A comprehensive evaluation integrating thermodynamics and mechanism kinetics for the Bunsen reaction in a sustainable iodine–sulfur cycle

Abstract

Carbon neutrality makes hydrogen a promising alternative source of energy. Iodine-sulfur cycle shows the greatest potential among hydrogen production methods. Bunsen reaction holds significant research value as the core reaction of the iodine-sulfur cycle. This paper presents an innovative method for evaluating Bunsen reactions, integrating equilibrium thermodynamics and kinetics to explore the influence of temperature, pressure, and reactant concentration on the Bunsen reaction. The thermodynamic results show that the influence of pressure on reaction balance is weak; with the gradual excess of I2, the amount of H2O required for Bunsen reaction decreases; the optimal operation ratio of H2O:I2:SO2 is 16:4:1 at 360K; the Bunsen reaction system should be carried out in an acidic system, while H2O promotes the spontaneous exothermic reaction of Bunsen. Additionally, we propose 8 reactions as Bunsen reaction mechanisms, and derive the rate equation. Bunsen reaction rates are promoted by [I2], [I3−], and [SO2] concentrations, inhibited by [I−] and [H+] concentrations, and the reaction rate of the whole solution system is sensitive to pH, [I−] and [H+] concentration changes. Added H2O improves pH, whereas acidic systems benefit from higher pH. Lastly, the interconnection of thermodynamic and kinetic results is discussed and compared with other literature. The method proposed in this study has universal application value for Bunsen reaction. It contributes to system process optimization and Bunsen reactor amplification, and facilitating carbon neutralization and hydrogen energy.