Temperature and concentration dependence of liquid phase diffusion coefficients

A study of experimental techniques for the determination of diffusion coefficients for binary mixtures and a study of the existing relationships for these coefficients were carried out. A new three-compartment diffusion cell was developed capable of measuring diffusion coefficients at temperatures up to the normal boiling point (24). By means of this cell, diffusion coefficients were measured for the systems ethanol-water, acetone-water and acetone- chloroform for a range of temperatures up to the normal boiling points. Thus diffusion coefficients for the above mixtures including those at boiling points and at infinite dilution are presented. A relationship was developed to relate diffusion coefficients with temperature and concentration (equation 3-1.21) in binary systems. It agrees better with the experimental data for the associated systems than some literature correlations. By application of parachors a new equation (3-2.4) was developed for the prediction of diffusion coefficients at infinite dilution , (201). This equation, because of the ease of calculating parachors, is more convenient to use than other equations based on the Stokes-Einstein equation. An additive method for the prediction of self-diffusion coefficients was introduced and a correlating equation (3-3.4) was developed. The bond and structural contributions to the constant of the equation were calculated on the basis of a limited amount of experimental data. Despite this the correlation gives reasonable predictions for the temperature range between melting point and boiling point. Another correlation for the prediction of self-diffusion coefficients was developed (203) (equation 3-3.6) by modifying an existing equation. This was possible by applying the relationship between the molal volume at the boiling point and the critical molal volume developed in this work (202). The new equation is more convenient to use. The correlating property of the critical temperature was used to devise a relationship between diffusion coefficients, critical temperature and the working temperature. The two correlating equations (3-4.6) and (3-4.7) can predict diffusion coefficients at various temperatures if one value of the diffusion coefficient at a single temperature is known.