HI purification method and system based on extraction and electrodialysis coupling

Abstract

The invention provides an HI purification method and system based on extraction and electrodialysis coupling. The method comprises the following steps: 1) carrying out selective complexation extraction on free iodine and triiodide ions in an HIx phase by adopting tri-n-octylphosphine oxide (TOPO) as an extracting agent; 2) performing low-temperature methanol desorption on the TOPO-I2 complex to realize Irecovery and TOPO regeneration; 3) deeply concentrating through an acid-resistant anion exchange electrodialysis membrane (perfluorosulfonic acid-CNT composite AEM), and increasing the HI concentration to be more than or equal to 70%; and 4) performing high-temperature thermal cracking on the HI to generate hydrogen and I2. The method integrates extraction and electrodialysis technologies to realize sulfur-iodine hydrogen production HI purification and two-stage separation, and free I2 is removed in advance through TOPO extraction, so that the content of iodine in a solution entering an electrodialysis system is greatly reduced, the iodine is prevented from being deposited on the surface of a membrane, the electrodialysis process is inhibited, the selectivity and flux of long-term operation of the membrane are ensured, the service life of the membrane is prolonged, and the quality of the membrane is improved. The operation and maintenance cost is reduced.

Description

TECHNICAL FIELD

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

[0002] The thermochemical sulfur-iodine cycle hydrogen production is the most ideal and mature method in the thermochemical cycle hydrogen production process. The main three reactions are Bunsen reaction, sulfuric acid decomposition and hydrogen iodide decomposition. Through the circulation of materials, the sulfur-containing material and the iodine-containing material are not consumed in the process, and only water is consumed as the source of hydrogen and oxygen generation. The total reaction is that water is decomposed into hydrogen and oxygen. The whole process only needs to add water, without adding other chemicals, and is green and environmentally friendly.

[0003] The Bunsen reaction uses iodine, SO2 and water as raw materials to occur the Bunsen reaction. In the Bunsen reaction, iodine and water are excessive, and the excessive iodine is used to make I2 and I - The combination enables the HIx phase and the sulfuric acid phase to be completely separated; the mixture enters the demixing column for two-phase separation; the HIx phase with a larger density is in the lower layer, and the sulfuric acid phase is in the upper layer.

[0004] For the HIx phase containing I2, HI, H2O, H2SO4 and the like, HI purification is needed before hydrogen iodide decomposition. The prior art has proposed many studies on the purification process of HI, mainly including:

[0005] (1) TBP single extraction HI technology: only TBP is used as an extractant, which has a certain extraction effect on HI and I2 in the HIx phase, and then HI and I2 are separated by subsequent operation to purify HI. However, TBP can also co-extract I2 under the condition of containing I2, which leads to a decrease in purification efficiency, and a separation operation of HI and I2 is needed later.

[0006] (2) Phosphoric acid extraction rectification: the U.S. GA company uses phosphoric acid to remove I2 in the HI-H2O-I2 mixed solution, and distills the remaining solution to obtain high-concentration HI. However, the phosphoric acid extraction rectification will introduce phosphoric acid impurities, and the phosphoric acid and impurities need to be further removed later.

[0007] (3) Direct rectification: CN114517714A directly uses a rectification tower to rectify the HI-H2O-I2 mixed solution. The light phase HI flows out after being vaporized from the top of the rectification tower, and the heavy phase I2 solution is collected at the bottom. This method cannot directly break the azeotropic balance, and the upper limit of the HI concentration is limited. In order to break through the azeotropic limit, the reflux ratio needs to be increased or the pressure needs to be reduced, which leads to an increase of 30%~50% in energy consumption.

[0008] (4) Electrochemical membrane separation: CN107904617B introduces a method of electrochemical decomposition of HI to produce hydrogen. HIx phase (containing HI, I2, H2O) is injected into the anode chamber, and platinum / carbon (Pt / C) catalyst is used. Deionized water is injected into the cathode chamber, and Pt / C catalyst is also used. Through anodic oxidation and cathodic reduction, HI is concentrated at the cathode and I2 is concentrated at the anode, realizing the separation of HI and I2. The operation conditions of electrochemical membrane separation are harsh, and the temperature and humidity need to be strictly controlled. It is sensitive to impurities in HIx phase. I2 on the anode side crystallizes at a temperature less than 40°C, which can easily pierce the membrane layer and form microporous defects.

[0009] (5) Cascade gas stripping method: CN114852960A gradually reduces the pressure and temperature through multiple gas stripping towers to make HI and a small amount of H2O overflow from the HIx solution in the form of gas, thereby realizing the separation and purification of HI. The impurity separation efficiency of the cascade gas stripping method is insufficient. Since I2 is extremely volatile, it is difficult to completely separate I2 during the gas stripping process, and I2 remains in the purified HI, which may cause poisoning of the subsequent decomposition catalyst and reduce the HI decomposition rate.

[0010] (6) CN114195094A uses high-temperature gas generated by sulfuric acid decomposition to heat the HI phase solution, causing water vapor to evaporate and thus achieving the purpose of concentrating the HI phase solution. This method does not separate I2 from the HI phase solution. Water vaporization also causes HI vaporization.

[0011] (7) CN107904617A proposes a method and device for electrochemical decomposition of HI to produce hydrogen in a sulfur-iodine cycle hydrogen production process. This technical solution uses an electrochemical decomposition method to produce hydrogen from HI obtained in the sulfur-iodine cycle hydrogen production process. CN107904617A electrochemically decomposes the HI obtained after the Bunsen reaction to produce hydrogen. This method does not consider removing I2 impurities from the solution, and directly sends the HIx solution containing a large amount of free I2 into the electrodialysis. I2 is easy to precipitate or oxidize on the membrane surface, causing membrane blockage or affecting membrane life, reducing system stability.

[0012] In summary, traditional distillation or direct membrane concentration of HIx phase solution, or direct electrodialysis of HIx phase solution, cannot selectively remove free I2, leading to crystallization and blockage of the distillation column, I2 fouling or corrosion of the membrane assembly, frequent shutdown for cleaning or replacement of the membrane material. Most membrane concentration or distillation processes can only concentrate HI to below 60%, resulting in low efficiency and high energy consumption in the high-temperature decomposition process. SUMMARY

[0013] The present application aims to overcome the deficiencies of the prior art, and provides a HI purification method and system based on coupling of extraction and electrodialysis. The present application uses TOPO (tri-n-octylphosphine oxide) / inert diluent organic phase high-efficiency complex extraction I2 before electrodialysis, which greatly reduces the content of I2 in the downstream process, avoiding plugging and corrosion. In addition, the present application can increase the HI concentration to ≥70% by connecting AEM / CEM electrodialysis, providing high-purity and high-concentration feed for the HI decomposition tower, and synchronously improving the cracking efficiency and hydrogen production rate.

[0014] The technical scheme of the present application is as follows:

[0015] The present application provides a HI purification method based on coupling of extraction and electrodialysis in a sulfur-iodine cycle hydrogen production system, which comprises the following steps:

[0016] 1) The HI phase solution obtained by the Bunsen reaction is sent to an extraction tower, and an extractant is used for extraction to obtain an aqueous phase and an organic phase rich in TOPO-I2 complex. The extractant is TOPO (tri-n-octylphosphine oxide) diluted with an inert diluent.

[0017] 2) The organic phase is transported to a desorption unit, and a pre-cooled polar solvent is added to the desorption unit. I2 in the organic phase is precipitated to form crystals, and the crystals are recycled back to the Bunsen reaction. The remaining organic phase is subjected to removal of the polar solvent and water to obtain regenerated TOPO, which is recycled to the extraction tower for reuse.

[0018] 3) The aqueous phase of step 1) is transported to an electrodialysis system, and concentration separation is carried out under the action of an external direct current electric field. The electrodialysis system is a series-type heterogeneous ion exchange membrane structure, which is composed of cation exchange membranes and anion exchange membranes arranged alternately to form membrane pairs. The electrodialysis system contains 50-100 pairs of membrane stacks. The electrodialysis system obtains a high-concentration HI solution, which is transported to a downstream HI decomposition tower.

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

[0020] According to a preferred embodiment of the present application, a jacket or a coil heater is installed outside the extraction tower, and the material temperature is controlled to be 45-50℃ by the jacket or the coil heater. A stirring device is arranged in the extraction tower to stir the material.

[0021] According to a preferred embodiment of the present application, the desorption unit is a desorption tank with stirring. The polar solvent is methanol, ethanol or isopropyl alcohol, and the pre-cooled polar solvent has a temperature of -30 to -10℃. The volume ratio of the polar solvent to the organic phase is 2-5:1.

[0022] According to the preferred scheme of the present application, the crystals separated out in the organic phase are recovered by a vacuum filter; and the remaining organic phase is subjected to removal of the polar solvent and water by a molecular sieve rotary evaporator.

[0023] According to the preferred scheme of the present application, the operating current density of the electrodialysis system is 15 A / dm 2 25 A / dm 2 , and the temperature is kept at 40-60℃; the mass percentage concentration of the high-concentration HI solution obtained by the electrodialysis system is ≥70%.

[0024] According to the preferred scheme of the present application, a baffle is arranged between the anion exchange membrane and the cation exchange membrane of the electrodialysis system, the thickness of the baffle is 2-5mm, and the fluid passage in the baffle adopts a slit type structure.

[0025] According to another application of the present application, the present application further provides an HI purification system for implementing the aforementioned method, which comprises:

[0026] an extraction tower for carrying out extraction of the HI phase solution to obtain an aqueous phase and an organic phase rich in TOPO-I2 complex, and the extraction agent used in the extraction is TOPO diluted by an inert diluent;

[0027] a desorption unit for carrying out desorption of the organic phase obtained by the extraction, and the desorption uses pre-cooled polar solvent;

[0028] a vacuum filter for filtering the crystal-containing organic phase obtained by the desorption unit to obtain I2 crystals and filtered organic phase;

[0029] a molecular sieve rotary evaporator for removing the polar solvent and water from the organic phase filtered by the vacuum filter to recover TOPO;

[0030] an electrodialysis system for concentrating the aqueous phase obtained by the extraction to obtain a high-concentration HI solution for carrying out HI decomposition.

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

[0032] 1) The present application constructs a combined process of “extraction + electrodialysis” for HI phase purification, realizing two-stage separation: first deiodination, and then HI concentration, that is, the present application removes free I2 in advance by TOPO extraction, so that the iodine content in the solution entering the electrodialysis system is greatly reduced, avoiding its deposition on the membrane surface, inhibiting the electrodialysis process, ensuring the selectivity and flux of the AEM / CEM membrane during long-term operation, prolonging the service life of the membrane, and reducing the operation and maintenance cost. The present application improves the HI separation efficiency and purity as a whole, while avoiding the blockage of pipelines by I2 and the influence on the subsequent process.

[0033] 2) The present application improves the extractant system, and the selectivity is greatly improved. The traditional HI phase purification technology through extraction process often uses TBP, which has extraction capacity for both HI and I2, and subsequent secondary separation of HI and I2 is required. This process discards TBP and uses pure TOPO system, which only targets I2 for coordination complexation, almost without taking HI, so that the extraction selectivity is improved from <50% (TBP) to >95% (TOPO), significantly simplifying the subsequent separation steps.

[0034] 3) The traditional composite solvent recovery often uses high-temperature distillation, which has high energy consumption and is easy to decompose the organic phase; the present application uses low-temperature methanol washing, low-temperature desorption of TOPO-I2 complex, and high-efficiency release of I2 (recovery rate >99%), while retaining the complete structure of TOPO (loss <5%), reducing material loss, and the process is mild and has high recycling efficiency. The I2 separated by the present application is recycled back to the Bunsen reaction tower for reuse, and the TOPO extractant can also be recycled, reducing the operating cost of the system. The present application realizes the recycling of the extractant, reduces the production cost and environmental burden of H2, and is suitable for low-carbon hydrogen production. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The present application is based on the flowchart of the HI purification method coupled with extraction and electrodialysis.

[0036] Figure 2 The present application is based on the flowchart of the HI purification method coupled with extraction and electrodialysis.

[0037] Figure 3 The present application is based on the flowchart of the HI purification method coupled with extraction and electrodialysis.

[0038] Figure 4 The present application is based on the flowchart of the HI purification method coupled with extraction and electrodialysis.

[0039] Figure 5 The present application is based on the flowchart of the HI purification method coupled with extraction and electrodialysis. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present application will be described in more detail below. Although the preferred embodiments of the present application are described below, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present application more thorough and complete, and to fully convey the scope of the present application to those skilled in the art.

[0041] As shown in Figure 1 The present application is based on the flowchart of the HI purification method coupled with extraction and electrodialysis. The present application is used to realize the concentration and purification of HI phase in the thermochemical sulfur-iodine cycle hydrogen production process, and the upstream process is the Bunsen reaction unit, and the 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 shows that it has a heavy phase inlet (introducing HI phase solution) and a light phase outlet (extracting organic phase enriched with TOPO-I2 complex) at the top of the tower, and a heavy phase outlet (extracting aqueous phase) and a light phase inlet (extractant inlet) at the bottom of the tower. The extraction tower is equipped with a jacket or has a built-in coil heater. 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 outside 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, 5238.8 mol I2 are put into the Bunsen reaction tower 1, and the Bunsen reaction occurs under the conditions of 5-15 atm and 100-150°C:

[0053]

[0054] Among them, SO2 mainly comes from sulfuric acid decomposition, I2 comes from HIx phase solution HIx purification separation and HI decomposition, and water mainly comes from sulfuric acid decomposition, circulating water for dissolving HI acid and system supplemented raw material water. Due to the excess of H2O and I2 when feeding, SO2 is completely reacted into H2SO4. After the reaction, the product flows from the bottom of the reaction tower into the stratification tower 2, and under the conditions of 5-15 atm and 100-150°C, it is static for 25 minutes to realize the stratification of HI phase and H2SO4 phase;

[0055] (2) Purification and decomposition of HI phase: the HI phase solution obtained by Bunsen reaction contains 4945.6 mol I2, 816.5 mol HI, 4219 mol H2O and a small amount of sulfuric acid impurities, which is mixed with the HI solution not decomposed in the HI decomposition tower, and then the HI phase solution is first sent to the HI extraction-electrodialysis module of Figure 1 for purification.

[0056] The HI phase solution is input into the extraction tower 10, and the equipment diagram of the extraction tower is as follows: Figure 2As shown, the extraction liquid after dehydration and methanol removal enters the extraction column from the light phase inlet, and the extraction liquid is TOPO (tri-n-octyl phosphine oxide), and a certain amount of inert diluent n-hexane needs to be added to the extraction agent, wherein TOPO:diluent = 1:9; the HIx phase solution enters the extraction column from the heavy phase inlet, and the HI phase solution is mixed with the extraction agent at a volume ratio of 1:1. A jacket or an internally built tube-plate heater is installed outside the extraction column, and the liquid temperature is controlled at 45-50°C through the jacket or the tube-plate heater. The motor drives the rotating shaft and the turntable to stir at a speed of 300-400 rpm for 20 minutes, so that the free I2 is complexed into the organic phase, and the extraction rate can reach more than 95%, while the HI mainly remains in the aqueous phase. The upper organic phase is rich in TOPO-I2 complex, which is transported to the methanol desorption unit 12 through the light phase solution outlet, and is kept at -10°C in the low-temperature methanol desorption tank, and pre-cooled methanol is added, and stirred for 10-15 minutes, and I2 is precipitated to form crystals, and I2 crystals are collected through a vacuum filter, and 1193.4 kg of I2 crystals are obtained, and the extraction separation rate of iodine reaches 95%, and is recovered to the Bunsen reaction column 1. The filtrate is transported to the organic phase dehydration and methanol removal unit 13, and the methanol and water are removed by a molecular sieve rotary evaporator. First, the TOPO, methanol and water solution in which I2 is precipitated is transported to the rotating cylinder of the rotary evaporator, the cylinder is driven by the motor to rotate at a high speed, the rotating speed is controlled at 100 rpm, the temperature is controlled at 60°C, and the vacuum degree in the cylinder is -0.09 MPa. At this time, the centrifugal force uniformly spreads the solution on the inner wall of the cylinder to form a thin liquid film. At the same time, the cylinder is heated, and the volatile water and methanol in the cylinder are rapidly evaporated and vaporized. The vapor (mainly methanol and water vapor) generated by evaporation then passes through the 3A molecular sieve layer filled at the top of the cylinder, which selectively adsorbs water molecules with smaller sizes, and methanol molecules with slightly larger sizes leave the cylinder and enter the condenser, where they are cooled and liquefied. The TOPO and n-hexane mixture in the cylinder is not evaporated, and finally the extraction agent and methanol are regenerated, and the extraction agent 0.47 m 3 , the extraction agent recovery rate is about 94.1%, and the regenerated extraction agent is recovered to the extraction column 10 for reuse.

[0057] (3) The heavy phase solution is basically a HI solution, and the mass fraction of HI is about 43%, which is transported from the heavy phase outlet at the bottom of the extraction column to the electrodialysis system. The aqueous solution has effectively removed free I2 through the previous TOPO extraction, and is suitable as the feed for subsequent electrodialysis concentration. The operating current density of the electrodialysis system is 15-25 A / dm 2temperature is kept at 40-60℃, which can reduce the solution viscosity and improve the ion mobility; the plate spacing is 2-5mm, and the channel adopts a slit structure to promote fluid disturbance and reduce the polarization layer effect. Under the action of an external direct current electric field, the HI is concentrated to ≥70%. Finally, 1197.5mol of HI and 3286.9mol of H2O are obtained in the high-concentration HI solution, and the HI solution concentration is 72.2%. The high-concentration HI solution is transported to the HI decomposition tower 3 for decomposition.

[0058] (4) Before the solution enters the HI decomposition tower 3, the HI solution is warmed to 300℃ and vaporized through a heat exchanger, and after entering the decomposition tower, the HI gas is cracked in an environment of 450-500℃: The output product of the HI decomposition tower 3 is cooled to 60℃ through a heat exchanger and then transported to a gas-liquid separator 4, and 571.6mol of undecomposed HI and 369.8mol of mixed solution of I2 produced by decomposition and residual extraction are recovered to the HI extraction-electrodialysis module, and 312.9mol of gaseous H2 is further dried and collected.

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

[0060] The concentrated sulfuric acid and the undecomposed sulfuric acid in the sulfuric acid storage tank 8 are jointly input into a sulfuric acid decomposition reactor 6 to undergo two-stage decomposition reactions. The first-stage decomposition reaction is carried out at: , and the reaction conditions are 430-450℃; the second-stage decomposition reaction is carried out at 850-900℃ with the catalysis of a catalyst: The input substances of the sulfuric acid decomposition reactor 6 contain 711.5mol of H2SO4, 970.2mol of H2O; the output products contain 193.2mol of O2, 325.1mol of SO3, 1681.7mol of H2O, and 386.4mol of SO2. The output products are cooled to 150-200℃ and then sent to a gas-liquid separator 7 for gas-liquid separation, during which the reaction: The gas-liquid separated sulfuric acid liquid is sent into the sulfuric acid storage tank 8, and is pumped into the sulfuric acid decomposition reactor 6 by a circulating pump. The remaining SO2 and O2 are cooled and pressurized to 30-50℃ and 0.1-0.5MPa, and then are sent to the adsorption tower 9. The adsorption tower is filled with MFI type silica zeolite as an adsorbent, and SO2 is adsorbed and desorbed for recovery, and is sent back to the Bunsen reaction tower 1. O2 is directly discharged.

[0061] Example 2

[0062] The same process as in Example 1 is used, except that the inert diluent is selected. In this example, cyclohexane is used as the inert diluent of TOPO, instead of n-hexane in Example 1. The volume of TOPO and cyclohexane is 1:9, the HI phase solution and the extractant are mixed at a volume ratio of 1:1, and all other operating parameters remain the same as in Example 1. The extraction results show that the extraction efficiency of the TOPO-cyclohexane system is slightly lower than that of the TOPO-n-hexane system in Example 1. The final extraction separation rate of iodine reaches 92.1%, and 1156.9 kg of iodine crystals are obtained. The HI solution concentration at the outlet of the electrodialysis reaches 71.7%, containing 1163.4 mol of HI and 3264.9 mol of H2O.

[0063] Example 3

[0064] The same process as in Example 1 is used, except that the dilution ratio of the extractant is adjusted to TOPO:n-hexane=1:8, and all other operating parameters remain the same as in Example 1. The extraction results show that the extraction rate of free I2 is 92.6, and I2 crystals with a mass of 1165.8 are obtained. After entering the electrodialysis, the concentration is increased to 71.1%, obtaining 1160.3 mol of HI and 3300.5 mol of H2O.

[0065] Example 4

[0066] The same process as in Example 1 is used, except that the operating current density of the electrodialysis is increased to 25A / dm 2 , and all other operating parameters remain the same as in Example 1. The HI concentration at the outlet of the electrodialysis is slightly increased to 73%, containing 1244.6 mol of HI and 3270.2 mol of H2O.

[0067] Comparative Example 1

[0068] The same process as example 1 was adopted, except for the selection of the extractant. In this comparative example, TBP was used as the extractant for the extraction of iodine. The extractant and the HIx solution were fed into the extraction column at a volume ratio of 1:1, and the same operation was used to recover iodine. The I2 crystal obtained was 845.4 kg, and the extraction 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 hydrogen production of 286.2 mol, which was 8.5% less than that of example 1.

[0069] From the above results, it can be seen that the present application couples the extraction technology with the electrodialysis technology and applies it to the HI phase purification and concentration process of the 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 more than 70%. The extraction process of the present application uses TOPO to selectively complex and extract I2, achieving the separation of HI and I2. The ratio of TOPO to diluent is 1:9, and the volume ratio of the organic phase to the aqueous phase is 1:1, optimizing the extraction efficiency and selectivity of I2. The present application uses a molecular sieve rotary evaporator to regenerate TOPO, achieving the recycling of the extractant, reducing the production cost and environmental burden of H2, and adapting to the target of low-carbon hydrogen production.

[0070] The above has described various embodiments of the present application, and the above description is exemplary and is not exhaustive, and is also not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for purifying HI based on coupling of extraction and electrodialysis in a hydrogen production process by the sulfur-iodine cycle, characterized in that Comprising the following steps: 1) The HI phase solution obtained by the Bunsen reaction is sent to an extraction tower, and an extractant is used for extraction to obtain an aqueous phase and an organic phase rich in TOPO-I2 complex; the extractant is TOPO diluted by inert diluent; 2) The organic phase is transported to a desorption unit, and pre-cooled polar solvent is added to the desorption unit, I2 in the organic phase is precipitated to form crystals, the crystals are recovered and returned to the Bunsen reaction, and the remaining organic phase is removed of polar solvent and water to obtain regenerated TOPO, which is recycled to the extraction tower for reuse; 3) The aqueous phase of step 1) is transported to an electrodialysis system, and concentrated separation is performed under the action of an applied direct current electric field; the electrodialysis system is a series type heterogeneous ion exchange membrane structure, which is composed of cation exchange membranes and anion exchange membranes arranged alternately to form membrane pairs, and the electrodialysis system comprises 50-100 pairs of membrane stacks; the electrodialysis system obtains a high-concentration HI solution, which is transported to a downstream HI decomposition tower.

2. The method of claim 1, wherein, In the extraction liquid of step 1), the volume ratio of TOPO to inert diluent is 1:8-10; in the extraction tower, the volume ratio of the HI phase solution to the extractant is 1:0.8-1.

5.

3. The method of claim 1, wherein, The inert diluent is one or more of n-hexane and cyclohexane.

4. The method of claim 1, wherein, The extraction tower is externally equipped with a jacket or internally provided with a coil heater, the material temperature is controlled to be 45-50℃ by the jacket or the coil heater, and a stirring device is arranged in the extraction tower to stir the material.

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

1.

6. The method of claim 1, wherein, In step 2), the crystals precipitated in the organic phase are recovered by a vacuum filter; the remaining organic phase is removed of polar solvent and water by a molecular sieve rotary evaporator; wherein the cylinder of the molecular sieve rotary evaporator is heated to a temperature of 50-70℃, the pressure is controlled to be-0.08 to 0.095 MPa, and the rotation speed is kept at 0-120 rpm; the molecular sieve rotary evaporator is filled with 3A molecular sieve with a particle diameter of 2-3 mm, and the purity of the extractant recovered by the molecular sieve rotary evaporator is ≥90%.

7. The method of claim 1, wherein, In step 3), the running current density of the electrodialysis system is 15 A / dm 2 25 A / dm 2 The temperature is kept at 40-60℃; the mass percentage concentration of the high-concentration HI solution obtained by the electrodialysis system is ≥70%.

8. The method of claim 1, wherein, In step 3), a partition plate is arranged between the anion exchange membrane and the cation exchange membrane of the electrodialysis system, the thickness of the partition plate is 2-5 mm, and the fluid passage in the partition plate adopts a slit type structure.

9. A HI purification system for use in the method of any one of claims 1-8, characterized in that Comprising: an extraction tower for extracting the HI phase solution to obtain an aqueous phase and an organic phase rich in TOPO-I2 complex, and the extractant used for extraction is TOPO diluted by inert diluent; a desorption unit for desorbing the organic phase obtained by extraction, and pre-cooled polar solvent is used for desorption; a vacuum filter for filtering the crystal-containing organic phase obtained by the desorption unit to obtain I2 crystals and filtered organic phase; a molecular sieve rotary evaporator for removing polar solvent and water from the organic phase filtered by the vacuum filter to recover TOPO; an electrodialysis system for concentrating the aqueous phase obtained by extraction to obtain a high-concentration HI solution for HI decomposition.

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