Membrane preparation method for regulating and controlling membrane structure of phase conversion membrane by using mixed solvent

Abstract

The invention discloses a membrane preparation method for regulating and controlling a phase conversion membrane structure by using a mixed solvent, which comprises the following steps: (1) preparing a membrane casting solution, dissolving a high-molecular polymer in more than two mixed solvents, stirring at 20-120 DEG C until the high-molecular polymer is completely dissolved, and standing at 20-100 DEG C for defoaming; (2) under a certain temperature and humidity condition, uniformly coating a substrate with the defoamed membrane casting solution, and entering a coagulating bath to form a membrane; and (3) fully removing the solvent after coagulating bath for a certain time, then drying and storing at a certain temperature, and regulating and controlling the polymer casting solution solvent system by two or more mixed solvents, so that the aperture of the surface of the separation membrane approaches to the structure of one solvent, and the loose section structure is in the middle structure of the two or more solvents. Membrane pores of the separation membrane are in the ultra / microfiltration category, and the separation membrane can be used as a base membrane of nanofiltration, reverse osmosis, gas separation membranes and the like, so that the mass transfer resistance is better reduced, and the separation effect is improved.

Description

[0001] This invention relates to the field of separation membrane technology, and more specifically to a method for fabricating a phase inversion membrane with a mixed solvent controlling the membrane structure. Background Technology

[0002] Phase inversion method, as one of the main methods for preparing separation membranes, has the advantages of wide availability of membrane materials and simple operation process, and is widely used in industrial production.

[0003] Phase inversion membranes typically have pore sizes ranging from 0.02 to 10 μm and are commonly used as ultrafiltration or microfiltration membranes, as well as base membranes for nanofiltration, reverse osmosis, gas separation, and pervaporation. The membrane structure of a phase inversion membrane affects its permeability and selectivity. To overcome the trade-off effect in permeability and selectivity, the ideal membrane structure is one with an ultrathin, dense skin layer with small pores on the surface and a loose, porous cross-section.

[0004] Currently, the most direct methods for controlling the membrane structure of phase inversion membranes (PIMs) include changing the polymer concentration, adjusting the solvent composition, altering the coagulation bath conditions, and introducing additives. Changing the polymer concentration is a simple and direct method, but it often leads to a decrease in other membrane properties such as mechanical strength or permeability. Changing the coagulation bath conditions is also an effective method, but the composition and temperature of the coagulation bath are often limited by experimental equipment and operational difficulties. While introducing additives can control the membrane pore structure, the residue of these additives may negatively impact membrane performance.

[0005] Regarding the control of membrane pores using mixed solvents, this patent proposes a membrane fabrication method for controlling the structure of phase inversion membranes using mixed solvents to address the aforementioned issues. Summary of the Invention

[0006] The purpose of this invention is to provide a method for fabricating phase inversion membranes by controlling the structure of the membrane with mixed solvents in order to solve the above-mentioned problems and overcome the defects of the prior art, as detailed below.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a method for preparing a phase inversion membrane structure controlled by a mixed solvent, (1) preparing a casting solution by dissolving a polymer in two or more mixed solvents, stirring at 20-120°C until completely dissolved, and then allowing it to stand at 20-100°C to remove bubbles; (2) At a temperature of 20-30℃ and a humidity of 30-70%, the degassed casting liquid is evenly coated on the substrate and then placed in a coagulation bath to form a film. (3) After a certain time in the coagulation bath, the solvent is completely removed, and then dried and stored at a certain temperature.

[0008] Preferably, the polymer in step (1) is a hydrophobic polymer, which is selected from one of polyvinylidene fluoride, polysulfone, polyethersulfone, polyetherimide, cellulose acetate or its derivatives.

[0009] Preferably, the mixed solvent in step (1) consists of at least two polar organic solvents, wherein the difference in solubility parameters of the polar organic solvents is ≤5 MPa. （1 / 2） It can also dissolve high molecular polymers to form a homogeneous casting solution.

[0010] Preferably, the polar organic solvent includes, but is not limited to, N-dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and triethyl phosphate.

[0011] Preferably, the temperature and humidity conditions in step (2) are 20°C and 40% respectively, and the difference in the replacement rate between the coagulation bath and the casting solution solvent is ≥15%, which is used to adjust the pore size of the membrane surface to 10-30nm and the cross-sectional double-layer loose structure.

[0012] Preferably, the coagulation bath is at least one of water, methanol, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, low molecular weight polyethylene glycol, benzene, toluene, aliphatic hydrocarbons, aromatic hydrocarbons, and aliphatic alcohols.

[0013] Preferably, the soaking time in the coagulation bath in step 3 is more than 12 hours, and the drying temperature is 40-80℃.

[0014] A method for fabricating a phase inversion membrane structure by regulating the structure of a mixed solvent is disclosed. The resulting porous membrane structure has a top layer with a pore size of 10-30 nm and a cross-sectional structure of a two-layer composite structure. The upper layer has a finger-like pore structure with a dense membrane structure between the finger-like pores, while the lower layer has a loose honeycomb structure.

[0015] The porous filter membrane prepared by the membrane fabrication method of controlling the phase inversion membrane structure using a mixed solvent has the following applications: as a microfiltration and ultrafiltration membrane, and also as a base membrane for nanofiltration, reverse osmosis, and gas separation pervaporation membranes.

[0016] The beneficial effects are: By controlling the solvent system of the polymer casting solution with two or more mixed solvents, the pore size of the separation membrane surface can be made to approach the structure of one of the solvents, while the loose cross-sectional structure is in between the structures of the two or more solvents. The membrane pores of this separation membrane fall within the ultrafiltration / microfiltration range and can be used as a base membrane for nanofiltration, reverse osmosis, gas separation membranes, etc., to better reduce mass transfer resistance and improve separation efficiency. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 These are surface and cross-sectional morphology diagrams of the porous filter membrane of Embodiment 1 of the present invention; Figure 2 These are surface and cross-sectional morphology diagrams of the porous filter membrane in Embodiment 2 of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0020] A method for fabricating phase inversion membranes with mixed solvents to regulate the membrane structure. (1) Prepare the casting solution by dissolving the polymer in two or more mixed solvents, stirring at 20-120℃ until completely dissolved, and then allowing it to stand at 20-100℃ to remove bubbles; wherein the polymer is a hydrophobic polymer, selected from one of polyvinylidene fluoride, polysulfone, polyethersulfone, polyetherimide, cellulose acetate or its derivatives. The mixed solvent consists of at least two polar organic solvents, wherein the difference in solubility parameters of the polar organic solvents is ≤5MPa (1 / 2), and they are capable of dissolving the polymer to form a homogeneous casting solution. The polar organic solvents include, but are not limited to, N-dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and triethyl phosphate.

[0021] (2) Under conditions of 20-30℃ and 30-70% humidity, the degassed casting solution is uniformly coated onto the substrate and then placed in a coagulation bath to form a film; wherein the difference in the replacement rate between the coagulation bath and the casting solution solvent is ≥15%, which is used to control the pore size of the film surface to 10-30nm and the cross-sectional double-layer loose structure. The coagulation bath is at least one of water, methanol, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, low molecular weight polyethylene glycol, benzene, toluene, aliphatic hydrocarbons, aromatic hydrocarbons, and aliphatic alcohols.

[0022] (3) After 12 hours in the coagulation bath, the solvent is completely removed, and then dried and stored at 40-80℃.

[0023] The prepared porous membrane structure has a pore size of 10-30 nm in the top layer and a two-layer composite structure in the cross section. The upper layer is a finger-shaped pore structure with a dense membrane structure between the finger-shaped pores, and the lower layer is a loose honeycomb structure.

[0024] Porous filter membranes can be used as microfiltration and ultrafiltration membranes, as well as as base membranes for nanofiltration, reverse osmosis, gas separation membranes, and pervaporation membranes.

[0025] Example 1: A method for fabricating a phase inversion membrane with mixed solvent-controlled membrane structure, wherein the preparation steps are as follows: (1) Dissolve 7g of polyvinylidene fluoride in a mixed solvent of 30g of N-methyl-2-pyrrolidone and 13g of triethyl phosphate, stir magnetically at 80°C for about 12h, and then let stand for 12h to remove bubbles.

[0026] (2) The film was scraped at a temperature of 20℃ and a humidity of 40%RH and placed in deionized water to form a phase conversion film.

[0027] (3) After the scraped membrane is soaked in coagulation bath water for 24 hours, it is taken out and dried in an oven at 50°C to obtain a porous filter membrane.

[0028] The surface and cross-sectional morphology of the porous filter membrane prepared by the above method are as follows: Figure 1 As shown in the figure, the surface morphology reveals that the membrane surface pores are approximately 20 nm in size, and the cross-section exhibits a loose, double-layered structure composed of finger-like and honeycomb-like pores. Further magnification of the intermediate structure between the finger-like pores reveals that the finger-like pores are formed by fibrous entanglements, creating a porous structure. This structure, with its smaller surface pores and looser cross-section, is more conducive to improving the membrane's separation efficiency.

[0029] Example 2: A method for fabricating a phase inversion membrane with mixed solvent-controlled membrane structure, wherein the preparation steps are as follows: (1) Dissolve 7g of polyvinylidene fluoride in a mixed solvent of 3g of dimethyl sulfoxide and 40g of triethyl phosphate, stir magnetically at 80°C for about 12h, and then let stand for 12h to remove bubbles.

[0030] (2) The film was scraped at a temperature of 20℃ and a humidity of 40%RH and placed in deionized water to form a phase conversion film.

[0031] (3) After the scraped membrane is soaked in coagulation bath water for 24 hours, it is taken out and dried in an oven at 50°C to obtain a porous filter membrane.

[0032] The surface and cross-sectional morphology of the porous filter membrane prepared by the above method are as follows: Figure 2 As shown, the morphology of the membrane is similar to... Figure 1Similarly, the surface has small pores, while the cross-section consists of a double-layered loose structure made up of finger-like pores and honeycomb-like pores.

[0033] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for fabricating a phase inversion membrane with a structure controlled by a mixed solvent, characterized in that, (1) Prepare the casting solution by dissolving the polymer in two or more mixed solvents, stirring at 20-120℃ until completely dissolved, and then letting it stand at 20-100℃ to remove bubbles; (2) Under the conditions of temperature of 20-30℃ and humidity of 30-70%, the deaerated casting liquid is evenly coated on the substrate and then placed in the coagulation bath to form a film. (3) Remove the solvent completely in the coagulation bath, then dry and store.

2. The method for fabricating a phase inversion membrane structure controlled by a mixed solvent according to claim 1, characterized in that: The polymer in step (1) is a hydrophobic polymer, which is selected from one of polyvinylidene fluoride, polysulfone, polyethersulfone, polyetherimide, cellulose acetate or its derivatives.

3. The method for fabricating a phase inversion membrane with mixed solvent controlled according to claim 2, characterized in that: The mixed solvent in step (1) consists of at least two polar organic solvents, wherein the difference in solubility parameters of the polar organic solvents is ≤5 MPa. （1 / 2） It can also dissolve high molecular polymers to form a homogeneous casting solution.

4. The method for fabricating a phase inversion membrane structure controlled by a mixed solvent according to claim 3, characterized in that: The polar organic solvents include, but are not limited to, N,N-dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and triethyl phosphate.

5. The method for fabricating a phase inversion membrane structure controlled by a mixed solvent according to claim 3, characterized in that: The temperature and humidity conditions in step (2) are 20°C and 40% respectively. The difference in the replacement rate between the coagulation bath and the casting solution solvent is ≥15%, which is used to adjust the pore size of the membrane surface to 10-30nm and the cross-sectional double-layer loose structure.

6. The method for fabricating a phase inversion membrane structure controlled by a mixed solvent according to claim 5, characterized in that: The coagulation bath is at least one of water, methanol, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, low molecular weight polyethylene glycol, benzene, toluene, aliphatic hydrocarbons, aromatic hydrocarbons, and aliphatic alcohols.

7. The method for fabricating a phase inversion membrane structure controlled by a mixed solvent according to claim 5, characterized in that: The coagulation bath soaking time in step 3 is more than 12 hours, and the drying temperature is 40-80℃.

8. A method for fabricating a phase inversion membrane structure controlled by a mixed solvent as described in any one of claims 1-7, wherein the porous membrane structure obtained is characterized in that: The membrane pore size of its top layer is 10-30 nm, and the cross-sectional structure of the membrane is a two-layer composite structure. The upper layer is a finger-shaped pore structure, and the space between the finger-shaped pores is also a dense membrane structure. The lower layer is a loose honeycomb structure.

9. An application of a porous filter membrane prepared using the membrane fabrication method for controlling the phase inversion membrane structure with a mixed solvent as described in claim 1 or 8, characterized in that, As a microfiltration and ultrafiltration membrane, it can also serve as a base membrane for nanofiltration, reverse osmosis, and gas separation membranes and pervaporation membranes.

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