The solubility of avocado oil in scCO2 was calculated from the
slope of the extraction curves in the constant extraction step, as
shown in Table 3.
The solubility of avocado oil in scCO2 as a function of temperature
and pressurewas correlated by the Chrastil equation (1982), as
written by equation (3). The parameters k, a, and b were obtained
by fitting the experimental data to the model, according to Eq. (5),
using a computer program which minimizes an objective function,
using the modified Nelder and Mead simplex method
The comparison between experimental values and those
calculated by the model is shown in Table 3 and Fig. 5. In addition, a
comparison between the experimental values is shown in Fig 6 to
illustrate the solubility behavior as a function of temperature and
pressure.
The solubility of a solute depends on the solvent density and
solute vapor pressure, as indicated by the Chrastil equation. The
increase in temperature decreases the density of the solvent, but
increases its vapor pressure, resulting in a pressure condition
where the effects are offset and the solubility behavior is reversed
with temperature. Below the crossover pressure, solubility decreases
with the increase in temperature, and above this point the
higher temperature increases the solubility. The crossover pressures
for solubility of various substances in scCO2 have been reported
by several authors, including 250 bar for squalene