Escape Of CO2 Research Articles

Fluid Inclusions and Hydrogen, Oxygen, Sulfur Isotopes of Nuri Cu‐W‐Mo Deposit in the Southern Gangdese, Tibet

AbstractThe Nuri Cu‐W‐Mo deposit is located in the southern subzone of the Cenozoic Gangdese Cu‐Mo metallogenic belt. The intrusive rocks exposed in the Nuri ore district consist of quartz diorite, granodiorite, monzogranite, granite porphyry, quartz diorite porphyrite and granodiorite porphyry, all of which intrude in the Cretaceous strata of the Bima Group. Owing to the intense metasomatism and hydrothermal alteration, carbonate rocks of the Bima Group form stratiform skarn and hornfels. The mineralization at the Nuri deposit is dominated by skarn, quartz vein and porphyry type. Ore minerals are chalcopyrite, pyrite, molybdenite, scheelite, bornite and tetrahedrite, etc. The oxidized orebodies contain malachite and covellite on the surface. The mineralization of the Nuri deposit is divided into skarn stage, retrograde stage, oxide stage, quartz‐polymetallic sulfide stage and quartz‐carbonate stage. Detailed petrographic observation on the fluid inclusions in garnet, scheelite and quartz from the different stages shows that there are four types of primary fluid inclusions: two‐phase aqueous inclusions, daughter mineral‐bearing multiphase inclusions, CO2‐rich inclusions and single‐phase inclusions. The homogenization temperature of the fluid inclusions are 280°C–386°C (skarn stage), 200°C–340°C (oxide stage), 140°C–375°C (quartz‐polymetallic sulfide stage) and 160°C–280°C (quartz‐carbonate stage), showing a temperature decreasing trend from the skarn stage to the quartz‐carbonate stage. The salinity of the corresponding stages are 2.9%–49.7 wt% (NaCl) equiv., 2.1%–7.2 wt% (NaCl) equiv., 2.6%–55.8 wt% (NaCl) equiv. and 1.2%–15.3 wt% (NaCl) equiv., respectively. The analyses of CO2‐rich inclusions suggest that the ore‐forming pressures are 22.1 M Pa–50.4 M Pa, corresponding to the depth of 0.9 km–2.2 km. The Laser Raman spectrum of the inclusions shows the fluid compositions are dominated in H2O, with some CO2 and very little CH4, N2, etc. δD values of garnet are between −114.4‰ and −108.7‰ and δ18OH2O between 5.9‰ and 6.7‰; δD of scheelite range from −103.2‰ to −101.29‰ and δ18OH2O values between 2.17‰ and 4.09‰; δD of quartz between −110.2‰ and −92.5‰ and δ18OH2O between −3.5‰ and 4.3‰. The results indicate that the fluid came from a deep magmatic hydrothermal system, and the proportion of meteoric water increased during the migration of original fluid. The δ34S values of sulfides, concentrated in a rage between −0.32‰ to 2.5‰, show that the sulfur has a homogeneous source with characteristics of magmatic sulfur. The characters of fluid inclusions, combined with hydrogen‐oxygen and sulfur isotopes data, show that the ore‐forming fluids of the Nuri deposit formed by a relatively high temperature, high salinity fluid originated from magma, which mixed with low temperature, low salinity meteoric water during the evolution. The fluid flow through wall carbonate rocks resulted in the formation of layered skarn and generated CO2 or other gases. During the reaction, the ore‐forming fluid boiled and produced fractures when the pressure exceeded the overburden pressure. Themeteoric water mixed with the ore‐forming fluid along the fractures. The boiling changed the pressure and temperature, oxygen fugacity, physical and chemical conditions of the whole mineralization system. The escape of CO2 from the fluid by boiling resulted in scheelite precipitation. The fluid mixing and boiling reduced the solubility of metal sulfides and led the precipitation of chalcopyrite, molybdenite, pyrite and other sulfide.

Re–Os sulfide (chalcopyrite, pyrite and molybdenite) systematics and fluid inclusion study of the Duobaoshan porphyry Cu (Mo) deposit, Heilongjiang Province, China

The Duobaoshan porphyry deposit, located in the northwestern part of the Lesser Hinggan Range, is one of the biggest porphyry Cu (Mo) deposits in the Central Asian orogenic belt in China. The Duobaoshan porphyry deposit occurs in granodiorite and volcanic rocks of the Middle Ordovician Duobaoshan Formation. Six types of veins have been identified in three ore-forming stages as follows: a quartz–potassic feldspar vein in the early ore-forming stage, an early stage quartz–molybdenite vein, late stage quartz–molybdenite and quartz–chalcopyrite–pyrite veins in the middle ore-forming stage, and quartz–pyrite and calcite–quartz veins in the late ore-forming stage. The following four types of fluid inclusions are distinguished from various quartz veins: two-phase aqueous, pure gas phase, CO2-bearing and daughter mineral-bearing inclusions.The ore-forming fluid for the early ore-forming stage belongs to the H2O–CO2–NaCl system, which is characterized by high temperatures (>550°C), intermediate salinities (16.2–18.1wt% NaCl eqv.) and high CO2 content. The ore-forming fluid from the middle ore-forming stage evolved to the H2O–CO2–NaCl system, which is characterized by intermediate to high temperatures (230–450°C) and high/low salinities (0.8 to >65.3wt% NaCl eqv.) and is also rich in CO2 and metals. The ore-forming fluid finally reached cool temperatures (110–200°C), low salinities (3.9–8.4wt% NaCl eqv.) and was CO2-poor. Intensive fluid immiscibility or boiling occurred when the ore-forming fluid with temperatures of 230–450°C and pressures of 10–41MPa ascended to 4.1km, inducing the escape of CO2, depressing the solubility of fluid, and depositing abundant metal sulfides.The total Re and Os concentrations of chalcopyrite and pyrite range from 0.15 to 2.95μg/g and 0.74 to 15.01ng/g, respectively. Analyses of seven chalcopyrite and pyrite samples yielded isochron ages of 482–486Ma, and the model age of one molybdenite sample is 485.6±3.7Ma. The mineralization age of the Duobaoshan deposit is between 482 and 486Ma, and mantle fluid and materials were involved in the mineralization process. The Duobaoshan deposit is a classic porphyry Cu (Mo) deposit that formed in an early Palaeozoic island arc tectonic setting.

Oxygen, pH, and oral-aboral axis specification in the sea urchin embryo

The oral-aboral axis of the sea urchin embryo is specified via the redox-regulated activation of nodal (Coffman et al., 2009, and references therein). Embryos cultured at high density under cover glass develop a radialized phenotype owing to inhibition of nodal expression (Coffman et al. 2004), an effect that we attributed to hypoxia. Recently Agca et al. (2009) reported that controlled hypoxia does inhibit nodal expression as well as ectoderm differentiation, but only when it is maintained until pluteus stage. However, we found that embryos developed under cover glass become radialized even when the cover glass is removed at early blastula stage (Supplemental Figure 1). We therefore asked whether other factors might contribute to this teratogenic effect. Since embryos cultured under otherwise identical conditions develop normally, it is clear that the relevant effect of cover glass is to limit gas exchange, which in addition to hypoxia will promote acidification by preventing escape of CO2. To determine which of these factors causes radialized development, embryos were developed to hatching blastula stage under normoxic (∼10 ppm O2) or hypoxic (≤1 ppm O2) conditions in culture medium buffered to pH 8, 7.5, 7, or 6.5. While acidic pH was mildly radializing, hypoxia alone produced significant radialization, which was enhanced by acidification (Fig. 1 A, Supplemental Table 1 and Supplemental Fig. 2). Since the embryos were released from hypoxia at blastula stage, these results differ from those of Agca et al. (2009), for reasons that remain unclear. One difference that may be relevant is that we determined the level of hypoxia by measuring dissolved oxygen, whereas Agca et al. (2009) monitored atmospheric oxygen. In addition, we scored morphology at prism stage, whereas Agca et al. did so at pluteus stage, which may have allowed for recovery by regulative development. Finally, Agca et al. did not quantify the phenotypes they reported. Figure 1 Hypoxia induces radialized development and reduces mitochondrial H2O2 levels in sea urchin embryos. (A) Differential effects of controlled hypoxia and pH on development of oral-aboral polarity. Embryos were developed under the indicated conditions (see ... Ratiometric imaging was used to measure the effect of limiting gas exchange on intracellular H2O2 and pH (Fig. 1 B, Supplemental Fig. 3). Both mitochondrial and cytoplasmic H2O2 were reduced by this treatment, with a decrease in mitochondrial H2O2 comparable in magnitude to that produced by a mitochondrially-targeted catalase (Mt-Cat) shown previously to both inhibit nodal activation and entrain oral-aboral polarity (Coffman et al. 2009) (Fig. 1B). This decrease in H2O2, a major reactive oxygen species (ROS), contradicts the untested assumption of Agca et al. (2009) that hypoxia elevates ROS. As would be expected, limiting gas exchange also lowers intracellular pH, but less so than the decrease produced by pH buffering that did not induce radialization (Supplemental Fig. 3), suggesting that the relevant pH effects are extracellular. We conclude that hypoxia is the major cause of the radialization caused by development under cover glass. This is probably attributable at least in part to decreased H2O2 levels, as the window of vulnerability corresponds to the initial H2O2-dependent activation phase of nodal expression (Supplemental Figure 1; Coffman et al., 2009). Extracellular acidification appears to play an ancillary role, perhaps weakening ligand-receptor interactions and thus by dampening the feedback amplification of nodal expression.

Quantification techniques for potential CO2 leakage from geological storage sites

CO2 storage monitoring programmes aim to demonstrate the effectiveness of the project in controlling atmospheric CO2 levels, by providing confidence in predictions of the long-term fate of stored CO2 and identifying and measuring any potentially harmful leaks to the environment. In addition, the EU Emissions Trading Scheme (ETS) treats leakages of stored CO2 from the geosphere in to the ocean or atmosphere as emissions, and as such they need to be accounted for. An escape of CO2 from storage may be detected through losses from the reservoir, or migration through the overburden, into shallow groundwater systems, through topsoil and into the atmosphere, or through a seabed into the water column. Various monitoring techniques can be deployed to detect and in some cases quantify leakage in each of these compartments. This paper presents a portfolio of monitoring methods that are appropriate for CO2 leakage quantification, with a view to minimising both uncertainties and costs.

The role of interseam strata in the retention of CO2 and CH4 in a coal seam gas system

Abstract Clastic sedimentary rocks associated with coal seams affect the retention of gas and the rate of escape of CO 2 and CH 4 from a coal seam gas (CSG) system. Quantifying sealing properties using a parameter based on molecular diffusion and permeation of gases through rock and coal matrices allows the effects to be evaluated. Observations made on a CSG system in the Hunter Coalfield, Sydney Basin, Australia, show that the gas contents vary between ∼0.5 m 3 /t and ∼10 m 3 /t. The CSG consists predominantly (>80%) of CH 4 . Analyses of stable carbon isotopes indicate that the CH 4 is mainly biogenic, with gases in deeper seams showing mixing with thermogenic sources. At depths less than about 500 m, the coal seams containing elevated gas contents are generally overlain by low permeability, fine-grained clastic rocks such as mudstone and carbonaceous shale. Using a purpose-built system to measure matrix permeability and diffusivity of a coal and its roof and floor rocks allows characterisation of long-term permeation and diffusive flow. Measurements indicate that permeation and diffusion take place at different rates depending on gas type. A main finding of the study is that CH 4 permeates more rapidly than CO 2 whereas CO 2 diffuses more rapidly than CH 4 . For the studied samples, gas diffusion in coal is slower than in the clastic rocks, indicating that the minor coal seams are even better seals compared to the interseam clastic rocks for the main coal seam reservoir. Differences in flow regimes vary with lithology and therefore differences in lithology affect the retention of CO 2 versus CH 4 . For example, the permeation of both CO 2 and CH 4 is several times more rapid in the sandstone than for the claystone analysed, but diffusive flow is similar for these two samples. Carrying out analyses such as those done in the present study will assist in evaluating gas containment properties of interseam strata in CSG systems over given periods of time. Quantification of these properties will assist in evaluating the potential for CO 2 injection and long-term storage in coal seams.

Efficiency of small scale carbon mitigation by patch iron fertilization

Abstract. While nutrient depletion scenarios have long shown that the high-latitude High Nutrient Low Chlorophyll (HNLC) regions are the most effective for sequestering atmospheric carbon dioxide, recent simulations with prognostic biogeochemical models have suggested that only a fraction of the potential drawdown can be realized. We use a global ocean biogeochemical general circulation model developed at GFDL and Princeton to examine this and related issues. We fertilize two patches in the North and Equatorial Pacific, and two additional patches in the Southern Ocean HNLC region north of the biogeochemical divide and in the Ross Sea south of the biogeochemical divide. We evaluate the simulations using observations from both artificial and natural iron fertilization experiments at nearby locations. We obtain by far the greatest response to iron fertilization at the Ross Sea site, where sea ice prevents escape of sequestered CO2 during the wintertime, and the CO2 removed from the surface ocean by the biological pump is carried into the deep ocean by the circulation. As a consequence, CO2 remains sequestered on century time-scales and the efficiency of fertilization remains almost constant no matter how frequently iron is applied as long as it is confined to the growing season. The second most efficient site is in the Southern Ocean. The North Pacific site has lower initial nutrients and thus a lower efficiency. Fertilization of the Equatorial Pacific leads to an expansion of the suboxic zone and a striking increase in denitrification that causes a sharp reduction in overall surface biological export production and CO2 uptake. The impacts on the oxygen distribution and surface biological export are less prominent at other sites, but nevertheless still a source of concern. The century time scale retention of iron in this model greatly increases the long-term biological response to iron addition as compared with simulations in which the added iron is rapidly scavenged from the ocean.

EXPERIMENTAL ERRORS IN HYPOBARIC LABORATORY RESEARCH

The hypobaric method (LP) controls [O 2 ] by regulating the storage pressure, and without imposing a significant refrigeration load decreases the concentrations of [CO 2 ], ethylene, and volatile contaminants in the incoming air-changes by up to >99% due to expansion during entry into the vacuum chamber. The high gaseous diffusion rate at a low pressure eliminates the commodity's surface to center [O 2 ] gradient created by respiratory O 2 consumption, causing different commodity types to have nearly identical low [O 2 ] tolerances, near 0.1%. Increased gaseous conductivity at a low pressure also promotes the escape of CO 2 , ethylene, and NH 3 from within the commodity, and air-changes flush the released gases from the storage chamber. The low [0 21 concentration intensely inhibits respiration, and even in 0.14% [O 2 ] a respiratory CO 2 inversion point is not reached. Humidity is kept close to saturation, and so little respiratory heat is produced that water loss is minimized. Without injuring the commodity, LP reduces [O 2 ] and [CO 2 ] sufficiently to inhibit ethylene production and prevent bacterial and mold growth, while low [CO 2 ]causes stomates to open in darkness, prevents CO 2 -damage, inhibits toxic succinate formation, limits ascorbic acid loss, and inactivates ethylene forming enzyme. Differences between insect and plant gas-exchange systems cause all insect life stages to perish at the low hypobaric pressures which benefit horticultural commodity storage. Hypobaric intermodal containers are structurally less demanding than the simplest ISO tank container class and do not pose an insurance or implosion problem. They consume the same amount of energy as standard refrigerated intermodal containers and are mechanically simpler than CA containers. The cost per shipment is similar in LP and CA. Experimental errors in published laboratory LP research are reviewed.

Variation of <sup>13</sup>C value in authigenic carbonates from Zigetang Co,Tibetan Plateau since 1950 AD

兹格塘错是青藏高原中部-个典型的半混合型咸水湖泊。本文在²¹⁰Pb和¹³⁷Cs定年的基础上,研究了兹格塘错重力岩芯（ZGTC A-1）小于38.5μm细颗粒组分碳酸盐稳定碳同位素1950年以来的变化及其影响因素。对冬夏季湖水水化学特征的分析表明,夏季湖水溶解CO₂呈逸出状态,冬季湖水钙离子浓度是夏季湖水的10倍,据此可以得出兹格塘错碳酸盐矿物主要在夏季沉淀。通过与那曲气象站气象记录对比发现,1950年以来A-1岩芯碳酸盐碳同位素变化与年均温度有很好的相关性,表现出年均温度高时碳同位素偏重,而年均温度低时碳同位素偏轻的特征。兹格塘错1950年以来自生碳酸盐碳同位素的变化是由湖区及水体碳循环（如碳酸盐沉淀,有机质的沉淀与分解,有机碳和无机碳的转化等）的变化引起的,但各种因素的相互作用非常复杂。碳酸盐含量也与温度有关,温度越高,碳酸盐含量越高,同时降水量与碳酸盐含量也存在明显的相关关系。1950年以来有机质含量与温度呈反相关,可能与湖泊生产力的下降有关。;Zigetang Co, located on the central Tibetan Plateau, is a meromictic saline lake. A 96-cm-long core(ZGTC A-1)wastaken from Zigetang Co(the water depth 25m) in summer 2006. The age of the upper 9. 25cm(since 1890AD) of the core wasgot through CIC model of ²¹⁰Pb. The ¹³C during the past 60 years had good correlation with the average temperature in Naqu Sta-lion,which indicated that it was mainly controlled by average temperature in a year. When the annual mean temperature was high-er, the ¹³C value in the sediment became heavier and vice versa. In Zigetang Co, the main factor controlling the ¹³C was theCO₂exchange between lake water and atmosphere. Seasonal variation of Ca²⁺and dissolved inorganic carbon(DIC) indicated thatthe calcium carbonate(mainly composed of calcite and aragonite) mainly precipitated in summer. The dissolved CO₂ in the lakewater escaped into the atmosphere due to the relatively high temperature in summer. When the average temperature in a year washigher, the escape of CO₂ into the atmosphere became larger due to the shorter frozen time on the lake surface in winter and higherwater temperature in summer, which induced the ¹³C of the dissolved inorganic carbon in the lake water was more positive, so dothe ¹³C in carbonates.

Synthesis and formation of alumina whiskers from hydrothermal solution

Al2O3 whiskers with an average length of 5 μm have been synthesized from hydrothermal solution. Al(NO3)3 and urea were mixed and put into a Teflon-lined stainless steel autoclave and then treated at 120 °C to fabricate precursor whiskers NH4Al(OH)2CO3 (AACH). AACH whiskers were heated at 1200 °C in a furnace to obtain Al2O3 whiskers. The time-dependent examinations revealed that the formation process of AACH whiskers involves two sequential processes: a short liquid–solid deposition process in the initial stage and a long Ostwald ripening process. During calcinations, AACH transforms to amorphism then to α-Al2O3. The escape of NH3 and CO2 induced the distortion and toothlike morphology on the surface of the Al2O3 whiskers.

Sodium alginate polymeric floating beads for the delivery of cefpodoxime proxetil

AbstractSodium alginate (SA) floating beads containing cefpodoxime proxetil, a third‐generation cephalosporin antibiotic, were prepared by precipitation method using calcium carbonate as gas generating agent.Hydroxypropyl methylcellulose (HPMC) was used in all the four formulations in different proportions (F1, F2, F3, and F4) as swelling agent to control the release of the drug. Gas generating agent forms pores on the surface of the beads because of the rapid escape of CO2 during the curing process in precipitating media. Scanning electron microscopy confirmed their porous and grossly spherical structure, and the size of the beads were in the range of 700–1000 μm. The size of the beads increases with the increase in the concentration of gas‐forming agent and decreases with the increase in the concentration SA. The drug entrapment efficiency was found to be in the range of 85.3–91.1%. F2 shows least entrapment, whereas F3 shows maximum entrapment. The percentage porosity was 82.1–89.1%, and the mean pore diameter was 0.41–0.52 μm. The porosity depends on the concentration of gas‐forming agent. The mechanical strength of the beads was 591–1073 g. All the formulations showed good floating time. The in vitro release was performed in glycine dissolution media according to USP for about 12 h. The cumulative % drug release was found to be 67.5–87.3%. The in vitro dissolution study reveals that the concentration of the gas generating agent and SA affects the release rate. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Some geomechanical aspects of geological CO2 sequestration

Reservoir depletion and subsequent CO2 injection into the depleted geological reservoir induce stress changes that may mechanically damage top seal and wells, or trigger existing faults, creating the leakage pathways for CO2 escape from the reservoir. The role of geomechanics is to assess the mechanical impact of stress changes on seals, wells and faults. Since many hydrocarbon fields are geometrically complex and irregular, and the rock properties are spatially variable, such an assessment can be conveniently done with a numerical modeling of the field. Based on numerical analyses, recommendations can be given regarding the overall suitability of the depleted geological reservoir for CO2 disposal and safe CO2 injection.

Carbon isotopic constraints on CO2 degassing in cold-water Geysers, Green River, Utah

Cold-water geysers at Green River, in east central Utah are sourced by natural springs situated along the Little Grand Wash and Salt Wash faults zones, as well as abandoned oil and water wells. The intermittent geysers are driven by degassing of CO2 from CO2-rich waters sourced from the Jurassic Navajo sandstone. Here we discuss use of del13C analyses of water and gases to estimate the depth at which the ascending waters become CO2 saturated. This is a potentially important control in the unlikely event of rapid CO2 escape from CO2 reservoirs. In Green River, it is also important for calculation of the kinetics of fluid-mineral reactions in the Navajo sandstone as an analogue for predicting the fate of CO2 in carbon storage reservoirs

A Preliminary Study on Fluid Inclusions and Mineralization of Xitieshan Sedimentary‐Exhalative (SEDEX) Lead‐Zinc Deposit

AbstractThe Xitieshan lead‐zinc deposit is located at the northern margin of the Qaidam Basin, Qinghai Province, China, and had developed a complete marine sedimentary‐exhalative system. Our preliminary study of ore‐forming fluids shows that fluid inclusions in quartz from altered stockwork rocks that represent the pipe facies have a wide range of temperature and salinity. The intense fluid activities are characteristics of the pipe facies of the exhalative system. Fluid inclusions in carbonates near the unstratified ore bodies hosted in the thick‐bedded marble which represents vent‐proximal facies are large in size and have moderate to high temperatures. They represent unerupted sub‐seafloor fluid activity. Fluids in altered stockwork rocks and carbonates have similar H2O‐NaCl‐CO2 system, both belonging to the sedimentary‐exhalative system. The fluids migrate from the pipe facies to the unstratified ore bodies. Boiling of the fluids causes the separation of CO2 vapor and liquid H2O. When the fluids migrate into the unconsolidated thick‐bedded marble, the escape of CO2, decreasing temperature and pressure as well as some involvement of seawater into the fluids result in the unmixing of fluids with high and low salinity and deposition of ore‐forming materials. The two unmixed fluids were trapped in unconsolidated carbonates and the ore‐forming materials were deposited in the unconsolidated carbonates to form the sedimentary‐exhalative type unstratified ore bodies. The ore‐forming temperature of unstratified ore bodies is up to high temperature indicating that there is a huge ore‐forming potential in its deep.

Thermal stability of artinite, dypingite and brugnatellite—Implications for the geosequestration of green house gases

The approach to remove green house gases by pumping liquefied carbon dioxide several kilometres below the ground implies that many carbonate containing minerals will be formed. Among these minerals the formation of dypingite, artinite and if the ferric iron is present brugnatellite are possible; thus necessitating a study of the thermal stability of such minerals. The thermal stability of two carbonate bearing minerals dypingite and artinite together with brugnatellite with a hydrotalcite related formulae have been characterised by a combination of thermogravimetry and evolved gas mass spectrometry. Artinite is thermally stable up to 352 °C. Two mass loss steps are observed at 219 and 355 °C. Dypingite decomposes at a similar temperature but over a large number of steps. Brugnatellite shows greater stability with decomposition not occurring until after 577 °C. The thermal decomposition of brugnatellite occurs over a number of mass decomposition steps. It is concluded that pumping liquefied green house gases into magnesium bearing mineral deposits is feasible providing a temperature of 350–355 °C is not exceeded to prevent escape of CO 2 towards the surface. In contrast, the water loss occurring at lower temperatures could have a positive effect on the geosequestration of CO 2 as it probably causes a decrease in the molar volume of secondary carbonate minerals and consequently an increase in aquifer porosity.

The pH Dependence of Heme Pocket Hydration and Ligand Rebinding Kinetics in Photodissociated Carbonmonoxymyoglobin

We monitored the occupancy of a functionally important non-coordinated water molecule in the distal heme pocket of sperm whale myoglobin over the pH range 4.3-9.4. Water occupancy was assessed by using time-resolved spectroscopy to detect the perturbation of the heme visible band absorption spectrum caused by water entry after CO photodissociation ( Goldbeck, R. A., Bhaskaran, S., Ortega, C., Mendoza, J. L., Olson, J. S., Soman, J., Kliger, D. S., and Esquerra, R. M. (2006) Proc. Natl. Acad. Sci. U. S. A. 103, 1254-1259 ). We found that the water occupancy observed during the time interval between ligand photolysis and diffusive recombination decreased by nearly 20% as the pH was lowered below 6. This decrease accounted for most of the concomitant increase in the observed CO bimolecular recombination rate constant, as the lower water occupancy presented a smaller kinetic barrier to CO entry into the pocket at lower pH. These results were consistent with a model in which the distal histidine, which stabilizes the water molecule within the distal pocket by accepting a hydrogen bond, tends to swing out of the pocket upon protonation and destabilize the water occupancy at low pH. Extrapolation of this model to lower pH suggests that the additional increase in ligand association rate constant observed previously in stopped-flow studies at pH 3 may also be due in part to reduced distal water occupancy concomitant with further His64 protonation and coupled protein conformational change.

Reservoir simulation of CO2 sequestration pilot in Frio brine formation, USA Gulf Coast

Reservoir simulation studies were performed to investigate compositional effects between aquifer fluid (brine) and injected supercritical CO2 during the sequestration process in the Frio brine formation. Accurate data calibrations of CO2 solubility and density, as well as brine density and viscosity, were performed. Hysteresis relative permeability was taken into consideration to account for the effect of trapped gas in the aquifer. In addition, real aquifer data obtained from the test site were used in order to characterize the Frio aquifer. The Frio Brine Storage Project is a study in USA that was conducted by the Bureau of Economic Geology (BEG) at the University of Texas at Austin as a pilot to investigate the CO2 sequestration process in an aquifer as the first closely monitored case study. The objective of monitoring this pilot study, which was conducted by a collaboration of several research organizations including BEG, Lawrence Berkley National Laboratory (LBNL), Sandia Technologies LLC, US Geological Survey (USGS), and Schlumberger, and funded by the DOE's National Energy Technology Laboratory (NETL), was to observe the behavior of supercritical CO2 in the subsurface, investigate the physics of the process, and obtain data for further validation of simulation results. This simulation study was carried out before the pilot began, and the results were verified against the early results of the field experiment. Different scenarios were simulated to investigate the lateral and vertical spread of the CO2 plume in the aquifer. Local grid refinement around both injection and monitoring wells helped to obtain accurate results. According to our studies, at the end of the simulation period (10 years from the injection date), a significant part of the injected CO2 will be in the form of trapped gas or will be dissolved in the aqueous phase. Considering the proposed injection plan, and since only a small portion of the injected CO2 will be in the form of free gas, the possibility of CO2 escape through the shale cap rock will be very low.

Sorption and swelling of poly(DL‐lactic acid) and poly(lactic‐co‐glycolic acid) in supercritical CO2: An experimental and modeling study

AbstractTissue engineering scaffolds require a controlled pore size and structure to host tissue formation from cell populations. Supercritical carbon dioxide (scCO2) processing can be used to form porous scaffolds in which the escape of CO2 from a plasticized polymer melt generates gas bubbles that shape the pores. The process is difficult to control with respect to changes in final pore size, porosity, and interconnectivity, while the solubility of CO2 in the polymers strongly affects the foaming process. An in‐depth understanding of polymer CO2 interaction will enable a successful scaffold processing. Amorphous poly(DL‐lactic acid) (PDLLA) and poly(lactic acid‐co‐glycolic acid) (PLGA) polymers are attractive candidates for fabricating scaffolds. In this study, CO2 sorption and swelling isotherms at 35 °C and up to 200 bar on a variety of homo‐ and copolymers of lactic acid and glycolic acids are presented. Sorption is measured through a gravimetric technique using a suspension microbalance and swelling by visualization. The obtained results are modeled using the Sanchez‐Lacombe equation of state. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 483–496, 2008

Control of pore size and structure of tissue engineering scaffolds produced by supercritical fluid processing

Tissue engineering scaffolds require a controlled pore size and structure to host tissue formation. Supercritical carbon dioxide (scCO2) processing may be used to form foamed scaffolds in which the escape of CO2 from a plasticized polymer melt generates gas bubbles that shape the developing pores. The process of forming these scaffolds involves a simultaneous change in phase in the CO2 and the polymer, resulting in rapid expansion of a surface area and changes in polymer rheological properties. Hence, the process is difficult to control with respect to the desired final pore size and structure. In this paper, we describe a detailed study of the effect of polymer chemical composition, molecular weight and processing parameters on final scaffold characteristics. The study focuses on poly(DL-lactic acid) (PDLLA) and poly(DL-lactic acid-co-glycolic acid) (PLGA) as polymer classes with potential application as controlled release scaffolds for growth factor delivery. Processing parameters under investigation were temperature (from 5 to 55 degrees C) and pressure (from 60 to 230 bar). A series of amorphous PDLLA and PLGA polymers with various molecular weights (from 13 KD to 96 KD) and/or chemical compositions (the mole percentage of glycolic acid in the polymers was 0, 15, 25, 35 and 50 respectively) were employed. The resulting scaffolds were characterised by optical microscopy, scanning electron microscopy (SEM), and micro X-ray computed tomography (microCT). This is the first detailed study on using these series polymers for scaffold formation by supercritical technique. This study has demonstrated that the pore size and structure of the supercritical PDLLA and PLGA scaffolds can be tailored by careful control of processing conditions.

CO escape from myoglobin with metadynamics simulations

The relatively small size of myoglobin makes it suitable for the investigation of the ligand escape process in respiratory proteins and, in general, an ideal model system for the study of the more general structure-function paradigm. In this work, we use Molecular Dynamics simulations combined with an accelerated algorithm, the metadynamics, to probe the escape of CO from myoglobin. Our approach permits to quantitatively describe the escape process via the reconstruction of the associated free energy surface. Additionally, hints on the involvement of a larger numbers of residues than hitherto assumed in the gating process are extracted from our data.

Origin of the Oceanic Lithosphere

In a global examination of mid-ocean ridge basalt (MORB) glass compositions, we find that Na8–Fe8–depth variations do not support modeling of MORBs as aggregates of melt compositions generated over a large range of temperature and pressure. However, the Na8–Fe8 variations are consistent with the compositional systematics of solidus melts in the plagioclase–spinel lherzolite transition in the CaO–MgO–Al2O3–SiO2–Na2O–FeO (CMASNF) system. For natural compositions, the P–T range for melt extraction is estimated to be ∼1·2–1·5 GPa and ∼1250–1280°C. This P–T range is a close match with the maximum P–T conditions for explosive pressure-release vaporization of carbonate-bearing melts. It is proposed that fracturing of the lithosphere induces explosive formation and escape of CO2 vapor. This provides the vehicle for extraction of MORBs at a relatively uniform T and P. The upper portion of the CO2-bearing and slightly melted seismic low-velocity zone flows toward the ridge, rises at the ridge axis to lower-lithosphere depths, melts much more extensively during this rise, and releases MORB melts to the surface driven by explosively escaping CO2 vapor. The residue and overlying crust produced by this melting then migrate away from the ridge axis as new oceanic lithosphere. The entire process of oceanic lithosphere creation involves only the upper ∼140 km. When lithospheric stresses shift fracture formation to other localities, escape of CO2 ceases, the vehicle for transporting melt to the surface disappears, and ridges die. Inverse correlations of Na8 vs Fe8 for MORB glasses are explained by mantle heterogeneity, and positive variations superimposed on the inverse variations are consistent with progressive extraction of melts from short, ascending melting columns. The uniformly low temperatures of MORB extraction are not consistent with the existence of hot plumes on or close to ocean ridges. In this modeling, the southern Atlantic mantle from Bouvet to about 26°N is relatively homogeneous, whereas the Atlantic mantle north of about 26°N shows significant long-range heterogeneity. The mantle between the Charlie Gibbs and Jan Mayen fracture zones is strongly enriched in FeO/MgO, perhaps by a trapped fragment of basaltic crust. Iceland is explained as the product of this enrichment, not a hot plume. The East Pacific Rise, Galapagos Ridge, Gorda Ridge, and Juan de Fuca Ridge sample mantle that is heterogeneous over short distances. The mantle beneath the Red Sea is enriched in FeO/MgO relative to the mantle beneath the northern Indian Ocean.