Binderless composite molecular sieve, method for preparing the same, and use thereof

Abstract

The application provides a binder-free composite molecular sieve, a preparation method and application thereof. The preparation raw material of the composite molecular sieve comprises at least two molecular sieves with a silicon aluminum atomic ratio of 150-700, wherein the difference c between the silicon aluminum atomic ratios of any two molecular sieves satisfies 0 The composite molecular sieve of the application does not contain a binder, can be used as a catalyst for an olefin cracking reaction, can improve the ethylene propylene yield, and has high catalyst stability.

Description

Technical Field

[0001] This invention belongs to the field of porous materials, specifically relating to a binder-free composite molecular sieve, its preparation method, and its application. Background Technology

[0002] Ethylene and propylene are essential raw materials for the petrochemical industry, and with my country's continuous economic development, the demand for ethylene and propylene will remain high. Mixed C4 and higher olefins are byproducts of ethylene plants, FCC units in oil refineries, and coal-to-gas plants, and are typically used only as low-value-added products such as fuel. Due to the large-scale and integrated development of my country's petrochemical enterprises and the lengthening of their industrial chains, developing technologies to increase the production of ethylene and propylene from C4 and higher olefins will allow for more optimized and rational utilization of light olefin resources, increase the production of the important raw material ethylene and propylene, create significant economic benefits for petrochemical enterprises, and improve the overall energy utilization rate.

[0003] ZSM-5 molecular sieve catalyst is a common MFI zeolite molecular sieve catalyst used in the cracking of C4 and above olefins to produce ethylene and propylene. ZSM-5 zeolite molecular sieves are widely used in catalysis due to their uniform and ordered micropores, large specific surface area, and high hydrothermal stability. However, zeolite powder, due to its small particle size, is inconvenient to use in practical applications and generally requires the addition of binders to shape the catalyst into a specific shape and mechanical strength. However, binders are generally inert components, and their addition effectively "dilutes" the active centers of the molecular sieve, increasing the actual reaction space velocity and accelerating catalyst deactivation. Binders also have a pore-blocking effect on the molecular sieve, affecting its diffusion performance.

[0004] ZSM-5 molecular sieve catalysts with different silica-to-alumina ratios exhibit completely different catalytic performance in the catalytic cracking of C4 olefins to ethylene and propylene. In existing technologies, the catalytic activity, product yields (such as ethylene and propylene), and reaction stability of single-component ZSM-5 molecular sieves in the catalytic cracking of olefins to ethylene and propylene still fall short of ideal requirements. Therefore, developing more composite ZSM-5 molecular sieves, especially binder-free composite ZSM-5 molecular sieves, holds promise for solving these problems. Summary of the Invention

[0005] To address the aforementioned technical problems in the prior art, this invention provides a binder-free composite molecular sieve and its preparation method. This invention combines molecular sieves with different silicon-to-aluminum atomic ratios and employs a binder conversion method to obtain a binder-free composite molecular sieve. Furthermore, the different molecular sieves exhibit synergistic catalytic effects, significantly improving the catalytic activity of the composite molecular sieve. In the catalytic cracking of olefins to produce ethylene and propylene, it demonstrates high reaction stability and a high yield of ethylene and propylene.

[0006] In a first aspect, the present invention provides a binder-free composite molecular sieve, the raw materials for which include at least two molecular sieves with a silicon-to-aluminum atomic ratio of 150-700, wherein the difference c between the silicon-to-aluminum atomic ratios of any two molecular sieves satisfies: 0 < c ≤ 300.

[0007] This invention combines at least two molecular sieves with a silicon-to-aluminum atomic ratio difference within a specific range to obtain a composite molecular sieve that simultaneously possesses a high content of zeolite structure and a large number of macroporous and microporous composite structures. This is more conducive to the rapid diffusion of products in catalytic reactions, slows down coking, and improves catalytic activity while enhancing reaction stability.

[0008] In this invention, the raw materials for preparation include at least two molecular sieves with a silicon-to-aluminum atomic ratio of 150-700. For example, the silicon-to-aluminum atomic ratio of the molecular sieves can be 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, or any value between them. In some embodiments, the raw materials for preparation include at least two molecular sieves with a silicon-to-aluminum atomic ratio of 200-600.

[0009] In this invention, the difference *c* between the silicon-to-aluminum atomic ratios of any two molecular sieves in the raw materials for preparing the composite molecular sieve can be 5, 10, 30, 50, 80, 100, 120, 150, 180, 200, 220, 250, 280, 300, or any value between them. In some embodiments, the difference *c* between the silicon-to-aluminum atomic ratios of any two molecular sieves in the raw materials for preparing the composite molecular sieve satisfies: 0 < c ≤ 200, preferably 50 ≤ c ≤ 200, and more preferably 50 ≤ c ≤ 150.

[0010] In some embodiments, the raw materials for preparation include a first molecular sieve and a second molecular sieve. The first molecular sieve has a silicon-to-aluminum atomic ratio of 300-700, such as 300, 350, 400, 450, 500, 550, 600, 650, 700 or any value between them, preferably 300-600, more preferably 350-500; the second molecular sieve has a silicon-to-aluminum atomic ratio of 150-600, such as 150, 200, 250, 300, 350, 400, 450, 500, 550, 600 or any value between them, preferably 200-400, more preferably 250-350.

[0011] In some embodiments, the raw materials for preparation include a first molecular sieve and a second molecular sieve, wherein the difference between the silicon-aluminum atomic ratio of the first molecular sieve and the silicon-aluminum atomic ratio of the second molecular sieve is 50-200, for example, 50, 80, 100, 120, 150, 180, 200 or any value between them, preferably 50-150, more preferably 100-150.

[0012] In some embodiments, the raw materials for preparation include a first molecular sieve and a second molecular sieve, wherein the silicon-to-aluminum atomic ratio of the first molecular sieve is 300-700, the silicon-to-aluminum atomic ratio of the second molecular sieve is 150-600, and the difference between the silicon-to-aluminum atomic ratio of the first molecular sieve and the silicon-to-aluminum atomic ratio of the second molecular sieve is greater than 0 and less than or equal to 200.

[0013] In some preferred embodiments, the raw materials for preparation include a first molecular sieve and a second molecular sieve, wherein the silicon-to-aluminum atomic ratio of the first molecular sieve is 300-600, the silicon-to-aluminum atomic ratio of the second molecular sieve is 200-400, and the difference between the silicon-to-aluminum atomic ratio of the first molecular sieve and the silicon-to-aluminum atomic ratio of the second molecular sieve is 50-200.

[0014] In some preferred embodiments, the raw materials for preparation include a first molecular sieve and a second molecular sieve, wherein the silicon-to-aluminum atomic ratio of the first molecular sieve is 350-500, the silicon-to-aluminum atomic ratio of the second molecular sieve is 250-350, and the difference between the silicon-to-aluminum atomic ratio of the first molecular sieve and the silicon-to-aluminum atomic ratio of the second molecular sieve is 50-150.

[0015] In some embodiments, the mass ratio of the first molecular sieve to the second molecular sieve is 1:(0.5-2).

[0016] In some embodiments, the raw materials used in the preparation include at least two molecular sieves with different silicon-to-aluminum atomic ratios, both of which are zeolite molecular sieves with MFI structures, such as ZSM-5 molecular sieves.

[0017] In this invention, there is no specific limitation on the mass percentage of each molecular sieve in the raw materials. In some embodiments, each molecular sieve accounts for 5%-95% of the total mass of the raw materials.

[0018] In a second aspect, the present invention provides a method for preparing the binder-free composite molecular sieve described in the first aspect, comprising the following steps:

[0019] (1) The raw materials are mixed with the binder and molded, and then mixed with organic amine and water to carry out a crystallization reaction;

[0020] (2) Mix the product after the crystallization reaction with a solution containing ammonium ions to carry out ion exchange;

[0021] (3) The ion-exchange product is placed in an atmosphere containing water vapor for steam treatment.

[0022] In step (1) above, the raw materials include at least two molecular sieves with a silicon-to-aluminum atomic ratio of 150-700, wherein the difference c between the silicon-to-aluminum atomic ratios of any two molecular sieves satisfies: 0 < c ≤ 300. For example, the value of c can be 5, 10, 30, 50, 80, 100, 120, 150, 180, 200, 220, 250, 280, 300 or any value between them. Preferably, 0 < c ≤ 200, more preferably, 50 ≤ c ≤ 200, and even more preferably, 100 ≤ c ≤ 150.

[0023] In step (1) above, the silicon-aluminum atomic ratio of at least two molecular sieves with different silicon-aluminum atomic ratios in the raw materials is selected from any value between 150 and 700, for example, it can be 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700 or any value between them, preferably 200-600.

[0024] In some embodiments, the raw materials for preparation include a first molecular sieve and a second molecular sieve. The first molecular sieve has a silicon-to-aluminum atomic ratio of 300-700, such as 300, 350, 400, 450, 500, 550, 600, 650, 700 or any value between them, preferably 300-600, more preferably 350-500; the second molecular sieve has a silicon-to-aluminum atomic ratio of 150-600, such as 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600 or any value between them, preferably 200-400, more preferably 250-350. In some specific embodiments, the difference between the silicon-aluminum atomic ratio of the first molecular sieve and the silicon-aluminum atomic ratio of the second molecular sieve is 50-200, such as 50, 80, 100, 120, 150, 180, 200 or any value between them, preferably 100-150.

[0025] In some embodiments, the raw materials for preparation include a first molecular sieve and a second molecular sieve, wherein the silicon-to-aluminum atomic ratio of the first molecular sieve is 300-700, the silicon-to-aluminum atomic ratio of the second molecular sieve is 150-600, and the difference between the silicon-to-aluminum atomic ratio of the first molecular sieve and the silicon-to-aluminum atomic ratio of the second molecular sieve is greater than 0 and less than or equal to 200.

[0026] In some preferred embodiments, the raw materials for preparation include a first molecular sieve and a second molecular sieve, wherein the silicon-to-aluminum atomic ratio of the first molecular sieve is 300-600, the silicon-to-aluminum atomic ratio of the second molecular sieve is 200-400, and the difference between the silicon-to-aluminum atomic ratio of the first molecular sieve and the silicon-to-aluminum atomic ratio of the second molecular sieve is 50-200.

[0027] In some preferred embodiments, the raw materials for preparation include a first molecular sieve and a second molecular sieve, wherein the silicon-to-aluminum atomic ratio of the first molecular sieve is 350-500, the silicon-to-aluminum atomic ratio of the second molecular sieve is 250-350, and the difference between the silicon-to-aluminum atomic ratio of the first molecular sieve and the silicon-to-aluminum atomic ratio of the second molecular sieve is 100-150.

[0028] In some embodiments, the mass ratio of the first molecular sieve to the second molecular sieve is 1:(0.5-2).

[0029] In some embodiments, the raw materials used in the preparation include at least two molecular sieves with different silicon-to-aluminum atomic ratios, both of which are zeolite molecular sieves with MFI structures, such as ZSM-5 molecular sieves.

[0030] This invention does not impose a specific limit on the mass percentage of each molecular sieve in the raw materials used for preparation. In some embodiments, each molecular sieve accounts for 5%-95% of the total mass of the raw materials.

[0031] In some embodiments, in step (1), the binder is selected from one or more of silica sol, water glass, and alumina.

[0032] In some embodiments, in step (1), the organic amine is selected from C1-C8 monoamines, C1-C8 diamines and C1-C8 imines, preferably at least one of ethylamine, propylamine, butylamine, hexamethyleneimine, triethylamine, ethylenediamine and hexamethylenediamine.

[0033] In some embodiments, in step (1), the temperature of the crystallization reaction is 120-200°C, for example 120°C, 140°C, 160°C, 180°C, 200°C or any value between them.

[0034] In some embodiments, the crystallization reaction in step (1) takes 10-100 hours, for example 12 hours, 24 hours, 36 hours, 48 ​​hours, 56 hours, 72 hours, 84 hours, 96 hours or any value between them.

[0035] In step (1) above, the molded body obtained after molding is preferably columnar. The cross-section of the column can be circular, square, four-leaf clover-shaped, three-leaf clover-shaped, ring-shaped or gear-shaped, etc., with a length of 0.3-1.0 cm and a maximum radial dimension of 0.1-0.5 cm.

[0036] In some embodiments, step (1) further includes: preparing the raw materials and binder, followed by drying and calcination. Preferably, based on the weight of the calcined molded body, the total percentage content of the molecular sieve is 40%-80%, and the percentage content of the binder is 20%-60%.

[0037] In some embodiments, in step (2), the crystallized product is first dried and calcined, and then mixed with a solution containing ammonium ions for ion exchange. Preferably, the drying temperature is 80-140°C, for example 82°C, 85°C, 90°C, 95°C, 100°C, 110°C, 120°C, 130°C, 140°C or any value between them, and the drying time is 4-10 hours. Preferably, the calcination temperature is 500-600°C, for example 520°C, 540°C, 560°C, 580°C, 600°C or any value between them; and the calcination time is 4-8 hours.

[0038] In some embodiments, in step (2), the solution containing ammonium ions is an ammonium salt solution with a mass concentration of 3%-10%. The present invention does not impose any particular limitation on the ammonium salt; those skilled in the art can select commonly used ammonium salts as needed. For example, the ammonium salt includes, but is not limited to, at least one of ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium carbonate, and ammonium bicarbonate.

[0039] In some implementations, in step (2), the temperature during ion exchange is 80-90°C, for example 82°C, 84°C, 86°C, 88°C, 90°C or any value between them.

[0040] In step (2) of the present invention, in order to obtain better results, the ion exchange can be performed multiple times, for example, 2-6 times.

[0041] In some embodiments, step (2) further includes: after ion exchange, solid-liquid separation, and drying and calcination of the solid to obtain a binder-free composite molecular sieve. Preferably, the drying temperature is 80-120°C, for example 82°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C or any value between them, and the drying time is 4-10 hours. Preferably, the calcination temperature is 500-600°C, for example 520°C, 540°C, 560°C, 580°C, 600°C or any value between them; and the calcination time is 4-8 hours.

[0042] In some embodiments, in step (3), steam treatment is performed in an atmosphere with a water vapor content of 10%-100% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or any value between them). Optionally, the water vapor-containing atmosphere also contains nitrogen, air, or a mixture thereof. In some embodiments, the water vapor-containing atmosphere contains both water vapor and air. In some specific embodiments, the water vapor flow rate is 10-30 g / h, for example, 10 g / h, 15 g / h, 18 g / h, 20 g / h, 22 g / h, 25 g / h, 28 g / h, 30 g / h, or any value between them, preferably 15-25 g / h. In some specific embodiments, the air flow rate is 10-30 L / h, such as 10 L / h, 15 L / h, 18 L / h, 20 L / h, 22 L / h, 25 L / h, 28 L / h, 30 L / h or any value between them, preferably 15-25 L / h.

[0043] In some embodiments, the water vapor intake rate is 0.1-10 h⁻¹ for the mass hourly space velocity (MSV) of the ion-exchange products. -1 .

[0044] In some embodiments, in step (3), the temperature of the steam treatment is 400-800°C, for example, 400%, 500%, 600%, 700%, 800% or any value between them, preferably 500-700°C. In some embodiments, in step (3), the steam treatment time is 1-48 hours, preferably 3-20 hours.

[0045] Thirdly, the present invention provides the application of the binder-free composite molecular sieve described in the first aspect in olefin pyrolysis reactions.

[0046] The present invention provides that the binder-free composite molecular sieve described in the first aspect can be used as a catalyst in olefin cracking reactions.

[0047] Preferably, the olefin cracking reaction is a reaction in which olefins having four or more carbon atoms are cracked to produce ethylene and / or propylene.

[0048] Compared with the prior art, the beneficial effects of the present invention are:

[0049] Composite molecular sieves are prepared by combining two or more molecular sieves with specific silicon-to-aluminum atomic ratio differences. This leverages the synergistic catalytic effect between molecular sieves with different silicon-to-aluminum atomic ratios. Furthermore, the binder is converted through organic amine treatment and ion exchange, resulting in a binder-free composite molecular sieve. Activation of the obtained composite molecular sieve using steam treatment technology further enhances its catalytic activity, particularly in the catalytic cracking of olefins to produce ethylene and propylene, where the catalyst exhibits high stability and high ethylene and propylene yield. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way.

[0051] In this article, "at least two" and "multiple" have the same meaning, both referring to two or more.

[0052] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0053] In this article, "C1-Cn" refers to the group having 1-n carbon atoms. For example, "C1-C8" refers to the group having 1-8 carbon atoms. "C1-C8 monoamine" refers to a monoamine having 1-8 carbon atoms, including but not limited to ethylamine, propylamine, butylamine, etc.

[0054] In this article, the "silicon-to-aluminum atomic ratio" refers to the molar ratio of silicon atoms to aluminum atoms in the molecular sieve.

[0055] Unless otherwise specified, the term "ethylene + propylene yield" in this article refers to the sum of the yields of ethylene and propylene.

[0056] Unless otherwise specified, all reagents used in the following embodiments of the present invention are commercially available.

[0057] Example 1

[0058] Step (1): Mix 15g of ZSM-5 molecular sieve (first molecular sieve raw powder) with a silicon-to-aluminum atomic ratio of 500, 15g of ZSM-5 molecular sieve (second molecular sieve raw powder) with a silicon-to-aluminum atomic ratio of 300, and 30g of silica sol (SiO2 mass content of 40%), and extrude it into particles with a diameter of 0.4cm, a length of 0.3-1.0cm, and a circular cross-section. Dry at 120℃ for 8 hours. Add 20g of triethylamine and 20g of water to a reaction vessel, place 40g of the above particle sample in the upper stainless steel mesh inside the reaction vessel, seal it, and perform gas-solid treatment at 190℃ for 120 hours. After the product is removed, wash it with distilled water, dry it at 120℃ for 8 hours, and calcine it in a muffle furnace in air atmosphere at 550℃ for 4 hours to obtain the binder-free ZSM-5 molecular sieve precursor.

[0059] Step (2): The binderless ZSM-5 molecular sieve precursor obtained in step (1) is subjected to ion exchange three times in a 5% ammonium nitrate solution at 80°C. After washing and drying again, it is calcined in a muffle furnace at 550°C for 6 hours to obtain the hydrogen-form binderless ZSM-5 molecular sieve precursor.

[0060] Step (3): Place 20 grams of the hydrogen-type binderless ZSM-5 molecular sieve precursor obtained in step (2) above into a quartz reaction tube, introduce water vapor at a flow rate of 18 grams per hour and air at a flow rate of 20 liters per hour, and steam treat for 10 hours at a temperature of 550°C to obtain the binderless ZSM-5 molecular sieve catalyst.

[0061] Example 2

[0062] In step (1), replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum atomic ratio of 500” with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum atomic ratio of 400”, and the rest of the steps are the same as in Example 1.

[0063] Example 3

[0064] In step (1), replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum atomic ratio of 500” with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum atomic ratio of 450”, and the rest of the steps are the same as in Example 1.

[0065] Example 4

[0066] In step (1), replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 300” with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 400”, and replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 500” with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 600”. The remaining steps are the same as in Example 1.

[0067] Example 5

[0068] In step (1), replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 300” with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 200”, and replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 500” with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 300”. The remaining steps are the same as in Example 1.

[0069] Example 6

[0070] In step (1), replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum atomic ratio of 500” with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum atomic ratio of 350”, and the rest of the steps are the same as in Example 1.

[0071] Example 7

[0072] Replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 300” with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 200”, and follow the same steps as in Example 1.

[0073] Example 8

[0074] Replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 300” with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 600”, and replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 500” with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 700”. The remaining steps are the same as in Example 1.

[0075] Comparative Example 1

[0076] In step (1), “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 500” is replaced with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 200”, and “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 300” is replaced with “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 100”. The remaining steps are the same as in Example 1.

[0077] Comparative Example 2

[0078] Change the steam treatment conditions: No steam treatment is performed in step (3); the remaining steps are the same as in Example 2.

[0079] Comparative Example 3

[0080] Replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 300 and 15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 500” with “30 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 200”, and the remaining steps are the same as in Example 1.

[0081] Comparative Example 4

[0082] Replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 300 and 15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 500” with “30 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 300”, and the remaining steps are the same as in Example 1.

[0083] Comparative Example 5

[0084] Replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 300 and 15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 500” with “30 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 400”, and the remaining steps are the same as in Example 1.

[0085] Comparative Example 6

[0086] Replace “15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 300 and 15 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 500” with “30 grams of ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 500”, and the remaining steps are the same as in Example 1.

[0087] Comparative Example 7

[0088] Step (1): Mix 15g of ZSM-5 molecular sieve (first molecular sieve raw powder) with a silicon-to-aluminum atomic ratio of 500, 15g of ZSM-5 molecular sieve (second molecular sieve raw powder) with a silicon-to-aluminum atomic ratio of 300, and 30g of silica sol (SiO2 mass content of 40%), extrude into particles with a diameter of 0.4 cm, a length of 0.3-1.0 cm, and a circular cross-section, and dry at 120℃ for 8 hours to obtain ZSM-5 molecular sieve precursor containing binder.

[0089] Step (2): The ZSM-5 molecular sieve precursor containing binder obtained in step (1) is subjected to ion exchange three times in a 5% ammonium nitrate solution at 80℃. After washing and drying again, it is calcined in a muffle furnace at 550℃ for 6 hours to obtain the hydrogen form ZSM-5 molecular sieve precursor containing binder.

[0090] Step (3): Place 20 grams of the hydrogen-type ZSM-5 molecular sieve precursor with binder obtained in step (2) above into a quartz reaction tube, introduce water vapor at a flow rate of 18 grams per hour and air at a flow rate of 20 liters per hour, and steam treat for 10 hours at a temperature of 550°C to obtain the ZSM-5 molecular sieve catalyst with binder.

[0091] The silica-alumina atomic ratios of the two molecular sieve raw powders in Examples 1-8 and Comparative Examples 1-7 are shown in Table 1.

[0092] Evaluation of the reactivity of C4 cracking to ethylene and propylene

[0093] A fixed-bed catalytic cracking reactor with a stainless steel tube reactor was used. The composite molecular sieves prepared in Examples 1-8 and Comparative Examples 1-7 were used as catalysts, and a mixture of C4 atoms prepared with standard gas was used as feedstock to evaluate the activity of the C4 cracking reaction to produce ethylene and propylene. The evaluation results are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] In Table 1 above, "ethylene + propylene yield" refers to the sum of the ethylene yield and the propylene yield.

[0098] Experimental conclusion:

[0099] As can be seen from Table 1, the composite molecular sieves provided in Examples 1-8 of the present invention have high catalytic activity and high ethylene + propylene yield (above 38%) in the C4 cracking reaction.

[0100] Compared with Comparative Examples 4 and 5, Example 2 of this application, using molecular sieves with a silicon-to-aluminum ratio of 400 and 300, under the same molecular sieve dosage, showed a higher yield of ethylene + propylene compared to using a molecular sieve catalyst with a silicon-to-aluminum ratio of 400 alone, and using a molecular sieve catalyst with a silicon-to-aluminum ratio of 300 alone. Similarly, in Examples 1, 3, and 5-6, compared with Comparative Example 4, under the same molecular sieve dosage, the composite molecular sieves obtained by combining molecular sieves with silicon-to-aluminum ratios of 500, 400, 450, 200, and 350 with a molecular sieve with a silicon-to-aluminum ratio of 300, all showed higher yields of ethylene + propylene than the yield of Comparative Example 4 using a molecular sieve with a silicon-to-aluminum ratio of 300 alone, and also higher than the yields of Comparative Examples 3, 5, and 6 using molecular sieves with silicon-to-aluminum ratios of 200, 400, and 500 alone, respectively. This demonstrates that in the above reaction, the composite molecular sieve of the present invention exhibits superior catalytic performance compared to a single molecular sieve, and the two molecular sieves exert a synergistic catalytic effect.

[0101] In Comparative Example 1, although the difference between the silicon-aluminum atomic ratio a of the first molecular sieve and the silicon-aluminum atomic ratio b of the original powder of the second molecular sieve is 100, the composite molecular sieve has low catalytic activity and reduced selectivity for the reaction products due to the low silicon-aluminum atomic ratios of both the first and second molecular sieves, resulting in a low yield of ethylene + propylene.

[0102] The results of Comparative Example 2 and Example 2 show that the molecular sieve without high-temperature steam treatment has slightly poorer catalytic performance and a lower yield of the final product ethylene + propylene.

[0103] The results of Comparative Example 7 and Example 1 show that the yield of ethylene + propylene in the C4 cracking reaction of the molecular sieve catalyst containing binder is much lower than that of the binder-free composite molecular sieve catalyst of the present invention.

[0104] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A binder-free composite molecular sieve, the raw materials for which are prepared include at least two molecular sieves with a silicon-to-aluminum atomic ratio of 150-700, wherein the difference c between the silicon-to-aluminum atomic ratios of any two molecular sieves satisfies: 0 < c ≤ 300; The raw materials for preparation include a first molecular sieve and a second molecular sieve, wherein the silicon-to-aluminum atomic ratio of the first molecular sieve is 300-700. The silicon-to-aluminum atomic ratio of the second molecular sieve is 200-400.

2. The composite molecular sieve according to claim 1, characterized in that, The difference *c* between the silicon-to-aluminum atomic ratios of any two molecular sieves satisfies: 0 < *c* ≤ 200; and / or, The first molecular sieve has a silicon-to-aluminum atomic ratio of 300-600; the second molecular sieve has a silicon-to-aluminum atomic ratio of 250-350.

3. The composite molecular sieve according to claim 1, characterized in that, The difference c between the silicon-aluminum atomic ratios of any two molecular sieves satisfies: 50 ≤ c ≤ 200.

4. The composite molecular sieve according to claim 1, characterized in that, The difference c between the silicon-aluminum atomic ratios of any two molecular sieves satisfies: 100≤c≤150.

5. The composite molecular sieve according to claim 1, characterized in that, The silicon-to-aluminum atomic ratio of the first molecular sieve is 350-500.

6. The composite molecular sieve according to claim 1, characterized in that, The difference between the silicon-aluminum atomic ratio of the first molecular sieve and the silicon-aluminum atomic ratio of the second molecular sieve is 50-200.

7. The composite molecular sieve according to claim 1, characterized in that, The difference between the silicon-aluminum atomic ratio of the first molecular sieve and the silicon-aluminum atomic ratio of the second molecular sieve is 50-150.

8. The composite molecular sieve according to claim 1, characterized in that, The at least two types of molecular sieves with different silicon-to-aluminum atomic ratios are all zeolite molecular sieves with MFI structure.

9. The composite molecular sieve according to claim 1, characterized in that, The at least two molecular sieves with different silicon-aluminum atomic ratios are both ZSM-5 molecular sieves.

10. A method for preparing the binder-free composite molecular sieve according to any one of claims 1-9, comprising the following steps: (1) The raw materials are mixed with the binder and molded, and then mixed with organic amine and water to carry out a crystallization reaction; (2) Mix the product after the crystallization reaction with a solution containing ammonium ions to carry out ion exchange; (3) Place the ion-exchange product in an atmosphere containing water vapor for steam treatment.

11. The preparation method according to claim 10, characterized in that, In step (1), the binder is selected from one or more of silica sol, water glass, and alumina; and / or, The organic amine is selected from at least one of C1-C8 monoamines, C1-C8 diamines, and C1-C8 imines; and / or, The crystallization reaction is carried out at a temperature of 120-200℃ for 10-100 hours.

12. The preparation method according to claim 10, characterized in that, The organic amine is selected from at least one of ethylamine, propylamine, butylamine, hexamethyleneimine, triethylamine, ethylenediamine, and hexamethylenediamine.

13. The preparation method according to claim 10, characterized in that, Step (1) also includes the steps of preparing raw materials and binders, mixing them into a mold, and then drying and calcining them.

14. The preparation method according to claim 13, characterized in that, Based on the weight of the calcined molded body, the total percentage content of the molecular sieve is 40%-80%, and the percentage content of the binder is 20%-60%.

15. The preparation method according to claim 10, characterized in that, In step (2), the solution containing ammonium ions is an ammonium salt solution with a mass concentration of 3%-10%; And / or, in step (2), the temperature during ion exchange is 80-90°C.

16. The preparation method according to claim 15, characterized in that, The ammonium salt is selected from at least one of ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium carbonate, and ammonium bicarbonate.

17. The preparation method according to claim 10, characterized in that, Step (2) also includes: after ion exchange, solid-liquid separation, the solid is dried and calcined to obtain a binder-free composite molecular sieve.

18. The preparation method according to claim 17, characterized in that, The drying temperature is 80-120℃, and the time is 4-10 hours.

19. The preparation method according to claim 17, characterized in that, The roasting temperature is 500-600℃, and the time is 4-8 hours.

20. The preparation method according to claim 10, characterized in that, In step (3), steam treatment is carried out in an atmosphere with a water vapor content of 10%-100%; and / or, The steam treatment temperature is 400-800℃, and the steam treatment time is 1-48 hours.

21. The preparation method according to claim 20, characterized in that, The atmosphere containing water vapor also contains nitrogen and / or air.

22. The application of the binderless composite molecular sieve according to any one of claims 1-9 or the binderless composite molecular sieve prepared by the preparation method according to any one of claims 10-21 in olefin cracking reaction.

23. The application according to claim 22, characterized in that, The olefin cracking reaction is a reaction in which olefins having four or more carbon atoms are cracked to produce ethylene and / or propylene.

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