High-quality potassium hydroxide refining and impurity removing process

Abstract

The invention provides a high-quality potassium hydroxide refining and impurity removal process, belongs to the field of potassium hydroxide impurity removal, and aims to overcome the defect that the purity of a potassium hydroxide product is reduced due to defects in removal precision and process stability during potassium hydroxide impurity removal in the prior art. The method comprises the following steps: carrying out oxidation decomposition on organic matters and precipitating calcium and magnesium ions, carrying out coarse filtration to remove large-particle impurities, carrying out graded filtration by adopting a three-stage series inorganic membrane module, carrying out efficient interception on impurities with different particle sizes by accurately controlling the pressure, temperature and flow rate of each membrane layer, and carrying out hydrochloric acid neutralization and potassium sulfite dechlorination to optimize the indexes of the brine. And finally, trace calcium and magnesium ions are deeply removed by utilizing the selective adsorption characteristics of the chelate resin and the strong acid cation resin, and after the resin is saturated, the resin is eluted, regenerated and recycled through acid and alkali with specific concentration, so that the impurity removal effect of potassium hydroxide is improved.

Description

Technical Field

[0001] The invention relates to the technical field of potassium hydroxide impurity removal, in particular to a process for refining and removing impurities from high-quality potassium hydroxide. Background Art

[0002] When potassium hydroxide is used to remove impurities from saturated crude brine obtained by dissolving solid potassium chloride, multiple processes are coordinated through the addition of composite refining agents for chemical precipitation, coarse filtration to intercept large particles of impurities, three-stage series inorganic membrane cross-flow filtration to remove micron-sized particles, and ion exchange resin to adsorb trace calcium and magnesium ions. These processes can remove organic matter, calcium and magnesium ions, and mechanical impurities from the brine, so that the brine purity meets the requirements of ion membrane electrolysis, forming a process to ensure the high quality of potassium hydroxide products.

[0003] Chinese patent application number CN103274550A discloses a method for removing impurities from brine during sodium chlorate production. When crude brine is used as the raw material for sodium chlorate production, this method includes three steps: chemical removal, ion exchange, and microfiltration. When brine or seawater is used as the raw material for sodium chlorate production, this method includes five steps: microfiltration, reverse osmosis concentration, chemical removal, ion exchange, and microfiltration. This method reduces the total calcium and magnesium ion content of the brine to less than 0.5 mg / L, which helps mitigate corrosion of the electrolytic cell anode, reduces power consumption, extends the tank cleaning cycle, and improves production efficiency.

[0004] The above patent is in operation, but the existing potassium hydroxide impurity removal process has defects in impurity removal accuracy and process stability. Most traditional processes rely on a single chemical precipitation method, which makes it difficult to reduce the concentration of calcium and magnesium ions to below 20ppb required for ion membrane electrolysis. In addition, the precipitation process is easily affected by temperature and pH fluctuations, making the removal efficiency unstable, which ultimately leads to the problem of reduced purity of the potassium hydroxide product.

[0005] To this end, we proposed a high-quality potassium hydroxide refining and impurity removal process. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defect in the prior art that the purity of the potassium hydroxide product is reduced due to defects in removal accuracy and process stability during potassium hydroxide impurity removal. The present invention proposes a high-quality potassium hydroxide refining and impurity removal process, which solves the problem in the background technology.

[0007] In order to solve the above technical problems, the present invention adopts a technical solution: a high-quality potassium hydroxide refining and impurity removal process, comprising the following steps:

[0008] S1: First, potassium hypochlorite, potassium carbonate, and potassium hydroxide composite refining agent are added sequentially to the saturated crude brine inside the reaction tank, wherein potassium hypochlorite oxidizes and decomposes organic matter, potassium carbonate reacts with calcium ions to form calcium carbonate crystal precipitation, and potassium hydroxide reacts with magnesium ions to form magnesium hydroxide colloidal precipitation. By controlling the reaction temperature of the liquid at 50°C-60°C and pH 11.0-12.0, and then controlling the precipitation residence time at 60-90 minutes during liquid precipitation, the preliminary removal of organic matter and calcium and magnesium ions is achieved, creating conditions for subsequent filtration;

[0009] S2: The crude brine that has completed the refining reaction flows into the intermediate tank by gravity. The membrane filtration feed pump is used to intercept mechanical impurities larger than 1.0 mm through the coarse filter and then sent to the inorganic membrane filtration unit. This reduces the risk of mechanical damage to the subsequent membrane filtration unit and ensures that the particle size of the feed impurities meets the tolerance range of the membrane module.

[0010] S3: The pretreated brine adopts a three-stage series cross-flow filtration process. The crude brine is transported to the circulation pump through the feed pump, and then pressurized by the circulation pump and sent to the membrane filtration system for graded filtration. Subsequently, part of the concentrated brine after filtration is discharged proportionally into the salt mud pool, and the rest returns to the inlet of the membrane filtration circulation pump and is mixed with the crude brine sent by the feed pump to adjust the solid-liquid ratio of the feed liquid, thereby controlling the solid content of the concentrated liquid and ensuring the flow rate on the membrane surface. The brine is then returned to the inorganic membrane filter through the membrane filtration circulation pump for circulation filtration, improving filtration stability and efficiency, and reducing the turbidity of the brine.

[0011] S4: The pH value of hydrochloric acid is then adjusted to 9.0-9.5 and added to the brine flowing out of the inorganic membrane filtration unit to neutralize excess alkalinity and optimize the subsequent ion exchange environment. Potassium sulfite is then added to remove residual free chlorine through chemical reaction before entering the primary brine tank to ensure that all brine indicators meet the feed requirements of the ion exchange resin tower;

[0012] S5: Finally, the initially treated brine is preheated by the brine heater and flows into the ion exchange resin tower. The resin functional groups utilize the selective adsorption characteristics of calcium and magnesium ions to further remove trace multivalent cations, thereby reducing the calcium and magnesium ion content in the secondary refined brine, ultimately meeting the brine purity requirements of the ion membrane electrolysis process and ensuring the high quality of potassium hydroxide products.

[0013] Furthermore, the amount of potassium hypochlorite added in S1 is 50g / ton-80g / ton of crude brine, with an effective chlorine content of ≥10%, and is used to oxidize and decompose organic matter, so that the total removal rate of carbon elements contained in organic pollutants in the liquid is ≥90%;

[0014] The amount of potassium carbonate added is 2.5kg / ton-3.0kg / ton of crude brine, with an excess of 10% to remove calcium ions. The reaction generates CaCO3 precipitation, reducing the calcium ion concentration from 400ppm-600ppm to 10ppm-15ppm;

[0015] The amount of potassium hydroxide added is 3.5kg / ton-4.0kg / ton of crude brine, with an excess of 15% to remove magnesium ions. The reaction generates magnesium hydroxide colloid, reducing the magnesium ion concentration from 250ppm-350ppm to 5ppm-8ppm.

[0016] Furthermore, the pore size of the coarse filter used in S2 is 1.0 mm, and the filtration flow rate is 1.5 m / s-2.0 m / s, so that the impurity removal rate is greater than 95%, and the pressure difference between the inlet and outlet of the coarse filter is less than 0.05 MPa, ensuring that the inorganic membrane filtration unit feed is not damaged by large particles.

[0017] Furthermore, a three-stage series inorganic membrane assembly is used in S3, which is a first-stage 5μm alumina ceramic membrane, a second-stage 1μm titanium filter membrane, and a third-stage 0.1μm zirconium oxide membrane. When the first-stage alumina ceramic membrane is filtering, the equipment controls the operating pressure to be 0.15MPa-0.2MPa, and the brine solution temperature is maintained at 50℃-60℃. This temperature helps to reduce the viscosity of the solution and improve the filtration efficiency. The liquid flows parallel to the membrane surface at a cross-flow speed of 2.0m / s-2.5m / s, and the fluid shear force is used to reduce the deposition of impurities on the membrane surface. Under this condition, the retention rate of impurities with a particle size greater than 5μm is ≥99%.

[0018] Furthermore, when the secondary titanium filter membrane is filtering, the equipment adjusts the operating pressure to 0.2MPa-0.25MPa, maintains the brine temperature at 50℃-60℃ to continue the high-efficiency filtration state, and increases the liquid cross-flow speed to 2.5m / s-3.0m / s to enhance the flushing effect on tiny particles. At this stage, the retention rate of impurities with a particle size of 1-5μm is ≥98%.

[0019] Furthermore, when the tertiary zirconia membrane is filtering, the equipment further sets the operating pressure to 0.25MPa-0.3MPa, the brine temperature is stabilized at 50℃-60℃, and the liquid passes through the membrane surface at a high-speed cross-flow of 3.0m / s-3.5m / s, ensuring efficient retention of 0.1μm-1μm impurities. During this process, the retention rate of impurities with a particle size of 0.1μm-1μm is ≥95%.

[0020] Furthermore, in the inorganic membrane filtration link of step S3, the solid-liquid ratio and flow rate are adjusted through the concentrated liquid circulation system to adjust the reflux volume of the tertiary concentrated liquid, and the feed solid-liquid ratio is stably controlled at 1:8-1:10. Specifically, the fluctuation of the feed solid-liquid ratio is detected online, and the circulation ratio is automatically adjusted to achieve dynamic balance. The flow rate control is based on the grading characteristics of the primary ceramic membrane, the secondary titanium filter membrane, and the tertiary zirconium oxide membrane, and is linked to the variable frequency pump through the pressure sensor. When the pressure on the membrane surface of each level approaches the threshold, the flow rate is automatically increased by 0.1m / s-0.2m / s to enhance scouring, ensuring that the membrane flux decrease rate is ≤1.5% / h and the daily increase in the transmembrane pressure difference is ≤0.005MPa, while maintaining the salt recovery rate ≥95%.

[0021] Furthermore, the ion exchange resin tower in S5 adopts resin functional groups for adsorption, and the resin functional groups are divided into chelating resin and strong acid cation resin. The selectivity coefficient of chelating resin for calcium ions is 1200-1500, and the selectivity coefficient of magnesium ions is 800-1000. The dynamic adsorption capacity is 200mmol / L-250mmol / L and 150mmol / L-200mmol / L respectively, which is suitable for pH 6-10 environment, so chelating resin is selected to adsorb calcium ions.

[0022] Furthermore, the strong acid cationic resin has a selectivity coefficient of 800-900 for calcium ions and a selectivity coefficient of 600-700 for magnesium ions, and adsorption capacities of 180 mmol / L-220 mmol / L and 130 mmol / L-170 mmol / L, respectively, and is suitable for a pH 5-12 environment. Therefore, the strong acid cationic resin is selected for adsorption treatment of magnesium ions.

[0023] Furthermore, when the adsorption capacity of the resin functional groups is saturated, 31% hydrochloric acid is used to elute calcium ions, while 32% potassium hydroxide is used to elute magnesium ions. The hydrochloric acid concentration of the reagent is controlled at 5%-8%, and the potassium hydroxide concentration is controlled at 4%-6%. The cleaned resin functional groups are then regenerated and put back into use to restore the adsorption capacity for calcium and magnesium ions.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention proposes a high-quality potassium hydroxide refining and impurity removal process. A composite refining agent of potassium hypochlorite, potassium carbonate, and potassium hydroxide is first added to saturated crude brine to oxidatively decompose organic matter and precipitate calcium and magnesium ions. After the crude brine passes through a coarse filter to intercept large particles of impurities, it is then subjected to cross-flow filtration through a three-stage series-connected inorganic membrane assembly to remove impurities of varying particle sizes step by step. Hydrochloric acid is then used to neutralize alkalinity, and potassium sulfite is used to remove residual chlorine. Finally, the brine is passed through an ion exchange resin tower, where chelating resin and strong acid cationic resin are used to adsorb calcium and magnesium ions, respectively. Once the resin is saturated, it undergoes acid-base elution and regeneration. These multiple steps work together to ensure that the brine purity meets the requirements of ion-exchange membrane electrolysis, thereby enhancing the potassium hydroxide impurity removal effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The disclosure of the present 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 the present invention. In the accompanying drawings, the same reference numerals are used to refer to the same components. Among them:

[0027] Figure 1 The figure schematically shows a process flow diagram proposed according to one embodiment of the present invention. DETAILED DESCRIPTION

[0028] It is easy to understand that according to the technical solution of the present invention, without changing the essential spirit of the present invention, a person skilled in the art can propose a variety of interchangeable structural modes and implementation modes. Therefore, the following specific embodiments and drawings are only exemplary descriptions of the technical solution of the present invention and should not be regarded as the entire invention or as a limitation or restriction of the technical solution of the present invention.

[0029] Example 1

[0030] like Figure 1 As shown, the following preferred technical solution is provided: a high-quality potassium hydroxide refining and impurity removal process, comprising the following steps:

[0031] S1: First, potassium hypochlorite, potassium carbonate, and potassium hydroxide composite refining agent are added sequentially to the saturated crude brine inside the reaction tank, wherein potassium hypochlorite oxidizes and decomposes organic matter, potassium carbonate reacts with calcium ions to form calcium carbonate crystal precipitation, and potassium hydroxide reacts with magnesium ions to form magnesium hydroxide colloidal precipitation. By controlling the reaction temperature of the liquid at 50°C-60°C and pH 11.0-12.0, and then controlling the precipitation residence time at 60-90 minutes during liquid precipitation, the preliminary removal of organic matter and calcium and magnesium ions is achieved, creating conditions for subsequent filtration;

[0032] S2: The crude brine that has completed the refining reaction flows into the intermediate tank by gravity. The membrane filtration feed pump is used to intercept mechanical impurities larger than 1.0 mm through the coarse filter and then sent to the inorganic membrane filtration unit. This reduces the risk of mechanical damage to the subsequent membrane filtration unit and ensures that the particle size of the feed impurities meets the tolerance range of the membrane module.

[0033] S3: The pretreated brine adopts a three-stage series cross-flow filtration process. The crude brine is transported to the circulation pump through the feed pump, and then pressurized by the circulation pump and sent to the membrane filtration system for graded filtration. Subsequently, part of the concentrated brine after filtration is discharged proportionally into the salt mud pool, and the rest returns to the inlet of the membrane filtration circulation pump and is mixed with the crude brine sent by the feed pump to adjust the solid-liquid ratio of the feed liquid, thereby controlling the solid content of the concentrated liquid and ensuring the flow rate on the membrane surface. The brine is then returned to the inorganic membrane filter through the membrane filtration circulation pump for circulation filtration, improving filtration stability and efficiency, and reducing the turbidity of the brine.

[0034] S4: The pH value of hydrochloric acid is then adjusted to 9.0-9.5 and added to the brine flowing out of the inorganic membrane filtration unit to neutralize excess alkalinity and optimize the subsequent ion exchange environment. Potassium sulfite is then added to remove residual free chlorine through chemical reaction before entering the primary brine tank to ensure that all brine indicators meet the feed requirements of the ion exchange resin tower;

[0035] S5: Finally, the initially treated brine is preheated by the brine heater and flows into the ion exchange resin tower. The resin functional groups utilize the selective adsorption characteristics of calcium and magnesium ions to further remove trace multivalent cations, thereby reducing the calcium and magnesium ion content in the secondary refined brine, ultimately meeting the brine purity requirements of the ion membrane electrolysis process and ensuring the high quality of potassium hydroxide products.

[0036] The amount of potassium hypochlorite added to S1 is 50g / ton-80g / ton of crude brine, with an effective chlorine content of ≥10%, and is used to oxidize and decompose organic matter, so that the total removal rate of carbon elements contained in organic pollutants in the liquid is ≥90%;

[0037] The amount of potassium carbonate added is 2.5kg / ton-3.0kg / ton of crude brine, with an excess of 10% to remove calcium ions. The reaction generates CaCO3 precipitation, reducing the calcium ion concentration from 400ppm-600ppm to 10ppm-15ppm;

[0038] The amount of potassium hydroxide added is 3.5kg / ton-4.0kg / ton of crude brine, with an excess of 15% to remove magnesium ions. The reaction generates magnesium hydroxide colloid, which reduces the magnesium ion concentration from 250ppm-350ppm to 5ppm-8ppm. Through the addition amount, excess ratio and effective ingredient requirements of potassium hypochlorite, potassium carbonate and potassium hydroxide, the effect of each agent in removing organic matter, calcium ions and magnesium ions is accurately quantified, laying the foundation for the subsequent impurity removal process.

[0039] The pore size of the coarse filter used in S2 is 1.0mm, and the filtration flow rate is 1.5m / s-2.0m / s, so that the impurity removal rate is greater than 95%, and the pressure difference between the inlet and outlet of the coarse filter is less than 0.05MPa, ensuring that the inorganic membrane filtration unit feed is not damaged by large particles. Large particle impurities are intercepted by the coarse filter to prevent them from damaging subsequent inorganic membrane filtration units, thereby ensuring process continuity and stability.

[0040] S3 uses a three-stage series inorganic membrane assembly, which is a first-stage 5μm alumina ceramic membrane, a second-stage 1μm titanium filter membrane, and a third-stage 0.1μm zirconium oxide membrane. When filtering the first-stage alumina ceramic membrane, the equipment controls the operating pressure to 0.15MPa-0.2MPa, and the brine solution temperature is maintained at 50℃-60℃. This temperature helps to reduce the solution viscosity and improve the filtration efficiency. The liquid flows parallel to the membrane surface at a cross-flow speed of 2.0m / s-2.5m / s, and the fluid shear force is used to reduce the deposition of impurities on the membrane surface. Under this condition, the retention rate of impurities with a particle size greater than 5μm is ≥99%. By adopting a graded cross-flow filtration process, through the synergistic effect of membrane assemblies of different materials and the optimized control of temperature, pressure, and flow rate, the filtration efficiency is improved and the deposition on the membrane surface is reduced, thereby achieving efficient retention of impurities of different particle sizes.

[0041] When the secondary titanium filter membrane is filtering, the equipment adjusts the operating pressure to 0.2MPa-0.25MPa, maintains the brine temperature at 50℃-60℃ to maintain high-efficiency filtration, and increases the liquid cross-flow velocity to 2.5m / s-3.0m / s to enhance the flushing effect on tiny particles. At this stage, the retention rate of impurities with a particle size of 1-5μm is ≥98%. By optimizing the operating pressure, maintaining a specific temperature and increasing the cross-flow velocity through the secondary titanium filter membrane, the flushing and retention effects on tiny particles are enhanced to ensure filtration accuracy.

[0042] During filtration, the tertiary zirconia membrane sets the operating pressure to 0.25MPa-0.3MPa, stabilizes the brine temperature at 50℃-60℃, and the liquid cross-flows through the membrane surface at a high speed of 3.0m / s-3.5m / s, ensuring efficient retention of 0.1μm-1μm impurities. During this process, the retention rate of impurities with a particle size of 0.1μm-1μm is ≥95%. The tertiary zirconia membrane increases the pressure, stabilizes the temperature, and accelerates the cross-flow speed of the liquid on the membrane surface. By utilizing the enhanced flushing force, the interception of tiny particle impurities is strengthened, thereby further improving the accuracy of brine filtration.

[0043] In the inorganic membrane filtration link of step S3, the solid-liquid ratio and flow rate are adjusted through the concentrated liquid circulation system to adjust the reflux volume of the tertiary concentrated liquid, and the feed solid-liquid ratio is stably controlled at 1:8-1:10. Specifically, the fluctuation of the feed solid-liquid ratio is detected online, and the circulation ratio is automatically adjusted to achieve dynamic balance. The flow rate control is based on the grading characteristics of the first-level ceramic membrane, the second-level titanium filter membrane, and the third-level zirconia membrane, and is linked to the frequency conversion pump through the pressure sensor. When the pressure on the membrane surface of each level approaches the threshold, the flow rate is automatically increased by 0.1m / s-0.2m / s to enhance scouring, ensuring that the membrane flux decrease rate is ≤1.5% / h and the daily increase in transmembrane pressure difference is ≤0.005MPa, while maintaining a salt recovery rate of ≥95%. The solid-liquid ratio and flow rate are dynamically adjusted through the concentrated liquid circulation system in the inorganic membrane filtration link, and the pressure sensor and frequency conversion control are linked based on the grading characteristics of the membrane components to achieve dual guarantees of impurity retention and stable membrane performance, while maintaining a high salt recovery rate.

[0044] The ion exchange resin tower in S5 uses resin functional groups for adsorption, and the resin functional groups are divided into chelating resins and strong acid cation resins. The selectivity coefficient of chelating resin for calcium ions is 1200-1500, and the selectivity coefficient of magnesium ions is 800-1000. The dynamic adsorption capacity is 200mmol / L-250mmol / L and 150mmol / L-200mmol / L respectively, which are suitable for pH 6-10 environment. Therefore, chelating resin is selected to adsorb calcium ions. Through the high selective adsorption characteristics of chelating resin for calcium ions and the adaptation to pH environment, the trace calcium ions in the brine can be accurately removed, thereby improving the purity of the brine.

[0045] The selectivity coefficient of strong acid cationic resin for calcium ions is 800-900, and the selectivity coefficient of magnesium ions is 600-700. The adsorption capacity is 180mmol / L-220mmol / L and 130mmol / L-170mmol / L respectively, which is suitable for pH 5-12 environment. Therefore, strong acid cationic resin is selected to adsorb magnesium ions. The selective adsorption capacity and wide pH adaptability of strong acid cationic resin for magnesium ions can be used to achieve efficient removal of trace magnesium ions in brine and ensure the brine refining effect.

[0046] When the adsorption capacity of the resin functional groups is saturated, 31% hydrochloric acid is used to elute calcium ions, while 32% potassium hydroxide is used to elute magnesium ions. The hydrochloric acid concentration of the reagent should be controlled at 5%-8%, and the potassium hydroxide concentration should be controlled at 4%-6%. The cleaned resin functional groups are then regenerated and put back into use to restore the adsorption capacity for calcium and magnesium ions. The calcium and magnesium ions on the saturated resin functional groups are respectively eluted with hydrochloric acid and potassium hydroxide of specific concentrations. After regeneration, the adsorption performance for calcium and magnesium ions is restored, thereby realizing the recycling of the resin.

[0047] Specifically, potassium hypochlorite, potassium carbonate, and potassium hydroxide composite refining agent are first added to the saturated crude brine in the reaction tank in sequence, wherein potassium hypochlorite can decompose organic matter in the brine, so that the total removal rate of carbon elements contained in organic pollutants in the liquid reaches ≥90%, and 10% excess potassium carbonate will react with calcium ions to generate calcium carbonate crystals and precipitate, at which time the calcium ion concentration will drop from 400ppm-600ppm to 10ppm-15ppm, and 15% excess potassium hydroxide will react with magnesium ions to form magnesium hydroxide colloidal precipitation, so that the magnesium ion concentration drops from 250ppm-350ppm to 5ppm-8ppm, and finally the temperature of the liquid reaction is controlled at 50℃-60℃ and pH The value is 11.0-12.0, and the liquid precipitation time is controlled at 60-90 minutes to complete the preliminary removal of organic matter and calcium and magnesium ions. Then, the crude brine that has completed the refining reaction flows into the intermediate pool by gravity. At this time, after the membrane filtration feed pump is started, the crude brine in the intermediate pool is pressurized and transported to the coarse filter. Since the pore size of the coarse filter is fixed at 1.0mm, mechanical impurities larger than 1.0mm in the liquid cannot pass through the filter pores and can only be intercepted on the filter surface, thereby achieving the retention of large particles of mechanical impurities. The liquid flow rate during filtration is 1.5m / s-2.0m / s. Under this flow rate condition, the brine can pass through the filter more evenly and stably, ensuring that the impurities are fully in contact with the filter and are intercepted. This filtration method can maximize the impurity removal rate. After the brine is above 95%, it will enter the three-stage series inorganic membrane assembly and pass through the first-stage 5μm alumina ceramic membrane, the second-stage 1μm titanium filter membrane, and the third-stage 0.1μm zirconium oxide membrane in sequence for filtration. When the liquid enters the surface of the first-stage 5μm alumina ceramic membrane for filtration, the brine flows through the membrane surface in parallel at a cross-flow speed of 2.0m / s-2.5m / s under the operating pressure of 0.15MPa-0.2MPa and the temperature of 50℃-60℃, achieving a retention rate of ≥99% for impurities with a particle size greater than 5μm. Subsequently, when the liquid enters the surface of the second-stage 1μm titanium filter membrane, the pressure of the brine is adjusted to 0.2MPa-0.25MPa, the temperature is maintained at 50℃-60℃, and the cross-flow speed is increased to 2.5m / s-3.0m / s. The system achieves a ≥98% retention rate for impurities with a particle size of 1-5μm. Finally, when the liquid enters the surface of the third-stage 0.1μm zirconia membrane, the brine flows through the membrane at a high speed of 3.0m / s-3.5m / s under pressure of 0.25MPa-0.3MPa and temperature of 50°C-60°C, achieving a high efficiency retention of ≥95% for impurities with a particle size of 0.1-1μm. During this process, the concentrate circulation system regulates the return flow of the third-stage concentrate to maintain a stable feed solid-liquid ratio of 1:8-1:10. Based on the membrane's grading characteristics, a pressure sensor and variable frequency pump are linked to dynamically adjust the flow rate to ensure stable membrane flux and transmembrane pressure differential, while maintaining a salt recovery rate of ≥95%. The pH value of the hydrochloric acid is then adjusted to 9.0-9.5 is then added to the filtered brine to neutralize excess alkalinity. Potassium sulfite is then added to remove residual free chlorine. The treated brine then enters the primary brine tank. After being preheated in a brine heater, it flows into the ion exchange resin tower, where the chelating resin adsorbs calcium ions, while the strong acid cation resin adsorbs magnesium ions, further removing trace polyvalent cations. When the chelating resin and strong acid cation resin reach saturation, the calcium ions are eluted with 31% hydrochloric acid, while the magnesium ions are simultaneously eluted with 32% potassium hydroxide. The resin is then regenerated and put back into use. This significantly reduces the calcium and magnesium ion contents in the secondary refined brine, meeting the brine purity requirements of the ion membrane electrolysis process and improving the potassium hydroxide's impurity removal effectiveness.

[0048] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A high-quality potassium hydroxide refining and impurity removal process, characterized in that: The following steps are involved: S1: First, potassium hypochlorite, potassium carbonate, and potassium hydroxide composite refining agent are added sequentially to the saturated crude brine inside the reaction tank, wherein potassium hypochlorite oxidizes and decomposes organic matter, potassium carbonate reacts with calcium ions to form calcium carbonate crystal precipitation, and potassium hydroxide reacts with magnesium ions to form magnesium hydroxide colloidal precipitation. By controlling the reaction temperature of the liquid at 50°C-60°C and pH 11.0-12.0, and then controlling the precipitation residence time at 60-90 minutes during liquid precipitation, the preliminary removal of organic matter and calcium and magnesium ions is achieved, creating conditions for subsequent filtration; S2: The crude brine that has completed the refining reaction flows into the intermediate tank by gravity. The membrane filtration feed pump is used to intercept mechanical impurities larger than 1.0 mm through the coarse filter and then sent to the inorganic membrane filtration unit. This reduces the risk of mechanical damage to the subsequent membrane filtration unit and ensures that the particle size of the feed impurities meets the tolerance range of the membrane module. S3: The pretreated brine adopts a three-stage series cross-flow filtration process. The crude brine is transported to the circulation pump through the feed pump, and then pressurized by the circulation pump and sent to the membrane filtration system for graded filtration. Subsequently, part of the concentrated brine after filtration is discharged proportionally into the salt mud pool, and the rest returns to the inlet of the membrane filtration circulation pump and is mixed with the crude brine sent by the feed pump to adjust the solid-liquid ratio of the feed liquid, thereby controlling the solid content of the concentrated liquid and ensuring the flow rate on the membrane surface. The brine is then returned to the inorganic membrane filter through the membrane filtration circulation pump for circulation filtration, improving filtration stability and efficiency, and reducing the turbidity of the brine. S4: The pH value of hydrochloric acid is then adjusted to 9.0-9.5 and added to the brine flowing out of the inorganic membrane filtration unit to neutralize excess alkalinity and optimize the subsequent ion exchange environment. Potassium sulfite is then added to remove residual free chlorine through chemical reaction before entering the primary brine tank to ensure that all brine indicators meet the feed requirements of the ion exchange resin tower; S5: Finally, the initially treated brine is preheated by the brine heater and flows into the ion exchange resin tower. The resin functional groups utilize the selective adsorption characteristics of calcium and magnesium ions to further remove trace multivalent cations, thereby reducing the calcium and magnesium ion content in the secondary refined brine, ultimately meeting the brine purity requirements of the ion membrane electrolysis process and ensuring the high quality of potassium hydroxide products.

2. The high-quality potassium hydroxide refining and impurity-removing process according to claim 1, wherein: The amount of potassium hypochlorite added in S1 is 50g-80g / ton of crude brine, with an effective chlorine content of ≥10%, which is used to oxidize and decompose organic matter, so that the total removal rate of carbon elements contained in organic pollutants in the liquid is ≥90%; The amount of potassium carbonate added is 2.5kg / ton-3.0kg / ton of crude brine, with an excess of 10% to remove calcium ions. The reaction generates CaCO3 precipitation, reducing the calcium ion concentration from 400ppm-600ppm to 10ppm-15ppm; The amount of potassium hydroxide added is 3.5kg / ton-4.0kg / ton of crude brine, with an excess of 15% to remove magnesium ions. The reaction generates magnesium hydroxide colloid, reducing the magnesium ion concentration from 250ppm-350ppm to 5ppm-8ppm.

3. The high-quality potassium hydroxide refining and impurity-removing process according to claim 1, wherein: The pore size of the coarse filter used in S2 is 1.0 mm, and the filtration flow rate is 1.5 m / s-2.0 m / s, so that the impurity removal rate is greater than 95%, and the pressure difference between the inlet and outlet of the coarse filter is less than 0.05 MPa, ensuring that the inorganic membrane filtration unit feed is not damaged by large particles.

4. The high-quality potassium hydroxide refining and impurity-removing process according to claim 1, wherein: The S3 uses a three-stage series inorganic membrane assembly, which is a first-stage 5μm alumina ceramic membrane, a second-stage 1μm titanium filter membrane, and a third-stage 0.1μm zirconium oxide membrane. When the first-stage alumina ceramic membrane is filtering, the equipment controls the operating pressure to be 0.15MPa-0.2MPa, and the brine solution temperature is maintained at 50°C-60°C. This temperature helps to reduce the solution viscosity and improve the filtration efficiency. The liquid flows parallel to the membrane surface at a cross-flow speed of 2.0m / s-2.5m / s, and the fluid shear force is used to reduce the deposition of impurities on the membrane surface. Under these conditions, the retention rate of impurities with a particle size greater than 5μm is ≥99%.

5. The high-quality potassium hydroxide refining and impurity-removing process according to claim 4, wherein: When the secondary titanium filter membrane is filtering, the equipment adjusts the operating pressure to 0.2MPa-0.25MPa, maintains the brine temperature at 50℃-60℃ to maintain high-efficiency filtration, and increases the liquid cross-flow speed to 2.5m / s-3.0m / s to enhance the flushing effect on tiny particles. At this stage, the retention rate of impurities with a particle size of 1-5μm is ≥98%.

6. The high-quality potassium hydroxide refining and impurity-removing process according to claim 5, wherein: During filtration, the three-stage zirconia membrane further sets the operating pressure to 0.25MPa-0.3MPa, the brine temperature is stabilized at 50°C-60°C, and the liquid passes through the membrane surface at a high-speed cross-flow of 3.0m / s-3.5m / s, ensuring efficient retention of impurities in the 0.1μm-1μm range. During this process, the retention rate of impurities with a particle size of 0.1μm-1μm is ≥95%.

7. The high-quality potassium hydroxide refining and impurity-removing process according to claim 6, wherein: In the inorganic membrane filtration link of step S3, the solid-liquid ratio and flow rate are adjusted through the concentrated liquid circulation system to adjust the reflux volume of the tertiary concentrated liquid, and the feed solid-liquid ratio is stably controlled at 1:8-1:

10. Specifically, the fluctuation of the feed solid-liquid ratio is detected online, and the circulation ratio is automatically adjusted to achieve dynamic balance. The flow rate control is based on the grading characteristics of the primary ceramic membrane, the secondary titanium filter membrane, and the tertiary zirconium oxide membrane, and is linked to the frequency conversion pump through the pressure sensor. When the pressure on the membrane surface of each level approaches the threshold, the flow rate is automatically increased by 0.1m / s-0.2m / s to enhance scouring, ensuring that the membrane flux decrease rate is ≤1.5% / h and the daily increase in the transmembrane pressure difference is ≤0.005MPa, while maintaining the salt recovery rate ≥95%.

8. The high-quality potassium hydroxide refining and impurity-removing process according to claim 1, wherein: The ion exchange resin tower in S5 adopts resin functional groups for adsorption, and the resin functional groups are divided into chelating resin and strong acid cation resin. The selectivity coefficient of chelating resin for calcium ions is 1200-1500, and the selectivity coefficient of magnesium ions is 800-1000. The dynamic adsorption capacity is 200mmol / L-250mmol / L and 150mmol / L-200mmol / L respectively, which is suitable for pH 6-10 environment. Therefore, chelating resin is selected to adsorb calcium ions.

9. The high-quality potassium hydroxide refining and impurity-removing process according to claim 8, wherein: The strong acid cationic resin has a selectivity coefficient of 800-900 for calcium ions and a selectivity coefficient of 600-700 for magnesium ions, and adsorption capacities of 180mmol / L-220mmol / L and 130mmol / L-170mmol / L, respectively. It is suitable for a pH 5-12 environment, so the strong acid cationic resin is selected for adsorption of magnesium ions.

10. The high-quality potassium hydroxide refining and impurity-removing process according to claim 9, wherein: When the adsorption capacity of the resin functional groups is saturated, 31% hydrochloric acid is used to elute calcium ions, while 32% potassium hydroxide is used to elute magnesium ions. The hydrochloric acid concentration of the reagent is controlled at 5%-8%, and the potassium hydroxide is controlled at 4%-6%. The cleaned resin functional groups are then regenerated and put back into use to restore their adsorption capacity for calcium and magnesium ions.

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