Method for preparing mfi molecular sieve membrane at low temperature and application thereof

Abstract

The application provides a method for preparing MFI molecular sieve membrane at low temperature and application. The preparation method comprises the following steps: introducing a dense continuous MFI seed layer on the surface of a porous carrier; dissolving a silicon source and an organic template agent in deionized water, stirring and aging at 50-120 DEG C to obtain solution A, dissolving ammonium fluoride in deionized water to obtain solution B, slowly dropping solution B into solution A and continuing to stir and age to obtain a synthesis mother liquor; placing the MFI seed layer in the synthesis mother liquor to perform hydrothermal reaction; after the reaction is completed, washing, drying and calcining are performed to obtain a high-quality MFI molecular sieve membrane. The MFI molecular sieve membrane prepared by the application has good connectivity, small intracrystalline / intercrystalline defect density and controllable membrane layer thickness, and has high separation performance for important industrial isomers such as n-butane / isobutane and o-xylene / p-xylene mixtures. The preparation process of the membrane material is simple, the synthesis temperature can be reduced to room temperature while ensuring high separation performance, is far lower than that reported in the existing literature, and has good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molecular sieve membrane synthesis, and particularly relates to a method for preparing MFI molecular sieve membrane at low temperature and application. BACKGROUND

[0002] Zeolite membrane is an inorganic membrane developed in recent 20 years. As a separation membrane material, it has the advantages of general inorganic membranes and the excellent properties of zeolite molecular sieve, such as uniform microporous channel, excellent thermal stability and chemical stability, controllable pore size and hydrophilic / hydrophobic property, and good catalytic activity. These properties enable the zeolite molecular sieve membrane to achieve good separation and catalytic performance at the molecular level.

[0003] Among the various types of zeolite molecular sieve membranes, the research on the zeolite membrane with MFI type topological structure is the most extensive. The research is extensive due to the following reasons: (1) MFI molecular sieve has unique pore size and structure, and its pore size is similar to the molecular kinetic diameter of many important substances in industry, which can be applied to the separation of n-butane / isobutane and o-xylene / p-xylene isomers, and due to the adjustable hydrophilic / hydrophobic property, it can also be widely applied to the separation of acid / water and alcohol / water systems; (2) MFI molecular sieve has diversified morphology and structure; (3) the membrane material is easy to process, modify and synthesize controllably.

[0004] The synthesis temperature is an important factor affecting the morphology and separation performance of the zeolite membrane. In order to ensure sufficient growth power of the crystal in the secondary growth process, the temperature for preparing the MFI molecular sieve membrane is generally high (120-180℃) at present, which leads to the fact that the reaction must be carried out in a sealed high-temperature and high-pressure reaction kettle. This undoubtedly increases the difficulty of membrane preparation operation, production energy consumption and equipment cost, and the high reaction temperature also easily leads to uncontrollable membrane thickness and the generation of intercrystalline defects of the membrane layer. Reducing the synthesis temperature can achieve better control of the nucleation and growth of the MFI molecular sieve membrane, reduce the membrane thickness and avoid the generation of defects in the membrane layer. Through the methods of heat reflux, single-mode microwave heating and use of high-activity silicon source, researchers can reduce the synthesis temperature of the MFI molecular sieve membrane to 100℃, and further reducing the synthesis temperature while ensuring good connectivity of the membrane material still faces great challenges. SUMMARY

[0005] The present application provides a method for preparing high-quality MFI molecular sieve membrane at low temperature, which reduces the synthesis temperature of the MFI molecular sieve membrane by adjusting the stirring and aging of the precursor solution and introducing the mineralizer to prepare a high-activity secondary growth solution, and explores the application thereof in industrial separation. The prepared MFI molecular sieve membrane has good connectivity, excellent thermal stability, chemical stability and mechanical stability. It has high separation performance for n-butane / isobutane and o-xylene / p-xylene mixtures, thereby providing a good industrial application prospect for the preparation of high-performance MFI molecular sieve membrane.

[0006] The application is achieved by the following technical solutions:

[0007] The method for preparing MFI molecular sieve membrane at low temperature comprises the following steps:

[0008] S1 uniformly coating MFI seeds on the surface of a porous carrier to form a dense and continuous seed layer, drying and then calcining to solidify the seed layer;

[0009] S2 dissolving a silicon source and an organic template in deionized water, stirring and aging at 50-120 DEG C to obtain solution A, dissolving ammonium fluoride in deionized water to obtain solution B, slowly adding solution B to solution A and continuing to stir and age to obtain a synthesis mother liquor;

[0010] S3 performing low-temperature hydrothermal reaction of the seed layer obtained in S1 and the synthesis mother liquor obtained in S2 at 30-90 DEG C;

[0011] S4 washing, drying and calcining the membrane material obtained in S3 to remove the organic template to obtain MFI molecular sieve membrane.

[0012] In step S2, the molar ratio of ammonium fluoride to the silicon source is NH4F / SiO2=0.2-2.0.

[0013] In step S1, the seed is MFI molecular sieve with a particle size of 20 nm-2 μm.

[0014] In step S1, the specific method for coating the MFI seeds is spin coating, dip coating, rubbing or spraying; the calcination temperature of the seed layer is 200-800 DEG C; and the calcination time is 20 min-100 h.

[0015] In step S1, the shape of the carrier includes single-channel tubular, multi-channel tubular, flat plate or hollow fiber tubular; the material of the carrier includes ceramic, stainless steel, alumina, titania, zirconia, silica, silicon carbide or silicon nitride; and the pore size is 2-2000 nm.

[0016] In step S2, the silicon source is one or more of methyltrimethoxysilane, ethyltrimethoxysilane, water glass, silica sol and silica aerogel; and the molar ratio of deionized water to the silicon source is H2O / SiO2=8-100.

[0017] In step S2, the organic template is one or more of tetrapropylammonium bromide, tetrapropylammonium hydroxide solution, tetraethylammonium hydroxide solution and methyltributylammonium hydroxide solution; and the molar ratio of the organic template to the silicon source is organic template / SiO2=0.05-0.4.

[0018] In step S2, the silicon source and the organic template are dissolved in deionized water, and the aging time is 4-20 h.

[0019] After the solution B is slowly added to the solution A in step S2, the aging temperature is 50-120℃ and the aging time is 4-20h.

[0020] The A solution in step S2 further comprises an aluminum source or a titanium source, the aluminum source is sodium metaaluminate, aluminum sulfate, aluminum chloride or aluminum nitrate, the titanium source is tetrabutyl titanate, titanium chloride or titanium isopropoxide, the molar ratio of the aluminum source to the silicon source is Al2O3 / SiO2=0.001-0.05, and the molar ratio of the titanium source to the silicon source is TiO2 / SiO2=0.002-0.1.

[0021] The hydrothermal reaction time in step S3 is 12h-84 days.

[0022] The MFI molecular sieve membrane in step S4 is calcined by a muffle furnace, an ozone atmosphere tube furnace or a rapid heating process, the calcination temperature is 150-700℃, and the calcination time is 0.3-50h. Further, the calcination method is the ozone atmosphere tube furnace, and the calcination temperature is 150-250℃, so that the required calcination temperature is lower, the time is shorter, and the integrity of the membrane is ensured to the maximum extent.

[0023] The application further provides an MFI molecular sieve membrane obtained by the above method.

[0024] The application further provides an application of the MFI molecular sieve membrane in separating a n-butane / isobutane mixed gas and separating an o-xylene / p-xylene mixed liquid, and the MFI molecular sieve membrane has good separation performance for the n-butane / isobutane mixed gas and the o-xylene / p-xylene mixed liquid system.

[0025] The application has the following beneficial effects: the application prepares a high-activity synthesis mother liquor by regulating and controlling stirring aging and introduction of a mineralizer solution, and a MFI molecular sieve membrane with good intergrowth is prepared at a lower synthesis temperature. By coupling low-temperature synthesis and fluorine ion mineralization, a high-quality MFI molecular sieve membrane with small intracrystalline / intercrystalline defect density, controllable thickness and morphology is obtained. Compared with a traditional MFI molecular sieve membrane preparation process, the synthesis temperature is greatly reduced (to room temperature 30℃), which greatly reduces the difficulty of membrane preparation and production cost. At the same time, the membrane material prepared at room temperature in the application has a n-butane / isobutane gas mixture (n-butane permeation flux 5.16x10 -7 mol·m -2 ·s -1 ·Pa -1 , separation factor 96.7) and an o-xylene / p-xylene liquid mixture (p-xylene flow rate 350g·m -2 ·h -1, separation factor 37) all show high separation performance and have good prospects for industrial applications. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is (a) SEM and (b) XRD of MFI seed prepared in Example 1.

[0027] Figure 2 is SEM of MFI seed layer prepared in Example 1.

[0028] Figure 3 is (a) planar and (b) cross-sectional SEM of Ml membrane prepared in Example 1.

[0029] Figure 4 is XRD of Ml membrane prepared in Example 1.

[0030] Figure 5 is single gas permeation test of Ml membrane prepared in Example 1.

[0031] Figure 6 is test of n- / iso-butane separation performance of Ml membrane prepared in Example 1 as a function of feed pressure.

[0032] Figure 7 is test of n- / iso-butane separation performance of Ml membrane prepared in Example 1 as a function of feed composition.

[0033] Figure 8 is comparison of n- / iso-butane separation performance of Ml membrane prepared in Example 1 with literature reported values.

[0034] Figure 9 is long-term stability of n- / iso-butane separation performance of Ml membrane prepared in Example 1.

[0035] Figure 10 is SEM of MFI seed prepared in Example 2.

[0036] Figure 11 is SEM of MFI seed monolayer prepared in Example 2.

[0037] Figure 12 is (a) SEM and (b) XRD of M2 membrane prepared in Example 2.

[0038] Figure 13 is SEM of M3 membrane prepared in Example 3.

[0039] Figure 14 is SEM of M4 membrane prepared in Example 4.

[0040] Figure 15 is SEM of M5 membrane prepared in Example 5.

[0041] Figure 16 is an SEM image of M6 membrane prepared in Example 6.

[0042] Figure 17 is an SEM image of M7 membrane prepared in Example 7.

[0043] Figure 18 is an SEM image of M8 membrane prepared in Example 8.

[0044] Figure 19 is an SEM image of M9 membrane prepared in Comparative Example 1.

[0045] Figure 20 is an SEM image of M10 membrane prepared in Comparative Example 2.

[0046] Figure 21 is an SEM image of M11 membrane prepared in Comparative Example 3.

[0047] Figure 22 is an SEM image of M12 membrane prepared in Comparative Example 4. DETAILED DESCRIPTION

[0048] The application will be further described in conjunction with specific examples. The following examples will help those skilled in the art to further understand the application, but in no way limit the application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the application. These all belong to the protection scope of the application.

[0049] The gas separation test conditions in this application are all at room temperature. If not specified, the mixed gas feed ratio is 1:1, the permeation side is at atmospheric pressure, the transmembrane pressure difference is 1 bar, and helium is used as the purge gas. The pervaporation test temperature in this application is 75℃, the molar ratio of o- / p-xylene is 1:1, and the transmembrane pressure difference is 1 bar.

[0050] Example 1

[0051] (1) Seed layer preparation: First, MFI nanocrystalline seeds were prepared by the clear solution method (see reference Angew. Chem. Int. Ed. 2021, 60, 7659-7663 for detailed synthesis process), and the prepared seeds were dispersed in deionized water to prepare a seed solution with a mass concentration of 0.6 wt.%. Then, the MFI seeds were uniformly coated on the surface of the porous support by the suspension coating process. During the suspension coating process, 0.3 mL of seed solution was dropped on the surface of the porous alumina sheet. After the suspension coating was completed, the support was placed in a 70℃ oven for drying for 12 h, and then placed in a muffle furnace for calcination at 550℃ for 6 h, to remove the organic template in the seeds and improve the bonding force between the seeds and the support.

[0052] (2) Synthesis mother liquor preparation: Tetraethyl orthosilicate (TEOS) was slowly added into a mixed solution of tetrapropylammonium hydroxide solution (25 wt.%) and deionized water, and the solution was stirred and aged at 90 °C for 12 h to obtain solution A; then ammonium fluoride was uniformly dissolved in deionized water to obtain solution B; and solution B was slowly added into solution A, and the solution was continuously stirred and aged at 90 °C for 12 h to obtain the synthesis mother liquor. The molar composition of the above synthesis mother liquor was 1 TEOS: 0.1 TPAOH: 0.4 NH4F: 22 H2O.

[0053] (3) MFI zeolite membrane prepared by secondary growth method: The support piece coated with the seed layer was placed in the synthesis mother liquor, and after sealing, it was placed in an oven and reacted at 30 °C for 84 days. After the reaction was completed, the membrane piece was taken out, washed with deionized water until neutral, and then dried overnight and placed in a tubular furnace in an ozone atmosphere at 200 °C for 3 h to remove the template, and the heating and cooling rates were both 0.5 °C / min. The MFI zeolite membrane prepared in this process is denoted as M1.

[0054] The scanning electron microscopy characterization of the MFI seed is shown in Figure 1 a, and the morphology of the zeolite is regular hexagonal prism, and the particle size is uniformly distributed at about 250 nm. The XRD result Figure 1 b) shows that the zeolite is a pure MFI crystal type with high crystallinity and no other impurity peaks. The scanning electron microscopy characterization of the seed layer prepared is shown in Figure 2 , and the seeds are continuously and densely arranged on the surface of the support. As can be seen from Figure 3 a, after secondary growth, the surface of the MFI zeolite membrane layer prepared is uniform, the crystals intergrow well, and the membrane layer is dense and continuous. The cross-sectional scanning electron microscopy characterization is shown in Figure 3 b, and the thickness of the MFI zeolite membrane is about 910 nm. The XRD result Figure 4 shows that the membrane material prepared is a pure MFI structure with high crystallinity. Subsequently, the gas separation performance test of the membrane M1 was carried out, as shown in Figure 5 , at normal temperature and pressure (25 °C, 1 bar), the permeation flux gradually decreases with the increase of the size of the single-component gas molecules on the raw material side, and there is an obvious cut-off phenomenon between n-butane and isobutane. The permeation flux of n-butane through the membrane M1 is 3.77 x 10 -7 mol·m -2 ·s -1 ·Pa -1 , and the ideal separation selectivity is 57.6. The feed pressure test of the membrane M1 for n-butane / isobutane mixed components (1:1) was carried out Figure 6 , and the results show that with the increase of the feed pressure, the permeation flux of n-butane and the separation factor both decrease. The feed composition test of the membrane M1 for n-butane / isobutane mixed components (1 bar) was carried out Figure 7The results showed that as the molar concentration of n-butane in the feed gas decreased, both the n-butane permeation flux and the separation factor increased significantly. Notably, when the molar ratio of n-butane to isobutane in the feed was 1:9, the n-butane permeation flux reached 5.16 × 10⁻⁶. -7 mol·m -2 ·s -1 ·Pa -1 The separation factor was 96.7, which exceeds the values ​​reported in all literature. Figure 8 Furthermore, studies have shown that the prepared MFI molecular sieve membrane also exhibits good long-term operational stability at 25℃ and 1 bar, with the n / isobutane separation factor and n-butane permeability remaining essentially unchanged after 24 hours of continuous testing. Figure 9 Finally, a pervaporation test was conducted on membrane M1 using a 1:1 mixture of o- and p-xylene. The test results showed that the p-xylene flow rate of membrane M1 was 350 g·m³. -2 ·h -1 The separation factor reached 37.

[0055] Example 2

[0056] The difference from Example 1 lies in the preparation method of the seed layer in step 1. Specifically, brick-shaped MFI seeds are first prepared using a clear solution method (detailed synthesis process can be found in reference Sci.Adv.2020,6,eaay5993). Then, the seed layer is coated using a hand-coating method, as follows: the porous alumina support surface is pre-modified with a 6.5 wt.% polyvinyl alcohol solution; an appropriate amount of MFI seed powder is poured onto the support surface and hand-coated using fingers wearing nitrile gloves; after calcination in a muffle furnace (550℃, 6h), a highly b-axis oriented MFI seed monolayer is obtained. Meanwhile, the synthesis time for the MFI molecular sieve membrane in step 3 is 56 days, with the remaining steps the same as in Example 1. The MFI molecular sieve membrane prepared in this process is denoted as M2.

[0057] Scanning electron microscopy characterization of MFI seeds, as follows: Figure 10 As shown, the molecular sieve morphology is a regular brick shape with a uniform particle size distribution of approximately 1.0 μm and almost no twinning. The scanning electron microscopy characterization of the prepared seed layer is as follows. Figure 11 As shown, the seed crystals are continuously and densely arranged on the carrier surface, and are highly b-axis oriented. After secondary growth, the voids between the seed crystals are completely filled, forming a continuous and dense film material on the carrier, with almost no twinning on the surface. Figure 12 a). XRD patterns show ( Figure 12b), only (0k0) diffraction peaks exist in the whole XRD diffraction angle range, which indicates that the MFI zeolite membrane is highly b-axis oriented. The membrane M2 is tested by n- / iso-butane mixed components (1:1) at normal temperature and pressure, and the results show that the permeation flux of n-butane can reach 3.1×10 - 7 mol·m -2 ·s -1 ·Pa -1 , and the separation factor is 42. The membrane M2 is tested by o / p-xylene mixed components (1:1) by pervaporation, and the results show that the p-xylene flow rate of the membrane M2 is 420 g·m -2 ·h -1 , and the separation factor reaches 43.

[0058] Example 3

[0059] The difference from Example 1 is that the temperature for secondary growth in step 3 is 90℃, and the time is 12h, and the other steps are the same as Example 1, and the MFI zeolite membrane prepared in the process is recorded as M3. The scanning electron microscope characterization of M3 is shown in Figure 13 , the membrane layer surface is continuous and dense, and the intergrowth is good. The membrane M3 is tested by n- / iso-butane mixed components (1:1) at normal temperature and pressure, and the results show that the permeation flux of n-butane can reach 2.4×10 -7 mol·m -2 ·s -1 ·Pa -1 , and the separation factor is 36.

[0060] Example 4

[0061] The difference from Example 1 is that the stirring aging temperature before and after the addition of ammonium fluoride solution in step 2 is 50℃, and the other steps are the same as Example 1, and the MFI zeolite membrane prepared in the process is recorded as M4. The scanning electron microscope characterization of M4 is shown in Figure 14 , the grain size of the membrane layer surface is reduced, and the membrane layer is continuous and dense and has good intergrowth.

[0062] Example 5

[0063] The difference from Example 1 is that the molar ratio of deionized water to silicon source in step 2 is H2O / SiO2=100, and the other steps are the same as Example 1, and the MFI zeolite membrane prepared in the process is recorded as M5. The scanning electron microscope characterization of M5 is shown in Figure 15 , the grain size of the membrane layer surface is significantly reduced, and the membrane layer still maintains good intergrowth.

[0064] Example 6

[0065] The difference from Example 1 is that the molar ratio of ammonium fluoride to silicon source in Step 2 is NH4F / SiO2=1.3. The remaining steps are the same as Example 1, and the MFI molecular sieve membrane prepared in the process is recorded as M6. The scanning electron microscope characterization of M6 is shown in Figure 16 The grain size on the surface of the membrane layer is large, and the membrane layer surface grows well.

[0066] Example 7

[0067] The difference from Example 1 is that the temperature of the secondary growth in Step 3 is 50°C, and the time is 50 days. The remaining steps are the same as Example 1, and the MFI molecular sieve membrane prepared in the process is recorded as M7. The scanning electron microscope characterization of M7 is shown in Figure 17 The surface of the membrane still maintains good intergrowth.

[0068] Example 8

[0069] The difference from Example 1 is that aluminum chloride is additionally added during the preparation of solution A in Step 2, and the molar ratio of aluminum chloride to tetraethyl orthosilicate is Al2O3 / SiO2=0.02. The remaining steps are the same as Example 1, and the MFI molecular sieve membrane prepared in the process is recorded as M8. The scanning electron microscope characterization of M8 is shown in Figure 18 The surface of the membrane maintains good intergrowth.

[0070] Comparative Example 1

[0071] The difference from Example 1 is that the molar ratio of ammonium fluoride to silicon source in Step 2 is NH4F / SiO2=0. The remaining steps are the same as Example 1, and the MFI molecular sieve membrane prepared in the process is recorded as M9. The scanning electron microscope characterization of M9 is shown in Figure 19 The seed size only slightly increases, and the intergrowth of the membrane surface is poor.

[0072] Comparative Example 2

[0073] The difference from Example 1 is that the mineralizer in Step 2 is NH4Cl. The remaining steps are the same as Example 1, and the MFI molecular sieve membrane prepared in the process is recorded as M10. The scanning electron microscope characterization of M10 is shown in Figure 20 The seed size almost has no obvious change, and the intergrowth of the membrane surface is very poor.

[0074] Comparative Example 3

[0075] The difference from Example 1 is that the mineralizer in Step 2 is NaF. The remaining steps are the same as Example 1, and the MFI molecular sieve membrane prepared in the process is recorded as M11. The scanning electron microscope characterization of M11 is shown in Figure 21 There are still a large number of gaps between the seeds that are not filled, and the intergrowth of the membrane surface is poor.

[0076] Comparative Example 4

[0077] The difference from Example 1 is that the stirring aging at 90°C for 12h is not carried out before the addition of the ammonium fluoride solution in Step 2, and the rest of the steps are the same as Example 1. The MFI zeolite membrane prepared in this process is denoted as M12. The scanning electron microscope characterization of M12 is shown in Figure 2. Figure 22 As shown, the crystal seed size has not changed significantly, and the film layer is poorly connected.

[0078] Although preferred embodiments of the application have been described, those skilled in the art will be able to make additional modifications and variations to the described embodiments without departing from the spirit and scope of the application. Accordingly, the appended claims are intended to encompass all such modifications and variations as falling within the scope of the application.

[0079] Obviously, various modifications and changes can be made to the present application by those skilled in the art without departing from the spirit and scope of the present application. Thus, it is intended that the present application encompass all such modifications and changes as fall within the scope of the appended claims and their equivalents.

Claims

1. A method for preparing MFI molecular sieve membranes at low temperature, characterized in that: Includes the following steps: S1 uniformly coats MFI seed crystals onto the surface of a porous carrier to form a dense and continuous seed crystal layer, which is then dried and calcined to solidify the seed crystal layer. S2 dissolves the silicon source and organic template agent in deionized water, stirs and ages at 50-120℃ to obtain solution A, dissolves ammonium fluoride in deionized water to obtain solution B, slowly adds solution B dropwise to solution A and continues stirring and aging to obtain synthesis mother liquor; S3 involves a low-temperature hydrothermal reaction between the seed layer obtained in S1 and the synthesis mother liquor obtained in S2 at 30–90 °C. S4 involves washing, drying, and calcining the membrane material obtained in S3 to remove the organic template agent, thus obtaining the MFI molecular sieve membrane.

2. The method for preparing MFI molecular sieve membranes at low temperature as described in claim 1, characterized in that: In step S2, the molar ratio of ammonium fluoride to silicon source is NH4F / SiO2 = 0.2 to 2.

0.

3. The method for preparing MFI molecular sieve membranes at low temperature as described in claim 1, characterized in that: The seed crystals mentioned in step S1 are MFI molecular sieves with a particle size of 20 nm to 2 μm.

4. The method for preparing MFI molecular sieve membranes at low temperature as described in claim 1, characterized in that: The silicon source mentioned in step S2 is one or more of methyl orthosilicate, ethyl orthosilicate, water glass, silica sol, and silica aerogel; the molar ratio of deionized water to silicon source is H2O / SiO2 = 8 to 100.

5. The method for preparing MFI molecular sieve membranes at low temperature as described in claim 1, characterized in that: The organic template agent mentioned in step S2 is one or more of tetrapropylammonium bromide, tetrapropylammonium hydroxide solution, tetraethylammonium hydroxide solution and methyltributylammonium hydroxide solution, and the molar ratio of organic template agent to silicon source is organic template agent / SiO2 = 0.05 to 0.

4.

6. The method for preparing MFI molecular sieve membranes at low temperature as described in claim 1, characterized in that: In step S2, the silicon source and organic template agent are dissolved in deionized water and aged for 4–20 hours.

7. The method for preparing MFI molecular sieve membranes at low temperature as described in claim 1, characterized in that: The hydrothermal reaction time in step S3 is 12 hours to 84 days.

8. The method for preparing MFI molecular sieve membranes at low temperature as described in claim 1, characterized in that: Solution A in step S2 further includes an aluminum source or a titanium source. The aluminum source is sodium aluminate, aluminum sulfate, aluminum chloride, or aluminum nitrate. The titanium source is tetrabutyl titanate, titanium chloride, or titanium isopropoxide. The molar ratio of the aluminum source to the silicon source is Al2O3 / SiO2 = 0.001 to 0.05, and the molar ratio of the titanium source to the silicon source is TiO2 / SiO2 = 0.002 to 0.

1.

9. An MFI molecular sieve membrane obtained by the method of claim 1.

10. The application of the MFI molecular sieve membrane of claim 9 in the separation of n / isobutane mixtures and o / p-xylene mixtures.

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