Phase Equilibria and Spectroscopic Identification of Structure II Hydrates with New Hydrate-Forming Agents (Cyclopropylamine and Cyclopentylamine)
Ki Hun Park, Dong Hyun Kim, Minjun Cha
Abstract
In this study, the phase equilibria of binary (cyclopropylamine (CPrA) + methane (CH4)) and (cyclopentylamine (CPeA) + CH4) hydrates were investigated using a conventional isochoric pressure–temperature trace method. The equilibrium temperatures of the binary (CPrA + CH4) and (CPeA + CH4) hydrates were higher than those of pure CH4 hydrate. The guest conformation and inclusion behaviors of the binary (CPrA + CH4) and (CPeA + CH4) hydrates were also examined through 13C solid-state nuclear magnetic resonance spectroscopy, and the results confirmed the formation of structure II hydrates with new hydrate-forming agents, CPrA and CPeA, in the presence of CH4. The crystal structures and possible host–guest interactions of the proposed hydrate systems were investigated through Rietveld analysis using the direct space method, and the results demonstrated the formation of sII hydrates (with cubic Fd-3m) and the possibility of host–guest interactions in the binary (CPrA + CH4) and (CPeA + CH4) hydrates. These observations provide an improved understanding of the unique nature of host–guest inclusion phenomena.