Influence of the initial CH4-hydrate system properties on CO2 capture kinetics.

• Exchange kinetic in CH 4 -hydrates using CO 2 or CO 2 -N 2 gas. • Impact of the initial CH 4 -hydrate system properties on the kinetic. • Structure, cage occupancy and phase composition monitored by Raman spectroscopy. • Quantitative and qualitative estimates of factors influencing the kinetic. Recovering methane from natural gas hydrate deposits using carbon dioxide injection is currently of great environmental and energetic interest as it shows potential for producing an energy resource while mitigating CO 2 emissions through CO 2 sequestration. This work investigates the exchange kinetic between CH 4 and CO 2 (or CO 2 -N 2 (v)) in synthetic hydrates, with an emphasis on the impact of CH 4 hydrate formation conditions (e.g. driving force Δ p) on the subsequent exchange reactions. Different driving forces Δ p are utilized and show that the exchange kinetic is improved by a factor of ~3 when the exchange is performed with low Δ p CH 4 hydrates, for which there is a higher relative amount of free H 2 O(liq) (277 K); the kinetic is further improved when stirring is applied. Isobaric CH 4 hydrates exhibit a fast primary hydrate dissociation and CH 4 release, followed by a slower exchange kinetic, possibly limited by solid-state exchange diffusion or secondary CO 2 -rich hydrate formation within the stability field of CH 4 hydrates. Upon exposure to a mixed CO 2 -N 2 (v) gas stream, secondary hydrate production is governed by the effective Δ p remaining after dissolution of the gas mixture, and results in an even slower exchange reaction rate. These results may help optimizing recovery processes in field trial experiments, where both hydrates and liquid water coexist, and aid in predicting the risk of geo-hazards induced by unstable secondary hydrate formation. Furthermore, the exchange kinetic dependencies highlighted here are important as they affect the overall energy efficiency and energy cost of CH 4 recovery processes in gas hydrate field trials. [ABSTRACT FROM AUTHOR]