Post-modified molecular sieve catalyst applied to naphtha catalytic cracking as well as preparation method and application of post-modified molecular sieve catalyst

Abstract

The invention belongs to the technical field of preparation of low-carbon olefins, and relates to a post-modified molecular sieve catalyst applied to naphtha catalytic cracking and a preparation method of the post-modified molecular sieve catalyst. The modified molecular sieve catalyst comprises a modified molecular sieve catalyst, wherein the modified molecular sieve catalyst comprises a carrier, and a phosphorus element and a lanthanum element which are loaded on the carrier; wherein the carrier comprises an alkali treatment modified HZSM-5 molecular sieve, a water vapor treatment modified HBeta molecular sieve and an aluminum oxide binder. Compared with an unmodified molecular sieve, the method has the advantages that the phosphorus-lanthanum loaded post-treatment modified molecular sieve is used as the catalyst, so that the yield of low-carbon olefins is obviously improved. The preparation method of the catalyst disclosed by the invention is simpler, controllable and lower in cost, and has extremely high popularization and application values.

Description

Technical Field

[0001] The invention belongs to the technical field of preparing low-carbon olefins, and in particular relates to a post-modified molecular sieve catalyst used for catalytic cracking of naphtha, and a preparation method and application thereof. Background Art

[0002] Low-carbon olefins include ethylene, propylene and butene, which are important organic chemicals and are widely used in the fields of chemical industry, medicine, materials, etc. The industrial production of low-carbon olefins mainly relies on tubular furnace steam cracking, and the reaction needs to be carried out at a temperature above 800°C, which consumes a lot of energy. Catalytic cracking to produce olefins can overcome the above shortcomings. The catalytic cracking temperature is 100-200°C lower than that of steam cracking, and the energy consumption is greatly reduced.

[0003] CN104549410 A provides a catalyst for producing propylene by catalytic cracking of naphtha, a preparation method thereof, and a method for producing propylene by catalytic cracking of naphtha. The catalyst contains 50-95% by weight of a molecular sieve and 5-50% by weight of a matrix, wherein the molecular sieve includes a first molecular sieve and a second molecular sieve, the first molecular sieve is a molecular sieve with an MWW structure, and the second molecular sieve is a zeolite and / or a non-zeolite molecular sieve with a twelve-membered ring channel.

[0004] CN114425417A provides a naphtha catalytic cracking catalyst and its preparation method and application. The catalyst contains 50-85% by weight of a carrier and 15-50% by weight of a core-shell molecular sieve. The ratio of the peak height of 2θ=22.4° to the peak height of 2θ=23.1° in the X-ray diffraction spectrum of the core-shell molecular sieve is 0.110:1, and the total specific surface area is greater than 420m 2 / g.

[0005] Researching and developing new and efficient catalysts suitable for the catalytic cracking of naphtha can increase the yield of low-carbon olefins and reduce energy consumption in the reaction process, which is of great significance for improving the economic benefits of petrochemical and oil companies. Summary of the invention

[0006] The main technical problem solved by the present invention is to provide a post-modified molecular sieve catalyst for catalytic cracking of naphtha and a preparation method thereof. The present invention adopts two specific molecular sieves including an alumina binder and post-treated in a specific manner as carriers, loads phosphorus elements and lanthanum elements, and obtains a new type of modified molecular sieve catalyst. The modified molecular sieve catalyst of the present invention significantly improves the yield of light olefins compared to the catalyst obtained by the molecular sieve that is not loaded with the above elements or is not modified by the method of the present invention. The catalyst preparation method of the present invention is simple and controllable, the raw materials are easily available, and it has extremely high application value.

[0007] The first aspect of the present invention is to provide a modified molecular sieve catalyst, the modified molecular sieve catalyst comprising: a carrier and phosphorus and lanthanum elements carried on the carrier;

[0008] The carrier comprises an alkali-treated modified HZSM-5 molecular sieve, a steam-treated modified HBeta molecular sieve and an alumina binder.

[0009] In a preferred embodiment of the present invention, based on the total weight of the carrier as 100wt%, the content of the alkali-treated modified HZSM-5 molecular sieve is 15-50wt%, preferably 35-45wt%, the content of the steam-treated modified HBeta molecular sieve is 15-35wt%, preferably 20-30wt%, and the content of the alumina binder is 15-50wt%, preferably 30-40wt%.

[0010] In a preferred embodiment of the present invention, the silicon-to-aluminum ratio of the carrier is 30-250; more preferably,

[0011] The silicon-aluminum ratio of the HZSM-5 molecular sieve modified by alkali treatment is 80-200, and / or the silicon-aluminum ratio of the HBeta molecular sieve modified by steam treatment is 50-120.

[0012] In a preferred embodiment of the present invention, the alkali-treated modified HZSM-5 molecular sieve is prepared by the following method:

[0013] The NaZSM-5 molecular sieve is mixed with an alkali solution, and the obtained powder is subjected to ammonium exchange and then calcined to obtain the alkali-treated modified HZSM-5 molecular sieve; more preferably:

[0014] The NaZSM-5 molecular sieve and the alkali solution are mixed at 50-90° C. for 1-4 hours; and / or the mass ratio of the NaZSM-5 molecular sieve to the alkali solution is 1:(15-40), and / or the alkali solution is selected from at least one of a NaOH solution and a potassium hydroxide solution; and / or the concentration of the alkali solution is 0.2-0.8 mol / L.

[0015] Preferably, the calcination conditions include: calcination at 450-650° C. for 2-8 hours.

[0016] As an example, in a more preferred embodiment of the present invention, in the present invention, the alkali treatment procedure of HZSM-5 is: pouring NaZSM-5 powder into NaOH solution and stirring at 50-90°C for 1-4 hours, the mass ratio of NaZSM-5 to NaOH solution is 1:15-1:40, and the molar concentration of NaOH solution is 0.2-0.8 mol / L. The obtained powder is ammonium exchanged and calcined at 450-650°C for 2-8h to obtain alkali-treated modified HZSM-5.

[0017] The ammonium exchange method in the present invention belongs to conventional experimental methods, and the ammonium ion compound is selected from ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium oxalate or ammonium acetate, which can realize the present invention.

[0018] In a preferred embodiment of the present invention, the steam-treated modified HBeta molecular sieve is prepared by treating the HBeta molecular sieve with steam at 450-650° C. for 2-4 hours.

[0019] In a preferred embodiment of the present invention, the carrier is obtained by kneading raw materials including alkali-treated modified HZSM-5 molecular sieve, steam-treated modified HBeta molecular sieve and alumina binder with sesbania powder and nitric acid solution.

[0020] According to the present invention, preferably, HZSM-5 modified by alkali treatment, HBeta modified by steam treatment and alumina binder powder are poured into a kneader, and sesbania powder and nitric acid solution are added and kneaded to obtain a modified molecular sieve catalyst carrier. Among them, the weight proportion of HZSM-5 modified by alkali treatment is 15-50%, preferably 35-45%, the weight proportion of HBeta modified by steam treatment is 15-35%, preferably 20-30%, and the weight proportion of alumina binder is 15-50%, preferably 30-40%.

[0021] The amount of sesbania powder used in the present invention belongs to the conventional molding technology in the field, and those skilled in the art can flexibly select it.

[0022] The dosage and concentration of the nitric acid solution in the present invention belong to conventional technical means formed in the field, and those skilled in the art can flexibly select them.

[0023] In a preferred embodiment of the present invention, in the modified molecular sieve catalyst, the mass ratio of phosphorus element to the carrier is (0.5-4):100, preferably (1-2):100, and the mass ratio of lanthanum element to the carrier is (0.1-2):100, preferably (0.2-1.1):100; preferably, the carrier is measured by the total mass of HZSM-5 modified by alkali treatment, HBeta modified by steam treatment and alumina binder.

[0024] The second aspect of the present invention is to provide a method for preparing the modified molecular sieve catalyst described in the first aspect, comprising loading a phosphorus precursor and a lanthanum precursor on the carrier, optionally drying, and then calcining to obtain the modified molecular sieve catalyst.

[0025] According to the present invention, the loading method can be selected in a wide range. In a preferred embodiment of the present invention, the loading method is an ion exchange method or an impregnation method.

[0026] According to the present invention, the roasting conditions can be selected within a wide range. In a preferred embodiment of the present invention, the roasting conditions include: a roasting temperature of 450-650° C., and / or a roasting time of 2-6 hours.

[0027] According to the present invention, the phosphorus precursor can be selected from a wide range. In a preferred embodiment of the present invention, the phosphorus precursor is selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and ammonium phosphate.

[0028] According to the present invention, the lanthanum precursor can be selected from a wide range. In a preferred embodiment of the present invention, the lanthanum precursor is selected from at least one of nitrate, sulfate, chloride and acetate of lanthanum.

[0029] According to the present invention, the amount of the phosphorus precursor and the amount of the lanthanum precursor can be selected within a wide range. In a preferred embodiment of the present invention, the mass ratio of the phosphorus element to the carrier is (0.5-4):100, preferably (1-2):100, and the amount of the lanthanum precursor is such that the mass ratio of the lanthanum element to the carrier is (0.1-2):100, preferably (0.2-1.1):100; preferably, the carrier is based on the total mass of the alkali-treated modified HZSM-5, the steam-treated modified HBeta and the alumina binder.

[0030] In a more preferred embodiment of the present invention, the loading methods are independently ion exchange or equal volume impregnation, and the final catalyst is obtained by drying and calcining after loading, and the calcination temperature is 450-650°C and the calcination time is 2-6h.

[0031] The third aspect of the present invention is to provide the use of the modified molecular sieve catalyst described in the first aspect or the modified molecular sieve catalyst prepared by the preparation method described in the second aspect in the catalytic cracking of naphtha.

[0032] The fourth aspect of the present invention is to provide a method for catalytic cracking of naphtha, comprising contacting naphtha with a catalyst to catalyze a cracking reaction of the naphtha, preferably to obtain ethylene and / or propylene, wherein:

[0033] The catalyst is the modified molecular sieve catalyst described in the first aspect or the modified molecular sieve catalyst prepared by the preparation method described in the second aspect.

[0034] In a preferred embodiment of the present invention, the temperature of the pyrolysis reaction is 500-800°C, and / or the mass space velocity is 4-15h -1 .

[0035] The present invention has the following advantages:

[0036] (1) The present invention uses a post-treated modified molecular sieve catalyst as a carrier, which includes HZSM-5 modified by alkali treatment, HBeta modified by steam treatment and an alumina binder. Compared with unmodified molecular sieves HZSM-5 and HBeta, the yield of light olefins is significantly improved.

[0037] (2) The present invention uses a phosphorus lanthanum metal-supported catalyst, which significantly improves the yield of light olefins compared to a carrier without a metal catalyst.

[0038] (3) The present invention adopts a post-treatment method for the existing specific molecular sieve, combined with the loading of phosphorus lanthanum, and the resulting catalyst preparation method is simpler and has lower cost.

[0039] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0040] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0041] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0042] In the following examples, the raw material used for the catalytic reaction is naphtha, wherein, in terms of mass percentage, the naphtha contains:

[0043] n-Decane: 55%

[0044] Isooctane: 25%

[0045] Methylcyclohexane: 15%

[0046] Benzene: 5%.

[0047] In the following examples, the contents of ethylene and propylene in the products were detected by gas chromatography;

[0048] The calculation method of ethylene yield is: product ethylene mass / raw material mass*100%

[0049] The calculation method of propylene yield is: product propylene mass / raw material mass*100%.

[0050] The raw materials in the following examples of the present invention, unless otherwise specified, are conventional commercially available products.

[0051] Example 1

[0052] NaZSM-5 powder with a silicon-aluminum ratio of 150 was poured into a NaOH solution and stirred at 80°C for 2 hours. The mass ratio of NaZSM-5 to NaOH solution was 1:30, and the molar concentration of the NaOH solution was 0.5 mol / L. The obtained powder was ammonium exchanged and calcined at 500°C for 4 hours to obtain alkali-treated modified HZSM-5.

[0053] The HBeta molecular sieve with a silicon-aluminum ratio of 100 was treated with steam at 550°C for 3 hours to obtain the steam-treated modified HBeta.

[0054] 40 g of alkali-treated modified HZSM-5, 20 g of steam-treated modified HBeta and 40 g of alumina binder powder were poured into a kneader, and appropriate amounts of sesbania powder and nitric acid solution were added, and kneaded to obtain a modified molecular sieve catalyst carrier.

[0055] The phosphorus element was loaded on the above-mentioned carrier by an ion exchange method using diammonium hydrogen phosphate as a precursor, and the mass ratio of the phosphorus element to the molecular sieve catalyst carrier was 1.5:100. Subsequently, the lanthanum element was loaded by an ion exchange method using lanthanum nitrate as a precursor, and the mass ratio of the lanthanum element to the molecular sieve catalyst carrier was 0.3:100. The catalyst was then dried and calcined at 550°C for 3 hours to obtain a finished catalyst.

[0056] The reaction conditions are as follows: 5 g of the modified molecular sieve catalyst is loaded into a fixed bed reactor, the raw material is naphtha, the reaction temperature is 650°C, the reaction pressure is 0.1 MPa, and the mass space velocity is 10 h -1 The reaction results and main product yields are shown in Table 1.

[0057] Example 2

[0058] Pour NaZSM-5 powder with a silicon-aluminum ratio of 80 into NaOH solution and stir for 2 hours at 70°C. The mass ratio of NaZSM-5 to NaOH solution is 1:35, and the molar concentration of NaOH solution is 0.2 mol / L. The obtained powder is ammonium exchanged and calcined at 550°C for 2h to obtain alkali-treated modified HZSM-5. HBeta molecular sieve with a silicon-aluminum ratio of 50 is treated with steam at 500°C for 2 hours to obtain steam-treated modified HBeta. 45g of alkali-treated modified HZSM-5, 25g of steam-treated modified HBeta and 30g of alumina binder powder are poured into a kneader, and an appropriate amount of sesbania powder and nitric acid solution are added, and kneaded to obtain a modified molecular sieve catalyst carrier. The phosphorus element was loaded on the above-mentioned carrier by an ion exchange method using diammonium hydrogen phosphate as a precursor, and the mass ratio of the phosphorus element to the molecular sieve catalyst carrier was 1.8:100. Subsequently, the lanthanum element was loaded by an ion exchange method using lanthanum nitrate as a precursor, and the mass ratio of the element to the molecular sieve catalyst carrier was 0.5:100. The catalyst was then dried and calcined at 550°C for 3 hours to obtain a finished catalyst.

[0059] The reaction conditions are as follows: 5 g of the modified molecular sieve catalyst is loaded into the fixed bed reactor, the reaction temperature is 620°C, the reaction pressure is 0.1 MPa, and the space velocity is 6 h -1 The reaction results and main product yields are shown in Table 1.

[0060] Example 3

[0061] Pour NaZSM-5 powder with a silicon-aluminum ratio of 250 into NaOH solution and stir for 2 hours at 50°C. The mass ratio of NaZSM-5 to NaOH solution is 1:15, and the molar concentration of NaOH solution is 0.8 mol / L. The obtained powder is ammonium exchanged and calcined at 550°C for 6 hours to obtain alkali-treated modified HZSM-5. HBeta molecular sieve with a silicon-aluminum ratio of 250 is treated with steam at 500°C for 3 hours to obtain steam-treated modified HBeta. 50g of alkali-treated modified HZSM-5, 15g of steam-treated modified HBeta and 35g of alumina binder powder are poured into a kneader, and an appropriate amount of sesbania powder and nitric acid solution are added, and kneaded to obtain a modified molecular sieve catalyst carrier. The phosphorus element was loaded on the above-mentioned carrier using diammonium hydrogen phosphate as a precursor by an equal volume impregnation method, and the mass ratio of the phosphorus element to the molecular sieve catalyst carrier was 3.2:100. Subsequently, the lanthanum element was loaded by an ion exchange method using lanthanum nitrate as a precursor, and the mass ratio of the element to the molecular sieve catalyst carrier was 1.8:100. The catalyst was then dried and calcined at 550°C for 3 hours to obtain a finished catalyst.

[0062] The reaction conditions are as follows: 5 g of the modified molecular sieve catalyst is loaded into the fixed bed reactor, the reaction temperature is 650°C, the reaction pressure is 0.1 MPa, and the space velocity is 12 h -1The reaction results and main product yields are shown in Table 1.

[0063] Example 4

[0064] Pour NaZSM-5 powder with a silicon-aluminum ratio of 30 into NaOH solution and stir for 3 hours at 80°C. The mass ratio of NaZSM-5 to NaOH solution is 1:25, and the molar concentration of NaOH solution is 0.8 mol / L. The obtained powder is ammonium exchanged and calcined at 550°C for 6 hours to obtain alkali-treated modified HZSM-5. HBeta molecular sieve with a silicon-aluminum ratio of 30 is treated with steam at 500°C for 2 hours to obtain steam-treated modified HBeta. 50g of alkali-treated modified HZSM-5, 15g of steam-treated modified HBeta and 35g of alumina binder powder are poured into a kneader, and an appropriate amount of sesbania powder and nitric acid solution are added, and kneaded to obtain a modified molecular sieve catalyst carrier. The phosphorus element was loaded on the above-mentioned carrier by an equal volume impregnation method using diammonium hydrogen phosphate as a precursor, and the mass ratio of the phosphorus element to the molecular sieve catalyst carrier was 3.2:100. Subsequently, the lanthanum element was loaded by an ion exchange method using lanthanum nitrate as a precursor, and the mass ratio of the lanthanum element to the molecular sieve catalyst carrier was 1.8:100. The catalyst was then dried and calcined at 550°C for 3 hours to obtain a finished catalyst.

[0065] The reaction conditions are as follows: 5 g of the modified molecular sieve catalyst is loaded into the fixed bed reactor, the reaction temperature is 650°C, the reaction pressure is 0.1 MPa, and the space velocity is 12 h -1 The reaction results and main product yields are shown in Table 1.

[0066] Example 5

[0067] The modified molecular sieve catalyst was prepared according to the method of Example 1, except that the silicon-aluminum ratio of NaZSM-5 was changed to 50, and the silicon-aluminum ratio of Hbeta was changed to 40. The rest of the preparation method and catalytic reaction conditions were the same as those of Example 2.

[0068] Example 6

[0069] The modified molecular sieve catalyst was prepared according to the method of Example 1, except that the mass ratio of phosphorus element to molecular sieve catalyst carrier was changed to 4:100. The rest of the preparation method and catalytic reaction conditions were the same as those of Example 2.

[0070] Comparative Example 1

[0071] The reaction conditions and phosphorus lanthanum element loading conditions used in this comparative example are exactly the same as those in Example 1, except that the catalyst carrier used is an unmodified HZSM-5 molecular sieve with a silicon-aluminum ratio of 150. The reaction results and main product yields are shown in Table 1.

[0072] Comparative Example 2

[0073] The reaction conditions used in this comparative example are exactly the same as those in Example 1, except that the catalyst used is the molecular sieve catalyst carrier prepared in Example 1 without the phosphorus lanthanum element loading. The reaction results and the yields of the main products are shown in Table 1.

[0074] Comparative Example 3

[0075] The reaction conditions used in this comparative example are exactly the same as those in Example 1, except that the Hbeta molecular sieve is not modified. The reaction results and the yields of the main products are shown in Table 1.

[0076] Table 1 Test results

[0077]

[0078] It can be seen from Table 1 that, compared with Comparative Example 1, Comparative Example 2, and Comparative Example 3, the yield of light olefins in Examples 1-6 is significantly improved.

[0079] The catalyst in the present invention is a novel naphtha catalytic cracking catalyst. In terms of preparation method, it can be prepared by post-treating an existing specific molecular sieve model and then combining it with loaded lanthanum phosphorus. The catalyst preparation method is simpler, controllable, and has lower cost, and has extremely high promotion and application value.

[0080] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0081] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0082] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

[0083] All publications, patent applications, patents and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings conventionally understood by those skilled in the art. In the event of a conflict, the definition in this specification shall prevail.

[0084] When this specification uses the prefix "well-known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, etc., the objects introduced by the prefix cover those commonly used in the art when this application is filed, but also include those that are not commonly used at present but will become recognized in the art as being suitable for similar purposes.

[0085] The endpoints and any values ​​of the scope disclosed in the present application document are not limited to the precise scope or value, and these scopes or values ​​should be understood to include values ​​close to these scopes or values. For numerical ranges, between the endpoint values ​​of each scope, between the endpoint values ​​of each scope and a separate point value, and between separate point values, one or more new numerical ranges can be combined with each other, and these numerical ranges should be considered as specifically disclosed in this article. Hereinafter, in principle, each technical solution can be combined with each other to obtain a new technical solution, which should also be considered as specifically disclosed in this article.

[0086] In the context of the present specification, any matters or items not mentioned are directly applicable to those known in the art without any changes except those explicitly stated.

[0087] Moreover, any embodiment described in this document may be freely combined with one or more other embodiments described in this document, and the technical solutions or technical ideas formed thereby are deemed to be part of the original disclosure or original record of the present invention, and should not be regarded as new content that has not been disclosed or anticipated in this document, unless a person skilled in the art considers that the combination is obviously unreasonable.

Claims

1. A modified molecular sieve catalyst, comprising: A carrier and phosphorus and lanthanum elements carried on the carrier; The carrier comprises an alkali-treated modified HZSM-5 molecular sieve, a steam-treated modified HBeta molecular sieve and an alumina binder.

2. The modified molecular sieve catalyst according to claim 1, characterized in that: Based on the total weight of the carrier as 100wt%, the content of the alkali-treated modified HZSM-5 molecular sieve is 15-50wt%, preferably 35-45wt%, the content of the steam-treated modified HBeta molecular sieve is 15-35wt%, preferably 20-30wt%, and the content of the alumina binder is 15-50wt%, preferably 30-40wt%.

3. The modified molecular sieve catalyst according to claim 1, characterized in that: The silicon-to-aluminum ratio of the carrier is 30-250; preferably: The silicon-aluminum ratio of the HZSM-5 molecular sieve modified by alkali treatment is 80-200, and / or the silicon-aluminum ratio of the HBeta molecular sieve modified by steam treatment is 50-120.

4. The modified molecular sieve catalyst according to claim 1, characterized in that: The alkali-treated modified HZSM-5 molecular sieve is prepared by the following method: The NaZSM-5 molecular sieve is mixed with an alkali solution, and the obtained powder is subjected to ammonium exchange and then calcined to obtain the alkali-treated modified HZSM-5 molecular sieve; preferably, Mixing NaZSM-5 molecular sieve and alkali solution at 50-90° C. for 1-4 hours; and / or, the mass ratio of NaZSM-5 molecular sieve to alkali solution is 1:(15-40), and / or, the alkali solution is selected from at least one of NaOH solution and potassium hydroxide solution; and / or, The concentration of the alkali solution is 0.2-0.8 mol / L; and / or, The calcination conditions include: calcination at 450-650° C. for 2-8 hours.

5. The modified molecular sieve catalyst according to claim 1, characterized in that: The steam-treated modified HBeta molecular sieve is prepared by treating the HBeta molecular sieve with steam at 450-650° C. for 2-4 hours.

6. The modified molecular sieve catalyst according to claim 1, characterized in that: The carrier is obtained by kneading raw materials including HZSM-5 molecular sieve modified by alkali treatment, HBeta molecular sieve modified by steam treatment and alumina binder with sesbania powder and nitric acid solution.

7. The modified molecular sieve catalyst according to any one of claims 1 to 6, characterized in that: In the modified molecular sieve catalyst, the mass ratio of phosphorus element to the carrier is (0.5-4):100, preferably (1-2):100, and the mass ratio of lanthanum element to the carrier is (0.1-2):100, preferably (0.2-1.1):

100.

8. The method for preparing the modified molecular sieve catalyst according to any one of claims 1 to 7, comprising loading a phosphorus precursor and a lanthanum precursor on the carrier, optionally drying, and then calcining to obtain the modified molecular sieve catalyst.

9. The preparation method according to claim 8, characterized in that: The loading method is an ion exchange method or an impregnation method; and / or, The calcination conditions include: a calcination temperature of 450-650° C., and / or a calcination time of 2-6 hours.

10. The preparation method according to claim 8, characterized in that: The phosphorus precursor is selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and ammonium phosphate; and / or, The lanthanum precursor is selected from at least one of nitrate, sulfate, chloride and acetate of lanthanum; and / or, The amount of the phosphorus precursor used is such that the mass ratio of the phosphorus element to the carrier is (0.5-4):100, preferably (1-2):100, and the amount of the lanthanum precursor used is such that the mass ratio of the lanthanum element to the carrier is (0.1-2):100, preferably (0.2-1.1):

100.

11. Use of the modified molecular sieve catalyst according to any one of claims 1 to 7 or the modified molecular sieve catalyst prepared by the preparation method according to any one of claims 8 to 10 in catalytic cracking of naphtha.

12. A method for catalytic cracking of naphtha, comprising contacting naphtha with a catalyst to catalyze a cracking reaction of the naphtha, preferably to obtain ethylene and / or propylene, wherein: The catalyst is a modified molecular sieve catalyst according to any one of claims 1 to 7 or a modified molecular sieve catalyst prepared by the preparation method according to any one of claims 8 to 10; Preferably, the temperature of the pyrolysis reaction is 500-800°C, and / or the mass space velocity is 4-15h -1 .

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