Preparation method of biomass liquid fuel for vehicles

Abstract

The invention relates to the technical field of liquid fuel, and discloses a preparation method of automotive biomass liquid fuel, which comprises the following steps: (1) mixing lignocellulose with microalgae to obtain a mixed raw material; (2) preparing a bifunctional catalyst, wherein the catalyst comprises a hydrodeoxygenation active site and an isomerization active site; (3) putting the mixed raw material and a bifunctional catalyst into a hydrothermal reaction system, and carrying out catalytic reaction in the presence of CO2 to generate a liquid hydrocarbon product; and (4) separating and purifying the liquid hydrocarbon product to obtain the biomass liquid fuel for vehicles. And (5) regenerating and recycling the catalyst. According to the method, a gradient oxidation-step phosphorization regeneration process is adopted, irreversible damage of traditional roasting to active sites is broken through, through cooperation of gradient temperature control and lattice oxygen, the carbon deposition removal rate is increased to 98%, the cycle life of the catalyst is prolonged by three times or above, and the regeneration cost is directly reduced by 40%.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid fuels, and particularly to a preparation method of a vehicle - used biomass liquid fuel. Background Art

[0002] The preparation of vehicle - used biomass liquid fuel mainly relies on renewable raw materials such as lignocellulose and microalgae oil, and is converted into hydrocarbon fuels through processes such as hydrothermal liquefaction and catalytic hydrodeoxygenation. In the prior art, raw material pretreatment mostly uses steam explosion or acid hydrolysis, and the catalyst system mainly consists of transition metal sulfides (such as NiMoS) or noble metals (such as Pt / Al2O3), and the reaction path focuses on a single deoxygenation or condensation route. Such methods have been partially applied to replace gasoline and diesel components, meeting the needs of the low - carbon transformation of transportation energy.

[0003] In traditional processes, catalyst regeneration relies on high - temperature oxidation, leading to metal sintering and irreversible loss of active sites; the fixed raw material ratio exacerbates the phase separation of lignocellulose and microalgae oil, limiting the carbon conversion efficiency; the deoxygenation path depends on high - pressure hydrogen, and the out - of - control side - reaction path causes tar accumulation; the preparation of multi - metal catalysts uses the co - impregnation method, and the mutual dissolution of active components masks the interfacial synergistic effect; uneven mass transfer in the hydrothermal reaction causes local supersaturation, resulting in insufficient product branching degree; the mismatch between the pretreatment intensity and raw material characteristics causes pore structure collapse, inhibiting oil penetration. The above defects jointly lead to systematic bottlenecks in the prior art, such as high energy consumption, large fluctuations in product quality, and short catalyst life, making it difficult to meet the stability and economic requirements of industrial production of vehicle fuels. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a preparation method of a vehicle - used biomass liquid fuel, which solves the problems in the prior art that high - temperature sintering during catalyst regeneration causes irreversible attenuation of activity, fixed raw material ratio exacerbates phase separation, resulting in low carbon conversion rate, deoxygenation path relying on high - pressure hydrogen triggering out - of - control side - reactions, multi - metal co - impregnation process masking the interfacial synergistic effect of activity, uneven mass transfer inhibiting the selective and directional generation of branched alkanes, and the mismatch between pretreatment intensity and raw material heterogeneity causing pore collapse.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A preparation method of a vehicle - used biomass liquid fuel, comprising the following steps: (1) Mix lignocellulose and microalgae to obtain a mixed raw material; After lignocellulose and microalgae are mixed in a specific ratio, the oil component (triglyceride) in microalgae can serve as a hydrogen donor, providing reducing power for the sugar intermediates derived from lignocellulose in subsequent reactions to achieve in-situ hydrodeoxygenation. The phospholipid component contained in the microalgae cell wall has a natural emulsifying effect, which can promote the homogeneous dispersion of lignocellulose and oil, and avoid the phase separation problem caused by the polarity difference of raw materials in traditional processes. After lignocellulose is pretreated by steam explosion, the fiber structure is loosened, and part of the hemicellulose remains as a soluble sugar source. Microalgae maintain the activity of phospholipids through low-temperature drying. The two work together to provide a mixed raw material system with high reaction activity for subsequent catalytic reactions.

[0006] (2) Prepare a bifunctional catalyst, which contains hydrodeoxygenation active sites and isomerization active sites; The bifunctional catalyst forms an atomic-level heterojunction interface by stepwise loading Ni2P and MoP active components. The Ni2P active sites have strong hydrodeoxygenation (HDO) ability, which can selectively break the C-O bonds in biomass-derived oxygenates (fatty acids, sugar dehydration products) to generate straight-chain alkanes; the MoP active sites convert straight-chain alkanes into branched-chain structures through skeletal isomerization, significantly improving the octane number of the product. The spatial proximity and electronic interaction of the two active sites enable the deoxygenation and isomerization reactions to be completed synchronously in a single reactor, breaking through the limitations of traditional multi-step processes.

[0007] (3) Place the mixed raw materials and the bifunctional catalyst in a hydrothermal reaction system and carry out a catalytic reaction in the presence of CO2 to generate liquid hydrocarbon products; In the hydrothermal reaction environment in the presence of CO2, the weak acidic property of CO2 promotes the hydrolysis of microalgae oil into free fatty acids, and at the same time inhibits the condensation and coking of lignin during the pyrolysis of lignocellulose. CO2 molecules can also serve as a mild oxidation medium to generate carbonate compounds with reaction intermediates (glycerol), further reducing the reaction energy barrier. The bifunctional catalyst directionally regulates the reaction path in this environment: the Ni2P sites drive the hydrodeoxygenation of fatty acids and sugar derivatives to generate straight-chain alkanes, and the MoP sites immediately initiate branched-chain isomerization, ultimately directly obtaining liquid hydrocarbon products mainly composed of C10-C18 branched-chain alkanes. This process does not require external hydrogen supply, and the reaction temperature is about 100 °C lower than that of traditional hydrogenation processes.

[0008] (4) Separate and purify the liquid hydrocarbon products to obtain vehicle-use biomass liquid fuels; After the liquid hydrocarbon product is centrifuged to remove solid residues, the light components (water, low-boiling impurities) and the target fraction are precisely separated by distillation cutting. Atmospheric distillation removes the light components to avoid product cracking caused by subsequent high-temperature distillation, while vacuum distillation efficiently extracts the main fraction of C10-C18 branched alkanes at low temperature. An optional hydrorefining step selectively saturates trace unsaturated hydrocarbons to further improve the oxidation stability of the fuel. However, this step is not essential because deep deoxygenation has been achieved in the main reaction.

[0009] (5) Regenerate and recycle the catalyst.

[0010] After the deactivated catalyst is calcined at high temperature to remove surface carbon deposits, it is secondarily phosphated in a reducing atmosphere to repair the surface active sites. The phosphide structures of Ni2P and MoP are reformed during the regeneration process, and the heterojunction interface is retained due to the characteristics of stepwise phosphating preparation.

[0011] Preferably, the mass ratio of the lignocellulose to the microalgae in step (1) is 3:1 ± 0.2; Lignocellulose is rich in cellulose and hemicellulose (accounting for 60-80%), but the hydrogen element in its carbon skeleton is relatively scarce; while the microalgae (high-lipid Chlorella) have an oil content as high as 30-50% and are rich in long-chain fatty acids (C16-C18), which can be used as hydrogen donors. At this ratio, the hydrogen atoms provided by the microalgae (fatty acids generated by oil decomposition) can fully meet the reducing power required for the deoxygenation of the hydrolysis products (glucose, xylose) of lignocellulose, avoiding incomplete reactions or the formation of by-products (coke) caused by insufficient hydrogen in traditional processes. At the same time, this ratio ensures that the total oxygen content of the mixed raw materials is controlled within the range of 15-20%, providing a reasonable reaction load for subsequent catalytic deoxygenation.

[0012] The phospholipid component (phosphatidylcholine) in the microalgae cell wall plays the role of a natural emulsifier in this step. Its hydrophilic end binds to the hydroxyl groups on the surface of lignocellulose, and its hydrophobic end wraps the oil molecules, forming a stable oil-water-solid three-phase dispersion system. When the mass ratio deviates from 3:1 ± 0.2, if the proportion of microalgae is too high (>1.2), the excessive phospholipids will increase the viscosity of the system and hinder mass transfer; if the proportion of lignocellulose is too high (>3.2), the hydrophobicity of cellulose will increase, leading to phase separation.

[0013] At a ratio of 3:1 ± 0.2, the molar ratio of triglycerides (each molecule contains 3 fatty acid chains) in microalgae oil to the hydrolyzed sugars of lignocellulose (each molecule contains 5-6 hydroxyl groups) is close to 1:2. This ratio enables the fatty acids generated by oil decomposition to precisely match the number of hydrogen atoms required for the deoxygenation of sugars, achieving efficient in-situ hydrogen transfer. Specifically, about 12 hydrogen atoms are required for each molecule of sugar (glucose) to be deoxygenated to form hydrocarbons, while 3 molecules of fatty acids (stearic acid) can provide 54 hydrogen atoms, and the redundant hydrogen atoms are used to inhibit the coking side reaction.

[0014] Preferably, the lignocellulose in step (1) is pretreated by steam explosion under the conditions of: steam pressure 0.8 - 1.2 MPa, temperature 185 - 205 °C, and time 5 - 8 minutes.

[0015] Under the action of high-temperature and high-pressure steam, hemicellulose in lignocellulose undergoes partial hydrolysis to generate oligosaccharides, and at the same time, steam penetrates into the fiber pores to form a local high-pressure area. When the pressure is released instantaneously, the dense structure of cellulose undergoes physical explosion due to the internal stress difference, forming a loose and porous structure, and the specific surface area is increased to 10 - 15 m 2 / g, providing a channel for the contact and mass transfer of the catalyst in the subsequent hydrothermal reaction.

[0016] Setting of the steam explosion time (5 - 8 minutes). When the time is too short (< 5 minutes), the hydrolysis of hemicellulose is insufficient and the porosity is insufficient; when the time is too long (> 8 minutes), it will lead to excessive depolymerization of cellulose to generate glucose monomers, which are prone to dehydration to form furan by-products in the subsequent high-temperature reaction. By dynamically regulating the explosion time in the present invention, hemicellulose is partially degraded into oligosaccharides (degree of polymerization 2 - 5), which not only retains its reaction activity but also avoids the product inhibition effect caused by excessive decomposition.

[0017] Preferably, the microalgae in step (1) are Chlorella with an oil content ≥ 30 wt%, and are vacuum dried at 40 - 50 °C until the water content ≤ 5%.

[0018] Chlorella with a high oil content (oil content 30 - 50%) can provide abundant triglycerides, and its fatty acid chains (C16:0, C18:1) are both hydrogen donors and precursors of branched-chain alkanes in the subsequent catalytic reaction. Compared with low-oil microalgae species (Spirulina, oil < 10%), the carbon-hydrogen ratio (C / H ≈ 6 - 7) of high-oil microalgae is closer to the ideal ratio of the target fuel (C / H ≈ 5 - 6), thereby reducing hydrogen consumption and by-product generation during the reaction process.

[0019] Strict control of the vacuum drying conditions (40 - 50 °C) aims to retain the phospholipid component (phosphatidylethanolamine) in the microalgae cell wall. Phospholipid molecules have an amphiphilic structure, with their hydrophilic ends binding to the hydroxyl groups of lignocellulose and their hydrophobic ends wrapping the oil molecules, forming a stable "oil-cellulose" emulsion system. If the drying temperature exceeds 50 °C, the phospholipids will be oxidized or denatured, losing their emulsifying function and resulting in phase separation of the mixed raw materials; while when it is lower than 40 °C, the drying efficiency is significantly reduced and the water content is difficult to meet the standard. Through low-temperature drying in a vacuum environment (pressure -0.08 - 0.1 MPa), the water can be quickly removed while maintaining the cell wall integrity, maximizing the synergistic effect of oil and phospholipids.

[0020] The significance of controlling the water content to ≤ 5% lies in: Suppressing hydrolysis side reactions: Excessive moisture is prone to cause excessive hydrolysis of oil and fat to produce free fatty acids (FFA) during subsequent high-temperature reactions, and FFA is prone to condense into tar-like substances without catalyst regulation. Low moisture content limits the hydrolysis of oil and fat within a controllable range, ensuring that the main hydrolysis product is the partially hydrolyzed product (monoacylglycerol) of triglyceride required for the reaction.

[0021] Optimizing the reaction system pressure: The vaporization of water at high temperature and high pressure will significantly increase the pressure inside the reactor, while low moisture content can reduce the generation of unnecessary steam, stabilize the total pressure within the target range of 15 - 20 MPa, and reduce equipment load and energy consumption.

[0022] Maintaining phospholipid activity: Excessive residual moisture will weaken the interfacial activity of phospholipids, while a moisture content of ≤5% can maintain the ability of phospholipid molecules to be oriented in the mixed raw materials, ensuring the stability of the emulsion system in subsequent reactions.

[0023] Preferably, the bifunctional catalyst described in step (2) is Ni2P-MoP heterojunction supported on a γ-Al2O3 carrier and prepared by a stepwise impregnation-phosphidation method.

[0024] Ni2P serves as the hydrodeoxygenation active center. Its electron-rich property (the hybridization of the d electrons of Ni and the p orbitals of P) can preferentially adsorb the O atoms in oxygen-containing compounds (fatty acids, dehydration products of sugars), generate straight-chain alkanes by breaking the C-O bond and supplementing H atoms. The electron-deficient property of MoP (the d-orbital vacancy of Mo) can induce the isomerization of the alkane skeleton and form a branched structure through a hydrocracking-recombination mechanism. The heterojunction interface of the two active phases forms a continuous electron transfer channel through lattice matching (partial coherency between the hexagonal crystal system of Ni2P and the cubic crystal system of MoP), enabling the deoxygenation product to be captured and isomerized by adjacent MoP sites without diffusion, significantly shortening the reaction path.

[0025] The innovation of the stepwise impregnation-phosphidation method lies in the controllable construction of active sites. The traditional co-impregnation method will cause the Ni and Mo precursors to compete for adsorption on the surface of the carrier, forming disordered alloys or independent particles. The stepwise process ensures the formation of an atomic-level contact heterojunction interface by first fixing the Ni2P crystal nuclei and then epitaxially growing MoP. Specifically, the Ni precursor is first uniformly dispersed on the surface of γ-Al2O3 and forms Ni2P nanoparticles with uniform size (5 - 8 nm) after phosphidation; subsequently, the loaded Mo precursor preferentially nucleates at the edge of the Ni2P particles during phosphidation, forming a "core-shell" structure with MoP wrapping Ni2P (verified by STEM-EDS mapping). This directional growth mode not only avoids the spatial isolation of active sites but also modulates the electronic state of MoP through the interfacial strain effect, enhancing its isomerization activity.

[0026] The selection of the γ-Al2O3 support combines physical and chemical functions: its high specific surface area (200 - 250 m 2 / g) provides sufficient active site loading sites, while the surface acidic sites (Lewis acid centers) can promote the dehydration reaction of lignocellulose-derived sugars to generate furan intermediates (5-hydroxymethylfurfural), providing key reactants for subsequent hydrodeoxygenation. In addition, the thermal stability of the support (tolerating ≥500 °C) ensures the structural integrity of the catalyst in a high-temperature hydrothermal environment.

[0027] Preferably, the stepwise impregnation-phosphating method includes: A. Impregnate the Ni(NO3)2 solution onto γ-Al2O3, and generate Ni2P / Al2O3 through calcination and phosphating; B. Impregnate the MoO3 solution onto Ni2P / Al2O3, and perform secondary phosphating to generate Ni2P-MoP / γ-Al2O3.

[0028] Step a: Oriented construction of Ni2P / Al2O3: Impregnate the Ni(NO3)2 solution (0.5 - 1.5 mol / L) onto the pretreated γ-Al2O3 support, and through capillary action, make Ni 2+ ions be uniformly adsorbed on the surface and within the pores of the support. The impregnated sample is dried at 110 - 130 °C for 4 - 6 hours to remove moisture and immobilize the precursor, and then calcined in an air atmosphere at 450 - 550 °C for 2 - 4 hours to decompose Ni(NO3)2 into NiO, and form Ni-O-Al bonds with the hydroxyl groups on the support surface, achieving strong anchoring of Ni species. The key to this step is to control the dispersion of NiO (particle size 3 - 5 nm), and too high a concentration or calcination temperature will lead to particle agglomeration and reduce the density of active sites.

[0029] Subsequent phosphating is carried out in a H2 / PH3 mixed gas (volume ratio 10:1), heated to 380 - 420 °C at a rate of 3 - 5 °C / min, and maintained for 1.5 - 2.5 hours. PH3 decomposes into P atoms at high temperature and undergoes a topological reaction with NiO to generate Ni2P crystals (hexagonal crystal system, space group P-62m). At the same time, H2 reduces the residual NiO to metallic Ni, forming a Ni2P / Ni biphasic structure. In this stage, through the precise matching of the phosphating temperature and time, it is ensured that Ni species are completely phosphated into Ni2P, while avoiding over-phosphating to generate the inactive NiP2 phase. The Ni2P grain size is controlled within 5 - 8 nm, and its high dispersion provides nucleation sites for subsequent MoP loading.

[0030] Step b: Interface regulation of the MoP / Ni2P heterojunction: Immerse the ammonium oxalate solution of MoO3 (0.3 - 0.8 mol / L) on the surface of Ni2P / Al2O3. The oxalate ions coordinate with the P atoms on the surface of Ni2P, inducing the preferential adsorption of the MoO3 precursor on the edges of Ni2P particles. After drying at 110 - 130 °C for 4 - 6 hours and calcining at 450 - 550 °C for 2 - 4 hours, MoO3 is converted into MoO X species, and form Mo - O - P interfacial bonds with the surface of Ni2P. Secondary phosphidation is carried out by heating to 430 - 470 °C at a rate of 4 - 6 °C / min in a H2 / PH3 mixed gas for 2.5 - 3.5 hours. MoO X is gradually phosphidated to MoP (cubic crystal system, space group Fm - 3m) under the action of PH3. At the same time, Ni2P undergoes partial surface reconstruction due to high temperature, forming a coherent interface of Ni2P - MoP.

[0031] Interface formation mechanism: MoP epitaxially grows on the edges of Ni2P particles. Due to lattice mismatch (the lattice constant of Ni2P is a = 5.69 Å, and that of MoP is 4.82 Å), compressive strain is generated, resulting in the upward shift of the d - band center of MoP and enhancing its catalytic activity for alkane isomerization. The simultaneously formed Ni - P - Mo interfacial atomic channels enable the directional migration of electrons from Ni2P to MoP, optimizing the energy barrier matching of deoxygenation and isomerization reactions.

[0032] The step - by - step phosphidation method forces MoP to cover Ni2P in a hetero - epitaxial mode through the "spatial confinement adsorption - interface - induced growth" mechanism, avoiding the formation of Ni - Mo alloy phases in the traditional co - impregnation method and ensuring the independence and synergy of the dual active sites.

[0033] Preferably, the hydrothermal reaction conditions in step (3) are: temperature 300 - 350 °C, pressure 15 - 20 MPa, CO2 partial pressure 2.0 - 3.0 MPa, and reaction time 25 - 35 minutes.

[0034] In the range of 300 - 350 °C, water is in a sub - critical state (density 0.1 - 0.3 g / cm 3 ), and its dielectric constant is significantly reduced, which can dissolve non - polar organic substances (microalgae oil) while maintaining the stability of polar components (sugars). This temperature range precisely matches the activity window of the bifunctional catalyst (Ni2P - MoP / γ - Al2O3): Ni2P exhibits high hydrodeoxygenation activity above 300 °C, while the isomerization function of MoP is significantly enhanced after 320 °C. The two work together to avoid the problem of active site mismatch caused by temperature gradients in traditional processes.

[0035] The total pressure design of 15 - 20 MPa is achieved through the synergistic pressurization of CO2 and N2. The CO2 partial pressure of 2.0 - 3.0 MPa brings it to the supercritical state (critical point: 31.1 °C, 7.38 MPa). At this time, CO2 has both the high diffusivity of a gas and the strong dissolving ability of a liquid, and can penetrate into the pores of lignocellulose, promoting the homogeneous mixing of oil and sugar. Meanwhile, the weak acidity of supercritical CO2 (pH ≈ 3 - 4) can selectively hydrolyze triglycerides in microalgae oil to produce free fatty acids (FFA), while avoiding the excessive degradation of hemicellulose in lignocellulose. N2, as an inert gas, supplements the pressure to the target range, and its low reactivity ensures that the reaction system focuses on the target path and reduces the occurrence of oxidation side reactions.

[0036] The correlation between reaction time and path orientation: The reaction time design of 25 - 35 minutes is based on the dual optimization of reaction kinetics and thermodynamic equilibrium. In the initial heating stage (8 - 12 °C / min), the hydrolysis of oil and the dehydration of sugar are quickly completed, generating FFA and furan intermediates; within the first 15 minutes of the constant temperature stage, the Ni2P sites dominate the hydrodeoxygenation reaction, converting FFA into straight-chain alkanes, while the sugar derivatives condense into long-chain hydrocarbons; in the subsequent 10 - 20 minutes, the MoP sites drive the isomerization of straight-chain alkanes to form branched structures. A reaction time exceeding 35 minutes will lead to the excessive cracking of branched alkanes to produce low-carbon hydrocarbons (C5 - C9), while a reaction time shorter than 25 minutes will result in insufficient octane number of the product due to incomplete isomerization. Through the precise control of the time window, the dynamic balance of deoxygenation and isomerization reactions is ensured, and the main product of C10 - C18 branched alkanes is directly obtained.

[0037] The CO2-mediated reaction path: Weak acid catalysis: Carbonic acid (H2CO3) formed by CO2 and water provides a mild acidic environment, promoting the hydrolysis of triglycerides to FFA, while inhibiting the condensation and coking of lignin; In-situ hydrogen source regulation: CO2 reacts with the intermediate glycerol to form glycerol carbonate, which releases CO2 and supplies active H under the catalysis of Ni2P + , reducing the dependence on external hydrogen sources; Solvent effect: The high diffusivity of supercritical CO2 accelerates the mass transfer of reactants to the active sites of the catalyst, increasing the reaction rate by 40 - 50%; Oxygen atom capture: CO2 combines with the O atom generated by deoxygenation to form CO3 2- , achieving the directional removal of oxygen elements through the recovery of CO2 by pressure relief and reducing the formation of oxygen-containing by-products (ketones, ethers).

[0038] Preferably, in step (3), the catalytic reaction simultaneously completes the hydrodeoxygenation of oil and the condensation and isomerization of sugar, directly generating branched alkanes.

[0039] Synergistic pathway of hydrodeoxygenation of oils and sugars condensation isomerization: In a bifunctional catalyst (Ni2P-MoP / γ-Al2O3) and CO2-mediated hydrothermal reaction environment, the conversion pathways of oils (triglycerides) and sugars (cellulose / hemicellulose derivatives) are synchronized in time and space for the first time. The hydrodeoxygenation (HDO) of oils is dominated by the Ni2P active site: triglycerides are hydrolyzed into free fatty acids (FFAs) in the weakly acidic environment of supercritical CO2, and then the carboxylic acid groups (-COOH) of FFAs are adsorbed on the electron-rich Ni sites of Ni2P, and linear alkanes (C16-C18) are generated by breaking the C-O bond and hydrogenation. At the same time, the sugars condensation isomerization is completed through the following pathway: the monosaccharides (glucose) derived from lignocellulose are dehydrated into furan compounds (5-hydroxymethylfurfural, HMF) under the catalysis of the acidic sites of the γ-Al2O3 support, and HMF is further adsorbed on the MoP site, and the carbon chain is extended to C10-C15 through aldol condensation reaction, and skeletal isomerization occurs under the drive of the electron-deficient Mo sites of MoP to form branched alkanes.

[0040] Through the interfacial electron transfer of the Ni2P-MoP heterojunction, the linear alkanes generated by deoxygenation are directly coupled with the long-chain intermediates derived from sugars on the catalyst surface to form a branched structure. This process does not require the separation and reprocessing of intermediate products. Dynamic synergistic mechanism of bifunctional catalyst: The heterojunction interface of Ni2P and MoP is the core of the synchronous reaction. The Ni2P active site preferentially adsorbs oxygen-containing compounds (FFA, HMF) through the d-electron enrichment characteristic to complete the deoxygenation or dehydration reaction; the deoxygenation product (linear alkane) then diffuses to the adjacent MoP active site through the interface, and its electron-deficient characteristic induces the cleavage and recombination of C-C bonds to achieve chain length adjustment and branching. This "deoxygenation-isomerization" tandem pathway is significantly accelerated due to the atomic-level proximity of the active sites (interface distance < 1nm).

[0041] Role of the carrier γ-Al2O3: The Brønsted acid sites (-OH groups) on the carrier surface not only promote the dehydration of sugars to generate HMF, but also stabilize the reaction intermediates through hydrogen bonding to prevent their excessive polymerization to form coke. The mesoporous structure of the carrier (pore diameter 5-10nm) provides a channel for the diffusion of long-chain alkanes to avoid catalyst deactivation caused by pore blockage.

[0042] Multiple regulatory roles of CO2: Reaction medium regulation: The high diffusivity of supercritical CO2 (scCO2) (diffusion coefficient is 10 2 times that of liquid water) promotes the homogeneous mixing of oils and sugar derivatives, enabling them to co-adsorb on the catalyst surface and providing a physical basis for the synergistic reaction.

[0043] Hydrogen transfer promotion: CO2 combines with the reaction by-product glycerol to form glycerol carbonate, which decarboxylates under the catalysis of Ni2P to release active H + , providing a proton source for sugar condensation and avoiding the high-pressure input of external hydrogen.

[0044] Oxygen removal path optimization: The O atoms generated by deoxygenation combine with CO2 to form CO3 2- ions, and the directional removal of oxygen elements is achieved through the pressure relief of CO2 after the reaction.

[0045] Preferably, the separation and purification described in step (4) includes: A. Centrifugally separating the catalyst from the liquid product; B. Removing the light components at 80 - 150°C by atmospheric distillation; C. Collecting the fraction at 150 - 350°C by vacuum distillation as the target fuel.

[0046] Efficient mass transfer and catalyst protection in centrifugal separation: The liquid hydrocarbon product is first rapidly separated from the catalyst by centrifugal separation (3000 - 5000 rpm, 10 - 15 minutes). The dynamic gradient design of the centrifugal force (linearly increasing to the target speed) prevents the exfoliation of surface active sites of the catalyst particles (particle size 5 - 8 nm) due to shear force during sedimentation. At the same time, the solid-liquid interfacial tension is optimized by adjusting the inclination angle of the centrifuge tube (45 - 60°), so that the recovery rate of the liquid product is ≥98%. Compared with the traditional filtration or static stratification process, the centrifugal separation time is shortened by 80%, and the risk of secondary pollution caused by filter membrane blockage or solvent cleaning is avoided. The key innovation of this step lies in the "gentle separation - activity retention" mechanism: the centrifugal conditions are precisely matched with the Stokes sedimentation rate of the catalyst particles, ensuring efficient separation while maintaining the structural integrity of the catalyst, and providing a highly active precursor for the subsequent regeneration step.

[0047] Targeted removal of light components in atmospheric distillation: The separated liquid product is subjected to atmospheric distillation (80 - 150°C) to remove light components (water, unreacted fatty acids, short-chain hydrocarbons). The upper limit of the distillation temperature (150°C) is strictly controlled below the initial boiling point of the target product (C10 - C18 branched alkanes) to avoid the co-distillation loss of the main product. The targeted removal of light components relies on their boiling point distribution characteristics: the boiling point differences among water (100°C), C5 - C9 alkanes (<150°C), and residual fatty acids (150 - 180°C). Through the cascade condensation of the fractionating column (theoretical plate number ≥3), the water content in the light components is reduced to ≤0.5 wt%, and the residual short-chain hydrocarbons are ≤1 wt%, providing a high-purity raw material for the subsequent vacuum distillation. By narrow boiling range cutting (80 - 150°C), the excessive heat load of traditional wide boiling range distillation is avoided, and the thermal cracking of the main product is reduced.

[0048] Low-temperature and High-selectivity Separation by Vacuum Distillation: The final purification of the target fuel is completed by vacuum distillation (absolute pressure 10 - 30 kPa, 150 - 350 °C). The vacuum environment reduces the boiling points of C10 - C18 branched alkanes by 80 - 120 °C, enabling efficient fractionation in the low-temperature range of 150 - 350 °C. This temperature range precisely matches the carbon chain length and degree of branching of the main products: fractions of C10 - C12 branched alkanes (boiling point 150 - 250 °C) and C13 - C18 branched alkanes (boiling point 250 - 350 °C) are separately collected by fractional condensation, with the octane number (RON) difference controlled within 2 units to ensure uniform fuel performance. The innovation lies in the "pressure-boiling point coupling regulation" mechanism: by dynamically adjusting the system pressure (10 - 30 kPa) and heating rate (2 - 5 °C / min), narrow fraction cutting of products with a wide carbon chain distribution is achieved.

[0049] Preferably, the catalyst regeneration in step (5) includes: A. Calcining in an air atmosphere at 550 - 650 °C to remove carbon deposits; B. Second phosphating in a H2 / PH3 mixed gas to repair active sites.

[0050] Orientation Oxidation Mechanism of High-temperature Calcination to Remove Carbon Deposits: The deactivated catalyst is calcined in an air atmosphere at 550 - 650 °C for 2 - 3 hours, and efficient removal of carbon deposits is achieved through controllable oxidation. The carbon deposits mainly come from the polymerization products of oxygen-containing intermediates (phenols, ketones) that are not completely deoxygenated in the reaction, and their forms include amorphous carbon (oxidizable at <500 °C) and graphitized carbon (oxidized at >600 °C). In this step, by ramping up the temperature in stages (initially rising to 400 °C at 5 °C / min and holding for 1 hour to remove amorphous carbon; then rising to the target temperature at 3 °C / min), gradient oxidation of carbon deposits is achieved: amorphous carbon is preferentially oxidized to CO2 by O2 in the low-temperature region (400 - 500 °C), while graphitized carbon is oxidized with the assistance of lattice oxygen (O released by the carrier γ-Al2O3) in the high-temperature region (600 - 650 °C), avoiding sintering of the carrier caused by local overheating. This temperature window precisely matches the phase transition critical point of the carrier γ-Al2O3 (<800 °C to maintain the γ phase), ensuring the stability of the catalyst skeleton structure. 2- ), avoiding sintering of the carrier caused by local overheating. This temperature window precisely matches the phase transition critical point of the carrier γ-Al2O3 (<800 °C to maintain the γ phase), ensuring the stability of the catalyst skeleton structure.

[0051] Active Site Repair and Interface Reconstruction of Second Phosphating: The calcined catalyst is secondarily phosphated in a H2 / PH3 mixed gas (volume ratio 8:1), heated to 400 - 450 °C at a rate of 4 - 6 °C / min and maintained for 2 - 3 hours to regenerate the active sites. The oxides (NiO, MoO3) formed on the surface of Ni and Mo during the calcination process react with PH3 to form Ni2P and MoP crystals respectively. The P atoms generated by the decomposition of PH3 preferentially fill the metal site defects exposed due to coke oxidation, restoring the hexagonal lattice of Ni2P and the cubic lattice structure of MoP. At the same time, H2 reduces the residual oxides to the metallic state and forms new Ni - P - Mo bonds at the heterojunction interface through surface migration, reconstructing the electron transfer channel.

[0052] Interface repair mechanism: During the secondary phosphating process, the epitaxial growth of MoP on the surface of Ni2P particles is limited by the preset phosphating temperature and gas ratio, forcing the formation of an atomic - level coherent interface (verified by HAADF - STEM observation). This process not only repairs the active sites but also modulates the d - band center of MoP through interface strain (lattice mismatch rate ≈ 4.5%), increasing its isomerization activity compared to the fresh catalyst.

[0053] The present invention provides a preparation method for vehicle - used biomass liquid fuel. It has the following beneficial effects: 1. The present invention adopts a gradient oxidation - step - by - step phosphating regeneration process, breaking through the irreversible damage of traditional calcination to active sites. In the prior art, metal sintering is caused by high - temperature oxidation. The present invention combines gradient temperature control and lattice oxygen to increase the coke removal rate to 98%, extend the catalyst cycle life by more than 3 times, and directly reduce the regeneration cost by 40%.

[0054] 2. The present invention adopts an adaptability design of raw material ratio and steam explosion to solve the problem of heterogeneous conversion of biomass. In traditional processes, fixed ratios lead to phase separation. The present invention dynamically matches the pores of lignocellulose and the particle size of microalgae oil, increasing the carbon conversion rate to exceed 85%, which is 37% higher than conventional methods, and reducing the tar generation amount to less than 1.5%.

[0055] 3. The present invention adopts a CO2 - mediated bifunctional reaction path to subvert the conflict between the deoxygenation and condensation paths. The prior art relies on high - pressure hydrogen for deoxygenation. The present invention uses the weak acidity of supercritical CO2 to selectively capture oxygen atoms, increasing the selectivity of branched - chain alkanes to 85%, reducing the oxygen impurity content by 70%, and saving 32% of energy consumption.

[0056] 4. The present invention adopts step - by - step impregnation - phosphating to construct a heterojunction interface, ending the situation where the activities of multi - metal catalysts are mutually entrapped. The traditional co - impregnation method results in the masking of active sites. The present invention forces the formation of an atomic - level coherent interface, increasing the electron transfer efficiency by 40%, enhancing the isomerization activity by 8%, and breaking through the 95% mark for the qualified rate of catalyst preparation. Description of the Drawings

[0057] Figure 1 Schematic diagram of the method flow of the present invention. Specific implementation mode

[0058] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0059] Example 1: Synergistic conversion of high-lipid microalgae and broad-leaved lignocellulose: Raw materials and parameters: Raw material ratio: Lignocellulose: Eucalyptus sawdust (cellulose 48%, hemicellulose 26%, lignin 18%), particle size 0.5 - 1.0 mm; Microalgae: Chlorella with 42% oil content (C16:0 accounts for 35%, C18:1 accounts for 45%), water content 4.8%; Mass ratio: Lignocellulose: Microalgae = 3:1.

[0060] Pretreatment: Steam explosion: Pressure 1.1 MPa, temperature 200 °C, time 6 minutes; Microalgae drying: Vacuum drying temperature 48 °C, absolute pressure -0.09 MPa, water content ≤ 4.5%.

[0061] Catalyst preparation: Stepwise impregnation - phosphating: Ni impregnating solution: 1.2 mol / L Ni(NO3)2 solution, impregnation amount 8 wt%; Primary phosphating: H2 / PH3 volume ratio 10:1, temperature 410 °C, time 2 hours; Mo impregnating solution: 0.6 mol / L (NH4)6Mo7O 24 Solution, impregnation amount 5 wt%; Secondary phosphating: H2 / PH3 volume ratio 8:1, temperature 450 °C, time 3 hours.

[0062] Hydrothermal reaction: Temperature 340 °C, total pressure 18 MPa (CO2 partial pressure 2.8 MPa), reaction time 28 minutes.

[0063] Separation and purification: Centrifugal separation: 4500 rpm, time 12 minutes; Atmospheric distillation: Collect light components at 80 - 150 °C; Vacuum distillation: absolute pressure 20 kPa, collect the fraction at 150 - 350 °C.

[0064] Catalyst regeneration: Calcination: in air atmosphere, temperature 600 °C, time 2.5 hours; Secondary phosphating: H2 / PH3 volume ratio 8:1, temperature 420 °C, time 2.5 hours.

[0065] Example 2: Adaptation process of needle - leaf lignocellulose and medium - lipid microalgae: Raw materials and parameters: Raw material ratio: Lignocellulose: pine sawdust (cellulose 40%, hemicellulose 22%, lignin 30%), particle size 0.3 - 0.8 mm; Microalgae: Chlorella with 35% lipid content (C16:0 accounts for 40%, C18:1 accounts for 38%), water content 4.2%; Mass ratio: lignocellulose: microalgae = 2.8:1.

[0066] Pretreatment: Steam explosion: pressure 0.9 MPa, temperature 190 °C, time 7.5 minutes; Microalgae drying: vacuum drying temperature 42 °C, absolute pressure - 0.1 MPa, water content ≤ 4.0%.

[0067] Catalyst preparation: Step - by - step impregnation - phosphating: Ni impregnation solution: 0.9 mol / L Ni(NO3)2 solution, impregnation amount 6 wt%; Primary phosphating: H2 / PH3 volume ratio 12:1, temperature 390 °C, time 2.2 hours; Mo impregnation solution: 0.4 mol / L(NH4)6Mo7O 24 Solution, impregnation amount 4 wt%; Secondary phosphating: H2 / PH3 volume ratio 7:1, temperature 440 °C, time 2.8 hours.

[0068] Hydrothermal reaction: Temperature 320 °C, total pressure 16 MPa (CO2 partial pressure 2.2 MPa), reaction time 32 minutes.

[0069] Separation and purification: Centrifugal separation: 3800 rpm, time 15 minutes; Atmospheric distillation: collect the light components at 80 - 150 °C; Vacuum distillation: absolute pressure 15 kPa, collect the fraction at 150 - 350 °C.

[0070] Catalyst regeneration: Roasting: in air atmosphere, temperature 580 °C, time 3 hours; Secondary phosphating: H2 / PH3 volume ratio 9:1, temperature 400 °C, time 3 hours.

[0071] Example 3: Enhanced treatment of high-lignin raw materials and low-moisture microalgae: Raw materials and parameters: Raw material ratio: Lignocellulose: oak sawdust (cellulose 35%, hemicellulose 20%, lignin 35%), particle size 0.2 - 0.5 mm; Microalgae: Chlorella with 45% oil content (C16:0 accounts for 30%, C18:1 accounts for 50%), moisture content 3.8%; Mass ratio: lignocellulose: microalgae = 3.2:1.

[0072] Pretreatment: Steam explosion: pressure 1.2 MPa, temperature 205 °C, time 5 minutes; Microalgae drying: vacuum drying temperature 50 °C, absolute pressure -0.08 MPa, moisture content ≤ 3.5%.

[0073] Catalyst preparation: Stepwise impregnation - phosphating: Ni impregnation solution: 1.5 mol / L Ni(NO3)2 solution, impregnation amount 10 wt%; Primary phosphating: H2 / PH3 volume ratio 9:1, temperature 430 °C, time 1.8 hours; Mo impregnation solution: 0.8 mol / L (NH4)6Mo7O 24 Solution, impregnation amount 6 wt%; Secondary phosphating: H2 / PH4 volume ratio 6:1, temperature 460 °C, time 3.2 hours.

[0074] Hydrothermal reaction: Temperature 350 °C, total pressure 20 MPa (CO2 partial pressure 3.0 MPa), reaction time 25 minutes.

[0075] Separation and purification: Centrifugal separation: 5000 rpm, time 10 minutes; Atmospheric distillation: collect light components at 80 - 150 °C; Vacuum distillation: absolute pressure 25 kPa, collect fractions at 150 - 350 °C.

[0076] Catalyst regeneration: Roasting: in air atmosphere, temperature 620 °C, time 2 hours; Secondary phosphating: H2 / PH3 volume ratio of 7:1, temperature of 440 °C, time of 2.5 hours.

[0077] Comparative Example 1 (corresponding to Example 1): Difference from Example 1: Catalyst preparation method: The traditional co-impregnation method was used (Ni(NO3)2 and (NH4)6Mo7O 24 solution were simultaneously impregnated on the γ-Al2O3 support), primary phosphating (H2 / PH3 volume ratio of 10:1, temperature of 410 °C, time of 2 hours), and stepwise phosphating was not carried out.

[0078] Hydrothermal reaction conditions: CO2 partial pressure was 0 MPa (the total pressure was supplemented with N2 to 18 MPa).

[0079] Comparative Example 2 (corresponding to Example 1): Difference from Example 1: Raw material ratio: Lignocellulose: Microalgae = 5:1.

[0080] Microalgae pretreatment: The drying temperature was increased to 70 °C, and the moisture content was increased to 8%.

[0081] Comparative Example 3 (corresponding to Example 2): Difference from Example 2: Catalyst support: γ-Al2O3 was replaced with SiO2 (same specific surface area, but no acidic sites).

[0082] Hydrothermal reaction temperature: Reduced to 280 °C.

[0083] Comparative Example 4 (corresponding to Example 2) Difference from Example 2: Catalyst regeneration process: The secondary phosphating step was cancelled, and only air calcination (600 °C, 3 hours) was carried out.

[0084] Hydrothermal reaction pressure: The total pressure was reduced to 10 MPa (CO2 partial pressure was still 2.2 MPa).

[0085] Comparative Example 5 (corresponding to Example 3) Difference from Example 3: Steam explosion pretreatment parameters: The pressure was adjusted to 0.5 MPa, and the time was extended to 15 minutes.

[0086] CO2 partial pressure: Increased to 4.0 MPa.

[0087] Comparative Example 6 (corresponding to Example 3): Difference from Example 3: The order of stepwise phosphating is reversed: first load the Mo precursor and phosphorate to form MoP, and then load the Ni precursor for secondary phosphating.

[0088] Vacuum distillation pressure: adjusted to 50 kPa.

[0089] Experiment 1: Verification of the synergistic effect between the catalyst preparation process and the CO2-mediated pathway: Description of experimental steps: Catalyst preparation: Example 1: Prepare the Ni2P-MoP / γ-Al2O3 catalyst according to the stepwise phosphating process (first Ni impregnation and phosphating, then Mo impregnation and phosphating).

[0090] Comparative Example 1: Use the traditional co-impregnation method (simultaneously impregnate Ni-Mo precursors), and prepare the catalyst by one-step phosphating. Cancel the CO2 partial pressure (replace with N2) in the hydrothermal reaction.

[0091] Comparative Example 5: Use the catalyst of Example 1, but increase the CO2 partial pressure to 4.0 MPa.

[0092] Comparative Example 6: Reverse the phosphating order (first Mo then Ni), and the rest is the same as Example 1.

[0093] Hydrothermal reaction: Unify the reaction conditions: temperature 340 °C, total pressure 18 MPa, time 28 minutes, only adjust the CO2 partial pressure and the catalyst type.

[0094] Raw materials: eucalyptus sawdust and high-lipid Chlorella vulgaris (mass ratio 3:1), steam explosion pretreatment (1.1 MPa, 200 °C, 6 minutes).

[0095] Product analysis: After centrifugal separation, measure the yield of branched-chain alkanes and the oxygen impurity content by GC-MS; Measure the carbon deposition amount of the catalyst by TPO (temperature-programmed oxidation); Characterize the proportion of heterojunction interfaces by HAADF-STEM.

[0096] Experimental data: Table 1 Effects of catalyst preparation and CO2 partial pressure on reaction performance Stepwise phosphating and interfacial electron synergy: The high yield (85.2%) and low oxygen content (0.7%) in Example 1 result from the Ni2P-MoP heterojunction interface formed by forced stepwise phosphidation. The Ni (electron-rich) and Mo (electron-deficient) sites at the interface form an electron transfer channel through d-orbital hybridization, enabling the straight-chain alkanes generated by deoxygenation to be directly transferred to adjacent MoP sites for isomerization, thus avoiding side reactions (coke formation) caused by the detachment of intermediates. In contrast, in Comparative Example 6, due to the reversed phosphidation order, the interface structure becomes disordered (interface ratio is only 29.4%), resulting in the disconnection of the deoxygenation and isomerization paths and a significant decrease in the yield (57.9%).

[0097] Oxygen removal and path regulation under CO2 partial pressure: When the CO2 partial pressure is 2.8 MPa (Example 1), the weak acidity (pH≈3.5) of supercritical CO2 selectively promotes the hydrolysis of triglycerides into FFA. At the same time, it acts as an oxygen carrier and combines with the generated O atoms to form CO3 2- , achieving the directional removal of oxygen elements (oxygen content 0.7%). In Comparative Example 1 (without CO2), due to the lack of an oxygen removal path, O atoms combine with intermediates to form oxygen-containing by-products (ketones, ethers), and the oxygen impurities soar to 4.1%. In Comparative Example 5 (CO2 partial pressure 4.0 MPa), due to the excessive deposition of CO3 2- blocking the catalyst pores, although the interface ratio is relatively high (88.9%), the yield is still limited (68.7%).

[0098] Constraints of process sequence on dynamic equilibrium: The "Ni first then Mo" sequence of stepwise phosphidation ensures the preferential nucleation of Ni2P crystals and serves as a template for the epitaxial growth of MoP, forming an atomic-level coherent interface (lattice mismatch rate 4.5%). This interface structure modulates the d-band center of MoP through the strain effect, increasing its isomerization activity by 8%. In contrast, the co-impregnation method in Comparative Example 1 leads to the mutual dissolution of Ni and Mo to form an inactive NiMoO4 phase (verified by XRD), significantly reducing the density of effective active sites at the interface (coke formation amount 6.8%). The experimental data verify the decisive role of the process sequence in the dynamic activity equilibrium of the catalyst.

[0099] Experiment 2: Verification of the adaptability boundary of raw material ratio and pretreatment parameters: Description of experimental steps: Raw material ratio and pretreatment: Example 1: Lignocellulose (eucalyptus sawdust): microalgae = 3:1; steam explosion pressure 1.1 MPa, temperature 200 °C, microalgae drying temperature 48 °C.

[0100] Example 3: Lignocellulose (oak sawdust): microalgae = 3.2:1; steam explosion pressure 1.2 MPa, temperature 205 °C, microalgae drying temperature 50 °C.

[0101] Comparative Example 2: Lignocellulose: microalgae = 5:1; steam explosion pressure 1.1 MPa, temperature 200 °C, microalgae drying temperature 70 °C.

[0102] Comparative Example 5: Lignocellulose: microalgae = 3:1; steam explosion pressure 0.5 MPa, temperature 200 °C, microalgae drying temperature 48 °C.

[0103] Hydrothermal reaction: Uniform reaction conditions: The catalyst is Ni2P-MoP / γ-Al2O3, temperature 340 °C, total pressure 18 MPa, CO2 partial pressure 2.8 MPa, time 28 minutes.

[0104] Product analysis: The yield of branched-chain alkanes was measured after centrifugal separation; The proportion of tar by-products was determined by Soxhlet extraction; The porosity of lignocellulose was determined by mercury intrusion porosimetry (MIP); The octane number (RON) was tested by a CFR engine.

[0105] Experimental data: Table 2 Influence of raw material ratio and pretreatment parameters on product performance Carbon-hydrogen balance constraint of raw material ratio: The yield difference between Example 1 and Example 3 (84.9% vs 81.1%) is due to the difference in lignin content (18% vs 35%) of lignocellulose types (eucalyptus sawdust vs oak sawdust). Oak sawdust with a higher lignin content releases more phenols during steam explosion to inhibit the condensation reaction, but partially compensates for the porosity loss (64.2%) by increasing the steam explosion pressure (1.2 MPa), maintaining the carbon-hydrogen balance. In Comparative Example 2 (5:1), due to excessive lignocellulose, the microalgae oil could not fully penetrate the pores, resulting in phase separation, and the tar proportion soared to 23.4%, and the yield dropped precipitously (53.6%).

[0106] Porosity regulation threshold of steam explosion pressure: Steam explosion pressure of 1.1 - 1.2 MPa (Examples 1, 3) depolymerizes hemicellulose partially into oligosaccharides (cellobiose, cellotriose), and at the same time forms through-pores with a pore size of 5 - 10 μm, providing a mass transfer channel for the oil-sugar composite precursor. In Comparative Example 5 (0.5 MPa), due to insufficient pressure, only closed micropores (pore size < 2 μm) are generated, and the porosity drops to 37.9%, and the oil cannot effectively penetrate into the interior of cellulose, resulting in limited condensation reaction (yield 62.8%).

[0107] Critical point of coking risk for microalgae drying temperature: The drying temperature of Example 1 (48 °C) retains the lipid-coated structure of the microalgae cell wall through mild dehydration, preventing cell wall rupture and lipid oxidation caused by high temperature (Comparative Example 2, 70 °C). Oxidized lipids generate conjugated olefins during subsequent hydrothermal reactions and polymerize into tar through the Diels-Alder reaction (the tar content in Comparative Example 2 is 23.4%). The low-temperature drying in Example 1 allows the oil to be uniformly dispersed in the cellulose pores in a free state, leading to a dominant increase in the condensation path (octane number 94).

[0108] Experiment 3: Verification of the stability of the carrier-regeneration system and reaction conditions: Description of the experimental procedure: Catalyst preparation and regeneration: Example 2: A γ-Al2O3 carrier was used to prepare a Ni2P-MoP catalyst by stepwise phosphating. The regeneration process was secondary phosphating (H2 / PH3 = 9:1, 400 °C) after calcination (580 °C).

[0109] Comparative Example 3: A SiO2 carrier (with the same specific surface area) was used, and the preparation and regeneration processes were the same as those in Example 2.

[0110] Comparative Example 4: For the γ-Al2O3 carrier, the regeneration process was only calcination (580 °C), and the secondary phosphating was cancelled.

[0111] Hydrothermal reaction: Uniform raw materials: Pine sawdust and medium-oil microalgae (mass ratio 2.8:1), steam explosion pretreatment (0.9 MPa, 190 °C, 7.5 minutes).

[0112] Example 2: Temperature 320 °C, total pressure 16 MPa (CO2 partial pressure 2.2 MPa); Comparative Example 3: Temperature 320 °C, total pressure 16 MPa (CO2 partial pressure 2.2 MPa); Comparative Example 4: Temperature 320 °C, total pressure 10 MPa (CO2 partial pressure 2.2 MPa).

[0113] Product analysis: Determine the proportion of C10-C16 branched alkanes; TPO was used to determine the carbon deposition amount on the catalyst; After 3 cycles of use, the catalyst activity retention rate was tested.

[0114] Experimental data: Table 3 Influence of carrier type and regeneration process on reaction stability Catalytic effect of sugar condensation on the acidic sites of the carrier: The surface acidic sites (B acid and L acid) of the γ-Al2O3 support activate the xylose oligomers (xylobiose) generated by the depolymerization of hemicellulose through protonation, promoting their Aldol condensation reaction with microalgal fatty acids to form C10-C16 branched alkane precursors (accounting for 81.7%). In contrast, the SiO2 support in Comparative Example 3 lacks acidic sites, and the xylose oligomers cannot be effectively activated, and the condensation reaction turns to produce short-chain hydrocarbons (C5-C9 accounting for 55%), resulting in a significant decrease in the yield of the target product (52.1%).

[0115] Dynamic repair mechanism of secondary phosphidation on active sites: The regeneration process of Example 2 selectively fills the metal defects exposed due to carbon deposition oxidation on the surface of Ni2P through secondary phosphidation (P atoms decomposed from PH3), restoring the integrity of its hexagonal lattice (the XRD half-peak width is reduced by 0.15°), and the activity retention rate is increased to 83.5%. In contrast, in Comparative Example 4 (only calcination), since the defect sites are not repaired, the metal particles agglomerate after cycling (TEM shows that the particle size increases from 5 nm to 12 nm), the carbon deposition amount rises to 8.3%, and the activity retention rate is less than 50%.

[0116] Threshold effect of reaction pressure on mass transfer-reaction equilibrium: The total pressure of 16 MPa in Example 2 makes the density of supercritical CO2 reach 0.8 g / cm 3 , enhancing the dissolution and diffusion ability of the oil-sugar complex, and the condensation reaction rate is increased by 2.1 times. In contrast, in Comparative Example 4 (total pressure 10 MPa), due to insufficient CO2 density (0.5 g / cm 3 ), mass transfer limitation leads to too high local concentration of reactants, triggering parallel side reactions (dehydration to form furan compounds), and the yield drops to 61.2%.

[0117] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing biomass liquid fuel for vehicle, characterized in that: The following steps are involved: (1) mixing lignocellulose with microalgae to obtain a mixed raw material; (2) preparing a bifunctional catalyst, wherein the catalyst comprises a hydrodeoxygenation active site and an isomerization active site; (3) placing the mixed raw material and the bifunctional catalyst in a hydrothermal reaction system, and performing a catalytic reaction in the presence of CO2 to generate liquid hydrocarbon products; (4) Separating and purifying liquid hydrocarbon products to obtain biomass liquid fuel for vehicles; (5) Regenerate and recycle the catalyst.

2. The method for preparing a biomass liquid fuel for vehicle according to claim 1, characterized in that: The mass ratio of lignocellulose to microalgae in step (1) is 3:1±0.

2.

3. The method for preparing a biomass liquid fuel for vehicle according to claim 1, characterized in that: The wood cellulose in step (1) is pretreated by steam explosion under the following conditions: steam pressure 0.8-1.2 MPa, temperature 185-205° C., time 5-8 minutes.

4. The method for preparing a biomass liquid fuel for vehicle according to claim 1, characterized in that: The microalgae in step (1) is Chlorella with a lipid content of ≥30wt%, and is vacuum dried at 40-50°C to a moisture content of ≤5%.

5. The method for preparing a biomass liquid fuel for vehicle according to claim 1, characterized in that: The bifunctional catalyst in step (2) is a Ni2P-MoP heterojunction loaded on a γ-Al2O3 carrier, and is prepared by a stepwise impregnation-phosphating method.

6. The method for preparing a biomass liquid fuel for vehicle according to claim 5, characterized in that: The step-by-step impregnation-phosphating method comprises: A. Impregnate Ni(NO3)2 solution into γ-Al2O3, and generate Ni2P / Al2O3 through roasting and phosphating; B. Impregnate MoO3 solution into Ni2P / Al2O3 and perform secondary phosphating to generate Ni2P-MoP / γ-Al2O3.

7. The method for preparing a biomass liquid fuel for vehicle according to claim 1, characterized in that: The hydrothermal reaction conditions in step (3) are: temperature 300-350°C, pressure 15-20MPa, CO2 partial pressure 2.0-3.0MPa, and reaction time 25-35 minutes.

8. The method for preparing a biomass liquid fuel for vehicle according to claim 1, characterized in that: The catalytic reaction in step (3) simultaneously completes oil hydrodeoxygenation and sugar condensation isomerization to directly generate branched alkanes.

9. The method for preparing a biomass liquid fuel for vehicle according to claim 1, characterized in that: The separation and purification in step (4) includes: A. Centrifugal separation of catalyst and liquid product; B. Remove light components at 80-150℃ by atmospheric distillation; C. Collect the 150-350°C fraction by vacuum distillation as the target fuel.

10. The method for preparing a biomass liquid fuel for vehicle according to claim 1, characterized in that: The catalyst regeneration in step (5) comprises: A. Calcination in air atmosphere at 550-650℃ to remove carbon deposits; B. Repair active sites by secondary phosphating in H2 / PH3 gas mixture.

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