Slit-shaped Pores Research Articles

Influence of porosity parameters and electrolyte chemical composition on the power densities of non-aqueous and ionic liquid based supercapacitors

Influence of specific surface area (SDFT), total pore volume (Vtot) and other porosity characteristics on the electrochemical parameters and power density of two electrode electric double layer capacitors based on 1 M 3-ethyl-methylammonium tetrafluoroborate (Et3MeNBF4) solution in acetonitrile and on 1-ethyl-3-methylimidazolium tetrafluoroborate (EtMeImBF4) has been analysed. The pore size distribution data calculated from nitrogen, CO2 and Ar adsorption isotherms using mainly Carbon 2D non-local density functional theory for heterogeneous surface (2D-NLDFT-HS) model have been compared with crystallographic characteristics obtained by Raman, X-ray diffraction, photoelectron spectroscopy, etc. methods. It was shown that, chemical composition and crystallographic structure of precursor material, synthesis and activation conditions have decisive influence on the shape (spherical, cylindrical or slit-shape pores) and hierarchical porous structure and electrical conductivity of the carbon materials. Noticeable increase in series and parallel capacitances from 50 to 138 F g−1 in 1 M Et3MeNBF4 and up to 155 F g−1 in EtMeImBF4, gravimetric power density (up to 35 kW kg−1) and volumetric power density (up to 25 kW dm−3, both at discharge time 3.6 s in 1 M Et3MeNBF4 + AN electrolyte) for optimised EDLC has been demonstrated. For EtMeImBF4 based cells lower gravimetric (25 kW kg−1) and volumetric (10 kW dm−3) power densities have been achieved. For completing the EDLCs with high power and energy densities, highly micro-and mesoporous materials with optimum specific surface area (1200–1500 m2 g−1) but maximum (meso) pore volume (Vtot > 1.5 cm3 g−1) should be applied. Only for optimised EDLCs the very short characteristic charging/discharging times (lower than 0.3 s in Et3MeNBF4 + AN and 1.0 s in EtMeImBF4) can be achieved.

Reduction of mild-dehydrated, low-grade iron ore by ethanol

Low-grade iron ore with high combined water (CW) content (e.g., goethite) has been first dehydrated at low temperatures mildly to be slit-shaped nano-order pore, then has been reduced by ethanol (C2H5OH) charging under the heating conditions. Bioethanol as derived from biomass, regarded as a renewable and carbon-neutral resource, is a promising candidate as a reducing agent for ironmaking. In the experiments, ethanol was dropwise added to the mild-dehydrated, porous iron ore beds at heating conditions using the temperature-program. As a result, the ethanol was soon decomposed to CO and H2, which then reduced the iron oxides. Porous iron ore acts as a good catalyst for ethanol decomposition as it simultaneously reduces to metallic iron. Interestingly, iron oxides were reduced at a lower temperature, compared to conventional coal-based ironmaking in the blast furnace. Metallic Fe was obtained at only 750 °C, showing a reduction degree of 81%, due to the contribution of hydrogen reduction. The longer charging time of ethanol promotes the higher reduction degree as well as sufficient compositions of reducing gas (H2-CO) for the reduction process. The results of experiments using different iron ores revealed the general rule that the higher CW content in ore makes the larger surface area of the iron ore by mild-dehydration, causing higher reactivity in the reduction process. The results appealed that mild-dehydrated iron ore is good raw materials of bioethanol ironmaking, due to its nanopores.

Aqueous Hydrogen Sulfide in Slit-Shaped Silica Nanopores: Confinement Effects on Solubility, Structural, and Dynamical Properties

Confinement in nanometer-size pores affects structural and transport properties of water and coexisting volatile species. It has for example been reported that confinement can enhance the solubility of gases in water. We report here equilibrium molecular dynamics simulations for aqueous H2S confined in slit-shaped silica pores at 313 K. We investigated the effect of pore width on the H2S solubility in water. We quantified the molecular distribution of the fluid molecules within the pores, the hydration structure for solvated H2S molecules, and the dynamical properties of the confined fluids. The results show that confinement reduces the H2S solubility in water and that the solubility increases with the pore size. Our analysis suggests that these results are due to perturbations on the coordination of water molecules around H2S due to confinement. Confinement is found to dampen the dynamical properties of aqueous H2S as well. Comparing the results obtained for aqueous H2S to those, reported elsewhere, for ...

Pore structure of kapok fiber

Kapok is a natural fiber with an extremely high degree of hollowness. Numerous pores in its cell wall form the pathways for gas molecules. The delamination of the cell wall in scanning electron microscopy images and the hysteresis loop in nitrogen adsorption–desorption isotherms are interpreted to indicate that the kapok fiber has slit-shaped pores. Nitrogen adsorption method based on Brunauer–Emmett–Teller theory was used to analyze the mesopore. The specific surface area of kapok fiber is evaluated as 2.99 m2/g in the relative pressure range (0.05–0.35). The pore size of the fiber is distributed in 4–40 nm and mainly concentrated on 3–4 nm. The volume of the pores with diameters of 2–40 nm accounted for about 80% of the total pore volume, and those with diameters over 40 nm accounted for about 20%. By the Va ~ αs micropore evaluating method, it is found that the micropore volume of the fiber is about 7.0399×10−11 ml/g.

COMPARISON OF PORE FRACTAL CHARACTERISTICS BETWEEN MARINE AND CONTINENTAL SHALES

Fractal characterization offers a quantitative evaluation on the heterogeneity of pore structure which greatly affects gas adsorption and transportation in shales. To compare the fractal characteristics between marine and continental shales, nine samples from the Lower Silurian Longmaxi formation in the Sichuan basin and nine from the Middle Jurassic Dameigou formation in the Qaidam basin were collected. Reservoir properties and fractal dimensions were characterized for all the collected samples. In this study, fractal dimensions were originated from the Frenkel–Halsey–Hill (FHH) model with N[Formula: see text] adsorption data. Compared to continental shale, marine shale has greater values of quartz content, porosity, specific surface area and total pore volume but lower level of clay minerals content, permeability, average pore diameter and methane adsorption capacity. The quartz in marine shale is mostly associated with biogenic origin, while that in continental shale is mainly due to terrigenous debris. The N[Formula: see text] adsorption–desorption isotherms exhibit that marine shale has fewer inkbottle-shaped pores but more plate-like and slit-shaped pores than continental shale. Two fractal dimensions ([Formula: see text] and [Formula: see text] were obtained at [Formula: see text] of 0–0.5 and 0.5–1. The dimension [Formula: see text] is commonly greater than [Formula: see text], suggesting that larger pores (diameter [Formula: see text][Formula: see text]nm) have more complex structures than small pores (diameter [Formula: see text][Formula: see text]nm). The fractal dimensions (both [Formula: see text] and [Formula: see text]) positively correlate to clay minerals content, specific surface area and methane adsorption capacity, but have negative relationships with porosity, permeability and average pore diameter. The fractal dimensions increase proportionally with the increasing quartz content in marine shale but have no obvious correlation with that in continental shale. The dimension [Formula: see text] is correlative to the TOC content and permeability of marine shale at a similar degree with dimension [Formula: see text], while the dimension [Formula: see text] is more sensitive to those of continental shale than dimension [Formula: see text]. Compared with dimension [Formula: see text], for two shales, dimension [Formula: see text] is better associated with the content of clay minerals but has worse correlations with the specific surface area and average pore diameter.

In Russian

Sorption materials for rare earth elements based on ethylene glycol dimethacrylate and methacrylic acid copolymers with different cross-link ratio have been synthesized by ion-imprinting method. Two approaches of ion-imprinted polymers elaboration – chemical immobilization and trapping – have been applied. The obtained materials have been characterized via scanning electron microscopy and IR-spectroscopy. The synthesized polymers exist as aggregates of plate-like particles with slit-shaped pores. The specific surface area of obtained sorbents varies from 109 to 350 m 2 /g. Sorption performance of synthesized polymers towards rare earth ions as well as its dependence on cross-link ratio and ion-imprinting version has been investigated. The sorption materials under study exhibit best sorption efficiency towards rare earth elements in solutions with pH 6. The maximum sorption capacity of the obtained sorbents is around 0.3 mmol/g. According to these results, imprinted polymer with cross-link ratio 80 % synthesized via trapping approach is characterized by the highest distribution coefficient values. The observed tetrad effect for rare earth elements adsorption reflects the chemical nature of adsorption process on the synthesized materials.

Effect of Water Saturation on Pressure-Dependent Permeability of Carboniferous Shale of the Qaidam Basin, China

Permeability is the most important parameter that describes gas flow characteristics in shale. Water saturation and effective pressure have a considerable effect on shale permeability. This paper presents the results of a laboratory study of the effects of water saturation and effective pressure on gas permeability in Carboniferous shales of the Qaidam Basin, China. The permeability of shale samples with varying water saturation (0–33 wt%) was measured at effective pressure of 6.9 to 27.59 MPa and at low mean pore pressure (< 6.89 MPa) at room temperature, using a pressure pulse decay permeameter. The results indicate that the water saturation and the effective pressure are the main factors affecting the shale permeability. Permeability of sample C034, which has a high clay content and is dominated by nanoscale slit-shaped pores, shows a large decrease (up to 90%) with increasing water saturation (from 0 to 31.7 wt%), depending on the effective pressure. A much larger permeability reduction with increasing water saturation fraction is associated with the swelling of clay minerals. For each sample with varying water saturation, our analyses revealed a consistent line relationship between log permeability and effective pressure variation. The impact of effective pressure on the measured permeability becomes more significant as water saturation increases. With increasing water saturation, the gas slippage factor decreases and calculated effective pore size increases, and gas–water flow in the shale samples occurs as channel flow. This study provides practical information for further studies of stress-dependent permeability of shale with water and the gas slippage effect in two-phase, gas–water flow.

Geochemical and petrophysical characteristics of Permian shale gas reservoirs of Raniganj Basin, West Bengal, India

Thick shale horizons of Permian age emerged as the potential source of gas through primary investigation, and resulted into the first Indian pilot-scale gas recovery demonstration project in the Raniganj basin. However, the relation of geochemical properties with shale pore matrix, porosity and permeability mechanism are yet to be evaluated for better dealing the phenomena of diffusion, transport and gas recovery. In this study, the analyses like proximate, Rock-Eval, TOC, VRo, low pressure N2 sorption, porosity, permeability, SEM-EDX and image processing have been carried out. The values of S1, S2, TOC and Tmax indicated fair to excellent source rock potential of the shales having type III/IV kerogens prone to thermal gas genesis. The low pressure N2 desorption curve of Raniganj Formation shales shows the Type H3 hysteresis comprising slit-shaped pores. The Barren Measures shales have Type H2 and H3 hysteresis patterns specifying to ink bottle-shaped pores and slit-shaped pores. Whereas, the oldest Barakar Formation shales are having ink bottle-shaped pores caused due to blocking effect. The slit-shaped pores favour the pore network and characteristically excellent for the flow of gas. The results of SEM-EDX are indicating alteration stability in the order of O<C<Si<Al<Fe<K<Na<Ca following the trend of least to strong weathering (Barakar<Barren Measures<Raniganj). The siliciclastic facies (Al-Si-Fe) signifying massive and laminated shale beds deposited under fluvio-lacustrine palaeoenvironment favouring alteration and accumulation of K-feldspar and aluminous minerals to clay.The increasing Tmax values with a centric decrease in porosity and permeability, specifying the role of devolatilization, disintegration and blocking of pore spaces/openings is a function of the thermal gradient. The linear evolution of multipoint BET surface area with increasing porosity suggests that the porosity values from 2.0 to 6.5% mainly corresponds to pore size of 3.0–11.0nm. Similarly, the inverse relationship between average pore size and porosity attributed to a greater contribution of smaller pores in total porosity. The pore network model derived through the SEM image processing has shown two types of connectivity - i) various pore sizes of diverse pore throats with dual opening directions, and ii) interlinked large and small pores obeying similar normal distributions. The Barren Measures shales have shown higher pore connectivity than the Raniganj and Barakar Formation shales.

Dispersion Peculiarities of Crystalline Cellulose Upon its Moistening

A modernized scheme of the structure of native cotton cellulose microfibrils is proposed, providing for the presence of slit-shaped pores in its structure and satisfying most of the results of modern studies of its supramolecular structure and sorption properties. It is shown that within the framework of this scheme it is possible to determine the content of elementary fibrils in microfibrils and the degree of crystallinity of cellulose using 1H-NMR and sorption measurements. The mechanism and character of dispersion of microfibrils, accompanied by supramolecular rearrangements of moistened cellulose, was investigated.

The Nitric Oxide Dimer Reaction in Carbon Nanopores.

When confined within nanoporous carbons (activated carbon fibers or carbon nanotubes) having pore widths of about 1 nm, nitric oxide is found to react completely to form the dimer, (NO)2, even though almost no dimers are present in the bulk gas phase in equilibrium with the pore phase. Moreover, the yield of dimer is unchanged upon varying the temperature over the range studied in the experiments. Earlier molecular simulation studies showed a significant increase in dimer formation in carbon nanopores, but the dimer yield was considerably less than that found in the experiments, and decreased rapidly as the temperature was raised. Here, we report an ab initio and molecular simulation study of this reaction in both slit-shaped pores and single-walled carbon nanotubes. The ab initio calculations show that the nitric oxide dimer forms a weak chemical bond with the carbon, and the bonding energy is more than 20 times stronger than the van der Waals energy assumed in the previous studies. When this is accounted for, the predicted dimer yield is in good agreement with the experimental values, as is its temperature dependence. We also report results for the pressure tensor components for this confined reactive mixture. Local tangential pressures near the pore walls are as high as millions of bar, reflecting the strong nanoscale forces.

Investigating Gas–Adsorption, Stress–Dependence, and Non–Darcy–Flow Effects on Gas Storage and Transfer in Nanopores by Use of Simplified Local Density Model

Summary As an unconventional rock, shale contains all the features of coalbed and tight sandstone specified as gas-adsorption capacity, microscale and nanoscale porosity, and extremely low permeability. The gas-storage mechanism of shale rocks not only is dominated by free gas in macropores and natural fractures, but also is controlled by adsorbed gas in microporous organic matter (kerogen) and clay minerals. Furthermore, Darcy's law is no longer applicable to describe gas transport in nanopores (Javadpour 2009; Wu et al. 2015). Therefore, developing a reliable model to calculate effective porosity and permeability in nanopores considering the effects of gas adsorption, stress dependence, and non-Darcy flow is crucial to characterize properties of shale-gas reservoirs and explain gas-flow behavior in nanopores. In this study, the simplified local density (SLD) model, which has been successfully applied to analyze gas adsorption on coal, activated carbon, and shale in recent studies, is used to analyze methane-adsorption data measured from five shale-core plugs in the laboratory (Mohammad et al. 2011; Chareonsuppanimit et al. 2012; Clarkson and Haghshenas 2016). A new approach to determine the thickness of adsorbed gas dependent on the density profile of the SLD model is proposed, which in turn provides the correction of methane adsorption to pore volume (PV). Furthermore, stress-dependence effect is incorporated into the gas-adsorption effect to generate an effective porosity function in shale rocks. In addition, non-Darcy-flow effect on gas transfer in nanopores is derived from the slit-shaped pore geometry of the SLD model and is represented by a weighted sum of second-order gas slippage and Knudsen diffusion. Consequently, the effective permeability is established as a function of the effects of gas adsorption, stress dependence, and non-Darcy flow. Moreover, the functions of effective porosity and permeability are incorporated into a numerical simulator to perform history matching for gas-production data from a horizontal well with multistage hydraulic fractures in a Barnett Shale reservoir. The simulation results properly match the gas-production data at the field scale. Finally, sensitivity studies on gas adsorption, stress dependence, and non-Darcy-flow effects are conducted to investigate their contributions to evaluating and estimating gas production from shale-gas reservoirs. The results of this study suggest that gas adsorption and non-Darcy-flow effects are two competitive aspects that have major influences on shale-gas production. The developed model including gas-adsorption, stress-dependence, and non-Darcy-flow effects provides insight into the characterization of rock properties and the description of gas-transport behavior in shale-gas reservoirs.

Pressure Enhancement in Confined Fluids: Effect of Molecular Shape and Fluid-Wall Interactions.

Recently, several experimental and simulation studies have found that phenomena that normally occur at extremely high pressures in a bulk phase can occur in nanophases confined within porous materials at much lower bulk phase pressures, thus providing an alternative route to study high-pressure phenomena. In this work, we examine the effect on the tangential pressure of varying the molecular shape, strength of the fluid-wall interactions, and pore width, for carbon slit-shaped pores. We find that, for multisite molecules, the presence of additional rotational degrees of freedom leads to unique changes in the shape of the tangential pressure profile, especially in larger pores. We show that, due to the direct relationship between the molecular density and the fluid-wall interactions, the latter have a large impact on the pressure tensor. The molecular shape and pore size have a notable impact on the layering of molecules in the pore, greatly influencing both the shape and scale of the tangential pressure profile.

Effect of pore structure on shale oil accumulation in the lower third member of the Shahejie formation, Zhanhua Sag, eastern China: Evidence from gas adsorption and nuclear magnetic resonance

As shale oil occurs primarily in micro–nano pores and fractures, research about the effect of pore structure on shale oil accumulation has great significance for shale oil exploration and development. The effect of pore structure on shale oil accumulation in the lower third member of the Shahejie formation (Es3l), Zhanhua Sag, eastern China was investigated using gas adsorption, soxhlet extraction, nuclear magnetic resonance (NMR) analysis, and field emission scanning electron microscope (FE-SEM) observation. The results indicated that the samples contained a larger amount of ink-bottle-shaped and slit-shaped pores after extraction than before extraction. The pore volume and specific surface area of the samples were approximately 2.5 times larger after extraction than before extraction. Residual hydrocarbon occurred primarily in the free-state form in pores with diameters of 10–1000 nm, which can provide sufficient pore volume for free hydrocarbon accumulation. Therefore, pores with diameters of 10–1000 nm were regarded as “oil-enriched pores”, which are effective pores for shale oil exploration, whereas pores with diameters smaller than 10 nm were regarded as “oil-ineffective pores”. Samples with only well-developed small pores with diameters smaller than 1000 nm showed high oil saturation, whereas samples with both small pores and also relatively large pores and micro-fractures presented low oil saturation. As the minimum pore size allowing fluid expulsion is 1000 nm, pores with diameters greater than 1000 nm were considered as “oil-percolated pores”. Large pores and micro-fractures are generally interconnected and may even form a complex fracture mesh, which greatly improves the permeability of shale reservoirs and is beneficial to fluid discharge.

Promising use of waste coal in the production of insulating material without the use of traditional natural materials

It is shown that one of the promising directions for the production of thermal insulation materials are waste coal (waste of the fuel and energy complex). Insulation materials (ceramic lightweight bricks) with the density not higher than 1250 kg/m3 were derived from waste coal without using the traditional natural raw materials. The innovative proposals for the use of waste coal in the manufacture of insulation materials were developed and their novelty was confirmed by four RF Patents. The investigated coal waste is characterized by high calorific value (1800–2800 kcal/kg); thus, such waste should be used not only as nonplastic materials but also as combustible additives so as to exclude the use of anthracite, coke breeze, etc., in the compositions of ceramic masses. Combustible additives containing increased amounts of organic compounds (the loss of ignition of >15%) and iron oxide (Fe2O3 of more than 3%) not only increase the porosity of ceramic products but also facilitate the uniform sintering of a ceramic crock. It was shown that there are three types of pores that mainly occur in samples of insulation materials: slitlike ones, isothermal ones, and bizarre pores. In addition, the samples contain relatively large oval pores and “channel” isometric pores. These pores determine the water absorption of ceramic materials. The presence of pores and, consequently, the heterogeneity of the material adversely affect the properties of ceramic products, and the harmful effect on the mechanical strength of the elongated (slitlike) pores is estimated at about 5 times higher than that for round ones. In addition, the presence of slit-shaped pores indicates the incompleteness of the sintering processes. The use of waste from the fuel and energy complex in the production of ceramic materials makes it possible to efficiently utilize industrial waste, to save scarce traditional natural materials, to expand the range of raw materials for construction materials, and to make a significant contribution to environmental protection.

Pore characteristics of lacustrine mudstones from the Cretaceous Qingshankou Formation, Songliao Basin

Cretaceous Qingshankou ([Formula: see text]) mudstone of lacustrine origin is the major source rock for conventional hydrocarbon currently being produced in the Daqing and Jilin oilfields of the Songliao Basin, which is one of the largest continental basins in the world. Therefore, elucidating the geochemical and petrological characteristics of the [Formula: see text] mudstone is important to help determine its quality as an economically viable source for shale oil production. In our study, eight dark mudstone core samples from the [Formula: see text] formation were subjected to total organic carbon (TOC), Rock-Eval pyrolysis, X-ray diffraction, scanning electron microscopy (SEM), field emission SEM (FE-SEM), and low-pressure [Formula: see text] gas adsorption (LPGA-[Formula: see text]) experiments. Geochemical and petrological analysis results indicated the presence of a high TOC content, which originated mainly from alginate and some plant-derived organic matter, whereas bitumen was frequently present in mudstones with thermal maturity in the oil-generation stage. The [Formula: see text] mudstones were comprised mainly of clay minerals, followed by quartz, feldspar, and carbonates. The LPGA-[Formula: see text] experiments revealed the presence of nanoscale slit-shaped pores, and the contribution from mesopores to the total pore volume was the highest in most of the samples. The average pore diameters (APDs) of the mudstone samples were all smaller than 20 nm (4.36–17.79 nm). We determined that there was a clear positive correlation between the APD and the free oil content; however, there were no clear correlations between the APDs and the quartz, carbonate, and TOC contents. FEM studies revealed the presence of intergranular pores with widths of approximately 10 μm, micron-level autogenetic organic matter pores within spores, organic matter pores caused by the hydrocarbon generation effect within organic matter or clay-organic complexes, and intraparticle pores within clays or pyrite framboids. The microlevel intergranular pores might play an important role in shale oil accumulation from source rock of lacustrine origin.

Glaucomatous changes in lamina pores shape within the lamina cribrosa using wide bandwidth, femtosecond mode-locked laser OCT.

PurposeThe lamina cribrosa (LC) is known to play a critical role in the pathogenesis of glaucoma. Although it has been reported that striae-shaped or slit-shaped lamina pores are more frequent in eyes with primary open angle glaucoma (POAG), this observation is based only on fundus photography. The primary object of this study is to perform layer-by-layer comparisons of the shape of lamina pores within the LC in vivo.DesignCross-sectional study.MethodsOptic nerve head B-scans were obtained using custom-made broad-wavelength optical coherence tomography with a mode-locked laser. A total of 300 single B-scans per eye were obtained and three-dimensional images were rendered from these image sequences to obtain 2-μm thin-slice en face images of the LC. Elongation indices (EIs) of the lamina pores were measured from the anterior surface (AS) of the LC to the deeper layers in 40-μm increments.ResultsThirteen eyes from 10 primary open angle glaucoma (POAG) patients of mean deviation -15.2 (-16.5, -12.9) (median [25,75 percentile]) dB and 10 eyes from 7 normal controls were studied. Although the EI value was not significantly different between the superior, temporal and inferior regions of the LC at any depth level in either group, it was greater at the AS than at the 40 μm and 80 μm depth levels (P < .001) in both groups, and was greater in the POAG group only at the AS and 40 μm depth level (P ≤ .05). After adjustment for age and refraction, the effects of depth and presence of POAG on the EI value remained significant. Also, the severity of glaucoma and depth were significant factors associated with EI in multivariate analysis.ConclusionsElongation of lamina pores was significantly more evident at the anterior surface and the 40-μm depth level of the LC in POAG eyes than in normal eyes, suggesting that nerve fiber bundles passing through the LC were under greater stress in the anterior layers of the LC.

Studies on the correlation between nanostructure and pore development of polymeric precursor-based activated hard carbons: II. Transmission electron microscopy and Raman spectroscopy studies

Abstract In a previous study, we reported on activated polymer-based hard carbons (APHCs), which were prepared using CO 2 activation and characterized according to activation conditions, including textural properties such as specific surface area and pore volume. This paper was focused on the correlation between nanostructure and pore development of APHCs by using Cs-corrected-field emission transmission electron microscopy (Cs-corrected FE-TEM) and Raman spectroscopy to supplement the in-depth explanation. In the TEM analysis, the APHCs were observed to contain slit-shaped pores (SPs) and little cylindrical pores (CPs). And Raman spectroscopy was used in order to determine the degree of development of the crystal size (L a ) in the APHCs. The size of L a increased with increasing activation time until it was nearly 3 nm. These small crystallites might cause the SPs development, resulting in the high micropore volume of the APHCs. From a result of Raman analysis, it was confirmed that the L a value and the ratio of I D /I G value were in a proportional relation. The reason for this relation is that the L a value has grown up to about 3 nm, which is consistent with the Ferrari equation.

Cooperative CO2 adsorption promotes high CO2 adsorption density over wide optimal nanopore range

Separation of CO2 based on adsorption, absorption, and membrane techniques is a crucial technology necessary to address current global warming issues. Porous media are essential for all these approaches and understanding the nature of the porous structure is important for achieving highly efficient CO2 adsorption. Porous carbon is considered to be a suitable porous media for investigating the fundamental mechanisms of CO2 adsorption, because of its simple morphology and its availability in a wide range of well-defined pore sizes. In this study, we investigated the dependence of CO2 adsorption on pore structures such as pore size, volume, and specific surface area. We also studied slit-shaped and cylindrical pore morphologies based on activated carbon fibers of 0.6–1.7 nm and carbon nanotubes of 1–5 nm, respectively, with relatively uniform structures. Porous media with larger specific surface areas gave higher CO2 adsorption densities than those of media having larger pore volumes. Narrower pores gave higher adsorption densities because of deep adsorption potential wells. However, at a higher pressure CO2 adsorption densities increased again in nanopores including micropores and small mesopores. The optimal pore size ranges of CO2 adsorption in the slit-shaped and cylindrical carbon pores were 0.4–1.2 and 1.0–2.0 nm, respectively, although a high adsorption density was only expected for the narrow carbon nanopores from adsorption potentials. The wider nanopore ranges than expected nanopore ranges are reasonable when considering intermolecular interactions in addition to CO2–carbon pore interactions. Therefore, cooperative adsorption among CO2 in relatively narrow nanopores can allow for high density and high capacity adsorption.

Transport Mechanism of Guest Methane in Water-Filled Nanopores

We computed the transport of methane through 1 nm wide slit-shaped pores carved out of selected solid substrates using classical molecular dynamics simulations. The transport mechanism was elucidated via the implementation of the well-tempered metadynamics algorithm, which allowed for the quantification and visualization of the free energy landscape sampled by the guest molecule. Models for silica, magnesium oxide, alumina, muscovite, and calcite were used as solid substrates. Slit-shaped pores of width 1 nm were carved out of these materials and filled with liquid water. Methane was then inserted at low concentration. The results show that the diffusion of methane through the hydrated pores is strongly dependent on the solid substrate. While methane molecules diffuse isotropically along the directions parallel to the pore surfaces in most of the pores considered, anisotropic diffusion was observed in the hydrated calcite pore. The differences observed in the various pores are due to local molecular prope...

Pore Structure Characterization of Different Rank Coals Using N2 and CO2 Adsorption and Its Effect on CH4 Adsorption Capacity: A Case in Panguan Syncline, Western Guizhou, China

To determine the pore structure characteristics of different coal ranks in Panguan syncline, both N2 adsorption–desorption (LP-N2GA) and CO2 adsorption (LP-CO2GA) were carried out with the goal of revealing the differentiation evolution of total pore volume (TPV), specific surface area (SSA), pore size distribution (PSD), and pore shape of 14 coal samples, and the influences of SSA to adsorption capability at different sizes (supermicroporous < 2 nm, micropore: 2–10 nm, transition pore: 10–100 nm) were further discussed. Density functional theory (DFT) is used for the determination of pore structure parameters to ensure its accuracy. Results show that the pore shape in the Panguan area is mostly the semi-open pores with poor connectivity (e.g., wedge-shaped, cylindrical, and slit-shaped pores with one closed side). Only a small amount of the pores is in open shapes (e.g., slit-shaped pores or cylindrical pores with two ends open). For most of the coal samples, the PSDs of pores tested by LP-N2GA appear to be multimodal, and the N2-TPV is mainly from the contribution of the transition pore (73.69–95.21%), followed by the micropore. The PSDs of supermicroporous (tested by LP-CO2GA) appear to be bimodal, with two peak values present at 0.52–0.61 nm and 0.82–0.87 nm, respectively, and a bigger pore volume distribution interval corresponds to a higher specific surface area. The N2-SSA (pore diameter ranges from 2 to 100 nm) mainly comes from the contribution of the pores 2–3 nm in diameter, and a bigger N2-TPV means a higher N2-SSA. The CO2-SSA (pore diameter ranges from 0.489 to 1.083 nm) which has a better positive linear correlation with Langmuir volume is related to CO2-TPV and the distribution frequency of pore volume at different pore sizes, and the contribution rate of CO2-SSA to the total SSA (CO2-SSA + N2-SSA) reaches 99%, indicating that supermicroporous has a significant effect on the coal adsorption capacity. With the increase of the vitrinite reflectance (Ro,ran, 0.83 → 2.27%), the N2-SSA increase gradually, and its increase tendency presents to be a half-reversed “U” shape in the whole, while the CO2-SSA presents an extremely significant linear increase tendency. Accordingly, the Langmuir volume (2.61 → 21.26 m3/t) also displays a linear growth tendency with the increasing vitrinite reflectance. The results of this study will provide guidance to the CBM development in the Panguan area.