Catalyst-free photo-induced direct alkane cracking method

Abstract

The invention discloses a catalyst-free photo-induced direct alkane cracking method. The method comprises the following steps: vacuumizing a reactor; alkane is introduced into the reactor subjected to the vacuumizing treatment; and irradiating the alkane by adopting a light source containing ultraviolet rays with the wavelength of 100-400nm on the premise of not adding a catalyst so as to excite a C-H bond at the tail end of the alkane to generate uniform cracking, thereby generating a hydrogen free radical and carbon free radical intermediate, the hydrogen free radicals are coupled to generate hydrogen, and the carbon free radical intermediates are subjected to self-reaction to form coupling products. Alkane molecules are excited by high-energy photons to realize direct homocracking of C-H bonds, and then homocracked hydrogen free radicals and carbon free radical intermediates react respectively.

Description

Technical Field

[0001] The present application belongs to the technical field of alkane conversion, and specifically relates to a method for direct photoinduced cracking of alkanes without a catalyst. Background Art

[0002] As an important chemical raw material, alkanes are widely used in the production of industrial products. The current research on alkane cracking to produce hydrogen and reaction products is of great significance to energy structure and carbon emission reduction.

[0003] The technical routes for alkane cracking to produce hydrogen and reaction products mainly include:

[0004] Thermal catalytic cracking, which drives the pyrolysis of methane at high temperature (>700°C) to produce hydrogen and solid carbon (such as CNT), requires metal catalysts (Ni, Fe-based, etc.). However, the reaction energy consumption is extremely high, the catalyst is easily deactivated due to carbon deposition, and the selectivity of gaseous hydrocarbons (such as ethane) in the product is extremely low (see McConnachie M, Konarova M, Smart S. Literature review of the catalytic pyrolysis of methane for hydrogen and carbon production [J]. International journal of hydrogen energy, 2023, 48 (66): 25660-25682);

[0005] Electrocatalytic conversion uses an electrochemical device to activate methane on the electrode surface, which can regulate product distribution (such as CO2 co-electrolysis to produce ethylene). However, the system consumes a lot of electricity, has poor electrode stability, and the co-production efficiency of hydrogen and ethane in the product is less than 5% (see Fan Z, Xiao W. Electrochemical splitting of methane in molten salts to produce hydrogen [J]. Angewandte Chemie International Edition, 2021);

[0006] The fuel cell pathway, which indirectly produces hydrogen through a methane fuel cell, is limited by the cost of the proton exchange membrane and the problem of catalyst poisoning, and has not yet been applied on a large scale (see Mirkarimi SMR, Bensaid S, Chiaramonti VN. Review of methane cracking over carbon-based catalyst for energy and fuels [J]. Renewable & sustainable energy reviews, 2023, 187 (Nov.): 113747.1-113747.16);

[0007] Benzene hydrogenation is a process in which benzene and hydrogen react under high temperature (150-250°C) and high pressure (1-5 MPa) in the presence of a catalyst (such as a nickel, platinum, or ruthenium-based catalyst) to produce cyclohexane. Although this method is mature and accounts for more than 90% of global production capacity, it relies on highly toxic benzene as a raw material and requires a high-purity hydrogen supply (usually from fossil fuel reforming), resulting in a high carbon footprint and high safety risks. In addition, precious metal catalysts are susceptible to sulfide poisoning and deactivation, requiring frequent regeneration or replacement, further increasing costs (see Dada EA, Achenie L. Production of Cylohexane from Hydrogenation of Benzene using Microreactor Technology [J]. Computer Aided Chemical Engineering, 2012, 31: 240-244).

[0008] The petroleum fraction separation method separates cyclohexane from crude oil straight-run gasoline or reformate by distillation. This method is highly dependent on the quality of the raw materials and is only applicable to specific crude oils with high cycloalkane content (such as crude oil from the Middle East). The product purity is low (usually less than 95%) and requires multi-stage distillation purification. The separation process requires the treatment of a large number of components with similar boiling points (such as methylcyclopentane), resulting in a sharp increase in energy consumption and poor economic and environmental compatibility (see Zhao Yueqiang, Wu Zhengming, Liu Weiwei, et al. Dynamic method-assisted screening of solvents for extractive distillation separation of cyclohexane-benzene mixtures [J]. Journal of Process Engineering, 2007, 7(4): 6);

[0009] Photocatalytic method: TiO2-based catalysts can promote the partial oxidation of methane to produce methanol under ultraviolet light (see Xu Zhenmin, Bian Zhenfeng. Research progress of photocatalytic methane conversion [J]. Acta Physico-Chimica Sinica, 2020(3): 11); or methane and water vapor reforming to produce hydrogen through Z-type heterojunction design (see Zhang Mengfan, Zhang Zhenmin, Jia Jingwen, et al. Research progress on the design, preparation and application of Z-type heterojunction photocatalysts [J]. Nonferrous Metals Science and Engineering, 2020, 11(3): 15);

[0010] The catalytic dehydrogenation and cyclization method utilizes a metal-acid bifunctional catalyst (such as Pt / Al2O3) to promote the dehydrogenation and cyclization of n-hexane to cyclohexane at high temperatures (>400°C) in the presence of hydrogen. However, this process requires continuous external heating to maintain the high temperature, which consumes extremely high energy. The catalyst also rapidly deactivates due to carbon deposition (usually with a lifespan of less than 100 hours), requiring frequent shutdowns for regeneration. Furthermore, cracking side reactions (such as the formation of methane and propylene) are difficult to suppress during the reaction, resulting in a cyclohexane selectivity of only 60-80%, and hydrogen, as a reaction product, is not effectively utilized (see Luo Xiaoyuan, Zhang Zhi, Yang Yu, et al. Preparation of Cyclohexene [P]. Hunan: CN201810088526.8, July 20, 2018).

[0011] To overcome the above limitations, some researchers have attempted to improve photocatalytic performance through precious metal loading (such as Au / TiO2), defect engineering (oxygen vacancy construction), or plasmon resonance effects (Ag nanoparticles) (see [1] Li Q, Ouyang Y, LiH, et al. Photocatalytic Conversion of Methane: Recent Advancements and Prospects [J]. Angewandte Chemie International Edition, 2021). However, the introduction of catalysts significantly increases process complexity and cost, and it is difficult to avoid the generation of reaction products (CO, CO2). Summary of the Invention

[0012] In order to overcome the shortcomings of the existing technology, the present application provides a method for catalyst-free light-induced direct cracking of alkanes, develops an efficient catalyst-free direct light-driven alkane conversion technology, realizes the co-production of highly selective hydrogen and carbon free radical coupling products, and avoids the defects of the existing technology such as strong catalyst dependence, high energy consumption, and low product selectivity.

[0013] In order to achieve the above objectives, this application adopts the following technical solutions:

[0014] A method for direct photocatalytic cracking of alkanes, comprising:

[0015] The reactor is vacuumed;

[0016] introducing alkane into the vacuum-treated reactor; and

[0017] In the absence of added catalyst, the alkane is irradiated with a light source containing ultraviolet rays with a wavelength of 100-400 nm to stimulate homolytic cleavage of the terminal C-H bond of the alkane, thereby generating hydrogen free radicals and carbon free radical intermediates; the hydrogen free radicals couple to generate hydrogen, and the carbon free radical intermediates react with themselves to form coupling products.

[0018] Furthermore, the reactor was vacuumed, including three cycles of vacuuming and filling the reactor with alkane to remove air residue, and then the reactor was vacuumed at 10 mL min -1 The alkane was continuously introduced at a flow rate of .

[0019] Furthermore, the alkane is methane; and the carbon radical intermediate forms ethane through a coupling reaction.

[0020] Furthermore, the wavelength range of the ultraviolet light is 100-272nm; the intensity of the light source is 10-200mW / cm 2 , the temperature is 10-60℃.

[0021] Furthermore, the alkane is n-hexane; and the carbon radical intermediate forms cyclohexane through an intramolecular ring-closure reaction.

[0022] Furthermore, the wavelength range of the ultraviolet light is 200-400nm; the intensity of the light source is 50-200mW / cm 2 , the temperature is 25-40℃.

[0023] Furthermore, the wavelength of the ultraviolet light is 254 nm.

[0024] Furthermore, the self-reaction includes an intermolecular coupling reaction or an intramolecular ring-closing reaction.

[0025] Furthermore, the alkane introduced into the vacuum-treated reactor includes an inert carrier gas, and the volume ratio of the alkane to the inert carrier gas is 1:1-1:4.

[0026] Furthermore, online gas chromatography is used to analyze gaseous hydrogen and coupling products in real time, and the purity of the coupling products is detected by condensation separation-mass spectrometry; the coupling products include RR, alkane + alkene or cyclic compounds.

[0027] Compared with the prior art, this application has the following advantages:

[0028] Ultraviolet light excites alkane molecules to directly split the C-H bond, followed by the homolytic splitting of hydrogen radicals (H·) and carbon radical intermediates. The hydrogen radicals (H·) and carbon radical intermediates then react separately. The hydrogen radicals combine with each other to generate hydrogen, and the carbon radical intermediates combine to generate coupling products. This allows for efficient co-production of hydrogen and coupling products at room temperature and pressure, breaking through the quantum efficiency bottleneck of traditional photocatalytic systems and eliminating the problems caused by catalysts.

[0029] No reliance on catalysts, completely abandoning traditional metal catalysts or photosensitive materials, avoiding catalyst deactivation, poisoning and cost issues;

[0030] Mild reaction conditions, operating at room temperature and pressure, energy consumption is reduced by more than 70% compared with thermal catalytic method;

[0031] Innovative mechanism, using photon energy to directly drive C-H bond cleavage, breaking through the limit of photocatalytic quantum efficiency (measured photon utilization rate reaches 12%);

[0032] The process is simple, does not require complex catalyst loading or reactor design, and is easy to scale up;

[0033] Environmentally friendly, no solid waste is generated during the entire process, meeting the requirements of green chemical industry;

[0034] In summary, the catalyst-free light-driven alkane conversion method of the present invention achieves efficient co-production of carbon free radical intermediate coupling products and hydrogen under mild conditions through precise light energy excitation and directional regulation of free radicals, providing a clean, economical and practical technical path for the high-value utilization of alkanes. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application but do not constitute an improper limitation on the present application. In the drawings:

[0036] Figure 1 A flowchart of the application method;

[0037] Figure 2 This is the result diagram of pure methane cracking to produce hydrogen and ethane;

[0038] Figure 3 This is the result of cracking methane and nitrogen (1:1) to produce hydrogen and ethane. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0040] In the description of this application, it should be understood that the relationship between the method steps can be in sequence or not, as long as it does not affect the overall technical effect, and therefore cannot be understood as a limitation on this application. The following description of this application is only to be understood as a description of individual embodiments of the technical solution of this application. Other embodiments are not reflected in the following description, but it does not mean that this application excludes these other embodiments, and the technical solution of this application is not limited to the specific implementation methods described below, and the scope of protection of this application is not limited to only the specific implementation methods described below. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of this application.

[0041] It should be noted that, if the terms "first", "second", etc. appear in the specification and claims of the present application and the above-mentioned drawings, the description is only used to distinguish similar objects and is not necessarily used to describe a specific order or sequential order. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in a sequence other than those illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0042] In some embodiments, as Figure 1 As shown, the present application provides a method for direct photo-induced cracking of alkanes without a catalyst, comprising:

[0043] S1: vacuum the reactor;

[0044] Specifically, the vacuum treatment of the reactor includes three vacuum-alkane filling cycles to remove air residues, and then -1 The alkane was continuously introduced at a flow rate of .

[0045] S2: introducing alkane into the vacuum-treated reactor;

[0046] Specifically, the alkane introduced into the vacuum-treated reactor includes an inert carrier gas, and the volume ratio of the alkane to the inert carrier gas is 1:1-1:4.

[0047] S3: In the absence of added catalyst, the alkane is irradiated with a light source containing ultraviolet rays with a wavelength of 100-400 nm to stimulate homolytic cleavage of the terminal C-H bond of the alkane, thereby generating hydrogen radicals and carbon radical intermediates; the hydrogen radicals couple to generate hydrogen, and the carbon radical intermediates react with themselves to form coupling products.

[0048] Specifically, the self-reaction includes an intermolecular coupling reaction or an intramolecular ring-closure reaction; online gas chromatography is used to analyze gaseous hydrogen and coupling products in real time, and the purity of the coupling products is detected by condensation separation-mass spectrometry; the coupling products include RR, alkane + alkene or cyclic compounds.

[0049] The present application specifically includes molecular excitation and energy relaxation: high-energy ultraviolet photons of a specific wavelength are used to directly irradiate the alkane gas in the quartz reactor, and the alkane molecules absorb the photon energy and transition to an electronically excited state; vibrational energy transfer: the excited state molecules transfer energy to the terminal C-H bond through a femtosecond vibrational relaxation process; C-H bond homolysis: when the energy exceeds the C-H bond dissociation energy, the bond homolysis is triggered to generate hydrogen radicals (H·) and carbon radical intermediates; radical-directed coupling: H· generates hydrogen (2H·→H2) through bimolecular coupling, and the carbon radical intermediates form coupling products through self-reaction.

[0050] In some embodiments, the alkane is methane; and the carbon radical intermediate forms ethane through a coupling reaction.

[0051] Specifically, the wavelength range of the ultraviolet light is 100-272nm; the intensity of the light source is 10-200mW / cm 2 , the temperature is 10-60℃.

[0052] Example: Production of ethane and hydrogen from pure methane by photoirradiation

[0053] In this example, pure methane was used as the reactant, a quartz reaction tube was used as the photoreactor, and the gas composition was analyzed by online gas chromatography (GC) in the following steps:

[0054] (1) A 25 mL quartz photoreactor was subjected to three cycles of vacuuming and methane filling to remove residual air, and then the reactor was heated at 10 mL min -1 High-purity methane (99.999%) was continuously introduced at a flow rate of 5 minutes to ensure the purity of the gas environment in the reaction system (residual O2 < 10ppm). A UV LED light source (spectrum 200-400nm, peak 254nm, light power density 8mW·cm -2) was used to irradiate the closed reaction system, and the reaction temperature was maintained at 20°C. After irradiation for 30 minutes, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 5.2 μL and 4.9 μL, respectively. Figure 2 shown.

[0055] (2) Keeping other conditions unchanged, after 30 minutes of illumination, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 12.6 μL and 9.0 μL, respectively. Figure 2 shown.

[0056] (3) Keeping other conditions unchanged, after 30 minutes of illumination, the samples were analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 15.9 μL and 12 μL, respectively. Figure 2 shown.

[0057] (4) Keeping other conditions unchanged, after 30 minutes of illumination, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 23.7 μL and 19.2 μL, respectively. Figure 2 shown.

[0058] Example: Production of ethane and hydrogen from pure methane by photoirradiation

[0059] In this example, pure methane was used as the reactant, a quartz reaction tube was used as the photoreactor, and the gas composition was analyzed by online gas chromatography (GC) in the following steps:

[0060] (1) A 25 mL quartz photoreactor was subjected to three cycles of vacuuming and methane filling to remove residual air, and then the reactor was heated at 10 mL min -1 High-purity methane (99.999%) was continuously introduced for 5 minutes to ensure the purity of the gas environment in the reaction system (residual O2 < 10 ppm). A mercury lamp (254 nm, optical power density 200 mW·cm -2 The sealed reaction system was irradiated with 1% CO 2 and the reaction temperature was maintained at 20° C. After irradiation for 30 minutes, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan), and the quantitative volumes of hydrogen and ethane were 15.7 μL and 14.9 μL respectively.

[0061] (2) Keeping other conditions unchanged, after 30 minutes of illumination, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 25.8 μL and 22.4 μL respectively.

[0062] (3) Keeping other conditions unchanged, after 30 minutes of illumination, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 33.2 μL and 29.0 μL respectively.

[0063] (4) Keeping other conditions unchanged, after 30 minutes of illumination, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 39.9 μL and 32.6 μL respectively.

[0064] Example: Production of ethane and hydrogen from pure methane by photoirradiation

[0065] In this example, pure methane was used as the reactant, a quartz reaction tube was used as the photoreactor, and the gas composition was analyzed by online gas chromatography (GC) in the following steps:

[0066] (1) A 25 mL quartz photoreactor was subjected to three cycles of vacuuming and methane filling to remove residual air, and then the reactor was heated at 10 mL min -1 High-purity methane (99.999%) was continuously introduced at a flow rate of 5 minutes to ensure the purity of the reaction system (residual O₂ <10 ppm). The sealed reaction system was irradiated using a solar simulator (AM1.5G) and the reaction temperature was maintained at 20°C. After 1 hour of irradiation, analysis by gas chromatography (GC, Shimadzu, Japan) revealed quantitative volumes of 1.9 μL for hydrogen and 0 μL for ethane.

[0067] (2) Keeping other conditions unchanged, after 1 hour of illumination, the samples were analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 3.8 μL and 1.2 μL respectively.

[0068] (3) Keeping other conditions unchanged, after 1 hour of illumination, the samples were analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 4 μL and 2 μL respectively.

[0069] (4) Keeping other conditions unchanged, after 2 h of illumination, the samples were analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 10 μL and 8.4 μL respectively.

[0070] Example: Producing ethane and hydrogen from methane (50% nitrogen) by photoirradiation

[0071] In this example, pure methane was used as the reactant, a quartz reaction tube was used as the photoreactor, and the gas composition was analyzed by online gas chromatography (GC) in the following steps:

[0072] (1) A 25 mL quartz photoreactor was subjected to three cycles of vacuuming and methane filling to remove residual air, and then the reactor was heated at 10 mL min-1 High-purity methane (99.999%) was continuously introduced for 5 minutes to ensure the purity of the gas environment in the reaction system (residual O2 < 10 ppm). A mercury lamp (254 nm, optical power density 200 mW·cm -2 ) was used to irradiate the closed reaction system, and the reaction temperature was maintained at 20°C. After irradiation for 30 minutes, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 4.6 μL and 2.9 μL, respectively. Figure 3 shown.

[0073] (2) Keeping other conditions unchanged, after 30 minutes of illumination, the samples were analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 10 μL and 8 μL, respectively. Figure 3 shown.

[0074] (3) Keeping other conditions unchanged, after 30 minutes of illumination, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 24.4 μL and 21.7 μL, respectively. Figure 3 shown.

[0075] (4) Keeping other conditions unchanged, after 30 minutes of illumination, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The quantitative volumes of hydrogen and ethane were 37.9 μL and 30.5 μL, respectively. Figure 3 shown.

[0076] In some embodiments, the alkane is n-hexane; and the carbon radical intermediate forms cyclohexane through an intramolecular ring closure reaction.

[0077] Specifically, the wavelength range of the ultraviolet light is 200-400nm; the intensity of the light source is 50-200mW / cm 2 , the temperature is 25-40° C. Further, the wavelength of the ultraviolet rays is preferably 254 nm.

[0078] Example: Photoreaction of n-hexane to produce cyclohexane and hydrogen - UV LED

[0079] In this example, n-hexane was used as the reactant and a quartz reaction tube was used as the photoreactor. The gas composition was analyzed by online gas chromatography (GC). The steps were as follows: a 25 mL quartz photoreactor was subjected to three cycles of vacuuming and n-hexane filling to remove residual air. The 25 mL quartz photoreactor was then heated at 10 mL min. -1 The flow rate of n-hexane was continuously introduced for 5 minutes to ensure the purity of the gas environment in the reaction system. A UV LED light source (spectrum 200-400nm, peak 254nm, light power density 8mW·cm -2) The sealed reaction system was irradiated, and the reaction temperature was maintained at 20°C. After each 30-minute irradiation, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The yields of hydrogen and cyclohexane were as follows:

[0080] Table 1 Photoreaction of n-hexane to produce cyclohexane and hydrogen (UV LED)

[0081]

[0082] Example: Photoreaction of n-hexane to produce cyclohexane and hydrogen-mercury lamp

[0083] In this example, n-hexane was used as the reactant and a quartz reaction tube was used as the photoreactor. The gas composition was analyzed by online gas chromatography (GC). The steps were as follows: a 25 mL quartz photoreactor was subjected to three cycles of vacuuming and n-hexane filling to remove residual air. The 25 mL quartz photoreactor was then heated at 10 mL min. -1 The flow rate of n-hexane was continuously introduced for 5 minutes to ensure the purity of the gas environment in the reaction system. A mercury lamp light source (spectrum 200-1000nm, peaks 238nm, 254nm, 313nm, 365nm, light power density 150mW·cm -2 ) The sealed reaction system was irradiated, and the reaction temperature was maintained at 20°C. After each 30-minute irradiation, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The yields of hydrogen and cyclohexane were as follows:

[0084] Table 2 Photoreaction of n-hexane to produce cyclohexane and hydrogen (mercury lamp)

[0085]

[0086] Example: Photoreaction of n-hexane to produce cyclohexane and hydrogen (sunlight AM 1.5G)

[0087] In this example, n-hexane was used as the reactant and a quartz reaction tube was used as the photoreactor. The gas composition was analyzed by online gas chromatography (GC). The steps were as follows: a 25 mL quartz photoreactor was subjected to three cycles of vacuuming and n-hexane filling to remove residual air. The 25 mL quartz photoreactor was then heated at 10 mL min. -1 n-Hexane was continuously introduced at a constant flow rate for 5 minutes to ensure the purity of the gas environment within the reaction system. The closed reaction system was irradiated with AM1.5G sunlight (2:00 PM, sunny), and the reaction temperature was maintained at 30°C. After each 30-minute irradiation period, the gas was analyzed by gas chromatography (GC, Shimadzu, Japan). The hydrogen and cyclohexane yields were as follows:

[0088] Table 3 Photoreaction of n-hexane to produce cyclohexane and hydrogen (sunlight)

[0089]

[0090]

[0091] The above-described embodiments only express several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they should not be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present application, and these all fall within the scope of protection of the present application. Therefore, the scope of protection of the patent in this application should be based on the attached claims, and the selection and description of the implementation methods are to best illustrate the principles of the present application and its practical application, so as to enable other technicians in this field to best use the present application with various modifications suitable for the specific purpose envisioned and the various described implementation methods.

Claims

1. A method for direct photocatalytic cracking of alkanes, characterized in that: include: The reactor is vacuumed; introducing alkane into the vacuum-treated reactor; as well as In the absence of added catalyst, the alkane is irradiated with a light source containing ultraviolet rays with a wavelength of 100-400 nm to stimulate homolytic cleavage of the terminal C-H bond of the alkane, thereby generating hydrogen free radicals and carbon free radical intermediates; the hydrogen free radicals couple to generate hydrogen, and the carbon free radical intermediates react with themselves to form coupling products.

2. The method for direct photocatalytic cracking of alkanes according to claim 1, wherein: The reactor was vacuumed for treatment, including three cycles of vacuuming and filling the reactor with alkane to remove residual air, and then the reactor was vacuumed at 10 mL min -1 The alkane was continuously introduced at a flow rate of .

3. The method for direct photocatalytic cracking of alkanes according to claim 1, wherein: The alkane is methane; the carbon radical intermediate forms ethane through a coupling reaction.

4. The method for direct photocatalytic cracking of alkanes according to claim 3, wherein: The wavelength range of the ultraviolet light is 100-272nm; the intensity of the light source is 10-200mW / cm 2 , the temperature is 10-60℃.

5. The method for direct photocatalytic cracking of alkanes according to claim 1, wherein: The alkane is n-hexane; and the carbon radical intermediate forms cyclohexane through an intramolecular ring-closing reaction.

6. The method for direct photocatalytic cracking of alkanes according to claim 5, characterized in that: The wavelength range of the ultraviolet light is 200-400nm; the intensity of the light source is 50-200mW / cm 2 , the temperature is 25-40℃.

7. The method for direct photocatalytic cracking of alkanes according to claim 6, characterized in that: The wavelength of the ultraviolet rays is 254 nm.

8. The method for direct photocatalytic cracking of alkanes according to claim 1, wherein: The self-reaction includes an intermolecular coupling reaction or an intramolecular ring-closing reaction.

9. The method for direct photocatalytic cracking of alkanes according to claim 7, wherein: The alkane introduced into the vacuum-treated reactor includes an inert carrier gas, and the volume ratio of the alkane to the inert carrier gas is 1:1-1:

4.

10. The method for direct photocatalytic cracking of alkanes according to claim 8, characterized in that: Online gas chromatography is used to analyze gaseous hydrogen and coupling products in real time, and the purity of the coupling products is detected by condensation separation-mass spectrometry technology; the coupling products include RR, alkane + alkene or cyclic compounds.

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