A theoretical revision of the derivation of liquid property expressions from an equation of state and its application

The thermodynamic properties of a liquid are generally determined from an e quation of state (EOS) through isothermal integration. Kahl (1967. Physical Review, 155, 78-80) and Nitsche (1992. Fluid Phase Equilibria, 78, 157-190 ) both questioned the validity of performing isothermal integration on a li quid and devised a Kahl's integration path to obtain liquid properties. In this paper, an alternate approach to revise the isothermal integration on l iquid was presented. A temperature-dependent revision factor alpha>(*) over bar * (T) was introduced to the liquid fugacity coefficient expression der ived from traditional isothermal integration, and the vapor pressure of pur e liquids can be reproduced. In er;tension to mixtures, since the vapor-liq uid equilibrium (VLE) has been taken into account by the revision factor al pha>(*) over bar * (T), simple mixing rules are adequate for EOS parameters even for highly non-ideal systems. Two types of mixing rule have been deve loped for a(T) depend on the VLE complexity. The proposed revision method a nd its application were illustrated through a modified Redlich-Kwong (MRK) EOS aiming at improving the description of volumetric properties. The test results on the VLE and PVT behavior of 43 pure substances and 17 binary mix tures are impressive. The comparisons with the widely used Soave-Redlich-Kw ong and Peng-Robinson equations of state indicate the advantages of the pro posed revision method and the superiority of MRK EOS. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.