Catalytic cracking catalyst, preparation method thereof and process for producing propylene through catalytic cracking

Abstract

The invention provides a catalytic cracking catalyst, a preparation method thereof and a process for producing propylene through catalytic cracking. The preparation method comprises the following steps: mixing a first silicon source, a first aluminum source, inorganic alkali, water and amorphous molecular sieve pre-crystallization liquid, and aging to obtain a first raw material mixture; adding a second silicon source into the first raw material mixture to obtain a second raw material mixture, crystallizing, filtering, washing, drying and roasting to obtain the nano ZSM-5 molecular sieve, wherein the second silicon source comprises white carbon black; the preparation method comprises the following steps: mixing and pulping a nano ZSM-5 molecular sieve, a Y molecular sieve, a binder, a phosphorus source, clay and water to form slurry of a catalyst raw material, and carrying out spray drying and roasting on the slurry of the catalyst raw material to obtain the catalytic cracking catalyst. The catalytic cracking catalyst provided by the invention has the characteristics of high liquefied gas yield and good propylene selectivity.

Description

Technical Field

[0001] This invention relates to the field of catalytic cracking catalyst technology, and in particular to a catalytic cracking catalyst, its preparation method, and a process for catalytic cracking to produce propylene. Background Technology

[0002] Propylene is an important chemical raw material, and the main process for producing propylene is the petroleum route, with catalytic cracking being one of the main processes. Currently, refining capacity continues to grow strongly, but demand for refined oil products has bottomed out, resulting in severe overcapacity in refining. Meanwhile, demand for low-carbon olefins such as propylene continues to grow, making "refining to chemical transformation" a crucial way for refining companies to enhance their competitiveness. The advantages of catalytic cracking technology in increasing the production of low-carbon olefins make it an important means for enterprises to transform and upgrade. CN101491772A, CN115869988A, CN102861604A, CN116174024A, CN115990513A, and CN115990508A disclose catalytic cracking catalysts for olefin production. From these existing technologies, it can be seen that the catalyst is the core technology for catalytic cracking, and the ZSM-5 molecular sieve, as its key active component, has a significant impact on its cracking selectivity.

[0003] Currently, ZSM-5 molecular sieves remain the main active component of catalytic cracking catalysts. Optimizing the physicochemical properties of ZSM-5 molecular sieves can significantly improve the reaction performance of catalytic cracking catalysts. Nano-ZSM-5 molecular sieves, due to their good accessibility of active centers and short diffusion channels, can effectively enhance cracking activity, reduce the probability of side reactions, and thus improve propylene selectivity. Therefore, based on the wide application of ZSM-5 and the catalytic reaction characteristics of nano-ZSM-5 molecular sieves, the preparation of nano-ZSM-5 molecular sieves has always been a research hotspot in the field.

[0004] CN104525245A (application number 201410808475) discloses a nanocrystalline stacked mesoporous ZSM-5 catalyst, its preparation, and its application. This technology, using only a first template agent, pretreats a solid silicon source to induce varying degrees of depolymerization, further adjusts the material ratio of the system, adds sodium salt to regulate the growth rate of the molecular sieve, and employs a two-stage crystallization method: low-temperature nucleation and high-temperature growth. This synthesizes a series of aggregated ZSM-5 molecular sieves with primary particle sizes ranging from 20-100 nm.

[0005] CN103626203A (application number 201310507311) discloses a method for preparing nano-ZSM-5 molecular sieves. The method involves further introducing a dispersant into a synthesis system comprising a silicon source, an aluminum source, an alkaline solution, and a template agent. The resulting ZSM-5 molecular sieve has a particle size of approximately 200 nm.

[0006] CN105293522A (application number 201510805744) discloses a method for preparing a narrow-distribution, small-grained ZSM-5 molecular sieve. 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.

[0007] It can be seen that template agents are still widely used in the current preparation process of small-crystal ZSM-5 molecular sieves. The 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. Reducing the introduction of template agents during the synthesis process by using seed crystal directing agents or pre-crystallization solutions is an effective method.

[0008] CN1915819A (application number 2005100287816) discloses a method for synthesizing ZSM-5 zeolite. Its key technical feature is the preparation of a seed crystal directing agent. The seed crystal directing agent uses tetraethyl orthosilicate, silica sol, or silica as the silicon source, and tetrapropylammonium hydroxide or tetrapropylammonium bromide as the template agent, and is prepared by aging under certain conditions. The seed crystal directing agent can serve as the nucleus for the growth of ZSM-5 molecular sieves, yielding ZSM-5 crystals of 100 nm in size.

[0009] CN116078421A (application number 2023103137876) discloses a method for preparing a highly stable nano-ZSM-5 catalyst and its application. The preparation method includes the following steps: (1) preparing all-silica molecular sieve silicalite-1 using template agent, silicon source and water as raw materials by pre-crystallization method; (2) using seed crystal method, using the silicalite-1 as seed crystal, mixing it with reaction raw materials including silicon source, aluminum source, template agent and water, and then treating it again by pre-crystallization method, and then sequentially passing it through crystallization, ammonium exchange and metal loading to obtain ZSM-5 molecular sieve. This method yields a highly stable ZSM-5 catalyst composed of secondary small particles of about 50 nm.

[0010] It can be seen that in the existing methods for synthesizing ZSM-5 molecular sieves using seed-directing agents or pre-crystallization solutions, the grain size of the resulting ZSM-5 molecular sieve is directly related to the size of the ZSM-5 molecular sieve seed crystals in the seed-directing agent or pre-crystallization solution. The product ZSM-5 grains are larger than or close to the size of the seed crystals in the seed-directing agent or pre-crystallization solution; generally, the smaller the seed crystal, the smaller the corresponding ZSM-5 molecular sieve grains. Moreover, this method usually yields ZSM-5 nanocrystalline aggregates. These polycrystalline aggregates are prone to close packing and mutual growth during the growth process, leading to the dissolution of mesoporous and macroporous structures. Therefore, although using seed-directing agents or pre-crystallization solutions can obtain nano-ZSM-5 molecular sieve aggregates with lower template agent dosages, it is still necessary to develop low-cost and green preparation methods to reduce the degradation of mesoporous and macroporous structures caused by mutual growth during nanocrystal aggregation.

[0011] In summary, further efforts are needed to improve the propylene selectivity of catalytic cracking catalysts by developing ZSM-5 nanocrystal aggregates with abundant mesoporous and macroporous structures. Summary of the Invention

[0012] To address the aforementioned problems, the present invention aims to provide a catalytic cracking catalyst, its preparation method, and a process for producing propylene via catalytic cracking. This catalytic cracking catalyst features high liquefied gas yield and good propylene selectivity.

[0013] To achieve the above objectives, the present invention provides a method for preparing a catalytic cracking catalyst, the method comprising:

[0014] S1. Mix the first silicon source, the first aluminum source, inorganic alkali, water, and amorphous molecular sieve precrystallization liquid, and age them to obtain the first raw material mixture;

[0015] S2. Add a second silicon source to the first raw material mixture to obtain a second raw material mixture, crystallize, filter, wash, dry, and calcine to obtain nano ZSM-5 molecular sieve; wherein, the second silicon source includes silica; the second raw material mixture satisfies the following molar ratio: m(Na2O):m(SiO2):m(Al2O3):m(H2O)=0.07-0.16:1:0.01-0.05:14-30;

[0016] S3. The nano ZSM-5 molecular sieve is mixed with Y molecular sieve, binder, phosphorus source, clay and water, pulped to form a slurry, spray dried and calcined to obtain the catalytic cracking catalyst.

[0017] Compared to conventional nano-zeolite seeds, the preparation method of the nano-ZSM-5 molecular sieve of this invention uses an amorphous molecular sieve pre-crystallization solution to provide growth sites. The amorphous molecular sieve pre-crystallization solution contains a large number of primary and secondary structural units, which can further reduce the primary particle size of the ZSM-5 molecular sieve. By reducing the crystallite size of the ZSM-5 molecular sieve, ZSM-5 molecular sieve nano-polymers can be obtained, which is beneficial for constructing multi-level channels in the ZSM-5 molecular sieve. Furthermore, the amorphous molecular sieve pre-crystallization solution eliminates the need for separation treatment, saving costs and being environmentally friendly.

[0018] According to a specific embodiment of the present invention, the preparation method of the amorphous molecular sieve precrystallization liquid may include: mixing a third silicon source, an organic template agent, and a second aluminum source to obtain a precrystallization liquid raw material, aging it, and obtaining the amorphous molecular sieve precrystallization liquid.

[0019] In the above-mentioned method for preparing amorphous molecular sieve precrystallization liquid, the aging temperature is 60℃-120℃, for example, specific values ​​such as 60℃, 70℃, 80℃, 90℃, 100℃, 105℃, 110℃, 120℃, etc., and a range with any two of the above specific values ​​as endpoints; the aging time is 2h-16h, for example, specific values ​​such as 2h, 4h, 8h, 9h, 10h, 12h, 14h, 16h, etc., and a range with any two of the above specific values ​​as endpoints.

[0020] In the above-mentioned method for preparing amorphous molecular sieve precrystallization liquid, the raw materials of the precrystallization liquid, based on oxides, satisfy the following molar ratio: SiO2:MO:Al2O3:H2O=1:0.02-0.06:0.01-0.05:15-25; wherein, MO is the oxide corresponding to the organic template agent, for example, when the organic template agent is TPAOH, MO is (TPA)2O. In some specific embodiments, the molar ratio of SiO2:MO:Al2O3:H2O can be 1:0.02-0.06:0.01-0.04:15-25.

[0021] In some specific implementations, based on molar parts, when SiO2 is 1 part, MO can be 0.02 parts, 0.025 parts, 0.03 parts, 0.035 parts, 0.04 parts, 0.045 parts, 0.05 parts, 0.055 parts, 0.06 parts, etc., and a range with any two of the above specific values ​​as endpoints; Al2O3 can be 0.01 parts, 0.015 parts, 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 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, 25 parts, etc., and a range with any two of the above specific values ​​as endpoints.

[0022] In the above method for preparing amorphous molecular sieve precrystallization liquid, the third silicon source includes tetraethyl orthosilicate and / or methyl orthosilicate.

[0023] In the above method for preparing amorphous molecular sieve precrystallization liquid, the organic template agent includes tetrapropylammonium hydroxide (TPAOH) and / or tetrapropylammonium bromide.

[0024] In the above-mentioned method for preparing amorphous molecular sieve precrystallization liquid, the second aluminum source includes one or more of sodium aluminate, aluminum sulfate, aluminum chloride, and aluminum nitrate.

[0025] In the above-mentioned method for preparing the catalytic cracking catalyst, the silicon source used to prepare the molecular sieve includes a first silicon source and a second silicon source, which are added in stages. Specifically, by mixing and aging the first silicon source with other raw materials, the formation of molecular sieve nuclei can be promoted; after aging, the second silicon source is added, which utilizes its abundant pores and good reactivity to improve the structure and performance of the molecular sieve. Through the above process, the interaction growth of nanocrystals can be reduced while maintaining a small grain size, thereby obtaining a hierarchical porous ZSM-5 molecular sieve with abundant medium and macroporous pores.

[0026] In the above-mentioned method for preparing the catalytic cracking catalyst, the first silicon source includes one or more of water glass, silica gel, silica sol, and fumed silica.

[0027] In the above-mentioned method for preparing the catalytic cracking catalyst, the second silicon source includes silica, which is formed by the loose stacking of silica nanoparticles and has good porosity and good reactivity. The main component of the silica in this invention is silica, and specifically, the silica can be one or a combination of two or more of precipitated silica, fumed silica, or ultrafine silica gel.

[0028] In the above-mentioned method for preparing the catalytic cracking catalyst, the first aluminum source includes one or more of aluminum sulfate, sodium aluminate, aluminum chloride, and aluminum nitrate.

[0029] In the above-mentioned method for preparing the catalytic cracking catalyst, the inorganic base includes one or a combination of two or more of sodium hydroxide, sodium carbonate, ammonia, and water glass. The inorganic base of this invention refers to an inorganic compound in a broad sense that can ionize hydroxide ions in aqueous solution. It is understood that when the second raw material mixture contains water glass, the water glass can simultaneously serve as both an inorganic base and a first silicon source.

[0030] In the above-described method for preparing the catalytic cracking catalyst, the mass of the amorphous molecular sieve precrystallization liquid, the first silicon source, and the second silicon source is based on the mass of SiO2, and the mass of the amorphous molecular sieve precrystallization liquid is 1%-10% of the sum of the masses of the first silicon source and the second silicon source. In some specific embodiments, the mass of the amorphous molecular sieve precrystallization liquid can be a specific value such as 1%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% of the sum of the masses of the first silicon source and the second silicon source, or a range with any two of the above specific values ​​as endpoints.

[0031] In the above-mentioned method for preparing the catalytic cracking catalyst, in step S1, aging treatment can promote the reduction of molecular sieve particle size and the increase of external surface area, and facilitate the mutual stacking of particles to form mesopores and macropores (including mesopores and macropores, referring to pores with a diameter of 2 nm or more), thereby increasing the specific surface area of ​​the molecular sieve. The aging temperature is 100℃-150℃, for example, specific values ​​such as 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, etc., and any two of the above specific values ​​as endpoints; the aging time is 2h-16h, for example, specific values ​​such as 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, etc., and any two of the above specific values ​​as endpoints.

[0032] In the above-mentioned method for preparing the catalytic cracking catalyst, the mass of the first silicon source and the second silicon source is based on the mass of SiO2. The mass of the second silicon source is 28%-60% of the sum of the masses of the first silicon source and the second silicon source, for example, specific values ​​such as 28%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, and any two of the above specific values ​​as endpoints.

[0033] In the above-mentioned method for preparing the catalytic cracking catalyst, in step S2, the second raw material mixture satisfies the following molar ratio:

[0034] The ratio of m(Na₂O):m(SiO₂):m(Al₂O₃):m(H₂O) is 0.07-0.16:1:0.01-0.05:14-30. In this ratio, m...

[0035] It represents Molar.

[0036] 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 inorganic bases, but also to other factors affecting sodium oxide or alkalinity. For example, when using alkaline sodium aluminate as the first aluminum source, the sodium oxide content in the sodium aluminate must also be included in the above molar ratios; if aluminum sulfate is used as the first aluminum source, since aluminum sulfate is acidic, 1 mol of sulfate 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 inorganic bases for this expression are not limited to sodium hydroxide.

[0037] In the above-mentioned second raw material mixture, in molar parts, when SiO2 is 1 part, Na2O can be 0.07 parts, 0.08 parts, 0.09 parts, 0.10 parts, 0.11 parts, 0.12 parts, 0.13 parts, 0.14 parts, 0.15 parts, 0.16 parts, etc., and a range with any two of the above specific values ​​as endpoints; Al2O3 can be 0.01 parts, 0.015 parts, 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, 20 parts, 25 parts, 30 parts, etc., and a range with any two of the above specific values ​​as endpoints.

[0038] In some specific embodiments, the second raw material mixture satisfies the following molar ratio: m(Na2O):m(SiO2):m(Al2O3):m(H2O)=0.08-0.16:1:0.015-0.04:20-30.

[0039] In the above-mentioned method for preparing the catalytic cracking catalyst, in S2, the crystallization temperature is 140℃-190℃, for example, specific values ​​such as 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, and a range with any two of the above specific values ​​as endpoints; the crystallization time is 8h-48h, for example, specific values ​​such as 8h, 10h, 12h, 16h, 18h, 20h, 24h, 26h, 28h, 30h, 32h, 36h, 40h, 48h, and a range with any two of the above specific values ​​as endpoints.

[0040] In the above-mentioned method for preparing the catalytic cracking catalyst, in step S2, the calcination temperature is 500℃-700℃, for example, specific values ​​such as 500℃, 550℃, 600℃, 650℃, 700℃, etc., and a range with any two of the above specific values ​​as endpoints; the calcination time is 3h-7h, for example, specific values ​​such as 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, etc., and a range with any two of the above specific values ​​as endpoints.

[0041] In the above-mentioned method for preparing the catalytic cracking catalyst, in S2, the primary particle size of the nano ZSM-5 molecular sieve is 20nm-90nm, for example, specific values ​​such as 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, etc., and a range with any two of the above specific values ​​as endpoints.

[0042] In the above-mentioned method for preparing the catalytic cracking catalyst, in step S2, the specific surface area of ​​the nano-ZSM-5 molecular sieve is 340 m². 2 ·g -1 -450m 2 ·g -1 .

[0043] In the above-mentioned method for preparing the catalytic cracking catalyst, in step S2, the pore volume of the nano-ZSM-5 molecular sieve is 0.3 cm³. 3 ·g -1 -0.6cm 3 ·g -1 .

[0044] In the above-mentioned method for preparing the catalytic cracking catalyst, in step S2, the mesopore volume of the nano-ZSM-5 molecular sieve is 0.15 cm³. 3 ·g -1 -0.40cm 3 ·g -1 .

[0045] In the above-mentioned method for preparing catalytic cracking catalyst, the catalyst comprises the following components by dry weight, calculated as 100% of the total dry weight of the catalyst: 20%-50% nano ZSM-5 molecular sieve, 5%-15% Y-type molecular sieve, 3%-8% binder, 5%-10% P2O5, and 30%-50% clay.

[0046] According to a specific embodiment of the present invention, the amount of nano ZSM-5 molecular sieve, Y molecular sieve, binder, phosphorus source, and clay added in S3 can be determined according to the above ratio.

[0047] According to a specific embodiment of the present invention, the mass percentage of the nano ZSM-5 molecular sieve in the catalyst, on a dry basis, can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc., and a range with any two of the above specific values ​​as endpoints.

[0048] According to a specific embodiment of the present invention, the mass percentage of the Y-type molecular sieve in the catalyst, based on dry weight, can be a specific value such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc., and a range with any two of the above specific values ​​as endpoints.

[0049] According to a specific embodiment of the present invention, the mass percentage of the binder in the catalyst, based on dry weight, can be 3%, 4%, 5%, 6%, 7%, 8%, or a range with any two of the above specific values ​​as endpoints.

[0050] According to a specific embodiment of the present invention, the mass percentage of P2O5 in the catalyst, based on dry weight, can be a specific value such as 5%, 6%, 7%, 8%, 9%, 10%, or a range with any two of the above specific values ​​as endpoints.

[0051] According to a specific embodiment of the present invention, the mass percentage of the clay in the catalyst, based on dry weight, can be 30%, 35%, 40%, 45%, 50%, or a range with any two of the above specific values ​​as endpoints.

[0052] According to a specific embodiment of the present invention, the amount of water added in S3 can be determined based on the solid content (solid mass content) of the slurry. In some specific embodiments, the solid content of the slurry can be controlled to be 30%-50%, for example, specific values ​​such as 30%, 35%, 40%, 45%, 50%, etc., and a range with any two of the above specific values ​​as endpoints.

[0053] In the above-described method for preparing the catalytic cracking catalyst, in step S3, the Y molecular sieve may include one or a combination of two or more of the following: USY molecular sieve, HY molecular sieve, REY molecular sieve (rare earth Y molecular sieve), REHY molecular sieve (rare earth hydrogen Y), and REUSY molecular sieve (rare earth ultrastable Y molecular sieve). In some specific embodiments, the Y molecular sieve may include USY molecular sieve and / or REHY molecular sieve.

[0054] In the above-mentioned method for preparing the catalytic cracking catalyst, in step S3, the clay may include one or more of the following: kaolin, halloysite, porous stone, diatomite, and sepiolite.

[0055] The binder includes one or more of aluminum sol, acidified boehmite, silica sol, and phosphoaluminate sol.

[0056] In some specific embodiments, the mass ratio of acid to aluminum oxide in the acidified pseudoboehmite can be 0.05-0.3:1. The acid contained in the acidified pseudoboehmite may include hydrochloric acid and / or nitric acid, etc.

[0057] In the above-described method for preparing the catalytic cracking catalyst, in step S3, the phosphorus source can be converted into P2O5 during the preparation process. The phosphorus source may include one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

[0058] In the above-described method for preparing the catalytic cracking catalyst, in step S3, the calcination temperature is 400℃-600℃, for example, specific values ​​such as 400℃, 450℃, 500℃, 550℃, 600℃, etc., and a range with any two of the above specific values ​​as endpoints. The calcination time is 0.3h-3.0h, for example, specific values ​​such as 0.3h, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, etc., and a range with any two of the above specific values ​​as endpoints.

[0059] In the above-mentioned method for preparing the catalytic cracking catalyst, S3 may further include the operation of ion-exchanging nano ZSM-5 molecular sieves into hydrogen-type molecular sieves.

[0060] That is, S3 may include: ion-exchanging the nano ZSM-5 molecular sieve obtained in S2 to obtain a hydrogen-type molecular sieve, mixing the hydrogen-type molecular sieve with a Y molecular sieve, a binder, a phosphorus source, clay and water to form a slurry, spray drying and calcining to obtain the catalytic cracking catalyst.

[0061] According to a specific embodiment of the present invention, the specific process of the above-mentioned ion exchange can be as follows: mixing nano ZSM-5 molecular sieve with ammonium salt solution, exchanging at 70℃-100℃ for 30min-100min, filtering and washing to obtain the hydrogen-form molecular sieve.

[0062] According to a specific embodiment of the present invention, the preparation method of the above-mentioned catalytic cracking catalyst may include:

[0063] S0. The third silicon source, organic template agent, and second aluminum source are mixed to obtain a precrystallization liquid raw material, which is aged at 60℃-120℃ for 2h-16h to obtain the amorphous molecular sieve precrystallization liquid; the molar ratio of the precrystallization liquid raw material based on oxides is: SiO2:MO:Al2O3:H2O=1:0.02-0.06:0.01-0.05:15-25;

[0064] S1. Mix the first silicon source, the first aluminum source, inorganic alkali, water, and amorphous molecular sieve precrystallization liquid, and age at 100℃-150℃ for 2h-16h to obtain the first raw material mixture.

[0065] S2. Add a second silicon source to the first raw material mixture to obtain a second raw material mixture, wherein the second silicon source includes silica.

[0066] The molar ratio of the second raw material mixture is: m(Na2O):m(SiO2):m(Al2O3):m(H2O)=0.07-0.16:1:0.01-0.05:14-30; the mass of the amorphous molecular sieve precrystallization liquid, the first silicon source, and the second silicon source is based on the mass of SiO2. The mass of the amorphous molecular sieve precrystallization liquid is 1%-10% of the sum of the masses of the first and second silicon sources, and the mass of the second silicon source is 28%-60% of the sum of the masses of the first and second silicon sources.

[0067] The second raw material mixture is crystallized at 140℃-190℃ for 8h-48h, filtered, washed, dried, and calcined at 500℃-700℃ for 3h-7h to obtain the nano ZSM-5 molecular sieve.

[0068] S3. The nano ZSM-5 molecular sieve is mixed with Y molecular sieve, binder, phosphorus source, clay and water, and pulped to form a slurry with a solid content of 30%-50%. The slurry is spray-dried and calcined at 400℃-600℃ for 0.3h-3.0h to obtain the catalytic cracking catalyst.

[0069] The catalyst, calculated on a dry basis as 100%, comprises the following components on a dry basis: 20%-50% nano ZSM-5 molecular sieve, 5%-15% Y-type molecular sieve, 3%-8% binder, 5%-10% P2O5, and 30%-50% clay.

[0070] This invention also provides a catalytic cracking catalyst, which is obtained by the above-described method for preparing the catalytic cracking catalyst. The catalytic cracking catalyst provided by this invention uses nano-ZSM-5 molecular sieve as the active component. This molecular sieve has abundant nanocrystalline aggregates with mesoporous and macroporous structures, thereby obtaining a catalytic cracking catalyst with high propylene selectivity.

[0071] This invention also provides a process for catalytic cracking to produce propylene, which uses the aforementioned catalytic cracking catalyst. When applied to the catalytic cracking process, the aforementioned catalytic cracking catalyst exhibits high propylene selectivity.

[0072] The beneficial effects of this invention include:

[0073] 1. The preparation method provided by the present invention utilizes an amorphous pre-crystallization liquid to provide growth sites and adds the first silicon source and the second silicon source in stages, which can reduce the primary particle size of ZSM-5 molecular sieve and reduce the aggregation and interactive growth of nanocrystals. The resulting hierarchical porous ZSM-5 molecular sieve is a hierarchical porous ZSM-5 molecular sieve nanocrystal aggregate with a large specific surface area and abundant pore structure (especially abundant medium and large pore structure).

[0074] 2. The catalytic cracking catalyst provided by this invention contains nano-ZSM-5 molecular sieves, whose large specific surface area significantly improves the accessibility of reactants to active sites. Simultaneously, the abundant pores promote rapid diffusion of product molecules, which is beneficial for improving reaction conversion rate and product selectivity. When applied to propylene production, this catalytic cracking catalyst exhibits high propylene selectivity. Attached Figure Description

[0075] Figure 1 This is a TEM image of the ZSM-5 molecular sieve prepared in Example 3.

[0076] Figure 2 TEM image of the ZSM-5 molecular sieve prepared in Comparative Example 1.

[0077] Figure 3 This is a TEM image of the ZSM-5 molecular sieve prepared in Comparative Example 2.

[0078] Figure 4 This is a TEM image of the ZSM-5 molecular sieve prepared in Comparative Example 3. Detailed Implementation

[0079] 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.

[0080] The analytical methods used in the following examples and comparative examples are as follows:

[0081] The morphology and particle size of the samples were characterized using an EM-2010 transmission electron microscope (TEM). The pore structure was characterized using a Micron ASAP 2010 nitrogen adsorption analyzer. Samples were degassed at 300℃ for 12 hours before testing. Specific surface area was calculated using the BET method, while pore volume, micropore volume, and external specific surface area were calculated using the t-plot method. The volume of mesopores was calculated as: pore volume - micropore volume.

[0082] The sources of raw materials used in the following examples and comparative examples are as follows:

[0083] 1. Tetrapropylammonium hydroxide (TPAOH), 25% (w / w) aqueous solution;

[0084] 2. NaOH and NaAlO2, commercially available;

[0085] 3. Water glass (SiO2, 250 g / L; Na2O, 88 g / L), aluminum sulfate (Al2O3, 90 g / L);

[0086] 4. Silica sol (40% silica by mass);

[0087] 5. White carbon black (SiO2 dry basis content, 99%), reduced by 13.04wt% (moisture content), model: ZQ-602, Zhuzhou Xinglong New Material Co., Ltd.

[0088] 6. Tetraethyl orthosilicate, analytical grade;

[0089] 7. Phosphoric acid, ammonium phosphate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate, purchased commercially;

[0090] 8. Kaolin (loss on ignition 15.96%), purchased commercially;

[0091] 9. Aluminum sol (alumina mass content, 20.15%), REUSY (loss on ignition 3.8%, cell constant 2.455 nm), boehmite (loss on ignition 37.26%);

[0092] 10. Silica gel, reduce (moisture content) by 12.74 wt%.

[0093] Example 1

[0094] This embodiment provides a catalytic cracking catalyst, the preparation method of which includes:

[0095] 1. Dissolve sodium aluminate in water. After complete dissolution, add tetrapropylammonium hydroxide (TPAOH) aqueous solution (TPAOH mass fraction 25%) and tetraethyl orthosilicate while stirring. Stir at room temperature for 4.5 h to hydrolyze the tetraethyl orthosilicate, obtaining a mixed solution. The molar ratio of the materials in the mixed solution satisfies:

[0096] SiO2:(TPA)2O:Al2O3:H2O=1:0.034:0.018:21.

[0097] The mixed solution was then transferred to a reaction vessel and aged at 96°C for 10.2 hours to obtain a clear amorphous precrystallized solution.

[0098] 2. Add 1305.42g of water to 35.35g of sodium aluminate, 7.70g of sodium hydroxide, and 1.13g of sodium carbonate, and stir for 41 minutes. Then, while stirring, slowly add 355.3g of silica sol as the first silicon source. After the silica sol is added, continue stirring for 77 minutes. Then, add amorphous pre-crystallization liquid to the system to form the first raw material mixture, and continue stirring for 1.1 hours. After stirring, transfer the material to a reactor and age it at 106℃ for 14 hours. After aging, add 94.74g of silica as the second silicon source to form a gel (as the second raw material mixture). The molar ratio of the resulting gel is: m(Na2O):m(SiO2):m(Al2O3):m(H2O)=0.08:1:0.038:22. After stirring for 1.5 hours, raise the reactor temperature to 183℃ and stir for 10.3 hours for crystallization. After crystallization, the obtained material was filtered, washed, dried, and calcined at 600℃ for 4.4 h to obtain nano-ZSM-5 molecular sieve NZ-1. The amount of pre-crystallization solution added was as follows: based on the SiO2 in the pre-crystallization solution, the first silicon source, and the second silicon source, the weight ratio of the pre-crystallization solution to the total SiO2 of the first and second silicon sources was 8%, and the mass of the second silicon source was 40% of the sum of the masses of the first and second silicon sources.

[0099] TEM analysis revealed that NZ-1 was composed of primary nanoparticles with a particle size of 83 nm. N2 adsorption analysis showed that NZ-1 had a BET specific surface area of ​​361.8 m². 2 ·g -1 The pore volume is 0.33 cm³. 3 ·g -1 The pore volume of medium to large pores is 0.20 cm³. 3 ·g -1 .

[0100] 3. Take 80g of HNZ-1 molecular sieve and mix it evenly with 410g of water. Then add 16.5g of solid NH4Cl to the slurry, heat to 89℃, stir and exchange at 89℃ for 33min, then filter, wash and dry to obtain hydrogen-form molecular sieve HNZ-1.

[0101] The prepared HNZ-1 molecular sieve was mixed with water to form a slurry with a solid content of 41%. The mixture was then spray-molded and calcined at 455℃ for 48 min to obtain the catalytic cracking catalyst CAT-1.

[0102] Example 2

[0103] This embodiment provides a catalytic cracking catalyst, the preparation method of which includes:

[0104] 1. Dissolve sodium aluminate in water. After complete dissolution, add tetrapropylammonium hydroxide (TPAOH) aqueous solution (TPAOH mass fraction 25%) and tetraethyl orthosilicate while stirring. Stir at room temperature for 3.4 h to hydrolyze the tetraethyl orthosilicate, obtaining a mixed solution. The molar ratio of the materials in the mixed solution satisfies:

[0105] SiO2:(TPA)2O:Al2O3:H2O=1:0.025:0.025:16.

[0106] The mixed solution was then transferred to a reaction vessel and aged at 85°C for 9.4 hours to obtain a clear amorphous precrystallized solution.

[0107] 2. 1651.13g of water, 1107.75g of water glass (used as the first silicon source) and inorganic alkali were mixed evenly. 167.92g of aluminum sulfate solution was added while stirring, and stirring continued for 38 minutes. Then, an amorphous pre-crystallized liquid was added to the system to form the first raw material mixture, and stirring continued for 0.9 hours. After stirring, the material was transferred to a reactor and aged at 135℃ for 8 hours. After aging, 251.55g of silica (used as the second silicon source) was added to form a gel. The molar ratio of the resulting gel was: m(Na₂O):m(SiO₂):m(Al₂O₃):m(H₂O) = 0.12:1:0.016:20. After stirring for 1.2 hours, the reactor temperature was raised to 159℃, and the crystallization reaction was carried out for 20 hours. After crystallization, the resulting material was filtered, washed, dried, and calcined at 620℃ for 5.2 hours to obtain nano-ZSM-5 molecular sieve NZ-2.

[0108] The amount of precrystallization liquid added is as follows: based on the SiO2 in the precrystallization liquid, the first silicon source, and the second silicon source, its weight ratio with the total SiO2 in the first and second silicon sources is 3%, and the mass of the second silicon source is 50% of the sum of the masses of the first and second silicon sources.

[0109] TEM analysis revealed that the obtained NZ-2 was composed of primary nanoparticles with a particle size of 63 nm. N2 adsorption showed that the BET specific surface area of ​​NZ-2 was 379.2 m².2 ·g -1 The pore volume is 0.38 cm³. 3 ·g -1 The pore volume of medium to large pores is 0.25 cm³. 3 ·g -1 .

[0110] 3. Take 100g of NZ-2 molecular sieve and mix it evenly with 745g of water. Then add 10.6g of solid (NH4)2SO4 to the slurry, heat to 84℃, stir and exchange at 84℃ for 48min, then filter, wash and dry to obtain hydrogen-form molecular sieve HNZ-2.

[0111] The prepared HNZ-2 molecular sieve was mixed with water to form a slurry with a solid content of 43%. The slurry was then spray-molded and calcined at 490℃ for 1.9 h to obtain the catalytic cracking catalyst CAT-2.

[0112] Example 3

[0113] This embodiment provides a catalytic cracking catalyst, the preparation method of which includes:

[0114] 1. Dissolve sodium aluminate in water. After complete dissolution, add tetrapropylammonium hydroxide (TPAOH) aqueous solution (TPAOH mass fraction 25%) and tetraethyl orthosilicate while stirring. Stir at room temperature for 2.5 h to hydrolyze the tetraethyl orthosilicate, obtaining a mixed solution. The molar ratio of the materials in the mixed solution satisfies:

[0115] SiO2:(TPA)2O:Al2O3:H2O=1:0.04:0.015:22.

[0116] The mixed solution was then transferred to a reaction vessel and aged at 110°C for 4 hours to obtain a clear amorphous precrystallized solution.

[0117] 2. Mix 1487.07g of water, 874.14g of water glass (as the first silicon source), and inorganic alkali evenly. Add 143.93g of aluminum sulfate solution while stirring, and continue stirring for 65 minutes. Then, add 450ml of amorphous pre-crystallization liquid to the system to form the first raw material mixture, and continue stirring for 2.1 hours. After stirring, transfer the material to a reactor and age it at 130℃ for 9 hours. After aging, add 88.98g of silica (as the second silicon source) to form a gel. The molar ratio of the resulting gel is: m(Na2O):m(SiO2):m(Al2O3):m(H2O) = 0.16:1:0.024:30. Stir for 1.7 hours, then raise the reactor temperature to 150℃ and stir for crystallization for 30 hours. After crystallization, filter, wash, and dry the resulting material, and calcine it at 570℃ for 5.1 hours to obtain nano-ZSM-5 molecular sieve NZ-3.

[0118] The amount of precrystallization liquid added is as follows: based on the SiO2 in the precrystallization liquid, the first silicon source, and the second silicon source, the weight ratio of the precrystallization liquid to the total SiO2 of the first and second silicon sources is 5%, and the mass of the second silicon source is 31% of the sum of the masses of the first and second silicon sources.

[0119] TEM analysis revealed that the obtained NZ-3 was composed of primary nanoparticles with a particle size of 25 nm. N2 adsorption showed that the BET specific surface area of ​​NZ-3 was 410.5 m². 2 ·g -1 The pore volume is 0.51 cm³. 3 ·g -1 The pore volume of the medium-to-large pores is 0.39 cm³. 3 ·g -1 .

[0120] 3. Take 100g of NZ-3 molecular sieve and mix it evenly with 830g of water. Then add 5.9g of solid NH4NO3 to the slurry, add hydrochloric acid solution to adjust the pH to 2.4, heat to 99℃, stir and exchange at 99℃ for 98min, then filter, wash and dry to obtain hydrogen-form molecular sieve HNZ-3.

[0121] The prepared HNZ-3 molecular sieve was mixed with water to form a slurry with a solid content of 45%. The mixture was then spray-molded and calcined at 542℃ for 1.2 h to obtain the catalytic cracking catalyst CAT-3.

[0122] Example 4

[0123] This embodiment provides a catalytic cracking catalyst, the preparation method of which includes:

[0124] 1. Dissolve sodium aluminate in water. After complete dissolution, add tetrapropylammonium hydroxide (TPAOH) aqueous solution (TPAOH mass fraction 25%) and tetraethyl orthosilicate while stirring. Stir at room temperature for 1.9 h to hydrolyze the tetraethyl orthosilicate, obtaining a mixed solution. The molar ratio of the materials in the mixed solution satisfies:

[0125] SiO2:(TPA)2O:Al2O3:H2O=1:0.029:0.031:18.

[0126] The mixed solution was then transferred to a reaction vessel and aged at 103°C for 8.1 hours to obtain a clear amorphous precrystallized solution.

[0127] 2. Mix 854.91g of water, 666.91g of water glass (as the first silicon source), and inorganic alkali evenly. Add 143.93g of aluminum sulfate solution while stirring, and continue stirring for 73 minutes. Then, add amorphous pre-crystallized liquid to the system to form the first raw material mixture, and continue stirring for 2.2 hours. After stirring, transfer the material to a reactor and age it at 142℃ for 4.6 hours. After aging, add 64.17g of silica (as the second silicon source) to form a gel. The molar ratio of the resulting gel is: m(Na2O):m(SiO2):m(Al2O3):m(H2O) = 0.14:1:0.032:26. Stir for 1.5 hours, then raise the reactor temperature to 169℃ and stir for crystallization for 12.3 hours. After crystallization, filter, wash, and dry the resulting material, and calcine it at 550℃ for 5.6 hours to obtain nano-ZSM-5 molecular sieve NZ-4.

[0128] The amount of precrystallization liquid added is as follows: based on the SiO2 in the precrystallization liquid, the first silicon source, and the second silicon source, the weight ratio of the precrystallization liquid to the total SiO2 of the first and second silicon sources is 4%, and the mass of the second silicon source is 30% of the sum of the masses of the first and second silicon sources.

[0129] TEM analysis revealed that the obtained NZ-4 was composed of primary nanoparticles with a particle size of 58 nm. N2 adsorption showed that the BET specific surface area of ​​NZ-4 was 384.6 m². 2 ·g -1 The pore volume is 0.42 cm³. 3 ·g -1 The pore volume of the medium-to-large pores is 0.29 cm³. 3 ·g -1 .

[0130] 3. Take 100g of NZ-4 molecular sieve and mix it evenly with 670g of water. Then add 24g of solid (NH4)2SO4 to the slurry, heat to 78℃, stir and exchange at 78℃ for 73min, then filter, wash and dry to obtain hydrogen-form molecular sieve HNZ-4.

[0131] The prepared HNZ-4 molecular sieve was mixed with water to form a slurry with a solid content of 44%. The slurry was then spray-molded and calcined at 520℃ for 1.4 h to obtain the catalytic cracking catalyst CAT-4.

[0132] Example 5

[0133] This embodiment provides a catalytic cracking catalyst, the preparation method of which includes:

[0134] 1. Dissolve sodium aluminate in water. After complete dissolution, add tetrapropylammonium hydroxide (TPAOH) aqueous solution (TPAOH mass fraction 25%) and tetraethyl orthosilicate while stirring. Stir at room temperature for 3.9 h to hydrolyze the tetraethyl orthosilicate, obtaining a mixed solution. The molar ratio of the materials in the mixed solution satisfies:

[0135] SiO2:(TPA)2O:Al2O3:H2O=1:0.053:0.035:25.

[0136] The mixed solution was then transferred to a reaction vessel and aged at 68°C for 14.6 hours to obtain a clear amorphous precrystallized solution.

[0137] 2. Add 1616.55g of water to 16.50g of sodium aluminate solution and 21.68g of sodium hydroxide, and stir for 51min. Then, slowly add 221.05g of silica sol as the first silicon source while stirring. After the silica sol is added, continue stirring for 79min. Then, add amorphous pre-crystallization liquid to the system to form the first raw material mixture, and continue stirring for 1.5h. After stirring, transfer the material to a reactor and age it at 114℃ for 6.3h. After cooling the material, add 132.63g of silica as the second silicon source to form a gel. The molar ratio of the resulting gel is: m(Na2O):m(SiO2):m(Al2O3):m(H2O)=0.10:1:0.019:27. After stirring for 1.7h, raise the temperature of the reactor to 145℃ and stir for 46h for crystallization. After crystallization, the resulting material was filtered, washed, dried, and calcined at 650℃ for 3.9 hours to obtain nano ZSM-5 molecular sieve NZ-5.

[0138] The amount of precrystallization solution added is as follows: based on the SiO2 in the precrystallization solution, the weight ratio of the precrystallization solution to the total SiO2 of the first and second silicon sources is 6%. The mass of the second silicon source is 60% of the sum of the masses of the first and second silicon sources.

[0139] TEM analysis revealed that the obtained NZ-5 was composed of primary nanoparticles with a particle size of 46 nm. N2 adsorption showed that the BET specific surface area of ​​NZ-5 was 398.1 m². 2 ·g -1 The pore volume is 0.47 cm³. 3 ·g -1 The pore volume of the medium-to-large pores is 0.34 cm³. 3 ·g -1 .

[0140] Take 150g of NZ-5 molecular sieve and mix it evenly with 940g of water. Then add 48g of solid NH4Cl to the slurry, heat it to 72℃, stir and exchange it at 72℃ for 77min, and then filter, wash and dry to obtain hydrogen-form molecular sieve HNZ-5.

[0141] The prepared HNZ-5 molecular sieve was mixed with water to form a slurry with a solid content of 42%. The slurry was then spray-molded and calcined at 530℃ for 1.7 h to obtain the catalytic cracking catalyst CAT-5.

[0142] Comparative Example 1

[0143] This comparative example provides a catalytic cracking catalyst, the preparation method of which includes:

[0144] 1. Dissolve sodium aluminate in water. After complete dissolution, add tetrapropylammonium hydroxide (TPAOH) aqueous solution (TPAOH mass fraction 25%) and tetraethyl orthosilicate while stirring. Stir at room temperature for 2.5 h to hydrolyze the tetraethyl orthosilicate, obtaining a mixed solution. The molar ratio of the materials in the mixed solution satisfies:

[0145] SiO2:(TPA)2O:Al2O3:H2O=1:0.04:0.015:22.

[0146] The mixed solution was then transferred to a reaction vessel and aged at 110°C for 4 hours to obtain a clear amorphous precrystallized solution.

[0147] 2. 1487.07g of water, 874.14g of water glass (as the first silicon source), and inorganic alkali were mixed evenly. 143.93g of aluminum sulfate solution was added while stirring, and stirring continued for 65 minutes. Then, 450ml of amorphous pre-crystallization solution and 88.98g of silica (as the second silicon source) were added to the system to form a gel. The molar ratio of the resulting gel was: m(Na₂O):m(SiO₂):m(Al₂O₃):m(H₂O) = 0.16:1:0.024:30. After stirring for 1.7 hours, the reactor was heated to 150℃, and the crystallization reaction was carried out for 30 hours. After crystallization, the resulting material was filtered, washed, dried, and calcined at 570℃ for 5.1 hours to obtain nano-ZSM-5 molecular sieve DZ-1.

[0148] The amount of precrystallization solution added is 5% by weight, based on the SiO2 in the precrystallization solution, the first silicon source, and the second silicon source, and the total SiO2 in the first and second silicon sources. The mass of the second silicon source is 31% of the sum of the masses of the first and second silicon sources.

[0149] TEM analysis revealed that DZ-1 was composed of primary nanoparticles with a particle size of 70 nm. N2 adsorption analysis showed that DZ-1 had a BET specific surface area of ​​345.2 m². 2 ·g -1 The pore volume is 0.24 cm³. 3 ·g -1 The pore volume of the medium-to-large pores is 0.11 cm³. 3 ·g -1 .

[0150] Take 100g of DZ-1 molecular sieve and mix it evenly with 830g of water. Then add 5.9g of solid NH4NO3 to the slurry, add hydrochloric acid solution to adjust the pH to 2.4, heat to 99℃, stir and exchange at 99℃ for 98min, then filter, wash and dry to obtain hydrogen-form molecular sieve HDZ-1.

[0151] The prepared HDZ-1 molecular sieve was mixed with water to form a slurry with a solid content of 45%. The mixture was then spray-molded and calcined at 542℃ for 1.2 h to obtain the catalytic cracking catalyst DC-1.

[0152] Compared with Example 3, in the preparation method of the nano ZSM-5 molecular sieve in this comparative example, the second silicon source is directly added to the first raw material mixture.

[0153] Comparative Example 2

[0154] This comparative example provides a catalytic cracking catalyst, the preparation method of which includes:

[0155] 1. Dissolve sodium aluminate in water. After complete dissolution, add tetrapropylammonium hydroxide (TPAOH) aqueous solution (TPAOH mass fraction 25%) and tetraethyl orthosilicate while stirring. Stir at room temperature for 2.5 h to hydrolyze the tetraethyl orthosilicate, obtaining a mixed solution. The molar ratio of the materials in the mixed solution satisfies:

[0156] SiO2:(TPA)2O:Al2O3:H2O=1:0.04:0.015:22.

[0157] The mixed solution was then transferred to a reaction vessel and aged at 110°C for 4 hours to obtain a clear amorphous precrystallized solution.

[0158] 2. Mix 1487.07g of water, 874.14g of water glass (as the first silicon source), and inorganic alkali evenly. Add 143.93g of aluminum sulfate solution while stirring, and continue stirring for 65 minutes. Then add 450ml of amorphous pre-crystallization solution to the system and continue stirring for 2.1 hours. After stirring, transfer the material to a reactor and age it at 130℃ for 9 hours. After cooling, add 88.98g of silica gel as the second silicon source to form a gel. The molar ratio of the resulting gel is: m(Na2O):m(SiO2):m(Al2O3):m(H2O) = 0.16:1:0.024:30. Stir for 1.7 hours, then raise the reactor temperature to 150℃ and stir for 30 hours for crystallization. After crystallization, filter, wash, and dry the resulting material, and calcine it at 570℃ for 5.1 hours to obtain nano-ZSM-5 molecular sieve DZ-2.

[0159] The amount of precrystallization solution added is 5% by weight, based on the SiO2 in the precrystallization solution, the first silicon source, and the second silicon source, and the total SiO2 in the first and second silicon sources. The mass of the second silicon source is 31% of the sum of the masses of the first and second silicon sources.

[0160] TEM analysis revealed that the obtained DZ-2 was composed of primary nanoparticles with a particle size of 60 nm. N2 adsorption showed that the BET specific surface area of ​​DZ-2 was 354.7 m². 2 ·g -1 The pore volume is 0.26 cm³. 3 ·g -1 The pore volume of the medium-to-large pores is 0.14 cm³. 3 ·g -1 .

[0161] 3. Take 100g of DZ-2 molecular sieve and mix it evenly with 830g of water. Then add 5.9g of solid NH4NO3 to the slurry, add hydrochloric acid solution to adjust the pH to 2.4, heat to 99℃, stir and exchange at 99℃ for 98min, then filter, wash and dry to obtain hydrogen-form molecular sieve HDZ-2.

[0162] The prepared HDZ-2 molecular sieve was mixed with water to form a slurry with a solid content of 45%. The mixture was then spray-molded and calcined at 542℃ for 1.2 h to obtain the catalytic cracking catalyst DC-2.

[0163] Compared with Example 3, in the preparation method of the nano ZSM-5 molecular sieve in this comparative example, silica sol is used instead of silica as the second silicon source.

[0164] Comparative Example 3

[0165] This comparative example provides a catalytic cracking catalyst, the preparation method of which includes:

[0166] 1. Dissolve sodium aluminate in water. After complete dissolution, add tetrapropylammonium hydroxide (TPAOH) aqueous solution (TPAOH mass fraction 25%) and tetraethyl orthosilicate while stirring. Stir at room temperature for 2.5 h to hydrolyze the tetraethyl orthosilicate, obtaining a mixed solution. The molar ratio of the materials in the mixed solution satisfies:

[0167] SiO2:(TPA)2O:Al2O3:H2O=1:0.04:0.015:22.

[0168] The mixed solution was then transferred to a reaction vessel and aged at 110°C for 4 hours to obtain a clear amorphous precrystallized solution.

[0169] 2. Mix 1199.98g of water and 1265.98g of water glass thoroughly. Add 143.93g of aluminum sulfate solution and 23.55ml of concentrated sulfuric acid while stirring. Continue stirring for 65 minutes. Then add 450ml of amorphous pre-crystallization solution and continue stirring for 2.1 hours. After stirring, transfer the material to a reactor and age at 130℃ for 9 hours to obtain a gel. The molar ratio of the obtained gel is: m(Na₂O):m(SiO₂):m(Al₂O₃):m(H₂O) = 0.16:1:0.024:30. After stirring for 1.7 hours, raise the reactor temperature to 150℃ and stir for crystallization for 30 hours. After crystallization, filter, wash, and dry the obtained material, then calcine at 570℃ for 5.1 hours to obtain nano-ZSM-5 molecular sieve DZ-3.

[0170] The amount of precrystallization liquid added is: based on the weight ratio of the precrystallization liquid to the SiO2 in the first silicon source, the weight ratio of the precrystallization liquid to the SiO2 in the first silicon source is 5%.

[0171] TEM analysis revealed that the obtained DZ-3 was composed of primary nanoparticles with a particle size of 60 nm. N2 adsorption showed that the BET specific surface area of ​​DZ-3 was 335.4 m². 2 ·g -1 The pore volume is 0.22 cm³. 3 ·g -1 The pore volume of medium and large pores is 0.10 cm³. 3 ·g -1 .

[0172] 3. Take 100g of DZ-3 molecular sieve and mix it evenly with 830g of water. Then add 5.9g of solid NH4NO3 to the slurry, add hydrochloric acid solution to adjust the pH to 2.4, heat to 99℃, stir and exchange at 99℃ for 98min, then filter, wash and dry to obtain hydrogen-form molecular sieve HDZ-2.

[0173] The prepared HDZ-3 molecular sieve was mixed with water to form a slurry with a solid content of 45%. The mixture was then spray-molded and calcined at 542℃ for 1.2 h to obtain the catalytic cracking catalyst DC-3.

[0174] Compared to Example 3, this comparative example only has a first silicon source and no second silicon source is added. Water glass is used as the first silicon source and is added all at once.

[0175] Test Example 1

[0176] This test example provides the structural characterization results of the nano ZSM-5 molecular sieves prepared in the above embodiments and comparative examples.

[0177] The structural parameters of the nano ZSM-5 molecular sieves prepared in the above examples and comparative examples are summarized in Table 1.

[0178] Table 1

[0179]

[0180] Figure 1 , Figure 2 , Figure 3 , Figure 4 The images are TEM images of nano ZSM-5 molecular sieves from Example 3, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively.

[0181] Will Figures 1 to 4It can be seen that, Figure 2 The aging process before adding the second silicon source is omitted. Figure 3 In this study, silica gel was used instead of silica as the second silicon source. Figure 4 The presence of only the first silicon source will cause the molecular sieve crystals to pack tightly together during growth, growing interactively with each other, which will cause the mesoporous and macroporous structures to dissolve.

[0182] In comparison, Figure 1 The molecular sieve crystals are relatively small, and the aggregation and interactive growth between the crystals are weak, resulting in a distinct medium-to-large pore structure in the molecular sieve samples.

[0183] The above results demonstrate that by adding a second silicon source containing silica and aging it before adding the second silicon source, this invention can reduce the aggregation and cross-growth between molecular sieve grains, resulting in a molecular sieve with abundant channel structure (especially mesoporous and macroporous structures) and small grain structure. The large external surface area of ​​the nano-molecular sieve can significantly improve the accessibility of reactants to active centers, while the small particle size can promote the rapid diffusion of products, which is beneficial to improving reaction conversion rate and product selectivity.

[0184] Test Example 2

[0185] This test case provides the performance test results of the catalytic cracking catalysis of the above embodiments and comparative examples.

[0186] The reaction performance was evaluated using a fixed-flow particle bed reactor. The feedstock used was from the 3 million tons / year heavy oil catalytic cracking unit of Lanzhou Petrochemical, and its properties are shown in Table 2. The catalyst was aged at 800℃ with 100% steam for 10 hours before evaluation. The reaction temperature was 600℃, and the catalyst-to-oil mass ratio was 4.0.

[0187] Table 2 Properties of feedstock used for catalyst selectivity assessment

[0188]

[0189] The reaction evaluation data of the catalytic cracking catalysts in the above embodiments and the comparative catalytic cracking catalysts are shown in Table 3. All values ​​in Table 3 are in mass percentage.

[0190] Table 3 Reaction performance of catalytic cracking catalysts

[0191]

[0192] *Total liquid yield = Gasoline yield + Diesel yield + LPG yield

[0193] As shown in the fixed-bed evaluation data in Table 3, compared with the comparative catalyst, the catalytic cracking catalyst prepared by the present invention has significantly improved the liquefied gas yield and propylene yield, demonstrating excellent propylene production enhancement performance.

[0194] The test results above show that by adding silica as a second silicon source during the preparation of nano-ZSM-5 molecular sieves and performing aging treatment before the second silicon source, this invention can reduce the aggregation and cross-growth between molecular sieve grains. This results in a molecular sieve with abundant channel structure (especially mesopore and macropore structure) and small grain structure, thereby increasing the specific surface area, pore volume, and mesopore and macropore volume of the ZSM-5 molecular sieve. The large external specific surface area of ​​the molecular sieve can significantly improve the accessibility of reactants to active sites, while the small particle size can promote the rapid diffusion of products, which is beneficial to improving reaction conversion rate and product selectivity, thereby improving the catalytic activity and propylene selectivity of the catalytic cracking catalyst made from this molecular sieve.

Claims

1. A method for preparing a catalytic cracking catalyst, the method comprising: S1. Mix the first silicon source, the first aluminum source, inorganic alkali, water, and amorphous molecular sieve precrystallization liquid, and age them to obtain the first raw material mixture; S2. Add a second silicon source to the first raw material mixture to obtain a second raw material mixture, crystallize, filter, wash, dry, and calcine to obtain nano ZSM-5 molecular sieve; wherein, the second silicon source includes silica. The second raw material mixture satisfies the following molar ratio: m(Na2O):m(SiO2):m(Al2O3):m(H2O)=0.07-0.16:1:0.01-0.05:14-30; S3. The nano ZSM-5 molecular sieve is mixed with Y molecular sieve, binder, phosphorus source, clay and water, pulped to form a slurry, spray dried and calcined to obtain the catalytic cracking catalyst.

2. The production method according to claim 1, wherein, The preparation method of the amorphous molecular sieve precrystallization liquid includes: mixing a third silicon source, an organic template agent, and a second aluminum source to obtain a precrystallization liquid raw material, aging it, and obtaining the amorphous molecular sieve precrystallization liquid.

3. The preparation method according to claim 2, wherein, In the preparation method of amorphous molecular sieve precrystallization liquid, the raw materials of the precrystallization liquid, based on oxides, satisfy the following molar ratio: SiO2:MO:Al2O3:H2O=1:0.02-0.06:0.01-0.05:15-25; MO stands for the oxide corresponding to the organic template agent.

4. The preparation method according to claim 2, wherein, In the preparation method of amorphous molecular sieve precrystallization liquid, the aging temperature is 60℃-120℃ and the aging time is 2h-16h.

5. The preparation method according to claim 1, wherein, The second raw material mixture satisfies the following molar ratio: m(Na2O):m(SiO2):m(Al2O3):m(H2O)=0.08-0.16:1:0.015-0.04:20-30.

6. The preparation method according to claim 1, wherein, The mass of the amorphous molecular sieve precrystallization liquid, the first silicon source, and the second silicon source is based on the mass of SiO2, and the mass of the amorphous molecular sieve precrystallization liquid is 1%-10% of the sum of the masses of the first silicon source and the second silicon source.

7. The preparation method according to claim 1, wherein, The masses of the first silicon source and the second silicon source are expressed as SiO2 mass, and the mass of the second silicon source is 28%-60% of the sum of the masses of the first silicon source and the second silicon source.

8. The preparation method according to claim 1, wherein, The first silicon source includes one or more of water glass, silica gel, silica sol, and precipitated silica.

9. The preparation method according to claim 1, wherein, The first aluminum source includes one or a combination of two or more of aluminum sulfate, sodium aluminate, aluminum chloride, and aluminum nitrate.

10. The preparation method according to claim 1, wherein, In S1, the aging temperature is 100℃-150℃, and the aging time is 2h-16h.

11. The preparation method according to claim 1, wherein, In S2, the crystallization temperature is 140℃-190℃, and the crystallization time is 8h-48h.

12. The preparation method according to claim 1, wherein, In S3, the catalyst comprises the following components by dry weight, calculated as 100% of the total dry weight of the catalyst: 20%-50% nano ZSM-5 molecular sieve, 5%-15% Y-type molecular sieve, 3%-8% binder, 5%-10% P2O5, and 30%-50% clay.

13. The preparation method according to claim 1, wherein, In S3, the Y molecular sieve includes one or more of USY molecular sieve, HY molecular sieve, REY molecular sieve, REHY molecular sieve, and REUSY molecular sieve; The clay includes one or more of the following: kaolin, halloysite, porous stone, diatomite, and sepiolite. The binder includes one or more of aluminum sol, acidified boehmite, silica sol and phosphogypsum sol; The phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

14. A catalytic cracking catalyst, wherein the catalytic cracking catalyst is obtained by the preparation method according to any one of claims 1-13.

15. A process for catalytic cracking to produce propylene, wherein the process uses the catalytic cracking catalyst of claim 14.

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