An indigo electrochemical reduction reactor and method using a microchannel carbon felt electrode

Abstract

The application provides an indigo electrochemical reduction reactor and method using a micro-channel carbon felt electrode. The reactor device comprises a cathode shell, an insulating gasket, a current collector, a micro-channel carbon felt electrode, a diaphragm, an oxygen electrode, an anode channel, and an anode shell. The micro-channel carbon felt electrode is internally provided with a micro-channel network for the flow of a cathode solution. The oxygen electrode is arranged in parallel with the carbon felt channel electrode, with a diaphragm in between. The current collector is arranged in close contact with the outer surface of the micro-channel carbon felt electrode. The insulating gasket is arranged in close contact with the outer surface of the current collector. The cathode shell is arranged in close contact with the outer surface of the insulating gasket. The oxygen electrode and the anode shell are provided with an anode channel, with an anode solution channel inside. The cathode shell and the anode shell are internally provided with heat exchange pipes. The application also provides an indigo electrochemical reduction method based on the above reactor. The application can directly electro-reduce indigo in the presence of a chemical reducing agent.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of using microchannel carbon felt electrode indigo electrochemical reduction reactor and indigo electrochemical reduction reaction method, belong to electrochemistry technical field. BACKGROUND

[0002] Indigo is a kind of compound that is widely used in textile industry, it needs to be reduced into water-soluble leuco salt in alkaline condition during dyeing process to effectively combine with clothing fiber, and then color after oxidation. Reducing indigo commonly uses caustic soda sodium dithionite, its reaction is complete, fast, but a large amount of waste salt is generated, pollutes water source, and raw material is easy to decompose, flammable, 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 the above substances all have problems such as high cost, chemical pollutants generated, poor reduction effect, etc. Catalytic hydrogenation of indigo in alkaline aqueous solution can greatly reduce the amount of sodium dithionite, but due to the high risk of explosion and fire, the hydrogenation reduction process cannot be directly used in dyeing factory, and the obtained solution with water content greater than 60% significantly increases transportation cost, so it is necessary to design a new type of indigo reduction reactor to safely and efficiently produce leuco salt solution without reducing agent.

[0003] Direct electrochemical reduction of indigo is a green synthesis method of leuco salt, which directly uses electrons provided on the electrode as reducing agent without using hydrogen. The existing electrochemical reduction reactor of indigo uses fixed or fluidized carbon particles as anode (such as US8333881), which has problems such as low contact efficiency of reactants with cathode surface, difficult to control flow state in reactor, high power consumption and low production efficiency. SUMMARY

[0004] To solve the above technical problems, the purpose of the present application is to provide an indigo electrochemical reduction reactor, which is provided with a microchannel carbon felt electrode inside, and can directly electro-reduce indigo without chemical reducing agent.

[0005] The present application also provides an indigo electrochemical reduction reaction method based on the above-mentioned indigo electrochemical reduction reactor.

[0006] To achieve the above purpose, the present application provides an indigo electrochemical reduction reactor using 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 arranged in sequence.

[0008] The micro-channel carbon felt electrode is internally provided with a micro-channel network for the flow of cathode solution;

[0009] The oxygen evolution electrode is arranged in parallel with the micro-channel carbon felt electrode, and is separated by the separator in the middle;

[0010] The current collector is arranged in close contact with the outer surface of the micro-channel carbon felt electrode;

[0011] The insulating gasket is arranged in close contact with the outer surface of the current collector;

[0012] The cathode shell is arranged in close contact with the outer surface of the insulating gasket;

[0013] The oxygen evolution electrode and the anode shell are provided with the anode channel, and the anode channel is internally provided with an anode solution channel;

[0014] The inside of the cathode shell and the inside of the anode shell are respectively provided with heat exchange pipelines.

[0015] In the above 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 respectively connected to the cathode and the anode of the power supply, and specifically can be connected to the cathode terminal and the anode terminal, and then connected to the cathode and the 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 micro-channel network, and the outlet of the micro-channel 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 micro-channel carbon felt electrode is made of calcined modified carbon felt.

[0020] The carbon felt is a kind of carbon material with high conductivity, high porosity and large specific surface area, and since the pores in the carbon felt are tiny, 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 generate a 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 novel indigo electrochemical reduction reactor based on a micro-channel carbon felt electrode.

[0021] 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.

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

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

[0024] In the above-mentioned 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 the carbon felt, degreasing (for example, washing and degreasing by using acetone and deionized water in sequence), drying (for example, drying at 80 DEG C for 24h), and then calcining at 300-800 DEG C for 1-3h in an acetic acid or oxygen atmosphere, 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, 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

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

[0034] 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.

[0035] 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.

[0036] 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, which can be connected with the external heat exchange medium device.

[0037] 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.

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

[0039] The cathode solution and the anode solution are respectively introduced into the micro-channel carbon felt electrode and the anode channel;

[0040] 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 to heat the cathode solution and the anode solution;

[0041] When the reaction temperature reaches 30-70℃ and the flow rate is stable, power is supplied to perform the reaction, wherein the current density of the power supply is not less than 50 mA / cm 2 After the reaction is completed, the power supply is stopped, the heat exchange medium is cut off, and the material is discharged to end the reaction.

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

[0043] The cathode solution is introduced into the micro-channel network in the micro-channel carbon felt electrode, and the anode solution is introduced into the anode solution channel in 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;

[0044] 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 to heat the cathode solution and the anode solution;

[0045] 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 50 mA / cm 2 ;

[0046] After a certain period of time, the power supply is turned off, the heat exchange medium is cut off, and the material is discharged to end the reaction.

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

[0048] According to a specific embodiment of the present application, preferably, the flow rate of the cathode solution and the anode solution is controlled to be 5-5000 mL / min.

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

[0050] According to a specific embodiment of the present application, preferably, the anode solution is an alkaline aqueous solution without indigo, and preferably, the concentration of the alkaline compound is 0.5-2 mol / L, based on the volume of the alkaline aqueous solution without indigo;

[0051] 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.

[0052] 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. The fluid distribution state in the cathode chamber is improved by modification and channel structure design, the adsorption and electrochemical reaction process of indigo particles are strengthened, the mass transfer efficiency between the electrode surface and the reactants is increased, the energy consumption of the reduction reaction is reduced, and direct electro-reduction of indigo without chemical reducing agent is realized.

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

[0054] (1) The present application controls 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.

[0055] (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 does not use 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

[0056] Figure 1 The structure schematic diagram of the reaction device of the indigo electrochemical reduction reactor using the micro-channel carbon felt electrode is provided for Example 1.

[0057] Figure 2 The structure schematic diagram of the indigo electrochemical reduction reactor using the micro-channel carbon felt electrode is provided for Example 1.

[0058] Figure 3 The structure schematic diagram of the indigo electrochemical reduction reactor using the micro-channel carbon felt electrode is provided for Example 1.

[0059] Figure 4 The structure schematic diagram of the indigo electrochemical reduction reactor using the micro-channel carbon felt electrode is provided for Example 1.

[0060] Figure 5Structure diagram of serpentine channel.

[0061] Figure 6 Structure diagram of stacked microchannel carbon felt electrode.

[0062] Figure 7 Structure diagram of dendritic channel.

[0063] Figure 8 Structure diagram of straight channel.

[0064] Figure 9 Structure diagram of zigzag channel.

[0065] Main figure number explanation:

[0066] 1 - microchannel 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 - microchannel 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

[0067] 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 should not be understood as limiting the scope of the present application.

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

[0069] Indigo conversion rate = (amount of substance of leucoindigo in cathode solution after reaction (mol) / amount of substance of indigo in cathode solution at the beginning of reaction (mol)) x 100%;

[0070] Current efficiency = (2 x amount of substance of leucoindigo in cathode solution after reaction (mol) x 96485 (C / mol)) / (current density (A / cm 2 ) x electrode area (cm 2 ) x electrolysis time (s)) x 100%.

[0071] Example 1

[0072] This example provides an indigo electrochemical reduction reactor comprising a carbon felt channel electrode, the structure of which is shown in Figure 1 、 Figure 2 、 Figure 3

[0073] ​The indigo electrochemical reduction reactor includes 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 shell 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 shell 6 arranged sequentially.

[0075] in:

[0076] The microchannel carbon felt electrode 1 has a cathode solution channel inside, specifically a microchannel network 11;

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

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

[0079] The insulating gasket 8 is positioned in close contact with the outer surface of the current collector 7;

[0080] The cathode housing 5 is disposed in close contact with the outer surface of the insulating gasket 8, and the cathode housing 5 is provided with a first heat exchange pipe 13 inside;

[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. An anode solution channel 12 is provided inside the anode channel 4.

[0082] The anode housing 6 is equipped with a second heat exchange pipe 14 inside;

[0083] Cathode terminal 9 and anode terminal 10 are connected to the cathode and anode of power supply 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 The diagram shown illustrates 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. The preparation method of calcined modified carbon felt includes: cleaning and degreasing a 1 mm thick carbon felt with acetone and deionized water in an ultrasonic bath, drying at 80°C for 24 h, and then calcining at 600°C for 2 h in an acetic acid atmosphere to obtain calcined modified carbon felt.

[0088] The specific surface area of ​​the carbon felt before and after the above treatment was determined using BET, and the calculated specific surface areas before and after treatment were 4.09 m². 2 / g and 60.28m 2 / g, measured by mercury porosimetry: the porosity of the calcined modified carbon felt is 57%.

[0089] The microchannel carbon felt electrode 1 is manufactured through the following steps: a serpentine channel (e.g., a width of 1 mm and a depth of 1 mm, i.e., the depth to which the channel penetrates the surface of the carbon felt during processing) is formed on a calcined modified carbon felt (10 mm × 10 mm × 1 mm) by mechanical machining. Figure 5 As shown), further stacking of three layers of carbon felt containing channels and connecting holes (as shown) Figure 6 (As shown) a cathode solution channel is provided, with the stacked carbon felt serving as the cathode;

[0090] 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 iridium dioxide loading is 2mg / cm³. 2 Based on the total area of ​​the titanium mesh;

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

[0092] The electrochemical reduction reaction of indigo was carried out in an electrochemical reduction reactor containing microchannel carbon felt electrodes, following the steps below:

[0093] 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;

[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, with the flow rate set to 5 mL / min.

[0095] 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.

[0096] The circulating water is input into the first heat exchange pipe 13 in the cathode shell 5 and the second heat exchange pipe 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℃;

[0097] When the reaction temperature 50℃ is reached and the flow rates of the cathode solution and the anode solution are stable, the power supply (for example, an electrochemical workstation) is turned on to perform the reaction, wherein the current density of the power supply is 50mA / cm 2 ;

[0098] The electrolysis is stopped after 4 hours of electrolysis, the amount of substance of the indigo white in the cathode solution is determined by using the potentiometric titration method, and the conversion rate of the indigo blue and the current efficiency are calculated.

[0099] The amount of substance of the indigo white in the cathode solution obtained by the potentiometric titration method is 3.57mmol, and the calculation shows that the conversion rate of the indigo blue is 93.5% and the current efficiency is 95.6%.

[0100] Example 2

[0101] The difference between this example 2 and the example 1 is that the current density is controlled at 110mA / cm 2 , the electrolysis is stopped after 2 hours of electrolysis, the amount of substance of the indigo white in the cathode solution is determined by using the potentiometric titration method, and the conversion rate of the indigo blue and the current efficiency are calculated, and the others are the same as the example 1.

[0102] The amount of substance of the indigo white in the cathode solution obtained by the potentiometric titration method is 3.74mmol, and the calculation shows that the conversion rate of the indigo blue is 98.2% and the current efficiency is 91.2%.

[0103] Comparative Example 1

[0104] The difference between this comparative example 1 and the example 2 is that the reaction channel is made of the carbon felt which is not treated in the example 1, the current density is controlled at 50mA / cm 2 , the electrolysis is stopped after 4 hours of electrolysis, the amount of substance of the indigo white in the cathode solution is determined by using the potentiometric titration method, and the conversion rate of the indigo blue and the current efficiency are calculated, and the others are the same as the example 1.

[0105] The results show that, compared with the example 1, the reaction tank pressure is increased by 1.8V, the electrolysis water phenomenon occurs, the conversion rate of the indigo blue is reduced to 52.0%, and the current efficiency is 53.2%.

[0106] Comparative Example 2

[0107] The comparative example 2 uses the reaction device of the comparative example 1, and the current density is reduced to 20mA / cm 2 , the tank pressure similar to the example 1 is obtained, the electrolysis is stopped after 10 hours of electrolysis, and the others are the same as the example 1.

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

[0109] The comparison of the experimental results of the comparative example 2 and the example 1 shows that the specific surface area of the carbon felt after the treatment is increased, and the reaction efficiency is improved.

[0110] Example 3

[0111] The example 3 is different from the example 1 in that 100 mL of the aqueous NaOH solution containing 2 g of indigo and having a concentration of 2 mol / L is used as the cathode solution, 100 mL of the aqueous NaOH solution having a concentration of 2 mol / L is used as the anode solution, and the current density is controlled at 50 mA / cm 2 After electrolysis for 8 hours, the electrolysis is stopped, the conversion rate of indigo and the current efficiency are calculated, and the other conditions are the same as those of the example 1.

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

[0113] The comparison of the experimental results of the example 3 and the example 1 shows that the appropriate increase of the content of the reactant indigo mainly affects the reaction time.

[0114] Example 4

[0115] The example 4 is different from the example 1 in that the temperature of the circulating water is 30℃, the electrolysis is stopped after 4 hours, the conversion rate of indigo and the current efficiency are calculated, and the other conditions are the same as those of the example 1.

[0116] The calculation shows that the conversion rate of indigo is 91.2% and the current efficiency is 93.2%.

[0117] Example 5

[0118] The example 5 is different from the example 1 in that the temperature of the heat exchange device is set to 70℃ for heat preservation, the electrolysis is stopped after 4 hours, the conversion rate of indigo and the current efficiency are calculated, and the other conditions are the same as those of the example 1.

[0119] The calculation shows that the conversion rate of indigo is 87.6% and the current efficiency is 89.5%.

[0120] Examples 6-12

[0121] The examples 6-12 are different from the example 1 in that the carbon felt is calcined at different temperatures and for different time, and the other conditions are the same as those of the example 1. The specific parameters and the reaction effects are shown in Table 1.

[0122] Table 1

[0123] Serial number Calcination temperature / °C Calcination time / h Specific surface area / m 2 / g]] Conversion of indigo / % 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 Example 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 was reduced to 200°C, and the measurement results showed that the specific surface area of ​​the carbon felt was only 5.24 m². 2 / g, essentially the same as untreated carbon felt; current density controlled at 50mA / cm². 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%, while 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, while the rest is the same as Example 6.

[0129] As a result, the surface carbon felt showed a small amount of cracking, the material became sparse and highly graphitized, and it was not successfully processed into a reaction channel.

[0130] Example 13

[0131] The difference between Example 13 and Example 1 is that the serpentine microchannel is replaced with a dendritic channel (e.g., Figure 7 As shown in the figure, after 4 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.

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

[0133] Example 14

[0134] The difference between Example 14 and Example 1 is that the serpentine microchannel is replaced with a straight channel (e.g., Figure 8 As shown in the figure, after 4 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.

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

[0136] Example 15

[0137] The difference between Example 15 and Example 1 is that the serpentine microchannel is replaced with a zigzag channel (e.g., Figure 9 As shown in the figure, after 4 hours of electrolysis, the electrolysis was stopped, and the conversion rate and current efficiency of indigo were calculated. Other parameters were the same as 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] The comparative example 5 is to remove the micro-channel carbon felt electrode 1 in the example 1, leaving a 10mm x 10mm x 2mm cavity, tightly filling solid carbon particles with a diameter of 2mm in the cavity and closely packing the flow collector 7, and the carbon particle bed layer is in communication with 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 x 10mm x 0.2mm, and the loading amount of the 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 x 12cm.

[0143] The indigo electrochemical reduction reactor of the comparative example 5 is used to carry out the indigo electrochemical reduction reaction, and the following steps are carried out:

[0144] 100mL of an aqueous NaOH solution containing 1g of indigo and having a concentration of 2mol / L of NaOH is used as the cathode solution, and 100mL of an aqueous NaOH solution having a concentration of 2mol / 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;

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

[0146] 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, and the flow rate is set to 5mL / min;

[0147] The 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℃;

[0148] When the reaction temperature 50℃ 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 is only 10mA / cm 2 at the same voltage as in the example 1.

[0149] The electrolysis is stopped after 4 hours of electrolysis, and the conversion rate of indigo and the current efficiency are calculated.

[0150] The calculation shows that the conversion rate of indigo is 25.2%, and the current efficiency is 97%.

[0151] By comparing the experimental results of the comparative example 5 and the 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 electrochemical reduction reactor for indigo using a microchannel carbon felt electrode, wherein, The indigo electrochemical reduction reactor includes a reaction apparatus; The reaction device includes a cathode shell (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 shell (6) arranged in sequence. The microchannel carbon felt electrode (1) is provided with a microchannel network (11) for the cathode solution to flow through. The oxygen evolution electrode (3) is arranged in parallel with the microchannel carbon felt electrode (1), and is separated by the diaphragm (2); The current collector (7) is disposed in close contact with the outer surface of the microchannel carbon felt electrode (1); The insulating pad (8) is disposed in close contact with the outer surface of the current collector (7); The cathode housing (5) is disposed in close contact with the outer surface of the insulating pad (8); The oxygen evolution electrode (3) is provided with an anode channel (4) between it and the anode shell (6), and the anode channel (4) is provided with an anode solution channel (12). Heat exchange pipes are respectively provided inside the cathode shell (5) and the anode shell (6); The microchannel network (11) is located inside the carbon felt and is placed in the center along the thickness direction of the carbon felt. The microchannel network (11) is formed by carving hollow microchannels on the carbon felt in the center and then bonding the carbon felts on both sides without microchannels with the carbon felts containing hollow microchannels.

2. The indigo electrochemical reduction reactor according to claim 1, wherein, The indigo electrochemical reduction reactor also includes a power source (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 modified carbon felt.

4. The indigo electrochemical reduction reactor according to claim 3, wherein, The geometric area of ​​the calcined modified carbon felt is 1-5000 cm². 2 .

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

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

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

8. The indigo electrochemical reduction reactor according to claim 3, wherein, The microchannels in the microchannel network (11) are selected from one or more combinations of straight channels, curved channels, broken line channels, cross-grid channels, and dendritic channels.

9. The indigo electrochemical reduction reactor according to claim 3, wherein, The cross-section of the microchannels in the microchannel network (11) is rectangular.

10. The indigo electrochemical reduction reactor according to claim 9, wherein, The width and depth of the rectangle are 0.5-5 mm.

11. The indigo electrochemical reduction reactor according to claim 3, wherein, The spacing between the microchannels in the microchannel network (11) on the same plane is less than 10 mm.

12. The indigo electrochemical reduction reactor according to claim 3, wherein, The microchannel network (11) is provided with an inlet, an outlet and a dendritic fluid distribution structure.

13. The indigo electrochemical reduction reactor according to claim 1, wherein, The oxygen evolution electrode (3) is a mesh electrode supported on a metal oxide electrocatalyst.

14. The indigo electrochemical reduction reactor according to claim 13, wherein, The support for 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 or more of iridium oxide, ruthenium oxide, iron oxide, and nickel oxide.

15. The indigo electrochemical reduction reactor according to claim 1, wherein, The oxygen evolution electrode (3) has the same area as the microchannel carbon felt electrode (1).

16. The indigo electrochemical reduction reactor according to claim 1, wherein, The diaphragm (2) is a proton exchange membrane; And / or, the current collector (7) is a metal sheet structure; And / or, the material of the insulating pad (8) is selected from polytetrafluoroethylene, polytrifluoroethylene, and polypropylene.

17. The indigo electrochemical reduction reactor according to claim 16, wherein, The proton exchange membrane is selected from one of Nafion N115, Nafion N117, Nafion N1110, Nafion N324, Nafion N424, and Nafion N438.

18. The indigo electrochemical reduction reactor according to claim 1, wherein, The material of the current collector (7) is selected from one of titanium, nickel, 316L stainless steel, and Hastelloy.

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

20. The indigo electrochemical reduction reactor according to claim 1, wherein, The thickness of the insulating pad (8) is 0.1-0.5 mm.

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

22. The indigo electrochemical reduction reactor according to claim 1, wherein, The anode channel (4) is made of insulating material.

23. The indigo electrochemical reduction reactor according to claim 22, wherein, The insulating material is selected from one or more of polytetrafluoroethylene, polytrifluoroethylene, PEEK, and polyvinyl chloride.

24. The indigo electrochemical reduction reactor according to claim 1, wherein, The cathode shell (5) and anode shell (6) are made of materials with good thermal conductivity.

25. The indigo electrochemical reduction reactor according to claim 24, wherein, The cathode shell (5) and anode shell (6) are made of stainless steel, copper, aluminum and titanium, respectively.

26. A method for electrochemical reduction of indigo using a microchannel carbon felt electrode, wherein the method is carried out using the electrochemical reduction reactor for indigo using a microchannel carbon felt electrode as described in any one of claims 1-25.

27. The electrochemical reduction reaction method for indigo according to claim 26, wherein, The electrochemical reduction method for indigo includes the following steps: The cathode solution and the anolyte solution are respectively introduced into the microchannel carbon felt electrode (1) and the anolyte channel (4); Heat exchange medium is introduced into the cathode shell (5) and anode shell (6) respectively for heat exchange; Once the reaction temperature reaches 30-70℃ and the flow rate stabilizes, an electric current is applied to initiate the reaction, with a current density of not less than 50 mA / cm². 2 After the reaction is complete, stop the power supply, disconnect the heat exchange medium, vent the material, and then end the reaction.

28. The electrochemical reduction reaction method for indigo according to claim 26, wherein, The cathode solution is an alkaline aqueous solution containing indigo particles; The anolyte solution is an alkaline aqueous solution that does not contain indigo.

29. The electrochemical reduction reaction method for indigo according to claim 28, wherein, 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.

30. The electrochemical reduction reaction method for indigo according to claim 28, wherein, The concentration of the alkaline compound is 0.5-2 mol / L based on the volume of the alkaline aqueous solution that does not contain indigo.

31. The method for electrochemical reduction of indigo according to claim 29 or 30, wherein, The alkaline compound is selected from one or more combinations of NaOH, KOH, Na2CO3, K2CO3, Na3PO4, and K3PO4.

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