Raman spectroscopy and molecular dynamics simulations of aqueous two-phase systems for the purification of phosphoric acid

Abstract

In this work, Raman spectroscopy and molecular dynamics simulations were used to elucidate key interactions between polyethylene glycol (PEG) and phosphoric acid (H₃PO₄) in aqueous two-phase systems for the extraction of phosphoric acid. Extensive molecular dynamics simulations were performed, and radial distribution functions as well as hydrogen bonds between PEG and other molecules were measured. Experimental data were used in combination with the slope method to infer PEG–H₃PO₄ interactions, and the interpretation is consistent with molecular simulation results. Based on our experimental and simulation results, we propose a solvation mechanism governed by hydrogen bonding interactions: at low concentrations of H₃PO₄ within the polymer-rich aqueous solution, entropy dominates and phosphoric acid molecules have weak interactions with PEG; as the concentration of phosphoric acid increases above a certain critical value, enthalpy dominates with PEG molecules interacting strongly with H₃PO₄ molecules via hydrogen bonds.