Modified Y molecular sieve and preparation method thereof

Abstract

The invention belongs to the technical field of catalytic cracking, and relates to a modified Y-type molecular sieve and a preparation method thereof, the modified Y-type molecular sieve contains more than 0-2% by mass of Nb, the acid amount of strong L acid of the modified Y-type molecular sieve is increased by 15-45 [mu] mol.g <-1 > compared with that of HY-type molecular sieve, and the acid amount of weak L acid of the modified Y-type molecular sieve is increased by 10-80 [mu] mol.g <-1 > compared with that of HY-type molecular sieve. The preparation method comprises the following steps: dipping and dissolving the exchanged molecular sieve in Nb (OH) 5 of an oxalic acid solution, drying and roasting. When the modified Y molecular sieve is used for catalytically cracking cycloalkanes, the conversion rate and the low-carbon olefin yield are obviously increased.

Description

Technical Field

[0001] The invention belongs to the field of catalytic cracking and relates to a modified Y molecular sieve and a preparation method thereof. Background Art

[0002] Y-type zeolites have a larger diffusion range and, due to their supercage structure, can accommodate larger molecules. Consequently, they exhibit poor selectivity for hydrocarbon diffusion and reaction. Y-type zeolites are currently the primary active component in catalytic cracking catalysts. Commonly synthesized zeolites are sodium-type, which exhibit low hydrocarbon cracking activity and poor selectivity. Numerous researchers have conducted research on modifying Y-type zeolites to improve their catalytic performance. Common modification methods include hydrothermal, acid-base, and metal modification.

[0003] Hydrothermal modification is a classic method that can regulate the acidity, silicon-aluminum ratio, and pore structure of molecular sieves, thereby improving the stability and catalytic performance of molecular sieve catalysts. Acid treatment can facilitate dealumination of Y molecular sieves, regulating their acid center distribution and pore structure. The acid dealumination method also offers simple and mild reaction conditions. Small molecule inorganic acids are the most commonly used acids in acid treatment processes. They have relatively low steric resistance and rapid diffusion rates, allowing them to effectively enter the molecular sieve pores for dealumination. Modifying molecular sieves with rare earth metals can improve their stability, imparting them with improved thermal and hydrothermal stability.

[0004] Petroleum distillates contain a large number of cyclohexane rings. Recently developed processing technologies, particularly to fully utilize the heavy aromatic hydrocarbon resources in distillates such as LCO and HCO, hydrogenate these aromatic heavy petroleum fractions to saturate them, producing hydrocarbon molecules containing cyclohexane rings that are then converted through catalytic cracking. During this conversion process, cyclohexane rings may undergo reactions such as ring-opening cracking, dehydrogenation, hydrogen transfer, and condensation.

[0005] However, existing modified Y-type molecular sieves, when used for the conversion of cycloalkane molecules, lack sufficient ring-opening cracking of cyclic hydrocarbons, resulting in low conversion rates. The prior art does not provide information on how to further utilize Y-type molecular sieves to improve the conversion of cycloalkane-containing molecular sieves, nor does it address how to further improve the conversion rate of cycloalkanes using Y-type molecular sieves, or how to achieve higher butene and propylene yields. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a modified Y molecular sieve and a preparation method thereof in view of the deficiencies in the prior art. The modified Y molecular sieve provided by the present invention significantly increases the conversion rate and / or butene yield and / or propylene yield when catalytically cracking cycloalkanes.

[0007] The present invention provides a modified Y-type molecular sieve containing a modifying element, niobium, wherein the niobium content calculated as niobium element is greater than 0 and not more than 2% by mass. Compared with the HY-type molecular sieve, the modified Y-type molecular sieve has an increased strong L-acid content of 15 to 45 μmol·g -1 , the amount of weak L-acid increases by 10 to 80 μmol·g -1 .

[0008] The acid amount was measured by pyridine adsorption infrared spectroscopy, B acid ( Acid) Acid amount used at 1540cm -1 The absorption peak at 1450cm is measured, and the acidity of L acid (Lewis acid) is measured at 1450cm -1 The total acid amount is the acid amount measured after vacuum desorption at 200°C, the strong acid amount is the acid amount measured after vacuum desorption at 350°C, and the weak acid amount is the difference between the total acid amount and the acid amount measured after vacuum desorption at 350°C.

[0009] Furthermore, the present invention provides a modified Y-type molecular sieve, wherein the niobium content calculated as niobium element is greater than 0 and not more than 2% by mass; the weak L-acid amount of the modified Y-type molecular sieve is 30 to 100 μmol·g -1 , the acidity of strong L-acid is 100~160μmol·g -1 In one embodiment, the weak B acid content of the modified Y-type molecular sieve is preferably 30 to 100 μmol·g -1 The amount of strong B acid in the modified Y-type molecular sieve is preferably 70 to 100 μmol·g -1 .

[0010] According to any of the above technical solutions, in one embodiment, compared with the HY type molecular sieve, the modified Y type molecular sieve has a strong L acid content increased by 15 to 45 μmol·g -1 For example, 20 to 40 μmol·g -1 Above or 20-30 μmol·g -1 or 30 μmol·g -1 above.

[0011] According to any of the above technical solutions, compared with the HY type molecular sieve, the weak L acid content of the modified Y type molecular sieve is increased by 10 to 80 μmol·g -1 For example, 13 to 70 μmol·g -1 or 14-35 μmol·g -1 or 20 μmol·g -1 above.

[0012] According to the modified Y-type molecular sieve provided by any of the above technical solutions of the present invention, in one embodiment, the amount of weak L acid in the modified Y-type molecular sieve is 30 to 100 μmol·g-1 Preferably 40 to 80 μmol·g -1 For example, 55 to 85 μmol·g -1 .

[0013] According to the modified Y-type molecular sieve provided by any of the above technical solutions of the present invention, in one embodiment, the strong L-acid content of the modified Y-type molecular sieve is 100-160 μmol·g -1 For example, 100 to 120 μmol·g -1 or 120-160 μmol·g -1 Preferably 133 to 155 μmol·g -1 .

[0014] According to the modified Y-type molecular sieve provided by any of the above technical solutions of the present invention, in one embodiment, the amount of weak B acid in the modified Y-type molecular sieve is 30 to 100 μmol·g -1 For example, 40 to 80 μmol·g -1 or 43.5-55 μmol·g -1 .

[0015] According to the modified Y-type molecular sieve provided by any of the above technical solutions of the present invention, in one embodiment, the acid amount of the strong B acid of the modified Y-type molecular sieve is 70 to 100, for example, 90 to 99 μmol·g -1 .

[0016] According to the modified Y-type molecular sieve provided by any of the above technical solutions of the present invention, in one embodiment, the acid amount ratio of the strong B acid of the modified Y-type molecular sieve to the strong L acid of the modified Y-type molecular sieve is: 0.5-0.85:1, for example, 0.7-0.8:1.

[0017] According to the modified Y-type molecular sieve provided by any of the above technical solutions of the present invention, in one embodiment, the acid amount ratio of the weak B acid of the modified Y-type molecular sieve to the weak L acid of the modified Y-type molecular sieve is: 0.45-0.9:1, for example, 0.55-0.8:1 or 0.8-0.85:1.

[0018] According to the modified Y-type molecular sieve provided by any of the above technical solutions of the present invention, in one embodiment, the niobium content in the modified Y-type molecular sieve can be 0.1-2 mass %, such as 0.2-1 mass % or 0.3-1.5 mass %, calculated as Nb.

[0019] According to the modified Y-type molecular sieve provided by any of the above technical solutions of the present invention, in one embodiment, the silicon-aluminum ratio (SiO2 / Al2O3 molar ratio) of the modified Y-type molecular sieve is 3 to 6, such as 3.5 to 6 or 4.5 to 6.

[0020] According to the modified Y-type molecular sieve provided by any of the above technical solutions of the present invention, in one embodiment, the sodium oxide content of the modified Y-type molecular sieve is preferably less than 1 mass %, for example, the sodium oxide content is preferably less than 0.5 mass %, for example, 0.01-0.5 mass % or less than 0.2 mass %.

[0021] According to any of the above technical solutions of the present invention, the sodium oxide content of the HY type molecular sieve is preferably less than 1 mass %, preferably less than 0.5 mass %, for example, 0.01 to 0.5 mass % or less than 0.2 mass %.

[0022] According to any of the above technical solutions of the present invention, preferably, the sodium oxide content of the HY type molecular sieve is equal to the sodium oxide content of the modified Y type molecular sieve.

[0023] According to the modified Y-type molecular sieve provided by any of the above technical solutions of the present invention, in one embodiment, the modified Y-type molecular sieve and the HY-type molecular sieve have the same silicon-to-aluminum ratio.

[0024] The niobium modified Y molecular sieve of the present invention has a mass fraction of niobium greater than 0 and not more than 2%. The low Nb loading of the present invention can be used for The acid and Lewis (L) acid are redistributed, preferably, the amount of B acid and L acid are increased; combined with other characteristics, the ring-opening cracking performance of the modified Y molecular sieve is improved.

[0025] The present invention further provides a method for preparing a modified Y molecular sieve, comprising:

[0026] A Y-type molecular sieve having a sodium oxide content of no more than 1% by mass is contacted with a niobium compound dissolved in a 0.1 to 0.3 mol / L oxalic acid solution to introduce niobium into the Y-type molecular sieve, followed by drying and calcination. The niobium compound is preferably Nb(OH)5.

[0027] The Y-type molecular sieve having a sodium oxide content of no more than 1% by mass, preferably has a sodium oxide content of less than 0.5% by mass, for example, less than 0.2% by mass. The Y-type molecular sieve having a sodium oxide content of no more than 1% by mass may be a HY molecular sieve, an NH4Y molecular sieve, or an NH4-HY molecular sieve.

[0028] In one embodiment, the present invention provides a method for preparing a modified Y molecular sieve, comprising:

[0029] a. obtaining a Y-type molecular sieve having a sodium oxide content not exceeding 1% by mass;

[0030] b. Dissolve Nb(OH)5 in an oxalic acid solution with a concentration of 0.1 to 0.3 mol / L to obtain an impregnation solution, wherein Nb: oxalic acid = 0.5 to 1.1:1, and then use the impregnation solution to impregnate, for example, the Y-type molecular sieve obtained in the supersaturated impregnation step a, wherein the sodium oxide content does not exceed 1% by mass. The impregnation is performed, for example, at room temperature for 1 to 40 hours, preferably 20 to 30 hours, dried, heated to a calcination temperature, and calcined at a constant temperature at the calcination temperature; the calcination temperature is 400-700°C, and the calcination time is 0.5-8 hours. Preferably, the calcination temperature is 450 to 600°C, and the calcination time is 1 to 4 hours.

[0031] According to the preparation method of the modified Y-type molecular sieve provided by the present invention, the Y-type molecular sieve with a sodium oxide content not exceeding 1% by mass described in step a can be purchased commercially or synthesized by itself.

[0032] In one embodiment, the Y-type molecular sieve having a sodium oxide content not exceeding 1% by mass can be obtained by washing and exchanging NaY molecular sieve with sodium.

[0033] According to the preparation method of the modified Y-type molecular sieve provided by the present invention, the sodium wash exchange is a sodium wash exchange method well known to those skilled in the art. For example, the NaY molecular sieve can be exchanged at a mass ratio of molecular sieve: ammonium salt: H2O = 1: (0.1-1): (5-10) at room temperature to 100°C, for example, room temperature to 60°C or 50-90°C, for 0.5-3 hours or 0.5-2 hours, and then filtered. In order to make the Na2O content in the molecular sieve meet the requirements, the sodium wash exchange process can be repeated once or multiple times, that is, one or more sodium wash exchanges are performed, for example, the sodium wash exchange process is repeated 1, 2 or 3 times. Each sodium wash exchange can be calcined or not after calcination. The ammonium salt can be an inorganic ammonium salt commonly used for molecular sieve exchange, for example, the ammonium salt can be selected from at least one of ammonium chloride, ammonium sulfate and ammonium nitrate. The sodium wash exchange is such that the sodium oxide content in the obtained Y-type molecular sieve after the sodium wash exchange is not higher than 1% by mass, for example, 0.01-1% by mass, preferably less than 0.5% by mass or less than 0.2% by mass.

[0034] The NaY molecular sieve can be purchased commercially or synthesized. In one embodiment, the NaY molecular sieve can be obtained by crystallizing the NaY molecular sieve and then washing it with water. The method for crystallizing the NaY molecular sieve can be, for example, synthesized according to the method disclosed in USP3639099, USP3671191, or CN1621349A.

[0035] According to the preparation method of modified Y-type molecular sieve provided by the present invention, in step b, Nb(OH)5 is dissolved in an oxalic acid solution with a concentration of 0.1 to 0.3 mol / L, and the molar ratio of Nb to oxalic acid is preferably 0.7-1.05:1, for example, 0.9 to 1:1 or 1:1.

[0036] According to the preparation method of the modified Y-type molecular sieve provided by the present invention, Nb(OH)5 is dissolved in an oxalic acid solution with a concentration of 0.1 to 0.3 mol / L. The dissolving of Nb(OH)5 in the oxalic acid solution can be carried out by mixing the oxalic acid solution with Nb(OH)5 under stirring at a certain temperature, such as 70 to 90°C, such as 75°C, 80°C or 85°C, and stirring to dissolve Nb(OH)5. The molecular sieve obtained by the supersaturated impregnation step b is then impregnated with the obtained oxalic acid solution in which Nb(OH)5 is dissolved. The impregnation can be carried out at room temperature for 20 to 30 hours, such as 22 hours, 24 hours, 26 hours or 28 hours, and then dried, such as at 100 to 150°C, for a drying time of, for example, 0.5 to 5 hours, such as at 110°C for 2 hours, to obtain a dried molecular sieve; the dried molecular sieve is heated to a calcination temperature for calcination. The calcination temperature can be 400-700°C, and the calcination time can be 0.5-8 hours.

[0037] According to the preparation method of the modified Y-type molecular sieve provided by the present invention, in step b, the dried molecular sieve is heated to a calcination temperature for calcination. The heating to the calcination temperature can be performed by directly heating the dried molecular sieve or cooling the dried molecular sieve, for example, cooling it to room temperature before the heating is performed. For example, the temperature can be raised from the temperature at the beginning of the heating, for example, from room temperature for 1 to 3 hours, for example, 2 hours, to the calcination temperature, for example, 450 to 600°C or 500 to 600°C, and the calcination time is 1 to 6 hours, for example, it can be calcined at a constant temperature of 550°C for 3 hours. In the present invention, the room temperature is 15 to 40°C.

[0038] Preferably, the impregnation is performed so that the Nb loading mass fraction in terms of niobium element in the obtained modified Y-type molecular sieve (or the niobium content in the modified Y-type molecular sieve) is 0.1 to 2 mass %.

[0039] In one embodiment, the preparation method of the modified Y-type molecular sieve provided by the present invention comprises: a. washing and exchanging the NaY molecular sieve with an ammonium salt solution so that the sodium oxide content therein is less than 0.5% by mass; b. preparing an oxalic acid solution with a concentration of 0.1 to 0.3 mol / L, for example, a concentration of 0.15 mol / L, 0.2 mol / L or 0.25 mol / L, dissolving Nb(OH)5 to form an impregnation solution, wherein the molar ratio of Nb to oxalic acid in the impregnation solution is 0.7 to 1.05:1, and supersaturating the impregnation solution with an appropriate amount of the molecular sieve obtained in step a, the impregnation time is preferably 20 to 30 hours, and the impregnation can be carried out at room temperature, dried, and calcined; the calcination can be carried out under hydrothermal conditions or under air atmosphere conditions; to obtain the modified Y-type molecular sieve.

[0040] The present invention also provides a method for using the modified Y-type molecular sieve for catalytic cracking of cycloalkanes, comprising the steps of contacting and reacting cycloalkanes with the modified Y-type molecular sieve under catalytic cracking conditions. The cycloalkanes may be pure cycloalkanes or cycloalkanes in a hydrocarbon oil containing cycloalkanes. The catalytic cracking reaction conditions include, for example, a reaction temperature of 480 to 530°C, a reaction time of 1 to 100 seconds, and a mass hourly space velocity of 0.1 to 100 h / min. -1 .

[0041] The modified Y molecular sieve provided by the present invention, when used in the catalytic cracking of hydrocarbons containing cycloalkanes, has higher conversion rates, higher butene yields, and surprisingly, higher propylene yields. The modified Y molecular sieve provided by the present invention can be used to prepare catalytic cracking catalysts for converting cycloalkanes.

[0042] The modified Y molecular sieve preparation method provided by the present invention can improve the binding effect between niobium and molecular sieve, and can The catalyst can be used to better redistribute the Lewis (L) acid and Lewis (L) acid, increasing the L acid content and, in preferred cases, also achieving a higher B acid content. This enhances the synergistic catalytic effect of niobium and molecular sieves. The catalyst prepared using this catalyst can be used in acid-catalyzed processes such as catalytic cracking, catalytic cracking, and hydrocracking.

[0043] The catalytic cracking method for cycloalkane provided by the present invention has significantly higher conversion rate, and significantly higher butene yield and propylene yield. DETAILED DESCRIPTION

[0044] The present invention will be further illustrated by the following examples, but the present invention is not limited thereto. Unless otherwise specified, the instruments and reagents used in the examples of the present invention are commonly used by those skilled in the art.

[0045] Catalytic cracking reaction evaluation was conducted using molecular sieves obtained from the examples and comparative examples using pure hydrocarbon microreactors. The method was as follows: the modified Y molecular sieve was aged at 800°C and 100% water vapor for 17 hours. 5g of modified Y molecular sieve with a particle size of 20-40 mesh was weighed and loaded into a fixed-bed reactor. The reaction was evaluated on a pure hydrocarbon microreactor. The feed oil was butylcyclohexane, and a 30mL / min high-purity nitrogen purge was used for more than 20 minutes before the reaction. The feed was automatically fed using a microinjection pump, with an oil feed rate of 1.56g and an oil feed time of 70s. The reaction temperature was 520°C, and the reaction mass space velocity was 16h. -1 .

[0046] The type of acid center and its acid content were determined by pyridine adsorption infrared in-situ measurement. Experimental instrument: Bruker IFS113V FT-IR (Fourier Transform Infrared) spectrometer. Method for determining acid content by pyridine adsorption infrared method: The sample was pressed into a self-supporting pellet and sealed in the in-situ cell of the infrared spectrometer. The temperature was raised to 400°C and the vacuum was reduced to 10 -3 Pa, keep the temperature constant for 2 hours, remove the gas molecules adsorbed by the sample. Cool down to room temperature, introduce pyridine vapor with a pressure of 2.67Pa and maintain adsorption equilibrium for 30 minutes. Then heat up to 200℃ and evacuate to 10 -3 Desorb at 30 min under Pa, cool to room temperature and take spectrum. Scanning wave number range: 1400 cm -1 -1700cm -1 The pyridine adsorption infrared spectrum of the sample was obtained after desorption at 200℃. -1 and 1450cm -1 The intensity of the characteristic adsorption peak is used to obtain the total The relative amount of acid centers (B acid centers) and Lewis acid centers (L acid centers).

[0047] After adsorption, the temperature is raised to 350℃ and the vacuum is drawn to 10 -3 After desorption at Pa for 30 minutes, the measured acid amounts are strong B acid and strong L acid. The weak B acid is obtained by subtracting the strong B acid from the total B acid, and the weak L acid is obtained by subtracting the strong L acid from the total L acid.

[0048] In the following examples and comparative examples, the room temperature is 25°C.

[0049] Example 1

[0050] HY molecular sieve (produced by the Changling Catalyst Plant of Sinopec Catalyst Co., Ltd., having a sodium oxide content of 0.84% ​​by mass, a silicon-aluminum ratio of 4.3, and a relative crystallinity of 86% (see RIPP 146-90 Ultrastable Y Molecular Sieve Relative Crystallinity Determination Method, Yang Cuiding et al., ed., Petrochemical Analysis Methods (RIPP Test Method), Science Press, 1990). 10 times the mass of water and 0.5 times the mass of ammonium chloride were added to exchange sodium at a temperature of 60° C. for 2 h. After the exchange, the mixture was filtered, and the filter cake was taken and exchanged once again according to the above method, filtered, and dried to obtain the exchanged molecular sieve with a Na O content of 0.1% by mass.

[0051] A 0.2 mol / L oxalic acid solution was prepared and stirred to dissolve Nb(OH)5 at 80°C, where the molar ratio of Nb to oxalic acid was 1:1. This solution was then supersaturated with the exchanged molecular sieve, where the mass ratio of niobium to molecular sieve was 0.5:100. After impregnation at room temperature for 24 hours, the solution was placed in an oven, dried at 110°C for 2 hours, ground, and then placed in a muffle furnace at room temperature. The temperature was raised to 550°C over 2 hours and then calcined at 550°C for 3 hours. The prepared molecular sieve was subjected to acidity measurement and microreaction evaluation. The results are shown in Tables 1 and 2.

[0052] Example 2

[0053] HY molecular sieve (same as Example 1) was added with 10 times the mass of water and 0.5 times the mass of ammonium chloride to exchange sodium. The exchange temperature was 60° C. and the exchange time was 2 h. After the exchange was completed, the mixture was filtered. The filter cake was taken and the exchange was repeated once, filtered, and dried. The Na2O content was 0.1% by mass to obtain the exchanged Y molecular sieve.

[0054] A 0.2 mol / L oxalic acid solution was prepared and stirred to dissolve Nb(OH)5 at 80°C, with a molar ratio of Nb to oxalic acid of 1:1. This solution was then supersaturated with the exchanged Y molecular sieve, with a mass ratio of niobium to molecular sieve of 1:100. After impregnation at room temperature for 24 hours, the solution was dried in an oven at 110°C for 2 hours, ground, and then placed in a muffle furnace at room temperature. The temperature was raised to 550°C over 2 hours and then calcined at 550°C for 3 hours. The prepared molecular sieve was then subjected to micro-reaction evaluation.

[0055] Comparative Example 1

[0056] HY (same as in Example 1) was added with 10 times the amount of water and 0.5 times the amount of ammonium chloride to exchange sodium at 60°C for 2 hours. After the exchange, the mixture was filtered. The filter cake was taken and exchanged once more, filtered, dried, and calcined at 550°C for 3 hours to obtain hydrogen-type Y molecular sieve (HY molecular sieve) with a Na2O content of 0.1% by mass. The prepared molecular sieve was subjected to micro-reaction evaluation.

[0057] Comparative Example 2

[0058] The method of Example 2 was followed, except that oxalic acid was not used for impregnation.

[0059] Comparative Example 3

[0060] The method of Example 2 was followed, except that the concentration of oxalic acid was 0.5 mol / L.

[0061] Comparative Example 4

[0062] The modified Y-type molecular sieve was prepared according to the method of Example 2, except that citric acid solution of equal concentration was mixed and stirred with Nb(OH)5.

[0063] Comparative Example 5

[0064] The modified Y-type molecular sieve was prepared according to the method of Example 2, except that the molar ratio of Nb to oxalic acid was 0.4:1.

[0065] Example 3

[0066] The modified Y molecular sieve was prepared according to the method of Example 1, except that during the impregnation, the mass ratio of Nb to the exchanged Y molecular sieve was 0.2:100.

[0067] Example 4

[0068] The modified Y molecular sieve was prepared according to the method of Example 1, except that during the impregnation, the mass ratio of Nb to the exchanged Y molecular sieve was 1.5:100.

[0069] Example 5

[0070] The modified Y molecular sieve was prepared according to the method of Example 1, except that the mass ratio of Nb to the exchanged Y molecular sieve was 0.8:100.

[0071] Example 6

[0072] Modified Y molecular sieve was prepared according to the method of Example 1, except that the concentration of the oxalic acid solution was 0.1 mol / L.

[0073] Example 7

[0074] Modified Y molecular sieve was prepared according to the method of Example 1, except that the concentration of oxalic acid was 0.3 mol / L.

[0075] Table 1 Total acid content and acid distribution of modified Y-type molecular sieves in Examples and Comparative Examples

[0076]

[0077] Table 2 Yield and selectivity of pure hydrocarbon micro-reaction light olefin products

[0078]

Claims

1. A modified Y-type molecular sieve containing a modifying element, niobium, wherein the niobium content, calculated as niobium element, is greater than 0-2% by mass. Compared with the HY-type molecular sieve, the modified Y-type molecular sieve has a strong L-acid content increased by 15-45 μmol·g -1 , the amount of weak L-acid increases by 10 to 80 μmol·g -1 ; The acidity was measured by pyridine adsorption infrared spectroscopy, and the acidity of B acid was measured at 1540 cm -1 The absorption peak at 1450cm -1 The total acid amount is the acid amount measured after vacuum desorption at 200°C, the weak acid amount is the difference between the total acid amount and the acid amount measured after vacuum desorption at 350°C, and the strong acid amount is the acid amount measured after vacuum desorption at 350°C.

2. The modified Y-type molecular sieve according to claim 1, wherein The modified Y-type molecular sieve has a weak L acid content of 30 to 100 μmol·g -1 , the acidity of strong L-acid is 100~160μmol·g -1 In one embodiment, the modified Y-type molecular sieve has a weak B acid content of 30 to 100 μmol·g -1 ; The modified Y-type molecular sieve has a strong B acid content of 70 to 100 μmol·g -1 In one embodiment, the ratio of the amount of strong B acid to the amount of strong L acid is: 0.5~0.85:1; the acid ratio of weak B acid to weak L acid is: 0.45～0.9：1。 3. The modified Y-type molecular sieve according to claim 1 or 2, wherein The niobium content is 0.1-2 mass % in terms of Nb, for example, 0.2-1 mass %; the sodium oxide content in the modified Y-type molecular sieve is preferably less than 1 mass %, and the sodium oxide content in the HY-type molecular sieve is preferably less than 1 mass %.

4. The modified Y-type molecular sieve according to any one of claims 1 to 3, wherein The silicon-aluminum ratio of the modified Y-type molecular sieve is 3 to 6 in terms of SiO2 / Al2O3 molar ratio. In one embodiment, the modified Y-type molecular sieve has the same silicon-aluminum ratio as the HY-type molecular sieve.

5. A method for preparing a modified Y molecular sieve, the method comprising: a. obtaining a Y-type molecular sieve having a sodium oxide content not exceeding 1% by mass; b. Dissolve Nb(OH)5 in 0.1-0.3 mol / L oxalic acid solution. The molar ratio of Nb to oxalic acid in the oxalic acid solution is greater than 0.5:1 and less than 1.1:1, and the Y-type molecular sieve obtained in step a is impregnated, dried, and calcined.

6. The method according to claim 5, wherein The content of sodium oxide in the Y-type molecular sieve in step a is 0.01 to 1% by mass.

7. The method according to claim 5, wherein The Y-type molecular sieve in step a is obtained by washing the NaY molecular sieve with an ammonium salt solution for sodium exchange; In one embodiment, the sodium washing exchange conditions are: According to the mass ratio of molecular sieve: ammonium salt: H2O = 1: (0.1-1): (5-10), the exchange is carried out at room temperature to 100°C for 0.5-3 hours, and then filtered; the sodium washing exchange can be carried out one or more times, and each exchange can be calcined or not after calcination, so that the sodium oxide content in the molecular sieve is not higher than 1% by mass; The ammonium salt may be one or more of ammonium chloride, ammonium sulfate and ammonium nitrate.

8. The method according to claim 5, wherein In step b, the molar ratio of Nb to oxalic acid in the oxalic acid solution is 0.7-1.05:1, preferably 1:

1.

9. The method according to claim 5, wherein In step b, the impregnation is carried out at room temperature for 20 to 30 hours; the calcination temperature is 400-700° C. and the calcination time is 0.5-8 hours; the impregnation is, for example, supersaturated impregnation, and the mass content of niobium in the modified Y-type molecular sieve obtained by the impregnation is preferably 0.1 to 2 mass % in terms of niobium element.

10. The method according to claim 5, wherein In step b, the molecular sieve obtained after drying is heated to a calcination temperature and then calcined. The heating to the calcination temperature can be carried out from room temperature over 1 to 3 hours. The calcination temperature is preferably 450-600°C, and the calcination time is preferably 1 to 6 hours.

11. Use of the modified molecular sieve according to any one of claims 1 to 4 in catalytic cracking of cycloalkanes and cyclopentanes.

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