An encapsulated composite catalyst and its application in oxidative cracking of naphtha to produce light olefins

Abstract

The present invention provides an encapsulated composite catalyst, and the composition of the encapsulated composite catalyst is: oxide oxygen carrier@molecular sieve, wherein the oxide oxygen carrier is selected from any one of CaMnO3, CaMn 0.8 Cu 0.2 O3, MgMn2O4, NiMn2O4, and the molecular sieve is selected from any one of ZSM-5 molecular sieve, Silicate-1 molecular sieve, and Beta molecular sieve. This catalyst overcomes the problems in the preparation of traditional metal molecular sieves, such as easy aggregation of metal ions, blockage of pore structures, and weak interaction between metal and molecular sieve; effectively inhibits the disadvantages of easy sintering and agglomeration of metal oxide oxygen carriers under high-temperature reaction conditions. The present invention also provides the application of the encapsulated composite catalyst in the oxidative cracking of naphtha to produce light olefins, realizing the transformation of the cracking reaction from highly endothermic to self-heating, greatly reducing process consumption, with high conversion rate and high mass selectivity of light olefins.

Description

Technical Field

[0001] The present invention relates to the field of oxidative cracking of naphtha to produce light olefins, and particularly relates to an encapsulated composite catalyst and its application in the oxidative cracking of naphtha to produce light olefins. Background Art

[0002] Light olefins (C2 = ~ C4 = ), such as ethylene, propylene, 1,3-butadiene, etc., as bulk products of the modern chemical industry, are widely used in fields such as plastics, rubber, medicine, and fine chemicals. Currently, the most common methods for producing ethylene and propylene are steam thermal cracking and catalytic cracking of hydrocarbon raw materials (mainly naphtha).

[0003] For example: CN101190865A discloses a method for catalytic oxidative cracking of naphtha to produce ethylene and propylene. In this invention, naphtha containing C4~C 10 hydrocarbons is used as the raw material. After the raw material hydrocarbon is vaporized, it is mixed with a gas containing oxygen. At a reaction temperature of 580~750°C, a reaction pressure of 0.05~0.5 MPa in gauge pressure, a weight hourly space velocity of 0.5~1.5 h -1 , a water / naphtha weight ratio of 0~5:1, and a naphtha / O2 molar ratio in the raw material mixture of 0.3~5.0:1, the raw material mixture reacts with the catalyst to produce ethylene and propylene. The catalyst used is selected from at least one of ZSM-5 / mordenite symbiotic molecular sieve or ZSM-5 / β zeolite symbiotic molecular sieve.

[0004] Steam thermal cracking of naphtha has disadvantages such as large equipment investment, high reaction temperature, harsh process conditions, high requirements for the reaction furnace tube material, large losses, and low production capacity. Catalytic cracking has problems that the co-feeding of oxygen makes the cracking reaction difficult to control, and various side reactions such as over-cracking, oxidative dehydrogenation, and deep oxidation are likely to occur; during the catalytic cracking reaction process, CO X emissions are excessive; the reaction energy consumption is large, and the oxygen production process requires a high-energy-consuming air separation device (about 1 / 3 of the energy consumption of the entire dehydrogenation process); the mixing of petroleum hydrocarbons and O2 for feeding has great potential safety hazards during the reaction process, and it is difficult for industrial applications; the distribution of the cracking reaction products is not easy to flexibly adjust and other technical problems.

[0005] In the industrial production of traditional naphtha catalytic cracking, zeolite molecular sieves are often used, such as ZSM-5 molecular sieve, Y-type molecular sieve, Beta molecular sieve, SAPO molecular sieve, etc. However, during the catalytic cracking process, the molecular sieve catalyst is easily deactivated due to reasons such as carbon deposition and poisoning, reducing the catalytic efficiency. Although the molecular sieve catalyst can be regenerated by air / oxygen and partially compensate for the reaction heat, the reaction process is still highly endothermic. In addition, the regeneration process is complex and costly, which further increases the production cost and difficulty. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a encapsulated composite catalyst and its application in the oxidative cracking of naphtha to produce light olefins.

[0007] The technical solution of the present invention is as follows:

[0008] An encapsulated composite catalyst, the composition of the encapsulated composite catalyst is: oxide oxygen carrier @ molecular sieve, wherein the oxide oxygen carrier is selected from any one of CaMnO3, CaMn 0.8 Cu 0.2 O3, MgMn2O4, NiMn2O4, Fe2O3, Mn2O3, Co3O4, and the molecular sieve is selected from any one of ZSM-5 molecular sieve, Silicate-1 molecular sieve and Beta molecular sieve.

[0009] Preferably, the preparation method of the encapsulated composite catalyst includes: using the sol-gel method to prepare CaMnO3, CaMn 0.8 Cu 0.2 O3 perovskite metal oxide oxygen carrier or MgMn2O4, NiMn2O4 spinel oxide oxygen carrier, or using the precipitation method to prepare Fe2O3, Mn2O3, Co3O4 single-component metal oxide oxygen carrier, and then using the hydrothermal seed induction method to prepare the encapsulated composite catalyst.

[0010] Preferably, the steps of preparing the encapsulated composite catalyst by the hydrothermal seed induction method include: adding 1 - 3 g of seed molecular sieve to the mixed solution of silicon source, template agent and 20 - 30 mL of deionized water to form a mixed aqueous solution, and stirring at 20 - 30 °C for 2 - 3 h; then adding 0.5 - 1.5 g of oxide oxygen carrier and 0.03 - 0.05 mol of surfactant to 20 - 30 mL of deionized water, and stirring at room temperature for 1 - 3 h to obtain an oxide oxygen carrier mixed suspension; mixing the mixed aqueous solution with the oxide oxygen carrier mixed suspension to form a mixed system, stirring the mixed system at 80 - 90 °C for 2 - 5 h to obtain a precursor mixed suspension, after the precursor mixed suspension is kept warm and aged for 24 - 48 h, the precursor mixed suspension is hydrothermally treated at 170 - 180 °C for 1 - 3 h; the precursor mixed suspension is centrifuged and washed with deionized water 2 - 4 times to obtain a solid product, the solid product is dried in an oven at 100 °C - 120 °C for 8 - 12 h and then calcined in a muffle furnace at 500 - 600 °C for 8 - 12 h, and after cooling to room temperature and grinding into a powdery solid smaller than 10 mesh, the encapsulated composite catalyst is prepared.

[0011] More preferably, the seed molecules are selected from any one of ZSM-5 zeolite, Silicate-1 zeolite, and Beta zeolite.

[0012] More preferably, the molar ratio of the silicon source to the template agent is 0.5 - 1.0 : 0.15 - 0.25.

[0013] More preferably, the silicon source is selected from any one of methyl orthosilicate, ethyl orthosilicate, silica sol, polyethoxydisiloxane, methyltrimethoxysilane, and methyltriethoxysilane.

[0014] More preferably, the template agent is selected from any one of tetrapropylammonium hydroxide, cetyltrimethylammonium bromide, triethylamine, and cyclohexylamine.

[0015] More preferably, the surfactant is selected from polyvinylpyrrolidone.

[0016] More preferably, the mass ratio of the seed zeolite to the metal oxide oxygen carrier is 2 - 3:1.

[0017] Preferably, the sol-gel method includes: According to the molecular formulas of the perovskite and spinel oxygen carriers to be prepared, CaMnO3, CaMn 0.8 Cu 0.2 O3,, MgMn2O4, NiMn2O4, confirm the metal cation composition, and weigh the nitrates containing the corresponding cations and dissolve them in deionized water to form a nitrate solution. Then, add citric acid and ethylene glycol to the nitrate solution to form a mixed system. Finally, heat and stir the mixed system at 70 °C - 90 °C until a sol is formed. The sol is dried at 80 °C - 100 °C, calcined at 350 °C - 500 °C for 1 h - 3 h, and calcined at 850 °C - 1000 °C for 6 - 9 h, cooled to room temperature and ground into powder to obtain oxide oxygen carriers doped with different metals.

[0018] Preferably, citric acid with a molar ratio of 1.5 - 3:1 to the metal cations is added, and ethylene glycol with a molar ratio of 1 - 2.5:1 to citric acid is added.

[0019] Preferably, the precipitation method includes: Weigh the nitrates corresponding to the cations of the single-component metal oxide oxygen carrier and dissolve them in deionized water, where the molar concentration of the metal cations is 0.1 - 0.2 mol / L to obtain a metal precursor solution; then accurately weigh sodium carbonate and dissolve it in deionized water, where CO3 2-The molar concentration is 0.3 - 0.4 mol / L. Under stirring, the sodium carbonate solution is added dropwise to the metal precursor solution until the pH value of the mixed solution is 10 - 11. The mixed solution is continuously stirred at 90 °C - 100 °C for 20 - 24 h, then centrifuged and washed until neutral. The obtained solid product is dried overnight at 70 °C - 90 °C, and then calcined in a muffle furnace at 550 °C - 700 °C for 5 h - 7 h to prepare a single-component metal oxide oxygen carrier.

[0020] The room temperature is generally 20 °C - 30 °C, and the overnight is generally 10 - 20 hours.

[0021] The present invention also provides a new method for oxidative cracking of naphtha to produce light olefins. The naphtha raw material is contacted with the catalyst, and the oxidative cracking reaction of the catalyst is carried out under the conditions of 500 - 800 °C, an air flow rate of 25 - 200 mL / min, a naphtha feed rate of 0.1 - 0.5 g, and a reaction time of 300 - 420 s for each redox cycle. The reaction stream is separated to obtain the target product light olefins.

[0022] The catalyst is any one of the above-mentioned encapsulated composite catalysts;

[0023] Or, the catalyst is selected from any one of CaMnO3, CaMn 0.8 Cu 0.2 O3, MgMn2O4, NiMn2O4, Fe2O3, Mn2O3, Co3O4.

[0024] Preferably, after the cracking reaction, the encapsulated composite catalyst is oxidized and regenerated by an air flow of 80 - 200 mL / min.

[0025] The following further explains and illustrates the present invention.

[0026] The naphtha chemical looping oxidative cracking process of the present invention is based on the chemical looping combustion technology. By constructing an encapsulated composite catalyst with the ability to carry oxygen and oxidative cracking, the high-efficiency oxidative cracking of naphtha to produce light olefins is realized under the condition of no gaseous oxygen. This process includes the steps of oxidative cracking and oxygen carrier regeneration. In the oxidative cracking reaction, naphtha cracks on the active component to form light olefins. At the same time, the lattice oxygen in the metal oxide oxygen carrier in-situ oxidizes part of the generated hydrogen into water vapor, promoting the cracking reaction equilibrium to move in the positive direction and improving the conversion of the substrate. After the reaction, the oxygen carrier that has lost lattice oxygen can be oxidized and regenerated in the air, replenishing the lattice oxygen and removing carbon deposition at the same time, and restoring the catalytic activity of the catalyst.

[0027] Compared with the traditional industrial naphtha cracking technology, the chemical-looping oxidative cracking technology decomposes the cracking reaction into two gas-solid reactions (oxidation reaction and reduction reaction) with the help of the lattice oxygen of the oxygen carrier, eliminating both the resource- and energy-intensive air separation process and the direct contact between naphtha and air, removing potential safety hazards, enabling the reaction to proceed at a relatively high partial pressure of petroleum hydrocarbons, and further improving the reaction conversion rate. At the same time, a large amount of heat is released during the oxidation regeneration process of the lattice oxygen consumed by the oxygen carrier in the air to supply the cracking reaction, realizing the self-heating operation of the cracking process and significantly reducing the process energy consumption.

[0028] In the traditional naphtha catalytic oxidative cracking technology, the intracrystalline diffusion limitation of the micropores of zeolite molecular sieves inhibits the diffusion of reactant and product molecules, resulting in the easy deactivation of the acidic centers of zeolite molecular sieves due to carbon deposition. Although zeolite molecular sieves can form a hierarchical structure through desilication or dealumination post-treatment methods to improve the mass transfer process of the cracking reaction, the post-treatment process is difficult to control and the enlarged pore structure is easily damaged during the reaction process, severely limiting its further industrial application. In addition, the lattice oxygen of metal oxide oxygen carriers is thermodynamically stable at low temperatures, and high-temperature conditions (>750 °C) are usually required for their application in naphtha oxidative cracking reactions. At high temperatures, metal oxide oxygen carriers are prone to sintering and agglomeration, resulting in coking and a decrease in catalytic performance.

[0029] Based on this, the present invention designs and constructs a series of encapsulated composite catalysts (oxide oxygen carrier@molecular sieve), encapsulating metal oxide oxygen carrier nanoparticles inside the molecular sieve and applying them to the chemical-looping oxidative cracking reaction of naphtha to produce light olefins. Among them, the types of metal oxide oxygen carriers include: perovskite type, spinel type, and single-component metal oxides, where the metal composition is transition metal and / or rare earth metal, and the metal oxide oxygen carriers are synthesized by sol-gel method or precipitation method. Using several molecular sieves as seeds and the hydrothermal seeding induction method, the metal oxide oxygen carriers are encapsulated inside the molecular sieve without changing the topological structure of the molecular sieve. The core-shell structure of the encapsulated composite catalyst can effectively inhibit the sintering and agglomeration of metal oxide nanoparticles. In addition, the lattice oxygen of the metal oxide oxygen carrier promotes the forward movement of the cracking reaction through selective hydrogen combustion reaction, improving the cracking reaction activity; at the same time, the coking of the molecular sieve can be inhibited through the oxidation reaction to improve its coke resistance. This effectively combines the cracking reaction performance and recyclability of the composite catalyst.

[0030] The calculation methods for the yield and selectivity in the examples of the present invention are as follows:

[0031] FU Li97Plus and Techcomp 7900 gas chromatographs are used to analyze the components of the gas products (light olefins, alkanes, aromatics, CO X, carbon deposition), and their contents are determined by the external standard method. The conversion rate of naphtha and the selectivity of the product are calculated based on mass, and the specific formulas are as follows:

[0032]

[0033]

[0034] The target product is light olefins, and our goal is to have a high conversion rate and a high selectivity for light olefins.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1. The encapsulated composite catalyst (oxide oxygen carrier @ molecular sieve) of the present invention overcomes the problems such as easy aggregation of metal ions, blockage of pore structures, and weak interaction between metal and molecular sieve during the preparation of traditional metal molecular sieves; at the same time, it effectively inhibits the disadvantage of easy sintering and agglomeration of metal oxide oxygen carriers under high-temperature reaction conditions.

[0037] 2. The rich and appropriately strong acidic centers of zeolite molecular sieves in the encapsulated composite catalyst of the present invention can effectively reduce the activation energy of hydrocarbon C-H bond cleavage in naphtha substrates, effectively reducing the naphtha cracking reaction temperature; during the chemical looping oxidative cracking of naphtha, the SHC reaction between the lattice oxygen of the oxygen carrier and the by-product hydrogen in the cracking reaction shifts the reaction equilibrium to the positive direction, promoting the conversion of the substrate.

[0038] 3. The oxidation reaction of the lattice oxygen of the metal oxide oxygen carrier in the encapsulated composite catalyst of the present invention effectively inhibits the defect of carbon deposition deactivation of zeolite molecular sieves due to micropore internal diffusion limitations, greatly improving the coke resistance of the encapsulated composite catalyst.

[0039] 4. The present invention applies the encapsulated composite catalyst to the oxidative cracking of naphtha to produce light olefins. By using the role of the lattice oxygen of the oxygen carrier, the cracking reaction is decomposed into two gas-solid reactions (oxidation reaction and reduction reaction), removing the energy- and capital-intensive air separation oxygen production process in the traditional naphtha oxidative cracking technology, and avoiding the direct contact process between naphtha hydrocarbon substances and gaseous oxygen in the traditional oxidative cracking process, eliminating potential safety hazards. At the same time, both the selective hydrogen combustion reaction of lattice oxygen in the reduction reaction step and the re-oxidation of the oxygen carrier in the air stream in the oxidation reaction step are exothermic processes, which can supply heat energy for the cracking reaction, realizing the transformation of the cracking reaction from highly endothermic to self-heating, greatly reducing process consumption.

[0040] 5. The present invention applies the encapsulated composite catalyst to the oxidative cracking of naphtha to produce light olefins, not only reducing the reaction temperature, but also having a high conversion rate, high mass selectivity of olefins, and less carbon deposition. The experimental results are shown in Table 4 and Table 5.

[0041] The detailed structure of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. Description of the Drawings

[0042] Figure 1 It is a graph of the test data of the application performance for Example 1;

[0043] Figure 2 It is a graph of the test data of the application performance for Example 2;

[0044] Figure 3 It is a graph of the test data of the application performance for Example 3;

[0045] Figure 4 It is a graph of the test data of the application performance for Example 4;

[0046] Figure 5 It is a graph of the test data of the application performance for Example 5. Specific Embodiments

[0047] Example 1 Synthesis of CaMnO3 and CaMn 0.8 Cu 0.2 O3

[0048] (1) Synthesis of CaMnO3:

[0049] Dissolve Ca(NO3)2 and Mn(NO3)2 with a stoichiometric ratio of Ca:Mn = 1:1 in 40 mL of deionized water and stir at 40 °C for 0.5 h. After the metal salts are fully dissolved, using citric acid as a complexing agent, add citric acid with a molar ratio of 2.5:1 to the metal cations (Ca, Mn) to the mixture, and stir at a speed of 500 rpm and 40 °C for 1 h. Then, add ethylene glycol (99.8%) with a molar ratio of 1:1 to citric acid, and then raise the temperature to 85 °C and continue stirring until the mixture forms a sol. Place the obtained solid product in a vacuum drying oven at 90 °C and dry overnight, and then place it in a muffle furnace and program the temperature to 450 °C and calcine for 1 h, and then raise the temperature to 950 °C and calcine for 8 h (heating rate is 10 °C / min). After cooling to room temperature, grind it into a powdery solid with a particle size less than 10 mesh to prepare the CaMnO3 perovskite composite oxide.

[0050] (2)CaMn 0.8 Cu 0.2 O3 synthesis:

[0051] Dissolve Ca(NO3)2, Mn(NO3)2, and Cu(NO3)2 with a stoichiometric ratio of Ca:Mn:Cu = 5:4:1 in 40 mL of deionized water and stir at 40 °C for 0.5 h. After the metal salts are fully dissolved, use citric acid as a complexing agent and add citric acid with a molar ratio of 2:1 to the metal cations (Ca, Mn, Cu) to the mixed solution. Stir at 600 rpm and 50 °C for 2 h. Then, add ethylene glycol (99.8%) with a molar ratio of 1.5:1 to citric acid, and then heat up to 80 °C and continue stirring until the mixed solution forms a sol. Place the obtained solid product in a vacuum drying oven at 80 °C and dry overnight, and then place it in a muffle furnace and heat it up to 400 °C at a programmed rate and calcine for 2 h, and then heat it up to 1000 °C and calcine for 9 h (heating rate is 10 °C / min). Wait until it cools to room temperature and grind it into a powdery solid smaller than 10 mesh, CaMn 0.8 Cu 0.2 O3 perovskite composite oxide.

[0052] Press the CaMnO3 and CaMn 0.8 Cu 0.2 O3 oxygen carriers prepared in Example 1 into tablets, sieve them through a 20-40 mesh sieve, and pack them in a fixed-bed reactor. Feed naphtha and nitrogen into the reactor. Carry out catalytic oxidative cracking reaction under certain reaction conditions, and separate the reaction stream to obtain the target product light olefins. The specific catalytic reaction performance data are shown in Table 1. The perovskite oxygen carrier after the reaction is oxidized and regenerated in an air stream of 80 mL / min to supplement the consumed lattice oxygen.

[0053] The specific reaction conditions in this example: 0.5 g of catalyst, reaction temperature 800 °C, space velocity 25 mL / min, naphtha feed rate 0.5 g, and the reaction time for each redox cycle is 420 s.

[0054] Table 1 Catalytic reaction performance data of Example 1

[0055]

[0056] As can be seen from Table 1, the prepared perovskite composite metal oxide oxygen carrier has good naphtha conversion ability and light olefin selectivity. At the same time, the B-site doped CaMn 2+ with Cu 0.8 Cu 0.2 O3 perovskite composite oxide increases its surface lattice oxygen reaction activity and release rate, improves the selectivity of the target product, and reduces the formation of carbon deposition and coking.

[0057] Synthesis of AMn2O4 (A = Ni, Mg) in Example 2

[0058] (1) Synthesis of MgMn₂O₄:

[0059] Dissolve Mg(NO₃)₂ and Mn(NO₃)₂ with a stoichiometric ratio of Mg:Mn:Cu = 1:2 in 20 mL of deionized water and stir at room temperature for 1 h. After the metal salts are fully dissolved, using citric acid as a complexing agent, add citric acid with a molar ratio of 1.5:1 to the metal cations (Mg, Mn) to the mixed solution, and stir at 400 rpm and 60 °C for 1.5 h. Then, add ethylene glycol (99.8%) with a molar ratio of 5:2 to citric acid, and then raise the temperature to 90 °C and continue stirring until the mixed solution forms a sol. Place the obtained solid product in a vacuum drying oven at 100 °C and dry overnight, and then place it in a muffle furnace and program the temperature to 500 °C for calcination for 2.5 h, and then raise the temperature to 900 °C for calcination for 6 h (heating rate is 10 °C / min). After cooling to room temperature, grind it into a powdery solid with a particle size less than 10 mesh to prepare the MgMn₂O₄ spinel composite oxide.

[0060] (2) Synthesis of NiMn₂O₄:

[0061] Dissolve Ni(NO₃)₂ and Mn(NO₃)₂ with a stoichiometric ratio of Ni:Mn:Cu = 1:2 in 30 mL of deionized water and stir at room temperature for 1.5 h. After the metal salts are fully dissolved, using citric acid as a complexing agent, add citric acid with a molar ratio of 3:1 to the metal cations (Ni, Mn) to the mixed solution, and stir at 450 rpm and 55 °C for 2.5 h. Then, add ethylene glycol (99.8%) with a molar ratio of 2:1 to citric acid, and then raise the temperature to 70 °C and continue stirring until the mixed solution forms a sol. Place the obtained solid product in a vacuum drying oven at 90 °C and dry overnight, and then place it in a muffle furnace and program the temperature to 350 °C for calcination for 3 h, and then raise the temperature to 850 °C for calcination for 7 h (heating rate is 10 °C / min). After cooling to room temperature, grind it into a powdery solid with a particle size less than 10 mesh to prepare the NiMn₂O₄ spinel composite oxide.

[0062] Press the AMn₂O₄ (A = Ni, Mg) oxygen carriers prepared in Example 2 into tablets, sieve them through a 20 - 40 mesh sieve, and load them into a fixed-bed reactor. Pass n-heptane and nitrogen into the reactor. Carry out catalytic oxidative cracking reaction under certain reaction conditions, and separate the reaction stream to obtain the target product light olefins. The specific catalytic reaction performance data are shown in Table 2. The perovskite oxygen carriers after the reaction are oxidized and regenerated in an air stream of 85 mL / min to supplement the consumed lattice oxygen.

[0063] Specific reaction conditions in this example: 0.5 g of catalyst, reaction temperature of 800 °C, space velocity of 25 mL / min, naphtha feed rate of 0.5 g, and reaction time for each redox cycle of 420 s.

[0064] Table 2 Catalytic reaction performance data of Example 2

[0065]

[0066] As can be seen from Table 2, the prepared spinel composite oxide has good naphtha conversion ability (conversion rate greater than 90%) and certain light olefin selectivity. However, the too strong conversion ability of the spinel composite oxide leads to the easy peroxidation of naphtha to form more carbon deposition and coking.

[0067] Synthesis of Fe2O3, Mn2O3, and Co3O4 in Example 3

[0068] (1) Synthesis of Fe2O3:

[0069] Dissolve ferric nitrate hexahydrate in 60 mL of deionized water, with the molar concentration of Fe 3+ being 0.1 mol / L, denoted as solution A1; accurately weigh sodium carbonate and dissolve it in 60 mL of deionized water, with the molar concentration of CO3 2- being 3 times that of Fe 3+ . Denote it as solution B1. Under vigorous stirring, slowly add solution B2 dropwise to solution A1 until the pH value of the solution is 10 - 11. The obtained mixed solution is continuously stirred at 90 °C for 24 h, and then centrifuged and washed until neutral. The obtained solid product is dried overnight at 70 °C, and then calcined in a muffle furnace at 550 °C for 5 h. After cooling to room temperature, it is ground into a powdery solid with a particle size less than 10 mesh to prepare Fe2O3.

[0070] The synthesis of other metal oxide oxygen carriers (Mn2O3, Co3O4) is consistent with that in Example 3 above. The Fe2O3, Mn2O3, and Co3O4 oxygen carriers prepared in Example 3 are pressed into tablets, screened through a 20 - 40 mesh sieve, and filled into a fixed - bed reactor. Naphtha and nitrogen are introduced into the reactor. Under certain reaction conditions, catalytic oxidative cracking reaction is carried out, and the reaction stream is separated to obtain the target product light olefins. The specific catalytic reaction performance data are shown in Table 3. The perovskite oxygen carrier after the reaction is oxidized and regenerated in an air stream at 90 mL / min to supplement the consumed lattice oxygen.

[0071] Specific reaction conditions in this example: 0.5 g of catalyst, reaction temperature of 800 °C, space velocity of 25 mL / min, naphtha feed rate of 0.5 g, and reaction time for each redox cycle of 420 s.

[0072] Table 3 Catalytic reaction performance data of Example 3

[0073]

[0074] As can be seen from Table 3, the prepared single-component metal oxide oxygen carriers have good naphtha conversion ability. However, under high-temperature reaction conditions, the metal oxide oxygen carriers are prone to sintering and agglomeration, resulting in low selectivity for light olefins and simultaneously leading to the formation of excessive CO X and excessive carbon deposition.

[0075] Example 4 Synthesis of metal oxide - zeolite (oxide oxygen carrier @ ZSM-5) encapsulated composite catalyst

[0076] (1) Synthesis of CaMnO3@ZSM-5:

[0077] 3 g of ZSM-5 was mixed with 1.46 g of tetraethyl orthosilicate (TEOS), 0.711 g of tetrapropylammonium hydroxide (concentration 40 - 50%) and 30 mL of aqueous solution. The resulting mixture was stirred at 30 °C for 3 h to obtain a mixed suspension A2. Among them, the molar ratio of tetraethyl orthosilicate (TEOS) to tetrapropylammonium hydroxide was 1.0:0.25. 1.5 g of CaMnO3 prepared in Example 1 above and 10.92 g of polyvinylpyrrolidone (PVP) were dispersed in 30 mL of deionized water, and stirred at room temperature for 3 h until evenly dispersed to obtain a mixed suspension B2. The mixed suspensions A2 and B2 were mixed and heated to 90 °C, and stirred vigorously for 5 h, and then the temperature was maintained and left to age for 48 h. After aging, the mixed suspension was hydrothermally treated at 180 °C for 3 h. After hydrothermal treatment and cooling to room temperature, the mixed suspension was centrifuged and washed 3 times with deionized water. The obtained solid product was dried in an oven at 120 °C for 12 h and calcined at 600 °C for 12 h (heating rate 5 °C / min), cooled to room temperature and ground into a powdery solid smaller than 10 mesh to obtain the CaMnO3@ZSM-5 encapsulated composite catalyst.

[0078] (2) Synthesis of NiMn2O4@ZSM-5:

[0079] 2 g of ZSM-5 was mixed with 0.80 g of tetramethoxysilane (TMOS), 0.510 g of cetyltrimethylammonium bromide (CTAB), and 25 mL of aqueous solution. The resulting mixture was stirred at 25 °C for 2.5 h to obtain a mixed suspension A3. Among them, the molar ratio of tetramethoxysilane (TMOS) to cetyltrimethylammonium bromide (CTAB) was: 0.75:0.2. 1 g of NiMn2O4 prepared in Example 2 above and 13.65 g of polyvinylpyrrolidone (PVP) were dispersed in 25 mL of deionized water, and stirred at room temperature for 2 h until uniformly dispersed to obtain a mixed suspension B3. The mixed suspensions A3 and B3 were mixed and heated to 85 °C, and stirred vigorously for 3.5 h, then the temperature was maintained and allowed to age statically for 36 h. After aging, the mixed suspension was hydrothermally treated at 175 °C for 2 h. After the hydrothermal treatment and cooling to room temperature, the mixed suspension was centrifuged and washed 3 times with deionized water. The obtained solid product was dried in an oven at 110 °C for 10 h, and calcined at 550 °C for 10 h (heating rate 5 °C / min), cooled to room temperature and ground into a powdery solid smaller than 10 mesh to obtain the NiMn2O4@ZSM-5 encapsulated composite catalyst.

[0080] (3)Fe2O3@ZSM-5

[0081] 1 g of ZSM-5 was mixed with 0.421 g of polyethoxydisiloxane (PEDS), 0.106 g of triethylamine, and 20 mL of aqueous solution. The resulting mixture was stirred at 20 °C for 2 h to obtain a mixed suspension A4. Among them, the molar ratio of polyethoxydisiloxane (PEDS) to triethylamine was: 0.5:0.15. 0.5 g of Fe2O3 prepared in Example 2 above and 8.19 g of polyvinylpyrrolidone (PVP) were dispersed in 20 mL of deionized water, and stirred at room temperature for 1 h until uniformly dispersed to obtain a mixed suspension B3. The mixed suspensions A3 and B3 were mixed and heated to 80 °C, and stirred vigorously for 2 h, then the temperature was maintained and allowed to age statically for 24 h. After aging, the mixed suspension was hydrothermally treated at 170 °C for 1 h. After the hydrothermal treatment and cooling to room temperature, the mixed suspension was centrifuged and washed 3 times with deionized water. The obtained solid product was dried in an oven at 100 °C for 8 h, and calcined at 500 °C for 8 h (heating rate 5 °C / min), cooled to room temperature and ground into a powdery solid smaller than 10 mesh to obtain the Fe2O3@ZSM-5 encapsulated composite catalyst.

[0082] The encapsulated composite catalyst oxygen carrier prepared in Example 4 was tableted, sieved through a 20-40 mesh sieve, and filled into a fixed bed reactor. Naphtha and nitrogen were introduced into the reactor. The catalytic oxidative cracking reaction was carried out under certain reaction conditions, and the reaction stream was separated to obtain the target product of light olefins. The specific catalytic reaction performance data are shown in Table 4. The perovskite oxygen carrier after the reaction was oxidized and regenerated in an air stream of 80 mL / min to supplement the consumed lattice oxygen.

[0083] The specific reaction conditions in this example are as follows: 0.5 g of catalyst, reaction temperature of 600 °C, space velocity of 25 mL / min, naphtha feed rate of 0.5 g, and reaction time for each redox cycle of 420 s.

[0084] Table 4 Catalytic reaction performance data of Example 4

[0085]

[0086] As can be seen from Table 4, using ZSM-5 molecular sieve as the seed and the hydrothermal seed induction method, the prepared encapsulated metal oxide-molecular sieve composite catalyst has a core-shell structure that can effectively inhibit the sintering and agglomeration of metal oxide nanoparticles and reduce the generation of CO X during the reaction. In addition, the lattice oxygen of the oxygen carrier inhibits the formation of coke through the oxidation reaction and promotes the forward movement of the cracking reaction through the selective hydrogen combustion reaction, improving the reaction activity and light olefin selectivity; the encapsulated composite catalyst in Example 4 is applied to the oxidative cracking of naphtha to produce light olefins, which not only reduces the reaction temperature, but also has high conversion rate, high mass selectivity of olefins, and less carbon deposition.

[0087] Example 5 Synthesis of encapsulated composite catalysts of metal oxide - molecular sieve (CaMn 0.8 Cu 0.2 O3@S-1, CaMn 0.8 Cu 0.2 O3@MCM-41, CaMn 0.8 Cu 0.2 O3@Beta)

[0088] (1) Synthesis of CaMn 0.8 Cu 0.2 O3@S-1:

[0089] 3 g of ZSM-5 was mixed with 1.06 g of silica sol, 0.174 g of cyclohexylamine, and 30 mL of aqueous solution. The resulting mixture was stirred at 30 °C for 3 h to obtain a mixed suspension A5. Among them, the molar ratio of tetraethyl orthosilicate (TEOS) to cyclohexylamine was 1.0:0.25. 1.5 g of CaMn 0.8 Cu0.2 0.3 g of O3 and 12.29 g of polyvinylpyrrolidone (PVP) were dispersed in 30 mL of deionized water. Among them, and stirred at room temperature for 3 h until evenly dispersed to obtain a mixed suspension B5. The A5 and B5 mixed suspensions were mixed and heated to 85 °C and stirred vigorously for 4 h, then the temperature was maintained and allowed to stand for aging for 48 h. After the aging was completed, the mixed suspension was hydrothermally treated at 180 °C for 2 h. After the hydrothermal treatment and cooling to room temperature, the mixed suspension was centrifuged and washed 3 times with deionized water. The obtained solid product was dried in an oven at 110 °C for 12 h and calcined at 550 °C for 12 h (heating rate 5 °C / min), cooled to room temperature and ground into a powdery solid smaller than 10 mesh to obtain CaMn 0.8 Cu 0.2 O3@S-1 encapsulated composite catalyst.

[0090] (2)Synthesis of CaMn 0.8 Cu 0.2 O3@MCM-41:

[0091] 2 g of MCM-41 was mixed with 0.954 g of methyltrimethoxysilane, 0.711 g of tetrapropylammonium hydroxide (concentration 40 - 50%) and 30 mL of aqueous solution. The obtained mixture was stirred at 30 °C for 3 h to obtain a mixed suspension A6. Among them, the molar ratio of tetraethyl orthosilicate (TEOS) to tetrapropylammonium hydroxide was: 1.0 : 0.25. 1.5 g of CaMn prepared in the above Example 1 0.8 Cu 0.2 O3 and 9.56 g of polyvinylpyrrolidone (PVP) were dispersed in 30 mL of deionized water. Among them, and stirred at room temperature for 3 h until evenly dispersed to obtain a mixed suspension B6. The A6 and B6 mixed suspensions were mixed and heated to 80 °C and stirred vigorously for 5 h, then the temperature was maintained and allowed to stand for aging for 40 h. After the aging was completed, the mixed suspension was hydrothermally treated at 170 °C for 3 h. After the hydrothermal treatment and cooling to room temperature, the mixed suspension was centrifuged and washed 3 times with deionized water. The obtained solid product was dried in an oven at 120 °C for 8 h and calcined at 600 °C for 9 h (heating rate 5 °C / min), cooled to room temperature and ground into a powdery solid smaller than 10 mesh to obtain CaMn 0.8 Cu 0.2 O3@MCM-41 encapsulated composite catalyst.

[0092] (3)Synthesis of CaMn 0.8 Cu 0.2 O3@Beta:

[0093] 2.5 g of Beta was mixed with 1.25 g of methyltriethoxysilane, 0.729 g of cetyltrimethylammonium bromide (CTAB), and 30 mL of aqueous solution. The resulting mixture was stirred at 30 °C for 3 h to obtain a mixed suspension A7. Among them, the molar ratio of tetraethyl orthosilicate (TEOS) to tetrapropylammonium hydroxide was 1.0:0.25. 1.5 g of CaMnO3 prepared in Example 1 above and 8.19 g of polyvinylpyrrolidone (PVP) were dispersed in 30 mL of deionized water, and stirred at room temperature for 3 h until uniformly dispersed to obtain a mixed suspension B7. The mixed suspensions A7 and B7 were mixed and heated to 90 °C, and vigorously stirred for 3.5 h, then the temperature was maintained and allowed to age statically for 30 h. After aging, the mixed suspension was hydrothermally treated at 175 °C for 1 h. After hydrothermal treatment and cooling to room temperature, the mixed suspension was centrifuged and washed 3 times with deionized water. The obtained solid product was dried in an oven at 115 °C for 11 h, and calcined at 600 °C for 8 h (heating rate 5 °C / min), cooled to room temperature and ground into a powdery solid smaller than 10 mesh, to obtain CaMn 0.8 Cu 0.2 O3@Beta encapsulated composite catalyst.

[0094] The encapsulated composite catalyst oxygen carrier prepared in Example 5 was tableted, passed through a 20-40 mesh sieve, and loaded into a fixed-bed reactor. Naphtha and nitrogen were introduced into the reactor. Under certain reaction conditions, a catalytic oxidative cracking reaction was carried out, and the reaction stream was separated to obtain the target product light olefins. The specific catalytic reaction performance data are shown in Table 5. The perovskite oxygen carrier after the reaction was oxidized and regenerated in an air stream at 80 mL / min to supplement the consumed lattice oxygen.

[0095] The specific reaction conditions in this example were as follows: 0.5 g of catalyst, reaction temperature 600 °C, space velocity 25 mL / min, naphtha feed rate 0.5 g, and the reaction time for each redox cycle was 420 s.

[0096] Table 5 Catalytic reaction performance data of Example 5

[0097]

[0098] As can be seen from Table 5, using different molecular sieves as seeds and combining with the hydrothermal seed induction method, the prepared encapsulated metal oxide-molecular sieve composite catalysts with different core-shell structures can effectively inhibit the sintering and aggregation of metal oxide nanoparticles and reduce CO during the reaction process XAnd the formation of carbon deposition. At the same time, the oxidation and reduction reactions of the lattice oxygen of the metal oxide oxygen carrier are both exothermic reactions that can supply heat energy to the reaction system, which can effectively reduce the reaction temperature and enable it to obtain good naphtha conversion rate and light olefin selectivity under low-temperature conditions.

[0099] The above are the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the claims of the present invention.

Claims

1. An encapsulated composite catalyst, characterized in that, The composition of the encapsulated composite catalyst is: oxide oxygen carrier@molecular sieve, where the oxide oxygen carrier is selected from any one of CaMnO3, CaMn 0.8 Cu 0.2 O3, MgMn2O4, NiMn2O4, and the molecular sieve is selected from any one of ZSM-5 molecular sieve, Silicate-1 molecular sieve, and Beta molecular sieve; the encapsulated composite catalyst is prepared by a hydrothermal seed-induced method, and the specific steps include: adding 1 - 3 g of seed molecular sieve to a mixed solution of a silicon source, a template agent, and 20 - 30 mL of deionized water to form a mixed aqueous solution, and stirring at 20 - 30 °C for 2 - 3 h; then adding 0.5 - 1.5 g of oxide oxygen carrier and 0.03 - 0.05 mol of surfactant to 20 - 30 mL of deionized water, and stirring at room temperature for 1 - 3 h to obtain an oxide oxygen carrier mixed suspension; mixing the mixed aqueous solution with the oxide oxygen carrier mixed suspension to form a mixed system, stirring the mixed system at 80 - 90 °C for 2 - 5 h to obtain a precursor mixed suspension, after the precursor mixed suspension is aged at a constant temperature for 24 - 48 h, the precursor mixed suspension is hydrothermally treated at 170 - 180 °C for 1 - 3 h; the precursor mixed suspension is centrifuged and washed with deionized water 2 - 4 times to obtain a solid product, the solid product is dried in an oven at 100 °C - 120 °C for 8 - 12 h and then calcined in a muffle furnace at 500 - 600 °C for 8 - 12 h, and after cooling to room temperature and grinding into a powdery solid smaller than 10 mesh, the encapsulated composite catalyst is obtained.

2. The encapsulated composite catalyst according to claim 1, wherein The CaMnO3, CaMn 0.8 Cu 0.2 O3 perovskite metal oxide oxygen carriers or MgMn2O4, NiMn2O4 spinel oxide oxygen carriers are prepared by the sol-gel method.

3. The encapsulated composite catalyst according to claim 1, wherein, The molar ratio of the silicon source to the template agent is 0.5 - 1.0 : 0.15 - 0.

25.

4. The encapsulated composite catalyst according to claim 3, wherein, The silicon source is selected from any one of methyl orthosilicate, ethyl orthosilicate, silica sol, polyethoxydisiloxane, methyltrimethoxysilane, and methyltriethoxysilane.

5. The encapsulated composite catalyst according to claim 1, wherein The template agent is selected from any one of tetrapropylammonium hydroxide, cetyltrimethylammonium bromide, triethylamine, and cyclohexylamine; the surfactant is selected from polyvinylpyrrolidone.

6. The encapsulated composite catalyst according to claim 2, wherein The sol-gel method includes: According to the molecular formulas of the perovskite and spinel oxygen carriers to be prepared, CaMnO3, CaMn 0.8 Cu 0.2 O3, MgMn2O4, NiMn2O4, confirm the metal cation composition, and weigh the nitrates containing the corresponding cations and dissolve them in deionized water to form a nitrate solution. Then, add citric acid and ethylene glycol to the nitrate solution to form a mixed system. Finally, heat and stir the mixed system at 70 °C - 90 °C until a sol is formed. The sol is dried at 80 °C - 100 °C, calcined at 350 °C - 500 °C for 1 h - 3 h, and calcined at 850 °C - 1000 °C for 6 - 9 h. After cooling to room temperature and grinding into a powdery solid smaller than 10 mesh, different metal-doped oxide oxygen carriers are obtained.

7. A new method for producing light olefins by oxidative cracking of naphtha, characterized in that, The naphtha feedstock contacts with the catalyst, and the oxidative cracking reaction is carried out under the conditions of 500 - 800 °C, an air flow rate of 25 - 200 mL / min, a naphtha feed rate of 0.1 - 0.5 g, and a reaction time of 300 - 420 s for each redox cycle. The reaction stream is separated to obtain the target product of light olefins; the catalyst is any one of the encapsulated composite catalysts in claims 1 - 6.

8. The new method for producing light olefins by oxidative cracking of naphtha according to claim 7, characterized in that, After the cracking reaction, the encapsulated composite catalyst is regenerated by oxidation with an air flow of 80 - 200 mL / min.

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