A method for preparing IM-5 molecular sieve membrane

Abstract

This invention discloses a method for preparing an IM-5 molecular sieve membrane, comprising the following steps: (1) preparation of IM-5 molecular sieve seed crystals; (2) coating of IM-5 seed crystals; and (3) preparation of the IM-5 molecular sieve membrane. This invention is the first to prepare an IM-5 molecular sieve membrane on a single-channel carrier via a two-stage hydrothermal synthesis. The method for preparing the IM-5 molecular sieve membrane is simple in its synthesis steps and has high reproducibility. The obtained IM-5 molecular sieve membrane has a uniform and dense membrane layer without macroporous defects, and can be applied to gas separation, exhibiting separation selectivity for H2 / SF6 and p-xylene / o-xylene systems.

Description

Technical Field

[0001] This invention provides a method for preparing an IM-5 molecular sieve membrane, belonging to the field of membrane separation. Background Technology

[0002] Zeolite molecular sieves possess uniform molecular size, high porosity, and excellent thermal and chemical stability, making them widely used in the petrochemical industry. Zeolite molecular sieve membranes are thin films prepared from zeolite at the micrometer or even nanometer scale, utilizing the differences in zeolite pore diameter or the adsorption capacity of different molecules to separate them. As an emerging membrane separation material, zeolite molecular sieve membranes, with their uniform pore size, adjustable pore structure, excellent hydrothermal and chemical stability, and continuous separation capabilities, hold a crucial position and significant development potential in the fields of separation and catalysis.

[0003] IM-5 molecular sieves possess two-dimensional ten-membered ring channels, along with a finite number of short three-dimensional channels. IM-5 exhibits better hydrothermal stability than ZSM-5, and boasts a larger cell volume and lower framework density. The superior physicochemical properties of IM-5 also enable its wider application in the petrochemical industry.

[0004] IM-5 molecular sieve was first successfully synthesized by a French oil company under dynamic hydrothermal conditions using pyrrolidine bis-quaternary ammonium salts as templates, and the synthesis method was disclosed under WO98 / 17581A1. The general structure of IM-5 was reported by Professor Corma's group in 2000 (JOURNAL OF CATALYSIS, 2000. 189(2): 382-394.), but its specific crystal structure parameters were not discovered until 2007. Baerlocher et al. (SCIENCE, 2007. 315(5815): 1113-1116.) used the Charge-Flipping structure analysis algorithm, combined with XRD and HRTEM characterization of IM-5 molecular sieve, to accurately resolve the topological structure of IM-5 for the first time.

[0005] To date, research on the synthesis of IM-5 molecular sieves is limited, with the main synthesis method based on the patent disclosed by PETROUS, also known as the stepwise synthesis method. Specifically, this method uses N-methylpyrrole bis-quaternary ammonium salt as a template agent and employs dynamic hydrothermal synthesis under conditions of high alkalinity and a high sodium-to-silicon ratio. Building upon the original patent, Ji Xiangfei et al. (JOURNAL OF POROUS MATERIALS, 2019. 26(2): 343-351.) proposed a one-pot synthesis method for IM-5. This method successfully synthesized pure IM-5 molecular sieves with high crystallinity and uniform morphology.

[0006] IM-5 molecular sieve is considered a promising catalyst due to its strong acidity, excellent hydrothermal stability and catalytic cracking activity. A series of modification studies have been conducted on reactions such as methane aromatization (KINETICS AND CATALYSIS, 2013. 54(4): 443-450.) and methanol alkylation (NEW JOURNAL OF CHEMISTRY, 2019. 43(29): 11758-11770.).

[0007] Unlike the aforementioned applications of powdered IM-5 molecular sieve synthesis and catalysis, this invention discloses for the first time a method for preparing continuous IM-5 molecular sieve membranes on a porous support. The method utilizes the uniform pores (size [size missing]) within the continuous membrane layer of the IM-5 molecular sieve to separate gas mixtures such as H2 / SF6 and o-xylene / p-xylene. The preparation process includes at least three steps: seed crystal preparation, seed crystal loading on the support surface, and hydrothermal film growth. Compared to conventional distillation separation, membrane separation of these gas mixtures is achieved solely through a molecular sieving mechanism without phase change, thus significantly reducing separation energy consumption. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing IM-5 molecular sieve membranes for the first time. The synthesis steps are simple and highly reproducible, and the prepared membranes are thin, dense, and continuous, exhibiting good H2 / SF6 and o-xylene / p-xylene gas separation performance.

[0009] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0010] A method for preparing an IM-5 molecular sieve membrane, comprising the following steps:

[0011] (1) Preparation of IM-5 molecular sieve seed crystals:

[0012] A sol was formed by mixing silicon source, aluminum source, alkali source and structure directing agent (SDA). The molar ratio of the sol components was: SiO2 / Al2O3=10~50, Na2O / SiO2=0.1~0.5, NaBr / SiO2=0.05~0.3, SDA / SiO2=0.05~0.6, H2O / SiO2=10~100. After aging at 80 °C for 72 h, the sol was poured into a reaction vessel and hydrothermally synthesized at 150~200 °C for 0.5~11 days. After completion, the product was removed, centrifuged, washed until neutral, and dried in an oven at 60 °C for 24 h to obtain IM-5 molecular sieve seed crystals.

[0013] (2) IM-5 seed coating:

[0014] First, the tubular carrier is washed and dried with boiling water. Then, the seed crystal synthesized in step (1) is ground and dispersed in an ethanol solution to obtain a suspension, which is then coated on the outer wall of the tubular carrier. The carrier is a porous tubular carrier of α-Al2O3 and ZrO2-Al2O3. The seed crystal coating method is dip coating and vacuum coating, and the seed crystal coating time is 30-120 s.

[0015] (3) Preparation of IM-5 molecular sieve membrane:

[0016] A sol was formed by mixing silicon source, aluminum source, alkali source and structure directing agent. The molar ratio of each component of the sol was: SiO2 / Al2O3=10~50, Na2O / SiO2=0.1~0.5, NaBr / SiO2=0.05~0.3, SDA / SiO2=0.05~0.6, H2O / SiO2=10~100. After aging at 25-100 ℃ for 3-100 h, the synthesized sol and the carrier coated with molecular sieve seed crystals in step (2) were placed together in a reaction vessel and hydrothermally synthesized at 150~200 ℃ for 0.5~11 days. After the reaction was completed, the membrane tube was taken out, rinsed with water until neutral, dried in an oven at 60 °C for 24 h, and calcined to obtain IM-5 molecular sieve membrane.

[0017] The molecular sieve seed crystals mentioned in step (1) have a size of 250 nm. The seed crystal suspension mentioned in step (2) has a mass concentration of 0.01-0.05 wt% and its solvent is ethanol or water. In step (2), the time for coating the seed crystal layer on the porous carrier is 30-120 s.

[0018] The silicon source is one of silica sol, silica gel, tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass, or silicon powder.

[0019] The aluminum source is one of aluminum hydroxide, sodium aluminate, aluminum foil, aluminum isopropoxide, aluminum n-butoxide, aluminum foil, aluminum powder, or aluminum oxide.

[0020] The structure-directing agent is a salt of 1,5-bis(N-methylpyrrolidine)pentane. The alkali source in steps (1) and (3) is sodium hydroxide.

[0021] Further, in step (3), the calcination atmosphere is air, oxygen or ozone, with ozone atmosphere being preferred, the calcination temperature is 150-530 ℃, the calcination time is 4-100 h, and the heating and cooling rate is 0.5-2℃ / min.

[0022] The IM-5 molecular sieve membrane prepared by the above method is mainly used for gas separation.

[0023] The beneficial effects of this invention are:

[0024] The method for secondary hydrothermal synthesis of IM-5 molecular sieve membranes of the present invention employs a dip-coating method to coat seed crystals onto a support, combined with support pretreatment and sol aging, to prepare IM-5 molecular sieve membranes on porous supports for the first time. This enables the application of IM-5 molecular sieves in gas separation membranes, achieving a high selectivity of 12.3 for H2 / SF6 separation and 3.7 for p-xylene / o-xylene separation. This preparation method offers advantages such as thin and dense IM-5 molecular sieve membranes and high reproducibility of synthesis. Separating homogeneous gas mixtures using phase equilibrium mechanisms typically requires multiple phase transitions, resulting in high energy consumption. The separation technology based on the membrane material prepared in this invention eliminates phase transitions during the separation process, achieving separation through a molecular sieving mechanism, thus significantly reducing separation energy consumption. Attached Figure Description

[0025] Figure 1 (a) Scanning electron microscope image and (b) XRD diffraction peak pattern of the synthesized IM-5 molecular sieve seed crystals. The XRD pattern includes the standard IMF structure (1) and the seed crystal (2).

[0026] Figure 2 Scanning electron microscope (SEM) images of the surface (a) and cross-section (b) of the seed layer.

[0027] Figure 3 Scanning electron microscope (SEM) images of the surface and cross-section of the IM-5 molecular sieve membrane (a) prepared for fabrication.

[0028] Figure 4 The XRD diffraction peak pattern of the obtained IM-5 molecular sieve membrane M1 is shown. The XRD pattern includes the standard IMF structure (a), the zirconia support (b), and the IM-5 molecular sieve membrane M1 (c). Specific implementation methods

[0029] To further describe the present invention, specific embodiments of the invention are given below, but the scope of protection sought by the present invention is not limited to these embodiments.

[0030] Example 1

[0031] (1) Preparation of IM-5 molecular sieve seed crystals:

[0032] Deionized water, sodium hydroxide, and sodium aluminate were mixed in a certain proportion and stirred at room temperature to form a homogeneous solution. Fumed silica powder, sodium bromide, and SDA [1,5-bis(N-methylpyrrolidine)pentane bromide] were then added to the solution. The molar ratio of the resulting synthetic sol was: SiO2 / Al2O3 = 20, Na2O / SiO2 = 0.28, NaBr / SiO2 = 0.1, SDA / SiO2 = 0.16, and H2O / SiO2 = 40. After aging at 80 °C for 24 h, the sol was poured into a high-pressure reactor lined with polytetrafluoroethylene and hydrothermally synthesized and crystallized at 160 °C for 9 days. The crystallization reaction was then stopped, and the product was washed with deionized water and centrifuged 2-3 times until neutral. Finally, the obtained molecular sieve was dried in a 60 °C oven to obtain IM-5 molecular sieve seed crystals.

[0033] (2) IM-5 seed coating:

[0034] Using a tubular porous zirconia ceramic support as a carrier, the substrate was first washed with boiling water and dried. Then, the IM-5 seed crystals prepared in step (1) were dispersed in an ethanol solution to prepare a seed crystal suspension with a concentration of 0.025 wt%, and ultrasonicated to form a homogeneous solution. Both ends of the tubular carrier were sealed with PTFE plugs, and the seed crystal suspension was coated onto the outer wall of the support by dip-coating. The immersion time was maintained for 40 s, and after drying in a 60 ℃ oven for 24 h, a continuous and dense molecular sieve crystal layer was formed on the surface of the support.

[0035] (3) Preparation of IM-5 molecular sieve membrane:

[0036] Deionized water, sodium hydroxide, and sodium aluminate were mixed in a certain proportion and stirred at room temperature to form a homogeneous solution. Fumed silica powder, sodium bromide, and SDA [1,5-bis(N-methylpyrrolidine)pentane bromide] were then added to the solution. The molar ratio of the resulting synthetic sol was: SiO2 / Al2O3=20, Na2O / SiO2=0.28, NaBr / SiO2=0.1, SDA / SiO2=0.16, and H2O / SiO2=40. After aging at 80°C for 72 h, the synthetic sol and the carrier coated with molecular sieve seeds in step (2) were placed together in a reactor and reacted at 175°C for 7 days. After the reaction, the membrane was removed, the membrane tube was rinsed with tap water until neutral, dried at 60℃, and the structure directing agent was removed under an ozone atmosphere. The calcination temperature was 200℃, the calcination time was 72 h, and the heating rate was 1℃ / min. The calcined IM-5 molecular sieve membrane was labeled as M1.

[0037] Figure 1The images show (a) scanning electron microscope (SEM) image and (b) XRD diffraction peak pattern of the synthesized IM-5 molecular sieve seed crystals. The synthesized IM-5 molecular sieve seed crystals exhibit typical rod-like shapes, with uniform grain size, regular morphology, and no amorphous material present. The XRD peaks of the seed crystals all correspond to the IMF structure, indicating that the crystals are pure IMF phases with high crystallinity and an average particle size of 200-300 nm.

[0038] Figure 2 Scanning electron microscope (SEM) images of the surface (a) and cross-section (b) of the prepared seed layer. Surface SEM image ( Figure 2 a) The surface of the carrier is uniformly covered with crystals; cross-sectional scanning electron microscope image ( Figure 2 b) The seed layer thickness is approximately 300 nm.

[0039] Figure 3 Scanning electron microscopy (SEM) images of the surface and cross-section of the prepared IM-5 molecular sieve membrane (a). Figure 2 It can be seen that there are no obvious defects on the surface of the film, the crystal growth is dense, and the cross-sectional image shows that the film thickness is about 600 nm.

[0040] Figure 4 XRD diffraction peak patterns of (a) standard IMF, (b) porous zirconia support, and (c) the obtained IM-5 molecular sieve membrane M1. Figure 4 This indicates that the synthesized IM-5 molecular sieve membrane has a pure IMF structure.

[0041] The gas separation performance of a membrane is represented by two parameters: gas permeation rate P and separation selectivity α. 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 × ΔP), with units of mol / (m²). 2 s Pa); Separation selectivity α is used to evaluate the efficiency of membrane separation, α=P A / P B The separation performance of the prepared IM-5 molecular sieve membrane for H2 / SF6 and p-xylene / o-xylene gases was tested. The test results are shown in Tables 1 and 2, respectively. It should be noted that when the separation selectivity is 1, it indicates that the membrane has no separation selectivity, and the magnitude of the permeation rate is meaningless.

[0042] Example 2

[0043] The difference from Example 1 is that in steps (1) and (3), the Na2O / SiO2 ratio in the seed crystal and membrane synthesis sol is 0.1, NaBr / SiO2 ratio is 0.05, SDA / SiO2 ratio is 0.6, and H2O / SiO2 ratio is 35. The remaining steps are the same as in Example 1. The prepared membrane is labeled M2. The H2 / SF6 and p-xylene / o-xylene gas separation performance of the prepared IM-5 molecular sieve membrane were tested. The test results are shown in Tables 1 and 2, respectively.

[0044] Example 3

[0045] The difference from Example 1 is that: the seed coating time in step (2) is 120 s; the NaBr / SiO2 = 0.3, SiO2 / Al2O3 = 10, and H2O / SiO2 = 30 in the seed and membrane synthesis sol in steps (1) and (3); the calcination rate for removing the template agent is 2 ℃ / min; and the remaining steps are the same as in Example 1. The prepared membrane is labeled M3. The H2 / SF6 and p-xylene / o-xylene gas separation performance of the prepared IM-5 molecular sieve membrane were tested. The test results are shown in Tables 1 and 2, respectively.

[0046] Example 4

[0047] The difference from Example 1 is that the concentration of the seed suspension used in step (2) was 0.05 wt%, the seed coating time was 30 s, and the hydrothermal conditions for membrane synthesis in step (3) were 11 days at 150°C. The remaining steps were the same as in Example 1. The prepared membrane was labeled M4, and the H2 / SF6 and p-xylene / o-xylene gas separation performance of the prepared IM-5 molecular sieve membrane were tested. The test results are shown in Tables 1 and 2, respectively.

[0048] Example 5

[0049] The difference from Example 1 is that the concentration of the seed suspension used in step (2) is 0.05 wt%, and in step (3), the sol is reacted at 175 °C for 5 days. The remaining steps are the same as in Example 1. The prepared membrane is labeled M5, and the gas separation performance of the membrane is shown in Table 1.

[0050] Example 6

[0051] The difference from Example 1 is that in steps (1) and (3), the Na2O / SiO2 ratio in the sol for synthesizing the seed crystals and the membrane is 0.5, the SDA / SiO2 ratio is 0.05, and the H2O / SiO2 ratio is 100. In step (2), the concentration of the seed crystal suspension used is 0.01 wt%, and the seed crystals are coated by vacuum suction. The remaining steps are the same as in Example 1. The prepared membrane is labeled M6, and the gas separation performance of the membrane is shown in Table 1.

[0052] Example 7

[0053] The difference from Example 1 is that the carrier used in step (2) is a tubular porous alumina support, the silicon source used in the membrane synthesis sol in step (3) is tetraethyl orthosilicate and the aluminum source is aluminum hydroxide, and the sol in step (3) is aged at 100°C for 3 h. The remaining steps are the same as in Example 1. The prepared membrane is labeled M7, and the gas separation performance of the membrane is shown in Table 1.

[0054] Example 8

[0055] The difference from Example 1 is that in step (3), calcination was carried out in a muffle furnace under an air atmosphere at a temperature of 530 °C for 4 h with a heating rate of 0.5 °C / min. The remaining steps were the same as in Example 1. The prepared membrane was labeled M8, and its gas separation performance is shown in Table 1.

[0056] Example 9

[0057] The difference from Example 1 is that in step (3), the membrane synthesis hydrothermal conditions were 200℃ for 0.5 days, and the calcination in step (3) was carried out in a tubular furnace under an oxygen atmosphere at a temperature of 150℃ for 100 h with a heating rate of 0.5℃ / min. The remaining steps were the same as in Example 1. The prepared membrane was labeled M9, and its gas separation performance is shown in Table 1.

[0058] Example 10

[0059] The difference from Example 1 is that in steps (1) and (3), the sol for seed crystal and membrane synthesis has SiO2 / Al2O3 = 30, Na2O / SiO2 = 0.35, NaBr / SiO2 = 0.2, SDA / SiO2 = 0.3, and H2O / SiO2 = 50. In step (3), the sol is aged at 25 °C for 100 h. The remaining steps are the same as in Example 1. The prepared membrane is labeled M10, and the gas separation performance of the membrane is shown in Table 1.

[0060] Comparative Example 1

[0061] Step (1) is the same as in Example 1.

[0062] Step (3) is the same as in Example 1, except that the in-situ synthesis method is used, the seed coating in step (2) is not performed, the hydrothermal temperature is 180°C, and the reaction time is 11 days.

[0063] The separation performance of the prepared IM-5 molecular sieve membrane for H2 / SF6 and p-xylene / o-xylene was tested. The test results are shown in Tables 1 and 2, respectively. The prepared membrane showed no separation performance in either system.

[0064] Comparative Example 2

[0065] Step (1) is the same as in Example 1.

[0066] Step (3) is the same as in Example 1, except that the in-situ synthesis method is used, the seed coating in step (2) is not performed, the hydrothermal temperature is 160°C, and the reaction time is 14 days.

[0067] The separation performance of the prepared IM-5 molecular sieve membrane for H2 / SF6 and p-xylene / o-xylene was tested. The test results are shown in Tables 1 and 2, respectively. The prepared membrane showed no separation performance in either system.

[0068] Tables 1 and 2 show that the molecular sieve membranes prepared by the secondary hydrothermal method all exhibit high separation selectivity for H2 / SF6 and p-xylene / o-xylene, indicating small membrane defects and high membrane quality. Meanwhile, the in-situ synthesis method requires a longer hydrothermal reaction time and lacks separation selectivity. This demonstrates that the secondary hydrothermal method for preparing IM-5 molecular sieve membranes is superior to that synthesized by the in-situ synthesis method.

[0069] Table 1. Single-gas permeation performance of the examples and comparative examples

[0070] .

[0071] Table 2. Separation performance of p-xylene / o-xylene in the Examples and Comparative Examples

[0072]

Claims

1. A method for preparing an IM-5 molecular sieve membrane, characterized in that, Comprising the following steps: (1) IM-5 molecular sieve seed preparation: a silica source, an aluminum source, an alkali source and a structure directing agent SDA are mixed to form a sol, the structure directing agent being 1,5-bis(N-methylpyrrolidine)pentane bromide salt, the molar ratio of the components of the obtained sol being: SiO2 / Al2O3=10-50, Na2O / SiO2=0.1-0.5, NaBr / SiO2=0.05-0.3, SDA / SiO2=0.05-0.6, H2O / SiO2=10-100, after aging at 80 ℃ for 72 h, the sol is poured into a reaction kettle, and hydrothermal synthesis is carried out at a temperature of 150-200 ℃ for 0.5-11 days, after completion, the product obtained in the reaction is taken out, centrifuged, washed to neutral, dried in an oven at 60 ℃ for 24 h, and the IM-5 molecular sieve seed is obtained; (2) IM-5 seed coating: the tubular carrier is first cleaned with boiling water and dried, then the seed synthesized in step (1) is ground and dispersed in an ethanol solution to prepare a suspension, and the suspension is coated on the outer wall of the tubular carrier; the carrier is a porous tubular carrier of α-Al2O3 or ZrO2-Al2O3; the seed coating method is dip coating or vacuum suction coating; (3) IM-5 molecular sieve membrane preparation: a silica source, an aluminum source, an alkali source and a structure directing agent SDA are mixed to form a sol, the structure directing agent being 1,5-bis(N-methylpyrrolidine)pentane bromide salt, the molar ratio of the components of the obtained sol being: SiO2 / Al2O3=10-50, Na2O / SiO2=0.1-0.5, NaBr / SiO2=0.05-0.3, SDA / SiO2=0.05-0.6, H2O / SiO2=10-100, after aging at 25-100 ℃ for 3-100 h, the carrier coated with the molecular sieve seed in step (2) is placed in a reaction kettle, and hydrothermal synthesis is carried out at a temperature of 150-200 ℃ for 0.5-11 days, after completion, the membrane tube is taken out, washed with water to neutral, dried in an oven at 60 ℃ for 24 h, and calcined to obtain the IM-5 molecular sieve membrane.

2. The method of claim 1, wherein the IM-5 molecular sieve membrane is prepared by the steps of: The size of the molecular sieve seed in step (1) is 250 nm.

3. The method for preparing an IM-5 molecular sieve membrane according to claim 1, characterized in that, The silica source in steps (1) and (3) is selected from one of a silica sol, tetraethyl orthosilicate, tetramethyl orthosilicate, sodium silicate, water glass or silicon powder.

4. The method of claim 1, wherein the IM-5 molecular sieve membrane is prepared by the steps of: The aluminum source in steps (1) and (3) is one of aluminum hydroxide, sodium metaaluminate, aluminum phyllosilicate, aluminum isopropoxide, aluminum n-butylate, aluminum foil, aluminum powder or alumina.

5. The method for preparing an IM-5 molecular sieve membrane according to claim 1, characterized in that, The alkali source in steps (1) and (3) is sodium hydroxide.

6. The method of claim 1, wherein the IM-5 molecular sieve membrane is prepared by the steps of: In step (2), the time for coating the seed layer on the porous carrier is 30-120 s.

7. The method of claim 1, wherein the IM-5 molecular sieve membrane is prepared by the steps of: In step (2), the concentration of the seed suspension is 0.01-0.05 wt%.

8. The method of claim 1, wherein the IM-5 molecular sieve membrane is prepared by the steps of: The calcination in step (3) uses air, oxygen or ozone as the calcination atmosphere, the calcination temperature is 150-530 ℃, the calcination time is 4-100 h, and the temperature rising and falling rate is 0.5-2 ℃ / min.

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