Method and system for photocatalytic oxidation of gaseous alkane

Abstract

The invention belongs to the technical field of photocatalytic oxidation of gaseous alkanes, and particularly relates to a method and system for photocatalytic oxidation of gaseous alkanes, and the method comprises the following steps: under illumination, enabling a photocatalyst, bubbles containing gaseous alkanes and chlorine-containing active substances to react at an interface of a two-phase system containing an organic phase and a water phase to generate an oxidation product, the oxidation product comprises one or more of acid, alcohol and aldehyde, and the organic phase can dissolve the chlorine-containing active substance. The method provided by the invention is beneficial to improving the generation rate of oxidation products and the apparent light quantum efficiency of photocatalytic reaction.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic oxidation of gaseous alkanes, and particularly relates to a method and system for photocatalytic oxidation of gaseous alkanes. BACKGROUND

[0002] Steam methane reforming process is generally used in industry, in which water vapor is used to convert methane into carbon monoxide and hydrogen at 700-1100℃ under the action of metal-based catalysts, and then liquid fuels such as methanol are prepared. This process has high energy consumption. In recent years, new type of catalytic materials for direct selective oxidation of methane have been developed, but the requirements for purity and concentration of raw materials are harsh, and the cost is high.

[0003] A method for light-driven selective oxidation of methane is reported, in which chlorine dioxide is excited by a xenon lamp with a wavelength greater than 320 nm and a power of 500 W to generate chlorine radicals, and the chlorine radicals can selectively oxidize methane dissolved in perfluorohexane solution within 15 minutes. The methane conversion rate of this method is as high as 99%, and the selective generation rates of methanol and formic acid are 14% and 85%, respectively. However, this method has the following problems: (1) methane needs to be dissolved in perfluorohexane before oxidation reaction, and the reaction is limited by the solubility and dissolution time of methane in perfluorohexane, and the generation rate of products is slow; (2) the reaction needs to be carried out under high light power, and the apparent photo quantum efficiency of the reaction is not high.

[0004] Therefore, the existing method for oxidizing gaseous alkanes such as methane needs to be improved. SUMMARY

[0005] The first aspect of the application provides a method for photocatalytic oxidation of gaseous alkanes, in which a photocatalyst, gas bubbles containing gaseous alkanes, and a chlorine-containing active substance are reacted at the interface of a two-phase system containing an organic phase and an aqueous phase under light to generate oxidation products, the oxidation products include one or more of acids, alcohols, and aldehydes, and the organic phase can dissolve the chlorine-containing active substance.

[0006] The method described in the application has at least the following beneficial effects: the method described in the application directly reacts the photocatalyst, gas bubbles containing gaseous alkanes, and a chlorine-containing active substance at the interface of a two-phase system containing an organic phase and an aqueous phase, which can improve the generation rate of products; the method described in the application uses light absorption by the photocatalyst to excite the reaction, and cooperates with the design of the multi-phase reaction system, which is beneficial to improve the apparent photo quantum efficiency of the reaction. In addition, the oxidation of gaseous alkanes can be realized at normal temperature and pressure using the method described in the application, which has low energy consumption.

[0007] In some embodiments, the two-phase system containing an organic phase and an aqueous phase is prepared by the following steps: An aqueous solution containing a chlorine-containing active substance is mixed with a first organic phase to obtain a two-phase system comprising a first aqueous phase and a first organic phase. The first organic phase in the two-phase system comprising a first aqueous phase and a first organic phase is separated, and the first organic phase is mixed with water to form the two-phase system containing both an organic phase and an aqueous phase. Thus, a two-phase system containing an aqueous phase and an organic phase dissolved with chlorine-containing active substances can be obtained.

[0008] In some embodiments, the aqueous solution containing the chlorine-containing active substance is prepared by the following method: Formulating a mixture containing ClO - and Cl - An aqueous solution is prepared by adjusting the pH of the aqueous solution to < 7.0, thereby obtaining the aqueous solution containing the chlorine-containing active substance; Alternatively, electrolysis containing Cl - An aqueous solution containing chlorine-containing active substances is obtained by dissolving the electrolysis product Cl2 in the aqueous solution on the anode side to obtain an anolyte solution, adjusting the pH of the anolyte solution to < 7.0.

[0009] In some embodiments, the gaseous alkane includes methane, and the oxidation product includes one or more of formic acid, methanol, and formaldehyde. Based on the similarity of the molecular structures of gaseous alkanes, in some embodiments, the gaseous alkane may include alkanes that are gaseous in their native state or at room temperature and pressure. As an example, the gaseous alkane may also include one or more of ethane, propane, n-butane, and isobutane, and the oxidation product includes one or more of an acid, alcohol, and aldehyde corresponding to the gaseous alkane.

[0010] In some embodiments, the method for generating the gaseous alkanes includes: introducing a gas containing the gaseous alkanes below the interface of the two-phase system. Since the gas containing the gaseous alkanes has a low density and low solubility, it will rise to the interface of the two-phase system in the form of bubbles, thereby forming gaseous alkanes at the interface.

[0011] In some embodiments, the gas containing the gaseous alkane is introduced into the interior of the organic phase. This facilitates the generation of gaseous alkane-containing bubbles.

[0012] In some embodiments, the gas containing the gaseous alkane is introduced at a rate of 0.01 mL / min to 20 mL / min.

[0013] In some embodiments, the average diameter of the bubbles containing the gaseous alkane is 50 nm to 500 μm. This is beneficial for increasing the yield.

[0014] In some embodiments, the wavelength of the illumination is 200 nm to 800 nm. This is beneficial for improving the efficiency of the photocatalytic reaction.

[0015] In some embodiments, the illumination power is greater than 0 W and less than or equal to 10 W. This is beneficial for improving the efficiency of the photocatalytic reaction.

[0016] In some embodiments, the photocatalyst comprises one or more of titanium dioxide, bismuth oxybromide, carbon nitride, bismuth vanadate, noble metal photocatalysts, metal-organic framework materials, covalent organic framework materials, hydrogen-bonded organic framework materials, and two-dimensional materials such as MXene. This is beneficial for improving the efficiency of the photocatalytic reaction.

[0017] In some embodiments, the gas containing gaseous alkanes includes one or more of the following: bio-fermentation source gas, waste treatment source gas, associated fossil fuel gas, combustion exhaust gas, and natural source gas. The method described in this application has a high tolerance for the concentration of gaseous alkanes in the gas containing gaseous alkanes and is applicable to the oxidation of various types of gaseous alkanes. Optionally, the bio-fermentation source gas includes one or more of the following: animal intestinal fermentation gas, fecal fermentation gas, and biomass digestion gas; and / or, the waste treatment source gas includes one or more of the following: solid waste landfill gas and wastewater treatment exhaust gas; and / or, the associated fossil fuel gas includes one or more of the following: oil and gas extraction escape gas, coalbed methane, and oil and gas pipeline leakage gas; and / or, the combustion exhaust gas includes one or more of the following: biomass fuel combustion exhaust gas, fossil fuel combustion exhaust gas, and engine exhaust gas; and / or, the natural source gas includes freshwater wetland biogas.

[0018] In some embodiments, the chlorine-containing active substance includes HClO, Cl2O, Cl2, polychlorinated monoanions, and Cl-. n - One or more of them.

[0019] In some embodiments, the organic phase includes one or more of perfluorooctane, perfluorohexane, perfluoropentane, perfluoronaphthane, perfluorocyclohexane, perfluoropolyether, polyfluoroether, perfluorotertiary amine, tetrachloroethylene, and carbon tetrachloride. Thus, the organic phase can form a stable two-phase system with the aqueous phase.

[0020] In some embodiments, the free chlorine concentration in the aqueous solution containing the chlorine-containing active substance is greater than or equal to 2 mg Cl2 / L. This is beneficial for improving the efficiency of the photocatalytic reaction.

[0021] In some embodiments, the organic phase includes the photocatalyst. During the reaction, the organic phase is disturbed, thereby allowing the photocatalyst to be better dispersed at the interface between the organic phase and the two-phase system, which is beneficial to improving the efficiency of the photocatalytic reaction.

[0022] In some embodiments, the aqueous phase is shielded from light during the reaction process. This reduces the occurrence of side reactions in the aqueous phase.

[0023] In some embodiments, the reaction temperature is greater than or equal to 0°C. This is beneficial for improving the efficiency of the photocatalytic reaction.

[0024] The second aspect of this application provides a system for the photocatalytic oxidation of gaseous alkanes, comprising: A photocatalytic oxidation device, comprising a two-phase system containing an organic phase and an aqueous phase, wherein the organic phase contains a chlorine-containing active substance and a photocatalyst; the photocatalytic oxidation device is provided with an inlet containing gaseous alkanes; and A light source is used to irradiate the interface between the organic phase and the two-phase system, causing the photocatalyst, gaseous alkanes, and chlorine-containing active substances to react at the interface between the organic phase and the two-phase system to generate oxidation products, wherein the oxidation products include one or more of acids, alcohols, and aldehydes.

[0025] The system described in this application allows for direct reaction of the photocatalyst, gaseous alkanes, and chlorine-containing active substances at the interface of a two-phase system containing an organic and an aqueous phase. This improves the product formation rate and enhances the apparent quantum efficiency of the reaction. Furthermore, the oxidation of gaseous alkanes can be achieved at room temperature and pressure, resulting in low energy consumption.

[0026] In some embodiments, the inlet for the gas containing gaseous alkanes is located below the interface of the two-phase system, for introducing the gas containing gaseous alkanes into the photocatalytic oxidation device, thereby forming gaseous alkanes-containing bubbles at the interface of the two-phase system.

[0027] In some embodiments, the device further includes an extraction apparatus for chlorine-containing active substances, which comprises an aqueous solution containing the chlorine-containing active substance and a first organic phase, wherein... The chlorine-containing active substance extraction device corresponding to the first organic compound is provided with a first liquid outlet and a first liquid inlet; The photocatalytic oxidation device corresponding to the organic compound is provided with a second inlet and a second outlet; the second inlet is connected to the first outlet, and the second outlet is connected to the first inlet. Thus, an organic phase containing chlorine-containing active substances can be obtained in the chlorine-containing active substance extraction device and supplied to the photocatalytic oxidation device.

[0028] In some embodiments, the chlorine-containing active substance extraction device corresponding to the aqueous solution containing the chlorine-containing active substance is provided with a third inlet and a third outlet; The system also includes an electrolysis device, which contains Cl... - The electrolysis device has a fourth outlet on the anode side and a fourth inlet on the cathode side. The fourth outlet is connected to the third inlet, and vice versa. Thus, the electrolysis device can generate Cl2 through electrolysis. The Cl2, after dissolving in water, can provide a chlorine source for the aqueous solution containing chlorine-containing active substances in the chlorine-containing active substance extraction device.

[0029] In some embodiments, the photocatalytic oxidation device corresponding to the water is further provided with a fifth liquid outlet and a fifth liquid inlet. The system also includes a product purification device, which has a sixth inlet and a sixth outlet. The sixth inlet is connected to the fifth outlet, and the sixth outlet is connected to the fifth inlet. This allows the product obtained from the photocatalytic reaction to be separated from the aqueous phase.

[0030] In some embodiments, the photocatalytic oxidation device has an inlet for gaseous alkanes at the bottom and an outlet for exhaust gas at the top, the outlet being connected to the inlet for gaseous alkanes. Thus, by introducing gaseous alkanes from the bottom of the device and recovering unreacted gas from the top for further reaction, the utilization rate of gaseous alkanes can be improved.

[0031] In some embodiments, the photocatalytic oxidation device containing the aqueous phase is equipped with a light-shielding device. This application does not limit the specific structure and arrangement of the light-shielding device, as long as it achieves the purpose of shielding the aqueous phase. As an example, the light-shielding device may include a light-shielding film, which may wrap around the outer wall of the photocatalytic oxidation device corresponding to the aqueous phase or be attached to the inner wall of the photocatalytic oxidation device corresponding to the aqueous phase; furthermore, multiple light-shielding membranes may be provided in the aqueous phase, or both a light-shielding film and multiple light-shielding membranes may be provided simultaneously. Attached Figure Description

[0032] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application; irrelevant details have been omitted for clarity. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a schematic diagram of the structure of a system for photocatalytic oxidation of gaseous alkanes according to some embodiments of this application; Figure 2 This is a schematic diagram of the structure of a system for photocatalytic oxidation of gaseous alkanes according to some embodiments of this application.

[0033] Explanation of reference numerals in the attached figures: 1 Photocatalytic oxidation device; 11 Organic phase; 12 Aqueous phase; 13 Inlet for gas containing gaseous alkanes; 14 Interface of the two-phase system; 15 Second inlet; 16 Second outlet; 17 Fifth outlet; 18 Fifth inlet; 19 Tail gas outlet; 2 Light source; 3 Chlorine-containing active substance extraction device; 31 Aqueous solution containing chlorine-containing active substances; 32 First organic phase; 33 First outlet; 34 First inlet; 35 Third inlet; 36 Third outlet; 4 Electrolysis device; 41 Fourth outlet; 42 Fourth inlet; 5 Product purification device; 51 Sixth inlet; 52 Sixth outlet. Detailed Implementation

[0034] The present application will now be described in detail with reference to the accompanying drawings and specific embodiments. The embodiments shown below are not intended to limit the scope of the invention as described in the claims. Furthermore, the complete contents of the configurations illustrated in the following embodiments are not limited to those necessary for the solution of the invention as described in the claims.

[0035] As used herein, the term "comprising" should be interpreted as inclusive and open-ended, not exclusive. Specifically, when used in the specification and claims, the term "comprising" and its variations mean including the specified features, steps, or components. These terms should not be construed as excluding the presence of other features, steps, or components.

[0036] In this document, the terms "first," "second," "third," "fourth," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," "third," "fourth," etc., may explicitly or implicitly include at least one of those features.

[0037] Wherever a range of values ​​is given herein, the range includes its endpoints, as well as all individual integers and fractions within the range, and also includes each narrower range formed by all the various possible combinations of those endpoints and internal integers and fractions, to form a subgroup of a larger group of values ​​within the same extent as each of those narrower ranges is explicitly given.

[0038] The first aspect of this application provides a method for photocatalytic oxidation of gaseous alkanes, wherein under light irradiation, a photocatalyst, gas bubbles containing gaseous alkanes, and a chlorine-containing active substance react at the interface of a two-phase system containing an organic phase and an aqueous phase to generate oxidation products, wherein the oxidation products include one or more of acids, alcohols, and aldehydes, and the organic phase is capable of dissolving the chlorine-containing active substance.

[0039] The method described in this application directly causes the photocatalyst, gaseous alkanes, and chlorine-containing active substances to react at the interface of a two-phase system containing an organic phase and an aqueous phase. This eliminates the need to first dissolve the gaseous alkanes in the organic phase before oxidation, thus avoiding or reducing the limitations imposed by the solubility and dissolution time of the gaseous alkanes in the organic phase on the reaction, thereby increasing the product formation rate. Furthermore, the method described in this application utilizes light absorption by the photocatalyst to excite the reaction, which improves photon utilization efficiency. The fact that the reaction occurs at the interface of the organic and aqueous phases facilitates rapid product transfer to the aqueous phase, reducing side reactions and further improving the apparent quantum efficiency of the photocatalytic oxidation reaction. Moreover, the method described in this application can achieve the oxidation of gaseous alkanes at room temperature and pressure, resulting in low energy consumption.

[0040] The apparent quantum efficiency (AQE) described in this application refers to the proportion of incident photons absorbed by a material that can successfully trigger a photochemical or photoelectric reaction at the target.

[0041] The ambient temperature mentioned in this application refers to the temperature range commonly found in natural environments, and the atmospheric pressure refers to the normal atmospheric pressure range at the Earth's surface. The reaction described in this application can be carried out at ambient temperature and atmospheric pressure, but this application does not limit the reaction to being carried out only at ambient temperature and atmospheric pressure.

[0042] The method described in this application does not limit the specific locations of the organic phase and the aqueous phase, as long as a two-phase system can be formed and a stable two-phase interface can be formed. As an example, the organic phase can be located below the aqueous phase (i.e., the density of the organic phase can be greater than the density of the aqueous phase), or the organic phase can be located above the aqueous phase (i.e., the density of the organic phase can be less than the density of the aqueous phase).

[0043] It should be noted that the method described in this application can achieve the oxidation of gaseous alkanes at room temperature and pressure. However, this application does not necessarily limit the method to only achieving the oxidation of gaseous alkanes at room temperature and pressure. As an example, the reaction can occur at a temperature greater than or equal to about 0°C. For example, the reaction temperature can be 0°C, 10°C, 20°C, 25°C, 30°C, 40°C, 50°C, 80°C, 90°C, or any range between any two of the above values.

[0044] In some embodiments, the aqueous phase is shielded from light during the reaction. This reduces or prevents the decomposition of small amounts of chlorine-containing reactive substances entering the aqueous phase by light, thereby reducing or preventing the formation of oxidizing intermediates in the aqueous phase, and thus reducing or preventing further oxidation of the products entering the aqueous phase.

[0045] It should be noted that this application does not particularly limit the method of shading the aqueous phase. Those skilled in the art can choose according to actual needs, as long as it can reduce the light exposure of the aqueous phase.

[0046] In some embodiments, the two-phase system containing an organic phase and an aqueous phase is prepared using the following steps: S100: An aqueous solution containing a chlorine-containing active substance is mixed with a first organic phase, thereby allowing the chlorine-containing active substance to be extracted from the aqueous solution using the first organic phase, resulting in a two-phase system comprising a first aqueous phase and a first organic phase, wherein the organic phase contains a chlorine-containing active substance dissolved in it.

[0047] It should be noted that the mixing of the aqueous solution containing the chlorine-containing active substance with the first organic phase in this step can be one or more of the following: stirring, shaking, or other mixing methods involving relatively vigorous disturbance. After mixing, the mixture is allowed to stand and separate into layers, which is more conducive to the transfer of the chlorine-containing active substance from the aqueous solution to the organic phase. S200: Separate the first organic phase from the two-phase system containing the first aqueous phase and the first organic phase, and mix the first organic phase with water, thereby forming the two-phase system containing the organic phase and the aqueous phase.

[0048] It should be noted that after separating the first organic phase from the first aqueous phase in step S200, the first organic phase is then mixed with water again to obtain a two-phase system. This minimizes the content of chlorine-containing active substances in the aqueous phase and prevents oxidation products from entering the aqueous phase and being further oxidized. The mixing in this step includes pouring the organic phase into the aqueous phase or vice versa. Preferably, the mixing is done without drastic disturbance, thereby reducing or preventing chlorine-containing active substances in the organic phase from entering the aqueous phase.

[0049] It should be noted that the organic phase mentioned in this application refers to the organic phase in the two-phase system containing both an organic phase and an aqueous phase, wherein the chlorine-containing active substance is dissolved in the organic phase; the first organic phase refers to the organic phase before the formation of the two-phase system. Furthermore, in this application, the first aqueous phase refers to the aqueous phase after the aqueous solution containing the chlorine-containing active substance is mixed with the first organic phase and allowed to stand and separate into layers.

[0050] This application does not limit the specific source and preparation method of the aqueous solution containing the chlorine-containing active substance, as long as it contains the chlorine-containing active substance.

[0051] As an example, the aqueous solution containing the chlorine-containing active substance can be prepared by the following method: Formulating a mixture containing ClO - and Cl - An aqueous solution is prepared by adjusting the pH of the aqueous solution to be less than 7.0. Specifically, the pH can be 1, 2, 3, 4, 5, 6, or any range between two of the above values, thereby obtaining the aqueous solution containing the chlorine-containing active substance. As an example, the ClO... - It can originate from HClO; in a low pH environment, HClO reacts with H+. + and Cl - Cl2 is generated through ion exchange, and Cl2 reacts with excess Cl... - Combined to form highly active polychloride monoanion Cl n - (such as Cl3) - ); Cl n - With HClO / ClO - Nucleophilic substitution occurs, and the highly reactive non-radical oxidant Cl2O is generated through O-Cl bond recombination. The entire process is dominated by chemical equilibrium, ultimately yielding an aqueous solution containing chlorine-containing reactive substances.

[0052] As an example, the aqueous solution containing the chlorine-containing active substance can also be prepared by the following method: Electrolysis containing Cl - An anolyte is obtained by electrolyzing an aqueous solution to obtain an anolyte solution. The pH of the anolyte solution is adjusted to be less than 7.0. Specifically, the pH can be 1, 2, 3, 4, 5, 6, or any range between two of the above values, thereby obtaining the aqueous solution containing the chlorine-containing active substance. It should be noted that, in this application, the anolyte solution refers to the solution obtained by electrolyzing a solution containing Cl. - The solution obtained by dissolving the anolyte Cl2, obtained from an aqueous solution, in an aqueous solution is described in this application. This application does not limit the content of Cl2 in the solution. - The specific composition of the aqueous solution, as an example, may include one or more of NaCl, KCl, etc. In this example, the solution is driven by an external electric field to contain Cl... -Chloride ions (Cl) in aqueous solutions (such as NaCl solution) - At the anode, an oxidation reaction occurs to produce chlorine gas (Cl2). The mechanism is that the positive voltage applied to the anode forces chloride ions to lose electrons (2Cl2). - → Cl2 + 2e - This process requires overcoming the electrochemical energy barrier and lowering the activation energy of the reaction through a catalytic electrode (such as a titanium electrode coated with RuO2). The Cl2 generated on the anode side partially dissolves in water and undergoes a reversible reaction with water (Cl2 + H2O). H + + Cl - + HClO), therefore the anolyte solution may contain Cl2, HClO, Cl... - and H + Components such as... When the pH of the anolyte solution is adjusted to <7 (acidic conditions), H... + Increased concentration will push the above equilibrium forward, promoting the formation of HClO; at the same time, excess Cl... - It combines with Cl2 in the solution to form polychlorinated anions (such as Cl3). - These polychlorinated anions further undergo nucleophilic substitution reactions with HClO, forming the highly reactive non-radical oxidant Cl2O through O-Cl bond recombination. The entire process is also dominated by chemical equilibrium, ultimately yielding an aqueous solution containing chlorinated reactive substances.

[0053] In some embodiments, the chlorine-containing active substance includes HClO, Cl2O, Cl2, polychlorinated monoanions, and Cl-. n - One or more of the above. This application specifies that the chlorine-containing active substance meets the above conditions. On the one hand, HClO can generate Cl under the action of light and photocatalyst. ,ClO Active species; Cl2O can decompose into Cl under light and photocatalysis. and oxygen-containing reactive species (such as O) Cl2 can be converted into Cl under light and photocatalysis. Polychloride ions and monoanions (Cl) n - (such as Cl3) - Cl5 - (etc.) can gradually dissociate into Cl under the action of light and photocatalyst. This facilitates the formation of active chlorine species, thereby improving the efficiency of photocatalytic oxidation reactions. It should be noted that the above explanation of the active chlorine species formation pathway is only a possible mechanistic hypothesis and not an absolute limitation on the nature of the reaction. On the other hand, the byproducts that may be generated during the reaction of the aforementioned chlorine-containing active substances are mainly inorganic chlorine species such as HCl, without the formation of persistent organic pollutants or recalcitrant toxic substances. These inorganic chlorine byproducts can be effectively treated through simple separation, neutralization, or recycling processes, thus better meeting the application requirements of green chemistry.

[0054] In this application, the polychlorinated monoanion Cl... n - This includes mononuclear anionic species formed by multiple chlorine atoms bonded together by covalent bonds, each carrying an overall negative charge. This application does not limit the polychlorinated monoanion Cl to this specific species. n - The amount of Cl in the present application, as an example, is Cl. n - It can include Cl3 - Cl5 - One or two of them.

[0055] In some embodiments, the organic phase includes one or more of perfluorooctane, perfluorohexane, perfluoropentane, perfluoronaphthane, perfluorocyclohexane, perfluoropolyether, polyfluoroether, perfluorotertiary amine, tetrachloroethylene, and carbon tetrachloride. Therefore, the organic phase is chemically stable and insoluble or sparingly soluble in water, allowing it to form a stable two-phase system with the aqueous phase and a stable phase interface between the two phases.

[0056] In some embodiments, the free chlorine concentration in the aqueous solution containing the chlorine-containing active substance is greater than or equal to 2 mg Cl2 / L. This application specifies that the free chlorine concentration meets the above condition, which is beneficial for improving the efficiency of the photocatalytic reaction. As an example, the free chlorine concentration can be 2 mg Cl2 / L, 4 mg Cl2 / L, 6 mg Cl2 / L, 8 mg Cl2 / L, 10 mg Cl2 / L, 20 mg Cl2 / L, 50 mg Cl2 / L, 100 mg Cl2 / L, 200 mg Cl2 / L, etc., or any range between two of the above values. It should be noted that the free chlorine includes the sum of oxidizing chlorine species existing in an unbound state, including molecular chlorine (Cl2), hypochlorous acid (HClO), dichlorvos (Cl2O), and / or intermediates that can partially dissociate into active chlorine (such as Cl3). - (e.g., the dissociation states of polychloride ions and monoanions). In this application, the concentration of free chlorine is expressed as the equivalent mass concentration of Cl2 (i.e., the content converted to Cl2), which can reflect the total amount of active chlorine in the organic phase that can directly participate in the activation reaction of gaseous alkanes.

[0057] In some embodiments, the organic phase includes the photocatalyst. During the reaction, the organic phase is disturbed to allow the photocatalyst to be better dispersed at the interface between the organic phase and / or the two-phase system. This increases the area of ​​the photocatalyst exposed to light and / or its contact rate with chlorine-containing active substances, thereby improving the efficiency of the photocatalytic reaction. It should be noted that this application does not limit the specific method and intensity of the disturbance. As an example, the disturbance can be achieved by stirring the organic phase using any suitable stirring device. It is important to note that the intensity of the disturbance is limited to promoting the dispersion of the photocatalyst without disrupting the stability at the two-phase interface.

[0058] In some embodiments, the photocatalyst includes one or more of titanium dioxide, bismuth oxybromide, carbon nitride, bismuth vanadate, noble metal photocatalysts, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), and two-dimensional materials MXene. This application limits the photocatalyst to the above-mentioned range, which is beneficial for improving the light absorption performance of the photocatalyst and its chemical stability in the reaction system described in this application; it is also beneficial for improving the dispersion performance of the photocatalyst at the interface of the two-phase system, thereby further improving the efficiency of the photocatalytic reaction.

[0059] In some embodiments, the wavelength of the illumination can be 200 nm-800 nm, where 200 nm-400 nm belongs to the ultraviolet region, 400 nm-760 nm belongs to the visible light region, and 760 nm-800 nm belongs to the near-infrared region. As an example, the wavelength of the illumination can specifically be 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, etc., or any range between two of these values. This application further limits the wavelength of the illumination to the above range, which can more efficiently excite the photocatalyst to generate photogenerated carriers with oxidizing properties, thereby improving the efficiency of the photocatalytic reaction.

[0060] This application does not impose excessive limitations on the light intensity or light power. Theoretically, any light intensity or light power greater than 0 is acceptable. As an example, the light power can be 0-10W, specifically 0.1 W, 0.5 W, 1 W, 2 W, 4 W, 6 W, 8 W, 10 W, or any range between any two of the above values.

[0061] In the reaction process described in this application, under light irradiation, the photocatalyst can catalyze the generation of highly reactive chlorine species (such as chlorine free radicals Cl) from chlorine-containing reactive substances. ,ClO Highly reactive chlorine species can contact gaseous alkanes at the interface between the bubble and the organic phase, thereby mediating the selective activation and oxidation of the CH bonds of the gaseous alkanes. This ultimately leads to the selective oxidation of the gaseous alkanes to generate oxidation products, which include one or more of acids, alcohols, and aldehydes. Since the above reaction continuously consumes the gaseous alkanes at the interface between the bubble and the organic phase, the gaseous alkanes within the bubble continuously diffuse towards the interface, providing gaseous alkane feedstock for the reaction until the gaseous alkanes in the bubble are completely consumed. Based on the similarity between the molecular structure and reaction characteristics of gaseous alkanes, the method described in this application is applicable to various gaseous alkanes. As an example, the gaseous alkanes may include one or more of methane, ethane, propane, n-butane, and isobutane, and the oxidation products include one or more of the acids, alcohols, and aldehydes corresponding to the gaseous alkanes. As an example, when the gaseous alkanes include methane, the oxidation products include formic acid, methanol, and / or formaldehyde.

[0062] The method described in this application does not have strict requirements on the concentration of gaseous alkanes in the gas containing gaseous alkanes. Theoretically, as long as the gas contains gaseous alkanes, this reaction can occur. Therefore, the method described in this application is applicable to the oxidation of various types of gaseous alkanes. For example, the gas containing gaseous alkanes may include one or more of the following: bio-fermentation source gas, waste treatment source gas, associated fossil fuel gas, combustion exhaust gas, and natural source gas. For example, the bio-fermentation source gas includes one or more of the following: animal intestinal fermentation gas, fecal fermentation gas, and biomass digestion gas; for example, the waste treatment source gas includes one or more of the following: solid waste landfill gas and wastewater treatment exhaust gas; for example, the associated fossil fuel gas includes one or more of the following: oil and gas extraction escape gas, coalbed methane, and oil and gas pipeline leakage gas; for example, the combustion exhaust gas includes one or more of the following: biomass fuel combustion exhaust gas, fossil fuel combustion exhaust gas, and engine exhaust gas; for example, the natural source gas includes freshwater wetland biogas.

[0063] In some embodiments, the method for generating the gaseous alkanes includes: introducing a gaseous alkane into the space below the interface of the two-phase system. Because the gaseous alkane has a low density and low solubility, it will rise to the interface of the two-phase system in the form of bubbles. Due to interfacial tension and other factors, the bubbles at the interface reach a force equilibrium and thus remain at the interface. In the reaction process described in this application, the gaseous alkanes in the bubbles remaining at the interface come into contact with chlorine-containing active substances, photocatalysts, and / or decomposition products of chlorine-containing active substances at the bubble boundary, and are selectively oxidized to generate oxidation products, which include one or more of acids, alcohols, and aldehydes. The generated oxidation products then transfer from the bubble boundary to the aqueous phase.

[0064] In some embodiments, the organic phase is located below the aqueous phase (i.e., the density of the organic phase is greater than that of the aqueous phase). In this case, the gas containing the gaseous alkane is introduced into the interior of the organic phase. This facilitates the generation of gaseous alkane-containing bubbles.

[0065] This application does not impose many restrictions on the rate of introduction of the gas containing the gaseous alkane. Theoretically, as long as the gas is introduced, the reaction can occur. As an example, the introduction rate can be 0.01 mL / min to 20 mL / min, for example, specifically 0.01 mL / min, 0.05 mL / min, 0.1 mL / min, 1 mL / min, 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, etc., or any range between any two of the above values.

[0066] In some embodiments, the average diameter of the bubbles containing the gaseous alkane is 50 nm to 500 μm. This is beneficial for improving the yield. As an example, the average diameter of the bubbles containing the gaseous alkane can be 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc., or any range between two of the above values. It should be noted that the bubbles containing gaseous alkane mentioned here refer to the average diameter of the bubbles containing gaseous alkane in the organic phase, and the diameter of the bubbles containing gaseous alkane is measured according to ISO 13320 laser diffraction or ISO 9276 electron microscopy statistical method.

[0067] The second aspect of this application provides a system for the photocatalytic oxidation of gaseous alkanes, see reference. Figure 1 The system includes a photocatalytic oxidation device 1 and a light source 2.

[0068] Using the system described in this application, the photocatalyst, gaseous alkanes, and chlorine-containing active substances can directly react at the interface 14 between the organic and aqueous phases, which can increase the product formation rate and improve the apparent quantum efficiency of the reaction. Furthermore, the oxidation of gaseous alkanes can be achieved at room temperature and pressure, resulting in low energy consumption.

[0069] refer to Figure 1 The photocatalytic oxidation device 1 includes a two-phase system containing an organic phase 11 and an aqueous phase 12. The organic phase 11 contains a chlorine-containing active substance and a photocatalyst. The photocatalytic oxidation device 1 is provided with an inlet 13 containing gaseous alkanes.

[0070] In the system described in this application, the relative positions of the organic phase 11 and the aqueous phase 12 are not specifically limited, as long as a two-phase system can be formed and a stable two-phase interface exists.

[0071] As an example, the organic phase 11 can be located above the aqueous phase 12, and a photocatalyst with a density lower than water can be used, so that the organic phase 11 includes chlorine-containing active substances and photocatalysts. Gas bubbles containing gaseous alkanes can be formed in the aqueous phase 12 and then float to the interface, at which point the photocatalytic oxidation reaction mainly occurs at the interface 14; in addition, some gaseous alkanes in the gaseous alkanes dissolve into the organic phase 11, and photocatalytic oxidation reactions can also occur in the organic phase 11.

[0072] As an example, the organic phase 11 can be located below the aqueous phase 12, in which case the aqueous phase 12 can act as a water seal for the organic phase 11, preventing its volatilization. For example, a photocatalyst with a density greater than water can be used, so that the organic phase 11 includes chlorine-containing active substances and the photocatalyst. Gas bubbles containing gaseous alkanes can be formed in the organic phase 11 and then float to the interface, where the photocatalytic oxidation reaction mainly occurs at the interface 14.

[0073] refer to Figure 2 In some embodiments, the inlet 13 for the gas containing gaseous alkanes is located below the interface 14 of the two-phase system, for introducing the gas containing gaseous alkanes into the photocatalytic oxidation device 1. Since the gas containing gaseous alkanes has a low density and low solubility, it will float to the interface 14 of the two-phase system in the form of bubbles, thereby forming gaseous alkanes bubbles at the interface 14 of the two-phase system.

[0074] refer to Figure 2 In some embodiments, the photocatalytic oxidation device 1 has an inlet 13 for gaseous alkanes at its bottom and an outlet 19 at its top, the outlet 19 being connected to the inlet 13. This application further specifies that the system structure satisfies the above limitations, allowing gaseous alkanes to be introduced from the bottom of the photocatalytic oxidation device 1, while unreacted gaseous alkanes can flow out from the top and return to the device through the inlet to continue participating in the reaction. This improves the utilization rate of gaseous alkanes in the gaseous alkanes.

[0075] refer to Figure 2In some embodiments, the photocatalytic oxidation device 1 containing the aqueous phase 12 is equipped with a light-shielding device. This application does not limit the specific structure and arrangement of the light-shielding device, as long as it achieves the purpose of shielding the aqueous phase. As an example, to facilitate light exposure at the interface 14 and the organic phase 11, the photocatalytic oxidation device 1 can be made of a transparent material. In this case, the light-shielding device can include a light-shielding film, which can be wrapped around the outer wall of the photocatalytic oxidation device 1 corresponding to the aqueous phase 12 or attached to the inner wall of the photocatalytic oxidation device 1 corresponding to the aqueous phase 12. Furthermore, the light-shielding device can also include multiple layers of light-shielding membranes disposed in the aqueous phase 12, or it can simultaneously include a light-shielding film and multiple layers of light-shielding membranes, or it can include other structures or other forms of light-shielding components, either individually or simultaneously. This application does not impose any limitations on this.

[0076] refer to Figure 1 The light source 2 is used to irradiate the interface 14 between the organic phase 11 and the two-phase system. Under normal temperature and pressure, the photocatalyst, gaseous alkanes, and chlorine-containing active substances react at the interface 14 to generate oxidation products, which include one or more of acids, alcohols, and aldehydes. In the system described in this application, the connection relationship between the light source 2 and the photocatalytic oxidation device 1 is not limited, as long as the above functions can be achieved.

[0077] In the system described in this application, the specific type and quantity of the light source 2 are not limited. For example, the light source 2 can be one or more of ultraviolet light sources, visible light sources, and infrared light sources. As an example, the light source 2 can specifically be one or more of mercury lamps, LED arrays, xenon lamps, etc.

[0078] refer to Figure 2(The arrows in the figure indicate the material flow direction.) In some embodiments, the system further includes a chlorine-containing active substance extraction device 3, which includes an aqueous solution 31 containing chlorine-containing active substances and a first organic phase 32. The chlorine-containing active substance extraction device corresponding to the first organic phase 32 is provided with a first outlet 33 and a first inlet 34. The photocatalytic oxidation device corresponding to the organic phase 11 is provided with a second inlet 15 and a second outlet 16. The second inlet 15 is connected to the first outlet 33, and the second outlet 16 is connected to the first inlet 34. Therefore, the first organic phase 32 can be connected to the organic phase 11. The first organic phase 32 extracts chlorine-containing active substances from the aqueous solution 31 containing chlorine-containing active substances in the chlorine-containing active substance extraction device 3. Then, the first organic phase 32 containing dissolved chlorine-containing active substances can be transported to the organic phase 11 in the photocatalytic oxidation device 1 to replenish the chlorine-containing active substances in the organic phase 11. After the chlorine-containing active substances in the organic phase 11 are consumed, they can also be transported to the chlorine-containing active substance extraction device 3 to continue extracting the chlorine-containing active substances as a new first organic phase 32. Thus, the recycling of organic phases can be achieved.

[0079] refer to Figure 2 In some embodiments, the system further includes an electrolysis device 4, which contains Cl... - The electrolysis device 4 has a fourth outlet 41 on the anode side and a fourth inlet 42 on the cathode side. The chlorine-containing active substance extraction device 3, corresponding to the aqueous solution 31 containing chlorine-containing active substances, has a third inlet 35 and a third outlet 36. The fourth outlet 41 is connected to the third inlet 35, and the fourth inlet 42 is connected to the third outlet 36. The electrolysis device 4 can electrolyze solutions containing Cl... - The aqueous solution produces Cl2, which dissolves in water to obtain an aqueous solution 31 containing chlorine-containing active substances. The system described in this application connects the electrolysis device 4 to the aqueous solution in the chlorine-containing active substance extraction device 3, providing the aqueous solution with chlorine-containing active substances. Then, the chlorine-containing active substances in the aqueous solution of the chlorine-containing active substance extraction device 3 are transferred to the first organic phase 32 based on differences in solubility. Afterward, the aqueous solution can be returned to the electrolysis device 4 to replenish the electrolyte, thereby achieving water recycling.

[0080] refer to Figure 2In some embodiments, the system further includes a product purification device 5, which has a sixth inlet 51 and a sixth outlet 52. The photocatalytic oxidation device 1 corresponding to the aqueous phase 12 also has a fifth outlet 17 and a fifth inlet 18. The sixth inlet 51 is connected to the fifth outlet 17, and the sixth outlet 52 is connected to the fifth inlet 18. By connecting the aqueous phase 12 to the product purification device 5, the aqueous phase 12 can be transported to the product purification device 5 for separation and purification to obtain the product. Alternatively, the aqueous phase in the product purification device 5 can be returned to the photocatalytic oxidation device 1, thereby achieving the recycling of the aqueous phase.

[0081] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0082] Example 1

[0083] A method for photocatalytic oxidation of methane, in this embodiment, is implemented using a system for photocatalytic methane oxidation, and specifically includes the following steps: (1) Prepare a mixed aqueous solution containing NaClO (concentration of 100 ppm) and NaCl (concentration of 3 M), add HCl to the mixed aqueous solution to adjust the pH to about 3.5, and test the concentration of free chlorine in the mixed aqueous solution (the test results are shown in Table 1); then add perfluorooctane to the mixed aqueous solution, control the volume ratio of the mixed aqueous solution to perfluorooctane to be 3:1, shake well and let stand to separate the layers. The upper layer is the first aqueous phase and the lower layer is the perfluorooctane phase containing chlorine-containing active substances. After separation, the perfluorooctane phase is obtained. (2) Take 5 mL of the perfluorooctane phase obtained in step (1) and add it to a colorimetric tube (i.e., photocatalytic oxidation device) with a diameter of 20 mm and a volume of 25 mL. Then slowly add 10 mL of pure water to it and let it stand to obtain a two-phase system with a perfluorooctane phase in the lower layer and an aqueous phase in the upper layer. Wrap tin foil around the wall of the colorimetric tube corresponding to the aqueous phase to keep the aqueous phase in a light-shielding environment. Then add 60 mg of bismuth oxybromine (BiOBr) material in tetragonal layered crystal form as a photocatalyst to the perfluorooctane phase. The equivalent circle diameter of the BiOBr material is in the micrometer range. (3) Magnetic stirring of the perfluorooctane phase, adjusting the stirring speed to 400 rpm, so that the stirring does not damage the stability of the two-phase interface, and at the same time, the photocatalyst powder can be dispersed in the perfluorooctane phase and the two-phase interface. (4) Use LED lamps as light sources with a wavelength of 420nm and a power of 5W to irradiate the perfluorooctane phase and the interface between the two phases; control the temperature of the perfluorooctane phase and the interface between the two phases at around 25℃ under normal pressure (1 standard atmosphere); introduce pure methane gas into the perfluorooctane phase through a gas pipe and control the distance between the outlet of the methane-containing gas and the interface between the two phases to be around 2.5cm. Methane-containing bubbles are generated in the perfluorooctane phase. The bubbles float to the interface between the two phases and stay and accumulate. Control the rate of methane gas introduction to be 3mL / min and the median diameter Dv50 of the methane-containing bubbles in the perfluorooctane phase to be 110μm. (5) After the reaction for 1 hour, take 1 mL of the upper aqueous phase, filter it with a 0.22 μm filter membrane, and detect the concentration of the product in the filtered aqueous phase.

[0084] Example 2

[0085] The difference between this embodiment and Example 1 is that titanium dioxide (average particle size <20nm) is used as the photocatalyst, and step (1) is also different, while other conditions are the same.

[0086] Step (1) of this embodiment is as follows: Electrolyzing a substance containing Cl in an electrolysis device - An aqueous solution, with the temperature controlled at 25℃, Cl... - The concentration was 0.03M, pH < 8, the anode of the electrolytic cell was a ruthenium-iridium titanium electrode, the cathode was a titanium electrode, and the electrolysis current was 0.03A. The solution from the anode side of the electrolytic device was taken to obtain an anolyte containing dissolved Cl2. The pH of the anolyte was adjusted to approximately 3.5, and then perfluorooctane was added. After standing and separating the layers, the upper layer was the first aqueous phase, and the lower layer was the perfluorooctane phase containing dissolved chlorine-containing active substances. After separation, the perfluorooctane phase was obtained.

[0087] The difference between Examples 3-5 and Example 1 is that the light wavelength is different, but all other conditions are the same, as detailed in Table 1.

[0088] The difference between Examples 6-8 and Example 1 is that the light power is different, but all other conditions are the same, as detailed in Table 1.

[0089] The difference between Examples 9-12 and Example 1 is that the concentration of free chlorine is different, while all other conditions are the same, as detailed in Table 1.

[0090] The difference between Examples 13-15 and Example 1 is that the types of organic phases are different, while all other conditions are the same, as detailed in Table 1.

[0091] The difference between Example 16 and Example 1 is that the reaction temperature is different, but all other conditions are the same, as detailed in Table 1.

[0092] The difference between Examples 17-19 and Example 1 is that the concentration of methane in the methane-containing gas is different, while all other conditions are the same, as detailed in Table 1.

[0093] Comparative Example 1

[0094] The difference between this comparative example and Example 13 lies in steps (1) and (4), while the other steps are the same, as follows: (1) Prepare a mixed aqueous solution containing NaClO and NaCl, adjust the pH of the mixed aqueous solution to about 3.5, then add a perfluorohexane solution saturated with methane CH4 to the mixed aqueous solution, let it stand and separate into layers, the upper layer is the first aqueous phase, and the lower layer is the perfluorohexane phase containing chlorine-containing active substances and methane. After separation, the perfluorohexane phase is obtained. (2) Take 5 mL of the perfluorohexane phase obtained in step (1) and add it to a colorimetric tube (i.e., photocatalytic oxidation device) with a diameter of 20 mm and a volume of 25 mL. Then slowly add 10 mL of pure water to it and let it stand to obtain a two-phase system with a perfluorohexane phase at the bottom and an aqueous phase at the top. Wrap tin foil around the wall of the colorimetric tube corresponding to the aqueous phase to keep the aqueous phase in a light-proof environment. Then add photocatalyst powder to the perfluorohexane phase. (3) Magnetic stirring of the perfluorohexane phase, adjusting the stirring speed to ensure that it does not damage the stability of the two-phase interface, and at the same time, the photocatalyst powder can be dispersed in the perfluorohexane phase and at the two-phase interface. (4) Use LED lights as the light source to illuminate the perfluorohexane phase and the interface between the two phases; control the temperature of the perfluorohexane phase and the interface between the two phases to about 25°C; slowly introduce methane gas into the bottom of the colorimetric tube through the vent pipe, and control the rate of methane introduction so that no bubbles are generated (i.e., replenish the methane consumed in the perfluorohexane phase to keep the methane in the phase saturated). (5) After the reaction has been going on for 1 hour, take 1 mL of the upper aqueous phase, filter it with a 0.22 μm filter membrane, and detect the concentration of the product in the filtered aqueous phase.

[0095] Comparative Example 2

[0096] The difference between this comparative example and Example 1 is that no photocatalyst is added, while all other conditions are the same.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 1 is that perfluorooctane is not used. The specific steps are as follows: (1) Prepare a mixed aqueous solution containing NaClO (concentration of 100ppm) and NaCl (concentration of 3M), and add HCl to the mixed aqueous solution to adjust the pH to about 3.5; (2) Take 5 mL of the aqueous solution obtained in step (1) and add it into a colorimetric tube (i.e., photocatalytic oxidation device) with a diameter of 20 mm and a volume of 25 mL, and add 60 mg of bismuth oxybromine photocatalyst to it; (3) Magnetic stirring, adjust the stirring speed to 400 rpm to disperse the photocatalyst powder; (4) Use LED lamps as light sources with a wavelength of 420nm and a power of 5W to irradiate the aqueous solution containing the catalyst; control the temperature at around 25℃ under normal pressure (1 standard atmosphere); introduce pure methane gas into the aqueous solution through a gas pipe and control the distance between the outlet of the methane-containing gas and the liquid surface to be around 2.5cm to generate methane-containing bubbles in the aqueous solution; control the rate of methane gas introduction to be 3mL / min and the median diameter Dv50 of the methane-containing bubbles in the aqueous solution to be 110 μm. (5) After reacting for 1 hour, take 1 mL of the aqueous solution, filter it using a 0.22 μm filter membrane, and detect the concentration of the product in the filtered aqueous phase.

[0099] Comparative Example 4

[0100] The difference between this comparative example and Example 1 is that step (2) does not involve the addition of pure water, and specifically includes the following steps: (1) Prepare a mixed aqueous solution containing NaClO (concentration of 100 ppm) and NaCl (concentration of 3 M). Add HCl to the mixed aqueous solution to adjust the pH to about 3.5. Then add perfluorooctane to the mixed aqueous solution and control the volume ratio of the mixed aqueous solution to perfluorooctane to be 3:1. Shake well and let stand to separate the layers. The upper layer is the first aqueous phase and the lower layer is the perfluorooctane phase containing chlorine-containing active substances. After separation, the perfluorooctane phase is obtained. (2) Take 5 mL of the perfluorooctane phase obtained in step (1) and add it into a colorimetric tube (i.e., photocatalytic oxidation device) with a diameter of 20 mm and a volume of 25 mL. Add 60 mg of bismuth oxybromine photocatalyst to the perfluorooctane phase. (3) Magnetic stirring of the perfluorooctane phase, adjusting the stirring speed to 400 rpm, to disperse the photocatalyst powder in the perfluorooctane phase; (4) Use LED lamps as light sources with a wavelength of 420 nm and a power of 5 W to irradiate the perfluorooctane phase; control the temperature of the perfluorooctane phase at around 25 °C under normal pressure (1 standard atmosphere); introduce pure gaseous alkane gas into the perfluorooctane phase through a venting pipe and control the distance between the outlet of the gas containing gaseous alkane gas and the liquid surface to be around 2.5 cm, so that gaseous alkane bubbles are generated in the perfluorooctane phase and float to the liquid surface. Control the gaseous alkane gas introduction rate to be 3 mL / min and the median diameter Dv50 of the gaseous alkane bubbles in the perfluorooctane phase to be 110 μm. (5) After 1 hour of reaction, 1 mL of perfluorooctane was taken from the liquid surface and filtered through a 0.22 μm filter membrane. The concentration of the product in the filtered aqueous phase was then measured. No aqueous phase was added in this comparative example, and the reaction occurred only in the perfluorooctane. The reason for measuring the content of oxidation products in the perfluorooctane on the liquid surface in this comparative example is that formic acid, methanol, and formaldehyde are not easily soluble in perfluorooctane and have a lower density than perfluorooctane. Therefore, theoretically, the products generated by the reaction would float from the perfluorooctane phase to the liquid surface.

[0101] The following are some of the detection and calculation methods used in the embodiments and comparative examples of this application: The method for detecting free chlorine concentration is as follows: Refer to the N,N-diethyl-p-phenylenediamine spectrophotometric method in GB / T 5750.11-2023 Standard Examination Methods for Drinking Water.

[0102] Formic acid detection method: The concentration of formic acid was determined using ion chromatography. Specifically, the column and conductivity cell were controlled at 30℃ and 35℃ respectively, and the flow rate was kept constant at 1.0 mL / min. Potassium hydroxide eluent was automatically generated online, and a gradient elution program was executed (10 mM concentration for 0-10 minutes, increased to 40 mM for 10.1-15 minutes, and decreased back to 10 mM for 15.1-23 minutes). Each injection was 50 μL, and the entire analysis cycle was 23 minutes, during which the suppressor current was maintained at a constant 120 mA. The limit of quantitation for this method is 0.6 μmol / L.

[0103] The method for detecting methanol was as follows: 1H nuclear magnetic resonance (NMR) with dimethyl sulfoxide (DMSO) as an internal standard was used to analyze and quantify methanol (CH3OH): 0.2 mL of the test solution was mixed with 0.4 mL of deuterated water (D2O) and 0.07 μmol of DMSO; then, the concentration of the methanol standard solution was compared with the corresponding DMSO area ratio to plot a calibration curve, thereby obtaining the concentration of methanol in the test solution.

[0104] Formaldehyde detection method: Based on the formaldehyde (HCHO) detection method in "Determination of Formaldehyde in Water - Acetylacetone Spectrophotometric Method" (GB 13197-91).

[0105] Methods for calculating apparent quantum efficiency (AQE):

[0106] Where n1 and n2 represent the number of product molecules (unit: mol); N1 and N2 represent the charge transfer number in the photocatalytic oxidation of gaseous alkanes into oxidation product molecules (the charge transfer number for the formation of formic acid from gaseous alkanes and oxygen is 6 electrons); R is the total charge transfer; N A For Avogadro's constant (6.02 × 10⁻⁶) 23 mol -1 I represents the optical power density (W·m). -2 S is the incident light illumination area (m²) 2 ); t is the reaction time (s); h is Planck's constant; c is the speed of light; λ is the wavelength of the incident light (unit: nm).

[0107] The parameter settings for the embodiments and comparative examples of this application are shown in Table 1.

[0108] Table 1

[0109] The product concentrations and apparent quantum efficiency (AQE) data for the embodiments and comparative examples of this application are shown in Table 2.

[0110] Table 2

[0111] As shown in Table 2, the method described in this application can achieve the oxidation of methane at room temperature and pressure. Furthermore, analysis of the oxidation products using the detection methods of the above embodiments of this application reveals that, in addition to formic acid, the oxidation products of the above embodiments generally also include methanol and / or formaldehyde. Among these, the formation rate of formic acid, the oxidation product, is faster in the embodiments of this application compared to the comparative examples. Formic acid is used to characterize the apparent quantum efficiency in the above embodiments of this application. Based on the test results, the apparent quantum efficiency of the embodiments of this invention is equal to or higher than 0.18%, while the apparent quantum efficiency of the comparative examples is not higher than 0.06%. Moreover, in the prior art, the apparent quantum efficiency of photocatalytic reactions is typically lower than 0.1%, thus demonstrating that the method described in this invention has a high quantum efficiency.

[0112] Table 2 shows that the detection result of formic acid in Comparative Example 4 was 0. It is speculated that the reason may be that the product was directly exposed on the liquid surface, part of which evaporated and the other part was further photocatalytically oxidized to generate carbon dioxide and / or carbon monoxide, resulting in its content being lower than the detection limit of the detection method used in this application, hence the detection result was 0.

[0113] The method described in this application also yielded similar results to that for methane when used for the photocatalytic oxidation of gaseous alkanes such as ethane, propane, n-butane, and isobutane.

[0114] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for photocatalytic oxidation of gaseous alkanes, characterized in that, Under light irradiation, a photocatalyst, gaseous alkanes, and chlorine-containing active substances react at the interface of a two-phase system containing an organic phase and an aqueous phase to generate oxidation products, which include one or more of acids, alcohols, and aldehydes. The organic phase can dissolve the chlorine-containing active substances.

2. The method according to claim 1, characterized in that, The two-phase system containing an organic phase and an aqueous phase is prepared using the following steps: An aqueous solution containing a chlorine-containing active substance is mixed with a first organic phase to obtain a two-phase system comprising a first aqueous phase and a first organic phase. The first organic phase in the two-phase system containing the first aqueous phase and the first organic phase is separated, and the first organic phase is mixed with water to form the two-phase system containing the organic phase and the aqueous phase.

3. The method according to claim 2, characterized in that, The aqueous solution containing the chlorine-containing active substance is prepared by the following method: Formulating a mixture containing ClO - and Cl - An aqueous solution is prepared by adjusting the pH of the aqueous solution to < 7.0 to obtain the aqueous solution containing the chlorine-containing active substance; or, Electrolysis containing Cl - An anolyte solution is obtained by adjusting the pH of the anolyte solution to < 7.0, thereby obtaining the aqueous solution containing the chlorine-containing active substance.

4. The method according to claim 1, characterized in that, The gaseous alkanes include one or more of methane, ethane, propane, n-butane, and isobutane; and / or, The method for generating bubbles containing gaseous alkanes includes: introducing a gas containing the gaseous alkanes below the interface of the two-phase system.

5. The method according to claim 4, characterized in that, One or more of the following conditions must be met: The gas containing the gaseous alkane is introduced into the interior of the organic phase; The average diameter of the bubbles containing the gaseous alkane is 50 nm-500 μm.

6. The method according to any one of claims 1-5, characterized in that, One or more of the following conditions must be met: The wavelength of the light is 200 nm-800 nm; The photocatalyst includes one or more of the following: titanium dioxide, bismuth oxybromide, carbon nitride, bismuth vanadate, noble metal photocatalysts, metal-organic framework materials, covalent organic framework materials, hydrogen-bonded organic framework materials, and two-dimensional material MXene. The gas containing gaseous alkanes includes one or more of the following: bio-fermentation source gas, waste treatment source gas, associated fossil fuel gas, combustion exhaust gas, and natural source gas; optionally, the bio-fermentation source gas includes one or more of the following: animal intestinal fermentation gas, fecal fermentation gas, and biomass digestion gas; and / or, the waste treatment source gas includes one or more of the following: solid waste landfill gas and wastewater treatment exhaust gas; and / or, the associated fossil fuel gas includes one or more of the following: oil and gas extraction escape gas, coalbed methane, and oil and gas pipeline leakage gas; and / or, the combustion exhaust gas includes one or more of the following: biomass fuel combustion exhaust gas, fossil fuel combustion exhaust gas, and engine exhaust gas; and / or, the natural source gas includes freshwater wetland biogas. The chlorine-containing active substances include HClO, Cl2O, Cl2, and polychlorinated monoanions (Cl). n One or more of the following; The organic phase includes one or more of perfluorooctane, perfluorohexane, perfluoropentane, perfluoronaphthane, perfluorocyclohexane, perfluoropolyether, polyfluoroether, perfluorotertiary amine, tetrachloroethylene, and carbon tetrachloride; The free chlorine concentration in the aqueous solution containing the chlorine-containing active substance is greater than or equal to 2 mg Cl2 / L; The organic phase includes the photocatalyst, and the organic phase is disturbed during the reaction to disperse the photocatalyst; The aqueous phase is shielded from light during the reaction process; The reaction temperature is greater than or equal to 0°C.

7. A system for photocatalytic oxidation of gaseous alkanes, characterized in that, include: A photocatalytic oxidation device, comprising a two-phase system containing an organic phase and an aqueous phase, wherein the organic phase contains a chlorine-containing active substance and a photocatalyst; the photocatalytic oxidation device is provided with an inlet containing gaseous alkanes; and A light source is used to irradiate the interface between the organic phase and the two-phase system, so that the photocatalyst, the gaseous alkanes-containing bubbles, and the chlorine-containing active substances react at the interface between the organic phase and the two-phase system to generate oxidation products, the oxidation products including one or more of acids, alcohols, and aldehydes. Optionally, the inlet for the gas containing gaseous alkanes is located below the interface of the two-phase system, for introducing the gas containing gaseous alkanes into the photocatalytic oxidation device to form gaseous alkanes-containing bubbles at the interface of the two-phase system.

8. The system according to claim 7, characterized in that, It also includes a chlorine-containing active substance extraction device, which comprises an aqueous solution containing the chlorine-containing active substance and a first organic phase, wherein... The chlorine-containing active substance extraction device corresponding to the first organic compound is provided with a first liquid outlet and a first liquid inlet; The photocatalytic oxidation device corresponding to the organic is provided with a second liquid inlet and a second liquid outlet; the second liquid inlet is connected to the first liquid outlet, and the second liquid outlet is connected to the first liquid inlet.

9. The system according to claim 8, characterized in that, The chlorine-containing active substance extraction device corresponding to the aqueous solution containing the chlorine-containing active substance is provided with a third inlet and a third outlet; The system also includes an electrolysis device, which contains Cl... - The electrolysis device has a fourth liquid outlet on the anode side and a fourth liquid inlet on the cathode side. The fourth liquid outlet is connected to the third liquid inlet, and the fourth liquid inlet is connected to the third liquid outlet.

10. The system according to any one of claims 7-9, characterized in that, One or more of the following conditions must be met: The photocatalytic oxidation device corresponding to the water is also provided with a fifth liquid outlet and a fifth liquid inlet. The system also includes a product purification device, which is provided with a sixth liquid inlet and a sixth liquid outlet. The sixth liquid inlet is connected to the fifth liquid outlet, and the sixth liquid outlet is connected to the fifth liquid inlet. The bottom of the photocatalytic oxidation device is provided with an inlet for gas containing gaseous alkanes, and the top of the photocatalytic oxidation device is provided with a tail gas outlet, which is connected to the inlet for gas containing gaseous alkanes. The photocatalytic oxidation device containing the aqueous phase is equipped with a light-shielding device.

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