WO2023028728A1

WO2023028728A1 - Electrochemical packed bed reactor and use thereof

Info

Publication number: WO2023028728A1
Application number: PCT/CN2021/115211
Authority: WO
Inventors: 杨宏昀; 杨晓航
Original assignee: 湘潭大学
Priority date: 2021-08-30
Filing date: 2021-08-30
Publication date: 2023-03-09

Abstract

An electrochemical packed bed reactor and a use thereof. The reactor utilizes a tubular packed bed structure, wherein one electrode is a three-dimensional electrode that forms an entire packed bed, and the other electrode serves as a support structure; an ionic conductive film (3) is located between the two electrodes and separates fluid flowing at two sides thereof; the three-dimensional electrode comprises a plurality of layers of open cell metal foam and catalyst particles (8) fixed within the metal foam, an electrode post (2) passes through a center thereof, and the three-dimensional electrode as a whole is in a state of equivalent electric potential; a reactant-containing fluid passes through a whole three-dimensional electrode bed layer, and a desired chemical reaction is performed on a surface of the three-dimensional electrode and a surface of a catalyst; the electrochemical packed bed utilizes a means of sample addition resembling that of a traditional packed bed: adding a sample at a bottom portion when a liquid phase reaction is performed; and adding a sample from a top portion when an added material is in a gas phase; the electrochemical packed bed can be operated at a specific pressure and temperature just like a traditional packed bed, and different reactions can also be performed in segments.

Description

Electrochemical packed bed reactor and its application

technical field

The invention relates to an electrochemical synthesis reactor, in particular to an electrochemical packed bed reactor and its application.

Background technique

Electrochemistry is the science of mutual conversion between electrical energy and chemical energy. The reaction in which chemical energy is converted into electrical energy is called battery reaction; the reaction in which electrical energy is converted into new substances is called electrolysis reaction. Through battery reactions, we convert a variety of substances into electrical energy, such as dry batteries, lithium batteries, and fuel cells, and also protect materials through battery principles. Through electrolytic reactions, we can synthesize and create a variety of new substances. Compared with traditional chemical synthesis, electrolytic reaction does not need to use toxic reagents and produces less "three wastes", so it has gradually developed into a new type of green chemical synthesis technology. Electrochemical synthesis technology also provides new ideas for synthetic chemistry. Compared with traditional chemical synthesis, electrochemical synthesis has the following advantages:

(1) The electrode reaction rate can be changed by adjusting the electrode potential. According to Professor Ma Chun'an's estimation, when the electrode overpotential increases by 1V, the activation energy decreases by about 40kJ, and the reaction rate increases by ¹⁰⁷ times. Therefore, electrochemical synthesis can obtain a higher reaction rate at room temperature by appropriately increasing the electrode position, which also makes Industrial production becomes possible. In traditional synthesis, the reaction rate can also be increased by increasing the temperature, but it is necessary to increase the reaction temperature by 600°C to obtain a 10 ⁷ -fold rate increase. Such a high temperature rise will pose considerable challenges to reaction equipment and materials.

(2) It is easier to control the direction of the electrode reaction. By controlling the potential and selecting appropriate electrodes, solvents, etc., the reaction can proceed in the desired direction, reduce side reactions, improve yield and product purity, and obtain substances that are difficult to prepare by general chemical synthesis methods, such as strong reducing properties. Strong oxidizing substances.

(3) less environmental pollution. The oxidizing and reducing agents required for electrochemical reactions are electrons, which are clean substances. The electrochemical synthesis process is easy to realize automatic and continuous operation. The electrolyzer is also easy to be sealed, so the discharge of "three wastes" is less.

Electrochemical synthesis has developed rapidly in recent years. New electrode materials emerge in endlessly. From metals to semiconductors, to non-metallic materials, from the original macroscopic structure to the current new electrode materials with nano- and micro-structured structures, these have greatly accelerated the development of electrochemical synthesis.

The chemical synthesis process and industrial production using electrochemistry are still a chemical process in essence, that is, the transfer problem required by the electrochemical reaction must be solved. For common electrochemical reactions, the temperature is close to room temperature, the flow rate of the liquid is not large, and mass transfer is the main problem of electrochemical synthesis. Laboratory-scale reactions can rely on high-speed rotating electrodes to eliminate transfer resistance, and industrial electrochemical reactors (electrolyzers) also have various designs according to the needs of the reaction. Traditional electrochemical reactors include traditional box-type electrolyzer and compact filter press type (plate-and-frame type). The former only relies on simple structure, easy design and manufacture, and convenient maintenance, but the space-time reaction rate is low, and it is difficult to meet the needs of continuous production and electrochemical processes that require high mass transfer. The latter adopts a compact and regular structure to obtain a higher space-time reaction rate, because the reaction volume can be expanded by increasing the number of reaction electrolyzers, and the reaction production capacity can be increased. This type of electrolyzer is also widely used in industry, such as the electrolysis of water device. However, the electrode area per unit reaction volume is still very limited; in addition, due to the limited space in the reactor, the mass transfer cannot be further enhanced, so the space-time reaction rate is not large. In order to increase the specific electrode area of the reactor, enhance mass transfer, and increase the space-time reaction rate, more novel electrochemical reactors have been developed, and the three-dimensional electrode is one of them.

As the name suggests, the three-dimensional electrode is to expand the electrode from a flat plate (2D) to an electrode structure with a 3D spatial structure. Compared with the traditional electrode, the three-dimensional electrode has a high specific electrode area. Early three-dimensional electrodes mostly used tiny particles or spherical materials, including carbon particles, graphite particles, and various metal particles. Three-dimensional electrode materials are not limited to granular materials, and the range of materials is very wide, including: conductive fiber materials (including metal fibers, carbon fibers, conductive rubber, etc.); conductive foam materials (metal foam and carbon foam); regular microelectrodes (including A three-dimensional electrode composed of a variety of mesh electrodes and porous electrodes); a three-dimensional electrode composed of porous materials loaded with electrochemical catalysts, active materials and conductive materials through impregnation, coating, electroplating and other processes.

There are many reports on 3D electrode testing. The most common is to use three-dimensional electrodes instead of ordinary flat electrodes and place them in electrolytic cells for electrolytic testing. For example, C.J.Brown et al. (J.App.Elec.94(24),95-106) tested a variety of three-dimensional electrodes made of Ni, including a variety of mesh electrodes, in an experimental electrolyzer to prepare carboxylic acids by oxidation of alcohols and a 3mm thick metal nickel foam plate electrode. They demonstrate the high specific electrode area and high space-time reaction rate of metal foams compared to flat-plate electrodes. However, because their electrolytes flow by from both sides of the electrode instead of flowing through, the mass transfer rate of the metal foam electrode is not improved compared with that of the flat electrode. Most of the tests of three-dimensional electrodes reported in the literature are similar to Brown's method. Under this configuration, the gap between the electrolytic cell and the three-dimensional electrode is large. For the flow system, part of the fluid (electrolyte) or even most of the fluid (electrolyte) entering the electrolytic cell flows out without long-term contact with the electrode. electrolyzer. The entire electrode is maintained at a relatively uniform reactant concentration, and the conversion rate is not large. This approach is very similar to the differential reactor in a chemical reactor, and is very suitable for testing the performance of the electrode. Because a large amount of reactants flow out or leave the three-dimensional electrode without reacting, batch or cyclic operation has to be adopted in order to obtain sufficient conversion in industrial applications.

For flow electrochemical reactors, especially in applications with high conversion requirements, it is common to fill the entire reactor or most of the reactor with three-dimensional electrodes. At this time we also call it an electrochemical packed bed reactor. The most common type of this type is that the entire packed bed consists of conductive particles, which are both packed bed and electrode. For example, Xu Wenlin and Yuan Weikang of East China University of Science and Technology reported an electrochemical packed bed composed of metallic copper particles (Chemical Reaction Engineering and Technology, 1996, 12(1), 17-24). Xu Wenlin and Wang Yaqiong also introduced several common packing The layout mode between the electrodes of the bed, the ion membrane and the flow direction (Chemical Metallurgy, 1995, 16(3), 263-270). The lead ball-filled tower-type fixed-bed electrochemical reactor used by the American Nalco Company to electrolytically synthesize tetraethyl lead also belongs to this early three-dimensional electrode type (Green Electrochemical Synthesis, Ma Chun'an). The difference is that these lead balls are both electrodes and reactants. In the flow reaction system of the sewage treatment industry, the conversion rate and residual degree of toxic and harmful substances in the fluid are relatively high, and electrochemical packed bed reactors are widely used. Yang et al. (Journal of Cleaner Production 308(2021) 127324) described in detail the application of electrochemical reactors in sewage treatment in their review. Among them, the packing particles of the packed bed are mostly activated carbon, conductive plastic, composite metal particles, etc. Most of these particles are about a few millimeters, and there are also nano-scale. Due to the gaps between the particles, the current density of this type of electrochemical packed bed converted from the cross-sectional area of the electrode is relatively small, mostly 10-100mA/cm ² . Because the content of harmful substances in wastewater is generally not too high, low current density also meets its application needs. Due to the resistance of particle contact, at low current densities, even when the reactor size is large, the potential distribution is not obvious, or does not affect the electrochemical reaction, but this severely limits the size of the packed bed reactor. expand.

Although the fluidized bed three-dimensional electrode has been developed based on the bipolar conduction mechanism. This type of three-dimensional electrode uses a dielectric material to be placed between two metal electrodes, and there is no gas separator or membrane material between the two metal electrodes. A high voltage is applied between the two electrodes, so that both ends of each fine dielectric material particle are polarized, which is equivalent to generating countless fine electrodes for electrochemical reactions, which greatly expands the bed space and effectively electrode area. He et al. (Applied Clay Science, 2014, 99, 178-186) demonstrated a three-dimensional granular Feton method for oxidation treatment of wastewater. The kaolin ceramic particle electrode containing iron element produces H ₂ O ₂ , and the H ₂ O ₂ reacts with the iron-containing catalyst in the packed bed particles to generate OH radicals. The OH radical oxidation activity is very high (oxidation potential of 2.8 V), and can indiscriminately oxidize common organic matter in wastewater to _CO2 and water. However, high operating voltage, uncontrollable polarization potential, particle wear in the fluidized state, significant current loss, and process safety issues all plague this type of system. In addition, the design of this type of reactor is difficult to be used in large-scale organic synthesis due to its own limitations on current density and the inability to separate the generated gases.

He et al. (Ind.Eng.Chem.Res.2004, 43, 7965-7974) reported that two packed beds (3cm and 7.6cm inner diameter) and A metal copper rod is placed in the middle to form a three-dimensional electrode, which is applied to the liquid-phase electrochemical dechlorination process. This three-dimensional packed bed solves the problem of liquid distribution very well, but the resistance between the metal foam cubes makes it face the same problem as the early metal particle packed bed, that is, it cannot solve the potential distribution under high current and large size reactors question. Ma Jingwei and others invented a mixed packed reaction bed composed of foamed nickel particles and graphite particles for sewage treatment (CN207483433U), but the reactor design also faces the problem of scaling up. Continuous metal foam or other metal structures will help to solve the problem of potential distribution at high current and large reactor size.

Tatarchuk et al. developed a metal microfibrous structure embedded activated carbon electrode (US5,080,963), which was successfully used in supercapacitors (US5,096,663) by virtue of the high conductivity of metal materials and the high specific surface area of activated carbon. His team developed a microfibrous structure with embedded catalysts and adsorbents that were also used in heterogeneous chemical reactions (US8,420,023). The small particle size (0.1-0.2mm) catalyst in the microfiber structure has a faster mass transfer and reaction rate than the traditional packed bed with large particles (3-6mm); the use of metal microfibers can also accelerate heat transfer and solve many problems. Heat transfer bottlenecks in chemical processes. The team has yet to see the catalytic material used as an electrode or in an electrochemical reactor. In addition, due to the high cost of metal microfibers, limited types of materials, and only two or three manufacturers monopolizing this industry, the application of such materials is very limited.

Summarizing the above literature, the use of porous metal structures as electrodes is conducive to mass transfer enhancement, and the current density can be increased by virtue of its high specific electrode area (the current density may still be low). From the perspective of the reactor, the current electrochemical packed bed reinforced by three-dimensional electrodes still needs to be improved in bed design and practical application, and large-scale organic synthesis cannot be carried out yet. In addition, my country's metal foam production and processing industry has recently developed rapidly. It can not only provide a variety of metals (aluminum, iron, copper, nickel, zinc, manganese, lead, etc.) inch), the pore size is uniform, and the material can be customized, which provides a good material support for the development of electrochemical packed beds.

Contents of the invention

In view of the above technical problems, the present invention provides an electrochemical packed bed reactor and its application.

The electrochemical packed bed reactor provided by the invention adopts a tubular packed bed structure. One of the electrodes is a three-dimensional electrode that can radiate the entire reaction space and can pass through the fluid; the other electrode is used as a supporting structure to form the outer wall of the reactor, and there are holes on it, and the fluid contacts the electrode. The conductive film material is located between the two electrodes, is in contact with the fluid on both sides, and is in close contact with the two electrodes.

Preferably, the three-dimensional electrode includes an electrode column in the center of the packed bed and several stacked metal foams radiating along the electrode column to the outer wall of the reactor, and catalyst particles are placed inside the metal foam.

Preferably, surface modification of the metal foam, such as carbon coating, coating, etc., is also included.

Preferably, the catalyst is conductive or non-conductive.

Preferably, the catalyst particles are dispersed and fixed inside the metal foam.

Preferably, the conductive membrane material is an ion exchange membrane or a ceramic material with ion exchange function.

Preferably, the metal foam is a whole piece of metal foam, rather than shredded small pieces of metal foam. Therefore, the three-dimensional electrodes are in an equipotential state, that is, the potential difference between any two points on the metal foam in the same packed bed is not greater than 1mV, 5mV, 10mV or the maximum potential difference set according to the reaction that does not affect the reaction selectivity.

Preferably, the metal foam is a monolithic metal foam with open cells, and the size of the open cells is between 5-200ppi.

Preferably, the direction of the reactor and the flow are both vertical; when there is gas or only gas in the sample, the top sample is used; when there is no gas in the sample or the reaction generates gas, the bottom sample is used.

Preferably, the electrochemical packed bed reactor works at the same temperature and pressure, or performs segmental control, and the electrodes, catalysts, and operating conditions (temperature, voltage, etc.) of each segment are partly the same or completely different.

The above-mentioned electrochemical packed bed reactor is applied to electrochemical reactions or heterogeneous catalytic reactions, such as electrolysis of water, electrochemical reduction of carbon dioxide (CO ₂ ), electrochemical reduction of nitrobenzene, oxidation conversion of methyl orange, etc. .

The present invention has the following characteristics:

(1) The electrochemical packed bed reactor is an extension of the traditional packed bed, which is a reactor formed by combining electrochemical reaction and heterogeneous catalytic reaction. Architecturally, an electrochemical reactor is closer to a packed bed than to an electrochemical cell/cell.

(2) The reactor adopts a tubular packed bed structure. One of the electrodes is a three-dimensional electrode that constitutes the entire packed bed, and a fluid passes through the bed formed by the entire three-dimensional electrode; the other electrode is used as a support structure, and on the outside of the three-dimensional electrode, constitutes the outer wall of the reactor, and there are holes on it for fluid ( Electrolyte) contacts and flows with the electrode. A conductive membrane material sits between the two electrodes, separating the fluids on both sides. Without power, this is a normal packed bed.

(3) The conductive membrane material is an ion-exchange membrane, including a cation-exchange membrane and an anion-exchange membrane, and may also be a ceramic material with an ion-exchange function. The conductive film is in close contact with the two electrodes, and the resistance between the conductive film and the electrodes is reduced as much as possible. The conductive membrane is in contact with the fluid on both sides, allowing cations or anions to pass through the membrane from one side of the membrane to the other.

(4) The three-dimensional electrode consists of two parts. The first part is the main part of the metal foam. When one piece of metal foam is not thick enough, multiple pieces of metal foam can be laminated together. In the center of the packed bed there are electrode posts for powering the metal foam layer (Figure 1 or Figure 2). The second part of the three-dimensional electrode is various catalyst particles placed inside the metal foam. Catalyst particles can accelerate the reaction of free radical particles or intermediate product molecules, thereby selectively obtaining target products. Catalysts can be processed into conductive and non-conductive types according to needs. There can be many types of catalysts in the three-dimensional electrode, so as to carry out more complicated chemical reactions. Because the catalyst particles are dispersed and fixed inside the metal foam, the loss of catalyst particles due to fluid flow is greatly reduced.

(5) The whole packed bed reactor is equipotential. This is very important, equipotential can very effectively suppress the occurrence of side reactions. By virtue of the excellent electrical conductivity of the metal foam material, a whole piece of metal foam is used instead of chopped small pieces of metal foam to realize the equipotential of the bed. For example, metal copper foam (5vol%), according to actual measurement and calculation, can achieve a potential difference of more than 1mV within a diameter of 230cm at a current density of 100mA/cm ² (this diameter is called an equipotential size), thereby achieving a large reaction The device is almost equipotential and avoids the occurrence of side reactions. When metal nickel foam is used, the equipotential size is smaller, but it can still be maintained above 55cm. In contrast, a packed bed composed of copper particles (0.1 mm) exhibits a potential difference of 1 mV or higher at a distance of 2 cm due to the degree of contact between particles. The conductivity of carbon foam is too low, but carbon-coated copper foam can be used to increase the conductivity. If the selectivity of the reaction is not very strict on the potential difference, a potential difference of 5 mV or even 10 mV can be accepted, and the above-mentioned equipotential diameter can be further expanded.

(6) The physical characteristics of the metal foam are optional and adjustable. There are many commercially available open-cell metal foams, including aluminum, iron, copper, nickel, zinc, manganese, lead, etc., the size of the open cells is between 10-140ppi, and the size of the pores is uniform. The internal metal surface area is huge and can fully contact with the reaction fluid. With the development of the metal foam processing industry, the above metal foam physical characteristics can now be customized. In addition, the internal surface of the metal foam can be further modified by electroplating, chemical replacement, vapor deposition, etc., such as tinning, galvanizing, and platinum plating on the inner surface of the copper foam, thereby changing the surface properties of the metal foam. If necessary, a larger specific electrode area, that is, the electrode area per unit volume, can also be obtained through surface modification (electroplating, vapor deposition, etc.) or by filling conductive catalyst particles.

(7) Convenient and flexible choice of catalyst. When carrying out liquid-phase electrochemical reaction, the diffusion speed of the liquid phase inside the catalyst particles is slow, and the external specific surface area of the catalyst has a great influence on the reaction, so try to choose particles with large pores or small particle sizes; while performing gas-phase reactions, The area inside the catalyst has a great influence on the reaction, and the catalyst particles with a large specific surface area should be selected as much as possible.

(8) The operation mode is similar to that of packed bed. The electrolyte containing reactants passes through the entire three-dimensional electrode bed, and reacts on the surface of the three-dimensional electrode and the surface of the catalyst. The electrochemical packed bed adopts the same sampling method as the traditional packed bed: when the liquid phase reaction is carried out, the sampling is taken from the bottom; when the feed has a gas phase, the sampling is injected from the top. Similarly, the electrochemical packed bed can also be operated at a specific pressure and temperature like a traditional packed bed, and it can also perform different reactions at different temperatures, voltages, and pressures in sections.

The invention is suitable for organic electrochemical synthesis, through the high specific electrode area, the current intensity under the limitation of current density is greatly improved, and the coupling effect between the electrocatalytic reaction on the foam electrode and the heterogeneous catalytic reaction on the catalyst particles inside the three-dimensional electrode, A significant improvement in the performance of the catalytic reaction can be achieved.

Description of drawings

Fig. 1 is the structural representation of common electrochemical packed bed reactor, and wherein, 1, metal foam layer, 2, electrode post, 1 and 2 collectively call three-dimensional electrode, constitute the anode (cathode) pole of electrochemical reactor, 3, The ion-conducting membrane, 4, the supporting electrode constituting the cathode (anode), and 5, the opening.

Fig. 2 is a schematic diagram of the layered structure of the metal foam, wherein, 6, the metal skeleton, 7, the cavity of the metal foam, 8, the catalyst particles, and 9, the pores of the metal foam.

Figure 3 is a schematic diagram of sampling in a common electrochemical packed bed reactor suitable for liquid phase sampling.

Figure 4 is a schematic diagram of sampling in a common electrochemical packed bed reactor suitable for gas-liquid or gas-phase sampling. .

Fig. 5 is a schematic diagram of reactions in which the whole reactor of the present invention operates at one voltage, with different types of electrode materials and catalysts in the packed bed, wherein the three-dimensional electrodes are segmented.

Fig. 6 is a reaction diagram showing that the reactor of the present invention works under different voltages, and the catalysts and electrode materials of each section are different, wherein, 10, the insulating sheet of the three-dimensional electrode, and 11, the insulating sheet of the supporting electrode.

Figure 7 shows the electrolytic water performance of copper foam and nickel foam.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

As shown in Figure 1 or 2, the electrochemical packed bed reactor of the present invention adopts a tubular packed bed structure. The electrode 101 is a three-dimensional electrode, including an electrode column in the center of the packed bed and a plurality of stacked metal foams radiating along the electrode column to the outer wall of the reactor. Catalyst particles are placed inside the metal foam; another electrode 102 is used as a supporting structure, It has openings to allow the electrolyte to pass through and contact the conductive film material 103 between the two electrodes.

Embodiment 1 Electrolysis of water

Metallic copper foam is used as the cathode, metal Ti mesh with iridium-tantalum coating is used as the anode, Nifion N117 cation exchange membrane is used, and dilute sulfuric acid (0.5mol/L) is used as the electrolyte of both the cathode and the anode. When the electrolysis voltage of the cathode and anode of the reactor is 4.0V, the current is 14A, the collection speeds of hydrogen and oxygen on both sides are 104ml/min and 52ml/min respectively, and the energy conversion efficiency is about 37% (see Figure 5). When the voltage is 2V, the current is 220mA, the energy efficiency is as high as 74%, and the production rates of hydrogen and oxygen are 1.67ml/min and 0.84ml/min. If metal nickel foam is used as the electrode material, the hydrogen evolution overvoltage can be reduced, thereby increasing the current intensity at the same voltage. For example, at 4V, the energy efficiency is 37%, the current intensity of nickel foam can reach 18A, and the gas extraction speed of hydrogen and oxygen can reach 133ml/min and 66ml/min; at 2V, the energy efficiency is 74%, nickel foam The current intensity is up to 1A, and the gas extraction rates of hydrogen and oxygen are 7.5ml/min and 3.8ml/min.

Example 2 Carbon dioxide (CO ₂ ) electrochemical reduction

Carbon dioxide is the main greenhouse gas and the goal of carbon neutrality. It is of great scientific and social significance to convert _CO2 into high-value organic compounds (methanol, formaldehyde, formic acid, ethanol) using low-cost electric energy obtained from renewable resources (wind power, hydropower, photovoltaics, etc.). In this embodiment, 12ml of surface-modified copper foam metal is used as the cathode of the electrochemical packed bed reactor, and 1M potassium bicarbonate solution (4ml/min) and CO _gas (10ml/min) are injected from the top of the packed bed reactor. The current intensity was adjusted to 100mA/cm ² to obtain the following product distribution (as shown in Table 1). A catalyst particle containing a transition metal (such as Ni, Cu, Zn, Fe, Ce, P, Pd or its oxide or its alloy) and a catalyst support (such as Al ₂ O ₃ , SiO ₂ , molecular sieve, activated carbon, etc.) Implanted and immobilized inside the surface-modified metallic copper foam bed, it was observed that the concentration of CO in the gas phase and the concentrations of formaldehyde and formic acid in the liquid phase were greatly increased, while the contents of hydrogen and _CO2 in the gas phase were greatly reduced. Table 1 presents the _CO2 electrochemical reduction product distribution, taking the catalyst containing Ni and activated carbon support as an example. The results showed that the catalyst enhanced the conversion of _CO2 to CO and organics.

Table 1 CO ₂ electrochemical reduction product distribution (unit mg/min)

Embodiment 3 Nitrobenzene electrochemical reduction

Nitrobenzene is a common organic compound, mostly used in the synthesis of dyes and pharmaceutical intermediates. Nitrobenzene can be electrochemically reduced to phenylhydroxylamine and aniline. Among them, the reduction potential of phenylhydroxylamine is about -0.4 to -0.6V, and that of aniline is about -1.3V. Copper metal foam is used to form an electrochemical reactor, potassium sulfate is used as catholyte, and dilute sulfuric acid is used as anolyte. Nitrobenzene and potassium sulfate solution were sonicated and injected from the bottom of the reactor. Phenylhydroxylamine can be obtained by controlling the cathode potential at around -0.58V, and the Faradaic efficiency can be obtained at a current density of 100mA/cm ² with a Faradaic efficiency of about 95%, and only a small amount of hydrogen is generated. The reaction rate of nitrobenzene in this electrochemical reactor can reach 6kg/L-day. Because the hydrogen evolution overpotential of the copper electrode is not high enough to reduce nitrobenzene to aniline. After electroplating Zn or Sn film or using metal zinc or metal nickel foam electrolysis, the reduction potential of the metal foam can be reduced to -1.3V or lower. Taking tin-plated metal copper foam as an example, nitrobenzene can be reduced to aniline at this potential, and the yield is about 2.5kg/L-day (Faraday efficiency is about 63%), but a large amount of hydrogen is still produced by-product, 0.13kg /L-day (Faraday efficiency close to 35%). In order to suppress hydrogen generation and increase the yield of aniline, a catalyst containing transition metal (Pd, Pt, Ni, Fe, Co, Cr, Ti or their alloys) and catalyst support (Al ₂ O ₃ , TiO ₂ , activated carbon, molecular sieve etc.) catalyst particles embedded in the metal foam. Taking the catalyst containing Ni and _TiO2 support as an example, the catalyst significantly increased the yield of aniline to 3.7 kg/L-day, and the hydrogen yield decreased to 0.1 kg/L-day. Because the amount of by-product hydrogen is still large, the structure and surface characteristics of the metal foam electrode and the formulation of the catalyst need to be further optimized.

The oxidative transformation of embodiment 4 methyl orange

Nitrobenzene, which often occurs in wastewater, was completely converted to _CO2 and water via electrochemical Fenton oxidation. Among them, molecular oxygen is electrochemically reduced to low-concentration hydrogen peroxide, and hydrogen peroxide generates OH radicals and Fe ³⁺ under the catalytic action of Fe ²⁺ ions. OH radicals have a very high oxidation potential (2.8V), second only to elemental fluorine. OH radicals indiscriminately convert organic matter in wastewater into _CO2 and water. Fe ³⁺ is reduced to Fe ²⁺ on the cathode surface. The traditional Fenton process requires iron ions to participate in the reaction, and then recovers iron ions through precipitation to avoid leakage and pollution of iron ions. In this embodiment, copper foam is used as the cathode, catalyst particles containing iron are fixed inside the copper foam, 0.05M potassium sulfate is added as the electrolyte, and the concentration of methyl orange is 100mg/L. The air and electrolyte injection rates were controlled at 5ml/min and 2ml/min respectively, the cathode potential was controlled at about -0.6V, and the current density was 10mA/cm ² . Adjust the volume of the electrochemical packed bed to 24ml, and the residence time at this time is 3.4 minutes, and the single-pass conversion rate of methyl orange can reach 90%, but more documents report that the electrochemical sewage treatment experimental device needs significantly more to achieve this conversion rate. long time.

Claims

An electrochemical packed bed reactor, characterized in that:

(1) Adopt tubular packed bed structure;

(2) One electrode is a three-dimensional electrode that constitutes the entire packed bed, and fluid flows in the electrode;

(3) Another electrode and another fluid are outside the three-dimensional electrode;

(4) There is a conductive film material between the two electrodes to separate the fluids on both sides.
The electrochemical packed bed reactor according to claim 1, wherein the three-dimensional electrode comprises an electrode column in the center of the packed bed and several layers of metal foams stacked along the electrode column to radiate to the outer wall of the reactor, so that Catalyst particles are placed inside the metal foam.
The electrochemical packed bed reactor according to claim 1, characterized in that the desired chemical reaction is carried out on the surface of the metal foam and on the catalyst particles.
The electrochemical packed bed reactor according to claim 2, characterized in that: the metal foam is a monolithic open-pore metal foam, and the size of the openings is between 5-200ppi; the three-dimensional electrodes are in an equipotential state , that is, the potential difference between any two points on the metal foam in the same packed bed is not more than 1mV, 5mV, 10mV or the maximum potential difference set according to the reaction that does not affect the reaction selectivity.
The electrochemical packed bed reactor according to claim 2, characterized in that, the catalyst is conductive or non-conductive; the catalyst particles are dispersed and fixed inside the metal foam; the conductive film material is ion An exchange membrane or a ceramic material with ion exchange function, the conductive membrane material is in close contact with the two electrodes, and is wetted or contacted by the fluid on both sides thereof.
The electrochemical packed bed reactor according to claim 1, wherein the two fluids are a mixture of liquid, gas or liquid and gas, and the liquid includes homogeneous liquid and heterogeneous liquid; reactor The placement direction and fluid flow direction are both vertical to the ground, or other non-horizontal directions; the fluid flows in the three-dimensional electrode; when there is gas or only gas in the sample, the top sample is taken; when there is no gas in the sample or the reaction generates gas, Bottom injection was used.
The electrochemical packed bed reactor according to claim 1, wherein the other electrode is a plate-shaped, strip-shaped, strip-shaped, sheet-shaped or mesh electrode with holes, or a three-dimensional electrode; The electrochemical packed bed reactor described above works at the same temperature and pressure, or performs segmental control, and the electrodes, catalysts and operating conditions of each segment are partly the same or completely different.
The electrochemical packed bed reactor according to claim 1, further comprising surface modification of the metal foam.
The application of the electrochemical packed bed reactor described in any one of claims 1 to 8 in electrochemical reaction or heterogeneous catalytic reaction.
The application according to claim 9, wherein said electrochemical reaction or heterogeneous catalytic reaction comprises electrolytic water reaction, electrochemical reduction reaction of carbon dioxide, electrochemical reduction reaction of nitrobenzene and oxidation conversion of methyl orange reaction.