A modified Y-type molecular sieve and its preparation method and application

Abstract

The present invention discloses a modified Y-type molecular sieve and a preparation method and application thereof. The preparation method comprises the following contents: (1) using an ammonium salt solution to perform ammonium exchange on a NaY molecular sieve, so that ammonium ions are exchanged with part of the Na ions in the NaY molecular sieve to obtain a partially ammonium exchanged molecular sieve NH4NaY; (2) the NH4NaY molecular sieve obtained in step (1) is subjected to a hydrothermal dealumination treatment to obtain a modified Y-type molecular sieve SRY after the hydrothermal dealumination treatment; (3) the modified Y-type molecular sieve SRY obtained in step (2) is subjected to an acid treatment, and after washing and drying, a final modified Y-type molecular sieve SSRY is obtained. The method can obtain a modified Y-type molecular sieve with developed secondary pores, a high specific surface area and a high silicon-aluminum ratio.

Description

Technical Field

[0001] The invention relates to a modified Y-type molecular sieve and a preparation method and application thereof, and in particular to a Y-type molecular sieve with a high silicon-aluminum ratio and a high specific surface area and a preparation method and application thereof. Background Art

[0002] The Y-type molecular sieve is composed of two cage-shaped structural units, a hexagonal prism cage and a β cage. Two adjacent β cages are connected to each other through oxygen bridges to form an eight-sided zeolite FAU-type skeleton structure. The eight-sided zeolite cages are connected through the twelve-membered ring at the pore opening to form a three-dimensional pore system of the Y molecular sieve. The pore diameter and inner diameter of the Y molecular sieve are 0.74nm and 1.2nm respectively, and the internal cavity volume is about 50%. Although there are more than 100 kinds of artificially synthesized molecular sieves, due to its unique pore structure, suitable acid properties and excellent stability, the Y molecular sieve still plays an irreplaceable role in the field of catalysis.

[0003] For different catalytic reactions, there are certain differences in the strength and number of acid centers required for the reaction. Therefore, it is very important to be able to regulate the acid properties and pore structure of Y molecular sieves within a large range to adapt to different production needs. Since the silicon-aluminum ratio of Y molecular sieve is relatively low, most of the synthesized Y molecular sieves in industry need to be modified to improve the stability of the molecular sieve. The silicon-aluminum ratio of the modified Y molecular sieve is greatly improved, and the pore structure and acid properties of the molecular sieve can be regulated at the same time. At present, the means to increase the silicon-aluminum ratio of Y molecular sieve in industry are mainly high-temperature hydrothermal dealumination and chemical solvent dealumination.

[0004] The high-temperature hydrothermal dealumination method is to first perform several ammonium exchanges on the NaY molecular sieve, and then introduce a certain amount of water vapor at a high temperature of 600-900°C. The molecular sieve framework aluminum is detached in the form of Al(OH)x, and at the same time, part of the framework collapses, and the dissociated SiO2 fills the hydroxyl vacancies through polycondensation, resulting in a dealumination and silicon filling reaction to produce secondary pores. The high-temperature hydrothermal dealumination reaction is fast and simple to operate. After dealumination, the thermal stability of the molecular sieve is significantly improved, but the detached non-framework aluminum will cover the active site surface or remain in the molecular sieve pores, affecting the adsorption and diffusion of the reactant molecules. CN 106692995 discloses a method for preparing a high-silicon, high-crystallinity modified mesoporous Y molecular sieve, which is cumbersome to operate.

[0005] Chemical solvent dealumination refers to the removal of aluminum on the framework in a solution by means of the coordination dissolution effect of an acid or a chelating agent. The molecular sieve treated with the solvent can be deeply dealuminated, and the removed non-framework aluminum will not cover the outer surface of the molecular sieve. However, the crystallinity of the molecular sieve after dealumination is greatly reduced, the lattice is severely damaged, and the degree of dealumination is not easy to control, which cannot meet the needs of producing industrial catalysts. CN 100572275 discloses a method for acid dealumination modification of Y molecular sieve under the protection of a surfactant. The method is relatively costly and not suitable for large-scale industrial production. CN 110498424 discloses a modification method using an alkali metal / alkaline earth metal salt solution for protection and then acid dealumination. The method can achieve uniform dealumination of the inner and outer surfaces of the Y molecular sieve, but the degree of dealumination is not high.

[0006] In summary, although the high temperature hydrothermal treatment and chemical solvent treatment methods in the prior art have their own advantages and disadvantages, both the single dealumination method and the combined treatment method have certain limitations and cannot solve their respective shortcomings. How to ensure that the molecular sieve has a high crystallinity, a large surface area and a large pore volume while dealumination is a technical challenge faced by the modified Y molecular sieve. Summary of the invention

[0007] In view of the deficiencies of the prior art, the present invention provides a modified Y-type molecular sieve and a preparation method and application thereof, wherein the method can obtain a modified Y-type molecular sieve with developed secondary pores, high specific surface area and high silicon-aluminum ratio.

[0008] A method for preparing a modified Y-type molecular sieve comprises the following contents:

[0009] (1) using an ammonium salt solution to perform ammonium exchange on the NaY molecular sieve, so that the ammonium ions are exchanged with part of the Na ions in the NaY molecular sieve to obtain a partially ammonium exchanged molecular sieve NH4NaY;

[0010] (2) subjecting the NH4NaY molecular sieve obtained in step (1) to a hydrothermal dealumination treatment to obtain a modified Y-type molecular sieve SRY after the hydrothermal dealumination treatment;

[0011] (3) The modified Y-type molecular sieve SRY obtained in step (2) is treated with acid, and the final modified Y-type molecular sieve SSRY is obtained after washing and drying.

[0012] In the above method, the ammonium salt in step (1) is one or more of ammonium nitrate, ammonium chloride and ammonium sulfate. The concentration of the prepared ammonium salt solution is 0.1-2.0 mol / L, and the ammonium exchange reaction is carried out at room temperature (25°C)-80°C. The exchange time is 0.5-2.5 hours, preferably 0.6-1.5 hours. The solid-liquid ratio in this process is 1g / 5ml-1g / 50ml, preferably 1g / 10ml-1g / 30ml.

[0013] In the above method, the Na2O content in the NH4NaY molecular sieve in step (1) is controlled to be 3.0 to 11.5 wt%, preferably 3.5 to 11.5 wt%, and more preferably 4.5 to 8.0 wt%, based on the weight of the NH4NaY molecular sieve.

[0014] In the above method, step (2) is to hydrothermally treat the NH4NaY molecular sieve obtained in step (1) at a temperature of 200-800°C and a pressure of 0.01-0.5 MPa for 0.5-4 hours, preferably at 450-600°C and 0.05-0.3 MPa for 1-2 hours.

[0015] In the above method, the acid treatment in step (3) adopts an organic acid solution for impregnation treatment, and either equal volume impregnation or excess volume impregnation can be adopted, preferably excess volume impregnation. The organic acid is one of citric acid, oxalic acid, tartaric acid and oxalic acid, and the concentration of the organic acid solution is 0.05~1.0 mol / L, preferably 0.05~0.5 mol / L. The impregnation treatment process is to perform an excess volume impregnation treatment on the SRY molecular sieve obtained in step (2) at 0~50°C for 0.1~5 hours, preferably at 0~35°C for 0.2~2 hours. The organic acid modification treatment is carried out under low temperature conditions to effectively slow down the rate at which the organic acid removes aluminum from the molecular sieve framework, while achieving Na + Ion exchange to H + , enhance the acidity of molecular sieve.

[0016] In the above method, after the acid treatment in step (3), the modified molecular sieve SSRY is washed to a pH between 6 and 7, and placed in an oven at a set temperature of 100 to 150° C. and dried for 12 to 24 hours.

[0017] A modified Y-type molecular sieve SSRY obtained by the above method has the following physical and chemical properties: SiO2 / Al2O3 ratio of 8 to 80, preferably 12 to 60; specific surface area of ​​600 to 1050 m 2 / g, preferably 750 ~ 970 m 2 / g; the pore volume is 0.30~0.50 ml / g, preferably 0.36~0.48 ml / g; the unit cell parameter is 2.438 ~ 2.452 nm, and the relative crystallinity is 50% ~ 98%.

[0018] The modified Y-type molecular sieve is used as a cracking component for preparing a hydrocracking catalyst, and can improve the ability to convert and crack condensed-ring polycyclic hydrocarbon macromolecules.

[0019] A hydrocracking catalyst, which contains, by weight percentage of the hydrocracking catalyst, 6-65%, preferably 10-55%, of the modified Y-type molecular sieve component prepared by the above method; 5-25%, preferably 8-20%, of aluminum oxide; 10-35%, preferably 15-28%, of the VIB group metal in terms of oxide; and 2-10%, preferably 4-8%, of the VIII group metal in terms of oxide; the VIB group metal is preferably tungsten (W) and molybdenum (Mo), and the VIII group metal is preferably cobalt (Co) and nickel (Ni).

[0020] The above catalyst is used for hydrocracking, and the reaction conditions are as follows: in the presence of hydrogen, the reaction pressure is 4~20MPa, the reaction temperature is 300~430℃, the hydrogen-oil volume ratio is 500~1800, and the liquid hourly volume space velocity is 0.5~5.0h -1 .

[0021] In the method of the present invention, a partial ammonium exchange method is used to exchange the conventional NaY molecular sieve to leave a proper amount of sodium oxide, Na + It plays a role in protecting the aluminum in the framework. During the hydrothermal treatment, the aluminum separated from the framework exists in the molecular sieve pores in various forms and covers the acid centers on the surface of the molecular sieve. Organic acid is needed to remove the aluminum in the pores and remove part of the aluminum in the molecular sieve framework to make up for the problem of surface aluminum enrichment caused by the hydrothermal treatment process and the single use of organic acid to modify the Y-type molecular sieve or the combination of the two, which easily causes the molecular sieve to be severely dealuminated and the framework collapses. Low temperature conditions can slow down the problem of too fast reaction rate of the organic acid-treated molecular sieve, which is beneficial to maintain the stability of the framework and avoid the collapse of the molecular sieve framework caused by rapid dealumination of organic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The XRD comparison diagram of the samples of Example 1 (B) and Comparative Example 2 (A).

[0023] Figure 2 This is the TEM image of Comparative Example 1.

[0024] Figure 3 This is the TEM image of Example 4. DETAILED DESCRIPTION

[0025] The following examples and comparative examples are used to further illustrate the effects and functions of the method of the present invention, but the following examples do not constitute limitations of the method of the present invention. In the context of the present invention, % should be understood as mass percentage unless otherwise specified.

[0026] The properties of the conventional NaY molecular sieve in the following examples and comparative examples are as follows: SiO2 / Al2O3 ratio is 4.96, specific surface area is 781.3 m 2 / g, the pore volume is 0.35ml / g, and the unit cell parameter is 2.468nm.

[0027] Example 1

[0028] A 0.25 mol / L ammonium nitrate solution was prepared, and conventional NaY molecular sieves were subjected to ammonium exchange reaction at room temperature (25°C) for 1.0 hour. The solid-liquid ratio in this process was 1g / 10ml, and a primary ammonium exchange molecular sieve NH4NaY-1 was obtained. The Na2O content was controlled to be 6.23% based on the weight of the NH4NaY molecular sieve.

[0029] The NH4NaY molecular sieve was subjected to a hydrothermal treatment at a temperature of 600 °C and a pressure of 0.1 MPa for 1.5 hours to obtain a modified Y-type molecular sieve SRY-1.

[0030] A 0.15 mol / L citric acid solution was prepared to perform secondary modification on the molecular sieve SRY. The SRY-1 molecular sieve was impregnated at 20°C for 30 min with a liquid-to-solid ratio of 1 g / 10 ml to obtain the final product SSRY-1. The SSRY-1 molecular sieve was washed to a pH value between 6 and 7 and dried at 120°C for 12 hours. The properties of the final product SSRY-1 are shown in Table 1, and the same applies to the following.

[0031] Example 2

[0032] Prepare a 0.5 mol / L ammonium nitrate solution, and perform an ammonium exchange reaction on a conventional NaY molecular sieve at 80°C for 2.0 hours. The solid-liquid ratio in this process is 1g / 10ml, and obtain a primary ammonium exchange molecular sieve NH4NaY-2. The Na2O content is controlled to be 4.87% based on the weight of the NH4NaY molecular sieve. Perform a hydrothermal treatment on the NH4NaY-2 molecular sieve at a temperature of 550°C and a pressure of 0.1 MPa for 1.5 hours to obtain a primary modified Y molecular sieve SRY-2;

[0033] Prepare 0.3mol / L citric acid solution to modify the molecular sieve SRY-2 for the second time, treat the SRY-1 molecular sieve at 10℃ for 20min, and the liquid-solid ratio is 1g / 10ml to obtain the final product SSRY-2. Wash the SSRY-2 molecular sieve to a pH value between 6 and 7, and dry it at 120℃ for 12 hours to obtain the final product SSRY-2.

[0034] Example 3

[0035] Prepare an ammonium nitrate solution with a concentration of 0.5 mol / L, and perform an ammonium exchange reaction on a conventional NaY type molecular sieve at 50°C for 1.5 hours. The solid-liquid ratio in this process is 1g / 8ml, and a primary ammonium exchange molecular sieve NH4NaY-3 is obtained. The Na2O content is controlled to be 4.92% based on the weight of the NH4NaY molecular sieve. The NH4NaY-3 molecular sieve is hydrothermally treated at a temperature of 500°C and a pressure of 0.1 MPa for 1.5 hours to obtain a primary modified Y type molecular sieve SRY-3;

[0036] Prepare 0.5 mol / L citric acid solution to perform secondary modification on molecular sieve SRY-3, treat SRY-1 molecular sieve at 10°C for 10 min, with a liquid-to-solid ratio of 1 g / 15 ml to obtain the final product SSRY-3, wash the SSRY-3 molecular sieve to a pH value between 6 and 7, and dry at 120°C for 12 hours to obtain the final product SSRY-3.

[0037] Example 4

[0038] Prepare a 0.5 mol / L ammonium nitrate solution, and perform an ammonium exchange reaction on a conventional NaY molecular sieve at 80°C for 2.0 hours. The solid-liquid ratio in this process is 1g / 20ml, and a primary ammonium exchange molecular sieve NH4NaY-4 is obtained. The Na2O content is controlled to be 4.59% based on the weight of the NH4NaY molecular sieve. The NH4NaY-4 molecular sieve is hydrothermally treated at a temperature of 600°C and a pressure of 0.1 MPa for 0.5 hours to obtain a primary modified Y molecular sieve SRY-4;

[0039] Prepare 0.10mol / L citric acid solution to modify the molecular sieve SRY-4 for the second time, treat the SRY-1 molecular sieve at 20℃ for 60min, and the liquid-solid ratio is 1g / 8ml to obtain the final product SSRY-4. Wash the SSRY-4 molecular sieve to a pH value between 6 and 7, and dry it at 120℃ for 12 hours. The final product SSRY-4

[0040] Example 5

[0041] Prepare an ammonium nitrate solution with a concentration of 0.25 mol / L, and perform an ammonium exchange reaction on a conventional NaY type molecular sieve at room temperature for 1.0 hour. The solid-liquid ratio in this process is 1g / 10ml, and a primary ammonium exchange molecular sieve NH4NaY-5 is obtained. The Na2O content is controlled to be 6.21% based on the weight of the NH4NaY molecular sieve. The NH4NaY-5 molecular sieve is hydrothermally treated at a temperature of 550 °C and a pressure of 0.2 MPa for 1.0 hour to obtain a primary modified Y type molecular sieve SRY-5;

[0042] A 0.10 mol / L citric acid solution was prepared to perform secondary modification on the molecular sieve SRY-5. The SRY-1 molecular sieve was treated at 10°C for 60 min with a liquid-to-solid ratio of 1 g / 8 ml to obtain the final product SSRY-5. The SSRY-5 molecular sieve was washed to a pH value between 6 and 7 and dried at 120°C for 12 hours to obtain the final product SSRY-5.

[0043] Example 6

[0044] Prepare an ammonium nitrate solution with a concentration of 0.25 mol / L, and perform an ammonium exchange reaction on a conventional NaY type molecular sieve at room temperature for 1.0 hour. The solid-liquid ratio in this process is 1g / 10ml, and a primary ammonium exchange molecular sieve NH4NaY-6 is obtained. The Na2O content is controlled to be 6.13% based on the weight of the NH4NaY molecular sieve. The NH4NaY-6 molecular sieve is hydrothermally treated at a temperature of 500 °C and a pressure of 0.3 MPa for 1.0 hour to obtain a primary modified Y type molecular sieve SRY-6;

[0045] Prepare 0.05mol / L citric acid solution to perform secondary modification on molecular sieve SRY-6, treat SRY-1 molecular sieve at 10℃ for 100min, with a liquid-solid ratio of 1g / 5ml, and obtain the final product SSRY-6. Wash the SSRY-6 molecular sieve to a pH value between 6 and 7, and dry it at 120℃ for 12 hours to obtain the final product SSRY-6.

[0046] Comparative Example 1

[0047] Prepare an ammonium nitrate solution with a concentration of 1.0 mol / L, and perform ammonium exchange reactions twice on conventional NaY molecular sieves at 95°C, each time for 1 hour, with a solid-liquid ratio of 1g / 15ml, to obtain molecular sieve NH4Y, and control the Na2O content to 2.55% based on the weight of the NH4Y molecular sieve. Perform a hydrothermal treatment on the NH4Y molecular sieve at a temperature of 600°C and a pressure of 0.1MPa for 1.5 hours to obtain a modified Y-type molecular sieve SRY-7;

[0048] Prepare 0.15mol / L citric acid solution to perform secondary modification on molecular sieve SRY-7, with a liquid-to-solid ratio of 1g / 10ml, treat SRY-1 molecular sieve at 20℃ for 0.5 hours to obtain the final product SSRY-7, and wash the SSRY-7 molecular sieve to a pH value between 6 and 7, and dry it at 120℃ for 12 hours to obtain the final product SSRY-7.

[0049] Comparative Example 2

[0050] Prepare an ammonium nitrate solution with a concentration of 0.5 mol / L, and perform an ammonium exchange reaction on a conventional NaY molecular sieve at room temperature (25°C) for 1.0 hour. The solid-liquid ratio in this process is 1g / 10ml, and a primary ammonium exchange molecular sieve NH4NaY-8 is obtained. The Na2O content is controlled to be 6.31% based on the weight of the NH4NaY molecular sieve. The NH4NaY molecular sieve is subjected to a hydrothermal treatment at a temperature of 600°C and a pressure of 0.1 MPa for 1.5 hours to obtain a primary modified Y-type molecular sieve SRY-8;

[0051] Prepare 0.2mol / L citric acid solution to modify the molecular sieve SRY for the second time, with a liquid-to-solid ratio of 1g / 10ml, treat the SRY-8 molecular sieve at 80℃ for 1 hour to obtain the final product SSRY-8, and wash the SSRY-8 molecular sieve to a pH value between 6-7, and dry it at 120℃ for 12 hours to obtain the final product SSRY-8.

[0052] Comparative Example 3

[0053] Prepare an ammonium nitrate solution with a concentration of 1.0 mol / L, and perform ammonium exchange reactions twice on conventional NaY molecular sieves at 95°C, each time for 1 hour, with a solid-liquid ratio of 1g / 10ml, to obtain molecular sieve NH4Y, and control the Na2O content to 2.45% based on the weight of the NH4Y molecular sieve. Perform a hydrothermal treatment on the NH4NaY molecular sieve at a temperature of 600°C and a pressure of 0.1 MPa for 1.5 hours to obtain a modified Y-type molecular sieve SRY-9;

[0054] A 0.6 mol / L nitric acid solution was prepared to perform secondary modification on the molecular sieve SRY, with a liquid-to-solid ratio of 1 g / 10 ml. The SRY-9 molecular sieve was treated at 90°C for 60 min to obtain the final product SSRY-9. The SSRY-9 molecular sieve was washed to a pH value between 6 and 7, and dried at 120°C for 12 hours to obtain the final product SSRY-9.

[0055] from Figure 1 It can be seen that the relative crystallinity of the Y-type molecular sieve in Comparative Example 2 is low after being treated with high-temperature organic acid, indicating that the molecular sieve framework collapses. After the molecular sieve in Example 1 is modified, the framework still maintains a high crystallinity. Figure 2 It can be seen that the surface of the modified Y-type molecular sieve is rough and has obvious holes, that is, the modified Y-type molecular sieve has a larger pore distribution.

[0056] Application of modified Y-type molecular sieve in hydrocracking catalyst:

[0057] The modified Y-type molecular sieve and alumina powder were mixed uniformly in a certain proportion, and a certain concentration of dilute nitric acid was prepared as a binder. The powders were fully mixed and rolled into a shape, and then dried and taken out and calcined at 550°C for 8 hours to obtain a hydrocracking catalyst carrier, and its water absorption rate was measured; Mo and Ni metal impregnation solutions were prepared, and the above catalyst carrier was impregnated for 2 hours, and then dried and taken out, and calcined at 500°C for 6 hours to obtain a hydrocracking catalyst. The properties are shown in Table 2.

[0058] This series of hydrocracking catalysts were presulfurized and evaluated using a 200ml small hydrogenation unit. The stock oil passed through the hydrotreating catalyst bed and the hydrocracking catalyst bed in succession. When passing through the hydrotreating catalyst bed, the organic nitrogen content in the stock oil was controlled to be < 10ppm. The properties of the stock oil used are shown in Table 3, and the evaluation process conditions and catalyst reaction performance comparison results are shown in Table 4.

[0059] Table 1 Pore structure information of modified Y-type molecular sieve

[0060]

[0061] Table 2 Composition of hydrocracking catalyst with modified Y-type molecular sieve as component

[0062]

[0063] Table 3 Raw oil properties

[0064]

[0065] Table 4 Process conditions and catalyst reaction performance

[0066]

[0067] As shown in Table 4, the results of the evaluation of the catalyst prepared by using the modified Y-type molecular sieve in the embodiment and the Y-type molecular sieve in the comparative example show that when the same reaction conversion rate is controlled, the reaction temperature is 14-25°C lower, and the heavy naphtha yield is increased by 6.3-8.6 percentage points. The experimental results show that the hydrocracking catalyst prepared by the modified Y-type molecular sieve obtained by the method of the present invention has better activity and target product selectivity.

Claims

1. A method for preparing a modified Y-type molecular sieve, wherein the modified Y-type molecular sieve has the following physicochemical properties: SiO2 / Al2O3 ratio of 33.6 to 80; specific surface area of ​​803.1 to 1050 m 2 / g; the pore volume is 0.40-0.50 ml / g; the unit cell parameter is 2.438-2.452 nm, and the relative crystallinity is 50%-98%. The preparation method comprises the following steps: (1) using an ammonium salt solution to perform ammonium exchange on the NaY molecular sieve, so that the ammonium ions are exchanged with part of the Na ions in the NaY molecular sieve to obtain a partially ammonium exchanged molecular sieve NH4NaY; (2) subjecting the NH4NaY molecular sieve obtained in step (1) to a hydrothermal dealumination treatment to obtain a modified Y-type molecular sieve SRY after the hydrothermal dealumination treatment; (3) The modified Y-type molecular sieve SRY obtained in step (2) is subjected to acid treatment, and after washing and drying, the final modified Y-type molecular sieve SSRY is obtained; The Na2O content in the NH4NaY molecular sieve in step (1) is controlled to be 4.5-8.0wt% based on the weight of the NH4NaY molecular sieve; In step (2), the NH4NaY molecular sieve obtained in step (1) is hydrothermally treated at a temperature of 550-600° C. and a pressure of 0.05-0.3 MPa for 1-2 hours; In step (3), the acid treatment process is to perform a volumetric impregnation treatment on the SRY molecular sieve obtained in step (2) at 0-20° C. for 0.1-5 hours; the acid treatment is performed using an organic acid solution, and the concentration of the organic acid solution is 0.05-0.3 mol / L; The ammonium salt in step (1) is one or more of ammonium nitrate, ammonium chloride and ammonium sulfate; The organic acid in step (3) is one of citric acid, oxalic acid, tartaric acid and oxalic acid.

2. The method according to claim 1, characterized in that: The concentration of the ammonium salt solution in step (1) is 0.1-2.0 mol / L.

3. The method according to claim 1, characterized in that: In step (1), the ammonium exchange reaction is carried out at room temperature to 80°C, the exchange time is 0.5 to 2.5 hours, and the solid-liquid ratio is 1g / 5ml to 1g / 50ml.

4. The method according to claim 3, characterized in that: The exchange time in step (1) is 0.6 to 1.5 hours, and the solid-liquid ratio in this process is 1 g / 10 ml to 1 g / 30 ml.

5. The method according to claim 1, characterized in that: In step (2), the NH4NaY molecular sieve obtained in step (1) is hydrothermally treated at a temperature of 200-800°C and a pressure of 0.01-0.5 MPa for 0.5-4 hours.

6. The method according to claim 1, characterized in that: The impregnation treatment in step (3) is equal volume impregnation or excess volume impregnation.

7. The method according to claim 1, characterized in that: After the acid treatment in step (3), the modified molecular sieve SSRY is washed to a pH between 6 and 7, and dried at 100 to 150° C. for 12 to 24 hours.

8. A modified Y-type molecular sieve prepared by the method of any one of claims 1 to 7.

9. The modified Y-type molecular sieve according to claim 8, characterized in that: The physicochemical properties of the modified Y-type molecular sieve are as follows: SiO2 / Al2O3 ratio is 37.4-60; specific surface area is 831.6-970 m 2 / g; pore volume is 0.42~0.48 ml / g.

10. Use of the modified Y-type molecular sieve according to claim 8 or 9 as a cracking component of a hydrocracking catalyst.

11. A hydrocracking catalyst, characterized in that: Calculated by weight percentage of the hydrocracking catalyst, it contains 6% to 65% of the modified Y-type molecular sieve according to claim 9 or 10; 5% to 25% of alumina; 10% to 35% of the VIB group metal in terms of oxide; and 2% to 10% of the VIII group metal in terms of oxide.

12. The hydrocracking catalyst according to claim 11, characterized in that: Calculated by weight percentage, the hydrocracking catalyst contains 10-55% of the modified Y-type molecular sieve according to claim 8 or 9; 8-20% of aluminum oxide; 15-28% of the VIB group metal in terms of oxide; 4-8% of the VIII group metal in terms of oxide; the VIB group metal is selected from tungsten and molybdenum, and the VIII group metal is selected from cobalt and nickel.

13. A hydrocracking method, characterized in that: The catalyst according to claim 11 or 12 is used, and the reaction conditions of hydrocracking are as follows: in the presence of hydrogen, the reaction pressure is 4-20 MPa, the reaction temperature is 300-430°C, the hydrogen-to-oil volume ratio is 500-1800, and the liquid hourly volume space velocity is 0.5-5.0 h -1 .

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