Butene cracking catalyst for producing ethylene and propylene, and preparation method and application thereof

Abstract

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

Description

Technical Field

[0001] This invention relates to the field of catalysis technology, specifically to a catalyst for the cracking of butene to produce ethylene and propylene, its preparation method, and its application. Background Technology

[0002] Ethylene and propylene, as building blocks of many important chemicals, are widely used in the production of polyethylene, polypropylene, and acrylonitrile, holding significant positions in industries such as packaging, textiles, electronics, and automobiles. Traditionally, the main technology for producing low-carbon olefins involves the catalytic cracking of petroleum products such as naphtha, petroleum gas, and condensate. In recent years, new coal chemical technologies for producing low-carbon olefins have seen unprecedented development, gradually becoming an important technological route for olefin production. However, these processes generate large amounts of carbon dioxide as a byproduct. 4+ Long-chain olefins. Therefore, olefin catalytic cracking (OCC) technology is used to process low-value-added byproduct C... 4+ The conversion of long-chain olefins into ethylene and propylene can not only promote integrated refining and chemical production, but also connect and support coal chemical industry and improve carbon resource utilization.

[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 sieves, olefin cracking technology using H-ZSM-5 as a catalyst has developed rapidly. However, current OCC technology still has some drawbacks, such as rapid catalyst deactivation due to coking, numerous byproducts (approximately 300 types), and difficulty in improving diene (ethylene, propylene) yields. Further improving catalyst activity and diene selectivity is a major challenge for OCC technology.

[0004] Currently, there are three main methods for improving the catalytic cracking performance of olefins:

[0005] (1) Regulation of ZSM-5 molecular sieve catalyst Acidity. This method is now quite mature, through... There is limited room for optimizing the catalytic cracking performance of olefins by adjusting the amount of acid.

[0006] (2) Regulating the effective diffusion distance of H-ZSM-5 molecular sieve. By reducing the grain size of the molecular sieve, creating a hierarchical pore structure, and constructing a molecular sieve morphology with a specific crystal face exposure, the effective diffusion distance of the molecular sieve catalyst can be effectively shortened, the intracrystalline diffusion resistance can be reduced, and the catalytic efficiency can be significantly improved. However, there are a series of technical difficulties in the implementation process. Among them, there are problems in the separation of small particle size molecular sieves in the production process, and the production cost is high. In addition, since the molecular sieve catalyst used in industry is a shaped catalyst, more binders are needed in the shaping process of small particle size molecular sieves, which further increases the cost of industrial application, hindering the industrial application of small particle size molecular sieves. For hierarchical pore molecular sieves, a large amount of expensive template agent is needed in the synthesis process, and a large amount of template agent in the calcination process can easily pollute the environment and is difficult to apply to industrial production. At the same time, the post-processing process can easily damage the framework structure of the molecular sieve, and the controllability is poor. The ZSM-5 molecular sieve with a specific morphology needs to add expensive additive raw materials in the preparation process, which is not conducive to industrial scale production from the aspects of cost and environmental protection.

[0007] (3) Modification of H-ZSM-5 molecular sieve. The common modification methods at present include acid etching method, SiO2 deposition method, element modification method (such as phosphorus, potassium, sodium, etc.) and other strategies. However, this method has poor controllability and repeatability, and can easily damage the framework structure of the molecular sieve.

[0008] Therefore, it is essential to find new methods to improve the performance of butene catalytic cracking to ethylene and propylene for the design of high-performance industrial catalysts. SUMMARY

[0009] In view of the problems of low diene yield and poor reaction stability of conventional microporous ZSM-5 molecular sieve catalysts in olefin catalytic cracking technology, the present application provides a new butene cracking to ethylene and propylene catalyst, its preparation method and application. The catalyst applied in olefin catalytic cracking technology can 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 application provides a butene cracking to ethylene and propylene catalyst, which is a core-shell H-ZSM-5@MCM-41 molecular sieve, and the thickness of the MCM-41 shell layer is 10-60 nm, preferably, the thickness of the shell layer is 20-40 nm.

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

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

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

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

[0015] The second aspect of the present application provides a preparation method of the above-mentioned catalyst, comprising the following steps:

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

[0017] (2) adding a basic solution and an organic template agent 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), and stirring to hydrolyze to obtain a modified solid-liquid mixture;

[0019] (4) aging and calcining the modified solid-liquid mixture obtained in step (3) to obtain the catalyst.

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

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

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

[0023] Further, in step (2), the basic 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 basic solution is a solution of at least one of ammonium carbonate, ammonium hydroxide, and ammonia water. ​​​

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

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

[0026] Further, 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] Further, 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] Further, in step (3), the mass ratio of the silicon source (calculated as SiO2) to H-ZSM-5 is 0.2 to 1.2, preferably 0.6 to 1.2.

[0029] Further, in step (3), the stirring hydrolysis condition is as follows: the temperature is 20 to 50℃, and the time is 2 to 10h; preferably, the temperature is 25 to 40℃, and the time is 4 to 6h.

[0030] Further, in step (4), the aging condition is as follows: the temperature is 20 to 50℃, and the time is 0.5 to 5h; preferably, the temperature is 25 to 40℃, and the time is 1 to 3h.

[0031] Further, in step (4), after aging, the product is subjected to conventional operations such as solid-liquid separation, water washing, and drying. The drying condition is as follows: the temperature is 80 to 150℃, and the time is 4 to 12h; preferably, the temperature is 90 to 110℃, and the time is 5 to 8h.

[0032] Further, in step (4), the calcination condition is as follows: the temperature is 500 to 650℃, and the time is 3 to 12h; preferably, the temperature is 530 to 600℃, and the time is 4 to 8h.

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

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

[0035] Compared with the prior art, the present application has the beneficial effects that:

[0036] 1. The present application provides a new catalyst for preparing ethylene and propylene by butene catalytic cracking, which has a core structure of H-ZSM-5 molecular sieve and a shell structure of MCM-41 molecular sieve. The introduction of the shell structure has no effect on the microporous structure of the H-ZSM-5 molecular sieve core, and the mesopore specific surface area of the catalyst is greatly increased. When applied to an olefin catalytic cracking reaction, a layer of mesoporous structure is created on the outer surface of the microporous active molecular sieve through the construction of the core-shell molecular sieve catalyst, which can effectively enrich the concentration of reactant molecules on the surface of the molecular sieve, increase the efficiency of entering the microporous channel of the active molecular sieve, and improve the accessibility of the active site, thereby effectively improving the catalytic efficiency, increasing the yield of the target product, prolonging the reaction life, and making it possible to efficiently catalyze the preparation of ethylene and propylene from low-value butene, which is convenient for industrial production.

[0037] 2. In the process of olefin catalytic cracking, it is urgent to develop a new H-ZSM-5 molecular sieve catalyst. The present application has found that, through the method of secondary growth and the comprehensive coordination of each step, a core-shell H-ZSM-5@MCM-41 molecular sieve catalyst with a suitable thickness can be obtained, which can greatly improve the catalytic efficiency while maintaining the internal structure of the molecular sieve crystal unchanged, thereby providing a new method for olefin catalytic cracking technology. Moreover, the preparation method of the present application has low cost and has important potential for industrial scale-up production.

[0038] 3. The catalyst of the present application is applied to the reaction of preparing ethylene and propylene by butene catalytic cracking, and the yield of ethylene and propylene is greatly improved, the deactivation rate of the catalyst is reduced, and the reaction stability is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

[0042] Figure 4TEM 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;

[0043] Figure 5 Reaction performance 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 in the reaction of preparing ethylene and propylene by catalytic cracking of olefins. DETAILED DESCRIPTION

[0044] The application will be further described below in conjunction with specific examples. However, the application is not limited to the following examples.

[0045] In the application, XRD and argon physical adsorption are used to determine the crystallinity and pore structure properties of the molecular sieve before and after modification. Among them, XRD characterization is tested on a model 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 ground in a mortar, and scanning is performed at a speed of 1° / min, and the scanning range of 2θ angle is 5°-50°.

[0046] In the application, argon physical adsorption is tested on a model Micromeritics TriStar3000 specific surface area analyzer. Before testing, the sample is treated by vacuumizing at 350℃ for 3h under vacuum state.

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

[0048] The technical solutions of the application will be further described below through specific examples.

[0049] In the application, the deactivation rate = (reaction 10h C 2-3 ＝ Yield-reaction 70h C 2-3 ＝ Yield) / (reaction 10h C 2-3 ＝ Yield) x 100%.

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

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

[0052] The specific steps of the ammonium exchange method are as follows: 2 g of the molecular sieve catalyst was dispersed in 80 mL of a 1 mol / L ammonium chloride solution, stirred at 90°C for 2 h, and after being suction-filtered and washed, the filter cake was dried in an oven at 90°C overnight and calcined at 550°C for 6 h to obtain a hydrogen-type ZSM-5 molecular sieve.

[0053] Example 1

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

[0055] (1) 3 g of the ZSM-5 molecular sieve powder (H-ZSM-5-p) obtained above was weighed into 60 mL of a 60% ethanol aqueous solution, and stirred uniformly to obtain a liquid-solid mixture I; the mass ratio of the molecular sieve bulk to the mixed solution was 1:20.

[0056] (2) 10 g of an aqueous ammonia solution (28%) and 3 g of cetyltrimethylammonium bromide (CTAB) organic template were added to the liquid-solid mixture I obtained in step (1), and after being thoroughly mixed, a liquid-solid mixture II was obtained.

[0057] (3) 7.92 g of tetraethyl orthosilicate was slowly added dropwise to the liquid-solid mixture II obtained in step (2), and after being slowly hydrolyzed at 30°C for 5 h, a modified liquid-solid mixture was obtained; the mass ratio of the silicon source (calculated as SiO2) to the H-ZSM-5 molecular sieve bulk was 0.6.

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

[0059] The core-shell molecular sieve catalyst obtained in Example 1 is denoted 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 above obtained core-shell H-ZSM-5@MCM-41-1 molecular sieve catalyst was applied to the reaction of preparing ethylene and propylene by catalytic cracking of butene. The reaction conditions of butene catalytic cracking were as follows: the reaction temperature was 550 ℃, the catalyst amount was 0.3 g, the butene volume space velocity was 30 h-1, and the reaction pressure was 0.5 bar. -1 The yield of product C 2-3 olefins is shown in Table 1, and the deactivation rate (after 70 h of reaction) of the obtained catalyst compared with the corresponding H-ZSM-5 molecular sieve bulk 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 Table 1. It can be seen from the XRD spectrum of H-ZSM-5@MCM-41-1 that, compared with the ZSM-5 molecular sieve bulk (H-ZSM-5-p), the crystallinity and framework structure of the molecular sieve with core-shell structure obtained in the present embodiment 1 do not change obviously, and the typical MFI topology can still be maintained, indicating that the secondary growth strategy can effectively prevent the destruction of the molecular sieve framework structure in the preparation process, so that the topology of the core-shell H-ZSM-5@MCM-41-1 molecular sieve catalyst obtained in the present embodiment 1 is consistent with the bulk. Figure 1

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

[0064] Figure 3 The mesopore size distribution results 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 bulk, the core-shell structure molecular sieve catalyst obtained in the present embodiment 1 contains rich mesopores, and the pore size is 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 are shown in Table 1. The results show that the morphology characteristics of the core-shell molecular sieve catalyst (H-ZSM-5@MCM-41-1) obtained in the present embodiment 1 are that a layer of uniform MCM-41 mesoporous structure is grown on the surface of the microporous molecular sieve, and the thickness is 30 nm.

[0066] Figure 5 ​The results of the reaction of butene catalytic cracking to ethylene and propylene catalyzed by H-ZSM-5-p and H-ZSM-5@MCM-41-1 molecular sieve are shown in Table 1. The results show that the diene yield in the reaction of butene catalytic cracking to ethylene and propylene catalyzed by the core-shell molecular sieve catalyst (H-ZSM-5@MCM-41-1) obtained in this embodiment is significantly improved, and the reaction stability is better, compared with the ZSM-5 molecular sieve bulk (H-ZSM-5-p). The specific data of diene yield and deactivation rate in the reaction of butene catalytic cracking to ethylene and propylene catalyzed by H-ZSM-5-p and H-ZSM-5@MCM-41-1 molecular sieve are shown in Table 1. It can be seen from the results that the initial diene yield of the molecular sieve bulk (H-ZSM-5-p) is 38.1%, which decreases to 19.8% after 70 hours of reaction, and the deactivation rate is 48%; while the initial activity of the core-shell ZSM-5 molecular sieve catalyst obtained in this embodiment is 42.3%, which can be maintained at 35.3% after 70 hours of reaction, and the deactivation rate is only 16.5%.

[0067] In summary Figures 1 to 5 It can be seen from the results of Table 1 that 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 keeping the framework structure and topological structure intact, and the diene yield and reaction stability are greatly improved when it is used in the reaction of butene catalytic cracking to ethylene and propylene.

[0068]

Embodiment 2

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

[0070] (1) 3 g of the ZSM-5 molecular sieve powder (H-ZSM-5-p) obtained above was weighed into 60 mL of 60% ethanol aqueous solution, and stirred to obtain a liquid-solid mixture I; the mass ratio of the molecular sieve bulk to the mixed solution was 1:20.

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

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

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

[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 similar to that of H-ZSM-5@MCM-41-1, and the crystallinity and framework structure do not change significantly, and still have typical MFI structure; the argon physical adsorption characterization results and mesopore size distribution results show that the core-shell molecular sieve catalyst obtained in Example 2 has obvious mesoporous structure characteristics; the morphology characterization results show that a layer of uniform MCM-41 mesoporous structure is grown on the surface of the microporous molecular sieve, and the thickness is 25nm. Figure 1

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

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

[0077]

Example 3

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

[0079] (1) 3g of the ZSM-5 molecular sieve powder (H-ZSM-5-p) obtained above was weighed into 60mL of 60% ethanol aqueous solution, and stirred uniformly to obtain a liquid-solid mixture I; the mass ratio of the molecular sieve bulk to the mixed solution is 1:20.

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

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

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

[0083] The core-shell molecular sieve catalyst obtained in Example 3 is designated H-ZSM-5@MCM-41-3, with a mass ratio of H-ZSM-5 to MCM-41 molecular sieves of 1:0.2. The XRD pattern of H-ZSM-5@MCM-41-3 is shown in the figure. Figure 1 Similarly, the crystallinity and framework structure did not change significantly, and it still had a typical MFI structure; the results of argon physical adsorption characterization and mesopore size distribution showed that the core-shell molecular sieve catalyst obtained in Example 3 had obvious mesoporous structure characteristics; the morphology characterization results showed that a uniform MCM-41 mesoporous structure with a thickness of 10 nm was grown on the surface of the microporous molecular sieve.

[0084] The evaluation methods and conditions for the catalyst used in the catalytic cracking of butene to produce ethylene and propylene in Example 3 are the same as those in Example 1.

[0085] Evaluation results show that, compared with the ZSM-5 molecular sieve bulk (H-ZSM-5-p), the core-shell molecular sieve catalyst (H-ZSM-5@MCM-41-3) obtained in Example 3 exhibits improved diene yield and reaction stability during the catalytic cracking of butene to ethylene and propylene. Table 1 shows the specific data on diene yield and deactivation rate during the catalytic cracking of butene to ethylene and propylene using H-ZSM-5@MCM-41-3 molecular sieve. The results indicate that the core-shell molecular sieve catalyst obtained in Example 3 has an initial activity of 39.2%, which remains at 25% after 70 hours of reaction, with a deactivation rate of 36.2%.

[0086]

Example 4

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

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

[0089] (2) To the liquid-solid mixture I obtained in step (1), 10 g of ammonia water solution (28%) and 3 g of cetyltrimethylammonium bromide (CTAB) organic template were added, and after being mixed thoroughly, liquid-solid mixture II was obtained.

[0090] (3) To the liquid-solid mixture II obtained in step (2), 15.84 g of tetraethyl orthosilicate was slowly added dropwise, and after being slowly hydrolyzed at 30°C for 5 h, a modified liquid-solid mixture was obtained; the mass ratio of the silicon source (calculated as SiO2) to the H-ZSM-5 molecular sieve body was 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 similar to that of H-ZSM-5, and the crystallinity and framework structure do not change significantly, and still have a typical MFI structure; the argon physical adsorption characterization results and the mesopore pore size distribution results show that the core-shell molecular sieve catalyst obtained in Example 4 has obvious mesopore structure characteristics; the morphology characterization results show that a layer of uniform MCM-41 mesopore structure is grown on the surface of the microporous molecular sieve, and the thickness is 60 nm. Figure 1

[0093] The evaluation method and conditions of the catalyst of Example 4 for the reaction of catalytic cracking of butene to ethylene and propylene are the same as those of 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 this example has a certain improvement in the yield of dienes in the reaction of catalytic cracking of butene to ethylene and propylene, and has a certain improvement in reaction stability. Table 1 is the specific data of the yield of dienes and the deactivation rate in the reaction of catalytic cracking of butene to ethylene and propylene over the H-ZSM-5@MCM-41-4 molecular sieve. It can be known from the results that the initial activity of the core-shell molecular sieve catalyst obtained in this example is 41.4%, and after 70 h 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 lies in that the amount of the core-shell molecular sieve catalyst in the olefin catalytic cracking reaction conditions is reduced to 0.15 g, and the reaction space velocity is increased to 60 h -1 ​.

[0098] The results of the butene catalytic cracking reaction to produce ethylene and propylene show that, compared with the ZSM-5 molecular sieve bulk (H-ZSM-5-p), under the reaction conditions of Example 5, the yield of dienes in the reaction of butene catalytic cracking to produce ethylene and propylene still has a certain increase, and the reaction stability has a certain increase. Table 1 is the specific data of the yield of dienes and the deactivation rate in the reaction of butene cracking to produce ethylene and propylene under the reaction conditions of Example 5. It can be known from the results that the initial activity of the molecular sieve catalyst under the reaction conditions of Example 5 is 38.5%, which can be maintained at 26% after 70 hours of reaction, and the deactivation rate is 32.5%.

[0099]

Example 6

[0100] The molecular sieve was prepared according to 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 results of the butene catalytic cracking reaction to produce ethylene and propylene show that, compared with the ZSM-5 molecular sieve bulk (H-ZSM-5-p), under the reaction conditions of Example 6, the yield of dienes in the reaction of butene catalytic cracking to produce ethylene and propylene still has a certain increase, and the reaction stability has a certain increase. Table 1 is the specific data of the yield of dienes and the deactivation rate in the reaction of butene cracking to produce ethylene and propylene under the reaction conditions of Example 6. It can be known from the results that the initial activity of the molecular sieve catalyst under the reaction conditions of Example 6 is 39.3%, which can be maintained at 28.1% after 70 hours of reaction, and the deactivation rate is 28.5%.

[0103]

Comparative Example 1

[0104] (1) 31.25 g of tetraethyl orthosilicate, 10 g of ammonia water solution (28%), 70 g of cetyltrimethylammonium bromide (CTAB), and 45 g of distilled water were weighed in a polytetrafluoroethylene lined tube to obtain a mixed solution A, which was transferred to a stainless steel crystallization kettle after being stirred thoroughly, 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) was applied in the reaction of butene catalytic cracking to produce ethylene and propylene. The olefin catalytic cracking reaction conditions were as follows: the reaction temperature was 550°C, the catalyst dosage was 0.3 g, the reaction space velocity was 30 h -1 , and the reaction pressure was 0.5 bar. The product C 2-3The yield of olefins is shown in Table 1, and the deactivation rate (after 70h of reaction) of the catalyst obtained compared with the corresponding H-ZSM-5 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, 31.25g of tetraethyl orthosilicate, 30g of tetrapropylammonium hydroxide (25%) and 45g of distilled water were weighed into a polytetrafluoroethylene-lined tube, and after being thoroughly stirred, a mixed solution A was obtained; second, 10g of distilled water, 0.1405g of aluminum nitrate nonahydrate and 0.6g of sodium hydroxide were weighed into another polytetrafluoroethylene-lined tube, and after being thoroughly stirred, a mixed solution B was obtained; then, the B solution was added to the A solution, which was thoroughly stirred and then transferred to a stainless steel crystallization kettle, and crystallization was carried out at 170°C for 48h. Finally, the product was washed, centrifuged, dried, calcined and ammonium-exchanged to obtain a ZSM-5 bulk (H-ZSM-5-p, Si / Al atomic ratio of 400).

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

[0109] (3) 3g of the H-ZSM-5-p molecular sieve in step (1) and 1.8g of the MCM-41 material in step (2) were weighed into a mortar and ground for 5 minutes to obtain a H-ZSM-5 / MCM-41 physically mixed molecular sieve catalyst; the mass ratio of MCM-41 to H-ZSM-5-p molecular sieve in the physically mixed catalyst was 0.6:1.

[0110] (4) The physically mixed H-ZSM-5 / MCM-41 molecular sieve catalyst obtained in step (3) was used in a reaction for preparing ethylene and propylene by catalytic cracking of butene. The catalytic cracking reaction conditions for olefins were as follows: reaction temperature was 550°C, catalyst dosage was 0.3g, reaction space velocity was 30h -1 , and reaction pressure was 0.5bar. The products C 2-3The olefin yield 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 bulk molecular sieve is shown in Table 1. According to the results, the initial diene yield of the molecular sieve bulk is 38.1%, which decreases 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 from 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 from the present Comparative Example 2 is 40.2%, which decreases 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 bulk molecular sieve, but is significantly lower than that of the core-shell molecular sieve catalyst obtained from Example 1.

[0111]

Comparative Example 3

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

[0113] The core-shell molecular sieve catalyst obtained from Comparative Example 3 is denoted as H-ZSM-5@MCM-41-D3. The results of the reaction of butene catalytic cracking to prepare ethylene and propylene show that, compared with the ZSM-5 bulk molecular sieve, the diene yield of the catalyst (H-ZSM-5@MCM-41-D3) obtained from the present Comparative Example 3 in the reaction of butene catalytic cracking to prepare ethylene and propylene decreases significantly, and the reaction stability also decreases significantly, which is probably due to the fact that the excess SiO2 modification causes the micropore channels of the ZSM-5 bulk molecular sieve to be blocked, and the effective active sites are covered, resulting in a significant decrease in the catalytic reaction activity and stability. Table 1 shows the specific data of the diene yield and the deactivation rate of the H-ZSM-5@MCM-41-D3 molecular sieve in the reaction of butene catalytic cracking to prepare ethylene and propylene. According to the results, the initial activity of the core-shell molecular sieve catalyst obtained from the present Comparative Example 3 is 31.4%, which decreases 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 is synthesized, which is denoted as ZSM-5@MCM-41-D4.

[0116] The obtained ZSM-5@MCM-41-D4 molecular sieve catalyst is applied to the reaction of butene catalytic cracking to prepare ethylene and propylene. The olefin catalytic cracking reaction conditions are as follows: the reaction temperature is 550℃, the catalyst amount is 0.3 g, the reaction space velocity is 30 h -1 , and the reaction pressure is 0.5 bar. The product C 2-3The yield of olefins is shown in Table 1, and the deactivation rate of the obtained catalyst (after 70 h of reaction) compared with the corresponding H-ZSM-5 bulk is shown in Table 1. According to the results, the initial activity of the core-shell molecular sieve catalyst obtained from Comparative Example 4 is 25.2%, and after 70 h of reaction, it decreases to 1.9%, with a deactivation rate of 92.5%. The results of the reaction of butene catalytic cracking to produce ethylene and propylene show that, compared with the ZSM-5 bulk, the catalyst (H-ZSM-5@MCM-41-D4) obtained from Comparative Example 4 has a significant decrease in the yield of diolefins and a significant decrease in reaction stability in the reaction of butene catalytic cracking to produce ethylene and propylene. This is probably because the silicon-aluminum ratio of the ZSM-5 molecular sieve is too low, resulting in excessive acid strength and acid amount, which exacerbates hydrogen transfer, causing the olefin products to be converted into alkanes and species, the effective active sites are covered, the yield of diolefins is reduced, and the catalytic reaction activity and stability are significantly decreased.

[0117]

Comparative Example 5

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

[0119] (1) 3 g of the ZSM-5 molecular sieve powder (H-ZSM-5-p) obtained above was added to 60 mL of 60% ethanol aqueous solution, and stirred to obtain a liquid-solid mixture I; the mass ratio of the molecular sieve bulk to the mixed solution was 1:20.

[0120] (2) 10 g of an aqueous ammonia solution (28%) and 1 g of cetyltrimethylammonium bromide (CTAB) organic template were added to the liquid-solid mixture I obtained in step (1), and after being fully mixed, a liquid-solid mixture II was obtained.

[0121] (3) 7.92 g of tetraethyl orthosilicate was slowly added dropwise to the liquid-solid mixture II obtained in step (2), and after slow hydrolysis at 30°C for 5 h, a modified liquid-solid mixture was obtained; the mass ratio of the silicon source (calculated as SiO2) to the H-ZSM-5 molecular sieve bulk was 0.6:1.

[0122] (4) The liquid-solid mixture obtained in step (3) was stirred, aged at 30°C for 2 h, suction 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 and the XRD spectrum of H-ZSM-5@MCM-41-D4 are shown in FIG. 1. Figure 1Similarly, the crystallinity and framework structure do not change obviously, and still have typical MFI structure; the argon physical adsorption characterization results and mesopore pore size distribution results show that the core-shell molecular sieve catalyst obtained from Comparative Example 5 has obvious mesoporous structure characteristics, and the micropore specific surface area decreases significantly; the morphology characterization results show that a layer of uniform MCM-41 mesoporous structure is grown on the surface of the microporous molecular sieve, and the thickness is 14 nm.

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

[0125] The reaction results show that, compared with the ZSM-5 molecular sieve bulk (H-ZSM-5-p), the core-shell molecular sieve catalyst (H-ZSM-5@MCM-41-D5) obtained from the present comparative example 5 has a significant decrease in the diene yield in the reaction of catalytic cracking of butene to ethylene and propylene, and the reaction stability is also reduced, which may be due to the insufficient template agent CTAB for forming mesoporous MCM-41 structure, resulting in a large amount of SiO2 existing in amorphous structure, blocking the micropores of the ZSM-5-p molecular sieve, and reducing the accessibility of the active sites of the molecular sieve catalyst, and the initial activity and reaction stability are significantly reduced. Table 1 shows the specific data of the diene yield and deactivation rate of the H-ZSM-5@MCM-41-D5 molecular sieve catalyst in the reaction of catalytic cracking of butene to ethylene and propylene. According to the results, the initial activity of the core-shell molecular sieve catalyst obtained from the present comparative example 5 is 30.9%, and after 70 hours of reaction, it is reduced to 5.3%, and the deactivation rate is 82.8%.

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

[0127]

[0128]

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

[0130]

[0131] The above detailed description of the specific embodiments of the present application, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application, and are within the protection scope of the present application.

Claims

1. A butene cracking catalyst for preparing ethylene and propylene, the catalyst being a core-shell H-ZSM-5@MCM-41 molecular sieve, the thickness of the MCM-41 shell layer being 10-60 nm;in the core-shell H-ZSM-5@MCM-41 molecular sieve, the silicon-aluminum atomic ratio of the H-ZSM-5 molecular sieve being 100-600;the mass ratio of the H-ZSM-5 molecular sieve to the MCM-41 molecular sieve being 1:1.2-1:0.2;the specific surface area of the core-shell H-ZSM-5@MCM-41 molecular sieve being 547-650 cm 2 ·g -1 ;the mesopore volume of the core-shell H-ZSM-5@MCM-41 molecular sieve being 0.280-0.350 cm 3 ·g -1 .

2. The catalyst of claim 1, wherein: The shell thickness of the MCM-41 is 20-40 nm.

3. The catalyst of claim 1, wherein: In the core-shell H-ZSM-5@MCM-41 molecular sieve, the silicon-aluminum atomic ratio of the H-ZSM-5 molecular sieve is 300-500; and the mass ratio of the H-ZSM-5 to the MCM-41 molecular sieve is 1:0.8-1:0.

4.

4. The catalyst of claim 1, wherein: The specific surface area of the core-shell H-ZSM-5@MCM-41 molecular sieve is 580-600 cm 2 ·g -1 .

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

6. The method of claim 5, wherein: In step (1), the solvent is a mixed solvent composed of ethanol and deionized water, wherein the volume ratio of ethanol to deionized water is 0.5-1:2-1; and in step (1), the mass ratio of the H-ZSM-5 molecular sieve to the solvent is 1:10-1:

50.

7. The method of claim 6, wherein: In step (1), the mass ratio of the H-ZSM-5 molecular sieve to the solvent is 1:20-1:

30.

8. The method of claim 5, wherein: 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; In step (2), the organic template agent is one of cetyltrimethylammonium bromide, tetrapropylammonium bromide, block copolymer P123 and tetrapropylammonium hydroxide; In step (3), the silicon source is one or more of tetraethyl orthosilicate, silica sol, tetramethyl orthosilicate, trimethylchlorosilane, triethylchlorosilane and tripropylchlorosilane.

9. The method of claim 8, wherein: In step (2), the alkaline solution is a solution of at least one of ammonium carbonate, ammonium hydroxide and ammonia water; In step (2), the selected organic template agent is cetyltrimethylammonium bromide; In step (3), the silicon source is selected from tetraethyl orthosilicate or silica sol.

10. The method of claim 5, wherein: In step (2), the mass concentration of the alkaline solution is 0.5%-30%; In step (2), the mass ratio of the alkaline solution to the organic template agent is 1:1-5:1; In step (3), the mass ratio of the silicon source (calculated as SiO2) to H-ZSM-5 is 0.2-1.

2.

11. The method of claim 10, wherein: In step (2), the mass ratio of the alkaline solution to the organic template agent is 2:1-4:1; In step (3), the mass ratio of the silicon source (calculated as SiO2) to H-ZSM-5 is 0.8-0.

4.

12. The method of claim 5, wherein: In step (3), the stirring hydrolysis conditions are as follows: the temperature is 20-50 ℃, and the time is 2-10 h; In step (4), the aging conditions are as follows: the temperature is 20-50 ℃, and the time is 0.5-5 h; In step (4), the calcining conditions are as follows: the temperature is 500-650 ℃, and the time is 3-12 h.

13. The method of claim 12, wherein: In step (3), the stirring hydrolysis conditions are as follows: the temperature is 25-40 ℃, and the time is 4-6 h; In step (4), the aging conditions are as follows: the temperature is 25-40 ℃, and the time is 1-3 h; In step (4), the calcination conditions are as follows: the temperature is 530-600 ℃, and the time is 4-8 h.

14. Use of the catalyst of any one of claims 1-4 in a reaction of butene cracking to produce ethylene and propylene.

15. The use according to claim 14, characterized in that: The reaction temperature is 300-700 ℃, the volume space velocity of butene is 5-60 h -1 , and the reaction pressure is 0.1-3 bar.

16. The use according to claim 15, characterized in that: The reaction temperature is 540-600 ℃, the reaction space velocity is 20-35 h -1 , and the reaction pressure is 0.3-0.8 bar.

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