Catalyst for preparing ethylene and propylene through butene cracking as well as preparation method and application of catalyst

Abstract

The invention discloses a catalyst for preparing ethylene and propylene through butene cracking as well as a preparation method and application of the catalyst. The catalyst is a core-shell H-ZSM-5 (at) MCM-41 molecular sieve, and the thickness of the shell layer of the MCM-41 is 10-60 nm; the preparation method comprises the following steps: dispersing an H-ZSM-5 molecular sieve into a solvent to obtain a mixture I; adding an alkaline solution and an organic template agent into the mixture I to obtain a mixture II; slowly dropwise adding a silicon source into the mixture II, stirring and hydrolyzing to obtain a modified solid-liquid mixture; and aging and roasting the modified solid-liquid mixture to obtain the catalyst. The catalyst is applied to a reaction for preparing ethylene and propylene through catalytic cracking of butene, and can improve the catalytic efficiency and prolong the reaction life.

Description

Technical Field

[0001] The invention relates to the technical field of catalysis, and in particular to a catalyst for preparing ethylene and propylene by cracking butene, and a preparation method and application thereof. Background Art

[0002] As building blocks of many important chemicals, ethylene and propylene are widely used in the production of chemicals such as polyethylene, polypropylene and acryl alcohol, and occupy an important position in the packaging, textile, electronics and automotive industries. The main technology for the traditional production of low-carbon olefins is the catalytic cracking of petroleum products such as naphtha, petroleum gas and condensate. In recent years, the new coal chemical industry has achieved unprecedented development in the production of low-carbon olefins and has gradually become an important technical route for olefin production. However, the above process will produce a large amount of C 4+ Therefore, the low value-added by-product C 4+ The conversion of long-chain olefins into ethylene and propylene can not only promote the integration of refining and chemical industries, but also connect and assist coal chemical industry and improve the utilization rate of carbon resources.

[0003] Olefin catalytic cracking is a typical acid-catalyzed reaction. In recent years, due to the suitable acidity and unique pore structure network of H-ZSM-5 molecular sieve, the olefin cracking technology using it as a catalyst has developed rapidly. However, the current OCC technology still has some disadvantages, such as rapid catalyst carbon deposition and deactivation, many by-products (about 300 kinds), and it is difficult to increase the yield of dienes (ethylene, propylene). Further improving catalyst activity and diene selectivity is a major challenge for OCC technology.

[0004] At present, there are three common methods to improve the performance of olefin catalytic cracking:

[0005] (1) Regulating the performance of ZSM-5 molecular sieve catalyst Acid amount. At present, this method is very mature. There is limited room for optimizing the catalytic cracking performance of olefins by regulating the amount of acid.

[0006] (2) Regulating the effective diffusion distance of H-ZSM-5 molecular sieve. By reducing the size of molecular sieve grains, creating a multi-level pore structure, and constructing a molecular sieve morphology with a specific crystal surface exposure, the effective diffusion distance of the molecular sieve catalyst can be effectively shortened, the intracrystalline diffusion resistance can be reduced, and its catalytic efficiency can be significantly improved. However, there are a series of technical difficulties in the implementation of this method. Among them, there is a problem of separation difficulty in the production process of small-particle molecular sieves, so the production cost is relatively high; in addition, since the molecular sieve catalysts used in industry are all formed catalysts, more binders are required in the forming process of small-particle molecular sieves, which further increases the cost of industrial application and hinders the industrial application of small-particle molecular sieves; for the synthesis process of multi-level pore molecular sieves, a large amount of expensive template agents are required, and the calcination process of a large amount of template agents is easy to cause environmental pollution, making it difficult to apply to industrial production. At the same time, the post-treatment process is easy to damage the molecular sieve skeleton structure and has poor controllability. ZSM-5 molecular sieves with specific morphology require the addition of expensive additive raw materials during the preparation process, which is not conducive to industrial scale-up production from the perspective of cost and environmental protection.

[0007] (3) Modification of H-ZSM-5 molecular sieve. Common modification methods include acid etching, SiO2 deposition, element modification (such as phosphorus, potassium, sodium, etc.) and other strategies. However, this method has poor controllability and repeatability, and is prone to damage the molecular sieve skeleton structure.

[0008] Therefore, finding new methods to improve the performance of catalytic cracking of butene to ethylene and propylene is crucial for the design of high-performance industrial catalysts. Summary of the invention

[0009] In view of the problems of low diene yield and poor reaction stability in the application of conventional microporous ZSM-5 molecular sieve catalysts in olefin catalytic cracking technology in the prior art, the present invention provides a new catalyst for butene cracking to produce ethylene and propylene, and a preparation method and application thereof. The catalyst is applied to olefin catalytic cracking technology to effectively inhibit the occurrence of secondary reactions such as polymerization and carbon deposition, and improve the diene yield and reaction life.

[0010] The first aspect of the present invention provides a catalyst for preparing ethylene and propylene by cracking butene, wherein the catalyst is a core-shell H-ZSM-5@MCM-41 molecular sieve, the shell thickness of MCM-41 is 10 to 60 nm, preferably, the shell thickness is 20 to 40 nm.

[0011] Furthermore, in the core-shell H-ZSM-5@MCM-41 molecular sieve, the atomic ratio of silicon to aluminum of the H-ZSM-5 molecular sieve is 100-600, preferably 300-500.

[0012] Furthermore, in the core-shell H-ZSM-5@MCM-41 molecular sieve, the mass ratio of H-ZSM-5 to MCM-41 molecular sieve is 1:1.2 to 1:0.2, and preferably, the mass ratio of H-ZSM-5 to MCM-41 molecular sieve is 1:0.8 to 1:0.4.

[0013] Furthermore, the specific surface area of ​​the core-shell H-ZSM-5@MCM-41 molecular sieve is 393-650 cm 2 ·g -1 , preferably 580-600cm 2 ·g -1 .

[0014] Furthermore, the mesopore volume in the core-shell H-ZSM-5@MCM-41 molecular sieve is 0.280-0.350 cm 3 ·g -1 .

[0015] The second aspect of the present invention provides a method for preparing the above catalyst, comprising the following steps:

[0016] (1) dispersing H-ZSM-5 molecular sieve into a solvent to obtain a mixture I;

[0017] (2) adding an alkaline solution and an organic template to the mixture I obtained in step (1) to obtain a mixture II;

[0018] (3) slowly adding a silicon source to the mixture II obtained in step (2), stirring and hydrolyzing to obtain a modified solid-liquid mixture;

[0019] (4) The modified solid-liquid mixture obtained in step (3) is aged and calcined to obtain the catalyst.

[0020] Furthermore, in step (1), the atomic ratio of silicon to aluminum of the H-ZSM-5 molecular sieve is 100 to 600, preferably 300 to 500.

[0021] Furthermore, in step (1), the solvent is a mixed solvent consisting of ethanol and deionized water, wherein the volume ratio of ethanol to deionized water is 0.5-1:2-1.

[0022] Furthermore, in step (1), the mass ratio of H-ZSM-5 molecular sieve to solvent is 1:10 to 1:50, preferably 1:20 to 1:30.

[0023] Furthermore, in step (2), the alkaline solution is a solution of at least one of sodium hydroxide, ammonium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, ammonium carbonate, and ammonia water; preferably, the alkaline solution is a solution of at least one of ammonium carbonate, ammonium hydroxide, and ammonia water.

[0024] Furthermore, in step (2), the mass concentration of the alkaline solution is 0.5% to 30%.

[0025] Furthermore, in step (2), the organic template is one of hexadecyltrimethylammonium bromide, tetrapropylammonium bromide, block copolymer P123, and tetrapropylammonium hydroxide; preferably, the selected organic template is hexadecyltrimethylammonium bromide.

[0026] Furthermore, in step (2), the mass ratio of the alkaline solution to the organic template is 1:1 to 5:1, preferably 2:1 to 4:1.

[0027] Furthermore, in step (3), the silicon source is one or more of tetraethyl orthosilicate, silica sol, tetramethyl orthosilicate, trimethylchlorosilane, triethylchlorosilane, and tripropylchlorosilane; preferably, the silicon source is selected from tetraethyl orthosilicate or silica sol.

[0028] Furthermore, in step (3), the mass ratio of the silicon source in terms of SiO2 to H-ZSM-5 is 0.2 to 1.2, preferably 0.6 to 1.2.

[0029] Furthermore, in step (3), the stirring hydrolysis conditions are as follows: temperature is 20-50°C, time is 2-10 hours, preferably, temperature is 25-40°C, time is 4-6 hours.

[0030] Furthermore, in step (4), the aging conditions are as follows: temperature is 20-50°C, and time is 0.5-5h. Preferably, the temperature is 25-40°C, and time is 1-3h.

[0031] Furthermore, in step (4), after aging, conventional operations such as solid-liquid separation, water washing, and drying are performed. The drying conditions are as follows: temperature of 80-150° C., time of 4-12 h, preferably, temperature of 90-110° C., time of 5-8 h.

[0032] Furthermore, in step (4), the calcination conditions are as follows: temperature is 500-650° C., and time is 3-12 h. Preferably, the temperature is 530-600° C., and time is 4-8 h.

[0033] The third aspect of the present invention provides the use of the above catalyst in the reaction of butene cracking to produce ethylene and propylene.

[0034] Further, the reaction conditions are as follows: the reaction temperature is 300-700°C, the butene volume space velocity is 5-60h -1 , the reaction pressure is 0.1 to 3 bar; preferably, the reaction temperature is 540 to 600°C, and the reaction space velocity is 20 to 35 h -1, the reaction pressure is 0.3~0.8bar.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention provides a novel catalyst for preparing ethylene and propylene by cracking butene. The catalyst has an H-ZSM-5 molecular sieve as a core structure and an MCM-41 molecular sieve as a shell structure, wherein the introduction of the shell structure has no effect on the microporous structure of the H-ZSM-5 molecular sieve core, and the mesoporous specific surface area of ​​the catalyst is greatly increased. The catalyst is applied to olefin catalytic cracking reactions. By constructing a core-shell molecular sieve catalyst, a layer of mesoporous structure is manufactured on the outer surface of the microporous active molecular sieve, which can effectively enrich the concentration of reactant molecules on the surface of the molecular sieve, thereby increasing the efficiency of the reactant molecules entering the microporous channels of the active molecular sieve and improving the accessibility of the active sites, thereby effectively improving the catalytic efficiency, increasing the yield of the target product, and prolonging the reaction life, making it possible to prepare ethylene and propylene by efficient catalytic conversion of low-value-added butene, and facilitating industrial production.

[0037] 2. In the process of olefin catalytic cracking reaction, it is urgent to develop new H-ZSM-5 molecular sieve catalysts. The inventors have found that by adopting the secondary growth method and comprehensively coordinating various steps, a core-shell H-ZSM-5@MCM-41 molecular sieve catalyst with suitable thickness can be obtained. The catalyst can greatly improve its catalytic efficiency while keeping the crystal structure of the molecular sieve basically unchanged, providing a new method for olefin catalytic cracking technology. In addition, the method of the present invention has low preparation cost and has important potential for industrial scale-up production.

[0038] 3. The catalyst of the present invention is used in the catalytic cracking of butene to prepare ethylene and propylene, the yield of ethylene and propylene is greatly improved, the catalyst deactivation rate is reduced, and the reaction stability is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The XRD characterization results of the H-ZSM-5@MCM-41-1 core-shell molecular sieve and the H-ZSM-5-p microporous molecular sieve obtained in Example 1;

[0040] Figure 2 The argon physical adsorption characterization results of the H-ZSM-5@MCM-41-1 core-shell molecular sieve and the H-ZSM-5-p microporous molecular sieve obtained in Example 1;

[0041] Figure 3 The mesopore size distribution characterization results of the H-ZSM-5@MCM-41-1 core-shell molecular sieve and the H-ZSM-5-p microporous molecular sieve obtained in Example 1;

[0042] Figure 4TEM characterization results of H-ZSM-5@MCM-41-1 core-shell molecular sieve and H-ZSM-5-p microporous molecular sieve obtained in Example 1;

[0043] Figure 5 The results are as follows: the reaction performance of the H-ZSM-5@MCM-41-1 core-shell molecular sieve and the H-ZSM-5-p microporous molecular sieve obtained in Example 1 in the catalytic cracking of olefins to prepare ethylene and propylene. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0045] In the present invention, XRD and argon physical adsorption are used to respectively determine the crystallinity and pore structure properties of the molecular sieve before and after modification. Among them, the XRD characterization is tested on a Bruker D8 Advance diffractometer. The experimental parameters are: tube voltage is 40kV, tube current is 40mA, Cu (Kα) (λ=5.1540589nm). Before testing, the sample needs to be fully ground in a mortar and scanned at a speed of 1° / min, and the scanning range of the 2θ angle is 5°-50°.

[0046] In the present invention, the argon physical adsorption is tested on a Micromeritics TriStar 3000 specific surface area analyzer. Before the test, the sample is vacuumed at 350° C. for 3 hours.

[0047] In the present invention, a high-resolution transmission electron microscope is used to measure the morphology of the molecular sieve before and after modification, wherein the transmission electron microscope model is Tecnai 20 STWIN, and the operating voltage is 200 kV.

[0048] The technical solution of the present invention is further described below through specific embodiments.

[0049] In the present invention, the inactivation rate = (reaction time 10 h C 2-3 ＝ Yield - reaction 70h C 2-3 ＝ Yield) / (reaction 10h C 2-3 ＝ Yield)×100%.

[0050] In the embodiments and comparative examples of the present invention, the H-ZSM-5 molecular sieve is prepared by the following method:

[0051] First, 31.25g of tetraethyl orthosilicate, 30g of tetrapropylammonium hydroxide (25%) and 45g of distilled water were weighed in a polytetrafluoroethylene lined tube, and mixed solution A was obtained after sufficient stirring; secondly, 10g of distilled water, 0.1405g of aluminum nitrate nonahydrate and 0.6g of sodium hydroxide were weighed in another polytetrafluoroethylene lined tube, and mixed solution B was obtained after sufficient stirring; then, solution B was added to solution A, and after sufficient stirring, it was transferred to a stainless steel crystallization kettle and crystallized at 170°C for 48h. Finally, the product was washed, centrifuged, dried at 100°C overnight, calcined at 550°C for 5h and ammonium exchanged to obtain the ZSM-5 molecular sieve body (H-ZSM-5-p, silicon-aluminum atomic ratio of 400).

[0052] The specific steps of the ammonium exchange method are as follows: disperse 2 g of the molecular sieve catalyst in 80 mL of 1 mol / L ammonium chloride solution, stir at 90°C for 2 h, filter and wash, dry the filter cake in a 90°C oven overnight, and calcine at 550°C for 6 h to obtain the hydrogenated ZSM-5 molecular sieve.

[0053] [Example 1]

[0054] Preparation of H-ZSM-5@MCM-41 molecular sieve:

[0055] (1) Weigh 3 g of the ZSM-5 molecular sieve powder (H-ZSM-5-p) obtained above and add it to 60 mL of 60% ethanol aqueous solution, stir evenly, and obtain a liquid-solid mixture I; the mass ratio of the molecular sieve body to the mixed solution is 1:20.

[0056] (2) Add 10 g of aqueous ammonia solution (28%) and 3 g of cetyltrimethylammonium bromide (CTAB) organic template to the liquid-solid mixture I obtained in step (1), and mix thoroughly to obtain a liquid-solid mixture II.

[0057] (3) Slowly drop 7.92 g of tetraethyl orthosilicate into the liquid-solid mixture II obtained in step (2), and slowly hydrolyze at 30° C. for 5 h to obtain a modified liquid-solid mixture; the mass ratio of the silicon source, calculated as SiO2, to the H-ZSM-5 molecular sieve body is 0.6.

[0058] (4) The liquid-solid mixture obtained in step (3) was stirred, aged at 30° C. for 2 h, filtered, washed with water, dried at 100° C. for 6 h, and calcined at 550° C. for 5 h to obtain a molecular sieve catalyst with a core-shell structure.

[0059] The core-shell molecular sieve catalyst obtained in Example 1 is recorded as H-ZSM-5@MCM-41-1, and the mass ratio of H-ZSM-5 to MCM-41 molecular sieve is 1:0.6.

[0060] Catalyst Evaluation:

[0061] The core-shell H-ZSM-5@MCM-41-1 molecular sieve catalyst obtained above was applied to the catalytic cracking of butene to produce ethylene and propylene. The reaction conditions of butene catalytic cracking were: reaction temperature of 550°C, catalyst dosage of 0.3g, butene volume space velocity of 30h -1 , the reaction pressure is 0.5 bar. Product C 2-3 The yield of olefins is shown in Table 1, and the deactivation rate of the obtained catalyst compared with the corresponding H-ZSM-5 molecular sieve body (after 70 hours of reaction) is shown in Table 1.

[0062] Figure 1 The XRD characterization results of H-ZSM-5-p and H-ZSM-5@MCM-41-1 are shown in Figure 2. Figure 1 It can be seen from the XRD spectrum that compared with the ZSM-5 molecular sieve body (H-ZSM-5-p), the crystallinity and skeleton structure of the molecular sieve with a core-shell structure (H-ZSM-5@MCM-41-1) obtained in Example 1 do not change significantly, and the typical MFI topological structure can still be maintained, indicating that the secondary growth strategy can effectively prevent the preparation process from destroying the molecular sieve skeleton structure, so that the topological structure of the core-shell H-ZSM-5@MCM-41-1 molecular sieve catalyst obtained in Example 1 remains consistent with the body.

[0063] Figure 2 The results of argon physical adsorption characterization of H-ZSM-5-p and H-ZSM-5@MCM-41-1 molecular sieve catalysts show that the core-shell molecular sieve catalyst obtained in Example 1 has obvious mesoporous structure characteristics, indicating that the molecular sieve structure contains abundant mesoporous structures.

[0064] Figure 3 The results of mesopore pore size distribution of H-ZSM-5-p and H-ZSM-5@MCM-41-1 molecular sieve catalysts are shown in Table 1. The results show that compared with the ZSM-5 molecular sieve body, the core-shell molecular sieve catalyst obtained in Example 1 contains abundant mesopores with a pore size of 2-3 nm.

[0065] Figure 4 The TEM characterization results of H-ZSM-5-p and H-ZSM-5@MCM-41-1 molecular sieve catalysts show that the morphological characteristics of the core-shell molecular sieve catalyst (H-ZSM-5@MCM-41-1) obtained in Example 1 are as follows: a uniform layer of MCM-41 mesoporous structure grows on the surface of the microporous molecular sieve, and its thickness is 30nm.

[0066] Figure 5The results of the reaction of H-ZSM-5-p and H-ZSM-5@MCM-41-1 molecular sieves catalyzing the cracking of butene to produce ethylene and propylene. The results show that compared with the ZSM-5 molecular sieve body (H-ZSM-5-p), the core-shell molecular sieve catalyst (H-ZSM-5@MCM-41-1) obtained by this Example 1 significantly improves the diene yield in the reaction process of catalytic cracking of butene to produce ethylene and propylene, and has better reaction stability. Table 1 shows the specific data of diene yield and deactivation rate in the reaction of H-ZSM-5-p and H-ZSM-5@MCM-41-1 molecular sieves catalyzing the cracking of butene to produce ethylene and propylene. From the results, it can be seen that the initial diene yield of the molecular sieve body (H-ZSM-5-p) is 38.1%, which drops to 19.8% after 70 hours of reaction, and the deactivation rate is 48%; while the initial activity of the core-shell molecular sieve catalyst obtained in Example 1 is 42.3%, which can be maintained at 35.3% after 70 hours of reaction, and the deactivation rate is only 16.5%.

[0067] comprehensive Figures 1 to 5 As can be seen from the results in Table 1, the core-shell ZSM-5 molecular sieve catalyst (H-ZSM-5@MCM-41-1) obtained in this embodiment can grow an ordered mesoporous MCM-41 film on the surface of the microporous molecular sieve while maintaining its skeleton structure and topological structure. When used in the reaction process of catalytic cracking of butene to produce ethylene and propylene, the diene yield and reaction stability are greatly improved.

[0068] [Example 2]

[0069] Preparation of H-ZSM-5@MCM-41 molecular sieve:

[0070] (1) Weigh 3 g of the ZSM-5 molecular sieve powder (H-ZSM-5-p) obtained above and add it to 60 mL of 60% ethanol aqueous solution, stir evenly, and obtain a liquid-solid mixture I; the mass ratio of the molecular sieve body to the mixed solution is 1:20.

[0071] (2) Add 10 g of ammonium carbonate aqueous solution (28%) and 3 g of cetyltrimethylammonium bromide (CTAB) organic template to the liquid-solid mixture I obtained in step (1), and mix thoroughly to obtain a liquid-solid mixture II.

[0072] (3) Slowly drop 4.5 g of silica sol (40%) into the liquid-solid mixture II obtained in step (2), and slowly hydrolyze at 30° C. for 5 h to obtain a modified liquid-solid mixture; the mass ratio of the silicon source, calculated as SiO2, to the H-ZSM-5 molecular sieve body is 0.6.

[0073] (4) The liquid-solid mixture obtained in step (3) was stirred, aged at 30° C. for 2 h, filtered, washed with water, dried at 100° C. for 6 h, and calcined at 550° C. for 5 h to obtain a molecular sieve catalyst with a core-shell structure.

[0074] The core-shell molecular sieve catalyst obtained in Example 2 is denoted as H-ZSM-5@MCM-41-2, and the mass ratio of H-ZSM-5 to MCM-41 molecular sieve is 1:0.6. The XRD spectrum of H-ZSM-5@MCM-41-2 is Figure 1 Similarly, there is no obvious change in crystallinity and skeleton structure, and it still has a typical MFI structure; the argon physical adsorption characterization results and the mesopore size distribution results show that the core-shell molecular sieve catalyst obtained by Example 2 has obvious mesoporous structural characteristics; the morphology characterization results show that a layer of uniform MCM-41 mesoporous structure grows on the surface of the microporous molecular sieve, and its thickness is 25nm.

[0075] Example 2 The evaluation method and conditions for the catalyst used in the catalytic cracking of butene to produce ethylene and propylene are the same as those in Example 1.

[0076] The evaluation results show that compared with the ZSM-5 molecular sieve body (H-ZSM-5-p), the core-shell molecular sieve catalyst (H-ZSM-5@MCM-41-2) obtained in Example 2 has a certain improvement in the diene yield during the reaction of butene catalytic cracking to produce ethylene and propylene, and the reaction stability has a certain improvement. Table 1 is the specific data of the diene yield and deactivation rate in the reaction of H-ZSM-5@MCM-41-2 molecular sieve catalyzing butene cracking to produce ethylene and propylene. It can be seen from the results that the initial activity of the core-shell molecular sieve catalyst obtained in Example 2 is 41.8%, and after 70 hours of reaction, it can be maintained at 33.5%, and the deactivation rate is 19.9%.

[0077] [Example 3]

[0078] Preparation of H-ZSM-5@MCM-41 molecular sieve:

[0079] (1) Weigh 3 g of the ZSM-5 molecular sieve powder (H-ZSM-5-p) obtained above and add it to 60 mL of 60% ethanol aqueous solution, stir evenly, and obtain a liquid-solid mixture I; the mass ratio of the molecular sieve body to the mixed solution is 1:20.

[0080] (2) Add 10 g of aqueous ammonia solution (28%) and 3 g of cetyltrimethylammonium bromide (CTAB) organic template to the liquid-solid mixture I obtained in step (1), and mix thoroughly to obtain a liquid-solid mixture II.

[0081] (3) Slowly drop 2.64 g of tetraethyl orthosilicate into the liquid-solid mixture II obtained in step (2), and slowly hydrolyze at 50° C. for 3 h to obtain a modified liquid-solid mixture; the mass ratio of the silicon source, calculated as SiO2, to the H-ZSM-5 molecular sieve body is 0.2.

[0082] (4) The liquid-solid mixture obtained in step (3) was stirred, aged at 50° C. for 1 h, filtered, washed with water, dried at 110° C. for 6 h, and calcined at 530° C. for 8 h to obtain a molecular sieve catalyst with a core-shell structure.

[0083] The core-shell molecular sieve catalyst obtained in Example 3 is denoted as H-ZSM-5@MCM-41-3, and the mass ratio of H-ZSM-5 to MCM-41 molecular sieve is 1:0.2. The XRD spectrum of H-ZSM-5@MCM-41-3 is Figure 1 Similarly, there is no obvious change in crystallinity and skeleton structure, and it still has a typical MFI structure; the argon physical adsorption characterization results and the mesopore size distribution results show that the core-shell molecular sieve catalyst obtained by Example 3 has obvious mesoporous structural characteristics; the morphology characterization results show that a layer of uniform MCM-41 mesoporous structure with a thickness of 10nm grows on the surface of the microporous molecular sieve.

[0084] The evaluation method and conditions of the catalyst for the catalytic cracking of butene to produce ethylene and propylene are the same as those in Example 1.

[0085] The evaluation results show that compared with the ZSM-5 molecular sieve body (H-ZSM-5-p), the core-shell molecular sieve catalyst (H-ZSM-5@MCM-41-3) obtained in Example 3 has a certain improvement in the diene yield during the reaction of butene catalytic cracking to produce ethylene and propylene, and the reaction stability has a certain improvement. Table 1 is the specific data of the diene yield and deactivation rate in the reaction of H-ZSM-5@MCM-41-3 molecular sieve catalyzing butene cracking to produce ethylene and propylene. It can be seen from the results that the initial activity of the core-shell molecular sieve catalyst obtained in Example 3 is 39.2%, and after 70 hours of reaction, it can be maintained at 25%, and the deactivation rate is 36.2%.

[0086] [Example 4]

[0087] Preparation of H-ZSM-5@MCM-41 molecular sieve:

[0088] (1) Weigh 3 g of the ZSM-5 molecular sieve powder (H-ZSM-5-p) obtained above and add it to 60 mL of 60% ethanol aqueous solution, stir evenly, and obtain a liquid-solid mixture I; the mass ratio of the molecular sieve body to the mixed solution is 1:20.

[0089] (2) Add 10 g of aqueous ammonia solution (28%) and 3 g of cetyltrimethylammonium bromide (CTAB) organic template to the liquid-solid mixture I obtained in step (1), and mix thoroughly to obtain a liquid-solid mixture II.

[0090] (3) Slowly drop 15.84 g of tetraethyl orthosilicate into the liquid-solid mixture II obtained in step (2), and slowly hydrolyze at 30° C. for 5 h to obtain a modified liquid-solid mixture; the mass ratio of the silicon source, calculated as SiO2, to the H-ZSM-5 molecular sieve body is 1.2.

[0091] (4) The liquid-solid mixture obtained in step (3) was stirred, aged at 50° C. for 2 h, filtered, washed with water, dried at 100° C. for 8 h, and calcined at 550° C. for 5 h to obtain a molecular sieve catalyst with a core-shell structure.

[0092] The core-shell molecular sieve catalyst obtained in Example 4 is denoted as H-ZSM-5@MCM-41-4, and the mass ratio of H-ZSM-5 to MCM-41 molecular sieve is 1:1.2. The XRD spectrum of H-ZSM-5@MCM-41-4 is Figure 1 Similarly, there is no obvious change in crystallinity and skeleton structure, and it still has a typical MFI structure; the argon physical adsorption characterization results and the mesopore size distribution results show that the core-shell molecular sieve catalyst obtained by Example 4 has obvious mesoporous structural characteristics; the morphology characterization results show that a layer of uniform MCM-41 mesoporous structure grows on the surface of the microporous molecular sieve, and its thickness is 60nm.

[0093] Example 4 The evaluation method and conditions for the catalyst used in the catalytic cracking of butene to produce ethylene and propylene are the same as those in Example 1.

[0094] The evaluation results show that compared with the ZSM-5 molecular sieve body (H-ZSM-5-p), the core-shell molecular sieve catalyst (H-ZSM-5@MCM-41-4) obtained in Example 4 has a certain improvement in the diene yield during the reaction of catalytic cracking of butene to produce ethylene and propylene, and the reaction stability has a certain improvement. Table 1 is the specific data of the diene yield and deactivation rate in the reaction of H-ZSM-5@MCM-41-4 molecular sieve catalyzing butene cracking to produce ethylene and propylene. It can be seen from the results that the initial activity of the core-shell molecular sieve catalyst obtained in Example 4 is 41.4%, and after 70 hours of reaction, it can be maintained at 32%, and the deactivation rate is 22.8%.

[0095] [Example 5]

[0096] The molecular sieve was prepared in the same manner as in Example 1.

[0097] Compared with Example 1, the difference is that the amount of core-shell molecular sieve catalyst in the olefin catalytic cracking reaction conditions is reduced to 0.15g, and the reaction space velocity is increased to 60h -1.

[0098] The reaction results of catalytic cracking of butene to produce ethylene and propylene show that compared with the ZSM-5 molecular sieve body (H-ZSM-5-p), under the reaction conditions of Example 5, the amount of core-shell molecular sieve catalyst is reduced, and the raw material space velocity is increased. The diene yield in the reaction process of catalytic cracking of butene to produce ethylene and propylene is still improved to a certain extent, and the reaction stability is improved to a certain extent. Table 1 is the specific data of diene yield and deactivation rate in the reaction of butene cracking to produce ethylene and propylene under the reaction conditions of Example 5. It can be seen from the results that the initial activity of the molecular sieve catalyst under the reaction conditions of Example 5 is 38.5%, and after 70 hours of reaction, it can be maintained at 26%, and the deactivation rate is 32.5%.

[0099] [Example 6]

[0100] The molecular sieve was prepared in the same manner as in Example 1.

[0101] Compared with Example 1, the difference is that the reaction temperature in the olefin catalytic cracking reaction conditions is 520°C.

[0102] The reaction results of catalytic cracking of butene to produce ethylene and propylene show that compared with the ZSM-5 molecular sieve body (H-ZSM-5-p), under the reaction conditions of Example 6, the catalytic reaction temperature is reduced to 520°C, and the diene yield in the reaction process of catalytic cracking of butene to produce ethylene and propylene is still improved to a certain extent, and the reaction stability is improved to a certain extent. Table 1 is the specific data of diene yield and deactivation rate in the reaction of butene cracking to produce ethylene and propylene under the reaction conditions of Example 6. It can be seen from the results that the initial activity of the molecular sieve catalyst under the reaction conditions of Example 6 is 39.3%, and after 70 hours of reaction, it can be maintained at 28.1%, and the deactivation rate is 28.5%.

[0103] [Comparative Example 1]

[0104] (1) 31.25 g of tetraethyl orthosilicate, 10 g of ammonia solution (28%), 70 g of hexadecyltrimethylammonium bromide (CTAB) and 45 g of distilled water were weighed into a polytetrafluoroethylene lined tube to obtain a mixed solution A, which was fully stirred and transferred to a stainless steel crystallization kettle and crystallized at 110° C. for 48 h. The product was washed, centrifuged, dried and calcined to obtain MCM-41 mesoporous material.

[0105] (2) The MCM-41 mesoporous material obtained in step (1) is applied to the catalytic cracking of butene to produce ethylene and propylene. Olefin catalytic cracking reaction conditions: reaction temperature is 550°C, catalyst dosage is 0.3g, reaction space velocity is 30h -1 , the reaction pressure is 0.5 bar. Product C 2-3The yield of olefins is shown in Table 1, and the deactivation rate (after 70 hours of reaction) of the obtained catalyst compared with the corresponding H-ZSM-5 molecular sieve bulk (H-ZSM-5-p) is shown in Table 1. From the results, it can be seen that MCM-41 has no catalytic activity.

[0106] [Comparative Example 2]

[0107] (1) First, weigh 31.25g of tetraethyl orthosilicate, 30g of tetrapropylammonium hydroxide (25%) and 45g of distilled water in a polytetrafluoroethylene lined tube, and stir thoroughly to obtain a mixed solution A; secondly, weigh 10g of distilled water, 0.1405g of aluminum nitrate nonahydrate and 0.6g of sodium hydroxide in another polytetrafluoroethylene lined tube, and stir thoroughly to obtain a mixed solution B; then, add solution B to solution A, stir thoroughly, transfer to a stainless steel crystallization kettle, and crystallize at 170°C for 48h. Finally, the product is washed, centrifuged, dried, calcined and ammonium exchanged to obtain a ZSM-5 molecular sieve body (H-ZSM-5-p, silicon-aluminum atomic ratio of 400).

[0108] (2) 31.25 g of tetraethyl orthosilicate, 10 g of ammonia solution (28%), 70 g of hexadecyltrimethylammonium bromide (CTAB) and 45 g of distilled water were weighed into a polytetrafluoroethylene lined tube to obtain a mixed solution A, which was fully stirred and transferred to a stainless steel crystallization kettle and crystallized at 110° C. for 48 h. The product was washed, centrifuged, dried and calcined to obtain MCM-41 mesoporous material.

[0109] (3) Weigh 3 g of the H-ZSM-5-p molecular sieve prepared in step (1) and 1.8 g of the MCM-41 material prepared in step (2) in a mortar, and grind for 5 minutes to obtain a H-ZSM-5 / MCM-41 physical mixed molecular sieve catalyst; the mass ratio of MCM-41 to H-ZSM-5-p molecular sieve in the physical mixed catalyst is 0.6:1.

[0110] (4) The physically mixed H-ZSM-5 / MCM-41 molecular sieve catalyst obtained in step (3) is applied to the catalytic cracking of butene to produce ethylene and propylene. Olefin catalytic cracking reaction conditions: reaction temperature is 550°C, catalyst dosage is 0.3g, reaction space velocity is 30h -1 , the reaction pressure is 0.5 bar. Product C 2-3The yield of olefins is shown in Table 1, and the deactivation rate of the obtained catalyst compared with the corresponding H-ZSM-5 molecular sieve body (after 70 hours of reaction) is shown in Table 1. It can be seen from the results that the initial diene yield of the molecular sieve body is 38.1%, which drops to 19.8% after 70 hours of reaction, and the deactivation rate is 48%; the initial activity of the core-shell molecular sieve catalyst obtained in Example 1 is 42.3%, which can be maintained at 35.3% after 70 hours of reaction, and the deactivation rate is only 16.5%. The initial activity of the molecular sieve catalyst obtained in this comparative example 2 is 40.2%, which drops to 25.2% after 70 hours of reaction, and the deactivation rate is 37.3%. The deactivation rate is lower than that of the ZSM-5 molecular sieve body, but significantly lower than that of the core-shell molecular sieve catalyst obtained in Example 1.

[0111] [Comparative Example 3]

[0112] Compared with Example 1, the only difference is that in the preparation of H-ZSM-5@MCM-41 molecular sieve, the amount of tetraethyl orthosilicate added is 32 g; the mass ratio of the silicon source, calculated as SiO2, to the H-ZSM-5 body is 2.4:1.

[0113] The core-shell molecular sieve catalyst obtained in Comparative Example 3 is recorded as H-ZSM-5@MCM-41-D3. The reaction results of catalytic cracking of butene to produce ethylene and propylene show that compared with the ZSM-5 molecular sieve body, the catalyst obtained in this Comparative Example 3 (H-ZSM-5@MCM-41-D3) has a significantly reduced diene yield during the reaction of catalytic cracking of butene to produce ethylene and propylene, and the reaction stability is also significantly reduced. This may be due to excessive SiO2 modification, which causes the micropores of the ZSM-5 molecular sieve body to be blocked and the effective active sites to be covered, resulting in a significant decrease in catalytic reaction activity and stability. Table 1 is the specific data of diene yield and deactivation rate in the reaction of H-ZSM-5@MCM-41-D3 molecular sieve catalyzing butene cracking to produce ethylene and propylene. It can be seen from the results that the initial activity of the core-shell molecular sieve catalyst obtained in this Comparative Example 3 is 31.4%, which drops to 6.2% after 70 hours of reaction, and the deactivation rate is 80.3%.

[0114] [Comparative Example 4]

[0115] According to the preparation method of patent CN103861637A, ZSM-5@MCM-41 molecular sieve was synthesized and recorded as ZSM-5@MCM-41-D4.

[0116] The obtained ZSM-5@MCM-41-D4 molecular sieve catalyst was used in the catalytic cracking of butene to produce ethylene and propylene. The reaction conditions of olefin catalytic cracking were: reaction temperature of 550°C, catalyst dosage of 0.3g, reaction space velocity of 30h -1 , the reaction pressure is 0.5 bar. Product C 2-3The yield of olefins is shown in Table 1, and the deactivation rate of the obtained catalyst compared with the corresponding H-ZSM-5 molecular sieve body (after 70 hours of reaction) is shown in Table 1. As can be seen from the results, the initial activity of the core-shell molecular sieve catalyst obtained by this comparative example 4 is 25.2%, which drops to 1.9% after 70 hours of reaction, and the deactivation rate is 92.5%. The reaction results of catalytic cracking of butene to prepare ethylene and propylene show that compared with the ZSM-5 molecular sieve body, the catalyst obtained by this comparative example 4 (H-ZSM-5@MCM-41-D4) has a significant decrease in the diene yield during the reaction of catalytic cracking of butene to prepare ethylene and propylene, and the reaction stability also decreases significantly, which may be due to the low silicon-aluminum ratio of the ZSM-5 molecular sieve, resulting in strong acid and excess acid, aggravating hydrogen transfer, causing the olefin product to enter and be converted into alkanes and species, and the effective active sites are covered, reducing the diene yield, resulting in a significant decrease in catalytic reaction activity and stability.

[0117] [Comparative Example 5]

[0118] Preparation of H-ZSM-5@MCM-41 molecular sieve:

[0119] (1) Weigh 3 g of the ZSM-5 molecular sieve powder (H-ZSM-5-p) obtained above and add it to 60 mL of 60% ethanol aqueous solution, stir evenly, and obtain a liquid-solid mixture I; the mass ratio of the molecular sieve body to the mixed solution is 1:20.

[0120] (2) Add 10 g of aqueous ammonia solution (28%) and 1 g of cetyltrimethylammonium bromide (CTAB) organic template to the liquid-solid mixture I obtained in step (1), and mix thoroughly to obtain a liquid-solid mixture II.

[0121] (3) Slowly drop 7.92 g of tetraethyl orthosilicate into the liquid-solid mixture II obtained in step (2), and slowly hydrolyze at 30° C. for 5 h to obtain a modified liquid-solid mixture; the mass ratio of the silicon source, calculated as SiO2, to the H-ZSM-5 molecular sieve body is 0.6:1.

[0122] (4) The liquid-solid mixture obtained in step (3) was stirred, aged at 30° C. for 2 h, filtered, washed with water, dried at 90° C. for 8 h, and calcined at 550° C. for 5 h to obtain a molecular sieve catalyst with a core-shell structure.

[0123] The core-shell molecular sieve catalyst obtained in Comparative Example 5 is denoted as H-ZSM-5@MCM-41-D5, and the mass ratio of H-ZSM-5 to MCM-41 molecular sieve is 1:0.6. The XRD spectrum of H-ZSM-5@MCM-41-D5 is Figure 1Similarly, there is no obvious change in crystallinity and skeleton structure, and it still has a typical MFI structure; the argon physical adsorption characterization results and the mesopore size distribution results show that the core-shell molecular sieve catalyst obtained by Comparative Example 5 has obvious mesoporous structure characteristics, and the micropore specific surface area is greatly reduced; the morphology characterization results show that a layer of uniform MCM-41 mesoporous structure grows on the surface of the microporous molecular sieve, and its thickness is 14nm.

[0124] The evaluation method and conditions of the catalyst of Comparative Example 5 for the catalytic cracking of butene to produce ethylene and propylene are the same as those of Example 1.

[0125] The reaction results show that compared with the ZSM-5 molecular sieve body (H-ZSM-5-p), the core-shell molecular sieve catalyst (H-ZSM-5@MCM-41-D5) obtained by this comparative example 5 has a significant decrease in the diene yield during the reaction of catalytic cracking of butene to produce ethylene and propylene, and the reaction stability is also reduced. This may be due to the fact that the template agent CTAB that forms the mesoporous MCM-41 structure is relatively small, resulting in a large amount of SiO2 existing in an amorphous structure, blocking the micropores of the ZSM-5-p molecular sieve, resulting in a decrease in the accessibility of the active sites of the molecular sieve catalyst, and the initial activity and reaction stability are significantly reduced. Table 1 is the specific data of the diene yield and deactivation rate in the reaction of H-ZSM-5@MCM-41-D5 molecular sieve catalyzing butene cracking to produce ethylene and propylene. As can be seen from the results, the initial activity of the core-shell molecular sieve catalyst obtained by this comparative example 5 is 30.9%, which is reduced to 5.3% after 70 hours of reaction, and the deactivation rate is 82.8%.

[0126] Table 1 Evaluation results of the catalysts obtained in each example

[0127]

[0128]

[0129] Table 2 Physicochemical properties of the catalysts obtained in each example

[0130]

[0131] The specific implementation modes 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 catalyst for preparing ethylene and propylene by cracking butene, wherein the catalyst is a core-shell H-ZSM-5@MCM-41 molecular sieve, and the thickness of the MCM-41 shell layer is 10 to 60 nm, preferably 20 to 40 nm.

2. The catalyst according to claim 1, characterized in that: In the core-shell H-ZSM-5@MCM-41 molecular sieve, the atomic ratio of silicon to aluminum of the H-ZSM-5 molecular sieve is 100 to 600, preferably 300 to 500; And / or, the mass ratio of H-ZSM-5 to MCM-41 molecular sieve is 1:1.2 to 1:0.2, preferably 1:0.8 to 1:0.

4.

3. The catalyst according to claim 1, characterized in that: The specific surface area of ​​core-shell H-ZSM-5@MCM-41 molecular sieve is 393~650cm 2 ·g -1 , preferably 580-600cm 2 ·g -1 ; And / or, the mesopore volume of the core-shell H-ZSM-5@MCM-41 molecular sieve is 0.280-0.350cm 3 ·g -1 .

4. The method for preparing the catalyst according to any one of claims 1 to 3, comprising the following steps: (1) dispersing H-ZSM-5 molecular sieve into a solvent to obtain a mixture I; (2) adding an alkaline solution and an organic template to the mixture I obtained in step (1) to obtain a mixture II; (3) slowly adding a silicon source to the mixture II obtained in step (2), stirring and hydrolyzing to obtain a modified solid-liquid mixture; (4) The modified solid-liquid mixture obtained in step (3) is aged and calcined to obtain the catalyst.

5. The preparation method according to claim 4, characterized in that: In step (1), the solvent is a mixed solvent consisting of ethanol and deionized water, wherein the volume ratio of ethanol to deionized water is 0.5-1:2-1; And / or, in step (1), the mass ratio of H-ZSM-5 molecular sieve to solvent is 1:10 to 1:50, preferably 1:20 to 1:

30.

6. The preparation method according to claim 4, characterized in that: In step (2), the alkaline solution is a solution of at least one of sodium hydroxide, ammonium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, ammonium carbonate, and ammonia water; preferably, the alkaline solution is a solution of at least one of ammonium carbonate, ammonium hydroxide, and ammonia water; And / or, in step (2), the organic template is one of hexadecyltrimethylammonium bromide, tetrapropylammonium bromide, block copolymer P123, and tetrapropylammonium hydroxide; preferably, the selected organic template is hexadecyltrimethylammonium bromide; And / or, in step (3), the silicon source is one or more of tetraethyl orthosilicate, silica sol, tetramethyl orthosilicate, trimethylchlorosilane, triethylchlorosilane, tripropylchlorosilane; preferably, the silicon source is selected from tetraethyl orthosilicate or silica sol.

7. The preparation method according to claim 4, characterized in that: In step (2), the mass concentration of the alkaline solution is 0.5% to 30%; And / or, in step (2), the mass ratio of the alkaline solution to the organic template is 1:1 to 5:1, preferably 2:1 to 4:1; And / or, in step (3), the mass ratio of the silicon source in terms of SiO2 to H-ZSM-5 is 0.2 to 1.2, preferably 0.8 to 0.

4.

8. The preparation method according to claim 4, characterized in that: In step (3), the stirring hydrolysis conditions are as follows: temperature is 20-50°C, time is 2-10h, preferably, temperature is 25-40°C, time is 4-6h; And / or, in step (4), the aging conditions are as follows: temperature is 20-50°C, time is 0.5-5h, preferably, temperature is 25-40°C, time is 1-3h; And / or, in step (4), the calcination conditions are as follows: temperature of 500-650° C., time of 3-12 h, preferably, temperature of 530-600° C., time of 4-8 h.

9. Use of the catalyst according to any one of claims 1 to 3 in the reaction of butene cracking to produce ethylene and propylene.

10. The use according to claim 9, characterized in that: The reaction temperature is 300-700°C, and the butene volume space velocity is 5-60h -1 , the reaction pressure is 0.1 to 3 bar; preferably, the reaction temperature is 540 to 600°C, and the reaction space velocity is 20 to 35 h -1 , the reaction pressure is 0.3~0.8bar.

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