Critical properties (pc, Tc, and ρc) and phase equilibria of binary mixtures of CO2, CHF3, CH2F2, and SF6

Measurements of the critical properties pc, Tc, and ρc of the pure substances CO2, CHF3, CH2F2, SF6 and their binary mixtures were performed by observing the critical opalescence in a static equilibrium cell. The experimental uncertainties of the critical properties are ±6 kPa, ±60 mK, and ±2% for the determination of the density. The composition was determined by gas-chromatographic analysis within ±0.3 mol%. The experimental results for the binary mixtures are described by several simple cubic equations of state with van der Waals mixing and combining rules, using only the experimental critical data of the pure components and those of an approximately equimolar mixture to fit the binary interaction parameters. The capability of the cubic equations of state with these binary interaction parameters not only to describe the critical loci but also to describe VLE data is demonstrated by additional VLE measurements for the binary systems (CHF3+SF6) and (SF6+CH2F2). Furthermore, VLE data published by other authors for some of the systems investigated are considered.