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

Abstract

An indigo electrochemical reduction reactor and indigo electrochemical reduction reaction method using a micro-channel carbon felt electrode. A reaction device of the reactor comprises a cathode casing, an insulating gasket, a current collector, a micro-channel carbon felt electrode, a separator, an oxygen evolution electrode, an anode channel, and an anode casing. A micro-channel network for a cathode solution to flow is provided inside the micro-channel carbon felt electrode; the oxygen evolution electrode and the carbon felt channel electrode are arranged in parallel, and are separated by the separator therebetween; the current collector is closely attached to the outer surface of the micro-channel carbon felt electrode; the insulating gasket is closely attached to the outer surface of the current collector; the cathode casing is closely attached to the outer surface of the insulating gasket. Further provided in the present invention is an indigo electrochemical reduction reaction method based on the reactor. The present invention can implement direct electroreduction of indigo without a chemical reducing agent.

Description

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

[0001] Cross-reference information

[0002] The present application claims priority to the Chinese patent application No. 202411360074.6, filed on September 27, 2024, and entitled "Indigo electrochemical reduction reactor using micro-channel carbon felt electrode and indigo electrochemical reduction reaction method", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to an indigo electrochemical reduction reactor using micro-channel carbon felt electrode and an indigo electrochemical reduction reaction method, and belongs to the technical field of electrochemistry. BACKGROUND

[0004] Indigo is a compound widely used in the textile industry. In the dyeing process, it needs to be reduced to water-soluble leuco sodium salt under alkaline conditions to effectively combine with clothing fibers, and then oxidized to develop color. The common method for reducing indigo is caustic soda safety powder, which has complete reaction and fast speed, but produces a large amount of waste salt, pollutes water sources, and the raw material is easy to decompose and flammable, which is a process to be eliminated. Current research focuses on finding other alternative reducing agents, such as sulfur dioxide, sugar, hydroxyacetone, divalent iron salt complex, sodium borohydride, etc., but all the above substances have problems such as high cost, generation of chemical pollutants, poor reduction effect, etc. Catalytic hydrogenation of indigo in alkaline aqueous solution can significantly reduce the use of safety powder, but due to the high risk of explosion and fire, the hydrogenation reduction process cannot be directly used in dyeing plants, and can only be directly provided by dye suppliers. The obtained solution has a water content of more than 60%, which significantly increases the transportation cost, so it is necessary to design a new type of indigo reduction reactor to safely and efficiently produce leuco sodium salt solution without reducing agent.

[0005] Direct electrochemical reduction of indigo is a green synthesis method of leuco sodium salt, which directly uses electrons provided by the electrode as a reducing agent without the use of hydrogen. The existing electrochemical reduction reactor for indigo uses fixed or fluidized carbon particles as an anode (such as US8333881), which has the problems of low contact efficiency of reactants with the surface of the cathode, difficult control of flow state in the reactor, high power consumption, and low production efficiency. SUMMARY

[0006] To solve the above technical problems, the purpose of the present application is to provide an indigo electrochemical reduction reactor, which is internally provided with a micro-channel carbon felt electrode, and can provide direct electro-reduction of indigo without chemical reducing agent.

[0007] The application also provides an indigo electrochemical reduction reaction method based on the above-mentioned indigo electrochemical reduction reactor.

[0008] To achieve the above-mentioned purpose, the application provides an indigo electrochemical reduction reactor using a micro-channel carbon felt electrode, wherein the indigo electrochemical reduction reactor comprises a reaction device;

[0009] The reaction device comprises a cathode shell, an insulating gasket, a current collector, a micro-channel carbon felt electrode, a diaphragm, an oxygen evolution electrode, an anode channel and an anode shell arranged in sequence.

[0010] The micro-channel carbon felt electrode is internally provided with a micro-channel network for the flow of a cathode solution.

[0011] The oxygen evolution electrode is arranged in parallel with the micro-channel carbon felt electrode and is separated by the diaphragm.

[0012] The current collector is arranged in close contact with the outer surface of the micro-channel carbon felt electrode.

[0013] The insulating gasket is arranged in close contact with the outer surface of the current collector.

[0014] The cathode shell is arranged in close contact with the outer surface of the insulating gasket.

[0015] The anode channel is arranged between the oxygen evolution electrode and the anode shell, and the anode channel is internally provided with an anode solution channel.

[0016] The cathode shell and the anode shell are respectively internally provided with heat exchange pipelines.

[0017] 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.

[0018] The current collector and the oxygen evolution electrode are respectively connected to the cathode and the anode of the power supply, and specifically, the current collector and the oxygen evolution electrode are respectively connected to a cathode terminal and an anode terminal and then connected to the cathode and the anode of the power supply.

[0019] 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 micro-channel network, and the outlet of the micro-channel network is connected to the inlet of the cathode solution storage tank.

[0020] 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.

[0021] In the above-mentioned indigo electrochemical reduction reactor, preferably, the micro-channel carbon felt electrode is made of calcined modified carbon felt.

[0022] The carbon felt is a kind of carbon material with high conductivity, high porosity and large specific surface area. Since the pores in the carbon felt are small, the carbon felt electrode is modified and the exquisite fluid channel structure design is implemented, so that the carbon felt is fully contacted with the indigo solution and uniformly adsorbs indigo particles to occur reduction reaction, which is an important means to make the carbon felt electrode practical. Based on this, the application proposes a cathode design scheme for the indigo direct electrochemical reduction reactor, forms a complete electrochemical reactor structure with the cathode as the core, and provides a new type of indigo electrochemical reduction reactor based on the micro-channel carbon felt electrode.

[0023] The application applies micro-chemical technology to the direct electrochemical reduction of indigo, designs and constructs a micro-channel carbon felt electrode. By adding micro-channels in the carbon felt electrode, the reliability and stability of fluid flow can be ensured, and the flow state in the reactor can be easily controlled. Meanwhile, by using the characteristics of high specific surface area, electron transfer can be accelerated, mass transfer can be strengthened, and the contact efficiency of reactants and cathode can be improved, so that indigo can be directly electrochemically reduced without chemical reducing agent.

[0024] In the above-mentioned indigo electrochemical reduction reactor, preferably, the geometric area of the calcined modified carbon felt is 1-5000 cm 2 The reactor size can be adjusted.

[0025] In the above-mentioned indigo electrochemical reduction reactor, preferably, the thickness of the calcined modified carbon felt is 0.5-10 mm.

[0026] In the above-mentioned indigo electrochemical reduction reactor, preferably, the porosity of the calcined modified carbon felt is > 30%.

[0027] In the above-mentioned indigo electrochemical reduction reactor, preferably, the modification method of the calcined modified carbon felt comprises the following steps: washing, degreasing (for example, washing and degreasing with acetone and deionized water in sequence), drying (for example, drying at 80 DEG C for 24 h), and then calcining at 300-800 DEG C for 1-3 h in an acetic acid or oxygen atmosphere to complete the modification.

[0028] 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, intersecting or staggered manner to form a three-dimensional electrode structure, while the inlet, outlet and fluid distribution structure are provided. The microchannel network in the carbon felt electrode serves as a cathode solution channel. When the indigo-containing alkaline aqueous solution flows through the microchannel network formed by the carbon felt stack, the indigo particles are adsorbed by the carbon felt and undergo reduction reaction to convert into water-soluble leuco sodium salt. Preferably, the cathode solution channel is selected from one or a combination of two or more of a straight channel, a curved channel (e.g. a serpentine channel), a broken line channel, an intersecting grid channel, and a dendritic channel. 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 provided simultaneously, which can be connected to form a network or can be parallel channels.

[0029] In the above-mentioned indigo electrochemical reduction reactor, preferably, the microchannel network is located inside the carbon felt and placed centrally 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 bonding the carbon felt on both sides without microchannels with the carbon felt containing hollow microchannels.

[0030] In the above-mentioned indigo electrochemical reduction reactor, preferably, the microchannels in the microchannel network have a spacing of less than 10 mm in the same plane.

[0031] In the above-mentioned indigo electrochemical reduction reactor, preferably, the cathode solution channel is provided with an inlet, an outlet and a dendritic fluid distribution structure at the end, respectively, for inputting the cathode solution, outputting the cathode solution and distributing and transporting the cathode solution among multiple cathode solution channels.

[0032] In the above-mentioned indigo electrochemical reduction reactor, preferably, the oxygen evolution electrode as the reaction anode is a mesh electrode loaded with metal oxide electrocatalyst. The oxygen evolution electrode has an area equal to that of the microchannel carbon felt electrode. The edge of the oxygen evolution electrode can be connected to an anode lead, and the anode channel is a parallel straight channel structure, with alkaline aqueous solution as the anode liquid, to undergo oxygen evolution reaction 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 can be selected from one or a combination of two or more of iridium oxide, ruthenium oxide, iron oxide and nickel oxide.

[0033] In the above-mentioned indigo electrochemical reduction reactor, preferably, the separator is a proton exchange membrane. In the reaction, the separator 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, for example, one of Nafion N115, Nafion N117, Nafion N1110, Nafion N324, Nafion N424, Nafion N438.

[0034] In the above-mentioned indigo electrochemical reduction reactor, the current collector is used to power the micro-channel 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, hastelloy.

[0035] In the above-mentioned indigo electrochemical reduction reactor, preferably, the thickness of the current collector is 0.1-1mm.

[0036] In the above-mentioned indigo electrochemical reduction reactor, an insulating gasket is used to ensure the insulation between the current collector and the cathode shell, preferably, the material of the insulating gasket is selected from one of polytetrafluoroethylene, polytrifluoroethylene, polypropylene. The thickness of the insulating gasket can be 0.1-0.5mm.

[0037] In the above-mentioned indigo electrochemical reduction reactor, the anode channel is used to transport the anode electrolyte to the anode while ensuring the insulation between the anode shell and the anode shell, preferably, the width and depth of the anode channel are 1-10mm respectively. The material of the anode channel is an insulating material, for example, selected from one or more combinations of polytetrafluoroethylene, polytrifluoroethylene, PEEK, polyvinyl chloride.

[0038] In the above-mentioned indigo electrochemical reduction reactor, the cathode shell and the anode shell 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 shell and the anode shell is preferably a material with good thermal conductivity; more preferably, the material of the cathode shell and the anode shell is selected from one of stainless steel, copper, aluminum, titanium respectively. The heat exchange pipes arranged inside the cathode shell and the anode shell are used to control the reaction temperature by heat exchange medium, and these heat exchange pipes can be connected with external heat exchange medium device.

[0039] The present application also provides an indigo electrochemical reduction reaction method, which is carried out by using the above-mentioned indigo electrochemical reduction reactor using micro-channel carbon felt electrode.

[0040] According to the specific embodiments of the present application, preferably, the indigo electrochemical reduction reaction method comprises the following steps:

[0041] The cathode solution and the anode solution are respectively introduced into the micro-channel carbon felt electrode and the anode channel;

[0042] Heat exchange medium is introduced into the cathode shell and the anode shell respectively to perform heat exchange;

[0043] When the reaction temperature reaches 30-70℃ and the flow rate is stable, power is supplied to perform the reaction, wherein the current density is not less than 50mA / cm 2 After the reaction is completed, the power supply is stopped, the heat exchange medium is cut off, the material is discharged, and the reaction is ended.

[0044] According to the specific embodiment of the present application, preferably, the indigo electrochemical reduction reaction method comprises the following specific steps:

[0045] The cathode solution is introduced into the micro-channel network of the micro-channel carbon felt electrode, and the anode solution is introduced into the anode solution channel of the anode channel; the circulation of the cathode solution can be realized by means of the circulation channel formed by the cathode solution storage tank, the cathode feed pump and the cathode micro-channel network, and the circulation of the anode solution can be realized by means of the circulation channel formed by the anode solution storage tank, the anode feed pump and the anode solution channel;

[0046] The heat exchange medium is introduced into the first heat exchange pipeline in the cathode shell and the second heat exchange pipeline in the anode shell respectively to heat the cathode solution and the anode solution;

[0047] When the reaction temperature (set temperature between 30-70℃) is reached and the flow rate of the cathode solution and the anode solution is stable, the power supply (such as an electrochemical workstation) is turned on to perform the reaction, wherein the current density of the power supply is not less than 50mA / cm 2 ;

[0048] After a certain period of time, the power supply is turned off, the heat exchange medium is cut off, the material is discharged, and the reaction is ended.

[0049] According to the specific embodiment of the present application, preferably, the current density of the power supply is controlled to be 50-110mA / cm 2 during the reaction.

[0050] According to the specific embodiment of the present application, preferably, the flow rate of the cathode solution and the anode solution is respectively controlled to be 5-5000mL / min.

[0051] According to the specific embodiment of the present application, preferably, the cathode solution is an alkaline aqueous solution containing indigo particles; preferably, the concentration of the indigo is 10-100g / L and the concentration of the alkaline compound is 0.2-2mol / L, based on the volume of the alkaline aqueous solution containing indigo particles.

[0052] According to a specific embodiment of the present application, preferably, the anode solution is an alkaline aqueous solution without indigo, and the concentration of the alkaline compound is 0.5-2 mol / L, preferably, based on the volume of the alkaline aqueous solution without indigo;

[0053] According to a specific embodiment of the present application, 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, and K3PO4.

[0054] The technical solution of the present application solves the problems of low contact efficiency of reactants with the cathode surface and difficult to control the flow state in the traditional indigo reduction electrochemical reactor, improves the fluid distribution state in the cathode chamber through modification and channel structure design, strengthens the adsorption and electrochemical reaction process of indigo particles, increases the mass transfer efficiency between the electrode surface and the reactants, reduces the energy consumption of the reduction reaction, and realizes the direct electro-reduction of indigo without chemical reducing agent.

[0055] Compared with the prior art, the present application has the following advantages:

[0056] (1) The present application adjusts and optimizes the cathode liquid flow field distribution by calcination modification and careful design of micro-channel structure, improves the adsorption effect of indigo in the cathode micro-channel network, enhances the contact between the reactants and the electrode, reduces the reaction potential, and improves the reaction efficiency.

[0057] (2) The present application realizes high-efficiency electrochemical reduction of indigo without using chemical reducing agent, the reaction is carried out at normal pressure and without using hydrogen, avoids subsequent separation steps, the reaction is safe and controllable, and the produced water-soluble leuco body sodium salt can be directly used for dyeing. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is a structural schematic diagram of the reaction device of the indigo electrochemical reduction reactor using a micro-channel carbon felt electrode provided in Example 1.

[0059] Figure 2 is a structural schematic diagram of the indigo electrochemical reduction reactor using a micro-channel carbon felt electrode provided in Example 1.

[0060] Figure 3 is a schematic diagram of the three-dimensional structure of the indigo electrochemical reduction reactor using a micro-channel carbon felt electrode provided in Example 1.

[0061] Figure 4 is a schematic diagram of another structure connection mode of the indigo electrochemical reduction reactor using a micro-channel carbon felt electrode provided in Example 1.

[0062] Figure 5 is a structural schematic diagram of a serpentine channel.

[0063] Figure 6 is a schematic diagram of the stacking mode of the micro-channel carbon felt electrode.

[0064] Figure 7 is a schematic diagram of the structure of the dendritic channel.

[0065] Figure 8 is a schematic diagram of the structure of the straight-line channel.

[0066] Figure 9 is a schematic diagram of the structure of the zigzag channel.

[0067] Main figure number explanation: 1-micro-channel carbon felt electrode; 2-separator; 3-oxygen evolution electrode; 4-anode channel; 5-cathode shell; 6-anode shell; 7-current collector; 8-insulating gasket; 9-cathode terminal post; 10-anode terminal post; 11-micro-channel network; 12-anode solution channel; 13-first heat exchange pipe; 14-second heat exchange pipe; 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 device. DETAILED DESCRIPTION

[0068] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present application, the technical solutions of the present application will be described in detail below, but it cannot be understood as limiting the scope of the implementation of the present application.

[0069] In the following examples and comparative examples, the indigo conversion rate and the current efficiency are calculated according to the following formula:

[0070] Indigo conversion rate = (amount of substance of leucoindigo in the cathode liquid after the reaction (mol) / amount of substance of indigo in the cathode liquid at the beginning of the reaction (mol)) x 100%;

[0071] Current efficiency = (2 x amount of substance of leucoindigo in the cathode liquid after the reaction (mol) x 96485 (C / mol)) / (current density (A / cm 2 ) x electrode area (cm 2 ) x electrolysis time (s)) x 100%.

[0072] Example 1

[0073] This example provides an indigo electrochemical reduction reactor comprising a carbon felt channel electrode, the structure of which is shown in Figures 1, 2 and 3.

[0074] 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, an anode feed pump 19;

[0075] The reaction device comprises, in sequence, a cathode shell 5, an insulating gasket 8, a current collector 7, a micro-channel carbon felt electrode 1, a separator 2, an oxygen evolution electrode 3, an anode channel 4, and an anode shell 6.

[0076] Wherein:

[0077] The micro-channel carbon felt electrode 1 is internally provided with a cathode solution channel, specifically a micro-channel network 11;

[0078] The oxygen evolution electrode 3 is arranged in parallel with the micro-channel carbon felt electrode 1, and is separated by a separator 2 in the middle;

[0079] The current collector 7 is arranged in close contact with the outer surface of the micro-channel carbon felt electrode 1, and one end of the current collector 7 is connected with a cathode terminal post 9;

[0080] The insulating gasket 8 is arranged in close contact with the outer surface of the current collector 7;

[0081] The cathode shell 5 is arranged in close contact with the outer surface of the insulating gasket 8, and the cathode shell 5 is internally provided with a first heat exchange pipeline 13;

[0082] The oxygen evolution electrode 3 and the anode shell 6 are provided with an anode channel 4, and one end of the oxygen evolution electrode 3 is connected with an anode terminal post 10, and the anode channel 4 is internally provided with an anode solution channel 12;

[0083] The anode shell 6 is internally provided with a second heat exchange pipeline 14;

[0084] The cathode terminal post 9 and the anode terminal post 10 are respectively connected with the cathode and the anode of a power supply 15;

[0085] The outlet of a cathode solution storage tank 17 is connected with the inlet of a cathode feed pump 16, the outlet of the cathode feed pump 16 is connected with the inlet of the micro-channel network 11, and the outlet of the micro-channel network 11 is connected with the inlet of the cathode solution storage tank 17;

[0086] The outlet of an anode solution storage tank 18 is connected with the inlet of an anode feed pump 19, the outlet of the anode feed pump 19 is connected with the inlet of the anode solution channel 12, and the outlet of the anode solution channel 12 is connected with the inlet of the anode solution storage tank 18; Fig. 4 shows a schematic diagram of another structural connection mode, wherein part of the structure is omitted;

[0087] The first heat exchange pipeline 13 and the second heat exchange pipeline 14 are respectively connected with an external heat exchange medium device 20;

[0088] The micro-channel carbon felt electrode 1 is made of calcined modified carbon felt, wherein the preparation method of the calcined modified carbon felt comprises: 1mm thick carbon felt is sequentially cleaned and degreased in an ultrasonic bath with acetone and deionized water, dried at 80℃ for 24h, and then calcined at 600℃ in an acetic acid atmosphere for 2h to obtain the calcined modified carbon felt.

[0089] The specific surface area of the carbon felt before and after the treatment is measured by BET, and the specific surface area before and after the treatment is calculated to be 4.09m2 / g and 60.28 m 2 / g, measured by mercury intrusion method: the porosity of the calcined modified carbon felt is 57%.

[0090] The microchannel carbon felt electrode 1 is made by the following steps: forming a serpentine channel with a width of 1 mm and a depth (i.e. the depth of the channel into the surface of the carbon felt during machining) of 1 mm on a calcined modified carbon felt (outer shape 10 mm x 10 mm x 1 mm) by mechanical machining (as shown in Fig. 5), and further stacking three layers of carbon felt containing channels and communication holes (as shown in Fig. 6) to form a cathode solution channel, using the stacked carbon felt as a cathode;

[0091] The oxygen evolution electrode 3 is a titanium mesh loaded with iridium dioxide, wherein the size of the titanium mesh is 10 mm x 10 mm x 0.2 mm, and the loading amount of iridium dioxide is 2 mg / cm 2 , based on the total area of the titanium mesh;

[0092] The separator 2 is Nafion N324, with a size of 12 cm x 12 cm.

[0093] The indigo electrochemical reduction reaction is carried out using an indigo electrochemical reduction reactor containing a microchannel carbon felt electrode, according to the following steps:

[0094] 100 mL of an aqueous NaOH solution containing 1 g of indigo and having a concentration of 2 mol / L of NaOH is used as the cathode solution, and 100 mL of an aqueous NaOH solution having a concentration of 2 mol / L of NaOH is used as the anode solution; before electrolysis, nitrogen is passed into the cathode solution for 30 minutes to remove oxygen in the solution;

[0095] The cathode solution in the cathode solution storage tank 17 is input into the microchannel network 11 in the microchannel carbon felt electrode 1 through the cathode feed pump 16, with a flow rate set to 5 mL / min;

[0096] The anode solution in the anode solution storage tank 18 is input into the anode solution channel 12 of the anode channel 4 through the anode feed pump 19, with a flow rate set to 5 mL / min;

[0097] Circulating water is input into the first heat exchange pipeline 13 in the cathode shell 5 and the second heat exchange pipeline 14 in the anode shell 6, respectively, to heat the cathode solution and the anode solution, and the temperature of the circulating water is 50°C;

[0098] When the reaction temperature of 50°C is reached and the flow rates of the cathode solution and the anode solution are stable, the power supply (such as an electrochemical workstation) is turned on for reaction, wherein the current density of the power supply is 50 mA / cm 2 ;

[0099] The electrolysis was stopped after 4 hours of electrolysis, and the amount of substance of indigo white in the catholyte was determined by potentiometric titration, and the conversion rate of indigo blue and the current efficiency were calculated.

[0100] The amount of substance of indigo white in the catholyte obtained by potentiometric titration was 3.57 mmol, and the calculation showed that the conversion rate of indigo blue was 93.5%, and the current efficiency was 95.6%.

[0101] Example 2

[0102] The difference between this example 2 and example 1 is that the current density is controlled at 110 mA / cm 2 , the electrolysis was stopped after 2 hours of electrolysis, and the amount of substance of indigo white in the catholyte was determined by potentiometric titration, and the conversion rate of indigo blue and the current efficiency were calculated, and the others were the same as example 1.

[0103] The amount of substance of indigo white in the catholyte obtained by potentiometric titration was 3.74 mmol, and the calculation showed that the conversion rate of indigo blue was 98.2%, and the current efficiency was 91.2%.

[0104] Comparative Example 1

[0105] The difference between this comparative example 1 and example 2 is that the reaction channel is made of carbon felt which is not treated in example 1, and the current density is controlled at 50 mA / cm 2 , the electrolysis was stopped after 4 hours of electrolysis, and the amount of substance of indigo white in the catholyte was determined by potentiometric titration, and the conversion rate of indigo blue and the current efficiency were calculated, and the others were the same as example 1.

[0106] The results show that compared with example 1, the reaction tank pressure is increased by 1.8V, the electrolysis of water occurs, the conversion rate of indigo blue is reduced to 52.0%, and the current efficiency is 53.2%.

[0107] Comparative Example 2

[0108] This comparative example 2 uses the reaction device of comparative example 1, and the current density is reduced to 20 mA / cm 2 , and the tank pressure similar to example 1 is obtained, and the electrolysis is stopped after 10 hours of electrolysis, and the others are the same as example 1.

[0109] The results show that the conversion rate of indigo blue is 92.0%, and the current efficiency is 94.1%.

[0110] From the comparison of the experimental results of this comparative example 2 and example 1, it can be seen that the specific surface area of the treated carbon felt is increased, and the reaction efficiency is improved.

[0111] Example 3

[0112] The difference between this embodiment 3 and embodiment 1 is that 100 mL of aqueous solution of NaOH with 2 g of indigo and 2 mol / L of NaOH is used as the cathode solution, and 100 mL of aqueous solution of NaOH with 2 mol / L of NaOH is used as the anode solution; the current density is controlled at 50 mA / cm 2 , and the electrolysis is stopped after 8 hours of electrolysis, and the conversion rate of indigo and the current efficiency are calculated, and the others are the same as in embodiment 1.

[0113] The results show that the conversion rate of indigo is 91.7%, and the current efficiency is 93.7%.

[0114] By comparing the experimental results of this embodiment 3 and embodiment 1, it can be seen that the appropriate increase of the content of the reactant indigo mainly affects the reaction time.

[0115] Embodiment 4

[0116] The difference between this embodiment 4 and embodiment 1 is that the temperature of the circulating water is 30℃; the electrolysis is stopped after 4 hours of electrolysis, and the conversion rate of indigo and the current efficiency are calculated, and the others are the same as in embodiment 1.

[0117] The calculation shows that the conversion rate of indigo is 91.2%, and the current efficiency is 93.2%.

[0118] Embodiment 5

[0119] The difference between this embodiment 5 and embodiment 1 is that the heat exchange device is set to a temperature of 70℃ for heat preservation; the electrolysis is stopped after 4 hours of electrolysis, and the conversion rate of indigo and the current efficiency are calculated, and the others are the same as in embodiment 1.

[0120] The calculation shows that the conversion rate of indigo is 87.6%, and the current efficiency is 89.5%.

[0121] Embodiments 6-12

[0122] The difference between this embodiment 6-12 and embodiment 1 is that the carbon felt calcination temperature and the calcination time are different, and the others are the same as in embodiment 1. The specific parameters and reaction effects are shown in Table 1.

[0123] Table 1

[0124] Comparative Example 3

[0125] The difference between this comparative example 3 and embodiment 6 is that the calcination temperature is reduced to 200℃, and the measurement results show that the specific surface area of the carbon felt is only 5.24 m 2 / g, which is basically the same as that of the untreated carbon felt; the current density is controlled at 50 mA / cm 2 , and the electrolysis is stopped after 4 hours of electrolysis, and the others are the same as in embodiment 6.

[0126] The calculation shows 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 this comparative example 4 and example 6 is that the calcination temperature is increased to 1000℃, and the other conditions are the same as in example 6.

[0129] The result shows that the surface carbon felt has a small amount of fragmentation, the material becomes sparse and the degree of graphitization is high, and the reaction channel is not successfully processed.

[0130] Example 13

[0131] The difference between this example 13 and example 1 is that the serpentine microchannel is replaced by a dendritic channel (as shown in Figure 7), the electrolysis is stopped after 4 hours of electrolysis, the conversion rate of indigo and the current efficiency are calculated, and the other conditions are the same as in example 1.

[0132] The calculation shows that the conversion rate of indigo is 90.6% and the current efficiency is 92.6%.

[0133] Example 14

[0134] The difference between this example 14 and example 1 is that the serpentine microchannel is replaced by a straight channel (as shown in Figure 8), the electrolysis is stopped after 4 hours of electrolysis, the conversion rate of indigo and the current efficiency are calculated, and the other conditions are the same as in example 1.

[0135] The result shows that the conversion rate of indigo is 91.4% and the current efficiency is 93.4%.

[0136] Example 15

[0137] The difference between this example 15 and example 1 is that the serpentine microchannel is replaced by a polyline channel (as shown in Figure 9), the electrolysis is stopped after 4 hours of electrolysis, the conversion rate of indigo and the current efficiency are calculated, and the other conditions are the same as in example 1.

[0138] The result shows that the conversion rate of indigo is 93.1% and the current efficiency is 95.2%.

[0139] Comparative Example 5

[0140] This comparative example 5 is to remove the microchannel carbon felt electrode 1 in example 1, leaving a 10mm×10mm×2mm cavity, tightly filling solid carbon particles with a diameter of 2mm in the cavity and tightly contacting the current collector 7, and the carbon particle bed layer 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 10mm×10mm×0.2mm, and the loading amount of iridium dioxide is 2mg / cm 2 , based on the total area of the titanium mesh;

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

[0143] The electrochemical reduction reaction of indigo was carried out using the indigo electrochemical reduction reactor of Comparative Example 5, and was conducted according to the following steps:

[0144] Use 100 mL of NaOH aqueous solution containing 1 g of indigo and a concentration of 2 mol / L as the cathode solution, and 100 mL of NaOH aqueous solution with a concentration of 2 mol / L as the anode solution; before electrolysis, purge the cathode solution with nitrogen gas for 30 minutes to remove oxygen from 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, with the flow rate set to 5 mL / min.

[0146] The anolyte in the anolyte storage tank 18 is fed into the anolyte channel 12 of the anolyte channel 4 via the anolyte feed pump 19, with a flow rate of 5 mL / min.

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

[0148] Once the reaction temperature of 50°C is reached and the flow rates of the cathode and anolyte solutions stabilize, the power supply (e.g., an electrochemical workstation) is turned on to proceed with the reaction. Under the same voltage as in Example 1, the current density is only 10 mA / cm². 2 ;

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

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

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

Claims

1. An indigo electrochemical reduction reactor using a microchannel carbon felt electrode, wherein, The indigo electrochemical reduction reactor comprises a reaction device; The reaction device comprises a cathode shell (5), an insulating gasket (8), a current collector (7), a micro-channel carbon felt electrode (1), a diaphragm (2), an oxygen evolution electrode (3), an anode channel (4), an anode shell (6) arranged in sequence; The micro-channel carbon felt electrode (1) is internally provided with a micro-channel network (11) for the flow of cathode solution; The oxygen evolution electrode (3) is arranged in parallel with the micro-channel carbon felt electrode (1) and is separated by the diaphragm (2) in the middle; The current collector (7) is arranged in close contact with the outer surface of the micro-channel carbon felt electrode (1); The insulating gasket (8) is arranged in close contact with the outer surface of the current collector (7); The cathode shell (5) is arranged in close contact with the outer surface of the insulating gasket (8); The oxygen evolution electrode (3) and the anode shell (6) are provided with the anode channel (4), and the anode channel (4) is internally provided with an anode solution channel (12); The inside of the cathode shell (5) and the inside of the anode shell (6) are respectively provided with heat exchange pipelines.

2. The indigo electrochemical reduction reactor of 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), an anode feed pump (19); The current collector (7) and the oxygen evolution electrode (3) are respectively connected with the cathode and the anode of the power supply (15); The outlet of the cathode solution storage tank (17) is connected with the inlet of the cathode feed pump (16), the outlet of the cathode feed pump (16) is connected with the inlet of the micro-channel network (11), and the outlet of the micro-channel network (11) is connected with the inlet of the cathode solution storage tank (17); The outlet of the anode solution storage tank (18) is connected with the inlet of the anode feed pump (19), the outlet of the anode feed pump (19) is connected with the inlet of the anode solution channel (12), and the outlet of the anode solution channel (12) is connected with the inlet of the anode solution storage tank (18).

3. The indigo electrochemical reduction reactor of claim 1, wherein, The micro-channel carbon felt electrode (1) is made of calcined modified carbon felt.

4. The indigo electrochemical reduction reactor of claim 3, wherein, The geometric area of the calcined modified carbon felt is 1-5000 cm 2 .

5. The indigo electrochemical reduction reactor of claim 3, wherein, The thickness of the calcined modified carbon felt is 0.5-10mm.

6. The indigo electrochemical reduction reactor of claim 3, wherein, The porosity of the calcined modified carbon felt is >30%.

7. The indigo electrochemical reduction reactor of claim 3, wherein, The modification method of the calcined modified carbon felt comprises the following steps: washing, degreasing, drying the carbon felt, and then calcining at 300-800℃ for 1-3h in an acetic acid or oxygen atmosphere to complete the modification.

8. The indigo electrochemical reduction reactor of claim 3, wherein, The micro-channels in the micro-channel network (11) are selected from one or more than two combinations of straight channels, curved channels, zigzag channels, cross grid channels, and dendritic channels; The micro-channel network (11) is located inside the carbon felt and is placed in the middle along the thickness direction of the carbon felt.

9. The indigo electrochemical reduction reactor of claim 8, wherein, The micro-channel network (11) is formed by engraving the micro-channels on the middle carbon felt, and then bonding the carbon felt on both sides without micro-channels with the carbon felt containing the engraved micro-channels.

10. The indigo electrochemical reduction reactor of claim 8, wherein, The cross section of the micro-channels in the micro-channel network (11) is rectangular.

11. The indigo electrochemical reduction reactor of claim 10, wherein, The width and depth of the rectangle are 0.5-5mm respectively.

12. The indigo electrochemical reduction reactor of claim 8, wherein, The spacing of the micro-channels in the micro-channel network (11) on the same plane is less than 10mm.

13. The indigo electrochemical reduction reactor of claim 8, wherein, The micro-channel network (11) is provided with an inlet, an outlet and a dendritic fluid distribution structure at the end.

14. The indigo electrochemical reduction reactor of claim 1, wherein, The oxygen evolution electrode (3) is a mesh electrode loaded with a metal oxide electrocatalyst.

15. The indigo electrochemical reduction reactor of claim 14, wherein, The carrier of the oxygen evolution electrode (3) is selected from one of titanium, nickel, titanium-niobium alloy and titanium-zirconium alloy; and 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.

16. The indigo electrochemical reduction reactor of claim 14, wherein, The area of the oxygen evolution electrode (3) is equal to that of the micro-channel carbon felt electrode (1).

17. The indigo electrochemical reduction reactor of claim 1, wherein, The separator (2) is a proton exchange membrane.

18. The indigo electrochemical reduction reactor of claim 17, wherein, The proton exchange membrane is selected from one of Nafion N115, Nafion N117, Nafion N1110, Nafion N324, Nafion N424 and Nafion N438.

19. The indigo electrochemical reduction reactor of claim 1, wherein, The current collector (7) is a metal sheet structure.

20. The indigo electrochemical reduction reactor of claim 19, wherein, The material of the current collector (7) is selected from one of titanium, nickel, 316L stainless steel and hastelloy.

21. The indigo electrochemical reduction reactor of claim 19, wherein, The thickness of the current collector (7) is 0.1-1 mm.

22. The indigo electrochemical reduction reactor of claim 1, wherein, The material of the insulating gasket (8) is selected from one of polytetrafluoroethylene, polytrifluoroethylene and polypropylene.

23. The indigo electrochemical reduction reactor of claim 22, wherein, The thickness of the insulating gasket (8) is 0.1-0.5 mm.

24. The indigo electrochemical reduction reactor of claim 1, wherein, The width and depth of the anode channel (4) are 1-10 mm respectively.

25. The indigo electrochemical reduction reactor of claim 24, wherein, The material of the anode channel (4) is an insulating material.

26. The indigo electrochemical reduction reactor of claim 25, wherein, The insulating material is selected from one of polytetrafluoroethylene, polytrifluoroethylene, PEEK and polyvinyl chloride or a combination of two or more thereof.

27. The indigo electrochemical reduction reactor of claim 1, wherein, The materials of the cathode shell (5) and the anode shell (6) are materials with good heat conduction performance.

28. The indigo electrochemical reduction reactor of claim 27, wherein, The materials of the cathode shell (5) and the anode shell (6) are selected from one of stainless steel, copper, aluminum and titanium respectively.

29. A method for the electrochemical reduction of indigo using a micro-channel carbon felt electrode, which is performed by using the electrochemical reduction reactor for indigo using a micro-channel carbon felt electrode according to any one of claims 1-28.

30. The indigo electrochemical reduction reaction process according to claim 29, wherein, The method for the electrochemical reduction of indigo comprises the following steps: The cathode solution and the anode solution are respectively introduced into the micro-channel carbon felt electrode (1) and the anode channel (4); Heat exchange medium is introduced into the cathode shell (5) and the anode shell (6) to perform heat exchange; When the reaction temperature reaches 30-70℃ and the flow is stable, the reaction is carried out by passing electricity, wherein the current density is not less than 50 mA / cm 2 After the reaction is completed, the electricity is stopped, the heat exchange medium is cut off, the material is emptied, and the reaction is ended.

31. The indigo electrochemical reduction reaction process according to claim 29, wherein, The cathode solution is an alkaline aqueous solution containing indigo particles, and the anode solution is an alkaline aqueous solution not containing indigo.

32. The indigo electrochemical reduction reaction process according to claim 31, wherein, The concentration of indigo is 10-100 g / L and the concentration of alkaline compound is 0.2-2 mol / L, based on the volume of the alkaline aqueous solution containing indigo particles.

33. The indigo electrochemical reduction reaction process according to claim 31, wherein, The concentration of alkaline compound is 0.5-2 mol / L, based on the volume of the alkaline aqueous solution not containing indigo.

34. The indigo electrochemical reduction reaction process according to claim 32 or 33, wherein, The alkaline compound is selected from one of NaOH, KOH, Na2CO3, K2CO3, Na3PO4 and K3PO4 or a combination of two or more thereof.

Images