Solubility behavior for aqueous polyethylene glycol monododecyl ether systems up to 30 MPa: measurement and correlation

Nonionic surfactant aqueous solutions exhibit phase separation into two distinct liquid micellar phases: a dilute phase with a low surfactant concentration and a surfactant-rich phase, known as coacervate. The application of these surfactants in solute extraction processes from aqueous media has been increasing, highlighting the importance of understanding their solubility behavior. This work reports cloud point data of a systematic series of binary aqueous mixtures of polyethylene glycol monododecyl ethers, ranging the degree of ethoxylation (6, 7, 8, 9, and 10). The cloud points were detected in a high-pressure apparatus by monitoring the turbidity appearance and disappearance of the mixtures as the temperature changed at a constant rate of 0.1 K/min, under constant pressures up to 30 MPa (4 isobarics). The miscibility behavior of the studied systems was positively affected by both the degree of ethoxylation and the applied pressure. The Flory-Huggins (FH) equation was applied to correlate the solubility curves, allowing the generation of pseudo-experimental tie lines across the observed temperature range. These tie lines were further correlated using the nonrandom two-liquid (NRTL) model with a linear temperature dependence for the interaction parameters. The Flory-Huggins and NRTL models showed agreement within the bounds of experimental uncertainty, with root-mean-square deviations (RMSD) of 0.5 K for temperature and 0.1 % for composition, respectively. Feasible process applications of these models, including enhanced oil recovery through chemical flooding, are indicated.