A method for the photoelectrocatalytic conversion of propane to isopropanol

Abstract

This invention relates to a method for the photoelectrocatalytic conversion of propane to prepare isopropanol, comprising the following steps: (1) constructing a zero-gap membrane electrode assembly using iridium oxide supported on titanium felt as the anode catalyst and Pt / C catalyst supported on carbon paper as the cathode catalyst, wherein one or more membrane electrode assemblies constitute an electrocatalytic reaction cell; (2) using KBr solution as the electrolyte in the electrocatalytic reaction cell, electrolyzing the KBr solution, obtaining an anolyte containing Br2 at the anode and a catholyte containing KOH at the cathode; (3) mixing the anolyte obtained in step (2) with propane and then passing it into a photochemical microreactor for photocatalytic reaction under illumination, wherein the resulting 2-bromopropane gas is absorbed by H2O; (4) mixing the absorbent containing 2-bromopropane obtained in step (3) with the KOH solution generated at the cathode and heating to obtain isopropanol product. Compared with the prior art, this invention has excellent isopropanol selectivity and production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of propane conversion to isopropanol, and in particular relates to a method for propane photoelectrocatalytic conversion to isopropanol. Background Technology

[0002] Isopropanol, also known as sec-propanol, is a colorless, transparent liquid with an odor similar to a mixture of ethanol and acetone. It is soluble in water and also in most organic solvents such as alcohols, ethers, benzene, and chloroform. Isopropanol is an important organic chemical raw material and solvent with wide applications in pesticides, pharmaceuticals, electronic chemistry, and daily chemical products. In pharmaceuticals, high-purity isopropanol can be used as a raw material for the production of drugs such as indomethacin. In the daily chemical industry, isopropanol can be used as a disinfectant and cleaning agent. In water treatment, isopropanol can be used as a hard water treatment agent and detergent. As a petroleum fuel additive, isopropanol is used in automotive and aviation fuels. Isopropanol can also be used as a raw material for the production of acetone, hydrogen peroxide, methyl isopropyl ketone, diisopropyl ketone, isopropylamine, isopropyl ether, isopropyl chloride, and isopropyl esters of fatty acids and chlorinated fatty acids.

[0003] Currently, the industrial production of isopropanol involves propylene hydration at 20 bar and 473 K, while propylene is produced by dehydrogenating propane under high temperature and pressure. This process involves the emission of large amounts of pollutants and is energy-intensive.

[0004] Patent application 202410131332.7 discloses a method for producing acetone isopropanol by low-temperature oxidation of propane. The key technical points are: using oxygen as an oxidant, propane is converted into oxygen-containing compounds by high-pressure reaction in a low-temperature environment below 200°C and in a reaction medium containing organic solvents. Although the technology mentions oxidation at low temperature, it still requires reaction under high pressure, and the selectivity of isopropanol is low.

[0005] Direct synthesis of alcohols from alkanes using renewable electricity and water is one way to reduce carbon emissions from the chemical industry. However, 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. 2 This 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

[0006] The purpose of this invention is to overcome the defects of the prior art and provide a method for the photoelectrocatalytic conversion of propane to prepare isopropanol. By introducing light irradiation to excite the associative cleavage of the Br-Br bond in the Br2 molecule, active bromine is formed, thereby accelerating the activation of propane and achieving an order-of-magnitude increase in yield.

[0007] The objective of this invention can be achieved through the following technical solution: a method for the photoelectrocatalytic conversion of propane to isopropanol, comprising the following steps:

[0008] (1) Using iridium oxide supported on titanium felt as the anode catalyst and Pt / C catalyst supported on carbon paper as the cathode catalyst, the anode catalyst and the cathode catalyst are sandwiched on both sides of the proton exchange membrane to construct a zero-gap membrane electrode assembly. One or more membrane electrode assemblies constitute an electrocatalytic reaction cell.

[0009] (2) Using KBr solution as the electrolyte in the electrocatalytic reaction cell, the KBr solution is electrolyzed, and the anode produces an anolyte containing Br2, and the cathode produces a catholyte containing KOH.

[0010] (3) After mixing the anolyte obtained in step (2) with propane, the mixture is introduced into a photochemical microreactor and photocatalytic reaction is carried out under light irradiation. The resulting 2-bromopropane gas is absorbed by H2O.

[0011] (4) The absorbent containing 2-bromopropane obtained in step (3) and the cathode electrolyte containing KOH generated in step (2) are mixed and heated to obtain isopropanol product.

[0012] Furthermore, the current density applied during the electrolysis of the KBr solution in step (1) is 300-1000 mA / cm². 2 The concentration of the KBr solution is 1–3 M.

[0013] Further, the cathode catalyst described in step (1) is prepared by the following method: Pt / C is dispersed in isopropanol, Nafion solution is added, the dispersion is uniform, and the mixture is sprayed onto hydrophilic carbon paper, wherein the loading of Pt / C is 0.5–2 mg / cm³. 2 .

[0014] Further, the anode catalyst described in step (1) is prepared by the following method: titanium felt is impregnated in an aqueous solution of iridium chloride, with the pH controlled at 7-8, for 20-40 minutes, followed by calcination in air at a temperature of 300-400℃ for 2-4 hours, with an iridium loading of 0.05-0.2 mg / cm³. 2 .

[0015] Furthermore, in step (3), the propane flow rate is 15-200 mL / min, and the anolyte flow rate is 1-15 mL / min.

[0016] Furthermore, the photochemical microreactor described in step (3) includes a transparent microchannel and a xenon lamp, with the xenon lamp positioned above the transparent microchannel.

[0017] Furthermore, the inner diameter of the transparent microchannel is 3.5-10 mm, and its internal pressure is 0.5-5 bar;

[0018] Its material is PFA, glass or quartz.

[0019] Furthermore, the xenon lamp has an output power of 200-400W and a wavelength of 300-1000nm.

[0020] Furthermore, in step (4), the heating temperature of the absorbent containing 2-bromopropane is 60–90°C.

[0021] Compared with the prior art, the present invention has the following superior effects:

[0022] (1) This invention activates propane by selecting Br radicals with higher selectivity for methylene sites and introduces light irradiation to excite the Br-Br bond breaking in bromine molecules, thereby forming active Br and accelerating propane activation, thus promoting the conversion of propane to isopropanol. Operating at 300 mA / cm² for 230 hours, the system consistently maintained approximately 85% Faraday efficiency and approximately 60% power conversion efficiency. At a maximum of 1000 mA / cm²... 2 At current density, with a Faraday efficiency exceeding 71%, the isopropanol yield reached 15 mol / gcat / h, making it the most advanced and efficient propane selective oxidation system reported to date for the preparation of isopropanol.

[0023] (2) This invention utilizes the KBr solution from the electrolytic anolyte to generate a solution of elemental Br2. This solution is then reacted with propane in a microreactor to form a Taylor flow with a gas-liquid interface, thereby improving mass transfer. A continuous-flow quartz photocatalytic reaction cell with an inner diameter of 3.5-10 mm achieves gas-liquid closure. Photoexcitation decomposes Br2 into active Br, which reacts with propane to selectively generate bromopropane, thus activating propane to bromopropane. The continuous-flow quartz photocatalytic reaction cell is a transparent spiral tube. The oscillation of surface waves formed at the gas-liquid interface within the tube accelerates interface renewal, thereby increasing the propane mass transfer coefficient and ultimately achieving photoelectric reaction rate matching. After generating bromopropane, it is coupled with OH- generated at the cathode for hydrolysis, achieving efficient and selective propanol production. The bromide ions generated from the hydrolysis of bromopropane can be reused for anolyte electrolysis to produce elemental bromine, realizing a Br cycle.

[0024] Compared to previous reports, the maximum bias current density of this system exceeds 750 mA / cm². 2 (Currently reported technologies are all below 20mA / cm) 2 ), at 300mA / cm 2 It maintains excellent isopropanol selectivity and production efficiency even after running continuously for more than 230 hours, making it a more efficient and stable reaction system compared to currently reported electrocatalytic or photocatalytic technologies. Attached Figure Description

[0025] Figure 1 Schematic diagram of a reaction system for the continuous electro-photocatalytic preparation of isopropanol from propane;

[0026] Figure 2 This is a schematic diagram of the mixing state of the gas section and liquid section in a photochemical microreactor;

[0027] Figure 3 This invention is compared with previously reported techniques for the selective electro-oxidation of propane to produce alcohols.

[0028] Figure 4 The Faraday efficiency of isopropanol in the photoelectric cascade propane preparation at different current densities was determined. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0030] This invention provides a highly efficient, stable, and continuous method for the photoelectrocatalytic conversion of propane to isopropanol, comprising the following steps:

[0031] (1) A titanium felt was used as a supporting electrode and immersed in an aqueous solution of iridium chloride at a pH of 7-8 for 20-40 minutes, preferably 30 minutes. It was then calcined in air at 300-400℃ for 2-4 hours. The iridium loading was 0.05-0.2 mg / cm³. 2 0.1 mg / cm³ is preferred. 2 The titanium felt-supported iridium oxide prepared was used as the anode catalyst.

[0032] (2) A commercially available 50% Pt / C catalyst was dispersed in ethanol, and Nafion solution was added. The dispersion was then uniformly dispersed under ultrasonic conditions. The catalyst was then sprayed layer by layer onto carbon paper (in a preferred embodiment, H-060 carbon paper from Toray Industries, Japan) and vacuum dried at room temperature. The loading of the Pt / C catalyst was controlled at 0.5-2 mg / cm³. 2 1 mg / cm 2 A cathode catalyst was obtained.

[0033] (3) Using zero-gap membrane electrodes as electrocatalytic partial reaction devices, such as Figure 1 As shown, the electrocatalytic reaction cell 1 includes one or more membrane electrode assemblies, each of which includes an anode, a cathode, a proton exchange membrane, and an electrolyte. Both the cathode and anode electrolytes use 1-3 M KBr, preferably 2 M KBr. The cathode uses the cathode catalyst prepared in step (2), and the anode uses the anode catalyst prepared in step (1). The cathode and anode are placed on opposite sides of the proton exchange membrane. The current density applied to the electrocatalytic reaction cell 1 is controlled to be 300-1000 mA / cm². 2 Electrolysis of KBr solution yields a solution containing elemental Br2 at the anode and a catholyte containing KOH at the cathode.

[0034] (4) The obtained anolyte (a solution containing Br2) is mixed with propane through a three-way valve 2 and then introduced into a photochemical microreactor 3. The flow rate of propane gas is controlled at 15-200 mL / min and the flow rate of anolyte is controlled at 1-15 mL / min, using a 1 bar pressure gauge.

[0035] (5) The photochemical microreactor 3 is a transparent microchannel with an inner diameter of 3.5-10 mm. The illumination conditions include: xenon lamp output power of 200-400 W and wavelength of 300-1000 nm; reaction pressure of 1 bar. The transparent microchannel is made of PFA, glass, or quartz. Figure 2 The gas and liquid sections shown are mixed and enter the photochemical microreactor 3. The yellow part represents the liquid and the white part represents the gas. It can be seen that the gas and liquid sections alternate in the photochemical microreactor 3.

[0036] (6) The gas and solution obtained from the reaction in the photochemical microreactor 3 are separated by a gas-liquid separator. The resulting solution is returned to the electrolyte storage container, and the resulting 2-bromopropane gas is absorbed in the storage bottle 4 with H2O solution.

[0037] (7) The absorbent containing 2-bromopropane obtained in step (6) and the cathode electrolyte containing KOH generated in step (3) are mixed and heated to a temperature of 60–90°C. The final isopropanol product can be collected by distillation and separation from the absorbent.

[0038] like Figure 3 The figure shows a comparison between the present invention (i.e., the present work in the figure) and the prior art (i.e., the industrial current density in the figure) for the selective oxidation of propane to propanol. It can be seen that the present invention achieves this at 1000 mA / cm². 2 At current densities, the invention achieves a Faraday efficiency exceeding 75%, and a maximum bias current density exceeding 750 mA / cm² compared to previously reported methods. 2(Currently reported technologies all have a bias current density below 20 mA / cm²) 2 (It is impossible to achieve both high total current density and high Faraday efficiency simultaneously), at 300 mA / cm². 2 It maintains excellent isopropanol selectivity and production efficiency even after running continuously for more than 230 hours, making it a more efficient and stable reaction system compared to currently reported electrocatalytic or photocatalytic technologies.

[0039] Unless otherwise specified, the raw materials and equipment used in this invention are all commercially available or commonly used equipment.

[0040] Example 1

[0041] A highly efficient, stable, and continuous method for the photoelectrocatalytic conversion of propane to isopropanol includes the following steps:

[0042] (1) 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 350°C for 3 hours. The iridium loading was 0.1 mg / cm³. 2 The titanium felt-supported iridium oxide prepared was used as the anode catalyst.

[0043] (2) 20 mg of commercially available 50% Pt / C catalyst (i.e., 10 mg Pt, 10 mg C) was dispersed in 1.5 mL of ethanol, and 100 μL of Nafion solution was added. The dispersion was then uniformly dispersed under ultrasonic conditions. The catalyst was then sprayed layer by layer onto H-060 carbon paper from Toray Industries, Inc. of Japan, and vacuum dried at room temperature. The loading of the Pt / C catalyst was controlled at 1 mg / cm³. 2 A cathode catalyst was obtained.

[0044] (3) The anode catalyst obtained in step (1) and the cathode catalyst obtained in step (2) are placed on both sides of the proton exchange membrane to form a "three-in-one" membrane electrode. Multiple membrane electrodes are stacked to form an electrocatalytic reaction cell 1. Both the cathode and anode electrolytes are 2M KBr. The current density applied to the electrocatalytic reaction cell 1 is controlled to be 1000 mA / cm². 2 Electrolysis of KBr solution yields a solution containing elemental Br2 at the anode and a catholyte containing KOH at the cathode.

[0045] (4) The obtained anolyte (a solution containing Br2) and propane are mixed through a three-way valve 2 and then introduced into a photochemical microreactor 3. The flow rate of propane gas is controlled at 100 mL / min and the flow rate of anolyte is controlled at 5 mL / min, using a 1 bar pressure gauge.

[0046] (5) The photochemical microreactor 3 is a transparent microchannel with an inner diameter of 3.5 mm and a length of 2 m. The illumination conditions include: xenon lamp output power of 300 W and wavelength of 300-1000 nm; reaction pressure of 1 bar. The transparent microchannel is made of PFA.

[0047] (6) The gas and solution obtained from the reaction in the photochemical microreactor 3 are separated by a gas-liquid separator. The resulting solution is returned to the electrolyte storage container, and the resulting 2-bromopropane gas is absorbed in the storage bottle 4 with H2O solution.

[0048] (7) The absorbent containing 2-bromopropane obtained in step (6) and the cathode electrolyte containing KOH generated in step (3) are mixed and heated to 80°C. The final isopropanol product can be collected by distillation and separation from the absorbent.

[0049] Finally at 1000mA / cm 2 At the given current density, the partial current density of isopropanol can reach 710 mA / cm². 2 .

[0050] Example 2

[0051] In step (3), the current density applied to the electrocatalytic reaction cell is 300 mA / cm². 2 The rest is the same as in Example 1.

[0052] Example 3

[0053] In step (3), the current density applied to the electrocatalytic reaction cell is 750 mA / cm². 2 The rest is the same as in Example 1.

[0054] Example 4

[0055] In step (4), the propane gas flow rate is 15 mL / min, the anolyte flow rate is 5 mL / min, and a 1 bar pressure gauge is used. The rest is the same as in Example 1.

[0056] Example 5

[0057] In step (4), the propane gas flow rate is 100 mL / min, the anolyte flow rate is 1 mL / min, and a 1 bar pressure gauge is used. The rest is the same as in Example 1.

[0058] Example 6

[0059] In step (4), the propane gas flow rate is 50 mL / min, the anolyte flow rate is 15 mL / min, and a 1 bar pressure gauge is used. The rest is the same as in Example 1.

[0060] The products obtained in each embodiment and comparative example were subjected to performance testing, as follows:

[0061] 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.

[0062] Yield calculation formula:

[0063]

[0064] Where, m a It is the amount of isopropanol produced in the reaction, m cat t is the amount of catalyst used in the reaction, and t is the reaction time.

[0065] Faraday efficiency calculation formula:

[0066]

[0067] Where F is the Faraday constant, n a c is the number of electrons transferred during the formation of 1 mole of isopropanol from propane. a Through nuclear magnetic resonance hydrogen spectrum ( 1 The concentration of isopropanol or ethanol detected by H NMR, where V is the volume of the absorption solution and Q is the total current.

[0068] Formula for calculating electricity conversion efficiency:

[0069]

[0070] 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.

[0071] The test results are as follows:

[0072]

[0073] As shown in the table above, this technical solution can ensure high selectivity and energy efficiency in the selective activation of propane to prepare isopropanol under different current densities, while also exhibiting extremely high yield per unit catalyst mass. Higher current densities result in higher isopropanol yield, but lower current densities lead to higher Faradaic efficiency and energy utilization. Within the current density range of this invention, the overall performance is high. However, the flow rates of the reactants need to be controlled to match the flow rates of propane and electrolyte within a set range. A propane flow rate of 15-200 mL / min and an anolyte flow rate of 1-15 mL / min both yield good results. This method demonstrates feasibility and universality.

[0074] Figure 4 The Faradaic efficiency of isopropanol in the photoelectric cascade propane preparation at different current densities was measured at 1000 mA / cm². 2 At current density, it still maintains a 71% isopropanol Faradaic efficiency, which is superior to other reported electrocatalytic activation of propane to prepare alcohols. Figure 3 ).

Claims

1. A method for the photoelectrocatalytic conversion of propane to isopropanol, characterized in that, Includes the following steps: (1) Using iridium oxide supported on titanium felt as the anode catalyst and Pt / C catalyst supported on carbon paper as the cathode catalyst, the anode catalyst and the cathode catalyst are sandwiched on both sides of the proton exchange membrane to construct a zero-gap membrane electrode assembly. One or more membrane electrode assemblies constitute an electrocatalytic reaction cell. (2) Using KBr solution as the electrolyte in the electrocatalytic reaction cell, the KBr solution is electrolyzed, and the anode produces an anolyte containing Br2, and the cathode produces a catholyte containing KOH. (3) After mixing the anolyte obtained in step (2) with propane, the mixture is introduced into a photochemical microreactor and photocatalytic reaction is carried out under light irradiation. The resulting 2-bromopropane gas is absorbed by H2O. (4) The absorbent containing 2-bromopropane obtained in step (3) and the cathode electrolyte containing KOH generated in step (2) are mixed and heated to obtain isopropanol product.

2. The method for photoelectrocatalytic conversion of propane to isopropanol according to claim 1, characterized in that, The current density applied to the electrolytic KBr solution in step (1) is 300-1000 mA / cm 2 , and the concentration of the KBr solution is 1-3 M.

3. The method for photoelectrocatalytic conversion of propane to isopropanol according to claim 1, characterized in that, The cathode catalyst described in step (1) is prepared by dispersing Pt / C in isopropyl alcohol, adding a Nafion solution, uniformly dispersing, and spraying on a hydrophilic carbon paper, wherein the loading of Pt / C is 0.5-2 mg / cm 2 .

4. The method for photoelectrocatalytic conversion of propane to isopropanol according to claim 3, characterized in that, The anode catalyst described in step (1) is prepared by dipping a titanium felt into an aqueous iridium chloride solution, the pH being controlled to be between 7 and 8, the dipping time being between 20 and 40 minutes, and then calcining under air at a temperature of between 300 and 400°C for a time of between 2 and 4 hours, the loading of metallic iridium being between 0.05 and 0.2 mg / cm 2 .

5. The method for photoelectrocatalytic conversion of propane to isopropanol according to claim 1, characterized in that, In step (3), the propane flow rate is 15-200 mL / min, and the anolyte flow rate is 1-15 mL / min.

6. The method of claim 1, wherein the method is characterized by: The photochemical microreactor described in step (3) includes a transparent microchannel and a xenon lamp, with the xenon lamp positioned above the transparent microchannel.

7. The method of claim 6, wherein the method is characterized by, The inner diameter of the transparent microchannel is 3.5-10 mm, and the internal pressure is 0.5-5 bar.

8. The method of claim 6, wherein the method is characterized by, The transparent microchannel is made of PFA, glass, or quartz.

9. The method of claim 6, wherein the method is characterized by, The xenon lamp has an output power of 200-400W and a wavelength of 300-1000nm.

10. The method of claim 1, wherein the method is characterized by, In step (4), the heating temperature of the absorbent is 60–90℃.

Images