A method and system for purification of hi based on coupling of extraction and electrodialysis

Abstract

The application provides a HI purification method and system based on coupling of extraction and electrodialysis. The method comprises the following steps: 1) using tri-n-octylphosphine oxide (TOPO) as an extractant to selectively complex and extract free iodine and triiodide ions in HIx phase; 2) desorbing the TOPO-I2 complex by low-temperature methanol to realize I2 recovery and TOPO regeneration; 3) deeply concentrating HI by using acid-resistant anion exchange electrodialysis membranes (perfluorosulfonic acid-CNT composite AEM) to increase the concentration of HI to ≥70 %; and 4) generating hydrogen and I2 by high-temperature pyrolysis of HI. The application integrates extraction and electrodialysis technologies to realize HI purification for hydrogen production from sulfur and iodine, realizes two-stage separation, removes free I2 in advance by TOPO extraction, greatly reduces the iodine content in the solution entering the electrodialysis system, avoids the deposition of iodine on the membrane surface, inhibits the electrodialysis process, ensures the selectivity and flux of the membrane during long-term operation, prolongs the service life of the membrane, and reduces the operation and maintenance cost.

Description

Technical Field

[0001] This invention belongs to the field of sulfur-iodine cycle hydrogen production, and relates to a HI purification method and system based on the coupling of extraction and electrodialysis. Background Technology

[0002] Thermochemical sulfur-iodine cycle hydrogen production is currently the most ideal and mature method among thermochemical cycle hydrogen production processes. Its three main reactions are the Bunsen reaction, sulfuric acid decomposition, and hydrogen iodide decomposition. Through material recycling, sulfur-containing and iodine-containing materials are not consumed in the process; only water is consumed as a source of hydrogen and oxygen. The overall reaction is the decomposition of water into hydrogen and oxygen. The entire process only requires the addition of water, without the need for other chemical substances, making it green and environmentally friendly.

[0003] The Bunsen reaction uses iodine, SO2, and water as raw materials. In the Bunsen reaction, iodine and water are in excess. The excess iodine is used to react I2 and I3. - The combination allows the HIx phase and the sulfuric acid phase to be completely separated; the mixture enters a layered column for two-phase separation; the HIx phase has a higher density and is located in the lower layer, while the sulfuric acid phase is in the upper layer.

[0004] The HIx phase contains substances such as I2, HI, H2O, and H2SO4. Before hydrogen iodide decomposition, HI purification is required. Existing technologies have yielded numerous studies on the HI purification process, mainly including:

[0005] (1) Tributyl phosphate (TBP) single extraction technology for HI: TBP is used as the extractant, which has a certain extraction effect on both HI and I2 in the HIx phase. HI and I2 are then separated and purified by other operations. However, TBP can also co-extract I2 in the presence of I2, which leads to a decrease in purification efficiency. HI and I2 need to be separated in the later stage.

[0006] (2) Phosphoric acid extractive distillation: GA Company in the United States developed a method to remove I2 from a HI-H2O-I2 mixed solution using phosphoric acid, and then distilled the remaining solution to obtain a high concentration of HI. However, phosphoric acid extractive distillation introduces phosphate impurities, which need to be further removed later.

[0007] (3) Direct distillation: CN114517714A directly uses a distillation column to distill the HI-H2O-I2 mixed solution. The light phase HI vaporizes from the top of the distillation column and flows out, while the heavy phase I2 solution is collected at the bottom. This method cannot directly break the azeotropic equilibrium, and the upper limit of HI concentration purification is limited. To break the azeotropic limit, the reflux ratio needs to be increased or the pressure needs to be reduced, resulting in an increase in energy consumption of 30%~50%.

[0008] (4) Electrochemical membrane separation: CN107904617B introduces an electrochemical method for hydrogen production by decomposing HI. The HIx phase (containing HI, I2, and H2O) is injected into the anode chamber using a platinum / carbon (Pt / C) catalyst, while deionized water is injected into the cathode chamber, also using a Pt / C catalyst. Through anodic oxidation and cathodic reduction reactions, HI accumulates at the cathode while I2 accumulates at the anode, thus achieving the separation of HI and I2. The electrochemical membrane separation method requires stringent operating conditions, demanding strict control of temperature and humidity. It is also sensitive to impurities in the HIx phase. I2 crystallizes on the anode side at temperatures below 40°C, easily piercing the membrane and forming microporous defects.

[0009] (5) Step-by-step stripping method: CN114852960A uses a multi-stage stripping tower to gradually reduce the pressure and temperature, causing HI and a small amount of H2O to escape from the HIx solution in gaseous form, thereby achieving the separation and purification of HI. The step-by-step stripping method has insufficient impurity separation efficiency. Since I2 is highly volatile, it is difficult to completely separate I2 during the stripping process. I2 residues still remain in the purified HI, which may lead to poisoning of the subsequent decomposition catalyst and a decrease in the HI decomposition rate.

[0010] (6) CN114195094A utilizes the high-temperature gas generated by the decomposition of sulfuric acid to heat the HI phase solution, thereby causing water vapor to evaporate and concentrating the HI phase solution. This method does not separate the I2 in the HI phase solution, and the HI will also vaporize during the evaporation of water.

[0011] (7) CN107904617A proposes a method and apparatus for producing hydrogen by electrochemical decomposition of HI in sulfur-iodine cycle hydrogen production. This technical solution uses electrochemical decomposition to produce hydrogen from HI obtained in sulfur-iodine hydrogen production. CN107904617A electrolyzes HI obtained after Bunsen reaction to produce hydrogen. This method does not consider the removal of I2 impurities in the solution. It directly sends the HIx solution containing a large amount of free I2 into electrodialysis. I2 is easy to precipitate or oxidize on the membrane surface, which can lead to membrane blockage or affect membrane life and reduce system stability.

[0012] In summary, traditional distillation, direct membrane concentration of the HIx phase solution, or direct electrodialysis of the HIx phase solution for hydrogen production struggles to selectively remove free I2. This leads to crystallization blockage in the distillation column, easy scaling or corrosion of membrane modules by I2, and frequent shutdowns for cleaning or replacement of membrane materials. Most membrane concentration or distillation processes can only concentrate HI to below 60%, resulting in low efficiency and high energy consumption in downstream high-temperature decomposition. Summary of the Invention

[0013] This invention aims to overcome the shortcomings of existing technologies and provide a HI purification method and system based on the coupling of extraction and electrodialysis. Before electrodialysis, this method employs TOPO (tri-n-octylphosphine oxide) / inert diluent organic phase for efficient complexation extraction of I2, significantly reducing the I2 content in downstream processes and avoiding clogging and corrosion. Furthermore, this invention, through series AEM / CEM electrodialysis, can increase the HI concentration to ≥70%, providing a high-purity, high-concentration feed to the HI decomposition tower, simultaneously improving cracking efficiency and hydrogen production rate.

[0014] The technical solution of the present invention is as follows:

[0015] This invention provides a HI purification method based on the coupling of extraction and electrodialysis in sulfur-iodine cycle hydrogen production, which includes the following steps:

[0016] 1) The HI phase solution obtained from the Bunsen reaction was fed into an extraction tower and extracted with an extractant to obtain an aqueous phase and an organic phase enriched with TOPO-I2 complex. The extractant was TOPO (tri-n-octylphosphine oxide) diluted with an inert diluent.

[0017] 2) The organic phase is transported to the desorption unit, and a pre-cooled polar solvent is added to the desorption unit. I2 in the organic phase precipitates to form crystals. The crystals are recovered and returned to the Bunsen reaction. The remaining organic phase is depolarized to remove the polar solvent and water to obtain regenerated TOPO. The regenerated TOPO is recovered to the extraction tower for reuse.

[0018] 3) The aqueous phase from step 1) is transported to the electrodialysis system and concentrated and separated under the action of an applied DC electric field. The electrodialysis system is a series heterogeneous ion exchange membrane structure, consisting of alternating cation exchange membranes and anion exchange membranes forming membrane pairs. The electrodialysis system contains 50-100 membrane pairs. The electrodialysis system obtains a high-concentration HI solution, which is then transported to the downstream HI decomposition tower.

[0019] According to a preferred embodiment of the present invention, the inert diluent is one or more of n-hexane and cyclohexane.

[0020] According to a preferred embodiment of the present invention, the extraction tower is equipped with an external jacket or a built-in coil heater, and the material temperature is controlled at 45~50℃ by the jacket or coil heater. A stirring device is installed inside the extraction tower to stir the material.

[0021] According to a preferred embodiment of the present invention, the desorption unit is a desorption tank with stirring; the polar solvent is methanol, ethanol or isopropanol, and the temperature of the pre-cooled polar solvent is -30 to -10°C; the volume ratio of the polar solvent to the organic phase is 2 to 5:1.

[0022] According to a preferred embodiment of the present invention, the crystals precipitated in the organic phase are recovered by a vacuum filter; and the remaining organic phase is treated with a molecular sieve rotary evaporator to remove polar solvents and water.

[0023] According to a preferred embodiment of the present invention, the operating current density of the electrodialysis system is 15 A / dm³. 2 ~25A / dm 2 The temperature is maintained at 40-60℃; the mass percentage concentration of the high-concentration HI solution obtained by the electrodialysis system is ≥70%.

[0024] According to a preferred embodiment of the present invention, a partition is provided between the anion exchange membrane and the cation exchange membrane in the electrodialysis system. The partition has a thickness of 2-5 mm, and the fluid channel inside the partition adopts a slit-type structure.

[0025] According to another invention of the present invention, the present invention also provides an HI purification system for implementing the aforementioned method, comprising:

[0026] The extraction tower is used to extract the HI phase solution to obtain an aqueous phase and an organic phase enriched with TOPO-I2 complex. The extractant used is TOPO diluted with an inert diluent.

[0027] The desorption unit is used to desorb the organic phase obtained by extraction, and the desorption uses a pre-cooled polar solvent;

[0028] A vacuum filter is used to filter the crystalline organic phase obtained from the desorption unit to obtain I2 crystals and the filtered organic phase.

[0029] Molecular sieve rotary evaporators are used to remove polar solvents and water from organic phases filtered by vacuum filters and to recover TOPO.

[0030] An electrodialysis system is used to concentrate the aqueous phase obtained from extraction to obtain a highly concentrated HI solution for HI decomposition.

[0031] Compared with the prior art, the present invention has the following effects and advantages:

[0032] 1) This invention constructs a combined "extraction + electrodialysis" process for HI phase purification, achieving two-stage separation: first, iodine removal, then HI concentration. Specifically, this invention pre-removes free I2 through TOPO extraction, significantly reducing the iodine content in the solution entering the electrodialysis system, preventing its deposition on the membrane surface, inhibiting the electrodialysis process, ensuring the selectivity and flux of the AEM / CEM membrane for long-term operation, extending membrane life, and reducing maintenance costs. This invention comprehensively improves HI separation efficiency and purity while avoiding I2 clogging of pipelines and its impact on subsequent processes.

[0033] 2) This invention improves the extractant system, significantly enhancing selectivity. Traditional techniques for HI phase purification using extraction processes often employ TBP, which has extraction capabilities for both HI and I2, requiring subsequent secondary separation of HI and I2. This process eliminates TBP, using a pure TOPO system that coordinates and complexes only with I2, almost completely eliminating HI. This increases the extraction selectivity from <50% (TBP) to >95% (TOPO), significantly simplifying subsequent separation steps.

[0034] 3) Traditional composite solvent recovery often employs high-temperature distillation, which is energy-intensive and prone to organic phase decomposition. This invention utilizes low-temperature methanol washing and low-temperature desorption of the TOPO-I2 complex, efficiently releasing I2 (recovery rate > 99%) while preserving the intact TOPO structure (loss < 5%), reducing material loss. The process is gentle and has high recycling efficiency. The I2 separated by this invention is recovered and returned to the Bunsen reactor for reuse, and the TOPO extractant can also be recycled, reducing system operating costs. This invention achieves the recycling of the extractant, reducing H2 production costs and environmental burden, and is suitable for low-carbon hydrogen production goals. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the HI purification method based on the coupling of extraction and electrodialysis according to the present invention.

[0036] Figure 2 This is a simplified diagram of the extraction tower of the present invention.

[0037] Figure 3 This is a schematic diagram of the electrodialysis system of the present invention.

[0038] Figure 4 This is a schematic diagram of the slit-type partition in the electrodialysis system of the present invention.

[0039] Figure 5 This is a flowchart of a sulfur-iodine cycle hydrogen production scheme based on the extraction-electrodialysis HI phase purification method of the present invention. Detailed Implementation

[0040] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0041] like Figure 1 The diagram shows a flowchart of the HI purification process based on the coupling of extraction and electrodialysis according to the present invention. The present invention is used to achieve the concentration and purification of the HI phase in the thermochemical sulfur-iodine cycle hydrogen production process. Its upstream process is the Bunsen reaction unit and its downstream process is the hydrogen iodide decomposition unit.

[0042] To fully understand this invention, a brief introduction to the thermochemical sulfur-iodine cycle hydrogen production process is provided below. The thermochemical sulfur-iodine cycle hydrogen production mainly includes three reactions: Bunsen reaction, sulfuric acid decomposition, and hydrogen iodide decomposition. In addition, it involves several purification or separation processes, such as phase separation and separation of Bunsen reaction products, purification and concentration of the sulfuric acid phase, and purification and concentration of the HI phase. It should be noted that this invention mainly involves improvements to the purification and concentration process of the HI phase. For other reaction units and separation units, existing technologies can still be used.

[0043] Reference Figure 1 The main steps of HI purification based on the coupling of extraction and electrodialysis in this invention include:

[0044] 1) The HI phase solution obtained from the Bunsen reaction is fed into an extraction tower and extracted with an extractant to obtain an aqueous phase and an organic phase enriched with TOPO-I2 complex; the extractant is TOPO diluted with an inert diluent, and the volume ratio of TOPO to the inert diluent is 1:8~10, preferably 1:9; the inert diluent is one or more of n-hexane and cyclohexane, and the volume ratio of the HI phase solution to the extractant in the extraction tower is 1:0.8~1.5, preferably 1:1.

[0045] like Figure 2 The schematic diagram of the extraction tower of the present invention shown indicates that it has a heavy phase inlet (introducing HI phase solution) and a light phase outlet (extracting organic phase enriched with TOPO-I2 complex) located at the top of the tower, and a heavy phase outlet (extracting aqueous phase) and a light phase inlet (extractant inlet) located at the bottom of the tower. The extraction tower is equipped with an external jacket or has a built-in coil heater, and the material temperature is controlled at 45~50℃ by the jacket or coil heater. A stirring shaft is installed inside the extraction tower, and a stirring motor is installed externally to drive the stirring shaft to stir the material.

[0046] 2) The organic phase is transported to the desorption unit, and a pre-cooled polar solvent is added to the desorption unit. I2 in the organic phase precipitates to form crystals. The crystals are recovered and returned to the Bunsen reaction. The remaining organic phase is de-polarized to remove the polar solvent and water, thereby regenerating TOPO. The regenerated TOPO is recovered to the extraction tower for reuse. The desorption unit is a desorption tank with stirring. The polar solvent is methanol, ethanol or isopropanol. The temperature of the pre-cooled polar solvent is -30℃ to -10℃, preferably -10℃. The volume ratio of polar solvent to organic phase is 2 to 5:1, preferably 3:1.

[0047] In a preferred embodiment of the invention, crystals precipitated in the organic phase are recovered by a vacuum filter; and polar solvents and water are removed from the remaining organic phase using a molecular sieve rotary evaporator.

[0048] 3) The aqueous phase from step 1) is transported to the electrodialysis system, where it is concentrated and separated under the action of an applied DC electric field; the principle of the electrodialysis system is as follows: Figure 3 As shown, 14 is the cathode, 15 is the cation exchange membrane, 16 is the anion exchange membrane, and 17 is the anode. The electrodialysis system is a series-connected heterogeneous ion exchange membrane structure, consisting of alternating cation exchange membranes 15 (CEM) and anion exchange membranes 16 (AEM) to form a membrane stack. A slit-type partition is arranged between the anion exchange membrane 16 and the cation exchange membrane 17 as a fluid flow channel. Figure 4 As shown, the slit-type partition is composed of serpentine slit channels 19. Each end of the slit channel 19 has a liquid guide hole 18 connected to the inlet and outlet. The slit channel 19 is formed by ribs arranged in a ribbed pattern; the area between adjacent ribs forms the slit channel for solution flow. The slit-type partition also supports the adjacent ion exchange membranes on both sides, preventing membrane bulging or collapse. This structure ensures a stable fluid channel while inducing moderate fluid disturbance at the rib boundaries, thereby reducing polarization and improving electrodialysis efficiency. This invention does not restrict the selection of membrane materials for the electrodialysis system. For AEM, anion exchange membranes with excellent chemical stability and mechanical strength under strongly acidic conditions (pH < 1), such as Fumasep FAA series anion exchange membranes, can be selected. Chemically cross-linked or CNT / acid-resistant polymer-modified anion exchange composite membranes can also be selected. For CEM, Nafion membranes or equivalent materials are used, possessing high selectivity for ion conduction and good acid resistance, enabling long-term stable operation in environments with ≥70% HI concentrations. With 50-100 membrane stacks, the scale and efficiency can be flexibly adjusted.

[0049] The operating current density of the electrodialysis system is 15~25 A / dm³. 2 Within the specified range, the temperature is maintained at 40-60℃, which reduces solution viscosity and increases ion mobility. The plate spacing is 2-5mm, and the channel adopts a slit-type structure to promote fluid turbulence and reduce polarization layer effects. Under the action of an applied DC electric field, HI is concentrated to ≥70%. The high-concentration HI solution obtained by the electrodialysis system is then transported to the downstream HI decomposition tower.

[0050] like Figure 5 The diagram shown is a flow chart of a sulfur-iodine cycle hydrogen production scheme based on the extraction-electrodialysis HI phase purification method of this invention. The following examples are combined with… Figure 5 The complete process of hydrogen production through sulfur-iodine cycle is described.

[0051] Example 1

[0052] (1) Bunsen reaction unit: 6827.8 mol H2O, 415.3 mol SO2, and 5238.8 mol I2 are introduced into Bunsen reaction tower 1; the Bunsen reaction occurs under the conditions of 5~15 atm and 100~150℃:

[0053]

[0054] SO2 mainly originates from sulfuric acid decomposition, I2 is obtained from the purification and separation of HIx phase solution and HI decomposition, and water mainly comes from sulfuric acid decomposition, circulating water for dissolving HI acid, and raw material water for system replenishment. Due to excess H2O and I2 during feeding, SO2 completely reacts to become H2SO4. The reaction product flows from the bottom of the reaction tower into the separation tower 2, where it is allowed to stand for 25 minutes at 5-15 atm and 100-150°C to achieve separation of the HI phase and the H2SO4 phase.

[0055] (2) Purification and decomposition of the HI phase: The HI phase solution obtained from the Bunsen reaction contains 4945.6 mol I2, 816.5 mol HI, 4219 mol H2O, and a small amount of sulfuric acid impurities. After being mixed with the HI solution that has not been decomposed in the HI decomposition tower, the HI phase solution is first transported to... Figure 1 Purification is performed using the HI extraction-electrodialysis module.

[0056] The HI phase solution is fed into extraction tower 10. The diagram of the extraction tower equipment is shown below. Figure 2As shown, the extract after dehydration and methanol removal enters the extraction tower through the light phase inlet. The extract is TOPO (tri-n-octylphosphine oxide), and a certain amount of inert diluent, n-hexane, is added to the extractant, with a TOPO:diluent ratio of 1:9. The HIx phase solution enters the extraction tower through the heavy phase inlet, with a volume ratio of 1:1 between the HI phase solution and the extractant. The extraction tower is externally jacketed or internally equipped with a coil heater. The liquid temperature is controlled at 45~50℃ by the jacket or coil heater. The motor drives the rotating shaft and disc to stir at a speed of 300~400 rpm for 20 minutes, causing the free I2 to complex into the organic phase. The extraction rate can reach over 95%, while HI is mainly retained in the aqueous phase. The upper organic phase enriches the TOPO-I2 complex and is transported to the methanol desorption unit 12 through the light phase solution outlet. It is maintained at -10°C in a low-temperature methanol desorption tank, and pre-cooled methanol is added. After stirring for 10-15 minutes, I2 precipitates and forms crystals. The I2 crystals are collected through a vacuum filter, yielding 1193.4 kg of I2 crystals. The iodine extraction and separation rate reaches 95%, and the crystals are recovered and returned to the Bunsen reaction tower 1. The filtrate is then passed through the organic phase dehydration and methanol removal unit 13, where methanol and water are removed using a molecular sieve rotary evaporator. First, the TOPO, methanol, and aqueous solution containing precipitated I2 are transported to the rotating cylinder of the rotary evaporator. The cylinder rotates at high speed under motor drive, controlled at 100 rpm, with a temperature of 60°C and a vacuum of -0.09 MPa inside the cylinder. Centrifugal force evenly spreads the solution on the inner wall of the cylinder, forming a thin liquid film. Simultaneously, the cylinder is heated, and the volatile water and methanol rapidly evaporate and vaporize. The vapor generated by evaporation (mainly methanol and water vapor) then passes through a 3A-type molecular sieve layer filling the top of the cylinder. Its special structure selectively adsorbs smaller water molecules, while slightly larger methanol molecules leave the cylinder and enter the condenser, where they are cooled and liquefied. Simultaneously, a mixture of unevaporated TOPO and n-hexane remains inside the cylinder, ultimately regenerating the extractant and methanol, yielding 0.47m of extractant. 3 The extractant recovery rate is approximately 94.1%, and the regenerated extractant is recycled back to the extraction tower 10 for reuse.

[0057] (3) The heavy phase solution is primarily an HI solution with a HI mass fraction of approximately 43%. It is fed to the electrodialysis system from the heavy phase outlet at the bottom of the extraction tower. This aqueous solution has already undergone effective removal of free I2 through the preceding TOPO extraction, making it suitable as feed for subsequent electrodialysis concentration. The operating current density of the electrodialysis system is 15~25 A / dm³. 2Within the specified range, the temperature is maintained at 40-60℃, which reduces solution viscosity and increases ion mobility. The plate spacing is 2-5mm, and the channel adopts a slit-type structure to promote fluid turbulence and reduce polarization layer effect. Under the action of an external DC electric field, HI is concentrated to ≥70%. The final high-concentration HI solution contains 1197.5mol HI and 3286.9mol H2O, with an HI solution concentration of 72.2%. The high-concentration HI solution is then transported to HI decomposition tower 3 for decomposition.

[0058] (4) Before the solution enters the HI decomposition tower 3, the HI solution is heated to 300℃ and vaporized by a heat exchanger. After entering the decomposition tower, the HI gas undergoes pyrolysis in an environment of 450~500℃: The output product of HI decomposition tower 3 is cooled to 60°C through a heat exchanger and then sent to gas-liquid separator 4. The 571.6 mol of undecomposed HI and the 369.8 mol of I2 produced by decomposition and the residue from extraction are mixed and sent to the HI extraction-electrodialysis module to obtain 312.9 mol of gaseous H2, which is then further dried and collected.

[0059] (5) Sulfuric acid purification and decomposition unit: The H2SO4 phase solution obtained from the Bunsen reaction is fed into the multi-effect evaporator 5 to concentrate the sulfuric acid solution. The mass fraction of sulfuric acid in the solution input into the multi-effect evaporator 5 is 37.9%, and the solution contains 415.3 mol H2SO4, 177 mol H2O, 72.8 mol HI, 14.1 mol I2, and a small amount of oxygen impurities. The multi-effect evaporator 5 finally produces concentrated sulfuric acid with a mass fraction of about 80%, which contains 396.4 mol H2SO4 and 534.1 mol H2O.

[0060] The concentrated sulfuric acid and the undecomposed sulfuric acid in sulfuric acid storage tank 8 are fed together into sulfuric acid decomposition reactor 6 to undergo a two-stage decomposition reaction. The first-stage decomposition reaction occurs in: The reaction conditions are 430~450℃; the second-stage decomposition reaction is carried out at 850~900℃ under catalytic conditions. The input materials to sulfuric acid decomposition reactor 6 include 711.5 mol H₂SO₄ and 970.2 mol H₂O; the output products include 193.2 mol O₂, 325.1 mol SO₃, 1681.7 mol H₂O, and 386.4 mol SO₂. After being cooled to 150-200℃, the output products are sent to gas-liquid separator 7 for gas-liquid separation, during which the following reaction occurs: The sulfuric acid liquid after gas-liquid separation is sent to sulfuric acid storage tank 8 and then pumped into sulfuric acid decomposition reactor 6. The remaining SO2 and O2 are cooled and pressurized to 30~50℃ and 0.1~0.5MPa and then sent to adsorption tower 9. The adsorption tower is filled with MFI type silica zeolite as adsorbent to adsorb and desorb SO2 for recovery and return to Bunsen reaction tower 1. O2 is discharged directly.

[0061] Example 2

[0062] The same procedure as in Example 1 was used, except for the choice of inert diluent. Cyclohexane was used as the inert diluent for TOPO in this example, replacing n-hexane in Example 1. The volume ratio of TOPO to cyclohexane was also 1:9, and the HI phase solution and extractant were mixed at a volume ratio of 1:1. All other operating parameters remained consistent with Example 1. Extraction results showed that the extraction efficiency of the TOPO-cyclohexane system was slightly lower than that of the TOPO-n-hexane system in Example 1. The final iodine extraction and separation rate reached 92.1%, yielding 1156.9 kg of iodine crystals. The concentration of the HI solution at the electrodialysis outlet reached 71.7%, containing 1163.4 mol HI and 3264.9 mol H2O.

[0063] Example 3

[0064] The same procedure as in Example 1 was used, except that the extractant dilution ratio was adjusted to TOPO:n-hexane = 1:8, while other operating parameters remained the same as in Example 1. Extraction results showed that the free I2 extraction rate was 92.6%, yielding 1165.8 mol of I2 crystals. After electrodialysis, the crystals were concentrated to 71.1%, yielding 1160.3 mol HI and 3300.5 mol H2O.

[0065] Example 4

[0066] The process is the same as in Example 1, except that the electrodialysis operating current density is increased to 25 A / dm³. 2 Other operating parameters were the same as in Example 1, but the HI concentration at the electrodialysis outlet was slightly increased to 73%, containing 1244.6 mol HI and 3270.2 mol H2O.

[0067] Comparative Example 1

[0068] The same process as in Example 1 was used, except for the choice of extractant. In this comparative example, TBP was used as the extractant to extract iodine. The extractant and HIx solution were added into the extraction tower at a volume ratio of 1:1, and the iodine was recovered through the same operation, yielding 845.4 kg of I2 crystals. The extraction and separation rate of iodine was only 67.3%. However, since TBP also has a certain extraction capacity for HI, the mass fraction of HI in the heavy phase solution after extraction was only 40%, resulting in a subsequent hydrogen production of 286.2 mol, which was 8.5% less than that in Example 1.

[0069] The results above demonstrate that this invention couples extraction and electrodialysis technologies and applies them to the HI phase purification and concentration process in thermochemical sulfur-iodine cycle hydrogen production, achieving efficient separation of HI and I2 and efficient concentration of HI. The mass fraction of HI in the HI solution is increased from 50-60% to over 70%. This invention uses a TOPO selective complexation extraction process for I2 to achieve HI and I2 separation. The TOPO to diluent ratio is 1:9, and the organic phase to aqueous phase volume ratio is 1:1, optimizing I2 extraction efficiency and selectivity. This invention is equipped with a molecular sieve rotary evaporator to regenerate TOPO, enabling the recycling of the extractant, reducing H2 production costs and environmental burden, and aligning with the goal of low-carbon hydrogen production.

[0070] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for HI purification based on the coupling of extraction and electrodialysis in sulfur-iodine cycle hydrogen production, characterized in that... Includes the following steps: 1) The HI phase solution obtained from the Bunsen reaction was fed into an extraction tower and extracted with an extractant to obtain an aqueous phase and an organic phase enriched with TOPO-I2 complex; the extractant was TOPO diluted with an inert diluent. 2) The organic phase is transported to the desorption unit, and a pre-cooled polar solvent is added to the desorption unit. I2 in the organic phase precipitates to form crystals. The crystals are recovered and returned to the Bunsen reaction. The remaining organic phase is depolarized to remove the polar solvent and water to obtain regenerated TOPO. The regenerated TOPO is recovered to the extraction tower for reuse. 3) The aqueous phase from step 1) is transported to the electrodialysis system and concentrated and separated under the action of an applied DC electric field. The electrodialysis system is a series heterogeneous ion exchange membrane structure, consisting of alternating cation exchange membranes and anion exchange membranes forming membrane pairs. The electrodialysis system contains 50-100 membrane pairs. The electrodialysis system obtains a high-concentration HI solution, which is then transported to the downstream HI decomposition tower.

2. The method according to claim 1, characterized in that, In step 1), the volume ratio of TOPO to inert diluent in the extract is 1:8~10; in the extraction tower, the volume ratio of HI phase solution to extractant is 1:0.8~1.

5.

3. The method according to claim 1, characterized in that, The inert diluent is one or more of n-hexane and cyclohexane.

4. The method according to claim 1, characterized in that, The extraction tower is equipped with an external jacket or a built-in coil heater. The material temperature is controlled at 45~50℃ by the jacket or coil heater. A stirring device is installed inside the extraction tower to stir the material.

5. The method according to claim 1, characterized in that, In step 2), the desorption unit is a desorption tank with stirring; the polar solvent is methanol, ethanol or isopropanol, and the temperature of the pre-cooled polar solvent is -30℃ to -10℃; the volume ratio of polar solvent to organic phase is 2 to 5:

1.

6. The method according to claim 1, characterized in that, In step 2), the crystals precipitated in the organic phase are recovered through a vacuum filter; the remaining organic phase is treated with a molecular sieve rotary evaporator to remove polar solvents and water; the cylinder temperature of the molecular sieve rotary evaporator is maintained at 50~70℃, the pressure is controlled between -0.095~-0.08MPa, and the rotation speed is maintained at 0~120rpm; the molecular sieve rotary evaporator is filled with type 3A molecular sieve with a particle diameter of 2~3mm, and the purity of the extractant recovered by the molecular sieve rotary evaporator is ≥90%.

7. The method according to claim 1, characterized in that, In step 3), the operating current density of the electrodialysis system is 15 A / dm³. 2 ~25A / dm 2 The temperature is maintained at 40-60℃; the mass percentage concentration of the high-concentration HI solution obtained by the electrodialysis system is ≥70%.

8. The method according to claim 1, characterized in that, In step 3), a partition is installed between the anion exchange membrane and the cation exchange membrane in the electrodialysis system. The partition is 2-5 mm thick, and the fluid channel inside the partition adopts a slit-type structure.

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