A method for stabilizing the active chlorine content of sodium hypochlorite solutions

Abstract

The present application relates to the technical field of automatic control, and particularly relates to a sodium hypochlorite solution effective chlorine content stabilization control method. In the cooling stage of the sodium hypochlorite solution, the concentration signal of free trace metal ions in the solution is obtained through an online electrochemical sensor. When the signal reaches a preset threshold value of a controller, the controller instructs a peristaltic pump to add a compounded stabilizer to the solution, and the compounded stabilizer is prepared by mixing a specific short peptide containing cysteine and histidine and a silicate buffer. After adding the compounded stabilizer, the solution is subjected to short-time ultrasonic cavitation treatment. The method replaces the traditional aminopolycarboxylate with a specific short peptide, avoids the carbon-nitrogen bond breakage failure in a strong oxidation environment, prevents the secondary release of metal ions from causing catalytic decomposition, prolongs the effective chlorine half-life, and reduces the generation amount of chlorate byproducts.

Description

Technical Field

[0001] This invention relates to the field of automatic control technology, and specifically to a method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solution. Background Technology

[0002] Sodium hypochlorite solution is susceptible to decomposition during storage due to the catalytic action of trace free metal ions, leading to a decrease in available chlorine content. A common stabilization method in current industrial production is the addition of aminopolycarboxylic acid chelating agents, such as ethylenediaminetetraacetic acid (EDTA), to the sodium hypochlorite solution. In actual operation, after the sodium hypochlorite solution is generated by electrolysis and undergoes initial cooling, operators typically pour a measured amount of alkaline aqueous solution containing EDTA directly into the storage tank based on experience or periodic test results. The multiple nitrogen and oxygen atoms in the EDTA molecule can combine with trace metal ions such as iron and copper ions in the solution to form stable cyclic complexes, thereby masking the active sites of the metal ions and blocking the catalytic pathway of the decomposition reaction of hypochlorite ions.

[0003] The core technical problem with the aforementioned existing solutions lies in the fact that aminopolycarboxylic acid salts such as ethylenediaminetetraacetic acid (EDTA) cannot maintain their structural stability in the highly oxidizing microenvironment of sodium hypochlorite. Hypochlorite molecules possess strong oxidizing properties and directly attack the carbon-nitrogen bonds within the EDTA molecule, causing the chelating agent to undergo ring-opening and chain-breaking reactions, leading to degradation and ineffectiveness. As the EDTA molecules degrade, trace amounts of metal ions that were previously masked by its complexation are released back into the solution system. These released metal ions, no longer masked, trigger a secondary catalytic decomposition reaction of sodium hypochlorite with higher activity. This means that conventional stabilization methods involving the addition of aminopolycarboxylic acid salts cannot maintain stable control over the available chlorine content during long-term storage. Summary of the Invention

[0004] To address the shortcomings of existing technologies that use aminopolycarboxylic acid chelating agents for stabilizing sodium hypochlorite solutions, which are prone to degradation and failure in the strong oxidizing microenvironment of sodium hypochlorite, leading to the secondary release of complexed metal ions and triggering secondary catalytic decomposition of sodium hypochlorite, and the inability of manual addition methods to accurately match the concentration of free metal ions to achieve dynamic and timely stabilization control, this invention provides a method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solutions.

[0005] To address the aforementioned technical problems, this invention provides a method for stabilizing and controlling the effective chlorine content of a sodium hypochlorite solution, comprising the following technical features: During the cooling stage of the sodium hypochlorite solution, the concentration signal of free trace metal ions in the sodium hypochlorite solution is acquired in real time using an online electrochemical sensor; the free trace metal ion concentration signal is transmitted to the input terminal of a controller, which has a preset metal ion concentration threshold; when the controller determines that the free trace metal ion concentration signal reaches the preset metal ion concentration threshold, the controller outputs a control command to a peristaltic pump actuator; after receiving the control command, the peristaltic pump actuator adds a compound stabilizer to the sodium hypochlorite solution, the compound stabilizer being prepared by mixing a specific short peptide containing cysteine ​​and histidine with a silicate buffer solution; after adding the compound stabilizer, an ultrasonic cavitation device electrically connected to the controller is activated to perform short-term ultrasonic cavitation treatment on the sodium hypochlorite solution.

[0006] The core inducing factor for the effective chlorination degradation of sodium hypochlorite is the catalytic effect of trace amounts of free metal ions in solution on the decomposition reaction of hypochlorite. In this scheme, during the critical window period of sodium hypochlorite cooling for catalytic decomposition, the concentration changes of free metal ions are captured in real time by an online electrochemical sensor to achieve precise control of the timing of stabilization intervention. The specific short peptides in the compound stabilizer have sulfhydryl groups of cysteine ​​residues with strong reducing properties, which are preferentially oxidized in the strong oxidizing microenvironment of sodium hypochlorite. This protects the peptide bond backbone of the short peptides and the imidazole groups of histidine residues from being attacked and degraded by hypochlorite, fundamentally avoiding the failure problem caused by the breakage of carbon-nitrogen bonds in traditional chelating agents. Meanwhile, the histidine imidazole group and the sulfur atom site of cysteine ​​in the short peptide can form polydentate coordination bonds with trace amounts of free metal ions, stabilizing the chelation of metal ions and completely masking their catalytic active sites, thus blocking their catalytic pathway for the decomposition of hypochlorite. The silicate buffer solution can maintain the strongly alkaline environment of the system, inhibiting the protonation and self-decomposition reactions of hypochlorite. The short-term ultrasonic cavitation treatment after addition, through the microjets and local turbulence generated by the collapse of cavitation bubbles, greatly improves the dispersion uniformity of short peptide molecules in sodium hypochlorite solution, shortens the equilibrium time of the chelation reaction, and achieves rapid and system-wide masking of free metal ions, avoiding the occurrence of catalytic decomposition reactions.

[0007] Furthermore, in the above technical solution, the specific short peptide containing cysteine ​​and histidine is prepared by solid-phase synthesis, and the amino acid sequence of the specific short peptide is cysteine-histidine-histidine-cysteine; when preparing the compound stabilizer, the specific short peptide is dissolved in the silicate buffer solution, the silicate buffer solution is an aqueous solution of sodium metasilicate, and the mass fraction of the specific short peptide in the compound stabilizer accounts for 0.5% to 2.0% of the total mass of the compound stabilizer.

[0008] In practice, the tetrapeptide sequence employs a symmetrical structure design with cysteine ​​residues at both ends and two histidine residues in the middle, forming a multidentate coordination structure. The thiol groups of the cysteine ​​residues at both ends provide two coordination sites, while the imidazole rings of the two histidine residues in the middle provide four coordination sites. This allows it to form a stable hexadentate chelate with transition metal ions, exhibiting a chelation stability constant far higher than that of monodentate or bidentate ligands, significantly enhancing the metal ion masking effect. The solid-phase synthesis method allows for precise control of the amino acid linkage sequence, avoiding byproduct generation and ensuring the stability of the short peptide's coordination activity. The 0.5%-2.0% mass fraction design ensures both the solubility and dispersibility of the short peptide in the buffer solution, preventing aggregation and inactivation between short peptide molecules at high concentrations, while also enabling rapid achievement of a chelation concentration matching the free metal ions after addition, achieving highly efficient masking. The sodium metasilicate aqueous solution serves as a buffer system, providing a stable, strongly alkaline environment. Simultaneously, the silicate ions can form a passivation film on the surface of the metal ions, producing a synergistic effect with the chelation of the short peptide, further inhibiting the catalytic activity of the metal ions.

[0009] Furthermore, in the above technical solution, the molar concentration of the sodium metasilicate aqueous solution is 0.1 mol / L to 0.5 mol / L, and the pH value of the sodium metasilicate aqueous solution is adjusted to 11.5 to 12.5; during the process of dissolving the specific short peptide in the sodium metasilicate aqueous solution, the temperature of the dissolution environment is controlled at 4°C to 10°C, and a magnetic stirrer is used to continuously stir at a speed of 50 to 100 revolutions per minute for 30 to 60 minutes until a homogeneous compound stabilizer is formed.

[0010] In practice, a sodium metasilicate concentration of 0.1-0.5 mol / L provides sufficient buffer capacity to maintain the strongly alkaline environment of the sodium hypochlorite solution system, preventing hypochlorite self-decomposition caused by pH fluctuations after addition. The pH range of 11.5-12.5 is the optimal pH range for sodium hypochlorite stability, while ensuring the reduced stability of the thiol groups in the short peptide molecules, preventing oxidative dimerization after thiol protonation and loss of coordination activity. The low-temperature dissolution environment of 4-10℃ can inhibit the oxidative degradation of short peptides during dissolution. The low-speed stirring of 50-100 rpm and the stirring time of 30-60 minutes can achieve complete dissolution and uniform dispersion of short peptides in the buffer solution without introducing a large amount of air that would cause oxidation, ensuring the consistency of activity between batches of the compound stabilizer.

[0011] Furthermore, in the above technical solution, the online electrochemical sensor includes a working electrode, a counter electrode, and a reference electrode. The working electrode is a glassy carbon electrode with a polypyrrole film modified on its surface. The online electrochemical sensor is installed in the overflow bypass of the sodium hypochlorite solution cooling tank. The overflow bypass is equipped with a thermostatic jacket, and cooling water circulates in the thermostatic jacket to maintain the temperature of the sodium hypochlorite solution in the overflow bypass at a constant 20°C to 25°C.

[0012] In practical implementation, the polypyrrole membrane exhibits excellent conductivity and cation selectivity. It can enrich free metal cations in the solution through electrostatic interaction, while simultaneously repelling the adsorption of anions such as hypochlorite on the electrode surface. This avoids the corrosion of the electrode surface and interference of the detection signal by the strongly oxidizing hypochlorite, significantly improving the sensitivity and anti-interference ability of trace metal ion detection. The overflow bypass design allows for continuous acquisition of the detection solution without affecting the main solution flow. The constant temperature jacket maintains the detection solution temperature at a constant 20-25℃, completely eliminating the influence of temperature fluctuations on the electrochemical detection signal. This ensures the accuracy and stability of the metal ion concentration detection results and provides a reliable basis for triggering the controller's dosing command.

[0013] Furthermore, in the above technical solution, the controller has a built-in proportional-integral-differential algorithm module, and the preset metal ion concentration threshold includes an upper limit threshold and a lower limit threshold. When the free state trace metal ion concentration signal continues to rise and reaches the upper limit threshold, the controller calculates the addition time through the proportional-integral-differential algorithm module and outputs a pulse signal with a corresponding duty cycle to the peristaltic pump actuator to control the addition amount of the compound stabilizer.

[0014] In practice, the dual threshold design of upper and lower limits can avoid frequent additions caused by small fluctuations in metal ion concentration, ensuring the stability of the system operation. The proportional-integral-differential algorithm module can dynamically calculate the required amount of compound stabilizer to be added based on the deviation between the real-time detected rate of change of metal ion concentration and the set threshold. It can achieve precise closed-loop control of the addition amount through the pulse signal with the corresponding duty cycle, avoiding the waste of raw materials caused by over-addition, and preventing the problem of insufficient addition that cannot completely mask free metal ions. This enables dynamic and precise control of the concentration of free metal ions in sodium hypochlorite solution.

[0015] Furthermore, in the above technical solution, the peristaltic pump actuator includes a metering peristaltic pump and a dosing pipe extending below the surface of the sodium hypochlorite solution. The end of the dosing pipe is provided with a microporous atomizing nozzle. When the peristaltic pump actuator responds to the pulse signal, the metering peristaltic pump operates in a stepping mode, dispersing the compound stabilizer into the sodium hypochlorite solution in the form of microdroplets through the microporous atomizing nozzle. The particle size of the microdroplets is 10 micrometers to 50 micrometers.

[0016] In practice, the metering peristaltic pump operates in step mode, which can accurately respond to the pulse signal of the controller and achieve micron-level precise control of the dosage of the compound stabilizer. The microporous atomizing nozzle can break the compound stabilizer into microdroplets of 10-50 micrometers, which greatly increases the contact surface area between the compound stabilizer and the sodium hypochlorite solution. This allows short peptide molecules to quickly diffuse to all areas of the solution system, shortens the collision and chelation time with free metal ions, avoids the problem of incomplete metal ion masking caused by uneven local concentration, and further improves the effect of stabilization control.

[0017] Furthermore, in the above technical solution, the ultrasonic cavitation device includes an ultrasonic transducer array fixed to the inner wall of the sodium hypochlorite solution cooling tank, and the ultrasonic transducer array is electrically connected to the controller; the ultrasonic frequency of the short-time ultrasonic cavitation treatment is set to 20kHz to 40kHz, and the straight-line distance between the emitting end face of the ultrasonic cavitation device and the microporous atomizing nozzle of the dosing pipeline is maintained within the range of 5 cm to 15 cm.

[0018] In practice, low-frequency ultrasound of 20-40kHz can generate a strong cavitation effect in the solution. The microjets and local high-pressure turbulence generated when the cavitation bubbles collapse can further enhance the dispersion effect of the compound stabilizer microdroplets in the solution. At the same time, it provides activation energy for the coordination and chelation reaction between short peptide molecules and metal ions, accelerating the chelation reaction rate. The 5-15 cm distance design ensures that the atomized compound stabilizer microdroplets are in the region of strongest ultrasonic cavitation effect as soon as they enter the solution system, maximizing the enhancement effect of ultrasound on dispersion and chelation reaction, and avoiding the attenuation of cavitation effect due to excessive distance, which would prevent the expected enhancement effect from being achieved.

[0019] Furthermore, in the above technical solution, while the peristaltic pump actuator starts to add the compound stabilizer, the controller outputs a start signal to the ultrasonic cavitation device after a delay of 5 to 10 seconds; the running time of the ultrasonic cavitation device is dynamically set by the controller based on the total addition time of the peristaltic pump actuator, and the running time of the ultrasonic cavitation device is 1.2 to 1.5 times the total addition time of the peristaltic pump actuator.

[0020] In practice, a 5-10 second delay in start-up design ensures that the microdroplets of the compound stabilizer enter the solution system first, and then disperse and enhance the reaction through ultrasonic cavitation effect. This avoids the solution temperature rise caused by premature ultrasonic start-up and prevents the cavitation effect from affecting the microdroplet formation process of the atomizing nozzle. The ultrasonic running time is set to 1.2-1.5 times the addition time to ensure that there is still sufficient ultrasonic action time after the compound stabilizer is added, so that the chelation reaction between short peptide molecules and metal ions can be completed. At the same time, it avoids the solution temperature rise caused by continuous ultrasonication, preventing sodium hypochlorite from thermally decomposing due to temperature rise, thus balancing the chelation reaction efficiency and the stability of sodium hypochlorite.

[0021] Furthermore, in the above technical solution, a redox potential sensor is connected in parallel next to the online electrochemical sensor, and the signal output terminal of the redox potential sensor is connected to another input terminal of the controller; the controller has a two-dimensional mapping table of metal ion concentration and redox potential pre-stored in it, and after receiving the free state trace metal ion concentration signal and the potential signal of the redox potential sensor, the controller checks the two-dimensional mapping table to confirm whether the triggering condition for adding the compound stabilizer is met.

[0022] In practice, the redox potential sensor can monitor the redox state of the sodium hypochlorite solution system in real time. The increase in the concentration of free metal ions will directly lead to the change in the redox potential of the system. By performing dual-parameter verification through a two-dimensional mapping table of metal ion concentration and redox potential, false triggering or missed triggering caused by the failure of a single electrochemical sensor or signal interference can be avoided. This greatly improves the reliability and safety of the dosing command triggering and ensures the continuous and stable operation of the stabilization control process.

[0023] Furthermore, in the above technical solution, the cooling stage of the sodium hypochlorite solution is the process of the sodium hypochlorite solution entering the heat exchanger for cooling after being generated by electrolysis. The initial temperature of the sodium hypochlorite solution entering the heat exchanger is 75°C to 85°C, and the final temperature of the sodium hypochlorite solution flowing out of the heat exchanger is 30°C to 35°C. The online electrochemical sensor, the peristaltic pump actuator, and the ultrasonic cavitation device are all installed on the outlet pipe of the heat exchanger.

[0024] In practice, sodium hypochlorite is generated at temperatures as high as 75-85℃ after electrolysis. Under high-temperature conditions, the thermal decomposition of hypochlorite ions and the catalytic decomposition of metal ions are extremely rapid. After being cooled to 30-35℃ by a heat exchanger, the thermal decomposition rate of the solution is significantly reduced, which is the optimal window period for metal ion masking and stabilization control. By setting all execution and detection devices in the heat exchanger outlet pipeline, free metal ions can be detected and masked immediately after the solution has cooled down and the risk of thermal decomposition has been greatly reduced. This completely blocks the catalytic decomposition reaction initiated by metal ions during the cooling stage, inhibits the effective chlorine degradation of sodium hypochlorite from the source, and maximizes the stabilization control effect.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This application uses a specific short peptide containing cysteine ​​and histidine to replace ethylenediaminetetraacetic acid (EDTA) as the metal ion masking component. The thiol groups in the short peptide molecule are preferentially consumed in a strong oxidizing environment, while the remaining histidine imidazole groups and peptide backbone can still form coordination bonds with metal ions after losing the thiol groups. The concentration of free trace metal ions in the solution is monitored in real time by an online electrochemical sensor, and the timing and amount of the compound stabilizer are dynamically controlled by a controller based on a concentration threshold, allowing the short peptide to bind to the metal ions before they initiate catalytic decomposition. This approach avoids the problem of chelating agent failure caused by the cleavage of carbon-nitrogen bonds by hypochlorite ions, overcomes the secondary catalytic decomposition phenomenon caused by the re-release of metal ions, prolongs the effective chlorine half-life of sodium hypochlorite solution, and reduces the formation of chlorate byproducts.

[0026] 2. A glassy carbon electrode with a surface-modified polypyrrole film is used to monitor metal ions within a constant-temperature jacket, eliminating interference from temperature fluctuations and improving the reliability of triggering the dosing command. The compounded stabilizer is injected into the solution as microdroplets through a microporous atomizing nozzle. Combined with the cavitation effect generated by the ultrasonic cavitation device, this increases the probability of collisions between the short peptides and metal ions in the solution. The controller activates the ultrasonic device after a delay following dosing and dynamically sets the ultrasonic duration. Ultrasonic energy promotes the coordination and binding process between short peptide molecules and metal ions, while simultaneously preventing the thermal decomposition of sodium hypochlorite due to additional heat generated by continuous ultrasonic exposure. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the present invention. Non-inventive improvements made by those skilled in the art based on the core technical solutions of the present invention are all within the protection scope of the present invention.

[0028] Unless otherwise specified, the raw materials, reagents, and instruments used in the following embodiments and comparative examples of this invention are all commercially available products in the art, and the detection methods used are all standard detection methods in the art. Specifically, the specific short peptide with the sequence cysteine-histidine-histidine-cysteine ​​was prepared by solid-phase peptide synthesis and purified by high-performance liquid chromatography with a purity ≥98%; sodium metasilicate, disodium ethylenediaminetetraacetate (EDTA-2Na), and other reagents were all analytical grade; the sodium hypochlorite solution was an initial solution prepared by industrial electrolysis, with an initial available chlorine content of 10.0% ± 0.2% and an initial free iron and copper total ion concentration of 52 ± 3 ppb; the online electrochemical sensor, redox potential (ORP) sensor, controller, metering peristaltic pump, and ultrasonic cavitation device were all conventional industrial equipment. The working electrode of the online electrochemical sensor was a glassy carbon electrode modified with a polypyrrole film, the reference electrode was an Ag / AgCl electrode, and the counter electrode was a platinum electrode.

[0029] Example 1: This example demonstrates the optimal implementation method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution. The specific steps are as follows: Preparation of the compound stabilizer: Prepare a sodium metasilicate aqueous solution with a molar concentration of 0.3 mol / L, and adjust the pH value to 12.0 with sodium hydroxide solution; place the above sodium metasilicate aqueous solution in a low temperature water bath, control the solution temperature at 6℃, add a specific short peptide with the sequence cysteine-histidine-histidine-cysteine, and control the mass fraction of the short peptide to be 1.0% of the total mass of the compound stabilizer; turn on the magnetic stirrer and stir continuously at 80 rpm for 45 minutes until the short peptide is completely dissolved, forming a homogeneous and transparent compound stabilizer, and store at 4℃ in the dark for later use.

[0030] Sodium hypochlorite solution cooling and online stabilization control: After being generated by electrolysis, the sodium hypochlorite solution has an initial temperature of 80℃ and is sent to a shell-and-tube heat exchanger for cooling. The temperature of the sodium hypochlorite solution at the heat exchanger outlet is controlled at 32℃. The online electrochemical sensor, ORP sensor, metering peristaltic pump dosing pipeline, and ultrasonic cavitation device are all installed on the outlet pipeline of the heat exchanger. The online electrochemical sensor and ORP sensor are installed in parallel in the overflow bypass of the cooling tank. The overflow bypass is equipped with a constant temperature jacket, and cooling water circulates in the jacket to maintain a constant solution temperature of 22℃ in the bypass. The ultrasonic transducer array of the ultrasonic cavitation device is fixed to the inner wall of the cooling tank. The straight-line distance between the transducer emitting end face and the microporous atomizing nozzle at the end of the dosing pipeline is 10cm.

[0031] The controller has built-in preset thresholds for free metal ion concentration, with an upper limit of 50 ppb and a lower limit of 20 ppb. It also incorporates a proportional-integral-derivative (PID) algorithm module and a two-dimensional mapping table of metal ion concentration and oxidation-reduction potential (ORP). An online electrochemical sensor acquires the concentration signal of free trace metal ions in the sodium hypochlorite solution in real time, while an ORP sensor acquires the redox potential signal of the solution in real time. Both signals are transmitted synchronously to the input of the controller. The controller verifies the two signals by querying the two-dimensional mapping table. When it determines that the free metal ion concentration signal has continuously risen to the upper limit threshold of 50 ppb, the PID algorithm module calculates that the addition time of the compound stabilizer is 60 seconds and outputs a pulse signal with the corresponding duty cycle to the metering peristaltic pump.

[0032] After receiving the pulse signal, the metering peristaltic pump operates in step mode, dispersing the compound stabilizer into the sodium hypochlorite solution as microdroplets with a particle size of 30μm through the microporous atomizing nozzle at the end of the dosing pipeline. At the same time as the metering peristaltic pump starts dosing, the controller outputs a start signal to the ultrasonic cavitation device after a delay of 8 seconds, setting the ultrasonic frequency to 30kHz and the ultrasonic running time to 1.3 times the dosing time (i.e., 78s). After the ultrasonic cavitation treatment is completed, the controller monitors the concentration of free metal ions in real time. When the concentration drops below the lower limit threshold of 20ppb, the dosing and ultrasonic treatment are stopped, completing the stabilization control process. The treated sodium hypochlorite solution is then sent to the storage tank for storage in the dark.

[0033] Example 2: The method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solution in this example is the same as that in Example 1, except that in the preparation of the compound stabilizer in step 1, the mass fraction of the specific short peptide is 0.5% of the total mass of the compound stabilizer.

[0034] Example 3: The method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solution in this example is the same as that in Example 1, except that in the preparation of the compound stabilizer in step 1, the mass fraction of the specific short peptide is 2.0% of the total mass of the compound stabilizer.

[0035] Example 4: The method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solution in this example is the same as that in Example 1, except that the molar concentration of sodium metasilicate aqueous solution is 0.1 mol / L in the preparation of the compound stabilizer in step 1.

[0036] Example 5: The method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution in this example is the same as that in Example 1, except that the molar concentration of sodium metasilicate aqueous solution is 0.5 mol / L in the preparation of the compound stabilizer in step 1.

[0037] Example 6: The method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solution in this example is the same as that in Example 1, except that the pH value of the sodium metasilicate aqueous solution is adjusted to 11.5 in the preparation of the compound stabilizer in step 1.

[0038] Example 7: The method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solution in this example is the same as that in Example 1, except that the pH value of the sodium metasilicate aqueous solution is adjusted to 12.5 in the preparation of the compound stabilizer in step 1.

[0039] Example 8: The method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solution in this example is the same as that in Example 1. The only difference is that in the preparation of the compound stabilizer in step 1, the temperature of the dissolution environment is controlled at 4°C, the speed of the magnetic stirrer is 50 rpm, and the stirring time is 30 minutes.

[0040] Example 9: The method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solution in this example is the same as that in Example 1. The only difference is that in the preparation of the compound stabilizer in step 1, the temperature of the dissolution environment is controlled at 10°C, the speed of the magnetic stirrer is 100 rpm, and the stirring time is 60 minutes.

[0041] Example 10: The method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solution in this example is exactly the same as that in Example 1 in terms of the formulation and preparation steps of the compound stabilizer. The remaining process parameters are the same as those in Example 1. The only difference is that in the stabilization control of step 2, the ultrasonic frequency of the ultrasonic cavitation device is set to 20kHz, and the straight-line distance between the transmitting end face of the ultrasonic transducer and the microporous atomizing nozzle is 5cm.

[0042] Example 11: The method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solution in this example is exactly the same as that in Example 1 in terms of the formulation and preparation steps of the compound stabilizer. The remaining process parameters are the same as those in Example 1. The only difference is that in the stabilization control of step 2, the ultrasonic frequency of the ultrasonic cavitation device is set to 40kHz, and the straight-line distance between the transmitting end face of the ultrasonic transducer and the microporous atomizing nozzle is 15cm.

[0043] Example 12: The method for stabilizing and controlling the effective chlorine content of sodium hypochlorite solution in this example is exactly the same as that in Example 1 in terms of the formulation and preparation steps of the compound stabilizer. The remaining process parameters are the same as those in Example 1. The only difference is that in the stabilization control of step 2, the controller outputs a start signal to the ultrasonic cavitation device after a 5-second delay when the metering peristaltic pump starts adding the solution. The ultrasonic running time is 1.2 times the addition time (i.e., 72 seconds).

[0044] Comparative Example 1: This comparative example is a control experiment lacking the core component. The remaining steps and parameters are the same as in Example 1. The only difference is that in the preparation of the compound stabilizer in step 1, no specific short peptide is added, and only a 0.3 mol / L sodium metasilicate aqueous solution with pH 12.0 is used as the stabilizer.

[0045] Comparative Example 2: This comparative example is a prior art control test, using the traditional stabilization process described in the background art, as follows: After the sodium hypochlorite solution is generated by electrolysis, it is cooled to 32°C by a heat exchanger and sent to a storage tank. A 0.3 mol / L EDTA-2Na aqueous solution with pH 12.0 is manually added to the storage tank. The amount added is the same as the volume of the compound stabilizer added in Example 1. After addition, the solution is mechanically stirred for 30 minutes to complete the stabilization treatment and stored under light-protected conditions. The initial conditions of the remaining sodium hypochlorite solutions are exactly the same as those in Example 1.

[0046] Comparative Example 3: This comparative example is a control experiment with parameters exceeding the specified range. The remaining steps and parameters are the same as in Example 1, except that in the preparation of the compound stabilizer in step 1, the pH value of the sodium metasilicate aqueous solution is adjusted to 10.0, which exceeds the range of 11.5-12.5 specified in this invention.

[0047] Comparative Example 4: This comparative example is a control experiment with missing key process steps. The remaining steps and parameters are the same as in Example 1. The only difference is that in the stabilization control of step 2, the ultrasonic cavitation treatment step is omitted, and only the addition process of the compound stabilizer is completed.

[0048] Test method: All tests were conducted under the same environmental conditions. The initial available chlorine content of all samples was 10.0% ± 0.2%, and the initial total free iron and copper ion concentration was 52 ± 3 ppb. After treatment, all samples were stored at 25°C in a light-proof and sealed environment. The specific detection methods are as follows: Determination of available chlorine content: The iodometric method was used, and the determination was carried out in accordance with the national standard GB19106-2013 "Sodium hypochlorite". The initial available chlorine content and the available chlorine content after 30 days of storage were tested separately. The 30-day available chlorine retention rate was calculated using the following formula: 30-day available chlorine retention rate (%) = (available chlorine content after 30 days of storage / initial available chlorine content) × 100%.

[0049] Determination of available chlorine half-life: The available chlorine content of the sample was measured every 5 days. The available chlorine degradation curve was fitted based on the first-order degradation kinetic model, and the time required for the available chlorine content to drop to 50% of the initial value was calculated, which is the available chlorine half-life.

[0050] Determination of chlorate byproduct content: Ion chromatography was used, with the optimized method referring to HJ778-2015 "Determination of Iodides in Water by Ion Chromatography", to determine the concentration of chlorate ions in the solution after 30 days of sample storage.

[0051] Determination of free metal ion concentration: Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the total concentration of free iron and copper ions in the sample after stabilization treatment.

[0052] Test results: The test results for all embodiments and comparative examples are shown in Table 1 below: Table 1. Test results of the stabilization effect of sodium hypochlorite solution

[0053] Results analysis: In all Examples 1-12 of this invention, the 30-day available chlorine retention rate reached over 88%, the available chlorine half-life exceeded 130 days, the 30-day chlorate content was below 220 mg / L, and the concentration of free metal ions after treatment was below 15 ppb, significantly better than all comparative examples. This demonstrates that the technical solution of this invention can efficiently mask trace amounts of free metal ions in the solution, completely block their catalytic effect on the decomposition of hypochlorite, significantly extend the available chlorine storage period of sodium hypochlorite solution, greatly reduce the generation of chlorate byproducts, and achieve stable control of the available chlorine content of sodium hypochlorite solution.

[0054] Comparative Example 1 lacked the core functional component of the present invention, the specific short peptide, and was treated only with sodium metasilicate buffer. Its 30-day effective chlorine retention rate was only 32.1%, and its effective chlorine half-life was only 22 days, showing a sharp decline compared with Example 1. After treatment, the concentration of free metal ions was still as high as 48 ppb, which was not significantly different from the initial concentration. This proves that the specific short peptide is the core substance for achieving metal ion chelation and masking and inhibiting catalytic decomposition, and is the key basis for the excellent stabilization effect of the technical solution of the present invention.

[0055] Comparative Example 2, using conventional EDTA chelating agents and manual addition processes, showed an effective chlorine retention rate of only 45.6% after 30 days and an effective chlorine half-life of only 35 days, far lower than Example 1 of this invention. Simultaneously, the chlorate byproduct content was as high as 950 mg / L, and the free metal ion concentration after treatment was 32 ppb. The core reason for its poor performance is that in the strongly oxidizing microenvironment of sodium hypochlorite, the carbon-nitrogen bonds of EDTA molecules are easily attacked by hypochlorite ions, leading to chain breakage and degradation. This causes the chelating agent to fail, and the previously complexed metal ions are released again, triggering secondary catalytic decomposition of sodium hypochlorite. Furthermore, manual addition cannot achieve dynamic and precise control based on the metal ion concentration, and cannot mask the metal ions before they trigger catalytic decomposition. This invention utilizes a specific short peptide that preferentially oxidizes the peptide bond backbone through the thiol group, avoiding the core defect of chelating agent degradation and failure. Combined with online closed-loop control, it achieves precise and timely masking of metal ions, solving a long-standing technical problem in existing technologies and achieving unexpected technical results.

[0056] Comparative Example 3 adjusted the pH of the sodium metasilicate aqueous solution to 10.0, which exceeds the 11.5-12.5 range specified in this invention. Its stabilization effect was significantly lower than that of Example 1. This is because: at pH values ​​below 11.5, hypochlorite ions readily undergo protonation to generate hypochlorous acid. The self-decomposition rate of hypochlorous acid is much higher than that of hypochlorite ions. Simultaneously, under low pH conditions, the thiol groups in short peptide molecules readily undergo protonation and oxidative dimerization, losing their coordination activity and failing to effectively chelate metal ions. This leads to the continuous occurrence of catalytic decomposition reactions, proving that the pH parameter range specified in this invention is a necessary condition for achieving excellent stabilization effects.

[0057] Comparative Example 4 omitted the key process step of ultrasonic cavitation treatment in this invention. Its 30-day effective chlorine retention rate decreased by 16.7 percentage points compared to Example 1, the effective chlorine half-life was shortened by 90 days, and the concentration of free metal ions increased to 18 ppb after treatment. The reason is that without the microjets and turbulence generated by ultrasonic cavitation, the microdroplets of the compound stabilizer could not achieve uniform dispersion throughout the system in a short time. The collision probability between short peptide molecules and free metal ions was significantly reduced, resulting in a slow chelation reaction rate and incomplete masking, failing to completely block the catalytic effect of metal ions. This proves that the ultrasonic cavitation step is an important component of the technical solution of this invention, which can significantly enhance the chelation masking effect and further improve the storage stability of sodium hypochlorite.

[0058] Examples 2-9, within the scope defined by this invention, adjusted the formulation and preparation parameters of the compound stabilizer, and all achieved excellent stabilization effects, proving that the compound stabilizer formulation of this invention has a wide range of applications and good process robustness; Examples 10-12, within the scope defined by this invention, adjusted the process parameters for stabilization control, and still maintained excellent technical effects, proving that the control method of this invention has good universality and industrial operability, and can be adapted to different industrial production conditions.

Claims

1. A method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution, characterized in that, The method includes: During the cooling stage of the sodium hypochlorite solution, the concentration signal of free trace metal ions in the sodium hypochlorite solution is acquired in real time by an online electrochemical sensor. The concentration signal of the free trace metal ions is transmitted to the input terminal of the controller, which has a preset metal ion concentration threshold. When the controller determines that the concentration signal of the free trace metal ions reaches the preset metal ion concentration threshold, the controller outputs a control command to the peristaltic pump actuator. After receiving the control command, the peristaltic pump actuator adds a compound stabilizer to the sodium hypochlorite solution. The compound stabilizer is prepared by mixing a specific short peptide with the amino acid sequence of cysteine-histidine-histidine-cysteine ​​with an aqueous solution of sodium metasilicate. The mass fraction of the specific short peptide in the compound stabilizer accounts for 0.5% to 2.0% of the total mass of the compound stabilizer. The pH value of the sodium metasilicate aqueous solution is adjusted to 11.5 to 12.

5. After adding the compound stabilizer, the ultrasonic cavitation device electrically connected to the controller is activated to perform short-term ultrasonic cavitation treatment on the sodium hypochlorite solution.

2. The method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution according to claim 1, characterized in that, The specific short peptide was prepared by solid-phase synthesis. In preparing the compound stabilizer, the specific short peptide is dissolved in the sodium metasilicate aqueous solution.

3. The method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution according to claim 2, characterized in that, The molar concentration of the sodium metasilicate aqueous solution is from 0.1 mol / L to 0.5 mol / L; During the process of dissolving the specific short peptide in the sodium metasilicate aqueous solution, the temperature of the dissolution environment is controlled at 4°C to 10°C, and a magnetic stirrer is used to continuously stir at a speed of 50 to 100 revolutions per minute for 30 to 60 minutes until a homogeneous compound stabilizer is formed.

4. The method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution according to claim 1, characterized in that, The online electrochemical sensor includes a working electrode, a counter electrode, and a reference electrode. The working electrode is a glassy carbon electrode with a polypyrrole film modified on its surface. The online electrochemical sensor is installed in the overflow bypass of the sodium hypochlorite solution cooling tank. The overflow bypass is equipped with a thermostatic jacket, and cooling water is circulated in the thermostatic jacket to maintain the temperature of the sodium hypochlorite solution in the overflow bypass at a constant 20°C to 25°C.

5. The method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution according to claim 1, characterized in that, The controller has a built-in proportional-integral-differential algorithm module, and the preset metal ion concentration threshold includes an upper limit threshold and a lower limit threshold. When the concentration signal of the free trace metal ions continues to rise and reaches the upper limit threshold, the controller calculates the addition time through the proportional-integral-derivative algorithm module and outputs a pulse signal with the corresponding duty cycle to the peristaltic pump actuator to control the addition amount of the compound stabilizer.

6. The method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution according to claim 5, characterized in that, The peristaltic pump actuator includes a metering peristaltic pump and a dosing pipeline extending below the surface of the sodium hypochlorite solution, with a microporous atomizing nozzle at the end of the dosing pipeline; When the peristaltic pump actuator responds to the pulse signal, the metering peristaltic pump operates in step mode, dispersing the compound stabilizer into the sodium hypochlorite solution in the form of microdroplets through the microporous atomizing nozzle. The particle size of the microdroplets is 10 micrometers to 50 micrometers.

7. The method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution according to claim 6, characterized in that, The ultrasonic cavitation device includes an ultrasonic transducer array fixed to the inner wall of a sodium hypochlorite solution cooling tank, and the ultrasonic transducer array is electrically connected to the controller. The ultrasonic frequency of the short-time ultrasonic cavitation treatment is set to 20kHz to 40kHz, and the straight-line distance between the emitting end face of the ultrasonic cavitation device and the microporous atomizing nozzle of the dosing pipeline is maintained within the range of 5cm to 15cm.

8. The method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution according to claim 7, characterized in that, While the peristaltic pump actuator starts to add the compound stabilizer, the controller outputs a start signal to the ultrasonic cavitation device after a delay of 5 to 10 seconds. The operating time of the ultrasonic cavitation device is dynamically set by the controller based on the total injection time of the peristaltic pump actuator. The operating time of the ultrasonic cavitation device is 1.2 to 1.5 times the total injection time of the peristaltic pump actuator.

9. The method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution according to claim 1, characterized in that, A redox potential sensor is connected in parallel with the online electrochemical sensor, and the signal output terminal of the redox potential sensor is connected to another input terminal of the controller. The controller has a two-dimensional mapping table of metal ion concentration and redox potential pre-stored in it. After receiving the free state trace metal ion concentration signal and the potential signal of the redox potential sensor, the controller checks the two-dimensional mapping table to confirm whether the triggering condition for adding the compound stabilizer is met.

10. The method for stabilizing and controlling the available chlorine content of sodium hypochlorite solution according to claim 1, characterized in that, The cooling stage of the sodium hypochlorite solution is the process of the sodium hypochlorite solution entering the heat exchanger after being generated by electrolysis and then being cooled down. The initial temperature of the sodium hypochlorite solution entering the heat exchanger is 75°C to 85°C, and the final temperature of the sodium hypochlorite solution flowing out of the heat exchanger is 30°C to 35°C. The online electrochemical sensor, the peristaltic pump actuator, and the ultrasonic cavitation device are all located on the outlet pipe of the heat exchanger.

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