Analysis of sulfur species in the residua fractions of Kazakhstan and Russia crude oils by pyrolysisgas chromatography

The sulfur species and their distribution in the residua of Kazakhstan and Russia crude oils were investigated by using pyrolysisgas chromatography (PY-GC) with the pulsed flame photometric detector (PFPD). The major sulfur-containing products from the residua pyrolysis were H2S, thiophene species, benzothiophene (BT) species and dibenzothiophene (DBT) species; therefore, the pyrolysis of the model compounds thiophene, BT and DBT under 400℃~1000℃ for 5s～10s was carried out to determine the origin of sulfur species in the residua. Thiophene can easily be cracked into H2S, while BT and DBT are partially cracked into H2S. The reactivity of BT and DBT can be inhibited for pyrolysis in the blend of thiophene, BT and DBT; thus the sulfur pyrolysates can illustrate the origin of BT and DBT, while thiophene may be under estimated since it can easily be cracked. The residua of Kazakhstan and Russia crude oils were separated into 18 and 19 narrow cuts, respectively, by supercritical fluid extraction and fractionation. The sulfur species distribution for sulfides, thiophenes, BTs and DBTs in these narrow cuts and non extractable end cuts were obtained through the pyrolysis at 1000℃ for 10s. As the cuts become heavier, the sulfur content in each cut increases; the relative fraction of thiophene sulfur in total sulfur content also increases, while the relative sulfide sulfur fraction decreases. Russia vacuum residue and its cuts show higher total thiophene contents than Kazakhstan vacuum residue and its corresponding cuts.