Composite molecular sieve, method for preparing the same, and use thereof

Abstract

The present application relates to the field of catalytic material synthesis, and discloses a composite molecular sieve, a preparation method and application thereof, and the composite molecular sieve has CHA structure and AFN structure. The synthesis method of the composite molecular sieve comprises the following steps: in the presence of a persulfate, an initial gel mixture containing a phosphorus source, a silicon source, an aluminum source, a template agent and water is crystallized. The CHA structure and AFN structure composite molecular sieve synthesized by the method has high crystallinity, large micropore specific surface area and micropore volume, and has potential application prospects in the fields of acid catalytic reaction and gas adsorption.

Description

Technical Field

[0001] This invention relates to the field of catalytic material synthesis, and more specifically, to a composite molecular sieve having a CHA structure and an AFN structure, its preparation method, and its application. Background Technology

[0002] Composite molecular sieves are a type of molecular sieve with a special structure. They are co-crystallizations formed by two or more molecular sieves, or composite crystals possessing the structural characteristics of two or more molecular sieves. Due to the special structure of composite molecular sieves, they possess a more rationally distributed pore structure and acidity, overcoming the limitations of individual molecular sieves. This allows them to better meet the needs of applications such as catalysis and has broad application prospects.

[0003] AFN-structured molecular sieves belong to the triclinic crystal system, with space group P-1 and unit cell parameters of _____. With α = 77.81°, β = 77.50°, and γ = 87.69°, this molecular sieve possesses a three-dimensional octagonal pore structure. The octagonal pore diameter along the

[100] direction is 0.19 × 0.46 nm, along the

[010] direction it is 0.21 × 0.49 nm, and along the

[001] direction it is 0.33 × 0.4 nm, classifying it as a small-pore molecular sieve. The CHA-structured molecular sieve belongs to the trigonal crystal system, with space group R-3m and cell parameters... With α = 94.47°, β = 94.47°, and γ = 94.47°, it has an octagonal ellipsoidal cage (cha cage) formed by stacking double six-membered rings in an ABC pattern and a three-dimensional cross-channel structure. The pore size is 0.38nm × 0.38nm, and the cage size is 1.0nm × 0.67nm × 0.67nm, which belongs to small-pore molecular sieves.

[0004] CN114054081A reports a SAPO-34 / SAPO-14 composite molecular sieve, its preparation method, and its application. The synthesis requires the addition of seed crystals and two crystallization processes. The SAPO-34 molecular sieve seed crystals are first prepared through a process of crystallization, filtration, washing, and drying. Then, the SAPO-34 molecular sieve seed crystals are added to the SAPO-14 molecular sieve synthesis gel system for a second crystallization, filtration, washing, and drying process. The preparation method is cumbersome. Summary of the Invention

[0005] To address the shortcomings of existing preparation techniques for composite molecular sieves with CHA and AFN structures, the present invention aims to provide a simple and convenient method for directly synthesizing composite molecular sieves with CHA and AFN structures, along with their preparation methods and applications.

[0006] The inventors of this invention have discovered that by adding persulfate ions to the synthesis system, a composite molecular sieve with both CHA and AFN structures can be obtained, solving the problem that existing technologies cannot directly synthesize composite molecular sieves with both CHA and AFN structures. Therefore, this invention provides a method for preparing a composite molecular sieve with both CHA and AFN structures. This method includes: crystallizing an initial gel mixture containing a phosphorus source, a silicon source, an aluminum source, a template agent, and water in the presence of persulfate ions, wherein the template agent is an organic amine with no more than 3 carbon atoms.

[0007] This invention also provides a composite molecular sieve with CHA and AFN structures and its applications.

[0008] This invention enables the production of composite molecular sieves with CHA and AFN structures. These sieves exhibit high crystallinity, large micropore specific surface area, and large micropore volume, and have potential applications in acid catalysis and gas adsorption. The synthesis method is simple and solves the problem that existing technologies cannot directly synthesize composite molecular sieves with CHA and AFN structures. Attached Figure Description

[0009] Figure 1 The XRD pattern of the molecular sieve sample synthesized in Example 1;

[0010] Figure 2 The XRD pattern of the molecular sieve sample synthesized in Example 2;

[0011] Figure 3 The image shows the XRD pattern of the molecular sieve sample synthesized in Example 3. Detailed Implementation

[0012] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0013] This invention provides a method for preparing a composite molecular sieve with CHA and AFN structures. The method is characterized by comprising: crystallizing an initial gel mixture containing a phosphorus source, a silicon source, an aluminum source, a template agent, and water in the presence of persulfate, wherein the template agent is an organic amine with no more than 3 carbon atoms.

[0014] In the initial gel mixture of the present invention, the molar ratio of phosphorus source to aluminum source can be 0.6-1.22:1, preferably 0.8-1.2:1 (such as 0.9, 0.95, 0.98, 0.99, 1, 1.1, 1.2 or any value between the above values).

[0015] In the initial gel mixture of the present invention, the molar ratio of silicon source to aluminum source can be 0.01-1:1, preferably 0.1-0.9:1 (such as 0.3, 0.35, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any value between the above values).

[0016] In the initial gel mixture of the present invention, the molar ratio of template agent to aluminum source can be 1-10:1, preferably 1.1-5:1 (such as 1.1, 1.5, 2, 3, 4, 5 or any value between the above values).

[0017] In the initial gel mixture of the present invention, the molar ratio of water to aluminum source can be 10-200:1, preferably 12-80:1 (such as 15, 20, 30, 40, 50, 60, 70, 80 or any value between the above values).

[0018] In the initial gel mixture of the present invention, the molar ratio of persulfate to aluminum source can be 0.001-0.02:1, preferably 0.002-0.018:1 (such as 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.01, 0.013, 0.014, 0.017, 0.018 or any value between the above values).

[0019] In this invention, the phosphorus source is calculated as P2O5, the aluminum source is calculated as Al2O3, and the silicon source is calculated as SiO2.

[0020] In this invention, the persulfate ions can be provided by various substances capable of providing persulfate ions in the initial gel mixture, preferably by alkali metal persulfates, and more preferably by sodium persulfate and / or potassium persulfate.

[0021] In this invention, the phosphorus source and aluminum source can be substances commonly found in the art capable of providing P and / or Al. According to a preferred embodiment of the invention, the phosphorus source and aluminum source are provided by a phosphorus-aluminum complex. The molar ratio of P (based on P2O5) to Al (based on Al2O3) in the phosphorus-aluminum complex is 0.8-1.2, and the phosphorus-aluminum complex has a phosphorus-aluminum crystal framework structure. The phosphorus-aluminum complex can be prepared according to the method described in CN111422843A. Using the phosphorus-aluminum complex as the phosphorus and aluminum source to synthesize the composite molecular sieve of this invention results in low cost, good reproducibility, high crystallinity of the molecular sieve product, and the ability to synthesize under low water-to-aluminum ratio conditions, thus improving the problems of low single-batch yield and high wastewater discharge caused by high water-to-aluminum ratios in traditional hydrothermal synthesis.

[0022] According to another preferred embodiment of the present invention, the phosphorus source and the aluminum source are provided by different substances. For example, the phosphorus source may be phosphoric acid, preferably orthophosphoric acid; the aluminum source may be alumina and / or aluminum hydroxide, preferably at least one of anhydrous alumina, aluminum hydroxide and boehmite.

[0023] In this invention, the silicon source can be a material commonly used in the art that can provide Si. For example, the silicon source can be silicon dioxide, preferably silica and / or silica gel.

[0024] According to a preferred embodiment of the present invention, the template agent (or structure directing agent) is an alkylamine with no more than 3 carbon atoms, more preferably isopropylamine. Using isopropylamine as a template agent can be more beneficial for the synthesis of composite molecular sieves having CHA and AFN structures.

[0025] In this invention, there are no particular requirements for the crystallization method. A single-stage crystallization can be used, which can be performed at 170-205°C for 20-80 hours. Alternatively, a two-stage crystallization can be used. In a preferred embodiment of this invention, the crystallization includes sequentially performing a first-stage crystallization and a second-stage crystallization, with the temperature of the first-stage crystallization being lower than the temperature of the second-stage crystallization. More preferably, the temperature of the first-stage crystallization is 25-55°C lower than the temperature of the second-stage crystallization (e.g., 26, 28, 32, 35, 38, 42, 45, 48, 52, 54°C or any value between these values). More preferably, the time for the first-stage crystallization is 5-10 hours shorter than the time for the second-stage crystallization (e.g., 5.2, 5.8, 6.2, 6.5, 6.8, 7.2, 8.5, 9.8 hours or any value between these values).

[0026] More preferably, the conditions for the first stage of crystallization include: a temperature of 140-160℃ (such as 141, 142, 145, 148, 152, 155, 158, 159℃ or any value between the above). More preferably, the conditions for the first stage of crystallization also include: a time of 33-40h (such as 34, 35, 36, 37, 38, 39, 40h or any value between the above).

[0027] More preferably, the conditions for the second stage of crystallization include: a temperature of 170-190℃ (e.g., 175, 176, 178, 180, 182, 184, 185, 189℃ or any value between the above). More preferably, the conditions for the second stage of crystallization also include: a time of 25-50h (e.g., 27, 29, 40, 41, 43, 45, 47, 49, 50, 52, 54h or any value between the above).

[0028] In this invention, the crystallization process does not have specific pressure requirements and can be performed under self-generated pressure. The crystallization can be static or dynamic, with dynamic crystallization being preferred. As a condition for dynamic crystallization, a rotational speed of 15-40 r / min is preferred.

[0029] According to a more preferred embodiment of the present invention, the first stage of crystallization is carried out under autogenous pressure and at 145-155°C for 35-39 hours, and the second stage of crystallization is carried out under autogenous pressure and at 175-185°C for 30-45 hours.

[0030] In this invention, to obtain molecular sieves (raw powder), the method may further include solid-liquid separation of the crystallized product, followed by sequential washing, drying, and optionally calcination of the obtained solid phase to obtain the molecular sieve. Specifically, the solid-liquid separation method can be performed using conventional methods, such as filtration and centrifugation. Furthermore, the solid phase obtained from the solid-liquid separation is washed before drying. The washing can be performed using conventional methods; to avoid introducing other impurities, it is preferable to wash with deionized water until neutral. The drying can be carried out at a temperature of 70-110°C, and the drying time can be selected according to the drying temperature, generally 4-12 hours. The calcination temperature can be 500-600°C, and the calcination time can be 3-5 hours.

[0031] The present invention also provides a composite molecular sieve having a CHA structure and an AFN structure, characterized in that the composite molecular sieve is prepared by the method described above;

[0032] Alternatively, the weight percentage of CHA structure molecular sieve in the composite molecular sieve is 10-95% (preferably 70-78%), and the weight percentage of AFN structure molecular sieve is 5-90% (preferably 22-30%).

[0033] According to the present invention, the anhydrous chemical composition of the composite molecular sieve is (SixAlyPz)O2, where x, y, and z represent the mole fractions of Si, Al, and P, respectively, and their values ​​range from x = 0.01-0.2 (preferably 0.05-0.07), y = 0.3-0.49 (preferably 0.4-0.45), and z = 0.4-0.6 (preferably 0.5-0.55), and x+y+z = 1; and the weight percentage of Na2O is 0-0.3%, preferably 0.05-0.2%.

[0034] According to the present invention, the microporous specific surface area of ​​the composite molecular sieve is not less than 340 m². 2 / g, preferably 350-400m 2 / g.

[0035] According to the present invention, the micropore volume of the composite molecular sieve is not less than 0.155 cm³. 3 / g, preferably 0.16-0.18cm 3 / g.

[0036] Furthermore, this invention also provides the application of the composite molecular sieve described above as a catalyst in acid-catalyzed reactions. The acid-catalyzed reaction is preferably a reaction involving the conversion of oxygen-containing compounds (such as alcohols, preferably methanol) to olefins or a straight-chain alkane isomerization reaction.

[0037] The present invention also provides the application of the composite molecular sieve described above in gas adsorption treatment.

[0038] The present invention will be described in detail below through embodiments. In the following embodiments and comparative examples:

[0039] X-ray powder diffraction (XRD) phase analysis was performed using a Panaco Empyrean diffractometer from the Netherlands, equipped with a PIXcel... 3D Detector. Test conditions: Cu target, Kα radiation, Ni filter, tube voltage 40kV, tube current 40mA, scanning range 5°-50°. The weight percentage of different phase structures in the composite molecular sieve is determined based on the characteristic peaks of each molecular sieve in the XRD pattern. Specifically, the weight percentage of each phase is calculated based on the peak height of the unique highest intensity characteristic peak of each molecular sieve. The specific calculation method is as follows: the highest intensity characteristic peak of the CHA structure molecular sieve is 9.4°, and the characteristic peak of the AFN structure molecular sieve is 8.9°. The peak heights of the characteristic peaks of the CHA and AFN structure molecular sieves are denoted as S1 and S2, respectively; the weight percentage of the CHA structure molecular sieve in the composite molecular sieve = S1 / (S1+S2)×100%; the weight percentage of the AFN structure molecular sieve = S2 / (S1+S2)×100%.

[0040] The inorganic elemental composition (XRF) of the molecular sieve samples was determined using a Philips MagiX fluorescence spectrometer.

[0041] The BET analysis was performed using a Micromeritics ASAP 2010 adsorption analyzer. Test conditions: The weighed sample was evacuated to a vacuum of 1.33 × 10⁻⁶ at 350°C. -2 Sample pretreatment was performed at constant temperature and pressure for 15 hours. The adsorption and desorption of nitrogen by the sample were measured at liquid nitrogen temperature -196℃ under different specific pressures p / p0, yielding nitrogen adsorption-desorption isotherms. The micropore specific surface area and micropore volume of the sample were calculated using the t-plot method.

[0042] In the following examples, R represents the organic template agent: isopropylamine.

[0043] The examples illustrate the synthesis of the composite molecular sieve with CHA and AFN structures described in this invention.

[0044] Example 1

[0045] Crystalline aluminum phosphate was prepared according to the method described in Example 2 of CN111422843A, with a solid content of 100% and a P2O5 / Al2O3 ratio of 0.99 (molar ratio).

[0046] Add 10.999 g of deionized water to the polytetrafluoroethylene liner, then add isopropylamine (99% by mass), followed by crystalline aluminum phosphate, and then solid silica gel (93.3% by mass of SiO2). Stir and mix thoroughly. Add 7 g of sodium persulfate (99% by mass) to water, stir to dissolve, and then add to the above mixture. Stir and mix thoroughly. The molar ratios of the components are: P2O5 / Al2O3 = 0.99, SiO2 / Al2O3 = 0.3, R / Al2O3 = 2, H2O / Al2O3 = 40, Na2S2O8 / Al2O3 = 0.004.

[0047] The polytetrafluoroethylene liner containing the above reaction mixture was capped, placed in a stainless steel autoclave and sealed, and then placed in a rotating convection oven at a speed of 20 r / min for crystallization under autogenous pressure: crystallization at 150℃ for 36 hours and at 180℃ for 45 hours. After crystallization, the product was removed by cooling to room temperature, filtered, washed, and dried at 110℃ for 12 hours to obtain a solid powder sample.

[0048] The obtained solid powder sample was subjected to X-ray diffraction analysis, and the XRD pattern is shown in the figure. Figure 1Referring to the XRD patterns of the CHA structure in CN107915237B and the AFN structure in CN112624137B, it was confirmed that the obtained solid powder sample is a composite molecular sieve with both CHA and AFN structures. Quantitative XRD analysis revealed that the CHA structure molecular sieve comprised 73.67% by weight, and the AFN structure molecular sieve comprised 26.33% by weight. XRF elemental analysis of the obtained composite molecular sieve showed its chemical composition to be (Si... 0.07 Al 0.42 P 0.51 The composite molecular sieve contained 0.0681% Na₂O by weight. After calcination at 550℃ for 3 hours, BET analysis revealed a micropore specific surface area of ​​351 m². 2 / g, micropore volume is 0.162cm³ 3 / g, the obtained composite molecular sieve has good micropore specific surface area and micropore volume, indicating that the composite molecular sieve has a complete crystal structure and high crystallinity.

[0049] Example 2

[0050] The preparation method of Example 1 is the same, except that the molar ratio of each component is: P2O5 / Al2O3 = 0.99, SiO2 / Al2O3 = 0.35, R / Al2O3 = 3, H2O / Al2O3 = 60, Na2S2O8 / Al2O3 = 0.007.

[0051] The obtained solid powder sample was subjected to X-ray diffraction analysis, and the XRD pattern is shown in the figure. Figure 2 The resulting composite molecular sieve exhibits both CHA and AFN structures. XRD diffraction analysis revealed that the CHA structure molecular sieve comprised 73.01% by weight, while the AFN structure molecular sieve comprised 26.99% by weight. XRF elemental analysis further confirmed its chemical composition as (Si...). 0.06 Al 0.44 P 0.50 The composite molecular sieve contained 0.0912% Na₂O by weight. After calcination at 550℃ for 3 hours, BET analysis revealed a micropore specific surface area of ​​364 m². 2 / g, micropore volume is 0.169cm³ 3 / g, the obtained composite molecular sieve has good micropore specific surface area and micropore volume, indicating that the composite molecular sieve has a complete crystal structure and high crystallinity.

[0052] Example 3

[0053] The preparation method is the same as in Example 1, except that Na2S2O8 / Al2O3 = 0.014.

[0054] The obtained solid powder sample was subjected to X-ray diffraction analysis, and the XRD pattern is shown in the figure. Figure 3 The resulting molecular sieve is a composite molecular sieve with both CHA and AFN structures. Quantitative analysis using XRD diffraction revealed that the CHA structure molecular sieve comprised 76.3% by weight, while the AFN structure molecular sieve comprised 23.7% by weight. XRF elemental analysis of the obtained molecular sieve powder sample revealed its chemical composition to be (Si... 0.06 Al 0.42 P 0.52 The composite molecular sieve contained 0.174% Na₂O by weight. After calcination at 550℃ for 3 hours, BET analysis revealed a micropore specific surface area of ​​357 m² / h. 2 / g, micropore volume is 0.165cm³ 3 / g, the obtained composite molecular sieve has good micropore specific surface area and micropore volume, indicating that the composite molecular sieve has a complete crystal structure and high crystallinity.

[0055] Example 4

[0056] The preparation method was followed as in Example 2, except that phosphoric acid was added separately as the phosphorus source and boehmite as the aluminum source for synthesis. X-ray diffraction analysis of the obtained solid powder sample revealed it to be a composite molecular sieve with both CHA and AFN structures.

[0057] Comparative Example 1

[0058] The preparation method was the same as in Example 2, except that isopropylamine was not added; instead, the same amount of isobutylamine was added as a template agent. X-ray diffraction analysis of the obtained solid powder sample showed that it belonged to other molecular sieve crystal phases and did not contain CHA or AFN structures.

[0059] Comparative Example 2

[0060] The preparation method was the same as in Example 2, except that sodium persulfate was not added. X-ray diffraction analysis of the obtained solid powder sample revealed it to be an AFN-structured molecular sieve.

[0061] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0062] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0063] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a composite molecular sieve having a CHA structure and an AFN structure, characterized in that, The preparation method includes: crystallizing an initial gel mixture containing a phosphorus source, a silicon source, an aluminum source, a template agent, and water in the presence of persulfate, wherein the template agent is an organic amine with no more than 3 carbon atoms; In the initial gel mixture, the molar ratio of phosphorus source, silicon source, aluminum source, template agent, water and persulfate is 0.6-1.22 : 0.01-1 : 1 : 1-10 : 10-200 : 0.001-0.02, wherein the phosphorus source is calculated as P2O5, the aluminum source is calculated as Al2O3, and the silicon source is calculated as SiO2; The crystallization process includes sequentially performing a first-stage crystallization and a second-stage crystallization, wherein the temperature of the first-stage crystallization is lower than the temperature of the second-stage crystallization. The first stage of crystallization is carried out under autogenous pressure and at 140-160℃ for 33-40 hours, and the second stage of crystallization is carried out under autogenous pressure and at 170-190℃ for 25-50 hours.

2. The preparation method according to claim 1, wherein, In the initial gel mixture, the molar ratio of phosphorus source, silicon source, aluminum source, template agent, water and persulfate is 0.8-1.2 : 0.1-0.9 : 1 : 1.1-5 : 12-80 : 0.002-0.018, wherein the phosphorus source is calculated as P2O5, the aluminum source is calculated as Al2O3, and the silicon source is calculated as SiO2.

3. The preparation method according to claim 1 or 2, wherein, The persulfate ions are provided by alkali metal persulfates.

4. The preparation method according to claim 3, wherein, The persulfate ions are provided by sodium persulfate and / or potassium persulfate.

5. The preparation method according to claim 1 or 2, wherein, The phosphorus source and aluminum source are provided by a phosphorus-aluminum composite, wherein the molar ratio of P (calculated as P2O5) to Al (calculated as Al2O3) in the phosphorus-aluminum composite is 0.8-1.2, and the phosphorus-aluminum composite has a phosphorus-aluminum crystal framework structure.

6. The preparation method according to claim 1 or 2, wherein, The phosphorus source is phosphoric acid; And / or, the silicon source is silicon dioxide; And / or, the aluminum source is aluminum oxide and / or aluminum hydroxide; And / or, the template agent is isopropylamine.

7. The preparation method according to claim 1 or 2, wherein, The phosphorus source is orthophosphoric acid; And / or, the silicon source is silica and / or silica gel; And / or, the aluminum source is at least one of anhydrous alumina, aluminum hydroxide, and boehmite.

8. The preparation method according to claim 1 or 2, wherein, The first stage of crystallization is carried out under autogenous pressure and at 145-155℃ for 35-39 hours, and the second stage of crystallization is carried out under autogenous pressure and at 175-185℃ for 30-45 hours.

9. The preparation method according to claim 1 or 2, wherein, The method further includes: sequentially performing solid-liquid separation, washing, drying, and calcination on the crystallized product.

10. The preparation method according to claim 9, wherein, The drying temperature is 70-110℃, and the drying time is 4-12 hours; And / or, the calcination temperature is 500-600℃, and the calcination time is 3-5h.

11. A composite molecular sieve having a CHA structure and an AFN structure, characterized in that, The composite molecular sieve is prepared by the preparation method described in any one of claims 1-10; Alternatively, the weight percentage of CHA structure molecular sieve in the composite molecular sieve is 10-95%, and the weight percentage of AFN structure molecular sieve is 5-90%.

12. The composite molecular sieve according to claim 11, wherein, The anhydrous chemical composition of the composite molecular sieve is (SixAlyPz)O2, where x, y, and z represent the mole fractions of Si, Al, and P, respectively, with values ​​ranging from x=0.01-0.2, y=0.3-0.49, and z=0.4-0.6, and x+y+z=1; and the Na2O weight percentage content is 0-0.3%. And / or, the microporous specific surface area of ​​the composite molecular sieve is not less than 340 m². 2 / g; And / or, the micropore volume of the composite molecular sieve is not less than 0.155 cm³. 3 / g.

13. The composite molecular sieve according to claim 12, wherein, The composite molecular sieve has a microporous specific surface area of ​​350-400 m². 2 / g; And / or, the micropore volume of the composite molecular sieve is 0.16-0.18 cm³. 3 / g.

14. The use of the composite molecular sieve according to any one of claims 11-13 as a catalyst in acid-catalyzed reactions.

15. The application according to claim 14, wherein, The acid-catalyzed reaction is a reaction in which oxygen-containing compounds are converted into olefins or a reaction in which straight-chain alkane isomerizes.

16. The application of the composite molecular sieve according to any one of claims 11-13 in gas adsorption treatment.

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