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Highlights • A novel method for identifying pore-body to pore-throat aspect ratio is defined. • This 'Morphological Aspect Ratio' scales linearly with non-wetting phase trapping. • Critical pore sizes are derived from connectivity and morphology of pore spaces. • Pore size relevant for capillary-dominated flow is defined by morphological opening. • The Morphological Aspect Ratio is applicable to a wide range of porous media. Abstract We introduce a new method for defining a pore-body to pore-throat aspect ratio from segmented 3D image data, based on a connectivity metric applicable to porous media with widely varying pore-space connectivity and pore-space morphology. The 'Morphological Aspect Ratio' (MAR) is identified from the pore-space connectivity, using the Euler number (χ) as a function of a pore-space size defined by a morphological opening (erosion and dilation) of the pore space. We show that residual non-wetting phase trapping in porous media resulting from secondary imbibition scales with the MAR. Trapping was investigated in a Bentheimer sandstone core and five columns of partially sintered glass-particle packs with different combinations of glass beads and crushed glass ranging in size from 0.3 to 1.2 mm, resulting in porosity levels of 22–36%. Residual non-wetting phase trapping scales with the MAR, in contrast to the aspect ratio calculated with the traditional Maximum Inscribed Sphere (MIS) algorithm applied after partitioning the pore space into pore bodies and pore throats with a watershed transform followed by a region merging algorithm. This novel aspect ratio is a robust method that is less affected by segmentation errors compared to other methods for calculating aspect ratio and is applicable to residual non-wetting phase trapping resulting from capillary-driven flow of a wetting fluid through water-wet porous media. [ABSTRACT FROM AUTHOR]

We investigate trapping of a nonwetting (NW) phase, air, within Bentheimer sandstone cores during drainage–imbibition flow experiments, as quantified on a three dimensional (3D) pore-scale basis via x-ray computed microtomography (X-ray CMT). The wetting (W) fluid in these experiments was deionized water doped with potassium iodide (1:6 by weight). We interpret these experiments based on the capillary–viscosity–gravity force dominance exhibited by the Bentheimer–air–brine system and compare to a wide range of previous drainage–imbibition experiments in different media and with different fluids. From this analysis, we conclude that viscous and capillary forces dominate in the Bentheimer–air–brine system as well as in the Bentheimer–supercritical CO 2 –brine system. In addition, we further develop the relationship between initial (post-drainage) NW phase connectivity and residual (post-imbibition) trapped NW phase saturation, while also taking into account initial NW phase saturation and imbibition capillary number. We quantify NW phase connectivity via a topological measure as well as by a statistical percolation metric. These metrics are evaluated for their utility and appropriateness in quantifying NW phase connectivity within porous media. Here, we find that there is a linear relationship between initial NW phase connectivity (as quantified by the normalized Euler number, χ ˆ ) and capillary trapping efficiency; for a given imbibition capillary number, capillary trapping efficiency (residual NW phase saturation normalized by initial NW phase saturation) can decrease by up to 60% as initial NW phase connectivity increases from low connectivity ( χ ˆ ≈ 0) to very high connectivity ( χ ˆ ≈ 1). We propose that multiphase fluid-porous medium systems can be efficiently engineered to achieve a desired residual state (optimal NW phase saturation) by considering the dominant forces at play in the system along with the impacts of NW phase topology within the porous media, and we illustrate these concepts by considering supercritical CO 2 sequestration scenarios. [ABSTRACT FROM AUTHOR]

Abstract: Microporous materials such as zeolites, metal organic frameworks, activated carbons and aluminum phosphates are suitable for catalysis and separation applications. These high surface area materials are invariably produced in particulate forms and need to be transformed into hierarchically porous structures for high performance adsorbents or catalysts. Structuring of porous powders enables an optimized structure with high mass transfer, low pressure drop, good heat management, and high mechanical and chemical stability. The requirements and important properties of hierarchically porous structures are reviewed with a focus on applications in gas separation and catalysis. Versatile powder processing routes to process porous powders into hierarchically porous structures like extrusion, coatings of scaffolds and honeycombs, colloidal processing and direct casting, and sacrificial approaches are presented and discussed. The use and limitations of the use of inorganic binders for increasing the mechanical strength is reviewed, and the most important binder systems, e.g. clays and silica, are described in detail. Recent advances to produce binder-free and complex shaped hierarchically porous monoliths are described and their performance is compared with traditional binder-containing structured adsorbents. Needs related to better thermal management and improved kinetics and volume efficiency are discussed and an outlook on future research is also given. [Copyright &y& Elsevier]

We show that water-based porosimetry ( WBP), a facile, simple, and nondestructive porosimetry technique, accurately evaluates both the pore size distribution and throat size distribution of sacrificially templated macroporous alumina. The pore size distribution and throat size distribution derived from the WBP evaluation in uptake (imbibition) and release (drainage) mode, respectively, were corroborated by mercury porosimetry and X-ray micro-computed tomography (μ-CT). In contrast with mercury porosimetry, the WBP also provided information on the presence of 'dead-end pores' in the macroporous alumina. [ABSTRACT FROM AUTHOR]

Abstract: In general, the post-combustion capture of CO2 is costly; however, swing adsorption processes can reduce these costs under certain conditions. This review highlights the issues related to adsorption-based processes for the capture of CO2 from flue gas. In particular, we consider studies that investigate CO2 adsorbents for vacuum swing or temperature swing adsorption processes. Zeolites, carbon molecular sieves, metal organic frameworks, microporous polymers, and amine-modified sorbents are relevant for such processes. The large-volume gas flows in the gas flue stacks of power plants limit the possibilities of using regular swing adsorption processes, whose cycles are relatively slow. The structuring of CO2 adsorbents is crucial for the rapid swing cycles needed to capture CO2 at large point sources. We review the literature on such structured CO2 adsorbents. Impurities may impact the function of the sorbents, and could affect the overall thermodynamics of power plants, when combined with carbon capture and storage. The heat integration of the adsorption-driven processes with the power plant is crucial in ensuring the economy of the capture of CO2, and impacts the design of both the adsorbents and the processes. The development of adsorbents with high capacity, high selectivity, rapid uptake, easy recycling, and suitable thermal and mechanical properties is a challenging task. These tasks call for interdisciplinary studies addressing this delicate optimization process, including integration with the overall thermodynamics of power plants. [Copyright &y& Elsevier]

A lightweight and strong porous cellulose material hasbeen preparedby drying aqueous foams stabilized with surface-modified nanofibrillatedcellulose (NFC). This material differs from other dry, particle stabilizedfoams in that renewable cellulose is used as stabilizing particles.Confocal microscopy and high speed video imaging show that the octylamine-coated,rod-shaped NFC nanoparticles residing at the air–liquid interfaceprevent the air bubbles from collapsing or coalescing. Stable wetfoams can be achieved at solids content around 1% by weight. Carefulremoval of the water results in a cellulose-based material with aporosity of 98% and a density of 30 mg cm–3. Theseporous cellulose materials have a higher Young’s modulus thanporous cellulose materials made from freeze-drying, at comparabledensities, and have a compressive energy absorption of 56 kJ m–3at 80% strain. Measurement with the aid of an autoporosimeterrevealed that most pores are in the range of 300 to 500 μm. [ABSTRACT FROM AUTHOR]

Abstract: Sacrificial templating of suspension cast and subsequently thermally treated zeolite monoliths with glassy carbon spheres and fibers yielded zeolite 13X and silicalite-1 monoliths with macroporosities up to 50vol%. Homogeneous distribution of the macroporosity in hierarchically porous monoliths was obtained by tailoring the surface chemistry of the carbon particles by polyelectrolyte-assisted adsorption of zeolite particles. The effect of amount of kaolin binder and temperature for the thermal treatment on the monoliths strength, surface area and CO2 uptake was studied by diametral compression tests, electron microscopy, X-ray diffraction and gas adsorption. Cyclic adsorption and regeneration measurements showed that zeolite 13X monoliths display a high CO2 uptake while the silicalite-1 monoliths could be regenerated with a relatively low energy penalty. [Copyright &y& Elsevier]

Abstract: We have regulated the permeability in macroporous alumina materials by manipulating the connectivity of the pore phase and the sizes of the smallest constrictions between connected pores. Templating with particle-coated expandable polymeric spheres (EPS) significantly increased the fraction of isolated pore clusters, and reduced both the sizes and the number of connections with neighboring pores, as determined by three-dimensional evaluation with X-ray micro-computed tomography. The stable particle coating, applied onto the EPS surfaces using polyelectrolyte multilayers, reduced the volume expansion and the coalescence of the EPS at elevated temperatures, which reduced the simulated permeability by as much as two orders of magnitude compared to templating with uncoated EPS in materials of similar porosities. We show that the Katz–Thompson model accurately predicts the permeability for the macroporous alumina materials with porosities of 46–76%. This suggests that the permeability to fluid flow in these materials is governed by the smallest constrictions between connected pores: the critical pore throat diameter. [Copyright &y& Elsevier]

Abstract: The three-dimensional (3D) structures of macroporous alumina, produced by a novel method that combines gel casting with expandable polymeric microspheres as a sacrificial templating material, have been characterised by X-ray micro-computed tomography (μ-CT). The grey-scale intensity tomogram data produced by the X-ray μ-CT was segmented into porous and solid phases and the individual pores were identified. We compared two-dimensional slices of the analysed data with the corresponding scanning electron microscopy images and showed that the structural features of the pores were well reproduced in the X-ray μ-CT images. 3D visualisations of the pore structure and the pore network were also shown. The open porosity obtained from X-ray μ-CT corresponded well with the porosity derived from mercury porosimetry for pores larger than the voxel dimension (3μm). The quantitative analysis also yielded information on the spatial variations in porosity and the number of connected neighbours of pores. The 3D data was used to relate the calculated permeability to the open porosity. [Copyright &y& Elsevier]

Abstract: Expandable microspheres have been used as a sacrificial template to produce macroporous ceramic materials by a gel-casting process. The temperature range for the gel-casting process has been tuned to allow the gas-filled polymer spheres to expand prior to the setting of the powder body. It is demonstrated that by controlling the amount and size of the expandable microspheres it is possible to tune and tailor the porosity up to 86% and the pore size distribution from 15 up to 150μm. The expandable microspheres add a relatively low amount of organic material that allows rapid and facile burn-out. The temperature-induced expansion of the microspheres and the associated volume increase of the suspension has been used as a simple zero-pressure near-net shaping method to yield complex-shaped macroporous alumina bodies. [Copyright &y& Elsevier]

• X-ray microtomography imaging of three-phase fluid distributions during quasi-static drainage-imbibition cycles of three-phase flow in water-wet porous media. • Initial water saturation (at the point of air injection) in three-phase flow does not affect the capillary pressure-saturation relationship or the interfacial area-saturation relationship under quasi-equilibrium conditions. • For the oil-water fluid pair in a three-phase flow system, hysteresis in the interfacial area-saturation relationship is minimal, and the capillary pressure-saturation-interfacial area relationship fully eliminates hysteresis. • For air-oil, the same conclusion can be drawn, as long as the system is in a quasi-equilibrated state. • Our results suggest that interface relaxation greatly affects formation of interfacial area, but it does not notably affect capillary pressure. We encounter three-phase flow in porous media within a range of settings, such as enhanced oil recovery, geologic CO 2 sequestration, and groundwater remediation. While an abundance of studies has been performed on the behavior of two fluid phases (e.g. oil/water or air/water) in porous media, relatively little information exists for three-phase flow systems (e.g. oil/water/air). This work explores the relationships between capillary pressure (P c), saturation (S) and fluid-fluid interfacial area (a) for water-wet three-phase flow systems where water is the wetting phase, oil is the intermediate-wet phase, and air (or gas) is the non-wetting phase. Specifically, we examine whether the P c - S - a relationships exhibit hysteresis during drainage and imbibition cycles. We present data collected via x-ray microtomography resulting in high-resolution three-dimensional images of the fluid configurations for varying degrees of saturation. Among the findings of the study (based on the available data), we highlight that (1) the P c - S - a relationship is non-hysteretic for both the oil-water fluid pair, and the air-oil fluid pair, and (2) that this same relationship is independent of the initial water saturation at the point of air injection. This finding suggests that both the oil-water and air-oil fluid pairs in a three-phase system can be adequately described by the thermodynamics-based theory originally proposed by Hassanizadeh and Gray (1993), as is the case for the equivalent two-phase system. [ABSTRACT FROM AUTHOR]

Background: Red blood cell (RBC) transfusions are associated with risks including immunological reactions and volume overload. Current guidelines suggest a restrictive transfusion strategy in most patients with sepsis but based on previous randomized controlled trials and observational studies, there are still uncertainties about the safety in giving low-grade RBC transfusions to patients with sepsis. Methods: Critically ill patients with severe sepsis or septic shock admitted to a university hospital intensive care unit between 2007 and 2018 that received less or equal to 2 units of RBCs during the first 5 days of admission were propensity score matched to controls. Outcomes were 90- and 180-day mortality, highest acute kidney injury network (AKIN) score the first 10 days, days alive and free of organ support the first 28 days after admission to the intensive care unit and highest sequential organ failure assessment score (SOFA-max). Results: Of 9490 admissions, 1347 were diagnosed with severe sepsis or septic shock. Propensity-score matching resulted in two well-matched groups with 237 patients in each. The annual inclusion rate in both groups was similar. The median hemoglobin level before RBC transfusion was 95 g/L (interquartile range 88–104) and the majority of the patients were transfused in first 2 days of admission. Low-grade RBC transfusion was associated with increased 90- and 180-day mortality with an absolute risk increase for death 9.3% (95% confidence interval: 0.6–18%, P = 0.032) and 11% (95% confidence interval: 1.7–19%, P = 0.018), respectively. Low-grade RBC transfusion also correlated with increased kidney, circulatory and respiratory failure and higher SOFA-max score. Conclusions: Low-grade RBC transfusion during the first 5 days of admission was associated with increased mortality and morbidity in a liberal transfusion setting. The results support the current practice of a restrictive transfusion strategy in septic critically ill patients. [ABSTRACT FROM AUTHOR]

Highlights: [•] We examine the effect of NW phase connectivity on capillary trapping in porous media. [•] We establish relationships of NW connectivity as a function of NW saturation. [•] High initial NW connectivity results in reduced trapping for Bentheimer sandstone. [•] Multiple drainage-imbibition cycles do not change the NW connectivity of the media. [•] A WAG injection scheme reduces connectivity and promotes capillary trapping of CO2. [Copyright &y& Elsevier]

We explore how X-ray computed microtomography can be used to generate highly-resolved 3D biofilm datasets on length scales that span multiple pore bodies. The data is integrated into a study of the effects of flow rate on three-dimensional growth of biofilm in porous media. Three flow rates were investigated in model packed-bed columns. Biofilm growth was monitored during an 11-day growth period using a combination of differential pressure and effluent dissolved oxygen measurements. At the end of the growth period, all columns were scanned using X-ray computed microtomography and a barium sulfate-based contrast agent. The resulting images were prepared for quantitative analysis using a novel image processing workflow that was tailored to this specific system. The reduction in permeability due to biofilm growth was studied using both transducer-based pressure drop measurements and image-based calculations using the Kozeny–Carman model. In addition, a set of structural measures related to the spatial distribution of biofilms were computed and analyzed for the different flow rates. We generally observed 1 to 2 orders of magnitude decrease in permeability as a result of bioclogging for all columns (i.e, across flow rates). The greatest average permeability and porosity reduction was observed for the intermediate flow rate (4.5 ml/h). A combination of results from different measurements all suggest that biofilm growth was oxygen limited at the lowest flow rate, and affected by shear stresses at the highest flow rate. We hypothesize that the interplay between these two factors drives the spatial distribution and quantity of biofilm growth in the class of porous media studied here. Our approach opens the way to more systematic studies of the structure-function relationships involved in biofilm growth in porous media and the impact that such growth may have on physical properties such as hydraulic conductivity. [ABSTRACT FROM AUTHOR]