Towards the development of a second-order approximation in activity coefficient models based on group contributions

A simple modification of group contribution based models for estimation of liquid phase activity coefficients is proposed. The main feature of this modification is that contributions estimated from the present first-order groups in many instances are found insufficient since the first-order groups do not provide all the important molecular structural information. Therefore, addition of second-order terms, which provide the needed extra molecular structural information, is proposed. The scope of the new approach is demonstrated through the well-known UNIFAC model in terms of improved correlation/prediction capabilities, distinction between isomers and ability to overcome proximity effects.