Modified ZSM-5 molecular sieve catalyst, preparation method and application thereof

Abstract

The invention discloses a modified ZSM-5 molecular sieve catalyst, a preparation method and application thereof, and the preparation method of the catalyst comprises the following steps: S1, molecular sieve pretreatment; S2, preparing manganese-doped mesoporous ferrosoferric oxide microspheres; S3, preparing active microsphere modifiers; S4, modifying active microsphere modifiers on the molecular sieve pretreated by step S1, and obtaining a modified ZSM-5 molecular sieve catalyst. The present invention has prepared a modified ZSM-5 molecular sieve catalyst that exhibits excellent catalytic ability in both heavy oil catalytic cracking and catalytic chloromethane coupling to prepare light olefins, which can effectively improve the catalytic activity of the catalyst when used for heavy oil catalytic cracking, promote the generation of free radicals, improve the yield of olefins, and suppress the generation of aromatics such as benzene and toluene; when used for catalytic chloromethane coupling to prepare light olefins, the conversion rate of chloromethane can be improved, and the selectivity of light olefins can be improved.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to a modified ZSM-5 molecular sieve catalyst, a preparation method thereof and application thereof in the selective catalytic cracking of heavy oil or the catalytic methyl chloride coupling to prepare light olefins. Background Art

[0002] Low-carbon olefins, especially ethylene and propylene, are very important basic chemical raw materials. At present, there is a huge demand for light oil worldwide, and light oil as a raw material for the production of low-carbon olefins is becoming increasingly scarce. Therefore, the technology of directly catalytic cracking heavy oil to produce low-carbon olefins is increasingly valued. Catalytic thermal cracking (CPP) is based on traditional catalytic cracking technology, using heavy oil such as wax oil, wax oil mixed with residual oil or atmospheric heavy oil as raw materials, using proprietary catalysts, and operating in a continuous reaction-regeneration cycle in a riser reactor. Ethylene and propylene are produced under milder operating conditions than steam cracking. Catalysts play a very important role in these processes. Molecular sieve catalysts are widely used products, and their research has received widespread attention. For example, patent CN102114429B provides a method for increasing the B acid content of ZSM5 molecular sieves and increasing the production of low-carbon olefins.

[0003] Generally speaking, hydrocarbon feedstocks are mainly composed of alkane, olefin and aromatic components. Under the same cracking environment, long-chain olefins are easier to crack into light olefins, but long-chain alkanes and alkyl aromatics are more difficult to crack. Therefore, how to improve the performance of molecular sieves so that they can crack more long-chain alkanes and aromatics with alkyl side chains is a key to improving the catalytic selectivity and catalytic activity of heavy oil catalytic cracking to produce light olefins. It is generally believed that the main sources of olefin generation are free radical reactions and positive carbon ion reactions (Xie Chaogang, Wei Xiaoli, Gong Jianhong, et al. Research progress on catalytic cracking reaction mechanism and practical application [J]. Acta Petrolei Sinica (Petroleum Processing), 2017, 33(2): 9. DOI: 10.3969 / j.issn.1001-8719.2017.02.001.).

[0004] Kenichi et al. (W. Kenichi, S. Ko-ichi, S. Goro, et al. "Catalytic cracking of n-butane over rare earth loaded HZSM-5 catalysts", Stud. Surf. Sci. Catal., 1999; 125: 449-456) used ZSM-5 molecular sieve loaded with rare earth to study the cracking of n-butane. The results showed that after loading rare earth metal ions, the formation of aromatic hydrocarbons such as benzene, toluene, and xylene (BXT) was significantly inhibited, resulting in an increase in the yield of light olefins (ethylene and propylene).

[0005] Studies have shown that the introduction of transition metals into ZSM-5 molecular sieves or catalysts changes the distribution of reaction products and the mechanism of catalytic thermal cracking reactions. In particular, the introduction of silver increases the yield of ethylene without reducing the yield of propylene. This indicates that silver can not only promote the formation of positive carbon ions in catalytic thermal cracking reactions, but also partially change the reaction mechanism through oxidation-reduction and promote the formation of free radicals. (Liu Hongzhou, Wang Xieqing. Effect of the introduction of transition metals into ZSM-5 molecular sieves on catalytic thermal cracking reactions [J]. Petroleum Refining and Chemical Engineering, 2001, 32(2):4. DOI:10.3969 / j.issn.1005-2399.2001.02.013.) It can be seen that rare earth doping and transition metal doping are expected to improve the catalytic performance of molecular sieve catalysts, and the generation of free radicals can promote the production of low-carbon rare earths.

[0006] In addition, with the shortage of global oil resources and the rise in oil prices, it is of great strategic significance to seek non-petroleum routes to prepare low-carbon olefins. From the perspective of economy and raw materials, the route of preparing low-carbon olefins via chloromethane using natural gas (methane) as raw material is a more ideal choice with good development prospects. For example, patent CN107175127B provides a supported composite metal molecular sieve catalyst for catalyzing chloromethane coupling to prepare low-carbon olefins.

[0007] Therefore, it is of great significance to develop a molecular sieve catalyst that can be used for both the selective catalytic cracking of heavy oil and the catalytic coupling of methyl chloride to produce light olefins. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a modified ZSM-5 molecular sieve catalyst, a preparation method and application thereof in view of the deficiencies in the above-mentioned prior art.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is: In a first aspect of the present invention, a method for preparing a modified ZSM-5 molecular sieve catalyst is provided, comprising the following steps: S1, molecular sieve pretreatment; S2, preparing manganese-doped mesoporous ferroferric oxide microspheres; S3, modifying ruthenium-doped carbon dots on manganese-doped ferroferric oxide microspheres to obtain an active microsphere modifier; S4, modifying the molecular sieve pretreated in step S1 with an active microsphere modifier to obtain a modified ZSM-5 molecular sieve catalyst.

[0010] Preferably, step S1 specifically includes: Take 5-20g HZSM-5 molecular sieve and add it to 50-200mL sodium hydroxide solution with a concentration of 0.1-0.3mol / L, disperse it ultrasonically for 15-60min, stir it for 1.5-6h, centrifuge it, wash the solid product with deionized water and ethanol in sequence, and then vacuum dry it at 80-120℃ for 6-24 to obtain the pretreated molecular sieve.

[0011] Preferably, step S2 specifically includes: FeCl3·6H2O, MnCl2·4H2O, sodium acetate and sodium hydroxide were added to ethylene glycol, and then ethylenediamine was added and stirred evenly. The obtained mixture was transferred to a reactor, reacted under heating, cooled to room temperature, filtered, and the product solid was washed with deionized water and vacuum dried to obtain manganese-doped mesoporous ferrosoferric oxide microspheres.

[0012] Preferably, step S2 specifically includes: Take 0.376-2.704g FeCl3·6H2O, 0.198-0.792g MnCl2·4H2O, 2.05-8.25g sodium acetate, and 0.125-0.5g sodium hydroxide and add them to 10-40mL ethylene glycol, then add 0.7-2.8mL ethylenediamine and stir evenly. Transfer the resulting mixture to a reactor, react at 150-185°C for 4-16h, cool to room temperature, filter, wash the product solid with deionized water, and vacuum dry at 80-110°C for 6-24h to obtain manganese-doped mesoporous ferrosoferric oxide microspheres.

[0013] Preferably, step S3 specifically includes: S3-1, adding the manganese-doped mesoporous ferroferric oxide microspheres prepared in step S2 and ethanol into deionized water, and performing ultrasonic dispersion to obtain a precursor solution A; S3-2, add tannic acid, ethylenediaminetetraacetic acid, citric acid, and RuCl3·3H2O into deionized water, and disperse by ultrasonic to obtain precursor solution B; S3-3. Add precursor solution B to precursor solution A under stirring, continue stirring and then transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, heat and react. After the reaction is completed, cool to room temperature and centrifuge. Wash the solid product with ethanol and deionized water in turn, and vacuum dry to obtain an active microsphere modifier.

[0014] Preferably, step S3 specifically includes: S3-1, take 1-4 g of the manganese-doped mesoporous ferroferric oxide microspheres prepared in step S2 and add 25-100 mL of ethanol to 50-200 mL of deionized water, and ultrasonically disperse for 15-60 min to obtain a precursor solution A; S3-2, add 169-676 mg of tannic acid, 292-1168 mg of ethylenediaminetetraacetic acid, 384-1536 mg of citric acid, and 103.5-414 mg of RuCl3·3H2O into 25-100 mL of deionized water, and disperse by ultrasonic for 5-30 min to obtain precursor solution B; S3-3. Add precursor solution B to precursor solution A under stirring, continue stirring for 15-60 minutes, then transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 170-210°C for 3-12 hours, cool to room temperature and centrifuge, wash the solid product with ethanol and deionized water in turn, and vacuum dry at 85-100°C for 6-24 hours to obtain an active microsphere modifier.

[0015] Preferably, step S4 specifically includes: S4-1, add La(NO3)3·6H2O to deionized water, stir, then add the pretreated molecular sieve prepared in step S1, stir, and obtain mixture 1; S4-2, adding the active microsphere modifier prepared in step S3 into deionized water, and performing ultrasonic dispersion to obtain a mixture 2; S4-3. Add mixture 2 to mixture 1 under stirring, continue stirring, transfer the obtained mixture to a reactor, react under heating, cool to room temperature after the reaction is completed, centrifuge and filter, wash the solid product with deionized water and ethanol in turn, and dry to obtain a modified ZSM-5 molecular sieve catalyst.

[0016] Preferably, step S4 specifically includes: S4-1, add 1.88-7.52 g La(NO3)3·6H2O to 75-300 mL deionized water, stir for 5-20 min, then add 10-40 g of the pretreated molecular sieve prepared in step S1, stir for 0.5-3 h, and obtain mixture 1; S4-2, taking 2.5-10 g of the active microsphere modifier prepared in step S3, adding it to 50-200 mL of deionized water, and ultrasonically dispersing it for 30-90 min to obtain a mixture 2; S4-3. Add mixture 2 to mixture 1 under stirring, continue stirring for 1-4 hours, transfer the obtained mixture to a reactor, react at 120-160°C for 6-24 hours, cool to room temperature, centrifuge and filter, wash the solid product with deionized water and ethanol in turn, and dry at 90-115°C for 6-24 hours to obtain a modified ZSM-5 molecular sieve catalyst.

[0017] The second aspect of the present invention provides a modified ZSM-5 molecular sieve catalyst, which is prepared by the method as described above.

[0018] The third aspect of the present invention provides a use of the modified ZSM-5 molecular sieve catalyst as described above in the selective catalytic cracking of heavy oil.

[0019] The beneficial effects of the present invention are: The present invention adopts active microsphere modifier and rare earth lanthanum doping to prepare a modified ZSM-5 molecular sieve catalyst that exhibits excellent catalytic ability in both heavy oil catalytic cracking and catalytic chloromethane coupling to prepare light olefins. When used for heavy oil catalytic cracking, the modified ZSM-5 molecular sieve catalyst can effectively improve the catalytic activity of the catalyst, promote the generation of free radicals, increase the yield of olefins, and inhibit the generation of aromatic hydrocarbons such as benzene and toluene; when used for catalytic chloromethane coupling to prepare light olefins, the modified ZSM-5 molecular sieve catalyst can improve the conversion rate of chloromethane and improve the selectivity of light olefins. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

[0021] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0022] The test methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples are all commercially available unless otherwise specified. In the following examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional products that can be purchased commercially.

[0023] The present invention provides a method for preparing a modified ZSM-5 molecular sieve catalyst, comprising the following steps: S1. Molecular sieve pretreatment: Take 5-20g HZSM-5 molecular sieve and add it to 50-200mL sodium hydroxide solution with a concentration of 0.1-0.3mol / L, disperse it ultrasonically for 15-60min, stir it for 1.5-6h, centrifuge it, wash the solid product with deionized water and ethanol in sequence, and then vacuum dry it at 80-120℃ for 6-24 to obtain the pretreated molecular sieve.

[0024] S2. Preparation of manganese-doped mesoporous ferroferric oxide microspheres: Take 0.376-2.704g FeCl3·6H2O, 0.198-0.792g MnCl2·4H2O, 2.05-8.25g sodium acetate, and 0.125-0.5g sodium hydroxide and add them to 10-40mL ethylene glycol, then add 0.7-2.8mL ethylenediamine and stir evenly. Transfer the resulting mixture to a reactor, react at 150-185°C for 4-16h, cool to room temperature, filter, wash the product solid with deionized water, and vacuum dry at 80-110°C for 6-24h to obtain manganese-doped mesoporous ferrosoferric oxide microspheres.

[0025] S3, modifying ruthenium-doped carbon dots on manganese-doped ferroferric oxide microspheres to obtain an active microsphere modifier: S3-1, take 1-4 g of the manganese-doped mesoporous ferroferric oxide microspheres prepared in step S2 and add 25-100 mL of ethanol to 50-200 mL of deionized water, and ultrasonically disperse for 15-60 min to obtain a precursor solution A; S3-2, add 169-676 mg of tannic acid, 292-1168 mg of ethylenediaminetetraacetic acid, 384-1536 mg of citric acid, and 103.5-414 mg of RuCl3·3H2O into 25-100 mL of deionized water, and disperse by ultrasonic for 5-30 min to obtain precursor solution B; S3-3. Add precursor solution B to precursor solution A under stirring, continue stirring for 15-60 minutes, then transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 170-210°C for 3-12 hours, cool to room temperature and centrifuge, wash the solid product with ethanol and deionized water in turn, and vacuum dry at 85-100°C for 6-24 hours to obtain an active microsphere modifier.

[0026] S4, modifying the molecular sieve pretreated in step S1 with an active microsphere modifier to obtain a modified ZSM-5 molecular sieve catalyst: S4-1, add 1.88-7.52 g La(NO3)3·6H2O to 75-300 mL deionized water, stir for 5-20 min, then add 10-40 g of the pretreated molecular sieve prepared in step S1, stir for 0.5-3 h, and obtain mixture 1; S4-2, taking 2.5-10 g of the active microsphere modifier prepared in step S3, adding it to 50-200 mL of deionized water, and ultrasonically dispersing it for 30-90 min to obtain a mixture 2; S4-3. Add mixture 2 to mixture 1 under stirring, continue stirring for 1-4 hours, transfer the obtained mixture to a reactor, react at 120-160°C for 6-24 hours, cool to room temperature, centrifuge and filter, wash the solid product with deionized water and ethanol in turn, and dry at 90-115°C for 6-24 hours to obtain a modified ZSM-5 molecular sieve catalyst.

[0027] The present invention also provides an application of the above modified ZSM-5 molecular sieve catalyst in the selective catalytic cracking of heavy oil.

[0028] The present invention adopts active microsphere modifier and rare earth lanthanum doping to prepare a modified ZSM-5 molecular sieve catalyst that exhibits excellent catalytic ability in both heavy oil catalytic cracking and catalytic chloromethane coupling to prepare light olefins. When used for heavy oil catalytic cracking, the modified ZSM-5 molecular sieve catalyst can effectively improve the catalytic activity of the catalyst, promote the generation of free radicals, increase the yield of olefins, and inhibit the generation of aromatic hydrocarbons such as benzene and toluene; when used for catalytic chloromethane coupling to prepare light olefins, the modified ZSM-5 molecular sieve catalyst can improve the conversion rate of chloromethane and improve the selectivity of light olefins.

[0029] The present invention firstly uses alkali solution to pretreat the molecular sieve, then prepares a manganese-doped mesoporous ferroferric oxide microsphere by hydrothermal method, then loads ruthenium-doped carbon dots on the manganese-doped mesoporous ferroferric oxide microsphere in situ to obtain an active microsphere modifier; finally, the active microsphere modifier and rare earth lanthanum are co-grafted onto the pretreated molecular sieve to achieve the modification of ZSM-5 molecular sieve. In the modification process, the active microsphere modifier is a manganese-doped mesoporous ferroferric oxide microsphere with a large number of carbon dots connected to the surface, and La is added to the active microsphere modifier. 3+ On the one hand, it combines with the hydroxyl groups on the surface of the molecular sieve through coordination and / or electrostatic action, and on the other hand, it combines with the carboxyl, hydroxyl and other functional groups on the carbon dots through coordination, playing the role of intermediate bridge, so that the active microsphere modifier can be connected to the molecular sieve in large quantities and evenly. At the same time, the doping of rare earth lanthanum can greatly improve the selectivity of the catalyst for olefins and increase the yield of low-carbon rare earth.

[0030] Manganese doped mesoporous Fe3O4 microspheres synthesized based on transition metals can promote the generation of positive carbon ions in the catalytic thermal cracking reaction, and can also promote the generation of free radicals through oxidation-reduction. Free radicals can promote the production of olefins (Xie Chaogang, Wei Xiaoli, Gong Jianhong, et al. Research progress on the mechanism of catalytic cracking reaction and practical application [J]. Acta Petrolei Sinica (Petroleum Processing), 2017, 33(2):9. DOI:10.3969 / j.issn.1001-8719.2017.02.001.); manganese doping can improve the stability and catalytic activity of the microspheres; at the same time, the mesoporous structure of manganese doped mesoporous Fe3O4 microspheres can not only facilitate the loading of ruthenium doped carbon dots, but also increase the specific surface area and the number of active sites. Ruthenium-doped carbon dots can form a convex structure on manganese-doped mesoporous ferroferric oxide microspheres, further increasing the specific surface area and increasing the active sites. Ruthenium-doped carbon dots can promote the generation of free radicals during thermal cracking. The large amount of free radicals generated can promote the formation of olefins, thereby improving the selectivity and yield of olefins.

[0031] The above is the overall concept of the present invention, and detailed embodiments and comparative examples are provided below on the basis of the overall concept of the present invention to further illustrate the present invention.

[0032] HZSM-5 molecular sieve, SiO2 / Al2O3=40, D50:4μm, moisture 5wt%, Aos Catalytic Materials (Dalian) Co., Ltd.; Tannic acid, Jiangsu Jiujia Biotechnology Co., Ltd.; EDTA, Jiangsu Caiwei Biotechnology Co., Ltd.; Citric acid, Jiangsu Caiwei Biotechnology Co., Ltd.; La(NO3)3·6H2O, Shandong Desheng New Materials Co., Ltd.

[0033] Example 1 A method for preparing a modified ZSM-5 molecular sieve catalyst comprises the following steps: S1. Molecular sieve pretreatment: Take 10g HZSM-5 molecular sieve (SiO2 / Al2O3=40) and add it to 100mL of 0.15mol / L sodium hydroxide solution. After ultrasonic dispersion for 30min, stir for 3h and centrifuge. The solid product is washed with deionized water and ethanol in turn, and then vacuum dried at 100℃ for 12 to obtain the pretreated molecular sieve.

[0034] S2. Preparation of manganese-doped mesoporous ferroferric oxide microspheres: Take 1.352g FeCl3·6H2O, 0.396g MnCl2·4H2O, 4.15g sodium acetate, and 0.25g sodium hydroxide and add them to 20mL ethylene glycol, then add 1.4mL ethylenediamine and stir evenly. The resulting mixture is transferred to a reactor, reacted at 170°C for 8h, cooled to room temperature, filtered, and the product solid is washed with deionized water and vacuum dried at 90°C for 12h to obtain manganese-doped mesoporous ferrosoferric oxide microspheres.

[0035] S3, modifying ruthenium-doped carbon dots on manganese-doped ferroferric oxide microspheres to obtain an active microsphere modifier: S3-1, take 2g of manganese-doped mesoporous ferroferric oxide microspheres and 50mL of ethanol, add them into 100mL of deionized water, and ultrasonically disperse for 30min to obtain precursor solution A; S3-2, add 338 mg of tannic acid, 584 mg of ethylenediaminetetraacetic acid, 768 mg of citric acid, and 207 mg of RuCl3·3H2O into 50 mL of deionized water, and disperse by ultrasonic for 15 min to obtain precursor solution B; S3-3. Add precursor solution B to precursor solution A under stirring, continue stirring for 30 minutes, then transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 190°C for 6 hours, cool to room temperature and centrifuge, wash the solid product with ethanol and deionized water in turn, and vacuum dry at 95°C for 12 hours to obtain an active microsphere modifier.

[0036] S4, modifying the molecular sieve pretreated in step S1 with an active microsphere modifier to obtain a modified ZSM-5 molecular sieve catalyst: S4-1, take 3.76g La(NO3)3·6H2O and add it into 150mL deionized water, stir for 10min, then add 20g pretreated molecular sieve prepared in step S1, stir for 1h, and obtain mixture 1; S4-2, taking 5 g of the active microsphere modifier prepared in step S3, adding it to 100 mL of deionized water, and ultrasonically dispersing it for 45 min to obtain a mixture 2; S4-3. Add mixture 2 to mixture 1 under stirring, continue stirring for 2 hours, transfer the obtained mixture to a reactor, react at 145°C for 12 hours, cool to room temperature, centrifuge and filter, wash the solid product with deionized water and ethanol in turn, and dry at 100°C for 12 hours to obtain a modified ZSM-5 molecular sieve catalyst.

[0037] Example 2 A method for preparing a modified ZSM-5 molecular sieve catalyst comprises the following steps: S1. Molecular sieve pretreatment: Take 10g HZSM-5 molecular sieve (SiO2 / Al2O3=40) and add it to 100mL of 0.15mol / L sodium hydroxide solution. After ultrasonic dispersion for 30min, stir for 3h and centrifuge. The solid product is washed with deionized water and ethanol in turn, and then vacuum dried at 100℃ for 12 to obtain the pretreated molecular sieve.

[0038] S2. Preparation of manganese-doped mesoporous ferroferric oxide microspheres: Take 1.352g FeCl3·6H2O, 0.396g MnCl2·4H2O, 4.15g sodium acetate, and 0.25g sodium hydroxide and add them to 20mL ethylene glycol, then add 1.4mL ethylenediamine and stir evenly. The resulting mixture is transferred to a reactor, reacted at 170°C for 8h, cooled to room temperature, filtered, and the product solid is washed with deionized water and vacuum dried at 90°C for 12h to obtain manganese-doped mesoporous ferrosoferric oxide microspheres.

[0039] S3, modifying ruthenium-doped carbon dots on manganese-doped ferroferric oxide microspheres to obtain an active microsphere modifier: S3-1, take 2g of manganese-doped mesoporous ferroferric oxide microspheres and 50mL of ethanol, add them into 100mL of deionized water, and ultrasonically disperse for 30min to obtain precursor solution A; S3-2, add 338 mg of tannic acid, 584 mg of ethylenediaminetetraacetic acid, 768 mg of citric acid, and 310.5 mg of RuCl3·3H2O into 50 mL of deionized water, and ultrasonically disperse for 15 min to obtain precursor solution B; S3-3. Add precursor solution B to precursor solution A under stirring, continue stirring for 30 minutes, then transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 190°C for 6 hours, cool to room temperature and centrifuge, wash the solid product with ethanol and deionized water in turn, and vacuum dry at 95°C for 12 hours to obtain an active microsphere modifier.

[0040] S4, modifying the molecular sieve pretreated in step S1 with an active microsphere modifier to obtain a modified ZSM-5 molecular sieve catalyst: S4-1, take 3.76g La(NO3)3·6H2O and add it into 150mL deionized water, stir for 10min, then add 20g pretreated molecular sieve prepared in step S1, stir for 1h, and obtain mixture 1; S4-2, taking 6 g of the active microsphere modifier prepared in step S3, adding it to 100 mL of deionized water, and ultrasonically dispersing it for 45 min to obtain a mixture 2; S4-3. Add mixture 2 to mixture 1 under stirring, continue stirring for 2 hours, transfer the obtained mixture to a reactor, react at 145°C for 12 hours, cool to room temperature, centrifuge and filter, wash the solid product with deionized water and ethanol in turn, and dry at 100°C for 12 hours to obtain a modified ZSM-5 molecular sieve catalyst.

[0041] Example 3 A method for preparing a modified ZSM-5 molecular sieve catalyst comprises the following steps: S1. Molecular sieve pretreatment: Take 10g HZSM-5 molecular sieve (SiO2 / Al2O3=40) and add it to 100mL of 0.2mol / L sodium hydroxide solution. After ultrasonic dispersion for 30min, stir for 3h and centrifuge. The solid product is washed with deionized water and ethanol in turn, and then vacuum dried at 100℃ for 12 to obtain the pretreated molecular sieve.

[0042] S2. Preparation of manganese-doped mesoporous ferroferric oxide microspheres: Take 1.352g FeCl3·6H2O, 0.396g MnCl2·4H2O, 4.15g sodium acetate, and 0.25g sodium hydroxide and add them to 20mL ethylene glycol, then add 1.4mL ethylenediamine and stir evenly. The resulting mixture is transferred to a reactor, reacted at 170°C for 8h, cooled to room temperature, filtered, and the product solid is washed with deionized water and vacuum dried at 90°C for 12h to obtain manganese-doped mesoporous ferrosoferric oxide microspheres.

[0043] S3, modifying ruthenium-doped carbon dots on manganese-doped ferroferric oxide microspheres to obtain an active microsphere modifier: S3-1, take 2.5g of manganese-doped mesoporous ferroferric oxide microspheres and 50mL of ethanol, add them into 100mL of deionized water, and ultrasonically disperse for 30min to obtain precursor solution A; S3-2, add 338 mg of tannic acid, 584 mg of ethylenediaminetetraacetic acid, 768 mg of citric acid, and 207 mg of RuCl3·3H2O into 50 mL of deionized water, and disperse by ultrasonic for 15 min to obtain precursor solution B; S3-3. Add precursor solution B to precursor solution A under stirring, continue stirring for 30 minutes, then transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 190°C for 6 hours, cool to room temperature and centrifuge, wash the solid product with ethanol and deionized water in turn, and vacuum dry at 95°C for 12 hours to obtain an active microsphere modifier.

[0044] S4, modifying the molecular sieve pretreated in step S1 with an active microsphere modifier to obtain a modified ZSM-5 molecular sieve catalyst: S4-1, take 3.76g La(NO3)3·6H2O and add it into 150mL deionized water, stir for 10min, then add 22g pretreated molecular sieve prepared in step S1, stir for 1.5h, and obtain mixture 1; S4-2, taking 5 g of the active microsphere modifier prepared in step S3, adding it to 100 mL of deionized water, and ultrasonically dispersing it for 45 min to obtain a mixture 2; S4-3. Add mixture 2 to mixture 1 under stirring, continue stirring for 2 hours, transfer the obtained mixture to a reactor, react at 140°C for 12 hours, cool to room temperature, centrifuge and filter, wash the solid product with deionized water and ethanol in turn, and dry at 100°C for 12 hours to obtain a modified ZSM-5 molecular sieve catalyst.

[0045] Comparative Example 1 A method for preparing a modified ZSM-5 molecular sieve catalyst comprises the following steps: S1. Molecular sieve pretreatment: Take 10g HZSM-5 molecular sieve (SiO2 / Al2O3=40) and add it to 100mL of 0.15mol / L sodium hydroxide solution. After ultrasonic dispersion for 30min, stir for 3h and centrifuge. The solid product is washed with deionized water and ethanol in turn, and then vacuum dried at 100℃ for 12 to obtain the pretreated molecular sieve.

[0046] S2. Take 3.76 g of La(NO3)3·6H2O and add it to 150 mL of deionized water. After stirring for 10 min, add 20 g of the pretreated molecular sieve prepared in step S1 and stir for 1 h to obtain a mixture. The obtained mixture is transferred to a reactor, reacted at 145° C. for 12 h, cooled to room temperature, and centrifuged. The solid product is washed with deionized water and ethanol in sequence, and dried at 100° C. for 12 h to obtain a modified ZSM-5 molecular sieve catalyst.

[0047] Comparative Example 2 A method for preparing a modified ZSM-5 molecular sieve catalyst comprises the following steps: S1. Molecular sieve pretreatment: Take 10g HZSM-5 molecular sieve (SiO2 / Al2O3=40) and add it to 100mL of 0.15mol / L sodium hydroxide solution. After ultrasonic dispersion for 30min, stir for 3h and centrifuge. The solid product is washed with deionized water and ethanol in turn, and then vacuum dried at 100℃ for 12 to obtain the pretreated molecular sieve.

[0048] S2. Preparation of manganese-doped mesoporous ferroferric oxide microspheres: Take 1.352g FeCl3·6H2O, 0.396g MnCl2·4H2O, 4.15g sodium acetate, and 0.25g sodium hydroxide and add them to 20mL ethylene glycol, then add 1.4mL ethylenediamine and stir evenly. The resulting mixture is transferred to a reactor, reacted at 170°C for 8h, cooled to room temperature, filtered, and the product solid is washed with deionized water and vacuum dried at 90°C for 12h to obtain manganese-doped mesoporous ferrosoferric oxide microspheres.

[0049] S3, modifying the molecular sieve pretreated in step S1 with manganese-doped mesoporous ferrosoferric oxide microspheres to obtain a modified ZSM-5 molecular sieve catalyst: S4-1, take 3.76g La(NO3)3·6H2O and add it into 150mL deionized water, stir for 10min, then add 20g pretreated molecular sieve prepared in step S1, stir for 1h, and obtain mixture 1; S4-2, taking 5 g of the manganese-doped mesoporous ferroferric oxide microspheres prepared in step S2, adding them to 100 mL of deionized water, and ultrasonically dispersing them for 45 min to obtain a mixture 2; S4-3. Add mixture 2 to mixture 1 under stirring, continue stirring for 2 hours, transfer the obtained mixture to a reactor, react at 145°C for 12 hours, cool to room temperature, centrifuge and filter, wash the solid product with deionized water and ethanol in turn, and dry at 100°C for 12 hours to obtain a modified ZSM-5 molecular sieve catalyst.

[0050] Performance Testing: 1. Heavy oil catalytic cracking performance test Using Daqing heavy oil as raw material, catalytic cracking experiments were carried out in a micro fixed bed reactor. The catalyst reaction conditions were: reaction temperature of 520°C, 1.5 g of reaction raw material was added within 60 s, the catalyst loading was 3.5 g, and the mass space velocity was 12 h -1 The product was analyzed by chromatography. The test results are shown in Table 1 below: Table 1 It can be seen from the test results that compared with Comparative Examples 1 and 2, the conversion rate of light olefins in Examples 1-3 is significantly improved.

[0051] 2. Performance test of catalytic chloromethane coupling to prepare light olefins This experiment was carried out in a three-stage temperature-controlled fixed-bed glass reaction tube. The modified ZSM-5 molecular sieve catalyst prepared in the embodiment and the comparative example was used to catalyze methyl chloride to prepare light olefins. The modified ZSM-5 molecular sieve catalyst was loaded into the fixed-bed reaction tube. The reaction raw material methyl chloride was diluted with nitrogen and then entered the reaction tube. The reaction conditions were: reaction temperature 400°C, pressure 0.5MPa, and methyl chloride mass space velocity 4h-1 , the volume flow ratio of methyl chloride to nitrogen is 1:5, and the reaction product is analyzed by Agilent 8860 GC gas chromatograph. The test results are shown in Table 2 below: Table 2 It can be seen from the test results that, compared with Comparative Example 1-2, the conversion rate of methyl chloride in Example 1-3 is improved, and the selectivity of low-carbon olefins is significantly improved.

[0052] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for preparing a modified ZSM-5 molecular sieve catalyst, characterized in that: The following steps are involved: S1, molecular sieve pretreatment; S2, preparing manganese-doped mesoporous ferroferric oxide microspheres; S3, modifying ruthenium-doped carbon dots on manganese-doped ferroferric oxide microspheres to obtain an active microsphere modifier; S4, modifying the molecular sieve pretreated in step S1 with an active microsphere modifier to obtain a modified ZSM-5 molecular sieve catalyst.

2. The method for preparing the modified ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: Step S1 specifically includes: Take 5-20g HZSM-5 molecular sieve and add it to 50-200mL sodium hydroxide solution with a concentration of 0.1-0.3mol / L, disperse it ultrasonically for 15-60min, stir it for 1.5-6h, centrifuge it, wash the solid product with deionized water and ethanol in sequence, and then vacuum dry it at 80-120℃ for 6-24 to obtain the pretreated molecular sieve.

3. The method for preparing the modified ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: Step S2 specifically includes: FeCl3·6H2O, MnCl2·4H2O, sodium acetate and sodium hydroxide were added to ethylene glycol, and then ethylenediamine was added and stirred evenly. The obtained mixture was transferred to a reactor, reacted under heating, cooled to room temperature, filtered, and the product solid was washed with deionized water and vacuum dried to obtain manganese-doped mesoporous ferrosoferric oxide microspheres.

4. The method for preparing the modified ZSM-5 molecular sieve catalyst according to claim 3, characterized in that: Step S2 specifically includes: Take 0.376-2.704g FeCl3·6H2O, 0.198-0.792g MnCl2·4H2O, 2.05-8.25g sodium acetate, and 0.125-0.5g sodium hydroxide and add them to 10-40mL ethylene glycol, then add 0.7-2.8mL ethylenediamine and stir evenly. Transfer the resulting mixture to a reactor, react at 150-185°C for 4-16h, cool to room temperature, filter, wash the product solid with deionized water, and vacuum dry at 80-110°C for 6-24h to obtain manganese-doped mesoporous ferrosoferric oxide microspheres.

5. The method for preparing the modified ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: Step S3 specifically includes: S3-1, adding the manganese-doped mesoporous ferroferric oxide microspheres prepared in step S2 and ethanol into deionized water, and performing ultrasonic dispersion to obtain a precursor solution A; S3-2, add tannic acid, ethylenediaminetetraacetic acid, citric acid, and RuCl3·3H2O into deionized water, and disperse by ultrasonic to obtain precursor solution B; S3-3. Add precursor solution B to precursor solution A under stirring, continue stirring and then transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, heat and react. After the reaction is completed, cool to room temperature and centrifuge. Wash the solid product with ethanol and deionized water in turn, and vacuum dry to obtain an active microsphere modifier.

6. The method for preparing the modified ZSM-5 molecular sieve catalyst according to claim 5, characterized in that: Step S3 specifically includes: S3-1, take 1-4 g of the manganese-doped mesoporous ferroferric oxide microspheres prepared in step S2 and add 25-100 mL of ethanol to 50-200 mL of deionized water, and ultrasonically disperse for 15-60 min to obtain a precursor solution A; S3-2, add 169-676 mg of tannic acid, 292-1168 mg of ethylenediaminetetraacetic acid, 384-1536 mg of citric acid, and 103.5-414 mg of RuCl3·3H2O into 25-100 mL of deionized water, and disperse by ultrasonic for 5-30 min to obtain precursor solution B; S3-3. Add precursor solution B to precursor solution A under stirring, continue stirring for 15-60 minutes, then transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 170-210°C for 3-12 hours, cool to room temperature and centrifuge, wash the solid product with ethanol and deionized water in turn, and vacuum dry at 85-100°C for 6-24 hours to obtain an active microsphere modifier.

7. The method for preparing the modified ZSM-5 molecular sieve catalyst according to claim 1, characterized in that: Step S4 specifically includes: S4-1, add La(NO3)3·6H2O to deionized water, stir, then add the pretreated molecular sieve prepared in step S1, stir, and obtain mixture 1; S4-2, adding the active microsphere modifier prepared in step S3 into deionized water, and performing ultrasonic dispersion to obtain a mixture 2; S4-3. Add mixture 2 to mixture 1 under stirring, continue stirring, transfer the obtained mixture to a reactor, react under heating, cool to room temperature after the reaction is completed, centrifuge and filter, wash the solid product with deionized water and ethanol in turn, and dry to obtain a modified ZSM-5 molecular sieve catalyst.

8. The method for preparing the modified ZSM-5 molecular sieve catalyst according to claim 7, characterized in that: Step S4 specifically includes: S4-1, add 1.88-7.52 g La(NO3)3·6H2O to 75-300 mL deionized water, stir for 5-20 min, then add 10-40 g of the pretreated molecular sieve prepared in step S1, stir for 0.5-3 h, and obtain mixture 1; S4-2, taking 2.5-10 g of the active microsphere modifier prepared in step S3, adding it to 50-200 mL of deionized water, and ultrasonically dispersing it for 30-90 min to obtain a mixture 2; S4-3. Add mixture 2 to mixture 1 under stirring, continue stirring for 1-4 hours, transfer the obtained mixture to a reactor, react at 120-160°C for 6-24 hours, cool to room temperature, centrifuge and filter, wash the solid product with deionized water and ethanol in turn, and dry at 90-115°C for 6-24 hours to obtain a modified ZSM-5 molecular sieve catalyst.

9. A modified ZSM-5 molecular sieve catalyst, characterized in that: It is prepared by the method according to any one of claims 1 to 8.

10. Use of the modified ZSM-5 molecular sieve catalyst as claimed in claim 9 in the selective catalytic cracking of heavy oil or the catalytic methyl chloride coupling to prepare light olefins.

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