Method for rapidly guiding cascade pore X molecular sieve with ultralow silica-alumina ratio based on electronegative ion collaborative matching

Abstract

The invention discloses a method for rapidly guiding a cascade pore X molecular sieve with an ultralow silica-alumina ratio based on electronegative ion collaborative matching. The preparation method comprises the following steps: dissolving an alkali source, an aluminum source and electronegative ions in water, adding a silicon source, and continuously stirring and aging to form uniform gel; and carrying out hydrothermal crystallization reaction on the gel to obtain the cascade pore X molecular sieve. Electronegative ions have strong ion affinity, form positive charges in a solution, and provide electrons for silicon-aluminum species under certain conditions. According to the method, electronegative ions with different ion radiuses are cooperatively matched, depolymerization nucleation of silicon-aluminum species is regulated and controlled, formation of a micro-mesoporous structure of the X molecular sieve is promoted, and the cascade pore X molecular sieve with the ultralow silicon-aluminum ratio is rapidly synthesized. The cascade pore X molecular sieve with an ultralow silica-alumina ratio can be prepared by regulating and controlling the electronegative ions, the synthesized X molecular sieve has a microporous, mesoporous or macroporous structure, and the problems of low mass transfer efficiency and poor accessible active sites of the conventional microporous X molecular sieve are effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieve preparation, and particularly relates to a method for rapidly guiding a hierarchical pore X molecular sieve with an ultra-low silicon-aluminum ratio based on the synergistic matching of electronegative ions. Background Art

[0002] The low silicon-aluminum ratio X molecular sieve was first synthesized by G.H. Kühl. It has the FAU topological structure, namely a hexagonal ring structure and a supercage structure with a relatively large window diameter. The confined environment inside the cage can serve as the reaction center for guest molecules, showing good molecular selectivity and excellent crystal structure stability. The low silicon-aluminum ratio X molecular sieve is one of the most commercially valuable and widely used molecular sieves in industry. However, only microporous structures exist in the low silicon-aluminum ratio X molecular sieve, which limits the molecular diffusion during the reaction process, thus affecting its adsorption / catalytic performance. In order to improve the diffusion environment of the molecular sieve and increase the mass transfer rate, hierarchical pore molecular sieves have emerged. Hierarchical pore molecular sieves refer to molecular sieves with micropores, mesopores or macropores. Hierarchical pore molecular sieves have been proven to have better molecular transfer efficiency than microporous molecular sieves, greatly improving the adsorption and catalytic performance of the molecular sieve.

[0003] The common synthesis method of the low silicon-aluminum ratio hierarchical pore X molecular sieve is the direct synthesis method. Usually, a hard or soft template agent and the required silicon and aluminum sources for the reaction are simultaneously introduced into the synthesis system at the initial stage of synthesis. After crystallization, the template agent is removed by high-temperature calcination, and finally a hierarchical pore molecular sieve rich in mesopores or even macropores is obtained. However, the template agent is not only expensive, but its removal process may also cause the collapse of the molecular sieve framework structure and produce pollution emissions, which is a high-cost and non-green process. Therefore, it is urgent to develop a template-free green synthesis method for the low silicon-aluminum ratio hierarchical pore X molecular sieve. The open literature (Journal of Cleaner Production, 372(2022)133591.) uses fly ash as the raw material, adds a foaming agent, and crystallizes for 48 h under saturated steam at 80 °C to obtain a hierarchical pore X molecular sieve. The open literature (Journal of Materials Science, 59(2024)10169-10181.) adopts a route without additives and synthesizes a hierarchical pore X molecular sieve (Si / Al = 1.2) with a layered morphology at a crystallization temperature of 90 °C for 24 h. The open literature (Materials Today Communications, 39(2024)109047.) ages at room temperature for 5 days in a tubular reactor, with a crystallization temperature of 90 °C and a crystallization time of 40 min at 1.1 atmospheres to obtain a low silicon-aluminum ratio hierarchical pore X molecular sieve.

[0004] The above-mentioned literature successfully prepared the hierarchical pore X molecular sieve without adding an organic template agent, but the required aging or crystallization time is relatively long and the energy consumption is high. Summary of the Invention

[0005] The object of the present invention is to provide a method for rapidly guiding a hierarchical pore X zeolite with an ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions. Without adding expensive mesoporous templating agents, different morphologies of hierarchical pore X zeolites can be rapidly synthesized by using electronegative ions, which is an efficient and green zeolite synthesis process. The synthesized X zeolite with a low silica-alumina ratio has both micropores, mesopores or macropores, forming a hierarchical pore structure, effectively solving the problems of low mass transfer efficiency and poor accessibility of active sites existing in conventional microporous X zeolites.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for rapidly guiding a hierarchical pore X zeolite with an ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions: The electronegative ions provide charges to the silica-alumina species, promoting the depolymerization and nucleation of the silica-alumina species, and synergistically matching the electronegative ions to effectively regulate the formation of the micro-mesoporous structure of the ultra-low silica-alumina ratio X zeolite, realizing the green synthesis of the hierarchical pore X zeolite with an ultra-low silica-alumina ratio without a template method. The specific steps of the method are as follows:

[0008] (1) Aging: Dissolve the alkali source, aluminum source and electronegative ions in deionized water, continuously stir for 20 - 30 minutes, then add the silica source, and continuously stir and age to form a uniform gel;

[0009] (2) Crystallization: Transfer the gel obtained after aging into a stainless steel autoclave for hydrothermal crystallization reaction, and then filter, wash and dry the product to obtain a hierarchical pore X zeolite with an ultra-low silica-alumina ratio.

[0010] As a preference of the present invention, the alkali source is one or both of sodium hydroxide and potassium hydroxide.

[0011] As a preference of the present invention, the aluminum source is one or more of sodium aluminate, aluminum sulfate and aluminum isopropoxide.

[0012] As a preference of the present invention, the electronegative ions are provided by one or more of FeO2, Na2O, NaBr, KBr or Mg3N2.

[0013] As a preference of the present invention, the silica source is one or more of water glass, silica sol, white carbon black and tetraethyl orthosilicate.

[0014] As a preference of the present invention, the gel composition in step (1) satisfies the following molar ratio: 1.0Al2O3:2.0 - 2.2SiO2:2.0 - 4.0Na2O:0.4 - 0.5K2O:100 - 120H2O:0.5 - 7.0 electronegative ions.

[0015] Preferably in the present invention, the aging time in step (1) is 3 to 30 min.

[0016] Preferably in the present invention, the temperature of the crystallization reaction in step (2) is 60 to 90 °C, and the crystallization reaction time is 0.5 to 4 h.

[0017] The mesopore aperture of the ultra-low silica-alumina ratio hierarchical pore X zeolite is 3 to 20 nm, the silica-alumina molar ratio is 2.01 to 2.04, the specific surface area is 666 to 920 m 2 / g, and the relative crystallinity is 80 to 98%.

[0018] Advantages of the present invention:

[0019] (1) The present invention can rapidly synthesize a hierarchical pore X zeolite with good crystallinity and a microporous-mesoporous composite under the condition of not adding an organic template and in the ultra-low silica-alumina ratio range by adjusting the concentration of electronegative ions. The required synthesis time is short, and there is no need to calcine the zeolite to remove the template, avoiding the problems of high energy consumption and environmental pollution caused by high-temperature calcination, and achieving the purpose of efficiently and greenly synthesizing the ultra-low silica-alumina ratio hierarchical pore X zeolite.

[0020] (2) Electronegative ions have strong ionic affinity, form positive charges in solution, and provide electrons to silicon-aluminum species under certain conditions. In the present invention, by synergistically matching electronegative ions with different ionic radii, the depolymerization and nucleation of silicon-aluminum species are regulated, promoting the formation of the micro-mesoporous structure of the ultra-low silica-alumina ratio X zeolite, and rapidly synthesizing the hierarchical pore X zeolite, and the zeolite has an ultra-low silica-alumina ratio (n(SiO2 / Al2O3) = 2.01 to 2.04).

[0021] (3) The present invention applies the synthesized ultra-low silica-alumina ratio hierarchical pore X zeolite to heavy metal adsorption, and has achieved remarkable effects. Compared with commercial X zeolite, under the same reaction conditions, the removal rate of heavy metals in sewage by the ultra-low silica-alumina ratio hierarchical pore X zeolite synthesized in the present invention is as high as 99.6%. Description of the drawings

[0022] Figure 1 It is the X-ray diffraction (XRD) pattern of the ultra-low silica-alumina ratio hierarchical pore X zeolite prepared in Examples 1, 2, and 3 of the present invention.

[0023] Figure 2 It is the scanning electron microscope (SEM) photograph of the ultra-low silica-alumina ratio hierarchical pore X zeolite prepared in Example 1 of the present invention.

[0024] Figure 3 It is the SEM photograph of the ultra-low silica-alumina ratio hierarchical pore X zeolite prepared in Example 2 of the present invention.

[0025] Figure 4SEM photograph of the hierarchical pore X zeolite with ultra-low silica-alumina ratio prepared in Example 3 of the present invention. Detailed implementation manners

[0026] The present invention will be further described in detail below with reference to the embodiments, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0027] The relative crystallinity in the examples is determined according to the ASTM D 3906-03 (2013) standard. The ratio of the sum of the integrated areas of 2θ at 15.7°±0.2°, 18.7±0.2°, 20.4°±0.3°, 23.7°±0.4°, 27.1°±0.5°, 30.8°±0.5°, 31.5°±0.5°, 34.2°±0.5° in the XRD patterns of the obtained product and the low silica-alumina ratio X zeolite standard sample is expressed as a percentage. The standard sample is an X zeolite with a silica-alumina molar ratio of 2.13 synthesized from conventional chemical reagents (produced by Nankai University Catalyst Factory), and its relative crystallinity is defined as 100%.

[0028] The experimental method for the adsorption of lead ions in the examples is as follows: Using a lead ion solution with an initial concentration of 500 mg / L as the adsorbate, 0.1 g of zeolite is added to 50 mL of the above lead ion solution, and stirred at 40 °C and a rotation speed of 400 rpm for 6 h. The zeolite solid is separated by centrifugation, and the supernatant is subjected to inductively coupled plasma detection.

[0029] Example 1

[0030] A method for rapidly guiding a hierarchical pore X zeolite with ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions, the steps are as follows:

[0031] (1) Aging: Dissolve sodium hydroxide, potassium hydroxide, sodium aluminate, sodium bromide and magnesium nitride in deionized water, stir continuously for 20 minutes, then add water glass and stir continuously to form a uniform gel. Control the molar ratio of the system as: Al2O3:SiO2:Na2O:K2O:H2O:NaBr:Mg3N2 = 1.0:2.0:3.5:0.5:110:6.2:0.6, and stir and age continuously for 5 min.

[0032] (2) Crystallization: Transfer the aged gel into a stainless steel autoclave, and carry out static crystallization at 80 °C for 2 h. After the crystallization is completed, the obtained sample is filtered, washed and dried to obtain a hierarchical pore X zeolite with ultra-low silica-alumina ratio.

[0033] The XRD diffraction pattern of the product obtained in this example is as Figure 1 shown, and the obtained solid powder phase belongs to the hierarchical pore X zeolite with ultra-low silica-alumina ratio. The SiO2 / Al2O3 measured by ICP is 2.01.

[0034] AsFigure 2 As shown, the diameter of the prepared molecular sieve particles characterized by SEM is 1.0 μm, which is a bulk-packed spherical ultra-low silica-alumina ratio X molecular sieve.

[0035] As shown in Table 1, from the N2 adsorption-desorption results, the mesopore diameter is concentrated at 8 nm, the specific surface area is 666 m 2 / g, and the pore volume is 0.35 cm 3 / g. Its adsorption rate for lead ions is 90.8%.

[0036] Example 2

[0037] A method for rapidly guiding a hierarchical pore X molecular sieve with ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions is as follows:

[0038] (1) Aging: Dissolve sodium hydroxide, potassium hydroxide, sodium aluminate, potassium bromide, and iron oxide in deionized water, continuously stir for 20 minutes, then add water glass, and continuously stir to form a homogeneous gel. Control the molar ratio of the system as: Al2O3:SiO2:Na2O:K2O:H2O:KBr:FeO2 = 1.0:2.05:3.2:0.4:115:5.5:0.5, and continuously stir and age for 10 min.

[0039] (2) Crystallization: Transfer the aged gel into a stainless steel autoclave and perform static crystallization at 75 °C for 4 h. After the crystallization is completed, the obtained sample is filtered, washed, and dried to obtain a hierarchical pore X molecular sieve with ultra-low silica-alumina ratio.

[0040] The XRD diffraction pattern of the product obtained in this example is as Figure 1 shown. The solid powder phase obtained belongs to the ultra-low silica-alumina ratio X molecular sieve, and the SiO2 / Al2O3 measured by ICP is 2.03.

[0041] As Figure 3 shown, the SEM characterization shows that the prepared molecular sieve is a bulk-packed hollow ultra-low silica-alumina ratio X molecular sieve.

[0042] As shown in Table 1, from the N2 adsorption-desorption results, the mesopore diameter is concentrated at 10 nm, the specific surface area is 850 m 2 / g, and the pore volume is 0.39 cm 3 / g. Its adsorption rate for lead ions is 95.4%.

[0043] Example 3

[0044] A method for rapidly guiding a hierarchical pore X molecular sieve with ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions is as follows:

[0045] (1) Aging: Dissolve sodium hydroxide, potassium hydroxide, sodium aluminate, magnesium nitride, and iron oxide in deionized water, stir continuously for 20 minutes, then add sodium silicate and stir continuously to form a homogeneous gel. Control the molar ratio of the system as: Al2O3:SiO2:Na2O:K2O:H2O:Mg3N2:FeO2 = 1.0:2.1:2.1:0.45:116:3.0:1.1, and stir continuously for aging for 30 min.

[0046] (2) Crystallization: Transfer the aged gel into a stainless-steel autoclave and perform static crystallization at 90 °C for 0.5 h. After the crystallization is completed, the obtained sample is filtered, washed, and dried to obtain an ultra-low silica-alumina ratio hierarchical pore X zeolite.

[0047] The XRD diffraction pattern of the product obtained in this example is as Figure 1 shown. The obtained solid powder phase belongs to an ultra-low silica-alumina ratio X zeolite, and the SiO2 / Al2O3 measured by ICP is 2.04.

[0048] As Figure 4 shown, the SEM characterization shows that the diameter of the prepared zeolite particles is 1.0 μm, which is a flaky stacked ultra-low silica-alumina ratio X zeolite.

[0049] As shown in Table 1, from the N2 adsorption and desorption results, it is known that the mesopore diameter is concentrated at 15 nm, the specific surface area is 920 m 2 / g, and the pore volume is 0.42 cm 3 / g. Its adsorption rate for lead ions is 99.6%.

[0050] Table 1 Structural characteristics of the hierarchical pore zeolites prepared in Examples 1-3

[0051]

[0052] Table 2 Adsorption performance of zeolite for lead ions

[0053]

[0054] Comparative Example 1

[0055] Do not add sodium bromide and magnesium nitride, and the others are the same as in Example 1. The phase of the obtained product determined by XRD is amorphous.

[0056] Comparative Example 2

[0057] Do not add potassium bromide and iron oxide, and the others are the same as in Example 2. The phase of the obtained product determined by XRD is amorphous.

[0058] Comparative Example 3

[0059] Do not add magnesium nitride and iron oxide, and the others are the same as in Example 3. The phase of the obtained product determined by XRD is amorphous.

[0060] As can be seen from the results of the above embodiments, the present invention successfully prepares hierarchical pore X zeolite with an ultra-low silica-alumina ratio by adding electronegative ions. The crystallization time required for this preparation process is short (0.5 - 4 h), and no organic template needs to be added. Moreover, by regulating the type and dosage of electronegative ions, the morphology and mesoporous structure of the hierarchical pore X zeolite with an ultra-low silica-alumina ratio can be adjusted. The prepared zeolite has excellent adsorption capacity for heavy metal lead ions. Therefore, the method of the present invention is practical, green and efficient.

Claims

1. A method for rapidly guiding a hierarchical pore X zeolite with an ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions, characterized in that, It includes the following steps: (1) Aging: Dissolve the alkali source, aluminum source and electronegative ions in water, continuously stir for 20 - 30 minutes, then add the silicon source, and continuously stir and age to form a uniform gel; (2) Crystallization: Transfer the gel obtained after aging into a stainless - steel autoclave for hydrothermal crystallization reaction, then filter, wash and dry the product to obtain the hierarchical - pore X zeolite with an ultra - low silica - alumina ratio.

2. A method for a hierarchical pore X zeolite with an ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions for rapid orientation, characterized in that, The electronegative ions are provided by one or more of FeO₂, Na₂O, NaBr, KBr or Mg₃N₂.

3. A method for a hierarchical pore X zeolite with an ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions for rapid orientation, characterized in that, The alkali source is one or two of sodium hydroxide or potassium hydroxide.

4. A method for the stepwise pore X zeolite with ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions and rapid orientation, characterized in that, The aluminum source is one or more of sodium aluminate, aluminum sulfate, aluminum isopropoxide.

5. A method for a hierarchical pore X zeolite with an ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions and rapid orientation, characterized in that, The silicon source is one or more of water glass, silica sol, fumed silica, tetraethyl orthosilicate.

6. A method for a hierarchical pore X zeolite with an ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions for rapid orientation, characterized in that, The gel composition in step (1) satisfies the following molar ratio: 1.0Al₂O₃:2.0 - 2.2SiO₂:2.0 - 4.0Na₂O:0.4 - 0.5K₂O:100 - 120H₂O:0.5 - 7.0 electronegative ions.

7. A method for a hierarchical pore X zeolite with an ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions and rapid orientation, characterized in that, The aging time in step (1) is 3 - 30 min.

8. A method for a hierarchical pore X zeolite with an ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions and rapid guidance, characterized in that The temperature of the crystallization reaction described in step (2) is 60~90 o °C, and the time of the crystallization reaction is 0.5~4 h.

9. A method for a hierarchical pore X zeolite with an ultra-low silica-alumina ratio based on the synergistic matching of electronegative ions for rapid orientation, characterized in that, The mesopore diameter of the described hierarchical pore X zeolite is 8 - 15 nm, the silica-alumina molar ratio is 2.01 - 2.04, and the specific surface area is 666 - 920 m 2 / g.

10. Application of the hierarchical - pore X zeolite obtained by the method according to any one of claims 1 - 9 in heavy - metal adsorption.

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