Preparation method of composite molecular sieve and application thereof in heavy oil cracking
By preparing ZSM-5/Y composite molecular sieves with a low silicon-to-aluminum ratio, a mesoporous-microporous structure is formed, which solves the problem that heavy oil macromolecules are difficult to enter the pores, improves the efficiency of heavy oil catalytic cracking and propylene yield, and reduces coke production, making it suitable for petrochemical catalytic cracking.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANDONG CHAMBROAD PETROCHEMICALS CO LTD
- Filing Date
- 2024-03-14
- Publication Date
- 2026-06-23
AI Technical Summary
Existing composite molecular sieves have small pore sizes in the heavy oil catalytic cracking process, making it difficult for large heavy oil molecules to enter the pores, resulting in low catalytic efficiency. Existing catalysts also perform poorly in heavy oil cracking.
A method for preparing ZSM-5/Y composite molecular sieves with a low silicon-to-aluminum ratio was adopted. By forming a hollow structure in the Y-type molecular sieve and combining it with ZSM-5 seed crystals, a mesoporous-microporous composite structure was formed, and a molded catalyst was prepared for heavy oil catalytic cracking.
It improves the activity and selectivity of heavy oil catalytic cracking, increases the yield of liquefied petroleum gas and propylene, and reduces the yield of coke, making it suitable for the petrochemical catalytic cracking field.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalytic cracking catalysts and their preparation, and particularly relates to a method for preparing a composite molecular sieve and its application in heavy oil cracking. Background Technology
[0002] Fluid catalytic cracking (FCC) is a core technology in modern oil refining, primarily used to convert high-boiling-point, high-molecular-weight petroleum fractions into more valuable fuels such as gasoline, diesel, liquefied petroleum gas (LPG), and olefins. The active component of the cracking catalyst used in FCC units is mainly Y-type molecular sieves (crystal size of approximately 1 μm), which exhibit high activity and selectivity. The resulting gasoline fraction contains a higher proportion of alkanes and aromatics, and a lower proportion of olefins. However, with the increasing weight and deterioration of crude oil quality, refineries are blending heavier oils year by year, placing higher demands on the FCC process.
[0003] The key to innovation in FCC technology lies primarily in the development of catalysts. Various molecular sieve catalytic cracking catalysts generally consist of an active component and a matrix. Catalysts with Y-type molecular sieves as the main active component are widely used in catalytic cracking. Commonly used molecular sieve types in the gas industry include A-type, X-type, Y-type, and -M-type. Among them, ZSM-5 molecular sieve is a zeolite molecular sieve containing organic amine cations, belonging to the orthorhombic crystal system. Its silicon-aluminum molar ratio can be varied over a wide range, making it one of the important catalytic materials for shape-selective reactions in the petroleum industry. However, in heavy oil cracking applications, due to the small pore size of ZSM-5 molecular sieves, large heavy oil molecules have difficulty entering the pores, resulting in low utilization of its internal surface active centers and consequently, low efficiency in catalytic cracking of heavy oil.
[0004] Many researchers hope to synthesize novel catalytic materials for the catalytic cracking of heavy oil by achieving a gradient distribution of pore structures and a rational combination of acidity. Mesoporous-microporous composite materials and hierarchical zeolite materials have attracted widespread attention. Recent research results show that novel composite molecular sieve materials containing different acidity centers and pore structures, synthesized using special techniques, such as the ZSM-5-encapsulated Y-type composite molecular sieve, often exhibit superior performance compared to single molecular sieves and mechanically mixed molecular sieves in solid acid catalysis. However, existing composite or mixed-structure catalysts are not well-suited for the catalytic cracking of heavy oil macromolecules, exhibiting poor catalytic performance. Summary of the Invention
[0005] To address the above problems, this invention provides a method for preparing a composite molecular sieve and its application in heavy oil cracking. The method of this invention can synthesize a ZSM-5 / Y composite molecular sieve with a low silica-alumina ratio, exhibiting high activity and high selectivity. When this sieve is used to prepare a catalyst for heavy oil catalytic cracking, it can meet the current needs of the transformation from oil refining to chemical products.
[0006] This invention provides a method for preparing a composite molecular sieve, comprising the following steps:
[0007] Aluminum source, silicon source and structure guiding agent are mixed and dissolved in water, and then crystallization treatment is performed to obtain ZSM-5 seed solution;
[0008] The Y-type molecular sieve is etched in water with an alkaline substance to form a hollow structure, and then mixed with acidic silica sol to obtain a solution containing hollow Y-type molecular sieve.
[0009] The ZSM-5 seed solution and the solution containing hollow Y-type molecular sieve are mixed and heated to crystallize. The crystallized product is then separated, washed, dried, and calcined to obtain the ZSM-5 / Y composite molecular sieve.
[0010] The ZSM-5 / Y composite molecular sieve was subjected to an ion exchange reaction with an ammonium salt, and then calcined to obtain an H-type ZSM-5 / Y composite molecular sieve product.
[0011] This invention mainly designs a method for synthesizing ZSM-5 / Y composite molecular sieves, and the catalyst prepared from them for application in the field of heavy oil catalytic cracking. The composite molecular sieve synthesized in this invention, when prepared into a catalyst, exhibits advantages such as high activity and good selectivity, achieving high yields of liquefied petroleum gas and propylene. It is particularly suitable for the petrochemical catalytic cracking field and has significant implications for the development of catalytic cracking technology.
[0012] In embodiments of the present invention, a low silicon-to-aluminum ratio ZSM-5 seed solution is first synthesized at a relatively low temperature and time. Specifically, an aluminum source, a structure-directing agent, and a silicon source are dissolved in a certain proportion to form a clear solution, which is then crystallized at a certain temperature for 2–72 hours to obtain the ZSM-5 seed solution. The aluminum source is one or more of aluminate, aluminum sol, and aluminum hydroxide, and more specifically sodium aluminate, aluminum sol, or aluminum hydroxide. The silicon source is one or more of tetraethyl orthosilicate, tetrabutyl orthosilicate, and silica gel, for example, tetraethyl orthosilicate is used as the silicon source. The structure-directing agent is mainly one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, and n-butylamine to synthesize the seed solution, with a silicon-to-aluminum ratio of 10–50. Furthermore, the crystallization treatment temperature is 343K–373K, and the mixture can be treated in a reaction vessel for 4–50 hours, such as 5–15 hours. The silicon-aluminum ratio = silicon oxide / aluminum oxide (molar ratio). This refers to the ratio of silicon and aluminum raw materials added during seed crystal synthesis when converted into oxides. Theoretically, it is consistent with the silicon-aluminum ratio of the final seed crystal.
[0013] Some embodiments of the present invention utilize alkali treatment of NaY-type molecular sieves to obtain hollow Y-type molecular sieves; the steps include: adding an alkaline substance to water, stirring evenly, then adding NaY-type molecular sieves, and stirring at a certain temperature for 2 to 10 hours; adding a certain amount of acidic silica sol to the obtained NaY-type molecular sieve suspension, and stirring for 0.5 to 2 hours.
[0014] The alkaline substance is one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, and sodium hydroxide. The alkaline substance, when mixed with water, forms an etching solution. After adding a Y-type molecular sieve (preferably a NaY-type molecular sieve) and stirring, a hollow structure is formed. The alkalinity of the etching solution is preferably 2–10; the mass ratio of the Y-type molecular sieve to the etching solution is 0.05–0.2. Alkalinity is a parameter representing the ability of water to absorb protons, usually determined by the total amount of substances in water that can quantitatively react with strong acids. The stirring temperature is 293K–313K, and the time is 2–10 hours, with a further stirring time of 2 hours–6 hours. After the addition of the acidic silica sol, the pH value of the solution is preferably 10–12. The acidic silica sol, also known as silica hydrosol, is a colloidal solution of high-molecular-weight silica particles dispersed in water. Commercially available products are acceptable; for example, the silica mass fraction of acidic silica sol is 30%, and the pH value is 2–4.
[0015] In this embodiment of the invention, the treated NaY molecular sieve solution is mixed with a ZSM-5 seed solution and crystallized under dynamic conditions. Preferably, the mixture is stirred evenly and then crystallized under dynamic conditions with increased temperature for 10–120 h to obtain a ZSM-5 / Y composite molecular sieve. In this embodiment, the ZSM-5 crystal growth involves two processes: first, the formation of numerous crystal nuclei at a temperature of 343 K–373 K; and second, the growth and bonding of crystals that have diffused into the hollow structure of the Y molecular sieve. In this embodiment, a certain amount of acidic silica sol is added to the Y molecular sieve suspension formed after alkali treatment of the NaY molecular sieve. Its main function is to adjust the pH, and it can also serve as a silicon source for ZSM-5 crystal growth along with the extracted silicon species. During the secondary crystallization process, the ZSM-5 crystals grow and combine with the Y molecular sieve.
[0016] Preferably, the mass ratio of the ZSM-5 seed solution to the Y-type molecular sieve is 0.5–2. The preferred temperature for the heated crystallization is 373 K–398 K, for example, 393 K; the time can be 10–120 h, with further heated crystallization for 15–90 h, etc. Because the ZSM-5 seed has a low silica-alumina ratio, by controlling the ratio of ZSM-5 seed to Y-type molecular sieve suspension, secondary growth of ZSM-5 crystals in the hollow Y-type molecular sieve can be achieved. In this embodiment of the invention, the ZSM-5 molecular sieve grows within the treated hollow structure of the Y-type molecular sieve, and the relatively low crystallization temperature does not excessively damage the Y-type molecular sieve structure. Due to the potential presence of new acidic sites and interfacial effects, the composite molecular sieve not only provides cooperative acidic centers and pore structures but also reduces carbon deposition, which is beneficial for maintaining catalyst activity.
[0017] After temperature-induced crystallization, the crystallized product is separated in this embodiment of the invention, and after washing, drying, and calcination, ZSM-5 / Y composite molecular sieve is obtained. In this embodiment, the ZSM-5 / Y composite molecular sieve is placed in an ammonium salt solution of a certain concentration for ion exchange reaction, and after washing, drying, and calcination, H-type ZSM-5 / Y molecular sieve is obtained. The separation, washing, drying, and calcination are operations well known to those skilled in the art. The drying temperature can be 333K–373K, and the time can be 12–24h; the calcination temperature can be 723K–773K, and the time can be 2h–6h. The ammonium salt is preferably ammonium chloride and / or ammonium nitrate, and the solution concentration can be 0.1M–0.6M. The ion exchange reaction temperature is preferably 303K–333K, and the exchange time can be 4–10h.
[0018] The composite molecular sieve obtained in the embodiments of this invention is mainly a composite of ZSM-5 and hollow Y-type sieves, containing large microporous and mesoporous structures, with a specific surface area of 650-690 m². 2 / g, with a low silicon-to-aluminum ratio. The Y molecular sieve contains a macroporous structure, which is conducive to molecular diffusion, etc. ZSM-5 seed crystals are adsorbed in the hollow Y molecular sieve and grow crystals. In application, heavy oil macromolecules can react in the Y molecular sieve, and the intermediate products formed by the reaction can then be further cracked on the surface of the ZSM-5 molecular sieve, which is beneficial to the stratified cracking of heavy oil.
[0019] The H-type ZSM-5 / Y composite molecular sieve prepared in this embodiment of the invention, when further prepared into a heavy oil cracking catalyst, exhibits high cracking activity, high liquefied petroleum gas (LPG) and gasoline yields, and significantly improves propylene yield. In particular, it effectively reduces coke yield. The oil / gas ratio of the product can be easily adjusted by modifying the synthesis conditions within the scope of the synthesis process of this invention.
[0020] This invention provides a heavy oil cracking catalyst, comprising a matrix and an active component, wherein the active component is an H-type ZSM-5 / Y composite molecular sieve product obtained by the preparation method described above.
[0021] In some embodiments, the heavy oil cracking catalyst is prepared by spray molding after mixing the active components with a matrix. The matrix includes kaolin, alumina sol, and boehmite. Specifically, the obtained H-type ZSM-5 / Y composite molecular sieve is mixed with kaolin, alumina sol, boehmite, acid, and water (generally deionized water), and spray molded to obtain the catalyst. The acid is hydrochloric acid; and the mass percentages of kaolin, alumina sol, hydrochloric acid, and H-type ZSM-5 / Y composite molecular sieve are 20%–60%, 2%–12%, 1%–3%, and 10%–40%, respectively. The embodiments of the present invention do not have special restrictions on the source of the matrix raw materials; kaolin is used as a carrier with a Na content of less than 0.1%, alumina sol is used as a binder with a solid content of 25%–30%, and a pH of 3–6.
[0022] In this embodiment of the invention, the formed catalyst is used as a heavy oil cracking catalyst, and its evaluation is performed using a fixed fluidized bed. This invention provides a method for heavy oil catalytic cracking, comprising: using the aforementioned heavy oil cracking catalyst as a catalyst, and performing a cracking reaction on the heavy oil feedstock using a fixed fluidized bed. The feedstock is preheated, preferably at a temperature of 853 K; the reaction temperature can be 803 K; and the fixed fluidized bed is a commonly used FCC device in the art, without any particular limitation.
[0023] The composite molecular sieve prepared in this invention exhibits high activity and selectivity. Its application as a catalyst in heavy oil catalytic cracking can meet the current needs of the transformation from oil refining to chemical production. The preparation process of this invention is simple and requires a low synthesis temperature, thus reducing catalyst costs. Detailed Implementation
[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention.
[0025] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods. Specifically, the Na content of the kaolin is less than 0.1%; the aluminum sol solid content is 25%-30%, and the pH is 3-6.
[0026] Example 1
[0027] (1) Sodium aluminate, tetraethyl orthosilicate and tetrapropylammonium hydroxide were used as aluminum source, silicon source and structure directing agent respectively to synthesize seed solution. Sodium aluminate, tetrapropylammonium hydroxide (40%) and tetraethyl orthosilicate were added to 250mL of water in a ratio of 3.5g:150mL:100mL and mixed evenly. The mixture was crystallized in a reactor at 353K for 8h to obtain ZSM-5 seed solution with silicon-aluminum ratio (SiO2 / Al2O3) = 21, which was then used for later use.
[0028] (2) Add 450g of sodium hydroxide to 1000mL of water, stir evenly, then add 200g of NaY molecular sieve (commercial NaY molecular sieve, silicon-to-aluminum ratio = 2), stir at 323K for 4h to obtain hollow NaY molecular sieve slurry.
[0029] (3) Add 50g of acidic silica sol (30% silica by mass, pH 2-4) to the NaY molecular sieve slurry and stir for 1h.
[0030] (4) Add 200 mL of ZSM-5 seed solution to the solution treated in step (3) above, stir evenly, pack into a reactor, and place in a rotary oven to crystallize at 393 K for 72 h.
[0031] (5) The crystallized product was separated, washed, dried (353K overnight), and then calcined at 813K for 3h to obtain ZSM-5 / Y composite molecular sieve.
[0032] (6) The obtained ZSM-5 / Y composite molecular sieve was placed in a 0.3M ammonium nitrate solution for ion exchange reaction at a temperature of 333K and a time of 6h. After washing and drying, it was calcined in air at 773K for 3h to obtain the H-type ZSM-5 / Y composite molecular sieve product.
[0033] (7) Add 150g of pseudoboehmite to 1390.5g of deionized water, add 36g of 37% hydrochloric acid and acidify for 1h, add 266.7g of aluminum sol and 352.6g of kaolin, stir for 30min, add 200g of H-type ZSM-5 / Y composite molecular sieve and stir for 30min; the mixed slurry is ball-milled and filtered, and then microspheres are formed by high-temperature spray centrifugation equipment, and calcined at 873K for 2h to obtain shaped catalyst particles.
[0034] Example 2
[0035] The synthesis temperature of the ZSM-5 seed solution was changed to 373K, the crystallization time was changed to 5h, and other conditions were the same as in Example 1.
[0036] Example 3
[0037] The sodium hydroxide used in the NaY type molecular sieve alkali treatment was replaced with 400 mL of tetrapropylammonium hydroxide, and other conditions were the same as in Example 1.
[0038] Example 4
[0039] The mass of sodium aluminate used to synthesize the ZSM-5 seed solution was increased to 7g, and other conditions were the same as in Example 1.
[0040] The synthesized molecular sieves were analyzed using the Quadrasorb evo™ fully automated specific surface area and porosity analyzer from Quantachrome, USA, according to the method in GB / T 21650.2-2008. The specific surface area and pore volume are shown in Table 1.
[0041] Table 1. Results of surface area and pore volume tests for molecular sieves
[0042]
[0043] Comparative Example 1
[0044] (1) The preparation of ZSM-5 seed solution is the same as in Example 1.
[0045] (2) Add 200g of NaY molecular sieve to 1000mL of water and stir at room temperature for 4h.
[0046] (3) Add 50g of acidic silica sol to the NaY molecular sieve slurry and stir for 1h.
[0047] (4) Add 200 mL of ZSM-5 seed solution to the above solution, stir evenly, pack into a reactor, and place in a rotary oven at 393 K for crystallization for 72 h.
[0048] (5) The separated crystallized products were washed, dried and then calcined at 813K for 3 hours to obtain ZSM-5 / Y composite molecular sieve.
[0049] (6) The ZSM-5 / Y composite molecular sieve was placed in a 0.3M ammonium nitrate solution for ion exchange reaction, washed, dried and then calcined in air at 773K for 3h to obtain the H-type molecular sieve product.
[0050] (7) Add 150g of pseudoboehmite to 1390.5g of deionized water, add 36g of 37% hydrochloric acid and acidify for 1h, add 266.7g of aluminum sol and 352.6g of kaolin, stir for 30min, add 200g of H-type ZSM-5 / Y composite molecular sieve and stir for 30min; after ball milling and filtration, the mixed slurry is formed into microspheres by high-temperature spray centrifugation equipment, and calcined at 873K for 2h to obtain the formed catalyst particles.
[0051] Comparative Example 2
[0052] (1) Sodium aluminate, tetraethyl orthosilicate and tetrapropylammonium hydroxide were used as aluminum source, silicon source and structure directing agent, respectively, to synthesize seed crystal solution. Sodium aluminate, tetrapropylammonium hydroxide (40%) and tetraethyl orthosilicate were added to 250mL of water in a ratio of 3.5g:150mL:100mL and mixed evenly. The mixture was crystallized in a reactor at 448K for 48h. The product was centrifuged, washed and dried for later use.
[0053] (2) Add 450g of sodium hydroxide to 1000mL of water, stir evenly, then add 200g of NaY molecular sieve, stir at 323K for 4h to obtain hollow NaY molecular sieve slurry.
[0054] (3) Add 50g of acidic silica sol to the NaY molecular sieve slurry and stir for 1h.
[0055] (4) Add 50g of ZSM-5 powder synthesized in step (1) to the above solution, stir evenly, pack into a reactor, and place in a rotary oven at 120℃ for crystallization for 72h.
[0056] (5) The separated crystallized products were washed, dried and then calcined at 813K for 3 hours.
[0057] (6) The product was placed in a 0.3M ammonium nitrate solution for ion exchange reaction, washed, dried and then calcined in air at 773K for 3h to obtain H-type molecular sieve product.
[0058] (7) Add 150g of pseudoboehmite to 1390.5g of deionized water, add 36g of 37% hydrochloric acid and acidify for 1h, add 266.7g of aluminum sol and 352.6g of kaolin, stir for 30min, add 200g of the above molecular sieve product and stir for 30min; after ball milling and filtration, the mixed slurry is formed into microspheres by high temperature spray centrifugation equipment, and calcined at 873K for 2h to obtain the formed catalyst particles.
[0059] Comparative Example 3
[0060] The catalyst was formed using commercial HY-type molecular sieves and ZSM-5 molecular sieves in a 1:1 ratio. 150g of boehmite was added to 1390.5g of deionized water, followed by acidification with 36g of 37% hydrochloric acid for 1 hour. Then, 266.7g of alumina sol and 352.6g of kaolin were added, and the mixture was stirred for 30 minutes. Next, 100g of HY-type molecular sieve and 100g of ZSM-5 molecular sieve were added, and the mixture was stirred for another 30 minutes. The resulting slurry was ball-milled, filtered, and then formed into microspheres using a high-temperature spray centrifuge. The microspheres were then calcined at 873K for 2 hours to obtain the formed catalyst particles.
[0061] Comparative Example 4
[0062] The catalyst was formed using commercial HY-type molecular sieves and ZSM-5 molecular sieves in a 4:1 ratio. 150g of boehmite was added to 1390.5g of deionized water, followed by acidification with 36g of 37% hydrochloric acid for 1 hour. Then, 266.7g of alumina sol and 352.6g of kaolin were added, and the mixture was stirred for 30 minutes. Next, 160g of HY-type molecular sieve and 40g of ZSM-5 molecular sieve were added, and the mixture was stirred for another 30 minutes. The resulting slurry was ball-milled, filtered, and then formed into microspheres using a high-temperature spray centrifuge. The microspheres were then calcined at 873K for 2 hours to obtain the formed catalyst particles.
[0063] During the evaluation of the molded catalysts in the fixed fluidized bed of the above embodiments and comparative examples, the properties of the raw materials and products are as follows.
[0064] The evaluation criteria for a fixed fluidized bed are as follows:
[0065] Table 2 Evaluation Criteria
[0066] reaction temperature K 803 Raw material preheating temperature K 853 Steam furnace temperature K 873 Feed rate g / min 20 Water inflow g / min 10 Nitrogen quantity mL / min 400
[0067] Table 3 Properties of Raw Materials
[0068]
[0069] Table 4 Product Properties
[0070]
[0071] As shown in the table above, the wear index of the prepared heavy oil cracking catalysts is less than 3% / h, which is acceptable compared to industrial propylene additives. Comparative Example 1 uses a NaY-type molecular sieve, which is difficult to form a composite structure with ZSM-5, resulting in poor catalytic performance. Comparative Example 2 also has difficulty in performing cascade reactions. Comparative Examples 3 and 4 are mainly used through mechanical mixing. The embodiments of this invention use a composite ZSM-5 / Y molecular sieve catalyst. Its mesoporous-microporous composite structure facilitates the conversion of macromolecules to C3 small molecules, thus resulting in a higher propylene yield. Simultaneously, the macroporous structure of the Y molecular sieve facilitates product diffusion, leading to lower coke production and higher economic benefits.
[0072] In the embodiments of this invention, due to the low silica-alumina ratio of ZSM-5 seed crystals, secondary growth of ZSM-5 crystals in hollow Y-type molecular sieves can be achieved by controlling the ratio of ZSM-5 seed crystals to Y-type molecular sieve suspension. The composite molecular sieve synthesized in this invention, when prepared as a catalyst, exhibits advantages such as high activity and good selectivity, and can achieve high yields of liquefied petroleum gas and propylene, making it particularly suitable for the petrochemical catalytic cracking field.
[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing a composite molecular sieve, characterized in that, Includes the following steps: Aluminum source, silicon source and structure guiding agent are mixed and dissolved in water, and then crystallization treatment is performed to obtain ZSM-5 seed solution; An etching solution is formed by mixing an alkaline substance with water. A Y-type molecular sieve is then added and stirred to form a hollow structure. The stirring process is carried out at a temperature of 293K~313K for 2~10 hours. This solution is then mixed with acidic silica sol to obtain a solution containing the hollow Y-type molecular sieve. The alkaline substance is one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, and sodium hydroxide. The pH value after mixing with the acidic silica sol is 10~12. The ZSM-5 seed solution and the solution containing hollow Y-type molecular sieve are mixed and heated to crystallize, then separated to obtain the crystallized product. After washing, drying, and calcination, a ZSM-5 / Y composite molecular sieve is obtained. The mass ratio of the ZSM-5 seed solution to the Y-type molecular sieve is 0.5~2. The temperature of the heated crystallization is 373K~398K, and the time is 10~120h. The ZSM-5 / Y composite molecular sieve was subjected to an ion exchange reaction with an ammonium salt, and then calcined to obtain an H-type ZSM-5 / Y composite molecular sieve product.
2. The method for preparing the composite molecular sieve according to claim 1, characterized in that, The aluminum source is one or more of aluminate, aluminum sol, and aluminum hydroxide; the silicon source is one or more of tetraethyl orthosilicate, tetrabutyl orthosilicate, and silica gel; and the structure directing agent is one or more of tetrapropylammonium hydroxide, tetrapropylammonium bromide, and n-butylamine.
3. The method for preparing the composite molecular sieve according to claim 2, characterized in that, The crystallization treatment is performed at a temperature of 343K~373K for a time of 2~72h.
4. The method for preparing the composite molecular sieve according to claim 1, characterized in that, The alkalinity of the etching solution is 2-10; the mass ratio of the Y-type molecular sieve to the etching solution is 0.05-0.
2.
5. The method for preparing the composite molecular sieve according to any one of claims 1-4, characterized in that, The ammonium salt is ammonium chloride and / or ammonium nitrate, and the ion exchange reaction is carried out at a temperature of 303K~333K and for a time of 4~10h.
6. A heavy oil cracking catalyst, comprising a matrix and an active component, characterized in that, The active component is the H-type ZSM-5 / Y composite molecular sieve product obtained by the preparation method according to any one of claims 1-5.
7. The heavy oil cracking catalyst according to claim 6, characterized in that, The heavy oil cracking catalyst is prepared by spray molding after mixing the active components with a matrix, wherein the matrix includes kaolin, alumina sol and boehmite.
8. A method for catalytic cracking of heavy oil, characterized in that, include: Using the heavy oil cracking catalyst described in claim 6 as a catalyst, a fixed fluidized bed is used to carry out the cracking reaction of heavy oil feedstock.