Indigo electrochemical reduction reactor using micro-channel carbon felt electrode and indigo electrochemical reduction reaction method

Abstract

The invention provides an indigo electrochemical reduction reactor using a micro-channel carbon felt electrode and an indigo electrochemical reduction reaction method. A reaction device of the reactor comprises a cathode shell, an insulating spacer, a current collector, a micro-channel carbon felt electrode, a diaphragm, an oxygen evolution electrode, an anode channel and an anode shell, a micro-channel network through which a cathode solution flows is arranged in the micro-channel carbon felt electrode; the oxygen evolution electrode and the carbon felt channel electrode are arranged in parallel and are separated by a diaphragm; the current collector clings to the outer surface of the micro-channel carbon felt electrode; the insulating spacer clings to the outer surface of the current collector; the cathode shell clings to the outer surface of the insulating spacer; an anode channel is arranged between the oxygen evolution electrode and the anode shell, and an anode solution channel is arranged in the anode channel; and heat exchange pipelines are arranged in the cathode shell and the anode shell. The invention further provides an indigo electrochemical reduction reaction method based on the reactor. According to the invention, direct electro-reduction of indigo can be realized in the presence of a chemical reducing agent.

Description

Technical Field

[0001] The invention relates to an indigo electrochemical reduction reactor using a microchannel carbon felt electrode and an indigo electrochemical reduction reaction method, belonging to the technical field of electrochemistry. Background Art

[0002] Indigo is a compound widely used in the textile industry. During the dyeing process, it needs to be reduced to a water-soluble sodium salt of leuco under alkaline conditions in order to effectively combine with clothing fibers, and then oxidized to develop color. The caustic soda insurance powder method is commonly used to reduce indigo. Its reaction is complete and fast, but it will produce a large amount of waste salt, pollute water sources, and the raw materials are easy to decompose and flammable, which is a process to be eliminated. Current research focuses on finding other alternative reducing agents, such as thiourea dioxide, sugar, hydroxyacetone, divalent iron salt complexes, sodium borohydride, etc., but all of the above substances have problems such as high cost, generation of chemical pollutants, and poor reduction effect. Catalytic hydrogenation in alkaline aqueous solution to reduce indigo can greatly reduce the amount of insurance powder used, but due to the high risk of explosion and fire, the hydrogenation reduction process cannot be used directly in the dyeing plant and can only be provided directly by the dye supplier. The water content of the resulting solution is greater than 60%, which significantly increases the transportation cost. Therefore, it is necessary to design a new indigo reduction reactor to safely and efficiently produce leuco sodium salt solution without the need for a reducing agent.

[0003] Direct electrochemical reduction of indigo is a green synthesis method for sodium salt of leucochrome, which directly uses the electrons provided by the electrode as a reducing agent without the use of hydrogen. The existing electrochemical reduction indigo reactor uses fixed or fluidized carbon particles as the anode (such as US8333881), which has engineering problems such as low contact efficiency between the reactant and the cathode surface, difficulty in regulating the flow state in the reactor, high power consumption, and low production efficiency. Summary of the invention

[0004] In order to solve the above technical problems, the object of the present invention is to provide an indigo electrochemical reduction reactor, which is provided with a microchannel carbon felt electrode inside the reactor, and can provide direct electroreduction of indigo without a chemical reducing agent.

[0005] The present invention also provides an indigo electrochemical reduction reaction method based on the indigo electrochemical reduction reactor.

[0006] To achieve the above object, the present invention provides an indigo electrochemical reduction reactor using a microchannel carbon felt electrode, wherein the indigo electrochemical reduction reactor comprises a reaction device;

[0007] The reaction device comprises a cathode shell, an insulating gasket, a current collector, a microchannel carbon felt electrode, a diaphragm, an oxygen evolution electrode, an anode channel, and an anode shell which are arranged in sequence;

[0008] The microchannel carbon felt electrode is provided with a microchannel network for cathode solution circulation inside;

[0009] The oxygen evolution electrode and the microchannel carbon felt electrode are arranged in parallel, separated by the diaphragm;

[0010] The current collector is arranged closely to the outer surface of the microchannel carbon felt electrode;

[0011] The insulating gasket is arranged closely against the outer surface of the current collector;

[0012] The cathode housing is arranged close to the outer surface of the insulating gasket;

[0013] The anode channel is provided between the oxygen evolution electrode and the anode shell, and an anode solution channel is provided inside the anode channel;

[0014] Heat exchange pipes are respectively arranged inside the cathode shell and inside the anode shell.

[0015] In the above-mentioned indigo electrochemical reduction reactor, preferably, the indigo electrochemical reduction reactor further comprises a power supply, a cathode feed pump, a cathode solution storage tank, an anode solution storage tank, and an anode feed pump;

[0016] The current collector and the oxygen evolution electrode are connected to the cathode and anode of the power supply respectively. Specifically, the current collector and the oxygen evolution electrode can be connected to the cathode terminal and the anode terminal respectively, and then connected to the cathode and anode of the power supply;

[0017] The outlet of the cathode solution storage tank is connected to the inlet of the cathode feed pump, the outlet of the cathode feed pump is connected to the inlet of the microchannel network, and the outlet of the microchannel network is connected to the inlet of the cathode solution storage tank;

[0018] The outlet of the anode solution storage tank is connected to the inlet of the anode feed pump, the outlet of the anode feed pump is connected to the inlet of the anode solution channel, and the outlet of the anode solution channel is connected to the inlet of the anode solution storage tank.

[0019] In the above indigo electrochemical reduction reactor, preferably, the microchannel carbon felt electrode is made of calcined modified carbon felt.

[0020] Carbon felt is a carbon material with high conductivity, high porosity and large specific surface area. Since the pores inside the carbon felt are tiny, the present invention modifies the carbon felt electrode and implements a sophisticated fluid channel structure design, so that the carbon felt is fully in contact with the indigo solution and uniformly adsorbs the indigo particles to undergo a reduction reaction, which is an important means to make the carbon felt electrode practical. Based on this, the present invention proposes a cathode design scheme for an indigo direct electrochemical reduction reactor, forms a complete electrochemical reactor structure with the cathode as the core, and provides a new indigo electrochemical reduction reactor based on a microchannel carbon felt electrode.

[0021] The present invention applies micro-chemical technology to the direct electrochemical reduction of indigo, designs and constructs a microchannel carbon felt electrode. By adding microchannels in the carbon felt electrode, the reliability and stability of the fluid flow can be guaranteed, and the flow state in the reactor can be easily regulated; at the same time, by utilizing its high specific surface area characteristics, it can accelerate electron transfer, strengthen mass transfer, and improve the contact efficiency between the reactant and the cathode, thereby realizing direct electrochemical reduction of indigo without a chemical reducing agent.

[0022] In the above indigo electrochemical reduction reactor, preferably, the geometric area of ​​the calcined modified carbon felt is 1-5000 cm 2 , which can be adjusted according to the reactor size.

[0023] In the above indigo electrochemical reduction reactor, preferably, the calcined modified carbon felt has a thickness of 0.5-10 mm.

[0024] In the above indigo electrochemical reduction reactor, preferably, the porosity of the calcined modified carbon felt is >30%.

[0025] In the above-mentioned indigo electrochemical reduction reactor, preferably, the modification method of the calcined modified carbon felt comprises the following steps: washing and degreasing the carbon felt (for example, washing and degreasing with acetone and deionized water in sequence), drying (for example, drying at 80°C for 24 hours), and then calcining at 300-800°C in an acetic acid or oxygen atmosphere for 1-3 hours to complete the modification.

[0026] In the above-mentioned indigo electrochemical reduction reactor, the modified carbon felt is first machined to form the required fluid channels, and then stacked in parallel, cross or staggered to form a three-dimensional electrode structure, and an inlet, outlet and fluid distribution structure are set at the same time. The microchannel network in the carbon felt electrode serves as a cathode solution channel. When the alkaline aqueous solution containing indigo flows through the microchannel network formed by the stacking of carbon felt, the indigo particles are adsorbed by the carbon felt, and a reduction reaction occurs to convert them into water-soluble leuco sodium salts. Preferably, the cathode solution channel is selected from one or more combinations of straight channels, curved channels (such as serpentine channels), broken line channels, cross-grid channels, and dendritic channels. The cross-section of the cathode solution channel is preferably rectangular; the width and depth of the rectangle can be 0.5-5 mm, respectively. In the reactor, multiple cathode solution channels can be set at the same time, and these cathode solution channels can be interconnected to form a network or can be parallel channels.

[0027] In the above-mentioned indigo electrochemical reduction reactor, preferably, the microchannel network is located inside the carbon felt and is placed in the center along the thickness direction of the carbon felt. More preferably, the microchannel network is formed by engraving hollow microchannels on the central carbon felt, and then laminating the carbon felt without microchannels on both sides with the carbon felt containing hollow microchannels.

[0028] In the above indigo electrochemical reduction reactor, preferably, the spacing between the microchannels in the microchannel network on the same plane is less than 10 mm.

[0029] In the above-mentioned indigo electrochemical reduction reactor, preferably, the cathode solution channel end is provided with an inlet, an outlet and a dendritic fluid distribution structure, which are respectively used for inputting cathode solution, outputting cathode solution and distributing and transporting cathode solution between multiple cathode solution channels.

[0030] In the above-mentioned indigo electrochemical reduction reactor, preferably, the oxygen evolution electrode is used as a reaction anode, which is a mesh electrode loaded with a metal oxide electrocatalyst. The area of ​​the oxygen evolution electrode and the microchannel carbon felt electrode must be equal. The edge of the oxygen evolution electrode can be connected to the anode wire, and the anode channel is a parallel straight channel structure. An alkaline aqueous solution is used as the anode liquid, and an oxygen precipitation reaction occurs to form oxygen. The carrier of the oxygen evolution electrode can be selected from one of titanium, nickel, titanium-niobium alloy, and titanium-zirconium alloy; the metal oxide electrocatalyst is selected from one of iridium oxide, ruthenium oxide, iron oxide, and nickel oxide, or a combination of two or more thereof.

[0031] In the above-mentioned indigo electrochemical reduction reactor, preferably, the diaphragm is a proton exchange membrane. During the reaction, the diaphragm should completely cover the oxygen evolution electrode and the edge of the carbon felt channel electrode. The proton exchange membrane can be selected from the Nafion membrane series, such as one of Nafion N115, Nafion N117, Nafion N1110, Nafion N324, Nafion N424, and Nafion N438.

[0032] In the above-mentioned indigo electrochemical reduction reactor, the current collector is used to power the microchannel carbon felt electrode. Preferably, the current collector is a metal sheet structure; more preferably, the material of the current collector is selected from one of titanium, nickel, 316L stainless steel, and Hastelloy.

[0033] In the above indigo electrochemical reduction reactor, preferably, the thickness of the current collector is 0.1-1 mm.

[0034] In the above indigo electrochemical reduction reactor, the insulating gasket is used to ensure the insulation between the current collector and the cathode housing. Preferably, the insulating gasket is made of one of polytetrafluoroethylene, polytrifluoroethylene and polypropylene. The thickness of the insulating gasket may be 0.1-0.5 mm.

[0035] In the above-mentioned indigo electrochemical reduction reactor, the anode channel is used to transport the anode electrolyte to the anode and ensure the insulation between the anode shell and the anode shell. Preferably, the width and depth of the anode channel are 1-10 mm respectively. The material of the anode channel is an insulating material, for example, one or a combination of two or more selected from polytetrafluoroethylene, polytrifluoroethylene, PEEK, and polyvinyl chloride.

[0036] In the above-mentioned indigo electrochemical reduction reactor, the cathode housing and the anode housing are fasteners with heat exchange pipes, which are used to support the overall structure of the reactor and control the reaction temperature. The material of the cathode housing and the anode housing is preferably a material with good thermal conductivity; more preferably, the material of the cathode housing and the anode housing is selected from one of stainless steel, copper, aluminum, and titanium. The heat exchange pipes arranged inside the cathode housing and the anode housing are used to control the reaction temperature through a heat exchange medium, and these heat exchange pipes can be connected to an external heat exchange medium device.

[0037] The present invention also provides an indigo electrochemical reduction reaction method, which is carried out by using the indigo electrochemical reduction reactor using the microchannel carbon felt electrode.

[0038] According to a specific embodiment of the present invention, preferably, the indigo electrochemical reduction reaction method comprises the following steps:

[0039] The cathode solution and the anode solution are respectively passed into the microchannel carbon felt electrode and the anode channel;

[0040] A heat exchange medium is introduced into the cathode housing and the anode housing respectively for heat exchange;

[0041] When the reaction temperature reaches 30-70°C and the flow rate is stable, power is turned on to react, where the current density is not less than 50mA / cm 2 After the reaction is completed, stop the power supply, cut off the heat exchange medium, and end the reaction after the material is vented.

[0042] According to a specific embodiment of the present invention, preferably, the indigo electrochemical reduction reaction method comprises the following specific steps:

[0043] The cathode solution is input into the microchannel network in the microchannel carbon felt electrode, and the anode solution is input into the anode solution channel of the anode channel; the circulation of the cathode solution can be realized by means of the circulation path formed by the cathode solution storage tank, the cathode feed pump, and the cathode microchannel network, and the circulation of the anode solution can be realized by means of the circulation path formed by the anode solution storage tank, the anode feed pump, and the anode solution channel;

[0044] Inputting heat exchange medium into the first heat exchange pipe in the cathode housing and the second heat exchange pipe in the anode housing respectively to heat the cathode solution and the anode solution;

[0045] When the reaction temperature (set temperature between 30-70°C) is reached and the flow rates of the cathode solution and the anode solution are stable, turn on the power supply (e.g., electrochemical workstation) to react, wherein the current density of the power supply is not less than 50 mA / cm 2 ;

[0046] After a certain reaction time, turn off the power, cut off the heat exchange medium, and end the reaction after venting the materials.

[0047] According to a specific embodiment of the present invention, preferably, during the reaction process, the current density of the power supply is controlled to be 50-110 mA / cm 2 .

[0048] According to a specific embodiment of the present invention, preferably, the flow rates of the cathode solution and the anode solution are respectively controlled to be 5-5000 mL / min.

[0049] According to a specific embodiment of the present invention, preferably, the cathode solution is an alkaline aqueous solution containing indigo particles; preferably, based on the volume of the alkaline aqueous solution containing indigo particles, the concentration of indigo is 10-100 g / L, and the concentration of the alkaline compound is 0.2-2 mol / L.

[0050] According to a specific embodiment of the present invention, preferably, the anode solution is an alkaline aqueous solution free of indigo, and preferably, the concentration of the alkaline compound is 0.5-2 mol / L based on the volume of the alkaline aqueous solution free of indigo;

[0051] According to a specific embodiment of the present invention, preferably, the alkaline compound used in the cathode solution and the anode solution is the same, and the alkaline compound can be selected from one or a combination of two or more of NaOH, KOH, Na2CO3, K2CO3, Na3PO4, K3PO4.

[0052] The technical solution of the present invention solves the problems of low contact efficiency between reactants and cathode surfaces and difficulty in regulating the flow state in the reactor in traditional indigo reduction electrochemical reactors. The fluid distribution state in the cathode chamber is improved through modification and channel structure design, the adsorption of indigo particles and the electrochemical reaction process are enhanced, the mass transfer efficiency between the electrode surface and the reactants is increased, the energy consumption of the reduction reaction is reduced, and direct electroreduction of indigo is achieved without a chemical reducing agent.

[0053] Compared with the prior art, the present invention has the following advantages:

[0054] (1) The present invention regulates and optimizes the cathode liquid flow field distribution through calcination modification and careful design of the microchannel structure, thereby improving the adsorption effect of indigo in the cathode microchannel network, enhancing the contact between the reactants and the electrode, reducing the reaction potential, and improving the reaction efficiency.

[0055] (2) The present invention achieves high-efficiency electrochemical reduction of indigo without using a chemical reducing agent. The reaction is carried out at normal pressure and does not use hydrogen, thus avoiding the subsequent separation step. The reaction is safe and controllable, and the generated water-soluble leuco-sodium salt can be directly used for dyeing. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a schematic structural diagram of the reaction device of the indigo electrochemical reduction reactor using microchannel carbon felt electrodes provided in Example 1.

[0057] Figure 2 This is a schematic diagram of the structure of an indigo electrochemical reduction reactor using microchannel carbon felt electrodes provided in Example 1.

[0058] Figure 3 This is a schematic diagram of the three-dimensional structure of the indigo electrochemical reduction reactor using microchannel carbon felt electrodes provided in Example 1.

[0059] Figure 4 A schematic diagram of another structural connection method of the indigo electrochemical reduction reactor using microchannel carbon felt electrodes provided in Example 1.

[0060] Figure 5This is a schematic diagram of the structure of the serpentine channel.

[0061] Figure 6 Schematic diagram of the stacking method of microchannel carbon felt electrodes.

[0062] Figure 7 Schematic diagram of the structure of the dendritic channel.

[0063] Figure 8 This is a schematic diagram of the structure of a straight channel.

[0064] Fig. 9 It is a structural diagram of a broken line channel.

[0065] Description of main figures:

[0066] 1-microchannel carbon felt electrode; 2-diaphragm; 3-oxygen evolution electrode; 4-anode channel; 5-cathode shell; 6-anode shell; 7-current collector; 8-insulating gasket; 9-cathode terminal; 10-anode terminal; 11-microchannel network; 12-anode solution channel; 13-first heat exchange pipeline; 14-second heat exchange pipeline; 15-power supply; 16-cathode feed pump; 17-cathode solution storage tank; 18-anode solution storage tank; 19-anode feed pump; 20-external heat exchange medium equipment. DETAILED DESCRIPTION

[0067] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0068] In the following examples and comparative examples, the indigo conversion rate and current efficiency were calculated according to the following formula:

[0069] Indigo conversion rate = (the amount of indigo in the cathode liquid after the reaction is completed (mol) / the amount of indigo in the cathode liquid at the beginning of the reaction (mol)) × 100%;

[0070] Current efficiency = (2 × the amount of indigo in the cathode liquid after the reaction (mol) × 96485 (C / mol)) / (current density (A / cm 2 )×electrode area (cm 2 )×electrolysis time (s))×100%.

[0071] Example 1

[0072] This embodiment provides an indigo electrochemical reduction reactor comprising a carbon felt channel electrode, the structure of which is as follows: Figure 1 , Figure 2 , Figure 3 shown.

[0073] The indigo electrochemical reduction reactor comprises a reaction device, a power supply 15, a cathode feed pump 16, a cathode solution storage tank 17, an anode solution storage tank 18, and an anode feed pump 19;

[0074] The reaction device includes a cathode housing 5, an insulating gasket 8, a current collector 7, a microchannel carbon felt electrode 1, a diaphragm 2, an oxygen evolution electrode 3, an anode channel 4, and an anode housing 6, which are arranged in sequence;

[0075] in:

[0076] A cathode solution channel is provided inside the microchannel carbon felt electrode 1, specifically a microchannel network 11;

[0077] The oxygen evolution electrode 3 is arranged in parallel with the microchannel carbon felt electrode 1, and is separated by a diaphragm 2;

[0078] The current collector 7 is arranged close to the outer surface of the microchannel carbon felt electrode 1, and one end of the current collector 7 is connected to a cathode terminal 9;

[0079] The insulating gasket 8 is arranged close to the outer surface of the current collector 7;

[0080] The cathode housing 5 is arranged close to the outer surface of the insulating gasket 8, and a first heat exchange pipe 13 is arranged inside the cathode housing 5;

[0081] An anode channel 4 is provided between the oxygen evolution electrode 3 and the anode housing 6, and one end of the oxygen evolution electrode 3 is connected to an anode terminal 10, and an anode solution channel 12 is provided inside the anode channel 4;

[0082] A second heat exchange pipe 14 is provided inside the anode housing 6;

[0083] The cathode terminal 9 and the anode terminal 10 are connected to the cathode and anode of the power source 15 respectively;

[0084] The outlet of the cathode solution storage tank 17 is connected to the inlet of the cathode feed pump 16, the outlet of the cathode feed pump 16 is connected to the inlet of the microchannel network 11, and the outlet of the microchannel network 11 is connected to the inlet of the cathode solution storage tank 17;

[0085] The outlet of the anode solution storage tank 18 is connected to the inlet of the anode feed pump 19, the outlet of the anode feed pump 19 is connected to the inlet of the anode solution channel 12, and the outlet of the anode solution channel 12 is connected to the inlet of the anode solution storage tank 18; Figure 4 Shown is a schematic diagram of another structural connection method, in which some structures are omitted;

[0086] The first heat exchange pipe 13 and the second heat exchange pipe 14 are respectively connected to the external heat exchange medium equipment 20;

[0087] The microchannel carbon felt electrode 1 is made of calcined modified carbon felt, wherein the preparation method of the calcined modified carbon felt comprises: cleaning and degreasing the 1 mm thick carbon felt with acetone and deionized water in an ultrasonic bath in turn, drying at 80°C for 24 hours, and then calcining at 600°C for 2 hours in an acetic acid atmosphere to obtain the calcined modified carbon felt.

[0088] The specific surface areas of the carbon felt before and after the treatment were measured by BET, and the specific surface areas before and after the treatment were calculated to be 4.09 m 2 / g and 60.28m 2 / g, measured by mercury intrusion method: the porosity of the calcined modified carbon felt is 57%.

[0089] The microchannel carbon felt electrode 1 is made by the following steps: a serpentine channel (such as a microchannel) with a width of 1 mm and a depth (i.e., the depth of the channel penetrating into the surface of the carbon felt during the processing) of 1 mm is formed on a calcined modified carbon felt (with an outer shape of 10 mm×10 mm×1 mm) by mechanical processing. Figure 5 As shown), three layers of carbon felt containing channels and connecting holes are further stacked (as shown Figure 6 ) a cathode solution channel, with the stacked carbon felt serving as a cathode;

[0090] The oxygen evolution electrode 3 is a titanium mesh loaded with iridium dioxide, wherein the size of the titanium mesh is 10 mm×10 mm×0.2 mm, and the loading amount of iridium dioxide is 2 mg / cm 2 , based on the total area of ​​the titanium mesh;

[0091] The separator 2 is Nafion N324 with a size of 12 cm×12 cm.

[0092] The indigo electrochemical reduction reaction is carried out using an indigo electrochemical reduction reactor comprising a microchannel carbon felt electrode, and is carried out according to the following steps:

[0093] 100 mL of an aqueous NaOH solution containing 1 g of indigo and a NaOH concentration of 2 mol / L was used as the cathode solution, and 100 mL of an aqueous NaOH solution with a concentration of 2 mol / L was used as the anode solution; before electrolysis, nitrogen was passed through the cathode solution for 30 minutes to remove oxygen in the solution;

[0094] The cathode solution in the cathode solution storage tank 17 is fed into the microchannel network 11 in the microchannel carbon felt electrode 1 through the cathode feed pump 16, and the flow rate is set to 5 mL / min;

[0095] The anode solution in the anode solution storage tank 18 is fed into the anode solution channel 12 of the anode channel 4 through the anode feed pump 19, and the flow rate is set to 5 mL / min;

[0096] The circulating water is respectively input into the first heat exchange pipe 13 in the cathode housing 5 and the second heat exchange pipe 14 in the anode housing 6 to heat the cathode solution and the anode solution. The temperature of the circulating water is 50°C.

[0097] When the reaction temperature reaches 50°C and the flow rates of the cathode solution and the anode solution are stable, turn on the power supply (e.g., electrochemical workstation) to react, wherein the current density of the power supply is 50 mA / cm 2 ;

[0098] After 4 hours of electrolysis, the electrolysis was stopped, and the amount of indigo in the cathode solution was determined by potentiometric titration to calculate the conversion rate of indigo and the current efficiency.

[0099] The amount of indigo in the cathode solution obtained by potentiometric titration was 3.57 mmol. Calculation showed that the conversion rate of indigo was 93.5% and the current efficiency was 95.6%.

[0100] Example 2

[0101] The difference between Example 2 and Example 1 is that the current density is controlled at 110 mA / cm 2 After 2 hours of electrolysis, the electrolysis was stopped, and the amount of indigo in the cathode liquid was determined by potentiometric titration. The conversion rate of indigo and the current efficiency were calculated. The rest was the same as in Example 1.

[0102] The amount of indigo in the cathode liquid obtained by potentiometric titration was 3.74 mmol. The conversion rate of indigo was calculated to be 98.2% and the current efficiency was 91.2%.

[0103] Comparative Example 1

[0104] The difference between Comparative Example 1 and Example 2 is that the reaction channel is made of carbon felt that has not been treated in Example 1, and the current density is controlled to 50 mA / cm 2 After 4 hours of electrolysis, the electrolysis was stopped, and the amount of indigo in the cathode liquid was determined by potentiometric titration. The conversion rate of indigo and the current efficiency were calculated. The rest was the same as in Example 1.

[0105] The results show that compared with Example 1, the reaction tank voltage was increased by 1.8 V, water electrolysis occurred, the indigo conversion rate was reduced to 52.0%, and the current efficiency was 53.2%.

[0106] Comparative Example 2

[0107] In this comparative example 2, the reaction device of comparative example 1 was used to reduce the current density to 20 mA / cm 2 , obtain a cell pressure similar to that in Example 1, stop electrolysis after 10 hours of electrolysis, and the rest is the same as in Example 1.

[0108] The results showed that the conversion rate of indigo was 92.0% and the current efficiency was 94.1%.

[0109] By comparing the experimental results of Comparative Example 2 with those of Example 1, it can be seen that the specific surface area of ​​the carbon felt increases after treatment, thereby improving the reaction efficiency.

[0110] Example 3

[0111] The difference between Example 3 and Example 1 is that 100 mL of NaOH aqueous solution containing 2 g of indigo and a NaOH concentration of 2 mol / L is used as the cathode solution, and 100 mL of NaOH aqueous solution with a concentration of 2 mol / L is used as the anode solution; the current density is controlled at 50 mA / cm 2 After 8 hours of electrolysis, the electrolysis was stopped and the conversion rate and current efficiency of indigo were calculated. The rest was the same as in Example 1.

[0112] The results showed that the conversion rate of indigo was 91.7% and the current efficiency was 93.7%.

[0113] By comparing the experimental results of Example 3 with those of Example 1, it can be seen that appropriately increasing the content of the reactant indigo mainly affects the reaction time.

[0114] Example 4

[0115] The difference between Example 4 and Example 1 is that the temperature of the circulating water is 30° C.; the electrolysis is stopped after 4 hours of electrolysis, and the conversion rate and current efficiency of indigo are calculated. The rest is the same as Example 1.

[0116] Calculations show that the conversion rate of indigo is 91.2% and the current efficiency is 93.2%.

[0117] Example 5

[0118] The difference between Example 5 and Example 1 is that the temperature of the heat exchange device is set to 70° C. for heat preservation; the electrolysis is stopped after 4 hours of electrolysis, and the conversion rate and current efficiency of indigo are calculated. The rest is the same as Example 1.

[0119] Calculations show that the conversion rate of indigo is 87.6% and the current efficiency is 89.5%.

[0120] Examples 6-12

[0121] The difference between Examples 6-12 and Example 1 is that the carbon felt calcination temperature and calcination time are different, and the rest are the same as Example 1. The specific parameters and reaction effects are shown in Table 1.

[0122] Table 1

[0123] Serial number Calcination temperature / ℃ Calcination time / h <![CDATA[Specific surface area / m 2 / g]]> Indigo conversion rate / % Example 6 300 2 22.34 57.5 Example 7 400 2 30.68 60.3 Example 8 500 2 55.29 88.2 Example 9 700 2 100.84 86.2 Example 10 800 2 120.81 82.7 Embodiment 11 600 1 32.34 61.3 Example 12 600 3 80.95 92.2

[0124] Comparative Example 3

[0125] The difference between Comparative Example 3 and Example 6 is that the calcination temperature is reduced to 200°C, and the measurement results show that the specific surface area of ​​the carbon felt is only 5.24m 2 / g, which is basically the same as the untreated carbon felt; the current density is controlled at 50mA / cm 2 , electrolysis was stopped after 4 hours, and the rest was the same as in Example 6.

[0126] Calculations show that the conversion rate of indigo is 55.1% and the current efficiency is only 56.4%.

[0127] Comparative Example 4

[0128] The difference between Comparative Example 4 and Example 6 is that the calcination temperature is increased to 1000° C., and the rest is the same as Example 6.

[0129] Results There was a small amount of fragmentation on the surface carbon felt, the material became sparse and highly graphitized, and was not successfully processed into a reaction channel.

[0130] Embodiment 13

[0131] The difference between this embodiment 13 and embodiment 1 is that the serpentine microchannel is replaced with a dendritic channel (such as Figure 7 After 4 hours of electrolysis, the electrolysis was stopped and the conversion rate and current efficiency of indigo were calculated. The rest were the same as in Example 1.

[0132] Calculations show that the conversion rate of indigo is 90.6% and the current efficiency is 92.6%.

[0133] Embodiment 14

[0134] The difference between this embodiment 14 and embodiment 1 is that the serpentine microchannel is replaced with a straight channel (such as Figure 8 After 4 hours of electrolysis, the electrolysis was stopped and the conversion rate and current efficiency of indigo were calculated. The rest were the same as in Example 1.

[0135] The results showed that the conversion rate of indigo was 91.4% and the current efficiency was 93.4%.

[0136] Embodiment 15

[0137] The difference between this embodiment 15 and embodiment 1 is that the serpentine microchannel is replaced with a zigzag channel (such as Fig. 9 After 4 hours of electrolysis, the electrolysis was stopped and the conversion rate and current efficiency of indigo were calculated. The other parameters were the same as those in Example 1.

[0138] The results showed that the conversion rate of indigo was 93.1% and the current efficiency was 95.2%.

[0139] Comparative Example 5

[0140] In comparative example 5, the microchannel carbon felt electrode 1 in example 1 is removed, leaving a 10mm×10mm×2mm cavity, in which solid carbon particles with a diameter of 2mm are tightly filled and closely attached to the current collector 7, and the carbon particle bed is connected to the inlet and outlet of the cathode solution.

[0141] The oxygen evolution electrode 3 is a titanium mesh loaded with iridium dioxide, wherein the size of the titanium mesh is 10 mm×10 mm×0.2 mm, and the loading amount of iridium dioxide is 2 mg / cm 2 , based on the total area of ​​the titanium mesh;

[0142] The separator 2 is Nafion N324 with a size of 12 cm×12 cm.

[0143] The indigo electrochemical reduction reaction was carried out using the indigo electrochemical reduction reactor of this comparative example 5, and the steps were as follows:

[0144] 100 mL of an aqueous NaOH solution containing 1 g of indigo and a NaOH concentration of 2 mol / L was used as the cathode solution, and 100 mL of an aqueous NaOH solution with a concentration of 2 mol / L was used as the anode solution; before electrolysis, nitrogen was passed through the cathode solution for 30 minutes to remove oxygen in the solution;

[0145] The cathode solution in the cathode solution storage tank 17 is fed into the carbon particle bed through the cathode feed pump 16, and the flow rate is set to 5 mL / min;

[0146] The anode solution in the anode solution storage tank 18 is fed into the anode solution channel 12 of the anode channel 4 through the anode feed pump 19, and the flow rate is set to 5 mL / min;

[0147] The circulating water is respectively input into the first heat exchange pipe 13 in the cathode housing 5 and the second heat exchange pipe 14 in the anode housing 6 to heat the cathode solution and the anode solution. The temperature of the circulating water is 50°C.

[0148] When the reaction temperature reaches 50°C and the flow rates of the cathode solution and the anode solution are stable, the power supply (e.g., electrochemical workstation) is turned on to carry out the reaction. At the same voltage as in Example 1, the current density is only 10 mA / cm 2 ;

[0149] After 4 hours of electrolysis, the electrolysis was stopped and the conversion rate of indigo and the current efficiency were calculated.

[0150] Calculations show that the conversion rate of indigo is 25.2% and the current efficiency is 97%.

[0151] By comparing the experimental results of Comparative Example 5 and Example 1, it can be seen that the low specific surface area of ​​the carbon particles will limit the improvement of the reaction efficiency.

Claims

1. An indigo electrochemical reduction reactor using microchannel carbon felt electrodes, wherein: The indigo electrochemical reduction reactor includes a reaction device; The reaction device comprises a cathode housing (5), an insulating gasket (8), a current collector (7), a microchannel carbon felt electrode (1), a diaphragm (2), an oxygen evolution electrode (3), an anode channel (4), and an anode housing (6) which are arranged in sequence; The microchannel carbon felt electrode (1) is provided with a microchannel network (11) inside for the cathode solution to circulate; The oxygen evolution electrode (3) and the microchannel carbon felt electrode (1) are arranged in parallel, separated by the diaphragm (2); The current collector (7) is arranged in close contact with the outer surface of the microchannel carbon felt electrode (1); The insulating gasket (8) is arranged in close contact with the outer surface of the current collector (7); The cathode housing (5) is arranged in close contact with the outer surface of the insulating gasket (8); The anode channel (4) is provided between the oxygen evolution electrode (3) and the anode housing (6), and an anode solution channel (12) is provided inside the anode channel (4); Heat exchange pipes are respectively provided inside the cathode housing (5) and inside the anode housing (6).

2. The indigo electrochemical reduction reactor according to claim 1, wherein: The indigo electrochemical reduction reactor further comprises a power supply (15), a cathode feed pump (16), a cathode solution storage tank (17), an anode solution storage tank (18), and an anode feed pump (19); The current collector (7) and the oxygen evolution electrode (3) are respectively connected to the cathode and anode of the power supply (15); The outlet of the cathode solution storage tank (17) is connected to the inlet of the cathode feed pump (16), the outlet of the cathode feed pump (16) is connected to the inlet of the microchannel network (11), and the outlet of the microchannel network (11) is connected to the inlet of the cathode solution storage tank (17); The outlet of the anode solution storage tank (18) is connected to the inlet of the anode feed pump (19), the outlet of the anode feed pump (19) is connected to the inlet of the anode solution channel (12), and the outlet of the anode solution channel (12) is connected to the inlet of the anode solution storage tank (18).

3. The indigo electrochemical reduction reactor according to claim 1, wherein: The microchannel carbon felt electrode (1) is made of calcined and modified carbon felt; Preferably, the geometric area of ​​the calcined modified carbon felt is 1-5000 cm 2 ; Preferably, the thickness of the calcined modified carbon felt is 0.5-10 mm; Preferably, the porosity of the calcined modified carbon felt is greater than 30%; Preferably, the modification method of the calcined modified carbon felt comprises the following steps: washing, degreasing, and drying the carbon felt, and then calcining it at 300-800° C. for 1-3 hours in an acetic acid or oxygen atmosphere to complete the modification.

4. The indigo electrochemical reduction reactor according to claim 3, wherein: The microchannels in the microchannel network (11) are selected from one or a combination of two or more of a straight channel, a curved channel, a broken line channel, a cross-grid channel, and a dendritic channel; The microchannel network (11) is located inside the carbon felt and is placed in the center along the thickness direction of the carbon felt; preferably, the microchannel network (11) is formed by engraving hollow microchannels on the central carbon felt, and then laminating the carbon felt without microchannels on both sides with the carbon felt containing hollow microchannels; Preferably, the cross-section of the microchannels in the microchannel network (11) is rectangular; more preferably, the width and depth of the rectangle are 0.5-5 mm respectively; Preferably, the spacing between the microchannels in the microchannel network (11) on the same plane is less than 10 mm; Preferably, the microchannel network (11) is provided with an inlet, an outlet and a dendritic fluid distribution structure at the end.

5. The indigo electrochemical reduction reactor according to claim 1, wherein: The oxygen evolution electrode (3) is a mesh electrode loaded with a metal oxide electrocatalyst; Preferably, the carrier of the oxygen evolution electrode (3) is selected from one of titanium, nickel, titanium-niobium alloy, and titanium-zirconium alloy; the metal oxide electrocatalyst is selected from one of iridium oxide, ruthenium oxide, iron oxide, and nickel oxide, or a combination of two or more thereof; Preferably, the area of ​​the oxygen evolution electrode (3) is equal to that of the microchannel carbon felt electrode (1).

6. The indigo electrochemical reduction reactor according to claim 1, wherein: The diaphragm (2) is a proton exchange membrane; preferably, the proton exchange membrane is selected from one of Nafion N115, Nafion N117, Nafion N1110, Nafion N324, Nafion N424, and Nafion N438; And / or, the current collector (7) is a metal sheet structure; preferably, the material of the current collector (7) is selected from one of titanium, nickel, 316L stainless steel, and Hastelloy; preferably, the thickness of the current collector (7) is 0.1-1 mm; And / or, the material of the insulating gasket (8) is selected from one of polytetrafluoroethylene, polytrifluoroethylene, and polypropylene; preferably, the thickness of the insulating gasket (8) is 0.1-0.5 mm.

7. The indigo electrochemical reduction reactor according to claim 1, wherein: The width and depth of the anode channel (4) are 1-10 mm respectively; Preferably, the material of the anode channel (4) is an insulating material, and more preferably, the insulating material is selected from one or a combination of two or more of polytetrafluoroethylene, polytrifluoroethylene, PEEK, and polyvinyl chloride.

8. The indigo electrochemical reduction reactor according to claim 1, wherein: The cathode housing (5) and the anode housing (6) are made of a material with good thermal conductivity. More preferably, the cathode housing (5) and the anode housing (6) are made of a material selected from stainless steel, copper, aluminum, and titanium.

9. A method for electrochemical reduction of indigo using a microchannel carbon felt electrode, which is carried out using the indigo electrochemical reduction reactor using a microchannel carbon felt electrode according to any one of claims 1 to 8; Preferably, the indigo electrochemical reduction reaction method comprises the following steps: Passing the cathode solution and the anode solution into the microchannel carbon felt electrode (1) and the anode channel (4) respectively; A heat exchange medium is introduced into the cathode housing (5) and the anode housing (6) respectively to perform heat exchange; When the reaction temperature reaches 30-70℃ and the flow rate is stable, power is turned on to carry out the reaction, wherein the current density is not less than 50mA / cm 2 After the reaction is completed, stop the power supply, cut off the heat exchange medium, and end the reaction after the material is emptied.

10. The indigo electrochemical reduction reaction method according to claim 9, wherein: The cathode solution is an alkaline aqueous solution containing indigo particles; preferably, based on the volume of the alkaline aqueous solution containing indigo particles, the concentration of indigo is 10-100 g / L, and the concentration of the alkaline compound is 0.2-2 mol / L; The anode solution is an alkaline aqueous solution free of indigo. Preferably, the concentration of the alkaline compound is 0.5-2 mol / L based on the volume of the alkaline aqueous solution free of indigo. Preferably, the alkaline compound is selected from one or a combination of two or more of NaOH, KOH, Na2CO3, K2CO3, Na3PO4, and K3PO4.

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