A method for producing high energy density space fuels from aromatics

Abstract

This invention discloses a method for preparing high-energy-density aerospace fuel from aromatics, belonging to the field of aerospace fuel preparation technology. The method uses aromatics and terpenoids as raw materials. First, an alkylation intermediate with a strained tricyclic skeleton is selectively constructed via cycloalkylation under the action of a Lewis acid catalyst. Then, hydrogenation saturation is performed on a supported noble metal catalyst to obtain a high-energy-density aerospace fuel mainly composed of C16-C18 polycyclic alkanes. The aromatics are one or more selected from toluene, benzene, ethylbenzene, propylbenzene, and xylene, and the terpenoids are one or more selected from 1,4-cineole, 1,8-cineole, terpinene, terpinene, α-pinene, β-pinene, and limonene. The density of the fuel obtained by this invention is not less than 0.90 g / cm³. 3 With a volumetric calorific value of not less than 38.0 MJ / L and a freezing point of not more than -55 ℃, it has the potential to replace traditional petroleum-based high-energy-density aerospace fuels.

Description

Technical Field

[0001] This invention belongs to the field of aerospace fuel preparation technology, specifically relating to a method for preparing high-energy-density aerospace fuel from aromatics. Background Technology

[0002] High-energy-density fuels (typically defined as fuels with a density greater than 0.90 g / mL and a volumetric calorific value greater than 38.0 MJ / L) are key materials for the propulsion systems of advanced aerospace vehicles. Given limited fuel tank volume, the fuel's density and volumetric calorific value directly determine the vehicle's range, speed, and payload. Traditional high-energy-density fuels, such as JP-10 and RJ-4, are produced from petroleum-based cyclopentadiene or methylcyclopentadiene via Diels-Alder cycloaddition, hydrogenation, and isomerization reactions, relying on non-renewable fossil resources. Under the dual constraints of energy security and carbon neutrality goals, developing new routes for producing high-energy-density aerospace fuels using renewable carbon resources is of great significance.

[0003] Terpenes are widely found in natural plant essential oils such as eucalyptus oil, turpentine oil, and citrus peel oil. Their molecules contain monocyclic or bicyclic skeletons, making them ideal renewable platform molecules for constructing high-density polycyclic alkane fuels. Existing technologies have reported methods for preparing terpenoid-based fuels using acid-catalyzed polymerization (dimerization)-hydroisomerization. However, the biomass-based dimer fuels obtained by this method have high viscosity and insufficient low-temperature fluidity, making their overall performance insufficient to meet the requirements of advanced aerospace vehicles. Furthermore, their performance is still inferior to petroleum-based fuels JP-10 and RJ-4.

[0004] To balance fuel density and low-temperature performance, some theoretical approaches have proposed linking terpenes with aromatics through ring-enlargement coupling. However, the presence of multiple reaction sites, such as ether bonds and carbon-carbon double bonds, in terpenes leads to intense competition between alkylation, polymerization, cracking, and ring-enlargement pathways during reactions with aromatics, making selective ring-enlargement and precise construction of polycyclic skeletons extremely difficult. Therefore, developing catalytic systems and processes capable of selectively catalyzing the ring-enlargement coupling of terpenes with aromatics is a crucial technical challenge for achieving high-energy-density space fuels from aromatics. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high-energy-density aerospace fuel from aromatics. This method can not only effectively avoid the excessive polymerization of terpenoid molecules during the reaction process, but also significantly improve the selectivity of ring-enhancing coupling, thereby obtaining high-performance aerospace fuel with high density and low freezing point.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing high-energy-density aerospace fuel from aromatics includes the following steps: (1) Aromatic hydrocarbons and terpenoids are subjected to cycloalkylation reaction under the action of Lewis acid catalyst to obtain an alkylation intermediate containing a tricyclic skeleton structure; wherein the aromatic hydrocarbon is one or more of toluene, benzene, ethylbenzene, propylbenzene and o-xylene, and the terpenoid is one or more of eucalyptus oil, 1,4-cineole, 1,8-cineole, terpinene, terpinene, α-pinene, β-pinene and limonene; (2) The cycloalkylated intermediate obtained in step (1) is subjected to hydrogenation reaction under the action of a hydrogenation catalyst to obtain the high energy density aerospace fuel.

[0007] Preferably, the Lewis acid catalyst in step (1) is selected from one or more of the following catalysts: AlCl3, FeCl3, Sc(OTf)3, Fe(OTf)3, Al(OTf)3, ZnCl2, Zn(OTf)2, CeCl3, La(OTf)3; AlCl3 / [Bmim]Cl, AlCl3 / [Emim]Cl, AlCl3 / Urea; the amount of the Lewis acid catalyst is 10%-100% of the mass of the terpene compound, preferably 50%.

[0008] Preferably, the molar ratio of the terpene compound to the aromatic hydrocarbon in step (1) is 1:1 to 1:40, and more preferably 1:5.

[0009] Preferably, the temperature of the cycloalkylation reaction in step (1) is 60-180 °C; and the reaction time is 3-24 h.

[0010] Preferably, the hydrogenation catalyst in step (2) is one of Pt / C, Pd / C, Ru / C, Ir / C, Rh / C, Co / C, Ni / C, Fe / C, Raney Ni, Raney Co, and Raney Cu; the amount of hydrogenation catalyst used is 1%-50% of the mass of the alkylation intermediate, preferably 10%.

[0011] Preferably, the temperature of the hydrogenation reaction in step (2) is 100-240 °C, the hydrogen pressure is 1.0-6.0 MPa, and the reaction time is 6-24 h.

[0012] Preferably, the solvent used in the hydrogenation reaction in step (2) is one of cyclohexane, n-hexane, n-octane, ethyl acetate, ethanol, methanol, isopropanol, tetrahydrofuran, or 2-methyltetrahydrofuran, and the substrate concentration range is 0.1-30 mol / L.

[0013] To achieve the aforementioned objectives, this invention also provides a high-energy-density aerospace fuel prepared by the above method, wherein the density of the high-energy-density aerospace fuel is not less than 0.90 g / cm³. 3Its volumetric calorific value is not less than 38.0 MJ / L, and its freezing point is not higher than -55 ℃.

[0014] The reaction mechanism of this invention is as follows (taking eucalyptol and toluene as an example): 1,4-Cephalophyllin or 1,8-Cephalophyllin, under acidic conditions, undergoes ether oxygen activation and CO bond cleavage to generate 4-terpineol and α-terpineol, respectively. Subsequently, acid-catalyzed dehydration generates conjugated dienes such as limonene, α-terpinene, and terpinene oleene. These conjugated dienes can interconvert under acid catalysis. Limonene, α-terpinene, and terpinene oleene undergo Friedel-Crafts alkylation reactions with equivalent amounts of aromatic hydrocarbons to generate alkylation intermediates, which then undergo intramolecular cyclization to form strained tricycloadditions. Finally, hydrogenation saturation yields polycyclic alkane fuels. Bicyclic terpenes such as α-pinene and β-pinene can isomerize under acidic conditions to generate the aforementioned conjugated diene intermediates. α-terpinene, terpinene oleene, and limonene are themselves the aforementioned conjugated dienes; therefore, all of the above terpenes can be directly used as raw materials for this invention.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, aromatics can be obtained by petroleum catalytic reforming, coal-based naphtha separation, or by biomass pyrolysis or biomass-based platform compounds (such as 2-methylfuran and ethylene via Diels-Alder cycloaddition), and have the potential to be supplied by the whole biomass route; this invention uses terpenoids and aromatics as raw materials, both of which can be derived from biomass, making the route sustainable and helping to reduce dependence on fossil resources; (2) The present invention uses Lewis acid-catalyzed cycloalkylation reaction to selectively construct a tricyclic framework, with a cycloalkylation intermediate yield of 75% and a total two-step yield of 68%; (3) The Pd / C hydrogenation catalyst used in this invention has good stability. Its activity only decreases slightly after four consecutive cycles, and it has good prospects for industrial application. (4) The high-energy-density aerospace fuel prepared by this invention has a density of 0.931 g / cm³. 3 Its volumetric calorific value reaches 40.8 MJ / L, and its freezing point is as low as -65°C. o C. With a freezing point and overall performance superior to petroleum-based RJ-4 fuel, it has the potential to replace traditional petroleum-based high-energy-density aerospace fuels. Attached Figure Description

[0016] Figure 1 This is the GC spectrum of the tricyclic alkylation intermediate 3, the product of the first step reaction in Example 1; Figure 2 The GC-MS spectrum of the tricyclic alkylation intermediate 3, the product of the first step reaction in Example 1; Figure 3 The GC-MS spectrum of tricycloalkane 9, the product of the second step reaction in Example 1; Figure 4 The 1H NMR spectrum of the tricycloalkylated intermediate 3, the product of the first step reaction in Example 1; Figure 5 The 1H NMR spectrum of the tricycloalkylated intermediate 7, the product of the first step reaction in Example 7; Figure 6 The 1H NMR spectrum of the tricycloalkylated intermediate 8, the product of the first step reaction in Example 8; Figure 7 The mechanism of the cycloalkylation reaction between toluene and 1,4-cineole; Figure 8 A schematic diagram of the preparation of high-energy-density fuels from toluene and eucalyptol. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto. In the following embodiments, the product composition was analyzed by gas chromatography-mass spectrometry (GC-MS), and the yield was determined by gas chromatography (GC) internal standard method; the fuel density was determined according to GB / T 1884, the freezing point according to GB / T 2430, and the calorific value according to GB / T 384. In the embodiments, unless otherwise stated, all reagents used can be purchased commercially or obtained in accordance with known literature.

[0018] Example 1

[0019] like Figure 7 and Figure 8 As shown, a method for preparing high-energy-density aerospace fuel from aromatics includes the following steps: (1) Cycloalkylation reaction: 1.00 g (6.5 mmol) of 1,4-cineole, 2.99 g (32.5 mmol, molar ratio of 1,4-cineole to toluene 1:5), and 0.50 g (50% of the mass of 1,4-cineole) were added to the reactor and stirred until homogeneous. The mixture was then reacted at 140 °C for 9 h. After the reaction was completed, the mixture was quenched, separated, and excess toluene was removed to obtain alkylation intermediate 3 containing a tricyclic framework, with a yield of 75%. The GC spectrum, GC-MS spectrum, and 1H NMR spectrum of alkylation intermediate 3 are shown below. Figure 1 , Figure 2 and Figure 4 As shown in the figure, this embodiment successfully achieved the toluene cycloalkylation reaction, yielding intermediate 3.

[0020] (2) Hydrogenation reaction: 0.30 g of the above alkylation intermediate, 0.03 g of Pd / C catalyst (Pd loading of 5%), and 2.0 mL of cyclohexane were added to a high-pressure reactor. Hydrogen gas was introduced to a pressure of 2.0 MPa, and the reaction was carried out at 200 °C for 10 h. After the reaction, the catalyst was separated by centrifugation and the solvent was removed to obtain high-energy-density aerospace fuel 9, which is mainly composed of C17 polycyclic alkanes. The overall yield of the two steps was 68%. The GC-MS spectrum of high-energy-density aerospace fuel 9 is shown below. Figure 3 As shown in the figure, this embodiment successfully achieved the hydrogenation saturation reaction and obtained polycyclic fuel 9.

[0021] The density of the fuel obtained in Example 1 was measured to be 0.931 g / cm³. 3 It has a volumetric calorific value of 40.8 MJ / L, a freezing point of -65 ℃, and a kinematic viscosity of 44.7 cSt at room temperature.

[0022] Example 2

[0023] Using the same process conditions as in Example 1, except that the terpene compound raw material 1,4-cineole was replaced with 1,8-cineole, the results were comparable to those in Example 1: an alkylation intermediate containing a tricyclic skeleton structure was obtained, which, after hydrogenation, yielded a high-energy-density aerospace fuel mainly composed of C17 polycyclic alkanes. The intermediate yield, the total yield of the two steps, and the density, volumetric calorific value, and freezing point of the fuel were all comparable to those in Example 1.

[0024] Example 3

[0025] Using the same process conditions as in Example 1, except that the terpene compound feedstock was replaced with eucalyptus oil (the main components of which are 1,4-cineole and 1,8-cineole), results comparable to those in Example 1 were obtained: an alkylated intermediate containing a tricyclic skeleton structure was obtained, which, after hydrogenation, yielded a high-energy-density aerospace fuel mainly composed of C17 polycyclic alkanes. The intermediate yield, the total yield of the two steps, and the density, volumetric calorific value, and freezing point of the fuel were all comparable to those in Example 1.

[0026] Example 4

[0027] Using the same process conditions as in Example 1, except that the terpene compound feedstock was replaced with limonene. Limonene is one of the conjugated diene intermediates in the cycloalkylation reaction of this invention. It can directly undergo Friedel-Crafts alkylation and intramolecular cyclization with toluene to obtain an alkylation intermediate with a tricyclic skeleton structure. After hydrogenation, a high-energy-density aerospace fuel mainly composed of C17 polycyclic alkanes is obtained. The overall yield of the two steps is 45%. This is because the dimerization reaction of limonene is also unavoidable, resulting in a relatively low yield of the target product.

[0028] Example 5

[0029] Using the same process conditions as in Example 4, except that the terpene compound raw material was replaced with terpene oil olefin, the same results as in Example 4 were obtained.

[0030] Example 6

[0031] Using the same process conditions as in Example 1, except that the terpene compound feedstock was replaced with α-pinene, α-pinene was isomerized under acidic conditions to generate a conjugated diene intermediate, which then underwent alkylation and intramolecular cyclization with toluene. After hydrogenation, a high-energy-density aerospace fuel mainly composed of C17 polycyclic alkanes was obtained. The overall yield of the two steps was also reduced to 40%, with pinene dimerization being the main side reaction.

[0032] Example 7

[0033] Using the same process conditions as in Example 1, except that the aromatic feedstock was replaced with benzene, 1,4-cineole and benzene could also undergo successful cycloalkylation to obtain product 7. The 1H NMR spectrum of product 7 is shown below. Figure 5 As shown in the figure, this embodiment successfully achieved the cycloalkylation reaction of benzene, and obtained the target alkylated product 7.

[0034] Product 7, after hydrogenation, yielded a high-energy-density aerospace fuel primarily composed of C16 polycyclic alkanes, with an overall two-step yield of 70%. The fuel had a density of 0.936 g / cm³. 3 It has a volumetric calorific value of 41.0 MJ / L, a freezing point of -60 ℃, and a kinematic viscosity of 68.2 cSt at room temperature.

[0035] Example 8

[0036] Using the same process conditions as in Example 1, except that the aromatic feedstock was replaced with ethylbenzene, 1,4-cineole and ethylbenzene could also undergo successful cycloalkylation to obtain product 8. The 1H NMR spectrum of product 8 is shown below. Figure 6 As shown in the figure, this embodiment successfully achieved the cycloalkylation reaction of ethylbenzene, and obtained the target alkylated product 8.

[0037] Product 8, after hydrogenation, yielded a high-energy-density aerospace fuel primarily composed of C18 cycloalkanes, with an overall two-step yield of 76% and a density of 0.941 g / cm³. 3 It has a volumetric calorific value of 42.0 MJ / L, a freezing point of -71 ℃, and a kinematic viscosity of 30.5 cSt at room temperature.

[0038] Example 9

[0039] Using the same process conditions as in Example 1, except that the aromatic feedstock was replaced with o-xylene, 1,4-cineole and o-xylene could also undergo successful cycloalkylation. The resulting product, after hydrogenation, yielded a high-energy-density aerospace fuel mainly composed of C18 polycyclic alkanes. The overall yield of the two steps reached 68%, and the density of the fuel was 0.928 g / cm³. 3 It has a volumetric calorific value of 41.2 MJ / L, a freezing point of -69 ℃, and a kinematic viscosity of 37.4 cSt at room temperature.

[0040] Example 10

[0041] Using the same process conditions as in Example 1, the terpene feedstock was replaced with a mixture of 1,4-cineole and limonene (molar ratio 1:1), and the aromatic feedstock was replaced with a mixture of toluene and benzene (molar ratio 1:1). After cycloalkylation and hydrogenation, a high-energy-density aerospace fuel mainly composed of C17 and C16 polycyclic alkanes was obtained, with a density of 0.920 g / cm³. 3 It has a volumetric calorific value of 39.8 MJ / L, a freezing point of -56.0 ℃, and a kinematic viscosity of 145.4 cSt at room temperature.

[0042] Example 11

[0043] The Pd / C catalyst recovered in Example 1 was investigated for recycling: the catalyst after centrifugation was used directly in the next batch of hydrogenation reaction without regeneration. After four consecutive cycles, the yield of polycyclic alkanes only decreased slightly, indicating that the Pd / C catalyst has good reusability.

[0044] Example 12

[0045] Using the same process conditions as in step (1) of Example 1, except that the catalyst was replaced with Sc(OTf)3 (at 20% of the mass of 1,4-eucalyptus leaves). The results showed that the catalyst had certain activity, with a target cycloalkylation product yield of 30%, but also a relatively high yield of terpene polymerization products. This indicates that excessively strong Lewis acids have poor selectivity and promote terpene polymerization side reactions; moderately strong Lewis acids, such as AlCl3, are the preferred catalyst.

[0046] Example 13

[0047] Using the same process conditions as step (1) in Example 1, only the amount of AlCl3 was increased to 70% of the 1,4-eucalyptus leaf mass. The results showed that the yield of the alkylation intermediate decreased to 40% due to the increased viscosity of the system leading to impaired mass transfer. This indicates that too much AlCl3 is not conducive to the reaction, and a 50% amount is more effective.

[0048] Example 14

[0049] Using the same process conditions as step (1) of Example 1, only the molar ratio of 1,4-cineole to toluene was adjusted to 1:10. The results showed that excess toluene promoted competitive dehydration and isomerization side reactions, resulting in a decrease in the yield of the cycloalkylation product to 60%. This indicates that excessive toluene is not suitable; too much toluene will solvate with the catalyst AlCl3, promoting the terpene isomerization side reaction. Therefore, a molar ratio of 1,4-cineole to toluene of 1:5 is more effective.

[0050] Example 15

[0051] Using the same process conditions as step (2) of Example 1 (220 °C, 12 h), only the hydrogenation catalysts were replaced with Rh / C, Ru / C, Pt / C, and Raney nickel, respectively. The results showed that the yields of polycyclic alkanes obtained by Rh / C and Ru / C catalysts were both 56%, while the catalytic activity of Pt / C (78%) and Raney nickel (78%) was significantly reduced, both being significantly lower than that of the Pd / C catalyst (91%). This indicates that the Pd / C catalyst has the best saturation capacity for benzene ring hydrogenation and is the optimal hydrogenation catalyst.

[0052] Comparative Example Using the same process conditions as in step (1) of Example 1, except that the catalyst was replaced with a strongly acidic cation exchange resin, Amberlyst-15 or Nafion (at 20% of the weight of 1,4-eucalyptus leaves). The results showed that the terpene carbocation intermediate mainly formed dimers through dimerization, and the target tricycloaddition was not obtained. This indicates that Bronsted acids preferentially promote the dimerization of terpenes, while Lewis acids (AlCl3) can promote the cycloalkylation reaction between toluene and terpenes.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-energy-density aerospace fuel from aromatics, characterized in that, Includes the following steps: (1) Aromatic hydrocarbons and terpenoids are subjected to cycloalkylation reaction under the action of Lewis acid catalyst to obtain an alkylation intermediate containing a tricyclic skeleton structure; wherein the aromatic hydrocarbon is one or more of toluene, benzene, ethylbenzene, propylbenzene and o-xylene, and the terpenoid is one or more of eucalyptus oil, 1,4-cineole, 1,8-cineole, terpinene, terpinene, α-pinene, β-pinene and limonene; (2) The cycloalkylated intermediate obtained in step (1) is subjected to hydrogenation reaction under the action of a hydrogenation catalyst to obtain the high energy density aerospace fuel.

2. The method for preparing high-energy-density aerospace fuel from aromatics according to claim 1, characterized in that, The Lewis acid catalyst in step (1) is selected from one or more of the following catalysts: AlCl3, FeCl3, Sc(OTf)3, Fe(OTf)3, Al(OTf)3, ZnCl2, Zn(OTf)2, CeCl3, La(OTf)3; AlCl3 / [Bmim]Cl, AlCl3 / [Emim]Cl, AlCl3 / Urea; the amount of the Lewis acid catalyst is 10%-100% of the mass of the terpene compound.

3. The method for preparing high-energy-density aerospace fuel from aromatics according to claim 1, characterized in that, In step (1), the molar ratio of the terpene compound to the aromatic hydrocarbon is 1:1 to 1:

40.

4. A method for preparing high-energy-density aerospace fuel from aromatics according to claim 2 or 3, characterized in that, In step (1), the amount of Lewis acid catalyst used is 50% of the mass of the terpene compound; the molar ratio of the terpene compound to the aromatic hydrocarbon is 1:

5.

5. The method for preparing high-energy-density aerospace fuel from aromatics according to claim 1, characterized in that, The temperature of the cycloalkylation reaction in step (1) is 60-180 °C; the reaction time is 3-24 h.

6. The method for preparing high-energy-density aerospace fuel from aromatics according to claim 1, characterized in that, The hydrogenation catalyst in step (2) is one of Pt / C, Pd / C, Ru / C, Ir / C, Rh / C, Co / C, Ni / C, Fe / C, Raney Ni, RaneyCo, and Raney Cu; the amount of hydrogenation catalyst used is 1%-50% of the mass of the alkylation intermediate.

7. A method for preparing high-energy-density aerospace fuel from aromatics according to claim 6, characterized in that, The amount of hydrogenation catalyst used in step (2) is 10% of the mass of the alkylation intermediate.

8. A method for preparing high-energy-density aerospace fuel from aromatics according to claim 1, characterized in that, The hydrogenation reaction in step (2) is carried out at a temperature of 100-240 °C, a hydrogen pressure of 1.0-6.0 MPa, and a reaction time of 6-24 h.

9. A method for preparing high-energy-density aerospace fuel from aromatics according to claim 1, characterized in that, The solvent used in the hydrogenation reaction in step (2) is one of cyclohexane, n-hexane, n-octane, ethyl acetate, ethanol, methanol, isopropanol, tetrahydrofuran, or 2-methyltetrahydrofuran, and the substrate concentration range is 0.1-30 mol / L.

10. The high-energy-density aerospace fuel prepared by the method according to any one of claims 1-9, characterized in that, The density of the high-energy-density aerospace fuel is not less than 0.90 g / cm³. 3 Its volumetric calorific value is not less than 38.0 MJ / L, and its freezing point is not higher than -55 ℃.

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