that the temperature control treatment after mixing is not performed in step (1), while the rest is the same as Example 4.

[0103] Comparative Example 3

[0104] This comparative example provides a composite nanofiltration membrane based on an oil-immersed gel coating and its preparation method. The difference between this example and Example 4 is that heat treatment is not performed in step (2), while the rest is the same as Example 4.

[0105] Performance testing

[0106] The water flux, inorganic salt ion selectivity, and surface roughness of the composite nanofiltration membranes based on oil-immersed gel coatings prepared in Examples 1-10 and Comparative Examples 1-3 were tested.

[0107] (1) Water flux and inorganic salt rejection performance of composite nanofiltration membrane: The tests were conducted in a high-pressure cross-flow apparatus (FloMem-0010-HP, purchased from Xiamen Shida Membrane Technology Co., Ltd.), with an effective volume of 2.5L in the feed tank and an effective membrane area of ​​16cm². 2 The filtration process employs a full circulation mode, operating at a cross-flow velocity of 6 L / min. The water flux is calculated using the following formula:

[0108]

[0109] Where P is the permeation flux (Lm) -2 h -1 bar -1 V p Let A be the volume (L) of permeate collected within time t. m Effective membrane area (m²) 2 ), where t is the running time (h) and TMP is the transmembrane pressure (bar).

[0110] The retention rate of inorganic salt ions is calculated using the following formula:

[0111]

[0112] Where C p and C r These represent the concentrations of the solute in the permeate and retentate, respectively. For inorganic salt ion solutions, the concentrations of the solute in the permeate and retentate are replaced by conductivity. The above tests were conducted at 25°C, and the concentration of the inorganic salt ion solution was 1 g / L.

[0113] (2) Roughness test:

[0114] The surface roughness of the composite nanofiltration membrane was analyzed using atomic force microscopy (FastScan Bio, Bruker, Germany). Membrane samples were cut to 1cm × 1cm size and placed on a glass slide. The surface roughness of the 5.0 × 5.0 μm membrane was analyzed using a tapping mode at 15–30°C. 2 Roughness was characterized on a membrane surface of varying sizes. Three different locations were randomly selected for measurement, and the average value was taken.

[0115] Table 1

[0116]

[0117]

[0118] Analysis of the data in Table 1 shows that the present invention improves the interfacial stability by constructing an oil-immersed gel coating, restricts the diffusion of organic phase monomers, reduces the intensity of interfacial polymerization reaction, and improves the uniformity of the separation layer, so that the composite nanofiltration membrane has a smooth and uniform separation layer structure; at the same time, the coating is resolidified by heat treatment, releasing unreacted monomers to carry out secondary polymerization reaction, further improving the crosslinking degree of the separation layer.

[0119] Analysis of Examples 1-8 shows that the water flux of the composite nanofiltration membrane is 12.3-31.4 Lm. -2 h -1 bar -1 The magnesium chloride rejection rate is 90-94.7%, and the average surface roughness is 17-32 nm.

[0120] A comparison of Examples 4 and 9 shows that the concentration of polystyrene-polyisoprene-polystyrene is not within a specific range. Excessive block copolymer increases the thickness of the gel interlayer, leading to increased mass transfer resistance, significantly reduced permeability of the composite nanofiltration membrane, and increased magnesium chloride rejection rate.

[0121] A comparison of Example 4 and Example 10 shows that replacing polystyrene-polyisoprene-polystyrene with polyisoprene molecules results in a decrease in the separation performance of the composite nanofiltration membrane and an increase in surface roughness due to the high affinity of polyisoprene for the solvent, which prevents gelation transformation at room temperature.

[0122] As can be seen from the comparison between Example 4 and Comparative Example 1, the composite nanofiltration membrane does not have an oil-immersed gel coating, and its interfacial polymerization has high instability. The separation performance of the composite nanofiltration membrane decreases, and the surface roughness of the separation layer increases.

[0123] As can be seen from the comparison between Example 4 and Comparative Example 2, the organic phase reactant solution in step (1) was not subjected to temperature control treatment, and the organic phase solution could not undergo sol-gel phase separation, which led to increased instability of the interfacial polymerization process, decreased separation performance of the composite nanofiltration membrane, and increased surface roughness of the separation layer.

[0124] As can be seen from the comparison between Example 4 and Comparative Example 3, the initial separation layer of the composite nanofiltration membrane was not heat-treated, and the oil-immersed gel coating could not be solidified, which resulted in the organic phase monomers being unable to undergo secondary reactions to improve the crosslinking degree of the separation layer, thus reducing the separation performance of the composite nanofiltration membrane and increasing the surface roughness of the separation layer.

[0125] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite nanofiltration membrane based on an oil-immersed gel coating, characterized in that, The composite nanofiltration membrane comprises a porous support membrane, an oil-impregnated gel coating, and an active separation layer; The raw material for the oil-immersed gel coating includes the gelation product of a block copolymer and an organic phase monomer; The active separation layer comprises an interfacial polymer formed by an aqueous phase monomer and an organic phase monomer; The block copolymer includes polystyrene-polyisoprene-polystyrene.

2. The composite nanofiltration membrane according to claim 1, characterized in that, The porous support membrane includes an inorganic porous support membrane or a polymer porous support membrane.

3. The composite nanofiltration membrane according to claim 2, characterized in that, The inorganic porous support membrane includes any one or a combination of at least two of the following: alumina ceramic porous support membrane, titanium oxide ceramic porous support membrane, silicon oxide ceramic porous support membrane, or zirconia ceramic porous support membrane.

4. The composite nanofiltration membrane according to claim 2, characterized in that, The polymer porous support membrane includes any one or a combination of at least two of the following: polysulfone porous support membrane, polyethersulfone porous support membrane, polyvinylidene fluoride porous support membrane, polytetrafluoroethylene porous support membrane, polyacrylonitrile porous support membrane, polyethylene porous support membrane, polyetherimide porous support membrane, polypropylene porous support membrane, polyimide porous support membrane, or polyamide porous support membrane.

5. The composite nanofiltration membrane according to claim 1, characterized in that, The thickness of the porous support membrane is 100~200μm.

6. The composite nanofiltration membrane according to claim 1, characterized in that, The thickness of the oil-impregnated gel coating is 30~150μm.

7. The composite nanofiltration membrane according to claim 1, characterized in that, The thickness of the active separation layer is 30~100nm.

8. The composite nanofiltration membrane according to claim 1, characterized in that, The mass ratio of the aqueous phase monomer, the organic phase monomer, and the block copolymer is (2~1000): (1~500): (1~500).

9. The composite nanofiltration membrane according to claim 8, characterized in that, The mass ratio of the aqueous phase monomer, the organic phase monomer, and the block copolymer is (10~200): (5~100): (1~100).

10. The composite nanofiltration membrane according to claim 1, characterized in that, The aqueous monomers include any one or a combination of at least two of polyethyleneimine, diethylenetriamine, piperazine, m-phenylenediamine, 3-aminobenzenesulfonamide, resorcinol, cyclohexanediamine, or triethylenetetramine.

11. The composite nanofiltration membrane according to claim 1, characterized in that, The organic phase monomers include acyl chloride monomers.

12. The composite nanofiltration membrane according to claim 11, characterized in that, The acyl chloride monomer includes any one or a combination of at least two of the following: trimesoyl chloride, trimesoyl chloride, isophenylenesulfonyl chloride, isophenylenesulfonyl chloride, o-phenylenesulfonyl chloride, o-phenylenesulfonyl chloride, terephthalenesulfonyl chloride, or terephthalenesulfonyl chloride.

13. A method for preparing a composite nanofiltration membrane according to any one of claims 1 to 12, characterized in that, The preparation method includes the following steps: (1) Mix the organic phase monomer solution and the block copolymer solution and coat them onto the surface of the porous support membrane to form an oil-impregnated gel coating containing the organic phase monomer; (2) The aqueous monomer solution is coated on the surface of the oil-immersed gel coating, and an active separation layer is formed through interfacial polymerization reaction to obtain the composite nanofiltration membrane.

14. The preparation method according to claim 13, characterized in that, The solvent in the organic phase monomer solution includes any one or a combination of at least two of the following: n-hexane, heptane, isoparaffin solvents, petroleum ether, cyclohexane, and ethyl acetate.

15. The preparation method according to claim 13, characterized in that, The organic monomer solution contains 0.01-5% organic monomer by mass.

16. The preparation method according to claim 13, characterized in that, The solvent in the aqueous monomer solution includes water.

17. The preparation method according to claim 13, characterized in that, The aqueous monomer solution contains 0.01-5% by mass of the aqueous monomer.

18. The preparation method according to claim 13, characterized in that, The solvent in the block copolymer solution includes any one or a combination of at least two of petroleum ether, n-hexane, cyclohexane, tetradecane, n-hexadecane, or 1-octadecene.

19. The preparation method according to claim 13, characterized in that, The block copolymer solution contains 0.01-5% by mass of block copolymer.

20. The preparation method according to claim 13, characterized in that, In step (1), the mixing process also includes temperature control.

21. The preparation method according to claim 20, characterized in that, In step (1), the temperature of the temperature control process is 80~120℃.

22. The preparation method according to claim 20, characterized in that, In step (1), the temperature control process takes 1 to 10 minutes.

23. The preparation method according to claim 13, characterized in that, In step (2), the temperature of the interfacial polymerization reaction is 20~60℃.

24. The preparation method according to claim 13, characterized in that, In step (2), the time for the interfacial polymerization reaction is 1 to 15 minutes.

25. The preparation method according to claim 13, characterized in that, In step (2), the interfacial polymerization reaction is followed by heat treatment.

26. The preparation method according to claim 25, characterized in that, In step (2), the temperature of the heat treatment is 60~100℃.

27. The preparation method according to claim 25, characterized in that, In step (2), the heat treatment time is 1~20 min.

28. The preparation method according to any one of claims 13-27, characterized in that, The preparation method includes the following steps: (1) Mix the organic phase monomer solution with the block copolymer solution, and treat it at 80~120℃ for 1~10 min, and coat it on the surface of the porous support membrane to form an oil-impregnated gel coating containing organic phase monomers; (2) Coat the surface of the porous support membrane with an aqueous monomer solution, perform interfacial polymerization reaction at 20~60℃ for 1~15min to form an active separation layer, and heat treat at 60~100℃ for 1~20min to obtain the composite nanofiltration membrane.

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