Sulfur release and its transformation behavior of sulfur-containing model compounds during pyrolysis under CO2 atmosphere

Sulfur release behavior of selected sulfur-containing compounds, tetradecyl mercaptan, dibutyl sulfide, phenyl sulfide, 2-methyl thiophene, benzo-thiophene and dibenzo-thiophene, were investigated by pyrolysis coupled with mass spectrometer (Py-MS) and pyrolysis connected with gas chromatogram (Py-GC) under CO2 atmosphere. It was found that the order of sulfur stability is tetradecyl mercaptan < dibutyl sulfide < phenyl sulfide < 2-methyl thiophene < benzo thiophene < dibenzo thiophene under CO2 atmosphere. The decomposition temperature of each sulfur compound is lower under CO2 atmosphere than that under inert atmosphere during pyrolysis, which indicates that CO2 can help breaking C-S bonds. For tetradecyl mercaptan and dibutyl sulfide, CO2 atmosphere can promote the release of H2S, COS and SO2 in the gas phase, especially with the sharp increase of the COS amount. However, for phenyl sulfide, dibenzo thiophene, 2-methyl thiophene and benzo thiophene, COS release amount under CO2 atmosphere is much higher than that under Ar atmosphere, while the release amount of H2S and SO2 under CO2 atmosphere is lower than that under Ar atmosphere. COS release of these thiophene compounds increases with the temperature increasing up to 850 °C under CO2 atmosphere, meanwhile CO release of these three sulfur-containing compounds are also increasing. This testifies that the COS formation is related to the CO formation at higher temperatures.