A GENERAL EQUATION OF STATE FOR SUPERCRITICAL-FLUID MIXTURES AND MOLECULAR-DYNAMICS SIMULATION OF MIXTURE PVTX PROPERTIES

A general Equation of State (EOS), which we previously developed for p ure nonpolar systems, is extended to polar systems such as water and t o mixtures in this study. This EOS contains only two parameters for ea ch pure component and two additional parameters for each binary mixtur e (no higher order parameters are needed for more complicated mixture systems). The two mixing parameters can be eliminated for nonaqueous m ixtures with a slight loss of accuracy in both total mole volume and i n excess volume (or nonideal mixing). Comparison with a large amount o f experimental PVTX data in pure systems (including H2O) and in the mi xtures, H2O-CO2, CO2-N-2 CH4-CO2, and N-2-CO2-CH4 results in an averag e error of 1.6% in density. Comparison with commonly used EOS for supe rcritical fluids shows that the EOS of this study covers far more T-P- X space with higher accuracy. We believe that it is accurate from supe rcritical temperature to 2000 K and from 0 to 25,000 bar or higher wit h an average error in density of less than 2% for both pure members an d mixtures in the system H2O-CO2-CH4-N-2-CO-H-2-O-2-H2S-Ar and possibl y with additional gases. Comparison with the published simulated data suggests that this EOS is approximately correct up to 300,000 bar and 2800 K. We also simulated the PVTX properties of a number of supercrit ical fluid mixtures using molecular dynamics (MD) simulation. These re sults and those of other authors are well predicted by the EOS of this study.