Method for producing acid and base based on high-salinity wastewater by bipolar membrane electrodialysis

Abstract

The application belongs to the technical field of wastewater treatment and resource, and discloses a method for generating acid and alkali based on bipolar membrane electrodialysis of high-salinity wastewater, which comprises the following steps: under constant voltage, based on the dynamic feedback control of the salt chamber conductivity, the high-salinity wastewater is intermittently fed in the mode of operation, so that the acid and alkali are stably generated in the bipolar membrane electrodialysis system; and the dynamic feedback interval of the salt chamber conductivity is 30-69 mS / cm. The application effectively inhibits the concentration polarization phenomenon under the condition of high-salinity feed of the bipolar membrane electrodialysis system, and improves the acid and alkali yield and the system operation stability.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment and resource utilization technology, and in particular to a method for producing acid and alkali from high-salt wastewater based on bipolar membrane electrodialysis. Background Technology

[0002] High-salinity wastewater is widely generated in industries such as metallurgy, chemicals, pharmaceuticals, printing and dyeing, seawater desalination, and coal chemicals. It is characterized by high total dissolved solids concentrations and complex compositions, making treatment challenging. Traditional treatment methods, such as evaporation crystallization and reverse osmosis, suffer from high energy consumption, severe secondary pollution, and low resource recovery rates. Bipolar membrane electrodialysis technology can directly convert salts into corresponding acids and bases without introducing external chemical reagents, enabling the resource utilization of high-salinity wastewater.

[0003] However, the inventors have noted that under high-salt feed conditions, bipolar membrane electrodialysis systems are prone to problems such as concentration polarization, membrane fouling, and decreased current efficiency, affecting acid and alkali yields and operational stability. Furthermore, in existing technologies, most bipolar membrane systems employ constant current or timed feeding modes, which are difficult to adapt to fluctuations in high salt concentrations, resulting in drastic conductivity fluctuations and unstable acid and alkali production efficiency.

[0004] Some literature employs a coupled process of electrodialysis (ED) and bipolar membrane electrodialysis (BMED), using electrodialysis as an intermediate concentration unit for cyclic concentration to produce desalinated and concentrated water, which is then treated using bipolar membrane electrodialysis. However, the inventors have noted that this coupled process has complex system integration, numerous control points, and poor operational stability.

[0005] Some literature also employs "non-steady-state" batch operations, for example, continuously concentrating a certain amount of concentrated water into the system until the conductivity reaches a set value, at which point the system is stopped, the product is discharged, or the flow is diverted. However, the inventors recognize that this batch operation is essentially a highly volatile "non-steady-state process." Key parameters within the system, such as resistance and current efficiency, change drastically as the reaction proceeds, leading to large fluctuations in the concentration of acid and alkali produced. Furthermore, frequent start-ups and shutdowns not only waste a significant amount of time but also generate ineffective Joule heat losses. It still fails to address issues such as concentration polarization and membrane fouling.

[0006] Therefore, there is an urgent need to develop a bipolar membrane electrodialysis method for producing acids and alkalis that is suitable for high-salt feed, has stable operation, and high acid and alkali yield. Summary of the Invention

[0007] According to one embodiment of the present invention, the purpose is to provide a method for producing acid and alkali from high-salt wastewater based on bipolar membrane electrodialysis. Based on a steady-state conversion mechanism of constant pressure and dynamic feedback control of salt chamber conductivity for intermittent feeding, stable generation of acid and alkali is achieved in the bipolar membrane electrodialysis system, which solves the problems of concentration polarization, unstable operation, and complex operation control that are prone to occur in existing bipolar membrane electrodialysis systems under high-salt feed conditions.

[0008] The above objective can be achieved through the following technical solutions: According to one aspect of the present invention, a method for producing acid and alkali from high-salinity wastewater based on bipolar membrane electrodialysis is provided, comprising: generating acid and alkali from high-salinity wastewater in a bipolar membrane electrodialysis system under constant pressure and based on an intermittent feeding operation mode; wherein the intermittent feeding is controlled based on dynamic feedback of salt chamber conductivity, and the dynamic feedback range of salt chamber conductivity is 30 to 69 mS / cm.

[0009] Preferably, the constant pressure range is 55-65V.

[0010] Preferably, the entire operating cycle is in a continuous cyclical state, and intermittent feeding is carried out by monitoring the conductivity of the salt chamber in real time.

[0011] Preferably, the intermittent feeding by real-time monitoring of the salt chamber conductivity includes: automatically stopping feeding when the salt chamber conductivity reaches the upper limit of the dynamic feedback range; and automatically resuming feeding when the salt chamber conductivity drops to the lower limit of the dynamic feedback range, so that the salt chamber conductivity recovers.

[0012] Preferably, the continuous cycle time is 65-120 minutes.

[0013] Preferably, the high-salinity wastewater has a TDS ≥ 40000 mg·L⁻¹. -1 .

[0014] Preferably, it further includes: controlling the calcium ion concentration, magnesium ion concentration, and turbidity of the high-salt wastewater; The concentrations of calcium ions and magnesium ions are both less than 1 mg / L, and the turbidity is less than 3 NTU.

[0015] Preferably, during operation, the conductivity of the membrane stack salt chamber is maintained in the range of 30.7 to 69 mS / cm, and the current fluctuates in the range of 23.5 to 63.4 A.

[0016] Preferably, after reaching a stable state, the HCl concentration on the acid side of the membrane stack is ≥6%, and the NaOH concentration on the alkaline side is ≥6.3%.

[0017] Preferably, after reaching a stable state, the average increase in conductivity on the acid side of the membrane stack is 4.21–4.55 mS·min. -1 The average increase in conductivity on the alkaline side was 1.62–1.69 mS·min. -1 .

[0018] Preferably, the bipolar membrane electrodialysis system comprises: A bipolar membrane electrodialysis device has a membrane stack, which includes a salt chamber, an acid chamber, an alkali chamber, and a bipolar chamber; The raw water tank is used to store high-salinity wastewater, and its outlet is connected to the inlet of the salt chamber through an inlet pipe. The salt circulation tank has its inlet connected to the salt chamber outlet via an output pipeline, and its outlet connected to the salt chamber inlet via a salt circulation pipeline. The acid circulation tank has its inlet connected to the acid chamber outlet via an acid output pipeline, and its outlet connected to the acid chamber inlet via an acid circulation pipeline. The alkali circulation tank has its inlet connected to the alkali chamber outlet via an alkali output pipeline, and its outlet connected to the alkali chamber inlet via an alkali circulation pipeline. The polar water tank is connected to the two polar chambers via circulation pipes. The salt chamber is equipped with a dynamic feedback control system for salt conductivity.

[0019] Preferably, the conductivity dynamic feedback control system includes: an online conductivity sensor, an automatic feed valve, and a controller. The online conductivity sensor is installed at the salt chamber outlet and is used to monitor the conductivity inside the salt chamber in real time. The controller is used to receive the signal emitted by the online conductivity sensor and issue instructions to the automatic feed valve according to preset logic. The automatic feed valve is installed at the salt chamber inlet and is used to receive the control signal from the controller and perform opening / closing actions.

[0020] Preferably, the acid circulation tank is pre-filled with an acid solution, the mass fraction of which is 1.5% to 3%.

[0021] Preferably, the alkali circulation tank is pre-filled with an alkali solution, the mass fraction of which is 1.5% to 3%.

[0022] Preferably, the polar water tank contains a sodium hydroxide solution, and the mass fraction of the sodium hydroxide solution is 1% to 3%.

[0023] Preferably, the salt conductivity dynamic feedback control system further includes a current monitoring device installed at the salt chamber outlet for monitoring the salt chamber current.

[0024] Preferably, the acid chamber is equipped with a dynamic feedback control system for acid conductivity.

[0025] Furthermore, the acid conductivity dynamic feedback control system includes at least an online conductivity sensor installed at the acid chamber outlet for real-time monitoring of the conductivity inside the acid chamber.

[0026] Preferably, the acid chamber is equipped with an acid concentration detector, which is located at the outlet of the acid chamber for detecting the acid concentration.

[0027] Preferably, the alkali chamber is equipped with an alkali conductivity dynamic feedback control system. Further, the alkali chamber equipped with the alkali conductivity dynamic feedback control system includes at least an online conductivity sensor installed at the outlet of the alkali chamber for real-time monitoring of the conductivity within the alkali chamber.

[0028] Preferably, the alkali chamber is equipped with an alkali concentration detector, which is located at the outlet of the alkali chamber for detecting the alkali concentration.

[0029] Beneficial effects: According to one embodiment of the present invention, a steady-state conversion mechanism based on constant pressure and dynamic feedback control of salt chamber conductivity for intermittent feeding is achieved, and the dynamic feedback range is optimized to 30-69 mS / cm. Stable generation of acid and alkali is realized in the bipolar membrane electrodialysis system, which effectively suppresses the concentration polarization phenomenon under high salt feed conditions and improves acid and alkali yield and system operation stability.

[0030] Compared with the prior art, the embodiments of the present invention also have the following advantages: 1) A lower upper limit for conductivity reduces the risk of scaling and concentration polarization. By controlling the upper limit of the dynamic conductivity feedback range to 69 mS / cm, the system is consistently maintained within a window of low resistance, low polarization, and high current efficiency, thus avoiding scaling and concentration polarization problems caused by high conductivity. This is especially beneficial for systems with total dissolved solids not less than 40,000 mg·L⁻¹. - ¹Highly concentrated saline solution is particularly effective.

[0031] 2) It operates under constant pressure and works in conjunction with "conductivity feedback control intermittent feeding".

[0032] On the one hand, constant pressure can perfectly adapt to the automated control of "dynamic steady state": In constant current mode, the current is a fixed value, which masks the real change in the resistance inside the membrane stack. It is difficult for the control system to accurately determine when to replenish the feed based solely on the current data. However, under the constant pressure condition of this invention, the change in current directly reflects the change in the resistance of the solution inside the membrane stack (i.e., the ion concentration). In constant pressure mode, the current is positively correlated with the salt conductivity (linearly), and the system response is more sensitive (when the conductivity drops to the lower limit, the resistance increases, and the current decreases accordingly. The system can trigger the feed command very smoothly and accurately). This characteristic makes the system more stable and responds faster, easily realizing the leap from "batch operation" to "quasi-steady-state continuous operation".

[0033] On the other hand, constant voltage can improve system safety: in order to maintain "constant current", the voltage is forced to rise, which can cause membrane stack breakdown and membrane damage, and also greatly increase safety hazards; while the present invention adopts constant voltage operation, and even if the salt chamber concentration decreases or increases, it can be intermittently fed through conductivity feedback, providing a physical safety barrier for the automated system and greatly extending the service life of expensive membrane stacks.

[0034] Thirdly, constant voltage can reduce energy consumption: Although constant current can ensure the acid and alkali production rate in the early stage, as the reaction proceeds, energy consumption will increase significantly in order to counteract the ever-increasing membrane stack resistance. However, this invention, through intermittent feeding, always locks the salt chamber conductivity in the high-efficiency operating range of low conductivity of 30-69 mS / cm. Combined with constant voltage mode, the system always operates at a lower voltage, avoiding the high-energy-consumption and low-efficiency range that the traditional constant current mode is forced into at low concentration stages. This design ensures production capacity while minimizing the power consumption per unit product.

[0035] 3) The entire operation of this invention is in a "quasi-steady-state continuous cyclic operation" state. This invention operates in a continuous cycle and intermittently replenishes the material by monitoring the conductivity of the salt chamber in real time. Here, "intermittent replenishment" emphasizes the method of material replenishment, while "continuous cyclic operation" refers to the continuity in reaction kinetics and production efficiency. Throughout the entire operating cycle, the electric field is never interrupted, acid and alkali production never stops, and the system is always in a dynamic balance of "reaction-automatic replenishment-re-reaction," eliminating the fatal "shutdown cooling and restart heating" link in traditional "batch operation" and achieving substantially uninterrupted production.

[0036] Unlike the "continuous operation within a single run": the existing (batch / intermittent) control logic is "feeding - processing to the set value and then stopping to unload - cleaning / restarting - proceeding to the next batch". Under this non-continuous operation mode of "stopping to unload", the material parameters (temperature, concentration, resistance, polarization state) in the reactor change greatly over time, which is a typical "non-steady-state process". This not only leads to large fluctuations in product quality (acid and alkali concentration) between batches, but also easily causes concentration polarization and fouling of the membrane stack during the start-up and shutdown phases.

[0037] Moreover, this invention constructs a 'conductivity upper and lower limit feedback control feeding mechanism' and controls the conductivity dynamic feedback range within a narrow range of 30-69 mS / cm. It breaks down the traditional 'large batch intermittent' process into countless tiny 'dynamic feeding units', achieving continuous cyclic operation through 'feeding-reaction-refeeding'. This not only achieves the continuity of the process flow but also keeps the bipolar membrane electrodialysis system in a 'quasi-steady-state operation' region. Within this region, key parameters such as membrane stack resistance, current efficiency, and acid and alkali production rates remain relatively constant. This 'continuous output under stable parameters' is far more industrially valuable than the volatile 'start-stop continuous' process of existing technologies.

[0038] 4) Further improve the lifespan of the bipolar membrane by controlling the influent water quality. By strictly controlling the influent water quality, limiting the calcium and magnesium content and turbidity, and combining the specific conductivity feedback control intermittent feeding mechanism and conductivity feedback control range of this invention, the lifespan of the expensive bipolar membrane can be greatly extended while improving acid and alkali yield and system operational stability. Attached Figure Description

[0039] Figure 1 This is a trend graph of salt cycle conductivity and current during acid and alkali production by bipolar membrane electrodialysis of high-salt solution in an embodiment of the present invention. Figure 2 This is a trend graph of acid cycle conductivity and alkali cycle conductivity during the acid-alkali production process of bipolar membrane electrodialysis in a high-salt solution according to an embodiment of the present invention. Detailed Implementation

[0040] In the following description, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that the embodiments can be modified in various ways without departing from the spirit and scope of the present invention.

[0041] The terminology used herein is for descriptive purposes only and is not intended to limit the scope of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should be further understood that, when used in this specification, the terms “comprising” and / or “including” specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0042] As used herein, unless specifically indicated or obvious in the context, the term "approximately" should be understood as being within the normal tolerances of the field, such as within 2 standard deviations of the mean. Unless otherwise stated in the context, all numerical values ​​provided herein are modified by the term "approximately".

[0043] Furthermore, it should be understood that the controller can perform one or more processes further described below, and the term controller refers to a hardware device including a memory and a processor. The memory is configured to store modules, and the processor is specifically configured to execute said modules to perform one or more processes further described below.

[0044] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Terms such as those commonly used and already found in dictionaries should be interpreted as having a meaning that matches the contextual meaning in this art. In this specification, unless explicitly defined, terms should not be ideally over-interpreted as having a formal meaning.

[0045] To address the problems of concentration polarization, unstable operation, complex operation control, unstable acid and alkali production efficiency, and short bipolar membrane lifespan in existing bipolar membrane electrodialysis systems under high-salt feed conditions, this invention proposes a method for acid and alkali production from high-salt wastewater using bipolar membrane electrodialysis. This method employs a constant-pressure, intermittent feeding operation mode based on dynamic feedback control of salt chamber conductivity, achieving stable acid and alkali production in the bipolar membrane electrodialysis system. This effectively suppresses concentration polarization under high-salt feed conditions, improving acid and alkali production rates and system operational stability.

[0046] In some embodiments, the method for producing acid and alkali from high-salinity wastewater based on bipolar membrane electrodialysis includes: generating acid and alkali from high-salinity wastewater in a bipolar membrane electrodialysis system based on a constant pressure and intermittent feeding operation mode; and the intermittent feeding is based on dynamic feedback control of salt chamber conductivity, wherein the dynamic feedback range of salt chamber conductivity is 30–69 mS / cm.

[0047] By employing a constant-pressure, intermittent feeding operation mode with dynamic feedback control of salt chamber conductivity, and setting an upper limit of 69 mS / cm and a lower limit of 30 mS / cm for salt chamber conductivity, the system can consistently maintain a window of low resistance, low polarization, and high current efficiency, avoiding problems such as scaling and concentration polarization caused by high conductivity. In particular, for total dissolved solids not less than 40,000 mg·L⁻¹, this is particularly effective. -1 The effect is particularly noticeable with highly concentrated saline solution.

[0048] This invention operates under constant voltage. In constant voltage mode, the current is positively correlated with the salt conductivity, resulting in a more sensitive system response. Further, the constant voltage range is 55-65V. More preferably, the operating pressure for constant voltage is 60V.

[0049] To further extend the lifespan of the bipolar membrane, the influent water quality is controlled. This includes controlling the turbidity, calcium ion concentration, and magnesium ion concentration of the high-salinity wastewater. Preferably, the calcium and magnesium ion concentrations in the influent are both controlled to be less than 1 mg / L, and the turbidity is controlled to be less than 3 NTU. By strictly controlling the influent water quality, limiting the calcium and magnesium content and turbidity, and combining this invention's specific intermittent feeding mechanism and its conductivity feedback control range, the lifespan of the expensive bipolar membrane can be significantly extended while improving acid and alkali yield and system operational stability.

[0050] This invention relates to intermittent feeding based on dynamic feedback control of salt chamber conductivity, which means intermittent feeding is performed by monitoring the conductivity of the salt chamber in real time. Specifically, it includes: Start-up phase: Raw water is introduced into the salt chamber. When the conductivity of the salt chamber reaches the upper limit of the dynamic feedback range, feeding automatically stops. Under the influence of the electric field, the salt is converted into acid and alkali, and the conductivity of the salt chamber continuously decreases. When the conductivity of the salt chamber drops to the lower limit of the dynamic feedback range, feeding automatically resumes, causing the conductivity to rise again. Throughout the entire operating cycle, the electric field is never interrupted, acid and alkali production never stops, and the system is always in a dynamic balance of "reaction-automatic replenishment-re-reaction," i.e., a "steady-state continuous operation" state. This eliminates the fatal "shutdown cooling and restart heating" stage in traditional batch operations, achieving virtually uninterrupted production.

[0051] In some embodiments, a dynamic conductivity feedback control system is configured for the salt chamber. Specifically, the bipolar membrane electrodialysis system includes a bipolar membrane electrodialysis device having a membrane stack, the membrane stack including a salt chamber, an acid chamber, an alkali chamber, and a bipolar chamber; wherein, the salt chamber is configured with a salt conductivity dynamic feedback control system.

[0052] Furthermore, the salt conductivity dynamic feedback control system includes: an online conductivity sensor, an automatic feed valve, and a controller. The online conductivity sensor is installed at the salt chamber outlet (it can be installed on the output pipeline or directly in the salt circulation tank) to monitor the conductivity inside the salt chamber in real time. The controller receives signals from the online conductivity sensor and issues commands to the automatic feed valve according to preset logic. The automatic feed valve is installed at the salt chamber inlet to receive control signals from the controller and perform opening / closing actions. By configuring the salt conductivity dynamic feedback control system for the salt chamber, an intermittent feeding operation mode based on the dynamic feedback control of the salt chamber conductivity is achieved.

[0053] Furthermore, the salt conductivity dynamic feedback control system may also include a current monitoring device for detecting current fluctuations in the salt chamber. Specifically, it can be installed on the output pipeline at the salt chamber outlet, or directly in the salt circulation tank, for example, at the salt circulation tank inlet.

[0054] In some preferred embodiments, each chamber of the membrane stack in the bipolar membrane electrodialysis system is equipped with a circulation box, and the entire operation cycle is in a continuous circulation state ("quasi-steady-state continuous circulation operation"), and intermittent feeding is carried out by real-time monitoring of the conductivity of the salt chamber.

[0055] Specifically, in some embodiments, the bipolar membrane electrodialysis system includes: a bipolar membrane electrodialysis device, a raw water tank, a salt circulation tank, an acid circulation tank, an alkali circulation tank, and an electrode water tank.

[0056] The raw water tank is used to store high-salinity wastewater, and its outlet is connected to the inlet of the salt chamber via an inlet pipe.

[0057] The bipolar membrane electrodialysis device, as described above, has a membrane stack, which includes a salt chamber, an acid chamber, an alkali chamber, and a bipolar chamber. The salt chamber is equipped with a dynamic feedback control system for salt conductivity.

[0058] The salt circulation tank has its inlet connected to the salt chamber outlet via an output pipeline, and its outlet connected to the salt chamber inlet via a salt circulation pipeline. High-salt wastewater is pumped from the raw water tank into the "salt chamber" of the membrane stack. Under the influence of an electric field, anions and cations in the salt migrate out through the anion and cation membranes, respectively, causing the salt solution to gradually become diluted (becoming dilute brine). This diluted brine then flows through the output pipeline to the salt circulation tank and circulates through the salt circulation pipeline. Furthermore, the salt circulation tank is connected to the salt chamber inlet via the raw water tank, allowing the circulating dilute brine to mix with the high-salt wastewater and enter the salt chamber as mixed influent.

[0059] The acid circulation tank has its inlet connected to the acid chamber outlet via an acid output pipeline, and its outlet connected to the acid chamber inlet via an acid circulation pipeline. Initially, it is pre-filled with a certain amount of dilute acid solution or pure water. Preferably, the acid circulation tank is pre-filled with an acid solution, the mass fraction of which is 1.5% to 3%. More preferably, the acid circulation tank is pre-filled with hydrochloric acid solution. The acid circulation tank is used to collect and circulate the generated acid solution. During operation, anions from the salt chamber enter the acid chamber and react with H+ generated by the bipolar membrane. + The resulting acid flows into the acid circulation tank and is circulated.

[0060] The alkali circulation tank has its inlet connected to the alkali chamber outlet via an alkali output pipeline, and its outlet connected to the alkali chamber inlet via an alkali circulation pipeline. It is initially pre-filled with a dilute alkali solution or pure water. Preferably, the alkali circulation tank is pre-filled with an alkali solution having a mass fraction of 1.5% to 3%. More preferably, the alkali circulation tank is pre-filled with a sodium hydroxide solution. The alkali circulation tank is used to collect and circulate the generated alkali solution. During operation, cations from the salt chamber enter the alkali chamber and react with OH- ions generated by the bipolar membrane. - The alkali that generates the response flows to the alkali circulation tank and is circulated.

[0061] The electrode water tank is connected to both electrode chambers via circulation pipelines and is specifically used for liquid circulation between the electrode chambers at both ends of the membrane stack. Electrode reactions generate gas and heat; the electrode water's role is to remove these byproducts and heat, protecting the electrode plates from corrosion. The electrode water maintains independent circulation and does not mix with other feed solutions. Furthermore, the electrode water tank contains a sodium hydroxide solution. Preferably, the sodium hydroxide solution has a mass fraction of 1% to 3%.

[0062] In addition, the bipolar membrane electrodialysis system may also include a pure water tank. The pure water tank is used for routine system maintenance. It stores deionized water or pure water and is primarily used for pipeline flushing before equipment startup, material ejection and replacement after shutdown, and periodic chemical cleaning of the membrane stack. Furthermore, the bipolar membrane electrodialysis system also includes equipment or instruments such as a circulating pump, flow meter, and pressure gauge to ensure system balance.

[0063] In addition, the acid chamber and / or alkali chamber are also equipped with corresponding dynamic conductivity feedback control systems for monitoring and controlling acid and alkali conductivity. The structure of the acid / alkali conductivity dynamic feedback control system is similar to that of the salt conductivity dynamic feedback control system, and it includes at least an online conductivity sensor installed on the pipeline at the outlet of the acid / alkali chamber.

[0064] Furthermore, the acid chamber and alkali chamber are also equipped with concentration detectors for real-time monitoring of the concentrations of the generated acid and alkali. These detectors can be installed on the pipeline at the outlet of the acid / alkali chamber or directly at the inlet of the acid / alkali circulation tank.

[0065] In some embodiments, the bipolar membrane electrodialysis system equipped with a circulation tank is used to produce acids and alkalis from high-salinity wastewater. Specifically, the water tank is injected with 1%–3% NaOH solution, the acid circulation tank is pre-charged with 1.5%–3% HCl, and the alkali circulation tank is pre-charged with 1.5%–3% NaOH. The method for producing acids and alkalis from high-salinity wastewater based on bipolar membrane electrodialysis specifically includes the following steps: 1) Using TDS ≥ 40000 mg·L -1 The solution is a highly concentrated brine solution, with calcium and magnesium ion concentrations controlled to be < 1 mg / L and turbidity < 3 NTU.

[0066] 2) Under the constant voltage of 60 V and intermittent feeding mode based on salt chamber conductivity feedback, acid and alkali are stably produced from high-salt wastewater. The preset upper limit of salt chamber conductivity is 69 mS / cm, and the lower limit is 30 mS / cm.

[0067] The operation process includes: the start-up phase, where feeding stops once the conductivity reaches its upper limit; under the influence of the electric field, the salt is converted into acid and alkali, and the conductivity decreases; when the conductivity drops to the lower limit, automatic feeding is initiated.

[0068] Furthermore, the system operates in a continuous cycle. Preferably, the continuous cycle time is 65-120 minutes, during which time it enters a stable operating state and can stably generate acids and bases. More preferably, the continuous cycle time is 100-110 minutes, for example, 105 minutes.

[0069] 3) Dynamic characteristics are monitored during operation, including salt conductivity, current, acid conductivity, alkali conductivity, acid and alkali concentration, and average growth rate.

[0070] Furthermore, the salt conductivity fluctuates periodically within the range of 30.7–69 ms, while the current fluctuates synchronously within the range of 23.5–63.4 A. Under the intermittent feeding mode based on constant voltage and dynamic feedback control of salt chamber conductivity, the salt chamber conductivity is maintained within a specific low dynamic feedback range, and the current fluctuates synchronously within a specific range, exhibiting a sensitive response.

[0071] During operation, the acid conductivity increases linearly, while the alkali conductivity increases steadily. Furthermore, after reaching a steady state, the average increase in acid-side conductivity is 4.21–4.55 mS·min. -1 The average increase in conductivity on the alkaline side was 1.62–1.69 mS·min. -1 As the operating time progresses, the average rate of increase in acid and alkali does not slow down. Throughout the entire continuous operating cycle, this invention can maintain a higher average rate of increase in acid and alkali with minimal fluctuations, exhibiting extremely high current efficiency and stable production capacity. This also confirms the significant effect of the intermittent feeding control strategy based on constant voltage and dynamic feedback control of salt chamber conductivity on suppressing concentration polarization and reducing mass transfer resistance.

[0072] Furthermore, after reaching a stable state, the HCl concentration on the acid side is ≥6%, and the NaOH concentration on the alkali side is ≥6.3%. The bipolar membrane electrodialysis system operates in constant pressure mode, maintaining a stable acid-base generation rate and high conversion efficiency, without exhibiting a significant decrease in current efficiency due to concentration polarization.

[0073] As can be seen, this invention achieves automatic feeding through the aforementioned conductivity feedback, avoiding concentration polarization; in constant voltage mode, the current is positively correlated with the salt conductivity, resulting in a sensitive system response. Furthermore, the acid and alkali conductivity increase approximately linearly, leading to stable yield; the system control strategy effectively supports high salt conversion efficiency. In addition, no external reagents are required, making it environmentally friendly.

[0074] The technical solution and effects of the present invention will be described below with reference to specific embodiments: Example 1 Influent water quality: High-concentration brine from a steel plant, with a TDS of 42000 mg·L⁻¹. -1 Calcium ions 0.5 mg / L, magnesium ions 0.3 mg / L, turbidity 2.5 NTU.

[0075] System Configuration: The effective membrane area of ​​the bipolar membrane electrodialysis device is 0.5 m². 2 The membrane stack voltage is 60 V. Raw water tank: 10 L; Acid circulation tank: pre-charged with 5 L of 2% HCl solution; Alkali circulation tank: pre-charged with 5 L of 2% NaOH solution; Extreme water tank: 5 L of 2% NaOH solution.

[0076] Operation process: The system is started, raw water enters the brine chamber, and the conductivity rises to 69 ms, at which point feeding is stopped; it operates at a constant pressure of 60 V, and the salt is converted into acid and alkali, causing the conductivity of the brine chamber to decrease; when the conductivity drops to 30 ms, feeding is automatically started, and the conductivity of the brine chamber rises again; the above cycle is repeated, with a total operating time of 105 min.

[0077] Execution result: Salt conductivity fluctuation range: 30.7–69 ms; Current fluctuation range: 23.5~63.4 A; Acid conductivity: increased from 144 ms to 480.8 ms, with an average growth rate of 4.21 ms·min. -1 (60–105 min); Alkali conductivity: increased from 80 ms to 252.7 ms, with an average increase of 1.69 ms·min. -1 ; Final product concentrations: HCl 6.2%, NaOH 6.5%; The system did not exhibit significant concentration polarization and operated stably.

[0078] Figure 1 and Figure 2The trend graphs of salt cycle conductance and current, acid cycle conductance and alkali cycle conductance during the operation of this embodiment are shown respectively.

[0079] like Figure 1 As shown, during operation, the salt circulation conductivity fluctuates within a specific range, and the current fluctuates synchronously within a specific range. The current is positively correlated with the salt conductivity, and the system response is sensitive.

[0080] like Figure 2 As shown, with the increase of reaction time, the acid cycle conductivity and the alkali cycle conductivity increase steadily, and the acid and alkali conductivity increase approximately linearly with small fluctuations, indicating that the acid and alkali yields of this invention are stable.

[0081] In summary, the present invention employs a control strategy based on constant pressure and dynamic feedback control of salt chamber conductivity for intermittent feeding, which effectively suppresses concentration polarization and provides stable and high acid-base yield and operational stability for high-salt feed.

[0082] The foregoing description is provided for illustrative purposes only and is not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and other embodiments will be apparent to those skilled in the art. The embodiments were chosen and described to better illustrate the principles and practical application of the invention and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for particular purposes, and are not intended for limiting purposes.

Claims

1. A method for producing acid and alkali from high-salinity wastewater using bipolar membrane electrodialysis, characterized in that, include: Under constant pressure, based on the intermittent feeding operation mode, high-salt wastewater generates acid and alkali in the bipolar membrane electrodialysis system; The intermittent feeding is controlled based on dynamic feedback of the salt chamber conductivity, and the dynamic feedback range of the salt chamber conductivity is 30 to 69 mS / cm.

2. The method for producing acid and alkali from high-salinity wastewater based on bipolar membrane electrodialysis according to claim 1, characterized in that, The constant pressure range is 55-65V; And / or, the entire operating cycle is in a continuous cyclic operation state, and intermittent feeding is performed by monitoring the conductivity of the salt chamber in real time; wherein, the step of intermittent feeding by monitoring the conductivity of the salt chamber in real time includes: automatically stopping feeding when the conductivity of the salt chamber reaches the upper limit of the dynamic feedback range; and automatically resuming feeding when the conductivity of the salt chamber drops to the lower limit of the dynamic feedback range, so that the conductivity of the salt chamber recovers.

3. The method for producing acid and alkali from high-salinity wastewater based on bipolar membrane electrodialysis according to claim 2, characterized in that, The continuous cycle operation time is 65-120 minutes.

4. The method for producing acid and alkali from high-salinity wastewater based on bipolar membrane electrodialysis according to claim 1, characterized in that, The high-salinity wastewater has a TDS ≥ 40000 mg·L⁻¹ -1 .

5. The method for producing acid and alkali from high-salinity wastewater based on bipolar membrane electrodialysis according to claim 3, characterized in that, It also includes controlling the calcium ion concentration, magnesium ion concentration, and turbidity of the high-salt wastewater; The concentrations of calcium ions and magnesium ions are both less than 1 mg / L, and the turbidity is less than 3 NTU.

6. The method for producing acid and alkali from high-salinity wastewater based on bipolar membrane electrodialysis according to claim 1, characterized in that, During operation, the conductivity of the membrane stack salt chamber remained in the range of 30.7 to 69 mS / cm, and the current fluctuated in the range of 23.5 to 63.4 A.

7. The method for producing acid and alkali from high-salinity wastewater based on bipolar membrane electrodialysis according to claim 1, characterized in that, After reaching a stable state, the HCl concentration on the acid side of the membrane stack is ≥6%, and the NaOH concentration on the alkaline side is ≥6.3%.

8. The method for producing acid and alkali from high-salinity wastewater based on bipolar membrane electrodialysis according to claim 1, characterized in that, After reaching a stable state, the average increase in conductivity on the acid side of the membrane stack was 4.21–4.55 mS·min. -1 The average increase in conductivity on the alkaline side was 1.62–1.69 mS·min. -1 .

9. The method for producing acid and alkali from high-salinity wastewater based on bipolar membrane electrodialysis according to claim 2, characterized in that, The bipolar membrane electrodialysis system includes: A bipolar membrane electrodialysis device has a membrane stack, which includes a salt chamber, an acid chamber, an alkali chamber, and a bipolar chamber; The raw water tank is used to store high-salinity wastewater, and its outlet is connected to the inlet of the salt chamber through an inlet pipe. The salt circulation tank has its inlet connected to the salt chamber outlet via an output pipeline, and its outlet connected to the salt chamber inlet via a salt circulation pipeline. The acid circulation tank has its inlet connected to the acid chamber outlet via an acid output pipeline, and its outlet connected to the acid chamber inlet via an acid circulation pipeline. The alkali circulation tank has its inlet connected to the alkali chamber outlet via an alkali output pipeline, and its outlet connected to the alkali chamber inlet via an alkali circulation pipeline. The polar water tank is connected to the two polar chambers via circulation pipes. The salt chamber is equipped with a dynamic feedback control system for salt conductivity. The dynamic feedback control system for salt conductivity includes an online conductivity sensor, an automatic feed valve, and a controller. The online conductivity sensor is located at the outlet of the salt chamber and is used to monitor the conductivity inside the salt chamber in real time. The controller is used to receive the signal emitted by the online conductivity sensor and issue instructions to the automatic feed valve according to preset logic. The automatic feed valve is located at the inlet of the salt chamber and is used to receive the control signal from the controller and perform opening / closing actions.

10. The method for producing acid and alkali from high-salinity wastewater based on bipolar membrane electrodialysis according to claim 9, characterized in that, The acid circulation tank is pre-filled with an acid solution, the mass fraction of which is 1.5% to 3%. The alkali circulation tank is pre-filled with an alkali solution, the mass fraction of which is 1.5% to 3%. The electrode tank contains a sodium hydroxide solution, and the mass fraction of the sodium hydroxide solution is 1% to 3%. The salt conductivity dynamic feedback control system further includes: a current monitoring device, installed at the salt chamber outlet, for monitoring the salt chamber current; The acid chamber is equipped with an acid conductivity dynamic feedback control system and an acid concentration detector; wherein, the acid conductivity dynamic feedback control system includes at least an online conductivity sensor installed at the outlet of the acid chamber for real-time monitoring of the conductivity inside the acid chamber; the acid concentration detector is installed at the outlet of the acid chamber. The alkali chamber is equipped with an alkali conductivity dynamic feedback control system and an alkali concentration detector; wherein, the alkali conductivity dynamic feedback control system includes at least an online conductivity sensor installed at the outlet of the alkali chamber for real-time monitoring of the conductivity inside the alkali chamber; the alkali concentration detector is installed at the outlet of the alkali chamber.

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