Influence of the molecular weight of polymer, temperature and pH on phase diagrams of poly (ethylene glycol) + di-potassium tartrate aqueous two-phase systems

Abstract

Phase diagrams and liquid – liquid equilibrium (LLE) data for aqueous two-phase systems (ATPSs) containing di-potassium tartrate (DPT) and poly (ethylene glycols) (PEG) (1500 and 6000) have been determined experimentally at different pH values (6.41, 7.74 and 9.05) and temperatures (298.15 and 308.15 K). The effect of molecular weights of the PEG, temperatures, and pH on the binodal curve, tie-line length (TLL) and slope of tie line (STL) was studied. It was found that an increasing in PEG molecular weight, temperature and pH led to the binodal curve displacement towards the origin and increasing two-phase region. Accordingly, the various empirical equations were used to correlate the binodal curves of these systems such as Merchuk equation and Pirdashti equation and the tie-line compositions were correlated using Guan equation. Also, the refractive index and density of ternary (PEG 1500/6000 + di-potassium tartrate (DPT) + water) system have been measured. The density and refractive index were employed as the physical properties to obtain the phase composition and the tie-lines ends and show a linear variation with mass fraction of the polymers and the salt. Also, it was found that TLL affects the density of ATPS. The density difference between the phases (Δρ) increased with an increment in the TLL and pH values and PEG molecular weights and temperatures. Finally, the salting-out ability of the systems were explained by using “Effective Excluded Volume (EEV) model”.