ZIF-8 membrane as well as in-situ synthesis method and application thereof

Abstract

The invention provides a ZIF-8 membrane and an in-situ synthesis method and application thereof, and belongs to the technical field of MOF materials, and specifically, the in-situ synthesis method of the ZIF-8 membrane provided by the invention comprises the following steps: S1, mixing zinc salt, 2-methylimidazole and water to prepare a precursor solution; s2, immersing a carrier in the precursor solution, and standing to form a film; and S3, soaking the carrier after film formation in water, and after soaking is completed, transferring the carrier into methanol for activation to obtain the ZIF-8 film. The in-situ synthesis method has the advantage of simple operation, and the prepared ZIF-8 membrane has the advantages of low preparation cost and high propylene / propane selectivity, and has wide industrial application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of MOF materials, and in particular to a ZIF-8 membrane and an in-situ synthesis method and application thereof. Background Art

[0002] Propylene is one of the most abundant basic organic chemical raw materials in the world. Currently, the primary method for industrially producing propylene is through propane cracking. However, the final product often contains a certain proportion of propane feedstock. Traditionally, the separation of propylene / propane mixtures relies primarily on cryogenic distillation technology. However, the boiling point difference between propane and propylene is small, and cryogenic distillation separation consumes significant energy and has low separation efficiency. Therefore, it is necessary to seek a more efficient and cost-effective propylene / propane separation technology. Membrane separation is a green separation technology that has emerged in recent years. Driven by pressure or chemical potential differences, membrane separation is not constrained by phase or thermodynamic equilibrium. Compared to traditional separation processes such as distillation and adsorption, membrane separation technology offers lower energy consumption and significantly higher separation efficiency. New membrane separation technologies offer a new, energy-efficient approach for propylene / propane separation.

[0003] Metal-organic frameworks (MOFs) have shown great potential in gas separation applications such as hydrocarbon separation and carbon capture due to their tunable pore structures and excellent adsorption properties. ZIF-8, one of the most representative MOF materials, has an effective kinetic sieving size between propylene (4.02 Å) and propane (4.16 Å) molecules and exhibits excellent kinetic sieving performance for propylene / propane separation (kinetic selectivity of 125), making it considered an ideal membrane material for propylene / propane separation. However, existing ZIF-8 membrane preparation processes often face technical challenges such as cumbersome synthesis steps, poor reproducibility, and low membrane formation efficiency, which severely restrict the scalable preparation and large-scale application of ZIF-8 membranes. Therefore, the development of simple synthesis strategies with mild synthesis conditions to achieve controllable and large-scale preparation of ZIF-8 membranes is a key focus of current research. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to improve the separation efficiency of propylene / propane mixed gas and reduce the separation cost.

[0005] In order to solve the above technical problems, the first aspect of the present invention provides an in-situ synthesis method of a ZIF-8 membrane, comprising the following steps: S1: Mix zinc salt, 2-methylimidazole and water to prepare a precursor solution; S2: Immerse the support in the precursor solution and let it stand to form a film; S3: Soaking the membrane-formed support in water, and then transferring it to methanol for activation to obtain a ZIF-8 membrane.

[0006] The present invention directly forms a film under mild conditions through a one-step immersion static method, avoiding the multi-step operations such as seed modification and interface treatment required by the traditional secondary growth method, and greatly simplifying the process flow; in step S3, the present invention adopts a step-by-step treatment method of water and methanol, which can effectively remove residual ligands and loose grains in the membrane while activating ZIF-8.

[0007] Preferably, in step S1, the molar ratio of the zinc salt, 2-methylimidazole and water is 1: (30-60): (1500-3990).

[0008] The invention uses an excessive amount of imidazole ligand to slow down the generation speed of crystal nuclei, thereby promoting the directional and orderly growth of crystals and obtaining a continuous film layer with uniform pore size distribution.

[0009] Preferably, in step S2, the temperature for static film formation is 268-303K.

[0010] Preferably, in step S3, the time length for soaking the carrier in water after film formation is 0.5 to 1 hour.

[0011] Preferably, in step S3, the activation time is 0.5 to 2 hours.

[0012] Preferably, in step S2, the carrier is an alumina carrier or a polymer PAN carrier.

[0013] The second aspect of the present invention provides a ZIF-8 membrane, which is prepared by the in-situ synthesis method described in the first aspect.

[0014] The third aspect of the present invention provides an application of the ZIF-8 membrane described in the second aspect, wherein the application is to use the ZIF-8 membrane for separating a mixed gas of C3H6 and C3H8.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention achieves controlled growth of ZIF-8 crystals on the carrier surface by optimizing the synthesis reaction conditions. This method abandons the complexity of traditional high-temperature and high-pressure or secondary growth processes. Through in-situ film formation technology, a continuous and dense ZIF-8 crystal layer is directly formed on the carrier surface, avoiding membrane defects caused by uneven grain stacking. At the same time, the water / methanol step-by-step post-treatment process effectively removes loose surface grains and solvent residues, maintaining the integrity of the membrane structure and optimizing the pore microenvironment. The pore size of the resulting ZIF-8 membrane is precisely controlled to close to the kinetic diameter of propylene (4.0 Å), significantly improving the propylene / propane separation selectivity through the molecular sieving effect, while the propylene permeability is stabilized at 3.0×10 -8 mol m -2 s -1 Pa-1 The above takes into account both high flux and high selectivity, providing an efficient solution for the large-scale preparation of industrial-grade gas separation membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the SEM characterization result of product M1 in Example 1 of the present invention; Figure 2 This is the SEM characterization result of product M9 in Example 3 of the present invention; Figure 3 This is the SEM characterization result of product M14 in Example 5 of the present invention; Figure 4 This is the SEM characterization result of product M15 in Example 6 of the present invention; Figure 5 This is the SEM characterization result of product M16 in Example 7 of the present invention. DETAILED DESCRIPTION

[0017] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only intended to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter ranges described in the present invention. Reasonable variations derived therefrom are still within the scope of protection of the claims of the present invention.

[0018] It should be noted that the endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0019] As described in the background technology, although existing MOF membranes can be used for gas separation, they still have defects such as high preparation cost and unstable performance. Based on this, the specific embodiment of the present invention provides an in situ synthesis method of ZIF-8 membrane, which specifically includes the following steps: S1: Mix zinc salt, 2-methylimidazole and water to prepare a precursor solution; S2: Immerse the support in the precursor solution and let it stand to form a film; S3: Soaking the membrane-formed support in water, and then transferring it to methanol for activation to obtain a ZIF-8 membrane.

[0020] Unlike existing technologies, this embodiment directly forms the membrane under isothermal conditions at room temperature through a one-step immersion and static method, avoiding the multiple steps required for secondary growth methods, such as seed modification and interface treatment, significantly simplifying the process. Furthermore, compared with hydrothermal and solvothermal methods, this embodiment can produce MOF membranes at room temperature, using milder reaction conditions and avoiding the membrane defects caused by uneven grain packing in these methods. In this embodiment, a step-by-step water / methanol post-treatment process effectively removes loose surface grains and solvent residues, maintaining the integrity of the membrane structure while optimizing the pore microenvironment. The resulting ZIF-8 membrane has a precisely controlled pore size close to the kinetic diameter of propylene (4.0 Å).

[0021] In step S1 of the above embodiment, the molar ratio of zinc salt, 2-methylimidazole and water is 1:(30-60):(1500-3990).

[0022] More specifically, in the above embodiment, the molar ratio of zinc salt, 2-methylimidazole and water is 1:30:1995.

[0023] In step S2 of the above embodiment, the temperature of the static film formation is 268-303K.

[0024] More specifically, in the above embodiment, the temperature for static film formation is preferably 268 to 283K, and most preferably 273 to 283K.

[0025] In step S2 of the above embodiment, the film-forming period is 0.5 to 12 hours.

[0026] In step S3 of the above embodiment, the carrier after film formation is immersed in water for 0.5 to 1 hour.

[0027] In step S2 of the above embodiment, the support is an alumina support or a polymer PAN support.

[0028] In the above embodiment, the alumina carrier forms a chemical bond with the ZIF-8 crystal layer by virtue of its high mechanical strength. In the solvent thermal reaction, it can not only enhance the adhesion of the membrane layer through interfacial interaction to prevent the structural collapse of the membrane layer under high pressure or swelling conditions, but also enhance the interface stability through the coordination effect between the surface hydroxyl groups and the metal nodes. The polymer PAN carrier provides a flexible support base for ZIF-8 through the topological matching of the molecular chain segments. Its porous structure can guide the crystals to grow in a directional manner along the preset channels, and maintain the continuity of the membrane layer in a dynamic synthesis environment. Both carriers can promote the uniform nucleation and dense stacking of ZIF-8 crystals through interfacial synergistic effects, providing an adaptive support system for the in situ synthesis of high-integrity separation membranes.

[0029] More specifically, in the above embodiment, the alumina support is selected from any one of a flaky alumina support, a tubular alumina support, and a capillary alumina support.

[0030] The in-situ ZIF-8 membrane synthesis method provided by the above embodiment can effectively achieve higher solution utilization and controllable synthesis, and can avoid defects in the membrane preparation process, resulting in a relatively continuous and dense ZIF-8 membrane with advantages such as simple operation, good reproducibility, and strong economic efficiency. The resulting ZIF-8 membrane is continuous, uniform, dense, and defect-free. At the same time, the ZIF-8 membrane has excellent propylene / propane mixture separation selectivity and stability.

[0031] The technical scheme of the present invention is further described below by specific examples, unless otherwise defined, all terms, symbols and other scientific terms used herein are intended to have the same meaning as those skilled in the art to which the present invention belongs. In some cases, this paper defines the terms with conventional understanding meaning for the purpose of illustrating or facilitating quoting, and such limitations herein should not be construed as representing that there are significant differences with conventional understandings in this area. The technical methods described herein or cited are generally fully understood by those skilled in the art and are adopted by conventional methods. Unless otherwise stated, the use of commercially available reagents and instruments is carried out according to the scheme and parameters given by the manufacturer.

[0032] Example 1 Preparation of ZIF-8 membrane S1: Prepare a precursor solution by mixing 0.184 g zinc acetate dihydrate, 2.05 g 2-methylimidazole, and 25 mL water. S2: At 293K, the α-Al2O3 support was immersed in the precursor solution and allowed to stand for 6h to complete the in situ growth of the ZIF-8 film; S3: The membrane-forming support was immersed in water for 30 minutes. After immersion, it was transferred to methanol for activation for 30 minutes. After drying, the ZIF-8 membrane was obtained. The product number was recorded as M1.

[0033] The SEM characterization of product M1 is as follows Figure 1 As shown by Figure 1 It can be seen that the surface grains of product M1 are cross-linked and intergrown and the particle size is uniform.

[0034] The propylene permeability and propylene / propane propylene / propane selectivity of product M1 were measured. The results are shown in Table 1. As can be seen from Table 1, product M1 has high propylene permeability and propylene / propane propylene / propane selectivity, and can be used for separating propylene from propylene / propane propylene / propane mixed gas.

[0035] Table 1 Example 2 Inter-batch stability determination of ZIF-8 S1: Prepare three precursor solutions by taking three portions of 0.184 g zinc acetate dihydrate, three portions of 2.05 g 2-methylimidazole, and three portions of 25 mL water; S2: At 293K, three α-Al2O3 supports were immersed in three precursor solutions respectively and allowed to stand for 6h to complete the in situ growth of ZIF-8 membranes; S3: The membrane-forming support was immersed in water for 30 min. After immersion, it was transferred to methanol for activation for 30 min. After drying, the ZIF-8 membrane was obtained. The product numbers were recorded as M2, M3, and M4.

[0036] The propylene permeability and propylene / propane selectivity of products M1, M2, M3, and M4 were measured. The results are shown in Table 2. As can be seen from Table 2, products M1, M2, M3, and M4 have high propylene permeability and propylene / propane selectivity, and can be used for separating propylene from propylene / propane mixtures. In addition, the ZIF-8 prepared by the present invention has excellent batch-to-batch synthesis repeatability.

[0037] Table 2 Example 3 Preparation of ZIF-8 at different film-forming temperatures S1: Prepare five precursor solutions by taking five parts of 0.184 g zinc acetate dihydrate, five parts of 2.05 g 2-methylimidazole, and five parts of 25 mL water; S2: Five precursor solutions were placed at 273K, 278K, 283K, 293K and 303K, respectively. Five α-Al2O3 supports were immersed in the corresponding precursor solutions and allowed to stand for 6 h to complete the in situ growth of the ZIF-8 film. S3: The membrane-forming support was soaked in water for 30 minutes. After soaking, it was transferred to methanol for activation for 30 minutes. After drying, the ZIF-8 membrane was obtained. The product numbers were recorded as M5, M6, M7, M8, and M9.

[0038] The propylene permeability and propylene / propane selectivity of products M5, M6, M7, M8, and M9 were measured. The results are shown in Table 3. As can be seen from Table 3, when the film formation temperature is 273~283K, the prepared ZIF-8 membrane is suitable for the separation of propylene in propylene / propane mixture.

[0039] Table 3 The product M9 was characterized by SEM, and the results are as follows Figure 2 As shown by Figure 2It can be seen that the surface uniformity of product M9 is poor, which is one of the reasons why the propylene / propane selectivity of product M9 is poor.

[0040] Example 4 Preparation of ZIF-8 with different precursor concentrations S1: Mix 0.184 g zinc acetate dihydrate, 2.05 g 2-methylimidazole and 25 mL water to prepare precursor solution I; mix 0.092 g zinc acetate dihydrate, 2.05 g 2-methylimidazole and 25 mL water to prepare precursor solution II; mix 0.092 g zinc acetate dihydrate, 4.1 g 2-methylimidazole and 25 mL water to prepare precursor solution III; mix 0.092 g zinc acetate dihydrate, 1.025 g 2-methylimidazole and 25 mL water to prepare precursor solution IV; S2: At 278K, four α-Al2O3 supports were immersed in four precursor solutions and allowed to stand for 6h to complete the in situ growth of the ZIF-8 film; S3: Soak the carrier after film formation in water for 30 minutes. After soaking, transfer it to methanol for activation for 30 minutes. After drying, ZIF-8 membranes are obtained. The product numbers are recorded as M10 (precursor solution I), M11 (precursor solution II), M12 (precursor solution III), and M13 (precursor solution IV).

[0041] The propylene permeability and propylene / propane selectivity of products M10, M11, M12, and M13 were measured, and the results are shown in Table 3. As can be seen from Table 3, M10 has a higher propylene / propane selectivity but a lower propylene permeability, while M12 and M13 have lower propylene / propane selectivity but higher propylene permeability. Table 4 proves that the preparation of ZIF-8 membrane products with different propylene / propane separation performance can be achieved by simply controlling the precursor concentration.

[0042] Table 4 Example 5 Preparation of ZIF-8 on a commercial tubular support S1: Prepare a precursor solution by mixing 0.4465 g zinc acetate dihydrate, 4.9747 g 2-methylimidazole, and 60 mL water. S2: At 293K, a 10cm long α-Al2O3 tubular support was immersed in the precursor solution and allowed to stand for 6h to complete the in situ growth of the ZIF-8 film; S3: The membrane-forming support was immersed in water for 30 min. After immersion, it was transferred to methanol for activation for 30 min. After drying, the ZIF-8 membrane was obtained. The product number was recorded as M14.

[0043] The product M14 was characterized by SEM, and the results are as follows Figure 3As shown by Figure 3 It can be seen that the surface grains of product M14 are continuous and dense, with no obvious defects, proving that this method can synthesize a dense ZIF-8 membrane layer on a tubular carrier with good scalability.

[0044] The propylene permeability and propylene / propane selectivity of product M14 were measured. The results are shown in Table 5. As can be seen from Table 5, product M14 has high propylene permeability and propylene / propane selectivity and can be used for separating propylene from propylene / propane mixed gas.

[0045] Table 5 Example 6 Preparation of ZIF-8 on a commercial capillary support S1: Prepare a precursor solution by mixing 0.184 g zinc acetate dihydrate, 2.05 g 2-methylimidazole, and 25 mL water. S2: At 293K, a 5cm long α-Al2O3 capillary support was immersed in the precursor solution and allowed to stand for 6h to complete the in situ growth of the ZIF-8 film; S3: The membrane-forming support was immersed in water for 30 minutes. After immersion, it was transferred to methanol for activation for 30 minutes. After drying, the ZIF-8 membrane was obtained. The product number was recorded as M15.

[0046] The SEM characterization of product M15 is as follows Figure 4 As shown by Figure 4 It can be seen that the surface grains of product M15 are continuous and dense, with no obvious defects, proving that this method can synthesize a dense ZIF-8 membrane layer on a capillary carrier with good scalability.

[0047] The propylene permeability and propylene / propane selectivity of product M15 were measured. The results are shown in Table 6. As can be seen from Table 6, product M15 has high propylene permeability and propylene / propane selectivity, and can be used for separating propylene from propylene / propane mixed gas.

[0048] Table 6 Example 7 Preparation of ZIF-8 on commercial polymer supports S1: Prepare a precursor solution by mixing 0.184 g zinc acetate dihydrate, 2.05 g 2-methylimidazole, and 25 mL water. S2: At 293K, a PAN substrate with a length and width of 2 cm was immersed in the precursor solution and allowed to stand for 6 h to complete the in situ growth of the ZIF-8 film; S3: The membrane-forming support was immersed in water for 30 min. After immersion, it was transferred to methanol for activation for 30 min. After drying, the ZIF-8 membrane was obtained. The product number was recorded as M16.

[0049] The product M16 was characterized by SEM, and the results are as follows Figure 5 As shown by Figure 5 It can be seen that the surface grains of product M16 are continuous and dense, with no obvious defects, proving that this method can synthesize a dense ZIF-8 membrane layer on a PAN carrier with good scalability.

[0050] The propylene permeability and propylene / propane selectivity of product M16 were measured. The results are shown in Table 7. As can be seen from Table 7, product M16 has high propylene permeability and propylene / propane selectivity and can be used for separating propylene from propylene / propane mixed gas.

[0051] Table 7 Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for in-situ synthesis of a ZIF-8 membrane, characterized in that: The following steps are involved: S1: Mix zinc salt, 2-methylimidazole and water to prepare a precursor solution; S2: Immerse the support in the precursor solution and let it stand to form a film; S3: Soaking the membrane-formed support in water, and then transferring it to methanol for activation to obtain a ZIF-8 membrane.

2. The in-situ synthesis method according to claim 1, wherein In step S1, the molar ratio of the zinc salt, 2-methylimidazole and water is 1: (30-60): (1500-3990).

3. The in-situ synthesis method according to claim 1, wherein In the step S2, the temperature of the static film formation is 268-303K.

4. The in-situ synthesis method according to claim 1, wherein In the step S2, the film is left to stand for 0.5 to 12 hours.

5. The in-situ synthesis method according to claim 1, wherein In the step S3, the film-formed carrier is immersed in water for 0.5 to 1 hour.

6. The in-situ synthesis method according to claim 1, wherein In step S3, the activation time is 0.5 to 2 hours.

7. The in situ synthesis method according to claim 1, wherein In the step S2, the support is an alumina support or a polymer PAN support.

8. A ZIF-8 membrane, characterized in that The compound is prepared by the in-situ synthesis method according to any one of claims 1 to 7.

9. An application of the ZIF-8 membrane according to claim 8, characterized in that: The application is to use the ZIF-8 membrane for separation of C3H6 and C3H8 mixed gases.

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