H2O CO2 Research Articles

SAFT2 equation of state for the CH4–CO2–H2O–NaCl quaternary system with applications to CO2 storage in depleted gas reservoirs

Understanding the phase equilibria and physical-chemical characteristics of the CH4–CO2–H2O–NaCl quaternary system is important for evaluating costs and risks for the storage of CO2 in depleted natural gas reservoirs as well as fluid inclusion studies. In this study, phase equilibria and thermodynamic properties of this system were investigated through the utilization of a statistical association fluid theory-based (SAFT) equation of state (EOS) at temperatures from 298 to 513 K (25–240 °C), pressures up to 600 bar (60 MPa) and concentration of NaCl up to 6 mol/kgH2O. The model parameters were obtained from the fitting of available experimental data of subsystems (i.e., CH4–H2O, CH4–CO2, and CH4–H2O–NaCl) that were judged to be reliable and incorporation of available parameters for the subsystems (i.e., pure component, CO2–H2O, and CO2–H2O–NaCl). Using the SAFT EOS developed in this study, we predicted the solubility of (CH4 + CO2) gas mixtures in pure H2O and compared it with the available experimental data and the predicted values from four popular numerical simulators. The results indicate that our model can provide reliable predictions for the CH4–CO2–H2O ternary system. Subsequently, we further predicted the phase equilibria and density of the CH4–CO2–H2O–NaCl system with NaCl varying from 0 to 6 mol/kgH2O. We also employed the SAFT EOS to predict the solubility of CO2 and CH4 in the water-alternating-gas process for CO2-enhanced oil recovery, demonstrating good agreement with the simulation results obtained through the Peng-Robinson EOS for predicting the CO2 and CH4 solubility. These predicted thermodynamic properties and phase behaviors in the CH4–CO2–H2O–NaCl system provide quantitative insights into the implications of CO2 storage in depleted oil and gas reservoirs.

Marble-hosted noble spinel deposits from the Luc Yen District (Vietnam): mineral equilibria involving corundum and spinel

Thermodynamic analysis is carried out for the model systems: (1) Na–Ca–Mg–A1–Si–CO2–H2O and (2) Ca–Mg–A1–Si–CO2–H2O. In each systems the mineral equilibria involving dolomite, calcite, spinel, corundum, pargasite, hydroxylclinohumite, and diaspore are considered. A diagram of the multisystem in coordinates μH2O-μCO2is constructed. Analysis showed a significant influence of chemical potentials of water and carbon dioxide in the mineral-forming medium on stability of corundum and spinel in marbles. The conditions of the spinel formation during metamorphism of protolith consisting of carbonate sediments with evaporites lenses and terrigenous material (smectites, bauxites, etc.), are considered in detail. The conditions of the replacement of spinel by corundum during retrograde metamorphism are determined depending on the mole fraction of CO2 in the fluid and temperature at pressure of 5 kbar.

Supercritical CO2 and Subcritical H2O Analysis Instrument: Automated Lipid Analysis for In Situ Planetary Life Detection.

The search for extraterrestrial extant or extinct life in our Solar System will require highly capable instrumentation and methods for detecting low concentrations of biosignatures. This paper introduces the Supercritical CO2 and Subcritical H2O Analysis (SCHAN) instrument, a portable and automated system that integrates supercritical fluid extraction (SFE), supercritical fluid chromatography (SFC), and subcritical water extraction coupled with liquid chromatography. The instrument is compact and weighs 6.3 kg, making it suitable for spaceflight missions to planetary bodies. Traditional techniques, such as gas chromatography-mass spectrometry (MS), face challenges with involatile and thermally labile analytes, necessitating derivatization. The SCHAN instrument, however, eliminates the need for derivatization and cosolvents by utilizing neat supercritical CO2 with water as an additive. This SFE-SFC-MS method gives efficient lipid biosignature separations with median detection limits of 10 pg/g (ppt) for fatty acids and 50 pg/g (ppt) for sterols. Several free fatty acids and cholesterol were among the detected peaks in biologically lean samples from the Atacama Desert, demonstrating the instrument's potential for in situ life detection missions. The SCHAN instrument addresses the challenges of conventional systems, offering a compact, portable, and spaceflight-compatible tool for the analysis of organics for future astrobiology-focused missions.

Photothermal Synergistic Effect Induces Bimetallic Cooperation to Modulate Product Selectivity of CO2 Reduction on Different CeO2 Crystal Facets.

Product selectivity of solar-driven CO2 reduction and H2O oxidation reactions has been successfully controlled by tuning the spatial distance between Pt/Au bimetallic active sites on different crystal facets of CeO2 catalysts. The replacement depth of Ce atoms by monatomic Pt determines the distance between bimetallic sites, while Au clusters are deposited on the surface. This space configuration creates a favourable microenvironment for the migration of active hydrogen species (*H). The *H is generated via the activation of H2O on monatomic Pt sites and migrate towards Au clusters with a strong capacity for CO2 adsorption. Under concentrated solar irradiation, selectivity of the (100) facet towards CO is 100 %, and the selectivity of the (110) and (111) facets towards CH4 is 33.5 % and 97.6 %, respectively. Notably, the CH4 yield on the (111) facet is as high as 369.4 μmol/g/h, and the solar-to-chemical energy efficiency of 0.23 % is 33.8 times higher than that under non-concentrated solar irradiation. The impacts of high-density flux photon and thermal effects on carriers and *H migration at the microscale are comprehensively discussed. This study provides a new avenue for tuning the spatial distance between active sites to achieve optimal product selectivity.

Sr(Ti0·3Fe0.7)O3−δ-based perovskite with in-situ exsolved Fe–Ru nanoparticles: A highly stable fuel electrode material for solid oxide electrochemical cells with efficient electrocatalytic CO2 reduction ability and preferential selectivity

The development of solid-oxide cells requires fuel electrodes capable of promoting highly catalytic activities for CO2 electrochemical reduction (CO2R). This study develops a fuel electrode material, Sr(Ti0·3Fe0·63Ru0.07)O3-δ (STFR) perovskite, enhance with in-situ exsolved Fe–Ru nanoparticles (STFR–FeRu), demonstrating excellent electrochemical catalytic activity for CO2R, considerable stability, and high selectivity for CO2 electrolysis. Notably, the study discovered for the first time that STFR–FeRu exhibits significantly enhanced catalytic activity in a CO2-containing atmosphere compares to that in hydrogen-based fuels. At 800 °C and 1.3 V, La0·8Sr0.2Ga0.8Mg0·2O3-δ electrolyte-supported cells with STFR–FeRu fuel electrode, for direct CO2 electrolysis, realizes a current density of 1.77 A cm−2. This current density is 50 % higher than that of H2O electrolysis under the same conditions. Additionally, the cell achieves a current density of 1.54 A cm−2 for CO2–H2O co-electrolysis, with a high CO2 electrolysis selectivity (CO concentration exceeding 60 % in the electrolysis products).

Seasonal precipitation distribution determines ecosystem CO2 and H2O exchange by regulating spring soil water–salt dynamics in a brackish wetland

Abstract The intensification of the global hydrological cycle is anticipated to increase the variability of precipitation patterns. Brackish wetlands respond to changes in precipitation patterns by regulating the absorption and release of CO2 and H2O to maintain the stability of ecosystem functions. However, there is limited understanding of how the inter‐seasonal precipitation distribution (SPD) affects ecosystem CO2 and H2O exchange compared with annual precipitation totals. Here, we conducted four consecutive years of field experiments in a brackish wetland, manipulating the proportion of precipitation across different seasons while maintaining a constant annual precipitation total. We utilized five inter‐SPD proportions (+73%, +56%, control (CK), −56%, −73%) to examine the effects of SPD on ecosystem CO2 and H2O exchange. Our findings revealed that the annual ecosystem CO2 and H2O fluxes showed a trend of decreasing with the decrease in spring precipitation distribution. Among them, the annual net ecosystem CO2 exchange, evapotranspiration, carbon use efficiency and water use efficiency were shown to be more sensitive to decrease in spring precipitation distribution and increase in summer and autumn precipitation distribution. This negative asymmetric response pattern suggests that annual ecosystem CO2 and H2O exchange is primarily governed by seasonal precipitation variability, with spring soil water–salt dynamics identified as the key driver. Therefore, this association can be explained by the fact that drought of the early growth stage exacerbates soil salinization and inhibits vegetation colonization and growth, thereby greatly impairing the annual CO2–H2O exchange capacity of brackish wetlands. Our results emphasized that the spring extreme precipitation‐induced soil water–salt conditions will greatly influence CO2 and H2O exchange in brackish wetlands in the future. These findings are crucial for improving predictions of the carbon sequestration and water‐holding capacity of brackish wetlands. Read the free Plain Language Summary for this article on the Journal blog.

Bayesian analysis of the molecular emission and dust continuum of protoplanetary disks

Context. The MIRI instrument on board the James Webb Space Telescope probes the chemistry and dust mineralogy of the inner regions of protoplanetary disks. The observed spectra are unprecedented in their detail and reveal a rich chemistry with strong diversity between objects. This complicates interpretations that are mainly based on manual continuum subtraction and 0D slab models. Aims. We investigate the physical conditions under which the gas emits in protoplanetary disks. Based on MIRI spectra, we apply a full Bayesian analysis that provides the posterior distributions of dust and molecular properties, such as column densities and emission temperatures. Methods. To do so, we introduced the Dust Continuum Kit with Line emission from Gas (DuCKLinG), a Python-based model simultaneously describing the molecular line emission and the dust continuum of protoplanetary disks without large computational cost. The model describes the dust continuum emission by dust models with precomputed dust opacities. The molecular emission is based on LTE slab models but from extended radial ranges with gradients in column densities and emission temperatures. We compare the model to observations using Bayesian analysis with linear regression techniques to reduce the dimension of the parameter space. We benchmarked this model to a complex thermo-chemical ProDiMo model of AATau and fit the MIRI spectrum of GW Lup. The latter allowed for a comparison to the previous results obtained with single slab models and hand-fitted continuum. Results. We successfully decrease the computational time of the fitting method by a factor of 80 by eliminating linear parameters, such as the emission areas, from the Bayesian run. This approach does not significantly change the retrieved molecular parameters, and only the calculated errors on the optically thin dust masses slightly decrease. For an AA Tau ProDiMo mock observation, we find that the retrieved molecular conditions from DuCKLinG (column densities from 3 × 1018 cm−2 to 4 × 1020 cm−2, radial range from 0.2 au to 1.2 au, and temperature range from about 200 K to 400 K) fall within the true values from ProDiMo (column densities between 4 × 1017 cm-2 to 5 × 1020 cm−2, radial extent 0.1 au to 6.6 au, and temperature range from about 120 to 1000 K). The smaller DuCKLinG ranges can be explained by the relative flux contributions of the different parts of ProDiMo. The parameter posterior of GW Lup reinforces previously found results. The previously determined column densities fall within the retrieved ranges in this study for all examined molecules (CO2, H2O, HCN, and C2H2). Similar overlap is found for the temperatures with only the temperature range of HCN (from 570−60+60 to 750−70+90 K) not including the previously found value (875 K). This discrepancy may be due to the simultaneous fitting of all molecules compared to the step-by-step fitting of the previous study. There is statistically significant evidence for radial temperature and column density gradients for H2O and CO2 compared to the constant temperature and column density assumed in the 0D slab models. Additionally, HCN and C2H2 emit from a small region with near constant conditions. Due to the small selected wavelength range 13.6–16.3 µm, the dust properties are not well constrained for GW Lup. DuCKL inG can become an important tool to analyse the molecular emission and dust mineralogy of large samples based on JWST /MIRI spectra in an automated way.

Sublimation of volatiles from H2O:CO2 bulk ices in the context of comet 67P/Churyumov-Gerasimenko

Context. Comets are considered to be remnants from the formation of the Solar System. ESA’s Rosetta mission targeted comet 67P/Churyumov-Gerasimenko and was able to record high-quality data on its chemical composition and outgassing behaviour, including low abundances of N2 that are observed to be correlated with H2O and CO2 in approximately a 63:37 ratio. Aims. In this work, the thermal desorption behaviour of N2 in H2O:CO2 ices was studied in the laboratory to investigate the co-desorption behaviour of N2 within the two most abundant cometary ices in 67P and to derive desorbing fractions in different temperature regimes. Methods. H2O:CO2:N2 ices of various ratios were prepared in a gas mixing system and co-deposited at 15 K onto a copper sample holder. Sublimation of the ice was measured using temperature programmed desorption mass spectrometry. Quantitative values were derived for the fraction of N2 co-desorbing with CO2 and H2O respectively. To validate the results, H2O:CO2:13CO ices were prepared as well. Results. The experiments show that the co-desorption of N2 with CO2 in H2O:CO2:N2 ices depends on the bulk amount of CO2 present in the ice. The fraction of N2 trapped in H2O reduces as more N2 and CO2 are added to the mixture. CO behaves qualitatively similar to N2, but more CO is found to co-desorb with CO2. To reproduce the ratio of N2 desorbing with H2O over that of CO2 (N2(H2O)/N2(CO2)), our ice analogues need to contain ≥15% CO2, while 67P contains ≤7.5% CO2. Large fractions of N2 can be removed from the ice due to heating up to 70 K, but for ice that most closely resembles that of 67P, the loss fraction of pure phase N2 is expected to be ≤20%. Therefore, N2 is suggested to be a minor carrier of nitrogen in the comet.

Retrieved Atmospheres and Inferred Surface Properties for Terrestrial Exoplanets Using Transmission and Reflected-light Spectroscopy

Future astrophysics missions will seek extraterrestrial life via transmission and direct-imaging observations. To assess habitability and biosignatures, we need robust retrieval tools to analyze observed spectra, and infer surface and atmospheric properties with their uncertainties. We use a novel retrieval tool to assess accuracy in characterizing near-surface habitability and biosignatures via simulated transmission and direct-imaging spectra, based on the Origins Space Telescope (Origins) and LUVOIR mission concepts. We assess our ability to discriminate between an Earth-like and a false-positive O3 TRAPPIST-1 e with transmission spectroscopy. In reflected light, we assess the robustness of retrieval results to unmodeled cloud extinction. We find that assessing habitability using transmission spectra may be challenging due to relative insensitivity to surface temperature and near-surface H2O abundances. Nonetheless, our order-of-magnitude H2O constraints can discriminate extremely desiccated worlds. Direct imaging is insensitive to surface temperature and subject to the radius/albedo degeneracy, but this method proves highly sensitive to surface water abundance, achieving retrieval precision within 0.1% even with partial clouds. Concerning biosignatures, Origins-like transmission observations (t = 40 hr) may detect the CO2/CH4 pair on M-dwarf planets and differentiate between biological and false-positive O3 using H2O and abundant CO. In contrast, direct-imaging observations with LUVOIR-A (t = 10 hr) are better suited to constraining O2 and O3, and may be sensitive to wavelength-dependent water cloud features, but will struggle to detect modern-Earth-like abundances of methane. For direct imaging, we weakly detect a stratospheric ozone bulge by fitting the near-UV wings of the Hartley band.

Laboratory simulations of ice growth in space: An expected nonuniform ice mantle composition

Context. In dense, cold molecular regions, gas-phase chemical species freeze out onto grain surfaces. These icy condensates become an important reservoir of volatile elements and feedstock for molecular diversity. Aims. While there is a fairly general agreement on the chemical composition of icy mantles, there are differences in how the various molecular components are perceived to be present. Should the materials composing the ice be mixed or are they segregated into distinct chemical zones? Methods. To answer such a question, we performed a few exploratory experiments that allowed the adsorbing surface (mimic dust grains) to slowly relax to very low temperatures while gas-phase mixtures of H2O, NH3, and CO embed onto it. Results. We find that mantles are far from being uniform, and they could evolve into completely mixed ices only if the ambient temperature undergoes a catastrophic collapse. Conclusions. Under the typical conditions of an interstellar dense cloud, ices present a high degree of molecular segregation, with possible consequences on the ice chemistry and the desorption mechanisms.

Mixing of endogenous CO2 and meteoric H2O causes extremely efficient carbonate dissolution

Karst corrosion of carbonate rocks by water with dissolved gases proceeds in most cases along two major scenarios: (i) meteoric water absorbs CO2 from soil and atmosphere, or (ii) ascending water of deep circulation carries with it dissolved endogenous gases, mainly CO2 and H2S. We have observed a peculiar variant where meteoric water absorbs ascending endogenous gases at a natural gas vent on a travertine mound in Slovakia. Carbonate dissolution's extreme effectiveness is demonstrated by mineralization of rainwater ponded at a gas vent, rising to 3.2 g/L of dissolved solids shortly after the rainfall. One liter of water ponded at the vent and mixing with the venting gas, dissolved up to 800 mg of calcium at a rate exceeding 5.8 mg/L·min. Limestone tablets placed at the vent show signs of significant corrosion, at rates up to 126 mm/ka. The rate is comparable to those in coastal karst, where freshwater is mixing with seawater and to those in sulfuric acid speleogenesis (SAS), both the highest hitherto known rates of karst corrosion in carbonates. The geomorphic effects of the process described are depressions on the surface of travertine near the vents of endogenous CO2. This type of corrosion seems to be universal and probably occurs everywhere where endogenous CO2 is exhaled to the surface from carbonate rocks.

Gas emissivities and absorptivities for H2O–CO2–CO mixtures

AbstractIn this work, an approximate solution is given to compute the gas emissivities and absorptivities for H2O–CO2–CO mixtures. The proposed model is valid for temperatures from 300 to 2700 K and pressure path‐length from 0.06 to 40 atm m. In the calculation of the analytical solution (AS), the nonlinear methods of Galerkin and Ritz were implemented based on the residual solution of the differential roots of the Finite Element Method. For each point value using the AS, the spectral absorptivity and emissivity were determined, while for the gas mixture the emissivity and absorptivity were computed using the Hottel Graphical Method (HGM) and the proposed method. In the emissivity calculations, the HGM shows less adjustment, with values of ±20% and ±15% for 79.1% and 56.2% of the available analytical data, while the proposed model correlates adequately with the available data, showing an average deviation of ±15% and ±10% for 91.4% and 76.2% of the available data. In the absorptivity estimations, the HGM shows a weaker fit, with values of ±20% and ±15% for 77.3% and 51.4% of the experimental data, respectively, while the proposed model shows good agreement with the available data, with a mean deviation of ±15% and ±10% for 89.8% and 74.1% of the test made.

Fluid–Melt–Rock Interaction during the Transition from Magmatism to HT-UHT-Granulite- and Amphibolite-Facies Metamorphism in the Ediacaran Adrar–Suttuf Metamafic Complex, NW Margin of the West African Craton (Southern Morocco)

Abstract Underplated mafic intrusions ponded at the base of the lower continental crust in extensional settings can experience ultra-high-temperature (UHT) granulite-facies metamorphism during tens of My due to slow cooling rates. These intrusions are also the source of heat and carbonic fluids for regional high-temperature (HT) granulite-facies metamorphism in the continental crust. This work analyses the fluid–melt–rock interaction processes that occurred during the magmatic to HT-UHT-granulite- and amphibolite-facies metamorphic evolution of high-grade mafic rocks from the Eastern Ediacaran Adrar–Suttuf Metamafic Complex (EASMC) of the Oulad Dlim Massif (West African Craton Margin, Southern Morocco). P–T conditions were determined using Ti-in-amphibole thermometry, two-pyroxene and amphibole–plagioclase thermobarometry, and phase diagram calculations. The thermobarometric study reveals the presence of tectonically juxtaposed lower- and mid-crustal blocks in EASMC that experienced decompression-cooling paths from, respectively, UHT and HT granulite-facies conditions at ca. 1.2 ± 0.28 GPa and 975 ± 50°C, and ca. 0.82 ± 0.15 GPa and 894 ± 50°C, to amphibole-facies conditions at ca. 0.28 ± 0.28 GPa and 787 ± 45°C (precision reported for the calibrations at 1 s level). An age for the magmatic to UHT granulite-facies metamorphic transition of 604 Ma was constrained from published SHRIMP Th–U–Pb zircon ages of the igneous protoliths. An amphibole 40Ar–39Ar cooling age of 499 ± 8 Ma (precision at 2 s level) was obtained for the lower-crustal blocks. Amphibole 40Ar–39Ar closure temperatures of 520–555°C were obtained for an age range of 604–499 Ma and an average constant cooling rate of 4.2°C/My, suggesting that the lower-crustal blocks cooled down to the greenschist–amphibolite facies transition in ca. 100 My. During the high-temperature stage, interstitial hydrous melts assisted textural maturation of the rock matrix and caused incongruent dissolution melting of olivine and pyroxenes, and, probably, development of An-rich spikes at the grain rims of plagioclase, and local segregation of pargasite into veins. Subsequent infiltration of reactive hydrous metamorphic fluids along mineral grain boundaries during cooling down to amphibolite-facies conditions promoted mineral replacements by coupled dissolution-precipitation mechanisms and metasomatism. Ubiquitous dolomite grains, with, in some cases, evidence for significant textural maturation, appear in the granoblastic aggregates of the high-grade mafic rocks. However, calculated phase relationships reveal that dolomite could not coexist with H2O–CO2 fluids at HT-UHT granulite- and low-medium P amphibolite-facies conditions. Therefore, it is proposed that it may have been generated from another CO2-bearing phase, such as an immiscible carbonatitic melt exsolved from the parental mafic magma, and preserved during cooling due to the prevalence of fluid-absent conditions in the granoblastic matrix containing dolomite. The lower-crustal mafic intrusions from EASMC can represent an example of a source of heat for granulitisation of the mid crust, but a sink for carbon due to the apparent stability of dolomite under fluid-absent conditions.

Integration of Co Single Atoms and Ni Clusters on Defect-Rich ZrO2 for Strong Photothermal Coupling Boosts Photocatalytic CO2 Reduction.

We report a solvothermal method for the synthesis of an oxygen vacancy-enriched ZrO2 photocatalyst with Co single atoms and Ni clusters immobilized on the surface. This catalyst presents superior performance for the reduction of CO2 in H2O vapor, with a CO yield reaching 663.84 μmol g-1 h-1 and a selectivity of 99.52%. The total solar-to-chemical energy conversion efficiency is up to 0.372‰, which is among the highest reported values. The success, on one hand, depends on the Co single atoms and Ni clusters for both extended spectrum absorption and serving as dual-active centers for CO2 reduction and H2O dissociation, respectively; on the other hand, this is attributed to the enhanced photoelectric and thermal effect induced by concentrated solar irradiation. We demonstrate that an intermediate impurity state is formed by the hybridization of the d-orbital of single-atom Co with the molecular orbital of H2O, enabling visible-light-driven excitation over the catalyst. In addition, Ni clusters play a crucial role in altering the adsorption configuration of CO2, with the localized surface plasmon resonance effect enhancing the activation and dissociation of CO2 induced by visible-near-infrared light. This study provides valuable insights into the synergistic effect of the dual cocatalyst toward both efficient photothermal coupling and surface redox reactions for solar CO2 reduction.

Information content of JWST spectra of WASP-39b

The era of James Webb Space Telescope (JWST) transmission spectroscopy of exoplanetary atmospheres commenced with the study of the Saturn-mass gas giant WASP-39b as part of the Early Release Science (ERS) program. WASP-39b was observed using several different JWST instrument modes (NIRCam, NIRISS, NIRSpec G395H and NIRSpec PRISM) and the spectra were published in a series of papers by the ERS team. The current study examines the information content of these spectra measured using the different instrument modes, focusing on the complexity of the temperature-pressure profiles and number of chemical species warranted by the data. We examine if the molecules H2O CO CO2 K H2S CH4 and SO2 are detected in each of the instrument modes. Two Bayesian inference methods are used to perform atmospheric retrievals: the standard nested sampling method, as well as the supervised machine learning method of the random forest (trained on a model grid). For nested sampling, Bayesian model comparison is used as a guide to identify the set of models with the required complexity to explain the data. Generally, non-isothermal transit chords are needed to fit the transmission spectra of WASP-39b, although the complexity of the temperature-pressure profile required is mode-dependent. The minimal set of chemical species needed to fit a spectrum is mode-dependent as well, and also depends on whether grey or non-grey clouds are assumed. When a non-grey cloud model is used to fit the NIRSpec G395H spectrum, it generates a spectral continuum that compensates for the water opacity. The same compensation is absent when fitting the non-grey cloud model to the NIRSpec PRISM spectrum (which has broader wavelength coverage), suggesting that it is spurious. The interplay between the cloud spectral continuum and the water opacity determines if sulphur dioxide is needed to fit either spectrum. The inferred elemental abundances of carbon and oxygen and the carbon-to-oxygen (C/O) ratios are all mode- and model-dependent, and should be interpreted with caution. Bayesian model comparison does not always offer a clear path forward for favouring specific retrieval models (e.g. grey versus non-grey clouds) and thus for enabling unambiguous interpretations of exoplanet spectra.

Competitive adsorption mechanisms of multicomponent gases in kaolinite under electric fields: A molecular perspective

The investigation of the competitive adsorption mechanisms of gas mixtures within the inorganic nanopores of shale influenced by an electric field holds paramount importance for improving shale gas recovery and enhancing CO2 storage efficiency. This study employs molecular dynamics (MD) simulations to investigate the competitive adsorption mechanisms of gas mixtures on kaolinite surfaces. Subsequently, the engineering parameters governing electric field-enhanced CO2 sequestration and enhanced gas recovery (CS-EGR) are explored and optimized. In the absence of an electric field, the analysis reveals that water molecules exhibit the highest adsorption capacity in a ternary H2O–CO2–CH4 mixture, resulting in the formation of a water film of a specific thickness. CO2 displays a superior adsorption capability over CH4. As the CO2 volume injected into the reservoir increases, CH4 undergoes desorption due to the dominant adsorption effect of CO2. However, the efficiency of CO2 displacing CH4 diminishes significantly. The introduction of an electric field alters the equilibrium state of the gas mixture, leading to a further increase in CO2 adsorption and enhancing its selectivity relative to that of CH4 by 33%. These findings lay the foundation for the practical implementation of electric field-enhanced CS-EGR in shale reservoirs.

Calculations of solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in aqueous solutions with accurate thermodynamic models

Determining solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in aqueous solutions is essential for various applications of noble gases in geological processes and for understanding the migration and accumulation of helium. This study developed two thermodynamic models for calculations of solubilities of five pure noble gases (i.e. He, Ne, Ar, Kr, and Xe) and He–CO2/CH4/N2 gas mixtures in water and in aqueous NaCl solution. The first model is constructed by extending the improved SAFT-LJ equation of state (EOS) to five binary H2O-noble gas systems and four ternary systems (i.e. H2O–He–NaCl, H2O–He–CO2, H2O–He–CH4, and H2O–He–N2). Both the non-ideality of aqueous phase and that of vapor phase of these systems were described using the improved SAFT-LJ EOS (φ-φ model). The second model is developed by modifying the gas solubility model proposed by Duan and his coworkers (one type of γ-φ model). The Pitzer theory was used to describe the non-ideality of aqueous phase and the improved SAFT-LJ EOS was used to describe the non-ideality of vapor phase. Both binary adjustable parameters of the improved SAFT-LJ EOS and parameters of the modified solubility model for pure gas were evaluated from experimental solubility data for pure gas. Both models are predictive for solubilities of gas mixtures since there is no need to evaluate their parameters from solubility data of gas mixtures.Comparisons of calculations of two models with experimental data show that both models can well represent solubilities and Henry's coefficients of five noble gases in pure water, as well as the solubility of He in aqueous NaCl solutions over a wide P-T range (273–600 K, 1–2000 bar for the solubility of He in water). The absolute average deviation of the improved SAFT-LJ EOS from experimental solubility data for five noble gases in pure water is 3.14% and that of the modified solubility model is 2.21%. Predictions of the improved SAFT-LJ EOS for Henry's coefficients for He in the He–CO2–H2O system are consistent with available experimental data. According to predictions of the improved SAFT-LJ EOS, Henry's coefficient for He in the He–CO2–H2O system is always lower than that in the He–H2O system at the same depth. Within 0–5 km depth, He solubility of He–CO2 gas mixture is much greater than that of pure He at the same depth and He partial pressure, He solubility of He–N2 mixture is a little greater than that of pure He, and He solubility of He–CH4 mixture is between that of He–CO2 mixture and that of He–N2 mixture. A computer program for calculations of solubilities of pure noble gases and He–CO2/CH4/N2 gas mixtures in pure water and in aqueous NaCl solutions can be obtained from the corresponding author via email.

Revealing the effect of O2, SO2 and H2O in supercritical CO2 on the corrosion behavior of 316 L steel at elevated temperature

Closed supercritical CO2 (sCO2) power systems require steels that can resist corrosion in high temperature CO2 containing different impurities at ppm levels. However, potential impurity effects on Fe-16Cr steels are not well understood. Herein we evaluated the corrosion behavior of 316 L steel in sCO2 containing 100 ppm O2, SO2 or H2O at 600 °C and 20 MPa. All investigated impurities enhanced Fe-oxide nodule formation, leading to higher carburization in underlying substrate. Presence of O2 caused transition of chromia scale into Fe-Cr spinel, because Cr supply from underlying substrate could not meet the consumption. Spallation occurred when 316 L was exposed with SO2 impurity, attributed to the formation of sulfides within and beneath the oxide scales. H2O impurity showed relatively low damage to protective chromia layer with localized aggravation. Corrosion mechanisms related to impurities were unraveled based on experimental results and thermodynamic analysis.

Molecular dynamics insights into gas-water interfacial tension: Optimizing hydrogen storage in subsurface conditions

This study presents a comprehensive analysis of interfacial tension (IFT) between pore water and hydrogen-cushion gas mixtures in subsurface porous media, a key variable in the distribution of gas mixtures for hydrogen storage. Employing molecular dynamics simulations, we developed two IFT models at 20 MPa and 373 K: one for an H2–CO2–H2O system and another for an H2–CH4–H2O system. The models reveal that increasing cushion gas concentration reduces gas-water IFT. Notably, for H2–CO2–H2O mixtures, the IFT substantially decreases with CO2 concentration up to 40%, after which the reduction rate diminishes. In H2–CH4–H2O mixtures, the IFT decreases linearly with CH4 concentration. The study attributes these variations to local density distributions and molecular orientation effects. Specifically, CO2 adsorption at the interface up to 40% concentration significantly lowers IFT, while CH4 adsorption proportionally decreases IFT. The influence of CO2 on water molecule orientation at the interface, in contrast to the non-effect of CH4, is also critical in enhancing IFT reduction. Our results also highlight the reduction of H2 self-diffusion at the interface caused by CO2 and CH4, an essential factor in optimizing subsurface hydrogen storage operations.

Formation of Richterite in the Enstatite–Diopside System in the Presence of K2CO3–Na2CO3–CO2–H2O Fluid: Implications for the Processes of Mantle Metasomatism

Formation of Richterite in the Enstatite–Diopside System in the Presence of K2CO3–Na2CO3–CO2–H2O Fluid: Implications for the Processes of Mantle Metasomatism