103 results found
Ward A, Pini R, 2022, Efficient Bayesian Optimisation of Industrial-scale Pressure-Vacuum Swing Adsorption Processes for CO2 Capture, Industrial and Engineering Chemistry Research, ISSN: 0888-5885
Azzan H, Rajagopalan AK, L'Hermitte A, et al., 2022, Simultaneous estimation of gas adsorption equilibria and kinetics of individual shaped adsorbents, Chemistry of Materials, ISSN: 0897-4756
Shaped adsorbents (e.g. pellets, extrudates) are typically employed in several gasseparation and sensing applications. The performance of these adsorbents is dictated bytwo key factors, their adsorption equilibrium capacity and kinetics. Often, adsorptionequilibrium and textural properties are reported for materials. Adsorption kinetics areseldom presented due to the challenges associated with measuring them. The overarching goal of this work is to develop an approach to characterize the adsorption propertiesof individual shaped adsorbents with less than 100 mg of material. To this aim, we havedeveloped an experimental dynamic sorption setup, complemented it with mathematical models, to describe the mass transport in the system. We embed these models into a derivative-free optimizer to predict model parameters for adsorption equilibrium andkinetics. We evaluate and independently validate the performance of our approach onthree adsorbents that exhibit di↵erences in their chemistry, synthesis, formulation andtextural properties. Further, we test the robustness of our mathematical frameworkusing a digital twin. We show that framework can rapidly (i.e. in a few hours) andquantitatively characterize adsorption properties at a milligram scale, making it suitedfor screening of novel porous materials.
Pini R, Siderius DW, Siepmann JI, 2022, Preface to Adsorption and Diffusion in Porous Materials Special Issue: Equilibrium Adsorption Data for Energy and Environmental Applications, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 67, Pages: 1597-1598, ISSN: 0021-9568
Hwang J, Azzan H, Pini R, et al., 2022, H2, N2, CO2, and CH4 unary adsorption isotherm measurements at low and high pressures on zeolitic imidazolate framework ZIF-8, Journal of Chemical & Engineering Data, Vol: 67, Pages: 1674-1686, ISSN: 0021-9568
Excess adsorption of CO2, CH4, N2, and H2 on ZIF-8 was measured gravimetrically in the pressure range ranging from vacuum to 30 MPa at 298.15, 313.15, 333.15, 353.15, and 394.15 K using a magnetic suspension balance. The textural properties of the adsorbent material─i.e., skeletal density, surface area, pore volume, and pore-size distribution─were estimated by helium gravimetry and N2 (77 K) physisorption. The adsorption isotherms were fitted with the Sips isotherm model and the virial equation, and the values of isosteric heat of adsorption and Henry constants for the gases were determined using the latter.
Fan D, Chapman E, Khan A, et al., 2022, Anomalous transport of colloids in heterogeneous porous media: a multi-scale statistical theory, Journal of Colloid and Interface Science, Vol: 617, Pages: 94-105, ISSN: 0021-9797
HypothesisTransport of suspended colloids in heterogeneous porous media is a multi-scale process that exhibits anomalous behavior and cannot be described by the Fickian dispersion theory. Although many studies have documented colloids’ transport at different length scales, a theoretical basis that links pore- to core-scale observations remains lacking. It is hypothesized that a recently proposed pore-scale statistical kinetic theory is able to capture the results observed experimentally.ExperimentsWe implement a multi-scale approach via conducting core-flooding experiments of colloidal particles in a sandstone sample, simulating particles flowing through a sub-volume of the rock’s digital twin, and developing a core-scale statistical theory for particles’ residence times via upscaling the pore-scale kinetic theory. Experimental and computational results for solute transport are used as benchmark.FindingsBased on good agreement across the scales achieved in our investigation, we show that the macroscopically observed anomalous transport is particle-type dependent and stems from particles’ microscopic dispersion and deposition in heterogeneous flow fields. In particular, we reveal that residence-time distributions (i.e., breakthrough curve) obey a closed-form function that encompasses particles’ microscopic dynamics, which allows investigations of a whole transition from pre-asymptotic to asymptotic behavior. The physical insights attained could be useful for interpreting experimental data and designing colloidal tracers.
Ward A, Pini R, 2022, Integrated uncertainty quanti cation and sensitivity analysis of single-component dynamic column breakthrough experiments, Adsorption, Vol: 28, Pages: 161-183, ISSN: 0929-5607
We have carried out the traditional analysis of a set of dynamic breakthrough experiments on the CO2/He system adsorbing onto activated carbon by fitting a 1D dynamic column breakthrough model to the transient experimental profiles. We have quantified the uncertainties in the fitted model parameters using the techniques of Bayesian inference, and have propagated these parametric uncertainties through the dynamic model to assess the robustness of the modelling. We have found significant uncertainties in the outlet mole fraction profile, internal temperature profile and internal adsorption profiles of approximately ±15%. To assess routes to reduce these uncertainties we have applied a global variance-based sensitivity analysis to the dynamic model using the Sobol method. We have found that approximately 70% of the observed variability in the modelling outputs can be attributed to uncertainties in the adsorption isotherm parameters that describe its temperature dependence. We also make various recommendations for practitioners, using the developed Bayesian statistical tools, regarding the choice of the isotherm model, the choice of the fitting data for the extraction of system specific parameters and the simplification of the wall energy balance.
Ansari H, Gong S, Trusler J, et al., 2022, Hybrid pore-scale adsorption model for CO2 and CH4 storage in shale, Energy and Fuels, Vol: 36, ISSN: 0887-0624
Making reliable estimates of gas adsorption in shale remains a challenge becausethe variability in their mineralogy and thermal maturity results in a broad distributionof pore-scale properties, including size, morphology and surface chemistry. Here, wedemonstrate the development and application of a hybrid pore-scale model that usessurrogate surfaces to describe supercritical gas adsorption in shale. The model is basedon the lattice Density Functional Theory (DFT) and considers both slits and cylindrical pores to mimic the texture of shale. Inorganic and organic surfaces associatedwith these pores are accounted for by using two distinct adsorbate-adsorbent interaction energies. The model is parameterised upon calibration against experimentaladsorption data acquired on adsorbents featuring either pure clay or pure carbon surfaces. Therefore, in its application to shale, the hybrid lattice DFT model only requiresknowledge of the shale-specific organic and clay content. We verify the reliability ofthe model predictions by comparison against high-pressure CO2 and CH4 adsorptionisotherms measured at 40 ◦C in the pressure range 0.01–30 MPa on four samples fromthree distinct plays, namely the Bowland (UK), Longmaxi (China) and Marcellus shale1(USA). Because it uses only the relevant pore-scale properties, the proposed model canbe applied to the analysis of other shales, minimising the heavy experimental burdenassociated with high pressure experiments. Moreover, the proposed development hasgeneral applicability meaning that the hybrid lattice DFT can be used to the characterisation of any adsorbent featuring morphologically and chemically heterogeneoussurfaces.
Huang Z, Kurotori T, Pini R, et al., 2022, Three-Dimensional Permeability Inversion Using Convolutional Neural Networks and Positron Emission Tomography, WATER RESOURCES RESEARCH, Vol: 58, ISSN: 0043-1397
Siepmann JI, Gardas R, Kofke DA, et al., 2022, The Journal of Chemical & Engineering Data: Introduction of Topical Sections and Updates from the Editorial Team, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 67, Pages: 1-2, ISSN: 0021-9568
Joewondo N, Garbin V, Pini R, 2022, Nonuniform collective dissolution of bubbles in regular pore networks, Transport in Porous Media, Vol: 141, Pages: 649-666, ISSN: 0169-3913
Understanding the evolution of solute concentration gradients underpins the prediction of porous media processes limited by mass transfer. Here, we present the development of a mathematical model that describes the dissolution of spherical bubbles in two-dimensional regular pore networks. The model is solved numerically for lattices with up to 169 bubbles by evaluating the role of pore network connectivity, vacant lattice sites and the initial bubble size distribution. In dense lattices, diffusive shielding prolongs the average dissolution time of the lattice, and the strength of the phenomenon depends on the network connectivity. The extension of the final dissolution time relative to the unbounded (bulk) case follows the power-law function, Bk/ℓ, where the constant ℓ is the inter-bubble spacing, B is the number of bubbles, and the exponent k depends on the network connectivity. The solute concentration field is both the consequence and a factor affecting bubble dissolution or growth. The geometry of the pore network perturbs the inward propagation of the dissolution front and can generate vacant sites within the bubble lattice. This effect is enhanced by increasing the lattice size and decreasing the network connectivity, yielding strongly nonuniform solute concentration fields. Sparse bubble lattices experience decreased collective effects, but they feature a more complex evolution, because the solute concentration field is nonuniform from the outset.
Delle Piane C, Ansari H, Li Z, et al., 2022, Influence of organic matter type on porosity development in the Wufeng-Longmaxi Shale: A combined microscopy, neutron scattering and physisorption approach, International Journal of Coal Geology, Vol: 249, Pages: 1-15, ISSN: 0166-5162
The upper Ordovician Wufeng Shale and lower Silurian Longmaxi Shale are part of the Fuling shale gas play located in the south-eastern part of the Sichuan Basin, southern China, representing the first commercial shale gas production project outside North America. We studied the occurrence of porosity at the micro- and nano-scale in samples of contrasting organic richness representing the typical lithofacies from the post-mature part of the Wufeng-Longmaxi gas play. Using a combination of site specific, high-resolution scanning and transmission electron microscopy with bulk measurements based on small angle neutron scattering and cryogenic Argon physisorption, along with conventional organic petrology, we highlight the impact of different types of organic matter (OM) (primary versus secondary) on the development of OM-hosted porosity. The results indicate that at the bulk scale the overall porosity in the samples is proportional to their organic content and organic hosted pore account for 30–40% of the total pore volume of the rocks. Nevertheless, most of the pores identified via electron microscopy imaging seem to reside in the organic matter, indicating that potentially a large part of the pores volume detected by neutron scattering and Argon physisorption is visually not detected. Organic matter focused nanoscale imaging revealed that mesopores are preferentially present in the solid bitumen and not in the primary detrital organic particles. Organic lean samples show low porosity and dominance of micropores, while organic-rich samples show higher porosity and a broader spectrum of pore sizes. Importantly, most of the meso pores are located in organic matter petrographically interpreted as solid bitumen, while detrital organic particles like graptolites show minimal visible porosity under high resolution electron microscopy and pore sizes in the micro pore range (i.e. <2 nm).Distinguishing between primary and secondary OM is therefore important for underst
Kuusela P, Pour-Ghaz M, Pini R, et al., 2021, Imaging of reactive transport in fractured cement-based materials with X-ray CT, Cement and Concrete Composites, Vol: 124, Pages: 1-12, ISSN: 0958-9465
The need to improve the understanding of the properties of cement-based materials calls for the development of tools for visualizing and quantifying chemicalreactions and flows of fluids within them. In this paper, we report the results ofan experimental study where a sample of fractured cement-paste was subjectedto injection of fluids (krypton, CO2 and water) and imaged simultaneously byX-ray computed tomography (CT). Initial porosity of the sample was estimatedusing a subtraction method based on CT scans taken initially and during krypton injection. The CT reconstructions were segmented to visualize crack patterns and fluid flow in three-dimensions and to quantify the evolution of porosityduring the experiment. The results show that CT captures the formation of acarbonate phase in the sample during CO2 injection, and the flow of water inthe fractured media. We quantify the reduction of porosity resulting from thecarbonation reaction. We observe that the newly formed carbonated layer impedes water flow and, locally, can lead to crack healing. The results demonstratethe ability of CT to image reactive transport in cement-based materials, andsupport the feasibility of this imaging tool for their characterization.
Ansari H, Rietmann E, Joss L, et al., 2021, A shortcut pressure swing adsorption analogue model to estimate gas-in-place and CO2 storage potential of gas shales, Fuel: the science and technology of fuel and energy, Vol: 301, Pages: 1-13, ISSN: 0016-2361
Natural gas extraction from shale formations has experienced a rapid growth in recent years, but the low recovery observed in many field operations demonstrates that the development of this energy resource is far from being optimal. The ambiguity in procedures that account for gas adsorption in Gas-in-Place calculations represents an important element of uncertainty. Here, we present a methodology to compute gas production curves based on quantities that are directly accessed experimentally, so as to correctly account for the usable pore-space in shale. We observe that adsorption does not necessarily sustain a larger gas production compared to a non-adsorbing reservoir with the same porosity. By analysing the entire production curve, from initial to abandonment pressure, we unravel the role of the excess adsorption isotherm in driving this behaviour. To evaluate scenarios of improved recovery by means of gas injection, we develop a proxy reservoir model that exploits the concept of Pressure Swing Adsorption used in industrial gas separation operations. The model has three stages (Injection/Soak/Production) and is used to compare scenarios with cyclic injection of CO2 or N2. The results show that partial pressure and competitive adsorption enhance gas production in complementary ways, and reveal the important trade-off between CH4 recovery and CO2 storage. In this context, this proxy model represents a useful to tool to explore strategies that optimise these quantities without compromising the purity of the produced stream, as the latter may introduce a heavy economic burden on the operation.
Fan D, Pini R, Striolo A, 2021, A seemingly universal particle kinetic distribution in porous media, Applied Physics Letters, Vol: 119, Pages: 1-6, ISSN: 0003-6951
We study many-particle transport in randomly jammed packing of spheres at different particle Péclet numbers (𝑃𝑒∗). We demonstrate that a modified Nakagami-m function describes particle velocity probability distributions when particle deposition occurs. We assess the universality of said function through comparison against Lagrangian simulations of various particle types as well as experimental data from the literature. We construe the function's physical meaning as its ability to explain particle deposition in terms of 𝑃𝑒∗ and the competition between distributions of energy barriers for particle release and particles' diffusive energy.
Ma L, Fauchille A-L, Ansari H, et al., 2021, Linking multi-scale 3D microstructure to potential enhanced natural gas recovery and subsurface CO2 storage for Bowland Shale, UK, Energy and Environmental Science, Vol: 14, Pages: 4481-4498, ISSN: 1754-5692
Injection of CO2 into shale reservoirs to enhance gas recovery and simultaneously sequester greenhouse gases is a potential contributor towards the carbon-neutral target. It offers a low-carbon, low-cost, low-waste and large-scale solution during energy transition period. A precondition to efficient gas storage and flow is a sound understanding of how the shale’s micro-scale impacts on these phenomena. However, the heterogeneous and complex nature of shales limits the understanding of microstructure and pore systems, making feasibility analysis challenging. This study qualitatively and quantitatively investigates the Bowland shale microstructure in 3D at five length scales: artificial fractures at 10-100 µm scale, matrix fabric at 1-10 µm-scale, individual mineral grains and organic matter particles at 100 nm- 1 µm scale, macropores and micro-cracks at 10-100 nm scale and organic matter and mineral pores at 1-10 nm-scale. For each feature, the volume fraction variations along the bedding normal orientation, the fractal dimensions and the degrees of anisotropy were analysed at all corresponding scales for a multi-scale heterogeneity analysis. The results are combined with other bulk laboratory measurements, including supercritical CO2 and CH4 adsorption at reservoir conditions, pressure-dependent permeability and nitrogen adsorption pore size distribution, to perform a comprehensive analysis on the storage space and flow pathways. A cross-scale pore size distribution, ranging from 2 nm to 3 µm, was calculated with quantified microstructure. The cumulative porosity is calculated to be 8%. The cumulative surface area is 17.6 m2/g. A model of CH4 and CO2 flow pathways and storage with quantified microstructure is presented and discussed. The feasibility of simultaneously enhanced gas recovery and subsurface CO2 storage in Bowland shale, the largest shale gas potential formation in the UK, was assessed based using multi-scale microstructure
Savulescu GC, Rücker M, Scanziani A, et al., 2021, Atomic force microscopy for the characterisation of pinning effects of seawater micro-droplets in n-decane on a calcite surface, Journal of Colloid and Interface Science, Vol: 592, Pages: 397-404, ISSN: 0021-9797
Hypothesis: Roughness is an important parameter in applications where wetting needs to be characterized. Micro-computed tomography is commonly used to characterize wetting in porous media but the main limitation of this approach is the incapacity to identify nanoscale roughness. Atomic force microscopy, AFM, however, has been used to characterize the topography of surfaces down to the molecular scale. Here we investigate the potential of using AFM to characterize wetting behavior at the nanoscale.Experiments: Droplets of water on cleaved calcite under decane were imaged using quantitative imaging QI atomic force microscopy where a force-distance curve is obtained at every pixel.Findings: When the AFM tip passed through the water droplet surface, an attraction was observed due to capillary effects, such that the thickness of the water film was estimated and hence the profile of the droplet obtained. This enables parameters such as the contact angle and contact angle distribution to be obtained at a nanometer scale. The contact angles around the 3-phase contact line are found to be quasi-symmetrically distributed between 10–30°. A correlation between the height profile of the surface and contact angle distribution demonstrates a quasi-proportional relationship between roughness on the calcite surface and contact angle.
Eckel A-M, Pini R, 2021, Spreading and mixing during solutal convection in uniform porous media with application to geologic CO2 storage, Physics of Fluids, Vol: 33, ISSN: 1070-6631
Convective dissolution in saline aquifers is expected to positively impact subsurface storage of carbon dioxide (CO2) by accelerating its dissolution rate into reservoir brines. By largely focusing on the dissolution flux, previous studies lack a systematic evaluation of the mixing process following CO2 emplacement, including a quantitative analysis at conditions representative of subsurface traps (Rayleigh number, Ra≤1 000). Here, we investigate solutal convection numerically in a two-dimensional uniform porous medium in the regime Ra=100−10 000. The macroscopic evolution of the convective process is characterized by means of fundamental macroscopic measures of mixing that use the local spatial structure of the solute concentration field. It is shown that the intensity of segregation closely mimics the evolution of the in situ convective pattern arising from the stretching and merging of downwelling plumes. The spreading length and the dilution index both confirm that the mixing process accelerates over time (t) with a power law scaling (∝tα) that transitions from diffusive (α=0.5) to superdiffusive mixing (α≥1) irrespective of Ra. This transition time scales τon∝Ra−2 and is used as a measure of the onset time of convection. The dilution index indicates that the time needed to reach close-to-complete mixing reduces linearly with Ra. On the contrary, the non-dimensional mass flux, expressed in terms of the Sherwood number, Sh, reveals a natural logarithmic scaling for Ra≤2 500.
Kurotori T, Pini R, 2021, A general capillary equilibrium model to describe drainage experiments in heterogeneous laboratory rock cores, Advances in Water Resources, Vol: 152, Pages: 1-12, ISSN: 0309-1708
Macroscopic observations of two-phase flow in porous rocks are largely affected by the heterogeneity in continuum properties at length scales smaller than a typical laboratory sample. The ability to discriminate among therock properties at the origin of the heterogeneity is key to the development of numerical models to be used forprediction. Here, we present a capillary equilibrium model that represents spatial heterogeneity in dual-porosityporous media in terms of the capillary entry pressure, 1∕𝛼, and the irreducible wetting phase saturation, 𝑆ir. Bothparameters are used to scale local capillary pressure curves by using three-dimensional imagery acquired duringmulti-rate gas/liquid drainage displacements. We verify the proposed approach by considering the case studyof a dual-porosity limestone core and use the spatial variation in 𝑆ir as proxy for microporosity heterogeneity.The latter places potentially next-to-leading order controls on the observed fluid saturation distribution, whichis strongly correlated to the distribution of 1∕𝛼. While microporosity is by and large uniform at the observationscale on the order of 0.1 cm3, the spatial correlation of 1∕𝛼 is on the order of 1 cm and is therefore not statisticallyrepresented in the volume of typical laboratory core samples.
Tian T, Hou J, Ansari H, et al., 2021, Mechanically stable structured porous boron nitride with high volumetric adsorption capacity, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 9, Pages: 13366-13373, ISSN: 2050-7488
Pini R, Ansari H, Hwang J, 2021, Measurement and interpretation of unary supercritical gas adsorption isotherms in micro-mesoporous solids, Adsorption, Vol: 27, Pages: 659-671, ISSN: 0929-5607
Gas adsorption at high pressures in porous solids is commonly quantified in terms of the excess amount adsorbed. Despite the wide spectrum of adsorbent morphologies available, the analysis of excess adsorption isotherms has mostly focused on microporous materials and the role of mesoporosity remains largely unexplored. Here, we present supercritical CO2 adsorption isotherms measured at 𝑇=308 K in the pressure range 𝑝=0.02−21 MPa on three adsorbents with distinct fractions of microporosity, 𝜙2, namely a microporous metal-organic framework (𝜙2=70%), a micro-mesoporous zeolite (𝜙2=38%) and a mesoporous carbon (𝜙2<0.1%). The results are compared systematically in terms of excess and net adsorption relative to two distinct reference states–the space filled with gas in the presence/absence of adsorbent–that are defined from two separate experiments using helium as the probing gas. We discuss the inherent difficulties in extracting from the supercritical adsorption isotherms quantitative information on the properties of the adsorbed phase (its density or volume), because of the nonuniform distribution of the latter within and across the different classes of pore sizes. Yet, the data clearly reveal pore-size dependent adsorption behaviour, which can be used to identify characteristic types of isotherm and to complement the information obtained using the more traditional textural analysis by physisorption.
Gardas RL, Kofke DA, Pini R, et al., 2021, Historical Perspective of the Journal of Chemical & Engineering Data's Published Topics, 1956-2020, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 66, Pages: 1555-1556, ISSN: 0021-9568
Hwang J, Pini R, 2021, Enhanced sorption of supercritical CO2 and CH4 in the hydrated interlayer pores of smectite, Langmuir: the ACS journal of surfaces and colloids, Vol: 37, Pages: 3778-3788, ISSN: 0743-7463
Understanding the long-term confinement of supercritical fluids in the clay pores of subsurface rocks is important for many geo-energy technologies, including geological CO2 storage. However, the adsorption properties of hydrated clay minerals remain largely uncertain because competitive adsorption experiments of supercritical fluids in the presence of water are difficult. Here, we report on the sorption properties of four source clay minerals—Ca-rich montmorillonite (STx-1b), Na-rich montmorillonite (SWy-2), illite–smectite mixed layer (ISCz-1), and illite (IMt-2)—for water at 20 °C up to relative humidity of 0.9. The measurements unveil the unsuitability of physisorption analysis by N2 (at 77 K) and Ar (at 87 K) gases to quantify the textural properties of clays because of their inability to probe the interlayers. We further measure the sorption of CO2 and CH4 on swelling STx-1b and nonswelling IMt-2, both in the absence (dehydrated at 200 °C) and the presence of sub-1W preadsorbed water (following dehydration) up to 170 bar at 50 °C. We observe enhanced sorption of CO2 and CH4 in STx-1b (50 and 65% increase at 30 bar relative to dry STx-1b, respectively), while their adsorption on IMt-2 remains unchanged, indicating the absence of competition with water. By describing the supercritical adsorption isotherms on hydrated STx-1b with the lattice density functional theory model, we estimate that the pore volume has expanded by approximately 6% through the formation of sub-nanometer pore space. By presenting a systematic approach of quantifying the smectite clay mineral’s hydrated state, this study provides an explanation for the conflicting literature observations of gas uptake capacities in the presence of water.
Burridge HC, Pini R, Shah SMK, et al., 2021, Identifying Efficient Transport Pathways in Early-Wood Timber: Insights from 3D X-ray CT Imaging of Softwood in the Presence of Flow (vol 136, pg 813, 2021), TRANSPORT IN POROUS MEDIA, Vol: 137, Pages: 799-800, ISSN: 0169-3913
Wenning QC, Madonna C, Kurotori T, et al., 2021, Chemo-Mechanical Coupling in Fractured Shale With Water and Hydrocarbon Flow, GEOPHYSICAL RESEARCH LETTERS, Vol: 48, ISSN: 0094-8276
Siepmann JI, Gardas RL, Kofke DA, et al., 2021, Journal of Chemical & Engineering Data: Why Change the Cover Page?, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 66, Pages: 859-860, ISSN: 0021-9568
Siepmann JI, Gardas RL, Kofke DA, et al., 2021, Journal of Chemical & Engineering Data: An Update from the Editorial Team, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 66, Pages: 1-2, ISSN: 0021-9568
Burridge HC, Pini R, Shah SMK, et al., 2021, Identifying efficient transport pathways in early-wood timber: insights from 3D X-ray CT imaging of softwood in the presence of flow, Transport in Porous Media, Vol: 136, Pages: 813-830, ISSN: 0169-3913
Wider use of timber has the potential to greatly reduce the embodied carbon of construction. Improved chemical treatment could help overcome some of the barriers to wider application of timber, by furthering the durability and/or mechanical properties of this natural material. Improving timber treatment by treating the whole volume of a piece of timber, or tailored sections thereof, requires sound understanding and validated modelling of the natural paths for fluid flow through wood. In this study we carry out a robust analysis of three-dimensional X-ray CT measurements on kiln-dried softwood in the presence of flow and identify small portions of early-wood which are uniquely capable of transporting fluids—herein ‘efficient transport pathways’. We successfully model the effects of these pathways on the liquid uptake by timber by introducing a spatial variability in the amount of aspiration of the bordered pits following kiln drying. The model demonstrates that fluid advances along these efficient transport paths between 10 and 30 times faster than in the remainder of the timber. Identifying these efficient transport pathways offers scope to improve and extend the degree to which timber properties are enhanced at an industrial scale through processes to impregnate timber.
Wenning QC, Madonna C, Petrini C, et al., 2021, X-ray CT imaging of displacement-and swelling-induced fracture aperture changes in clay-rich rock
The study of permeability in fracture shale is challenging because coupled processes of mechanical damage, flow, and self-sealing are largely affected by the abundance of clay mineral in such systems. Yet the understanding of the coupling of these processes is fundamental to successful implementation of subsurface energy and waste storage technologies. Here, we present experimental results that combine simultaneous X-ray Computed Tomography with shear-flow experiments to study fracture deformation, fluid sorption, and flow in shale. In both experiments, the average mechanical aperture increases with shear displacement under constant radial stress (1.5 MPa). Upon subsequent brine injection the aperture is reduced to below the initial mated state. Digital image correlation is used to quantify the divergent displacement of the two sample halves, which is likely caused by fluid sorption. Fracture aperture reduction and divergent displacement were not observed in a control experiment with decane. Thus, at low confining pressures, the self-sealing process in clay-rich shales is dominated by swelling, rather than creep, and can occur relatively quickly (< 30 minutes).
Ansari H, Joss L, Hwang J, et al., 2020, Supercritical adsorption in micro- and meso-porous carbons and its utilisation for textural characterisation, Microporous and Mesoporous Materials, Vol: 308, ISSN: 1387-1811
Understanding supercritical gas adsorption in porous carbons requires consistency between experimental measurements at representative conditions and theoretical adsorption models that correctly account for the solid’s textural properties. We have measured unary CO2 and CH4 adsorption isotherms on a commercial mesoporous carbon up to 25 MPa at 40 °C, 60 °C and 80 °C. The experimental data are successfully described using a model based on the lattice Density Functional Theory (DFT) that has been newly developed for cylindrical pores and used alongside Ar (87K) physisorption to extract the representative pore sizes of the adsorbent. The agreement between model and experiments also includes important thermodynamic parameters, such as Henry constants and the isosteric heat of adsorption. The general applicability of our integrated workflow is validated by extending the analysis to a comprehensive literature data set on a microporous activated carbon. This comparison reveals the distinct pore-filling behaviour in micro- and mesopores at supercritical conditions, and highlights the limitations associated with using slit-pore models for the characterisation of porous carbons with significant amounts of mesoporosity. The lattice DFT represents a departure from simple adsorption models, such as the Langmuir equation, which cannot capture pore size dependent adsorption behaviour, and a practical alternative to molecular simulations, which are computationally expensive to implement.
Pini R, Joss L, Hosseinzadeh Hejazi SA, 2020, Quantitative imaging of gas adsorption equilibrium and dynamics by X-ray Computed Tomography, Adsorption, Vol: 27, Pages: 801-818, ISSN: 0929-5607
We present the development and application of X-ray Computed Tomography (CT) for the determination of the adsorption properties of microporous adsorbents and the study of breakthrough experiments in a laboratory fixed-bed adsorption column. Using the model system CO2/helium on activated carbon, equilibrium and dynamic adsorption/desorption measurements by X-ray CT are described, and the results are successfully compared to those obtained from conventional methods, including the application of a one-dimensional dynamic column breakthrough model. The study demonstrates the practical feasibility of applying X-ray CT to measure internal and transient concentration profiles in adsorbent systems on the length-scales from a single adsorbent pellet to a packed column.
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