(279c) Molecular and Thermal Diffusion Coefficients of Binary Hydrocarbon Mixtures

The Ludwig-Soret effect (that is, thermal diffusion) describes the formation of a concentration gradient in a mixture under a temperature gradient. The effect is quantified by the Soret coefficient, which is in turn related to the molecular and thermal diffusion coefficients of a mixture. Thermal diffusion is important in a myriad of applications, such as in petroleum reservoirs, material sciences, oceanography, biological systems and chemical engineering. There has been extensive theoretical and experimental work to model and measure thermal and molecular diffusion coefficients. However, there is no accurate predictive model for the explicit dependency of these coefficients on molecular shape and composition. There are also a large number of important mixtures for which these coefficients have not been determined. We have embarked on a major research effort to measure an extensive set of data on molecular and thermal diffusion coefficients of aromatic-alkane and alkane-alkane binary mixtures of various compositions. A major objective of this work is to study the influence of composition and molecular shape on the molecular and thermal diffusion coefficients of hydrocarbon binary mixtures. This study is intended to provide a framework for development of theoretical models. Our experimental results indicate that thermal diffusion coefficients for aromatic-alkane binary mixtures have a different dependency than alkane-alkane binary mixtures, which suggests a strong dependency of these coefficients on molecular shape.