The excess enthalpies of (carbon dioxide + cyclohexane) at 308.15, 358.15, and 413.15 K from 7.50 to 12.50 MPa

The excess molar enthalpies H_m^E for (carbon dioxide + cyclohexane) were measured in the vicinity of their critical locus and in the supercritical region. Mixtures at 308.15 K and at 7.50 MPa show very exothermic mixing and a region where H_m^E varies linearly with mole fraction x while at 10.50 and 12.50 MPa they show only moderately endothermic mixing. Mixtures at 358.15 and 413.15 K and at all pressures studied except for 358.15 K and 12.50 MPa have an exothermic section in the cyclohexane-rich region, a linear section which starts at a mole fraction x corresponding very closely to that of the minimum value of H_m^E, and an endothermic section in the carbon-dioxide-rich region. The H_m^E results exhibiting a linear section allow the determination of values for the vapor and liquid equilibrium-phase compositions. The changes observed in the excess enthalpy with both pressure and temperature are discussed in terms of liquid-vapor equilibrium and critical constants for (carbon dioxide + cyclohexane).