A method of making and product of a mixed matrix MOF membrane for the extraction of helium from natural gas

Abstract

The application relates to a preparation method and product of a mixed matrix MOF membrane for extracting helium from natural gas, and belongs to the technical field of mixed matrix membrane material preparation. The application discloses a preparation method of a mixed matrix MOF membrane for extracting helium from natural gas, mainly a mixed matrix MOF membrane (Zn-BDC / PIM-1) prepared by means of an in-situ growth method. The in-situ growth of MOF filling materials in a linear structure self-porous polymer (PIM-1) enhances the interaction between the polymer and the MOF particles, avoids the process of pre-synthesis, drying and re-dispersion of the MOF materials, effectively solves the problems of particle agglomeration and interface defects, and improves the natural gas helium extraction performance of the material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of preparation of mixed matrix membrane materials, and relates to a preparation method and product of a mixed matrix MOF membrane for extracting helium from natural gas. BACKGROUND

[0002] Helium (He) is a rare strategic resource and an inert gas indispensable for many high-tech applications. Although He is abundant in the universe, its terrestrial sources are limited, and the world's helium is currently mainly derived from natural gas. Compared with traditional separation methods such as distillation and adsorption, membrane separation technology has the advantages of relatively low cost, no phase change in the separation process, continuous operation, high energy efficiency, and no secondary pollution in extracting helium from natural gas. However, there are some problems in the separation membranes reported in the current membrane separation technology, which limit its application prospect, such as the difficulty in balancing the selectivity and permeability of polymer membranes, and the good separation performance of inorganic membranes such as silicon dioxide, but the commercialization is complex and the cost is high.

[0003] Therefore, in the technical research, inorganic particles are tried to be incorporated into the polymer matrix to form a mixed matrix membrane, trying to eliminate or reduce the weaknesses of the polymer matrix membrane, which is also the most potential membrane separation material. Among the existing porous materials, metal organic frameworks (MOFs) have become excellent filling materials for mixed matrix membranes due to their highly porous structure, adjustable functional groups and adjustable pore structure. However, the mixed matrix MOF membranes prepared by physical mixing have problems such as agglomeration of MOF particles, invalid accumulation of polymers, and poor compatibility of MOF-polymer interface, which leads to defects in the interface, blocks the gas transport channel, and significantly reduces the He permeability and selectivity. In addition, due to the insufficient interaction between the polymer phase and the particles, non-selective voids may occur, which increases the permeation amount of gas molecules with larger kinetic diameters such as CH4 and N2, which is not conducive to gas separation.

[0004] Therefore, it is necessary to conduct in-depth research on the mixed matrix MOF membrane for extracting helium from natural gas, so as to obtain a mixed matrix MOF membrane with good performance and simple preparation method. SUMMARY

[0005] Therefore, one of the purposes of the present application is to provide a preparation method of a mixed matrix MOF membrane for extracting helium from natural gas; the second purpose of the present application is to provide a mixed matrix MOF membrane for extracting helium from natural gas; and the third purpose of the present application is to provide an application of a mixed matrix MOF membrane in extracting helium from natural gas.

[0006] To achieve the above-mentioned purposes, the present application provides the following technical solutions:

[0007] 1.A method for preparing a mixed matrix MOF membrane for extracting helium from natural gas, the method comprising the following steps:

[0008] (1) preparing a linear structure self-porous polymer (PIM-1) : anhydrous K2CO3, 5, 5', 6, 6'-tetrahydroxy-3, 3', 3, 3'-tetramethyl-1, 1'-spirobiindoline and 2, 3, 5, 6-tetrafluoroterephthalonitrile are added to 20-45 mL of N, N-dimethylformamide (DMF), heated and stirred to dissolve, and then deionized water is added to dissolve after cooling, and the crude product is collected by filtration, and the linear structure self-porous polymer (PIM-1) is obtained by repeating purification in methanol and vacuum drying.

[0009] (2) preparing a ZIF-8 / PIM-1 material: 1-3.5 g of the linear structure self-porous polymer (PIM-1) prepared in step (1) is dissolved in chloroform (CHCl3), stirred to form a uniform solution, an aqueous solution of zinc nitrate hexahydrate (Zn (NO3) 2·6H2O) is added, an aqueous solution of terephthalic acid (BDC) is added after mixing uniformly, and stirring is performed at a speed of 6000-10000 rpm for 6-10 h, and then the mixture is poured into methanol, and the ZIF-8 / PIM-1 material is obtained by filtration and drying.

[0010] (3) preparing a mixed matrix MOF membrane (Zn-BDC / PIM-1) : the ZIF-8 / PIM-1 material prepared in step (2) is dissolved in chloroform (CHCl3), cast in a mold, and the membrane obtained after evaporation of the solvent is soaked in methanol for 24-48 h, and dried at 80℃ for 12-36 h to obtain the mixed matrix MOF membrane (Zn-BDC / PIM-1).

[0011] Preferably, in step (1), the molar ratio of the anhydrous K2CO3, 5, 5', 6, 6'-tetrahydroxy-3, 3', 3, 3'-tetramethyl-1, 1'-spirobiindoline and 2, 3, 5, 6-tetrafluoroterephthalonitrile is 1-2.4: 3-6: 3-7.5.

[0012] The molar volume ratio of the 5, 5', 6, 6'-tetrahydroxy-3, 3', 3, 3'-tetramethyl-1, 1'-spirobiindoline, N, N-dimethylformamide (DMF) and methanol is 3-4.7: 20-50: 30-75, mmol: mL: mL.

[0013] Preferably, in step (1), the temperature for heating and stirring to dissolve is 60-80℃, and the time is 56-80 h.

[0014] The vacuum drying is specifically drying at 80℃ for 12-24 h.

[0015] Preferably, in step (2), the mass-volume ratio of the linear structured self-porous polymer (PIM-1) and chloroform (CHCl3) is 1-3.6:20-45, g:mL;

[0016] The molar volume ratio of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and water in the aqueous solution of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) is 3-5.2:15-45, mmol:mL;

[0017] The molar volume ratio of terephthalic acid (BDC) and water in the aqueous solution of terephthalic acid (BDC) is 2.5-4:50-80, mmol:mL.

[0018] Preferably, in step (2), the mass-molar ratio of the linear structured self-porous polymer (PIM-1), zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and terephthalic acid (BDC) is 0.6-1.4:3-5.8:2.9-5, g:mmol:mmol.

[0019] Preferably, in step (3), the mass-volume ratio of the ZIF-8 / PIM-1 and chloroform is 1.5-3.6:6-8.5, g:mL.

[0020] 2. The mixed matrix MOF membrane (Zn-BDC / PIM-1) prepared by the above preparation method.

[0021] 3. The application of the above mixed matrix MOF membrane (Zn-BDC / PIM-1) in extracting helium from natural gas.

[0022] The beneficial effects of the present application are:

[0023] 1. The present application discloses a preparation method of a mixed matrix MOF membrane for extracting helium from natural gas, which mainly prepares a mixed matrix MOF membrane (Zn-BDC / PIM-1) by means of in-situ growth method, fills the MOFs material in the linear structured self-porous polymer (PIM-1) by in-situ growth, enhances the interaction between the polymer and the MOFs particles, avoids the process of pre-synthesis, drying and re-dispersion of the MOFs material, effectively solves the problems of particle agglomeration and interface defects, and improves the performance of the material in extracting helium from natural gas.

[0024] 2. The application also discloses a mixed matrix MOF membrane for extracting helium from natural gas, which can simultaneously improve the permeability and selectivity of helium (He) and maintain excellent helium (He) separation performance in long-term tests, in particular, when the amount of the mixed matrix MOF membrane Z is 18 wt%, the selectivity of He / CH4 and He / N2 reaches 320 and 260, respectively, which is 2.6 times and 2.4 times that of the pure linear structure self-porous polymer (PIM-1), respectively.

[0025] Other advantages, objects, and features of the present application will be understood and appreciated by those skilled in the art upon reading this specification, some of which will become apparent to those skilled in the art from the foregoing description, or can be learned by practice of the application. The advantages, objects and novel features of the application can be realized and attained by the instrumentalities and combinations pointed out in this specification. DETAILED DESCRIPTION

[0026] The embodiments of the present application will be described in detail with specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the disclosure of the specification. The present application can also be implemented or applied by other different specific embodiments, and the details in the specification can be modified or changed in various ways based on different views and applications without departing from the spirit of the present application.

[0027] Example 1

[0028] A preparation method of a mixed matrix MOF membrane for extracting helium from natural gas, specifically comprising the following steps:

[0029] (1) Preparation of linear structure self-porous polymer (PIM-1): anhydrous K2CO3 (0.14 g, 1 mmol), 5,5',6,6'-tetrahydroxy-3,3',3,3'-tetramethyl-1,1'-spirobiindoline (1.02 g, 3 mmol) and 2,3,5,6-tetrafluoroterephthalonitrile (0.60 g, 3 mmol) are added to 20 mL of N,N-dimethylformamide (DMF), heated to 65°C and stirred for 72 h to make them uniformly mixed, after cooling, deionized water (30 mL) is added, the crude product is collected by filtration, purified three times in methanol, and then dried at 80°C under vacuum for 12 h to obtain the linear structure self-porous polymer (PIM-1).

[0030] (2) Preparation of mixed matrix MOF membrane (Zn-BDC / PIM-1): 1 g of linear structured microporous polymer (PIM-1) was dissolved in 20 mL of chloroform (CHCl3) and stirred for 5 h to form a uniform solution, then an aqueous solution of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) (Zn(NO3)2·6H2O (0.89 g, 3 mmol) was dissolved in 20 mL of water) was added, and after being fully mixed for 30 min under continuous stirring, an aqueous solution of terephthalic acid (BDC) (BDC (0.60 g, 3 mmol) was dissolved in 50 mL of water) was added, and after being continuously stirred vigorously for 6 h, it was poured into excess methanol, and after being filtered and dried, a uniform ZIF-8 / PIM-1 material was obtained.

[0031] (3) The ZIF-8 / PIM-1 material was dissolved in chloroform according to a mass-volume ratio of 1:2, g:mL, and then cast in a mold, and after the solvent was evaporated, the obtained membrane was soaked in methanol for 24 h, and then dried at 80 °C for 12 h to obtain a Zn-BDC / PIM-1 mixed matrix MOF membrane.

[0032] Example 2

[0033] A method for preparing a mixed matrix MOF membrane for extracting helium from natural gas, specifically comprising the following steps:

[0034] (1) Preparation of linear structured microporous polymer (PIM-1): Anhydrous K2CO3 (0.14 g, 1 mmol), 5,5',6,6'-tetrahydroxy-3,3',3,3'-tetramethyl-1,1'-spirobiindoline (2.04 g, 6 mmol) and 2,3,5,6-tetrafluoroterephthalonitrile (1.5 g, 7.5 mmol) were added to 100 mL of N,N-dimethylformamide (DMF), heated to 60 °C and stirred for 80 h to mix uniformly, then deionized water (150 mL) was added after cooling, the crude product was collected by filtration, purified three times in methanol, and then dried at 80 °C under vacuum for 24 h to obtain a linear structured microporous polymer (PIM-1).

[0035] (2) Preparation of mixed matrix MOF membrane (Zn-BDC / PIM-1): 3.6 g of linear structured microporous polymer (PIM-1) was dissolved in 20 mL of chloroform (CHCl3) and stirred for 5 h to form a uniform solution, then an aqueous solution of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) (Zn(NO3)2·6H2O (5.34 g, 18 mmol) was dissolved in 90 mL of water) was added, and after being fully mixed for 30 min under continuous stirring, an aqueous solution of terephthalic acid (BDC) (BDC (4.8 g, 17.4 mmol) was dissolved in 348 mL of water) was added, and after being continuously stirred vigorously for 6 h, it was poured into excess methanol, and after being filtered and dried, a uniform ZIF-8 / PIM-1 material was obtained.

[0036] (3) The ZIF-8 / PIM-1 material was dissolved in chloroform according to a mass-volume ratio of 3.6:6, g:mL, and then cast in a mold, and after the solvent was evaporated, the obtained membrane was soaked in methanol for 24 h, and then dried at 80 °C for 36 h to obtain a Zn-BDC / PIM-1 mixed matrix MOF membrane.

[0037] Example 3

[0038] A method for preparing a mixed matrix MOF membrane for extracting helium from natural gas, specifically comprising the following steps:

[0039] (1) Preparation of linear structured microporous polymer (PIM-1): Anhydrous K2CO3 (0.336 g, 2.4 mmol), 5,5',6,6'-tetrahydroxy-3,3',3,3'-tetramethyl-1,1'-spirobiindoline (1.02 g, 3 mmol), and 2,3,5,6-tetrafluoroterephthalonitrile (0.60 g, 3 mmol) were added to 12.8 mL of N,N-dimethylformamide (DMF), heated to 80 °C and stirred for 56 h to mix uniformly, then deionized water (19.2 mL) was added after cooling, the crude product was collected by filtration, purified three times in methanol, and then dried at 80 °C under vacuum for 18 h to obtain a linear structured microporous polymer (PIM-1).

[0040] (2) Preparation of mixed matrix MOF membrane (Zn-BDC / PIM-1): 1.4 g of linear structured microporous polymer (PIM-1) was dissolved in 7.78 mL of chloroform (CHCl3) and stirred for 5 h to form a uniform solution, then an aqueous solution of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) (Zn(NO3)2·6H2O (0.89 g, 3 mmol) was dissolved in 8.65 mL of water) was added, and after fully mixing under continuous stirring for 30 min, an aqueous solution of terephthalic acid (BDC) (BDC (0.58 g, 2.9 mmol) was dissolved in 36.25 mL of water) was added, and after continuous vigorous stirring for 10 h, it was poured into excess methanol, and after filtration and drying, a uniform ZIF-8 / PIM-1 material was obtained.

[0041] (3) The ZIF-8 / PIM-1 material was dissolved in chloroform according to a mass-volume ratio of 1.5:8.5, g:mL, and then cast in a mold, and after evaporation of the solvent, the obtained membrane was soaked in methanol for 24 h, and dried at 80°C for 12 h to obtain a Zn-BDC / PIM-1 mixed matrix MOF membrane.

[0042] Performance test

[0043] The Zn-BDC / PIM-1 mixed matrix MOF membranes prepared in Example 1, Example 2 and Example 3 were subjected to performance tests, and the results are shown in Table 1.

[0044] Table 1 Permeability and selectivity of Zn-BDC / PIM-1 mixed matrix MOF membranes prepared in different examples

[0045] Sample Zn content (wt. %) He permeability Selectivity of He / CH4 Selectivity of He / N2 Example 1 18 232 GPU 320 260 Example 2 30 217 GPU 235 216 Example 3 13 256 GPU 279 234 PIM-1 0 148 GPU 123 108

[0046] From Table 1, it can be seen that compared with pure linear structured microporous polymer (PIM-1), the Zn-BDC / PIM-1 mixed matrix MOF membrane prepared by the method of the present application has better permeability and helium (He) separation performance, and as the content of zinc ions (Zn 2+ ) in the mixed matrix MOF membrane increases, the He permeability, He / CH4 selectivity and He / N2 selectivity all show a trend of first increasing and then decreasing.

[0047] In summary, the application discloses a preparation method of a mixed matrix MOF membrane for extracting helium from natural gas, mainly using an in-situ growth method to prepare a mixed matrix MOF membrane (Zn-BDC / PIM-1), growing MOF filling materials in a linear structure self-microporous polymer (PIM-1) in-situ, enhancing the interaction between the polymer and the MOF particles, avoiding the process of pre-synthesis, drying and re-dispersion of the MOF materials, effectively solving the problems of particle agglomeration and interface defects, and improving the helium extraction performance of the material from natural gas. The mixed matrix MOF membrane prepared by the application can improve the permeability and selectivity of helium (He) at the same time, and can maintain excellent helium (He) separation performance in long-term tests, especially when the amount of Zn in the mixed matrix MOF membrane is 18wt.%, the selectivity of He / CH4 and He / N2 reaches 320 and 260 respectively, which is 2.6 times and 2.4 times of the pure linear structure self-microporous polymer (PIM-1) respectively.

[0048] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the application and not to limit the application, although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced equivalently without departing from the purpose and scope of the technical solutions, which should be covered in the scope of the claims of the application.

Claims

1. A method for the preparation of a mixed matrix MOF membrane for the extraction of helium from natural gas, characterized in that, The preparation method comprises the following steps: (1) preparing a linear structure self-porous polymer: anhydrous K2CO3, 5, 5', 6, 6'-tetrahydroxy-3, 3', 3, 3'-tetramethyl-1, 1'-spirobiindoline and 2, 3, 5, 6-tetrafluoroterephthalonitrile are added into N, N-dimethylformamide, heated and stirred to dissolve, after cooling, deionized water is added to dissolve, the crude product is collected by filtration, and after repeated purification in methanol, the linear structure self-porous polymer can be obtained by vacuum drying; (2) preparing a ZIF-8 / PIM-1 material: 1-3.5 g of the linear structure self-porous polymer prepared in step (1) is dissolved in chloroform, stirred to form a uniform solution, an aqueous zinc nitrate hexahydrate solution is added, after mixing uniformly, an aqueous terephthalic acid solution is added, stirring is carried out at a speed of 6000-10000 rpm for 6-10 h, and then the mixture is poured into methanol, and after filtration and drying, the ZIF-8 / PIM-1 material is obtained; (3) preparing a mixed matrix MOF membrane: the ZIF-8 / PIM-1 material prepared in step (2) is dissolved in chloroform, cast in a mold, and after evaporation of the solvent, the obtained membrane is soaked in methanol for 24-48 h, dried at 80 ℃ for 12-36 h, and the mixed matrix MOF membrane is obtained.

2. The production method according to claim 1, characterized by, In step (1), the molar ratio of the anhydrous K2CO3, 5, 5', 6, 6'-tetrahydroxy-3, 3', 3, 3'-tetramethyl-1, 1'-spirobiindoline and 2, 3, 5, 6-tetrafluoroterephthalonitrile is 1-2.4:3-6:3-7.5; The molar volume ratio of the 5, 5', 6, 6'-tetrahydroxy-3, 3', 3, 3'-tetramethyl-1, 1'-spirobiindoline, N, N-dimethylformamide and methanol is 3-4.7:20-50:30-75, mmol:mL:mL.

3. The preparation method according to claim 1, characterized in that, In step (1), the temperature for heating and stirring to dissolve is 60-80 ℃, and the time is 56-80 h; The vacuum drying is specifically drying at 80 ℃ for 12-24 h under vacuum.

4. The method of claim 1, wherein, In step (2), the mass-volume ratio of the linear structure self-porous polymer and chloroform is 1-3.6:20-45, g:mL; The molar volume ratio of zinc nitrate hexahydrate and water in the aqueous zinc nitrate hexahydrate solution is 3-5.2:15-45, mmol:mL; and the molar volume ratio of terephthalic acid and water in the aqueous terephthalic acid solution is 2.5-4:50-80, mmol:mL.

5. The method of claim 1, wherein, In step (2), the mass-molar ratio of the linear structure self-porous polymer, zinc nitrate hexahydrate and terephthalic acid is 0.6-1.4:3-5.8:2.9-5, g:mmol:mmol.

6. The method of claim 1, wherein, In step (3), the mass-volume ratio of the ZIF-8 / PIM-1 and chloroform is 1.5-3.6:6-8.5, g:mL.

7. The mixed matrix MOF membrane prepared by the preparation method according to any one of claims 1-6.

8. Application of the mixed matrix MOF membrane according to claim 7 to extraction of helium from natural gas.