Chemical reactor network modeling of a microwave plasma thermal decomposition of H ₂S into hydrogen and sulfur

The conventional treatment method for H ₂S is the Claus process, which produces sulfur and water. This results in a loss of the valuable potential product hydrogen. H ₂S treatment would be more economically valuable if both hydrogen and sulfur products could be recovered. Based on standard heats of formation analysis, the theoretical energy required to produce hydrogen from H ₂S dissociation is only 20.6 kJ/mol of H ₂ as compared to 63.2 kJ/mol of H ₂ from steam methane reforming and 285.8 kJ/mol of H ₂ from water electrolysis. Among the many thermal decomposition methods that have been explored in the literature, Micro-wave plasma dissociation of H ₂S prevails as the method of choice to attain the best conversion and energy efficiency. Chemical kinetics simulations using an ideal flow reactor network have been carried out on the CHEMKIN-PRO software package and they support these findings. The reactor network simulates the thermal plasma behavior in the plasma torch, the plasma reactor, and the sulfur condenser. Two chemical kinetics mechanisms have been used and the results show an almost complete conversion of H ₂S into hydrogen and sulfur in the plasma reactor at an optimum temperature of about 2400 K at atmospheric pressure. While the most challenging task of the process is found to be the plasma cooling rate at the sulfur condenser where very fast quenching is required to conserve the hydrogen product from converting back to H ₂S.