Method for preparing ethylene and co-producing ethylene oxide through carbon dioxide electro-catalysis

Abstract

The invention discloses a method for preparing ethylene and co-producing ethylene oxide through carbon dioxide electro-catalysis, which realizes efficient conversion of carbon dioxide into ethylene and ethylene oxide by optimizing the composition and structure of a catalyst, improving the activity and selectivity of the catalyst and combining an innovative reaction system design. By using the Cu-Ag nano-alloy catalyst, the dispersity and the stability of the catalyst are enhanced, so that the selectivity of ethylene is improved. The BaOx / IrO2 catalyst is prepared by loading metal barium oxide on an industrial catalyst iridium oxide (IrO2), so that cracking of hypochlorous acid is efficiently inhibited, and the conversion rate of preparing ethylene oxide from ethylene is increased. By constructing a novel oxidation-reduction electrochemical system, the reaction of preparing ethylene from CO2 and the reaction of preparing ethylene oxide from ethylene are carried out in the same electrolyzer, so that the total Faraday efficiency from carbon dioxide (CO) to ethylene oxide in the whole electrochemical system reaches 35.2%, the total battery voltage is about 2V, the ethylene oxide selectivity exceeds 90%, and the electrochemical performance is good. The selectivity is far higher than that of ethylene oxide in industry.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical catalysis, and specifically relates to a method for preparing ethylene and co-producing ethylene oxide by electrocatalysis of carbon dioxide, as well as an electrocatalyst and a novel redox electrocatalytic system for implementing the method. Technical Background

[0002] With the acceleration of global industrialization, chemical production has become one of the important areas to reduce energy consumption and carbon emissions. Ethylene and ethylene oxide, as important chemical raw materials, are widely used in many industries such as plastics, textiles, and medicine. However, traditional ethylene and ethylene oxide production methods mainly rely on fossil resources such as petroleum, which not only have limited resources but also have serious environmental pollution problems.

[0003] Ethylene is widely used in the production of synthetic fibers, synthetic rubber, synthetic plastics (such as polyethylene), synthetic ethanol and other chemical products. The traditional method of producing ethylene mainly relies on oil cracking, which is to heat oil or natural gas to a high temperature (about 800°C or above) to crack it into lighter hydrocarbon compounds. However, this method consumes a large amount of fossil fuels, and the cracking of each ton of ethylene will produce about 1-2 tons of CO2.

[0004] In recent years, with the development of sustainable energy and environmentally friendly technologies, the direct conversion of carbon dioxide (CO2) to ethylene through electrocatalysis has become a research field that has attracted much attention. This method can effectively utilize carbon dioxide in the atmosphere and reduce dependence on fossil fuels.

[0005] Ethylene oxide is the main raw material of polyethylene terephthalate, with an annual output of 20 million tons. The traditional method of producing ethylene oxide mainly relies on the direct oxidation of ethylene, that is, using a silver catalyst to react ethylene with O2 under high temperature and high pressure conditions (about 200°C and 100 atmospheres) to produce ethylene oxide. Higher temperatures and pressures require a lot of energy consumption and place higher demands on equipment. In addition, high-quality silver catalysts are expensive, which increases the cost of production. Every ton of ethylene oxide produced will emit about 0.9 tons of CO2.

[0006] Compared with the traditional direct oxidation method, the electrocatalytic method has higher selectivity and lower energy consumption potential. The electrocatalytic preparation of ethylene needs to be carried out in two steps, first reducing CO2 to ethylene and then oxidizing ethylene to ethylene oxide. The Faraday efficiency of the total CO2 to ethylene oxide in this process is only 6%. It should be noted that the cracking reaction of hypochlorous acid (HOCl) during the ethylene oxidation process will generate a large amount of unreactive ClO-, which seriously reduces the selectivity of ethylene oxide and the economic efficiency of the overall process.

[0007] Existing electrocatalytic technology provides a possible path for converting carbon dioxide (CO2) into high-value chemicals. However, it still faces many challenges in practical applications, such as high energy consumption, low conversion efficiency and low selectivity. In particular, under high temperature and high pressure or certain specific environments (such as extreme pH values ​​and high salinity), the solubility and mass transfer efficiency in the electrolyte are limited, resulting in unsatisfactory reaction rate and conversion rate of the electrocatalytic process. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention proposes a method for preparing ethylene and co-producing ethylene oxide by electrocatalysis of carbon dioxide. The method aims to improve the activity and selectivity of the catalyst by optimizing the composition and structure of the catalyst, and at the same time, combine innovative reaction system design to achieve efficient conversion of carbon dioxide and efficient production of chemicals, so as to meet the urgent demand of the chemical production industry for green and low-carbon technologies.

[0009] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0010] A method for preparing ethylene and co-producing ethylene oxide by electrocatalysis of carbon dioxide comprises the following steps: constructing a novel redox electrochemical system, directly coupling a carbon dioxide reduction reaction (CO2RR) and an ethylene oxidation reaction (EtOR) in the same electrolyzer, a carbon dioxide reduction reaction occurs at the cathode, CO2 is reduced to ethylene at the cathode, O2 obtained by electrolysis of water is introduced into the anode, ethylene oxidation reaction occurs at the anode to obtain ethylene oxide, a Cu-Ag nanoparticle / copper / polytetrafluoroethylene electrode is used as the cathode, a BaOx / IrO2 / Ti electrode is used as the anode, a phosphate buffer solution (containing a small amount of potassium chloride) is used as the electrolyte solution, the conductivity is increased, a certain buffering capacity is provided, the pH value of the solution near the surface of the anode and the cathode is relatively stable, and an efficient electrochemical cycle is formed.

[0011] Furthermore, the method for preparing ethylene and co-producing ethylene oxide by electrocatalytic production of carbon dioxide comprises the following steps:

[0012] A: Preparation of Cu-Ag nanoparticles / copper / PTFE electrode for CO2RR (cathode);

[0013] B: Preparation of BaOx / IrO2 / Ti electrode for EtOR (anode);

[0014] C: Construct a new redox electrochemical system: Use phosphate buffer solution (containing a small amount of potassium chloride) as the electrolyte, introduce CO2 into the air inlet of the cathode chamber, reduce CO2 to ethylene on the Cu-Ag nanoparticle / copper / PTFE electrode, absorb the ethylene generated by the reaction using an ethylene absorption device, and transport it to the anode through a gas delivery pipeline. In addition, introduce oxygen and chloride inhibitors generated by electrolysis of water into the anode to improve the selectivity of the product. Oxidize ethylene to produce ethylene oxide on the BaOx / IrO2 / Ti electrode and collect it in the ethylene oxide absorption device.

[0015] Further, the Cu-Ag nanoparticle / copper / polytetrafluoroethylene electrode for cathode was prepared by uniformly mixing the Cu-Ag nanoalloy catalyst and the polymer binder and spray-depositing them on the copper / polytetrafluoroethylene (PTFE) substrate until the density reached 1.25 mg / cm 2 catalyst loading; wherein the copper / polytetrafluoroethylene (PTFE) substrate was prepared by evaporation: a copper target was sputtered on a hydrophobic PTFE substrate with an average pore size of 450 μm at a sputtering rate of 0.5 A / s, and sputtering was continued until a target thickness of 150 nm was reached.

[0016] Further, the preparation of BaOx / IrO2 / Ti electrode for EtOR (anode): a high-purity titanium mesh was selected as the electrode substrate, and the prepared BaO x / IrO2 catalyst was mixed with an appropriate amount of polytetrafluoroethylene, and an appropriate amount of isopropanol was added to make a slurry. The slurry was evenly coated on the pretreated titanium substrate by spray deposition until it reached 2 mg / cm 2 of catalyst loading.

[0017] Furthermore, the Cu-Ag nano alloy catalyst is composed of an active component, an auxiliary agent and a carrier, and has a general structural formula of Cu-Ag / X, wherein X is the carrier silicon carbide, the loading mass percentage of metal Cu and Ag in the catalyst is 20-70%, the auxiliary agent is potassium carbonate, the mass percentage of potassium carbonate is 5%, and the rest is the carrier, and the surface area of ​​metal Cu in the catalyst powder is 14.5-25.8m 2 / g, the surface area of ​​metal Ag is 18.7~31.4m 2 / g, the catalyst specific surface area is 118~209m 2 / g, the dispersion of Cu in the catalyst is 67.8-74.3%, the dispersion of Ag is 72.6-81.9%, and the catalyst zero-valent copper Cu 0 Surface area 14.7~17.6m 2 / g, catalyst zero-valent silver Ag 0 Surface area 17.1~23.9m 2 / g, the average size of Cu particles in the catalyst is 1.8-3.3nm, and the average size of Ag particles in the catalyst is 1.6-2.9nm.

[0018] Further, the preparation method of Cu-Ag nano alloy catalyst is as follows:

[0019] (1) According to the Cu:Ag mass ratio of 2:1 and the Cu-Ag loading of 70%, 35.21 g of copper nitrate trihydrate and 7.32 g of silver nitrate were weighed and added into a round-bottom flask. 125 mL of distilled water was added and stirred to dissolve. 6 g of SiC support was washed several times with deionized water until the pH was close to neutral;

[0020] (2) drying the cleaned SiC carrier at 80° C. until the water is completely removed;

[0021] (3) adding the SiC carrier to the copper-silver mixed solution and dropping 10 wt % sodium hydroxide solution and stirring to precipitate until the pH value is 10, adding 5.00 g of 20 wt % potassium carbonate solution, centrifugally dispersing on a magnetic stirrer, heating the water bath to 80° C., and aging for 4 h;

[0022] (4) The precipitate obtained in step (3) was washed with deionized water until the pH value was neutral, dried at 120° C. for 12 h, placed in a muffle furnace, and calcined at 500° C. in a nitrogen flow for 4 h.

[0023] (5) Grinding through a 60-80 mesh sieve to obtain a catalyst powder, and reducing and activating it in a hydrogen atmosphere at 400° C. for 3 h to obtain a Cu-Ag nano alloy catalyst.

[0024] A high-efficiency catalyst was prepared on an industrial catalyst (IrO2) to determine the composite catalyst with the best inhibitory effect on the cracking reaction of hypochlorous acid (HOCl).

[0025] A composite electrocatalyst for inhibiting the cracking reaction of hypochlorous acid (HOCl), the preparation principle is as follows:

[0026] Density functional theory (DFT) was used to computationally study the HOCl cracking process on bare IrO2, and oxides of four metals in the sixth period (known to have good stability in chlorine solution) were selected as candidate promoters. Their effects on the Faradaic efficiency of ethylene to ethylene oxide were observed, and the metal oxides with the best inhibitory effect on the cracking reaction of HOCl were selected and combined with bare IrO2 as composite electrocatalysts.

[0027] Furthermore, the four metal oxides are barium oxide (BaO x ), lanthanum oxide (LaO x ), cerium oxide (CeO x ) and bismuth oxide (BiOx ).

[0028] Furthermore, iridium oxide (IrO2) catalyst was loaded on bare IrO2 and the four metal oxides at a loading amount of 3 wt%. All electrochemical reactions were performed in 2 M KCl electrolyte at 100 mA / cm 2 The current density is carried out.

[0029] Preferably, BaO x Supported IrO2 catalyst (BaO x / IrO2) showed the best inhibition effect.

[0030] Preferably, BaO x The molar ratio of Ba / Ir in BaO / IrO2 is 3, and x The nanoparticles need to be loaded on IrO2.

[0031] Furthermore, BaO x / IrO2 limits the Faradaic efficiency to inactive ClO- to less than 10%, thereby increasing the Faradaic efficiency of ethylene to ethylene oxide to 90%.

[0032] Furthermore, BaO x The preparation method of the / IrO2 catalyst is as follows: a titanium mesh is placed in 3M HCl and etched at a temperature of 75°C for 40 minutes, dehydrated iridium oxide, dilute hydrochloric acid and barium chloride dihydrate are dissolved in isopropanol and mixed evenly to obtain a catalyst ink, wherein the molar ratio of Ba / Ir is 3, the etched titanium mesh is immersed in the above-prepared catalyst ink, the titanium mesh is taken out and dried at 120°C, and the titanium mesh is sintered at 500°C to form a BaOx / IrO2 catalyst on its surface, and the immersion, drying and sintering steps are repeated until 2 mg / cm 2 The target BaOx / IrO2 catalyst loading amount is 3wt%, and the mass percentage of BaOx in the BaOx / IrO2 catalyst is 3wt%.

[0033] Further, ethylene oxide is produced using the same gas supply as the industrial direct oxidation process.

[0034] Furthermore, the novel redox electrochemical system constructed by the present invention has the following advantages: 2 The Faraday efficiency and full cell voltage of ethylene to ethylene oxide were measured at an applied current density of .

[0035] Furthermore, the novel redox electrochemical system constructed by the present invention has an applied current density of 300 mA / cm 2When the reaction is carried out, the total Faraday efficiency from carbon dioxide (CO2) to ethylene oxide reaches 35.2%, the full cell voltage is about 2V, the duration is more than 100h, and about 0.17MJ of energy can be saved for every ton of ethylene oxide produced.

[0036] Furthermore, the novel redox electrochemical system constructed by the present invention has an ethylene oxide selectivity of over 90%, which is much greater than the ethylene oxide selectivity in industry.

[0037] On the basis of the above technical solution, compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0038] 1. The present invention adopts copper-silver alloy, and through the synergistic effect between the two metals, the activation ability of the catalyst to CO2 is enhanced, thereby improving the conversion rate of CO2. The presence of silver can adjust the electronic structure of the copper surface, making the reaction intermediates easier to form or stabilize, thereby promoting the reaction. SiC as a carrier can effectively prevent the catalyst from sintering and deactivation at high temperatures, and prolong the life of the catalyst. The interaction between copper, silver and SiC is optimal, the raw materials are easy to obtain, the cost is low, the process is simple and controllable, the structure is stable, the operability is strong, and it has good industrial application prospects.

[0039] 2. In the present invention, the carbon dioxide reduction reaction and the ethylene oxidation reaction are coupled in the same electrolyzer, and the selectivity of ethylene oxide exceeds 90%, achieving a total Faraday efficiency of 35.2% from carbon dioxide (CO2) to ethylene oxide in the entire electrochemical system, and compared with the existing electrochemical system, the energy consumption of producing 1kg of ethylene oxide is reduced by 0.17MJ. The selectivity of ethylene oxide exceeds 90%, which is much greater than the selectivity of ethylene oxide in industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention is a flow chart of a method for preparing ethylene and co-producing ethylene oxide by electrocatalytic production of carbon dioxide.

[0041] Figure 2 This is the flow chart for the preparation of Cu-Ag nanoalloy catalyst.

[0042] Figure 3 BaO x / IrO2 catalyst preparation flow chart.

[0043] Figure 4 The Faraday efficiency of ethylene oxide of bare IrO2 and 3 wt% IrO2 catalyst loaded on Ba, La, Ce, and Bi oxides respectively.

[0044] Figure 5 This is a schematic diagram of the new redox electrochemical system.

[0045] Reference numerals: 1. power supply, 2. ethylene absorption device, 3. Cu-Ag nano alloy catalyst, 4. phosphate buffer solution (containing a small amount of potassium chloride), 5. Nafion membrane, 6. BaO x / IrO2 catalyst, 7. Ethylene oxide absorption device. DETAILED DESCRIPTION

[0046] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0047] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0048] Example 1

[0049] The Cu-Ag nano alloy catalyst for the co-production of ethylene oxide from carbon dioxide in this embodiment is prepared by a coprecipitation method (CP), and the steps are as follows:

[0050] (1) According to the Cu:Ag mass ratio of 1:1 and the Cu-Ag loading of 70%, 26.60 g of copper nitrate trihydrate and 11.06 g of silver nitrate were weighed and added into a round-bottom flask. 125 mL of distilled water was added and stirred to dissolve. 6 g of SiC carrier was washed several times with deionized water until the pH was close to neutral.

[0051] (2) The cleaned SiC carrier was dried at 80° C. until the water was completely removed.

[0052] (3) The SiC carrier was added to the copper-silver mixed solution and 10 wt % sodium hydroxide solution was dropped and stirred to precipitate until the pH value was 10, 5.00 g of 20 wt % potassium carbonate solution was added, and the mixture was dispersed by centrifugation on a magnetic stirrer, and the temperature was raised to 80° C. in a water bath and aged for 4 h.

[0053] (4) The obtained precipitate was washed with deionized water until the pH value was neutral, dried at 120° C. for 12 h, placed in a muffle furnace, and calcined at 500° C. in a nitrogen flow for 4 h.

[0054] (5) Grind and sieve through 60-80 mesh to obtain catalyst powder, and reduce and activate it in a hydrogen atmosphere at 400° C. for 3 h to obtain catalyst 1.

[0055] Example 2: According to the Cu:Ag mass ratio of 1:2 and the Cu-Ag loading of 70%, 18.07 g of copper nitrate trihydrate and 14.64 g of silver nitrate were weighed, and the remaining operations were the same as in Example 1 to obtain Catalyst 2.

[0056] Example 3: According to the Cu:Ag mass ratio of 1:3 and the Cu-Ag loading of 70%, 13.46 g of copper nitrate trihydrate and 16.38 g of silver nitrate were weighed, and the remaining operations were the same as in Example 1 to obtain Catalyst 3.

[0057] Example 4: According to the Cu:Ag mass ratio of 2:1 and the Cu-Ag loading of 70%, 35.21 g of copper nitrate trihydrate and 7.32 g of silver nitrate were weighed, and the remaining operations were the same as those in Example 1 to obtain catalyst 4.

[0058] Example 5: According to the Cu:Ag mass ratio of 3:1 and the Cu-Ag loading of 70%, 40.15 g of copper nitrate trihydrate and 5.46 g of silver nitrate were weighed, and the remaining operations were the same as those in Example 1 to obtain Catalyst 5.

[0059] Example 6: According to the Cu:Ag mass ratio of 2:3 and the Cu-Ag loading of 70%, 21.68g of copper nitrate trihydrate and 13.08g of silver nitrate were weighed, and the remaining operations were the same as those in Example 1 to obtain Catalyst 6.

[0060] The performance of the catalysts prepared in Examples 1 to 6 was evaluated respectively.

[0061] The carbon dioxide electrode reaction in the present invention is carried out in a fixed bed reactor in a closed hydrogen atmosphere environment. The prepared alloy catalyst is used as a working electrode, and a potassium carbonate (K2CO3) aqueous solution is used as an electrolyte. A silver / silver chloride (Ag / AgCl) electrode is used as a reference electrode, a platinum mesh (Pt mesh) is used as a counter electrode, and a three-electrode system and an electrochemical workstation are used to apply a constant voltage of -0.8V vs. RHE at room temperature for electrochemical testing. A sufficient amount of CO2 is passed through the reaction electrode, and the flow rate of CO2 is controlled to be 50mL / min. After 10 minutes of reaction, a sufficient amount of O2 is passed through the reaction electrode, and the flow rate of O2 is controlled to be 50mL / min. After 10 minutes of reaction, a qualitative and quantitative analysis is performed by observing the Faraday efficiency and current density of the electrode where the catalyst is located.

[0062] Table 1: Performance evaluation of catalyst powders prepared at different metal mass ratios

[0063]

[0064] It can be seen from Table 1 that the selectivity for the target product can be effectively improved by adjusting the metal mass ratio. The ethylene selectivity varies significantly with the metal ratio. Cu:Ag=2:1 is the best ratio with the highest ethylene selectivity, indicating that an appropriate amount of Ag can significantly improve the surface properties of Cu.

[0065] Example 7

[0066] BaO x The preparation method of the / IrO2 catalyst is as follows:

[0067] The titanium mesh was placed in 3M HCl (≥98%) and etched at 75°C for 40 minutes. Dehydrated iridium oxide (99.99%), hydrochloric acid (37%) and barium chloride dihydrate (>99.999%) were dissolved in isopropanol and mixed evenly (Ba / Ir molar ratio was 3) to obtain catalyst ink. The etched titanium mesh was immersed in the above-prepared catalyst ink. The titanium mesh was taken out and dried at 120°C. The titanium mesh was sintered at 500°C to form BaOx / IrO2 catalyst on its surface. The impregnation, drying and sintering steps were repeated until the target BaOx / IrO2 loading, i.e., 2 mg / cm2, was reached. 2 , wherein the mass percentage of BaOx in the BaOx / IrO2 catalyst is 3wt%, to obtain the active catalyst (I) BaOx / IrO2 required by the present invention.

[0068] Example 8: The operation is the same as that of Example 7, except that barium chloride dihydrate (>99.999%) is replaced by lanthanum chloride hydrate (99.9%) to obtain the active catalyst (II) LaOx / IrO2 required by the present invention.

[0069] Example 9: The operation is the same as that of Example 7, except that barium chloride dihydrate (>99.999%) is replaced by cerium chloride hydrate (99.9%) to obtain the active catalyst (III) CeOx / IrO2 required by the present invention.

[0070] Example 10: The operation is the same as that of Example 7, except that barium chloride dihydrate (>99.999%) is replaced by bismuth chloride hydrate (99.9%) to obtain the active catalyst (IV) BiOx / IrO2 required by the present invention.

[0071] Example 11: The operation is the same as that of Example 7, except that iridium oxide dehydrate (99.99%) and an appropriate amount of hydrochloric acid (37%) are added to isopropanol, and no lanthanide metal chloride is added to obtain the control group (V) naked IrO2 required by the present invention.

[0072] The performance of catalysts I to V prepared in Examples 7 to 11 was evaluated by conducting electrochemical reactions in a 2M potassium chloride electrolyte to determine the Faraday efficiency of ethylene to ethylene oxide and the selectivity of ethylene oxide. In particular, the current density was 100 mA / cm 2 .

[0073] Table 2: Performance evaluation of composite electrocatalysts synthesized from different sixth-period metal oxides and iridium oxide

[0074]

[0075] from Figure 4 As can be seen from Table 2, by comparing the various properties of Examples 7-10 and conducting a comparative experiment with Example 11, the IrO2 catalyst supported by barium oxide (BaOx / IrO2) performs best, which converts the inactive ClO - The Faradaic efficiency is limited to less than 10%, reducing the inactive ClO - The production of ethylene oxide increases the Faraday efficiency of ethylene to ethylene oxide to 90%.

[0076] At 100mA / cm 2 The BaOx / IrO2 catalyst was tested for 300 hours of continuous operation at a current density of 1.5 MW and showed that it maintained stable performance. Specifically, the Faradaic efficiency of ethylene oxide was greater than 80% on average.

[0077] Example 12: Figure 5 As shown in the figure, the novel redox electrochemical system consists of 2 electrolytic chambers and 2 electrodes. A phosphate buffer solution (containing a small amount of potassium chloride) is selected as the electrolyte. The chamber sides are the cathode chamber for CO2RR and the anode chamber for EtOR. The Nafion membrane is used in the middle to separate the reactants and products at the positive and negative electrodes.

[0078] (1) Preparation of Cu-Ag nanoparticle / copper / PTFE electrode for CO2RR (cathode)

[0079] Copper / polytetrafluoroethylene (PTFE) substrate: used to support Cu-Ag nano alloy catalyst, prepared by evaporation. Sputtering was performed on a hydrophobic PTFE substrate (average pore size 450 μm) using a copper target at a sputtering rate of 0.5 A / s until the target thickness of 150 nm was reached.

[0080] Cu-Ag nanoparticles / copper / PTFE electrode: prepared by spray deposition. The Cu-Ag nanocatalyst prepared in Example 4 and the polymer binder were uniformly mixed and spray-deposited on the copper / PTFE substrate until the concentration reached 1.25 mg / cm 2 of catalyst loading.

[0081] (2) Preparation of BaOx / IrO2 / Ti electrode for EtOR (anode)

[0082] BaOx / IrO2 / Ti electrode: A high-purity titanium mesh was selected as the electrode substrate. The BaO prepared in Example 7 was x / IrO2 catalyst was mixed with an appropriate amount of polytetrafluoroethylene, and an appropriate amount of isopropanol was added to make a slurry. The slurry was evenly coated on the pretreated titanium substrate by spray deposition until it reached 2 mg / cm 2 of catalyst loading.

[0083] (3) Construct a new redox electrochemical system.

[0084] A phosphate buffer solution (containing a small amount of potassium chloride) is used as an electrolyte, CO2 is introduced into the air inlet of the cathode chamber, CO2 is reduced to ethylene on the Cu-Ag nanoparticle / copper / PTFE electrode, the ethylene generated by the reaction is absorbed by an ethylene absorption device, and transported to the anode through a gas delivery pipeline, and oxygen and chloride inhibitors generated by electrolysis of water are introduced into the anode, and ethylene is oxidized to ethylene oxide on the BaOx / IrO2 / Ti electrode and collected in the ethylene oxide absorption device.

[0085] Example 13: Based on the novel redox electrochemical system designed in Example 12, the performance evaluation and assessment are performed, and the specific steps are as follows:

[0086] (1) The electricity price is set at $0.05 / kWh and the current density is 100 mA / cm 2 The system was run for 1 h under the conditions of , and the collected ethylene and ethylene oxide were quantitatively analyzed using a gas chromatograph.

[0087] (2) Based on the amount of ethylene oxide collected and the number of electrons in the reaction equation, Faraday's law is used to calculate the theoretical amount of electricity that should be consumed.

[0088] (3) The actual amount of electricity consumed is obtained by integrating the change in current over time and calculating the Faraday efficiency.

[0089] (4) Use an electrochemical workstation to directly read and record the operating voltage of the full cell.

[0090] Example 14: The operation is the same as in Example 13, except that 100 mA / cm 2 The current density was changed to 200 mA / cm 2 , determine the system's Faradaic efficiency and full-cell voltage.

[0091] Example 15: The operation is the same as Example 13, except that 100 mA / cm2 The current density was changed to 300 mA / cm 2 , determine the system's Faradaic efficiency and full-cell voltage.

[0092] Example 16: The operation is the same as in Example 13, except that 100 mA / cm 2 The current density was changed to 400 mA / cm 2 , determine the system's Faradaic efficiency and full-cell voltage.

[0093] Table 3: Performance evaluation and energy consumption assessment of new redox electrocatalytic systems at different current densities

[0094]

[0095] It can be seen from Table 3 that as the current density increases, the Faraday efficiency from carbon dioxide to ethylene oxide increases significantly, and the full-cell voltage of the system rises in a parabolic trend. 2 After 300 mA / cm, the Faraday efficiency dropped significantly. The reason is that high current density will promote the formation of non-target products, thereby inhibiting the target reaction. 2 is the optimal current density.

[0096] At 300mA / cm 2 The system was tested for 100 hours of continuous operation at a current density of 1.5 %. The results showed that it maintained stable performance.

[0097] In actual production, the conversion rate of ethylene to ethylene oxide will not reach 100%, but will be about 85%-90% or even higher. As can be seen from Table 3, when the product ratio of ethylene to ethylene oxide is 1:9, the system has the lowest energy consumption, and compared with the existing electrocatalytic technology for producing ethylene oxide, the energy consumption is reduced by about 0.17 MJ to produce 1 kg of ethylene oxide.

[0098] The present invention optimizes the composition and structure of the catalyst to improve the activity and selectivity of the catalyst, and combines innovative reaction system design to achieve efficient conversion of carbon dioxide into ethylene and ethylene oxide. The Cu-Ag nano alloy catalyst is used to enhance the dispersibility and stability of the catalyst, thereby improving the selectivity of ethylene. BaO is prepared by loading metal barium oxide on industrial catalyst iridium oxide (IrO2). x / IrO2 catalyst, which effectively inhibits the cracking of hypochlorous acid and improves the conversion rate of ethylene to ethylene oxide. By constructing a new redox electrochemical system, the reaction of CO2 to ethylene and ethylene to ethylene oxide is carried out in the same electrolyzer, achieving a total Faraday efficiency of 35.2% from carbon dioxide (CO2) to ethylene oxide in the entire electrochemical system, a full cell voltage of about 2V, and an ethylene oxide selectivity of more than 90%, which is much greater than the ethylene oxide selectivity in industry.

[0099] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.

Claims

1. A method for preparing ethylene and co-producing ethylene oxide by electrocatalysis of carbon dioxide, characterized in that The following steps are involved: A new redox electrochemical system was constructed, and the carbon dioxide reduction reaction (CO2RR) and the ethylene oxidation reaction (EtOR) were directly coupled in the same electrolyzer. The carbon dioxide reduction reaction occurred at the cathode, where CO2 was reduced to ethylene, and the O2 obtained by electrolysis of water was passed into the anode, where ethylene oxidation reaction occurred to obtain ethylene oxide. The cathode used Cu-Ag nanoparticles / copper / polytetrafluoroethylene electrode, and the anode used BaOx / IrO2 / Ti electrode, and phosphate buffer solution was used as the electrolyte solution.

2. The method for preparing ethylene and co-producing ethylene oxide by electrocatalytic production of carbon dioxide according to claim 1, characterized in that: The following steps are involved: A: Preparation of Cu-Ag nanoparticles / copper / PTFE electrode for CO2RR (cathode); B: Preparation of BaOx / IrO2 / Ti electrode for EtOR (anode); C: Construct a new redox electrochemical system: Use phosphate buffer solution as the electrolyte, introduce CO2 into the air inlet of the cathode chamber, reduce CO2 to ethylene on the Cu-Ag nanoparticle / copper / PTFE electrode, absorb the ethylene generated by the reaction using an ethylene absorber, and transport it to the anode through a gas delivery pipeline. In addition, introduce oxygen and chloride inhibitors generated by electrolysis of water into the anode, oxidize ethylene to ethylene oxide on the BaOx / IrO2 / Ti electrode and collect it in the ethylene oxide absorber.

3. The method for preparing ethylene and co-producing ethylene oxide by electrocatalytic production of carbon dioxide according to claim 2, characterized in that: Preparation of Cu-Ag nanoparticle / copper / polytetrafluoroethylene electrode for cathode: The Cu-Ag nanoalloy catalyst and polymer binder were uniformly mixed and spray-deposited on a copper / polytetrafluoroethylene (PTFE) substrate until a catalyst loading of 1.25 mg / cm² was reached; the copper / polytetrafluoroethylene (PTFE) substrate was prepared by evaporation: a copper target was sputtered on a hydrophobic PTFE substrate with an average pore size of 450 µm at a sputtering rate of 0.5 A / s, and sputtering was continued until a target thickness of 150 nm was reached.

4. The method for preparing ethylene and co-producing ethylene oxide by electrocatalytic production of carbon dioxide according to claim 2, characterized in that: Preparation of BaOx / IrO2 / Ti electrode for EtOR (anode): High-purity titanium mesh was selected as the electrode substrate. X / IrO2 catalyst was mixed with an appropriate amount of polytetrafluoroethylene, and an appropriate amount of isopropanol was added to make a slurry. The slurry was evenly coated on the pretreated titanium substrate by spray deposition until the catalyst loading reached 2 mg / cm².

5. The method for preparing ethylene and co-producing ethylene oxide by electrocatalytic production of carbon dioxide according to claim 3, characterized in that: The Cu-Ag nano alloy catalyst is composed of an active component, an auxiliary agent and a carrier, and has a general structural formula of Cu-Ag / X, wherein X is a carrier silicon carbide, the loading mass percentage of metal Cu and Ag in the catalyst is 20-70%, the auxiliary agent is potassium carbonate, the mass percentage of potassium carbonate is 5%, and the rest is the carrier. The surface area of ​​metal Cu in the catalyst powder is 14.5-25.8 m2 / g, the surface area of ​​metal Ag is 18.7-31.4 m2 / g, the specific surface area of ​​the catalyst is 118-209 m2 / g, the dispersion degree of Cu in the catalyst is 67.8-74.3%, the dispersion degree of Ag is 72.6-81.9%, and the catalyst zero-valent copper Cu is 1.34-1.

64. 0 The surface area is 14.7~17.6m² / g, the catalyst is zero-valent silver Ag 0 The surface area is 17.1~23.9m² / g, the average size of Cu particles in the catalyst is 1.8~3.3nm, and the average size of Ag particles in the catalyst is 1.6~2.9nm.

6. The method for preparing ethylene and co-producing ethylene oxide by electrocatalytic production of carbon dioxide according to claim 5, characterized in that: The preparation method of Cu-Ag nano alloy catalyst is as follows: (1) According to the Cu:Ag mass ratio of 2:1 and the Cu-Ag loading of 70%, weigh 35.21g of copper nitrate trihydrate and 7.32g of silver nitrate, add them into a round-bottom flask, add 125mL of distilled water and stir to dissolve, and wash 6g of SiC carrier with deionized water several times until the pH is close to neutral; (2) drying the cleaned SiC carrier at 80° C. until the water is completely removed; (3) Add the SiC carrier to the copper-silver mixed solution and drop 10 wt% sodium hydroxide solution and stir to precipitate until the pH is 10, add 5.00 g of 20% potassium carbonate solution, centrifuge and disperse on a magnetic stirrer, heat the water bath to 80 °C, and age for 4 h; (4) washing the precipitate obtained in step (3) with deionized water until the pH value is neutral, drying at 120° C. for 12 h, placing it in a muffle furnace, and calcining it at 500° C. in a nitrogen flow for 4 h; (5) Grinding through a 60-80 mesh sieve to obtain a catalyst powder, which was reduced and activated in a hydrogen atmosphere at 400°C for 3 h to obtain a Cu-Ag nano-alloy catalyst.

7. The method for preparing ethylene and co-producing ethylene oxide by electrocatalytic production of carbon dioxide according to claim 4, characterized in that: BaO X The preparation method of / IrO2 catalyst is as follows: placing a titanium mesh in 3M HCl and etching it at a temperature of 75°C for 40 minutes, dissolving dehydrated iridium oxide, dilute hydrochloric acid and barium chloride dihydrate in isopropanol and mixing them evenly to obtain a catalyst ink, wherein the molar ratio of Ba / Ir is 3, immersing the etched titanium mesh in the above-prepared catalyst ink, taking out the titanium mesh and drying it at 120°C, sintering the titanium mesh at 500°C to form a BaOx / IrO2 catalyst on its surface, repeating the impregnation, drying and sintering steps until a target BaOx / IrO2 catalyst loading of 2 mg / cm² is reached, and the mass percentage of BaOx in the BaOx / IrO2 catalyst is 3 wt%.

8. The method for preparing ethylene and co-producing ethylene oxide by electrocatalytic production of carbon dioxide according to claim 1 or 2, characterized in that: The Faradaic efficiency and full cell voltage of ethylene to ethylene oxide were measured at applied current densities of 100, 200, 300 and 400 mA / cm².

9. The method for preparing ethylene and co-producing ethylene oxide by electrocatalytic production of carbon dioxide according to claim 8, characterized in that: At an applied current density of 300 mA / cm², the total Faradaic efficiency from carbon dioxide (CO2) to ethylene oxide reached 35.2%, the full cell voltage was about 2 V, the duration was more than 100 hours, and about 0.17 MJ of energy could be saved for every ton of ethylene oxide produced.

10. The method for preparing ethylene and co-producing ethylene oxide by electrocatalytic production of carbon dioxide according to claim 1 or 2, characterized in that: The selectivity of ethylene oxide exceeds 90%, which is much higher than that in industry.

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