Enhanced methane storage in sH clathrate hydrates directly derived from sII hydrate seeds

Abstract

Storing gaseous energy, such as methane, using clathrate hydrates is highly promising due to environmentfriendliness, economic feasibility, and mild operating conditions. To develop a feasible hydrate-based methane storage system, pinacolone (PCN) was utilized as a thermodynamic promoter with pre-constructed cyclopentane hydrate seeds under static conditions. Introducing hydrate seeds and PCN resulted in instantaneous nucleation events, leading to the predominant formation of structure H (sH) hydrates containing methane and PCN. In-situ Raman and PXRD analyses supported the prominent formation of sH hydrates, indicating that methane can be easily stored in thermodynamically stable sH hydrates. Kinetic studies at varying pressure conditions (6.0, 4.5, and 3.5 MPa) were also conducted to investigate the impact of PCN under broader operating conditions. Through kinetic evaluations and ex-situ Raman spectra, we confirmed facile methane storage in sH hydrate under all pressure conditions without induction time, overcoming a major hurdle of hydrate-based technologies. Furthermore, the use of PCN resulted in higher methane uptakes compared to other structure II hydrate formers owing to cage occupancies of methane molecules in different structures. These findings suggest an efficient way to store methane with a high storage capacity in sH hydrates.