阅读说明：本技术 耐溶剂聚合物纳滤膜及其制备方法和应用 (Solvent-resistant polymer nanofiltration membrane as well as preparation method and application thereof ) 是由 靳健 王正宫 于 2020-05-11 设计创作，主要内容包括：本发明涉及一种耐溶剂聚合物纳滤膜及其制备方法和应用,其制备方法包括以下步骤：将二胺单体与二酐单体在催化剂的作用下,在第一极性有机溶剂中于160～230℃条件下发生环化酰亚胺,反应完全后形成聚酰亚胺；二胺单体包括含羧基的二胺单体与不含羧基的二胺单体；将聚酰亚胺溶于第二极性有机溶剂,形成浓度为10wt％～40wt％的成膜溶液；然后将成膜溶液成膜后进行相转化,得到中间体膜；采用金属盐的有机溶液处理中间体膜,以使得金属离子与聚酰亚胺中的羧基配位交联,交联完毕后得到耐溶剂聚合物纳滤膜；其中,金属盐选自金属盐和/或多价金属盐。本发明还公开了耐溶剂聚合物纳滤膜在分离和/或纯化有机溶液中化合物的应用。(The invention relates to a solvent-resistant polymer nanofiltration membrane as well as a preparation method and application thereof, wherein the preparation method comprises the following steps: under the action of a catalyst, a diamine monomer and a dianhydride monomer are subjected to cyclic imide in a first polar organic solvent at 160-230 ℃, and polyimide is formed after complete reaction; the diamine monomer comprises a diamine monomer containing carboxyl and a diamine monomer containing no carboxyl; dissolving polyimide in a second polar organic solvent to form a film forming solution with the concentration of 10 wt% -40 wt%; then, carrying out phase transformation after the film forming solution is formed into a film to obtain an intermediate body film; treating the intermediate membrane by using an organic solution of metal salt to coordinate and crosslink metal ions and carboxyl in polyimide, and obtaining a solvent-resistant polymer nanofiltration membrane after crosslinking is finished; wherein the metal salt is selected from metal salt and/or polyvalent metal salt. The invention also discloses application of the solvent-resistant polymer nanofiltration membrane in separation and/or purification of compounds in organic solution.)

1. The preparation method of the solvent-resistant polymer nanofiltration membrane is characterized by comprising the following steps of:

(1) reacting a diamine monomer and a dianhydride monomer in a first polar organic solvent at 160-230 ℃ under the action of a catalyst to form polyimide;

the diamine monomer comprises at least one diamine monomer containing carboxyl and at least one diamine monomer containing no carboxyl; the structural formula of the polyimide comprises a first repeating unit and a second repeating unit, wherein the first repeating unit comprises a polymerized chain segment of at least one dianhydride monomer and a diamine monomer containing a carboxyl group, and the second repeating unit comprises a polymerized chain segment of at least one dianhydride monomer and a diamine monomer containing no carboxyl group;

the boiling point of the first polar organic solvent is higher than 160 ℃;

(2) dissolving the polyimide in a second polar organic solvent to form a film forming solution with the concentration of 10-40 wt%; then, carrying out phase transformation after the film forming solution is formed into a film to obtain an intermediate film;

(3) treating the intermediate membrane by using an organic solution of metal salt to enable metal ions to be coordinated and crosslinked with carboxyl in polyimide, and obtaining the solvent-resistant polymer nanofiltration membrane after crosslinking is finished; wherein the metal salt is selected from one or more divalent metal salts and/or polyvalent metal salts.

2. The method of claim 1, wherein: in the step (1), the diamine monomer containing carboxyl is selected from at least one diamine monomer with the structural formula of NH₂-R”-NH₂Wherein R' in each monomer is selected from one of the following structural formulas:

3. the method of claim 1, wherein: in the step (1), the diamine monomer having no carboxyl group is selected from at least one diamine monomer having the formula NH₂-R’-NH₂Wherein R' in each monomer is selected from one of the following structural formulas:

4. the method of claim 1, wherein: in step (1), the dianhydride monomer is selected from at least one dianhydride monomer having the structural formulaWherein R in each monomer is selected from one of the following structural formulas:

5. the method of claim 1, wherein: in the step (1), the molar ratio of the dianhydride monomer, the diamine monomer containing a carboxyl group and the diamine monomer containing no carboxyl group is 10:0.1-9.9: 0.1-9.9.

6. The method of claim 1, wherein: in the step (2), the film-forming solution is formed into a film by a method of preparing a flat sheet film or a method of preparing a hollow fiber film.

7. The method of claim 1, wherein: in the step (3), the divalent metal salt includes one or more of copper salt, nickel salt, zinc salt, cobalt salt, magnesium salt and calcium salt, and the polyvalent metal salt includes one or more of iron salt, lanthanum salt and aluminum salt.

8. A solvent-resistant polymeric nanofiltration membrane prepared by the preparation method of any one of claims 1 to 7, wherein the nanofiltration membrane comprises: the polyimide resin comprises a plurality of polyimide polymer chain segments, wherein each polyimide polymer chain segment comprises a first repeating unit and a second repeating unit, and the polymerization degree ratio of the first repeating unit to the second repeating unit is 1-100: 1-100; the carboxyl groups in different polyimide polymer chain segments are coordinated and crosslinked with metal ions.

9. The solvent-resistant polymeric nanofiltration membrane of claim 8, wherein: in each polyimide polymer chain segment, the number of the first repeating units is 10-1000; the number of the second repeating units is 10-1000.

10. Use of the solvent resistant polymeric nanofiltration membrane according to claim 8 for the separation and/or purification of compounds in organic solutions.

Technical Field

The invention relates to the technical field of membrane separation, in particular to a solvent-resistant polymer nanofiltration membrane and a preparation method and application thereof.

Background

Organic Solvent Nanofiltration (OSN) is a novel nanofiltration membrane separation technology that has been rapidly developed in recent years. OSN is driven by 5-30bar of transmembrane pressure, and can realize separation and purification of solute molecules with molecular weight of 200-1000Da in organic solvent through the sieving effect of nanofiltration membrane pores. The OSN technology has important and wide application in the aspects of homologue separation, medicine purification, dye separation, solvent recovery and the like, and has special significance in the fields of petrochemical industry, medicines, foods, textiles and the like. However, the common nanofiltration membrane is mainly applied to an aqueous solution system, and the used membrane material has poor tolerance to an organic solvent and is not suitable for an organic solvent system, particularly a strong polar solvent system. Therefore, the development of solvent-resistant nanofilteration (SRNF) membranes is the key and core of OSN technology development.

The nanofiltration membrane suitable for an organic solvent system needs to have the characteristics of swelling resistance, corrosion resistance and high flux, so that special requirements are required for selection of membrane materials of the solvent-resistant nanofiltration membrane and a preparation method. The polyimide is used as a polymer material with good film forming property, high thermal stability, oxidation resistance and good mechanical property, is widely applied and has good application prospect in the preparation of solvent-resistant nanofiltration membranes. However, polyimide is inferior in swelling resistance and also in chlorine resistance in a highly polar organic solvent.

In order to solve the problems, in the prior art, a plurality of methods are adopted to crosslink the polyimide membrane, so that the swelling resistance and the physical and chemical stability of the solvent-resistant nanofiltration membrane are improved. For example, CN 110801736 a discloses a method for preparing a nanofiltration membrane containing a metal framework compound intermediate layer, which comprises preparing an HKUST-1 intermediate layer on the surface of a polyimide porous base membrane containing a large amount of amino groups by an in-situ growth method, and preparing a separation layer on the intermediate layer by an interfacial polymerization method, thereby obtaining a nanofiltration membrane which has excellent separation performance, good solvent resistance and is not easy to peel. CN 106459590a discloses a porous membrane comprising a metal-organic framework material, comprising at least one porous metal-organic framework material, at least one at least bidentate organic compound coordinated to at least one metal ion, at least one fibrillated fluoropolymer and additives. CN104689727A discloses a semipermeable membrane, a forward osmosis and reverse osmosis water treatment device and a method for preparing the same, wherein the semipermeable membrane comprises a first surface and a support layer, an active layer, wherein the support layer comprises a porous structure with a polymer and at least one metal oxide or metalloid oxide therein.

However, the currently adopted crosslinking method often causes the polyimide molecular chain to be dense, thereby causing the membrane flux to be greatly reduced and seriously affecting the separation efficiency of the nanofiltration membrane. Therefore, a preparation method capable of improving the swelling resistance and the physical and chemical stability of the solvent-resistant polymer nanofiltration membrane without affecting the membrane flux is needed.

Disclosure of Invention

In order to solve the problem that the membrane flux of the existing nanofiltration membrane is reduced after cross-linking, the invention aims to provide a solvent-resistant polymer nanofiltration membrane as well as a preparation method and application thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

on one hand, the invention discloses a preparation method of a solvent-resistant polymer nanofiltration membrane, which comprises the following steps:

(1) under the action of a catalyst, a diamine monomer and a dianhydride monomer are subjected to cyclic imide in a first polar organic solvent at 160-230 ℃, and polyimide is formed after complete reaction;

the diamine monomer comprises at least one diamine monomer containing carboxyl and at least one diamine monomer containing no carboxyl; the polyimide has a structural formula comprising a first repeating unit and a second repeating unit, wherein the first repeating unit comprises a polymerized chain segment of at least one dianhydride monomer and a diamine monomer containing a carboxyl group, and the second repeating unit comprises a polymerized chain segment of at least one dianhydride monomer and a diamine monomer containing no carboxyl group;

the boiling point of the first polar organic solvent is higher than 160 ℃;

(2) dissolving polyimide in a second polar organic solvent to form a film forming solution with the concentration of 10 wt% -40 wt%; then, carrying out phase transformation after the film forming solution is formed into a film to obtain an intermediate body film;

(3) treating the intermediate membrane by using an organic solution of metal salt to coordinate and crosslink metal ions and carboxyl in polyimide, and obtaining a solvent-resistant polymer nanofiltration membrane after crosslinking is finished; wherein the metal salt is selected from one or more divalent metal salts and/or polyvalent metal salts.

Further, in the step (1), the diamine monomer containing carboxyl is selected from at least one diamine monomer having a formula of NH₂-R”-NH₂Wherein R' in each monomer is selected from one of the following structural formulas:

in the above structural formula, the connection site of the "-" group represents the connection site of the amine group in the diamine monomer.

In the invention, the carboxyl in the diamine monomer containing carboxyl forms a metal coordination bond with subsequent metal ions to realize non-covalent crosslinking of a plurality of polyimide chain segments, thereby improving the solvent resistance and the pressure resistance of the polymer nanofiltration membrane.

Further, in the step (1), the diamine monomer having no carboxyl group is selected from at least one diamine monomer having the formula NH₂-R’-NH₂Wherein R' in each monomer is selected from one of the following structural formulas:

in the above structural formula, the connection site of the "-" group represents the connection site of the amine group in the diamine monomer.

In the invention, the diamine monomer without carboxyl has the effects of adjusting the carboxyl content in polyimide, improving the molecular weight of the polymer to a certain extent and ensuring that the polymer nanofiltration membrane has better film-forming property and mechanical property.

Further, in the step (1), the dianhydride monomer is selected from at least one dianhydride monomer having the structural formulaWherein R in each monomer is selected from one of the following structural formulas:

in the above structural formula, the connection site of "-" on the group represents the connection site of the carbonyl group in the dianhydride monomer.

Preferably, the dianhydride monomer is aromatic acid dianhydride monomer, and R in the dianhydride monomer is preferably one of the following structural formulas:

further, in the step (1), the molar ratio of the dianhydride monomer, the carboxyl group-containing diamine monomer, and the diamine monomer not containing a carboxyl group is 10:0.1 to 9.9, preferably 10:0.1:9.9, 10:1:9, 10:2:8, 10:3:7, 10:4:6, 10:5:5, 10:6:4, 10:7:3, 10:8:2, 10:9:1, 10:9.9: 0.1.

According to the invention, by controlling the molar ratio of the diamine monomer containing carboxyl and the diamine monomer containing no carboxyl, the film forming solution can be ensured to have good film forming property and mechanical property, and the density of coordination crosslinking points in polyimide is ensured to be in a proper range, so that the flux reduction of the finally prepared nanofiltration membrane caused by excessive coordination crosslinking points is prevented.

Further, in step (1), the catalyst includes triethylamine, quinoline, pyrazine, and the like.

Further, in the step (1), the first polar organic solvent comprises one or more of m-cresol and/or N-methylpyrrolidone.

Preferably, in the step (1), the diamine monomer is dissolved in the first polar organic solvent, then the dianhydride monomer is added in batches, and after uniform mixing, a reaction system with a total solid content of 100-500g/L is formed, and then the reaction is carried out for 5-10 h at 160-230 ℃.

Preferably, in the step (1), during the reaction, the water generated by the reaction is removed by azeotropic dehydration of toluene, thereby promoting the reaction.

Further, in the step (2), the second polar organic solvent includes one or more of m-cresol, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone and 1, 4-dioxane. Since the polyimide of the present invention contains a large amount of carboxyl groups, and is difficult to dissolve in a common solvent, the second polar organic solvent is selected to ensure sufficient dissolution of the polyimide synthesized in step (1).

Further, in the step (2), the film-forming solution is formed into a film by a method of preparing a flat sheet film or a method of preparing a hollow fiber film.

Further, the method for preparing the flat sheet membrane comprises the following steps:

coating the film forming solution on the surface of a substrate to form a uniform bubble-free film, transferring the substrate with the film into a phase inversion bath for phase inversion, and obtaining an intermediate film after the phase inversion is completed. Preferably, the coating is carried out by a knife coating method, and the thickness of the film on the surface of the substrate is 50 to 500. mu.m. Preferably, the coating is carried out at a humidity of 10-80%.

Further, the method for preparing the hollow fiber membrane comprises the following steps:

(S1) filtering the film-forming solution through a screen, transferring the film-forming solution into a film tank, and degassing the film-forming solution at 15 to 50 ℃;

(S2) solution spinning the degassed solution to form a hollow fiber membrane.

Preferably, in the step (S2), the solution spinning process means that the bore fluid is extruded through the central hole of the concentric hole spinneret, and the degassed filtrate is extruded through the annular gap of the concentric hole spinneret.

Preferably, the bore fluid comprises one or more of water, ethanol, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone.

Further, the phase inversion bath used in the film forming process comprises water and/or ethanol.

Further, in the step (3), the divalent metal salt includes one or more of copper salt, nickel salt, zinc salt, cobalt salt, magnesium salt and calcium salt, and the polyvalent metal salt includes iron salt, lanthanum salt and/or aluminum salt. Preferably, the metal salt comprises a copper salt or a lanthanum salt.

More preferably, the metal salt comprises one or more of copper sulfate, copper nitrate, copper chloride, ferric nitrate, ferric chloride, nickel nitrate, nickel chloride, zinc nitrate, zinc chloride, cobalt nitrate, magnesium chloride, magnesium nitrate, aluminum chloride, aluminum nitrate, calcium nitrate, lanthanum chloride and calcium chloride.

Further, in the step (3), the concentration of the organic solution of the metal salt is 0.01 to 1 mol/L.

Preferably, in step (3), the organic solvent used in the organic solution of the metal salt includes an alcohol solvent, preferably methanol, ethanol, isopropanol, acetone, or the like. The organic solvent used in the organic solution of the metal salt can influence the crosslinking degree of the finally formed nanofiltration membrane, the integrity of the membrane structure and the like, and the alcohol organic solvent can ensure that the crosslinking degree of the nanofiltration membrane is in a proper range and the integrity of the membrane structure.

Further, in the step (3), the treatment time is 12-72h, and the treatment temperature is 20-50 ℃.

On the other hand, the invention also discloses a solvent-resistant polymer nanofiltration membrane prepared by the preparation method, which comprises a plurality of polyimide polymer chain segments, wherein the polyimide polymer chain segments comprise a first repeating unit and a second repeating unit, and the polymerization degree ratio of the first repeating unit to the second repeating unit is 1-100: 1-100; the carboxyl groups in different polyimide polymer chain segments are coordinated and crosslinked with metal ions.

Furthermore, in each polyimide polymer chain segment, the number of the first repeating units is 10-1000; the number of the second repeating units is 10 to 1000.

In the present invention, the polyimide polymer segment includes the following structural formula:

wherein m is 10-1000; n is 10-1000; m: n is 1-100: 1-100; unless otherwise specified, m and n are as defined herein; r is derived from dianhydride, R 'is derived from diamine without carboxyl, and R' is derived from diamine with carboxyl; specifically, the method comprises the following steps:

r is selected from one of the following structural formulas:

r' is selected from one of the following structural formulas:

r' is selected from one of the following structural formulas:

with R' asFor example, the structural formula of the polyimide polymer chain segment and the structure after the polyimide polymer chain segment is coordinated with metal ions are as follows in sequence:

furthermore, the cut-off molecular weight of the solvent-resistant polymer nanofiltration membrane is 850Da, and the flux is 10-50Lm under the operation pressure of 1MPa^-2h^-1bar^-1。

In a specific embodiment of the invention, under the operation pressure of 1MPa, the rejection rate of the solvent-resistant polymer nanofiltration membrane to Coomassie brilliant blue in a methanol solvent can reach up to 99%, and the membrane flux reaches 30Lm^-2h^-1bar^-1。

The solvent-resistant polymer nanofiltration membrane has good swelling resistance and compaction resistance in polar organic solvents such as methanol, ethanol, acetone, chloroform, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone and 1, 4-dioxane, and has high flux.

In another aspect, the invention also discloses the application of the solvent-resistant polymer nanofiltration membrane in separating and/or purifying compounds in organic solution.

Further, the solvent in the organic solution comprises one or more of methanol, ethanol, acetone, chloroform, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone and 1, 4-dioxane.

Further, the isolated compounds include dye molecules, drug molecules, and natural biomolecules.

The invention provides a preparation method which can improve the swelling resistance and the physical and chemical stability of a solvent-resistant polymer nanofiltration membrane and does not influence the membrane flux. The invention prepares the target membrane material through steps of polyimide carboxylation, phase conversion and ion crosslinking. Performing a cyclized imide reaction on a diamine monomer containing carboxyl, a diamine monomer containing no carboxyl and an aromatic acid dianhydride monomer under a selected condition to form a polyimide material, wherein the polyimide material comprises a polyimide copolymer containing carboxyl groups; after phase inversion, soaking carboxyl in a plurality of polyimide copolymerization chains and a divalent or polyvalent metal salt solution to perform coordination crosslinking on metal ions and the carboxyl; thereby improving the swelling resistance, the physical and chemical stability, the organic solvent resistance and the mechanical property of the membrane material and solving the problem of the reduction of the membrane flux of the polyimide membrane caused by the cross-linking treatment.

Compared with the prior art, the invention has the following advantages and effects:

1. the invention adopts the strong coordination crosslinking technology of divalent or polyvalent metal ions and carboxyl, so that the main chain structure of the polyimide is kept complete. The obtained membrane material has better physical and chemical stability and obviously improved mechanical strength (see figure 5).

2. Due to the strong coordination crosslinking effect of divalent or polyvalent metal ions and carboxyl, the obtained membrane material has better swelling resistance to various organic solvents such as methanol, ethanol, acetone, chloroform, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, 1, 4-dioxane and the like.

3. In the prior art, a covalent bond is formed between a cross-linking agent and polyimide, and the membrane flux of the obtained membrane material is greatly reduced compared with that before cross-linking. The chemical bond energy of the coordination bond is obviously weaker than that of the covalent bond, so that the coordination bond is formed by the cross-linking agent and the polyimide, the membrane flux of the obtained membrane material is not greatly reduced compared with that before cross-linking, and the higher membrane flux can be still maintained.

4. Due to the adoption of a multiple coordination crosslinking mode, the membrane material prepared by the invention has a stable structure and good compaction resistance, and can keep relatively stable membrane flux and high retention rate within a long test time (see figure 7).

5. The preparation process of the solvent-resistant polymer nanofiltration membrane provided by the invention is simple and controllable, has good repeatability, is suitable for large-scale industrial production, and has good application prospect in the field of organic solution system separation.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following description is made with reference to the preferred embodiments of the present invention and the accompanying detailed drawings.

Drawings

FIG. 1 is a schematic illustration of the ionic crosslinking of solvent resistant polymeric nanofiltration membranes in an embodiment of the present invention;

FIG. 2 is a schematic diagram of a synthetic route for a carboxyl group-containing polyimide copolymer in an embodiment of the present invention;

FIG. 3 is a schematic diagram of the ionic crosslinking of solvent resistant polymer nanofiltration membranes according to an embodiment of the present invention;

FIG. 4 is a photograph showing the stable presence of the solvent-resistant polymer nanofiltration membrane in various organic solvents in example 4 of the present invention;

FIG. 5 is a comparison of the mechanical strength of the solvent-resistant polymeric nanofiltration membrane and the uncrosslinked polyimide membrane in example 4 of the present invention;

FIG. 6 is a scanning electron microscope image of the cross section of the nanofiltration membrane made of the solvent-resistant polymer in example 4 of the present invention;

FIG. 7 is a comparison of the pressure proof performance of the solvent-resistant polymer nanofiltration membrane and the uncrosslinked polyimide membrane in example 4 of the present invention;

fig. 8 is a graph of the flux of a solvent resistant polymer nanofiltration membrane according to example 4 of the present invention as a function of time.

The meaning of the symbols in the drawings:

wherein, M in FIG. 1ⁿ⁺Represents a divalent or polyvalent metal ion.

Detailed Description

The following examples are given to further illustrate the embodiments of the present invention. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.