Fickian diffusion coefficient of binary liquid mixtures in a thermogravitational column

By measuring the mass fraction difference between the top and the bottom of a thermogravitational column as a function of time, we show that this transient evolution of the separation toward its steady value gives the isothermal mass diffusion coefficient, at least in the validity limit of the Furry-Jones-Onsager theory, whereas the final steady separation produces the thermodiffusion coefficient. The following mixtures have been considered: water-ethanol (39.12 wt% ethanol), toluene-hexane (51.7 wt% toluene), and the three systems of the so-called "benchmark of Fontainebleau", which are the three binaries composed of isobutylbenzene and/or dodecane and/or 1,2,3,4 tetrahydronaphthalene (50 wtl/o in each component for each case). The obtained results indicate that reliable values of the isothermal diffusion coefficlent can be determined by using the thermogravitational method.