Reutilization method of ZIF-8 synthesis waste liquid and ZIF-8 film

Abstract

The invention provides a recycling method of ZIF-8 synthesis waste liquid and a ZIF-8 membrane, and belongs to the technical field of metal organic framework materials.The recycling method of the ZIF-8 synthesis waste liquid comprises the following steps that S1, the ZIF-8 synthesis waste liquid is collected and diluted with an N, N-dimethylacetamide aqueous solution, and ligand recovery liquid is obtained; and S2, coating the surface of a carrier with the ligand recovery liquid obtained in the step S11, and reacting under a heating condition to prepare the ZIF-8 film. The method provides a new theoretical basis for synthesis of the ZIF-8 film, and opens up a new way for cyclic utilization of the MOF material and cost benefit improvement.

Description

Technical Field

[0001] The present invention relates to the technical field of metal framed materials, and more particularly, to a method for recycling waste liquid from ZIF-8 synthesis and a ZIF-8 membrane. Background Art

[0002] Metal-organic framework (MOF) materials are crystalline porous materials with a periodic network structure formed by the self-assembly of inorganic metal centers (metal ions or metal clusters) and bridging organic ligands. ZIF-8 materials (zeolitic imidazolate framework-8) are a type of MOF material composed of zinc ions and 2-methylimidazole ligands. ZIF-8 membranes have excellent molecular sieving properties and have broad application prospects in fields such as hydrogen purification, carbon dioxide capture, and dehydration of organic solvents. However, the large-scale preparation of ZIF-8 membranes still faces many challenges, and the development of efficient and economical synthesis technologies is of great significance for promoting the commercial application process of ZIF-8 membranes.

[0003] Currently, the preparation methods of ZIF-8 membranes mainly include in-situ growth method, secondary growth method, and interfacial synthesis method, etc. However, no matter which method is used, a large amount of supernatant will be generated during the synthesis process, which contains unreacted metal salts (such as zinc nitrate), organic ligands (such as 2-methylimidazole), solvents (such as methanol, N,N-dimethylformamide), and a small amount of ZIF-8 nanoparticles. These supernatants are usually regarded as waste and directly discharged, which not only causes waste of resources but also pollutes the environment. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to reduce the environmental pollution caused by the waste liquid from ZIF-8 synthesis.

[0005] To solve the above technical problem, the first aspect of the present invention provides a method for recycling waste liquid from ZIF-8 synthesis, including the following steps: S1: Collect the waste liquid from ZIF-8 synthesis and dilute it with an aqueous solution of N,N-dimethylacetamide to obtain a ligand recovery solution; S2: Coat the ligand recovery solution obtained in step S11 on the surface of the carrier and react under heating conditions to obtain a ZIF-8 membrane.

[0006] Preferably, in step S1, the volume ratio of N,N-dimethylacetamide to water in the aqueous solution of N,N-dimethylacetamide is 1:(0.5~2).

[0007] Preferably, in step S1, the dilution multiple is 1~4 times.

[0008] Preferably, in the step S2, the carrier is any one of α-Al2O3 carrier, γ-Al2O3 carrier, anodic aluminum oxide carrier, TiO2 carrier, PVDF carrier, PAN carrier, PES carrier, PTFE carrier, and PEI carrier.

[0009] Preferably, in the step S2, the heating temperature is 100~250 °C, and the heating duration is 10~30 min.

[0010] Preferably, the ZIF-8 synthesis waste liquid is the final waste liquid obtained by the dip-coating thermal conversion method for preparing ZIF-8 membranes. The steps of preparing ZIF-8 membranes by the dip-coating thermal conversion method are as follows: Step 1: Dissolve zinc acetate dihydrate and 2-methylimidazole in a mixed solvent of water and N,N-dimethylacetamide to form a metal salt solution and a ligand solution respectively; Step 2: Add the ligand solution to the metal salt solution to form a synthesis solution, and let it stand for reaction to obtain ZIF-8 membranes.

[0011] Preferably, in the step 2, by mole fraction, the synthesis solution comprises the following components: 1 part of Zn, 0.2~4 parts of 2-methylimidazole, 50~400 parts of water, and 20~200 parts of N,N-dimethylacetamide.

[0012] Preferably, in the step 2, the temperature for standing reaction is -5~20 °C, and the duration for standing reaction is 1~24 h.

[0013] The method for recycling the ZIF-8 synthesis waste liquid provided by the present invention aims at the synthesis waste liquid for preparing ZIF-8 by the dip-coating thermal conversion method. By collecting the ZIF-8 synthesis waste liquid, its utilization rate is increased, and a high-performance ZIF-8 membrane is prepared by controlling the dilution ratio.

[0014] The second aspect of the present invention provides a method for preparing ZIF-8 membranes, and the ZIF-8 membranes are prepared by the method for recycling the ZIF-8 synthesis waste liquid described in the first aspect.

[0015] The ZIF-8 membranes prepared by the method for recycling the ZIF-8 synthesis waste liquid provided by the present invention have excellent gas separation performance and can be used for the separation of mixed gases such as carbon dioxide-methane mixed gas, carbon dioxide-nitrogen mixed gas, and propylene-propane mixed gas.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The method for recycling the waste liquid in the synthesis of ZIF-8 provided by the present invention can recover the waste liquid in the synthesis of ZIF-8 and prepare it into a ZIF-8 membrane. This makes the whole process of preparing the ZIF-8 membrane simple in operation, greatly improves the utilization rate of the waste liquid in the synthesis of ZIF-8, reduces the generation of chemical waste, and is an environmentally friendly technology. The present invention can repeat the performance of the ZIF-8 membrane by finely regulating the synthesis conditions, realize the synthesis of a high-performance ZIF-8 membrane from the waste liquid in the synthesis of ZIF-8, provide a new theoretical basis for the synthesis of the ZIF-8 membrane, and also open up a new path for the recycling and cost-benefit improvement of MOF materials. Detailed implementation manners

[0017] To make the above objects, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention will be described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not used to limit the parameter range described in the present invention. Reasonable changes derived therefrom are still within the protection scope of the claims of the present invention.

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

[0019] Unless otherwise defined, all terms, symbols and other scientific terms used herein are intended to have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. In some cases, terms with conventional understood meanings are defined herein for the purpose of clarification or convenient reference. Such definitions herein should not be construed as indicating a significant difference from the conventional understanding in the art. The technical methods described or cited herein are generally well 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 schemes and parameters given by the manufacturers.

[0020] The existing ZIF-8 is prepared by the dip-coating thermal conversion method, and waste liquid will be generated during the preparation process. To reduce the environmental pollution caused by the waste liquid in the synthesis of ZIF-8, the detailed implementation manners of the present invention provide a method for recycling the waste liquid in the synthesis of ZIF-8, including the following steps: S1: Collect the waste liquid in the synthesis of ZIF-8 and dilute it with an N,N-dimethylacetamide aqueous solution to obtain a ligand recovery solution; S2: Coat the ligand recovery solution obtained in step S11 onto the surface of the support, and react under heating conditions to obtain a ZIF-8 membrane.

[0021] In step S1 of some embodiments, the volume ratio of N,N-dimethylacetamide to water in the N,N-dimethylacetamide aqueous solution is 1:(0.5 - 2).

[0022] In step S2 of some embodiments, the support is any one of α-Al2O3 support, γ-Al2O3 support, anodic aluminum oxide support, TiO2 support, PVDF support, PAN support, PES support, PTFE support, and PEI support.

[0023] In step S2 of some embodiments, the heating temperature is 100 - 250 °C, and the heating duration is 10 - 30 min.

[0024] The technical solution of the present invention will be further described below through specific embodiments.

[0025] Example 1 This example provides a method for preparing a ZIF-8 membrane using the supernatant of a ZIF-8 synthesis solution, which specifically includes the following steps: Dissolve 0.33 g (15 mmol) of Zn(OAc)2·2H2O and 0.25 g of 2-methylimidazole in 5 ml of H2O. After ultrasonic dissolution, add 10 ml of DMAc, mark as solution A and solution B. After ice-bath stirring for 8 min, add solution B to solution A within 90 s. After stirring for 30 s, obtain the precursor solution of the ZIF-8 membrane. Immerse the Al2O3 support in the precursor solution for 30 s, take it out, blot dry the moisture, and react in a blast drying oven at 200 °C for 15 min. After natural cooling, obtain the ZIF-8 polycrystalline membrane, denoted as C1 - C2 respectively.

[0026] Let the obtained ZIF-8 synthesis solution settle naturally for 12 h. Centrifuge the settled synthesis solution, and take out the upper clarified liquid after centrifugation as the supernatant. Mix and dilute it by one time with H2O / DMAc (2 / 1) under ice-bath conditions to obtain a new ZIF-8 synthesis solution. After stirring for 30 s, obtain the precursor solution of the ZIF-8 membrane. Immerse the Al2O3 support in the precursor solution for 30 s, take it out, blot dry the moisture, and react in a blast drying oven at 200 °C for 15 min. After natural cooling, obtain the ZIF-8 polycrystalline membrane synthesized using the supernatant, marked as C3 - C4.

[0027] The detection results of the propylene / propane separation selectivity and permeability of products C1 - C4 are shown in Table 1. Comparing the performance data before and after, the ZIF-8 membrane synthesized using the supernatant has excellent separation and selection performance comparable to that of the ZIF-8 membrane synthesized for the first time.

[0028] Example 2 This example provides a method for preparing ZIF-8 membranes using the supernatant of the ZIF-8 synthesis solution, which specifically includes the following steps: Dissolve 0.33 g (15 mmol) of Zn(OAc)2·2H2O and 0.25 g of 2-methylimidazole in 5 ml of H2O. After ultrasonic dissolution, add 10 ml of DMAc, and label them as solution A and solution B. After stirring in an ice bath for 8 min, add solution B to solution A within 90 s, and stir for 30 s to obtain the precursor solution of the ZIF-8 membrane. Immerse the Al2O3 support in the precursor solution for 30 s, take it out, blot dry the water, and react in a forced-air oven at 200 °C for 15 min. After natural cooling, obtain the ZIF-8 polycrystalline membranes, denoted as C5 - C6 respectively.

[0029] Let the obtained ZIF-8 synthesis solution settle naturally for 12 h, centrifuge the settled synthesis solution, take out the upper clear liquid after centrifugation as the supernatant, mix and dilute it two-fold with H2O / DMAc (2 / 1) under the condition of an ice bath to prepare a new ZIF-8 synthesis solution. After stirring for 30 s, obtain the precursor solution of the ZIF-8 membrane. Immerse the Al2O3 support in the precursor solution for 30 s, take it out, blot dry the water, and react in a forced-air oven at 200 °C for 15 min. After natural cooling, obtain the ZIF-8 polycrystalline membranes synthesized using the supernatant, denoted as C7 - C8.

[0030] The detection results of the propylene / propane separation selectivity and permeability of products C5 - C8 are shown in Table 2. Among them, when the dilution factor becomes two-fold, the selectivity of the newly synthesized ZIF-8 membrane for propylene / propane is improved, and the permeability of propylene is also significantly improved.

[0031] Example 3 This example provides a method for preparing ZIF-8 membranes using the supernatant of the ZIF-8 synthesis solution, which specifically includes the following steps: Dissolve 0.33 g (15 mmol) of Zn(OAc)2·2H2O and 0.25 g of 2-methylimidazole in 5 ml of H2O. After ultrasonic dissolution, add 10 ml of DMAc, and label them as solution A and solution B. After stirring in an ice bath for 8 min, add solution B to solution A within 90 s, and stir for 30 s to obtain the precursor solution of the ZIF-8 membrane. Immerse the Al2O3 support in the precursor solution for 30 s, take it out, blot dry the water, and react in a forced-air oven at 200 °C for 15 min. After natural cooling, obtain the ZIF-8 polycrystalline membranes, denoted as C9 - C10 。

[0032] The obtained ZIF-8 synthesis solution was allowed to settle naturally for 12 h, and the settled synthesis solution was centrifuged. The upper clear liquid after centrifugation was taken out as the supernatant, and was mixed and diluted four times with H2O / DMAc (2 / 1) under the condition of an ice bath to prepare a new ZIF-8 synthesis solution. After stirring for 30 s, a precursor solution of the ZIF-8 membrane was obtained. The Al2O3 support was dip-coated in the precursor solution for 30 s, taken out, dried, and reacted in a forced-air oven at 200 °C for 15 min. After natural cooling, a ZIF-8 polycrystalline membrane synthesized using the supernatant was obtained, labeled as C 11 ~C 12 。

[0033] Products C9~C 12 The detection results of the propylene / propane separation selectivity and permeability of product C9~C are shown in Table 3. Among them, when the dilution multiple became four times, the selectivity of the newly synthesized ZIF-8 membrane for propylene / propane did not show an obvious increase, and the permeability of propylene did not show an obvious increase either. Therefore, it can be determined that the optimal dilution multiple is two times.

[0034] By comparing the separation performance, it can be seen that the present invention not only successfully reused the supernatant of the ZIF-8 synthesis solution to synthesize the ZIF-8 membrane, but also the performance of the ZIF-8 membrane is the same as that of the ZIF-8 prepared from the original solution. These findings not only provide a new theoretical basis for the synthesis of ZIF-8 membranes, but also open up a new path for the recycling and cost-benefit improvement of MOF materials.

[0035] 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 all fall within the protection scope of the present invention.

Claims

1. A method for recycling ZIF-8 synthesis waste liquid, characterized in that: The following steps are involved: S1: Collect the ZIF-8 synthesis waste liquid, dilute it with N,N-dimethylacetamide aqueous solution, and obtain the ligand recovery liquid; S2: The ligand recovery solution obtained in step S1 is coated on the surface of the carrier, and reacted under heating conditions to obtain a ZIF-8 membrane.

2. The method for recycling ZIF-8 synthetic waste liquid as claimed in claim 1, characterized in that: In the step S1, the volume ratio of N,N-dimethylacetamide to water in the N,N-dimethylacetamide aqueous solution is 1:(0.5-2).

3. The method for recycling ZIF-8 synthetic waste liquid as claimed in claim 1, characterized in that, In step S1, the dilution multiple is 1 to 4 times.

4. The method for recycling ZIF-8 synthetic waste liquid as claimed in claim 1, characterized in that, In the step S2, the carrier is any one of an α-Al2O3 carrier, a γ-Al2O3 carrier, an anodized aluminum carrier, a TiO2 carrier, a PVDF carrier, a PAN carrier, a PES carrier, a PTFE carrier, and a PEI carrier.

5. The method for recycling ZIF-8 synthetic waste liquid as claimed in claim 1, characterized in that, In step S2, the heating temperature is 100-250° C., and the heating time is 10-30 minutes.

6. The method for recycling ZIF-8 synthetic waste liquid as claimed in claim 1, characterized in that, The ZIF-8 synthesis waste liquid is the final waste liquid of preparing the ZIF-8 membrane by the dip-coating thermal conversion method. The steps of preparing the ZIF-8 membrane by the dip-coating thermal conversion method are as follows: Step 1: Dissolve zinc acetate dihydrate and 2-methylimidazole in a mixed solvent of water and N,N-dimethylacetamide to form a metal salt solution and a ligand solution respectively; Step 2: Add the ligand solution to the metal salt solution to form a synthetic solution, let it stand for reaction, and obtain the ZIF-8 membrane.

7. The method for recycling ZIF-8 synthetic waste liquid as claimed in claim 6, characterized in that, In step 2, the synthetic solution includes the following components by mole: 1 part of Zn, 0.2-4 parts of 2-methylimidazole, 50-400 parts of water and 20-200 parts of N,N-dimethylacetamide.

8. The method for recycling ZIF-8 synthetic waste liquid as claimed in claim 6, characterized in that, In the step 2, the temperature of the static reaction is -5 to 20° C., and the duration of the static reaction is 1 to 24 hours.

9. A method for preparing a ZIF-8 membrane, characterized in that: The product is prepared by the method for recycling ZIF-8 synthesis waste liquid as described in any one of claims 1 to 8.

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