Jiwoong Seol

Spectroscopic Observation of Atomic Hydrogen Radicals Entrapped in Icy Hydrogen Hydrate

A hydrogen molecule entrapped in the cages of icy hydrogen hydrate is confined in host water framework and thus behaves unlike pure solid or liquid hydrogen. The gamma-irradiated hydrogen radicals are for the first time observed from ESR and solid-state MAS 1H NMR spectra to stably exist in the icy hydrate channels without any collapse of the host framework, confirming the chemical shift consistency of ionized hydrogen derivatives. We discuss the confined icy hydrate channels, which can act as potential storage sites for simultaneously imprisoning both molecular and ionized hydrogen and further as icy nanoreactors.

Effect of Interlayer Ions on Methane Hydrate Formation in Clay Sediments

Natural methane hydrates occurring in marine clay sediments exhibit heterogeneous phase behavior with high complexity, particularly in the negatively charged interlayer region. To date, the real clay interlayer effect on natural methane hydrate formation and stability remains still much unanswered, even though a few computer simulation and model studies are reported. We first examined the chemical shift difference of 27Al, 29Si, and 23Na between dry clay and clay containing intercalated methane hydrates (MH) in the interlayer. We also measured the solid-state 13C MAS NMR spectra of MH in Na-montmorillonite (MMT) and Ca-montmorillonite (MMT) to reveal abnormal methane popularity established in the course of intercalation and further performed cryo-TEM and XRD analyses to identify the morphology and layered structure of the intercalated methane hydrate. The present findings strongly suggest that the real methane amount contained in natural MH deposits should be reevaluated under consideration of the compositional, structural, and physical characteristics of clay-rich sediments. Furthermore, the intercalated methane hydrate structure should be seriously considered for developing the in situ production technologies of the deep-ocean methane hydrate.

Abnormal methane occupancy of natural gas hydrates in deep sea floor sediments

Natural gas hydrates were recovered from near-seafloor sediments and analysed to compare two distinctive methane inclusion phenomena. We document the first observation of abnormal methane occupancy in sediment-rich NGH deposits.

Natural gas hydrate as a potential energy resource: From occurrence to production

Natural gas hydrate reservoirs have been strongly suggested as a potential energy resource. However, this potential is expected to be limited by geological factors, reservoir properties, and phase-equilibria considerations. Accordingly, sufficient understanding and accurate analyses for the complex surroundings in a natural gas hydrate system have to occur before methane recovery. In this paper, we discuss the formation and structure patterns of global natural gas hydrate, including the origins of hydrocarbon, crystal structures, and unique structure transition. We also summarize two important anomalies related to methane occupancy and chlorinity which were revealed very recently. Furthermore, we review the geological and chemical surroundings of the shallow hydrate deposits, the so-called brine patch discovered in the Cascadia Margin and Ulleung Basin, which are significantly related to tectonic conduits for methane gas and positive chlorinity.

Magnetic transition and long-time relaxation behavior induced by selective injection of guest molecules into clathrate hydrates.

Magnetic molecules physisorbed into low-dimensional nanostructures of microporous materials such as graphite and metal-organic frameworks have been verified to exhibit an unusual magnetic behavior. We demonstrate that the selective injection of both magnetic and nonmagnetic guest molecules into the water-ice cages of clathrate hydrates to form a 3D superstructure with tetrahedral and diamond-like sublattices can modify the inherent magnetism.

Molecular cage occupancy of clathrate hydrates at infinite dilution: experimental determination and thermodynamic significance.

This study focuses on the cage occupancy of guest molecules in the infinitely dilute state. At the extreme conditions of highly diluted guest concentrations the direct measurements of the cage occupancy ratio representing the competitive inclusion of multiguest species appear to be so difficult because of spectroscopic intensity limitation, but its thermodynamic significance might be considerable due to the fact that the infinite-dilution value of the cage occupancy ratio can provide the valuable thermodynamic information as a very unique and guest-specific parameter. To experimentally identify gaseous guest populations in structure I (sI) and structure II (sII) cages, we used the solid-state nuclear magnetic resonance (NMR), gas chromatography, and direct gas measurements. Furthermore, we derived the simple and generalized thermodynamic equation related to cage occupancies at infinite dilution from the van der Waals-Platteeuw model. Both experimental and predicted values agree well within the experimental error range.

Phase and kinetic behavior of the mixed methane and carbon dioxide hydrates

Large amounts of CH4 are stored as hydrates on continental margins and permafrost regions. If the CH4 hydrates could be converted into CO2 hydrate, they would serve double duty as CH4 sources and CO2 storage sites in the deep ocean sediments. As preliminary investigations, both the phase behavior of CH4 hydrates and kinetic behavior of CO2 hydrate were measured at versatile conditions that can simulate actual marine sediments. When measuring three-phase equilibria (H-LW-V) containing CH4 hydrate, we also closely examined pore and electrolyte effects of clay and NaCl on hydrate formation. These two effects inhibited hydrate nucleation and thus made the hydrate equilibrium line shift to a higher pressure region. In addition, the kinetic data of CO2 hydrate in the mixtures containing clay and NaCl were determined at 2.0 MPa and 274.15 K. Clay mineral accelerated an initial formation rate of CO2 hydrate by inducing nucleation as initiator, but total amount of formed CO2, of course, decreased due to the capillary effect of clay pores. Also, the addition of NaCl in sample mixtures made both initial formation rate and total amount of CO2 consumption decrease.

Experimental Verifications of Abnormal Chlorinity appearing in Natural Deep- Sea Gas Hydrate

The chloride anion is known to be the most abundant salt ion in sea water. At the regions such as ODP Sites 1249 and 1250 the highly enriched chloride concentration is observed in a zone extended from near the sediment surface (~1 mbsf) to depths about 25 mbsf. Here, we designed the in-situ electric circuit system for measuring chloride concentration within reliable accuracy. In the cylindrical cell the 5-10 tubes having holes on the wall and electrodes were equipped around clay mixture. The open holes were made to regulate to a certain degree the interface area between methane gas and clay sample. As may be anticipated, the chloride concentration abnormally increased under fast rate condition for forming methane hydrate, but no noticeable concentration change was detected under relatively low rate. In fact, the present experiment seems to be a lot deficient to investigate the ion diffusion and moreover does not fully reflect the real deep-sea floor condition, but the meaningful results for describing the abnormal salinity enrichment might be drawn. The physical effects of chloride anions on surface morphologies of methane hydrate formed in the sediments were additionally examined with the Field Emission-Scanning Electronic Microscope (FE-SEM).