Phosphorus-doped hierarchical pore ZSM-5 zeolite, and preparation method and application thereof

Abstract

The application belongs to the technical field of petroleum processing and petrochemical catalysts, and particularly relates to a phosphorus-doped hierarchical pore ZSM-5 zeolite and a preparation method and application thereof. The phosphorus-doped hierarchical pore ZSM-5 zeolite is prepared by a one-step hydrothermal synthesis method. The phosphorus element enters the zeolite framework in a stable four-coordinated form, forms a strong chemical bond with silicon and aluminum atoms, and simultaneously realizes the framework-level coordinated doping of the phosphorus element and the precise construction of micro-mesopore-macropore hierarchical channels, successfully solving the contradiction between the insufficient hydrothermal stability of the hierarchical pore zeolite and the channel blockage caused by phosphorus modification. The prepared zeolite has a crystallinity retention rate of > 85% after hydrothermal treatment at 800 DEG C, has excellent physical structure, chemical stability and outstanding catalytic performance, provides an ideal material solution for developing a new generation of long-life and high-efficiency petrochemical catalysts (especially for processes such as olefin cracking and MTO), and has great scientific value and broad industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of petroleum processing and petrochemical catalyst technology, specifically relating to a phosphorus-doped hierarchical porous ZSM-5 zeolite, its preparation method, and its application. Background Technology

[0002] ZSM-5 zeolite, due to its unique shape-selective catalytic properties and tunable acidity, has become an indispensable catalytic material in the petrochemical industry. However, in industrial applications, especially in reactions involving high temperatures and high water vapor partial pressures (such as catalytic cracking) and regenerated coke cycles, ZSM-5 catalysts face two major challenges:

[0003] Micropore mass transfer limitation and structural deactivation: Traditional ZSM-5 zeolites are predominantly microporous (<2 nm), and their narrow channels severely restrict the diffusion of macromolecular reactants (such as heavy oil components) and products, resulting in low utilization of internal active sites and a high susceptibility to deep reactions leading to carbon deposition and rapid catalyst deactivation. To address this issue, constructing hierarchical porous structures containing mesopores (2-50 nm) and even macropores has proven to be an effective strategy. This structure can significantly shorten molecular diffusion paths, improve macromolecular accessibility, thereby inhibiting carbon deposition and extending catalyst lifetime.

[0004] Insufficient hydrothermal stability and chemical deactivation: While the construction of hierarchical porous structures improves mass transfer, it also introduces new problems. The increased external specific surface area exposes more framework aluminum atoms to high-temperature water vapor, exacerbating the framework dealuminization process. The removal of framework aluminum not only directly destroys the strongly acidic Brønsted acid (B acid) sites, leading to an irreversible decrease in catalytic activity, but the generated non-framework aluminum species also clog the pores. Therefore, the structural stability of hierarchical porous zeolites often becomes a major bottleneck in their industrial applications.

[0005] Phosphorus (P) modification is a widely studied and effective post-treatment technique for improving the hydrothermal stability of zeolites. Studies have confirmed that phosphorus species can interact with aluminum in the zeolite framework, effectively inhibiting dealumination under high-temperature hydrothermal conditions, maintaining crystal structure stability, and modulating acidity. For example, modification of ZSM-5 with phosphorus oxides improves its acid center density, strength, and hydrothermal stability. However, existing technologies still face bottlenecks.

[0006] On the one hand, while the traditional post-impregnation phosphorus modification method (such as that used in patent CN114887647A) is simple to operate, phosphorus species tend to accumulate on the outer surface of zeolite and at the pore inlets during high-temperature calcination, forming polyphosphates. This modification method physically blocks the pore openings, severely covering acidic sites. For hierarchical ZSM-5, this actually stifles its mass transfer advantages, leading to a decrease in the accessibility of active centers. Although this patent achieves synergistic regulation of the carrier acidity and metal dispersion by co-impregnating phosphorus with noble metal precursors, its modification logic mainly serves the noble metal hydrogenation active centers, and the method of introducing phosphorus fails to avoid the risk of physical blockage of the pores.

[0007] On the other hand, in-situ synthesis methods have attracted attention to avoid post-processing clogging problems. Patent CN121222495A, by introducing phosphorus additives into the synthesis of alumina supports, achieved a framework integration between the additives and the support, significantly enhancing water and acid resistance. This suggests the possibility of introducing phosphorus elements in the early stages of support synthesis to achieve uniform doping and strong interactions. However, direct hydrothermal synthesis of phosphorus-doped zeolites for the ZSM-5 zeolite system faces significant challenges: conventional inorganic phosphate salts (such as phosphates) are too reactive in the hydrothermal synthesis environment, readily reacting preferentially with the aluminum source to form amorphous aluminum phosphate impurities, rather than entering the silica-alumina zeolite framework at the atomic level, leading to synthesis failure or impure products. Therefore, existing technologies often force the use of expensive and toxic organic phosphorus sources (such as triethyl phosphate) as precursors, which is not only costly but also brings environmental and safety pressures.

[0008] Therefore, providing a green and stable new method for preparing phosphorus-doped hierarchical porous ZSM-5 zeolite has important scientific value and urgent industrial application prospects for developing next-generation high-performance petrochemical catalysts, improving heavy oil processing efficiency, light hydrocarbon resource value and plant operation cycle. Summary of the Invention

[0009] The technical problem to be solved by this invention is to provide a phosphorus-doped hierarchical porous ZSM-5 zeolite, its preparation method, and its applications. The method employs in-situ hydrothermal synthesis, using inorganic phosphate salts as the phosphorus source, long-chain quaternary ammonium salts as template agents, and also adding silicon-aluminum sources. By controlling the crystallization temperature, a phosphorus-based framework-doped ZSM-5 containing micro-meso-multi-hierarchical pores is obtained in one step. Phosphorus and aluminum exist in a stable four-coordinated form within the framework. The prepared phosphorus-doped hierarchical porous ZSM-5 zeolite can be used for olefin catalytic cracking and MTO reactions, exhibiting high diene yields and slow carbon deposition.

[0010] The technical solution adopted is as follows:

[0011] A method for preparing phosphorus-doped hierarchical porous ZSM-5 zeolite includes the following steps:

[0012] (1) Mix aluminum source, phosphorus source and silicon source in water and stir, adjust pH to 8-9 to form a gel; add long carbon chain quaternary ammonium salt to the gel and stir to obtain a homogeneous mixture; wherein, the molar ratio of silicon source, phosphorus source and aluminum source is 30-300:0.5-2:1, and the molar ratio of silicon element to long carbon chain quaternary ammonium salt molecule is 100:2.5-5;

[0013] (2) The mixture is crystallized, and the crystallized product is washed, dried and calcined to obtain phosphorus-doped hierarchical porous ZSM-5 zeolite; wherein the hydrothermal reaction temperature during crystallization is 150℃, the calcination temperature is 550~650℃, and the calcination time is 4h~6h.

[0014] The aluminum source is aluminum sulfate octadecahydrate or sodium aluminate;

[0015] The silicon source is silica sol or water glass;

[0016] The phosphorus source is one or a combination of two of ammonium dihydrogen phosphate and disodium hydrogen phosphate;

[0017] The long-chain quaternary ammonium salt is an alkyl trimethyl quaternary ammonium salt, wherein the alkyl group is a straight-chain alkyl group with 12-18 carbons.

[0018] Preferably, the long-chain quaternary ammonium salt is any one or a combination of two of dodecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0019] Preferably, the silica sol used has a mass fraction of 40%; or, the water glass used has a mass fraction of 30% SiO2 and a mass fraction of 9% Na2O.

[0020] Preferably, in step (1), the molar ratio of silicon to water molecules is 1:18 to 25.

[0021] Preferably, in step (1), the molar ratio of silicon source, phosphorus source and aluminum source is 70:0.82:1; and the pH is 9.

[0022] Preferably, in step (1), the pH value of the solution is adjusted by an alkaline source and / or an acid source; the alkaline source is a sodium hydroxide or potassium hydroxide solution, and the acid source is any one or a combination of inorganic acids such as phosphoric acid, concentrated sulfuric acid, and nitric acid.

[0023] Preferably, in step (2), the crystallization time is 24h to 72h.

[0024] Preferably, the crystals precipitated after the hydrothermal reaction are washed, dried, and then calcined; the drying temperature is controlled at 100-120℃.

[0025] The phosphorus-doped hierarchical porous ZSM-5 zeolite prepared by this invention has a specific surface area of ​​402–440 m² / g, contains 2–4 nm intracrystalline mesopores and 30–50 nm intercrystalline macropores, and phosphorus and aluminum exist in the framework in a stable tetracoordinate form, with an acid content B / L ratio of 6.7–12.3.

[0026] The phosphorus-doped hierarchical porous ZSM-5 zeolite prepared by this invention can be applied to olefin catalytic cracking and MTO reactions, exhibiting high diene yield and slow carbon deposition. The phosphorus-doped hierarchical porous ZSM-5 zeolite has a lifetime of 265 hours in olefin catalytic cracking and 35 hours in MTO reactions.

[0027] The phosphorus-doped hierarchical porous ZSM-5 zeolite prepared by the method of this invention forms a PO-Al bonded framework structure, and the sample has micro-meso-multi-hierarchical channels. Phosphorus is deposited in the framework rather than in the channels, and the micropores and mesopores remain unobstructed, so the mass transfer efficiency of the hierarchical pores is not impaired. The phosphorus-doped hierarchical porous ZSM-5 zeolite prepared in this application has excellent hydrothermal stability, and still retains 90% crystallinity after being treated at a high temperature of 800℃ for 17 hours. Compared with the post-impregnation method to cover acidic sites, the in-situ doping of this invention retains more framework aluminum and increases the number of Brønsted acid sites (increasing the B / L ratio).

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) In the preparation method of the present invention, phosphorus element successfully enters the zeolite framework in a stable four-coordinate form and forms strong chemical bonds with silicon and aluminum atoms. This atomic-level doping fundamentally solves the problem of easy migration and pore blockage of phosphorus species in the traditional impregnation method, provides the catalyst with long-lasting and intrinsic stability, and achieves the synergistic unity of "stable doping" and "unobstructed pores".

[0030] (2) The material prepared by the present invention simultaneously possesses intracrystalline mesopores of 2-4 nm and intercrystalline macropores of 30-50 nm, which together with the inherent micropores constitute a three-dimensional interconnected hierarchical pore system. This structure not only greatly shortens the diffusion path between reactants and products and avoids micropore blockage, but also provides abundant mass transfer channels and greater accessibility to surface active sites for the reaction.

[0031] (3) The material prepared by this invention effectively inhibits skeleton dealuminization under high temperature and water vapor due to the strong anchoring effect of skeletal phosphorus on neighboring aluminum atoms. After harsh hydrothermal treatment at 800℃, the crystallinity retention rate is >85%, which is significantly better than conventional and most modified ZSM-5 zeolites. This means that the catalyst has an ultra-long structural life in industrial devices that require frequent regeneration (such as catalytic cracking), and has achieved excellent "hydrothermal stability", thus achieving a performance breakthrough.

[0032] (4) The material prepared by this invention has a multi-level pore structure that accelerates the diffusion and release of macromolecular intermediates (such as carbon deposit precursors), thus physically inhibiting carbon deposition. Simultaneously, the introduction of phosphorus finely modulates the strength and distribution of acid centers. In olefin catalytic cracking and methanol-to-olefins (MTO) reactions, this unique synergistic effect of "unobstructed structure + modified acidity" manifests as: high yield of target products, significantly improving the overall yield of low-carbon olefins (diolefins) such as ethylene and propylene; a slow carbon deposition rate, significantly reducing the catalyst activity decay rate and significantly extending the operating cycle; and the optimized pore structure combined with acidity, which is beneficial to the formation of target products.

[0033] (5) This invention directly uses inexpensive inorganic phosphates as the phosphorus source, and simultaneously completes phosphorus doping and hierarchical pore construction through a one-step hydrothermal method. This completely avoids the pore blockage problem of the traditional "post-impregnation method" and the high cost and safety risks of the "organic phosphorus source method", opening up a green and efficient new synthetic route for catalyst preparation. Furthermore, it achieves effective control over mesopore size, phosphorus doping morphology and content, and the product has good reproducibility, laying a solid foundation for industrial-scale production.

[0034] In summary, this invention, through an innovative one-step hydrothermal synthesis method, simultaneously achieves the framework-level coordination doping of phosphorus and the precise construction of micro-meso-multilevel pores, successfully overcoming the long-standing contradiction between insufficient hydrothermal stability of multilevel porous zeolites and pore blockage caused by phosphorus modification. The prepared zeolite possesses excellent physical structure, intrinsic chemical stability, and outstanding catalytic performance, providing an ideal material solution for developing a new generation of long-life, high-efficiency petrochemical catalysts (especially for processes such as olefin cracking and MTO), and has significant scientific value and broad industrial application prospects. Attached Figure Description

[0035] Figure 1 The images are XRD patterns of the samples prepared in Examples 1-3 and Comparative Examples 1-2 of this invention; wherein, a is the XRD pattern of Examples 1-3, and b is the XRD pattern of Comparative Examples 1 and 2.

[0036] Figure 2 The images show isotherms and pore size distribution diagrams of zeolites prepared in Examples 1-3 of this invention; wherein, a is an adsorption isotherm diagram of zeolites prepared in Examples 1-3, and b is a pore size distribution diagram of zeolites prepared in Examples 1-3.

[0037] Figure 3 This is a comparison diagram of the pore size distribution of Comparative Examples 1 and 2.

[0038] Figure 4 This refers to the scanning electron microscope and EDS mapping of Embodiment 2 of the present invention.

[0039] Figure 5The diagram shows the structural characterization of the zeolites prepared in Example 2 and Comparative Example 1 of this invention; where a is the Al NMR of the zeolite prepared in Example 2 and Comparative Example 1 of this invention. 27 Al NMR comparison diagram, b is the NMR of zeolite P prepared in Example 2 of this invention. 31 PMAS NMR image.

[0040] Figure 6 The crystallinity changes of zeolites prepared in Examples 1-3 and Comparative Examples 1-2 of this invention before and after hydrothermal treatment are shown.

[0041] Figure 7 The amount of coke produced by the zeolite preparations after 8 hours of reaction in Example 2 and Comparative Example 2 of this invention is the amount of coke produced by the calciner. Detailed Implementation

[0042] The accompanying drawings are for illustrative purposes only; in order to enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples, but they should not be construed as limiting the present patent.

[0043] Unless otherwise specified, the test methods or experimental methods described in the following examples are conventional methods or obtained from conventional commercial sources.

[0044] Example 1: A method for preparing a phosphorus-doped hierarchical porous ZSM-5 molecular sieve, comprising:

[0045] Weigh 0.58g of aluminum sulfate octadechydrate, 0.10g of ammonium dihydrogen phosphate, and 2.5g of phosphoric acid (98% by mass) and mix with 40g of deionized water. Stir until the solids are completely dissolved to obtain a clear solution. Add 25g of water glass (with a mass fraction of 30% SiO2 and 9% Na2O) and stir to form a gel (pH 9). Add 2g of dodecyltrimethylammonium chloride to the gel and stir for 1 hour. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization treatment at 150℃ for 48 hours. After crystallization, wash the obtained solid product with water and dry it at 100℃. Place the dried solid product in a muffle furnace and calcine at 550℃ for 4 hours to obtain phosphorus-doped hierarchical porous PHZ-70-0.5 zeolite molecular sieve.

[0046] Example 2, a method for preparing a phosphorus-doped hierarchical porous ZSM-5 molecular sieve, comprising:

[0047] Weigh 0.58g of aluminum sulfate octadechydrate, 0.20g of ammonium dihydrogen phosphate, and 2.5g of phosphoric acid (98% by mass) and mix with 40g of deionized water. Stir until the solids are completely dissolved to obtain a clear solution. Add 25g of water glass (with a mass fraction of 30% SiO2 and 9% Na2O) and stir to form a gel (pH 9). Add 2g of dodecyltrimethylammonium chloride to the gel and stir for 1 hour. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization treatment at 150℃ for 48 hours. After crystallization, wash the obtained solid product with water and dry it at 100℃. Place the dried solid product in a muffle furnace and calcine at 550℃ for 4 hours to obtain phosphorus-doped hierarchical porous PHZ-70-1 zeolite molecular sieve.

[0048] Example 3, a method for preparing a phosphorus-doped hierarchical porous ZSM-5 molecular sieve, comprising:

[0049] Weigh 0.58g of aluminum sulfate octadechydrate, 0.31g of ammonium dihydrogen phosphate, and 2.3g of phosphoric acid (98% by mass) and mix with 40g of deionized water. Stir until the solids are completely dissolved to obtain a clear solution. Add 25g of water glass (with a mass fraction of 30% SiO2 and 9% Na2O) and stir to form a gel (pH 9). Add 2.2g of dodecyltrimethylammonium chloride to the gel and stir for 1 hour. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization treatment at 150℃ for 48 hours. After crystallization, wash the obtained solid product with water and dry it at 100℃. Place the dried solid product in a muffle furnace and calcine at 550℃ for 4 hours to obtain phosphorus-doped hierarchical porous PHZ-70-1.5 zeolite molecular sieve.

[0050] Example 4, a method for preparing a phosphorus-doped hierarchical porous ZSM-5 molecular sieve, comprising:

[0051] Weigh 1.16g of aluminum sulfate octadechydrate, 0.21g of ammonium dihydrogen phosphate, and 1.8g of phosphoric acid (98% by mass) and mix with 40g of deionized water. Stir until the solids are completely dissolved to obtain a clear solution. Add 25g of water glass (with a mass fraction of 30% SiO2 and 9% Na2O) and stir to form a gel (pH 9). Add 3g of octadecyltrimethylammonium bromide to the gel and stir for 1 hour. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization treatment at 150℃ for 48 hours. After crystallization, wash the obtained solid product with water and dry it at 100℃. Place the dried solid product in a muffle furnace and calcine at 550℃ for 4 hours to obtain phosphorus-doped hierarchical porous PHZ-35-1 zeolite molecular sieve.

[0052] Example 5, a method for preparing a phosphorus-doped hierarchical porous ZSM-5 molecular sieve, comprising:

[0053] Weigh 0.14g of aluminum sulfate octadechydrate, 0.21g of ammonium dihydrogen phosphate, and 4g of sulfuric acid (98% by mass) and mix with 40g of deionized water. Stir until the solid is completely dissolved to obtain a clear solution. Add 25g of water glass (with a mass fraction of 30% SiO2 and 9% Na2O) and stir to form a gel (pH 8). Add 2.8g of octadecyltrimethylammonium bromide to the gel and stir for 1 hour. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization treatment at 150℃ for 48 hours. After crystallization, wash the obtained solid product with water and dry it at 100℃. Place the dried solid product in a muffle furnace and calcine at 550℃ for 4 hours to obtain phosphorus-doped hierarchical porous PHZ-300-1 zeolite molecular sieve.

[0054] Example 6, a method for preparing a phosphorus-doped hierarchical porous ZSM-5 molecular sieve, comprising:

[0055] Weigh 0.27g sodium aluminate, 0.47g disodium hydrogen phosphate, 2g sulfuric acid (98% by mass), and 15g deionized water, mix and stir until completely dissolved. Dissolve 0.8g sodium hydroxide in 10g water and stir until completely dissolved to form a clear liquid. Add the sodium hydroxide solution dropwise to the mixed solution and stir, then add 30g silica sol (40% SiO2 by mass) to form a gel. Add 2.5g hexadecyltrimethylammonium bromide to the gel and stir for 1 hour. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization at 140℃ for 60 hours. After crystallization, wash the resulting solid product with water and dry at 100℃. Place the dried solid product in a muffle furnace and calcine at 550℃ for 6 hours to obtain phosphorus-doped hierarchical porous PHZ-60-1 zeolite molecular sieve.

[0056] Example 7, a method for preparing a phosphorus-doped hierarchical porous ZSM-5 molecular sieve, comprising:

[0057] Weigh 0.11g sodium aluminate, 0.19g disodium hydrogen phosphate, 2g sulfuric acid (98% by mass), and 15g deionized water, mix and stir until completely dissolved. Dissolve 1.0g sodium hydroxide in 10g water and stir until completely dissolved to form a clear liquid. Add the sodium hydroxide solution dropwise to the mixed solution and stir, then add 30g silica sol (40% by mass) to form a gel. Add 2.5g hexadecyltrimethylammonium bromide to the gel and stir for 1 hour. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization at 140℃ for 60 hours. After crystallization, wash the resulting solid product with water and dry at 100℃. Place the dried solid product in a muffle furnace and calcine at 550℃ for 6 hours to obtain phosphorus-doped hierarchical porous PHZ-150-1 zeolite molecular sieve.

[0058] Example 8, a method for preparing a phosphorus-doped hierarchical porous ZSM-5 molecular sieve, comprising:

[0059] Weigh 0.09g sodium aluminate, 0.23g disodium hydrogen phosphate, 2g sulfuric acid (98% by mass), and 15g deionized water, and mix until completely dissolved. Dissolve 1.0g sodium hydroxide in 64g water and stir until completely dissolved to form a clear liquid. Add the sodium hydroxide solution dropwise to the mixed solution and stir, then add 12g of silica and mix thoroughly. Add 2.5g hexadecyltrimethylammonium bromide to the mixture and stir for 1 hour. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization at 140℃ for 60 hours. After crystallization, wash the resulting solid product with water and dry at 100℃. Place the dried solid product in a muffle furnace and calcine at 550℃ for 6 hours to obtain phosphorus-doped hierarchical porous PHZ-180-1.5 zeolite molecular sieve.

[0060] Comparative Example 1: Preparation of hierarchical porous ZSM-5 catalyst.

[0061] Weigh 0.58g of aluminum sulfate octahydrate and 2.5g of concentrated sulfuric acid (98% by mass) and mix with 40g of deionized water until the solid is completely dissolved to obtain a clear solution. Add 25g of water glass (with a mass fraction of 30% SiO2 and 9% Na2O) and stir to form a gel (pH 9). Add 2.5g of cetyltrimethylammonium bromide to the gel and stir for 1h. Transfer the stirred gel to a polytetrafluoroethylene-lined reactor for crystallization treatment at a temperature of 150℃ for 48h. After crystallization, wash the obtained solid product with water and dry it at 100℃. Place the dried solid product in a muffle furnace and calcine at 550℃ for 4h to obtain hierarchical porous ZSM-5(70) zeolite molecular sieve, where 70 is the silicon-aluminum molar ratio.

[0062] Comparative Example 2: Preparation of supported P / hierarchical porous ZSM-5 catalyst.

[0063] The preparation steps of hierarchical ZSM-5 are described in Comparative Example 1. 1 g of the prepared hierarchical ZSM-5 molecular sieve was placed in a flask. 0.03 g of ammonium dihydrogen phosphate was weighed and dissolved in 2 g of deionized water. The ammonium dihydrogen phosphate solution was uniformly added dropwise onto the hierarchical ZSM-5 molecular sieve in three stages until no impregnation solution remained. The sieve was then dried in an oven at 100℃ for 5 h. After drying, it was removed and placed in a muffle furnace and calcined at 550℃ for 3 h to prepare P / ZSM-5 zeolite molecular sieve. The P / Al molar ratio of the impregnated sample was 1.

[0064] Comparative Example 3: Preparation of microporous ZSM-5 molecular sieve.

[0065] 5.85 g of tetrapropylammonium hydroxide (TPAOH mass fraction of 25%) and 0.70 g of NaOH were dissolved in 12.00 g of deionized water and stirred until the solution was clear. Then, 0.03 g of sodium aluminate was added and stirred for about 30 min to form a clear solution. 5.00 g of ethyl silicate was added to the clear solution and stirred at room temperature for 2 h. The mixture was loaded into a self-pressurized autoclave and crystallized at 180 °C for 24 h. After crystallization, the obtained solid product was washed and dried. The dried solid was calcined at 550 °C for 6 h to obtain conventional microporous ZSM-5 (60) zeolite molecular sieve raw powder.

[0066] Comparative Example 4: Preparation of supported P / ZSM-5 catalyst.

[0067] The preparation steps for microporous ZSM-5 are described in Comparative Example 3. 1 g of the prepared hierarchical ZSM-5 molecular sieve was placed in a gai-shaped flask. 0.03 g of ammonium dihydrogen phosphate was weighed and dissolved in 2 g of deionized water. The ammonium dihydrogen phosphate solution was uniformly added dropwise onto the hierarchical ZSM-5 molecular sieve in three stages until no impregnation solution remained. The sieve was then dried in a 100℃ oven for 5 hours. After drying, it was removed and placed in a muffle furnace. Calcination was performed at 550℃ for 3 hours to prepare P / ZSM-5 zeolite molecular sieve. The P / Al molar ratio of the impregnated sample was 1.

[0068] Test Example 1:

[0069] XRD pattern analysis of the ZSM-5 zeolite prepared in Examples 1-3 is shown in the figure. Figure 1 As shown in (a), both exhibit characteristic peaks of the MFI type structure, indicating good crystallinity. Figure 1 (b) shows the XRD patterns of the samples prepared in Comparative Example 1 and Comparative Example 2. The results show that after the phosphorus impregnation modification, the crystallinity of Comparative Example 2 was slightly reduced compared with that of Comparative Example 1.

[0070] Test Example 2:

[0071] The mesopore distribution of the molecular sieve products prepared in Examples 1-3 and Comparative Examples 1-2 was tested using N2 adsorption-desorption isotherms. Figure 2 As shown in (a), the zeolite isotherms prepared in Examples 1-3 have hysteresis loops, indicating the presence of a mesoporous structure. Figure 2 (b) shows the pore size distribution of the zeolites prepared in Examples 1-3. The results show that all samples have a three-dimensional pore structure of micro-meso-macro, with mesopores adjustable in size from 2-4 nm and macropores concentrated in size from 30-50 nm. The pore size distributions of Comparative Examples 1 and 2 are compared. Figure 3 A comprehensive analysis of the data in Table 1 and Table 2 shows that the impregnation method for phosphorus modification causes a dual effect of micropore blockage and mesopore loss. Figure 3The comparative example 2 shows a significant decrease in the micropore size distribution signal at locations smaller than 1 nm, indicating that phosphorus species are deposited at the micropore openings; however, the micropore volume (V) in Table 1... micro The concentration remained constant at 0.08 cm³ / g, indicating that the internal space of the micropores was not filled, but rather formed a "bottleneck" blockage. This prevents reactants from entering the micropores and contacting the active sites through the blocked pore openings. Table 1 shows the mesoporous pore volume (V) of Comparative Example 2. meso The phosphorus content decreased from 0.21 to 0.17 cm³ / g, and the external specific surface area (Sext) decreased from 235 to 167 m² / g, indicating that phosphorus species simultaneously caused the collapse or blockage of the mesoporous structure. This combined effect of micropore blockage and mesopore loss means that although the impregnation-modified samples retain micropore volume, their actual mass transfer capacity and catalytic activity are reduced. Specific pore distribution data for the molecular sieves are shown in Table 1; the embodiments of this invention all exhibit larger specific surface areas and pore volumes.

[0072] Table 1. Comparison of pore properties of zeolites prepared in Examples 1-3 and Comparative Examples 1-2

[0073]

[0074] Test Example 3:

[0075] This experimental example demonstrates the scanning electron microscopy analysis of the molecular sieve prepared in Example 2, as shown in the attached figure. Figure 4 The scanning electron microscope and mapping shown in the figure indicate that the sample morphology is a stacked spherical morphology, and P is highly dispersed within the molecular sieve.

[0076] Test Example 4:

[0077] The zeolite prepared in Example 2 was subjected to NMR analysis for Al and P. Figure 5 (a) in the text is the sample from Example 2. 27 AlMAS NMR results, compared with Comparative Example 1 27 A new signal appeared in Al MAS NMR at a chemical shift of 40.1 ppm, which is the signal of twisted four-coordinated aluminum formed by the combination of framework aluminum and phosphorus. Figure 5 (b) in the example is Example 2. 31 The P MAS NMR results, with a P signal at −24.1 ppm, further confirm the formation of a four-coordinated P group. IV –O–Al IV The framework structure indicates that phosphorus enters the molecular sieve framework.

[0078] Test Example 5:

[0079] The crystallinity comparison charts of the zeolites prepared in Examples 1-3 and Comparative Examples 1-2 after hydrothermal treatment at 800℃ (hydrothermal treatment refers to placing the samples in a reactor and passing 100% steam at high temperature for a certain period of time) are attached. Figure 6 As shown in the figure, the crystallinity of the zeolites prepared in Examples 1-3 after aging was above 85% compared to that before hydrothermal treatment, indicating good hydrothermal stability. The zeolite prepared in Comparative Example 1, without phosphorus modification, exhibited poor hydrothermal stability. Comparative Example 2 shows that the hydrothermal stability of the sample after post-impregnation modification was improved, but the relative decrease in crystallinity was still greater than that in Examples 1-3. This demonstrates that the phosphorus-doped hierarchical porous molecular sieve prepared by the method of this invention has better hydrothermal stability than the post-impregnation method.

[0080] Test Example 6:

[0081] The acidity of the molecular sieve products prepared in Examples 1-3, Comparative Example 1, and Comparative Example 2 was tested using NH3-TPD and infrared pyridine adsorption to determine the acid content and type. Specific sample acidity data are shown in Table 2. Compared with Comparative Example 1, the total acid content of Examples 1-3 did not change much before and after the introduction of phosphorus. However, Examples 1-3 showed more B acid sites, while the acid content of Comparative Example 2 was significantly lower than that of Comparative Example 1. This indicates that the acid content was lower in the post-impregnation method because phosphorus covered some of the acid sites.

[0082] Table 2 Comparison of acid properties of zeolites prepared in Examples 1-3 and Comparative Examples 1-2

[0083]

[0084] Test Example 7:

[0085] The amount of coke produced was determined in the catalytic reaction residues of the zeolite molecular sieves prepared in Example 2 and Comparative Example 2 after 8 hours. The reaction process was as follows: the obtained zeolite molecular sieves were pressed into tablets and ground to 40-80 mesh. 1.0 g of sample was weighed and loaded into a fixed-bed reactor for catalytic cracking reaction evaluation, using 1-hexene as raw material, at a reaction temperature of 550 °C and a space velocity of 6 h⁻¹. -1 The results of the coking amount of the preservative are as follows: Figure 7 As shown in the results, compared with impregnation with P, the phosphorus-doped hierarchical porous molecular sieve prepared by the present invention has a lower coke production, indicating that the phosphorus homogeneous part of the sample prepared by the present invention does not experience pore blockage, inhibiting secondary reactions and reducing coke formation.

[0086] Test Example 8:

[0087] The catalytic performance of the zeolite molecular sieves prepared in Examples 1-3 and Comparative Examples 1, 2 and 4 was tested after aging at 800 degrees Celsius for 17 hours.

[0088] The zeolite molecular sieve tablets obtained from Examples 1-3 and Comparative Examples 1, 2, and 4 were ground to 40-80 mesh. 1.0 g of sample was weighed and loaded into a fixed-bed reactor for catalytic cracking reaction evaluation, using 1-hexene as the raw material, at a reaction temperature of 550°C and a space velocity of 6 h⁻¹. -1 The evaluation results are shown in Table 3.

[0089] Table 3 Comparison of evaluation data of zeolite catalytic cracking prepared in Examples 1-3 and Comparative Examples 1, 2, and 4

[0090]

[0091] The catalyst lifespan in Table 3 refers to the time during which the 1-hexene conversion rate decreases by no more than 3 percentage points.

[0092] The catalytic cracking results of Examples 1-3 are shown in Table 3. Compared with Comparative Example 1 (unmodified hierarchical porous structure), the phosphorus-doped hierarchical porous ZSM-5 prepared in this application maintained a high conversion rate (>95%) after hydrothermal treatment, while the conversion rate of Comparative Example 1 decreased to 71.7%, indicating that phosphorus doping inhibited framework dealumination and maintained excellent catalytic activity after harsh hydrothermal treatment. Compared with Comparative Example 2 (post-phosphorus impregnation modification), the propylene yield of Example 2 increased by 16 percentage points (66.3% vs. 50.2%), and the lifetime was extended by 2 times (265 h vs. 126 h), proving that in-situ doping avoids micropore blockage and improves catalytic stability. Comparative Example 3 (micropore post-phosphorus impregnation) had a lifetime of only 60 h due to the lack of mesoporous and macroporous channels, indicating that mesopores and phosphorus doping need to work synergistically to improve catalytic stability.

[0093] Test Example 9: Methanol to Olefins (MTO) reaction.

[0094] The phosphorus-doped hierarchical porous ZSM-5 molecular sieve prepared in Example 2 was granulated into tablets (40-80 mesh) and packed into a fixed-bed reactor with a catalyst loading of 1 g. Reaction conditions: temperature 480 °C, methanol weight hourly space velocity (WHSV) 6.0 h⁻¹. -1 At atmospheric pressure. The catalyst was treated with steam at 800℃ for 17 h before the reaction, and the evaluation results are shown in Table 4.

[0095] Table 4 Comparison of product distribution in methanol-to-olefins (MTO) reaction

[0096]

[0097] Results: The zeolite prepared in Example 2 of this invention, when used as a catalyst, maintained a methanol conversion rate of >99%, a total yield of ethylene + propylene (diene) of 72.1%, a propylene / ethylene mass ratio of 3.7, and a catalyst lifetime (time with conversion >95%) of 35 h. In contrast, the sample prepared in Comparative Example 2 (post-impregnation method), when used as a catalyst, had a lifetime of only 16 h and a diene yield of 68.7% under the same conditions.

[0098] In summary, the zeolite catalyst prepared by this invention provides abundant mass transfer channels and greater accessibility to surface active sites for the reaction, resulting in high yield and good product reproducibility. It offers an ideal material solution for developing a new generation of long-life, high-efficiency petrochemical catalysts.

[0099] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A phosphorus-doped hierarchical porous ZSM-5 zeolite, characterized in that, The zeolite has a specific surface area of ​​402–440 m² / g, contains 2–4 nm intracrystalline mesopores and 30–50 nm intercrystalline macropores, and phosphorus and aluminum exist in the framework in a stable four-coordinated form. The acid content B / L ratio is 6.7–12.

3. The method for preparing the zeolite includes the following steps: (1) Mix aluminum source, phosphorus source and silicon source in water and stir, adjust pH to 9 to form a gel; add long carbon chain quaternary ammonium salt to the gel and stir to obtain a homogeneous mixture; wherein, the molar ratio of silicon source, phosphorus source and aluminum source is 70:0.82:1; the molar ratio of silicon element to long carbon chain quaternary ammonium salt molecule is 100:2.5~5; the molar ratio of silicon element to water molecule is 1:18~25; (2) The mixture is crystallized, and the crystallized product is washed, dried and calcined to obtain phosphorus-doped hierarchical porous ZSM-5 zeolite; wherein the hydrothermal reaction temperature during crystallization is 150℃, the calcination temperature is 550~650℃, and the calcination time is 4h~6h. The aluminum source is aluminum sulfate octadecahydrate or sodium aluminate; The silicon source is silica sol or water glass; The phosphorus source is one or a combination of two of ammonium dihydrogen phosphate and disodium hydrogen phosphate; The long-chain quaternary ammonium salt is an alkyl trimethyl quaternary ammonium salt, wherein the alkyl group is a straight-chain alkyl group with 12-18 carbons.

2. The phosphorus-doped hierarchical porous ZSM-5 zeolite according to claim 1, characterized in that, The long-chain quaternary ammonium salt is any one or a combination of two of dodecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

3. The phosphorus-doped hierarchical porous ZSM-5 zeolite according to claim 1, characterized in that, The silica sol used has a mass fraction of 40%; or, the water glass used has a mass fraction of 30% SiO2 and a mass fraction of 9% Na2O.

4. The phosphorus-doped hierarchical porous ZSM-5 zeolite according to claim 1, characterized in that, In step (1), the pH value is adjusted using an alkaline source and / or an acid source; the alkaline source is sodium hydroxide or potassium hydroxide solution, and the acid source is any one or a combination of inorganic acids such as phosphoric acid, concentrated sulfuric acid, and nitric acid.

5. The phosphorus-doped hierarchical porous ZSM-5 zeolite according to claim 1, characterized in that, In step (2), the crystallization time is 24h to 72h.

6. The phosphorus-doped hierarchical porous ZSM-5 zeolite according to claim 5, characterized in that, After the hydrothermal reaction, the precipitated crystals are washed, dried, and then calcined; the drying temperature is controlled at 100-120℃.

7. The application of a phosphorus-doped hierarchical porous ZSM-5 zeolite as described in any one of claims 1-6 in olefin catalytic cracking and MTO reaction, characterized in that, The phosphorus-doped hierarchical porous ZSM-5 zeolite has a lifetime of 265 hours in olefin catalytic cracking and 35 hours in MTO reaction.

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