A post-modified molecular sieve catalyst for naphtha catalytic cracking, its preparation method and application.

Abstract

This invention belongs to the technical field of preparing low-carbon olefins, and relates to a post-modified molecular sieve catalyst for naphtha catalytic cracking and its preparation method. The modified molecular sieve catalyst comprises: a modified molecular sieve catalyst, which includes: a support and phosphorus and lanthanum elements supported on the support; wherein the support comprises alkali-treated modified HZSM-5 molecular sieve, steam-treated modified HBeta molecular sieve, and an alumina binder. This invention has the following advantages: Using a phosphorus-lanthanum supported post-treated modified molecular sieve as a catalyst, the yield of low-carbon olefins is significantly improved compared to unmodified molecular sieves. The preparation method of the catalyst is simpler, more controllable, and lower in cost, possessing extremely high application value.

Description

Technical Field

[0001] This invention belongs to the technical field of preparing low-carbon olefins, specifically relating to a post-modified molecular sieve catalyst for naphtha catalytic cracking, its preparation method, and its application. Background Technology

[0002] Low-carbon olefins, including ethylene, propylene, and butene, are an important class of organic chemicals widely used in chemical, pharmaceutical, and materials industries. The industrial production of low-carbon olefins mainly relies on tubular furnace steam cracking, which requires reactions above 800°C and consumes enormous amounts of energy. Catalytic cracking to olefins can effectively overcome these drawbacks, as catalytic cracking operates at temperatures 100-200°C lower than steam cracking, significantly reducing energy consumption.

[0003] CN104549410 A discloses a catalyst for catalytic cracking of naphtha to produce propylene, a method for preparing the catalyst, and a method for catalytic cracking of naphtha to produce propylene. The catalyst contains 50-95 wt% molecular sieves and 5-50 wt% matrix, wherein the molecular sieves include a first molecular sieve and a second molecular sieve, the first molecular sieve being a molecular sieve with a MWW structure, and the second molecular sieve being a zeolite and / or non-zeolite molecular sieve with twelve-membered ring channels.

[0004] CN114425417A discloses a naphtha catalytic cracking catalyst, its preparation method, and its application. The catalyst contains 50-85% by weight of a support and 15-50% by weight of a core-shell molecular sieve. The X-ray diffraction pattern of the core-shell molecular sieve shows a peak height ratio of 0.110:1 at 2θ = 22.4° to 2θ = 23.1°, and a total specific surface area greater than 420 m². 2 / g.

[0005] Researching and developing novel, highly efficient catalysts suitable for the catalytic cracking of naphtha can improve 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 this invention is to provide a post-modified molecular sieve catalyst for naphtha catalytic cracking and its preparation method. This invention uses two specific molecular sieves, including an alumina binder and a specific post-treatment method, as supports to load phosphorus and lanthanum elements, resulting in a novel modified molecular sieve catalyst. Compared with catalysts obtained from molecular sieves not loaded with the above elements, or those not modified using the method of this invention, the modified molecular sieve catalyst of this invention significantly improves the yield of low-carbon olefins. The catalyst preparation method of this invention is simple and controllable, uses readily available raw materials, and has extremely high application value.

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

[0008] The carrier comprises alkali-treated modified HZSM-5 molecular sieve, steam-treated modified HBeta molecular sieve, and 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 alkali-treated modified HZSM-5 molecular sieve has a silica-to-alumina ratio of 80-200, and / or the steam-treated modified HBeta molecular sieve has a silica-to-alumina ratio of 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] NaZSM-5 molecular sieve is mixed with an alkaline solution, and the resulting powder is then subjected to ammonium exchange followed by calcination to obtain the alkali-treated modified HZSM-5 molecular sieve; more preferably:

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

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

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

[0017] The ammonium exchange method in this invention is a conventional experimental method. The ammonium ion compound is selected from ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium oxalate, or ammonium acetate, all of which can achieve this invention.

[0018] In a preferred embodiment of the present invention, the steam-treated modified HBeta molecular sieve is prepared by steam-treating the HBeta molecular sieve 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 guar gum powder and nitric acid solution.

[0020] According to the present invention, preferably, alkali-treated modified HZSM-5, steam-treated modified HBeta, and alumina binder powder are poured into a kneader, and guar gum powder and nitric acid solution are added and kneaded to obtain a modified molecular sieve catalyst support. The alkali-treated modified HZSM-5 accounts for 15-50% by weight, preferably 35-45%, the steam-treated modified HBeta accounts for 15-35% by weight, preferably 20-30%, and the alumina binder accounts for 15-50% by weight, preferably 30-40%.

[0021] The amount of guar gum powder used in this invention is a conventional technique in the field, and those skilled in the art can choose flexibly.

[0022] The amount and concentration of nitric acid solution used in this invention are conventional techniques established in the field, and those skilled in the art can choose flexibly.

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

[0024] A 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 onto the support, optionally drying them, and then calcining them to obtain the modified molecular sieve catalyst.

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

[0026] According to the present invention, the calcination conditions can be selected within a wide range. In a preferred embodiment of the present invention, the calcination conditions include: a calcination temperature of 450-650°C and / or a calcination 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 lanthanum nitrate, sulfate, chloride and acetate.

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

[0030] In a more preferred embodiment of the present invention, the loading method is independently either ion exchange or equal volume impregnation. After loading, the catalyst is dried and calcined to obtain the final catalyst. The calcination temperature is 450-650℃ and the calcination time is 2-6h.

[0031] A third aspect of the present invention is to provide the application 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] A 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 yielding 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 hourly space velocity is 4-15 h⁻¹. -1 .

[0035] The present invention has the following advantages:

[0036] (1) The present invention uses post-treated modified molecular sieve catalyst as support, including alkali-treated modified HZSM-5, steam-treated modified HBeta and alumina binder. Compared with unmodified molecular sieves HZSM-5 and HBeta, the yield of low carbon olefins is significantly improved.

[0037] (2) The present invention uses a lanthanum phosphate metal supported catalyst, which significantly improves the yield of low-carbon olefins compared with a support without metal catalyst.

[0038] (3) The present invention adopts a post-treatment method for existing specific molecular sieves, combined with supported lanthanum phosphate, resulting in a simpler and lower-cost catalyst preparation method.

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

[0040] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0041] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0042] In the following examples, the feedstock used in the catalytic reaction is naphtha, wherein, by mass percentage, the naphtha contains:

[0043] n-Decane: 55%

[0044] Isooctane: 25%

[0045] Methylcyclohexane: 15%

[0046] Benzene: 5%.

[0047] In the following examples, the content of ethylene and propylene in the product was detected by gas chromatography.

[0048] The yield of ethylene is calculated as follows: (mass of ethylene product / mass of feedstock) * 100%

[0049] The yield of propylene is calculated as: (mass of propylene product / mass of raw material) * 100%.

[0050] Unless otherwise specified, the raw materials used in the following embodiments of this invention are all conventional commercially available products.

[0051] Example 1

[0052] NaZSM-5 powder with a silicon-to-aluminum ratio of 150 was poured into 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 NaOH solution was 0.5 mol / L. The resulting powder was subjected to ammonium exchange and calcined at 500°C for 4 hours to obtain alkali-treated modified HZSM-5.

[0053] HBeta molecular sieves with a silica-to-alumina ratio of 100 were steam-treated at 550°C for 3 hours to obtain steam-treated modified HBeta.

[0054] 40g of alkali-treated modified HZSM-5, 20g of steam-treated modified HBeta, and 40g of alumina binder powder were poured into a kneader, and an appropriate amount of guar gum powder and nitric acid solution were added. The mixture was kneaded to obtain the modified molecular sieve catalyst support.

[0055] Phosphorus was loaded onto the aforementioned support using diammonium hydrogen phosphate as a precursor via ion exchange, with a phosphorus-to-molecular sieve catalyst support mass ratio of 1.5:100. Lanthanum was then loaded onto the support using lanthanum nitrate as a precursor via ion exchange, with a lanthanum-to-molecular sieve catalyst support mass ratio of 0.3:100. The catalyst was then dried and calcined at 550°C for 3 hours to obtain the final catalyst.

[0056] The reaction conditions were as follows: 5g of the modified molecular sieve catalyst was loaded into a fixed-bed reactor; naphtha was used as the feedstock; the reaction temperature was 650℃; the reaction pressure was 0.1 MPa; and the mass hourly space velocity (WHSV) was 10 h⁻¹. -1 The reaction results and yields of the main products are shown in Table 1.

[0057] Example 2

[0058] NaZSM-5 powder with a silicon-to-aluminum ratio of 80 was added to a NaOH solution and stirred at 70°C for 2 hours. The mass ratio of NaZSM-5 to NaOH solution was 1:35, and the molar concentration of the NaOH solution was 0.2 mol / L. The resulting powder underwent ammonium exchange and was calcined at 550°C for 2 hours to obtain alkali-treated modified HZSM-5. HBeta molecular sieve with a silicon-to-aluminum ratio of 50 was steam-treated at 500°C for 2 hours to obtain steam-treated modified HBeta. 45 g of alkali-treated modified HZSM-5, 25 g of steam-treated modified HBeta, and 30 g of alumina binder powder were added to a kneader, along with appropriate amounts of guar gum powder and nitric acid solution, and kneaded to obtain a modified molecular sieve catalyst support. Phosphorus was loaded onto the aforementioned support using diammonium hydrogen phosphate as a precursor via ion exchange, with a phosphorus-to-molecular sieve catalyst support mass ratio of 1.8:100. Lanthanum was then loaded onto the support using lanthanum nitrate as a precursor via ion exchange, with a lanthanum-to-molecular sieve catalyst support mass ratio of 0.5:100. The catalyst was then dried and calcined at 550°C for 3 hours to obtain the final catalyst.

[0059] The reaction conditions were as follows: 5g of the modified molecular sieve catalyst was loaded into a fixed-bed reactor; the reaction temperature was 620℃; the reaction pressure was 0.1MPa; and the space velocity was 6h⁻¹. -1 The reaction results and yields of the main products are shown in Table 1.

[0060] Example 3

[0061] NaZSM-5 powder with a silicon-to-aluminum ratio of 250 was added to a NaOH solution and stirred at 50°C for 2 hours. The mass ratio of NaZSM-5 to NaOH solution was 1:15, and the molar concentration of the NaOH solution was 0.8 mol / L. The resulting powder underwent ammonium exchange and was calcined at 550°C for 6 hours to obtain alkali-treated modified HZSM-5. HBeta molecular sieve with a silicon-to-aluminum ratio of 250 was steam-treated at 500°C for 3 hours to obtain steam-treated modified HBeta. 50 g of alkali-treated modified HZSM-5, 15 g of steam-treated modified HBeta, and 35 g of alumina binder powder were added to a kneader, along with appropriate amounts of guar gum powder and nitric acid solution, and kneaded to obtain a modified molecular sieve catalyst support. Phosphorus was loaded onto the aforementioned support using diammonium hydrogen phosphate as a precursor via an equal-volume impregnation method, with a phosphorus-to-molecular-sieve catalyst support mass ratio of 3.2:100. Subsequently, lanthanum was loaded onto the support using ion exchange method with lanthanum nitrate as a precursor, with a lanthanum-to-molecular-sieve catalyst support mass ratio of 1.8:100. The catalyst was then dried and calcined at 550°C for 3 hours to obtain the final catalyst.

[0062] The reaction conditions were as follows: 5g of the modified molecular sieve catalyst was loaded into a fixed-bed reactor; the reaction temperature was 650℃; the reaction pressure was 0.1MPa; and the space velocity was 12h⁻¹. -1The reaction results and yields of the main products are shown in Table 1.

[0063] Example 4

[0064] NaZSM-5 powder with a silicon-to-aluminum ratio of 30 was added to a NaOH solution and stirred at 80°C for 3 hours. The mass ratio of NaZSM-5 to NaOH solution was 1:25, and the molar concentration of the NaOH solution was 0.8 mol / L. The resulting powder underwent ammonium exchange and was calcined at 550°C for 6 hours to obtain alkali-treated modified HZSM-5. HBeta molecular sieve with a silicon-to-aluminum ratio of 30 was steam-treated at 500°C for 2 hours to obtain steam-treated modified HBeta. 50 g of alkali-treated modified HZSM-5, 15 g of steam-treated modified HBeta, and 35 g of alumina binder powder were added to a kneader, along with appropriate amounts of guar gum powder and nitric acid solution, and kneaded to obtain a modified molecular sieve catalyst support. Phosphorus was loaded onto the aforementioned support using diammonium hydrogen phosphate as a precursor via an equal-volume impregnation method, with a phosphorus-to-molecular-sieve catalyst support mass ratio of 3.2:100. Lanthanum was then loaded onto the support using ion exchange method with lanthanum nitrate as a precursor, with a lanthanum-to-molecular-sieve catalyst support mass ratio of 1.8:100. The catalyst was then dried and calcined at 550°C for 3 hours to obtain the final catalyst.

[0065] The reaction conditions were as follows: 5g of the modified molecular sieve catalyst was loaded into a fixed-bed reactor; the reaction temperature was 650℃; the reaction pressure was 0.1MPa; and the space velocity was 12h⁻¹. -1 The reaction results and yields of the main products 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-to-aluminum ratio of NaZSM-5 was changed to 50 and the silicon-to-aluminum ratio of Hbeta was changed to 40. The rest of the preparation method and catalytic reaction conditions were the same as in 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 to molecular sieve catalyst support was changed to 4:100, and the rest of the preparation method and catalytic reaction conditions were the same as in Example 2.

[0070] Comparative Example 1

[0071] The reaction conditions and lanthanum phosphorus loading conditions used in this comparative example are exactly the same as those in Example 1. The difference is that the catalyst support used is an unmodified HZSM-5 molecular sieve with a silicon-to-aluminum ratio of 150. The reaction results and yields of the main products 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. The difference is that the catalyst used is the molecular sieve catalyst support without lanthanum phosphorus element prepared in Example 1. The reaction results and the yield 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 was not modified. The reaction results and yields of the main products are shown in Table 1.

[0076] Table 1. Experimental Results

[0077]

[0078] As can be seen from Table 1, the yield of low-carbon olefins in Examples 1-6 is significantly improved compared to Comparative Examples 1, 2, and 3.

[0079] The catalyst in this invention is a novel naphtha catalytic cracking catalyst. In terms of preparation method, it can be prepared by post-processing existing molecular sieves of a specific type and then combining them with supported lanthanum phosphate. The catalyst preparation method is simpler, more controllable, and lower in cost, and has extremely high value for promotion and application.

[0080] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations 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 herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0082] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on 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 terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[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 commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0084] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application’s filing, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0085] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0086] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0087] Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas shall be regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination to be obviously unreasonable.

Claims

1. A modified molecular sieve catalyst, said modified molecular sieve catalyst comprising: The carrier and the phosphorus and lanthanum elements supported on the carrier; The carrier includes alkali-treated modified HZSM-5 molecular sieve, steam-treated modified HBeta molecular sieve, and alumina binder; Based on the total weight of the carrier as 100wt%, the content of the alkali-treated modified HZSM-5 molecular sieve is 15-50wt%, and the content of the steam-treated modified HBeta molecular sieve is 15-35wt%.

2. The modified molecular sieve catalyst according to claim 1, characterized in that: Based on a total weight of 100 wt% for the carrier, the content of the alumina binder is 15-50 wt%.

3. 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 35-45wt%, the content of the steam-treated modified HBeta molecular sieve is 20-30wt%, and the content of the alumina binder is 30-40wt%.

4. The modified molecular sieve catalyst according to claim 1, characterized in that: The silicon-to-aluminum ratio of the carrier is 30-250.

5. The modified molecular sieve catalyst according to claim 1, characterized in that: The alkali-treated modified HZSM-5 molecular sieve has a silica-to-alumina ratio of 80-200, and / or the steam-treated modified HBeta molecular sieve has a silica-to-alumina ratio of 50-120.

6. The modified molecular sieve catalyst according to claim 1, characterized in that: The alkali-treated modified HZSM-5 molecular sieve was prepared by the following method: NaZSM-5 molecular sieve was mixed with an alkaline solution, and the resulting powder was subjected to ammonium exchange and then calcined to obtain the alkali-treated modified HZSM-5 molecular sieve.

7. The modified molecular sieve catalyst according to claim 6, characterized in that: NaZSM-5 molecular sieve was reacted with alkaline solution at 50-90°C. o Mixing at C conditions for 1-4 hours; and / or, the mass ratio of NaZSM-5 molecular sieve to alkaline solution is 1:(15-40); and / or, the alkaline solution is selected from at least one of NaOH solution and potassium hydroxide solution; and / or, The concentration of the alkaline solution is 0.2-0.8 mol / L; And / or, The calcination conditions include: at 450-650°C. o C Roast for 2-8 hours.

8. The modified molecular sieve catalyst according to claim 1, characterized in that: The steam-treated modified HBeta molecular sieve is obtained by steam-treating the HBeta molecular sieve at 450-650°C. o It is prepared by steam treatment for 2-4 hours under C conditions.

9. The modified molecular sieve catalyst according to claim 1, characterized in that: 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 guar gum powder and nitric acid solution.

10. The modified molecular sieve catalyst according to any one of claims 1-9, characterized in that: In the modified molecular sieve catalyst, the mass ratio of phosphorus to the support is (0.5-4):100, and the mass ratio of lanthanum to the support is (0.1-2):

100.

11. The modified molecular sieve catalyst according to any one of claims 1-9, characterized in that: In the modified molecular sieve catalyst, the mass ratio of phosphorus to the support is (1-2):100, and the mass ratio of lanthanum to the support is (0.2-1.1):

100.

12. A method for preparing a modified molecular sieve catalyst according to any one of claims 1-11, comprising loading a phosphorus precursor and a lanthanum precursor onto the support, optionally drying them, and then calcining them to obtain the modified molecular sieve catalyst.

13. The preparation method according to claim 12, characterized in that: The loading method is ion exchange or impregnation; and / or, The calcination conditions for the modified molecular sieve catalyst include: a calcination temperature of 450-650°C. o C, and / or, the roasting time is 2-6 h.

14. The preparation method according to claim 12, characterized in that: The phosphorus precursor is selected from at least one of phosphoric acid, diammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate; and / or, The lanthanum precursor is selected from at least one of lanthanum nitrate, sulfate, chloride, and acetate; and / or, The amount of the phosphorus precursor is such that the mass ratio of phosphorus to the support is (0.5-4):100, and the amount of the lanthanum precursor is such that the mass ratio of lanthanum to the support is (0.1-2):

100.

15. The preparation method according to claim 12, characterized in that: The amount of phosphorus precursor used is such that the mass ratio of phosphorus to the support is (1-2):100, and the amount of lanthanum precursor used is such that the mass ratio of lanthanum to the support is (0.2-1.1):

100.

16. The application of a modified molecular sieve catalyst according to any one of claims 1-11 or a modified molecular sieve catalyst prepared by any one of claims 12-15 in the catalytic cracking of naphtha.

17. A method for catalytic cracking of naphtha, comprising contacting naphtha with a catalyst to catalyze a cracking reaction in the naphtha, wherein, The catalyst is the modified molecular sieve catalyst according to any one of claims 1-11 or the modified molecular sieve catalyst prepared by any one of claims 12-15.

18. The catalytic cracking method according to claim 17, characterized in that: The pyrolysis reaction yields ethylene and / or propylene.

19. The catalytic cracking method according to claim 17, characterized in that: The temperature of the pyrolysis reaction is 500-800°C. o C, and / or, mass hourly space velocity of 4-15 h⁻¹ -1 .

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