Institute of Petroleum Engineering

Centre for Gas Hydrate Research Publications

Abstract 139

Low-Pressure Molecular Hydrogen Storage in Semi-clathrate Hydrates of Quaternary Ammonium Compounds

Chapoy, A., Anderson, R., and Tohidi, B.

Journal of the American Chemical Society, 129, 746-747 (2007).

Previously, the molecular diameter of hydrogen was considered too small to stabilize clathrate cavities, even in hydrates formed from gas mixtures. However, recent studies demonstrate that significant H2 can be accommodated in simple (single guest) and binary cubic structure-II clathrate hydrates under specific conditions. This discovery has prompted considerable research into clathrate hydrates as potential hydrogen storage materials. In this communication, we report that substantial volumes of molecular hydrogen can be stored in the structural cavities of a class of lesser known clathrate hydrates, namely the semi-clathrate hydrates of quaternary ammonium salts (QAS). Phase equilibrium studies of tetra-n-butylammonium bromide (TBAB, (C4H9)4N+Br-) and tetra-n-butylammonium fluoride (TBAF, (C4H9)4N+F-) aqueous systems under H2 pressure confirm the formation of binary H2-TBAB and H2-TBAF semi-clathrate hydrates which are stable at ambient temperatures (≤ 29 °C) to atmospheric pressure. Such favorable stability conditions, combined with ease of formation/H2 regeneration and low parent QAS solution vapor pressures (thus high H2 purity), make semi-clathrates particularly attractive as potential H2 storage media.

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