Preparation method of oxalic acid

Abstract

The invention provides a preparation method of oxalic acid, which comprises the following steps: carrying out electrolytic reduction treatment on carbon dioxide to obtain an oxalic acid solution; performing electrolytic oxidation treatment on the ethylene glycol aqueous solution to obtain an oxalic acid solution; the electrolytic reduction treatment and the electrolytic oxidation treatment are mutually coupled in an electrolytic tank. The preparation method of oxalic acid provided by the invention can be used for efficiently preparing oxalic acid, and is environment-friendly and low in energy consumption.

Description

Technical Field

[0001] The invention relates to a method for preparing oxalic acid and belongs to the field of electrochemistry. Background Art

[0002] Oxalic acid is an important chemical product, widely used in the pharmaceutical, dye, pesticide, plastic, rubber, leather and other industries. For example, oxalic acid can chelate many metal ions and minerals, so oxalic acid can be used as a cleaning agent. For example, oxalic acid can combine with certain chemicals to form dyes, and can also serve as a stabilizer for dyes, thereby extending the life of the dyes. For example, oxalic acid can penetrate into leather fibers, making the leather fibers more stable and preventing them from rotting and hardening.

[0003] Currently, the main method for producing oxalic acid is the carbon oxidation process, which involves reacting carbon monoxide with water vapor under high temperature and pressure to produce oxalic acid. However, this method is energy-intensive, requires sophisticated equipment, and produces large amounts of the greenhouse gas carbon dioxide.

[0004] Therefore, those skilled in the art are in urgent need of developing a method for preparing oxalic acid that can efficiently prepare oxalic acid while reducing environmental pollution and saving energy consumption. Summary of the Invention

[0005] The invention provides a method for preparing oxalic acid. The method can efficiently prepare oxalic acid, reduce environmental pollution, save energy consumption, and has simple process and is easy to operate.

[0006] The present invention provides a method for preparing oxalic acid, which comprises the following steps:

[0007] The carbon dioxide is subjected to electrolytic reduction treatment to obtain an oxalic acid solution;

[0008] Electrolytically oxidizing the ethylene glycol aqueous solution to obtain an oxalic acid solution;

[0009] The electrolytic reduction treatment and the electrolytic oxidation treatment are coupled with each other in one electrolytic cell.

[0010] The method for preparing oxalic acid as described above, wherein the electrolytic reduction treatment includes an electrolytic reduction catalyst, and the electrolytic reduction catalyst includes a P-doped Pb and Zn diatomic catalyst;

[0011] The atomic molar ratio of P, Pb and Zn in the P-doped Pb and Zn diatomic catalyst is (1-10): (0.5-0.9): (0.5-0.1).

[0012] In the above-mentioned method for preparing oxalic acid, the particle size of the electrolytic reduction catalyst is 1-100 nm.

[0013] The method for preparing oxalic acid as described above, wherein the electrolytic reduction catalyst is prepared by the following steps:

[0014] Ammonia water is added to a raw material system including a lead source and a zinc source to perform a first reaction to obtain a first product, and then the first product is calcined with NaH2PO3 to obtain the electrolytic reduction catalyst;

[0015] The reaction temperature of the first reaction is 60-100° C., and the reaction time is 1-5 hours; the calcination temperature of the calcination treatment is 300-400° C., and the calcination time is 1-5 hours.

[0016] The method for preparing oxalic acid as described above, wherein the electrolytic cell comprises a gas chamber and an electrolyte chamber separated by a gas diffusion electrode;

[0017] The gas chamber is used to receive carbon dioxide, and the carbon dioxide diffuses into the electrolyte chamber through the gas diffusion electrode, and the carbon dioxide undergoes the electrolytic reduction treatment on the surface of the gas diffusion electrode; the gas diffusion electrode includes a mesh substrate and the electrolytic reduction catalyst;

[0018] The electrolytic oxidation process is performed in the electrolyte chamber.

[0019] In the above-mentioned method for preparing oxalic acid, the volume ratio of the gas chamber to the electrolyte chamber is 1:(10-50).

[0020] In the above-mentioned method for preparing oxalic acid, the feed temperature of the carbon dioxide is 20-80° C., and the feed pressure is 0.1-1 MPaG.

[0021] The method for preparing oxalic acid as described above, wherein the feed temperature of the ethylene glycol aqueous solution is 20-80° C. and the feed pressure is 0.1-1 MPaG;

[0022] And / or, the mass percentage of ethylene glycol in the ethylene glycol aqueous solution is 10-30%.

[0023] The method for preparing oxalic acid as described above, wherein the current density of the electrolytic reduction treatment and the electrolytic oxidation treatment is 500-2000A / m 2 , the voltage is lower than 5V.

[0024] In the method for preparing oxalic acid as described above, the anode in the electrolyte chamber includes an anode plate and an anode coating, the anode coating includes an anode catalyst, and the anode catalyst includes a RuO2 / TiO2 catalyst.

[0025] In the preparation method of oxalic acid provided by the present invention, oxalic acid can be obtained by electrolytic reduction of carbon dioxide and electrolytic oxidation of ethylene glycol aqueous solution. Two oxalic acid preparation reactions can be carried out in one electrolysis device, which greatly improves the efficiency of the reaction, can efficiently prepare oxalic acid, and can effectively reduce the equipment investment and maintenance costs required for the electrolysis device, and can effectively save energy consumption. At the same time, carbon dioxide is used as the raw material, greenhouse gas can be recycled and utilized, and it is environmentally friendly. In addition, the preparation method of oxalic acid is simple in process and easy to operate, which is conducive to the large-scale production of oxalic acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the operation of an electrolytic cell including gas diffusion electrodes. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0028] The present invention provides a method for preparing oxalic acid, which comprises the following steps:

[0029] The carbon dioxide is subjected to electrolytic reduction treatment to obtain an oxalic acid solution;

[0030] Electrolytically oxidizing the ethylene glycol aqueous solution to obtain an oxalic acid solution;

[0031] The electrolytic reduction treatment and the electrolytic oxidation treatment are coupled with each other in one electrolytic cell.

[0032] The electrolytic reduction treatment and the electrolytic oxidation treatment are coupled with each other in one electrolytic cell in the present invention, which means that an electrolytic voltage is applied in one electrolytic cell, and the electrolytic reduction treatment and the electrolytic oxidation treatment occur simultaneously, both of which generate oxalic acid.

[0033] Specifically, in an electrolytic cell, carbon dioxide obtains electrons under the action of the cell voltage for electrolytic reduction treatment to obtain oxalic acid solution, while ethylene glycol aqueous solution loses electrons under the action of the cell voltage for electrolytic oxidation treatment to obtain oxalic acid solution.

[0034] The electrolytic ion equation for electrolytic reduction treatment is:

[0035] 4CO2+8e - +8H + →4H2C2O4;

[0036] The ionic equation for electrolytic oxidation treatment is:

[0037] C2H6O2+2H2O→H2C2O4+8e - +8H + .

[0038] Carbon dioxide is electrolytically reduced to produce oxalate ions, which are combined with hydrogen ions obtained through electrolytic oxidation to produce oxalic acid.

[0039] The present invention does not limit the choice of electrolytic cell, which can be selected according to actual needs, as long as it can electrolytically reduce carbon dioxide and electrolytically oxidize ethylene glycol aqueous solution.

[0040] The present invention does not limit the specific parameters of the electrolytic reduction treatment and the electrolytic oxidation treatment, and they can be selected according to actual needs.

[0041] The present invention does not limit the amount of carbon dioxide introduced, and it can be selected according to actual needs.

[0042] The present invention does not limit the concentration of the ethylene glycol aqueous solution, and the concentration can be selected according to actual needs.

[0043] The preparation method of oxalic acid provided by the present invention can efficiently prepare oxalic acid, and can reduce environmental pollution, save energy consumption, and the method process is simple, easy to operate. The inventor has analyzed this principle and believes that the reason may be that both electrolytic reduction treatment of carbon dioxide and electrolytic oxidation treatment of ethylene glycol aqueous solution can obtain oxalic acid, that is, the preparation reaction of two oxalic acids can be carried out in one electrolysis device, which greatly improves the efficiency of the reaction, so as to efficiently prepare oxalic acid, and can effectively reduce the equipment investment and maintenance cost required for the electrolysis device, and can effectively save energy consumption; while the raw material adopts carbon dioxide, greenhouse gas can be recycled, and is environmentally friendly. In addition, the preparation method of the oxalic acid is simple, easy to operate, which is conducive to the large-scale production of oxalic acid.

[0044] In a specific embodiment, the electrolytic reduction treatment includes an electrolytic reduction catalyst, which includes a P-doped Pb and Zn diatomic catalyst, wherein the atomic molar ratio of P, Pb and Zn is (1-10): (0.5-0.9): (0.5-0.1), for example, 1:0.5:0.5, 1:0.6:0.4, 1:0.7:0.3, 1:0.8:0.2, 1:0.9:0.1, 5:0.5:0.5, 5:0.6:0.4, 5:0.7:0.3, 5:0.8:0.2, 5:0.9:0.1, 10:0.5:0.5, 10:0.6:0.4, 10:0.7:0.3, 10:0.8:0.2, 10:0.9:0.1, etc. This P-doped Pb and Zn diatomic catalyst features active sites composed of Pb and Zn atoms. P is incorporated into the catalyst's spatial structure, serving as the catalyst's skeleton. The high specific surface area of ​​this P-doped Pb and Zn diatomic catalyst increases the catalyst's chemically active area. The P's multi-electron holes coordinate with multiple catalysts, exposing sufficient catalytically active sites and promoting charge transport, thereby aiding the electrolytic reduction of carbon dioxide to oxalate ions, and subsequently, to form oxalic acid. Furthermore, this electrolytic reduction catalyst accelerates the efficiency of the electrolytic reduction process, improving the efficiency of oxalic acid production.

[0045] In a specific embodiment, the particle size D50 of the electrolytic reduction catalyst is 10-100 nm, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm. When the particle size of the electrolytic reduction catalyst is within the above range, the electrolytic reduction catalyst can better catalyze the electrolytic reduction reaction of carbon dioxide, which is beneficial to improving the efficiency of the electrolytic reduction reaction of carbon dioxide, thereby being able to more efficiently improve the production efficiency of oxalic acid. Preferably, the particle size D50 of the electrolytic reduction catalyst is 10-50 nm.

[0046] Specifically, the present invention performs SEM testing on the electrolytic reduction catalyst to obtain the particle size of the electrolytic reduction catalyst.

[0047] In one embodiment, the electrolytic reduction catalyst is prepared by the following steps:

[0048] Ammonia water is added to a raw material system including a lead source and a zinc source to perform a first reaction to obtain a first product, and then the first product is calcined with NaH2PO3 to obtain an electrolytic reduction catalyst;

[0049] The reaction temperature of the first reaction is 60-100° C., and the reaction time is 1-5 hours; the calcination temperature of the calcination treatment is 300-400° C., and the calcination time is 1-5 hours.

[0050] Specifically, a lead source, a zinc source and a solvent are mixed to prepare a raw material system including a lead source and a zinc source, and then aqueous ammonia is added to the raw material system to carry out a first reaction. The reaction temperature of the first reaction is 60-100° C., for example, 60° C., 65° C., 70° C., 75° C., 80° C., 85° C., 90° C., 95° C. or 100° C., and the reaction time is 1-5 h, for example, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, followed by cooling and crystallization, solid-liquid separation, to obtain a first product, and then the first product is mixed with NaH2PO3 and heated in an inert atmosphere. The calcination treatment is carried out in a gas environment, the calcination temperature of the calcination treatment is 300-400°C, for example, 300°C, 305°C, 310°C, 315°C, 320°C, 325°C, 330°C, 335°C, 340°C, 345°C, 350°C, 355°C, 360°C, 365°C, 370°C, 375°C, 380°C, 385°C, 390°C, 395°C or 400°C, and the calcination time is 1-5h, for example, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, to obtain an electrolytic reduction catalyst.

[0051] The present invention does not limit the specific selection of the lead source and the zinc source, and they can be selected according to actual needs. For example, lead nitrate, zinc chloride, etc. can be selected.

[0052] The present invention does not limit the specific choice of solvent, as long as it can dissolve the lead source and the zinc source to form a solution, for example, water can be selected.

[0053] The addition ratio of the lead source and the zinc source in the present invention can be determined according to the molar ratio of lead to zinc in the P-doped Pb and Zn diatomic catalyst.

[0054] In the present invention, the ratio of the molar amount of ammonia water to the total molar amount of the lead source and the zinc source is (1:0.5).

[0055] The present invention does not limit the specific operation of solid-liquid separation, which can be selected according to actual needs, for example, centrifugal separation can be performed.

[0056] The addition ratio of the first product to NaH2PO3 in the present invention can be determined according to the molar ratio of lead, zinc and phosphorus in the P-doped Pb and Zn diatomic catalyst.

[0057] The present invention utilizes the above-mentioned method to prepare an electrolytic reduction catalyst that catalyzes the electrolytic reduction reaction of carbon dioxide, thereby improving the efficiency of the carbon dioxide electrolytic reduction reaction and further enhancing the efficiency of oxalic acid production. Furthermore, the preparation method of the electrolytic reduction catalyst is simple to operate and the raw materials are readily available, facilitating large-scale production of the electrolytic reduction catalyst.

[0058] In one embodiment, the electrolytic cell comprises a gas chamber and an electrolyte chamber separated by a gas diffusion electrode;

[0059] The gas chamber is used to receive carbon dioxide, which diffuses into the electrolyte chamber through the gas diffusion electrode, and the carbon dioxide undergoes electrolytic reduction on the surface of the gas diffusion electrode; the gas diffusion electrode includes a mesh substrate and an electrolytic reduction catalyst;

[0060] The electrolytic oxidation treatment is carried out in an electrolyte chamber.

[0061] Specifically, if Figure 1 As shown, the electrolytic cell includes a gas chamber and an electrolyte chamber, which are separated by a gas diffusion electrode. Carbon dioxide is fed from the gas chamber and diffuses into the electrolyte chamber through the gas diffusion electrode, so that the carbon dioxide undergoes electrolytic reduction treatment on the surface of the gas diffusion electrode, and electrolytic oxidation treatment is carried out in the electrolyte chamber; wherein, the gas diffusion electrode includes a mesh substrate and a coating layer coated on the surface of the mesh substrate, and the coating layer includes an electrolytic reduction catalyst.

[0062] The present invention does not limit the specific selection of the mesh substrate, as long as it can conduct electricity during the electrolysis process and allow gas to diffuse therein, for example, a gold mesh or a silver mesh can be selected.

[0063] The present invention does not limit the preparation method of the gas diffusion electrode, as long as the gas diffusion electrode includes a mesh substrate and an electrolytic reduction catalyst.

[0064] The present invention uses a gas diffusion electrode including a mesh substrate and an electrolytic reduction catalyst. Carbon dioxide can diffuse through the gas diffusion electrode and undergo an electrolytic reduction reaction on the surface of the gas diffusion electrode, which is beneficial to improving the electrolytic reduction efficiency of carbon dioxide, thereby enabling more efficient preparation of oxalic acid. In addition, the electrolytic cell eliminates the need for a diaphragm, preventing the diaphragm from reacting with oxalic acid, ethylene glycol, etc., which would lead to the generation of side reactions and save subsequent oxalic acid purification treatment.

[0065] In one embodiment, the gas diffusion electrode is prepared by the following steps:

[0066] 1) mixing an electrolytic reduction catalyst with a thickener, a dispersant, an ionomer, and a hydrophobic fluoropolymer to prepare a slurry to obtain slurry A;

[0067] 2) mixing the thickener and the hydrophobic fluoropolymer to prepare slurry to obtain slurry B;

[0068] 3) coating slurry B on the mesh substrate;

[0069] Alternatively, the ionomer is brush-coated on a mesh substrate and covered with a PTFE membrane or a PFA membrane, wherein the thickness of the PTFE membrane or the PFA membrane is 100 μm-500 μm and the pore size is 100 nm-500 nm;

[0070] 4) coating slurry A on the other side of the mesh substrate;

[0071] 5) The electrodes are pressed and fixed, and sintered at high temperature to obtain a gas diffusion electrode.

[0072] The present invention does not limit the specific selection of thickeners, dispersants, ionic polymers and hydrophobic fluoropolymers. For example, the thickener includes at least two of polyacrylic acid, polyacrylate, hydroxyethyl cellulose and methyl cellulose, the dispersant includes polyvinyl pyrrolidone and / or polyacrylamide, the ionic polymer includes perfluorosulfonic acid resin, such as Nafion, the hydrophobic fluoropolymer includes PTFE and / or PFA, and the hydrophobic fluoropolymer is in the form of powder or film.

[0073] The present invention does not limit the mass ratio of the electrolytic reduction catalyst to the thickener, dispersant, ion polymer, and hydrophobic fluoropolymer. For example, the mass ratio of the electrolytic reduction catalyst to the thickener, dispersant, ion polymer, and hydrophobic fluoropolymer is 1:(0.1-0.5):(1-5):(0.1-0.5):(0.05-0.2), preferably 1:(0.1-0.2):(1-3):(0.1-0.3):(0.08-0.15).

[0074] The present invention does not limit the viscosity of the slurry A. For example, the viscosity of the slurry A is 2-20 Pa·s, preferably 5-10 Pa·s.

[0075] The present invention does not limit the viscosity of the slurry B. For example, the viscosity of the slurry B is 2-20 Pa·s, preferably 5-10 Pa·s.

[0076] The present invention does not limit the specific selection and parameters of the mesh substrate. For example, a gold mesh or a silver mesh may be selected. The thickness of the mesh substrate is 100-500 μm, preferably 300-500 μm.

[0077] The present invention does not limit the loading mass ratio of slurry A and slurry B on the mesh substrate. For example, the loading amount of slurry B is 0.5-5 times the loading amount of slurry A.

[0078] The present invention does not limit the specific operation of coating, for example, casting or coating methods can be used.

[0079] The present invention does not limit the method for pressing the electrodes. For example, a roll-to-roll or hydraulic process may be used for pressing and fixing. Preferably, the pressure of the process is 10-100 MPa.

[0080] The present invention does not limit specific parameters of high-temperature sintering, for example, sintering at 180-400° C. for 20-100 min.

[0081] The thickness of the gas diffusion electrode prepared in the present invention is 300-1500 μm, preferably 500-800 μm, and the pore size of the gas diffusion electrode is 100-2000 nm, preferably 500-1200 nm.

[0082] In one specific embodiment, the volume ratio of the gas chamber to the electrolyte chamber is 1:(10-50), for example, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, or 1:50. When the volume ratio of the gas chamber to the electrolyte chamber is within the above range, carbon dioxide and ethylene glycol can undergo sufficient electrolytic reduction and electrolytic oxidation, avoiding excessive carbon dioxide or ethylene glycol that would otherwise waste raw materials, thereby reducing costs.

[0083] In a specific embodiment, the feed temperature of carbon dioxide is 20-80° C., for example, 20° C., 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., or 80° C., and the feed pressure is 0.1-1 MPaG, for example, 0.1 MPaG, 0.2 MPaG, 0.3 MPaG, 0.4 MPaG, 0.5 MPaG, 0.6 MPaG, 0.7 MPaG, 0.8 MPaG, 0.9 MPaG, or 1 MPaG, etc. When the feed temperature and feed pressure of carbon dioxide are within the above ranges, carbon dioxide can diffuse rapidly in the gas diffusion electrode, and is conducive to the electrolytic reduction reaction of carbon dioxide on the surface of the gas diffusion electrode, thereby improving the efficiency of the electrolytic reduction reaction of carbon dioxide and further improving the efficiency of oxalic acid preparation.

[0084] In a specific embodiment, the feed temperature of the ethylene glycol aqueous solution is 20-80° C., for example, 20° C., 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., or 80° C., and the feed pressure is 0.1-1 MPaG, for example, 0.1 MPaG, 0.2 MPaG, 0.3 MPaG, 0.4 MPaG, 0.5 MPaG, 0.6 MPaG, 0.7 MPaG, 0.8 MPaG, 0.9 MPaG, or 1 MPaG, etc. When the feed temperature and feed pressure of the ethylene glycol aqueous solution are within the above ranges, the ethylene glycol aqueous solution can undergo an efficient electrolytic oxidation reaction, thereby further improving the efficiency of oxalic acid preparation.

[0085] In one specific embodiment, the mass percentage of ethylene glycol in the ethylene glycol aqueous solution is 10-30%, for example, 10%, 15%, 20%, 25%, or 30%. When the mass percentage of ethylene glycol is within this range, ethylene glycol can undergo a sufficient electrolytic oxidation reaction with water, avoiding excess ethylene glycol or water. Furthermore, hydrogen ions can be rapidly conducted in the electrolyte, facilitating the binding of oxalate radicals with hydrogen ions, thereby increasing the efficiency of oxalic acid production.

[0086] In one embodiment, the current density of the electrolytic reduction treatment and the electrolytic oxidation treatment is 500-2000 A / m 2 , the voltage is lower than 5 V. When the current density and voltage of the electrolytic reduction treatment and the electrolytic oxidation treatment are within the above ranges, the electrolytic reduction treatment and the electrolytic oxidation treatment can be carried out efficiently, thereby enabling oxalic acid to be quickly produced, saving electricity consumption, and reducing production costs.

[0087] In one embodiment, the anode in the electrolyte chamber includes an anode plate and an anode coating, the anode coating including an anode catalyst, and the anode catalyst including a RuO2 / TiO2 catalyst. The anode is disposed in the electrolyte chamber and includes an anode plate and an anode coating, the anode coating including an anode catalyst, and the anode catalyst including a RuO2 / TiO2 catalyst. The anode catalyst can rapidly electrolytically oxidize ethylene glycol, thereby improving the efficiency of the electrolytic oxidation reaction and thereby improving the efficiency of oxalic acid production.

[0088] Hereinafter, the present invention will be further described in detail through specific examples.

[0089] Example 1

[0090] This embodiment prepares oxalic acid by the following steps:

[0091] In the electrolytic cell, the electrolytic cell includes a gas chamber and an electrolyte chamber separated by a gas diffusion electrode. The volume ratio of the gas chamber to the electrolyte chamber is 1:10. Both reaction chambers are made of corrosion-resistant titanium alloy material, and the inner walls are coated with a graphene coating with good conductivity.

[0092] A 99.9% pure carbon dioxide gas was introduced into the gas chamber at a pressure of 800 kPaG and a temperature of 60°C. A 10% by weight ethylene glycol aqueous solution was introduced into the reaction chamber at a pressure of 800 kPaG and a temperature of 60°C. A 2000 A / m 2 The current density is 1.5 and the voltage is 4.8 V to produce oxalic acid.

[0093] Among them, the electrolytic reduction catalyst in the gas diffusion electrode is prepared by the following steps: mixing lead nitrate, zinc chloride and water to prepare a raw material system including lead nitrate and zinc chloride, then adding ammonia water to the raw material system, the molar ratio of lead nitrate, zinc chloride and ammonia water is 0.8:0.2:2, and performing a first reaction. The reaction temperature of the first reaction is 100°C and the reaction time is 3 hours. Then the temperature is lowered for crystallization and solid-liquid separation to obtain a first product. Then the first product is mixed with NaH2PO3, the molar ratio of the first product to NaH2PO3 is 1:2, and calcination is carried out under an inert gas environment. The calcination temperature of the calcination treatment is 350°C and the calcination time is 3 hours to obtain a P-doped Pb and Zn diatomic catalyst. The D50 of the catalyst is 50 nm, and the atomic molar ratio of P, Pb and Zn in the P-doped Pb and Zn diatomic catalyst is 2:0.8:0.2.

[0094] The gas diffusion electrode is prepared by the following steps: 1) mixing the above-mentioned electrolytic reduction catalyst with thickeners methyl cellulose and hydroxyethyl cellulose, dispersant polyvinyl pyrrolidone, ion polymer Nafion, and adhesive PTFE to prepare slurry, wherein the mass ratio of the electrolytic reduction catalyst to the thickener, dispersant, ion polymer, and hydrophobic fluoropolymer is 1:0.1:2:0.1:0.1 to obtain slurry A, and the viscosity of slurry A is 5 Pa·s; 2) mixing the adhesive PTFE and the dispersant methyl cellulose in a mass ratio of 1:1 to prepare slurry B, and the viscosity of slurry B is 5 Pa·s; 3) coating slurry B on a mesh substrate; 4) coating slurry A on the other side of the mesh substrate; the loading amount of slurry B is 5 times the loading amount of slurry A; 5) pressing and fixing the electrode by a hydraulic process at a pressure of 5 MPa, and sintering at 150°C for 30 minutes to obtain a gas diffusion electrode.

[0095] Mercury intrusion testing was performed on the gas diffusion electrode, and the thickness of the gas diffusion electrode was found to be 0.5 mm and the pore size was 100-1000 nm.

[0096] The anode catalyst in the anode includes RuO2 / TiO2 catalyst.

[0097] Example 2

[0098] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the particle size of the electrolytic reduction catalyst is 10 nm.

[0099] Example 3

[0100] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the particle size of the electrolytic reduction catalyst is 100 nm.

[0101] Example 4

[0102] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the particle size of the electrolytic reduction catalyst is 120 nm.

[0103] Example 5

[0104] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the reaction temperature of the first reaction is 100° C. and the reaction time is 1 h; the calcination temperature of the calcination treatment is 350° C. and the calcination time is 2 h.

[0105] Example 6

[0106] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the reaction temperature of the first reaction is 60° C. and the reaction time is 5 h; the calcination temperature of the calcination treatment is 400° C. and the calcination time is 1 h.

[0107] Example 7

[0108] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the reaction temperature of the first reaction is 120° C. and the reaction time is 6 h; the calcination temperature of the calcination treatment is 450° C. and the calcination time is 0.5 h.

[0109] Example 8

[0110] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the volume ratio of the gas chamber to the electrolyte chamber is 1:30.

[0111] Example 9

[0112] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the volume ratio of the gas chamber to the electrolyte chamber is 1:50.

[0113] Example 10

[0114] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the volume ratio of the gas chamber to the electrolyte chamber is 1:60.

[0115] Example 11

[0116] The steps for preparing oxalic acid in this example are substantially the same as those in Example 1, except that the feed temperature of carbon dioxide is 20° C. and the feed pressure is 1 MPaG.

[0117] Example 12

[0118] The steps for preparing oxalic acid in this example are substantially the same as those in Example 1, except that the feed temperature of carbon dioxide is 80° C. and the feed pressure is 0.1 MPaG.

[0119] Example 13

[0120] The steps for preparing oxalic acid in this example are substantially the same as those in Example 1, except that the feed temperature of carbon dioxide is 10° C. and the feed pressure is 1.2 MPaG.

[0121] Example 14

[0122] The steps for preparing oxalic acid in this example are substantially the same as those in Example 1, except that the feed temperature of the ethylene glycol aqueous solution is 20° C. and the feed pressure is 1 MPaG.

[0123] Example 15

[0124] The steps for preparing oxalic acid in this example are substantially the same as those in Example 1, except that the feed temperature of the ethylene glycol aqueous solution is 80° C. and the feed pressure is 0.1 MPaG.

[0125] Example 16

[0126] The steps for preparing oxalic acid in this example are substantially the same as those in Example 1, except that the feed temperature of the ethylene glycol aqueous solution is 10° C. and the feed pressure is 1.2 MPaG.

[0127] Example 17

[0128] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the mass percentage of the ethylene glycol aqueous solution is 20%.

[0129] Example 18

[0130] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the mass percentage of the ethylene glycol aqueous solution is 30%.

[0131] Example 19

[0132] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the mass percentage of the ethylene glycol aqueous solution is 40%.

[0133] Example 20

[0134] The steps for preparing oxalic acid in this embodiment are similar to those in embodiment 1, except that the current density is 2000 A / m 2 , the voltage is 4.9V.

[0135] Example 21

[0136] The steps for preparing oxalic acid in this embodiment are similar to those in embodiment 1, except that the current density is 100 A / m 2 , the voltage is 2.5V.

[0137] Example 22

[0138] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the atomic molar ratio of P, Pb, and Zn in the P-doped Pb and Zn diatomic catalyst is 1:0.5:0.5.

[0139] Example 23

[0140] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the atomic molar ratio of P, Pb, and Zn in the P-doped Pb and Zn diatomic catalyst is 10:0.5:0.5.

[0141] Example 24

[0142] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the atomic molar ratio of P, Pb, and Zn in the P-doped Pb and Zn diatomic catalyst is 1:0.9:0.1.

[0143] Example 25

[0144] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the atomic molar ratio of P, Pb, and Zn in the P-doped Pb and Zn diatomic catalyst is 10:0.9:0.1.

[0145] Example 26

[0146] The steps for preparing oxalic acid in this embodiment are substantially the same as those in Example 1, except that the atomic molar ratio of P, Pb, and Zn in the P-doped Pb and Zn diatomic catalyst is 0.5:0.8:0.2.

[0147] Comparative Example 1

[0148] The steps for preparing oxalic acid in this comparative example are substantially the same as those in Example 1, except that the electrolyte chamber contains methanol aqueous solution.

[0149] Comparative Example 2

[0150] This comparative example prepares oxalic acid and comprises the following steps:

[0151] In the electrolytic cell comprising a cathode chamber and an anode chamber, which is separated by a diaphragm, both reaction chambers are made of corrosion-resistant titanium alloy material, and the inner walls are coated with a graphene coating with good conductivity.

[0152] N2 was introduced into the gas chamber at a temperature of 60°C. A 10% ethylene glycol aqueous solution was introduced into the reaction chamber at a pressure of 800 kPa at a temperature of 60°C. A 2000 A / m 2 The current density is 100 and the voltage is 7V to produce oxalic acid.

[0153] Test example

[0154] In a flow electrolyzer, CO2 was introduced into the cathode gas chamber, and an ethylene glycol aqueous solution was introduced into the anode electrolysis chamber. The electrochemical reaction was carried out under constant current conditions for 4 hours. The electrolyte was collected and tested for oxalic acid concentration, and the amount of oxalic acid generated was calculated. The oxalic acid current efficiency was calculated based on the generated amount. The theoretical oxalic acid yield at the anode was 0.42 g / Ah, and the theoretical oxalic acid yield at the cathode was 1.68 g / Ah. The total theoretical oxalic acid yield at the cathode and anode was 2.1 g / Ah. The average oxalic acid current efficiency was calculated by ratioing the generated amount to the theoretical yield.

[0155] Oxalic acid was analyzed by HPLC.

[0156] Table 1

[0157]

[0158]

[0159] As shown in Table 1, based on the comparison between Examples 1-26 and Comparative Examples 1 and 2, the method for preparing oxalic acid provided by the present invention can efficiently prepare oxalic acid, and the average current efficiency of oxalic acid can reach up to 62%. Therefore, it can be seen that the method for preparing oxalic acid provided by the present invention can efficiently prepare oxalic acid, improve the average current efficiency of oxalic acid, and the preparation method can reduce environmental pollution and save energy consumption, thereby facilitating the industrial application of the preparation method.

[0160] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing oxalic acid, characterized in that: The following steps are involved: The carbon dioxide is subjected to electrolytic reduction treatment to obtain an oxalic acid solution; Electrolytically oxidizing the ethylene glycol aqueous solution to obtain an oxalic acid solution; The electrolytic reduction treatment and the electrolytic oxidation treatment are coupled to each other in one electrolytic cell.

2. The method for preparing oxalic acid according to claim 1, characterized in that: The electrolytic reduction treatment includes an electrolytic reduction catalyst, wherein the electrolytic reduction catalyst includes a P-doped Pb and Zn diatomic catalyst; Among them, the atomic molar ratio of P, Pb and Zn in the P-doped Pb and Zn diatomic catalyst is (1-10): (0.5-0.9): (0.5-0.1).

3. The method for preparing oxalic acid according to claim 2, characterized in that: The particle size D50 of the electrolytic reduction catalyst is 10-100 nm.

4. The method for preparing oxalic acid according to claim 2 or 3, characterized in that: The electrolytic reduction catalyst is prepared by the following steps: Ammonia water is added to a raw material system including a lead source and a zinc source to perform a first reaction to obtain a first product, and then the first product is reacted with NaH2PO3 and then calcined to obtain the electrolytic reduction catalyst; The reaction temperature of the first reaction is 60-100°C, and the reaction time is 1-5h; the calcination temperature of the calcination treatment is 300-400°C, and the calcination time is 1-5h.

5. The method for preparing oxalic acid according to any one of claims 2 to 4, characterized in that: The electrolytic cell comprises a gas chamber and an electrolyte chamber separated by a gas diffusion electrode; The gas chamber is used to receive carbon dioxide, the carbon dioxide diffuses into the electrolyte chamber through the gas diffusion electrode, and the carbon dioxide undergoes the electrolytic reduction treatment on the surface of the gas diffusion electrode; The gas diffusion electrode comprises a mesh substrate and the electrolytic reduction catalyst; The electrolytic oxidation treatment is performed in the electrolyte chamber.

6. The method for preparing oxalic acid according to claim 5, characterized in that: The volume ratio of the gas chamber to the electrolyte chamber is 1:(10-50).

7. The method for preparing oxalic acid according to any one of claims 1 to 6, characterized in that: The feed temperature of the carbon dioxide is 20-80°C, and the feed pressure is 0.1-1 MPaG.

8. The method for preparing oxalic acid according to any one of claims 1 to 7, characterized in that: The feed temperature of the ethylene glycol aqueous solution is 20-80°C, and the feed pressure is 0.1-1MPaG; And / or, the mass percentage of ethylene glycol in the ethylene glycol aqueous solution is 10-30%.

9. The method for preparing oxalic acid according to any one of claims 1 to 8, characterized in that: The current density of the electrolytic reduction treatment and the electrolytic oxidation treatment is 500-2000A / m 2 , the voltage is lower than 5V.

10. The method for preparing oxalic acid according to any one of claims 5 to 9, characterized in that: The anode in the electrolyte chamber includes an anode plate and an anode coating, the anode coating includes an anode catalyst, and the anode catalyst includes a RuO2 / TiO2 catalyst.

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