Experiment and a New Thermodynamic Model Based on Group Contribution for Correlation Liquid-Liquid Equilibria in Aqueous Two Phase Systems of PEG and (K2HPO4 or Na2SO4)

A new thermodynamic model based on group contribution has been proposed for studying the phase behavior of aqueous two phase polymer-salt systems. The assumptions of NRTL-NRF model and the activity coefficient equation of UNIQUACNRF model have been used for the groups. In this new model, UNIFAC-NRF, the nonrandom state of groups were selected as a refrence state . The binary interaction parameters were adjusted using the data of binary salt–water systems and the ternary systems were correlated with only six binary adjustable parameters. The Debye-Huckel equation based on Fowller-Guggenheim equation was used to calculate the long range electrostatic interaction of the ions. The UNIFAC-NRF model was applied to correlate the experimental data of aqueous two phase systems: PEG-K2HPO4–water and PEG– Na2SO4–water for two different molecular weight of PEG at different pH. The results of the new model showed that it can be used to correlate the LLE in aqueous solution of polymer-salt very well.

Keywords:

Aqueous two phase system , Activity coefficient , UNIFAC-NRF , Polyethylene glycol , Liquid-Liquid Equilibria