Hydrous pyrolysis of organic sulfur compounds: Species and distribution of secondary derivatives

The species and distributions of secondary compounds generated from eight organic sulfur compounds by way of hydrous pyrolysis were investigated. The results indicate that the formation of the secondary compounds and their structures and distribution depend on their thermal stability and the types of initial model compounds, as well as hydrous pyrolysis temperatures, while a large number and higher abundance of the secondary compounds appear to be formed mainly between 200 and 270 °C. Assignment of these secondary compounds indicates that alkyl thiols and sulfides are the most reactive compounds, producing a large number and relatively high amount of secondary organic thiols, sulfides, disulfides, sulfoxides and sulfones; while the secondary compounds generated from the thiophenic compounds are mainly low abundant methylated isomers of their own. Disulfidization, sulfidization and oxidation are the most significant mechanism(s) associated with the transformation of the initial thiols and sulfides model compounds. Alkyl thiophenes are only found to be formed from the alkyl thiol and sulfides, while it is noticed that thiophene, benzothiophene and dibenzothiophene are not genetically connected as they are not precursors of each other. Methylated thiophenic compounds are quantitatively insignificant but commonly present in the pyrolysates of thiophenes, benzothiophenes and dibenzothiophenes.