NEW PHYSICAL CONSTRAINTS FOR FLUID MIXTURE EQUATIONS OF STATE AND MIXTURE COMBINING RULES

Using thermodynamic identities and equilibrium relations, we prove that cubic equations of state with their usual mixture combining rules (EOS/MCR) must provide collinearity of isochores at their own predicted temperature extremum (CT). The conditions for collinearity are supported from simulated vapor-liquid-equilibrium (VLE) data using the Redlich-Kwong EOS. Cricondenbar (CB) and cricondentherm (CT) loci are presented as powerful physical constraints to develop and/or to improve the density-dependent MCR so as to provide future VLE calculations with more nearly correct physics. The relationships among CB, CT, and circondencomps (CC), are developed so that ordinary experimental VLE data may be used together with these constraints to yield information about the MCR for each mixture.