CN109487298B - Method for preparing ethylene glycol by electrocatalysis of formaldehyde - Google Patents
Method for preparing ethylene glycol by electrocatalysis of formaldehyde Download PDFInfo
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- CN109487298B CN109487298B CN201811493422.1A CN201811493422A CN109487298B CN 109487298 B CN109487298 B CN 109487298B CN 201811493422 A CN201811493422 A CN 201811493422A CN 109487298 B CN109487298 B CN 109487298B
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Abstract
A method for preparing ethylene glycol by electrocatalysis of formaldehyde belongs to the field of electrocatalysis, and comprises the following steps: 1) adding a cathode electrolyte and an anode electrolyte into a double-chamber electrolytic cell respectively and separating by using an ion exchange membrane, wherein the cathode electrolyte is an electrolyte solution containing formaldehyde, and the anode electrolyte is a pure electrolyte solution containing no formaldehyde; 2) inserting a Pt electrode serving as a counter electrode into the anolyte, placing a carbon material treated by a modifier serving as a working electrode into the catholyte, and taking a calomel electrode as a reference electrode; 3) before the reaction starts, introducing inert gas into the cathode, and simultaneously externally connecting a constant-temperature water tank to heat a double-chamber electrolytic cell so as to heat the anolyte and the catholyte to the reaction temperature; 4) adjusting the applied voltage to start reaction to obtain a product ethylene glycol; the carbon material treated by the modifier is used as a working electrode, so that the reaction can be continuously and stably carried out on the premise of higher Faraday efficiency, and the yield of the ethylene glycol can be improved.
Description
Technical Field
The invention belongs to the field of electrocatalysis, and particularly relates to a method for preparing ethylene glycol by electrocatalysis of formaldehyde.
Background
Ethylene glycol is an important monomer for synthesizing polyester compounds, is very important in the aspect of clothes and food industry, and has an increasing demand for ethylene glycol from 2010 to 2015 according to data statistics, but the serious problem is that more than 60% of domestic ethylene glycol depends on import, so that the problem how to improve the yield of domestic ethylene glycol is urgently needed to be solved at present. At present, the industrial synthesis method of ethylene glycol mainly comprises the steps of preparing ethylene glycol by oxidizing ethylene which is a cracking product of petroleum into ethylene oxide and then hydrating the ethylene oxide, and preparing the ethylene glycol by taking synthetic gas as a raw material through a dimethyl oxalate intermediate. It can be seen that the current industrial synthesis method of ethylene glycol mainly takes petroleum or coal as raw material, is carried out at higher temperature and pressure, and the reaction needs a plurality of intermediate steps, which is not in accordance with the concept of green chemistry.
The ethylene glycol is prepared by the formaldehyde electrocatalysis, and the ethylene glycol is prepared by one-step coupling of the formaldehyde which is a simple and easily available industrial raw material, so that the high selectivity and yield of the ethylene glycol can be realized, the production cost can be greatly reduced for the industrially existing ethylene oxide hydration method, the reaction condition is mild, and the product is single. US patent US4517062 discloses the use of graphite rods as working electrodes to investigate the effect of different catholyte on the reaction performance. In 1989, the article "electrochemical study of the reduction of formaldehyde in neutral concentrated aqueous solutions" specifically explored the effect of different cathode materials on the activity of formaldehyde to electrocatalytic ethylene glycol production, and proposed the unique activity of graphite electrodes for the reaction. US patent 4950368 discloses the effect of different anodic reactions and different cell membranes on the electrocatalytic formaldehyde to ethylene glycol reaction, and also achieves better faradaic efficiency at high currents.
In the existing reports about preparing ethylene glycol by electrocatalysis of formaldehyde, graphite is used as a working electrode, the influence of reaction conditions or reaction modes on reaction performance is researched, the described performance can only be maintained within 1h, and when the reaction time exceeds 1h, the faradaic efficiency of the ethylene glycol is rapidly reduced, and the electrode almost loses activity. For example, in 1990, "Electrochemical hydrogenation of formaldehyde to ethylene glycol", graphite was used as a working electrode to perform a reaction for preparing ethylene glycol by electrocatalysis of formaldehyde, and the faradaic efficiency of ethylene glycol was reduced from 100% to less than 50% within 2 hours. At present, no research report is reported on improvement of reaction activity and reaction stability by modifying a carbon electrode, and in order to realize industrial application of preparing ethylene glycol by formaldehyde electrocatalysis, a more efficient and stable electrode needs to be found, so that the reaction can be continuously and stably carried out on the premise of higher faradaic efficiency, and the yield of ethylene glycol is improved.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provide a method for preparing ethylene glycol by electrocatalysis of formaldehyde, which adopts a carbon material with a modified surface as a catalytic material, can greatly improve the reaction activity, and enables the reaction to maintain higher Faraday efficiency within 10 hours.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for preparing ethylene glycol by electrocatalysis of formaldehyde comprises the following steps:
1) adding a cathode electrolyte and an anode electrolyte into a double-chamber electrolytic cell respectively and separating by using an ion exchange membrane, wherein the cathode electrolyte is an electrolyte solution containing formaldehyde, and the anode electrolyte is a pure electrolyte solution containing no formaldehyde;
2) inserting a Pt electrode serving as a counter electrode into the anolyte, placing a carbon material treated by a modifier serving as a working electrode into the catholyte, and taking a calomel electrode as a reference electrode;
3) before the reaction starts, introducing inert gas into the cathode, and simultaneously externally connecting a constant-temperature water tank to heat a double-chamber electrolytic cell so as to heat the anolyte and the catholyte to the reaction temperature;
4) adjusting the applied voltage to start reaction to obtain the product ethylene glycol.
In the method for preparing the ethylene glycol by electrocatalysis of formaldehyde, the reaction temperature is 20-90 ℃, the applied voltage is-1.0-3.0V, the reaction time is 1-10 h, and the molar concentration of the formaldehyde in the cathode electrolyte is 1.6-13.3M; a double-chamber electrolytic cell which takes a proton exchange membrane or an anion exchange membrane as a diaphragm is adopted; the reaction can be carried out in a non-flowing or flowing manner.
The modifier is a polymer, perfluorothiol or perfluorosilane, has a hydrophobic group, can be well modified on a carbon substrate, and changes the surface property of the substrate; the carbon material comprises at least one of carbon paper, carbon cloth, graphite flake, foam carbon and carbon nano tube, and the carbon material has good conductivity and coatability and can be used as a good substrate for preparing an electrode.
In the present invention, when a polymer is used as a modifier, the carbon material treated with the polymer is prepared as follows:
1) sequentially carrying out ultrasonic treatment on a carbon material by using acetone, ethanol and water, and then drying in an oven;
2) soaking the carbon material dried in the step 1) in a polymer solution or a suspension, taking out the carbon material completely soaked in the polymer solution or the suspension, and placing the carbon material on a rotating disc to rotate to obtain the carbon material uniformly wrapped by the polymer solution or the suspension;
3) drying the carbon material rotated in the step 2) in a vacuum drying oven to obtain a dried carbon material uniformly coated by a polymer;
4) placing the dried carbon material uniformly wrapped by the polymer in the step 3) into a tubular furnace, and carrying out high-temperature roasting treatment by taking inert gas as carrier gas;
in the step 1), the mass percentage concentration of the polymer in the polymer solution or suspension is 5-80%; the polymer comprises at least one of polytetrafluoroethylene, polyvinyl chloride and polymethyl methacrylate.
In the invention, when the perfluoro-mercaptan or the perfluoro-silane is used as the modifier, the preparation method of the carbon material treated by the perfluoro-mercaptan or the perfluoro-silane comprises the following steps:
1) sequentially carrying out ultrasonic treatment on a carbon material by using acetone, ethanol and water, and drying in an oven;
2) dissolving perfluorothiol or perfluorosilane in ethanol or acetone to prepare a modifier-organic solvent solution, and soaking the carbon material dried in the step 1) in the modifier-organic solvent solution;
3) taking out the carbon material soaked in the step 2), cleaning the carbon material by using ethanol, and then placing the carbon material in a vacuum drying oven for drying to obtain a carbon material modified by perfluorothiol or perfluorosilane;
in the step 2), the mass percentage concentration of the perfluorinated mercaptan or the perfluorinated silane in the modifier-organic solvent solution is 0.1-10%; the perfluorinated mercaptan comprises at least one of heptadecafluoro-1-decylthiol, perfluorooctanethiol and perfluorododecanethiol; the perfluorosilane comprises at least one of tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, heptadecadecyltrimethoxysilane and heptadecadecyltriethoxysilane.
The modification method of the carbon material treated by the modifier can also adopt a pulling coating method, a dropping coating method, a dipping method, a spray pyrolysis method and an ion exchange method, and a uniform modification layer can be formed on the surface of the modified carbon material.
In the present invention, a typical reaction process for preparing ethylene glycol by electrocatalysis of formaldehyde is as follows:
and (3) cathode reaction: 2HCHO +2H++2e-→HOCH2CH2OH
And (3) anode reaction: h2O→1/2O2+2H++2e-
And (3) total reaction: 2HCHO + H2O→HOCH2CH2OH+1/2O2
Cathode competition side reaction: 2H++2e-→H2
The carbon material modified by the hydrophobic modifier has better hydrophobicity, and the carbon material modified by the hydrophobic modifier is used as a catalyst for preparing the ethylene glycol from the formaldehyde, so that the hydrogen evolution side reaction can be effectively inhibited, the activity and Faraday efficiency of preparing the ethylene glycol from the formaldehyde are improved, and meanwhile, the stability of the catalyst is also obviously improved.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1. the carbon material treated by the modifier has better activity in the reaction of preparing the ethylene glycol by formaldehyde electrocatalysis compared with the untreated carbon material.
2. The carbon material modified by the modifier is used in the reaction of preparing the ethylene glycol by electrocatalysis formaldehyde, and compared with the carbon material which is not modified by the modifier, the carbon material can effectively improve the reaction activity, so that the reaction can maintain higher Faraday efficiency within 10h, and the yield of the ethylene glycol is improved to a great extent.
Drawings
FIG. 1 is an SEM image of an unmodified carbon paper;
FIG. 2 is an SEM image of a carbon paper modified with a 60 wt% polytetrafluoroethylene suspension;
FIG. 3 is a graph of contact angle of an unmodified carbon paper surface;
FIG. 4 is a contact angle diagram of a carbon paper surface modified with a 60 wt% concentration polytetrafluoroethylene suspension;
FIG. 5 is a graph showing the change of the Faraday efficiencies of ethylene glycol in 1-5 h for unmodified carbon paper and carbon paper modified by polytetrafluoroethylene suspension with the concentration of 60 wt%;
FIG. 6 is a graph showing the change of the yield of ethylene glycol in 1-5 h for unmodified carbon paper and carbon paper modified by polytetrafluoroethylene suspension with the concentration of 60 wt%.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects of the present invention clearer and clearer, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.
The present invention modifies a carbon material with a polymer, perfluorothiol, or perfluorosilane to obtain a surface-modified carbon material, and the method for producing the surface-modified carbon material will be described below with reference to examples 1 and 2.
Example 1
In this embodiment, the preparation method of the carbon material modified by polytetrafluoroethylene suspension using carbon paper as a substrate is as follows:
1) taking carbon paper as a substrate material, sequentially carrying out ultrasonic treatment on acetone, ethanol and water for 10min respectively, and drying in an oven at 60 ℃;
2) soaking the dried and clean carbon paper obtained in the step 1) in a polytetrafluoroethylene suspension with the concentration of 60 wt%, taking out the carbon paper completely soaked by the polytetrafluoroethylene suspension, placing the carbon paper on a rotating disc, and rotating for 1min to obtain the carbon paper uniformly wrapped by the polytetrafluoroethylene suspension;
3) placing the carbon paper rotated in the step 2) in a vacuum drying oven, and drying at 50 ℃ for 0.5h to obtain dried carbon paper uniformly wrapped by polytetrafluoroethylene;
4) placing the carbon paper dried in the step 3) in a tube furnace, and carrying out high-temperature roasting treatment by taking argon as carrier gas: heating to 100-105 ℃ at a heating rate of 5-10 ℃/min, calcining at a constant temperature of 100-105 ℃ for 25-30 min, heating to 260-280 ℃ at a heating rate of 5-10 ℃/min, calcining at a constant temperature of 260-280 ℃ for 15-20 min, heating to 360-380 ℃ at a heating rate of 10-15 ℃/min, calcining at a constant temperature of 360-380 ℃ for 15-30 min, and controlling the temperature to decrease.
According to the embodiment, the loading capacity of the polytetrafluoroethylene on the surface of the carbon paper can be adjusted by changing the concentration of the impregnated polytetrafluoroethylene suspension, so that the hydrophilic and hydrophobic strength of the surface of the carbon paper can be adjusted.
Fig. 1 is an SEM image of an unmodified carbon paper, and it can be seen from fig. 1 that the carbon fibers have smooth surfaces and no fillers therebetween, and referring to fig. 3, the contact angle of the surface of the unmodified carbon paper is 80 °, and the surface is hydrophilic, which indicates that the unmodified carbon paper has better hydrophilicity; fig. 2 is an SEM image of the carbon paper modified by the suspension of 60 wt% ptfe, and it can be seen from fig. 2 that the surfaces of the carbon fibers are covered by ptfe, and a certain amount of ptfe is filled between the carbon fibers, and referring to fig. 4, the contact angle of the surface of the carbon paper modified by ptfe is 129 °, and the surface is approximately in a superhydrophobic state, which indicates that the modified carbon paper has better hydrophobicity.
Example 2
In the embodiment, the preparation method for modifying the carbon cloth by using the carbon cloth as a substrate and a small amount of tridecafluorooctyltrimethoxysilane as a modifier comprises the following steps:
1) sequentially carrying out ultrasonic treatment on the carbon cloth by using acetone, ethanol and water, and drying in an oven at 60 ℃;
2) dissolving a small amount of tridecafluorooctyltrimethoxysilane reagent in ethanol or acetone to prepare a modifier-organic solvent solution with the concentration of 5 wt%, and soaking the carbon cloth dried in the step 1) in the modifier-organic solvent solution for 1-2 h;
3) taking out the carbon cloth soaked in the step 2), cleaning the carbon cloth by using ethanol, and then drying the carbon cloth in a vacuum drying oven at 60 ℃ to obtain the carbon material modified by the tridecafluorooctyl trimethoxysilane.
Example 3
The carbon material modified by polytetrafluoroethylene and prepared in example 1 is used as a catalytic material in the reaction of preparing ethylene glycol by electrocatalysis of formaldehyde, and the specific steps are as follows:
1) adding catholyte and anolyte into a double-chamber electrolytic cell, wherein the volumes of the catholyte and the anolyte are respectively 30mL and are separated by a fluorinated Tosoh TSK (TM) proton exchange membrane, and the catholyte is separated by Na containing formaldehyde with certain concentration2SO4The solution composition is that the anolyte is Na without formaldehyde2SO4Solution, and Na in anolyte and catholyte2SO4The concentration of the solution is equal;
2) a Pt electrode is used as a counter electrode to be inserted into the anolyte, unmodified carbon paper and carbon paper modified by polytetrafluoroethylene suspension solution with the concentration of 60 wt% are respectively used as working electrodes to be placed in the catholyte, and a calomel electrode is used as a reference electrode to keep good sealing performance of both the anode and the cathode;
3) before the reaction, N is firstly introduced into the cathode2Half an hour, simultaneously, externally connecting a constant temperature water tank to heat a double-chamber electrolytic cell to keep the temperature at about 60 ℃, and heating the anolyte and the catholyte to the reaction temperature;
4) controlling the applied voltage to be-2.3V by a CHI 600D electrochemical workstation, and carrying out the reaction for 5h to obtain a product ethylene glycol, wherein the reaction of formaldehyde reduction coupling is carried out at the cathode of the electrolytic cell, and the reaction of water oxidation and oxygen generation is carried out at the corresponding anode.
After the reaction is finished, collecting samples, analyzing the concentration of ethylene glycol when different catalytic materials are used as working electrodes by adopting liquid chromatography, drawing a graph of the change of efficiency and yield with time by adopting an ethylene glycol method, and comparing the influence of unmodified carbon paper and carbon paper modified by a polytetrafluoroethylene suspension solution with a certain concentration on the reaction performance.
FIG. 5 is a graph showing the change of the Faraday efficiencies of ethylene glycol in 1-5 h for unmodified carbon paper and carbon paper modified by polytetrafluoroethylene suspension with the concentration of 60 wt%; a represents an unmodified carbon paper, and B represents a carbon paper modified by a 60 wt% polytetrafluoroethylene suspension. FIG. 6 is a graph showing the change of the yield of ethylene glycol in 1-5 h for unmodified carbon paper and carbon paper modified by polytetrafluoroethylene suspension with the concentration of 60 wt%; a represents an unmodified carbon paper, and B represents a carbon paper modified by a 60 wt% polytetrafluoroethylene suspension. The results of fig. 5 to 6 show that the faradaic efficiency of the unmodified carbon paper after 1h of reaction is only 45%, and the faradaic efficiency of the ethylene glycol is rapidly reduced after 1h, and the concentration of the ethylene glycol is not increased any more; the carbon electrode modified by polytetrafluoroethylene can realize the Faraday efficiency of nearly 100% within 1 hour of reaction, and can maintain better stability within 5 hours of reaction, the Faraday efficiency is kept at 75%, and the yield of ethylene glycol is 10% after 5 hours. The surface of the carbon paper which is not treated is hydrophilic, and the surface of the carbon paper which is modified by the polytetrafluoroethylene suspension is approximately in a super-hydrophobic state, so that the hydrophilicity and the hydrophobicity of the surface of the carbon electrode are key factors influencing the activity of the electrode in the reaction of preparing ethylene glycol by electrocatalysis.
Example 4
The carbon cloth modified with tridecafluorooctyltrimethoxysilane prepared in example 2 was used as a working electrode, and the reaction for preparing ethylene glycol by formaldehyde electrocatalysis was carried out at a reaction temperature of 60 ℃ and an applied voltage of-2.3V in the same manner as in example 3. After the reaction was carried out for 5 hours, the obtained product was analyzed and calculated. Compared with unmodified carbon cloth, the yield of the ethylene glycol is improved by 50 percent after the carbon cloth modified by the tridecafluorooctyltrimethoxysilane reacts for 5 hours.
Example 5
According to the mode of example 2, thirteen fluorine octyl trimethoxy silane is changed into heptadecafluoro-1-deca mercaptan, carbon cloth modified by the heptadecafluoro-1-deca mercaptan is prepared, the modified carbon cloth is used as a working electrode, and then the formaldehyde electrocatalytic ethylene glycol preparation reaction is carried out under the conditions that the reaction temperature is 60 ℃ and the applied voltage is-2.3V according to the mode of example 3. After the reaction is carried out for 5 hours, the obtained product is analyzed and calculated, the yield of the ethylene glycol is 16%, and the Faraday efficiency can be maintained at 57% and is far higher than the performance of the unmodified carbon cloth.
Example 6
Graphite flakes modified with polymethyl methacrylate were prepared by replacing carbon paper with graphite flakes and polytetrafluoroethylene with polymethyl methacrylate in the same manner as in example 1, and the modified graphite flakes were used as working electrodes, followed by electrocatalytic reaction of formaldehyde to ethylene glycol in the same manner as in example 3 at a reaction temperature of 60 ℃ and an applied voltage of-2.3V. After 5 hours of reaction time, the product was analyzed and the yield of ethylene glycol was increased by 60% relative to untreated graphite flake.
Example 7
The carbon electrode modified by the 60 wt% polytetrafluoroethylene suspension prepared in example 1 was used as a working electrode, and the influence of the working electrode on the reaction performance of preparing ethylene glycol from formaldehyde through electrocatalysis was investigated by changing the conditions of temperature, applied voltage, formaldehyde concentration and the like in the manner of example 3.
1) The reaction temperature is adjusted from 20 to 90 ℃, and the faradaic efficiency of the glycol is found to increase along with the increase of the reaction temperature, and the faradaic efficiency is 95 percent at the maximum when the temperature is 70 ℃. The method is characterized in that the electrocatalysis reaction for preparing ethylene glycol from formaldehyde is influenced by temperature, the number of free formaldehyde molecules is increased along with the increase of the temperature in a certain temperature range, so that the reaction for preparing ethylene glycol from formaldehyde by coupling is easier to occur, but the formaldehyde is volatilized seriously along with the continuous increase of the temperature, so that the reaction performance is influenced.
2) The applied voltage is adjusted from-1.0 to-3.0V, and the reaction current is gradually increased along with the increase of the applied voltage, and can reach 179mA when the applied voltage is-2.3V, and the high faradaic efficiency of 95 percent is maintained under high current.
3) The concentration of formaldehyde is changed from 1.6-13.3M by adjusting the amount of the formaldehyde solution added into the catholyte, and the results show that the concentration of non-electrolyte in the catholyte is gradually increased along with the increase of the concentration of the formaldehyde, so that the current is gradually reduced, but free formaldehyde molecules are increased along with the increase of the concentration of the formaldehyde, the faradaic efficiency of ethylene glycol is gradually increased, the current is 179mA when the concentration of the formaldehyde is 6.7M, the faradaic efficiency reaches 95%, and the yield of the ethylene glycol reaches 2.4% within 1 hour.
Example 8
After 10 hours of reaction using carbon paper modified with a 60 wt% polytetrafluoroethylene suspension as a working electrode in the same manner as in example 3 and under the conditions of temperature, voltage, formaldehyde concentration and the like preferred in example 7, the concentration of ethylene glycol in the sample was 600mM and the Faraday efficiency of ethylene glycol was about 60% after 10 hours of reaction, and the yield of ethylene glycol was 17%, which was the most preferable reaction performance reported so far.
Comparative example 1
The untreated carbon paper was used as a working electrode, and the formaldehyde electrocatalytic ethylene glycol preparation reaction was carried out at a reaction temperature of 60 ℃ and an applied voltage of-2.3V in the manner of example 3 for 5 hours, and the obtained product was analyzed and calculated. The Faraday efficiency of the obtained glycol in 1h is 45%, the Faraday efficiency in 2h is reduced to 19%, after 5h of reaction, the Faraday efficiency of the glycol is only 9%, and the yield of the glycol is 1%.
Comparative example 2
The untreated graphite sheet was used as a working electrode, and the reaction for producing ethylene glycol by formaldehyde electrocatalysis was carried out at a reaction temperature of 60 ℃ and an applied voltage of-2.3V in the same manner as in example 3, and the obtained product was analyzed and calculated. The faradaic efficiency of the ethylene glycol obtained in 1h was 50% and decreased to 29% in 2 h.
Claims (8)
1. A method for preparing ethylene glycol by electrocatalysis of formaldehyde is characterized in that: the method comprises the following steps:
1) adding a cathode electrolyte and an anode electrolyte into a double-chamber electrolytic cell respectively and separating by using an ion exchange membrane, wherein the cathode electrolyte is an electrolyte solution containing formaldehyde, and the anode electrolyte is a pure electrolyte solution containing no formaldehyde;
2) inserting a Pt electrode serving as a counter electrode into the anolyte, placing a carbon material treated by a modifier serving as a working electrode into the catholyte, and taking a calomel electrode as a reference electrode;
3) before the reaction starts, introducing inert gas into the catholyte, and simultaneously externally connecting a constant-temperature water tank to heat a double-chamber electrolytic cell so as to heat the anolyte and the catholyte to the reaction temperature;
4) adjusting the applied voltage to start reaction to obtain a product ethylene glycol;
the modifier is polymer, heptadecafluoro-1-decylthiol, perfluorooctanethiol, perfluorododecanethiol, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, heptadecafluorodecyltrimethoxysilane or heptadecafluorodecyltriethoxysilane; the carbon material comprises at least one of carbon paper, carbon cloth, graphite flakes, carbon foam and carbon nanotubes; the polymer comprises at least one of polytetrafluoroethylene, polyvinyl chloride and polymethyl methacrylate.
2. The method for preparing ethylene glycol by electrocatalysis of formaldehyde as claimed in claim 1, wherein: the reaction temperature is 20-90 ℃, the applied voltage is-1.0 to-3.0V, and the molar concentration of formaldehyde in the cathode electrolyte is 1.6-13.3M.
3. The method for preparing ethylene glycol by electrocatalysis of formaldehyde as claimed in claim 1, wherein: the double-chamber electrolytic cell adopts a double-chamber electrolytic cell which takes a proton exchange membrane or an anion exchange membrane as a diaphragm; the reaction is carried out in a non-flowing or flowing manner.
4. The method for preparing ethylene glycol by electrocatalysis of formaldehyde as claimed in claim 1, wherein: the modification method of the carbon material treated with the modifier includes a lift coating method, a drop coating method, a dipping method, a spray pyrolysis method, an ion exchange method.
5. The method for preparing ethylene glycol by electrocatalysis of formaldehyde as claimed in claim 1, wherein: the method for preparing a polymer-treated carbon material comprises the steps of:
1) sequentially carrying out ultrasonic treatment on a carbon material by using acetone, ethanol and water, and then drying in an oven;
2) soaking the carbon material dried in the step 1) in a polymer solution or a suspension, taking out the carbon material completely soaked in the polymer solution or the suspension, and placing the carbon material on a rotating disc to rotate to obtain the carbon material uniformly wrapped by the polymer solution or the suspension;
3) drying the carbon material rotated in the step 2) in a vacuum drying oven to obtain a dried carbon material uniformly coated by a polymer;
4) and (3) placing the dried carbon material uniformly wrapped by the polymer in the step 3) into a tubular furnace, and carrying out high-temperature roasting treatment by taking inert gas as carrier gas.
6. The method for preparing ethylene glycol by electrocatalysis of formaldehyde as claimed in claim 1, wherein: a method for producing a carbon material treated with heptadecafluoro-1-decylthiol, perfluorooctanethiol, perfluorododecylmercaptan, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, heptadecafluorodecyltrimethoxysilane or heptadecafluorodecyltriethoxysilane, comprises the steps of:
1) sequentially carrying out ultrasonic treatment on a carbon material by using acetone, ethanol and water, and drying in an oven;
2) dissolving heptadecafluoro-1-decylthiol, perfluorooctanethiol, perfluorododecanethiol, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, heptadecafluorodecyltrimethoxysilane or heptadecafluorodecyltriethoxysilane in ethanol or acetone to prepare a modifier-organic solvent solution, and soaking the carbon material dried in the step 1) in the modifier-organic solvent solution;
3) taking out the carbon material soaked in the step 2), washing the carbon material with ethanol, and then placing the carbon material in a vacuum drying oven for drying to obtain the carbon material modified by heptadecafluoro-1-decylthiol, perfluorooctanethiol, perfluorododecanethiol, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, heptadecafluorodecyltrimethoxysilane or heptadecafluorodecyltriethoxysilane.
7. The method for preparing ethylene glycol by electrocatalysis of formaldehyde as claimed in claim 5, wherein: the mass percentage concentration of the polymer in the polymer solution or suspension is 5-80%.
8. The method for preparing ethylene glycol by electrocatalysis of formaldehyde as claimed in claim 6, wherein: the mass percentage concentration of heptadecafluoro-1-decylthiol, perfluorooctanethiol, perfluorododecanethiol, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, heptadecafluorodecyltrimethoxysilane or heptadecafluorodecyltriethoxysilane in the modifier-organic solvent solution is 0.1-10%.
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