CN114804146A - Preparation method of all-silicon CHA molecular sieve membrane - Google Patents

Preparation method of all-silicon CHA molecular sieve membrane Download PDF

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CN114804146A
CN114804146A CN202210390502.4A CN202210390502A CN114804146A CN 114804146 A CN114804146 A CN 114804146A CN 202210390502 A CN202210390502 A CN 202210390502A CN 114804146 A CN114804146 A CN 114804146A
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silicon
cha molecular
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周荣飞
王娜娜
杜靖
柳波
王斌
邢卫红
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Nanjing Tech University
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B39/00—Compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites; Their preparation; After-treatment, e.g. ion-exchange or dealumination
    • C01B39/02—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof; Direct preparation thereof; Preparation thereof starting from a reaction mixture containing a crystalline zeolite of another type, or from preformed reactants; After-treatment thereof
    • C01B39/46—Other types characterised by their X-ray diffraction pattern and their defined composition
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B37/00—Compounds having molecular sieve properties but not having base-exchange properties
    • C01B37/005—Silicates, i.e. so-called metallosilicalites or metallozeosilites
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    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2004/03—Particle morphology depicted by an image obtained by SEM

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Abstract

The invention relates to a preparation method of an all-silicon CHA molecular sieve membrane, which is used for preparing the all-silicon CHA molecular sieve membrane in a fluorine-free system by utilizing a secondary growth method. The method comprises the following steps: (1) preparing all-silicon CHA molecular sieve seed crystal; (2) pre-coating seed crystals on the porous carrier; (3) and preparing the all-silicon CHA molecular sieve membrane by a secondary growth method. The sol-state fluorine-free secondary growth method adopted by the invention greatly improves the repeatability of film preparation and the environmental friendliness of the process. The all-silicon CHA molecular sieve membrane prepared by the invention has uniform and compact membrane layer and is used for CO 2 /CH 4 And CO 2 /N 2 The mixed gas has good preferential CO permeation 2 And the method can be used for natural gas purification and flue gas carbon capture.

Description

Preparation method of all-silicon CHA molecular sieve membrane
Technical Field
The invention relates to a preparation method of an all-silicon CHA molecular sieve membrane, in particular to a preparation method of an all-silicon CHA molecular sieve membrane in a fluorine-free sol-state synthetic liquid system by utilizing a secondary growth method, belonging to the field of preparation and separation application of molecular sieve membranes.
Background
CO as the main impurity gas in natural gas 2 Mainly, since the acidic nonflammable CO2 gas reduces the calorific value of natural gas and has strong corrosivity to a transmission pipeline in a wet state, the removal of CO2 from natural gas (effective component methane) becomes an important link of natural gas production. In the seventies of the twentieth century, Methyldiethanolamine (MEDA) absorbents were developed by BASF corporation, germany, for the removal of CO2 from natural gas, after which the use of polymeric membranes, such as cellulose acetate membranes, was reported for industrial natural gas separations. The molecular sieve membrane has excellent chemical stability, thermal stability and high mechanical strength, and is an ideal material for removing CO2 from high-pressure natural gas.
Yu et al (Journal of Membrane Science, 2009, 335: 32-36) reported SAPO-34 molecular sieve membranes for CO 2 /CH 4 Separating; at a feed pressure of 4.6 MPa, CO 2 Permeability of 1X 10 -6 mol/(m 2 s Pa)，CO 2 /CH 4 The selectivity was 60. The zeolite molecular sieve membrane of the phosphor-aluminum type has a high hydrophilicity, resulting in poor moisture resistance. The literature (Chemical Engineering Research Design, 2020, 153: 37-48) reports CO of SAPO-34 molecular sieve membranes under a small amount (0.6%) of water vapor 2 The permeation rate is greatly reduced by 60%. Thus, hydrophilic low-silicon molecular sieve membranes present challenges in high-humidity flue gas carbon capture and natural gas purification applications. The all-silicon CHA (also called all-silicon CHA) molecular sieve membrane has a three-dimensional channel structure with eight-membered rings, the channel size is 0.38 nm, and the molecular sieve membrane is in a CO state 2 /CH 4 And CO 2 /N 2 Has excellent sieving effect in gas separation of the mixture. Meanwhile, the membrane is endowed with super-strong hydrophobicity by the all-silicon framework.
The molecular sieve synthesis route in which a fluoride such as hydrofluoric acid is added as a specific mineralizer is called fluoridation, and is also a general method for synthesizing the all-silicon CHA molecular sieve. The prior all-silicon CHA molecular sieve membrane adopts a fluorine route synthesis method. WO2017081841A1 discloses a method for preparing an all-silicon CHA molecular sieve membrane by fluorine route, and H for preparing the membrane 2 /SF 6 Selectivity isGreater than 10. US2014315709a1 discloses a method for the ultrasonic selective deposition of a layer of all-silicon CHA molecular sieve crystals and the preparation of all-silicon CHA molecular sieve membranes under fluorine route. The literature (Separation and Purification Technology, 2018, 197: 116- 2 /CH 4 The separation selectivity is as high as 130. The authors also found that the CO of the membrane under high pressure and humidification 2 Permeation rate and CO 2 /CH 4 The selectivity performance was comparable to that in the dry system, well indicating the moisture resistance and stability of the all-silicon CHA molecular sieve membranes. Literature (Separation and Purification Technology, 2021, 274: 119104) synthesis using silicon hexafluoride as fluorine and silicon source for CO 2 /CH 4 The use of fluoride in isolated all-silicon CHA molecular sieve membranes is still not environmentally friendly.
The synthesis of the all-silicon CHA molecular sieve membrane at present has two problems: (1) all the existing reports prepare pure phase all-silicon CHA crystals and films under fluorine route, and fluoride is not environment-friendly. (2) At lower and narrow n (H) 2 O)/n(SiO 2 ) The all-silicon CHA crystal and the film are prepared in a ratio range (the ratio =4-7), a film layer with controllable thickness and continuous compactness is difficult to form in a semi-solid gel system, and the repeatability of the preparation of the all-silicon CHA molecular sieve film is difficult to guarantee.
How to prepare an all-silicon CHA molecular sieve membrane that is environmentally friendly and has high reproducibility has been a challenge and difficulty of research in the field. The fluorine route causes the synthetic route of the all-silicon CHA molecular sieve membrane not to be green; and the semi-solid gel is difficult to ensure the material fluidity so as to greatly reduce the film synthesis repeatability.
At present, because how components such as silicon-oxygen tetrahedron are assembled into molecular sieve crystals with specific pore channel structures cannot be determined, the nucleation and crystallization mechanisms of the molecular sieve crystals under different reaction conditions are not clear (Xue et al 'molecular sieve and porous material chemistry', 2015, scientific publishing house, page 281), the film forming mechanism of the molecular sieve film is more complex, and the reference of different types of molecular sieves and molecular sieve films is very small.
Disclosure of Invention
The invention adopts a sol-state alkali mineralization route to replace a semisolid gel fluorine route, thereby greatly improving the repeatability of membrane preparation and the environmental friendliness of the process. In order to avoid the phenomenon that the ratio of n (Si)/n (Al) in the film crystal is reduced because aluminum elements in the common pure alumina carrier migrate into the crystal, the invention adopts metal oxide carriers such as zirconia, titania and the like. The invention aims to improve the defects of the prior art and provides a preparation method of an all-silicon CHA molecular sieve membrane. The fluorine-free green all-silicon CHA molecular sieve membrane can be repeatedly prepared by carrying out secondary hydrothermal synthesis on the all-silicon CHA molecular sieve membrane by adopting a sol alkali mineralization route.
The technical scheme of the invention is as follows: the all-silicon CHA molecular sieve membrane is synthesized on a porous carrier by adopting a sol-state alkali mineralization route and utilizing a secondary hydrothermal synthesis method. The method comprises the following specific steps:
(1) preparing all-silicon CHA molecular sieve seed crystal: mixing a silicon source, lithium hydroxide, an organic structure directing agent OSDA and water, stirring and aging for 1-100 h, wherein the molar composition of the formed sol is as follows: SiO 2 2 : OSDA: LiOH: H 2 O =1 (0.1-1) (0.01-0.8) (15-50), pouring the sol into a reaction kettle, adding 0-1 wt% of all-silicon CHA molecular sieve crystals into the reaction kettle, performing hydrothermal synthesis for 1-100 h at 100-250 ℃, centrifuging, washing to neutrality, drying and calcining the molecular sieve crystals obtained by the reaction to obtain the all-silicon CHA molecular sieve seed crystals.
(2) Porous carrier coated seed: dispersing the molecular sieve seed crystals synthesized in the step 1 in an ethanol solution, performing ultrasonic treatment to obtain a seed crystal suspension, sealing two ends of a carrier by using tetrafluoro plugs, coating a layer of seed crystals on the carrier, and performing drying treatment in an oven to obtain a continuous and compact seed crystal layer.
(3) Preparing an all-silicon CHA molecular sieve membrane: mixing a silicon source, lithium hydroxide, OSDA and water, stirring and aging for 1-100 h, wherein the molar composition of the formed sol is as follows: SiO 2 2 : OSDA: LiOH: H 2 O =1 (0.1-1) (0.01-0.8) (15-500), pouring the sol into a reaction kettle, putting the carrier coated with the seed crystal in the step 2 into the sol, performing hydrothermal synthesis for 1-100 h at 100-250 ℃, taking out the membrane tube after the reaction is finished, and then washing the membrane tube with water until the membrane tube is flushedAnd (4) neutralizing, drying and calcining to obtain the all-silicon CHA molecular sieve membrane.
Preferably, the silicon source in steps 1 and 3 is tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, silica sol, water glass or silicon powder.
Preferably, the OSDA in steps 1 and 3 isN-N-N-trimethyladamantyl ammonium hydroxide,N-N-N-trimethyladamantyl ammonium bromide,N-N-N-one or more of trimethyladamantyl ammonium iodide or tetraethylammonium hydroxide.
Preferably, in step 2, the method for coating the seed layer on the porous support is a dip coating method, a vacuum suction method, a wiping method or a spin coating method.
Preferably, in the step 2, the method for coating the seed crystal layer on the porous carrier is a dip coating method, and the concentration of the seed crystal suspension is 0.01-0.5 wt%.
Preferably, in the step 2, the size of the all-silicon CHA molecular sieve seed crystal is 50-1000 nm, and the thickness of the seed crystal layer coated on the porous carrier is 50-1000 nm.
Preferably, the material of the carrier in steps 2 and 3 is one or more of zirconia, titania, mullite, silicon carbide or silica or a composite material thereof.
Preferably, the carrier in steps 2 and 3 is in the form of a sheet, a tube or a hollow fiber, and the average pore size is 50-2000 nm.
Preferably, air, oxygen or ozone is adopted for calcination removal of OSDA in the steps 1 and 3, the calcination temperature is 150-600 ℃, the calcination time is 5-50 h, and the temperature increase and decrease rate is 0.2-2 ℃/min.
Preferably, the heating manner in step 3 is oven heating, oil bath heating or microwave heating.
The invention has the beneficial effects that:
the method for in-situ preparation of the Si-CHA molecular sieve membrane provided by the invention avoids the steps of preparing CHA molecular sieve seed crystals and loading the seed crystals on the surface of a carrier when a secondary growth method is adopted, the influence of the seed crystal quality (crystallinity, particle size and the like) on membrane preparation is not required to be considered, and the membrane synthesis efficiency and repeatability are greatly improved. The invention adopts a fluorine-free route to synthesize the Si-CHA molecular sieve membrane, thereby reducing pollution and improving the separation performance of the membrane. The invention adopts a sol alkali mineralization route to replace a semisolid gel fluorine route, and greatly improves the repeatability of membrane preparation and the environmental friendliness of the process. In order to avoid the phenomenon that the ratio of n (Si)/n (Al) in the film crystal is reduced because aluminum elements in the common pure alumina carrier migrate into the crystal, the invention adopts metal oxide carriers such as zirconia, titania and the like.
Drawings
Fig. 1 is a SEM image at different magnifications of all-silicon CHA molecular sieve seeds prepared in example 1.
Fig. 2 is SEM images of (a) the surface and (b) the cross section of the zirconia support in example 1.
FIG. 3 is SEM images of (a) the surface and (b) the cross section of the support after the seed crystal coating in example 1.
Fig. 4 is an XRD pattern of (a) simulated CHA peaks, (b) zirconia support, (c) all-silicon CHA molecular sieve seeds, and (d) CHA molecular sieve membrane prepared in example 1.
FIG. 5 is a surface SEM image of all-silicon CHA molecular sieve prepared in example 1.
FIG. 6 is a cross-sectional SEM image of the all-silicon CHA molecular sieve prepared in example 1.
Detailed Description
The present invention will be further explained with reference to examples. The following examples are provided only for illustrating the present invention and are not intended to limit the scope of the present invention.
Example 1
The preparation method of the all-silicon CHA molecular sieve membrane comprises the following steps:
(1) preparing all-silicon CHA molecular sieve seed crystal: silicon powder as silicon source andN, N, N-trimethyl-1-adamantyl ammonium hydroxide is OSDA, and silicon powder (fused silica, 99 wt%), lithium hydroxide (LiOH, 99.8 wt%) and,N, N, N-trimethyl-1-adamantyl ammonium hydroxide (TMAdaOH, 25 wt%) and water, stirred and aged for 6 h, the sol formed having a molar composition: SiO 2 2 : OSDA: LiOH: H 2 O=1: 0.And 3: 0.3: 20, pouring the sol into a reaction kettle, adding 0.1 wt% of all-silicon CHA molecular sieve crystals into the reaction kettle, carrying out hydrothermal synthesis for 36 h at 150 ℃, centrifuging, washing to be neutral, drying the molecular sieve crystals obtained by the reaction, removing OSDA under an ozone atmosphere, wherein the calcination temperature is 200 ℃, the calcination time is 48 h, and the heating rate is 0.5 ℃/min, so as to obtain all-silicon CHA molecular sieve seed crystals with the size of 300 nm.
(2) Porous carrier coated seed: dispersing the molecular sieve seed crystals synthesized in the step 1 in an ethanol solution, performing ultrasonic treatment to obtain 0.05 wt% of seed crystal suspension, sealing two ends of a tubular zirconia carrier by using tetrafluoro plugs, coating a layer of seed crystals on a porous carrier, and performing drying treatment in an oven to obtain a continuous and compact seed crystal layer, wherein the thickness of the seed crystal layer is about 400 nm.
(3) Preparing an all-silicon CHA molecular sieve membrane: silicon powder as silicon source andN, N, N-trimethyl-1-adamantyl ammonium hydroxide is OSDA, and silicon powder (fused silica, 99 wt%), lithium hydroxide (LiOH, 99.8 wt%) and,N, N, N-trimethyl-1-adamantyl ammonium hydroxide (TMAdaOH, 25 wt%) and water, stirred and aged for 6 h, the sol formed having a molar composition: SiO 2 2 : OSDA: LiOH: H 2 O =1: 0.3: 0.3: 35, and the support coated with the seed crystal in step 2 was put into the sol. Putting a stainless steel reaction kettle filled with sol and a carrier into an oven, carrying out hydrothermal synthesis for 36 h at 150 ℃, carrying out cleaning, drying and calcining after reaction to obtain the all-silicon CHA molecular sieve membrane, drying at 100 ℃, removing OSDA under the ozone atmosphere, wherein the calcining temperature is 200 ℃, the calcining time is 48 h, the heating rate is 0.5 ℃/min, and the prepared membrane is marked as M1.
Fig. 1 is a SEM image at different magnifications of prepared all-silicon CHA molecular sieve seeds. The synthesized all-silicon CHA crystals were typically cubic with an average particle size of 300 nm.
Fig. 2 is a surface and cross-sectional SEM image of a zirconia support. The average pore diameter of the carrier is 200 nm.
FIG. 3 is an SEM image of the surface and cross-section of a seed coated zirconia support. The seed crystal completely covers the surface of the carrier, and the thickness of the seed crystal layer is about 400 nm.
Fig. 4 is an XRD pattern of simulated CHA peaks, zirconia support, all-silicon CHA molecular sieve seeds, and prepared CHA molecular sieve membrane. Compared with the simulated CHA peak term, both the all-silicon CHA molecular sieve seed crystals and the prepared CHA molecular sieve membrane are pure CHA molecular sieve crystals. The characteristic peak of the carrier contained in the molecular sieve membrane is caused by the fact that the carrier crystal phase is detected by X-rays penetrating through the membrane.
FIG. 5 is a surface SEM image of all-silicon CHA molecular sieve prepared in example 1. It can be seen that the film surface has no obvious defect and the crystal growth is compact.
FIG. 6 is a cross-sectional SEM image of the all-silicon CHA molecular sieve prepared in example 1. It can be seen that the grown film is dense and continuous, the thickness of the film is about 1.8 microns, and the film is thin.
The gas separation performance of a membrane is represented by two parameters, gas permeation rate P and separation coefficient α. The 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 × Δ P) in mol/(m) 2 s Pa); the separation coefficient alpha is used for evaluating the membrane separation efficiency, and alpha = P A /P B 。
The prepared all-silicon CHA molecular sieve membrane M1 is subjected to CO 2 /CH 4 And (5) testing the gas separation performance of the system. The test conditions were: the temperature is 25 ℃, the transmembrane pressure drop is 0.2 MPa, the osmotic side pressure is maintained at 0.103 MPa, the molar composition is 50/50 percent, and the flow rate of feed gas is 4L/min. The gas flow rate on the permeate side was measured with a bubble flow meter, and the gas composition on the permeate side was analyzed with a gas chromatograph (shimadzu, GC 2014). The test results are shown in Table 1.
Preparation of all-silicon CHA molecular sieve membrane M1 for CO 2 /CH 4 And (5) testing the gas separation performance of the system. The test conditions were: the temperature is 25 ℃, the transmembrane pressure drop is 0.2 MPa, the osmotic side pressure is maintained at 0.103 MPa, the molar composition is 50/50 percent, and the flow rate of feed gas is 4L/min. The gas flow rate on the permeate side was measured with a bubble flow meter, and the gas composition on the permeate side was analyzed with a gas chromatograph (shimadzu, GC 2014). The test results are shown in Table 1.
Preparation of all-silicon CHA molecular sieve membrane M1 for CO 2 /N 2 And (5) testing the gas separation performance of the system. The test conditions were the same as in example 1. CO2 2 The permeation rate was 6.3X 10 -7 mol/(m 2 s Pa) and CO 2 /N 2 The selectivity was 24.
Example 2
The procedure was the same as in example 1, except that in steps 1 and 3, the silicon source was silica sol and the OSDA wasN, N, N-trimethyl-1-adamantylammonium bromide, the sol molar composition being: SiO 2 2 : OSDA: LiOH: H 2 O =1: 0.1: 0.1: 15, the synthesis temperature is 120 ℃, the synthesis time is 96 h, the used carrier is a tubular titanium oxide carrier, and the average pore diameter is 50 nm. The film produced was designated M2.
Preparation of all-silicon CHA molecular sieve membrane M2 for CO 2 /CH 4 And (5) testing the gas separation performance of the system. The test conditions were the same as in example 1, and the test results are shown in Table 1.
Example 3
The procedure was the same as in example 1, except that in steps 1 and 3, the silicon source was tetraethyl orthosilicate and the OSDA was tetraethyl orthosilicateN, N, N-trimethyl-1-adamantylammonium hydroxide and tetraethylammonium hydroxide in a molar ratio of 1: 1, the sol molar composition is: SiO 2 2 : OSDA: LiOH: H 2 O =1: 0.5: 0.5: 50, and the used carrier is a hollow fibrous silica/mullite composite carrier having an average pore diameter of 1000 nm. The resulting film was labeled M3.
Preparation of all-silicon CHA molecular sieve membrane M3 for CO 2 /CH 4 And (5) testing the gas separation performance of the system. The test conditions were the same as in example 1, and the test results are shown in Table 1.
Example 4
The preparation process is the same as example 1, except that in steps 1 and 3, the sol aging time is 96 h, the reaction temperature is 230 ℃, the reaction time is 5 h, the used carrier is a flaky zirconia carrier, the average pore diameter is 500 nm, the OSDA is removed under the oxygen atmosphere, the calcination temperature is 450 ℃, the calcination time is 6 h, and the temperature rise rate is 2 ℃/min. The resulting film was labeled M4.
The prepared all-silicon CHA molecular sieve membrane M4 is subjected to CO 2 /CH 4 And (5) testing the gas separation performance of the system. The test conditions were the same as in example 1, andthe results are shown in Table 1.
Example 5
The preparation process is the same as example 1, except that in steps 1 and 3, the sol aging time is 1 h, the reaction temperature is 180 ℃, the reaction time is 36 h, the OSDA is removed under the oxygen atmosphere, the calcination temperature is 550 ℃, the calcination time is 6 h, and the temperature rise rate is 1 ℃/min. The resulting film was labeled M5.
Preparation of all-silicon CHA molecular sieve membrane M5 for CO 2 /CH 4 And (5) testing the gas separation performance of the system. The test conditions were the same as in example 1, and the test results are shown in Table 1.
Example 6
The procedure was the same as in example 1, except that no seed crystal was added in step 1, and the average particle size of the synthesized crystals (as seed crystals for film preparation) was about 1000 nm; in the step 2, the seed crystal is coated by adopting a vacuum suction method, the suction time is 30 s, the concentration of the seed crystal liquid is 0.5 wt%, and the thickness of the seed crystal layer is 1000 nm. The resulting film was labeled M6.
Preparation of all-silicon CHA molecular sieve membrane M6 for CO 2 /CH 4 And (5) testing the gas separation performance of the system. The test conditions were the same as in example 1, and the test results are shown in Table 1.
Example 7
The procedure was the same as in example 1 except that 1 wt% of seed crystal was added in step 1 and the average particle size of the synthesized crystals (as seed crystals for film formation) was about 100 nm; step 2, coating seed crystal by adopting a vacuum suction method, wherein the suction time is 60 s, the concentration of seed crystal liquid is 0.02 wt%, and the thickness of the seed crystal layer is 100 nm; the molar composition of the sol in the step 3 is SiO 2 : OSDA: LiOH: H 2 O =1: 1: 0.8: 400. The resulting film was labeled M7.
Preparation of all-silicon CHA molecular sieve membrane M7 for CO 2 /CH 4 And (5) testing the gas separation performance of the system. The test conditions were the same as in example 1, and the test results are shown in Table 1.
Example 8
The preparation process was the same as in example 1, except that in step 3, the sol had a molar composition of 1SiO 2 : 1OSDA: 0.8LiOH: 400H 2 O, microwave heating is adopted, the reaction temperature is 170 ℃, and the reaction is carried outThe reaction time is 1 h. The resulting film was labeled M8.
Preparation of all-silicon CHA molecular sieve membrane M8 for CO 2 /CH 4 And (4) testing the gas separation performance of the system. The test conditions were the same as in example 1, and the test results are shown in Table 1.
Comparative example 1 preparation of all-silica CHA molecular sieve membranes with a fluorochemical gel System
(1) Preparation of Si-CHA seed crystal: silicon powder (fused silica, 99 wt%) and N-N-N-trimethyl-1-adamantyl ammonium hydroxide (TMADAOH, 25 wt%) were mixed with deionized water, stirred well at room temperature until completely dissolved, then Si-CHA molecular sieve was added thereto, the mixture was heated at 60 ℃ and stirred well until dry powder, and hydrofluoric acid (HF, 40 wt%) was added thereto until the sol became neutral. Heating to evaporate water to the required water content, wherein the molar composition of the synthesized sol is as follows: SiO 2 2 : TMAdaF: H 2 O =1: 0.8: 6.5. And (2) putting the sol into a stainless steel reaction kettle, carrying out hydrothermal synthesis for 72 h at the temperature of 150 ℃, taking out after the reaction is finished, centrifuging, washing to be neutral, drying and calcining a product obtained by the reaction to obtain Si-CHA molecular sieve seed crystals, wherein the size of the seed crystals is about 200-300 nm.
(2) Porous carrier coated seed: dispersing the seed crystals synthesized in the step 1 in an ethanol solution, obtaining 0.05 wt% of seed crystal suspension through ultrasound, sealing two ends of a tubular porous zirconia carrier by using tetrafluoro plugs, coating a layer of seed crystals on the tubular porous carrier (zirconia/alumina composite carrier with the average pore diameter of 100 nm) through a dip-coating method, and drying in an oven to obtain a continuous and compact seed crystal layer.
(3) Preparation of Si-CHA molecular sieve membrane: the sol preparation is the same as step 1, except that the molar composition of the synthetic sol: SiO 2 2 : TMAdaF: H 2 O =1: 0.5: 5.5; putting the carrier coated with the seed crystal into a stainless steel reaction kettle filled with the sol, performing hydrothermal synthesis at 150 ℃ for 36 hours, and cleaning, drying and calcining after reaction to obtain a Si-CHA molecular sieve membrane; drying at 100 deg.C, removing structure directing agent under ozone atmosphere, calcining at 200 deg.C for 48 h, and heating at 0.2 deg.C/min. The film produced was designated M9.
The prepared Si-CHA molecular sieve membrane M9 is subjected to CO 2 /CH 4 And (5) testing the gas separation performance. The test methods and conditions were in accordance with example 1. The test results are shown in Table 1.
TABLE 1 example and comparative example to CO 2 /CH 4 Separation performance of mixed gas
Figure 745724DEST_PATH_IMAGE002

Claims (10)

1. A preparation method of an all-silicon CHA molecular sieve membrane is characterized in that the all-silicon CHA molecular sieve membrane is prepared in a fluorine-free system by a secondary growth method; the method comprises the following steps:
(1) preparing all-silicon CHA molecular sieve seed crystal: mixing a silicon source, lithium hydroxide, an organic structure directing agent OSDA and water, stirring and aging for 1-100 h, wherein the molar composition of the formed sol is as follows: SiO 2 2 : OSDA: LiOH: H 2 O =1, (0.1-1), (0.01-0.8), (15-50), pouring the sol into a reaction kettle, adding 0-1 wt% of all-silicon CHA molecular sieve crystals into the reaction kettle, performing hydrothermal synthesis for 1-100 h at 100-250 ℃, centrifuging, washing to neutrality, drying and calcining the molecular sieve crystals obtained by the reaction to obtain all-silicon CHA molecular sieve seed crystals;
(2) porous carrier coated seed: dispersing the molecular sieve seed crystals synthesized in the step 1 in an ethanol solution, obtaining a seed crystal suspension through ultrasound, sealing two ends of a carrier by using tetrafluoro plugs, coating a layer of seed crystals on the carrier, and obtaining a continuous and compact seed crystal layer after drying treatment of an oven;
(3) preparing an all-silicon CHA molecular sieve membrane: mixing a silicon source, lithium hydroxide, OSDA and water, stirring and aging for 1-100 h, wherein the molar composition of the formed sol is as follows: SiO 2 2 : OSDA: LiOH: H 2 O =1, (0.1-1), (0.01-0.8), (15-500), pouring the sol into a reaction kettle, putting the carrier coated with the seed crystal in the step 2 into the sol, performing hydrothermal synthesis for 1-100 h at 100-250 ℃, taking out a membrane tube after the reaction is finished, washing the membrane tube with water to be neutral, drying and calcining to obtain the all-silicon CHA molecular sieve membrane.
2. The method of claim 1, wherein the silicon source in steps 1 and 3 is tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, silica sol, water glass, or silica powder.
3. The method of claim 1, wherein the OSDA in steps 1 and 3 is OSDAN-N-N-trimethyladamantyl ammonium hydroxide,N-N-N-trimethyladamantyl ammonium bromide,N-N-N-one or more of trimethyladamantyl ammonium iodide or tetraethylammonium hydroxide.
4. The method of claim 1, wherein the step 2 of applying the seed layer to the porous support is dip coating, vacuum pumping, wiping or spin coating.
5. The method of claim 1, wherein the step 2, the step of applying the seed layer on the porous support is a dip coating method, and the seed suspension concentration is 0.01-0.5 wt%.
6. The method of claim 1, wherein in step 2, the size of the all-silicon CHA molecular sieve seed crystal is 50-1000 nm, and the thickness of the seed crystal layer coated on the porous carrier is 50-1000 nm.
7. The method of claim 1, wherein the support material in steps 2 and 3 is one or more of zirconia, titania, mullite, silicon carbide, or silica, or a composite thereof.
8. The method of claim 1, wherein the support in steps 2 and 3 is in the form of a sheet, a tube or a hollow fiber, and has an average pore size of 50-2000 nm.
9. The method of claim 1, wherein the calcination in steps 1 and 3 is carried out with air, oxygen or ozone, the calcination temperature is 150-600 ℃, the calcination time is 5-50 h, and the temperature increase/decrease rate is 0.2-2 ℃/min.
10. The method of claim 1, wherein the heating in step 3 is oven heating, oil bath heating or microwave heating.
CN202210390502.4A 2022-04-14 2022-04-14 Preparation method of all-silicon CHA molecular sieve membrane Pending CN114804146A (en)

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CN104289115A (en) * 2014-08-25 2015-01-21 南京工业大学 Preparation method of high-silicon CHA type SSZ-13 molecular sieve membrane
CN109867294A (en) * 2019-03-19 2019-06-11 南开大学 Cupric CHA type zeolite, its manufacturing method and purposes
CN110683559A (en) * 2019-08-22 2020-01-14 上海工程技术大学 Green synthesis method of ultrathin SSZ-13 molecular sieve membrane
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