951045.fig.003a
(a)
951045.fig.003b
(b)
Figure 3: (a) 2D contour plot and (b) 3D response surface curve of the constructed model displaying sulfur removal at different O/S and time. Oxidation condition: T = 65°C; aqueous phase pH = 1.5; acid/S = 20. Extraction condition: T = 22°C; solvent-to-oil volume ratio = 1; number of extraction stages = 2.