Density, Speed of Sound, Compressibility and Related Excess Properties of Methane + n-Heptane at T = 303.15 K and p = 10 to 70 MPa

Abstract

Density and speed of sound of methane + n-heptane binary mixtures were measured at a temperature equal to 303.15 K and at pressures ranging from 10 MPa to 70 MPa. The measurements were performed in pure n-heptane and eight different mixtures with methane molar percentage ranging from 20 % to 95 %. Speed of sound data was obtained by a pulse-echo technique working at 3 MHz whereas density data were acquired from a vibrating U-tube densimeter. Isothermal and isentropic compressibilities were derived from both measurements in the same conditions. Finally, partial molar volumes, excess molar volume, excess isothermal compressibility as well as excess speed of sound and excess isentropic compressibility were estimated at the same conditions and the relative excess properties were represented as a function of methane content. From these measurements, it was observed that the large difference in compressibility of pure components provoked significant deviations to ideal behavior with relative excess values that can reach − 20 %, − 100 % and 200 % of the ideal properties for molar volume, isothermal compressibility and speed of sound, respectively. Moreover, a small clustering effect at high dilution of n-heptane at 30 MPa was brought forth to light by evaluating the partial molar volumes.