Sulfur removal and release behaviors of sulfur-containing model compounds during pyrolysis under inert atmosphere by TG-MS connected with Py-GC

Abstract

Sulfur containing model compounds, tetradecyl mercaptan, dibutyl sulfide, phenyl sulfide, 2-methyl thiophene, benzothiophene and dibenzothiophene, were selected to investigate their sulfur removal and release behaviors during pyrolysis under inert atmosphere by thermo-gravimetric analyzer with mass spectrometer (TG-MS) and pyrolysis connected with gas chromatogram (Py-GC). It was found that the order of sulfur removal was tetradecyl mercaptan > dibutyl sulfide > 2-methyl thiophene > benzo thiophene > phenyl sulfide > dibenzothiophene. Except for phenylsulfide, this rule is contrary to the decomposition temperature order of the sulfur functional groups. SO2 evolution was detected by MS and GC for all those model compounds and COS evolution was also found except for phenylsulfide and dibenzothiophene; while H2S evolution was measured only for tetradecyl mercaptan, dibutyl sulfide and 2-methyl thiophene. However, SO2 content was much higher than H2S and COS in pyrolysis gas for each model compound, which may be caused by that indigenous hydrogen was much less than indigenous oxygen under inert atmosphere, when activated carbon was used as carrier. Thus, most of sulfur radicals can connect with indigenous oxygen and release in the form of SO2. For phenyl sulfide, benzothiophene and dibenzothiophene, as their indigenous hydrogen was not enough to react with sulfur radicals, no H2S was detected during pyrolysis under inert atmosphere, while SO2 was found and its content was very high in pyrolysis gas.