Ultrasound-assisted oxidative desulfurization of Arabian extra light oil (AXL) with molecular characterization of the sulfur compounds

The oxidative desulfurization (ODS) of model oil (BT, DBT, and 4,6-DMDBT) was studied with Mo/Ti-TUD-1 catalyst under mechanical stirring and ultrasonic-assisted conditions. ODS of DBT followed the pseudo-first-order kinetic model under both conditions and achieved a maximum conversion of 99%. The use of ultrasound instead of mechanical stirring significantly shortens the reaction time from 80 to 15 min. The oxidative reactivity of sulfur compounds in the model oil followed the same order under the mechanical stirring and ultrasound: 4,6-DMDBT > DBT > BT. Then ultrasound-assisted oxidative desulfurization of Arabia extra light oil was performed at 60 °C. It removed 56.5% of sulfur from the Arabian extra light oil feedstock. APPI FT-ICR characterized the sulfur compounds distribution. The S1, S2, O2S1, and O4S2 class species were identified in Arabian extra light oil feedstock, raffinate, and methanol extraction phase samples. The abundant O2S1 class species which had 9–15 Double Bond Equivalent (DBE) values and 15–30 carbon numbers, O4S2 class species with 11–20 DBE and 20 < carbon number < 40 were detected in the extraction phase. 1H NMR and 13C NMR results revealed that the molecular structure in Arabian extra light oil is aromatic-base with a high alkylation degree. Combined with the FT-ICR and NMR results, those sulfur-containing compounds with lower alkylation degrees were converted to sulfone over Mo/Ti-TUD-1 catalyst and extracted by methanol.