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

Abstract

The invention provides a Y / ZSM-5 composite molecular sieve, a preparation method thereof and a catalytic cracking catalyst. The preparation method comprises the following steps: mixing a first Y molecular sieve and a second Y molecular sieve, mixing with an alkaline solution of a structure-directing agent, and crystallizing to obtain the Y / ZSM-5 composite molecular sieve, or mixing a second Y molecular sieve or a mixture of the first Y molecular sieve and the second Y molecular sieve with a structure-directing agent, and then carrying out pressurization treatment and crystallization to obtain the Y / ZSM-5 composite molecular sieve, the silica-alumina ratio of the first Y molecular sieve being greater than 0 and less than 14, the silica-alumina ratio of the second Y molecular sieve being greater than or equal to 9, and the silica-alumina ratio of the second Y molecular sieve being greater than the silica-alumina ratio of the first Y molecular sieve; the mass ratio of the first Y molecular sieve to the second Y molecular sieve is less than or equal to 7: 3. The invention also provides the composite molecular sieve obtained by the preparation method and a catalytic cracking catalyst comprising the composite molecular sieve. The Y / ZSM-5 composite molecular sieve has two molecular sieve phases and relatively high catalytic performance.

Description

Technical Field

[0001] The 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

[0002] Through the catalytic cracking process, the production of low-carbon olefins and aromatics can not only greatly digest the excess refining capacity, achieve balanced development of refining and downstream high-end petrochemical product production, further improve corporate benefits and market competitiveness, but also greatly increase the self-sufficiency rate of low-carbon olefins, alleviate the contradiction between insufficient supply and demand of petrochemical raw materials, and play a huge supporting role in economic development. The occurrence of positive carbon ion reaction in the catalytic cracking process of heavy oil requires the catalysis of acidic catalysts. Therefore, the development of high-performance solid acid catalysts has become the core of catalytic cracking technology research and innovation. Zeolite molecular sieves are the most studied type of catalyst additives in catalytic cracking catalysts. In the catalytic cracking process of heavy oil, ZSM-5 molecular sieves can be used in combination with Y molecular sieves to increase the selectivity of low-carbon olefins by cracking hydrocarbon molecules in gasoline fractions. However, in the prior art, when Y-type molecular sieves and ZSM-5 molecular sieves are used in combination, there is usually a significant spatial distance between the two, resulting in the linear hydrocarbons and simple isomerized hydrocarbons from the Y-type molecular sieve usually leaving the FCC catalyst surface directly as the final reaction products, and it is difficult to continue to react further on the surface of the ZSM-5 molecular sieve as intermediates.

[0003] 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.

[0004] 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. Summary of the invention

[0005] In order to solve the above problems, the object of the present invention is to provide a Y / ZSM-5 composite molecular sieve and a preparation method thereof and a catalytic cracking catalyst. The Y / ZSM-5 composite molecular sieve has 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, which is beneficial to improving the catalytic activity of the molecular sieve.

[0006] 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:

[0007] Synthesis method 1: Mix and slurry the first Y molecular sieve and the second Y molecular sieve, filter and dry the slurry to obtain a Y molecular sieve raw material; fully mix the Y molecular sieve raw material with an alkaline solution of a structure directing agent, and crystallize to obtain the Y / ZSM-5 composite molecular sieve;

[0008] 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;

[0009] 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;

[0010] 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.

[0011] 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).

[0012] 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, mix the two molecular sieves thoroughly after pulping, filter and dry them, 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 containing the alkaline solution of the structure directing agent in a high-temperature hydrothermal environment. Synthesis method 2 is to dry the Y molecular sieve raw material mixed with the structure directing agent and then compact it, and transfer the compacted mixed Y molecular sieve to a high-temperature hydrothermal environment for in-situ dissolution and crystallization; in the process of in-situ dissolution and crystallization in the high-temperature hydrothermal environment, the silicon and aluminum dissolved in the Y molecular sieve undergo structural rearrangement and crystallization, thereby obtaining a Y / ZSM-5 composite molecular sieve.

[0013] The second synthesis method provided by the present invention is to use a second Y molecular sieve with a relatively high silicon-aluminum ratio as a raw material, introduce a structure directing agent into the pores of the second Y molecular sieve, and then compact the second Y molecular sieve containing the structure directing agent, and then perform in-situ dissolution and crystallization treatment on the compacted second Y molecular sieve in a high-temperature hydrothermal environment, so that the silicon-aluminum ratio of the dissolved second Y molecular sieve undergoes structural rearrangement and crystallization, thereby obtaining a Y / ZSM-5 composite molecular sieve.

[0014] The third synthesis method provided by the present invention is to use two Y molecular sieves with different silicon-aluminum ratios as raw materials at the same time, and compact the Y molecular sieve raw material containing the alkaline solution of the structure directing agent before crystallization, so that the Y molecular sieve undergoes structural rearrangement and crystal transformation during the crystallization process, thereby obtaining a Y / ZSM-5 composite molecular sieve.

[0015] In the above preparation method, Fig.21 As shown, 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 the crystallization temperature) and high alkali (provided by the alkaline solution of the 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; in contrast, 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 not at all. 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 also be physically confined by compaction treatment. In contrast, Fig.21 As shown, in the case where no compaction treatment is performed and only the second Y molecular sieve is used as a raw material, although a certain degree of solid phase crystallization will occur in the single second Y molecular sieve during the crystallization process, the generated ZSM-5 molecular sieve is not affected by physical confinement, and obvious agglomeration will occur between the grains. The present invention suppresses the flow and exchange of materials during rearrangement and crystallization 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 crystallization process of the present invention is conducive to the formation of ultrafine nano-sized ZSM-5 molecular sieve phases, and improves the degree of uniform dispersion of the ZSM-5 molecular sieve phase in the composite molecular sieve.

[0016] Compared with conventional micron-sized ZSM-5 molecular sieves, the nano-sized ZSM-5 molecular sieves formed by 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 clogging of pores by coking and carbon formation. Therefore, the catalytic activity (such as conversion rate) of the composite molecular sieve can be significantly improved, the deactivation rate of the composite molecular sieve can be reduced, and the service life can be extended.

[0017] 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, the silicon-aluminum ratio of the first Y molecular sieve may be greater than 0 and less than 14, and the silicon-aluminum ratio of the second Y molecular sieve may 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 may be any one of 9-14, for example, it may 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.

[0018] In the present invention, the m value can be adjusted according to 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 value of the structure directing alkaline solution. The m value can also vary according to the type of structure directing agent. For the same type of structure directing agent (such as a structure directing agent that is a quaternary ammonium salt), the larger the ionic volume of the structure directing agent (such as the longer the side chain 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 value 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.

[0019] 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 specific values ​​such as 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, and the range with any two of the above specific values ​​as endpoints.

[0020] 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.

[0021] 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; it can be further controlled 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.

[0022] 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, according to 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 ​​and a range with any two of the above specific values ​​as endpoints.

[0023] 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.

[0024] 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.

[0025] In 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: in 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.

[0026] In the above three synthesis methods, by controlling the amount of the 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 is "limitedly dissolved", which can achieve the effect of retaining part of the Y molecular sieve framework and making the final product contain the Y molecular sieve phase, and 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 the 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.

[0027] 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, it can be (0.1-1): (0.1-1). In some specific embodiments, in parts by mass, 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 accordingly, 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.

[0028] In the above three synthesis methods, the cation of the structure directing agent can be used as a structure directing agent for the ZSM-5 molecular sieve to promote the formation of the ZSM-5 molecular sieve phase; the anion hydroxide in the alkaline solution of the structure directing agent can dissolve the silicon and aluminum in the Y molecular sieve as the silicon source and aluminum source of the ZSM-5 molecular sieve phase, and on the other hand, it 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 proportion 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, and a tertiary ammonium base.

[0029] 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.

[0030] In the above three synthesis methods, the tertiary ammonium base may include choline hydroxide.

[0031] 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.

[0032] In the above three synthesis methods, the pH value of the alkaline solution of the structure directing agent can be 10-14, specifically, it can be 10, 11, 12, 13, 14 and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0033] 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. The inorganic base may specifically include one or a combination of two or more of LiOH, NaOH, and KOH.

[0034] 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 Y molecular sieve raw material, the structure directing agent, and the water in 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-like system. Due to the low fluidity of the system and the confinement effect of the first Y molecular sieve, the silicon and aluminum dissolved in the second Y molecular sieve are crystallized in situ to generate a ZSM-5 phase, and the confinement effect of the first Y molecular sieve can promote the ZSM-5 molecular sieve phase to form uniformly dispersed nano-sized small crystals.

[0035] 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 specific manner by immersing the Y molecular sieve raw material in the 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 pressurized impregnation method, or a combination of two or more thereof. Alternatively, the Y molecular sieve raw material and the alkaline solution of the structure directing agent may also be mixed by dropping the alkaline solution of the structure directing agent into the Y molecular sieve raw material.

[0036] In the above three synthesis methods, 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-250°C, for example, 80°C-200°C. In some specific embodiments, the crystallization temperature can be 50°C, 80°C, 100°C, 150°C, 200°C, 250°C and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0037] In the above three synthesis methods, the crystallization time is 0.1h-120h, for example, 0.5-72h. In some specific embodiments, the crystallization time can be 0.1h, 0.5h, 1h, 5h, 10h, 20h, 24h, 30h, 40h, 48h, 50h, 60h, 70h, 72h, 80h, 90h, 96h, 120h and other specific values, as well as ranges with any two of the above specific values ​​as endpoints.

[0038] In the above preparation method, the crystallization pressure is generally 0.1-10MPa, for example, 0.1MPa, 0.5MPa, 1MPa, 2MPa, 3MPa, 4MPa, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa, 10MPa and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0039] In the above three synthesis methods, the crystallization process can be in-situ crystallization, and no liquid solvent exists during the crystallization process. The crystallization method can specifically include one or a combination of two or more of solid phase hydrothermal crystallization, quasi-solid phase hydrothermal crystallization, steam-assisted solid phase hydrothermal crystallization, etc.

[0040] 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, taking 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 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, 99.5%, 99.9% and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0041] 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.

[0042] 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:

[0043] 1. Mix and slurry a first Y molecular sieve and a second Y molecular sieve in a mass ratio of less than or equal to 7:3, and dry 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;

[0044] 2. Immerse the Y molecular sieve raw material in the solution of the structure directing agent. After sufficient immersion, 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-120 h to obtain the Y / ZSM-5 composite molecular sieve.

[0045] In the above-mentioned synthesis method 2, the second Y molecular sieve with a higher silicon-aluminum ratio after compaction is subjected to in-situ dissolution and crystallization treatment in a high-temperature and high-alkali hydrothermal environment, so that the silicon and aluminum dissolved in the Y molecular sieve undergo structural rearrangement and crystallization, thereby obtaining a Y / ZSM-5 composite molecular sieve. The compaction treatment can increase the density between particles and increase the difficulty of mass transfer, thereby inhibiting the aggregation of large particles of the ZSM-5 phase during the crystallization process.

[0046] 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 ZSM-5 molecular sieve phase in the composite molecular sieve, and the particle size of the formed ZSM-5 molecular sieve is smaller.

[0047] In the above synthesis method 2, the pressure of the compaction treatment can be controlled to be 0.1MPa-60MPa, for example, 1-30MPa. Specifically, the pressure of the compaction treatment can be 0.1MPa, 0.5MPa, 1MPa, 5MPa, 10MPa, 20MPa, 30MPa, 40MPa, 50MPa, 60MPa and other specific values, and a range with any two of the above specific values ​​as endpoints.

[0048] According to a specific embodiment of the present invention, the second synthesis method of the preparation method of the above-mentioned Y / ZSM-5 composite molecular sieve may specifically include:

[0049] 1. Use the second Y molecular sieve with a silicon-aluminum ratio greater than or equal to m as the Y molecular sieve raw material, where m is any value between 9 and 14;

[0050] 2. Immerse the Y molecular sieve raw material in an alkaline solution of a structure directing agent, take out the Y molecular sieve raw material after sufficient immersion, and dry and compact the taken out Y molecular sieve raw material at a pressure of 0.1 MPa-60 MPa;

[0051] 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.

[0052] According to a specific embodiment of the present invention, the synthesis method 3 of the preparation method of the above Y / ZSM-5 composite molecular sieve may specifically include:

[0053] 1. Mix and slurry a first Y molecular sieve and a second Y molecular sieve in a mass ratio of less than or equal to 7:3, and dry 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;

[0054] 2. Immerse the Y molecular sieve raw material in the solution of the 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 0.1MPa-60MPa; the compacted Y molecular sieve raw material is transferred to a sealed reactor and crystallized at 50-250°C for 0.1h-120h to obtain the Y / ZSM-5 composite molecular sieve.

[0055] The present invention also provides a Y / ZSM-5 composite molecular sieve, which is obtained by the above preparation method.

[0056] 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 proportion of the ZSM-5 molecular sieve phase in the Y / ZSM-5 composite molecular sieve can be greater than or equal to 1%. Further, the mass ratio of the Y molecular sieve phase to the ZSM-5 molecular sieve phase can be 50-99:1-50, for example, 64-93:7-36. In some specific embodiments, the mass ratio of the Y molecular sieve phase to the ZSM-5 molecular sieve phase can be 99:1, 93:7, 90:10, 85:15, 80:20, 70:30, 64:36, 60:40, 50:50 and other specific values ​​and a range with any two of the above specific values ​​as endpoints.

[0057] The present invention also provides a catalytic cracking catalyst, which includes the above-mentioned Y / ZSM-5 composite molecular sieve. The ZSM-5 molecular sieve phase in the above-mentioned Y / ZSM-5 composite molecular sieve is an ultrafine nanophase, which is evenly distributed with the Y molecular sieve phase, which is conducive to the molecules decomposed in the Y molecular sieve phase entering the ZSM-5 molecular sieve phase for further cracking and decomposition, and is conducive to the production of more low-carbon olefins.

[0058] The beneficial effects of the present invention include:

[0059] The preparation method of the Y / ZSM-5 composite molecular sieve provided by the present invention is crystallized by using molecular sieves with different silicon-aluminum ratios as raw materials, and the dissolution, rearrangement and crystal transformation of part of the Y molecular sieve can occur during the crystallization process, and the formation of the ZSM-5 molecular sieve phase is promoted, and the ZSM-5 molecular sieve phase is an ultrafine nano phase and is uniformly dispersed in the composite molecular sieve. In addition, by selecting molecular sieves with different silicon-aluminum ratios, the regulation of the skeleton aluminum content in the composite molecular sieve can also be achieved, thereby adjusting the acid amount of the composite molecular sieve. The two phases in the composite molecular sieve thus obtained are evenly distributed, and the catalytic performance is effectively improved, which can be applied to the catalytic cracking process. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 Composite molecular sieve Y C1 / ZSM-5 C1 Sample and composite molecular sieve Y B / ZSM-5 B X-ray diffraction spectrum of the sample.

[0061] Figure 2 Composite molecular sieve Y C1 / ZSM-5 C1 Scanning electron microscope image of the sample.

[0062] Figure 3 Composite molecular sieve Y C2 / ZSM-5 C2 Sample and composite molecular sieve Y B / ZSM-5 B X-ray diffraction spectrum of the sample.

[0063] Figure 4 Composite molecular sieve Y C2 / ZSM-5 C2 Scanning electron microscope image of the sample.

[0064] Figure 5 Composite molecular sieve Y C3 / ZSM-5 C3 Sample and composite molecular sieve Y B / ZSM-5 B X-ray diffraction spectrum of the sample.

[0065] Figure 6 Composite molecular sieve Y C3 / ZSM-5 C3 Scanning electron microscope image of the sample.

[0066] Figure 7 , Figure 8 Composite molecular sieve Y C3 / ZSM-5 C3 Transmission electron microscopy image of the sample.

[0067] Fig. 9 Composite molecular sieve Y C4 / ZSM-5 C4 Sample and composite molecular sieve Y B / ZSM-5 B X-ray diffraction spectrum of the sample.

[0068] Fig.10 Composite molecular sieve Y C4 / ZSM-5 C4 Scanning electron microscope image of the sample.

[0069] Fig.11 , Fig.12 Composite molecular sieve Y C4 / ZSM-5 C4 Transmission electron microscopy image of the sample.

[0070] Fig.13 Composite molecular sieve Y C5 / ZSM-5 C5 Sample and composite molecular sieve Y B / ZSM-5 B X-ray diffraction spectrum of the sample.

[0071] Fig.14Composite molecular sieve Y C5 / ZSM-5 C5 Scanning electron microscopy images of the samples.

[0072] Fig.15 Composite molecular sieve Y C6 / ZSM-5 C6 Sample and composite molecular sieve Y E / ZSM-5 E X-ray diffraction spectrum of the sample.

[0073] Fig.16 Composite molecular sieve Y C6 / ZSM-5 C6 Scanning electron microscope image of the sample.

[0074] Fig.17 Composite molecular sieve Y B / ZSM-5 B Scanning electron microscope image of the sample.

[0075] Fig.18 Composite molecular sieve Y B / ZSM-5 B Transmission electron microscopy image of the sample.

[0076] Fig.19 , Fig. 20 Composite molecular sieve Y E / ZSM-5 E Scanning electron microscope image of the sample.

[0077] Fig.21 It is a schematic diagram of the crystallization process in the preparation method of the present invention. DETAILED DESCRIPTION

[0078] In order to have a clearer understanding of the technical features, purposes 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 construed as limiting the applicable scope of the present invention.

[0079] In the present invention, the silicon-to-aluminum ratio is the molar ratio of Si / Al. The first Y molecular sieve and the second Y molecular sieve used in the following examples are both ammonium-type USY molecular sieves, which are commercially available.

[0080] Example 1

[0081] This embodiment provides a Y / ZSM-5 composite molecular sieve, the preparation method of which includes:

[0082] 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, and dried to obtain Y molecular sieve raw materials (named Y C1 ).

[0083] 2. Weigh 0.9 g of 25 wt% tetrapropylammonium hydroxide solution and 1 g 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.

[0084] 3. Then the fully 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 C1 / ZSM-5 C1 ).

[0085] The X-ray diffraction patterns and scanning electron microscope images of the product samples obtained in this example are shown in Figure 1 and Figure 2 shown.

[0086] Example 2

[0087] This embodiment provides a Y / ZSM-5 composite molecular sieve, the preparation method of which includes:

[0088] 1. 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, and dried to obtain Y molecular sieve raw materials (named Y C2 ).

[0089] 2. Weigh 0.9 g of 25 wt% tetrapropylammonium hydroxide solution and 1 g of Y molecular sieve raw material Y C2 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.

[0090] 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 ).

[0091] The X-ray diffraction patterns and scanning electron microscope images of the product samples obtained in this example are shown in Figure 3 and Figure 4 shown.

[0092] Example 3

[0093] This embodiment provides a Y / ZSM-5 composite molecular sieve, the preparation method of which includes:

[0094] 1. 3g of the first Y molecular sieve (sample name Y A ; Silicon-aluminum 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 Y molecular sieve raw materials with different silicon-aluminum ratios (named Y C3 ).

[0095] 2. Weigh 0.9g of 25wt% tetrapropylammonium hydroxide solution and 1g of mixed Y C3 Molecular sieve: At room temperature, 0.9 g of the tetrapropylammonium hydroxide solution is slowly and evenly added to the molecular sieve pores to impregnate them evenly.

[0096] 3. After the fully impregnated sample was dried at room temperature for 24 hours, it was subjected to high pressure (25MPa) compaction treatment. The treated sample was transferred into 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 ).

[0097] The X-ray diffraction pattern, scanning electron microscope image and transmission electron microscope image of the product sample of this embodiment are respectively as follows: Figure 5 , Figure 6 , Figure 7 and Figure 8 shown.

[0098] Example 4

[0099] This embodiment provides a Y / ZSM-5 composite molecular sieve, the preparation method of which includes:

[0100] 1. Weigh 0.9 g of 25 wt% tetrapropylammonium hydroxide solution and 1 g of Y molecular sieve (sample name Y B ; Silicon-aluminum 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.

[0101] 2. After the fully impregnated sample was dried at room temperature for 24 hours, it was subjected to high pressure (25MPa) compaction treatment. The treated sample was transferred into a 5 ml polytetrafluoroethylene lined stainless steel pressure-resistant 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 ).

[0102] The X-ray diffraction pattern, scanning electron microscope image and transmission electron microscope image of the product sample of this embodiment are respectively as follows: Fig. 9 , Fig.10 , Fig.11 and Fig.12 shown.

[0103] Example 5

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

[0105] 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, and dried to obtain Y molecular sieve raw materials (named Y C5 ).

[0106] 2. Weigh 0.9 g of 25 wt% tetrapropylammonium hydroxide solution and 1 g 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.

[0107] 3. Then the fully 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 C5 / ZSM-5 C5 ).

[0108] The X-ray diffraction patterns and scanning electron microscope images of the product samples obtained in this example are shown in Fig.13 and Fig.14 shown.

[0109] Example 6

[0110] This embodiment provides a Y / ZSM-5 composite molecular sieve, the preparation method of which includes:

[0111] 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, and dried to obtain Y molecular sieve raw materials (named Y C6 ).

[0112] 2. Weigh 0.9 g of 25 wt% tetrapropylammonium hydroxide solution and 1 g 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.

[0113] 3. Then the fully 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 C6 / ZSM-5 C6 ).

[0114] The X-ray diffraction patterns and scanning electron microscope images of the product samples obtained in this example are shown in Fig.15 and Fig.16 shown.

[0115] Comparative Example 1

[0116] This comparative example provides a Y / ZSM-5 composite molecular sieve, the preparation method of which comprises:

[0117] 1. Weigh 0.9 g of 25 wt% tetrapropylammonium hydroxide solution and 1 g of Y molecular sieve (sample name Y B ; Silicon-aluminum 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.

[0118] 2. Then the fully 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 B / ZSM-5 B ).

[0119] The scanning electron microscope images and transmission electron microscope images of the product samples of this comparative example are shown as follows: Fig.17 and Fig.18 shown.

[0120] Comparative Example 2

[0121] This comparative example provides a Y / ZSM-5 composite molecular sieve, the preparation method of which comprises:

[0122] 1. Weigh 0.9 g of 25 wt% tetrapropylammonium hydroxide solution and 1 g of Y molecular sieve (sample name Y E ; Silicon-aluminum 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.

[0123] 2. Then the fully 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 E / ZSM-5 E ).

[0124] The scanning electron microscope images and transmission electron microscope images of the product samples of this comparative example are shown as follows: Fig.15 and Fig.19 , Fig. 20 shown.

[0125] Test Example 1

[0126] This test example provides an analysis of the test results of the structural characterization of the above-mentioned embodiment and comparative example samples.

[0127] Figure 1 , Figure 3 , Figure 5 , Fig. 9 , Fig.13 , Fig.15 The XRD diagrams of the composite molecular sieve samples of Examples 1 to 6 and Comparative Examples 1 and 2 are shown. It can be seen that Examples 1 to 6 and Comparative Examples 1 and 2 all contain Y molecular sieve phase and ZSM-5 molecular sieve phase. Based on the above XRD results, the mass ratio of the two phases in the composite molecular sieve is calculated and summarized in Table 1.

[0128] 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 area of ​​the molecular sieve phase. A mixture of a standard Y molecular sieve and a standard ZSM-5 molecular sieve in a mass ratio of 1:1 is used as a standard sample, and the diffraction peak area is selected for comparison. The mass ratio is recorded as 1:1, and then the calculation is performed based on the diffraction conditions of each sample to be tested.

[0129] Table 1

[0130]

[0131] As can be seen from Table 1, compared with the composite molecular sieve prepared by 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. It can be seen from Example 1 to Example 2 that as the content of the first Y molecular sieve with a low silicon-aluminum ratio decreases, the ZSM-5 content increases, proving 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 the regulation of the relative proportion of the two phases of the composite molecular sieve by regulating the raw material ratio.

[0132] By comparing Example 2 with Example 3, and Example 4 with Comparative Example 1, it is found that under the same raw material composition, the ZSM-5 content in the product is reduced by the pressure treatment compared with the product obtained without the pressure treatment, which proves that the pressure process also has an inhibitory effect on the growth of the ZSM-5 molecular sieve during the crystallization process. Combined with the crystallization principle (solid phase crystallization, in-situ dissolution), it is speculated that this inhibitory effect can also reduce the agglomeration of ZSM-5 and the formation of large particles.

[0133] Comparing the composition of the composite molecular sieves of Example 1 with that of Example 5, and comparing the composition of the composite molecular sieves of Example 2 with that of 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 obviously adjust the ratio of the two phases of the composite molecular sieve. Further comparing the morphology of the molecular sieves of Example 1 with that of Example 5 and combining the above-mentioned analysis of the composition of the composite molecular sieve, it can be seen that for the same second Y molecular sieve, when obtaining a composite molecular sieve with similar composition and morphology, the silicon-aluminum ratio of the corresponding first Y molecular sieve can be selected in a larger range, which shows that the preparation method of the present invention has diversity and universality for the selection of the Y molecular sieve raw material (i.e., the first Y molecular sieve) with a low silicon-aluminum ratio.

[0134] By comparing Example 6 with Comparative Example 2, it is found that when the Y molecular sieve with a higher silicon-aluminum ratio is used as the second molecular sieve, the addition of the first Y molecular sieve with a low silicon-aluminum ratio can still play a good inhibitory role. Fig.19 , Fig. 20 ), the ZSM-5 molecular sieve obtained from the product of comparative example 2, which only adds the second Y molecular sieve with a high silicon-aluminum ratio, appears in a typical plate-like molecular sieve morphology with a smooth surface of 3-5 microns after crystallization; in contrast, the ZSM-5 molecular sieve in the product of Example 6, which uses the same second Y molecular sieve and further adds the first Y molecular sieve, still appears in the form of smaller nanoparticles attached to the surface of the Y-type molecular sieve. The above results further prove the inhibitory effect of adding the first Y molecular sieve with a low silicon-aluminum ratio on the formation of large particles of ZSM-5, and prove the diversity of the selection of the silicon-aluminum ratio of the second molecular sieve.

[0135] Furthermore, 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 raw material ratio, compaction treatment, etc.), thereby affecting the overall silicon-aluminum ratio of the composite molecular sieve and achieving regulation of the amount of acid.

[0136] Figure 7 , Figure 8 , Fig.11 , Fig.12 , Fig.18 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 of Example 3 and Example 4 retains the original faujasite shape, and fine particles of about 20 nm appear on the surface, and lattice fringes with different lattice fringes width from the Y-type molecular sieve appear on the sample surface. Combined with the XRD results showing the presence of the Y molecular sieve phase and the 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 morphology characterization results of the composite molecular sieve sample of Comparative Example 1, the ZSM-5 molecular sieve is agglomerated large particles.

[0137] Figure 2 , Figure 4 , Figure 6 , Fig.10 , Fig.17 It is an SEM image of the composite molecular sieve sample of Example 1 to Example 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 Example 1 and Example 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 increase significantly. For Example 3 and Example 4, which 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 dendritic nanoparticles appear in both Example 3 and Example 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 is a ZSM-5 molecular sieve. 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 in the embodiment, the growth of ZSM-5 can be inhibited and the formation of large particles of ZSM-5 can be reduced.

[0138] Test Example 2

[0139] This test example provides a catalytic performance test of the composite molecular sieve samples of Examples 2 to 4.

[0140] 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 a comparative sample 2-1.

[0141] The Y molecular sieve (corresponding to the Y molecular sieve phase in Example 3) and the 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 a comparative sample 3-1.

[0142] 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 a comparative sample 4-1.

[0143] 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.

[0144] The above samples were subjected to catalytic cracking micro-reaction performance tests.

[0145] Catalyst preparation: Dry and cool the molecular sieve sample to be tested, stir kaolin, molecular sieve, silica sol and water at 100℃ for 4h and mix them evenly according to the mass ratio of 5:4:2:20, dry them at 100℃ overnight, and then hydrothermally age them at 100℃ for 4h. The obtained sample is pressed into tablets at 20MPa and sieved into 20-40 mesh to obtain the catalyst used in the FCC micro-reactor. Before the catalytic reaction evaluation, fill the catalyst bed, heat it to 100℃ at a heating rate of 2℃ / min in a nitrogen atmosphere, keep it at a constant temperature for 2h at 100℃, heat it to 550℃ at a heating rate of 2℃ / min, calcine it at a constant temperature for 2h at 550℃, and then cool it down to the reaction temperature naturally for use. This process is the in-situ activation of the catalyst.

[0146] Catalytic cracking: In this experiment, the catalytic performance of the prepared molecular sieve catalyst was evaluated using a Beijing Weikendu catalytic cracking fixed-bed reactor. Nitrogen was used as a carrier gas, and the feed rate was changed by adjusting the nitrogen flow rate, thereby adjusting the reaction space velocity. The inner diameter of the reaction tube was 2 cm, and the catalyst loading was 5 g.

[0147] Operating parameters: reaction temperature: 510°C; regeneration temperature: 650°C; carrier gas flow rate: 200 mL / min

[0148] Steps:

[0149] (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;

[0150] (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;

[0151] (3) nitrogen was introduced into the reaction tube, and the temperature was gradually raised to 510° C. to activate the catalyst in situ;

[0152] (4) adjusting the carrier gas flow rate to an appropriate level, and passing the feedstock oil into the reaction tube to contact the catalyst to start the reaction;

[0153] (5) After the reaction is completed, the liquid and gas phase products are collected, subjected to chromatographic analysis, and the product distribution is calculated;

[0154] (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.

[0155] The test results are summarized in Table 2, Table 3 and Table 4.

[0156] Table 2

[0157]

[0158]

[0159] As can be seen from Table 2, the comparative sample 1 formed by mechanically mixing the two molecular sieves reduces the coke yield by 0.90 relative to the conventional USY molecular sieve, and increases the propylene yield by 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 by 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.

[0160] Table 3

[0161]

[0162] As can be seen from Table 3, the comparative sample 1 formed by mechanically mixing the two molecular sieves increases the coke yield by 0.93 and the propylene yield by 2.35% relative to the conventional USY molecular sieve; and the Y / ZSM-5 composite molecular sieve of Example 2 can not only further increase the propylene yield, but also significantly reduce the coke yield (reduction by 26%). 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 2 is also significantly improved relative to the catalytic performance of the existing industrial catalytic cracking catalyst.

[0163] Table 4

[0164]

[0165] As can be seen from Table 4, the comparative sample 1 formed by mechanically mixing the two molecular sieves reduces the coke yield by 0.46 relative to the conventional USY molecular sieve, and increases the propylene yield by 5.99%; and the Y / ZSM-5 composite molecular sieve of Example 4 can not only further increase the propylene yield, but also significantly reduce the coke yield (the reduction is up to 41%). 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 4 is also significantly improved relative to the catalytic performance of the existing industrial catalytic cracking catalyst.

[0166] 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, reducing coke, etc., which can prove 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.

[0167] The above results show that the preparation method provided by the present invention can produce a composite molecular sieve product having both a Y molecular sieve phase and a ZSM-5 molecular sieve phase by utilizing the difference in solubility of two Y molecular sieves with different silicon-aluminum ratios. Fig.15 As shown, in the process of generating the ZSM-5 molecular sieve phase, the first Y molecular sieve with a relatively low silicon-aluminum ratio and / or compaction treatment can play a physical confinement role, 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 Y / ZSM-5 composite molecular sieve in which the ZSM-5 molecular sieve crystals are highly nano-sized and the ZSM-5 molecular sieve phase and the Y molecular sieve phase are uniformly distributed and in close contact.

Claims

1. A method for preparing a Y / ZSM-5 composite molecular sieve, the method 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; 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 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.

3. The preparation method according to claim 2, wherein The organic amine includes one or a combination of two or more of tetrapropylammonium bromide, hexadecyltrimethylammonium bromide, triethylamine, and ethylenediamine.

4. The preparation method according to claim 2, wherein The quaternary ammonium base includes one or a combination of two or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.

5. The preparation method according to claim 2, wherein: The tertiary ammonium base includes choline hydroxide.

6. 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).

7. 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, preferably 5-30.

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

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

10. A Y / ZSM-5 composite molecular sieve obtained by the preparation method according to any one of claims 1 to 9.

11. The Y / ZSM-5 composite molecular sieve according to claim 10, wherein: The Y / ZSM-5 composite molecular sieve comprises a Y molecular sieve phase and a ZSM-5 molecular sieve phase.

12. The Y / ZSM-5 composite molecular sieve according to claim 11, wherein: The mass ratio of the Y molecular sieve phase to the ZSM-5 molecular sieve phase is 50-99:1-50.

13. A catalytic cracking catalyst comprising the Y / ZSM-5 composite molecular sieve according to any one of claims 10 to 12.

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