Thermal and Mass Diffusivities of Linear Alcohols Containing Dissovled Gases by Dynamic Light Scattering

Abstract: In the present work, simultaneous measurements of thermal diffusivities and Fick diffusion coefficients in the liquid phase of binary mixtures of primary alcohols containing dissovled gases were performed by dynamic light scattering. The total average expanded uncertainties (k=2) were 14.2 for thermal and 6.8 for Fick diffusivities. By the investigation of 1-hexanol or 1-decanol with H2, He, N2 or CO at infinite dilution of the gas between 303 K and 423 K, the dependences of thermal and Fick diffusivities on temperature and on solute as well as solvent were studied. The thermal diffusivity was found to decrease with increasing temperature and agrees for all solutes with values calculated from literature for the pure solvents. The Fick diffusion coefficient shows Arrhenius-like behaviour with temperature and is considerably larger for the systems with light gases compared to the same systems with N2 or CO. It was observed that the Fick diffusion coefficient is higher for the He than for H2, despite its larger molar mass, while no considerable difference between N2 and CO was found over a wide temperature range. Thermal diffusivities are larger in 1-decanol than in 1-hexanol, while the opposite is the case for the Fick diffusion coefficient. In the binary mixture of 1-hexanol with dissolved CO2, thermal and Fick diffusivities were measured over a wide range of concentrations at different temperatures between 303 K and 353 K. The Fick diffusion coefficient shows a strongly non-ideal behaviour, which is expressed by a maximum around 20 mol% of CO2, followed by a pronounced decrease with increasing concentration of CO2. Due to the experimental limitations, a minimum expected between 75 and 95 mol% of CO2 could not be resolved. The method of polarization difference Raman spectroscopy was applied to experimentally determine the mixture concentration. The determination of CO2 molar fractions has an estimated uncertainty (k=2) of 12% and the comparison with literature data yields an average absolute relative deviation of 3.8%.