A MOLECULAR SIMULATION-BASED METHOD FOR THE ESTIMATION OF ACTIVITY-COEFFICIENTS FOR ALKANE SOLUTIONS

In a recent study Sheng et al. (1995, A.I. Ch.E. J. 41 (10) 2306-2313) presented activity coefficients calculated by molecular simulation (M S) for athermal model polymer-solvent systems. Both activity coefficie nts of the monomeric solvent in the polymer (gamma(1)(infinity)) and o f the polymer in the solvent (gamma(2)(infinity)) were calculated at i nfinite dilution conditions. The MS data cover a broad range of system asymmetry with respect to size in the area of oligomer-solvent mixtur es (up to segment ratio 60/1 which corresponds to e.g. a system of n-h eptane with nC(460)). The MS results were compared with classical and recently proposed free-volume (FV) activity coefficient models in orde r to conclude on the suitability of the models for phase equilibrium c alculations for asymmetric systems. On the basis of the work by Sheng et al., extrapolation methods for estimating the activity coefficient of a solvent and that of a polymer in real solvent-polymer systems are developed here. The so-obtained MS-based activity coefficients are co mpared with experimental data (in the case of solvent activities) and with the predictions of various activity coefficients models (in the c ase of polymer activities). Copyright (C) 1996 Elsevier Science Ltd.