Clustering and Sorption of Sulfolane and Pyridine onto Silicates

Sulfolane and pyridine are used for sour gas sweetening and carbon capture, and they are found as cocontaminants in groundwater. They are known to be miscible in water, but their mixing behavior in ternary aqueous mixtures containing sulfolane, pyridine, and water is unknown. Pyridine and sulfolane are hydrogen bond acceptors, and they increase the proportion of water molecules that donate hydrogen bonds in ternary mixtures, as revealed by Fourier transform infrared spectroscopy. Small-angle neutron scattering demonstrates that sulfolane and pyridine form molecular clusters in water. These have a core-shell structure, with a pyridine core and a sulfolane shell. Computer simulations indicate that clusters are composed of nine pyridine molecules, surrounded by five to six sulfolane molecules. While sulfolane does not sorb onto clay minerals in the absence of pyridine, pyridine promotes its sorption. This potentially limits the risk of sulfolane migration in clayey aquifers copolluted by pyridine.