Preparation method and application of silicalite-1 zeolite membrane

Abstract

This invention belongs to the field of membrane separation technology, specifically relating to a method for preparing a Silicalite-1 zeolite membrane and its application. The method involves preparing sizable and highly crystallizable sheet-like and disc-shaped Silicalite-1 crystals, which are then sequentially coated onto a rough macroporous support surface to form a seed double layer. A composite template agent, such as bis-[1,5-(tripropylammonium)]pentamethylene diiodide, is introduced to regulate the crystallization and growth of the Silicalite-1 zeolite membrane, resulting in a continuous and dense thin-film Silicalite-1 membrane exhibiting high selectivity for N₂ / SF₆. The Silicalite-1 zeolite membrane of this invention demonstrates excellent sieving performance for N₂ and SF₆, which have significantly different kinetic diameters, making it particularly suitable for SF₆ recovery and inert gas purification in industrial waste gas. This method is simple and operates under mild conditions, making it valuable for energy conservation and environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a method for preparing a Silicalite-1 zeolite membrane and its application. Background Technology

[0002] Sulfur hexafluoride (SF6) is an important functional gas widely used in the power industry. Due to its high dielectric strength, excellent arc-quenching performance, and good heat transfer properties, and its colorless, odorless, non-flammable, and chemically stable characteristics at room temperature and pressure, it has long been widely used as an insulating and arc-quenching medium in gas-insulated switchgear, circuit breakers, and related high-voltage power equipment, playing a crucial role in ensuring the safe and stable operation of power systems and improving equipment compactness. Because SF6 has extremely high greenhouse gas potential, its effective recovery and emission reduction have become a key focus of the industry. Existing N2 / SF6 separation and recovery technologies mainly include cryogenic distillation separation, adsorption separation, hydrate separation, and membrane separation. Cryogenic distillation relies on the difference in boiling points and the inconsistency in volatility between gas and liquid components, thus requiring multiple phase transitions, resulting in high energy consumption and operating costs. While adsorption methods avoid phase transitions, they currently face challenges such as difficulty in balancing adsorption capacity and selectivity, bed pressure drop and pulverization, and the disconnect between experimental systems and continuous industrial processes. Hydrate methods offer relatively mild operating conditions, but current research shows limited advantages in product purity and kinetic separation. Membrane separation of N2 / SF6 typically uses polymer membranes, but these have low permeability and selectivity. SAPO-34 molecular sieve membranes have been reported for zeolite membranes, but their small pore size results in low permeability for N2. In contrast, MFI membranes exhibit excellent sieving performance for N2 (~3.64 Å) and SF6 (~5.5 Å), which have significantly different kinetic diameters. Their regular sub-nanopores, good thermochemical stability, and compact continuous membrane process setup demonstrate unique potential for low-flow, decentralized waste gas recovery scenarios.

[0003] For example, a method for preparing an MFI-type zeolite membrane and its application in gas separation (CN118079676A) involves the inventors first preparing sheet-like Silicalite-1 crystals with controllable size and high crystallinity using Silicalite-1 nanocrystals. Then, these sheet-like Silicalite-1 crystals are coated onto a rough macroporous support surface as a seed layer. Finally, the seed layer is subjected to secondary hydrothermal growth to obtain an MFI-type molecular sieve membrane. Although n- / isobutane separation and N2 / SF6 separation differ in their separation targets and application scenarios, they share certain similarities in MFI-type zeolite membrane separation. Both rely on the regulation of mass transfer behavior of different gas molecules by the regular sub-nanopores of the MFI zeolite, achieving selective separation through molecular sieving effects and differences in adsorption-diffusion behavior. For N2 / SF6 separation, the interaction between small N2 molecules and Silicalite-1 is weak. Due to the reliance on molecular sieving selectivity, there are unique and high requirements for membrane density, continuity, integrity, and intergranular defects.

[0004] Therefore, there is an urgent need to develop a method for preparing silicalite-1 zeolite membranes that can form highly dense, continuous, complete and uniform thickness membranes to meet the application requirements of efficient separation and recovery of N2 / SF6. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing Silicalite-1 zeolite membranes and their applications. The method first uses urea and acetamide as seed growth regulators to synergistically control the growth of Silicalite-1 crystals with controllable size and high crystallinity, preparing sheet-like Silicalite-1 crystals. Then, disc-shaped Silicalite-1 crystals are prepared. Subsequently, the sheet-like Silicalite-1 crystals are coated onto a rough, macroporous support surface, followed by coating with the synthesized disc-shaped Silicalite-1 crystals to form a double seed layer. Crucially, a composite template agent (especially bis-[1,5-(tripropylammonium)]pentamethylene diiodide) is introduced into the membrane synthesis solution to regulate the crystallization and growth behavior of MFI, preparing a continuous and dense MFI thin film with high selectivity for N2 / SF6. The technical solution of this invention is as follows: A method for preparing a Silicalite-1 zeolite membrane and its application, comprising the following steps: Step (1) Preparation of sheet-like Silicalite-1 crystals: Silicon source, tetrapropylammonium hydroxide (TPAOH), urea, acetamide and deionized water are mixed and stirred and aged to obtain a clear sol; the sol is placed in a hydrothermal reactor for crystallization. After the reaction is completed, the product is centrifuged, washed and dried to obtain sheet-like Silicalite-1 crystals. Step (2) Preparation of disc-shaped Silicalite-1 crystals: The silicon source, tetrapropylammonium hydroxide and deionized water are mixed, stirred and aged to obtain a clear synthesis solution. The synthesis solution is placed in a hydrothermal reactor for high-temperature crystallization. The product is centrifuged, washed and dried to obtain disc-shaped Silicalite-1 crystals. Step (3) Coating the seed layer: Disperse the sheet-like Silicalite-1 crystals obtained in step (1) and the disk-like Silicalite-1 crystals obtained in step (2) in deionized water to obtain two seed solutions; vertically immerse the rough macroporous carrier in the seed solutions of the sheet-like crystals and the disk-like crystals in sequence, keep it for a period of time, and then pull it out at a uniform speed. After drying and calcining, a smooth Silicalite-1 double seed layer is obtained. Step (4) Preparation of Silicalite-1 molecular sieve membrane: Prepare a secondary growth synthesis solution by mixing and stirring a silicon source, template agent OSDA and deionized water; place the flat Silicalite-1 seed layer obtained in step (3) into a hydrothermal reactor, and then slowly add the secondary growth synthesis solution into the reactor until the seed layer is completely submerged, and carry out a hydrothermal crystallization reaction to obtain Silicalite-1 molecular sieve membrane. After the reaction is completed, remove the Silicalite-1 molecular sieve membrane from the reactor, wash it with water, dry it, and then calcine it to remove the template agent.

[0006] Furthermore, in steps (1), (2) and (4), the silicon source is one or more of tetraethyl orthosilicate, silica sol, fumed silica, silicic acid, and sodium silicate, preferably tetraethyl orthosilicate.

[0007] Further, in step (1), the molar ratio of SiO2:TPAOH:H2O:acetamide:urea in the solution is 1:0.32:165:(0-1.0):(0-1.0); the crystallization temperature is 160-200℃, the crystallization time is 18-60 h; the drying temperature is 60-100℃, and the drying time is 12-24 h.

[0008] Furthermore, in step (1), the size of the sheet-like Silicalite-l nanocrystals is 1.0 μm-4.0 μm.

[0009] Further, in step (2), the molar ratio of SiO2:TPAOH:H2O in the solution is 1:(0.25-0.35):(140-200); the crystallization temperature is 160-175℃, the crystallization time is 16-24 h; the drying temperature is 60-100℃, and the drying time is 12-24 h.

[0010] Furthermore, in step (2), the size of the disk-shaped Silicalite-1 crystal is 400-600 nm.

[0011] Further, in step (3), the mass content of the flaky Silicalite-1 crystals in the flaky Silicalite-1 seed solution is 0.1-1%; the mass content of the disc-shaped Silicalite-1 crystals in the disc-shaped Silicalite-1 seed solution is 0.1-1%; the material of the rough macroporous carrier is alumina, zirconium oxide or mullite; the shape of the rough macroporous carrier is tubular, flat or porous; and the pore size of the rough macroporous carrier is 1-10 μm.

[0012] Furthermore, in step (3), the seed crystals introduced into the rough macroporous carrier are held for 10-60 s, the drying temperature is 60-100℃, the drying time is 6-12 h, the calcination temperature is 400-550℃, the calcination time is 4-8 h, and the heating / cooling rate is 0.5-1.5℃ / min.

[0013] Further, in step (4), the template agent OSDA is one or a mixture of two or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium iodide, tetrabutylammonium hydroxide, tetrabutylammonium bromide and bis-[1,5-(tripropylammonium)]pentamethylene diiodide (dC5); the molar ratio of SiO2:OSDA:H2O in the secondary growth synthesis solution is 1:(0.1-0.32):(60-200); the stirring temperature for preparing the secondary growth synthesis solution is 20-40℃ and the stirring time is 2-24 h.

[0014] Further, in step (4), the crystallization temperature is 100-180℃, the crystallization time is 12-96h; the drying temperature is 80-160℃, the drying time is 6-12h; the calcination temperature is 150-550℃, the calcination time is 4-24h; the heating or cooling rate is 0.5-1.5℃ / min; and the calcination atmosphere can be air or ozone atmosphere.

[0015] The Silicalite-1 zeolite membrane prepared by the above method can be applied to the separation process of N2 and SF6 mixed gases. In specific applications, the Silicalite-1 zeolite membrane is assembled in a membrane separation assembly to form a sealed membrane separation unit, which includes an inlet side (high-pressure side) and a permeate side (low-pressure side). A mixed gas containing SF6 and N2 is introduced into the inlet side of the membrane separation unit, and separation is carried out under certain operating pressure and temperature conditions. Utilizing the difference in permeation rates of different gas molecules through the Silicalite-1 zeolite membrane, N2 preferentially permeates through the membrane layer into the permeate side, while SF6 is retained on the inlet side, thereby achieving the enrichment and recovery of SF6. Preferably, the operating temperature is room temperature to 150°C, the inlet side pressure is 0.05–0.2 MPa, and the permeate side is under atmospheric or reduced pressure conditions to improve the separation driving force. As needed, the membrane separation process can be configured in single-stage or multi-stage series / parallel configurations to further improve the recovery purity and recovery rate of SF6.

[0016] The beneficial effects of this invention are: Preparing dense zeolite molecular sieve membranes for gas separation on macroporous supports is extremely challenging. To address this, this invention proposes a method that utilizes large-sized sheet-like and disk-like Silicalite-1 seed layers. By introducing a composite template agent (especially bis-[1,5-(tripropylammonium)]pentamethylene diiodide) into the membrane synthesis solution, the crystallization and growth behavior of MFI are controlled, resulting in a continuous and dense MFI thin-layer membrane for efficient separation of nitrogen (N2) and sulfur hexafluoride (SF6). The method for preparing sheet-like Silicalite-1 crystals in this invention is simple and easy to implement, yields high production volumes, and achieves sheet-like molecular sieves with complete morphology, controllable size, and high crystallinity without the need for complex and expensive template agents. In particular, by introducing dC5 into the membrane synthesis solution to form a composite template agent, this invention achieves precise control over the crystallization path and membrane formation process of the MFI molecular sieve. This composite template agent promotes regular crystal growth and continuous membrane coverage, reducing problems such as loose membranes, numerous defects, and uneven thickness caused by crystallization competition in traditional hydrothermal membrane formation processes. The resulting MFI thin-layer membrane exhibits higher density, continuity, and integrity, and can effectively shorten the mass transfer path, reduce non-selective leakage, and improve the membrane's separation performance for target gas systems. Therefore, it has significant industrial application value and environmental significance in the fields of sulfur hexafluoride recovery and greenhouse gas emission reduction. Attached Figure Description

[0017] Figure 1 Scanning electron microscope image of the sheet-like Silicalite-1 seed crystals prepared in Example 1; Figure 2 X-ray diffraction pattern of the sheet-like Silicalite-1 seed crystals prepared in Example 1; Figure 3 A scanning electron microscope image of the disk-shaped Silicalite-1 seed crystals prepared in Example 1; Figure 4 X-ray diffraction pattern of the disk-shaped Silicalite-1 seed crystals prepared in Example 1; Figure 5 Scanning electron microscope (SEM) images of the surface and cross-section of the Silicalite-1 membrane prepared in Example 1; Figure 6 X-ray diffraction pattern of the Silicalite-1 film prepared in Example 1; Figure 7 The image shows a scanning electron microscope (SEM) image of the surface of the Silicalite-1 membrane prepared in Example 4. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0019] Example 1 (1) Preparation of Silicalite-1 seed crystals: A solution was prepared by mixing and stirring tetrapropylammonium hydroxide (TPAOH), acetamide, and deionized water at a molar ratio of 1:0.32 SiO2:0.32 TPAOH:165 H2O:0.3 urea:0.3 acetamide. The solution was then aged to obtain a clear sol. The sol was placed in a hydrothermal reactor and crystallized at 175℃ for 48 h. After the reaction, the product was centrifuged, washed, and dried at 60℃ for 24 h to obtain silicalite-1 seed crystals. The average size of the silicalite-1 seed crystals was approximately 2 μm. Its scanning electron microscope (SEM) image and X-ray diffraction (XRD) pattern are shown below. Figure 1 and Figure 2 As shown.

[0020] (2) Preparation of disc-shaped Silicalite-1 seed crystals: A solution was prepared by mixing and stirring tetrapropylammonium hydroxide (TPAOH) and deionized water at a molar ratio of 1 SiO2:0.32 TPAOH:165 H2O to obtain a clear sol. The sol was placed in a hydrothermal reactor and crystallized at 175℃ for 17 h. After the reaction, the product was washed by centrifugation and dried at 60℃ for 24 h to obtain plate-shaped Silicalite-1 crystals. The scanning electron microscope image and X-ray diffraction pattern of the Silicalite-1 crystals are shown below. Figure 3 , Figure 4 As shown, the average size of Silicalite-1 seed crystals is approximately 500 nm.

[0021] (3) Coating of the dual seed layer: The two ends of a 2 μm macroporous alumina carrier tube with a length of 5 cm were sealed with polytetrafluoroethylene plugs and placed in an oven preheated to 80 °C for 4 h. The preheated tube was vertically immersed in a suspension of 1 wt% plate-like seed crystals for 20 seconds. The macroporous alumina carrier coated with plate-like silicalite-1 crystals (single seed layer) was first dried at room temperature, and then transferred to an oven to dry overnight at 80 °C. The same procedure was repeated to coat the disk-like silicalite-1 crystals onto the single seed layer to form a dual seed layer.

[0022] (4) Preparation of silicalite-1 zeolite membrane: The preparation steps of the secondary synthesis solution are the same as those of the molecular sieve crystal synthesis solution. The formula of the secondary growth synthesis solution is n(TEOS): n(TPAOH): n(H2O) = 1:0.15:60. The obtained smooth silicalite-1 seed layer is placed in a hydrothermal reactor, and then the secondary growth synthesis solution is slowly added to the reactor until the seed layer is completely submerged. The hydrothermal crystallization reaction is carried out to obtain the silicalite-1 molecular sieve membrane. After the reaction is completed, the silicalite-1 molecular sieve membrane is taken out from the reactor, washed with water, dried, and then calcined to remove the template agent. The surface and cross-section of the prepared zeolite membrane are shown in the figure. Figure 5 As shown, the X-ray diffraction pattern is as follows: Figure 6 As shown. The prepared silicalite-1 zeolite membrane was tested under conditions of 0.1 MPa and 28℃ with a mixed gas of N2 and SF6 fed in equal proportions. The N2 / SF6 separation factor was 152, and the N2 permeation flux was 4.25 × 10⁻⁶. -7 mol / (m 2 ·s·Pa).

[0023] Example 2 The seed crystal synthesis solution formulation for the plate-like seeds in Example 1 was changed to 1 SiO2:0.32 TPAOH:165 H2O:1 acetamide, resulting in silicalite-1 seeds with a size of 1.1 μm. The formulation for the disc-shaped seed crystal synthesis solution was changed to 1 SiO2:0.25 TPAOH:140 H2O, with a crystallization temperature of 160℃ and a crystallization time of 16 h, resulting in silicalite-1 seeds with a size of 400 nm. A seed suspension with a concentration of 0.5 wt% was prepared and coated to form a double seed layer. The formulation of the secondary growth synthesis solution was n(TEOS):n(TPAOH):n(H2O) = 1:0.3:200. The template agent was removed using an ozone atmosphere at 150℃, with other conditions being the same as in Example 1. The prepared silicalite-1 zeolite membrane was tested under conditions of 0.05 MPa and 50℃ with a mixed gas of N2 and SF6 fed in equal proportions. The N2 / SF6 separation factor was 66, and the N2 permeation flux was 4.9 × 10⁻⁶. -7 mol / (m 2 ·s·Pa).

[0024] Example 3 The seed crystal synthesis solution formula for the plate-like seeds in Example 1 was changed to 1 SiO2:0.32 TPAOH:165 H2O:1 urea. The treatment method was the same as in Example 1, and the size of the prepared silicalite-1 seeds was 3.8 μm. The formula for the disk-like seed crystal synthesis solution was changed to 1 SiO2:0.35 TPAOH:200 H2O. The crystallization temperature was 175℃ and the crystallization time was 24 h. The size of the prepared silicalite-1 seeds was 600 nm. A seed crystal suspension with a concentration of 0.8 wt% was prepared and coated to form a double seed layer. The formula of the secondary growth synthesis solution was n(TEOS):n(TPAOH):n(H2O) = 1:0.3:200. Other conditions were the same as in Example 1. The prepared silicalite-1 zeolite membrane was tested under conditions of 0.1 MPa and 150 °C with a mixed gas of N2 and SF6 fed in equal proportions. The N2 / SF6 separation factor was 21, and the N2 permeation flux was 5.6 × 10⁻⁶. -7 mol / (m 2 ·s·Pa).

[0025] Example 4 The secondary growth synthesis solution from Example 1 was supplemented with dC5 as a template agent, and the formulation was changed to n(TEOS):n(TPAOH):n(dC5):n(H2O) = 1:0.15:0.04:60. Other conditions remained the same as in Example 1. The scanning electron microscope image of the prepared silicalite-1 zeolite film is shown below. Figure 7 As shown, the addition of dC5 as a template agent promotes further interlayer aggregation and crystallization, resulting in a denser zeolite membrane. The prepared silicalite-1 zeolite membrane was tested with a mixed gas of N2 and SF6 fed in equal proportions at 0.1 MPa and 25 °C. The N2 / SF6 separation factor was 175, and the N2 permeation flux was 5.9 × 10⁻⁶. -7 mol / (m 2 ·s·Pa).

[0026] Example 5 The secondary growth synthesis solution from Example 2 was supplemented with dC5 as a template agent, and the formulation was changed to n(TEOS):n(TPAOH):n(dC5):n(H2O) = 1:0.3:0.08:200. Other conditions remained the same as in Example 2. The prepared silicalite-1 zeolite membrane was tested with a mixed gas of N2 and SF6 fed in equal proportions at 0.1 MPa and 80°C. The N2 / SF6 separation factor was 78, and the N2 permeation flux was 6.8 × 10⁻⁶. -7 mol / (m 2 ·s·Pa).

[0027] Example 6 The concentration of the plate-like and disc-shaped seed crystal suspensions in Example 4 was changed to 0.1 wt%, while other conditions remained the same as in Example 4. The prepared silicalite-1 zeolite membrane was tested with a mixed gas of N2 and SF6 fed in equal proportions at 0.15 MPa and 35°C. The N2 / SF6 separation factor was 25, and the N2 permeation flux was 6.9 × 10⁻⁶. -7 mol / (m 2 ·s·Pa).

[0028] Example 7 The silicon source used in step (1) of Example 1 was changed to fumed silica, the crystallization time was changed to 18 h, and the crystallization temperature was changed to 200 °C. Other conditions remained the same as in Example 1. The prepared silicalite-1 zeolite membrane was tested with a mixed gas of N2 and SF6 fed in equal proportions at 0.1 MPa and 28 °C. The N2 / SF6 separation factor was 139, and the N2 permeation flux was 4.5 × 10⁻⁶. -7 mol / (m2 ·s·Pa).

[0029] Example 8 The silicon source used in step (1) of Example 1 was changed to fumed silica, the crystallization time was changed to 60 h, and the crystallization temperature was changed to 160 °C. Other conditions remained the same as in Example 1. The prepared silicalite-1 zeolite membrane was tested with a mixed gas of N2 and SF6 fed in equal proportions at 0.1 MPa and 28 °C. The N2 / SF6 separation factor was 125, and the N2 permeation flux was 4.9 × 10⁻⁶. -7 mol / (m 2 ·s·Pa).

[0030] Example 9 The formulation of Example 4 was changed to n(TEOS): n(TPABr): n(dC5): n(H2O) = 1:0.15:0.02:60. Other conditions remained the same as in Example 4. The prepared silicalite-1 zeolite membrane was tested with a mixed gas of N2 and SF6 fed in equal proportions at 0.06 MPa and 35°C. The N2 / SF6 separation factor was 146, and the N2 permeation flux was 4.6 × 10⁻⁶. -7 mol / (m 2 ·s·Pa).

[0031] Example 10 The crystallization temperature in step 4 of Example 1 was changed to 100℃, and the crystallization time was changed to 48 h. Other conditions remained the same as in Example 1. The prepared silicalite-1 zeolite membrane was tested with a mixed gas of N2 and SF6 fed in equal proportions at 0.09 MPa and 32℃. The N2 / SF6 separation factor was 86, and the N2 permeation flux was 6.2 × 10⁻⁶. -7 mol / (m 2 ·s·Pa).

[0032] Comparative Example 1 The double seed layer in Example 1 was replaced with a single seed layer using only 500 nm seed crystals, while other conditions remained the same as in Example 1. The prepared silicalite-1 zeolite membrane was tested with a mixed gas of N2 and SF6 fed in equal proportions at 0.2 MPa and 28°C. The N2 / SF6 separation factor was 120, and the N2 permeation flux was 1.27 × 10⁻⁶. -7 mol / (m 2 ·s·Pa).

[0033] Comparative Example 2 The macroporous alumina support tubes in Example 1 were replaced with 100nm and 200nm support tubes, while other conditions remained the same as in Example 1. The resulting silicalite-1 zeolite membrane detached from the support and showed no effect on N2 / SF6 separation.

Claims

1. A method for preparing a Silicalite-1 zeolite membrane and its application, characterized in that, Includes the following steps: Step (1) Preparation of sheet-like Silicalite-1 crystals: Silicon source, tetrapropylammonium hydroxide (TPAOH), urea, acetamide and deionized water are mixed and stirred and aged to obtain a clear sol; the sol is placed in a hydrothermal reactor for crystallization. After the reaction is completed, the product is centrifuged, washed and dried to obtain sheet-like Silicalite-1 crystals. Step (2) Preparation of disc-shaped Silicalite-1 crystals: The silicon source, tetrapropylammonium hydroxide and deionized water are mixed, stirred and aged to obtain a clear synthesis solution. The synthesis solution is placed in a hydrothermal reactor for high-temperature crystallization. The product is centrifuged, washed and dried to obtain disc-shaped Silicalite-1 crystals. Step (3) Coating the seed layer: Disperse the sheet-like Silicalite-1 crystals obtained in step (1) and the disk-like Silicalite-1 crystals obtained in step (2) in deionized water to obtain two seed solutions; vertically immerse the rough macroporous carrier in the seed solutions of the sheet-like crystals and the disk-like crystals in sequence, keep it for a period of time, and then pull it out at a uniform speed. After drying and calcining, a smooth Silicalite-1 double seed layer is obtained. Step (4) Preparation of Silicalite-1 molecular sieve membrane: Prepare a secondary growth synthesis solution by mixing and stirring silicon source, template agent OSDA and deionized water; place the flat Silicalite-1 seed layer obtained in step (3) in a hydrothermal reactor, and then slowly add the secondary growth synthesis solution to the reactor until the seed layer is completely submerged, and carry out a hydrothermal crystallization reaction to obtain Silicalite-1 molecular sieve membrane. After the reaction is completed, take the Silicalite-1 molecular sieve membrane out of the reactor, wash it with water, dry it and then calcine it to remove the template agent.

2. The method for preparing a Silicalite-1 zeolite membrane according to claim 1 and its application, characterized in that, In steps (1), (2) and (4), the silicon source is one or a mixture of two or more of tetraethyl orthosilicate, silica sol, fumed silica, silicic acid, and sodium silicate.

3. The method for preparing a Silicalite-1 zeolite membrane according to claim 1 and its application, characterized in that, In step (1), the molar ratio of SiO2:TPAOH:H2O:acetamide:urea in the solution is 1:0.32:165:(0-1.0):(0-1.0); the crystallization temperature is 160-200℃, the crystallization time is 18-60 h; the drying temperature is 60-100℃, and the drying time is 12-24 h.

4. The method for preparing a Silicalite-1 zeolite membrane according to claim 1 and its application, characterized in that, In step (1), the size of the sheet-like Silicalite-1 nanocrystals is 1.0 μm-4.0 μm; in step (2), the size of the disk-like Silicalite-1 crystals is 400-600 nm.

5. The method for preparing a Silicalite-1 zeolite membrane according to claim 1 and its application, characterized in that, In step (2), the molar ratio of SiO2:TPAOH:H2O in the solution is 1:(0.25-0.35):(140-200); the crystallization temperature is 160-175℃, the crystallization time is 16-24 h; the drying temperature is 60-100℃, and the drying time is 12-24 h.

6. The method for preparing a Silicalite-1 zeolite membrane according to claim 1 and its application, characterized in that, In step (3), the mass content of Silicalite-1 crystals in the flaky Silicalite-1 seed solution is 0.1-1%; the mass content of Silicalite-1 crystals in the disc-shaped Silicalite-1 seed solution is 0.1-1%; the material of the rough macroporous carrier is alumina, zirconium oxide or mullite; the shape of the rough macroporous carrier is tubular, flat or porous; the pore size of the rough macroporous carrier is 1-10 μm.

7. The method for preparing a Silicalite-1 zeolite membrane according to claim 1 and its application, characterized in that... In step (3), the seed crystals introduced into the rough macroporous carrier are held for 10-60 s, the drying temperature is 60-100℃, the drying time is 6-12 h, the calcination temperature is 400-550℃, the calcination time is 4-8 h, and the heating / cooling rate is 0.5-1.5℃ / min.

8. The method for preparing a Silicalite-1 zeolite membrane according to claim 1 and its application, characterized in that, In step (4), the template agent OSDA is one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrapropylammonium iodide, tetrabutylammonium hydroxide, tetrabutylammonium bromide and bis-[1,5-(tripropylammonium)]pentamethylene diiodide; the molar ratio of SiO2:OSDA:H2O in the secondary growth synthesis solution is 1:(0.1-0.32):(60-200); the stirring temperature for preparing the secondary growth synthesis solution is 20-40℃ and the stirring time is 2-24 h.

9. The method for preparing a Silicalite-1 zeolite membrane according to claim 1 and its application, characterized in that, In step (4), the crystallization temperature is 100-180℃ and the crystallization time is 12-96 h; the drying temperature is 80-160℃ and the drying time is 6-12 h; the calcination temperature is 150-550℃ and the calcination time is 4-24 h; the heating or cooling rate is 0.5-1.5℃ / min; and the calcination atmosphere is air or ozone.

10. The Silicalite-1 zeolite membrane prepared by the method according to any one of claims 1-9 is applied to the separation process of N2 and SF6 mixed gas, characterized in that, The Silicalite-1 zeolite membrane is assembled in a membrane separation assembly to form a sealed membrane separation unit, which includes an inlet side and a permeate side. A mixed gas containing SF6 and N2 is introduced into the inlet side of the membrane separation unit and separated under certain operating pressure and temperature conditions. The operating temperature is from room temperature to 150°C, the inlet side pressure is 0.05 to 0.2 MPa, and the permeate side is under atmospheric or reduced pressure conditions.

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