Gas Diffusion Research Articles

Insight into CO2/CH4 separation by ionic liquids confined in MXene membrane from molecular level

Composite membranes incorporating ionic liquids (ILs) within MXene demonstrate promising potential for CO2 separation. However, studies on the separation of CO2/CH4 using MXene-confined ILs membranes are limited, especially in terms of understanding the mechanisms at the molecular level. In this work, the system of CO2/CH4 in MXene-confined ILs membranes was studied by molecular dynamic simulations. The number density results reveal that MXene stratifies the ILs between the layers, with higher concentrations of ILs near MXene and lower concentrations in the middle layer. Notably, MXene has a greater impact on cations distribution compared to anions. As the layer spacing of MXene expands from 1.5 to 3 nm, the interaction between MXene and IL weakens, while that between the cations and anions strengthens. The confined ILs enhance gas solubility capability but impede gas diffusion. CO2 is distributed closer to anions, while CH4 tends to be closer to cations, with the distance between CH4 and cations decreasing as the layer spacing increases. Additionally, with the increase of layer distance, the proportion of confined ILs gradually decreases, and the gas diffusion coefficient gradually increases. Furthermore, compared to 1-Ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and 1-Ethyl-3-methylimidazolium hexafluorophosphate ([EMIM][PF6]), MXene-confined 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TF2N]) is identified as the most effective for CO2/CH4 separation, owing to its superior CO2 solubility and highest diffusion selectivity.

Analysis of pore formation and carburizing mechanism of magnetite reduction by CO

To investigate the porosity and expansion mechanism of CO-reduced magnetite, the reduced microstructures of magnetite under conventional heating and microwave heating were compared. The microstructure characteristics of magnetite with various reduction degrees were examined in a 60%CO-Ar reduction atmosphere, and the formation and evolution mechanism of the structure were analyzed in conjunction with the reduction effect. The results indicate that the reduction product of CO reduced magnetite possesses a porous structure. Nevertheless, when the gas diffusion is restricted, the reduction process is sluggish and the porous structure is not readily formed. Microwave heating enhances the gas-phase diffusion capacity, thermodynamic carburizing capacity, and solid-phase carbon-oxygen diffusion capacity, resulting in a higher oxygen loss rate than that of conventional heating. Under the experimental conditions, the lattice shrinkage during the Fe3O4 → Fe0.88O transformation and the rapid expansion of Fe0.88O → Fe0.94O are the causes of the crack. Microwaves facilitate the formation of pores and cracks in the product. This study offers a novel concept for the development of foam steel.

2D MOF‐Based Filtration‐Sensing Strategy for Trace Gas Sensing Under Intense F‐Gas Interference at Room Temperature

AbstractThe detection of trace impurity gases in fluorinated gas (F‐gas) that are widely used in the industry offers a significant avenue for equipment status monitoring and mitigating unnecessary emissions. However, the formidable electron affinity (EA) and adsorption propensity of F‐gas molecules render the identification of trace impurities within a high‐concentration F‐gas atmosphere exceptionally challenging. Herein, the filtration‐sensing strategy is proposed to realize highly sensitive and selective Room Temperature (RT) sensing of trace gases in the F‐gas environment. Through the innovative construction of a bilayer structure, comprising Co3(HITP)2 as the overlayer and SnO2 nanofibers (NFs) as the sensing layer, remarkably sensitive detection of trace impurity gases under intense F‐gas interference conditions is achieved. The efficacy of the Co3(HITP)2 overlayer is further corroborated through the incorporation of Pd‐SnO2 and MoS2‐SnO2 sensors, concurrently facilitating targeted quantitative identification within a complex gas mixture environment. The underlying sensing mechanism is predominantly attributed to interatomic adsorption interactions and the modulation of gas diffusion by microporous structures. This work provides pioneering insights into trace impurity detection within high‐concentration F‐gas atmosphere while presenting a potentially viable solution for the operational maintenance of F‐gas‐based industrial equipment (F‐equipment) in industrial applications.

Hierarchically conductive electrodes unlock stable and scalable CO2 electrolysis.

Electrochemical CO2 reduction has emerged as a promising CO2 utilization technology, with Gas Diffusion Electrodes becoming the predominant architecture to maximize performance. Such electrodes must maintain robust hydrophobicity to prevent flooding, while also ensuring high conductivity to minimize ohmic losses. Intrinsic material tradeoffs have led to two main architectures: carbon paper is highly conductive but floods easily; while expanded Polytetrafluoroethylene is flooding resistant but non-conductive, limiting electrode sizes to just 5 cm2. Here we demonstrate a hierarchically conductive electrode architecture which overcomes these scaling limitations by employing inter-woven microscale conductors within a hydrophobic expanded Polytetrafluoroethylene membrane. We develop a model which captures the spatial variability in voltage and product distribution on electrodes due to ohmic losses and use it to rationally design the hierarchical architecture which can be applied independent of catalyst chemistry or morphology. We demonstrate C2+ Faradaic efficiencies of ~75% and reduce cell voltage by as much as 0.9 V for electrodes as large as 50 cm2 by employing our hierarchically conductive electrode architecture.

Various Cultivars of Citrus Fruits: Effects of Construction on Gas Diffusion Resistance and Internal Gas Concentration of Oxygen and Carbon Dioxide

Various cultivars of citrus fruits have unique constructions, such as thick outer skin. These constructions generate gas diffusion resistance between the atmosphere and the fruit, which can limit the gas exchange of O2 and CO2.This has not been sufficiently investigated. This study on seven cultivars of citrus fruit firstly aimed to investigate gas diffusion resistance utilizing the ethane efflux method; secondly, this study aimed to investigate the internal gas concentration of O2 and CO2. As a result, a cultivar of citrus fruit with slimmer outer skin thickness had lower resistance. For the internal gas, a high CO2 concentration in comparison with the atmosphere was observed even in the fruits with the minimum resistance, and no considerable difference was observed among all cultivars, regardless of the gas diffusion resistance value. However, when the fruits were stored at 25 °C for 2 weeks, CO2 gas concentration tended to increase and O2 gas concentration tended to decrease, with an increase in the resistance value. Therefore, when the respiration of citrus fruits is activated at ambient temperature, the self-control system of internal gas concentration can be driven to suppress the respiration which was induced by gas diffusion resistance generated from their construction.

Toward revolutionizing PEMFC manufacturing for clean energy conversion: a review on the innovative contribution of 3D printing techniques

AbstractThree-dimensional printing (3DP) is a technology useful for fabricating both structural and energy devices. Of great concern to this review is promising nature of additive manufacturing (AM) for engineering fuel cells (FCs) for clean energy conversion. 3DP technique is useful for the fabrication of fuel cell components, and they offer waste minimization, low-cost, and complex geometric structures. In this review, significance of different 3DP techniques toward revolutionizing fuel cell fabrication is given. The aim is to unravel the importance and status of 3D-printed fuel cells and hence provides researchers and scientists with extensive opportunities of 3DP techniques for fuel cell engineering. After careful selection of state-of-the-art literatures, different kinds of 3DP techniques of relevance to electrolytes, electrodes, and other key components (e.g., gas diffusion layers (GDLs), bipolar plates (BPs), and membrane electrode assembly (MEA)) fabrication are explicitly discussed. Among the techniques, the best approaches are recommended for further studies. Advantages associated with these techniques are indicated for the benefit of those whose interests matter most on clean energy production. The challenges researchers are facing in the use of 3DP for fuel cell fabrications are identified. Possible solutions to the identified challenges are suggested as way forward to further development in this research area. It is expected that this review article will benefit engineers and scientists who have interest on clean energy conversion devices.

CATALYST BASED ON PALLADIUM‐MODIFIED MIL‐53(AL) PYROLYSATE FOR ORR IN ALKALINE MEDIA

A catalyst for the oxygen reduction reaction (ORR) based on the metal‐organic framework material MIL‐53(Al) modified with palladium was synthesized. Its textural and morphological characteristics were studied using the method of adsorption porosimetry, SEM, TEM, energy dispersive X‐ray analysis (EDAX) , X‐ray diffraction (XRD), Raman –spectroscopy, X‐ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA‐DSC). The electrocatalytic properties of the synthesized material in ORR were studied by voltammetry using a rotating disk electrode. Corrosion resistance was studied in the CV mode. It was found that the synthesized catalyst is characterized by high corrosion resistance. The tolerance of synthetized catalyst Pyr_MIL‐53(Al)_Pd to the methanol was studied. The obtained catalyst was studied in a membrane electrode assembly (MEA) formed by spraying an ionomer suspension onto a gas diffusion layer (GDL). The synthesized Pyr‐MIL‐53 (Al)_Pd and commercial platinum (60% Pt) (HiSPEC 9100) catalysts were compared in the cathode composition, and 10% PtM (M = Ni, Mo)/CNT catalysts were used on the anode. The power density of the FC (P) was calculated based on the obtained current‐voltage curves. Based on the set of characteristics, the synthesized catalyst based on MIL‐53 (AL) doped with palladium is superior in efficiency to the commercial platinum catalyst.

Integration of Pre‐Activated Carbon‐Fabric Layers for Ampere‐Hour‐Scale Quasi‐Solid‐State Pouch‐Type Zinc–Air Batteries

AbstractAchieving ampere‐hour‐scale capacities in pouch‐type zinc–air batteries (ZABs) requires optimizing key factors, such as preventing inactive ZnO dendrite formation on zinc anodes and enhancing catalytic activity with efficient gas diffusion in the air cathode. Here, a pioneering flexible, large‐area, ampere‐hour‐scale quasi‐solid‐state ZAB is introduced, addressing these challenges through a novel preactivation strategy combined with a layered assembly approach. This method employs mass‐producible fibrous carbon textiles to form flexible fabrics that separate functions within multi‐stacked layers. Preactivated carbon fabric layers, independently functionalized and easily reassembled, enhance scalability and manufacturability. A bilayer catalytic air electrode, incorporating hydrophilic NiFe hydroxide and hydrophobic FeNC regions, ensures efficient charge and mass transfer, significantly boosting catalytic activity. To prevent dendrite formation on the zinc anode, a zincophilic copper interlayer is implemented. This configuration supports rapid, stable charge–discharge cycles at a high current density of 20 mA cm⁻2. The large‐area stacked bipolar structure pouch cells, exceeding 36 cm2, achieve a discharge capacity of up to 2500 mAh, maintaining high cycle stability through discharge–charge cycles with 200 mAh per cycle. This approach significantly enhances the scalability, manufacturability, and production potential of ultrahigh‐capacity wearable ZABs, making them practical for widespread application in various portable and flexible devices.

Oxygen Abundance Throughout the Dwarf Starburst Galaxy IC 10

Measurements of oxygen abundance throughout galaxies provide insight to the formation histories and ongoing processes. Here we present a study of the gas-phase oxygen abundance in the H ii regions and diffuse gas of the nearby starburst dwarf galaxy, IC 10. Using the Keck Cosmic Web Imager at W. M. Keck Observatory, we map the central region of IC 10 from 3500 to 5500 Å. The auroral [O III] 4363 Å line is detected with a high signal-to-noise ratio in 12 of 46 H II regions observed, allowing for direct measurement of the oxygen abundance, yielding a median and standard deviation of 12+log(O/H)=8.37±0.25 . We investigate trends between these directly measured oxygen abundances and other H II region properties, finding weak negative correlations with the radius, velocity dispersion, and luminosity. We also find weak negative correlations between the oxygen abundance and the derived quantities of turbulent pressure and ionized gas mass, and a moderate correlation with the derived dynamical mass. Strong line, R 23 abundance estimates are used in the remainder of the H II regions and on a resolved spaxel-by-spaxel basis. There is a large offset between the abundances measured with R 23 and the auroral line method. We find that the R 23 method is unable to capture the large range of abundances observed via the auroral line measurements. The extent of this variation in the measured abundances further indicates a poorly mixed interstellar medium in IC 10, which is not typical of dwarf galaxies and may be partly due to the ongoing starburst, accretion of pristine gas, or a late stage merger.

Proton Pool for the Mitigation of Salt Precipitate Enhancing CO2 Electroreduction in a Flow Cell

Flow cells featuring a gas diffusion electrode (GDE) have emerged as an attractive platform for electrochemical CO2 reduction, offering high current densities (~300 mA·cm−2) and low energy consumption. However, the formation of salt precipitates, particularly carbonate and bicarbonate, poses a significant deficiency by reducing the cell’s operational longevity. In this study, we present a novel approach to mitigate salt precipitates in real-time through acid–base interaction. Recovery efficiency and partial current density of the cell were used to evaluate the capability of removing salt precipitates and the maintenance of CO2 reduction reactions (CO2RRs). It was suggested that the direct treatment of intermittent acid rinse recovers the performance of CO2RRs to a large extent (>97%), and the modification of the proton exchange resin reduces the reduction rate of partial current densities to 1/15 than that of the unmodified. This improvement enhances the cell’s catalytic performance, enabling the stability test for catalysts within the GDE-based flow cell.

Study on the Control Effect of Borehole Gas Extraction in Coal Seams Based on the Stress–Seepage Coupling Field

In order to determine the reasonable parameters of high-gas and extra-thick coal seam drainage, considering the factors of the coal seam metamorphic degree, stress condition, gas occurrence state, and permeability dynamic change, the gas desorption, diffusion, and transport process of coal seam gas are analyzed. A secondary distribution model of coal around the borehole, a porosity variation model of coal around the borehole, a stress–seepage coupling model, a pore flow model of the pressure-driven transition flow zone, and a free molecular flow zone are established. Taking the gas drainage of Zhangcun Coal Mine of Lu’an Group as the research object, the influence of drilling hole diameter, coal seam permeability, gas original pressure, and other factors on the control range of coal seam drainage drilling is simulated by ANSYS Fluent 6.3.26. The results show that secondary stress distribution occurs in the coal seam drill hole under the action of lead stress, which leads to the change in porosity; the seepage zone, transition zone, molecular flow zone, and original rock stress zone are presented around the drill hole; and the range of influence of the drill hole is mainly based on the seepage zone and the transition zone, supplemented by the molecular flow zone. The control range of the drill hole is in a positive proportional relationship to the diameter of the drill hole, the porosity of the coal seam, and the original pressure of the gas.

Effects of liquid fraction and contact angle on structure and coarsening in two-dimensional foams

Aqueous foams coarsen with time due to gas diffusion through the liquid between the bubbles. The mean bubble size grows, and small bubbles vanish. However, coarsening is little understood for foams with an intermediate liquid content, particularly in the presence of surfactant-induced attractive forces between the bubbles, measured by the interface contact angle where thin films meet the bulk liquid. Rigorous bubble growth laws have yet to be developed, and the evolution of bulk foam properties is unclear. We present a quasistatic numerical model for coarsening in two-dimensional wet foams, focusing on growth laws and related bubble properties. The deformation of bubble interfaces is modelled using a finite-element approach, and the gas flow through both films and Plateau borders is approximated. We give results for disordered two-dimensional wet foams with $256$ to $1024$ bubbles, at liquid fractions from $2\,\%$ to $25\,\%$ , beyond the zero-contact-angle unjamming transition, and with contact angles up to $10^\circ$ . Simple analytical models for the bubble pressures, film lengths and coarsening growth rates are developed to aid interpretation. If the contact angle is non-zero, we find that a prediction of the coarsening rate approaches a non-zero value as the liquid fraction is increased. We also find that an individual bubble's effective number of neighbours determines whether it grows or shrinks to a good approximation.

Enhancement of the quality of mc-Si ingot grown by vacuum directional solidification furnace with growth rate increase reducing the cost of the wafer for PV application: Carbon and oxygen analysis

In this paper, we propose a numerical model to investigate the dissolution of oxygen atoms from the porous silica crucible, SiO gas formation, back diffusion of CO gas and segregation of carbon and oxygen during the growth of multi-crystalline silicon (mc-Si) by vacuum directional solidification (VDS) at different growth rates (3, 6 and 9 mm/h) by silt valve opening rate. The dissolution of oxygen decreases during the rapid growth of ingot because the reaction between the molten silicon and the porous silica crucible is constrained. This limitation on oxygen dissolution from the porous silica crucible further diminishes chemical reaction inside the VDS furnace. Consequently, the segregation pattern of the carbon and oxygen is affected at higher growth rate. During the VDS mc-Si growth, a growth rate of 9mm/h yields better quality of the VDS grown mc-Si ingots compared to other growth rates, this rate reduces SiC precipitation and SiO2 cluster formation due to lower concentration of carbon and oxygen. The obtained carbon concentration minimizes the wire saw defects. Based on these numerical results (9 mm/h), we have implemented experimental work. Prepared samples are analyzed using FTIR spectra and minority carrier lifetime measurements. The effect of oxygen concentration in the samples is analyzed in the minority carrier lifetime measurements. The oxygen and carbon concentrations are calculated by FTIR spectra and their results are compared with the numerical simulation.

Research on the Calculation Method and Diffusion Pattern of VCE Injury Probability in Oil Tank Group Based on SLAB-TNO Method

Accidental leakage from oil–gas storage tanks can lead to the formation of liquid pools. These pools can result in vapor cloud explosions (VCEs) if combustible vapors encounter ignition energy. Conducting accurate and comprehensive consequence analyses of such explosions is crucial for quantitative risk assessments (QRAs) in industrial safety. In this study, a methodology based on the SLAB-TNO model to calculate the overpressure resulting from a VCE is presented. Based on this method, the consequences of the VCE accident considering the gas cloud concentration diffusion are studied. The probit model is employed to evaluate casualty probabilities under varying environmental and operational conditions. The effects of key parameters, including gas diffusion time, wind speed, lower flammability limit (LFL), and environment temperature, on casualty diffusion are systematically investigated. The results indicate that when the diffusion time is less than 100 s, the VCE consequences are significantly more severe due to the rapid spread of the gas cloud. Furthermore, increasing wind speed accelerates gas dispersion, reducing the spatial extent of casualty isopleths. The LFL is shown to have a direct impact on both the mass and diffusion of the flammable gas cloud, with higher LFL values shifting the explosion’s epicenter upward. The environmental temperature promotes gas diffusion in the core area and increases the mass of the combustible gas cloud. These findings provide critical insights for improving the safety protocols in oil and gas storage facilities and can serve as a valuable reference for consequence assessment and emergency response planning in similar industrial scenarios.

Mapping of drought-induced changes in tissue characteristics across the leaf profile of Populus balsamifera.

Leaf architecture impacts the ease of gases diffusion, biochemical process, and photosynthetic performance. For balsam poplar, a widespread North American species, the influence of water availability on leaf anatomy and subsequent photosynthetic performance remains unknown. To address this shortcoming, we characterized the anatomical changes across the leaf profile in three-dimensional space for saplings subjected to soil drying and rewatering using X-ray microcomputed tomography. Our hypothesis was that higher abundance of bundle sheet extensions (BSE) minimizes drought-induced changes in intercellular airspace volume relative to mesophyll volume (i.e. mesophyll porosity, θIAS) and aids recovery by supporting leaf structural integrity. Leaves of 'Carnduff-9' with less abundant BSEs exhibited greater θIAS, higher spongy mesophyll surface area, reduced palisade mesophyll surface area, and less veins compared with 'Gillam-5'. Under drought conditions, Carnduff-9 showed significant changes in θIAS across leaf profile while that was little for 'Gillam-5'. Under rewatered conditions, drought-induced changes in θIAS were fully reversible in 'Gillam-5' but not in 'Carnduff-9'. Our data suggest that a 'robust' leaf structure with higher abundance of BSEs, reduced θIAS, and relatively large mesophyll surface area provides for improved photosynthetic capacity under drought and supports recovery in leaf architecture after rewatering in balsam poplar.

High-sensitivity NO2 fluorescence sensor based on a QDs@Aerogels/SM composite nanofilm.

Quantum dots (QDs) exhibit excellent optical and chemical properties, making them advantageous for fluorescence sensing. However, gas sensor using QDs is often hampered by challenges such as gas diffusion and low concentration. This work describes the development of a nitrogen dioxide (NO2) fluorescence gas sensor that utilizes a QDs@Aerogels/SM composite nanofilm containing CdTe QDs modified by reduced glutathione (GSH), silica microspheres (SMs), and silica aerogel. The SM and porous aerogels create a uniform porous structure that enhances the distribution of QDs. Compared to the pure QDs film, the QDs@Aerogels/SM composite film exhibits enhanced fluorescence intensity. The porous structure promotes the adsorption of NO2, which improves the detection sensitivity. The QDs@Aerogels/SM composite film was applied in a portable gas sensor. The sensor demonstrates a good linear response to NO2 gas in the range of 0-10 ppm, with an ultra-low detection limit of 0.096 ppm and high selectivity. The uniform distribution of aerogel and SM enhances the stability of the composite nanofilm, and the fluorescence of the films remains virtually unchanged over a period of 60 days which ensures its optimal performance over extended periods of use. The fluorescent NO2 sensor demonstrated selective and sensitive quenching upon exposure to NO2, making it ideal for environmental monitoring and further applications.

In-situ Raman Observation on Gas Diffusion Electrode/Polyelectrolyte Interface

Polyelectrolytes (PEs) serve as the critical medium for electrochemical reactions in membrane-based electrochemical devices, such as fuel cells and membrane electrolyzers. To optimize membrane-based electrochemical device performance and elucidate reaction mechanisms, there is a pressing need for detailed microscopic molecular information at gas diffusion electrode/PE interfaces. In this work, we designed a novel membrane-based-electrochemical-device-like gas diffusion electrode/polyelectrolyte electrochemical in-situ Raman cell. The cell's configuration and gas transfer characteristics closely mimic those of MBEDs under working conditions. We created a Pt/Nafion(s) interface by hot-pressing satellite Au@SiO2-Pt loaded carbon cloth with a Nafion membrane, and used this interface for electrochemical in-situ surface enhanced Raman spectroscopy (SERS) observation, including oxygen adsorption/desorption processes, structure of interfacial water and functional groups of Nafion under Ar. The cell enables negatively polarize the potential down to -1.6 V vs. RHE without stripping of the solid/solid interface, despite vigorous H2 generation. The stability of the interface under extreme conditions demonstrates rapid gas transfer at the interface. This observation underscores the potential of our in-situ Raman cell for studying various gas-involved reactions under conditions that closely resemble those in operational MBEDs.

CO2 hydrate formation in superabsorbent hydrogels for carbon capture—A comparison of water-confined framework vs non-water framework

This study investigates the kinetics of CO2 hydrate formation in saturated hydrogel particles—water-confined frameworks—through both experimental and numerical methods, and compares the results with those obtained in silica gels, silicon-based frameworks. Three hydrogel materials with varying swelling ratios were synthesized via radical polymerization. An advanced shrinking core model was developed, incorporating factors of CO2 solubility, gas diffusion, gas–water reaction, capillary effects, and hydrogel functional groups. Results showed rapid CO2 hydrate growth within the first 100 min, with CO2 uptake reaching 78%–82% of the final amount by 600 min. The highest percent water conversion achieved was 96.6%. Simulations indicated a significant decrease in CO2 diffusion coefficient through the hydrate shell over time, especially in hydrogels with higher methacrylic acid content. Capillary effects diminished as the reaction proceeded, with final water consumption via capillaries accounting for 14.4%–26.7% of the total. Hydrogels with higher swelling ratios and higher agglomeration degree formed more porous hydrate shells, enhancing CO2 diffusion but resulting in lower overall CO2 uptake due to their lower water content. Comparisons with hydrophilic porous silica gel revealed that, although hydrogels initially posed greater mass transfer resistance, they ultimately exhibited superior CO2 absorption capacity and rate.

Efficient membrane separation of SO2 by choline chloride-based natural deep eutectic solvents: The role of hydrogen bonding sites

Natural deep eutectic solvents (NDESs) are recognized as promising membrane materials for sustainable SO2 separation. Evaluating their separation performances is necessary, as well as understanding of the role that each hydrogen bonding site (including anion and functional groups in NDESs) plays in SO2 separation. Herein, three choline chloride (ChCl)-based NDESs bearing different number and type of functional groups were firstly incorporated into Pebax matrix to fabricate blended membranes for removing SO2 from CO2 and N2. The Pebax/NDES membranes show SO2 permeability up to 10502 Barrer (0.20 bar and 40 °C), with excellent SO2/N2 and SO2/CO2 selectivity of 1808 and 62.5 obtained, respectively, which are enhanced by 156 %, 61.5 % and 56.1 % compared with those in neat Pebax membrane. By means of gas solubility and diffusivity measurements, quantum chemical calculations and spectral characterizations, the highly-reversible multi-site interactions between SO2 and hydrogen bonding sites in NDESs (Cl−···SO2, carbonyl O···SO2 and hydroxyl O···SO2) were revealed. Meanwhile, the strength of hydrogen bonding network inside the NDESs, which is governed by the hydrogen bonding sites, is found to significantly influence the gas diffusion. More importantly, SO2/CO2/N2 (2.5/15/82.5 mol%) mixed gas separation experiment also displays the superior separation performance and long-term stability of Pebax/NDES membrane.

Multiphase flow and reactive transport benchmark for radioactive waste disposal

AbstractCompacted bentonite is part of the multi-barrier system of radioactive waste repositories. The assessment of the long-term performance of the barrier requires using reactive transport models. Here we present a multiphase flow and reactive transport benchmark for radioactive waste disposal. The numerical model deals with a 1D column of unsaturated bentonite through which water, dry air and $${\hbox {CO}_{2{(g)}}}$$ CO 2 ( g ) may flow and with the following reactions; aqueous complexation, calcite and gypsum dissolution/precipitation, cation exchange and gas dissolution. INVERSE-FADES-CORE V2, $$\hbox {DuMu}^X$$ DuMu X , TOUGHREACT and iCP were benchmarked with 6 test cases of increasing complexity, starting with conservative tracer transport under variably unsaturated conditions and ending with water flow, gas diffusion, minerals and cation exchange. The solutions of all codes exhibit similar trends. Small discrepancies are found in conservative tracer transport due to differences in hydrodynamic dispersion. Computed $${\hbox {CO}_{2{(g)}}}$$ CO 2 ( g ) pressures agree when a sufficiently refined grid is used. Small discrepancies in $${\hbox {CO}_{2{(g)}}}$$ CO 2 ( g ) and pH are found near the no-flow boundary at early times which vanish later. Discrepancies are due differences in the formulations used for gas flow at nearly water-saturated conditions. Computed $${\hbox {CO}_{2{(g)}}}$$ CO 2 ( g ) pressures show a fluctuation between $$10^{-4}$$ 10 - 4 and $$10^{-3}$$ 10 - 3 years which slows down the in-diffusion of $${\hbox {CO}_{2{(g)}}}$$ CO 2 ( g ) . This fluctuation is associated with chemical reactions involving $${\hbox {CO}_{2}}$$ CO 2 . There are discrepancies in solute concentrations due to differences in the Debye–Hückel (DH) formulation. They are overcome when all codes use the same DH formulation. The results of this benchmark will contribute to increase the confidence on multiphase reactive transport models for radioactive waste disposal.