A method for preparing an internally pressurized MOF-based hollow fiber composite membrane module

Abstract

This invention discloses a method for preparing an internally pressurized MOF-based hollow fiber composite membrane module, belonging to the field of membrane separation technology. The invention involves introducing an aqueous solution containing metal ions and an organic solution containing organic ligands into the shell side and tube side of a hollow fiber membrane module, respectively. By controlling the number of reactions between metal ions and organic ligands on the inner surface of the hollow fiber membrane, a continuous MOF functional layer is precisely constructed. Subsequently, a low-concentration polymer solution is used to repair defects in the MOF layer, resulting in an internally pressurized MOF-based hollow fiber composite membrane module, which is then applied to pervaporation ethanol / water separation. This method simplifies the preparation process of the internally pressurized hollow fiber composite membrane module; the thin inner surface MOF layer reduces molecular diffusion resistance and enhances molecular mass transfer; the surface-coated polymer matrix effectively repairs MOF layer defects, further enhancing molecular separation selectivity and effectively protecting the MOF functional layer; and it enhances the long-term stability of the membrane module.

Description

Technical Field

[0001] This invention relates to a method for preparing an internally pressurized MOF-based hollow fiber composite membrane module, belonging to the field of membrane separation technology. Background Technology

[0002] Carbon neutrality has become a crucial means of reducing global energy consumption and environmental pollution. Membrane separation technology, due to its advantages such as low energy consumption, mild separation conditions, ease of operation, and small footprint, has been widely used in water treatment and gas separation. Molecular separation technologies, represented by membrane separation techniques such as pervaporation and gas separation, are one of the important strategies for achieving carbon neutrality. As the core of membrane separation technology, the effective design and preparation of membrane materials are of paramount importance. Molecular separation processes are mainly based on the differences in the dissolution and diffusion behavior of components in a densely structured membrane to achieve the separation of target molecules. For densely structured membranes, common polymer membranes are widely used in the preparation of molecular separation membranes due to their good ductility, ease of processing, and low cost. However, the inherent trade-off between permeability and selectivity of polymer membranes limits their application in pervaporation separation.

[0003] Metal-organic frameworks (MOFs), as an emerging crystalline material, are widely used in liquid and gas separation and catalysis due to their large specific surface area, regular pore structure, and strong adsorption capacity. In recent years, researchers have conducted extensive and meaningful studies on the preparation of continuous, defect-free MOF-based membranes based on flat sheet membranes. Conventional blending-coating methods produce membranes with relatively thick separation layers and suffer from interfacial defects caused by MOF filler agglomeration. Water-oil interfacial synthesis has been proven to prepare thin MOF-based membranes, reducing mass transfer resistance in molecular separation processes and improving membrane separation performance. Li et al. prepared MOF membranes on the surface of polyethersulfone flat sheet membranes based on the water-oil interface and used them for effective dye removal (Chemica Communication, 2015, 51, 918-920). Zhao et al. prepared MOF membranes on the surface of polyethersulfone flat sheet membranes using water-oil interfacial synthesis, followed by interfacial polymerization on the MOF membrane surface to prepare polyamide membranes. The prepared composite membrane can remove various dyes from water (Jurnal of Membrane Science, 2021, 625, 119154). These studies have actively promoted the development of MOF-based molecular separation membranes based on flat sheet membranes. However, flat sheet membrane modules are difficult to seal and have poor packing density, which limits their industrial applications. Compared with planar membrane modules, hollow fiber membrane modules have advantages such as high packing density, large effective surface area, and good self-supporting performance, and have now become one of the most important separation membranes in industrial applications. Patent CN201510378308.4 discloses the preparation of MOF-based membranes for gas separation by passing metal salt solutions and organic ligand solutions into hollow fiber membrane modules. This preparation method requires continuous pumping of MOF synthesis solution, resulting in low raw material utilization, long synthesis time, and the continuous flow process easily washes away the synthesized MOF, leading to poor continuity and stability of the MOF layer and low preparation efficiency. Patent 202211241762.1 discloses the effective construction of an ultrathin silicone rubber / MOF composite membrane on the outer surface of a hollow fiber membrane for the recovery of ethanol from water. Compared with constructing a functional layer on the outer surface of a hollow fiber membrane, preparing a MOF-based membrane module on the inner surface of a hollow fiber membrane can more effectively protect the separation layer, achieve high separation efficiency, and reduce the impact of feed flow conditions on the separation process, resulting in low pressure drop. However, the small cavity structure of the hollow fiber membrane is easily clogged during membrane preparation, which increases the difficulty of preparing an internally pressurized MOF-based hollow fiber membrane module. Preparing a thin, continuous, and stable MOF-based separation layer on the inner surface of a hollow fiber membrane with a high curvature surface structure places higher demands on the membrane preparation process and the structure of the separation layer. Therefore, developing a simple and effective method for preparing an internally pressurized MOF-based hollow fiber membrane module is of great significance. Summary of the Invention

[0004] The purpose of this invention is to prepare a thin, continuous, and uniform high-performance MOF-based separation membrane on the inner surface of a polymer hollow fiber membrane, forming an internally pressurized MOF-based hollow fiber membrane module that facilitates molecular separation. Conventional coating methods struggle to uniformly coat the casting solution onto the surface of a hollow fiber membrane with a curved structure to form a thin and continuous separation layer. Coating the inner surface of the hollow fiber membrane also presents challenges, as the casting solution easily clogs the pores of the membrane cavity. To address these issues, an internally pressurized MOF-based hollow fiber composite membrane module and its preparation method are provided.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] This invention relates to a method for preparing an internally pressurized MOF-based hollow fiber composite membrane module, the specific method of which is as follows:

[0007] 1) The polymer hollow fiber membrane is filled and sealed in the tube, and dried at 25°C for 24 to 48 hours to obtain the hollow fiber membrane module. The internal space of the polymer hollow fiber membrane is the tube side of the membrane module, and the space between the polymer hollow fiber membrane and the outer shell of the membrane module is the shell side of the membrane module.

[0008] The polymer hollow fiber membrane is an ultrafiltration membrane or a polymer nanofiltration membrane;

[0009] The polymer used in the polymer hollow fiber membrane is polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or polyethersulfone (PES); preferably, it is a PVDF hollow fiber membrane.

[0010] 2) Add metal salt to deionized water according to the ratio of 0.5g to 3g of metal salt per 100ml of deionized water, and stir at room temperature for 10 to 40 minutes to dissolve it completely to obtain solution 1;

[0011] The metal salt is selected from any one or more of zinc and / or cobalt nitrates, acetates, and chlorides, mixed in any proportion;

[0012] 3) According to the ratio of 1g to 5g of organic ligand per 100ml of organic solution 1, add organic ligand to organic solution 1, stir at room temperature for 10 to 60 minutes to fully dissolve it, and obtain solution 2;

[0013] The organic solution 1 is a mixed solution of n-hexane, ethanol and methanol, wherein the volume ratio of n-hexane, ethanol and methanol is 100-40:1:1.5-2.

[0014] The organic ligand is any one or more of 2-methylimidazole, 4,5-dichloroimidazole, and benzimidazole, mixed in any proportion;

[0015] 4) Inject the solution 1 obtained in step 2) into the tube side and shell side of the hollow fiber membrane module obtained in step 1), respectively, and let it stand for 0.5 to 2 hours to allow the solution 1 to fill the membrane pores of the polymer hollow fiber membrane; then drain the solution 1 from the tube side, and use the solution 1 in the shell side as a metal source for subsequent interface synthesis to ensure the effective preparation of the MOF layer.

[0016] 5) Pass the solution 2 obtained in step 3 into the tube side of the hollow fiber membrane module after step 4), let it stand for 0.5 to 2 hours, then drain the solution 1 in the shell side and the solution 2 in the tube side, and treat it at 50 to 120°C for more than 8 hours to obtain a hollow fiber membrane module with MOF seed crystals on the inner surface.

[0017] 6) Repeat the operation of steps 4) to 5) 1 to 20 times, preferably 2 to 8 times, on the hollow fiber membrane module containing MOF seeds obtained in step 5) to obtain a hollow fiber membrane module with a MOF layer grown on the inner surface of the hollow fiber.

[0018] 7) Add silicone rubber, crosslinking agent and catalyst to organic solution 2, stir for 0.5-2 hours to obtain solution 3. The mass ratio of organic solution 2, silicone rubber, crosslinking agent and catalyst is 1000-200:1-2:0.5-2:1.

[0019] The organic solution 2 is selected from any one or more of n-heptane, n-hexane, and n-pentane, mixed in any proportion;

[0020] The silicone rubber is any one or more of polydimethoxysiloxane (PDMS), polymethyloctylsiloxane (POMS), and polytrimethylsilyl-1-propyne solution (PTMSP) in any proportion;

[0021] The crosslinking agent is any one or more of tetraethyl orthosilicate (TEOS), phenyltrimethoxysilane (PTMOS), octyltrimethoxysilane (OTMOS), and γ-aminopropyltriethoxysilane (APTEOS) mixed in any proportion;

[0022] The catalyst is any one of dibutyltin dilaurate (DBTDL) and dioctyltin dilaurate (DOTDL) or a combination thereof;

[0023] 8) Introduce the solution 3 obtained in step 7) into the tube of the hollow fiber membrane module in which the MOF layer is grown on the inner surface of the hollow fiber obtained in step 6), and treat it under a pressure of 0.01-0.05 MPa for 10-60 seconds. Then drain the solution 3 and heat-treat it at 70-90℃ for 2-12 hours to repair the intercrystalline defects of the MOF layer, thereby obtaining the internal pressure MOF-based hollow fiber composite membrane module.

[0024] Beneficial effects

[0025] 1. This invention prioritizes the use of interfacial synthesis to construct a thin MOF layer on the inner surface of a hollow fiber membrane, followed by defect repair of the MOF layer using a low-concentration polymer solution. This MOF-based separation membrane preparation strategy effectively avoids the problem of MOF particle agglomeration leading to membrane separation performance degradation in MOF-based mixed matrix membranes prepared by traditional blending-coating methods.

[0026] 2: Synthesize MOF membranes using the water-oil interface. Due to the self-termination effect of MOF membranes, the formation of MOF layers can be effectively controlled. This makes it easy to prepare thin and relatively continuous MOF membranes, thereby enhancing mass transfer behavior during the separation process.

[0027] 3. This invention precisely constructs a thin MOF functional layer on the inner surface of a hollow fiber membrane and prepares a nanoscale ultrathin polymer repair layer using a low-concentration polymer solution by controlling the number of interfacial synthesis steps. The thickness of this layer is only 378±5 nm, achieving the preparation of a thin, continuous, and uniform MOF-based separation layer on the inner surface of the polymer hollow fiber membrane. The prepared MOF-based separation membrane, while ensuring good selectivity, significantly reduces the diffusion resistance of permeable molecules, enhances membrane permeability, and breaks the "trade-off" effect of permeability and selectivity in traditional polymer membranes.

[0028] 4: The nanoscale ultrathin polymer layer prepared by using low-concentration polymer solution effectively repairs the intergranular defects of MOF layer and enhances the physical and chemical stability of MOF layer during molecular separation process, thus realizing the stable operation of MOF base film during molecular separation process.

[0029] 5. This invention simplifies the fabrication process of functional hollow fiber membrane modules by constructing a MOF-based functional layer on the inner surface of the hollow fiber membrane module, effectively protecting the MOF layer. It avoids the problem of damage to the functional layer due to friction and other external forces that occurred during the previous process of preparing the separation membrane first and then the membrane module. The resulting internally pressurized MOF-based hollow fiber membrane module fabrication strategy opens up new avenues for constructing high-performance hollow fiber membrane modules. Attached Figure Description

[0030] Figure 1 The image shows a surface SEM image of the MOF-4 / PVDF hollow fiber composite membrane obtained in Example 3.

[0031] Figure 2 The image shows the surface SEM image of the PDMS@MOF-4 / PVDF hollow fiber composite membrane obtained in Example 3.

[0032] Figure 3 SEM images of cross-sections of the PDMS@MOF-4 / PVDF hollow fiber composite membrane obtained in Example 3 at different magnifications;

[0033] Figure 4 The image shows a cross-sectional SEM image of the hollow fiber membrane in the internally compressed polymer / MOF hybrid matrix obtained in Comparative Example 1.

[0034] Figure 5 Here is a SEM image of the surface of the hollow fiber composite membrane with internal pressure MOF layer obtained in Comparative Example 3.

[0035] Figure 6 Here is a SEM image of the surface of the hollow fiber composite membrane with internal pressure MOF layer obtained in Comparative Example 4.

[0036] Figure 7 The graph shows a comparison of the pervaporation separation performance of each embodiment and comparative example. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings, embodiments, and comparative examples.

[0038] Example 1:

[0039] A method for preparing an internally pressurized MOF-based hollow fiber membrane module, the specific steps of which are as follows:

[0040] 1) Seven PVDF hollow fiber membrane filaments were packed into a glass tube, encapsulated with 704 silicone rubber, and dried at room temperature for 48 hours to obtain a hollow fiber membrane module. Methanol was then introduced into the tube side of the membrane module for 30 minutes to obtain a hollow fiber membrane module in which the membrane filaments were fully wetted by methanol.

[0041] 2) Add 1.5g of zinc nitrate hexahydrate to 100mL of deionized water and stir at 300rpm for 30min to obtain solution 1. Add 1.614g of dimethylimidazole to 95.6g of n-hexane solution, followed by the addition of 1.9g of methanol and 2.5g of ethanol, and stir at 300rpm for 30min to obtain solution 2. Pass solution 1 into the tube side of a hollow fiber membrane module that is fully wetted with methanol for 1h, and inject solution 1 into the shell side; then pass solution 2 into the tube side of the module, let it stand (interfacial synthesis) for 30min, and then treat it at 100℃ for 8h to obtain an internal pressure MOF-1 / PVDF hollow fiber membrane module;

[0042] 3) Add 0.2 g PDMS to 39.8 mL n-heptane and stir at 300 rpm for 20 min to obtain solution 3. Then, add 0.04 g TEOS and 0.008 g DBTDL to solution 3 and stir at 300 rpm for 20 min to obtain solution 4. Pass solution 4 into the tubing of the internal pressure MOF-1 / PVDF hollow fiber membrane module obtained in step 2, treat it at a pressure of 0.02 MPa for 30 s, and then place it in an 80℃ forced-air drying oven for 4 h to obtain the PDMS@MOF-1 / PVDF hollow fiber composite membrane module.

[0043] Example 2:

[0044] A method for preparing an internally pressurized MOF-based hollow fiber membrane module, the specific steps of which are as follows:

[0045] 1) Seven PVDF hollow fiber membrane filaments were packed into a glass tube, encapsulated with 704 silicone rubber, and dried at room temperature for 48 hours to obtain a hollow fiber membrane module. Methanol was then introduced into the tube side of the membrane module for 30 minutes to obtain a hollow fiber membrane module in which the membrane filaments were fully wetted by methanol.

[0046] 2) Add 1.5g of zinc nitrate hexahydrate to 100mL of deionized water and stir at 300rpm for 30min to obtain solution 1. Add 1.614g of dimethylimidazole to 95.6g of n-hexane solution, followed by the addition of 1.9g of methanol and 2.5g of ethanol, and stir at 300rpm for 30min to obtain solution 2. Pass solution 1 into the tube side of a hollow fiber membrane module that is fully wetted with methanol for 1h, and inject solution 1 into the shell side; then pass solution 2 into the tube side of the module, let it stand (interfacial synthesis) for 30min, and then treat it at 100℃ for 8h. Then repeat the above steps - interfacial synthesis twice to obtain an internal pressure MOF-2 / PVDF hollow fiber membrane module;

[0047] 3) Add 0.2 g PDMS to 39.8 mL n-heptane and stir at 300 rpm for 20 min to obtain solution 3. Then, add 0.04 g TEOS and 0.008 g DBTDL to solution 3 and stir at 300 rpm for 20 min to obtain solution 4. Pass solution 4 into the tubing of the internal pressure MOF-2 / PVDF hollow fiber membrane module obtained in step 2, treat it at a pressure of 0.02 MPa for 30 s, and then place it in an 80℃ forced-air drying oven for 4 h to obtain the PDMS@MOF-2 / PVDF hollow fiber composite membrane module.

[0048] Example 3:

[0049] A method for preparing an internally pressurized MOF-based hollow fiber membrane module, the specific steps of which are as follows:

[0050] 1) Seven PVDF hollow fiber membrane filaments were packed into a glass tube, encapsulated with 704 silicone rubber, and dried at room temperature for 48 hours to obtain a hollow fiber membrane module. Methanol was then introduced into the tube side of the membrane module for 30 minutes to obtain a hollow fiber membrane module in which the membrane filaments were fully wetted by methanol.

[0051] 2) Add 1.5g of zinc nitrate hexahydrate to 100mL of deionized water and stir at 300rpm for 30min to obtain solution 1. Add 1.614g of dimethylimidazole to 95.6g of n-hexane solution, followed by the addition of 1.9g of methanol and 2.5g of ethanol, and stir at 300rpm for 30min to obtain solution 2. Pass solution 1 into the tube side of a hollow fiber membrane module that is fully wetted with methanol for 1h, and inject solution 1 into the shell side; then pass solution 2 into the tube side of the module, let it stand (interfacial synthesis) for 30min, and then treat it at 100℃ for 8h. Repeat the above steps - interfacial synthesis 4 times to obtain an internal pressure MOF-4 / PVDF hollow fiber membrane module;

[0052] 3) Add 0.2 g PDMS to 39.8 mL of n-heptane and stir at 300 rpm for 20 min to obtain solution 3. Then, add 0.04 g TEOS and 0.008 g DBTDL to solution 3 and stir at 300 rpm for 20 min to obtain solution 4. Pass solution 4 into the tubing of the internal pressure MOF-4 / PVDF hollow fiber membrane module obtained in step 2, treat at a pressure of 0.02 MPa for 30 s, and then place in an 80℃ forced-air drying oven for 4 h to obtain the PDMS@MOF-4 / PVDF hollow fiber composite membrane module. The inner surface of the inner membrane fibers of the internal pressure MOF-4 / PVDF hollow fiber membrane module was observed by scanning electron microscopy, as shown... Figure 1 As shown. Scanning electron microscopy was used to observe the inner surface and cross-section of the inner membrane filaments in the PDMS@MOF-4 / PVDF hollow fiber membrane module. Figure 2 and Figure 3 As shown.

[0053] Example 4:

[0054] A method for preparing an internally pressurized MOF-based hollow fiber membrane module, the specific steps of which are as follows:

[0055] 1) Seven PVDF hollow fiber membrane filaments were packed into a glass tube, encapsulated with 704 silicone rubber, and dried at room temperature for 48 hours to obtain a hollow fiber membrane module. Methanol was then introduced into the tube side of the membrane module for 30 minutes to obtain a hollow fiber membrane module in which the membrane filaments were fully wetted by methanol.

[0056] 2) Add 1.5g of zinc nitrate hexahydrate to 100mL of deionized water and stir at 300rpm for 30min to obtain solution 1. Add 1.614g of dimethylimidazole to 95.6g of n-hexane solution, followed by the addition of 1.9g of methanol and 2.5g of ethanol, and stir at 300rpm for 30min to obtain solution 2. Pass solution 1 into the tube side of a hollow fiber membrane module that is fully wetted with methanol for 1h, and inject solution 1 into the shell side; then pass solution 2 into the tube side of the module, let it stand (interfacial synthesis) for 30min, and then treat it at 100℃ for 8h. Repeat the above steps - interfacial synthesis 5 times to obtain an internal pressure MOF-4 / PVDF hollow fiber membrane module;

[0057] 3) Add 0.2 g PDMS to 39.8 mL n-heptane and stir at 300 rpm for 20 min to obtain solution 3. Then, add 0.04 g TEOS and 0.008 g DBTDL to solution 3 and stir at 300 rpm for 20 min to obtain solution 4. Pass solution 4 into the tubing of the internal pressure MOF-4 / PVDF hollow fiber membrane module obtained in step 2, treat it at a pressure of 0.02 MPa for 30 s, and then place it in an 80℃ forced-air drying oven for 4 h to obtain the PDMS@MOF-4 / PVDF hollow fiber composite membrane module.

[0058] Comparative Example 1:

[0059] A method for preparing an internally pressurized polymer / MOF hybrid matrix hollow fiber membrane module, the specific steps of which are as follows:

[0060] 1) Seven PVDF hollow fiber membrane filaments were filled into a glass tube, encapsulated with 704 silicone rubber, and dried at room temperature for 48 hours to obtain a hollow fiber membrane module.

[0061] 2) Dissolve 2.933 g of zinc nitrate hexahydrate and 6.489 g of 2-methylimidazole in 200 mL of methanol (designated as solution A and solution B, respectively). Then, add solution A to solution B at a molar ratio of 1:4 (Zn:Hmim) and stir vigorously. After reacting for 1.5 h, centrifuge at 10000 r / min for 10 min and wash twice with ethanol. Finally, place the collected ZIF-8 nanoparticles in a vacuum drying oven and dry overnight at 100 °C. The prepared ZIF-8 nanoparticles were collected and stored for later use.

[0062] 3) 0.1 g of ZIF-8 nanoparticles synthesized in step 2 were added to 89.1 mL of n-heptane and ultrasonically dispersed for 30 min. Then, 0.9 g of PDMS was added to the above solution, and the mixture was stirred at 300 rpm for 30 min. Next, 0.2 g of TEOS and 0.035 g of DBTDL were added to the above solution, and the mixture was stirred at 300 rpm for 20 min to obtain the casting solution. The casting solution was pumped into the tube of the hollow fiber membrane module prepared in step 1, and coated at a pressure of 0.02 MPa for 30 s. Excess casting solution was then removed from the module, and the module was placed in an 80°C drying oven for 4 h to obtain an internally pressurized PDMS / MOFs hybrid matrix hollow fiber membrane module. The cross-section of the fabricated membrane was observed using a scanning electron microscope, as shown... Figure 4 As shown, the separation layer of the polymer / MOFs mixed matrix membrane prepared by the blending-coating method on the surface of the hollow fiber membrane is relatively thick, and the casting solution leakage is serious. This will greatly increase the molecular diffusion resistance and is not conducive to molecular separation.

[0063] Comparative Example 2

[0064] A method for preparing an internally pressurized MOF layer hollow fiber membrane module, the specific steps of which are as follows:

[0065] 1) Seven PVDF hollow fiber membrane filaments were packed into a glass tube, encapsulated with 704 silicone rubber, and dried at room temperature for 48 hours to obtain a hollow fiber membrane module. Methanol was then introduced into the tube side of the membrane module for 30 minutes to obtain a hollow fiber membrane module in which the membrane filaments were fully wetted by methanol.

[0066] 2) Add 1.5g of zinc nitrate hexahydrate to 100mL of deionized water and stir at 300rpm for 30min to obtain solution 1. Add 1.614g of dimethylimidazole to 95.6g of n-hexane solution, followed by the addition of 1.9g of methanol and 2.5g of ethanol, and stir at 300rpm for 30min to obtain solution 2. Pass solution 1 into the tube side of a hollow fiber membrane module that is fully wetted with methanol for 1h, and inject solution 1 into the shell side; then pass solution 2 into the tube side of the module, let it stand (interfacial synthesis) for 30min, and then treat it at 100℃ for 8h. Repeat the above steps - interfacial synthesis 4 times to obtain an internal pressure MOF-4 / PVDF hollow fiber membrane module;

[0067] Comparative Example 3:

[0068] MOF-based hollow fiber composite membranes were prepared by solvent evaporation and self-crystallization.

[0069] The difference from Example 3 is that this comparative example uses a solvent evaporation self-crystallization method to prepare a ZIF-8 layer on the inner surface of a hollow fiber membrane, and the preparation process is based on the published patent CN202211241762.1.

[0070] Patent CN202211241762.1 describes a method for precisely controlling the ZIF-8 layer thickness through solvent evaporation cycles to prepare an ultrathin silicone rubber / MOF hollow fiber composite membrane on the outer surface of a hollow fiber membrane. A ZIF-8 layer was prepared on the inner surface of the hollow fiber membrane using the same method, and subsequent observations were performed using scanning electron microscopy. Figure 5 As shown, although ZIF-8 particles are generated on the inner surface, a continuous ZIF-8 film is not formed, and many voids and defects exist on the surface. This indicates that this method is difficult to effectively prepare MOF-based hollow fiber composite membranes on the inner surface of hollow fiber membranes.

[0071] Comparative Example 4:

[0072] The difference from Example 3 is that in this comparative example, the metal salt and organic ligand for synthesizing the MOF were dissolved in methanol, respectively. Then, the two methanol solutions were placed on the inner and outer sides of a hollow fiber membrane, respectively, to react on the surface of the hollow fiber membrane and thus prepare the MOF membrane. Subsequently, the reaction was observed using a scanning electron microscope. Figure 6 As shown, the lack of a phase interface leads to an excessively fast and uncontrollable reaction rate. This results in discontinuous MOF films with numerous defects, making it difficult to produce dense MOF layers.

[0073] The hollow fiber composite membrane modules obtained in each embodiment were used to verify the molecular separation performance by separating and recovering ethanol in an aqueous ethanol solution. The specific test standards are as follows:

[0074] The effective area of ​​the membrane used in the test was 21 cm². 2 The feed solution was a 5 wt% ethanol-water solution, with a circulation rate of 0.5 m / s, and the test system temperature was maintained at 40℃. A vacuum pump was used to maintain the permeate pressure below 3 kPa, and the collector was immersed in liquid nitrogen to collect the permeate vapor. The composition of the feed solution and permeate was then analyzed using a GC-7890II gas chromatograph (China Tianmei Scientific Instruments Co., Ltd.), with at least three measurements taken for each membrane module. The total permeate flux (J, gm³) was calculated according to the following equation. -2 .h -1 ) and separation factor (β):

[0075]

[0076]

[0077] J i =J×m i (3)

[0078] Where W(g) is the total mass of permeate collected within t hours, and A(m) is the total mass of permeate collected within t hours. 2 (m) represents the effective area of ​​the membrane. f and m pThese are the ethanol concentrations (wt%) on the feed side and the permeate side, respectively.

[0079] Ethanol permeation flux and separation factor of each hollow fiber composite membrane module, as follows: Figure 7 As shown, from Example 1 to Example 3, the prepared membrane modules gradually achieved optimal beneficial effects, with ethanol permeation flux and separation factor reaching 1.3 kg / m². -2 .h -1 And 8.64. The beneficial effects obtained in Example 4 and Example 3 are similar because Example 3 has already formed a continuous and uniform MOF layer. Subsequent interface synthesis will hinder the diffusion of metal ions and organic ligands to the phase interface, inhibiting the continued growth of the MOF layer, thus the beneficial effects obtained are similar. Compared with Example 3, Comparative Example 2 achieved poorer beneficial effects, which indicates that the MOF layer has non-selective molecular diffusion channels, further proving the importance of Example 3.

Claims

1. A method for preparing an internally pressurized MOF-based hollow fiber composite membrane module, characterized in that: The specific method is as follows: 1) The polymer hollow fiber membrane is filled and sealed in the tube, and dried at 25°C for 24 to 48 hours to obtain the hollow fiber membrane module. The internal space of the polymer hollow fiber membrane is the tube side of the membrane module, and the space between the polymer hollow fiber membrane and the outer shell of the membrane module is the shell side of the membrane module. The polymer hollow fiber membrane is an ultrafiltration membrane or a polymer nanofiltration membrane; The polymer used in the polymer hollow fiber membrane is polyvinylidene fluoride, polytetrafluoroethylene, or polyethersulfone. 2) Add metal salt to deionized water according to the ratio of 0.5g to 3g of metal salt per 100ml of deionized water, and stir at room temperature for 10 to 40 minutes to fully dissolve it to obtain solution 1; The metal salt is selected from any one or more of zinc and / or cobalt nitrates, acetates, and chlorides, mixed in any proportion; 3) According to the ratio of 1g to 5g of organic ligand per 100ml of organic solution 1, add organic ligand to organic solution 1, stir at room temperature for 10 to 60 minutes to fully dissolve it, and obtain solution 2; The organic solution 1 is a mixed solution of n-hexane, ethanol and methanol, wherein the volume ratio of n-hexane, ethanol and methanol is 100-40:1:1.5-2. The organic ligand is any one or more of 2-methylimidazole, 4,5-dichloroimidazole, and benzimidazole, mixed in any proportion; 4) Inject the solution 1 obtained in step 2) into the tube side and shell side of the hollow fiber membrane module obtained in step 1), let it stand for 0.5 to 2 hours, and then drain the solution 1 from the tube side. 5) Pass solution 2 obtained in step 3 into the tube side of the hollow fiber membrane module after step 4), let it stand for 0.5 to 2 hours, then drain solution 1 from the shell side and solution 2 from the tube side, and treat it at 50 to 120°C for more than 8 hours to obtain a hollow fiber membrane module with MOF seed crystals on the inner surface. 6) Repeat steps 4) and 5) 1 to 20 times to obtain a hollow fiber membrane module with an MOF layer grown on the inner surface of the hollow fiber. 7) Add silicone rubber, crosslinking agent and catalyst to organic solution 2, stir for 0.5-2 hours to obtain solution 3. The mass ratio of organic solution 2, silicone rubber, crosslinking agent and catalyst is 1000-200:1-2:0.5-2:

1. The organic solution 2 is selected from any one or more of n-heptane, n-hexane, and n-pentane, mixed in any proportion; The silicone rubber is any one or more of polydimethoxysiloxane, polymethyloctylsiloxane, and polytrimethylsilyl-1-propyne solution mixed in any proportion; The crosslinking agent is any one or more of tetraethyl orthosilicate, phenyltrimethoxysilane, octyltrimethoxysilane, and γ-aminopropyltriethoxysilane, mixed in any proportion; The catalyst is any one or a combination of dibutyltin dilaurate and di-n-octyltin dilaurate. 8) Pass the solution 3 obtained in step 7) into the hollow fiber membrane module tube obtained in step 6), and treat it under a pressure of 0.01 to 0.05 MPa for 10 to 60 seconds. Then discharge the solution 3 and heat treat it at 70 to 90°C for 2 to 12 hours to obtain the internal pressure MOF-based hollow fiber composite membrane module.

2. The method for preparing an internally pressurized MOF-based hollow fiber composite membrane module as described in claim 1, characterized in that: In step 6), the number of times steps 4) and 5) are repeated is 2 to 8.

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