Mutual solubility and VLLE correlation for the R32 + R290 system

Following our recent study on vapour–liquid-equilibrium (VLE) of the difluoromethane (R32) + propane (R290) system, that covered the temperature range between 248.13 and 294.91 K, the present study focused on the behaviour of the liquid phase down to 215 K. The immiscibility of the liquid phase was observed at temperatures below 230 K and the mutual solubility was ascertained by the visual observation of the cloud point with a new apparatus. The experimental results were used to develop a method for deriving vapour–liquid–liquid-equilibrium (VLLE) parameters using an equation of state. The azeotropic pressures found from VLE at temperatures above UCST and the heteroazeotropic pressures derived from VLLE formed a common trend well represented by the Antoine equation. A common trend was exhibited also by the azeotropic compositions found from the VLE data above UCST and those found from the VLLE data correlation. Both regularities observed may be considered as an internal consistency of two independent experiments within the estimated uncertainty.