An afx-type zeolite molecular sieve, a preparation method therefor and an application thereof

Abstract

The present application belongs to the technical field of zeolite molecular sieve, and particularly relates to an AFX type zeolite molecular sieve, a preparation method and application thereof. An initial gel obtained by mixing an aluminum source, a silicon source, an inorganic base (sodium carbonate and / or sodium hydroxide), seeds and water is subjected to a hydrothermal crystallization reaction, and a crystallization product obtained is subjected to solid-liquid separation, washing and solid drying in sequence to obtain the AFX type zeolite molecular sieve. The AFX type zeolite molecular sieve with no organic template agent and low silicon-aluminum ratio is synthesized by using a traditional hydrothermal synthesis method, using seeds and an inorganic cation double-oriented design, and has great potential application value in the future catalysis field of diesel vehicles and non-road mobile machinery and the industrial adsorption separation industry due to the properties of no organic template agent and low silicon-aluminum ratio, and the synthesis does not use an organic template agent, reduces industrial production cost, and also reduces environmental pollution, and has great economic advantages in industrial production.

Description

Technical Field

[0001] This invention belongs to the field of zeolite molecular sieve technology, specifically relating to an AFX type zeolite molecular sieve, its preparation method, and its application. Background Technology

[0002] AFX-type zeolite molecular sieves were first reported by Zones in 1985, and they consist of d6r, gme, and aft cages. The AFX structure has a straight 8-ring channel. The three-dimensional porous system it forms belongs to the ABC6 group of zeolites, and its silicon-to-aluminum ratio is generally greater than 3; this unique structure enables the zeolite to be used in heterogeneous catalytic reactions.

[0003] Existing technologies often use complex organic templates or other small molecule templates to synthesize AFX-type zeolite molecular sieves. However, the presence of organic templates causes wastewater pollution during the synthesis process. In addition, to obtain complete molecular sieve channels, it is often necessary to calcine the organic templates, which leads to energy consumption and the generation of toxic gases. Moreover, organic templates themselves are expensive, making their use unfavorable for industrial applications. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an AFX-type zeolite molecular sieve, its preparation method and application. The preparation method is simple, does not use organic template agents, is low in cost, and does not produce toxic gases. The AFX-type zeolite molecular sieve prepared by this method has a low silica-alumina ratio, high purity and high crystallinity.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing AFX-type zeolite molecular sieves, comprising the following steps:

[0007] The initial gel obtained by mixing aluminum source, silicon source, inorganic alkali, seed crystal and water was subjected to hydrothermal crystallization reaction to obtain crystallized product;

[0008] The crystallized product was subjected to solid-liquid separation, washing, and solid drying in sequence to obtain the AFX type zeolite molecular sieve.

[0009] The inorganic base includes sodium carbonate and / or sodium hydroxide.

[0010] Preferably, the aluminum source includes one or more of sodium aluminate, aluminum isopropoxide, boehmite, aluminum chloride, aluminum sulfate, and aluminum hydroxide.

[0011] Preferably, the silicon source includes one or more of silica, silica sol, sodium silicate, tetraethyl orthosilicate, and water glass.

[0012] Preferably, the mass of the seed crystal is 5-15% of the mass of SiO2 in the silicon source.

[0013] Preferably, the temperature of the hydrothermal crystallization reaction is 120–200°C.

[0014] Preferably, the hydrothermal crystallization reaction takes 1 to 5 days.

[0015] Preferably, the ratio of the amount of silicon source to aluminum source, expressed as the molar ratio of SiO2 to Al2O3, is 1:(0.01 to 0.1).

[0016] Preferably, the ratio of the amount of silicon source and inorganic base used is 1:(0.25~0.6, based on the molar ratio of SiO2 to Na2O).

[0017] The present invention also provides an AFX-type zeolite molecular sieve prepared by the preparation method described above, wherein the silicon-to-aluminum ratio in the AFX-type zeolite molecular sieve is 2.8 to 2.9.

[0018] This invention also provides the application of the AFX-type zeolite molecular sieve described above in catalytic and / or adsorption separation.

[0019] This invention provides a method for preparing AFX-type zeolite molecular sieves, comprising the following steps: hydrothermal crystallization of an initial gel obtained by mixing an aluminum source, a silicon source, an inorganic base, seed crystals, and water to obtain a crystallized product; sequentially subjecting the crystallized product to solid-liquid separation, washing, and solid drying to obtain the AFX-type zeolite molecular sieve; the inorganic base includes sodium carbonate and / or sodium hydroxide. This invention synthesizes AFX-type zeolite molecular sieves using a dual-directed synthesis method involving seed crystals and inorganic cations. Analysis of its crystalline phase region reveals that it can crystallize only in specific phase regions under organic template agent-free conditions, ultimately yielding the AFX-type zeolite molecular sieve without an organic template agent. This invention avoids the use of expensive and toxic organic template agents, thereby reducing synthesis costs and generating significant economic advantages. Furthermore, it does not produce toxic gases, making it green, economical, and environmentally friendly. Moreover, the AFX-type zeolite molecular sieve prepared by this invention has a silicon-to-aluminum ratio of 2.8–2.9. The AFX type zeolite molecular sieve has a low silicon-to-aluminum ratio, high purity, and high crystallinity. Its low silicon-to-aluminum ratio makes it a potential application in the catalytic field of diesel vehicles and off-road mobile machinery, as well as in the industrial adsorption and separation industry. Attached Figure Description

[0020] Figure 1 The XRD patterns of AFX-type zeolite molecular sieves synthesized with different silicon or aluminum sources in Examples 1-3 are shown.

[0021] Figure 2 The XRD patterns are of AFX-type zeolite molecular sieves obtained by different seed-assisted synthesis in Examples 2 and 4.

[0022] Figure 3 Here is a scanning electron microscope image of the AFX zeolite molecular sieve synthesized in Example 1;

[0023] Figure 4 The image shows a scanning electron microscope (SEM) image of the AFX zeolite molecular sieve synthesized in Example 2.

[0024] Figure 5 Here is a scanning electron microscope image of the AFX zeolite molecular sieve synthesized in Example 3;

[0025] Figure 6 The image shows a scanning electron microscope (SEM) image of the AFX zeolite molecular sieve synthesized in Example 4.

[0026] Figure 7 This is the powder X-ray diffraction (PXRD) pattern of the template-free AFX zeolite molecular sieve synthesized in this invention.

[0027] Figure 8 This is a scanning electron microscope image of the template-free AFX zeolite molecular sieve synthesized in this invention. Detailed Implementation

[0028] This invention provides a method for preparing AFX-type zeolite molecular sieves, comprising the following steps:

[0029] The initial gel obtained by mixing aluminum source, silicon source, inorganic alkali, seed crystal and water was subjected to hydrothermal crystallization reaction to obtain crystallized product;

[0030] The crystallized product was subjected to solid-liquid separation, washing, and solid drying in sequence to obtain the AFX type zeolite molecular sieve.

[0031] The inorganic base includes sodium carbonate and / or sodium hydroxide.

[0032] Unless otherwise specified, the present invention does not have special requirements on the source of the raw materials used in the preparation, and commercially available products well known to those skilled in the art can be used.

[0033] This invention mixes an aluminum source, a silicon source, an inorganic alkali, seed crystals, and water to obtain an initial gel.

[0034] In this invention, the silicon source preferably includes one or more of silica, silica sol, sodium silicate, tetraethyl orthosilicate and water glass, and more preferably silica or silica sol.

[0035] In this embodiment of the invention, the SiO2 content in the silica sol is specifically 30%.

[0036] In this invention, the aluminum source preferably includes one or more of sodium aluminate, aluminum isopropoxide, boehmite, aluminum chloride, aluminum sulfate, and aluminum hydroxide, more preferably aluminum isopropoxide or boehmite; the ratio of the amount of silicon source to aluminum source, based on the molar ratio of SiO2 to Al2O3, is preferably 1:(0.01-0.1), more preferably 1:(0.01-0.05).

[0037] In this invention, the mass of the seed crystal is preferably 5-15% of the mass of SiO2 in the silicon source, more preferably 7-12%. In this invention, the seed crystal is preferably SAPO-56 or SSZ-16, more preferably SAPO-56. This invention does not have a particular limitation on the source of the seed crystal; it can be prepared using commercially available related products or methods well known to those skilled in the art.

[0038] In this invention, the inorganic base includes sodium carbonate and / or sodium hydroxide, preferably sodium hydroxide; the ratio of the amount of silicon source and inorganic base is based on the molar ratio of SiO2 to Na2O, preferably 1:(0.25-0.6), more preferably 1:(0.3-0.5).

[0039] In this invention, the ratio of the amount of silicon source and water used is preferably 1:(10-60), more preferably 1:(20-50), based on the molar ratio of SiO2 to H2O.

[0040] In this invention, the preferred method for mixing the aluminum source, silicon source, inorganic alkali, seed crystal, and water is to first mix the aluminum source and water and stir until completely dissolved, then add the inorganic alkali and stir a third time, then add the seed crystal and stir a fourth time until completely dissolved, and finally add the silicon source to the resulting suspension and stir a fifth time. In this invention, the first stirring is preferably performed at room temperature; the first stirring speed is preferably 40-60 rpm, more preferably 50 rpm; the first stirring time is preferably 5-20 min, more preferably 10 min; the second stirring is preferably performed at room temperature; the second stirring speed is preferably 40-60 rpm, more preferably 50 rpm; the second stirring time is preferably 5-20 min, more preferably 10 min; the third stirring is preferably performed at room temperature; the third stirring speed is preferably 40-60 rpm, more preferably 50 rpm; the invention does not have a specific limitation on the third stirring time, as long as the seed crystal is uniformly dissolved; the fourth stirring is preferably performed at room temperature; the fourth stirring speed is preferably 40-60 rpm, more preferably 50 rpm; the fourth stirring time is preferably 12-36 h, more preferably 24 h.

[0041] After obtaining the initial gel, the present invention performs a hydrothermal crystallization reaction on the initial gel to obtain a crystallized product.

[0042] In this invention, the temperature of the hydrothermal crystallization reaction is preferably 120-200°C, more preferably 150-170°C; the time of the hydrothermal crystallization reaction is preferably 1-5 days, more preferably 2-4 days.

[0043] After obtaining the crystallized product, the present invention performs solid-liquid separation on the crystallized product to obtain a solid.

[0044] In this invention, the solid-liquid separation is preferably performed by filtration. The present invention does not specifically limit the filtration process; any filtration process well-known in the art can be used.

[0045] After obtaining the solid, the present invention washes the solid to obtain a washed solid.

[0046] In this invention, the reagent used for washing is preferably water, more preferably deionized water; the number of washing cycles is preferably 2 to 5 times, more preferably 3 times.

[0047] After obtaining the washed solid, the present invention performs solid drying on the washed solid to obtain the AFX type zeolite molecular sieve.

[0048] In this invention, the drying temperature is preferably 70-80°C, more preferably 75°C; the drying time is preferably 12-36 hours, more preferably 24 hours.

[0049] This invention synthesizes AFX-type zeolite molecular sieves using a dual-directed synthesis method involving seed crystals and inorganic cations. Analysis of its crystalline phase regions reveals that crystallization occurs only within specific phase regions of the AFX-type zeolite molecular sieve under organic template-free conditions. This method yields AFX-type zeolite molecular sieves without the use of organic templates, resulting in significant economic advantages. Furthermore, it eliminates the production of toxic gases, making it a green, economical, and environmentally friendly option. The prepared AFX-type zeolite molecular sieves, characterized by a low silica-to-alumina ratio, high purity, and high crystallinity, also hold immense potential for future applications in catalysis of diesel vehicles and off-road mobile machinery, as well as in industrial adsorption and separation.

[0050] The present invention also provides an AFX-type zeolite molecular sieve prepared by the preparation method described above, wherein the silicon-to-aluminum ratio in the AFX-type zeolite molecular sieve is 2.8 to 2.9.

[0051] In this invention, the silica-alumina ratio in the AFX type zeolite molecular sieve is preferably 2.8.

[0052] In this invention, the crystal structure of the AFX-type zeolite molecular sieve belongs to the hexagonal space group P63 / mmc and ABC-6, with a stacking sequence of AABBCCBB and a framework density of 15.1 t atoms / AFX-type zeolite molecular sieves are formed through the construction of d6r, GME, and AFT cages. The AFX structure has a straight 8-ring channel. A three-dimensional pore system.

[0053] The AFX-type zeolite molecular sieve provided by this invention has a low silica-to-alumina ratio, high purity, and high crystallinity.

[0054] This invention also provides the application of the AFX-type zeolite molecular sieve described above in catalytic and / or adsorption separation.

[0055] The present invention does not impose any particular limitation on the application of the AFX type zeolite molecular sieve in catalysis and / or adsorption separation; any application method known in the art can be used.

[0056] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] 0.097 g of sodium aluminate was added to 7.350 mL of water and stirred at 50 rpm for 10 min at room temperature until uniformly dissolved. Then, 0.379 g of sodium hydroxide was added and stirred at 50 rpm for 10 min at room temperature. Next, 0.070 g of SAPO-56 seed crystals were added and stirred at 50 rpm at room temperature until uniformly dissolved. Then, 0.701 g of silica was added to the resulting suspension and stirred at 50 rpm at room temperature until uniform. The stirring time was 24 h to obtain a mixture. The resulting mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and subjected to hydrothermal crystallization at 150 °C for 3 days. Crystallization occurred. The obtained crystallization product was filtered, washed three times with deionized water, and dried at 75 °C for 24 h to obtain AFX type zeolite molecular sieve.

[0059] Example 2

[0060] 0.042 g of boehmite was added to 5.800 mL of water and stirred at 50 rpm for 10 min at room temperature until uniformly dissolved. Then, 0.333 g of sodium hydroxide was added and stirred at 50 rpm for 10 min at room temperature. Next, 0.060 g of SAPO-56 seed crystals were added and stirred at 50 rpm at room temperature until uniformly dissolved. Then, 2.003 g of silica sol (SiO2 content of 30%) was added to the resulting suspension and stirred at 50 rpm at room temperature until uniform for 24 h to obtain a mixture. The resulting mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and subjected to hydrothermal crystallization at 160 °C for 1 day. Crystallization occurred. The obtained crystallization product was filtered, washed with deionized water three times, and dried at 75 °C for 24 h to obtain AFX type zeolite molecular sieve.

[0061] Example 3

[0062] 0.081 g of aluminum isopropoxide was added to 5.148 mL of water and stirred at 50 rpm for 10 min at room temperature until uniformly dissolved. Then, 0.251 g of sodium hydroxide was added and stirred at 50 rpm for 10 min at room temperature. Next, 0.045 g of SAPO-56 seed crystals were added and stirred at 50 rpm at room temperature until uniformly dissolved. Then, 0.450 g of silica was added to the resulting suspension and stirred at 50 rpm at room temperature until uniform. The stirring time was 24 h to obtain a mixture. The resulting mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and subjected to hydrothermal crystallization at 160 °C for 2 days. Crystallization occurred. The obtained crystallization product was filtered, washed three times with deionized water, and dried at 75 °C for 24 h to obtain AFX type zeolite molecular sieve.

[0063] Example 4

[0064] 0.034 g of boehmite was added to 6.000 mL of water and stirred at 50 rpm for 10 min at room temperature until uniformly dissolved. Then, 0.277 g of sodium hydroxide was added and stirred at 50 rpm for 10 min at room temperature. Next, 0.050 g of SSZ-16 seed crystals were added and stirred at 50 rpm at room temperature until uniformly dissolved. Then, 0.669 g of silica was added to the resulting suspension and stirred at 50 rpm at room temperature until uniform. The stirring time was 24 h to obtain a mixture. The resulting mixture was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and subjected to hydrothermal crystallization at 170 °C for 5 days. Crystallization occurred. The obtained crystallization product was filtered, washed three times with deionized water, and dried at 75 °C for 24 h to obtain AFX type zeolite molecular sieve.

[0065] Comparative Example 1

[0066] The Si / Al ratio of AFX-type zeolite molecular sieves synthesized in the prior art (M. Onishi, N. Tsunoji, M. Sadakane, T. Sano, Synthesis of Phosphorus-Modified AFX Zeolite by the Hydrothermal Conversion of Tetraalkylphosphonium Hydroxide Impregnated FAU Zeolite, Bull. Chem. Soc. Jpn. 94 (2021) 1-7) is 3.3 to 5.5.

[0067] Comparative Example 2

[0068] The Si / Al ratio of the AFX-type zeolite molecular sieve synthesized in the prior art (P. Hrabanek, A. Zikanova, T. Supinkova, J. Drahokoupil, V. Fila, M. Lhotka, H. Dragounova, F. Laufek, L. Brabec, I. Jirka, B. Bernauer, O. Prokopova, V. Martin-Gil, M. Kocirik, Static in-situ hydrothermal synthesis of small porezeolite SSZ-16 (AFX) using heated and pre-aged synthesis mixtures, Micropor. Mesopor. Mater. 228 (2016) 107-115) is 9.1.

[0069] Performance testing

[0070] (1) XRD tests were performed on the AFX-type zeolite molecular sieves synthesized with different silicon or aluminum sources in Examples 1-3, and the results were compared with the standard spectra of AFX zeolite molecular sieves. Figure 1 As shown.

[0071] Depend on Figure 1 It can be seen that the AFX type zeolite molecular sieve provided by the present invention has a high degree of crystallinity, with 90% in Example 1, 95% in Example 2, and 85% in Example 3.

[0072] (2) XRD tests were performed on the AFX-type zeolite molecular sieves obtained by different seed-assisted synthesis in Examples 2 and 4, and the results were compared with the standard spectra of AFX zeolite molecular sieves. Figure 2 As shown.

[0073] Depend on Figure 2 It can be seen that the AFX type zeolite molecular sieve provided by the present invention has a high degree of crystallinity, which is 95% in Example 4.

[0074] (3) The AFX zeolite molecular sieves synthesized in Examples 1-4 were scanned using a scanning electron microscope, and the results are as follows: Figures 3-6 As shown.

[0075] Depend on Figures 3-6 As shown, the AFX type zeolite molecular sieve provided by this invention has high purity.

[0076] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A process for the preparation of an AFX-type zeolite molecular sieve, characterized by, The method comprises the following steps: mixing an aluminum source, a silicon source, an inorganic base, seeds and water to obtain an initial gel, and then performing a hydrothermal crystallization reaction on the initial gel to obtain a crystallization product; performing solid-liquid separation, washing and solid drying on the crystallization product in sequence to obtain the AFX-type zeolite molecular sieve; the inorganic base is sodium hydroxide; the aluminum source comprises sodium metaaluminate, aluminum isopropoxide or pseudo-boehmite; the silicon source is white carbon black; the seeds are SAPO-56; the silicon-aluminum ratio in the AFX-type zeolite molecular sieve is 2.8-2.

9.

2. The production method according to claim 1, characterized by, The mass of the seeds is 5-15% of the mass of SiO2 in the silicon source.

3. The preparation method according to claim 1, characterized in that, The temperature of the hydrothermal crystallization reaction is 120-200 ℃.

4. The production method according to claim 1 or 3, characterized by, The time of the hydrothermal crystallization reaction is 1-5 days.

5. The preparation method according to claim 1, characterized in that, The amount of the silicon source and the aluminum source is in a molar ratio of SiO2 to Al2O3 of 1:(0.01-0.1).

6. The method of claim 1, wherein, The amount of the silicon source and the inorganic base is in a molar ratio of SiO2 to Na2O of 1:(0.25-0.6).

7. The zeolite molecular sieve of AFX type prepared according to the preparation process of any one of claims 1 to 6, characterized in that, The silicon-aluminum ratio in the AFX-type zeolite molecular sieve is 2.8-2.

9.

8. The AFX-type zeolite molecular sieve of claim 7 is applied to catalysis and / or adsorption separation.

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