A method for preparing a PDMS-based pervaporation membrane with a continuous intermediate layer

Abstract

The present invention provides a method for preparing a PDMS-based pervaporation membrane with a continuous intermediate layer. First, a TA-APTES@ODS intermediate layer is prepared, and then a metal source is uniformly dispersed in a PDMS polymer and spin-coated onto the membrane surface. MOFs nanoparticles are formed in situ by chemical vapor deposition, and finally a hydrophobic silane coupling agent is coated on the membrane surface to improve the performance of the membrane. The prepared intermediate layer optimizes the surface structure and performance of the base membrane, prevents the pore permeation effect of PDMS, and promotes the dense formation of the PDMS selective layer. The metal source uniformly distributed in the PDMS matrix is ​​combined with a ligand by CVD and converted in situ into uniformly dispersed MOFs nanoparticles, which alleviates the aggregation of MOFs. At the same time, the surface of the composite membrane is modified, and the preferential adsorption of butanol on the PDMS surface and permeation is promoted by coating the surface with a hydrophobic silane coupling agent, thereby improving the separation performance and permeation flux of the pervaporation membrane.

Description

Technical Field

[0001] The invention belongs to the technical field of membranes, and in particular relates to a preparation method of a PDMS pervaporation composite membrane with a spherical continuous intermediate layer for preferential alcohol permeation. Background Art

[0002] Bioenergy has attracted widespread attention as a recyclable energy source. Among them, biobutanol has the advantages of high calorific value, moderate corrosivity, low volatility, and good compatibility with petroleum, and is considered to be one of the most promising and effective biofuels. At present, the most commonly used method for producing n-butanol is acetone-butanol-ethanol (ABE) fermentation technology. However, the final product inhibits the activity of microorganisms during the fermentation process, resulting in low butanol concentration and low butanol yield, which increases the cost of subsequent separation processes. In order to minimize the energy consumption of butanol separation, many separation methods have been studied. Among these methods, pervaporation (PV) has become an ideal membrane-based butanol recovery technology due to its high butanol selectivity, low energy consumption, little impact on microorganisms, and easy integration with fermentation units.

[0003] Membrane separation performance is primarily determined by the properties of the membrane material. For alcohol recovery, the most commonly used materials for hydrophobic membranes include polymers such as polydimethylsiloxane (PDMS), polyether block polyamide (PEBA), and polyvinylidene fluoride (PVDF). PDMS is widely used in the preparation of PV membranes due to its high hydrophobicity, excellent thermal properties, and chemical stability. However, the selectivity and flux of PDMS membranes need to be further improved to meet the requirements of industrial applications.

[0004] In recent years, PDMS composite membranes have attracted increasing attention due to their excellent separation performance. PDMS composite membranes consist of a thin separation layer on a porous support layer. However, due to insufficient cross-linking between PDMS polymer molecules, immersion of polymer chains in the macropores of the substrate, or irregular arrangement of polymer chains, it is difficult to construct a thin selective layer without non-selective defects or pinholes. In addition, according to simulation models, the transmembrane transport resistance of the PDMS composite membrane is composed of the porous region of the substrate, the "dense region" of the substrate, the PDMS matrix immersed in the pores of the substrate, and the top selective layer. The support membrane of the general PDMS composite membrane is an ultrafiltration membrane, which can allow water and butanol molecules to pass through quickly. In contrast, the non-porous PDMS matrix greatly reduces the molecular diffusion rate. Therefore, the immersion layer and the top dense layer are the main transmembrane transport resistance of the PDMS composite membrane.

[0005] To reduce the impact of the intrusion layer, several attempts have been made to prevent the infiltration of the PDMS matrix. Despite some progress, significant room for improvement remains. Constructing an interlayer on the surface of a porous substrate is a promising approach to prevent polymer penetration into the pores of the base membrane and has been widely used in the preparation of various membranes. Due to the chemical inertness of the commonly used support PVDF, it is difficult to form a stable interlayer with strong adhesion to the base membrane and the dense PDMS layer. Fortunately, tannic acid (TA) and 3-aminopropyltriethoxysilane (APTES) can be used to construct a layered coating (TA-APTES) on various membranes using a facile and simple strategy. Furthermore, TA-APTES layered coatings have the potential to form functional surfaces with higher surface area through secondary reactions. Therefore, functionalized TA-APTES layered coatings may be an ideal interlayer option for the preparation of high-performance PDMS composite membranes, minimizing the PDMS intrusion layer. MOF nanoparticles can provide preferential permeation pathways for organic compounds, improving membrane separation performance. MOFs, composed of metal centers coordinated by organic ligands, have high porosity and tunable pore size. These advantages of MOFs have enhanced their application in the preparation of PV membranes. Combining the intermediate layer with MOFs nanoparticles provides a new idea for constructing high-performance PDMS-based composite membranes with preferential alcohol permeability. Summary of the Invention

[0006] In order to overcome the upper limit of the pore permeation effect of PDMS polymer and the "trade-off" effect of pervaporation membrane, the present invention provides a preparation method for constructing a spherical continuous intermediate layer of PDMS pervaporation composite membrane with preferential alcohol permeation.

[0007] The technical solutions of the present invention are as follows:

[0008] A method for preparing a PDMS-based pervaporation membrane having a continuous intermediate layer, the method comprising:

[0009] (1) Hydrophilic modification of ultrafiltration membrane

[0010] Dissolving tannic acid in a buffer solution having a pH of 7.5-8.5 (preferably 8.5) to obtain a 1-4 g / L tannic acid solution (preferably 2 g / L), adding an ethanolic solution of 3-aminopropyltriethoxysilane to obtain a reaction solution A; immersing the pretreated hydrophobic ultrafiltration membrane in the reaction solution A at room temperature, shaking and soaking for 6-14 hours (preferably 12 hours), and washing to obtain a hydrophilically modified ultrafiltration membrane; the mass ratio of tannic acid to 3-aminopropyltriethoxysilane contained in the ethanolic solution of 3-aminopropyltriethoxysilane is 1:0.5-2 (preferably 1:1);

[0011] (2) Secondary hydrophobic modification of ultrafiltration membrane

[0012] Dissolve octadecyltrimethoxysilane (ODS) in anhydrous ethanol to obtain an octadecyltrimethoxysilane solution with a concentration of 1.0-4.0 g / L (preferably 2.5 g / L), add deionized water, and adjust the pH to 4.0-5.0 (5.0 in one embodiment of the present invention) (using acetic acid) to obtain a reaction solution B; immerse the hydrophilic modified ultrafiltration membrane described in step (1) in the reaction solution B, shake and react for 4-12 hours (preferably 6 hours), and then wash to obtain a TA-APTES@ODS membrane (TAO); the volume ratio of the anhydrous ethanol to the deionized water is 6-12:1 (preferably 10:1);

[0013] (3) Preparation of composite PDMS membranes by chemical vapor deposition (CVD) loading MOFs

[0014] Dissolving polydimethylsiloxane (PDMS) in a good solvent to obtain a PDMS solution having a concentration of 10 wt% to 30 wt% (preferably 20 wt%); adding zinc acetylacetonate (Zn(acac)2) and tetraethyl orthosilicate (TEOS, a crosslinker) and mixing uniformly; adding dibutyltin dilaurate (DBTDL, a catalyst) and carrying out a catalytic reaction for 8 to 30 minutes to obtain a coating solution; the mass ratio of the polydimethylsiloxane, zinc acetylacetonate, tetraethyl orthosilicate, and dibutyltin dilaurate being 100:0.5-6:5-15:1-3 (preferably 100:1.5:10:2);

[0015] The coating liquid is completely spin-coated on the TA-APTES@ODS membrane described in step (2), and the membrane is placed in a reaction kettle containing an organic ligand, and subjected to a thermal cross-linking reaction at 60-140° C. for 6-14 h (preferably 80° C. for 12 h) under closed conditions to obtain a TAO / ZIF-8 / PDMS composite membrane;

[0016] The mass of the coating solution is 0.2-0.3 g / cm based on the area of ​​the TA-APTES@ODS membrane. 2 (Preferably 0.28 g / cm 2 ); the mass ratio of zinc acetylacetonate to the organic ligand is 1:25-100 (preferably 1:76);

[0017] When the ratio of polydimethylsiloxane to zinc acetylacetonate is outside the range of 100:0.5-6, too little zinc acetylacetonate results in low flux and poor separation performance. Too much zinc acetylacetonate prevents it from being fully dispersed in the solvent, resulting in waste and a slight decrease in performance. The organic ligand should be in excess, at least 25 times the amount of zinc acetylacetonate.

[0018] (4) Hydrophobic modification of TAO / ZIF-8 / PDMS composite membrane surface

[0019] The TAO / ZIF-8 / PDMS composite membrane described in step (3) is shaken in a 2-6 wt% (preferably 4 wt%) silane coupling agent solution for 20-100 min (preferably 60 min) to obtain the continuous intermediate layer PDMS-based pervaporation membrane.

[0020] In one embodiment of the present invention, the pretreatment in step (1) is: soaking the hydrophobic ultrafiltration membrane in ethanol for 20 minutes.

[0021] In one embodiment of the present invention, the concentration of the ethanol solution of 3-aminopropyltriethoxysilane in step (1) is 6-14 g / L, preferably 10 g / L.

[0022] Furthermore, the hydrophobic ultrafiltration membrane in step (1) is one of polyvinylidene fluoride ultrafiltration membrane (PVDF), polysulfone ultrafiltration membrane (PSF), and polytetrafluoroethylene ultrafiltration membrane (PTFE), and in one embodiment of the present invention, it is PVDF ultrafiltration membrane.

[0023] Furthermore, the buffer in step (1) is at least one of tris-HCl buffer, tris buffer, tris-phosphate buffer, and phosphate buffer, preferably tris-HCl buffer.

[0024] In one embodiment of the present invention, the cleaning in step (1) is: washing with ethanol and deionized water in sequence.

[0025] In one embodiment of the present invention, the cleaning in step (2) is: washing with ethanol and deionized water in sequence.

[0026] Furthermore, the good solvent in step (3) is at least one of n-heptane, n-hexane, chloroform, dichloromethane, and toluene, preferably at least one of n-heptane and n-hexane.

[0027] Furthermore, the organic ligand in step (3) is at least one of 2-methylimidazole, 1-ethylimidazole, benzimidazole, and 1-butylimidazole, preferably at least one of 2-methylimidazole and 1-ethylimidazole.

[0028] Furthermore, the silane coupling agent contained in the silane coupling agent solution in step (4) is at least one of γ-mercaptopropyltrimethoxysilane (KH-590), 3-aminopropyltriethoxysilane (KH-550), γ-glycidoxypropyltrimethoxysilane (KH-560), and γ-methacryloxypropyltrimethoxysilane (KH-570), preferably at least one of KH-590 and KH-550.

[0029] Furthermore, the solvent in the silane coupling agent solution in step (4) is at least one of methanol, water, ethanol, benzene, and toluene, preferably at least one of methanol and water.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] A hierarchical interlayer fabricated by co-deposition of TA and APTES and co-functionalization with ODS optimizes the substrate's surface structure and properties, inhibiting the penetration of the PDMS matrix into the substrate's channels. This facilitates the preparation of a defect-free, thin PDMS separation layer and increases flux. Through chemical vapor infiltration of ligands, the uniformly distributed metal source is converted in situ into MOF nanoparticles, mitigating MOF aggregation and reducing the transmembrane transport resistance of n-butanol, thereby enhancing permeation flux. The hydrophobic surface modification of the PDMS composite membrane facilitates the preferential adsorption of n-butanol, which rapidly adsorbs to the membrane surface along the hydrophobic chains of the silane coupling agent, improving permeation and separation performance. For the recovery of low-concentration n-butanol, the defect-free TAO / ZIF-8 / KH-590 / PDMS composite membrane exhibits excellent permeation-separation performance, making it highly competitive. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the process of the TAO / ZIF-8 / KH-590 / PDMS pervaporation composite membrane prepared in Example 1.

[0033] Figure 2 This is a scanning electron microscope image of the intermediate layer TA-APTES@ODS material prepared in Example 1.

[0034] Figure 3 This is a scanning electron microscope image of the intermediate layer TAO / ZIF-8 / KH-590 / PDMS pervaporation composite membrane prepared in Example 1.

[0035] Figure 4 A diagram of a homemade device for performance testing in a specific implementation manner. DETAILED DESCRIPTION

[0036] The present invention is further described below by means of specific examples, but the protection scope of the present invention is not limited thereto.

[0037] The performance test method is as follows:

[0038] The performance of the prepared pervaporation membrane was evaluated using a homemade device. The effective test area of ​​the membrane pool was 7 cm 2 The test temperature was 70° C., the feed liquid was a 1 wt % n-butanol aqueous solution, and the concentration of n-butanol in the permeate solution and the feed liquid was determined by gas chromatography (GC-14B).

[0039] The specific process is as follows: the feed liquid enters the evaluation tank through a peristaltic pump, n-butanol contacts and permeates the PDSM surface of the membrane (a small amount of water can also pass through), and is collected through vacuum cooling.

[0040] (1) Permeation flux:

[0041]

[0042] Where, J(gm -2 h -1 ) is the total permeate flux; W (g) is the total mass of the permeate collected in the PV performance test, S (m 2 ) is the effective membrane area, and T(h) is the duration of the performance test.

[0043] (2) Separation factor:

[0044]

[0045] Where α is the separation factor; Y p and X f are the n-butanol contents (wt%) in the permeate and feed liquid, respectively.

[0046] (3) Pervaporation separation index:

[0047] PSI=J(α-1)

[0048] Where, PSI is the separation index factor; J(gm -2 h -1 ) is the total permeation flux; α is the separation factor.

[0049] The PVDF ultrafiltration membrane used in the following examples was manufactured by Zhongke Ruiyang Membrane Technology (Beijing) Co., Ltd., with a product number of SG-UF050-8040 and a molecular weight cut-off of 50,000 Da.

[0050] The PVDF ultrafiltration membrane used in the experiment was used by cutting the membrane module into circular membranes with a diameter of 4.5 cm.

[0051] In the following examples, the rotation speed of the spin coater during spin coating is 1500 rpm.

[0052] Example 1

[0053] (1) Hydrophilic modification of PVDF ultrafiltration membrane

[0054] First, prepare 50mM Tris-HCl buffer with a pH of 8.5, then dissolve 2g / L of TA in the buffer and set aside, which is recorded as solution A. Mark 10g / L of APTES ethanol solution as solution B. Then add solution B to solution A (V DI :VEtOH =5:1), designated as Solution C. The PVDF membrane was soaked in ethanol for 20 minutes, then allowed to react in Solution C for 12 hours at room temperature with shaking to form a TA-APTES coating. Finally, the membrane was washed sequentially with ethanol and deionized water with shaking to remove unreacted substances.

[0055] (2) Secondary hydrophobic modification of PVDF ultrafiltration membrane

[0056] 0.05 g of ODS was added to 20 mL of ethanol and completely dissolved, followed by the addition of 2 mL of deionized water. The pH was adjusted to 5 with acetic acid (Solution D). The PVDF membrane hydrophilically modified with TA-APTES was then immersed in Solution D and allowed to react on a shaker for 6 hours. After several washes with ethanol and then deionized water, the membrane was immersed in deionized water to remove any unreacted reagents. The modified coating, or intermediate layer, was designated TA-APTES@ODS(TAO).

[0057] (3) Preparation of composite PDMS membrane by CVD loading MOFs

[0058] 0.855g of PDMS was added to 5ml (3.42g) of n-heptane to obtain a 20wt% solution (Solution A), which was dissolved by stirring at room temperature. 0.0132g of Zn(acac)2 was then added and mixed uniformly for 30 minutes. 0.0855g of the crosslinker TEOS was then added and mixed uniformly for 15 minutes. Finally, 0.0171g of the catalyst DBTDL was added to accelerate the reaction, which lasted for approximately 10 minutes. The mass ratio of PDMS:TEOS:DBTDL was 100:10:2. After uniform mixing, the solution was sonicated and allowed to stand to remove bubbles. After approximately 20 minutes, the coating solution reached a desired viscosity. The PDMS coating solution was then spin-coated onto a PVDF substrate with an intermediate layer of TAO using a spin coater to produce a PDMS composite membrane. The membrane was then placed in a reaction vessel containing 1g of 2-methylimidazole and cross-linked in an 80°C oven for 12 hours, resulting in a TAO / ZIF-8 / PDMS composite membrane.

[0059] (4) Preparation of TAO / ZIF-8 / KH-590 / PDMS membrane

[0060] The TAO / ZIF-8 / PDMS composite membrane was shaken in a 4 wt % methanol solution of KH-590 for 60 minutes to perform surface hydrophobic modification, thereby obtaining the pervaporation composite membrane that preferentially permeates alcohol.

[0061] The total flux of the obtained TAO / ZIF-8 / KH-590 / PDMS composite membrane was 2890 g m -2 h -1 , the separation factor is 40.3 and the PSI is 113577.

[0062] Example 2

[0063] (1) Hydrophilic modification of PVDF ultrafiltration membrane

[0064] First, prepare 50mM Tris-HCl buffer with a pH of 8.5, then dissolve 2g / L of TA in the buffer and set aside, which is recorded as solution A. Mark 10g / L of APTES ethanol solution as solution B. Then add solution B to solution A (V DI :V EtOH =5:1), designated as Solution C. The PVDF membrane was soaked in ethanol for 20 minutes, then allowed to react in Solution C for 12 hours at room temperature with shaking to form a TA-APTES coating. Finally, the membrane was washed sequentially with ethanol and deionized water with shaking to remove unreacted substances.

[0065] (2) Secondary hydrophobic modification of PVDF ultrafiltration membrane

[0066] 0.05 g of ODS was added to 20 mL of ethanol and completely dissolved, followed by the addition of 2 mL of deionized water. The pH was adjusted to 5 with acetic acid solution, designated Solution D. The PVDF membrane hydrophilically modified with TA-APTES was then immersed in Solution D and allowed to react on a shaker for 12 hours. After several washes with ethanol and then deionized water, the membrane was immersed in deionized water to remove any unreacted reagents. The modified coating, or intermediate layer, was designated TA-APTES@ODS(TAO).

[0067] (3) Preparation of composite PDMS membrane by CVD loading MOFs

[0068] 0.855g of PDMS was added to 5ml of n-heptane to obtain a 20wt% solution (Solution A), which was stirred and dissolved at room temperature. 0.0132g of Zn(acac)2 was then added and mixed thoroughly for 30 minutes. 0.0855g of the crosslinker TEOS was then added and stirred for 15 minutes. Finally, 0.0171g of the catalyst DBTDL was added to accelerate the reaction for approximately 10 minutes. The mass ratio of PDMS:TEOS:DBTDL was 100:10:2. After uniform mixing, the solution was sonicated and allowed to stand to remove bubbles. After approximately 20 minutes, the coating solution reached a desired viscosity. The PDMS coating solution was then spin-coated onto a PVDF substrate with an intermediate layer of TAO using a spin coater to produce a PDMS composite membrane. The membrane was then placed in a reaction vessel containing 1g of 2-methylimidazole and subjected to a crosslinking reaction in an 80°C oven for 12 hours, resulting in a TAO / ZIF-8 / PDMS composite membrane.

[0069] (4) Preparation of TAO / ZIF-8 / KH-590 / PDMS membrane

[0070] The TAO / ZIF-8 / PDMS composite membrane was shaken in a 4 wt % methanol solution of KH-590 for 60 minutes to perform surface hydrophobic modification, thereby obtaining the pervaporation composite membrane that preferentially permeates alcohol.

[0071] The total flux of the obtained TAO / ZIF-8 / KH-590 / PDMS composite membrane was 2473 g m -2 h -1 , the separation factor is 43.1 and the PSI is 106586.3.

[0072] Example 3

[0073] (1) Hydrophilic modification of PVDF ultrafiltration membrane

[0074] First, prepare 50mM Tris-HCl buffer with a pH of 8.5, then dissolve 2g / L of TA in the buffer and set aside, which is recorded as solution A. Mark 10g / L of APTES ethanol solution as solution B. Then add solution B to solution A (V DI :V EtOH =5:1), designated as Solution C. The PVDF membrane was soaked in ethanol for 20 minutes, then allowed to react in Solution C for 12 hours at room temperature with shaking to form a TA-APTES coating. Finally, the membrane was washed sequentially with ethanol and deionized water with shaking to remove unreacted substances.

[0075] (2) Secondary hydrophobic modification of PVDF ultrafiltration membrane

[0076] 0.05 g of ODS was added to 20 mL of ethanol and completely dissolved, followed by the addition of 2 mL of deionized water. The pH was adjusted to 5 with acetic acid solution, designated Solution D. The PVDF membrane hydrophilically modified with TA-APTES was then immersed in Solution D and allowed to react on a shaker for 6 hours. After several washes with ethanol and then deionized water, the membrane was immersed in deionized water to remove any unreacted reagents. The modified coating, or intermediate layer, was designated TA-APTES@ODS(TAO).

[0077] (3) Preparation of composite PDMS membrane by CVD loading MOFs

[0078] 0.855g of PDMS was added to 5ml of n-heptane to obtain a 20wt% solution (Solution A), which was stirred and dissolved at room temperature. 0.0264g of Zn(acac)2 was then added and mixed thoroughly for 30 minutes. 0.0855g of the crosslinker TEOS was then added and stirred for 15 minutes. Finally, 0.0171g of the catalyst DBTDL was added to accelerate the reaction for approximately 10 minutes. The mass ratio of PDMS:TEOS:DBTDL was 100:10:2. After uniform mixing, the solution was sonicated and allowed to stand to remove bubbles. After approximately 15 minutes, the coating solution reached a desired viscosity. The PDMS coating solution was then spin-coated onto a PVDF substrate with an intermediate layer of TAO using a spin coater to produce a PDMS composite membrane. The membrane was then placed in a reaction vessel containing 1g of 2-methylimidazole and cross-linked in an 80°C oven for 12 hours to produce a TAO / ZIF-8 / PDMS composite membrane.

[0079] (4) Preparation of TAO / ZIF-8 / KH-590 / PDMS membrane

[0080] The TAO / ZIF-8 / PDMS composite membrane was shaken in a 4 wt % methanol solution of KH-590 for 60 minutes to perform surface hydrophobic modification, thereby obtaining the pervaporation composite membrane that preferentially permeates alcohol.

[0081] The total flux of the obtained TAO / ZIF-8 / KH-590 / PDMS composite membrane was 2540 g m -2 h -1 , the separation factor is 38.3 and the PSI is 94742.

[0082] Example 4

[0083] (1) Hydrophilic modification of PVDF ultrafiltration membrane

[0084] First, prepare 50mM Tris-HCl buffer with a pH of 8.5, then dissolve 2g / L of TA in the buffer and set aside, which is recorded as solution A. Mark 10g / L of APTES ethanol solution as solution B. Then add solution B to solution A (V DI :V EtOH =5:1), designated as Solution C. The PVDF membrane was soaked in ethanol for 20 minutes, then allowed to react in Solution C for 12 hours at room temperature with shaking to form a TA-APTES coating. Finally, the membrane was washed sequentially with ethanol and deionized water with shaking to remove unreacted substances.

[0085] (2) Secondary hydrophobic modification of PVDF ultrafiltration membrane

[0086] 0.05 g of ODS was added to 20 mL of ethanol and completely dissolved, followed by the addition of 2 mL of deionized water. The pH was adjusted to 5 with acetic acid solution, designated Solution D. The PVDF membrane hydrophilically modified with TA-APTES was then immersed in Solution D and allowed to react on a shaker for 6 hours. After several washes with ethanol and then deionized water, the membrane was immersed in deionized water to remove any unreacted reagents. The modified coating, or intermediate layer, was designated TA-APTES@ODS(TAO).

[0087] (3) Preparation of composite PDMS membrane by CVD loading MOFs

[0088] 0.855g of PDMS was added to 5ml of n-heptane to obtain a 20wt% solution (Solution A), which was stirred and dissolved at room temperature. 0.0264g of Zn(acac)2 was then added and mixed thoroughly for 30 minutes. 0.0855g of the crosslinker TEOS was then added and mixed thoroughly for 15 minutes. Finally, 0.0171g of the catalyst DBTDL was added to accelerate the reaction for approximately 10 minutes. The mass ratio of PDMS:TEOS:DBTDL was 100:10:2. After mixing thoroughly, the solution was sonicated and allowed to stand to remove bubbles. After approximately 15 minutes, the coating solution reached a desired viscosity. The PDMS coating solution was then spin-coated onto a PVDF substrate with an intermediate layer of TAO using a spin coater to produce a PDMS composite membrane. The membrane was then placed in a reaction vessel containing 1g of 2-methylimidazole and cross-linked in an oven at 120°C for 6 hours to produce a TAO / ZIF-8 / PDMS composite membrane.

[0089] (4) Preparation of TAO / ZIF-8 / KH-590 / PDMS membrane

[0090] The TAO / ZIF-8 / PDMS composite membrane was shaken in a 4 wt % methanol solution of KH-590 for 60 minutes to perform surface hydrophobic modification, thereby obtaining the pervaporation composite membrane that preferentially permeates alcohol.

[0091] The total flux of the obtained TAO / ZIF-8 / KH-590 / PDMS composite membrane was 3201 g m -2 h -1 , the separation factor is 30.1 and the PSI is 93149.1.

[0092] Example 5

[0093] (1) Hydrophilic modification of PVDF ultrafiltration membrane

[0094] First, prepare 50mM Tris-HCl buffer with a pH of 8.5, then dissolve 2g / L of TA in the buffer and set aside, which is recorded as solution A. Mark 10g / L of APTES ethanol solution as solution B. Then add solution B to solution A (V DI :V EtOH =5:1), designated as Solution C. The PVDF membrane was soaked in ethanol for 20 minutes, then allowed to react in Solution C for 12 hours at room temperature with shaking to form a TA-APTES coating. Finally, the membrane was washed sequentially with ethanol and deionized water with shaking to remove unreacted substances.

[0095] (2) Secondary hydrophobic modification of PVDF ultrafiltration membrane

[0096] 0.05 g of ODS was added to 20 mL of ethanol and completely dissolved, followed by the addition of 2 mL of deionized water. The pH was adjusted to 5 with acetic acid solution, designated Solution D. The PVDF membrane hydrophilically modified with TA-APTES was then immersed in Solution D and allowed to react on a shaker for 6 hours. After several washes with ethanol and then deionized water, the membrane was immersed in deionized water to remove any unreacted reagents. The modified coating, or intermediate layer, was designated TA-APTES@ODS(TAO).

[0097] (3) Preparation of composite PDMS membrane by CVD loading MOFs

[0098] 0.855g of PDMS was added to 5ml of n-heptane to obtain a 20wt% solution (Solution A), which was stirred and dissolved at room temperature. 0.0264g of Zn(acac)2 was then added and mixed thoroughly for 30 minutes. 0.0855g of the crosslinker TEOS was then added and stirred for 15 minutes. Finally, 0.0171g of the catalyst DBTDL was added to accelerate the reaction for approximately 10 minutes. The mass ratio of PDMS:TEOS:DBTDL was 100:10:2. After uniform mixing, the solution was sonicated and allowed to stand to remove bubbles. After approximately 15 minutes, the coating solution reached a desired viscosity. The PDMS coating solution was then spin-coated onto a PVDF substrate with an intermediate layer of TAO using a spin coater to produce a PDMS composite membrane. The membrane was then placed in a reaction vessel containing 1g of 2-methylimidazole and cross-linked in an 80°C oven for 12 hours to produce a TAO / ZIF-8 / PDMS composite membrane.

[0099] (4) Preparation of TAO / ZIF-8 / KH-590 / PDMS membrane

[0100] The TAO / ZIF-8 / PDMS composite membrane was shaken in a 5 wt % methanol solution of KH-590 for 60 minutes to perform surface hydrophobic modification, thereby obtaining the pervaporation composite membrane that preferentially permeates alcohol.

[0101] The total flux of the obtained TAO / ZIF-8 / KH-590 / PDMS composite membrane was 2679 g m -2 h -1 , the separation factor is 43.3 and the PSI is 113321.7.

[0102] Example 6 Different reaction times of the intermediate layer

[0103] The other steps are the same as those in Example 1, except for the duration of the shaking and soaking reaction in step (1). The corresponding results are shown in the following table:

[0104]

[0105]

[0106] Comparative Example 1

[0107] (1) Preparation of pure PDMS film

[0108] Add 0.855g of PDMS to 5ml of n-heptane to obtain a 20wt% solution (solution a), and stir and dissolve at room temperature. Then add 0.0855g of cross-linking agent TEOS and stir, mixing evenly for 15 minutes. Finally, add 0.0171g of catalyst DBTDL to accelerate the reaction for about 10 minutes. Among them, the mass ratio of PDMS:TEOS:DBTDL is 100:10:2. After uniform mixing, ultrasonicate and stand to remove bubbles. After about 30 minutes, the coating liquid reaches a certain viscosity. Use a spin coater to spin-coat the PDMS coating liquid on the PVDF ultrafiltration membrane to obtain a PDMS composite membrane. The membrane is cross-linked in an 80°C oven for 12 hours to obtain a PDMS pure membrane.

[0109] The total flux of the obtained PDMS pure membrane was 1469 g m -2 h -1 , the separation factor is 34.7 and the PSI is 49505.3.

[0110] Comparative Example 2

[0111] (1) Hydrophilic modification of PVDF ultrafiltration membrane

[0112] First, prepare 50mM Tris-HCl buffer with a pH of 8.5, then dissolve 2g / L of TA in the buffer and set aside, which is recorded as solution A. Mark 10g / L of APTES ethanol solution as solution B. Then add solution B to solution A (V DI :V EtOH=5:1), designated as Solution C. The PVDF membrane was soaked in ethanol for 20 minutes, then allowed to react in Solution C for 12 hours at room temperature with shaking to form a TA-APTES coating. Finally, the membrane was washed sequentially with ethanol and deionized water with shaking to remove unreacted substances.

[0113] (2) Secondary hydrophobic modification of PVDF ultrafiltration membrane

[0114] 0.05 g of ODS was added to 20 mL of ethanol and completely dissolved, followed by the addition of 2 mL of deionized water. The pH was adjusted to 5 with acetic acid solution, designated Solution D. The PVDF membrane hydrophilically modified with TA-APTES was then immersed in Solution D and allowed to react on a shaker for 6 hours. After several washes with ethanol and then deionized water, the membrane was immersed in deionized water to remove any unreacted reagents. The modified coating, or intermediate layer, was designated TA-APTES@ODS(TAO).

[0115] (3) Preparation of PDMS composite membrane

[0116] Add 0.855g of PDMS to 5ml of n-heptane to obtain a 20wt% solution (solution a), and stir and dissolve at room temperature. Then add 0.0855g of crosslinker TEOS and stir, mixing evenly for 15 minutes. Finally, add 0.0171g of catalyst DBTDL to accelerate the reaction for about 10 minutes. Among them, the mass ratio of PDMS:TEOS:DBTDL is 100:10:2. After uniform mixing, ultrasonicate and stand to remove bubbles. After about 30 minutes, the coating liquid reaches a certain viscosity. Use a spin coater to spin-coat the PDMS coating liquid on a PVDF substrate with an intermediate layer of TAO to obtain a PDMS composite membrane. The membrane is cross-linked in an 80°C oven for 12 hours to obtain a TAO / PDMS composite membrane.

[0117] The total flux of the obtained TAO / PDMS composite membrane was 1895 g m -2 h -1 , the separation factor is 38.2 and the PSI is 70494.

[0118] Comparative Example 3

[0119] (1) Preparation of composite PDMS membranes by CVD loading of MOFs

[0120] 0.855g of PDMS was added to 5ml of n-heptane to obtain a 20wt% solution (Solution A), which was stirred and dissolved at room temperature. 0.0132g of Zn(acac)2 was then added and mixed uniformly for 30 minutes. 0.0855g of the crosslinker TEOS was then added and mixed uniformly for 15 minutes. Finally, 0.0171g of the catalyst DBTDL was added to accelerate the reaction for approximately 10 minutes. The mass ratio of PDMS:TEOS:DBTDL was 100:10:2. After uniform mixing, the solution was sonicated and allowed to stand to remove bubbles. After approximately 20 minutes, the coating solution reached a certain viscosity. The PDMS coating solution was then spin-coated onto a PVDF ultrafiltration membrane using a spin coater to obtain a PDMS composite membrane. The membrane was then placed in a reaction vessel containing 1g of 2-methylimidazole and cross-linked in an 80°C oven for 12 hours to obtain a ZIF-8 / PDMS composite membrane.

[0121] The total flux of the obtained ZIF-8 / PDMS composite membrane was 1894 g m -2 h -1 , the separation factor is 45 and the PSI is 83336.

[0122] Comparative Example 4

[0123] (1) Hydrophilic modification of PVDF ultrafiltration membrane

[0124] First, prepare 50mM Tris-HCl buffer with a pH of 8.5, then dissolve 2g / L of TA in the buffer and set aside, which is recorded as solution A. Mark 10g / L of APTES ethanol solution as solution B. Then add solution B to solution A (V DI :V EtOH =5:1), designated as Solution C. The PVDF membrane was soaked in ethanol for 20 minutes, then allowed to react in Solution C for 12 hours at room temperature with shaking to form a TA-APTES coating. Finally, the membrane was washed sequentially with ethanol and deionized water with shaking to remove unreacted substances.

[0125] (2) Secondary hydrophobic modification of PVDF ultrafiltration membrane

[0126] 0.05 g of ODS was added to 20 mL of ethanol and completely dissolved, followed by the addition of 2 mL of deionized water. The pH was adjusted to 5 with acetic acid solution, designated Solution D. The PVDF membrane hydrophilically modified with TA-APTES was then immersed in Solution D and allowed to react on a shaker for 6 hours. After several washes with ethanol and then deionized water, the membrane was immersed in deionized water to remove any unreacted reagents. The modified coating, or intermediate layer, was designated TA-APTES@ODS(TAO).

[0127] (3) Preparation of PDMS composite membrane

[0128] Add 0.855g of PDMS to 5ml of n-heptane to obtain a 20wt% solution (solution a), and stir and dissolve at room temperature. Then add 0.0855g of TEOS as a crosslinker and stir, and mix evenly for 15 minutes. Finally, add 0.0171g of catalyst DBTDL to accelerate the reaction for about 10 minutes. Among them, the mass ratio of PDMS:TEOS:DBTDL is 100:10:2. After uniform mixing, ultrasonicate and stand to remove bubbles. After about 30 minutes, the coating liquid reaches a certain viscosity. Use a spin coater to spin-coat the PDMS coating liquid on a PVDF substrate with an intermediate layer of TAO to obtain a PDMS composite membrane. The membrane is cross-linked in an 80°C oven for 12 hours to obtain a TAO / PDMS composite membrane. (4) Preparation of TAO / KH-590 / PDMS membrane

[0129] The TAO / PDMS composite membrane was shaken in a 4 wt % methanol solution of KH-590 for 60 minutes to perform surface hydrophobic modification, thereby obtaining the pervaporation composite membrane that preferentially permeates alcohol.

[0130] The total flux of the obtained TAO / KH-590 / PDMS composite membrane was 2269 g m -2 h -1 , the separation factor is 40.9 and the PSI is 90533.1.

[0131] Comparative Example 5 Non-in-situ

[0132] (1) Hydrophilic modification of PVDF ultrafiltration membrane

[0133] First, prepare 50mM Tris-HCl buffer with a pH of 8.5, then dissolve 2g / L of TA in the buffer and set aside, which is recorded as solution A. Mark 10g / L of APTES ethanol solution as solution B. Then add solution B to solution A (V DI :V EtOH =5:1), designated as Solution C. The PVDF membrane was soaked in ethanol for 20 minutes, then allowed to react in Solution C for 12 hours at room temperature with shaking to form a TA-APTES coating. Finally, the membrane was washed sequentially with ethanol and deionized water with shaking to remove unreacted substances.

[0134] (2) Secondary hydrophobic modification of PVDF ultrafiltration membrane

[0135] 0.05 g of ODS was added to 20 mL of ethanol and completely dissolved, followed by the addition of 2 mL of deionized water. The pH was adjusted to 5 with acetic acid solution, designated Solution D. The PVDF membrane hydrophilically modified with TA-APTES was then immersed in Solution D and allowed to react on a shaker for 6 hours. After several washes with ethanol and then deionized water, the membrane was immersed in deionized water to remove any unreacted reagents. The modified coating, or intermediate layer, was designated TA-APTES@ODS(TAO).

[0136] (3) Synthesis of ZIF-8

[0137] ZIF-8 was generated by mixing equal volumes of a 0.018M aqueous solution of zinc nitrate hexahydrate (Zn(NO₃)₂ 6H₂O) and a 1.38M aqueous solution of 2-methylimidazole. The mixture was stirred at room temperature for 1 hour, resulting in a turbid solution. The resulting solid was centrifuged and washed five times with methanol and then water, followed by drying in an 80°C oven to yield ZIF-8.

[0138] (4) Preparation of PDMS mixed matrix membrane

[0139] 0.855g of PDMS was added to 5ml of n-heptane to obtain a 20wt% solution (Solution A), which was stirred and dissolved at room temperature. 0.0132g of ZIF-8 was then added and stirred for 30 minutes. 0.0855g of the crosslinker TEOS was then added and stirred for 15 minutes. Finally, 0.0171g of the catalyst DBTDL was added to accelerate the reaction for approximately 10 minutes. The mass ratio of PDMS:TEOS:DBTDL was 100:10:2. After uniform mixing, the solution was sonicated and allowed to stand to remove bubbles. After approximately 20 minutes, the coating solution reached a certain viscosity. The PDMS coating solution was then spin-coated onto a PVDF substrate with an intermediate layer of TAO using a spin coater to produce a PDMS composite membrane. The crosslinking reaction was allowed to proceed in an 80°C oven for 12 hours to obtain a TAO / ZIF-8@PDMS composite membrane.

[0140] (5) Preparation of TAO / ZIF-8@PDMS / KH-590 membrane

[0141] The TAO / ZIF-8 / PDMS composite membrane was shaken in a 4 wt % methanol solution of KH-590 for 60 minutes to perform surface hydrophobic modification, thereby obtaining the pervaporation composite membrane that preferentially permeates alcohol.

[0142] The total flux of the obtained TAO / ZIF-8@PDMS / KH-590 mixed matrix membrane was 1993 g m -2 h -1 , the separation factor is 42.7 and the PSI is 83108.1.

[0143] Comparative Example 6 without intermediate layer

[0144] (1) Preparation of composite PDMS membranes by CVD loading of MOFs

[0145] 0.855g of PDMS was added to 5ml of n-heptane to obtain a 20wt% solution (Solution A), which was stirred and dissolved at room temperature. 0.0132g of Zn(acac)2 was then added and mixed uniformly for 30 minutes. 0.0855g of the crosslinker TEOS was then added and mixed uniformly for 15 minutes. Finally, 0.0171g of the catalyst DBTDL was added to accelerate the reaction for approximately 10 minutes. The mass ratio of PDMS:TEOS:DBTDL was 100:10:2. After uniform mixing, the solution was sonicated and allowed to stand to remove bubbles. After approximately 20 minutes, the coating solution reached a certain viscosity. The PDMS coating solution was then spin-coated onto a PVDF ultrafiltration membrane using a spin coater to obtain a PDMS composite membrane. The membrane was then placed in a reaction vessel containing 1g of 2-methylimidazole and cross-linked in an 80°C oven for 12 hours to obtain a ZIF-8 / PDMS composite membrane.

[0146] (2) Preparation of ZIF-8 / KH-590 / PDMS membrane

[0147] The ZIF-8 / PDMS composite membrane was shaken in a 4 wt % methanol solution of KH-590 for 60 minutes to perform surface hydrophobic modification, thereby obtaining the pervaporation composite membrane that preferentially permeates alcohol.

[0148] The total flux of the obtained ZIF-8 / KH-590 / PDMS composite membrane was 2137 g m -2 h -1 , the separation factor is 39.5 and the PSI is 82274.5.

Claims

1. A method for preparing a PDMS-based pervaporation membrane having a continuous intermediate layer, characterized in that The method is: (1) Hydrophilic modification of ultrafiltration membrane Dissolving tannic acid in a pH 7.5-8.5 buffer to obtain a 1-4 g / L tannic acid solution, adding an ethanol solution of 3-aminopropyltriethoxysilane to obtain a reaction solution A; immersing a pretreated hydrophobic ultrafiltration membrane in the reaction solution A at room temperature, shaking and soaking for 6-14 hours, and then washing to obtain a hydrophilically modified ultrafiltration membrane; the mass ratio of tannic acid to 3-aminopropyltriethoxysilane contained in the ethanol solution of 3-aminopropyltriethoxysilane is 1:0.5-2; (2) Secondary hydrophobic modification of ultrafiltration membrane Dissolve octadecyltrimethoxysilane (ODS) in anhydrous ethanol to obtain an octadecyltrimethoxysilane solution with a concentration of 1.0-4.0 g / L, add deionized water, adjust the pH to 4.0-5.0, and obtain a reaction solution B; immerse the hydrophilic modified ultrafiltration membrane described in step (1) in the reaction solution B, shake and react for 4-12 hours, and then wash to obtain a TA-APTES@ODS membrane; the volume ratio of the anhydrous ethanol to the deionized water is 6-12:1; (3) Preparation of composite PDMS membranes by chemical vapor deposition of MOFs Dissolving polydimethylsiloxane in a good solvent to obtain a PDMS solution with a concentration of 10 wt% to 30 wt%; adding zinc acetylacetonate and tetraethyl orthosilicate, mixing evenly, adding dibutyltin dilaurate to carry out a catalytic reaction for 8 to 30 minutes to obtain a coating solution; the mass ratio of the polydimethylsiloxane, zinc acetylacetonate, tetraethyl orthosilicate to dibutyltin dilaurate is 100:0.5-6:5-15:1-3; The coating liquid is completely spin-coated on the TA-APTES@ODS membrane described in step (2), placed in a reaction kettle containing an organic ligand, and subjected to a thermal cross-linking reaction at 60-140°C under closed conditions for 6-14 hours to obtain a TAO / ZIF-8 / PDMS composite membrane; The mass of the coating solution is 0.2-0.3 g / cm based on the area of ​​the TA-APTES@ODS membrane. 2 ; The mass ratio of zinc acetylacetonate to the organic ligand is 1: 25-100; (4) Hydrophobic modification of TAO / ZIF-8 / PDMS composite membrane surface The TAO / ZIF-8 / PDMS composite membrane described in step (3) is shaken in a 2-6 wt% silane coupling agent solution for 20-100 min to obtain the continuous intermediate layer PDMS-based pervaporation membrane.

2. The method for preparing a PDMS-based pervaporation membrane having a continuous intermediate layer according to claim 1, characterized in that The pretreatment in step (1) is as follows: soaking the hydrophobic ultrafiltration membrane in ethanol for 20 minutes.

3. The method for preparing a PDMS-based pervaporation membrane having a continuous intermediate layer according to claim 1, wherein: The concentration of the ethanol solution of 3-aminopropyltriethoxysilane in step (1) is 6-14 g / L.

4. The method for preparing a PDMS-based pervaporation membrane having a continuous intermediate layer according to claim 1, wherein: The hydrophobic ultrafiltration membrane in step (1) is one of polyvinylidene fluoride ultrafiltration membrane, polysulfone ultrafiltration membrane and polytetrafluoroethylene ultrafiltration membrane.

5. The method for preparing a PDMS-based pervaporation membrane having a continuous intermediate layer according to claim 1, wherein: The buffer in step (1) is at least one of tris-HCl buffer, tris-phosphate buffer, and phosphate buffer.

6. The method for preparing a PDMS-based pervaporation membrane having a continuous intermediate layer according to claim 1, wherein The cleaning in step (1) is as follows: washing with ethanol and deionized water in sequence; The cleaning in step (2) is: washing with ethanol and deionized water in sequence.

7. The method for preparing a PDMS-based pervaporation membrane having a continuous intermediate layer according to claim 1, wherein: The good solvent in step (3) is at least one of n-heptane, n-hexane, chloroform, dichloromethane, and toluene.

8. The method for preparing a PDMS-based pervaporation membrane having a continuous intermediate layer according to claim 1, wherein: The organic ligand in step (3) is at least one of 2-methylimidazole, 1-ethylimidazole, benzimidazole, and 1-butylimidazole.

9. The method for preparing a PDMS-based pervaporation membrane having a continuous intermediate layer according to claim 1, wherein: The silane coupling agent contained in the silane coupling agent solution in step (4) is at least one of γ-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane.

10. The method for preparing a PDMS-based pervaporation membrane having a continuous intermediate layer according to claim 1, wherein: The solvent in the silane coupling agent solution in step (4) is at least one of methanol, water, ethanol, benzene and toluene.

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