Preparation method and application of coal-based high-energy-density fuel

Abstract

The invention belongs to the technical field of aerospace fuels, and particularly relates to a preparation method and application of a coal-based high-energy-density fuel, and the preparation method comprises the following three steps: firstly, analyzing the content of aromatic hydrocarbon in a coal-based liquid product, and determining the molar weight of the aromatic hydrocarbon; secondly, adding cycloolefin or cycloalcohol according to a molar ratio of 1: (1-1.2), carrying out alkylation reaction under the action of an acid catalyst, and carrying out solid-liquid separation and reduced pressure distillation to obtain an alkylated product; and finally, adding a supported noble metal catalyst for hydrogenation saturation reaction, and separating impurities to obtain the high-energy-density fuel. The coal-based fuel prepared by the method disclosed by the invention not only realizes a major breakthrough from complex separation to integrated reaction in process, but also shows high density, high calorific value and high thermal oxidation stability, has proper viscosity and freezing point performance, and can meet strict requirements of advanced aircrafts under extreme working conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of aerospace fuel, and in particular relates to a preparation method and application of a coal-based high-energy-density fuel. Background Art

[0002] With the rapid development of aerospace technology and aircraft, the demand for fuel energy density continues to increase. Fuel energy density directly determines the amount of heat released per unit volume of combustion. Therefore, it is necessary to simultaneously improve both fuel density and mass calorific value to balance the dual requirements of aircraft size constraints and high energy output. Furthermore, aerospace fuels must exhibit excellent thermal and oxidative stability and low-temperature performance to meet the stringent requirements of advanced aircraft operating under extreme operating conditions.

[0003] Currently, high-energy-density fuels mainly rely on petroleum resources. However, my country is relatively short of petroleum resources, while coal resources are abundant. Therefore, the production of high-energy-density fuels from coal has become a research hotspot. In the existing technology, the method of obtaining fuels by hydrorefining coal-based liquid products (such as coal-based diesel, coal-based kerosene, coal tar, and coal direct liquefaction oil) has been widely explored, but the density of the fuels produced by these methods can usually only reach about 0.85g / cm 3 , which cannot meet the requirements of advanced aircraft for high energy density of fuel.

[0004] In order to improve fuel density, the existing technology mostly adopts the aromatic alkylation reaction of coal-based liquid products, and improves fuel density by introducing new ring structures and increasing the degree of cyclization of molecules. However, due to the complex composition of coal-based liquid products, the traditional process adopts the method of first separating the components of coal-based liquid products, extracting light aromatics, and then alkylating the obtained light aromatics to introduce new ring structures. Although this step can reduce the interference of other complex components in the reaction to a certain extent, the light aromatics obtained after separation still contain polycyclic aromatic hydrocarbons (aromatic hydrocarbons with a ring number ≥ 2), and these polycyclic aromatic hydrocarbons will cause diffusion and mass transfer restrictions in the subsequent alkylation reaction. In addition, the catalysts used in the alkylation process of the traditional process, such as strong acids such as aluminum chloride and sulfuric acid or acidic molecular sieves with a small pore size (about 0.5nm) (such as ZSM-5, ZSM-35, ZSM-48, MCM-22), generally have low selectivity, easy to coke and carbon deposition, etc., which ultimately leads to low reaction conversion rate and difficulty in meeting the expected high energy density fuel requirements.

[0005] Therefore, there is an urgent need for a method that can directly utilize a coal-based liquid product mixture system to prepare a fuel with high energy density, excellent thermal oxidation stability and low-temperature performance.

[0006] In order to solve the above problems, the present invention is proposed. Summary of the Invention

[0007] In response to the problems of cumbersome steps, limited mass transfer and low catalytic selectivity in existing processes, the present invention aims to provide a preparation method and application of coal-based high-energy density fuel. This method directly subjects the coal-based liquid product to an alkylation reaction, introduces alkylating functional groups such as cycloolefins or cycloalcohols, and uses HY molecular sieves or USY molecular sieves with a FAU structure or their modified molecular sieves or metal-modified phosphotungstic acid (wherein phosphotungstic acid can be abbreviated as HPW) as a catalyst to cause the coal-based aromatic hydrocarbon molecules to undergo a directed alkylation reaction to adjust the coal-based molecular structure, and finally undergoes a complete hydrogenation saturation reaction. The coal-based fuel prepared by the method of the present invention not only achieves a major breakthrough in the process from complex separation to integrated reaction, but also exhibits high density, high calorific value, high thermal oxidation stability, and has suitable viscosity and freezing point performance, which can meet the stringent requirements of advanced aircraft under extreme working conditions.

[0008] The present invention adopts the following technical solutions:

[0009] A first aspect of the present invention provides a method for preparing a coal-based high energy density fuel, the method comprising the following steps:

[0010] Step (1), testing the molar amount of aromatics in the coal-based liquid product:

[0011] Step (2), carrying out an alkylation reaction between the coal-based liquid product and a cycloolefin or cycloalcohol having a molar ratio of 1:1-1.2 to the aromatic hydrocarbon in the coal-based liquid product under an inert atmosphere and catalyzed by a large-pore acidic catalyst, after which the catalyst and insoluble solid impurities are removed, followed by vacuum distillation to selectively remove light components, and collecting non-volatile components to obtain an alkylated product;

[0012] Step (3), subjecting the collected alkylation product and hydrogen to a hydrogenation saturation reaction under the catalysis of a supported noble metal, and after the reaction is completed, removing the catalyst and solid impurities to obtain the coal-based high energy density fuel.

[0013] Preferably, the amount of the acidic catalyst added in step (2) is 10-20 wt% of the coal-based liquid product, and the reaction time is 1-2 h under the conditions of a reaction temperature of 180-200° C. and a reaction pressure of 4 MPa;

[0014] The reduced pressure distillation conditions are: temperature 60-160°C, vacuum degree 3kPa-30kPa.

[0015] Preferably, in step (2), the large-pore acidic catalyst is one of HY molecular sieve or its modified product, USY molecular sieve or its modified product, and metal-modified phosphotungstic acid.

[0016] Preferably, the coal-based liquid product is directly used as the raw material for the alkylation reaction without prior separation of aromatic hydrocarbons.

[0017] Preferably, the cycloolefin in step (2) is one or more of cyclopentene, cyclohexene, norbornene, and norbornadiene; and the cyclic alcohol is one or more of cyclohexanol, cyclopentanol, and norbornyl alcohol.

[0018] Preferably, in step (3), a supported precious metal is added at 1-10 wt% of the collected alkylation product, and hydrogen is introduced at a pressure of 5-6 MPa under temperature control conditions at a reaction temperature of 150-200° C. for 2-24 hours. After the reaction is completed, the catalyst and insoluble solid impurities are removed to obtain the high energy density fuel.

[0019] Preferably, the supported precious metal is Ru / C containing 5 wt% Ru or Pd / Al2O3 containing 5 wt% Pd.

[0020] The second aspect of the present invention provides a coal-based high-energy density fuel prepared by the preparation method described in the first aspect, wherein the coal-based high-energy density fuel comprises benzene, indene, naphthalene, acenaphthene, fluorene, phenanthrene and anthracene and their branched and hydrogenated derivatives.

[0021] A third aspect of the present invention provides an application of the high energy density fuel prepared by the preparation method described in the first aspect as an aerospace fuel.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. First of all, it should be noted that the composition of coal-based liquid products is complex. The main components include: benzene, indene, naphthalene, acenaphthene, fluorene, phenanthrene and anthracene, as well as their branched and hydrogenated derivatives. Their molecular sizes are generally between 0.8 and 1.5 nm. Traditional microporous molecular sieves (such as ZSM-5 with a pore size of 0.55 nm) cannot accommodate such molecules, resulting in obstructed mass transfer. The standard pore size of the HY / USY molecular sieve of the present invention is 0.74 nm, which is significantly larger than that of ZSM-5. This allows dicyclic / tricyclic aromatic hydrocarbons to diffuse freely to the active sites of the catalyst. Furthermore, the modified HY / USY molecular sieve in the prior art further achieves pore expansion, accelerates the mass transfer of large molecules (such as anthracene derivatives), and reduces coking caused by the retention of intermediates.

[0024] 2. Strong acid catalysts such as aluminum chloride and sulfuric acid, although highly acidic, cannot control the direction of the reaction and are prone to generate polysubstituted products. Small-pore molecular sieves such as ZSM-5 have uneven distribution of acid sites, resulting in low reaction activity. In contrast, the HY / USY molecular sieves and their derivatives selected in the present invention also have moderate strong acid sites (0.7-0.9 mmol / g), which can efficiently catalyze the Friedel-Crafts alkylation reaction of aromatic hydrocarbons while suppressing over-alkylation or polymerization side reactions.

[0025] 3. In addition, the present invention selects metal (such as Sn, etc.) modified phosphotungstic acid as a catalyst to achieve synergistic effect of Bronsted acid and Lewis acid. Lewis acid enhances the activation ability of cycloolefins or cycloalcohols, and Bronsted acid directionally guides aromatic hydrocarbons to attack for alkylation. The introduction of metal by modification can also stabilize the phosphotungstic acid skeleton, reduce the loss of acidic sites, and extend the catalyst life.

[0026] 4. The traditional process requires the separation of aromatics from coal-based liquid products, which is complex and has high energy consumption costs. The present invention innovatively directly performs an alkylation reaction on the coal-based liquid products, adapts the large-pore catalyst to the mass transfer requirements of polycyclic aromatic hydrocarbons, eliminates the aromatics separation step, simplifies the process flow, and retains high-density components such as indenes, naphthalenes, acenaphthenes, fluorenes, phenanthrenes and anthracenes, further ensuring the energy density of the fuel.

[0027] 5. Traditional alkylation reaction processes require complex catalyst systems (such as bifunctional metal-acid catalysts), while the present invention only requires a single catalyst (HY / , USY or modified phosphotungstic acid), the reaction conditions are mild, and the catalyst is a heterogeneous solid that can be centrifuged and reused, which is energy-saving and environmentally friendly. DETAILED DESCRIPTION

[0028] The following examples illustrate the process described in the present invention, but the present invention is not limited to these examples.

[0029] Example 1

[0030] This embodiment provides a method for preparing a coal-based high energy density fuel, comprising the following steps:

[0031] Step (1): A batch of coal-based diesel was analyzed for composition using a Shimadzu GC-MS QP2020 and an Rtx-5MS (100% dimethylpolysiloxane, 50 m × 0.25 mm × 0.25 μm) column. The temperature program was as follows: 40°C for 3 min, then 10°C / min to 220°C for 7 min, then 10°C / min to 300°C for 5 min. The calculated number of aromatic moles in the raw material was 137 mmol.

[0032] Step (2), after three nitrogen replacements, the air in the reactor was completely exhausted, and then 50g of coal-based diesel was added to the quartz glass lining of the batch reactor, followed by the addition of 12.87g of norbornene and 10g of mesoporous USY molecular sieve (silicon-aluminum ratio of 10-12), and then the system was maintained at a reaction temperature of 180°C and a pressure of 4MPa (nitrogen environment) for 1h;

[0033] After the reaction, centrifuge at 6000 rpm and room temperature for 3 minutes, then remove the catalyst and insoluble solid impurities, and distill using a self-built vacuum distillation apparatus at 60-160° C. and a vacuum degree of 3 kPa-30 kPa until no liquid flows out, and collect the non-volatile components to obtain 57 g of alkylation product;

[0034] The amount of norbornene added is calculated based on the analysis results of step (1), where the molar ratio of the two substrates, aromatic hydrocarbon and norbornene, in the reaction system is 1:1;

[0035] Step (3): Add 2 g of Pd / Al2O3 containing 5 wt% Pd to the alkylation product obtained in step (2), introduce hydrogen (maintaining the pressure at 5 MPa), and then react at a temperature of 150° C. for 10 h. After the reaction is completed, centrifuge at 6000 rpm for 3 min to remove the catalyst and insoluble solid impurities, thereby obtaining the coal-based high energy density fuel, which is recorded as fuel A.

[0036] Example 2

[0037] Compared with Example 1, the difference between this embodiment is that the amount of coal-based diesel raw material is increased to 670 g, and the amount of norbornene is increased in proportion, and the amount of mesoporous USY molecular sieve (silicon-aluminum ratio of 10-12) is reduced to 10 wt% of the coal-based diesel. The remaining parameters and steps are consistent with Example 1. The high energy density fuel prepared is recorded as B fuel.

[0038] Example 3

[0039] The only difference between this embodiment and Example 1 is that norbornene is replaced by cyclohexene. The remaining parameters and steps are consistent with those of Example 1. The high energy density fuel prepared is denoted as C fuel.

[0040] Example 4

[0041] Compared with Example 1, the only difference between this embodiment is that the mesoporous USY is replaced by Sn1.5TPA (stannous chloride modified phosphotungstic acid, n(SnCl2):n(HPW)=1.5:1), and norbornene is replaced by cyclopentene. The other parameters and steps are consistent with Example 1. The high energy density fuel prepared is denoted as D fuel.

[0042] Example 5

[0043] The only difference between this embodiment and Example 1 is that norbornene is replaced by a mixture of cyclohexene and norbornene, specifically n(cyclohexene):n(norbornene) = 1:1. The remaining parameters and steps are consistent with Example 1. The high energy density fuel prepared is recorded as E fuel.

[0044] Example 6

[0045] The only difference between this embodiment and embodiment 2 is that the mesoporous USY is replaced with modified 0.1USY (0.1 mol / L HNO3-modified mesoporous USY). The remaining parameters and steps are consistent with those of embodiment 2. The high energy density fuel prepared is recorded as F fuel.

[0046] The modification method of USY is as follows: 20g USY, 200ml 0.1mol / L HNO3, stirred at 60℃ for 0.5h, filtered to pH 7, dried overnight, and calcined at 550℃ for 4h.

[0047] Example 7

[0048] Compared with Example 4, the only difference between this example is that the modified 0.1 USY is replaced by modified 0.3 USY (0.3 mol / L HNO3-modified mesoporous USY). The other parameters and steps are consistent with Example 4. The high energy density fuel prepared is recorded as G fuel.

[0049] The modification method of USY is as follows: 20g USY was mixed with 200ml 0.1mol / L HNO3, stirred at 60℃ for 0.5h, washed and filtered until the pH value of the filtrate was 7, dried overnight, and calcined at 550℃ for 4h.

[0050] Example 8

[0051] The only difference between this embodiment and embodiment 2 is that the mesoporous USY is replaced with 0.3HY (HY modified with 0.3 mol / L NaOH, where the HY silicon-aluminum ratio is 10-12). The remaining parameters and steps are consistent with those of embodiment 2. The high energy density fuel prepared is recorded as H fuel.

[0052] The HY modification method involved stirring the HY molecular sieve in a 0.3 mol / L NaOH solution at 60°C for 2 hours, with a solid-to-liquid ratio of 1 g:10 ml. The alkali-treated molecular sieve was filtered until the filtrate was neutral. The zeolite was then dried at 100°C for 12 hours. The treated zeolite was then ammonium exchanged three times with a 1.0 M NH4Cl solution for 4 hours. The sample was washed, filtered, and dried at 100°C overnight before being calcined at 550°C for 4 hours.

[0053] Example 9

[0054] The only difference between this embodiment and Example 1 is that norbornene is replaced by norbornenol and the time is extended to 2 hours. The remaining parameters and steps are consistent with Example 1. The high energy density fuel prepared is recorded as I fuel.

[0055] Example 10

[0056] The only difference between this embodiment and embodiment 1 is that coal-based diesel is replaced by coal direct liquefaction oil and the hydrogenation reaction catalyst is replaced by Ru / C. The remaining parameters and steps are consistent with those of embodiment 1. The high energy density fuel prepared is recorded as J fuel.

[0057] Example 11

[0058] The only difference between this embodiment and embodiment 1 is that norbornene is replaced by norbornadiene. The remaining parameters and steps are consistent with those of embodiment 1. The high energy density fuel prepared is denoted as K fuel.

[0059] Example 12

[0060] Compared with Example 1, the only difference between this example is that the mesoporous USY is replaced by HY (silicon-aluminum ratio = 10-12), norbornene is replaced by cyclohexanol, and the alkylation reaction time is extended to 2.0 hours. The remaining parameters and steps are consistent with Example 1. The high energy density fuel prepared is recorded as L fuel.

[0061] Comparative Example 1

[0062] The only difference between this comparative example and Example 1 is that the mesoporous USY is replaced by HZSM-5. The other parameters and steps are consistent with Example 1. The high energy density fuel prepared is recorded as 1# fuel.

[0063] Comparative Example 2

[0064] The only difference between this comparative example and Example 1 is that the mesoporous USY is replaced by HZSM-35. The other parameters and steps are consistent with Example 1. The high energy density fuel prepared is recorded as 2# fuel.

[0065] Comparative Example 3

[0066] The only difference between this comparative example and Example 1 is that the mesoporous USY is replaced by HZSM-48. The other parameters and steps are consistent with those of Example 1. The high energy density fuel prepared is recorded as 3# fuel.

[0067] Comparative Example 4

[0068] The only difference between this comparative example and Example 1 is that the mesoporous USY is replaced by MCM-22. The other parameters and steps are consistent with those of Example 1. The high energy density fuel prepared is recorded as 4# fuel.

[0069] Test Example 1

[0070] In order to verify the difference in performance between the high energy density fuel prepared by the present invention and the fuel prepared by conventional catalysts, this test example shows the performance index test results of the fuels prepared in the above embodiments and comparative examples. The test method is as follows: first, the heat of combustion (NHOC) is measured using an IKA-C6000 calorimeter according to the ASTM D240-02 standard; secondly, the fuel density is measured using a Mettler-Toledo DE40 density meter according to the ASTM D4052 standard; then, the freezing point is measured according to the ASTM D2386 standard; finally, the kinematic viscosity is measured using a glass capillary viscometer according to the ASTM D445 standard. Each indicator is measured three times, and the average value is taken. The error is controlled within ±0.2%. The final performance parameters of each fuel are summarized in Table 1 and Table 2:

[0071] Table 1 Fuel performance test results

[0072]

[0073] Table 2 Fuel density test results

[0074]

[0075] It can be seen that the density of fuels A through M prepared by the present invention is higher than that of conventional fuels 1#-4#. While the heat of combustion per unit mass of fuel AE is slightly lower than that of conventional fuels, its higher density increases its energy density per unit volume by approximately 1.5–3%, significantly outperforming fuels produced by conventional processes. Furthermore, all of the aforementioned samples have freezing points below –60°C, demonstrating excellent ultra-low-temperature anti-condensation properties. At both 0°C and 20°C, the kinematic viscosities of fuels A through E are within the same range as conventional fuels, ensuring excellent flow properties at both room and low temperatures.

[0076] Test Example 2

[0077] Fuel B, fuel C, and coal-based diesel were selected for testing. The heat exchange performance of different fuels was tested under a simulated advanced aircraft working environment (flow rate 1 g / s, pressure 4 MPa, Φ3×0.5×1000 mm 316L stainless steel heat exchange tube). The results are listed in Table 2 (fuel B, density 0.9029 g / cm 3 ), Table 3 (C fuel, density 0.8862g / cm 3 ) and Table 4 (coal-based diesel, density 0.8813 g / cm3 ).

[0078] Table 2B Fuel heat transfer performance test results

[0079]

[0080] Table 3C fuel heat transfer performance test results

[0081]

[0082] Table 4 Coal-based diesel heat transfer performance test results

[0083]

[0084] It can be seen that compared with traditional coal-based diesel, the B and C fuels prepared by the method of the present invention not only have higher heat sink and higher cracking gas yield, but also have significantly improved heat exchange stability at high temperatures, fully meeting the requirements of large heat flow and high-reliability operation of aircraft.

Claims

1. A method for preparing a coal-based high energy density fuel, characterized in that: The preparation method comprises the following steps: Step (1), testing the molar amount of aromatics in the coal-based liquid product: Step (2), carrying out an alkylation reaction between the coal-based liquid product and a cycloolefin or cycloalcohol having a molar ratio of 1:1-1.2 to the aromatic hydrocarbon in the coal-based liquid product under an inert atmosphere and catalyzed by a large-pore acidic catalyst, after which the catalyst and insoluble solid impurities are removed, followed by vacuum distillation to selectively remove light components, and collecting non-volatile components to obtain an alkylated product; Step (3), subjecting the collected alkylation product and hydrogen to a hydrogenation saturation reaction under the catalysis of a supported noble metal, and after the reaction is completed, removing the catalyst and solid impurities to obtain the coal-based high energy density fuel.

2. The method for preparing a coal-based high energy density fuel according to claim 1, characterized in that: In step (2), the amount of the acidic catalyst added is 10-20 wt% of the coal-based liquid product, and the reaction time is 1-2 h under the conditions of a reaction temperature of 180-200° C. and a reaction pressure of 4 MPa; The reduced pressure distillation conditions are: temperature 60-160°C, vacuum degree 3kPa-30kPa.

3. The method for preparing a coal-based high energy density fuel according to claim 1, characterized in that: In the step (2), the large-pore acid catalyst is one of HY molecular sieve or its modified product, USY molecular sieve or its modified product, and metal-modified phosphotungstic acid.

4. The method for preparing a coal-based high energy density fuel according to claim 3, characterized in that: The coal-based liquid product does not need to be separated from aromatic hydrocarbons in advance and can be directly used as the raw material for the alkylation reaction.

5. The method for preparing a coal-based high energy density fuel according to claim 1, characterized in that: In the step (2), the cycloolefin is one or more of cyclopentene, cyclohexene, norbornene, and norbornadiene; and the cyclic alcohol is one or more of cyclohexanol, cyclopentanol, and norbornyl alcohol.

6. The method for preparing a coal-based high energy density fuel according to claim 1, characterized in that: In the step (3), a supported noble metal is added according to 1-10 wt% of the collected alkylation product, and hydrogen is introduced at a pressure of 5-6 MPa under the temperature control condition of a reaction temperature of 150-200° C. for 2-24 hours. After the reaction is completed, the catalyst and insoluble solid impurities are removed to obtain the high energy density fuel.

7. The method for preparing a coal-based high energy density fuel according to claim 6, characterized in that: The supported noble metal is Ru / C containing 5 wt% Ru or Pd / AI2O3 containing 5 wt% Pd.

8. A coal-based high energy density fuel prepared by the preparation method according to claim 1, characterized in that: The high energy density fuel comprises benzene, indene, naphthalene, acenaphthene, fluorene, phenanthrene and anthracene and their branched and hydrogenated derivatives.

9. Use of the high energy density fuel prepared by the preparation method according to claim 1 as aerospace fuel.

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