Application of ionic liquids as electrolytes in flow electrode capacitive deionization technology

Abstract

This invention belongs to the field of water desalination and purification, and relates to the application of ionic liquids as electrolytes in flow electrode capacitive deionization technology. An ionic liquid is prepared by mixing it with active electrode materials and organic solvents to obtain a flow electrode slurry, which is then applied in flow electrode capacitive deionization. The flow electrode capacitive deionization system of this invention can withstand an applied voltage of 3.5V, which is 2.5 times the voltage that aqueous electrolytes can withstand. It achieves a single-cycle desalination efficiency of over 99% and features low energy consumption, high efficiency, no pollution, and continuous and stable operation. The method provided by this invention has advantages such as high desalination efficiency, no pollution, and continuous and stable operation, and has good industrial application prospects in water desalination, heavy metal removal, organic matter removal, water resource recovery, and high-salinity wastewater treatment.

Description

Technical Field

[0001] This invention belongs to the field of water desalination and purification, and relates to the application of ionic liquids as electrolytes in flow electrode capacitive deionization technology. Background Technology

[0002] Rapid societal development and overpopulation have not only led to excessive consumption of freshwater resources but also resulted in varying degrees of water pollution, exacerbating freshwater shortages. Seawater desalination technology is currently an effective means of addressing water scarcity, primarily including reverse osmosis, forward osmosis, multi-stage flash evaporation, ion exchange, multi-effect evaporation, and electrodialysis. However, these technologies require significant time, energy, and labor. On the other hand, wastewater treatment and recycling can improve water resource utilization and is also an effective way to alleviate water scarcity. High-salinity wastewater, as one of the main types of industrial wastewater, generally originates from the continuous accumulation of salt during industrial production and recycling processes. Due to its wide range of sources, high hazard, high recyclability, and relatively easy treatment, it is a preferred wastewater for recycling. Currently, high-salinity wastewater treatment technologies mainly include thermal concentration, membrane methods, and biological methods. The first two methods are prone to system or membrane corrosion and scaling, while biological methods are sensitive to environmental conditions and difficult to control.

[0003] Capacitive deionization (CDO) is an emerging water desalination technology based on the double-layer principle. As a green and economical water treatment technology, it requires no chemical additives in seawater desalination, high-salinity wastewater desalination, heavy metal ion removal, and special ion recovery, showing great promise. However, the inability of current common CDO technologies to operate continuously restricts their large-scale application. Flow electrode CDO uses a slurry composed of active electrode materials and electrolytes to replace the original fixed electrodes, becoming the core of electron transport and ion adsorption in the system. This overcomes the inability of previous CDO systems to operate continuously, enhancing the desalination effect. Furthermore, it offers higher energy efficiency and more flexible operating modes, making it a superior choice for efficient, continuous, and low-energy desalination.

[0004] Current research and development in flow electrode capacitive deionization mainly focuses on device structure improvement, innovation of active electrode materials and their dosage ratio, and device operation modes. Few studies have paid attention to the importance of the electrolyte in the electrode slurry. Commonly used aqueous electrolytes have low boiling points and are easily volatile. Furthermore, when the operating voltage exceeds 1.2V, the aqueous electrolyte may decompose, leading to reduced cycle stability during circulation due to solvent evaporation or decomposition.

[0005] Ionic liquids are characterized by their non-volatility, non-flammability, conductivity, stable electrochemical performance, large voltage window, and easy recyclability. They are widely used in fields such as supercapacitors, organic synthesis, and catalysis. However, there are currently no inventions or researches that apply them to the field of capacitor deionization. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the shortcomings of existing technologies by providing a flow electrode capacitive deionization system using ionic liquid as the electrolyte and its application in water desalination. This system uses a mixed solution of ionic liquid, organic solvent, and active electrode material as the flow electrode slurry. This flow electrode slurry is used in a flow electrode capacitive deionization module for water desalination, exhibiting characteristics such as a high withstand voltage threshold, high desalination efficiency, and stable operation.

[0007] Invention Concept: This invention provides a flowing electrode capacitive deionization system using ionic liquid as the electrolyte and its application in water desalination. The main technical principle is as follows: Under the action of an electric field, the anions and cations in the brine to be treated are adsorbed onto the active electrode materials at both electrodes. The electrode slurry flowing out of the electric field undergoes charge neutralization in a storage tank, and the adsorbed ions are desorbed into the ionic liquid electrolyte, thus continuously achieving desalination and regeneration of the active electrode materials. Simultaneously, since the viscosity of ionic liquid is relatively higher than that of aqueous electrolyte at room temperature, to reduce the cost and viscosity of the electrolyte, an organic solvent can be used as a diluent and mixed with the ionic liquid in a certain proportion, which can effectively solve this problem.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] This invention discloses the application of ionic liquids as electrolytes in the deionization of flowing electrode capacitors.

[0010] In some embodiments, the ionic liquid includes, but is not limited to, any one or a combination of several of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-butylimidazolium tetrafluoroborate, and 1-n-butyl-1-methylpyrrolidine di(trifluoromethanesulfonyl)imide.

[0011] Wherein, the 1-ethyl-3-methylimidazolium tetrafluoroborate is abbreviated as EMIMBF4; the 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is abbreviated as EMIM-NTf2; the 1-butyl-3-methylimidazolium hexafluorophosphate is abbreviated as BMIPF6; the 1-butyl-3-butylimidazolium tetrafluoroborate is abbreviated as BMIBF4; and the 1-n-butyl-1-methylpyrrolidine di(trifluoromethanesulfonyl)imide is abbreviated as PYR14-TFSI.

[0012] In some embodiments, preferably, the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, or 1-butyl-3-methylimidazolium hexafluorophosphate.

[0013] In some embodiments, the ionic liquid is mixed with active electrode materials and organic solvents as an electrolyte to prepare a flow electrode slurry, which is then applied to the deionization of flow electrode capacitors.

[0014] In some embodiments, the active electrode material is a porous carbon electrode material; the organic solvent is any one or a combination of several of N,N-dimethylformamide, acetonitrile, dimethyl sulfoxide, and N-methylpyrrolidone.

[0015] In some embodiments, preferably, the porous carbon electrode material is activated carbon; the mesh size of the activated carbon is 100 to 325 mesh, more preferably 100 mesh.

[0016] The activated carbon mentioned above is commercially available.

[0017] In some embodiments, the volume ratio of the ionic liquid to the organic solvent is 1:(1-6); the concentration of the active electrode material in the flowing electrode slurry is 0.005-0.075 g / mL.

[0018] In some embodiments, preferably, the volume ratio of the ionic liquid to the organic solvent is 1:(1-4); and the concentration of the active electrode material in the flowing electrode slurry is 0.025-0.050 g / mL.

[0019] In some embodiments, the flow electrode capacitor deionization process is carried out in a flow electrode capacitor deionization device; the flow electrode capacitor deionization device includes a flow electrode capacitor deionization module, a DC power supply, a first peristaltic pump, a second peristaltic pump, a flow electrode slurry storage tank, a water storage tank, and a conductivity meter; the flow electrode capacitor deionization module includes a cathode flow electrode chamber, a desalination chamber, and an anode flow electrode chamber; wherein, the DC power supply is connected to both ends of the flow electrode capacitor deionization module to form a closed loop, and the DC power supply applies voltage to the flow electrode capacitor deionization module; the water storage tank... The outlet of the device is connected in series with the first peristaltic pump and the inlet of the desalination chamber via connecting pipes. The outlet of the desalination chamber is connected to the inlet of the water storage tank via a pipe, forming a closed loop. The probe of the conductivity meter is placed in the water storage tank. The outlet of the slurry storage tank of the flowing electrode is connected to one end of the second peristaltic pump via a connecting pipe. The other end of the second peristaltic pump is connected to the inlet of the cathode flowing electrode chamber and the inlet of the anode flowing electrode chamber via Y-shaped pipes. The outlets of the cathode flowing electrode chamber and the anode flowing electrode chamber are connected to the inlet of the flowing electrode slurry storage tank via Y-shaped pipes, forming a closed loop.

[0020] In this system, a DC power supply applies voltage to the flow electrode capacitor deionization module. The positive terminal of the DC power supply is connected to the anode flow electrode chamber in the flow electrode capacitor deionization module, and the negative terminal of the DC power supply is connected to the cathode flow electrode chamber in the flow electrode capacitor deionization module.

[0021] In some embodiments, the flowing electrode capacitor deionization module is assembled sequentially in the following order: end plate, silicone pad, graphite current collector, silicone pad, cation exchange membrane, silicone pad, separator, silicone pad, anion exchange membrane, silicone pad, graphite current collector, silicone pad, and end plate to obtain the flowing electrode capacitor deionization module; wherein, the flow channels in the two graphite current collectors are the cathode flowing electrode chamber and the anode flowing electrode chamber, respectively, the cavity in the separator is the desalination chamber, a cation exchange membrane is provided between the cathode flowing electrode chamber and the desalination chamber, and an anion exchange membrane is provided between the desalination chamber and the anode flowing electrode chamber.

[0022] In some embodiments, a first peristaltic pump pumps the brine to be treated from the storage tank into the desalination chamber of the flow electrode capacitor deionization module for desalination. The desalinated brine flows out of the outlet of the desalination chamber and returns to the storage tank, forming a circulation loop. While the first peristaltic pump is working, a second peristaltic pump pumps the flow electrode slurry from the flow electrode slurry storage tank into the cathode flow electrode chamber and the anode flow electrode chamber of the flow electrode capacitor deionization module, respectively. After salt ion adsorption is completed, the slurry flows out from the outlet of the cathode flow electrode chamber and the anode flow electrode chamber, respectively, and returns to the flow electrode slurry storage tank to complete charge neutralization and salt ion desorption, forming a circulation loop. The conductivity of the brine in the storage tank is monitored in real time using a conductivity meter.

[0023] Among them, the conductivity meter monitors the conductivity of the brine in the water storage tank in real time.

[0024] After desalination, the active electrode material can be recovered by filtering, washing with water, and drying the flowing electrode slurry.

[0025] In some embodiments, a DC power supply applies a voltage to the flow electrode capacitor deionization module, the voltage ranging from 0.5 to 4.0V.

[0026] In some embodiments, preferably, a DC power supply applies a voltage to the flow electrode capacitor deionization module, the voltage range being 1.5 to 3.5V.

[0027] In some embodiments, the salt concentration in the brine is 0.1–2.0 g / L; the brine is a solution containing inorganic salt ions; the inorganic salt ions, including but not limited to cations such as Na+, are also present. + Ca 2+ Mg 2+ Cu 2+ Cr 3+ Cd 2+ Pb 2+ and NH4 + Any one or more of the following, anions including but not limited to Cl. - I - SO 2 4 - NO 2 3 - and PO 3 4 - Any one or more of the following combinations.

[0028] In some embodiments, preferably, the salt concentration in the brine is 0.5–2.0 g / L; the brine is a solution containing inorganic salt ions; and the inorganic salt ions, wherein the cation is Na+. + and NH4 + Any one or a combination of two of them, the anion is Cl. - and SO 2 4 - Any one or a combination of two of them.

[0029] In some embodiments, the first peristaltic pump pumps the brine to be treated into the flow electrode capacitor deionization module at a flow rate of 10-60 mL / min; the second peristaltic pump pumps the flow electrode slurry into the flow electrode capacitor deionization module at a flow rate of 10-60 mL / min.

[0030] In some embodiments, preferably, the first peristaltic pump pumps the brine to be treated into the flow electrode capacitor deionization module at a flow rate of 45-55 mL / min; the second peristaltic pump pumps the flow electrode slurry into the flow electrode capacitor deionization module at a flow rate of 35-45 mL / min.

[0031] Specifically, in the brine desalination process, there are adsorption and desorption processes. In the adsorption process, under the action of an electric field, anions and cations in the brine are adsorbed by the active electrode materials in the anolyte and cathode flow electrode slurries, respectively, to achieve continuous desalination. In the desorption process, the flow electrode slurries adsorbed with anions and cations are simultaneously circulated back to the flow electrode slurry storage tank for charge neutralization, and the adsorbed ions are desorbed into the ionic liquid electrolyte of the flow electrode slurry to achieve the regeneration of the active electrode materials.

[0032] Specifically, the desalination efficiency of the flow electrode capacitor deionization system of the present invention is more efficient and stable than that of the flow electrode capacitor deionization system using aqueous electrolyte, and the desalination rate can still reach 95% after 20 cycles.

[0033] Beneficial effects:

[0034] (1) The ionic liquid used in this invention as the electrolyte to prepare the flowing electrode slurry gives the flowing electrode capacitor deionization module a wider voltage window, good thermal stability, low volatility, and low flammability. Its unique physicochemical properties make it superior to aqueous and organic electrolytes, and it can withstand higher applied voltages, thus achieving higher and faster desalination efficiency. The ionic liquid of this invention still maintains a desalination rate of over 95% after 20 cycles at 3.5V.

[0035] (2) The flow electrode capacitor deionization system of the present invention can withstand an applied voltage of 3.5V, which is 2.5 times the voltage that aqueous electrolyte can withstand (1.4V). The single desalination efficiency is over 99%, and it has the characteristics of low energy, high efficiency, no pollution, and continuous and stable operation.

[0036] (3) The method provided by the present invention has the advantages of high desalination efficiency, no pollution and continuous and stable operation, and has good industrial application prospects in the fields of water desalination, heavy metal removal, organic matter removal, water resource recovery and high-salt wastewater treatment. Attached Figure Description

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0038] Figure 1 SEM images of activated carbon before and after use; Figure 1 a is the SEM image of the activated carbon before use. Figure 1 b is a SEM image of the activated carbon after drying and recovery following desalination.

[0039] Figure 2 The process flow diagram and structural diagram of the flow electrode capacitor deionization system are shown. Figure 2 a is the process flow diagram of the flow electrode capacitive deionization system. Figure 2 b is a structural diagram of the flow electrode capacitor deionization module.

[0040] Figure 3 Experimental results on the voltage of flow electrode capacitive deionization systems with different electrolytes; Figure 3 Figure a shows the change in the conductivity of salt water in the ionic liquid system under different voltages. Figure 3 b is a comparison chart of desalination rates for different electrolyte systems.

[0041] Figure 4 The diagram shows the continuous desalination performance of water desalination using a mixture of EMIMBF4 and DMF as the electrolyte in a flow electrode capacitive deionization technique.

[0042] Figure 5 Electrochemical performance testing of activated carbon electrode sheets; among which, Figure 5 a represents the cyclic voltammetry curves of the activated carbon electrode at different scan rates. Figure 5 b represents the constant current charge-discharge curves of the activated carbon electrode sheet under different current densities. Figure 5 c is the Nyquist plot of the activated carbon electrode sheet in the frequency range of 10 mHz to 100 kHz. Detailed Implementation

[0043] To further understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] Unless otherwise specified, all reagents involved in the embodiments of this invention are commercially available products and can be purchased through commercial channels.

[0045] The formula for calculating the desalination rate in this embodiment of the invention is as follows:

[0046]

[0047] Where C0 is the initial concentration of the saline solution (g·L⁻¹) -1 C is the brine concentration at the end of desalination (g·L). -1 ).

[0048] Example 1

[0049] In the following embodiments of the present invention, the deionization process of the flow electrode capacitor deionization is carried out in a flow electrode capacitor deionization device; the flow electrode capacitor deionization device includes a flow electrode capacitor deionization module 1, a DC power supply 2, a first peristaltic pump 3, a second peristaltic pump 4, a flow electrode slurry storage tank 5, a water storage tank 6, and a conductivity meter 7 (see details). Figure 2 a).

[0050] The flow electrode capacitive deionization module 1 includes a cathode flow electrode chamber, a desalination chamber, and an anode flow electrode chamber. The flow electrode capacitive deionization module 1 is assembled sequentially in the following order: end plate a, silicone gasket f, graphite current collector b, silicone gasket f, cation exchange membrane c, silicone gasket f, separator d, silicone gasket f, anion exchange membrane e, silicone gasket f, graphite current collector b, silicone gasket f, and end plate a, to obtain the flow electrode capacitive deionization module (see details). Figure 2 b); wherein the flow channels in the two graphite current collectors are the cathode flow electrode chamber and the anode flow electrode chamber, respectively, the cavity in the partition is the desalination chamber, a cation exchange membrane is provided between the cathode flow electrode chamber and the desalination chamber, and an anion exchange membrane is provided between the desalination chamber and the anode flow electrode chamber.

[0051] DC power supply 2 is connected to both ends of the flowing electrode capacitor deionization module 1, forming a closed loop. The DC power supply applies voltage to the flowing electrode capacitor deionization module. The outlet of the water storage tank 6 is connected in series with the first peristaltic pump 3 and the inlet of the desalination chamber through connecting pipes. The outlet of the desalination chamber is connected to the inlet of the water storage tank 6 through a pipe, forming a closed loop. The probe of the conductivity meter 7 is placed in the water storage tank 6 to monitor the conductivity of the brine in the water storage tank in real time. The outlet of the flowing electrode slurry storage tank 5 is connected to one end of the second peristaltic pump 4 through a connecting pipe. The other end of the second peristaltic pump 4 is connected to the inlet of the cathode flowing electrode chamber and the inlet of the anode flowing electrode chamber through Y-shaped pipes, respectively. The outlet of the cathode flowing electrode chamber and the outlet of the anode flowing electrode chamber are connected to the inlet of the flowing electrode slurry storage tank 5 through Y-shaped pipes, forming a closed loop. In this system, a DC power supply applies voltage to the flow electrode capacitor deionization module. The positive terminal of the DC power supply is connected to the anode flow electrode chamber in the flow electrode capacitor deionization module, and the negative terminal of the DC power supply is connected to the cathode flow electrode chamber in the flow electrode capacitor deionization module.

[0052] During operation, the first peristaltic pump 3 pumps the brine to be treated from the storage tank 6 into the desalination chamber of the flow electrode capacitor deionization module 1 for desalination. The desalinated brine flows out of the outlet of the desalination chamber and returns to the storage tank 6, forming a circulation loop. While the first peristaltic pump 3 is working, the second peristaltic pump 4 pumps the flow electrode slurry from the flow electrode slurry storage tank 5 into the cathode flow electrode chamber and the anode flow electrode chamber of the flow electrode capacitor deionization module 1, respectively. After the salt ion adsorption is completed through the flow channel of the graphite collector plate in the flow electrode chamber, the slurry flows out from the outlet of the cathode flow electrode chamber and the anode flow electrode chamber, respectively, and returns to the flow electrode slurry storage tank 5 to complete charge neutralization and salt ion desorption, forming a circulation loop. The conductivity of the brine in the storage tank 6 is monitored in real time using a conductivity meter 7.

[0053] In the brine desalination process, there are adsorption and desorption processes. In the adsorption process, under the action of an electric field, anions and cations in the brine are adsorbed by the active electrode materials in the anolyte and catholyte flow electrode slurries, respectively, to achieve continuous desalination. In the desorption process, the flow electrode slurries with adsorbed anions and cations are simultaneously circulated back to the flow electrode slurry storage tank for charge neutralization, and the adsorbed ions are desorbed into the ionic liquid electrolyte of the flow electrode slurry to achieve the regeneration of the active electrode materials.

[0054] Example 2

[0055] 1.25 g of activated carbon (100 mesh) was added to a mixed solution of 10 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) and 40 mL of N,N-dimethylformamide (DMF). The mixture was magnetically stirred for 1 h to disperse the activated carbon, resulting in a flowing electrode slurry (with an activated carbon concentration of 0.025 g / mL). This slurry was then stored in a flowing electrode slurry tank for later use. A DC power supply was connected to the flowing electrode capacitor deionization module to form a closed loop. The DC voltage circuit applied 3.5 V to the module. A first peristaltic pump delivers a 1.0 g / L sodium chloride aqueous solution from the storage tank into the desalination chamber of the flow electrode capacitor deionization module for desalination. The desalinated brine flows out of the desalination chamber and back into the storage tank, forming a circulation loop. The pumping flow rate of the brine is 45 mL / min. Simultaneously with the first peristaltic pump, a second peristaltic pump pumps the flow electrode slurry from the flow electrode slurry storage tank into the cathode and anode flow electrode chambers of the flow electrode capacitor deionization module, respectively. After salt ion adsorption through the graphite collector channels in the flow electrode chambers, the slurry flows out from the outlets of the cathode and anode flow electrode chambers, respectively, back into the flow electrode slurry storage tank to complete charge neutralization and salt ion desorption, forming a circulation loop. The pumping flow rate of the flow electrode slurry is 35 mL / min. A conductivity meter probe is placed in the storage tank to monitor the brine concentration in real time. After 2 hours of desalination, the desalination rate was calculated to be 89%.

[0056] After desalination, the flowing electrode slurry was filtered to recover the activated carbon material. After repeated rinsing with deionized water, it was dried in a 60℃ oven to obtain the recovered activated carbon. SEM images of the activated carbon before and after use are shown below. Figure 1 As shown in the figure, the morphology of the activated carbon did not change significantly before and after use, indicating that the morphology of the activated carbon was stable in this system.

[0057] Example 3

[0058] The experimental method was the same as in Example 2, except that the voltage of 3.5V was replaced with 2.5V, the concentration of sodium chloride aqueous solution was replaced with 0.5g / L instead of 1.0g / L, and the pump flow rate of sodium chloride aqueous solution was replaced with 55mL / min instead of 45mL / min. After 2 hours of desalination, the desalination rate was 79%.

[0059] Example 4

[0060] The experimental method was the same as in Example 2, except that 1.25g of activated carbon (100 mesh) was replaced with 2.5g of activated carbon (100 mesh), and the concentration of activated carbon in the flowing electrode slurry was 0.05g / mL. After 2 hours of desalination, the desalination rate was 93%.

[0061] Example 5

[0062] The experimental method was the same as in Example 4, except that 10 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) and 40 mL of N,N-dimethylformamide (DMF) were replaced with 25 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) and 25 mL of N,N-dimethylformamide (DMF). After desalting for 2 hours, the desalination rate was 87%.

[0063] Example 6

[0064] The experimental method was the same as in Example 4, except that 40 mL of N,N-dimethylformamide (DMF) was replaced with 40 mL of acetonitrile, and the pump flow rate of sodium chloride aqueous solution was changed from 45 mL / min to 55 mL / min. After 2 hours of desalination, the desalination rate was 95%.

[0065] Example 7

[0066] The experimental method was the same as in Example 5, except that 25 mL of N,N-dimethylformamide (DMF) was replaced with 25 mL of acetonitrile, 25 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) was replaced with 25 mL of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM-NTf2), and the pump flow rate of the sodium chloride aqueous solution was changed from 45 mL / min to 55 mL / min. After 2 hours of desalination, the desalination rate was 86%.

[0067] Example 8

[0068] The experimental method was the same as in Example 7, except that the sodium chloride aqueous solution was replaced with an ammonium chloride aqueous solution, and the concentration was changed from 1.0 g / L to 2.0 g / L. After 2 hours of desalination, the desalination rate was 82%.

[0069] Example 9

[0070] The experimental method was the same as in Example 5, except that 25 mL of N,N-dimethylformamide (DMF) was replaced with 25 mL of dimethyl sulfoxide (DMSO), 25 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) was replaced with 25 mL of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6), and the sodium chloride aqueous solution was replaced with ammonium sulfate aqueous solution. After desalination for 2 hours, the desalination rate was 84%.

[0071] Example 10

[0072] The experimental method was the same as in Example 2, except that 40 mL of N,N-dimethylformamide (DMF) was replaced with 40 mL of N-methylpyridinone (NMP), 10 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) was replaced with 10 mL of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6), and the sodium chloride aqueous solution was replaced with an ammonium chloride aqueous solution, with the concentration changed from 1.0 g / L to 1.5 g / L. After 2 hours of desalination, the desalination rate was 85%.

[0073] Example 11

[0074] Aqueous electrolyte system with flowing electrode capacitance for deionization:

[0075] 2.50 g of activated carbon (100 mesh) was added to 50 mL of deionized water and dispersed by magnetic stirring for 1 hour to obtain a flowing electrode slurry (the concentration of activated carbon in the slurry was 0.05 g / mL), which was then placed in a flowing electrode slurry storage tank for later use. A DC power supply was connected to the flowing electrode capacitive deionization module to form a closed loop, and the DC voltage circuit applied voltages of 1.0 V, 1.2 V, and 1.4 V to the module, respectively. A first peristaltic pump delivers a 1.0 g / L sodium chloride aqueous solution from the storage tank into the desalination chamber of the flow electrode capacitor deionization module for desalination. The desalinated brine flows out of the desalination chamber and back into the storage tank, forming a circulation loop. The pumping flow rate of the brine is 55 mL / min. Simultaneously with the first peristaltic pump, a second peristaltic pump pumps the flow electrode slurry from the flow electrode slurry storage tank into the cathode and anode flow electrode chambers of the flow electrode capacitor deionization module, respectively. After salt ion adsorption through the graphite collector channels in the flow electrode chambers, the slurry flows out from the outlets of the cathode and anode flow electrode chambers, respectively, back into the flow electrode slurry storage tank to complete charge neutralization and salt ion desorption, forming a circulation loop. The pumping flow rate of the flow electrode slurry is 45 mL / min. A conductivity meter probe is placed in the storage tank to monitor the brine concentration in real time. The desalination time is 2 hours.

[0076] ionic liquid electrolyte system with flow electrode capacitance for deionization:

[0077] 2.50 g of activated carbon (100 mesh) was added to a mixed solution of 10 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) and 40 mL of N,N-dimethylformamide (DMF). The mixture was magnetically stirred for 1 h to disperse the activated carbon, resulting in a flowing electrode slurry (with an activated carbon concentration of 0.05 g / mL). This slurry was then stored in a flowing electrode slurry tank for later use. A DC power supply was connected to the flowing electrode capacitor deionization module to form a closed loop. The DC voltage circuit applied voltages of 1.5 V, 2.5 V, and 3.5 V to the module, respectively. A first peristaltic pump delivers a 1.0 g / L sodium chloride aqueous solution from the storage tank into the desalination chamber of the flow electrode capacitor deionization module for desalination. The desalinated brine flows out of the desalination chamber and back into the storage tank, forming a circulation loop. The pumping flow rate of the brine is 55 mL / min. Simultaneously with the first peristaltic pump, a second peristaltic pump pumps the flow electrode slurry from the flow electrode slurry storage tank into the cathode and anode flow electrode chambers of the flow electrode capacitor deionization module, respectively. After salt ion adsorption through the graphite collector channels in the flow electrode chambers, the slurry flows out from the outlets of the cathode and anode flow electrode chambers, respectively, back into the flow electrode slurry storage tank to complete charge neutralization and salt ion desorption, forming a circulation loop. The pumping flow rate of the flow electrode slurry is 45 mL / min. A conductivity meter probe is placed in the storage tank to monitor the brine concentration in real time. The desalination time is 2 hours.

[0078] Comparison of desalination rates:

[0079] The results are as follows Figure 3 As shown, ionic liquid systems can withstand greater applied voltages and significantly reduce the conductivity of salt water in a short period of time. Figure 3 a) The desalination rate of aqueous electrolyte systems is below 40%, while the desalination rate of ionic liquid systems can reach as high as 99.6% at 3.5V. Figure 3 b).

[0080] Example 12

[0081] 2.50 g of activated carbon (100 mesh) was added to a mixed solution of 10 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) and 40 mL of N,N-dimethylformamide (DMF). The mixture was magnetically stirred for 1 h to disperse the activated carbon, resulting in a flowing electrode slurry (with an activated carbon concentration of 0.05 g / mL). This slurry was then stored in a flowing electrode slurry tank for later use. A DC power supply was connected to the flowing electrode capacitor deionization module to form a closed loop. The DC voltage circuit applied 3.5 V to the module. A first peristaltic pump delivers a 1.0 g / L sodium chloride aqueous solution from the storage tank into the desalination chamber of the flow electrode capacitor deionization module for desalination. The desalinated brine flows out of the desalination chamber and back into the storage tank, forming a circulation loop. The pumping flow rate of the brine is 55 mL / min. Simultaneously with the first peristaltic pump, a second peristaltic pump pumps the flow electrode slurry from the flow electrode slurry storage tank into the cathode and anode flow electrode chambers of the flow electrode capacitor deionization module, respectively. After salt ion adsorption through the graphite collector channels in the flow electrode chambers, the slurry flows out from the outlets of the cathode and anode flow electrode chambers, respectively, back into the flow electrode slurry storage tank to complete charge neutralization and salt ion desorption, forming a circulation loop. The pumping flow rate of the flow electrode slurry is 45 mL / min. A conductivity meter probe is placed in the storage tank to monitor the brine concentration in real time.

[0082] A desalination experiment was conducted every 2 hours. Conductivity data were recorded at the beginning and end of each experiment and converted into brine concentration. The desalination rate (SRE, %) was calculated using the formula below. The brine in the reservoir was replaced before the next experiment, while maintaining the initial concentration; the slurry for the flowing electrode was not replaced. The experiment was repeated 20 times.

[0083]

[0084] Where C0 is the initial concentration of the saline solution (g·L⁻¹) -1 C is the brine concentration at the end of desalination (g·L). -1 The result is as follows: Figure 4As shown, after 20 cycles of experiments, the desalination rate of the ionic liquid system is still above 95%, which shows that the stability of the ionic liquid system is excellent.

[0085] Example 13

[0086] Activated carbon (100 mesh), acetylene black, and polyvinylidene fluoride (PVDF) were mixed on nickel foam in a weight ratio of 8:1:1 and dried overnight at 80°C to obtain the working electrode. Ten times the mass of activated carbon (100 mesh) were used to prepare the counter electrode using the same method. A silver disk electrode was selected as the reference electrode. The experiment used a three-electrode system on a CHI660E (Shanghai Chenhua) electrochemical workstation to perform electrochemical tests on the samples in EMIMBF4 ionic liquid.

[0087] Electrochemical performance testing of activated carbon electrode sheets, such as Figure 5 As shown, Figure 5 a represents the activated carbon electrode sheet under different scanning speeds (15mV·s). -1 ~100mV·s -1 The cyclic voltammetry curves of the activated carbon electrode in the EMIMBF4 ionic liquid, with a potential window of -0.5 to 2 V, showed no redox peaks and exhibited symmetry. This indicates that the electrode reaction of the activated carbon electrode in the EMIMBF4 ionic liquid is highly reversible, with no redox reaction occurring, i.e., no pseudocapacitance is generated. The electroadsorption process is a stable and reversible process.

[0088] Figure 5 b shows the constant current charge-discharge curves of the activated carbon electrode sheet under different current densities. In the constant current charge-discharge test, the lower the current density, the longer the charge-discharge time per cycle. Each charge-discharge curve has good symmetry, approximating an isosceles triangle, indicating that the activated carbon electrode has electrochemical reversibility.

[0089] Figure 5 c is the Nyquist plot of the activated carbon electrode sheet in the frequency range of 10 mHz to 100 kHz, which shows the high charge transfer efficiency of the system.

[0090] This invention provides a concept and method for applying ionic liquids as electrolytes in flowing electrode capacitive deionization technology. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. Use of ionic liquid as electrolyte in flow-electrode capacitive deionization; The ionic liquid is any one or a combination of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis-trifluoromethylsulfonylimide, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate and 1-n-butyl-1-methylpyrrolidinium di(trifluoromethylsulfonyl)imide; The ionic liquid as electrolyte is mixed with active electrode material and organic solvent to prepare flow-electrode slurry, and is applied in flow-electrode capacitive deionization; The active electrode material is porous carbon electrode material; the organic solvent is any one or a combination of N,N-dimethylformamide, acetonitrile, dimethyl sulfoxide and N-methyl pyrrolidone; The porous carbon electrode material is activated carbon; the mesh number of the activated carbon is 100-325 mesh; the volume ratio of the ionic liquid to the organic solvent is 1:(1-6); the concentration of the active electrode material in the flow-electrode slurry is 0.005-0.075 g / mL.

2. Use according to claim 1, characterized in that, The flow-electrode capacitive deionization is carried out in a flow-electrode capacitive deionization device; The flow-electrode capacitive deionization device comprises a flow-electrode capacitive deionization module (1), a direct current power supply (2), a first peristaltic pump (3), a second peristaltic pump (4), a flow-electrode slurry storage tank (5), a water storage pool (6) and a conductivity meter (7); the flow-electrode capacitive deionization module (1) comprises a cathode flow-electrode chamber, a desalination chamber and an anode flow-electrode chamber; wherein the direct current power supply (2) is connected to both ends of the flow-electrode capacitive deionization module (1) to form a closed loop, and the direct current power supply applies voltage to the flow-electrode capacitive deionization module; the water outlet of the water storage pool (6) is connected to the water inlet of the desalination chamber through a connecting pipe in series, and the water outlet of the desalination chamber is connected to the water inlet of the water storage pool (6) through a pipe to form a closed loop; the probe of the conductivity meter (7) is placed in the water storage pool (6); the slurry outlet of the flow-electrode slurry storage tank (5) is connected to one end of the second peristaltic pump (4) through a connecting pipe, the other end of the second peristaltic pump (4) is connected to the slurry inlet of the cathode flow-electrode chamber and the slurry inlet of the anode flow-electrode chamber through a Y-shaped pipe respectively, and the slurry outlets of the cathode flow-electrode chamber and the anode flow-electrode chamber are connected to the slurry inlet of the flow-electrode slurry storage tank (5) through a Y-shaped pipe to form a closed loop.

3. Use according to claim 2, characterized in that, The flow-electrode capacitive deionization module is assembled in the order of end plate, silica gel gasket, graphite current collector, silica gel gasket, cation exchange membrane, silica gel gasket, separator, silica gel gasket, anion exchange membrane, silica gel gasket, graphite current collector, silica gel gasket and end plate to obtain the flow-electrode capacitive deionization module; wherein the flow channels in the two graphite current collectors are the cathode flow-electrode chamber and the anode flow-electrode chamber respectively, the cavity in the separator is the desalination chamber, a cation exchange membrane is arranged between the cathode flow-electrode chamber and the desalination chamber, and an anion exchange membrane is arranged between the desalination chamber and the anode flow-electrode chamber.

4. Use according to claim 3, characterized in that, The first peristaltic pump (3) pumps the salt water to be treated from the water storage tank (6) into the desalination chamber of the flow electrode capacitive deionization module (1) for desalination, and the desalinated salt water flows out from the water outlet of the desalination chamber back into the water storage tank (6), forming a circulating loop; while the first peristaltic pump (3) is working, the second peristaltic pump (4) pumps the flow electrode slurry in the flow electrode slurry storage tank (5) into the cathode flow electrode chamber and the anode flow electrode chamber of the flow electrode capacitive deionization module (1) respectively, and after the salt ions are adsorbed, they flow out from the slurry outlets of the cathode flow electrode chamber and the anode flow electrode chamber respectively back into the flow electrode slurry storage tank (5) to complete charge neutralization and salt ion desorption, forming a circulating loop; the conductivity meter (7) is used to monitor the conductivity of the salt water in the water storage tank (6) in real time.

5. Use according to claim 2, characterized in that, The direct current power supply applies a voltage to the flow electrode capacitive deionization module, and the voltage ranges from 0.5 to 4.0 V.

6. Use according to claim 4, characterized in that, The concentration of salt in the salt water is 0.1-2.0 g / L; the salt water is a solution containing inorganic salt ions; the inorganic salt ions are any one or combination of several of Na + , Ca 2+ , Mg 2+ , Cu 2+ , Cr 3+ , Cd 2+ , Pb 2+ and , and the anions are any one or combination of several of Cl - , I - , and .

7. Use according to claim 4, characterized in that, The flow rate of the first peristaltic pump for pumping the salt water to be treated into the flow electrode capacitive deionization module is 10-60 mL / min; and the flow rate of the second peristaltic pump for pumping the flow electrode slurry into the flow electrode capacitive deionization module is 10-60 mL / min. The direct current power supply applies a voltage to the flow electrode capacitive deionization module, and the voltage ranges from 0.5 to 4.0 V. The flow rate of the first peristaltic pump for pumping the salt water to be treated into the flow electrode capacitive deionization module is 10-60 mL / min; and the flow rate of the second peristaltic pump for pumping the flow electrode slurry into the flow electrode capacitive deionization module is 10-60 mL / min.

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