A closed-loop electrochemical alkaline production method and system based on seawater decalcification and dechlorination pretreatment and sulfate radical migration regeneration

Abstract

The application discloses a closed-loop electrochemical alkali production method and system based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration, and comprises the following steps: S1, making seawater pass through a cation exchange resin unit and an anion exchange resin unit in sequence to remove Ca 2+ and Cl ‑ in the seawater, and obtaining sulfate-containing seawater; S2, introducing the sulfate-containing seawater into a middle cabin of a three-tank electrochemical device, applying an electric field, and forming an acid solution containing sulfuric acid in an anode cabin; and S3, taking the acid sulfate-containing solution as a regeneration liquid, and recycling the regeneration liquid to regeneration of the cation exchange resin and the anion exchange resin in the step S1, and making the regenerated cation exchange resin and the anion exchange resin perform the step S1 again. The application removes Ca 2+ in seawater in advance before electrochemical alkali production, avoids the Ca ‑ from forming deposition in a high OH ‑ environment, reduces membrane pollution and electrode scaling problems, and improves the continuous operation stability of the system.

Description

Technical Field

[0001] This invention belongs to the field of seawater resource utilization and electrochemical technology, and in particular relates to a closed-loop electrochemical alkali production method and system based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration. Background Technology

[0002] Electrochemical alkali production using seawater has broad application prospects in seawater resource utilization, green chemical engineering, and carbon capture. However, existing direct electrochemical alkali production technologies using seawater mainly suffer from the following problems: First, the Ca in seawater 2+ Ions of equal hardness can easily induce scaling on the film or electrode surface during electrochemical alkali production.

[0003] Due to the OH in the alkali production chamber - As the concentration gradually increases, Ca 2+ Easily reacts with OH - CO3 2- These substances combine to form insoluble deposits, causing membrane fouling, increased mass transfer resistance, increased voltage, and decreased operating efficiency. In severe cases, this can lead to system blockage or failure.

[0004] Second, Cl in seawater - There are safety risks involved in electrochemical processes.

[0005] Under anodic conditions, Cl - It may undergo oxidation reactions to generate Cl2 or other chlorine-containing reactive species, which not only bring toxicity and corrosion risks, but also affect the safety of system operation, product purity and equipment life. Therefore, it is not suitable to be directly introduced into the alkali electrochemical system.

[0006] Third, existing pretreatment processes typically rely on the addition of external acids and alkalis to regenerate the resin, resulting in high operating costs and low system closed-loop characteristics.

[0007] If ion exchange resin is used to remove Ca from seawater 2+ and Cl - Conventional methods require additional acid or alkali solutions to regenerate the resin, which not only increases reagent consumption and operational complexity but also leads to the problem of treating by-product salt waste liquid.

[0008] Fourth, existing technologies do not adequately utilize the anion migration behavior in electrochemical systems and fail to achieve coupling between pretreatment and electrolysis processes.

[0009] In a three-cell electrochemical system containing sulfate, SO4 2- It can migrate towards the anode side and interact with H + Together they form an acidic medium, but existing technologies typically do not use this acid-generating process for upstream resin regeneration, resulting in the underutilization of material circulation within the system.

[0010] Therefore, there is an urgent need to develop a method to remove Ca before seawater enters the electrochemical alkali production unit. 2+ and Cl - Furthermore, a closed-loop process is used to regenerate the pretreated resin by utilizing the acid solution generated inside the electrochemical process, so as to balance the alkali production efficiency, operational safety, resin regeneration cost and overall system stability. Summary of the Invention

[0011] In view of this, the present invention aims to propose a closed-loop electrochemical alkali production method and system based on seawater decalcification and dechlorination pretreatment and sulfate migration and regeneration, so as to solve at least one technical problem in the background art.

[0012] To achieve the above objectives, the technical solution of the present invention is implemented as follows: A closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration includes the following steps: S1: Seawater is passed sequentially through a cation exchange resin unit and an anion exchange resin unit to remove Ca from the seawater. 2+ and Cl - Seawater containing sulfate was obtained; S2: The sulfate-containing seawater obtained in step S1 is introduced into the intermediate chamber of a three-cell electrochemical device, which includes an anode chamber, an intermediate chamber, and a cathode chamber. An anion exchange membrane is installed between the anode chamber and the intermediate chamber, and a bipolar membrane is installed between the intermediate chamber and the cathode chamber. An electric field is applied to cause the OH- ions generated by the hydrolysis of the bipolar membrane. - Entering the intermediate compartment and Na + Combined to form NaOH, while simultaneously causing SO4 2- Driven by an electric field, it migrates through the anion exchange membrane to the anode chamber, where an acidic solution containing sulfuric acid is formed. S3: Using the acidic sulfate-containing solution generated in step S2 as the regenerator, and following the reverse order of step S1, first pass it through the anion exchange resin unit for regeneration, then through the cation exchange resin unit for regeneration; the two regenerated resins are then subjected to step S1 again; simultaneously, SO42- is released during the regeneration process. 2- It returns to the resin unit with the regenerated liquid and re-enters the intermediate chamber after resin regeneration, forming SO4. 2- The system operates in a completely closed loop, requiring no external addition of sulfate.

[0013] Furthermore, in step S1, the cation exchange resin is a weak acid type, and the weak acid cation exchange resin is used to preferentially adsorb and remove Ca from seawater. 2+ ; The anion exchange resin is a sulfate-type strong-base anion exchange resin, used for adsorbing and removing Cl.- At the same time, it exchanges the anions in the solution for SO4. 2- .

[0014] Furthermore, in step S2, by controlling the running time and / or current, the acidic sulfate-containing solution formed in the anode chamber is made to reach an acidity condition suitable for regenerating the cation exchange resin. Furthermore, the concentration of sodium sulfate formed in the anode chamber is made to a level suitable for regenerating the anion exchange resin and restoring it to a sulfate-type working state. Furthermore, during step S2, within 2 to 3 hours of operation, the pH value of the acidic sulfate-containing solution formed in the anode chamber drops below 3, which serves as the regeneration solution for the weak acid cation exchange resin in step S3. In step S2, the electrochemical device continues to operate, so that the concentration of sodium sulfate formed in the anode chamber reaches 0.45~0.55 mol / L, which is directly used as the regeneration liquid of the strong base anion exchange resin in step S3 to restore the saturated resin to the sulfate-type working state.

[0015] Furthermore, in step S2, the applied electric field is in constant current mode or constant voltage mode.

[0016] Preferably, in step S2, the constant current applied during electrochemical operation is 2-3A, the system voltage is 4-6V, and the solution circulation rate is 50-70mL / min.

[0017] Furthermore, the regeneration process of the cation exchange resin and the regeneration process of the anion exchange resin are carried out in any one of the following methods: series regeneration, parallel regeneration, or stepwise regeneration.

[0018] The system used in the aforementioned closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration includes: Seawater feeding unit; The cation exchange resin unit, whose inlet is connected to the seawater feed unit, is used to remove Ca from seawater. 2+ ; The anion exchange resin unit, with its inlet connected to the outlet of the cation exchange resin unit, is used to remove Cl from seawater. - And the solution is converted into sulfate-containing seawater; The three-cell electrochemical alkali production unit has an intermediate chamber inlet connected to the outlet of an anion exchange resin unit; the three-cell electrochemical alkali production unit includes an anode chamber, an intermediate chamber, and a cathode chamber; an anion exchange membrane is installed between the anode chamber and the intermediate chamber; a bipolar membrane is installed between the intermediate chamber and the cathode chamber; The anode acid-generating liquid return pipeline has its inlet connected to the outlet of the anode chamber of the three-cell electrochemical alkali-generating unit, and its outlet connected to the regenerated liquid inlet of the cation exchange resin unit and the regenerated liquid inlet of the anion exchange resin unit, respectively. The anode acid-generating liquid return pipeline has its inlet connected to the outlet of the anode chamber of the three-cell electrochemical alkali-generating unit, and its outlet connected to the regenerated liquid inlet of the anion exchange resin unit. A regenerated liquid series pipeline has its inlet connected to the regenerated liquid outlet of the anion exchange resin unit and its outlet connected to the regenerated liquid inlet of the cation exchange resin unit. During regeneration, the acidic solution produced at the anode flows sequentially through the anion exchange resin unit and the cation exchange resin unit, and the regeneration sequence is the reverse of the seawater treatment process. The alkali output unit is connected to the outlet of the intermediate chamber of the three-tank electrochemical alkali production unit.

[0019] Furthermore, the cation exchange resin unit is filled with a weak acid type or a strong acid type resin; the anion exchange resin unit is filled with a strong base type or a weak base type anion exchange resin.

[0020] Furthermore, the anode and cathode of the three-cell electrochemical alkali production unit are made of electrode materials resistant to chlorine corrosion and / or with high oxygen evolution overpotential; Preferably, in the three-cell electrochemical alkali production unit, both the anode and cathode are ruthenium-iridium-titanium electrodes.

[0021] The aforementioned closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration, or the system used in the aforementioned closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration, is characterized in that: the seawater is simulated seawater, real seawater, or high-salinity calcium- and chlorine-containing wastewater.

[0022] Compared with existing technologies, the closed-loop electrochemical alkali production method and system based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration described in this invention has the following advantages: 1. This invention can significantly reduce the risk of membrane fouling by pre-removing Ca from seawater before electrochemical alkali production. 2+ To avoid it in high OH - Deposits are formed in the environment, thereby reducing membrane fouling and electrode scaling problems and improving the stability of continuous system operation.

[0023] 2. This invention can reduce the safety risks of chlorine-containing systems by removing Cl before it enters the electrochemical unit. - It can effectively suppress chlorine evolution at the anode and related side reactions, reducing equipment corrosion, toxic gas release, and safety control pressure.

[0024] 3. This invention achieves self-supply of the regeneration medium within the system and a closed-loop circulation of sulfate ions. On one hand, this invention utilizes SO4... 2- The acid-producing solution migrates and accumulates towards the anode side, allowing it to be directly reused for resin regeneration, reducing or even eliminating the need for external acid or alkali reagents. More importantly, this invention utilizes a front-end anion exchange resin to remove Cl- from seawater. - Replace with SO4 2- SO4 2- It becomes the only shuttle anion in the system: it is consumed in the intermediate chamber, migrates to the anode chamber under the drive of the electric field, returns to the front end with the regenerator, regenerates after being regenerated by the anion exchange resin, and re-enters the intermediate chamber to form complete SO4. 2- Internal circulation. This fundamentally avoids the problem of needing to continuously replenish sulfate to the intermediate compartment due to the net migration of sulfate ions in traditional solutions, achieving a true material closed loop and significantly reducing operating costs and complexity.

[0025] 4. This invention enables the coupled closed-loop operation of the pretreatment and electrochemical units. Instead of treating seawater pretreatment, electrolytic alkali production, and resin regeneration as independent units, this invention establishes a material recycling relationship through acid reuse, making the overall system more compact, synergistic, and sustainable.

[0026] 5. This invention is beneficial for seawater resource utilization and green alkali production. This invention enables stable alkali production using seawater as one of the raw material sources, while also considering system safety, ion balance, and resin recycling. It is suitable for application in green chemical engineering, seawater resource utilization, and carbon capture and regeneration alkali production. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This invention presents a closed-loop electrochemical alkali production process based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration (solid lines in the diagram represent the main material flow, and dashed lines represent SO4). 2- (Circulation path and reverse regeneration path of regenerated liquid). Figure 2 The present invention describes the removal of Ca 2+ Solid resin adsorption and regeneration diagram (a is the adsorption and regeneration of Ca in simulated seawater by a weak acid cation exchange resin) 2+ (b) is the breakthrough curve, and b is the elution curve of the weak acid cation exchange resin after adsorption saturation, which is regenerated by using an acid solution with pH < 3 generated in situ on the anode side. Figure 3 The Cl removal method described in this invention -Solid resin adsorption and regeneration diagram (a is the adsorption and regeneration of a strong base anion exchange resin (sulfate type) on Cl in simulated seawater) - The removal and anion conversion curves are shown in Figure b. Figure b shows the regeneration curve of the strong base anion exchange resin after adsorption saturation, which is regenerated by using 0.5 mol / L sodium sulfate solution generated in situ on the anode side to restore it to the sulfate form. Figure 4 The diagrams for the acid-base production of the asymmetric electrochemical device described in this invention are as follows: (a) is the pH change curve of the intermediate chamber (alkali-producing side) over time, and (b) is the pH change curve of the anode chamber (acid-producing side) over time. Figure 5 The graphs show a voltage / power comparison between untreated seawater and seawater pretreated according to the present invention (a is a voltage comparison graph, b is a power comparison graph). Detailed Implementation

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0029] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] Example 1: Closed-loop alkali production based on simulated seawater decalcification and dechlorination pretreatment and three-tank electrochemical coupling This embodiment provides a closed-loop electrochemical alkali production method based on simulated seawater decalcification and dechlorination pretreatment and sulfate migration and regeneration.

[0031] Figure 1 This indicates that the process of the present invention includes simulated seawater pretreatment and ion exchange to remove Ca. 2+ With Cl - The three-cell electrochemical unit produces alkali and forms an acidic medium on the anode side, and the resin is recycled through a regeneration unit. Simulated seawater is used as feed, first entering a decalcification resin column. The decalcification resin is a weak acid cation exchange resin, specifically Zhejiang Zhengguang's D113; this preferentially removes Ca from the system. 2+ The simulated seawater, after being decalcified, then enters a dechlorination resin column. The dechlorination resin is a strong base anion exchange resin, specifically Zhejiang Zhengguang's D201. Used to remove Cl from the system - The treated solution is then converted into sulfate-containing seawater suitable for subsequent electrochemical operation. The feed, after two-stage resin pretreatment, enters the intermediate chamber of the three-tank electrochemical unit, where alkali production and acidic medium formation on the anode side are achieved under the influence of an electric field. The resulting acidic and sulfate media are further used for upstream resin regeneration, thus forming a closed-loop operation process of pretreatment-electrochemistry-resin recycling. This overall process is similar to... Figure 1 Consistent with the above.

[0032] The three-cell electrochemical apparatus used in this embodiment includes an anode chamber, an intermediate chamber, and a cathode chamber. An anion exchange membrane (AEM) is installed between the anode chamber and the intermediate chamber, and a bipolar membrane (BPM) is installed between the intermediate chamber and the cathode chamber. The effective area of ​​the membrane is 6cm × 6cm. The anode is a ruthenium-iridium-titanium electrode (i.e., an electrode with a titanium substrate coated with ruthenium and iridium oxide coatings; this electrode is a commonly used oxygen evolution anode in the art and can be obtained commercially or prepared by conventional methods), with an effective area of ​​6cm × 6cm. Each chamber has a body size of 6cm × 6cm × 1cm and is connected to an external 1L circulating solution to form a circulation loop at a flow rate of 60mL / min.

[0033] A constant current of 2.5A was applied during electrochemical operation, with an operating voltage of approximately 5V, which fluctuated during operation. The total operating time was 6 hours, with acidic conditions suitable for resin regeneration typically achieved within approximately 2–3 hours. During operation, BPM underwent water dissociation, generating H₂. + and OH - , of which OH - It enters the intermediate chamber, gradually alkalizing the solution there; SO4 2- Driven by an electric field, the anode migrates to the anode side via an AEM, forming an acidic sulfate-containing environment there. Figure 4 It can be seen that after the device is put into operation, the pH on the alkali-producing side increases significantly, while the pH on the acid-producing side continues to decrease, indicating that the device can achieve alkali and acid production in the same system respectively.

[0034] In this embodiment, during the operation of the three-cell electrochemical device, an acidic sulfate-containing medium can be formed on the anode side while alkali is produced in the intermediate chamber. Experiments show that under conditions of a constant current of 2.5A, a system voltage of approximately 5V, and a circulation flow rate of 60mL / min, an acidic solution with a pH below 3 can be obtained on the anode side after approximately 2–3 hours of operation; during continued operation, the sodium sulfate concentration in the system can reach 0.5mol / L. Therefore, the electrochemical unit can directly generate the medium required for resin regeneration in situ without the need for additional external regeneration solution. During regeneration, the anode acid-producing solution is passed through the two resin columns sequentially in the reverse order of seawater pretreatment (i.e., first anion exchange resin, then cation exchange resin), without the need for a split pipeline or distribution unit, thus simultaneously completing the SO42-regeneration of the anion exchange resin. 2- Type regeneration and acid elution decalcification regeneration of cation exchange resins. This reverse tandem regeneration method is related to the attached... Figure 1 The process shown is completely consistent, with simple piping, easy control, and high industrial feasibility.

[0035] The generated acidic solution with a pH below 3 can be directly used for the regeneration of weak acid cation exchange resins, allowing the Ca adsorbed on the resins to be released. 2+The resin is displaced and eluted, thus restoring its decalcification ability. The resulting 0.5 mol / L sodium sulfate solution can be directly used to regenerate strong base anion exchange resins or restore them to a sulfate-type operating state, enabling them to regain their ability to react with Cl-. - The removal capacity is improved. The two types of regenerated resins are then reintroduced into the front-end simulated seawater pretreatment process, thus forming a closed-loop operating system of pretreatment—electrochemical alkali production—in-situ generation of regeneration medium—resin reuse.

[0036] This embodiment illustrates that the present invention does not simply separate seawater pretreatment, electrolytic alkali production, and resin regeneration. Instead, it establishes a recyclable and interconnected process relationship between the units through sulfate migration, anodic acidification, and in-situ generation of the regeneration medium.

[0037] Cation exchange resins can be weakly acidic or strongly acidic; anion exchange resins can be strongly basic, weakly basic, or other types capable of achieving Cl- - Removal and SO4 2- Functional materials for replacement.

[0038] The membrane module configuration, chamber arrangement, regenerator reflux path, and resin regeneration sequence in the three-cell electrochemical reactor can all be adjusted according to actual operating conditions. As long as a closed-loop operation can be achieved, integrating seawater pretreatment, electrochemical alkali production, and anode acid production for resin regeneration, it should be considered an equivalent alternative to the present invention. Example 2: The effect of weak acid cation exchange resin on Ca 2+ Removal and Regeneration Examples This embodiment illustrates the effect of a weak acid cation exchange resin on Ca in simulated seawater. 2+ The removal capacity and regeneration feasibility.

[0039] Containing Ca 2+ Simulated seawater is passed into a resin column filled with a weak acid cation exchange resin, causing the Ca in the feed to... 2 + It exchanges with exchangeable ions on the resin, thereby realizing Ca 2+ Remove. According to Figure 2 a, in the feed Ca 2+ The initial concentration was approximately 50 mg / L. -1 Under these conditions, as the treatment bed volume increases, the effluent Ca... 2+ The concentration remained at a low level in the early stage, indicating that the resin column could effectively remove Ca. 2+ When the bed volume is increased, the effluent Ca... 2+ The significant increase in concentration indicates that the resin gradually reached adsorption saturation and breakthrough occurred. This result demonstrates that, before entering the subsequent electrochemical alkali production unit, using a weak acid cation exchange resin to remove Ca from simulated seawater is effective. 2+Pre-removal is feasible.

[0040] When the weak acid cation exchange resin is nearly saturated, it is regenerated using an acidic solution with a pH below 3 generated in situ on the anode side of a three-cell electrochemical device. According to... Figure 2 b, During the regeneration process, the Ca in the regenerated solution 2+ The concentration initially increased rapidly, then gradually decreased, indicating that the Ca loaded on the resin... 2+ The resin is gradually eluted and released, and the exchange sites are restored. This result indicates that weak acid cation exchange resins can effectively remove Ca2+. 2+ Furthermore, it can be directly regenerated through the acid solution generated electrochemically within the system, making it suitable for recycling in the system of this invention. Because Ca... 2+ Is it a subsequent high OH - The environment is a major source of deposits and fouling on the membrane surface, so this decalcification step can significantly reduce the risk of fouling in subsequent electrochemical units.

[0041] Example 3: Strong base anion exchange resin for Cl - Examples of removal and restoration to sulfate form This embodiment illustrates the effect of strong base anion exchange resins on Cl- in simulated seawater. - The feasibility of removing and restoring the product to its sulfate-type working state.

[0042] Simulated seawater, after decalcification treatment, is passed into a resin column packed with strong base anion exchange resin, causing the Cl- in the solution to... - It exchanges with exchangeable anions on the resin, thereby realizing Cl - Removal. Preferably, the strong base anion exchange resin operates in the sulfate form to remove Cl. - At the same time, the treated solution is gradually constructed into a sulfate system suitable for subsequent electrochemical operation.

[0043] according to Figure 3 During the operation of the resin column, Cl in the effluent - Concentration and SO4 2- The concentration showed a corresponding change, indicating that the resin column effectively removed Cl. - Simultaneously, the conversion of the anion system was completed. This result demonstrates that strong-base anion exchange resins can not only achieve dechlorination but also transform the system from a high-chlorine environment to one suitable for SO4. 2- Operating environment for migration and anodic acid production.

[0044] Once the strong base anion exchange resin has adsorbed to a certain extent, it is regenerated using a 0.5 mol / L sodium sulfate solution generated in situ during the operation of the three-tank electrochemical unit. This restores the resin to its sulfate-type working state, allowing it to be reused in the dechlorination process. This demonstrates that the restoration process of the dechlorination resin in this invention can also be accomplished by the sulfate medium generated electrochemically within the system, without the need for additional external regeneration solution.

[0045] This embodiment illustrates that the front-end dechlorination step does not merely remove Cl. - It also plays an important role in providing the sulfate system for the subsequent three-cell electrochemical unit, and is one of the key links in forming a closed-loop coupling relationship in this invention.

[0046] Example 4: Acid and Alkali Production Example of a Three-Tank Electrochemical Unit This embodiment illustrates the ability of the three-cell electrochemical device to simultaneously produce acid and alkali in this invention.

[0047] The sulfate-containing simulated seawater treated in Examples 2 and 3 was introduced into the intermediate chamber of the three-cell electrochemical apparatus. The anode chamber and the intermediate chamber were separated by an anion exchange membrane, and the intermediate chamber and the cathode chamber were separated by a bipolar membrane. A constant current of 2.5A was applied during operation, the system voltage was approximately 5V, the total solution circulation time was 6 hours, and the circulation flow rate was 60 mL / min.

[0048] During operation, OH groups generated by the bipolar membrane dissociation... - Upon entering the intermediate chamber, SO4 rapidly increases the pH of the solution there and forms an alkaline product. 2－ Under the influence of an electric field, they migrate to the anode side, creating an acidic sulfate-containing environment on the anode side. According to... Figure 4 a and Figure 4 b. The pH on the alkali-producing side rises significantly in a short period of time, while the pH on the acid-producing side continues to decrease, indicating that the three-tank device used in this invention can achieve spatial separation of acid and alkali. Typically, after about 2 to 3 hours of operation, an acidic solution with a pH below 3, sufficient for resin regeneration, can be formed on the anode side; during continued operation, the concentration of sodium sulfate formed in the system can reach 0.5 mol / L, which can be further used to restore the strong base anion exchange resin to the sulfate form.

[0049] This embodiment illustrates that the three-cell electrochemical device used in this invention can not only produce alkali in the intermediate chamber and produce acid on the anode side, but also generate the medium required for the regeneration of the front-end resin in situ within a short operating time, thus combining the functions of alkali production and regeneration medium supply, providing direct support for the closed-loop operation of the entire system.

[0050] Example 5: Closed-Loop Operation Example This embodiment is used to illustrate that the overall process of the present invention has the capability of closed-loop operation.

[0051] Following the process described in Example 1, simulated seawater is sequentially treated through a weak acid cation exchange resin column and a strong base anion exchange resin column before entering the intermediate chamber of a three-cell electrochemical device for electrolysis. During electrolysis, an alkaline solution is generated in the intermediate chamber, while an acidic solution with a pH below 3 is formed in situ on the anode side. Simultaneously, a sodium sulfate solution with a concentration of up to 0.5 mol / L is formed in the system. The acidic solution is used to regenerate the weak acid cation exchange resin, and the sodium sulfate solution is used to restore the strong base anion exchange resin to its sulfate form. The regenerated resin is then reused for simulated seawater pretreatment. This cyclical operation constitutes a closed-loop system of pretreatment, electrolysis, in-situ generation of regeneration media, resin regeneration, and resin reuse.

[0052] according to Figure 1 The overall process shown in this invention does not involve a traditional linear flow; instead, a circular connection is formed between the front-end resin unit and the back-end electrochemical unit via the reflux of acid and sulfate media. Figure 2 , Figure 3 and Figure 4 The results show that the resin removal of target ions, resin regeneration, and electrochemical acid and alkali production processes can all be established. Therefore, the present invention has the technical basis and direct experimental support for constructing a closed-loop operating system.

[0053] like Figure 5 As shown, Ca in untreated seawater 2+ and Cl - This can lead to membrane fouling and electrode scaling, causing a continuous increase in voltage and power. However, after the decalcification and dechlorination pretreatment of this invention, the system operates more stably, and the increase in voltage and power is significantly reduced.

[0054] Comparative Example 1: Direct Electrolysis of Untreated Simulated Seawater This comparative example illustrates the impact of simulated seawater without decalcification and dechlorination pretreatment on membrane fouling, voltage variation, and system stability when it enters a three-cell electrochemical device directly, and compares it with the pretreated electrochemical alkali production system described in this invention.

[0055] In this comparative example, simulated seawater that had not undergone decalcification with cation exchange resin and dechlorination with anion exchange resin was directly introduced into the intermediate chamber of a three-cell electrochemical device. The structure, membrane area, electrode material, circulation flow rate, and current conditions of the three-cell electrochemical device were consistent with those in Example 4, namely, an anion exchange membrane was installed between the anode chamber and the intermediate chamber, and a bipolar membrane was installed between the intermediate chamber and the cathode chamber. The effective membrane area was 6cm × 6cm, the effective electrode area was 6cm × 6cm, the circulation flow rate was 60mL / min, and a constant current of 2.5A was applied during operation.

[0056] During operation, it was found that untreated Ca in simulated seawater... 2+ The OH level gradually rises in the intermediate compartment - Easily reacts with OH in the environment - The carbonate components in the system form insoluble deposits, which gradually accumulate on the membrane surface, near the electrodes, and in the flow channel region. With prolonged operation, the mass transfer resistance of the system increases, manifested as a gradual increase in operating voltage, and the rate of voltage increase is significantly higher than that of the sulfate-containing feed system pretreated according to this invention. This phenomenon indicates that during direct electrolysis of simulated seawater without decalcification treatment, Ca... 2+ Inorganic fouling caused by this process can exacerbate membrane fouling and electrode surface deposition, thereby reducing the long-term operational stability of the electrochemical device.

[0057] Meanwhile, due to the high concentration of Cl in the untreated simulated seawater... - Under the influence of an electric field, it may migrate to the anode side and participate in chlorine evolution or other chlorine-containing side reactions in the anode environment. This process may not only cause equipment corrosion and safety risks, but also interfere with the anode side's reaction to produce SO4. 2- The migration-based acid production process makes the composition of the acid solution on the anode side more complex, which is not conducive to its direct reuse in resin regeneration.

[0058] In contrast, in Examples 1 to 5 of this invention, simulated seawater is first passed through a weak acid cation exchange resin to remove Ca. 2+ Then, Cl is removed by a sulfate-type strong base anion exchange resin. - It is then converted into a sulfate-containing system. After pretreatment, the feed enters the three-cell electrochemical unit, where Ca can be induced to precipitate. 2+ The content is significantly reduced, the risk of chlorine-containing side reactions is reduced simultaneously, the tendency of membrane fouling and electrode scaling during operation is alleviated, the rate of increase in system voltage is reduced, and the alkali-producing and acid-producing sides can maintain a more stable operating state.

[0059] This comparative example shows that if untreated simulated seawater is directly used for electrochemical alkali production, it is easy to cause problems due to Ca. 2+ Deposition and Cl - Side reactions lead to increased membrane fouling, faster voltage rise, and decreased operational safety. However, this invention, through the front-end decalcification, dechlorination, and sulfate system, can mitigate membrane fouling and electrode scaling at the source, reduce the voltage rise rate under constant current operation, and improve electrochemical efficiency.

[0060] This embodiment illustrates that the present invention can not only solve the problem of Ca that may be generated when simulated seawater is directly introduced into an electrochemical device. 2+ Scale and Cl - It eliminates the chlorine precipitation problem and enables resin regeneration through in-situ generated regeneration media within the system, reducing the consumption of external acid and alkali reagents and improving the overall synergy and sustainable operation of the system.

[0061] This invention can significantly reduce Ca 2+ The risk of scaling caused by calcium in seawater 2+ In high OH - In the presence of precipitates, insoluble deposits easily form, which is a significant cause of membrane fouling, electrode scaling, and increased system voltage drop. This invention addresses this by incorporating a weak acid cation exchange resin unit before the electrochemical unit to remove Ca from the feed. 2+ .from Figure 2 It can be seen that the resin column can dissolve Ca during its effective working phase. 2+ Maintaining a low water output level, while Figure 2 b further indicates that the resin can be eluted by acid generated electrochemically within the system to remove Ca. 2+ And it restores the exchange capacity. Therefore, this invention, through a front-end decalcification step, can reduce the risk of inorganic scaling during subsequent alkali production from the source.

[0062] This invention can reduce Cl - The resulting chlorine precipitation and safety risks, Cl in seawater - High chloride content, if directly introduced to the anode side or involved in improper electrochemical processes, may induce chlorine evolution and related chlorine-containing side reactions, leading to safety, corrosion, and product purity issues. This invention addresses this by pre-removing chloride using a strong-base anion exchange resin. - At the same time, SO4 was introduced 2- Construct a suitable subsequent electrochemical system. Figure 3 This indicates that the resin column can achieve Cl - Removal, accompanied by SO4 2－ The concentration change completes the conversion of the anion system. This step helps reduce the probability of chlorine-containing side reactions, thereby improving the overall safety of the process.

[0063] This invention enables the simultaneous coupling of alkali production in the intermediate chamber and acid production on the anode side. This invention utilizes AEM and BPM to construct a three-cell asymmetric electrochemical device, which simultaneously realizes the generation of alkali solution and the formation of acidic medium in one device. Figure 4 The results show that the pH on the alkali-producing side rises rapidly after operation, while the pH on the acid-producing side continues to decrease, indicating that the acid and alkali products can be spatially separated and output separately. This means that the present invention is not just a seawater pretreatment method, nor just an electrolytic alkali production method, but a comprehensive system that couples pretreatment with subsequent acid and alkali generation.

[0064] This invention enables in-situ generation of the resin regeneration medium within the system. Traditional ion exchange pretreatment processes typically require the preparation of additional acid or salt solutions for resin regeneration, resulting in high reagent consumption, complex operation, and a heavy burden of wastewater treatment. This invention utilizes a three-tank electrochemical device to generate the resin regeneration medium in situ simultaneously with alkali production. Experiments show that under the operating conditions described in this invention, the device can generate an acid solution with a pH below 3 within approximately 2-3 hours, which can be directly used for the regeneration of weak acid cation exchange resins; simultaneously, the sodium sulfate concentration formed in the system can reach 0.5 mol / L, which can be used to restore strong base anion exchange resins to the sulfate form. Thus, this invention truly achieves self-sufficiency of the regeneration medium within the system, rather than relying on external chemicals. Figure 2 , Figure 3 and Figure 4 The results show that there is a clear coupling relationship between the resin adsorption / regeneration process and the electrochemical acid generation process.

[0065] After each cycle, the exchange capacity of the cation exchange resin (decalcification) and the anion exchange resin (dechlorination) almost completely recovered, with no cumulative adsorption residue. Three repeated runs showed that key parameters such as pH on the alkali-producing side, pH of the acid solution on the anode side, and sodium sulfate concentration remained essentially consistent, indicating that irreversible fouling or scaling did not occur in the membrane (AEM / BPM) or electrodes. SO4 2- The system operates in a completely closed loop, and its concentration did not decrease during the three runs.

[0066] This invention can construct a truly closed-loop operating system, connecting simulated seawater decalcification and dechlorination, three-tank electrochemical alkali production, in-situ generation of acid and sulfate regeneration medium on the anode side, resin regeneration and resin reuse into an internal circulation system. Figure 1 This closed-loop process has been visually demonstrated, and Figures 2 to 4 The feasibility of decalcification, dechlorination, and acid and alkali production processes was further verified.

[0067] Therefore, this invention not only has the potential for closed-loop operation, but has also demonstrated that the electrochemical unit can directly supply the medium required for the regeneration of pretreatment resin, thereby significantly reducing the consumption of external chemicals and improving the system integration and greenness.

[0068] This invention is beneficial for simulating seawater resource utilization and green alkali production applications. Using simulated seawater as the research object, it reduces the adverse effects of high hardness and high chlorine systems through pretreatment, and then outputs alkali solution through an electrochemical unit. Simultaneously, a regeneration medium is generated in situ internally, completing resin recycling. This system balances safety, membrane stability, regeneration cost, and process closed-loop characteristics, making it suitable for promotion in seawater resource utilization, green chemical process alkali preparation, and coupled scenarios related to carbon capture and regeneration.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration, characterized in that: Includes the following steps: S1: Seawater is passed sequentially through a cation exchange resin unit and an anion exchange resin unit to remove Ca from the seawater. 2+ and Cl - Seawater containing sulfate was obtained; S2: The sulfate-containing seawater obtained in step S1 is introduced into the intermediate chamber of a three-cell electrochemical device, which includes an anode chamber, an intermediate chamber, and a cathode chamber. An anion exchange membrane is installed between the anode chamber and the intermediate chamber, and a bipolar membrane is installed between the intermediate chamber and the cathode chamber. An electric field is applied to cause the OH- ions generated by the hydrolysis of the bipolar membrane. - Entering the intermediate compartment and Na + Combined to form NaOH, while simultaneously causing SO4 2- Driven by an electric field, it migrates through the anion exchange membrane to the anode chamber, where an acidic solution containing sulfuric acid is formed. S3: Using the acidic sulfate-containing solution generated in step S2 as the regenerator, and following the reverse order of step S1, first pass it through the anion exchange resin unit for regeneration, then through the cation exchange resin unit for regeneration; the two regenerated resins are then subjected to step S1 again; simultaneously, SO42- is released during the regeneration process. 2- It returns to the resin unit with the regenerated liquid and re-enters the intermediate chamber after resin regeneration, forming SO4. 2- The system operates in a completely closed loop, requiring no external addition of sulfate.

2. The closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration according to claim 1, characterized in that: In step S1, the cation exchange resin is a weak acid type. The weak acid cation exchange resin is used to preferentially adsorb and remove Ca from seawater. 2+ ; The anion exchange resin is a sulfate-type strong-base anion exchange resin, used for adsorbing and removing Cl. - At the same time, it exchanges anions in the solution for SO4. 2- .

3. The closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration according to claim 1, characterized in that: In step S2, by controlling the running time and / or current, the acidic sulfate-containing solution formed in the anode chamber is made to reach an acidity condition suitable for regenerating the cation exchange resin. Furthermore, the concentration of sodium sulfate formed in the anode chamber is made to a level suitable for regenerating the anion exchange resin and restoring it to a sulfate-type working state.

4. The closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration according to claim 1, characterized in that: During step S2, within 2 to 3 hours of operation, the pH value of the acidic sulfate-containing solution formed in the anode chamber drops below 3, which serves as the regeneration solution for the weak acid cation exchange resin in step S3. In step S2, the electrochemical device continues to operate, so that the concentration of sodium sulfate formed in the anode chamber reaches 0.45~0.55 mol / L, which is directly used as the regeneration liquid of the strong base anion exchange resin in step S3 to restore the saturated resin to the sulfate-type working state.

5. The closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration according to claim 1, characterized in that: In step S2, the applied electric field is in constant current mode or constant voltage mode. Preferably, in step S2, the constant current applied during electrochemical operation is 2-3A, the system voltage is 4-6V, and the solution circulation rate is 50-70mL / min.

6. The closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration according to claim 1, characterized in that: The regeneration process of the cation exchange resin and the regeneration process of the anion exchange resin are carried out in any one of the following methods: series regeneration, parallel regeneration, or step regeneration.

7. The system used in the closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration as described in any one of claims 1 to 6, characterized in that: include: Seawater feeding unit; The cation exchange resin unit, whose inlet is connected to the seawater feed unit, is used to remove Ca from seawater. 2+ ; The anion exchange resin unit, with its inlet connected to the outlet of the cation exchange resin unit, is used to remove Cl from seawater. - And the solution is converted into sulfate-containing seawater; The three-cell electrochemical alkali production unit has an intermediate chamber inlet connected to the outlet of an anion exchange resin unit; the three-cell electrochemical alkali production unit includes an anode chamber, an intermediate chamber, and a cathode chamber; an anion exchange membrane is installed between the anode chamber and the intermediate chamber; a bipolar membrane is installed between the intermediate chamber and the cathode chamber; The anode acid-generating liquid return pipeline has its inlet connected to the outlet of the anode chamber of the three-cell electrochemical alkali-generating unit, and its outlet connected to the regenerated liquid inlet of the anion exchange resin unit. A regenerated liquid series pipeline has its inlet connected to the regenerated liquid outlet of the anion exchange resin unit and its outlet connected to the regenerated liquid inlet of the cation exchange resin unit. During regeneration, the acidic solution produced at the anode flows sequentially through the anion exchange resin unit and the cation exchange resin unit, and the regeneration sequence is the reverse of the seawater treatment process. The alkali output unit is connected to the outlet of the intermediate chamber of the three-tank electrochemical alkali production unit.

8. The system used in the closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration according to claim 7, characterized in that: The cation exchange resin unit is filled with a weak acid or strong acid resin; the anion exchange resin unit is filled with a strong base or weak base anion exchange resin.

9. The system used in the closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration according to claim 7, characterized in that: The anode and cathode of the three-cell electrochemical alkali production unit are made of electrode materials that are resistant to chlorine corrosion and / or have a high oxygen evolution overpotential. Preferably, in the three-cell electrochemical alkali production unit, both the anode and cathode are ruthenium-iridium-titanium electrodes.

10. The system used in the closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration according to any one of claims 1 to 6, or the closed-loop electrochemical alkali production method based on seawater decalcification and dechlorination pretreatment and sulfate migration regeneration according to claims 8 to 9, characterized in that: The seawater in question is simulated seawater, real seawater, or high-salinity wastewater containing calcium and chlorine.

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