Experimental study of the critical and supercritical phenomena in ternary mixture of water + 1-propanol + n-hexane

Abstract

The liquid-gas phase transition (PS, TS, ρS) and PρT properties of the ternary water + 1-propanol + n-hexane mixture with fixed concentration of 0.3333 mole fraction of each component (equimolar mixture) were measured. Measurements were focused in the immediate vicinity of the critical and supercritical regions in order to closely observe the features of the mixture critical behavior. Measurements were made along 29 liquid and vapor isochores between (25.03 and 646.59) kg·m−3 and over the temperature range from (373.15 to 673.15) K at pressures up to 60 MPa. For each isochore most measurements were made in the immediate vicinity of the liquid-gas phase transition temperature (in the single- and two-phase regions) where the break of the P-T isochore's slopes is observing. Temperatures and pressures (TS, PS) at the liquid-gas phase transition point for each fixed density (isochore, ρ) were measured using the isochoric P–T break point technique in the immediate vicinity of the critical point of the mixture. The critical property data TC = 510.85 K, PC = 6.09 MPa, and ρC = 255.22 kg·m−3 for the ternary mixture were extracted from the detailed PρT and (PS, TS, ρS) measurements near the critical point. The combined expanded uncertainty of the density, ρ, pressure, P, temperature, T, and concentration, x, measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 0.2% (density in the liquid phase), 0.3% (density in the gas phase); 0.5% (density in the critical and supercritical regions); 0.05% (pressure), 15 mK (temperature), and 0.01 mol% (concentration). The excess molar volumes (VmE) of the ternary mixture were calculated using the measured molar volumes Vm of the mixture and the reference molar volumes of the pure components for various experimental temperatures and pressures in the supercritical region. Also, the measured PρT data at low densities (vapor phase) were used to calculated the second and third virial coefficients of the mixture at high temperatures.