PREDICTION AND CORRELATION OF TRIGLYCERIDE-SOLVENT SOLID-LIQUID EQUILIBRIA WITH ACTIVITY-COEFFICIENT MODELS

Solid-liquid equilibria (SLE) for solvent-triacylglyceride (TAG) syste ms are studied with activity coefficient models. Systems consisted of 29 data sets of C10:0 to Cls:0 saturated triglycerides in nine solvent s, benzene, acetone, carbon disulfide, carbon tetrachloride, chlorofor m, diethyl ether, ethanol, ethyl acetate, and n-hexane making up 562 d ata points. Eighteen activity coefficient models containing 0-2 fittin g parameters were evaluated including a number of Flory Free Volume (F FV) and Entropic Free Volume (FEFV) models evaluated by Coutinho et al . [J.A.P. Coutinho, S.I. Andersen, E.H. Stenby, Evaluation of activity coefficient models in prediction of alkane solid-liquid equilibria, F luid Phase Equilibria 103 (1995) 23-39], the UNIFAC model and its vari ations, the Wilson, UNIQUAC, and van Laar equations and some proposed modifications of the FEFV and UNIFAC models. The modifications were as follows: (i) a Flory type chi parameter was added to the FEFV model ( EFFV-X) and (ii) the exponent in the UNIFAC combinatorial term was tre ated as a fitting parameter (UNIFAC-C). Models were compared in terms of absolute average percent deviation (AAPD) in temperature. The best predictive model for TAG-solvent systems was found to be the Dortmund version of UNIFAC. Addition of a fitting parameter to the UNIFAC model s provided significant improvement. For the UNIFAC-1977, UNIFAC (Lyngb y) and UNIFAC (Dortmund), these exponents were found to be 0.897, 0.85 8, and 0.749, respectively. The best single parameter correlative mode l was found to be the FEFV-X model, which gave an AAPD of 0.305%. The Wilson equation was the best two parameter correlation equation and pr ovided an AAPD of 0.154%. (C) 1998 Elsevier Science B.V.