Comparison of excess molar enthalpies and excess molar volumes as a function of temperature and pressure for mixtures of (ethane, propane, and butane) with (methanol, ethanol, propan-1-ol, and butan-1-ol)

Measurements of the excess molar enthalpies H-m(E) as a function of pressure and temperature have now been completed for all of the binary mixtures of ethane, propane, and butane with methanol, ethanol, propan-1-ol, and butan-1-ol. Excess molar volumes V-m(E) were also obtained for selected systems. This paper summarizes the results obtained and compares the effect of molar mass, temperature, and pressure on H-m(E), V-m(E), (partial derivative H-m(E)/partial derivative p)T, and C-p,m(E). The effect of (fluid + fluid) equilibria on H-m(E) is described. The UNIFAC-II prediction of H-m(E) is also compared with the experimental results. The effect of molar mass of the alkane and the alkanol, temperature, and pressure are qualitatively explained by a model that includes contributions to H-m(E) and V-m(E) by a positive hydrogen bonding term and a negative packing term. The hydrogen bonding term is most important at high mole fraction of alkane and is dependent on temperature and the molar mass of the alkane. The packing term is most important at low mole fraction of alkane and is dependent on the molar masses of the alkane and the alkanol, temperature, and pressure. The packing term increases in importance in liquid (alkane + alkanol) mixtures as the temperature approaches the critical temperature of the alkane, and becomes large and at temperatures where the alkane is a supercritical fluid. (C) 1996 Academic Press Limited