Estimation of molecular diffusivity in liquid phase systems by the Wilke-Chang equation.

This study deals with the application of the Wilke-Chang equation to the estimation of molecular diffusivity (Dm) in liquid phase systems including polar solutes and/or solvents. First, Dm of benzene in six different organic solvents was experimentally measured by the peak parking method. The value of association coefficient (α) was calculated from the Dm values by assuming that Dm can be represented by the Wilke-Chang equation. Then, the α value was correlated with the solubility parameter (δ) and ET of the solvents. Two different curved correlations were observed between α and the two physico-chemical parameters. This means that α of given solutes and solvents can be obtained from the values of δ and/or ET. Finally, Dm was estimated by a modified Wilke-Chang equation, which is derived by considering the aggregation of not only solvent molecules but also solute molecules. Although α is necessary for the estimation, it was calculated from δ for various solutes and solvents. The Dm values estimated were compared with those reported in literature. The mean square deviation between the Dm values was calculated less than 19% for 71 Dm data. It was demonstrated that the modified Wilke-Chang equation can be used for estimating Dm in liquid phase systems containing polar solutes and solvents.