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The use of natural gas hydrate (NGH) as a natural gas transportation and storage medium is expected to meet further energy demand in the near future. To exploit NGH for industrial porposes, it is necessary to establish NGH storage systems using their self-preservation properties. In this report, NGH pellets containing CH 4 , C 2 H 6 , and C 3 H 8 were produced by continuous production using a bench-scale unit and successfully stored for 3 months at 253 K under atmospheric pressure. Qualitative and quantitative analyses [phase-contrast X-ray computed tomography (CT) by means of diffraction-enhanced imaging, cryogenic scanning electron microscopy, powder X-ray diffraction, and gas chromatography] were conducted to investigate the progression of dissociation. Some of the NGH pellets were also examined for their thermal history dependence between approximately 85 and 253 K after storage for 1 day or less to assess their stability under a rapid temperature change. The internal texture of the original NGH pellets was dense with hydrate even after 3 months of storage. On the other hand, thermal cracks covered with ice had formed in the hydrate pellet after the temperature rise (from 85 to 253 K). These cracks were assumed to be dissociation sites, but the dissociation was stopped only near the cracks. The mass fractions of NGH were larger than 70% after 3 months of storage and undergoing thermal history. These results demonstrate the excellent characteristics of NGH pellets produced by continuous production, improving their suitability for use as natural gas storage media.

Storage of natural gas (NG) is required for a range of applications. In this study, we succeeded to maintain NG within water cages of anomalously preserved NG hydrate crystal for more than three weeks under thermodynamically unstable conditions at 253 K and atmospheric pressure. This anomalous preservation phenomenon of NG hydrate pellet was measured quantitatively by powder X-ray diffraction and gas chromatography as well as measuring the change in weight caused by hydrate dissociation. In addition, two different types of phase contrast X-ray imaging techniques, X-ray interferometric imaging and diffraction enhanced imaging, also revealed that the NG hydrate was maintained inside the pellet. Also, scanning electron microscopy showed that the outer ice layer formed contained many pores while the internal microstructure of NG hydrate pellet was dense without pores. These experimental results suggest that formation of the outer ice layer may not be related to anomalous preservation of NG hydrate, but formation of pore space may cause hydrate dissociation.

Stabilization by a silyl group on the methylene carbon and a diamine ligand led to the isolation of gem-dichromiomethane species. X-ray crystallography confirmed the identity of the structure of this rare example of reactive gem-dimetalloalkane species. The isolated gem-dichromiomethane complex acted as a storable silylmethylidene carbene equivalent, with reactivity that could be changed dramatically upon addition of a Lewis acid (ZnCl) and a base (TMEDA) to promote both silylalkylidenation of polar aldehydes and silylcyclopropanation of nonpolar alkenes. Identification of a key reactive species also identified the catalytic version of these transformations and provided insights into the reaction mechanism. In contrast to Simmons-Smith cyclopropanation, the real reactive species for the current cyclopropanation was a chromiocarbene species, not a chromium carbenoid species.