Thermodynamics of the nitromethane + 1-butanol system near the upper critical point

A thermodynamic study for the nitromethane+1-butanol binary liquid system near its upper critical point UCP is presented. Densities, isentropic compressibilities, and isobaric molar heat capacities were measured throughout the composition range at atmospheric pressure and temperatures of 288.15, 293.15, 298.15 and 308.15 K. In addition, liquid–liquid equilibrium data are reported. Density data were used to obtain isobaric thermal expansivities and, via appropriate thermodynamic relations, isothermal compressibilities and isochoric molar heat capacities were derived. The excess quantities for these properties were calculated using the ideality criterion of Benson and Kiyohara. Results are discussed in terms of a high degree of non-randomness in the mixture expected near the UCP. In particular, excess heat capacities are good indicators of the above-mentioned effect.