Process for the preparation of sustainable aviation fuel components by one-step coupling of aromatic and light hydrocarbons

Abstract

The application discloses a method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons, and belongs to the technical field of green fuel catalytic preparation. The zeolite-encapsulated sub-nanometer bimetallic cluster bifunctional catalyst is prepared by a hydrothermal crystallization method, and a catalytic material with stable structure and matching active sites is obtained by combining a low-oxygen controllable calcination, ammonium exchange and high-temperature reduction process. The catalyst is applied to a fixed bed system, and one-step direct coupling reaction of BTX and C2-C4 alkanes can be realized to directionally prepare aviation coal fraction alkylated aromatic hydrocarbon products. The zeolite mesocrystal structure is used to optimize the mass transfer effect, the sub-nanometer synergistic effect of the bimetallic active center and the acid site is used, the dehydrogenation and alkylation reactions of alkanes and aromatics are efficiently coupled, and the selectivity of the target product is significantly improved. Meanwhile, the catalyst has excellent anti-coking and anti-sintering performances, can be stably operated for more than 1000 hours after multiple regeneration cycles, can prepare high-quality sustainable aviation fuel components, and has good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of green and renewable fuel preparation and catalytic chemical technology, specifically relating to a zeolite-encapsulated bimetallic catalyst with a confined space structure, and its process for one-step coupling of aromatics and light hydrocarbons to prepare sustainable aviation fuel components. Background Technology

[0002] Long-chain alkyl aromatics with suitable carbon number ratios possess high density, high energy density, good low-temperature flow properties, and thermal stability, making them a core component of high-quality sustainable aviation fuels. They can effectively improve the volumetric calorific value and combustion stability of aviation kerosene, meet high-end aviation fuel standards, and have extremely high application value in the field of low-carbon emission reduction in the aviation industry. Currently, industrially produced alkylated aromatics are generally produced using benzene and low-carbon olefin alkylation processes, where the raw material low-carbon olefins mainly rely on energy-intensive processes such as catalytic cracking and alkane dehydrogenation. Due to the high bond energy of the CH bond in low-carbon alkanes and the difficulty in activation, traditional olefin preparation processes involve harsh reaction conditions, high equipment energy consumption, and high production costs. Furthermore, traditional processes are difficult to directionally synthesize long-chain alkyl aromatics suitable for aviation kerosene fractions, failing to meet the needs of large-scale production of sustainable aviation fuels.

[0003] In-situ coupling of the endothermic dehydrogenation reaction of C2-C4 low-carbon alkanes with the exothermic benzene alkylation reaction can achieve immediate in-situ conversion of dehydrogenation to olefins. This approach effectively reduces system energy consumption by utilizing complementary reaction heats, while simultaneously breaking the thermodynamic equilibrium limitations of the dehydrogenation reaction and improving alkane conversion efficiency, making it a highly promising green synthetic route. However, this coupled reaction system requires extremely high matching between catalyst structure and active sites. It necessitates a bifunctional catalyst possessing both matched dehydrogenation active centers and acidic alkylation active centers, with precise spatial distribution and site ratios between the two.

[0004] Existing traditional bifunctional catalysts have obvious technical defects: on the one hand, the spatial matching of active sites is poor and the mass transfer resistance is large, resulting in a low overall yield of alkylated aromatics; on the other hand, high-concentration aromatic systems are prone to carbon accumulation on the catalyst surface and high-temperature sintering of active metals, resulting in rapid catalyst deactivation, short service life, and difficulty in regeneration after deactivation and poor cycle stability, which seriously restricts the industrial application of the one-step coupling process of low-carbon alkane-benzene to alkylated aromatics.

[0005] In summary, developing a highly efficient and stable bifunctional catalyst with spatial matching between the metal active center and acidic sites, excellent mass transfer performance, and strong resistance to carbon deposition and sintering can enable efficient coupling of light hydrocarbons and aromatics and the directional preparation of long-chain alkyl aromatics from aviation kerosene fractions. This breakthrough overcomes the technical bottlenecks of traditional processes, such as single product, high energy consumption, and poor catalyst stability. It is key to achieving sustainable, green, efficient, and low-cost integrated production of aviation fuel and has significant engineering application value and industrial promotion significance. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a one-step method for preparing alkylated aromatics and sustainable aviation fuel components by coupling alkane dehydrogenation and olefin-aromatic coupling. This method solves the technical problems of easy catalyst carbonization and sintering, large mass transfer resistance, and low product selectivity and raw material utilization in traditional stepwise series processes. It achieves efficient and highly selective one-step direct coupling of light alkane and aromatic raw materials, which meets the needs of green and low-carbon fuel industrial production.

[0007] The technical solution adopted by the present invention to achieve the above objectives is as follows: a method for producing alkylated aromatics by combining alkane dehydrogenation and olefin-aromatic coupling, specifically comprising the following process steps: S1. Preparation of metal-doped zeolite precursor mixed gel: Tetrabutylammonium hydroxide, silicon source and deionized water are mixed evenly and stirred continuously until fully mixed. Then aluminum source is added and stirred until a uniform suspension is formed. Subsequently, auxiliary metal salt, noble metal salt solution and ethylenediamine are added in sequence and stirred continuously until uniform, finally obtaining a stable and uniform mixed gel.

[0008] S2. Preparation of zeolite precursor by hydrothermal crystallization: The mixed gel obtained in step S1 is transferred to a polytetrafluoroethylene-lined high-pressure reactor and hydrothermal crystallization reaction is carried out under the set temperature conditions; after the reaction is completed, the product is centrifuged, washed with deionized water and organic solvent in sequence and dried to obtain synthetic MEL zeolite powder.

[0009] S3. Low-oxygen controlled calcination to remove MEL molecular sieve template agent: The synthesized zeolite powder obtained in step S2 is placed in a tube furnace and calcined at a programmed temperature using an inert mixed atmosphere containing a low concentration of oxygen to gently remove the organic template agent inside the zeolite while retaining the complete pore structure and microscopic active sites, resulting in a template-free solid powder.

[0010] S4. Preparation of bifunctional catalyst by ion exchange and hydrogen reduction: The solid powder obtained in step S3 is dispersed in an ammonium salt aqueous solution and stirred continuously to complete the ion exchange modification; after modification, it is centrifuged, washed, and dried, and then placed in a hydrogen-containing reducing atmosphere for programmed heating and reduction to finally obtain a highly stable bifunctional catalyst of MEL zeolite-encapsulated sub-nanometer bimetallic clusters.

[0011] S5. Preparation of alkyl aromatic hydrocarbons for aviation fuel by one-step coupling reaction: The bifunctional catalyst prepared in step S4 is loaded into the reactor, and a mixed feed gas of benzene and C2-C4 light alkanes is introduced under heating conditions to carry out a direct coupling reaction of dehydrogenation-alkylation in situ. After the reaction is completed, the product is separated and purified to obtain highly selective alkylated aromatic hydrocarbons, which are the core components of sustainable aviation fuel.

[0012] Furthermore, in step S1, the auxiliary metal salt is selected from any one of the chloride, nitrate, and sulfate salts of cobalt, nickel, zinc, molybdenum, indium, and tin; the noble metal salt is selected from any one of chloroplatinic acid, palladium chloride, and ruthenium chloride.

[0013] Furthermore, in step S1, the Si / Al ratio of the system is controlled to be 10 to 100 based on the molar ratio of silicon to aluminum; based on the mass of the metal elements, the mass fraction of noble metal salt in the mixed gel is 0.1 to 0.5%, and the mass fraction of auxiliary metal salt is 0.5 to 2%.

[0014] Furthermore, in step S2, the hydrothermal crystallization reaction temperature is 100–250 °C, and the crystallization time is 1–2 days.

[0015] Furthermore, in step S3, the mixed atmosphere used for calcination is a mixture of 1-3% O2 ​​and 97-99% N2 by volume, preferably a low-oxygen, mild calcination atmosphere with 2% vol O2; the calcination temperature is controlled at 400-600 ℃. Low-oxygen, mild oxidation conditions can precisely control the combustion rate of the template agent, avoiding severe oxidation that could damage the zeolite's defective structure and metal active sites, while ensuring complete removal of the template agent, thus balancing the integrity of the zeolite structure and its catalytic activity.

[0016] Furthermore, in step S4, the reducing atmosphere is a hydrogen-argon mixture with a volume fraction of 5% H2, and the preferred reduction temperature is 300 ℃. The overall reduction temperature range is controlled between 200 and 400 ℃, which can achieve appropriate reduction and high dispersion of bimetallic clusters and ensure optimal catalytic synergy.

[0017] Furthermore, in step S5, a continuous flow fixed-bed reactor is selected for the catalytic reaction; the reaction temperature is controlled at 300-450 ℃, the reaction system is protected by a normal pressure nitrogen atmosphere, and the molar ratio of benzene to light alkane feedstock is fixed at 1:4; the reactor is sealed and pressure resistant as a whole, and is suitable for continuous and stable operation.

[0018] Specifically, this invention uses MEL zeolite as a framework carrier and introduces bimetallic active components in situ during the zeolite gel synthesis stage. This confines the noble metal and auxiliary metal clusters within the pores during molecular sieve crystallization, fundamentally preventing metal component loss, agglomeration, and high-temperature sintering. Leveraging the unique pore confinement effect and mesocrystalline mass transfer structure of zeolite, the mass transfer resistance of the reaction system is significantly reduced, achieving sub-nanometer precise synergy between dehydrogenation active sites and acidic alkylation sites.

[0019] Specifically, the light alkane raw materials applicable to this invention include one or more complex combinations of ethane, propane, n-butane, and isobutane, which can achieve efficient coupling of light hydrocarbons with different carbon chains and aromatics, and directionally prepare long-chain alkyl aromatics suitable for aviation kerosene fractions.

[0020] For the preferred operating conditions, when the Si / Al molar ratio of the catalyst is 25-50 and the feedstock is mainly propane, a ruthenium-nickel bimetallic catalytic system is preferred, wherein the ruthenium metal loading is preferably 0.1-0.2 wt% and the nickel metal loading is preferably 0.5-0.8 wt%. Under this ratio, the bimetallic synergistic effect is optimal, which can maximize the improvement of light hydrocarbon conversion rate and alkyl aromatic selectivity.

[0021] Compared with existing technologies, this invention has significant technical advantages and positive effects. This invention employs a one-pot hydrothermal method to achieve precise encapsulation of sub-nanometer bimetallic clusters within mesocrystalline aluminosilicate zeolites. Relying on the unique mesocrystalline structure formed by the self-assembly of zeolites, the molecular diffusion paths of reactants and products are significantly shortened, effectively reducing the mass transfer resistance of the system. This fundamentally alleviates the problem of catalyst deactivation due to hindered diffusion of aromatics and reaction products, and significantly improves the reaction stability of the catalyst.

[0022] This invention achieves precise confinement and encapsulation of bimetallic clusters within specific channels of MEL zeolite at the sub-nanometer scale. The auxiliary metal component acts as a co-catalyst, firmly anchoring the noble metal clusters through chemical bonds. This effectively suppresses the migration, aggregation, and sintering of noble metal particles during high-temperature reactions and under fluctuating operating conditions, ensuring the structural stability of the active center. Simultaneously, this confined structure maintains a sub-nanometer spatial proximity (less than 1 nm) between the unsaturated coordinated noble metal dehydrogenation active sites and the zeolite framework Brønsted acid alkylation sites, achieving a high degree of synergy between the dehydrogenation active center and the acidic catalytic center. This allows dehydrogenation reaction intermediates to rapidly participate in the alkylation reaction in situ, significantly improving the catalytic efficiency and reaction rate of the coupled reaction.

[0023] This invention innovatively regulates the oxygen concentration during the roasting stage, preferably using a 2% low-oxygen atmosphere to complete the removal of the template agent. This allows for precise control of the combustion and decomposition rate of the organic template agent, avoiding violent combustion that could damage the microscopic defect structure inside the zeolite, thus fully preserving the pore characteristics and structural advantages of the zeolite. At the same time, it further enhances the dispersibility and structural stability of the bimetallic clusters, providing structural assurance for long-term stable catalytic reactions.

[0024] Based on the catalyst's unique mesocrystalline mass transfer structure, bimetallic confinement synergistic effect, and stable microstructure characteristics, this invention effectively breaks the thermodynamic limitations of the traditional stepwise reaction of alkane dehydrogenation-aromatic alkylation, achieving efficient and directional conversion of C2-C4 alkanes with benzene coupling reaction. The selectivity of benzene substitution products can reach over 90%, and it can efficiently and directionally prepare long-chain alkyl aromatic components suitable for sustainable aviation fuels with high product purity and few by-products.

[0025] Furthermore, this invention effectively suppresses carbon buildup and zeolite framework damage during the reaction process through zeolite mesocrystalline structure optimization and bimetallic confinement modification, significantly improving the catalyst's resistance to carbon buildup, sintering, and structural collapse. Under multiple rounds of continuous reaction-regeneration cycles, the catalyst can operate stably for over 1000 hours without significant structural damage or activity decay, demonstrating excellent cycle stability. This meets the requirements of continuous industrial production and provides reliable technical support for the large-scale, green, and low-cost preparation of sustainable aviation fuel. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments. The described embodiments are only some embodiments of the present invention, not all embodiments, and are only used to illustrate the technical solutions of the present invention. They are not intended to be limiting. Any substitutions, modifications, and improvements made within the spirit, principles, and protection scope of the present invention shall fall within the protection scope of the present invention.

[0027] Example 1

[0028] This embodiment prepares a PtZn@MEL-25-2%O2 zeolite-encapsulated bimetallic catalyst and applies it to the coupling reaction of benzene and ethane to prepare aromatic components of jet fuel. The specific steps are as follows: S1. Preparation of precursor gel: At room temperature, 4.55 g of 40 wt% tetrabutylammonium hydroxide solution, 5.0 g of tetraethyl orthosilicate and 2.33 g of deionized water were mixed and stirred continuously for 12 h; then 0.72 g of aluminum nitrate was added to adjust the silicon-to-aluminum ratio Si / Al=25, and stirring was continued for 3 h to mix thoroughly; then 150 μL of chloroplatinic acid / zinc chloride mixed aqueous solution (corresponding to Pt and Zn metal loading of 0.3 wt% and 1 wt%, respectively) and 150 μL of ethylenediamine were added and stirred for 30 min to obtain a uniform and stable catalytic precursor gel system.

[0029] S2. Hydrothermal Crystallization Synthesis: The prepared precursor gel was transferred to a polytetrafluoroethylene-lined high-pressure reactor and subjected to hydrothermal crystallization at a constant temperature of 150 °C for 2 days. After the reaction, the product was centrifuged (10,000 rpm for 5 min) and washed repeatedly with deionized water and acetone to remove residual impurities and unreacted raw materials. Finally, it was dried overnight at 60 °C to obtain a solid powder precursor.

[0030] S3. Low-oxygen atmosphere calcination: The dried solid powder is placed in a tube furnace and a mixed atmosphere of 2% O2 + 99% N2 is continuously introduced at a gas flow rate of 50 mL / min. The temperature is increased to 550 ℃ at a heating rate of 4 ℃ / min and calcined at a constant temperature for 5 h to complete the controllable removal of the template agent and the crystal structure stabilization, thus obtaining the PtZn@MEL-25-2%O2 catalyst semi-finished product.

[0031] S4. Ion exchange and reduction molding: Take 1.0 g of the above catalyst semi-finished product, disperse it in 30 mL of ammonium acetate solution with a concentration of 0.5 mol / L, stir at room temperature for 6 h for ion exchange modification, centrifuge, wash and dry, place the solid powder in a tube furnace, and reduce it to 400 ℃ at 5 ℃ / min in a 5% H2 / Ar reducing atmosphere for 2 h; after reduction, press and sieve the powder to select 40-60 mesh particles for later use.

[0032] S5. Fixed-bed catalytic evaluation: Accurately weigh 250 mg of molded catalyst and fill it into the center of the isothermal section of the fixed-bed reactor. Set the reaction conditions to atmospheric pressure and a reaction temperature of 400 °C, introduce a mixed reaction gas with a benzene to ethane molar ratio of 1:4, and control the benzene mass hourly space velocity (WHSV) to be 1.6 h⁻¹. - ¹, Aromatic coupling reactions were continuously carried out. The duration of a single continuous reaction was nearly 400 h. After the reaction was deactivated, the catalyst was regenerated by carbon removal and hydrogen reduction in a 2% O2 atmosphere at 550 °C. Multiple cycles of testing were conducted.

[0033] Online gas chromatography analysis showed that the catalyst prepared in this embodiment achieved a selectivity of 80.6% for ethylbenzene in the aromatic products during the initial reaction stage. The test results indicate that the catalyst exhibits a complete and undamaged zeolite framework, with no obvious sintering or agglomeration of bimetallic clusters, demonstrating excellent structural stability and catalytic selectivity.

[0034] Example 2

[0035] This embodiment prepares a RuNi@MEL-12.5-2%O2 zeolite-encapsulated bimetallic catalyst and applies it to the coupling reaction of benzene and propane to prepare aromatic components of jet fuel. The specific steps are as follows: S1. Preparation of precursor gel: At room temperature, 4.55 g of 40 wt% tetrabutylammonium hydroxide solution, 5.0 g of tetraethyl orthosilicate and 2.33 g of deionized water were mixed and stirred continuously for 12 h; then 1.44 g of aluminum nitrate was added to adjust the silicon-to-aluminum ratio Si / Al = 12.5, and stirring was continued for 3 h to mix thoroughly; then 150 μL of ruthenium chloride / nickel chloride mixed aqueous solution (corresponding to Ru and Ni metal loadings of 0.2 wt% and 1.5 wt%, respectively) and 150 μL of ethylenediamine were added and stirred for 30 min to obtain a uniform and stable catalytic precursor gel system.

[0036] S2. Hydrothermal Crystallization Synthesis: The prepared precursor gel was transferred to a polytetrafluoroethylene-lined high-pressure reactor and subjected to hydrothermal crystallization at a constant temperature of 150 °C for 2 days. After the reaction, the product was centrifuged (10,000 rpm for 5 min) and washed repeatedly with deionized water and acetone to remove residual impurities and unreacted raw materials. Finally, it was dried overnight at 60 °C to obtain a solid powder precursor.

[0037] S3. Low-oxygen atmosphere calcination: The dried solid powder is placed in a tube furnace and a mixed atmosphere of 2% O2 + 99% N2 is continuously introduced at a gas flow rate of 50 mL / min. The temperature is increased to 550 ℃ at a heating rate of 4 ℃ / min and calcined at a constant temperature for 5 h to complete the controllable removal of the template agent and the crystal structure stabilization, thus obtaining the RuNi@MEL-12.5-2%O2 catalyst semi-finished product.

[0038] S4. Ion exchange and reduction molding: Take 1.0 g of the above catalyst semi-finished product, disperse it in 30 mL of ammonium acetate solution with a concentration of 0.5 mol / L, stir at room temperature for 6 h for ion exchange modification, centrifuge, wash and dry, place the solid powder in a tube furnace, and reduce it to 400 ℃ at 5 ℃ / min in a 5% H2 / Ar reducing atmosphere for 2 h; after reduction, press and sieve the powder to select 40-60 mesh particles for later use.

[0039] S5. Fixed-bed catalytic evaluation: Accurately weigh 250 mg of molded catalyst and fill it into the center of the isothermal section of the fixed-bed reactor. Set the reaction conditions to atmospheric pressure and a reaction temperature of 400 °C, introduce a mixed reaction gas with a benzene to propane molar ratio of 1:4, and control the benzene mass hourly space velocity (WHSV) to be 2 h⁻¹. - ¹, Aromatic coupling reactions were continuously carried out. The duration of a single continuous reaction was nearly 400 h. After the reaction was deactivated, the catalyst was regenerated by carbon removal and hydrogen reduction in a 2% O2 atmosphere at 550 °C. Multiple cycles of testing were conducted.

[0040] Online gas chromatography analysis showed that the catalyst prepared in this embodiment achieved a propylbenzene selectivity of 92.6% in the initial reaction stage of the aromatic products. After three reaction-regeneration cycles, with a cumulative stable operating time exceeding 1000 h, the catalyst activity was fully recovered, and the final ethylbenzene product selectivity remained at 90.3%. The test results indicate that the catalyst has a stable zeolite framework structure, and the bimetallic active clusters exhibit no sintering or agglomeration, demonstrating extremely high catalytic selectivity and cycle stability, enabling efficient and stable preparation of alkyl aromatic components for aviation kerosene.

[0041] Example 3

[0042] This embodiment prepares a PdCo@MEL-20-2%O2 zeolite-encapsulated bimetallic catalyst and applies it to the coupling reaction of benzene and propane to prepare aromatic components of jet fuel. The specific steps are as follows: S1. Preparation of precursor gel: At room temperature, 4.55 g of 40 wt% tetrabutylammonium hydroxide solution, 5.0 g of tetraethyl orthosilicate and 2.33 g of deionized water were mixed and stirred continuously for 12 h; then 0.90 g of aluminum nitrate was added to adjust the silicon-to-aluminum ratio Si / Al=20, and stirring was continued for 3 h to mix thoroughly; then 150 μL of palladium chloride / cobalt chloride mixed aqueous solution (corresponding to Pd and Co metal loadings of 0.25 wt% and 1.2 wt%, respectively) and 150 μL of ethylenediamine were added and stirred for 30 min to obtain a uniform and stable catalytic precursor gel system.

[0043] S2. Hydrothermal Crystallization Synthesis: The prepared precursor gel was transferred to a polytetrafluoroethylene-lined high-pressure reactor and subjected to hydrothermal crystallization at a constant temperature of 150 °C for 2 days. After the reaction, the product was centrifuged (10,000 rpm for 5 min) and washed repeatedly with deionized water and acetone to remove residual impurities and unreacted raw materials. Finally, it was dried overnight at 60 °C to obtain a solid powder precursor.

[0044] S3. Low-oxygen atmosphere calcination: The dried solid powder is placed in a tube furnace and a mixed atmosphere of 2% O2 + 99% N2 is continuously introduced at a gas flow rate of 50 mL / min. The temperature is increased to 550 ℃ at a heating rate of 4 ℃ / min and calcined at a constant temperature for 5 h to complete the controllable removal of the template agent and the crystal structure stabilization, thus obtaining the PdCo@MEL-20-2%O2 catalyst semi-finished product.

[0045] S4. Ion exchange and reduction molding: Take 1.0 g of the above catalyst semi-finished product, disperse it in 30 mL of ammonium acetate solution with a concentration of 0.5 mol / L, stir at room temperature for 6 h for ion exchange modification, centrifuge, wash and dry, place the solid powder in a tube furnace, and reduce it to 400 ℃ at 5 ℃ / min in a 5% H2 / Ar reducing atmosphere for 2 h; after reduction, press and sieve the powder to select 40-60 mesh particles for later use.

[0046] S5. Fixed-bed catalysis evaluation: Accurately weigh 250 mg of molded catalyst and fill it into the center of the isothermal section of the fixed-bed reactor. Set the reaction conditions to atmospheric pressure and a reaction temperature of 400 °C, introduce a mixed reaction gas with a benzene to propane molar ratio of 1:4, and control the benzene mass hourly space velocity (WHSV) to be 1.8 h⁻¹. - ¹, Aromatic coupling reactions were continuously carried out. The duration of a single continuous reaction was nearly 400 h. After the reaction was deactivated, the catalyst was regenerated by carbon removal and hydrogen reduction in a 2% O2 atmosphere at 550 °C. Multiple cycles of testing were conducted.

[0047] According to online gas chromatography analysis, the catalyst prepared in this embodiment achieved a selectivity of 82.3% for propylbenzene in the aromatic products during the initial reaction stage.

[0048] Example 4

[0049] This embodiment prepares a PtNi@MEL-15-2%O2 zeolite-encapsulated bimetallic catalyst and applies it to the coupling reaction of benzene and butane to prepare aromatic components of jet fuel. The specific steps are as follows: S1. Preparation of precursor gel: At room temperature, 4.55 g of 40 wt% tetrabutylammonium hydroxide solution, 5.0 g of tetraethyl orthosilicate and 2.33 g of deionized water were mixed and stirred continuously for 12 h; then 1.20 g of aluminum nitrate was added to adjust the silicon-to-aluminum ratio Si / Al=15, and stirring was continued for 3 h to mix thoroughly; then 150 μL of chloroplatinic acid / nickel chloride mixed aqueous solution (corresponding to Pt and Ni metal loadings of 0.2 wt% and 1.3 wt%, respectively) and 150 μL of ethylenediamine were added and stirred for 30 min to obtain a uniform and stable catalytic precursor gel system.

[0050] S2. Hydrothermal Crystallization Synthesis: The prepared precursor gel was transferred to a polytetrafluoroethylene-lined high-pressure reactor and subjected to hydrothermal crystallization at a constant temperature of 150 °C for 2 days. After the reaction, the product was centrifuged (10,000 rpm for 5 min) and washed repeatedly with deionized water and acetone to remove residual impurities and unreacted raw materials. Finally, it was dried overnight at 60 °C to obtain a solid powder precursor.

[0051] S3. Low-oxygen atmosphere calcination: The dried solid powder is placed in a tube furnace and a mixed atmosphere of 2% O2 + 99% N2 is continuously introduced at a gas flow rate of 50 mL / min. The temperature is increased to 550 ℃ at a heating rate of 4 ℃ / min and calcined at a constant temperature for 5 h to complete the controllable removal of the template agent and the crystal structure stabilization, thus obtaining the PtNi@MEL-15-2%O2 catalyst semi-finished product.

[0052] S4. Ion exchange and reduction molding: Take 1.0 g of the above catalyst semi-finished product, disperse it in 30 mL of ammonium acetate solution with a concentration of 0.5 mol / L, stir at room temperature for 6 h for ion exchange modification, centrifuge, wash and dry, place the solid powder in a tube furnace, and reduce it to 400 ℃ at 5 ℃ / min in a 5% H2 / Ar reducing atmosphere for 2 h; after reduction, press and sieve the powder to select 40-60 mesh particles for later use.

[0053] S5. Fixed-bed catalytic evaluation: Accurately weigh 250 mg of molded catalyst and fill it into the center of the isothermal section of the fixed-bed reactor. Set the reaction conditions to atmospheric pressure and a reaction temperature of 400 °C, introduce a mixed reaction gas with a benzene to butane molar ratio of 1:4, and control the benzene mass hourly space velocity (WHSV) at 2.0 h⁻¹. - ¹, Aromatic coupling reactions were continuously carried out. The duration of a single continuous reaction was nearly 400 h. After the reaction was deactivated, the catalyst was regenerated by carbon removal and hydrogen reduction in a 2% O2 atmosphere at 550 °C. Multiple cycles of testing were conducted.

[0054] According to online gas chromatography analysis, the catalyst prepared in this embodiment achieved a selectivity of 85.9% for butylbenzene and isobutylbenzene in the aromatic products during the initial reaction stage.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications, substitutions, and variations can be made to the technical solutions and process parameters of the present invention without departing from the core spirit and scope of the present invention, and all such modifications and variations should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons, characterized in that, Includes the following steps: S1. Preparation of mixed gel: Tetrabutylammonium hydroxide, silicon source and deionized water are mixed and stirred evenly. Aluminum source is added and stirring is continued to form a uniform suspension. Then auxiliary metal salt, noble metal salt solution and ethylenediamine are added and stirred evenly to obtain a stable mixed gel. S2. Hydrothermal crystallization: The mixed gel is transferred to a polytetrafluoroethylene-lined high-pressure reactor, and after hydrothermal crystallization, it is centrifuged, washed and dried to obtain synthetic MEL zeolite powder. S3. Low-oxygen controlled calcination: The synthesized zeolite powder is placed in a tube furnace and calcined using a low-oxygen inert mixed atmosphere with programmed temperature rise to remove the organic template agent and obtain calcined solid powder. S4. Modification and reduction: The calcined solid powder is dispersed in an ammonium salt aqueous solution for ion exchange. After centrifugation, washing and drying, it is reduced at high temperature in a hydrogen atmosphere to obtain a zeolite-encapsulated sub-nanometer bimetallic cluster bifunctional catalyst. S5. One-step coupling reaction: The bifunctional catalyst is loaded into the reactor, and a mixture of BTX aromatics and C2-C4 light alkanes is introduced under heating conditions to carry out an in-situ dehydrogenation-alkylation coupling reaction. After the reaction, the alkylated aromatics product is separated, which is the core component of sustainable aviation fuel.

2. The method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons according to claim 1, characterized in that: In step S1, the auxiliary metal salt is any one of the chloride, nitrate, and sulfate salts of cobalt, nickel, zinc, molybdenum, indium, and tin; the noble metal salt is any one of chloroplatinic acid, palladium chloride, and ruthenium chloride.

3. The method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons according to claim 1, characterized in that: In step S1, the silicon-to-aluminum molar ratio Si / Al in the system is 10 to 100; based on the mass of the metal elements, the mass fraction of noble metal salt in the mixed gel is 0.1 to 0.5%, and the mass fraction of auxiliary metal salt is 0.5 to 2%.

4. The method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons according to claim 1, characterized in that: In step S2, the hydrothermal crystallization temperature is 100–250 °C, and the crystallization time is 1–2 days.

5. The method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons according to claim 1, characterized in that: In step S3, the calcination atmosphere is a mixture of 1-3% O2 ​​and 97-99% N2 by volume, preferably 2% volO2; the calcination temperature is 400-600 ℃, and the heating rate is 4 ℃ / min.

6. The method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons according to claim 1, characterized in that: In step S4, the ammonium salt solution used for ion exchange is an ammonium acetate solution with a concentration of 0.5 mol / L; the reducing atmosphere is a hydrogen-argon mixture with a volume fraction of 5% H2, and the reduction temperature is 200–400 °C, preferably 300 °C.

7. The method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons according to claim 1, characterized in that: In step S5, the reaction reactor is a continuous flow fixed bed reactor, the reaction temperature is 300-450 ℃, the reaction system is under normal pressure nitrogen protection atmosphere, and the molar ratio of BTX aromatics to light alkanes is 1:

4.

8. The method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons according to claim 1, characterized in that: The C2-C4 light alkanes include one or more combinations of ethane, propane, n-butane, and isobutane.

9. The method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons according to claim 1, characterized in that: The catalyst is a MEL zeolite confined encapsulated bimetallic cluster structure, with the distance between the bimetallic active center and the zeolite Brønsted acid site being less than 1 nm, forming a sub-nanometer synergistic catalytic system.

10. The method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons according to claim 3, characterized in that: When the Si / Al molar ratio of the catalyst is 25 to 50 and the raw material is mainly propane, a ruthenium-nickel bimetallic system is selected, with a ruthenium loading of 0.1 to 0.2 wt% and a nickel loading of 0.5 to 0.8 wt%.

11. The method for preparing sustainable aviation fuel components by one-step coupling of aromatics and light hydrocarbons according to claim 1, characterized in that: The catalyst is calcined to remove carbon and then regenerated by hydrogen reduction and reused. Its cumulative stable operating life can reach more than 1000 hours, and the selectivity of the alkylated aromatics is ≥90%.