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

Abstract

The application 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 with a second Y molecular sieve, mixing the first Y molecular sieve and the second Y molecular sieve with an alkaline solution of a structure directing agent, and crystallizing to obtain the Y / ZSM-5 composite molecular sieve; or mixing the second Y molecular sieve or a mixture of the first Y molecular sieve and the second Y molecular sieve with a structure directing agent, performing pressure treatment and crystallization 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, the silicon-aluminum ratio of the second Y molecular sieve is greater than that of the first Y molecular sieve, and the mass ratio of the first Y molecular sieve to the second Y molecular sieve is less than or equal to 7:3. The application further provides the composite molecular sieve obtained by the above 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 high catalytic performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molecular sieve synthesis, and particularly relates to a Y / ZSM-5 composite molecular sieve, a preparation method thereof and a catalytic cracking catalyst. BACKGROUND

[0002] The catalytic cracking process can digest excess low-carbon olefins and aromatics, realize balanced development of oil refining and production of high-end petrochemical products, further improve enterprise benefits and market competitiveness, greatly improve the self-sufficiency rate of low-carbon olefins, and alleviate the contradiction between supply and demand of petroleum chemical raw materials, which has a great supporting role for economic development. The occurrence of carbonium ion reaction in the heavy oil catalytic cracking process needs the catalysis of acidic catalyst. Therefore, the development of high-performance solid acid catalyst has become the core of the research and innovation of catalytic cracking technology. Zeolite molecular sieve is the most studied catalyst additive in catalytic cracking catalysts. In the heavy oil catalytic cracking process, ZSM-5 molecular sieve can be used together 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-type molecular sieve and ZSM-5 molecular sieve are used together, there is usually a clear spatial distance between them, which causes the straight-chain hydrocarbons and simple isomeric hydrocarbons produced by the Y-type molecular sieve to usually directly leave the surface of the FCC catalyst as final reaction products, and it is difficult for them to continue to react further on the surface of the ZSM-5 molecular sieve as intermediate products.

[0003] In the current research on Y-type molecular sieve and ZSM-5 molecular sieve composite molecular sieve, some methods use single starting Y molecular sieve as raw material to generate ZSM-5 phase through crystal transformation. However, block-shaped molecular sieve appears 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 of Y / ZSM-5 composite molecular sieve capable of obtaining ZSM-5 phase with nanometer size and uniform dispersion. SUMMARY

[0005] In order to solve the above problems, the purpose of the present application is to provide a Y / ZSM-5 composite molecular sieve, a preparation method thereof and a catalytic cracking catalyst. The Y / ZSM-5 composite molecular sieve has a Y molecular sieve phase and a ZSM-5 molecular sieve phase with nanometer size, and the ZSM-5 molecular sieve phase is uniformly dispersed in the composite molecular sieve, which is conducive to improving the catalytic activity of the molecular sieve.

[0006] In order to achieve the above purpose, the present application provides a preparation method of Y / ZSM-5 composite molecular sieve, which comprises the following steps:

[0007] Synthesis method one: the first Y molecular sieve is mixed with the second Y molecular sieve to make a slurry, the slurry is filtered and dried to obtain a Y molecular sieve raw material; the Y molecular sieve raw material is mixed with an alkaline solution of a structure directing agent, and crystallization is performed to obtain the Y / ZSM-5 composite molecular sieve;

[0008] Synthesis method two: the second Y molecular sieve is mixed with an alkaline solution of a structure directing agent, dried, compacted, and crystallized to obtain the Y / ZSM-5 composite molecular sieve;

[0009] Synthesis method three: the first Y molecular sieve is mixed with the second Y molecular sieve to make a slurry, the slurry is filtered and dried to obtain a Y molecular sieve raw material; the Y molecular sieve raw material is mixed with an alkaline solution of a structure directing agent, dried, compacted, and crystallized to obtain the Y / ZSM-5 composite molecular sieve;

[0010] 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 synthesis method one and synthesis method two, 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) based on the total mass of the first Y molecular sieve and the second Y molecular sieve being 100%.

[0012] The above synthesis method one provided by the present application uses two Y molecular sieves with different silicon-aluminum ratios as raw materials, mixes the two molecular sieves after slurry making, and then filters and dries them to obtain a Y molecular sieve raw material formed by Y molecular sieves with different silicon-aluminum ratios, and then introduces a structure directing agent into the pores of the Y molecular sieve raw material; without any washing and drying treatment, the Y molecular sieve raw material containing the alkaline solution of the structure directing agent is directly subjected to in-situ dissolution and crystallization treatment in a high-temperature hydrothermal environment. Synthesis method two is to dry the Y molecular sieve raw material mixed with the structure directing agent, compact the mixture, and then transfer the compacted mixture to a high-temperature hydrothermal environment for in-situ dissolution and crystallization; during the in-situ dissolution and crystallization in the high-temperature hydrothermal environment, the dissolved silicon-aluminum of the Y molecular sieve undergoes structural rearrangement and crystal transformation, thereby obtaining the Y / ZSM-5 composite molecular sieve.

[0013] The above synthesis method two provided by the present application uses a second Y molecular sieve with a relatively high silicon-aluminum ratio as a raw material, introduces a structure directing agent into the pores of the second Y molecular sieve, and then compacts the second Y molecular sieve containing the structure directing agent, and then performs in-situ dissolution and crystallization treatment on the compacted second Y molecular sieve in a high-temperature hydrothermal environment, so that the dissolved silicon-aluminum of the second Y molecular sieve undergoes structural rearrangement and crystal transformation, thereby obtaining the Y / ZSM-5 composite molecular sieve.

[0014] The third synthesis method provided by the present application is to use two Y zeolites with different silicon to aluminum ratios as raw materials, and to compact the Y zeolite raw material containing an alkaline solution of a structure directing agent before crystallization, so that the Y zeolite undergoes structural rearrangement and recrystallization during the crystallization process, thereby obtaining a Y / ZSM-5 composite zeolite.

[0015] In the above preparation method, as shown in Figure 21 the second Y zeolite with a higher silicon to aluminum ratio undergoes a large degree of dissolution in a hydrothermal environment with high temperature (provided by the crystallization temperature) and high alkalinity (provided by the alkaline solution of the structure directing agent), and the dissolved silicon and aluminum, etc. can be used as raw materials for the formation of the ZSM-5 zeolite phase; in contrast, the first Y zeolite with a smaller silicon to aluminum ratio undergoes a smaller degree of dissolution in the hydrothermal environment with high temperature and high alkalinity, and only a small amount of the framework is dissolved or not dissolved at all. Therefore, the first Y zeolite can physically confine the newly formed ZSM-5 zeolite during the recrystallization process. Alternatively, the newly formed ZSM-5 zeolite can also be physically confined by compaction treatment. In contrast, as shown in Figure 21 without compaction treatment and only using the second Y zeolite as the raw material, the single second Y zeolite will also undergo a certain degree of solid-phase recrystallization during the crystallization process, but the generated ZSM-5 zeolite is not subject to the effect of physical confinement, and obvious agglomeration will occur between the crystal grains. The present application inhibits the flow and exchange of substances during the rearrangement and recrystallization process through the above-mentioned physical confinement means, and since the silicon and aluminum source for the ZSM-5 zeolite phase is limited (mainly from the dissolved silicon and aluminum in the Y zeolite raw material) and the mass transfer is limited, the rearrangement and recrystallization process of the present application is conducive to the formation of ultra-fine nanoscale ZSM-5 zeolite phase, and improves the uniform dispersion degree of the ZSM-5 zeolite phase in the composite zeolite.

[0016] Compared with conventional micron-sized ZSM-5 zeolite, the nanoscale ZSM-5 zeolite crystal formed by the present application has a relatively reduced crystal size and an increased specific surface area, can provide more active sites, reduce the resistance to pore diffusion, and reduce the plugging of the pore by coking and carbon deposition, can significantly improve the catalytic activity (such as conversion rate) of the composite zeolite, reduce the deactivation rate of the composite zeolite, and prolong the service life.

[0017] In the above three synthesis methods, the first Y zeolite generally does not undergo solid phase transformation or undergos very little transformation during the above crystallization process, and is mainly used for physical confinement of the newly formed ZSM-5 zeolite. The second Y zeolite is a Y zeolite capable of solid phase transformation. The silicon-aluminum ratio of the second Y zeolite is generally greater than the silicon-aluminum ratio of the first Y zeolite, and the silicon-aluminum ratio of the first Y zeolite can be greater than 0 and less than 14, and the silicon-aluminum ratio of the second Y zeolite can be greater than or equal to 9. Specifically, the silicon-aluminum ratio of the first Y zeolite is generally less than m, and the silicon-aluminum ratio of the second Y zeolite is generally greater than or equal to m. In some specific embodiments, the value of m 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, etc. Specific values and ranges with any two of the above specific values as endpoints.

[0018] In the present application, the value of m can be adjusted according to factors such as the alkaline solution of the structure directing agent, the crystallization temperature, etc. For example, the value of m can increase with the increase of the crystallization temperature, and the value of m can decrease with the increase of the pH value of the alkaline solution of the structure directing agent. The value of m can also vary according to the type of the structure directing agent. For the same type of structure directing agent (such as quaternary ammonium salt structure directing agent), the larger the ionic volume of the structure directing agent (such as the longer the branched chain of the quaternary ammonium salt), the larger the value of m. 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 value of m can be 12.

[0019] In the above three synthesis methods, the silicon-aluminum ratio of the second Y zeolite 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 zeolite 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. Specific values and ranges with any two of the above specific values as endpoints.

[0020] In the above three synthesis methods, the second Y zeolite can be ammonium type Y zeolite, hydrogen type Y zeolite, rare earth type Y zeolite, etc. Specifically, the second Y zeolite can include one or a combination of two or more of NH4Y zeolite, HY zeolite, USY zeolite, RY zeolite.

[0021] In the above synthesis method one and synthesis method three, the first Y molecular sieve has a silica-alumina ratio 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 first Y molecular sieve can have a silica-alumina ratio of 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 the like, and a range between any two of the above values as the end points. In some embodiments, a first Y molecular sieve with a lower silica-alumina ratio, such as a first Y molecular sieve with a silica-alumina ratio of 7 or less, can be used to save cost.

[0022] In the above synthesis method one and synthesis method three, the second Y molecular sieve has a silica-alumina ratio that is greater than or equal to 5 different from the silica-alumina ratio of the first Y molecular sieve, i.e., the silica-alumina ratio of the second Y molecular sieve is greater than or equal to 5 than the silica-alumina ratio of the first Y molecular sieve. In some embodiments, according to the silica-alumina ratio range of a conventional Y molecular sieve, the difference between the silica-alumina ratio of the second Y molecular sieve and the silica-alumina ratio of the first Y molecular sieve can be 5-30, and can be 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22.9, 23, 25, 30, and the like, and a range between any two of the above values as the end points.

[0023] In the above synthesis method one and synthesis method three, 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, or the like. 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 first Y molecular sieve and the second Y molecular sieve can be the same or different.

[0024] In the above three synthesis methods, by adjusting the silica-alumina ratio of the first Y molecular sieve and / or the second Y molecular sieve, and adjusting the relative ratio of the first Y molecular sieve to the second Y molecular sieve in the synthesis method one and 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 to 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 role of structure directing in the above crystallization process: in the crystallization process, the silicon and aluminum dissolved out of the Y molecular sieve raw material, especially the second Y molecular sieve, can undergo structural rearrangement under the action of hydroxyl ions to generate 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 zeolite raw material, the degree of dissolution of the intermediate Y zeolite can be controlled, so that the Y zeolite undergoes "limited dissolution", on the one hand, the effect of retaining part of the Y zeolite framework, so that the final product contains a Y zeolite phase, on the other hand, a certain amount of ZSM-5 zeolite can be formed using the dissolved fragments. And by adjusting the amount of the structure-directing agent relative to the Y zeolite raw material, the conversion degree of the Y zeolite to the ZSM-5 zeolite and the uniformity of the distribution of the two zeolite phases in the composite zeolite can be adjusted.

[0027] In the above three synthesis methods, the mass ratio of the Y zeolite raw material to the structure-directing agent can be (0.1-1):(0.01-1), for example, it can be (0.1-1):(0.1-1). In some specific embodiments, the mass of the Y zeolite 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, etc. specific values and 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, etc. specific values and 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 act as a structure-directing agent for the ZSM-5 zeolite, promoting the formation of the ZSM-5 zeolite phase; the anion hydroxyl in the alkaline solution of the structure-directing agent can dissolve the silicon and aluminum in the Y zeolite as the silicon source and aluminum source of the ZSM-5 zeolite phase, on the one hand, and on the other hand, it can also provide an alkaline environment, promoting the generation of the ZSM-5 zeolite phase. By adjusting the type of cation in the structure-directing agent, the relative proportion of the two zeolite phases in the composite Y zeolite can be adjusted. Specifically, the structure-directing agent includes one or a combination of two or more of organic amine, quaternary ammonium base, and tertiary ammonium base.

[0029] In the above three synthesis methods, the quaternary ammonium base can 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 can include choline hydroxide.

[0031] In the above three synthesis methods, the organic amine can include one or a combination of two or more of tetrapropylammonium bromide, cetyltrimethylammonium 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, and can be specifically 10, 11, 12, 13, 14, and the like, or a range defined by any two of the above values.

[0033] In the above three synthesis methods, the alkaline solution of the structure directing agent can further comprise an inorganic base for adjusting the pH value of the solution. The inorganic base can specifically comprise 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 comprises 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 or quasi-solid system. Due to the low fluidity of the system and the confinement effect of the first Y molecular sieve, the dissolved silicon and aluminum in the second Y molecular sieve are crystallized in situ to form ZSM-5 phase, and the confinement effect of the first Y molecular sieve can promote the formation of uniformly dispersed nanoscale small crystals of ZSM-5 molecular sieve phase.

[0035] In the above three synthesis methods, the mixing method of the Y molecular sieve raw material and the alkaline solution of the structure directing agent can be specifically impregnation of the Y molecular sieve raw material in the alkaline solution of the structure directing agent. The impregnation method can comprise one or a combination of two or more of volume impregnation, equal volume impregnation, multiple impregnation, impregnation precipitation, fluidized bed spray impregnation, vapor phase impregnation, vacuum impregnation, and pressurized impregnation. Alternatively, the mixing method of the Y molecular sieve raw material and the alkaline solution of the structure directing agent can also be dropwise addition of the alkaline solution of the structure directing agent to the Y molecular sieve raw material.

[0036] In the above three synthesis methods, by adjusting the crystallization conditions, the relative proportion of the two molecular sieve phases in the composite molecular sieve can be adjusted. The crystallization temperature can be 50-250°C, for example, 80-200°C. In some specific embodiments, the crystallization temperature can be 50°C, 80°C, 100°C, 150°C, 200°C, 250°C, and the like, or a range defined by any two of the above values.

[0037] In the above three synthesis methods, the crystallization time is 0.1 h to 120 h, for example, can be 0.5 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 the like specific values and ranges with any two of the above specific values as endpoints.

[0038] In the above preparation method, the crystallization pressure is generally 0.1 to 10 MPa, for example, 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 the like specific values and ranges 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 is present during the crystallization process. The crystallization method can specifically include one or a combination of two or more of solid phase hydrothermal crystallization, solid phase-like hydrothermal crystallization, and vapor-assisted solid phase hydrothermal crystallization.

[0040] The present application finds that in the Y molecular sieve raw material of synthesis method one and synthesis method three, by controlling the mass content of the first Y molecular sieve with a low silicon-aluminum ratio to be 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 can be ensured that the Y molecular sieve raw material undergoes solid phase transformation during the crystallization process. That is, taking the total mass of the first Y molecular sieve and the second Y molecular sieve raw material as 100%, the mass of the first Y molecular sieve is less than or equal to 70% and greater than 0%, and correspondingly, 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 the like specific values and ranges with any two of the above specific values as endpoints. Correspondingly, 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 the like specific values and ranges with any two of the above specific values as endpoints.

[0041] In the Y zeolite raw material of the synthesis method one and the synthesis method three, the mass ratio of the first Y zeolite to the second Y zeolite is generally less than or equal to 7:3, which 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 ranges with any two of the above specific values as the end points.

[0042] According to a specific embodiment of the present application, the synthesis method one in the preparation method of the Y / ZSM-5 composite zeolite can specifically include:

[0043] 1. A first Y zeolite and a second Y zeolite with a mass ratio of less than or equal to 7:3 are mixed and pulped, and the slurry is dried to obtain a Y zeolite raw material; wherein the silicon-aluminum ratio of the first Y zeolite is less than m, and the silicon-aluminum ratio of the second Y zeolite is greater than or equal to m, m being any one of 9-14;

[0044] 2. The Y zeolite raw material is immersed in a solution of a structure directing agent, and after sufficient immersion, the Y zeolite raw material is taken out, without washing or drying, and directly transferred to a sealed reaction kettle for crystallization at 50-250°C for 0.1h-120h to obtain the Y / ZSM-5 composite zeolite.

[0045] In the above-mentioned synthesis method two, the second Y zeolite with a high silicon-aluminum ratio that has undergone compaction treatment is subjected to in-situ dissolution and crystallization treatment in a high-temperature and high-alkali hydrothermal environment, so that the silicon-aluminum dissolved from the Y zeolite is subjected to structural rearrangement and crystal transformation, thereby obtaining the Y / ZSM-5 composite zeolite. The compaction treatment can increase the compactness between particles and increase the mass transfer difficulty, thereby inhibiting the generation of large particle aggregates of ZSM-5 phase during the crystallization process.

[0046] In the above-mentioned synthesis method two, the compaction treatment can inhibit the phase transformation of Y zeolite to ZSM-5 zeolite to a certain extent. For example, compared with the Y / ZSM-5 composite zeolite prepared without compaction treatment, the Y / ZSM-5 composite zeolite obtained by compaction treatment has a lower content of ZSM-5 zeolite phase in the composite zeolite, and the particle size of the formed ZSM-5 zeolite is smaller.

[0047] In the above-mentioned synthesis method two, the pressure of the compaction treatment can be controlled to be 0.1MPa-60MPa, for example, 1-30MP. Specifically, the pressure of the compaction treatment can be 0.1MPa, 0.5MPa, 1MPa, 5MPa, 10MPa, 20MPa, 30MPa, 40MPa, 50MPa, 60MPa, and the like, and ranges with any two of the above specific values as the end points.

[0048] According to the specific embodiment of the present application, the synthesis method two of the preparation method of the Y / ZSM-5 composite molecular sieve can specifically include:

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

[0050] 2. The Y molecular sieve raw material is immersed in an alkaline solution of a structure-directing agent, and after sufficient immersion, the Y molecular sieve raw material is taken out, dried, and compacted at a pressure of 0.1-60 MPa;

[0051] The compacted Y molecular sieve raw material is directly transferred to a sealed reaction kettle without washing or drying, and is crystallized at 50-250℃ for 0.1-120 h to obtain the Y / ZSM-5 composite molecular sieve.

[0052] According to the specific embodiment of the present application, the synthesis method three of the preparation method of the Y / ZSM-5 composite molecular sieve can specifically include:

[0053] 1. The first Y molecular sieve and the second Y molecular sieve are mixed and slurried at a mass ratio of less than or equal to 7:3, and the slurry is dried 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 in the range of 9-14;

[0054] 2. The Y molecular sieve raw material is immersed in a solution of a structure-directing agent, and after sufficient immersion, the Y molecular sieve raw material is taken out and dried, and the dried Y molecular sieve raw material is compacted at a pressure of 0.1-60 MPa; the compacted Y molecular sieve raw material is transferred to a sealed reaction kettle, and is crystallized at 50-250℃ for 0.1-120 h to obtain the Y / ZSM-5 composite molecular sieve.

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

[0056] According to a specific embodiment of the present application, the Y / ZSM-5 composite molecular sieve comprises a Y molecular sieve phase and a ZSM-5 molecular sieve phase. By controlling the amount and type of alkaline solution of 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 percentage 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 and 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 and 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 the like specific values and ranges with any two of the above specific values as endpoints.

[0057] The present application also provides a catalytic cracking catalyst comprising 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 ultra-fine nanophase uniformly distributed with the Y molecular sieve phase, which is beneficial to the molecules decomposed by the Y molecular sieve phase to further crack and decompose in the ZSM-5 molecular sieve phase, and is beneficial to the production of low-carbon olefins.

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

[0059] The preparation method of the Y / ZSM-5 composite molecular sieve provided by the present application can promote the formation of a ZSM-5 molecular sieve phase, which is an ultra-fine nanophase and uniformly dispersed in the composite molecular sieve, by using molecular sieves with different silicon-aluminum ratios as raw materials for crystallization, and by causing partial dissolution, rearrangement and recrystallization of Y molecular sieves during the crystallization process. In addition, by selecting molecular sieves with different silicon-aluminum ratios, the framework aluminum content in the composite molecular sieve can also be adjusted, thereby adjusting the acid amount of the composite molecular sieve. The two-phase distribution in the composite molecular sieve obtained in this way is uniform, and the catalytic performance is effectively improved, which can be applied in catalytic cracking processes. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 For 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 For composite molecular sieve Y C1 / ZSM-5 C1 Scanning electron micrograph of the sample.

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

[0063] Figure 4 Composite zeolite Y C2 / ZSM-5 C2 Scanning electron micrograph of the sample.

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

[0065] Figure 6 Composite zeolite Y C3 / ZSM-5 C3 Scanning electron micrograph of the sample.

[0066] Figure 7 、 Figure 8 Composite zeolite Y C3 / ZSM-5 C3 Transmission electron micrograph of the sample.

[0067] Figure 9 Composite zeolite Y C4 / ZSM-5 C4 Sample and composite zeolite Y B / ZSM-5 B X-ray diffraction pattern of the sample.

[0068] Figure 10 Composite zeolite Y C4 / ZSM-5 C4 Scanning electron micrograph of the sample.

[0069] Figure 11 、 Figure 12 Composite zeolite Y C4 / ZSM-5 C4 Transmission electron micrograph of the sample.

[0070] Figure 13 Composite zeolite Y C5 / ZSM-5 C5 Sample and composite zeolite Y B / ZSM-5 B X-ray diffraction pattern of the sample.

[0071] Figure 14Composite molecular sieve Y C5 ZSM-5 C5 Scanning electron microscope image of the sample.

[0072] Figure 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] Figure 16 Composite molecular sieve Y C6 ZSM-5 C6 Scanning electron microscope image of the sample.

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

[0075] Figure 18 Composite molecular sieve Y B ZSM-5 B Transmission electron microscope image of the sample.

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

[0077] Figure 21 Schematic diagram of the crystallization process in the preparation method of the present application. DETAILED DESCRIPTION

[0078] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present application, the technical solutions of the present application are described in detail below, but it should not be understood as limiting the scope of the present application.

[0079] In the present application, the silicon-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] The present embodiment provides a Y / ZSM-5 composite molecular sieve, and a preparation method thereof.

[0082] 1. 5 g of the first Y molecular sieve (sample name Y A ; silicon-aluminum ratio: 6.1) and 5 g of the second Y molecular sieve (sample name Y B; silicon-aluminum ratio: 6.1) and 7g of the second Y zeolite (sample name Y B ; silicon-aluminum ratio: 19.1) are mixed with 100g of water, stirred for 2 hours at room temperature, and dried to obtain a Y zeolite raw material formed by Y zeolites with different silicon-aluminum ratios (named Y C2 ). C1

[0083] 2. 0.9g of a tetrapropylammonium hydroxide solution with a concentration of 25wt% and 1g of the Y zeolite raw material Y C1 are weighed respectively. The 0.9g of the above-mentioned tetrapropylammonium hydroxide solution is slowly and uniformly dropped into the above-mentioned molecular sieve channels to impregnate uniformly at room temperature.

[0084] 3. The sample after impregnation is then directly transferred into a polytetrafluoroethylene-lined stainless steel pressure-resistant reaction kettle with a volume of 5ml. The sealed reaction kettle is then placed in an oven at 140°C for crystallization for 24 hours. After washing and drying, a Y / ZSM-5 composite zeolite product (sample name Y C1 / ZSM-5 C1 ) is obtained.

[0085] The X-ray diffraction pattern and the scanning electron microscope image of the product sample obtained in this example are shown in Figure 1 and Figure 2 respectively.

[0086] Example 2

[0087] This example provides a Y / ZSM-5 composite zeolite, and a preparation method thereof includes:

[0088] 1. 3g of the first Y zeolite (sample name Y A ; silicon-aluminum ratio: 6.1) and 7g of the second Y zeolite (sample name Y B ; silicon-aluminum ratio: 19.1) are mixed with 100g of water, stirred for 2 hours at room temperature, and dried to obtain a Y zeolite raw material formed by Y zeolites with different silicon-aluminum ratios (named Y C2 ).

[0089] 2. 0.9g of a tetrapropylammonium hydroxide solution with a concentration of 25wt% and 1g of the Y zeolite raw material Y C2 are weighed respectively. The 0.9g of the above-mentioned tetrapropylammonium hydroxide solution is slowly and uniformly dropped into the above-mentioned molecular sieve channels to impregnate uniformly at room temperature.

[0090] 3. The sample after impregnation is then directly transferred into a polytetrafluoroethylene-lined stainless steel pressure-resistant reaction kettle with a volume of 5ml. The sealed reaction kettle is then placed in an oven at 140°C for crystallization for 24 hours. After washing and drying, a Y / ZSM-5 composite zeolite product (sample name Y C2 / ZSM-5 C2 ) is obtained.

[0091] The X-ray diffraction pattern and the scanning electron microscope image of the product sample obtained in this example are shown inFigure 3 and Figure 4 As shown.

[0092] Example 3

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

[0094] 1. Take 3g of the first Y molecular sieve (sample name Y) A ;Silicon-to-aluminum ratio: 6.1), 7g of second Y molecular sieve (sample name Y) B (Silicon-to-aluminum ratio: 19.1) was mixed with 100g of water and stirred at room temperature for 2 hours. After drying, Y molecular sieve raw materials with different silicon-to-aluminum ratios (named Y) were obtained. C3 ).

[0095] 2. Weigh out 0.9g of a 25wt% tetrapropylammonium hydroxide solution and 1g of a mixture of Y. C3 Molecular sieve. At room temperature, 0.9 g of the above tetrapropylammonium hydroxide solution was slowly and evenly added dropwise into the pores of the above molecular sieve to impregnate it evenly.

[0096] 3. The fully impregnated sample was then dried at room temperature for 24 hours and then subjected to high-pressure (25 MPa) compaction. The treated sample was then transferred to a 5 mL PTFE-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) was obtained. C3 / ZSM-5 C3 ).

[0097] The X-ray diffraction pattern, scanning electron microscope (SEM) image, and transmission electron microscope (TEM) image of the product sample in this embodiment are shown below. Figure 5 , Figure 6 , Figure 7 and Figure 8 As shown.

[0098] Example 4

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

[0100] 1. Weigh out 0.9g of a 25wt% tetrapropylammonium hydroxide solution and 1g of Y molecular sieve (sample name Y). B (Silicon-to-aluminum ratio: 19.1). At room temperature, 0.9 g of the above tetrapropylammonium hydroxide solution was slowly and evenly added dropwise into the molecular sieve channels to impregnate them evenly.

[0101] 2. The fully impregnated sample is then dried at room temperature for 24 hours, and then subjected to high pressure (25 MPa) compaction treatment. The treated sample is then placed in a polytetrafluoroethylene-lined stainless steel pressure-resistant autoclave with a volume of 5 mL. The sealed autoclave is then placed in an oven at 140°C for 24 hours of crystallization. After washing and drying, the Y / ZSM-5 composite molecular sieve product (sample name Y / ZSM-5) is obtained. 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 example are shown in Figure 9 , Figure 10 , Figure 11 and Figure 12 , respectively.

[0103] Example 5

[0104] This example provides a Y / ZSM-5 composite molecular sieve, and a preparation method thereof, which comprises:

[0105] 1. 5 g of a first Y molecular sieve (sample name Y D ; silicon-aluminum ratio: 2.7) and 5 g of a second Y molecular sieve (sample name Y B ; silicon-aluminum ratio: 19.1) are weighed separately, mixed with 100 g of water, and stirred at room temperature for 2 hours. After drying, a Y molecular sieve raw material (named Y C5 ) is obtained.

[0106] 2. 0.9 g of a 25 wt% tetrapropylammonium hydroxide solution and 1 g of the Y molecular sieve raw material Y C5 are weighed separately. The 0.9 g of the tetrapropylammonium hydroxide solution is slowly and uniformly added to the molecular sieve channels at room temperature to impregnate uniformly.

[0107] 3. The fully impregnated sample is then directly placed in a polytetrafluoroethylene-lined stainless steel pressure-resistant autoclave with a volume of 5 mL. The sealed autoclave is then placed in an oven at 140°C for 24 hours of crystallization. After washing and drying, the Y / ZSM-5 composite molecular sieve product (sample name Y C5 / ZSM-5 C5 ) is obtained.

[0108] 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.

[0109] Example 6

[0110] This example provides a Y / ZSM-5 composite molecular sieve, and a preparation method thereof, which comprises:

[0111] 1. Take 3 g of first Y zeolite (sample name Y A ; Si / Al ratio: 6.1) and 7 g of second Y zeolite (sample name Y E ; Si / Al ratio: 29.0) and 100 g of water, mix them and stir for 2 hours at room temperature, dry, and obtain Y zeolite raw material (named Y C6 ) with different Si / Al ratios.

[0112] 2. Take 0.9 g of 25 wt% tetrapropylammonium hydroxide solution and 1 g of Y zeolite raw material Y C6 , respectively. Slowly and uniformly add 0.9 g of the above-mentioned tetrapropylammonium hydroxide solution into the above-mentioned molecular sieve channels at room temperature to impregnate uniformly.

[0113] 3. Then, directly transfer the fully impregnated sample into a 5-milliliter polytetrafluoroethylene-lined stainless steel pressure-resistant reaction kettle, then place the sealed reaction kettle in a 140°C oven for crystallization for 24 hours, and after washing and drying, obtain Y / ZSM-5 composite zeolite product (sample name Y C6 / ZSM-5 C6 ).

[0114] 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.

[0115] Comparative Example 1

[0116] This comparative example provides a Y / ZSM-5 composite zeolite, and the preparation method thereof comprises:

[0117] 1. Take 0.9 g of 25 wt% tetrapropylammonium hydroxide solution and 1 g of Y zeolite (sample name Y B ; Si / Al ratio: 19.1), respectively. Slowly and uniformly add 0.9 g of the above-mentioned tetrapropylammonium hydroxide solution into the above-mentioned molecular sieve channels at room temperature to impregnate uniformly.

[0118] 2. Then, directly transfer the fully impregnated sample into a 5-milliliter polytetrafluoroethylene-lined stainless steel pressure-resistant reaction kettle, then place the sealed reaction kettle in a 140°C oven for crystallization for 24 hours, and after washing and drying, obtain Y / ZSM-5 composite zeolite product (sample name Y B / ZSM-5 B ).

[0119] The scanning electron microscope image and transmission electron microscope image of the product sample of this comparative example are shown in Figure 17 and Figure 18 , respectively.

[0120] Comparative Example 2

[0121] The present comparative example provides a Y / ZSM-5 composite molecular sieve, and a preparation method thereof, which comprises:

[0122] 1. 0.9 g of tetrapropylammonium hydroxide solution with a concentration of 25 wt% and 1 g of Y molecular sieve (sample name Y E ; silicon-aluminum ratio: 29.0) were weighed respectively. The 0.9 g of the above-mentioned tetrapropylammonium hydroxide solution was slowly and uniformly added into the above-mentioned molecular sieve channels for impregnation at room temperature.

[0123] 2. Then, the fully impregnated sample was directly transferred into a polytetrafluoroethylene-lined stainless steel pressure-resistant reaction kettle with a volume of 5 mL, and then the sealed reaction kettle was placed in an oven at 140°C for crystallization for 24 hours. After washing and drying, a Y / ZSM-5 composite molecular sieve product (sample name Y E / ZSM-5 E ) was obtained.

[0124] The scanning electron microscope images and transmission electron microscope images of the product sample of the present comparative example are shown in Figure 15 and Figure 19 、 Figure 20 respectively.

[0125] Test Example 1

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

[0127] Figure 1 、 Figure 3 、 Figure 5 、 Figure 9 、 Figure 13 、 Figure 15 The XRD patterns of the composite molecular sieve samples of Example 1 to Example 6 and Comparative Examples 1 and 2 are shown in FIG. 1. As can be seen, the Y molecular sieve phase and the ZSM-5 molecular sieve phase are contained in Example 1 to Example 6 and Comparative Examples 1 and 2. According to the above XRD results, the mass ratio of the two phases in the composite molecular sieve is calculated and the results are 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 according to the characteristic peak area of the molecular sieve phase. A mixture of standard Y molecular sieve and standard ZSM-5 molecular sieve with a mass ratio of 1:1 is used as a standard sample, the diffraction peak area is selected for comparison, and the mass ratio is recorded as 1:1. Then, the diffraction of each sample to be tested is calculated.

[0129] Table 1

[0130]

[0131] From Table 1, it can be seen that, compared with the composite molecular sieve prepared by using only one Y molecular sieve raw material with a certain silicon-aluminum ratio, the present application can effectively adjust the relative proportion of ZSM-5 molecular sieve phase in the composite molecular sieve by using two Y molecular sieves with different silicon-aluminum ratios as raw materials. As can be seen from Example 1 to Example 2, with the decrease of the content of the first Y molecular sieve with a low silicon-aluminum ratio, the content of ZSM-5 increases, which proves that the addition of the first Y molecular sieve with a low silicon-aluminum ratio can inhibit the growth of ZSM-5 molecular sieve in the solid phase crystallization process, so as to realize the adjustment of the relative proportion of the two phases of the composite molecular sieve by regulating the proportion of the raw materials.

[0132] It can be found from the comparison between Example 2 and Example 3, and the comparison between Example 4 and Comparative Example 1 that, under the same raw material composition, the pressure treatment makes the content of ZSM-5 in the product decrease compared with the product obtained without pressure treatment, which proves that the pressure process also has an inhibitory effect on the growth of ZSM-5 molecular sieve in the crystallization process. Combined with the principle of crystallization (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 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 of the second Y molecular sieve with a high silicon-aluminum ratio can more obviously adjust the relative proportion of the two phases of the composite molecular sieve. Further comparing the morphologies of the molecular sieves of Example 1 and Example 5 and combining the above analysis of the composition of the composite molecular sieve, it can be seen that, for the same second Y molecular sieve, the silicon-aluminum ratio of the corresponding first Y molecular sieve can be selected in a larger range to obtain a composite molecular sieve with similar composition and morphology, which indicates that the preparation method of the present application has diversity and universality for the selection of the Y molecular sieve raw material with a low silicon-aluminum ratio (i.e. the first Y molecular sieve).

[0134] It can be found from the comparison between Example 6 and Comparative Example 2 that, when a Y molecular sieve with a higher silicon-aluminum ratio is used as the second molecular sieve, the first Y molecular sieve with a low silicon-aluminum ratio still has a good inhibitory effect. In the scanning electron microscope images (Figs. 1 to 4), Figure 19 、 Figure 20 In the scanning electron microscope images (Figs. 1 to 4), the product of Comparative Example 2, which only adds the second Y molecular sieve with a high silicon-aluminum ratio, after crystallization, the ZSM-5 molecular sieve appears in the typical plate-like molecular sieve morphology with a smooth surface of 3-5 microns; in contrast, the product of Example 6, which uses the same second Y molecular sieve and further adds the first Y molecular sieve, the ZSM-5 molecular sieve still appears in the form of small nanoparticles attached to the surface of the Y molecular sieve. The above results further prove the inhibitory effect of the addition of 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] And, embodiments 1 to 4 can prove that the present application can regulate the relative proportion of two phases in the composite molecular sieve by regulating the reaction conditions (such as the proportion of raw materials, compaction treatment, etc.), and further can affect the overall silicon-aluminum ratio of the composite molecular sieve, and achieve the regulation of the acid amount.

[0136] Figure 7 、 Figure 8 、 Figure 11 、 Figure 12 、 Figure 18 The TEM images of the composite molecular sieve of Example 3, Example 4 and Comparative Example 1 are shown. It can be seen that the Y-type molecular sieve phase of Example 3 and Example 4 after crystallization retains the original shape of the faujasite zeolite, and small particles of about 20 nm appear on the surface, and crystal lattice stripes different from the crystal lattice stripe width of the Y-type molecular sieve appear on the surface of the sample. Combined with the XRD results showing that the Y molecular sieve phase and the ZSM-5 molecular sieve phase exist in the sample, it can be proved that the nanoparticles in the molecular sieve sample prepared by the present application are ZSM-5 molecular sieve. In contrast, in the morphology characterization results of the composite molecular sieve sample of Comparative Example 1, the ZSM-5 molecular sieve is an aggregated large particle.

[0137] Figure 2 、 Figure 4 、 Figure 6 、 Figure 10 、 Figure 17 The SEM images of the composite molecular sieve samples of Example 1 to Example 4 and Comparative Example 1 are shown. It can be seen that in the SEM images of Examples 1 to 4, the overall molecular sieve presents a relatively uniform morphology. As can be seen from Example 1 and Example 2, with the increase of the proportion of high-silicon molecular sieve (second Y molecular sieve), the small particles on the surface of the Y-type molecular sieve (typical faujasite structure) in the SEM image increase significantly. For Examples 3 and 4 which are subjected to compaction treatment before crystallization, the small particles on the surface of the Y molecular sieve in the electron micrographs of both are more dense, and in Examples 3 and 4, tree-like growth of nanoparticles is observed. In Comparative Example 1, large particles (3-5 microns) with smooth surface and stacked morphology of micrometer-sized zeolite are observed, which are ZSM-5 molecular sieve. Combined with the formation of ZSM-5 nanoparticles in the TEM images of the examples, it can be proved that by adding a low-silicon-aluminum ratio Y molecular sieve to the raw materials and compaction treatment of the molecular sieve raw materials, 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 test of the catalytic performance of the composite molecular sieve samples of Examples 2 to 4.

[0140] Y zeolite (corresponding to Y zeolite phase in Example 2) and ZSM-5 zeolite (corresponding to ZSM-5 zeolite phase in Example 2) were mixed in a mass ratio of 85:15 to obtain Comparative Sample 2-1.

[0141] Y zeolite (corresponding to Y zeolite phase in Example 3) and ZSM-5 zeolite (corresponding to ZSM-5 zeolite phase in Example 3) were mixed in a mass ratio of 92:8 to obtain Comparative Sample 3-1.

[0142] Y zeolite (corresponding to Y zeolite phase in Example 4) and ZSM-5 zeolite (corresponding to ZSM-5 zeolite phase in Example 4) were mixed in a mass ratio of 64:36 to obtain Comparative Sample 4-1.

[0143] USY zeolite with a silicon-aluminum ratio of 19.1 used as a raw material in Example 2 was used as Comparative Sample 2-2, USY zeolite with a silicon-aluminum ratio of 19.1 used as a raw material in Example 3 was used as Comparative Sample 3-2, and USY zeolite with a silicon-aluminum ratio of 19.1 used as a raw material in Example 4 was used as Comparative Sample 4-2.

[0144] The above samples were subjected to catalytic cracking microreaction performance tests.

[0145] Catalyst preparation: The molecular sieve sample to be tested was dried and cooled, kaolin, molecular sieve, silica sol, and water were mixed uniformly at 100°C for 4h in a mass ratio of 5:4:2:20, and then dried overnight at 100°C, followed by hydrothermal aging treatment at 100°C for 4h. The obtained sample was pressed into a tablet at 20MPa and sieved into 20-40 mesh to obtain a catalyst for an FCC microreaction device. Before the catalytic reaction evaluation, the catalyst bed was filled, and the temperature was increased to 100°C at a rate of 2°C / min under a nitrogen atmosphere, and then the temperature was kept constant at 100°C for 2h, and then the temperature was increased to 550°C at a rate of 2°C / min, and then the temperature was kept constant at 550°C for 2h, and then the temperature was naturally lowered to the reaction temperature for standby, and this process was used to activate the catalyst in situ.

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

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

[0148] Operating steps:

[0149] (1) Use quartz sand and quartz wool to fix the molecular sieve particles at the middle of the reaction tube at the thermocouple end point position;

[0150] (2) Install and fix the reaction tube, check the air tightness of the device and related heat preservation, etc., to ensure that the air tightness and heat preservation performance of each pipeline are good;

[0151] (3) Introduce nitrogen into the reaction tube, and gradually heat to 510°C to activate the catalyst in situ;

[0152] (4) Adjust to the appropriate carrier gas flow rate, and introduce the raw oil into the reaction tube to contact the catalyst to start the reaction;

[0153] (5) After the reaction is completed, collect the liquid and gas products, and enter the chromatographic analysis and calculate the product distribution;

[0154] (6) Open the aging program to raise the temperature to 650°C for 1h, and repeat steps (3), (4), (5) for cyclic evaluation.

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

[0156] Table 2

[0157]

[0158]

[0159] As can be seen from Table 2, the coke yield of the comparative sample 1 formed by mechanically mixing two kinds of molecular sieves is reduced by 0.90, and the propylene yield is increased by 2.11% relative to the conventional USY molecular sieve; the Y / ZSM-5 composite molecular sieve of Example 3 not only can further improve the propylene yield, but also can greatly reduce the coke yield (the reduction rate reaches 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 also has obvious improvement 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 coke yield of comparative sample 1 formed by mechanically mixing two kinds of molecular sieves is increased by 0.93 relative to the conventional USY molecular sieve, and the propylene yield is increased by 2.35%; the Y / ZSM-5 composite molecular sieve of Example 2 can further increase the propylene yield and greatly reduce the coke yield (by 26%).

[0163] Table 4

[0164]

[0165] As can be seen from Table 4, the coke yield of comparative sample 1 formed by mechanically mixing two kinds of molecular sieves is reduced by 0.46 relative to the conventional USY molecular sieve, and the propylene yield is increased by 5.99%; the Y / ZSM-5 composite molecular sieve of Example 4 can further increase the propylene yield and greatly reduce the coke yield (by 41%). The total liquid yield (corresponding to "liquefied gas + gasoline + diesel" in Table 2) of the existing industrial catalytic cracking catalyst is 83-86%, the coke yield is 6-10%, and the propylene yield is about 5%. It can be seen that the catalytic performance of the Y / ZSM-5 composite molecular sieve of Example 4 is also obviously 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 application has more excellent effects in improving the propylene yield and reducing the coke, and thus it can be proved that the preparation method of the present application can control 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 application can produce a composite molecular sieve product having a Y molecular sieve phase and a ZSM-5 molecular sieve phase at the same time by using the solubility difference of two kinds of Y molecular sieves with different silicon-aluminum ratios. As shown in the above results, in the process of generating the ZSM-5 molecular sieve phase, the dissolution of the second Y molecular sieve crystal particles and the formation of the ZSM-5 molecular sieve crystals can be carried out locally in situ by the physical confinement effect of the first Y molecular sieve with a lower silicon-aluminum ratio and / or the compaction treatment, so that the ZSM-5 molecular sieve crystals are highly nanometerized, and the ZSM-5 molecular sieve phase and the Y molecular sieve phase are uniformly distributed and in close contact. Figure 15 The above results show that the preparation method provided by the present application can produce a composite molecular sieve product having a Y molecular sieve phase and a ZSM-5 molecular sieve phase at the same time by using the solubility difference of two kinds of Y molecular sieves with different silicon-aluminum ratios. As shown in the above results, in the process of generating the ZSM-5 molecular sieve phase, the dissolution of the second Y molecular sieve crystal particles and the formation of the ZSM-5 molecular sieve crystals can be carried out locally in situ by the physical confinement effect of the first Y molecular sieve with a lower silicon-aluminum ratio and / or the compaction treatment, so that the ZSM-5 molecular sieve crystals are highly nanometerized, 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 a first Y molecular sieve with a second Y molecular sieve to form a slurry, and filtering and drying the slurry to obtain a Y molecular sieve raw material; 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; or, mixing the second Y molecular sieve as a Y molecular sieve raw material with an alkaline solution of a structure-directing agent, and drying, compacting, and crystallizing to obtain the Y / ZSM-5 composite molecular sieve; or, mixing a first Y molecular sieve with a second Y molecular sieve to form a slurry, and filtering and drying the slurry to obtain a Y molecular sieve raw material; mixing the Y molecular sieve raw material with an alkaline solution of a structure-directing agent, and drying, compacting, and crystallizing to obtain the Y / ZSM-5 composite molecular sieve; wherein the first Y molecular sieve has a silica-alumina ratio greater than 0 and less than 14, the second Y molecular sieve has a silica-alumina ratio greater than or equal to 9, and the silica-alumina ratio of the second Y molecular sieve is greater than the silica-alumina ratio of the first Y molecular sieve, the silica-alumina ratio being a molar ratio of Si / Al; in the Y molecular sieve raw material, the first Y molecular sieve has a mass less than or equal to 70% based on a total mass of the first Y molecular sieve and the second Y molecular sieve being 100%; the structure-directing agent comprises one or a combination of two or more of an organic amine, a quaternary ammonium base, and a tertiary ammonium base; a mass ratio of the Y molecular sieve raw material to the structure-directing agent is (0.1-1) : (0.01-1).

2. The production method according to claim 1, wherein the organic amine comprises one or a combination of two or more of tetrapropylammonium bromide, cetyltrimethylammonium bromide, triethylamine, and ethylenediamine.

3. The production method according to claim 1, wherein the quaternary ammonium base comprises one or a combination of two or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

4. The production method according to claim 1, wherein the tertiary ammonium base comprises choline hydroxide.

5. The production method according to claim 1, wherein a difference between the silica-alumina ratio of the second Y molecular sieve and the silica-alumina ratio of the first Y molecular sieve is greater than or equal to 5.

6. The production method according to claim 1, wherein a difference between the silica-alumina ratio of the second Y molecular sieve and the silica-alumina ratio of the first Y molecular sieve is 5-30.

7. The production method according to claim 1, wherein the crystallization is performed at a temperature of 50-250℃ for a time of 0.1-120h.

8. The production method according to claim 1, wherein, the compacting is performed at a pressure of 0.1 MPa-60 MPa. 9.A Y / ZSM-5 composite molecular sieve obtained by the method of any one of claims 1-8.

10. The Y / ZSM-5 composite molecular sieve of claim 9, wherein, the Y / ZSM-5 composite molecular sieve comprises a Y molecular sieve phase and a ZSM-5 molecular sieve phase.

11. The Y / ZSM-5 composite molecular sieve of claim 10, wherein, a mass ratio of the Y molecular sieve phase to the ZSM-5 molecular sieve phase is 50-99:1-50. 12.A catalytic cracking catalyst comprising the Y / ZSM-5 composite molecular sieve of any one of claims 9-11.

Images