Method for removing chlorate produced in the preparation of potassium hydroxide by ion-exchange membrane electrolysis and operation system thereof

Abstract

The present application relates to the technical field of deep treatment of brine for preparation of potassium hydroxide by electrolysis, and discloses a method and operation system for removing chlorate produced in preparation of potassium hydroxide by ion-exchange membrane electrolysis, step one: introducing the brine discharged from the electrolysis procedure into a buffer homogenizing tank, mixing after stirring, proportionally shunting through a double-path variable frequency pump, and respectively conveying to a titanium-based electrolytic cell and a dechlorination raw material buffer tank, the titanium-based electrolytic cell being supplied with nitrogen until the oxygen content in the cell is ≤0.5%; step two: starting the power supply of the titanium-based electrolytic cell, setting the initial cell voltage, adjusting the current density through a rectifier, and simultaneously dynamically adjusting the electrolysis parameters based on the free chlorine concentration in the brine to control the hydrogen production. The method and operation system for removing chlorate produced in preparation of potassium hydroxide by ion-exchange membrane electrolysis can accurately control the generation and residual amount of chlorate in the electrolysis system, avoid the chlorate from passing through the ion-exchange membrane into the cathode to cause the chlorate in the finished product to exceed the standard, and significantly improve the purity and quality grade of the potassium hydroxide product.

Description

A method and operating system for removing chlorate produced during the preparation of potassium hydroxide by ion-exchange membrane electrolysis. Technical Field

[0001] This invention relates to the field of deep treatment technology for dilute brine in the preparation of potassium hydroxide by electrolysis, and particularly to a method and operating system for removing chlorate generated in the preparation of potassium hydroxide by ion-exchange membrane electrolysis. Background Technology

[0002] In the industrial production of potassium hydroxide using ion-exchange membrane electrolysis, chlorine gas generated in the anode zone of the electrolytic cell easily reacts with hydroxide ions from the cathode zone to form chlorate, while free chlorine remains in the brine. If the brine containing chlorate and free chlorine is directly reused in the salt treatment section, it will not only reduce the purity of the incoming refined brine and cause the ion-exchange membrane to foam and age, but also cause the chlorate content in the finished potassium hydroxide to exceed the standard, affecting product quality.

[0003] In the potassium hydroxide production process, Cl2 from the brine on the anode side of the electrolysis reacts with OH- from the reverse osmosis on the cathode side. - A reaction occurs, continuously producing chlorate. While chlorate itself has no direct impact on the ion-exchange membrane, it can pass through the membrane and enter the cathode, causing excessive chlorate levels in the finished alkali product and severely lowering product quality. Simultaneously, it reduces the concentration of the incoming brine, causing foaming of the ion-exchange membrane and affecting electrolysis efficiency. Traditional chlorate removal processes have significant shortcomings, exhibiting low removal efficiency and difficulty in effectively controlling the chlorate content in the brine. During brine circulation, chlorate continuously accumulates, not only reducing brine purity but also negatively impacting subsequent electrolysis processes, increasing the probability of side reactions, and leading to increased impurities in the potassium hydroxide product. Furthermore, accumulated chlorate corrodes production equipment such as evaporation devices, shortening equipment lifespan and increasing maintenance costs and replacement frequency. Summary of the Invention

[0004] The technical problem to be solved by this invention is that existing technologies have the disadvantage of being unable to achieve deep removal of both free chlorine and chlorate as single pollutants at the same time. To address this, we propose a method and operating system for removing chlorate generated during the preparation of potassium hydroxide by ion-exchange membrane electrolysis.

[0005] To achieve the above objectives, this application adopts the following technical solution: a method for removing chlorate produced during the preparation of potassium hydroxide by ion-exchange membrane electrolysis, comprising the following steps:

[0006] Step 1: The brine discharged from the electrolysis process is introduced into a buffer homogenizing tank. After stirring and mixing, it is proportionally divided by a dual-path variable frequency pump and delivered to the titanium-based electrolytic cell and the dechlorination raw material buffer tank respectively. Nitrogen gas is introduced into the titanium-based electrolytic cell until the oxygen content in the cell is ≤0.5%.

[0007] Step 2: Start the power supply of the titanium-based electrolyzer, set the initial cell voltage, adjust the current density through the rectifier, and dynamically adjust the electrolysis parameters based on the free chlorine concentration in the brine to control the hydrogen production. The generated hydrogen is then transported to the dechlorination reactor through a buffer tank for pressure stabilization.

[0008] Step 3: Fill the dechlorination reactor with Pd-Ru / CNTs-UiO-66 catalyst, purge with nitrogen, turn on the ultraviolet lamp to preheat to the set light intensity, and at the same time introduce the hydrogen generated in step 2 to form a gas-liquid-solid three-phase reaction system. During the process, the temperature of the reaction system in the dechlorination reactor is controlled to adapt to the reaction requirements of catalytic hydrodechlorination and preliminary decomposition of chlorate.

[0009] Step 4: Introduce the dechlorinated brine containing the catalyst into the ceramic ultrafiltration membrane system to retain the catalyst and return it to the dechlorination reactor; the brine that permeates through the membrane enters the pH adjustment tank, and NaOH is added to adjust the pH;

[0010] Step 5: Introduce the pH-adjusted brine into the decomposition tank;

[0011] Step 6: Before feeding into the decomposition tank, the brine first exchanges heat with the high-temperature brine at the outlet of the decomposition tank through a plate heat exchanger. After feeding, the temperature of the brine system in the decomposition tank is controlled. By adjusting the temperature, the deep decomposition efficiency of chlorate is enhanced, ensuring that chlorate removal meets the standards.

[0012] Step 7: Introduce the treated brine into the reuse buffer tank and test for SO4. 2- After being treated with chlorate and free chlorine, the solution is transported to the salt processing section and mixed with solid NaCl to prepare refined brine. After filtration, the brine is returned to the electrolytic cell for recycling, while SO4 levels are monitored. 2- Cumulative rate and electrolytic cell current efficiency.

[0013] Preferably, the ratio of the proportional diversion is 10%:90%, wherein 10% of the brine is pumped to the titanium-based electrolyzer via a flow branch pump, and 90% of the brine is pumped to the dechlorination raw material buffer tank via a flow branch pump.

[0014] Preferably, the dynamic adjustment of electrolysis parameters is based on a Cl2:H2 molar ratio of 1:1. The theoretical hydrogen production of H2 is calculated according to the free chlorine concentration and the target processing capacity, based on the required dechlorination reaction molar ratio, and the electrolysis current is dynamically adjusted.

[0015] Preferably, the current density adjustment adopts a stepped increase, starting from 300 A / m in the first 30 minutes. 2 Gradually increase to 500A / m 2 Then increase by 50 A / m every 10 minutes. 2 Until the target value is reached.

[0016] Preferably, the Pd-Ru / CNTs-UiO-66 catalyst has a particle size of 2-3 mm and a bed height of 1.5 m.

[0017] Preferably, the ultraviolet lamp has a wavelength of 254nm, a power of 500W, and a light intensity of 10MW / cm² after preheating for 10 minutes. 2 .

[0018] Preferably, the UV lamp preheating adopts a gradient power increase method, first running at 50% power for 5 minutes, and then increasing to 100% power for 5 minutes.

[0019] Preferably, the Pd-Ru / CNTs-UiO-66 catalyst is added in batches: 60% of the total amount is added initially, the chlorate concentration is checked after 10 minutes of reaction, and then the remaining 40% is added; the temperature is controlled by a step-by-step heating operation: from room temperature to 60°C at a rate of 2°C / min, held for 5 minutes, and then increased to 80-85°C at a rate of 1°C / min.

[0020] An operating system for removing chlorate produced by the ion-exchange membrane electrolysis method for preparing potassium hydroxide includes a hydrogen production unit, a catalytic dechlorination reaction unit, a catalyst separation unit, and a pH adjustment device connected in sequence.

[0021] Preferably, the hydrogen production unit includes:

[0022] An electrolytic cell, whose inlet is connected to the main brine delivery pipeline, is used to receive the diverted brine. The electrolytic cell uses titanium-based electrodes and generates hydrogen gas at the cathode through an electrolytic reaction.

[0023] A buffer tank, the inlet of which is connected to the hydrogen outlet of the electrolyzer, is used to stabilize the hydrogen pressure at 0.1-0.12 MPa;

[0024] A hydrogen delivery pipeline is connected at one end to the outlet of the buffer tank and at the other end to the catalytic dechlorination reaction unit.

[0025] The catalytic dechlorination reaction unit includes: a dechlorination reactor, which has a brine inlet at the top connected to the remaining part of the brine delivery pipeline and a hydrogen inlet at the bottom connected to the other end of the hydrogen delivery pipeline;

[0026] The catalyst separation unit includes a ceramic ultrafiltration membrane separator, the inlet of which is connected to the outlet of the dechlorination reactor;

[0027] pH adjustment device for adjusting the pH of saline solution.

[0028] The technical effects and advantages of this invention are as follows:

[0029] This invention, on the one hand, can precisely control the generation and residual amount of chlorate in the electrolysis system, preventing it from passing through the ion-exchange membrane into the cathode and causing excessive chlorate levels in the finished alkali, thus significantly improving the purity and quality grade of potassium hydroxide products. On the other hand, it can maintain a stable concentration of the brine entering the tank, preventing foaming of the ion-exchange membrane due to abnormal brine concentration, ensuring stable operation and electrolysis efficiency of the electrolysis process. Simultaneously, compared to traditional removal processes, its chlorate removal efficiency is significantly improved, effectively inhibiting chlorate accumulation during brine circulation, reducing subsequent electrolysis side reactions caused by chlorate accumulation, and lowering the impurity content in the potassium hydroxide product. Furthermore, it can reduce the corrosive effect of chlorate on evaporation equipment and other production devices, extending equipment lifespan, reducing equipment maintenance frequency and replacement costs, and providing strong support for improving quality, reducing consumption, and stabilizing efficiency in the industrial production of potassium hydroxide. Attached Figure Description

[0030] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0031] Figure 1 is a flowchart of the present invention;

[0032] Figure 2 is a system module diagram of the present invention. Detailed Implementation

[0033] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0034] Referring to Figures 1-2, the present invention provides a technical solution: a method for removing chlorate produced during the preparation of potassium hydroxide by ion-exchange membrane electrolysis, comprising the following steps:

[0035] Step 1: The brine discharged from the electrolytic cell first enters the buffer homogenizing tank, where it is thoroughly mixed for 10 minutes using an in-tank stirrer to ensure a highly uniform brine composition. After mixing, the dual-channel variable frequency pump system is activated, splitting the brine into a 10%:90% ratio as preset: one variable frequency pump controls approximately 10% of the total flow, directly delivering this portion of the brine to the titanium-based electrolytic cell; the other variable frequency pump controls the remaining 90% of the flow, stably delivering the brine to the dechlorination feed buffer tank for temporary storage.

[0036] By dividing the brine into 10% portions, 90% is designated as the main feedstock for the subsequent in-situ hydrogen production process, while the remaining 90% serves as the primary feedstock for the dechlorination reaction. The hydrogen electrolyzer undergoes inerting before the brine feedstock is introduced. Specifically, nitrogen is introduced into the electrolyzer at a pressure of 0.15 MPa and adjusted to a suitable flow rate. The inside of the cell is continuously purged for at least 20 minutes. After purging, an oxygen content detector is used to monitor the gas content, confirming that the residual oxygen content has stabilized and decreased to a safe threshold. Utilizing the inert nature of nitrogen, the original air in the electrolyzer is completely replaced and eliminated. This fundamentally prevents the subsequent hydrogen from mixing with residual oxygen to form an explosive mixture before the hydrogen production reaction begins. This safety measure effectively eliminates the potential explosion risk in the hydrogen production process and ensures a safe preparation environment for the feedstock required for the subsequent dechlorination reaction. Meanwhile, the 90% brine composition, after buffering and homogenization, remains highly stable, avoiding the problem of affecting the efficiency of subsequent dechlorination reactions due to fluctuations in concentration or impurities, reducing the frequency of process parameter adjustments, and lowering the overall operational complexity.

[0037] Step 2: Start the power supply of the hydrogen electrolyzer, and set the initial cell voltage to 1.8V and the target current density to 500A / m. 2 The current density is adjusted in a stepped manner, starting from 300 A / m in the first 30 minutes. 2 Gradually increase to 500A / m 2 Then increase by 50 A / m every 10 minutes. 2 The current is then slowly increased to the target value via a rectifier. Once the current stabilizes, the variable frequency pump is turned on and adjusted to 90% of its rated flow rate to ensure a stable sample flow for the online free chlorine detector. Real-time Cl2 monitoring and recording of the free chlorine concentration in the saline solution (Cl2:H2 = 1:1) are maintained. Based on the free chlorine concentration and target throughput, the theoretical hydrogen production from H2 is calculated according to the required dechlorination reaction molar ratio. Real-time matching of hydrogen production is achieved by dynamically adjusting the electrolysis current, ensuring that the hydrogen output meets reaction requirements while avoiding excess.

[0038] Hydrogen gas, generated by electrolysis (H2), first enters 0.1m. 3 The buffer tank, controlled by a closed-loop system comprised of a high-precision pressure sensor at its top, maintains a stable internal pressure within the range of 0.1-0.12 MPa. Hydrogen is then delivered via a 316L stainless steel check valve and a corrosion-resistant flow meter to a porous titanium plate gas distribution device at the bottom of the dechlorination reactor. An online hydrogen purity detector is integrated into the delivery pipeline to monitor and ensure the hydrogen purity meets the technical requirement of ≥99.5%.

[0039] This process utilizes the H+ contained in the brine itself. +Hypochlorite ions, through electrolysis reaction H + It is reduced to H2 chloride ions. Wherein 2H... + +2e - =H2↑, the hydrogen produced at the cathode is directly used as a reducing agent, and no additional external hydrogen source is needed; Cl2::H2=1:1.1, the on-site hydrogen production is precisely adjusted by the molar ratio to ensure that the supply of H2 hydrogen is moderately excessive with Cl2 to ensure the completeness of the reaction, while avoiding the abnormal increase in system pressure caused by excessive H2 hydrogen.

[0040] The above-mentioned process successfully replaced the traditional sodium sulfite dechlorination method, completely avoiding SO4. 2- This process eliminates the membrane fouling problem caused by byproduct accumulation and removes the inherent high-pressure leakage and explosion risks of traditional external hydrogen storage equipment during handling and storage. The process also reduces SO4 emissions. 2- No sulfur-containing byproducts are produced throughout the process, eliminating the harm of sulfate to the ion exchange membrane from the source; the hydrogen production feedstock is directly taken from the electrolysis of brine system, eliminating the need for external hydrogen procurement and transportation, and significantly reducing raw material costs; on-site hydrogen production is ready for immediate use, and is transported to the reactor through short-distance closed pipelines, increasing the hydrogen utilization rate to over 95%.

[0041] However, it is also important to note that, to ensure stable system operation, the following operational procedures must be strictly followed: The actual operating voltage of the electrolytic cell must be manually recorded once per hour. When the voltage exceeds 2.0V, the electrode surface must be immediately checked for scaling or passivation. If scaling is confirmed, the electrodes must be soaked and cleaned with a 0.5% dilute hydrochloric acid solution to restore their activity. When the pressure in the titanium alloy buffer tank unexpectedly exceeds the safety threshold of 0.15MPa, the safety valve installed in the tank must be able to reliably and automatically open to release pressure. At the same time, the interlocking device should immediately cut off the power supply to the electrolytic cell, providing double protection to prevent equipment damage due to overpressure.

[0042] Step 3: The dechlorination reactor is filled with a Pd-Ru / CNTs-UiO-66 catalyst, which consists of a support framework, active components, and a reinforcing phase. The support framework uses carbon nanotubes (CNTs) as a conductive network and structural support, providing high specific surface area and excellent electronic conductivity. The active components include palladium (Pd) and ruthenium (Ru), which are uniformly dispersed in the form of metal nanoparticles on the surface of CNTs and in the metal-organic framework channels of UiO-66, achieving high catalytic activity. The reinforcing phase is a porous UiO-66 structure, which further enhances the stability of the reaction interface. The catalyst particle size is 2-3 mm, and the bed height is set at 1.5 m to ensure uniform distribution within the reactor. In the Pd-Ru / CNTs-UiO-66 catalyst, the synergistic effect of the dual active sites of Pd-Ru promotes the adsorption and activation of chlorine species; the conductive network of CNTs accelerates the electron transfer process and improves the reaction kinetic efficiency; the porous nature of UiO-66 optimizes the gas-liquid-solid three-phase contact efficiency, and the temperature of the reaction system in the dechlorination reactor is controlled during the process to adapt to the reaction requirements of catalytic hydrodechlorination and preliminary decomposition of chlorate, thereby enhancing the mass transfer effect.

[0043] First, carbon nanotubes were acidified to enrich their surface with carboxyl functional groups. Then, the treated carbon nanotubes were dispersed in a DMF solution containing zirconium salt and terephthalic acid, and UiO-66 crystals were grown in situ on their surface via a solvothermal reaction, forming a CNTs-UiO-66 composite support. Next, using an equal-volume impregnation method, soluble salt precursor solutions of palladium (Pd) and ruthenium (Ru) were loaded onto the composite support at a predetermined mass ratio. After aging and drying, a programmed temperature reduction was performed in a hydrogen / nitrogen mixed atmosphere to finally obtain a highly dispersed Pd-Ru / CNTs-UiO-66 composite catalyst.

[0044] 10g of CNTs were added to a 500mL three-necked flask, followed by 200mL of concentrated nitric acid. The mixture was heated to 120℃ and refluxed for 6 hours with magnetic stirring. After the reaction was completed, the filtrate was washed with deionized water until the pH reached 5-6 to remove residual nitric acid. The filtrate was then placed in a vacuum drying oven and dried at 80℃ for 12 hours to obtain acidified CNTs with a surface rich in -COOH and -OH functional groups, which facilitated their combination with UiO-66. Using a ZrCl4:H2 ratio of 1:1, 0.86g of ZrCl4 and 0.61g of H2 were weighed and added to 200mL of LDMF. The mixture was ultrasonically dispersed for 30 minutes until completely dissolved. 0.15g of acidified CNTs was then added, and the mixture was ultrasonically dispersed for another 15 minutes to ensure uniform dispersion of the CNTs. The mixture was then transferred to a 500mL polytetrafluoroethylene reactor and reacted in a 120℃ oven for 24 hours.

[0045] After the reaction was completed, the mixture was cooled to room temperature, centrifuged to collect the solid, washed three times with DMF to remove unreacted monomers, washed twice with ethanol, and dried under vacuum at 60°C for 12 hours to obtain a black powdery CNTs-UiO-66 composite support.

[0046] Calculate the amount of precursor used. The target total loading is 5%, Pd:Ru = 3:1, and the mass ratio is 10g. Taking 10g of CNTs-UiO-66 carrier, it is necessary to load 0.375g of Pd and 0.125g of Ru.

[0047] Corresponding palladium nitrate dosage: 0.375g ÷ 47% = 0.798g;

[0048] Corresponding dosage of ruthenium trichloride: 0.125g ÷ 37% = 0.338g;

[0049] Dissolve the above precursor in 50 mL of deionized water and stir until completely dissolved to obtain a mixed solution of metal ions.

[0050] Add 10g of composite carrier to the solution and stir and soak at room temperature for 12 hours. The solution volume should match the water absorption rate of the carrier to ensure complete adsorption.

[0051] The catalyst precursor was dried at 80℃ for 6 hours to remove moisture, thus obtaining the supported precursor catalyst.

[0052] The catalyst precursor was placed in a quartz tube reactor and purged with nitrogen for 30 minutes to remove air.

[0053] Switch to a mixture of hydrogen and nitrogen gas, heat to 200°C at a rate of 2°C / min, and hold for 2 hours to remove Pd. 2+ Ru 3+ Restore to Pd 0 and Ru 0 Element;

[0054] After reduction, the catalyst was cooled to room temperature under a nitrogen atmosphere to obtain the final catalyst Pd-Ru / CNTs-UiO-66.

[0055] The Pd-Ru / CNTs-UiO-66 catalyst was added in batches: 60% of the total amount was added initially, and the chlorate concentration was checked after 10 minutes of reaction before the remaining 40% was added. Temperature control employed a stepped heating method: the temperature was increased from room temperature to 60°C at a rate of 2°C / min, held for 5 minutes, and then increased to 80-85°C at a rate of 1°C / min. At the start of the operation, nitrogen gas at 0.2 MPa was introduced at a flow rate of 15 m³ / min. 3 The reactor is purged continuously for 30 minutes at a rate of / h to remove residual oxygen and impurities, ensuring a pure reaction environment. After purging, the nitrogen inlet valve is closed, and the 254nm UV lamp assembly is turned on and preheated for 10 minutes until the light intensity stabilizes at 10MW / cm².2 To ensure full activation of the ultraviolet light source, the ultraviolet lamp preheating adopts a gradient power increase method: first run at 50% power for 5 minutes, then increase to 100% power for 5 minutes; the three-phase reaction system adopts countercurrent contact enhancement operation, hydrogen diffuses upward from the gas distribution device at the bottom of the reactor in the form of microbubbles, and dilute brine is sprayed downward from the top spray head at a 30° angle to form a liquid film, thereby enhancing gas-liquid contact.

[0056] Subsequently, the 90% saturated brine feed pump was started, and the flow rate was controlled at 4.5-7.2 m³ / h. 3 Within a certain range (e.g., brine is evenly sprayed through the spray nozzles at the top of the reactor to form a liquid film); simultaneously, the hydrogen inlet valve is opened, and the hydrogen flow rate is controlled to maintain a Cl2:H2 ratio of 1:1.1, establishing a stable gas-liquid-solid three-phase reaction system. The free chlorine concentration is monitored in real-time by a laser gas detector at the reactor outlet. If the detected value exceeds 0.03 mg / L, the system automatically triggers an adjustment mechanism: the hydrogen flow rate is immediately increased by 10% to increase the supply of reducing agent; the brine inlet valve opening is reduced by 20%, and the residence time is extended from 30 seconds to 40 seconds to optimize reaction contact efficiency until the free chlorine concentration drops to 0.03 mg / L or below.

[0057] This process utilizes 254nm ultraviolet light to efficiently break Cl-Cl bonds, reducing the activation energy of the Cl2 reaction and simultaneously decomposing trace amounts of organic chlorine pollutants. The countercurrent contact method extends the contact time between the brine and the H2 catalyst, ensuring that the chlorine removal reaction is thorough and complete, thereby improving the overall dechlorination efficiency and system stability.

[0058] Step 4: After dechlorination, the catalyst-containing brine enters the ceramic ultrafiltration membrane system. The operating pressure is controlled at 0.2 MPa and the temperature at 70-80℃. The catalyst is retained by the membrane and returned to the dechlorination reactor via a reflux pump. Next, the brine permeates through the membrane into the pH adjustment tank. The online pH meter in the tank is turned on, and 32% NaOH is injected via a metering pump. The alkali addition is adjusted in real time to stabilize the pH at 6-7. Finally, the ceramic ultrafiltration membrane is backwashed periodically: the feed valve is closed, and 0.5% hydrochloric acid is introduced at a flow rate of 1.5 m³ / h. 3 / h, backwash for 15 minutes to restore membrane flux.

[0059] Ceramic ultrafiltration membranes utilize the pore size sieving effect to trap catalyst particles, achieving solid-liquid separation; the brine after dechlorination is acidic, and 32% NaOH is added for neutralization, resulting in H+ ions. + +OH - =H2O adjusts the pH to neutral to prevent acidic brine from corroding downstream pipes and equipment. The catalyst is lost with the brine, reducing catalyst replenishment costs and preventing acidic brine from corroding downstream decomposition tanks, heat exchangers and other equipment.

[0060] Step 5: The pH-adjusted brine enters the decomposition tank. Turn on the online chlorate concentration meter in the tank. If the detected concentration is ≤15mg / L, start the Ce... 3+ The catalyst metering pump calculates the dosage based on the volume of brine in the tank, and controls the catalyst concentration to 5-10 mg / L.

[0061] Then, turn on the heating device of the decomposition tank and raise the temperature to 80-85℃. Turn on the stirrer and adjust the pH of the tank to 1.5-2.0 using the hydrochloric acid metering pump. The residence time is automatically adjusted according to the chlorate concentration. When the concentration is 10-12 mg / L, the residence time is 30 minutes, and when the concentration is 12-15 mg / L, the residence time is 15 minutes. After the reaction is completed, the chlorate concentration is measured to ensure that it is ≤5 mg / L.

[0062] Ce 3+ Metal ions can act as electron transfer mediators, accelerating the reaction of ClO3. - With Cl - The reaction, with the chemical formula as follows: ClO3 - +5Cl - +6H + =3Cl2↑+3H2O, by controlling the catalyst concentration and reaction conditions, optimizing the reaction kinetics, improving the removal rate of low-concentration chlorate, breaking through the bottleneck of low removal rate of low-concentration chlorate (<15mg / L) in traditional processes, and avoiding the downgrading of potassium hydroxide products due to excessive chlorate.

[0063] Step Six: Before feeding into the decomposition tank, the brine first enters a plate heat exchanger to fully exchange heat with the high-temperature brine from the decomposition tank outlet. After feeding, the temperature of the brine system in the decomposition tank is controlled. By regulating the temperature, the deep decomposition efficiency of chlorate is enhanced, ensuring that chlorate removal meets the standards. By recovering and utilizing the waste heat of the brine at the decomposition tank outlet, the inlet low-temperature brine is effectively preheated: under winter operating conditions, the temperature of the brine can be raised to 55℃ after heat exchange in the waste heat recovery section; while under summer operating conditions, it can be raised to 75℃. The brine that has completed the initial heat exchange then enters the precision heating section. Here, by precisely adjusting the hot water flow rate into the heater, and simultaneously monitoring and controlling the brine outlet temperature online in real time, the temperature of the brine finally entering the decomposition tank is ensured to be strictly stable within the target range of 80-85℃. This waste heat recovery design significantly reduces the energy load of subsequent heating units.

[0064] Step 7: The treated and qualified brine is returned to the salt processing section through a closed pipeline system. There, it is mixed with replenished solid sodium chloride (NaCl) in a predetermined ratio in the water distribution tank to prepare refined brine that meets the requirements for electrolysis. This achieves zero-discharge recycling of desalinated brine and SO4 throughout the entire system. 2-To ensure the long-term stability of the circulating brine quality and prevent the accumulation of impurities from negatively impacting the efficiency of the ion-exchange membrane electrolyzer and the quality of the final product, the system is equipped with multiple online monitoring and control mechanisms. The specific operating procedures are as follows:

[0065] The qualified brine from the decomposition tank outlet first enters a dedicated reuse buffer tank, simultaneously activating the integrated online monitoring instruments within the tank to continuously detect SO4. 2- Key indicators in the brine include sodium chloride concentration, chlorate content, and free chlorine concentration. After all analytical indicators are confirmed to be consistently within acceptable limits, the reuse pump is activated to quantitatively deliver the qualified brine from the buffer tank to the distribution tank in the salt treatment section. In the distribution tank, metered solid NaCl particles are uniformly added to the flowing brine according to process requirements. Simultaneously, a powerful stirrer is activated to ensure the solid salt is fully dissolved and uniformly mixed, strictly controlling the concentration of the refined brine within the process range of 305-315 g / L. During this process, the pH value of the refined brine is simultaneously monitored and recorded. The prepared refined brine is filtered to remove fine particulate matter and finally delivered to the electrolytic cell circulation main for electrolysis. Furthermore, online monitoring instruments are continuously operated at key points in the entire brine circulation system to monitor SO4 levels in real time. 2- Track and record the accumulation rate of specific impurities and related water quality data to provide data support for process optimization and preventive maintenance.

[0066] An operating system for removing chlorate produced by the ion-exchange membrane electrolysis method for preparing potassium hydroxide includes a hydrogen production unit, a catalytic dechlorination reaction unit, a catalyst separation unit, and a pH adjustment device connected in sequence.

[0067] The hydrogen production unit includes:

[0068] The electrolyzer has its inlet connected to the main brine delivery pipeline to receive the diverted brine. The electrolyzer uses titanium-based electrodes and generates hydrogen gas at the cathode through an electrolytic reaction.

[0069] A buffer tank, whose inlet is connected to the hydrogen outlet of the electrolyzer, is used to stabilize the hydrogen pressure at 0.1-0.12 MPa.

[0070] The hydrogen delivery pipeline connects to the outlet of the buffer tank at one end and extends to the catalytic dechlorination reaction unit at the other end.

[0071] The catalytic dechlorination reaction unit includes a dechlorination reactor, which has a brine inlet at the top connected to the remaining part of the brine delivery pipeline and a hydrogen inlet at the bottom connected to the other end of the hydrogen delivery pipeline.

[0072] The catalyst separation unit includes a ceramic ultrafiltration membrane separator, the inlet of which is connected to the outlet of the dechlorination reactor;

[0073] pH adjustment device for adjusting the pH of saline solution.

[0074] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A method for removing chlorate produced during the preparation of potassium hydroxide by ion-exchange membrane electrolysis, characterized in that, Includes the following steps: Step 1: The brine discharged from the electrolysis process is introduced into a buffer homogenizing tank. After stirring and mixing, it is proportionally divided by a dual-path variable frequency pump and separately delivered to a titanium-based electrolytic cell and a dechlorination feed buffer tank. Nitrogen gas is introduced into the titanium-based electrolytic cell until the oxygen content in the cell is ≤0.5%. Step 2: The power supply to the titanium-based electrolytic cell is started, the initial cell voltage is set, and the current density is adjusted by a rectifier. Simultaneously, based on the free chlorine concentration in the brine, the electrolysis parameters are dynamically adjusted to control the hydrogen production. The generated hydrogen is then delivered to the dechlorination reactor via a pressure-stabilized buffer tank. Step 3: A Pd-Ru / CNTs-UiO-66 catalyst is filled into the dechlorination reactor, and the gas is purged. After nitrogen purging, the ultraviolet lamp is turned on to preheat to the set light intensity, and hydrogen generated in step two is introduced simultaneously to form a gas-liquid-solid three-phase reaction system. During the process, the temperature of the reaction system in the dechlorination reactor is controlled to adapt to the reaction requirements of catalytic hydrodechlorination and preliminary decomposition of chlorate. Step four: The dechlorinated brine containing the catalyst is introduced into the ceramic ultrafiltration membrane system to retain the catalyst and return it to the dechlorination reactor. The brine that permeates through the membrane enters the pH adjustment tank, and NaOH is added to adjust the pH. Step five: The pH-adjusted brine is introduced into the decomposition tank, and the online chlorate concentration meter in the tank is turned on. If the detected concentration is ≤15mg / L, the Ce2000 decomposition tank is activated. 3+ Catalyst metering pump: Calculate the dosage based on the volume of brine in the tank, controlling the catalyst concentration to 5-10 mg / L. Then, turn on the decomposition tank heating device to raise the temperature to 80-85℃, turn on the stirrer, and simultaneously adjust the pH in the tank to 1.5-2.0 using the hydrochloric acid metering pump. Automatically adjust the residence time according to the chlorate concentration: 30 minutes for a concentration of 10-12 mg / L, and 15 minutes for a concentration of 12-15 mg / L. After the reaction, check the chlorate concentration to ensure it is ≤5 mg / L. Step Six: Before feeding into the decomposition tank, the brine is first exchanged with the high-temperature brine at the decomposition tank outlet via a plate heat exchanger. After feeding, the temperature of the brine system in the decomposition tank is controlled to enhance the deep decomposition efficiency of chlorate and ensure that chlorate removal meets the standards. Step Seven: Introduce the treated brine into a reuse buffer tank and check the SO4 levels. 2- After being treated with chlorate and free chlorine, the solution is transported to the salt processing section and mixed with solid NaCl to prepare refined brine. After filtration, the brine is returned to the electrolytic cell for recycling, while SO4 levels are monitored. 2- Cumulative rate and electrolytic cell current efficiency.

2. The method for removing chlorate produced during the preparation of potassium hydroxide by ion-exchange membrane electrolysis according to claim 1, characterized in that: The ratio of the proportional diversion is 10%:90%, wherein 10% of the brine is pumped to the titanium-based electrolyzer via a flow branch pump, and 90% of the brine is pumped to the dechlorination raw material buffer tank via a flow branch pump.

3. The method for removing chlorate produced during the preparation of potassium hydroxide by ion-exchange membrane electrolysis according to claim 1, characterized in that: The dynamically adjusted electrolysis parameters are based on a Cl2:H2 molar ratio of 1:

1. The theoretical hydrogen production from H2 is calculated according to the free chlorine concentration and target processing capacity, based on the required dechlorination reaction molar ratio, and the electrolysis current is dynamically adjusted.

4. The method for removing chlorate produced during the preparation of potassium hydroxide by ion-exchange membrane electrolysis according to claim 1, characterized in that: The current density is adjusted in a stepped manner, starting from 300A / m in the initial 30 minutes. 2 Gradually increase to 500A / m 2 Then increase by 50 A / m2 every 10 minutes until the target value is reached.

5. The method for removing chlorate produced during the preparation of potassium hydroxide by ion-exchange membrane electrolysis according to claim 1, characterized in that: The Pd-Ru / CNTs-UiO-66 catalyst has a particle size of 2-3 mm and a bed height of 1.5 m.

6. The method for removing chlorate produced during the preparation of potassium hydroxide by ion-exchange membrane electrolysis according to claim 1, characterized in that: The ultraviolet lamp has a wavelength of 254nm and a power of 500W. After preheating for 10 minutes, the light intensity reaches 10MW / cm². 2 .

7. The method for removing chlorate produced during the preparation of potassium hydroxide by ion-exchange membrane electrolysis according to claim 1, characterized in that: The UV lamp preheating adopts a gradient power increase method, first running at 50% power for 5 minutes, and then increasing to 100% power for 5 minutes.

8. The method for removing chlorate produced during the preparation of potassium hydroxide by ion-exchange membrane electrolysis according to claim 1, characterized in that: The Pd-Ru / CNTs-UiO-66 catalyst was added in batches: 60% of the total amount was added initially, and the chlorate concentration was checked after 10 minutes of reaction before the remaining 40% was added. Temperature control was carried out using a stepped heating operation: the temperature was increased from room temperature to 60℃ at a rate of 2℃ / min, held for 5 minutes, and then increased to 80-85℃ at a rate of 1℃ / min.

9. The operating system for the method of removing chlorate produced by the ion-exchange membrane electrolysis method for preparing potassium hydroxide according to any one of claims 1-8: characterized in that, It includes a hydrogen production unit, a catalytic dechlorination reaction unit, a catalyst separation unit, and a pH adjustment device connected in sequence.

10. The operating system for the method of removing chlorate generated during the preparation of potassium hydroxide by ion-exchange membrane electrolysis according to claim 9, characterized in that: The hydrogen production unit includes: an electrolyzer with its inlet connected to the main brine delivery pipeline for receiving diverted brine; the electrolyzer uses titanium-based electrodes to generate hydrogen gas at the cathode through an electrolytic reaction; a buffer tank with its inlet connected to the hydrogen outlet of the electrolyzer for stabilizing the hydrogen pressure at 0.1-0.12 MPa; and a hydrogen delivery pipeline, one end connected to the outlet of the buffer tank and the other end extending to the catalytic dechlorination reaction unit. The catalytic dechlorination reaction unit includes: a dechlorination reactor with a brine inlet at the top connected to the remaining portion of the main brine delivery pipeline and a hydrogen inlet at the bottom connected to the other end of the hydrogen delivery pipeline. The catalyst separation unit includes: a ceramic ultrafiltration membrane separator with its inlet connected to the outlet of the dechlorination reactor; and a pH adjustment device for adjusting the pH of the brine.

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