The oil yields of Eucalyptus leaves obtained by SFE under all conditions, hydro-distillation and Soxhlet extraction with ethanol and hexane are summarised in Fig. 6. It can be seen that Soxhlet extraction with ethanol brought out the highest oil yield of 36.33%, while hydro-distillation had the lowest yield of 3.77% and the SFE showed an intermediate yield. The SFE yield was up to 4.78%, comparable in magnitude with the hexane Soxhlet results. Similar results have been reported by other authors [22,23]. Glisic et al. [22] investigated the SC-CO2 extraction of Dalmatian sage and
compared that with Soxhlet extraction using ethanol–water (70:30) mixture and hydro-distillation. Their results revealed that the Soxhlet extraction achieved the highest yield of 26.5 wt%, while SC-CO2 extraction at 30 MPa resulted in a yield of 4.82 wt% and hydro-distillation only gave a yield of 0.5% (v/w) of essential oil. They explained that the SFE allowed a wide range of chemicals to be isolated, while hydro-distillation was limited to volatile compounds and Soxhlet extraction was limited to high molecular compounds. Vági et al. [24] have also compared the extracts from
marjoram using SC-CO2 (50 C and 45 MPa), ethanol Soxhlet extraction and hydro-distillation and the oil yields were 3.8 g/ 100 g, 9.1 g/100 g, and 0.8 ml/100 g, respectively. However, the SFE comprised 21% essential oil, while the alcoholic extract contained only 9% volatile oil substance. Zhao and Zhang [25] also compared the supercritical fluid extraction of M. oleifera leaves oil with the Soxhlet hexane extraction. The yield of the SFE process (the highest yield was 6.3%) was lower than that of the Soxhlet hexane extraction (9.3%).