Experimental High-Pressure Isochoric/Isoplethic Equilibrium for the Systems Propane + n‑Pentane and Propane + Diethyl Ether

In this work, loci of isochoric (constant global density)–isoplethic (constant global composition) phase equilibria, generally made of heterogeneous and homogeneous segments, were experimentally studied for the binary systems propane (C3) + n-pentane and C3 + diethyl ether. The temperature and pressure ranges of the new binary experimental data are, roughly, from 320 to 470 K and from 1 to 25 MPa, respectively. The binary experiments were performed at varying overall density (ρ) and varying propane mole fraction (X C3). The obtained experimental loci made it possible to determine phase boundaries for the studied mixtures. Experimental results show that, at constant global composition, a decrease in the isochore global mass density implies both an increase in the isochore break-point temperature (bubble temperature) and a decrease in the isochoric pressure–temperature coefficient (slope) of the isochore homogeneous-liquid segment. Besides, at constant global mass density, the break-point temperature decreases with the increase in the light component global mole fraction. The experimental data obtained were correlated using the perturbed-chain statistical associating fluid theory equation of state. The model, at the set values for the model parameters, is capable of reproducing the single-phase pressure versus temperature behavior and the phase transitions.