A saPO-31 molecular sieve based hydroisomerization catalyst, its preparation method and application

Abstract

The application relates to the technical field of heterogeneous catalytic materials, and particularly discloses a SAPO-31 molecular sieve-based hydroisomerization catalyst as well as a preparation method and application thereof. The preparation process of the SAPO-31 molecular sieve-based hydroisomerization catalyst is as follows: an aluminum source, a phosphorus source, a silicon source, a microporous structure directing agent and a mesoporous pore-forming agent are mixed to form a synthesis gel, dry gel powder is obtained after drying and grinding, gas phase assisted crystallization is carried out at 170-210 DEG C, and then SAPO-31 molecular sieve is obtained after washing, drying and calcination; and finally, the SAPO-31 molecular sieve is used as a carrier, and metal active components are loaded to obtain the catalyst. The SAPO-31 molecular sieve-based hydroisomerization catalyst can be used in the preparation of low-condensation-point biodiesel through the hydrogenation isomerization reaction of a biomass oil hydrogenation deoxygenation product, has high isomerization selectivity, and significantly improves the low-temperature fluidity and yield of the product.

Description

Technical Field

[0001] This application relates to the field of heterogeneous catalytic materials technology, and more specifically, to a SAPO-31 molecular sieve-based hydroisomer catalyst, its preparation method, and its application. Background Technology

[0002] With the accelerating global energy structure transformation and increasingly stringent environmental requirements, the development of renewable and low-pollution alternative energy sources has become a major issue that urgently needs to be addressed. Biomass oils (such as jatropha oil, palm oil, and waste cooking oil) are widely available and sustainably renewable raw materials for the production of biodiesel / jet fuel, and have become a research hotspot in the energy field due to their ability to effectively reduce dependence on fossil fuels and decrease carbon emissions.

[0003] In the process of converting biomass oils into high-quality biodiesel, hydroisomerization catalysts are crucial in determining product performance. Their core objectives are twofold: first, to convert long-chain n-alkanes in hydrodeoxygenation products into isoalkanes, significantly improving the product's low-temperature fluidity; and second, to maximally suppress cracking side reactions during the conversion process, ensuring product yield. Among numerous catalyst support materials, SAPO-31 molecular sieve is considered an ideal support due to its unique pore topology. However, in practical applications, traditional material preparation processes have revealed significant limitations in their adaptability.

[0004] SAPO-31 synthesized by the traditional hydrothermal method is typically a microporous, micron-sized crystal. For long-chain alkanes, this structure is like a "maze," with extremely high intracrystalline diffusion resistance leading to a significant reduction in the utilization rate of active sites. To overcome this diffusion limitation, the process is forced to operate at high temperatures, which directly changes the reaction pathway from ideal isomerization to uncontrolled cracking. This excessive breakage of long-chain alkanes results in a precipitous drop in liquid yield, with a large amount of raw material wasted as low-value byproducts.

[0005] To alleviate diffusion problems, the industry has attempted solutions such as introducing mesoporous templates or post-processing etching. However, the inventors have found that these methods often only address the symptoms, not the root cause. They either lead to the collapse of the molecular sieve framework and loss of acidity, or the generated mesopores are not interconnected. In some cases, the agglomeration caused by nano-sizing even creates new transport barriers. Current technologies have not yet found a balance between improving diffusion efficiency and maintaining framework stability. Therefore, developing a nano-SAPO-31 catalyst that can achieve precise positioning of active metals and possesses a highly efficient mesoporous transport network is imperative. Summary of the Invention

[0006] To improve the selectivity of the isomerization reaction of biomass oil hydrodeoxygenation products and enhance the low-temperature fluidity and yield of the products, this application provides a SAPO-31 molecular sieve-based hydroisomerization catalyst, its preparation method, and its application.

[0007] In a first aspect, this application provides a preparation process for a SAPO-31 molecular sieve-based hydroisomerization catalyst, employing the following technical solution: A process for preparing a SAPO-31 molecular sieve-based hydroisomerization catalyst includes the following steps: S1: Mix aluminum source, phosphorus source, silicon source and dual template agent to form a synthetic gel, wherein the dual template agent includes a microporous structure guiding agent and a mesoporous pore-forming agent; S2: The synthesized gel is dried and ground to obtain dry gel powder; S3: Place the dry adhesive powder on the upper part of a sealed reaction container, place a mixture containing water and organic amine at the bottom of the reaction container, perform gas-phase assisted crystallization at 170-210℃, and obtain SAPO-31 molecular sieve by washing, drying and calcining the crystallized product. S4: It is obtained by loading metal active components onto SAPO-31 molecular sieve.

[0008] Optionally, the molar ratio between the aluminum source, phosphorus source and silicon source is 1:1:(0.1-0.3).

[0009] By employing the above-mentioned technical solution, a multi-porous network structure with interconnected and ordered micropores and mesopores coexisting was constructed using a synergistic dual-template agent system of micropore directing agents and mesopore pore-forming agents. The gel was then dried and ground to form a dry gel powder, which was subsequently crystallized. This process significantly limited the physical space for subsequent crystal growth, effectively confining the environment and ensuring that the SAPO-31 molecular sieve product was a nanostructure. This effectively shortened the diffusion path of molecules within the micropores, resulting in a significantly improved apparent reaction rate compared to micron-sized SAPO-31 catalysts. Simultaneously, the unobstructed pore structure prevented local enrichment and retention of reactants and intermediates, reducing the formation of carbon precursors. The localized loading of active metals in the mesoporous region also prevented the "suffocation" of metal active sites due to pore blockage, thus enabling the catalyst to exhibit a longer single-pass operating life and higher stability.

[0010] The vapor-phase assisted crystallization process effectively prevents the over-hydration problem of the traditional hydrothermal method. The prepared SAPO-31 molecular sieve support takes into account both framework stability and pore integrity, effectively overcoming the problems of framework collapse and acid loss caused by the introduction of traditional mesoporous template agents or post-processing etching.

[0011] Optionally, the mesoporous pore-forming agent is selected from any one of carbon nanotubes, hexadecyltrimethylammonium bromide, and polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer.

[0012] Optionally, the amount of the mesoporous pore-forming agent is 1-5 wt% of the total mass of the aluminum source, phosphorus source, and silicon source.

[0013] Optionally, the microporous structure directing agent is di-n-propylamine.

[0014] Optionally, the amount of di-n-propylamine used is 0.8-1.5 times the total molar amount of the aluminum source, phosphorus source, and silicon source.

[0015] Optionally, the drying temperature in step S2 is 80-100℃, and the crystallization time in step S3 is 24-72h.

[0016] By adopting the above technical solution, the drying temperature and crystallization time are adapted to the gas-phase assisted process, ensuring sufficient crystal growth while avoiding particle agglomeration or mesopore blockage caused by over-crystallization. This solves the problems of uneven crystal size and disordered mesopore distribution caused by insufficient drying in traditional methods, ensuring that the product is 50-200nm nanocrystals and guaranteeing diffusion efficiency from the perspective of process parameters.

[0017] Optionally, the SAPO-31 molecular sieve has a particle size of 50-200 nm and has intracrystalline mesopores formed after the removal of the dual template agent. The pore size of the intracrystalline mesopores is 3-10 nm, and the proportion of the intracrystalline mesopores to the total pore volume is >40%.

[0018] Optionally, the metal active component includes Pt and Pd, and the loading is 0.3-1 wt% of the mass of the SAPO-31 molecular sieve support.

[0019] Optionally, the molar ratio of Pt to Pd is 1:(1-4), and the particle size is 2-5 nm.

[0020] Optionally, the Pt and Pd metal active components are loaded onto the support via an impregnation solution containing a competing adsorbent.

[0021] Secondly, this application provides a SAPO-31 molecular sieve-based hydroisomerization catalyst, which is prepared by the preparation process of the SAPO-31 molecular sieve-based hydroisomerization catalyst of this application.

[0022] Thirdly, this application provides the application of SAPO-31 molecular sieve-based hydroisomerization catalyst in the hydroisomerization reaction of biomass oil hydrodeoxygenation products to prepare low-pour-point biodiesel.

[0023] Optionally, the biomass oil includes jatropha oil, palm oil, and waste cooking oil.

[0024] Optionally, the conditions for the hydroisomerization reaction are: reaction temperature 280-320℃.

[0025] By adopting the above technical solution, a hydroisomerization catalyst prepared by loading metal active components onto SAPO-31 molecular sieve has a uniform distribution of acidic sites, providing structural support for inhibiting cracking reactions. The efficient diffusion effect allows long-chain alkane molecules in bio-oils to quickly approach the active sites distributed on the micropore openings and mesopore walls. Combined with suitable acidity, this promotes a deeper isomerization reaction. The isomerization reaction can be carried out at lower temperatures, generating more isoalkanes with multi-branched structures. This fundamentally avoids high-temperature-induced cracking side reactions, significantly improves the yield of liquid products, and allows the product's pour point to stably reach below -30℃, greatly expanding the application scenarios and fields of biodiesel.

[0026] In summary, this application has the following beneficial effects: 1. Because this application uses a gas-phase assisted dry gel conversion method combined with dual template agents to synergistically create pores, it successfully constructs a continuous and ordered mesoporous network inside nanoscale SAPO-31 crystals. Mesopores, as highways for material transport, allow long-chain alkane molecules to quickly approach the active sites distributed on the micropore openings and mesopore walls. The nanoscale SAPO-31 molecular sieve support further shortens the diffusion path of molecules in the micropores, enabling the intrinsic reaction rate to shift from diffusion control to reaction kinetic control. Compared with traditional micron-scale SAPO-31 supports, the diffusion resistance is smaller and the apparent reaction rate is significantly improved.

[0027] 2. This application uses SAPO-31 molecular sieve as a support to prepare a hydroisomerization catalyst. The significant improvement in diffusion resistance allows the isomerization reaction to proceed efficiently at lower temperatures (e.g., 260-280℃), effectively avoiding high-temperature-induced cracking side reactions. The yield of liquid products is significantly improved. The combination of efficient diffusion and suitable acidity promotes a deeper isomerization reaction, generating more isoalkanes with multi-branched structures. The produced biodiesel can stably reach a pour point below -30℃, which is significantly better than existing technology products (usually above -20℃), greatly expanding the application areas and seasons of biodiesel.

[0028] 3. This application adopts a gas-phase assisted dry gel conversion method, which uses very little water and has a high utilization rate of template agent. By controlling the amount of template agent, dry gel treatment conditions and crystallization parameters, it is possible to achieve precise control over the crystal size, mesopore size and distribution, and acidity of SAPO-31 molecular sieve carrier. The process is continuous and controllable, more green and environmentally friendly, and highly repeatable, effectively improving the problem of large fluctuations in product performance of traditional processes. Detailed Implementation

[0029] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0030] Preparation Example 1 SAPO-31 molecular sieve, its preparation method includes the following steps: S1: Dissolve 10.2g aluminum isopropoxide in 40mL of deionized water, add 11.5g 85% phosphoric acid under stirring to obtain aluminum phosphate gel, continue stirring for 1h and then add 2.1g tetraethyl orthosilicate, stir for 2h and then add 12g di-n-propylamine and 1g hexadecyltrimethylammonium bromide in sequence, stir for 6h to form a synthetic gel. S2: The synthesized gel was dried in an oven at 100°C for 24 hours, and then ground into dry gel powder. S3: Place the dry adhesive powder on the upper support of a 100mL hydrothermal reactor with a polytetrafluoroethylene liner, add 5mL of a mixture of water and ethylamine with a volume ratio of 4:1 to the bottom of the reactor, seal the reactor, and carry out gas-phase assisted crystallization at 190℃ for 36h. S4: After cooling, filtering, washing and drying the crystallized product, it was calcined in a muffle furnace at 600℃ for 5 hours to obtain a white powdery hierarchical porous nano-SAPO-31 molecular sieve. After SEM characterization, its particle size was 80-150nm, and it had a nanosphere structure. Obvious "wormhole-like" or "cavity-like" intracrystalline mesopores were visible inside the crystal, and the pore size of the intracrystalline mesopores was 3-6nm.

[0031] Preparation Example 2 SAPO-31 molecular sieve, its preparation method includes the following steps: S1: Dissolve 10.2g aluminum isopropoxide in 40mL of deionized water, add 11.5g 85% phosphoric acid under stirring to obtain aluminum phosphate gel, continue stirring for 1h and then add 2.1g tetraethyl orthosilicate, stir for 2h and then add 12g di-n-propylamine and 1g carbon nanotubes with a diameter of 5-20nm in sequence, stir for 6h to form a synthetic gel; S2: The synthesized gel was dried in an oven at 80°C for 24 hours and then ground into dry gel powder. S3: Place the dry adhesive powder on the upper support of a 100mL hydrothermal reactor with a polytetrafluoroethylene liner, add 5mL of a mixture of water and ethylamine with a volume ratio of 4:1 to the bottom of the reactor, seal the reactor, and carry out gas-phase assisted crystallization at 170℃ for 48h. S4: After cooling, filtering, washing and drying the crystallized product, it was calcined in a muffle furnace at 650℃ for 4 hours to obtain a white powdery hierarchical porous nano-SAPO-31 molecular sieve. After SEM characterization, its particle size was 120-200nm, and it had a nanosphere structure. Obvious "wormhole-like" or "cavity-like" intracrystalline mesopores were visible inside the crystal, and the pore size of the intracrystalline mesopores was 6-10nm.

[0032] Preparation Example 3 SAPO-31 molecular sieve, its preparation method includes the following steps: S1: Dissolve 10.2g of aluminum isopropoxide in 40mL of deionized water, add 11.5g of 85% phosphoric acid under stirring to obtain aluminum phosphate gel, continue stirring for 1h and then add 2.1g of tetraethyl orthosilicate, stir for 2h and then add 12g of di-n-propylamine and 1g of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer in sequence, stir for 6h to form a synthetic gel; S2: The synthesized gel was dried in an oven at 90°C for 24 hours and then ground into dry gel powder. S3: Place the dry adhesive powder on the upper support of a 100mL hydrothermal reactor with a polytetrafluoroethylene liner, add 5mL of a mixture of water and ethylamine with a volume ratio of 4:1 to the bottom of the reactor, seal the reactor, and perform gas-phase assisted crystallization at 210℃ for 24h. S4: After cooling, filtering, washing and drying the crystallized product, it was calcined in a muffle furnace at 550℃ for 6 hours to obtain a white powdery hierarchical porous nano-SAPO-31 molecular sieve. After SEM characterization, its particle size was 50-120nm, and it had a nanosphere structure. Obvious "wormhole-like" or "cavity-like" intracrystalline mesopores were visible inside the crystal, and the pore size of the intracrystalline mesopores was 5-8nm.

[0033] Preparation Example 4 SAPO-31 molecular sieve, its preparation method includes the following steps: S1: Dissolve 10.2g aluminum isopropoxide in 40mL of deionized water, add 11.5g 85% phosphoric acid while stirring to obtain aluminum phosphate gel, continue stirring for 1h and then add 2.1g tetraethyl orthosilicate, stir for 6h to form a synthetic gel; S2: The synthesized gel was placed in a 100mL hydrothermal reactor with a polytetrafluoroethylene liner, the reactor was sealed, and vapor-assisted crystallization was carried out at 190℃ for 36h. S4: After cooling, filtering, washing and drying the crystallized product, it was calcined in a muffle furnace at 600℃ for 5h to obtain white powdery micron-sized SAPO-31 molecular sieve. After SEM characterization, its particle size was 1-3μm and it had a micron rod structure.

[0034] Preparation Example 5 The preparation method of SAPO-31 molecular sieve differs from that of Preparation Example 1 only in that the template agent hexadecyltrimethylammonium bromide was not added in step S1. After SEM characterization, its particle size is 60-100 nm, and it is in the form of nanoparticles with virtually no mesopores.

[0035] Example 1 A SAPO-31 molecular sieve-based hydroisomerization catalyst, the preparation method of which includes the following steps: S1: Take 5g of SAPO-31 molecular sieve prepared in Example 1 as a carrier, and dehydrate it under vacuum at 150℃ for 3h to obtain pretreated SAPO-31 molecular sieve carrier. S2: Prepare a 20 mL aqueous solution containing 0.017 g H2PtCl6·6H2O, 0.038 g PdCl2 and 0.2 g citric acid. Add the pretreated SAPO-31 molecular sieve support to the aqueous solution, apply a vacuum of 20 kPa for 30 s, then impregnate at room temperature for 8 h, filter out the solid, dry at 100 °C for 12 h, and finally reduce at 400 °C under H2 atmosphere for 3 h to obtain a SAPO-31 molecular sieve-based hydroisomerization catalyst with a total metal loading of about 0.5 wt% and a Pt:Pd molar ratio of about 1:2.

[0036] Example 2 A SAPO-31 molecular sieve-based hydroisomerization catalyst, the preparation method of which includes the following steps: S1: Take 5g of SAPO-31 molecular sieve prepared in Example 1 as a carrier and dehydrate it in a vacuum at 150℃ for 4h to obtain a pretreated SAPO-31 molecular sieve carrier. S2: Prepare a 20 mL aqueous solution containing 0.011 g H2PtCl6·6H2O, 0.023 g PdCl2 and 0.12 g citric acid. Add the pretreated SAPO-31 molecular sieve support to the aqueous solution, apply a vacuum of 10 kPa for 30 s, then impregnate at room temperature for 12 h, filter out the solid, dry at 90 °C for 12 h, and finally reduce at 450 °C under H2 atmosphere for 2 h to obtain a SAPO-31 molecular sieve-based hydroisomerization catalyst with a total metal loading of about 0.3 wt% and a Pt:Pd molar ratio of about 1:2.

[0037] Example 3 A SAPO-31 molecular sieve-based hydroisomerization catalyst, the preparation method of which includes the following steps: S1: Take 5g of SAPO-31 molecular sieve prepared in Example 1 as a carrier, and dehydrate it under vacuum at 200℃ for 2h to obtain pretreated SAPO-31 molecular sieve carrier. S2: Prepare a 20 mL aqueous solution containing 0.034 g H2PtCl6·6H2O, 0.076 g PdCl2 and 0.4 g citric acid. Add the pretreated SAPO-31 molecular sieve support to the aqueous solution, apply a vacuum of 30 kPa for 30 s, then impregnate at room temperature for 4 h, filter out the solid, dry at 80 °C for 12 h, and finally reduce at 350 °C under H2 atmosphere for 4 h to obtain a SAPO-31 molecular sieve-based hydroisomerization catalyst with a total metal loading of about 1 wt% and a Pt:Pd molar ratio of about 1:2.

[0038] Example 4 A SAPO-31 molecular sieve-based hydroisomerization catalyst, differing from Example 1 only in that the SAPO-31 molecular sieve support in step S1 is prepared by Example 2.

[0039] Example 5 A SAPO-31 molecular sieve-based hydroisomerization catalyst, differing from Example 1 only in that the SAPO-31 molecular sieve support in step S1 is prepared by Preparation Example 3.

[0040] Comparative Example 1 A micron-sized SAPO-31 molecular sieve-based hydroisomerization catalyst differs from Example 1 in that step S1 uses the SAPO-31 molecular sieve prepared in Preparation Example 4 as a support, step S2 uses a conventional impregnation method, does not add the competing adsorbent citric acid, does not use vacuum assistance, and loads the same amount of Pt-Pd.

[0041] Comparative Example 2 A SAPO-31 molecular sieve-based hydroisomerization catalyst, differing from Example 1 only in that the SAPO-31 molecular sieve support in step S1 is prepared by Example 5.

[0042] Performance testing Test Example 1: Characterization of SAPO-31 Molecular Sieves The crystal morphology and size, BET specific surface area, total pore volume, mesopore volume and mesopore ratio of the SAPO-31 molecular sieves obtained in Examples 1-7 were characterized by scanning electron microscopy (SEM) and gas phase adsorption analysis, respectively. The characterization results are shown in Table 1.

[0043] Table 1

[0044] As can be seen from the performance test results in Table 1, the SAPO-31 molecular sieve prepared by the dual-template agent pore-forming method combined with the gas-phase assisted dry gel conversion method has a multi-level nanostructure with a particle size of 50-200 nm. It has intracrystalline mesopores formed after the removal of the dual-template agent, and the proportion of mesopores in the total pore volume is >40%. It has successfully realized the construction of a through-hole and ordered mesoporous network inside the nanoscale SAPO-31 crystal.

[0045] Test Example 2: Catalytic Performance Evaluation Raw materials: Simulated jatropha oil plus hydrodeoxygenated oil (a mixture of n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, etc. by mass); Reaction conditions: Fixed-bed reactor, catalyst loading 2 mL, pressure 4.0 MPa, volumetric space velocity 1.0 h⁻¹ -1The hydrogen-to-oil ratio was 800:1. The catalytic performance of the SAPO-31 molecular sieve-based hydroisomer catalysts obtained in Examples 1-7 and Comparative Examples 1-2 was tested at different temperatures, and the relevant test results are recorded in Table 2.

[0046] Table 2

[0047] As can be seen from the performance test results in Table 2, at the same temperature of 280℃, the hydroisomerization catalyst prepared by this application using SAPO-31 molecular sieve as a support through dual-template agent pore-forming combined with gas-phase assisted dry gel conversion significantly outperformed the conventional catalyst in Comparative Example 1 (63.8%) in the hydroisomerization reaction of biomass oil hydrodeoxygenation products, exhibiting excellent low-temperature activity. Even when the catalytic reaction temperature of the conventional catalyst in Comparative Example 1 was increased to 320℃ to achieve a similar conversion rate, its diesel yield (82.1%) was still significantly lower than that of the SAPO-31 molecular sieve-based hydroisomerization catalyst in this application at 280℃, and its gas yield (18.5%) was extremely high. This also proves the significant advantages of the hydroisomerization catalyst prepared by this application using nano-scale SAPO-31 molecular sieve as a support in suppressing cracking and improving the selectivity of isomerization reaction.

[0048] The SAPO-31 molecular sieve support used in Comparative Example 2 only has nanostructures and lacks abundant mesopores. Its yield and freezing point are inferior to those of Examples 1-5. It can be seen that the SAPO-31 molecular sieve with multi-level nanopores in this application is significantly better in terms of yield and freezing point when used as a catalyst support. This also shows that the introduction of mesoporous network plays a decisive role in performance improvement, and its effect is significantly better than simple crystal nano-sizing.

[0049] This also demonstrates that mesopores, acting as highways for mass transport, allow long-chain alkane molecules to quickly approach active sites distributed at the pore openings and mesopore walls. Nanoscale SAPO-31 molecular sieve supports further shorten the diffusion path of molecules within the micropores, enabling intrinsic reaction rates to shift from diffusion control to reaction kinetic control. Compared to traditional micron-sized SAPO-31 supports, diffusion resistance is significantly reduced, and apparent reaction rates are significantly improved.

[0050] Furthermore, the biodiesel produced by the hydroisomerization catalyst of this application has a stable pour point below -30℃, which is significantly better than that produced by traditional catalysts, fully meeting the requirements for low-temperature fluidity of diesel in cold regions and significantly enhancing its application value. This also demonstrates that the significant improvement in diffusion resistance not only enables the isomerization reaction to proceed efficiently at lower temperatures (260-280℃), effectively avoiding high-temperature-induced cracking side reactions and significantly increasing liquid product yield, but also, the combination of efficient diffusion and suitable acidity promotes a deeper isomerization reaction, generating more isoalkanes with multi-branched structures, enabling the produced biodiesel to have a stable pour point below -30℃, greatly expanding the application areas and seasons of biodiesel.

[0051] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A preparation process for a SAPO-31 molecular sieve-based hydroisomerization catalyst, characterized in that, Includes the following steps: S1: Mix aluminum source, phosphorus source, silicon source and dual template agent to form a synthetic gel, wherein the dual template agent includes a microporous structure guiding agent and a mesoporous pore-forming agent; S2: The synthesized gel is dried and ground to obtain dry gel powder; S3: Place the dry adhesive powder on the upper part of a sealed reaction container, place a mixture containing water and organic amine at the bottom of the reaction container, perform gas-phase assisted crystallization at 170-210℃, and obtain SAPO-31 molecular sieve by washing, drying and calcining the crystallized product. S4: It is obtained by loading metal active components onto SAPO-31 molecular sieve.

2. The preparation process of the SAPO-31 molecular sieve-based hydroisomerization catalyst according to claim 1, characterized in that, The mesoporous pore-forming agent is selected from any one of carbon nanotubes, hexadecyltrimethylammonium bromide, and polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer.

3. The preparation process of the SAPO-31 molecular sieve-based hydroisomerization catalyst according to claim 1, characterized in that, The microporous structure directing agent is di-n-propylamine.

4. The preparation process of the SAPO-31 molecular sieve-based hydroisomerization catalyst according to claim 1, characterized in that, The drying temperature in step S2 is 80-100℃, and the crystallization time in step S3 is 24-72h.

5. The preparation process of the SAPO-31 molecular sieve-based hydroisomerization catalyst according to claim 1, characterized in that, The SAPO-31 molecular sieve has a particle size of 50-200 nm and has intracrystalline mesopores formed after the removal of the dual template agent. The pore size of the intracrystalline mesopores is 3-10 nm, and the proportion of intracrystalline mesopores to the total pore volume is >40%.

6. The preparation process of the SAPO-31 molecular sieve-based hydroisomerization catalyst according to claim 1, characterized in that, The active metal components include Pt and Pd, and the loading amount is 0.3-1 wt% of the mass of the SAPO-31 molecular sieve support.

7. A SAPO-31 molecular sieve-based hydroisomerization catalyst, characterized in that, It is prepared by the preparation process of the SAPO-31 molecular sieve-based hydroisomer catalyst according to any one of claims 1-6.

8. The application of the hydroisomerization catalyst according to claim 7 in the preparation of low-pour-point biodiesel by hydroisomerization reaction of biomass oil hydrodeoxygenation products.

9. The application according to claim 8, characterized in that, The conditions for the hydroisomerization reaction are: reaction temperature 260-320℃.

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