Calculation of excess molar enthalpy of binary liquid mixtures at high pressures from experimental data at low pressures

• Excess molar enthalpy at high pressure was calculated by excess molar volume data.
• Redlich-Kister, Wilson and NRTL equations were modified by depending to pressure and temperature.
• Excess molar volume data were correlated by modified Redlich-Kister, Wilson and NRTL equations.
• Calculated excess molar enthalpies were compared with the experimental values in the literature.

A new approach for calculating the excess molar enthalpies of binary liquid mixtures at entire pressure range of interest based on the experimental excess molar enthalpy (HmE) data at low pressure, is proposed. The method is a simple thermodynamic relation combined with the modified Redlich-Kister equation and modified local composition model (NRTL and Wilson) in which the binary parameters were temperature and pressure dependent that are determined by using experimental excess molar volume (VmE) at different temperatures and pressures. The calculation has been carried out for seven binary systems which include light hydrocarbon-alcohol systems plus water-ethanol. A comparison of the calculated and experimental HmE at different temperatures and pressures of seven binary mixtures indicate that the models describe the excess molar enthalpies very well quantitatively.