Conjugated microporous organic solvent-resistant nanofiltration composite membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of separation membranes, and discloses a conjugated microporous organic solvent-resistant nanofiltration composite membrane and a preparation method and application thereof, the nanofiltration composite membrane comprises a base membrane and a separation layer compounded in pores and / or on the surface of the base membrane; a polymer forming the separation layer comprises repeated structural units containing aromatic rings, and the aromatic rings of part of the repeated structural units are connected with halogen substituents; on the basis of the total molar weight of chemical elements contained in the separation layer, the molar content of halogen is 2-26%; and the porosity of the nanofiltration composite membrane separation layer is 20-65%. The nanofiltration composite membrane has excellent acid and alkali resistance, excellent non-polar solvent permeability and good chemical stability.

Description

Technical Field

[0001] The invention relates to the technical field of separation membranes, and in particular to a conjugated microporous organic solvent-resistant nanofiltration composite membrane and a preparation method and application thereof. Background Art

[0002] Organic solvents are a class of organic compounds widely used in the fields of petroleum, chemical industry, catalysis, food and medicine. If they are not properly handled, they will cause serious environmental pollution. Among the methods used to treat organic solvents, the organic solvent-resistant nanofiltration process has significant advantages due to its low energy consumption, high separation efficiency, simple operation and environmental friendliness. Under pressure-driven, organic solvent-resistant nanofiltration membranes can efficiently separate molecules with a molecular weight between 200-1000Da, and can achieve the purification and concentration of high-value organic small molecules, the recovery and reuse of organic solvents, and have broad application prospects.

[0003] At present, organic solvent resistant nanofiltration membranes generally have low flux for non-polar solvents, poor chemical stability, and insufficient long-term stability. Commercial organic solvent resistant nanofiltration membranes have low flux for non-polar solvents (<2.0 L / (m 2 ·h·bar)). To meet the growing demand for membrane separation in non-polar solvent systems, researchers have made many attempts. For example, hydrophobic polymers such as polydimethylsiloxane are coated on the porous support layer. Although non-polar solvents are easier to penetrate than polar solvents, their permeability is not ideal due to the irregular stacking of polymer chains; hydrophobic block functional amines or acyl chloride functional groups are introduced during the interfacial polymerization reaction to optimize the hydrophobicity of the selective layer, which is conducive to the adsorption and diffusion of non-polar solvents. However, due to the very limited amount of introduced hydrophobic segments, high permeability of non-polar solvents cannot be obtained; in addition, self-microporous polymers can avoid the disadvantage of low porosity caused by the close stacking of segments in traditional polymer membranes due to their intrinsic microporous structure, and can increase porosity while reducing liquid transmission resistance, but they have problems with swelling and poor long-term stability, and the pore size can undergo irreversible changes, resulting in a significant decrease in separation selectivity. In summary, it is crucial to develop high-throughput and high-stability organic solvent-resistant nanofiltration membranes.

[0004] The conjugated microporous polymer membrane has a CC rigid skeleton, is insoluble in organic solvents, has good chemical and structural stability, has excellent tolerance to organic solvents, and can be used for fluid separation under harsh conditions. Wang et al. used multifunctional acetyl monomers to prepare an unsupported conjugated microporous polymer membrane under methanesulfonic acid catalysis (Journal of Materials Chemistry A, 2020, 8, 15891-15899), but this unsupported membrane is very brittle, not conducive to industrial amplification, and has a low flux for non-polar solvents; CN113461912A and CN114524962A respectively disclose a polycyclic aromatic skeleton polymer and a composite membrane preparation method. By dissolving the acetyl reaction monomer in an organic solvent and forming a prepolymer solution under acid catalysis, the prepolymer solution is modified on the surface of the polymer substrate membrane and thermally cured to obtain a composite membrane. The prepared composite membrane has a very high flux for polar solvents such as methanol and ethanol, but a very low permeation flux for non-polar solvents. Therefore, how to overcome the problem of poor flux of composite membranes for non-polar solvents is the key to the application of composite separation membranes in the fields of hydrocarbon separation, drug purification and organic solvent recovery and reuse. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems of poor flux and poor separation effect of composite membranes for non-polar solvents in the prior art, and to provide a conjugated microporous organic solvent-resistant nanofiltration composite membrane and its preparation method and application. The nanofiltration composite membrane has good permeability to non-polar solvents and good chemical stability.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a nanofiltration composite membrane, the nanofiltration composite membrane comprising a base membrane and a separation layer composited in the pores and / or on the surface of the base membrane; the polymer forming the separation layer comprises repeating structural units containing aromatic rings, wherein the aromatic rings of some repeating structural units are connected to halogen substituents; The molar content of halogen is 2-26% based on the total molar amount of chemical elements contained in the separation layer; The porosity of the nanofiltration composite membrane separation layer is 20-65%.

[0007] A second aspect of the present invention provides a method for preparing a nanofiltration composite membrane, comprising: (1) in the presence of a catalyst, subjecting compound I and compound II to a prepolymerization reaction to obtain a prepolymerization solution; the molar ratio of compound I to compound II is (0.1-10):1; Wherein, compound I has a structure as shown in formula (1), Formula (1), Wherein, R1, R2, R3, R4, R5, and R6 are each independently selected from any one of H, C1-C6 substituted or unsubstituted alkyl, C6-C12 substituted or unsubstituted aryl, amine, acetyl, and halogen substituents, and R1, R2, R3, R4, R5, and R6 contain at least one acetyl group and one halogen substituent; Compound II has a structure as shown in formula (2), Formula (2), Wherein, R1', R2', R3', R4', R5', and R6' are each independently selected from any one of H, a C1-C6 substituted or unsubstituted alkyl group, a C6-C12 substituted or unsubstituted aryl group, an amine group, and an acetyl group, and R1', R2', R3', R4', R5', and R6' contain at least one acetyl group, preferably contain at least two acetyl groups; (2) contacting the base film with the prepolymerization solution to perform deep polymerization to obtain a composite film precursor; (3) Washing and drying the composite membrane precursor.

[0008] The third aspect of the present invention provides the use of the nanofiltration composite membrane described in the first aspect or the nanofiltration composite membrane prepared by the above preparation method in hydrocarbon separation, catalyst recovery, drug purification and organic solvent recovery.

[0009] The nanofiltration composite membrane provided by the present invention, the polymer forming the separation layer includes a repeating structural unit containing an aromatic ring, which can form a CC-coupled conjugated microporous structure, and the aromatic rings in some of the repeating structural units containing aromatic rings are connected with halogen substituents. By controlling the appropriate halogen content and membrane porosity, the interaction between non-polar solvents and the membrane pore structure can be significantly improved, and an ultrafast transmission channel for non-polar solvents can be constructed. The nanofiltration composite membrane has excellent acid and alkali resistance, excellent non-polar solvent permeability, and good chemical stability. The reason may be that by introducing an appropriate amount of halogen substituents into the CC-coupled conjugated microporous structure, on the one hand, the appropriate hydrophobicity of the pores inside the membrane can be adjusted, and on the other hand, the porosity of the conjugated microporous polymer membrane can be regulated. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a physical picture of the conjugated microporous nanofiltration composite membrane in Example 1 of the present invention; Figure 2 This is the FTIR graph of the conjugated microporous nanofiltration composite membrane in Example 1 of the present invention. DETAILED DESCRIPTION

[0011] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0012] The first aspect of the present invention provides a nanofiltration composite membrane, comprising a base membrane and a separation layer composited in the pores and / or on the surface of the base membrane; the polymer forming the separation layer comprises repeating structural units containing aromatic rings, wherein the aromatic rings of some repeating structural units are connected to halogen substituents; based on the total molar amount of chemical elements in the separation layer, the molar content of the halogen is 2-26%; The porosity of the nanofiltration composite membrane separation layer is 20-65%.

[0013] In the present invention, the polymer forming the separation layer includes repeating structural units containing aromatic rings, and the polymer has a CC-coupled conjugated microporous structure. Halogen substituents are connected to the aromatic rings of some repeating structural units. It can be understood that the polymer contains some repeating structural units connected to halogen substituents and the remaining repeating structural units not connected to halogen substituents. The inventors of the present invention have found in their research that by controlling the appropriate halogen content and porosity, the interaction between non-polar solvents and membrane pore structures can be significantly improved, and an ultrafast transmission channel for non-polar solvents can be constructed. The nanofiltration composite membrane has excellent acid and alkali resistance, excellent non-polar solvent permeability, and good chemical stability.

[0014] Preferably, FTIR is used to characterize the surface chemical structure of the nanofiltration composite membrane at 1000-1300 cm -1 There is a vibration absorption peak of the CF bond.

[0015] According to some preferred embodiments of the present invention, based on the total molar amount of chemical elements in the separation layer, the molar content of halogen is 2-26%, preferably 10-15%, for example, 10%, 11%, 12%, 13%, 14%, 15%, etc. Controlling the content of halogen within the above preferred range is conducive to further adjusting the appropriate hydrophobicity of the pores inside the membrane and forming an appropriate pore size, thereby facilitating further improving the permeability and molecular interception performance of the nanofiltration separation membrane to non-polar solvents.

[0016] In the present invention, the halogen content in the separation layer is measured by X-ray photoelectron spectroscopy.

[0017] According to the present invention, preferably, the porosity of the separation layer of the nanofiltration composite membrane is 20-65%, preferably 40-60%.

[0018] In the present invention, the porosity of the nanofiltration composite membrane separation layer is measured by the Archimedes buoyancy method.

[0019] According to some preferred embodiments of the present invention, the pore size of the base membrane is in the range of 0.1-5 μm, preferably 0.1-1 μm.

[0020] In the present invention, the polymer forming the separation layer includes repeating structural units containing aromatic rings, wherein the aromatic rings of some repeating structural units are connected to halogen substituents. The polymer forming the separation layer can be obtained by polymerization of compounds of any structural composition, as long as the CC coupled conjugated microporous structure can be constructed, and there is no particular limitation on the source of the repeating structural units mentioned above.

[0021] According to some preferred embodiments of the present invention, the repeating structural unit connected with a halogen substituent is derived from a compound I as shown in formula (1), Formula (1), Among them, R1, R2, R3, R4, R5, and R6 are each independently selected from any one of H, C1-C6 substituted or unsubstituted alkyl, C6-C12 substituted or unsubstituted aryl, amine, acetyl, and halogen substituents, and R1, R2, R3, R4, R5, and R6 contain at least one acetyl group and one halogen substituent.

[0022] In the present invention, the C1-C6 alkyl group may be, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, or the like, or isomers thereof, and the alkyl group may or may not contain a substituent, and the substituent may be selected from any one of an aromatic group, an amino group, an acetyl group, and a halogen substituent.

[0023] In the present invention, the C6-C12 substituted or unsubstituted aryl group may be, for example, a substituted or unsubstituted phenyl group, a biphenyl group, etc., and the substituent in the aryl group may also be selected from any one of an aryl group, an amine group, an acetyl group, and a halogen substituent group.

[0024] According to some preferred embodiments of the present invention, the remaining repeating structural units not containing halogen substituents are derived from compound II represented by formula (2), Formula (2), Wherein, R1', R2', R3', R4', R5', R6' are each independently selected from any one of H, C1-C6 substituted or unsubstituted alkyl, C6-C12 substituted or unsubstituted aryl, amine, and acetyl, and R1', R2', R3', R4', R5', R6' contain at least one acetyl, preferably at least two acetyl. In the above preferred case, it is beneficial for super acid to catalyze acetyl cross-linking to form a network structure and improve chemical stability.

[0025] The specific selection range of each of the above substituents is the same as above and will not be repeated here.

[0026] In the present invention, the halogen substituent may be any substituent containing halogen, preferably containing fluorine and / or chlorine, for example, a halogen atom or a halogenated hydrocarbon group. The halogenated hydrocarbon group is preferably a C1-C6 halogenated hydrocarbon, specifically at least one of a fluoromethyl, a fluoroethyl, a fluoropropyl, and a fluorocyclohexyl group. The present invention has no particular limitation on the number of halogen atoms in the halogenated hydrocarbon. Preferably, the halogenated hydrocarbon is selected from at least one of a difluoromethyl, a trifluoromethyl, a fluorocyclohexyl, and a fluoroaromatic hydrocarbon.

[0027] According to some preferred embodiments of the present invention, some of the repeating structural units connected with halogen substituents are derived from acetyl compounds containing halogen substituents, preferably 2-fluoroacetophenone, 3-fluoroacetophenone, 4-fluoroacetophenone, 2,3-difluoroacetophenone, 3,4-difluoroacetophenone, 3,5-difluorobenzophenone, 2,6-difluoroacetophenone, 2,2,2-trifluoroacetophenone, 2,4,6-trifluoroacetophenone, 2′-(trifluoromethyl)acetophenone, 4′-(trifluoromethyl)acetophenone, 2,3,4,5-tetrafluoroacetophenone, 2′,3′,4′,5′,6′-pentafluoroacetophenone, 2′,4′-di(trifluoromethyl)acetophenone, 3,5- At least one of bis(trifluoromethyl)acetophenone, 2,2,2-trifluoro-3′-(trifluoromethyl)acetophenone, 2′-fluoro-4′,6′-bis(trifluoromethyl)acetophenone, 1-(2,6-difluoro-4-methylphenyl)ethanone, 2,2,2-trifluoro-4′-methylacetophenone, 1-(2-fluorocyclohexyl)ethanone and 2,4-difluoro-3-trifluoromethylacetophenone; more preferably at least one of 4-fluoroacetophenone, 3,4-difluoroacetophenone, 4′-(trifluoromethyl)acetophenone, 2,3,4,5-tetrafluoroacetophenone, 2′,3′,4′,5′,6′-pentafluoroacetophenone and 2′,4′-bis(trifluoromethyl)acetophenone.

[0028] According to some preferred embodiments of the present invention, the remaining repeating structural units that do not contain halogen substituents are derived from multifunctional acetyl compounds, preferably at least one of 1,2-diacetylbenzene, 1,3-diacetylbenzene, 1,4-diacetylbenzene, N,N′-acetyl-1,4-phenylenediamine, 1,3,5-triacetylbenzene, diacetylaminobenzene, N,N-diacetyl-o-[extended]phenylenediamine, 4,4′-diacetylbiphenyl, 2,2′-diacetylbiphenyl, 4,4′-diacetyldiarylethane, 4,4′-diacetyl-o-terphenyl and 1,3,5-tri(4-acetylphenyl)benzene, and further preferably at least one of 1,3-diacetylbenzene, 1,4-diacetylbenzene, 1,3,5-triacetylbenzene and 4,4′-diacetylbiphenyl.

[0029] The use of the above-mentioned preferred multifunctional acetyl compound and the acetyl compound containing a halogen substituent to form a polymer having a CC conjugated microporous structure is beneficial to improving the affinity of the membrane for non-polar solvents and the flux of non-polar solvents.

[0030] On the other hand, the present invention provides a nanofiltration composite membrane, which includes a base membrane and a separation layer composited in the pores and / or on the surface of the base membrane; the separation layer includes a repeating structure unit i and a repeating structure unit ii, the repeating structure unit i is derived from an acetyl aromatic compound containing a halogen substituent, and the repeating structure unit ii is derived from an acetyl aromatic compound not containing a halogen substituent; based on the total molar amount of chemical elements in the separation layer, the molar content of halogen is not less than 2%; the porosity of the separation layer of the nanofiltration composite membrane is not less than 20%.

[0031] A second aspect of the present invention provides a method for preparing a nanofiltration composite membrane, comprising: (1) in the presence of a catalyst, subjecting compound I and compound II to a prepolymerization reaction to obtain a prepolymerization solution; the molar ratio of compound I to compound II is (0.1-10):1; Wherein, compound I has a structure as shown in formula (1), Formula (1), Wherein, R1, R2, R3, R4, R5, and R6 are each independently selected from any one of H, C1-C6 substituted or unsubstituted alkyl, C6-C12 substituted or unsubstituted aryl, amine, acetyl, and halogen substituents, and R1, R2, R3, R4, R5, and R6 contain at least one acetyl group and one halogen substituent; Compound II has a structure as shown in formula (2), Formula (2), Wherein, R1', R2', R3', R4', R5', and R6' are each independently selected from any one of H, a C1-C6 substituted or unsubstituted alkyl group, a C6-C12 substituted or unsubstituted aryl group, an amine group, and an acetyl group, and R1', R2', R3', R4', R5', and R6' contain at least one acetyl group, preferably contain at least two acetyl groups; (2) contacting the base film with the prepolymerization solution to perform deep polymerization to obtain a composite film precursor; (3) Washing and drying the composite membrane precursor.

[0032] The preparation method of the nanofiltration composite membrane provided by the present invention adopts compound I and compound II as polymerization reaction monomers to undergo prepolymerization, and then contacts with a base membrane for deep polymerization, so that a separation layer with a CC-coupled conjugated microporous structure can be formed in the pores and / or on the surface of the base membrane. By controlling the ratio of compound I and compound II, the content of the halogen substituent can be adjusted, and then the hydrophobicity and pore structure of the separation layer can be adjusted. The conjugated microporous composite membrane prepared by the present invention has excellent acid and alkali resistance due to its CC-coupled chemical structure, and can overcome the shortcomings of poor non-polar solvent permeability and poor chemical stability.

[0033] In the present invention, the specific structures of compound I and compound II have been described in detail in the first aspect and will not be repeated here.

[0034] According to the present invention, in step (1), the molar ratio of compound I to compound II is (0.1-10):1, for example, it can be 0.1:1, 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 and other specific but non-limiting molar ratios. Preferably, the molar ratio of compound I to compound II is (0.3-6):1. Controlling the molar ratio of compound I to compound II within the above preferred range is conducive to obtaining a suitable halogen content and separation layer porosity, thereby ensuring high non-polar solvent permeability and good molecular separation performance. A higher halogen content will form steric hindrance, resulting in a decrease in the conjugated micropore porosity, while a lower halogen content has limited ability to enhance non-polar solvents.

[0035] According to the present invention, the selection range of the conditions for the prepolymerization reaction in step (1) is relatively wide, as long as the conditions can allow compound I and compound II to undergo preliminary polymerization.

[0036] According to some preferred embodiments of the present invention, in step (1), the temperature of the prepolymerization reaction is 40-90°C, preferably 60-70°C, and the reaction time is 2-30h, preferably 4-24h. The above preferred embodiments are used to facilitate the uniform occurrence of the superacid-catalyzed acetyl reaction and obtain a relatively viscous prepolymerization solution suitable for coating on a porous substrate.

[0037] The present invention has a wide range of selection for the catalyst in step (1), which is based on the ability to catalyze the prepolymerization reaction. Preferably, the catalyst is an organic acid, particularly preferably an organic strong acid, such as at least one of trifluoromethanesulfonic acid, carborane acid, fluorosulfonic acid, fluoroantimonic acid, chlorosulfonic acid, magic acid, methanesulfonic acid and p-toluenesulfonic acid, preferably at least one of trifluoromethanesulfonic acid, methanesulfonic acid and p-toluenesulfonic acid. The use of the preferred organic strong acid to catalyze the cyclotrimerization reaction of the acetyl monomer is conducive to the construction of a chemically inert CC rigid skeleton, avoiding the problem of easy swelling of existing membrane materials.

[0038] According to the present invention, preferably, in step (1), the prepolymerization reaction is carried out in the presence of an organic solvent.

[0039] Preferably, step (1) comprises: mixing compound I, compound II, a catalyst and an organic solvent, performing a prepolymerization reaction, and obtaining a prepolymerization solution. The present invention has no particular requirements for the mixing order of the catalyst, compound I, compound II and organic solvent. Preferably, compound I and compound II are first dissolved in an organic solvent and then mixed with the catalyst. The above preferred embodiment is adopted to facilitate uniform dispersion of the compounds, avoid excessively fast and uneven reaction of compound I or compound II, and thus further improve the separation performance of the obtained nanofiltration composite membrane.

[0040] The present invention has no particular limitation on the amount of the organic solvent, as long as it can fully disperse the reaction components. Preferably, the total molar amount of compound I and compound II is 0.1-5 mol, preferably 0.1-1 mol, relative to the total volume of 1L of catalyst and organic solvent.

[0041] Further preferably, the volume ratio of the organic solvent to the catalyst is 1:(0.05-1), preferably 1:(0.1-0.5).

[0042] The present invention has a wide range of choices for the base membrane, and any conventional base membrane that can be used for solvent-resistant nanofiltration composite membranes in the art can be applied to the present invention, for example, the material of the base membrane is selected from at least one of polytetrafluoroethylene, polypropylene, polyvinylidene fluoride, polyamide, polyetheretherketone and polybenzimidazole, preferably polytetrafluoroethylene and / or polypropylene. The use of the above preferred base membrane is conducive to further exerting the synergistic effect of the base membrane and the separation membrane, thereby further improving the permeability and chemical stability of the non-polar solvent of the prepared nanofiltration composite membrane.

[0043] The present invention has no particular limitation on the contact method between the base film and the prepolymer solution in step (2). Preferably, the contact method in step (2) includes: impregnating the base film with the prepolymer solution, or coating the prepolymer solution on the surface of the base film.

[0044] When the contacting is performed by immersion, preferably, the contacting time is 1-15 min, preferably 3-5 min.

[0045] When the contact is performed by coating, any conventional coating process in the art may be used, such as scraping, spin coating, dip coating, etc., and the present invention has no particular limitation on this.

[0046] Preferably, the reaction temperature of the deep polymerization is 50-150° C., preferably 70-110° C., and the reaction time is 2-30 h, preferably 4-24 h.

[0047] In the present invention, by controlling the above-mentioned preferred prepolymerization and deep polymerization conditions, it is advantageous to control the speed and film-forming properties of the superacid-catalyzed acetyl cyclotrimerization reaction.

[0048] In the present invention, the catalyst, monomers and oligomers not involved in the reaction, etc. are removed by washing in step (3). The present invention has no particular limitation on the specific manner of washing, so long as the above washing purpose is achieved. Preferably, the washing agent is selected from at least one of water, methanol and tetrahydrofuran.

[0049] According to some preferred embodiments of the present invention, the washing comprises: immersing the composite membrane precursor in water, methanol and tetrahydrofuran in sequence for washing.

[0050] According to some preferred embodiments of the present invention, the preparation method further comprises: contacting the washed composite membrane precursor with a pore preserving agent, and then performing the drying. Preferably, the pore preserving agent is selected from at least one of glycerol, polyethylene glycol, camphorsulfonic acid, triethylamine, and sodium dodecyl sulfate. The above preferred embodiments are used to protect the porosity of the nanofiltration membrane to a greater extent and avoid shrinkage and deformation of the membrane.

[0051] The third aspect of the present invention provides the use of the nanofiltration composite membrane described in the first aspect or the nanofiltration composite membrane prepared by the above preparation method in hydrocarbon separation, catalyst recovery, drug purification and organic solvent recovery.

[0052] The present invention will be described in detail below through examples.

[0053] Example 1 1) 0.66 mmol of 1,3,5-triacetylbenzene and 0.66 mmol of 2′,3′,4′,5′,6′-pentafluoroacetophenone were placed in a 25 mL round-bottom flask, 6 mL of tetrahydrofuran was added at room temperature, and then the temperature was raised to 60 °C for stirring; after the monomer was fully dissolved, 0.6 mL of trifluoromethanesulfonic acid was quickly added, the monomer concentration was 0.2 mol / L, and the reaction was carried out for 24 h to obtain a prepolymer solution; 2) The prepolymerized solution was poured into a culture dish, and a polytetrafluoroethylene-based membrane (pore size of 0.45 μm) was placed in the dish and immersed for 5 min. After being taken out, the mixture was further polymerized in a 70 °C oven for 24 h to obtain a composite membrane precursor. 3) The composite membrane precursor is sequentially immersed in water, methanol and tetrahydrofuran for washing, and then immersed in glycerol and dried to obtain a composite membrane denoted as P1.

[0054] Actual picture Figure 1 The surface chemical structure was characterized by FTIR, and the results are shown in Figure 2 As shown, it can be seen that at 1000-1300 cm -1 The vibration absorption peak of the CF bond was observed nearby, proving that the fluorine element was successfully introduced into the conjugated microporous structure.

[0055] The physicochemical characteristics of the composite membrane P1 are shown in Table 1.

[0056] Comparative Example 1 1) Place 0.66 mmol of 1,3,5-triacetylbenzene in a 25 mL round-bottom flask, add 6 mL of tetrahydrofuran at room temperature, and then heat to 60 °C for stirring; after the monomer is fully dissolved, quickly add 0.6 mL of trifluoromethanesulfonic acid and react for 24 h to obtain a prepolymer solution.

[0057] 2) Pour the prepolymerized solution into a culture dish and quickly place it into a polytetrafluoroethylene-based membrane (pore size 0.45 μm) and immerse it for 5 min. After taking it out, place it in a 70 °C oven for further polymerization for 24 h.

[0058] 3) The composite membrane was sequentially immersed in water, methanol and tetrahydrofuran for washing, and then immersed in glycerol and dried to obtain a composite membrane denoted as DP1. The physicochemical characteristics of the composite membrane DP1 are shown in Table 1.

[0059] Comparative Example 2 (Polyamide Nanofiltration Composite Membrane) 1) dissolving polyimide in N,N-dimethylformamide to obtain a 22 wt% polymer solution, standing overnight and centrifuging to obtain a degassed polymer casting solution; 2) The casting solution was coated on the polyester non-woven fabric with a coating thickness of 250 μm, and then the fabric was quickly immersed in water for phase inversion to obtain a polyimide base membrane; the base membrane was then transferred to pure water and soaked for 2 h, and then immersed in 120 g / L hexamethylenediamine / isopropanol solvent for cross-linking for 16 h, and finally washed with isopropanol for 3 h to obtain an organic solvent-resistant base membrane.

[0060] 3) Interfacial polymerization was carried out on the polyimide-based membrane. It was first immersed in a 3 wt% aqueous solution of m-phenylenediamine for 5 minutes. After the aqueous phase was discarded, the surface moisture was blown dry with an air gun; then a 0.15 w / v% n-hexane solution of trimesoyl chloride was poured onto the membrane surface for 1 minute; after the oil phase was discarded, the membrane surface was immediately rinsed with n-hexane, and then placed in a 60 °C oven for curing for 10 minutes to obtain an organic solvent-resistant nanofiltration membrane, which was recorded as DP2. The physicochemical characteristics of the composite membrane DP2 are shown in Table 1.

[0061] Example 2 1) Place 0.5 mmol of 1,3,5-triacetylbenzene and 3 mmol of 2′,3′,4′,5′,6′-pentafluoroacetophenone in a 25 mL round-bottom flask, add 6 mL of tetrahydrofuran at room temperature, and then heat to 60 °C for stirring; after the monomer is fully dissolved, add 3 mL of trifluoromethanesulfonic acid, the monomer concentration is 0.4 mol / L, and react for 24 h to obtain a prepolymer solution; 2) Pour the prepolymerized solution into a culture dish, quickly put in a polytetrafluoroethylene-based membrane (pore size 1 μm) and immerse for 5 min, then take it out and place it in a 110 °C oven for further polymerization for 4 h to obtain a composite membrane precursor; 3) The composite membrane precursor was sequentially soaked in water, methanol and tetrahydrofuran for washing, then soaked in glycerol and dried to obtain a composite membrane denoted as P2. The physicochemical characteristics of the composite membrane P2 are shown in Table 1.

[0062] Example 3 1) 5.4 mmol of 1,3-diacetobenzene and 1.8 mmol of 4′-(trifluoromethyl)acetophenone were placed in a 25 mL round-bottom flask, 6 mL of toluene was added at room temperature, and then the temperature was raised to 50 °C for stirring; after the monomer was fully dissolved, 1.2 mL of p-toluenesulfonic acid was quickly added, the monomer concentration was 0.75 mol / L, and the reaction was carried out for 4 hours to obtain a prepolymer solution; 2) Pour the prepolymerized solution into a culture dish, quickly put in a polytetrafluoroethylene-based membrane (pore size 0.1 μm) and immerse for 5 min, then take it out and place it in a 90 °C oven for further polymerization for 12 h to obtain a composite membrane precursor; 3) The composite membrane precursor was sequentially soaked in water, methanol and tetrahydrofuran for washing, then soaked in glycerol and dried to obtain a composite membrane denoted as P3. The physicochemical characteristics of the composite membrane P3 are shown in Table 1.

[0063] Example 4 1) Place 2.34 mmol of 2,2′-diacetylbiphenyl and 0.26 mmol of 2,3-difluoroacetophenone in a 25 mL round-bottom flask, add 8 mL of acetonitrile at room temperature, and then heat to 40 °C for stirring; after the monomer is fully dissolved, add 0.4 mL of chlorosulfonic acid, the monomer concentration is 0.3 mol / L, and react for 26 hours to obtain a prepolymer solution.

[0064] 2) The prepolymerized solution was poured into a culture dish, and a polytetrafluoroethylene-based membrane (pore size of 2 μm) was quickly placed in the dish and immersed for 15 min. After being taken out, the dish was placed in a 130 °C oven for further polymerization for 2 h to obtain a composite membrane precursor.

[0065] 3) The composite membrane precursor was sequentially soaked in water, methanol and tetrahydrofuran for washing, then soaked in glycerol and dried to obtain a composite membrane denoted as P4. The physicochemical characteristics of the composite membrane P4 are shown in Table 1.

[0066] Example 5 1) Place 0.5 mmol of diethylaminobenzene and 4.9 mmol of 3,5-bis(trifluoromethyl)acetophenone in a 25 mL round-bottom flask, add 6 mL of N,N-dimethylacetamide at room temperature, and then heat to 40 °C for stirring; after the monomer is fully dissolved, add 0.5 mL of fluorosulfonic acid, the monomer concentration is 0.8 mol / L, and react for 30 hours to obtain a prepolymer solution.

[0067] 2) Pour the prepolymerized solution into a culture dish, put in a polytetrafluoroethylene-based membrane (pore size 2 μm) and immerse for 15 min, take it out and place it in a 120°C oven for further polymerization for 4 h to obtain a composite membrane precursor; 3) The composite membrane precursor was sequentially soaked in water, methanol and tetrahydrofuran for washing, then soaked in glycerol and dried to obtain a composite membrane denoted as P5. The physicochemical characteristics of the composite membrane P5 are shown in Table 1.

[0068] Example 6 1) Place 0.4 mmol of 4,4′-diacetyl o-terphenyl and 3.3 mmol of 2,4-difluoro-3-trifluoromethylacetophenone in a 25 mL round-bottom flask, add 3 mL of acetone at room temperature, and then heat to 90 °C for stirring; after the monomer is fully dissolved, quickly add 3 mL of fluoroantimonic acid, the monomer concentration is 0.62 mol / L, react for 2 hours, and obtain a prepolymer solution; 2) Pour the prepolymerized solution into a culture dish, quickly put in a polytetrafluoroethylene-based membrane (pore size 5 μm) and immerse for 1 min, then take it out and place it in a 120 °C oven for further polymerization for 4 h to obtain a composite membrane precursor; 3) The composite membrane precursor was alternately soaked in water, methanol and tetrahydrofuran for washing, then soaked in glycerol and dried to obtain a composite membrane denoted as P6. The physicochemical characteristics of the composite membrane P6 are shown in Table 1.

[0069] Example 7 The method of Example 1 is followed, except that the glycerol soaking step is not performed, and the composite membrane precursor after washing in step 3) is directly dried to obtain a composite membrane P7.

[0070] Comparative Example 3 1) Place 0.66 mmol of 1,3,5-triacetophenone and 0.66 mmol of 2′,3′,4′,5′,6′-pentafluoroacetophenone in a 25 mL round-bottom flask, add 6 mL of tetrahydrofuran at room temperature, and quickly add 0.6 mL of trifluoromethanesulfonic acid after the monomers are fully dissolved; 2) The solution was quickly poured into a culture dish, and a polytetrafluoroethylene-based membrane (pore size: 0.45 μm) was placed in the dish and immersed for 5 min. After being taken out, the dish was placed in a 70 °C oven for polymerization for 24 h to obtain a composite membrane precursor. 3) The composite membrane precursor was sequentially immersed in water, methanol and tetrahydrofuran for washing, and then immersed in glycerol and dried to obtain a composite membrane denoted as DP3.

[0071] The physicochemical characteristics of composite membrane DP3 are shown in Table 1.

[0072] Table 1

[0073] Test Case (1) Separation membrane performance test: Solvent flux test of separation membrane. Solvent flux is the amount of solvent that passes through a unit membrane area (A, m2) per unit time (t, h) under unit pressure (P, bar) under certain operating pressure conditions. 2) of the solvent volume (V, L); put the separation membrane into a dead-end filtration device (HP4750, Sterlitech), operate it under a certain pressure, and record the flow rate of the solvent per unit time; finally, the solvent flux is calculated according to the following formula: P = V / (A·t·∆P); The interception performance test of the separation membrane is that the interception rate is the ability of the membrane to prevent the components in the feed liquid from passing through or to intercept a certain component. The interception rate test is performed by measuring the concentration difference (C P ) and the solute concentration of the raw material solution (C F ), the calculation formula is as follows: R = (1-C P / C F )×100%; The raw materials are methanol containing 50 mg / L of acid fuchsin (molecular weight: 585.5 g / mol) and methyl blue (molecular weight: 799.80 g / mol) small molecule dyes; the flux of pure solvent n-hexane. A dead-end test device was used, and the test was conducted at room temperature and 5 bar pressure for 72 h.

[0074] The long-term operating flux and molecular retention rate of the nanofiltration composite membranes prepared in the above examples and comparative examples are shown in Table 2.

[0075] Table 2

[0076] It can be seen from the test results of Table 2 that under long-term testing, relative to the comparative example, the composite nanofiltration membrane prepared in the embodiment of the present invention has excellent retention performance for small molecule acid fuchsin and methyl blue. Comparative Example 1 and Comparative Example DP1 test results show that compared with the composite membrane prepared without adding fluorinated acetyl monomers, that is, only constructing a CC rigid skeleton, the fluorinated conjugated microporous organic solvent-resistant nanofiltration membrane significantly improves the permeation flux of non-polar solvents while reducing the molecular weight cutoff. Comparative Example 1 and Comparative Example DP3 test results show that the base membrane is difficult to be infiltrated without the pre-polymerization stage, and the film-forming property is very poor, resulting in no formation of a dense separation layer. By comparing DP2, it can be found that the conjugated microporous composite membrane has a significant non-polar solvent flux advantage over the polyamide composite membrane prepared by the traditional interfacial polymerization method, which is mainly due to the high porosity of the conjugated microporous skeleton, and the introduction of fluorine-containing elements enhances the interaction between the non-polar solvent and the membrane.

[0077] (2) Test of acid and alkali resistance of separation membrane: At room temperature, the composite membranes prepared in the above embodiments and comparative examples were immersed in 5M hydrochloric acid solution and 5M sodium hydroxide solution for 15 days, respectively, and finally transferred to pure water for rinsing, and the aqueous solution was replaced with methanol to test its organic solvent nanofiltration separation performance. The test raw materials were methanol containing 50 mg / L of Congo red (molecular weight: 696.68 g / mol) small molecule dye and pure solvent n-hexane. A dead-end test device was used, and the test was carried out at room temperature at a pressure of 5 bar for 72 h.

[0078] Table 3 shows the permeation flux of n-hexane and methanol and the retention rate of Congo red in methanol of the composite nanofiltration membrane before and after immersion in 5M hydrochloric acid solution.

[0079] Table 3

[0080] Table 4 shows the permeation flux of the composite nanofiltration membrane for n-hexane and methanol and the retention rate of Congo red in methanol before and after soaking in 5M sodium hydroxide solution.

[0081] Table 4

[0082] Combining the results in Table 3 and Table 4, it can be seen that, compared with the comparative example, the nanofiltration composite membrane prepared in the embodiment of the present invention has excellent acid and alkali resistance and good chemical stability.

[0083] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A nanofiltration composite membrane, characterized in that: The nanofiltration composite membrane comprises a base membrane and a separation layer composited in the pores and / or on the surface of the base membrane; the polymer forming the separation layer comprises repeating structural units containing aromatic rings, wherein the aromatic rings of some repeating structural units are connected to halogen substituents; The molar content of halogen is 2-26% based on the total molar amount of chemical elements contained in the separation layer; The porosity of the separation layer of the nanofiltration composite membrane is 20-65%.

2. The nanofiltration composite membrane according to claim 1, wherein Based on the total molar amount of chemical elements contained in the separation layer, the molar content of halogen is 10-15%; The porosity of the separation layer of the nanofiltration composite membrane is 40-60%; The pore size of the base film is 0.1-5 μm.

3. The nanofiltration composite membrane according to claim 1 or 2, wherein: Some of the repeating structural units connected with halogen substituents are derived from compound I as shown in formula (1), Formula (1), Wherein, R1, R2, R3, R4, R5, and R6 are each independently selected from any one of H, C1-C6 substituted or unsubstituted alkyl, C6-C12 substituted or unsubstituted aryl, amine, acetyl, and halogen substituents, and R1, R2, R3, R4, R5, and R6 contain at least one acetyl group and one halogen substituent; The remaining repeating structural units not containing halogen substituents are derived from compound II represented by formula (2), Formula (2), Wherein, R1', R2', R3', R4', R5', and R6' are each independently selected from any one of H, C1-C6 substituted or unsubstituted alkyl, C6-C12 substituted or unsubstituted aryl, amine, and acetyl, and at least one acetyl is contained in R1', R2', R3', R4', R5', and R6'; The halogen substituent is at least one of a halogen atom and a C1-C6 halogenated hydrocarbon.

4. The nanofiltration composite membrane according to claim 3, wherein: Some of the repeating structural units with halogen substituents attached are derived from 2-fluoroacetophenone, 3-fluoroacetophenone, 4-fluoroacetophenone, 2,3-difluoroacetophenone, 3,4-difluoroacetophenone, 3,5-difluorobenzophenone, 2,6-difluoroacetophenone, 2,2,2-trifluoroacetophenone, 2,4,6-trifluoroacetophenone, 2′-(trifluoromethyl)acetophenone, 4′-(trifluoromethyl)acetophenone, 2,3,4,5-tetrafluoroacetophenone, 2′,3′,4′,5′, At least one of 6′-pentafluoroacetophenone, 2′,4′-bis(trifluoromethyl)acetophenone, 3,5-bis(trifluoromethyl)acetophenone, 2,2,2-trifluoro-3′-(trifluoromethyl)acetophenone, 2′-fluoro-4′,6′-bis(trifluoromethyl)acetophenone, 1-(2,6-difluoro-4-methylphenyl)ethanone, 2,2,2-trifluoro-4′-methylacetophenone, 1-(2-fluorocyclohexyl)ethanone and 2,4-difluoro-3-trifluoromethylacetophenone; The remaining repeating structural units without halogen substituents are derived from at least one of 1,2-diacetylbenzene, 1,3-diacetylbenzene, 1,4-diacetylbenzene, N,N′-diacetyl-1,4-phenylenediamine, 1,3,5-triacetylbenzene, diacetylaminobenzene, N,N-diacetyl-o-[extended]phenylenediamine, 4,4′-diacetylbiphenyl, 2,2′-diacetylbiphenyl, 4,4′-diacetyldiarylethane, 4,4′-diacetyl-o-terphenyl and 1,3,5-tri(4-acetylphenyl)benzene; The halogen substituent is selected from at least one of a fluorine atom, a difluoromethyl group, a trifluoromethyl group, a fluorocyclohexyl group, and a fluoroaromatic group.

5. A method for preparing a nanofiltration composite membrane, comprising: (1) in the presence of a catalyst, subjecting compound I and compound II to a prepolymerization reaction to obtain a prepolymerization solution; The molar ratio of compound I to compound II is (0.1-10): 1; Wherein, compound I has a structure as shown in formula (1), Formula (1), Wherein, R1, R2, R3, R4, R5, and R6 are each independently selected from any one of H, C1-C6 substituted or unsubstituted alkyl, C6-C12 substituted or unsubstituted aryl, amine, acetyl, and halogen substituents, and R1, R2, R3, R4, R5, and R6 contain at least one acetyl group and one halogen substituent; Compound II has a structure as shown in formula (2), Formula (2), wherein R1', R2', R3', R4', R5', and R6' are each independently selected from any one of H, a C1-C6 substituted or unsubstituted alkyl group, a C6-C12 substituted or unsubstituted aryl group, an amine group, and an acetyl group, and at least one of R1', R2', R3', R4', R5', and R6' contains an acetyl group; (2) contacting the base film with the prepolymerization solution to perform deep polymerization to obtain a composite film precursor; (3) Washing and drying the composite membrane precursor.

6. The preparation method according to claim 5, wherein: In step (1), the molar ratio of compound I to compound II is (0.3-6):1; In step (1), the prepolymerization reaction temperature is 40-90° C., and the reaction time is 2-30 hours.

7. The preparation method according to claim 5 or 6, wherein: In step (1), the catalyst is selected from at least one of trifluoromethanesulfonic acid, carborane acid, fluorosulfonic acid, fluoroantimonic acid, chlorosulfonic acid, magic acid, methanesulfonic acid and p-toluenesulfonic acid; In step (1), the prepolymerization reaction is carried out in the presence of an organic solvent, and the volume ratio of the organic solvent to the catalyst is 1:(0.05-1); Relative to the total volume of 1L of the catalyst and the organic solvent, the total molar amount of the compound I and the compound II is 0.1-1 mol.

8. The preparation method according to claim 5 or 6, wherein: In step (2), the material of the base film is selected from at least one of polytetrafluoroethylene, polypropylene, polyvinylidene fluoride, polyamide, polyetheretherketone and polybenzimidazole; The contacting method in step (2) includes: impregnating the base film with a prepolymer solution, or coating the prepolymer solution on the surface of the base film; The reaction temperature of the deep polymerization is 50-150°C, and the reaction time is 2-30h.

9. The preparation method according to claim 5 or 6, wherein: The washing in step (3) comprises: immersing the composite membrane precursor in a detergent; the detergent is selected from at least one of water, methanol and tetrahydrofuran; The preparation method further comprises: contacting the washed composite membrane precursor with a pore preserving agent, and then performing the drying; the pore preserving agent is selected from at least one of glycerol, polyethylene glycol, camphorsulfonic acid, triethylamine, and sodium dodecyl sulfate.

10. Use of the nanofiltration composite membrane according to any one of claims 1 to 4 or the nanofiltration composite membrane prepared by the preparation method according to any one of claims 5 to 9 in hydrocarbon separation, catalyst recovery, drug purification and organic solvent recovery.

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