High-permeability and high-selectivity polyamide composite membrane as well as preparation method and application thereof

Abstract

The invention discloses a high-permeability and high-selectivity polyamide composite membrane as well as a preparation method and application thereof, and belongs to the technical field of membrane separation. A compound HCX or HCXH with a hydrophilic imidazole group is used as an intermediate layer material, and then an interfacial polymerization reaction is carried out on the intermediate layer to prepare the polyamide composite membrane. The middle layer constructed by the invention not only effectively regulates and controls the physicochemical properties of the polyamide layer and optimizes the transmission path of water molecules, but also reduces the invasion of the polyamide matrix into the pores of the support layer, thereby reducing the hydraulic resistance. Besides, the intermediate layer improves the concentration of the amine monomer on the surface of the substrate through hydrogen-bond interaction, limits the diffusion rate of the amine monomer to an organic phase, remarkably reduces the effective thickness of the polyamide layer, and finally obtains the high-permeability and high-selectivity polyamide composite membrane.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of preparation and application of separation membranes, and particularly relates to a high-permeability and high-selectivity polyamide composite membrane. BACKGROUND

[0002] Under the dual challenges of global water resource shortage and water pollution, efficient and environmentally friendly water treatment technology has become the key to guarantee water resource safety and sustainable utilization. In this context, membrane separation technology has been widely used in water treatment due to its high treatment efficiency, wide application range, and easy integration with other processes.

[0003] Polyamide composite membranes are dominant in the production and application of reverse osmosis, nanofiltration and forward osmosis due to their excellent chemical stability, mechanical strength and good separation performance. They are usually prepared by interfacial polymerization on a porous support layer. Specifically, the porous support layer is sequentially immersed in an aqueous solution containing a polyamine and an organic phase solution containing a polyacyl chloride, and an interfacial polymerization reaction occurs at the water / organic phase to form a polyamide separation layer. Researchers have found that the construction of an intermediate layer can improve the properties of the support layer (surface pore size and porosity, wettability, etc.), and by affecting the storage of water phase monomers and the diffusion rate of monomers during interfacial polymerization, it can reduce the thickness of the polyamide layer and reduce the mass transfer resistance. On the other hand, the intermediate layer can optimize the water molecule transport path by enhancing the drainage channel effect. Both of the above can improve the permeation and separation performance of the membrane. Patent CN 115672030 A discloses a composite reverse osmosis membrane containing a alginate hydrogel intermediate layer and a preparation method thereof. The alginate hydrogel intermediate layer is generated in situ on the surface of the base membrane, and the diffusion rate of the water phase monomer is regulated by its space network structure, and the interfacial polymerization process is optimized, thereby obtaining a polyamide separation layer with lower crosslinking degree, which is beneficial to increasing the water permeability of the membrane. Patent CN 116272410 A discloses a high-flux nanocomposite membrane containing an ultrathin nanomaterial intermediate layer. The nanomaterial is used to construct an intermediate layer on the surface of the base membrane, and the nanomaterial is doped in the interfacial polymerization aqueous solution, which effectively utilizes the inherent pores of the material and cooperates with the interfacial polymerization reaction to construct an ultrathin separation layer with nanometer mass transfer channels, thereby effectively improving the water flux of the membrane. It can be understood that by adding an intermediate layer, the thickness of the polyamide layer is effectively reduced, and the water flux is improved, but the selectivity is inevitably reduced, and it is difficult to obtain a polyamide composite membrane with high flux and high salt rejection rate. Therefore, the present application provides a polyamide composite membrane that can improve permeability while maintaining selectivity by preparing a compound HC X or HC X H and using it as an intermediate layer. SUMMARY

[0004] Therefore, the present application uses a compound HCX or HC X H builds the intermediate layer and effectively regulates the physicochemical properties of the polyamide layer, promotes the rapid transport of water molecules between the polyamide layer and the support layer, and also shortens the water molecule transport path through the drain effect. At the same time, the coverage of the intermediate layer on the substrate surface reduces the invasion of the polyamide matrix into the pores of the support layer, further reducing the hydraulic resistance. In addition, the imidazole groups in the intermediate layer increase the amine monomer concentration on the substrate surface through hydrogen bonding, and limit the diffusion rate of amine monomers to the organic phase, significantly reducing the effective thickness of the polyamide layer, thereby realizing the preparation of high-performance polyamide composite membranes.

[0005] To achieve the above purpose, the first aspect of the present application provides a preparation method of a high-permeability high-selectivity polyamide composite membrane, specifically comprising the following steps:

[0006] (1) Preparation of compound HC X or HC X H: nucleophilic addition reaction of isocyanate or diisocyanate and histamine to generate compound HC X or HC X H, the structure of isocyanate is R x -N=C=O, the molar ratio of isocyanate to histamine is 1:1, and the structure of diisocyanate is O=C=N-R x -N=C=O, the molar ratio of diisocyanate to histamine is 1:2, wherein R x is an alkyl chain, and x represents the number of carbon atoms in the alkyl chain, preferably 4-10.

[0007] (2) Preparation of the intermediate layer: uniformly spread the ethanol / water solution of compound HC X or HC X H on the surface of the support layer, pour off the excess liquid after standing for a period of time, and air dry.

[0008] (3) Preparation of a polyamide composite membrane: sequentially immerse the surface of the intermediate layer obtained in step (2) in an aqueous solution containing a polyamine and an organic phase solution containing a polyacyl chloride in n-hexane, and generate a polyamide separation layer through interfacial polymerization for a period of time. Finally, the polyamide composite membrane is obtained through post-processing.

[0009] Specifically, the isocyanate includes, but is not limited to, any one of butyl isocyanate, pentyl isocyanate, hexyl isocyanate, heptyl isocyanate. The diisocyanate includes, but is not limited to, any one of 1,4-butane diisocyanate, 1,6-hexane diisocyanate, 1,8-diisocyanatooctane, 1,10-decane diisocyanate. The diisocyanate includes, but is not limited to, any one of 1,4-butane diisocyanate, 1,6-hexane diisocyanate, 1,8-diisocyanatooctane, 1,10-decane diisocyanate. Compound HC X or HC X The preparation of H, specifically: first, the isocyanate or diisocyanate and histamine are added to a mixed organic solvent of tetrahydrofuran, ethyl acetate and acetonitrile, heated to 70-90°C and refluxed for 2-6h. After the mixed solution is cooled, the excess solvent is removed by rotary evaporation. Subsequently, the obtained substance is dissolved in a small amount of ethanol to obtain a saturated solution, and then an excess of n-hexane is added and stirred and centrifuged.

[0010] Further, the volume ratio of ethanol to water in the ethanol / water solution in step (2) is 0.5-8, preferably 1-5. Compound HC X or HC X The concentration of H in the ethanol / water solution is 0.001-0.2 m / v%, preferably 0.0075-0.05 m / v%, for example 0.001 m / v%, 0.002 m / v%, 0.00375 m / v%, 0.0075 m / v%, 0.015 m / v%, 0.025 m / v%, 0.05 m / v%, 0.1 m / v%, 0.2 m / v%, or a range defined by any two of the above values, m is g and v is mL. The deposition time is 1-8 min, preferably 2-4 min.

[0011] The polyamine in step (3) includes, but is not limited to, any one of ethylenediamine, propylenediamine, hexanediamine, m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, piperazine, diethylenetriamine, triethylenetetramine, triaminotriole, N-aminoethylpiperazine, 2,4-diaminotoluene, 2,2-difluoropropane-1,3-diamine, 4-morpholine-m-phenylenediamine, 4-piperazine-m-phenylenediamine, and the concentration of the polyamine in the aqueous solution is 0.1-5 wt.%, preferably 0.5-2 wt.%, and the aqueous solution is immersed for 0.5-8 min, preferably 1-4 min.

[0012] The polybasic acid chloride in the step (3) includes but is not limited to one of benzene triformyl chloride, terephthaloyl chloride, isophthaloyl chloride, phthaloyl chloride, benzene tetracarboxylic acid chloride, cyclohexane diacyl chloride, cyclohexane triformyl chloride, oxalyl chloride, 2,4,4',6-biphenyl tetracarboxylic acid chloride, 2,2',4,4',6,6'-biphenyl tetracarboxylic acid chloride, 2,3',4,5',6-biphenyl pentacarboxylic acid chloride, and the concentration of the polybasic acid chloride in the organic phase solution is 0.01-1 wt.%, preferably 0.05-0.5 wt.%. The time for the organic phase solution to be immersed is 0.1-3 min, preferably 0.5-2 min.

[0013] The temperature for the post-treatment in the step (3) is 40-100℃, preferably 50-70℃; and the time is 2-5 min.

[0014] The support layer material in the step (2) includes but is not limited to any one of polysulfone, polyether sulfone, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyimide, polystyrene, polyester.

[0015] The second aspect of the present application provides a high-permeability and high-selectivity polyamide composite membrane prepared by the method of the first aspect, which comprises a support layer, an intermediate layer and a polyamide layer from bottom to top, the intermediate layer is a compound HC X or HC X H crystal, the crystal structure has a pore structure with a pore size of 0.26 nm, the thickness of the polyamide layer is 22-100 nm, preferably 22-82 nm, for example, 22 nm, 24 nm, 26 nm, 28 nm, 30 nm, 32 nm, 34 nm, 36 nm, 38 nm, 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, 50 nm, 52 nm, 54 nm, 56 nm, 58 nm, 60 nm, 62 nm, 64 nm, 66 nm, 68 nm, 70 nm, 72 nm, 74 nm, 76 nm, 78 nm, 80 nm, 82 nm, 84 nm, 86 nm, 88 nm, 90 nm, 92 nm, 94 nm, 96 nm, 98 nm, 100 nm, or a range defined by any two of the above values.

[0016] Further, the third aspect of the present application provides the application of the high-permeability and high-selectivity polyamide composite membrane in a solution separation process, which can be used in the fields of brackish water treatment and seawater desalination, and has higher water permeability compared with the traditional polyamide composite membrane.

[0017] Compared with the prior art, the present application has the following beneficial effects: (1) the compound HC Xor HC X H is a kind of molecular configuration and synthesis method relatively simple organic molecular compound, as intermediate layer material can effectively improve the interface compatibility with polyamide layer;At the same time, compound HC X or HC X H crystallization forms intermediate layer with specific pore structure, overcomes the problem that polyamide layer may produce defects when using traditional nanomaterials to prepare intermediate layer due to uneven material size and distribution;(2) The intermediate layer prepared in the application promotes the rapid transport of water molecules between the polyamide separation layer and the support layer, and shortens the water molecule transport path through the drainage ditch effect, effectively reducing the problem of increased water molecule transport resistance across the membrane caused by traditional coating type intermediate layer;(3) The application uses compound HC X or HC X H The hydrogen bond between the imidazole group and the amine monomer improves the concentration of the amine monomer stored on the substrate surface and limits its diffusion rate, significantly reducing the effective thickness of the polyamide separation layer and shortening the water transport path;In addition, compound HC X or HC X H Covering on the substrate surface is conducive to reducing the invasion of polyamide matrix into the pores of the support layer, and cooperatively reduces the hydraulic resistance, so that the polyamide composite membrane can maintain high salt retention rate while improving water permeability. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 SEM images of the surface and section of the polyamide layer in Comparative Examples 1-2.

[0019] Figure 2 SEM images of the surface and section of the polyamide layer in Example 1-2.

[0020] Figure 3 SEM images of the section of the polyamide layer in Examples 3-5.

[0021] Figure 4 SEM images of the surface and section of the polyamide layer in Example 6. DETAILED DESCRIPTION

[0022] The application will be further described below through specific examples and comparative examples, which are only used to explain the application, not to limit the application.

[0023] Example 1:

[0024] (1) Preparation of HC4H compound: First, 2 mmol of 1,4-diisocyanatobutane was mixed with 4 mmol of histamine (at a molar ratio of 1:2) and then added to 4 mL of tetrahydrofuran, 2 mL of ethyl acetate and 4 mL of acetonitrile, and the mixture was warmed to 80°C and refluxed for 4 h. After the mixture was cooled, the excess solvent was removed by rotary evaporation as much as possible. Subsequently, the resulting substance was dissolved in a small amount of ethanol to obtain a saturated solution, and then an excess of n-hexane was added and stirred for 30 min, followed by centrifugation (6000 rpm, 10 min). Finally, the product was dried in a vacuum oven at 40°C overnight to obtain a pure white HC4H compound powder.

[0025] (2) Preparation of intermediate layer: The HC4H powder was uniformly dispersed in an ethanol / water solution at a volume ratio of 3 to obtain a solution with a mass concentration of 0.05 m / v%, and the solution was uniformly spread on the surface of the polysulfone support layer. After standing for 3 min, the excess liquid was poured off and naturally air-dried.

[0026] (3) Preparation of polyamide composite membrane: A water phase solution containing 2 wt.% of m-phenylenediamine was uniformly poured onto the surface of the HC4H intermediate layer, and after standing for 2 min, the water phase solution was poured out. After naturally air-drying, an organic phase solution containing 0.1 wt.% of trimesoyl chloride was poured onto the surface, and after interfacial polymerization for 1 min, the excess organic phase solution was poured out and rinsed with a small amount of n-hexane. Finally, it was placed in an oven at 80°C for 3 min to obtain a polyamide composite membrane.

[0027] Example 2:

[0028] (1) Preparation of HC6H compound: Except that 1,4-diisocyanatobutane was replaced by 1,6-diisocyanatohexane, the remaining steps were the same as in Example 1.

[0029] (2) Preparation of intermediate layer: Except that HC4H was replaced by HC6H, the remaining steps were the same as in Example 1.

[0030] (3) Preparation of polyamide composite membrane: Except that HC4H was replaced by HC6H, the remaining steps were the same as in Example 1.

[0031] Examples 3-5:

[0032] Except that the mass concentration of HC6H in step (2) was different, the others were the same as in Example 2 (see Table 1).

[0033] Example 6:

[0034] (1) Preparation of HC6 compound: First, 2 mmol of hexyl isocyanate and 2 mmol of histamine (in a 1 : 1 molar ratio) were mixed and added to 4 mL of tetrahydrofuran, 2 mL of ethyl acetate and 4 mL of acetonitrile, warmed to 80°C and refluxed for 4 h. After the mixture was cooled, the excess solvent was removed as much as possible by rotary evaporation. Subsequently, the resulting material was dissolved in a small amount of ethanol to obtain a saturated solution, and then an excess of n-hexane was added and stirred for 30 min before centrifugation (6000 rpm, 10 min). Finally, the product was dried in a vacuum oven at 40°C overnight to obtain a pure white HC6 compound powder.

[0035] (2) Preparation of intermediate layer: HC6 powder was uniformly dispersed in an ethanol / water solution with a volume ratio of 3 to obtain a solution with a mass concentration of 0.05 m / v%, and then uniformly spread on the surface of the polysulfone support layer. After standing for 3 min, the excess liquid was poured off and naturally air-dried.

[0036] (3) Preparation of polyamide composite membrane: A water phase solution containing 2 wt.% m-phenylenediamine was poured onto the surface of the HC6 intermediate layer, and after standing for 2 min, the water phase solution was poured out. After naturally air-drying, an organic phase solution containing 0.1 wt.% trimesoyl chloride was poured onto its surface, and after interfacial polymerization for 1 min, the excess organic phase solution was poured out and washed with a small amount of n-hexane. Finally, it was placed in an 80°C oven for heat treatment for 3 min to obtain a polyamide composite membrane.

[0037] Example 7:

[0038] (1) The preparation method of HC4H was the same as step (1) in Example 1.

[0039] (2) The preparation method of intermediate layer was the same as step (2) in Example 1.

[0040] (3) Preparation of polyamide composite membrane: A water phase solution containing 2 wt.% m-phenylenediamine and an organic phase solution containing 0.1 wt.% trimesoyl chloride were sequentially added to a circular reactor, and free interfacial polymerization was carried out for 1 min. The excess solution was removed, and the formed polyamide layer was transferred to the surface of the HC4H intermediate layer formed in step (2) and washed with a small amount of n-hexane. Finally, it was placed in an 80°C oven for heat treatment for 3 min to obtain a polyamide composite membrane.

[0041] Example 8:

[0042] (1) The preparation method of HC6H was the same as step (1) in Example 2.

[0043] (2) The preparation method of intermediate layer was the same as step (2) in Example 2.

[0044] (3) Preparation of polyamide composite membrane: except that HC4H was replaced by HC6H, the rest of the steps were the same as step (3) in Example 7.

[0045] Comparative Example 1:

[0046] (1) A volume ratio of 3 of ethanol / water solution was evenly spread on the surface of the polysulfone support layer, and after standing for 3 min, the excess liquid was poured off and naturally air-dried.

[0047] (2) Preparation of polyamide composite membrane: the aqueous solution containing 2 wt.% m-phenylenediamine was poured onto the surface of the above substrate, and after standing for 2 min, the aqueous solution was poured out. After natural air-drying, an organic phase solution containing 0.1 wt.% trimesoyl chloride was poured onto its surface, and after 1 min of interfacial polymerization, the excess organic phase solution was poured out and washed with a small amount of n-hexane. Finally, it was placed in an 80°C oven for heat treatment for 3 min to obtain a polyamide composite membrane.

[0048] Comparative Example 2:

[0049] Preparation of polyamide composite membrane: the aqueous solution containing 2 wt.% m-phenylenediamine was poured onto the surface of the polysulfone support layer, and after standing for 2 min, the aqueous solution was poured out. After natural air-drying, an organic phase solution containing 0.1 wt.% trimesoyl chloride was poured onto its surface, and after 1 min of interfacial polymerization, the excess organic phase solution was poured out and washed with a small amount of n-hexane. Finally, it was placed in an 80°C oven for heat treatment for 3 min to obtain a polyamide composite membrane.

[0050] Comparative Example 3:

[0051] (1) A volume ratio of 3 of ethanol / water solution was evenly spread on the surface of the polysulfone support layer, and after standing for 3 min, the excess liquid was poured off and naturally air-dried.

[0052] (2) Preparation of polyamide composite membrane: except that the surface of the support layer did not contain an intermediate layer, the rest of the steps were the same as step (3) in Example 7.

[0053] Test Example:

[0054] Performance test conditions of polyamide composite membrane: the feed liquid was a 2000 ppm NaCl aqueous solution, the test pressure was 20 bar, and the test temperature was 25±2°C. Before measurement, all membranes were compacted for 1 h, and after the flux was stable, the water permeability and salt rejection rate of the membrane were tested. The corresponding water permeability (L·m –2 ·h –1 ·bar –1 ) and salt rejection rate (R, %) were calculated according to the following formula: where A is the effective area of the solution through the membrane (m 2∆V(L) is the volume of permeate collected during the permeation time (∆t, h). ∆P(bar) is the average transmembrane pressure difference during membrane operation. C p and C f These are the salt concentrations of the permeate and feed solution, respectively.

[0055]

[0056]

[0057] Depend on Figure 1 It was observed that the membrane surfaces of Comparative Examples 1-2 exhibited more large leaf-shaped polyamide structures. The formation of this structure is primarily attributed to the interfacial polymerization reaction being essentially an exothermic, acid-producing process. This process promotes the release of dissolved gases from the aqueous solution, subsequently generating nanobubbles and inducing the formation of leaf-shaped polyamide structures. Compared to Comparative Examples 1-2, the membrane surface morphology in Examples 1-2 showed significant changes (…). Figure 2 In Example 1, the polyamide leaflet size decreased while the number of leaflets increased, and this trend was even more pronounced in Example 2. The hydrophilic imidazole groups in the interlayer slowed the diffusion-reaction rate of the amine monomer through hydrogen bonding, which further reduced the intensity of the exothermic reaction between the amine monomer and the acyl chloride monomer, resulting in a relatively slow formation and release of nanobubbles. Ultimately, smaller leaf-shaped polyamides formed on the membrane surface. Compared to the HC4H compound (Example 1), the HC6H compound (Example 2) exhibited a stronger inhibitory effect on amine monomer diffusion, possibly due to its longer alkyl chain and larger molecular size, thus demonstrating a stronger steric hindrance effect.

[0058] like Figure 1 As shown, the membranes in Comparative Examples 1–2 have thicker polyamide separation layers, measuring 139 ± 75 nm and 134 ± 40 nm, respectively. After constructing the intermediate layer, the effective thickness of the polyamide layer is significantly reduced ( Figure 2 This is mainly attributed to two advantages provided by the intermediate layer: on the one hand, the "active" region surrounded by imidazole groups increases the affinity for the amine monomer-aqueous solution, thereby increasing the local concentration of the amine monomer; on the other hand, the compound HC... X or HC XThe hydrogen bonding between H and amine monomer reduces its diffusion rate into the organic phase. According to the Freger theory, the thickness of the polyamide layer is related to the initial concentration of amine monomer and its diffusion rate into the organic phase. The higher the initial concentration of amine monomer and the lower its diffusion rate, the smaller the thickness of the polyamide layer. The reduction of the polyamide layer thickness in Examples 1-2 effectively shortens the water molecule transport path, thus facilitating the improvement of water permeability. It is worth noting that the polyamide layer in Example 2 prepared with HC6H is thinner than that in Example 1 with HC4H interlayer, with an average thickness of only 26 nm, which is related to its lower amine monomer diffusion rate.

[0059] Table 1. Separation performance of polyamide composite membranes in Examples and Comparative Examples

[0060] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Intermediate compound HC4H HC6H HC6H HC6H HC6H HC6 / / Mass concentration / m / v% 0.05 0.05 0.025 0.015 0.0075 0.05 0 / Water permeability / L m –2 ·h –1 ·bar –1 ]]> 2.12 3.19 2.57 2.27 2.16 2.06 1.47 1.56 Salt rejection rate / % 99.23 99.28 99.27 99.27 99.38 98.74 99.21 99.19 Polyamide layer thickness / nm 54 ± 22 26 ± 4 38 ± 10 49 ± 13 55 ± 27 66 ± 16 139 ± 75 134 ± 40

[0061] From the performance test results in Table 1, since there is no significant difference in water permeability and salt rejection between Comparative Example 1 and Comparative Example 2, the influence caused by ethanol / water solution immersion can be ruled out. The water permeability of the membranes in Example 1 and Example 2 is 2.12 L-m -2 ·h -1 ·bar -1 and 3.19 L-m -2 ·h -1 ·bar -1 , respectively, which is 44% and 117% higher than that of the membrane in Comparative Example 1, respectively. The improvement of water permeability is mainly attributed to the construction of the interlayer and its regulation of the physicochemical properties of the polyamide layer. Compared with Comparative Example 1, the HC X H interlayer promotes the rapid transport of water molecules between the polyamide layer and the support layer, and shortens the water molecule transport path across the membrane through the gutter effect. At the same time, the thinner separation layer in Examples 1-2 significantly reduces the water molecule transport resistance in the membrane. In addition, the coverage of the HC X H interlayer on the substrate surface also reduces the intrusion of the polyamide matrix into the pores of the support layer, further reducing the hydraulic resistance. It is worth noting that the HC4H interlayer (Example 1) and the HC6H interlayer (Example 2) effectively improve the water permeability while maintaining a high salt rejection rate of the membrane.

[0062] The change in membrane permeability is mainly related to the structure of the HC X H interlayer and the polyamide separation layer. This means that the permeability enhancement factor (f PA-IL ) of the polyamide composite membrane in Examples 1 and 2 is composed of the HC X H interlayer (f IL ) and the polyamide layer (f PA ), i.e. f PA-IL=Water permeability of the membrane in the example ÷Water permeability of the membrane in Comparative Example 1 = f IL + f PA The permeability enhancement factor f of the membranes in Examples 1 and 2 was calculated. PA-IL The values ​​are 1.44 and 2.17 respectively.

[0063] To further quantify HC of different chain lengths X The contribution of the intermediate layer formed by compound H to the performance of the polyamide composite membrane was demonstrated in Examples 7-8 and Comparative Example 3 prepared by free interface polymerization, with water permeability of 1.16 L·m⁻¹, respectively. -2 ·h -1 ·bar -1 1.09 L·m -2 ·h -1 ·bar -1 and 0.98 L·m -2 ·h -1 ·bar -1 The prepared polyamide layer structure depends only on the composition of the monomer solution and the reaction time, while eliminating substrate interference. Therefore, the permeability enhancement factor (f) of the membranes in Examples 7-8 is [not specified]. fPA-IL ) solely attributed to HC X H. Contribution of the intermediate layer to water permeability (f) IL ), that is, f fPA-IL =Water permeability of the membrane in the example ÷Water permeability of the membrane in Comparative Example 3 = f IL The calculated permeability enhancement factors for the membranes in Examples 7 and 8 were 1.18 and 1.11, respectively. The permeability enhancement factor for Example 7 was slightly higher than that for Example 8. This indicates that the HC4H interlayer had a slightly greater effect on improving permeability than the HC6H interlayer.

[0064] The indirect improvement of permeability by the polyamide layer (i.e., f) PA ) can be achieved through the f of the membrane in Examples 1-2 PA-IL and the f of the membrane in Examples 7-8 fPA-IL (i.e. f) IL The difference between them was calculated. The calculation results show that the f of the membrane in Example 2 PA It is 1.06, approximately the same as the membrane in Example 1 (f PA =0.26) is 4 times thicker. This significant difference is related to the regulation of interfacial monomer diffusion by the HC6H interlayer, resulting in a thinner polyamide layer (~26 nm), about half the thickness of the membrane in Example 1 (54 nm). Therefore, compared to the direct contribution of the interlayer to membrane permeability, the indirect regulation of the physicochemical structure of the polyamide layer by the HC6H interlayer contributes to the membrane's higher water permeability.

[0065] In addition, we also prepared HC6 compound with the same alkyl chain length as HC6H, but only containing imidazole group on one side. Similar to the film prepared with HC6H interlayer (Example 2), the surface of the film prepared with HC6 interlayer (Example 6) also exhibited small size polyamide structures. However, compared to HC6H, the HC6 molecule has less imidazole group, which results in a lower degree of inhibition of amine monomer diffusion, and eventually leads to a significant increase in the thickness of the polyamide layer, thus increasing the resistance of water molecules to transport within the film. Therefore, Example 6 exhibited a lower water permeability than Example 2 (Table 1). In addition, due to the difference in molecular size between HC6H and HC6, there are more HC6 molecules on the surface of the substrate at the same mass concentration. The excess HC6 molecules can affect the compactness of the internal network structure of the polyamide, resulting in a decrease in salt rejection rate.

Claims

1. A method for preparing a high permeability, high selectivity polyamide composite membrane, characterized by, Specifically comprising the following steps: (1) Compound HC X or HC X H is prepared by nucleophilic addition reaction of isocyanate or diisocyanate and histamine to form compound HC X or HC X H, the isocyanate has a structure of R x -N=C=O, the molar ratio of isocyanate to histamine is 1:1, and the diisocyanate has a structure of O=C=N-R x -N=C=O, the molar ratio of diisocyanate to histamine is 1:2, wherein R x is an alkyl chain, and x represents the number of carbon atoms in the alkyl chain; (2) Preparation of the intermediate layer: An ethanol / water solution of compound HC X or HC X H was spread evenly on the surface of the support layer, and after a period of time the excess liquid was poured off and allowed to dry naturally; (3) Preparation of the polyamide composite membrane: the surface of the intermediate layer obtained in step (2) is sequentially immersed in an aqueous solution containing a polyamine and an organic phase solution containing a polyacyl chloride, and a polyamide separation layer is generated through interfacial polymerization for a period of time, and finally a polyamide composite membrane is obtained through post-processing.

2. The method of claim 1, wherein the high permeability, high selectivity polyamide composite membrane is prepared by the steps of: The isocyanate is any one of butyl isocyanate, amyl isocyanate, hexyl isocyanate, and heptyl isocyanate, and the diisocyanate is any one of 1,4-butane diisocyanate, 1,6-hexane diisocyanate, 1,8-diisocyanatooctane, and 1,10-decane diisocyanate.

3. The method for preparing the high-permeability, high-selectivity polyamide composite membrane according to claim 1, characterized in that, The volume ratio of ethanol to water in the ethanol / water solution in step (2) is 0.5 - 8, and the compound HC X or HC X The concentration of H in the ethanol / water solution is 0.001 - 0.2 m / v%.

4. The method of claim 1, wherein the high permeability, high selectivity polyamide composite membrane is prepared by the steps of: The deposition time in step (2) is 1-8 min.

5. The method for preparing a high-permeability, high-selectivity polyamide composite membrane according to claim 1, characterized in that, The polyamine in step (3) is any one of ethylenediamine, propylenediamine, hexanediamine, m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, piperazine, diethylenetriamine, triethylenetetramine, triaminotriethylamine, N-aminoethylpiperazine, 2,4-diaminotoluene, 2,2-difluoropropane-1,3-diamine, 4-morpholine-m-phenylenediamine, and 4-piperazine-m-phenylenediamine, the concentration of the polyamine in the aqueous solution is 0.1-5 wt.%, and the aqueous solution immersion time is 0.5-8 min.

6. The method of claim 1, wherein the high permeability, high selectivity polyamide composite membrane is prepared by the steps of: The polyacyl chloride in step (3) is any one of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, phthaloyl chloride, pyromellitic chloride, cyclohexane dicarboxylic acid chloride, cyclohexane tricarboxylic acid chloride, oxalyl chloride, 2,4,4',6-biphenyl tetracarboxylic acid chloride, 2,2',4,4',6,6'-biphenyl tetracarboxylic acid chloride, and 2,3',4,5',6-biphenyl pentacarboxylic acid chloride, the concentration of the polyacyl chloride in the organic phase solution is 0.01-1 wt.%, and the organic phase solution immersion time is 0.1-3 min.

7. The method for preparing a high-permeability, high-selectivity polyamide composite membrane according to claim 1, characterized in that, The post-processing temperature in step (3) is 40-100°C, and the time is 2-5 min.

8. The method for preparing a high-permeability, high-selectivity polyamide composite membrane according to claim 1, characterized in that, The support layer material in step (2) is any one of polysulfone, polyethersulfone, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylonitrile, polyimide, polystyrene, and polyester.

9. A high permeability, high selectivity polyamide composite membrane prepared by the method of any one of claims 1-8, wherein, It sequentially comprises a support layer, an intermediate layer, and a polyamide layer from bottom to top, and the thickness of the polyamide layer is 22-100 nm.

10. Use of the high-permeability and high-selectivity polyamide composite membrane of claim 9 in a solution separation process.

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