A method for electrocatalytic reduction of carbon dioxide and membrane-coupled production of ethanol

Abstract

The application discloses a method for electrocatalytically reducing carbon dioxide and producing ethanol by membrane coupling, and belongs to the technical field of electrochemical reduction and membrane separation coupling. After a perm-ethanol membrane is arranged in an electrolytic cell, the selectivity of the perm-ethanol membrane is utilized to separate liquid-phase product ethanol and remove the product, so that the chemical balance is pushed to proceed in a positive direction, the electrochemical reaction is promoted to occur, the selectivity and overall conversion efficiency of the reaction are improved, and high-purity ethanol is obtained. The structure of the electro-reduction ethanol production device is scientific and reasonable, safe and convenient to use, low in cost, and short in processing flow, and the selectivity of ethanol in the reaction process and the collection process is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical reduction and membrane separation coupling, and particularly relates to a method for electrocatalytic reduction of carbon dioxide and membrane coupling production of ethanol. BACKGROUND

[0002] Carbon dioxide electro-reduction technology is a technology that uses electrical energy to reduce carbon dioxide into high-value chemical products, which can effectively realize the resource utilization of greenhouse gases and the storage of renewable energy, and has potential economic and social value.

[0003] The reduction products of CO2 are diverse, such as CO, ethylene, methanol, ethanol, formic acid, etc. Among them, the value of C2+ products such as ethanol in terms of energy density and industrial application is significantly higher than that of C1 products. For example, ethanol is often used as a fuel mixture ingredient, a key precursor for the synthesis of various compounds, and the medical and food industries. However, the generation of C2+ products requires a high-energy carbon-carbon coupling process, and CO2 reduction produces a variety of intermediates that each lead to different final products, so the efficiency of catalyzing CO2 reduction to C2+ products is low and the selectivity of a single product is low.

[0004] In recent years, electrochemical reduction of CO2 has attracted the attention of researchers as a more effective and sustainable reduction scheme. And some progress has been made on how to efficiently electrocatalytically reduce CO2 to C2+ compounds. Specific C2+ products can be obtained with high selectivity, but their high selectivity is usually only achieved at low activity, and the C2+ yield is still much lower than that of traditional thermal catalytic CO2 hydrogenation. Therefore, developing efficient catalysts and exploring new electrocatalytic processes to achieve high current density, high C2+ selectivity and high stability of the reduction process is still the key to promoting the practical application of electrocatalytic reduction of CO2.

[0005] In the process of electro-reduction of carbon dioxide to ethanol, a catalyst (such as a single-atom catalyst or a copper-silver composite catalyst) is usually used to reduce carbon dioxide to ethanol. However, during the reaction, various by-products such as formic acid and ethylene may be generated, which will affect the selectivity and efficiency of the reaction. Based on the principle of chemical reaction, if the main product can be effectively separated and removed during the reaction, it will help to move the chemical equilibrium towards the generation of products, i.e. to promote the forward reaction, thereby helping to obtain more products. Therefore, removing the ethanol produced during the reduction process is a feasible way to improve the selectivity of the reaction.

[0006] There are many methods for product separation, and membrane separation technology is one of the high-precision separation technologies in the 21st century, which has the advantages of low energy consumption and simple operation. Membrane separation technology is based on the selective permeability of membrane materials to specific components to separate different components. The ethanol-permeable membrane is one of the membrane materials with specific permeability, which can selectively permeate ethanol molecules and block the passage of other impurities or reaction intermediates, thereby improving the selectivity and efficiency of the reaction and helping to maintain the stability and continuity of the reaction system. In the process of electro-reducing CO2 to produce ethanol, if the ethanol produced can be successfully separated and removed by using the ethanol-permeable membrane, the concentration of the reactants can be kept stable, thereby improving the reaction efficiency and yield.

[0007] The existing technology mainly focuses on finding high-performance catalysts for electro-catalytic reduction of CO2 to produce ethanol, and there is no report on the process design of CO2 electro-reduction to produce methanol coupled with membrane separation technology, and the corresponding technology has a lot of exploration space. SUMMARY

[0008] In view of the above problems, the present application aims to provide a device and method for membrane separation coupled with electro-catalytic reduction of CO2 to produce ethanol, which separates and collects the ethanol produced by electrolysis in time by setting an ethanol-permeable membrane in the cathode chamber, promotes the reduction reaction, and improves the selectivity and overall conversion efficiency of the reaction.

[0009] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: a method for electro-catalytic reduction of carbon dioxide and membrane coupling production of ethanol, comprising the following steps:

[0010] 1) adding an electrolyte into an electrolytic cell, and forming an electrolytic cell with a working electrode loaded with an electro-catalyst, a reference electrode and a counter electrode;

[0011] 2) setting an ethanol-permeable membrane in the cathode chamber of the electrolytic cell;

[0012] 3) performing constant potential electrolysis on the electrolytic cell under the condition of continuously introducing CO2, and collecting the generated ethanol after passing through the ethanol-permeable membrane.

[0013] Further, the electrolytic cell is selected from one of an H-type electrolytic cell, a flow-type electrolytic cell or a membrane electrode electrolytic cell.

[0014] Further, the rate of continuously introducing CO2 is CO2 volume: electrolytic solution volume = 1:1-10.

[0015] Further, the electro-catalyst can catalyze the reduction of CO2 to generate ethanol under the action of constant potential, and the electro-catalyst is one of a metal catalyst, an enzyme catalyst, a molecular catalyst and a composite catalyst.

[0016] As preferred, the metal catalyst is one of a copper-based catalyst, a silver-based catalyst, a tin-based catalyst, a nickel-based catalyst, and a zinc-based catalyst.

[0017] Further, the alcohol-permeable membrane is one of an organic membrane, an inorganic membrane, and an organic / inorganic composite membrane material.

[0018] As preferred, the organic alcohol-permeable membrane material is one of a PDMS (polydimethylsiloxane) membrane, a PVTES (polyvinyltriethoxysilane) membrane, a COF (covalent organic framework) membrane, and a mixed matrix membrane.

[0019] As preferred, the inorganic membrane is one of a porous membrane, and is one of a zeolite molecular sieve membrane, a silicon membrane, a MOF (metal-organic framework) membrane, a carbon molecular sieve membrane, and a ceramic membrane.

[0020] Further, the alcohol collection method is one of vacuum condensation collection and purge gas purge collection.

[0021] The application also discloses a device for preparing ethanol by coupling membrane separation with electrocatalytic reduction of CO2, which comprises an electrolytic cell, wherein a working electrode, a reference electrode, a counter electrode, and an alcohol-permeable membrane are arranged in the electrolytic cell, and the working electrode is loaded with an electrocatalyst for catalyzing the electrolysis of carbon dioxide to generate ethanol; the electrolytic cell is divided into a cathode chamber and an anode chamber by a proton exchange membrane, the working electrode, the reference electrode, and the alcohol-permeable membrane are arranged in the cathode chamber, and the counter electrode is arranged in the anode chamber; the retentate side of the alcohol-permeable membrane is connected with an electrolyte, and the permeate side of the alcohol-permeable membrane is connected with an ethanol collection device, and ethanol is collected by vacuum condensation collection or purge gas purge collection.

[0022] The application has the following beneficial effects:

[0023] 1. The application couples the technology of preparing ethanol by electrocatalytic reduction of CO2 with the technology of membrane separation, separates the liquid-phase product ethanol by using the selectivity of the alcohol-permeable membrane, and removes the ethanol by vacuum condensation or purge gas purge, so that the removal of the liquid-phase product can promote the chemical equilibrium to proceed in a positive direction, promote the electrochemical reaction to occur, improve the selectivity and overall conversion efficiency of the reaction, and help to obtain high-purity ethanol.

[0024] 2. The application couples the technology of electrocatalytic reduction of CO2 with the technology of membrane separation to prepare ethanol, which not only can effectively reduce the emission of carbon dioxide, but also can convert this greenhouse gas into a useful resource, and is expected to become one of important means for realizing the carbon neutralization target, and has a wide application prospect in the fields of environmental protection and energy conversion. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a structural schematic diagram of the device for preparing ethanol by coupling membrane separation with electrocatalytic reduction of CO2 provided in Example 1;

[0026] Wherein, 1-electrochemical workstation, 2-H-type electrolytic cell, 3-counter electrode, 4-working electrode, 5-reference electrode, 6-methanol permeable membrane, 7-ethanol collection tank, 8-CO2 gas source;

[0027] 21-cathode chamber, 22-anode chamber. DETAILED DESCRIPTION

[0028] In order to make the ordinary skilled in the art better understand the technical solutions of the present application, the technical solutions of the present application are further described below in combination with the drawings and examples. Example 1

[0029] The working electrode 4 (loaded with copper-based catalyst), the reference electrode 5 (saturated calomel electrode) and the counter electrode 3 (platinum electrode) are assembled together into an H-type electrolytic cell (see Figure 1 ), the cathode chamber 21 and the anode chamber 22 of the H-type electrolytic cell 2 are separated by a proton exchange membrane, and the cathode chamber 21 and the anode chamber 22 are filled with CO2-saturated KHCO3 electrolyte (0.1 M), and the methanol permeable membrane 6 is installed in the cathode chamber.

[0030] The working electrode 4 is the core of the reaction and is placed in the cathode chamber 21. It is used to apply a reduction potential to make CO2 undergo a reduction reaction on the electrode surface to generate products such as ethanol.

[0031] The reference electrode 5 is used to measure and control the electrode potential to ensure that the reaction is carried out at a set potential. It is usually placed in the same electrolyte as the working electrode 4 and is isolated from the working electrode 4 by a proton exchange membrane.

[0032] The counter electrode 3 is used to balance the current in the circuit and is usually placed in the anode chamber 22. It consumes electrons through an oxidation reaction (such as oxygen evolution) to maintain the current loop of the entire electrolytic cell.

[0033] The methanol permeable membrane 6 used is a silicalite-1 molecular sieve membrane, which is an outer membrane, and the outside is in contact with the electrolyte, and the inside is the permeation side; the outer diameter of the membrane tube is 8 mm, the inner diameter is 4 mm, and the length is 30 cm.

[0034] CO2 is continuously introduced into the electrolytic cell at a rate of 30 mL min -1 , and constant potential electrolysis is carried out at a potential of -0.5 V to obtain liquid and gas phase products. The gas phase product enters the chromatograph for analysis, and the ethanol in the liquid phase product permeates the methanol permeable membrane 6 and is collected by vacuum condensation. The vacuum pump is turned on, and when the vacuum degree is reduced to below 200 Pa, the ethanol collection tank 7 is used to collect ethanol.

[0035] The H-type electrolytic cell is connected to the electrochemical workstation 1, and CO2 is continuously introduced into the electrolytic cell at a rate of 30 mL min -1The constant potential electrolysis was carried out at different potentials with the continuous input of CO2, and the gaseous and liquid phase products were obtained, the liquid phase product ethanol was collected, and the Faraday efficiency of ethanol was calculated.

[0036] When the constant potential electrolysis was carried out at a potential of-0.5 V, the Faraday efficiency of ethanol was 30.73%, the current density of ethanol was 19.24 mA·cm -2 The flux of the ethanol permeable membrane was 1.17 kg·m -2 ·h -1 The purity of the collected ethanol reached 90.7%; when the constant potential electrolysis was carried out at a potential of-0.8 V, the Faraday efficiency of ethanol increased to 44.53%, the current density of ethanol was 31.64 mA·cm -2 The flux of the ethanol permeable membrane was 1.5 kg·m -2 ·h -1 After 60 min of operation, the purity of the collected ethanol reached 88.1%.

[0037] Comparative Example 1

[0038] The difference between the example 1 and the comparative example 1 is that the ethanol permeable membrane is not set in the cathode chamber. When the constant potential electrolysis is carried out at a potential of-0.5 V and-0.8 V, the Faraday efficiency of ethanol is only 19.58% and 42.14% respectively, and the purity of the collected ethanol is 84.5%. Example 2

[0039] The difference between the example 1 and the example 2 is that the ethanol collection method used in the example 2 is changed to nitrogen blowing gas blowing collection. When the constant potential electrolysis is carried out at a potential of-0.8 V, the Faraday efficiency of ethanol increases to 37.69%, the current density of ethanol is 25 mA·cm -2 The flux of the ethanol permeable membrane is 1.26 kg·m -2 ·h -1 Compared with the scheme of preparing ethanol by electrocatalytic reduction of CO2 without coupling membrane separation technology, the Faraday efficiency of ethanol can be increased by more than 5% by using the method disclosed in the example. Example 3

[0040] The catalyst-loaded gas diffusion electrode (loaded with copper-based catalyst), reference electrode (saturated calomel) and counter electrode (platinum electrode) were assembled into a flow type electrolytic cell, the cathode chamber and anode chamber of the flow type electrolytic cell were separated by a proton exchange membrane, the cathode chamber and anode chamber were respectively filled with continuously flowing CO2 saturated electrolyte (1 M KOH), and CO2 gas was introduced from the channel on the same side as the gas diffusion layer; the experiment was carried out at normal temperature and pressure, and the flow rate was 30 mLmin -1CO2 is continuously introduced into a flow electrolyzer at a rate of -0.8V, and electrolysis is performed at a constant potential. The carbon dioxide continuously passes through a porous hydrophobic gas diffusion layer and reacts with the catalyst and electrolyte at the gas-liquid-solid three-phase interface, yielding liquid and gaseous products. The gaseous product is analyzed by a gas chromatograph via a gas tube. Ethanol in the liquid product is collected by vacuum condensation after passing through an alcohol permeabilization membrane. The vacuum pump is turned on, and ethanol collection begins once the vacuum level drops below 200 Pa.

[0041] During testing, the prepared flow electrolytic cell was connected to an electrochemical workstation, and constant potential electrolysis was performed at a potential of -0.8V to obtain the liquid product ethanol. The Faraday efficiency of ethanol was then calculated.

[0042] Because the carbon dioxide mass transfer efficiency on the gas diffusion electrode is higher than that on a conventional electrode, and because the flow-type electrolytic cell shortens the distance between the cathode and anode chambers, effectively reducing the electrolyte impedance and the potential of the entire reaction system, the Faraday efficiency of ethanol reaches 70.38%, and the current density of ethanol reaches 400 mA·cm⁻¹. -2 The flux of the percolate membrane is 2.2 kg·m. -2 ·h -1 Compared to a flow electrolyzer without membrane separation technology, the Faraday efficiency of ethanol can be increased by more than 20% when using a flow electrolyzer with membrane separation technology disclosed in this embodiment for electrocatalytic CO2 reduction.

Claims

1. A method for electrocatalytic reduction of carbon dioxide coupled with membrane coupling to produce ethanol, characterized in that, Includes the following steps: 1) Add the electrolyte to the electrolytic cell to form an electrolytic cell with the working electrode, reference electrode and counter electrode loaded with electrocatalyst; 2) Install an alcohol-permeable membrane in the cathode chamber of the electrolytic cell; 3) The electrolytic cell performs constant potential electrolysis under the condition of continuous CO2 introduction, and the generated ethanol is collected after being separated by a percolation membrane.

2. The method for electrocatalytic reduction of carbon dioxide and membrane coupling to produce ethanol as described in claim 1, characterized in that, The electrolytic cell is selected from one of the following: H-type electrolytic cell, flow electrolytic cell, or membrane electrode electrolytic cell.

3. The method for electrocatalytic reduction of carbon dioxide and membrane coupling to produce ethanol as described in claim 1, characterized in that, The rate at which CO2 is continuously introduced is given by the ratio of CO2 volume to solution volume in the electrolytic cell: 1:1-10.

4. The method for electrocatalytic reduction of carbon dioxide and membrane coupling to produce ethanol as described in claim 1, characterized in that, The electrocatalyst can catalyze the reduction of CO2 to ethanol under constant potential. The electrocatalyst is one of the following: metal catalyst, enzyme catalyst, molecular catalyst, and composite catalyst.

5. The method for electrocatalytic reduction of carbon dioxide and membrane coupling to produce ethanol as described in claim 4, characterized in that, The metal catalyst is one of copper-based catalysts, silver-based catalysts, tin-based catalysts, nickel-based catalysts, and zinc-based catalysts.

6. The method for electrocatalytic reduction of carbon dioxide and membrane coupling to produce ethanol as described in claim 1, characterized in that, The alcohol-permeable membrane is one of the following: organic membrane, inorganic membrane, and organic / inorganic composite membrane material.

7. The method for electrocatalytic reduction of carbon dioxide and membrane coupling to produce ethanol as described in claim 6, characterized in that, The organic permeable membrane material is selected from one of PDMS membrane, PVTES membrane, COF membrane and mixed matrix membrane.

8. The method for electrocatalytic reduction of carbon dioxide and membrane coupling to produce ethanol as described in claim 6, characterized in that, Inorganic membranes are one of the following: zeolite molecular sieve membranes, silicon membranes, MOF membranes, carbon molecular sieve membranes, and ceramic membranes.

9. The method for electrocatalytic reduction of carbon dioxide and membrane coupling to produce ethanol as described in claim 1, characterized in that, The method for collecting ethanol is selected from either vacuum condensation collection or purge gas purging collection.

10. An apparatus for the electrocatalytic reduction of carbon dioxide coupled with membrane coupling to produce ethanol, characterized in that, The device includes an electrolytic cell containing a working electrode, a reference electrode, a counter electrode, and a permeabilized membrane. The working electrode is loaded with an electrocatalyst for the electrolysis of carbon dioxide to produce ethanol. The electrolytic cell is divided into a cathode chamber and an anode chamber by a proton exchange membrane. The working electrode, reference electrode, and permeabilized membrane are placed in the cathode chamber, and the counter electrode is placed in the anode chamber. The filtration side of the permeabilized membrane is connected to the electrolyte, and the permeation side of the permeabilized membrane is connected to an ethanol collection device. Ethanol is collected by vacuum condensation or by purge gas.

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