Description: Two new cyclic peroxides, 2 and 3, were isolated from a sample of the Norwegian sponge Plakortis simplex. Their structures including relative stereochemistry were elucidated by interpretation of MS and NMR data. Compound 3 exhibited moderate in vitro activity against six solid human tumor cell lines with IC50 values in the range 7−15 μg/mL.

Description: In the colloidal synthesis of iron sulfides, a series of dialkyl disulfides, alkyl thiols, and dialkyl disulfides (allyl, benzyl, tert-butyl, and phenyl) were employed as sulfur sources. Their reactivity was found to tune the phase between pyrite (FeS2), greigite (Fe3S4), and pyrrhotite (Fe7S8). DFT was used to show that sulfur-rich phases were favored when the C–S bond strength was low in the organosulfurs, yet temperature dependent studies and other observations indicated the reasons for phase selectivity were more nuanced; the different precursors decomposed through different reaction mechanisms, some involving the oleylamine solvent. The formation of pyrite from diallyl disulfide was carefully studied as it was the only precursor to yield FeS2. Raman spectroscopy indicated that FeS2 forms directly without an FeS intermediate, unlike most synthetic procedures to pyrite. Diallyl disulfide releases persulfide (S–S)2– due to the lower C–S bond strength relative to the S–S bond strength, as well as facile decomposition in the presence of amines through SN2′ mechanisms at elevated temperatures.

Description: We describe a new and efficient technique to grow aggregates of pure methane hydrate in quantities suitable for physical and material properties testing. Test specimens were grown under static conditions by combining cold, pressurized CH4 gas with granulated H2O ice, and then warming the reactants to promote the reaction CH4(g) + 6H2O(s→l) → CH4·6H2O (methane hydrate). Hydrate formation evidently occurs at the nascent ice/liquid water interface on ice grain surfaces, and complete reaction was achieved by warming the system above the ice melting point and up to 290 K, at 25−30 MPa, for approximately 8 h. The resulting material is pure, cohesive, polycrystalline methane hydrate with controlled grain size and random orientation. Synthesis conditions placed the H2O ice well above its melting temperature while reaction progressed, yet samples and run records showed no evidence for bulk melting of the unreacted portions of ice grains. Control experiments using Ne, a non-hydrate-forming gas, showed that under otherwise identical conditions, the pressure reduction and latent heat associated with ice melting are easily detectable in our fabrication apparatus. These results suggest that under hydrate-forming conditions, H2O ice can persist metastably to temperatures well above its ordinary melting point while reacting to form hydrate. Direct observations of the hydrate growth process in a small, high-pressure optical cell verified these conclusions and revealed additional details of the hydrate growth process. Methane hydrate samples were then tested in constant-strain-rate deformation experiments at T = 140−200 K, Pc = 50−100 MPa, and ε = 10-4−10-6 s-1. Measurements in both the brittle and ductile fields showed that methane hydrate has measurably different strength than H2O ice, and work hardens to an unusually high degree compared to other ices as well as to most metals and ceramics at high homologous temperatures. This work hardening may be related to a changing stoichiometry under pressure during plastic deformation; X-ray analyses showed that methane hydrate undergoes a process of solid-state disproportionation or exsolution during deformation at conditions well within its conventional stability field.

Description: Methane recovery from artificial hydrate-bearing sandstones by simulated flue gas swapping was tested using a core flooding experimental setup. Seven groups of experiments were conducted to investigate the effect of hydrate saturation as well as the initial porosity and permeability of sandstones on methane production and carbon dioxide capture. The results show that the CH4 recovery efficiency and the amount of CO2 captured increase with the increase of hydrate saturation at the same initial porosity and permeability of sandstone. The highest CH4 recovery obtained is 51.6% and 99.4% of CO2 in simulated flue gas is sequestered in the hydrate phase after swapping at 9.2 MPa and 277.15 K. Hydrate saturation was 82.5% and the initial porosity and permeability of sandstone are 25.1% and 49 mD, respectively. With the increase of initial porosity and permeability of sandstone, the CH4 recovery efficiency and the amount of CO2 captured increase when other conditions (the hydrate saturation and reaction time) are similar. For investigating the CH4-flue gas swapping mechanism, a micro-differential scanning calorimetry was used to test the heat changes in the whole reaction. No noticeable endothermic or exothermic phenomenon was detected in the CH4-flue gas swapping, which indicates that CH4 hydrate would form mixed hydrates directly instead of going through a dissociation and reformation process. Based on the observed experimental results, a CH4-flue gas swapping mechanism is proposed and the reaction process is found to be essentially controlled by mass transfer.

Description: The Ignik Sikumi Gas Hydrate Exchange Field Experiment was conducted by ConocoPhillips in partnership with the U.S. Department of Energy, the Japan Oil, Gas and Metals National Corporation, and the U.S. Geological Survey within the Prudhoe Bay Unit on the Alaska North Slope during 2011 and 2012. The primary goals of the program were to (1) determine the feasibility of gas injection into hydrate-bearing sand reservoirs and (2) observe reservoir response upon subsequent flowback in order to assess the potential for C02 exchange for CH4 in naturally occurring gas hydrate reservoirs. Initial modeling determined that no feasible means of injection of pure C02 was likely, given the presence of free water in the reservoir. Laboratory and numerical modeling studies indicated that the injection of a mixture of C02 and N2 offered the best potential for gas injection and exchange. The test featured the following primary operational phases: (1) injection of a gaseous phase mixture of C02, N2, and chemical tracers; (2) flowback conducted at downhole pressures above the stability threshold for native CH4 hydrate; and ( 3) an extended ( 30-days) flowback at pressures near, and then below, the stability threshold of native CH4 hydrate. The test findings indicate that the formation of a range of mixed-gas hydrates resulted in a net exchange of C02 for CH4 in the reservoir, although the complexity of the subsurface environment renders the nature, extent, and efficiency of the exchange reaction uncertain. The next steps in the evaluation of exchange technology should feature multiple well applications; however, such field test programs will require extensive preparatory experimental and numerical modeling studies and will likely be a secondary priority to further field testing of production through depressurization. Additional insights gained from the field program include the following: (1) gas hydrate destabilization is self-limiting, dispelling any notion of the potential for uncontrolled destabilization; (2) gas hydrate test wells must be carefully designed to enable rapid remediation of wellbore blockages that will occur during any cessation in operations; (3) sand production during hydrate production likely can be managed through standard engineering controls; and ( 4) reservoir heat exchange during depressurization was more favorable than expected-mitigating concerns for near-wellbore freezing and enabling consideration of more aggressive pressure reduction.

Description: Microbial mats collected at cold methane seeps in the Black Sea carry out anaerobic oxidation of methane (AOM) to carbon dioxide using sulfate as the electron acceptor. These mats, which predominantly consist of sulfate-reducing bacteria and archaea of the ANME-1 and ANME-2 type, contain large amounts of proteins very similar to methyl-coenzyme M reductase from methanogenic archaea. Mass spectrometry of mat samples revealed the presence of two nickel-containing cofactors in comparable amounts, one with the same mass as coenzyme F430 from methanogens (m/z = 905) and one with a mass that is 46 Da higher (m/z = 951). The two cofactors were isolated and purified, and their constitution and absolute configuration were determined. The cofactor with m/z = 905 was proven to be identical to coenzyme F430 from methanogens. For the m/z = 951 species, high resolution ICP-MS pointed to F430 + CH2S as the molecular formula, and LA-ICP-SF MS finally confirmed the presence of one sulfur atom per nickel. Esterification gave two stereoisomeric pentamethyl esters with m/z = 1021, which could be purified by reverse phase HPLC and were subjected to comprehensive NMR analysis, allowing determination of their constitution and configuration as (172S)−172-methylthio-F430 pentamethyl ester and (172R)−172-methylthio-F430 pentamethyl ester. The corresponding diastereoisomeric pentaacids could also be separated by HPLC and were correlated to the esters via mild hydrolysis of the latter. Equilibration of the pentaacids under acid catalysis showed that the (172S) isomer is the naturally occurring albeit thermodynamically less stable one. The more stable (172R) isomer (80% at equilibrium) is an isolation artifact generated under the acidic conditions necessary for the isolation of the cofactors from the calcium carbonate-encrusted mats.

Description: We determined the coordination environment of Zn2+ in aqueous Cl- brines at 25 °C and 300 °C using ab initio molecular dynamics simulations. The ZnCl+ and ZnCl2 complexes exist as pseudo-octahedral ZnClm(H2O)6-m clusters at 25 °C but occur as pseudo-tetrahedral ZnClm(H2O)4-m clusters at 300 °C. The ZnCl3- complex occurs as the pseudo-tetrahedral ZnCl3(H2O)- cluster at 25 and 300 °C. The tetrahedral ZnCl42- complex, however, is the dominant Zn−Cl complex at 25 °C, at least in highly concentrated (7.4 m) Cl- brines. The change in hydration number with temperature for the ZnCl+ and ZnCl2 complexes will complicate extrapolations of solvation energies to hydrothermal conditions using a Born-model-based equation of state.

Description: Microscopy, confocal Raman spectroscopy and powder X-ray diffraction (PXRD) were used for in situ investigations of the CO2-hydrocarbon exchange process in gas hydrates and its driving forces. The study comprises the exposure of simple structure I CH4 hydrate and mixed structure II CH4–C2H6 and CH4–C3H8 hydrates to gaseous CO2 as well as the reverse reaction, i.e., the conversion of CO2-rich structure I hydrate into structure II mixed hydrate. In the case of CH4–C3H8 hydrates, a conversion in the presence of gaseous CO2 from a supposedly more stable structure II hydrate to a less stable structure I CO2-rich hydrate was observed. PXRD data show that the reverse process requires longer initiation times, and structural changes seem to be less complete. Generally, the exchange process can be described as a decomposition and reformation process, in terms of a rearrangement of molecules, and is primarily induced by the chemical potential gradient between hydrate phase and the provided gas phase. The results show furthermore the dependency of the conversion rate on the surface area of the hydrate phase, the thermodynamic stability of the original and resulting hydrate phase, as well as the mobility of guest molecules and formation kinetics of the resulting hydrate phase.

Description: Marine methane hydrate in sands has huge potential as an unconventional gas resource; however, no field test of their production potential had been conducted. Here, we report the world’s first offshore methane hydrate production test conducted at the eastern Nankai Trough and show key findings toward future commercial production. Geological analysis indicates that hydrate saturation reaches 80% and permeability in the presence of hydrate ranges from 0.01 to 10 mdarcies. Permeable (1–10 mdarcies) highly hydrate-saturated layers enable depressurization-induced gas production of approximately 20,000 Sm3/D with water of 200 m3/D. Numerical analysis reveals that the dissociation zone expands laterally 25 m at the front after 6 days. Gas rate is expected to increase with time, owing to the expansion of the dissociation zone. It is found that permeable highly hydrate-saturated layers increase the gas–water ratio of the production fluid. The identification of such layers is critically important to increase the energy efficiency and the technical feasibility of depressurization-induced gas production from hydrate reservoirs.