Metal-organic framework mixed matrix membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of gas membrane separation, in particular to a metal-organic framework mixed matrix membrane and a preparation method and application thereof. The mixed matrix membrane is prepared by taking a water-stable metal-organic framework material Zn-bzc-2CH3 synthesized by a solvothermal method as a filler dispersion phase and cross-linked polyethylene glycol XLPEO as a polymer matrix continuous phase through ultraviolet cross-linking polymerization. The Zn-bzc-2CH3 material has a dynamic screening capability on propylene / propane, so that the mixed matrix membrane shows enhanced propylene / propane separation performance.

Description

Technical Field

[0001] The invention belongs to the technical field of gas membrane separation, and in particular relates to a metal-organic framework mixed matrix membrane and a preparation method and application thereof. Background Art

[0002] Polymer-grade propylene (C3H6) with a purity of more than 99.5% is a key raw material for the production of polypropylene, which is one of the most produced synthetic plastics in the world. The main impurity in propylene is propane (C3H8), so the removal of propane is an important step in obtaining high-purity propylene. At present, the industry mainly relies on cryogenic distillation to separate propylene / propane, which has high investment costs and energy consumption. Therefore, the development of energy-saving and efficient propylene / propane separation methods is of great significance for energy conservation and emission reduction in chemical processes.

[0003] Compared with traditional separation methods, membrane separation is a more energy-efficient and efficient separation technology. Among the many types of membrane materials, mixed matrix membranes can combine the good processability of polymers with the good diffusion and screening capabilities of new porous materials. It is expected to break through the limitations of polymer membrane separation performance while maintaining good large-scale preparation and application potential. It is a type of separation membrane material that is expected to be applied in the short term. One of the cores of mixed matrix membrane material design lies in the design and regulation of filler structure and function. Metal-organic framework materials, as a new type of nano-microstructured porous materials, have outstanding advantages in structural diversity, designability and controllability. They are an ideal filler for the preparation of mixed matrix membranes. However, metal-organic framework mixed matrix membranes with high propylene / propane separation performance are still relatively lacking.

[0004] Therefore, the development of metal-organic framework mixed matrix membrane materials that can efficiently separate propylene / propane has important research significance and value. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a metal-organic framework mixed matrix membrane and a preparation method and application thereof.

[0006] The present invention is achieved through the following technical solutions: A metal-organic framework mixed matrix membrane, wherein the filler used in the preparation of the mixed matrix membrane is a water-stable metal-organic framework material Zn-bzc-2CH3 with propylene / propane kinetic screening ability, and the polymer matrix is ​​cross-linked polyethylene glycol.

[0007] The present invention also provides a method for preparing the metal-organic framework mixed matrix membrane, comprising the following steps: S1: The Zn-bzc-2CH3 filler powder is uniformly dispersed in methanol by ultrasonic treatment to obtain a suspension A; S2: adding polyethylene glycol diacrylate oligomer PEGDA to suspension A, and mixing the filler particles and the oligomer uniformly by stirring and ultrasonic treatment to obtain suspension B; S3: adding a photoinitiator to the suspension B, mixing evenly by stirring and ultrasonic treatment, volatilizing the methanol in the obtained suspension B, increasing the viscosity of the casting liquid, and reducing the aggregation and sedimentation of particles; then, dropping the obtained casting liquid between two quartz glass plates with a certain gap, and then placing it in a UV cross-linking instrument, irradiating it under UV light, so that the oligomers in the casting liquid are cross-linked and cured to form a film; S4: The cross-linked and cured membrane is taken out from between the quartz glass plates and immersed in methanol for 3 days to fully dissolve the oligomers that are not fully cross-linked; then the membrane is taken out and the solvent is slowly evaporated at room temperature to reduce the curling and breakage of the membrane caused by stress; after the solvent is fully evaporated, the membrane is vacuum treated to further evaporate the residual solvent, and then the membrane is stored in a vacuum environment.

[0008] Further, the Zn-bzc-2CH3 filler used in step S1 comprises the following steps: (1) 0.42 g of 3,5-dimethylpyrazole-4-carboxylic acid and 0.89 g of zinc nitrate hexahydrate were dissolved in 40 mL of N,N-diethylformamide (DEF) to obtain a reaction solution A; (2) Add reaction solution A into a stainless steel reactor lined with polytetrafluoroethylene, and then place the reactor in a forced air drying oven. Through program temperature control, raise the temperature to 140°C in 6 hours, maintain it for 12 hours, and then reduce it to 30°C in 2 hours; (3) The reaction solution is centrifuged, and the crystals generated in the solution are collected to separate the crude Zn-bzc-2CH3 product; then, the product is soaked and centrifuged in methanol for several times to remove unreacted metal salts and organic ligands, thereby obtaining the Zn-bzc-2CH3 filler required for the preparation of the mixed matrix membrane.

[0009] Preferably, in step S2, the molecular weight of the PEGDA oligomer is 700 g / mol.

[0010] Preferably, in step S2, the mass ratio of Zn-bzc-2CH3 filler to PEGDA oligomer is 30:70.

[0011] Preferably, in step S3, the wavelength of the ultraviolet light used is 302 nm, and the irradiation time is 90 s.

[0012] Preferably, in step S3, the photoinitiator used is 2,2-dimethoxy-2-phenylacetophenone (DMPA), and the amount used is 0.1 wt %.

[0013] The present invention also provides application of the metal-organic framework mixed matrix membrane in propylene / propane separation.

[0014] The beneficial effects of the present invention are as follows: 1. The present invention uses a water-stable metal-organic framework material Zn-bzc-2CH3 as a filler to prepare a mixed matrix membrane. The membrane material belongs to a mixed matrix membrane, which can combine the advantages of polymer membranes in terms of cost and large-scale preparation and has good application prospects. In addition, the high water stability of the filler is conducive to the application of the membrane material under real separation conditions.

[0015] 2. The Zn-bzc-2CH3 material used in the present invention has a kinetic screening capability for propylene / propane, and the propylene / propane separation selectivity of the mixed matrix membrane is significantly improved compared with the pure XLPEO membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the Zn-bzc-2CH3 material used in the present invention; Figure 2 It is the propylene and propane adsorption isotherms of the Zn-bzc-2CH3 material synthesized in the present invention; Figure 3 It is the propylene and propane kinetic adsorption curve of the Zn-bzc-2CH3 material synthesized in the present invention; Figure 4 It is the XRD spectra of the synthesized Zn-bzc-2CH3 material and the mixed matrix membranes prepared in Examples 1-5 and Comparative Example 1; Figure 5 is a cross-sectional scanning electron micrograph of the mixed matrix membranes prepared in Examples 1-5 and Comparative Example 1; Figure 6 The propylene / propane separation performance of the mixed matrix membranes prepared in Examples 1-5 and Comparative Example 1. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0018] The present invention provides a metal-organic framework mixed matrix membrane, which is prepared by ultraviolet cross-linking polymerization using water-stable metal-organic framework material Zn-bzc-2CH3 synthesized by a solvent thermal method as a filler (dispersed phase) and cross-linked polyethylene glycol (XLPEO) as a polymer matrix (continuous phase).

[0019] The method for preparing the metal-organic framework mixed matrix membrane comprises the following steps: S1: The Zn-bzc-2CH3 filler powder is uniformly dispersed in methanol by ultrasonic treatment to obtain a suspension A; S2: Add polyethylene glycol diacrylate (PEGDA) oligomer to suspension A, and mix the filler particles and the oligomer uniformly by stirring and ultrasonic treatment to obtain suspension B; S3: adding a photoinitiator to the suspension B, mixing evenly by stirring and ultrasonic treatment, and then volatilizing a proper amount of methanol in the obtained suspension B to increase the viscosity of the casting liquid and reduce the aggregation and sedimentation of particles; then, dropping a proper amount of the obtained casting liquid between two quartz glass plates with a certain gap, and then placing it in a UV cross-linking instrument and irradiating it under UV light to cross-link and solidify the oligomers in the casting liquid into a film; S4: The cross-linked and cured membrane is taken out from between the quartz glass plates and immersed in methanol for 3 days to fully dissolve the oligomers that are not fully cross-linked. The membrane is then taken out and the solvent is slowly evaporated at room temperature to reduce the curling and breakage of the membrane caused by stress. After the solvent is fully evaporated, the membrane is vacuum treated to further evaporate the residual solvent, and then the membrane is stored in a vacuum environment for characterization and testing.

[0020] Wherein, the synthesis method of the Zn-bzc-2CH3 filler comprises the following steps: (i) dissolving 0.42 g of 3,5-dimethylpyrazole-4-carboxylic acid and 0.89 g of zinc nitrate hexahydrate in 40 mL of N,N-diethylformamide (DEF) to obtain a reaction solution A; (ii) Add reaction solution A into a stainless steel reactor with a polytetrafluoroethylene liner (volume: 100 mL), then place the reactor in a forced air drying oven, and through programmed temperature control, raise the temperature to 140°C over 6 h, maintain it for 12 h, and then reduce it to 30°C for 2 h; (iii) The reaction solution is centrifuged to collect the crystals generated in the solution to separate the crude Zn-bzc-2CH3 product; then, the product is soaked and centrifuged in methanol for several times to remove unreacted metal salts and organic ligands to obtain the Zn-bzc-2CH3 filler required for the preparation of the mixed matrix membrane.

[0021] Example 1 S1: 0.6 g Zn-bzc-2CH3 powder was uniformly dispersed in 2.0 g methanol by ultrasonic treatment to obtain suspension A; S2: Add 1.4 g of polyethylene glycol diacrylate (PEGDA) oligomer to suspension A, and mix the filler particles and the oligomer uniformly by stirring and ultrasonic treatment to obtain suspension B; S3: Add 0.004 g of photoinitiator DMPA to the suspension B, mix well by stirring and ultrasonic treatment, and then volatilize the methanol in the obtained suspension B appropriately to increase the viscosity of the casting liquid and reduce the aggregation and sedimentation of particles; then, drop an appropriate amount of the obtained casting liquid between two quartz glass plates with a certain gap, and then place it in a UV cross-linking instrument and irradiate it under UV light with a wavelength of 302 nm for 90 seconds to cross-link and solidify the oligomers in the casting liquid into a film; S4: The cross-linked and cured membrane is taken out from between the quartz glass plates and immersed in methanol for 3 days to fully dissolve the oligomers that are not fully cross-linked; then the membrane is taken out and the solvent is slowly evaporated at room temperature to reduce the curling and breakage of the membrane caused by stress; after the solvent is fully evaporated, the membrane is vacuum treated to further evaporate the residual solvent to obtain the metal-organic framework mixed matrix membrane.

[0022] Example 2 The difference between Example 2 and Example 1 is that the mass of Zn-bzc-2CH3 in step S1 is 0.2 g, the mass of PEGDA in step S2 is 1.8 g, and the other conditions are exactly the same.

[0023] Example 3 The difference between Example 3 and Example 1 is that the mass of Zn-bzc-2CH3 in step S1 is 0.4 g, the mass of PEGDA in step S2 is 1.6 g, and the other conditions are exactly the same.

[0024] Example 4 The difference between Example 3 and Example 1 is that the mass of Zn-bzc-2CH3 in step S1 is 0.8 g, the mass of PEGDA in step S2 is 1.2 g, and the other conditions are exactly the same.

[0025] Example 5 The difference between Example 5 and Example 1 is that the mass of Zn-bzc-2CH3 in step S1 is 1.0 g, the mass of PEGDA in step S2 is 1.0 g, and the other conditions are exactly the same.

[0026] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the mass of Zn-bzc-2CH3 in step S1 is 0 g, the mass of PEGDA in step S2 is 2.0 g, and the other conditions are exactly the same.

[0027] The metal-organic framework mixed matrix membrane of the present invention, the metal-organic framework material Zn-bzc-2CH3 used in the preparation of the membrane has a structure as follows Figure 1The Zn-bzc-2CH3 material has a cage-like pore structure with a large pore cavity and a small pore window. The pore window size allows the passage of propylene and propane molecules. Therefore, the thermodynamic adsorption isotherm of the material for propylene and propane is approximately (see Figure 2 ), with no apparent selectivity. However, there are differences in the diffusion behavior of propylene and propane molecules when they pass through the smaller pore windows of the material (see Figure 3 ), relatively small propylene molecules can pass through the pores of the material faster. Therefore, the material has a high kinetic adsorption selectivity for propylene and propane (~17.1), and using this material as a filler can improve the propylene / propane separation factor of the membrane.

[0028] Figure 4 XRD spectra of the mixed matrix membranes and the synthesized Zn-bzc-2CH3 materials prepared in Examples 1-5 and Comparative Example 1. As can be seen from the figure, with the increase of the loading amount of the Zn-bzc-2CH3 material, the characteristic peaks of the metal-organic framework material in the spectrum become more and more obvious, while the characteristic peaks of the polymer gradually weaken. Figure 5 The scanning electron microscope images of the cross-sections of the mixed matrix membranes prepared in Examples 1-5 and Comparative Example 1 show that the Zn-bzc-2CH3 material particles are uniformly distributed throughout the membrane. As the loading amount increases, more metal-organic framework particles can be observed in the images.

[0029] Propylene / propane separation performance test of the mixed matrix membrane obtained in Examples 1-5 and Comparative Example 1 The propylene / propane separation performance of the mixed matrix membranes prepared in Examples 1-5 and Comparative Example 1 was tested using a 50:50 propylene / propane mixed gas at a pressure of 0.2 MPa. The test results are as follows: Figure 6 As shown in Table 1. It can be seen that the mixed matrix membrane obtained in Example 1 has the highest propylene / propane separation factor. A higher doping amount is likely to introduce defects into the membrane, thereby reducing the separation selectivity of the membrane. It can be seen that the preferred filler doping amount of the Zn-bzc-2CH3 / XLPEO mixed matrix membrane is 30wt%.

[0030] Table 1. Test results of propylene / propane separation performance of mixed matrix membranes obtained in Examples 1-5 and Comparative Example 1

Claims

1. A metal-organic framework mixed matrix membrane, characterized in that: The mixed matrix membrane uses water-stable metal-organic framework material Zn-bzc-2CH3 as a filler dispersed phase and cross-linked polyethylene glycol XLPEO as a polymer matrix continuous phase, and is prepared by ultraviolet cross-linking polymerization.

2. The metal-organic framework mixed matrix membrane according to claim 1, characterized in that: The preparation method of the metal-organic framework material Zn-bzc-2CH3 comprises the following steps: (1) 0.42 g of 3,5-dimethylpyrazole-4-carboxylic acid and 0.89 g of zinc nitrate hexahydrate were dissolved in 40 mL of N,N-diethylformamide DEF to obtain a reaction solution A; (2) Add reaction solution A into a stainless steel reactor lined with polytetrafluoroethylene, and then place the reactor in a forced air drying oven. Through program temperature control, raise the temperature to 140°C in 6 hours, maintain it for 12 hours, and then reduce it to 30°C in 2 hours; (3) The reaction solution is centrifuged, and the crystals generated in the solution are collected to separate the crude Zn-bzc-2CH3 product; then, the unreacted metal salt and organic ligand are removed by immersion-centrifugation washing with methanol to obtain the Zn-bzc-2CH3 filler required for the preparation of the mixed matrix membrane.

3. A method for preparing a metal-organic framework mixed matrix membrane, characterized in that: The following steps are involved: S1: The Zn-bzc-2CH3 filler powder is uniformly dispersed in methanol by ultrasonic treatment to obtain a suspension A; S2: adding polyethylene glycol diacrylate PEGDA oligomer to suspension A, and mixing the filler particles and the oligomer uniformly by stirring and ultrasonic treatment to obtain suspension B; S3: adding a photoinitiator to the suspension B, mixing evenly by stirring and ultrasonic treatment, volatilizing the methanol in the obtained suspension B, and then dropping the obtained casting liquid between two quartz glass plates, and then placing it in a UV cross-linking instrument, irradiating it under UV light, so that the oligomers in the casting liquid are cross-linked and cured to form a film; S4: The cross-linked and cured membrane is taken out from between the quartz glass plates and immersed in methanol for 3 days to fully dissolve the oligomers that are not fully cross-linked; then the membrane is taken out and the solvent is slowly evaporated at room temperature to reduce the curling and breakage of the membrane caused by stress; after the solvent is fully evaporated, the membrane is vacuum treated to further evaporate the residual solvent, and then the membrane is stored in a vacuum environment.

4. The method for preparing a metal-organic framework mixed matrix membrane according to claim 3, characterized in that: In step S2, the molecular weight of the PEGDA oligomer is 700 g / mol.

5. The method for preparing a metal-organic framework mixed matrix membrane according to claim 3, characterized in that: In step S3, the wavelength of the ultraviolet light is 302 nm, and the irradiation time is 90 s.

6. The method for preparing a metal-organic framework mixed matrix membrane according to claim 3, characterized in that: In step S3, the photoinitiator is 2,2-dimethoxy-2-phenylacetophenone DMPA, and the amount used is 0.1 wt %.

7. Use of the metal-organic framework mixed matrix membrane according to any one of claims 1 or 2 in propylene / propane separation.

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