A New Model of Excess Gibbs Energy for Systems Containing Polymer-Salt-Water Applicable to Aqueous Two Phase Systems

摘要

A new thermodynamics model is presented for the phase equilibria calculations of 15 different aqueous two phase systems (ATPSs). The systems consist of water, polyethylene glycol and various salts (ammonium sulfate, sodium sulfate and sodium tartrate). The excess Gibbs energy model developed in the present study consists of three different terms. Long range and short range contributions and a combinatorial part of the excess Gibbs energy are used for obtaining the activity coefficient of species in the mixture. For the long range term, an extended Debye-Huckel equation is used and the Freed-FV equation is applied to calculate the combinatorial part of activity coefficient. For the short range contribution a new model based on the virial osmotic coefficient is developed to determine the equilibrium composition in ATPSs. Moreover, binary interaction parameters and calculated binodal curve data of each system are reported. The results show that the absolute average deviation percent (AAD%) of the model was less than 1% for the studied systems. Also, the phase equilibria calculations were done using UNIQUAC, UNIFAC, MNRTL-NRF and Modified Wilson equations to compare the results of the models with the results obtained by the new presented model. The results show that the new model can calculate the phase equilibria in ATPS systems better than most of the above equations.