Predicting the high-pressure phase equilibria of binary aqueous solutions of 1-butanol, n-butoxyethanol and n-decylpentaoxyethylene ether (C10E5) using the SAFT-HS approach

Abstract

The phase equilibria of water + n-butan-1-ol is characterized by the presence of so-called closed-loop curves which represent regions of liquid-liquid immiscibility in the phase diagram. The system exhibits lower critical solution temperatures (LCSTs), which denote the lower limit of immiscibility together with upper critical solution temperatures (UCSTs). This behaviour can be explained in terms of the competition between the incompatibility of the water with the alkyl chain and the hydrogen bonding between water and the hydroxyl group. To study the phase equilibria we have used a simplified version of the statistical associating fluid theory (SAFT), which is based on the thermodynamic perturbation theory of Wertheim for associating fluids: the original SAFT-LJ equation of state treats the molecules as chains of Lennard-Jones segments, while the simplified SAFT-HS equation treats molecules as chains of hardsphere repulsive segments with van der Waals interactions. The water molecules are modelled as hard...