Modified ZSM-5 molecular sieve, preparation method thereof and catalyst

Abstract

The invention provides a modified ZSM-5 molecular sieve, a preparation method thereof and a catalyst. The preparation method of the modified ZSM-5 molecular sieve comprises the following steps: carrying out first roasting and grinding on ZSM-5 molecular sieve seed crystals, mixing the ground ZSM-5 molecular sieve seed crystals with an alkali source and a silicon source, and carrying out heating treatment; mixing the heated product with an aluminum source to obtain a raw material solution, crystallizing, mixing the ZSM-5 molecular sieve obtained by crystallization with an acid solution and a zinc source, and carrying out zinc ion exchange; and mixing the ZSM-5 molecular sieve subjected to zinc ion exchange with a phosphorus source, and carrying out phosphorus modification, filtration, drying and secondary roasting to obtain the modified ZSM-5 molecular sieve. The invention also provides the modified ZSM-5 molecular sieve obtained by the preparation method and a catalyst prepared from the molecular sieve. The modified ZSM-5 molecular sieve has small crystal grains, has high catalytic activity as a catalyst, and can produce more propylene.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials technology, and in particular to a modified ZSM-5 molecular sieve, its preparation method, and its catalyst. Background Technology

[0002] Propylene, as an important chemical feedstock, accounts for about one-third of the production from catalytic cracking units. Therefore, increasing propylene production has become a key objective in adjusting the product distribution of catalytic cracking units. ZSM-5 molecular sieves, due to their unique pore structure, abundant acidic centers, and good thermal and hydrothermal stability, have excellent applications in catalytic cracking for high propylene production. With the increasing demand for propylene from refineries, the reactivity of ZSM-5, a key active component for increasing propylene production, needs further improvement.

[0003] Modifying ZSM-5 molecular sieves is one way to improve their pyrolysis performance and increase propylene production. Reducing the crystal size of ZSM-5 molecular sieves can further reduce side reactions and improve reaction performance. Specifically, in catalytic reactions, reducing the particle size of ZSM-5 molecular sieves can improve the accessibility of reactants to active sites and promote the rapid diffusion of products, which is beneficial to improving reaction conversion and product selectivity. Therefore, the preparation of small-crystal ZSM-5 molecular sieves is a hot research topic in this field.

[0004] CN20151080574.4 discloses a method for preparing narrow-distribution, small-grained ZSM-5 molecular sieves. In this method, a solution obtained by mixing a template agent, an aluminum source, and a silicon source is first reacted in an ultrasonic water bath for 0.5-2 hours, then reacted in a microwave environment for 0.5-2 hours, and the product is then subjected to hydrothermal crystallization. This yields a narrow-distribution, small-grained ZSM-5 molecular sieve.

[0005] CN202211435030.6 discloses a method for preparing single-crystal nano ZSM-5 molecular sieves rich in intercrystalline and intracrystalline mesopores and their applications. The invention involves sequentially mixing a template agent, water, alkali metal hydroxide, aluminum source and silicon source to obtain a gel, and then performing two-stage crystallization on the gel to obtain ZSM-5 molecular sieves. The ZSM-5 molecular sieves obtained by this method can have their crystal size reduced to the nanometer size.

[0006] The preparation process of existing small-crystal ZSM-5 molecular sieves still uses a large amount of template agents. The large use of template agents not only leads to a significant increase in synthesis costs, but also causes environmental problems due to the waste gas and waste liquid emissions resulting from the introduction of template agents.

[0007] In the preparation of small-crystal ZSM-5 molecular sieves, reducing the introduction of template agents during synthesis is still possible, and using seed-directing agents or pre-crystallization solutions is an effective method. Although using seed-directing agents or pre-crystallization solutions can yield small-crystal ZSM-5 molecular sieves with lower template agent addition amounts, the preparation of seed-directing agents or pre-crystallization solutions still requires the introduction of template agents, which still brings cost and environmental issues.

[0008] Therefore, it is necessary to overcome the technical problem that existing small-crystal ZSM-5 molecular sieves usually require the introduction of template agents, develop a green method for preparing small-crystal ZSM-5 molecular sieves, and optimize their propylene-producing performance.

[0009] Metal and phosphorus modification of ZSM-5 molecular sieves is also a way to improve catalytic performance and increase propylene production. However, existing modification methods are usually impregnation methods. When modifying with more than two elements, stepwise modification can be carried out, in which the precursor of one element is impregnated and then dried and calcined, and then the precursor of another element is impregnated. However, stepwise modification is a long process and requires more than two drying and calcination cycles, resulting in high energy consumption. If the modification is carried out simultaneously, the precursors of different elements are prone to interaction, which affects the reactivity of the modified molecular sieve. For example, in CN101440302A and CN103816936A, zinc and phosphorus are added in one step, requiring only one calcination. However, during the one-step addition process, the zinc-containing solution and the phosphorus-containing solution are prone to interaction, affecting the reactivity of the modified molecular sieve.

[0010] In summary, there is a need to develop a green synthesis method for small-crystal ZSM-5 molecular sieves, simplify the modification process, and optimize the propylene-producing performance of ZSM-5 molecular sieves. Summary of the Invention

[0011] To address the aforementioned technical problems, the present invention aims to provide a modified ZSM-5 molecular sieve, its preparation method, and a catalyst. This preparation method eliminates the need for template agents and organic additives, simplifies the modification steps, and yields a modified ZSM-5 molecular sieve with small crystallites. As a catalyst, it exhibits high catalytic activity and can produce a large yield of propylene.

[0012] To achieve the above objectives, the present invention provides a method for preparing modified ZSM-5 molecular sieves, the method comprising:

[0013] The ZSM-5 molecular sieve seed crystals were first calcined and ground. The ground ZSM-5 molecular sieve seed crystals were then mixed with an alkali source and a silicon source and subjected to a heating treatment to obtain the heated product.

[0014] The product of the heating treatment was mixed with an aluminum source to obtain a raw material solution, which was then crystallized to obtain ZSM-5 molecular sieve.

[0015] ZSM-5 molecular sieve is mixed with an acidic solution and a zinc source, and stirred to perform zinc ion exchange. Then, the zinc-ion-exchanged ZSM-5 molecular sieve is mixed with a phosphorus source, stirred to perform phosphorus modification, filtered, dried, and then calcined a second time to obtain the modified ZSM-5 molecular sieve.

[0016] In obtaining ZSM-5 molecular sieves, this invention involves high-temperature calcination (first calcination), grinding, and alkaline treatment of ZSM-5 molecular sieve seed crystals to obtain small-grained ZSM-5 molecular sieve seed crystals and primary and secondary structural units. Introducing a silicon source during alkaline treatment facilitates the interaction between the silicon source and the small-grained ZSM-5 molecular sieve seed crystals and primary and secondary structural units, thereby promoting the growth of the synthesized silica-alumina gel around the small-grained seed crystals and primary and secondary structural units. This allows for the direct synthesis of small-grained ZSM-5 molecular sieves without template agents or organic additives. Subsequently, under acidic conditions, the small-grained ZSM-5 molecular sieves are modified with zinc and phosphorus composites to prepare a modified ZSM-5 molecular sieve material with high propylene production properties.

[0017] In the above preparation method, the ZSM-5 molecular sieve seed crystals can be industrial ZSM-5 molecular sieves. This invention does not impose special restrictions on the silicon-to-aluminum ratio of the ZSM-5 molecular sieve seed crystals; both high-silicon and low-silicon ZSM-5 molecular sieves are suitable for this invention and have good seed crystal guiding effects, allowing ZSM-5 molecular sieves to be obtained through crystallization. From a cost-saving perspective, in specific embodiments, low-silicon ZSM-5 molecular sieves can be used as ZSM-5 molecular sieve seed crystals.

[0018] In the above preparation method, the first calcination can reduce the crystallinity of the ZSM-5 molecular sieve seed crystals and destroy the molecular sieve, so as to facilitate the separation between molecular sieve grains during subsequent grinding. The temperature of the first calcination can be controlled between 900℃ and 1100℃, for example, specific values ​​such as 900℃, 950℃, 1000℃, 1050℃, and 1100℃, and a range with any two of the above specific values ​​as endpoints; the time of the first calcination is between 1h and 18h, for example, specific values ​​such as 1h, 2h, 4h, 5h, 7h, 8h, 10h, 12h, 14h, 16h, and 18h, and a range with any two of the above specific values ​​as endpoints.

[0019] In the above preparation method, the grinding speed is 1000r / min-3000r / min, for example, specific values ​​such as 1000r / min, 1500r / min, 2000r / min, 2500r / min, 3000r / min, etc., and a range with any two of the above specific values ​​as endpoints; the grinding time is 1h-10h, for example, specific values ​​such as 1h, 2h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc., and a range with any two of the above specific values ​​as endpoints.

[0020] In the above preparation method, the median particle size of the milled ZSM-5 molecular sieve is less than or equal to 1 μm, specifically 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, etc., and a range with any two of the above specific values ​​as endpoints.

[0021] In some specific implementations, the grinding can be done by ball milling, performed in a ball mill.

[0022] In the above preparation method, the mass of the ground ZSM-5 molecular sieve is based on dry weight, the mass of the silicon source is based on the mass of SiO2, and the mass ratio of the ground ZSM-5 molecular sieve to the silicon source is 0.02-0.15:1.

[0023] In the above preparation method, the temperature of the heating treatment is 50℃-100℃, for example, specific values ​​such as 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, etc., and a range with any two of the above specific values ​​as endpoints; the time of the heating treatment is 1h-10h, for example, specific values ​​such as 1h, 2h, 2.5h, 3h, 4h, 4.5h, 5h, 6h, 7h, 8h, 9h, 10h, etc., and a range with any two of the above specific values ​​as endpoints. In some specific embodiments, the heating treatment can be carried out under stirring conditions.

[0024] In the above preparation method, the composition of the raw material solution satisfies the following molar ratio: m(Na2O):m(Al2O3):m(SiO2):m(H2O)=0.05-0.2:0.02-0.05:1:14-30. m represents molar.

[0025] According to a specific embodiment of the present invention, in molar parts, when SiO2 is 1 part, Na2O can be 0.05 parts, 0.1 parts, 0.11 parts, 0.12 parts, 0.13 parts, 0.14 parts, 0.15 parts, 0.16 parts, 0.17 parts, 0.18 parts, 0.2 parts, etc., and a range with any two of the above specific values ​​as endpoints; Al2O3 can be 0.02 parts, 0.025 parts, 0.03 parts, 0.035 parts, 0.04 parts, 0.045 parts, 0.05 parts, etc., and a range with any two of the above specific values ​​as endpoints; H2O can be 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, 25 parts, 30 parts, etc., and a range with any two of the above specific values ​​as endpoints.

[0026] The above synthesis ratios are general expressions for molecular sieve synthesis formulations. It is understood that the sodium oxide in these expressions refers not only to the sodium oxide corresponding to the alkali source, but also to other factors affecting sodium oxide or alkalinity. For example, when using alkaline sodium aluminate as the aluminum source, the sodium oxide contained in the sodium aluminate must also be factored in; if aluminum sulfate is used as the aluminum source, since aluminum sulfate is acidic, 1 mol of sulfate ions can neutralize 1 mol of sodium oxide, and the corresponding sodium oxide needs to be reduced in the formulation. Therefore, in the above expressions, sodium oxide indicates the sodium ions and alkalinity in the solution. Those skilled in the art will understand that the applicable alkali source for this expression is not limited to sodium hydroxide.

[0027] In the above preparation method, the crystallization temperature is 140℃-190℃, for example, specific values ​​such as 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, etc., and a range with any two of the above specific values ​​as endpoints; the crystallization time is 6h-48h, for example, specific values ​​such as 6h, 8h, 10h, 12h, 24h, 36h, 48h, etc., and a range with any two of the above specific values ​​as endpoints.

[0028] In the above preparation method, the alkali source added to the ZSM-5 molecular sieve seed crystals after grinding can promote the dissolution of molecular sieves and obtain small-grained molecular sieve seed crystals and primary and secondary structural units of ZSM-5 molecular sieves. On the other hand, it can also serve as the alkali source required in the subsequent synthesis of ZSM-5 molecular sieves.

[0029] In the above preparation method, the alkali source includes an inorganic alkaline compound. Specifically, the alkali source may include one or a combination of two or more of sodium hydroxide, ammonia, and water glass.

[0030] In the above preparation method, the silicon source includes one or more of silica sol, water glass, and precipitated silica. The precipitated silica used in this invention refers to precipitated silica, fumed silica, or ultrafine silica gel, etc.

[0031] In the above preparation method, the aluminum source can be a commonly used aluminum source for synthesizing ZSM-5 molecular sieves, specifically including aluminum sulfate and / or sodium aluminate. This invention does not impose any special limitations on the type of aluminum source.

[0032] In the above preparation method, the product of the heating treatment can be in gel form. The product of the heating treatment and the aluminum source are added slowly, and the gel is dispersed by rapid stirring during the mixing process to promote the full hydrolysis and condensation of the aluminum source and the silicon source. The mixing order of the product of the heating treatment and the aluminum source is not specifically limited; it can be that the product of the heating treatment is added to the aluminum source, or the aluminum source is added to the product of the heating treatment.

[0033] In the above preparation method, the crystallization of ZSM-5 molecular sieve has a particle size of 100nm-300nm, such as 100nm, 120nm, 150nm, 200nm, 250nm, 300nm, etc., and a range with any two of the above specific values ​​as endpoints.

[0034] In the above preparation method, the ZSM-5 molecular sieve obtained after crystallization is usually a sodium-type molecular sieve. In some specific embodiments, after crystallization is completed, the crystallized product can be filtered, washed with water, exchanged, and dried to finally obtain the hydrogen-type ZSM-5 molecular sieve.

[0035] In the above preparation method, the present invention does not specifically limit the exchange method. The exchange can be carried out in a way commonly used in the art. It is only necessary to exchange the product obtained after crystallization from sodium molecular sieve to hydrogen molecular sieve. For example, the exchange can be carried out by including the following steps: performing solid-liquid separation and washing on the crystallized product to obtain a solid phase; mixing the solid phase with deionized water and ammonium salt at a mass ratio of 1:(4-10):(0.05-1), or mixing the solid phase with water at a mass ratio of 1:(4-10) and adjusting the pH value to 1.0-4.0; then heating and stirring to perform solid-liquid separation, washing, and drying to obtain the ZSM-5 molecular sieve.

[0036] In the above-mentioned exchange process, the heating and stirring can specifically be heated to 60℃-100℃ and stirred for 0.4h-2h.

[0037] In the above-described exchange process preparation method, the exchange of the present invention is not limited to the type of ammonium salt, but is generally a soluble ammonium salt, such as one or more combinations of ammonium sulfate, ammonium nitrate, and ammonium chloride.

[0038] During the above exchange process, an inorganic acid can be used to adjust the pH value, and the inorganic acid may include hydrochloric acid, etc.

[0039] In the above preparation method, the reactivity of ZSM-5 molecular sieve can be further improved by phosphorus and zinc composite modification. Specifically, phosphorus modification of ZSM-5 molecular sieve can improve its thermal and hydrothermal stability, and optimize its acidity distribution, thereby reducing secondary reactions in catalytic cracking and promoting propylene selectivity. Zinc modification of ZSM-5 molecular sieve allows zinc to play a certain dehydrogenation role as a modifying element, promoting alkane conversion in catalytic cracking. In the bifunctional modification process of this invention, the dispersion of zinc in ZSM-5 and the interaction between phosphorus and ZSM-5 are important factors in improving product performance.

[0040] The preparation method provided by this invention involves stepwise zinc and phosphorus modification, and is carried out under acidic conditions. This eliminates the need for calcination after zinc modification, allowing direct phosphorus modification and reducing modification steps, thus simplifying the process. Zinc exchange of ZSM-5 molecular sieve under acidic conditions removes some of the framework aluminum and fragmented aluminum, promoting the reaction between zinc and ZSM-5 molecular sieve and further optimizing the pore structure, acidity distribution, and zinc dispersion within the ZSM-5 molecular sieve pores. Then, phosphorus modification is performed on the ZSM-5 molecular sieve; by controlling the reaction sequence of zinc and phosphorus modification, zinc phosphate precipitation can be avoided. The prepared modified ZSM-5 molecular sieve exhibits better propylene production performance in catalytic cracking and pyrolysis reactions.

[0041] In the above preparation method, the mass ratio of the acidic solution to the ZSM-5 molecular sieve (the ZSM-5 molecular sieve obtained in step 2) is 2-10:1. The acidic solution contains acidic substances, and the concentration of the acidic substances in the acidic solution is 0.1 mol / L-4 mol / L.

[0042] In some specific embodiments, the molar ratio of the acidic substance in the acidic solution to the mass of the ZSM-5 molecular sieve (the ZSM-5 molecular sieve obtained in step 2) can be 0.003-0.01 mol: 1 g.

[0043] In the above preparation method, the acidic substances in the acidic solution include organic acids and / or inorganic acids. Accordingly, the acidic solution includes organic acid solutions and / or inorganic acid solutions, such as hydrochloric acid solutions.

[0044] In the above preparation method, the mass of ZSM-5 molecular sieve is on a dry basis, and the mass of zinc source is based on zinc oxide. The mass of the zinc source is 0.1%-2% of the mass of ZSM-5 molecular sieve (ZSM-5 molecular sieve obtained in step 2, unmodified), for example, it can be a specific value such as 0.1%, 0.5%, 0.8%, 0.9%, 1%, 1.5%, 1.6%, 2%, etc., and a range with any two of the above specific values ​​as endpoints.

[0045] In the above preparation method, the zinc source can be a water-soluble zinc salt, specifically including one or more of zinc nitrate, zinc chloride, zinc acetate, and zinc sulfate.

[0046] In the above preparation method, the temperature of zinc ion exchange is 40℃-100℃, for example, it can be a specific value such as 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, or any two of the above specific values ​​as endpoints; the time of zinc ion exchange is 0.3h-3h, for example, it can be a specific value such as 0.3h, 0.5h, 0.8h, 1h, 1.3h, 1.5h, 2h, 2.1h, 2.5h, 2.6h, 3h, or any two of the above specific values ​​as endpoints.

[0047] In the above preparation method, the mass of ZSM-5 molecular sieve is on a dry basis, and the mass of phosphorus source is on a phosphorus pentoxide basis. The mass of the phosphorus source is 2%-8% of the mass of ZSM-5 molecular sieve (ZSM-5 molecular sieve obtained in step 2, unmodified), for example, it can be a specific value such as 2%, 3%, 3.3%, 3.4%, 3.5%, 3.6%, 4%, 4.5%, 5%, 5.5%, 5.6%, 5.7%, 6%, 6.5%, 6.7%, 6.8%, 7%, 7.5%, 8%, etc., and a range with any two of the above specific values ​​as endpoints.

[0048] In the above preparation method, the phosphorus source may include phosphoric acid and / or phosphate, specifically including one or more of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, and ammonium hydrogen phosphate.

[0049] In the above preparation method, the phosphorus modification temperature is 120℃-180℃, for example, specific values ​​such as 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, and any two of the above specific values ​​as endpoints; the phosphorus modification time is 0.2h-3h, for example, specific values ​​such as 0.2h, 0.5h, 0.7h, 1h, 1.3h, 1.6h, 2h, 2.4h, 2.5h, 3h, and any two of the above specific values ​​as endpoints.

[0050] In the above preparation method, the drying temperature of the phosphorus-modified product can be controlled at 100℃-120℃.

[0051] In the above preparation method, the second calcination temperature is 400℃-700℃, for example, specific values ​​such as 400℃, 450℃, 470℃, 500℃, 540℃, 550℃, 600℃, 630℃, 650℃, 670℃, 700℃, etc., and a range with any two of the above specific values ​​as endpoints; the second calcination time is 0.5h-4h, for example, specific values ​​such as 0.5h, 0.7h, 1h, 1.1h, 1.5h, 1.7h, 2h, 2.5h, 3h, 3.4h, 3.5h, 4h, 4.5h, 5h, etc., and a range with any two of the above specific values ​​as endpoints.

[0052] According to a specific embodiment of the present invention, the preparation method of the modified ZSM-5 molecular sieve may specifically include:

[0053] 1. The ZSM-5 molecular sieve seed crystals are first calcined at 900℃-1100℃ for 1h-18h. The calcined product is then ground at a speed of 1000r / min-3000r / min for 1h-10h. The ground ZSM-5 molecular sieve seed crystals are then mixed with an alkali source and a silicon source and heated at 50℃-100℃ for 1h-10h to obtain the heated product.

[0054] The mass ratio of the ground ZSM-5 molecular sieve seed crystals to SiO2 in the silicon source is 0.02-0.15:1.

[0055] 2. The product of the heating treatment is mixed with an aluminum source to obtain a raw material solution, wherein the composition of the raw material solution satisfies the following molar ratio: m(Na2O):m(Al2O3):m(SiO2):m(H2O)=0.05-0.2:0.02-0.05:1:14-30;

[0056] The raw material solution was crystallized at 140-190℃ for 6-48 hours. The crystallized product was filtered, washed with water, exchanged, and dried to obtain hydrogen-form ZSM-5 molecular sieve.

[0057] 3. Mix hydrogen-form ZSM-5 molecular sieve with acidic solution and zinc source, and stir at 40-100℃ for 0.3-3h to carry out zinc modification; mix zinc ion-exchanged crystalline molecular sieve with phosphorus source, and stir at 120-180℃ for 0.2h-3h to carry out phosphorus modification;

[0058] The mass of ZSM-5 molecular sieve is on a dry basis, the mass of zinc source is based on oxides, the mass of phosphorus source is based on phosphorus pentoxide, the mass of zinc source is 0.1%-2% of the mass of ZSM-5 molecular sieve, and the mass of phosphorus source is 2%-8% of the mass of ZSM-5 molecular sieve.

[0059] The phosphorus-modified ZSM-5 molecular sieve was filtered, washed, dried at 100-120℃, and then calcined at 400℃-700℃ for 0.5h-4h to obtain the modified ZSM-5 molecular sieve.

[0060] The present invention also provides a modified ZSM-5 molecular sieve, which is obtained by the above preparation method.

[0061] According to a specific embodiment of the present invention, taking the total mass of the modified ZSM-5 molecular sieve as 100%, the mass content of zinc oxide in the modified ZSM-5 molecular sieve is 0.1%-2%, for example, it can be specific values ​​such as 0.1%, 0.4%, 0.5%, 0.8%, 0.9%, 1%, 1.3%, 1.5%, 1.6%, 2%, etc., and a range with any two of the above specific values ​​as endpoints; the mass content of phosphorus pentoxide in the modified ZSM-5 molecular sieve is 2%-8%, for example, it can be specific values ​​such as 2%, 3%, 3.3%, 3.5%, 3.6%, 4%, 4.5%, 4.7%, 5%, 5.5%, 6%, 6.5%, 6.9%, 7%, 7.5%, 8%, etc., and a range with any two of the above specific values ​​as endpoints.

[0062] According to a specific embodiment of the present invention, the modified ZSM-5 molecular sieve has a small grain size, which can be 100nm-300nm.

[0063] This invention also provides a catalyst made from the aforementioned modified ZSM-5 molecular sieve. This catalyst, when applied in catalytic cracking or catalytic propylene production processes, exhibits the effect of increasing propylene production.

[0064] The beneficial effects of this invention include:

[0065] 1. The modified ZSM-5 molecular sieve preparation method provided by the present invention can obtain small-grained ZSM-5 molecular sieve seeds and primary and secondary structural units of ZSM-5 molecular sieve by high-temperature calcination, grinding and alkaline treatment of industrial ZSM-5 molecular sieve seeds. The introduction of silicon source during alkaline treatment is beneficial to the interaction between silicon source and ZSM-5 molecular sieve small-grained seeds and primary and secondary structural units, thereby promoting the growth of synthesized silica-alumina gel around small-grained seeds and primary and secondary structural units. Small-grained ZSM-5 molecular sieves can be directly synthesized without the presence of template agents and organic additives.

[0066] 2. The preparation method provided by this invention performs zinc modification and phosphorus modification in steps under acidic conditions. This eliminates the need for calcination after zinc modification, allowing direct phosphorus modification and reducing modification steps, thus simplifying the process. Zinc exchange in the acidic medium removes some of the framework aluminum and fragmented aluminum from the ZSM-5 molecular sieve, further optimizing the pore structure, acidity distribution, and zinc dispersion within the ZSM-5 sieve pores. Then, phosphorus modification is performed on the ZSM-5 molecular sieve, resulting in a modified ZSM-5 molecular sieve with improved propylene production performance in catalytic cracking and pyrolysis reactions. Attached Figure Description

[0067] Figure 1 The SEM image of the NZ-3 molecular sieve prepared in Example 3 is shown.

[0068] Figure 2 SEM spectra of DMZ-1 molecular sieve prepared for Comparative Example 1.

[0069] Figure 3 SEM spectra of DMZ-2 molecular sieve prepared for Comparative Example 2.

[0070] Figure 4 SEM spectra of DMZ-2 molecular sieve prepared for Comparative Example 3. Detailed Implementation

[0071] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0072] The surface morphology of the samples was characterized using an Ultra-Plus field emission scanning electron microscope from Zeiss GmbH, Germany.

[0073] The raw materials used in the following examples and comparative examples are:

[0074] 1. Industrial ZSM-5 molecular sieve, SiO2 / Al2O3 = 30 (molar ratio);

[0075] 2. NaOH, NaAlO2, zinc chloride, zinc nitrate, zinc acetate, and hydrochloric acid, purchased commercially;

[0076] 3. Water glass (SiO2, 250 g / L; Na2O, 88 g / L), aluminum sulfate (Al2O3, 90 g / L);

[0077] 4. Silica sol (40%);

[0078] 5. Silica, with a reduction of 13.04% (moisture content), model: ZQ-602, Zhuzhou Xinglong New Material Co., Ltd.

[0079] 6. Phosphoric acid, ammonium phosphate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate, purchased commercially;

[0080] 7. Kaolin (loss on ignition 15.96%);

[0081] 8. Aluminum sol (alumina content, 20.15%), USY (loss on ignition 15.6%, cell constant 2.450 nm), provided by Catalyst Division of Lanzhou Petrochemical Company, China National Petroleum Corporation.

[0082] Example 1

[0083] This embodiment provides a modified ZSM-5 molecular sieve, the preparation method of which includes:

[0084] 1. Industrial ZSM-5 molecular sieve was used as seed crystals and calcined at 1090℃ for 5 hours (i.e., the first calcination). The calcined industrial ZSM-5 molecular sieve was then added to a ball mill at a speed of 2800 r / min for 6 hours, after which the sample was removed. 30 g of the ground ZSM-5 molecular sieve (median particle size 0.95 μm) was weighed and added to 1500 ml of water. The mixture was stirred until homogeneous. Then, 349.65 g of silica and 99.97 g of sodium hydroxide were added to the mixture, and the mixture was stirred for 32 minutes. The temperature was then raised to 60℃ and stirred for 2.5 hours to obtain mixture A (i.e., the product of the temperature treatment).

[0085] The mass ratio of the ground ZSM-5 molecular sieve to SiO2 in the silicon source (white carbon black) is 10%.

[0086] 2. Mix 127.5 ml of aluminum sulfate and 868.6 ml of water, stirring thoroughly to obtain mixture B. Then, slowly add mixture B to mixture A while stirring rapidly. After the addition of mixture B is complete, maintain stirring for 0.6 hours to obtain the raw material solution. Transfer the raw material solution to a reaction vessel, heat to 180°C, and crystallize at 180°C for 10 hours. After crystallization, filter and wash the crystallized product (i.e., molecular sieve). Then, mix the product at a mass ratio of molecular sieve dry basis: deionized water: ammonium sulfate = 1:5.5:0.35, heat to 83°C, stir for 1.1 hours, filter, wash, and dry to obtain NZ-1. Analysis shows that the crystal size of the obtained NZ-1 is 270 nm.

[0087] The components of the raw material solution satisfy the following molar ratio: m(Na2O):m(Al2O3):m(SiO2):m(H2O)=0.18:0.0222:1:28.

[0088] 3. Take 110 mL of 1.8 mol / L hydrochloric acid solution, add 0.99 g of (CH3COO)2Zn, stir until completely dissolved, add 50 g of NZ-1 molecular sieve (dry basis, the same below), heat to 52℃, stir for 2.1 h, then add 3.78 g of (NH4)3PO4, stir until completely dissolved, heat to 151℃, stir for 1.3 h, filter, dry at 108℃ for 26 h, then calcine at 470℃ for 1.7 h to obtain modified ZSM-5 molecular sieve sample MNZ-1. XRF shows that MNZ-2 contains 0.88 wt% ZnO and 3.6 wt% P2O5.

[0089] Example 2

[0090] This embodiment provides a modified ZSM-5 molecular sieve, the preparation method of which includes:

[0091] 1. Industrial ZSM-5 molecular sieve was calcined at 938℃ for 8 hours. The calcined ZSM-5 molecular sieve was then added to a ball mill at a speed of 2000 r / min for 8 hours. The sample was then removed. 5.0 g of the ground ZSM-5 molecular sieve (median particle size 0.7 μm) was weighed and added to 500 ml of water. The mixture was stirred until homogeneous. Then, 143.74 g of silica and 31.67 g of sodium hydroxide were added to the mixture, and the mixture was stirred for 45 minutes. The temperature was then raised to 95℃, and the mixture was stirred for 6 hours to obtain mixture A.

[0092] The mass ratio of the ground ZSM-5 molecular sieve to SiO2 in the silicon source (white carbon black) is 4%.

[0093] 2. Mix 70.8 ml of aluminum sulfate and 121.4 ml of water, stirring until homogeneous to obtain mixture B. Then, slowly add mixture B to mixture A while stirring rapidly. After the addition of mixture B is complete, maintain stirring for 1.3 hours to obtain the raw material solution. Transfer the raw material solution to a reaction vessel, heat to 160℃, and crystallize at 160℃ for 18 hours. After crystallization, filter and wash the crystallization product. Then, mix the product at a mass ratio of molecular sieve dry basis: deionized water: ammonium chloride = 1:8.2:0.49, heat to 74℃, stir for 48 minutes, filter, wash, and dry to obtain NZ-2. Analysis shows that the crystal size of the obtained NZ-2 is 160 nm.

[0094] The components of the raw material solution satisfy the following molar ratio: m(Na2O):m(Al2O3):m(SiO2):m(H2O)=0.10:0.0303:1:19.

[0095] 3. Take 220 mL of 0.7 mol / L hydrochloric acid solution, add 0.88 g of Zn(NO3)2·6H2O, stir until completely dissolved, add 50 g of NZ-2 molecular sieve (dry basis, the same below), heat to 75℃, stir for 1.3 h, then add 6.29 g of (NH4)2HPO4, stir until completely dissolved, heat to 170℃, stir for 0.7 h, filter, dry at 113℃ for 18 h, then calcine at 495℃ for 2.0 h to obtain modified ZSM-5 molecular sieve sample MNZ-2. XRF shows that MNZ-2 contains 0.48 wt% ZnO and 6.9 wt% P2O5.

[0096] Example 3

[0097] This embodiment provides a modified ZSM-5 molecular sieve, the preparation method of which includes:

[0098] 1. Industrial ZSM-5 molecular sieve was calcined at 1060℃ for 7 hours. Then, the industrial ZSM-5 molecular sieve was added to a ball mill, and the milling speed was set to 2300 r / min for 4 hours. The sample was then removed. 17.3 g of the milled ZSM-5 molecular sieve (median particle size 0.6 μm) was weighed, and 477.26 g of water glass was added. The mixture was stirred until homogeneous. Then, 28.52 g of silica was added to the mixture, and the mixture was stirred for 1.1 hours. The temperature was then raised to 85℃, and the mixture was stirred for 8 hours to obtain mixture A.

[0099] The mass ratio of the ground ZSM-5 molecular sieve to SiO2 in the silicon source (water glass) is 12%.

[0100] 2. Mix 119.94g of aluminum sulfate and 447.4ml of water, stirring until homogeneous to obtain mixture B. Then, slowly add mixture B to mixture A while stirring rapidly. After the addition of mixture B is complete, maintain stirring for 0.8 hours to obtain the raw material solution. Transfer the raw material solution to a reaction vessel, heat to 150℃, and crystallize at 150℃ for 30 hours. After crystallization, filter and wash the crystallization product. Then, mix the product at a mass ratio of molecular sieve dry basis: deionized water: ammonium nitrate = 1:6.3:0.42, heat to 88℃, stir for 33 minutes, filter, wash, and dry to obtain NZ-3. Figure 1 The image shows the SEM image of the NZ-3 molecular sieve prepared in Example 3. SEM analysis revealed that the crystal size of the obtained NZ-3 was 120 nm.

[0101] The components of the raw material solution satisfy the following molar ratio: m(Na2O):m(Al2O3):m(SiO2):m(H2O)=0.14:0.0435:1:25.

[0102] 3. Take 260 ml of 1.8 mol / L hydrochloric acid solution, add 0.69 g of ZnCl2, stir until completely dissolved, add 50 g of NZ-3 molecular sieve, heat to 91℃, stir for 2.6 h, then add 3.55 g of (NH4)3PO4, stir until completely dissolved, heat to 153℃, stir for 2.5 h, filter, dry at 107℃ for 23 h, then calcine at 630℃ for 1.1 h to obtain modified ZSM-5 molecular sieve sample MNZ-3. XRF shows that MNZ-3 contains 0.83 wt% ZnO and 3.3 wt% P2O5.

[0103] Example 4

[0104] This embodiment provides a modified ZSM-5 molecular sieve, the preparation method of which includes:

[0105] 1. Industrial ZSM-5 molecular sieve was calcined at 980℃ for 4 hours. Then, the industrial ZSM-5 molecular sieve was added to a ball mill, and the milling speed was set to 1500 r / min for 7 hours. The sample was then removed. 8.61 g of the milled ZSM-5 molecular sieve (median particle size 0.8 μm) was weighed, and 700.0 g of water was added. The mixture was stirred until homogeneous. Then, 190.87 g of silica was added to the mixture, and the mixture was stirred for 1.4 hours. The temperature was then raised to 73℃, and the mixture was stirred for 4.5 hours to obtain mixture A.

[0106] The mass ratio of the ground ZSM-5 molecular sieve to SiO2 in the silicon source (white carbon black) is 7%.

[0107] 2. Mix 15.91g of sodium aluminate solid with 313.0ml of water and stir until homogeneous to obtain mixture B. Then, slowly add mixture B to mixture A while stirring rapidly. After the addition of mixture B is complete, continue stirring for 1.1 hours to obtain the raw material solution. Transfer the raw material solution to a reaction vessel, heat to 146℃, and crystallize at 146℃ for 47 hours. After crystallization, filter and wash the crystallization product. Then, mix the product at a mass ratio of molecular sieve dry basis: deionized water: ammonium nitrate = 1:6.8:0.78, heat to 78℃, stir for 72 minutes, filter, wash, and dry to obtain NZ-4. Analysis showed that the crystal size of the obtained NZ-4 was 210nm.

[0108] The components of the raw material solution satisfy the following molar ratio: m(Na2O):m(Al2O3):m(SiO2):m(H2O)=0.13:0.0244:1:21.

[0109] 3. Take 156 ml of 2.9 mol / L hydrochloric acid solution, add 1.8 g of (CH3COO)2Zn, stir until completely dissolved, add 50 g of NZ-4 molecular sieve, heat to 63℃, stir for 0.8 h, then add 3.88 g of H3PO4, stir until completely dissolved, heat to 136℃, stir for 1.6 h, filter, dry at 119℃ for 33 h, then calcine at 545℃ for 3.4 h to obtain modified ZSM-5 molecular sieve sample MNZ-4. XRF shows that MNZ-4 contains 1.6 wt% ZnO and 4.7 wt% P2O5.

[0110] Example 5

[0111] This embodiment provides a modified ZSM-5 molecular sieve, the preparation method of which includes:

[0112] 1. Industrial ZSM-5 molecular sieve was calcined at 1040℃ for 2 hours. Then, the industrial ZSM-5 molecular sieve was added to a ball mill, and the milling speed was set to 2500 r / min for 2 hours. The sample was then removed. 15.2 g of the milled ZSM-5 molecular sieve (median particle size 0.75 μm) was weighed, and 413.13 g of water glass and 150 ml of water were added. The mixture was stirred until homogeneous. Then, 30.73 g of silica was added to the mixture, and the mixture was stirred for 1.3 hours. The temperature was then raised to 79℃, and the mixture was stirred for 9.1 hours to obtain mixture A.

[0113] The mass ratio of the ground ZSM-5 molecular sieve to SiO2 in the silicon source (water glass + silica) is 14%.

[0114] 2. Mix 71.97g of aluminum sulfate and 267.7ml of water, stirring until homogeneous to obtain mixture B. Then, slowly add mixture B to mixture A while stirring rapidly. After the addition of mixture B is complete, maintain stirring for 1.5 hours to obtain the raw material solution. Transfer the raw material solution to a reaction vessel, heat to 171℃, and crystallize at 171℃ for 21 hours. After crystallization, filter and wash the crystallization product. Then, mix the product at a mass ratio of molecular sieve dry basis to deionized water of 1:4.7, add hydrochloric acid to adjust the pH to 2.6, heat to 64℃, stir for 87 minutes, filter, wash, and dry to obtain NZ-5 molecular sieve. Analysis shows that the crystal size of the obtained NZ-5 is 190nm.

[0115] The components of the raw material solution satisfy the following molar ratio: m(Na2O):m(Al2O3):m(SiO2):m(H2O)=0.17:0.0278:1:24.

[0116] 3. Take 170 ml of 0.8 mol / L hydrochloric acid solution, add 2.34 g of Zn(NO3)2·6H2O, stir until completely dissolved, add 50 g of NZ-5 molecular sieve, heat to 88℃, stir for 1.5 h, then add 4.46 g of NH4H2PO4, stir until completely dissolved, heat to 139℃, stir for 2.4 h, filter, dry at 113℃ for 25 h, then calcine at 670℃ for 0.7 h to obtain modified ZSM-5 molecular sieve sample MNZ-5. XRF shows that MNZ-5 contains 1.3 wt% ZnO and 5.5 wt% P2O5.

[0117] Example 6

[0118] This embodiment provides a catalyst, the preparation method of which includes:

[0119] The MNZ-3 molecular sieve prepared in Example 3, along with kaolin, alumina sol, and USY, were mixed in a mass ratio of MNZ-3:kaolin:alumina sol:USY = 2:50:15:33 to prepare a slurry. The slurry was then spray-dried to prepare model catalyst microspheres. The catalyst microspheres were calcined at 550°C for 1.5 h. Subsequently, deionized water and ammonium chloride were added at 7 times and 0.35 times the mass of the catalyst microspheres, respectively. The mixture was heated to 92°C and stirred at a constant temperature for 45 minutes. After filtration and washing, catalyst CAT-1 was obtained.

[0120] Comparative Example 1

[0121] This comparative example provides a modified ZSM-5 molecular sieve, the preparation method of which includes:

[0122] 1. Weigh 17.3g of ZSM-5 molecular sieve, add 477.26g of water glass, stir evenly, then add 28.52g of silica to the mixture, stir for 1.1h, then heat to 85℃ and stir for 8h to obtain mixture A.

[0123] The mass ratio of ZSM-5 molecular sieve to SiO2 in the silicon source is 12%.

[0124] 2. Mix 119.94g of aluminum sulfate and 447.4ml of water, stirring until homogeneous to obtain mixture B. Then, slowly add mixture B to mixture A while stirring rapidly. After the addition of mixture B is complete, maintain stirring for 0.8 hours to obtain the raw material solution. Transfer the raw material solution to a reaction vessel, heat to 150℃, and crystallize at 150℃ for 30 hours. After crystallization, filter and wash the crystallization product. Then, mix the product at a mass ratio of molecular sieve dry basis: deionized water: ammonium nitrate = 1:6.3:0.42, heat to 88℃, stir for 33 minutes, filter, wash, and dry to obtain DNZ-1. Figure 2 SEM images of the prepared DMZ-1 molecular sieve for Comparative Example 1 are shown. Analysis revealed that the crystallite size of the obtained DNZ-1 was 2.5 μm.

[0125] The components of the raw material solution satisfy the following molar ratio: m(Na2O):m(Al2O3):m(SiO2):m(H2O)=0.14:0.0435:1:25.

[0126] 3. Take 260 ml of 1.8 mol / L hydrochloric acid solution, add 0.69 g of ZnCl2, stir until completely dissolved, add 50 g of DNZ-1 molecular sieve, heat to 91℃, stir for 2.6 h, then add 3.55 g of (NH4)3PO4, stir until completely dissolved, heat to 153℃, stir for 2.5 h, filter, dry at 107℃ for 23 h, then calcine at 630℃ for 1.1 h to obtain modified ZSM-5 molecular sieve sample DMZ-1. XRF shows that DMZ-1 contains 0.83 wt% ZnO and 3.3 wt% P2O5.

[0127] Compared to Example 3, step 1 of the comparative molecular sieve preparation method did not involve calcination and grinding.

[0128] This comparative example also provides a catalyst, the preparation method of which includes:

[0129] The prepared DMZ-1 molecular sieve, along with kaolin, alumina sol, and USY, were mixed in a mass ratio of DMZ-1:kaolin:alumina sol:USY = 2:50:15:33 to prepare a slurry. The slurry was then spray-dried to prepare model catalyst microspheres. The catalyst microspheres were calcined at 550℃ for 1.5 h. Subsequently, deionized water and ammonium chloride were added at 7 times and 0.35 times the mass of the catalyst microspheres, respectively. The mixture was heated to 92℃ and stirred at a constant temperature for 45 minutes. After filtration and washing, catalyst CAT-2 was obtained.

[0130] Compared to Example 3, step 1 of the comparative molecular sieve preparation method did not involve calcination and grinding.

[0131] Comparative Example 2

[0132] This comparative example provides a modified ZSM-5 molecular sieve, the preparation method of which includes:

[0133] 1. Add industrial ZSM-5 molecular sieve to a ball mill, set the speed to 2300 r / min, and grind for 4 hours. Take out the sample. Weigh 477.26 g of water glass, stir evenly, then add 28.52 g of silica to the mixture, stir for 1.1 hours, then heat to 85℃ and stir for 8 hours. Then add 17.3 g of ground ZSM-5 molecular sieve (median particle size 0.6 μm) to obtain mixture A.

[0134] The mass ratio of the ground ZSM-5 molecular sieve to SiO2 in the silicon source is 12%.

[0135] 2. Mix 119.94g of aluminum sulfate and 447.4ml of water, stirring until homogeneous to obtain mixture B. Then, slowly add mixture B to mixture A while stirring rapidly. After the addition of mixture B is complete, maintain stirring for 0.8 hours to obtain the raw material solution. Transfer the raw material solution to a reaction vessel, heat to 150℃, and crystallize at 150℃ for 30 hours. After crystallization, filter and wash the crystallization product. Then, mix the product at a mass ratio of molecular sieve dry basis: deionized water: ammonium nitrate = 1:6.3:0.42, heat to 88℃, stir for 33 minutes, filter, wash, and dry to obtain DNZ-2. Figure 3 The SEM image of the DMZ-2 molecular sieve prepared for Comparative Example 2 is shown. SEM analysis revealed that the crystallite size of the obtained DNZ-2 was 950 nm.

[0136] The components of the raw material solution satisfy the following molar ratio: m(Na2O):m(Al2O3):m(SiO2):m(H2O)=0.14:0.0435:1:25.

[0137] 3. Take 260 ml of 1.8 mol / L hydrochloric acid solution, add 0.69 g of ZnCl2, stir until completely dissolved, add 50 g of DNZ-2 molecular sieve, heat to 91℃, stir for 2.6 h, then add 3.55 g of (NH4)3PO4, stir until completely dissolved, heat to 153℃, stir for 2.5 h, filter, dry at 107℃ for 23 h, then calcine at 630℃ for 1.1 h to obtain modified ZSM-5 molecular sieve sample DMZ-2. XRF shows that DMZ-2 contains 0.83 wt% ZnO and 3.3 wt% P2O5.

[0138] Compared to Example 3, step 1 of the comparative molecular sieve preparation method does not involve calcination, but only grinding.

[0139] This comparative example also provides a catalyst, the preparation method of which includes:

[0140] The prepared DMZ-2 molecular sieve, along with kaolin, alumina sol, and USY, were mixed in a mass ratio of DMZ-2:kaolin:alumina sol:USY = 2:50:15:33 to prepare a slurry. The slurry was then spray-dried to prepare model catalyst microspheres. The catalyst microspheres were calcined at 550℃ for 1.5 h. Subsequently, deionized water and ammonium chloride were added at 7 times and 0.35 times the mass of the catalyst microspheres, respectively. The mixture was heated to 92℃ and stirred at a constant temperature for 45 minutes. After filtration and washing, catalyst CAT-3 was obtained.

[0141] Comparative Example 3

[0142] This comparative example provides a modified ZSM-5 molecular sieve, the preparation method of which includes:

[0143] 1. The industrial ZSM-5 molecular sieve was calcined at 1060℃ for 7 hours. 17.3g of the calcined ZSM-5 molecular sieve was weighed, 477.26g of water glass was added, and the mixture was stirred evenly. Then 28.52g of silica was added to the mixture, and the mixture was stirred for 1.1 hours. The temperature was then raised to 85℃ and stirred for 8 hours to obtain mixture A.

[0144] The mass ratio of ZSM-5 molecular sieve to SiO2 in the silicon source is 12%.

[0145] 2. Mix 119.94g of aluminum sulfate and 447.4ml of water, stirring until homogeneous to obtain mixture B. Then, slowly add mixture B to mixture A while stirring rapidly. After the addition of mixture B is complete, maintain stirring for 0.8 hours to obtain the raw material solution. Transfer the raw material solution to a reaction vessel, heat to 150℃, and crystallize at 150℃ for 30 hours. After crystallization, filter and wash the crystallization product. Then, mix the product at a mass ratio of molecular sieve dry basis: deionized water: ammonium nitrate = 1:6.3:0.42, heat to 88℃, stir for 33 minutes, filter, wash, and dry to obtain DNZ-3. Figure 4 The SEM image of the DMZ-2 molecular sieve prepared for Comparative Example 3 is shown. SEM analysis revealed that the crystallite size of the obtained DNZ-3 was 800 nm.

[0146] The components of the raw material solution satisfy the following molar ratio: m(Na2O):m(Al2O3):m(SiO2):m(H2O)=0.14:0.0435:1:25.

[0147] 3. Take 260 ml of 1.8 mol / L hydrochloric acid solution, add 0.69 g of ZnCl2, stir until completely dissolved, add 50 g of DNZ-3 molecular sieve, heat to 91℃, stir for 2.6 h, then add 3.55 g of (NH4)3PO4, stir until completely dissolved, heat to 153℃, stir for 2.5 h, filter, dry at 107℃ for 23 h, then calcine at 630℃ for 1.1 h to obtain modified ZSM-5 molecular sieve sample DMZ-3. XRF shows that DMZ-3 contains 0.83 wt% ZnO and 3.3 wt% P2O5.

[0148] Compared to Example 3, step 1 of the comparative molecular sieve preparation method only involves calcination and does not involve grinding.

[0149] This comparative example also provides a catalyst, the preparation method of which includes:

[0150] The prepared DMZ-3 molecular sieve, along with kaolin, alumina sol, and USY, were mixed in a mass ratio of DMZ-3:kaolin:alumina sol:USY = 2:50:15:33 to prepare a slurry. The slurry was then spray-dried to prepare model catalyst microspheres. The catalyst microspheres were calcined at 550℃ for 1.5 h. Subsequently, deionized water and ammonium chloride were added at 7 times and 0.35 times the mass of the catalyst microspheres, respectively. The mixture was heated to 92℃ and stirred at a constant temperature for 45 minutes. After filtration and washing, catalyst CAT-4 was obtained.

[0151] Will Figure 1 and Figures 2 to 4 The comparison of the results shows that: Figures 2 to 4 The ZSM-5 molecular sieve prepared in the comparative example shown has individual particle sizes close to or exceeding 1 μm; while the ZSM-5 molecular sieve in Example 3 has significantly smaller individual particle sizes, approximately 120 nm. This comparison demonstrates that the calcination and grinding treatments of the ZSM-5 molecular sieve in this invention have a synergistic effect, jointly reducing the crystal size of the molecular sieve, whereas individual calcination or grinding treatments do not have this effect. Specifically, this invention, through the synergistic calcination and grinding of the seed crystals, can reduce the crystal size of the ZSM-5 molecular sieve seed crystals and promote the dissolution of the molecular sieve surface during subsequent alkaline treatment, further reducing the crystal size of the ZSM-5 molecular sieve and promoting dispersion; the resulting solution contains a large number of fine ZSM-5 molecular sieve particles and the primary and secondary structural units of the ZSM-5 molecular sieve. The above-mentioned calcination and grinding treatment can enhance the interaction between the fine particles of ZSM-5 molecular sieve and the primary and secondary structural units of ZSM-5 molecular sieve and the silicon source, thereby guiding the formation of small-crystal ZSM-5 molecular sieve with MFI structure without template agent and organic additive.

[0152] Test Example 1

[0153] This test example provides an evaluation of the reaction performance of catalysts prepared from the modified ZSM-5 molecular sieves of the examples and the comparative modified ZSM-5 molecular sieves.

[0154] The reaction performance was evaluated using a fixed fluidized bed reactor. The feedstock used was from the 3 million tons / year heavy oil catalytic cracking unit of Lanzhou Petrochemical. The properties of the feedstock are shown in Table 1. The catalyst was aged at 800℃ with 100% steam for 10 hours before evaluation. The reaction evaluation data are shown in Table 2.

[0155] Table 1 Properties of feedstock oils used for catalyst selectivity assessment

[0156]

[0157]

[0158] Table 2. Reaction performance of catalysts prepared from modified ZSM-5 molecular sieves

[0159]

[0160] As shown in the ACE evaluation data in Table 2, when used in catalytic cracking reactions, the catalyst containing 2wt% modified ZSM-5 molecular sieve material prepared in this invention significantly improves the liquefied gas yield and propylene yield compared with the comparative ZSM-5 molecular sieve material catalyst, demonstrating excellent propylene production performance.

[0161] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing modified ZSM-5 molecular sieve, the method comprising: The ZSM-5 molecular sieve seed crystals were first calcined and ground. The ground ZSM-5 molecular sieve seed crystals were then mixed with an alkali source and a silicon source and subjected to a heating treatment to obtain the heated product. The product of the heating treatment was mixed with an aluminum source to obtain a raw material solution, which was then crystallized to obtain ZSM-5 molecular sieve. ZSM-5 molecular sieve is mixed with an acidic solution and a zinc source, and stirred to perform zinc ion exchange. Then, the zinc-ion-exchanged ZSM-5 molecular sieve is mixed with a phosphorus source, stirred to perform phosphorus modification, filtered, dried, and then calcined a second time to obtain the modified ZSM-5 molecular sieve.

2. The preparation method according to claim 1, wherein, The first roasting temperature is 900℃-1100℃, and the first roasting time is 1h-18h.

3. The preparation method according to claim 1, wherein, The grinding speed is 1000r / min-3000r / min, and the grinding time is 1h-10h.

4. The production method according to claim 1 or 3, wherein The median particle size of the ground ZSM-5 molecular sieve is no greater than 1.0 μm.

5. The production method according to claim 1, wherein The mass of the ground ZSM-5 molecular sieve seed crystals is on a dry basis, and the mass of the silicon source is SiO2. The mass ratio of the ground ZSM-5 molecular sieve seed crystals to the silicon source is 0.02-0.15:

1.

6. The production method according to claim 1 or 5, wherein The silicon source includes one or more of silica sol, water glass, and silica.

7. The production method according to claim 1, wherein The temperature of the heating treatment is 50℃-100℃, and the heating treatment time is 1h-10h.

8. The production method according to claim 1, wherein The components of the raw material solution satisfy the following molar ratio: m(Na2O):m(Al2O3):m(SiO2):m(H2O)=0.05-0.2:0.02-0.05:1:14-30.

9. The production method according to claim 1, wherein The crystallization temperature is 140℃-190℃, and the crystallization time is 6h-48h.

10. The production method according to claim 1, wherein, The ZSM-5 molecular sieve has a crystal size of 100nm-300nm.

11. The method of producing according to claim 1, wherein, The mass of the ZSM-5 molecular sieve is on a dry basis, and the mass of the zinc source is on a zinc oxide basis, wherein the mass of the zinc source is 0.1%-2% of the mass of the ZSM-5 molecular sieve.

12. The production method according to claim 1 or 11, wherein The zinc ion exchange temperature is 40℃-100℃, and the zinc ion exchange time is 0.3h-3h.

13. The method of producing according to claim 1, wherein, The mass of ZSM-5 molecular sieve is on a dry basis, and the mass of phosphorus source is on a phosphorus pentoxide basis, wherein the mass of phosphorus source is 2%-8% of the mass of ZSM-5 molecular sieve.

14. The production method according to claim 1 or 13, wherein The phosphorus modification temperature is 120℃-180℃, and the phosphorus modification time is 0.2h-3h.

15. A modified ZSM-5 molecular sieve, wherein the molecular sieve is obtained by the preparation method according to any one of claims 1-14.

16. The modified ZSM-5 molecular sieve of claim 15, wherein, Based on the total mass of the modified ZSM-5 molecular sieve as 100%, the mass content of zinc oxide in the modified ZSM-5 molecular sieve is 0.1%-2%, and the mass content of phosphorus pentoxide in the modified ZSM-5 molecular sieve is 2%-8%.

17. A catalyst made from the modified ZSM-5 molecular sieve as described in claim 15 or 16.

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