Ammonia found as a catalyst in rapid and efficient all-vapor clathrate hydrate formation
Ammonia found as a catalyst in rapid and efficient all-vapor clathrate hydrate formation lead image
Clathrate hydrates are icelike crystalline structures composed of water and small trapped molecules in cagelike structures formed by hydrogen bonds. Methane and CO2 are common gases that become trapped in clathrate hydrates, typically at high pressures and low temperatures, both in nature in oceans and in natural-gas pipelines. Clathrate hydrates can be both beneficial, as in gas storage and transportation, or detrimental, such as in pipeline clogs.
New research in The Journal of Chemical Physics shows the rapid and efficient formation of clathrate hydrates from a mixtue of ammonia and water vapor. While past work focused on the formation of clathrates at much higher pressures and temperatures, this work considers clathrate formation at subatmospheric pressures and temperatures around 180 K. Ammonia not only induces the clathrate to form at less extreme conditions, it also greatly accerlerated the reaction. These clathrates form routinely in less than a second.
Researchers performed spectroscopic measurements and ab initio simulations using density functional theory to determine the underlying time-dependent mechanism of clathrate formation. Ammonia was unique in its rapid penetration of the water network as a catalyst that creates defects with mobilities responsible for the rapid clathrate formation.
All-vapor clathrate formation using premixtures of water vapor and one or more gases enable rapid gas entrapment. This may potentially be extended to applications including carbon dioxide sequestration. The authors have begun work focused on extending this method to operation at higher temperatures. This could enable larger clathrate particle sizes, which would increase the potential practical uses of this discovery.
Source: “NH3 as simple clathrate-hydrate catalyst: Experiment and theory,” by Murat Kılıç, J. Paul Devlin, and Nevin Uras-Aytemiz, The Journal of Chemical Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5029908 .
