Desulphurization of gas oil in a packed bed extractor: Optimization of operating parameters for simultaneous maximization of efficiency and yield by desirability approach†

A full factorial central composite design (CCD) method was used to design the experiments for extractive desulphurization of straight run gas oil (SRGO) containing 0.013 g/g (1.3 wt%) sulphur in a packed bed extractor using N-N-dimethyl formamide (DMF) as solvent. The operational parameters, namely water concentration (W-C) in main solvent, solvent-to-feed ratio (S/F), and extraction temperature (T-E) which affect the sulphur removal and yield were used as input variables in design of experiments. Considering the trade-off between sulphur removal and yield, multi-response optimization with a desirability function approach has been used to estimate the optimized value of these operating parameters so as to maximize sulphur removal and yield of extracted straight run gas oil (ESRGO). Optimum values of selected variables were: water content in solvent = 2.91, solvent-to-feed ratio = 1.70, and extraction temperature = 46.4 degrees C. At the maximum desirability value, ESRGO yield and percent sulphur removal were 81.67 and 60.53 %, respectively. Since importance of sulphur removal and yield would depend on the secondary process to be selected for reducing the sulphur to 50-10 ppm, an analysis of goal importance effect on the optimized value of operational parameters for maximum desirability was also presented and discussed.