Self-supporting zeolite molecular sieve-MOF crystalline glass composite membrane, its preparation method and application

Abstract

This invention relates to the field of membrane separation materials, specifically to a self-supporting zeolite molecular sieve-MOF crystal glass composite membrane, its preparation method, and its application. The method includes: uniformly mixing a metal salt and a ligand, ball milling the mixture using a planetary ball mill, filtering the milled mixture, and washing it with methanol to obtain ZIF-62 particles; uniformly mixing the ZIF-62 particles and zeolite molecular sieve powder, and preparing them into discs using a mechanical pressing machine; and calcining the discs under inert gas protection to obtain the self-supporting zeolite molecular sieve-MOF crystal glass composite membrane. In this invention, ZIF-62 and zeolite molecular sieve crystal powder are mixed and mechanically pressed into discs of a certain thickness. The discs are then heated under an inert gas atmosphere. The heating temperature is such that the ZIF-62 particles melt and encapsulate the zeolite molecular sieve, thereby eliminating defects in the membrane and forming a dense, monolithic film.

Description

Technical Field

[0001] This invention relates to the field of membrane separation materials, specifically to a self-supporting zeolite molecular sieve-MOF crystal glass composite membrane, its preparation method, and its application. Background Technology

[0002] 1,3-Butadiene (C4H6) is an important light olefin and a major chemical raw material for the industrial production of synthetic rubber, plastics, and fibers. 1,3-C4H6 is typically produced by petroleum cracking, which also yields a mixture of C4 hydrocarbons (including n-butane (n-C4H6)). 10 n-Butene (n-C4H8), isobutane (i-C4H8) 10 ) and isobutylene (i-C4H8). Developing high-performance membranes for hydrocarbon separation in industry is a potential energy-saving approach. Currently, there are two main types of C4H6 separation membranes: polymer membranes and mixed matrix membranes (MMMs). MMMs have become a highly attractive research area in the field of separation membranes due to their combination of high separation performance of the dispersed phase and easy processability of the continuous phase. These MMMs are made of porous materials (mainly zeolites and metal-organic frameworks (MOFs)) dispersed in a polymer matrix. Zeolite molecular sieves are typically aluminosilicates with a tetrahedral framework structure. This inorganic framework has a rigid and ordered porous structure, enabling efficient molecular sieving with separation efficiency superior to the flexible framework materials used in membrane separation. However, zeolite-based MMMs still face some challenges in the separation of C4 hydrocarbons. First, the uneven dispersion of the packing material in the membrane and the underdeveloped pores in the MMM lead to reduced permeability. Plasticization, a phenomenon that occurs when the concentration of adsorbed gases (such as C2H4, C3H6, and C4H6) in the polymer matrix increases, causes polymer expansion, which in turn leads to a decrease in membrane performance. In polymer membranes, the problems of plasticization and underdeveloped pores are more pronounced, leading to a further decrease in permeability.

[0003] As an emerging material in recent years, MOF (Metal-Organic Fabric) glasses can maintain the same coordination geometry in their crystalline state and possess a certain degree of porosity, making them very suitable as membrane materials and a promising option for overcoming grain boundary defects. MOF glasses are typically obtained by melting the crystals into a liquid state at a certain temperature and then quenching them. Combining the advantages of processability, isotropy, grain boundary absence, and reusability, MOF glasses have been studied in the field of gas separation. However, the porosity of MOF glasses decreases during melting, leading to low flux, which hinders their practical application. Summary of the Invention

[0004] Based on this, the present invention proposes a self-supporting zeolite molecular sieve-MOF crystal glass composite membrane that is free from the limitation of flux by the support, as well as its preparation method and application.

[0005] According to a first aspect of the present invention, a method for preparing a self-supporting zeolite molecular sieve-MOF crystalline glass composite membrane is provided, comprising:

[0006] The metal salt and ligand were mixed evenly and then ball-milled using a planetary ball mill. After ball milling, the mixture was filtered and washed with methanol to obtain ZIF-62 particles.

[0007] After the ZIF-62 particles and zeolite molecular sieve powder are mixed evenly, they are prepared into round tablets using a mechanical tablet press.

[0008] Under inert gas protection, the discs are calcined to obtain a self-supporting zeolite molecular sieve-MOF crystal glass composite membrane.

[0009] According to an embodiment of the present invention, the metal salt is a zinc ion source;

[0010] In the metal salt, the molar ratio of zinc ion source to ligand is 1:2.

[0011] According to an embodiment of the present invention, the zinc ion source is a mixture of zinc hydroxide and zinc acetate;

[0012] The molar ratio of zinc hydroxide to zinc acetate is 99:1 to 70:30.

[0013] According to an embodiment of the present invention, the ligand is a mixture of imidazole and benzimidazole.

[0014] According to an embodiment of the present invention, the molar ratio of the zinc ion source, the imidazole and the benzimidazole is 1:1.75:0.25.

[0015] According to an embodiment of the present invention, the zeolite molecular sieve is one of SSZ-13 molecular sieve, Cu-SSZ-13 molecular sieve, SAPO-34 molecular sieve, ZSM-5 molecular sieve, 3A molecular sieve, 4A molecular sieve, and 5A molecular sieve.

[0016] The mass ratio of the zeolite molecular sieve to the ZIF-62 particles is 1-60:99-40.

[0017] According to an embodiment of the present invention, the calcination temperature range is from room temperature to 380-450°C, the heating rate is 3°C / min, argon or nitrogen is used as a protective gas, and the gas flow rate is 120-140 mL / min.

[0018] According to a second aspect of the present invention, a pressure-responsive membrane obtained by the above-described preparation method is provided.

[0019] According to a third aspect of the present invention, an application of the above-described self-supporting zeolite molecular sieve-MOF crystal glass composite membrane in the gas separation of difficult-to-separate systems is provided.

[0020] According to embodiments of the present invention, it includes systems for C4H6 / i-C4H8 and C4H6 / i-C4H 10 System, C4H6 / n-C4H8 system or C4H6 / n-C4H 10 System separation.

[0021] As can be seen from the above technical solutions, the MOF material with glass transition properties, its preparation method, and its applications provided by the present invention have the following beneficial effects:

[0022] The preparation method provided by this invention synthesizes ZIF-62 MOF material by ball milling, mixes it uniformly with zeolite molecular sieve material, and prepares a self-supporting zeolite molecular sieve-MOF crystal glass composite membrane by mechanical pressing. The supportless MOF glass membrane is free from the limitation of flux by the support, and the zeolite molecular sieve material in the membrane greatly improves the membrane porosity. While improving the flux, it can accurately identify small molecule gases, which has practical value for industrial separation of difficult-to-separate systems.

[0023] This invention proposes to prepare MOF materials with vitrification properties by ball milling, and then mix them evenly with zeolite molecular sieve materials before mechanical pressing and calcination to obtain a high-throughput, self-supporting porous zeolite molecular sieve-MOF crystal glass composite membrane for difficult-to-separate systems (C4H6 / C4). This method broadens the range of membrane materials to be selected in the field of membrane separation and lays the foundation for the practical application of vitrified MOF membranes. Attached Figure Description

[0024] Figure 1 Here is a scanning electron microscope image of the ZIF-62 particles obtained in the embodiments of the present invention;

[0025] Figure 2 Thermogravimetric curves of ZIF-62 and SSZ-13 mixed in different mass ratios in this embodiment of the invention are shown.

[0026] Figure 3 X-ray diffraction patterns of zeolite molecular sieve-MOF crystal glass composite membranes prepared with ZIF-62 and SSZ-13 in different mass ratios in the embodiments of the present invention.

[0027] Figure 4 These are scanning electron microscope (SEM) images of the surface and cross-section of sample 2 of the present invention;

[0028] Figure 5 Here are scanning electron microscope (SEM) images of the surface and cross-section of sample 3 of the present invention;

[0029] Figure 6 Here are scanning electron microscope (SEM) images of the surface and cross-section of sample 4 of this invention;

[0030] Figure 7 The gas permeation separation performance of samples 1, 2, 3, and 4 of this invention;

[0031] Figure 8 This is to show the selectivity of C4H6 in sample 4 of the present invention for the other four C4 gases. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0033] As an emerging material in recent years, MOF (Metal-Oxide-Flecked) glass can maintain the same coordination geometry in its crystalline state and possesses a certain degree of porosity, making it very suitable as a membrane material and a promising option for overcoming grain boundary defects. MOF glass is typically obtained by melting the crystals into a liquid state at a certain temperature and then quenching it. Combining the advantages of processability, isotropy, grain boundary absence, and reusability, MOF glass has been studied in the field of gas separation. However, the porosity of MOF glass decreases during melting, leading to low flux, which hinders its practical application. Zeolite molecular sieve-MOF crystal glass composite membranes (zeolite CGC membranes) refer to materials prepared by mixing glassy MOF with zeolite molecular sieves. The glassy MOF melts into a viscous liquid at a certain temperature, encapsulating the zeolite molecular sieve, and after quenching to room temperature, a composite material with excellent compatibility is produced. This strategy is very flexible, allowing CGC to be prepared into specific shapes, making it a feasible method for preparing self-supporting membranes.

[0034] Because 1,3-C4H6 and other C4 hydrocarbon gases share similar physicochemical properties, traditional industrial distillation purification methods cannot provide high-purity C4H6 with low energy consumption. By using the molten state of ZIF-62 to uniformly disperse zeolite molecular sieves into a membrane, a self-supporting porous zeolite molecular sieve-MOF crystal glass composite membrane is prepared. The zeolite molecular sieves in the membrane can recognize C4H6, ensuring preferential permeation of C4H6.

[0035] Therefore, there is a need for a MOF membrane that can overcome the flux limitation imposed by the support and a method for its preparation.

[0036] According to a first aspect of the present invention, a method for preparing a self-supporting zeolite molecular sieve-MOF crystalline glass composite membrane is provided, comprising:

[0037] S1: Mix the metal salt and ligand evenly, and then ball mill them using a planetary ball mill. After ball milling, filter the mixture and wash it with methanol to obtain ZIF-62 particles.

[0038] S2: After mixing ZIF-62 particles and zeolite molecular sieve powder evenly, prepare round tablets using a mechanical tablet press;

[0039] S3: Under inert gas protection, the discs are calcined to obtain a self-supporting zeolite molecular sieve-MOF crystal glass composite membrane.

[0040] The preparation method provided by this invention utilizes a ball milling method, which is characterized by high yield, fast reaction rate, and environmental friendliness, to prepare ZIF-62 crystal particles with high-temperature melting characteristics. ZIF-62 and zeolite molecular sieve crystal powder are uniformly mixed and then pressed into discs using mechanical pressing. These discs are then heated under an inert atmosphere, causing the ZIF-62 particles to melt and encapsulate the zeolite molecular sieve, thereby eliminating defects in the membrane and forming a dense, monolithic film. This membrane exhibits self-support, high selectivity, and high throughput, providing a solution for the separation of difficult-to-separate gases.

[0041] The preparation method provided by this invention synthesizes ZIF-62 MOF material by ball milling, mixes it uniformly with zeolite molecular sieve material, and prepares a self-supporting zeolite molecular sieve-MOF crystal glass composite membrane by mechanical pressing. The supportless MOF glass membrane is free from the limitation of flux by the support, and the zeolite molecular sieve material in the membrane greatly improves the membrane porosity. While improving the flux, it can accurately identify small molecule gases, which has practical value for industrial separation of difficult-to-separate systems.

[0042] This invention proposes to prepare MOF materials with vitrification properties by ball milling, and then mix them evenly with zeolite molecular sieve materials before mechanical pressing and calcination to obtain a high-throughput, self-supporting porous zeolite molecular sieve-MOF crystal glass composite membrane for difficult-to-separate systems (C4H6 / C4). This method broadens the range of membrane materials to be selected in the field of membrane separation and lays the foundation for the practical application of vitrified MOF membranes.

[0043] According to an embodiment of the present invention, S1 specifically involves uniformly mixing a mixed metal salt with a ligand in different molar ratios, ball milling the mixture using a planetary ball mill, filtering the resulting product, washing it with methanol, and obtaining ZIF-62 particles.

[0044] According to an embodiment of the present invention, in S1, the metal salt is a zinc ion source.

[0045] According to an embodiment of the present invention, in S1, the molar ratio of zinc ion source to ligand in the metal salt is 1:2.

[0046] According to an embodiment of the present invention, in S1, the zinc ion source is a mixture of zinc hydroxide and zinc acetate.

[0047] According to an embodiment of the present invention, in S1, the molar ratio of zinc hydroxide to zinc acetate is 99:1 to 70:30.

[0048] According to an embodiment of the present invention, in S1, the molar ratio of zinc hydroxide to zinc acetate can be 99:1, 90:10, 80:20, or 70:30.

[0049] According to an embodiment of the present invention, in S1, the ligand is a mixture of imidazole and benzimidazole.

[0050] According to an embodiment of the present invention, in S1, the molar ratio of zinc ion source, imidazole and benzimidazole is 1:1.75:0.25.

[0051] According to an embodiment of the present invention, in S1, the volume of the ball mill jar is 50-500 mL, the rotation speed is 300-500 r, and the ball milling time is 0.5-2 h.

[0052] According to an embodiment of the present invention, in S1, anhydrous methanol is used, and the cleaning and soaking time is 12 hours.

[0053] According to an embodiment of the present invention, S2 specifically involves uniformly mixing ZIF-62 and zeolite molecular sieve powders of different mass ratios and preparing them into discs of a certain diameter and thickness using a mechanical tablet press.

[0054] According to an embodiment of the present invention, in S2, the zeolite molecular sieve is one of SSZ-13 molecular sieve, Cu-SSZ-13 molecular sieve, SAPO-34 molecular sieve, ZSM-5 molecular sieve, 3A molecular sieve, 4A molecular sieve, and 5A molecular sieve.

[0055] According to an embodiment of the present invention, in S2, the mass ratio of zeolite molecular sieve to ZIF-62 particles is 1-60:99-40.

[0056] According to an embodiment of the present invention, in S2, the diameter of the tablet is 1-9.5 cm.

[0057] According to an embodiment of the present invention, in S2, the pressure used for tablet compression is 10 MPa.

[0058] According to an embodiment of the present invention, in S2, tableting is performed at room temperature.

[0059] According to an embodiment of the present invention, S3 specifically involves calcining the discs in a tube furnace under inert gas protection to obtain a self-supporting zeolite molecular sieve / ZIF-62 crystal-glass composite membrane.

[0060] According to an embodiment of the present invention, in S3, the calcination temperature range is from room temperature to 380 to 450°C, the heating rate is 3°C / min, argon or nitrogen is used as a protective gas, and the gas flow rate is 120 to 140 mL / min.

[0061] According to an embodiment of the present invention, in S3, the diameter of the tubular furnace tube is 10cm.

[0062] According to a second aspect of the present invention, a pressure-responsive membrane obtained by the above-described preparation method is provided.

[0063] This invention melts ZIF-62 particles and encapsulates zeolite molecular sieves, thereby eliminating defects in the membrane and forming a monolithic, dense film. This membrane possesses characteristics such as self-support, high selectivity, and high throughput, providing a solution for the separation of difficult-to-separate gases.

[0064] According to a third aspect of the present invention, an application of the above-described self-supporting zeolite molecular sieve-MOF crystal glass composite membrane in the gas separation of difficult-to-separate systems is provided.

[0065] According to embodiments of the present invention, it includes systems for C4H6 / i-C4H8 and C4H6 / i-C4H 10 System, C4H6 / n-C4H8 system or C4H6 / n-C4H 10 System separation.

[0066] The technical solution of the present invention will be described in detail below through preferred embodiments. It should be noted that the specific embodiments in the following text are for illustrative purposes only and are not intended to limit the present invention.

[0067] Example:

[0068] Figure 1 This is a scanning electron microscope image of the ZIF-62 particles obtained in an embodiment of the present invention.

[0069] 2.978 g of imidazole, 0.738 g of benzimidazole, 1.740 g of zinc hydroxide, 1.647 g of zinc acetate dihydrate, and 2.5 mL of N,N-dimethylformamide were added to a 100 mL stainless steel grinding jar. Twenty stainless steel grinding balls were added to the jar. The mixture was milled at 300 rpm for 30 min at room temperature using a QM-3SP04L planetary ball mill. After the reaction was complete, the product was soaked in anhydrous methanol for 12 h, washed three times, and then dried to obtain ZIF-62.

[0070] ZIF-62 and SSZ-13 zeolite molecular sieve powders of 150 mg and 0 mg (mass ratio 1:0), 135 mg and 15 mg (mass ratio 9:1), 120 mg and 30 mg (mass ratio 8:2), and 105 mg and 45 mg (mass ratio 7:3) were mixed evenly and then prepared into discs with a diameter of 2 cm and a thickness of 334-368 μm using a mechanical tablet press.

[0071] Under inert gas protection, the discs were calcined in a tube furnace to obtain self-supporting SSZ-13 / ZIF-62 zeolite molecular sieve-MOF crystal glass composite membranes, which were used as samples 1, 2, 3 and 4, respectively.

[0072] Material characterization

[0073] Figure 2 The thermogravimetric curves of ZIF-62 and SSZ-13 mixed in different mass ratios in this embodiment of the invention are shown.

[0074] Figure 3 The X-ray diffraction patterns are of zeolite molecular sieve-MOF crystal glass composite membranes prepared with ZIF-62 and SSZ-13 in different mass ratios in the embodiments of the present invention.

[0075] Figure 4 The images show scanning electron microscope (SEM) images of the surface and cross-section of sample 2 of this invention.

[0076] Figure 5 The images show scanning electron microscope (SEM) images of the surface and cross-section of sample 3 of the present invention.

[0077] Figure 6 The images show scanning electron microscope (SEM) images of the surface and cross-section of sample 4 of this invention.

[0078] like Figure 2 As shown, when ZIF-62 and SSZ-13 are mixed in different mass ratios, the two materials are stable and do not decompose at 500℃.

[0079] like Figure 3 As shown, the disappearance of the diffraction peak of ZIF-62 crystal in the composite membrane indicates that ZIF-62 has transformed from a crystal to an amorphous glass, and the zeolite molecular sieve material in the membrane retains its crystalline form.

[0080] Figures 4-6 This indicates that the self-supporting zeolite molecular sieve-MOF crystal glass composite membranes (samples 2-4) have dense and defect-free membrane surfaces and cross-sections.

[0081] Experimental Example 1:

[0082] Figure 7 The gas permeation separation performance of samples 1, 2, 3 and 4 of this invention is shown.

[0083] Under single-gas testing conditions at 25℃, samples 1, 2, 3, and 4 were tested in C4H6 / n-C4H 10 The permeability coefficient of C4H6 in the system is shown in the figure. Figure 7 It can be seen that the permeability coefficients of samples 1-4 are 94, 296, 397 and 693 GPU, respectively; C4H6 / n-C4H 10 The selectivity values ​​were 1.4, 4.1, 6.1, and 11.2, respectively. The results indicate that Sample 1, as a pure ZIF-62 glass membrane, has low C4H6 permeability and selectivity, while the self-supporting zeolite molecular sieve-MOF crystal glass composite membranes prepared by mixing ZIF-62 and SSZ-13 in this invention (i.e., Samples 2, 3, and 4) have higher C4H6 permeability and selectivity.

[0084] Experimental Example 2:

[0085] Figure 8 This is to show the selectivity of C4H6 in sample 4 of the present invention for the other four C4 gases.

[0086] Under single-gas testing conditions at 25℃, tests were conducted on C4H6 / i-C4H8 and C4H6 / i-C4H... 10 C4H6 / n-C4H8, C4H6 / n-C4H 10 The selectivity of sample 4 for C4H6 in the system is shown in the figure. Figure 8 , Figure 8 This indicates that under single-gas testing conditions at 25℃, the C4H6 / i-C4H8 and C4H6 / i-C4H6 components of sample 4... 10 C4H6 / n-C4H8, C4H6 / n-C4H 10 The selectivity values ​​were 9.72, 9.93, 10.31, and 11.24, respectively. The results indicate that the membrane possesses C4H6 recognition capability and can separate C4H6 gas independently in a C4 system, demonstrating excellent sieving ability.

[0087] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a self-supporting zeolite-molecular-organic-framework (MOF) crystal glass composite membrane, comprising: uniformly mixing a metal salt and a ligand, ball-milling with a planetary ball mill, and then performing suction filtration and methanol washing to obtain ZIF-62 particles; uniformly mixing the ZIF-62 particles and zeolite powder, and then using a mechanical tablet press to prepare a round tablet; under the condition of inert gas protection, calcining the round tablet to obtain a self-supporting zeolite-MOF crystal glass composite membrane, wherein the calcination temperature is in the range of room temperature to 380-450 ℃, and the temperature rising rate is 3 ℃ / min, so that the ZIF-62 particles melt and wrap the zeolite. 2.The method according to claim 1, wherein the metal salt is a zinc ion source; and the molar ratio of the zinc ion source to the ligand in the metal salt is 1:

2. 3.The method according to claim 2, wherein the zinc ion source is a mixture of zinc hydroxide and zinc acetate; and the molar ratio of the zinc hydroxide to the zinc acetate is 99:1-70:

30. 4.The method according to claim 2, wherein the ligand is a mixture of imidazole and benzimidazole. 5.The method according to claim 4, wherein the molar ratio of the zinc ion source, the imidazole and the benzimidazole is 1:1.75:0.

25. 6.The method according to claim 1, wherein the zeolite is one of SSZ-13, Cu-SSZ-13, SAPO-34, ZSM-5, 3A, 4A and 5A; and the mass ratio of the zeolite to the ZIF-62 particles is 1-60:99-40. 7.Under the condition of inert gas protection, the inert gas is argon or nitrogen, and the gas flow of the inert gas is 120-140 mL / min. 8.A self-supporting zeolite-MOF crystal glass composite membrane obtained by the method according to any one of claims 1-7. 9.Use of the self-supporting zeolite-MOF crystal glass composite membrane according to claim 8 in gas separation of a difficult separation system. ​ ​ ​ ​ ​ ​ 7. The production method according to claim 1, wherein ​ ​ ​ 10. Use according to claim 9, comprising separation of C4H6 / i-C4H8 systems, C4H6 / i-C4H 10 systems, C4H6 / n-C4H8 systems or C4H6 / n-C4H 10 systems.

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