Composite molecular sieve hydroisomerization catalyst, preparation and application

Abstract

The invention belongs to the technical field of catalysts, and discloses a composite molecular sieve hydroisomerization catalyst, a preparation method and application in biological aviation kerosene hydroisomerization reaction. The catalyst is a bifunctional hydroisomerization catalyst with SAPO-11, ZSM-22 and USY molecular sieves compounded in a specific proportion as carriers and precious metal as an active component, and belongs to a composite molecular sieve hydroisomerization catalyst with unique acidity and pore channel synergistic effect, the C9-C16 yield of the catalyst reaches 82% or above, and the freezing point is lower than-55 DEG C. According to the method, carrier properties are optimized through a key pretreatment process, and stability and high efficiency of catalytic performance are ensured.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a composite molecular sieve hydroisomerization catalyst, its preparation method, and its application in the hydroisomerization reaction of bio-jet fuel. Background Technology

[0002] In response to climate change, the aviation industry has an increasingly urgent need for sustainable aviation fuel (SAF). The most mature and reliable technology for producing SAF is through hydroprocessing (HEFA), using animal and vegetable oils and waste oils as raw materials. The key to this route lies in the hydroisomerization (HI) process, which converts the straight-chain alkanes (mainly C15-C18) produced by hydrodeoxygenation (HDO) into isoalkanes with abundant branched chains. This significantly lowers the freezing point of the product to meet the stringent specifications of aviation kerosene (such as the JetA-1 standard requiring a freezing point ≤ -47°C).

[0003] The performance of hydroisomerization catalysts directly determines the yield and quality of SAFs. An ideal catalyst should possess both high isomerization selectivity (to lower the freezing point) and moderate selective cracking capability (to adjust the carbon number distribution to the C9-C16 jet fuel range), while suppressing excessive cracking to generate lighter components. Currently, industrial and research focus is on bifunctional (metal-acid) catalysts supported on shape-selective molecular sieves.

[0004] SAPO-11 molecular sieves, due to their unique ten-membered ring one-dimensional channel structure and suitable acidity, can selectively promote the formation of monomethyl branched isomers and are widely recognized as one of the best supports in this field. ZSM-22 has a similar channel structure to SAPO-11 but is more acidic and is often used to improve the overall activity of catalysts. USY molecular sieves possess three-dimensional macropores and strong acid centers, exhibiting outstanding ability to crack long-chain alkanes.

[0005] However, existing technologies have significant limitations: CN201510465351.4 (Hydroisomerization and Cracking Catalyst for the Preparation of Bio-aviation Kerosene from Castor Oil): discloses a catalyst using Al-modified titanium silicate molecular sieve (TS-1) as a support and NixW / NixMo as the active component, with urea dispersant used to improve the dispersibility of the active component. However, this catalyst uses a single TS-1 support, lacks the synergistic effect of isomerization and selective cracking, and has limited ability to adjust the carbon number of C17+ long-chain alkanes, resulting in a jet fuel fraction yield of only about 76%, which is difficult to meet the needs of large-scale production. CN201610412721.2 (An Isomerization Dewaxing Method for the Production of Bio-aviation Kerosene and a Catalyst for the Method): discloses a hydroisomerization catalyst using silicon surface-modified mesoporous molecular sieve (such as ZSM-22) as a support and Pt / Pd as the active component. It adjusts the silicon-to-aluminum ratio through surface silicon modification, but the acidity and pore structure of a single modified molecular sieve are limited, failing to simultaneously meet the requirements of high heterogeneity selectivity and moderate cracking. The product's freezing point is only -47 to -53°C, and the C9-C16 selectivity is less than 60%. CN202510873484.9 (A composite catalyst and its preparation method and a method for preparing bio-jet fuel): discloses a composite catalyst composed of a heterogeneous catalyst (support ZSM-22, etc.) and a cracking catalyst (support ZSM-5, etc.), using a cross-layered stacking method. Although it can achieve synergy between heterogeneity and cracking, the process of separate preparation and cross-packing of the two catalysts is complex, with high operating costs, and the active sites of the two catalysts are difficult to achieve synergy at the microscopic level, resulting in a jet fuel yield of only about 75%. CN202310343810.6 (An isomeric dewaxing catalyst for the production of bio-jet fuel and its application method): Discloses a catalyst with nickel supported on a Y-type molecular sieve. While this catalyst has lower cost, the hydrogenation isomerization activity of nickel is lower than that of precious metals. Furthermore, the pore structure of a single Y-type molecular sieve is insufficient for selective control of isomer products, resulting in an isomerization rate of only 40%~53%, and the freezing point is difficult to stably remain below -45℃. CN202410147759.6 (A core-shell structured bio-jet fuel catalyst and its application): Discloses a core-shell structured catalyst (the core is ZSM-5 supported on Pt and divalent metals, and the shell is a large-pore molecular sieve). Its core-shell preparation process is complex (requiring multiple steps such as hydrothermal encapsulation and activation), making large-scale production difficult. Moreover, the interfacial resistance between the core and shell affects mass transfer efficiency, resulting in a maximum jet fuel yield of only 63%. CN201711023173.5 (A method for producing an isomeric dewaxing catalyst and bio-jet fuel): discloses an isomeric dewaxing catalyst containing two twelfth-membered ring silica-alumina molecular sieves (such as Beta and ZSM-12). The dewaxing effect is improved by combining molecular sieves. However, the selected molecular sieves lack precise cracking control of long-chain alkanes and do not carry out targeted acid regulation, which can easily lead to excessive cracking (increase in C5-C7 light components) or insufficient isomerization (exceeding the freezing point).

[0006] In summary, while SAPO-11 alone offers high isomer selectivity, its cracking capacity is weak, particularly its selective cracking ability for C17+ heavy alkanes, resulting in limited jet fuel fraction yield and potential residues of high-carbon fractions in the product. Using USY alone or in excessively high proportions can lead to deep, random cracking reactions due to its strong acidity and large pore size, causing a sharp decline in the selectivity of the target jet fuel, an increase in light byproducts, and difficulty in achieving the desired freezing point due to side reactions. Simple two-component composites (such as SAPO-11 / USY) cannot effectively synergize their functions if the proportions or treatment are improper; instead, strong acid sites become the centers of disruptive side reactions.

[0007] Therefore, developing a novel, highly efficient catalyst that can precisely balance isomerization and selective cracking to simultaneously optimize jet fuel yield and freezing point performance is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0008] To address the above-mentioned technical problems, the primary objective of this invention is to provide a composite molecular sieve hydroisomerization catalyst. This catalyst is a bifunctional hydroisomerization catalyst using a specific ratio of SAPO-11, ZSM-22, and USY molecular sieves as a support and noble metals as the active component. It belongs to a type of composite molecular sieve hydroisomerization catalyst with unique acidity and pore synergistic effects. This catalyst can efficiently convert straight-chain alkanes derived from bio-oils into high-yield, low-freezing-point bio-jet fuel under mild conditions.

[0009] The second objective of this invention is to provide a method for preparing a composite molecular sieve hydroisomerization catalyst, which optimizes the support properties through key pretreatment processes to ensure stable and efficient catalytic performance.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A composite molecular sieve hydroisomerization catalyst, wherein the catalyst comprises, by weight (100%): The composite molecular sieve carrier comprises 80-95%, active metal 0.2-1.5%, and binder 4.8-18.5%. The composite molecular sieve support is composed of the following molecular sieves in a dry basis mass ratio as follows: SAPO-11 molecular sieve and ZSM-22 molecular sieve are mixed at a mass ratio of (1.5~3):1; The total mass ratio of USY molecular sieve to composite molecular sieve carrier is 0.1~0.3:1; The relative crystallinity of both the SAPO-11 molecular sieve and the ZSM-22 molecular sieve is >90% to ensure the integrity of the support pore structure and catalytic stability. The silica-to-alumina ratio of the USY molecular sieve is 10-50. This avoids excessive acidity leading to over-cracking while ensuring adequate selective cracking capability.

[0011] Preferably, the USY molecular sieve has a particle size of 0.15~0.25.

[0012] Preferably, the active metal includes platinum and / or palladium; The binder includes any one of boehmite, silica, and clay.

[0013] Preferably, the active metal is platinum; The binder is boehmite.

[0014] A method for preparing a composite molecular sieve hydroisomerization catalyst includes the following steps: S1. Molecular sieve composite and pretreatment: Dry SAPO-11 molecular sieve, ZSM-22 molecular sieve and USY molecular sieve were selected and mechanically mixed in proportion to obtain a mixture. The mixture was then subjected to hydrothermal treatment to obtain composite molecular sieve carrier powder. S2, Carrier molding: The obtained composite molecular sieve carrier powder is mixed with binder, extrusion aid and adhesive solvent, rolled, extruded into strips, dried and calcined at high temperature to obtain composite carrier; S3, Active Metal Loading: The catalyst precursor is obtained by uniformly loading the impregnation solution containing the active metal precursor onto the composite support using the equal volume impregnation method. After impregnation, room temperature aging, drying and low temperature calcination, the catalyst precursor is obtained. S4. Catalyst activation: Before use, the catalyst precursor is placed in a hydrogen atmosphere and reduced to obtain the composite molecular sieve hydroisomerization catalyst.

[0015] Preferably, in step S1, the hydrothermal treatment conditions are: treatment at 400~550℃ and a water vapor partial pressure of 0.1~0.5 atm for 2~6 hours.

[0016] Step S1 above is used to modulate the acid strength and acid quantity of USY and ZSM-22, moderately remove some of the framework aluminum to reduce the density of strong acid centers, and at the same time promote the formation of beneficial mesoporous structures in SAPO-11, thereby achieving the "homogenization" and optimization of the acid properties of the three molecular sieves.

[0017] Preferably, in step S2, the extrusion aid is guar gum powder; the adhesive solvent is a dilute nitric acid solution. The mass ratio of the composite molecular sieve carrier powder, extrusion aid, and adhesive solvent is 0.85:0.05:0.145. The drying temperature is 100~120℃; the high-temperature calcination temperature is 500~600℃, and the duration is 3~6h.

[0018] Preferably, in step S3, the drying temperature is 100~120℃ and the low-temperature calcination temperature is 300~450℃.

[0019] Preferably, in step S4, the reduction conditions are: reduction at 350~450℃ for 2~6 hours.

[0020] The application of a composite molecular sieve hydroisomerization catalyst in the hydroisomerization reaction of bio-jet kerosene, wherein the reaction conditions are: reaction pressure 3.0~8.0 MPa, temperature 280~360℃, hydrogen-to-oil volume ratio (500~1000):1, and liquid hourly space velocity 0.5~2.0 h⁻¹. -1 ; The bio-jet fuel is a mixture mainly composed of C15-C20 straight-chain alkanes obtained by hydrodeoxygenation of bio-oils; The bio-oils include one or more of palm oil, waste cooking oil, and microalgae oil.

[0021] Compared with the prior art, the present invention has at least the following technical effects: This invention provides a composite molecular sieve hydroisomerization catalyst, which is a bifunctional hydroisomerization catalyst with a specific ratio of SAPO-11, ZSM-22 and USY molecular sieves as supports and noble metals as active components. It belongs to a composite molecular sieve hydroisomerization catalyst with unique acidity and pore synergistic effect.

[0022] The preparation method of this composite molecular sieve hydroisomer catalyst optimizes the support properties through key pretreatment processes to ensure stable and efficient catalytic performance. Detailed Implementation

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention will be briefly introduced below in conjunction with the description of the embodiments or the prior art. Obviously, the following description of the technical solutions is merely some embodiments of the present invention. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention.

[0024] One specific embodiment of the present invention is as follows: I. Catalyst Preparation and Preparation Methods: In all the examples and comparative examples below, the USY molecular sieve (SiO2 / Al2O3=25) was purchased from the catalyst factory of Nankai University, and the SAPO-11 and ZSM-22 molecular sieves were synthesized according to the literature method (relative crystallinity >95%). Unless otherwise specified, the catalyst with a Pt loading of 0.5 wt% was prepared according to the following general steps: 1. Composite and pretreatment: The molecular sieves were mixed according to the proportions in Table 1, placed in a fixed bed, and 30 vol% water vapor / N2 mixture was introduced and treated at 480℃ for 4 hours; 2. Molding: Take 70g of the treated composite molecular sieve, 25g of pseudoboehmite, and 5g of guar gum powder, add an appropriate amount of 5% nitric acid solution, knead, extrude (Φ1.6mm), dry (120℃ / 12h), and calcine (550℃ / 4h); 3. Loading and calcination: Impregnate with chloroplatinic acid solution of equal volume, age, dry (120℃ / 6h), and calcinate (400℃ / 3h); 4. Reduction: Before use, reduce in situ in the reactor at 400℃ under H2 atmosphere for 4 hours.

[0025] II. Example and Comparative Examples: Formulation and Catalytic Performance Evaluation 2.1 Evaluation Method: Raw materials: a model compound consisting of n-pentadecane (n-C15), n-hexadecane (n-C16), n-heptadecane (n-C17), and n-octadecane (n-C18) in a mass ratio of 20:30:30:20.

[0026] Apparatus: 100 mL fixed-bed hydrogenation reactor.

[0027] Conditions: Pressure 5.0 MPa, temperature 320℃, hydrogen-to-oil volume ratio 800:1, weight hourly space velocity (WHSV) 1.0 h⁻¹ -1 .

[0028] Analysis: After the reaction stabilized for 24 hours, online samples were taken, and the carbon number distribution was analyzed by gas chromatography (GC) simulating distillation. The isomers were analyzed by multidimensional gas chromatography (GC×GC), and the freezing point was determined according to the ASTM standard method.

[0029] 2.2 Examples and Comparative Data Table 1: Composition and Performance Evaluation Results of Different Catalysts

[0030] III. Results Analysis 3.1 Proportional Effect: The data clearly show that when the ratio of SAPO-11, ZSM-22, and USY is around 60:25:15, the overall performance of the catalyst reaches its peak (Example 1).

[0031] At this ratio, the "pyrolysis-heterogeneity" cascade function of the three molecular sieves achieves optimal synergy, realizing an excellent balance of near-complete C18 conversion, jet fuel yield exceeding 82%, and freezing point below -58℃.

[0032] 3.2 Component Function Verification: Comparative Example 1 (single SAPO-11) confirmed that the lack of pyrolysis components led to incomplete conversion of heavy feedstocks; Comparative Example 2 (single USY) proved that strong pyrolysis function alone cannot achieve high-selectivity isomerization; Comparative Example 3 (binary composite without ZSM-22) and Examples 3 and 4 showed that an excessively high proportion of USY or a lack of ZSM-22 transition would disrupt the synergy between acidity and pores, leading to a decrease in selectivity.

[0033] 3.3 The criticality of the pretreatment step: Comparative Example 4 (same as Example 1 but without pretreatment) had an initial freezing point as high as -48°C and lower selectivity than the pretreated sample. This strongly demonstrates that hydrothermal treatment is an essential step for harmonizing the acidity of the composite support, passivating harmful strong acid centers, and thus obtaining stable and excellent initial and long-term catalytic performance. Untreated catalysts have an induction period, resulting in unstable product properties that cannot meet the requirements of industrial plants for immediate catalyst performance.

[0034] in conclusion: This invention successfully prepared a hydroisomerization catalyst by combining SAPO-11, ZSM-22, and USY molecular sieves in a specific ratio and employing a key hydrothermal pretreatment process. This catalyst exhibits significant advantages in bio-jet kerosene production, including high yield, low freezing point, and high selectivity. Its overall performance far surpasses existing single or binary molecular sieve catalysts, solving the technical challenge of simultaneously achieving isomerization and selective cracking, and possesses extremely high industrial application value.

[0035] Finally, it should be noted that 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. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite molecular sieve hydroisomerization catalyst, characterized in that, The catalyst, by total mass, comprises the following components: The composite molecular sieve carrier comprises 80-95%, active metal 0.2-1.5%, and binder 4.8-18.5%. The composite molecular sieve support is composed of the following molecular sieves in a dry basis mass ratio as follows: SAPO-11 molecular sieve and ZSM-22 molecular sieve are mixed at a mass ratio of (1.5~3):1; The total mass ratio of USY molecular sieve to composite molecular sieve carrier is 0.1~0.3:1; The relative crystallinity of both the SAPO-11 molecular sieve and the ZSM-22 molecular sieve is >90%. The silica-alumina ratio of the USY molecular sieve is 10~50.

2. The composite molecular sieve hydroisomerization catalyst according to claim 1, characterized in that, The USY molecular sieve has a thickness of 0.15~0.

25.

3. The composite molecular sieve hydroisomerization catalyst according to claim 1, characterized in that, The active metal includes platinum and / or palladium; The binder includes any one of boehmite, silica, and clay.

4. The composite molecular sieve hydroisomerization catalyst according to claim 3, characterized in that, The active metal is platinum; The binder is boehmite.

5. A method for preparing a composite molecular sieve hydroisomerization catalyst as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Molecular sieve composite and pretreatment: Dry SAPO-11 molecular sieve, ZSM-22 molecular sieve and USY molecular sieve were selected and mechanically mixed in proportion to obtain a mixture. The mixture was then subjected to hydrothermal treatment to obtain composite molecular sieve carrier powder. S2, Carrier molding: The obtained composite molecular sieve carrier powder is mixed with binder, extrusion aid and adhesive solvent, rolled, extruded into strips, dried and calcined at high temperature to obtain composite carrier; S3, Active Metal Loading: The catalyst precursor is obtained by uniformly loading the impregnation solution containing the active metal precursor onto the composite support using the equal volume impregnation method. After impregnation, room temperature aging, drying and low temperature calcination, the catalyst precursor is obtained. S4. Catalyst activation: Before use, the catalyst precursor is placed in a hydrogen atmosphere and reduced to obtain the composite molecular sieve hydroisomerization catalyst.

6. The method for preparing the composite molecular sieve hydroisomerization catalyst according to claim 5, characterized in that, In S1, the hydrothermal treatment conditions are: treatment at 400~550℃ and a water vapor partial pressure of 0.1~0.5 atm for 2~6 hours.

7. The method for preparing the composite molecular sieve hydroisomerization catalyst according to claim 5, characterized in that, In S2, the extrusion aid is guar gum powder; the adhesive solvent is a dilute nitric acid solution. The mass ratio of the composite molecular sieve carrier powder, extrusion aid, and adhesive solvent is 0.85:0.05:0.

145. The drying temperature is 100~120℃; the high-temperature calcination temperature is 500~600℃, and the duration is 3~6h.

8. The method for preparing the composite molecular sieve hydroisomerization catalyst according to claim 5, characterized in that, In S3, the drying temperature is 100~120℃ and the low-temperature calcination temperature is 300~450℃.

9. The method for preparing the composite molecular sieve hydroisomerization catalyst according to claim 5, characterized in that, In step S4, the reduction conditions are: reduction at 350~450℃ for 2~6 hours.

10. The application of a composite molecular sieve hydroisomerization catalyst as described in any one of claims 1 to 4 in the hydroisomerization reaction of bio-jet fuel, characterized in that, The reaction conditions are: reaction pressure 3.0~8.0 MPa, temperature 280~360℃, hydrogen-to-oil volume ratio (500~1000):1, and liquid hourly space velocity (LHSV) 0.5~2.0 h⁻¹. -1 ; The bio-jet fuel is a mixture mainly composed of C15-C20 straight-chain alkanes obtained by hydrodeoxygenation of bio-oils; The bio-oils include one or more of palm oil, waste cooking oil, and microalgae oil.

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