Si-CHA molecular sieve membrane as well as preparation method and application thereof

Abstract

The invention relates to a Si-CHA molecular sieve membrane as well as a preparation method and application thereof. The preparation method of the Si-CHA molecular sieve membrane comprises the following steps: coating growth gel on the surface of a support body loaded with Si-CHA seed crystal, and carrying out crystallization reaction to obtain a Si-CHA molecular sieve membrane precursor; the Si-CHA molecular sieve membrane precursor is cleaned, the cleaned Si-CHA molecular sieve membrane precursor is subjected to first drying treatment and first calcination treatment, and the Si-CHA molecular sieve membrane is obtained. According to the preparation method of the Si-CHA molecular sieve membrane, the growth orientation of the Si-CHA molecular sieve can be conveniently controlled, and the continuous and compact molecular sieve membrane layer with few defects can be rapidly and efficiently prepared. According to the Si-CHA molecular sieve membrane prepared by the method, the flux and the selectivity of the molecular sieve membrane are effectively improved, the problem that the selectivity of the surface of a traditional membrane is poor due to impurities is well solved, and the Si-CHA molecular sieve membrane has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve membrane preparation technology, and in particular to Si-CHA molecular sieve membranes, their preparation methods and applications. Background Technology

[0002] Carbon dioxide is the primary cause of global warming. Human-generated carbon dioxide emissions mainly originate from the combustion of fossil fuels. To reduce carbon dioxide levels in the atmosphere and achieve "carbon peaking and carbon neutrality," it is necessary to separate CO2 and N2 from flue gas for utilization or storage (CCUS). Traditional gas separation technologies include absorption, cryogenic distillation, and pressure swing adsorption, but these suffer from high energy consumption and costs. Membrane separation technology, on the other hand, offers advantages such as low operating costs, environmental friendliness, simple equipment and operation, small footprint, and strong adaptability, making it a very promising gas separation technology. Currently, membrane separation shows excellent application prospects in flue gas purification, biogas purification, and CO2 capture.

[0003] Zeolite molecular sieve membranes are inorganic membranes with a unique and regular pore structure and uniform pore size. They also possess good mechanical and thermal stability, making them suitable for gas separation under industrial conditions. Zeolite molecular sieves mainly include aluminosilicate (SAPO-34) and aluminosilicate (low-silica chalcogenide, SSZ-13, and Si-CHA) molecular sieves. Gas separation using zeolite molecular sieve membranes primarily utilizes the sieving effect and preferential adsorption selectivity of the molecular sieve channels. Among them, Si-CHA molecular sieves, with a pore size of 0.38 nm × 0.38 nm, are considered ideal materials for CO2 gas separation due to their suitable pore size and preferential adsorption selectivity.

[0004] Si-CHA molecular sieve membranes are usually prepared by a secondary growth hydrothermal method, but the prepared membranes are usually thick and contain impurities, and the growth orientation cannot be controlled, resulting in low separation efficiency for CO2 / N2. Summary of the Invention

[0005] Therefore, it is necessary to provide Si-CHA molecular sieve membranes that can improve the separation selectivity and permeability of CO2 / N2, their preparation methods, and applications.

[0006] One aspect of the present invention provides a method for preparing a Si-CHA molecular sieve membrane, comprising the following steps: coating the surface of a support loaded with Si-CHA seeds with a growth gel and performing a crystallization reaction to obtain a Si-CHA molecular sieve membrane precursor; the crystallization reaction time is 24 h to 48 h; cleaning the Si-CHA molecular sieve membrane precursor; and subjecting the cleaned Si-CHA molecular sieve membrane precursor to a first drying treatment and a first calcination treatment to obtain a Si-CHA molecular sieve membrane.

[0007] In some embodiments, the support for the Si-CHA seeds is prepared by a method comprising the following steps:

[0008] A seed gel is prepared, wherein the seed gel comprises a first silicon source, a first template agent, a first fluoride, and water;

[0009] The seed gel is subjected to a first crystallization treatment. The product of the first crystallization treatment is washed and then subjected to a second drying treatment and a second calcination treatment to prepare Si-CHA seed crystals.

[0010] The Si-CHA seed crystals are covered on the surface of the support, and a third calcination treatment is performed to prepare a support loaded with Si-CHA seed crystals.

[0011] In some embodiments, the method for preparing Si-CHA molecular sieve membranes satisfies at least one of the following features (1)-(10):

[0012] (1) In the seed gel, the molar ratio of the first silicon source to the first template agent is 1: (0.3-0.8);

[0013] (2) In the seed gel, the molar ratio of the first silicon source to the first fluoride is 1: (0.4-0.5);

[0014] (3) In the seed gel, the molar ratio of the first silicon source to the water is 1: (10-20);

[0015] (4) The first silicon source is selected from any one or more of fumed silica and silica sol;

[0016] (5) The first template agent is selected from any one or more of N,N,N-trimethyladamantane ammonium hydroxide, tetraethylammonium hydroxide, and triethylamine;

[0017] (6) The first fluoride includes any one or more of hydrogen fluoride, ammonium fluoride, and ammonium bifluoride;

[0018] (7) The temperature of the first crystallization treatment is 150℃-170℃, and the time of the first crystallization treatment is 24h-72h;

[0019] (8) The temperature of the second calcination treatment is 500 ℃-550 ℃, and the time of the second calcination treatment is 12h-24h;

[0020] (9) The step of covering the Si-CHA seed crystals onto the surface of the support includes: mixing the seed crystals and a solvent to prepare a seed crystal suspension, wherein the mass concentration of the seed crystals in the seed crystal suspension is 1wt%-2wt%; wherein the solvent is selected from any one or more of ethanol and water; mixing the support with the seed crystal suspension and drying;

[0021] (10) The temperature of the third calcination treatment is 500 ℃-550 ℃, and the time of the third calcination treatment is 12h-24h.

[0022] In some embodiments, the seed crystals obtained after the second calcination treatment are added to the seed crystal gel again for a second crystallization treatment. After the product after the second crystallization treatment is washed, a third drying treatment and a third calcination treatment are performed to obtain Si-CHA seed crystals. Optionally, the average particle size of the Si-CHA seed crystals is 500 nm-700 nm.

[0023] In some embodiments, the growth gel comprises a second silicon source, a second template agent, a second fluoride, and water;

[0024] Optionally, the growth gel includes at least one of the following features (1)-(4):

[0025] (1) The molar ratio of the second silicon source, the second template agent, the second fluoride and water is (1-1.3):(0.5-0.8):(0.5-0.8):(3-4);

[0026] (2) The second silicon source is selected from any one or more of fumed silica and silica sol;

[0027] (3) The second template agent is selected from any one or more of N,N,N-trimethyladamantane ammonium hydroxide, tetraethylammonium hydroxide, and triethylamine;

[0028] (4) The second fluoride is selected from any one or more of the second hydrogen fluoride, ammonium fluoride, and ammonium hydrogen fluoride.

[0029] In some embodiments, the temperature of the crystallization reaction is 150°C-170°C.

[0030] In some embodiments, the method for preparing the Si-CHA molecular sieve membrane includes at least one of the following features (1)-(3):

[0031] (1) The support body includes a ceramic tube;

[0032] (2) The temperature of the first drying treatment is 100 ℃-120 ℃, and the time is 8 h-10 h;

[0033] (3) The temperature of the first calcination treatment is 500 ℃-550 ℃ and the time is 12 h-24 h.

[0034] In a second aspect, this application provides a Si-CHA molecular sieve membrane, which is prepared by any of the above-described methods for preparing Si-CHA molecular sieve membranes.

[0035] In a third aspect, this application provides an application of the Si-CHA molecular sieve membrane as described above in the separation of mixed gases.

[0036] In some embodiments, the above application includes at least one of the following features (1)-(3):

[0037] (1) The mixed gas includes carbon dioxide and nitrogen; optionally, the volume percentage of carbon dioxide in the mixed gas is 10%-20% and the volume percentage of nitrogen is 80%-90%;

[0038] (2) The separation of the mixed gas is carried out at a temperature of 25℃-50℃;

[0039] (3) The pressure of the mixed gas during separation is 1 bar to 3 bar.

[0040] The aforementioned method for preparing Si-CHA molecular sieve membranes involves encapsulating a growth gel on the surface of a support loaded with Si-CHA crystals for crystallization. This facilitates control over the growth orientation of the Si-CHA molecular sieve, enabling rapid and efficient preparation of a continuous and dense molecular sieve membrane layer with fewer defects. Furthermore, encapsulating the growth gel on the surface of the support loaded with Si-CHA crystals reduces the amount of growth gel used, thereby lowering the preparation cost of the Si-CHA molecular sieve membrane. The Si-CHA molecular sieve membrane prepared by this method effectively improves the flux and selectivity of the molecular sieve membrane, effectively solving the problem of poor selectivity caused by impurities on the surface of traditional membranes, and has broad application prospects. Attached Figure Description

[0041] Figure 1 The image shows a scanning electron microscope (5 μm) image of the Si-CHA molecular sieve membrane prepared in Example 1.

[0042] Figure 2 The image shows a scanning electron microscope (SEM) image (20 μm) of the Si-CHA molecular sieve membrane prepared in Example 1. Detailed Implementation

[0043] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0045] Since carbon dioxide and nitrogen have similar kinetic diameters (0.33 nm for carbon dioxide and 0.364 nm for nitrogen), separating them requires high-quality molecular sieve membranes. Typical Si-CHA molecular sieve membranes exhibit poor selectivity for separating carbon dioxide and nitrogen. To address this issue, this application provides at least one Si-CHA molecular sieve membrane, its preparation method, and its applications.

[0046] According to a typical embodiment of this application, a method for preparing a Si-CHA molecular sieve membrane is provided, comprising the following steps: coating the surface of a support loaded with Si-CHA seeds with a growth gel and carrying out a crystallization reaction to obtain a Si-CHA molecular sieve membrane precursor; the crystallization reaction time is 24 h to 48 h; cleaning the Si-CHA molecular sieve membrane precursor; and subjecting the cleaned Si-CHA molecular sieve membrane precursor to a first drying treatment and a first calcination treatment to obtain a Si-CHA molecular sieve membrane.

[0047] The aforementioned method for preparing Si-CHA molecular sieve membranes involves encapsulating a growth gel on the surface of a support loaded with Si-CHA seeds for crystallization. This facilitates control over the growth orientation of the Si-CHA molecular sieve, enabling rapid and efficient preparation of a continuous and dense molecular sieve membrane layer with fewer defects. Encapsulating the growth gel on the support surface also allows for the formation of a thinner growth gel layer, reducing the amount of growth gel required and lowering the preparation cost of the Si-CHA molecular sieve membrane. Furthermore, it enhances the growth competitiveness of the seed layer, leading to preferential growth and splitting to form a dense membrane layer. On the other hand, since the growth gel crystallizes into a pure-phase Si-CHA molecular sieve membrane, the possibility of impurity formation is reduced. Therefore, the Si-CHA molecular sieve membrane prepared by this method effectively improves the flux and selectivity of the molecular sieve membrane, effectively solving the problem of poor selectivity caused by impurities on the surface of traditional membranes, and has broad application prospects.

[0048] In some embodiments, the support for Si-CHA seeds is prepared by a method comprising the following steps: preparing a seed gel, the seed gel comprising a first silicon source, a first template agent, a first fluoride, and water; subjecting the seed gel to a first crystallization treatment, washing the product of the first crystallization treatment, and then subjecting it to a second drying treatment and a second calcination treatment to obtain Si-CHA seeds; covering the surface of the support with the Si-CHA seeds, and subjecting it to a third calcination treatment to obtain the support for Si-CHA seeds. In-situ growth of molecular sieve seeds, after crystallization, is similar to the growth gel, also resulting in a pure-phase Si-CHA molecular sieve, which helps reduce impurities in the molecular sieve membrane and improves the separation efficiency of the obtained Si-CHA molecular sieve membrane for carbon dioxide gas.

[0049] For example, the crystallization reaction time can be 24 h, 26 h, 28 h, 30 h, 32 h, 34 h, 36 h, 38 h, 40 h, 42 h, 44 h, 46 h, 48 h, etc., but is not limited to these.

[0050] In some embodiments, the first silicon source is selected from any one or more of fumed silica and silica sol. In particular, when fumed silica is used as the first silicon source, the prepared Si-CHA molecular sieve membrane exhibits better separation performance for nitrogen and carbon dioxide gases.

[0051] In some embodiments, the first template agent is selected from any one or more of N,N,N-trimethyladamantane ammonium hydroxide, tetraethylammonium hydroxide, and triethylamine.

[0052] Furthermore, in the seed gel, the molar ratio of the first silicon source to the first template agent is 1: (0.3-0.8), and non-limitingly, it can be 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, etc.

[0053] In some embodiments, the first fluoride includes any one or more of hydrogen fluoride, ammonium fluoride, and ammonium bifluoride; further, in the seed gel, the molar ratio of the first silicon source to the first fluoride is 1:(0.4-0.5); non-limitingly, it can be 1:0.4, 1:0.45, 1:0.5, etc.

[0054] Furthermore, in the seed gel, the molar ratio of the first silicon source to water is 1:(10-20); non-limitingly, the molar ratio of the first silicon source to water can be 1:10, 1:12, 1:14, 1:16, 1:18, 1:20, etc.

[0055] In some embodiments, the temperature of the first crystallization treatment is 150℃-170℃, and the time of the first crystallization treatment is 24h-72h, such as 24h, 36h, 48h, 60h, 72h, etc.

[0056] The purpose of the second drying process described above is to remove moisture from the crystallized product after washing. For example, the second drying can be carried out by heating, and the temperature of the second drying can be 100 ℃-120 ℃.

[0057] After drying, the template agent of the crystallized product is removed by calcination. In some embodiments, the temperature of the second calcination treatment is 500 ℃-550 ℃, and the time of the second calcination treatment is 12 h-24 h.

[0058] In some embodiments, to obtain seed crystals with smaller particle sizes, the seed crystals obtained after the second calcination treatment are added to the seed gel again for a second crystallization treatment. The product after the second crystallization treatment is washed, then subjected to a third drying treatment and a third calcination treatment to obtain Si-CHA seed crystals. Through secondary growth crystallization, the seed crystals generated in the first crystallization are split into smaller Si-CHA seed crystals under the action of the second crystallization treatment. Further reducing the size of the Si-CHA seed crystals reduces the particle size of the Si-CHA molecular sieve, which is beneficial for improving the separation selectivity of the membrane for CO2 / N2. Simultaneously, reducing the seed crystal size also allows for better bonding with the support, thereby increasing the membrane's density. This enables the Si-CHA molecular sieve membrane to maintain high separation selectivity and permeability under different nitrogen and carbon dioxide mixed gas concentrations. The process of the second crystallization treatment and the processes for washing, drying, and calcining the product of the second crystallization treatment can refer to the first crystallization treatment process and the second drying and second calcination process described above. Optionally, the average particle size of the Si-CHA seed crystals is 500 nm-700 nm.

[0059] In some embodiments, the step of coating the support surface with Si-CHA seeds includes: mixing the seeds and a solvent to prepare a seed suspension, optionally with a seed concentration of 1wt%-2wt%; optionally, the solvent is selected from any one or more of ethanol and water; mixing the support with the seed suspension and drying. For example, the step of mixing the support with the seed suspension includes: immersing the support in the suspension. To ensure sufficient Si-CHA seeds are loaded on the support, the immersed and dried support can be immersed again in the seed suspension; this immersion and drying process can be repeated multiple times, such as 5-7 times. Optionally, each immersion time can be 30-60 seconds.

[0060] In some embodiments, the support body comprises a ceramic tube; optionally, the support body is an inorganic porous alumina ceramic tube.

[0061] Furthermore, the temperature of the third calcination treatment is 500 ℃-550 ℃, and the time of the third calcination treatment is 12 h-24 h.

[0062] A growth gel was coated onto the surface of a support loaded with Si-CHA seeds, and a crystallization reaction was carried out to prepare a Si-CHA molecular sieve membrane precursor.

[0063] In some embodiments, the method of coating the surface of a support for supporting Si-CHA seeds with a growth gel includes uniformly coating the surface of the support for supporting Si-CHA seeds with a growth gel.

[0064] In some embodiments, the growth gel comprises a second silicon source, a second template agent, a second fluoride, and water; further, the molar ratio of the second silicon source, the second template agent, the second fluoride, and water is (1-1.3):(0.5-0.8):(0.5-0.8):(3-4). The growth gel with this composition is convenient to be coated on the surface of the support on which Si-CHA seeds are loaded, which is beneficial to forming a Si-CHA molecular sieve membrane of suitable thickness, thereby improving the separation effect of the Si-CHA molecular sieve membrane for carbon dioxide and nitrogen. Non-limitingly, the molar ratio of the second silicon source, the second template agent, the second fluoride, and water can be (1-1.3):(0.5-0.8):(0.5-0.8):3, (1-1.3):(0.5-0.8):(0.5-0.8):3.05, (1-1.3):(0.5-0.8):(0.5-0.8):3.1, (1-1.3):(0.5-0.8):(0.5-0.8):3.2, (1-1.3):(0.5-0.8):(0.5-0.8):3.5, (1-1.3):(0.5-0.8):(0.5-0.8):3.8, (1-1.3):(0.5-0.8):(0.5-0.8):4, etc.

[0065] Optionally, when preparing the above-mentioned gel, a pre-prepared gel with a high water content can be prepared first. For example, the molar ratio of the second silicon source, the second template agent, the second fluoride and water can be (1-1.3):(0.5-0.8):(0.5-0.8):(6-8). Then, some water is removed by heating to obtain a growth gel with the above composition.

[0066] Furthermore, the second silicon source is selected from any one or more of fumed silica and silica sol.

[0067] Optionally, the second template agent is selected from any one or more of N,N,N-trimethyladamantane ammonium hydroxide, tetraethylammonium hydroxide, and triethylamine.

[0068] Optionally, the second fluoride is selected from any one or more of hydrogen fluoride, ammonium fluoride, and ammonium bifluoride.

[0069] In some embodiments, the temperature of the crystallization reaction is 150°C-170°C.

[0070] The Si-CHA molecular sieve membrane precursor obtained by the crystallization reaction is cleaned, for example, by rinsing with deionized water. After separating the water, it undergoes a first drying treatment and a first calcination treatment to obtain the Si-CHA molecular sieve membrane.

[0071] In some embodiments, the temperature of the first drying process is 100 ℃-120 ℃, and the time is 8 h-10 h.

[0072] In some embodiments, the temperature of the first calcination treatment is 500 ℃-550 ℃, and the time is 12 h-24 h.

[0073] In some embodiments, the first calcination treatment, the second calcination treatment, and the third calcination treatment described above can each be carried out independently in air, oxygen, or a mixture of both. Optionally, the heating rate during the first calcination treatment, the second calcination treatment, and the third calcination treatment can each be independently 0.5℃ / min-1℃ / min, which is beneficial for further improving the calcination effect.

[0074] In some embodiments, the Si-CHA molecular sieve membrane prepared by the above method has a thickness of 2.5 μm to 3.5 μm and exhibits suitable permeability and good separation effect for carbon dioxide and nitrogen.

[0075] According to another typical embodiment of this application, a Si-CHA molecular sieve membrane is provided, which is prepared by any of the above-described methods for preparing Si-CHA molecular sieve membranes. The Si-CHA molecular sieve membrane prepared by the above methods not only has a lower cost but also effectively improves the flux and selectivity of the molecular sieve membrane, thus effectively solving the problem of poor selectivity caused by impurities on the surface of traditional membranes.

[0076] According to another typical embodiment of this application, an application of the above-described Si-CHA molecular sieve membrane in the separation of mixed gases is provided. The above-described Si-CHA molecular sieve membrane exhibits excellent flux and selectivity for carbon dioxide, and can efficiently separate carbon dioxide and nitrogen.

[0077] In some embodiments, the above-mentioned mixed gas includes carbon dioxide and nitrogen; optionally, the volume percentage of carbon dioxide in the mixed gas is 10%-20%, and the volume percentage of nitrogen is 80%-90%.

[0078] In some embodiments, the gas mixture separation is carried out at a temperature of 25°C to 50°C. Within the above temperature range, the Si-CHA molecular sieve membrane of this application can stably and efficiently separate carbon dioxide.

[0079] In some embodiments, the pressure of the mixed gas during separation is 1 bar to 3 bar. Within this pressure range, the Si-CHA molecular sieve membrane exhibits good selective separation of carbon dioxide and nitrogen. However, when the pressure is too high, the separation selectivity decreases because the Si-CHA molecular sieve membrane's ability to inhibit nitrogen permeation weakens.

[0080] The following examples and comparative examples further illustrate the technical effects that this application can achieve.

[0081] Example 1

[0082] (1) Seed crystal preparation: A gel was prepared by mixing SiO2, 0.6 template agent, 0.6 fluoride, and 6H2O in a molar ratio. An aqueous solution of N,N,N-trimethyl-1-adamantane ammonium hydroxide (TMAdaOH) was added to the fumed silica and stirred until homogeneous. An aqueous solution of hydrofluoric acid was added to the gel and stirred until homogeneous. Excess water was evaporated by heating. The reaction was carried out at 150°C for 48 hours. The template agent was removed by washing and centrifugation, followed by calcination at 550°C for 10 hours. The average size of the prepared primary-grown Si-CHA crystals was 3 μm.

[0083] To obtain Si-CHA seed crystals with smaller particle sizes, we opted for secondary growth-induced preparation. First, the prepared Si-CHA was ground uniformly and then added to a gel with the same proportions as in the primary synthesis for secondary growth, where the mass ratio of the primary-grown Si-CHA crystals to the gel was 0.09:1. The reaction conditions were the same as those used for preparing the primary-grown Si-CHA crystals, resulting in secondary-grown seed crystals with an average size of 4 μm.

[0084] (2) Preparation of seed layer: Tubular α-Al2O3 was selected as the support, with an outer diameter of 12 mm, an inner diameter of 8 mm, and an average pore size of 0.5 μm. First, the tubular α-Al2O3 support was pretreated. The surface of the support was sanded with sandpaper, and the secondary growth seed prepared in step (1) was uniformly coated onto the support by the immersion method. Specifically, the secondary growth Si-CHA molecular sieve prepared in step (1) was prepared into a 1 wt% seed dispersion, the support was immersed in the seed dispersion for 40 s, taken out and placed in an oven to dry, and the immersion was repeated 6 times. The pre-coated seed support was dried at 100 °C for 2 hours. The support was placed in a tube furnace and calcined at 550 °C for 5 hours to obtain the support loaded with Si-CHA seed.

[0085] (3) Preparation of Si-CHA molecular sieve membrane: A gel was prepared by mixing SiO2: 0.5 template agent: 0.5 fluoride: 12H2O in a molar ratio. A TMAdaOH aqueous solution was added to the fumed silica. Hydrofluoric acid aqueous solution was added to the gel and stirred evenly. The mixture was heated until H2O / SiO2 = 3 to form a thick gel.

[0086] The prepared supported Si-CHA seed support was uniformly coated with a thick gel and fixed in a reaction vessel, where it was crystallized at 150°C for 36 hours.

[0087] After the reaction, the molecular sieve membrane was removed and rinsed with deionized water for 10 min, then soaked in pure water for 12 h, and finally dried in an oven at 100 °C. The membrane was then placed in a tube furnace and calcined at 550 °C for 12 h at a heating rate of 1 °C / min to remove the template agent.

[0088] The scanning electron microscope image of the Si-CHA molecular sieve membrane prepared in Example 1 is shown below. Figure 1 and Figure 2 As shown. By Figure 1 and Figure 2 It can be seen that the Si-CHA molecular sieve membrane has a dense surface growth and good crystal structure.

[0089] Example 2

[0090] Steps (1) and (2) are the same as in Example 1.

[0091] The preparation process of step (3) is basically the same as that of step (3) in Example 1. The difference is that the molar ratio of H2O / SiO2 in the final gel that encapsulates the molecular sieve membrane is 2.9.

[0092] Example 3

[0093] Steps (1) and (2) are the same as in Example 1.

[0094] Step (3) is basically the same as step (3) in Example 1, except that the final H2O / SiO2 molar ratio in the gel encapsulating the molecular sieve membrane is 3.1. The resulting molecular sieve membrane is labeled as 3.1-Si-CHA.

[0095] Example 4

[0096] Steps (1) and (3) are the same as in Example 1.

[0097] The preparation process in step (2) is basically the same as that in step (2) of Example 1, except that the seed dispersion is prepared using the Si-CHA molecular sieve prepared in step (1).

[0098] Example 5

[0099] The preparation process of seed crystals in step (1) is detailed as follows: A gel is prepared by mixing 1SiO2: 0.6 template agent: 0.6 fluoride: 6H2O. First, N,N,N-trimethyl-1-adamantane ammonium hydroxide (TMAdaOH), tetraethyl orthosilicate, and ball-milled Si-CHA molecular sieve (calculated as SiO2, the molar ratio of tetraethyl orthosilicate to Si-CHA molecular sieve is 1:0.8) in a certain proportion and stirring at room temperature for about 6 hours to form sol A. Then, the temperature of the magnetic stirrer is raised to 80°C, and stirring and heating are continued while evaporating water to obtain dry gel B. At room temperature, a certain amount of hydrofluoric acid (HF, 40%) is slowly added to it, and heating and stirring are continued to evaporate water to obtain dry gel C. Then, the dry gel is poured into a stainless steel reactor with a polytetrafluoroethylene liner and placed in a constant temperature oven at 160°C for 48 hours. After the reaction is complete, remove the stainless steel reactor and cool it in cold water. Pour out the yellowish-brown dry gelatinous substance from the liner and centrifuge. Then wash it several times with deionized water by centrifugation. Repeat this process 2-3 times to obtain 200 nm cubic Si-CHA molecular sieve crystals. Dry them at 60 °C for later use.

[0100] The same steps (2) and (3) were performed as in Example 1 to obtain the Si-CHA molecular sieve membrane.

[0101] Example 6

[0102] Step (2) is the same as in Example 1.

[0103] Steps (1) and (3) are basically the same as in Example 1, except that the same amount of fumed silica (calculated as SiO2) is replaced with silica sol.

[0104] Example 7

[0105] Steps (1) and (2) are the same as in Example 1.

[0106] The preparation process in step (3) is basically the same as that in step (3) of Example 1, except that the crystallization reaction time is 24 hours.

[0107] Example 8

[0108] Steps (1) and (2) are the same as in Example 1.

[0109] The preparation process in step (3) is basically the same as that in step (3) of Example 1, except that the crystallization reaction time is 48h.

[0110] Experimental Example 1

[0111] Gas separation performance is represented by permeability P (Barrer) and separation coefficient α. At a test temperature of 25℃, the pressure difference before and after the membrane... Under the conditions of H2 as carrier gas, the carrier gas flow rate is 50 mL / min, the test mixed gas flow rate is 100 mL / min, and CO2 / N2 = 20% / 80% is selected as the feed gas for performance testing. Gas chromatography is used to determine the gas composition on the permeate side, and a soap membrane flow meter is used to determine the gas flow rate. The gas separation performance test results of different membranes are shown in Table 1.

[0112] Table 1

[0113]

[0114] As shown in Table 1, compared with Example 4, the molecular sieve membranes prepared using seeds synthesized through secondary growth have higher permeability than those prepared using seeds synthesized through primary growth. This is because the membrane layer prepared by small-particle-size Si-CHA is thinner, resulting in higher permeability. Compared with Examples 7-8, the membrane flux prepared after 24h, 36h, and 48h of reaction in Example 1 decreases sequentially. The Si-CHA molecular sieve membrane in Example 1 has a membrane thickness of 3 μm. This is because the membrane thickness decreases as the reaction time increases, but the membrane layer is thinner after 24h of reaction, resulting in poor selectivity.

[0115] Experimental Example 2

[0116] Using the Si-CHA molecular sieve membrane prepared in Example 1, the pressure difference before and after the membrane was measured at a test temperature of 25-50°C. Under the conditions of H2 as carrier gas, the carrier gas flow rate is 50 mL / min, the test mixed gas flow rate is 100 mL / min, and CO2 / N2 = 20% / 80% is selected as the feed gas for performance testing. The gas composition on the permeate side is determined by gas chromatography, and the gas flow rate is determined by soap film flow meter. The test results of Si-CHA membrane gas separation performance at different temperatures are shown in Table 2.

[0117] Table 2

[0118]

[0119] As shown in Table 2, the selectivity and permeability of the Si-CHA molecular sieve membrane remained relatively stable with temperature changes; the selectivity was slightly higher than other systems at 30℃, and then decreased slightly with increasing temperature. The Si-CHA molecular sieve membrane exhibited good separation performance and stability at 25-50℃.

[0120] Using the Si-CHA molecular sieve membrane prepared in Example 1, at a test temperature of 25°C, the pressure difference before and after the membrane was measured. Under the conditions of H2 as carrier gas, the carrier gas flow rate is 50 mL / min, the test mixed gas flow rate is 100 mL / min, and CO2 / N2 = 20% / 80% is selected as the feed gas for performance testing. The gas composition on the permeate side is determined by gas chromatography, and the gas flow rate is determined by soap film flow meter. The test results of Si-CHA membrane gas separation performance under different pressures are shown in Table 3.

[0121] Table 3

[0122]

[0123] As shown in Table 3, the Si-CHA membrane exhibits higher pressure and permeability compared to other systems at 2 bar. Between 2 and 6 bar, selectivity decreases with increasing pressure, CO2 permeability declines, while N2 permeability increases. This is because the Si-CHA membrane preferentially adsorbs CO2 and inhibits N2 permeation, and this inhibition weakens with increasing pressure.

[0124] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0125] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A method for preparing a Si-CHA molecular sieve membrane, characterized in that, The method comprises the following steps: The support surface loaded with Si-CHA seeds is wrapped with a growth gel, and a crystallization reaction is performed to obtain a Si-CHA molecular sieve membrane precursor; the crystallization reaction is performed for 24 h to 48 h; The Si-CHA molecular sieve membrane precursor is washed, and the washed Si-CHA molecular sieve membrane precursor is subjected to first drying treatment and first calcination treatment to obtain a Si-CHA molecular sieve membrane.

2. The method of making a Si-CHA molecular sieve membrane of claim 1, wherein, The support loaded with Si-CHA seeds is prepared by a method comprising the following steps: A seed gel is prepared, and the components of the seed gel include a first silicon source, a first template agent, a first fluoride, and water; The seed gel is subjected to first crystallization treatment, and the product of the first crystallization treatment is washed, subjected to second drying treatment, and subjected to second calcination treatment to prepare Si-CHA seeds; The Si-CHA seeds are coated on the surface of the support, and third calcination treatment is performed to prepare a support loaded with Si-CHA seeds.

3. The method of making a Si-CHA molecular sieve membrane of claim 2, wherein, At least one of the following characteristics (1)-(10) is met: (1) In the seed gel, the molar ratio of the first silicon source to the first template agent is 1:(0.3-0.8); (2) In the seed gel, the molar ratio of the first silicon source to the first fluoride is 1:(0.4-0.5); (3) In the seed gel, the molar ratio of the first silicon source to water is 1:(10-20); (4) The first silicon source is selected from any one or more of fumed silica and silica sol; (5) The first template agent is selected from any one or more of N,N,N-trimethyladamantammonium hydroxide, tetraethylammonium hydroxide, and triethylamine; (6) The first fluoride includes any one or more of hydrogen fluoride, ammonium fluoride, and ammonium bifluoride; (7) The temperature of the first crystallization treatment is 150°C-170°C, and the time of the first crystallization treatment is 24 h-72 h; (8) The temperature of the second calcination treatment is 500°C-550°C, and the time of the second calcination treatment is 12 h-24 h; (9) The step of coating the Si-CHA seeds on the surface of the support includes mixing the seeds and a solvent to prepare a seed suspension, and optionally, the mass concentration of the seeds in the seed suspension is 1wt%-2wt%; Optionally, the solvent is selected from any one or more of ethanol and water; the support is mixed with the seed suspension and dried; (10) The temperature of the third calcination treatment is 500°C-550°C, and the time of the third calcination treatment is 12 h-24 h.

4. The method of making a Si-CHA molecular sieve membrane of claim 2, wherein, The seeds obtained after the second calcination treatment are added to the seed gel again for second crystallization treatment, and the product after the second crystallization treatment is washed, subjected to third drying treatment, and subjected to third calcination treatment to obtain Si-CHA seeds; optionally, the average particle size of the Si-CHA seeds is 500 nm-700 nm.

5. The method of making a Si-CHA molecular sieve membrane according to any one of claims 1 to 4, characterized in that, The growth gel includes a second silicon source, a second template agent, a second fluoride, and water; Optionally, the growth gel comprises at least one of the following features (1)-(4): (1) the molar ratio of the second silicon source, the second template agent, the second fluoride and water is (1-1.3):(0.5-0.8):(0.5-0.8):(3-4); (2) the second silicon source is selected from any one or more of fumed silica and silica sol; (3) the second template agent is selected from any one or more of N,N,N-trimethyladamantammonium hydroxide, tetraethylammonium hydroxide and triethylamine; (4) the second fluoride is selected from any one or more of hydrogen fluoride, ammonium fluoride and ammonium bifluoride.

6. The method of making a Si-CHA molecular sieve membrane according to any one of claims 1 to 4, characterized in that, The temperature of the crystallization reaction is 150-170°C.

7. The method of making a Si-CHA molecular sieve membrane according to any one of claims 1 to 4, characterized in that, comprises at least one of the following features (1)-(3): (1) the support comprises a ceramic tube; (2) the temperature of the first drying treatment is 100-120°C and the time is 8-10 hours; (3) the temperature of the first calcination treatment is 500-550°C and the time is 12-24 hours.

8. A Si-CHA molecular sieve membrane characterized by, The Si-CHA molecular sieve membrane is prepared by the method of any one of claims 1-7.

9. The Si-CHA molecular sieve membrane of claim 8 for use in mixed gas separation.

10. Use according to claim 9, characterized in that, comprises at least one of the following features (1)-(3): (1) the mixed gas comprises carbon dioxide and nitrogen; optionally, in the mixed gas, the volume percentage of carbon dioxide is 10-20% and the volume percentage of nitrogen is 80-90%; (2) the mixed gas separation is carried out at a temperature of 25-50°C; (3) the pressure of the mixed gas during the separation is 1-3 bar.

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