ABSTRACT
Mass transport by diffusion plays an essential role in chemical engineering processes (solid and liquid extractions, distillation, etc.) but also in chemical reactions and biological systems. Thermodiffusion, also called thermal diffusion or the Ludwig–Soret effect, describes the coupling between a temperature gradient and a resulting mass flux in a multicomponent system. For the determination of diffusion coefficients in liquids, various techniques are usually employed: diaphragm cell, conductometric and optical cells, dynamic light scattering and Taylor dispersion technique. The latter has become a fast and reliable method for the measurement of mutual diffusion coefficients (Dik ), with the advantage of relative simplicity of the equipment used. In the case of Soret effect there has been great improvement on experimental techniques, especially modern optical methods, which will be here discussed and the new developments on the optical beam deflection technique are described.
The diffusion and thermodiffusion coefficients attained for some relevant hydrocarbon mixtures with three components are presented and discussed and the results are compared, when available, with literature results obtained using different experimental methods.
