A method for preparing high-purity hydriodic acid based on an electrodialysis system

Abstract

This invention discloses a method for preparing high-purity hydroiodic acid based on an electrodialysis system, belonging to the fields of chemical engineering and new energy technology. The method includes: introducing a first iodide solution into the material chamber of a three-compartment bipolar membrane electrodialysis system; after acid-base preparation, a second iodide solution is obtained; the obtained second iodide solution is then introduced into the desalination and concentration chambers of a two-compartment homogeneous membrane electrodialysis system for electrodialysis concentration, yielding a third and fourth iodide solution; the products from each stage can be reused or sold after processing. This invention avoids the generation of the byproduct iodate, directly generating a high-purity, high-concentration hydroiodic acid solution, eliminating cumbersome and expensive purification steps, and completely achieving product separation. The process is simple, safe, and environmentally friendly. The acid produced by the three-compartment bipolar membrane electrodialysis system becomes a qualified hydroiodic acid product after passing through an MVR evaporation system, and the produced alkali, as a byproduct, can be sold or utilized, turning waste into treasure.

Description

Technical Field

[0001] This invention belongs to the fields of chemical engineering and new energy technology, and specifically relates to a method for preparing high-purity hydroiodic acid based on an electrodialysis system. Background Technology

[0002] Hydroiodic acid is an aqueous solution of hydrogen iodide. It is a strong acid with a pungent, irritating odor and is mainly used as an analytical reagent, reducing agent, auxiliary catalyst, and raw material for the synthesis of some iodides. Traditional methods for producing hydroiodic acid include direct synthesis, hydrogen sulfide reduction, and iodine and red phosphorus synthesis. The direct synthesis method requires stringent reaction conditions, needing temperatures above 500°C and using Pt as a catalyst, making it expensive. The hydrogen sulfide reduction method requires toxic hydrogen sulfide gas and has a complex production route, making it unsuitable for large-scale applications. The iodine and red phosphorus synthesis method produces byproducts such as phosphorous acid along with hydroiodic acid, and the yield is low.

[0003] Currently, an industrial production method for hydroiodic acid has been proposed. This method uses iodine, soluble iodides, soluble alkalis or soluble oxyacid salts, and water as raw materials. It utilizes an electrosynthesis unit cell composed of electrodes, electrode support components, a bipolar membrane, and a tank as the synthesis equipment, and produces hydroiodic acid through electrochemical synthesis (CN 110724968 B). However, its drawbacks are as follows:

[0004] (1) The product separation and purity are poor, and hydroiodic acid is mixed with iodine, resulting in a complex and impure product;

[0005] (2) Poor safety, as the system contains corrosive and volatile elemental iodine;

[0006] (3) The process is complex, the electrolysis process cannot be operated continuously, and it requires supporting purification unit operations such as reduction and distillation;

[0007] (4) Iodate, a byproduct, is of low value and difficult to process;

[0008] (5) The overall energy consumption is high, and there is a side reaction that generates iodate. It requires more electrical energy to produce a unit mass of HI.

[0009] (6) The main materials of the equipment have a short service life and need to be replaced frequently, resulting in high costs and poor overall economic benefits.

[0010] Therefore, there is an urgent need to provide a new method for preparing high-purity hydroiodic acid based on an electrodialysis system. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing high-purity hydroiodic acid based on an electrodialysis system. This invention avoids the generation of the byproduct iodate, directly producing a high-purity, high-concentration hydroiodic acid solution, eliminating cumbersome and expensive purification steps, and achieving complete product separation. The process is simple, safe, and environmentally friendly. The acid produced by the three-compartment bipolar membrane electrodialysis system becomes a qualified hydroiodic acid product after passing through an MVR evaporation system. The produced alkali, as a byproduct, can be sold or utilized, turning waste into treasure. The dilute fraction and concentrated alkali water from the MVR evaporation system can be reused in the three-compartment bipolar membrane system, meeting the industry's zero-emission requirements.

[0012] The specific technical solution adopted in this invention is as follows:

[0013] This invention provides a method for preparing high-purity hydroiodic acid based on an electrodialysis system, as detailed below:

[0014] S1: A first iodide solution is introduced into the material chamber of the three-compartment bipolar membrane electrodialysis system, a hydroiodic acid solution and / or water is introduced into the acid product chamber, a corresponding soluble alkali solution and / or water is introduced into the alkali product chamber, and an alkali solution is introduced into the water chamber. After energizing, acid and alkali preparation is carried out, and a second iodide solution is obtained from the material chamber, a hydroiodic acid solution is obtained from the acid product chamber, and an alkali solution is obtained from the alkali product chamber.

[0015] S2: The second iodide solution obtained in S1 is passed into the desalination chamber and the concentration chamber of the two-compartment homogeneous membrane electrodialysis system, respectively. A salt solution is passed into the electrode chamber. After electrodialysis, the solution is concentrated to obtain the third iodide solution and the fourth iodide solution from the desalination chamber and the concentration chamber, respectively.

[0016] S3: The fourth iodide solution obtained in S2 is de-hardened and then introduced into the material chamber of S1. The third iodide solution obtained in S2 is mixed with a high-concentration soluble iodide solution and de-hardened before being introduced into the material chamber of S1.

[0017] S4: The hydroiodic acid solution obtained in S1 is passed into the MVR evaporation system for concentration treatment to obtain hydroiodic acid product and dilute fraction. The dilute fraction is used to be passed into the acid product chamber of S1.

[0018] S5: The alkaline solution obtained in S1 is passed into the desalination chamber and the concentrate chamber of the two-compartment homogeneous membrane electrodialysis system, respectively. The alkaline solution is passed into the electrode chamber. After energizing, electrodialysis is performed to concentrate the solution. The first sodium hydroxide solution and the second sodium hydroxide solution are obtained from the desalination chamber and the concentrate chamber, respectively.

[0019] S6: The second sodium hydroxide solution obtained in S5 is used to prepare the first iodide solution, and the first sodium hydroxide solution is used to pass into the alkali product chamber described in S1.

[0020] Preferably, the three-compartment bipolar membrane electrodialysis system includes an anode plate, a cathode plate, and a first membrane stack sandwiched between the anode plate and the cathode plate, all connected to a DC power supply. The first membrane stack consists of at least one first electrodialysis unit, and both ends of the first membrane stack are bipolar membranes. The first electrodialysis unit is a three-compartment structure composed of a bipolar membrane, an anion exchange membrane, a cation exchange membrane, and a bipolar membrane arranged in sequence. The three compartments are respectively an acid product compartment composed of a bipolar membrane and anion exchange membrane, a material compartment composed of an anion exchange membrane and a cation exchange membrane, and an alkali product compartment composed of a cation exchange membrane and a bipolar membrane.

[0021] Preferably, the two-compartment homogeneous membrane electrodialysis system includes an anode plate, a cathode plate, and a second membrane stack sandwiched between the anode plate and the cathode plate, all connected to a DC power supply. The second membrane stack consists of at least one second electrodialysis unit, and both ends of the second membrane stack are cation exchange membranes. The second electrodialysis unit is a two-compartment structure consisting of a cation exchange membrane, an anion exchange membrane, and a cation exchange membrane arranged in sequence. The two compartments are a desalination chamber and a concentrate chamber, respectively.

[0022] Preferably, the MVR evaporation system includes a preheater, a falling film evaporator, a gas-liquid separator, a steam compressor, and a discharge pump; the material outlet of the preheater is connected to the material inlet of the falling film evaporator, the vapor-liquid outlet of the falling film evaporator is connected to the inlet of the gas-liquid separator, the gas phase outlet of the gas-liquid separator is connected to the suction port of the steam compressor, and the exhaust port of the steam compressor is connected to the heating steam inlet of the falling film evaporator; the gas phase space of the gas-liquid separator is connected to an inert gas protection system through a pipeline, the liquid phase outlet is connected to the inlet of the discharge pump, and the outlet of the discharge pump is connected to the material inlet of the finished product cooler; the condensate outlet of the falling film evaporator is connected to the heat source inlet of the preheater.

[0023] Preferably, the first iodide solution is obtained by the following method:

[0024] Elemental iodine is reacted with an aqueous sodium hydroxide solution in a redox reaction to obtain a mixed solution of sodium iodide and sodium iodate. A reducing agent is then added to the mixed solution to completely reduce the byproduct sodium iodate to sodium iodide, yielding a sodium iodide reaction solution. This solution is then concentrated by evaporation, heated to a target concentration, and cooled to crystallize, resulting in sodium iodide crystals. Impurities (not present in the solution) are removed. Figure 7 (As shown in the figure) After obtaining pure sodium iodide solid, it is then dissolved in water to prepare the high-concentration soluble iodide solution, and after hardening treatment, the first iodide solution is obtained.

[0025] Preferably, the reducing agent is sodium sulfite; the mass fraction of the high-concentration soluble iodide solution is 10wt%-30wt%; and the hardening treatment is performed by removing metal cations through chelating resin.

[0026] Preferably, the operating temperature of the three-compartment bipolar membrane electrodialysis system and the two-compartment homogeneous membrane electrodialysis system is 20~35℃, and the operating voltage of the DC power supply is 20-35V.

[0027] Preferably, the anode plate and cathode plate are one or more of nickel plates, ruthenium-titanium plates, and graphite plates.

[0028] Preferably, the alkaline solution introduced into the electrode water chamber of the three-compartment bipolar membrane electrodialysis system is a sodium hydroxide aqueous solution with a concentration of 2wt%-4wt%.

[0029] Preferably, the operating current density of the three-compartment bipolar membrane electrodialysis system is 400-600 A / m³. 2 The operating current density of the two-compartment homogeneous membrane electrodialysis system is 300-400 A / m³. 2 .

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] (1) Compared with traditional processes, the three-compartment bipolar membrane electrodialysis technology used in this invention directly eliminates expensive and dangerous key chemical raw materials (such as red phosphorus and sulfiding agents) from the source, reducing raw material costs by more than 60%. At the same time, since the process does not require high temperature and high pressure, the unit acid energy consumption is reduced by more than 40%. According to comprehensive calculations, the unit product production cost is reduced by as much as 50%-70%, and the investment payback period is shortened to 9-12 months, resulting in significant economic benefits;

[0032] (2) This process route fundamentally eliminates the generation of highly toxic hazardous wastes such as sulfur and phosphorus, reduces the generation of by-products such as sodium iodate, and has no harmful gas emissions throughout the process. It only requires electric power to drive, is clean and environmentally friendly, and a single production line can reduce hazardous waste emissions by thousands of tons and carbon emissions by tens of thousands of tons per year. The environmental benefits are worth tens of millions of yuan per year.

[0033] (3) The core device of the three-compartment bipolar membrane electrodialysis process in this process route, the membrane stack, has a certain investment cost, but it operates stably during its lifespan, has low maintenance cost, and its lifespan can reach 2 years. The lifespan of other process components can reach 4-5 years.

[0034] (4) The three-compartment bipolar membrane electrodialysis process realizes flexible, precise and controllable hydroiodic acid concentration and continuous production. The product concentration of this process route can easily and stably reach the standard, and the product consistency far exceeds that of the traditional batch production method. The yield rate jumps to more than 99.9%, which greatly enhances the added value and market competitiveness of the product. The process by-product sodium hydroxide can be recycled and reused, forming a circular economy model, increasing additional revenue points, and enhancing the overall value of the industrial chain.

[0035] (5) This process will greatly stimulate the market demand and technological progress of upstream iodide (such as potassium iodide and sodium iodide) high-purity raw materials, while providing downstream semiconductor manufacturing companies with stable, green and low-cost core materials. It is expected to reduce their procurement costs by 30%-40% and promote the steady development of the entire industry chain. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the overall structure of a bipolar membrane electrodialysis system according to a preferred embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of the overall structure of a two-compartment homogeneous membrane electrodialysis system according to a preferred embodiment of the present invention;

[0038] Figure 3 for Figure 1 Schematic diagram of the first membrane stack structure;

[0039] Figure 4 for Figure 2 Schematic diagram of the second membrane stack structure;

[0040] Figure 5 for Figure 1 System schematic diagram;

[0041] Figure 6 for Figure 2 System schematic diagram;

[0042] Figure 7 This is a flowchart of the process method of the present invention. Detailed Implementation

[0043] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the present invention can be combined accordingly without mutual conflict.

[0044] like Figure 7 As shown, this invention provides a method for preparing high-purity hydroiodic acid based on an electrodialysis system, the specific method of which is as follows:

[0045] S1: A first iodide solution (a high-concentration soluble iodide solution) is introduced into the material chamber of the three-compartment bipolar membrane electrodialysis system. Figure 7In a preferred embodiment, a 30 wt% sodium iodide solution is used. Hydroiodic acid solution and / or water are introduced into the acid product chamber, a soluble alkali solution corresponding to the hydroiodic acid solution and / or water are introduced into the alkali product chamber, and an alkali solution is introduced into the electrode water chamber. After electrolysis, acid-base preparation is performed. After sufficient reaction, a second iodide solution (a low-concentration soluble iodide solution) is obtained from the material chamber of the three-compartment bipolar membrane electrodialysis system. Figure 7 In a preferred embodiment shown, a 10% sodium iodide solution (by mass) is used to obtain a hydroiodic acid solution (in the acid product chamber). Figure 7 In a preferred embodiment shown, a 256 g / L sodium iodide solution was used to obtain an alkaline solution (in the alkaline product chamber). Figure 7 In a preferred embodiment shown, the sodium hydroxide solution is 80 g / L.

[0046] As a preferred embodiment of the present invention, such as Figure 1 , 3 Figures 5 and 6 show a preferred system schematic, a first membrane stack schematic, and a system principle schematic for operation of the three-compartment bipolar membrane electrodialysis system of the present invention, respectively. As can be seen from the figures, the three-compartment bipolar membrane electrodialysis system mainly includes an anode plate, a cathode plate connected to a DC power supply, and a first membrane stack sandwiched between the anode plate and the cathode plate. The first membrane stack consists of at least one first electrodialysis unit, with bipolar membranes at both ends. Each first electrodialysis unit is a three-compartment structure composed of a bipolar membrane, an anion exchange membrane, a cation exchange membrane, and a bipolar membrane arranged sequentially. The three compartments are respectively an acid product compartment composed of a bipolar membrane and anion exchange membrane, a material compartment composed of an anion exchange membrane and a cation exchange membrane, and an alkali product compartment composed of a cation exchange membrane and a bipolar membrane.

[0047] Specifically, such as Figure 3 As shown, the first membrane stack includes, in sequence: a water distribution plate, an electrode water separator, a bipolar membrane, an acid chamber separator, an anion exchange membrane, a material separator, a cation exchange membrane, an alkali chamber separator, a bipolar membrane, an acid chamber separator, an anion exchange membrane, a material separator, a cation exchange membrane, an alkali chamber separator, ... bipolar membrane, electrode water separator, and water distribution plate. The electrode water is connected to the entire membrane stack system through the electrode water separator, forming the electrode water chamber.

[0048] As a preferred embodiment of the present invention, such as Figure 7 As shown, the first iodide solution can be obtained in the following manner:

[0049] 1) High-purity elemental iodine is reacted with an aqueous solution of sodium hydroxide in a reaction vessel to produce a mixed solution of sodium iodide and sodium iodate. The chemical formula for this reaction is 3I₂ + 6NaOH = 5NaI + NaIO₃ + 3H₂O.

[0050] For industrial-grade preparation, industrial-grade iodine with a purity ≥99.5% is required. For pharmaceutical-grade or electronic-grade NaI (such as contrast agents and optoelectronic materials), the purity must be increased to high-purity iodine (≥99.9% or 99.99%). Industrial-grade preparation commonly uses industrial-grade caustic soda flakes or liquid caustic soda (NaOH purity ≥98%), with a sodium hydroxide aqueous solution concentration of 30wt%-50wt%. The specific choice can be made based on the actual situation.

[0051] 2) Subsequently, reducing agents such as sodium sulfite are added to the resulting mixed solution to completely reduce the byproduct sodium iodate (NaIO3) to sodium iodide, yielding a sodium iodide reaction solution. The chemical formula for this reaction is NaIO3 + 3Na2SO3 = NaI + 3Na2SO4.

[0052] 3) Subsequently, the obtained sodium iodide reaction solution was heated to the target concentration by evaporation and concentration, and then cooled to crystallize, precipitating sodium iodide crystals. The obtained sodium iodide crystals were then subjected to impurity removal operations such as filtration and washing (to remove impurities such as sodium sulfate) to obtain pure sodium iodide solid.

[0053] 4) The obtained pure sodium iodide solid was dissolved in water to prepare a high-concentration soluble iodide solution (i.e. Figure 7 Sodium iodide (30% by mass) is subjected to a chelating resin to remove impurities such as metal cations, resulting in a first iodide solution.

[0054] In a preferred embodiment of the present invention, the positive and negative electrode plates in the three-compartment bipolar membrane electrodialysis system can be one or more of nickel plates, ruthenium titanium plates, and graphite plates, and the membrane material used can be one or more of PES, PVC, PE, PS, and PP.

[0055] In a preferred embodiment of the present invention, during the acid-base preparation process of the three-compartment bipolar membrane electrodialysis system, the electrode water chamber, alkali product chamber, acid product chamber, and material chamber are independent of each other, operating at a temperature of 20~35℃, and the supporting equipment includes circulating cooling water. The operating current density is 400-600A / m³. 2 The operating voltage of the DC power supply is 20-35V. The alkaline solution introduced into the electrode water chamber can be a sodium hydroxide aqueous solution with a concentration of 2wt%-4wt%.

[0056] In a preferred embodiment of the present invention, the iodide is sodium iodide, and the concentration of sodium iodide solution in the material chamber of the three-compartment bipolar membrane electrodialysis system is maintained at 10wt%-30wt%.

[0057] In a preferred embodiment of the present invention, deionized water is initially added to both the acid product chamber and the alkali product chamber in the three-compartment bipolar membrane electrodialysis system, with an initial volume ratio of 1:1 between the acid and alkali product chambers.

[0058] In practical applications, when a direct current is applied to the three-compartment bipolar membrane electrodialysis system, the bipolar membrane can convert H2O into H+. + With OH - They migrate to the anther and anode sides of the membrane, respectively. Under electric drive, monovalent metal cations in the material chamber pass through the cation exchange membrane and react with OH groups generated on the anther side of the bipolar membrane. - A base is formed by combining; anions pass through the anion exchange membrane and simultaneously react with H+ generated on the anode side of the bipolar membrane. + Combine to form acids, such as Figure 5 As shown.

[0059] The hydroiodic acid and sodium hydroxide solution prepared by the three-compartment bipolar membrane electrodialysis system of the present invention has a concentration greater than 2 mol / L, and the metal ion impurities in the prepared hydroiodic acid can be reduced to below 50 ppm.

[0060] S2: The second iodide solution obtained in S1 (in...) Figure 7 In a preferred embodiment, a 10% sodium iodide solution is introduced into the desalination chamber and the concentrate chamber of a two-compartment homogeneous membrane electrodialysis system. A salt solution (e.g., a 2wt%-4wt% sodium iodide solution) is introduced into the electrode chamber. After electrodialysis, the solution is concentrated, and a third iodide solution (a low-concentration iodide solution) is obtained from the desalination chamber and the concentrate chamber, respectively. Figure 7 In a preferred embodiment shown, the solutions are a 10 g / L sodium iodide solution and a fourth iodide solution (a high-concentration iodide solution, in...). Figure 7 In a preferred embodiment shown, a sodium iodide solution of 300 g / L with a concentration of 25 wt% or higher is used.

[0061] As a preferred embodiment of the present invention, such as Figure 2 , 4 Figures 6 and 7 show a preferred system schematic, a second membrane stack schematic, and a system principle schematic for operation of the two-compartment homogeneous membrane electrodialysis system of the present invention, respectively. As can be seen from the figures, the two-compartment homogeneous membrane electrodialysis system mainly includes an anode plate, a cathode plate connected to a DC power supply, and a second membrane stack sandwiched between the anode plate and the cathode plate. The second membrane stack consists of at least one second electrodialysis unit, with cation exchange membranes at both ends. Each second electrodialysis unit is a two-compartment structure composed of cation exchange membranes, anion exchange membranes, and cation exchange membranes arranged sequentially. The two compartments refer to the concentrate compartment formed by the cation exchange membrane and the anion exchange membrane, and the desalination compartment formed by the anion exchange membrane and the cation exchange membrane, respectively.

[0062] Specifically, such as Figure 4As shown, the second membrane stack includes, in sequence: a water distribution plate, an electrode water separator, a cation exchange membrane, a concentrate chamber separator, an anion exchange membrane, a desalination chamber separator, a cation exchange membrane, a concentrate chamber separator, an anion exchange membrane, a desalination chamber separator, ... a cation exchange membrane, an electrode water separator, and a water distribution plate. The electrode water is connected to the entire membrane stack system through the electrode water separator, forming the electrode water chamber.

[0063] In a preferred embodiment of the present invention, the positive and negative electrode plates in the two-compartment homogeneous membrane electrodialysis system can be one or more of nickel plates, ruthenium titanium plates, and graphite plates, and the membrane material used can be one or more of PES, PVC, PE, PS, and PP.

[0064] In a preferred embodiment of the present invention, during the electrodialysis concentration process of the two-compartment homogeneous membrane electrodialysis system, the electrode water chamber, concentrate chamber, and dilute water chamber are independent of each other, operating at a temperature of 20~35℃, and the supporting equipment includes circulating cooling water. The operating current density is 300-400A / m³. 2 The operating voltage of the DC power supply is 20-35V. The initial volume ratio of the freshwater chamber to the concentrated water chamber can be 3:1.

[0065] S3: The fourth iodide solution obtained in S2 (in...) Figure 7 In a preferred embodiment, a 300 g / L sodium iodide solution is treated with a chelating resin to remove impurities such as metal cations, and then introduced into the material chamber of the three-compartment bipolar membrane electrodialysis system in S1. The third iodide solution obtained in S2 (in...) Figure 7 In a preferred embodiment shown, a 10 g / L sodium iodide solution (concentration below 10 wt%) and a high-concentration soluble iodide solution (in... Figure 7 In a preferred embodiment shown, a 30% sodium iodide solution is mixed and then treated with chelating resin to remove impurities such as metal cations before being introduced into the material chamber of the three-compartment bipolar membrane electrodialysis system in S1.

[0066] S4: The hydroiodic acid solution obtained in S1 (in...) Figure 7 In a preferred embodiment shown, a 256 g / L sodium iodide solution was passed into an MVR evaporation system for concentration to obtain hydroiodic acid product (in... Figure 7 In a preferred embodiment shown, the product is 57% hydroiodic acid (by mass) and a dilute fraction. The hydroiodic acid product can be sold directly, while the dilute fraction can be recycled into the acid product chamber of the three-compartment bipolar membrane electrodialysis system in S1.

[0067] In a preferred embodiment of the present invention, the MVR evaporation system mainly includes a preheater, a falling film evaporator, a gas-liquid separator, a steam compressor, and a discharge pump. The material outlet of the preheater is connected to the material inlet of the falling film evaporator; the vapor-liquid outlet of the falling film evaporator is connected to the inlet of the gas-liquid separator; the gas phase outlet of the gas-liquid separator is connected to the suction port of the steam compressor; and the exhaust port of the steam compressor is connected to the heating steam inlet of the falling film evaporator. The gas phase space of the gas-liquid separator is connected to an inert gas protection system via a pipeline; the liquid phase outlet is connected to the inlet of the discharge pump; and the outlet of the discharge pump is connected to the material inlet of the finished product cooler. The condensate outlet of the falling film evaporator is connected to the heat source inlet of the preheater.

[0068] Specifically, components in the MVR evaporation system that come into direct contact with iodine require non-metallic corrosion-resistant materials to resist iodine corrosion. These materials can be one or more of high-purity graphite, polytetrafluoroethylene (PTFE), or fusible polytetrafluoroethylene (PFA) enamel. The inert gas protection system is connected to the gas phase space of the falling film evaporator and gas-liquid separator and is equipped with an oxidation-reduction potential (ORP) sensor, which automatically adjusts the inert gas flow rate based on the ORP value. The ORP sensor in the system monitors in real time and controls the nitrogen supply valve to maintain the system ORP value below -200 mV. An online density meter controls the discharge concentration to remain stable at 57 wt%. The flow-through components of the steam compressor are made of graphite, ceramic, or a metal substrate coated with a fluoroplastic anti-corrosion layer. The heat exchange tubes of the falling film evaporator are graphite tubes, the separator is carbon steel lined with PFA, and all pipes and valves are PTFE-lined tubes or high-purity graphite tubes.

[0069] In practical use, before starting the MVR evaporation system, it is purged with 99.999% nitrogen for 30 minutes to ensure the system oxygen content is <50 ppm. The centrifugal compressor is then started, providing a 10°C temperature rise. The system operates under a micro-vacuum of -10 kPa (absolute pressure approximately 91 kPa), lowering the boiling point of hydroiodic acid to approximately 100°C. The evaporation rate is controlled by adjusting the compressor speed.

[0070] A preferred embodiment of the MVR evaporation system is as follows:

[0071] Inerting: Before startup, the entire system is purged with inert gas until the oxygen content detector shows a standard (e.g., <10 ppm); Feeding and Preheating: Low-concentration HI feedstock is preheated to near boiling point in a preheater (made of graphite or PTFE); Falling Film Evaporation: The preheated feed liquid is fed into the top of the falling film evaporator, where it is evenly distributed into a liquid film that flows down the inner wall of the heat exchange tubes. Heating steam from the compressor outside the tubes provides a heat source, causing partial evaporation of the HI liquid film inside the tubes; Separation and Compression: The generated secondary steam (HI + H2O) is separated from the concentrate in the separator. The pure secondary steam is drawn into the steam compressor, and after compression, its saturation temperature increases, becoming heating steam that is fed into the shell side of the falling film evaporator; Condensation and Discharge: The heating steam is condensed into distilled water in the shell side (which may contain trace amounts of HI and requires further treatment), and discharged by the condensate pump. After the concentrated HI acid at the bottom of the separator reaches the predetermined concentration, it is cooled by the finished product cooler (graphite cooler) before being discharged to prevent high-temperature decomposition. Full-process protection: Throughout the entire process, the inert gas protection system operates continuously to maintain a slight positive pressure in the system.

[0072] S5: The alkaline solution obtained in S1 (in...) Figure 7 In a preferred embodiment, an 80 g / L sodium hydroxide solution is introduced into the desalination chamber and the concentrate chamber of a two-compartment homogeneous membrane electrodialysis system. An alkaline solution (e.g., a 2 wt%-4 wt% sodium hydroxide solution) is introduced into the electrode chamber. After electrodialysis concentration, a first sodium hydroxide solution (a low-concentration sodium hydroxide solution) is obtained from the desalination chamber and the concentrate chamber, respectively. Figure 7 In a preferred embodiment shown, the first solution is a 10 g / L sodium hydroxide solution, and the second solution is a high-concentration sodium hydroxide solution. Figure 7 In a preferred embodiment shown, a sodium hydroxide solution of 160 g / L is used, with a concentration that can reach over 16 wt%.

[0073] S6: The second sodium hydroxide solution obtained in step S5 can be returned to the front end and reacted with elemental iodine to prepare the first iodide solution, or it can be sold directly. The first sodium hydroxide solution obtained in step S5 can be recycled by passing it into the alkali product chamber of the three-compartment bipolar membrane electrodialysis system in S1.

[0074] The method and effects of the present invention will be specifically illustrated below through examples.

[0075] Example 1

[0076] This embodiment utilizes, as Figure 1The three-compartment bipolar membrane electrodialysis system shown above is used to prepare hydroiodic acid, specifically step S1. Specifically, sodium iodide solutions with concentrations of 1.0, 1.5, 2.0, and 2.5 mol / L (i.e., the initial material concentrations in Table 1) are introduced into the material compartment of the three-compartment bipolar membrane electrodialysis system for acid-base preparation. Both the acid and base product compartments initially contain deionized water in a 1:1 volume ratio. The designed experimental parameters are: membrane partial voltage ≤ 2V, current density 500 A / m³. 2 The operating temperature was 20-35℃. The results are shown in Table 1. It was found that the yield of hydroiodic acid (HI) was high, all above 90%, and the content of metal impurities was less than 50ppm.

[0077] Table 1 Current density at 500 A / m 2 Below, the yield and impurity content of materials with different contents are compared.

[0078]

[0079] Table 1 shows that the current efficiency initially increases and then decreases with increasing initial sodium iodide solution concentration. The current efficiency is highest when the sodium iodide solution concentration is 2 mol / L, but decreases when the concentration exceeds 2 mol / L. This suggests that in the initial stage of the experiment, the conductivity of the entire system gradually increases with increasing sodium iodide solution concentration, leading to a decrease in overall resistance and a corresponding increase in current efficiency. However, when the sodium iodide solution concentration continues to rise above 2 mol / L, the ionization rate of sodium iodide decreases due to the excessively high concentration, and the ion migration rate also decreases within the same operating time. Furthermore, the significant difference between the concentrations in the material chamber and the alkali product chamber reduces the membrane's selective permeability to ions, causing reverse ion permeation and resulting in a decrease in current efficiency.

[0080] In a preferred embodiment of the present invention, in order to improve current efficiency and reduce costs, the concentration of sodium iodide solution entering the three-compartment bipolar membrane electrodialysis system after hardening should be maintained between 10wt% and 30wt%.

[0081] Example 2

[0082] This embodiment utilizes, as Figure 2 The two-compartment homogeneous membrane electrodialysis system shown above performs HI concentration, i.e., step S2 above, specifically at 400 A / m 2 A 10 wt% sodium iodide solution was concentrated at a current density of 400 A / m³. Both the desalination and concentration chambers initially contained 10 wt% sodium iodide solution in a volume ratio of 3:1. The experimental parameters were designed as follows: membrane partial voltage ≤ 0.5 V, current density 400 A / m³. 2 Operating temperature: 20-35℃.

[0083] The results showed that the concentrate chamber could produce a 30 wt% sodium iodide solution, while the desalination chamber produced a sodium iodide solution with a concentration of <1 wt%. The current efficiency of this ED concentration stage (i.e., the stage of concentrating low-concentration sodium iodide in the two-compartment homogeneous membrane electrodialysis system) was 93.8%. Therefore, the above method can achieve highly efficient concentration of sodium iodide from low to high concentrations, ensuring continuous operation of the subsequent bipolar membrane electrodialysis, with a very high conversion rate and a safe and environmentally friendly process throughout.

[0084] This invention utilizes a three-compartment bipolar membrane electrodialysis system to convert industrial sodium iodide solution into hydroiodic acid and sodium hydroxide solution. The products obtained by this method are completely separated, with a hydroiodic acid yield of no less than 90% and no additional impurities introduced. The hydroiodic acid has extremely high purity, eliminating the need for complex purification operations. The low-concentration sodium iodide solution remaining in the material chamber can be reconcentrated using a two-compartment homogeneous membrane electrodialysis system. The resulting high-concentration sodium iodide solution is then reintroduced into the three-compartment bipolar membrane electrodialysis system for hydroiodic acid production. The sodium hydroxide solution produced by the three-compartment bipolar membrane electrodialysis system can be concentrated to over 16 wt% using a two-compartment homogeneous membrane electrodialysis system. The resulting high-concentration alkali solution can be reused at the front end to produce pure sodium iodide salt. The remaining desalinated water after sodium hydroxide concentration can be reused in the alkali product chamber of the three-compartment bipolar membrane electrodialysis system. The experimental process generates no wastewater or waste gas, achieving recycling and a green process within the system.

[0085] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A method for preparing high-purity hydroiodic acid based on an electrodialysis system, characterized in that, Specifically as follows: S1: A first iodide solution is introduced into the material chamber of the three-compartment bipolar membrane electrodialysis system, a hydroiodic acid solution and / or water is introduced into the acid product chamber, a corresponding soluble alkali solution and / or water is introduced into the alkali product chamber, and an alkali solution is introduced into the water chamber. After energizing, acid and alkali preparation is carried out, and a second iodide solution is obtained from the material chamber, a hydroiodic acid solution is obtained from the acid product chamber, and an alkali solution is obtained from the alkali product chamber. S2: The second iodide solution obtained in S1 is passed into the desalination chamber and the concentration chamber of the two-compartment homogeneous membrane electrodialysis system, respectively. A salt solution is passed into the electrode chamber. After electrodialysis, the solution is concentrated to obtain the third iodide solution and the fourth iodide solution from the desalination chamber and the concentration chamber, respectively. S3: The fourth iodide solution obtained in S2 is de-hardened and then introduced into the material chamber of S1. The third iodide solution obtained in S2 is mixed with a high-concentration soluble iodide solution and de-hardened before being introduced into the material chamber of S1. S4: The hydroiodic acid solution obtained in S1 is passed into the MVR evaporation system for concentration treatment to obtain hydroiodic acid product and dilute fraction. The dilute fraction is used to be passed into the acid product chamber of S1. S5: The alkaline solution obtained in S1 is passed into the desalination chamber and the concentrate chamber of the two-compartment homogeneous membrane electrodialysis system, respectively. The alkaline solution is passed into the electrode chamber. After energizing, electrodialysis is performed to concentrate the solution. The first sodium hydroxide solution and the second sodium hydroxide solution are obtained from the desalination chamber and the concentrate chamber, respectively. S6: The second sodium hydroxide solution obtained in S5 is used to prepare the first iodide solution, and the first sodium hydroxide solution is used to pass into the alkali product chamber described in S1.

2. The method for preparing high-purity hydroiodic acid based on an electrodialysis system according to claim 1, characterized in that, The three-compartment bipolar membrane electrodialysis system includes an anode plate, a cathode plate, and a first membrane stack sandwiched between the anode plate and the cathode plate, all connected to a DC power supply. The first membrane stack consists of at least one first electrodialysis unit, and both ends of the first membrane stack are bipolar membranes. The first electrodialysis unit is a three-compartment structure composed of a bipolar membrane, an anion exchange membrane, a cation exchange membrane, and a bipolar membrane arranged in sequence. The three compartments are respectively an acid product compartment composed of a bipolar membrane and anion exchange membrane, a material compartment composed of an anion exchange membrane and a cation exchange membrane, and an alkali product compartment composed of a cation exchange membrane and a bipolar membrane.

3. The method for preparing high-purity hydroiodic acid based on an electrodialysis system according to claim 1, characterized in that, The two-compartment homogeneous membrane electrodialysis system includes an anode plate, a cathode plate, and a second membrane stack sandwiched between the anode plate and the cathode plate, all connected to a DC power supply. The second membrane stack consists of at least one second electrodialysis unit, and both ends of the second membrane stack are cation exchange membranes. The second electrodialysis unit is a two-compartment structure consisting of a cation exchange membrane, an anion exchange membrane, and a cation exchange membrane arranged in sequence. The two compartments are a desalination chamber and a concentrate chamber, respectively.

4. The method for preparing high-purity hydroiodic acid based on an electrodialysis system according to claim 1, characterized in that, The MVR evaporation system includes a preheater, a falling film evaporator, a gas-liquid separator, a steam compressor, and a discharge pump. The material outlet of the preheater is connected to the material inlet of the falling film evaporator; the vapor-liquid outlet of the falling film evaporator is connected to the inlet of the gas-liquid separator; the gas phase outlet of the gas-liquid separator is connected to the suction port of the steam compressor; and the exhaust port of the steam compressor is connected to the heating steam inlet of the falling film evaporator. The gas phase space of the gas-liquid separator is connected to an inert gas protection system via a pipeline; the liquid phase outlet is connected to the inlet of the discharge pump; and the outlet of the discharge pump is connected to the material inlet of the finished product cooler. The condensate outlet of the falling film evaporator is connected to the heat source inlet of the preheater.

5. The method for preparing high-purity hydroiodic acid based on an electrodialysis system according to claim 1, characterized in that, The first iodide solution was obtained as follows: Elemental iodine is subjected to a redox reaction with an aqueous sodium hydroxide solution to obtain a mixed solution of sodium iodide and sodium iodate. A reducing agent is then added to the mixed solution to completely reduce the byproduct sodium iodate to sodium iodide, resulting in a sodium iodide reaction solution. The sodium iodide reaction solution is then concentrated by evaporation, heated to a target concentration, and cooled to crystallize, precipitating sodium iodide crystals. After impurity removal, pure sodium iodide solid is obtained, which is then dissolved in water to prepare the high-concentration soluble iodide solution. After hardening treatment, the first iodide solution is obtained.

6. The method for preparing high-purity hydroiodic acid based on an electrodialysis system according to claim 5, characterized in that, The reducing agent is sodium sulfite; the mass fraction of the high-concentration soluble iodide solution is 10wt%-30wt%; the hardening treatment is to remove metal cations by chelating resin.

7. The method for preparing high-purity hydroiodic acid based on an electrodialysis system according to claim 1, characterized in that, The operating temperature of both the three-compartment bipolar membrane electrodialysis system and the two-compartment homogeneous membrane electrodialysis system is 20~35℃, and the operating voltage is 20-35V.

8. A method for preparing high-purity hydroiodic acid based on an electrodialysis system according to claim 2 or 3, characterized in that, The anode plate and cathode plate are one or more of nickel plates, ruthenium-titanium plates, and graphite plates.

9. The method for preparing high-purity hydroiodic acid based on an electrodialysis system according to claim 1, characterized in that, The alkaline solution introduced into the electrode water chamber of the three-compartment bipolar membrane electrodialysis system is a sodium hydroxide aqueous solution with a concentration of 2wt%-4wt%.

10. The method for preparing high-purity hydroiodic acid based on an electrodialysis system according to claim 1, characterized in that, The operating current density of the three-compartment bipolar membrane electrodialysis system is 400-600 A / m³. 2 The operating current density of the two-compartment homogeneous membrane electrodialysis system is 300-400 A / m³. 2 .

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