The effects of pressure and temperature on the yield of
total oil extract were studied under the following conditions:
pressures at 10–30 MPa; temperatures at 313–353
K. Figure 3(a) shows the effect of pressure on the yield
of essential oil extract. At pressures of 20 and 30 MPa,
the yields of oil extract were higher compared to 10
MPa. At 353 K, under a pressure of 10 MPa, the density
of CO2 is 0.222 g/cm3, which is close to that of a gas. In
general, it is thought that increasing pressure at a
constant temperature increases extraction rate due to
apparent increase in SC-CO2 density [24]. However, on
the contrary, results in Figure 3(b) show that the yield of
oil extract was obviously increasing with decreasing SCCO2
density. For example, at temperatures of 313, 333,
and 353 K, the density of SC-CO2 is 0.910, 0.830, and
0.746 g/cm3, respectively, under a pressure of 30 MPa. If
the density of SC-CO2 is sufficient enough to dissolve the
target compounds such as terpenes, then the temperature
should also have an effect on the yield. These results indicate
that solubility of essential oil in SC-CO2 depends on
both density and temperature.