New Model to Predict Infinite Dilution Activity Coefficients Based on (∂p/∂x)_{T,x → 0}

Accurate prediction of infinite dilution activity coefficient (γ^∞) is essential for the calculation of phase equilibria, solubility, and related properties in molecular thermodynamics. Here, we propose a new model to accurately predict the value of γ^∞. It is applicable to calculate γ^∞ for compounds in aqueous solution at different temperatures. The model is based on the relationship of (∂p/∂x)_T,x→0 with γ^∞ and temperature at low pressure. First, we introduce the new idea of using the group contribution method to estimate (∂p/∂x)_T,x→0 and then obtain the activity coefficient of a solute at infinite dilution in water based on the relationship between (∂p/∂x)_T,x→0 and γ^∞. The accuracy of this model is verified using experimental data from 46 systems and more than 450 data points. The result shows that the total average relative deviation of the predicted values from the experimental values for training data is 4.73%. Besides, we test the applicability of the model using solutes that are not part of the training data set. The result shows that the model is satisfactory for the prediction of testing data. Compared with other models, the results prove that the developed model outperforms the UNIFAC model, the modified UNIFAC model, and previous predictive models for aqueous systems. The final equation with only simple arithmetic is more easily applied in engineering practices.