A method for preparing single crystal multi-level pore chiral crystal form A enriched Beta molecular sieve

Abstract

The present invention adopts a hydrothermal synthesis method to prepare a Beta zeolite molecular sieve with chiral pore crystal form A enrichment in an alkali-fluorine system, the proportion of crystal form A is as high as more than 90%, and it has a single crystal multi-level pore structure. This molecular sieve exhibits excellent catalytic activity, selectivity and stability in the performance of catalytic cracking, and has great potential application value in the fields of petrochemicals, fine chemicals and life sciences.

Description

Technical Field

[0001] The invention belongs to the technical field of zeolite molecular sieve preparation, and in particular relates to a method for preparing a single crystal multi-level pore chiral crystal form A-enriched Beta molecular sieve. Background Art

[0002] Beta molecular sieve has three-dimensional crossed twelve-membered ring channels, with straight channels in the X-axis and Y-axis directions, and a pore size of 0.67×0.66nm, and curved channels in the Z-axis direction, and a pore size of 0.56×0.56nm. Due to its through three-dimensional channels and good thermal and hydrothermal stability, Beta molecular sieve is widely used in the adsorption and separation of aromatics, alkylation, acylation and cracking reactions, and is one of the few molecular sieves currently used in industry.

[0003] Generally, the synthesized Beta molecular sieve is a symbiotic structure of crystal form A and crystal form B, with a ratio of 44:56 [Treacy MMJ, Newsam JM. Two new three-dimensional twelve-ring zeolite frameworks of which zeolite beta is a disordered intergrowth [J]. Nature, 1988, 332 (6161): 249-251]. In 2001, researchers discovered another crystal form C of Beta molecular sieve [Corma A, Navarro MT, Rey F, et al. Pure polymorph C of zeolite beta synthesized by using framework isomorphous substitution as a structure-directing mechanism [J]. Angewandte Chemie, 2001, 113 (12): 2337-2340]. Among the various crystal forms of Beta molecular sieve, crystal form A has a 12-membered chiral helical channel in the c-axis direction, and its chiral space group is P4322 or P4122, which has great application potential in enantioselective catalysis and separation processes.

[0004] However, the synthesis of pure phase A Beta molecular sieve is extremely challenging, and researchers have been working hard to increase the proportion of form A. In the early days, researchers used chiral organic templates to synthesize Beta zeolites rich in form A and obtained 5% enantiomeric excess in enantioselective catalysis [Davis ME, Lobo R F. Zeolite and molecular sieve synthesis [J]. Chemistry of Materials, 1992, 4 (4): 756-768]. Later, the use of non-chiral organic templates in high-concentration fluoride routes significantly increased the proportion of form A in Beta molecular sieves to ~ 65% [Zhang G, Wang B, Zhang W, et al. Synthesis of polymorph A-enriched beta zeolites in a HF-concentrated system [J]. Dalton Transactions, 2016, 45 (15): 6634-6640]. Recently, researchers have obtained Beta zeolite containing 70% of crystalline form A by dry gel method and adding additives [Lu T, Zhu L, Wang X, et al. A green route for the crystallization of a chiral polymorph A-enriched zeolite beta [J]. Inorganic Chemistry Frontiers, 2018, 5 (4): 802-805]. Although great progress has been made in the enrichment of chiral crystalline form A, the proportion of crystalline form A is still relatively low. In addition, most of the current A-enriched Beta molecular sieves are all-silicon molecular sieves, which have no acidic active sites and cannot be directly used in catalytic reactions. Therefore, the development of a preparation method for chiral crystalline form A-enriched Beta aluminosilicate molecular sieves has important economic value for its application.

[0005] On the other hand, one of the biggest limitations of molecular sieves in catalytic reactions is the carbon deposition problem. The generation of carbon deposition will cause the pores of the molecular sieve to be blocked, and eventually lead to the deactivation of the catalyst. Single crystal multi-level pore molecular sieves can effectively improve the mass transfer problem, significantly reduce the carbon deposition rate and improve the catalytic efficiency. Therefore, multi-level pore molecular sieve materials have great application potential in industrial catalysis. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing a chiral crystal form A-enriched Beta molecular sieve, and obtain the chiral crystal form A-enriched Beta molecular sieve by a common hydrothermal synthesis method. The prepared molecular sieve has a single crystal multi-level pore structure, the proportion of crystal form A exceeds 90%, and exhibits higher activity and selectivity than ordinary Beta zeolite catalysts in catalyzing alkylbenzene cracking reactions.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a Beta molecular sieve enriched in crystal form A comprises the following steps:

[0009] (1) mixing a silicon source material, a boron group element compound, a tetravalent element compound other than silicon and germanium, an organic template, a fluorine source material and water in proportion under stirring, and the reaction can be carried out under static or dynamic stirring to obtain a reaction gel, the chemical composition of the reaction gel is: rROH:aHF:xX2O3:yYO2:SiO2:wH2O, wherein R represents a positively charged group of the organic template; X represents one or more trivalent elements; Y represents one or more tetravalent elements other than silicon and germanium; r = 0.1-1.0, a = 0-1.0, x = 0-0.1, y = 0-0.1, w = 1-50;

[0010] (2) after removing excess solvent from the reaction gel, the reaction gel is transferred to a stainless steel reactor and reacted at 120-200° C. for 1-30 days, preferably at 160-180° C. for 14-20 days under sealed conditions;

[0011] (3) After washing and drying the product crystallized in step (2), calcining it in an air atmosphere at 500-650° C. for 2-5 hours obtains the Beta aluminosilicate molecular sieve with the template removed.

[0012] The preparation method of the above-mentioned Beta molecular sieve preferably comprises a reaction gel rROH:aHF:xX2O3:yYO2:SiO2:wH2O, wherein X is Al or B; Y is Ti; r=0.3-1, a=0.3-1, x=0-0.08, y=0-0.08, and w=2-20.

[0013] The preferred silicon source is one or more of water glass, silica sol, ethyl orthosilicate or butyl orthosilicate. The boron compound is preferably one or more of sodium aluminate, aluminum isopropoxide, aluminum sulfate hexahydrate, aluminum hydroxide or boric acid. The preferred fluorine source is hydrofluoric acid and / or ammonium fluoride. The preferred tetravalent element compound other than silicon and germanium is tetrabutyl titanate and tin dioxide.

[0014] In the above-mentioned method for preparing molecular sieves, the organic template is an azaspirane base, and the positively charged group R is preferably listed in Table 1.

[0015] Table 1

[0016]

[0017]

[0018] In the above method, before preparing the reaction gel, the organic template is exchanged into the form of hydroxide (ROH) by ion exchange resin, and its concentration is calibrated by 0.1M hydrochloric acid solution before use.

[0019] Generally, the tetravalent element other than silicon is first added to the obtained basic template solution, stirred to dissolve, and then the silicon source is added and continued to stir, and finally the corresponding boron group element compound is added, stirred evenly, and then the fluorine source is added or no fluorine source is added (fluorine-free system), and the excess solvent in the system is removed by heating under an infrared lamp or in an oven to obtain the target gel.

[0020] The method of the present invention can obtain a Beta molecular sieve enriched in form A with a single crystal multi-level pore structure by adjusting the ratio of each reactant r=0.5-1.0, a=0.3-0.7, x=0.02-0.08, y=0-0.1, and w=1-30.

[0021] The single crystal multi-level pore chiral crystal form A enriched Beta molecular sieve prepared by the method of the present invention has a proportion of crystal form A exceeding 90% and a chemical composition form of p(M 1 / n XO2)·qYO2·SiO2, wherein M represents a proton or an inorganic cation with a valence of +n; X represents a trivalent element; Y represents a tetravalent element except Si and germanium; n represents 1 or 2, p=0-0.2; q=0-0.2. M is preferably a proton or sodium, X is preferably Al, Y is preferably titanium, preferably p=0-0.08; preferably q=0-0.08.

[0022] Another object of the present invention is to provide the use of the Beta molecular sieve prepared by the method of the present invention as an adsorption material, separation material, and catalyst in the field of chemistry and chemical engineering.

[0023] Another object of the present invention is to provide the use of Beta aluminosilicate molecular sieve as a catalyst in catalytic cracking of alkylbenzene. In a specific example, in the catalytic cracking of 1,3,5-triisopropylbenzene, a molecular sieve synthesis gel is prepared according to a molar ratio of 1SiO2:1ROH:0.004Al2O3:0.5HF:10H2O, and a molecular sieve is further prepared. The reaction temperature is 400°C, and the feed rate of 1,3,5-triisopropylbenzene is 10.6mL h -1 , the catalyst loading amount is 3.0g.

[0024] Advantages of the present invention:

[0025] The present invention uses a low-cost template agent to obtain a chiral crystal form A-enriched Beta molecular sieve through a common hydrothermal synthesis method, wherein the proportion of crystal form A is as high as more than 90%. At the same time, the prepared molecular sieve also has a single crystal multi-level pore structure and has excellent catalytic alkylbenzene cracking performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Comparison of the X-ray powder diffraction pattern of the synthesized product with the simulated X-ray powder diffraction pattern of Beta molecular sieve with different A / B ratios (Cu target).

[0027] Figure 2 This is a scanning electron microscope image of the synthesized molecular sieve sample.

[0028] Figure 3 This is the N2 adsorption-desorption characterization diagram of the synthesized molecular sieve sample.

[0029] Figure 4 The catalytic performance of the synthesized molecular sieve samples. DETAILED DESCRIPTION

[0030] The specific steps of the present invention are described below by way of examples, but are not limited to the examples.

[0031] The terms used in the present invention, unless otherwise specified, generally have the meanings commonly understood by those of ordinary skill in the art.

[0032] The present invention is further described in detail below in conjunction with specific examples and with reference to data. It should be understood that these embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention in any way.

[0033] In the following examples, various processes and methods not described in detail are conventional methods well known in the art.

[0034] Example 1: Taking the template cation 1 in Table 1 as an example, the synthesis process of the template ROH is described.

[0035] First, 15 mL of piperidine, 19 mL of 1,5-dibromopentane and 41.5 g of K2CO3 (0.3 mol) were added to acetonitrile (150 mL). The mixture was heated at 80 ° C for 12 hours. Then the filtrate was filtered to obtain a solid, which was recrystallized in ether and dried overnight at 80 ° C to obtain a white product with a yield of 94%. The product was characterized by liquid nuclear magnetic resonance (D2O) and electrospray mass spectrometry and confirmed to be the bromide salt of the target cation.

[0036] The obtained product was dissolved in 200 mL of deionized water and ion exchanged through 717 strong alkaline anion exchange resin to obtain a template alkaline aqueous solution in the form of hydroxide. An appropriate amount of this solution was weighed and calibrated with 0.1 mol / L hydrochloric acid solution, using phenolphthalein as an indicator. The calibration results confirmed that the exchange efficiency of the template 1 bromide salt to the hydroxide base reached 95%.

[0037] The template cations 2-4 in Table 1 can be prepared by referring to the above method.

[0038] Example 2: Prepare the gel for molecular sieve synthesis in a molar ratio of 1SiO2:1ROH:0.004Al2O3:0.5HF:10H2O, the steps are as follows: weigh the measured template 1 alkaline solution, add 0.008mmol (0.0016g) aluminum isopropoxide and 1mmol (0.2084g) ethyl orthosilicate, stir at room temperature for about two hours to completely dissolve, then add the designed amount of hydrofluoric acid solution and stir evenly. Place the mixed gel under an infrared lamp or in an 80°C oven to remove excess solvent to the theoretical weight. Transfer the resulting reaction gel to a 15mL stainless steel reactor with a polytetrafluoroethylene liner, react at 160°C under sealed conditions for 15 days, wash the product twice with water, wash twice with ethanol, and dry for use. X-ray powder diffraction phase identification shows that the product is a Beta aluminosilicate molecular sieve enriched in form A ( Figure 1 ). Scanning electron microscopy and N2 adsorption-desorption characterization show that the product crystal has a single crystal multi-level pore structure ( Figure 2 and Figure 3 ).

[0039] Example 3: Prepare a molecular sieve synthesis gel according to the molar ratio of 1SiO2: 1ROH: 0.004Al2O3: 1HF: 10H2O, the steps are as follows: weigh a measured amount of template 1 alkaline solution, first add 0.008mmol (0.0016g) of aluminum isopropoxide and 1mmol (0.2084g) of tetraethyl orthosilicate thereto, stir at room temperature for about two hours to completely dissolve the tetraethyl orthosilicate, then add a designed amount of hydrofluoric acid solution, stir evenly, and finally place the mixed gel under an infrared lamp or in an 80°C oven to remove excess solvent to the theoretical weight. The resulting reaction gel is transferred to a 15mL stainless steel reactor with a polytetrafluoroethylene liner, reacted at 160°C under sealed conditions for 15 days, and the product is washed twice with water and twice with ethanol. X-ray powder diffraction phase identification shows that the product is an ordinary Beta aluminosilicate molecular sieve ( Figure 1 ). Scanning electron microscopy shows that the crystal size is about 200nm ( Figure 2 ), and N2 adsorption and desorption results showed that it is a microporous material ( Figure 3 ).

[0040] Example 4: Prepare the gel for molecular sieve synthesis according to the molar ratio of 1SiO2:1ROH:0.02TiO2:0.5HF:10H2O, the steps are as follows: weigh the measured template agent 1 alkaline solution, first add 0.02mmol (0.0108g) of tetrabutyl titanate thereto, stir for about half an hour, then add 1mmol (0.2084g) of ethyl orthosilicate, stir for about two hours at room temperature to completely dissolve the ethyl orthosilicate, then add the designed amount of hydrofluoric acid solution, stir evenly, finally place the mixed gel under an infrared lamp or in an 80℃ oven, remove excess solvent to theoretical weight. Transfer the resulting reaction gel to a 15mL stainless steel reactor with a polytetrafluoroethylene liner, react at 160℃ under sealed conditions for 15 days, and wash the product twice with water and twice with ethanol. The X-ray powder diffraction pattern of the product is the same as that of Example 2, which is a Beta titanate molecular sieve enriched in crystal form A.

[0041] Example 5: Prepare the gel for molecular sieve synthesis in a molar ratio of 1SiO2:1ROH:0.5HF:10H2O, and the steps are as follows: Weigh a measured amount of template 1 alkaline solution, first add 1mmol (0.2084g) of tetraethyl orthosilicate thereto, stir at room temperature for about two hours to completely hydrolyze the tetraethyl orthosilicate, then add a designed amount of hydrofluoric acid solution and stir evenly. Place the mixed gel under an infrared lamp or in an 80°C oven to remove excess solvent to the theoretical weight. Transfer the final reaction gel to a 15mL stainless steel reactor with a polytetrafluoroethylene liner, react at 160°C under sealed conditions for 15 days, and wash the product twice with water and twice with ethanol. The X-ray powder diffraction pattern of the product is the same as that of Example 2, which is a Beta silicate molecular sieve enriched in crystalline form A. Scanning electron microscopy and N2 adsorption and desorption characterization show that the crystal single crystal has multi-level pore properties ( Figure 2 and Figure 3 ).

[0042] Example 6: Performance of single crystal multi-level pore form A enriched Beta aluminosilicate molecular sieve as a catalyst in catalyzing the cracking of 1,3,5-triisopropylbenzene (1,3,5-TIPB).

[0043] The molecular sieve-catalyzed 1,3,5-TIPB cracking reaction was carried out in a fixed-bed microreactor under the following reaction conditions: reaction temperature was 400 °C, the feed rate of 1,3,5-TIPB was 10.6 mL h -1 The catalyst loading amount is 3.0 g. The reaction results are as follows Figure 4 Under the catalysis of the single crystal multi-level pore type A enriched Beta aluminosilicate molecular sieve material obtained in Example 2, the conversion rate and benzene selectivity of 1,3,5-TIPB are higher than those of the common Beta aluminosilicate molecular sieve catalytic material obtained in Example 3.

Claims

1. A method for preparing a single crystal multi-level pore chiral crystal form A enriched Beta molecular sieve, characterized in that The steps include: (1) A silicon source material, a boron group element compound, a tetravalent element compound other than silicon and germanium, an organic template, a fluorine source material and water are mixed uniformly in proportion under stirring to obtain a reaction gel. The chemical composition of the reaction gel is: r ROH: a HF: x X2O3: y YO2:SiO2: w H2O, where R represents the positively charged group of the organic template, ; X represents one or more trivalent boron group elements; Y represents one or more tetravalent elements other than silicon and germanium, r =0.5-1.0, a =0.3-0.7, x =0-0.05, y =0-0.1, w =1-30; (2) removing excess solvent from the reaction gel, transferring the reaction gel to a stainless steel reactor, and reacting at 120-200° C. for 1-60 days under sealed conditions; (3) The product crystallized in step (2) is washed and dried, and then calcined in an air atmosphere at 500-650° C. for 2-5 hours to obtain the Beta molecular sieve with the template removed.

2. The method for preparing the single crystal multi-level pore chiral crystal form A enriched Beta molecular sieve according to claim 1, characterized in that The silicon source material is selected from one or more of white carbon black, water glass, silica sol, ethyl orthosilicate or butyl orthosilicate; the boron group element compound is selected from one or more of sodium aluminate, aluminum isopropoxide, aluminum sulfate hexahydrate, aluminum hydroxide or boric acid; the fluorine source material is hydrofluoric acid and / or ammonium fluoride; the tetravalent element compound other than silicon and germanium is oxides or esters of titanium and tin.

3. A single crystal multi-level pore chiral crystal form A enriched Beta molecular sieve, characterized in that Prepared by the method of claim 1 or 2, the chemical composition is p (M 1 / n XO2) q YO2·SiO2, wherein M represents a proton; X represents one or more trivalent boron group elements; Y represents one or more tetravalent elements except silicon and germanium; p=0-0.2; q=0-0.

2.

4. The single crystal multi-level pore chiral crystal form A enriched Beta molecular sieve according to claim 3, characterized in that X is Al, Y is Ti, p =0-0.08, q =0-0.

08.

5. A single crystal multi-level pore chiral crystal form A enriched Beta molecular sieve, characterized in that Prepared by the method of claim 1 or 2, the chemical composition is p (M 1 / n XO2) q YO2·SiO2, wherein M represents an inorganic cation with a valence of +n; X represents one or more trivalent boron group elements; Y represents one or more tetravalent elements except silicon and germanium; n represents 1 or 2; p=0-0.2; q=0-0.

2.

6. The single crystal multi-level pore chiral crystal form A enriched Beta molecular sieve according to claim 5, characterized in that M represents sodium, X represents Al, Y represents Ti, p =0-0.08, q =0-0.

08.

7. Use of the single crystal multi-level pore chiral crystal form A enriched Beta molecular sieve prepared by the method of claim 1 or 2 as an adsorption material and catalyst in the field of chemistry and chemical engineering.

8. The use according to claim 7, characterized in that The Beta molecular sieve is used as a catalyst to catalyze the cracking of alkylbenzene.

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