Optimization of Extractive Desulfurization of Diesel Oil in a Continuous Oldshue-Rushton Column Pilot Plant

In this study, a continuous sulfur extraction process in a pilot plant Oldshue-Rushton column has been studied, and its operating cost has been optimized, where the feed of the column was earlier produced in an oxidative desulfurization reactor. Dimethylformamide was used as a polar solvent to remove the sulfur-containing compounds of the oxidized diesel in the extraction column. The effects of agitation speed (100-200 rpm) and inlet flow rate of the solvent to the column (33-165 mL/min) on the holdup, sulfur removal, diesel recovery, and solvent recovery were investigated, utilizing the response surface methodology. The operating cost during the continuous-flow extraction process, consisting of the chemical cost, electricity cost, and the health cost related to the SO2 emission, was also applied as a criterion to optimize the process. The best performance of the extraction process was achieved at ambient temperature, where the inlet flow rate of the oxidized diesel was 99 mL/min, agitation speed was 107 rpm, and inlet flow rate of the solvent was 35 mL/min. In these conditions, dispersed phase holdup, sulfur removal, diesel recovery, and solvent recovery were 0.0101, 92.75, 91.80, and 96.90%, respectively. In addition, a considerable improvement in the sulfur removal as well as chemical consumption cost was achieved.