High-Temperature and High-Pressure PVT Measurements of the Binary n-Hexane + Methyl Octanoate Mixture near the Critical Point of the Pure Solvent (n-Hexane)

Abstract

PρT and phase transition properties (P S ,ρ S ,T S ) of the dilute binary mixture of n-hexane + methyl octanoate (at a concentration of 0.057 mol fraction of methyl octanoate) have been studied using the constant-volume piezometer technique. The measurements were performed along 16 liquid, vapor, and nearcritical isochores between 32.38 and 615.57 kg•m −3 over a temperature range from 291 to 633 K at pressures up to 16 MPa. Measurements were concentrated in the immediate vicinity of the critical point of pure n-hexane and liquid−gas phase transition points (bubble and dew point curve) in order to study the effect of critical fluctuations in pure n-hexane on the thermodynamic properties of the dilute mixture and to closely observe the phase transition changes and precise measurements of the (P S ,ρ S ,T S ) and critical point (P C ,ρ C ,T C ) data. The measured critical property data for the mixture were used to study the isomorphic critical behavior of strongly (isothermal compressibility K TX and isobaric heat capacity C PX ) and weakly (isochoric heat capacity C VX ) singular properties along the critical isochore and the critical isotherm. The measured PρT data were also used to estimate the values of physical meaning (theoretically important) parameters, namely, characteristic reduced temperature ( , ) 1 2 and density differences ( , ) 1 2 of the mixture. Based on the measured critical property data, the value of the Krichevskii parameter K kr has been estimated, which defines the structural (N exc )and thermodynamic (V H C , , 2 2 2 P ) properties of the dilute mixture near the critical point of the pure solvent (n-hexane).