Cage occupancy and structural changes during hydrate formation from initial stages to resulting hydrate phase

Abstract

Hydrate formation processes and kinetics are still not sufficiently understood on a molecular level based on experimental data. In particular, the cavity formation and occupancy during the initial formation and growth processes of mixed gas hydrates are rarely investigated. In this study, we present the results of our time-depending Raman spectroscopic measurements during the formation of hydrates from ice and gases or gas mixtures such as CH4, CH4-CO2, CH4-H2S, CH4-C3H8, CH4-iso-C4H10, and CH4-neo-C5H12 at constant pressure and temperature conditions and constant composition of the feed gas phase. All investigated systems in this study show the incorporation of CH4 into the 5(12) cavities as first step in the initial stages of hydrate formation. Furthermore, the results imply that the initial hydrate phases differ from the resulting hydrate phase having reached a steady state regarding the occupancy and ratio of the small and large cavities of the hydrate.

Keywords: 5(12) Cavities; Hydrate formation kinetics; Mixed gas hydrates; Raman spectroscopy.