Nucleation and dissociation of methane clathrate embryo at the gas–water interface

Abstract

Among natural energy resources, methane clathrate has attracted tremendous attention because of its strong relevance to current energy and environment issues. Yet little is known about how the clathrate starts to nucleate and disintegrate at the molecular level, because such microscopic processes are difficult to probe experimentally. Using surface-specific sum-frequency vibrational spectroscopy, we have studied in situ the nucleation and disintegration of methane clathrate embryos at the methane-gas–water interface under high pressure and different temperatures. Before appearance of macroscopic methane clathrate, the interfacial structure undergoes 3 stages as temperature varies, namely, dissolution of methane molecules into water interface, formation of cage-like methane–water complexes, and appearance of microscopic methane clathrate, while the bulk water structure remains unchanged. We find spectral features associated with methane–water complexes emerging in the induction time. The complexes are present over a wide temperature window and act as nuclei for clathrate growth. Their existence in the melt of clathrates explains why melted clathrates can be more readily recrystallized at higher temperature, the so-called “memory effect.” Our findings here on the nucleation mechanism of clathrates could provide guidance for rational control of formation and disintegration of clathrates.

Magnesium-Promoted Rapid Nucleation of Carbon Dioxide Hydrates

“…Slow nucleation of hydrates is one of the key challenges associated with hydrate formation. Nucleation refers to the formation of the first “stable” crystal of hydrate that can subsequently grow. − While nucleation is undoubtedly influenced by thermodynamic conditions, the induction (wait) time for hydrates to nucleate can range from hours to days in the absence of any external promotion techniques . Additional key challenges associated with hydrate formation involve slow growth rates and low gas-to-hydrate conversion.…”

Explicating the amino acid effects for methane storage in hydrate form

“…It does not allow further gas to interact with water hindering hydrate growth. 22,23 Several mechanical techniques are being adopted to overcome these challenges and enhance the gas water interaction and higher surface area for hydrate growth. 24,25 These include mixing/agitating the sample using stirred reactor, rocking cells, and spraying the water into pressurized reactors using the high-pressure pumps.…”

Reduced phase stability and faster formation/dissociation kinetics in confined methane hydrate

“…There are abundant literature data indicating that confinement leads to faster kinetics compared with their bulk counterpart (16,20,28), but the underlying mechanisms remain to be unraveled. Theoretically, much work has been done to elucidate the molecular routes that lead to the nucleation of bulk hydrates (29)(30)(31)(32)(33), but the case of confined hydrates has not been considered. Several authors have used molecular modeling to investigate the growth of an already formed methane or carbon dioxide hydrate in the vicinity of a surface (34)(35)(36)(37)(38), but microscopic nucleation remains largely unexplored.…”