阅读说明：本技术 一种多产双甲基异构烃的高稳定性改性y型分子筛及其制备方法 (High-stability modified Y-type molecular sieve for producing more dimethyl isomeric hydrocarbon and preparation method thereof ) 是由 袁帅 周灵萍 田辉平 陈振宇 张蔚琳 沙昊 于 2018-06-29 设计创作，主要内容包括：一种多产双甲基异构烃的高稳定性改性Y型分子筛及其制备方法,该改性Y型分子筛的CaO含量为0.7～6.3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1040℃,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,具有较低的焦炭选择性,具有更高的汽油收率、液化气收率,汽油中具有更高的异构烃含量,双甲基异构烃含量/单甲基异构烃含量较高。(High-stability modified Y-type molecular sieve for increasing yield of dimethyl isomeric hydrocarbon and preparation method thereof, wherein CaO content of the modified Y-type molecular sieve is 0.7-6.3 wt%, and Na content 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 1040 ℃, and the ratio of the B acid content to the L acid content measured by a pyridine adsorption infrared method at 200 ℃ is not lower than 2.30. The preparation methodComprises 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 the advantages of low coke selectivity, high gasoline yield and high liquefied gas yield, and the gasoline has high content of isomeric hydrocarbon and high content of dimethyl isomeric hydrocarbon/monomethyl isomeric hydrocarbon.)

1. A modified Y-type molecular sieve is characterized in that the content of calcium oxide in the modified Y-type molecular sieve is 0.7-6.3 wt%, the content of sodium oxide is 0.1-0.5 wt%, the total pore volume is 0.33-0.39 mL/g, the percentage of the pore volume of secondary pores with the pore diameter of 2-100 nm in the modified Y-type molecular sieve in the total pore volume is 10-25%, the unit cell constant is 2.440-2.455 nm, the percentage of non-framework aluminum content in the modified Y-type molecular sieve in the total aluminum content is not higher than 20%, the lattice collapse temperature is not lower than 1040 ℃, 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 modified Y-type molecular sieve has a lattice collapse temperature of 1040 ℃ to 1080 ℃, such as 1040 ℃ to 1055 ℃.

4. 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 is 2.4 to 4.2.

5. 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.

6. The modified Y-type molecular sieve of claim 1, wherein the modified Y-type molecular sieve has a relative crystal retention of 33% or more, for example, 35 to 45%, 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 75%.

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 0.9 to 5.9 wt%, for example, 1.5 to 6 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 8.5 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 solution to perform an ion exchange reaction, filtering, washing, and optionally drying to obtain a calcium-containing Y-type molecular sieve with a conventional unit cell size and reduced sodium oxide content;

(2) roasting the calcium-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-containing Y-type molecular sieve having a conventional unit cell size and 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 step (1), the calcium content of the calcium-containing Y-type molecular sieve with the reduced sodium oxide content comprises 0.8-10 wt% of calcium calculated as CaO, 4-8.8 wt% of sodium oxide, such as 5-7.5 wt%, and the cell constant is 2.465 nm-2.472 nm.

12. The method of claim 9, wherein the step (1) of contacting the NaY molecular sieve with the soluble calcium salt solution to perform the ion exchange reaction is performed according to the following formula: soluble calcium salt: h₂O is 1: 0.009-0.28: 5-15, mixing NaY molecular sieve, soluble calcium salt and water, and stirring, wherein the soluble calcium salt can be calcium chloride and/or calcium nitrate.

13. The method of claim 9 or 12, wherein the step (1) of contacting the NaY molecular sieve with a soluble calcium salt solution for an ion exchange reaction comprises: mixing NaY molecular sieve with water, adding soluble calcium salt and/or soluble calcium 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.

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

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

16. The method of claim 9, wherein the washing method in 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 Y-type molecular sieve for heavy oil catalytic cracking to produce more dimethyl isomeric hydrocarbon and a preparation method thereof.

Background

At present, the industrial preparation of the high-silicon Y-type zeolite mainly adopts a hydrothermal method, and the NaY zeolite is subjected to rare earth ion exchange for many times and high-temperature roasting for many times, so that 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. Moreover, the content of the isomeric hydrocarbon in the gasoline produced by the catalyst prepared in the conventional Y molecular sieve is stabilized in a certain range and is difficult to improve, the content of the isomeric hydrocarbon in the gasoline is mainly monomethyl isomeric hydrocarbon generally, and the ratio of the monomethyl isomeric hydrocarbon to the dimethyl isomeric hydrocarbon is low, so that the improvement of the quality of the catalytic cracking gasoline is limited, and the competitiveness of the catalytic cracking gasoline product is reduced.

In U.S. Pat. Nos. 4,849,287 and 4,4429053, NaY zeolite is exchanged with rare earth ions and then treated with steam, the aluminum removal of the zeolite is difficult in the steam treatment process, the unit cell parameters of the zeolite before the steam treatment are increased to 2.465-2.475 nm, the unit cell parameters after the treatment are 2.420-2.464 nm, and the temperature required for reducing the unit cell parameters is higher (593-733 ℃). The heavy oil cracking activity of zeolite is not high and coke selectivity is not good.

In the processes provided in US5340957 and US5206194, SiO of NaY zeolite is used as the starting material₂/Al₂O₃The ratio is 6.0, and this method also has the disadvantages of the aforementioned U.S. Pat. Nos. 4,84287 and 4429053, in which NaY is subjected to rare earth exchange and then to hydrothermal treatment.

Gas phase chemical processes are another important process for preparing high silica zeolites first reported by Beyer and Mankui in 1980. The gas phase chemical method generally adopts SiCl under the protection of nitrogen₄Reacting 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 not beneficial to the isomerization reaction in the hydrocarbon catalytic cracking process.

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 strong heavy oil conversion capability, high hydrogen transfer reaction activity and higher isobutane product content. However, the Y-type molecular sieve containing Mg and Ca prepared by the existing method has poor thermal and hydrothermal stability, can only improve the content of isobutane generally, cannot effectively improve the content of isomeric hydrocarbon in gasoline, and cannot improve the content of dimethyl isomeric hydrocarbon.

Disclosure of Invention

One of the technical problems to be solved by the invention is to provide a Y-type molecular sieve (also called Y-type zeolite) which is suitable for heavy oil catalytic cracking processing, can produce more dimethylisohydrocarbon 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 inventors have made extensive fundamental studies to obtain the following new findings: the higher octane number of the bis-methyl isomeric hydrocarbon can greatly improve the quality of FCC gasoline, for example, the higher octane number of the gasoline can be maintained under the condition of reducing the content of olefin or aromatic hydrocarbon. However, the existing Y-type molecular sieve has poor stability and isomerization performance, and is not beneficial to the generation of isomeric hydrocarbon in the catalytic cracking process.

The invention provides a modified Y-type molecular sieve, which contains 0.7-6.3 wt% of calcium oxide, 0.1-0.5 wt% of sodium oxide and 0.33-0.39 mL/g of total pore volume, wherein 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) is₂/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 1040 ℃, 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 2.0-100 nm accounting for 10-25% of the total pore volume, preferably 15-21%, for example 17-21%.

The modified Y-type molecular sieve provided by the invention has a lattice collapse temperature (structure collapse temperature) of not less than 1040 ℃, such as 1040-1080 ℃ or 1041-1055 ℃.

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, which is measured at 200 ℃ by using a pyridine adsorption infrared method, is preferably 2.4-4.2, for example, 2.42-3.5.

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 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 14.0, for example 8.5 to 12.6 or 8.1 to 12.

According to the modified Y-type molecular sieve provided by the invention, the percentage of non-framework aluminum content in the molecular sieve in the total aluminum content is not higher than 20%, for example, 13-19 wt%.

The modified Y-type molecular sieve provided by the invention has a crystal retention of over 33%, such as 36-40%, 39-45% or 35-45%, after aging for 17 hours at 800 ℃ under normal pressure and in a 100 volume% steam atmosphere. The normal pressure is 1 atm.

The modified Y-type molecular sieve provided by the invention has a relative crystallinity of not less than 58%, such as 58-75% or 58-68%, preferably, the modified Y-type molecular sieve has a relative crystallinity of 59-70%, such as 59-63%.

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, for example, 0.26-0.32 mL/g.

The modified Y-type molecular sieve contains calcium element, and the calcium content in the modified Y-type molecular sieve calculated by CaO is 0.7-6.3 wt%, preferably 0.9-5.9 wt%, for example 1.5-6.0 wt% or 0.7-4.3 wt%.

The modified Y-type molecular sieve provided by the invention has the sodium oxide content of not more than 0.5 wt%, and can be 0.15-0.5 wt%, such as 0.20-0.5 wt% or 0.3-0.46 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 a soluble calcium salt solution to perform an ion exchange reaction, filtering and washing to obtain a Y-type molecular sieve with a conventional unit cell size and reduced sodium oxide content and containing calcium; wherein the soluble calcium salt solution is also called calcium salt solution;

(2) modifying the calcium-containing Y-type molecular sieve with the reduced sodium oxide content and the conventional unit cell size, and optionally drying to obtain a Y-type molecular sieve with a reduced unit cell constant, wherein the modifying is to roast the calcium-containing Y-type molecular sieve with the reduced sodium oxide content and the conventional unit cell size 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) reducing the unit cell constant of the Y-type molecular sieve and SiCl₄Gas 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 sample obtained by roasting in the step (2) is not more than 1 weight percent, the Y-type molecular sieve sample 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 weight percent, the Y-type molecular sieve obtained by roasting in the step (2) is dried to ensure that the water content of the Y-type molecular sieve with the reduced unit cell constant is less than 1 weight percent.

The modified Y-type molecular sieve provided by the invention has high thermal and hydrothermal stability, is used for heavy oil catalytic cracking, has higher activity stability and lower coke selectivity, has higher gasoline yield, light oil yield and total liquid yield compared with the existing Y-type molecular sieve, and has more dimethyl isomeric hydrocarbon in gasoline.

In the present invention, the isoparaffin refers to a chain isoparaffin and a chain isoolefin. The term "bis-methyl isomeric hydrocarbons" means that the carbon chain contains two methyl branches, and the term "mono-methyl isomeric hydrocarbons" means that the carbon chain contains one methyl branch. The content of the isomeric hydrocarbon is increased, which is beneficial to improving the quality of FCC gasoline.

The preparation method of the calcium modified Y-shaped molecular sieve can prepare the high-silicon Y-shaped molecular sieve with high crystallinity, high thermal stability and high hydrothermal stability and a certain secondary pore structure, the calcium-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 gasoline yield, the light oil yield, the liquefied gas yield and the total liquid yield of the molecular sieve used for heavy oil conversion can be improved, and the content of the dimethyl isohydrocarbon in the gasoline is higher.

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 catalytic cracking catalyst taking the molecular sieve as an active component has the advantages of strong heavy oil conversion capability, high stability, high coke selectivity, high light oil yield, high total liquid yield and high gasoline yield; and the content of the dimethyl isomeric hydrocarbon in the gasoline is higher. The modified Y-type molecular sieve provided by the invention can also be used for reducing octane number loss by gasoline hydrogenation adsorption desulfurization, lubricating oil hydrogenation pour point depression and hydrocarbon isomerization.

Detailed Description

The modified Y-type molecular sieve provided by the invention has an embodiment that the calcium oxide content is 0.7-6.3 wt%, preferably 0.9-5.9 wt% or 1.5-6 wt%, the sodium oxide content is 0.1-0.5 wt%, for example 0.13-0.4 wt% or 0.3-0.5 wt%, the total pore volume is 0.33-0.39 mL/g, the percentage of the secondary pores with the pore diameter of 2-100 nm in the total pore volume is 10-25%, preferably 15-21%, the unit cell constant is 2.440-2.455 nm, and the framework silicon-aluminum ratio (SiO/Al ratio)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%, preferably 13-19, the relative crystallinity is not lower than 58%, the lattice collapse temperature is 1040-1060 ℃, 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, 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-shaped molecular sieve, the NaY molecular sieve and soluble calcium salt solution are subjected to ion exchange reaction in the step (1) to obtain sodium oxide containing sodiumReduced amounts of calcium containing Y-type molecular sieve of conventional unit cell size. 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 and the soluble calcium 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), soluble calcium salt (CaO) and H₂O is 1: 0.009-0.28: 5-15 by weight. In one embodiment, the ion exchange reaction of the NaY molecular sieve with the soluble calcium salt solution comprises the following steps of₂The method comprises the steps of mixing NaY molecular sieve (also called NaY zeolite), soluble calcium salt and water in a weight ratio of 1: 0.009-0.27: 5-15, and carrying out exchange of calcium ions and sodium ions by stirring at 15-95 ℃, for example, 65-95 ℃, preferably for 30-120 minutes, wherein the water is decationized water, deionized water or a mixture thereof. The NaY molecular sieve, the soluble calcium salt and the water are mixed to form a mixture, the NaY molecular sieve and the water can be formed into slurry, and then the soluble calcium salt and/or a soluble calcium salt solution are added into the slurry, wherein the soluble calcium salt solution is an aqueous solution of the soluble calcium salt, and the soluble calcium salt can be one or two of calcium chloride and calcium nitrate. 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-containing Y-type molecular sieve with conventional unit cell size and reduced sodium oxide content obtained in step (1) is 0.7-11 wt% calculated on CaO, such as 0.8-10 wt% or 4-10 wt% or 0.9-7.5 wt% or 1.5-6 wt% or 0.7-4.5 wt%, the sodium oxide content is not more than 9 wt%, such as 4-8.8 wt% or 4.5-8.5 wt% or 5-7.5 wt%, and the unit cell constant is 2.465 nm-2.472 nm.

In the preparation method of the modified Y-type molecular sieve, the Y-type molecular sieve with the conventional unit cell size containing calcium 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 molecular sieve with reduced unit cell constant (calculated by 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 zeolite (also called molecular sieve)⁺，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) carrying out ion exchange reaction on a NaY molecular sieve (also called NaY zeolite) and a soluble calcium salt solution, filtering and washing to obtain a Y-type molecular sieve with conventional unit cell size and reduced sodium oxide content and containing calcium; 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-containing Y-type molecular sieve with the conventional unit cell size and the 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.