The solid phase mass transfer coefficients (kXA) resulted rather
similar in the fitting of all OECs (see Table 4). In general, kXA values
were two orders of magnitude lower than kYA values, indicating a
strong limitation of caffeine mass transfer in the solid phase. This
limitation become evident from the beginning of the extraction and
thus, it is possible that the saturation of the supercritical phase was
not attained. Furthermore, kXA values resulted reasonably similar
for all cosolvents used, representing similar mass transfer in the
solid phase. Regarding fluid phase mass transfer coefficient (kYA),
values were 1.8 and 2.6 times higher for, respectively, CO2 + ETOH
and CO2 + EL, with respect to pure CO2 or CO2 + EA.