Green preparation method of hollow spherical stepped hole LSX molecular sieve

Abstract

The invention discloses a green preparation method of a hollow spherical stepped hole LSX molecular sieve. The preparation method comprises the following steps: dissolving an alkali source in water to prepare a solution A, and dissolving a silicon source in water to prepare a solution B; adding an aluminum source and an acidic inorganic salt into the solution A to prepare a solution C; dropwise adding the solution B into the solution C to prepare a solution D; and continuously stirring the solution D to form gel, transferring the gel into a stainless steel reaction kettle, carrying out a hydrothermal crystallization reaction, filtering, and drying to obtain the stepped pore LSX molecular sieve. According to the invention, the traditional organic template agent is replaced by the acid inorganic salt, and acid radical ions and aluminum species are subjected to a double hydrolysis reaction under a mild hydrothermal crystallization condition, so that nucleation of the cascade pore LSX molecular sieve and formation of a hollow structure are promoted. According to the invention, the problems of high energy consumption, high cost, environmental pollution and the like caused by a template agent are avoided, and the prepared stepped pore LSX molecular sieve has larger specific surface area and mesoporous rate, and has excellent performance in the fields of ion exchange and adsorption.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieve preparation, and particularly relates to a green preparation method of hollow spherical hierarchical pore LSX molecular sieve. Background Art

[0002] X molecular sieve is a kind of synthetic molecular sieve with a cubic octahedral zeolite structure, and the silica-alumina ratio (SiO2 / Al2O3) generally ranges from 2.0 to 3.0. Usually, the low-silica X molecular sieve with a silica-alumina ratio between 2.0 and 2.2 is called LSX molecular sieve, which has more framework negative charges and is an excellent adsorbent for cation modification, and is used as an ion exchanger and adsorbent.

[0003] Traditional LSX molecular sieve only has microporous channels with a specific spatial structure, and its pore diameter is less than 2 nm, while hierarchical pore LSX molecular sieve has both microporous, mesoporous or macroporous structures, eliminating the mass transfer resistance and diffusion limitation due to the existence of micropores in the molecular sieve and improving the catalytic activity. Hierarchical pore molecular sieves are usually prepared by the following two methods, one is the bottom-up method with hard template or soft template, and the other method is the top-down method of dealumination or desilication. Since the LSX molecular sieve structure contains a high content of aluminum, the silicon species are protected by the aluminum species and are difficult to be removed. Moreover, the dealumination process causes an increase in the silica-alumina ratio of the molecular sieve, making it not have the excellent properties of low silica-alumina ratio. And the mesopores obtained by the top-down method are randomly distributed and cannot be flexibly adjusted. Therefore, the bottom-up method has become the most suitable method for preparing hierarchical pore LSX molecular sieve. The public literature (Colloids And Surfaces A: Physicochemical And Engineering Aspects, 2008, 318(1): 269-274.) reported the synthesis of hierarchical pore LSX molecular sieve with mesopore size of 4-50 nm using polydiallyldimethylammonium chloride and spirulina. The public literature (Angewandte Chemie International Edition, 2012, 51(8): 1962-1965.) reported the synthesis of hierarchical pore LSX molecular sieve with intracrystalline mesopores with an average pore diameter of 7 nm using cetyltrimethoxysilyl ammonium chloride. The public literature (Microporous and Mesoporous Materials, 2022, 330: 111-618.) reported the synthesis of hierarchical pore LSX molecular sieve using anionic surfactant sodium dodecylbenzenesulfonate as a template agent, and this hierarchical pore LSX molecular sieve showed higher catalytic activity than microporous molecular sieve in oleic acid deoxygenation.

[0004] The organic template agents reported in the above literature need to be removed by high-temperature calcination. This process consumes a large amount of energy and produces a large amount of harmful gases, and the template agents are expensive and cannot be recycled after the structure is damaged. Summary of the Invention

[0005] The object of the present invention is to provide a green preparation method for hollow spherical hierarchical pore LSX molecular sieve, aiming to solve the problems such as the use of expensive templates and environmental pollution caused by high-temperature calcination of templates in the preparation process of hierarchical pore LSX molecular sieve. The preparation method uses acid salts instead of organic templates to direct the formation of hierarchical pore LSX molecular sieve.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A green preparation method for hollow spherical hierarchical pore LSX molecular sieve, comprising the following steps:

[0008] (1) Dissolve the alkali source in deionized water to form solution A, and dissolve the silicon source in deionized water to form solution B;

[0009] (2) Add the aluminum source and acid salt to solution A under continuous stirring to form solution C;

[0010] (3) Continuously stir solution C for 15 - 17 min, and then drop solution B into solution C to form solution D;

[0011] (4) Continuously stir solution D for 20 - 22 min, transfer the formed gel into a stainless steel autoclave, carry out hydrothermal crystallization reaction at 70 - 110 °C for 2 - 10 h, and then filter and dry the product to obtain hierarchical pore LSX molecular sieve.

[0012] In the process of preparing hierarchical pore LSX molecular sieve by the template method, the template is difficult to obtain, expensive, and its removal process may also cause the collapse of the molecular sieve framework structure and generate pollution emissions, which is a high-cost and non-green process. Through a large number of experimental studies, the present invention finds that acid salts can replace organic templates to prepare hierarchical pore LSX molecular sieve with a hollow spherical particle morphology, which has a large specific surface area and good adsorption performance. It avoids the use of expensive organic templates and environmental pollution problems, and greatly reduces the preparation cost and energy consumption of hierarchical pore LSX molecular sieve.

[0013] As a preference of the present invention, the composition of the gel satisfies the following molar ratio: 1.0 Al2O3: 2.0 - 2.2 SiO2: 2.0 - 5.0 Na2O: 0.4 - 0.7 K2O: 90 - 110 H2O: 5.0 - 8.0 acid salt.

[0014] As a preference of the present invention, the alkali source is one or two of sodium hydroxide or potassium hydroxide.

[0015] Preferably, the silicon source is one or more of water glass, silica sol, tetraethyl orthosilicate, and sodium silicate.

[0016] Preferably, the aluminum source is one or more of sodium aluminate, aluminum sulfate, and aluminum isopropoxide.

[0017] Preferably, the acid-type inorganic salt is one or more of potassium dihydrogen phosphate, sodium dihydrogen phosphate, sodium bisulfate, disodium hydrogen pyrophosphate, and sodium bicarbonate.

[0018] The hierarchical pore LSX molecular sieve prepared by the present invention has both microporous, mesoporous and macroporous structures, with SiO2 / Al2O3 being 2.01 - 2.20, the mesoporous pore diameter concentrated at 10 - 50 nm, and the specific surface area being 766 - 930 m 2 / g.

[0019] The present invention uses an acid-type inorganic salt to replace the traditional organic template agent, and utilizes the double hydrolysis reaction of acid radical ions and aluminum species under mild hydrothermal crystallization conditions to promote the nucleation of the hierarchical LSX molecular sieve and the formation of a hollow structure. The present invention has the following beneficial effects:

[0020] 1. The present invention uses an acid-type inorganic salt to replace the organic template agent to prepare a hierarchical pore LSX molecular sieve, avoiding problems such as high energy consumption, high cost, and environmental pollution caused by the template agent.

[0021] 2. The process of the present invention does not require high-temperature calcination, is convenient for industrial application, and has the characteristics of high efficiency and greenness.

[0022] 3. The hierarchical pore LSX molecular sieve prepared by the present invention has a larger specific surface area and mesoporous ratio than the commercial LSX molecular sieve, and has excellent performance in the fields of ion exchange and adsorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the X-ray diffraction (XRD) pattern of the hierarchical pore LSX molecular sieve prepared in Example 1 of the present invention.

[0024] Figure 2 It is the scanning electron microscope (SEM) photograph of the hierarchical pore LSX molecular sieve prepared in Example 1.

[0025] Figure 3 It is the SEM photograph of the hierarchical pore LSX molecular sieve prepared in Example 2.

[0026] Figure 4 It is the SEM photograph of the hierarchical pore LSX molecular sieve prepared in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be further described below in conjunction with examples, but the present invention is not limited thereby.

[0028] It should be noted that the relative crystallinity described in the examples is based on the ASTM D 3906-03(2013) standard. It is 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 LSX molecular sieve standard sample. The standard sample is the LSX molecular sieve with a silica-alumina ratio of 2.13 produced by the Catalyst Factory of Nankai University, and its crystallinity is defined as 100%.

[0029] Example 1

[0030] A green preparation method of hollow spherical hierarchical pore LSX molecular sieve is as follows:

[0031] (1) Dissolve sodium hydroxide and potassium hydroxide in deionized water to form solution A, and dissolve water glass in deionized water to form solution B;

[0032] (2) Under continuous stirring conditions, add sodium aluminate, potassium dihydrogen phosphate and sodium bisulfate to solution A to form solution C;

[0033] (3) Continuously stir solution C for 15 min, and then add solution B to solution C to form solution D;

[0034] (4) Continuously stir solution D for 20 min to obtain a gel. The molar composition of the obtained gel is 1.0Al2O3:2.0SiO2:2.7Na2O:0.6K2O:98H2O:3.4NaHSO4:2.4KH2PO4. Transfer the formed gel into a stainless steel autoclave and carry out static hydrothermal crystallization at 80 °C for 4 h;

[0035] (5) After the crystallization reaction is completed, vacuum filter the obtained product, wash it with deionized water until neutral, and dry it in an 80 °C drying oven to obtain hierarchical pore LSX molecular sieve.

[0036] The XRD diffraction pattern of the LSX molecular sieve prepared in this example is as Figure 1 shown. The obtained solid powder phase belongs to the LSX molecular sieve, and the SiO2 / Al2O3 measured by ICP is 2.01.

[0037] As Figure 2 shown, the SEM characterization shows that the diameter of the prepared molecular sieve is about 1.4 μm, and it is a hollow spherical particle morphology LSX molecular sieve.

[0038] As shown in Table 1, the N2 adsorption and desorption results show that the mesopore diameter is concentrated at 10 nm, and the specific surface area is 766 m 2 / g, the pore volume is 0.39 cm 3 / g.

[0039] Example 2

[0040] A green preparation method of hollow spherical hierarchical pore LSX molecular sieve is as follows:

[0041] (1) Dissolve sodium hydroxide and potassium hydroxide in deionized water to form solution A, and dissolve silica sol in deionized water to form solution B;

[0042] (2) Under continuous stirring, add sodium aluminate, disodium hydrogen pyrophosphate and sodium dihydrogen phosphate to solution A to form solution C;

[0043] (3) Continuously stir solution C for 15 min, and then add solution B to solution C to form solution D;

[0044] (4) Continuously stir solution D for 20 min to obtain a gel. The molar composition of the obtained gel is 1.0Al2O3:2.1SiO2:2.7Na2O:0.4K2O:98H2O:3.4Na2H2P2O7:2.4NaH2PO4. Transfer the formed gel into a stainless steel autoclave and carry out static hydrothermal crystallization at 85 °C for 2 h;

[0045] (5) After the crystallization reaction is completed, vacuum filter the obtained product, wash it with deionized water until neutral, and dry it in an oven at 80 °C to obtain hierarchical pore LSX molecular sieve.

[0046] The solid powder phase obtained by XRD characterization of the LSX molecular sieve prepared in this example belongs to the LSX molecular sieve, and ICP measures that SiO2 / Al2O3 is 2.08.

[0047] As Figure 3 shown, the SEM characterization shows that the prepared molecular sieve is a hollow spherical particle assembled from nanoparticles.

[0048] 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 745 m 2 / g, and the pore volume is 0.30 cm 3 / g.

[0049] Example 3

[0050] A green preparation method of hollow spherical hierarchical pore LSX molecular sieve is as follows:

[0051] (1) Dissolve sodium hydroxide and potassium hydroxide in deionized water to form solution A, and dissolve water glass in deionized water to form solution B;

[0052] (2) Under continuous stirring conditions, sodium aluminate, sodium dihydrogen phosphate, and sodium bicarbonate are added to solution A to prepare solution C;

[0053] (3) Solution C is continuously stirred for 15 min, and then solution B is added to solution C to prepare solution D;

[0054] (4) Solution D is continuously stirred for 20 min to obtain a gel. The molar composition of the obtained gel is 1.0Al2O3:2.2SiO2:2.7Na2O:0.7K2O:100H2O:4.2NaHCO3:3.6Na2H2P2O7. The formed gel is transferred into a stainless-steel autoclave and subjected to static hydrothermal crystallization at 90 °C for 6 h;

[0055] (5) After the crystallization reaction is completed, the obtained product is vacuum filtered, washed with deionized water until neutral, and dried in an oven at 80 °C to obtain hierarchical pore LSX molecular sieve.

[0056] The solid powder phase obtained by XRD characterization of the LSX molecular sieve prepared in this example belongs to the LSX molecular sieve, and SiO2 / Al2O3 measured by ICP is 2.20.

[0057] As Figure 4 shown, the SEM characterization shows that the prepared molecular sieve is a lamellar stacked LSX molecular sieve.

[0058] As shown in Table 1, from the N2 adsorption-desorption results, the mesopore aperture is concentrated at 50 nm, the specific surface area is 930 m 2 / g, and the pore volume is 0.42 cm 3 / g.

[0059] Table 1 Structural parameters of the hierarchical pore LSX molecular sieve prepared in Examples 1-3

[0060]

[0061] Comparative Example 1

[0062] No acid-type inorganic salt is added, and the others are the same as in Example 1. The phase of the obtained product determined by XRD is amorphous.

[0063] Comparative Example 2

[0064] No acid-type inorganic salt is added, and the others are the same as in Example 2. The phase of the obtained product determined by XRD is amorphous.

[0065] Comparative Example 3

[0066] No acid-type inorganic salt is added, and the others are the same as in Example 3. The phase of the obtained product determined by XRD is amorphous.

[0067] Comparative Example 4

[0068] No acid inorganic salt was added, and the others were the same as in Example 4. The phase of the product obtained by XRD measurement was amorphous.

Claims

1. A green preparation method of hollow spherical stepped pore LSX molecular sieve, characterized in that, It includes the following steps: (1) Dissolve the alkali source in water to form solution A, and dissolve the silicon source in water to form solution B; (2) Add the aluminum source and the acid salt into solution A under continuous stirring to form solution C; (3) Continuously stir solution C for 15-17 min, and then drop solution B into solution C to form solution D; (4) Continuously stir solution D for 20 - 22 min, transfer the formed gel into a stainless-steel reactor, and hydrothermally crystallize at 70 - 110 o °C for 2 - 10 h. Then filter and dry the product to obtain hierarchical pore LSX molecular sieve.

2. The green preparation method of a hollow spherical stepped pore LSX molecular sieve according to claim 1, characterized in that, The composition of the gel satisfies the following molar ratio: 1.0Al2O3:2.0-2.2SiO2:2.0-5.0Na2O:0.4-0.7K2O:90-110H2O:5.0-8.0 acid salt.

3. The green preparation method of a hollow spherical stepped pore LSX molecular sieve according to claim 1, characterized in that, The alkali source is one or both of sodium hydroxide and potassium hydroxide.

4. The green preparation method of a hollow spherical stepped pore LSX molecular sieve according to claim 1, characterized in that, The silicon source is one or several of water glass, silica sol, tetraethyl orthosilicate, and sodium silicate.

5. The green preparation method of a hollow spherical stepped pore LSX molecular sieve according to claim 1, characterized in that, The aluminum source is one or several of sodium aluminate, aluminum sulfate, and aluminum isopropoxide.

6. The green preparation method of a hollow spherical stepped pore LSX molecular sieve according to claim 1, characterized in that, The acid salt is one or several of potassium dihydrogen phosphate, sodium dihydrogen phosphate, sodium bisulfate, disodium hydrogen pyrophosphate, and sodium bicarbonate.

7. The green preparation method of a hollow spherical stepped pore LSX molecular sieve according to claim 1, characterized in that, The SiO2 / Al2O3 of the described stepped pore LSX molecular sieve is 2.01 - 2.20, the mesopore diameter is concentrated at 10 - 50 nm, and the specific surface area is 766 - 930 m 2 / g.

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