Organic solvent-resistant composite nanofiltration membrane, preparation method thereof and application

Abstract

The present invention relates to a solvent-resistant composite nanofiltration membrane, its preparation method and application. Among them, the solvent-resistant composite nanofiltration membrane comprises the following steps: preparing a polyimide porous membrane from a polyimide casting solution by the non-solvent induced phase separation method, and the coagulation bath is an aqueous solution of aliphatic diamine; mixing a hydroxyl-containing polymer, a silicate ester and water to prepare a mixed solution, the mixed solution is acidic, and the mass ratio of the hydroxyl-containing polymer to the silicate ester is 1:1 - 1:20; sequentially placing an aqueous solution of a hydrophilic compound and the mixed solution on the same surface of the polyimide porous membrane, and forming a separation layer by heat treatment to obtain a solvent-resistant composite nanofiltration membrane, and the hydrophilic compound has amino and hydroxyl groups. The solvent-resistant composite nanofiltration membrane prepared by this preparation method not only has the properties of high solvent resistance, high solvent flux and high rejection rate, but also can be simultaneously applicable to the efficient separation of polar organic solvent systems and non-polar organic solvent systems.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and particularly to an organic solvent-resistant composite nanofiltration membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Organic solvent nanofiltration (OSN) is a new type of membrane separation technology that is green, efficient, energy-saving, and easy to operate, and has broad application prospects in related fields such as chemical engineering, pharmaceuticals, energy, and the environment. However, most of the existing organic solvent-resistant nanofiltration membranes prepared by the phase inversion method have limitations such as a relatively thick skin layer and low flux. The organic solvent-resistant composite nanofiltration membrane composed of a base membrane and a separation layer has the advantages of a thin skin layer, high solvent flux, and high rejection rate. However, in practical applications, the separation layer of the organic solvent-resistant composite nanofiltration membrane is prone to peeling due to insufficient bonding force between the base membrane and the separation layer, and at the same time, the rejection rate of small molecule organic compounds needs to be improved. In addition, due to the extremely small pore size (0.5 nm - 2 nm) of the organic solvent-resistant composite nanofiltration membrane, when an organic solvent passes through such a small membrane pore, the interaction forces such as hydrogen bonding or hydrophobic interaction between the organic solvent and the separation layer are relatively significant, resulting in different mass transfer behaviors for polar and non-polar organic solvents. Therefore, the organic solvent-resistant composite nanofiltration membrane is usually only suitable for the efficient separation of a single polar organic solvent system or non-polar organic solvent system, and it is difficult to be simultaneously suitable for the efficient separation of polar and non-polar organic solvent systems. Summary of the Invention

[0003] Based on this, in view of the above problems, it is necessary to provide an organic solvent-resistant composite nanofiltration membrane, a preparation method thereof, and an application thereof. The organic solvent-resistant composite nanofiltration membrane prepared by this preparation method not only has high solvent resistance, high solvent flux, and high rejection rate performance, but also can be simultaneously suitable for the efficient separation of polar and non-polar organic solvent systems.

[0004] An organic solvent-resistant composite nanofiltration membrane, comprising the following steps:

[0005] Prepare a polyimide porous membrane from a polyimide casting solution by the non-solvent induced phase separation method, wherein the coagulation bath used in the non-solvent induced phase separation method is an aqueous solution of an aliphatic diamine;

[0006] Mix a high molecular polymer containing hydroxyl groups, a silicate ester, and water to prepare a mixed solution, wherein the mixed solution is acidic, and the mass ratio of the high molecular polymer containing hydroxyl groups to the silicate ester is 1:1 - 1:20;

[0007] Place an aqueous solution of a hydrophilic compound and the mixed solution in sequence on the same surface of the polyimide porous membrane, and form a separation layer by heat treatment to obtain an organic solvent-resistant composite nanofiltration membrane, wherein the hydrophilic compound has amino and hydroxyl groups.

[0008] In one embodiment, the mass fraction of polyimide in the polyimide casting solution is 10% - 30%;

[0009] and / or, the mass fraction of the aliphatic diamine in the aqueous solution of the aliphatic diamine is 1% - 8%.

[0010] In one embodiment, the mass fraction of the high molecular polymer containing hydroxyl groups in the mixed solution is 1% - 5%;

[0011] and / or, the mass fraction of the silicate ester in the mixed solution is 2% - 20%.

[0012] In one embodiment, the pH of the mixed solution is 2 - 5;

[0013] and / or, the temperature of the mixed solution is 20°C - 40°C.

[0014] In one embodiment, the mass fraction of the hydrophilic compound in the aqueous solution of the hydrophilic compound is 0.1% - 3%.

[0015] In one embodiment, the molecular weight of the hydrophilic compound is 50 - 150.

[0016] In one embodiment, the aliphatic diamine is selected from at least one of 1,2 - propanediamine, pentanediamine, and hexanediamine;

[0017] and / or, the hydrophilic compound is selected from at least one of diethanolamine, tris(hydroxymethyl)aminomethane, and 1,3 - diamino - 2 - hydroxypropane;

[0018] and / or, the high molecular polymer containing hydroxyl groups is selected from polyvinyl alcohol and / or hydroxypropyl methylcellulose;

[0019] and / or, the silicate ester is selected from at least one of tetraethyl orthosilicate and tetramethyl orthosilicate.

[0020] In one embodiment, the temperature of the heat treatment is 50°C - 80°C, and the time is 10 min - 30 min.

[0021] An organic solvent - resistant composite nanofiltration membrane prepared by using the preparation method of the organic solvent - resistant composite nanofiltration membrane described above.

[0022] An application of the organic solvent - resistant composite nanofiltration membrane described above in an organic solvent treatment device.

[0023] In the preparation method of the organic solvent-resistant composite nanofiltration membrane of the present invention, an aqueous solution of aliphatic diamine is used as the coagulation bath. While inducing phase separation to form a polyimide porous membrane, a cross-linking reaction occurs with polyimide to form a highly cross-linked polyimide network structure, endowing the polyimide porous membrane with excellent solvent resistance. When an aqueous solution of a hydrophilic compound having amino and hydroxyl groups is introduced, the amino group it carries reacts with the imide group on the surface of the polyimide porous membrane, and hydroxyl groups are successfully introduced onto the surface of the polyimide porous membrane. The silicate ester in the mixed solution hydrolyzes to form Si(OH)4 under acidic conditions. When the mixed solution is placed on the surface of the polyimide porous membrane, three reactions will occur under the action of heat treatment: ① Si(OH)4 undergoes self-condensation to form a Si-O-Si hydrophobic network structure; ② Si(OH)4 can act as a cross-linking agent, that is, Si-OH reacts with the hydroxyl groups in the polymer to cause a cross-linking reaction to form a hydrophilic network structure; ③ The remaining Si-OH in the hydrophobic network structure and the hydrophilic network structure can react with each other to form a separation layer with nano-pores. At the same time, it can also react with the hydroxyl groups on the surface of the polyimide porous membrane, so that the separation layer and the polyimide porous membrane are connected by chemical bonds, thereby effectively preventing the separation layer from falling off in the solvent and ensuring the stable operation of the entire composite nanofiltration membrane in the solvent. At the same time, the hydrophobic network structure and the hydrophilic network structure can respectively provide extremely fast mass transfer channels for non-polar solvents and polar solvents, realizing the rapid transmission of non-polar organic solvents and polar organic solvents. In addition, by controlling the mass ratio of the hydroxyl-containing polymer and the silicate ester, the cross-linking density of the separation layer can be effectively controlled, which is beneficial to the formation of a thin and uniformly dense separation layer, and improves the solvent flux and rejection rate of the organic solvent-resistant composite nanofiltration membrane.

[0024] Therefore, the organic solvent-resistant composite nanofiltration membrane prepared by the present invention not only has high solvent resistance, high solvent flux and high rejection rate, but also can be simultaneously applied to the efficient separation of polar organic solvent systems and non-polar organic solvent systems. Brief Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a structural cross-sectional view of the organic solvent-resistant composite nanofiltration membrane prepared in Example 1 of the present invention. Among them, the curve similar to S in the figure represents a chemical bond;

[0027] Figure 2 is Figure 1Enlarged schematic diagram of the middle elliptical part;

[0028] Figure 3 Electron micrograph of the organic solvent-resistant composite nanofiltration membrane prepared in Example 1 of the present invention;

[0029] Figure 4 Electron micrograph of the organic solvent-resistant composite nanofiltration membrane prepared in Comparative Example 9 of the present invention.

[0030] Description of the drawings: 1. Polyimide porous membrane; 2. Separation layer. Detailed implementation manners

[0031] To facilitate the understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments or examples and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of the related listed items. The any and all combinations include any two related listed items, any more related listed items, or all related listed items.

[0033] The organic solvent-resistant composite nanofiltration membrane provided by the present invention includes the following steps:

[0034] Prepare a polyimide porous membrane from a polyimide casting solution by the non-solvent induced phase separation method, wherein the coagulation bath used in the non-solvent induced phase separation method is an aliphatic diamine aqueous solution;

[0035] Mix a high molecular polymer containing hydroxyl groups, a silicate ester, and water to prepare a mixed solution, wherein the mixed solution is acidic, and the mass ratio of the high molecular polymer containing hydroxyl groups to the silicate ester is 1:1 - 1:20;

[0036] Place an aqueous solution of a hydrophilic compound and the mixed solution in sequence on the same surface of the polyimide porous membrane, and form a separation layer by heat treatment to obtain an organic solvent-resistant composite nanofiltration membrane, wherein the hydrophilic compound has amino groups and hydroxyl groups.

[0037] In the present invention, when preparing a polyimide porous membrane from a polyimide casting solution by the non-solvent induced phase separation method, an aqueous solution of an aliphatic diamine is used as the coagulation bath. In this process, on the one hand, water in the aqueous solution of the aliphatic diamine acts as a non-solvent and can rapidly exchange with the solvent in the polyimide casting solution, causing the polyimide casting solution to phase separate and form a polyimide porous membrane. On the other hand, the aliphatic diamine acts as a cross-linking agent and can undergo a cross-linking reaction with the polyimide to form a highly cross-linked polyimide network structure, significantly increasing the rigidity of the polyimide chains, thereby effectively resisting the swelling and erosion of organic solvents and endowing the polyimide porous membrane with excellent solvent resistance.

[0038] When an aqueous solution of a hydrophilic compound is placed on the surface of the polyimide porous membrane, since the hydrophilic compound has amino and hydroxyl groups, the hydrophilic compound reacts with the imide groups on the surface of the polyimide porous membrane through the amino groups it carries and is loaded on the surface of the polyimide porous membrane, successfully introducing hydroxyl groups on the surface of the polyimide porous membrane, thereby achieving the activation of the surface of the polyimide porous membrane and providing sufficient chemical anchoring sites for the subsequent fixation of the nano-porous separation layer.

[0039] When the mixed solution is placed on the surface of the polyimide porous membrane, since the mixed solution is acidic, the silicate ester in the mixed solution will hydrolyze to form Si(OH)4, and three reactions will occur under the action of heat treatment: ① Si(OH)4 undergoes self-condensation to form a Si-O-Si hydrophobic network structure; ② Si(OH)4 can act as a cross-linking agent, that is, Si-OH reacts with the hydroxyl groups in the polymer to cause a cross-linking reaction to form a hydrophilic network structure; ③ The remaining Si-OH in the hydrophobic network structure and the hydrophilic network structure can react with each other to form a separation layer with nano-pore diameters (0.5 nm - 2 nm), and at the same time can also react with the hydroxyl groups on the surface of the polyimide porous membrane, so that the separation layer and the polyimide porous membrane are connected by chemical bonds.

[0040] For the organic solvent-resistant composite nanofiltration membrane constructed in the above manner, the polyimide porous membrane and the separation layer composed of the two network structures themselves have excellent solvent resistance, and the polyimide porous membrane and the separation layer are connected by chemical bonds, which can effectively prevent the separation layer from falling off in the solvent and ensure the stable operation of the entire organic solvent-resistant composite nanofiltration membrane in the solvent; at the same time, the hydrophobic network structure and the hydrophilic network structure can provide extremely fast mass transfer channels for non-polar solvents and polar solvents respectively, realizing the rapid transmission of non-polar organic solvents and polar organic solvents.

[0041] In addition, by controlling the mass ratio of the hydroxyl-containing polymer and the silicate ester, the crosslinking density of the separation layer can be effectively controlled, which is beneficial to the formation of a thin and uniformly dense separation layer, and improves the solvent flux and rejection rate of the organic solvent-resistant composite nanofiltration membrane.

[0042] Therefore, the organic solvent-resistant composite nanofiltration membrane prepared by the present invention not only has high solvent resistance, high solvent flux and high rejection rate, but also can be simultaneously applicable to the efficient separation of polar organic solvent systems and non-polar organic solvent systems.

[0043] It should be noted that in the present invention, controlling the mixed solution to be acidic is beneficial to promoting the hydrolysis of the silicate ester into Si-OH groups in the mixed solution, providing conditions for the subsequent reaction of Si-OH with itself, the surface of the porous membrane or the hydroxyl groups in the polymer; and after being placed on the surface of the polyimide porous membrane, under the action of heat treatment, it is beneficial to promote the self-polymerization of Si-OH to form a Si-O-Si hydrophobic network structure, providing a mass transfer channel for non-polar organic solvents; the crosslinking reaction of Si-OH with the hydroxyl groups in the polymer forms a hydrophilic network structure, providing a mass transfer channel for polar solvents; at the same time, the rapid transmission of polar organic solvents and non-polar organic solvents is realized, so that the organic solvent-resistant composite nanofiltration membrane is simultaneously applicable to the efficient separation of polar organic solvent systems and non-polar organic solvent systems.

[0044] In the present invention, the specific steps of preparing a polyimide porous membrane from a polyimide casting solution by the non-solvent induced phase separation method are as follows: dissolving polyimide in an organic solvent to prepare a homogeneous polyimide casting solution, and then placing the polyimide casting solution in a coagulation bath for phase separation to obtain a polyimide porous membrane, wherein the coagulation bath is an aqueous solution of aliphatic diamine. It can be understood that since polyimide itself has excellent chemical stability, high temperature resistance and mechanical strength, the prepared polyimide porous membrane and the organic solvent-resistant composite nanofiltration membrane both have excellent chemical stability, high temperature resistance and mechanical strength.

[0045] Optionally, the mass fraction of polyimide in the polyimide casting solution is 10%-30%; the mass fraction of the aliphatic diamine in the aqueous solution of the aliphatic diamine is 1%-8%. By setting in this way, on the one hand, the rate of phase separation can be accurately regulated by adjusting the mass fraction of polyimide in the polyimide casting solution and the mass fraction of the aliphatic diamine in the aqueous solution of the aliphatic diamine, which is beneficial to the formation of a polyimide porous membrane with a uniform pore size distribution, ensuring the solvent flux, rejection rate and structural stability of the polyimide porous membrane; on the other hand, it can enable a sufficient reaction between polyimide and aliphatic diamine, better form a highly crosslinked polyimide network structure, which is beneficial to further improving the rigidity of the polyimide chain, more effectively resisting the swelling and erosion of organic solvents, and improving the solvent resistance of the polyimide porous membrane.

[0046] Further, the aliphatic diamine is selected from at least one of 1,2-propanediamine, pentanediamine, and hexanediamine.

[0047] In the present invention, the specific steps of preparing a mixed solution by mixing a hydroxyl-containing polymer, a silicate ester, and water are as follows: Dissolve the hydroxyl-containing polymer in water and adjust the pH to acidic, then add the silicate ester, and finally heat and stir evenly in a water bath. After stirring, a mixed solution is prepared. At this time, the mixed solution is acidic, and the silicate ester is hydrolyzed into Si(OH)4.

[0048] Optionally, the mass fraction of the hydroxyl-containing polymer in the mixed solution is 1% - 5%; the mass fraction of the silicate ester in the mixed solution is 2% - 20%. By setting it in this way, the mass ratio of the hydroxyl-containing polymer and the silicate ester can be better regulated by adjusting the mass fraction of the hydroxyl-containing polymer in the mixed solution and the mass fraction of the silicate ester in the mixed solution. On the one hand, it is beneficial to better form a thin, dense, uniform, and small-pore separation layer, thereby improving the solvent flux and rejection rate of the organic solvent-resistant composite nanofiltration membrane. On the other hand, it is beneficial to better form a silicon network structure that interpenetrates with the separation layer, enabling the organic solvent-resistant composite nanofiltration membrane to be better applicable to the efficient separation of non-polar organic solvent systems and polar organic solvent systems.

[0049] Further, the hydroxyl-containing polymer is selected from polyvinyl alcohol and / or hydroxypropyl methylcellulose.

[0050] Optionally, the silicate ester is selected from at least one of tetraethyl orthosilicate and tetramethyl orthosilicate.

[0051] Optionally, the pH of the mixed solution is 2 - 5. By setting it in this way, it is beneficial for the silicate ester to be better hydrolyzed into Si(OH)4, which can self-polymerize and react with the hydroxyl groups on the surface of the polyimide porous membrane and the hydroxyl groups in the hydroxyl-containing polymer to form a separation layer, better realizing the chemical bond connection between the separation layer and the polyimide porous membrane, improving the bonding force between the separation layer and the polyimide porous membrane, and further improving the structural stability of the organic solvent-resistant composite nanofiltration membrane.

[0052] In one embodiment, hydrochloric acid is used to adjust the pH of the mixed solution to 2 - 5.

[0053] Optionally, the temperature of the mixed solution is 20°C - 40°C. By setting it in this way, it is beneficial to make the components in the mixed solution mix evenly, and at the same time, it is beneficial for the silicate ester to be hydrolyzed to form Si(OH)4.

[0054] Optionally, the mass fraction of the hydrophilic compound in the aqueous solution of the hydrophilic compound is 0.1% - 3%. With such a setting, it is beneficial to introduce sufficient hydroxyl groups on the surface of the polyimide porous membrane, facilitating the further construction of a thin and stable separation layer.

[0055] Optionally, the molecular weight of the hydrophilic compound is 50 - 150. With such a setting, it is beneficial to more tightly fix the separation layer on the surface of the polyimide porous membrane through chemical bonds, avoiding the decrease in rejection rate caused by swelling of both in organic solvents.

[0056] Furthermore, the hydrophilic compound is selected from at least one of diethanolamine, tris(hydroxymethyl)aminomethane, and 1,3 - diamino - 2 - hydroxypropane.

[0057] Optionally, the temperature of the heat treatment is 50°C - 80°C, and the time is 10 min - 30 min. With such a setting, it is beneficial to form a more complete separation layer, further improving the solvent flux and rejection rate of the organic - solvent - resistant composite nanofiltration membrane.

[0058] Meanwhile, the present invention also provides an organic - solvent - resistant composite nanofiltration membrane prepared by using the preparation method of the organic - solvent - resistant composite nanofiltration membrane described above. As Figures 1 to 2 shown, the organic - solvent - resistant composite nanofiltration membrane includes a polyimide porous membrane 1 and a separation layer 2 arranged in a stacked manner, wherein the separation layer 2 is connected to the polyimide porous membrane 1 through chemical bonds. In this organic - solvent - resistant composite nanofiltration membrane, due to the excellent solvent - resistant performance of the polyimide porous membrane, and the separation layer having the characteristics of being thin, uniformly dense, and having a small pore size, and there are hydrophobic and hydrophilic network structures interspersed in the separation layer, the organic - solvent - resistant composite nanofiltration membrane has high solvent resistance, high solvent flux, and high rejection rate performance, and can be simultaneously applicable to the efficient separation of polar organic solvent systems and non - polar organic solvent systems.

[0059] In one embodiment, the thickness of the separation layer 2 is 100 nm - 150 nm.

[0060] In addition, the present invention also provides an application of the organic - solvent - resistant composite nanofiltration membrane described above in an organic solvent treatment device.

[0061] Hereinafter, the organic - solvent - resistant composite nanofiltration membrane, its preparation method, and application will be further described through the following specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples, the operations are carried out under conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified in the manufacturer are all conventional products that can be obtained through commercial purchase.

[0062] Example 1

[0063] The polyimide was dissolved in the organic solvent N,N-dimethylformamide to prepare a homogeneous polyimide casting solution, and then the polyimide casting solution was placed in a coagulation bath for phase separation and crosslinking to obtain a polyimide porous membrane. Among them, the mass fraction of polyimide in the polyimide casting solution was 15%, and the coagulation bath was an aqueous solution of 1,2-propanediamine with a mass fraction of 5%.

[0064] Diethanolamine (molecular weight 105) was dissolved in pure water to prepare an aqueous solution of diethanolamine. Among them, the mass fraction of diethanolamine in the aqueous solution of diethanolamine was 1%; polyvinyl alcohol was dissolved in water and the pH was adjusted to 3.5, and then tetraethyl orthosilicate was added, and the mixture was heated and stirred evenly in a water bath to obtain a mixed solution. Among them, in the mixed solution, the mass fraction of polyvinyl alcohol was 2.0%, the mass fraction of tetraethyl orthosilicate was 6%, and the temperature of the mixed solution was 30 °C.

[0065] The above polyimide porous membrane was immersed in the above aqueous solution of diethanolamine for 5 min and then taken out; the above mixed solution was coated on one surface of the polyimide porous membrane treated with the aqueous solution of diethanolamine, and the excess mixed solution on the membrane surface was removed, and then it was heat-treated at 50 °C for 30 min to form a separation layer, and then taken out to obtain an organic solvent-resistant composite nanofiltration membrane. Among them, the thickness of the separation layer was 120 nm.

[0066] From Figures 1 to 2 it can be seen that the organic solvent-resistant composite nanofiltration membrane of this example includes a polyimide porous membrane and a separation layer arranged in a stacked manner. Among them, the separation layer is connected to the polyimide porous membrane by chemical bonds. From Figure 3 it can be seen that the separation layer on the surface of the organic solvent-resistant composite nanofiltration membrane of this example is thin, has uniform denseness and a small pore size.

[0067] Example 2

[0068] The polyimide was dissolved in the organic solvent N,N-dimethylacetamide to prepare a homogeneous polyimide casting solution, and then the polyimide casting solution was placed in a coagulation bath for phase separation and crosslinking to obtain a polyimide porous membrane. Among them, the mass fraction of polyimide in the polyimide casting solution was 10%, and the coagulation bath was an aqueous solution of pentanediamine with a mass fraction of 1%.

[0069] Dissolve tris(hydroxymethyl)aminomethane (molecular weight: 121) in pure water to prepare an aqueous solution of tris(hydroxymethyl)aminomethane, wherein the mass fraction of tris(hydroxymethyl)aminomethane in the aqueous solution of tris(hydroxymethyl)aminomethane is 0.1%; dissolve polyvinyl alcohol in water and adjust the pH to 2, then add tetraethyl orthosilicate, and stir evenly by water bath heating to obtain a mixed solution, wherein, in the mixed solution, the mass fraction of polyvinyl alcohol is 1.0%, the mass fraction of tetraethyl orthosilicate is 20%, and the temperature of the mixed solution is 40 °C.

[0070] Immerse the above polyimide porous membrane in the above aqueous solution of tris(hydroxymethyl)aminomethane for 5 min and then take it out; coat the above mixed solution on one surface of the polyimide porous membrane treated with the aqueous solution of tris(hydroxymethyl)aminomethane, remove the excess mixed solution on the membrane surface, and then place it in a heat treatment at 70 °C for 20 min, and take it out to obtain an organic solvent-resistant composite nanofiltration membrane, wherein the thickness of the separation layer is 125 nm.

[0071] Example 3

[0072] Dissolve polyimide in an organic solvent of N-methylpyrrolidone to prepare a homogeneous polyimide casting solution, and then subject the polyimide casting solution to phase separation in a coagulation bath to obtain a polyimide porous membrane, wherein the mass fraction of polyimide in the polyimide casting solution is 30%, and the coagulation bath is an aqueous solution of hexamethylenediamine with a mass fraction of 8%.

[0073] Dissolve 1,3-diamino-2-hydroxypropane (molecular weight: 90) in pure water to prepare an aqueous solution of 1,3-diamino-2-hydroxypropane, wherein the mass fraction of 1,3-diamino-2-hydroxypropane in the aqueous solution of 1,3-diamino-2-hydroxypropane is 3%; dissolve hydroxypropyl methylcellulose in water and adjust the pH to 5, then add methyl orthosilicate, and stir evenly by water bath heating to obtain a mixed solution, wherein, in the mixed solution, the mass fraction of hydroxypropyl methylcellulose is 5.0%, the mass fraction of methyl orthosilicate is 5%, and the temperature of the mixed solution is 35 °C.

[0074] Immerse the above polyimide porous membrane in the above aqueous solution of 1,3-diamino-2-hydroxypropane for 5 min and then take it out; coat the above mixed solution on one surface of the polyimide porous membrane treated with the aqueous solution of 1,3-diamino-2-hydroxypropane, remove the excess mixed solution on the membrane surface, and then place it in a heat treatment at 80 °C for 10 min, and take it out to obtain an organic solvent-resistant composite nanofiltration membrane, wherein the thickness of the separation layer is 128 nm.

[0075] Example 4

[0076] Example 4 is different from Example 1 only in that the mass fraction of polyimide in the polyimide casting solution is 5%, and the remaining conditions are the same. A composite nanofiltration membrane resistant to organic solvents is obtained, wherein the thickness of the separation layer is 118 nm.

[0077] Example 5

[0078] Example 5 is different from Example 1 only in that the mass fraction of polyimide in the polyimide casting solution is 35%, and the remaining conditions are the same. A composite nanofiltration membrane resistant to organic solvents is obtained, wherein the thickness of the separation layer is 123 nm.

[0079] Example 6

[0080] Example 6 is different from Example 1 only in that the coagulation bath is an aqueous solution of 1,2-propanediamine with a mass fraction of 0.5%, and the remaining conditions are the same. A composite nanofiltration membrane resistant to organic solvents is obtained, wherein the thickness of the separation layer is 115 nm.

[0081] Example 7

[0082] Example 7 is different from Example 1 only in that the coagulation bath is an aqueous solution of 1,2-propanediamine with a mass fraction of 9%, and the remaining conditions are the same. A composite nanofiltration membrane resistant to organic solvents is obtained, wherein the thickness of the separation layer is 125 nm.

[0083] Example 8

[0084] Example 8 is different from Example 1 only in that in the mixed solution, the mass fraction of polyvinyl alcohol is 0.5%, and the remaining conditions are the same. A composite nanofiltration membrane resistant to organic solvents is obtained, wherein the thickness of the separation layer is 113 nm.

[0085] Example 9

[0086] Example 9 is different from Example 1 only in that in the mixed solution, the mass fraction of polyvinyl alcohol is 6%, and the remaining conditions are the same. A composite nanofiltration membrane resistant to organic solvents is obtained, wherein the thickness of the separation layer is 135 nm.

[0087] Example 10

[0088] Example 10 is different from Example 1 only in that in the mixed solution, the mass fraction of tetraethyl orthosilicate is 1%, and the remaining conditions are the same. A composite nanofiltration membrane resistant to organic solvents is obtained, wherein the thickness of the separation layer is 105 nm.

[0089] Example 11

[0090] Example 11 is different from Example 1 only in that the mass fraction of tetraethyl orthosilicate in the mixed solution is 22%, and the rest of the conditions are the same, obtaining a composite nanofiltration membrane resistant to organic solvents. Among them, the thickness of the separation layer is 132 nm.

[0091] Example 12

[0092] Example 12 is different from Example 1 only in that the mass fraction of diethanolamine in the aqueous solution of diethanolamine is 0.05%, and the rest of the conditions are the same, obtaining a composite nanofiltration membrane resistant to organic solvents. Among them, the thickness of the separation layer is 115 nm.

[0093] Example 13

[0094] Example 13 is different from Example 1 only in that the mass fraction of diethanolamine in the aqueous solution of diethanolamine is 4%, and the rest of the conditions are the same, obtaining a composite nanofiltration membrane resistant to organic solvents. Among them, the thickness of the separation layer is 127 nm.

[0095] Example 14

[0096] Example 14 is different from Example 1 only in that an equal mass of glucosamine (molecular weight of 179) is used to replace diethanolamine, and the rest of the conditions are the same, obtaining a composite nanofiltration membrane resistant to organic solvents. Among them, the thickness of the separation layer is 123 nm.

[0097] Comparative Example 1

[0098] Comparative Example 1 is different from Example 1 only in that the coagulation bath is water, and the rest of the conditions are the same, obtaining a composite nanofiltration membrane. Among them, the thickness of the separation layer is 119 nm.

[0099] Comparative Example 2

[0100] Comparative Example 2 is different from Example 1 in that the coagulation bath is water, and the polyimide porous membrane is crosslinked with 5% polyethyleneimine, without hydrophilic compounds, mixed solution and heat treatment, and the rest of the conditions are the same, obtaining a composite nanofiltration membrane resistant to organic solvents. Among them, the thickness of the separation layer is 255 nm.

[0101] Comparative Example 3

[0102] Comparative Example 3 is different from Example 1 only in that glutaraldehyde is used to replace tetraethyl orthosilicate, and the rest of the conditions are the same, obtaining a composite nanofiltration membrane resistant to organic solvents. Among them, the thickness of the separation layer is 105 nm.

[0103] Comparative Example 4

[0104] Comparative Example 4 is different from Example 1 only in that polyvinyl alcohol is dissolved in water and the pH is adjusted to 7, and the remaining conditions are the same, obtaining an organic solvent-resistant composite nanofiltration membrane, wherein the thickness of the separation layer is 108 nm.

[0105] Comparative Example 5

[0106] Comparative Example 5 is different from Example 1 only in that isopropanol is used to replace diethanolamine, and the remaining conditions are the same, obtaining an organic solvent-resistant composite nanofiltration membrane, wherein the thickness of the separation layer is 111 nm.

[0107] Comparative Example 6

[0108] Comparative Example 6 is different from Example 1 only in that in the mixed solution, the mass fraction of polyvinyl alcohol is 1.0% and the mass fraction of tetraethyl orthosilicate is 0.5%, and the remaining conditions are the same, obtaining an organic solvent-resistant composite nanofiltration membrane, wherein the thickness of the separation layer is 117 nm.

[0109] Comparative Example 7

[0110] Comparative Example 7 is different from Example 1 only in that in the mixed solution, the mass fraction of polyvinyl alcohol is 0.5% and the mass fraction of tetraethyl orthosilicate is 14%, and the remaining conditions are the same, obtaining an organic solvent-resistant composite nanofiltration membrane, wherein the thickness of the separation layer is 140 nm.

[0111] Comparative Example 8

[0112] Comparative Example 8 is different from Example 1 only in that it does not contain the step of preparing the polyimide porous membrane treated with the diethanolamine aqueous solution, that is, directly applying the above mixed solution to one surface of the polyimide porous membrane, removing the excess mixed solution on the membrane surface, and then placing it at 60 °C for heat treatment for 25 min to form a separation layer, and taking out to obtain an organic solvent-resistant composite nanofiltration membrane, wherein the thickness of the separation layer is 113 nm.

[0113] Comparative Example 9

[0114] Comparative Example 9 is different from Example 1 only in that it does not contain the step of applying the above mixed solution to one surface of the polyimide porous membrane treated with the diethanolamine aqueous solution, that is, directly placing the polyimide porous membrane treated with the diethanolamine aqueous solution at 60 °C for heat treatment for 25 min to form a separation layer, and taking out to obtain the organic solvent-resistant composite nanofiltration membrane as shown in Figure 4 The thickness of the separation layer is 0 nm.

[0115] From Figure 4 it can be seen that for the organic solvent-resistant composite nanofiltration membrane of this comparative example, an effective dense separation layer cannot be formed.

[0116] The performance tests were carried out on the organic solvent-resistant composite nanofiltration membranes prepared in Examples 1 to 14 and Comparative Examples 1 to 9. The test results are shown in Table 1. The specific test methods are as follows:

[0117] Membrane flux and rejection rate test: The test pressure was 0.5 MPa, and the test temperature was 25 °C. The N,N-dimethylacetamide (DMAc) solution (100 mg / L) of methylene blue or the toluene solution (100 mg / L) of sudan blue II was used as the concentrated water. Among them, the membrane flux (F) was calculated by the volume of the solvent passing through the organic solvent-resistant composite nanofiltration membrane within a certain time. The formula is: F = V / (A×T), where V is the volume of the solvent passing through the organic solvent-resistant composite nanofiltration membrane per unit time, A is the effective membrane area, and T is the time; the rejection rate (R) was calculated from the concentration of the feed liquid and the concentration of the permeate. The calculation formula is: R = (1 - C1 / C0)×100%, where C1 is the concentration of the permeate and C0 is the concentration of the feed liquid.

[0118] Table 1

[0119]

[0120] It can be seen from the data in Table 1 that compared with Examples 1 and 4 to 5, controlling the mass fraction of polyimide in the polyimide casting solution within a suitable range is beneficial to improving the solvent resistance of the organic solvent-resistant composite nanofiltration membrane; compared with Examples 1 and 6 to 7, controlling the mass fraction of aliphatic diamine in the coagulation bath within a suitable range is beneficial to improving the flux, solvent resistance and rejection rate of the organic solvent-resistant composite nanofiltration membrane; compared with Examples 1 and 8 to 9, controlling the mass fraction of the high molecular polymer containing hydroxyl groups in the mixed solution within a suitable range is beneficial to improving the interfacial bonding strength, rejection rate and flux of the organic solvent-resistant composite nanofiltration membrane; compared with Examples 1 and 10 to 11, controlling the mass fraction of silicate ester in the mixed solution within a suitable range is beneficial to improving the rejection rate, membrane flux and rapid transmission of non-polar and polar organic solvents of the organic solvent-resistant composite nanofiltration membrane; compared with Examples 1 and 12 to 13, controlling the mass fraction of the hydrophilic compound in the aqueous solution of the hydrophilic compound within a suitable range is beneficial to improving the rejection rate, membrane flux and interfacial bonding strength of the organic solvent-resistant composite nanofiltration membrane.

[0121] Compared with Example 1 and Comparative Example 1, in Comparative Example 1, since the coagulation bath is water and cannot act as a cross-linking agent to react with polyimide by cross-linking reaction, the solvent resistance of the organic solvent-resistant composite nanofiltration membrane is poor. At the same time, during the operation, the polyimide porous membrane is likely to partially or even completely dissolve, resulting in the rupture of the separation layer and ultimately the loss of the retention performance. Compared with Example 1 and Comparative Example 2, since the polyimide porous membrane is prepared by the conventional phase inversion cross-linking method in Comparative Example 2, the thickness of the separation layer is relatively thick and the membrane flux is poor. Compared with Example 1 and Comparative Example 3, since glutaraldehyde is used in Comparative Example 3, a hydrophobic network structure cannot be formed to provide a mass transfer channel for non-polar organic solvents, making it difficult to be efficiently separated for both polar and non-polar organic solvent systems. Compared with Example 1 and Comparative Example 4, since the pH of the mixed solution in Comparative Example 4 is neutral, the hydrolysis rate of tetraethyl orthosilicate is slow, making it difficult to form sufficient Si-OH groups, and thus it is difficult to cross-link the hydroxyl-containing polymer and react with the hydroxyl groups of the polyimide porous membrane in the form of chemical bonds to form a separation layer, resulting in the easy detachment of the separation layer. Compared with Example 1 and Comparative Examples 6 to 7, since the mass ratio of the hydroxyl-containing polymer to the silicate ester in Comparative Examples 6 to 7 is not within a specific range, the pore size distribution of the formed separation layer is uneven, affecting the flux and rejection rate of the organic solvent-resistant composite nanofiltration membrane. Compared with Example 1 and Comparative Example 8, although a solvent-resistant polyimide porous membrane and a dense separation layer can be respectively formed because the polyimide porous membrane in Comparative Example 8 is not treated with a hydrophilic compound containing hydroxyl and amino groups, the two are not connected by chemical bonds and are prone to swelling and separation in organic solvents, ultimately resulting in the loss of the retention performance. Compared with Example 1 and Comparative Example 9, since the mixed solution is not coated to form a dense separation layer in Comparative Example 9, there is no retention performance.

[0122] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0123] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A preparation method of an organic solvent-resistant composite nanofiltration membrane, characterized in that, It includes the following steps: The polyimide casting solution is prepared into a polyimide porous membrane by the non-solvent induced phase separation method. Among them, the coagulation bath used in the non-solvent induced phase separation method is an aqueous solution of aliphatic diamine; A high molecular polymer containing hydroxyl groups, a silicate ester and water are mixed to prepare a mixed solution. Among them, the mixed solution is acidic, and the mass ratio of the high molecular polymer containing hydroxyl groups to the silicate ester is 1:1 - 1:20; An aqueous solution of a hydrophilic compound and the mixed solution are sequentially placed on the same surface of the polyimide porous membrane, and a separation layer is formed by heat treatment to obtain an organic solvent-resistant composite nanofiltration membrane. Among them, the hydrophilic compound has amino groups and hydroxyl groups.

2. The preparation method of the organic solvent-resistant composite nanofiltration membrane according to claim 1, characterized in that, The mass fraction of polyimide in the polyimide casting solution is 10% - 30%; And / or, the mass fraction of the aliphatic diamine in the aqueous solution of the aliphatic diamine is 1% - 8%.

3. The preparation method of the organic solvent-resistant composite nanofiltration membrane according to claim 1, characterized in that, The mass fraction of the high molecular polymer containing hydroxyl groups in the mixed solution is 1% - 5%; And / or, the mass fraction of the silicate ester in the mixed solution is 2% - 20%.

4. The preparation method of the organic solvent-resistant composite nanofiltration membrane according to claim 1, wherein The pH of the mixed solution is 2 - 5; And / or, the temperature of the mixed solution is 20°C - 40°C.

5. The preparation method of the organic solvent-resistant composite nanofiltration membrane according to claim 1, wherein, The mass fraction of the hydrophilic compound in the aqueous solution of the hydrophilic compound is 0.1% - 3%.

6. The preparation method of the organic solvent-resistant composite nanofiltration membrane according to claim 1, wherein, The molecular weight of the hydrophilic compound is 50 - 150.

7. The preparation method of the organic solvent-resistant composite nanofiltration membrane according to claim 1, characterized in that, The aliphatic diamine is selected from at least one of 1,2-propanediamine, pentanediamine, and hexanediamine; And / or, the hydrophilic compound is selected from at least one of diethanolamine, tris(hydroxymethyl)aminomethane, and 1,3-diamino-2-hydroxypropane; And / or, the high molecular polymer containing hydroxyl groups is selected from at least one of polyvinyl alcohol and / or hydroxypropyl methylcellulose; And / or, the silicate ester is selected from at least one of tetraethyl orthosilicate and tetramethyl orthosilicate.

8. The preparation method of the organic solvent-resistant composite nanofiltration membrane according to any one of claims 1 to 7, characterized in that, The temperature of the heat treatment is 50°C - 80°C, and the time is 10 min - 30 min.

9. An organic solvent-resistant composite nanofiltration membrane prepared by the preparation method of the organic solvent-resistant composite nanofiltration membrane according to any one of claims 1 to 8.

10. An application of the organic solvent-resistant composite nanofiltration membrane according to claim 9 in an organic solvent treatment device.

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