Inter- and intradiffusion in liquid mixtures of methane andn-decane

Abstract

The interdiffusion coefficient,D ₁₂, has been measured by Mach-Zehnder interferometry for liquid mixtures of methane andn-decane at 303 K. The mole fraction of methane was from 0.11 to 0.96 and the pressure was from 30 to 60 MPa. This includes measurements in the critical region, the critical locus being approached from supercritical pressures to within 0.4 MPa. The accuracy inD ₁₂ is estimated to be from 3 to 10%, depending on the composition. Our data are compared with the Sigmund correlation, which is widely used to estimate diffusion coefficients in hydrocarbons at high pressures. The deviation between estimate and measurement is one order of magnitude for some of the states. We have also compared with a more recent correlation used by Erkey, but this one is not found to be applicable to the compositions studied in the present work. Our data were related to recently measured intradiffusion coefficients,D ₁ andD ₂, at the same state points. On this basis, we have evaluated different mixing rules for obtaining the interdiffusion coefficient from intradiffusion coefficients, both close to and away from the critical region. It is found that the so-called Darken and Adamson relations have the right qualitative behavior.