Solubility of caffeine from green tea in supercritical CO2: a theoretical and empirical approach

Decaffeination of fresh green tea was carried out
with supercritical CO2 in the presence of ethanol as co-solvent.
The solubility of caffeine in supercritical CO2 varied from
44.19 × 10−6 to 149.55 × 10−6 (mole fraction) over a pressure
and temperature range of 15 to 35 MPa and 313 to 333 K,
respectively. The maximum solubility of caffeine was obtained
at 25 MPa and 323 K. Experimental solubility data were correlated
with the theoretical equation of state models Peng-
Robinson (PR), Soave Redlich-Kwong (SRK), and Redlich-
Kwong (RK). The RK model had regressed experimental data
with 15.52 % average absolute relative deviation (AARD). In
contrast, Gordillo empirical model regressed the best to experimental
data with only 0.96% AARD. Under supercritical conditions,
solubility of caffeine in tea matrix was lower than the
solubility of pure caffeine. Further, solubility of caffeine in
supercritical CO2 was compared with solubility of pure caffeine
in conventional solvents and a maximum solubility
90 × 10−3 mol fraction was obtained with chloroform.