Dual polymer-modified composite SSZ-13 molecular sieve membrane, preparation method and application

Abstract

This invention discloses a dual-polymer modified composite SSZ-13 molecular sieve membrane, its preparation method, and its application, belonging to the field of gas separation technology. The method involves first coating the SSZ-13 molecular sieve membrane with a layer of 6FDA-APAF. 0.5 -BIA 0.5 A polymer membrane is then coated with a PDMS membrane to prepare a composite membrane. Compared with unmodified membrane materials or membrane materials modified by only one polymer, the helium / methane separation performance of the composite membrane material co-modified by two polymers is significantly improved. Since the Young's modulus of the inorganic molecular sieve membrane is higher than that of the polymer membrane, the composite SSZ-13 molecular sieve membrane has higher mechanical stability than the polymer membrane. It performs well under different pressures, especially under high pressure, and can maintain good operational stability. It can be used to extract helium from low-concentration helium-containing natural gas in pipelines. This not only provides a new way for the successful separation and recovery of helium, but also provides new ideas for the performance optimization of other separation membranes.

Description

Technical Field

[0001] This invention belongs to the field of gas separation technology, specifically relating to a dual polymer-modified SSZ-13 molecular sieve membrane, its preparation method, and its application in separating He / CH4 mixed gas. Background Technology

[0002] Helium is a colorless, non-toxic, low-boiling-point monatomic inert gas that plays a vital role in fields such as magnetic resonance imaging, semiconductor manufacturing, aerospace, and nuclear power plants. In recent years, the demand for helium has been increasing annually. Helium originates from the decay of radioactive metals in the Earth's crust, initially emitted as a byproduct of natural gas along with other waste gases. Although helium is also distributed in the atmosphere and rock formations, its extremely low concentration makes it difficult to accumulate, and helium-containing natural gas is the only commercial source of helium.

[0003] The main methods for separating and recovering helium from natural gas include cryogenic separation, pressure swing adsorption (PSA), and membrane separation technology. Cryogenic separation is a traditional separation process, but the cryogenic liquefaction separation process is energy-intensive and expensive. PSA uses the difference in adsorption capacity of adsorbents on gas components for separation and purification, but it requires a large area and the adsorbent is difficult to regenerate, resulting in a high loss rate.

[0004] Membrane separation, a novel separation method developed in the 1950s, boasts advantages such as low energy consumption, ease of operation, flexible device design, and small footprint, leading to its wide range of applications. Membrane separation utilizes the difference in transport velocities between helium and methane within a membrane to selectively separate the two gases, showing significant enrichment and concentration effects for low-concentration helium. The core of membrane separation technology lies in the membrane material, among which polymer membranes are widely used in gas separation, liquid filtration, and ion exchange. They are typically made of polymeric materials, possessing specific pore sizes and selectivity, enabling effective separation of molecules or ions of different sizes. The advantages of polymer membranes include low cost, ease of processing, and good mechanical properties. However, existing polymer membrane materials generally exhibit low helium permeability and difficulty in achieving the required helium / methane selectivity for separation. To address these issues, Chinese patent CN113337095A proposes a self-polymerizing microporous polymer fluorinated membrane. This membrane is obtained by replacing hydrogen on the surface of a microporous polymer membrane with fluorine from a fluorine-nitrogen mixture. The resulting membrane material exhibits an ideal helium / methane selectivity exceeding 3000. However, it should be noted that while this membrane boasts superior performance, its preparation is challenging, and the resulting membrane material exhibits poor mechanical stability and thermal conductivity, limiting its practical application. Chinese patent CN115414793A discloses an STT molecular sieve membrane suitable for helium purification, providing a new method for helium separation. However, the separation performance of this membrane under specific environments (such as high-pressure conditions) still needs further investigation.

[0005] SSZ-13 molecular sieve membrane is a molecular sieve with a chalcogenide (CHA) structure, consisting of AlO4 and SiO4 tetrahedra linked by oxygen atoms to form an ellipsoidal cage-like structure with an eight-membered ring. The pore size of SSZ-13 is 0.38 nm × 0.38 nm, comparable to the kinetic diameter of many small molecule gases, and it has a high specific surface area (up to 700 m² / g). SSZ-13 molecular sieve membranes have shown great potential in gas separation due to their high catalytic performance, excellent selectivity, outstanding sulfur resistance, and unique three-dimensional pore structure, and hold promise for mass production to reduce costs. However, SSZ-13 molecular sieve membranes suffer from limitations such as limited hydrothermal stability, a limited number of acidic sites, pore size constraints, and aging issues. Existing technologies often employ methods such as optimizing the synthesis process, loading metal ions, and introducing modifiers to improve the performance of SSZ-13 molecular sieve membranes.

[0006] According to relevant reports, introducing specific polymers onto molecular sieve membranes can alter their surface properties and pore structure, such as changing their hydrophilic or hydrophobic properties, thereby improving the separation selectivity for mixed gases like CO2 / CH4 and H2 / CH4. Furthermore, polymer modification can enhance the mechanical strength and stability of molecular sieve membranes and reduce defects. Compared to polymer membranes, organic-inorganic composite membranes offer enhanced mechanical strength and stability, making them more suitable for industrial applications. However, there are few reports on polymer-modified SSZ-13 molecular sieve membranes. Successfully preparing a novel membrane material with excellent He / CH4 selectivity through polymer modification of SSZ-13 molecular sieve membranes would provide new possibilities for separating He / CH4. Summary of the Invention

[0007] To address the aforementioned problems, this invention aims to provide a dual-polymer modified composite SSZ-13 molecular sieve membrane, achieved by sequentially modifying the SSZ-13 molecular sieve membrane with 6FDA-APAF. 0.5 -BIA 0.5 The membrane layer and PDMS membrane layer effectively improve the He / CH4 separation performance of the base membrane, and it performs well even under high pressure conditions. Moreover, the membrane preparation process is simple, the preparation cost is low, and the resulting composite membrane material has a stable structure, making it suitable for widespread use in the field of gas separation.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing a dual polymer-modified composite SSZ-13 molecular sieve membrane, comprising the following steps:

[0009] 1) Polymer 6FDA-APAF 0.5 -BIA 0.5Dissolve in solvent, mix well, filter, defoam, and obtain 6FDA-APAF. 0.5 -BIA 0.5 Solution;

[0010] 2) Mix PDMS, curing agent and n-heptane, stir well, filter, defoam, and obtain PDMS solution;

[0011] 3) First, coat the SSZ-13 molecular sieve membrane and the support with the 6FDA-APAF prepared in step 1). 0.5 -BIA 0.5 Solution;

[0012] 4) Coated with 6FDA-APAF 0.5 -BIA 0.5 PDMS solution was coated onto the molecular sieve membrane and the support to obtain a composite SSZ-13 molecular sieve membrane modified with two polymers.

[0013] Further, in step 1), the solvent is N-methylpyrrolidone, and the mixture is stirred at a speed of 600 rpm-800 rpm for 6-12 hours; the prepared 6FDA-APAF 0.5 -BIA 0.5 6FDA-APAF in solution 0.5 -BIA 0.5 The mass percentage is 1-30 wt.%.

[0014] Further, in step 2), the mass percentage of PDMS in the prepared PDMS solution is 0.5-25 wt.%, and the solution is mixed by stirring at a speed of 600 rpm-800 rpm for 6-12 h.

[0015] Furthermore, the coating process in steps 3) and 4) is completed by means including dip coating, spraying, brushing, spin coating, and vacuum coating.

[0016] Preferably, 6FDA-APAF is coated onto the SSZ-13 molecular sieve membrane using the dip-coating method. 0.5 -BIA 0.5 With PDMS, the specific process is as follows:

[0017] S1. First, immerse the SSZ-13 molecular sieve membrane and carrier, which are sealed at both ends, into the prepared 6FDA-APAF solution. 0.5 -BIA 0.5The solution was immersed for 15–20 seconds, with an immersion and withdrawal rate of 40–60 mm / min. After removal, it was dried in an oven at 60–70 °C for 1–2 h, then heated to 180–200 °C in a vacuum oven at a rate of 1–5 °C / min to completely remove the solvent, and then cooled to 303 K at a rate of 1–5 °C / min to coat the SSZ-13 molecular sieve membrane with 6FDA-APAF. 0.5 -BIA 0.5 ;

[0018] S2, coated with 6FDA-APAF 0.5 -BIA 0.5 The SSZ-13 molecular sieve membrane and the support were immersed in PDMS solution for 1-30 min, with an immersion and extraction rate of 1-3 cm / s. After drying at room temperature for 1-3 h, they were placed in an oven and heated at a rate of 1-5 °C / min to 90-110 °C for 1-3 h. Then, the temperature was lowered to 333 K at a rate of 1-3 °C / min to coat the SSZ-13 molecular sieve membrane with PDMS.

[0019] Furthermore, the 6FDA-APAF 0.5 -BIA 0.5 6FDA-APAF in solution 0.5 -BIA 0.5 The mass percentage of the sample was 10 wt.%, and the mass percentage of PDMS in the PDMS solution was 5 wt.%; the immersion time in the PDMS solution was 5~25 min.

[0020] This application also provides a dual-polymer modified composite SSZ-13 molecular sieve membrane, wherein 6FDA-APAF are sequentially modified onto the SSZ-13 molecular sieve membrane. 0.5 -BIA 0.5 Membrane layer and PDMS membrane layer.

[0021] This dual-polymer modified composite SSZ-13 molecular sieve membrane can be applied in the field of gas separation, especially for separating He / CH4 mixtures, which are simulated natural gas components containing 0.097% helium and a certain concentration of carbon dioxide and ethane. The feed pressure during the gas separation process is 0.1~10 MPa, preferably 0.2~5 MPa; the feed flow rate is 1~300 mL•min. -1 5-200 mL•min is preferred. -1 .

[0022] This application also proposes a three-stage natural gas helium extraction apparatus, comprising:

[0023] The composite SSZ-13 molecular sieve membrane separation unit is a first-stage membrane separation component built based on the composite SSZ-13 molecular sieve membrane, used to separate helium from high-pressure pipeline natural gas.

[0024] The natural gas liquefaction unit, with its feed side connected to the permeate side of the composite SSZ-13 molecular sieve membrane separation unit, is used to liquefy helium-rich natural gas.

[0025] The SSZ-13 molecular sieve membrane separation unit is a 1-3 stage membrane separation component built based on the SSZ-13 molecular sieve membrane. The feed side is connected to the gas outlet of the natural gas liquefaction unit and is used for multi-stage extraction of helium from non-condensable gas to obtain crude helium.

[0026] The method for extracting helium from natural gas using the above-mentioned three-stage natural gas helium extraction device is as follows:

[0027] 1) High-pressure pipeline natural gas is fed into the composite SSZ-13 molecular sieve membrane separation unit for in-situ helium enrichment. Helium-rich natural gas is output from the permeate side, and the residual gas is returned to the natural gas pipeline.

[0028] 2) The helium-rich natural gas is liquefied using the natural gas liquefaction unit. The liquefied gas is directly output, and the obtained non-condensable gas is fed into the SSZ-13 molecular sieve membrane separation unit.

[0029] 3) The SSZ-13 molecular sieve membrane separation unit is used to perform multi-stage helium extraction from non-condensable gas, with crude helium obtained on the permeate side and residual gas returned to the natural gas liquefaction unit.

[0030] The beneficial effects of this invention are as follows:

[0031] 1. This application involves coating SSZ-13 molecular sieve membranes with polymer 6FDA-APAF. 0.5 -BIA 0.5 Modifying SSZ-13 molecular sieve membranes with polymer PDMS, 6FDA-APAF 0.5 -BIA 0.5 The coating of the membrane layer can optimize the gas separation performance of the base membrane, improve the membrane selectivity and permeability by forming a dense selective layer, and further improve the gas separation performance of the membrane while protecting the polyimide from water vapor erosion and maintaining good He / CH4 separation performance under high pressure. Compared with unmodified molecular sieve membranes and those modified by only a single polymer, the composite SSZ-13 molecular sieve membrane modified by two polymers prepared in this application has significantly improved helium / methane separation performance.

[0032] 2. The composite SSZ-13 molecular sieve membrane prepared in this application exhibits excellent molecular sieving effect and demonstrates good helium / methane separation performance under different feed pressures. Even under simulated gas (helium concentration of 0.097%) helium extraction tests at 5 MPa high pressure, the separation performance remains excellent, with a high He recovery rate. R He It can even reach 11.5%;

[0033] 3. The composite SSZ-13 molecular sieve membrane disclosed in this application was tested for helium extraction using simulated gas (helium concentration of 0.097%). The results showed that it can effectively increase the helium concentration factor. Moreover, as the feed pressure increases, the selectivity of helium / methane gas separation of this membrane decreases only slightly, and the He recovery rate gradually increases. Therefore, this molecular sieve membrane can be efficiently used to extract helium from low-concentration helium-containing natural gas in pipelines. It has the advantages of convenient operation, energy saving and environmental protection, and significant economic benefits.

[0034] 4. This application utilizes 6FDA-APAF 0.5 -BIA 0.5 After the SSZ-13 molecular sieve membrane was modified with polymers PDMS, the separation performance of the membrane was improved and good operational stability was maintained. After long-term use, the membrane structure did not show obvious damage, and the membrane's He gas permeability, He / CH4 gas separation selectivity and He recovery rate remained at a high level.

[0035] 5. This application utilizes two polymers to co-modify the SSZ-13 molecular sieve membrane to improve the membrane's gas permeability and separation performance. This not only provides a new method for the successful separation and recovery of helium, but also offers new ideas for optimizing the performance of other separation membranes.

[0036] 6. This application discloses a three-stage natural gas helium extraction process. First, a highly selective composite SSZ-13 molecular sieve membrane is used to separate high-pressure pipeline natural gas to obtain highly concentrated helium-rich natural gas. The non-condensable gas obtained after liquefying the helium-rich natural gas is then separated using a high-flux SSZ-13 molecular sieve membrane. The SSZ-13 molecular sieve membrane separation unit is a multi-stage membrane module, which can increase the membrane processing capacity, reduce the footprint, and save investment costs. Helium extraction through the SSZ-13 molecular sieve membrane module greatly reduces energy consumption compared to traditional cryogenic separation and pressure swing adsorption, providing a strong reference for obtaining high-purity helium. Attached Figure Description

[0037] Figure 1The images are characterizations of the SSZ-13 molecular sieve membrane; (a) is a small image of the surface of the SSZ-13 molecular sieve membrane, (b) is a small image of the cross-section of the SSZ-13 molecular sieve membrane, and (c) is a small image of the XRD pattern of the SSZ-13 molecular sieve membrane (a is the SSZ-13 molecular sieve, and b is the standard peak of the SSZ-13 molecular sieve).

[0038] Figure 2 The images show the XRD patterns of SSZ-13 molecular sieves modified with different concentrations of PDMS. In the image (a), the small image is the XRD pattern of SSZ-13 molecular sieves, and the small images (b)-(g) are the XRD patterns of SSZ-13 molecular sieves modified with 0 wt.%, 0.5 wt.%, 1 wt.%, 2 wt.%, 5 wt.%, and 16 wt.% PDMS solutions, respectively.

[0039] Figure 3 These are SEM images of SSZ-13 molecular sieve membranes modified with different concentrations of PDMS. In the images, (a)-(b) are surface SEM images of the SSZ-13 molecular sieve membrane modified with 0.5 wt.% PDMS solution at different magnifications; (c) is a cross-sectional SEM image of the SSZ-13 molecular sieve membrane modified with 0.5 wt.% PDMS solution; (d)-(e) are surface SEM images of the SSZ-13 molecular sieve membrane modified with 1 wt.% PDMS solution at different magnifications; (f) is a cross-sectional SEM image of the SSZ-13 molecular sieve membrane modified with 1 wt.% PDMS solution; (g)-(h) are surface SEM images of the SSZ-13 molecular sieve membrane modified with 2 wt.% PDMS solution at different magnifications; and (i) is a cross-sectional SEM image of the SSZ-13 molecular sieve membrane modified with 2 wt.% PDMS solution. Cross-sectional SEM images of SSZ-13 molecular sieve membrane modified with 5 wt.% PDMS solution; (j)-(k) are surface SEM images of SSZ-13 molecular sieve membrane modified with 5 wt.% PDMS solution at different magnifications; (l) is a cross-sectional SEM image of SSZ-13 molecular sieve membrane modified with 5 wt.% PDMS solution; (m)-(n) are surface SEM images of SSZ-13 molecular sieve membrane modified with 16 wt.% PDMS solution at different magnifications; (o) is a cross-sectional SEM image of SSZ-13 molecular sieve membrane modified with 16 wt.% PDMS solution.

[0040] Figure 4 To utilize 6FDA-APAF 0.5 -BIA 0.5 TG curves of SSZ-13 molecular sieve before and after modification. The modified SSZ-13 molecular sieve is denoted as SSZ-13-10 wt.%BIA.

[0041] Figure 5 This diagram illustrates the preparation process of the composite SSZ-13 molecular sieve membrane and the morphological changes of the membrane after gas separation. In the diagram, 1 represents the SSZ-13 molecular sieve membrane, and 2 represents the membrane coated with 6FDA-APAF. 0.5 -BIA 0.5 3- SSZ-13 molecular sieve membrane after PDMS coating, 4- pipeline natural gas (5MPa), 5- four-channel a -Al2O3 hollow fiber carrier, 6-6FDA-APAF exhibits significant deformation after gas separation. 0.5 -BIA 0.5 Polymer membrane, 7-coated with 6FDA-APAF after slight deformation following gas separation. 0.5 -BIA 0.5 Furthermore, the molecular sieve membrane with a carrier, 8-the composite SSZ-13 molecular sieve membrane that did not deform after gas separation;

[0042] Figure 6 The results of single-component gas permeation tests on the composite SSZ-13 molecular sieve membrane M12 are shown in (a) inset, which shows the permeability of gases with different molecular dynamic diameters, and (b) inset, which shows the ideal selectivity of M12 for different mixed gases at 0.2 MPaG.

[0043] Figure 7 The effect of feed pressure on the He / CH4 separation performance of SSZ-13 molecular sieve membrane and composite SSZ-13 molecular sieve membrane M12 is shown in the following figures: (a) Inset shows the He / CH4 gas separation selectivity and gas permeability of the molecular sieve membrane before and after modification under different pressures (orange curves represent He / CH4 gas separation selectivity, and purple curves represent He gas permeability); (b) Inset shows the recovery rate of the molecular sieve membrane before and after modification under different pressures.

[0044] Figure 8 The effect of feed pressure on the natural gas helium extraction performance of composite SSZ-13 molecular sieve membrane M12 is shown in the following figures: (a) Inset shows the He permeability and He / CH4 gas separation selectivity of M12 under different pressures; (b) Inset shows the He recovery rate and He concentration factor of M12 under different pressures.

[0045] Figure 9 The effect of feed flow rate on the natural gas helium extraction performance of composite SSZ-13 molecular sieve membrane M12 is shown in the following figures: (a) Inset shows the changes in He permeability and He / CH4 gas separation selectivity of M12 with increasing feed flow rate; (b) Inset shows the changes in He recovery rate and He concentration factor of M12 with increasing feed flow rate.

[0046] Figure 10The results of long-term stability tests on the composite SSZ-13 molecular sieve membrane M12 under conditions of 5 MPa and 298 K are shown. In the figure, (a) the inset shows the changes in He permeability and He / CH4 gas separation selectivity of M12 at different times; (b) the inset shows the changes in He recovery rate and He concentration factor of M12 at different times.

[0047] Figure 11 This is a schematic diagram of a three-stage natural gas helium extraction unit, where 1-high-pressure pipeline natural gas, 2-composite SSZ-13 molecular sieve membrane separation unit, 3-natural gas liquefaction unit, 4-pressurization device, 5-SSZ-13 molecular sieve membrane separation unit, 6-crude helium, and 7-liquefied gas;

[0048] Figure 12 Helium extraction performance data for BOG of primary SSZ-13 molecular sieve membrane (helium content of raw material is 2%).

[0049] Figure 13 Helium extraction performance data for BOG of secondary SSZ-13 molecular sieve membrane (raw material helium content 15%). Detailed Implementation

[0050] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0051] This application selects to utilize 6FDA-APAF 0.5 -BIA 0.5 SSZ-13 molecular sieve membranes were modified with PDMS. The effect of modifying SSZ-13 with a single polymer on the molecular sieve membrane was first investigated. The specific investigation process is as follows:

[0052] 1. Preparation of PDMS-modified SSZ-13 molecular sieve membranes

[0053] 1) Prepare dense SSZ-13 molecular sieve membranes according to existing technologies.

[0054] First, NaOH, Al(OH)3, and deionized water were sequentially added to a polytetrafluoroethylene bottle and stirred for 2 hours. Finally, colloidal silica was gradually added dropwise to the solution. The final synthesis solution had a molar ratio of SiO2, Al2O3, NaOH, TMAdaOH, and H2O of 100:2.5:20.5:16.9:4436.5. The mixture was then stirred at room temperature for another 12 hours. The synthesis solution was then placed in a reactor for hydrothermal synthesis. After the reaction, the SSZ-13 molecular sieve was washed repeatedly by high-speed centrifugation to neutralize it, and then dried overnight in a 60℃ oven. Finally, the SSZ-13 molecular sieve was calcined at 550℃ for 24 hours to remove the template agent, with a heating / cooling rate of 1℃·min.-1 The 7 cm commercial four-channel a The Al2O3 hollow fiber support was soaked in 0.1 M NaOH solution for 24 h, then washed with deionized water and dried in a 60℃ oven. A 0.5 wt.% seed solution was then prepared using the SSZ-13 molecular sieve described above. Seed crystals were coated onto the surface of the hollow fiber support using the dip-coating method. After two dip-coating cycles, the support was placed in a 60℃ oven overnight. The synthesis solution preparation process was the same as that for the SSZ-13 molecular sieve synthesis solution, with a molar composition of 20 TMAdaOH: 20.4 NaOH: 0.45 Al2O3: 105 SiO2: 4400 H2O. After synthesis, the molecular sieve membrane was removed, its surface was washed, and dried. Finally, the template agent was removed under an ozone atmosphere. This method successfully synthesized a well-grown SSZ-13 molecular sieve membrane free of other impurities. The membrane was characterized, and the results are as follows: Figure 1 As shown, from Figure 1 The small image in the middle (c) shows that SSZ-13 molecular sieve has been successfully produced.

[0055] 2) Preparation of polydimethylsiloxane (PDMS) solution: Weigh polydimethylsiloxane, curing agent (tetramethyltetravinylcyclotetrasiloxane), and n-heptane according to a mass ratio of 1:0.1:x (x=199, 99, 49, 19, 5.25) to prepare PDMS n-heptane mixed solutions with weight percentages of 0.5 wt.%, 1 wt.%, 2 wt.%, 5 wt.%, and 16 wt.%. Pour the prepared solutions into reagent bottles and stir vigorously at 600 rpm for 12 h to homogenize the solutions. Filter, defoam by ultrasonication, and set aside for use.

[0056] 3) The SSZ-13 molecular sieve membrane and hollow fiber carrier, which were sealed at both ends with raw material tape, were immersed in PDMS-n-heptane mixed solutions of different mass percentages for impregnation. Specifically, they were immersed for 40 s in 16 wt.% PDMS solution and for 15 min in other concentrations of PDMS solution. The immersion and extraction rate was 2 cm / s. After drying at room temperature for 1 h, they were placed in an oven and heated at a rate of 1℃ / min to 100℃ for 1 h. Then, they were cooled to 333 K at a rate of 1℃ / min to successfully coat the SSZ-13 molecular sieve membrane with PDMS.

[0057] To investigate whether PDMS modification of SSZ-13 molecular sieve membranes would damage the CHA crystal structure, XRD analysis was performed on SSZ-13 molecular sieves before and after modification. Figure 2 ), and SEM characterization was performed on SSZ-13 molecular sieves modified with different concentrations of PDMS (), Figure 3 ).

[0058] See XRD analysis results. Figure 2 As shown in the figure, the SSZ-13 molecular sieve retains the CHA crystal form after PDMS modification, and the CHA standard peak area of ​​the SSZ-13 molecular sieve gradually decreases with the increase of PDMS concentration.

[0059] Depend on Figure 3 It can be seen that when SSZ-13 molecular sieve membranes are modified with 0.5 wt.%, 1 wt.%, and 2 wt.% PDMS solutions, obvious cubic crystals of SSZ-13 molecular sieve and some large cracks can be seen on the surface of the SSZ-13 molecular sieve membrane. Figure 2 (a), (b), (d), (e), (g), (h) small figures) PDMS failed to effectively modify these defects; cross-section of SSZ-13 molecular sieve membrane modified with 0.5 wt.% PDMS solution ( Figure 2 (c) Small figure) No thickness of the PDMS coating is visible. At a PDMS solution concentration of 1 wt.%, a distinct PDMS polymer component is visible within the modified SSZ-13 molecular sieve membrane cross-section. Figure 2 (See small figure in f). This is because the SSZ-13 molecular sieve membrane has large defects, allowing PDMS to penetrate into the support through these defects, increasing the gas mass transfer resistance. When the PDMS solution concentration is 5 wt.%, a noticeable PDMS coating is visible on the surface of the SSZ-13 molecular sieve membrane, but it still does not completely cover the cubic crystals of the SSZ-13 molecular sieve. Figure 2 In the small figures (j) and (k), no obvious polymer thickness can be seen in the cross-section of the film layer (j) and (k). Figure 2 (middle (l) small figure). When the SSZ-13 molecular sieve membrane was modified with 16 wt.% PDMS solution, the surface of the molecular sieve membrane was completely covered by PDMS, and the SSZ-13 molecular sieve crystal particles were almost invisible. Figure 2 (m) and (n) small figures), a PDMS layer of a certain thickness can also be seen in the cross-section of the SSZ-13 molecular sieve membrane. Figure 2 The small (o) image is about 6 μm.

[0060] The results above show that PDMS modification of SSZ-13 molecular sieve membrane does not damage the CHA crystal form of the molecular sieve membrane, and low concentration of PDMS failed to modify SSZ-13 molecular sieve membrane.

[0061] 2. Preparation of 6FDA-APAF 0.5 -BIA 0.5 SSZ-13 molecular sieve membrane with individual modification

[0062] 1) Preparation of dense SSZ-13 molecular sieve membrane: The method is the same as above.

[0063] 2) Prepare 10% 6FDA-APAF solution by mass. 0.5 -BIA 0.5 The solution can be found in existing technical literature (LI Y, WANG L, WANG XR, et al., Asymmetric copolyimide membranes fabricated by nonsolvent-induced phase separation for He / CH4 and He / N2 separation, Frontiers of Chemical Science and Engineering, 2024, 18, 44.): A certain amount of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (APAF, >98%) and 5-amino-2-(4-aminophenyl)benzimidazole (BIA, 99%) were dissolved in 20 mL of N-methylpyrrolidone (NMP) in a four-necked round-bottom flask, and then 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA, 98%) monomer was added. The molar ratio was controlled at 6FDA:APAF:BIA = 1:0.5:0.5. The mixture was mechanically stirred under a flowing nitrogen atmosphere. The polymerization temperature was maintained at 278 K in an ice bath for 12 hours. The temperature was then increased to 453 K, and the reaction was carried out for 8 hours using a Dean-Stark reflux apparatus, with 10 mL of o-xylene used as an azeotropic agent to remove moisture. The resulting polymer was collected, washed with a 25% aqueous methanol solution, and dried in a vacuum oven at 180 °C. The resulting 6FDA-APAF... 0.5 -BIA 0.5 Dissolving in N-methylpyrrolidone solvent (mass ratio 1:9) yields 10% 6FDA-APAF. 0.5 -BIA 0.5 The solution was poured into a reagent bottle and stirred vigorously at 600 rpm for 12 hours to homogenize it. The solution was then filtered, ultrasonically defoamed, and set aside for later use.

[0064] 3) Immerse the SSZ-13 molecular sieve membrane and hollow fiber carrier, which are sealed at both ends with PTFE tape, in 6FDA-APAF. 0.5 -BIA 0.5 The solution was immersed for 15 seconds, and the immersion and extraction rates were 50 mm / min. After removal, it was heated and dried at a rate of 1℃ / min. After drying, it was cooled to 303 K at a rate of 1℃ / min.

[0065] To determine whether the polymer entered the molecular sieve channels, thermogravimetric analysis was performed on the SSZ-13 molecular sieve before and after polymer modification. The results are as follows: Figure 4 As shown. From Figure 4As you can see, when the thermogravimetric analysis (TGA) temperature is between 30 and 200°C, the weight loss of SSZ-13 molecular sieve is mainly caused by water desorbed from the molecular sieve and residual solvent that was not completely removed. At 200-500°C, this weight loss is caused by CO2 removal from the NMP and polymer within the SSZ-13 molecular sieve cages during thermally induced rearrangement. After 500°C, the weight loss is caused by the gradual decomposition of the polymer backbone. Using polymer 6FDA-APAF... 0.5 -BIA 0.5 When modifying SSZ-13 molecular sieve membranes, the polymer and solvent N-methylpyrrolidone can clog the molecular sieve channels, reducing the effective pore size of the molecular sieve.

[0066] Building upon the aforementioned research, further investigation was conducted on 10 wt.% 6FDA-APAF. 0.5 -BIA 0.5 The effects of solution modification on SSZ-13 molecular sieve membranes and supports, and the effects on 10 wt.% 6FDA-APAF 0.5 -BIA 0.5 The He / CH4 separation performance of the modified SSZ-13 molecular sieve membrane was tested (n He :n CH4 =1:1), the results are shown in Table 1.

[0067] Table 1, 6FDA-APAF 0.5 -BIA 0.5 Effect of Modification on the Performance of SSZ-13 Molecular Sieve Membranes

[0068]

[0069] a: Coat a polymer membrane, specifically polymer 6FDA-APAF, onto the SSZ-13 molecular sieve membrane or support. 0.5 -BIA 0.5 The concentration was 10 wt.%, and four repeatable membranes (M1-M4) were prepared, with a b: ×10⁻⁶. -8 mol·m -2 ·s -1 ·Pa -1 c:×10 -9 mol·m -2 ·s -1 ·Pa -1 Test conditions: 0.2 MPaG, n He :n CH4 =1:1, feed flow rate: 200 mL·min -1 50 mL·min -1 Argon gas was purged, and the test temperature was 298 K.

[0070] Furthermore, the effects of different mass fractions of PDMS solution on the modification of SSZ-13 molecular sieve membranes and supports were investigated, and the He / CH4 separation performance (n) of the SSZ-13 molecular sieve membranes before and after modification was tested. He :n CH4 =1:1), the results are shown in Table 2.

[0071] Table 2. Effects of different PDMS concentrations on the performance of SSZ-13 molecular sieve membranes

[0072]

[0073] a: Coat a layer of polymer PDMS membrane onto the SSZ-13 molecular sieve membrane or support. The PDMS solution concentration is in wt.%. The immersion time is 40 s when the PDMS solution concentration is 16 wt.%, and 15 min for other concentrations. b: ×10 -8 mol·m -2 ·s -1 ·Pa -1 c:×10 -9 mol·m -2 ·s -1 ·Pa -1 Test conditions: 0.2 MPaG, n He :n CH4 =1:1, feed flow rate: 200 mL·min -1 50 mL·min -1 Argon gas was purged, and the test temperature was 298 K.

[0074] As shown in Tables 1 and 2, polymer 6FDA-APAF alone... 0.5 -BIA 0.5 Modifying the SSZ-13 molecular sieve membrane with PDMS only slightly improved its He / CH4 separation performance. Table 2 shows that the modification effect was optimal when the PDMS concentration was 5 wt.%.

[0075] To improve the helium enrichment efficiency of the SSZ-13 molecular sieve membrane under high pressure, based on the above research, in subsequent embodiments, 10 wt.% of polymer 6FDA-APAF was coated onto the SSZ-13 molecular sieve membrane. 0.5 -BIA 0.5 After the solution was dissolved, a layer of PDMS (concentration of 5 wt.%) was coated on it to prepare a composite SSZ-13 molecular sieve membrane. The preparation process is described in [link to preparation process]. Figure 5 ,from Figure 5 It can also be seen that the composite SSZ-13 molecular sieve membrane has excellent mechanical stability compared to polymer membranes, which can prevent it from breaking under high pressure. Example

[0076] 1) Preparation of dense SSZ-13 molecular sieve membrane: The method is the same as above.

[0077] 2) Prepare 10 wt.% 6FDA-APAF 0.5 -BIA 0.5 Solution: Same method as above.

[0078] 3) Preparation of polydimethylsiloxane (PDMS) solution:

[0079] Weigh out polydimethylsiloxane, tetramethyltetravinylcyclotetrasiloxane, and n-heptane in a mass ratio of 1:0.1:19 to prepare a 5 wt.% PDMS solution in n-heptane. Pour the prepared solution into a reagent bottle and stir vigorously at 600 rpm for 12 h to homogenize the solution. Filter, defoam by sonication, and set aside for later use.

[0080] 4) Coat 6FDA-APAF onto SSZ-13 molecular sieve membrane using the dip-coating method. 0.5 -BIA 0.5 PDMS and PDMS were used to prepare composite SSZ-13 molecular sieve membranes:

[0081] S1. First, immerse the SSZ-13 molecular sieve membrane and hollow fiber carrier, which are sealed at both ends with PTFE tape, into the 6FDA-APAF prepared in step 2). 0.5 -BIA 0.5 The solution was immersed for 15 seconds, with an immersion and withdrawal rate of 50 mm / min. After removal, it was dried in a 60℃ oven for 1 h, then placed in a vacuum oven and heated to 200℃ at a rate of 1℃ / min to completely remove the solvent. Finally, it was cooled to 303 K at a rate of 1℃ / min to successfully coat the SSZ-13 molecular sieve membrane with 6FDA-APAF. 0.5 -BIA 0.5 ;

[0082] S2. Continue coating with 6FDA-APAF 0.5 -BIA 0.5 The SSZ-13 molecular sieve membrane and hollow fiber support were immersed in 5 wt.% PDMS solution for 1-30 min with an immersion and extraction rate of 2 cm / s. After drying at room temperature for 1 h, they were placed in an oven with a heating rate of 1℃ / min. After drying at 100℃ for 1 h, the temperature was reduced to 333 K at a rate of 1℃ / min to successfully coat the SSZ-13 molecular sieve membrane with PDMS, thus completing the preparation of the composite membrane modified by the two polymers.

[0083] The effects of different PDMS solution immersion times on the He / CH4 separation performance of the SSZ-13 molecular sieve membrane were tested, and the results are shown in Table 3.

[0084] Table 3. Effect of different PDMS impregnation times on the performance of SSZ-13 molecular sieve membranes

[0085]

[0086] a:min, first coat a layer of 6FDA-APAF onto the SSZ-13 molecular sieve membrane or carrier. 0.5 -BIA 0.5 A membrane was then formed, and a polymer PDMS membrane was coated on it. The PDMS solution concentration was 5 wt.%, b:×10 -8 mol·m -2 ·s -1 ·Pa -1 c:×10 - 9 mol·m -2 ·s -1 ·Pa -1 Test conditions: 0.2 MPaG, n He :n CH4 =1:1, feed flow rate: 200 mL·min -1 50 mL·min -1 Argon gas was purged, and the test temperature was 298 K.

[0087] As shown in Table 3, the He / CH4 selectivity of the composite SSZ-13 molecular sieve membrane was significantly improved at PDMS impregnation times of 5 min, 10 min, 15 min, 20 min, and 25 min. Particularly at a PDMS impregnation time of 15 min, the He / CH4 selectivity of M12 increased from 14.1 to 80.9, demonstrating a significant modification effect. Subsequently, corresponding performance tests were conducted using membrane M12 as the test object.

[0088] 1. The single-component gas permeability of the composite SSZ-13 molecular sieve membrane M12 was tested with a feed rate of 50 mL / min and argon purging at a rate of 20 mL / min (helium purging was used for SF6). The results are as follows: Figure 6 As shown in the figure, the permeability of all gases decreases monotonically with increasing molecular dynamic diameter. Figure 6 (middle (a) small figure) indicates that the membrane has a good molecular sieving effect. At 0.2 MPaG, the ideal selectivities of M12 for He / H2, He / N2, He / CH4, He / C2H6 and He / SF6 are 1.1, 33, 101, 110 and 6430, respectively, all of which are much higher than the Knudsen diffusion selectivity ( Figure 6(middle (b) small image).

[0089] 2. The effect of feed pressure on the separation performance of unmodified SSZ-13 molecular sieve membrane and composite SSZ-13 molecular sieve membrane M12 was investigated. The feed flow rate was 200 mL / min, and argon gas was purged at a rate of 50 mL / min. Results are shown below. Figure 7 As shown in the figure, compared with the unmodified SSZ-13 molecular sieve membrane, M12 exhibits a higher selectivity for He / CH4 gas separation at 0.2 MPa. a He / CH4 The selectivity of He / CH4 gas separation increased from 15 to 89, a 493% improvement, especially under a feed pressure of 5 MPa. a He / CH4 From 4 to 57, an increase of 1325% ( Figure 7 (middle (a) small figure); He recovery rate of M12 at 5 MPa R He Reaching 11.5% ( Figure 7 (small image in medium (b)).

[0090] 3. Testing of natural gas helium extraction performance of composite SSZ-13 molecular sieve membrane M12

[0091] Helium extraction tests were conducted on M12 using a simulated gas (helium concentration of 0.097%, containing a certain concentration of CO2 and C2H6) (200 mL / min feed gas, 20 mL / min argon purging). The results are shown below. Figure 8 .

[0092] from Figure 8 As the feed pressure increases, the He permeability of M12 decreases. P He The selectivity of He / CH4 gas separation decreased by 46%. a He / CH4 It dropped from 89 to 60, a decrease of only 33%. Figure 8 (middle (a) small figure), He recovery rate of M12 R He It gradually increased, rising from 1% to 8.6%. Figure 8 (small image in medium (b)).

[0093] 4. Performance testing of natural gas helium extraction from composite SSZ-13 molecular sieve membrane

[0094] At 5 MPa, the effect of feed flow rate (simulated helium concentration of 0.097%, containing a certain concentration of CO2 and C2H6) on the He / CH4 separation performance of the modified SSZ-13 molecular sieve membrane M12 was further investigated. The results are as follows: Figure 9 As shown, with the increase of feed flow rate, the permeability of He gas...P He It shows an upward trend, from 3.27 × 10 -9 mol·m -2 ·s -1 ·Pa -1 Increased to 3.75 × 10 -9 mol·m -2 ·s -1 ·Pa -1 Selectivity of He / CH4 gas separation a He / CH4 Increased from 54 to 67 ( Figure 9 (small figure in medium (a)). When the feed flow rate is from 10 mL·min -1 200 mL·min -1 At that time, the He concentration factor on the osmotic side β He It shows an upward trend, rising from 22 to 47. Figure 9 (middle (b) smaller figure). At a feed flow rate of 10 mL / min -1 At that time, the recovery rate of He on the permeate side R He Increased to 80%.

[0095] 5. Stability Test of Natural Gas Helium Extraction Performance of Composite SSZ-13 Molecular Sieve Membrane

[0096] The stability of the modified SSZ-13 molecular sieve membrane M12 in separating He and its helium enrichment effect under high pressure (5 MPa) were tested in simulated natural gas containing CO2 and C2H6. After a test of up to 96 h, the membrane M12 remained stable, its structure was not damaged, and the He gas permeability was [not specified]. P He It has remained at 3.7 × 10 -9 mol·m -2 ·s -1 ·Pa -1 Selectivity of He / CH4 gas separation a He / CH4 60 ( Figure 10 (small figure in medium (a)). He recovery rate was tested over a long period in a simulated natural gas containing CO2 and C2H6 impurities. R He The concentration factor remained at 8.1%, the He concentration factor. β He Up to 43 ( Figure 10 (small image in medium (b)).

[0097] Application examples

[0098] This application example proposes a three-stage natural gas helium extraction device based on the aforementioned composite SSZ-13 molecular sieve membrane. It combines the zeolite molecular sieve membrane separation and selection process with the natural gas liquefaction process, and successively separates high-pressure pipeline natural gas and non-condensable gas from the natural gas liquefaction unit to obtain high-purity helium.

[0099] Specifically, the device structure reference Figure 11 The three-stage natural gas helium extraction device includes a composite SSZ-13 molecular sieve membrane separation unit 2, a natural gas liquefaction unit 3, and an SSZ-13 molecular sieve membrane separation unit 5 connected in sequence.

[0100] The composite SSZ-13 molecular sieve membrane separation unit 2 is a first-stage membrane separation component constructed based on the composite SSZ-13 molecular sieve membrane (preferably M12) prepared in Example 1. High-pressure pipeline natural gas 1 (helium content of 0.02~0.3mol%) is input from its inlet end for separating helium in the high-pressure pipeline natural gas 1. The gas pressure on the feed side is 3~10 MPa, and the permeate side is under slightly positive pressure. A vacuum can also be applied to increase the driving force. Highly concentrated helium-rich natural gas is obtained on the permeate side, and the residual gas is returned to the natural gas pipeline for further helium extraction.

[0101] The feed side of the natural gas liquefaction unit 3 is connected to the permeation side of the composite SSZ-13 molecular sieve membrane separation unit 2, and is used to liquefy helium-rich natural gas. The obtained liquefied gas is directly output, and the non-condensable gas (BOG) is introduced into the SSZ-13 molecular sieve membrane separation unit 5.

[0102] Before the BOG is introduced into the SSZ-13 molecular sieve membrane separation unit 5, the non-condensable gas can be pressurized using the pressurization device 4.

[0103] The SSZ-13 molecular sieve membrane separation unit 5 is a 1-3 stage membrane separation component constructed based on the SSZ-13 molecular sieve membrane prepared above. It is used for multi-stage extraction of helium from pressurized non-condensable gas. The gas pressure on the feed side is 0.5~3.0MPa, and the permeate side is under slightly positive pressure. A vacuum can also be drawn to increase the driving force. Crude helium-6 is obtained on the permeate side. The residual gas of this unit is returned to the natural gas liquefaction unit 3 for liquefaction treatment.

[0104] The specific process of natural gas helium extraction based on the above-mentioned device is as follows: Pipeline natural gas has the characteristics of high pressure and low helium. It is sent to a highly selective composite SSZ-13 molecular sieve membrane unit for initial helium extraction. The permeate gas is returned to the natural gas pipeline, and the helium in the permeate gas is enriched (the helium concentration can be increased from the initial 0.075% to 4.4%). The helium-rich natural gas is fed into the natural gas liquefaction unit to obtain liquefied natural gas. The generated non-condensable gas (BOG) is compressed by a booster device and then purified again by the SSZ-13 molecular sieve membrane separation unit for 1-3 stages of helium purification to obtain crude helium.

[0105] When using a single-stage SSZ-13 molecular sieve membrane for helium extraction from non-condensable gases, 2% helium-containing natural gas was used as the feed gas at a feed flow rate of 0.75 L / min. The helium extraction performance of the single-stage membrane module under different feed pressures was tested, and the results are as follows: Figure 12 As shown, at 0.2 MPa, the He / CH4 selectivity is 14, the concentration factor is 10, and the helium recovery rate is 26.7%. Single-stage membrane separation can increase the helium concentration from 2% to 20%. With increasing feed pressure, the He / CH4 selectivity and concentration factor show a significant decreasing trend; however, the helium recovery rate significantly increases. At 5.1 MPa, the helium recovery rate significantly improves to 83%, but the He / CH4 selectivity decreases from 14 to 4, and the helium concentration factor decreases from 10 to 2.

[0106] When using a two-stage SSZ-13 molecular sieve membrane for helium extraction from non-condensable gases, with a helium content of 15% in the feed natural gas and a feed flow rate of 0.3 L / min, the helium extraction performance of the two-stage membrane module was tested under different feed pressures. The results are as follows: Figure 13 As shown, at 3.0 MPa, the helium enrichment factor decreased to 1.4, the He / CH4 selectivity decreased to 3, and the helium recovery rate was 95%.

[0107] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. However, the above description is merely a specific embodiment of the present invention, and the technical features of the present invention are not limited thereto. Any other embodiments derived by those skilled in the art without departing from the technical solution of the present invention should be covered within the scope of the present invention.

Claims

1. A method for preparing a dual-polymer modified composite SSZ-13 molecular sieve membrane, characterized in that, Includes the following steps: 1) Polymer 6FDA-APAF 0.5 -BIA 0.5 Dissolve in solvent, mix well, filter, defoam, and obtain 6FDA-APAF. 0.5 -BIA 0.5 Solution; 2) Mix PDMS, curing agent and n-heptane, stir well, filter, defoam, and obtain PDMS solution; 3) First, coat the SSZ-13 molecular sieve membrane and the support with the 6FDA-APAF prepared in step 1). 0.5 -BIA 0.5 Solution; 4) Coated with 6FDA-APAF 0.5 -BIA 0.5 PDMS solution was coated onto the molecular sieve membrane and the support to obtain a composite SSZ-13 molecular sieve membrane modified with two polymers. Among them, 6FDA-APAF 0.5 -BIA 0.5 To dissolve a certain amount of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 5-amino-2-(4-aminophenyl)benzimidazole in a four-necked round-bottom flask using 20 mL of N-methylpyrrolidone, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride monomer was added, with the molar ratio controlled at 6FDA:APAF:BIA = 1:0.5:0.

5.

2. The method for preparing a dual-polymer modified composite SSZ-13 molecular sieve membrane as described in claim 1, characterized in that, In step 1), the solvent is N-methylpyrrolidone, and the mixture is stirred at 600-800 rpm for 6-12 hours; the prepared 6FDA-APAF... 0.5 -BIA 0.5 6FDA-APAF in solution 0.5 -BIA 0.5 The mass percentage is 1-30 wt.%; In step 2), the mass percentage of PDMS in the prepared PDMS solution is 0.5-25 wt.%, and the solution is mixed by stirring at a speed of 600 rpm-800 rpm for 6-12 h.

3. The method for preparing a dual-polymer modified composite SSZ-13 molecular sieve membrane as described in claim 1, characterized in that, The coating process in steps 3) and 4) is completed by means of dip coating, spraying, brushing, spin coating or vacuum coating.

4. The method for preparing a dual-polymer modified composite SSZ-13 molecular sieve membrane as described in claim 3, characterized in that, 6FDA-APAF was coated onto the SSZ-13 molecular sieve membrane using the dip-coating method. 0.5 -BIA 0.5 With PDMS, the specific process is as follows: S1. First, immerse the SSZ-13 molecular sieve membrane and carrier, which are sealed at both ends, into the prepared 6FDA-APAF solution. 0.5 -BIA 0.5 The solution was immersed for 15–20 seconds, with an immersion and withdrawal rate of 40–60 mm / min. After removal, it was dried in an oven at 60–70 °C for 1–2 h, then heated to 180–200 °C in a vacuum oven at a rate of 1–5 °C / min to completely remove the solvent, and then cooled to 303 K at a rate of 1–5 °C / min to coat the SSZ-13 molecular sieve membrane with 6FDA-APAF. 0.5 -BIA 0.5 ; S2, coated with 6FDA-APAF 0.5 -BIA 0.5 The SSZ-13 molecular sieve membrane and the support were immersed in PDMS solution for 1-30 min, with an immersion and extraction rate of 1-3 cm / s. After drying at room temperature for 1-3 h, they were placed in an oven and heated at a rate of 1-5 °C / min to 90-110 °C for 1-3 h. Then, the temperature was lowered to 333 K at a rate of 1-3 °C / min to coat the SSZ-13 molecular sieve membrane with PDMS.

5. The method for preparing a dual-polymer modified composite SSZ-13 molecular sieve membrane as described in claim 4, characterized in that, The 6FDA-APAF 0.5 -BIA 0.5 6FDA-APAF in solution 0.5 -BIA 0.5 The mass percentage of the PDMS solution was 10 wt.%, and the mass percentage of PDMS in the PDMS solution was 5 wt.%; the immersion time in the PDMS solution was 5~25 min.

6. A composite SSZ-13 molecular sieve membrane modified with two polymers, characterized in that, It is prepared based on the preparation method of any one of claims 1-5, wherein 6FDA-APAF is successively modified onto the SSZ-13 molecular sieve membrane. 0.5 -BIA 0.5 Membrane layer and PDMS membrane layer.

7. The application of the dual polymer-modified composite SSZ-13 molecular sieve membrane as described in claim 6 in gas separation, characterized in that, The composite SSZ-13 molecular sieve membrane is used to separate He / CH4 mixed gas.

8. The application as described in claim 7, characterized in that, The He / CH4 mixture is a simulated natural gas composition, containing 0.097% helium and a certain concentration of carbon dioxide and ethane. The feed pressure during the gas separation process is 0.1–10 MPa, and the feed flow rate is 1–300 mL / min. -1 .

9. A three-stage natural gas helium extraction device, characterized in that, It is constructed based on the dual polymer-modified composite SSZ-13 molecular sieve membrane as described in claim 6, comprising: The composite SSZ-13 molecular sieve membrane separation unit is a first-stage membrane separation component built based on the composite SSZ-13 molecular sieve membrane, used to separate helium from high-pressure pipeline natural gas. The natural gas liquefaction unit is connected on the feed side to the permeate side of the composite SSZ-13 molecular sieve membrane separation unit, and is used to liquefy helium-rich natural gas. The SSZ-13 molecular sieve membrane separation unit is a 1-3 stage membrane separation component built based on the SSZ-13 molecular sieve membrane. The feed side is connected to the gas outlet of the natural gas liquefaction unit and is used for multi-stage extraction of helium from non-condensable gas to obtain crude helium.

10. The method for extracting helium from natural gas using the three-stage natural gas helium extraction apparatus according to claim 9, characterized in that, Includes the following steps: 1) High-pressure pipeline natural gas is fed into the composite SSZ-13 molecular sieve membrane separation unit for in-situ helium enrichment. Helium-rich natural gas is output from the permeate side, and the residual gas is returned to the natural gas pipeline. 2) The helium-rich natural gas is liquefied using the natural gas liquefaction unit. The liquefied gas is directly output, and the obtained non-condensable gas is fed into the SSZ-13 molecular sieve membrane separation unit. 3) The SSZ-13 molecular sieve membrane separation unit is used to perform multi-stage helium extraction from non-condensable gas, with crude helium obtained on the permeate side and residual gas returned to the natural gas liquefaction unit.

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