An empirical near-critical correction for a quasi-chemical nonrandom lattice fluid

Abstract

This paper proposes a simple empirical correction to improve the near-critical volumetric behavior of a classical equation of state (EOS) which overpredicts the critical point. The focus is on the alternative representation of long-range density fluctuation, an effect neglected in classical EOS, in terms of molecular clustering. To formulate the molecular clustering of interest, the Veytsman statistics is extended and fluctuation parameter is explicitly obtained as a solution to the quadratic equation. The proposed contribution was combined with a quasi-chemical nonrandom lattice fluid (QLF), which overpredicts the critical point. The combined model was found to require three clustering parameters besides three classical parameters and tested against vapor-liquid equilibrium data consisting of 43 nonpolar and polar components. The calculation results showed that the combined model satisfactorily represents the flattened part of the critical isotherm curve for methane as well as the top of the coexistence curve for the tested components.