Broad Pore Size Distribution Research Articles

Resolving the Effects of Surface Area and Porosity on the Capacitance of Activated Carbon

One strategy to improve the energy density of electrochemical double-layer capacitors is to maximize the capacitance per unit surface area. However, due to the intercoupled relationship between surface area and pore size distribution, the effect of pore size on capacitance remains unclear. In this study, two samples prepared from the same raw material, with similar specific surface areas and chemical compositions, but different pore size distributions are compared in order to investigate the effects of pore size on capacitance. The results demonstrate that in the microporous sample, the SSA-normalized capacitance is 15.1 µF cm-2, while the mesoporous sample has an SSA-normalized capacitance of 13.2 µF cm-2 for all charging rates. However, when normalized to mass, the enhanced micropore capacitance may be masked due to variations in a sample’s bulk density. Therefore, these results demonstrate in broad pore size distribution activated carbon samples, the SSA-normalized capacitance is enhanced in microporous materials.

Characterization of full pore size distribution and its significance to macroscopic physical parameters in tight glutenites

Characterization of microscopic pore structure plays an important role in understanding transport and accumulation mechanism of tight gas accumulation. Optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen gas adsorption (N2GA), mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) experiments were performed on tight glutenite samples from the Lower Cretaceous Shahezi Formation in the northern Songliao Basin of China in order to gain insight into the microscopic pore structure (e.g., pore types and full pore size distribution), and to discuss the control of full pore structure properties on macroscopic physical parameters. The results show that the tight glutenite samples in this study contain four types of pores: inter-granular pores, dissolution pores, inter-crystalline pores and even some pores associated to micro-fractures. The inter-crystalline pores and inter-granular/dissolution pores can be determined by the surface fractal dimensions and mercury intrusion features because of different pore connectivity. The combination of N2GA and MIP were applied as complementary techniques and revealed that the studied samples have a broad pore size distribution ranging from 2 nm to 200 μm (mainly from 10 nm to 2 μm). Nano-scaled pores become the crucial storage space in tight glutenite samples. A total porosity derived from full pore size distribution curves is between 1.18% and 5.64%, which is closer helium porosity than that originated from N2GA and MIP techniques, respectively. Tight glutenite samples with a greater proportion of small pores (diameter<50 nm) mainly corresponding to inter-crystalline pores always have worse macroscopic physical parameters. However, tight glutenite samples with a greater proportion of large pores (diameter>200 nm) mainly corresponding to inter-granular/dissolution pores always correspond to better macroscopic physical parameters. The development of different pore types controls the macroscopic physical parameters. A series of empirical equations developed from multiple regression analysis between permeability, porosity and pore radius were established in tight glutenite samples. Pore radius corresponding to 15% cumulative pore volume from the combination of N2GA and MIP techniques is the best permeability estimator for tight glutenite samples.

Platinum clusters supported on/in Dion–Jacobson phase HLaNb2O7 by topochemical method

Platinum clusters were supported on/in HLaNb2O7 nanosheets by topochemical reaction strategy for the first time. The as-prepared samples were analyzed using ICP OES and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption isotherms and X-ray photoelectron spectroscopy. The results showed that HLaNb2O7 nanosheets were modified with platinum clusters with good monodispersity. The product was a mesoporous solid with broad pore size distribution and large surface area. The oxidation state of platinum was zero and the size of Pt clusters was only about 1–2 nm. This study provides a novel approach to support metal clusters on layered compounds.

Nanofiltration Membranes with Narrow Pore Size Distribution via Contra-Diffusion-Induced Mussel-Inspired Chemistry.

Nanofiltration membranes (NFMs) are widely used in saline water desalination, wastewater treatment, and chemical product purification. However, conventional NFMs suffer from broad pore size distribution, which limits their applications for fine separation, especially in complete separation of molecules with slight differences in molecular size. Herein, defect-free composite NFMs with narrow pore size distribution are fabricated using a contra-diffusion method, with dopamine/polyethylenimine solution on the skin side and ammonium persulfate solution on the other side of the ultrafiltration substrate. Persulfate ions can diffuse through the ultrafiltration substrate into the other side and in situ trigger dopamine to form a codeposited coating with polyethylenimine. The codeposition is hindered on those sites completely covered by the polydopamine/polyethylenimine coating, although it is promoted at the defects or highly permeable regions because it is induced by the diffused persulfate ions. Such a "self-completion" process results in NFMs with highly uniform structures and narrow pore size distribution, as determined by their rejection of neutral solutes. These near electrically neutral NFMs show a high rejection of divalent ions with a low rejection of monovalent ions (MgCl2 rejection = 96%, NaCl rejection = 23%), majorly based on a steric hindrance effect. The as-prepared NFMs can be applied in molecular separation such as isolating cellulose hydrogenation products.

Simulating secondary waterflooding in heterogeneous rocks with variable wettability using an image‐based, multiscale pore network model

AbstractThe two‐phase flow properties of natural rocks depend strongly on their pore structure and wettability, both of which are often heterogeneous throughout the rock. To better understand and predict these properties, image‐based models are being developed. Resulting simulations are however problematic in several important classes of rocks with broad pore‐size distributions. We present a new multiscale pore network model to simulate secondary waterflooding in these rocks, which may undergo wettability alteration after primary drainage. This novel approach permits to include the effect of microporosity on the imbibition sequence without the need to describe each individual micropore. Instead, we show that fluid transport through unresolved pores can be taken into account in an upscaled fashion, by the inclusion of symbolic links between macropores, resulting in strongly decreased computational demands. Rules to describe the behavior of these links in the quasistatic invasion sequence are derived from percolation theory. The model is validated by comparison to a fully detailed network representation, which takes each separate micropore into account. Strongly and weakly water‐and oil‐wet simulations show good results, as do mixed‐wettability scenarios with different pore‐scale wettability distributions. We also show simulations on a network extracted from a micro‐CT scan of Estaillades limestone, which yields good agreement with water‐wet and mixed‐wet experimental results.

Resolving the Effects of Surface Area and Porosity on the Capacitance of Activated Carbon

Electrochemical double-layer capacitors (EDLCs) store energy at the interface of the electrode and electrolyte, known as the electrical double layer. One of the challenges facing EDLC technology is their moderate energy density compared to batteries and fuel cells. Therefore, improving EDLC performance requires identification of the key electrode and electrolyte parameters that affect energy density. Some of the key parameters that are known to impact the energy density of an electrode material are the material’s specific surface area (SSA), its pore size distribution, the macroscopic morphology, and the material’s chemical composition, relating to the wettability of the material and the faradaic reactions that may occur during charging. However, published research to date has not isolated the intercoupled relationship between specific surface area and pore size distribution. While high surface area materials often have high microporosity (pores less than 2 nm in diameter) due to the high surface to volume ratio of these small pores, as the pore size is increased into the mesopores range (2-50 nm diameter pores), the material’s SSA tends to decrease, since mesopores have a lower surface to volume ratio [1, 2]. As such, there remains an ongoing unresolved debate as to the relationship between pore size and SSA-normalized capacitance [2], with some researchers demonstrating an increased SSA-normalized capacitance in pores with diameters less than 1 nm [3], some researchers suggesting that there is no correlation between pore size and SSA-normalized capacitance [4], and some researchers demonstrating that there is a relationship between SSA-normalized capacitance and pores greater than 2 nm in diameter [5]. One of the main challenges to unravel the correlation between pore size and SSA-normalized capacitance is the variation in a material’s structural features, including total SSA, and its chemical composition. This makes it challenging to determine the effect of a single parameter [2]. In order to investigate the effect of pore size on SSA-normalized capacitance, the ideal materials for comparison would be those of similar specific surface area, and chemical composition, but differing pore size distribution. This approach ensures that the effects of the material’s total SSA are constant. When materials have different total SSA values, it is difficult to determine if the variations in performance are associated to differing pore size or differing surface area. Additionally, the relationship is more complicated in a sample with multiple pore sizes, which is common in activated carbon materials. It is critical to determine the relationship between pore size and capacitance in materials with narrow pore size distributions, and materials that have broad pore size distributions. By identifying the key structural features that improve the energy density of a material, the overall performance of EDLCs may also be improved. This study investigates the relationship between SSA-normalized capacitance and pore size distribution. Activated carbon materials were prepared with various pore size, but with similar specific surface area and chemical composition. The relationship between pore size and both SSA-normalized capacitance and gravimetric capacitance as well as the rate performance of the activated carbon materials is reported. Finally, the dependence of capacitance on maximum operating voltage is discussed in order to better elucidate the relationship between porosity and capacitance. Initial results have demonstrated that as the pore size increases, the SSA-normalized capacitance decreases. However, a similar decrease was not observed in the gravimetric capacitance. This indicates that the variation in bulk density of broad pore size distribution carbon materials may mask the effects of enhanced SSA-normalized capacitance in sub-nanometer pores. The results suggest that there may be a critical pore size distribution that will maximize both SSA-normalized capacitance and gravimetric capacitance.

Mechanical properties and thermal conductivity of a temperature resistance hollow glass microspheres/borosilicate glass buoyance material

A temperature resistance buoyancy material was fabricated through a tert-butyl alcohol gelcasting process with borosilicate glass (BG) and hollow glass microspheres (HGMs) as the matrix and filler, respectively. The effects of the mass ratio of HGMs to BG and sintering temperature on the microstructure, thermal conductivity, and mechanical properties of the composite were studied. The results show that HGMs were bonded together by the BG, and the sample sintered at 750°C exhibited a broad pore size distribution, from several microns to more than one hundred microns. The thermal conductivity experimental values of all the samples were less than that of Hashin-Shtrikman upper bound (HS+) prediction but agreed well with that predicted from effective medium percolation theory. The relationship between compressive strength and relative density was predicted by the Gibson-Ashby model, with the calibration factor phi below 0.7. Young′s modulus values obtained from the experiment were below that of HS+ prediction. The modulus values of the four types of samples sintered at 650°C agreed well with the Pabst model prediction, while the values of the samples sintered at 700°C and 750°C were distributed in a zone between Ashby-Gibson model and HS+ prediction.

Modeling of the lithium-air battery cathodes with broad pore size distribution

Achieving theoretical promises of 1000Wh/kg specific energy for lithium-air batteries is quite challenging due to limited transport in the cathode along with electrode passivation. Transport can be enhanced in the electrodes with complex hierarchical pore architecture. Here, using computer simulations we analyze the effects of cathode pore size distribution (PSD) on capacity and discharge curve shape. Calculations considering a broad PSD revealed that even small discharge product resistivity prevents larger pores from accumulating the discharge product and thus turning them into non-clogging oxygen supply channels. Thus optimization of cathode architecture by adding of large-scale cavities enables cell capacity enhancement.

The Influence of Electrode Microstructure on the Performance of Free-Standing Cathode for Aprotic Lithium-Oxygen Battery

Free-standing NiCo2O4@Ni cathodes for aprotic lithium-oxygen batteries were synthesized through a simple hydrothermal process followed by heat treatment in the air. The morphology of the NiCo2O4 deposit changed from nanosheet to nanowire with the increase of hydrothermal time. Further observation revealed that the nanosheet/nanowire NiCo2O4 were assembled by nanoparticles with a size of 10–20 nm. The directional assembly of the nanoparticles were not affected by the reaction time. The influence of catalyst microstructure on the electrochemical performance of Li-O2 batteries was studied. The results of battery tests in pure oxygen indicate that the cathode material with a high specific surface area, large pore volume and broad pore size distribution can facilitate the discharge reaction, leading to an improved cell performance. As a result, the cathode based on the NiCo2O4 nanowire array delivered a specific discharge capacity of 1682 mAh g−1 at 30 mA g−1 and a stable cyclability of 50 cycles with a capacity limitation of 500 mAh g−1.

Direct correlation of diffusion and pore size distributions with low field NMR

The time-dependent diffusion coefficient (D) is a powerful tool to probe microstructure in porous media, and can be obtained by the NMR method. In a real porous sample, molecular diffusion is very complex. Here we present a new method which directly measures the relationship between effective diffusion coefficients and pore size distributions without knowing surface relaxivity. This method is used to extract structural information and explore the relationship between D and a in porous media having broad pore size distributions. The diffusion information is encoded by the Pulsed Field Gradient (PFG) method and the pore size distributions are acquired by the Decay due to Diffusion in the Internal Field (DDIF) method. Two model samples were measured to verify this method. Restricted diffusion was analyzed, and shows that most fluid molecules experience pore wall. The D(a) curves obtained from correlation maps were fitted to the Padé approximant equation and a good agreement was found between the fitting lines and the measured data. Then a sandstone sample with unknown structure was measured. The state of confined fluids was analyzed and structural information, such as pore size distributions, were extracted. The D – T1 correlation maps were also obtained using the same method, which yielded surface relaxivities for different samples. All the experiments were conducted on 2MHz NMR equipment to obtain accurate diffusion information, where internal gradients can be neglected. This method is expected to have useful applications in the oil industry, particularly for NMR logging in the future.

Favorable Ion Packing in Porous Carbon for High Gravimetric Capacitance Supercapacitors

There is an increasing need for high power density to keep the stability and sustainability of the grid energy storage, as well as to meet the demand for high-power portable devices. Supercapacitor (SC) is an attractive energy storage option for high power application. However, the moderate energy densities of the SCs limit their wide-spread use(1, 2). The existing strategies to achieve high capacitance and hence the specific energy demands micropores to match the ion size(3) and narrow pore size distribution (PSD) for the micropores(4). However, limited type of the carbon materials could offer effectively controlled narrow PSD in microporous region. Moreover, the ion transportation resistance in the micropores is much higher than in the mesopores, leading to lower output power and worse rate capability. In this work, the high gravimetric capacitance of supercapacitor with good rate capability was achieved by a combine modeling and experimental approach(5). A large-scalable method was utilized to prepare a series of high-surface area (up to 3400 m2/g) and mesopores-rich carbon nanosponge (CNS) with varied PSD by tuning carbonization and activation conditions. The porous structure of the typical CNS is shown in Fig. 1a&b. The prepared materials were tested in carbon-ionic liquid (IL) SCs, and the gravimetric capacitances of SCs were varied from 121 to 290 F/g in neat ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) electrolyte (Fig. 1c). We developed a model of ion packing and demonstrated, quantitively, the significant impact of geometric factor (PSD and ionic size) on the ion-distribution in the pores and hence the gravimetric capacitance. The model predicts satisfactorily the gravimetric capacitance of the CNSs synthesized in our work (Fig. 1c) as well as the reported carbon materials in literatures. The model reveals that the capacitance is determined by the correlation between PSD and an ion-packing function which described the discipline of the ion-distribution in different pore sizes. Based on our model, systematic strategies for rational design of various carbon materials (both micro- and mesoporous and allows broad PSD) and ionic liquids to achieve ultrahigh gravimetric capacitance can be proposed. The mesopore-rich CNS with desired PSD promoted by our model delivered the capacitance up to 290 F/g at 20 oC, which is among one of the highest recorded DL capacitance(2). A better ion-packing at 60 oC results an ultrahigh gravimetric capacitance of 387 F/g of CNS in ionic liquid. The expected specific energy of the full-packaged cell was comparable to nickel–metal hydride (NiMH) batteries(1), while the cell still delivered good rate capability and good stability.

Coating of paper with highly filled powders

The purpose of this study was to evaluate the feasibility of using highly filled powders as electrostatically applied paper coatings. Powders prepared by two different methods were suitable for electrostatic deposition and they attached to the paper surface with a grounded backing. Pressing at elevated temperatures turned out to be a crucial process step for improving the adhesive and cohesive strengths of the powder coating layer on paper. Limited mechanical interlocking with the base paper and an uneven pressure profile were factors impairing the surface strength of the coated paper. On the other hand, factors such as higher polymer content, higher pressing temperature, pre-heating the paper prior to coating, and increasing the number of hot roll nips increased adhesion between the coating and the base paper. Powder coatings as such had uneven thickness, and they displayed a relatively broad pore size distribution.

Development of Ethenylene-Bridged Organosilica Membranes for Desalination Applications

A promising new ethenylene-bridged organosilica membrane has been developed for pervaporative desalination of water. Due to the introduction of polarizable and rigid ethenylene bridges in the silica networks, the membrane exhibited an improved water affinity and superior hydrothermal stability. The ethenylene-bridged organosilica membrane delivered a high water flux of up to 14.2 kg m–2 h–1 with a high NaCl rejection of 99.6% for pervaporative desalination 70 °C. Moreover, the membrane was highly applicable and stable for desalination of saline water under a wide range of salt concentrations. The rapid permeation of water molecules through the membrane was attributed to the open pore structure and the water–pore wall interactions, while the transport of hydrated salt ions was explained by the relatively broad pore size distribution of the ethenylene-bridged silica networks.

Toughening of Thermoresponsive Arrested Networks of Elastin-Like Polypeptides To Engineer Cytocompatible Tissue Scaffolds.

Formulation of tissue engineering or regenerative scaffolds from simple bioactive polymers with tunable structure and mechanics is crucial for the regeneration of complex tissues, and hydrogels from recombinant proteins, such as elastin-like polypeptides (ELPs), are promising platforms to support these applications. The arrested phase separation of ELPs has been shown to yield remarkably stiff, biocontinuous, nanostructured networks, but these gels are limited in applications by their relatively brittle nature. Here, a gel-forming ELP is chain-extended by telechelic oxidative coupling, forming extensible, tough hydrogels. Small angle scattering indicates that the chain-extended polypeptides form a fractal network of nanoscale aggregates over a broad concentration range, accessing moduli ranging from 5 kPa to over 1 MPa over a concentration range of 5-30 wt %. These networks exhibited excellent erosion resistance and allowed for the diffusion and release of encapsulated particles consistent with a bicontinuous, porous structure with a broad distribution of pore sizes. Biofunctionalized, toughened networks were found to maintain the viability of human mesenchymal stem cells (hMSCs) in 2D, demonstrating signs of osteogenesis even in cell media without osteogenic molecules. Furthermore, chondrocytes could be readily mixed into these gels via thermoresponsive assembly and remained viable in extended culture. These studies demonstrate the ability to engineer ELP-based arrested physical networks on the molecular level to form reinforced, cytocompatible hydrogel matrices, supporting the promise of these new materials as candidates for the engineering and regeneration of stiff tissues.

Facile fabrication of hierarchically porous NiO microspheres as anode materials for lithium ion batteries

In this work, we report a novel and facile route for the large-scale fabrication of hierarchically porous NiO microspheres, which involves the thermal decomposition of β-Ni(OH)2 precursor at 450 °C in air for 2 h. The superstructures exhibit high specific surface area, large porous volume, and broad pore size distribution. The electrochemical properties of the hierarchically porous NiO microspheres were examined by cyclic voltammetry and galvanostatic charge/discharge studies. The results demonstrate that the hierarchically porous NiO microspheres are promising anode materials with enhanced lithium storage capacity and excellent cycling stability. The hierarchically porous NiO microspheres can retain a reversible capacity of 612 mA h g−1 after 50 cycles at a current density of 100 mA g−1. The improved electrochemical performance is attributed to their hierarchical structure and large amounts of mesopores within the nanosheets, which can effectively improve structural stability, reduce the diffusion length for lithium ions and electrons, and buffer volume expansion during the charge/discharge processes.

Advanced Water Management in PEFCs: Diffusion Layers with Patterned Wettability II. Measurement of Capillary Pressure Characteristic with Neutron and Synchrotron Imaging

In this paper, we present an experimental study on the development of gas diffusion layer (GDL) materials for fuel cells with dedicated water removal pathways generated using radiation induced grafting of hydrophilic compounds onto the hydrophobic polymer coating. The impact of several material parameters was studied: the carbon substrate type, the coating load, the grafted chemical compound and the pattern design (width and separation of the hydrophilic pathways). The corresponding materials were characterized for their capillary pressure characteristic during water imbibition experiments, in which we also evidenced the differences between injection from a narrow distribution channel in the center of the material (and thus strongly relying on lateral transport) and homogeneous injection from one face of the material. All materials parameters were observed to have a significant influence on the water distribution. In particular, the type of substrate has a dramatic impact, with results ranging from a nearly perfect separation of water between hydrophilic and hydrophobic domains for substrates having a narrow pore size distribution to a fully random imbibition of the material for substrates having a broad pore size distribution.

Universal scaling of the formation factor in clays: Example from the Nankai Trough

AbstractElectrical conductivity is a fundamental characteristic describing how strongly a network opposes flow of electrical current. In fully water‐saturated porous media the conductivity, represented by the formation factor, is mainly controlled by porosity, connectivity of the conducting phases, and the tortuosity of electrical current paths. Previous work has shown that universal scaling derived from percolation and effective medium theories accurately describes the relationship between formation factor and porosity when the percolation threshold is taken account, as well as the porosity value at which the scaling switches from percolation theory to effective medium theory. We determined the formation factor in clay‐rich sediments based on cation exchange capacity measurements on samples from five scientific ocean drilling sites in the Nankai Trough. We then compared the results to predictions from universal scaling after determining the volume of clay‐bound water and the percolation threshold. We found that the previously reported universal scaling relations hold in these clay‐rich sediments once the corrections are made for the clay‐bound water and that percolation scaling appears to be valid over the entire range of observed porosities, probably due to relatively broad pore size distributions or low pore system connectivity. Our results show that universal scaling can be applied to describe the porosity dependence of the formation factor in clay‐rich sediments when appropriate corrections are made for the presence of clay‐bound water.

Influence of polymer morphology on the adsorption behaviors of molecularly imprinted polymer‐methacrylic acid functionalized β‐cyclodextrin

ABSTRACTThe influence of molecularly imprinted polymer‐methacrylic acid functionalized β‐cyclodextrin (MIP(MAA‐β‐CD)) morphology on the adsorption behavior studies towards benzylparaben (BzP) was explored. The effects of time, concentration, and temperature towards BzP uptake were extensively evaluated. The adsorption performance of MIP(MAA‐β‐CD) was compared with that on the molecularly imprinted polymer‐methacrylic acid (MIP(MAA)) synthesized without β‐CD. The MIP(MAA‐β‐CD) was synthesized to obtain a spherical and spongy‐porous texture with a broad pore size distribution. The MIP(MAA‐β‐CD) showed fast kinetic and the intra‐particle diffusion model demonstrated a three step (surface and pore) adsorption process. The Koble‐Corrigan isotherm was the most suitable model for data fitting, which indicated that MIP(MAA‐β‐CD) had homogeneous and heterogeneous surfaces. This finding clearly demonstrated that the large uptake and strong affinity of MIP(MAA‐β‐CD) did not only probably result from the monomer‐template interactions, but also due to the morphological MIP(MAA‐β‐CD) structure. In contrary to MIP(MAA‐β‐CD), MIP(MAA) synthesized with uniform morphology and narrow pore size distribution had lower adsorption capacities and its kinetic data fitted the pseudo‐second order diffusion model, indicating a two‐step (surface only) adsorption process. The MIP(MAA) adsorption process followed the Langmuir isotherm model referred to solely homogeneous uptake. The calculated thermodynamic parameters showed that the BzP uptake was exothermic, spontaneous, and physisorption process onto MIPs, which supported the results of kinetics and isotherm adsorption data. This study clearly revealed that the presence of β‐CD improved the morphology of synthesized MIP, and automatically enhanced the adsorption behavior of MIP. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42720.

Influence of the porous support on diffusion in composite membranes

Composite membranes used in gas separation, pervaporation and reverse osmosis applications typically consist of at least one nonporous layer on top of a porous structure. The porous support restricts diffusion in the top layer because molecules can exit the layer only where a pore is present. This not only increases the path length for diffusion, but also increases the concentration gradient of the diffusing molecules as they approach the pore opening. These two effects combine to give the top layer a diffusion resistance that is greater than the intrinsic resistance of the layer, which is calculated as the actual thickness of the top layer, H, divided by the diffusion coefficient, D. In membrane terms, this means that the effective permeance of the composite membrane is smaller than the intrinsic permeance, which is calculated as the permeability coefficient, P, divided by H. The relative reduction in permeance is expressed by the restriction factor, Ψ, and is independent of the solubility and diffusion coefficients.We simulated the diffusion process using computational fluid dynamics (CFD) and determined the restriction factor, Ψ, as a function of the support porosity, ϕ, and a normalized dimension, τ, defined as the top layer thickness divided by the pore radius. By defining a dimensionless Restriction Number, NR, we were able to very accurately correlate the restriction factor data to the following equation:ψ=ϕ+1.6⋅NR1.11+1.6⋅NR1.1withNR=τ⋅ϕ1−ϕThe correlation predicts the restriction factor within 5% for all cases evaluated, which included three different pore distribution patterns and multiple pore size distributions with up to four different pore sizes. Our analysis suggests that the correlation is also applicable to porous supports with more realistic properties, such as random pore location and broader pore size distributions. The correlation is useful to evaluate the influence of the porous support on the permeance of composite membranes and shows that the effect can be significant in high-performance membranes.A limited number of CFD simulations were performed for composite membranes containing a gutter layer and show convincingly that a high permeability gutter layer can significantly improve the permeance of composite membranes while reducing selectivity by only a modest degree.

Reduction behavior and crushing strength of carbon-containing iron ore sinters prepared from tar recovered from coke oven gas

The reduction behavior and crushing strength of carbon-containing iron ore sinters (SI–C) prepared from coke oven gas (COG) tar have been examined with a quartz-made fixed bed reactor and with a tensile and compression testing machine, respectively. When an as-received iron ore sinter (SI) is heated at 10°C/min up to 600°C in 55% H2/He, the resulting sample (SI/600) gives a very small, broad pore size distribution profile, the surface area (SBET) and pore volume (VBJH) being 1.5m2/g and 0.005cm3/g, respectively. On the other hand, SI-pretreated in 55% H2/He at 450°C for 4h (SI-450) provides the pore distribution profile peaking around 10nm, and SBET and VBJH are 4m2/g and 0.02cm3/g, respectively. When carbon-containing iron ore sinters (SI/600–C and SI-450–C) are prepared by pyrolysis of the mixture of the pretreated SI and COG tar, no measurable amounts of SBET and VBJH are detectable in any case. The crushing strength of SI-450 is improved significantly by the deposition of tar-derived carbonaceous materials into the pores formed during the pre-treatment. In a temperature-programed heat treatment in He, the evolution of CO, CO2 and H2O from the SI-450–C samples start after 600°C, and each rate profile observed shows a large peak around 700–850°C. The extent of reduction of SI–C, SI/600–C or SI-450–C is 3, 19 or 55% on SI basis, respectively, and it depends on SBET and/or VBJH of the feed sample.