J Phys Chem B. 2014 Nov 26;118(47):13371-7. doi: 10.1021/jp5042487. Epub 2014 Jul 01.

Experimental study on the effect of ammonia on the phase behavior of tetrahydrofuran clathrates.

The journal of physical chemistry. B

Tuan Hoang Vu, Elodie Gloesener, Mathieu Choukroun, Anaïs Ibourichene, Robert Hodyss

PMID: 24940841 DOI: 10.1021/jp5042487

Abstract

Clathrate hydrates, ice-like crystalline compounds in which small guest molecules are enclosed inside cages formed by tetrahedrally hydrogen-bonded water molecules, are naturally abundant on Earth and are generally expected to exist on icy celestial bodies. A prototypical example is Saturn's moon Titan, where dissociation of methane clathrates, a major crustal component, could contribute significantly to the replenishment of atmospheric methane. Ammonia is an important clathrate inhibiting agent that may be present (potentially at high concentrations) in Titan's interior. In this study, low-temperature Raman experiments are conducted to examine the dissociation point of tetrahydrofuran clathrates, an ambient-pressure analogue of methane clathrates, over a wide range of ammonia concentrations from 0 to 25 wt %. A phase diagram for the H2O-THF-NH3 system is generated, showing two main results: (i) ammonia lowers the dissociation point of clathrate hydrates to a similar extent compared to the melting of water ice and (ii) THF clathrate exhibits a "liquidus-like" behavior in the presence of ammonia, with a eutectic temperature of about 203.6 K. As temperatures higher than this estimated eutectic are anticipated within Titan's icy crust, these results imply that partial dissociation of clathrates can occur readily and may contribute to outgassing from the interior.

Publication Types

• Journal Article