A zwitterionic surfactant concentrates sulfolane in floating foams, to purify water

Sulfolane is a worldwide groundwater miscible pollutant, used for carbon capture and sour gas treatment. It is heavier than water and can sink when spilled in low salinity aquifers, posing remedial challenges. There are no strategies to prevent sulfolane plunging, other than pumping large groundwater volumes. We show that the zwitterionic surfactant cocamidopropyl betaine (CAPB) interacts with sulfolane, producing a stable floating foam, in which sulfolane is concentrated by >140 %. The foam forms by bubbling air or mild mixing. CAPB is surface active in either water or in aqueous sulfolane mixtures, and its films stabilize the air-water interface even upon significant deformation. CAPB-sulfolane interactions disrupt the water network, thereby decreasing the heat and onset of water evaporation from the foam. While CAPB successfully concentrated sulfolane, Tween 20 did not. Cationic cetyltrimethylammonium bromide binds sulfolane, but extraction of sulfolane was not possible due to foam instability.