Environmental implications of sulfolane demixing from water by phenolic co-contaminants

Sulfolane is a groundwater pollutant used to remove acidic components from petroleum. Phenolic compounds such as phenol, m-cresol, p-cresol and dimethylphenol can be found as co-pollutants because they are present in petroleum. Sulfolane is freely miscible in pure water, but phenolic compounds decrease its miscibility. Depending on the composition of the mixture, either larger droplets or molecular clusters form. Clusters are visible by small angle neutron scattering. Demixing occurs because sulfolane has higher affinity for phenols than water, as evident from activity coefficients estimated by COnductor like Screening MOdel for Realistic Solvents, COSMO-RS. Attenuated total reflectance – Fourier transform infrared spectroscopy reveals interactions between the -OH groups of phenols and the -SO groups of sulfolane. Sulfolane interacts more strongly with phenols than water, as seen by computer simulations. Demixing of sulfolane by phenols leads to entrapment into varying mineral substrates, potentially attenuating its migration in groundwater. It also enables its removal from ternary mixtures by polyurethane sponges, onto which sulfolane alone does not sorb in binary aqueous mixtures. • Phenols form clusters with sulfolane in ternary aqueous mixtures • In certain mixtures, larger droplets of sulfolane+phenols sink in water • Droplets of sulfolane+phenols are retained by sand and other minerals • Droplets of sulfolane+phenols are also retained by polyurethane sponges