Carbon dioxide hydrate kinetics in porous media with and without salts

Large amounts of methane (CH4) exist in the earth in the form of natural gas hydrates, an ice-like substance with guest gas molecules trapped within. One proposed method to recover methane from marine natural gas hydrates is to sequester carbon dioxide (CO2) as hydrates and produce methane. Fundamental understanding of CO2 hydrate in marine environments - the formation and dissociation behavior needs to be understood first in order to develop techniques to facilitate the exchange process. In this study, CO2 hydrate formation and dissociation was studied in Toyoura sand (100-500 mu m), pure water, saltwater of 1.5 wt%, 3 wt% and natural seawater at formation pressure of 3.5 MPa and driving force of 1.5 MPa. Slightly lower water conversions to hydrate were observed when comparing pure water to saline water, though initial gas uptake in saline water was higher than that in pure water. Multiple nucleation was observed in pure water systems, possibly explaining a slightly higher rate of gas uptake after extended periods of time. Dissociation behavior was investigated at two different temperature driving forces of 4 K and 10 K. The presence of NaCl might have a slight impact on dissociation kinetics, causing slightly quicker dissociation than in pure water systems at the lower driving force of 4 K. We did not observe evidence of kinetic inhibition during hydrate formation due to the presence of NaCl but as expected, we observed thermodynamic inhibition. (C) 2014 Elsevier Ltd. All rights reserved.