Solubility of cinnamic acid in supercritical carbon dioxide and subcritical 1,1,1,2-tetrafluoroethane: Experimental data and modelling

To promote the extraction of natural cinnamic acid with supercritical and subcritical fluids, the solubility of cinnamic acid was measured respectively in supercritical carbon dioxide (SCCO 2 ) by the dynamic method and in subcritical 1,1,1,2-tetrafluoroethane (sub-R134a) by the static method. The experiments were performed at temperatures from 308 K to 328 K and pressures of 9.0, 11.0, 13.0, 15.0, and 18.0 MPa. The solubility of cinnamic acid in SCCO 2 and sub-R134a were compared by calculating the enhancement factor ( δ ), which indicated that the value of δ in sub-R134a is greater than that in SCCO 2 ; meanwhile, the entrainment factor ( ψ ), which describes the influence of co-solvent (ethanol, ethyl acetate and n -pentane) on the cinnamic acid solubility in SCCO 2 , showed that the solubility of cinnamic acid in SCCO 2 increased with the co-solvent polarity increasing. Six semi-empirical models (Chrastil, A-L, K-J, S-S, M-S-T, and Bartle) were used to correlate cinnamic acid solubility in binary system (cinnamic acid + SCCO 2 or sub-R134a) and four models (Gonzalea, Sovova, Tang and Sauceau) were used to correlate cinnamic acid solubility in ternary system (cinnamic acid + SCCO 2 +co-solvent). The enthalpy values of cinnamic acid, including Δ H total , Δ H sub. and Δ H sol. , were estimated through Chrastil and Bartle models; and the partial molar volume of cinnamic acid was calculated by K-J model. A new model was proposed on the basis of the molecular association theory and verified by 47 solid solutes solubility in SCCO 2 or sub-R134a with satisfactory correlation results.