Gas Permeability Research Articles

Rubbery organic frameworks (ROFs) toward ultrapermeable CO 2 -selective membranes

The capture of CO 2 is of high interest in our society representing an essential tool to mitigate man-made climate warming. Membrane technology applied for CO 2 capture offers several advantages in terms of energy savings, simple operation, and easy scale-up. Glassy membranes are associated with low gas permeability that negatively affect on their industrial implementation. Oppositely, rubbery membranes offer high permeability, but their selectivity is low. Here we report rubbery organic frameworks (ROFs) combining the high permeability of soft matrices with the high sieving selectivity of molecular frameworks. The best performing membranes provide a CO 2 /N 2 selectivity up to 104 with a CO 2 permeability up to 1000 Barrer, representing relevant performances for industrial implementation. Water vapors have a positive effect on CO 2 permeability, and the CO 2 /N 2 selectivity is higher than in dry conditions, as most of CO 2 gas emissions are present in fully humidified gas streams. The synergetic high permeability/selectivity performances are superior to that observed with current state-of-the-art polymeric membranes.

Investigation aspects of the geogenic radon potential on Bulgarian territory

Radon (222Rn) is a radioactive gas formed as a result of the radioactive decay of radium (226Ra). Radon is identified as one of the dominant sources of population exposure that could lead to lung cancer, accounting for between 3% and 14% of all lung cancers. Rocks in the Earth’s crust are a primary source of radon in the atmosphere. In this context, the geogenic radon potential (GRP) of a terrain refers to the probability of high radon concentrations being present in a building. The radon index is a concept used to characterize the geogenic potential of the terrain, providing the likelihood of radon concentration in a building, which is directly related to the influence of the Earth's surface. One approach to quantifying the radon index is based on multivariate cross-tabulation, involving two parameters: radon concentration in soil gas and the gas permeability of the earth layer, both measured at 80 cm below the surface. In Bulgaria, focused investigations on the connection between radon gas and geology, resp. on GRP have begun in the last five. As a result of the accumulated experience from field studies conducted so far related to the characterization of GRP, two important aspects have been identified that impact field measurements and the determination of radon gas in the soil, thus the methodology for calculating the radon index. The first aspect is connected with the theoretical and model-based investigations about possible state of soil saturation. The second aspect is about the GRP and fault systems in Sofia. This article makes an attempt to summarize all the studies concerning these two aspects and to suggest some further steps in the geogenic radon potential studies.

Orderly Coating of Bilayer Polymer to Tailor Microenvironment for Efficient C−N Coupling Toward Highly Selective Urea Electrosynthesis

AbstractElectrosynthesis of urea from co‐reduction of carbon dioxide and nitrate is a promising alternative to the industrial process. However, the overwhelming existence of proton and nitrate as well as the insufficient supply of CO2 at the reaction interface usually result in complex product distributions from individual nitrate reduction or hydrogen evolution, instead of C−N coupling. In this work, we systematically optimize this microenvironment through orderly coating of bilayer polymer to specifically tackle the above challenges. Polymer of intrinsic microporosity is chosen as the upper polymer to achieve physical sieving, realizing low water diffusivity for suppressing hydrogen evolution and high gas permeability for smooth mass transfer of CO2 at the same time. Polyaniline with abundant basic amino groups is capable of triggering chemical interaction with acidic CO2 molecules, so that is used as the underlying polymer to serve as CO2 concentrator and facilitate the carbon source supply for C−N coupling. Within this tailored microenvironment, a maximum urea generation yield rate of 1671.6 μg h−1 mg−1 and a high Faradaic efficiency of 75.3 % are delivered once coupled with efficient electrocatalyst with neighboring active sites, which is among the most efficient system of urea electrosynthesis.

Evaluation of Pore-Former Size and Volume Fraction on Tape Cast Porous 430 Stainless Steel Substrates for Plasma Spraying

Porous 430L stainless steel disks made by tape casting with various pore-former sizes and volume fractions were evaluated as substrates for solid oxide cell (SOC) fabrication by plasma spraying. This work reports the substrate properties relevant to the SOC operation of disks made by using extra fine metal powder with dense sintering to minimize the fine porosity between particles. In contrast, the coarse porosity is introduced by the pore former. We found that the 60 μm pore former at a 45 vol% fraction has the best application fit; it gives an adequate gas permeability of 3.11 × 10−13 m2 and an average open pore size of 45.90 μm. Compared to a commercial substrate with a similar porosity perimeter/steel area ratio, the porosity and gas permeability are 1.6 and 3 times higher, respectively. The detected maximum surface pore is 49 μm, allowing gas-tight electrolytes fabricated by plasma spray deposition.

Enhancing CO2/N2 and CO2/CH4 Separation Properties of PES/SAPO-34 Membranes Using Choline Chloride-Based Deep Eutectic Solvents as Additives

CO2 separation is an important environmental method mainly used in reducing CO2 emissions to mitigate anthropogenic climate change. The use of mixed-matrix membranes (MMMs) arrives as a possible answer, combining the high selectivity of inorganic membranes with high permeability of organic membranes. However, the combination of these materials is challenging due to their opposing nature, leading to poor interactions between polymeric matrix and inorganic fillers. Many additives have been tested to reduce interfacial voids, some of which showed potential in dealing with compatibility problems, but most of them lack further studies and optimization. Deep eutectic solvents (DESs) have emerged as IL substitutes since they are cheaper and environmentally friendly. Choline chloride-based deep eutectic solvents were studied as additives in polyethersulfone (PES)/SAPO-34 membranes to improve CO2 permeability and CO2/N2 and CO2/CH4 selectivity. SAPO-34 crystals of 150 nm with a high surface area and microporosity were synthesized using dry-gel methodology. The PES/SAPO-34 membranes were optimized following previous work and used in a defined composition, using 5 or 10 w/w% of DES during membrane preparation. All MMMs were characterized by their ideal gas permeability using N2 and CO2 pure gasses. Selected membranes were also tested using CH4 pure gas. The results presented that 5 w/w%, in polymer mass, of ChCl–glycerol presented the best result over the synthesized membranes. An increase of 200% in CO2 permeability maintains the CO2/N2 selectivity for the non-modified PES/SAPO-34 membrane. A CO2/CH4 selectivity of 89.7 was obtained in PES/SAPO-34/ChCl-glycerol membranes containing 5 w/w% of this DES, which is an outstanding ideal separation performance for MMMs when compared to other results in the literature. FTIR analysis reiterates the presence of glycerol in the membranes prepared. Dynamic Mechanical Thermal Analysis (DMTA) shows that the addition of 5 w/w% of DES does not impact the membrane flexibility or polymer structure. However, in concentrations higher than 10 w/w%, the inclusion of DES could lead to high membrane rigidification without impacting the overall thermal resistance. SEM analysis of DES-enhanced membranes presented asymmetric final membranes and reaffirmed the results obtained in DMTA about rigidified structures and lower zeolite–polymer interaction with higher concentrations of DES.

Mechanical, thermal and gas separation properties of copolyimides and their thermal rearrangement copolymer membranes with spirobisindane structures

In this work, two kinds of dimaine monomers with spirocyclic structures, including 3,3,3′,3′-tetramethyl-6,6′-bis[3-amino-4-hydroxyphenoxy]-1,1′-spirobisindane (TBAHS) and 3,3,3′,3′-tetramethyl-bis(5-amino-6-hydroxyphenyl)-1,1′-spirobisindane (TBHAS) are firstly synthesized. Then, the two diamines TBAHS and TBHAS are copolymerized in different molar ratios with equimolar 4,4′-(hexafluoroisopropenyl)diphthalic anhydride (6FDA) to synthesize poly(amic acid) (PAA) solution, followed by thermal imidization to obtain a series of copolyimide (coPI) membranes. Next, these coPI(TBAHS-TBHAS) specimens are subjected to thermal rearrangement (TR) treatment at 450°C to obtain the corresponding coTR(TBAHS-TBHAS) copolymer membranes. The influences of the molar ratio of TBAHS to TBHAS, thermal treatment temperature and time on the microstructures and properties of the PI and TR copolymers are investigated. With the increase of rigid TBHAS molar ratio, the glass transition temperature ( Tg) and d-spacing value of the coPI(TBAHS-TBHAS) samples are significantly enhanced. Furthermore, as the thermal treatment temperature increases, the mechanical properties of the copolymer membranes display a sharply decline trend, but the d-spacing values are obviously increased. When the molar ratio of TBAHS to TBHAS is 7:3, the gas permeabilities of the coTR membrane reach 1140.5, 1180.6, 306.6, and 44.9 Barrer for H2, CO2, O2, and N2, respectively. Meanwhile, the ideal selectivity of O2/ N2 is 6.82, suggesting a superior separation performance close to the 2015 upper limit. Furthermore, with the increase of thermal treatment temperature and time, the gas permeabilities are also improved.

Flat biofilms extrusion of poly(lactic acid)/poly(butylene adipate‐co‐terephthalate) grafted with glycidyl methacrylate blends: Toward ecological packaging for sustainability

AbstractBlends of poly(lactic acid) (PLA)/poly(butylene adipate‐co‐terephthalate) grafted with glycidyl methacrylate (PBAT‐g‐GMA) were developed to produce flat and flexible biofilms through extrusion. The PLA/PBAT‐g‐GMA (90%/10%, 80%/20%, 70%/30%, and 60%/40% by mass) blends were processed in the internal mixer, injection molded, and manufactured into flat films. The optimal composition to produce flexible biofilms was PLA/PBAT‐g‐GMA (60/40%), as it demonstrated a decrease in elastic modulus of 53.2% and a significant gain in elongation at a break of 4923% about pure PLA. The incorporation of 40% PBAT‐g‐GMA in PLA increased the torque (Z) by 208%, while the melt flow index (MFI) decreased by 51.57%, compared to PLA. Additionally, the degradation rate (Rz) and molar mass loss (Rm) during processing were minimized, indicating that 40% PBAT‐g‐GMA enhanced stability of the PLA matrix. Fourier transform infrared spectroscopy indicated interactions between the GMA of PBAT‐g‐GMA and PLA, justifying the increase in viscosity and elongation at break. The PLA/PBAT‐g‐GMA (60/40%) composition showed a transmittance in the range of 20%–48% (400–800 nm) and an oxygen gas permeability of 1.56 × 10−5 cm3 STP/cm−2 h bar, indicating its potential for applications in packaging with optical barrier properties. Scanning electron microscopy (SEM) revealed ligaments in the interfacial region between PLA and PBAT‐g‐GMA, confirming the good performance in elongation at break. The results presented are essential for the plastics processing sector, aiming to develop eco‐friendly packaging.

Metal-Coordinated, Dual-Crosslinked PIM Polymer Membranes for Upgraded CO2 Separation: Aging and Plasticization Resistance.

The practical use of polymers of intrinsic microporosity (PIMs) in CO2 separation is often hindered by their moderate selectivity, performance instability over time, and pressure constraints. To address these limitations, a straightforward approach is presented to enhance the CO2 separation capability of PIM-1 by incorporating metal ions into uniformly hydrolyzed PIM-1 (cPIM). This dual linking strategy, achieved via ionic and coordination bonding of metal ions with the polymeric side chains including ─COOH and ─CONH2, restructures the polymer, disrupting hydrogen bonds between cPIM chains and creating active sites for CO2 via π-complexation. This modification enhances gas permeability while maintaining high selectivity. The optimized zinc-coordinated membrane achieves an impressive CO2 permeability of ≈2,500 Barrer with CO2/N2 and CO2/CH4 selectivities of 27.1 and 23, respectively, outperforming pristine cPIM (700 Barrer; CO2/N2=27; CO2/CH4=19). Notably, this performance surpasses the 2008 Robeson upper-bound limits for both gas pairs. Additionally, the metal-coordinated membranes exhibit remarkable long-term stability, resisting aging effects for up to 20 days and maintaining anti-plasticization properties at pressures up to 20 bar. These dual-crosslinked membranes demonstrate promising potential for mixed gas separation, indicating their suitability for real-world industrial applications.

Enhanced plasticization resistance of hollow fiber membranes via metal ion coordination for advanced helium recovery

Plasticization can significantly impair the gas separation performance of gas separation membranes, especially for hollow fiber membranes (HFMs) with ultrathin skin layer. While conventional thermal crosslinking is an effective method to address this issue, it often leads to the transition layer collapse in HFMs, resulting in a significant decrease in gas permeance. Herein, we fabricate polyimide-cerium (PI-Ce) complex HFMs using a carboxylic group-containing 6FDA-mPDA0.65-DABA0.3-TFMB0.05 copolyimide through metal ion coordination to achieve plasticization-resistance helium recovery from natural gas. We optimized dope compositions and spinning conditions to produce defect-free hollow fiber membranes with a skin layer as thin as 300 nm. The coordination between carboxyl groups and cerium ions was characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The polymer-metal coordinated membranes exhibited enhanced gas selectivities compared to the pristine HFMs due to the tailored microporosity achieved through polymer-metal coordination. Furthermore, the PI-Ce HFMs demonstrated only a 10.8% decline in mixed-gas He/CH4 selectivity, which is significantly lower than the 55.4% decline observed in pristine HFMs when exposed to CO2-containing feed pressures below 400 PSIA. Molecular dynamics simulations confirmed that coordination confined molecular chain swelling, thereby suppressing plasticization caused by CO2. The exceptional plasticization resistance of the PI-Ce complex HFMs provides a novel strategy for recovering helium from aggressive natural gas environments.

Liquid and gas permeabilities of nanostructured layers: Three-dimensional lattice Boltzmann simulation

Liquid water and gas permeabilities in nanostructured catalyst layers (CLs) (pore size ∼10–150 nm) and microporous layers (MPLs) (pore size ∼50 nm-5 μm) are crucial to reduce the mass transport loss in proton exchange membrane fuel cells (PEMFCs). Experimental measurement of their permeabilities poses great challenges due to their brittle and thin characteristics. Presently, considerable discrepancy exists in the reported permeability values for CLs and MPLs in the literature with variation spanning several orders of magnitude. This study digitally reconstructed various nanostructures of similar pore size as CLs and MPLs to calculate their permeabilities using the Lattice Boltzmann Method (LBM) based on no-slip (e.g. for liquid water flow in MPL and CL's secondary pores) or slip condition (e.g. for gas flow in MPL). Analysis was performed to evaluate the range of pore size in nanostructures for the two boundary conditions. A comprehensive investigation was conducted under various parameters such as the Reynolds number (Re), sphere diameter, porosity, and pore structure. The results revealed that permeability exhibits an increasing trend with the diameter and porosity. The predicted permeability of randomly arranged spheres agrees well with established correlations. The random sphere structure demonstrates higher permeability than their body-centered cubic (BCC) and face-centered cubic (FCC) counterparts. Under slip boundary condition, the permeability was enhanced, compared to the no-slip condition. This study's novelty lies in using distinct boundary conditions to assess the permeabilities of liquid and air, based on flow pattern analysis in the CL and MPL pore structures. A new empirical correlation describing the influence of the Knudsen number (Kn) on the slip permeability was developed, exhibiting consistency with simulation across the entire porosity spectrum.

Foamed calcium sulfoaluminate cement with controlled porous network for daily or seasonal heat storage in ettringite

Calcium sulfoaluminate (CSA) cement-based materials have high ettringite content enables heat storage, enhancing the thermal inertia of buildings. This study aims to optimize the porous network of foamed CSA material in terms of porosity, permeability and mechanical strength so that they can be effective in building applications as supporting structures with heat storage capacity. To achieve these goals, a foaming process method using hydrogen peroxide (H2O2) and surfactant was used to control the porous network. The H2O2 and surfactant contents varied from 0.5% to 1.2% and 0.01% to 0.05%, respectively, and generated a wide range of material densities from 589 to 1184 kg/m3 - and hence a wide range of properties in terms of porosity (43 - 70%), permeability (2.6 10-13 - 7.1 10-12 m2) and compressive strength (0.8 -9.4 MPa). Then, an abacus correlating material properties, found by surface fitting, linking porosity, gas permeability and compressive strength, allowed the material to be optimized in accordance with the needs of each building application. The CSA paste consisting of 1% H2O2 and 0.03% surfactant, with 66% porosity, 4.1 10-12 m2 permeability, and 1.8 MPa compressive strength, was the optimal mix-design for solar storage box applications (for short-term storage). The CSA paste consisting of 0.5% H2O2 and 0.01% surfactant, with 43% porosity, 5.6 10-13 m2 permeability, 9.4 MPa compressive strength, appeared to be optimal for self-supporting wall storing solar heat (long-term storage).

Mathematical Modeling of Gas-phase Mass Transfer in Hydrous Materials for a Total Heat Exchange Ventilator

Total heat exchange ventilation systems are effective in achieving energy savings by reducing the ventilation load in buildings, while maintaining a certain amount of fresh outdoor air intake. As the system's elemental materials exchange both latent and sensible heat, hydrophilic chemical compounds may be exchanged simultaneously. Proper control of the exchange of hazardous chemicals and pollutants via these heat exchange elements is an important issue in the development of total heat exchange ventilation systems. In this respect, the development of a numerical model that facilitates repeated sensitivity analysis is important in the development of a new total heat exchanger that has high heat exchange efficiency and suppresses the exchange of polluting chemicals. This study proposes new hygrothermal and chemical compound transfer models for paper-based hydrous materials, which are the main components of total heat exchangers in indoor ventilation systems. Through a series of numerical analyses and experimental measurements, the prediction accuracy of the mathematical model was compared with experimental results for the gas transfer rate in hydrous materials and a building-sized total heat exchanger. The results demonstrated that an increase in water content in hydrous material has a significant impact on the permeability of water-soluble gases, with NH3 and HCHO permeability coefficients increasing by factors of 250 and 20 respectively. Conversely, for low-solubility gases such as CO2, the permeability coefficient only slightly increased at low humidity and remained largely unaffected thereafter. These findings contribute to the advancement of more efficient and safer total heat exchange ventilation systems.

Measurements of Drying and Wetting Gas Diffusion Coefficients and Gas Permeability of Unsaturated Soils Using a New Flexible-Wall Device

Measurements of Drying and Wetting Gas Diffusion Coefficients and Gas Permeability of Unsaturated Soils Using a New Flexible-Wall Device

Modification of pore structure of coal under hot steam injection as revealed by nuclear magnetic resonance

Heat injection provides a feasible approach for the extremely efficient extraction of coalbed gas. Injecting hot steam can effectively improve the pore structure of coal and increase the permeability of coal. To observe the changes in the pore structure of coal during hot steam injection, low magnetic field nuclear magnetic resonance technology is used to study the variations in the pore structure of coal under different heat injection durations. The results show that hot steam can promote the formation, growth, and expansion of coal pore fissures, thereby enhancing the gas permeability of the coal seam. At the same time, the analysis of relevant nuclear magnetic parameters indicates that when the heat injection duration is 15 minutes, hot steam has the best effect on coal modification. In the early stage of hot steam injection, hot steam stimulates the development of the porous structure. In the middle stage, some pore structures collapse and get blocked due to local thermal stress. In the late stage of hot steam injection, hot steam accelerates the conversion of micropore and mesopore structures into macropore or fissure structures, and hot steam has a significant modification effect on coal.

Multifocal Rigid Gas Permeable Contact Lenses with Multi-Tangential Positioning and Corrected Spherical Aberration for Myopia Control

Slowing the progression of myopia has become an extensive concern for parents of children with myopia. According to research findings in animals, eye growth is primarily influenced by the peripheral retina. Treatment options such as orthokeratology, daytime bifocal or multifocal soft contact lens usage are available because they can induce relative myopia in the periphery. In this work, a new multifocal rigid gas permeable (MFRGP) contact lens for myopia prevention and control in adolescents was designed specifically for preventing and controlling myopia in adolescents. This lens features a multi-tangent alignment curve, smaller spherical aberration, and transition defocus. FocalPoints and UPC 100 Vision were used for lens design and lathing, respectively. The lens structure and power profile were measured using IS830 and CONTEST 2, respectively. The elimination of lens aberrations was achieved through design optimization using ZEMAX with ray tracing. Lens fitting was evaluated using slit-lamp microscopy and corneal topography.

Fabrication of high-performance SiC ceramic membranes modified using in situ grown mullite whiskers and high-temperature filtration

The gas permeance and particle removal efficiency of silicon carbide (SiC) membranes are the most important performance indicators for high-temperature gas filtration. The rational design of SiC membrane microstructure has a positive impact on the improvement of performance indicators. This work prepared SiC membranes modified by in situ grown mullite whiskers, optimized their preparation conditions and investigated their performance improvement. The membrane suspension composition and sintering temperature were optimized using Taguchi’s method and gas permeance as the target. The thickness of the membrane was regulated by adjusting the spraying cycles and solid content in membrane suspension. Results showed that best membrane performance was obtained when the content of sintering aids, MoO3, and AlF3·3H2O were 8, 12, and 12 wt%, respectively; the solid concentration in membrane suspension was 30 wt%; the number of spraying cycles was 2, and the temperature was 1350 °C. The resulting membrane obtained a pore size of 5.8 µm and the Darcy's permeability coefficient k was 8.58 × 10−12 m2. It also had good interfacial adhesion and thermal shock and corrosion resistances. The membrane achieved a PM2.5 removal rate of more than 99.9 % at room temperature and high temperatures (100 °C–400 °C) with a low pressure drop below 1.4 kPa. Overall, the SiC ceramic membranes are prospective candidates for dust-laden gas filtration at high temperatures.

Modification of ZIF-8 Membranes for Gas Separation Using X-ray Radiation.

We report an X-ray radiation-induced modification of the structure and gas permeation behavior of ZIF-8 membranes. With 300 min irradiation time, CO2 permeance decreases by only 9%, while N2 and CH4 permeances reduce by 75 and 65%, respectively, leading to 3.7- and 2.6-fold enhancements in ideal selectivity for CO2/N2 and CO2/CH4.

Processing and Properties of Polyhydroxyalkanoate/ZnO Nanocomposites: A Review of Their Potential as Sustainable Packaging Materials

The escalating environmental concerns associated with conventional plastic packaging have accelerated the development of sustainable alternatives, making food packaging a focus area for innovation. Bioplastics, particularly polyhydroxyalkanoates (PHAs), have emerged as potential candidates due to their biobased origin, biodegradability, and biocompatibility. PHAs stand out for their good mechanical and medium gas permeability properties, making them promising materials for food packaging applications. In parallel, zinc oxide (ZnO) nanoparticles (NPs) have gained attention for their antimicrobial properties and ability to enhance the mechanical and barrier properties of (bio)polymers. This review aims to provide a comprehensive introduction to the research on PHA/ZnO nanocomposites. It starts with the importance and current challenges of food packaging, followed by a discussion on the opportunities of bioplastics and PHAs. Next, the synthesis, properties, and application areas of ZnO NPs are discussed to introduce their potential use in (bio)plastic food packaging. Early research on PHA/ZnO nanocomposites has focused on solvent-assisted production methods, whereas novel technologies can offer additional possibilities with regard to industrial upscaling, safer or cheaper processing, or more specific incorporation of ZnO NPs in the matrix or on the surface of PHA films or fibers. Here, the use of solvent casting, melt processing, electrospinning, centrifugal fiber spinning, miniemulsion encapsulation, and ultrasonic spray coating to produce PHA/ZnO nanocomposites is explained. Finally, an overview is given of the reported effects of ZnO NP incorporation on thermal, mechanical, gas barrier, UV barrier, and antimicrobial properties in ZnO nanocomposites based on poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). We conclude that the functionality of PHA materials can be improved by optimizing the ZnO incorporation process and the complex interplay between intrinsic ZnO NP properties, dispersion quality, matrix–filler interactions, and crystallinity. Further research regarding the antimicrobial efficiency and potential migration of ZnO NPs in food (simulants) and the End-of-Life will determine the market potential of PHA/ZnO nanocomposites as active packaging material.

Effect of the Cathodic Gas Diffusion Layer on the Performance of a Proton Exchange Membrane Electrolyzer

Hydrogen production through electrolysis using renewable resources is highly promising for reducing greenhouse gas emissions. While significant efforts have focused on developing more efficient and cost-effective catalysts to lower hydrogen production costs, catalysts are not the primary expense in electrolyzer fabrication. In the case of Proton Exchange Membrane Water Electrolyzers (PEMWEs), other components—such as the proton membrane, gas diffusion layer (GDL), and bipolar plates—contribute more to overall costs. To explore this, a study was conducted on the performance of PEMWEs with various carbon paper GDLs, developed in the lab, on the cathodic side. This study examined how properties like electrical conductivity, porosity, and gas permeability affect performance. These findings emphasize the need to optimize components beyond catalysts to improve the cost-effectiveness of hydrogen production through electrolysis.

Impact of gas adsorption of nitrogen, argon, methane, and CO2 on gas permeability in nanoporous rocks

Gas adsorption on the surface of nanoporous rocks is an important process that occurs in many applied scenarios such as shale gas production or CO2 enhanced gas recovery or storage. While there are few theoretical considerations on the effect of gas adsorption on permeability, a systematic laboratory investigation of the impact of gas adsorption on gas flow and permeability is still lacking. In this paper, permeability of four adsorptive gases, i.e., nitrogen, argon, methane, and carbon dioxide, was measured, along with helium permeability, for two nanoporous rock samples that have high and low total organic carbon (TOC) content, respectively. The measurements were conducted at a range of pore pressures from 150 to 1500 psi (1.03–10.34 MPa). Gas adsorption isotherms were also measured at the same conditions. A mathematical model that considers adsorption with specific boundary conditions for the experimental setup was used for data analysis. The results show that gas adsorption causes larger drop in pressure decay and greater retardation in pressure equilibrium. However, the reduction of permeability relative to helium (25%–46%) is similar for gases with different levels of adsorption, indicating the occurrence of single-layer adsorption for these gases. Comparison between the two samples further supports the concept of single-layer adsorption and signifies the impact of pore size on the permeability reduction due to adsorption. These new findings deepen the fundamental understanding and provide important clarification on the effect of gas adsorption on gas flow and permeability in nanoporous rocks.