Methane storage in clathrate hydrates containing water-miscible oxirane promoters

As the share of natural gas in the global demand for energy continues to increase, there is a growing need for sustainable, energy-efficient, and cost-effective natural gas storage and transportation technologies. This study investigates methane hydrates (MHs) containing two oxirane compounds, namely, propylene oxide (PO) and epoxyisobutane (EIB), for their potential use in hydrate-based methane storage (HBMS) applications. The microstructures of the MHs containing both PO and EIB were identified as the sII type by high-resolution powder diffraction (HRPD), C-13 NMR, and Raman spectroscopy. Moreover, the addition of PO/EIB significantly improved the thermodynamic stability of simple MH. In particular, as EIB increased the equilibrium temperature by 15 K, the EIB + CH4 hydrate remained stable up to ambient temperature (19 degrees C) even under a mild pressure (30 bar). It was also clearly demonstrated that PO and EIB act as simple hydrate formers (SHFs) with good water miscibility. The EIB + CH4 hydrate also showed a remarkable CH4 capacity of 0.117 mol CH4/mol H2O or 117 m(3) CH4 (at STP)/m(3) hydrate, nearly identical to the theoretical maximum. It is believed that both PO and EIB could potentially be employed to facilitate sustainable and energy-efficient HBMS technologies owing to the combined excellence of their high promotion capability and energy density, and good water miscibility. Novelty statements Both PO and EIB act as powerful promoters with good water miscibility. Both PO and EIB act as simple sII hydrate formers. Approximately 120 m(3) of methane gas can be stored in 1 m(3) of EIB hydrate.