Preparation method of MFI molecular sieve membrane for carbon capture

Abstract

The invention discloses a preparation method of an MFI molecular sieve membrane for carbon capture, which specifically comprises the following steps: firstly, preparing an MFI molecular sieve seed crystal, and preparing into a seed crystal suspension; loading an MFI molecular sieve seed crystal layer on the surface of the porous carrier of which the surface is modified with the gas-phase SiO2 layer by adopting a dip-coating method; and introducing a W element to the surface of the porous carrier loaded with the MFI molecular sieve seed crystal layer by adopting a dry gel conversion method, a hydrothermal synthesis method or a super-dilute solution preparation method, and calcining to prepare the W-doped MFI molecular sieve membrane. The metal element W is introduced into the MFI molecular sieve membrane, so that the adsorption performance on CO2 is better, and the advantage of separating a CO2 mixture in an adsorption-diffusion mechanism is more obvious. Meanwhile, the introduction of the W element also eliminates a hydrophilic group Si-OH on the surface of the membrane, so that the hydrophobicity of the membrane is improved, and the W-MFI molecular sieve membrane can still have relatively high separation selectivity and stability on a CO2 mixture even in the presence of water vapor.

Description

Technical Field

[0001] The invention relates to a method for preparing an MFI molecular sieve membrane for carbon capture, and belongs to the technical field of molecular sieve membrane material preparation and gas separation. Background Art

[0002] As we all know, the greenhouse effect is caused by excessive emissions of greenhouse gases, and CO2 accounts for about 77% of global greenhouse gases [Journal of Materials Chemistry A, 2015, 3(23):12500-6]. Therefore, CO2 is one of the main factors leading to climate change. Because of its large proportion in human social life, it has attracted widespread attention from the scientific community at home and abroad. The Paris Agreement stipulates that the global average temperature rise should be controlled within 2°C compared with pre-industrial times, and actively strive to control the global average temperature rise within 1.5°C [Progress in Climate Change Research, 2016, 12(1):61-67].

[0003] At present, the separation and capture processes of CO2 mainly include cryogenic distillation, absorption, adsorption separation and membrane separation. Among them, membrane separation [Journal of Membranes Science, 2008, 307 (1): 88-95] is a new low-energy separation technology with advantages such as low investment cost, small footprint and easy amplification, so membrane separation technology is more and more widely used. Gas separation membrane has the characteristics of energy saving, high efficiency and environmental friendliness, and can play a vital role in the separation of typical industrial small molecule gases (CO2 / N2, etc.).

[0004] At present, a variety of membranes have been developed for the separation of CO2. Among them, zeolite molecular sieve membranes have a regular pore structure, better thermal stability, chemical stability and structural stability [Chem Soc Rev, 2015, 44 (20): 7128-54]. In addition, zeolite molecular sieve membranes can be used under high temperature and high pressure, and can be operated in harsh chemical environments, and are expected to be used for separation applications through molecular sieving and adsorption-diffusion mechanisms. At present, the main common zeolite molecular sieves are MFI type, CHA type, DD3R type, LTA type, FAU type zeolite molecular sieves, mordenite, etc. Among them, MFI type zeolite molecular sieve has become an important zeolite membrane material due to its unique pore structure. The basic structure of MFI molecular sieve is composed of 8 five-membered rings and has D2d symmetry. These unit structures are connected by sharing one side to form a five-silicon chain parallel to the c-axis, and then further linked between the mesh layers to form a three-dimensional structure. MFI molecular sieve has two groups of intersecting pores: one group is a ten-membered ring pore parallel to the a-axis direction, with a pore size of The other group is a ten-membered ring channel parallel to the b-axis, with an aperture size of

[0005] The pore size of MFI molecular sieves is similar to the kinetic diameter of many commonly used gas and solvent molecules. Therefore, MFI molecular sieves and MFI molecular sieve membranes can be used to separate a variety of important substances, such as organic isomers, H2 and CO2, H2 and CH4, and organic matter and water [Microporous and Mesoporous Materials, 2019, 289: 1-7]. CH. Nicolas [Ind. Eng. Chem. Res. 2012, 51, 10451-10461] et al. have studied the separation of water, NO x The influence of light hydrocarbons on the separation of CO2 / N2 by MFI molecular sieve membrane, where the CO2 / N2 separation selectivity is 3. Wang [Journal of Membrane Science 636, 2021, 119565] et al. used a double-layer membrane (inner layer SSZ-13 membrane, outer layer MFI membrane) to study the separation of CO2 / CH4 and CO2 / N2, where the optimal CO2 permeability was 1.5×10 -6 mol·m -2 ·s -1 ·Pa -1 and 1.4×10 -6 mol·m -2 ·s -1 ·Pa -1 , the separation factors are 153 and 22 respectively. MPBernal et al. [AIChE Journal. 2004, 50] prepared MFI molecular sieve membrane (ZSM-5) on alumina and stainless steel tube carriers, and tested its separation performance for CO2 / N2 mixture. The best separation performance was achieved by using Na-ZSM5 membrane, with a separation selectivity of up to 13.7.

[0006] In recent years, people have successfully introduced various metal elements into the framework of MFI molecular sieve membranes to explore new research areas. Pera-Titus [Microporous and Mesoporous Materials, 2010, 133 (1-3): 18-26] et al. synthesized B-MFI molecular sieve membranes. Compared with traditional aluminum-based MFI hollow fiber membranes, B-MFI hollow fiber membranes have improved separation performance for paraxylene. Zhang [Separation and Purification Technology, 2001, 25: 269-74] et al. synthesized crack-free Fe-MFI molecular sieve membranes. The Fe element was incorporated into the molecular sieve framework. The permeability of the synthesized Fe-MFI molecular sieve membrane H2 was 3.0×10 -6 mol·m-2 ·s -1 ·Pa -1 , the separation factor of H2 / C3H8 is 25.8.

[0007] Based on this, how to further improve the CO2 / N2 separation performance by introducing metal elements is still a problem that needs to be tackled. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing an MFI molecular sieve membrane for carbon capture. Compared with the all-silicon MFI molecular sieve membrane, the W-MFI molecular sieve membrane has better adsorption performance for CO2 due to the introduction of the metal element W into its skeleton, so the advantage of separating CO2 mixtures by adsorption-diffusion mechanism is more obvious. At the same time, the introduction of the W element also eliminates the hydrophilic group Si-OH on the membrane surface, thereby increasing the hydrophobicity of the membrane, so that even in the presence of water vapor, the W-MFI molecular sieve membrane can still have a high separation selectivity and stability for the CO2 mixture.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A method for preparing an MFI molecular sieve membrane for carbon capture comprises the following steps:

[0011] S1, preparing MFI molecular sieve seed crystals and configuring them into a seed crystal suspension; using an immersion and pulling method to load the MFI molecular sieve seed crystal layer on the surface of a porous carrier modified with a gas-phase SiO2 layer;

[0012] S2. The W element is introduced onto the surface of the porous carrier loaded with the MFI molecular sieve seed layer by using a dry gel conversion method, a hydrothermal synthesis method or an ultra-dilute solution preparation method, followed by calcination to obtain a W-doped MFI molecular sieve membrane.

[0013] Preferably, in step S1, the preparation method of MFI molecular sieve seed crystals is:

[0014] According to the molar ratio of H2O:TPAOH:SiO2:C2H5OH in the synthesis solution of (10-200):(0.1-0.5):(0.5-1.5):(2-6), water, tetrapropylammonium hydroxide and tetraethyl orthosilicate are mixed, stirred and aged for 1-5 hours, and then hydrothermally synthesized at 100-200°C for 1-72 hours;

[0015] After the reaction is completed, the product is cooled, centrifuged, washed, dried, and then calcined at 500-750°C for 5-8h.

[0016] Preferably, in step S1, the concentration of the seed suspension is 0.2-2wt%; and the porous carrier is hollow fiber Al2O3.

[0017] Preferably, in step S1, the operation time of the immersion pulling method is 5-60 seconds, and after completion, the immersion pulling method is dried at 120-160°C.

[0018] Preferably, before the impregnation and pulling method is performed, a step of sintering the porous carrier with a gas-phase SiO2 layer on the surface is performed, and the sintering conditions are: 450-700°C, 5-20h.

[0019] Preferably, in step S2, the specific method for preparing the W-doped MFI molecular sieve membrane by the dry gel conversion method is:

[0020] Mix H2O, template, silicon source and tungsten source in a molar ratio of (30-80):(0.1-0.3):(0.5-1.5):(0.02-0.07), stir and age for 2-5 hours to obtain a synthetic solution;

[0021] The porous carrier loaded with the MFI molecular sieve seed layer is placed in the synthesis liquid for 0.5-3 minutes, and then dried at 120-160°C for 0.5-2 hours; then placed in a reaction kettle containing 0.5-3g of water, dried at 160-200°C for 20-25 hours, quenched with cold water, and the membrane is taken out, washed with water and dried;

[0022] The membrane is then placed in an atmosphere of air, oxygen or ozone and calcined at 200-260° C. for 40-60 hours; wherein the heating rate is 0.5-3° C. / min.

[0023] Preferably, in step S2, the specific method for preparing the W-doped MFI molecular sieve membrane by hydrothermal synthesis is:

[0024] Mix H2O, template, silicon source and tungsten source in a molar ratio of (100-250):(0.1-0.3):(0.5-1.5):(0.04-0.09), stir and age for 4-7 hours to obtain a synthetic solution;

[0025] The porous carrier loaded with the MFI molecular sieve seed layer is placed in the synthesis solution, and then reacted at 120-160°C for 40-60h, quenched with cold water, and the membrane is taken out, washed with water and dried;

[0026] The membrane is calcined at 200-260°C for 40-60h in an ozone atmosphere, wherein the heating rate is 0.5-3°C / min.

[0027] Preferably, in step S2, the specific method for preparing the W-doped MFI molecular sieve membrane by the ultra-dilute solution preparation method is:

[0028] Mix H2O, template, silicon source and tungsten source in a molar ratio of (1000-2500):(0.1-0.3):(0.5-1.5):(0.02-0.07), stir and age for 4-7 hours to obtain a synthetic solution;

[0029] The porous carrier loaded with the MFI molecular sieve seed layer is placed in the synthesis solution, and then reacted at 120-160°C for 40-60h, quenched with cold water, and the membrane is taken out, washed with water and dried;

[0030] The membrane is calcined at 200-260°C for 40-60h in an ozone atmosphere, wherein the heating rate is 0.5-3°C / min.

[0031] Preferably, the template is tetrapropylammonium hydroxide; the silicon source is at least one of tetraethyl orthosilicate, gas-phase SiO2, and silica sol; and the tungsten source is at least one of sodium tungstate dihydrate and ammonium tungstate.

[0032] Application of the MFI molecular sieve membrane for carbon capture prepared by any of the above methods in CO2 / N2 separation.

[0033] The beneficial effects of the present invention are:

[0034] The prepared W-doped MFI molecular sieve membranes all conform to the crystal form of MFI molecular sieve, have good crystallinity, and good cross-growth between crystals. However, the membranes prepared by the dry gel conversion method are thinner and can significantly improve the gas permeability. At the same time, the introduction of the W element can enhance the adsorption of CO2 by the membrane on the one hand, and on the other hand, the introduction of W eliminates the hydrophilic group Si-OH on the membrane surface and increases the hydrophobicity of the membrane, so that even in the presence of water vapor, the W-MFI molecular sieve membrane can still have high separation selectivity and stability for CO2 mixtures. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 XRD patterns of the molecular sieve membranes prepared in Example 1 and Comparative Example 1;

[0036] Figure 2 XRD diagrams of the molecular sieve membranes prepared in Example 2 and Comparative Example 2;

[0037] Figure 3 XRD patterns of the molecular sieve membranes prepared in Example 3 and Comparative Example 3;

[0038] Figure 4 The SEM images of the molecular sieve membranes prepared in Example 1 and Comparative Example 1;

[0039] Figure 5 The SEM images of the molecular sieve membranes prepared in Example 2 and Comparative Example 2;

[0040] Figure 6 The SEM images of the molecular sieve membranes prepared in Example 3 and Comparative Example 3;

[0041] Figure 7 It is the N2 adsorption-desorption isotherm diagram of W-MFI molecular sieve and Si-MFI molecular sieve;

[0042] Figure 8 The surface water contact angle diagrams of the molecular sieve membranes prepared in Example 1 and Comparative Example 1;

[0043] Fig. 9 is the adsorption isotherm of CO2 on W-MFI molecular sieve at 273K and 298K;

[0044] Fig.10 It is the adsorption isotherm of CO2 of Si-MFI molecular sieve at 273K and 298K;

[0045] Fig.11 is the adsorption isotherm of W-MFI molecular sieve to N2 at 273K and 298K;

[0046] Fig.12 It is the adsorption isotherm of Si-MFI molecular sieve to N2 at 273K and 298K;

[0047] Fig.13 This is a CO2 / N2 / H2O stability test graph of the molecular sieve membranes prepared in Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0048] The present application prepares a film synthesis liquid containing tungsten on the surface of the SiO2-modified Al2O3 carrier as an induction seed, and then coats the film synthesis liquid containing tungsten on the surface of the coated carrier. The film synthesis liquid is then dried, loaded into an autoclave, water is added to the bottom of the autoclave, and high-temperature crystallization is performed to obtain a W-MFI molecular sieve membrane.

[0049] The present invention is described in detail below in conjunction with the accompanying drawings and examples. In the following examples and comparative examples, TPAOH is tetrapropylammonium hydroxide, TEOS is tetraethyl orthosilicate, and C2H5OH is ethanol.

[0050] Example 1

[0051] The dry gel conversion method is used to prepare the MFI molecular sieve membrane. The specific operation is as follows:

[0052] (1) Preparation of MFI molecular sieve seed crystals:

[0053] In-situ hydrothermal preparation of MFI molecular sieves was used as induction seeds, and the molar ratio of the synthetic liquid was H2O:TPAOH:SiO2:

[0054] C2H5OH=19.2:0.2:1:4. First, weigh deionized water and place it in a polytetrafluoroethylene bottle, then add tetrapropylammonium hydroxide and tetraethyl orthosilicate in sequence, and stir and age at room temperature for 4 hours. Pour the resulting synthetic solution into a reactor and place it in a 150℃ oven for hydrothermal synthesis for 2 days. After the reaction is completed, cool to room temperature, take out the molecular sieve, wash it by centrifugation until it is neutral, and then place it in an oven for drying, and finally calcine it at 550℃ for 6 hours to remove the organic template.

[0055] (2) Preparation of W-MFI molecular sieve seed crystals:

[0056] The preparation steps are the same as step (1), except that Na2WO4·2H2O needs to be added to the synthesis liquid, and the final synthesis liquid molar ratio is H2O:TPAOH:SiO2:C2H5OH:Na2WO4·2H2O=19.2:0.2:1:4:0.04.

[0057] (3) Preparation of seed layer:

[0058] A hollow fiber Al2O3 (outer diameter 4.06 mm; inner diameter 1.20 mm; porosity 45%; pore size 0.368 μm) with a surface modified with a gas-phase SiO2 layer (manual rubbing method, particle size 300 nm) was used as a carrier, and the carrier was calcined at 550°C for 10 h to sinter SiO2 on the carrier, washed with deionized water, and dried in an oven overnight. The seed crystals prepared in step (1) were prepared into a 0.5 wt.% seed crystal suspension, and then the carrier was placed in the seed crystal suspension for 30 s by an immersion pulling method, and finally placed in a 140°C oven for drying for use.

[0059] (4) Preparation of W-MFI molecular sieve membrane:

[0060] Deionized water, TPAOH, TEOS, and Na2WO4·2H2O were prepared in a molar ratio of 60:0.12:1:0.04, and the prepared membrane synthesis solution was stirred and aged at room temperature for 4 hours. The carrier coated with seed crystals in step (2) was placed in the membrane synthesis solution for 1 minute to coat the surface of the carrier with a layer of membrane synthesis gel, and then placed in a 140°C oven for 1 hour. After drying, it was placed in a reactor containing 1.5g of water, and the reactor was placed in a 180°C oven for 1 day. After the reaction was completed, the reactor was quenched with cold water, the membrane was taken, washed with water, and dried for use. Then the membrane was calcined in an ozone atmosphere to remove the template agent, the calcination temperature was 230°C, the calcination time was 2 days, and the heating rate was 1°C / min to obtain a W-MFI molecular sieve membrane.

[0061] Comparative Example 1

[0062] Step (1) and step (2) are the same as step (1) and step (3) in Example 1.

[0063] Step (3): Preparation of Si-MFI molecular sieve membrane:

[0064] The preparation steps are basically the same as step (4) of Example 1, except that Na2WO4·2H2O is not added to the membrane synthesis solution, and the prepared membrane is an all-silicon MFI molecular sieve membrane.

[0065] Example 2

[0066] The conventional hydrothermal method is used to prepare the MFI molecular sieve membrane. The specific operation is as follows:

[0067] Step (1) and step (2) are the same as step (1) and step (3) in Example 1.

[0068] Step (3): Preparation of W-MFI molecular sieve membrane:

[0069] First, deionized water, TPAOH, TEOS, and Na2WO4·2H2O were prepared in a molar ratio of 180:0.12:1:0.06. The prepared membrane synthesis solution was stirred and aged at room temperature for 6 hours. After the solution was clarified, it was poured into a reactor, and a carrier loaded with a seed layer was placed. The reactor was then placed in a 130°C oven for 2 days. After the reaction was completed, the reactor was quenched with cold water, the membrane was taken, washed with water, and dried for use. The membrane was calcined in an ozone atmosphere to remove the template agent. The calcination temperature was 230°C, the calcination time was 2 days, and the heating rate was 1°C / min to obtain a W-MFI molecular sieve membrane.

[0070] Comparative Example 2

[0071] Step (1) and step (2) are the same as step (1) and step (3) in Example 1.

[0072] Step (3): Preparation of Si-MFI molecular sieve membrane:

[0073] The preparation steps are basically the same as step (3) of Example 2, except that Na2WO4·2H2O is not added to the membrane synthesis solution, and the prepared membrane is an all-silicon MFI molecular sieve membrane.

[0074] Example 3

[0075] The MFI molecular sieve membrane is prepared from an ultra-dilute solution. The specific operation is as follows:

[0076] Step (1) and step (2) are the same as step (1) and step (3) in Example 1.

[0077] Step (3): Preparation of W-MFI molecular sieve membrane:

[0078] First, deionized water, TPAOH, TEOS, and Na2WO4·2H2O were prepared in a molar ratio of 1500:0.12:1:0.4. The prepared membrane synthesis solution was stirred and aged at room temperature for 6 hours. After the solution was clarified, it was poured into a reactor, and a carrier loaded with a seed layer was placed. The reactor was then placed in a 140°C oven for 2 days. After the reaction was completed, the reactor was quenched with cold water, the membrane was taken, washed with water, and dried for use. The membrane was calcined in an ozone atmosphere to remove the template agent. The calcination temperature was 230°C, the calcination time was 2 days, and the heating rate was 1°C / min to obtain a W-MFI molecular sieve membrane.

[0079] Comparative Example 3

[0080] Step (1) and step (2) are the same as step (1) and step (3) in Example 1.

[0081] Step (3): Preparation of Si-MFI molecular sieve membrane:

[0082] The preparation steps are basically the same as step (3) of Example 3, except that Na2WO4·2H2O is not added to the membrane synthesis solution, and the prepared membrane is an all-silicon MFI molecular sieve membrane.

[0083] The XRD patterns of the molecular sieve membranes prepared in Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3 are shown respectively. Figure 1 , Figure 2 and Figure 3 As shown, the membranes prepared by the three methods all conform to the crystal form of the MFI molecular sieve. The surface and cross-sectional SEM images of the molecular sieve membranes prepared in Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3 are shown respectively. Figure 4 , Figure 5 and Figure 6 As shown in the figure, it can be seen that the molecular sieve membranes prepared by the three methods provided in Examples 1-3 have good crystallinity and good intergrowth between crystals, but the membrane prepared by the dry gel conversion method is thinner.

[0084] N2 adsorption-desorption isotherm ( Figure 7 ) showed that the BET surface area and micropore volume (377.02 m 2 / g and 0.17m 3 / g) is lower than the BET surface area and micropore volume of the Si-MFI molecular sieve membrane prepared in Comparative Example 1 (501.45 m 2 / g and 0.21m 3 / g), which indicates that the introduction of W into the framework of MFI molecular sieve membrane will reduce the pore size of the membrane.

[0085] Surface water contact angle ( Figure 8) shows that the water contact angle of the W-MFI molecular sieve membrane prepared in Example 1 is greater than the water contact angle of the Si-MFI molecular sieve membrane prepared in Comparative Example 1, which indicates that the introduction of W into the skeleton of the MFI molecular sieve membrane will improve the hydrophobicity of the membrane.

[0086] The gas separation performance of the membrane is expressed by two parameters: gas permeation rate P and separation coefficient a. Gas permeation rate P represents the total amount of gas passing through a unit area of ​​the membrane per unit time and unit pressure, P = N / (A×△P), and the unit is mol·m -2 ·s -1 ·Pa -1 ; The separation coefficient a is used to evaluate the membrane separation efficiency, a = P A / P B .

[0087] The W-MFI and Si-MFI molecular sieve membranes prepared in the examples and comparative examples were tested for CO2 / N2 gas separation performance. The test conditions were: temperature 25°C, permeate end pressure maintained at 0.1MPa, feed gas composition 60:60mL / min, and feed gas total flow rate 170mL / min. The gas flow rate on the permeate side was measured with a soap bubble flowmeter; the gas composition on the permeate side was analyzed with a gas chromatograph; the test results are shown in Table 1.

[0088] Table 1 Gas separation performance test results

[0089]

[0090] It can be seen from Table 1 that, compared with the Si-MFI molecular sieve membrane, when the W-MFI molecular sieve membrane prepared in the embodiment and the comparative example is used for CO2 / N2 separation, the molecular sieve membrane prepared in the embodiment has better CO2 / N2 separation performance. And the CO2 / N2 separation factor of the W-MFI molecular sieve membrane prepared in Example 1 is as high as 38, which is better than the membrane performance prepared by other methods.

[0091] According to the Langmuir equation, the single component adsorption data obtained at different temperatures were fitted ( Fig. 9 , 10 , 11, 12), and then the adsorption heat data were obtained. The fitting related data are shown in Table 2.

[0092] Table 2 Adsorption heat fitting data

[0093]

[0094] From the data in Table 2, it can be seen that the introduction of W can increase the adsorption capacity of the membrane for CO2. Furthermore, from the CO2 / N2 / H2O stability test results ( Fig.13) It can be seen that even in the presence of water vapor, the W-MFI molecular sieve membrane can still have high separation selectivity and stability for CO2 mixtures.

[0095] The above is only a preferred implementation of the patent of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the patent of the present invention. These improvements and modifications should also be regarded as the scope of protection of the patent of the present invention.

Claims

1. A method for preparing an MFI molecular sieve membrane for carbon capture, characterized in that: The steps include: S1, preparing MFI molecular sieve seed crystals and configuring them into a seed crystal suspension; using an immersion and pulling method to load the MFI molecular sieve seed crystal layer on the surface of a porous carrier modified with a gas-phase SiO2 layer; S2. The W element is introduced onto the surface of the porous carrier loaded with the MFI molecular sieve seed layer by using a dry gel conversion method, a hydrothermal synthesis method or an ultra-dilute solution preparation method, followed by calcination to obtain a W-doped MFI molecular sieve membrane.

2. The method for preparing the MFI molecular sieve membrane for carbon capture according to claim 1, characterized in that: In step S1, the preparation method of MFI molecular sieve seed crystals is: According to the molar ratio of H2O:TPAOH:SiO2:C2H5OH in the synthesis solution of (10-200):(0.1-0.5):(0.5-1.5):(2-6), water, tetrapropylammonium hydroxide and tetraethyl orthosilicate are mixed, stirred and aged for 1-5 hours, and then hydrothermally synthesized at 100-200°C for 1-72 hours; After the reaction is completed, the product is cooled, centrifuged, washed, dried, and then calcined at 500-750°C for 5-8 hours.

3. The method for preparing the MFI molecular sieve membrane for carbon capture according to claim 1, characterized in that: In step S1, the concentration of the seed suspension is 0.2-2wt%; the porous carrier is hollow fiber Al2O3.

4. The method for preparing the MFI molecular sieve membrane for carbon capture according to claim 1, characterized in that: In step S1, the operation time of the immersion pulling method is 5-60 seconds, and after completion, the mixture is dried at 120-160°C.

5. The method for preparing the MFI molecular sieve membrane for carbon capture according to claim 1, characterized in that: Before the impregnation and pulling method is operated, a step of sintering the porous carrier with a gas-phase SiO2 layer on the surface is also carried out. The sintering conditions are: 450-700°C, 5-20h.

6. The method for preparing the MFI molecular sieve membrane for carbon capture according to claim 1, characterized in that: In step S2, the specific method for preparing the W-doped MFI molecular sieve membrane by the dry gel conversion method is: Mix H2O, template, silicon source and tungsten source in a molar ratio of (30-80):(0.1-0.3):(0.5-1.5):(0.02-0.07), stir and age for 2-5 hours to obtain a synthetic solution; The porous carrier loaded with the MFI molecular sieve seed layer is placed in the synthesis liquid for 0.5-3 minutes, and then dried at 120-160°C for 0.5-2 hours; then placed in a reaction kettle containing 0.5-3g of water, dried at 160-200°C for 20-25 hours, quenched with cold water, and the membrane is taken out, washed with water and dried; The membrane is then placed in an atmosphere of air, oxygen or ozone and calcined at 200-260° C. for 40-60 hours; wherein the heating rate is 0.5-3° C. / min.

7. The method for preparing the MFI molecular sieve membrane for carbon capture according to claim 1, characterized in that: In step S2, the specific method for preparing the W-doped MFI molecular sieve membrane by hydrothermal synthesis is: Mix H2O, template, silicon source and tungsten source in a molar ratio of (100-250):(0.1-0.3):(0.5-1.5):(0.04-0.09), stir and age for 4-7 hours to obtain a synthetic solution; The porous carrier loaded with the MFI molecular sieve seed layer is placed in the synthesis solution, and then reacted at 120-160°C for 40-60h, quenched with cold water, and the membrane is taken out, washed with water and dried; The membrane is calcined at 200-260°C for 40-60h in an ozone atmosphere, wherein the heating rate is 0.5-3°C / min.

8. The method for preparing the MFI molecular sieve membrane for carbon capture according to claim 1, characterized in that: In step S2, the specific method for preparing the W-doped MFI molecular sieve membrane by the ultra-dilute solution preparation method is: Mix H2O, template, silicon source and tungsten source in a molar ratio of (1000-2500):(0.1-0.3):(0.5-1.5):(0.02-0.07), stir and age for 4-7 hours to obtain a synthetic solution; The porous carrier loaded with the MFI molecular sieve seed layer is placed in the synthesis solution, and then reacted at 120-160°C for 40-60h, quenched with cold water, and the membrane is taken out, washed with water and dried; The membrane is calcined at 200-260°C for 40-60h in an ozone atmosphere, wherein the heating rate is 0.5-3°C / min.

9. The method for preparing the MFI molecular sieve membrane for carbon capture according to any one of claims 6, 7 and 8, characterized in that: The template agent is tetrapropylammonium hydroxide; the silicon source is at least one of tetraethyl orthosilicate, gas phase SiO2 and silica sol; and the tungsten source is at least one of sodium tungstate dihydrate and ammonium tungstate.

10. Use of the MFI molecular sieve membrane for carbon capture prepared by the method according to any one of claims 1 to 8 in CO2 / N2 separation.

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