A method for preparing a rare earth catalyst for petroleum cracking

Abstract

The present application relates to the technical field of catalysts, in particular to a preparation method of a rare earth catalyst for petroleum cracking. The preparation method first forms a stable ternary complex solution by reacting lanthanum nitrate and cerium nitrate with bidentate ligand and functional ionic liquid after dissolution; then the solution is mixed with silica-alumina gel formed by a template agent, a silicon source, an aluminum source and a mineralizer, and the catalyst is prepared through hydrothermal crystallization, programmed temperature calcination and other steps. The preparation method realizes the highly uniform dispersion and stable combination of rare earth elements in the molecular sieve carrier through the coordination and hydrogen bond anchoring synergistic effect. The prepared catalyst shows high heavy oil conversion rate, high low-carbon olefin selectivity, excellent hydrothermal stability, outstanding anti-coking and anti-metal poisoning capacity in the petroleum cracking reaction, and has performance advantages and industrial application economy, and is suitable for large-scale petroleum cracking production scenarios.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a method for preparing a rare earth catalyst for petroleum cracking. Background Technology

[0002] Catalytic cracking of petroleum is a core process in modern oil refining for the production of lightweight heavy oil and key chemical feedstocks such as low-carbon olefins. This process heavily relies on high-performance catalytic materials, with molecular sieve-based catalysts dominating due to their regular pore structure and tunable acidity. To further enhance the activity, selectivity, and stability of catalysts, the introduction of rare earth elements (such as lanthanum and cerium) has proven to be an effective strategy. Rare earth ions can modify the acidity of molecular sieves through exchange or loading, and can also enhance their framework thermal stability and resistance to heavy metal poisoning.

[0003] Currently, industrial applications commonly employ impregnation or ion exchange methods to introduce rare earth elements into pre-synthesized molecular sieve supports. However, these traditional methods have inherent limitations: during impregnation, rare earth salt solutions tend to accumulate and agglomerate on the outer surface and within the large pores of the support, making atomic-level dispersion difficult to achieve; subsequent drying and high-temperature calcination steps further exacerbate the migration and sintering of active components, leading to the formation of large rare earth oxide particles. This uneven distribution not only severely limits the effective utilization rate of rare earth atoms but also results in uneven acidity distribution in the catalyst, poor accessibility to active sites, and may exacerbate undesirable reactions (such as hydrogen transfer reactions) due to excessive concentration of local strong acid centers, thereby reducing the selectivity of the target olefin and accelerating carbon deposition and deactivation.

[0004] Furthermore, achieving a robust bond between rare earth active centers and the molecular sieve framework to withstand hydrothermal aging in harsh reaction-regeneration cycles, while simultaneously synergistically regulating the catalyst's cracking activity and resistance to carbon deposition and metal poisoning, remains a significant challenge for current technologies. Simple physical mixing or simple loading cannot achieve precise positioning and functional synergy of rare earth elements such as lanthanum and cerium at the molecular scale, thus limiting further improvements in the overall performance of the catalyst.

[0005] Therefore, developing a novel preparation method that can achieve highly uniform dispersion and stable anchoring of rare earth elements in molecular sieve supports, while also possessing multiple synergistic functions, is of significant technical importance and application value for obtaining high-performance petroleum cracking catalysts. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and propose a method for preparing rare earth catalysts for petroleum cracking.

[0007] To achieve the above objectives, the present invention provides a method for preparing a rare earth catalyst for petroleum cracking, comprising the following steps:

[0008] (1) Add lanthanum nitrate and cerium nitrate to deionized water, heat to 40-50℃ and stir to dissolve to form a rare earth salt solution. Add a bidentate complexing agent to the rare earth salt solution, then adjust the pH to 4.0-5.0 with dilute nitric acid, then heat to 60-70℃ and stir for 1-2 hours. Then add a functional ionic liquid and continue stirring for 1-2 hours to obtain a ternary complex solution.

[0009] (2) Add the template agent to the deionized water and stir at room temperature for 20-40 min; add the silicon source dropwise, stir for 0.5-1.5 h, then add the aluminum source and mineralizer in sequence, stir at room temperature for 1-3 h to form a silica-alumina gel, add the ternary complex solution dropwise to the silica-alumina gel, heat to 50-60℃ and stir for 3-4 h, adjust the pH to 9.0-10.0 with NaOH solution to obtain the precursor gel;

[0010] (3) Transfer the precursor gel to a high-pressure reactor, seal it, and heat it to 160-180℃ for hydrothermal crystallization for 24-36h. Stir for 10min every 6h during the crystallization process. After cooling to room temperature, the crystals are obtained.

[0011] (4) The crystallized material is separated by centrifugation, washed with deionized water until the pH of the filtrate is neutral, vacuum dried at 100-120℃ for 12-16h, and then calcined and pulverized by programmed temperature increase to obtain a rare earth catalyst for petroleum cracking.

[0012] Preferably, the bidentate ligand in (1) refers to ethylenediaminetetramethylenephosphonic acid or aminotrimethylenephosphonic acid.

[0013] Preferably, the functional ionic liquid in (1) refers to 1-butyl-3-methylimidazolium dihydrogen phosphate.

[0014] Preferably, in (1), the molar ratio of lanthanum nitrate, cerium nitrate, and bidentate ligand is 4-6:6-4:12-15.

[0015] Preferably, in (1), the weight ratio of lanthanum nitrate, deionized water and functional ionic liquid is 1:30-50:0.4-0.5.

[0016] Preferably, the concentration of dilute nitric acid in (1) is 0.1-0.5 mol / L.

[0017] Preferably, the template agent in (2) refers to tetrapropylammonium hydroxide.

[0018] Preferably, the silicon source in (2) refers to tetraethyl orthosilicate.

[0019] Preferably, the aluminum source in (2) refers to sodium aluminate.

[0020] Preferably, the mineralizing agent in (2) refers to sodium hydroxide.

[0021] Preferably, in (2), the template agent, deionized water, silicon source, aluminum source, mineralizer and ternary complex solution are in a weight ratio of 0.2-0.3:6-8:1:0.2-0.4:0.05-0.1:1.2-1.8.

[0022] Preferably, the concentration of the NaOH solution in (2) is 0.1-0.5 mol / L.

[0023] Preferably, in (2), the dropping rate of the silicon source is 3-5 g / min, and the dropping rate of the ternary complex solution is 2-5 g / min.

[0024] Preferably, in the (3) process, the precursor gel filling amount of the high-pressure reactor is 60%-70% of the reactor volume, and the heating rate is 1-3℃ / min.

[0025] Preferably, the conditions for programmed temperature rise calcination in (4) are as follows: heat up to 180-220℃ at 3-7℃ / min and hold for 0.5-1.5h, then heat up to 350-450℃ at 3-7℃ / min and hold for 1-3h, and finally heat up to 580-620℃ and hold for 4-6h. Air is introduced during the calcination process at a flow rate of 50-100mL / min.

[0026] Preferably, in step (4), the crushing and screening process uses a planetary ball mill with 10mm diameter zirconia balls as the grinding media, a ball-to-material ratio of 5-10:1, a rotation speed of 200-300 rpm, a crushing time of 30-60 min, and a 200-300 mesh standard sieve.

[0027] Furthermore, the present invention also provides a rare earth catalyst for petroleum cracking, which is prepared by the above-described method.

[0028] Preferably, the mechanism of action of a rare earth catalyst for petroleum cracking according to the present invention is explained as follows:

[0029] The formation of the ternary complex in the catalyst of this invention is the foundation for the precise construction of the active center. The tertiary amino group (containing a lone pair of electrons) and the phosphonic acid group (O atom as the hard base center) in the bidentate coordinating agent (ethylenediaminetetramethylenephosphonic acid or aminotrimethylenephosphonic acid) molecule, based on the HSAB theory and the La... 3+ Ce 3+ A multidentate stable coordination structure is formed, with the tertiary amine forming a strong coordination bond with rare earth ions, and the phosphonate group forming an auxiliary coordination bond with rare earth ions through the O atom, effectively inhibiting the aggregation of rare earth ions; the functional ionic liquid 1-butyl-3-methylimidazolium dihydrogen phosphate ([BMIM][H2PO4]) contains the anion [H2PO4]. -It forms an intermolecular hydrogen bond network with the phosphonic acid group of the bidentate ligand, and simultaneously wraps around the outside of the coordination layer through electrostatic interactions, forming an "outer electrostatic layer," further enhancing the stability of the ternary complex; cationic [BMIM] + The steric hindrance effect regulates the coordination environment of rare earth ions, reserving suitable sites for subsequent interactions with silica-alumina gel, ultimately forming a ternary complex solution with uniform particle size, laying the structural foundation for the uniform distribution of active centers.

[0030] The synergistic effect of the ternary complex and the silica-alumina gel enables the directional anchoring and skeletal embedding of rare earth ions. When the ternary complex is introduced into the forming silica-alumina gel system, its abundant phosphonic acid groups play a decisive role. These groups, through the oxygen atoms on their P=O and P-OH bonds, form strong hydrogen bonds with the large number of silanol and aluminol groups generated by the hydrolysis and condensation of silicon and aluminum sources in the gel network. This hydrogen bonding is not random adsorption, but driven by intermolecular forces, the entire rare earth complex is uniformly and firmly "woven" into the growing silica-alumina network as independent units. Under mild heat treatment at 50-60℃, this anchoring effect is strengthened, and the continued polymerization of the gel locks the rare earth species in a more rigid environment. This process ensures that the rare earth ions are atomically dispersed in the macroscopic gel, fundamentally avoiding the migration and aggregation problems of active components caused by subsequent drying and calcination in traditional impregnation methods, and achieving the "in-situ" uniform distribution of rare earth elements in the carrier.

[0031] The hydrothermal crystallization process achieves in-situ fusion and structural stabilization of rare earth elements and the molecular sieve framework. Under high-pressure hydrothermal conditions at 160-180℃, the precursor gel is used as a template agent to guide the reaction of Si(OH)4 and AlO2. - Directed polymerization forms a regular molecular sieve microporous structure, due to La 3+ Ce 3+ With their large ionic radius and high coordination number, rare earth elements cannot enter the molecular sieve framework lattice in a tetrahedral coordination form like silicon and aluminum. However, they may be fixed in the channels, cage structures, or ion exchange sites of the molecular sieve through strong interactions, forming ionic bonds or strong polar bonds with framework bridging oxygen atoms or terminal hydroxyl groups. Some rare earth elements may form non-framework oxide clusters that are tightly bound to the framework. Stirring every 6 hours during crystallization optimizes the mass transfer of the system, which helps rare earth elements to be evenly distributed in the molecular sieve structure and avoids uneven active sites caused by local aggregation. The mineralizing agent (sodium hydroxide) promotes the cross-linking polymerization of the molecular sieve framework by regulating the alkalinity of the system, further improving the structural stability, while providing a suitable chemical environment for the interaction between rare earth elements and the framework.

[0032] The calcination and reaction processes achieve synergistic optimization of catalytic performance. During programmed temperature calcination (180-220℃ for water removal, 350-450℃ for organic component decomposition, and 580-20℃ for enhanced bonding), the introduced air oxidizes and decomposes the template agent, ligand, and organic fragments of the ionic liquid, preventing residual carbon species from poisoning the active center. Simultaneously, the interaction between rare earth species and the molecular sieve framework is further strengthened, forming a stable active center structure. Lanthanum species, due to their high charge and large radius, significantly enhance the stability of the framework oxygen bonds, inhibiting the dealumination process and hydrothermal aging in the reaction-regeneration cycle, thereby greatly improving the overall stability and lifespan of the catalyst. Cerium species, with their variable valence state, play a key role as an oxidation promoter in the catalyst regeneration stage, effectively catalyzing the combustion and removal of carbon deposits. Simultaneously, during the reaction stage, they may inhibit excessive cracking and secondary reactions by regulating surface electronic properties. Ultimately, this composite system, consisting of highly dispersed rare earth oxides and a silica-alumina molecular sieve framework with modulating acidity, exhibits excellent C / C bond selective breaking ability, high low-carbon olefin yield, and outstanding resistance to carbon deposition and metal poisoning in petroleum cracking reactions.

[0033] The beneficial effects of this invention are:

[0034] 1. This invention achieves atomic-level dispersion of rare earth species by constructing a ternary complex system of "La-Ce composite rare earth + bidentate ligand + functional ionic liquid". The tertiary amino group and phosphonate group of the bidentate ligand form multidentate stable coordination with rare earth ions. Combined with the electrostatic encapsulation and steric hindrance regulation of the ionic liquid, rare earth agglomeration is avoided, forming high-density and uniform active centers. The La-Ce composite rare earth synergistically optimizes the distribution of acidic sites in the molecular sieve, enhances the synergistic effect of Bronsted acid and Lewis acid, precisely promotes the directional breaking of C-C bonds, significantly improves the selectivity of low-carbon olefin formation, effectively inhibits side reactions such as hydrogen transfer and excessive cracking, and ensures the high efficiency of the catalytic reaction.

[0035] 2. In this invention, La is utilized 3+ The high charge characteristics of the catalyst interact strongly with the bridging oxygen in the molecular sieve framework, significantly enhancing the bonding strength of the Si-O-Al network and suppressing dealumination and framework collapse during the reaction-regeneration cycle. The gradient heating mode of programmed temperature calcination allows for the gradual decomposition and volatilization of organic components, preventing damage to the pore structure while simultaneously strengthening the bonding between rare earth elements and the framework. The entire preparation process utilizes multiple mechanisms, including hydrogen bond anchoring and coordination stabilization, to ensure that the catalyst maintains its regular pore structure and the integrity of active centers even under high-temperature and steamy conditions, significantly improving hydrothermal stability and long-term performance stability.

[0036] 3. The phosphonic acid groups of the bidentate ligand used in this invention form a dense hydrogen bond network with the hydroxyl groups in the silica-alumina gel, precisely anchoring the rare earth-ligand complex near the active sites of the molecular sieve, thus preventing the migration and loss of rare earth ions during hydrothermal crystallization and subsequent processes. The synergistic stabilization of coordination and ionic liquids ensures uniform dispersion of rare earth species and their transformation into surface-active species, significantly improving the effective utilization rate of rare earths. Excellent catalytic effects can be achieved without increasing the amount of rare earths used, reducing the waste of rare earth resources and lowering the raw material cost of catalyst preparation, thus balancing performance advantages with the economics of industrial applications.

[0037] 4. This invention utilizes the variable valence state of Ce species through valence state cycling to efficiently catalyze the oxidative decomposition of carbon deposit precursors during the catalyst regeneration stage, thereby inhibiting carbon deposition at its source; La 3+ The catalyst stabilizes the strong acid sites of the molecular sieve, reducing carbon deposition caused by excessive adsorption and polymerization. Simultaneously, La and Ce species can form stable complexes with heavy metals such as V and Ni in heavy oil, blocking the migration of heavy metals to acidic sites and preventing poisoning and structural damage. This dual-function synergistic effect enables the catalyst to maintain stable catalytic performance in complex reaction systems, broadening its applicability to a wider range of feedstocks. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0039] Example 1: A specific preparation method of a rare earth catalyst for petroleum cracking, comprising the following steps:

[0040] (1) Add 10g of lanthanum nitrate and 15.06g of cerium nitrate to 300g of deionized water, heat to 40℃ and stir to dissolve to form a rare earth salt solution. Add 40.27g of ethylenediaminetetramethylenephosphonic acid to the rare earth salt solution, then adjust the pH to 4.0-5.0 with 0.1mol / L dilute nitric acid, then heat to 60℃ and stir for 1h. Then add 4g of 1-butyl-3-methylimidazolium phosphate and continue stirring for 1h to obtain a ternary complex solution.

[0041] (2) Add 40g of tetrapropylammonium hydroxide to 1.2kg of deionized water and stir at room temperature for 20min; add 200g of tetraethyl orthosilicate at a dropping rate of 3g / min and stir for 0.5h. Then add 40g of sodium aluminate and 10g of sodium hydroxide in sequence and stir at room temperature for 1h to form a silica-alumina gel. Add 240g of ternary complex solution to the silica-alumina gel at a dropping rate of 2g / min and heat to 50℃ and stir for 3h. Adjust the pH to 9.0-10.0 with 0.1mol / L NaOH solution to obtain the precursor gel.

[0042] (3) The precursor gel was transferred to a high-pressure reactor. The amount of precursor gel filled was 60% of the reactor volume. After sealing, the temperature was increased to 160℃ at a heating rate of 1℃ / min for hydrothermal crystallization for 24h. During the crystallization process, the mixture was stirred for 10min every 6h. After cooling to room temperature, the crystals were obtained.

[0043] (4) The crystallized material was separated by centrifugation, washed with deionized water until the pH of the filtrate was neutral, vacuum dried at 100℃ for 12h, and then calcined by programmed temperature increase (heating to 180℃ at 3℃ / min and holding for 0.5h, then heating to 350℃ at 3℃ / min and holding for 1h, and finally heating to 580℃ and holding for 4h, with air introduced during the calcination process at a flow rate of 50mL / min), and pulverized and sieved (using a planetary ball mill, with 10mm diameter zirconia balls as the grinding media, a ball-to-material ratio of 5:1, a rotation speed of 200rpm, pulverizing for 30min, and passing through a 200-300 mesh standard sieve) to obtain a rare earth catalyst for petroleum cracking.

[0044] Example 2: A specific preparation method of a rare earth catalyst for petroleum cracking, comprising the following steps:

[0045] (1) Add 10g of lanthanum nitrate and 10.04g of cerium nitrate to 400g of deionized water, heat to 45℃ and stir to dissolve to form a rare earth salt solution. Add 34.90g of ethylenediaminetetramethylenephosphonic acid to the rare earth salt solution, then adjust the pH to 4.0-5.0 with 0.3mol / L dilute nitric acid, then heat to 65℃ and stir for 1.5h. Then add 4.5g of 1-butyl-3-methylimidazolium phosphate and continue stirring for 1.5h to obtain a ternary complex solution.

[0046] (2) Add 50g of tetrapropylammonium hydroxide to 1.4kg of deionized water and stir at room temperature for 30min; add 200g of tetraethyl orthosilicate at a dropping rate of 4g / min and stir for 1h. Then add 60g of sodium aluminate and 16g of sodium hydroxide in sequence and stir at room temperature for 2h to form a silica-alumina gel. Add 300g of ternary complex solution to the silica-alumina gel at a dropping rate of 3g / min and heat to 55℃ and stir for 3.5h. Adjust the pH to 9.0-10.0 with 0.3mol / L NaOH solution to obtain the precursor gel.

[0047] (3) The precursor gel was transferred to a high-pressure reactor. The amount of precursor gel filled was 65% of the reactor volume. After sealing, the temperature was increased to 170℃ at a heating rate of 2℃ / min for hydrothermal crystallization for 30h. During the crystallization process, the mixture was stirred for 10min every 6h. After cooling to room temperature, the crystals were obtained.

[0048] (4) The crystallized material was separated by centrifugation, washed with deionized water until the pH of the filtrate was neutral, vacuum dried at 110℃ for 14h, and then calcined by programmed temperature increase (heating to 200℃ at 5℃ / min and holding for 1h, then heating to 400℃ at 5℃ / min and holding for 2h, and finally heating to 600℃ and holding for 5h, with air introduced during the calcination process at a flow rate of 80mL / min), and pulverized and sieved (using a planetary ball mill, with 10mm diameter zirconia balls as the grinding media, a ball-to-material ratio of 8:1, a rotation speed of 250rpm, pulverizing for 45min, and passing through a 200-300 mesh standard sieve) to obtain a rare earth catalyst for petroleum cracking.

[0049] Example 3: A specific preparation method of a rare earth catalyst for petroleum cracking, comprising the following steps:

[0050] (1) Add 10g of lanthanum nitrate and 6.69g of cerium nitrate to 500g of deionized water, heat to 50℃ and stir to dissolve to form a rare earth salt solution. Add 33.56g of ethylenediaminetetramethylenephosphonic acid to the rare earth salt solution, then adjust the pH to 4.0-5.0 with 0.5mol / L dilute nitric acid, then heat to 70℃ and stir for 2h. Then add 5g of 1-butyl-3-methylimidazolium phosphate and continue stirring for 2h to obtain a ternary complex solution.

[0051] (2) Add 60g of tetrapropylammonium hydroxide to 1.6kg of deionized water and stir at room temperature for 40min; add 200g of tetraethyl orthosilicate at a dropping rate of 5g / min and stir for 1.5h. Then add 80g of sodium aluminate and 20g of sodium hydroxide in sequence and stir at room temperature for 3h to form a silica-alumina gel. Add 360g of ternary composite solution to the silica-alumina gel at a dropping rate of 5g / min and heat to 60℃ and stir for 4h. Adjust the pH to 9.0-10.0 with 0.5mol / L NaOH solution to obtain the precursor gel.

[0052] (3) The precursor gel was transferred to a high-pressure reactor. The amount of precursor gel filled was 70% of the reactor volume. After sealing, the temperature was increased to 180℃ at a heating rate of 3℃ / min for hydrothermal crystallization for 36h. During the crystallization process, the mixture was stirred for 10min every 6h. After cooling to room temperature, the crystals were obtained.

[0053] (4) The crystallized material was separated by centrifugation, washed with deionized water until the pH of the filtrate was neutral, vacuum dried at 120℃ for 16h, and then calcined by programmed temperature increase (heating to 220℃ at 7℃ / min and holding for 1.5h, then heating to 450℃ at 7℃ / min and holding for 3h, and finally heating to 620℃ and holding for 6h, with air introduced during the calcination process at a flow rate of 100mL / min), and pulverized and sieved (using a planetary ball mill, with 10mm diameter zirconia balls as the grinding media, a ball-to-material ratio of 10:1, a rotation speed of 300rpm, pulverization for 60min, and passing through a 200-300 mesh standard sieve) to obtain a rare earth catalyst for petroleum cracking.

[0054] Example 4: The difference between Example 4 and Example 2 is that ethylenediaminetetramethylenephosphonic acid in step (1) is replaced with aminotrimethylenephosphonic acid.

[0055] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that ethylenediaminetetramethylenephosphonic acid is not added in step (1).

[0056] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that 1-butyl-3-methylimidazolium dihydrogen phosphate is not added in step (1).

[0057] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that neither ethylenediaminetetramethylenephosphonic acid nor 1-butyl-3-methylimidazolium dihydrogen phosphate is added in step (1).

[0058] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that lanthanum nitrate is not added in step (1), and the amount of cerium nitrate added is the same as the total molar amount of lanthanum nitrate and cerium nitrate in Example 2.

[0059] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that cerium nitrate is not added in step (1), and the amount of lanthanum nitrate added is the same as the total molar amount of lanthanum nitrate and cerium nitrate in Example 2.

[0060] Performance testing:

[0061] 1. Catalytic activity and selectivity testing: A fixed-bed microreactor was used to simulate industrial petroleum cracking reaction conditions, with heavy oil (density 0.90-0.95 g / cm³) being catalytically cracked. 3Using catalysts with a residual carbon value of 5.0%-7.0% as raw materials, 5g of the catalysts prepared in Examples 1-4 and Comparative Examples 1-5 were respectively loaded into the isothermal section of the reactor. The bed was fixed with quartz sand. The reaction conditions were set as follows: reaction temperature 550℃, reaction pressure 0.1MPa, raw material feed rate 1.0mL / min, carrier gas (nitrogen) flow rate 50mL / min, continuous reaction for 4h. After the reaction products were separated by condensation, the gas phase products were analyzed by online gas chromatography (GC-9860, equipped with HP-PONA capillary column) to determine the hydrocarbon composition. The liquid phase products were qualitatively and quantitatively analyzed by offline gas chromatography-mass spectrometry (GC-MS-QP2020). The yield of light olefins (ethylene + propylene + butene) (the percentage of the sum of the mass of ethylene, propylene and butene in the product to the total mass of the raw materials), the heavy oil conversion rate (the percentage of the mass of the converted heavy oil to the mass of the feed heavy oil) and the low-carbon alkane / olefin ratio were calculated. The experimental results are shown in Table 1.

[0062] 2. Hydrothermal Stability Test: Referring to the hydrothermal aging conditions of industrial catalyst regeneration cycle, each catalyst sample (2g) was placed in a hydrothermal aging furnace and aged for 16h at 800℃ in a 100% water vapor atmosphere. During the aging process, air was introduced (flow rate 80mL / min) to simulate the regeneration environment. After aging, the catalyst was cooled to room temperature, and the reaction performance was evaluated under the same conditions as in the "Catalytic Activity and Selectivity Test". The yield of light olefins of the aged catalyst was measured, and the activity retention rate was obtained by calculating "yield of light olefins after aging / yield of light olefins of fresh catalyst × 100%". The experimental results are shown in Table 1.

[0063] 3. Rare Earth Utilization Test: The total content of La and Ce in the catalyst was determined using inductively coupled plasma optical emission spectrometry (ICP-OES, Optima 8300). 0.1 g of catalyst sample was accurately weighed, and 10 mL of concentrated nitric acid and 5 mL of hydrofluoric acid were added. The mixture was digested in a microwave digester until clear, cooled, and then brought to a final volume of 100 mL. The La content in the solution was determined by ICP-OES. 3+ Ce 3+ The concentration of rare earth elements was determined, and the total rare earth mass fraction in the catalyst was calculated. The content of active rare earth species on the catalyst surface was analyzed using X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi). The catalyst sample was pressed into tablets and placed in the sample chamber. With Al Kα as the excitation source, the photoelectron spectra of the La3d and Ce3d orbitals were measured. The proportion of active La and Ce species that can participate in the catalytic reaction on the surface to the total rare earth elements was calculated by peak fitting. The rare earth utilization rate was calculated as follows: Rare earth utilization rate (%) = (total rare earth mass fraction in the catalyst × proportion of active rare earth elements on the surface) / (total mass of La and Ce added to the raw materials / total mass of the finished catalyst) × 100%. The experimental results are shown in Table 1.

[0064] 4. Anti-carbon deposition performance test: After reacting each catalyst sample continuously for 8 hours under the conditions of "catalytic activity and selectivity test", the feed was stopped, and the reactor bed was purged with nitrogen for 30 minutes to remove physically adsorbed hydrocarbons. 1.0 g of the reacted catalyst sample was accurately weighed and thermogravimetric analysis was performed using a simultaneous thermal analyzer (TG-DTA, STA 449F3): Under air atmosphere, the temperature was increased from room temperature to 800℃ at a rate of 10℃ / min, and the mass change curve of the sample with temperature was recorded. Based on the mass loss in the 300-700℃ range of the thermogravimetric curve (this temperature range is the characteristic temperature of carbon deposition oxidation decomposition), the amount of carbon deposition on the catalyst surface was calculated (carbon deposition amount = (mass of catalyst after reaction - mass of catalyst after carbon deposition oxidation) / mass of catalyst after reaction × 100%). The experimental results are shown in Table 1.

[0065] 5. Resistance to Metal Poisoning Test: Simulating heavy metal contamination in industrial heavy oil, ammonium vanadate and nickel nitrate were added to the catalytic cracking heavy oil feedstock to achieve a V and Ni mass fraction of 50 μg / g. Each catalyst sample (5g) was loaded into a fixed-bed reactor. The heavy oil feedstock containing heavy metals was introduced at a rate of 1.0 mL / min under conditions of 550℃ and 0.1 MPa for 6 hours. After the reaction, the yield of light olefins was determined according to the "Catalytic Activity and Selectivity Test" method. Simultaneously, the deposition amounts of V and Ni in the catalyst were determined using ICP-OES. The resistance to metal poisoning of the catalyst was evaluated by comparing the yield of light olefins after reaction with the heavy metal-containing feedstock / the yield of light olefins after reaction with the non-heavy metal-containing feedstock × 100%. The experimental results are shown in Table 1.

[0066] Table 1 Performance Test Results

[0067]

[0068] Performance Analysis:

[0069] As can be seen from the experimental data in Table 1, the catalysts prepared by the technical solution of the present invention in Examples 1-4 have excellent comprehensive performance. This may be because they construct a ternary complex synergistic system of "La-Ce composite rare earth + bidentate ligand + functional ionic liquid". Through coordination, hydrogen bond anchoring and electrostatic encapsulation, the rare earth species are dispersed at the atomic level. At the same time, the molecular sieve framework structure and acidic site distribution are precisely controlled to enhance the stable interaction between rare earth and framework, and suppress side reactions and performance decay. Among them, Example 2 has the best comprehensive performance.

[0070] Example 2 showed the best catalytic activity and selectivity, stemming from the pairing of the tertiary amino group and phosphonic acid group of the bidentate ligand in the ternary complex with La. 3+ Ce 3+A multidentate stable coordination structure is formed, with tertiary amines providing lone pairs of electrons to form strong coordination bonds, and phosphonic acid groups assisting in coordination. Combined with the electrostatic encapsulation of the functional ionic liquid [BMIM][H2PO4] anion and the steric hindrance effect of the cation, rare earth ion aggregation is inhibited, forming high-density, uniformly distributed active centers. La-Ce composite rare earth synergistically regulates the surface acidity of molecular sieves: La 3+ It forms strong polar bonds with skeletal oxygen, optimizes the density of bronsted acid sites, and promotes the protonation of hydrocarbons to form carbocations; Ce 3+ By modulating Lewis acid strength through electronic effects, hydrogen transfer and excessive cracking side reactions are suppressed. The two work together to significantly improve the selectivity of directional C-C bond cleavage to generate alkenes and reduce the ratio of low-carbon alkanes to alkenes.

[0071] Example 2 exhibits the best hydrothermal stability, which may be due to the lanthanum species (La). 3+ The strong interaction between La and the molecular sieve framework leads to the high dispersion of La, which is anchored by hydrogen bonds, during crystallization and calcination. 3+ The rare earth elements form strong bonds with the framework bridging oxygen (such as La-O-Si bonds). This strong ionic-covalent bond property can effectively stabilize the framework aluminum-oxygen tetrahedra and inhibit the process of framework dealuminization and structural collapse under high temperature and water vapor conditions. At the same time, the highly dispersed state avoids the sintering of rare earth species themselves, allowing this stabilizing effect to be widely and persistently exerted in the bulk phase of the molecular sieve. Thus, it can still maintain a high density of active centers and pore integrity after harsh aging. Furthermore, the gradient heating mode of programmed temperature calcination allows organic components such as template agents and coordinating agents to gradually decompose and volatilize, avoiding the instantaneous expansion and explosion of gas in the pores caused by rapid heating. This maximizes the preservation of the regular microporous structure of the molecular sieve. The calcination parameters of Example 2 not only thoroughly remove organic impurities, but also enhance the interaction between rare earth elements and the framework through gradient temperature, so that a large number of active centers can still be retained after aging, and the activity retention rate is significantly improved.

[0072] Example 2 showed the highest rare earth utilization rate, mainly because the phosphonic acid group of the bidentate ligand forms a dense hydrogen bond network with the silanol and aluminol groups in the silica-alumina gel, which precisely anchors the rare earth-ligand complex near the active sites of the molecular sieve, avoiding the migration and loss of rare earth ions during hydrothermal crystallization. During hydrothermal crystallization, the anchored rare earth species form a stable interaction with the oxygen atoms of the molecular sieve framework, transforming into active species on the surface that can participate in catalytic reactions, thus significantly improving the utilization rate.

[0073] Example 2 shows a lower carbon buildup due to the synergistic effect of the bifunctional approach and optimized pore accessibility. Firstly, highly dispersed cerium species (Ce...) 3+ / Ce 4+ It possesses a certain redox capability, which can gently oxidize some of the adsorbed polycyclic aromatic hydrocarbon precursors in the early stages of the reaction, inhibiting their deep dehydrogenation condensation into coke; secondly, La 3+The strong acid centers of the molecular sieve were stabilized, reducing excessive cleavage and secondary polymerization of olefins caused by strong acid sites. Finally, the uniformly dispersed active centers ensured smooth diffusion of reactants and products within the pores, reducing retention and coking caused by excessively high local concentrations.

[0074] Example 2 exhibits the best resistance to metal poisoning, possibly because La and Ce species form stable complexes with heavy metals (V, Ni) in heavy oil, blocking the migration of heavy metals to acidic sites on the catalyst through coordination, thus preventing the acidic sites from being occupied or destroyed; simultaneously, La... 3+ The strong polar bonds formed with the molecular sieve framework enhance the stability of the Si-O-Al network and inhibit heavy metal-induced framework dealuminization and structural collapse. The rare earth species in Example 2 are uniformly dispersed, have high binding strength with the framework, and have a greater complexation capacity for heavy metals. Furthermore, the integrity of the molecular sieve framework improves the tolerance to heavy metal poisoning, resulting in a significant reduction in the catalytic performance degradation after the reaction of raw materials containing heavy metals.

[0075] Comparative Example 1 (without bidentate ligand): Due to the lack of chelating stabilization from the bidentate ligand, rare earth ions are prone to hydrolysis and aggregation in the early stages of preparation, forming large rare earth hydroxide or oxide particles. This results in extremely poor dispersion of active sites, a sharp reduction in the number of effective acid sites, and an unreasonable acid distribution, thus significantly reducing catalytic activity and selectivity. Furthermore, the large rare earth particles cannot effectively stabilize the framework or provide uniform redox sites, leading to a comprehensive deterioration in stability, resistance to carbon deposition, and resistance to poisoning.

[0076] Comparative Example 2 (without functional ionic liquid): The lack of ionic liquid reinforcement and steric stabilization of the hydrogen bond network in the ternary complex reduced the homogeneity and stability of the precursor solution. The introduction of silica-alumina gel affected the anchoring uniformity of rare earth species, leading to slight aggregation in some areas. This resulted in a decrease in the dispersion and utilization rate of active rare earth species in the final catalyst, causing varying degrees of performance degradation.

[0077] Comparative Example 3 (without bidentate ligands and ionic liquids): The precursor was a simple mixed solution of rare earth salts. The rare earth ions severely precipitated and aggregated in the subsequent alkaline step, almost completely losing the opportunity for molecular-level dispersion. The structure and performance of the prepared catalyst were severely degraded, with all evaluation indicators being the worst.

[0078] Comparative Example 4 (containing only Ce): La lacking 3+ The strong stabilizing effect on the framework significantly reduces the overall hydrothermal stability of the catalyst. Although its initial activity is acceptable, its structure degrades severely after aging. Furthermore, the lack of La-Ce synergy may lead to uneven acid regulation and a weaker synergistic protective mechanism against heavy metal poisoning.

[0079] Comparative Example 5 (La only): Lacking the redox function of Ce species, the catalyst's in-situ inhibition of carbon deposition precursors and passivation of deposited heavy metals during the reaction were insufficient, resulting in a higher tendency for carbon deposition and a significantly weakened resistance to metal poisoning. Its product selectivity also failed to reach optimal levels due to the limited acid modulation.

[0080] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a rare earth catalyst for petroleum cracking, characterized in that, Includes the following steps: (1) Add lanthanum nitrate and cerium nitrate to deionized water, heat to 40-50℃ and stir to dissolve to form a rare earth salt solution. Add a bidentate complexing agent to the rare earth salt solution, then adjust the pH to 4.0-5.0 with dilute nitric acid, then heat to 60-70℃ and stir for 1-2 hours. Then add a functional ionic liquid and continue stirring for 1-2 hours to obtain a ternary complex solution. (2) Add the template agent to deionized water and stir at room temperature for 20-40 min; add the silicon source dropwise, stir for 0.5-1.5 h, then add the aluminum source and mineralizer in sequence, stir at room temperature for 1-3 h to form a silica-alumina gel, add the ternary complex solution dropwise to the silica-alumina gel, heat to 50-60℃ and stir for 3-4 h, adjust the pH to 9.0-10.0 with NaOH solution to obtain the precursor gel; (3) Transfer the precursor gel to a high-pressure reactor, seal it, and heat it to 160-180℃ for hydrothermal crystallization for 24-36h. Stir for 10min every 6h during the crystallization process. After cooling to room temperature, the crystals are obtained. (4) The crystallized material is separated by centrifugation, washed with deionized water until the pH of the filtrate is neutral, vacuum dried at 100-120℃ for 12-16h, and then calcined by programmed temperature increase, crushed and sieved to obtain a rare earth catalyst for petroleum cracking. The bidentate ligand in (1) refers to ethylenediaminetetramethylenephosphonic acid or aminotrimethylenephosphonic acid; the functional ionic liquid refers to 1-butyl-3-methylimidazolium dihydrogen phosphate. The conditions for programmed temperature rise calcination in (4) are as follows: heat up to 180-220℃ at 3-7℃ / min and hold for 0.5-1.5h, then heat up to 350-450℃ at 3-7℃ / min and hold for 1-3h, and finally heat up to 580-620℃ and hold for 4-6h. Air is introduced during the calcination process at a flow rate of 50-100mL / min.

2. The method for preparing rare earth catalysts for petroleum cracking according to claim 1, characterized in that, In (1), the molar ratio of lanthanum nitrate, cerium nitrate, and bidentate ligand is 4-6:6-4:12-15; the weight ratio of lanthanum nitrate, deionized water, and functional ionic liquid is 1:30-50:0.4-0.5; and the concentration of dilute nitric acid is 0.1-0.5 mol / L.

3. The method for preparing rare earth catalysts for petroleum cracking according to claim 1, characterized in that, In (2), the template agent refers to tetrapropylammonium hydroxide; the silicon source refers to tetraethyl orthosilicate; the aluminum source refers to sodium aluminate; and the mineralizer refers to sodium hydroxide.

4. The method for preparing a rare earth catalyst for petroleum cracking according to claim 1, characterized in that, In (2), the template agent, deionized water, silicon source, aluminum source, mineralizer and ternary complex solution are in a weight ratio of 0.2-0.3:6-8:1:0.2-0.4:0.05-0.1:1.2-1.8; the concentration of NaOH solution is 0.1-0.5 mol / L.

5. The method for preparing a rare earth catalyst for petroleum cracking according to claim 1, characterized in that, The dropping rate of the silicon source in (2) is 3-5 g / min, and the dropping rate of the ternary complex solution is 2-5 g / min.

6. The method for preparing a rare earth catalyst for petroleum cracking according to claim 1, characterized in that, The precursor gel filling amount of the high-pressure reactor in (3) is 60%-70% of the reactor volume, and the heating rate is 1-3℃ / min.

7. The method for preparing a rare earth catalyst for petroleum cracking according to claim 1, characterized in that, In step (4), the crushing and screening process uses a planetary ball mill with 10mm diameter zirconia balls as the grinding media. The ball-to-material ratio is 5-10:1, the rotation speed is 200-300rpm, the crushing time is 30-60min, and the material passes through a 200-300 mesh standard sieve.

8. A rare earth catalyst for petroleum cracking, prepared by the method described in any one of claims 1-7.

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