Method for producing ethanol through electrocatalytic reduction of carbon dioxide and membrane coupling

Abstract

The invention discloses a method for producing ethanol through electrocatalytic reduction of carbon dioxide and membrane coupling, and belongs to the technical field of electrochemical reduction and membrane separation coupling. After the alcohol-permeable membrane is arranged in the electrolytic tank, the selectivity of the alcohol-permeable membrane is utilized to separate the liquid-phase product ethanol and remove the product, so that the chemical equilibrium can be promoted to proceed forwards, the electrochemical reaction is promoted, the selectivity and the overall conversion efficiency of the reaction are improved, and the high-purity ethanol can be obtained; the device for preparing ethanol through electroreduction is scientific and reasonable in structure, safe and convenient to use, low in cost and short in treatment flow, and the selectivity of ethanol in the reaction process and the collection process is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical reduction and membrane separation coupling, and in particular relates to a method for producing ethanol by electrocatalytic reduction of carbon dioxide and membrane coupling. Background Art

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

[0003] CO 2 The reduction products are diverse, such as CO, ethylene, methanol, ethanol, formic acid, etc. Among them, C2+ products such as ethanol are significantly more valuable than C1 products in terms of energy density and industrial application. For example, ethanol is often used as a fuel blending component, a key precursor for the synthesis of various compounds, and the medical and food industries. However, the generation of C2+ products requires a carbon-carbon coupling process with a high reaction energy barrier, and CO 2 During the reduction, a variety of intermediates are generated, each leading to a different final product, thus catalyzing CO 2 The efficiency of reduction to C2+ products is low and the selectivity of a single product is low.

[0004] In recent years, CO 2 Electrochemical reduction of CO has attracted the attention of researchers as a potentially more effective and sustainable reduction method. 2 Some progress has been made in the preparation of C2+ compounds, and specific C2+ products can be obtained with high selectivity. However, the high selectivity can usually only be achieved at low activity, and the C2+ yield is still much lower than that of traditional thermal catalytic CO 2 Therefore, developing efficient catalysts and exploring new electrocatalytic processes to achieve high current density, high C2+ selectivity and high stability in the reduction process is still the key to promoting electrocatalytic reduction of CO 2 The key to practical application.

[0005] In the process of carbon dioxide electroreduction 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, a variety of by-products may be generated during the reaction, such as formic acid, ethylene, etc., which will affect the selectivity and efficiency of the reaction. Based on the principles of chemical reactions, if the main products can be effectively separated and removed during the reaction, the chemical equilibrium will be pushed toward the direction of product generation, that is, the reaction will be pushed forward, thereby helping to obtain more products. Therefore, removing the ethanol produced during the reduction process is a feasible idea to improve the selectivity of the reaction.

[0006] There are many methods for product separation. Membrane separation technology is one of the high-precision separation technologies in the 21st century, with advantages such as low energy consumption and simple operation. Membrane separation technology is based on the preferential permeability of membrane materials to specific components to achieve the separation of different components. Alcohol permeable membrane is one of the membrane materials with specific permeability, which can selectively pass 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. 2 In the process of producing ethanol, if the produced ethanol can be successfully separated and removed continuously using an alcohol permeable membrane, the concentration of the reactants will be kept stable, thereby improving the reaction efficiency and yield.

[0007] In the prior art, electrocatalytic CO 2 The research on reduction to ethanol is mainly focused on finding high-performance catalysts. 2 The process design of producing methanol by electro-reduction has not been reported yet, and there is still a lot of room for exploration of the corresponding technology. Summary of the invention

[0008] In view of the above problems, the present invention aims to provide a membrane separation coupled electrocatalytic CO 2 The invention discloses a device and method for producing ethanol by reduction, which timely separates and collects the ethanol produced by electrolysis by setting an alcohol permeable membrane in the cathode chamber, promotes the reduction reaction, and improves the selectivity of the reaction and the overall conversion efficiency.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is as follows: a method for producing ethanol by electrocatalytic reduction of carbon dioxide and membrane coupling, comprising the following steps: 1) Adding electrolyte into the electrolytic cell to form an electrolytic cell with a working electrode loaded with an electrocatalyst, a reference electrode and a counter electrode; 2) Arranging an alcohol permeable membrane in the cathode chamber of the electrolytic cell; 3) The electrolytic cell is continuously fed with CO 2 Constant potential electrolysis is carried out under conditions of , and the generated ethanol is collected after passing through the alcohol permeable membrane.

[0010] Furthermore, the electrolytic cell is selected from one of an H-type electrolytic cell, a flow-type electrolytic cell or a membrane electrode electrolytic cell.

[0011] Furthermore, continuous CO 2 The rate of CO 2 Volume: volume of solution in electrolytic cell = 1:1-10.

[0012] Furthermore, the electrocatalyst can catalyze CO under constant potential. 2 Reduction generates ethanol, and the electrocatalyst is one of a metal catalyst, an enzyme catalyst, a molecular catalyst, and a composite catalyst.

[0013] Preferably, 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.

[0014] Furthermore, the alcohol permeable membrane is one of an organic membrane, an inorganic membrane and an organic / inorganic composite membrane material.

[0015] Preferably, the organic alcohol permeable membrane material is selected from one of PDMS (polydimethylsiloxane) membrane, PVTES (polyvinyltriethoxysilane) membrane, COF (covalent organic framework) membrane and mixed matrix membrane.

[0016] Preferably, the inorganic membrane is a porous membrane selected from a zeolite molecular sieve membrane, a silicon membrane, a MOF (metal organic framework) membrane, a carbon molecular sieve membrane and a ceramic membrane.

[0017] Furthermore, the method of collecting ethanol is selected from one of vacuum condensation collection and purge gas purge collection.

[0018] The present application also discloses a membrane separation coupled electrocatalytic CO 2 The device for producing ethanol by reduction 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 an electrocatalyst for catalyzing the electrolysis of carbon dioxide to produce ethanol is loaded on the working electrode; 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 interception side of the alcohol permeable membrane is connected to an electrolyte, and the permeation side of the alcohol permeable membrane is connected to an ethanol collection device, and ethanol is collected by vacuum condensation collection or purge collection with purge gas.

[0019] The beneficial effects of the present invention are: 1. This application will electrocatalyze CO 2 The reduction-to-ethanol technology is coupled with the membrane separation technology. The selectivity of the alcohol-permeable membrane is used to separate the liquid product ethanol, and the ethanol is removed by vacuum condensation or purge gas purge. The removal of the liquid product can promote the chemical equilibrium in the positive direction, promote the occurrence of electrochemical reactions, improve the selectivity of the reaction and the overall conversion efficiency, and help to obtain high-purity ethanol. 2. This application couples electrocatalytic reduction of CO 2 The production of ethanol using membrane separation technology can not only effectively reduce carbon dioxide emissions, but also convert this greenhouse gas into useful resources. It is expected to become one of the important means to achieve the goal of carbon neutrality and has broad application prospects in the fields of environmental protection and energy conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The membrane separation coupled electrocatalytic CO provided in Example 1 2A schematic diagram of the structure of a device for producing ethanol by reduction; Among them, 1-electrochemical workstation, 2-H-type electrolytic cell, 3-counter electrode, 4-working electrode, 5-reference electrode, 6-alcohol permeable membrane, 7-ethanol collection tank, 8-CO 2 Gas source; 21- cathode chamber, 22- anode chamber. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments. Example 1

[0022] The working electrode 4 (loaded with a copper-based catalyst), the reference electrode 5 (saturated calomel) and the counter electrode 3 (platinum electrode) are assembled together to form 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 CO 2 Saturated KHCO 3 The electrolyte (0.1 M) and the alcohol permeable membrane 6 are installed in the cathode chamber.

[0023] 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 CO 2 A reduction reaction occurs on the electrode surface to produce products such as ethanol.

[0024] The reference electrode 5 is used to measure and control the electrode potential to ensure that the reaction proceeds at the set potential. It is usually placed in the same electrolyte as the working electrode 4 and isolated from the working electrode 4 by a proton exchange membrane.

[0025] 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 an oxygen evolution reaction) to maintain the current loop of the entire electrolytic cell.

[0026] The alcohol permeable membrane 6 used is a silicalite-1 molecular sieve membrane, which is an outer membrane, the outside of which is in contact with the electrolyte, and the inside of the tube 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.

[0027] At 30 mL min -1 CO is continuously introduced into the electrolytic cell at a rate of 2 , and constant potential electrolysis is performed at a potential of -0.5 V to obtain liquid products and gas products. The gas product enters the chromatograph for analysis, and the ethanol in the liquid product passes through the alcohol permeable membrane 6 and is collected by vacuum condensation. The vacuum pump is turned on, and when the vacuum degree drops below 200 Pa, the ethanol collection tank 7 is used to collect ethanol.

[0028] Connect the H-type electrolytic cell to the electrochemical workstation 1 and set the flow rate at 30 mL min -1 CO was continuously introduced at a rate of 2 Under the condition of constant potential electrolysis, gas phase products and liquid phase products are obtained at different potentials, the liquid phase product ethanol is collected, and the Faraday efficiency of ethanol is calculated.

[0029] When the electrolysis was carried out at a potential of -0.5 V, the Faradaic efficiency of ethanol was 30.73% and the current density of ethanol was 19.24 mA·cm -2 The flux of alcohol permeation membrane is 1.17 kg·m -2 ·h -1 The purity of the collected ethanol reached 90.7%. When constant potential electrolysis was performed at a potential of -0.8 V, the Faraday efficiency of ethanol increased to 44.53%, and the current density of ethanol was 31.64 mA·cm -2 The flux through the membrane is 1.5 kg·m -2 ·h -1 After running for 60 min, the purity of the collected ethanol reached 88.1%.

[0030] Comparative Example 1 The difference from Example 1 is that no alcohol permeable membrane is provided in the cathode chamber. Constant potential electrolysis is performed at potentials of -0.5 V and -0.8 V, respectively, and 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

[0031] The difference between this embodiment and embodiment 1 is that the ethanol collection method used in this embodiment is changed to nitrogen purge collection. At a potential of -0.8 V, the Faradaic efficiency of ethanol is increased to 37.69%, and the current density of ethanol is 25 mA cm -2 The flux through the membrane is 1.26 kg·m -2 ·h -1 Compared with the uncoupled membrane separation technology, electrocatalytic CO 2 For the preparation of ethanol, the method disclosed in this embodiment is used to electro-reduce CO 2 To produce ethanol, the Faraday efficiency of ethanol can be increased by more than 5%. Example 3

[0032] The catalyst-loaded gas diffusion electrode (loaded with a copper-based catalyst), the reference electrode (saturated calomel) and the counter electrode (platinum electrode) were assembled into a flow-type electrolytic cell. The cathode chamber and the anode chamber of the flow-type electrolytic cell were separated by a proton exchange membrane. The cathode chamber and the anode chamber were filled with continuously flowing CO 2Saturated electrolyte (1 M KOH), CO 2 The gas was introduced from the channel on the same side as the gas diffusion layer. The experiment was carried out at room temperature and pressure at a rate of 30 mL min -1 CO is continuously introduced into the flow-type electrolytic cell at a rate of 2 The constant potential electrolysis was carried out at a potential of -0.8 V. Carbon dioxide continuously passed through the porous hydrophobic gas diffusion layer and reacted with the catalyst and the electrolyte at the gas-liquid-solid three-phase interface to obtain liquid products and gas products. The gas products entered the gas chromatograph through the gas pipe for analysis. The ethanol in the liquid products was collected by vacuum condensation through the alcohol permeable membrane. The vacuum pump was turned on and the ethanol was collected when the vacuum degree dropped below 200 Pa.

[0033] During the test, the prepared flow-type electrolytic cell was connected to an electrochemical workstation, and constant potential electrolysis was performed at a potential of -0.8 V to obtain liquid product ethanol, and the Faraday efficiency of ethanol was calculated.

[0034] Since the mass transfer efficiency of carbon dioxide on the gas diffusion electrode is higher than that of the general electrode, and the flow-type electrolytic cell shortens the distance between the cathode chamber and the anode chamber, the impedance of the electrolyte and the potential of the entire reaction system are effectively reduced. The Faraday efficiency of ethanol reaches 70.38%, and the current density of ethanol reaches 400 mA cm -2 The flux through the alcohol membrane is 2.2 kg·m -2 ·h -1 Compared with the flow-type electrolytic cell without coupling membrane separation technology, the flow-type electrolytic cell with coupling membrane separation technology disclosed in this embodiment is used for electrocatalytic CO 2 Under reduced conditions, the Faradaic efficiency of ethanol can be increased by more than 20%.

Claims

1. A method for producing ethanol by electrocatalytic reduction of carbon dioxide and membrane coupling, characterized in that: The steps include: 1) Adding electrolyte into the electrolytic cell to form an electrolytic cell with the working electrode loaded with electrocatalyst, the reference electrode and the counter electrode; 2) Arranging 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 separated by an alcohol permeable membrane and then collected.

2. The method for producing ethanol by electrocatalytic reduction of carbon dioxide and membrane coupling according to claim 1, characterized in that: The electrolytic cell is selected from one of an H-type electrolytic cell, a flow-type electrolytic cell or a membrane electrode electrolytic cell.

3. The method for producing ethanol by electrocatalytic reduction of carbon dioxide and membrane coupling according to claim 1, characterized in that: The rate of continuous CO2 introduction is CO2 volume: solution volume in the electrolytic cell = 1:1-10.

4. The method for producing ethanol by electrocatalytic reduction of carbon dioxide and membrane coupling according to claim 1, characterized in that: The electrocatalyst can catalyze the reduction of CO2 to generate ethanol under constant potential, and the electrocatalyst is one of a metal catalyst, an enzyme catalyst, a molecular catalyst, and a composite catalyst.

5. The method for producing ethanol by electrocatalytic reduction of carbon dioxide and membrane coupling according to claim 4, characterized in that: 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.

6. The method for producing ethanol by electrocatalytic reduction of carbon dioxide and membrane coupling according to claim 1, characterized in that: The alcohol permeable membrane is one of organic membrane, inorganic membrane and organic / inorganic composite membrane materials.

7. The method for producing ethanol by electrocatalytic reduction of carbon dioxide and membrane coupling according to claim 6, characterized in that: The organic alcohol permeable membrane material is selected from one of a PDMS membrane, a PVTES membrane, a COF membrane and a mixed matrix membrane.

8. The method for producing ethanol by electrocatalytic reduction of carbon dioxide and membrane coupling according to claim 6, characterized in that: The inorganic membrane is a porous membrane selected from a zeolite molecular sieve membrane, a silicon membrane, an MOF membrane, a carbon molecular sieve membrane and a ceramic membrane.

9. The method for producing ethanol by electrocatalytic reduction of carbon dioxide and membrane coupling according to claim 1, characterized in that: The method of collecting ethanol is selected from one of vacuum condensation collection and purge gas purge collection.

10. A device for electrocatalytic reduction of carbon dioxide and membrane coupling to produce ethanol, characterized in that: The invention 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 an electrocatalyst for catalyzing the electrolysis of carbon dioxide to produce ethanol is loaded on the working electrode; the electrolytic cell is divided into a cathode chamber and an anode chamber by a proton exchange membrane, and 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 interception side of the alcohol permeable membrane is connected to an electrolyte, and the permeation side of the alcohol permeable membrane is connected to an ethanol collection device, and ethanol is collected by vacuum condensation collection or purge collection with purge gas.

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