Poly (ether) sulfone block copolymer separation membrane, preparation method and application

Abstract

The invention provides a poly (ether) sulfone block copolymer separation membrane and a preparation method thereof, the separation membrane comprises a porous substrate, and a support layer and a compact separation layer which are sequentially positioned on the porous substrate, and the support layer and the compact separation layer are of a continuous structure formed by a poly (ether) sulfone block copolymer; the thickness of the compact separation layer is less than 100nm, and the average membrane aperture is less than 10nm; the content of oxygen and nitrogen elements on the surface of the compact separation layer is greater than 17%; the porosity of the separation membrane is greater than 85%; the separation membrane does not contain a pore-foaming agent or a dissolved substance; the poly (ether) sulfone group segmented copolymer separation membrane can be used for separation and purification of liquid and gas.

Description

Technical Field

[0001] The invention relates to the technical field of membrane separation, in particular to a poly(ether)sulfone block copolymer separation membrane, a preparation method and application thereof. Background Art

[0002] In recent years, separation membranes have been widely used in food production, biomedicine, electronic products and other fields due to their low cost, high separation efficiency, green environmental protection, and strong continuous operability. Poly(ether) sulfone materials are one of the main materials commonly used to prepare separation membranes because of their excellent film-forming properties, thermal stability, chemical tolerance, food hygiene and high mechanical strength. They have been widely used to prepare porous membranes with different separation accuracies. However, due to the strong molecular chain rigidity and hydrophobicity of poly(ether) sulfone materials, when preparing separation membranes through phase transformation, the porosity of the formed membrane is low, and the dense cortex of the membrane is thick (greater than 200nm), resulting in poor water permeability of the membrane and a low water permeability coefficient of the membrane, which limits its application space. Therefore, how to reduce the cortex thickness and increase the porosity has always been an important issue to be solved when using poly(ether) sulfone materials to prepare separation membranes. For example: Invention patent CN12044290A uses polysulfone-based block copolymers as membrane materials to prepare loose nanofiltration membranes (pore size 2.2nm) with narrow pore size distribution and high porosity. However, the separation membrane still has problems such as thick membrane skin and low membrane flux, and the core problems of the separation membrane have not been effectively solved.

[0003] In addition, the composite solvent NIPS method is currently widely used to prepare separation membranes to solve this problem; for example: invention patent CN111757777A uses a composite solvent combined with a critical eutectic temperature to prepare a separation membrane with a relatively uniform pore size and a high flux, but the pore size of the separation membrane prepared by this method is generally greater than 15nm, and it is difficult to prepare a porous membrane below 10nm, so that its application space is limited; invention patent CN106432761B uses two polymer materials to mix in a single solvent to prepare a film, and then dissolves it in a second solvent to extract one of the polymer materials, thereby preparing a high-flux porous separation membrane with a porosity of not less than 20%, but the separation membrane has a large pore size, a thick skin, and a complex membrane preparation process, which is difficult to large-scale industrial production.

[0004] In order to solve the problems of low porosity, thick surface skin, and difficulty in balancing pore size and flux in the preparation of separation membranes using traditional commercial poly(ether) sulfone materials, and to achieve the purpose of streamlining the membrane preparation process, accurately controlling the pore size, and improving the application scope of the traditional NIPS method, the present application provides a method for preparing a thin-skinned, high-porosity, and high-flux separation membrane by using a selective solvent to promote microphase separation and pore formation of poly(ether) sulfone block copolymers. Summary of the invention

[0005] The method of the present invention uses a poly(ether) sulfone block copolymer to replace a traditional poly(ether) sulfone material, and uses a selective solvent to promote the microphase separation and pore formation of the poly(ether) sulfone block copolymer to prepare a porous separation membrane, which can make the average membrane pore size of the dense separation layer on the separation membrane below 10 nm, have a high porosity and an ultra-thin dense skin layer, and can accurately customize the pore size of the separation membrane according to the size of different separated objects. The prepared separation membrane can be widely used in the separation and purification of liquids and gases.

[0006] A poly(ether)sulfone block copolymer separation membrane, the separation membrane comprising a porous substrate and a support layer and a dense separation layer sequentially disposed on the porous substrate, wherein the support layer and the dense separation layer are a continuous structure composed of a poly(ether)sulfone block copolymer; and

[0007] The thickness of the dense separation layer is less than 100 nm, and the average membrane pore size is less than 10 nm;

[0008] The oxygen and nitrogen content on the surface of the dense separation layer is greater than 17%;

[0009] The porosity of the separation membrane is greater than 85%;

[0010] The separation membrane does not contain a porogen and no dissolved matter.

[0011] The method for preparing the poly(ether) sulfone block copolymer separation membrane is characterized by comprising the following steps:

[0012] (1) preparing a casting solution composed of 15 wt.% to 35 wt.% of a poly(ether) sulfone block copolymer and 65 wt.% to 85 wt.% of a composite solvent, wherein the composite solvent is composed of a good solvent for different blocks of the poly(ether) sulfone block copolymer and a selective solvent for one block, and both the casting solution and the composite solvent have an upper critical solution temperature, and the upper critical solution temperature is not less than 30° C., and the casting solution temperature is prepared to be higher than the upper critical solution temperature;

[0013] (2) coating the casting liquid on the surface of the porous substrate, and cooling the casting liquid to a temperature within 20°C of the upper critical solution temperature of the casting liquid, thereby inducing microphase separation of the casting liquid, wherein the microphase separation size is less than 100 nm;

[0014] (3) Immerse the coated casting solution in a coagulation bath for phase inversion to obtain a poly(ether)sulfone block copolymer separation membrane with an average membrane pore size of less than 10 nm.

[0015] Furthermore, the poly(ether)sulfone block copolymer is formed by chemical bonding of a hydrophilic block A and a poly(ether)sulfone block B, and has a number average molecular weight of ≥15 KDa, and a content of the hydrophilic block A of ≥3 wt.%.

[0016] Furthermore, the composite solvent is composed of good solvents of different blocks of the poly(ether)sulfone block copolymer and a selective solvent of one block, wherein the mass ratio of the good solvent to the selective solvent is not less than 4.3:1 and not greater than 39:1; the good solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, cyclopentane, dimethyl sulfoxide, tetramethyl sulfoxide, etc.; the selective solvent is one or more of water, methanol, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, propanol, propylene glycol, isopropanol, n-octanol, n-hexane, n-heptane, and n-octane.

[0017] Furthermore, the hydrophilic block A is one of dextran, polyacrylic acid, hyperbranched polyglycerol ether, chitosan, polypropylene alcohol, cyclodextrin, polyethylene glycol methacrylate, polyethylene glycol, polypropylene glycol, and polyvinyl alcohol; and the poly(ether) sulfone block B is one of polysulfone, polyether sulfone, and polyphenylene sulfone.

[0018] Furthermore, the coagulation bath is a mixture of one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone and water, the mass fraction of water in the coagulation bath is not less than 30wt.%, and the coagulation bath temperature is not higher than the upper critical solution temperature of the casting liquid.

[0019] The above-mentioned poly(ether)sulfone block copolymer separation membrane can be widely used in the separation and purification of liquids and gases.

[0020] The advantages and positive effects of the present invention are:

[0021] The present invention promotes microphase separation and pore formation of poly(ether)sulfone block copolymers through selective solvents to prepare a high-throughput separation membrane with a thin skin layer and high porosity. The method can adjust the composition and temperature of the polymer casting liquid system to make the average membrane pore size of the dense separation layer on the separation membrane less than 10nm and the overall porosity greater than 85%. The method can accurately customize the pore size of the separation membrane according to the size of different separated objects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The maximum critical solution temperature of the casting liquid system is measured using a rotational rheometer in Example 7 of the present invention;

[0023] Figure 2 The determination of the highest critical solution temperature of the composite solvent using a particle size analyzer in Example 7 of the present invention;

[0024] Figure 3 This is a transmission electron microscope image of a cross section of the separation membrane in Example 7 of the present invention;

[0025] Figure 4 This is the pore size analysis of the separation membrane in Example 7 of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the implementation of the present invention clearer, the technical scheme in the embodiment of the present invention will be described in more detail below in conjunction with the drawings in the embodiment of the present invention. The described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0028] Example 1

[0029] The method for preparing a poly(ether)sulfone block copolymer separation membrane comprises the following steps:

[0030] A poly(ether) sulfone block copolymer casting solution is prepared, wherein the casting solution is composed of 15wt.% to 35wt.% of the poly(ether) sulfone block copolymer by mass fraction and 65wt.% to 85wt.% of a composite solvent, wherein the composite solvent is composed of a good solvent for different blocks of the poly(ether) sulfone block copolymer and a selective solvent for one block; and both the casting solution and the composite solvent have an upper critical solubility temperature, the upper critical solubility temperature is not less than 30° C., and the temperature of the casting solution during preparation is higher than the upper critical solubility temperature;

[0031] According to the obtained casting solution, a separation membrane is prepared and obtained by a phase inversion method: the obtained poly(ether)sulfone block copolymer casting solution is uniformly coated on the surface of a porous substrate by a scraper, and the porous substrate is a non-woven fabric or a non-porous carrier; the porous substrate coated with the casting solution is cooled to a temperature not exceeding 20°C above or below the upper critical solubility temperature of the casting solution, and the cooled casting solution and the carrier are immersed in a coagulation bath to solidify into a membrane;

[0032] The poly(ether) sulfone block copolymer is formed by chemical bonding of a hydrophilic block A and a poly(ether) sulfone block B, and has a number average molecular weight of ≥15KDa and a content of the hydrophilic block A of ≥3wt.%; the poly(ether) sulfone block copolymer undergoes microphase separation in a casting solution, and the microphase separation size is less than 100nm; the hydrophilic block A is one of dextran, polyacrylic acid, hyperbranched polyglycerol ether, chitosan, polypropylene alcohol, cyclodextrin, polyethylene glycol methacrylate, polyethylene glycol, polypropylene glycol, and polyvinyl alcohol; the poly(ether) sulfone block B is one of polysulfone, polyether sulfone, and polyphenylene sulfone;

[0033] The composite solvent is composed of a good solvent and a selective solvent of different blocks of a poly(ether)sulfone block copolymer, wherein the mass ratio of the good solvent to the selective solvent is not less than 4.3:1 and not greater than 39:1, and an upper critical solution temperature exists; the good solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, cyclopentane, dimethyl sulfoxide, tetramethyl sulfoxide, etc.; the selective solvent is one or more of water, methanol, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, propanol, propylene glycol, isopropanol, n-octanol, n-hexane, n-heptane, and n-octane.

[0034] The coagulation bath is a mixture of one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone and water, the mass fraction of water in the coagulation bath is not less than 30wt.%, and the coagulation bath temperature is not higher than the upper critical solution temperature of the casting liquid.

[0035] The poly(ether) sulfone block copolymer separation membrane obtained by the above-mentioned poly(ether) sulfone block copolymer separation membrane preparation method comprises a porous substrate and a support layer and a dense separation layer sequentially disposed on the porous substrate, and the support layer and the dense separation layer are both continuous structures composed of poly(ether) sulfone block copolymers; and

[0036] The thickness of the dense separation layer is less than 100 nm, and the average membrane pore size is less than 10 nm;

[0037] The oxygen and nitrogen content on the surface of the dense separation layer is greater than 17%;

[0038] The porosity of the separation membrane is greater than 85%;

[0039] The separation membrane does not contain a porogen and no dissolved matter.

[0040] The poly(ether)sulfone block copolymer separation membrane obtained by the above-mentioned poly(ether)sulfone block copolymer separation membrane preparation method is used for separation and purification of liquid and gas.

[0041] In this embodiment, a poly(ether)sulfone block copolymer separation membrane was prepared according to the above method, as follows:

[0042] S1: preparing a casting solution containing a composite solvent and a polysulfone-based block copolymer at a temperature of 90° C., and fully stirring the casting solution at 90° C. to obtain a stable and uniform casting solution; the casting solution is composed of 16wt.% polysulfone-block-polyethylene glycol (number average molecular weight 25KDa, hydrophilic block content 23wt.%); 9wt.% n-octane (selective solvent in the composite solvent); and 75wt.% N,N-dimethylacetamide (good solvent in the composite solvent);

[0043] S2: Pour the casting liquid prepared according to S1 evenly onto a clean glass plate, use a 200um scraper to scrape the casting liquid into a liquid film state, cool the carrier coated with the casting liquid to 40°C, place the glass plate carrying the liquid film in a deionized water coagulation bath for phase transformation into a membrane, the coagulation bath temperature is 25°C, after the membrane separates from the glass plate by itself, take out the membrane and soak it in deionized water, change the water every 2 hours until the residual organic solvent in the membrane pores is completely removed, and obtain a polysulfone-based block copolymer separation membrane; after testing, the pure water permeability coefficient of the obtained polysulfone-based block copolymer is 862LMH / bar, and the retention of bovine serum albumin reaches 99.9%.

[0044] Example 2

[0045] Similarly, according to the method of Example 1, the components and ratios of the casting solution are changed, and the parameters such as the temperature in the preparation process are adjusted, for example, the composition of the poly(ether) sulfone block copolymer, the mass fraction of the block copolymer in the casting solution, the composition of the composite solvent, the carrier, the configuration of the casting solution temperature, the cooling temperature, the coagulation bath composition and other variables; as shown in Attached Table 1, a variety of poly(ether) sulfone block copolymer separation membranes are obtained, and the obtained poly(ether) sulfone block copolymer separation membranes are tested for performance. The pure water permeability coefficient and screening performance of the poly(ether) sulfone block copolymer separation membrane are shown in Attached Table 1:

[0046] Table 1

[0047]

[0048]

[0049]

[0050]

[0051] Appendix: The molecular weight of bovine serum albumin is 66500 kDa, the molecular weight of acid fuchsin is 585 Da, and the molecular weight of tylosin tartrate is 916.1 Da.

[0052] The present invention discloses a method for preparing a separation membrane using a poly(ether)sulfone block copolymer as a raw material, combining a unique cooling response mechanism to promote phase separation of a casting liquid system, and utilizing a composite solvent system to strengthen the phase separation of the casting liquid system, thereby preparing a high-throughput asymmetric poly(ether)sulfone block copolymer membrane with a thin skin layer in one step; by regulating the components of the casting liquid system, the design of the liquid membrane cooling process can affect the size of the phase separation of the casting liquid system, thereby achieving control of the pore size of the prepared separation membrane, and further achieving a high-throughput precision screening process for retained substances of different sizes. For example, the poly(ether)sulfone block copolymer membrane in Example 7 has a pure water permeability coefficient of about 40LMH / bar, and a retention rate of up to 94.6% for smaller molecule antibiotics (50ppm of tylosin tartrate), while the poly(ether)sulfone block copolymer membrane in Example 11 has a pure water permeability coefficient of 1433LMH / bar and a retention rate of up to 99.9% for larger molecule proteins (1000ppm of bovine serum albumin); both membranes show good size exclusion in the separation of smaller molecule antibiotics and larger molecule proteins, and have a pure water permeability coefficient far exceeding that of conventional membranes. Compared with conventional membranes, the poly(ether)sulfone block copolymer method for preparing membranes described in this patent can effectively improve the pure water permeability coefficient and separation performance of separation membranes; this shows that this method has a certain universality for preparing thin-skinned high-flux separation membranes, and is very easy to achieve large-scale production.

[0053] It should be noted that, taking Example 7 as an example, when determining the upper critical solution temperature of the casting solution and the composite solvent, a rotational rheometer and a particle size analyzer can be used for testing and analysis, as shown in the attached Figure 1 , 2 The upper critical solution temperatures of the casting liquid and the composite solvent were finally determined to be 73.5°C and 75°C, respectively. The casting liquid was prepared at a temperature of 90°C, which was higher than the upper critical solution temperature. The porous substrate coated with the casting liquid was cooled to near the upper critical solution temperature of the casting liquid (75°C). At this time, the phase separation size of the casting liquid system was the smallest, and the phase separation size continued to increase with the increase in the degree of system cooling until the system temperature was 20°C below the upper critical solution temperature. The phase separation size was too large to form a membrane. Finally, the porous substrate coated with the casting liquid was placed in a coagulation bath to solidify into a membrane, and a poly(ether) sulfone block copolymer separation membrane was obtained. The cross-section of the poly(ether) sulfone block copolymer separation membrane in Example 7 was analyzed by transmission electron microscopy as shown in FIG. Figure 3 ,Depend on Figure 3 It can be concluded that the thickness of the membrane's dense separation layer is 60 nm. In addition, the pore size of the membrane was analyzed by a specific surface area and porosity analyzer. Figure 4 ,Depend on Figure 4It can be concluded that the pore size of the membrane is concentrated at 0.7nm; the ultra-thin dense separation layer and the smaller pore size are the fundamental reasons why the membrane has high flux and excellent screening performance.

[0054] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A poly(ether)sulfone block copolymer separation membrane, characterized in that: The separation membrane comprises a porous substrate and a support layer and a dense separation layer sequentially disposed on the porous substrate, and the support layer and the dense separation layer are a continuous structure composed of a poly(ether)sulfone block copolymer; and The thickness of the dense separation layer is less than 100 nm, and the average membrane pore size is less than 10 nm; The oxygen and nitrogen content on the surface of the dense separation layer is greater than 17%; The porosity of the separation membrane is greater than 85%; The separation membrane does not contain a porogen and no dissolved matter.

2. The method for preparing the poly(ether)sulfone block copolymer separation membrane according to claim 1, characterized in that: The steps include: (1) preparing a casting solution composed of 15 wt.% to 35 wt.% of a poly(ether) sulfone block copolymer and 65 wt.% to 85 wt.% of a composite solvent, wherein the composite solvent is composed of a good solvent for different blocks of the poly(ether) sulfone block copolymer and a selective solvent for one block, and both the casting solution and the composite solvent have an upper critical solution temperature, and the upper critical solution temperature is not less than 30° C., and the casting solution temperature is prepared to be higher than the upper critical solution temperature; (2) coating the casting liquid on the surface of the porous substrate, and cooling the casting liquid to a temperature within 20°C of the upper critical solution temperature of the casting liquid, thereby inducing microphase separation of the casting liquid, wherein the microphase separation size is less than 100 nm; (3) Immerse the coated casting solution in a coagulation bath for phase inversion to obtain a poly(ether)sulfone block copolymer separation membrane with an average membrane pore size of less than 10 nm.

3. The method for preparing a poly(ether)sulfone block copolymer separation membrane according to claim 2, characterized in that: The poly(ether)sulfone block copolymer is formed by chemical bonding of a hydrophilic block A and a poly(ether)sulfone block B, and has a number average molecular weight of ≥15 KDa and a content of the hydrophilic block A of ≥3 wt.%.

4. The method for preparing a poly(ether)sulfone block copolymer separation membrane according to claim 2, characterized in that: The composite solvent is composed of good solvents of different blocks of poly(ether)sulfone block copolymers and a selective solvent of one block, wherein the mass ratio of the good solvent to the selective solvent is not less than 4.3:1 and not more than 39:1; the good solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, cyclopentane, dimethyl sulfoxide, tetramethyl sulfoxide, etc.; the selective solvent is one or more of water, methanol, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, propanol, propylene glycol, isopropanol, n-octanol, n-hexane, n-heptane, and n-octane.

5. The method for preparing a poly(ether)sulfone block copolymer separation membrane according to claim 3, characterized in that: The hydrophilic block A is one of dextran, polyacrylic acid, hyperbranched polyglycerol ether, chitosan, polypropylene alcohol, cyclodextrin, polyethylene glycol methacrylate, polyethylene glycol, polypropylene glycol, and polyvinyl alcohol; the poly(ether) sulfone block B is one of polysulfone, polyether sulfone, and polyphenylene sulfone.

6. The method for preparing a poly(ether)sulfone block copolymer separation membrane according to claim 2, characterized in that: The coagulation bath is a mixture of one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone and water, the mass fraction of water in the coagulation bath is not less than 30wt.%, and the coagulation bath temperature is not higher than the upper critical solution temperature of the casting liquid.

7. The poly(ether)sulfone block copolymer separation membrane according to any one of claims 1 to 6 can be widely used in the separation and purification of liquids and gases.

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