Theoretical study of vapor-liquid equilibrium inside capillary porous plates

A generalized thermodynamic framework is provided for vapor-liquid equilibr ium (VLE) in the presence of external fields and is utilized to develop a s emi-empirical model for VLE within porous materials that accounts for the e ffect of the long-range surface forces. The alteration of VLE of binary mix tures in capillary porous plates is explained on the basis of the effect of long-range surface forces exerted by the solid on the liquid, which alter the intermolecular interactions amongst the mixture components as well as t heir vapor pressure. The excess Gibbs energy, activity coefficients, and re lative volatility are studied in the presence of external fields in relatio n to those in their absence. The VLE of cyclohexane-ethanol (components of different polarity) system at 25 degrees C, and acetone-ethanol (similar po larity) system at 32 degrees C are predicted using an approximate approach developed in this study and compared with experimental results. It is found that the results obtained by the approximate approach are in agreement wit h the experimental ones. (C) 1999 Elsevier Science B.V. All rights reserved .