Apparent kinetics of a gas–liquid–liquid system of Bunsen reaction with iodine-toluene solution for hydrogen production through H2S splitting cycle

Abstract

A chemical splitting cycle of H2S to produce H2 for sustainable oil sands bitumen upgrading was recently developed in our research group which includes three reactions (Wang, H. Hydrogen production from a chemical cycle of H2S splitting. International Journal of Hydrogen Energy 2007; 32:3907–14):H2S + H2SO4 → S + SO2 + 2H2O (H2S Oxidation) (1)2H2O + I2+SO2 → H2SO4 + 2HI (Bunsen Reaction) (2)2HI → H2 + I2 (HI decomposition) (3)With iodine provided by iodine-toluene solution, the Bunsen reaction can be conducted at room temperature. Compared with the General Atomics stoichiometry and operation condition for the sulfur–iodine cycle, this modification can minimize or avoid problems such as side reactions, corrosion and iodine deposition. In addition, it reduces the unnecessary transportation of the excessive cycling agents in the cycle. This work studies the apparent reaction rate of the Bunsen reaction in a gas–liquid–liquid multiphase system resulted from the presence of toluene in a closed, fixed-volume batch reactor using the initial rate analysis method. The reaction rate was found to be the first order with respect to SO2 and I2, respectively. The temperature effect on the reaction rate showed activation energy of 6.02 kJ/mol, which suggests that the rate-controlling step of the Bunsen reaction in the gas–liquid–liquid system is the step of SO2 absorption into the liquid phases. The variation of operating conditions including toluene/water volume ratio, agitation speed, and temperature confirmed the mass transfer rate-limiting step.