A method for electrochemically co-producing chlorine and co

Abstract

The application discloses an electrochemical preparation method for co-production of chlorine gas and CO, and provides a simple and efficient method for co-production of chlorine gas and CO. The method solves the problems of complex electrode material preparation, high cost and easy pipeline blockage in the prior production technology.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of organic electrochemical synthesis, and particularly relates to a method for simultaneously preparing chlorine and CO by an electrochemical co-production process. BACKGROUND

[0002] Chlorine and CO are both important chemical raw materials and are widely used in various industries. Chlorine is mainly prepared by electrolysis in the chlor-alkali method, or is prepared by using HCl as a raw material and using air (oxygen) oxidation. CO is mainly prepared in large quantities by coal gasification devices, but a large amount of CO2 is produced as a byproduct, which is one of the main sources of greenhouse gases.

[0003] Advanced Energy Material, 2021, Vol. 11, 2100075 reports a method for simultaneously preparing chlorine and CO by electrolyzing seawater, which requires the use of cobalt phthalocyanine as a key electrode material. The electrode preparation process is complex, and the price of cobalt phthalocyanine and other additives is high, resulting in high overall electrode cost, which does not have large-scale application prospects.

[0004] Patent CN111575732 reports an experimental method using carbonates as a cathode liquid. Carbonate substances have poor stability and are easily reduced in a cathode reduction atmosphere, thereby causing the electrolyte to deteriorate. In addition, NaHCO3 and Na2CO3 generated in the process easily block the pipeline. Due to the low conductivity of carbonates, the cell voltage is high during the reaction process, and the power consumption is high.

[0005] Therefore, it can be seen that there are problems such as complex preparation of electrode catalysts and poor stability of electrode liquid in the co-production of chlorine to prepare CO, and a clean, safe and stable method is needed. SUMMARY

[0006] The main purpose of the present application is to provide a method for co-producing chlorine and CO. In order to achieve the above-mentioned purpose of the application, the technical scheme adopted by the present application is as follows:

[0007] An electrochemical co-production process and a preparation method of an electrode, comprising the following steps:

[0008] An oxidation reaction of chlorine ions occurs at the anode to generate chlorine; a CO2 electrochemical reduction reaction occurs at the cathode to generate CO; the anode electrolyte is a NaCl aqueous solution, and the cathode electrolyte is a mixture of an ionic liquid and water.

[0009] The reaction equations are as follows:

[0010] Anode: 2Cl - → Cl2 + 2e -

[0011] Cathode: 3CO2 + H2O + 2Na+ 2e - → CO + 2 NaHCO3

[0012] The ionic liquid has the following structural formula, wherein X = one of BF4, PF6, CF3SO3 (trifluoromethane sulfonic acid), (CF3SO2)2N (bistrifluoromethanesulfonylimide), (FSO2)2N (bisfluorosulfonylimide).

[0013]

[0014] In the present application, the concentration of the NaCl aqueous solution is 2wt%-10wt%;

[0015] Preferably, the mass ratio of the amount of the ionic liquid added to water in the cathode electrolyte is 1:1-3:1.

[0016] In the present application, the cathode is a gas diffusion electrode, which comprises a gas diffusion layer and a catalytic layer. The gas diffusion layer is selected from one of carbon paper, carbon felt, and polytetrafluoroethylene porous film. The catalytic layer comprises a host metal and a doped metal. The host metal is selected from one of silver, gold, and zinc; the doped metal is selected from one of platinum group metals, preferably one of rhodium, palladium, and platinum, and the mass ratio of the doped element to the host metal is 0.1%-5%.

[0017] The preparation method of the gas diffusion electrode comprises the following steps:

[0018] The host metal, the doped metal, the additive, and the Nafion aqueous solution are added to the solvent in a mass ratio, and after being uniformly dispersed, the catalyst slurry is uniformly sprayed on the gas diffusion layer by a watering can, and multiple spraying is performed to control the thickness of the catalytic layer. After completion, natural air drying is performed, and then the cathode material is obtained by drying in an oven.

[0019] The solvent is selected from one or more of isopropyl alcohol, ethanol, and methanol, and the amount of the solvent is 10-20wt% of the host metal;

[0020] The additive is selected from hydroxyethyl cellulose, hydroxymethyl cellulose, and hydroxypropyl methyl cellulose, and the amount of the additive is 1-5wt% of the host metal;

[0021] The concentration of the Nafion aqueous solution is 1-10wt%, and the amount of the Nafion aqueous solution is 5-10wt% of the host metal;

[0022] The thickness of the catalytic layer is 30-50 microns;

[0023] The drying temperature is 200-400℃, and the drying time is 12-36h.

[0024] The anode material is selected from one of titanium plating ruthenium dioxide, titanium plating iridium oxide and graphite.

[0025] The current density is 500-3000 A / m 2 , preferably 1000-2000 A / m 2 . The reduction reaction temperature is 40-60℃.

[0026] The reaction is carried out in an electrolytic cell, which can be a conventional diaphragm electrolytic cell, and the diaphragm is selected from Nafion ion exchange membrane, and the electrolytic cell can be provided with a stirrer, a thermometer and other accessories in addition to the electrodes.

[0027] In a specific embodiment, the anode and the cathode are rectangular electrodes, the anode electrode area is 1-10 cm 2 , the cathode electrode area is 1-10 cm 2 , and the two electrodes are placed in parallel, and the distance between the anode and the cathode is 2-10 mm.

[0028] In a specific embodiment, the preparation method comprises the following steps:

[0029] NaCl aqueous solution is added to the anode chamber of the electrolytic cell, and ionic liquid (X = BF4) and water are added to the cathode chamber, CO2 is introduced into the cathode liquid for 5-60 minutes before the reaction, the current density is controlled to be 1000 A / m 2 , and electrolysis is carried out at 40℃ for 10 hours. The yield of anode product chlorine is determined by titration, the yield of cathode product CO is determined by gas chromatography, and the main by-product is hydrogen.

[0030] In the method, the cathode material substrate is polytetrafluoroethylene porous fiber, the main metal of the catalytic layer is silver with a content of 99wt%, and the doping metal rhodium has a content of 1wt%; and the anode material is titanium plating ruthenium dioxide.

[0031] The anode and the cathode are rectangular electrodes, the anode electrode area is 10 cm 2 , the cathode electrode area is 10 cm 2 , the two electrodes are placed in parallel, and the distance between the anode and the cathode is 5 mm. Nafion 117 ion exchange membrane is used to separate the anode chamber and the cathode chamber.

[0032] Compared with the prior art, the present application has the following advantages:

[0033] (1) The present application uses a new type of ionic liquid, which has good water solubility and can be used as a mixed solvent to dissolve the sodium bicarbonate generated in the reaction process, thereby avoiding the precipitation of sodium bicarbonate on the electrode surface and the problems such as pipeline blockage;

[0034] (2) The application adopts a gas diffusion electrode doped with platinum group metals, improves the selectivity of CO, and effectively reduces the cost of electrode materials.

[0035] In conclusion, the application provides a simple and efficient method for co-production of chlorine and CO, and solves the problems of complex electrode material preparation, high cost, and easy pipeline blockage in the prior art. DETAILED DESCRIPTION

[0036] The application will be further described below in conjunction with examples, but the application is not limited to the listed examples, and also includes equivalent improvements and modifications of the technical solutions defined in the claims attached to the application.

[0037] The raw materials and equipment in the examples are described as follows:

[0038] Carbon paper, carbon felt, and polytetrafluoroethylene porous film were purchased from Shanghai Xianren Science and Technology Company.

[0039] Ionic liquid was purchased from Merni Chemical Technology Co., Ltd., with a purity of > 99%.

[0040] Anode material: Xi'an Taijin Material Company.

[0041] Methanol, ethanol, isopropyl alcohol, hydroxyethyl cellulose, hydroxymethyl cellulose, and hydroxypropyl methyl cellulose were purchased from Aldrin Reagent.

[0042] 5wt% Nafion aqueous solution, cation exchange membrane Nafion 115, Nafion 117, and Nafion 1110 were purchased from DuPont China Group Co., Ltd.

[0043] Metal powder was purchased from Shanghai Xianren Material Company.

[0044] Gas chromatography analysis conditions: instrument model: Shimadzu 2010 Plus, carrier gas: helium; flow rate: 1.0 ml / min; sample injection amount: 0.2 ul; sample injection port temperature: 300℃; split ratio: 30:1; chromatographic column: DB-5 (30m x 0.25mm x 0.25um); column temperature: 50℃ for 2 minutes, increased to 80℃ at a rate of 5℃ / min, maintained for 0min, increased to 300℃ at a rate of 15℃ / min, maintained for 10min; detector: TCD, temperature: 300℃.

[0045] Example 1

[0046] The preparation method of the cathode material is as follows: first, a catalyst slurry is prepared; 999 mg of silver powder, 1 mg of metal rhodium powder, 10 mg of hydroxyethyl cellulose, and 50 mg of 5 wt% Nafion aqueous solution are added into 100 mg of isopropyl alcohol solvent in a mass ratio, uniformly dispersed, and then the catalyst slurry is uniformly sprayed on the carbon paper through a watering can, and the thickness of the catalytic layer is controlled to be 30 microns through multiple spraying; after completion, the mixture is naturally air-dried, and then placed in an oven for drying at 300°C for 24 hours to obtain the cathode material.

[0047] 100 g of 2%wt NaCl aqueous solution is added to the anode chamber of the electrolytic cell, 50 g of ionic liquid (X = BF4) and 50 g of water are added to the cathode chamber, the cathode material substrate is carbon paper, the main metal of the catalytic layer is silver, and the content is 99.9wt%, and the doping metal rhodium content is 0.1wt%. The anode material is titanium coated with ruthenium dioxide. The anode and the cathode are both rectangular electrodes, the anode electrode area is 10 cm 2 , the cathode electrode area is 10 cm 2 , and the two electrodes are placed in parallel with a distance of 2 mm between the anode and the cathode. A cation exchange membrane Nafion 117 is used to separate the anode chamber and the cathode chamber. CO is introduced into the cathode liquid for 230 minutes before the reaction, and the current density is controlled to be 1000 A / m 2 , and electrolysis is carried out at 40°C for 10 hours. The yield of the anode product chlorine is determined by titration, and the current efficiency is 96%; the cathode product CO is determined by gas chromatography, and the current efficiency is 97%.

[0048] Example 2

[0049] The preparation method of the cathode material is as follows: first, a catalyst slurry is prepared; 999 mg of silver powder, 1 mg of metal rhodium powder, 10 mg of hydroxyethyl cellulose, and 50 mg of 5 wt% Nafion aqueous solution are added into 100 mg of isopropyl alcohol solvent in a mass ratio, uniformly dispersed, and then the catalyst slurry is uniformly sprayed on the carbon paper through a watering can, and the thickness of the catalytic layer is controlled to be 30 microns through multiple spraying; after completion, the mixture is naturally air-dried, and then placed in an oven for drying at 300°C for 24 hours to obtain the cathode material.

[0050] 100 g of 2%wt NaCl aqueous solution is added to the anode chamber of the electrolytic cell, 50 g of ionic liquid (X = BF4) and 50 g of water are added to the cathode chamber, the cathode material substrate is carbon paper, the main metal of the catalytic layer is silver, and the content is 99.9wt%, and the doping metal rhodium content is 0.1wt%. The anode material is titanium coated with ruthenium dioxide. The anode and the cathode are both rectangular electrodes, the anode electrode area is 10 cm 2 , the cathode electrode area is 10 cm 2, the two electrodes are placed in parallel, the distance between the cathode and the anode is 10 mm. The anode chamber and the cathode chamber are separated by a cation exchange membrane Nafion 115. CO is introduced into the cathode liquid for 30 minutes before the reaction, and the current density is controlled at 2000 A / m 2 , the electrolysis is carried out at 60℃ for 5h. The yield of the anode product chlorine is determined by titration, and the current efficiency is 95%; the yield of the cathode product CO is determined by gas chromatography, and the current efficiency is 96%.

[0051] Example 3

[0052] The preparation method of the cathode material is as follows: first, prepare a catalyst slurry, and then add 950 mg of zinc powder, 50 mg of platinum powder, 48 mg of hydroxypropyl methyl cellulose, and 95 mg of 5wt% Nafion aqueous solution into 143 mg of methanol solvent in a mass ratio, uniformly disperse, and then uniformly spray the catalyst slurry on the carbon felt through a sprinkler, control the thickness of the catalytic layer to be 50 microns by multiple spraying, and then naturally air dry, and then put it into an oven for drying at 300℃ for 24h to obtain the cathode material.

[0053] 100g of 10wt% NaCl aqueous solution is added to the anode chamber of the electrolytic cell, 66g of ionic liquid (X=CF3SO3 (trifluoromethanesulfonic acid)) and 33g of water are added to the cathode chamber, the cathode material substrate is carbon felt, and the main metal of the catalytic layer is zinc with a content of 95wt%, and the doping metal platinum content is 5wt%. The anode material is graphite. The anode and the cathode are both rectangular electrodes, the anode electrode area is 10cm 2 , the cathode electrode area is 10cm 2 , the two electrodes are placed in parallel, the distance between the cathode and the anode is 6 mm. The anode chamber and the cathode chamber are separated by a cation exchange membrane Nafion 1110. CO is introduced into the cathode liquid for 30 minutes before the reaction, and the current density is controlled at 1500 A / m 2 , the electrolysis is carried out at 50℃ for 7.5h. The yield of the anode product chlorine is determined by titration, and the current efficiency is 92%; the yield of the cathode product CO is determined by gas chromatography, and the current efficiency is 93%.

[0054] Example 4

[0055] The preparation method of the cathode material is as follows: first, prepare a catalyst slurry, and then add 950 mg of zinc powder, 50 mg of platinum powder, 48 mg of hydroxypropyl methyl cellulose, and 95 mg of 5wt% Nafion aqueous solution into 143 mg of methanol solvent in a mass ratio, uniformly disperse, and then uniformly spray the catalyst slurry on the carbon felt through a sprinkler, control the thickness of the catalytic layer to be 50 microns by multiple spraying, and then naturally air dry, and then put it into an oven for drying at 300℃ for 24h to obtain the cathode material.

[0056] The anode chamber of the electrolytic cell was fed with 100 g of a 7 wt% NaCl aqueous solution, and the cathode chamber was fed with 60 g of an ionic liquid (X = (CF3SO2)2N (bistrifluoromethylsulfonylimide)) and 40 g of water. The cathode material substrate was carbon paper, and the main metal of the catalytic layer was silver, with a content of 97.5 wt%, and the doping metal palladium had a content of 2.5 wt%. The anode material was titanium coated with ruthenium dioxide. Both the anode and the cathode were rectangular electrodes, with an anode electrode area of 10 cm 2 , and a cathode electrode area of 10 cm 2 . The two electrodes were placed in parallel, with a cathode-anode distance of 4 mm. A cation exchange membrane Nafion 117 was used to separate the anode chamber and the cathode chamber. CO was introduced into the cathode liquid for 30 minutes before the reaction, and the current density was controlled at 500 A / m 2 . Electrolysis was performed at 45°C for 8 h. The yield of the anode product, chlorine, was determined by titration, and the current efficiency was 90%; the yield of the cathode product, CO, was determined by gas chromatography, and the current efficiency was 96%.

[0057] Example 5

[0058] The cathode material was prepared as follows: a catalyst slurry was first prepared by adding 970 mg of gold powder, 30 mg of metal platinum powder, 20 mg of hydroxyethyl cellulose, and 78 mg of a 5 wt% Nafion aqueous solution into 156 mg of an ethanol solvent, and then uniformly dispersing the mixture. The catalyst slurry was uniformly sprayed onto a polytetrafluoroethylene porous film through a watering can, and multiple spraying was performed to control the thickness of the catalytic layer to be 35 microns. After completion, natural air drying was performed, and then the material was placed into an oven for drying at 300°C for 24 h to obtain the cathode material.

[0059] The anode chamber of the electrolytic cell was fed with 100 g of a 7 wt% NaCl aqueous solution, and the cathode chamber was fed with 60 g of an ionic liquid (X = (CF3SO2)2N (bistrifluoromethylsulfonylimide)) and 40 g of water. The cathode material substrate was carbon paper, and the main metal of the catalytic layer was silver, with a content of 97.5 wt%, and the doping metal palladium had a content of 2.5 wt%. The anode material was titanium coated with ruthenium dioxide. Both the anode and the cathode were rectangular electrodes, with an anode electrode area of 10 cm 2 , and a cathode electrode area of 10 cm 2 . The two electrodes were placed in parallel, with a cathode-anode distance of 4 mm. A cation exchange membrane Nafion 117 was used to separate the anode chamber and the cathode chamber. CO was introduced into the cathode liquid for 30 minutes before the reaction, and the current density was controlled at 500 A / m 2 . Electrolysis was performed at 45°C for 8 h. The yield of the anode product, chlorine, was determined by titration, and the current efficiency was 90%; the yield of the cathode product, CO, was determined by gas chromatography, and the current efficiency was 96%.

[0060] Comparative Example 1

[0061] The preparation method of the cathode material is as follows: first, a catalyst slurry is prepared; 999 mg of silver powder, 1 mg of rhodium powder, 10 mg of hydroxyethyl cellulose, and 50 mg of 5 wt% Nafion aqueous solution are added into 100 mg of isopropyl alcohol solvent according to the mass ratio, and then uniformly dispersed; the catalyst slurry is uniformly sprayed on the carbon paper through a watering can, and the thickness of the catalytic layer is controlled to be 30 microns through multiple spraying; after completion, it is naturally dried, and then placed in an oven for drying at 300°C for 24 hours to obtain the cathode material.

[0062] 100 g of 2%wt NaCl aqueous solution is added to the anode chamber of the electrolytic cell, 50 g of ionic liquid ([C12MIm]BF4) and 50 g of water are added to the cathode chamber, the cathode material substrate is carbon paper, the main metal of the catalytic layer is silver, and the content is 99.9 wt%, and the doping metal rhodium content is 0.1 wt%. The anode material is titanium coated with ruthenium dioxide. The anode and the cathode are both rectangular electrodes, the anode electrode area is 10 cm 2 , the cathode electrode area is 10 cm 2 , and the two electrodes are placed in parallel with a distance of 2 mm between the cathode and the anode. The anode chamber and the cathode chamber are separated by a cation exchange membrane Nafion 117. CO is introduced into the cathode liquid for 230 minutes before the reaction, the current density is controlled to be 1000 A / m 2 , and electrolysis is carried out at 40°C for 10 hours. The yield of the anode product chlorine is determined by titration, and the current efficiency is 96%; the cathode product CO is determined by gas chromatography, and the current efficiency is 17%, and the main byproduct is hydrogen.

[0063] Comparative Example 2

[0064] 100 g of 2%wt NaCl aqueous solution is added to the anode chamber of the electrolytic cell, 100 g of water is added to the cathode chamber, and the cathode material is silver foil. The anode material is titanium coated with ruthenium dioxide. The anode and the cathode are both rectangular electrodes, the anode electrode area is 10 cm 2 , the cathode electrode area is 10 cm 2 , and the two electrodes are placed in parallel with a distance of 2 mm between the cathode and the anode. The anode chamber and the cathode chamber are separated by a cation exchange membrane Nafion 117. CO is introduced into the cathode liquid for 230 minutes before the reaction, the current density is controlled to be 1000 A / m 2 , and electrolysis is carried out at 40°C for 10 hours. The yield of the anode product chlorine is determined by titration, and the current efficiency is 96%; the cathode product CO is determined by gas chromatography, and the current efficiency is 27%, and the main byproduct is hydrogen.

Claims

1. An electrochemical co-production process, comprising the following steps: chlorine is generated by oxidation of chloride ions at the anode, and CO is generated by electrochemical reduction of CO2 at the cathode; the anolyte is an aqueous NaCl solution, and the catholyte is a mixture of an ionic liquid and water, the ionic liquid having the following structure: wherein X = one of BF4, PF6, CF3SO3 (trifluoromethanesulfonic acid), (CF3SO2)2N (bistrifluoromethanesulfonylimide), (FSO2)2N (bisfluorosulfonylimide), 2. The electrochemical coproduction process of claim 1 wherein, the concentration of the aqueous NaCl solution is 2 wt% to 10 wt%, and the mass ratio of the ionic liquid to water in the catholyte is 1:1 to 3:

1.

3. The electrochemical coproduction process of claim 1 wherein, The cathode is a gas diffusion electrode, comprising a gas diffusion layer and a catalytic layer, wherein the gas diffusion layer is selected from one of carbon paper, carbon felt, and polytetrafluoroethylene porous film, and the catalytic layer comprises a host metal and a doped metal; the host metal is selected from one of silver, gold, and zinc, and the doped metal is selected from one of platinum group metals, and the mass ratio of the doped element to the host metal is 0.1% to 5%.

4. The electrochemical coproduction process of claim 3, wherein, The doped metal is selected from one of rhodium, palladium, and platinum.

5. The electrochemical coproduction process of claim 3 wherein, The preparation method of the gas diffusion electrode comprises the following steps: The host metal, the doped metal, an additive, and an aqueous Nafion solution are added to a solvent in a mass ratio, and after being uniformly dispersed, the catalyst slurry is uniformly sprayed on the gas diffusion layer by a watering can, and the thickness of the catalytic layer is controlled by multiple spraying, and after completion, the gas diffusion electrode is naturally air-dried and then placed in an oven for drying to obtain the cathode material.

6. The electrochemical coproduction process of claim 5, wherein, The solvent is selected from one or more of isopropyl alcohol, ethanol, and methanol, and the amount of the solvent is 10 wt% to 20 wt% of the host metal; the additive is selected from hydroxyethyl cellulose, hydroxymethyl cellulose, and hydroxypropyl methyl cellulose, and the amount of the additive is 1 wt% to 5 wt% of the host metal; the thickness of the catalytic layer is 30 microns to 50 microns; and the drying temperature is 200°C to 400°C, and the drying time is 12 hours to 36 hours.

7. The electrochemical coproduction process according to any of claims 1 to 6, wherein the cathode is a solid oxide fuel cell. The anode material is selected from one of titanium coated with ruthenium dioxide, titanium coated with iridium oxide, and graphite.

8. The electrochemical coproduction process according to any one of claims 1 to 6, wherein the cathode is a solid oxide fuel cell. The current density of the electrochemical reduction reaction is 500-3000 A / m 2 ; the reduction reaction temperature range is 40-60℃.

9. The electrochemical coproduction process according to any of claims 1 to 6, wherein the cathode is a solid oxide fuel cell. The current density of the electrochemical reduction reaction is 1000-2000 A / m 2 .

10. The electrochemical coproduction process according to any of claims 1 to 6, wherein The electrochemical co-production process is performed in an electrolytic cell, and the electrolytic cell is a diaphragm electrolytic cell, and the diaphragm is selected from a Nafion ion exchange membrane.

11. The electrochemical coproduction process according to any of claims 1 to 6, wherein The anode electrode area in the electrochemical cogeneration process is 1-10 cm 2 The cathode electrode area is 1-10 cm 2 Two electrodes are placed in parallel, and the distance between the cathode and the anode is 2-10 mm.

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