Cascade system and method for preparing alcohol by converting alkane through photoelectrocatalysis and application

Abstract

The invention relates to a system and method for preparing alcohol through cascade photoelectrocatalysis alkane conversion and application, the system comprises an electro-catalysis reaction tank and a photocatalytic reaction tank, the electro-catalysis reaction tank is sequentially connected with a pump, a three-way valve and the photocatalytic reaction tank through pipelines, and a halogen elementary substance electrolyte generated by the electro-catalysis reaction tank is conveyed to the three-way valve through a peristaltic pump; the preparation method comprises the following steps: mixing a cathode electrolyte with alkane gas, introducing the mixture into a photocatalytic reaction tank, carrying out light source excitation catalytic reaction in the photocatalytic reaction tank, carrying out gas-liquid separation on the obtained mixture, mixing the obtained mixed gas with the cathode electrolyte after the reaction in the electro-catalytic reaction tank, introducing the obtained mixture into a microreactor, and heating to obtain an alcohol product. Compared with the prior art, the method provided by the invention has excellent alcohol selectivity and production efficiency, and is a more efficient and stable reaction system compared with the currently reported electro-catalysis or photocatalysis technology.

Description

Technical Field

[0001] This invention belongs to the field of alkane conversion to alcohol, and in particular relates to a system, method and application of cascade photoelectrocatalytic alkane conversion to alcohol. Background Technology

[0002] Methanol, ethanol, and propanol, among other low-carbon alcohols, are important bulk chemicals. Annual production of low-carbon alcohols exceeds 400 million tons, with a market value exceeding US$40 billion annually (of which, methanol production exceeds 100 million tons; ethanol is approximately 300 million tons; and propanol is between one million and ten million tons). Methanol is one of the most important bulk chemicals, serving as a fundamental organic raw material for the production of olefins, dimethyl ether, methylamine, and ethylene glycol. Ethanol is not only an important chemical raw material and a widely used solvent, but also, as a clean and renewable energy source, is used extensively globally for biofuel production, helping to reduce greenhouse gas emissions and decrease dependence on fossil fuels. Propanol (including n-propanol and isopropanol) can be used as a solvent, antifreeze, preservative, and a basic raw material for many chemicals, and can also be used to produce plasticizers, coatings, and resins.

[0003] Currently, industrial methanol production involves a multi-step process. One step involves the thermocatalytic conversion of methane (CH4) into syngas at 50 bar and 800 K, followed by CO hydrogenation to produce methanol. This process generates 3.2 tons of carbon dioxide per ton of methanol produced. The current lifecycle emissions from methanol production are close to 0.3 gigatons of carbon dioxide per year, accounting for approximately 10% of the carbon dioxide emissions from the chemical manufacturing industry. The methanol production process also consumes a significant amount of energy, accounting for about 10% of the total emissions from the chemical industry.

[0004] Ethanol is mainly produced through bio-fermentation. The average life cycle greenhouse gas emissions of bioethanol are about 0.5 to 1.5 tons of carbon dioxide. Its production process involves a large amount of land use, water consumption, and the use of fertilizers and pesticides, which will have environmental impact issues.

[0005] The industrial production of propanol (including n-propanol and isopropanol) uses a propylene hydration process at 50 bar and 473 K. Producing one ton of propanol generates 2.5 to 3.5 tons of carbon dioxide, resulting in significant pollutant emissions and high energy consumption.

[0006] Given the high carbon emissions and high energy consumption in current industrial production of alcohols, using renewable electricity and water to directly synthesize alcohols from small molecule alkanes through electro-oxidation under normal temperature and pressure conditions is a transformative technology for achieving low-energy and low-carbon chemical engineering.

[0007] Patent application CN202110456330.1 discloses a method for promoting the electrocatalytic oxidation of methane to chloromethane using chloride ions. First, a cobalt-nickel composite spinel oxide nanoparticle electrocatalyst for the electrocatalytic oxidation of methane to chloromethane is prepared. Then, using this electrocatalyst as the anode in a chloride-containing electrolyte, the cobalt-nickel composite oxide nanoparticles electrocatalyze the oxidation of methane in the presence of chloride ions, selectively generating chloromethane while suppressing side reactions such as carbon dioxide and oxygen. Although this technology uses chloride electrolytes to selectively activate methane via chlorine (Cl) as a redox medium, forming gaseous chloromethane (CH3Cl) and eliminating the over-oxidation of CH4 to CO2, the preparation of CH3Cl is achieved using active Cl species (*Cl) adsorbed on the electrode surface. Because the energy barrier of the *Cl-*Cl coupling reaction is much lower than that of the *Cl activation reaction of methane, the main product is Cl2, resulting in a Faraday efficiency of only 8% and a partial current density of less than 20 mA / cm² for the target product CH3Cl. 2 .

[0008] Patent application 202311313146.7 discloses a molybdenum-doped cuprous selenide electrocatalyst with high methane adsorption selenium defects, its preparation method, and its application. This catalyst exhibits high methane adsorption efficiency, strong hydrophobicity, and excellent electrocatalytic activity in the electrocatalytic oxidation of methane to ethanol in carbonate solutions. However, this technology utilizes reactive oxygen species to activate methane, which fails to address the methane peroxidation problem caused by potential increase at high current densities, resulting in an ethanol current density below 40 mA / cm². 2 .

[0009] Existing research reports the use of chloride electrolytes to selectively activate alkanes, such as methane (CH4), ethane (C2H6), and propane (C3H8), using chlorine (Cl) as a redox medium to form the corresponding gaseous haloalkanes. This selective activation effectively avoids the over-oxidation of alkanes to CO2. However, because the coupling barrier of Cl-Cl (forming Cl2) is lower than that of Cl* activating CH4, the selectivity for generating chloromethane is less than 10%, and the chlorination selectivity for ethane and propane is even lower. Furthermore, another problem with existing techniques is the low yield, mainly due to gas mass transfer, which causes the chlorine precipitation reaction to always dominate, resulting in the majority of products being Cl2 rather than the target haloalkanes.

[0010] Currently reported high-selectivity electrocatalytic alkane oxidation current densities are all below 10 mA / cm². 2 This is far lower than the industrial current density (300 mA / cm²) required for widespread industrial applications. 2This is because as the current density increases, the positive potential rises, leading to excessive oxidation of alkanes, which in turn forms carbon dioxide, resulting in a decrease in product selectivity. Summary of the Invention

[0011] The present invention aims to overcome the defects of the prior art and provide a highly efficient, stable and continuous cascade photoelectrocatalytic system and method for converting alkanes (including but not limited to methane, ethane and propane) into corresponding alcohols (such as methanol, ethanol, propanol, etc.).

[0012] This invention discloses a cascaded photocatalytic system for the efficient conversion of alkanes into alcohols. The system consists of an electrocatalytic reaction cell and a photocatalytic reaction cell, wherein the electrocatalytic reaction cell is sequentially connected to a peristaltic pump, a three-way valve, and the photocatalytic reaction cell via pipelines. Applying voltage to the electrocatalytic reaction cell generates an electrolyte containing halogen elements (X₂, X = Cl, Br, I). This halogen-containing electrolyte is pumped to the three-way valve via the peristaltic pump, while alkane gas is also introduced into the three-way valve. The volume ratio of the halogen-containing electrolyte to the alkane is adjusted by regulating the three-way valve. The mixed gas then enters the photocatalytic reaction cell, where catalytic conversion occurs under light source excitation. The resulting mixture undergoes gas-liquid separation, and the resulting gas is mixed with the cathode electrolyte from the electrocatalytic reaction cell and then introduced into a microreactor. Under heating conditions, the alcohol product is obtained.

[0013] Furthermore, the electrocatalytic reaction cell is a zero-gap membrane electrode cell, comprising one or more membrane electrode assemblies and an electrolyte, wherein each membrane electrode assembly comprises an anode, a cathode, and a proton exchange membrane;

[0014] The electrolyte can be either NaCl or KBr solution, both of which provide the corresponding halide ions as redox mediators and possess good conductivity and stability. In addition, NaBr, KCl, KI, and NaI solutions can also be used as electrolytes. The pH of the electrolyte is adjusted to 1-3 using H₂SO₄, and the appropriate solution can be selected based on production objectives and reaction potential.

[0015] Furthermore, the photocatalytic reaction cell is a transparent microchannel with an inner diameter of 1.5-10 mm;

[0016] Furthermore, a xenon lamp is used as the light source. The xenon lamp has an output power of 200-400W and a wavelength of 300-1000nm, suitable for reactions requiring high power and a wide spectral range. The reaction pressure is 0.5-5 bar.

[0017] The microreactor is a reactant with an inner diameter of 1.5-10 mm, and is made of PFA, glass or quartz.

[0018] This invention also provides a method for the cascade photoelectrocatalytic conversion of alkane to alcohol, comprising the following steps:

[0019] (1) Control the current of the electrocatalytic reaction cell, electrolyze the electrolyte, obtain an electrolyte containing halogen elements at the anode, and obtain H2 and NaOH or KOH solution at the cathode;

[0020] (2) The obtained anolyte and alkanes are mixed through a three-way valve and then introduced into a photocatalytic reaction cell to control the photocatalytic reaction conditions for catalytic reaction.

[0021] (3) The gas and solution obtained from the photocatalytic reaction tank are separated by a gas-liquid separator. The gas obtained is a mixture of alkane / monohaloalkane, and the solution obtained is returned to the electrolyte storage container.

[0022] (4) Mix the alkane / monohaloalkane mixed gas with the cathodic electrolyte after the reaction, and pass it into a microreactor for heating reaction;

[0023] (5) The gas and liquid after the reaction in the microreactor are separated by a gas-liquid separation device. The gas is unreacted alkanes, and the final alcohol product is collected in the liquid.

[0024] Furthermore, the current density of the electrocatalytic reaction cell in step (1) is 300 mA / cm². 2 This current density ensures high catalytic efficiency and product selectivity while preventing equipment overheating or catalyst degradation.

[0025] Furthermore, in step (2), the gas flow rate introduced into the three-way valve is 2-100 mL / min to ensure that the gas fully contacts the catalyst and has a high processing efficiency. The electrolyte flow rate is 1-15 mL / min to ensure that the electrolyte can be evenly distributed and maintain the ion concentration in the reaction medium, thereby improving the overall reaction efficiency.

[0026] Furthermore, in step (4), the heating temperature of the microreactor is 60-100℃. This temperature range is designed to optimize the selectivity and yield of the target product, taking into account both the reaction rate and the avoidance of side reactions, thereby achieving the best conversion effect.

[0027] The present invention also provides an application of the system described herein, in which the system is used to convert alkane into alcohol.

[0028] Furthermore, the alkane includes methane, ethane, or propane.

[0029] Compared with the prior art, the present invention has the following superior effects:

[0030] (1) This invention utilizes an extended gas-liquid two-phase interface photoinduced reaction to develop a novel cascaded electro-photochemical microreactor system, achieving effective synergy between electrocatalysis and photocatalysis. Halogen aqueous solutions are generated by electrolyzing the anolyte-halogen salt solution. A three-way valve is used to form a Taylor flow with a gas-liquid interface between the alkanes and the electrolyte within the microreactor, thereby improving mass transfer. In a novel photoreactor with an inner diameter of 1.5-10 mm made of quartz / PFA, gas-liquid closure is achieved. Photoexcitation decomposes elemental halogens into active halogen species. These active halogen species react with alkanes to selectively generate haloalkanes (such as those produced by electrolyzing NaCl and Cl). - Cl2 is generated, and photo-excited Cl2 homolytic cleavage promotes the isolytic cleavage of Cl-Cl bonds in the Cl2 molecule, forming active chlorine (·Cl), which activates alkanes to haloalkanes. The oscillation of surface waves formed at the gas-liquid interface within the photoreactor accelerates interface renewal, thereby increasing the alkane mass transfer coefficient and ultimately achieving photoelectric reaction rate matching. After the haloalkanes are generated, they are coupled with OH- generated at the cathode for hydrolysis, achieving efficient and selective alcohol production. Compared to existing technologies, this invention achieves a dual breakthrough in current density and selectivity, with a maximum bias current density exceeding 240 mA / cm². 2 (while currently reported technologies typically have an A / cm) 2 It maintains excellent alcohol selectivity and production efficiency even after continuous operation for over 100 hours. Compared to currently reported electrocatalytic or photocatalytic technologies, it is a more efficient and stable reaction system, suitable for high-selectivity alcohol preparation at industrial-grade current densities.

[0031] (2) This invention utilizes synchrotron radiation photoionization mass spectrometry (SR-PIMS) to synergistically study the reaction kinetics of cascade electro-photochemical reactions. By adjusting the applied current, the amount of halogen elements generated per unit time can be controlled, and the generation rate of halogen elements can be controlled by controlling the current density per unit area. Taking Cl as an example, SR-PIMS analysis revealed that the generation rate of CH3Cl and the concentration of Cl2 substrate exhibit a first-order reaction rate. Therefore, by changing the mass transfer coefficient of the photoreactor, the diffusion degree of methane and Cl2 substrate within the photoreactor can be controlled, achieving a matching control of the photoelectrochemical cascade reaction rate, thus realizing efficient, stable, and highly selective alcohol production.

[0032] (3) When the system of this invention is applied to propane, propane is preferably activated by selecting Br radicals with higher selectivity for methylene sites, and light irradiation is introduced to excite the Br-Br bond breaking in bromine molecules, thereby forming active Br and accelerating the activation of propane. This achieves an order-of-magnitude increase in yield. At 300 mA / cm 2At current density, with a Faraday efficiency exceeding 75%, the isopropanol yield exceeded 15 mol / g. cat / h is currently the most advanced and efficient system reported for the selective oxidation of propane to prepare isopropanol. Attached Figure Description

[0033] Figure 1 The rate order of the methane-halogen electrolyte reaction in SR-PIMS testing;

[0034] Figure 2 This is a continuous electro-photocatalytic reaction system for the preparation of alcohols from alkanes.

[0035] Figure 3 This is a comparison of the selective electro-oxidation techniques for preparing methanol from methane in Example 1 and the comparative example.

[0036] Figure 4 Selective oxidation of methane, ethane, and propane to produce methanol, ethanol, propanol, and isopropanol at 300 mA / cm 2 Faraday efficiency and half-cell energy utilization efficiency at current density;

[0037] Figure 5 The proton NMR spectrum of methanol (1H NMR spectrum) 1 1H NMR (H NMR) detection results;

[0038] Figure 6 The proton nuclear magnetic resonance spectrum of ethanol ( 1 1H NMR (H NMR) detection results;

[0039] Figure 7 The 1H NMR spectrum of isopropanol ( 1 1H NMR (H NMR) detection results;

[0040] Figure 8 The X-ray diffraction (XRD) spectrum of the catalyst IrO2 / Ti;

[0041] Figure 9 This is a scanning electron microscope (SEM) image of the catalyst IrO2 / Ti;

[0042] Figure 10 EDX-mapping image of the IrO2 / Ti catalyst obtained by scanning electron microscopy (SEM). Detailed Implementation

[0043] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0044] This invention constructs a continuous electro-photocatalytic reaction system, the reaction system of which is as follows: Figure 2As shown. The continuous electro-photocatalytic reaction system includes an electrocatalytic reaction cell and a photocatalytic reaction cell. The electrocatalytic reaction cell consists of a zero-gap membrane electrode cell 1 and a peristaltic pump 2. The zero-gap membrane electrode cell 1 includes one or more membrane electrode assemblies. Each membrane electrode assembly includes an anode, a cathode, a proton exchange membrane, and an electrolyte. The anode and cathode are attached to opposite sides of the proton exchange membrane to form a zero-gap membrane electrode. Both the anode and cathode use a 5.4M NaX (X = Cl, Br, I) solution as the electrolyte, and the applied current is controlled at 300 mA / cm². 2 The current is used for electrolysis of X. - X2 is prepared by oxidation.

[0045] The cathode and anode are prepared by the following method:

[0046] Titanium felt was used as the supporting electrode and immersed in an aqueous solution of iridium chloride at a pH of 7-8 for 30 minutes. It was then calcined in air at 300-400℃ for 2-4 hours. The iridium loading was 0.1 mg / cm³. 2 The titanium felt-supported iridium oxide prepared was used as the anode.

[0047] The XRD pattern of the obtained anode is as follows Figure 8 As shown in the figure, the prepared electrode is a composite material of IrO2 and Ti.

[0048] The morphology of the obtained anode under a scanning electron microscope is as follows: Figure 9 As shown in the figure, A is an electron microscope image at 20 μm and B is an electron microscope image at 600 nm. It can be seen from the figure that IrO2 micrometers are uniformly grown on the Ti fiber skeleton.

[0049] The morphology of the obtained anode under a transmission electron microscope is as follows: Figure 10 As shown, A is a TEM image of IrO2, B is a TEM image of IrO2 in HAADF mode, C and D are the elemental distributions of Ir and O, respectively, with Ir and O elements uniformly distributed.

[0050] The cathode uses a commercially available 50% Pt / C catalyst, sprayed onto H-060 carbon paper, with a loading of 1 mg / cm³. 2 .

[0051] Subsequently, the electrolyte and alkane gas prepared at the anode of the electrocatalytic reaction cell are mixed through a three-way valve 3 and then introduced into the photochemical microreactor 4 (such as a continuous flow quartz photocatalytic reaction cell, i.e., a transparent microchannel made of a transparent material such as PFA, glass, or quartz with an inner diameter of 1.5-10 mm). The gas flow rate is 2-100 mL / min, and the electrolyte flow rate is 1-15 mL / min, measured at a pressure of 1 bar. A xenon lamp 5 is used as the light source 5, with an output power of 300 W and a wavelength of 300-1000 nm; the reaction pressure is 1 bar, which excites the electrolyte containing X2 generated during the electrocatalytic process. Subsequently, CH3X products are generated in the continuous flow quartz photocatalytic reaction cell. The gas and solution obtained after the reaction in the photochemical microreactor 4 are separated by a gas-liquid separator 6. The obtained gas is a mixture of alkanes and halogenated alkanes such as methane / chloromethane, ethane / chloroethane, propane / bromopropane, etc., and the obtained solution is returned to the electrolyte storage container 7.

[0052] A mixture of alkanes and haloalkanes, such as methane / chloromethane, ethane / chloroethane, propane / bromopropane, etc., is mixed with the cathode electrolyte after reaction in the zero-gap membrane electrode cell 1. The mixed electrolyte / gas is then introduced into a microreactor 8 for heating. The microreactor has an inner diameter of 3.5-10 mm and is made of PFA, glass, or quartz. The heating temperature is 60-100℃.

[0053] The gas and liquid after the reaction in the microreactor 8 are separated by a gas-liquid separator 9. The gas is unreacted methane (ethane, propane), and the final product, methanol (ethanol, propanol, or isopropanol), is collected in the liquid.

[0054] The product is mixed with the cathode electrolyte in the electrocatalytic reaction cell to obtain methanol (ethanol, propanol or isopropanol).

[0055] The above system can be used in the photoelectrocatalytic conversion of alkanes to alcohols. This invention primarily utilizes this system to achieve efficient, stable, and continuous photoelectrocatalytic conversion of alkanes to alcohols. By introducing light irradiation to excite the associative cleavage of the XX bonds in the X2 molecule, active halogen radicals are formed, thereby accelerating the activation of the alkane. The implementation of this scheme achieves an order-of-magnitude increase in yield. The method for cascade photoelectrocatalytic conversion of alkanes to alcohols using the above system includes the following steps:

[0056] (1) Control the current in the electrocatalytic reaction cell to achieve a current density of 300 mA / cm². 2 Electrolysis of the electrolyte yields an electrolyte containing halogen elements;

[0057] The electrolytic preparation of halogens depends on the current density and reaction time, and the yield can be obtained from formula (1):

[0058] C=F*N*j*t*FE (1)

[0059] Where C represents the molar amount of halogenated element, F is the Faraday constant (96485C / mol), N is the number of electrons transferred, J is the applied current, t is the reaction time, and FE is the Faraday efficiency.

[0060] Therefore, according to formula (1), the amount of halogens generated per unit time depends on the applied current. The generation rate of halogens can be controlled by controlling the current density per unit area.

[0061] (2) The obtained anolyte and alkanes are mixed through a three-way valve and then introduced into a photocatalytic reaction cell. The photocatalytic reaction conditions are controlled to carry out the catalytic reaction: the gas flow rate through the three-way valve is 2-100 mL / min and the electrolyte flow rate is 1-15 mL / min.

[0062] Photoexcitation decomposes elemental halogens into reactive halogen species, which then react with alkanes to selectively generate haloalkanes (e.g., by electrolysis of NaCl, Cl). - Cl2 is generated, and photo-excitation of Cl2 homolytically cleaves to generate ·Cl, promoting the homolytic cleavage of the Cl-Cl bonds in the Cl2 molecule to form active chlorine, thereby activating the alkane to a haloalkanes.

[0063] The reaction rates of halogens and alkanes in the photoreaction process were measured using synchrotron radiation photoionization mass spectrometry (SR-PIMS).

[0064] Taking Cl2 as an example: Figure 1 As shown, during the gas-phase reaction, the formation rate of CH3Cl and the concentration of the halogen electrolyte exhibit a first-order reaction rate with a reaction order of k = 2.13. This means that during the gas-phase reaction, the product formation rate increases with the increase of substrate concentration.

[0065] However, at room temperature and pressure, the halogens prepared by the electrocatalytic process dissolve in the electrolyte, requiring alkanes to diffuse into the solution for the reaction to complete. Due to the low solubility of alkanes in solvents, improvements in mass transfer of alkanes are needed through reactor design.

[0066] Therefore, for photoelectric tandem systems, matching of photo-electric reaction rates is required to achieve efficient generation of haloalkanes. Mass transfer is improved by using a three-way valve to form a Taylor flow with a gas-liquid interface between the alkanes and electrolyte within the microreactor. The overall volumetric mass transfer coefficient is the product of the specific surface area (a) and the individual mass transfer coefficient (kL). Assuming the Taylor bubble is a long cylinder with two hemispherical caps, the specific surface area can be expressed as formula (2).

[0067]

[0068] Where, d B L represents the average bubble size. B V represents the length of the dispersed phase (bubbles in the gas-liquid mixture). B This represents the bubble volume. According to the Higby permeation model, the mass transfer coefficient can be expressed as equation (3).

[0069]

[0070] τ represents the Higby contact time, D L This represents the diffusion coefficient in a liquid.

[0071] According to the above formula, by adjusting the inner diameter of the three-way valve under different current densities, the bubble / liquid ratio can be controlled, thereby adjusting the mass transfer coefficient, improving the mass transfer effect of methane, and realizing the efficient conversion of halogenated elements produced by the electrolytic cell into haloalkanes.

[0072] Based on this, the present invention develops a novel photoreactor with an inner diameter of 1.5-10 mm and made of quartz / PFA, which enables gas-liquid sealing within a tiny reaction channel, controls the reaction pressure in the photocatalytic reaction cell to 0.5-5 bar, and simultaneously controls the output power of the light source to 200-400 W with a wavelength of 300-1000 nm; the oscillation of surface waves formed at the gas-liquid interface in the photoreactor accelerates interface renewal, thereby improving the alkane mass transfer coefficient and ultimately achieving photoelectric reaction rate matching.

[0073] (3) The gas and solution obtained after the photocatalytic reaction in the reactor are separated by a gas-liquid separator. The resulting gas is a mixture of alkane and haloalkane, and the resulting solution is returned to the electrolyte storage container. The general reaction formula between the alkane and the anolyte is:

[0074] C n H 2n+2 +2X - -2e - →C n H 2n+1 X+HX

[0075] (4) Mix the alkane / haloalkanes mixed gas with the cathodic electrolyte after the reaction, and pass it into a microreactor for heating reaction; the heating temperature is 60-100℃.

[0076] (5) The gas and liquid after the reaction in the microreactor are separated by a gas-liquid separation device. The gas is unreacted alkanes, and the final alcohol product is collected in the liquid.

[0077] Unless otherwise specified, the raw materials and equipment used in this invention are all commercially available or commonly used equipment.

[0078] Example 1

[0079] The specific steps for the photoelectric coupling selective oxidation of methane to methanol are as follows:

[0080] See Figure 2 A zero-gap membrane electrode was used as the electrocatalytic reaction device. Both the cathode and anolyte were 5.4M NaCl. The reaction was carried out at room temperature and atmospheric pressure, with a controlled application of 300 mA / cm². 2 The current is applied, and after the reaction, an anolyte (an aqueous solution containing Cl2) and a catholyte (NaOH solution) are obtained.

[0081] The resulting anolyte was mixed with methane through a three-way valve and then introduced into a photocatalytic reaction cell (in this embodiment, a quartz tube with an inner diameter of 1.5 mm was used). The gas flow rate was 50 mL / min, and the electrolyte flow rate was 5 mL / min, measured using a 1 bar pressure gauge. The gas and solution obtained after the reaction in the photocatalytic reaction cell were separated by a gas-liquid separator. The resulting gas was a methane / chloromethane mixture, and the resulting solution was returned to the anolyte storage container.

[0082] A methane / chloromethane gas mixture is mixed with the reacted cathode electrolyte. The mixed electrolyte / gas is then passed into a microreactor for heating. In this embodiment, a quartz tube with an inner diameter of 1.5 mm is used as the microreactor, and the heating temperature is 80°C.

[0083] The gas and liquid from the microreactor reaction are separated using a gas-liquid separator. The gas is unreacted methane, and the final methanol product is collected in liquid form. The collected liquid product is then analyzed by proton nuclear magnetic resonance (NMR) spectroscopy. 1 H NMR) confirmed, such as Figure 5 As shown in the figure, the main product is methanol.

[0084] Comparative Example 1

[0085] Methanol was prepared by selective electro-oxidation of methane using the method disclosed in patent application 202110456330.1.

[0086] like Figure 3 The figure shows a comparison between Example 1 (i.e., the work in the figure) and the comparative example (i.e., the industrial current density in the figure) of the selective electro-oxidation of methane to methanol. It can be seen that Example 1 achieves the desired methanol production at 300 mA / cm². 2 At the given current density, a Faraday efficiency exceeding 80% is achieved, whereas previously reported current densities for the selective oxidation of methane to methanol were all below 10 mA / cm². 2 Example 1 achieved a breakthrough in current density by two orders of magnitude while maintaining high methanol selectivity and Faraday efficiency.

[0087] The products obtained in Example 1 and Comparative Example 1 were subjected to performance testing, as follows:

[0088] Detection method: Collect the liquid phase containing the product and analyze it by nuclear magnetic resonance (NMR) 1H spectroscopy (NMR). 1 Confirmed by H NMR.

[0089] Yield calculation formula:

[0090]

[0091] Where, m a It is the amount of methanol produced in the reaction, m cat t is the amount of catalyst used in the reaction, and t is the reaction time.

[0092] Faraday efficiency calculation formula:

[0093]

[0094] Where F is the Faraday constant, n a c is the number of electrons transferred during the formation of 1 mole of methanol from methane. a Through nuclear magnetic resonance hydrogen spectrum ( 1 The concentration of methanol or ethanol detected by H NMR, where V is the volume of the absorption solution and Q is the total current.

[0095] Formula for calculating electricity conversion efficiency:

[0096]

[0097] in, It is the thermodynamic potential of the product, E cell It is the battery voltage (non-iR compensation), ΔG O It is the change in Gibbs free energy of the reaction.

[0098] Test results:

[0099]

[0100] As can be seen from the table above, Example 1 of this invention, utilizing a photoelectro-catalytic cascade device, achieves a comprehensive breakthrough in methanol yield, Faraday efficiency, and electrical energy utilization efficiency. Specifically, the methanol yield is increased by two orders of magnitude, while the electrical energy utilization efficiency increases from 4% in Comparative Example 1 to 40%. The methanol yield and Faraday efficiency are also significantly better than those of Comparative Example 1. This demonstrates that the photoelectro-catalytic cascade device of this invention achieves excellent results.

[0101] Figure 4 Selective oxidation of methane, ethane, and propane to methanol, ethanol, n-propanol, and isopropanol at 300 mA / cm 2 Faraday efficiency at current density and total cell energy utilization efficiency, from Figure 4 As can be seen from this, the current applied to the electrocatalytic reaction cell in Example 1 is controlled at 300 mA / cm. 2 At the given current density, the partial current density of methanol can reach 250 mA / cm². 2 The half-cell energy utilization efficiency reaches 69%, and the potential is only 1.7V.

[0102] Figure 5 The 1H NMR spectrum of the products after the reaction ( 1 The yield of methanol and the corresponding Faraday efficiency of methane conversion were determined by nuclear magnetic resonance (NMR) analysis.

[0103] Example 2: Photocoupled selective oxidation of ethane to ethanol, the specific steps are as follows:

[0104] A zero-gap membrane electrode assembly (MEA) was used as the electrocatalytic reaction device. The MEA assembly included an anode, cathode, proton exchange membrane, and electrolyte. Both the cathode and anode electrolytes were 5.4 M NaCl. Tests were conducted at room temperature and atmospheric pressure. An applied voltage of 300 mA / cm² was maintained. 2 The current was measured. The resulting anolyte was mixed with ethane via a three-way valve and then introduced into a photochemical microreactor. The gas flow rate was 100 mL / min, and the electrolyte flow rate was 15 mL / min, measured using a 1 bar pressure gauge. The gas and solution obtained after the reaction in the photochemical microreactor were separated using a gas-liquid separator. The resulting gas was an ethane / chloroethane mixture, and the resulting solution was returned to the anolyte storage container. The ethane / chloroethane mixture was then mixed with the reacted cathode electrolyte. The mixed electrolyte / gas was introduced into the microreactor for heating. The microreactor had an inner diameter of 1.5 mm, was made of PFA, and the heating temperature was 100 °C. The rest of the process was the same as in Example 1.

[0105] The resulting product current density and total current are as follows Figure 4 As shown. For example, at 300mA / cm 2 At the given current density, the partial current density of ethanol can reach 210 mA / cm². 2 The half-cell energy utilization efficiency reaches 65%, and the potential is only 1.77V.

[0106] Figure 6 The 1H NMR spectrum of the products after the reaction ( 1 The yield of ethanol and the corresponding Faraday efficiency of ethane conversion were determined by nuclear magnetic resonance (NMR) analysis.

[0107] Example 3

[0108] The photocoupled selective oxidation of propane to propanol involves the following steps:

[0109] A zero-gap membrane electrode was used as the electrocatalytic reaction device. Both the cathode and anolyte were 5.4M NaCl. The reaction was carried out at room temperature and atmospheric pressure, with a controlled application of 300 mA / cm². 2 The current is applied, and after the reaction, anolyte and catholyte are obtained.

[0110] The resulting anolyte was mixed with propane via a three-way valve and then introduced into a photochemical microreactor (in this embodiment, a quartz tube with an inner diameter of 3.5 mm was used). The gas flow rate was 50 mL / min, and the electrolyte flow rate was 5 mL / min, measured using a 1 bar pressure gauge. The gas and solution obtained after the reaction in the photochemical microreactor were separated by a gas-liquid separator. The resulting gas was a propane / chloromethane mixture, and the resulting solution was returned to the anolyte storage container. The resulting chloropropane gas was absorbed using a DMF / H₂O mixed solution. The absorbent containing chloropropane was heated to 80 °C. The final propanol product was collected in liquid form.

[0111] Figure 7 The 1H NMR spectrum of the products after the reaction ( 1 The H NMR results, after being analyzed by nuclear magnetic resonance, determined the yield of propanol and the corresponding Faraday efficiency of propane conversion.

[0112] The current density and total current of the obtained propanol and isopropanol products are as follows: Figure 4 As shown. For example, at 300mA / cm 2 At the given current density, the partial current density of propanol can reach 94 mA / cm². 2 The partial current density of isopropanol can reach 135 mA / cm². 2 .

[0113] Example 4

[0114] The photocoupled selective oxidation of propane to isopropanol involves the following steps:

[0115] A zero-gap membrane electrode was used as the electrocatalytic partial reaction device. Both the cathode and anolyte were 2MKBr. Tests were conducted at room temperature and atmospheric pressure. An applied current of 300 mA / cm² was controlled. 2The current was measured. The resulting anolyte was mixed with propane through a three-way valve and then introduced into the photochemical microreactor at a gas flow rate of 50 mL / min and an anolyte flow rate of 5 mL / min, measured at a pressure of 1 bar. The gas and solution obtained after the reaction in the photochemical microreactor were separated by a gas-liquid separator. The resulting solution was returned to the electrolyte storage container, and the obtained 2-bromopropane gas was absorbed by a water-mixed solution. The absorbent containing 2-bromopropane was heated to 80 °C. The final isopropanol product was collected in liquid form.

[0116] The final product's Faraday efficiency and half-cell energy utilization efficiency are as follows: Figure 4 As shown. For example, at 300mA / cm 2 At the given current density, the isopropanol Faraday efficiency is 82%.

[0117] The products obtained in Examples 2-4 were tested using the same method as in Example 1, and the results are as follows:

[0118]

[0119] The table above shows that this technical solution is a universal strategy for the selective activation of alkanes to prepare corresponding alcohol products, ensuring high selectivity and energy efficiency, while also achieving extremely high yield per unit catalyst mass. It demonstrates feasibility and universality.

Claims

1. A system for cascade photoelectrocatalytic conversion of alkanes to alcohols, characterized in that, It includes an electrocatalytic reaction tank and a photocatalytic reaction tank. The electrocatalytic reaction tank is connected to a pump, a three-way valve and the photocatalytic reaction tank in sequence through pipelines. The halogen-containing electrolyte generated in the electrocatalytic reaction tank is transported to the three-way valve by a peristaltic pump. After being mixed with alkane gas, it enters the photocatalytic reaction tank. In the photocatalytic reaction tank, a photocatalytic reaction occurs under the excitation of a light source to generate a monohaloalkane. The resulting mixture is separated into gas and liquid. The resulting mixed gas is mixed with the cathode electrolyte after the reaction in the electrocatalytic reaction tank. The resulting mixture is passed into a microreactor for heating to obtain the alcohol product.

2. The system for cascaded photoelectrocatalytic conversion of alkane to alcohol according to claim 1, characterized in that, The electrocatalytic reaction cell is a zero-gap membrane electrode cell, comprising one or more membrane electrode assemblies and an electrolyte. Each membrane electrode assembly includes an anode, a cathode, and a proton exchange membrane. The electrolyte is a solution of NaCl, KCl, NaBr, KBr, NaI, or KI.

3. The system for cascaded photoelectrocatalytic conversion of alkane to alcohol according to claim 1, characterized in that, The photocatalytic reaction cell is a transparent microchannel with an inner diameter of 1.5-10 mm; The light source used is a xenon lamp, with an output power of 200-400W and a wavelength of 300-1000nm; The reaction pressure inside the photocatalytic reaction tank is 0.5-5 bar.

4. The system for cascade photoelectrocatalytic conversion of alkane to alcohol according to claim 1, characterized in that, The microreactor is a reactor with an inner diameter of 1.5-10 mm, and is made of PFA, glass or quartz.

5. A method for preparing alcohols from alkane via photoelectrocatalytic conversion using the system described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Control the current of the electrocatalytic reaction cell, electrolyze the electrolyte, obtain an electrolyte containing halogen elements at the anode, and obtain H2 and NaOH or KOH solution at the cathode; (2) The obtained anolyte and alkanes are mixed through a three-way valve and then introduced into a photocatalytic reaction cell. The photocatalytic reaction conditions are controlled to carry out the photocatalytic reaction. (3) The gas and solution obtained after the photocatalytic reaction are separated by a gas-liquid separator. The gas obtained is a mixture of alkane / monohaloalkane, and the solution obtained is returned to the electrolyte storage container. (4) Mix the alkane / monohaloalkane mixed gas with the cathodic electrolyte after the reaction, and pass it into a microreactor for heating reaction; (5) The gas and liquid after the reaction in the microreactor are separated by a gas-liquid separation device. The gas is unreacted alkanes, and the final alcohol product is collected in the liquid.

6. The method for cascade photoelectrocatalytic conversion of alkane to alcohol according to claim 5, characterized in that, Step (1) The current density of the electrocatalytic reaction cell is 300 mA / cm². 2 .

7. The method for cascade photoelectrocatalytic conversion of alkane to alcohol according to claim 5, characterized in that, In step (2), the gas flow rate into the three-way valve is 2-100 mL / min, and the electrolyte flow rate is 1-15 mL / min.

8. The method for cascade photoelectrocatalytic conversion of alkane to alcohol according to claim 5, characterized in that, Step (4) The heating temperature of the microreactor is 60-100℃.

9. An application of the system as described in any one of claims 1-4, characterized in that, The system is used for the conversion of alkane into alcohol.

10. The application according to claim 9, characterized in that, The alkane mentioned includes methane, ethane, or propane.

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