In-situ synthesis all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve and preparation method thereof

Abstract

The invention relates to the technical field of molecular sieve preparation, in particular to an in-situ synthesis all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve and a preparation method thereof.The in-situ synthesis all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained according to the following method that firstly, a silicon source, a structure-directing agent and deionized water are mixed to be uniform, and white powder B is obtained after crystallization, filtering, washing, drying and roasting are conducted; then uniformly mixing a silicon source, a template agent and deionized water to obtain a mixed solution C; and finally, adding the white powder B into the mixed solution C, uniformly mixing, crystallizing, filtering, washing, drying and roasting to obtain the catalyst. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve not only has weak acidity, but also has a micro-mesoporous structure and good hydrothermal stability, is especially suitable for a system with weak acidity, widens the application of the molecular sieve, and overcomes the limitation of the use of the current single ZSM-5 molecular sieve and MCM-41 molecular sieve.

Description

Technical Field

[0001] The invention relates to the technical field of molecular sieve preparation, in particular to an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve and a preparation method thereof. Background Art

[0002] In the 1970s, Mobil Corporation of the United States developed a ZSM-5 zeolite molecular sieve, which has three-dimensional cross-pores, namely, ten-membered ring straight pores and ten-membered ring Zigzag-type pores. The diameter of the intersection is 0.9nm, which is between the size of small-pore zeolites and large-pore zeolites, so it has a unique shape selectivity. In addition, ZSM-5 zeolite molecular sieve also has good controllability, hydrothermal stability and ion exchangeability, and has been successfully used in a variety of reaction systems, such as alkylation, isomerization, methanol to hydrocarbons and catalytic cracking reactions. However, ZSM-5 zeolite molecular sieve is a microporous molecular sieve with a pore size of less than 2nm. It is not conducive to the entry and exit of large molecules in the reaction process, which is easy to cause blockage, leading to catalyst deactivation, affecting its stability, and to a certain extent limiting its promotion and application.

[0003] The MCM-41 molecular sieve is also a mesoporous molecular sieve synthesized by Mobil Corporation of the United States using a liquid crystal template mechanism. It has a hexagonal ordered pore structure, a pore size uniformly distributed between 1nm and 10nm, a large specific surface area and regular pores, but its pore wall is thin (<1nm), which makes it weak in acidity, poor in ion exchange capacity and poor in hydrothermal stability, which greatly limits its promotion and application in the field of catalysis. In order to improve its hydrothermal stability, it is generally necessary to increase the thickness of its pore wall or to grow other molecular sieves with good hydrothermal stability on its surface. Therefore, based on the good hydrothermal stability of ZSM-5 molecular sieve, ZSM-5 / MCM-41 molecular sieve can be synthesized, which can not only improve the hydrothermal stability of MCM-41, but also change its acidity and ion exchange performance, obtain a micro-mesoporous composite molecular sieve, and expand its application in the field of catalysis.

[0004] Chinese patent document with patent number CN103723741A discloses a ZSM-5 / MCM-41 zeolite molecular sieve and its preparation method and application. The patent uses hexadecyltrimethylammonium bromide as a template, and mixes silicon source, aluminum source, template (R), sodium hydroxide and water to form a sol. The molar ratio of the sol is: SiO2:Al2O3:R:Na2O:H2O=(7 to 8933):0.01:(0.61 to 732):(0.76 to 1496):(255 to 499500). The sol is hydrothermally crystallized at 140°C to 180°C for 2 to 3 days, and then cooled, filtered, washed and dried to obtain a ZSM-5 / MCM-41 composite molecular sieve sample. The specific synthesis steps are: first, hexadecyltrimethylammonium bromide is dissolved in deionized water under heating conditions, and then sodium hydroxide and aluminum sulfate are added in sequence, stirred until dissolved, and finally, a silica sol solution (SiO2, 30wt%) is added under stirring. After the addition, stirring is continued to mix evenly. The amount of substance composition of the reaction sol is SiO2:A l2 O3:R:Na2O:H2O=6.67:0.01:0.61:0.76:255 (R is hexadecyltrimethylammonium bromide, the same below). The reaction sol is sealed in a stainless steel high-pressure reactor with a polytetrafluoroethylene liner, crystallized at 170°C for 2 days, and the reactor is taken out and quickly cooled to room temperature, the solid product is filtered out, and washed with deionized water to neutrality, and dried at 100°C overnight to obtain the product. The ZSM-5 / MCM-41 zeolite molecular sieve prepared in this patent is still a sodium-type molecular sieve, which requires further ammonium exchange; at the same time, the ZSM-5 / MCM-41 molecular sieve is not an all-silicon molecular sieve, and has a strong acidity, and is not suitable for weakly acidic catalytic reaction systems. Summary of the invention

[0005] The present invention provides an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve and a preparation method thereof, which overcomes the deficiencies of the above-mentioned prior art. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve has weak acidity and is suitable for systems with weak acidity.

[0006] One of the technical solutions of the present invention is achieved by the following measures: an in-situ synthesis of all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, stirring the required amount of silicon source, structure directing agent and deionized water, and adjusting the pH value with a pH adjuster to obtain a mixed solution A; S2, crystallizing the mixed solution A, and then filtering, washing, drying and calcining to obtain a white powder B; S3, stirring the required amount of silicon source, template agent and deionized water uniformly, adjusting the pH value with a pH adjuster, and obtaining a mixed solution C; S4, adding white powder B to the mixed solution C and stirring evenly to obtain a mixed solution D, and then filtering, washing, drying and calcining the mixed solution D to obtain an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve.

[0007] The following is a further optimization and / or improvement of one of the above-mentioned technical solutions: In the above steps S1 and S3, the silicon source is one or more of silica sol, silica gel, tetraethyl orthosilicate, silicon dioxide and white carbon black.

[0008] In the above step S1, the structure directing agent is one or more of tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, n-butylamine and tetrabutylammonium bromide.

[0009] In the above steps S1 and S3, the pH adjuster is urea or ammonia water, and the pH value is adjusted to 8.5 to 10.5.

[0010] In the above step S3, the template agent is one or more of hexadecyltrimethylammonium bromide and dodecyltrimethylammonium bromide.

[0011] In the above step S1, the molar ratio of the silicon source, the structure directing agent and the deionized water is 1:(0.1 to 50):(5 to 200).

[0012] In the above step S3, the molar ratio of the silicon source, the template and the deionized water is 1:(0.002 to 1.0):(20 to 300).

[0013] In the above step S1, the stirring temperature is 10°C to 50°C, and the stirring time is 1h to 12h.

[0014] In the above step S3, the stirring temperature is 30° C. to 120° C., and the stirring time is 1 h to 12 h.

[0015] In the above step S2, the crystallization temperature is 100° C. to 200° C., and the crystallization time is 24 h to 96 h.

[0016] In the above step S4, the stirring time is 1 h to 6 h, the crystallization temperature is 80° C. to 200° C., and the crystallization time is 12 h to 108 h.

[0017] In the above step S2, the drying temperature is 50°C to 150°C, the drying time is 4h to 24h, the roasting temperature is 400°C to 800°C, and the roasting time is 4h to 10h.

[0018] In the above step S4, the drying temperature is 50°C to 150°C, the drying time is 4h to 24h, the roasting temperature is 400°C to 750°C, and the roasting time is 3h to 10h.

[0019] The second technical solution of the present invention is achieved by the following measures: an in-situ synthesis of all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is carried out according to the following method: S1, stirring the required amount of silicon source, structure directing agent and deionized water, and adjusting the pH value with a pH adjuster to obtain a mixed solution A; S2, crystallizing the mixed solution A, and then filtering, washing, drying and calcining to obtain a white powder B; S3, stirring the required amount of silicon source, template agent and deionized water uniformly, and adjusting the pH value with a pH adjuster to obtain a mixed solution C; S4, adding white powder B to the mixed solution C and stirring evenly to obtain a mixed solution D, and then filtering, washing, drying and calcining the mixed solution D to obtain an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve.

[0020] The invention provides a method for in-situ synthesizing an all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared by the method is sodium-free and does not require ammonium exchange, and is directly a hydrogen-type composite molecular sieve, thereby reducing the ammonium exchange step and simplifying the process flow. Meanwhile, the in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve not only has weak acidity, but also has a micro-mesoporous structure and good hydrothermal stability, and is particularly suitable for systems with weak acidity, thereby broadening its application and overcoming the limitations of the current use of single ZSM-5 molecular sieves and MCM-41 molecular sieves. DETAILED DESCRIPTION

[0021] The present invention is not limited by the following embodiments, and the specific implementation method can be determined according to the technical scheme of the present invention and the actual situation. Unless otherwise specified, the various chemical reagents and chemicals mentioned in the present invention are all chemical reagents and chemicals known and used in the prior art; unless otherwise specified, the percentages in the present invention are all mass percentages; unless otherwise specified, the solutions in the present invention are all aqueous solutions with water as the solvent, for example, hydrochloric acid solution is a hydrochloric acid aqueous solution; the normal temperature and room temperature in the present invention generally refer to a temperature of 15°C to 25°C, and are generally defined as 25°C.

[0022] The present invention will be further described below in conjunction with embodiments: Example 1: The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, stirring the required amount of silicon source, structure directing agent and deionized water, and adjusting the pH value with a pH adjuster to obtain a mixed solution A; S2, crystallizing the mixed solution A, and then filtering, washing, drying and calcining to obtain a white powder B; S3, stirring the required amount of silicon source, template agent and deionized water uniformly, and adjusting the pH value with a pH adjuster to obtain a mixed solution C; S4, adding white powder B to the mixed solution C and stirring evenly to obtain a mixed solution D, and then filtering, washing, drying and calcining the mixed solution D to obtain an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve.

[0023] Embodiment 2: As an optimization of the above embodiment, in steps S1 and S3, the silicon source is one or more of silica sol, silica gel, tetraethyl orthosilicate, silicon dioxide and white carbon black.

[0024] Example 3: As an optimization of the above example, in step S1, the structure directing agent is one or more of tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, n-butylamine and tetrabutylammonium bromide.

[0025] Example 4: As an optimization of the above example, in steps S1 and S3, the pH adjuster is urea or ammonia water, and the pH value is adjusted to 8.5 to 10.5.

[0026] Embodiment 5: As an optimization of the above embodiment, in step S3, the template agent is one or more of hexadecyltrimethylammonium bromide and dodecyltrimethylammonium bromide.

[0027] Example 6: As an optimization of the above example, in step S1, the molar ratio of the silicon source, the structure directing agent and the deionized water is 1: (0.1 to 50): (5 to 200).

[0028] Example 7: As an optimization of the above example, in step S3, the molar ratio of the silicon source, the template and the deionized water is 1: (0.002 to 1.0): (20 to 300).

[0029] Embodiment 8: As an optimization of the above embodiment, in step S1, the stirring temperature is 10°C to 50°C, and the stirring time is 1h to 12h.

[0030] Example 9: As an optimization of the above example, in step S3, the stirring temperature is 30°C to 120°C, and the stirring time is 1h to 12h.

[0031] Embodiment 10: As an optimization of the above embodiment, in step S2, the crystallization temperature is 100°C to 200°C, and the crystallization time is 24h to 96h.

[0032] Example 11: As an optimization of the above example, in step S4, the stirring time is 1 h to 6 h, the crystallization temperature is 80°C to 200°C, and the crystallization time is 12 h to 108 h.

[0033] Example 12: As an optimization of the above example, in step S2, the drying temperature is 50°C to 150°C, the drying time is 4h to 24h, the roasting temperature is 400°C to 800°C, and the roasting time is 4h to 10h.

[0034] Example 13: As an optimization of the above example, in step S4, the drying temperature is 50°C to 150°C, the drying time is 4h to 24h, the roasting temperature is 400°C to 750°C, and the roasting time is 3h to 10h.

[0035] Embodiment 14: The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, take 31.2g of silicon source (silica sol, mass fraction of 30%), 12.9g of structure directing agent (tetrabutylammonium bromide) and 108.5g of deionized water, stir at 30℃ for 1h, adjust the pH value to 9.3 with pH adjuster (ammonia water, mass fraction of 25%), and stir at 30℃ for 6h to obtain mixed solution A; S2, crystallizing the mixed solution A at 150°C for 96 hours, filtering and washing to neutrality after the crystallization, drying at 120°C for 9 hours, and calcining at 520°C for 5 hours to obtain a white powder B; S3, take 7.2g of silicon source (ethyl orthosilicate), 4.3g of template (hexadecyltrimethylammonium bromide) and 59g of deionized water, stir at 30°C for 2h, adjust the pH value to 9.8 with a pH adjuster (ammonia water, mass fraction 25%), and obtain a mixed solution C; S4, add white powder B to the mixed solution C, stir at room temperature for 3 hours to obtain a mixed solution D, transfer the mixed solution D to a crystallization kettle with a polytetrafluoroethylene liner, crystallize at 120°C for 48 hours, then filter, wash, and dry at 100°C for 15 hours. After calcining at 520°C for 8 hours, an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained.

[0036] The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared in Example 14 of the present invention has a sodium content of 0.001% and a specific surface area of ​​324 m 2 / g, pore volume 0.78m 3 / g, weak acid content 0.56mmol / g, strong acid content 0.12mmol / g.

[0037] Embodiment 15: The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, take 15g of silicon source (white carbon black), 220g of structure directing agent (tetrapropylammonium hydroxide, mass fraction of 25%) and 205g of deionized water, stir at 30°C for 2h, adjust the pH value to 8.5 with pH adjuster (urea), and stir at 30°C for 4h to obtain mixed solution A; S2, crystallizing the mixed solution A at 140°C for 72 hours, filtering and washing to neutrality after the crystallization, drying at 120°C for 12 hours, and calcining at 500°C for 6 hours to obtain a white powder B; S3, take 105.8g of silicon source (silica sol, mass fraction of 30%), 9.8g of template (dodecyltrimethylammonium bromide) and 254g of deionized water, stir at 35°C for 5h, adjust the pH value to 8.6 with pH adjuster (ammonia water, mass fraction of 25%), and obtain mixed solution C; S4, add white powder B to the mixed solution C, stir at room temperature for 4 hours to obtain a mixed solution D, transfer the mixed solution D to a crystallization kettle with a polytetrafluoroethylene liner, crystallize at 110°C for 48 hours, then filter, wash, and dry at 120°C for 24 hours. After calcining at 550°C for 8 hours, an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained.

[0038] The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared in Example 15 of the present invention has a sodium content of 0.002% and a specific surface area of ​​358 m 2 / g, pore volume 0.69m 3 / g, weak acid content 0.60mmol / g, strong acid content 0.10mmol / g.

[0039] Embodiment 16: The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, take 45g of silicon source (ethyl orthosilicate), 20g of structure directing agent (n-butylamine) and 162g of deionized water, stir at 40°C for 3h, adjust the pH value to 8.7 with pH adjuster (urea), and stir at 40°C for 3h to obtain mixed solution A; S2, crystallizing the mixed solution A at 180°C for 45 hours, filtering and washing to neutrality after the crystallization, drying at 90°C for 10 hours, and calcining at 550°C for 5 hours to obtain a white powder B; S3, taking 12.5 g of silicon source (silicon dioxide), 15.6 g of template (hexadecyltrimethylammonium bromide) and 212 g of deionized water, stirring at 40°C for 3 h, adjusting the pH value to 10.0 with a pH adjuster (ammonia water, mass fraction of 25%), and obtaining a mixed solution C; S4, add white powder B to the mixed solution C, stir at room temperature for 5 hours to obtain a mixed solution D, transfer the mixed solution D to a crystallization kettle with a polytetrafluoroethylene liner, crystallize at 160°C for 48 hours, then filter, wash, and dry at 90°C for 24 hours. After calcining at 480°C for 8 hours, the in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained.

[0040] The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared in Example 16 of the present invention has a sodium content of 0.0018% and a specific surface area of ​​391 m 2 / g, pore volume 0.53m 3 / g, weak acid content 0.65mmol / g, strong acid content 0.09mmol / g.

[0041] Embodiment 17: The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, take 15g of silicon source (10g of silica sol, mass fraction of 30% and 5g of white carbon black), 360g of structure directing agent (120g of n-butylamine and 240g of tetrapropylammonium hydroxide, mass fraction of 25%) and 135g of deionized water, stir at 50℃ for 2h, adjust the pH value to 9.7 with pH adjuster (ammonia water, mass fraction of 25%), and stir at 30℃ for 4h to obtain mixed solution A; S2, crystallizing the mixed solution A at 200°C for 48 hours, filtering and washing to neutrality after the crystallization, drying at 140°C for 8 hours, and calcining at 550°C for 4 hours to obtain a white powder B; S3, taking 10.2 g of silicon source (silica gel), 6.4 g of template (hexadecyltrimethylammonium bromide) and 326 g of deionized water, stirring at 30°C for 3 h, adjusting the pH value to 9.6 with a pH adjuster (urea), and obtaining a mixed solution C; S4, add white powder B to the mixed solution C, stir at room temperature for 3.5 hours to obtain a mixed solution D, transfer the mixed solution D to a crystallization kettle with a polytetrafluoroethylene liner, crystallize at 170°C for 48 hours, then filter, wash, and dry at 90°C for 24 hours. After calcining at 600°C for 6 hours, the in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained.

[0042] The sodium content of the in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared in Example 17 of the present invention is 0.001%, and the specific surface area is 314 m 2 / g, pore volume 0.51m 3 / g, weak acid content 0.48mmol / g, strong acid content 0.13mmol / g.

[0043] Embodiment 18: The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, take 2.3g silicon source (2g silicon dioxide and 0.3g white carbon black), 540g structure directing agent (tetrapropylammonium hydroxide, mass fraction of 25%) and 128g deionized water, stir at 30℃ for 5h, adjust pH value to 10.1 with pH adjuster (ammonia water, mass fraction of 25%), stir at 30℃ for 5h, and obtain mixed solution A; S2, crystallizing the mixed solution A at 170°C for 56 hours, filtering and washing to neutrality after the crystallization, drying at 110°C for 10 hours, and calcining at 540°C for 6 hours to obtain a white powder B; S3, take 45.2g of silicon source (ethyl orthosilicate), 35.6g of template (hexadecyltrimethylammonium bromide) and 264.3g of deionized water, stir at 20°C for 3h, adjust the pH value to 9.3 with a pH adjuster (ammonia water, mass fraction 25%), and obtain a mixed solution C; S4, add white powder B to the mixed solution C, stir at room temperature for 2 hours to obtain a mixed solution D, transfer the mixed solution D to a crystallization kettle with a polytetrafluoroethylene liner, crystallize at 150°C for 24 hours, then filter, wash, and dry at 100°C for 12 hours. After calcining at 500°C for 5 hours, an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained.

[0044] The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared in Example 18 of the present invention has a sodium content of 0.0015% and a specific surface area of ​​382 m 2 / g, pore volume 0.51m 3 / g, weak acid content 0.72mmol / g, strong acid content 0.20mmol / g.

[0045] Embodiment 19: The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, take 8g of silicon source (silicon dioxide), 125g of structure directing agent (tetrapropylammonium hydroxide, mass fraction of 25%) and 75g of deionized water, stir at 35°C for 2h, adjust the pH value to 8.8 with pH adjuster (ammonia water, mass fraction of 25%), and stir at 45°C for 6h to obtain mixed solution A; S2, crystallizing the mixed solution A at 160°C for 80 hours, filtering and washing to neutrality after the crystallization, drying at 100°C for 12 hours, and calcining at 580°C for 4 hours to obtain a white powder B; S3, take 52.3g of silicon source (silica sol, mass fraction of 30%), 45.2g of template (dodecyltrimethylammonium bromide) and 340.5g of deionized water, stir at 40°C for 2.5h, adjust the pH value to 8.7 with pH adjuster (urea), and obtain mixed solution C; S4, add white powder B to the mixed solution C, stir at room temperature for 5 hours to obtain a mixed solution D, transfer the mixed solution D to a crystallization kettle with a polytetrafluoroethylene liner, crystallize at 180°C for 60 hours, then filter, wash, and dry at 90°C for 24 hours. After calcining at 580°C for 9 hours, an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained.

[0046] The sodium content of the in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared in Example 19 of the present invention is 0.0039%, and the specific surface area is 412 m 2 / g, pore volume 0.69m 3 / g, weak acid content 0.64mmol / g, strong acid content 0.15mmol / g.

[0047] Embodiment 20: The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, take 6g of silicon source (silica sol, mass fraction of 30%), 89g of structure directing agent (tetrabutylammonium bromide) and 95g of deionized water, stir at 25℃ for 3h, adjust the pH value to 8.9 with pH adjuster (ammonia water, mass fraction of 25%), and stir at 40℃ for 5h to obtain mixed solution A; S2, crystallizing the mixed solution A at 160°C for 72 hours, filtering and washing to neutrality after the crystallization, drying at 110°C for 24 hours, and calcining at 480°C for 10 hours to obtain a white powder B; S3, take 13.9 g of silicon source (ethyl orthosilicate), 16.3 g of template (hexadecyltrimethylammonium bromide) and 189.6 g of deionized water, stir at 40 ° C for 3 h, adjust the pH value to 10.5 with a pH adjuster (ammonia water, mass fraction of 25%), and obtain a mixed solution C; S4, add white powder B to the mixed solution C, stir at room temperature for 5 hours to obtain a mixed solution D, transfer the mixed solution D to a crystallization kettle with a polytetrafluoroethylene liner, crystallize at 140°C for 96 hours, then filter, wash, and dry at 120°C for 16 hours. After calcining at 700°C for 24 hours, an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained.

[0048] The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared in Example 19 of the present invention has a sodium content of 0.0079% and a specific surface area of ​​360 m 2 / g, pore volume 0.46m 3 / g, weak acid content 0.52mmol / g, strong acid content 0.05mmol / g.

[0049] Embodiment 21: The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, take 5g of silicon source (white carbon black), 435g of structure directing agent (tetrapropylammonium hydroxide, mass fraction of 25%) and 158g of deionized water, stir at 30°C for 6h, adjust the pH value to 9.0 with pH adjuster (urea), and stir at 25°C for 6h to obtain mixed solution A; S2, crystallizing the mixed solution A at 160°C for 48 hours, filtering and washing to neutrality after the crystallization, drying at 80°C for 20 hours, and calcining at 600°C for 5 hours to obtain a white powder B; S3, taking 14.5 g of silicon source (ethyl orthosilicate), 18.1 g of template (hexadecyltrimethylammonium bromide) and 322 g of deionized water, stirring at 35°C for 5 h, adjusting the pH value to 9.8 with a pH adjuster (urea), and obtaining a mixed solution C; S4, add white powder B to the mixed solution C, stir at room temperature for 2.5 hours to obtain a mixed solution D, transfer the mixed solution D to a crystallization kettle with a polytetrafluoroethylene liner, crystallize at 180°C for 40 hours, then filter, wash, and dry at 120°C for 10 hours. After calcining at 550°C for 8 hours, an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained.

[0050] The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared in Example 20 of the present invention has a sodium content of 0.0058% and a specific surface area of ​​278 m 2 / g, pore volume 0.63m 3 / g, weak acid content 0.50mmol / g, strong acid content 0.16mmol / g.

[0051] Embodiment 21: The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, take 12.5g of silicon source (11g of silica sol, with a mass fraction of 30% and 1.5g of silicon dioxide), 513g of structure directing agent (335g of tetrapropylammonium hydroxide, with a mass fraction of 25% and 178g of n-butylamine) and 170g of deionized water, stir at 40°C for 2h, adjust the pH value to 8.5 with a pH adjuster (ammonia water, with a mass fraction of 25%), and stir at 50°C for 6h to obtain a mixed solution A; S2, crystallizing the mixed solution A at 180°C for 60 hours, filtering and washing to neutrality after the crystallization, drying at 150°C for 6 hours, and calcining at 720°C for 5 hours to obtain a white powder B; S3, take 35.7g of silicon source (silica sol, mass fraction of 30%), 6.9g of template (dodecyltrimethylammonium bromide) and 275g of deionized water, stir at 20°C for 4.5h, adjust the pH value to 9.2 with pH adjuster (urea), and obtain mixed solution C; S4, add white powder B to the mixed solution C, stir at room temperature for 3.5 hours to obtain a mixed solution D, transfer the mixed solution D to a crystallization kettle with a polytetrafluoroethylene liner, crystallize at 130°C for 48 hours, then filter, wash, and dry at 80°C for 24 hours. After calcining at 560°C for 5 hours, an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained.

[0052] The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared in Example 21 of the present invention has a sodium content of 0.0025% and a specific surface area of ​​452 m 2 / g, pore volume 0.71m 3 / g, weak acid content 0.76mmol / g, strong acid content 0.09mmol / g.

[0053] Embodiment 22: The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained by the following method: S1, take 3.6g of silicon source (white carbon black), 9.6g of structure directing agent (tetramethylammonium hydroxide, mass fraction of 25%) and 25g of deionized water, stir at 45°C for 4.5h, adjust the pH value to 8.8 with pH adjuster (ammonia water, mass fraction of 25%), and stir at 40°C for 4h to obtain mixed solution A; S2, crystallizing the mixed solution A at 130°C for 96 hours, filtering and washing to neutrality after the crystallization, drying at 140°C for 5 hours, and calcining at 560°C for 8 hours to obtain a white powder B; S3, taking 20.5 g of silicon source (silicon dioxide), 37.8 g of template (hexadecyltrimethylammonium bromide) and 220.5 g of deionized water, stirring at 45 ° C for 3 h, adjusting the pH value to 10.5 with a pH adjuster (ammonia water, mass fraction of 25%), and obtaining a mixed solution C; S4, add white powder B to the mixed solution C, stir at room temperature for 4.5 hours to obtain a mixed solution D, transfer the mixed solution D to a crystallization kettle with a polytetrafluoroethylene liner, crystallize at 170°C for 96 hours, then filter, wash, and dry at 150°C for 8 hours. After calcining at 640°C for 6 hours, an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve is obtained.

[0054] The sodium content of the in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared in Example 21 of the present invention is 0.0029%, and the specific surface area is 323 m 2 / g, pore volume 0.65m 3 / g, weak acid content 0.49mmol / g, strong acid content 0.18mmol / g.

[0055] In summary, the present invention provides a method for in-situ synthesis of all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieves. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve prepared by the method is sodium-free and does not require ammonium exchange, and is directly a hydrogen-type composite molecular sieve, thereby reducing the ammonium exchange step and simplifying the process flow. At the same time, the in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve of the present invention not only has weak acidity, but also has a micro-mesoporous structure and good hydrothermal stability, and is particularly suitable for systems with weak acidity, thereby broadening its application and overcoming the limitations of the current use of single ZSM-5 molecular sieves and MCM-41 molecular sieves.

[0056] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the requirements of different situations.

Claims

1. An in-situ synthesis of all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve, characterized in that Obtained as follows: S1, stirring the required amount of silicon source, structure directing agent and deionized water, and adjusting the pH value with a pH adjuster to obtain a mixed solution A; S2, crystallizing the mixed solution A, and then filtering, washing, drying and calcining to obtain a white powder B; S3, stirring the required amount of silicon source, template agent and deionized water uniformly, and adjusting the pH value with a pH adjuster to obtain a mixed solution C; S4, adding white powder B to the mixed solution C and stirring evenly to obtain a mixed solution D, and then filtering, washing, drying and calcining the mixed solution D to obtain an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve.

2. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve according to claim 1, characterized in that In steps S1 and S3, the silicon source is one or more of silica sol, silica gel, tetraethyl orthosilicate, silicon dioxide and white carbon black.

3. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve according to claim 1 or 2, characterized in that In step S1, the structure directing agent is one or more of tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, n-butylamine and tetrabutylammonium bromide.

4. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve according to claim 1, 2 or 3, characterized in that In steps S1 and S3, the pH adjuster is urea or ammonia water, and the pH value is adjusted to 8.5 to 10.

5.

5. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve according to any one of claims 1 to 4, characterized in that In step S3, the template agent is one or more of hexadecyltrimethylammonium bromide and dodecyltrimethylammonium bromide.

6. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve according to any one of claims 1 to 5, characterized in that In step S1, the molar ratio of the silicon source, the structure directing agent and deionized water is 1:0.1 to 50:5 to 200; or / and, in step S3, the molar ratio of the silicon source, the template and deionized water is 1:0.002 to 1.0:20 to 300.

7. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve according to any one of claims 1 to 6, characterized in that In step S1, the stirring temperature is 10°C to 50°C, and the stirring time is 1h to 12h; or / and, in step S3, the stirring temperature is 30°C to 120°C, and the stirring time is 1h to 12h.

8. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve according to any one of claims 1 to 7, characterized in that In step S2, the crystallization temperature is 100°C to 200°C, and the crystallization time is 24h to 96h; or / and, in step S4, the stirring time is 1h to 6h, the crystallization temperature is 80°C to 200°C, and the crystallization time is 12h to 108h.

9. The in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve according to any one of claims 1 to 8, characterized in that In step S2, the drying temperature is 50°C to 150°C, the drying time is 4h to 24h, the roasting temperature is 400°C to 800°C, and the roasting time is 4h to 10h; or / and, in step S4, the drying temperature is 50°C to 150°C, the drying time is 4h to 24h, the roasting temperature is 400°C to 750°C, and the roasting time is 3h to 10h.

10. A method for preparing an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve according to any one of claims 2 to 9, characterized in that Proceed as follows: S1, stirring the required amount of silicon source, structure directing agent and deionized water, and adjusting the pH value with a pH adjuster to obtain a mixed solution A; S2, crystallizing the mixed solution A, and then filtering, washing, drying and calcining to obtain a white powder B; S3, stirring the required amount of silicon source, template agent and deionized water uniformly, adjusting the pH value with a pH adjuster, and obtaining a mixed solution C; S4, adding white powder B to the mixed solution C and stirring evenly to obtain a mixed solution D, and then filtering, washing, drying and calcining the mixed solution D to obtain an in-situ synthesized all-silicon sodium-free ZSM-5 / MCM-41 composite molecular sieve.