CHEMICAL THEORY FOR MIXTURES CONTAINING ANY NUMBER OF ALCOHOLS

In a previous paper (Pradham et al., 1993. Fluid Phase Equilibria, 84: 183-206) Flory-Huggins theory, regular solution theory, and the use of chemical equilibria to model hydrogen bonding were combined to form a simple association model for ternary mixtures containing two alcohols and an alkane. In this paper the model is extended to represent systems containing any number of alcohols and alkanes. The chemical equilibria approach, thought to be complicated for systems containing more than two alcohols, is actually found to be quite feasible if a suitable means of counting the associated complexes is used. The model does not require cross-association equilibrium constants for alcohols to be the geometric mean of the self-association constants. However, this assumption is tested on binary vapor-liquid equilibrium data for alcohol systems and is found to provide acceptable results. In addition to binary mixtures of alcohols, the model is applied to binary mixtures of an alcohol and an alkane, ternary mixtures containing two alcohols and an alkane, and ternary mixtures comprising three alcohols. It compares favorably with the Wilson equation and has potentially fewer adjustable parameters. Finally, the model is compared with statistical associating fluid theory (SAFT) and the two approaches are found to be strikingly similar.