Temperature control auxiliary membrane capacitive deionization desalination system and desalination method

Abstract

The invention discloses a temperature control auxiliary membrane capacitive deionization desalination system and desalination method in the technical field of water treatment, and the system comprises a membrane capacitive deionization device, a water temperature control module and a data acquisition system, the membrane capacitive deionization device comprises an ionization pool made of a glass material, and a cation exchange membrane, an anion exchange membrane, a porous support frame, a pair of activated carbon electrodes and two power lines which are distributed in the ionization pool in parallel, and the two power lines are connected to the two activated carbon electrodes respectively; and a cation exchange membrane and an anion exchange membrane are respectively arranged on two sides of the porous support frame. According to the invention, the porous activated carbon electrode is combined with the ion exchange membrane to form the membrane capacitive deionization device, low voltage is applied to the desalination system to separate ions from the water inlet solution, the effluent desalination is realized, the water inlet temperature is stable through the temperature control module, and the energy consumption for operating the membrane capacitive deionization system is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, in particular to a temperature-controlled auxiliary membrane capacitor deionization and desalination system and a desalination method. Background Art

[0002] Faced with the challenge of water scarcity, it is particularly important to extract fresh water from non-traditional water sources. At present, a variety of technologies have been developed for seawater / saltwater desalination, mainly including pressure-driven, electrochemical-driven and thermal-driven desalination methods. Reverse osmosis (RO), as a classic process of pressure-driven desalination, has been widely used in seawater and saltwater treatment and resource recovery. Studies have shown that for every 1°C reduction in water temperature, the water output of RO will decrease by 3%. Given that the temperature of sea / saltwater varies significantly with the seasons (ranging from 15°C to 40°C), the feed water temperature has become a key factor affecting the performance of RO. At the same time, this technology also has the disadvantages of high energy consumption, huge infrastructure investment, easy scaling and high sensitivity to temperature changes. On this basis, capacitive deionization (CDI) is developing rapidly as an emerging electrochemical desalination technology. The core of this technology is to use porous carbon electrodes to achieve efficient adsorption and release of ions, thereby achieving the purpose of desalination of seawater / saltwater.

[0003] In the evolution of CDI technology, membrane capacitive deionization technology (MCDI) has attracted much attention due to its unique advantages and has become a hot spot in current research and commercial applications. The MCDI system effectively regulates the transmission path of ions by introducing high-charge-density ion exchange membranes (IEMs), that is, promoting the passage of counter ions and hindering common ions, which can significantly enhance the desalination efficiency and stability of the system. More importantly, the introduction of IEMs successfully inhibits the migration of dissolved oxygen to the cathode, reduces the occurrence of Faraday side reactions, and further improves the overall performance and operational stability of the MCDI system.

[0004] However, under standard operating conditions, since the feed water temperature affects the energy consumption and current efficiency of membrane capacitive deionization, the energy efficiency of CDI technology in desalination of brackish water is lower than that of RO technology, which is not conducive to expanding the application of CDI technology. Summary of the invention

[0005] The purpose of the present invention is to provide a temperature-controlled auxiliary membrane capacitor deionization desalination system and a desalination method. By setting a temperature auxiliary module, a stable desalination efficiency can be maintained under different temperature conditions, and the system has lower energy consumption and higher current efficiency, and has a higher desalination efficiency than the traditional reverse osmosis (RO) seawater desalination method.

[0006] In a first aspect, the present invention provides a temperature-controlled auxiliary membrane capacitor deionization and desalination system, comprising a membrane capacitor deionization device, a water temperature control module and a data acquisition system, wherein the membrane capacitor deionization device comprises an ionization cell made of organic glass material, and two activated carbon electrodes, a cation exchange membrane, an anion exchange membrane, a porous support frame and two power cords distributed in parallel in the ionization cell, wherein the two power cords are respectively connected to the two activated carbon electrodes, a cation exchange membrane and an anion exchange membrane are respectively arranged on both sides of the porous support frame, and the membrane capacitor deionization device realizes desalination of effluent water by intermittent ionization of synthesized influent water by applying an external voltage; The water inlet end of the water temperature control module is connected to one end of the ionization cell through a first pipe, and the water outlet end of the water temperature control module is connected to the inside of the ionization cell through a third pipe. The water temperature control module is used to maintain the stability of the water inlet temperature of the membrane capacitor deionization device, thereby reducing the energy consumption during the operation of the membrane capacitor deionization device. The membrane capacitor deionization module is formed by combining a porous carbon electrode with an ion exchange membrane, and is combined with a water temperature control module. Ions are separated from the inlet solution by applying a low voltage to achieve outlet water desalination. The inlet temperature is stabilized by the temperature control module, which can reduce the energy consumption of the membrane capacitor deionization system. The data acquisition system is electrically connected between the membrane capacitor deionization device and the water temperature control module, and is used to collect and process data from the membrane capacitor deionization device and the water temperature control module.

[0007] As a further solution of the present invention: the porous support frame is a planar support plate with multiple arrays of perforations, and the porous support frame is used to form a water inlet channel.

[0008] As a further solution of the present invention: the water temperature control module includes a constant temperature bath, a conductivity meter installed throughout the constant temperature bath, and a temperature control module fixed on the surface of the constant temperature bath. The constant temperature bath is loaded with synthetic inlet water. The temperature control module is used to monitor the temperature of pure water in the constant temperature bath. By maintaining the consistency of the temperature of the synthetic inlet water in the constant temperature bath, the consistency of experimental conditions can be ensured. The conductivity meter is electrically connected to the data acquisition system. The conductivity meter is used to monitor the conductivity of the synthetic inlet water in the constant temperature bath. The conductivity meter is a CON-BTA conductivity meter.

[0009] As a further solution of the present invention: the temperature control module is made of a material with photothermal conversion performance, the material with photothermal conversion performance is used to absorb light energy and convert the absorbed light energy into heat energy to achieve low-energy water temperature control, the material with photothermal conversion performance includes two-dimensional MXene nanomaterials, multilayer graphene, organic polymers or plasma metals, and by setting up the temperature control module, it is possible to maintain a stable desalination efficiency under different temperature conditions, and has lower energy consumption and higher current efficiency, which is higher than the desalination efficiency of the traditional reverse osmosis (RO) seawater desalination method. By controlling the stability of temperature, the positive effect on the migration of ions through IEMs and the negative effect of temperature on ion adsorption on the electrode can be offset, so that the membrane capacitor deionization system can maintain high-efficiency desalination performance and low energy consumption, and at the same voltage, the high-temperature feed aqueous solution can exhibit lower resistance and higher current efficiency.

[0010] As a further solution of the present invention: the concentration of the synthetic influent is 500 mg / L, the synthetic influent is prepared by dissolving sodium chloride in purified water, the purified water is Milli-Q purified water, and the resistivity of the purified water is 18.2 MΩ·cm.

[0011] As a further solution of the present invention: the activated carbon electrode includes an anode and a cathode, and the anode and the cathode are both made of polyvinylidene fluoride (PVDF), carbon black and activated carbon fully dissolved in N-methylpyrrolidone (NMP) solution, wherein the mass ratio of polyvinylidene fluoride (PVDF) is 4%, the mass ratio of carbon black is 5%, and the mass ratio of activated carbon is 91%. The solvent of polyvinylidene fluoride (PVDF) and carbon black fully dissolved and mixed in N-methylpyrrolidone (NMP) solution is applied to a graphite plate, and dried in an oven at 60°C for 12 hours to completely remove the solvent. The dried graphite plate is cut into a standard size of 5.8 cm × 5.8 cm for use.

[0012] As a further solution of the present invention: the data acquisition system includes a water circulation pump, a server, a DC power supply and a display. A second pipeline is connected between the constant temperature bath and the water circulation pump. The water circulation pump is used to drain synthetic water to the membrane capacitor deionization device. The water circulation pump is connected between the membrane capacitor deionization device and the water temperature control module. The positive and negative electrodes of the DC power supply are connected to the activated carbon electrodes through two power lines, and voltage is provided to the membrane capacitor deionization device. The water circulation pump is a double-head peristaltic pump, and the model of the double-head peristaltic pump is L100-1S-1.

[0013] As a further solution of the present invention: the voltage provided by the DC power supply is 0.3V-1.2V, and the temperature control module controls the synthetic water inlet temperature to increase from 20°C to 25°C, which can increase the effective pore size of the cation exchange membrane and / or the anion exchange membrane.

[0014] In the membrane capacitor deionization system, due to the effect of the Faraday reaction, the pH value of the feed water drops to about 4 during the charging stage regardless of the temperature change; while during the discharge stage, the pH value returns to the initial level. In addition, the experiment observed that higher feed water temperature accelerates the rate of pH decrease, which is similar to the performance of the CDI system under the same conditions, but the pH decrease rate of the CDI system is more significant in the early stage. Compared with the non-Faraday process, the Faraday reaction is the main mechanism causing pH changes. Under the applied voltage conditions, the main Faraday reactions in the membrane capacitor deionization device 1 include the electrolysis equation 4 of water and the carbon oxidation equation 5 on the anode, generating From the anode chamber through the anion exchange membrane into the compartment, thereby reducing the pH of the feed water. It is worth noting that due to the existence of electrostatic repulsion, the pH drop rate in the membrane capacitive deionization device 1 is slower than that in the CDI system.

[0015] (Equation 1) (Equation 2) (Equation 3) (Equation 4) (Equation 5) (Equation 6) Equation 7 shows the standard electrode potential E0 at different temperatures: (Equation 7) Where E 0 T is the standard electrode potential at temperature T, 298 K (temperature coefficient mV / K at 25°C.

[0016] For the chemical reaction under study, the temperature coefficient is a negative constant, indicating that E 0 T It is negatively correlated with temperature. Specifically, as the feed water temperature increases, E 0 T It can be inferred that under the condition of constant applied voltage, the temperature rise will intensify the occurrence of Faraday anode reaction equations 4 and 5, accelerating The generation of hydrogen ions in the water leads to a rapid decrease in pH value. In addition, when the temperature rises, the ion migration impedance in the solution decreases, and the ion embedding reaction rate and ion diffusion coefficient both increase. These changes work together to reduce the overpotential and increase the discharge voltage. Based on this, the charge transfer temperature is maintained by controlling the temperature, and the diffusion efficiency temperature of hydrogen ions in the feed water is maintained, so as to achieve a balance between electron transfer and hydrogen ion diffusion process, further inhibit the Faraday reaction equations 4 and 5 of the anode, maintain electrode stability, and help maintain the stability of the outlet pH value.

[0017] Therefore, by constructing a temperature-controlled assisted membrane capacitor deionization high-efficiency desalination system, the membrane capacitor deionization can maintain the quality and stability of water flux with low energy consumption under low / high temperature conditions, wherein the membrane capacitor deionization device 1 uses electrostatic force to drive ions to migrate to the electrode surface, while the temperature control system maintains the stability of the electrode, thereby effectively expanding the application prospects of the membrane capacitor deionization device 1 in extreme temperature environments. The performance stability of the temperature-controlled assisted membrane capacitor deionization high-efficiency desalination system under long-term operation conditions is further explored under different temperature environments.

[0018] Table 1 shows the desalination efficiency of the system in the 1st and 10th cycles;

[0019] After 10 cycles, the system's desalination efficiency remained at about 91%. The results show that the temperature-controlled assisted membrane capacitive deionization high-efficiency desalination system has advantages over the traditional RO system in terms of desalination efficiency and energy consumption of brine at different temperatures, especially in areas with large temperature fluctuations or cold areas. This technology has a wide range of applications, low processing energy consumption, and long-term stable operation, and has great commercial application prospects.

[0020] In a second aspect, the present invention further provides a temperature-controlled auxiliary membrane capacitor deionization and desalination method, which is applied to the temperature-controlled auxiliary membrane capacitor deionization and desalination system as described in the above scheme, and the temperature-controlled auxiliary membrane capacitor deionization and desalination method comprises: preparing synthetic feed water, anode and cathode of activated carbon electrodes; The DC power supply is charged at a preset voltage for 2400 seconds, and the discharge process is performed for 2400 seconds by changing the voltage direction to achieve electrode regeneration; Set the charging voltage group and water inlet flow rate group; Given the inlet water temperature; The effect of inlet water temperature on the desalination efficiency of the membrane capacitor deionization system under certain charging voltage and feed flow rate conditions was determined.

[0021] As a further solution of the present invention: the charging voltage group consists of 0V, 0.3V, 0.6V, 0.9V, 1.2V, and 1.5V, and the water inlet flow rate group consists of 3.6mL / min, 12.6mL / min, 18.6mL / min, 24.6mL / min, 30.6mL / min, 36.6mL / min, 40.6mL / min, and 44.6 mL / min.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. In the present invention, a membrane capacitor deionization module is formed by combining a porous carbon electrode with an ion exchange membrane, and a water temperature control module is combined at the same time. By applying a low voltage, ions are separated from the inlet solution to achieve effluent desalination. The inlet temperature is stabilized by the temperature control module, which can reduce the energy consumption of the membrane capacitor deionization system.

[0023] 2. In the present invention, by setting a water temperature control module, it is possible to maintain a stable desalination efficiency under different temperature conditions, and has lower energy consumption and higher current efficiency, and has a higher desalination efficiency than the traditional reverse osmosis (RO) seawater desalination method.

[0024] 3. In the present invention, the system can maintain a desalination efficiency of more than 90% at low / high temperatures. In addition, the system energy consumption can be reduced by 10% with the assistance of the temperature control module. The operation is simple and the desalination effect is stable.

[0025] 4. In the present invention, by controlling the stability of temperature, the positive effect on the migration of ions through IEMs and the negative effect of temperature on ion adsorption on electrodes can be offset, so that the membrane capacitor deionization system can maintain high-efficiency desalination performance and low energy consumption. At the same time, at the same voltage, the high-temperature feed aqueous solution can show lower resistance and higher current efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a diagram of the temperature-controlled auxiliary membrane capacitor deionization system of the present invention; Figure 2 This is a performance diagram of the deionization and desalination system under different voltage conditions of the present invention. Figure 2 (a) is the relationship between the change of inlet water conductivity and the change of voltage. Figure 2 (b) is the relationship between specific energy consumption and current efficiency as voltage changes. Figure 2 (c) is the desalination efficiency diagram at different flow rates. Figure 2 (d) is the relationship between system current efficiency and unit energy consumption at different flow rates; Figure 3 is a graph showing the relationship between conductivity and time under different applied voltage conditions of the present invention; Figure 4 It is a relationship diagram between the inlet water conductivity and different voltages under the charge and discharge conditions of the present invention; Figure 5 This is a graph of desalination efficiency when the water temperature is 15°C to 40°C according to the present invention; Figure 6 is a graph showing the relationship between the current efficiency and temperature of the present invention, Figure 6 (a) is the relationship between desalination efficiency and temperature. Figure 6 (b) is the relationship between current efficiency and specific energy consumption and temperature; Figure 7 This is a relationship diagram between water temperature and pH value after desalination according to the present invention; Figure 8 The present invention is a flow chart of the steps of the temperature-controlled auxiliary membrane capacitor deionization and desalination method.

[0027] In the figure: 1. membrane capacitor deionization device; 101. ionization cell; 102. activated carbon electrode; 103. cation exchange membrane; 104. anion exchange membrane; 105. porous support frame; 106. power cord; 2. water temperature control module; 201. constant temperature bath; 202. conductivity meter; 203. temperature control module; 3. data acquisition system; 301. water circulation pump; 302. server; 303. DC power supply; 304. display; 4. first pipeline; 5. second pipeline; 6. third pipeline. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0029] See also Figure 1The present invention discloses a temperature-controlled auxiliary membrane capacitor deionization and desalination system, comprising a membrane capacitor deionization device 1, a water temperature control module 2 and a data acquisition system 3. The membrane capacitor deionization device 1 comprises an ionization cell 101 made of organic glass plates, and a pair of activated carbon electrodes 102, a cation exchange membrane 103, an anion exchange membrane 104, a porous support frame 105 and two power lines 106 distributed in parallel in the ionization cell 101. The two power lines 106 are respectively connected to the two activated carbon electrodes 102, a cation exchange membrane 103 and an anion exchange membrane 104 are respectively arranged on both sides of the porous support frame, and the organic glass plate 102, a cation exchange membrane 103, an anion exchange membrane 104 and a porous support frame 105 are arranged in parallel with each other. The membrane capacitor deionization device 1 realizes desalination of effluent water by intermittent ionization of synthesized influent water through an applied voltage; The water inlet end of the water temperature control module 2 is connected to one end of the ionization cell 101 through the first pipe 4, and the water outlet end of the water temperature control module 2 is connected to the inside of the ionization cell 101 through the third pipe 6. The water temperature control module 2 is used to maintain the stability of the water inlet temperature of the membrane capacitor deionization device 1, thereby reducing the energy consumption of the membrane capacitor deionization device 1 during operation; The data acquisition system 3 is electrically connected between the membrane capacitor deionization device 1 and the water temperature control module 2 . The data acquisition system 3 is used to collect and process data from the membrane capacitor deionization device 1 and the water temperature control module 2 .

[0030] Preferably, the porous support frame 105 is a planar support plate having multiple arrays of perforations, and the porous support frame 105 is used to form a water inlet channel to facilitate the flow of synthetic inlet water in the thermostatic bath 201 .

[0031] Preferably, the water temperature control module 2 includes a thermostatic bath 201, a conductivity meter 202 installed in the thermostatic bath, and a temperature control module 203 fixed on the surface of the thermostatic bath 201. The thermostatic bath 201 is loaded with synthetic inlet water. The temperature control module 203 is used to monitor the temperature of pure water in the thermostatic bath 201. By maintaining the consistency of the synthetic inlet water temperature in the thermostatic bath 201, the consistency of the experimental conditions can be ensured, and the influence of the applied charging voltage value and the inlet water flow rate on the desalination efficiency under different temperature conditions can be studied; The conductivity meter 202 is electrically connected to the data acquisition system 3 . The monitoring probe of the conductivity meter 202 is located in the thermostatic bath 201 and is used to monitor the conductivity of the synthetic influent water in the thermostatic bath 201 . The conductivity meter 202 is a CON-BTA conductivity meter.

[0032] Preferably, the temperature control module 203 is made of a material with photothermal conversion performance. The material with photothermal conversion performance is used to absorb light energy and convert the absorbed light energy into heat energy to achieve low-energy water temperature control. The material with photothermal conversion performance includes two-dimensional MXene nanomaterials, multilayer graphene, organic polymers or plasma metals. By setting up the temperature control module, it is possible to maintain a stable desalination efficiency under different temperature conditions, and has lower energy consumption and higher current efficiency. The desalination efficiency is higher than that of the traditional reverse osmosis (RO) seawater desalination method. By controlling the stability of temperature, the positive effect on the migration of ions through IEMs and the negative effect of temperature on ion adsorption on the electrode can be offset, so that the membrane capacitor deionization system can maintain high-efficiency desalination performance and low energy consumption. At the same time, under the same voltage, the high-temperature feed aqueous solution can exhibit lower resistance and higher current efficiency.

[0033] Preferably, the concentration of the synthetic influent water is 500 mg / L, and the synthetic influent water is prepared by dissolving sodium chloride in purified water, and the purified water is Milli-Q purified water, and the resistivity of the purified water is 18.2 MΩ·cm.

[0034] Preferably, the activated carbon electrode 102 includes an anode and a cathode, both of which are made of polyvinylidene fluoride PVDF, carbon black and activated carbon fully dissolved in N-methylpyrrolidone NMP solution, wherein the mass ratio of polyvinylidene fluoride PVDF is 4%, the mass ratio of carbon black is 5%, and the mass ratio of activated carbon is 91%. The solvent of polyvinylidene fluoride PVDF and carbon black fully dissolved and mixed in N-methylpyrrolidone NMP solution is applied to a graphite plate, and dried in an oven at 60°C for 12 hours to completely remove the solvent. The dried graphite plate is cut into a standard size of 5.8 cm × 5.8 cm for use.

[0035] Preferably, the data acquisition system 3 includes a water circulation pump 301, a server 302, a DC power supply 303 and a display 304. The signal input end of the display 304 is electrically connected to the server 302. The server 302 uses the collected temperature, voltage, and water inlet flow rate data to process and obtain the current efficiency and the energy consumption value under the corresponding experimental conditions, and displays the data through the display 304. A second pipe 5 is connected between the thermostatic bath 201 and the water circulation pump 301. The water circulation pump 301 is used to drain the synthetic water inlet to the membrane capacitor deionization device 1. When the water circulation pump 301 is started, the synthetic water in the thermostatic bath 201 can be drained to the third pipe 6 through the second pipe 5, and the synthetic water inlet can be drained into the ionization cell 101 through the third pipe 6. The water circulation pump 301 is connected between the membrane capacitor deionization device 1 and the water temperature control module 2. The DC power supply 303 is used to provide voltage. The water circulation pump 301 is a double-head peristaltic pump, which can realize the pumping / draining operation of the synthetic water inlet. The model of the double-head peristaltic pump is L100-1S-1.

[0036] Preferably, the voltage provided by the DC power supply 303 is 0.3V-1.2V, and the temperature control module 203 controls the synthetic water inlet temperature to increase from 20°C to 25°C, so as to increase the effective pore size of the cation exchange membrane 103 and / or the anion exchange membrane 104. When the water inlet temperature is controlled to increase from 20°C to 50°C, the structure of the polymer chain is changed, thereby causing the effective pore size of the ion exchange membrane to expand from 0.58±0.03 nm to 0.66±0.01 nm. At the same time, due to the partial dissociation of water molecules in the ion hydration shell at high temperature, the thermal motion in the solution is accelerated. By controlling the temperature increase by the temperature control module 203, the radius of the hydrated ion can be reduced. However, too high a temperature will cause the adsorption capacity of the activated carbon electrode 106 to decrease. Therefore, by controlling the temperature of the synthetic water inlet to be within a suitable range of 20-25°C, the pore size of the ion exchange membrane and the smaller ion hydration radius are increased, which is beneficial for the salt ions to pass through the ion exchange membrane.

[0037] In summary, by controlling the temperature to be stable, the positive effect on ion migration through the ion exchange membrane and the negative effect of temperature on ion adsorption on the electrode can be offset, so that the membrane capacitive deionization device 1 can maintain high desalination performance and low energy consumption.

[0038] According to the current efficiency equation (SI, Eq. 4), at the same voltage, the high-temperature feed aqueous solution exhibits lower resistance and higher current efficiency at time t, while according to the specific energy consumption equation (SI, Eq. 3), the high-temperature feed aqueous solution achieves better specific energy consumption due to the increase in total energy consumption due to the high current.

[0039] like Figure 2 and Figure 3 As shown, by applying a voltage increasing from 0.3V to 1.2V to the data acquisition system 3 through the DC power supply 303, it can be clearly seen that the salt removal rate in the membrane capacitor deionization device 1 jumps from 16.1% to 93.7%, which can achieve a high salt removal rate while reducing energy consumption; at the same time, it is observed that as the voltage is increased from 1.2V to 1.5V, the energy consumption per unit of treated water also increases from 0.04 kWh / m³ to 0.93 kWh / m³.

[0040] like Figure 2 As shown in (b), it is worth noting that the current efficiency reaches a peak value of 95.8% at a voltage of 0.9 V, and then drops to 80.7% at 1.5 V, suggesting that the Faraday reaction and its accompanying adverse side reactions, such as water electrolysis, may be induced in this process, thereby affecting the stability of the current efficiency. Considering the salt removal efficiency and energy consumption factors, this embodiment preferably selects 1.2 V as the optimal operating voltage for in-depth discussion.

[0041] like Figure 2 As shown in (c), when the feed water flow rate increases from 3.6 mL / min to 24.6 mL / min, the salt removal efficiency in the membrane capacitor deionization device 1 increases from 90.0% to 96.1%. However, when the feed water flow rate further increases to 44.6 mL / min, the salt removal efficiency decreases to 89.5%. The slow flow rate leads to a decrease in the mass transfer rate, which reduces the chance of ions reaching the electrode surface for adsorption. In addition, too low a flow rate will also lead to a decrease in the average concentration of ions in the membrane capacitor deionization device 1, reducing the driving force for ion transmission to the electrode, thereby reducing the salt removal efficiency. On the other hand, a faster flow rate provides a higher pumping force, which limits the transfer rate of ions in the feed water. Therefore, when the feed water flow rate exceeds 24.6 mL / min, the salt removal efficiency will not increase but decrease. By controlling the feed water flow rate, the salt removal efficiency in the membrane capacitor deionization device 1 can be further controlled.

[0042] like Figure 2 As shown in (d), as the water feed flow rate increases from 3.6 mL / min to 30.6 mL / min, the unit energy consumption increases from 0.65 kWh / m³ to 0.75 kWh / m³. It is worth noting that after reaching 30.6 mL / min, although the water inlet flow rate of membrane capacitor deionization device 1 continues to increase, the unit energy consumption remains stable.

[0043] At the same time, when the inlet flow rate increased from 3.6 mL / min to 44.6 mL / min, the current efficiency showed a trend of decreasing from 89.5% to 74.1%. The difference in energy consumption under different inlet flow rates can be attributed to the partial relief of the current when the flow rate was increased. This phenomenon may be related to the heterogeneity of the solution ion concentration distribution in the membrane capacitive deionization device 1. Specifically, the electrosorption effect exceeds the ion transport caused by electromigration and convection, resulting in the formation of a low concentration area near the electrode accompanied by a significant current slowdown. In addition, a higher water flow rate helps to alleviate the ion concentration polarization effect, while a lower water flow rate reduces the internal dissipation of energy due to smaller ohmic losses. However, the total charge increases with the increase of the inlet flow rate. Too fast an inlet flow rate may hinder the effective adsorption of ions on the electrode surface, thereby reducing the effective Coulomb force in the electrosorption process. Therefore, the unit energy consumption increases with the increase of the inlet flow rate. The current efficiency is slightly improved in the initial stage, but as the water flow rate is further increased, the increase in the total charge is more significant.

[0044] In summary, in the present invention, the optimal water supply flow rate range of the membrane capacitor deionization device 1 is 18.6 mL / min~30.6 mL / min. Therefore, the present invention preferably selects 18.6 mL / min as the water supply flow rate in subsequent experiments.

[0045] like Figure 5 As shown, the operating procedure of the membrane capacitor deionization device 1 for batch operation based on the change of solution feed water temperature was tested, and the desalination performance of the membrane capacitor deionization device 1 was analyzed. The results showed that by controlling the water temperature to 15°C to 40°C, it was found that the desalination efficiency of the membrane capacitor deionization device 1 could be maintained at about 92%. By establishing a system at low / high temperature, the desalination efficiency can still be maintained at more than 90%. In addition, with the assistance of the temperature control module, the system energy consumption can be reduced by 10%. The operation is simple and the desalination effect is stable.

[0046] like Figure 6 As shown, the specific energy consumption increases with the increase of water temperature, that is, the specific energy consumption increases from 0.65k kWh / m³ to 0.76kkWh / m³. At the same time, with the change of solution water supply temperature, the current efficiency decreases by 14%. Therefore, by adding a temperature control module 203 to assist the water temperature, the desalination energy consumption of the membrane capacitor deionization device 1 can be effectively reduced, thereby improving the current efficiency.

[0047] like Figure 7 The figure shows the effect of water temperature on the pH value of synthetic inlet water after treatment by membrane capacitor deionization device 1. In the membrane capacitor deionization system, due to the effect of Faraday reaction, the pH value of the feed water drops to about 4 during the charging stage regardless of temperature changes; while during the discharge stage, the pH value returns to the initial level. In addition, the experiment observed that higher feed water temperature accelerates the rate of pH decrease, which is similar to the performance of the CDI system under the same conditions, but the pH decrease rate of the CDI system is more significant in the early stage. Compared with the non-Faraday process, the Faraday reaction is the main mechanism leading to pH changes. Under the applied voltage conditions, the main Faraday reactions in the membrane capacitor deionization device 1 include the electrolysis equation 4 of water and the carbon oxidation equation 5 on the anode. The generated H+ It passes through the anion exchange membrane from the anode chamber into the compartment, thereby reducing the pH value of the feed water. It is worth noting that due to the existence of electrostatic repulsion, the pH drop rate in the membrane capacitive deionization device 1 is slower than that in the CDI system. (Equation 1) (Equation 2) (Equation 3) (Equation 4) (Equation 5) (Equation 6) Equation 7 shows the standard electrode potential E0 at different temperatures: (Equation 7) Where E 0 T is the standard electrode potential at temperature T, 298 K (temperature coefficient mV / K at 25°C).

[0048] For the chemical reaction under study, the temperature coefficient is a negative constant, indicating that E 0 T It is negatively correlated with temperature. Specifically, as the feed water temperature increases, E 0 T It can be inferred that under the condition of constant applied voltage, the temperature rise will intensify the occurrence of Faraday anode reaction equations 4 and 5, accelerating The generation of hydrogen ions in the water leads to a rapid decrease in pH value. In addition, when the temperature rises, the ion migration impedance in the solution decreases, and the ion embedding reaction rate and ion diffusion coefficient both increase. These changes work together to reduce the overpotential and increase the discharge voltage. Based on this, the charge transfer temperature is maintained by controlling the temperature, and the diffusion efficiency temperature of hydrogen ions in the feed water is maintained, so as to achieve a balance between electron transfer and hydrogen ion diffusion process, further inhibit the Faraday reaction equations 4 and 5 of the anode, maintain electrode stability, and help maintain the stability of the outlet pH value.

[0049] Therefore, by constructing a temperature-controlled assisted membrane capacitor deionization high-efficiency desalination system, the membrane capacitor deionization can maintain the quality and stability of water flux with low energy consumption under low / high temperature conditions, wherein the membrane capacitor deionization device 1 uses electrostatic force to drive ions to migrate to the electrode surface, while the temperature control system maintains the stability of the electrode, thereby effectively expanding the application prospects of the membrane capacitor deionization device 1 in extreme temperature environments. The performance stability of the temperature-controlled assisted membrane capacitor deionization high-efficiency desalination system under long-term operation conditions is further explored under different temperature environments.

[0050] Table 1 shows the desalination efficiency of the system in the 1st and 10th cycles;

[0051] After 10 cycles, the system's desalination efficiency remained at about 91%. The results show that the temperature-controlled assisted membrane capacitive deionization high-efficiency desalination system has advantages over the traditional RO system in terms of desalination efficiency and energy consumption of salt water at different temperatures, especially in areas with large temperature fluctuations or cold areas. This technology has a wide range of applications, low processing energy consumption, and long-term stable operation.

[0052] like Figure 8The figure shows a flow chart of the steps of the temperature-controlled auxiliary membrane capacitor deionization and desalination method of the present invention, which provides a temperature-controlled auxiliary membrane capacitor deionization and desalination method, which is applied to the temperature-controlled auxiliary membrane capacitor deionization and desalination system of the above scheme, and the temperature-controlled auxiliary membrane capacitor deionization and desalination method comprises: S1: preparing synthetic feed water, anode and cathode of activated carbon electrode; S2: charging the DC power supply at a preset voltage for 2400 seconds, and performing a discharge process for 2400 seconds by changing the voltage direction to achieve electrode regeneration; S3: Setting the charging voltage group and the water inlet flow rate group; S4: given water inlet temperature; S5: Determine the effect of inlet water temperature on the desalination efficiency of the membrane capacitor deionization desalination system under certain charging voltage and feed flow rate conditions.

[0053] Preferably, the charging voltage group consists of 0V, 0.3V, 0.6V, 0.9V, 1.2V, and 1.5V, and the water inlet flow rate group consists of 3.6mL / min, 12.6mL / min, 18.6mL / min, 24.6mL / min, 30.6mL / min, 36.6mL / min, 40.6mL / min, and 44.6 mL / min.

[0054] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A temperature-controlled auxiliary membrane capacitor deionization and desalination system, characterized in that: include: A membrane capacitor deionization device, comprising an ionization cell made of organic glass, and a cation exchange membrane, an anion exchange membrane, a porous support frame, a pair of activated carbon electrodes and two power lines distributed in parallel in the ionization cell, the two power lines are respectively connected to the activated carbon electrodes, a cation exchange membrane and an anion exchange membrane are respectively arranged on both sides of the porous support frame, and the membrane capacitor deionization device realizes desalination of effluent water by intermittent ionization of synthesized influent water through an external voltage; A water temperature control module, wherein the water inlet end of the water temperature control module is connected to one end of the ionization cell through a first pipe, and the water outlet end of the water temperature control module is connected to the interior of the ionization cell through a third pipe, and the water temperature control module is used to maintain the stability of the water inlet temperature of the membrane capacitor deionization device; A data acquisition system is electrically connected between the membrane capacitor deionization device and the water temperature control module, and is used to collect and process data from the membrane capacitor deionization device and the water temperature control module.

2. The temperature-controlled auxiliary membrane capacitor deionization and desalination system according to claim 1, characterized in that: The porous support frame is a planar support plate having a plurality of arrays of perforations, and the porous support frame is used to form a water inlet channel.

3. The temperature-controlled auxiliary membrane capacitor deionization and desalination system according to claim 1, characterized in that: The water temperature control module includes a thermostatic bath, a conductivity meter installed in the thermostatic bath, and a temperature control module fixed on the surface of the thermostatic bath. The thermostatic bath is loaded with synthetic influent water. The temperature control module is used to monitor the temperature of pure water in the thermostatic bath. The conductivity meter is electrically connected to the data acquisition system, and the conductivity meter is used to monitor the conductivity of the synthetic influent water in the constant temperature bath.

4. The temperature-controlled auxiliary membrane capacitor deionization and desalination system according to claim 3, characterized in that: The temperature control module is made of a material with photothermal conversion performance, and the material with photothermal conversion performance is used to absorb light energy and convert the absorbed light energy into heat energy.

5. The temperature-controlled auxiliary membrane capacitor deionization and desalination system according to claim 1, characterized in that: The concentration of synthetic influent water is 500 mg / L. The synthetic influent water is prepared by dissolving sodium chloride in purified water. The resistivity of purified water is 18.2 MΩ·cm.

6. The temperature-controlled auxiliary membrane capacitor deionization and desalination system according to claim 4, characterized in that: The activated carbon electrode includes an anode and a cathode, both of which are made of polyvinylidene fluoride (PVDF), carbon black and activated carbon fully dissolved in N-methylpyrrolidone (NMP) solution, wherein the mass ratio of polyvinylidene fluoride (PVDF) is 4%, the mass ratio of carbon black is 5%, and the mass ratio of activated carbon is 91%.

7. The temperature-controlled auxiliary membrane capacitor deionization and desalination system according to claim 6, characterized in that: The data acquisition system includes a water circulation pump, a server, a DC power supply and a display. A second pipeline is connected between the constant temperature bath and the water circulation pump. The water circulation pump is used to drain synthetic water to the membrane capacitor deionization device. The water circulation pump is connected between the membrane capacitor deionization device and the water temperature control module. The water circulation pump is a double-head peristaltic pump.

8. The temperature-controlled auxiliary membrane capacitor deionization and desalination system according to claim 7, characterized in that: The voltage provided by the DC power supply is 0.3V-1.2V, and the temperature control module controls the synthetic water inlet temperature to increase from 20°C to 25°C, which is used to increase the effective pore size of the cation exchange membrane and / or the anion exchange membrane.

9. A temperature-controlled auxiliary membrane capacitor deionization and desalination method, applied to the temperature-controlled auxiliary membrane capacitor deionization and desalination system according to any one of claims 1 to 8, characterized in that: The temperature-controlled assisted membrane capacitive deionization and desalination method includes: preparing synthetic feed water, anode and cathode of activated carbon electrodes; The DC power supply is charged at a preset voltage for 2400 seconds, and the discharge process is performed for 2400 seconds by changing the voltage direction to achieve electrode regeneration; Set the charging voltage group and water inlet flow rate group; Given the inlet water temperature; The effect of inlet water temperature on the desalination efficiency of membrane capacitive deionization system under certain charging voltage and feed flow rate conditions was determined.

10. The temperature-controlled assisted membrane capacitor deionization and desalination method according to claim 9, characterized in that: The charging voltage group consists of 0V, 0.3V, 0.6V, 0.9V, 1.2V, and 1.5V. The water inlet flow rate group consists of 3.6mL / min, 12.6mL / min, 18.6mL / min, 24.6mL / min, 30.6mL / min, 36.6mL / min, 40.6mL / min, and 44.6 mL / min.

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