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.