Binder-free composite molecular sieve as well as preparation method and application thereof

Abstract

The invention provides a binder-free composite molecular sieve as well as a preparation method and application thereof. The preparation raw materials of the composite molecular sieve comprise at least two molecular sieves with the silicon-aluminum atomic ratio of 150-700, wherein the difference value c between the silicon-aluminum atomic ratios of any two molecular sieves is more than 0 and less than or equal to 300. The composite molecular sieve provided by the invention does not contain a binder, can be used as a catalyst for olefin cracking reaction, can improve the yield of ethylene and propylene, and has high catalyst stability.

Description

Technical Field

[0001] The invention belongs to the field of porous materials, and in particular relates to a binder-free composite molecular sieve and a preparation method and application thereof. Background Art

[0002] Ethylene and propylene are important basic raw materials for the petrochemical industry. With the continuous development of my country's economy, the demand for ethylene and propylene will continue to be high. Mixed C4 and above olefins are by-products of ethylene plants, refinery FCC units and coal-to-gas units, and can usually only be used as low value-added products such as fuel. Due to the large-scale and integrated development of my country's petrochemical enterprises and the extension of the industrial chain, the development of C4 and above olefin production ethylene and propylene technology will enable more optimized and reasonable utilization of light olefin resources, increase production of important raw materials ethylene and propylene, create huge economic benefits for petrochemical enterprises, and improve the comprehensive utilization rate of energy.

[0003] ZSM-5 molecular sieve catalyst is a common MFI zeolite molecular sieve catalyst used for the cracking of C4 and above olefins to produce ethylene and propylene. ZSM-5 zeolite molecular sieve is widely used in the field of catalysis because of its advantages such as uniform and ordered micropores, large specific surface area, and high hydrothermal stability. Zeolite powder is very inconvenient in practical applications due to its small particle size. Generally, it is necessary to add a binder to form the catalyst so that it has a certain specific shape and a certain mechanical strength. However, the binder is generally an inert component. The addition of the binder actually has a "dilution" effect on the active center of the molecular sieve, which increases the actual reaction space velocity and accelerates the deactivation of the catalyst. The binder has a certain pore blocking effect on the molecular sieve and affects the diffusion performance.

[0004] ZSM-5 molecular sieve catalysts with different silicon-aluminum ratios have completely different catalytic performances in the catalytic cracking of C4 olefins to produce ethylene and propylene. In the prior art, the use of a single-component ZSM-5 molecular sieve still cannot meet the ideal requirements in terms of catalytic activity, yield of ethylene and propylene and other products, and reaction stability in the catalytic cracking of olefins to produce ethylene and propylene. Therefore, the development of more composite ZSM-5 molecular sieves, especially binder-free composite ZSM-5 molecular sieves, is expected to solve the above problems. Summary of the invention

[0005] In order to solve the above technical problems existing in the prior art, the present invention provides a composite molecular sieve without binder and a preparation method thereof. The present invention compounded molecular sieves with different silicon-aluminum atomic ratios and adopted a binder conversion method to obtain a composite molecular sieve without binder, and different molecular sieves showed synergistic catalytic effects, greatly improving the catalytic activity of the composite molecular sieve, and in the reaction of catalyzing olefin cracking to prepare ethylene and propylene, it has high reaction stability and high ethylene and propylene yield.

[0006] In a first aspect, the present invention provides a binderless composite molecular sieve, wherein the raw materials for preparing the molecular sieves include 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<c≤300.

[0007] The present invention compounds at least two molecular sieves whose silicon-aluminum atomic ratio difference is within a specific range, and the obtained composite molecular sieve has a high content of zeolite structure and a large number of macropore and micropore composite structures, which is more conducive to the rapid diffusion of products in the catalytic reaction, slows down coking, improves catalytic activity, and improves reaction stability.

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

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

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

[0011] In some embodiments, the preparation raw materials include a first molecular sieve and a second molecular sieve, and 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 therebetween, preferably 50-150, and more preferably 100-150.

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

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

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

[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, in the preparation raw materials, at least two molecular sieves with different silicon-aluminum atomic ratios are both zeolite molecular sieves with MFI structure, for example, both are ZSM-5 molecular sieves.

[0017] In the present invention, there is no particular limitation on the mass percentage of each molecular sieve in the raw material. In some embodiments, each molecular sieve accounts for 5% to 95% of the total mass of the raw material.

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

[0019] (1) mixing the prepared raw material with a binder to form a mixture, and then mixing with an organic amine and water to perform a crystallization reaction;

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

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

[0022] In the above step (1), the preparation raw materials include 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<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 therebetween, preferably, 0<c≤200, more preferably, 50≤c≤200, and further preferably, 100≤c≤150.

[0023] In the above step (1), the silicon-aluminum atomic ratio of at least two molecular sieves with different silicon-aluminum atomic ratios in the preparation 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 therebetween, preferably 200-600.

[0024] In some embodiments, the preparation raw materials include a first molecular sieve and a second molecular sieve, the silicon-aluminum atomic ratio of the first molecular sieve is 300-700, for example, 300, 350, 400, 450, 500, 550, 600, 650, 700 or any value therebetween, preferably 300-600, more preferably 350-500; the silicon-aluminum atomic ratio of the second molecular sieve is 150-600, for example, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600 or any value therebetween, 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 therebetween, preferably 100-150.

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

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

[0027] In some more preferred embodiments, the preparation raw materials include a first molecular sieve and a second molecular sieve, wherein the silicon-aluminum atomic ratio of the first molecular sieve is 350-500, the silicon-aluminum atomic ratio of the second molecular sieve is 250-350, and 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 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, in the preparation raw materials, at least two molecular sieves with different silicon-aluminum atomic ratios are both zeolite molecular sieves with MFI structure, for example, both are ZSM-5 molecular sieves.

[0030] The present invention does not impose any particular limitation on the mass percentage of each molecular sieve in the raw material. In some embodiments, each molecular sieve accounts for 5% to 95% of the total mass of the raw material.

[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, such as 120°C, 140°C, 160°C, 180°C, 200°C or any value therebetween.

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

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

[0036] In some embodiments, step (1) further comprises: drying and calcining the prepared raw materials after mixing with the binder. Preferably, based on the weight of the calcined molded body, the total content of the molecular sieve is 40%-80%, and the 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 to perform ion exchange. Preferably, the drying temperature is 80-140°C, such as 82°C, 85°C, 90°C, 95°C, 100°C, 110°C, 120°C, 130°C, 140°C or any value therebetween, and the drying time is 4-10 hours. Preferably, the calcining temperature is 500-600°C, such as 520°C, 540°C, 560°C, 580°C, 600°C or any value therebetween; the calcining 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 specifically limit the ammonium salt, and those skilled in the art can select the ammonium salt commonly used in the art 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, ammonium bicarbonate, etc.

[0039] In some embodiments, in step (2), the temperature for ion exchange is 80-90°C, such as 82°C, 84°C, 86°C, 88°C, 90°C or any value therebetween.

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

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

[0042] In some embodiments, in step (3), steam treatment is carried out 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 therebetween). Optionally, the atmosphere containing water vapor also contains nitrogen, air or a mixture thereof. In some embodiments, the atmosphere containing water vapor contains water vapor and air. In some specific embodiments, the flow rate of the water vapor is 10-30 g / h, such as 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 therebetween, preferably 15-25 g / h. In some specific embodiments, the air flow rate is 10-30 L / h, for example 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 therebetween, preferably 15-25 L / h.

[0043] In some embodiments, the mass space velocity of the water vapor intake to the product after the ion exchange is 0.1-10h -1 .

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

[0045] In a third aspect, the present invention provides use of the binderless composite molecular sieve described in the first aspect in an olefin cracking reaction.

[0046] The present invention provides that the binderless 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 of cracking olefins having more than 4 carbon atoms to produce ethylene and / or propylene.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] Two or more molecular sieves with a specific difference in silicon-aluminum atomic ratios are compounded to form a composite molecular sieve, and the synergistic catalytic effect between the molecular sieves with different silicon-aluminum atomic ratios is exerted. The binder is converted through organic amine treatment and ion exchange to obtain a composite molecular sieve without a binder. The obtained composite molecular sieve is activated by steam treatment technology to improve the catalytic activity of the molecular sieve, especially in the reaction of catalytic olefin cracking to prepare ethylene and propylene, the catalyst has high stability and high ethylene and propylene yield. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to constitute any limitation to the present invention.

[0051] As used herein, "at least two" and "plurality" have the same meaning, and both refer to two or more than two.

[0052] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0053] Herein, the "C1-Cn" means that the group has 1-n carbon atoms, for example, "C1-C8" means that the group has 1-8 carbon atoms, and "C1-C8 monoamine" means a monoamine having 1-8 carbon atoms, including but not limited to ethylamine, propylamine, butylamine, etc.

[0054] Herein, the "silicon to aluminum atomic ratio" refers to the molar ratio of silicon atoms to aluminum atoms in the molecular sieve.

[0055] Herein, unless otherwise specified, the "ethylene + propylene yield" refers to the sum of the ethylene yield and the propylene yield.

[0056] Unless otherwise specified, the reagents used in the following examples of the present invention can be obtained through commercial channels.

[0057] Example 1

[0058] Step (1): 15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 500 (first molecular sieve original powder), 15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 300 (second molecular sieve original powder), and 30 g of silica sol (SiO2 mass content of 40%) are kneaded and extruded into particles with a diameter of 0.4 cm, a length of 0.3-1.0 cm, and a circular cross-section, and dried at 120° C. for 8 hours. 20 g of triethylamine and 20 g of water are added to a reactor, and 40 g of the above-mentioned particle sample is placed in the upper stainless steel mesh inside the reactor, sealed, and gas-solid treated at 190° C. for 120 hours. The product is taken out and washed with distilled water, dried at 120° C. for 8 hours, and calcined at 550° C. in an air atmosphere of a muffle furnace for 4 hours to obtain a 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% by mass ammonium nitrate solution at 80°C, washed and dried again, and then calcined in a muffle furnace at 550°C for 6 hours to obtain a hydrogen-type binderless ZSM-5 molecular sieve precursor.

[0060] Step (3): Place 20 g of the hydrogen-type binderless ZSM-5 molecular sieve precursor obtained in the above step (2) in a quartz reaction tube, introduce water vapor at a flow rate of 18 g 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 a binderless ZSM-5 molecular sieve catalyst.

[0061] Example 2

[0062] In step (1), "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 500" is replaced by "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 400", and the remaining steps are the same as in Example 1.

[0063] Example 3

[0064] In step (1), "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 500" is replaced by "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 450", and the remaining steps are the same as in Example 1.

[0065] Example 4

[0066] In step (1), "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 300" is replaced by "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 400", and "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 500" is replaced by "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 600", and the remaining steps are the same as in Example 1.

[0067] Example 5

[0068] In step (1), "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 300" is replaced by "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 200", and "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 500" is replaced by "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 300", and the remaining steps are the same as in Example 1.

[0069] Example 6

[0070] In step (1), "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 500" is replaced by "15 g of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 350", and the remaining steps are the same as in Example 1.

[0071] Example 7

[0072] Replace “15 g of ZSM-5 molecular sieve having a silicon-aluminum atomic ratio of 300” with “15 g of ZSM-5 molecular sieve having a silicon-aluminum atomic ratio of 200”, and the remaining steps are the same as in Example 1.

[0073] Example 8

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

[0075] Comparative Example 1

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

[0077] Comparative Example 2

[0078] Changing 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-aluminum atomic ratio of 300, 15 grams of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 500" with "30 grams of ZSM-5 molecular sieve with a silicon-aluminum atomic ratio of 200", and the remaining steps are the same as Example 1.

[0081] Comparative Example 4

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

[0083] Comparative Example 5

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

[0085] Comparative Example 6

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

[0087] Comparative Example 7

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

[0089] Step (2): The binder-containing ZSM-5 molecular sieve precursor obtained in step (1) is ion exchanged three times in a 5% ammonium nitrate solution at 80°C, washed and dried again, and then calcined in a muffle furnace at 550°C for 6 hours to obtain a hydrogen-type binder-containing ZSM-5 molecular sieve precursor.

[0090] Step (3): Place 20 g of the hydrogen-type binder-containing ZSM-5 molecular sieve precursor obtained in the above step (2) in a quartz reaction tube, introduce water vapor at a flow rate of 18 g 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 a binder-containing ZSM-5 molecular sieve catalyst.

[0091] The silicon-aluminum 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 Reaction Activity of C4 Cracking to Prepare Ethylene and Propylene

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

[0094] Table 1

[0095]

[0096]

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

[0098] Experimental conclusion:

[0099] It can be seen from Table 1 that the composite molecular sieves provided by Examples 1-8 of the present invention have higher catalytic activity and higher ethylene+propylene yield (more than 38%) in the carbon four cracking reaction.

[0100] Compared with Comparative Examples 4 and 5, Example 2 of the present application shows that, under the same molecular sieve dosage, the composite catalyst prepared by using molecular sieves with a silicon-aluminum atomic ratio of 400 and a silicon-aluminum atomic ratio of 300 is higher than the molecular sieve catalyst with a silicon-aluminum atomic ratio of 400 and the molecular sieve catalyst with a silicon-aluminum atomic ratio of 300. Similarly, in Example 1, Example 3, and Examples 5-6, compared with Comparative Example 4, under the same molecular sieve dosage, the composite molecular sieve obtained by compounding molecular sieves with silicon-aluminum atomic ratios of 500, 400, 450, 200, and 350 and molecular sieves with a silicon-aluminum atomic ratio of 300, the yield of ethylene + propylene of the reaction product is higher than the yield of molecular sieves with a silicon-aluminum atomic ratio of 300 used in Comparative Example 4 alone, and is also higher than the yields of molecular sieves with silicon-aluminum atomic ratios of 200, 400, and 500 used alone in Comparative Examples 3, Comparative Examples 5, and Comparative Examples 6, respectively. This indicates that in the above reaction, the composite molecular sieve of the present invention has better catalytic performance than a single molecular sieve, and the two molecular sieves play a synergistic catalytic role.

[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 second molecular sieve raw powder is 100, since the silicon-aluminum atomic ratios of the first molecular sieve and the second molecular sieve are both low, the resulting composite molecular sieve has low catalytic activity, reduced selectivity for reaction products, and low ethylene + propylene yield.

[0102] From the comparison of the results of Comparative Example 2 and Example 2, it can be seen that the molecular sieve that has not been treated with high-temperature steam has a slightly poor catalytic performance and a low yield of the final product ethylene + propylene.

[0103] From the comparison of the results of Comparative Example 7 and Example 1, it can be seen that in the reaction of preparing ethylene and propylene by carbon four cracking using the molecular sieve catalyst containing a binder, the yield of ethylene + propylene is much lower than that using the binderless composite molecular sieve catalyst of the present invention.

[0104] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A binderless composite molecular sieve, wherein the raw materials for preparing the molecular sieves include 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<c≤300.

2. 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: 0<c≤200, preferably 50≤c≤200, more preferably 100≤c≤150; and / or, The preparation raw materials include a first molecular sieve and a second molecular sieve, the silicon-aluminum atomic ratio of the first molecular sieve is 300-700, preferably 300-600, more preferably 350-500; the silicon-aluminum atomic ratio of the second molecular sieve is 150-600, preferably 200-400, more preferably 250-350; preferably, 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, preferably 50-150.

3. The composite molecular sieve according to claim 1 or 2, characterized in that: The at least two molecular sieves with different silicon-aluminum atomic ratios are both zeolite molecular sieves with MFI structure, preferably both are ZSM-5 molecular sieves.

4. The method for preparing the binder-free composite molecular sieve according to any one of claims 1 to 3, comprising the following steps: (1) mixing the prepared raw material with a binder to form a mixture, and then mixing with an organic amine and water to perform a crystallization reaction; (2) mixing the product after the crystallization reaction with a solution containing ammonium ions to perform ion exchange; (3) The ion exchange product is placed in an atmosphere containing water vapor for steam treatment.

5. The preparation method according to claim 4, 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 C1-C8 monoamines, C1-C8 diamines and C1-C8 imines, preferably at least one of ethylamine, propylamine, butylamine, hexamethyleneimine, triethylamine, ethylenediamine and hexamethylenediamine; and / or, The temperature of the crystallization reaction is 120-200° C., and the time of the crystallization reaction is 10-100 hours.

6. The preparation method according to claim 4 or 5, characterized in that: Step (1) also includes: after the raw materials are prepared and mixed with the binder, drying and calcining are performed; Preferably, based on the weight of the calcined molded body, the total content of the molecular sieve is 40%-80%, and the content of the binder is 20%-60%.

7. The preparation method according to any one of claims 4 to 6, characterized in that: In step (2), the solution containing ammonium ions is an ammonium salt solution with a mass concentration of 3% to 10%; Preferably, the ammonium salt is selected from at least one of ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium carbonate and ammonium bicarbonate; And / or, in step (2), the temperature during ion exchange is 80-90°C.

8. The preparation method according to any one of claims 4 to 7, characterized in that: Step (2) further comprises: after ion exchange, solid-liquid separation, and solid drying and calcination to obtain a binder-free composite molecular sieve; Preferably, the drying temperature is 80-120°C and the drying time is 4-10 hours. Preferably, the calcination temperature is 500-600° C. and the calcination time is 4-8 hours.

9. The preparation method according to any one of claims 4 to 8, characterized in that: In step (3), steam treatment is performed in an atmosphere containing 10% to 100% water vapor; optionally, the atmosphere containing water vapor also contains nitrogen and / or air; and / or, The temperature of the steam treatment is 400-800° C., and the time of the steam treatment is 1-48 hours.

10. Use of the binderless composite molecular sieve according to any one of claims 1 to 3 in olefin cracking reactions, Preferably, the olefin cracking reaction is a reaction of cracking olefins having more than 4 carbon atoms to produce ethylene and / or propylene.

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