Y / ZSM-5 composite molecular sieve and preparation method therefor, and catalytic cracking catalyst

Abstract

Provided are a Y / ZSM-5 composite molecular sieve and a preparation method therefor, and a catalytic cracking catalyst. The preparation method comprises: mixing a Y molecular sieve raw material containing a second Y molecular sieve with an alkaline solution of a structure directing agent and carrying out crystallization to obtain a Y / ZSM-5 composite molecular sieve. The method further comprises carrying out drying and compaction treatment before crystallization, and / or, the Y molecular sieve raw material contains a first Y molecular sieve. The composite molecular sieve has two molecular sieve phases and high catalytic performance.

Description

Y / ZSM-5 composite molecular sieve, preparation method thereof and catalytic cracking catalyst

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 10, 2023, with application number 202311499444.X and invention name “Y / ZSM-5 composite molecular sieve, its preparation method and catalytic cracking catalyst”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of molecular sieve synthesis, and in particular to a Y / ZSM-5 composite molecular sieve and a preparation method thereof, and a catalytic cracking catalyst. Background Art

[0003] The production of low-carbon olefins and aromatics through the catalytic cracking process can not only significantly reduce excess refining capacity, achieve balanced development between refining and downstream high-end petrochemical production, and further enhance corporate profitability and market competitiveness, but also significantly increase self-sufficiency in low-carbon olefins, alleviate the imbalance between supply and demand of petrochemical raw materials, and significantly support economic development. The carbonium ion reaction in the catalytic cracking of heavy oil requires the catalysis of an acidic catalyst. Therefore, the development of high-performance solid acid catalysts has become a core area of ​​research and innovation in catalytic cracking technology. Zeolite molecular sieves are the most widely studied type of catalyst additive in catalytic cracking catalysts. In the catalytic cracking of heavy oil, ZSM-5 molecular sieve can be used in combination with Y molecular sieve to increase the selectivity of low-carbon olefins by cracking hydrocarbon molecules in the gasoline fraction. However, in the prior art, when Y molecular sieve and ZSM-5 molecular sieve are used together, there is often a significant spatial distance between the two. As a result, the linear hydrocarbons and simple isomeric hydrocarbons released from the Y molecular sieve often leave the FCC catalyst surface directly as final reaction products, making it difficult for them to continue to react on the ZSM-5 molecular sieve surface as intermediates.

[0004] At present, in the research on composite molecular sieves of Y-type molecular sieve and ZSM-5 molecular sieve, some methods use a single starting Y molecular sieve as a raw material and generate a ZSM-5 phase through crystallization. However, blocky molecular sieves will appear in the ZSM-5 phase, and the dispersion uniformity of the ZSM-5 phase in the composite molecular sieve is poor, which is not conducive to shortening the distance between the ZSM-5 phase and the Y molecular sieve phase.

[0005] Therefore, it is necessary to provide a preparation method for obtaining a Y / ZSM-5 composite molecular sieve in which the ZSM-5 phase is nanosized and uniformly dispersed.

[0006] Summary of the Invention

[0007] To address the above-mentioned problems, the present invention provides a Y / ZSM-5 composite molecular sieve, a preparation method thereof, and a catalytic cracking catalyst. The Y / ZSM-5 composite molecular sieve comprises a Y molecular sieve phase and a nano-sized ZSM-5 molecular sieve phase, and the ZSM-5 molecular sieve phase is uniformly dispersed in the composite molecular sieve, thereby improving the catalytic activity of the molecular sieve.

[0008] In order to achieve the above object, the present invention provides a method for preparing a Y / ZSM-5 composite molecular sieve, the preparation method comprising: fully mixing a Y molecular sieve raw material containing a second Y molecular sieve with an alkaline solution of a structure directing agent, and crystallizing to obtain the Y / ZSM-5 composite molecular sieve;

[0009] Wherein, the preparation method further comprises: drying and compacting treatment before crystallization, and / or, the Y molecular sieve raw material contains a first Y molecular sieve;

[0010] wherein the silicon-aluminum ratio of the first Y molecular sieve is greater than 0 and less than 14, the silicon-aluminum ratio of the second Y molecular sieve is greater than or equal to 9, and the silicon-aluminum ratio of the second Y molecular sieve is greater than the silicon-aluminum ratio of the first Y molecular sieve;

[0011] In the Y molecular sieve raw material, based on the total mass of the first Y molecular sieve and the second Y molecular sieve being 100%, the mass of the first Y molecular sieve is less than or equal to 70%.

[0012] According to a specific embodiment of the present invention, the above preparation method may specifically include:

[0013] Synthesis method 1: mixing and slurrying a first Y molecular sieve and a second Y molecular sieve, filtering and drying the slurry to obtain a Y molecular sieve raw material; fully mixing the Y molecular sieve raw material with an alkaline solution of a structure directing agent, and crystallizing to obtain the Y / ZSM-5 composite molecular sieve;

[0014] Synthesis method 2: fully mixing the second Y molecular sieve with an alkaline solution of a structure directing agent, drying, compacting, and crystallizing to obtain the Y / ZSM-5 composite molecular sieve;

[0015] Synthesis method three: mixing and slurrying the first Y molecular sieve and the second Y molecular sieve, filtering and drying the slurry to obtain a Y molecular sieve raw material; fully mixing the Y molecular sieve raw material with an alkaline solution of a structure-directing agent, drying, compacting, and crystallizing to obtain the Y / ZSM-5 composite molecular sieve;

[0016] Among them, in synthesis method one, synthesis method two and synthesis method three (hereinafter referred to as the three synthesis methods), the silicon-aluminum ratio of the first Y molecular sieve is greater than 0 and less than or equal to 14, the silicon-aluminum ratio of the second Y molecular sieve is greater than or equal to 9, and the silicon-aluminum ratio of the second Y molecular sieve is greater than the silicon-aluminum ratio of the first Y molecular sieve.

[0017] In the synthesis method 1 and the synthesis method 2, based on the total mass of the first Y molecular sieve and the second Y molecular sieve as 100%, the mass of the first Y molecular sieve is less than or equal to 70% (the mass ratio of the first Y molecular sieve to the second Y molecular sieve is ≤7:3).

[0018] The above-mentioned synthesis method provided by the present invention is to use two Y molecular sieves with different silicon-aluminum ratios as raw materials, slurry the two molecular sieves, fully mix them, filter and dry them, and obtain a Y molecular sieve raw material formed by Y molecular sieves with different silicon-aluminum ratios, and then introduce a structure-directing agent into the pores of the Y molecular sieve raw material; then, without any washing or drying treatment, directly dissolve and crystallize the Y molecular sieve raw material in an alkaline solution containing the structure-directing agent in a high-temperature hydrothermal environment.

[0019] The second synthesis method provided by the present invention is to use a second Y molecular sieve with a high silicon-aluminum ratio as a raw material, introduce a structure directing agent into the pores of the second Y molecular sieve, and then dry the second Y molecular sieve containing the structure directing agent and perform a compaction treatment. The compacted second Y molecular sieve containing the structure directing agent (mixed Y molecular sieve) is then subjected to in-situ dissolution and crystallization treatment in a high-temperature hydrothermal environment, so that the silicon-aluminum ratio of the dissolved second Y molecular sieve undergoes structural rearrangement and crystallization to obtain a Y / ZSM-5 composite molecular sieve.

[0020] The third synthesis method provided by the present invention is to simultaneously use two Y molecular sieves with different silicon-aluminum ratios as raw materials, and dry and compact the Y molecular sieve raw materials containing the alkaline solution of the structure-directing agent before crystallization, and then transfer them to a high-temperature hydrothermal environment for in-situ dissolution and crystallization, so that the Y molecular sieve undergoes structural rearrangement and crystallization during the crystallization process, thereby obtaining a Y / ZSM-5 composite molecular sieve.

[0021] In the above preparation method, as shown in Figure 21, in the case of "before and after solid phase transformation of USY after doping", when the raw material contains both the first Y molecular sieve and the second Y molecular sieve, the second Y molecular sieve with a higher silicon-aluminum ratio dissolves to a greater extent in a hydrothermal environment of high temperature (provided by crystallization temperature) and high alkali (provided by an alkaline solution of a structure directing agent), and the dissolved silicon, aluminum, etc. can be used as raw materials for the generation of the ZSM-5 molecular sieve phase; while the first Y molecular sieve with a smaller silicon-aluminum ratio dissolves to a lesser extent in a hydrothermal environment of high temperature and high alkali, and the skeleton dissolves only a small amount or does not dissolve. Therefore, the first Y molecular sieve can physically confine the newly formed ZSM-5 molecular sieve during the crystallization process. Alternatively, the newly formed ZSM-5 molecular sieve can be physically confined by compaction treatment to form a crystalline state similar to the crystalline state of "before and after solid phase transformation of USY after doping" shown in Figure 21.

[0022] In contrast, as shown in Figure 21, in the case of “before and after USY solid phase conversion”, when no compaction treatment is performed and only the second Y molecular sieve is used as a raw material, a single second Y molecular sieve will undergo a certain degree of solid phase conversion during the crystallization process, but the generated ZSM-5 molecular sieve is not subject to the effect of physical confinement, and obvious agglomeration will occur between the grains. The present invention suppresses the flow and exchange of materials during rearrangement and conversion by the above-mentioned physical confinement means. Due to the limited source of silicon and aluminum of the ZSM-5 molecular sieve phase (mainly from the silicon and aluminum dissolved in the Y molecular sieve raw material) and limited mass transfer, the rearrangement and conversion process of the present invention is conducive to the formation of ultrafine nano-sized ZSM-5 molecular sieve phases, thereby improving the degree to which the ZSM-5 molecular sieve phase is uniformly dispersed in the composite molecular sieve.

[0023] Compared with conventional micron-sized ZSM-5 molecular sieves, the nano-sized ZSM-5 molecular sieves formed in the present invention have relatively smaller crystal sizes and larger specific surface areas, which can provide more active sites, reduce the resistance to pore diffusion, and reduce the blockage of pores by coking and carbon formation. It can significantly improve the catalytic activity (such as conversion rate) of the composite molecular sieve, reduce the deactivation rate of the composite molecular sieve, and extend its service life.

[0024] In the above three synthesis methods, the first Y molecular sieve generally does not undergo solid phase crystallization or undergoes a very small amount of crystallization during the above crystallization process, and is mainly used to physically confine the newly generated ZSM-5 molecular sieve. The second Y molecular sieve is a Y molecular sieve capable of solid phase crystallization. The silicon-aluminum ratio of the second Y molecular sieve is generally greater than the silicon-aluminum ratio of the first Y molecular sieve, and the silicon-aluminum ratio of the first Y molecular sieve can be greater than 0 and less than 14, and the silicon-aluminum ratio of the second Y molecular sieve can be greater than or equal to 9. Specifically, the silicon-aluminum ratio of the first Y molecular sieve is generally less than m, and the silicon-aluminum ratio of the second Y molecular sieve is generally greater than or equal to m. In some specific embodiments, the m value can be any one of 9-14, for example, it can be 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14 and other specific values ​​and a range with any two of the above specific values ​​as endpoints.

[0025] In the present invention, the m value can be adjusted based on factors such as the alkaline solution of the structure-directing agent and the crystallization temperature. For example, the m value can increase with increasing crystallization temperature, and the m value can decrease with increasing pH of the alkaline solution of the structure-directing agent. The m value can also vary depending on the type of structure-directing agent. For the same type of structure-directing agent (such as a quaternary ammonium salt), the larger the ionic volume of the structure-directing agent (such as the longer the side chains of the quaternary ammonium salt), the larger the m value. In some specific embodiments, when the structure-directing agent is a quaternary ammonium base, the pH of the alkaline solution of the structure-directing agent is 10-14, and the crystallization temperature is 50-250°C, the m value can be 12.

[0026] In the above three synthesis methods, the silicon-aluminum ratio of the second Y molecular sieve can be greater than or equal to 9, greater than or equal to 10, greater than or equal to 11, greater than or equal to 12, greater than or equal to 13, greater than or equal to 14, etc., and can be further controlled to be 12-30, 12-20. The silicon-aluminum ratio of the second Y molecular sieve can be specifically 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 29, 30, etc., and a range with any two of the above specific values ​​as endpoints.

[0027] In the above three synthesis methods, the second Y molecular sieve can be ammonium-type Y molecular sieve, hydrogen-type Y molecular sieve, rare earth-type Y molecular sieve, etc. Specifically, the second Y molecular sieve can include one or a combination of two or more of NH4Y molecular sieve, HY molecular sieve, USY molecular sieve, and RY molecular sieve.

[0028] In the above-mentioned synthesis method 1 and synthesis method 3, the silicon-aluminum ratio of the first Y molecular sieve is less than 14, less than 13, less than 12, less than 11, less than 10, less than 9; further controllable to be greater than or equal to 2 and less than 12, greater than 2 and less than 12, greater than or equal to 6 and less than 12, or greater than 6 and less than or equal to 12. The silicon-aluminum ratio of the first Y molecular sieve can be specifically 12, 11.5, 11, 10.5, 10, 9.5, 9, 8.5, 8, 7.5, 7, 6.5, 6.1, 6, 5.5, 5, 4.5, 4, 3.5, 3, 2.7, 2.5, 2, 1.5, 1, 0.5 and other specific values ​​and ranges with any two of the above specific values ​​as endpoints. In some specific embodiments, a first Y molecular sieve with a lower silicon-aluminum ratio, such as a first Y molecular sieve with a silicon-aluminum ratio of less than 7, can be selected to save costs.

[0029] In the above-mentioned synthesis method 1 and synthesis method 3, the difference between the silicon-aluminum ratio of the second Y molecular sieve and the silicon-aluminum ratio of the first Y molecular sieve is greater than or equal to 5, that is, the silicon-aluminum ratio of the second Y molecular sieve is greater than the silicon-aluminum ratio of the first Y molecular sieve by more than 5. In some specific embodiments, based on the silicon-aluminum ratio range of conventional Y molecular sieves, the difference between the silicon-aluminum ratio of the second Y molecular sieve and the silicon-aluminum ratio of the first Y molecular sieve can be 5-30, specifically 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22.9, 23, 25, 30 and other specific values, as well as ranges with any two of the above specific values ​​as endpoints.

[0030] In the above-mentioned synthesis method 1 and synthesis method 3, the first Y molecular sieve can be an ammonium type Y molecular sieve, a hydrogen type Y molecular sieve, a rare earth type Y molecular sieve, etc. Specifically, the first Y molecular sieve can include one or a combination of two or more of NH4Y molecular sieve, HY molecular sieve, USY molecular sieve, and RY molecular sieve (rare earth Y molecular sieve). The types of the first Y molecular sieve and the second Y molecular sieve can be the same or different.

[0031] In the above three synthesis methods, by regulating the silicon-aluminum ratio of the first Y molecular sieve and / or the second Y molecular sieve, and regulating the relative ratio of the first Y molecular sieve to the second Y molecular sieve in the synthesis method one and the synthesis method two, the framework aluminum content of the composite molecular sieve, the acid amount of the composite molecular sieve, and the relative ratio of the Y molecular sieve phase and the ZSM-5 molecular sieve phase in the composite molecular sieve can be adjusted.

[0032] During the crystallization process of the above three synthesis methods, the alkaline solution of the structure directing agent can play a structural guiding role in the above crystallization process: during the crystallization process, the Y molecular sieve raw material, especially the silicon and aluminum dissolved from the second Y molecular sieve, can undergo structural rearrangement under the action of hydroxide, and transform into a ZSM-5 molecular sieve phase.

[0033] In the above three synthesis methods, by controlling the amount of structure-directing agent relative to the Y molecular sieve raw material, the solubility of the intermediate Y molecular sieve can be controlled, so that the Y molecular sieve undergoes "limited dissolution". On the one hand, it can achieve the effect of retaining part of the Y molecular sieve framework and making the final product contain the Y molecular sieve phase. On the other hand, the dissolved fragments can be used to form a certain amount of ZSM-5 molecular sieve. In addition, by adjusting the amount of structure-directing agent relative to the Y molecular sieve raw material, the degree of conversion of the Y molecular sieve to the ZSM-5 molecular sieve and the uniformity of the distribution of the two molecular sieve phases in the composite molecular sieve can be adjusted.

[0034] In the above three synthesis methods, the mass ratio of the Y molecular sieve raw material to the structure-directing agent is (0.1-1):(0.01-1), for example, (0.1-1):(0.1-1). In some specific embodiments, the mass of the Y molecular sieve raw material can be 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1.0 parts, and other specific values, as well as ranges with any two of the above specific values ​​as endpoints, and correspondingly, the mass of the structure-directing agent can be 0.01 parts, 0.05 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 1.0 parts, and other specific values, as well as ranges with any two of the above specific values ​​as endpoints.

[0035] In the three synthesis methods mentioned above, the cation of the structure-directing agent can act as a structure-directing agent for the ZSM-5 molecular sieve, promoting the formation of the ZSM-5 molecular sieve phase; the anion hydroxide in the alkaline solution of the structure-directing agent can, on the one hand, dissolve the silicon and aluminum in the Y molecular sieve as silicon and aluminum sources for the ZSM-5 molecular sieve phase, and on the other hand, can also provide an alkaline environment to promote the formation of the ZSM-5 molecular sieve phase. By adjusting the type of cation in the structure-directing agent, the relative ratio of the two molecular sieve phases in the composite Y molecular sieve can be adjusted. Specifically, the structure-directing agent includes one or a combination of two or more of an organic amine, a quaternary ammonium base, or a tertiary ammonium base.

[0036] In the above three synthesis methods, the quaternary ammonium base may include one or a combination of two or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0037] In the above three synthesis methods, the tertiary ammonium base may include choline hydroxide.

[0038] In the above three synthesis methods, the organic amine may include one or a combination of two or more of tetrapropylammonium bromide, hexadecyltrimethylammonium bromide, triethylamine, and ethylenediamine.

[0039] In the above three synthesis methods, the pH value of the alkaline solution of the structure directing agent can be 10-14, specifically 10, 11, 12, 13, 14 and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0040] In the above three synthesis methods, the alkaline solution of the structure-directing agent may further include an inorganic base for adjusting the pH value of the solution. Specifically, the inorganic base may include one or a combination of two or more of LiOH, NaOH, and KOH.

[0041] In the above three synthesis methods, the solvent used in the alkaline solution of the structure directing agent generally includes water. In some specific embodiments, the mass ratio of the water in the Y molecular sieve raw material, the structure directing agent, and the alkaline solution of the structure directing agent can be (0.1-1): (0.01-1): (0.5-5), for example (0.1-1): (0.1-1): (0.5-5). By controlling the solid-liquid ratio in the reaction system, the crystallization process can be carried out in a solid phase or a solid-phase system. Due to the low fluidity of the system and the confinement of the first Y molecular sieve, the silicon and aluminum dissolved in the second Y molecular sieve are crystallized in situ to form a ZSM-5 phase, and the confinement of the first Y molecular sieve can promote the ZSM-5 molecular sieve phase to form uniformly dispersed small crystals of nanometer size.

[0042] In the above three synthesis methods, the Y molecular sieve raw material and the alkaline solution of the structure directing agent are mixed in a manner that the Y molecular sieve raw material is immersed in an alkaline solution of the structure directing agent. The impregnation method may include a quantitative impregnation method, an equal volume impregnation method, a multiple impregnation method, an impregnation precipitation method, a fluidized bed spray impregnation method, an impregnation vapor phase impregnation method, a vacuum impregnation method, and a pressure impregnation method. One or more combinations thereof. Alternatively, the Y molecular sieve raw material and the alkaline solution of the structure directing agent can also be mixed by adding the alkaline solution of the structure directing agent dropwise to the Y molecular sieve raw material.

[0043] In the three synthesis methods described above, the relative ratio of the two molecular sieve phases in the composite molecular sieve can be adjusted by adjusting the crystallization conditions. The crystallization temperature is 50°C to 250°C, for example, 80°C to 200°C. In some specific embodiments, the crystallization temperature can be 50°C, 80°C, 100°C, 150°C, 200°C, 250°C, or other specific values, as well as ranges with any two of the above specific values ​​as endpoints.

[0044] In the above three synthesis methods, the crystallization time is 0.1 h to 120 h, for example, 0.5 h to 72 h. In some specific embodiments, the crystallization time can be 0.1 h, 0.5 h, 1 h, 5 h, 10 h, 20 h, 24 h, 30 h, 40 h, 48 h, 50 h, 60 h, 70 h, 72 h, 80 h, 90 h, 96 h, 120 h, and other specific values, as well as ranges with any two of the above specific values ​​as endpoints.

[0045] In the above preparation method, the crystallization pressure is generally 0.1-10 MPa, for example, specific values ​​such as 0.1 MPa, 0.5 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, and ranges with any two of the above specific values ​​as endpoints.

[0046] In the three aforementioned synthesis methods, the crystallization process can be in situ crystallization, without the presence of a liquid solvent. The crystallization method can specifically include one or a combination of two or more of solid-phase hydrothermal crystallization, quasi-solid-phase hydrothermal crystallization, and steam-assisted solid-phase hydrothermal crystallization.

[0047] The present invention finds that in the Y molecular sieve raw materials of synthesis method one and synthesis method three, by controlling the mass content of the first Y molecular sieve with a relatively low silicon-aluminum ratio to less than 70% (the mass content of the first Y molecular sieve in synthesis method two is 0%, which also meets the range of less than 70%), it is possible to ensure that the Y molecular sieve raw material undergoes solid phase crystallization during the crystallization process. That is, based on the total mass of the first Y molecular sieve and the second Y molecular sieve raw materials as 100%, the mass of the first Y molecular sieve is less than or equal to 70% and greater than 0%, and accordingly, the mass of the second Y molecular sieve is greater than or equal to 30% and less than 100%, and the mass ratio of the first Y molecular sieve to the second Y molecular sieve is less than or equal to 7:3. In some specific embodiments, the mass of the first Y molecular sieve can be 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, 1%, 0.5%, 0.1% and other specific values ​​and a range with any two of the above specific values ​​as endpoints. Accordingly, the mass of the second Y molecular sieve can be specific values ​​such as 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, 99.5%, 99.9%, and a range with any two of the above specific values ​​as endpoints.

[0048] In the Y molecular sieve raw materials of synthesis method one and synthesis method three, the mass ratio of the first Y molecular sieve to the second Y molecular sieve is generally less than or equal to 7:3, and can be further controlled to be 3:7-5:5, for example, specific values ​​such as 3:7, 3.5:6.5, 4:6, 4.5:6.5, 5:5, and a range with any two of the above specific values ​​as endpoints.

[0049] According to a specific embodiment of the present invention, the first synthesis method in the preparation method of the above-mentioned Y / ZSM-5 composite molecular sieve may specifically include:

[0050] 1. Mixing and slurrying a first Y molecular sieve and a second Y molecular sieve in a mass ratio of less than or equal to 7:3, and drying the slurry to obtain a Y molecular sieve raw material; wherein the silicon-aluminum ratio of the first Y molecular sieve is less than m, and the silicon-aluminum ratio of the second Y molecular sieve is greater than or equal to m, and m is any value between 9 and 14;

[0051] 2. Immerse the Y molecular sieve raw material in a solution of a structure directing agent. After sufficient impregnation, take out the Y molecular sieve raw material, transfer the impregnated Y molecular sieve raw material directly to a sealed reactor without washing or drying, and crystallize it at 50-250° C. for 0.1 h to 120 h to obtain the Y / ZSM-5 composite molecular sieve.

[0052] In the second synthesis method, a compacted second Y molecular sieve with a high silicon-to-aluminum ratio undergoes in-situ dissolution and crystallization in a high-temperature, high-alkaline hydrothermal environment, causing the dissolved silicon and aluminum in the Y molecular sieve to undergo structural rearrangement and crystallization, thereby obtaining a Y / ZSM-5 composite molecular sieve. The compaction treatment increases the density between particles and improves the difficulty of mass transfer, thereby inhibiting the formation of large ZSM-5 particle aggregation during the crystallization process.

[0053] In the above-mentioned synthesis method 2, the compaction treatment can inhibit the crystallization of the Y molecular sieve to the ZSM-5 molecular sieve phase to a certain extent. For example, compared with the Y / ZSM-5 composite molecular sieve prepared without compaction treatment, the Y / ZSM-5 composite molecular sieve obtained after compaction treatment has a lower content of the ZSM-5 molecular sieve phase in the composite molecular sieve, and the particle size of the formed ZSM-5 molecular sieve is smaller.

[0054] In the above-mentioned synthesis method 2, the pressure of the compaction treatment can be controlled to be 0.1 MPa-60 MPa, for example, 1-30 MPa. Specifically, the pressure of the compaction treatment can be 0.1 MPa, 0.5 MPa, 1 MPa, 5 MPa, 10 MPa, 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, or other specific values, or ranges with any two of the above specific values ​​as endpoints.

[0055] According to a specific embodiment of the present invention, the second synthetic method of the preparation method of the above-mentioned Y / ZSM-5 composite molecular sieve may specifically include:

[0056] 1. Using a second Y molecular sieve having a silicon-aluminum ratio greater than or equal to m as a Y molecular sieve raw material, where m is any value between 9 and 14;

[0057] 2. Immerse the Y molecular sieve raw material in an alkaline solution of a structure directing agent. After sufficient immersion, take out the Y molecular sieve raw material, dry it, and compact it at a pressure of 0.1 MPa-60 MPa;

[0058] The compacted Y molecular sieve raw material is directly transferred to a sealed reactor without washing or drying, and crystallized at 50° C.-250° C. for 0.1-120 hours to obtain the Y / ZSM-5 composite molecular sieve.

[0059] According to a specific embodiment of the present invention, the third synthesis method of the preparation method of the above-mentioned Y / ZSM-5 composite molecular sieve may specifically include:

[0060] 1. Mixing and slurrying a first Y molecular sieve and a second Y molecular sieve in a mass ratio of less than or equal to 7:3, and drying the slurry to obtain a Y molecular sieve raw material; wherein the silicon-aluminum ratio of the first Y molecular sieve is less than m, and the silicon-aluminum ratio of the second Y molecular sieve is greater than or equal to m, and m is any value between 9 and 14;

[0061] 2. Immerse the Y molecular sieve raw material in a solution of a structure directing agent. After sufficient immersion, take out the Y molecular sieve raw material and dry it. The dried Y molecular sieve raw material is compacted at a pressure of 0.1 MPa-60 MPa. Transfer the compacted Y molecular sieve raw material to a sealed reactor and crystallize it at 50-250° C. for 0.1 h-120 h to obtain the Y / ZSM-5 composite molecular sieve.

[0062] The present invention also provides a Y / ZSM-5 composite molecular sieve, which is obtained by the above preparation method.

[0063] According to a specific embodiment of the present invention, the Y / ZSM-5 composite molecular sieve includes a Y molecular sieve phase and a ZSM-5 molecular sieve phase. By controlling the amount and type of the alkaline solution of the structure directing agent and the crystallization conditions, the ratio of the Y molecular sieve phase and the ZSM-5 molecular sieve phase in the composite molecular sieve can be controlled. In some specific embodiments, the mass ratio of the ZSM-5 molecular sieve phase in the Y / ZSM-5 composite molecular sieve can be greater than or equal to 1%, further 1%-50%. Furthermore, the mass ratio of the Y molecular sieve phase and the ZSM-5 molecular sieve phase can be 50-99:1-50, for example, 60-95:5-40, 60-94:6-40, 64-93:7-36, etc. In some specific embodiments, the mass ratio of the Y molecular sieve phase to the ZSM-5 molecular sieve phase can be 99:1, 98:2, 97:3, 96:4, 95:5, 94:6, 93:7, 92:8, 91:9, 90:10, 85:15, 80:20, 75:25, 70:30, 65:35, 64:36, 60:40, 55:45, 50:50 and other specific values, as well as ranges with any two of the above specific values ​​as endpoints.

[0064] The Y / ZSM-5 composite molecular sieve provided by the present invention can be used as a catalyst to produce more olefins.

[0065] The present invention also provides a catalytic cracking catalyst comprising the Y / ZSM-5 composite molecular sieve. The ZSM-5 molecular sieve phase in the Y / ZSM-5 composite molecular sieve is an ultrafine nanophase that is evenly distributed with the Y molecular sieve phase, facilitating the decomposition of molecules in the Y molecular sieve phase to enter the ZSM-5 molecular sieve phase for further cracking and decomposition, thereby facilitating the production of higher yields of light olefins.

[0066] The beneficial effects of the present invention include:

[0067] The preparation method of the Y / ZSM-5 composite molecular sieve provided by the present invention is crystallized as raw material using molecular sieves with different silicon-aluminum ratios, and the dissolution, rearrangement and crystallization of part of the Y molecular sieve can occur during the crystallization process, promote the formation of the ZSM-5 molecular sieve phase, and the ZSM-5 molecular sieve phase is ultrafine nanophase and uniformly dispersed in the composite molecular sieve. In addition, by selecting molecular sieves with different silicon-aluminum ratios, it is also possible to achieve the regulation of the skeleton aluminum content in the composite molecular sieve, so as to regulate the acid amount of the composite molecular sieve. The composite molecular sieve thus obtained has a uniform distribution of two phases, and catalytic performance is effectively improved, which can be applied to catalytic cracking processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 is a composite molecular sieve Y C1 / ZSM-5 C1 Sample and composite molecular sieve Y B / ZSM-5 B X-ray diffraction patterns of the samples.

[0069] Figure 2 is composite molecular sieve Y C1 / ZSM-5 C1 Scanning electron microscope image of the sample.

[0070] Figure 3 is a composite molecular sieve Y C2 / ZSM-5 C2 Sample and composite molecular sieve Y B / ZSM-5 B X-ray diffraction patterns of the samples.

[0071] Figure 4 shows composite molecular sieve Y C2 / ZSM-5 C2 Scanning electron microscope image of the sample.

[0072] Figure 5 is a composite molecular sieve Y C3 / ZSM-5 C3 Sample and composite molecular sieve Y B / ZSM-5 B X-ray diffraction patterns of the samples.

[0073] Figure 6 is a composite molecular sieve Y C3 / ZSM-5 C3 Scanning electron microscope image of the sample.

[0074] Figure 7 and Figure 8 are composite molecular sieves Y C3 / ZSM-5 C3 Transmission electron microscopy image of the sample.

[0075] Figure 9 is a composite molecular sieve Y C4 / ZSM-5 C4 Sample and composite molecular sieve Y B / ZSM-5 BX-ray diffraction patterns of the samples.

[0076] Figure 10 is a composite molecular sieve Y C4 / ZSM-5 C4 Scanning electron microscope image of the sample.

[0077] Figure 11 and Figure 12 are composite molecular sieves Y C4 / ZSM-5 C4 Transmission electron microscopy image of the sample.

[0078] Figure 13 is a composite molecular sieve Y C5 / ZSM-5 C5 Sample and composite molecular sieve Y B / ZSM-5 B X-ray diffraction patterns of the samples.

[0079] Figure 14 is a composite molecular sieve Y C5 / ZSM-5 C5 Scanning electron microscope image of the sample.

[0080] Figure 15 is a composite molecular sieve Y C6 / ZSM-5 C6 Sample and composite molecular sieve Y E / ZSM-5 E X-ray diffraction patterns of the samples.

[0081] Figure 16 is a composite molecular sieve Y C6 / ZSM-5 C6 Scanning electron microscope image of the sample.

[0082] Figure 17 is a composite molecular sieve Y B / ZSM-5 B Scanning electron microscope image of the sample.

[0083] Figure 18 is a composite molecular sieve Y B / ZSM-5 B Transmission electron microscopy image of the sample.

[0084] Figure 19 and Figure 20 are composite molecular sieves Y E / ZSM-5 E Scanning electron microscope image of the sample.

[0085] FIG21 is a schematic diagram of the crystallization process in the preparation method of the present invention. DETAILED DESCRIPTION

[0086] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0087] In the present invention, the silicon-to-aluminum ratio refers to the molar ratio of Si to Al. The first and second Y molecular sieves used in the following examples are both ammonium-type USY molecular sieves, which are commercially available.

[0088] Example 1

[0089] This embodiment provides a Y / ZSM-5 composite molecular sieve, the preparation method of which includes:

[0090] 1. Weigh 5g of the first Y molecular sieve (sample name Y A ; Si-Al ratio: 6.1) and 5g of the second Y molecular sieve (sample name Y B ; Silicon aluminum ratio: 19.1) was mixed with 100g of water and stirred at room temperature for 2 hours, dried, and obtained Y molecular sieve raw materials (named Y C1 ).

[0091] 2. Weigh 0.9g of 25wt% tetrapropylammonium hydroxide solution and 1g of Y molecular sieve raw material Y C1 At room temperature, 0.9 g of the tetrapropylammonium hydroxide solution was slowly and evenly added dropwise into the molecular sieve pores to impregnate them evenly.

[0092] 3. Then the fully impregnated sample was directly transferred into a 5 ml PTFE-lined stainless steel pressure-resistant reactor, and then the sealed reactor was placed in a 140 ° C oven for crystallization for 24 hours. After washing and drying, the Y / ZSM-5 composite molecular sieve product (sample name Y C1 / ZSM-5 C1 ).

[0093] The X-ray diffraction pattern and scanning electron microscope image of the product sample obtained in this example are shown in Figure 1 and Figure 2 respectively.

[0094] Example 2

[0095] This embodiment provides a Y / ZSM-5 composite molecular sieve, the preparation method of which includes:

[0096] 1. Add 3g of the first Y molecular sieve (sample name Y A ; Si-Al ratio: 6.1) and 7g of the second Y molecular sieve (sample name Y B ; Silicon aluminum ratio: 19.1) was mixed with 100g of water and stirred at room temperature for 2 hours, dried, and obtained Y molecular sieve raw materials (named Y C2 ).

[0097] 2. Weigh 0.9g of 25wt% tetrapropylammonium hydroxide solution and 1g of Y molecular sieve raw material Y C2At room temperature, 0.9 g of the tetrapropylammonium hydroxide solution was slowly and evenly added dropwise into the molecular sieve pores to impregnate them evenly.

[0098] 3. Then the impregnated sample was directly transferred into a 5 ml PTFE-lined stainless steel pressure reactor, and then the sealed reactor was placed in a 140 ° C oven for crystallization for 24 hours. After washing and drying, the Y / ZSM-5 composite molecular sieve product (sample name Y C2 / ZSM-5 C2 ).

[0099] The X-ray diffraction pattern and scanning electron microscope image of the product sample obtained in this example are shown in Figure 3 and Figure 4 respectively.

[0100] Example 3

[0101] This embodiment provides a Y / ZSM-5 composite molecular sieve, the preparation method of which includes:

[0102] 1. 3g of the first Y molecular sieve (sample name Y A ; Si-Al ratio: 6.1), 7g second Y molecular sieve (sample name Y B ; Silicon-aluminum ratio: 19.1) was mixed with 100g of water and stirred at room temperature for 2 hours, and dried to obtain different silicon-aluminum ratio Y molecular sieve raw materials (named Y C3 ).

[0103] 2. Weigh 0.9g of 25wt% tetrapropylammonium hydroxide solution and 1g of mixed Y C3 At room temperature, 0.9 g of the tetrapropylammonium hydroxide solution was slowly and evenly added dropwise into the molecular sieve pores to impregnate them evenly.

[0104] 3. The fully impregnated sample was dried at room temperature for 24 hours and then subjected to high pressure (25MPa) compaction treatment. The treated sample was transferred to a 5 ml polytetrafluoroethylene lined stainless steel pressure reactor. The sealed reactor was then placed in a 140°C oven for crystallization for 24 hours. After washing and drying, the Y / ZSM-5 composite molecular sieve product (sample name Y C3 / ZSM-5 C3 ).

[0105] The X-ray diffraction pattern, scanning electron microscope image and transmission electron microscope image of the product sample of this example are shown in Figure 5, Figure 6, Figure 7 and Figure 8 respectively.

[0106] Example 4

[0107] This embodiment provides a Y / ZSM-5 composite molecular sieve, the preparation method of which includes:

[0108] 1. Weigh 0.9g of 25wt% tetrapropylammonium hydroxide solution and 1g of Y molecular sieve (sample name Y B ; Si-Al ratio: 19.1). At room temperature, 0.9 g of the tetrapropylammonium hydroxide solution was slowly and evenly added dropwise into the molecular sieve pores to impregnate them evenly.

[0109] 2. The fully impregnated sample was dried at room temperature for 24 hours and then subjected to high pressure (25MPa) compaction treatment. The treated sample was transferred to a 5 ml polytetrafluoroethylene lined stainless steel pressure reactor. The sealed reactor was then placed in a 140°C oven for crystallization for 24 hours. After washing and drying, the Y / ZSM-5 composite molecular sieve product (sample name Y C4 / ZSM-5 C4 ).

[0110] The X-ray diffraction pattern, scanning electron microscope image and transmission electron microscope image of the product sample of this example are shown in Figure 9, Figure 10, Figure 11 and Figure 12 respectively.

[0111] Example 5

[0112] This embodiment provides a Y / ZSM-5 composite molecular sieve, the preparation method of which includes:

[0113] 1. Weigh 5g of the first Y molecular sieve (sample name Y D ; Si-Al ratio: 2.7) and 5g of the second Y molecular sieve (sample name Y B ; Silicon aluminum ratio: 19.1) was mixed with 100g of water and stirred at room temperature for 2 hours, dried, and obtained Y molecular sieve raw materials (named Y C5 ).

[0114] 2. Weigh 0.9g of 25wt% tetrapropylammonium hydroxide solution and 1g of Y molecular sieve raw material Y C5 At room temperature, 0.9 g of the tetrapropylammonium hydroxide solution was slowly and evenly added dropwise into the molecular sieve pores to impregnate them evenly.

[0115] 3. Then the fully impregnated sample was directly transferred into a 5 ml PTFE-lined stainless steel pressure-resistant reactor, and then the sealed reactor was placed in a 140 ° C oven for crystallization for 24 hours. After washing and drying, the Y / ZSM-5 composite molecular sieve product (sample name Y C5 / ZSM-5 C5 ).

[0116] The X-ray diffraction pattern and scanning electron microscope image of the product sample obtained in this example are shown in Figure 13 and Figure 14 respectively.

[0117] Example 6

[0118] This embodiment provides a Y / ZSM-5 composite molecular sieve, the preparation method of which includes:

[0119] 1. Weigh 3g of the first Y molecular sieve (sample name Y A ; Si-Al ratio: 6.1) and 7g of the second Y molecular sieve (sample name Y E ; Silicon aluminum ratio: 29.0) was mixed with 100g of water and stirred at room temperature for 2 hours, dried, to obtain Y molecular sieve raw materials (named Y) with different silicon aluminum ratios. C6 ).

[0120] 2. Weigh 0.9g of 25wt% tetrapropylammonium hydroxide solution and 1g of Y molecular sieve raw material Y C6 At room temperature, 0.9 g of the tetrapropylammonium hydroxide solution was slowly and evenly added dropwise into the molecular sieve pores to impregnate them evenly.

[0121] 3. Then the fully impregnated sample was directly transferred into a 5 ml PTFE-lined stainless steel pressure-resistant reactor, and then the sealed reactor was placed in a 140 ° C oven for crystallization for 24 hours. After washing and drying, the Y / ZSM-5 composite molecular sieve product (sample name Y C6 / ZSM-5 C6 ).

[0122] The X-ray diffraction pattern and scanning electron microscope image of the product sample obtained in this example are shown in Figure 15 and Figure 16 respectively.

[0123] Comparative Example 1

[0124] This comparative example provides a Y / ZSM-5 composite molecular sieve, the preparation method of which comprises:

[0125] 1. Weigh 0.9g of 25wt% tetrapropylammonium hydroxide solution and 1g of Y molecular sieve (sample name Y B ; Si-Al ratio: 19.1). At room temperature, 0.9 g of the tetrapropylammonium hydroxide solution was slowly and evenly added dropwise into the molecular sieve pores to impregnate them evenly.

[0126] 2. The fully impregnated sample was then directly transferred into a 5 ml PTFE-lined stainless steel pressure reactor. The sealed reactor was then placed in a 140°C oven for crystallization for 24 hours. After washing and drying, the Y / ZSM-5 composite molecular sieve product (sample name Y B / ZSM-5 B ).

[0127] The X-ray diffraction data of the product sample of this comparative example are recorded in Figures 1, 3, 5, 9 and 13, and the scanning electron microscope image and transmission electron microscope image are shown in Figures 17 and 18, respectively.

[0128] Comparative Example 2

[0129] This comparative example provides a Y / ZSM-5 composite molecular sieve, the preparation method of which comprises:

[0130] 1. Weigh 0.9g of 25wt% tetrapropylammonium hydroxide solution and 1g of Y molecular sieve (sample name Y E ; Si-Al ratio: 29.0). At room temperature, 0.9 g of the tetrapropylammonium hydroxide solution was slowly and evenly added dropwise into the molecular sieve pores to impregnate them evenly.

[0131] 2. The fully impregnated sample was then directly transferred into a 5 ml PTFE-lined stainless steel pressure reactor. The sealed reactor was then placed in a 140°C oven for crystallization for 24 hours. After washing and drying, the Y / ZSM-5 composite molecular sieve product (sample name Y E / ZSM-5 E ).

[0132] The X-ray diffraction pattern and scanning electron microscope image of the product sample of this comparative example are shown in Figure 15, Figure 19 and Figure 20 respectively.

[0133] Test Example 1

[0134] This test example provides an analysis of the test results of the structural characterization of the above-mentioned examples and comparative examples.

[0135] Figures 1, 3, 5, 9, 13, and 15 are XRD patterns of the composite molecular sieve samples of Examples 1 to 6 and Comparative Examples 1 and 2. It can be seen that Examples 1 to 6 and Comparative Examples 1 and 2 all contain both a Y molecular sieve phase and a ZSM-5 molecular sieve phase. Based on the above XRD results, the mass ratio of the two phases in the composite molecular sieve was calculated and summarized in Table 1.

[0136] The mass ratio of the Y molecular sieve phase to the ZSM-5 molecular sieve phase in the composite molecular sieve can be calculated based on the characteristic peak areas of the molecular sieve phases. Using a 1:1 mass ratio mixture of standard Y molecular sieve and standard ZSM-5 molecular sieve as the standard sample, select the diffraction peak areas for comparison and record this mass ratio as 1:1. Calculations are then performed based on the diffraction patterns of the individual samples tested.

[0137] Table 1

[0138] As can be seen from Table 1, compared to composite molecular sieves prepared using only one Y molecular sieve raw material with a silicon-aluminum ratio, the present invention can effectively adjust the relative proportion of the ZSM-5 molecular sieve phase in the composite molecular sieve by using two Y molecular sieves with silicon-aluminum ratios as raw materials. From Examples 1 and 2, it can be seen that as the content of the first Y molecular sieve with a low silicon-aluminum ratio decreases, the ZSM-5 content increases, demonstrating that the addition of the first Y molecular sieve with a low silicon-aluminum ratio can inhibit the growth of the ZSM-5 molecular sieve during the solid-phase crystallization process, thereby achieving regulation of the relative proportion of the two phases of the composite molecular sieve by regulating the raw material ratio.

[0139] Comparisons between Examples 2 and 3, and between Example 4 and Comparative Example 1, reveal that, given the same raw material composition, compaction treatment reduces the ZSM-5 content in the product compared to the uncompacted product, demonstrating that the pressurization process also inhibits the growth of ZSM-5 molecular sieve during the crystallization process. Combined with the principles of crystallization (solid-phase crystallization and in-situ dissolution), it is speculated that this inhibitory effect also reduces ZSM-5 agglomeration and the formation of large particles.

[0140] Comparing the compositions of the composite molecular sieves of Example 1 and Example 5, and comparing the compositions of the composite molecular sieves of Example 2 and Example 6, it can be seen that: compared with changing the silicon-aluminum ratio of the first Y molecular sieve with a low silicon-aluminum ratio, changing the silicon-aluminum ratio range of the second Y molecular sieve with a high silicon-aluminum ratio can more significantly adjust the two-phase ratio of the composite molecular sieve. Further comparing the molecular sieve morphology of Example 1 and Example 5 and combining the above-mentioned composite molecular sieve composition analysis, it can be seen that for the same second Y molecular sieve, when obtaining a composite molecular sieve with similar composition and morphology, the corresponding first Y molecular sieve has a wider range of silicon-aluminum ratios to select, which shows that the preparation method of the present invention has diversity and universality for the selection of Y molecular sieve raw materials (i.e., first Y molecular sieves) with low silicon-aluminum ratios.

[0141] By comparing between Example 6 and Comparative Example 2, it is found that when the Y molecular sieve of a higher silicon-aluminum ratio is used as the second molecular sieve, the addition of the first Y molecular sieve of low silicon-aluminum ratio can still play a better inhibitory effect. In the scanning electron microscope (SEM) diagram (Figure 19, Figure 20), the ZSM-5 molecular sieve obtained after crystallization of the comparative example 2 product of the second Y molecular sieve of only adding a high silicon-aluminum ratio appears with a typical plate-like molecular sieve morphology with a smooth surface of 3-5 microns; By contrast, the ZSM-5 molecular sieve still appears in the form of smaller nanoparticles attached to the surface of the Y-type molecular sieve using the same second Y molecular sieve and further adding the first Y molecular sieve in the product of Example 6. The above results further prove that the inhibitory effect of adding large particles of ZSM-5 by the first Y molecular sieve of low silicon-aluminum ratio is formed, and prove the diversity of the second molecular sieve silicon-aluminum ratio selection.

[0142] Moreover, Examples 1 to 4 demonstrate that the present invention can regulate the relative proportion of the two phases in the composite molecular sieve by regulating the reaction conditions (such as the raw material ratio, compaction treatment, etc.), thereby affecting the overall silicon-aluminum ratio of the composite molecular sieve and achieving regulation of the acid content.

[0143] Figures 7, 8, 11, 12, and 18 are TEM images of the composite molecular sieves of Example 3, Example 4, and Comparative Example 1. It can be seen that the Y-type molecular sieve phase after crystallization in Example 3 and Example 4 retains the original faujasite shape, with small particles of about 20 nm appearing on the surface, and lattice fringes with a width different from that of the Y-type molecular sieve appearing on the sample surface. Combined with the XRD results showing the presence of Y molecular sieve phase and ZSM-5 molecular sieve phase in the sample, it can be proved that the nanoparticles in the molecular sieve sample prepared by the present invention are ZSM-5 molecular sieves. In contrast, in the morphological characterization results of the composite molecular sieve sample of Comparative Example 1, the ZSM-5 molecular sieve is agglomerated large particles.

[0144] Figures 2, 4, 6, 10 and 17 are SEM images of the composite molecular sieve samples of Examples 1 to 4 and Comparative Example 1. It can be seen that in the SEM images of Examples 1 to 4, the overall molecular sieve presents a relatively uniform morphology. It can be seen from Examples 1 and 2 that as the ratio of high silicon molecular sieve (second Y molecular sieve) increases, the small particles on the surface of the Y-type molecular sieve (typical faujasite structure) in the SEM image significantly increase. For Examples 3 and 4 that are compacted before crystallization, the small particles on the surface of the Y molecular sieve in the electron microscope photos of the two are more dense, and nanoparticles with tree-like growth appear in both Examples 3 and 4. In Comparative Example 1, large particles (3-5 microns) of micron size with a smooth surface and a plate-like zeolite stacking morphology appear, which are ZSM-5 molecular sieves. Combined with the formation of ZSM-5 nanoparticles in the embodiment in the TEM image, it can be proved that by adding a low silicon-aluminum ratio Y molecular sieve to the raw material and compacting the molecular sieve raw material, the growth of ZSM-5 can be suppressed and the formation of large particles of ZSM-5 can be reduced.

[0145] Test Example 2

[0146] This test example provides a catalytic performance test of the composite molecular sieve samples of Examples 2 to 4.

[0147] The Y molecular sieve (corresponding to the Y molecular sieve phase in Example 2) and the ZSM-5 molecular sieve (corresponding to the ZSM-5 molecular sieve phase in Example 2) were mixed in a mass ratio of 85:15 to obtain comparative sample 2-1.

[0148] Y molecular sieve (corresponding to the Y molecular sieve phase in Example 3) and ZSM-5 molecular sieve (corresponding to the ZSM-5 molecular sieve phase in Example 3) were mixed in a mass ratio of 92:8 to obtain comparative sample 3-1.

[0149] The Y molecular sieve (corresponding to the Y molecular sieve phase in Example 4) and the ZSM-5 molecular sieve (corresponding to the ZSM-5 molecular sieve phase in Example 4) were mixed in a mass ratio of 64:36 to obtain comparative sample 4-1.

[0150] The USY molecular sieve with a silicon-aluminum ratio of 19.1 used as raw material in Example 2 was used as comparison sample 2-2, the USY molecular sieve with a silicon-aluminum ratio of 19.1 used as raw material in Example 3 was used as comparison sample 3-2, and the USY molecular sieve with a silicon-aluminum ratio of 19.1 used as raw material in Example 4 was used as comparison sample 4-2.

[0151] The above samples were subjected to catalytic cracking micro-reaction performance tests.

[0152] Catalyst Preparation: The prepared molecular sieve sample to be tested was dried and cooled. Kaolin, molecular sieve, silica sol, and water were stirred at 100°C for 4 hours to achieve uniformity, then dried overnight at 100°C and hydrothermally aged for 4 hours at 100°C. The resulting sample was pressed into tablets at 20 MPa and sieved to 20-40 mesh to obtain the catalyst for the FCC microreactor. Prior to catalytic reaction evaluation, the catalyst bed was loaded and, under a nitrogen atmosphere, heated at a rate of 2°C / min to 100°C. The temperature was then maintained at 100°C for 2 hours, then increased at a rate of 2°C / min to 550°C. The mixture was then calcined at 550°C for 2 hours, and then cooled naturally to the reaction temperature for use. This process constitutes in-situ catalyst activation.

[0153] Catalytic cracking: This experiment uses a Beijing Vikendu catalytic cracking fixed-bed reactor to evaluate the catalytic performance of the prepared molecular sieve catalyst. Nitrogen is used as the carrier gas. The feed rate is changed by adjusting the nitrogen flow rate, thereby adjusting the reaction space velocity. The inner diameter of the reaction tube is 2 cm, and the catalyst loading is 5 g.

[0154] Operating parameters: reaction temperature: 510°C; regeneration temperature: 650°C; carrier gas flow rate: 200 mL / min

[0155] Steps:

[0156] (1) Using quartz sand and quartz wool to fix the molecular sieve particles at the end point of the thermocouple in the middle of the reaction tube;

[0157] (2) Install and fix the reaction tube, check the air tightness of the device and related insulation, and ensure that the air tightness and insulation performance of each pipeline are intact;

[0158] (3) nitrogen was introduced into the reaction tube and the temperature was gradually raised to 510°C to activate the catalyst in situ;

[0159] (4) Adjusting the carrier gas flow rate to an appropriate level, introducing the crude oil into the reaction tube to contact the catalyst and initiate the reaction;

[0160] (5) After the reaction is completed, the liquid and gas phase products are collected, subjected to chromatographic analysis, and the product distribution is calculated;

[0161] (6) Start the aging program and raise the temperature to 650°C for 1 hour, then repeat steps (3), (4), and (5) for cyclic evaluation.

[0162] The test results are summarized in Table 2, Table 3 and Table 4.

[0163] Table 2

[0164] As can be seen from Table 2, the comparative sample 1 formed by mechanically mixing the two molecular sieves has a coke yield reduction of 0.90 relative to the conventional USY molecular sieve, and an increase in propylene yield of 2.11%; and the Y / ZSM-5 composite molecular sieve of Example 3 can not only further increase the propylene yield, but also significantly reduce the coke yield (reduction rate of up to 33%). The existing industrial catalytic cracking catalyst has a total liquid yield (corresponding to "liquefied gas + gasoline + diesel" in Table 2) of 83-86%, a coke yield of 6-10%, and a propylene yield of about 5%. It can be seen that the catalytic performance of the Y / ZSM-5 composite molecular sieve of Example 3 is also significantly improved relative to the catalytic performance of the existing industrial catalytic cracking catalyst.

[0165] Table 3

[0166] As can be seen from Table 3, the comparative sample 1 formed by mechanically mixing the two molecular sieves increased the coke yield by 0.93 relative to the conventional USY molecular sieve, and the propylene yield increased by 2.35%; and the Y / ZSM-5 composite molecular sieve of Example 2 can not only further improve the propylene yield, but also significantly reduce the coke yield (the reduction rate reaches 26%). The existing industrial catalytic cracking catalyst has a total liquid yield (corresponding to the "liquefied gas + gasoline + diesel" in Table 2) of 83-86%, a coke yield of 6-10%, and a propylene yield of about 5%. It can be seen that the catalytic performance of the Y / ZSM-5 composite molecular sieve of Example 2 is also significantly improved relative to the catalytic performance of the existing industrial catalytic cracking catalyst.

[0167] Table 4

[0168] As can be seen from Table 4, the comparative sample 1 formed by mechanically mixing the two molecular sieves reduced the coke yield by 0.46 relative to the conventional USY molecular sieve, and increased the propylene yield by 5.99%; and the Y / ZSM-5 composite molecular sieve of Example 4 can not only further improve the propylene yield, but also significantly reduce the coke yield (the reduction rate reaches 41%). The existing industrial catalytic cracking catalyst has a total liquid yield (corresponding to the "liquefied gas + gasoline + diesel" in Table 2) of 83-86%, a coke yield of 6-10%, and a propylene yield of about 5%. It can be seen that the catalytic performance of the Y / ZSM-5 composite molecular sieve of Example 4 is also significantly improved relative to the catalytic performance of the existing industrial catalytic cracking catalyst.

[0169] The above results can prove that the Y / ZSM-5 composite molecular sieve provided by the present invention has a more excellent effect in improving propylene yield and reducing coke. It can be proved that the preparation method of the present invention can regulate the structure of the composite molecular sieve and the Y / ZSM-5 composite molecular sieve obtained thereby has excellent catalytic performance.

[0170] The above results illustrate that the preparation method provided by the present invention utilizes the solubility difference of two Y molecular sieves with different silicon-aluminum ratios to produce a composite molecular sieve product having both a Y molecular sieve phase and a ZSM-5 molecular sieve phase. Wherein, as shown in Figure 15, in the process of generating the ZSM-5 molecular sieve phase, a physical confinement effect can be achieved by the first Y molecular sieve and / or compaction treatment having a relatively low silicon-aluminum ratio, so that the dissolution of the second Y molecular sieve crystal particles and the crystal formation of the ZSM-5 molecular sieve are both carried out locally in situ, thereby obtaining a ZSM-5 molecular sieve crystal that is highly nano-sized and the ZSM-5 molecular sieve phase is uniformly distributed and in close contact with the Y / ZSM-5 composite molecular sieve.

Claims

1. A method for preparing a Y / ZSM-5 composite molecular sieve, the method comprising: The Y molecular sieve raw material containing the second Y molecular sieve is fully mixed with the alkaline solution of the structure directing agent, and crystallized to obtain the Y / ZSM-5 composite molecular sieve; Wherein, the preparation method further comprises: drying and compacting treatment before crystallization, and / or, the Y molecular sieve raw material contains a first Y molecular sieve; The silicon-aluminum ratio of the first Y molecular sieve is greater than 0 and less than 14, the silicon-aluminum ratio of the second Y molecular sieve is greater than or equal to 9, and the silicon-aluminum ratio of the second Y molecular sieve is greater than the silicon-aluminum ratio of the first Y molecular sieve; In the Y molecular sieve raw material, based on the total mass of the first Y molecular sieve and the second Y molecular sieve being 100%, the mass of the first Y molecular sieve is less than or equal to 70%.

2. The method for preparing the Y / ZSM-5 composite molecular sieve according to claim 1, comprising: Mixing the first Y molecular sieve and the second Y molecular sieve and slurrying them, filtering and drying the slurry to obtain a Y molecular sieve raw material; The Y molecular sieve raw material is fully mixed with the alkaline solution of the structure directing agent, and crystallized to obtain the Y / ZSM-5 composite molecular sieve; Alternatively, the second Y molecular sieve is used as a Y molecular sieve raw material and is fully mixed with an alkaline solution of a structure directing agent, and then dried, compacted, and crystallized to obtain the Y / ZSM-5 composite molecular sieve; Alternatively, the first Y molecular sieve and the second Y molecular sieve are mixed and slurried, and the slurry is filtered and dried to obtain a Y molecular sieve raw material; the Y molecular sieve raw material is fully mixed with an alkaline solution of a structure directing agent, dried, compacted, and crystallized to obtain the Y / ZSM-5 composite molecular sieve, wherein the silicon-aluminum ratio of the first Y molecular sieve is greater than 0 and less than 14, the silicon-aluminum ratio of the second Y molecular sieve is greater than or equal to 9, and the silicon-aluminum ratio of the second Y molecular sieve is greater than the silicon-aluminum ratio of the first Y molecular sieve; In the Y molecular sieve raw material, based on the total mass of the first Y molecular sieve and the second Y molecular sieve being 100%, the mass of the first Y molecular sieve is less than or equal to 70%.

3. The preparation method according to claim 1, wherein The structure directing agent includes one or a combination of two or more of an organic amine, a quaternary ammonium base and a tertiary ammonium base.

4. The preparation method according to claim 3, wherein The organic amine includes one or a combination of two or more of tetrapropylammonium bromide, hexadecyltrimethylammonium bromide, triethylamine, and ethylenediamine.

5. The preparation method according to claim 3, wherein: The quaternary ammonium base includes one or a combination of two or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.

6. The preparation method according to claim 3, wherein: The tertiary ammonium base includes choline hydroxide.

7. The preparation method according to claim 1, wherein The mass ratio of the Y molecular sieve raw material to the structure directing agent is (0.1-1): (0.01-1).

8. The preparation method according to claim 1, wherein The pH value of the alkaline solution of the structure directing agent is 10-14.

9. The preparation method according to claim 1, wherein The mass ratio of the Y molecular sieve raw material, the structure directing agent, and the water in the alkaline solution of the structure directing agent is (0.1-1): (0.01-1): (0.5-5).

10. The preparation method according to claim 1, wherein: The difference between the silicon-to-aluminum ratio of the second Y molecular sieve and the silicon-to-aluminum ratio of the first Y molecular sieve is greater than or equal to 5.

11. The preparation method according to claim 1, wherein: The difference between the silicon-to-aluminum ratio of the second Y molecular sieve and the silicon-to-aluminum ratio of the first Y molecular sieve is 5-30.

12. The preparation method according to claim 1, wherein: The crystallization temperature is 50-250° C., and the crystallization time is 0.1-120 h.

13. The preparation method according to claim 1, wherein: The pressure of the compaction treatment is 0.1 MPa-60 MPa.

14. A Y / ZSM-5 composite molecular sieve obtained by the preparation method according to any one of claims 1 to 13.

15. The Y / ZSM-5 composite molecular sieve according to claim 14, wherein: The Y / ZSM-5 composite molecular sieve comprises a Y molecular sieve phase and a ZSM-5 molecular sieve phase.

16. The Y / ZSM-5 composite molecular sieve according to claim 15, wherein: The mass ratio of the Y molecular sieve phase to the ZSM-5 molecular sieve phase is 50-99:1-50.

17. A catalytic cracking catalyst comprising the Y / ZSM-5 composite molecular sieve according to any one of claims 14 to 16.

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