Mechanistic insight into the decomposition of sulfone compounds in supercritical water

Supercritical water gasification (SCWG) is famous for the clean utilization of organic wastes without SO_x emission. Investigating the decomposition mechanism of sulfone compounds, the dominant organic sulfur compounds of organic wastes, in supercritical water (SCW) is conducive to the development of SCWG technology. Herein, the comparative decomposition mechanism of phenyl vinyl sulfone (PVS), diphenyl sulfone (DS), and benzo[b]thiophene 1,1-dioxide (BD) are explored via experiments and density functional theoretical (DFT) calculations. Experiments on the decomposition characteristics of sulfone compounds in pyrolysis and SCW are conducted using a quartz tube reactor system at temperatures ranging from 400 °C to 700 °C. It is indicated that SCW can inhibit the generation of SO₂ during the decomposition of sulfone compounds. The multi-step decomposition pathways that sulfone compounds thermal decompose in pyrolysis and react with H₂O, H₂, and free radicals (H•/OH•) in SCW are proposed by DFT calculations. It is proved that the presence of H• and OH• in SCW changes the decomposition pathways of sulfone compounds to suppress the release of SO₂. This work contributes to a deeper understanding of the sulfur transformation of organic sulfur compounds and provides a theoretical foundation for the clean utilization of organic wastes in SCWG.