Method for preparing oriented MFI molecular sieve membrane by using mixed template and application of oriented MFI molecular sieve membrane

Abstract

The invention provides a method for preparing an oriented MFI molecular sieve membrane by using a mixed template and application of the oriented MFI molecular sieve membrane. The preparation method comprises the following steps: coating the compact and continuous MFI seed crystal layer on the surface of the porous carrier; the method comprises the following steps: dissolving a silicon source and a mixed organic template agent in deionized water, stirring and aging to obtain a synthetic mother solution; placing the carrier coated with the seed crystal layer in a synthetic mother solution for hydrothermal reaction; after the reaction is finished, washing, drying and roasting to obtain the (h0h)-oriented MFI molecular sieve membrane. The MFI molecular sieve membrane prepared by the invention has high orientation, good linkage property, relatively small intergranular defect density and controllable membrane thickness, and can efficiently separate industrial important isomeride such as a mixture of n- / isobutane and o- / p-xylene. The membrane material adopts hydro-thermal synthesis, the process is simple, the preparation cost of the membrane is reduced, the membrane material can be used for a sheet carrier, a tubular carrier and a multi-channel carrier while high separation performance is ensured, large-scale preparation of the oriented MFI molecular sieve membrane is expected to be realized, and application and popularization are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieve membrane preparation, and particularly relates to a method for preparing an oriented MFI molecular sieve membrane by using a mixed template and its application. Background Art

[0002] In petrochemical industry, the separation of hydrocarbons with the same carbon number (such as isomers of C4 alkanes or C5 olefins) is a key link in light hydrocarbon processing and clean fuel production. The separation and purification of such substances are extremely difficult due to their extremely similar physical and chemical properties such as molecular size and polarity. Traditional low-temperature distillation technology has high energy consumption and high separation cost, while membrane separation technology is gradually becoming an important way to solve the efficient separation of hydrocarbon mixtures with the same carbon number by virtue of its unique separation mechanism and material characteristics.

[0003] MFI-type zeolite molecular sieve membrane has become an ideal material for realizing the synergistic optimization of high flux and high selectivity in the industrial separation field due to its precisely controllable oriented structure. Among various zeolite membranes, the research system of MFI membrane is the most perfect, and its performance advantages stem from its unique anisotropic pore structure: composed of sinusoidal pores in the a-axis direction and straight pores in the b-axis direction which are three-dimensionally intertwined. By means of seed-directed assembly and synthesis kinetics regulation, membrane layers with different advantageous orientations can be prepared. A large number of studies have shown that the straight pores of the b-axis oriented MFI zeolite membrane are perpendicular to the carrier surface, and the diffusion path is shorter, showing excellent performance in the separation of xylene isomers (PX / OX). (h0h)- and a-axis orientations belong to sinusoidal curve pores, and the pore window size is beneficial to the separation of butane isomers. However, the pore channels of the a-axis oriented membrane layer form an angle with the membrane layer surface, while the pore channels of the (h0h)-oriented membrane layer are perpendicular to the pore orifice direction of the membrane layer surface, and the mass transfer resistance is relatively small. Therefore, the (h0h)-oriented MFI zeolite membrane is more suitable for the separation of n / i-C4H 10 .

[0004] At present, the synthesis of (h0h)-oriented MFI molecular sieve membrane mostly uses TPA + (tetrapropylammonium ion) as a single organic template agent to regulate the orientation during the secondary growth process. However, TPA + will preferentially adsorb on the (010) crystal plane of MFI crystals, promoting the growth of the membrane layer in the b-axis orientation. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a method for preparing an oriented MFI zeolite membrane using a mixed template and its application. By adding a quaternary ammonium cation with a longer alkyl chain as an organic template agent based on tetrapropylammonium ions to prepare a secondary growth solution, it promotes the preferential growth of the membrane layer in the (h0h)-orientation, improves the denseness of the membrane layer, and explores its application in industrial separation. The prepared MFI zeolite membrane is continuous and dense, with excellent thermal stability, chemical stability, and high orientation. It has high separation performance for n- / i-butane, o- / p-xylene, and H₂ / NH₃ mixtures, thus providing a good prospect for large-scale preparation of high-performance MFI zeolite membranes.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing an oriented MFI zeolite membrane using a mixed template, comprising the following steps:

[0008] S1 Uniformly coat MFI seeds on the surface of a porous support to form a dense and continuous seed layer, and after drying, calcine to solidify the seed layer;

[0009] S2 Dissolve a mixed organic template agent and a silicon source in deionized water, and stir and age to obtain a synthesis mother liquor; the mixed organic template agent includes a tetrapropylammonium cation compound and a quaternary ammonium cation compound with a longer alkyl chain;

[0010] S3 Hydrothermally react the support coated with the seed layer obtained in S1 and the synthesis mother liquor obtained in S2 at 100 - 200 °C;

[0011] S4 Wash, dry, and calcine the membrane material obtained in S3 to remove the organic template agent, and obtain an (h0h)-oriented MFI zeolite membrane.

[0012] The seeds in step S1 are MFI zeolites with a particle size of 50 nm - 1 μm. Further, the seeds are MFI zeolites with a particle size of 50 - 150 nm.

[0013] The method for coating the MFI seeds in step S1 is spin coating, dip coating, drop coating, wiping coating, spraying, or vacuum crystal coating.

[0014] The calcination temperature of the seed layer in step S1 is 100 - 800 °C; the calcination time is 10 min - 100 h.

[0015] The shape of the support in step S1 includes single-channel tubular, multi-channel tubular, flat, or hollow fiber tubular. The material of the support includes ceramics, stainless steel, alumina, titanium dioxide, zirconium dioxide, silicon dioxide, silicon carbide, or silicon nitride, and the pore size is 2 - 2000 nm.

[0016] The quaternary ammonium salt cationic compounds with long alkyl chains described in step S2 include one or more of tetrabutylammonium bromide, tetrabutylammonium hydroxide, tetrabutylammonium chloride, tetraamylammonium chloride, tetraamylammonium hydroxide, tetraamylammonium bromide, tetraamylammonium iodide, methyltributylammonium hydroxide, and ethyltrimethylammonium bromide.

[0017] The tetrapropylammonium cationic compounds described in step S2 include tetrapropylammonium hydroxide, tetrapropylammonium chloride, tetrapropylammonium bromide, tetrapropylammonium sulfate, or tetrapropylammonium nitrate.

[0018] The molar ratio of the tetrapropylammonium cationic compounds, quaternary ammonium salt cationic compounds with long alkyl chains, deionized water to the silicon source in step S2 is (0.05 - 0.08):(0.03 - 0.05):(20 - 400):1, where the silicon source is calculated as SiO₂.

[0019] The silicon source described in step S2 includes one or more of methyl orthosilicate, ethyl orthosilicate, water glass, silica sol, and silica aerogel.

[0020] The aging time in step S2 is 10 min to 100 h.

[0021] The synthesis mother liquor in step S2 further includes an aluminum source, and the molar ratio of the aluminum source to the silicon source is 0.001 - 0.5, where the silicon source is calculated as SiO₂ and the aluminum source is calculated as Al₂O₃.

[0022] The aluminum source includes metallic aluminum, aluminum hydroxide, sodium metaaluminate, aluminum sulfate, aluminum chloride, aluminum isopropoxide, or aluminum nitrate.

[0023] The hydrothermal reaction time in step S3 is 1 h to 20 days.

[0024] The calcination temperature in step S4 is 100 - 700 °C; the calcination time is 0.2 - 50 h. Further, the calcination method is muffle furnace calcination, tube furnace calcination in an ozone atmosphere, or rapid thermal process calcination. Still further, the calcination method is tube furnace calcination in an ozone atmosphere, and the calcination temperature is 150 - 300 °C, so that the required calcination temperature is lower, the time is shorter, and the integrity of the membrane is ensured to the greatest extent.

[0025] The thickness of the MFI zeolite membrane is 0.5 μm to 30 μm.

[0026] The present invention also provides an application of the MFI zeolite membrane obtained by the method in the separation of isomers.

[0027] The isomers include a mixture of n / i - butane, a mixture of o / p - xylene, or a mixture of H₂ / NH₃.

[0028] The beneficial effects of the present invention are as follows: By using tetrapropylammonium cation compound and quaternary ammonium salt cation compound with a longer alkyl chain as a mixed template agent to prepare a highly active synthesis mother liquor, a highly (h0h)-oriented MFI zeolite membrane with good connectivity is obtained under hydrothermal reaction. Replacing TPA with an appropriate amount of quaternary ammonium salt cation with a longer alkyl chain + , induces the formation of larger silicon-oxygen secondary units, facilitating the entry of TPA + , and thus accelerating the nucleation and growth of MFI seeds. In addition, the quaternary ammonium salt cation with a longer alkyl chain is preferentially adsorbed on the (100) crystal plane, which competes with the adsorption on the (010) crystal plane of TPA + , inhibiting the growth of the b-axis orientation and being beneficial to the growth of the (h0h)-orientation. At the same time, replacing a small amount of TPA with the quaternary ammonium salt cation with a longer alkyl chain + , the thermal decomposition temperature of the quaternary ammonium salt cation with a longer carbon chain is much lower than that of TPA + . Through the complementary molecular characteristics and thermal decomposition behaviors of the two, gases are released in a gradient during the removal of the template agent, reducing the volume shrinkage stress and the density of grain boundary cracks, thereby reducing the occurrence of intercrystalline defects in the MFI zeolite membrane and simultaneously improving the separation performance and industrial applicability. The membrane material prepared by the present invention has a high separation performance for the n-butane / i-butane gas mixture (n-butane permeation flux: 6.8×10 -8 mol·m -2 ·s -1 ·Pa -1 , separation factor: 52), the o-xylene / p-xylene liquid mixture (p-xylene flow rate: 0.8 kg·m -2 ·h -1 , separation factor: 89), and the hydrogen / ammonia gas (ammonia permeation flux: 1.5×10 -7 mol·m -2 ·s -1 ·Pa -1 , separation factor: 135) mixtures, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 are the (a) SEM image and (b) XRD pattern of the MFI seeds prepared in Example 1.

[0030] Figure 2 is the SEM image of the MFI seed layer prepared in Example 1.

[0031] Figure 3 are the (a) plan view and (b) cross-sectional SEM images of the M1 membrane prepared in Example 1.

[0032] Figure 4 is the XRD pattern of the M1 membrane prepared in Example 1.

[0033] Figure 5 These are the (a) plan view and (b) cross-sectional SEM images of the M2 membrane prepared in Example 2.

[0034] Figure 6 This is the XRD pattern of the M2 membrane prepared in Example 2.

[0035] Figure 7 This is the plan view SEM image of the M3 membrane prepared in Example 3.

[0036] Figure 8 This is the plan view SEM image of the M4 membrane prepared in Example 4.

[0037] Figure 9 This is the plan view SEM image of the M5 membrane prepared in Example 5.

[0038] Figure 10 This is the plan view SEM image of the M6 membrane prepared in Example 6.

[0039] Figure 11 This is the plan view SEM image of the M7 membrane prepared in Example 7.

[0040] Figure 12 This is the long-term stability graph of the separation performance of the M1 membrane prepared in Example 1 for n-butane / isobutane.

[0041] Figure 13 This is the test graph of the separation performance of the M1 membrane prepared in Example 1 for n-butane / isobutane varying with the feed composition.

[0042] Figure 14 This is the plan view SEM image of the M8 membrane prepared in Comparative Example 1.

[0043] Figure 15 This is the plan view SEM image of the M9 membrane prepared in Comparative Example 2.

[0044] Figure 16 This is the plan view SEM image of the M10 membrane prepared in Comparative Example 3.

[0045] Figure 17 These are the (a) plan view SEM and (b) XRD images of the M11 membrane prepared in Comparative Example 4. Detailed implementation manners

[0046] The present invention will be further described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. These all fall within the protection scope of the present invention.

[0047] In this application, the gas separation test conditions are all at room temperature. Without special instructions, the mixed gas feed ratio is 1:1, the permeate side is at atmospheric pressure, the transmembrane pressure difference is 1 bar, and helium is used as the purge gas. In this application, the pervaporation test temperature is 75 °C, the molar ratio of o-xylene / p-xylene is 1:1, and the transmembrane pressure difference is 1 bar.

[0048] Example 1

[0049] (1) Preparation of MFI seeds: First, weigh each raw material according to the molar ratio of tetrapropylammonium hydroxide:tetraethyl orthosilicate:deionized water of 0.36:1:14 to prepare a seed synthesis solution. Stir and age the synthesis solution at room temperature for 12 h and then filter. Next, transfer the obtained clear and transparent solution into a reaction kettle, crystallize it at 100 °C for 72 h, then cool and take it out. Pour out the supernatant, add an equal amount of deionized water, then centrifuge to obtain a precipitate, and dry it at 60 °C for 12 h to obtain MFI seeds;

[0050] (2) Coating and curing the seed layer: Disperse the prepared seeds in deionized water to prepare a seed solution with a mass concentration of 0.5 wt.%. Subsequently, uniformly coat the MFI seeds on the surface of the tubular porous alumina support by dip coating: dip the support in the seed dispersion liquid, and the dipping time for each time is 30 s. After dip coating, place the support in an oven at 70 °C and dry it for 12 h, and then put it into a muffle furnace and calcine it at 500 °C for 6 h to remove the organic template agent in the seeds while improving the bonding force between the seeds and the support to cure the seed layer.

[0051] (3) Preparation of the synthesis mother liquor: Slowly drip tetraethyl orthosilicate (TEOS) into the mixed solution of template agent A tetrapropylammonium hydroxide solution (25 wt.%), template agent B tetrabutylammonium hydroxide solution (25 wt.%) and deionized water, and stir and age it at room temperature for 6 h to obtain the synthesis mother liquor. The molar composition of the above synthesis mother liquor is 1 TEOS:0.07 TPAOH:0.03 TBAOH:130 H2O.

[0052] (4) Preparation of MFI zeolite membrane by secondary growth method: Place the carrier tube coated with the seed layer obtained in (1) into the synthesis mother liquor, seal it and put it into an oven, and react at 160 °C for 20 h. After the reaction is completed, take out the membrane tube, wash it with deionized water until it is neutral, dry it overnight, and then put it into a tubular furnace in an ozone atmosphere and calcine it at 250 °C for 6

[0053] h to remove the template agent, and the heating and cooling rates are both 1 °C / min. The MFI zeolite membrane prepared in this process is denoted as M1.

[0054] The scanning electron microscope characterization of the MFI seeds is as Figure 1 shown in a. The morphology of the zeolite is a regular hexagonal prism, and the particle size is evenly distributed at about 100 nm. The XRD results (Figure 1 b) indicates that the molecular sieve is of pure MFI crystal form, with high crystallinity and no other impurity peaks. The SEM characterization of the prepared seed layer is as shown in Figure 2 , where the seeds are closely arranged to form a continuous and dense seed layer. As can be seen from Figure 3 a, after secondary growth, the surface of the prepared MFI molecular sieve membrane is uniform, dense and continuous. The cross-sectional SEM characterization is as shown in Figure 3 b, and the thickness of the MFI molecular sieve membrane is 4.8 μm. The XRD pattern ( Figure 4 ) indicates that the prepared membrane material is of pure MFI structure. The relative peak intensities representing the 101 and 002 orientations can reflect the orientation of the MFI membrane layer grains. Only the (101) diffraction peak exists in membrane M1, which indicates that the MFI molecular sieve membrane has a highly (h0h)-axis orientation. The nitrogen and sulfur hexafluoride gas permeation tests were carried out on membrane M1 (at room temperature and atmospheric pressure). The results show that the nitrogen permeation flux is 4.8×10 -9 mol·m -2 ·s -1 ·Pa -1 , and the sulfur hexafluoride gas permeation flux is 3.5×10 -7 mol·m -2 ·s -1 ·Pa -1 . The ideal selectivity of membrane M1 for sulfur hexafluoride / nitrogen is 73, which indicates that the membrane layer has good denseness and almost no defects. This shows that the addition of TBA + accelerates the induction of the membrane layer to grow in the (h0h)-axis orientation and inhibits the generation of defects during the membrane growth process. The normal temperature and atmospheric pressure test of the n-butane / i-butane mixed component (1:1) was carried out on membrane M1. The results show that the n-butane permeation flux can reach 6.8×10 -8 mol·m -2 ·s -1 ·Pa -1 , and the separation factor is 52. The pervaporation test of the o-xylene / p-xylene mixed component (1:1) was carried out on membrane M1. The results show that the p-xylene flux of membrane M1 is 800 g·m -2 ·h -1 , and the separation factor reaches 89. The normal temperature and atmospheric pressure test of the hydrogen / ammonia mixed component (1:1) was carried out on membrane M1. The results show that the ammonia permeation flux can reach 1.5×10 -7 mol·m -2 ·s -1 ·Pa -1 , and the separation factor is 135.

[0055] Example 2

[0056] The difference from Example 1 is that: in Step 3, the molar ratio of tetrapropylammonium hydroxide solution, tetrabutylammonium hydroxide solution to the silicon source is 0.05 / 0.05 / 1, and the remaining steps are the same as those in Example 1. The MFI zeolite membrane prepared by this process is denoted as M2.

[0057] The SEM characterization of the MFI seeds is as Figure 5 shown in a. The crystal grains on the membrane surface are significantly larger, the growth of the membrane surface is good, and there are almost no twin crystals on the surface. The cross-sectional SEM characterization is as Figure 5 shown in b. The connectivity of the membrane layer is good, the thickness increases, about 11.6 μm. The corresponding XRD results show ( Figure 6 ), within the entire XRD diffraction angle range, there are (101) diffraction peak and (002) diffraction peak, and the peak intensity of the (101) orientation is much greater than that of (002), indicating that the membrane layer has a high (h0h) orientation advantage. The membrane M2 was tested with a normal-butane / isobutane mixed component (1:1) at normal temperature and pressure. The results show that the permeation flux of normal butane can reach 3.1×10 - 8 mol·m -2 ·s -1 ·Pa -1 , and the separation factor is 37. The membrane M2 was tested by pervaporation with an o-xylene / p-xylene mixed component (1:1). The results show that the flux of p-xylene through the membrane M2 is 420 g·m -2 ·h -1 , and the separation factor reaches 53.

[0058] Example 3

[0059] The difference from Example 1 is that: in Step 3, the template B is selected as tetraamylammonium hydroxide solution, and the molar ratio of tetraamylammonium hydroxide to tetrapropylammonium hydroxide is 0.03 / 0.07. The remaining steps are the same as those in Example 1. The MFI zeolite membrane prepared by this process is denoted as M3. The SEM characterization of M3 is as Figure 7 shown. The crystal grains on the membrane surface become larger, and the growth of the membrane surface is good. The membrane M3 was tested with a normal-butane / isobutane mixed component (1:1) at normal temperature and pressure. The results show that the permeation flux of normal butane can reach 4.3×10 -8 mol·m -2 ·s -1 ·Pa -1 , and the separation factor is 45.

[0060] Example 4

[0061] The difference from Example 1 is that: in Step 4, the secondary growth time is 15 h, and the remaining steps are the same as those in Example 1. The MFI zeolite membrane prepared by this process is denoted as M4. The SEM characterization of M4 is as Figure 8As shown, the grains on the surface of the membrane layer are significantly reduced, and the membrane layer is continuous, dense and has good connectivity. The membrane M4 was tested with a mixed component of n-butane / i-butane (1:1) at normal temperature and pressure. The results show that the permeation flux of n-butane can reach 1.2×10 -7 mol·m -2 ·s -1 ·Pa -1 , and the separation factor is 30.

[0062] Example 5

[0063] The difference from Example 1 is that in Step 3, the molar ratio of deionized water to silicon source is H2O / SiO2 = 100, and the other steps are the same as in Example 1. The MFI zeolite membrane prepared by this process is denoted as M5. The SEM characterization of M5 is as Figure 9 shown. The grains on the surface of the membrane layer are significantly reduced, and the membrane layer still maintains good connectivity at this time. The membrane M5 was tested with a mixed component of n-butane / i-butane (1:1) at normal temperature and pressure. The results show that the permeation flux of n-butane can reach 8.4×10 -8 mol·m -2 ·s -1 ·Pa -1 , and the separation factor is 44.

[0064] Example 6

[0065] The difference from Example 1 is that in Step 4, the temperature of secondary growth is 160 °C and the time is 20 h, and the other steps are the same as in Example 1. The MFI zeolite membrane prepared by this process is denoted as M6. The SEM characterization of M6 is as Figure 10 shown. The membrane layer has achieved connectivity on the basis of the seed layer, and the crystal gaps have been completely closed. The membrane M6 was tested with a mixed component of n-butane / i-butane (1:1) at normal temperature and pressure. The results show that the permeation flux of n-butane can reach 5.5×10 -8 mol·m -2 ·s -1 ·Pa -1 , and the separation factor is 41.

[0066] Example 7

[0067] The difference from Example 1 is that in Step 3, aluminum chloride is additionally added as an aluminum source during the preparation of the synthesis mother liquor, and the molar ratio of aluminum chloride to tetraethyl orthosilicate is Al2O3 / SiO2 = 0.02. The other steps are the same as in Example 1. The MFI zeolite membrane prepared by this process is denoted as M7. The SEM characterization of M7 is as Figure 11 shown. The connectivity of the membrane surface is good, and the size of the MFI crystal grains is small. The membrane M7 was tested with a mixed component of n-butane / i-butane (1:1) at normal temperature and pressure. The results show that the permeation flux of n-butane can reach 1.5×10 -7mol·m -2 ·s -1 ·Pa -1 , the separation factor is 34.

[0068] Example 8: Gas separation stability test was carried out on the prepared MFI membrane

[0069] The MFI membrane layer prepared in Example 1 was subjected to a normal / isobutane gas separation stability test to test its long-term stability. The test conditions were as follows: the test temperature was room temperature, the mixed gas feed ratio was 1:1, the permeate side was at atmospheric pressure, and the transmembrane pressure difference was 1 bar. The membrane layer was continuously treated at room temperature for 24 hours to examine its stability ( Figure 12 ). It was found that the performance of the MFI membrane remained stable without obvious changes, indicating that the membrane has excellent long-term stability and is conducive to industrial application.

[0070] Example 9: Separation performance test of the prepared MFI membrane with the change of feed composition

[0071] The MFI membrane layer prepared in Example 1 was subjected to a separation performance test with the change of the normal / isobutane feed composition. The test conditions were as follows: the test temperature was room temperature, the feed ratio of n-butane to isobutane in the mixed gas was between 1:9 and 9:1, the permeate side was at atmospheric pressure, and the transmembrane pressure difference was 1 bar. The membrane layer was continuously treated at room temperature for 6 hours at each feed composition until the membrane layer was stable. The membrane layer was continuously treated at room temperature to examine the influence of the change of feed composition on the separation performance ( Figure 13 ). The results showed that with the increase of the feed ratio, both n-butane and isobutane increased, but the separation selectivity showed a trend of first increasing and then decreasing. The results showed that when the molar ratio of n-butane to isobutane in the feed was 7:3, the permeation flux of n-butane could reach 7.5×10 -8 mol·m -2 ·s -1 ·Pa -1 , and the separation factor was 58.

[0072] Comparative Example 1

[0073] The difference from Example 1 was that in step 3, only tetrabutylammonium hydroxide was used as the organic template agent, and the molar composition of the synthesis mother liquor was 1TEOS:0.1TBAOH:130H2O. The other steps were the same as those in Example 1. The MFI zeolite membrane prepared in this process was denoted as M8. The SEM characterization of M8 is as Figure 14 shown. The seed crystals grew slightly, and a continuous membrane layer could not be obtained. The nitrogen and sulfur hexafluoride gas permeation tests (room temperature and atmospheric pressure) were carried out on the membrane M8 respectively. The results showed that the permeation flux of nitrogen was 3.4×10 -8 mol·m -2 ·s -1 ·Pa-1 , the permeation flux of sulfur hexafluoride gas is 4.7×10 -7 mol·m -2 ·s -1 ·Pa -1 , and the ideal selectivity of membrane M8 for sulfur hexafluoride / nitrogen is 13.8, which is much lower than the result measured for membrane M1, indicating that there are significant intercrystalline defects in the membrane layer.

[0074] Comparative Example 2

[0075] The difference from Example 1 is that: the synthesis mother liquor in Step 3 is not stirred and aged at room temperature for 6 h. The remaining steps are the same as those in Example 1, and the MFI zeolite membrane prepared in this process is denoted as M9. The scanning electron microscope characterization of M9 is as Figure 15 shown. The size of the seed crystals has no obvious change, and the connectivity of the membrane surface is extremely poor. The nitrogen and sulfur hexafluoride gas permeation tests (at normal temperature and pressure) were carried out on membrane M9 respectively. The results show that the permeation flux of nitrogen is 9.3×10 -8 mol·m -2 ·s -1 ·Pa -1 , the permeation flux of sulfur hexafluoride gas is 1.4×10 -6 mol·m -2 ·s -1 ·Pa -1 , and the ideal selectivity of membrane M8 for sulfur hexafluoride / nitrogen is 15.0, indicating that the membrane layer has defects.

[0076] Comparative Example 3

[0077] The difference from Example 1 is that: in Step 4, the secondary growth temperature is changed to 70 °C, and the remaining steps are the same as those in Example 1. The MFI zeolite membrane prepared in this process is denoted as M10. The scanning electron microscope characterization of M10 is as Figure 16 shown. The size of the seed crystals has no obvious change, nucleation is difficult, and the connectivity of the membrane layer is very poor. The nitrogen and sulfur hexafluoride gas permeation tests (at normal temperature and pressure) were carried out on membrane M10 respectively. The results show that the permeation flux of nitrogen is 7.6×10 -8 mol·m -2 ·s -1 ·Pa -1 , the permeation flux of sulfur hexafluoride gas is 1.2×10 -6 mol·m -2 ·s -1 ·Pa -1 , and the ideal selectivity of membrane M8 for sulfur hexafluoride / nitrogen is 15.8, indicating that there are many defects in the membrane.

[0078] Comparative Example 4

[0079] The difference from Example 1 is that in Step 3, only tetrapropylammonium hydroxide is used as the organic template agent, and the molar composition of the synthesis mother liquor is 1TEOS:0.3TPAOH:130H2O. The remaining steps are the same as those in Example 1. The MFI zeolite membrane prepared by this process is denoted as M11. The scanning electron microscope characterization of M11 is as Figure 17 shown in a. The seed crystals grow sufficiently to obtain a continuous film layer. The XRD pattern ( Figure 17 b) shows that only the (0k0) diffraction peak exists in the membrane M11, indicating that the MFI zeolite membrane has a high b-axis orientation. The membrane M11 is tested with a mixed component of n-butane / i-butane (1:1) at normal temperature and pressure. The results show that the permeation flux of n-butane can reach 2.6×10 -7 mol·m -2 ·s -1 ·Pa -1 , and the separation factor is 24.

[0080] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concepts. Therefore, the appended claims are intended to be construed to include the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0081] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing an oriented MFI zeolite membrane using a mixed template, characterized in that: It includes the following steps: S1 Uniformly coat MFI seeds on the surface of a porous support to form a dense and continuous seed layer, and after drying, calcine to solidify the seed layer; S2 Dissolve a mixed organic template agent and a silicon source in deionized water, stir and age to obtain a synthesis mother liquor; the mixed organic template agent includes a tetrapropylammonium cation compound and a quaternary ammonium salt cation compound with a longer alkyl chain; S3 Hydrothermally react the support coated with the seed layer obtained in S1 and the synthesis mother liquor obtained in S2 at 100-200 °C; S4 Wash, dry, and calcine the membrane material obtained in S3 to remove the organic template agent, and obtain an (h0h)-oriented MFI zeolite membrane.

2. The method for preparing an oriented MFI zeolite membrane using a mixed template according to claim 1, characterized in that: The seeds in step S1 are MFI zeolites with a particle size of 50 nm to 1 μm; and / or, The method for coating the MFI seeds in step S1 is spin coating, dip coating, drop coating, wiping coating, spraying, or vacuum crystal coating.

3. The method for preparing an oriented MFI zeolite membrane using a mixed template according to claim 1, characterized in that: The shape of the support in step S1 includes single-channel tubular, multi-channel tubular, flat, or hollow fiber tubular; the material of the support includes ceramics, stainless steel, alumina, titanium dioxide, zirconium dioxide, silicon dioxide, silicon carbide, or silicon nitride, and the pore diameter is 2-2000 nm.

4. The method for preparing an oriented MFI zeolite membrane using a mixed template according to claim 1, wherein: The quaternary ammonium salt cation compound with a longer alkyl chain in step S2 includes one or more of tetrabutylammonium bromide, tetrabutylammonium hydroxide, tetrabutylammonium chloride, tetraamylammonium chloride, tetraamylammonium hydroxide, tetraamylammonium bromide, tetraamylammonium iodide, methyltributylammonium hydroxide, and ethyltrimethylammonium bromide.

5. The method for preparing an oriented MFI zeolite membrane using a mixed template according to claim 1, characterized in that: In step S2, the molar ratio of the tetrapropylammonium cation compound, the quaternary ammonium salt cation compound with a longer alkyl chain, deionized water to the silicon source is (0.05-0.08):(0.03-0.05):(20-400):

1.

6. The method for preparing an oriented MFI zeolite membrane using a mixed template according to claim 1, characterized in that: The silicon source in step S2 includes one or more of methyl orthosilicate, ethyl orthosilicate, water glass, silica sol, and silica aerogel; and / or, The aging time in step S2 is 10 min to 100 h.

7. The method for preparing an oriented MFI zeolite membrane using a mixed template according to claim 1, wherein: The synthesis mother liquor in step S2 further includes an aluminum source, and the molar ratio of the aluminum source to the silicon source is 0.001-0.

5.

8. The method for preparing an oriented MFI zeolite membrane using a mixed template according to claim 1, wherein: The hydrothermal reaction time in step S3 is 1 h to 20 days, and / or, The calcination temperature in step S4 is 100-700 °C; the calcination time is 0.2-50 h.

9. Application of the MFI zeolite membrane obtained by the method according to any one of claims 1-8 in the separation of isomers.

10. Use of the MFI zeolite membrane according to claim 9 in the separation of isomers, characterized in that: The isomers include a mixture of n- / i-butane, a mixture of o- / p-xylene, or a mixture of hydrogen / ammonia.

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