Conjugated microporous organic solvent-resistant nanofiltration composite membrane and its preparation method and application

Abstract

The present invention relates to the technical field of separation membranes, and discloses a conjugated microporous organic solvent-tolerant nanofiltration composite membrane, a preparation method thereof and an application thereof. The nanofiltration composite membrane comprises a base membrane and a separation layer compounded in the pores and / or on the surface of the base membrane; the polymer forming the separation layer comprises a repeating structural unit containing an aromatic ring, wherein halogen substituents are connected to the aromatic rings of some of the repeating structural units; based on the total molar amount of chemical elements contained in the separation layer, the molar content of halogen is 2-26%; the porosity of the separation layer of the nanofiltration composite membrane is 20-65%. The nanofiltration composite membrane has excellent acid and alkali resistance, excellent non-polar solvent permeation performance, and good chemical stability.

Description

Technical Field

[0001] The present invention relates to the technical field of separation membranes, and particularly relates to a conjugated microporous organic solvent-resistant nanofiltration composite membrane, a preparation method thereof, and an 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 cannot be properly treated, they will cause serious environmental pollution. Among the methods for treating 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 drive, the organic solvent-resistant nanofiltration membrane can efficiently separate molecules with molecular weights between 200 and 1000 Da, and can achieve the purification and concentration of high-value organic small molecules, as well as the recovery and reuse of organic solvents, with broad application prospects.

[0003] At present, the flux of organic solvent-resistant nanofiltration membranes for non-polar solvents is generally low, the chemical stability is poor, and the long-term stability is insufficient. The commercial organic solvent-resistant nanofiltration membranes have a 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, coating hydrophobic polymers such as polydimethylsiloxane on a porous support layer. Although non-polar solvents are more easily permeable than polar solvents, due to the random packing of polymer chains, their permeability is not ideal; introducing hydrophobic block functional amines or acyl chloride functional groups during the interfacial polymerization reaction and optimizing the hydrophobicity of the selective layer helps the adsorption and diffusion of non-polar solvents. However, due to the very limited introduction of hydrophobic chain segments, high permeability of non-polar solvents cannot be obtained; in addition, intrinsically microporous polymers can avoid the disadvantage of low porosity caused by the close packing of chain segments in traditional polymer membranes, and can increase the porosity while reducing the liquid transport resistance, but they have problems of swelling and poor long-term stability, and the pore size can change irreversibly, resulting in a significant decrease in separation selectivity. In summary, it is crucial to develop high-flux and high-stability organic solvent-resistant nanofiltration membranes.

[0004] Conjugated microporous polymer membranes have a C-C rigid backbone, are insoluble in organic solvents, have good chemical and structural stability, excellent tolerance to organic solvents, and can be applied to fluid separation under harsh conditions. Wang et al. prepared unsupported conjugated microporous polymer membranes using multifunctional acetyl monomers under the catalysis of methanesulfonic acid (Journal of Materials Chemistry A, 2020, 8, 15891-15899). However, this unsupported membrane is very brittle, which is not conducive to industrial scale-up, and the non-polar solvent flux is relatively low; CN113461912A and CN114524962A respectively disclose a method for preparing a polycyclic aromatic skeleton polymer and a composite membrane. By dissolving an acetyl reaction monomer in an organic solvent and under the catalysis of an acid, a prepolymer solution is first formed, and then the prepolymer solution is modified on the surface of a 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 the permeation flux for non-polar solvents is very low. Therefore, how to overcome the problem of poor non-polar solvent flux of the composite membrane is the key to the application of the composite separation membrane in fields such as hydrocarbon separation, drug purification, and organic solvent recycling and reuse. Summary of the Invention

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

[0006] To achieve the above object, in the first aspect of the present invention, a nanofiltration composite membrane is provided. The nanofiltration composite membrane includes a substrate membrane and a separation layer composite in the pores and / or on the surface of the substrate membrane; the polymer forming the separation layer includes a repeating structural unit containing an aromatic ring, wherein halogen substituents are connected to the aromatic rings of some of the repeating structural units;

[0007] Based on the total molar amount of chemical elements contained in the separation layer, the molar content of halogen is 2-26%;

[0008] The porosity of the separation layer of the nanofiltration composite membrane is 20-65%.

[0009] In the second aspect of the present invention, a preparation method of a nanofiltration composite membrane is provided, including:

[0010] (1) Under the presence of a catalyst, a pre-polymerization reaction is carried out on Compound I and Compound II to obtain a pre-polymerization solution; the molar ratio of Compound I to Compound II is (0.1-10):1;

[0011] Among them, Compound I has the structure shown in Formula (1),

[0012] Formula (1),

[0013] wherein R 1 and R 2 and R 3 and R 4 and R 5 and R 6 are each independently selected from any one of H, substituted or unsubstituted alkyl having 1 to 6 carbon atoms, substituted or unsubstituted aryl having 6 to 12 carbon atoms, amino group, acetyl group, and halogen substituent, and at least one of R 1 and R 2 and R 3 and R 4 and R 5 and R 6 contains at least one acetyl group and at least one halogen substituent;

[0014] Compound II has a structure as shown in Formula (2),

[0015] Formula (2),

[0016] wherein R 1 ', R 2 ', R 3 ', R 4 ', R 5 ', R 6 ' are each independently selected from any one of H, substituted or unsubstituted alkyl having 1 to 6 carbon atoms, substituted or unsubstituted aryl having 6 to 12 carbon atoms, amino group, and acetyl group, and at least one of R 1 ', R 2 ', R 3 ', R 4 ', R 5 ', R 6 ' contains at least one acetyl group, preferably at least two acetyl groups;

[0017] (2) Contact the base film with the prepolymerization solution and perform deep polymerization to obtain a composite membrane precursor;

[0018] (3) Wash and dry the composite membrane precursor.

[0019] 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.

[0020] 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 conjugated microporous structure with C-C coupling, and a halogen substituent is connected to the aromatic ring in some of the repeating structural units containing an aromatic ring. 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 ultra-fast transport 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 conjugated microporous structure with C-C coupling, on the one hand, the appropriate hydrophobicity of the internal pores of 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

[0021] Figure 1 is a physical diagram of the conjugated microporous nanofiltration composite membrane in Example 1 of the present invention;

[0022] Figure 2 is an FTIR diagram of the conjugated microporous nanofiltration composite membrane in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] In the ranges disclosed herein, the endpoints and any values are not limited to the exact 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, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0024] The first aspect of the present invention provides a nanofiltration composite membrane, the nanofiltration composite membrane includes a base membrane and a separation layer composite in the pores and / or on the surface of the base membrane; the polymer forming the separation layer includes a repeating structural unit containing an aromatic ring, wherein a halogen substituent is connected to the aromatic ring in some of the repeating structural units; based on the total molar amount of the chemical elements of the separation layer, the molar content of halogen is 2-26%;

[0025] The porosity of the separation layer of the nanofiltration composite membrane is 20-65%.

[0026] In the present invention, the polymer forming the separation layer includes repeating structural units containing aromatic rings, and the polymer has a C-C coupled conjugated microporous structure. Halogen substituents are connected to the aromatic rings of some of the repeating structural units. It can be understood that the polymer contains some repeating structural units with halogen substituents and the remaining repeating structural units without halogen substituents. The inventors of the present invention found in their research that by controlling the appropriate halogen content and porosity, the interaction between non-polar solvents and the membrane pore structure can be significantly improved, and an ultra-fast transmission channel for non-polar solvents can be constructed. This nanofiltration composite membrane has excellent acid and alkali resistance, excellent non-polar solvent permeability, and good chemical stability.

[0027] Preferably, FTIR is used to characterize the surface chemical structure of the nanofiltration composite membrane, and there is a vibration absorption peak of the C-F bond at 1000 - 1300 cm -1 in it.

[0028] According to some preferred embodiments of the present invention, based on the total molar amount of the chemical elements in the separation layer, the molar content of halogen is 2 - 26%, preferably 10 - 15%, and for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, etc. Controlling the halogen content within the above preferred range is beneficial to further adjusting the appropriate hydrophobicity of the pores inside the membrane, forming appropriate pore sizes, and thus is beneficial to further improving the permeability of the nanofiltration separation membrane to non-polar solvents and the molecular retention performance.

[0029] In the present invention, the halogen content in the separation layer is obtained by X-ray photoelectron spectroscopy analysis and testing.

[0030] According to the present invention, preferably, the porosity of the separation layer of the nanofiltration composite membrane is 20 - 65%, preferably 40 - 60%.

[0031] In the present invention, the porosity of the separation layer of the nanofiltration composite membrane is measured by the Archimedes buoyancy method.

[0032] According to some preferred embodiments of the present invention, the pore size range of the substrate membrane is 0.1 - 5 μm, preferably 0.1 - 1 μm.

[0033] In the present invention, the polymer forming the separation layer includes repeating structural units containing aromatic rings, and among them, halogen substituents are connected to the aromatic rings of some of the repeating structural units. The polymer forming the separation layer can be obtained by polymerization of compounds with any structure, as long as it can construct a C-C coupled conjugated microporous structure, and there is no particular limitation on the source of the above-mentioned repeating structural units.

[0034] According to some preferred embodiments of the present invention, the repeating structural unit connected with a halogen substituent is derived from compound I shown in formula (1).

[0035] Formula (1)

[0036] wherein, R 1 、R 2 、R 3 、R 4 、R 5 、R 6 are each independently selected from any one of H, substituted or unsubstituted alkyl having 1 to 6 carbon atoms, substituted or unsubstituted aryl having 6 to 12 carbon atoms, amino group, acetyl group, and halogen substituent, and at least one of R 1 、R 2 、R 3 、R 4 、R 5 、R 6 contains at least one acetyl group and one halogen substituent.

[0037] In the present invention, the alkyl having 1 to 6 carbon atoms may be, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, etc. or their isomers, and the alkyl may or may not contain a substituent, and the substituent may be selected from any one of aryl, amino group, acetyl group, and halogen substituent.

[0038] In the present invention, the substituted or unsubstituted aryl having 6 to 12 carbon atoms may be, for example, substituted or unsubstituted phenyl, biphenyl, etc., and the substituent in the aryl may also be selected from any one of aryl, amino group, acetyl group, and halogen substituent.

[0039] According to some preferred embodiments of the present invention, the repeating structural unit without a halogen substituent in the remaining part is derived from compound II shown in formula (2).

[0040] Formula (2)

[0041] wherein, R 1 ’, R 2 ’, R 3 ’, R 4 ’, R 5 ’, R 6 ’ are each independently selected from any one of H, substituted or unsubstituted alkyl having 1 to 6 carbon atoms, substituted or unsubstituted aryl having 6 to 12 carbon atoms, amino group, and acetyl group, and R 1 ’, R 2 ’, R 3 ’, R 4 ’, R 5 ’, R 6It contains at least 1 acetyl group, preferably at least 2 acetyl groups. In the above preferred case, it is beneficial for superacid to catalyze the crosslinking of acetyl groups to form a network structure and improve chemical stability.

[0042] The specific selection ranges of the above substituents are the same as those described above and will not be elaborated here.

[0043] In the present invention, the halogen substituent can be any substituent group containing halogen, preferably containing fluorine and / or chlorine, such as a halogen atom or a halogenated hydrocarbon group. The halogenated hydrocarbon group is preferably a C1-C6 halogenated hydrocarbon, specifically can be at least one of fluoromethyl, fluoroethyl, fluoropropyl, fluorocyclohexyl, and the present invention has no special limitation on the number of substituted halogen atoms in the halogenated hydrocarbon. Preferably, the halogenated hydrocarbon is selected from at least one of difluoromethyl, trifluoromethyl, fluorocyclohexyl, and fluoroarene.

[0044] According to some preferred embodiments of the present invention, some of the repeating structural units connected with halogen substituents are from acetyl compounds containing halogen substituents, preferably at least one of 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'-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; 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.

[0045] According to some preferred embodiments of the present invention, the repeating structural unit without halogen substituents in the remainder is derived from a polyfunctional acetyl compound, preferably at least one of 1,2-diacetylbenzene, 1,3-diacetylbenzene, 1,4-diacetylbenzene, N,N'-acetyl-1,4-phenylenediamine, 1,3,5-triacetylbenzene, diacetamidobenzene, N,N-diacetyl-o-phenylenediamine, 4,4'-diacetylbiphenyl, 2,2'-biacetylbiphenyl, 4,4'-diacetyldiarylethane, 4,4'-diacetyl-o-terphenyl, and 1,3,5-tris(4-acetylphenyl)benzene, and further preferably at least one of 1,3-diacetylbenzene, 1,4-diacetylbenzene, 1,3,5-triacetylbenzene, and 4,4'-diacetylbiphenyl.

[0046] Using the above-mentioned preferred polyfunctional acetyl compound and an acetyl compound containing a halogen substituent to form a polymer with a C-C conjugated microporous structure is beneficial to improving the affinity of the membrane for non-polar solvents and the flux of non-polar solvents.

[0047] On the other hand, the present invention provides a nanofiltration composite membrane, which includes a base membrane and a separation layer composite in the pores and / or on the surface of the base membrane; the separation layer includes a repeating structural unit i and a repeating structural unit ii, the repeating structural unit i is derived from an acetyl aromatic compound containing a halogen substituent, and the repeating structural unit ii is derived from an acetyl aromatic compound without a halogen substituent; based on the total molar amount of the 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%.

[0048] The second aspect of the present invention provides a method for preparing a nanofiltration composite membrane, including:

[0049] (1) In the presence of a catalyst, pre-polymerize compound I and compound II to obtain a pre-polymerization solution; the molar ratio of compound I to compound II is (0.1-10):1;

[0050] Among them, compound I has the structure shown in formula (1),

[0051] Formula (1),

[0052] Among them, R 1 、R 2 、R 3 、R 4 、R 5 、R 6 are each independently selected from any one of H, a substituted or unsubstituted alkyl group with 1-6 carbon atoms, a substituted or unsubstituted aryl group with 6-12 carbon atoms, an amino group, an acetyl group, and a halogen substituent, and R 1 、R2 and R 3 and R 4 and R 5 and R 6 contains at least one acetyl group and one halogen substituent;

[0053] Compound II has the structure shown in formula (2),

[0054] Formula (2),

[0055] wherein R 1 ’, R 2 ’, R 3 ’, R 4 ’, R 5 ’, R 6 ’ are each independently selected from any one of H, substituted or unsubstituted alkyl of C1-C6, substituted or unsubstituted aryl of C6-C12, amino group, and acetyl group, and at least one of R 1 ’, R 2 ’, R 3 ’, R 4 ’, R 5 ’, R 6 ’ contains at least one acetyl group, preferably at least two acetyl groups;

[0056] (2) contacting the base film with the prepolymerization solution to carry out deep polymerization to obtain a composite film precursor;

[0057] (3) washing and drying the composite film precursor.

[0058] The preparation method of the nanofiltration composite membrane provided by the present invention uses Compound I and Compound II as polymerization monomers, undergoes prepolymerization, and then contacts with the base film for deep polymerization, which can form a separation layer with a conjugated microporous structure having C-C coupling in the pores and / or on the surface of the base film. By controlling the ratio of Compound I and Compound II, the content of halogen substituents can be adjusted, and thus 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 C-C coupling chemical structure, and can overcome the disadvantages of poor non-polar solvent permeability and poor chemical stability.

[0059] 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 elaborated here.

[0060] 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 specific non-limiting molar ratios such as 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, etc. Preferably, the molar ratio of compound I to compound II is (0.3 - 6):1. Controlling the molar ratio of compound I and compound II within the above preferred range is beneficial to obtaining a suitable halogen content and the porosity of the separation layer, thereby ensuring a high non-polar solvent permeability and good molecular separation performance. A higher halogen content will form steric hindrance, resulting in a decrease in the porosity of the conjugated micropores, while a lower halogen content has limited ability to enhance non-polar solvents.

[0061] According to the present invention, for the selection range of the conditions of the prepolymerization reaction in step (1) is relatively wide, as long as it can enable the preliminary polymerization of compound I and compound II.

[0062] 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 - 30 h, preferably 4 - 24 h. Adopting the above preferred embodiments is beneficial to the uniform occurrence of the superacid-catalyzed acetyl group reaction and obtaining a relatively viscous prepolymer solution suitable for coating on a porous substrate.

[0063] The present invention has a relatively wide selection range for the catalyst in step (1), as long as it can catalyze the progress of the prepolymerization reaction. Preferably, the catalyst is an organic acid, and 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. Using the above preferred organic strong acids to catalyze the cyclotrimerization reaction of acetyl monomers is beneficial to constructing a chemically inert C-C rigid framework and avoiding the problem of easy swelling of existing membrane materials.

[0064] According to the present invention, preferably, in step (1), the prepolymerization reaction is carried out in the presence of an organic solvent.

[0065] Preferably, step (1) includes: mixing compound I, compound II, a catalyst, and an organic solvent, and carrying out a prepolymerization reaction to obtain a prepolymer solution. The present invention has no particular requirements for the mixing order of the catalyst, compound I, compound II, and the organic solvent. Preferably, compound I and compound II are first dissolved in the organic solvent, and then mixed with the catalyst. Adopting the above preferred embodiments is beneficial to the uniform dispersion of the compounds, avoiding the too-fast and uneven reaction of compound I or compound II, thereby further improving the separation performance of the prepared nanofiltration composite membrane.

[0066] The present invention has no special limitation on the dosage of the organic solvent, as long as it can fully disperse each reaction component. Preferably, relative to the total volume of 1 L of the catalyst and the organic solvent, the total molar amount of Compound I and Compound II is 0.1 - 5 mol, preferably 0.1 - 1 mol.

[0067] Further preferably, the volume ratio of the organic solvent to the catalyst is 1:(0.05 - 1), preferably 1:(0.1 - 0.5).

[0068] The present invention has a wide selection range for the base film. Any conventional base film 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 film is selected from at least one of polytetrafluoroethylene, polypropylene, polyvinylidene fluoride, polyamide, polyether ether ketone, and polybenzimidazole, preferably polytetrafluoroethylene and / or polypropylene. Using the above-preferred base film is beneficial to further exert the synergistic effect between the base film and the separation membrane, thereby further improving the permeability and chemical stability of the prepared nanofiltration composite membrane to non-polar solvents.

[0069] The present invention has no special limitation on the contact method between the base film and the prepolymerization solution in step (2). Preferably, the contact method in step (2) includes: impregnating the base film with the prepolymerization solution, or coating the prepolymerization solution on the surface of the base film.

[0070] When the contact is carried out by the impregnation method, preferably, the contact time is 1 - 15 min, preferably 3 - 5 min.

[0071] When the contact is carried out by the coating method, any conventional coating process in the art can be used, such as blade coating, spin coating, dip coating, etc. The present invention has no special limitation on this.

[0072] Preferably, the reaction temperature for the deep polymerization is 50 - 150 °C, preferably 70 - 110 °C, and the reaction time is 2 - 30 h, preferably 4 - 24 h.

[0073] In the present invention, by controlling the above-preferred prepolymerization and deep polymerization conditions, it is beneficial to control the reaction rate and film-forming performance of the superacid-catalyzed acetyl cyclotrimerization reaction.

[0074] In the present invention, the catalyst, unreacted monomers, oligomers, etc. are removed by washing in step (3). The present invention has no special limitation on the specific method of the washing, as long as the above washing purpose is achieved. Preferably, the washing agent is selected from at least one of water, methanol, and tetrahydrofuran.

[0075] According to some preferred embodiments of the present invention, the washing includes: soaking the composite membrane precursor in water, methanol, and tetrahydrofuran in sequence for washing.

[0076] According to some preferred embodiments of the present invention, the preparation method further includes: contacting the washed composite membrane precursor with a pore - protecting agent, and then performing the drying. Preferably, the pore - protecting agent is selected from at least one of glycerol, polyethylene glycol, camphorsulfonic acid, triethylamine, and sodium dodecyl sulfate. By adopting the above - mentioned preferred embodiments, it is beneficial to protect the porosity of the nanofiltration membrane to a greater extent and avoid membrane shrinkage and deformation.

[0077] The third aspect of the present invention provides the application of the nanofiltration composite membrane described in the first aspect or the nanofiltration composite membrane prepared by the above - mentioned preparation method in hydrocarbon separation, catalyst recovery, drug purification, and organic solvent recovery.

[0078] The present invention will be described in detail below through examples.

[0079] Example 1

[0080] 1) Place 0.66 mmol of 1,3,5 - triacetylbenzene and 0.66 mmol of 2′,3′,4′,5′,6′ - pentafluorobenzophenone 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 monomers are fully dissolved, quickly add 0.6 mL of trifluoromethanesulfonic acid, the monomer concentration is 0.2 mol / L, and react for 24 h to obtain a prepolymerization solution;

[0081] 2) Pour the prepolymerization solution into a petri dish, immerse it in a polytetrafluoroethylene - based membrane (pore size 0.45 μm) for 5 min, take it out and place it in an oven at 70 °C for further polymerization for 24 h to obtain a composite membrane precursor;

[0082] 3) Soak the composite membrane precursor in water, methanol, and tetrahydrofuran in sequence for washing, and then soak it in glycerol and air - dry to obtain a composite membrane denoted as P1.

[0083] The physical picture is as Figure 1 shown. The surface chemical structure was characterized by FTIR, and the results are as Figure 2 shown. It can be seen that a vibration absorption peak of the C - F bond is observed near 1000 - 1300 cm -1 to prove that fluorine elements are successfully introduced into the conjugated microporous structure.

[0084] The physical and chemical characteristics of the composite membrane P1 are shown in Table 1.

[0085] Comparative Example 1

[0086] 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 monomers are fully dissolved, quickly add 0.6 mL of trifluoromethanesulfonic acid and react for 24 h to obtain a prepolymerization solution.

[0087] 2) Pour the prepolymerization solution into a petri dish, quickly place it in a polytetrafluoroethylene-based membrane (pore size 0.45 μm) for impregnation for 5 min, take it out and place it in an oven at 70 °C for further polymerization for 24 h.

[0088] 3) Immerse the composite membrane in water, methanol, and tetrahydrofuran in sequence for washing, then soak it in glycerol and air-dry it to obtain a composite membrane denoted as DP1. The physical and chemical characteristics of the composite membrane DP1 are shown in Table 1.

[0089] Comparative Example 2 (polyamide nanofiltration composite membrane)

[0090] 1) Dissolve polyimide in N,N-dimethylformamide to prepare a 22 wt% polymer solution, let it stand overnight and centrifuge to obtain a degassed polymer casting solution;

[0091] 2) Coat the casting solution on a polyester non-woven fabric with a coating thickness of 250 μm, quickly immerse it in water for phase inversion to obtain a polyimide substrate membrane; then transfer the substrate membrane to pure water and soak it for 2 h, then immerse the substrate membrane in a 120 g / L hexamethylenediamine / isopropanol solvent for crosslinking for 16 h, and finally wash it with isopropanol for 3 h to obtain an organic solvent-resistant substrate membrane.

[0092] 3) Conduct interfacial polymerization on the polyimide substrate membrane. First, immerse it in an aqueous solution of 3 wt% m-phenylenediamine for 5 min, pour off the aqueous phase and then use an air gun to dry the surface moisture; then pour a 0.15 w / v% hexane solution of trimesoyl chloride onto the membrane surface and react for 1 min; pour off the oil phase and immediately rinse the membrane surface with hexane, and then place it in an oven at 60 °C for curing for 10 min to obtain an organic solvent-resistant nanofiltration membrane denoted as DP2. The physical and chemical characteristics of the composite membrane DP2 are shown in Table 1.

[0093] Example 2

[0094] 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 monomers are fully dissolved, add 3 mL of trifluoromethanesulfonic acid, the monomer concentration is 0.4 mol / L, and react for 24 h to obtain a prepolymerization solution;

[0095] 2) Pour the pre-polymerization solution into a petri dish, quickly place it in a polytetrafluoroethylene-based membrane (with a pore size of 1 μm) for impregnation for 5 min, take it out and place it in an oven at 110 °C for further polymerization for 4 h to obtain a composite membrane precursor;

[0096] 3) Immerse the composite membrane precursor in water, methanol, and tetrahydrofuran in sequence for washing, then soak it in glycerol and air-dry it to obtain a composite membrane denoted as P2. The physical and chemical characteristics of composite membrane P2 are shown in Table 1.

[0097] Example 3

[0098] 1) Place 5.4 mmol of 1,3-diacetylbenzene and 1.8 mmol of 4'-(trifluoromethyl)acetophenone in a 25 mL round-bottom flask, add 6 mL of toluene at room temperature, and then heat it to 50 °C for stirring; after the monomers are fully dissolved, quickly add 1.2 mL of p-toluenesulfonic acid, the monomer concentration is 0.75 mol / L, and react for 4 h to obtain a pre-polymerization solution;

[0099] 2) Pour the pre-polymerization solution into a petri dish, quickly place it in a polytetrafluoroethylene-based membrane (with a pore size of 0.1 μm) for impregnation for 5 min, take it out and place it in an oven at 90 °C for further polymerization for 12 h to obtain a composite membrane precursor;

[0100] 3) Immerse the composite membrane precursor in water, methanol, and tetrahydrofuran in sequence for washing, then soak it in glycerol and air-dry it to obtain a composite membrane denoted as P3. The physical and chemical characteristics of composite membrane P3 are shown in Table 1.

[0101] Example 4

[0102] 1) Place 2.34 mmol of 2,2'-biacetylbiphenyl 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 it to 40 °C for stirring; after the monomers are fully dissolved, add 0.4 mL of chlorosulfonic acid, the monomer concentration is 0.3 mol / L, and react for 26 h to obtain a pre-polymerization solution.

[0103] 2) Pour the pre-polymerization solution into a petri dish, quickly place it in a polytetrafluoroethylene-based membrane (with a pore size of 2 μm) for impregnation for 15 min, take it out and place it in an oven at 130 °C for further polymerization for 2 h to obtain a composite membrane precursor.

[0104] 3) Immerse the composite membrane precursor in water, methanol, and tetrahydrofuran in sequence for washing, then soak it in glycerol and air-dry it to obtain a composite membrane denoted as P4. The physical and chemical characteristics of composite membrane P4 are shown in Table 1.

[0105] Example 5

[0106] 1) Place 0.5 mmol of diethylamide benzene 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 monomers are fully dissolved, add 0.5 mL of fluorosulfonic acid, with the monomer concentration being 0.8 mol / L, and react for 30 h to obtain a prepolymerization solution.

[0107] 2) Pour the prepolymerization solution into a petri dish, place it in a polytetrafluoroethylene-based membrane (with a pore size of 2 μm) for impregnation for 15 min, take it out and place it in an oven at 120 °C for further polymerization for 4 h to obtain a composite membrane precursor.

[0108] 3) Immerse the composite membrane precursor successively in water, methanol, and tetrahydrofuran for washing, and then soak it in glycerol and dry it to obtain a composite membrane denoted as P5. The physical and chemical characteristics of composite membrane P5 are shown in Table 1.

[0109] Example 6

[0110] 1) Place 0.4 mmol of 4,4′-diacetyl-o-terphenyl and 3.3 mmol of 2,4-difluoro-3-(trifluoromethyl)acetophenone 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 monomers are fully dissolved, quickly add 3 mL of fluoroantimonic acid, with the monomer concentration being 0.62 mol / L, and react for 2 h to obtain a prepolymerization solution.

[0111] 2) Pour the prepolymerization solution into a petri dish, quickly place it in a polytetrafluoroethylene-based membrane (with a pore size of 5 μm) for impregnation for 1 min, take it out and place it in an oven at 120 °C for further polymerization for 4 h to obtain a composite membrane precursor.

[0112] 3) Immerse the composite membrane precursor alternately in water, methanol, and tetrahydrofuran for washing, and then soak it in glycerol and dry it to obtain a composite membrane denoted as P6. The physical and chemical characteristics of composite membrane P6 are shown in Table 1.

[0113] Example 7

[0114] According to the method of Example 1, the difference is that the glycerol soaking step is not carried out, and the composite membrane precursor after washing in step 3) is directly dried to obtain a composite membrane P7.

[0115] Comparative Example 3

[0116] 1) Place 0.66 mmol of 1,3,5-triacetylbenzene 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.

[0117] 2) Pour the solution quickly into a petri dish, place it in a polytetrafluoroethylene-based membrane (pore size: 0.45 μm) and impregnate for 5 min. After taking it out, place it in an oven at 70 °C for polymerization for 24 h to obtain a composite membrane precursor;

[0118] 3) Immerse the composite membrane precursor in water, methanol, and tetrahydrofuran in sequence for washing, then soak it in glycerol and dry it to obtain a composite membrane denoted as DP3.

[0119] The physical and chemical characteristics of the composite membrane DP3 are shown in Table 1.

[0120] Table 1

[0121]

[0122] Test example

[0123] (1) Performance test of the separation membrane:

[0124] For the solvent flux test of the separation membrane, the solvent flux is the volume of solvent (V, L) passing through a unit membrane area (A, m 2 ) per unit time (t, h) under a unit pressure (P, bar) under certain operating pressure conditions; place the separation membrane in a dead-end filtration device (HP4750, Sterlitech), operate it under a certain pressure, and record the solvent flow rate per unit time; finally, calculate the solvent flux according to the following formula:

[0125] P = V / (A·t·∆P);

[0126] For the rejection performance test of the separation membrane, the rejection rate is the ability of the membrane to prevent components in the feed liquid from passing through or to retain a certain component; the rejection rate is tested by measuring the ratio of the concentration difference (C P ) of the solute in the feed liquid and the permeate during membrane filtration to the solute concentration (C F ) of the feed liquid, and its calculation formula is as follows:

[0127] R = (1 - C P / C F ) × 100%;

[0128] The feed liquids are methanol containing 50 mg / L of small molecule dyes acid fuchsin (molecular weight: 585.5 g / mol) and methylene blue (molecular weight: 799.80 g / mol); the flux of pure solvent n-hexane. Using a dead-end test device, test at a pressure of 5 bar for 72 h at room temperature.

[0129] The fluxes and molecular rejection rates of the nanofiltration composite membranes prepared in the above examples and comparative examples during long-term operation are shown in Table 2.

[0130] Table 2

[0131]

[0132] As can be seen from the test results in Table 2, under long-term testing, compared with the comparative examples, the composite nanofiltration membranes prepared in the embodiments of the present invention have excellent retention performance for both small molecule acid fuchsin and methylene blue. By comparing the test results of Example 1 and Comparative Example DP1, it can be found that compared with the composite membrane prepared without adding the fluorinated acetyl monomer, that is, only constructing a C-C rigid skeleton, the fluorinated conjugated microporous organic solvent-resistant nanofiltration membrane not only reduces the retention molecular weight but also significantly improves the permeation flux of non-polar solvents. By comparing the test results of Example 1 and Comparative Example DP3, it can be found that the base membrane without the pre-polymerization stage is difficult to be wetted and has very poor film-forming properties, resulting in the failure to form a dense separation layer. And through comparison with DP2, it can be found that the conjugated microporous composite membrane has an obvious non-polar solvent flux advantage compared with 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 elements enhancing the interaction between non-polar solvents and the membrane.

[0133] (2)Testing the acid and alkali resistance of the separation membrane:

[0134] Under normal temperature conditions, the composite membranes prepared in the above examples and comparative examples were respectively immersed in 5M hydrochloric acid solution and 5M sodium hydroxide solution for 15 days, and finally transferred to pure water for thorough rinsing and then replaced the aqueous solution with methanol to test their organic solvent nanofiltration separation performance. The test feed solutions were methanol containing 50 mg / L of Congo red (molecular weight: 696.68 g / mol) small molecule dye and pure solvent n-hexane respectively. Using a dead-end test device, at room temperature, the test was carried out at a pressure of 5 bar for 72 h.

[0135] Table 3 shows the permeation fluxes of n-hexane and methanol and the retention rate of Congo red in methanol of the above composite nanofiltration membranes before and after immersion in 5M hydrochloric acid solution.

[0136] Table 3

[0137]

[0138] Table 4 shows the permeation fluxes of n-hexane and methanol and the retention rate of Congo red in methanol of the above composite nanofiltration membranes before and after immersion in 5M sodium hydroxide solution.

[0139] Table 4

[0140]

[0141] Combining the results in Table 3 and Table 4, it can be seen that compared with the comparative examples, the nanofiltration composite membranes prepared in the embodiments of the present invention have excellent acid and alkali resistance and good chemical stability.

[0142] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within 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, diacetamidobenzene, N,N-diacetyl-o-phenylenediamine, 4,4′-diacetylbiphenyl, 2,2′-biacetylbiphenyl, 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 fluoroarene 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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