Polymer induced aqueous-two-phase-systems for extractive concentration of aqueous salt solutions

Among the most energy intensive processes in the chemical industry are water removal processes from polar mixtures with high boiling components, e.g., salts. Water is usually removed by multiple effect evaporation; an energy demanding operation due to the high evaporation enthalpy of water. In our approach to develop novel, energy-efficient processes for concentrating salt solutions, we found that Polymer Induced Phase Separation (PIPS) is a very interesting alternative. Here, the results of the PIPS-study for concentrating salt solutions are reported, whereby a range of commercially available polymers (e.g., linear, hyperbranched, surfactants and gels) has been applied for concentration of model salts NaCl, Na2SO4 and FeCl3. The formation behaviour of aqueous biphasic systems was studied for the various polymers and the three salts in aqueous solutions at atmospheric pressure and varying operational parameters: temperature (20–60 °C), solvent/feed ratio (0.5–2.0 wt%), pH (0–7.5) and initial salt concentration (5–30 wt%). For different groups of polymers, diverse aqueous biphasic system behaviour was observed, being highly dependent on the pH. For salt concentration purposes, obtaining a salt-rich phase with a high salt concentration is desired. The most promising results were obtained with polyethers, obtaining aqueous biphasic systems with high concentrations of salts in the polymer-rich phase. It was possible to concentrate diluted salt solutions up to a 3.4 factor based on this initial proof of concept. Further studies are currently in progress, aiming at conceptual processes for water removal to optimise the operations in order to minimise the use of energy.