Diffusivities in Binary Mixtures of Cyclohexane or Ethyl Butanoate with Dissolved CH4 or R143a Close to Infinite Dilution

Abstract

This work is part of a series of studies focusing on binary mixtures consisting of a liquid with a dissolved gas close to infinite dilution. A particular focus is on the study of the influence of molecular characteristics on mutual or self-diffusivity. Heterodyne dynamic light scattering (DLS) experiments and equilibrium molecular dynamics (EMD) simulations are applied to determine the Fick diffusion coefficient D11 and the self-diffusion coefficient of the gas solute in the mixture Dself,1. Often, the latter is referred to in the literature as the intradiffusion coefficient, which is equal to D11 in the limit of infinite dilution. Both DLS and EMD simulations are applied in macroscopic thermodynamic equilibrium at or close to saturation conditions. In the present study, mixtures of methane (CH4) or the refrigerant 1,1,1-trifluoroethane (R143a) dissolved in cyclohexane or ethyl butanoate are investigated at temperatures T between 303 and 423 K. The average expanded experimental uncertainty (coverage factor k = 2) of D11 from DLS experiments is 10%, and the average expanded statistical uncertainty (k = 2) of Dself,1 from EMD simulations is 6.4%. Unexpectedly, D11 in mixtures of CH4 dissolved in cyclohexane or ethyl butanoate essentially matches within uncertainties at a given T, and mixtures of cyclohexane with R143a show smaller D11 values in comparison to ethyl butanoate with R143a.