ALBERT

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: Numerical tools are essential for the prediction and evaluation of conventional hydrocarbon reservoir performance. Gas hydrates represent a vast natural resource with a significant energy potential. The numerical codes/tools describing processes involved during the dissociation (induced by several methods) for gas production from hydrates are powerful, but they need validation by comparison to empirical data to instill con fidence in their predictions. In this study, we successfully reproduce experimental data of hydrate dissociation using the TOUGH+HYDRATE (T+H) code. Methane(CH4)hydrate growth and dissociation in partially water- and gas-saturated Bentheim sandstone were spatially resolved using Magnetic Resonance Imaging (MRI), which allows the in situ monitoring of saturation and phase transitions. All the CH4 that had been initially converted to gas hydrate was recovered during depressurization. The physical system was reproduced numerically, usingboth a simplified 2D model and a 3D grid involving complex Voronoi elements. We modeled dissociation using both the equilibrium and the kinetic reaction options in T+H, and we used a range of kinetic parameters for sensitivity analysis and curve fitting. We successfully reproduced the experimental results, which confirmed the empirical data that demonstrated that heattransport was the limiting factor during dissociation. Dissociation was more sensitive to kinetic parameters than anticipated, which indicates that kinetic limitations may be important in short-term core studies and a necessity in such simulations. This is the first time T+H has been used to predict empirical nonmonotonic dissociation behavior, where hydrate dissociation and reformation occurred as parallel events.

Description: Methane hydrate, a potential future energy resource, is known to occur naturally in vast quantities beneath the ocean floor and in permafrost regions. It is important to evaluate how much methane is recoverable from these hydrate reserves. This article introduces the theoretical background of HydrateResSim, the National Energy Technology Laboratory (NETL) methane production simulator for hydrate-containing reservoirs, originally developed for NETL by Lawrence Berkeley National Laboratory (LBNL). It describes the mathematical model that governs the dissociation of methane hydrate by depressurization or thermal stimulation of the system, including the transport of multiple temperature-dependent components in multiple phases through a porous medium. The model equations are obtained by incorporating the multiphase Darcy’s law for gas and liquid into both the mass component balances and the energy conservation equations. Two submodels in HydrateResSim for hydrate dissociation are also considered: a kinetic model and a pure thermodynamic model. Contrary to more traditional reservoir simulations, the set of model unknowns or primary variables in HydrateResSim changes throughout the simulation as a result of the formation or dissociation of ice and hydrate phases during the simulation. The primary variable switch method (PVSM) is used to effectively track these phase changes. The equations are solved by utilizing the implicit time finite-difference method on the grid system, which can properly describe phase appearance or disappearance as well as the boundary conditions. The Newton-Raphson method is used to solve the linear equations after discretization and setup of the Jacobian matrix. We report here the application of HydrateResSim to a three-component, four-phase flow system in order to predict the methane produced from a laboratory-scale reservoir. The first results of HydrateResSim code in a peer-reviewed publication are presented in this article. The numerical solution was verified against the state-of-the art simulator TOUGH+Hydrate. The model was then used to compare twodissociation theories: kinetic and pure equilibrium. Generally, the kinetic model revealed a lower dissociation rate than the equilibrium model. The hydrate dissociation patterns differed significantly when the thermal boundary condition was shifted from adiabatic to constant-temperature. The surface area factor was found to have an important effect on the rate of hydrate dissociation for the kinetic model. The deviation between the kinetic and equilibrium models was found to increase with decreasing surface area factor.

Description: Calculations of the size and density of atmospheric aerosols are complicated by the fact that they can exist at concentrations highly supersaturated with respect to dissolved salts and supercooled with respect to ice. Densities and apparent molar volumes of solutes in aqueous solutions containing the solutes H2SO4, HNO3, HCl, Na2SO4, NaNO3, NaCl, (NH4)2SO4, NH4NO3, and NH4Cl have been critically evaluated and represented using fitted equations from 0 to 50 °C or greater and from infinite dilution to concentrations saturated or supersaturated with respect to the dissolved salts. Using extrapolated densities of high-temperature solutions and melts, the relationship between density and concentration is extended to the hypothetical pure liquid solutes. Above a given reference concentration of a few mol kg−1, it is observed that density increases almost linearly with decreasing temperature, and comparisons with available data below 0 °C suggest that the fitted equations for density can be extrapolated to very low temperatures. As concentration is decreased below the reference concentration, the variation of density with temperature tends to that of water (which decreases as temperature is reduced below 3.98 °C). In this region below the reference concentration, and below 0 °C, densities are calculated using extrapolated apparent molar volumes which are constrained to agree at the reference concentrations with an equation for the directly fitted density. Calculated volume properties agree well with available data at low temperatures, for both concentrated and dilute solutions. Comparisons are made with literature data for temperatures of maximum density. Apparent molar volumes at infinite dilution are consistent, on a single ion basis, to better than ±0.1 cm3 mol−1 from 0 to 50 °C. Volume properties of aqueous NaHSO4, NaOH, and NH3 have also been evaluated, at 25 °C only. In part 2 of this work (ref 1) an ion interaction (Pitzer) model has been used to calculate apparent molar volumes of H2SO4 in 0−3 mol kg−1 aqueous solutions of the pure acid and to represent directly the effect of the HSO4− ↔ H+ + SO42− reaction. The results are incorporated into the treatment of aqueous H2SO4 density described here. Densities and apparent molar volumes from −20 to 50 °C, and from 0 to 100 wt % of solute, are tabulated for the electrolytes listed in the title and have also been incorporated into the extended aerosol inorganics model (E-AIM, http://www.aim.env.uea.ac.uk/aim/aim.php) together with densities of the solid salts and hydrates.

Description: A total of 19 naturally occurring bromophenols, with six new and 13 known structures, were isolated and identified from the methanolic extract of the marine red alga Rhodomela confervoides. The new compounds were identified by spectroscopic methods as 3,4-dibromo-5-((methylsulfonyl)methyl)benzene-1,2-diol (1), 3,4-dibromo-5-((2,3-dihydroxypropoxy)methyl)benzene-1,2-diol (2), 5-(aminomethyl)-3,4-dibromobenzene-1,2-diol (3), 2-(2,3-dibromo-4,5-dihydroxyphenyl)acetic acid (4), 2-methoxy-3-bromo-5-hydroxymethylphenol (5), and (E)-4-(2-bromo-4,5-dihydroxyphenyl)but-3-en-2-one (6). Each compound was evaluated for free radical scavenging activity against DPPH (α,α-diphenyl-β-dipicrylhydrazyl) and ABTS [2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt] radicals. Most of them exhibited potent activities stronger than or comparable to the positive controls butylated hydroxytoluene (BHT) and ascorbic acid. The results from this study suggest that R. confervoides is an excellent source of natural antioxidants, and inclusion of these antioxidant-rich algal components would likely help prevent the oxidative deterioration of food.

Description: The current difficulty in visualizing the true extent of malignant brain tumors during surgical resection represents one of the major reasons for the poor prognosis of brain tumor patients. Here, we evaluated the ability of a hand-held Raman scanner, guided by surface-enhanced Raman scattering (SERS) nanoparticles, to identify the microscopic tumor extent in a genetically engineered RCAS/tv-a glioblastoma mouse model. In a simulated intraoperative scenario, we tested both a static Raman imaging device and a mobile, hand-held Raman scanner. We show that SERS image-guided resection is more accurate than resection using white light visualization alone. Both methods complemented each other, and correlation with histology showed that SERS nanoparticles accurately outlined the extent of the tumors. Importantly, the hand-held Raman probe not only allowed near real-time scanning, but also detected additional microscopic foci of cancer in the resection bed that were not seen on static SERS images and would otherwise have been missed. This technology has a strong potential for clinical translation because it uses inert gold-silica SERS nanoparticles and a hand-held Raman scanner that can guide brain tumor resection in the operating room.

Description: Consumer preference for natural food ingredients has increased in recent decades, and the natural food colorant market has grown to over one billion dollars annually. A variety of red, orange, and yellow natural colorants are approved and in use, but there still exists a lack of available blue and purple natural colorant options. The occurrence of blue colored compounds in the natural world is relatively rare. The isolation, identification, and characterization of natural blue and purple pigments obtained from underexplored natural sources such as from obscure terrestrial organisms and marine microorganisms will be discussed.

Description: Titanium (Ti) is present as a trace element in seawater at extremely low concentrations (5-350 pM, where 1 pM = 10(-12) mol L(-1)) throughout the water column. Presently, little is known about the marine biogeochemistry of Ti and there is a distinct lack of oceanic measurements of Ti, because of the combined difficulties of trace-metal clean sampling for an element at such low levels and the lack of a suitable shipboard method of analysis. Here, a new cathodic stripping voltammetry procedure is presented for the rapid determination of Ti at pM concentrations in seawater that is capable of being used directly at sea. This method utilizes the catalytic enhancement of the reduction of the complex formed between Cupferron (N-nitrosophenylhydroxylamine) and Ti(IV). While Cupferron itself acts as both a complexing agent and an oxidizing agent, it was found that the optimal sensitivity was with bromate as an auxiliary oxidant. An advantage of this method is that it is useable over the pH range of 5.5-8. Under the conditions employed in this work, detection limits ranged from 5 pM to 12 pM. This new catalytic method is significantly more sensitive than existing methods and has been extensively tested at sea in the Atlantic and Southern Oceans.

Description: Electrolytes can thermodynamically inhibit clathrate hydrate formation by lowering the activity of water in the surrounding liquid phase, causing the hydrates to form at lower temperatures and higher pressures compared to their formation in pure water. However, it has been reported that some thermodynamic hydrate inhibitors (THIs), when doped at low concentrations, could enhance the rate of gas hydrate formation. We here report a systematic study of model natural gas (a mixture of 90% methane and 10% propane) hydrate formation in strong monovalent salt solutions in a broad range of concentrations, using a high pressure automated lag time apparatus (HP-ALTA). HP-ALTA can apply a large number (〉100) of cooling ramps to a sample and construct probability distributions of gas hydrate formation for each sample. The probabilistic interpretation of data enables us to mitigate the stochastic variation inherent in the nucleation probability distributions and facilitates meaningful comparison among different samples. The electrolytes used in this work are lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), sodium chloride (NaCl), sodium bromide (NaBr), sodium iodide (NaI), potassium chloride (KCl), potassium bromide (KBr), and potassium iodide (KI). We found that (1) some salts may act as kinetic hydrate promoters at low concentrations; (2) the width of the probability distributions (stochasticity) of natural gas hydrate formation in these salt solutions was significantly narrower than that in pure water. To gain further insight, we extended the study of the solutions of the same nine salts to the formation of ice and model tetrahydrofuran (THF) hydrate for comparison.