Thermodynamic Properties of cis-1,1,1,4,4,4-Hexafluorobutene [R‑1336mzz(Z)]: Vapor Pressure, (p, ρ, T) Behavior, and Speed of Sound Measurements and Equation of State

We present experimental measurements of the density, speed of sound, vapor pressure, and dew-point pressure of cis-1,1,1,4,4,4-hexafluorobutene, which is also known as R-1336mzz­(Z). Vapor pressures were measured at temperatures from 330 to 440 K; the dew-point pressure was measured at T = 293.15 K. Densities were measured in the liquid and supercritical regions over the temperature range of 230 to 460 K, with pressures up to 36 MPa. Vapor-phase sound speeds were measured at temperatures between 280 and 480 K, with pressures from 0.021 to 2.2 MPa. Densities and dew points were measured in a two-sinker densimeter with a magnetic suspension coupling. Vapor pressures were measured with a static technique in the densimeter. Sound speed data were measured with a spherical acoustic resonator. An equation of state written in terms of the Helmholtz energy was developed based on these data together with additional data from the literature; it represents the present experimental data with relative average absolute deviations (AAD) of 0.0081% for densities, 0.027% for vapor pressure, and 0.017% for vapor-phase speed of sound. Literature data for liquid-phase speed of sound have an AAD of 0.023%, and for saturated liquid density data, the AAD is 0.049%.