Alkane-based fuel composition for small aircraft and preparation method of alkane-based fuel composition

Abstract

The invention discloses an alkane-based fuel composition for a small aircraft and a preparation method of the alkane-based fuel composition, and relates to the field of fuel preparation, the preparation method comprises the following steps: performing hydrolysis treatment on mixed grease containing triglyceride and free fatty acid, and obtaining a fatty acid phase and a glycerol aqueous solution phase after the treatment is finished; carrying out fermentation reaction on the glycerol aqueous solution phase and a hydrogen-producing strain to obtain biological hydrogen and fermentation liquor containing volatile fatty acid, then purifying the fermentation liquor, and carrying out electrolytic treatment on the purified fermentation liquor to obtain electrochemical hydrogen; reacting the fatty acid phase with a zirconia-based solid acid catalyst to obtain a ketone mixture, and carrying out hydrodeoxygenation treatment on the ketone mixture, biological hydrogen and electrochemical hydrogen to obtain a long-chain n-alkane mixture; and carrying out hydroisomerization cracking on the long-chain n-alkane mixture to obtain an isoparaffin mixture, and fractionating the isoparaffin mixture to obtain the alkane-based fuel composition. The problem of high hydrogen consumption in the prior art is effectively solved.

Description

Technical Field

[0001] This invention relates to the field of fuel preparation, and more particularly to an alkane-based fuel composition for small aircraft and a method for preparing the same. Background Technology

[0002] The HEFA-SP (hydrogenated ester and fatty acid synthetic paraffin kerosene) process converts triglycerides in animal and vegetable oils into specific alkane-based fuel compositions through hydrodeoxygenation, cracking, and isomerization reactions. The core component of this composition is C9-C16 isoalkanes, whose excellent low-temperature performance and high energy density make them ideal components for aviation kerosene. This process realizes the targeted conversion of biomass resources into high-performance green aviation fuels and is a key technological path for decarbonization in the aviation industry.

[0003] The traditional HEFA-SP process uses animal and vegetable oils as raw materials to produce bio-jet fuel through hydrogenation and isomerization. However, it suffers from high hydrogen consumption during hydrodeoxygenation. Specifically, triglycerides and free fatty acids in oil molecules contain a large number of oxygen atoms, which need to be removed in the form of water through hydrogenation. This process consumes a large amount of hydrogen, typically accounting for more than 60% of the total hydrogen used in the entire process. High hydrogen consumption directly leads to increased production costs, and since much of the hydrogen comes from fossil fuel reforming, it weakens the carbon emission reduction benefits throughout the entire life cycle. In addition, complex impurities in the raw materials can easily poison and deactivate the hydrogenation catalyst. To maintain reaction efficiency, it is necessary to increase the hydrogen partial pressure or frequently replace the catalyst, further exacerbating hydrogen consumption and operating costs.

[0004] Therefore, an alkane-based fuel composition for small aircraft and its preparation method are proposed to solve the problem of high hydrogen consumption during hydrodeoxygenation. Summary of the Invention

[0005] The purpose of this invention is to provide an alkane-based fuel composition for small aircraft and its preparation method, thereby solving the problem of high hydrogen consumption during hydrodeoxygenation.

[0006] To achieve this objective, the present invention adopts the following technical solution: An alkane-based fuel composition for small aircraft and a method for preparing the same, the method comprising the following steps: Step S1: Hydrolyze the mixed oil containing triglycerides and free fatty acids to obtain a fatty acid phase and a glycerol aqueous solution phase after the treatment is completed. Step S2: The aqueous glycerol phase is fermented with hydrogen-producing strain to obtain bio-hydrogen and fermentation broth containing volatile fatty acids. The fermentation broth is then purified and electrolyzed to obtain electrochemical hydrogen. Step S3: The fatty acid phase is reacted with a zirconium oxide-based solid acid catalyst to obtain a ketone mixture, which is then subjected to hydrodeoxygenation treatment with the biohydrogen and electrochemical hydrogen obtained in step S2 to obtain a long-chain n-alkanes mixture. Step S4: After hydroisomerization of the long-chain n-alkane mixture, an isoalkane mixture is obtained, which is then fractionated to obtain an alkane-based fuel composition.

[0007] Step S1 specifically includes the following steps: The mixed oils were reacted with deionized water at 180-220℃ and 1.5-2.5 MPa under weakly acidic conditions for 1-3 hours to obtain a fatty acid phase and a glycerol aqueous solution phase; wherein the glycerol aqueous solution phase includes glycerol (glycerol), and the fatty acid phase includes free fatty acid C. 12 -C 18 .

[0008] The mixed oil is obtained from waste oil through coarse filtration, solidification, and preliminary desalination.

[0009] Step S2 specifically includes the following steps: Step S21: After removing impurities from the glycerol aqueous solution phase, adjust its pH to obtain the glycerol aqueous solution substrate; Step S22: The glycerol aqueous solution substrate and the hydrogen-producing strain are fermented in an anaerobic fermentation reactor at a first temperature to obtain bio-hydrogen, carbon dioxide and fermentation broth including volatile fatty acids. Step S23: The fermentation broth is subjected to centrifugation, ultrafiltration and electrodialysis desalination in sequence to obtain a purified solution. The purified solution is used as the anode feed solution and deionized water is used as the cathode feed solution. The two solutions are sent to the anode chamber and cathode chamber of the anion exchange membrane electrolysis cell for electrolysis to obtain electrochemical hydrogen and carbon dioxide.

[0010] In step S21, the pH value after pH adjustment is 6.5-7.5; In step S22, the first temperature is 30-40℃, the fermentation reaction time is 24-48h, the inoculation amount of the hydrogen-producing strain is 5-20 vol% of the fermentation liquid volume, the total concentration of volatile fatty acids in the purified liquid is 5-50 g / L, the volume ratio of biological hydrogen to carbon dioxide is (2-4):(1-3), and the hydrogen-producing strain is hydrogen-producing Enterobacter. In step S23, the temperature of the anion exchange membrane electrolytic cell is 50-70℃, the cell voltage is 1.8-2.5V, and the operating current density is 100-400mA / cm². 2 .

[0011] Step S3 specifically includes the following steps: Step S31: After pretreating the fatty acid phase, a ketation reaction is carried out with a zirconium oxide-based solid acid catalyst to obtain a ketone mixture, carbon dioxide, and water vapor; wherein, the ketone mixture includes long-chain symmetrical ketone C. 31 -C 35 ; Step S32: The ketone mixture, bio-hydrogen, and electrochemical hydrogen are placed in a container equipped with a bifunctional catalyst for hydrogenation reaction. After the reaction is completed, a mixture of long-chain n-alkanes is obtained; wherein, the long-chain n-alkanes mixture includes n-alkanes C 30 -C 34 With water.

[0012] In step S31, the ketation reaction is carried out at a temperature of 320-360°C and a pressure of 0.5-1.0 MPa. In step S32, the catalyst is a Pt / WO3–ZrO2 bifunctional catalyst, the hydrogenation reaction temperature is 250-280℃, the pressure is 3.0-4.0MPa, and the time is 4-6h, and the molar ratio of the ketone mixture to the total molar amount of biological hydrogen and electrochemical hydrogen is 1:(3-5).

[0013] Step S4 specifically includes the following steps: Step S41: The long-chain n-alkane mixture and the hydrogen obtained in step S2 are placed in a container containing a hydroisomerization cracking catalyst for hydroisomerization cracking treatment to obtain an isomerized alkane mixture C9-C. 17 ; Step S42: The isoparaffin mixture is fractionated using a fractionating column. By controlling the temperatures at the top, side stream, and bottom of the column, a fraction with an initial boiling point ≥150℃ and a final boiling point ≤250℃ is collected from the side stream to obtain an alkane-based fuel composition; wherein the alkane-based fuel composition includes isoparaffins C9-C 17 .

[0014] In step S41, the hydroisomerization cracking treatment is carried out at a temperature of 320-360℃, a pressure of 5.0-7.0 MPa, and a weight hourly space velocity of 0.8-1.5 h⁻¹. -1 The hydroisomerization catalyst is a Pt / USY molecular sieve catalyst, and the volume ratio of hydrogen gas to long-chain n-alkane mixture obtained in step S2 is (300-600):1. In step S42, the aromatic hydrocarbon content of the alkane-based fuel composition is <0.1%, and the freezing point is <-47°C.

[0015] An alkane-based fuel composition for small aircraft, said alkane-based fuel composition for small aircraft is prepared by the preparation method described above.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides an alkane-based fuel composition for small aircraft and its preparation method. The method involves hydrolyzing a mixed oil into a fatty acid phase and a glycerol aqueous solution phase, and then differentially treating them to systematically reduce hydrogen consumption. Specifically, for the glycerol aqueous solution phase, a fermentation and electrolysis coupled process is used to convert it into bio-hydrogen and electrochemical hydrogen, constructing an internal hydrogen supply system to replace the external fossil-derived hydrogen required by traditional processes. For the fatty acid phase, a hydrogen-free catalytic ketation reaction is used to achieve deep deoxygenation and carbon chain growth, eliminating the need for direct hydrogenation. The hydrogen requirement for removing the oxygen atoms is reduced by using self-produced hydrogen to perform mild hydrodeoxygenation on the more reactive ketone intermediates, further reducing the hydrogen consumption in this step. Finally, the obtained long-chain alkanes are hydroisomerized, cracked, and fractionated to produce a compliant alkane-based fuel composition. This method reduces the total hydrogen consumption of the entire process through the synergistic effect of internal hydrogen production and hydrogen-free deoxygenation, while realizing the high-value utilization and green conversion of waste oil resources throughout the process. It effectively overcomes the economic and environmental bottlenecks caused by the high hydrogen consumption of the traditional HEFA-SP process. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] The structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0019] Figure 1 This is a flowchart of the preparation method in this invention. Detailed Implementation

[0020] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In the description of this invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component positioned centrally in the connection.

[0022] Example 1: Please see Figure 1 This embodiment describes an alkane-based fuel composition for small aircraft and its preparation method. The preparation method includes the following steps: Step S1: Hydrolyze the mixed oil containing triglycerides and free fatty acids to obtain a fatty acid phase and a glycerol aqueous solution phase after the treatment is completed. Step S2: The aqueous glycerol phase is fermented with hydrogen-producing strain to obtain bio-hydrogen and fermentation broth containing volatile fatty acids. The fermentation broth is then purified and electrolyzed to obtain electrochemical hydrogen. Step S3: The fatty acid phase is reacted with a zirconium oxide-based solid acid catalyst to obtain a ketone mixture, which is then subjected to hydrodeoxygenation treatment with the biohydrogen and electrochemical hydrogen obtained in step S2 to obtain a long-chain n-alkanes mixture. Step S4: After hydroisomerization of the long-chain n-alkane mixture, an isoalkane mixture is obtained, which is then fractionated to obtain an alkane-based fuel composition.

[0023] Specifically, in step S1, the mixed oil containing triglycerides and free fatty acids is hydrolyzed to obtain a fatty acid phase and a glycerol aqueous solution phase after the treatment is completed. Step S1 specifically includes the following steps: The mixed oils were reacted with deionized water at 180-220℃ and 1.5-2.5 MPa under weakly acidic conditions for 1-3 hours to obtain a fatty acid phase and a glycerol aqueous solution phase; wherein the glycerol aqueous solution phase includes glycerol (glycerol), and the fatty acid phase includes free fatty acid C. 12 -C 18 .

[0024] The mixed oil is obtained from waste oil through coarse filtration, solidification, and preliminary desalination.

[0025] It should be noted that during hydrolysis, high temperature and pressure conditions cause water molecules to directly attack and break the ester bonds in triglyceride molecules. Specifically, each triglyceride macromolecule, the main building block of lipids, reacts with three water molecules, breaking the three ester bonds (-COO-) in its molecular skeleton, ultimately generating three independent free fatty acid molecules and one glycerol molecule. This chemical transformation is fundamental, changing the basic chemical composition of the material and transforming the originally homogeneous oil phase system into a clear two-phase system. The upper layer is a hydrophobic fatty acid phase, which also contains fat-soluble pigments and sterols, among other impurities. The lower layer is a hydrophilic aqueous glycerol phase, which dissolves the glycerol and water generated in the reaction, as well as water-soluble salts, sugars, and protein degradation products originally present in the raw material.

[0026] It is known that the chemical composition of the fatty acid phase is transformed into that of long-chain free fatty acids, whose molecules possess higher reactivity. In particular, the carboxyl functional group can directly participate in the subsequent ketation reaction without prior transesterification, contributing to the reduction of hydrogen consumption. This allows the material to directly enter the hydrogen-free ketation deoxygenation pathway, avoiding the hydrogen consumption or other material consumption caused by the hydrogenation or alcoholysis of triglycerides required in traditional processes. Meanwhile, the glycerol aqueous solution phase highly enriches glycerol in the aqueous phase, achieving efficient physical separation of glycerol and fatty acids. This forms an independent purification and conversion channel for glycerol, enabling it to be extracted and utilized separately, rather than existing as an impurity in the main reaction stream, affecting catalyst efficiency or increasing hydrogen consumption in subsequent processing.

[0027] Understandably, the above method achieves precise separation and targeted enrichment of raw materials, and provides corresponding raw materials for subsequent processing techniques of completely different types, namely, the dehydrogenated ketogenesis of fatty acid phase and the bio-fermentation hydrogen production of glycerol aqueous solution phase. Specifically, by classifying the materials in the early stage, it is ensured that the glycerol component, which is easy to produce hydrogen through biological pathways, is directed to the fermentation hydrogen production unit in subsequent steps to produce bio-hydrogen and electrochemical hydrogen; while the fatty acid component that needs to be deoxygenated is directed to the catalytic ketogenesis unit, which does not consume hydrogen at all, avoiding the useless consumption of glycerol component under high temperature and high pressure hydrogenation environment, and the inability to utilize its hydrogen production potential, thus resulting in a net loss of hydrogen.

[0028] It is worth noting that the hydrolysis process simultaneously achieves the chemical transformation and physical phase separation of triglycerides, thus preparing ideal raw materials for subsequent differentiated processing. The corresponding temperature and pressure ensure a high reaction rate while avoiding fatty acid decomposition; the corresponding time ensures that the hydrolysis is fully completed. Under this approach, a characteristic fatty acid phase and a glycerol aqueous solution phase are stably produced, laying the foundation for the entire process chain.

[0029] In one specific embodiment, the mixed oils and deionized water were reacted under weakly acidic conditions of 200°C and 2.0 MPa for 2 hours to obtain a fatty acid phase and a glycerol aqueous solution phase. Specifically, in step S2, the glycerol aqueous solution phase is fermented with the hydrogen-producing strain to obtain bio-hydrogen and fermentation broth containing volatile fatty acids. The fermentation broth is then purified and electrolyzed to obtain electrochemical hydrogen. Step S2 specifically includes the following steps: Step S21: After removing impurities from the glycerol aqueous solution phase, adjust its pH to obtain the glycerol aqueous solution substrate; In step S21, the pH value after pH adjustment is 6.5-7.5; Step S22: The glycerol aqueous solution substrate and the hydrogen-producing strain are fermented in an anaerobic fermentation reactor at a first temperature to obtain bio-hydrogen, carbon dioxide and fermentation broth including volatile fatty acids. In step S22, the first temperature is 30-40℃, the fermentation reaction time is 24-48h, the inoculation amount of hydrogen-producing strain is 5-20 vol% of the fermentation liquid volume, the total concentration of volatile fatty acids in the purified liquid is 5-50 g / L, the volume ratio of biological hydrogen to carbon dioxide is (2-4):(1-3), and the hydrogen-producing strain is hydrogen-producing Enterobacter. Step S23: The fermentation broth is subjected to centrifugation, ultrafiltration and electrodialysis desalination in sequence to obtain a purified solution. The purified solution is used as the anode feed solution and deionized water is used as the cathode feed solution. The two solutions are sent to the anode chamber and cathode chamber of the anion exchange membrane electrolysis cell for electrolysis to obtain electrochemical hydrogen and carbon dioxide.

[0030] In step S23, the temperature of the anion exchange membrane electrolyzer is 50-70℃, the cell voltage is 1.8-2.5V, and the operating current density is 100-400mA / cm². 2 .

[0031] It should be noted that in step S21, the input material is the glycerol aqueous solution phase obtained from the upstream pretreatment. This material contains glycerol, water, and various impurities. The working principle of this step is to pretreat the material through physical and chemical methods. In this process, solid particles and some pigments and other impurities are removed through filtration, adsorption, and other operations. The hydrogen ion concentration is adjusted by adding acid or alkali to bring the pH value of the system to the range most suitable for subsequent microbial growth, thereby transforming the glycerol aqueous solution phase into a glycerol aqueous solution substrate. In step S22, the enzyme system inside the hydrogen-producing strain cells uses glycerol molecules as a carbon source and energy source for anaerobic metabolism. Under biochemical pathways (such as glycerol fermentation for hydrogen production), glycerol is decomposed, ultimately releasing hydrogen molecules and carbon dioxide gas. At the same time, some carbon sources are converted into volatile fatty acids and other organic acids and secreted extracellularly. In this process, the glycerol aqueous solution substrate is converted into a mixture of gaseous biological hydrogen and carbon dioxide, as well as a liquid, rich in... The fermentation broth contains volatile fatty acids. In step S23, the bacterial cells and macromolecules in the fermentation broth are first removed by physical separation methods such as centrifugation and ultrafiltration. Then, desalination is carried out by electrodialysis, selectively migrating and removing inorganic salt ions under the action of an electric field, thereby obtaining a pure organic acid aqueous solution, i.e., a purified solution. Subsequently, the purified solution is used as the anode feed liquid and enters the anion exchange membrane electrolytic cell. On the surface of the anode catalyst (the interface region where the electrocatalytic material loaded on the anode conductive substrate is in contact with its reaction environment), volatile fatty acid molecules undergo electrochemical oxidation, losing electrons to generate carbon dioxide and protons. These protons are transferred to the cathode through the membrane and combine with hydroxide ions generated from the reduction of water molecules in the cathode chamber, or directly gain electrons at the cathode to generate hydrogen molecules, thereby converting the purified solution into high-purity electrochemical hydrogen, carbon dioxide, and mineralized water. In addition, the electrolysis method using an anion exchange membrane electrolytic cell is well known to those skilled in the art, and will not be described in detail in this embodiment.

[0032] It is known that the glycerol aqueous solution substrate obtained in step S21 has reduced impurity content and its pH value is controlled within a specific range. This provides a repeatable initial reaction environment for the subsequent fermentation process, which is the foundation for ensuring biocatalytic efficiency. In step S22, the main organic components of the fermentation broth rich in volatile fatty acids have been transformed from glycerol to volatile fatty acids with smaller molecular weight and higher electrochemical activity. The role of bio-hydrogen is to serve as the initial source of hydrogen in the hydrogenation process, and the fermentation broth rich in volatile fatty acids can efficiently convert the energy carrier from glycerol into a fuel precursor suitable for efficient conversion in the subsequent electrochemical process. The electrochemical hydrogen obtained in step S23 has high purity, and its production process simultaneously achieves the complete mineralization of organic pollutants in the fermentation broth. The high-purity electrochemical hydrogen, as a high-quality hydrogen source, can meet the hydrogen source purity requirements of the catalysts used in subsequent steps to avoid poisoning and deactivation. In addition, the thorough treatment of the fermentation broth by this process enables the entire system to achieve near-zero discharge of organic wastewater, transforming environmental burden into resource benefits.

[0033] Understandably, step S21, through impurity removal and pH adjustment, prepares an aqueous glycerol substrate that eliminates the inhibition and toxicity of impurities and inappropriate pH levels on the hydrogen-producing strains. This provides a fundamental guarantee for the efficient and stable operation of step S22. Furthermore, by optimizing the quality of the reaction precursor, it improves the efficiency and reliability of the entire bio-hydrogen production process, providing a stable and efficient bioconversion basis for solving the hydrogen consumption problem. In step S22, by utilizing microbial metabolism, glycerol is directionally converted into hydrogen and highly electrochemically active volatile fatty acids, achieving the initial energy conversion. This not only produces initial bio-hydrogen but also prepares suitable... The fermentation broth processed by the electrochemical system transforms complex waste into materials that are easily powered by subsequent electricity through biocatalysis, contributing to solving the hydrogen consumption problem and increasing the total hydrogen production during the hydrogenation process. In step S23, the purified liquid containing volatile acids is effectively converted into high-purity hydrogen, completing the transformation from organic waste to high-quality energy. The resulting electrochemical hydrogen replaces externally purchased hydrogen, thus solving the problem of high hydrogen consumption. In addition, by producing high-purity hydrogen to replace external supply to the greatest extent, and with almost no new secondary pollution generated throughout the process, the problems of high hydrogen consumption and environmental compatibility are also solved.

[0034] It is important to emphasize that step S21, through the pretreatment of materials, ensures that the biocatalysis stage can achieve the highest hydrogen production rate and substrate conversion rate, thus contributing to the efficiency improvement and cost reduction of all subsequent steps. Step S22 achieves the initial self-production of hydrogen and completes the energy carrier transformation. It not only obtains the initially used bio-hydrogen but also creates the material conditions for the use of efficient electrochemical processes in step S23 by generating fermentation broth. Step S23 achieves the hydrogen consumption reduction target by directly and quantitatively providing electrochemical hydrogen to replace external hydrogen, thus enabling the overall process to achieve the goals of low hydrogen consumption and greening.

[0035] It is worth noting that the impurity removal and pH adjustment process in step S21 can avoid the severe inhibition of microbial activity by impurities and the original pH in the glycerol aqueous solution, thereby improving the biochemical reaction efficiency in step S22, and the resulting solution is also suitable for the growth of hydrogen-producing strains. The anaerobic fermentation process in step S22 allows the hydrogen-producing strains to convert glycerol into hydrogen and volatile acids, and the concentration of glycerol in the material and the first temperature matching the metabolic temperature of the hydrogen-producing strain maximize the yield of hydrogen and the target volatile acid. In step S23, the purified solution is obtained by first centrifuging, ultrafiltration and electrodialysis, which ensures that the subsequent electrolysis process can be carried out efficiently and stably.

[0036] In a specific embodiment, step S2 specifically includes: step S21, removing impurities and adjusting the pH of the glycerol aqueous solution phase to obtain a glycerol aqueous solution substrate with a pH of 7.0; step S22, anaerobic fermenting the glycerol aqueous solution substrate with hydrogen-producing Enterobacter at 35°C for 36 hours to obtain bio-hydrogen, carbon dioxide, and fermentation broth; wherein the inoculum amount of hydrogen-producing Enterobacter is 10% of the fermentation broth volume; step S23, centrifuging, ultrafiltration, and electrodialysis desalination treatment of the fermentation broth sequentially to obtain a purified solution; electrolyzing the purified solution and deionized water in an anion exchange membrane electrolysis cell at 60°C and a cell voltage of 2.2V to obtain electrochemical hydrogen and carbon dioxide. In addition, when obtaining the purified solution, impurities such as sulfur and nitrogen compounds are also cleaned and removed.

[0037] In an optional embodiment, the bio-hydrogen and electrochemical hydrogen obtained in step S2 can be purified to obtain purified bio-hydrogen and purified electrochemical hydrogen for use in subsequent step 31.

[0038] Specifically, in step S3, the fatty acid phase is reacted with a zirconium oxide-based solid acid catalyst to obtain a ketone mixture, which is then subjected to hydrogenation and deoxygenation treatment with the biohydrogen and electrochemical hydrogen obtained in step S2 to obtain a long-chain n-alkane mixture. Step S3 specifically includes the following steps: Step S31: After pretreating the fatty acid phase, a ketation reaction is carried out with a zirconium oxide-based solid acid catalyst to obtain a ketone mixture, carbon dioxide, and water vapor; wherein, the ketone mixture includes long-chain symmetrical ketone C. 31 -C 35 ; In step S31, the ketation reaction is carried out at a temperature of 320-360℃ and a pressure of 0.5-1.0 MPa. Step S32: The ketone mixture, bio-hydrogen, and electrochemical hydrogen are placed in a container equipped with a bifunctional catalyst for hydrogenation reaction. After the reaction is completed, a mixture of long-chain n-alkanes is obtained; wherein, the long-chain n-alkanes mixture includes n-alkanes C 30 -C 34 With water.

[0039] In step S32, the catalyst is a Pt / WO3–ZrO2 bifunctional catalyst, the hydrogenation reaction temperature is 250-280℃, the pressure is 3.0-4.0MPa, the time is 4-6h, and the molar ratio of the ketone mixture to the total molars of biological hydrogen and electrochemical hydrogen is 1:(3-5).

[0040] It should be noted that in step S31, during the ketation reaction, two free fatty acid molecules undergo decarboxylation condensation at the acidic sites of the zirconium oxide-based solid acid catalyst. Specifically, the carboxyl group of one fatty acid molecule interacts with the α-hydrogen atom of the other fatty acid molecule, synergistically removing one molecule of carbon dioxide and one molecule of water. Simultaneously, the two hydrocarbon chains are connected through newly formed carbon-carbon bonds, generating a long-chain symmetrical ketone molecule with a carbon number equal to the sum of the carbon numbers of the starting fatty acids minus one. This allows the input C... 12 -C 18 The fatty acid phase transformation results in a mixture of ketones with longer carbon chains, releasing gaseous byproducts. This process removes half of the oxygen atoms from the raw material without consuming any hydrogen, and completes the carbon chain growth, providing intermediates with larger molecular weights for subsequent steps. During the hydrodeoxygenation reaction in step S32, the carbonyl groups in the ketone mixture are adsorbed and hydrogenated at the metal site (Pt) of the Pt / WO3–ZrO2 bifunctional catalyst, generating an unstable semi-alcohol intermediate. This intermediate then migrates to the acidic site of the catalyst (WO3–ZrO2 support) and undergoes a dehydration reaction, forming the corresponding long-chain olefin. This olefin rapidly returns to the metal site to complete hydrogenation saturation, ultimately generating n-alkanes with a carbon skeleton identical to the raw ketone and water. This transforms the ketone mixture into a long-chain n-alkane mixture after reacting with hydrogen, with water as a byproduct. Furthermore, due to the carbon number distribution and reaction selectivity of the raw fatty acids, the generated ketone mixture exhibits a C10-C20 carbon structure. 31 -C 35 Primarily composed of ketones with trace amounts of other carbon numbers; after hydrogenation and deoxygenation, the corresponding ketones with C360 carbons are obtained. 30 -C34 A mixture of predominantly n-alkanes.

[0041] It is known that, according to step S31, the number of oxygen atoms in the ketone mixture is reduced by half compared to the raw fatty acid, and the average carbon chain length is increased. This achieves deep deoxygenation without consuming hydrogen. Furthermore, the increased carbon chain length raises the boiling point, making it easier to separate from unreacted raw materials or light components by distillation. This provides a well-defined intermediate for subsequent steps, thus achieving efficient removal of half of the oxygen atoms from the raw material without relying on external hydrogen. This reduces the absolute demand for hydrogen resources in the entire process, significantly decreasing the total amount of material and the total amount of oxygen atoms to be removed in subsequent hydrodeoxygenation treatments, directly alleviating the problem of high hydrogen consumption in the hydrodeoxygenation process. The n-alkane mixture obtained in step S32 is chemically stable and has a low oxygen content. It is mainly composed of carbon and hydrogen elements, which ensures the purity of the hydrocarbon composition and storage stability of the fuel product. This step marks the successful conversion of oxygen-containing intermediates into hydrocarbon compounds. It achieves efficient and low-hydrogen-consumption hydrogenation and deoxygenation of ketones under relatively mild conditions to generate pure n-alkanes. It also completes the qualitative change from oxygen-containing intermediates to saturated hydrocarbon molecules. Since the carbonyl group of ketone molecules is chemically more reactive than the carboxyl group of fatty acids and requires a lower hydrogenation activation energy, this process has lower hydrogen consumption and milder reaction conditions than direct hydrogenation and deoxygenation of fatty acids, and further achieves deoxygenation with a smaller hydrogen consumption.

[0042] It is important to emphasize that step S31 provides structural hydrogen consumption savings through hydrogen-free deoxygenation, changing the reaction route rather than saving hydrogen by optimizing hydrogenation conditions, thus eliminating the need for hydrogen required to directly remove these oxygen atoms; step S32 provides an efficient and economical terminal conversion, maximizing the reactivity advantage brought by step S31 while ensuring complete deoxygenation.

[0043] It is worth noting that in step S31, a fatty acid-catalyzed ketogenesis process is used to treat the fatty acid phase, achieving hydrogen-free deoxygenation and simultaneous carbon chain growth. During this process, the reaction temperature is controlled at 320-360℃ to provide sufficient activation energy for efficient decarboxylation coupling, while avoiding excessive cracking. A pressure of 0.5-1.0 MPa helps maintain sufficient contact and mass transfer of the reactants under suitable conditions, ensuring a sufficiently high concentration and probability of effective collisions and reactions of fatty acid molecules on the catalyst surface, thereby obtaining a high ketone yield. In step S32, the high reactivity of ketone molecules allows for a faster hydrogenation and deoxygenation process compared to direct lipid processing. The reaction is carried out at lower hydrogen pressure and temperature for fatty acids, which reduces the hydrogen consumption per unit product and the severity of equipment operating conditions, thereby achieving the technical effect of saving energy and costs. In this process, the reaction temperature is between 250-280℃, which is sufficient to efficiently activate the ketone carbonyl group for hydrogenation and dehydration, and can effectively suppress side reactions such as excessive cracking of C-C bonds. The hydrogen pressure is controlled at 3.0-4.0 MPa, which can ensure the hydrogen chemical potential and mass transfer motive force required for the reaction, promote the rapid completion of the hydrogenation step, and avoid the uneconomical equipment investment and energy consumption caused by excessive pressure. At the same time, the hydrogenation function of Pt in the catalyst and the weak acidity function of WO3-ZrO2 support achieve optimal synergy at this temperature and pressure.

[0044] In one specific embodiment, step S3 specifically includes: Step S31: The fatty acid phase is ketated with a zirconium oxide-based solid acid catalyst at 340℃ and 0.8MPa to obtain a ketone mixture; Step S32: The ketone mixture is reacted with bio-hydrogen and electrochemical hydrogen in the presence of a Pt / WO3–ZrO2 bifunctional catalyst at 265℃ and 3.5MPa for 5 hours to obtain a long-chain n-alkane mixture, and the molar ratio of the ketone mixture to the total molar ratio of bio-hydrogen and electrochemical hydrogen is 1:4.

[0045] Specifically, in step S4, the long-chain n-alkane mixture is subjected to hydroisomerization cracking to obtain an isoalkane mixture, which is then fractionated to obtain an alkane-based fuel composition.

[0046] Step S4 specifically includes the following steps: Step S41: The long-chain n-alkane mixture and the hydrogen obtained in step S2 are placed in a container containing a hydroisomerization cracking catalyst for hydroisomerization cracking treatment to obtain an isomerized alkane mixture C9-C. 17 ; In step S41, the hydroisomerization cracking treatment is carried out at a temperature of 320-360℃, a pressure of 5.0-7.0 MPa, and a weight hourly space velocity of 0.8-1.5 h⁻¹. -1The hydroisomerization catalyst is a Pt / USY molecular sieve catalyst, and the volume ratio of hydrogen gas to long-chain n-alkane mixture obtained in step S2 is (300-600):1. Step S42: The isoparaffin mixture is fractionated using a fractionating column. By controlling the temperatures at the top, side stream, and bottom of the column, a fraction with an initial boiling point ≥150℃ and a final boiling point ≤250℃ is collected from the side stream to obtain an alkane-based fuel composition; wherein the alkane-based fuel composition includes isoparaffins C9-C 17 .

[0047] In step S42, the aromatic content of the alkane-based fuel composition is <0.1%, and the freezing point is <-47°C.

[0048] It should be noted that in step S41, the metal sites (Pt) on the Pt / USY molecular sieve catalyst first catalyze the controlled dehydrogenation reaction of long-chain n-alkane molecules, generating the corresponding olefin intermediates. Subsequently, these olefin intermediates rapidly diffuse to the solid acid sites (USY molecular sieve) of the catalyst, where they form carbocations and undergo skeletal rearrangement and β-bond cleavage, simultaneously breaking the long carbon chains into medium-chain fragments and transforming their structure from straight-chain to branched. Finally, these medium-chain branched olefin intermediates migrate back to the metal sites to complete the hydrogenation reaction, generating stable medium-chain isoalkanes. This fundamentally changes the physicochemical properties of the feed, transforming it from a mixture of high-pour-point long-chain n-alkanes to a mixture of low-pour-point medium-chain isoalkanes, significantly improving fluidity. In this process, the synergistic effect of the hydrogenation-dehydrogenation active centers and the strongly acidic active centers is utilized, efficiently and selectively converting long-chain n-alkane molecules into medium-chain isoalkanes under a high hydrogen-affinity environment. Alkanes are cracked and isomerized into medium-chain branched alkanes with low pour points. Simultaneously, the cracking depth and product distribution are controlled by the shape selectivity of the catalyst, ensuring the yield of the target product. In step S42, due to the inherent differences in volatility (boiling point) between molecules with different carbon numbers in the isoalkane mixture, when the mixture enters the fractionation column, each component undergoes multiple vaporization and condensation processes within the temperature gradient field established from the bottom to the top of the column. During this process, lighter components with lower boiling points are more easily vaporized and enriched at the top of the column, while heavier components with higher boiling points are more enriched in liquid form at the bottom. By controlling the temperature, pressure, and reflux ratio within the column, and by setting a side stream at the tray corresponding to the target boiling range, the vapor enriched there, composed entirely of the target isoalkane, can be continuously condensed and collected, achieving clear segmentation of a single feed and producing three products with different boiling ranges. Furthermore, fractionation via a fractionation column is well known to those skilled in the art and will not be described further in this embodiment.

[0049] It is known that the mixture of isoparaffins C9-C 17The alkane molecules contained within have a highly branched chemical structure, giving the final product excellent low-temperature fluidity. The straight-chain alkane molecules have a regular structure and strong intermolecular forces, making them easy to arrange into a crystal structure at higher temperatures, thus causing the fuel to solidify. In contrast, the branched-chain alkane molecules, due to their steric hindrance, severely hinder the regular stacking of molecules and the formation of crystal lattices, thus exhibiting a sharp drop in freezing point or freezing point. This ensures that the final synthesized product meets the physicochemical requirements for use in harsh high-altitude and low-temperature environments. Furthermore, step S42, through the distillation range and clear component segmentation, precisely extracts the final product, whose initial boiling point, final boiling point, and the entire distillation temperature profile are strictly limited within the range specified by the ASTM D7566 standard, ensuring that the final product has highly uniform and predictable evaporation characteristics and combustion performance.

[0050] Understandably, the hydroisomerization in step S41 improves the low-temperature performance of the fuel, transforming it from the inherently easily solidified state of long-chain alkanes into a functional fluid that can remain liquid at low temperatures. This solves the problem of physical property defects in the products caused by the long-chain intermediates generated in the above steps, ensuring that the key performance of the final product is consistent with that of traditional products. Step S42, through the separation and purification of the hydroisomerization products, yields a target fuel with a single component and stable performance, achieving standardized preparation of the target fuel.

[0051] It is worth noting that step S41, using a dedicated catalyst at specific temperature, pressure, and hydrogen-to-hydrogen ratio, efficiently cracks and isomerizes the long-chain n-alkanes obtained in the previous step into medium-chain branched alkanes. This reduces the pour point of the material while ensuring high yield, thus solving the problem of low-temperature applicability of the fuel product. Step S42 employs a fractionation process to precisely cut the mixture after hydroisomerization cracking into fractions with different boiling ranges, efficiently and accurately separating C9-C fractions from the complex components that fully conform to the final product. 17 The target fraction is obtained while simultaneously separating byproducts. Furthermore, during the fractionation process, light naphtha components with predominantly C5-C8 carbon numbers are collected from the top of the fractionation column, while components with carbon numbers greater than C5 are collected from the bottom. 17 The heavy diesel oil component.

[0052] In a specific embodiment, step S4 specifically includes: step S41, mixing the long-chain n-alkane mixture with the hydrogen obtained in step S2, and then, in the presence of a Pt / USY molecular sieve catalyst, at 340°C, 6.0 MPa, and a weight hourly space velocity (WHSV) of 1.0 h⁻¹. -1 Under certain conditions, hydroisomerization cracking is carried out to obtain an isoalkane mixture; in step S42, the isoalkane mixture is fractionated in a fractionating tower, and the fraction with a distillation range of 150-250℃ is collected from the side stream to obtain an alkane-based fuel composition, and the volume ratio of hydrogen to long-chain n-alkane mixture is 500:1.

[0053] The following is a comparison of the preparation method of Example 1 with the data of the traditional HEFA-SP process, as shown in Tables 1 and 2: Table 1 Table 2 As can be seen from Tables 1 and 2, this invention demonstrates significant advantages in core indicators such as theoretical hydrogen consumption, operational severity, hydrogen self-sufficiency rate, glycerol value enhancement, and environmental friendliness, effectively solving the problem of high hydrogen consumption.

[0054] Example 2: This embodiment provides an alkane-based fuel composition for small aircraft, which is prepared using the preparation method described in Example 1.

[0055] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An alkane-based fuel composition for small aircraft and a method for preparing the same, characterized in that, The preparation method includes the following steps: Step S1: Hydrolyze the mixed oil containing triglycerides and free fatty acids to obtain a fatty acid phase and a glycerol aqueous solution phase after the treatment is completed. Step S2: The glycerol aqueous solution phase is fermented with hydrogen-producing strain to obtain bio-hydrogen and fermentation broth containing volatile fatty acids. The fermentation broth is then purified and electrolyzed to obtain electrochemical hydrogen. Step S3: The fatty acid phase is reacted with a zirconium oxide-based solid acid catalyst to obtain a ketone mixture, which is then subjected to hydrodeoxygenation treatment with the biohydrogen and electrochemical hydrogen obtained in step S2 to obtain a long-chain n-alkanes mixture. Step S4: After hydroisomerization of the long-chain n-alkane mixture, an isoalkane mixture is obtained, which is then fractionated to obtain an alkane-based fuel composition.

2. The alkane-based fuel composition for small aircraft and its preparation method according to claim 1, characterized in that, Step S1 specifically includes the following steps: The mixed oils were reacted with deionized water at 180-220℃ and 1.5-2.5 MPa under weakly acidic conditions for 1-3 hours to obtain a fatty acid phase and a glycerol aqueous solution phase; wherein the glycerol aqueous solution phase includes glycerol (glycerol), and the fatty acid phase includes free fatty acid C. 12 -C 18 .

3. The alkane-based fuel composition for small aircraft and its preparation method according to claim 2, characterized in that, The mixed oil is obtained from waste oil through coarse filtration, solidification, and preliminary desalination.

4. The alkane-based fuel composition for small aircraft and its preparation method according to claim 1, characterized in that, Step S2 specifically includes the following steps: Step S21: After removing impurities from the glycerol aqueous solution phase, adjust its pH to obtain the glycerol aqueous solution substrate; Step S22: The glycerol aqueous solution substrate and the hydrogen-producing strain are fermented in an anaerobic fermentation reactor at a first temperature to obtain bio-hydrogen, carbon dioxide and fermentation broth including volatile fatty acids. Step S23: The fermentation broth is subjected to centrifugation, ultrafiltration and electrodialysis desalination in sequence to obtain a purified solution. The purified solution is used as the anode feed solution and deionized water is used as the cathode feed solution. The two solutions are sent to the anode chamber and cathode chamber of the anion exchange membrane electrolysis cell for electrolysis to obtain electrochemical hydrogen and carbon dioxide.

5. The alkane-based fuel composition for small aircraft and its preparation method according to claim 4, characterized in that, In step S21, the pH value after pH adjustment is 6.5-7.5; In step S22, the first temperature is 30-40℃, the fermentation reaction time is 24-48h, the inoculation amount of the hydrogen-producing strain is 5-20 vol% of the fermentation liquid volume, the total concentration of volatile fatty acids in the purified liquid is 5-50 g / L, the volume ratio of biological hydrogen to carbon dioxide is (2-4):(1-3), and the hydrogen-producing strain is hydrogen-producing Enterobacter. In step S23, the temperature of the anion exchange membrane electrolytic cell is 50-70℃, the cell voltage is 1.8-2.5V, and the operating current density is 100-400mA / cm². 2 .

6. The alkane-based fuel composition for small aircraft and its preparation method according to claim 1, characterized in that, Step S3 specifically includes the following steps: Step S31: After pretreating the fatty acid phase, a ketation reaction is carried out with a zirconium oxide-based solid acid catalyst to obtain a ketone mixture, carbon dioxide, and water vapor; wherein, the ketone mixture includes long-chain symmetrical ketone C. 31 -C 35 ; Step S32: The ketone mixture, bio-hydrogen, and electrochemical hydrogen are placed in a container equipped with a bifunctional catalyst for hydrogenation reaction. After the reaction is completed, a mixture of long-chain n-alkanes is obtained; wherein, the long-chain n-alkanes mixture includes n-alkanes C 30 -C 34 With water.

7. The alkane-based fuel composition for small aircraft and its preparation method according to claim 6, characterized in that, In step S31, the ketation reaction is carried out at a temperature of 320-360°C and a pressure of 0.5-1.0 MPa. In step S32, the catalyst is a Pt / WO3–ZrO2 bifunctional catalyst, the hydrogenation reaction temperature is 250-280℃, the pressure is 3.0-4.0MPa, and the time is 4-6h, and the molar ratio of the ketone mixture to the total molar amount of biological hydrogen and electrochemical hydrogen is 1:(3-5).

8. The alkane-based fuel composition for small aircraft and its preparation method according to claim 1, characterized in that, Step S4 specifically includes the following steps: Step S41: The long-chain n-alkane mixture and the hydrogen obtained in step S2 are placed in a container containing a hydroisomerization cracking catalyst for hydroisomerization cracking treatment to obtain an isomerized alkane mixture C9-C. 17 ; Step S42: The isoparaffin mixture is fractionated using a fractionating column. By controlling the temperatures at the top, side stream, and bottom of the column, a fraction with an initial boiling point ≥150℃ and a final boiling point ≤250℃ is collected from the side stream to obtain an alkane-based fuel composition; wherein the alkane-based fuel composition includes isoparaffins C9-C 17 .

9. The alkane-based fuel composition for small aircraft and its preparation method according to claim 8, characterized in that, In step S41, the hydroisomerization cracking treatment is carried out at a temperature of 320-360℃, a pressure of 5.0-7.0 MPa, and a weight hourly space velocity of 0.8-1.5 h⁻¹. -1 The hydroisomerization catalyst is a Pt / USY molecular sieve catalyst, and the volume ratio of hydrogen gas to long-chain n-alkane mixture obtained in step S2 is (300-600):

1. In step S42, the aromatic hydrocarbon content of the alkane-based fuel composition is <0.1%, and the freezing point is <-47°C.

10. An alkane-based fuel composition for small aircraft, characterized in that, The alkane-based fuel composition for small aircraft is prepared using the preparation method described in claims 1-9.

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