(319d) Exploring Retrograde Vaporization and Derivative Properties of near-Critical Fluids Using Monte Carlo Simulations and Equations of State

Configurational-bias Monte Carlo simulations in the Gibbs, isobaric-isothermal, and canonical ensembles and various equations of state are applied to investigate two important phenomena found for near-critical fluids: (i) double retrograde vaporization in vapor-liquid phase equilibria of binary mixtures near the critical point of the lower-boiling compound, and (ii) non-monotonic behavior of thermodynamic derivative properties as function of density or pressure at temperatures above, but close to the critical temperature.  For the retrograde behavior, binary mixtures of methane/n-alkanes and carbon dioxide/(n-alkanes or alkylbenzenes) are discussed.  For the thermodynamic derivative properties, various butane-like models are investigated at a temperature of T/T_crit = 1.1, wherethe critical temperature is determined from Gibbs ensemble simulations for each molecular model to allow for comparison of all models at the same reduced temperature.  The molecular simulations allow one to provide molecular-level understanding of these near-critical phenomena, whereas the equations of state serve as supporting data and as guide for the set-up of Gibbs ensemble simulations (i.e., by providing information on appropriate overall composition and volume/pressure to be used).