Lattice-Level structural insight into cyclohexyl amine hydrate for Hydrate-Based CH4 storage

Abstract

Natural gas, a fossil fuel known for its relatively low carbon emissions, will be crucial during the transition to clean energy in climate scenarios. As energy consumption rises, the development of energy-efficient gas storage and transportation becomes critical. As an alternative approach, hydrate-based natural gas storage technology, which utilizes gas hydrates, offers advantages in terms of energy efficiency from a milder formation condition. Despite the benefit of hydrate-based natural gas storage technology, it is crucial to maximize storage capacity by increasing conversion rate and gas occupancy as well as the promotion effect in the selection of an organic compound called thermodynamic hydrate promoter to alleviate still harsh thermodynamic conditions. In this study, we introduce the cyclohexyl amine (CHA) molecule as a hydrate promoter with lattice-scale measurements of the CHA hydrate system. With crystallographic analysis, CHA forms tetragonal self-hydrate (P21n) itself; however, it has been observed that structure II (sII) hydrate forms when CH4 coexists. From the phase equilibria measurements, we revealed that CHA can perform the promotion effect with the CH4 hydrate system; subsequent dispersive Raman spectroscopy and 13C solid-state nuclear magnetic resonance measurements confirmed that most CH4 was occupied in the sII hydrate small cage in the CHA (5.6 mol%) + CH4 hydrate system. Gas uptake measurements revealed that a system consisting of stoichiometric concentration of the CHA system attained a CH4 storage capacity of 100.8 mmol of CH4/mol of H2O. Based on this result, we suggest that CHA has the potential to be considered as a promoter candidate for hydrate based CH4 storage technology. © 2025 Elsevier B.V.