(31d) On the Need for Improved Models of Activity Coefficient Temperature Dependence

Activity coefficients have long been used by chemical engineers and scientists to model liquid solution behavior.  They are key descriptors in the design of chemical separation operations, liquid product formulations, and other technologies where liquid composition is a key factor affecting performance.  Although many methods have been developed over the years to model activity coefficients as a function of composition, much less progress has been made in understanding how to quantify the effect of temperature.  Developing such a method will greatly enhance our ability to model and design a wide range of industrially important chemical technologies.

To begin addressing this gap, we have developed a new approach in which infinite-dilution (or limiting) activity coefficients of nonelectrolyte solute-solvent binary pairs are classified into seven general types.  Each type is defined in terms of characteristic temperature dependence, values of limiting activity coefficients, and specific kinds of molecular interactions.  The new method provides a framework for data that can serve as a useful guide.