The decomposition of aromatic hydrocarbons during coal pyrolysis in hydrogen plasma: A density functional theory study

Coal pyrolysis in hydrogen plasma has been proposed to undergo two steps. Volatiles such as aromatic hydrocarbons vaporize from coal and subsequently decompose to produce acetylene and hydrogen. We employed a density functional theory (DFT) to investigate the decomposition pathway of benzene, a model aromatic hydrocarbon, for understanding the coal pyrolysis in hydrogen plasma. The results indicate that there are two low-energy decomposition channels. Active hydrogen atoms in the plasma play an important role in the initiation of benzene decomposition, which leads to the formation of c-C6H5 particle and hydrogen molecule. The c-C6H5 could further decompose to yield acetylene, hydrogen and carbon soot, which is more favorable based on its lower activation energies. The decomposition makes the primary contribution to acetylene formation, and the dehydrogenation results in the additional hydrogen gas and serious coking. The active hydrogen atoms in plasma can remarkably lessen the energy barriers required for the reactions.