Vol.:(0123456789) International Journal of Thermophysics (2020) 41:115 https://doi.org/10.1007/s10765-020-02694-9 1 3 Density, Speed of Sound, Compressibility and Related Excess Properties of Methane + n‑Heptane at T = 303.15 K and p = 10 to 70 MPa Jean‑Patrick Bazile 1  · Djamel Nasri 1  · Hai Hoang 2,3  · Guillaume Galliero 1  · Jean‑Luc Daridon 1 Received: 30 May 2020 / Accepted: 9 June 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020 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 diferent 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 com- pressibilities 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 func- tion of methane content. From these measurements, it was observed that the large diference in compressibility of pure components provoked signifcant 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 efect at high dilution of n-heptane at 30 MPa was brought forth to light by evaluating the partial molar volumes. * Jean-Luc Daridon jean-luc.daridon@univ-pau.fr 1 Laboratoire des Fluides Complexes et leurs Réservoirs, LFCR, UMR 5150, Universite de Pau et des Pays de l’Adour, E2S UPPA, CNRS, TOTAL, 64000 Pau, France 2 Institute of Fundamental and Applied Sciences, Duy Tan University, 10C Tran Nhat Duat Street, District 1, Ho Chi Minh City 700000, Vietnam 3 Faculty of Natural Sciences, Duy Tan University, Da Nang 550000, Viet Nam