An Investigation on the Effect of Interfacial Tension on the Ultrasound Assisted Oxidative Desulfurization (UAOD)

Ultrasound assisted oxidative desulfurization (UAOD) is a new process for the sulfur removal from different middle distillate cuts. In the UAOD process, at first, the sulfur-containing compounds are oxidized using a suitable oxidation system under ultrasound irradiation. Then, the oxidized sulfur-containing compounds are separated by solvent extraction. In the present study, the effect of interfacial tension between aqueous and hydrocarbon phases on the sulfur removal of diesel fuel has been investigated for the first time. The selected oxidation system was hydrogen peroxide/formic acid system. In this regards, three different surfactants including anionic, cationic, and nonionic surfactants have been evaluated. The results revealed that the application of sodium dodecyl sulfate (SDS) as an anionic surfactant and cetyltrimethylammonium bromide (CTAB) as a cationic surfactant leads to the sulfur removal of 82.65 and 83.10% after oxidation followed by solvent extraction respectively. The sulfur removal in the absence of surfactants was 81.61% in the same oxidation and extraction conditions. The application of span 60 as a nonionic surfactant leads to a decrease in sulfur removal to 78.65% in the same oxidation and extraction conditions. However, the application of span 60 leads to about 3% increase in the sulfur removal in comparison with the case without surfactant after the oxidation step. Therefore, the addition of surfactants can lead to a positive effect on the oxidation step due to decreasing the interfacial tension between aqueous and hydrocarbon phases and a negative effect on the extraction step of the UAOD process.