A tankless continuous multistage countercurrent electrodialysis system and electrodialysis method

Abstract

The application belongs to the technical field of electrodialysis, and particularly relates to a tank-free continuous multistage countercurrent electrodialysis system and an electrodialysis method. The tank-free continuous multistage countercurrent electrodialysis system comprises two or more membrane stacks, each compartment of each membrane stack is not provided with a tank, and each compartment of each membrane stack is directly connected through a pipeline. The feed liquid in each compartment of each membrane stack in the electrodialysis system is organized in a countercurrent manner, and the feed liquid in each compartment realizes self-circulation in the stack through a circulating pump. The system is simple, convenient to connect, fast to start, and fast to respond. The inter-stage flow is stable, and the whole system is convenient to control.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrodialysis, and in particular, relates to a continuous multi-stage reverse flow electrodialysis system without a tank and an electrodialysis method. Mainly related to, in the treatment of salt-containing feed liquid by electrodialysis (ordinary electrodialysis, bipolar membrane electrodialysis, etc.), to realize desalination, salt concentration or acid-base regeneration, an electrodialysis system and an electrodialysis method for reducing the energy consumption of electrodialysis for treating salt-containing feed liquid, improving current efficiency and desalination rate are provided. BACKGROUND

[0002] Electrodialysis is a kind of membrane separation technology that uses the selective permeability of ion exchange membrane to make charged ions migrate across the membrane under the action of electric field, so as to realize desalination and salt concentration of solution. The traditional electrodialysis (hereinafter referred to as ordinary electrodialysis) membrane stack has alternating anion exchange membrane and cation exchange membrane. The membrane stack structure (taking sodium chloride as an example) and ion migration schematic diagram are as shown in Figure 1 , wherein AM is an anion exchange membrane, and CM is a cation exchange membrane. Ion exchange membrane is a thin film with ion selective permeability function, which can allow ions with opposite electric properties to the fixed groups on the membrane to pass through, while blocking ions with the same electric properties as the fixed groups on the membrane. That is, the cation exchange membrane (hereinafter referred to as the positive membrane) can allow positively charged ions to pass through, while blocking negatively charged ions; the anion exchange membrane (hereinafter referred to as the negative membrane) can allow negatively charged ions to pass through, while blocking positively charged ions. The raw material liquid (salt-containing solution) enters the desalination chamber (i.e. circulates between the desalination chamber and the tank), and under the action of electric field, anions and cations migrate across the membrane to the concentrated chambers on both sides, respectively, and finally desalination feed liquid is obtained in the desalination chamber, and concentrated salt solution is obtained in the concentrated chamber.

[0003] On the basis of ordinary electrodialysis, new electrodialysis technologies such as bipolar membrane electrodialysis, selective electrodialysis and displacement electrodialysis have been developed. Among them, bipolar membrane is a kind of ion exchange membrane with special function, which can dissociate water molecules into H + and OH - and release them outside the membrane under the action of electric field. The side of the bipolar membrane releasing H + is called the positive side, and the side releasing OH - is called the negative side. When the bipolar membrane is used in combination with anion and cation exchange membranes, bipolar membrane electrodialysis can regenerate the corresponding acid and base from salt, while the feed liquid is desalted (Industrial Water Treatment, 2021, 41(05): 36-41.).

[0004] Figure 2This diagram illustrates the membrane stack structure (using sodium sulfate as an example) and ion migration schematic of a conventional acid-salt-base three-compartment bipolar membrane electrodialysis system. AM is the anion exchange membrane (hereinafter referred to as the anion membrane), CM is the cation exchange membrane (hereinafter referred to as the cation membrane), and BM is the bipolar membrane. The compartment between AM and CM is called the salt compartment, initially filled with a salt solution (an aqueous solution of sodium sulfate). The compartment between AM and BM is called the acid compartment, and the compartment between CM and BM is called the base compartment. Under the influence of an electric field, water molecules within the bipolar membrane dissociate into H+. + and OH - They move towards the cathode and anode, respectively, into the acid chamber and the alkali chamber, H + With anions (SO4) migrating across the anion membrane from the salt chamber 2- ) combine in the acid chamber to form acid (H2SO4); OH - With cations (Na) migrating across the cation membrane from the salt chamber + The two molecules combine to form an alkali (NaOH) in the alkali chamber.

[0005] Will Figure 2 The removal of the anion exchange membrane in the "acid-salt-base" three-compartment bipolar membrane electrodialysis stack, i.e., merging the salt and acid compartments, yields a "salt-base" two-compartment structure. A schematic diagram of the conventional "salt-base" two-compartment bipolar membrane electrodialysis stack structure (taking sodium gluconate as an example) and ion migration is shown in Figure 3(a). Here, CM is the cation exchange membrane, BM is the bipolar membrane; the compartment between BM and CM is the salt compartment, initially filled with a salt-containing solution (an aqueous solution of sodium gluconate); the compartment between CM and BM is the base compartment; under the influence of an electric field, water molecules within the bipolar membrane dissociate into OH-. - and H + They migrate into the alkali chamber and the salt chamber respectively. The cations (Na+) in the salt chamber... + The solution migrates into the alkali chamber, where a base (NaOH) is obtained, and in the salt chamber, a mixture of acid and salt (a mixture of gluconic acid and the remaining sodium gluconate) is obtained.

[0006] Similarly, Figure 2 The removal of the cation exchange membrane in the "acid-salt-base" three-compartment bipolar membrane electrodialysis stack, i.e., merging the salt and base compartments, yields a "acid-salt" two-compartment structure. A schematic diagram of the conventional "acid-salt" two-compartment bipolar membrane electrodialysis stack structure (taking pentanediamine hydrochloride as an example) and ion migration is shown in Figure 3(b). AM is the anion exchange membrane, and BM is the bipolar membrane; the compartment between BM and AM is the acid compartment; the compartment between AM and BM is the salt compartment, initially filled with a salt-containing solution (an aqueous solution of pentanediamine hydrochloride); under the influence of an electric field, water molecules within the bipolar membrane dissociate into H+. + and OH - They migrate into the acid chamber and salt chamber respectively, and the anions in the salt chamber (Cl) -) migrate into the acid chamber, get acid (hydrochloric acid) in the acid chamber, and get a mixed solution of base and salt (a mixed solution of pentanediamine and residual pentanediamine hydrochloride) in the salt chamber.

[0007] In addition, there are other types of electrodialysis membrane stack structures, such as double decomposition electrodialysis and ion displacement electrodialysis (not shown).

[0008] Traditionally, the operation of ordinary electrodialysis is in batch mode, such as Figure 4 As shown: the initial feed solution of each chamber is added to the cylinder, the power supply and the circulating pump of each chamber are turned on, the feed solution circulates between the electrodialysis membrane stack and the cylinder, until the predetermined desalination rate or concentration or concentration factor is reached, and the feed solution of each chamber is discharged. The conventional batch operation mode requires many auxiliary equipment, and the feed solution needs to be frequently loaded and unloaded, especially in the later stage of the electrodialysis process, ion reverse concentration migration increases energy consumption. The case of bipolar membrane electrodialysis is similar, and the problem of reverse concentration migration is more serious in batch operation mode, because H + and OH - The migration activity in aqueous solution is significantly higher than that of other anions, and the blocking effect of anion exchange membrane on H + is limited, and the blocking effect of cation exchange membrane on OH - is also limited. With the increase of the regeneration acid and base concentration in the acid chamber and the base chamber, H + in the acid chamber easily "leaks into" the salt chamber through the anion exchange membrane, and OH - in the base chamber easily "leaks into" the salt chamber through the cation exchange membrane. In batch operation mode, the "leakage" of bipolar membrane electrodialysis in the later stage is more serious, which leads to the difficulty of regenerating high acid and base concentration in bipolar membrane electrodialysis, and the "leakage" reduces the current efficiency of bipolar membrane electrodialysis, resulting in increased energy consumption.

[0009] Therefore, people have proposed a multi-stage countercurrent electrodialysis method (CN113477090A; Process Engineering, 2010, 10(02):276-81.; CN201010034136.6, CN201010150056.7), which organizes the feed solution of each stage in a countercurrent manner. Compared with the same operating conditions without classification, the energy consumption is reduced and the acid concentration is increased, but no specific electrodialysis system scheme is given.

[0010] The conventional multi-stage countercurrent electrodialysis system is a batch multi-stage countercurrent electrodialysis system, such as Figure 5As shown, the feed liquid of each compartment (two or more compartments) of each membrane stack is organized in a countercurrent manner, but each stage still adopts batch operation, that is, the concentrated chamber and the desalination chamber of ordinary electrodialysis, or the acid chamber, the salt chamber, and the base chamber of bipolar membrane electrodialysis. The feed liquid of the entire process is organized in a countercurrent manner, but each stage is processed to a predetermined level like batch single-stage electrodialysis or bipolar membrane electrodialysis. When the process is completed, the completed liquid in the feed tank of the current stage is transferred to the feed tank of the next stage (as the initial liquid of the next stage), and the completed liquid in the feed tank of the previous stage is transferred to the feed tank of the current stage (as the initial liquid of the current stage), and a new batch begins. The batch multi-stage countercurrent electrodialysis system reduces the concentration difference on both sides of the membrane to a certain extent, alleviates the problem of high energy consumption when ions migrate against concentration, but the operation process is complicated and difficult to manage. Each stage (table) of equipment (electrodialysis) needs to go through a time-varying process, regardless of whether a constant voltage or a constant current mode is used.

[0011] Therefore, a continuous multi-stage countercurrent electrodialysis system is proposed, as shown in Figure 6 (shown as two compartments, such as ordinary electrodialysis or two-compartment bipolar membrane electrodialysis). Due to the need to maintain a sufficient linear velocity (usually the linear velocity of liquid flow is about 3 cm / s) inside the electrodialysis membrane stack to ensure mixing and mass transfer in the membrane stack, the feed liquid of each compartment of each stage of the membrane stack needs to be kept in high-speed self-circulation flow (circulating through the membrane stack outlet, the feed tank, and the membrane stack inlet), and a small part of the feed liquid is diverted from the membrane stack outlet to the feed tank of the next stage of the membrane stack (Desalination, 2003, 153(1-3): 371-6.).

[0012] Figure 6 The system shown still retains the feed tank of each compartment of each stage of the membrane stack, and the outlet of each stage of the membrane stack is connected to the feed tank of the next stage of the membrane stack to adjust the flow between stages by valves Figure 6 , and the flow meters are omitted), which has the disadvantage of being difficult to ensure consistent flow between stages unless a complex flow control system based on the feedback of the liquid level position of each feed tank is added.

[0013] Another continuous multi-stage countercurrent electrodialysis system similar to the system shown in Figure 6 is that the feed tank of each stage of the membrane stack is connected to the feed tank of the next stage of the membrane stack, and the feed liquid of each stage of the feed tank flows into the next stage in an overflow manner due to the difference in liquid level Figure 7 , which can basically ensure that the liquid level position of each feed tank is maintained within a certain range, but the flow between stages still fluctuates and has poor stability.

[0014] The above-mentioned continuous countercurrent multi-stage electrodialysis system Figure 6 , Figure 7The advantage of retaining the feed tank of each membrane stack is that the feed tank of each membrane stack is connected to the atmosphere, the fluid mechanics of each membrane stack is similar to the single-stage batch operation membrane stack, and the pressure distribution is similar. However, the disadvantage is that the system connection is complex, and the equipment is numerous. The presence of the feed tank increases the liquid volume of the entire system, resulting in slow start-up after system start-up / cleaning, slow dynamic response, unstable inter-stage flow, and difficulty in implementing automatic control. SUMMARY

[0015] To solve the problems of the continuous countercurrent multistage electrodialysis system with a feed tank, such as complex system connection, numerous equipment, slow start-up, slow dynamic response, unstable inter-stage flow, and difficulty in implementing automatic control, the present application provides a feed tank-free continuous multistage countercurrent electrodialysis system and an electrodialysis method.

[0016] The technical principle of the present application is as follows: In order to ensure mixing and mass transfer in the membrane stack, the internal linear velocity of the electrodialysis membrane stack needs to be sufficient. If the compartments of the electrodialysis membrane stacks are simply connected in series, the residence time of the feed liquid flowing through the membrane stack will be short, and the single-pass migration rate will be low. Therefore, the feed liquid in each compartment needs to be kept in high-speed self-circulation within the membrane stack (circulating through the membrane stack outlet, a circulating pump, and the membrane stack inlet). In the present application, each compartment of each membrane stack is kept in high-speed self-circulation (a flow meter, a valve, and a heat exchanger can be installed on the high-speed self-circulation loop as needed), but the high-speed self-circulation loop is not provided with a feed tank (i.e., the high-speed self-circulation loop is isolated from the atmosphere). On the other hand, a small part of the feed liquid is branched from any position of the high-speed self-circulation loop of the compartment of the upper membrane stack and directly introduced into any position of the high-speed self-circulation loop of the corresponding compartment of the present membrane stack, but the positions of the branched feed liquid from the high-speed self-circulation loop of the compartment of the present membrane stack to the corresponding compartment of the next membrane stack and the branched feed liquid from the high-speed self-circulation loop of the compartment of the next membrane stack to the corresponding compartment of the subsequent membrane stack are not overlapped. Thus, the number of system connections and equipment is reduced, the liquid volume of the entire system is greatly reduced, and the conditions for implementing automatic control are provided.

[0017] The feed tank-free continuous multistage countercurrent electrodialysis system of the present application comprises two or more membrane stacks, wherein each compartment of each membrane stack is not provided with a feed tank, and each compartment of each membrane stack is directly connected by a pipeline.

[0018] According to the feed tank-free continuous multistage countercurrent electrodialysis system of the present application, the feed liquid in each compartment of each membrane stack in the electrodialysis system is organized in a countercurrent manner, and the feed liquid in each compartment is self-circulated by a circulating pump.

[0019] According to the feed tank-free continuous multistage countercurrent electrodialysis system of the present application, preferably, the electrodialyzer of the electrodialysis system comprises a common electrodialyzer, a three-compartment bipolar membrane electrodialyzer, or a two-compartment bipolar membrane electrodialyzer.

[0020] According to the continuous multi-stage countercurrent electrodialysis system without feed tank, as an option, when the electrodialysis system is a common electrodialysis system, the membrane stack of the common electrodialysis system comprises two compartments, namely a desalination compartment and a concentration compartment.

[0021] The countercurrent organization comprises: the desalination compartment initial liquid enters the first-stage membrane stack and sequentially flows through the membrane stacks to the Nth-stage membrane stack; the concentration compartment initial liquid enters the Nth-stage membrane stack and sequentially flows through the membrane stacks to the first-stage membrane stack; wherein N≥2.

[0022] According to the continuous multi-stage countercurrent electrodialysis system without feed tank, as another option, when the electrodialysis system is a three-compartment bipolar membrane electrodialysis system, the membrane stack of the three-compartment bipolar membrane electrodialysis system comprises three compartments, namely an acid compartment, a salt compartment and a base compartment.

[0023] The countercurrent organization comprises: the salt compartment initial liquid enters the first-stage membrane stack and sequentially flows through the membrane stacks to the Nth-stage membrane stack; the acid compartment initial liquid and the base compartment initial liquid enter the Nth-stage membrane stack and sequentially flow through the membrane stacks to the first-stage membrane stack; wherein N≥2.

[0024] According to the continuous multi-stage countercurrent electrodialysis system without feed tank, as another option, when the electrodialysis system is a two-compartment bipolar membrane electrodialysis system, the membrane stack of the two-compartment bipolar membrane electrodialysis system comprises two compartments, namely a salt compartment and a base compartment.

[0025] The countercurrent organization comprises: the salt compartment initial liquid enters the first-stage membrane stack and sequentially flows through the membrane stacks to the Nth-stage membrane stack; the base compartment initial liquid enters the Nth-stage membrane stack and sequentially flows through the membrane stacks to the first-stage membrane stack; wherein N≥2.

[0026] Alternatively, the membrane stack of the two-compartment bipolar membrane electrodialysis system comprises two compartments, namely a salt compartment and an acid compartment; the countercurrent organization comprises: the salt compartment initial liquid enters the first-stage membrane stack and sequentially flows through the membrane stacks to the Nth-stage membrane stack; the acid compartment initial liquid enters the Nth-stage membrane stack and sequentially flows through the membrane stacks to the first-stage membrane stack; wherein N≥2.

[0027] According to the continuous multi-stage countercurrent electrodialysis system without feed tank, preferably, the direct connection between the compartments of each membrane stack through pipelines comprises:

[0028] The outlet of each compartment of each membrane stack is connected to the inlet of the corresponding compartment of the next-stage membrane stack; or,

[0029] The outlet of each compartment of each membrane stack is connected to the outlet of the corresponding compartment of the next-stage membrane stack; or,

[0030] The inlet of each compartment of each membrane stack is connected to the outlet of the corresponding compartment of the next membrane stack; or

[0031] The inlet of each compartment of each membrane stack is connected to the inlet of the corresponding compartment of the next membrane stack.

[0032] The application also provides an electrodialysis method based on any of the above-mentioned continuous multi-stage countercurrent electrodialysis systems, when the electrodialyzer in the electrodialysis system is a common electrodialyzer, comprising the following steps:

[0033] The outlet salt concentration of the last stage of the common electrodialyzer is fed back to adjust the operating voltage of the last stage, or the flow of the feed liquid of the first stage of the desalination chamber is fed back to adjust.

[0034] According to the electrodialysis method of the application, preferably, when the outlet salt concentration is lower than the set value, the operating voltage of the last stage is reduced; when the outlet salt concentration is higher than the set value and the current density of the last stage is lower than the maximum current density that the ion exchange membrane can withstand, the operating voltage of the last stage is increased; wherein the increment of the adjustment of the operating voltage of the last stage =-(the outlet salt concentration-set value)*K1; wherein K1 is a negative value, which is the correlation coefficient between the outlet salt concentration and the operating voltage of the last stage, obtained from the fitting relationship between the two;

[0035] Or,

[0036] When the outlet salt concentration is higher than the set value and the current density of the last stage is equal to or higher than the maximum current density that the ion exchange membrane can withstand, the flow of the feed liquid of the first stage of the desalination chamber is reduced, wherein the increment of the adjustment of the flow of the feed liquid of the first stage of the desalination chamber =-(the outlet salt concentration-set value)*K2; wherein K2 is a positive value, which is the correlation coefficient between the outlet salt concentration and the flow of the feed liquid of the first stage of the desalination chamber, obtained from the fitting relationship between the two.

[0037] According to the electrodialysis method of the application, preferably, the outlet salt concentration is represented by the conductivity value detected by a conductivity meter, wherein,

[0038] When the conductivity value of the outlet salt concentration is lower than the set value, the operating voltage of the last stage is reduced; when the conductivity value of the outlet salt concentration is higher than the set value and the current density of the last stage is lower than the maximum current density that the ion exchange membrane can withstand, the operating voltage of the last stage is increased; wherein the increment of the adjustment of the operating voltage of the last stage =-(the conductivity value of the outlet salt concentration-set value)*K3; wherein K3 is a negative value, which is the correlation coefficient between the conductivity value of the outlet salt concentration and the operating voltage of the last stage, obtained from the fitting relationship between the two.

[0039] Or,

[0040] The conductivity value of the outlet salt concentration is higher than a set value, and the current density of the last stage is equal to or higher than the maximum current density that the ion exchange membrane can withstand, the flow rate of the feed liquid of the first desalination chamber is reduced, wherein the increment of the flow rate adjustment of the feed liquid of the first desalination chamber = -(conductivity value of the outlet salt concentration - set value) * K4; wherein K4 is a positive value, which is the correlation coefficient of the conductivity value of the outlet salt concentration and the flow rate of the feed liquid of the first desalination chamber, obtained from the fitting relationship of the two.

[0041] The electrodialysis method based on any of the above-mentioned cylinder-free continuous multi-stage countercurrent electrodialysis systems of the application comprises the following steps when the electrodialysis device in the electrodialysis system is a bipolar membrane electrodialysis device:

[0042] The outlet salt concentration of the bipolar membrane electrodialysis device is fed back to adjust the operating voltage of the last stage, or the flow rate of the feed liquid of the first salt chamber is fed back to adjust.

[0043] According to the electrodialysis method of the application, further preferably, the outlet salt concentration is lower than a set value, and the operating voltage of the last stage is reduced; the outlet salt concentration is higher than a set value, and the current density of the last stage is lower than the maximum current density that the ion exchange membrane can withstand, and the operating voltage of the last stage is increased; wherein the increment of the operating voltage adjustment of the last stage = -(outlet salt concentration - set value) * K1; wherein K1 is a negative value, which is the correlation coefficient of the outlet salt concentration and the operating voltage of the last stage, obtained from the fitting relationship of the two;

[0044] Or,

[0045] The outlet salt concentration is higher than a set value, and the current density of the last stage is equal to or higher than the maximum current density that the ion exchange membrane can withstand, and the flow rate of the feed liquid of the first salt chamber is reduced, wherein the increment of the flow rate adjustment of the feed liquid of the first salt chamber = -(outlet salt concentration - set value) * K2; wherein K2 is a positive value, which is the correlation coefficient of the outlet salt concentration and the flow rate of the feed liquid of the first salt chamber, obtained from the fitting relationship of the two.

[0046] According to the electrodialysis method of the application, further preferably, the conductivity value of the outlet salt concentration is detected by a conductivity meter, wherein,

[0047] The conductivity value of the outlet salt concentration is lower than a set value, and the operating voltage of the last stage is reduced; the conductivity value of the outlet salt concentration is higher than a set value, and the current density of the last stage is lower than the maximum current density that the ion exchange membrane can withstand, and the operating voltage of the last stage is increased; wherein the increment of the operating voltage adjustment of the last stage = -(conductivity value of the outlet salt concentration - set value) * K3; wherein K3 is a negative value, which is the correlation coefficient of the conductivity value of the outlet salt concentration and the operating voltage of the last stage, obtained from the fitting relationship of the two;

[0048] Or,

[0049] The conductivity value of the outlet salt concentration is higher than a set value, and the current density of the last stage is equal to or higher than the maximum current density that the ion exchange membrane can withstand, and the flow rate of the feed liquid of the first stage salt chamber is reduced, wherein the increment of the flow rate adjustment of the feed liquid of the first stage salt chamber = -(conductivity value of outlet salt concentration - set value) * K4; wherein K4 is a positive value, which is the correlation coefficient of the conductivity value of the outlet salt concentration and the flow rate of the feed liquid of the first stage salt chamber, obtained from the fitting relationship of the two.

[0050] The ordinary electrodialysis and bipolar membrane electrodialysis device in the application is a conventional electrodialysis device, and a conventional operation method can be used, including constant current, constant voltage or variable voltage, variable current mode. The constant voltage mode is preferred.

[0051] The number of stages of the tankless continuous multistage countercurrent electrodialysis system of the application is preferably two or three.

[0052] The temperature of the liquid in each compartment of the application adopts the temperature of conventional electrodialysis operation, which is usually in the range of 5-50°C; the flow rate of each compartment adopts the conventional flow rate, which is usually in the range of 1-10 cm / s; and the current density adopts the conventional current density, which is usually in the range of 10-100 mA / cm 2 .

[0053] The ion exchange membrane used in the ordinary electrodialysis and bipolar membrane electrodialysis device of the application is not particularly limited, and a ion exchange membrane known to those skilled in the art can be used, which can be purchased from the market. For example, conventional electrodialysis anion exchange membrane, cation exchange membrane and bipolar membrane can also be used. Monovalent anion and cation selective membrane can also be used.

[0054] The advantages of the application are:

[0055] 1. The system is simple and easy to connect. The application solves the problems of complex connection and multiple devices of the continuous countercurrent multistage electrodialysis system with each stage tank, which is also greatly simplified compared with the overflow mode in which the liquid level difference of the liquid in each stage tank is used to flow into the next stage by overflow.

[0056] 2. Fast start and fast dynamic response. The application solves the problems of slow start and slow dynamic response of the continuous countercurrent multistage electrodialysis system with each stage tank, and realizes short start-up time, because the dead volume of the system is small.

[0057] 3. Stable flow between stages. The application solves the problem of unstable flow between stages of the continuous countercurrent multistage electrodialysis system with each stage tank. The high-speed self-circulation loop of each stage membrane stack of the application is isolated from the atmosphere, realizing stable transportation of the liquid between stages, and the flow between stages is consistent (the flow between stages depends on the flow of the feed pump. As long as the flow of the feed pump is stable, the flow between stages can be stable).

[0058] 4. The system is easy to control. The application solves the problem that the continuous multi-stage reverse flow electrodialysis system with material cylinders at each stage is not easy to implement automatic control. The continuous multi-stage reverse flow electrodialysis system with material cylinders at each stage needs to go through the changes of the flow of the feed pump, the position of the liquid surface of the material cylinder, the overflow flow, and the position of the liquid surface of the next stage material cylinder. The feedback regulation is slow and the process is long. The electrodialysis system of the application is fully closed, and the changes of the flow of the feed pump can be immediately reflected on the outlet flow and the treatment effect, and the control means responds quickly. Only by measuring / monitoring the electrical conductivity of the outlet material liquid at each stage, the running state of the membrane stack at the stage can be judged. Only by adjusting the operating voltage of the last stage membrane stack, the outlet salt concentration can be quickly affected. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 It is a schematic diagram of the membrane stack structure (taking sodium chloride as an example) and ion migration of ordinary electrodialysis; wherein AM is an anion exchange membrane, and CM is a cation exchange membrane.

[0060] Figure 2 It is a schematic diagram of the membrane stack structure (taking sodium sulfate as an example) and ion migration of the conventional “acid-salt-base” three-chamber bipolar membrane electrodialysis; wherein AM is an anion exchange membrane, CM is a cation exchange membrane, and BM is a bipolar membrane.

[0061] Fig. 3(a) is a schematic diagram of the membrane stack structure (taking sodium gluconate as an example) and ion migration of the conventional “salt-base” two-chamber bipolar membrane electrodialysis; wherein CM is a cation exchange membrane, and BM is a bipolar membrane.

[0062] Fig. 3(b) is a schematic diagram of the membrane stack structure (taking piperidine hydrochloride as an example) and ion migration of the conventional “acid-salt” two-chamber bipolar membrane electrodialysis; wherein AM is an anion exchange membrane, and BM is a bipolar membrane.

[0063] Figure 4 It is a batch operation mode of ordinary electrodialysis (three membrane stacks are shown to run independently).

[0064] Figure 5 It is a multi-stage reverse flow electrodialysis system of batch operation (a three-stage two-compartment system is shown).

[0065] Figure 6 It is a continuous multi-stage reverse flow electrodialysis system in which the outlet of each stage membrane stack is connected to the material cylinder of the next stage membrane stack (a three-stage two-compartment system is shown).

[0066] Figure 7 It is a continuous multi-stage reverse flow electrodialysis system in which the material cylinder of each stage membrane stack is connected to the material cylinder of the next stage membrane stack (a three-stage two-compartment system is shown).

[0067] Figure 8The no-tank continuous multi-stage countercurrent electrodialysis system (a two-compartment three-stage system) of the present application.

[0068] Figure 9 The no-tank continuous multi-stage countercurrent electrodialysis system (a three-stage system, only the connection of one compartment is shown, including flow meter, valve, and heat exchanger) of the present application (outlet-inlet mode).

[0069] Figure 10 The no-tank continuous multi-stage countercurrent electrodialysis system (a three-stage system, only the connection of one compartment is shown, including flow meter, valve, and heat exchanger) of the present application (outlet-outlet mode).

[0070] Figure 11 The no-tank continuous multi-stage countercurrent electrodialysis system (a three-stage system, only the connection of one compartment is shown, including flow meter, valve, and heat exchanger) of the present application (inlet-outlet mode).

[0071] Figure 12 The no-tank continuous multi-stage countercurrent electrodialysis system (a three-stage system, only the connection of one compartment is shown, including flow meter, valve, and heat exchanger) of the present application (inlet-inlet mode). DETAILED DESCRIPTION

[0072] The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

[0073] The no-tank continuous multi-stage countercurrent electrodialysis system of the present application is shown in Figure 8 The no-tank continuous multi-stage countercurrent electrodialysis system of the present application is shown in

[0074] Specifically, for ordinary electrodialysis, the two compartments refer to a desalination compartment and a concentration compartment (as shown in Figure 1As shown in FIG. 2(a), the "feed solution is organized in a counter-current manner" is: the desalination chamber initial liquid enters from the first stage membrane stack, sequentially passes through each stage membrane stack, and flows to the Nth stage (N≥2) membrane stack; the concentration chamber initial liquid enters from the Nth stage (N≥2) membrane stack, sequentially passes through each stage membrane stack, and flows to the first stage membrane stack. In the process of the desalination chamber initial liquid flowing from the first stage membrane stack to the Nth stage membrane stack, ions gradually migrate out, and the ion concentration in the desalination chamber gradually decreases along the flow direction; and in the process of the concentration chamber initial liquid flowing from the Nth stage membrane stack to the first stage membrane stack, ions gradually migrate from the desalination chamber into the concentration chamber, and the ion concentration in the concentration chamber gradually increases along the flow direction. The "feed solution is organized in a counter-current manner" makes the desalination liquid with high ion concentration and the concentration liquid with high ion concentration in the same stage, and the desalination liquid with low ion concentration and the concentration liquid with low ion concentration in the same stage, thereby reducing the concentration difference on both sides of the ion exchange membrane, and thus reducing the energy consumption when ions migrate against the concentration and improving the current efficiency.

[0075] Specifically, for three-compartment bipolar membrane electrodialysis, the three compartments refer to an acid chamber, a salt chamber, and a base chamber (as shown in FIG. 3(a)), or an acid chamber, a salt chamber, and a base chamber (as shown in FIG. 3(b)), and the "feed solution is organized in a counter-current manner" is: the salt chamber initial liquid enters from the first stage membrane stack, sequentially passes through each stage membrane stack, and flows to the Nth stage (N≥2) membrane stack; the acid chamber initial liquid and the base chamber initial liquid enter from the Nth stage (N≥2) membrane stack, sequentially pass through each stage membrane stack, and flow to the first stage membrane stack. Figure 2

[0076] Specifically, for two-compartment bipolar membrane electrodialysis, the two compartments refer to a salt chamber and a base chamber (as shown in FIG. 3(a)), or an acid chamber and a salt chamber (as shown in FIG. 3(b)), and the "feed solution is organized in a counter-current manner" is: the salt chamber initial liquid enters from the first stage membrane stack, sequentially passes through each stage membrane stack, and flows to the Nth stage (N≥2) membrane stack; the base chamber initial liquid enters from the Nth stage (N≥2) membrane stack, sequentially passes through each stage membrane stack, and flows to the first stage membrane stack; or the salt chamber initial liquid enters from the first stage membrane stack, sequentially passes through each stage membrane stack, and flows to the Nth stage (N≥2) membrane stack; the acid chamber initial liquid enters from the Nth stage (N≥2) membrane stack, sequentially passes through each stage membrane stack, and flows to the first stage membrane stack.

[0077] Specifically, the "direct connection between the compartments of each stage membrane stack" includes: the outlet of each compartment of each stage membrane stack is connected to the inlet of the corresponding compartment of the next stage membrane stack (hereinafter referred to as an "outlet-inlet" mode, as shown in FIG. 2(a)); Figure 9 the outlet of each compartment of each stage membrane stack is connected to the outlet of the corresponding compartment of the next stage membrane stack (hereinafter referred to as an "outlet-outlet" mode, as shown in FIG. 2(b)); Figure 10 the inlet of each compartment of each stage membrane stack is connected to the outlet of the corresponding compartment of the next stage membrane stack (hereinafter referred to as an "inlet-outlet" mode, as shown in FIG. 2(c)); Figure 11 ​and the inlet of each compartment of each membrane stack is connected to the inlet of the corresponding compartment of the next membrane stack (hereinafter referred to as "inlet-inlet" mode, as shown in FIG. 1) ; and Figure 12

[0078] It should be noted that the "feed tank" and "product tank" in the present application are not Figures 9-12 "material cylinders" in the present application. Figures 4-7 The "feed tank" and "product tank" in the present application do not participate in the self-circulation loop of the membrane stack, but only represent the source and destination of the material liquid, which is equivalent to a "material liquid temporary storage tank" in the industrial field, and the volume can be large or small. Figures 9-12 The "feed tank" and "product tank" in the present application do not participate in the self-circulation loop of the membrane stack, but only represent the source and destination of the material liquid, which is equivalent to a "material liquid temporary storage tank" in the industrial field, and the volume can be large or small.

[0079] The no-cylinder continuous multi-stage countercurrent electrodialysis system of the present application may be disturbed during actual industrial operation (i.e., continuous feeding and continuous discharging), for example, the concentration and flow rate of the feed liquid at the inlet of the first stage (1st stage) may fluctuate (due to the previous process) and affect the salt concentration at the outlet of the last stage (Nth stage). Therefore, the present application also provides an electrodialysis method based on the no-cylinder continuous multi-stage countercurrent electrodialysis system.

[0080] ​The electrodialysis method based on the continuous multi-stage reverse flow electrodialysis system without feed tank of the application feeds back and adjusts the operating voltage of the last stage (N stage) according to the salt concentration at the outlet of the last stage (N stage) of the ordinary electrodialysis desalination chamber, or the salt concentration at the outlet of the last stage (N stage) of the bipolar membrane electrodialysis chamber, or the flow of the feed liquid of the first stage (1 stage) desalination chamber or salt chamber. That is, if the outlet salt concentration is lower than the set value (i.e. target value), the operating voltage of the last stage (N stage) is reduced; if the outlet salt concentration is higher than the set value (i.e. target value) and the current density of the last stage (N stage) is lower than the maximum current density that the ion exchange membrane can withstand, the operating voltage of the last stage (N stage) is increased; wherein the increment of the operating voltage adjustment of the last stage (N stage) = -(outlet salt concentration-set value)*K1, K1 is the correlation coefficient of the outlet salt concentration and the operating voltage of the last stage (N stage) (note: K1 itself is negative), which is related to the membrane stack and the material system being treated, and is obtained from the fitting relationship of the two. The operating voltage of the last stage (N stage) can be manually adjusted near the set value, the corresponding outlet salt concentration can be detected, and one data point can be obtained. Repeat this process to obtain at least two data points, and the fitting relationship can be established. Of course, more data points will make the fitting relationship more accurate. If the outlet salt concentration is higher than the set value (i.e. target value) and the current density of the last stage (N stage) is equal to or higher than the maximum current density that the ion exchange membrane can withstand, the flow of the feed liquid of the first stage (1 stage) desalination chamber or salt chamber is reduced, wherein the increment of the flow adjustment of the feed liquid of the first stage (1 stage) desalination chamber or salt chamber = -(outlet salt concentration-set value)*K2, K2 is the correlation coefficient of the outlet salt concentration and the flow of the feed liquid of the first stage (1 stage) desalination chamber or salt chamber (note: K2 itself is positive), which is related to the membrane stack and the material system being treated, and is obtained from the fitting relationship of the two. The flow of the feed liquid of the first stage (1 stage) desalination chamber or salt chamber can be manually adjusted near the set value, the corresponding outlet salt concentration can be detected, and one data point can be obtained. Repeat this process to obtain at least two data points, and the fitting relationship can be established. Of course, more data points will make the fitting relationship more accurate.

[0081] Specifically, the outlet salt concentration is represented by the conductivity value detected by a conductivity meter, and the conductivity meter detection is preferably online monitoring.

[0082] Specifically, if the conductivity value of the outlet salt concentration is lower than the set value (i.e. target value), the operating voltage of the last stage (Nth stage) is reduced; if the conductivity value of the outlet salt concentration is higher than the set value (i.e. target value) and the current density of the last stage (Nth stage) is lower than the maximum current density that the ion exchange membrane can withstand, the operating voltage of the last stage (Nth stage) is increased; wherein the increment of the operating voltage adjustment of the last stage (Nth stage) = -(conductivity value of the outlet salt concentration - set value) * K3, K3 is the correlation coefficient of the conductivity value of the outlet salt concentration and the operating voltage of the last stage (Nth stage) (note: K3 itself is a negative value), which is related to the membrane stack and the material system being treated, and is obtained from the fitting relationship formula. The operating voltage of the last stage (Nth stage) can be manually adjusted near the set value, the conductivity value of the outlet salt concentration is detected, and one data point is obtained. Repeat the above steps to obtain at least two data points, and the fitting relationship formula can be established. Of course, more data points will make the fitting relationship formula more accurate. If the conductivity value of the outlet salt concentration is higher than the set value (i.e. target value) and the current density of the last stage (Nth stage) is equal to or higher than the maximum current density that the ion exchange membrane can withstand, the flow rate of the feed liquid of the first stage (1st stage) desalination chamber or salt chamber is reduced, wherein the increment of the flow rate adjustment of the feed liquid of the first stage (1st stage) desalination chamber or salt chamber = -(conductivity value of the outlet salt concentration - set value) * K4, K4 is the correlation coefficient of the conductivity value of the outlet salt concentration and the flow rate of the feed liquid of the first stage (1st stage) desalination chamber or salt chamber (note: K4 itself is a positive value), which is related to the membrane stack and the material system being treated, and is obtained from the fitting relationship formula. The flow rate of the feed liquid of the first stage (1st stage) desalination chamber or salt chamber can be manually adjusted near the set value, the conductivity value of the outlet salt concentration is detected, and one data point is obtained. Repeat the above steps to obtain at least two data points, and the fitting relationship formula can be established. Of course, more data points will make the fitting relationship formula more accurate.

[0083] Example 1

[0084] A sodium chloride aqueous solution was treated using the three-stage tankless continuous countercurrent ordinary electrodialysis system of the present application. The ordinary electrodialyzer was a plate-and-frame type, and the membrane stack was composed of 4 RXAM negative membranes (Hebei Yadisheng Environmental Protection Equipment Co., Ltd.) and 5 SHCM positive membranes (Shanghai Xiangfeng Chemical Co., Ltd.). The membrane stack structure is shown in Figure 1 The effective area of each membrane in the membrane stack was 0.0088 m 2 The anode plate was a titanium-coated ruthenium electrode, and the cathode plate was a stainless steel electrode. The separator and the screen were both made of polypropylene material. The separator was a non-return type, and the screen was a woven mesh type. The connection relationship of the three-stage membrane stack is shown in Figure 9 .

[0085] Pre-fill each stage of the membrane stack with water. Start the circulation pumps of the desalination and concentration chambers of each stage of the conventional electrodialysis membrane stack, with a liquid flow linear velocity of 3 cm / s in each compartment. Turn on the DC power supply of each stage of the membrane stack, using constant voltage mode, with operating voltages of 2.8V, 3V, and 3.2V for the first, second, and third stages, respectively. Introduce a 30 g / L sodium chloride aqueous solution at a flow rate of 800 mL / h into the desalination chamber inlet of the first stage membrane stack via a feed pump; introduce deionized water at a flow rate of 120 mL / h into the concentration chamber inlet of the third stage membrane stack via a feed pump; and introduce 0.3 L of a 30 g / L sodium sulfate solution into each electrode chamber of each stage of the membrane stack. Monitor the conductivity of the feed solution at the desalination chamber outlet of the third stage membrane stack online.

[0086] After 80 minutes, the conductivity of the feed solution at the desalination chamber outlet of the third-stage membrane stack stabilized at 3 mS / cm. Timing was then started, and the volumes of feed and effluent solutions in each compartment were measured. After 120 minutes, conventional electrodialysis was stopped. 1.59 L of a 3 g / L NaCl aqueous solution was obtained at the outlet of the desalination chamber of the third-stage membrane stack, and 0.25 L of a 174 g / L sodium chloride aqueous solution was obtained at the outlet of the concentration chamber of the first-stage membrane stack. Calculations showed that the energy consumption for conventional electrodialysis concentration and recovery of sodium chloride was 0.24 kWh / kg NaCl, and the membrane flux was 10.5 mol NaCl / m³. 2 / h, with an average current efficiency of 70.4%. During operation, the sodium chloride concentration in the salt chamber outlet solution of the third-stage membrane stack desalination fluctuated within the range of 3 g / L ± 0.04 g / L.

[0087] Comparative Example 1

[0088] refer to Figure 6 The continuous three-stage countercurrent conventional electrodialysis system shown is used to treat sodium chloride aqueous solution. The other settings of the electrodialysis apparatus are the same as in Example 1, but the connection relationship of the three membrane stacks is as described above. Figure 6 As shown. The feed tanks of the desalination and concentration chambers of each membrane stack have a volume of 50 mL and are connected between the membrane stack outlet and the circulation pump inlet of the corresponding compartment, forming a circulation loop of "membrane stack outlet, feed tank, circulation pump, membrane stack inlet"; at the same time, a small portion of the feed liquid is diverted from the membrane stack outlet to the feed tank of the next stage membrane stack.

[0089] The operation process is the same as in Example 1, except that water is pre-filled in each stage of the membrane stack and the feed tank; a 30 g / L sodium chloride aqueous solution is introduced into the feed tank inlet of the desalination chamber of the first-stage membrane stack via a feed pump; and deionized water is introduced into the feed tank inlet of the concentration chamber of the third-stage membrane stack via a feed pump. The conductivity of the feed solution at the outlet of the desalination chamber of the third-stage membrane stack is monitored online.

[0090] The conductivity of the third membrane stack desalination chamber outlet liquid was stabilized at 3-4 mS / cm after 160 minutes, at which time the timer was started and the volume of the feed and discharge of each compartment was measured. After 120 minutes, the normal electrodialysis operation was stopped, and 1.594 L of 3.7 g / L NaCl aqueous solution was obtained at the desalination chamber outlet of the third membrane stack, and 0.245 L of 172 / L NaCl aqueous solution was obtained at the concentration chamber outlet of the first membrane stack. The energy consumption of the normal electrodialysis concentration recovery of NaCl was calculated to be 0.244 kWh / kg NaCl, and the membrane flux was 10.17 NaCl / m 2 / h, and the current efficiency was 69.3%. During the operation, the fluctuation range of the NaCl concentration of the third membrane stack desalination chamber outlet liquid was 3.7 g / L ± 1.1 g / L, and the liquid level in the tank was difficult to stabilize, and the situation of constantly rising or constantly falling occurred, which had to be manually adjusted continuously.

[0091] Example 2

[0092] The lithium sulfate aqueous solution was treated by using the tankless continuous three-stage countercurrent "acid-salt-base" three-chamber bipolar membrane electrodialysis system of the present application to regenerate into sulfuric acid and lithium hydroxide. The three-chamber bipolar membrane electrodialyzer was a plate and frame type, and the membrane stack was composed of 4 AMVN negative membranes (Asahi Glass Company), 4 SHCM positive membranes (Shanghai Xiangfeng Chemical Industry Co., Ltd.), and 5 TRJBM bipolar membranes (Beijing Tingrun Membrane Technology Development Co., Ltd.), and the membrane stack structure is shown in Figure 2 The effective area of each membrane in the membrane stack was 0.0088 m 2 ; the anode plate was a titanium coated ruthenium electrode, and the cathode plate was a stainless steel electrode; the separator and the screen were both polypropylene materials, the separator was a non-return type, and the screen was a woven mesh type. The connection relationship of the three-stage membrane stack is shown in Figure 10 .

[0093] The water was filled in each membrane stack in advance. The circulation pumps of the acid chamber, the salt chamber, and the base chamber of the "acid-salt-base" three-chamber bipolar membrane electrodialysis of each membrane stack were started, and the liquid flow linear velocity in each compartment was 3 cm / s. The direct current power supply of each membrane stack was turned on, and the operating voltage of the first, second, and third membrane stacks was 12 V, 12 V, and 12 V, respectively. The 150 g / L lithium sulfate aqueous solution was introduced into the salt chamber outlet of the first membrane stack through the feed pump at a flow rate of 600 mL / h; the deionized water was introduced into the acid chamber outlet of the third membrane stack through the feed pump at a flow rate of 600 mL / h; the deionized water was introduced into the base chamber outlet of the third membrane stack through the feed pump at a flow rate of 600 mL / h; and the 0.35 mol / L sodium sulfate solution was introduced into the electrode chamber of each membrane stack at 0.3 L. The conductivity of the salt chamber outlet liquid of the third membrane stack was monitored online.

[0094] After 18 minutes, the conductivity of the feed solution at the salt chamber outlet of the third-stage membrane stack stabilized at 2.6 mS / cm. Timing was then started, and the volumes of feed and effluent in each compartment were measured. After 120 minutes, the "acid-salt-alkali" three-chamber bipolar membrane electrodialysis operation was stopped. 0.61 L of a 2.42 g / L lithium sulfate aqueous solution was obtained at the salt chamber outlet of the third-stage membrane stack; 1.51 L of a 1.08 mol / L sulfuric acid aqueous solution was obtained at the acid chamber outlet of the first-stage membrane stack; and 1.48 L of a 2.20 mol / L lithium hydroxide aqueous solution was obtained at the alkali chamber outlet of the first-stage membrane stack. The calculated energy consumption for treating lithium sulfate using the "acid-salt-alkali" three-chamber bipolar membrane electrodialysis was 3.20 kWh / kg LiOH. + The membrane flux was 14.09 mol / m³. 2 / h, SO4 2- The membrane flux is 6.77 mol / m 2 / h, with an average current efficiency of 78.5%. During operation, the lithium sulfate concentration in the salt chamber outlet solution of the third-stage membrane stack fluctuated within the range of 2.42 g / L ± 0.1 g / L.

[0095] Comparative Example 2

[0096] use Figure 6 The continuous three-stage countercurrent "acid-salt-base" three-compartment bipolar membrane electrodialysis system shown treats lithium sulfate aqueous solution and regenerates it into sulfuric acid and lithium hydroxide. The other settings of the three-compartment bipolar membrane electrodialysis device are the same as in Example 2, but the connection relationship of the three membrane stacks is as described above. Figure 6 As shown. The feed tanks of the acid, salt and alkali chambers of each stage of the membrane stack have a volume of 50 mL and are connected between the membrane stack outlet and the circulation pump inlet of the corresponding compartment, forming a circulation loop of "membrane stack outlet, feed tank, circulation pump, membrane stack inlet"; at the same time, a small portion of the feed liquid is diverted from the membrane stack outlet to the feed tank of the next stage membrane stack.

[0097] The operation process is the same as in Example 2, except that water is pre-filled in each stage of the membrane stack and the feed tank. A 150 g / L lithium sulfate aqueous solution is pumped into the salt chamber feed tank inlet of the first-stage membrane stack via a feed pump at a flow rate of 600 mL / h. Deionized water is pumped into the acid chamber feed tank inlet of the third-stage membrane stack via a feed pump at a flow rate of 600 mL / h. Deionized water is also pumped into the alkali chamber feed tank inlet of the third-stage membrane stack via a feed pump at a flow rate of 600 mL / h. The conductivity of the feed solution at the salt chamber outlet of the third-stage membrane stack is monitored online.

[0098] The conductivity of the solution at the outlet of the salt compartment of the third membrane stack stabilized at 6.6 mS / cm after 40 minutes, at which time the timing was started and the volumes of the feed and product solutions were measured. The "acid-salt-base" three-compartment bipolar membrane electrodialysis was stopped after 120 minutes, and 0.65 L of a 6.1 g / L aqueous lithium sulfate solution was obtained at the outlet of the salt compartment of the third membrane stack, 1.49 L of a 1.08 mol / L aqueous sulfuric acid solution was obtained at the outlet of the acid compartment of the first membrane stack, and 1.46 L of a 2.20 mol / L aqueous lithium hydroxide solution was obtained at the outlet of the base compartment of the first membrane stack. The energy consumption of the "acid-salt-base" three-compartment bipolar membrane electrodialysis for treating lithium sulfate was calculated to be 3.35 kWh / kg LiOH, Li + The membrane flux was 13.89 mol / m 2 / h, and the average current efficiency was 77.3%. During the operation, the lithium sulfate concentration of the solution at the outlet of the salt compartment of the third membrane stack fluctuated in the range of 6.1 g / L ± 0.2 g / L, and the liquid level in the tank was difficult to stabilize, and had to be manually adjusted continuously. 2- The membrane flux was 6.67 mol / m 2 / h, and the average current efficiency was 77.3%. During the operation, the lithium sulfate concentration of the solution at the outlet of the salt compartment of the third membrane stack fluctuated in the range of 6.1 g / L ± 0.2 g / L, and the liquid level in the tank was difficult to stabilize, and had to be manually adjusted continuously.

[0099] Example 3

[0100] A "salt-base" two-compartment bipolar membrane electrodialysis system without a tank was used to treat an aqueous sodium gluconate solution to regenerate gluconic acid and sodium hydroxide. The two-compartment bipolar membrane electrodialyzer was a plate-and-frame type, and the membrane stack was composed of 4 SHCM anode membranes (Shanghai Xiangfeng Chemical Co., Ltd.) and 5 TRJBM bipolar membranes (Beijing Tingrun Membrane Technology Development Co., Ltd.). The membrane stack structure is shown in Fig. 3(a), and the effective area of each membrane in the membrane stack was 0.0088 m 2 ; the anode plate was a titanium-coated ruthenium electrode, and the cathode plate was a stainless steel electrode; the separators and the spacer were both made of polypropylene, the separators were non-return separators, and the spacer was a woven mesh type. The connection relationship of the three membrane stacks is shown in Fig. 3(b). Figure 11

[0101] The three membrane stacks were filled with water in advance. The circulation pumps of the salt compartments and the base compartments of the "salt-base" two-compartment bipolar membrane electrodialysis of the three membrane stacks were started, and the linear velocity of the liquid flow in each compartment was 3 cm / s. The direct current power supply of each membrane stack was turned on, and the operating voltage of the first, second, and third membrane stacks was 12.5 V, 12.5 V, and 12 V, respectively. The outlet of the salt compartment of the first membrane stack was connected to a feed pump, and a 300 g / L aqueous sodium gluconate solution was fed at a flow rate of 830 mL / h; the outlet of the base compartment of the third membrane stack was connected to a feed pump, and deionized water was fed at a flow rate of 420 mL / h; and 0.3 L of a 0.5 mol / L sodium sulfate solution was fed to the electrode compartments of each membrane stack. The conductivity of the solution at the inlet of the salt compartment of the third membrane stack was monitored online.​

[0102] After 23 minutes, the conductivity of the feed solution at the salt chamber inlet of the third-stage membrane stack stabilized at 6.6 mS / cm. Timing began at this point, and the volumes of feed and effluent solutions in each compartment were measured. After 120 minutes, the "salt-alkali" two-chamber bipolar membrane electrodialysis operation was stopped. Na₂O₃ was obtained at the salt chamber inlet of the third-stage membrane stack. + 1.54 L of a 5 g / L gluconic acid aqueous solution was used to obtain 0.96 L of a 1.96 mol / L sodium hydroxide aqueous solution at the inlet of the alkali chamber of the first-stage membrane stack. Calculations show that the energy consumption for treating sodium gluconate using a two-chamber bipolar membrane electrodialysis process with a "salt-alkali" configuration is 2.24 kWh / kg NaOH. + The membrane flux is 9.08 mol / m 2 / h, with an average current efficiency of 67.01%. During operation, the Na+ content of the feed solution at the salt chamber inlet of the third-stage membrane stack... + The concentration fluctuated within the range of 5 g / L ± 0.2 g / L.

[0103] Comparative Example 3

[0104] refer to Figure 7 The continuous three-stage countercurrent "salt-alkali" two-chamber bipolar membrane electrodialysis system shown is used to treat sodium gluconate aqueous solution and regenerate it into gluconic acid and sodium hydroxide. The other settings of the two-chamber bipolar membrane electrodialysis device are the same as in Example 3, but the connection relationship of the three-stage membrane stacks is referenced. Figure 7 As shown. The feed cylinders of the salt and alkali chambers of each membrane stack have a volume of 50 mL and are connected between the membrane stack outlet and the circulation pump inlet of the corresponding compartment, forming a circulation loop of "membrane stack outlet, feed cylinder, circulation pump, membrane stack inlet". The feed cylinders of each membrane stack are connected to the feed cylinders of the next membrane stack, and the feed liquid in each feed cylinder flows into the next stage by overflow due to the liquid level difference.

[0105] The operation process is the same as in Example 3, except that water is pre-filled in each stage of the membrane stack and the feed tank. A 300 g / L sodium gluconate aqueous solution is pumped into the salt chamber feed tank inlet of the first-stage membrane stack via a feed pump at a flow rate of 830 mL / h; deionized water is pumped into the alkali chamber feed tank inlet of the third-stage membrane stack via a feed pump at a flow rate of 420 mL / h. The conductivity of the feed solution at the salt chamber feed tank outlet of the third-stage membrane stack is monitored online.

[0106] After 50 minutes, the conductivity of the feed solution at the salt chamber outlet of the third-stage membrane stack stabilized at 9.7 mS / cm. Timing began at this point, and the volumes of feed and effluent in each compartment were measured. After 120 minutes, the "salt-alkali" two-chamber bipolar membrane electrodialysis operation was stopped, and Na₂SO₄ was obtained at the salt chamber outlet of the third-stage membrane stack. +The glucose acid aqueous solution with a concentration of 7.2 g / L was 1.58 L, and the sodium hydroxide aqueous solution with a concentration of 1.91 mol / L was 0.92 L obtained from the alkali chamber cylinder outlet of the first-stage membrane stack. The energy consumption of the "salt-alkali" two-chamber bipolar membrane electrodialysis for treating sodium gluconate was 2.31 kWh / kg NaOH, and the Na + The membrane flux was 8.49 mol / m 2 / h, and the average current efficiency was 65.03%. During the operation, the fluctuation range of the Na + concentration of the material liquid at the salt chamber cylinder outlet of the third-stage membrane stack was 7.2 g / L±0.3 g / L.

[0107] Example 4

[0108] The pentanediamine hydrochloride aqueous solution was treated by using the tankless continuous two-stage countercurrent "acid-salt" two-chamber bipolar membrane electrodialysis system of the application to regenerate hydrochloric acid and pentanediamine. The two-chamber bipolar membrane electrodialyzer was a plate-and-frame type, the membrane stack was composed of 4 pieces of AMVN negative membrane (Asahi Glass Company) and 5 pieces of TRJBM bipolar membrane (Beijing Tingrun Membrane Technology Development Co., Ltd.), the membrane stack structure was shown in Fig. 3(b), the effective area of each membrane in the membrane stack was 0.0088 m 2 ; the anode plate was a titanium-coated ruthenium electrode, the cathode plate was a stainless steel electrode; the separator and the screen were both polypropylene materials, the separator was a non-return type, and the screen was a woven mesh type. The connection relationship of the two-stage membrane stack was shown in Fig. 2. Figure 12 The connection relationship of the two-stage membrane stack was shown in Fig. 2.

[0109] The water was filled in each stage of the membrane stack in advance. The circulation pumps of the acid chamber and the salt chamber of the "acid-salt" two-chamber bipolar membrane electrodialysis of each stage of the membrane stack were started, and the liquid flow linear velocity in each compartment was 3 cm / s. The direct current power supply of each stage of the membrane stack was turned on, and the operating voltage of the first-stage and the second-stage membrane stack was 12 V and 12 V, respectively. The pentanediamine hydrochloride aqueous solution with a concentration of 0.52 mol / L was introduced into the salt chamber inlet of the first-stage membrane stack through a feeding pump at a flow rate of 800 mL / h; the deionized water was introduced into the acid chamber inlet of the second-stage membrane stack through a feeding pump at a flow rate of 800 mL / h; and the sodium sulfate solution with a concentration of 0.25 mol / L was introduced into the electrode chamber of each stage of the membrane stack at 0.3 L. The conductivity of the material liquid at the salt chamber inlet of the second-stage membrane stack was monitored on line.

[0110] After 15 minutes, the conductivity of the feed solution at the salt chamber inlet of the second-stage membrane stack stabilized at 6.9 mS / cm. Timing was then started, and the volumes of feed and effluent in each compartment were measured. After 120 minutes, the acid-salt two-chamber bipolar membrane electrodialysis operation was stopped. 1.45 L of a 3.6 g / L Cl- solution of pentanediamine was obtained at the salt chamber inlet of the second-stage membrane stack, and 1.75 L of a 0.87 mol / L hydrochloric acid solution was obtained at the acid chamber inlet of the first-stage membrane stack. Calculations showed that the energy consumption for treating pentanediamine hydrochloride using the acid-salt two-chamber bipolar membrane electrodialysis was 0.109 kWh / mol HCl, and the Cl- membrane flux was 6.16 mol / m³. 2 / h, with an average current efficiency of 54.42%. During operation, the Cl- concentration of the feed solution at the salt chamber inlet of the second-stage membrane stack fluctuated within the range of 3.6 g / L ± 0.2 g / L.

[0111] Comparative Example 4

[0112] refer to Figure 7 The continuous two-stage countercurrent "acid-salt" two-compartment bipolar membrane electrodialysis system shown is used to treat pentamethylenediamine hydrochloride aqueous solution and regenerate it into hydrochloric acid and pentamethylenediamine. The other settings of the two-compartment bipolar membrane electrodialysis device are the same as in Example 4, but the connection relationship of the secondary membrane stacks is referenced. Figure 7 As shown. The feed cylinders of the acid and salt chambers of each membrane stack have a volume of 50 mL and are connected between the membrane stack outlet and the circulation pump inlet of the corresponding compartment, forming a circulation loop of "membrane stack outlet, feed cylinder, circulation pump, membrane stack inlet". The feed cylinders of each membrane stack are connected to the feed cylinders of the next membrane stack, and the feed liquid in each feed cylinder flows into the next stage by overflow due to the liquid level difference.

[0113] The operation process is the same as in Example 4, except that water is pre-filled in each stage of the membrane stack and the feed tank. A 0.52 mol / L pentanediamine hydrochloride aqueous solution is pumped into the salt chamber feed tank inlet of the first-stage membrane stack via a feed pump at a flow rate of 800 mL / h; deionized water is pumped into the acid chamber feed tank inlet of the second-stage membrane stack via a feed pump at a flow rate of 800 mL / h. The conductivity of the feed solution at the salt chamber feed tank outlet of the second-stage membrane stack is monitored online.

[0114] After 30 minutes, the conductivity of the feed solution at the salt chamber outlet of the second-stage membrane stack stabilized at 8.9 mS / cm. Timing was then started, and the volumes of feed and effluent in each compartment were measured. After 120 minutes, the acid-salt two-chamber bipolar membrane electrodialysis operation was stopped. 1.50 L of a 4.7 g / L Cl- concentration pentanediamine aqueous solution was obtained at the salt chamber outlet of the second-stage membrane stack, and 1.70 L of a 0.86 mol / L hydrochloric acid aqueous solution was obtained at the acid chamber outlet of the first-stage membrane stack. Calculations showed that the energy consumption for treating pentanediamine hydrochloride using the acid-salt two-chamber bipolar membrane electrodialysis was 0.118 kWh / mol HCl, and the Cl- membrane flux was 5.71 mol / m³.2 / h, with an average current efficiency of 50.3%. During operation, the Cl- concentration of the feed liquid at the salt chamber outlet of the second-stage membrane stack fluctuated within the range of 4.7 g / L ± 0.3 g / L.

[0115] Example 5

[0116] The present invention utilizes a feedless, continuous, three-stage countercurrent "acid-salt-alkali" three-chamber bipolar membrane electrodialysis system to treat sodium sulfate aqueous solution and regenerate it into sulfuric acid and sodium hydroxide. The three-chamber bipolar membrane electrodialysis unit is a plate-and-frame type, with the membrane stack consisting of 4 AMVN anion exchange membranes (Asahi Glass Co., Ltd.), 4 SHCM cation exchange membranes (Shanghai Xiangfeng Chemical Co., Ltd.), and 5 TRJBM bipolar membranes (Beijing Tingrun Membrane Technology Development Co., Ltd.). The membrane stack structure is referenced... Figure 2 As shown, the effective area of ​​each membrane in the membrane stack is 0.0088 m². 2 The anode plate is a titanium-coated ruthenium electrode, and the cathode plate is a stainless steel electrode; both the separators and mesh are made of polypropylene, with the separators being loop-free separators and the mesh being a woven mesh type. The connection relationships of the three-stage membrane stack are referenced. Figure 10 As shown.

[0117] Pre-fill each stage of the membrane stack with water. Start the circulation pumps for the acid, salt, and alkali chambers of each stage of the "acid-salt-alkali" three-chamber bipolar membrane electrodialysis stack, with a liquid flow linear velocity of 3 cm / s in each chamber. Turn on the DC power supply for each stage of the membrane stack, using constant voltage mode, with operating voltages of 12V, 12V, and 12V for the first, second, and third stages, respectively. In the first stage, a 200 g / L sodium sulfate aqueous solution is pumped into the salt chamber outlet via a feed pump at a flow rate of 600 mL / h; in the third stage, deionized water is pumped into the acid chamber outlet via a feed pump at a flow rate of 600 mL / h; in the third stage, deionized water is pumped into the alkali chamber outlet via a feed pump at a flow rate of 600 mL / h; and 0.3 L of 0.35 mol / L sodium sulfate solution is pumped into each electrode chamber of each stage of the membrane stack. Monitor the conductivity of the feed solution at the salt chamber outlet of the third stage membrane stack online.

[0118] After 17 minutes, the conductivity of the feed solution at the salt chamber outlet of the third-stage membrane stack stabilized at 6.9 mS / cm. A sodium sulfate aqueous solution with a concentration of 4.82 g / L was obtained at the salt chamber outlet of the third-stage membrane stack, a sulfuric acid aqueous solution with a concentration of 1.24 mol / L was obtained at the acid chamber outlet of the first-stage membrane stack, and a sodium hydroxide aqueous solution with a concentration of 2.52 mol / L was obtained at the alkali chamber outlet of the first-stage membrane stack.

[0119] After 30 minutes, the flow rate of the sodium sulfate aqueous solution into the salt chamber outlet of the first-stage membrane stack was artificially increased by 5% to 630 mL / h (simulating fluctuations in the flow rate of the raw material solution in production), and after about 15 minutes, the conductivity of the material solution at the salt chamber outlet of the third-stage membrane stack increased and stabilized at 10.8 mS / cm; through a pre-experiment (fitting relationship between the operating voltage and the conductivity of the outlet material solution), K3 = -0.122 / (mS / cm) was obtained, multiplied by -(10.8 mS / cm-6.9 mS / cm), to obtain an increase of 0.47 V in the operating voltage of the third-stage membrane stack, and this increase was implemented, and after about 5 minutes, the conductivity of the material solution at the salt chamber outlet of the third-stage membrane stack returned to about 7.1 mS / cm; after 30 minutes, the sodium sulfate aqueous solution into the salt chamber outlet of the first-stage membrane stack was artificially switched to a sodium sulfate aqueous solution with a concentration of 210 g / L (the concentration was increased by 5%, and the flow rate remained at 630 mL / h, simulating fluctuations in the concentration of the raw material solution in production), and after about 15 minutes, the conductivity of the material solution at the salt chamber outlet of the third-stage membrane stack increased and stabilized at 10.9 mS / cm; through a pre-experiment (fitting relationship between the flow rate of the feed solution and the conductivity of the outlet material solution), K4 = 8.66(mL / h) / (mS / cm) was obtained, multiplied by -(10.9 mS / cm-6.9 mS / cm), to obtain an increase of -35 mL / h in the flow rate of the sodium sulfate aqueous solution into the salt chamber outlet of the first-stage membrane stack, and this increase was implemented, and after about 5 minutes, the conductivity of the material solution at the salt chamber outlet of the third-stage membrane stack returned to about 6.9 mS / cm.

[0120] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the examples, those skilled in the art should understand that modifications or equivalent replacements to the technical solutions of the present application do not deviate from the spirit and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A cartridgeless continuous multistage countercurrent electrodialysis system comprising a membrane stack of two or more stages, characterized in that, Each compartment of each membrane stack is not provided with a cylinder, and each compartment of each membrane stack is directly connected through a pipeline; Among them, the feed liquid in each compartment of each membrane stack in the electrodialysis system is organized in a countercurrent manner, and the feed liquid in each compartment is self-circulated through a circulating pump.

2. The cartridgeless continuous multistage countercurrent electro dialysis system of claim 1, wherein, The electrodialyzer of the electrodialysis system includes a common electrodialyzer, a three-chamber bipolar membrane electrodialyzer, or a two-chamber bipolar membrane electrodialyzer.

3. The cartridgeless continuous multistage countercurrent electro dialysis system of claim 2, wherein, The electrodialyzer of the electrodialysis system is a common electrodialyzer, and the membrane stack of the common electrodialyzer includes two compartments, which are a desalination chamber and a concentration chamber. The countercurrent organization includes: the initial liquid of the desalination chamber enters the first-stage membrane stack, and then sequentially passes through each membrane stack to the Nth-stage membrane stack; the initial liquid of the concentration chamber enters the Nth-stage membrane stack, and then sequentially passes through each membrane stack to the first-stage membrane stack; wherein N≥2.

4. The cartridgeless continuous multistage countercurrent electro dialysis system of claim 2, wherein, The electrodialyzer of the electrodialysis system is a three-chamber bipolar membrane electrodialyzer, and the membrane stack of the three-chamber bipolar membrane electrodialyzer includes three compartments, which are an acid chamber, a salt chamber, and a base chamber. The countercurrent organization includes: the initial liquid of the salt chamber enters the first-stage membrane stack, and then sequentially passes through each membrane stack to the Nth-stage membrane stack; the initial liquid of the acid chamber and the initial liquid of the base chamber enter the Nth-stage membrane stack, and then sequentially pass through each membrane stack to the first-stage membrane stack; wherein N≥2.

5. The cartridgeless continuous multistage countercurrent electro dialysis system of claim 2, wherein, The electrodialyzer of the electrodialysis system is a two-chamber bipolar membrane electrodialyzer, and the membrane stack of the two-chamber bipolar membrane electrodialyzer includes two compartments, which are a salt chamber and a base chamber. The countercurrent organization includes: the initial liquid of the salt chamber enters the first-stage membrane stack, and then sequentially passes through each membrane stack to the Nth-stage membrane stack; the initial liquid of the base chamber enters the Nth-stage membrane stack, and then sequentially passes through each membrane stack to the first-stage membrane stack; wherein N≥2. Alternatively, the membrane stack of the two-chamber bipolar membrane electrodialyzer includes two compartments, which are a salt chamber and an acid chamber. The countercurrent organization includes: the initial liquid of the salt chamber enters the first-stage membrane stack, and then sequentially passes through each membrane stack to the Nth-stage membrane stack; the initial liquid of the acid chamber enters the Nth-stage membrane stack, and then sequentially passes through each membrane stack to the first-stage membrane stack; wherein N≥2.

6. The cartridgeless continuous multistage countercurrent electrodialysis system according to any one of claims 1-5, wherein, The direct connection between each compartment of each membrane stack through a pipeline includes: The outlet of each compartment of each membrane stack is connected to the inlet of the corresponding compartment of the next-stage membrane stack; or, The outlet of each compartment of each membrane stack is connected to the outlet of the corresponding compartment of the next-stage membrane stack; or, The inlet of each compartment of each membrane stack is connected to the outlet of the corresponding compartment of the next-stage membrane stack; or, The inlet of each compartment of each membrane stack is connected to the inlet of the corresponding compartment of the next-stage membrane stack.

7. An electrodialysis method based on the continuous multi-stage countercurrent electrodialysis system of any one of claims 1-5, wherein the electrodialyzer in the electrodialysis system is a common electrodialyzer, and the method comprises the following steps: The salt concentration at the outlet of the desalination chamber of the last-stage common electrodialyzer is fed back to adjust the operating voltage of the last-stage, or the flow rate of the feed liquid of the first-stage desalination chamber is fed back to adjust.

8. The electrodialysis method of claim 7, wherein the outlet salt concentration is lower than the set value, the operating voltage of the last stage is reduced; the outlet salt concentration is higher than the set value, and the current density of the last stage is lower than the maximum current density that the ion exchange membrane can withstand, the operating voltage of the last stage is increased; wherein the increment of the adjustment of the operating voltage of the last stage = -(the outlet salt concentration - the set value) * K1; wherein K1 is a negative value, which is the correlation coefficient of the outlet salt concentration and the operating voltage of the last stage, obtained from the fitting relationship between the two; or, the outlet salt concentration is higher than the set value, and the current density of the last stage is equal to or higher than the maximum current density that the ion exchange membrane can withstand, the flow rate of the feed liquid of the first desalination chamber is reduced, wherein the increment of the adjustment of the flow rate of the feed liquid of the first desalination chamber = -(the outlet salt concentration - the set value) * K2; wherein K2 is a positive value, which is the correlation coefficient of the outlet salt concentration and the flow rate of the feed liquid of the first desalination chamber, obtained from the fitting relationship between the two.

9. The electrodialysis method according to claim 8, characterized in that, the outlet salt concentration is represented by the conductivity value detected by a conductivity meter, wherein, the conductivity value of the outlet salt concentration is lower than the set value, the operating voltage of the last stage is reduced; the conductivity value of the outlet salt concentration is higher than the set value, and the current density of the last stage is lower than the maximum current density that the ion exchange membrane can withstand, the operating voltage of the last stage is increased; wherein the increment of the adjustment of the operating voltage of the last stage = -(the conductivity value of the outlet salt concentration - the set value) * K3; wherein K3 is a negative value, which is the correlation coefficient of the conductivity value of the outlet salt concentration and the operating voltage of the last stage, obtained from the fitting relationship between the two; or, the conductivity value of the outlet salt concentration is higher than the set value, and the current density of the last stage is equal to or higher than the maximum current density that the ion exchange membrane can withstand, the flow rate of the feed liquid of the first desalination chamber is reduced, wherein the increment of the adjustment of the flow rate of the feed liquid of the first desalination chamber = -(the conductivity value of the outlet salt concentration - the set value) * K4; wherein K4 is a positive value, which is the correlation coefficient of the conductivity value of the outlet salt concentration and the flow rate of the feed liquid of the first desalination chamber, obtained from the fitting relationship between the two.

10. An electrodialysis method based on the tankless continuous multi-stage countercurrent electrodialysis system according to any one of claims 1-5, wherein the electrodialyzer in the electrodialysis system is a bipolar membrane electrodialyzer, comprising the following steps: the outlet salt concentration of the last stage of the bipolar membrane electrodialyzer is fed back to adjust the operating voltage of the last stage, or the flow rate of the feed liquid of the first salt chamber is adjusted.

11. The electrodialysis method according to claim 10, wherein, the outlet salt concentration is lower than the set value, the operating voltage of the last stage is reduced; the outlet salt concentration is higher than the set value, and the current density of the last stage is lower than the maximum current density that the ion exchange membrane can withstand, the operating voltage of the last stage is increased; wherein the increment of the adjustment of the operating voltage of the last stage = -(the outlet salt concentration - the set value) * K1; wherein K1 is a negative value, which is the correlation coefficient of the outlet salt concentration and the operating voltage of the last stage, obtained from the fitting relationship between the two; or, The outlet salt concentration is higher than a set value, and the current density of the last stage is equal to or higher than the maximum current density that the ion exchange membrane can withstand, the flow rate of the feed liquid of the first stage salt chamber is reduced, wherein the increment of the flow rate adjustment of the feed liquid of the first stage salt chamber = -(the outlet salt concentration - the set value) * K2; wherein K2 is a positive value, which is the correlation coefficient of the outlet salt concentration and the flow rate of the feed liquid of the first stage salt chamber, obtained from the fitting relationship of the two.

12. The electrodialysis method according to claim 11, characterized in that, The outlet salt concentration is represented by the conductivity value detected by a conductivity meter, wherein, The conductivity value of the outlet salt concentration is lower than a set value, the operating voltage of the last stage is reduced; the conductivity value of the outlet salt concentration is higher than a set value, and the current density of the last stage is lower than the maximum current density that the ion exchange membrane can withstand, the operating voltage of the last stage is increased; wherein the increment of the operating voltage adjustment of the last stage = -(the conductivity value of the outlet salt concentration - the set value) * K3; wherein K3 is a negative value, which is the correlation coefficient of the conductivity value of the outlet salt concentration and the operating voltage of the last stage, obtained from the fitting relationship of the two; Or, The conductivity value of the outlet salt concentration is higher than a set value, and the current density of the last stage is equal to or higher than the maximum current density that the ion exchange membrane can withstand, the flow rate of the feed liquid of the first stage salt chamber is reduced, wherein the increment of the flow rate adjustment of the feed liquid of the first stage salt chamber = -(the conductivity value of the outlet salt concentration - the set value) * K4; wherein K4 is a positive value, which is the correlation coefficient of the conductivity value of the outlet salt concentration and the flow rate of the feed liquid of the first stage salt chamber, obtained from the fitting relationship of the two.

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