High-pressure phase equilibria and volumetric properties of the CO2 + hexadecane + butylcyclohexane system: Experimental and modeling study

The phase equilibria of two hexadecane + butylcyclohexane mixtures were investigated by adding carbon dioxide, for which no data are available in the literature, using a variable-volume high-pressure view cell. Five isopleths ranging from 13 to 85 mol% carbon dioxide were studied at five different temperature conditions. In addition, high-pressure density data were obtained for three different hexadecane + butylcyclohexane mixtures at five temperatures and pressures up to 100 MPa. The classical Peng-Robinson equation of state (PR EoS) was applied with a fully predictive mixing rule incorporating a temperature-dependent binary interaction parameter ($k_{\mathrm{ij}}$) to model the experimentally measured phase equilibria. The two ternary mixtures exhibited classical behavior across all global compositions investigated, presenting only simple liquid-vapor equilibrium. The PR EoS approach qualitatively captured the experimental phase behavior of both systems. Moreover, the experimental density data were correlated using the Tammann–Tait equation, and the following thermodynamic derivative properties were calculated: isothermal compressibility (${\kappa }_T$), isobaric thermal expansivity (${\alpha }_P)$, thermal pressure coefficient (${\gamma }_v$), and internal pressure ($P_i$).