The effects of the operation conditions on the extraction yield are shown in Figs. 2 and 3. During the initial period of any extraction curve, the solute’s accessibility results in a maximal extraction rate that is constant. Hence, the slope of the extraction curve, the mass of extract versus the mass of CO2, can be used to determine the solved content of RHSO in CO2. This value corresponds to apparent solubil-ity (S) if extraction process is in equilibrium. The initial extractionrate (RExt, g RHSO kg/dry solid/h) were obtained from the slope of the first linear extraction period of the extraction curves as given in these figures except for Fig. 3b. However, the solved content of RHSO in CO2 or S (g RHSO/kg CO2) was also obtained from the data which were plotted as the mass of RHSO extracted versus the mass of CO2 utilized.