Stimulation calculation of desulfurization mechanisms dominated by free radicals reactions during pyrolysis of thiophenes under water vapor atmosphere

Abstract

The desulfurization mechanisms of thiophene and 2-methyl thiophene were investigated by the density functional theory (DFT) during pyrolysis under water vapor atmosphere. Based on the transition state theory (TST), the rate constants corresponding to these elementary reactions are calculated, meanwhile the speed and spontaneity of every reaction can be obtained from the aspect of kinetics. Theoretically, it is found that H2O (g) directly attacking CS bonds of thiophene and 2-methyl thiophene cannot easily generate COS and H2S even at 1200 K in terms of thermodynamics and kinetics. If the desulfurization mechanisms of thiophenes are investigated by free radicals mechanisms under steam atmosphere, their initial energy barriers needing to be overcome significantly reduce. Therefore, desulfurization mechanisms of thiophenes and H2O (g) are the most possibly dominated by radical reactions at higher temperatures and H2S is mainly generated.