Critical points of mixtures: An analogy with pure fluids



The thermodynamic properties of vapor-liquid equilibrium (VLE) states near the critical locus of mixtures are correlated in very close analogy with the techniques used to correlate the properties of pure fluids near a critical point. The only mixture parameters used in the correlation are the values of pressure, volume, temperature, and mole fraction (PVTx) along the physical critical locus. We illustrate the power of the present approach by correlating the rather extensive PVTx data that exist near the critical loci of the binary mixtures: CO2[BOND]C2H6, SF6[BOND]C3H8, and C8H18[BOND]C3H8. Nearly all the data within 10% of the critical temperature may be described within their accuracy despite the occurrence of critical azeotropy or large regions of retrograde condensation.