Kinetics of methane clathrate formation and dissociation under Mars relevant conditions

Mathematics – Logic

Scientific paper

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

1

Scientific paper

Spectral observations have detected methane within the martian atmosphere (Formisano, V., Atreya, S., Encrenaz, T., Ignatiev, N., Giuranna, M. [2004]. Science 306, 1758-1761; Mumma, M.J. et al. [2009]. Science 323, 1041-1045), however, the origin of the methane has not been determined. Methane clathrate (also referred to as methane hydrate) has been suggested as a potential subsurface reservoir, storing and releasing biologic and/or abiogenic methane. In this study, rates of methane hydrate formation and dissociation were measured experimentally at 234-264 K and 1.4-4.7 MPa to test the clathrate reservoir hypothesis. Initial formation rates range from 4.3 × 10-6 to 8.1 × 10-5 mol m-2 s-1. Results show decreasing rates of formation over time in individual experiments, indicating initial rapid clathration, followed by diffusion-limited transport of methane into the ice through the previously formed hydrate. These experiments indicate increased pressure results in increased formation rates, likely the result of higher concentration gradients, enhancing the methane diffusion flux into the solid phase. Experiments conducted at elevated temperatures produced faster initial rates of formation, resulting from increased kinetic energy of methane molecules and/or thickening of the Quasi-Liquid Layer. Based on this temperature dependence, the activation energy for methane hydrate formation from ice was determined to be 35.9 kJ/mol. Hydrate dissociation experiments initiated by depressurization or warming at conditions between 222 K and 265 K and 0.1-2.0 MPa were conducted following each formation experiment, yielding methane hydrate dissociation rates from 3.01 × 10-6 to 9.92 × 10-5 mol m-2 s-1. While both hydrate dissociation and formation showed decreasing instantaneous rates over the course of each experiment, the transition between the initial rate of dissociation and the interpreted diffusion-limited period of continued dissociation was more abrupt than that observed in formation experiments, supporting an ice shielding effect. The initial concentration of methane in the solid phase had a significant effect on hydrate dissociation rates. Higher methane concentrations in the solid phase produce faster initial rates, likely due to increased concentration gradients, thus increasing the diffusion component of dissociation. Increased temperatures also produced faster dissociation rates, yielding an activation energy for dissociation of 32.7 kJ/mol. The rates determined within this study suggest that small near-surface methane hydrate reservoirs are a feasible source for recent methane plumes detected on Mars. Rates of methane release from gas hydrates also indicate that gas hydrate dissociation may have played a role in forming ancient chaos terrain and associated outflow channels.

No associations

LandOfFree

Say what you really think

Search LandOfFree.com for scientists and scientific papers. Rate them and share your experience with other people.

Rating

Kinetics of methane clathrate formation and dissociation under Mars relevant conditions does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Kinetics of methane clathrate formation and dissociation under Mars relevant conditions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Kinetics of methane clathrate formation and dissociation under Mars relevant conditions will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFWR-SCP-O-1560748

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.