Preparation method and use of molecular sieve with STW structure

Abstract

This invention utilizes a relatively low-cost template and a hydrothermal synthesis method to prepare STW-type silicate molecular sieves with helical channels in alkaline or fluorine systems. By optimizing the synthesis conditions, STW molecular sieves with nanometer-sized and hollow morphologies can be prepared. This molecular sieve exhibits excellent catalytic activity, selectivity, and stability in the alkylation of toluene and methanol to produce p-xylene, and has great potential applications in fields such as petrochemistry, fine chemicals, and life sciences.

Description

Technical Field

[0001] The present invention belongs to the technical field of zeolite molecular sieve preparation, and specifically relates to a preparation method of a spiral channel STW structure silicate molecular sieve material and its application in catalytic reactions such as toluene methanol alkylation to produce p-xylene. Background Art

[0002] Para-xylene is an important aromatic hydrocarbon chemical raw material, widely used in the chemical, pharmaceutical, pesticide, fuel, and solvent industries. Currently, the domestic para-xylene market is facing an increasingly severe supply shortage, necessitating the development of new technologies for its production. Producing para-xylene using toluene and methanol as raw materials and molecular sieves as catalysts is a promising approach that can alleviate para-xylene's dependence on petroleum resources. However, this approach presents challenges due to the similar size of xylene isomers and the fact that thermodynamic equilibrium favors the production of meta-xylene. Therefore, achieving high para-xylene selectivity is a challenge.

[0003] Currently, the most widely studied and applied molecular sieve in this reaction is ZSM-5. It was first reported by Mobil Oil Company in the United States in 1972 [Argauer RJ, Landolt GR, US Patent 3702886, 1972]. ZSM-5 has an MFI topology (MFI is the molecular sieve structure code defined by the International Molecular Sieve Association) consisting of two sets of intersecting pores: one set of straight pores parallel to the Z axis, with pore openings composed of elliptical ten-membered rings and a pore size of 0.58 nm x 0.52 nm; the other set of sinusoidal pores parallel to the XY plane, with a pore size of 0.53 nm x 0.56 nm. ZSM-5 exhibits low para-xylene selectivity when catalyzing the production of para-xylene. Most researchers use P, B, Mg, Pt, or SiO2 to modify ZSM-5 molecular sieves to reduce pore size and increase the diffusion resistance of o- and m-xylene in the pores, thereby improving the selectivity for p-xylene [Wang C., Zhang L., Huang X., et al. Maximizing sinusoidal channels of HZSM-5 for high shape-selectivity to p-xylene [J]. Nature Communications, 2019, 10, 4348]. However, the modification process will cover some active sites, reducing catalytic activity. Secondly, the modified material will fall off during the reaction, reducing the stability of the catalyst. Therefore, it is particularly urgent to find a molecular sieve with a better topological structure for the alkylation of toluene and methanol to produce p-xylene.

[0004] The STW structured molecular sieve has an octahedral straight pore with a pore size of 0.47 nm × 0.30 nm and a 10-membered helical pore with a pore size of 0.55 nm × 0.50 nm intersecting with it. It was first synthesized in the form of SU-32 silicate under the structural guidance of diisopropylamine [Tang L, Shi L, Bonneau C, et al. A zeolite family with chiral and achiral structures built from the same building layer [J]. Nature Materials, 2008, 7(5): 381-385]. Subsequently, researchers used 1,3,4-trimethyl-2-ethylimidazolium and pentamethylimidazolium as structure-directing agents to synthesize all-silica and aluminosilicate STW molecular sieves [Rojas A., Camblor MAA pure silica chiral polymorph with helical pores [J]. Angewandte Chemie, 2012, 124, 3920-3922; Rojas A., Arteaga O., Kahr B., et al. Synthesis, structure, and optical activity of HPM-1, a pure silica chiral zeolite [J]. Journal of the American Chemical Society, 2013, 135, 11975-11984]. The application of STW molecular sieves is limited by the high price of germanium, the poor hydrothermal stability of germanosilicate molecular sieves, and the high cost of the structure-directing agents used. Developing inexpensive methods to prepare all-silica and aluminosilicate STW molecular sieves is of great economic value for their application.

[0005] One of the biggest limitations of molecular sieves in catalytic reactions is carbon deposition. Carbon deposition can block the molecular sieve pores, ultimately leading to catalyst deactivation. The size and morphology of the molecular sieve can influence mass transfer during the catalytic process. Molecular sieves with specific sizes and morphologies, such as nano- and hierarchical-pore molecular sieves, can significantly reduce carbon deposition rates and improve catalytic efficiency. Therefore, these nano- and hierarchical-pore molecular sieve materials hold great potential for application in industrial catalysis. Summary of the Invention

[0006] The present invention aims to provide a cost-effective method for preparing a STW-structured silicate molecular sieve material. By using a specific organic structure-directing agent, the STW silicate is produced over a broad crystalline phase range. The present invention also provides a method for preparing nano- and hollow-structured STW molecular sieve materials by controlling synthesis conditions. Furthermore, the present invention provides the use of the STW-structured silicate molecular sieve in the alkylation of toluene with methanol to produce p-xylene, demonstrating excellent selectivity and stability.

[0007] The technical solutions of the present invention are as follows:

[0008] A method for preparing a STW structure silicate molecular sieve, wherein the molecular sieve has a STW framework structure and a chemical composition 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 other than Si and germanium; n represents 1 or 2, p = 0–0.2; and q = 0–0.2. M is preferably a proton or sodium, X is preferably Al, and Y is preferably titanium. Preferably, p = 0–0.08; and preferably, q = 0–0.08. The preparation method comprises the following steps:

[0009] (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, a molecular sieve seed crystal and water are mixed uniformly under stirring in proportion, 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, a = 0-1, x = 0-0.1, y = 0-0.1, w = 1-50, and the amount of the molecular sieve seed crystal added is 0-10wt% of the theoretical mass of the gel;

[0010] (2) removing excess solvent from the reaction gel (e.g., under an infrared lamp or in an 80°C oven) to a theoretical weight, transferring the reaction gel to a stainless steel reactor, and reacting at 120-200°C under sealed conditions for 1-30 days, preferably at 160-180°C for 14-20 days; (3) washing and drying the product crystallized in step (2), and calcining it in an air atmosphere at 500-650°C for 2-5 hours to obtain a STW structure silicate molecular sieve with the template removed.

[0011] The above-mentioned STW silicate molecular sieve preparation method preferably comprises a reaction gel of rROH:aHF:xX2O3:yYO2:SiO2:wH2O, where X is Al or B, Y is Ti, r=0.1-1, a=0-1, x=0-0.08, y=0-0.08, and w=2-20, and the amount of seed crystals added is 0-5wt% of the theoretical mass of the gel. Bipyramidal, rod-shaped, or flaky STW silicate molecular sieves can be produced.

[0012] Preferred silicon sources include one or more of water glass, silica sol, ethyl orthosilicate, or butyl orthosilicate. Preferred boron compounds include one or more of sodium metaaluminate, aluminum isopropoxide, aluminum sulfate hexadecahydrate, aluminum hydroxide, or boric acid. Preferred fluorine sources include hydrofluoric acid and / or ammonium fluoride. Preferred compounds of tetravalent elements other than silicon and germanium include tetrabutyl titanate and tin dioxide.

[0013] The STW structure silicate molecular sieve prepared by the method of the present invention has a space group of P6122 or P6522 and is composed of four, five, eight, or ten-membered rings [4 6 5 8 8 2 10 2 ] pore cavity, with an eight-membered ring straight channel with a pore size of 0.47nm×0.30nm and a ten-membered ring spiral channel with a pore size of 0.55nm×0.50nm.

[0014] In the preparation method of the above-mentioned STW structure silicate molecular sieve, the organic template is a 1,5-diazabicyclo[4.3.0]non-5-ene basic salt, and the positively charged group R is preferably listed in Table 1.

[0015] Table 1

[0016]

[0017] In the above method, before preparing the reaction gel, the organic template is exchanged into the form of hydroxide base (ROH) through ion exchange resin, and its concentration is calibrated with 0.1M hydrochloric acid solution before use.

[0018] Generally, tetravalent elements other than silicon and germanium are first added to the obtained basic template solution, stirred to dissolve, and then a silicon source is added and continued to stir. Finally, the corresponding boron group element compound is added and stirred evenly. A 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.

[0019] The method of the present invention can further obtain the following STW structure silicate molecular sieve by adjusting the ratio of each reactant: (1) r = 0.2-1, a = 0-1, x = 0-0.05, y = 0-0.1, w = 1-30, and when the amount of seed crystal added is 1-5wt% of the theoretical mass of the gel, a nano-sized STW structure silicate molecular sieve can be obtained;

[0020] (2) When r=0.4-1, a=0.1-0.8, x=0-0.05, y=0-0.1, w=1-20 and the amount of seed added is 0-5wt% of the theoretical mass of the gel, a hollow morphology STW structure silicate molecular sieve is obtained.

[0021] Another object of the present invention is to provide a crystalline STW structure silicate molecular sieve nanomaterial or a hollow STW structure silicate molecular sieve obtained by the above preparation method.

[0022] Another object of the present invention is to provide the use of the STW structure silicate 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 STW silicate molecular sieve materials in the alkylation of toluene with methanol to produce p-xylene. In the catalytic alkylation of toluene with methanol to produce p-xylene, the molar ratio of toluene to methanol is: n(toluene) / n(methanol) = 1-8; the reaction temperature is 350-500°C; the reaction pressure is 0.1-4 MPa; and the mass space velocity is 1-15 h / min. -1 The carrier gas is nitrogen or hydrogen. The catalyst is preferably STW aluminosilicate molecular sieve (Si / Al = 100). The molar ratio of toluene to methanol is preferably: n(toluene) / n(methanol) = 3. The reaction temperature is preferably 400°C. The reaction pressure is preferably 2 MPa. The mass space velocity is preferably 7.5 h / min. -1 ; Nitrogen is preferably the carrier gas.

[0024] Advantages of the present invention:

[0025] The present invention utilizes a specific template to prepare STW-structured silicate molecular sieves over a wide synthesis range. Compared with previous STW-structured molecular sieve synthesis conditions, the synthesis phase range is significantly expanded, and impurity phases such as ITW are not generated, resulting in pure-phase STW-structured molecular sieve materials. STW-structured molecular sieve materials can also be synthesized in a fluorine-free system. By varying the synthesis conditions, the crystal size can be regulated from the micron to the nanometer level, and hollow STW-structured molecular sieve materials can be prepared. The STW-structured aluminosilicate molecular sieve prepared by the present invention exhibits excellent catalytic performance in the alkylation of toluene and methanol to produce p-xylene. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 X-ray powder diffraction pattern of the synthesized product (Cu target).

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

[0028] Figure 3 This is a comparison chart of the reaction performance of toluene methanol alkylation to produce p-xylene catalyzed by molecular sieves. DETAILED DESCRIPTION

[0029] The specific steps of the present invention are described below by way of examples, but are not limited to the examples.

[0030] Unless otherwise specified, the terms used in the present invention generally have the meanings commonly understood by those skilled in the art.

[0031] The present invention will be described in further detail below in conjunction with specific examples and with reference to data. It should be understood that these examples are only for illustrating the present invention and are not intended to limit the scope of the present invention in any way.

[0032] In the following examples, various processes and methods not described in detail are conventional methods well known in the art.

[0033] Example 1: Taking the template cation 1 in Table 1 as an example, the synthesis process of the template is described.

[0034] 15 mL of 1,5-diazabicyclo[4.3.0]non-5-ene was added to 150 mL of tetrahydrofuran, followed by 20 mL of iodomethane. The mixture was allowed to react at 40°C for 24 hours. The temperature was then cooled to room temperature, and the solvent was removed by rotary evaporation to yield a viscous oily product. This product was washed with ether (3 × 10 mL) and dried under vacuum overnight with a yield of 91%. The product was characterized by liquid nuclear magnetic resonance (D2O) and electrospray ionization mass spectrometry, confirming it to be the iodine salt of the target cation.

[0035] The resulting product was dissolved in 200 mL of deionized water and ion exchanged with 717 strongly basic anion exchange resin to produce an aqueous solution of the template in the hydroxide form. 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 iodine salt of template 1 to the hydroxide base reached 95%.

[0036] The template cations 2-4 in Table 1 can be prepared by referring to the above method using 1-bromoethane, 1-bromopropane, and 1-bromoisobutane.

[0037] Example 2: Prepare the gel for molecular sieve synthesis in a molar ratio of 1SiO2:0.7ROH:0.5HF:30H2O, and the steps are as follows: weigh the measured template agent 1 alkaline solution, add 1mmol (0.2084g) of tetraethyl orthosilicate, stir at room temperature for about two hours to completely dissolve it, 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 final 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 it for use. X-ray powder diffraction phase identification analysis shows that the X-ray powder diffraction pattern of the product is the same as the X-ray powder diffraction pattern calculated based on the STW crystal structure, and it is a silicate molecular sieve with STW structure ( Figure 1 Scanning electron microscopy shows that the crystal has a bipyramidal morphology and a crystal size of about 5 μm ( Figure 2 ).

[0038] Example 3: Prepare a molecular sieve synthesis gel in a molar ratio of 1SiO2:0.3ROH:7H2O, the steps are as follows: weigh the measured template agent 1 alkaline solution, add 1mmol (0.2084g) of tetraethyl orthosilicate, stir at room temperature for about two hours to completely dissolve the tetraethyl orthosilicate, add 1wt% (0.0032g) of the product of Example 2 of the theoretical mass of the gel as a seed, 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 30 days, wash the product twice with water, wash twice with ethanol, and dry it for use. X-ray powder diffraction phase identification shows that the product is a silicate molecular sieve with a STW structure ( Figure 1 Scanning electron microscopy shows that the product crystals have a bipyramidal morphology and a crystal size of about 4 μm ( Figure 2 ).

[0039] Example 4: Prepare a molecular sieve synthesis gel according to the molar ratio of 1SiO2:0.5ROH:0.005Al2O3:0.5HF:15H2O, the steps are as follows: weigh the measured template agent 2 alkaline solution, first add 0.01mmol (0.0020g) of aluminum isopropoxide thereto, stir for about half an hour, then add 1mmol (0.2084g) of tetraethyl orthosilicate, stir at room temperature for about two hours to completely hydrolyze the tetraethyl orthosilicate, 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, and wash the product twice with water and twice with ethanol. X-ray powder diffraction phase identification shows that the product is an aluminosilicate molecular sieve with a STW structure ( Figure 1 ), the product crystals can be seen to have a bipyramidal morphology by scanning electron microscopy, and the crystal size is about 10 μm ( Figure 2 ).

[0040] Example 5: Prepare a molecular sieve synthesis gel according to the molar ratio of 1SiO2:0.7ROH:0.01Al2O3:0.5HF:2H2O, the steps are as follows: weigh the measured template agent 1 alkaline solution, first add 0.02mmol (0.0041g) of aluminum isopropoxide thereto, stir for about half an hour, then add 1mmol (0.2084g) of tetraethyl orthosilicate, stir at room temperature for about two hours to completely hydrolyze the tetraethyl orthosilicate, 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, and wash the product twice with water and twice with ethanol. X-ray powder diffraction phase identification shows that the product is an aluminosilicate molecular sieve with a STW structure ( Figure 1 ), the product crystals can be seen to be rod-shaped by scanning electron microscopy, with a crystal size of about 40μm×8μm ( Figure 2 ).

[0041] Example 6: Prepare a molecular sieve synthesis gel according to the molar ratio of 1SiO2:0.4ROH:0.002Al2O3:0.2HF:5H2O, the steps are as follows: weigh the measured template agent 1 alkaline solution, first add 0.001mmol (0.0002g) of aluminum isopropoxide thereto, stir for about half an hour, then add 1mmol (0.2084g) of tetraethyl orthosilicate, stir at room temperature for about two hours to completely hydrolyze the tetraethyl orthosilicate, 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 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. X-ray powder diffraction phase identification shows that the product is an aluminosilicate molecular sieve with a STW structure ( Figure 1 ), the product crystals can be seen to have a flake morphology through scanning electron microscopy ( Figure 2 ).

[0042] Example 7: A molecular sieve synthesis gel was prepared in a molar ratio of 1SiO2:0.8ROH:0.005Al2O3:0.6HF:30H2O. The steps were as follows: Weigh a measured amount of template 1 alkaline solution, first add 1wt% (0.0033g) of the product of Example 4 as a seed crystal, then add 0.01mmol (0.0020g) of aluminum isopropoxide and stir for about half an hour. Then add 1mmol (0.2084g) of tetraethyl orthosilicate and stir at room temperature for about two hours to completely hydrolyze the tetraethyl orthosilicate. Then add the designed amount of hydrofluoric acid solution and stir evenly. The mixed gel was placed under an infrared lamp or in an 80°C oven to remove excess solvent to the theoretical weight. The resulting reaction gel was transferred to a 15mL stainless steel reactor with a polytetrafluoroethylene liner and reacted at 160°C under sealed conditions for 15 days. The product was washed twice with water and twice with ethanol. X-ray powder diffraction phase identification showed that the product was an aluminosilicate molecular sieve with STW structure ( Figure 1 Scanning electron microscopy shows that the product crystal size is about 200nm ( Figure 2 ).

[0043] Example 8: A molecular sieve synthesis gel was prepared in a molar ratio of 1SiO2:0.2ROH:0.05Al2O3:0.2HF:10H2O. The steps were as follows: Weigh a measured amount of template 1 alkaline solution and first add 4 wt% (0.0130 g) of the product from Example 4 as a seed crystal, based on the theoretical mass of the gel. Then, add 0.1 mmol (0.0204 g) of aluminum isopropoxide and stir for about half an hour. Then, add 1 mmol (0.2084 g) of tetraethyl orthosilicate and stir at room temperature for about two hours to completely hydrolyze the tetraethyl orthosilicate. Then, add the desired amount of hydrofluoric acid solution and stir evenly. The mixed gel was placed under an infrared lamp or in an 80°C oven to remove excess solvent to the theoretical weight. The resulting reaction gel was transferred to a 15 mL stainless steel reactor lined with polytetrafluoroethylene and reacted at 160°C under sealed conditions for 15 days. The product was washed twice with water and twice with ethanol. The X-ray powder diffraction pattern of the product is the same as that of Example 7, indicating an aluminosilicate molecular sieve with a STW structure. Scanning electron microscopy shows that the crystal size of the product is about 200 nm, similar to that of Example 7.

[0044] Example 9: Prepare a molecular sieve synthesis gel according to the molar ratio of 1SiO2:1ROH:0.005Al2O3:0.8HF:5H2O, the steps are as follows: weigh the measured template agent 1 alkaline solution, first add 0.01mmol (0.0020g) of aluminum isopropoxide thereto, stir for about half an hour, then add 1mmol (0.2084g) of tetraethyl orthosilicate, stir at room temperature for about two hours to completely hydrolyze the tetraethyl orthosilicate, 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, and wash the product twice with water and twice with ethanol. X-ray powder diffraction phase identification shows that the product is an aluminosilicate molecular sieve with a STW structure ( Figure 1 ), the product crystals can be seen to be hollow by scanning electron microscopy ( Figure 2 ).

[0045] Example 10: A molecular sieve synthesis gel was prepared in a molar ratio of 1SiO2:0.4ROH:0.05Al2O3:0.1HF:20H2O. The steps were as follows: Weigh a measured amount of template 1 alkaline solution, first add 1 wt% (0.0032 g) of the product of Example 2 as a seed crystal based on the theoretical mass of the gel, then add 0.1 mmol (0.0204 g) of aluminum isopropoxide and stir for about half an hour. Then, add 1 mmol (0.2084 g) of tetraethyl orthosilicate and stir at room temperature for about two hours to completely hydrolyze the tetraethyl orthosilicate. Then, add the desired amount of hydrofluoric acid solution and stir evenly. The mixed gel was placed under an infrared lamp or in an 80°C oven to remove excess solvent to the theoretical weight. The resulting reaction gel was transferred to a 15 mL stainless steel reactor lined with polytetrafluoroethylene and reacted at 160°C under sealed conditions for 15 days. The product was washed twice with water and twice with ethanol. The X-ray powder diffraction pattern of the product is the same as that of Example 9, indicating that the product is an aluminosilicate molecular sieve with a STW structure. Scanning electron microscopy shows that the product crystals have a hollow morphology, similar to that of Example 9.

[0046] Example 11: A molecular sieve synthesis gel was prepared in a molar ratio of 1SiO2:0.7ROH:0.02TiO2:0.7HF:5H2O. The steps were as follows: Weigh a measured amount of the alkaline solution of the template agent 1, first add 0.02mmol (0.0108g) of tetrabutyl titanate, and stir for about half an hour. Then, add 1mmol (0.2084g) of ethyl orthosilicate and stir at room temperature for about two hours to completely dissolve the ethyl orthosilicate. Then, add the desired amount of hydrofluoric acid solution and stir evenly. Finally, add 2wt% (0.0065g) of the product of Example 2 as a seed crystal based on the theoretical mass of the gel. The mixed gel was placed under an infrared lamp or in an 80°C oven to remove excess solvent to the theoretical weight. The resulting reaction gel was transferred to a 15mL stainless steel reactor lined with polytetrafluoroethylene and reacted at 160°C under sealed conditions for 15 days. The product was washed twice with water and twice with ethanol. The X-ray powder diffraction pattern of the product is the same as that of Example 2, and is a titanosilicate molecular sieve with a STW structure.

[0047] Example 12: Performance of STW structure aluminosilicate molecular sieve as catalyst in the alkylation of toluene and methanol to produce p-xylene.

[0048] The molecular sieve-catalyzed alkylation of toluene with methanol to produce p-xylene was carried out in a fixed-bed microreactor under the following reaction conditions: the molar ratio of toluene to methanol was n(toluene) / n(methanol) = 3, the mixed feed of toluene and methanol was introduced into the fixed-bed reactor by a horizontal flow pump, the reaction temperature was 400°C, the reaction pressure was 2 MPa, and the mass space velocity was 7.5 h -1 , the catalyst loading amount is 3.0g, the reaction results are as follows Figure 3As shown. The toluene conversion rate of ZSM-5 aluminosilicate molecular sieve (Si / Al=100, synthesized according to the literature: Song W., Justice RE, et al. Synthesis, characterization, and adsorption properties of nanocrystalline ZSM-5[J]. Langmuir 2004, 20, 8301-8306) is about 23%, the p-xylene selectivity is about 30%, and the catalyst deactivates rapidly after 24 hours. Under the catalysis of STW aluminosilicate molecular sieve (Si / Al=100) obtained in Example 7, the toluene conversion rate is about 15%, the p-xylene selectivity reaches more than 90%, and the catalyst begins to deactivate after 10 hours. The STW aluminosilicate molecular sieve catalyst synthesized by the present invention shows excellent p-xylene selectivity in the reaction of toluene methanol alkylation to p-xylene.

[0049] Example 13: Performance of Hollow STW Structure Aluminosilicate Molecular Sieve as Catalyst in Toluene Methanol Alkylation to Para-Xylene

[0050] The molecular sieve-catalyzed alkylation of toluene with methanol to produce p-xylene was carried out in a fixed-bed microreactor under the following reaction conditions: the molar ratio of toluene to methanol was n(toluene) / n(methanol) = 3, the mixed feed of toluene and methanol was introduced into the fixed-bed reactor by a horizontal flow pump, the reaction temperature was 400°C, the reaction pressure was 2 MPa, and the mass space velocity was 7.5 h -1 , the catalyst loading amount is 3.0g, the reaction results are as follows Figure 3 As shown. Under the catalysis of the hollow STW aluminosilicate molecular sieve material (Si / Al=100) obtained in Example 9, the toluene conversion rate (about 17%) and para-xylene selectivity (over 90%) were comparable to those of the solid STW aluminosilicate molecular sieve obtained in Example 7, but the catalyst stability was significantly improved, with no deactivation observed within 80 hours, demonstrating even better para-xylene selectivity and catalytic stability.

Claims

1. A method for preparing a STW structure silicate 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, a STW molecular sieve seed crystal, and water are uniformly mixed in proportion under stirring to obtain a reaction gel, wherein the tetravalent element compound other than silicon and germanium is an oxide or ester of titanium and tin, and the chemical composition of the reaction gel is: r ROH: a HF: x X2O3: y YO2:SiO2: w H2O, wherein R represents a positively charged group of an organic template, the organic template is a basic salt of 1,5-diazabicyclo[4.3.0]non-5-ene, and R is selected from one or more of the following structures: 、 、 、 ; X represents one or more trivalent boron group elements; Y represents one or more tetravalent elements other than silicon and germanium, r =0.1-1, a =0-1, x =0-0.1, y =0-0.1, w =1-50, the amount of seed added is 0-10 wt% of the theoretical mass of the gel; (2) removing excess solvent from the reaction gel, transferring the reaction gel to a stainless steel reactor, and reacting at 120-200°C under sealed conditions for 1-60 days; (3) washing and drying the product crystallized in step (2), and then calcining it in an air atmosphere at 500-650° C. for 2-5 hours to obtain the STW silicate molecular sieve with the template removed; The STW structure silicate molecular sieve has a skeleton crystal structure of germanium silicate SU-32, and its chemical composition is p (M 1 / n XO2) q YO2·SiO2, wherein M represents a proton or an inorganic cation with a +n valence; X represents one or more trivalent elements; and Y represents one or more tetravalent elements other than silicon and germanium. p = 0–0.1, q = 0–0.

1.

2. The method for preparing the STW structure silicate molecular sieve according to claim 1, wherein M represents proton or sodium, X is Al or B, Y is Ti, p =0-0.08; q =0-0.

08.

3. The method for preparing the STW structure silicate molecular sieve according to claim 1, wherein 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 metaaluminate, aluminum isopropoxide, aluminum sulfate hexadecahydrate, aluminum hydroxide or boric acid; and the fluorine source material is hydrofluoric acid and / or ammonium fluoride.

4. The method for preparing the STW structure silicate molecular sieve according to claim 1, wherein The STW molecular sieve seed crystal is a STW structure molecular sieve of pure silicate, aluminosilicate, borosilicate, titanosilicate or stannosilicate.

5. The method for preparing the STW structure silicate molecular sieve according to claim 1, wherein r 、 a 、 x 、 y and w They are: r =0.1-1, a =0-1, x =0-0.08, y =0-0.08, w =2-30, and the amount of seed crystal added is 0-5wt% of the theoretical mass of the gel.

6. The method for preparing the STW structure silicate molecular sieve according to any one of claims 1 to 4, characterized in that r =0.2-1, a =0-1, x =0-0.05, y =0-0.1, w =1-30, and the amount of seed crystal added is 1-5 wt% of the theoretical mass of the gel to obtain a nano-sized STW structure silicate molecular sieve.

7. The method for preparing the STW structure silicate molecular sieve according to any one of claims 1 to 4, characterized in that r =0.4-1, a =0.1-0.8, x =0-0.05, y =0-0.1, w =1-20, and the amount of seed crystal added is 0-5 wt% of the theoretical mass of the gel to obtain a hollow morphology STW structure silicate molecular sieve.

8. A STW structure silicate molecular sieve, characterized in that The method according to claim 6 or 7 is used for preparation.

9. Use of the STW structure silicate molecular sieve prepared by the method according to any one of claims 1 to 7 as an adsorption material, separation material, or catalyst in the field of chemistry and chemical engineering.

10. Application of STW structure silicate molecular sieve as catalyst in the production of p-xylene by alkylation of toluene and methanol.

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