The effect of the extraction pressure (20–40 MPa) and temperature
(40–60 ◦C) on the extraction yield was examined under the
conditions of 0.75 mL/min and 355 < Dp < 500 m. The obtained
experimental findings are shown in Fig. 3c. Although the operating
temperature has a significant effect on the extraction yield at
a constant pressure of 20 MPa, but there is no such effect under
a pressure of 30 MPa or more. At a constant pressure of 20 MPa,
when the temperature was increased from 40 to 60 ◦C, the recovery
of oil in the seed improved at a ratio of 2/3–1/2 at 5 h. This is
caused by the low solvating power of scCO2 under a pressure of
20 MPa and a temperature between 40 and 60 ◦C. Therefore, it is
necessary to increase the operating time in order to fully recover
the oil in the seeds. Similarly Illes et al. [26] also found that small
amount of RHSO can be recovered by scCO2 at the lowest operating
pressure (10 MPa) and low scCO2 density (less than 600 g/L). At 30
and 40 MPa, for all operating temperatures examined, the oil can
be fully extracted in shorter operating time such as 150 and 90 min,
respectively. The extraction rate increases as the operating pressure
increases during the first periods of the separation process at a constant
operating temperature. The density of scCO2 increases with
increasing operating pressure at a constant operating temperature.
Therefore, the solubility of the oil also increases. Our experimental
results at 40 MPa showed a negligible effect of the operating
temperature increase on the initial extraction rate; i.e. the experimental
point at different operating temperature practically overlap
as shown in Fig. 3c. Indeed, the experiments performed at 40 MPa
and over give extraction rates at different temperature that could be
in agreement with the previous studies [27–29]. However, different
findings as stated by Machmudah et al.[31] have also been reported
in the literature. They reported that the extraction yield decreases
with increasing temperature at 15 and 30 MPa, but increases with
increasing temperature at 45 MPa. Therefore their high extraction
yields (13–16%wt.) were reached at the conditions of between 30
and 45 MPa of pressure at 40–80 ◦C