Laboratory simulation of gas hydrate formation at ice surfaces in Earth atmosphere

Abstract

<p>For fourteen days in November the world’s attention turned to the rise in atmospheric GHG levels, on this occasion with a special focus on methane (<em>Nature</em> 25 August 2021).  Methane had previously been the subject of a study on gas hydrate formation and, while noting the relevance of this property to climate change modelling, the authors in that case wrote: `<em>Curiously, gas hydrates seem to defy intuition about hydrophobic compounds, as the concentration of a nonpolar gas in the solid hydrate lattice is more than two orders of magnitude higher than the solubility of such a gas in liquid water’</em> (Walsh et al 2008 `Microsecond Simulations of Spontaneous Methane Hydrate Nucleation and Growth' ). </p><p>The term `non-polar’ applies to the gases of Earth’s atmosphere - so does the same concentration paradox apply to the inclusion of each of these species in atmospheric ice? For CO<sub>2</sub>, curves published by the University of Lille quantify hydrate formation across a range of partial pressures, and are projected to a zero pressure origin, thereby embracing the partial pressure of the gas in Earth atmosphere (Chazallon and Pirim (2018) `Selectivity and CO2 capture efficiency in CO2-N2 clathrate hydrates investigated by in-situ Raman spectroscopy', Figs 4A and 4B).  Moreover, in the presence of ice phase at -12°C our own results have shown that, from a CO<sub>2</sub>+N<sub>2</sub> mixture, more than 90% of CO<sub>2 </sub>goes into the ice/hydrate phase, which is three times higher that at 10°C (Hassanpouryouzband et al 2019 `<span>Geological CO<sub>2</sub> capture and storage with flue gas hydrate formation in frozen and unfrozen sediments'</span>).</p><p>We simulate hydrate formation in the Earth's atmosphere using laboratory apparatus designed to quantify the depletion of GHGs (including water vapour) from a chilled airstream at atmospheric pressure across a range of temperatures, followed by analysis of the condensate. </p>