Interfacial Synergy of Green Sophorolipids and Cyclodextrins: The Regulation Mechanism on Methane Hydrate Formation

To resolve the slow kinetics of methane hydrate formation and the environmental issues posed by conventional surfactants, this study investigated the interfacial modulation effects of a green biosurfactant-based system─comprising sophorolipids, cyclodextrin, and low-concentration KCl─on methane hydrate synthesis at 2 °C and 6 MPa. At a concentration of 2 wt %, sophorolipids achieved saturated adsorption at the interface. Compared to the pure water system, this reduced the induction time by 79.07%, increased methane uptake by 74.08%, and enhanced gas storage density by 302.4%. The synergistic effect was highly dependent on CD cavity size: α-CD exhibited synergistic enhancement with a 12.21% increase in methane uptake; β-CD reversed the inhibition, achieving a 201.68% improvement; and γ-CD exhibited an inhibitory effect due to active site shielding via inclusion complexation. Experiments under mild stirring at 300 rpm confirmed that interfacial molecular interactions serve as the core driving force for efficient methane hydrate formation. The addition of 300 ppm KCl induced mild inhibition on hydrate formation in the optimal hybrid system through ionic competition, inclusion antagonism, and interfacial adsorption interference. This study provides theoretical support for the development of green promoters for methane hydrate formation.