Thermostatic control assisted membrane capacitive deionization desalination system and desalination method

Abstract

The present invention discloses a temperature-controlled auxiliary membrane capacitive deionization desalination system and a desalination method in the field of water treatment technology, which includes a membrane capacitive deionization device, a water temperature control module, and a data acquisition system. The membrane capacitive deionization device includes an ionization cell made of glass material, a cation exchange membrane, an anion exchange membrane, a porous support frame, a pair of activated carbon electrodes, and two power lines that are parallelly distributed in the ionization cell. The two power lines are respectively connected to the two activated carbon electrodes, and a cation exchange membrane and an anion exchange membrane are respectively arranged on both sides of the porous support frame. In the present invention, a porous activated carbon electrode is combined with an ion exchange membrane to form a membrane capacitive deionization device, and a low voltage is applied externally in the desalination system to separate ions from the influent solution, achieving desalination of the effluent. The water temperature control module is used to stabilize the influent temperature and reduce the energy consumption of operating the membrane capacitive deionization system.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and specifically to a temperature-controlled assisted membrane capacitive deionization desalination system and a desalination method. Background Art

[0002] At present, a variety of technologies have been developed for seawater / brackish water desalination, mainly including pressure-driven, electrochemically-driven, and thermally-driven desalination methods. Reverse osmosis (RO), as a classic process for pressure-driven desalination, has been widely applied in the fields of seawater and brackish water treatment and resource recovery. Research shows that for every 1°C decrease in the water temperature, the water production of RO will decrease by 3%. Given that the temperature of sea / brackish water varies significantly with 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 disadvantages such as high energy consumption, huge infrastructure investment, easy scaling, and high sensitivity to temperature changes. On this basis, capacitive deionization (CDI), as an emerging electrochemically-driven desalination technology, is developing rapidly. The core of this technology lies in using porous carbon electrodes to achieve efficient adsorption and release of ions, thereby achieving the purpose of desalinating seawater / brackish water.

[0003] In the evolution process 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 ion transport path by introducing ion exchange membranes (IEMs) with high charge density, that is, it promotes the passage of counterions and hinders co-ions, and can significantly enhance the desalination efficiency and stability of the system. Particularly importantly, the introduction of IEMs successfully inhibits the migration process of dissolved oxygen to the cathode, reduces the occurrence of Faraday side reactions, and further improves the overall performance and operation stability of the MCDI system.

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

[0005] The purpose of the present invention is to provide a temperature-controlled assisted membrane capacitive deionization desalination system and a desalination method. By setting a temperature assistance module, it can maintain a stable desalination efficiency under different temperature conditions, and has low energy consumption and high 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 capacitive deionization desalination system, which includes a membrane capacitive deionization device, a water temperature control module, and a data acquisition system. The membrane capacitive deionization device includes an ionization cell made of plexiglass, two activated carbon electrodes parallelly distributed in the ionization cell, a cation exchange membrane, an anion exchange membrane, a porous support, and two power lines. The two power lines 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. The membrane capacitive deionization device realizes desalination of the effluent by intermittently ionizing and synthesizing the influent under an applied voltage.

[0007] The inlet end of the water temperature control module is connected to one end of the ionization cell through a first pipeline, and the outlet end of the water temperature control module is connected to the inside of the ionization cell through a third pipeline. The water temperature control module is used to maintain the stability of the influent temperature of the membrane capacitive deionization device, thereby reducing the energy consumption during the operation of the membrane capacitive deionization device. By combining a porous carbon electrode and an ion exchange membrane to form a membrane capacitive deionization module, and at the same time combining a water temperature control module, ions are separated from the influent solution by applying a low external voltage to achieve desalination of the effluent. By stabilizing the influent temperature through the temperature control module, the energy consumption of operating the membrane capacitive deionization system can be reduced.

[0008] The data acquisition system is electrically connected between the membrane capacitive deionization device and the water temperature control module, and the data acquisition system is used to collect and process the data of the membrane capacitive deionization device and the water temperature control module.

[0009] As a further solution of the present invention: the porous support is a planar support plate with multiple arrays of perforations, and the porous support is used to form an influent channel.

[0010] As a further solution of the present invention: the water temperature control module includes a constant temperature bath, a conductivity meter installed through the constant temperature bath, and a temperature control module fixed on the surface of the constant temperature bath. The constant temperature bath is filled with synthetic influent. The temperature control module is used to monitor the temperature of the pure water in the constant temperature bath. By maintaining the consistency of the temperature of the synthetic influent in the constant temperature bath, the consistency of the experimental conditions can be ensured. 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 in the constant temperature bath. The conductivity meter is a CON-BTA conductivity meter.

[0011] 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 consumption water temperature regulation. The material with photothermal conversion performance includes two-dimensional MXene nanomaterials, multi-layer graphene, organic polymers or plasmonic metals. By setting the temperature control module, it is possible to maintain a stable desalination efficiency under different temperature conditions, and it has low energy consumption and high current efficiency, and has a higher desalination efficiency than the traditional reverse osmosis (RO) seawater desalination method. By controlling the stability of the temperature, the positive effect of the ion migration through the IEMs can be offset by the negative effect of the temperature on the ion adsorption on the electrodes, so that the membrane capacitive 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 exhibit lower resistance and higher current efficiency.

[0012] As a further solution of the present invention: The concentration of the synthetic feed water is 500 mg / L. The synthetic feed water is made 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.

[0013] As a further solution of the present invention: The activated carbon electrode includes an anode and a cathode. Both the anode and the cathode are made of polyvinylidene fluoride (PVDF), carbon black and activated carbon fully dissolved in N-methylpyrrolidone (NMP) solution. Among them, 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%. By applying the solvent of polyvinylidene fluoride (PVDF) and carbon black fully dissolved and mixed in N-methylpyrrolidone (NMP) solution on a graphite plate and drying it 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 standby.

[0014] 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 divert the synthetic feed water to the membrane capacitive deionization device. The water circulation pump is connected between the membrane capacitive deionization device and the water temperature control module. The positive and negative poles of the DC power supply are connected to the activated carbon electrode through two power lines and provide voltage to the membrane capacitive deionization device. The water circulation pump is a double-headed peristaltic pump, and the model of the double-headed peristaltic pump is L100-1S-1.

[0015] As a further solution of the present invention: The voltage provided by the DC power supply is 0.3V - 1.2V. The temperature control module controls the temperature of the synthetic feed water to rise from 20°C to 25°C, which can increase the effective pore size of the cation exchange membrane and / or the anion exchange membrane.

[0016] In the membrane capacitive deionization system, due to the Faraday reaction, regardless of temperature changes, the pH value of the feed water drops to around 4 during the charging stage; while in the discharging stage, the pH value returns to the initial level. In addition, experimental observations show that a higher feed water temperature accelerates the rate of pH decline. This phenomenon is similar to the performance of the CDI system under the same conditions, but the rate of pH decline in the CDI system is more significant in the initial 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 capacitive deionization device 1 include the electrolysis equation of water 4 and the carbon oxidation equation 5 on the anode, generating passes through the anion exchange membrane from the anode chamber into the compartment, thereby reducing the pH value of the feed water. It should be noted that due to the existence of electrostatic repulsion, compared with the CDI system, the rate of pH decline in the membrane capacitive deionization device 1 is slower.

[0017] (Equation 1)

[0018] (Equation 2)

[0019] (Equation 3)

[0020] (Equation 4)

[0021] (Equation 5)

[0022] (Equation 6)

[0023] Equation 7 shows the standard electrode potential E0 at different temperatures:

[0024] (Equation 7)

[0025] where E 0 T is the standard electrode potential at temperature T, is the temperature coefficient mV / K at 298 K (25 °C).

[0026] For the chemical reaction under study, its temperature coefficient is a negative constant, indicating that E 0 T is negatively correlated with temperature. Specifically, as the feed water temperature increases, E 0 T decreases accordingly. It can be inferred that under a constant applied voltage condition, an increase in temperature will exacerbate the occurrence of the Faraday anode reaction equations 4 and 5, accelerating The generation then prompts a rapid decrease in the pH value. Additionally, when the temperature rises, the ion migration impedance in the solution decreases, and at the same time, both the ion intercalation reaction rate and the ion diffusion coefficient increase. These changes work together to reduce the overpotential and increase the discharge voltage. Based on this, by controlling the temperature to maintain the charge transfer temperature and the diffusion efficiency temperature of hydrogen ions in the feed water, the balance between the electron transfer and the hydrogen ion diffusion process is achieved, further inhibiting the Faraday reaction equations 4 and 5 at the anode, maintaining the electrode stability, and being conducive to maintaining the stability of the pH value of the effluent.

[0027] Therefore, by constructing a temperature-controlled auxiliary membrane capacitive deionization high-efficiency desalination system, membrane capacitive deionization can maintain the quality and stability of the water flux with lower energy consumption under low / high temperature conditions. Among them, the membrane capacitive deionization device 1 uses electrostatic force to drive ions to migrate towards the electrode surface, while the temperature control system maintains the electrode stability, thus effectively expanding the greater application prospects of the membrane capacitive deionization device 1 in extreme temperature environments. By further exploring the performance stability of the temperature-controlled auxiliary membrane capacitive deionization high-efficiency desalination system under different temperature environments in long-term operation conditions.

[0028] Table 1 shows the desalination efficiency of the system in the 1st cycle and the 10th cycle;

[0029]

[0030] After 10 cycles, the desalination efficiency of the system is maintained at about 91%. This result indicates that the temperature-controlled auxiliary membrane capacitive deionization high-efficiency desalination system has more advantages in desalination efficiency and energy consumption for different temperature brines compared with the traditional RO system. Especially in areas with large temperature fluctuations or cold regions, this technology has a wide application range, low processing energy consumption, and stable long-term operation, and has great commercial application prospects.

[0031] In the second aspect, the present invention also provides a temperature-controlled auxiliary membrane capacitive deionization desalination method, which is applied to the temperature-controlled auxiliary membrane capacitive deionization desalination system as described in the above solution. The temperature-controlled auxiliary membrane capacitive deionization desalination method includes:

[0032] Prepare synthetic influent, the anode and cathode of the activated carbon electrode;

[0033] Charge the DC power supply at a preset voltage for 2400 seconds, and perform a 2400-second discharge process by changing the voltage direction to achieve electrode regeneration;

[0034] Set the charging voltage group and the influent flow rate group;

[0035] Specify the influent temperature;

[0036] Measure the influence of the influent temperature on the desalination efficiency of the membrane capacitive deionization desalination system under certain charging voltage and feed flow rate conditions.

[0037] As a further solution of the present invention: the charging voltage group consists of 0V, 0.3V, 0.6V, 0.9V, 1.2V, 1.5V, and the influent flow rate group consists of 3.6 mL / min, 12.6 mL / min, 18.6 mL / min, 24.6 mL / min, 30.6 mL / min, 36.6 mL / min, 40.6 mL / min, 44.6 mL / min.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] 1. In the present invention, by combining a porous carbon electrode with an ion exchange membrane to form a membrane capacitive deionization module, and simultaneously combining a water temperature control module, ions are separated from the influent solution by applying a low external voltage to achieve desalination of the effluent. By the temperature control module, the influent water temperature is stabilized, which can reduce the energy consumption of operating the membrane capacitive deionization system.

[0040] 2. In the present invention, by setting the water temperature control module, a stable desalination efficiency can be maintained under different temperature conditions, and it has low energy consumption and high current efficiency, and the desalination efficiency is higher than that of the traditional reverse osmosis (RO) seawater desalination method.

[0041] 3. In the present invention, by establishing that the system can still maintain a desalination efficiency greater than 90% at low / high temperatures. 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.

[0042] 4. In the present invention, by controlling the stability of the temperature, the positive effect of the ion migration through the IEMs can be offset against the negative effect of the temperature on the ion adsorption on the electrode, so that the membrane capacitive deionization system can maintain high 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a diagram of the temperature control assisted membrane capacitive deionization system of the present invention;

[0044] Figure 2 It is a diagram of the performance of the deionization desalination system of the present invention under different voltage conditions, Figure 2 (a) is a diagram of the relationship between the influent conductivity and the change of voltage, Figure 2 (b) is a diagram of the relationship between the specific energy consumption and the current efficiency and the change of voltage, Figure 2 (c) is a desalination efficiency diagram at different flow rates, Figure 2 (d) is a diagram of the relationship between the system current efficiency and the unit energy consumption at different flow rates;

[0045] Figure 3 It is the graph of the relationship between conductivity and time under different applied voltage conditions of the present invention;

[0046] Figure 4 It is the graph of the relationship between the influent conductivity and different voltages under the charge and discharge conditions of the present invention;

[0047] Figure 5 It is the desalination efficiency graph of the present invention when the water temperature is from 15°C to 40°C;

[0048] Figure 6 It is the graph of the relationship between the current efficiency and temperature of the present invention, Figure 6 (a) is the graph of the relationship between desalination efficiency and temperature, Figure 6 (b) is the graph of the relationship between current efficiency and unit energy consumption and temperature;

[0049] Figure 7 It is the graph of the relationship between the water temperature and the pH value after desalination of the present invention;

[0050] Figure 8 It is the step flow chart of the temperature control assisted membrane capacitive deionization desalination method of the present invention.

[0051] In the figure: 1. Membrane capacitive deionization device; 101. Ionization cell; 102. Activated carbon electrode; 103. Cation exchange membrane; 104. Anion exchange membrane; 105. Porous support; 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 implementation manners

[0052] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0053] Embodiment

[0054] Please refer to Figure 1, the present invention discloses a temperature-controlled auxiliary membrane capacitive deionization desalination system, which includes a membrane capacitive deionization device 1, a water temperature control module 2 and a data acquisition system 3. The membrane capacitive deionization device 1 includes an ionization cell 101 made of plexiglass, and a pair of activated carbon electrodes 102, a cation exchange membrane 103, an anion exchange membrane 104, a porous support 105 and two power lines 106 that are parallelly distributed 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. The plexiglass 102, a cation exchange membrane 103, an anion exchange membrane 104 and a porous support 105 are arranged parallel to each other. The membrane capacitive deionization device 1 realizes desalination of the effluent through intermittent ionization synthesis of the influent by applying an external voltage;

[0055] The water inlet end of the water temperature control module 2 is connected to one end of the ionization cell 101 through a first pipeline 4, and the water outlet end of the water temperature control module 2 is connected to the inside of the ionization cell 101 through a third pipeline 6. The water temperature control module 2 is used to keep the influent temperature of the membrane capacitive deionization device 1 stable, thereby reducing the energy consumption during the operation of the membrane capacitive deionization device 1;

[0056] The data acquisition system 3 is electrically connected between the membrane capacitive deionization device 1 and the water temperature control module 2. The data acquisition system 3 is used to collect and process the data of the membrane capacitive deionization device 1 and the water temperature control module 2.

[0057] Preferably, the porous support 105 is a planar support plate with multiple arrays of perforations. The porous support 105 is used to form an influent channel to facilitate the flow of the synthesized influent in the constant temperature bath 201.

[0058] Preferably, the water temperature control module 2 includes a constant temperature bath 201, a conductivity meter 202 installed through the constant temperature bath, and a temperature control module 203 fixed on the surface of the constant temperature bath 201. The constant temperature bath 201 is filled with synthesized influent. The temperature control module 203 is used to monitor the temperature of the pure water in the constant temperature bath 201. By maintaining the consistency of the temperature of the synthesized influent in the constant temperature bath 201, the consistency of the experimental conditions can be ensured, and the influence of the applied charging voltage value and the influent flow rate on the desalination efficiency under different temperature conditions can be studied;

[0059] 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 constant temperature bath 201 and is used to monitor the conductivity of the synthesized influent in the constant temperature bath 201. The conductivity meter 202 is a CON-BTA conductivity meter.

[0060] 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 consumption water temperature regulation. The material with photothermal conversion performance includes two-dimensional MXene nanomaterials, multi-layer graphene, organic polymers or plasmonic metals. By setting the temperature control module, it is possible to maintain a stable desalination efficiency under different temperature conditions, and it has low energy consumption and high current efficiency, and the desalination efficiency is higher than that of the traditional reverse osmosis (RO) seawater desalination method. By controlling the stability of the temperature, the positive effect of ion migration through IEMs can be offset by the negative effect of temperature on ion adsorption on the electrodes, so that the membrane capacitive 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 exhibit lower resistance and higher current efficiency.

[0061] Preferably, the concentration of the synthetic feed water is 500 mg / L. The synthetic feed water is made 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.

[0062] Preferably, the activated carbon electrode 102 includes an anode and a cathode. Both the anode and the cathode are made of polyvinylidene fluoride PVDF, carbon black and activated carbon that are fully dissolved in N-methylpyrrolidone NMP solution. Among them, 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%. By applying the solvent of polyvinylidene fluoride PVDF and carbon black that are fully dissolved and mixed in N-methylpyrrolidone NMP solution on the graphite plate and drying it 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 standby.

[0063] 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 influent flow rate data for processing to obtain the current efficiency and the energy consumption value under the corresponding experimental conditions, and displays the data through the display 304;

[0064] There is a second pipeline 5 connected between the constant temperature bath 201 and the water circulation pump 301. The water circulation pump 301 is used to drain the synthetic feed water to the membrane capacitive deionization device 1. Starting the water circulation pump 301 can drain the synthetic feed water in the constant temperature bath 201 to the third pipeline 6 through the second pipeline 5, and then drain the synthetic feed water into the ionization cell 101 through the third pipeline 6. The water circulation pump 301 is connected between the membrane capacitive 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-headed peristaltic pump, which can realize the pumping / draining operation of the synthetic feed water. The model of the double-headed peristaltic pump is L100-1S-1.

[0065] Preferably, the voltage provided by the DC power supply 303 is 0.3V - 1.2V. The temperature control module 203 controls the temperature of the synthetic feed water to rise from 20°C to 25°C, which is used to increase the effective pore size of the cation exchange membrane 103 and / or the anion exchange membrane 104. When the control of the feed water temperature rises from 20°C to 50°C, by changing the structure of the polymer chain, the effective pore size of the ion exchange membrane is enlarged 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 through the temperature control module 203, the radius of the hydrated ion can be reduced. However, too high a temperature will lead to a decrease in the adsorption capacity of the activated carbon electrode 106. Therefore, controlling the temperature of the synthetic feed water within the suitable range of 20 - 25°C results in an increase in the pore size of the ion exchange membrane and a smaller radius of ion hydration, which is beneficial for salt ions to pass through the ion exchange membrane.

[0066] In summary, by controlling the temperature stability, the positive effect of the ion migration through the ion exchange membrane can be offset by the negative effect of the temperature on the ion adsorption on the electrode, so that the membrane capacitive deionization device 1 can maintain high-efficiency desalination performance and low energy consumption.

[0067] According to the current efficiency equation (SI, Eq. 4), at the same voltage, the high-temperature feed aqueous solution shows a lower resistance and a higher current efficiency at time t. And according to the specific energy consumption equation (SI, Eq. 3), the high-temperature feed aqueous solution has an increased total energy consumption due to the high current, thus achieving a more optimal specific energy consumption.

[0068] As Figure 2 and Figure 3 shown, by applying a voltage that increases 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 capacitive deionization device 1 jumps from 16.1% to 93.7%. While obtaining a high salt removal rate, the energy consumption can be reduced; at the same time, it is observed that as the voltage is increased from 1.2V to 1.5V, the energy consumption per unit treated water volume also increases from 0.04 kWh / m³ to 0.93 kWh / m³.

[0069] As Figure 2 shown in (b), it is worth noting that the current efficiency reaches a peak of 95.8% at a voltage of 0.9 V, and then drops to 80.7% at 1.5 V, suggesting that a Faraday reaction and its accompanying adverse side reactions, such as water electrolysis, may be induced during this process, thus affecting the stability of the current efficiency. Considering the salt removal efficiency and energy consumption factors comprehensively, 1.2 V is preferably selected as the optimal operating voltage in this example for in-depth discussion.

[0070] As Figure 2 shown in (c), when the feed water flow rate increases from 3.6 mL / min to 24.6 mL / min, the salt removal efficiency of the membrane capacitive 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 drops to 89.5%. The slow flow rate leads to a decrease in the mass transfer rate, reducing the chance of ions reaching the electrode surface for adsorption. Moreover, too low a flow rate also causes a decrease in the average ion concentration inside the membrane capacitive deionization device 1, reducing the driving force for ion transport to the electrode, thereby reducing the salt removal efficiency. On the other hand, a faster flow rate provides a higher pumping force, restricting the ion transfer rate in the feed water. Therefore, when the feed water flow rate exceeds 24.6 mL / min, the salt removal efficiency does not increase but decreases. By controlling the feed water flow rate, the salt removal efficiency of the membrane capacitive deionization device 1 can be further controlled.

[0071] As Figure 2 shown in (d), as the feed water 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 influent flow rate of the membrane capacitive deionization device 1 continues to increase, the unit energy consumption remains stable.

[0072] Meanwhile, when the influent flow rate increases from 3.6 mL / min to 44.6 mL / min, the current efficiency shows a decreasing trend from 89.5% to 74.1%. The difference in energy consumption at different influent flow rates can be attributed to the partial mitigation of the current when increasing the flow rate. This phenomenon may be related to the inhomogeneity of the solution ion concentration distribution inside the membrane capacitive deionization device 1;

[0073] Specifically, the electroadsorption effect exceeds the ion transport caused by electromigration and convection, resulting in the formation of a low-concentration region near the electrode and a significant slowdown in the current. In addition, a higher influent flow rate helps to alleviate the ion concentration polarization effect, while a lower influent flow rate reduces the internal dissipation of energy due to smaller ohmic losses;

[0074] However, the total charge increases with the increase of the influent flow rate. An overly fast influent flow rate may hinder the effective adsorption of ions on the electrode surface, thereby reducing the effective Coulomb force during the electro-adsorption process. Therefore, the unit energy consumption increases with the increase of the influent flow rate;

[0075] The initial current efficiency slightly increases, but as the influent flow rate further accelerates, the increase in the total charge is more significant.

[0076] In summary, in the present invention, the optimal feed water flow rate range of the membrane capacitive deionization device 1 is 18.6 mL / min to 30.6 mL / min. Therefore, the present invention preferably selects 18.6 mL / min as the feed water flow rate in the subsequent experiments.

[0077] As Figure 5 shown, the operating procedure of the membrane capacitive deionization device 1 for batch operation based on the change of the solution feed water temperature was tested, and the desalination performance of the membrane capacitive deionization device 1 was analyzed. The results show that by controlling the water temperature from 15 °C to 40 °C, it is found that the desalination efficiency of the membrane capacitive deionization device 1 can remain at about 92%. By establishing the system, the desalination efficiency can still remain greater than 90% at low / high temperatures. 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.

[0078] As Figure 6 shown, the specific energy consumption will increase with the increase of the water temperature, that is, the specific energy consumption ranges from 0.65 k kWh / m³ to 0.76 k kWh / m³. At the same time, with the change of the solution feed water temperature, the current efficiency decreases by 14%. Therefore, by adding the temperature control module 203 to assist the water temperature, the desalination energy consumption of the membrane capacitive deionization device 1 can be effectively reduced, thereby improving the current efficiency.

[0079] As Figure 7 shown, the pH value of the synthetic influent after being treated by the membrane capacitive deionization device 1 with the controlled water temperature is shown. In the membrane capacitive deionization system, due to the Faraday reaction, regardless of the temperature change, the pH value of the feed water during the charging stage drops to about 4; while in the discharging stage, the pH value returns to the initial level. In addition, it is experimentally observed that a higher feed water temperature will accelerate the rate of pH value decrease. This phenomenon is similar to the performance of the CDI system under the same conditions, but the rate of pH decrease in the CDI system is more significant in the initial stage. Compared with the non-Faraday process, the Faraday reaction is the main mechanism leading to the pH change. Under the applied voltage conditions, the main Faraday reactions in the membrane capacitive deionization device 1 include the electrolysis equation 4 of water and the carbon oxidation equation 5 on the anode, generating H+ It passes through the anion exchange membrane from the anode chamber into the compartment, thus reducing the pH value of the feed water. It is worth noting that due to the existence of electrostatic repulsion, compared with the CDI system, the pH drops more slowly in the membrane capacitive deionization device 1.

[0080] (Equation 1)

[0081] (Equation 2)

[0082] (Equation 3)

[0083] (Equation 4)

[0084] (Equation 5)

[0085] (Equation 6)

[0086] Equation 7 shows the standard electrode potential E0 at different temperatures:

[0087] (Equation 7)

[0088] where E 0 T is the standard electrode potential at temperature T, is the temperature coefficient mV / K at 298 K (25 °C).

[0089] For the chemical reaction under study, its temperature coefficient is a negative constant, indicating that E 0 T has a negative correlation with temperature. Specifically, as the feed water temperature increases, E 0 T decreases accordingly. It can be inferred that under a constant applied voltage, an increase in temperature will exacerbate the occurrence of Faraday anode reactions in Equations 4 and 5, accelerating generation, and thus prompting a rapid drop in pH value. In addition, when the temperature rises, the ionic migration impedance in the solution decreases, and at the same time, the ion intercalation reaction rate and ion diffusion coefficient both increase. These changes together reduce the overpotential and increase the discharge voltage. Based on this, by controlling the temperature to maintain the charge transfer temperature and the diffusion efficiency temperature of hydrogen ions in the feed water, the balance between the electron transfer and hydrogen ion diffusion processes can be achieved, further inhibiting the Faraday reactions in Equations 4 and 5 at the anode, maintaining electrode stability, and being beneficial to maintaining the stability of the effluent pH value.

[0090] Therefore, by constructing a temperature-controlled auxiliary membrane capacitive deionization high-efficiency desalination system, membrane capacitive deionization can maintain the quality and stability of water flux with low energy consumption under both low-temperature / high-temperature conditions. Among them, the membrane capacitive deionization device 1 uses electrostatic force to drive ions to migrate towards the electrode surface, while the temperature control system maintains the stability of the electrode, thus effectively expanding the greater application prospects of the membrane capacitive deionization device 1 in extreme temperature environments. By further exploring the performance stability of the temperature-controlled auxiliary membrane capacitive deionization high-efficiency desalination system under different temperature environments during long-term operation conditions.

[0091] Table 1 shows the desalination efficiency of the system in the 1st cycle and the 10th cycle;

[0092]

[0093] After 10 cycles, the desalination efficiency of the system remained at about 91%. This result indicates that the temperature-controlled auxiliary membrane capacitive deionization high-efficiency desalination system has more advantages in desalination efficiency and energy consumption of different temperature brines compared with the traditional RO system. Especially in areas with large temperature fluctuations or cold regions, this technology has a wide application range, low treatment energy consumption, and stable long-term operation.

[0094] Such as Figure 8 As shown in the flowchart of the steps of the temperature-controlled auxiliary membrane capacitive deionization desalination method of the present invention, a temperature-controlled auxiliary membrane capacitive deionization desalination method is provided, which is applied to the temperature-controlled auxiliary membrane capacitive deionization desalination system as described above. The temperature-controlled auxiliary membrane capacitive deionization desalination method includes:

[0095] S1: Prepare synthetic influent water, the anode and cathode of the activated carbon electrode;

[0096] S2: Charge the DC power supply at a preset voltage for 2400 seconds, and perform a 2400-second discharge process by changing the voltage direction to achieve electrode regeneration;

[0097] S3: Set the charging voltage group and the influent flow rate group;

[0098] S4: Specify the influent temperature;

[0099] S5: Measure the influence of the influent temperature on the desalination efficiency of the membrane capacitive deionization desalination system under certain charging voltage and feed flow rate conditions.

[0100] Preferably, the charging voltage group consists of 0V, 0.3V, 0.6V, 0.9V, 1.2V, 1.5V, and the influent flow rate group consists of 3.6 mL / min, 12.6 mL / min, 18.6 mL / min, 24.6 mL / min, 30.6 mL / min, 36.6 mL / min, 40.6 mL / min, 44.6 mL / min.

[0101] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within 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, 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, the membrane capacitor deionization device realizes effluent desalination by intermittent ionization of synthetic influent water by applying an external voltage, the concentration of the synthetic influent water is 500 mg / L, the synthetic influent water is prepared by dissolving sodium chloride in purified water, and the resistivity of the purified water is 18.2 MΩ·cm; 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. The data acquisition system is used to collect and process data from the membrane capacitor deionization device and the water temperature control module. The data acquisition system includes a DC power supply. The voltage provided by the DC power supply is 0.3V-1.2V. 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.

2. The temperature-controlled auxiliary membrane capacitor deionization and desalination system according to claim 1 is 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 is 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 is 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 capacitive deionization and desalination system according to claim 4 is characterized in that: The activated carbon electrode includes an anode and a cathode, both of which are made of polyvinylidene fluoride, carbon black and activated carbon fully dissolved in an N-methylpyrrolidone solution, wherein the mass ratio of polyvinylidene fluoride is 4%, the mass ratio of carbon black is 5%, and the mass ratio of activated carbon is 91%.

6. The temperature-controlled auxiliary membrane capacitor deionization and desalination system according to claim 5, characterized in that: The data acquisition system includes a water circulation pump, a server 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.

7. 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 6, 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 the membrane capacitor deionization system under certain charging voltage and feed flow rate conditions was determined.

8. The temperature-controlled assisted membrane capacitor deionization and desalination method according to claim 7, characterized in that: The charging voltage group consists of 0.3V, 0.6V, 0.9V, and 1.2V, and the water inlet flow rate group consists of 12.6mL / min, 18.6mL / min, 24.6mL / min, 30.6mL / min, 36.6mL / min, and 40.6mL / min.

Images