Method for preparing LaY molecular sieve with high rare earth exchange degree at low roasting temperature

Abstract

The invention discloses a method for preparing a LaY molecular sieve with a high rare earth exchange degree at a low roasting temperature. The method is a liquid-solid combined ion exchange method, i.e., part of residual liquid-phase rare earth is subjected to precipitation treatment, and is migrated into a sodalite cage of a molecular sieve in a solid-phase form in a subsequent roasting step. According to the method, liquid-phase exchange and solid-phase exchange are combined, the advantages of the liquid-phase exchange and the solid-phase exchange are brought into full play, meanwhile, the defects are avoided, the rare earth exchange degree can reach 60-100% only through one-time liquid-phase exchange and one-time roasting, and it is ensured that all rare earth ions are located in sodalite cages. Compared with a traditional method, the method has the advantages that the preparation process flow is simple, the roasting temperature is reduced, and the CO roasting atmosphere can effectively promote sodium ions in the small cage to migrate to the supercage.

Description

Technical Field

[0001] The invention belongs to the technical field of catalytic cracking catalyst preparation, and particularly relates to a method for preparing LaY molecular sieve with high rare earth exchange degree at a low calcination temperature. Background Art

[0002] Under high-temperature hydrothermal conditions, most catalysts face a pressing challenge: hydrothermal deactivation. Zeolite dealumination under extreme conditions presents a significant challenge. Therefore, improving the thermal and hydrothermal stability of zeolites is currently a key concern. To address this issue, molecular sieves are often modified with rare earth ions to enhance the hydrothermal stability of FCC (fluid catalytic cracking) catalysts.

[0003] Rare earth modified Y molecular sieve is mainly achieved through ion exchange and calcination. Calcination is a process in which high temperature is used to induce ions in the crystal cavity to migrate and change their reaction properties under a specific temperature and water vapor environment. Unable to pass through the hexagonal cage To enter the sodalite cage, the hydration layer must be removed through calcination, which promotes the migration of lanthanum ions to the small cage and the migration of sodium ions from the small cage to the super cage. High-performance REY molecular sieves require a high rare earth content (>15wt%) and a low sodium content (<1.5wt%). Residual sodium ions will neutralize the acid sites, reducing the acid density and catalytic activity. A high rare earth content is beneficial to improving the hydrogen transfer, isomerization, and aromatization activity of the molecular sieve, and is beneficial to enhancing its thermal and hydrothermal stability. Therefore, the calcination process plays a decisive role in regulating the rare earth distribution and sodium content, which directly affects the thermal / hydrothermal stability and catalytic performance of the molecular sieve.

[0004] Industrially, REY molecular sieves prepared using traditional liquid-phase exchange methods typically have an RE2O3 content of no more than 13wt%. Increasing the rare earth exchange rate requires a more complex rare earth exchange and roasting process. Two main processes are used to prepare REY molecular sieves with a rare earth content higher than 15wt%: a two-exchange, two-roasting method or a liquid-solid combined two-exchange, one-roasting method used in CDY production. The two-exchange, two-roasting process requires two exchanges and roasting steps, resulting in a complex process and less than 70% rare earth utilization in the first exchange. While the CDY preparation method is simple, it also suffers from the problem of excessively high roasting temperatures. Lowering the roasting temperature during the solid-phase exchange process is a pressing issue in CDY production.

[0005] Currently, the traditional process for modifying Y-type molecular sieves and rare earth exchange is limited by the method. There are no reports demonstrating that using solid-phase exchange, rare earth ions can completely enter the small cages as cations. Furthermore, using liquid-phase exchange, only a portion of the rare earth ions enter the molecular sieve's supercage structure, while the rest remain in the liquid phase. Summary of the Invention

[0006] To overcome the problems of lanthanum ion-modified Y molecular sieves, such as complicated preparation processes, high calcination temperatures, and low rare earth content, the present invention provides a method for preparing LaY molecular sieves with high rare earth exchange rates at low calcination temperatures. This method is a liquid-solid combined ion exchange method, in which some of the residual liquid-phase rare earths are precipitated and, in a subsequent calcination step, migrated into the sodalite cages of the molecular sieve in the form of a solid phase. The present invention combines liquid-phase exchange with solid-phase exchange, fully leveraging the advantages of each while simultaneously addressing their shortcomings. With only one liquid-phase exchange and one calcination, a rare earth exchange rate of 60-100% can be achieved, ensuring that all rare earth ions are located in the sodalite cages.

[0007] The first method for preparing LaY molecular sieve with high rare earth exchange degree at a low calcination temperature comprises: mechanically grinding LaCl3·7H2O and NaY molecular sieve for 10-60 minutes, and then calcining at 530-580°C for 1-4 hours under a CO atmosphere; then dispersing the calcined product in an ammonium chloride solution with a pH of 3.5-4.0, and conducting an exchange reaction at 60-80°C for 10-120 minutes; and finally filtering and washing with ammonium chloride solution and deionized water in sequence, and drying to obtain the LaY molecular sieve with high rare earth exchange degree.

[0008] The second method for preparing LaY molecular sieve with high rare earth exchange degree at a low calcination temperature comprises: ultrasonically dispersing NaY molecular sieve in deionized water, then adding LaCl3·7H2O and continuing ultrasonic dispersion, adjusting the pH of the mixed solution to 3.5-4.0 with hydrochloric acid, carrying out exchange reaction at room temperature for 0.5-3 hours, adding ammonia water to adjust the pH to 8.5-9.0 to obtain a precipitate, washing with deionized water, drying, and calcining at 530-580°C under a CO atmosphere for 1-4 hours; then dispersing the calcined product in an ammonium chloride solution with a pH of 3.5-4.0, carrying out exchange reaction at 60-80°C for 10-120 minutes; finally, filtering and washing with an ammonium chloride solution and deionized water in sequence, and drying to obtain the LaY molecular sieve with high rare earth exchange degree.

[0009] The concentration of the ammonium chloride solution is 4-8 wt%.

[0010] The present invention has the following beneficial effects:

[0011] (1) The rare earth modified LaY molecular sieve still maintains the typical structural characteristics of Y-type molecular sieve. Compared with air atmosphere, CO calcination atmosphere significantly promotes the La 3 + and Na+ ion exchange efficiency in the small cage.

[0012] (2) With La 3With increasing exchange capacity, the unit cell parameters of LaY molecular sieves gradually increase, significantly improving thermal stability. Using an optimized liquid-solid combined ion exchange method, a "two-exchange, one-baking" process is required to produce high-performance REY molecular sieves with a La2O3 content of 24.60wt%, a rare earth exchange degree of 100%, and a Na2O content reduced to 0.31wt%.

[0013] (3) Compared with the traditional method, the preparation process of the present invention is simple, which not only reduces the roasting temperature, but also the CO roasting atmosphere can effectively promote the migration of sodium ions in the small cage to the super cage. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the XRD scan of the LaY molecular sieve prepared in Example 1.

[0015] Figure 2 This is a SEM scan of the LaY molecular sieve prepared in Example 2.

[0016] Figure 3 This is a SEM scan of the LaY molecular sieve prepared in Example 3.

[0017] Figure 4 This is the TG-DSC scan of the LaY molecular sieve prepared in Example 3.

[0018] Figure 5 This is a SEM scan of the LaY molecular sieve prepared in Comparative Example 1.

[0019] Figure 6 This is the TG-DSC scan of the LaY molecular sieve prepared in Comparative Example 1. DETAILED DESCRIPTION

[0020] Example 1: Preparation of LaY molecular sieve by mechanical grinding

[0021] NaY molecular sieve (Changling Catalyst Plant, SiO2 / Al2O3 5.5) and LaCl·7H O were ground and mixed at a mass ratio of 1:0.4 for 30 min, and then calcined in a muffle furnace at 360-660℃ in air and CO atmosphere for 2 h at intervals of 20℃. -1 The pH value of 5 wt% ammonium chloride solution was adjusted to 3.7 with hydrochloric acid, and the calcined product and ammonium chloride solution were ultrasonically dispersed in a mass ratio of 1:20. After exchange in a water bath at 65°C for 15 minutes, the mixture was filtered and washed with ammonium chloride solution and deionized water in sequence, and dried at 120°C for 4 hours to obtain LaY molecular sieve.

[0022] For the same rare earth content, the unit cell parameters of LaY molecular sieve in air atmosphere increase with the calcination temperature, reaching In CO atmosphere, the unit cell parameters can reach the same value at 540℃. At this time, the La2O3 content is 13.71wt% and the rare earth exchange degree is 62.43%. This proves that CO atmosphere can effectively promote the super cage La 3 +The exchange process with the small cage Na+.

[0023] Table 1

[0024]

[0025]

[0026] Example 2: Preparation of LaY molecular sieve by liquid-solid combined ion exchange method

[0027] NaY molecular sieve (Changling Catalyst Plant, SiO2 / Al2O3 is 5.5) was mixed with deionized water at a mass ratio of 1:10 and ultrasonically dispersed. Lanthanum chloride heptahydrate was then added at a mass ratio of NaY molecular sieve: LaCl3·7H2O=1:0.2, and ultrasonic dispersion was continued. The slurry pH was adjusted to 3.7 with 0.1mol·L-1 hydrochloric acid, exchanged at room temperature for 1h, and then the pH was adjusted to 8.5 with 0.5mol·L-1 ammonia water to obtain a precipitate, washed with deionized water, dried at 120℃ for 4h, and calcined at 540℃ under CO atmosphere for 2-4h; -1 The pH value of a 5 wt% ammonium chloride solution was adjusted to 3.7 with hydrochloric acid, and the calcined product and the ammonium chloride solution were ultrasonically dispersed in a mass ratio of 1:20, exchanged in a water bath at 65° C. for 15 min, and finally filtered and washed with an ammonium chloride solution and deionized water in sequence. After drying, a LaY molecular sieve with a high rare earth exchange degree was obtained.

[0028] The unit cell parameters of the LaY molecular sieve prepared above are The La2O3 content is 13.14wt%, the rare earth exchange degree is 64.67%, and the structural collapse temperature is 1011℃.

[0029] Example 3: Preparation of LaY molecular sieve by liquid-solid combined ion exchange method

[0030] NaY molecular sieve (Changling Catalyst Plant, SiO2 / Al2O3 is 5.5) was mixed with deionized water at a mass ratio of 1:10 and ultrasonically dispersed. Lanthanum chloride heptahydrate was then added at a mass ratio of NaY molecular sieve: LaCl3·7H2O=1:0.4, and ultrasonic dispersion was continued. The slurry pH was adjusted to 3.7 with 0.1mol·L-1 hydrochloric acid, exchanged at room temperature for 1h, and then the pH was adjusted to 8.5 with 0.5mol·L-1 ammonia water to obtain a precipitate, washed with deionized water, dried at 120℃ for 4h, and calcined at 540℃ under CO atmosphere for 2h; -1The pH value of a 5 wt% ammonium chloride solution was adjusted to 3.7 with hydrochloric acid, and the calcined product and the ammonium chloride solution were ultrasonically dispersed in a mass ratio of 1:20, exchanged in a water bath at 65° C. for 15 min, and finally filtered and washed with an ammonium chloride solution and deionized water in sequence. After drying, a LaY molecular sieve with a high rare earth exchange degree was obtained.

[0031] The unit cell parameters of the LaY molecular sieve prepared above are The La2O3 content is 17.38wt%, the rare earth exchange degree is 79.09%, and the structural collapse temperature is 1027℃.

[0032] Example 4: Preparation of LaY molecular sieve by liquid-solid combined ion exchange method

[0033] NaY molecular sieve (Changling Catalyst Plant, SiO2 / Al2O3 is 5.5) was mixed with deionized water at a mass ratio of 1:10 and ultrasonically dispersed. Lanthanum chloride heptahydrate was then added at a mass ratio of NaY molecular sieve: LaCl3·7H2O=1:0.6, and ultrasonic dispersion was continued. The slurry pH was adjusted to 3.7 with 0.1mol·L-1 hydrochloric acid, exchanged at room temperature for 1h, and then the pH was adjusted to 8.5 with 0.5mol·L-1 ammonia water to obtain a precipitate, washed with deionized water, dried at 120℃ for 4h, and calcined at 540℃ under CO atmosphere for 2h; -1 The pH value of a 5 wt% ammonium chloride solution was adjusted to 3.7 with hydrochloric acid, and the calcined product and the ammonium chloride solution were ultrasonically dispersed in a mass ratio of 1:20, exchanged in a water bath at 65° C. for 15 min, and finally filtered and washed with an ammonium chloride solution and deionized water in sequence. After drying, a LaY molecular sieve with a high rare earth exchange degree was obtained.

[0034] The unit cell parameters of the LaY molecular sieve prepared above are The La2O3 content is 19.66wt%, the rare earth exchange degree is 89.46%, and the structural collapse temperature is 1016℃.

[0035] Example 5: Preparation of LaY molecular sieve by liquid-solid combined ion exchange method

[0036] NaY molecular sieve (Changling Catalyst Plant, SiO2 / Al2O3 is 5.5) was mixed with deionized water at a mass ratio of 1:10 and ultrasonically dispersed. Lanthanum chloride heptahydrate was then added at a mass ratio of NaY molecular sieve: LaCl3·7H2O=1:0.8, and ultrasonic dispersion was continued. The slurry pH was adjusted to 3.7 with 0.1mol·L-1 hydrochloric acid, exchanged at room temperature for 1h, and then the pH was adjusted to 8.5 with 0.5mol·L-1 ammonia water to obtain a precipitate, washed with deionized water, dried at 120℃ for 4h, and calcined at 540℃ under CO atmosphere for 2h; -1The pH value of a 5 wt% ammonium chloride solution was adjusted to 3.7 with hydrochloric acid, and the calcined product and the ammonium chloride solution were ultrasonically dispersed in a mass ratio of 1:20, exchanged in a water bath at 65° C. for 15 min, and finally filtered and washed with an ammonium chloride solution and deionized water in sequence. After drying, a LaY molecular sieve with a high rare earth exchange degree was obtained.

[0037] The unit cell parameters of the LaY molecular sieve prepared above are The La2O3 content is 24.60wt%, the Na2O content is as low as 0.31wt%, the rare earth exchange degree is 100%, and the structural collapse temperature is 1013℃.

[0038] Comparative Example 1:

[0039] The unit cell parameters of the unmodified NaY molecular sieve with a silicon-aluminum ratio of 5.5 are The La2O3 content is 0, the Na2O content is 11.29wt%, and the structural collapse temperature is 960℃.

Claims

1. A method for preparing LaY molecular sieve with high rare earth exchange degree at low calcination temperature, characterized in that: The specific operation of the method is as follows: after mechanically grinding LaCl3·7H2O and NaY molecular sieve for 10-60 minutes, calcining at 530-580°C for 1-4 hours under a CO atmosphere; then dispersing the calcined product in an ammonium chloride solution with a pH of 3.5-4.0, and performing an exchange reaction at 60-80°C for 10-120 minutes; finally, filtering and washing with the ammonium chloride solution and deionized water in sequence, and drying to obtain the LaY molecular sieve with a high rare earth exchange degree.

2. A method for preparing LaY molecular sieve with high rare earth exchange degree at low calcination temperature, characterized in that: The specific operation of the method is as follows: ultrasonically dispersing NaY molecular sieve in deionized water, then adding LaCl3·7H2O and continuing ultrasonic dispersion, adjusting the pH of the mixed solution to 3.5-4.0 with hydrochloric acid, performing exchange reaction at room temperature for 0.5-3 hours, adding ammonia water to adjust the pH to 8.5-9.0 to obtain a precipitate, washing with deionized water, drying, and calcining at 530-580°C for 1-4 hours under a CO atmosphere; then dispersing the calcined product in an ammonium chloride solution with a pH of 3.5-4.0, performing exchange reaction at 60-80°C for 10-120 minutes; finally, filtering and washing with the ammonium chloride solution and deionized water in sequence, and drying to obtain the LaY molecular sieve with a high rare earth exchange degree.

3. The method according to claim 1 or 2, characterized in that The concentration of the ammonium chloride solution is 4-8 wt%.

Images