The Sulfur-Iodine(SI) thermochemical hydrogen production process is one of the most promising thermochemical water splitting technologies. SI process consists of three sections, which are so called the Bunsen reaction section, the H2SO4 decomposition section and HI decomposition section.
In the integrated operation of the SI process, the O2 produced from a H2SO4 decomposition section could be supplied directly to the Bunsen reaction section without preliminary separation. A HIx(I2+HI+H2O) solution could be also provided as the reactants in a Bunsen reaction section, since the sole separation of I2 in a HIx solution recycled from a HI decomposition section was very difficult. Therefore, the Bunsen reaction using SO2-O2 mixture gases was carried out to identify the effect of O2. The experiments have been performed at I2 saturation points of each temperature with SO2 and SO2-O2 mixture gases. Furthermore, a series of experiment were performed at 333 K to identify the effect of the amount of O2 in SO2-O2 mixture gases.
In the first place, we investigated the Bunsen reaction using SO2-O2 mixture gases in the presence of I2/H2O mixture. As the results, the amount of I2 unreacted under the feed of SO2-O2 mixture gases was higher than that under the feed of SO2 gas only. In the phase separation of the products, the amount of a H2SO4 impurity in HIx phase increased, while the amount of HI and I2 in a H2SO4 phase decreased with feeding the SO2-O2 mixture gases. The effects of O2 in SO2-O2 mixture gases were decreased with increasing temperature. In addition, the volume fraction of a H2SO4 solution decreased with increasing the O2/SO2 molar ratio.
In the second place, the effect of O2 on the Bunsen reaction was investigated by supplying SO2-O2 mixture gases in the presence of HIx solution. As the results, the amount of I2 unreacted under the feed of SO2-O2 mixture gases was little higher than that under the feed of SO2 gas only, and the amount of HI produced was relatively decreased. The O2 in SO2-O2 mixture gases also played a role to decrease the amount of a impurity in HIx phase by only striping effect, while that in a H2SO4 phase was hardly affected.
On the basis of striping effect of O2 in SO2-O2 mixture gases, purification effect is confirmed at the purification section of each phase solution with O2.