Commercial-scale methane (CH 4 ) extraction from natural hydrate deposits remains a challenge due to, among other factors, a poor understanding of hydrate-host sediment interactions under low-temperature and high-pressure conditions that are conducive to their existence. We report the use of synchrotron X-ray computed microtomography (CMT) to image, for the first time, time-resolved pore-scale methane CH 4 hydrate growth from an aqueous solution containing 5 wt % barium chloride (BaCl 2 ) and pressurized CH 4 hosted in glass beads, all contained in an aluminum cell with an effective volume of 3.5 mL. Multiple two-dimensional (2-D) cross-sectional images show CH 4 hydrates, with 7.5 mm resolution, distributed in patches throughout the system without dependence on distance from the cell walls. The time-resolved three-dimensional (3-D) images, constructed from the 2-D slices, exhibited pore-filling hydrate formation from dissolved CH 4 gas, similar to natural CH 4 hydrates (sI) in the marine environment. Furthermore, the 3-D images show that the aqueous phase was the wetting phase of the glass beads, i.e., the host and the formed hydrate were separated by an aqueous layer. These results provide some fundamental understanding of the nucleation phenomenon of gas hydrate formation at the pore scale. Pore-filling CH 4 hydrate growth is likely to result in a reduced bulk modulus, and thus, could affect seafloor stability during the reverse phenomenon, i.e., dissociation of natural hydrate deposits.

Graphene-based nanocomposites possess excellent mechanical, electrical, thermal, optical, and chemical properties. These materials have potential applications in high-performance transistors, biomedical systems, sensors, and solar cells. This paper presents a critical review of the recent developments in graphene-based nanocomposite research, exploring synthesis methods, characterizations, mechanical properties, and thermal properties. Emphasis is placed on characterization techniques and mechanical properties with detailed examples from recent literature. The importance of characterization techniques including Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) for the characterization of graphene flakes and their composites were thoroughly discussed. Finally, the effect of graphene even at very low loadings on the mechanical properties of the composite matrix was extensively reviewed.

The occurrence state and molecular structure of extracellular proteins were analyzed to reveal the influencing factors on the water-holding capacities of protein-like substances in waste-activated sludge (WAS). The gelation process of extracellular proteins verified that advanced oxidation processes (AOPs) for WAS dewaterability improvement eliminated the water affinity of extracellular proteins and prevented these macromolecules from forming stable colloidal aggregates. Isobaric tags for relative and absolute quantitation proteomics identified that most of the extracellular proteins were originally derived from the intracellular part and the proteins originally located in the extracellular part were mainly membrane-associated. The main mechanism of extracellular protein transformation during AOPs could be represented by the damage of the membrane or related external encapsulating structure and the release of intracellular substances. For the selected representative extracellular proteins, the strong correlation (R > 0.97, p < 0.03) between the surface hydrophilicity index and α-helix percentages in the secondary structure indicated that the water affinity relied more on the spatial distribution of hydrophilic functional groups rather than the content. Destructing the secondary structure represented by the α-helix and stretching the polypeptide aggregation in the water phase through disulfide bond removal might be the key to eliminating the inhibitory effects of extracellular proteins on the interstitial water removal from WAS.

Sequestration of carbon dioxide (CO 2 ) in the form of its hydrates in natural methane (CH 4 ) hydrate reservoirs, via CO 2 /CH 4 exchange, is an attractive pathway that also yields valuable CH 4 gas as product. In this paper, we describe a macroscale experiment to form CO 2 and CH 4 -CO 2 hydrates, under seafloor-mimic conditions, in a vessel fitted with glass windows that provides visualization of hydrates throughout formation and dissociation processes. Time resolved pressure and temperature data as well as images of hydrates are presented. Quantitative gas conversions with pure CO 2 , calculated from gas chromatographic measurements yielded values that range from 23 -59% that correspond to the extent of formed hydrates. In CH 4 -rich CH 4 -CO 2 mixed gas systems, CH 4 hydrates were found to form preferentially.

Methane hydrate formation and dissociation kinetics were investigated in seawater-saturated consolidated Ottawa sand-pack under sub-seafloor conditions to study the influence of effective pressure on formation and dissociation kinetics. To simulate a sub-seafloor environment, the pore-pressure was varied relative to confining pressure in successive experiments. Hydrate formation was achieved by methane charging followed by sediment cooling. The formation of hydrates was delayed with increasing degree of consolidation. Hydrate dissociation by step-wise depressurization was instantaneous, emanating preferentially from the interior of the sand-pack. Pressure drops during dissociation and in situ temperature controlled the degree of endothermic cooling within sediments. In a closed system, the post-depressurization dissociation was succeeded by thermally induced dissociation and pressure-temperature conditions followed theoretical methane-seawater equilibrium conditions and exhibited excess pore pressure governed by the pore diameter. These post-depressurization equilibrium values for the methane hydrates in seawater saturated consolidated sand-pack were used to estimate the enthalpy of dissociation of 55.83 ± 1.41 kJ/mol. These values were found to be lower than those OPEN ACCESSEnergies 2013, 6 6226 reported in earlier literature for bulk hydrates from seawater (58.84 kJ/mol) and pure water (62.61 kJ/mol) due to excess pore pressure generated within confined sediment system under investigation. However, these observations could be significant in the case of hydrate dissociation in a subseafloor environment where dissociation due to depressurization could result in an instantaneous methane release followed by slow thermally induced dissociation. The excess pore pressure generated during hydrate dissociation could be higher within fine-grained sediments with faults and barriers present in subseafloor settings which could cause shifting in geological layers.