## 4 Experimental Procedure and Results  
### Partial Experimental Results and Discussion  
After the completion of the Bunsen reaction, a settling process is required to ensure complete phase separation. This settling time is particularly important for the iodine-sulfur hydrogen production system, as it is closely related to the stable operation of the system and hydrogen production rate. First, the molar ratio of the materials (H\({}_{2}\)SO\({}_{4}\):HI:\({}_{2}\):H\({}_{2}\)O = 1:2:2:12) is fixed, followed by precise metering and transfer to the reaction vessel. The external circulation pump is then activated. When the four-component mixed solution reaches 85 \({}^{\circ}\)C, the circulation pump is turned off, and the valve at the bottom of the Bunsen reaction tank is opened to release it into the liquid-liquid separation tank for gravity-driven separation. Samples were collected every 10 min over a 30 min period and analyzed via potentiometric titration. Figure 9 shows the trend of the H\({}_{2}\)SO\({}_{4}\) phase component concentrations in the liquid-liquid separation tank over time. After 25 min of settling, the component concentrations stabilize and remain almost constant. At this point, the upper-phase ratio is H\({}_{2}\)SO\({}_{4}\):HI:\({}_{2}\):H\({}_{2}\)O = 4.29:0.37:0.098:28.145, and the concentration of H\({}_{2}\)SO\({}_{4}\) is approximately 42 wt%. This phenomenon indicates that, under optimal molar ratios, the mixed solution can quickly achieve phase stratification, and as time progresses, the component concentrations stabilize. Therefore, the settling time for phase separation in the subsequent full-process pilot will be set to 25 min. During the experiment, the concept of purification efficiency was introduced to assess the purification effect. For the purification of the HI\({}_{\rm x}\) phase, the purification rate of the HI\({}_{\rm x}\) phase was obtained by measuring the concentration of sulfuric acid before and after purification. The calculation formula is as follows:  
\[\delta~{}=~{}\frac{C_{0}-C_{f}}{C_{0}}\times 100\% \tag{7}\]  
Figure 9: The trend of changes in the concentration of each component in the upper H\({}_{2}\)SO\({}_{4}\) phase over time. where \(C_{0}\) represents the initial concentration of impurities before purification, and \(C_{f}\) represents the concentration of remaining impurities after purification. Due to the low sulfuric acid content and high iodine and water content in the HIx phase, a slight reverse reaction occurs at 97 \({}^{\circ}\)C, while a side reaction involving the formation of sulfur occurs after 107 \({}^{\circ}\)C [26]. Based on these findings, during the operation of the HIx phase purification tower, the reaction temperature was set to 97 \({}^{\circ}\)C. Under these conditions, a four-component mixed solution with a total material molar ratio of H2 SO4:HI:I2:H2O = 1:2:2:12 was selected as the research object. After phase separation, the lower-phase HIx phase material had a molar ratio of H2 SO4:HI:I2:H2O = 0.13:1.56:2.62:6.81. The trend of the HIx phase purification rate in the experiment over time is shown in Figure 10. The purification efficiency of HI increased with time, reaching 88% after a residence time of 120 min, which essentially meets the requirements. During the HI distillation operation, the purified HIx phase mixture, as described above, was used as the research object. After purification, the molar ratio of H2 SO4:HI:I2:H2O in the HIx phase material was 0.025:0.61:2.2:6.1. A feeding flow rate of 1 L/min was used, and by properly controlling the reboiler discharge flow, reflux ratio, tower temperature, and other factors, a continuous and stable HI output was eventually achieved. Given that HI is the key product required for distillation, the separation capacity of the top and reboiler of the column was characterized using two parameters: the molar ratio of I2 to HI and the molar ratio of H2O to HI [27].