Ferulic acid solubility in supercritical carbon dioxide, ethanol and water mixtures

Ferulic acid (FA) is a phenolic compound present in many natural extracts. To obtain high FA extraction yields using supercritical carbon dioxide (scCO2), the extraction should be performed in the presence of co-solvents. This work reports FA solubility in scCO2/ethanol/water mixtures and its thermodynamic modelling using the Peng-Robinson equation of state. FA solubility in scCO2/ethanol was measured by a dynamic method at different temperatures (313, 323 and 333) K, pressures (20, 30 and 40) MPa and mole ratios of the scCO2/ethanol mixture (95:5 and 90:10). FA solubility in scCO2 with ethanol and water was evaluated at 323 K and 30 MPa, at three different mole ratios of the scCO2/ethanol/water mixture (97.4:2:0.6, 93.5:5:1.5 and 88:9.3:2.7). Also measured was the solubility of FA in water and in ethanol at ambient pressure. By using 10% ethanol, the FA solubility in (scCO2 + ethanol) attained values 120 times higher than FA solubility in pure scCO2 and about 50 times lower than solubility in ethanol. The lowest value was obtained at 313 K and 20 MPa and the highest at 333 K and 40 MPa (1.9 × 10−3); however, the co-solvent effect decreased when increasing pressure. Finally, the presence of the co-solvent is very important to obtain natural extracts rich in ferulic acid. The prediction of FA solubility in ternary and quaternary systems using the binary interaction parameters did not produce good results. Calculated values were smaller than the experimental values, probably due to the strong interactions between acid molecules and alcohol.