Mfi-type molecular sieve membrane, controllable preparation method and application thereof

Abstract

The application discloses an MFI type molecular sieve membrane and a controllable preparation method and application thereof, relates to the technical field of inorganic membrane material preparation, and realizes accurate control of membrane pore size by controlling ozone calcination conditions to adjust the residual amount of organic templates in the membrane pores; with the prolongation of calcination time, the organic templates in the pores are gradually oxidized and removed, leading to the change of the membrane pore size; the preparation steps comprise seed reaction gel preparation, MFI type molecular sieve seed preparation, support seed preparation, preliminary MFI type molecular sieve membrane preparation, and MFI type molecular sieve membrane preparation. The MFI type molecular sieve membrane prepared by the application has excellent performance in the separation of small-size molecules and large-size molecules, can be used for the separation of hydrogen / isobutane, methane / isobutane, n-butane / isobutane and other systems, the preparation process is simpler, the separation effect of small-size molecules and large-size molecules is higher, and thus the separation requirements under different conditions can be met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic membrane material preparation, in particular to a controllable preparation method of MFI type molecular sieve membrane, MFI type molecular sieve membrane obtained by the preparation method, and application of the MFI type molecular sieve membrane in separation of hydrogen and isobutane, methane and isobutane, and n-butane and isobutane. BACKGROUND

[0002] Separation processes are indispensable unit operations in many industries. Compared with traditional separation techniques such as rectification, adsorption and evaporation, membrane separation has the advantages of low energy consumption, high efficiency, and small footprint. Membrane separation technology has gradually become a replacement for traditional separation units. Zeolite molecular sieve membranes have uniform pore size, excellent separation performance and good chemical stability, and are considered to be good candidates for separating related mixtures. Among them, MFI type zeolite molecular sieve membranes have received extensive attention and have been used to separate various molecular mixtures, such as n / iso-butane and p / m-xylene systems based on molecular sieving mechanism. The preparation process of zeolite molecular sieve membranes usually needs to go through 2 steps: hydrothermal synthesis of membranes and removal of organic template agents in membrane pores. For a specific zeolite molecular sieve membrane, the pore size of the membrane is fixed. In order to obtain excellent separation performance, it is usually necessary to modify and control the pore size of the membrane.

[0003] Common methods for regulating the pore structure of zeolite molecular sieve membranes include chemical vapor deposition and ion exchange. Chemical vapor deposition effectively reduces the pore size of the molecular sieve membrane by depositing amorphous substances (such as SiO2, TiO2) on the zeolite channels / orifices, thereby improving the separation selectivity of the membrane. For example, Langmuir, 2009, 25.9: 4848-4852 The H2 / CO2 selectivity of the MFI molecular sieve membrane modified by vapor deposition method is significantly increased, while the unmodified membrane only shows Knudsen selectivity, however, in practical application, it is difficult to ensure the uniformity of the species on the surface and in the pores of the deposited membrane, and the process is complex, requiring high equipment requirements; while ion exchange adjusts the pore size and adsorption properties of the molecular sieve membrane by exchanging the ions in the molecular sieve framework with different metal ions (such as Li + , K + , Ag + and Ca 2+ ), the adjustment of the pore size of the ion exchange membrane may be limited by the types of available metal ions, resulting in a limited adjustment range, and certain metal ions may migrate or flow out under use conditions, affecting the long-term stability of the membrane.

[0004] In addition, encapsulating or wrapping metal species in the pores of molecular sieves can also reduce the pore size of the molecular sieves, for example, Science, 2021, 373 (6552), 315-320 prepared a self-assembled Fe-containing mordenite, which narrowed the channels of the molecular sieve due to the presence of Fe species, and showed good adsorption separation selectivity in the study, however, the method of encapsulating metal species in the molecular sieve is mainly used for adsorption, and its application in membrane separation is still under exploration.

[0005] In addition, a Chinese invention patent (grant announcement number CN114804139B) discloses a preparation method of a multi-channel MFI type molecular sieve membrane, the process is as follows: (1) preparing short columnar MFI type molecular sieve seeds; (2) coating a layer of uniform and dense MFI type molecular sieve seed layer on the inner wall of the multi-channel carrier; (3) then preparing a continuous and dense MFI type molecular sieve membrane on the inner surface of each channel of the multi-channel carrier by a one-time hydrothermal synthesis method. The molecular sieve membrane prepared by using the multi-channel carrier has a high surface area to volume ratio, can greatly improve the packing density of the membrane, can reduce the volume of the membrane module, and the membrane has good separation performance in a n-butane / isobutane (n-C4H 10 / i-C4H 10 ) mixed system. The innovation of the invention is mainly to provide a multi-channel MFI type molecular sieve membrane for n-butane / isobutane separation, and no innovation is proposed for the preparation of the microporous structure and pore size of the MFI type molecular sieve membrane; in addition, the large pore structure (b axis and a axis) inherent to the MFI molecular sieve cannot separate small molecule size gases, and the controllable preparation of the molecular sieve membrane has very little reference value.

[0006] In view of the deficiencies of the prior art, the present application provides an MFI type zeolite molecular sieve membrane which can be used for separating different molecular size gases, a controllable preparation method and application thereof, by controlling the removal degree of the template agent, adjusting the residual amount of the organic template in the membrane pores to effectively reduce the inherent large pores of the MFI molecular sieve to adjust the membrane pore size, and obtain excellent gas separation performance. SUMMARY

[0007] (I) Technical problems to be solved

[0008] In view of the deficiencies of the prior art, the present application provides an MFI type zeolite molecular sieve membrane which can be used for separating different molecular size gases, a controllable preparation method and application thereof, by controlling the removal degree of the template agent, adjusting the residual amount of the organic template in the membrane pores to effectively reduce the inherent large pores of the MFI molecular sieve to adjust the membrane pore size, and obtain excellent gas separation performance.

[0009] (II) Technical solutions

[0010] To achieve the above object, the present application provides the following technical solutions.

[0011] A controllable preparation method of MFI type molecular sieve membrane, which effectively adjusts the membrane pore size by controlling the removal degree of the template agent and adjusting the residual amount of the organic template agent in the membrane hole, and obtains excellent separation performance, and the specific steps are as follows:

[0012] S1, preparing seed reaction gel: preparing raw materials according to the molar ratio of silicon source: organic template agent SDA: alkali source (OH -1 ): distilled water = 10: (1.6-2.8): (0.44-1.3): (100-150), respectively adding to the stirring tank to mix uniformly to form a solution, continuously stirring and aging at room temperature for 6-48h, and preparing the first reaction gel;

[0013] In this step, during the stirring and aging process, the synthesis reaction at room temperature can be prolonged to increase the crystal nucleus density and promote the crystal growth during synthesis;

[0014] S2, preparing MFI type molecular sieve seed: pouring the prepared first reaction gel into a reaction kettle, hydrothermal synthesis at 80-120℃ for 48-96h, after the reaction is completed, the reaction product is centrifuged, washed to neutral pH, and freeze-dried in a vacuum environment to prepare high-dispersion MFI molecular sieve seed;

[0015] S3, preparing seed-coated support: the prepared MFI molecular sieve seed is added to ethanol or aqueous solution for ultrasonic dispersion to prepare a seed solution with a concentration of 0.06-2%, the seed solution is coated on the porous support, and the seed layer is formed by drying at 30-80℃ for 2h to prepare the seed-coated support;

[0016] S4, preparing MFI type molecular sieve membrane: silicon source, organic template agent SDA and distilled water are added to the stirring tank according to the molar ratio of 25: (2-8): (1000-1500) to mix uniformly to form a solution, continuously stirring at room temperature for 6-24h to prepare the second reaction gel, the second reaction gel and the seed-coated support prepared in step S3 are put into a reaction kettle, and synthesized at 75-140℃ for 24-85h, after the reaction is completed, the temperature is cooled to room temperature to obtain MFI type molecular sieve membrane, and the membrane is taken out, washed and dried;

[0017] S5, adjusting the pore size of MFI type molecular sieve membrane: the MFI type molecular sieve membrane in step S4 is placed in a flowing gas atmosphere furnace for calcination to remove the organic template agent in the membrane layer, and the MFI type molecular sieve membrane with high separation performance is prepared.

[0018] Preferably, the silicon source in steps S1 and S4 is one of, but not limited to, tetraethyl orthosilicate, ammonium fluorosilicate, silica sol and fumed silica.

[0019] Preferably, the organic template SDA in the step S1 and step S4 is one of but not limited to tetrapropylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium bromide.

[0020] Preferably, the alkali source in the step S1 is one of but not limited to sodium hydroxide and potassium hydroxide.

[0021] Preferably, the porous support in the step S3 is a ceramic support made of one of but not limited to silicon carbide, alumina and mullite material, and the shape is one of but not limited to tube, sheet and disc.

[0022] Preferably, the seed coating method in the step S3 is one of but not limited to dip coating and vacuum suction coating, wherein the suction pressure of the vacuum suction coating is negative pressure of 5-20kPa, and the suction time is 10-60s.

[0023] Preferably, in the step S4, the membrane is taken out and washed for 3-5 times, and dried at 50-100℃ for 2-4h.

[0024] Preferably, in the step S5, the atmosphere of the atmosphere furnace is ozone-containing mixed gas, the ozone concentration is 60-100mg / L, the calcination temperature is 30-250℃, and the calcination time is 6-60h.

[0025] In the ozone-containing mixed gas, in addition to ozone, other components can be nitrogen, oxygen or air. Since the stability of ozone is higher at lower temperature, but the reaction activity is weaker, as the temperature rises, the decomposition speed of ozone increases, more free radicals are generated, and thus the oxidation activity is enhanced; but since the half-life (life) of ozone is shortened, therefore, the calcination time can be extended at lower temperature, and the calcination time can be shortened at higher temperature, and the same effect can be achieved. If the temperature exceeds 250℃, the ozone will decompose instantaneously (1-2s), which will seriously reduce the effect of calcination and oxidation for removing the template.

[0026] Another object of the present application is to provide a MFI type molecular sieve membrane prepared by the controllable preparation method.

[0027] Still another object of the present application is to provide an application of the MFI type molecular sieve membrane prepared by the controllable preparation method, which is used for the separation of small size molecules and large size molecules, including but not limited to hydrogen and isobutane, methane and isobutane, and n-butane and isobutane.

[0028] The sizes of n-butane and isobutane molecules are different, the size of n-butane molecule is 0.47nm, and the size of isobutane molecule is 0.53nm, and the difference in the size of the molecules is large, so effective separation can be carried out.

[0029] (Three) beneficial effects

[0030] Compared with the prior art, the preparation method has the following beneficial effects:

[0031] (1) The present application effectively adjusts the pore size of the MFI type molecular sieve membrane by controlling the removal degree of the template agent, meets different separation needs, makes the separation performance of the membrane more excellent, and can realize precise separation for specific gas mixtures.

[0032] (2) Compared with the traditional membrane preparation method, the present application adopts a simple and efficient step to realize the pore size regulation of the membrane in the process of removing the organic template agent, thereby reducing the complex requirements for the equipment and the process difficulty, thereby improving the production efficiency of the MFI type molecular sieve membrane, effectively reducing the production cost, and having the characteristics of easy popularization.

[0033] (3) The MFI type molecular sieve membrane of the present application can be widely applied to the separation of small size molecules and large size molecules, such as hydrogen and isobutane, methane and isobutane, n-butane and isobutane, etc., has important industrial application value, and helps to improve the resource utilization rate and reduce the energy consumption. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 SEM characterization diagram of the MFI type molecular sieve seed prepared in Example 1 of the present application.

[0035] Figure 2 XRD diagram of the MFI type molecular sieve seed and the MFI type molecular sieve membrane prepared in Example 1 and Example 2 of the present application.

[0036] Figure 3 SEM characterization diagram of the seed coated support prepared in Example 1 of the present application.

[0037] Figure 4 SEM characterization diagram of the MFI type molecular sieve membrane prepared in Example 1 of the present application.

[0038] Figure 5 SEM characterization diagram of the seed coated support prepared in Example 2 of the present application.

[0039] Figure 6 SEM characterization diagram of the MFI type molecular sieve membrane prepared in Example 2 of the present application.

[0040] Figure 7 ATR-FTIR spectrum of the MFI type molecular sieve and tetrapropylammonium hydroxide under different calcination conditions corresponding to the embodiment of the present application.

[0041] Figure 8The separation results of the MFI type molecular sieve membrane prepared in the application for small size molecules and large size molecules are shown in the chart. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the application will be clearly and completely described in combination with the drawings of the embodiments of the application.

[0043] Embodiment 1

[0044] The controllable preparation method of the MFI type molecular sieve membrane is specifically as follows:

[0045] Step S1, preparing a seed reaction gel: a silica sol, tetrapropylammonium hydroxide, sodium hydroxide and water are added into a stirring tank in a molar ratio of SiO2:SDA:NaOH:H2O=10:2.4:0.87:119, and are uniformly mixed, and the solution is continuously stirred at room temperature for aging for 12 hours, and a first reaction gel is prepared;

[0046] Step S2, preparing MFI molecular sieve seeds: the first reaction gel prepared in step S1 is poured into a reaction kettle, and is hydrothermally synthesized at 100 DEG C for 72 hours, and after the reaction is completed, the reaction product is subjected to centrifugation, washing, and is washed until the pH is neutral, and then is placed in a vacuum freeze dryer, and high-dispersed MFI molecular sieve seeds are prepared;

[0047] Step S3, preparing a seed-coated support: the MFI molecular sieve seeds prepared in step S2 are added into an ethanol or aqueous solution and are ultrasonically dispersed, and a seed solution with a mass concentration of 0.6% is prepared; a seed layer is coated on a porous support (a tubular support structure prepared from an alumina material) by using a vacuum extraction coating method, wherein the coating pressure is-5 kPa, and the coating time is 20 seconds, and then the seed-coated support is dried at 80 DEG C for 2 hours to form a seed layer, and the seed-coated support is prepared;

[0048] Step S4, preliminarily preparing an MFI type molecular sieve membrane: tetraethyl orthosilicate, tetrapropylammonium hydroxide and water are added into a stirring tank in a molar ratio of 25:3:1450, and are uniformly mixed, and the solution is continuously stirred at room temperature for 8 hours, and a second reaction gel is prepared, and the second reaction gel and the seed-coated support prepared in step S3 are placed into a reaction kettle and are synthesized at 90 DEG C for 70 hours, and after the reaction is completed, the reaction kettle is cooled to room temperature, and the membrane is taken out and is washed 4 times, and is dried at 50 DEG C for 4 hours;

[0049] Step S5, regulating the pore size of the MFI type molecular sieve membrane: the MFI type molecular sieve membrane preliminarily prepared in step S4 is placed in a furnace in a flowing gas atmosphere, the calcination temperature is 200 DEG C, the calcination time is 36 hours, and the ozone concentration is 80 mg / L, and by partially removing the organic template agent in the membrane layer, the MFI type molecular sieve membrane M1 with high separation performance is prepared.

[0050] In this embodiment 1, the SEM results of the prepared MFI type molecular sieve seed crystal are shown in the attached Figure 1 Figure 1, the MFI molecular sieve seed crystal has a spherical shape, and its diameter is 40-100 nm; the XRD results of the seed crystal are shown in the attached Figure 2 Figure 2, the prepared MFI type molecular sieve seed crystal is a pure phase MFI; the SEM images of the prepared seed crystal coated support surface and cross section are shown in the attached Figure 3 Figure 3, it can be seen that the seed crystal layer has a high packing density, a small porosity between the seed crystals, and the seed crystal layer is very dense and has a thickness of 1.57 µm.

[0051] The surface and cross section SEM images of the final membrane product, the MFI type molecular sieve membrane M1 prepared in this embodiment 1, are shown in the attached Figure 4 Figure 4, the surface crystals of the membrane interpenetrate each other without large pore defects, the membrane layer is relatively dense and has a thickness of about 1.98 µm (increased by 0.41 um); the XRD spectrum of the MFI type molecular sieve membrane M1 is shown in the attached Figure 2 Figure 5, the diffraction peak of the prepared MFI type molecular sieve membrane M1 is consistent with the standard peak, indicating that the prepared membrane is a pure phase MFI type molecular sieve membrane; the separation experiment results of the prepared MFI type molecular sieve membrane M1 on equimolar n-butane / isobutane mixed gas and other systems at 60℃ are shown in the attached Figure 8 Figure 6.

[0052] Embodiment 2

[0053] Compared with embodiment 1, the preparation conditions in the embodiment 2 of the application are different in that:

[0054] In step S3, the seed crystal layer is coated on the porous support by vacuum extraction coating method, wherein the coating pressure is -15 kPa, and the coating time is 10 s, to obtain a seed crystal coated support.

[0055] In step S4, the synthesis temperature and time of the MFI type molecular sieve membrane are 80℃ and 80 h respectively, to obtain a MFI type molecular sieve membrane M2.

[0056] In the embodiment 2 of the application, the surface and cross section SEM images of the prepared seed crystal coated support are shown in the attached Figure 5 Figure 7, it can be seen that the seed crystal layer has a high packing density, a small porosity between the seed crystals, and the seed crystal layer is dense and has a thickness of 0.86 µm. The surface and cross section SEM images of the MFI type molecular sieve membrane M2 are shown in the attached Figure 6 Figure 8, the surface of the membrane is very smooth, the crystals of the membrane layer interpenetrate each other without large pore defects, the membrane layer is dense and has a thickness of about 1.54 µm; the XRD spectrum of the MFI type molecular sieve membrane M2 is shown in the attached Figure 2 Figure 9, which is a pure phase MFI molecular sieve membrane. The separation experiment results of the prepared membrane M1 on equimolar n-butane / isobutane mixed gas and other systems at 60℃ are shown in the attached Figure 8 Figure 10.

[0057] Example 3

[0058] Compared with Example 1, the preparation conditions in Example 3 of the application are different in that:

[0059] The ozone calcination time in step S5 is 24 h, and the MFI type molecular sieve membrane M3 is prepared.

[0060] The prepared membrane M3 has a membrane layer thickness of about 1.98 µm. The membrane separates equimolar n-butane / isobutane (50 / 50) mixed gas and other systems at 60 ℃, and the experimental results are shown in FIG. 3. Figure 8

[0061] Example 4

[0062] Compared with Example 1, the preparation conditions in Example 4 of the application are different in that:

[0063] The ozone calcination time in step S5 is 48 h, and the MFI type molecular sieve membrane M4 is prepared.

[0064] The prepared membrane M4 has a membrane layer thickness of about 1.98 µm. The membrane separates equimolar n-butane / isobutane (50 / 50) mixed gas and other systems at 60 ℃, and the experimental results are shown in FIG. 4. Figure 8

[0065] Example 5

[0066] Compared with Example 1, the preparation conditions in Example 5 of the application are different in that:

[0067] The ozone calcination time in step S5 is 60 h, and the MFI type molecular sieve membrane M5 is prepared for completely removing the organic template agent in the membrane pores.

[0068] The prepared membrane M5 has a membrane layer thickness of about 1.98 µm. The membrane separates equimolar n-butane / isobutane (50 / 50) mixed gas and other systems at 60 ℃, and the experimental results are shown in FIG. 5. Figure 8

[0069] Example 6

[0070] Compared with Example 1, the preparation conditions in Example 6 of the application are different in that:

[0071] In step S1, the seed crystal preparation reaction gel is prepared by using a first reaction gel prepared according to a molar ratio of SiO2:SDA:NaOH:H2O=10:2.4:0.44:119, and the MFI type molecular sieve membrane M6 is prepared.

[0072] ​​​In this embodiment 6, the diameter of the prepared MFI type molecular sieve seed crystal is 180 nm; the seed layer thickness of the prepared seed crystalized support is 2.65 µm; the prepared membrane layer thickness is about 3 µm (increased by 0.35 um); the prepared membrane M6 separates the equimolar n-butane / isobutane mixed gas and other systems at 60℃, and the separation experimental results are as shown in the following table 6. Figure 8

[0073] Embodiment 7

[0074] Compared with embodiment 1, the preparation conditions in the present embodiment 7 are different in that:

[0075] The seed crystal reaction gel prepared in step S1 is a first reaction gel prepared according to the molar ratio of SiO2:SDA:NaOH:H2O=10:2.4:1.3:119; and the MFI type molecular sieve membrane M7 is prepared.

[0076] In this embodiment 7, the diameter of the prepared MFI type molecular sieve seed crystal is 30 nm; the seed layer thickness of the prepared seed crystalized support is 1.4 µm; the prepared membrane layer thickness is about 2.3 µm (increased by 0.9 um); the prepared membrane M7 separates the equimolar n-butane / isobutane mixed gas and other systems at 60℃, and the separation experimental results are as shown in the following table 7. Figure 8

[0077] Embodiment 8

[0078] Compared with embodiment 1, the preparation conditions in the present embodiment 8 are different in that:

[0079] The synthesis temperature of the membrane in step S4 is 75℃ for 85h; and the MFI type molecular sieve membrane M8 is prepared.

[0080] The prepared MFI type molecular sieve membrane layer thickness is about 1.8 µm; the prepared membrane M8 separates the equimolar n-butane / isobutane mixed gas and other systems at 60℃, and the separation experimental results are as shown in the following table 8. Figure 8

[0081] Embodiment 9

[0082] Compared with embodiment 1, the present embodiment 9 is different in that:

[0083] The synthesis temperature of the membrane in step S4 is 140℃ for 24h; and the MFI type molecular sieve membrane M9 is prepared.

[0084] The prepared MFI type molecular sieve membrane layer thickness is about 2.2 µm; the prepared membrane M9 separates the equimolar n-butane / isobutane mixed gas and other systems at 60℃, and the separation experimental results are as shown in the following table 9.​​​Figure 8 As shown.

[0085] Example 10

[0086] Compared with Example 1, the preparation condition in Example 10 of the application is different in that:

[0087] In step S3, the concentration of the seed solution is 1.03%, and finally the MFI type molecular sieve membrane M10 is prepared.

[0088] The prepared MFI type molecular sieve membrane layer has a thickness of about 4.5 µm; the separation experiment results of the prepared membrane M8 on the equimolar n-butane / isobutane mixed gas and other systems at 60 ℃ are shown in the following table. Figure 8 As shown.

[0089] Example 11

[0090] Compared with Example 1, the preparation condition in Example 10 of the application is different in that:

[0091] In step S4, the concentration of the seed solution is 2%, and finally the MFI type molecular sieve membrane M11 is prepared.

[0092] The prepared MFI type molecular sieve membrane layer has a thickness of about 6.3 µm; the separation experiment results of the prepared membrane M8 on the equimolar n-butane / isobutane mixed gas and other systems at 60 ℃ are shown in the following table. Figure 8 As shown.

[0093] Example 12

[0094] Compared with Example 1, the preparation condition in Example 10 of the application is different in that:

[0095] In step S4, the molar ratio of tetraethyl silicate, tetrapropyl ammonium hydroxide and water is 25:2:1000, and finally the MFI type molecular sieve membrane M12 is prepared.

[0096] The prepared MFI type molecular sieve membrane layer has a thickness of about 1.85 µm; the separation experiment results of the prepared membrane M8 on the equimolar n-butane / isobutane mixed gas and other systems at 60 ℃ are shown in the following table. Figure 8 As shown.

[0097] Example 13

[0098] Compared with Example 1, the preparation condition in Example 10 of the application is different in that:

[0099] In step S4, the molar ratio of tetraethyl silicate, tetrapropyl ammonium hydroxide and water is 25:8:1500, and finally the MFI type molecular sieve membrane M13 is prepared.

[0100] The prepared MFI type molecular sieve membrane layer thickness is about 3.9 µm; the prepared membrane M8 is separated at 60℃ for equimolar n-butane / isobutane mixed gas and other systems, and the separation experiment results are as shown in the following table 1. Figure 8

[0101] Comparative Example 1

[0102] Compared with Example 1, the preparation conditions in Comparative Example 1 are different in that:

[0103] The ozone calcination time in step S5 is 72h, that is, the organic template agent in the membrane hole is completely removed, and the MFI type molecular sieve membrane B1 is prepared.

[0104] The prepared membrane B1 is separated at 60℃ for equimolar n-butane / isobutane (50 / 50) mixed gas and other systems, and the experiment results are as shown in the following table 2. Figure 8

[0105] Comparative Example 2

[0106] Compared with Example 1, the preparation conditions in Comparative Example 2 are different in that:

[0107] The seed preparation reaction gel in step S1 is to prepare a first reaction gel according to the molar ratio of SiO2: SDA: H2O = 10: 2.4: 119, and the MFI type molecular sieve membrane B2 is prepared.

[0108] The diameter of the MFI type molecular sieve seed prepared in Comparative Example 2 is 300nm; the seed layer thickness of the prepared seed coated support is 3.9 µm; the prepared membrane layer thickness is about 4.15 µm (increased by 0.25um); the prepared MFI type molecular sieve membrane B2 shows very high permeation rate at 60℃ for equimolar n-butane / isobutane mixed gas and other systems, but shows Nusselt selectivity, indicating that the membrane layer has many defects and no separation performance, and the separation experiment results are as shown in the following table 3. Figure 7

[0109] It should be particularly pointed out that we cannot list all the examples, and the specific embodiments of the present application are only for illustrative purposes. Among them, the synthesis temperature and synthesis time of the seed prepared in step S2 are 80℃ and 96h, and the synthesis temperature and synthesis time of 120℃ and 48h prepared MFI molecular sieve seed have the same morphology and size range of 40-100nm, and the separation effect is also similar, which is the optimal hydrothermal synthesis condition in the experimental research process.

[0110] The prepared MFI type molecular sieve membrane layer thickness is about 3.9 µm; the prepared membrane M8 is separated at 60℃ for equimolar n-butane / isobutane mixed gas and other systems, and the separation experiment results are as shown in the following table 1. Figure 8 ​​​It can be seen that with the extension of the ozone calcination time, the content of the organic template in the pore of the MFI zeolite molecular sieve gradually decreases, and the organic template is completely removed after 60 h of ozone calcination, i.e. the residual amount of the template in the pore of the MFI molecular sieve can be precisely controlled by regulating the calcination conditions.

[0111] It can be seen from the attached Figure 8 It can be seen from (Examples 1, 6, 7 and Comparative Example 2) that the size of the seed crystal of the MFI molecular sieve decreases with the increase of the alkali concentration, but it also needs to be controlled within an appropriate range, and too low or too high alkali concentration will affect the size of the crystal, and smaller seed crystal has higher activity and can promote the rapid growth of the membrane layer.

[0112] It can be seen from the attached Figure 8 It can be seen from (Examples 1, 3, 4, 5 and Comparative Example 1) that with the extension of the ozone calcination time, the content of the organic template in the pore of the MFI zeolite molecular sieve gradually decreases, resulting in the gradual increase of the pore size. At first, the removal of the template makes the size matching between the pore of the membrane and the n-butane product more ideal, and the molecular size of n-butane is smaller, which is more easily passed through the membrane pore, thereby improving the permeation rate of n-butane and the separation factor of the n- / isobutane mixed gas. However, when the calcination time continues to extend, excessive removal of the template leads to the excessive expansion of the membrane pore, which destroys the size matching. At this time, although the permeation rate of n-butane continues to increase, due to the expansion of the pore size, the selectivity between n-butane and isobutane is reduced, resulting in the decrease of the separation factor. At the same time, by extending the calcination time in the ozone environment, the essence is to control the ozone to generate more free radicals, thereby removing the organic template SDA, and with the increase of the ozone concentration, the oxidation reaction is accelerated, thereby shortening the active oxidation time of the ozone, so the concentration of the ozone has little effect on the performance of the molecular sieve membrane, and is closely related to the calcination time in the ozone environment, so a reasonable concentration of the ozone can be controlled.

[0113] It can be seen from the attached Figure 8 It can be seen from (Examples 1, 10 and 11) that the higher the concentration of the seed crystal solution, the more the number of the seed crystals deposited on the surface of the membrane substrate, and the higher the crystal nucleus density, which is helpful to promote the growth of the crystal of the membrane layer and make the membrane layer thicker, and the n- / isobutane separation factor tends to increase.

[0114] It can be seen from the attached Figure 8 It can be seen from (Examples 1, 2, 7, 8, 9, 10, 11, 12, 13 and Comparative Example 1) that although the MFI molecular sieve membranes with different microstructures (different thicknesses of the membrane layer) are used, excellent separation performance can be obtained by removing the organic template in the pore, and the performance of the MFI molecular sieve membrane obtained is not greatly affected by the different proportions of the organic template SDA, so only the optimal proportion of the organic template SDA is provided in the examples. It can be seen from the attached ​As can be seen, the MFI type molecular sieve membrane prepared by the application has good separation performance for hydrogen / isobutane and methane / isobutane.

[0115] Compared with the deficiencies of the traditional pore structure regulation method of the molecular sieve membrane, the preparation method of the MFI type molecular sieve membrane can be accurately controlled, the preparation process is simpler, the penetration analysis is more efficient, and the separation effect of small size molecules and large size molecules is better.

Claims

1. A method for the controllable preparation of MFI type molecular sieve membranes, characterized in that By controlling the removal degree of the template agent, the residual amount of the organic template agent in the membrane hole is adjusted to effectively adjust the membrane pore size, and excellent separation performance is obtained, and the specific steps are as follows: S1, preparing seed reaction gel: raw materials are prepared according to the molar ratio of silicon source: organic template agent SDA: alkali source: distilled water = 10: (1.6-2.8): (0.44-1.3): (100-150), respectively added to the stirring tank, mixed uniformly to form a solution, continuously stirred at room temperature for 6-48h, and the first reaction gel is prepared; S2, preparing MFI type molecular sieve seed: the prepared first reaction gel is poured into a reaction kettle, hydrothermal synthesis is carried out at 80-120℃ for 48-96h, after the reaction is completed, the reaction product is centrifuged, washed to neutral pH, and freeze-dried in a vacuum environment to prepare high-dispersion MFI molecular sieve seed; S3, preparing seed coated support: the prepared MFI molecular sieve seed is added to ethanol or aqueous solution and ultrasonically dispersed to prepare a seed solution with a concentration of 0.06-2%, the seed solution is coated on a porous support, and the seed layer is formed by drying at 30-80℃ for 2h to prepare a seed coated support; S4, preparing MFI type molecular sieve membrane: silicon source, organic template agent SDA and distilled water are added to the stirring tank according to the molar ratio of 25: (2-8): (1000-1500), mixed uniformly to form a solution, continuously stirred at room temperature for 6-24h, and the second reaction gel is prepared, the second reaction gel and the seed coated support prepared in step S3 are put into a reaction kettle, synthesized at 75-140℃ for 24-85h, cooled to room temperature after the reaction is completed, and the MFI type molecular sieve membrane is obtained, the membrane is taken out, washed and dried; S5, adjusting the pore size of the MFI type molecular sieve membrane: the MFI type molecular sieve membrane in step S4 is placed in a flowing gas atmosphere furnace for calcination to remove the organic template agent in the membrane layer, and a MFI type molecular sieve membrane with high separation performance is prepared.

2. The method for controllable preparation of MFI type molecular sieve membrane according to claim 1, characterized in that, The silicon source in steps S1 and S4 is one of tetraethyl orthosilicate, ammonium fluorosilicate, silica sol and fumed silica.

3. The method for controllable preparation of MFI-type molecular sieve membrane according to claim 1, characterized in that, The organic template agent SDA in steps S1 and S4 is one of tetrapropylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium bromide.

4. The method for controllable preparation of MFI-type molecular sieve membrane according to claim 1, characterized in that, The alkali source in step S1 is one of sodium hydroxide and potassium hydroxide.

5. The method for controllable preparation of MFI-type molecular sieve membrane according to claim 1, characterized in that, The porous support in step S3 is a ceramic support made of one of silicon carbide, alumina and mullite materials, and the shape is tubular, sheet or disc.

6. The method for controllable preparation of MFI-type molecular sieve membrane according to claim 1, characterized in that, The seed coating method in step S3 includes but is not limited to one of dip coating method and vacuum extraction coating method; wherein the extraction pressure of the vacuum extraction coating method is negative pressure of 5-20kPa, and the extraction time is 10-60s.

7. The method for controllable preparation of MFI-type molecular sieve membrane according to claim 1, characterized in that, In step S4, the membrane is taken out, washed 3-5 times, and dried at 50-100℃ for 2-4h.

8. The method for controllable preparation of MFI-type molecular sieve membrane according to claim 1, characterized in that: In step S5, the atmosphere of the atmosphere furnace is a mixed gas containing ozone, the ozone concentration is 60-100mg / L, the calcination temperature is 30-250℃, and the calcination time is 6-60h.

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