A W-SSZ-13 molecular sieve membrane, its preparation method, and its application in gas separation.

Abstract

This invention discloses a W-SSZ-13 molecular sieve membrane, its preparation method, and its application in gas separation. The preparation method of the W-SSZ-13 molecular sieve membrane includes the following steps: placing a carrier loaded with an SSZ-13 seed layer in a membrane synthesis gel and heating for primary crystallization; then adding a tungsten-containing compound and heating for secondary crystallization; followed by washing, drying, and calcination to obtain the W-SSZ-13 molecular sieve membrane. This invention, by incorporating tungsten (W) into the framework of the SSZ-13 molecular sieve membrane, reduces the pore size of the membrane, thereby improving the separation selectivity of the membrane for CO2 / N2 and CO2 / CH4. Simultaneously, the incorporation of W eliminates the silanol groups on the membrane surface, thereby increasing the membrane's hydrophobicity. This allows the W-SSZ-13 molecular sieve membrane to maintain high separation selectivity and stability for the aforementioned mixed gases even in the presence of water vapor.

Description

Technical Field

[0001] This invention relates to a W-SSZ-13 molecular sieve membrane, its preparation method, and its application in gas separation, belonging to the technical field of molecular sieve membrane material preparation and gas separation application. Background Technology

[0002] There are many methods for capturing CO2, mainly including physicochemical solvent absorption, solid adsorption, cryogenic distillation, and membrane separation. Among these, membrane separation has advantages such as energy saving, simple operation, environmental friendliness, and ease of control and scale-up, making it widely used in the field of gas separation.

[0003] Zeolite molecular sieve membranes possess a regular pore structure and better thermal, chemical, and structural stability, making them promising for CO2 separation through molecular sieving, selective adsorption, and differences in surface diffusion rates. Eight-membered ring molecular sieves (8MR), such as CHA, DDR, and AEI, are ideal for separating CO2 (0.33 nm) and other larger gas molecules (e.g., N2 (0.364 nm) and CH4 (0.38 nm)) and have attracted considerable attention from researchers. Due to the preferential adsorption of CO2 by CHA molecular sieve membranes, they are suitable for separating CO2 and other light gases. However, because water has a stronger affinity for hydrophilic frameworks, both the permeability and selectivity for CO2 are reduced.

[0004] Heteroatom doping is considered an effective method to modify the pore structure and surface properties of zeolites. The heteroatom doping process involves introducing transition metal cations to replace silicon (Si) in the zeolite framework, altering the TOT angle and TOT length (T = Si). This results in a reduction in the zeolite membrane pore size, changing the adsorption of gas molecules on the membrane surface, or influencing the pore size of the molecular sieve to produce different gas permeation behaviors, thereby affecting the intramembrane diffusion of gas molecules. By doping with metals, the microstructure and surface properties of SSZ-13 molecular sieve membranes can be controlled and modified to achieve more efficient separation.

[0005] Niu et al. (Journal of Solid State Chemistry, 2020, 287, 121330) synthesized Fe-SSZ-13 molecular sieves via in-situ doping and applied them to the selective catalytic reduction of NO by NH3. x(NH3-SCR) was found to have good catalytic performance. Patent CN114560475 A relates to a method for preparing a metal-modified M-SSZ-13 molecular sieve membrane, which encapsulates a transition metal within the pores of the molecular sieve via hydrothermal synthesis. Grand et al. (Nature Materials, 2017, 16, 1010-1015) synthesized nanoscale W-MFI zeolite crystals and found that introducing W into the MFI zeolite crystals can remove Si-OH groups on the surface by forming double bonds with oxygen. Peng et al. (Journal of Membrane Science, 2022, 659) successfully prepared a silanol-free W-MFI zeolite membrane with higher hydrophobicity and stability for the pervaporation separation of ethanol / water. To date, there have been no reports of adding W atoms to the framework structure of SSZ-13 molecular sieve membranes. Summary of the Invention

[0006] The purpose of this invention is to provide a W-SSZ-13 molecular sieve membrane, its preparation method, and its application in gas separation. By incorporating W into the framework of the SSZ-13 molecular sieve membrane, the pore size of the SSZ-13 molecular sieve membrane can be reduced, thereby improving the membrane's selectivity for separating CO2 / N2 and CO2 / CH4. At the same time, the incorporation of W also eliminates the silanol groups on the membrane surface, thereby increasing the membrane's hydrophobicity. This allows the W-SSZ-13 molecular sieve membrane to maintain high selectivity and stability for the aforementioned mixed gases even in the presence of water vapor.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a W-SSZ-13 molecular sieve membrane includes the following steps:

[0009] The carrier loaded with the SSZ-13 seed layer was placed in the membrane synthesis gel and heated for primary crystallization; then a tungsten-containing compound was added and heated for secondary crystallization; after washing, drying and calcination, the W-SSZ-13 molecular sieve membrane was obtained.

[0010] In the membrane synthesis gel, the molar ratio of SiO2, NaOH, Al2O3, TMAdaOH, and H2O is 1:(0.1-0.3):(0.01-0.05):(0.15-0.5):(30-50);

[0011] The molar ratio of the added tungsten-containing compound to SiO2 in the membrane synthesis gel was (0.01-0.1):1.

[0012] Preferably, the method for preparing the carrier loaded with the SSZ-13 seed layer is as follows:

[0013] A seed gel was prepared, and the gel was heated to crystallize. After centrifugation, washing, drying, and ball milling, SSZ-13 seed crystals were obtained. The molar ratio of SiO2, NaOH, Al2O3, TMAdaOH, and H2O in the seed gel was 1:(0.1-0.3):(0.01-0.05):(0.15-0.5):(30-50).

[0014] Prepare SSZ-13 seed crystals into a seed crystal suspension, and then coat the seed crystal suspension onto the surface of the carrier.

[0015] Preferably, the preparation methods of the membrane synthesis gel and the seed gel both include the following steps:

[0016] Mix the template agent, aluminum source and alkali source, then add water and silicon source respectively, mix and heat in a water bath until the solution is clear and transparent, then stop heating and age.

[0017] Preferably, the template agent is N,N,N-trimethyladamantane ammonium hydroxide; the alkali source is sodium hydroxide, and / or potassium hydroxide, and / or cesium hydroxide; the aluminum source is aluminum hydroxide, and / or sodium aluminate; and the silicon source is silica sol, and / or fumed silica.

[0018] Preferably, the aging time is 10-15 hours.

[0019] Preferably, in the seed suspension, the mass concentration of SSZ-13 seed crystals is 0.5-2wt%, and the coating time is 5-30s.

[0020] Preferably, the conditions for the primary crystallization are: 150-170℃, 72-120h;

[0021] The conditions for secondary crystallization are: 150-170℃, 12-36h.

[0022] Preferably, the tungsten-containing compound is Na2WO4·2H2O.

[0023] Preferably, the calcination conditions are: the environment is air, oxygen, ozone or an oxygen / ozone mixture, the heating rate is 0.2-0.5℃ / min, the calcination temperature is 200-450℃, and the calcination time is 24-96h.

[0024] Applications of W-SSZ-13 molecular sieve membranes prepared by any of the above methods in CO2 / N2 separation and CO2 / CH4 separation.

[0025] The beneficial effects of this invention are as follows:

[0026] By incorporating W into the framework of the SSZ-13 molecular sieve membrane, the pore size of the SSZ-13 molecular sieve membrane can be reduced, thereby improving the separation selectivity of the membrane for CO2 / N2 and CO2 / CH4. At the same time, the incorporation of W also eliminates the silanol groups on the membrane surface, thereby increasing the hydrophobicity of the membrane, so that it still has high separation selectivity and stability for the above-mentioned mixed gases in the presence of water vapor.

[0027] XPS and UV-Vis results indicate that tetrahedral coordinated tungsten atoms are bound to the CHA framework in the oxidized state of W(VI). W(VI) is bonded to the zeolite framework through two WO-Si bonds and simultaneously forms double bonds with the two terminal O atoms. N2 adsorption-desorption isotherms show that the BET surface area and micropore volume (599 m²) of the W-SSZ-13 molecular sieve membrane are... 2 / g and 0.215m 3 / g) lower than the BET surface area and micropore volume (661m) of the SSZ-13 molecular sieve membrane. 2 / g and 0.238m 3 / g), indicating that W was introduced on the membrane surface; and the adsorption capacities of CO2, N2 and CH4 of the SSZ-13 molecular sieve membrane were all higher than those of the W-SSZ-13 molecular sieve membrane, confirming the effect of W doping on reducing the pore size.

[0028] The W-SSZ-13 molecular sieve membrane prepared by this invention was used for CO2 / N2 and CO2 / CH4 separation. Compared with the SSZ-13 molecular sieve membrane, the maximum separation factor (max SF) for equimolar CO2 / N2 increased from 8.3 to 16.9. For equimolar CO2 / CH4, the maximum separation factor increased from 105 to 176. Furthermore, under humid conditions, the W-SSZ-13 molecular sieve membrane exhibited better separation performance and stability. Attached Figure Description

[0029] Figure 1 The XRD patterns are of the molecular sieve membranes prepared in Example 1 and Comparative Examples 1-2 of this invention.

[0030] Figure 2 The images show the surface and cross-sectional SEM images of the W-SSZ-13 molecular sieve membrane prepared in Example 1 of this invention.

[0031] Figure 3 The images show the surface and cross-sectional SEM images of the W-SSZ-13 molecular sieve membrane prepared in Example 2 of this invention.

[0032] Figure 4 The images show the surface and cross-sectional SEM images of the SSZ-13 molecular sieve membrane prepared in Comparative Example 1 of this invention.

[0033] Figure 5The images show the surface and cross-sectional SEM images of the W-SSZ-13-I molecular sieve membrane prepared in Comparative Example 2 of this invention.

[0034] Figure 6 The images show the DR UV-vis images of the bottom molecular sieves prepared in Example 1 and Comparative Example 1 of this invention.

[0035] Figure 7 XPS image of the surface of the W-SSZ-13 molecular sieve membrane prepared in Example 1 of this invention;

[0036] Figure 8 The surface water contact angle diagrams are shown for the molecular sieve membranes prepared in Example 1 and Comparative Example 1 of this invention.

[0037] Figure 9 The following are N2 adsorption-desorption isotherms of the bottom molecular sieves prepared in Example 1 and Comparative Example 1 of this invention;

[0038] Figure 10 The adsorption isotherms of the bottom molecular sieves prepared in Example 1 and Comparative Example 1 of this invention at 298 K for CO2, N2 and CH4.

[0039] Figure 11 The figures show the CO2 / CH4 / H2O stability test results of the molecular sieve membranes prepared in Example 1 and Comparative Example 1 of this invention.

[0040] Figure 12 The graphs show the CO2 / N2 / H2O stability test results of the molecular sieve membranes prepared in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0041] This invention uses ball-milled SSZ-13 molecular sieve as seed crystals. First, SSZ-13 molecular sieve membranes are synthesized under hydrothermal conditions. Then, Na2WO4·2H2O is added to the synthesis solution to introduce W onto the surface of the SSZ-13 molecular sieve membrane, resulting in a W-SSZ-13 molecular sieve membrane. The incorporation of W reduces the pore size of SSZ-13, improves the membrane's selectivity for separating CO2 / N2 and CO2 / CH4, and eliminates the silanol groups on the membrane surface, increasing the membrane's hydrophobicity. This allows the W-SSZ-13 membrane to maintain high selectivity and stability for the aforementioned mixed gases even in the presence of water vapor.

[0042] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0043] Example 1

[0044] The specific preparation method of W-SSZ-13 molecular sieve membrane is as follows:

[0045] (1) Preparation of seed crystals: Sodium hydroxide (NaOH, 96%), aluminum hydroxide (Al(OH)3, 98%), and N,N,N-trimethyl-1-adamantane ammonium hydroxide (TMAdaOH, 25%) were placed in a polytetrafluoroethylene bottle and stirred in a water bath until the aluminum hydroxide was completely dissolved. After the solution cooled to room temperature, water was added to the solution and stirring was continued for 3 hours. Silica sol (40% aqueous solution) was slowly added to the solution while stirring, and the solution was heated in a water bath until it became clear and transparent, and aged for 12 hours. The final molar ratio of the synthesized gel was SiO2:NaOH:Al2O3:TMAdaOH:H2O = 1:0.22:0.01:0.19:41.9. The obtained gel was hydrothermally crystallized at 160℃ for 96 hours. The obtained product was washed with deionized water, centrifuged 2-3 times at high speed, and dried at 60℃ for 24 hours. The dried product was then calcined at 550℃ for 24 hours and then ball-milled. The ball mill speed was 350 r / min and the ball milling time was 3 hours. After centrifugation and drying, the solid obtained from the ball milling was collected to obtain the ball-milled SSZ-13 molecular sieve.

[0046] (2) Preparation of seed layer: Four-channel hollow fiber α-Al2O3 was used as the carrier with an outer diameter of 3.6 mm and a diameter of 0.9 mm for the four internal cylindrical channels. The average pore size of the support was 0.5 μm and the porosity was ~40%. The seed crystals prepared in step (1) were uniformly coated on the carrier by dip-coating method. Specifically, the ball-milled SSZ-13 molecular sieve prepared in step (1) was used to make a seed crystal suspension of 0.5 wt%. The carrier was immersed in the seed crystal suspension for 15 seconds, then dried at room temperature for 3 hours, and then immersed in the seed crystal suspension for 15 seconds in the opposite direction. The carrier was dried at room temperature for 3 hours and then dried at 60°C for 12 hours.

[0047] (3) Preparation of W-SSZ-13 molecular sieve membrane: NaOH, Al(OH)3, TMAdaOH, and H2O were added to a polytetrafluoroethylene bottle and stirred under water bath heating until all Al(OH)3 was dissolved. Water was added and stirred at room temperature for 3 hours to form a homogeneous solution. Finally, silica sol was added and heated in a water bath until the solution became clear and transparent. The water bath heating was then stopped, and the solution was aged for 12 hours. The molar ratio of the synthesized gel was SiO2:NaOH:Al2O3:TMAdaOH:H2O = 1:0.22:0.01:0.19:41.9.

[0048] After fixing the carrier with the seed layer prepared in step (2), it was placed in a reaction vessel and reacted with the membrane to form a gel at 160℃ for 96 h. Na2WO4·2H2O was added to the gel after the reaction was completed and mixed evenly. The molar ratio of each substance in the final molecular sieve membrane gel was SiO2:NaOH:Al2O3:TMAdaOH:H2O:Na2WO4·2H2O=1:0.22:0.01:0.19:41.9:0.02. Crystallization was continued in an oven at 160℃ for 24 h.

[0049] The membrane after reaction was washed with deionized water, dried at 60℃ for 12 h, and then calcined in an ozone atmosphere to remove the template agent for 24 h at 200℃ at a heating rate of 0.5℃ / min. The product obtained from the bottom of the reactor was collected, centrifuged, dried, and calcined. The prepared molecular sieve membrane was labeled W-SSZ-13.

[0050] Example 2

[0051] Steps (1) and (2) are the same as in Example 1.

[0052] Step (3) of the preparation process is basically the same as step (3) in Example 1. The difference is that the molar ratio of each substance in the gel of the final synthesized molecular sieve membrane is SiO2:NaOH:Al2O3:TMAdaOH:H2O:Na2WO4·2H2O=1:0.22:0.01:0.19:41.9:0.04. The prepared molecular sieve membrane is labeled as W-0.04-SSZ-13.

[0053] Comparative Example 1

[0054] The specific preparation method of SSZ-13 molecular sieve membrane is as follows:

[0055] Steps (1) and (2) are the same as in Example 1.

[0056] Step (3): Preparation of SSZ-13 molecular sieve membrane. NaOH, Al(OH)3, TMAdaOH, and H2O were added to a polytetrafluoroethylene bottle and stirred under water bath heating until all Al(OH)3 was dissolved. Water was added and stirred at room temperature for 3 hours to form a homogeneous solution. Finally, silica sol was added and heated in a water bath until the solution became clear and transparent. The water bath heating was stopped, and the solution was aged for 12 hours. The final gel molar ratio was SiO2:NaOH:Al2O3:TMAdaOH:H2O = 1:0.22:0.01:0.19:41.9. The carrier with the seed layer prepared in step (2) was fixed and placed in a reaction vessel. The gel was reacted with the membrane at 160℃ for 96 hours. The membrane after reaction was washed with deionized water, dried at 60℃ for 12 hours, and then calcined under an ozone atmosphere to remove the template agent. The calcination time was 24 hours, the calcination temperature was 200℃, and the heating rate was 0.5℃ / min. The product obtained from the bottom of the reactor was collected, centrifuged, dried, and calcined. The prepared molecular sieve membrane was labeled SSZ-13.

[0057] Comparative Example 2

[0058] Step (3): Preparation of W-SSZ-13-I molecular sieve membrane. NaOH, Al(OH)3, TMAdaOH, and H2O were added to a polytetrafluoroethylene bottle and stirred under water bath heating until all Al(OH)3 was dissolved. Water and Na2WO4·2H2O were added and stirred at room temperature for 3 hours to form a homogeneous solution. Finally, silica sol was added and heated in a water bath until the solution became clear and transparent. The water bath heating was then stopped, and the solution was aged for 12 hours. The final gel molar ratio was SiO2:NaOH:Al2O3:TMAdaOH:H2O:Na2WO4·2H2O = 1:0.22:0.01:0.19:41.9:0.02. The carrier with the seeded crystal layer prepared in step (2) was fixed and placed in a reaction vessel. The gel was reacted with the membrane at 160℃ for 96 hours. The membrane after reaction was washed with deionized water, dried at 60℃ for 12 h, and then calcined in an ozone atmosphere to remove the template agent for 24 h at 200℃ at a heating rate of 0.5℃ / min. The product obtained from the bottom of the reactor was collected, centrifuged, dried, and calcined. The prepared molecular sieve membrane was labeled W-SSZ-13-I.

[0059] The gas separation performance of a membrane is represented by two parameters: the gas permeation rate P and the separation coefficient a. The gas permeation rate P represents the total amount of gas passing through a unit area of ​​the membrane per unit time and unit pressure, P = N / (A × ΔP), with units of mol / (m²). 2 s Pa); the separation coefficient a is used to evaluate the efficiency of membrane separation, a=PA / PB.

[0060] The XRD patterns of the molecular sieve membranes prepared in Example 1 and Comparative Examples 1-2 are shown below. Figure 1 As shown. Surface and cross-sectional SEM images of the W-SSZ-13, W-0.04-SSZ-13, and SSZ-13, W-SSZ-13-I molecular sieve membranes prepared in Examples 1-2 and Comparative Examples 1 and 2 are shown below. Figure 2-5 As shown. By Figure 2-5 It can be seen that the surface interaction growth of SSZ-13, W-SSZ-13, and W-0.04-SSZ-13 is good, and the crystal form is relatively good. The surface of W-SSZ-13-I shows walnut-shaped and cubical stacking together, with poor inter-crystal growth. The film thickness is 5-6 μm.

[0061] XPS ( Figure 7 ) and UV-vis( Figure 6 The results showed that the tetrahedral tungsten atoms were bound to the CHA framework in the oxidation state of W(VI). W(VI) was bonded to the zeolite framework through two WO-Si bonds and simultaneously formed double bonds with the two terminal O atoms. N2 adsorption-desorption isotherms ( Figure 9-10 This indicates that the BET surface area and micropore volume (599 m²) of the W-SSZ-13 molecular sieve membrane are... 2 / g and 0.215m 3 / g) lower than the BET surface area and micropore volume (661 m) of the SSZ-13 molecular sieve membrane. 2 / g and 0.238 m 3 / g), indicating that W was introduced on the membrane surface; and the adsorption capacities of CO2, N2, and CH4 in the SSZ-13 molecular sieve membrane were all higher than those in the W-SSZ-13 molecular sieve membrane, confirming the effect of W doping on reducing pore size. Figure 8 It can be seen that the surface water contact angle of the W-SSZ-13 molecular sieve membrane is larger than that of the SSZ-13 molecular sieve membrane, indicating that the incorporation of W element increases the hydrophobicity of the membrane.

[0062] The CO2 / CH4 and CO2 / N2 gas separation performance of the W-SSZ-13, W-0.04-SSZ-13, and SSZ-13 and W-SSZ-13-I molecular sieve membranes prepared in Examples 1-2, Comparative Examples 1 and 2 were tested. The test conditions were: temperature 25°C, permeate pressure maintained at 1 bar, molar composition 50 / 50%, and total feed gas flow rate 150 ml / min. The gas flow rate on the permeate side was measured using a soap bubble flow meter; the gas composition on the permeate side was analyzed using gas chromatography; the test results are shown in Table 1.

[0063] Table 1. Gas separation performance test results

[0064]

[0065] As shown in Table 1, the W-SSZ-13 molecular sieve membranes prepared in Examples 1-2, when used for CO2 / N2 and CO2 / CH4 separation, showed a significant increase in the maximum separation factor for equimolar CO2 / N2 compared to the SSZ-13 molecular sieve membrane. Furthermore, the maximum separation factor (max SF) for equimolar CO2 / N2 of the W-SSZ-13 molecular sieve membrane prepared in Example 1 increased from 8.8 to 16.9 compared to the SSZ-13 molecular sieve membrane. For equimolar CO2 / CH4, the maximum separation factor increased from 105 to 176.

[0066] Meanwhile, the stability of the molecular sieve membranes prepared in Example 1 and Comparative Example 1 under CO2 / CH4 and CO2 / N2 conditions was tested, and the results are as follows: Figure 11-12 As shown, by Figure 11-12 It can be seen that the W-SSZ-13 molecular sieve membrane exhibits better separation performance and stability under humid conditions.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a W-SSZ-13 molecular sieve membrane, characterized in that, Includes the following steps: The carrier loaded with the SSZ-13 seed layer was placed in the membrane synthesis gel and heated for primary crystallization. Then, a tungsten-containing compound was added to the gel after the primary crystallization reaction was completed, mixed evenly, and heated for secondary crystallization. After washing, drying, and calcination, the W-SSZ-13 molecular sieve membrane was obtained. In the membrane synthesis gel, the molar ratio of SiO2, NaOH, Al2O3, TMAdaOH, and H2O is 1:(0.1-0.3):(0.01-0.05):(0.15-0.5):(30-50); The molar ratio of the added tungsten-containing compound to SiO2 in the membrane synthesis gel was (0.01-0.1):

1.

2. The method for preparing the W-SSZ-13 molecular sieve membrane according to claim 1, characterized in that, The method for preparing the carrier loaded with the SSZ-13 seed layer is as follows: A seed gel was prepared, and the gel was heated to crystallize. After centrifugation, washing, drying, and ball milling, SSZ-13 seed crystals were obtained. The molar ratio of SiO2, NaOH, Al2O3, TMAdaOH, and H2O in the seed gel was 1:(0.1-0.3):(0.01-0.05):(0.15-0.5):(30-50). Prepare SSZ-13 seed crystals into a seed crystal suspension, and then coat the seed crystal suspension onto the surface of the carrier.

3. The method for preparing the W-SSZ-13 molecular sieve membrane according to claim 2, characterized in that, The preparation methods of the membrane synthesis gel and the seed gel both include the following steps: Mix the template agent, aluminum source and alkali source, then add water and silicon source respectively, mix and heat in a water bath until the solution is clear and transparent, then stop heating and age.

4. The method for preparing the W-SSZ-13 molecular sieve membrane according to claim 3, characterized in that, The template agent is N,N,N-trimethyladamantane ammonium hydroxide; the alkali source is sodium hydroxide, and / or potassium hydroxide, and / or cesium hydroxide; the aluminum source is aluminum hydroxide, and / or sodium aluminate; and the silicon source is silica sol, and / or fumed silica.

5. The method for preparing the W-SSZ-13 molecular sieve membrane according to claim 3, characterized in that, The aging time is 10-15 hours.

6. The method for preparing the W-SSZ-13 molecular sieve membrane according to claim 3, characterized in that, In the seed suspension, the mass concentration of SSZ-13 seed crystals is 0.5-2 wt%, and the coating time is 5-30 s.

7. The method for preparing the W-SSZ-13 molecular sieve membrane according to claim 1, characterized in that, The conditions for the primary crystallization are: 150-170℃, 72-120h; The conditions for secondary crystallization are: 150-170℃, 12-36h.

8. The method for preparing the W-SSZ-13 molecular sieve membrane according to claim 1, characterized in that, The tungsten-containing compound is Na2WO4·2H2O.

9. The method for preparing the W-SSZ-13 molecular sieve membrane according to claim 1, characterized in that, The calcination conditions are as follows: the environment is air, oxygen, ozone or a mixture of oxygen and ozone, the heating rate is 0.2-0.5℃ / min, the calcination temperature is 200-450℃, and the calcination time is 24-96h.

10. The application of the W-SSZ-13 molecular sieve membrane prepared by the preparation method according to any one of claims 1-9 in CO2 / N2 separation and CO2 / CH4 separation.

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