Thermal and mutual diffusivities in binary mixtures of alkanes with dissolved gases by dynamic light scattering (DLS)

Abstract

This work presents thermal diffusivities a and Fick diffusion coefficients D₁₁ of binary mixtures of the alkanes n-pentane, n-decane, n-hexadecane, or squalane (2,6,10,15,19,23-hexamethyltetracosane) with dissolved carbon dioxide (CO₂) or propane by dynamic light scattering (DLS). The investigations are performed over a temperature range from (293 to 393) K and cover a wide composition range from infinite dilution of the dissolved gas up to an amount fraction of the gas of 0.69. Using DLS, D₁₁ and a are accessed with average expanded experimental uncertainties (coverage factor k = 2) of (6.6 and 7.6)%. The results from this work are compared to the few experimental data available in the literature and are used to investigate the influences of the thermodynamic state and of the characteristics of the solvent and solute molecules on both transport properties. For all investigated binary mixtures, the influence of the dissolved gas on a is found to be small since most data agree with a of the pure solvent within combined uncertainties. The composition-dependent trend for D₁₁ varies strongly for the different binary mixtures, where both an increase or decrease with increasing amount fraction of the dissolved gas can be observed. For D₁₁ at infinite dilution, two prediction models from the literature are tested. While both models are able to qualitatively predict the temperature-dependent trend of D₁₁, the relative deviation of the predicted D₁₁ from the present experimental results varies strongly for the different mixtures between (9 and 95)%.