A dual-support hydrocracking catalyst, its preparation method and application

Abstract

This invention provides a dual-support hydrocracking catalyst, its preparation method, and its application. The dual-support hydrocracking catalyst comprises a composite support and an active metal. The composite support is composed of USY molecular sieve and MCM-41 mesoporous molecular sieve. The active metal comprises at least two transition metal elements. The mass ratio of the composite support to the active metal is (2~5):1; the mass ratio of the USY molecular sieve to the MCM-41 mesoporous molecular sieve is (0.5~2):1. The supported hydrocracking catalyst provided by this invention constructs a microporous-mesoporous synergistic pore structure, balancing activity and stability. By using a dual support composed of USY and MCM-41 in a specific ratio, the strong acidity and high shape selectivity of USY molecular sieve are retained, while the mesoporous structure of MCM-41 solves the problem of limited diffusion of macromolecular raw materials, significantly improving the catalyst's carbon-holding capacity and significantly improving its resistance to colloids and carbon deposition.

Description

Technical Field

[0001] This invention relates to the field of aviation fuel technology, and in particular to a dual-support hydrocracking catalyst, its preparation method, and its application. Background Technology

[0002] Sustainable aviation fuel (SAF) is the core path for the civil aviation industry to achieve deep decarbonization. Among them, the preparation of SAF using bio-based naphtha obtained from the conversion of waste oils, lignocellulose and other biomass as raw materials is one of the mainstream technical routes in the industry.

[0003] Bio-based naphtha feedstocks typically contain oxygen-containing impurities such as fatty acid esters, alcohols, and ketones, as well as large molecular weight hydrocarbon components. These need to be converted into C3-C8 light hydrocarbon middle fractions via hydrocracking, followed by dehydrogenation, oligomerization / oligomerization, and hydrogenation processes to produce SAF products that meet aerospace standards. The hydrocracking catalyst is the core of this process, directly determining the feedstock conversion efficiency, target product selectivity, and plant operational stability.

[0004] Existing hydrocracking catalysts have the following core defects: Poor adaptability of support structure: Although the single microporous USY molecular sieve support has strong acidity and good shape selectivity, its narrow pores restrict the diffusion of bio-based macromolecular raw materials, which easily leads to carbon deposition and deactivation, resulting in a short catalyst lifetime; although the single mesoporous MCM-41 molecular sieve has large pores and excellent diffusion performance, its weak acidity results in insufficient cracking activity and shape selectivity, and low selectivity for the C3~C8 target fractions, which cannot meet the yield requirements of SAF production.

[0005] Single function and complex process: Most existing hydrocracking catalysts only have cracking and hydrogenation functions. They have poor tolerance to oxygen-containing impurities in bio-based feedstocks and require a separate pre-deoxygenation unit before hydrocracking, which greatly prolongs the process and increases equipment investment and operating costs.

[0006] Insufficient isomerization performance: The existing catalyst has weak isomerization activity, and the isomer / normal ratio of hydrocracking products is low, resulting in poor low-temperature fluidity of the subsequently prepared SAF products, which cannot meet the core requirement that the freezing point of Jet A-1 aviation fuel should not be higher than -55℃.

[0007] Poor stability and resistance to impurities: Bio-based naphtha contains a certain amount of gum, sulfur and nitrogen impurities. Existing catalysts have weak resistance to gum, carbon deposits and sulfur and nitrogen, short continuous operation cycles, and rapid activity decay after regeneration, which cannot meet the needs of industrial continuous production.

[0008] CN111468171A discloses a solid acid catalytic reaction method for the long-chain alkylation of aromatic hydrocarbons. The method includes: first, feeding the raw aromatic hydrocarbons into a fixed-bed alkylation reactor and filling the reactor; then, feeding a mixture of the raw aromatic hydrocarbons, raw C6-C24 long-chain olefins, and additive long-chain alkyl aromatic hydrocarbon solvents or long-chain alkane solvents into the fixed-bed reactor, contacting them with MCM hydrocarbons and a mesoporous molecular sieve solid acid catalyst to carry out the long-chain alkylation reaction of aromatic hydrocarbons, generating long-chain alkyl aromatic hydrocarbons as products; a portion of the effluent from the alkylation reactor is recycled back to the reactor as circulating fluid, and another portion is used as effluent from the distillation separation system to separate excess raw materials and products. This method is environmentally friendly, has good catalyst activity and stability, high conversion rate, high selectivity, and high product linearity.

[0009] CN119909748A discloses a composite molecular sieve catalyst, its preparation method, and its application. The catalyst is composed of an ordered mesoporous molecular sieve (mass ratio 1:1-5) and a modified USY molecular sieve catalyst. The modified USY molecular sieve catalyst is obtained by treating USY molecular sieve with an inorganic solution and then calcining it. The inorganic solution is one of ammonium chloride, ammonium fluoride, or hydrofluoric acid. This method uses a composite molecular sieve of ordered mesoporous molecular sieve and inorganically modified USY molecular sieve as a catalyst for removing trace amounts of olefins from isopentane oil. It can deeply remove trace amounts of olefins from isopentane oil, improving the quality of isopentane oil. Furthermore, the composite molecular sieve catalyst exhibits good adsorption performance and minimal isopentane loss.

[0010] CN115286665A discloses a method for preparing fructose by isomerization of glucose. The method includes the following steps: heating an aqueous glucose solution under the action of a catalyst; the catalyst is a metal-organic ligand catalyst and / or a molecular sieve-supported gold-organic ligand catalyst; in the catalyst, the metal is selected from at least one of zirconium, aluminum, zinc, and cobalt, the organic ligand is 2-methylimidazole, and the molecular sieve is USY molecular sieve and / or MCM. This method is simple, convenient, and low in cost.

[0011] Existing catalysts are generally used alone, and combined technologies are less studied, while their application areas vary. Therefore, there is an urgent need to develop a hydrocracking catalyst that combines the functions of hydrodeoxygenation, isomerization, and hydrocracking, is suitable for bio-based naphtha feedstocks, and has high selectivity, good stability, and long lifespan. Summary of the Invention

[0012] The technical problem this invention aims to solve is that existing catalyst supports suffer from poor structural adaptability, limited functionality, and insufficient morphological properties in the process of preparing sustainable aviation fuel. The purpose of this invention is to provide a dual-support hydrocracking catalyst, its preparation method, and its application, enabling it to perform three functions—hydrodeoxygenation, isomerization, and hydrocracking—in the process of preparing sustainable aviation fuel. It can directly process oxygenated bio-based naphtha feedstock without the need for a pre-deoxygenation unit, and the process can ultimately achieve high selectivity for the target fraction, excellent isomerization performance, strong resistance to carbon deposition and impurities, and a long operating cycle.

[0013] To address the aforementioned technical problems, in a first aspect, this invention provides a dual-support hydrocracking catalyst, comprising a composite support and an active metal. The composite support is composed of a USY molecular sieve and an MCM-41 mesoporous molecular sieve, and the active metal comprises at least two transition metal elements. The mass ratio of the composite support to the active metal is (2~5):1, for example, 2:1, 3:1, 4:1, or 5:1; the mass ratio of the USY molecular sieve to the MCM-41 mesoporous molecular sieve is (0.5~2):1, for example, 0.5:1, 1:1, 1.5:1, 1.7:1, or 2:1. Mixing the two in the above proportions achieves synergistic complementarity between micropores and mesopores, balancing cracking activity and mass transfer performance. If the proportions change significantly, the overall performance of the catalyst will decrease.

[0014] In this invention, USY molecular sieve provides the acidic centers and shape-selective catalytic performance required for hydrocracking, while MCM-41 mesoporous molecular sieve provides diffusion channels for macromolecular feedstocks and carbon-containing spaces. At the same time, transition metal elements can provide core hydrogenation activity, adjust the acidity distribution of the catalyst, and improve the catalyst's resistance to sulfur and impurities. Through such catalyst design, the catalyst can simultaneously possess the triple functions of hydrodeoxygenation, isomerization, and hydrocracking.

[0015] In addition, USY molecular sieves have abundant strong acid sites and microporous structures, which can provide excellent cracking activity and promote the breaking of carbon-carbon bonds in long-chain hydrocarbons; MCM-41 mesoporous molecular sieves can effectively improve mass transfer efficiency and reduce the retention of intermediate products and secondary cracking.

[0016] Preferably, the transition metal element includes at least two of Ni, W, Pt, Pd, Mo, or Ag.

[0017] Preferably, the transition metal element is Ni and W.

[0018] In this invention, the Ni-W bimetallic system formed by Ni and W has a synergistic hydrogenation effect, and its hydrogenation activity is superior to that of common bimetallic systems such as Ni-Mo and Co-Mo. It can better match the cracking activity of the composite support, realize the dynamic balance between hydrogenation and cracking reaction, and further improve the selectivity of the target product.

[0019] Preferably, the mass ratio of Ni to W is (0.2~0.7):1, for example, it can be 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1 or 0.7:1, etc.

[0020] Preferably, the specific surface area of ​​the dual-supported hydrocracking catalyst is 350~550 m². 2 / g, for example, could be 350m 2 / g、400 m 2 / g、450 m 2 / g、500 m 2 / g or 550 m 2 / g, etc., with a pore volume of 0.35~0.65cm³. 3 / g, for example, could be 0.35cm 3 / g, 0.4 cm 3 / g, 0.5 cm 3 / g, 0.6 cm 3 / g or 0.65 cm 3 / g, etc., with an average pore size of 4~12nm, for example, it can be 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm or 12nm, etc.

[0021] In a second aspect, the present invention provides a method for preparing a dual-support hydrocracking catalyst as described in the first aspect, the method comprising: (1) Mix USY molecular sieve with MCM-41 mesoporous molecular sieve, add binder and extrusion aid to obtain a carrier precursor; (2) Mix the precursors of transition metal elements to obtain an impregnation solution, and then mix the carrier precursors in step (1) into the impregnation solution. After sonication, standing, drying and calcination, the dual-carrier hydrocracking catalyst is obtained.

[0022] Preferably, the binder in step (1) is a pseudoboehmite binder, and the amount of the binder is 10% to 20% of the total mass of the USY molecular sieve and the MCM-41 mesoporous molecular sieve, for example, it can be 10%, 15%, 16% or 20%, etc. Preferably, the extrusion aid in step (1) is guar gum powder extrusion aid, and the amount of the extrusion aid is 2% to 5% of the total mass of USY molecular sieve and MCM-41 mesoporous molecular sieve, for example, it can be 2%, 3%, 4% or 5%.

[0023] In this invention, the USY molecular sieve can be pretreated by placing the USY molecular sieve in a muffle furnace and calcining it at 500~600℃ for 3~6 hours to remove the template agent and surface impurities. After natural cooling, it is ground and passed through a 200~400 mesh sieve to obtain the pretreated USY molecular sieve.

[0024] In this invention, the MCM-41 mesoporous molecular sieve is synthesized by hydrothermal synthesis. Using tetraethyl orthosilicate (TEOS) as the silicon source, hexadecyltrimethylammonium bromide (CTAB) as the template agent, and ammonia as the pH adjuster, the raw materials were weighed according to a TEOS:CTAB:H2O molar ratio of 1:(0.15~0.3):(80~120). CTAB was dissolved in deionized water and stirred until completely dissolved. Ammonia was added to adjust the pH of the system to 10~12. TEOS was slowly added dropwise and stirred continuously for 1~3 hours to obtain the precursor sol. The precursor sol was transferred to a hydrothermal reactor and hydrothermally crystallized at 100~140℃ for 24~72 hours. After natural cooling, it was filtered, washed with deionized water until neutral, dried at 100~120℃ for 6~12 hours, and calcined at 550~650℃ for 4~8 hours to remove the template agent, resulting in MCM-41 mesoporous molecular sieve, which was then ground through a 200~400 mesh sieve for later use.

[0025] Preferably, the precursor of the transition metal element in step (2) is a salt compound of the transition metal element.

[0026] In this invention, the precursor of the transition metal element is a salt compound of the transition metal element. For example, the Ni precursor can be nickel nitrate or nickel acetate, and the W precursor can be ammonium metatungstate or ammonium tungstate, etc.

[0027] Preferably, the temperature of the ultrasound in step (2) is 25~60℃, for example, it can be 25℃, 40℃, 50℃ or 60℃, etc., and the time is 0.5~2h, for example, it can be 0.5h, 0.6h, 1h, 1.5h or 2h, etc.

[0028] Preferably, the settling time in step (2) is 4 to 12 hours, for example, 4 hours, 7 hours, 9 hours, 10 hours or 12 hours.

[0029] Preferably, the drying temperature in step (2) is 100~120℃, for example, 100℃, 110℃, 115℃ or 120℃, and the time is 6~12h, for example, 6h, 7h, 8h, 9h, 10h, 11h or 12h.

[0030] Preferably, the roasting temperature in step (2) is 500~600℃, for example, 500℃, 510℃, 520℃, 550℃, 580℃ or 600℃, and the time is 4~6h, for example, 4h, 5h or 6h.

[0031] Thirdly, the present invention provides the application of the dual-support hydrocracking catalyst described in the first aspect in the preparation of sustainable aviation fuel.

[0032] Specifically, renewable feedstocks (such as biomass oil, waste cooking oil, etc.) are mixed with hydrogen and subjected to hydrocracking reaction under the action of the dual-carrier hydrocracking catalyst to convert into C3~C8 fractions that meet aviation fuel standards, thus obtaining sustainable aviation fuel.

[0033] Implementing this invention has the following beneficial effects: The hydrocracking catalyst supported by this invention constructs a microporous-mesoporous synergistic pore structure, balancing activity and stability. It employs a dual-support composition of USY and MCM-41 in a specific ratio. This retains the strong acidity and high shape selectivity of the USY molecular sieve, ensuring hydrocracking reaction activity and selectivity for the target C3-C8 fractions; while the mesoporous structure of MCM-41 solves the problem of limited diffusion of large molecular feedstocks, significantly improving the catalyst's carbon-holding capacity, effectively inhibiting carbon deposition and deactivation, and significantly improving its resistance to gum formation and carbon deposition.

[0034] This invention enables the catalyst to simultaneously possess the triple functions of hydrodeoxygenation, isomerization, and hydrocracking through the synergistic regulation of Ni-W bimetals. It can directly process bio-based naphtha feedstock containing oxygen-containing impurities such as fatty acid esters, alcohols, and ketones, without the need for a separate pre-deoxygenation unit. This shortens the SAF production process by more than 30% and reduces equipment investment by more than 25%.

[0035] The catalyst of this invention achieves efficient isomerization simultaneously during hydrocracking by precisely matching acidity and hydrogenation activity. Under reaction conditions of 340~380℃ and 6.0~10.0MPa, the selectivity of C3~C8 middle fraction is higher than 70%, and the product isomer / normal ratio is higher than 3.5. This can significantly improve the low-temperature fluidity of subsequent SAF products and meet the core standard that the freezing point of aviation fuel is not higher than -55℃.

[0036] The catalyst of this invention exhibits outstanding resistance to sulfur, nitrogen, and colloids, as well as excellent regeneration performance, making it fully suitable for the needs of continuous industrial production and possessing broad application prospects and commercial value. Attached Figure Description

[0037] Figure 1This is the N2 adsorption-desorption isotherm of the dual-support hydrocracking catalyst prepared in Example 2 of this invention;

[0038] Figure 2 This is a pore size distribution diagram of the dual-support hydrocracking catalyst prepared in Example 2 of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] This embodiment provides a dual-support hydrocracking catalyst. The mass ratio of USY molecular sieve to MCM-41 mesoporous molecular sieve in the composite support is 2:1; based on 100 g of catalyst, the mass of active metal element Ni is 3 g, the mass of active metal element W is 15 g, the mass ratio of Ni to W is 0.2:1, and the mass ratio of composite support to active metal element is 4.56:1.

[0042] Preparation process: (1) Mix USY molecular sieve with MCM-41 mesoporous molecular sieve, add 15wt% boehmite and 3wt% guar gum powder, add an appropriate amount of deionized water and knead evenly, extrude into strips of φ2mm; dry at 110℃ for 8h, calcine at 550℃ for 5h to obtain the carrier precursor. Among them: USY molecular sieve pretreatment: USY molecular sieve is placed in a muffle furnace, calcined at 550℃ for 4 hours, naturally cooled and then ground, and passed through a 300-mesh sieve to obtain pretreated USY molecular sieve.

[0043] MCM-41 Synthesis: The raw materials were weighed according to the molar ratio of TEOS:CTAB:H2O 1:0.2:100. CTAB was dissolved in deionized water and stirred until completely dissolved. Ammonia was added to adjust the pH to 11. TEOS was slowly added dropwise and stirred continuously for 2 hours to obtain the precursor sol. The sol was transferred to a hydrothermal reactor and hydrothermally crystallized at 120℃ for 48 hours. After natural cooling, it was filtered, washed with deionized water until neutral, dried at 110℃ for 8 hours, and calcined at 600℃ for 6 hours to remove the template agent, thus obtaining MCM-41 molecular sieve. It was then ground through a 300-mesh sieve for later use.

[0044] (2) Mix nickel nitrate and ammonium metatungstate precursors to obtain impregnation solution, then mix the carrier precursor from step (1) into the impregnation solution, ultrasonically impregnate at 40°C for 1 h, let stand at room temperature for 8 h, dry at 110°C for 12 h, and calcine at 500°C for 4 h to obtain dual-carrier hydrocracking catalyst.

[0045] Example 2

[0046] This embodiment provides a dual-support hydrocracking catalyst. The mass ratio of USY molecular sieve to MCM-41 mesoporous molecular sieve in the composite support is 1:1. Based on 100 g of catalyst, the mass of active metal element Ni is 4.5 g, the mass of active metal element W is 20 g, the mass ratio of Ni to W is 0.225:1, and the mass ratio of the composite support to the active metal element is 3.08:1. The N2 adsorption-desorption isotherms and pore size distribution diagrams of the prepared catalyst are shown below. Figure 1 and Figure 2 As shown.

[0047] Example 3

[0048] This embodiment provides a dual-support hydrocracking catalyst. The mass ratio of MCM-41 mesoporous molecular sieve to USY molecular sieve in the composite support is 2:1; based on 100 g of catalyst, the mass of active metal element Ni is 6 g, the mass of active metal element W is 25 g, the mass ratio of Ni to W is 0.24:1, and the mass ratio of composite support to active metal element is 2.23:1.

[0049] Comparative Example 1 This comparative example is basically the same as Example 1, but does not use MCM-41 mesoporous molecular sieve.

[0050] Comparative Example 2 This comparative example is basically the same as Example 1, but does not use USY molecular sieve.

[0051] Comparative Example 3 This comparative example is basically the same as Example 1, but the mass ratio of USY molecular sieve to MCM-41 mesoporous molecular sieve is 4:1.

[0052] Comparative Example 4 This comparative example is basically the same as Example 1, but the mass ratio of USY molecular sieve to MCM-41 mesoporous molecular sieve is 1:4.

[0053] Comparative Example 5 This comparative example is basically the same as Example 1, but the mass percentage of Ni is 2% and the mass percentage of W is 10%.

[0054] Comparative Example 6 This comparative example is basically the same as Example 1, but the mass percentage of Ni is 7% and the mass percentage of W is 30%.

[0055] The performance of the dual-support hydrocracking catalysts prepared above was tested. The catalysts of Examples 1-3 and Comparative Examples 1-6 were evaluated using a fixed-bed hydrocracking reactor. The feedstock was industrial-grade bio-based naphtha with the following properties: density (20℃) 0.762 g / cm³. 3 Distillation range 65~320℃, oxygen content 1.2wt%, sulfur content 28ppm, nitrogen content 12ppm, gum content 120mg / 100mL. Process conditions: reaction temperature 360℃, reaction pressure 8.0MPa, hydrogen-to-oil ratio 500:1, mass hourly space velocity 1.0h⁻¹. -1 The catalyst loading was 100 mL, and samples were taken for analysis after the reaction had been running stably for 200 h. The results are shown in Table 1: Table 1

[0056] As can be seen from the experimental data in Table 1, the dual-support hydrocracking catalyst provided by this invention exhibits good catalytic selectivity and easy configuration, especially the catalytic performance provided by the dual supports. However, the effect decreases significantly when the composition of the support changes.

[0057] In addition, a 1000-hour continuous operation stability test was conducted on the catalyst of Example 2. The results showed that after 1000 hours of continuous operation, the selectivity of the catalyst for C3-C8 fractions remained above 72%, the isomer / normal fraction ratio was above 3.5, the deoxygenation rate was above 99.5%, the carbon deposition was only 4.2 wt%, and there was no obvious deactivation phenomenon. This verified the industrial application potential of the catalyst with a continuous operation cycle of not less than 1 year.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dual-support hydrocracking catalyst, characterized in that, The dual-support hydrocracking catalyst comprises a composite support and an active metal. The composite support comprises USY molecular sieve and MCM-41 mesoporous molecular sieve, and the active metal comprises at least two transition metal elements. The mass ratio of the composite support to the active metal is (2~5):1, and the mass ratio of the USY molecular sieve to the MCM-41 mesoporous molecular sieve is (0.5~2):

1.

2. The dual-support hydrocracking catalyst according to claim 1, characterized in that, The transition metal element includes at least two of Ni, W, Pt, Pd, Mo, or Ag.

3. The dual-support hydrocracking catalyst according to claim 2, characterized in that, The transition metal elements are Ni and W.

4. The dual-support hydrocracking catalyst according to claim 3, characterized in that, The mass ratio of Ni to W is (0.2~0.7):

1.

5. The dual-support hydrocracking catalyst according to claim 1, characterized in that, The specific surface area of ​​the dual-supported hydrocracking catalyst is 350~550 m². 2 / g, pore volume 0.35~0.65cm³ 3 / g, with an average pore size of 4~12nm.

6. The method for preparing the dual-supported hydrocracking catalyst according to any one of claims 1 to 5, characterized in that, The preparation method includes: (1) Mix USY molecular sieve with MCM-41 mesoporous molecular sieve, add binder and extrusion aid to obtain a carrier precursor; (2) Mix the precursors of transition metal elements to obtain an impregnation solution, and then mix the carrier precursors in step (1) into the impregnation solution. After sonication, standing, drying and calcination, the dual-carrier hydrocracking catalyst is obtained.

7. The preparation method according to claim 6, characterized in that, The binder mentioned in step (1) is a pseudoboehmite binder, and the amount of the binder is 10% to 20% of the total mass of USY molecular sieve and MCM-41 mesoporous molecular sieve; The extrusion aid mentioned in step (1) is guar gum powder extrusion aid, and the amount of the extrusion aid is 2% to 5% of the total mass of USY molecular sieve and MCM-41 mesoporous molecular sieve.

8. The preparation method according to claim 6, characterized in that, The precursor of the transition metal element mentioned in step (2) is a salt compound of the transition metal element; The temperature of the ultrasound in step (2) is 25~60℃, and the time is 0.5~2h; The settling time mentioned in step (2) is 4~12 hours; The drying temperature in step (2) is 100~120℃, and the time is 6~12h; The roasting temperature in step (2) is 500~600℃ and the time is 4~6h.

9. The application of the dual-support hydrocracking catalyst according to any one of claims 1 to 5 in the preparation of sustainable aviation fuel.

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