Modified small crystal y molecular sieve, preparation method and application thereof

Abstract

This disclosure relates to a modified small-crystal Y molecular sieve, its preparation method, and its application. The preparation method includes the following steps: (1) mixing small-crystal NaY molecular sieve, a phosphorus source, and water in a weight ratio of NaY:P2O5:water = 1:(0.01~0.15):(8~10), and performing a first exchange on the resulting material below 100°C to obtain a phosphorus-containing small-crystal Y molecular sieve; (2) mixing the phosphorus-containing small-crystal Y molecular sieve with a rare earth source solution in a weight ratio of NaY:RE2O3 = 1:(0.16~0.3), and performing a second exchange on the resulting material at 120~240°C. This preparation method improves the hydrothermal stability of the small-crystal Y molecular sieve and avoids the phenomenon of dealuminization or collapse of the molecular sieve framework when rare earth migrates to the small-crystal molecular sieve using conventional calcination methods.

Description

Technical Field

[0001] This disclosure relates to the field of molecular sieve technology, specifically to a modified small-crystal Y molecular sieve, its preparation method, and its application. Background Technology

[0002] Y-type molecular sieves have been widely used as the main active component of petrochemical catalysts. In recent years, with the increasing weight and quality of feedstock oils, improving the accessibility of active sites in refining catalysts and enhancing their macromolecular cracking capabilities has become particularly important. As the crystal size of Y-type molecular sieves decreases, the number of exposed active sites on their surface increases significantly, resulting in a greater number of active centers on the outer surface and thus improved catalytic activity. On the other hand, the shorter pores connecting small-crystal Y-type molecular sieves to the outside environment facilitate the diffusion of reactants and products, reduce diffusion resistance, and effectively decrease the reaction depth and coking rate. Therefore, compared with traditional Y-type molecular sieves, small-crystal Y-type molecular sieves exhibit superior catalytic performance and have become a key focus of research and development in novel petrochemical catalytic materials.

[0003] Conventional Y-type molecular sieves used in catalytic cracking catalysts typically have a crystallite size of around 1000 nm. As the crystallite size decreases (especially to below 600 nm), its structural stability significantly deteriorates, manifested in a marked decrease in the framework collapse temperature of small-crystal NaY molecular sieves. The modified hydrothermal stability also deteriorates significantly, as evidenced by the noticeably lower microreactor activity of modified small-crystal NaY molecular sieves after hydrothermal aging. These structural characteristics of small-crystal NaY molecular sieves severely limit their application in catalytic cracking units with demanding hydrothermal regeneration conditions.

[0004] Patent CN106276961B discloses a modification method for improving the stability of small-grained Y molecular sieves. The significant feature of this method is that it first contacts small-grained NaY molecular sieves with a grain size of 100–800 nm with silicon tetrachloride to perform vapor-phase aluminum extraction and silicon replenishment, followed by water washing and rare-earth exchange to obtain rare-earth-containing silicon tetrachloride vapor-phase ultrastable small-grained Y molecular sieves. This method has difficulty ensuring the uniformity of material contact during the vapor-phase ultrastable process, is technically challenging, and has high product production costs.

[0005] Patent CN104828840B discloses a method for modifying small-crystal NaY molecular sieves. This method first treats small-crystal NaY particles (200-700 nm in diameter) with NaOH solution, followed by ammonium ion exchange to wash away sodium, then liquid-phase aluminum extraction and silicon replenishment with ammonium fluorosilicate, followed by hydrothermal calcination, and finally sodium washing with ammonium and hydrochloric acid to remove non-framework aluminum, yielding an ultra-stable small-crystal Y molecular sieve with secondary pores, which can be used as an active component in hydrocracking. However, this method is costly to operate, involves the treatment of fluoride-containing wastewater, and is not conducive to clean production.

[0006] Patent CN1907854A discloses a method for preparing small-crystal REY with high rare earth content. The method involves first exchanging small-crystal NaY molecular sieves (200-700 nm particle size) at a weight ratio of NaY:rare earth of 1:0.18-0.38 at 10-100℃, then separating the sieves, collecting the filtrate, adjusting the pH to 8-11.2 to obtain a rare earth precipitate, adding water to the sieve filter cake, slurrying, filtering, washing, drying, and then calcining at 650-850℃. After ammonium leaching with sodium, a REY molecular sieve with a RE2O3 weight content of 14-21% is obtained. This small-crystal REY is used as an active component in catalytic cracking catalysts, exhibiting higher heavy oil conversion capacity and higher gasoline yield. While this method can improve the stability of the small-crystal Y molecular sieve by increasing the rare earth loading, the high-temperature calcination process causes a loss of crystallinity (specific surface area) in the small-crystal Y molecular sieve.

[0007] In summary, current methods for modifying small-crystal NaY molecular sieves include two approaches: aluminum extraction and silicon replenishment through the framework, and directly increasing the rare earth loading to improve framework stability. Aluminum extraction and silicon replenishment increase operational complexity and production costs, and also raise environmental pollution issues. Rare earth modification, on the other hand, is a simpler and potentially effective method for improving the stability of small-crystal Y molecular sieves. However, existing rare earth modification methods tend to reduce the specific surface area of ​​the small-crystal molecular sieves. Summary of the Invention

[0008] The purpose of this disclosure is to provide a modified small-crystal Y molecular sieve, its preparation method and application. This method improves the hydrothermal stability of the small-crystal Y molecular sieve and avoids the phenomenon of dealuminization or collapse of the molecular sieve skeleton that is easily caused when rare earth elements migrate to the small cage of the small-crystal molecular sieve by calcination.

[0009] To achieve the above objectives, the first aspect of this disclosure provides a method for preparing modified small-crystal Y molecular sieves, the method comprising the following steps:

[0010] (1) Mix small-crystal NaY molecular sieve, phosphorus source and water in a weight ratio of NaY:P2O5:water = 1:(0.01~0.15):(8~10), and perform a first exchange on the resulting material below 100℃ to obtain phosphorus-containing small-crystal Y molecular sieve;

[0011] (2) The phosphorus-containing small crystal Y molecular sieve and rare earth source solution are mixed at a weight ratio of NaY:RE2O3 = 1:(0.16~0.3), and the resulting second material is subjected to a second exchange at 120~240℃.

[0012] Optionally, in step (1), the phosphorus source is a water-soluble phosphorus-containing compound, preferably an oxyacid of phosphorus and / or an acidic phosphate. The oxyacid of phosphorus includes one or more of orthophosphoric acid, phosphorous acid, hypophosphoric acid, metaphosphoric acid, pyrophosphoric acid, metaphosphorous acid, diphosphoric acid and polyphosphoric acid. The acidic phosphate includes one or more of ammonium phosphate, diammonium hydrogen phosphate and diammonium dihydrogen phosphate.

[0013] Optionally, in step (1), the average particle size of the small-crystal NaY molecular sieve is 200-700 nm, and the Na2O content is 10-12% by weight, based on the total weight of the small-crystal NaY molecular sieve.

[0014] Optionally, in step (1), the conditions for the first exchange include: a temperature of 15 to 100°C, preferably 60 to 80°C; and a time of 5 to 45 minutes, preferably 10 to 30 minutes.

[0015] Optionally, in step (2), the rare earth source solution contains one or more rare earth sources selected from rare earth chloride, rare earth nitrate and rare earth acetate, and the rare earth elements in the rare earth source include one or more of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Er, Sc and Y.

[0016] Optionally, in step (2), the temperature of the second exchange is 180-200°C and the time is 0.5-2h; optionally, step (2) further includes washing and drying the product of the second exchange, wherein the drying temperature is 80-150°C and the time is 8-24h.

[0017] The second aspect of this disclosure provides a modified small-crystal Y molecular sieve prepared by the method described in the first aspect of this disclosure, wherein the modified small-crystal Y molecular sieve contains phosphorus and rare earth elements; based on the total weight of the modified small-crystal Y molecular sieve, the content of Na2O is less than 1.5% by weight, the content of phosphorus as P2O5 is 1 to 12% by weight, and the content of rare earth elements as RE2O3 is 14 to 21% by weight.

[0018] Optionally, the average particle size of the modified small-crystal Y molecular sieve is 200–700 nm.

[0019] Optionally, the modified small-crystal Y molecular sieve is subjected to ammonium ion exchange to remove sodium until the Na2O content in the modified small-crystal Y molecular sieve is below 0.3% by weight, and then aged at 800°C in a 100% by volume water vapor atmosphere for 17 hours. The specific surface area retention rate of the modified small-crystal Y molecular sieve after aging is 50-70%.

[0020] The third aspect of this disclosure provides an application of the modified small-grained Y molecular sieve described in the second aspect of this disclosure in petroleum catalytic cracking.

[0021] Through the above technical solution, the preparation method of modified small-crystal Y molecular sieve provided in this disclosure first loads P element onto the small-crystal molecular sieve under low temperature conditions to improve the hydrothermal stability of the small-crystal molecular sieve, so that the aluminum framework of the small-crystal molecular sieve is fully protected by P element. Then, under high temperature hydrothermal conditions, rare earth ions migrate directly into the cage of the small-crystal molecular sieve, avoiding the phenomenon of dealuminization or collapse of the molecular sieve framework that is easily caused when using conventional calcination to migrate rare earth elements into the cage of the small-crystal molecular sieve. Furthermore, under high temperature hydrothermal conditions, the P element loaded onto the molecular sieve in the first step can continue to diffuse fully within the molecular sieve crystals, which is beneficial to improving the distribution of P element in the bulk phase of the molecular sieve, increasing the effective loading of P element, and further improving the hydrothermal stability of the molecular sieve.

[0022] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0024] Figure 1 This is a scanning electron microscope (SEM) image of the modified small-crystal Y molecular sieve of Example 1 of this disclosure;

[0025] Figure 2 This is a scanning electron microscope (SEM) image of the modified small-crystal Y molecular sieve of Example 2 of this disclosure;

[0026] Figure 3 This is a scanning electron microscope (SEM) image of the modified small-crystal Y molecular sieve of Example 3 of this disclosure;

[0027] Figure 4 This is a scanning electron microscope (SEM) image of the modified small-crystal Y molecular sieve of Example 4 of this disclosure;

[0028] Figure 5 This is a scanning electron microscope (SEM) image of the modified small-crystal Y molecular sieve of Example 5 of this disclosure. Detailed Implementation

[0029] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0030] The first aspect of this disclosure provides a method for preparing modified small-crystal Y molecular sieves, the method comprising the following steps:

[0031] (1) Mix small-crystal NaY molecular sieve, phosphorus source and water in a weight ratio of NaY:P2O5:water = 1:(0.01~0.15):(8~10), and perform a first exchange on the resulting material below 100℃ to obtain phosphorus-containing small-crystal Y molecular sieve;

[0032] (2) The phosphorus-containing small crystal Y molecular sieve and rare earth source solution are mixed at a weight ratio of NaY:RE2O3 = 1:(0.16~0.3), and the resulting second material is subjected to a second exchange at 120~240℃.

[0033] The method for preparing modified small-crystal Y molecular sieve disclosed herein first loads phosphorus (P) onto the small-crystal molecular sieve at low temperature to improve its hydrothermal stability, ensuring that the aluminum framework of the small-crystal molecular sieve is adequately protected by P. Then, under high-temperature hydrothermal conditions, rare earth elements migrate directly into the cages of the small-crystal molecular sieve, avoiding the dealuminization or collapse of the framework that can occur when using conventional calcination methods to migrate rare earth elements into the cages of the small-crystal molecular sieve. Furthermore, under high-temperature hydrothermal conditions, the P loaded onto the molecular sieve in the first step can continue to diffuse fully within the molecular sieve crystals, which is beneficial for improving the distribution of P within the bulk phase of the molecular sieve, increasing the effective loading of P, and further improving the hydrothermal stability of the molecular sieve. In a preferred embodiment, steps (1) and (2) are both carried out in an acidic system, wherein the phosphorus source in step (1) is an acidic phosphorus source.

[0034] In one embodiment of this disclosure, in step (1), the phosphorus source is a water-soluble phosphorus-containing compound, preferably an oxyacid of phosphorus and / or an acidic phosphate. The oxyacid of phosphorus includes one or more of orthophosphoric acid, phosphorous acid, hypophosphoric acid, metaphosphoric acid, pyrophosphoric acid, metaphosphorous acid, diphosphoric acid, and polyphosphoric acid. The acidic phosphate includes one or more of ammonium phosphate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate. In the above embodiment, by selecting a water-soluble phosphorus-containing compound, it is beneficial to introduce phosphorus into the small-crystal molecular sieve, so that phosphorus reacts with aluminum on the framework of the small-crystal molecular sieve, thereby improving the hydrothermal stability and catalytic performance of the small-crystal molecular sieve.

[0035] In one embodiment of this disclosure, in step (1), the average particle size of the small-crystal NaY molecular sieve is 200-700 nm, and the Na2O content is 10-12% by weight, based on the total weight of the small-crystal NaY molecular sieve. In the above embodiment, the small-crystal NaY molecular sieve has a small average particle size and a large specific surface area, and the structural stability and hydrothermal stability of the molecular sieve are both poor.

[0036] In one embodiment of this disclosure, in step (1), the conditions for the first exchange include: a temperature of 15–100°C, preferably 60–80°C; and a time of 5–45 min, preferably 10–30 min. In the above embodiment, by selecting the preferred conditions for the first exchange, it is beneficial to further increase the loading of P element.

[0037] In one embodiment of this disclosure, in step (2), the rare earth source solution contains one or more rare earth sources selected from rare earth chloride, rare earth nitrate, and rare earth acetate. The rare earth elements in the rare earth source include one or more of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Er, Sc, and Y. In the above embodiment, by selecting a rare earth source, it is beneficial to introduce rare earth elements into the cages of the small-crystal molecular sieve, increase the loading of rare earth elements, thereby improving the stability of the small-crystal molecular sieve framework and thus improving the hydrothermal stability of the small-crystal molecular sieve.

[0038] In one embodiment of this disclosure, in step (2), the temperature of the second exchange is 180–200°C, and the time is 0.5–2 h, preferably 1–1.5 h. In a preferred embodiment, step (2) further includes washing and drying the product of the second exchange, wherein the drying temperature is 80–150°C, and the time is 8–24 h. In the above embodiments, by selecting the preferred second exchange conditions, it is beneficial for rare earth elements to migrate directly into the cages of phosphorus-containing small-crystal Y molecular sieves, avoiding the phenomenon that the partial removal or even collapse of the framework aluminum of the small-crystal molecular sieve is easily caused by conventional calcination. Moreover, it is beneficial for the P element loaded onto the molecular sieve in the first step to continue to diffuse fully within the molecular sieve crystals, improving the distribution of P element in the bulk phase of the molecular sieve, and ensuring that the framework aluminum of the molecular sieve is fully protected by P element.

[0039] A second aspect of this disclosure provides a modified small-crystal Y molecular sieve obtained by the preparation method described in the first aspect of this disclosure. The modified small-crystal Y molecular sieve contains phosphorus and rare earth elements. Based on the total weight of the modified small-crystal Y molecular sieve, the Na₂O content is less than 1.5% by weight, the phosphorus content (calculated as P₂O₅) is 1–12% by weight, and the rare earth element content (calculated as RE₂O₃) is 14–21% by weight. The modified small-crystal Y molecular sieve provided by this disclosure exhibits excellent hydrothermal stability and catalytic performance.

[0040] In one embodiment of this disclosure, the average particle size of the modified small-crystal Y molecular sieve is 200–700 nm. In the above embodiment, the smaller average particle size of the modified small-crystal Y molecular sieve facilitates the diffusion of reactants and products from the small-crystal molecular sieve to the outside, reduces diffusion resistance, and effectively reduces reaction depth and coking rate.

[0041] In one embodiment of this disclosure, the modified small-crystal Y molecular sieve undergoes ammonium ion exchange desodiuming treatment until the Na2O content in the modified small-crystal Y molecular sieve is below 0.3% by weight. Then, it is aged at 800°C in a 100% by volume water vapor atmosphere for 17 hours. The specific surface area retention rate of the aging modified small-crystal Y molecular sieve is 50-70%, preferably 55-65%. Here, the specific surface area retention rate refers to the percentage of the specific surface area retained by the aging modified small-crystal Y molecular sieve compared to the specific surface area of ​​the modified small-crystal Y molecular sieve before aging. In the above embodiment, the aging modified small-crystal Y molecular sieve exhibits a higher specific surface area retention rate and a higher light oil micro-reactivity index, resulting in better hydrothermal stability when used in petroleum catalytic cracking.

[0042] The third aspect of this disclosure provides an application of the modified small-grained Y molecular sieve described in the second aspect of this disclosure in petroleum catalytic cracking.

[0043] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited thereto.

[0044] Unless otherwise specified, all raw materials used in the following embodiments are commercially available products.

[0045] In the following embodiments, the specific testing methods are as follows:

[0046] The low-temperature nitrogen adsorption (BET) measurement of the sample was performed on the ASAP24000 adsorption instrument of Micromeritics, USA. Test conditions: The sample was degassed under vacuum at 300℃ for 6h, and N2 adsorption-desorption test was performed at 77.4K. The nitrogen adsorption-desorption isotherm curve was obtained, and the specific surface area was calculated using the BET formula.

[0047] Crystallinity was determined using the RIPP 146-90 standard method. For details of the RIPP standard method mentioned here, please refer to "Analytical Methods for Petrochemical Products", edited by Yang Cuiding et al., 1990 edition.

[0048] The silicon-to-aluminum ratio of the skeleton is determined using the following formula:

[0049] SiO2 / Al2O3 = 2 × (25.8575 - a0) / (a0 - 24.191); where a0 is the unit cell parameter of the molecular sieve, determined using the RIPP 145-90 standard method;

[0050] The morphology and average particle size of the samples were analyzed by scanning electron microscopy (SEM). The SEM analysis was performed on an ISI-60A electron microscope from ISI Corporation in the United States. The experimental conditions were: accelerating voltage 20 kV and sample tilt angle 30°.

[0051] The Na2O content, P element content, and rare earth element content of the samples were tested using an XRF analyzer, model Rigaku 3271E.

[0052] Example 1

[0053] (1) 60g of small-crystal NaY molecular sieve (dry basis weight), 1.7g of diammonium hydrogen phosphate, and 600g of deionized water were mixed evenly at a weight ratio of NaY:P2O5:H2O = 1:0.015:10. The resulting first material was placed in a 1L autoclave and subjected to a first exchange under stirring. The temperature of the first exchange was 25℃, and the time was 30min, resulting in a mixed solution containing phosphorus-containing small-crystal NaY molecular sieve. The small-crystal NaY molecular sieve was prepared in the laboratory, with an average particle size of 200-300nm and a specific surface area of ​​798cm². 2 / g, Na2O content is 12.4 wt%, relative crystallinity is 94%, and framework silicon-aluminum ratio is 5.4;

[0054] (2) According to the weight ratio of NaY:RE2O3 = 1:0.29, 155.9g of mixed rare earth source solution (provided by Changling Catalyst Company, the rare earth source is a mixture of lanthanum chloride and cerium chloride, and the content of rare earth elements calculated as RE2O3 is 11.16% by weight) is added to the mixture in step (1). The resulting second material undergoes a second exchange under stirring. The temperature of the second exchange is 240℃ and the time is 1h. Then the heating jacket is removed, and the material is discharged after the temperature of the material drops below 100℃. After filtration, washing and drying (drying temperature is 120℃ and time is 20h), modified small crystal Y molecular sieve 1 is obtained, which is denoted as PRSY-1.

[0055] Example 2

[0056] (1) 60g of small-crystal NaY molecular sieve (dry basis weight), 11.2g of diammonium hydrogen phosphate, and 480g of deionized water were mixed evenly at a weight ratio of NaY:P2O5:H2O = 1:0.1:8. The resulting first material was placed in a 1L autoclave and subjected to a first exchange under stirring. The temperature of the first exchange was 60℃, and the time was 20min, resulting in a mixed solution containing phosphorus-containing small-crystal NaY molecular sieve. The small-crystal NaY molecular sieve was prepared in the laboratory, with an average particle size of 300-400nm and a specific surface area of ​​786cm². 2 / g, the Na2O content is 12.3% by weight, the relative crystallinity is 93%, and the framework silicon-aluminum ratio is 5.4;

[0057] (2) According to the weight ratio of NaY:RE2O3 = 1:0.20, 107.5g of mixed rare earth source solution (provided by Changling Catalyst Company, the rare earth source is a mixture of lanthanum chloride and cerium chloride, and the content of rare earth elements calculated as RE2O3 is 11.16% by weight) is added to the mixture in step (1). The resulting second material undergoes a second exchange under stirring. The temperature of the second exchange is 200℃ and the time is 1.2h. Then the heating jacket is removed, and the material is discharged after the temperature drops below 100℃. After filtration, washing and drying (drying temperature is 120℃ and time is 20h), modified small crystal Y molecular sieve 2 is obtained, which is denoted as PRSY-2.

[0058] Example 3

[0059] (1) 60g of small-crystal NaY molecular sieve (dry basis weight), 13.4g of diammonium hydrogen phosphate, and 540g of deionized water were mixed evenly at a weight ratio of NaY:P2O5:H2O = 1:0.12:9. The resulting first material was placed in a 1L autoclave and subjected to a first exchange under stirring. The temperature of the first exchange was 75℃, and the time was 20min, resulting in a mixed solution containing phosphorus-containing small-crystal NaY molecular sieve. The small-crystal NaY molecular sieve was prepared in the laboratory, with an average particle size of 400-500nm and a specific surface area of ​​772cm². 2 / g, the Na2O content is 11.6% by weight, the relative crystallinity is 95%, and the framework silicon-aluminum ratio is 5.5;

[0060] (2) According to the weight ratio of NaY:RE2O3 = 1:0.17, add 91.4g of mixed rare earth source solution (provided by Changling Catalyst Company, the rare earth source is a mixture of lanthanum chloride and cerium chloride, and the content of rare earth elements calculated as RE2O3 is 11.16% by weight) to the mixture in step (1). The resulting second material undergoes a second exchange under stirring. The temperature of the second exchange is 190℃ and the time is 1.3h. Then, remove the heating jacket and discharge the material after the material temperature drops below 100℃. After filtration, washing and drying (drying temperature is 120℃ and time is 20h), the modified small-crystal Y molecular sieve 3 is obtained, which is denoted as PRSY-3.

[0061] Example 4

[0062] (1) 60g of small-crystal NaY molecular sieve (dry basis weight), 14.5g of diammonium hydrogen phosphate, and 540g of deionized water were mixed evenly at a weight ratio of NaY:P2O5:H2O = 1:0.13:9. The resulting first material was placed in a 1L autoclave and subjected to a first exchange under stirring. The temperature of the first exchange was 85℃, and the time was 15min, resulting in a mixed solution containing phosphorus-containing small-crystal NaY molecular sieve. The small-crystal NaY molecular sieve was prepared in the laboratory, with an average particle size of 500-600nm and a specific surface area of ​​746cm².2 / g, the Na2O content is 11.0% by weight, the relative crystallinity is 94%, and the framework silicon-aluminum ratio is 5.7;

[0063] (2) According to the weight ratio of NaY:RE2O3 = 1:0.16, add 86.0g of mixed rare earth source solution (provided by Changling Catalyst Company, the rare earth source is a mixture of lanthanum chloride and cerium chloride, and the content of rare earth elements calculated as RE2O3 is 11.16% by weight) to the mixture in step (1). The resulting second material undergoes a second exchange under stirring. The temperature of the second exchange is 220℃ and the time is 1h. Then, remove the heating jacket and discharge the material after the material temperature drops below 100℃. After filtration, washing and drying (drying temperature is 120℃ and time is 20h), the modified small-crystal Y molecular sieve 4 is obtained, which is denoted as PRSY-4.

[0064] Example 5

[0065] (1) 60g of small-crystal NaY molecular sieve (dry basis weight), 6.7g of diammonium hydrogen phosphate, and 480g of deionized water were mixed evenly at a weight ratio of NaY:P2O5:H2O = 1:0.06:8. The resulting first material was placed in a 1L autoclave and subjected to a first exchange under stirring. The temperature of the first exchange was 90℃, and the time was 10min, resulting in a mixed solution containing phosphorus-containing small-crystal NaY molecular sieve. The small-crystal NaY molecular sieve was prepared in the laboratory, with an average particle size of 600-700nm and a specific surface area of ​​732cm². 2 / g, the Na2O content is 12.1% by weight, the relative crystallinity is 93%, and the framework silicon-aluminum ratio is 5.6;

[0066] (2) According to the weight ratio of NaY:RE2O3 = 1:0.25, 134.4g of mixed rare earth source solution (provided by Changling Catalyst Company, the rare earth source is a mixture of lanthanum chloride and cerium chloride, and the content of rare earth elements calculated as RE2O3 is 11.16% by weight) is added to the mixture in step (1). The resulting second material undergoes a second exchange under stirring. The temperature of the second exchange is 180℃ and the time is 1.4h. Then the heating jacket is removed, and the material is discharged after the temperature drops below 100℃. After filtration, washing and drying (drying temperature is 120℃ and time is 20h), modified small-crystal Y molecular sieve 5 is obtained, which is denoted as PRSY-5.

[0067] Example 6

[0068] (1) 60g of small-crystal NaY molecular sieve (dry basis weight), 10.6g of diammonium hydrogen phosphate, and 540g of deionized water were mixed evenly at a weight ratio of NaY:P2O5:H2O = 1:0.095:9. The resulting first material was placed in a 1L autoclave and subjected to a first exchange under stirring. The temperature of the first exchange was 95℃, and the time was 10min, resulting in a mixed solution containing phosphorus-containing small-crystal NaY molecular sieve. The small-crystal NaY molecular sieve was prepared in the laboratory, with an average particle size of 500-600nm and a specific surface area of ​​746cm². 2 / g, the Na2O content is 11.0% by weight, the relative crystallinity is 94%, and the framework silicon-aluminum ratio is 5.7;

[0069] (2) According to the weight ratio of NaY:RE2O3 = 1:0.19, 102.2g of mixed rare earth source solution (provided by Changling Catalyst Company, the rare earth source is a mixture of lanthanum chloride and cerium chloride, and the content of rare earth elements calculated as RE2O3 is 11.16% by weight) is added to the mixture in step (1). The resulting second material undergoes a second exchange under stirring. The temperature of the second exchange is 120℃ and the time is 1.5h. Then the heating jacket is removed, and the material is discharged after the temperature of the material drops below 100℃. After filtration, washing and drying (drying temperature is 120℃ and time is 20h), modified small crystal Y molecular sieve 6 is obtained, which is denoted as PRSY-6.

[0070] Example 7

[0071] (1) 60g of small-crystal NaY molecular sieve (dry basis weight), 9.8g of diammonium hydrogen phosphate, and 540g of deionized water were mixed evenly at a weight ratio of NaY:P2O5:H2O = 1:0.088:9. The resulting first material was placed in a 1L autoclave and subjected to a first exchange under stirring. The temperature of the first exchange was 80℃, and the time was 20min, resulting in a mixed solution containing phosphorus-containing small-crystal NaY molecular sieve. The small-crystal NaY molecular sieve was prepared in the laboratory, with an average particle size of 400-500nm and a specific surface area of ​​772cm². 2 / g, the Na2O content is 11.6% by weight, the relative crystallinity is 95%, and the framework silicon-aluminum ratio is 5.5;

[0072] (2) According to the weight ratio of NaY:RE2O3 = 1:0.22, 118.3g of mixed rare earth source solution (provided by Changling Catalyst Company, the rare earth source is a mixture of lanthanum chloride and cerium chloride, and the content of rare earth elements calculated as RE2O3 is 11.16% by weight) is added to the mixture in step (1). The resulting second material undergoes a second exchange under stirring. The temperature of the second exchange is 140℃ and the time is 1.5h. Then the heating jacket is removed, and the material is discharged after the temperature drops below 100℃. After filtration, washing and drying (drying temperature is 120℃ and time is 20h), modified small-crystal Y molecular sieve 7 is obtained, which is denoted as PRSY-7.

[0073] Example 8

[0074] (1) 60g of small-crystal NaY molecular sieve (dry basis weight), 4.5g of diammonium hydrogen phosphate, and 480g of deionized water were mixed evenly at a weight ratio of NaY:P2O5:H2O = 1:0.04:8. The resulting first material was placed in a 1L autoclave and subjected to a first exchange under stirring. The temperature of the first exchange was 30℃, and the time was 30min, resulting in a mixed solution containing phosphorus-containing small-crystal NaY molecular sieve. The small-crystal NaY molecular sieve was prepared in the laboratory, with an average particle size of 300-400nm and a specific surface area of ​​786cm². 2 / g, the Na2O content is 12.3% by weight, the relative crystallinity is 93%, and the framework silicon-aluminum ratio is 5.4;

[0075] (2) According to the weight ratio of NaY:RE2O3 = 1:0.27, 145.2g of mixed rare earth source solution (provided by Changling Catalyst Company, the rare earth source is a mixture of lanthanum chloride and cerium chloride, and the content of rare earth elements calculated as RE2O3 is 11.16% by weight) is added to the mixture in step (1). The resulting second material undergoes a second exchange under stirring. The temperature of the second exchange is 160℃ and the time is 1.5h. Then the heating jacket is removed, and the material is discharged after the temperature drops below 100℃. After filtration, washing and drying (drying temperature is 120℃ and time is 20h), modified small-crystal Y molecular sieve 8 is obtained, which is denoted as PRSY-8.

[0076] Comparative Example 1

[0077] Using the same raw materials as in Example 2, the only difference was that, according to the weight ratio of NaY:RE2O3:H2O = 1:0.23:8, 60g of small-crystal NaY molecular sieve (dry basis weight), 96.8g of mixed rare earth source solution (provided by Changling Catalyst Company, the rare earth source being a mixture of lanthanum chloride and cerium chloride, with a rare earth element content of 11.16% by weight based on RE2O3), and 480g of deionized water were mixed evenly. The resulting material underwent rare earth exchange under stirring at a temperature of 80°C for 1 hour. After filtration, ammonia was added dropwise to the filtrate to adjust the pH to 9.5, resulting in a rare earth precipitate. This precipitate was then mixed with the molecular sieve filter cake and slurried with water. After filtration, washing, and drying, the sample before calcination was obtained, with a specific surface area of ​​668 m². 2 / g, denoted as DB-REY-A; DB-REY-A was calcined in a muffle furnace at 650℃ for 2h, and then subjected to ammonium ion exchange to remove sodium, yielding RE2O3 with a content of 16.5% by weight and a BET specific surface area of ​​591m². 2 The comparative molecular sieve 1, denoted as DB-REY-B, is 1 g.

[0078] Comparative Example 2

[0079] Using the same raw materials as in Example 2, the only difference was that 60g of small-crystal NaY molecular sieve (dry basis weight) was mixed evenly with 30g of ammonium sulfate, 11.2g of diammonium hydrogen phosphate, and 480g of deionized water. The mixture was heated to 85°C and exchanged for 50 minutes under stirring. Then, 96.8g of a mixed rare earth solution (provided by Changling Catalyst Company, the rare earth source being a mixture of lanthanum chloride and cerium chloride, with a rare earth element content of 11.16% by weight, calculated as RE2O3) was added, and the exchange continued for another 30 minutes. After filtration and washing, a filter cake sample before calcination was obtained, with a BET specific surface area of ​​685m². 2 / g, denoted as DB-PREY-A; the filter cake is then calcined at 620℃ and 80% steam for 1.5h, and then subjected to ammonium ion exchange to remove sodium, resulting in a RE2O3 content of 14.5 wt%, a P2O5 content of 9.0 wt%, and a BET specific surface area of ​​565 m². 2 The comparative molecular sieve 2, denoted as DB-PREY-B1, has a ratio of / g.

[0080] Comparative Example 3

[0081] Using the same raw materials as in Example 2, the only difference was that 60g of small-crystal NaY molecular sieve (dry basis weight) was mixed evenly with 30g of ammonium sulfate, 11.2g of diammonium hydrogen phosphate, and 480g of deionized water. The mixture was heated to 85°C and exchanged for 50 minutes under stirring. Then, 96.8g of a mixed rare earth solution (provided by Changling Catalyst Company, the rare earth source being a mixture of lanthanum chloride and cerium chloride, with a rare earth element content of 11.16% by weight, calculated as RE2O3) was added, and the exchange continued for another 50 minutes. The mixture was then filtered, and ammonia was added dropwise to the filtrate to adjust the pH to 9.5, resulting in a rare earth precipitate. This precipitate was then mixed with the molecular sieve filter cake and slurried with water. After filtration and washing, a filter cake sample before calcination was obtained, with a BET specific surface area of ​​672 m². 2 / g, designated DB-PREY-2A; the filter cake was then calcined at 620℃ and 80% steam for 1.5h, followed by ammonium ion exchange to remove sodium, resulting in a RE2O3 content of 16.5 wt%, a P2O5 content of 9.1 wt%, and a BET specific surface area of ​​571 m². 2 The comparative molecular sieve 3, denoted as DB-PREY-B2, has a ratio of / g.

[0082] Table 1. Composition and structural characteristics of molecular sieves

[0083]

[0084]

[0085] Test case

[0086] The modified small-crystal Y molecular sieves prepared in Examples 1-8 and the comparative molecular sieves prepared in Comparative Examples 1-3 were subjected to ammonium ion exchange desodiuming treatment until the Na2O content was below 0.3% by weight. After aging in a 100% by volume water vapor atmosphere at 800°C for 17 hours, their specific surface area and light oil micro-reaction activity index were tested. The light oil micro-reaction activity index was evaluated by using standard light diesel oil as raw material, the water vapor-deactivated molecular sieve as catalyst, and reacting at 460°C. The total conversion rate of light diesel oil by weight was calculated, and this total conversion rate was used as the light oil micro-reaction activity index. The light oil micro-reaction activity index = (1-(1-G)W1 / W)×100%, where G is the percentage content of gasoline fraction in the liquid product obtained from the reaction before 216°C as determined by chromatographic analysis, W1 is the amount of oil recovered, and W is the amount of oil fed in. The test results are shown in Table 2: The specific surface area retention rate of the modified small-crystal Y molecular sieve after aging = 100% × specific surface area of ​​the modified small-crystal Y molecular sieve after aging / specific surface area of ​​the modified small-crystal Y molecular sieve before aging.

[0087] Table 2. Specific surface area and light oil microreactive index of modified small-crystal Y molecular sieve after aging.

[0088]

[0089]

[0090] As can be seen from Table 2, the modified small-crystal Y molecular sieves prepared by the preparation method of this disclosure in Examples 1-8 have good hydrothermal stability, small specific surface area loss after aging, large specific surface area retention rate, and high light oil micro-reactivity index. In contrast, Comparative Examples 1-3 did not use the preparation method of this disclosure, and the specific surface area of ​​the comparative molecular sieves before calcination was similar to or even larger than that of the sample in Example 2. However, in order to achieve the migration of rare earth elements into the cages of the small-crystal molecular sieves, they were all subjected to high-temperature calcination, which caused the removal of some aluminum from the skeleton of the small-crystal molecular sieves or even the collapse of the skeleton. As a result, the specific surface area of ​​the molecular sieves after aging treatment decreased significantly, and the light oil micro-reactivity index decreased significantly. The modified small-crystal Y molecular sieve provided in this disclosure can achieve the migration of rare earth elements into the molecular sieve cages without calcination, and will not cause a loss of specific surface area during the modification process. In addition, the protective effect of P element on the aluminum of the molecular sieve skeleton results in a high specific surface area retention after hydrothermal aging, and the corresponding light oil micro-reactivity index is also high. Therefore, the modified small-crystal Y molecular sieve provided in this disclosure has better hydrothermal stability.

[0091] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0092] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0093] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for preparing modified small-grained Y molecular sieves, characterized in that, The preparation method includes the following steps: (1) Small-crystal NaY molecular sieve, phosphorus source, and water are mixed in a weight ratio of NaY:P2O5:water = 1:(0.01~0.15):(8~10). The resulting first material is subjected to a first exchange at below 100℃ to obtain phosphorus-containing small-crystal NaY molecular sieve. The average particle size of the small-crystal NaY molecular sieve is 200~700nm, and the specific surface area is 700cm². 2 / g or more; (2) The phosphorus-containing small-crystal Y molecular sieve and rare earth source solution are mixed at a weight ratio of NaY:RE2O3=1:(0.16~0.3). The resulting second material is subjected to a second exchange under high-temperature hydrothermal conditions at 120~240℃. The product of the second exchange is not calcined to obtain modified small-crystal Y molecular sieve. The modified small-crystal Y molecular sieve contains phosphorus and rare earth elements; based on the total weight of the modified small-crystal Y molecular sieve, the Na2O content is less than 1.5% by weight, the phosphorus content (calculated as P2O5) is 1-12% by weight, and the rare earth element content (calculated as RE2O3) is 14-21% by weight.

2. The preparation method according to claim 1, characterized in that, In step (1), the phosphorus source is a water-soluble phosphorus-containing compound.

3. The preparation method according to claim 1, characterized in that, In step (1), the phosphorus source is an oxyacid of phosphorus and / or an acidic phosphate. The oxyacid of phosphorus includes one or more of orthophosphoric acid, phosphorous acid, hypophosphoric acid, metaphosphoric acid, pyrophosphoric acid, metaphosphorous acid, diphosphoric acid and polyphosphoric acid. The acidic phosphate includes one or more of ammonium phosphate, diammonium hydrogen phosphate and diammonium dihydrogen phosphate.

4. The preparation method according to claim 1, characterized in that, In step (1), the conditions for the first exchange include: a temperature of 15~100℃ and a time of 5~45min.

5. The preparation method according to claim 4, characterized in that, In step (1), the conditions for the first exchange include: a temperature of 60~80℃ and a time of 10~30min.

6. The preparation method according to claim 1, characterized in that, In step (2), the rare earth source solution contains one or more rare earth sources selected from rare earth chloride, rare earth nitrate and rare earth acetate, and the rare earth elements in the rare earth source include one or more of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Er, Sc and Y.

7. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the second exchange is 180~200℃ and the time is 0.5~2h.

8. The preparation method according to claim 1, characterized in that, Step (2) further includes washing and drying the product of the second exchange, wherein the drying temperature is 80~150℃ and the time is 8~24h.

9. The preparation method according to claim 1, characterized in that, The average particle size of the modified small-crystal Y molecular sieve is 200~700nm.

10. The preparation method according to claim 1, characterized in that, The modified small-crystal Y molecular sieve is subjected to ammonium ion exchange to remove sodium until the Na2O content in the modified small-crystal Y molecular sieve is below 0.3% by weight. Then, it is aged at 800°C in a 100% by volume water vapor atmosphere for 17 hours. The specific surface area retention rate of the modified small-crystal Y molecular sieve after aging is 50-70%.

11. The application of the modified small-crystal Y molecular sieve prepared by the preparation method according to any one of claims 1 to 10 in petroleum catalytic cracking.

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