阅读说明：本技术 一种多产异构c4的高稳定性改性y型分子筛及其制备方法 (High-stability modified Y-type molecular sieve for producing more isomeric C4 and preparation method thereof ) 是由 袁帅 田辉平 周灵萍 陈振宇 张蔚琳 沙昊 于 2018-06-29 设计创作，主要内容包括：一种多产异构C4的高稳定性改性Y型分子筛及其制备方法,该改性Y型分子筛的CaO含量为0.3～4重量％,RE<Sub>2</Sub>O<Sub>3</Sub>含量为2～7重量％,Na<Sub>2</Sub>O含量为0.1～0.5重量％,总孔体积为0.33～0.39mL/g,2～100nm的二级孔的孔体积占总孔体积的10～25％,晶胞常数为2.440～2.455nm,非骨架铝含量占总铝含量比例不高于20％,晶格崩塌温度不低于1050℃,用吡啶吸附红外法在200℃时测定的B酸量与L酸量的比值不低于2.30。所述的制备方法包括离子交换、在一定的温度和水蒸汽条件下改性处理以及与四氯化硅反应的步骤。该改性Y型分子筛,具有更高的重油转化活性和较低的焦炭选择性,具有更高的汽油收率、异构C4收率,汽油中具有更高的异构烃含量。(The high-stability modified Y-type molecular sieve for producing more heterogeneous C4 and the preparation method thereof, wherein the CaO content of the modified Y-type molecular sieve is 0.3-4 wt%, and RE content of the modified Y-type molecular sieve 2 O 3 2 to 7% by weight of Na 2 The content of O is 0.1-0.5 wt%, the total pore volume is 0.33-0.39 mL/g, the pore volume of secondary pores with the diameter of 2-100 nm accounts for 10-25% of the total pore volume, the unit cell constant is 2.440-2.455 nm, the proportion of non-framework aluminum content in the total aluminum content is not higher than 20%, the lattice collapse temperature is not lower than 1050 ℃, and the ratio of B acid content to L acid content measured by a pyridine adsorption infrared method at 200 ℃ is not lower than 2.30. The preparation method comprises the steps of ion exchange, modification treatment under certain temperature and water vapor conditions and reaction with silicon tetrachloride. The modified Y-type molecular sieve has higher heavy oil conversion activity and higher heavy oil conversion activityLow coke selectivity, higher gasoline yield and isomeric C4 yield, and higher content of isomeric hydrocarbon in gasoline.)

1. A modified Y-type molecular sieve is characterized in that the content of calcium oxide in the modified Y-type molecular sieve is 0.3-4 wt%, the content of rare earth oxide is 2-7 wt%, the content of sodium oxide is not more than 0.5 wt%, the total pore volume is 0.33-0.39 mL/g, the pore volume of secondary pores with the pore diameter of 2-100 nm accounts for 10-25% of the total pore volume, the unit cell constant is 2.440-2.455 nm, the content of non-framework aluminum in the modified Y-type molecular sieve accounts for not more than 20% of the total aluminum content, the lattice collapse temperature is not lower than 1050 ℃, and the ratio of the B acid amount to the L acid amount in the total acid amount of the modified Y-type molecular sieve measured by a pyridine adsorption infrared method at 200 ℃ is not lower than 2.30.

2. The modified Y-type molecular sieve of claim 1, wherein the modified Y-type molecular sieve has secondary pores with a pore size of 2nm to 100nm, the pore volume percentage of which is 15% to 21% of the total pore volume.

3. The modified Y-type molecular sieve of claim 1, wherein the non-framework aluminum content of the modified Y-type molecular sieve is 13-19% of the total aluminum content, and the framework silica-alumina ratio is SiO₂/Al₂O₃The molar ratio is 7.3-14.

4. The modified Y-type molecular sieve of claim 1, wherein the modified Y-type molecular sieve has a lattice collapse temperature of 1050-1080 ℃ or 1050-1063 ℃.

5. The modified Y-type molecular sieve of claim 1, wherein the ratio of the amount of B acid to the amount of L acid in the total acid amount of the modified Y-type molecular sieve measured at 200 ℃ by pyridine adsorption infrared method is 2.3 to 5.0, or 2.4 to 4.2, or 2.4 to 3.5.

6. The modified Y-type molecular sieve of claim 1, wherein the modified Y-type molecular sieve has a relative crystal retention of 35% or more, for example, 36 to 45% or 35 to 48%, after aging at 800 ℃ under normal pressure in a 100% steam atmosphere for 17 hours.

7. The modified Y-type molecular sieve of claim 1, wherein the modified Y-type molecular sieve has a relative crystallinity of 58 to 68%.

8. The modified Y-type molecular sieve of any one of claims 1 to 7, wherein the modified Y-type molecular sieve has a calcium oxide content of 0.3 to 4 wt%, a rare earth oxide content of 2 to 7 wt%, a sodium oxide content of 0.2 to 0.5 wt%, a unit cell constant of 2.442 to 2.452nm, and a framework Si/Al ratio of 8 to 12.6.

9. A preparation method of a modified Y-type molecular sieve comprises the following steps:

(1) contacting the NaY molecular sieve with a soluble calcium salt and a rare earth salt solution to perform an ion exchange reaction, filtering, washing and optionally drying to obtain a Y-type molecular sieve with conventional unit cell size, wherein the content of sodium oxide is reduced, and the Y-type molecular sieve contains calcium and rare earth;

(2) roasting the calcium-and rare earth-containing Y-type molecular sieve with the conventional unit cell size and reduced sodium oxide content for 4.5-7 hours at the temperature of 350-480 ℃ in the atmosphere of 30-90 vol% of water vapor, and optionally drying to obtain the Y-type molecular sieve with the reduced unit cell constant;

(3) according to SiCl₄: the Y-type molecular sieve with reduced unit cell constant is 0.1-0.7: 1, carrying out contact reaction on the Y-shaped molecular sieve with the reduced unit cell constant and silicon tetrachloride gas at the reaction temperature of 200-650 ℃ for 10 minutes to 5 hours, washing and filtering to obtain the modified Y-shaped molecular sieve.

10. The process of claim 9, wherein the calcium and rare earth-containing Y-type molecular sieve having a conventional unit cell size with a reduced sodium oxide content in step (1) has a unit cell constant of 2.465 to 2.472nm and a sodium oxide content of not more than 8.8 wt.%.

11. The method according to claim 9, wherein in the step (1), the calcium content of the calcium and rare earth-containing Y-type molecular sieve of the conventional unit cell size with the reduced sodium oxide content is 0.4 to 10 wt% in terms of CaO, and the rare earth content is RE in terms of RE₂O₃2 to 8 wt%, a sodium oxide content of 4 to 8.8 wt%, for example, 5.5 to 8.5 wt%, and a cell constant of 2.465nm to 2.472 nm.

12. The method of claim 9, wherein the first and second optical elements are selected from the group consisting of,the method is characterized in that in the step (1), the NaY molecular sieve is contacted with soluble calcium salt and rare earth salt solution for ion exchange reaction, according to the NaY molecular sieve: soluble calcium salt: soluble rare earth salt: h₂O is 1: 0.009-0.28: 0.005-0.09: 5-15, mixing the NaY molecular sieve, the soluble calcium salt, the soluble rare earth salt and water, and stirring.

13. The method of claim 9 or 12, wherein the step (1) of contacting the NaY molecular sieve with a solution of a soluble calcium salt and a rare earth salt to perform an ion exchange reaction comprises: mixing NaY molecular sieve with water, adding soluble calcium salt and/or soluble calcium salt solution and soluble rare earth salt and/or soluble rare earth salt solution under stirring to perform ion exchange reaction, filtering and washing; the conditions of the ion exchange reaction are as follows: the exchange temperature is 15-95 ℃, and the exchange time is 30-120 minutes; the soluble calcium salt solution and the rare earth salt solution are aqueous solutions of soluble calcium salt and soluble rare earth salt; the soluble calcium salt is calcium chloride and/or calcium nitrate, and the soluble rare earth salt is rare earth chloride and/or rare earth nitrate.

14. The method according to claim 9, wherein the roasting temperature in the step (2) is 380 to 460 ℃, the roasting atmosphere is 40 to 80% of water vapor atmosphere, and the roasting time is 5 to 6 hours.

15. The method according to claim 9, wherein the unit cell constant of the Y-type molecular sieve having a decreased unit cell constant obtained in step (2) is 2.450nm to 2.462nm, and the water content of the Y-type molecular sieve having a decreased unit cell constant is not more than 1% by weight.

16. The method according to claim 9, wherein the washing method in the step (3) is washing with water under the washing conditions that the molecular sieve: h₂O is 1: 6-15, the pH value is 2.5-5.0, and the washing temperature is 30-60 ℃.

Technical Field

The invention relates to a high-stability modified Y-type molecular sieve for producing more isomeric C4 hydrocarbons and a preparation method thereof.

Background

At present, the industrial preparation of the high-silicon Y-type zeolite mainly adopts a hydrothermal method, the NaY zeolite is subjected to multiple rare earth ion exchange and multiple high-temperature roasting, and the rare earth-containing high-silicon Y-type zeolite can be prepared, which is the most conventional method for preparing the high-silicon Y-type zeolite, but the hydrothermal method for preparing the rare earth high-silicon Y-type zeolite has the defects that: because the structure of the zeolite can be damaged by too harsh hydrothermal treatment conditions, the Y-type zeolite with high silica-alumina ratio can not be obtained; although the generation of extra-framework aluminum is beneficial to improving the stability of the zeolite and forming new acid centers, the excessive extra-framework aluminum reduces the selectivity of the zeolite, and in addition, a plurality of dealumination cavities in the zeolite cannot be timely supplemented by silicon migrated from the framework, so that the lattice defect of the zeolite is often caused, and the crystal retention of the zeolite is low. And because the conventional Y molecular sieve only contains rare earth, silicon, aluminum and other elements, the adjustment of the structure and the performance of the conventional Y molecular sieve is limited in a certain range, and the composition of a product is often stabilized in a certain range. Therefore, the thermal and hydrothermal stability of the rare earth-containing high-silicon Y-type zeolite prepared by the hydrothermal method is poor, which is shown in that the lattice collapse temperature is low, the crystallinity retention rate and the specific surface area retention rate are low after hydrothermal aging, and the selectivity is poor. Another method for producing high-silicon Y-type zeolite is gas phase chemical, which generally employs SiCl under nitrogen protection₄Reacting with anhydrous NaY zeolite at a certain temperature. U.S. Pat. Nos. 4,42737,178, U.S. Pat. No. 4,4438178, Chinese patent Nos. CN1382525A, CN1194941A and CN1683244A disclose the use of SiCl₄A process for preparing ultra-stable Y-type zeolite by gas-phase chemical dealumination. However, the existing gas phase ultrastable molecular sieve is unfavorable for the isomerization reaction of the hydrocarbon catalytic cracking process. The content of isomeric hydrocarbon in the isomeric C4 and gasoline produced by the catalyst prepared by the conventional Y molecular sieve is stable in a certain range and is difficult to increase.

Zhuhuayuan (Petroleum institute, 2001, 17(6):6-10) et al proposed the effect of magnesium-containing modified molecular sieve on the performance of FCC catalyst. Researches find that the FCC catalyst containing the Mg and Ca molecular sieves has higher isobutane product content. However, the Y molecular sieve prepared by the method has poor thermal and hydrothermal stability, and can only increase the content of isobutane generally, but cannot effectively increase the content of isomeric hydrocarbon in gasoline.

Disclosure of Invention

One of the technical problems to be solved by the invention is to provide a high-yield isomeric C4 suitable for the catalytic cracking processing of heavy oil and a modified Y-type molecular sieve (Y-type molecular sieve is also called Y-type zeolite) which can improve the content of isomeric hydrocarbon in gasoline and has high stability. The second technical problem to be solved by the invention is to provide a preparation method of the modified Y-type molecular sieve.

The invention provides a modified Y-type molecular sieve, wherein the calcium oxide content of the modified molecular sieve is 0.3-4 wt%, the rare earth oxide content is 2-7 wt%, the sodium oxide content is not more than 0.5 wt%, such as 0.1-0.5 wt%, the total pore volume is 0.33-0.39 mL/g, the pore volume of secondary pores with the pore diameter of 2-100 nm accounts for 10-25% of the total pore volume of the modified Y-type molecular sieve, the unit cell constant is 2.440-2.455 nm, and the framework silicon-aluminum ratio (SiO is)₂/Al₂O₃Molar ratio) is: 7.3-14.0, the percentage of non-framework aluminum content in the molecular sieve to the total aluminum content is not higher than 20%, the lattice collapse temperature is not lower than 1050 ℃, and the ratio of the B acid amount to the L acid amount in the total acid amount of the modified Y-type molecular sieve measured by a pyridine adsorption infrared method at 200 ℃ is not lower than 2.30.

The modified Y-type molecular sieve provided by the invention has the pore volume of secondary pores with the pore diameter (diameter) of 2-100 nm accounting for 10-25% of the total pore volume, and preferably 15-21% or 15-23% or 17-21%.

The modified Y-type molecular sieve provided by the invention has the non-framework aluminum content accounting for not more than 20% of the total aluminum content, such as 10-20% or 13-19% by weight.

The modified Y-type molecular sieve provided by the invention is a high-silicon Y-type molecular sieve, and the framework silicon-aluminum ratio (SiO) of the high-silicon Y-type molecular sieve₂/Al₂O₃Molar ratio) of 7.3 to 14.0Examples are: 8 to 12.6.

The modified Y-type molecular sieve provided by the invention has a lattice collapse temperature (also called structure collapse temperature) of not less than 1050 ℃, for example, the lattice collapse temperature of the molecular sieve is 1050-1080 ℃, preferably 1050-1063 ℃ or 1052-1065 ℃.

The ratio of the B acid amount to the L acid amount in the total acid amount of the modified Y-type molecular sieve determined by a pyridine adsorption infrared method at 200 ℃ is preferably 2.4-4.2, 2.4-3.5 or 2.3-5.0.

The unit cell constant of the modified Y-type molecular sieve provided by the invention is 2.440-2.455 nm, such as 2.442-2.452 nm.

The modified Y-type molecular sieve provided by the invention has a crystal retention of over 35%, such as 36-45%, 38-44%, 35-48% or 39-45%, after aging for 17 hours at 800 ℃ under normal pressure and in a 100 volume% steam atmosphere. The normal pressure is 1 atm.

The relative crystallinity of the modified Y-type molecular sieve provided by the invention is not less than 58%, such as 58-68%, 59-63%, 60-70% or 60-66%.

The invention provides a modified Y-type molecular sieve, one embodiment of which has a specific surface area of 620-670 m²The/g is, for example, 630 to 660m²/g。

The modified Y-type molecular sieve provided by the invention has the preferable total pore volume of 0.35-0.39 mL/g, such as 0.35-0.375 mL/g.

In one embodiment, the modified Y-type molecular sieve provided by the invention has a micropore volume of 0.25-0.35 mL/g, such as 0.26-0.32 mL/g or 0.28-0.31 mL/g.

The modified Y-type molecular sieve contains calcium and rare earth elements, the calcium content of the modified Y-type molecular sieve is 0.3-4 wt% calculated by CaO, such as 0.5-3.5 wt% or 0.9-3 wt% or 0.9-4 wt%, and Re is added in the modified Y-type molecular sieve₂O₃The rare earth content is preferably 2 to 7 wt%, for example 2.5 to 6.5 wt%, for example 2.5 to 4.5 wt%.

The modified Y-type molecular sieve provided by the invention has the sodium oxide content of not more than 0.5%, and can be 0.15-0.5 wt%, such as 0.3-0.5 wt%, or 0.20-0.45 wt%, or 0.25-0.4 wt%.

The invention provides a preparation method of a modified Y-type molecular sieve, which comprises the following steps:

(1) contacting the NaY molecular sieve with soluble calcium salt and rare earth salt solution to perform ion exchange reaction, filtering and washing to obtain a Y-type molecular sieve with conventional unit cell size, reduced sodium oxide content and containing calcium and rare earth; wherein the soluble calcium salt solution is also called calcium salt solution, and the soluble rare earth salt solution is also called rare earth salt solution;

(2) modifying the Y-type molecular sieve with the conventional unit cell size and the reduced sodium oxide content and containing calcium and rare earth, and optionally drying to obtain the Y-type molecular sieve with the reduced unit cell constant, wherein the modifying treatment is to roast the Y-type molecular sieve with the conventional unit cell size and the reduced sodium oxide content and containing calcium and rare earth at the temperature of 350-480 ℃ in an atmosphere containing 30-90 vol% of water vapor (also called 30-90 vol% of water vapor atmosphere or 30-90 vol% of water vapor) for 4.5-7 hours;

(3) mixing the Y-type molecular sieve sample with SiCl, wherein the unit cell constant is reduced₄Gas is contacted and reacted at the temperature of 200-650 ℃, wherein SiCl is contained₄: the weight ratio of the Y-type molecular sieve with reduced unit cell constant obtained in the step (2) on a dry basis is 0.1-0.7: 1, reacting for 10 minutes to 5 hours, and then washing and filtering to obtain the modified Y-type molecular sieve. Wherein the water content of the Y-type molecular sieve having a reduced unit cell constant is preferably not more than 1% by weight; if the water content in the Y-type molecular sieve obtained by modification treatment in the step (2) (in a Y-type molecular sieve sample obtained by roasting) is not more than 1 wt%, the Y-type molecular sieve can be directly used for contacting silicon tetrachloride to carry out the reaction, and if the water content in the Y-type molecular sieve obtained by roasting in the step (2) is more than 1 wt%, the Y-type molecular sieve with the reduced unit cell constant obtained by roasting in the step (2) is dried to ensure that the water content is less than 1 wt%.

The modified Y-type molecular sieve provided by the invention has high thermal and hydrothermal stability and high selectivity of isomeric hydrocarbon. The catalyst is used for heavy oil catalytic cracking, has higher heavy oil conversion activity and lower coke selectivity than the prior Y-type molecular sieve, has higher gasoline yield and isomeric C4 yield, has higher light oil yield and total liquid yield, and has more isomeric hydrocarbons in gasoline.

The preparation method of the calcium and rare earth modified Y-shaped molecular sieve can prepare the high-silicon Y-shaped molecular sieve with a certain secondary pore structure and high crystallinity, high thermal stability and high hydrothermal stability, the calcium and rare earth containing molecular sieve has uniform aluminum distribution and less non-framework aluminum content, the modified Y-shaped molecular sieve is used for heavy oil conversion, the coke selectivity is good, the heavy oil cracking activity is high, the gasoline yield, the isomeric C4 yield and the isomeric hydrocarbon content in gasoline of the molecular sieve used for heavy oil conversion can be improved, and the liquefied gas yield, the light oil yield and the total liquid yield are improved.

In the present invention, the isoparaffin refers to a chain isoparaffin and a chain isoolefin.

The modified Y-type molecular sieve provided by the invention can be used as an active component of a catalytic cracking catalyst and used for converting heavy oil or poor oil; the method can also be used for adsorption desulfurization of gasoline so as to improve the octane number of the desulfurized gasoline; it can also be used for lubricating oil isomerization pour point depression. The catalytic cracking catalyst with the molecular sieve as an active component has the advantages of strong heavy oil conversion capability, high stability, good coke selectivity, high gasoline yield, high light oil yield, high total liquid yield and high yield of isomeric C4, and the gasoline has high content of isomeric hydrocarbon. Increasing the content of iso-hydrocarbons in gasoline may improve the quality of gasoline, for example, may allow gasoline to have a higher octane number with a reduced content of olefins or aromatics.

Detailed Description

In one embodiment, the modified Y-type molecular sieve has a calcium oxide content of 0.3 to 4 wt%, preferably 0.5 to 3.5 wt%, and a rare earth oxide content of 2 to 7 wt%, preferably 2.5 to 6.5 wt%, for example 2.5 to 4.5 wt%. The content of sodium oxide is 0.1 to 0.5 wt%, for example 0.3 to 0.5 wt% or 0.13 to 0.4 wt%, the total pore volume is 0.33 to 0.39mL/g, the percentage of the pore volume of the secondary pores having a pore diameter of 2 to 100nm to the total pore volume is 10 to 25%, preferably 15 to 21%, and the unit cell is usually a unit cellThe number of the silica-alumina particles is 2.440-2.455 nm, and the framework silicon-alumina ratio (SiO)₂/Al₂O₃Molar ratio) is: 7.3-14.0, the percentage of non-framework aluminum content in the molecular sieve in the total aluminum content is not higher than 20%, preferably 13-19, the relative crystallinity is not lower than 58%, the lattice collapse temperature is 1050-1080 ℃ or 1052-1065 ℃, and the ratio of the B acid amount to the L acid amount in the total acid amount of the modified Y-type molecular sieve measured at 200 ℃ by using a pyridine adsorption infrared method is not lower than 2.30, preferably 2.4-4.2.

The preparation process of the modified Y-type molecular sieve comprises the step of contacting the Y-type molecular sieve with silicon tetrachloride to carry out dealuminization and silicon supplementation reaction.

In the preparation method of the modified Y-type molecular sieve, in the step (1), the NaY molecular sieve is contacted with soluble calcium salt and rare earth salt solution to carry out ion exchange reaction, so as to obtain the Y-type molecular sieve with conventional unit cell size and reduced sodium oxide content and containing calcium. The soluble calcium salt and the rare earth salt are a calcium salt capable of being dissolved in a solvent and a rare earth salt capable of being dissolved in a solvent, and the contacting can be carried out by contacting the NaY molecular sieve with a soluble calcium salt solution and a soluble rare earth salt for ion exchange (for example, contacting with a rare earth salt solution and then a calcium salt solution, or contacting with a calcium salt solution and then a rare earth salt solution), or contacting with a solution containing a soluble calcium salt and a soluble rare earth salt (also referred to as a mixed solution of a soluble calcium salt and a rare earth salt in the invention), and the mixed solution of the soluble calcium salt and the soluble rare earth salt can be obtained by mixing the soluble calcium salt and the soluble rare earth salt with a solvent such as water. The NaY molecular sieve can be purchased commercially or prepared according to the existing method, and in one embodiment, the unit cell constant of the NaY molecular sieve is 2.465-2.472 nm, and the framework silicon-aluminum ratio (SiO)₂/Al₂O₃Molar ratio) of 4.5 to 5.2, a relative crystallinity of 85% or more, for example, 85 to 95%, and a sodium oxide content of 13.0 to 13.8% by weight. The NaY molecular sieve, the soluble calcium salt and the rare earth salt solution are subjected to ion exchange reaction, the exchange temperature is preferably 15-95 ℃, for example 65-95 ℃, and the exchange time is preferably 30-120 minutes, for example 45-90 minutes. NaY molecular sieve (dry basis) calciumSalts (calculated as CaO) rare earth salts (calculated as RE)₂O₃Meter): h₂O is 1: 0.009-0.28: 0.005-0.09: 5-15 by weight. The rare earth salt is soluble rare earth salt, and the calcium salt is soluble calcium salt. In one embodiment, the ion exchange reaction of the NaY molecular sieve in contact with the soluble calcium salt and the rare earth salt solution comprises the following steps of₂The method comprises the steps of mixing NaY molecular sieve (also called NaY zeolite), calcium salt, rare earth salt and water in a weight ratio of 1: 0.009-0.27: 0.005-0.09: 5-15, and carrying out exchange of calcium ions and rare earth ions with sodium ions by stirring at 15-95 ℃, such as 65-95 ℃, preferably for 30-120 minutes. The NaY molecular sieve, the calcium salt, the rare earth salt and water are mixed to form a mixture, the NaY molecular sieve and the water can be formed into slurry, and then the calcium salt and/or the calcium salt water solution, the rare earth salt and/or the rare earth salt water solution are added into the slurry. The calcium salt is preferably calcium chloride and/or calcium nitrate. The rare earth salt is preferably rare earth chloride and/or rare earth nitrate. The rare earth such as one or more of La, Ce, Pr, Nd and misch metal, preferably, the misch metal contains one or more of La, Ce, Pr and Nd, or further contains at least one of rare earth other than La, Ce, Pr and Nd. The washing in step (1) is intended to wash out exchanged sodium ions, and for example, deionized water or decationized water may be used for washing. Preferably, the calcium content of the calcium and rare earth-containing Y-type molecular sieve with a conventional unit cell size and reduced sodium oxide content obtained in step (1) is 0.3 to 10 wt%, for example, 0.4 to 9 wt%, or 0.4 to 6 wt%, or 1 to 5 wt%, or 2 to 4 wt%, or 0.3 to 4 wt%, or 3 to 6 wt%, or 3.5 to 5.5 wt%, or 4 to 9 wt% in terms of CaO, and the rare earth content is Re₂O₃2 to 8 wt% or 2.1 to 7 wt% or 3 to 7 wt% or 4 to 6 wt%, sodium oxide content of not more than 9 wt%, for example, 5.5 to 8.5 wt% or 5.5 to 7.5 wt%, and unit cell constant of 2.465nm to 2.472 nm.

In the preparation method of the modified Y-type molecular sieve, the Y-type molecular sieve containing calcium and rare earth in the conventional unit cell size is roasted for 4.5-7 hours at the temperature of 350-480 ℃ in the atmosphere of 30-90 vol% of water vapor in step (2), preferably, the roasting temperature in step (2) is 380-460 ℃, the roasting atmosphere is 40-80 vol% of water vapor, and the roasting time is 5-6 hours. The water vapor atmosphere contains 30-90% by volume, preferably 40-80% by volume of water vapor, and also contains other gases, such as one or more of air, helium or nitrogen. The Y-type molecular sieve with the reduced unit cell constant in the step (2) has the unit cell constant of 2.450 nm-2.462 nm. Preferably, the calcined molecular sieve is also dried in step (2) so that the water content in the Y-type molecular sieve having a reduced unit cell constant is preferably not more than 1 wt%.

In the preparation method of the modified Y-type molecular sieve, SiCl is adopted in the step (3)₄: the weight ratio of the Y-type zeolite (on a dry basis) is preferably 0.3-0.6: 1, the reaction temperature is preferably 350-500 ℃, and the washing method in the step (3) can adopt a conventional washing method, and can be washed by water, such as decationized water or deionized water, so as to remove Na remained in the zeolite⁺，Cl^-And Al³⁺Etc. soluble by-products, for example the washing conditions may be: the weight ratio of the washing water to the molecular sieve can be 5-20: 1, typically molecular sieve: h₂The weight ratio of O is 1: 6-15, the pH value is preferably 2.5-5.0, and the washing temperature is 30-60 ℃. Preferably, the washing is performed such that no free Na is detected in the washing solution after washing⁺，Cl^-And Al³⁺Plasma, Na in the washing liquid after washing in general⁺，Cl^-And Al³⁺The respective contents of ions do not exceed 0.05 wt.%.

The preparation method of the modified Y-type molecular sieve provided by the invention comprises the following steps:

(1) contacting a NaY molecular sieve (also called NaY zeolite) with a mixed solution of soluble calcium salt and rare earth salt for ion exchange reaction, filtering and washing to obtain a Y-type molecular sieve with conventional unit cell size, reduced sodium oxide content and containing calcium and rare earth; the ion exchange is carried out for 30-120 minutes under the conditions of stirring and the temperature of 15-95 ℃, preferably 65-95 ℃;

(2) roasting the calcium-and rare earth-containing Y-type molecular sieve with the conventional unit cell size and reduced sodium oxide content for 4.5-7 hours at the temperature of 350-480 ℃ in the atmosphere containing 30-90 vol% of water vapor, and drying to obtain the Y-type molecular sieve with the reduced unit cell constant and the water content of less than 1 wt%; the unit cell constant of the Y-type molecular sieve with the reduced unit cell constant is 2.450 nm-2.462 nm;

(3) mixing the Y-type molecular sieve with water content lower than 1 wt% and SiCl vaporized by heating₄Gas contact of SiCl₄: the weight ratio of the Y-type molecular sieve with the water content lower than 1 wt% and the reduced unit cell constant (calculated by dry basis) is 0.1-0.7: 1, carrying out contact reaction for 10 minutes to 5 hours at the temperature of 200-650 ℃, and washing and filtering to obtain the modified Y-type molecular sieve provided by the invention.

The following examples further illustrate the invention but are not intended to limit the invention thereto.