Impact of hydroxyl group in surfactant structure on methane hydrate formation, pelletization, and dissociation for...

This study investigates the impact of hydroxyl functionalization on biosurfactants for methane hydrate formation, emphasizing their potential in sustainable gas storage. Sodium oleate (SO) and hydroxylated sodium oleate (HSO), derived from oleic and ricinoleic acids, respectively, were synthesized and evaluated as eco-friendly promoters. HSO outperformed SO and conventional surfactants, such as sodium dodecyl sulfate (SDS), particularly at low concentrations (50 ppm). Methane hydrate formation with HSO achieved an impressive conversion efficiency of 94.95 % at 50 ppm, surpassing SDS. HSO significantly enhanced storage capacity up to 161.86 v/v, exceeding the 157.90 v/v capacity of SDS. The optimized balance of hydrophilic and hydrophobic properties in HSO enhanced gas-water interactions, enabling rapid hydrate crystallization and stabilization. Furthermore, HSO exhibited superior performance in saline environments, achieving higher methane consumption and water-to-hydrate conversion rates compared to SO and SDS. This highlights the advantages of using seawater as a medium for methane hydrate formation, as it reduces operational costs and enhances sustainability. Methane hydrate pellet formation experiments revealed that HSO led to a faster formation rate and higher conversion degree. The resulting pellets were more stable and exhibited greater methane storage capacity. In long-term stability tests, HSO-based pellets retained more methane than SO-based pellets after 15 days at -5 °C. Additionally, HSO demonstrated excellent thermal stability in both pure and saline water, remaining structurally intact at elevated temperatures. These findings highlight the potential of molecularly tailored biosurfactants, such as HSO, as green and efficient alternatives to conventional surfactants for methane storage and transportation. This advancement aligns with global sustainability goals and supports the broader adoption of hydrate-based solidified methane technology.