Surface Permeabilities Research Articles

Modeling of multi-mechanisms permeability for hydrogen separation using a membrane process

In gas separation using nanoporous membranes, both operating conditions and membrane properties are key to the process performance. Mathematical modeling is crucial for defining the optimal conditions and properties for the optimization and design of these processes. This research introduces a comprehensive model that integrates surface and pore permeabilities for studying the (PIM-1) membrane performance for H2/N2 separation. The model combines empirical and solution-diffusion models to examine temperature and pressure effects alongside a theoretical approach for assessing how pore size and porosity influence permeability and selectivity. Simulation results indicated that temperature increases from 298 K to 373 K significantly enhanced hydrogen and nitrogen permeability by 13% and 135%, respectively, while the selectivity dropped from 24.6 to 15.3. On the other hand, the pressure effect was less significant compared to the effect. The study also highlighted the critical roles of pore size and porosity in transport mechanisms and membrane performance, showing that increasing the pore size and porosity enhanced permeability and reduced selectivity. Remarkably, PIM-1 membranes with pore sizes of near 1 nm and porosity below 0.1 exceeded the Robeson 2008 upper limit, showcasing improved permeability with good selectivity. This model offers a predictive tool for PIM-1 membrane performance under various conditions, facilitating the design of efficient separation process.

Decorating the Node of a Zirconium-Based Metal-Organic Framework to Tune Adsorption Behavior and Surface Permeation.

Surface barriers are commonly observed in nanoporous materials. Although researchers have explored methods to repair defects or create flawless crystals to mitigate surface barriers, these approaches may not always be practical or readily achievable in targeted metal-organic frameworks (MOFs). In our study, we propose an alternative approach focusing on the introduction of diverse ligands onto a MOF-808 node to finely adjust its adsorption and mass transport characteristics. Significantly, our findings indicate that while adsorption curves can be inferred based on the MOF's chemical composition and the probing molecule, surface permeabilities exhibit variations dependent on the specific probe utilized and the incorporated ligand. Our investigation, considering van der Waals forces exclusively between the adsorbate (e.g., n-hexane, propane, and benzene) and the adsorbent, revealed that augmenting these interactions can indeed improve surface permeation to a certain extent. Conversely, strong adsorption resulting from hydrogen bonding interactions, particularly with water in modified MOFs, led to compromised permeation within the MOF crystals. These outcomes provide valuable insights for the porous materials community and offer guidance in the development of adsorbents with enhanced affinity and superior mass transport properties for gases and vapors.

Soap-Film Membranes for CO2/Air Separation.

Thin liquid films are a potential game changer in the quest for efficient gas separation strategies. Such fluid membranes, which are complementary to their solid counterparts involving porous materials, can achieve complex separation by combining permeability and adsorption mechanisms in their liquid core and at their surface. In addition, unlike porous solid membranes that must be regenerated between separation steps to recover a gas-free porosity, thus preventing continuous operation, liquid membranes can be regenerated using continuous liquid flow through the fluid film. Here, building on the self-sustained mobile film technique, we propose a simple experimental setup allowing direct quantitative assessment of the gas permeability of soap films stabilized by different surfactant types. Using a simple prototypical example involving O2/N2 mixtures, the measurement principle is first presented to establish a proof of concept. As the gas solubilities and diffusivities are known, the results of such experiments can be compared with microscopic models to disentangle the liquid core and surface permeabilities from a direct macroscopic transport response of the film subjected to a gas concentration difference. The same dynamical experiments performed for air enriched in CO2 indicate that the permeability of the soap film varies with the molar fraction in the gas compartment, a feature not observed for O2/N2. These experimental findings pave the way for the design of novel separation technologies in fields and situations where porous solid membranes are of limited efficiency.

Influence of Pore Size on Hydrocarbon Transport in Isostructural Metal-Organic Framework Crystallites.

Hydrocarbon separations using porous materials such as metal-organic frameworks (MOFs) have been proposed to reduce the energy demands associated with current distillation-based methods. Despite the potential of these materials to distinguish hydrocarbons through thermodynamic or kinetic mechanisms, experimental data quantifying hydrocarbon transport in MOFs is lacking. Such mass transfer measurements are vital to elucidate structure-property relationships and design future high-performing separation materials. In this work, we aim to isolate the influence of pore size on hydrocarbon diffusion by studying a pair of isoreticular MOFs, Co2Cl2BBTA and Co2Cl2BTDD. We use a volumetric method to extract mass transport coefficients for six hydrocarbon probe molecules of varying size and chemical functionality. From these nonequilibrium mass transport measurements, we determine the rate-limiting diffusion mechanism and identify trends in hydrocarbon surface permeabilities in the MOFs based on pore size, hydrocarbon chain length, and temperature.

CO2 and CH4 diffusivities through synthesized ZIF-8 nanocrystals: An experimental and theoretical investigation

CO 2 separation is of paramount importance owing to global warming abatement, as well as sour natural gas sweetening. Mixed matrix membranes (MMMs), containing porous zeolitic imidazolate frameworks (ZIFs), in particular ZIF-8, have drawn noticeable attention due to their favorable separation performance. However, there are evidences of discrepancies in the reported values of gas diffusion coefficients/diffusivities through ZIFs, even for common well-studied gases, such as CO 2 and CH 4 in the literature. These discrepancies might be attributed to the surface/barrier effects, which are intensified by ZIF-8 nanocrystals downsizing. In this paper, an effort has been made to determine the impact of these surface effects on diffusivities of CO 2 and CH 4 through ZIF-8 nanocrystals. To do so, ZIF-8 nanocrystals ( ~ 100 nm), pristine poly(ethylene glycol diacrylate) (PEGDA) membrane, and PEGDA/ZIF-8 mixed matrix membranes (MMMs) were prepared. Gas adsorption/sorption measurements for CO 2 and CH 4 over a temperature range of (308–348) K were conducted. The Maxwell model was applied to obtain gas permeabilities in pure ZIF-8 nanocrystals by employing the measured values of permeabilities through fabricated MMMs. The solubilities in ZIF-8 nanocrystals were found using adsorption isotherms, and the corrected/intracrystalline diffusivities were subsequently obtained using solution–diffusion theory. Moreover, the apparent/extracrystalline diffusivity values, affected by the surface effects, were attained from transient uptake rate measurements, and were compared to the corrected ones. The surface effects were eventually determined via a single-resistance model. • Surface effects of ZIF-8 nanocrystals against diffusion of CO 2 and CH 4 were investigated. • Surface permeabilities of CO 2 and CH 4 in ZIF-8 were obtained in the range of 10 −8 cm s −1 . • Corrected transport diffusivities were corresponding to intracrystalline diffusivities. • Extracrystalline diffusivities were found seven orders of magnitude lower than the intracrystalline diffusivities.

Asymmetric layer‐by‐layer polyelectrolyte nanofiltration membranes with tunable retention

AbstractNanofiltration (NF) membrane processes are attractive to remove multivalent ions. As ion retention in NF membranes is determined by both size and charge exclusion, negatively charged membranes are required to reject negatively charged ions. Layer‐by‐layer assembly of alternating polycation (PC) and polyanion layers on top of a support is a versatile method to produce membranes. Especially the polyelectrolyte (PE) couple polydiallyldimethylammoniumchloride and poly(sodium‐4‐styrenesulfonate) (PDADMAC/PSS) is extensively investigated. This PE couple cannot form highly negatively charged membrane surfaces, due to interdiffusion and charge overcompensation of PDADMAC into the PSS layers, which limits the operational window to tailor membrane properties. We propose the use of asymmetric layer formation and show how combining two charge densities of one PC can produce negatively charged NF membranes. Starting from hollow fiber ultrafiltration supports coated with base layers of PDADMAC/PSS, they are coated with PDADMAC/PSS or poly(acrylamide‐co‐diallyldimethylammoniumchloride), P(AM‐co‐DADMAC)/PSS layers. P(AM‐co‐DADMAC) has a charge density of only 32% compared to 100% for PDADMAC. The particular novel membranes coated with P(AM‐co‐DADMAC) have a highly negatively charged surface and high permeabilities (7–19 L/[m2hbar]), with high retentions for Na2SO4 of up to 95%. These values position the developed membranes in the top range compared to commercial and other layer‐by‐layer membranes.

Estimates for the Effective Permeability of Intact Granite Obtained from the Eastern and Western Flanks of the Canadian Shield

Granitic rock from the western part of the Canadian Shield is considered as a potential host rock for the siting of a deep geological repository for the storage of heat-emitting high-level nuclear fuel waste. The research program focused on the use of surface permeability measurements conducted at 54 locations on a 300 mm cuboid of granite, obtained from the Lac du Bonnet region in Manitoba, to obtain an estimate for the effective permeability of the cuboid. Companion experiments are conducted on a 280 mm cuboid of granite obtained from Stanstead, Quebec, located in the eastern part of the Canadian Shield. The surface permeabilities for the cuboids of granite are developed from theoretical relationships applicable to experimental situations where steady flow is initiated at a sealed annular surface region with a pressurized central domain. The experimental values for the surface permeability are used with a kriging procedure to estimate the permeability variations within the cuboidal region. The spatial variations of permeability are implemented in computational models of the cuboidal regions to determine the one-dimensional permeabilities in three orthogonal directions. The effective permeability of the granite cuboids is estimated by appeal to the geometric mean. The research provides a non-destructive methodology for estimating the effective permeability of large specimens of rock and the experiments performed give estimates for the effective permeability of the two types of granitic rock obtained from the western and eastern flanks of the Canadian Shield.

Flying too close to the Sun – The viability of perihelion-induced aqueous alteration on periodic comets

Comets are typically considered to be pristine remnants of the early solar system. However, by definition they evolve significantly over their lifetimes through evaporation, sublimation, degassing and dust release. This occurs once they enter the inner solar system and are heated by the Sun. Some comets (e.g. 1P/Halley, 9P/Tempel and Hale-Bopp) as well as chondritic porous cosmic dust – released from comets – show evidence of minor aqueous alteration resulting in the formation of phyllosilicates, carbonates or other secondary phases (e.g. Cu-sulphides, amphibole and magnetite). These observations suggest that (at least some) comets experienced limited interaction with liquid water under conditions distinct from the alteration histories of hydrated chondritic asteroids (e.g. the CM and CR chondrites).This synthesis paper explores the viability of perihelion-induced heating as a mechanism for the generation of highly localised subsurface liquid water and thus mild aqueous alteration in periodic comets. We draw constraints from experimental laboratory studies, numerical modelling, spacecraft observations and microanalysis studies of cometary micrometeorites. Both temperature and pressure conditions necessary for the generation and short-term (hour-long) survival of liquid water are plausible within the immediate subsurface (<0.5 m depth) of periodic comets with small perihelia (<1.5 A.U.), low surface permeabilities and favourable rotational states (e.g. high obliquities and/or slow rotational periods). We estimate that solar radiant heating may generate liquid water and perform aqueous alteration reactions in 3–9% of periodic comets. An example of an ideal candidate is 2P/Encke which has a small perihelion (0.33 A.U.), a high obliquity and a short orbital period. This comet should therefore be considered a high priority candidate in future spectroscopic studies of comet surfaces. Small quantities of phyllosilicate generated by aqueous alteration may be important in cementing together grains in the subsurface of older dormant comets, thereby explaining observations of unexpectedly high tensile strength in some bodies.Most periodic comets which currently pass close to the Sun are dormant, having experienced surface heating, significant cometary activity and dust release in the past. These bodies may be responsible for the partially hydrated cometary micrometeorites we find at the Earth's surface and their aqueous alteration histories may have been produced by perihelion-induced subsurface heating. This is in contrast to radiogenic and impact heating that operated during the early solar system on asteroids. This study has implications for the alteration history of the active asteroid Phaethon, the target of JAXA's DESTINY+ mission.

Investigating hydrological contributions to volcano monitoring signals: a time-lapse gravity example

SUMMARY Geophysical techniques are widely used to monitor volcanic unrest. A number of studies have also demonstrated that hydrological processes can produce or trigger geophysical signals. Hydrologically induced gravity signals have previously been recorded by specifically designed gravitysurveysaswellas,inadvertently,byvolcanomonitoringstudies.Watertablecorrections ofmicrogravitysurveysarecommonplace.However,thefluctuationsofthewatertablebeneath survey locations are often poorly known, and such a correction fails to account for changes in water-mass storage in the unsaturated zone. Here, we combine 2-D axis-symmetrical numerical fluid-flow models with an axis-symmetric, distributed-mass, gravity calculation to model gravity changes in response to fluctuating hydrological recharge. Flow simulations are based on tropical volcanic settings where high surface permeabilities promote thick unsaturated zones. Our study highlights that mass storage (saturation) changes within the unsaturated zone beneath a survey point can generate recordable gravity changes. We show that for a tropical climate, recharge variations can generate gravity variations of over 150 µGal; although, we demonstrate that for the scenarios investigated here, the probability of recording such large signals is low. Our modelling results indicate that microgravity survey corrections based on water table elevation may result in errors of up to 100 µGal. The effect of inter-annual recharge fluctuations dominate over seasonal cycles which makes prediction and correction of the hydrological contribution more difficult. Spatial hydrogeological heterogeneity can also impact on the accuracy of relative gravity surveys, and can even result in the introduction of additional survey errors. The loading fluctuations associated with saturation variations in the unsaturated zone may also have implications for other geophysical monitoring techniques, such as geodetic monitoring of ground deformation.

Imaging of transient guest profiles in nanoporous host materials: a new experimental technique to study intra-crystalline diffusion

The application of interference microscopy (IFM) and infrared microscopy (IRM) to monitoring transient concentration profiles during uptake and release of guest molecules in nanoporous materials has opened a novel technique for diffusion studies with adsorbed molecules. For the first time, the coefficients of transport diffusion and the surface permeabilities have become accessible by direct observation under non-equilibrium conditions. The examples presented in this communication include diffusion and permeation measurements with zeolites of the ferrierite type and with metal-organic frameworks (MOFs) of type ZIF-8

Assessing Surface Permeabilities from Transient Guest Profiles in Nanoporous Host Materials

Easy come, easy go? Transport resistances on particle surfaces are important for mass transfer in nanoporous materials and bulk diffusion in crystals. Interference microscopy and IR micro-imaging are shown to be excellent tools for determining such transport resistances. By studying short-chain-length alkane guest molecules in crystals of the metal-organic framework compound Zn(tbip) a data collection of surface permeabilities is established.

Mass transfer in one-dimensional nanoporous crystals with different surface permeabilities

Mass transfer in one-dimensional nanoporous crystals with different surface permeabilities

The options of interference microscopy to explore the significance of intracrystalline diffusion and surface permeation for overall mass transfer on nanoporous materials

After a short introduction into interference microscopy and its potentials in monitoring transient concentration profiles in nanoporous materials, we concentrate on the special options of an analysis of these profiles close to the crystal surfaces. We shall in particular introduce a novel route of correlating the overall uptake, at a certain instant of time, with the current boundary concentration. In this way, the significance of surface resistances to overall molecular uptake may be most vividly demonstrated. Considering a large variety of nanoporous host-guest systems, including methanol in zeolites ferrierite, methanol in MOF Manganese(II)-formate and methanol in SAPO STA-7, quite different patterns of surface resistivities may be observed. A generalized analysis is complicated by the fact that both the diffusivities and the surface permeabilities are found to notably depend on the actual concentration. As a consequence, for one and the same system and over identical pressure steps, the relative contributions of diffusion and surface permeation to the overall process may be quite different for desorption and adsorption.

Intracrystalline Diffusivities and Surface Permeabilities Deduced from Transient Concentration Profiles: Methanol in MOF Manganese Formate

The intracrystalline concentration profiles during molecular uptake of methanol by an initially empty, single crystal of microporous manganese(II) formate (Mn(HCO2)2), representing an ionic inorganic-organic hybrid within the MOF family, are monitored by interference microscopy. Within these profiles, a crystal section could be detected where over the total of its extension ( approximately 2 microm x 50 microm x 30 microm) molecular uptake ideally followed the pattern of one-dimensional diffusion. Analysis of the evolution of intracrystalline concentration in this section directly yields the permeability of the crystal surface and the intracrystalline diffusivity as a function of the concentration of the total range of 0 <or= theta <or= 0.57 covered in the experiments. Within this range, the surface permeability is found to increase by 1 order of magnitude, while, within the limits of accuracy (+/-30%), the transport diffusivity remains constant, thus reflecting the properties of the lattice gas model.

Numerical modeling of the origin of calcite mineralization in the Refugio‐Carneros fault, Santa Barbara Basin, California

AbstractMany faults in active and exhumed hydrocarbon‐generating basins are characterized by thick deposits of carbonate fault cement of limited vertical and horizontal extent. Based on fluid inclusion and stable isotope characteristics, these deposits have been attributed to upward flow of formation water and hydrocarbons. The present study sought to test this hypothesis by using numerical reactive transport modeling to investigate the origin of calcite cements in the Refugio‐Carneros fault located on the northern flank of the Santa Barbara Basin of southern California. Previous research has shown this calcite to have low δ13C values of about −40 to −30‰PDB, suggesting that methane‐rich fluids ascended the fault and contributed carbon for the mineralization. Fluid inclusion homogenization temperatures of 80–125°C in the calcite indicate that the fluids also transported significant quantities of heat. Fluid inclusion salinities ranging from fresh water to seawater values and the proximity of the Refugio‐Carneros fault to a zone of groundwater recharge in the Santa Ynez Mountains suggest that calcite precipitation in the fault may have been induced by the oxidation of methane‐rich basinal fluids by infiltrating meteoric fluids descending steeply dipping sedimentary layers on the northern basin flank. This oxidation could have occurred via at least two different mixing scenarios. In the first, overpressures in the central part of the basin may have driven methane‐rich formation waters derived from the Monterey Formation northward toward the basin flanks where they mixed with meteoric water descending from the Santa Ynez Mountains and diverted upward through the Refugio‐Carneros fault. In the second scenario, methane‐rich fluids sourced from deeper Paleogene sediments would have been driven upward by overpressures generated in the fault zones because of deformation, pressure solution, and flow, and released during fault rupture, ultimately mixing with meteoric water at shallow depth. The models in the present study were designed to test this second scenario, and show that in order for the observed fluid inclusion temperatures to be reached within 200 m of the surface, moderate overpressures and high permeabilities were required in the fault zone. Sudden release of overpressure may have been triggered by earthquakes and led to transient pulses of accelerated fluid flow and heat transport along faults, most likely on the order of tens to hundreds of years in duration. While the models also showed that methane‐rich fluids ascending the Refugio‐Carneros fault could be oxidized by meteoric water traversing the Vaqueros Sandstone to form calcite, they raised doubts about whether the length of time and the number of fault pulses needed for mineralization by the fault overpressuring mechanism were too high given existing geologic constraints.

Surface barriers on nanoporous particles: A new method of their quantitation by PFG NMR

The surface permeability of zeolite crystals of type NaCaA for small alkane molecules (methane and ethane) was estimated by using a novel method, analysing NMR tracer desorption measurements. It is based on the measurement of both the relative amount of tracer exchange and the corresponding effective coefficients of intracrystalline diffusion and their correlation with the results of model calculations by dynamic Monte Carlo simulations. For the two LTA specimens investigated, already in the as-synthesized zeolite crystals notable surface resistances have been observed. Surface permeabilities have been studied in dependence on temperature, sorbate and crystal size.

Exploring the surface permeability of nanoporous particles by pulsed field gradient NMR

A new method to determine the surface permeability of nanoporous particles is proposed. It is based on the comparison of experimental data on tracer exchange and intracrystalline molecular mean square displacements as obtained by the PFG NMR tracer desorption technique with the corresponding solutions of the diffusion equation via dynamical Monte Carlo simulations. The method is found to be particularly sensitive in the “intermediate” regime, when the influence of intracrystalline diffusion and surface resistances of the nanoporous crystal on molecular transport are comparable and the conventional method fails. As an example, the surface permeabilities of two samples of zeolite NaCaA with different crystal sizes are determined with methane, as a probe molecule, at room temperature.

Multiphase Flow Dynamics, Volume 1: Fundamentals; Volume 2: Thermal and Mechanical Interactions

Multiphase Flow Dynamics, Volume 1: Fundamentals; Volume 2: Thermal and Mechanical Interactions

THREE DIMENSIONAL NUMERICAL SIMULATION OF SHELL-AND-TUBE HEAT EXCHANGERS. PART I: FOUNDATION AND FLUID MECHANICS

A three-dimensional, colocated, fully implicit, control volume based calculation procedure, HEATX[1], has been used to simulate fluid flow and heal transfer in shell-and-tube heat exchangers. The three-dimensional numerical model uses the distributed resistance method along with volumetric porosities and surface permeabilities to model the tubes in the heat exchanger. Turbulence effects are modeled using a modified k-ϵ model with additional source terms for turbulence generation and dissipation by tubes. Shell and baffle walk are modeled using the wall function approach. Tubes and baffles are modeled using volumetric porosities and surface permeabilities. Baffle-shell and baffle-tube leakages are modeled using a Bernoulli type formulation. Specialized geometry generators compute baffle, nozzle, and tube region porosities and permeabilities. This article presents the foundation and fluid mechanics of the problem. A subsequent article will discuss modeling of shell-side and tube-side heat transfer. The three-dimensional numerical model is validated by comparison of computed pressure drops with the experiments conducted at Argonne National Labs [2] in E shell type heat exchangers. The effect of baffle cut and baffle spacing on the pressure drop is studied. Good agreement is obtained between the computed results and the experiments.

THREE-DIMENSIONAL NUMERICAL SIMULATION OF SHELL-AND-TUBE HEAT EXCHANGERS. PART II: HEAT TRANSFER

A three-dimensional, allocated, fully implicit control volume based calculation procedure HEATX [1] has been developed over the past 3 years to simulate flow and heat transfer in sheU-and-tube heat exchangers. The three-dimensional model uses the distributed resistance concept of Patankar and Spalding [2], in conjunction with surface permeabilities and volumetric porosities to model the tubes in the heat exchanger. Part I of this article describes the details of the distributed resistance formulation, leakage modeling, geometry modeling, and the turbulence model. Details of the shell-side and tube-side heat transfer are given in this second part. The tube-side temperature field is computed by solving an enthalpy equation for the tube-side fluid. Coupling between the shell-side and the tube-side equations is described, and numerical results are compared with the Delaware project experimental data. We have made use of the symmetry of the heat exchanger to speed up our calculations. Good agreement was obtained between our three-dimensional numerical simulations and experimental results for overall pressure drop and temperature differences. Computed overall pressure drops and temperature differences were within 15% of experimental results.