Changes In Pore Size Distribution Research Articles

Investigation on the anti-carbonation properties of alkali-activated slag concrete: Effect of activator types and dosages

In this paper, three alkaline activators, namely sodium hydroxide (SH), calcium oxide and sodium carbonate (COSC), calcium hydroxide and sodium sulfate (CHSS), and the influence of different alkali equivalents on the carbonation resistance of alkali-activated slag concrete (AASC) were investigated. By testing the mechanical properties at different carbonation ages of AASC with three types of activators at varying alkali equivalents (4%, 6%, and 8%), along with the changes in carbonation depth, this study aims to characterize hydration products and porosity through microstructural analysis. The objective is to explain the mechanism by which carbonation affects the AASC structure. The findings showed that the carbonation rate (i.e., the growth rate of the carbonation depth) of AASC was CHSS > COSC > SH when the exciter dosages were the same, and the carbonation rate of all samples tended to slow down as the alkali components increased. Calcite and spherulite were the calcium carbonate morphologies after SH, COSC, and CHSS carbonation according to XRD, TG/DSC, and pore structure tests; the calcium carbonate content decreased with increasing alkali equivalent after carbonation. Since the pore-increasing effect of carbonation due to the destruction of C–S–H is weaker than the filling effect produced by calcium carbonate, the total pore volume of SH, COSC, and CHSS decreased due to the activator effect after carbonation. Specifically, the calcium carbonate created by carbonation repairs pores and cracks of matrix, but its presence also reduces the calcium hydroxide concentration, leading to a decrease in the alkalinity of the pore solution, which disrupts the structure of the hydration products and loosens the matrix. The focus is on which aspect is more decisive. Interestingly, small pores however decreased, while there was an increase in larger pore sizes resulting in a change in pore size distribution. However, this negative impact on pore distribution decreased with increasing alkali dosage.

Study on Preparation Technology and Heat Conduction Mechanism of High-Purity & Ultra-Fine Alumina Powder from Scrap Aluminum Cans

In view of the increasing scarcity of bauxite resources in China, the high energy consumption and high pollution of electrolytic aluminum, and the requirements for energy conservation and environmental protection, aluminum recycling and high-value utilization of its derivatives have evolved into a crucial development requirement for the aluminum industry in the future. As an important part of the development of recycled aluminum resources, the high-value application of scrap aluminum cans has always been a hot research topic in various recycled aluminum processing enterprises and scientific research units. The traditional regeneration system of waste cans includes a series of complex technological processes such as pretreatment, paint removal, smelting system and casting system, which is difficult to control in the middle of the process. Most of the recycled scrap aluminum cans are cast and downgraded for later use, except for a part of them used as alloy materials for new cans. In this paper, combined with the research on the preparation of metal aluminum alkoxide, combined with recrystallization heat conduction to further study the effective dissolution or adsorption how to remove impurity elements to obtain high-purity aluminum alcohol salt mechanism research, and thermal effect of alcohols with different carbon chains on the synthesis of high-purity aluminum alkoxide was further investigated. Moreover, the changes in morphology and pore size distribution of hydrolyzed alumina precursor materials under different hydrothermal temperature conditions were discussed by means of the alkoxide hydrolysis-sol-gel process. Eventually, the aluminum alkoxide was obtained by the reaction of waste cans with isopropanol and heavy crystal thermal conductivity, and the high-purity aluminum alkoxide was purified by vacuum distillation. Under the hydrothermal condition of 160°C, the high-purity alumina material with a purity of 99.99% and an original crystal size of 200nm was prepared.

Dissipative Particle Dynamics Study on the Phase Region of Spatial Gradient Materials Produced by Photoinduced Isomerization

AbstractSpatial gradient materials occupy an important research position in the field of functional materials with their unique porous structure. Gradient changes in pore size and density distribution have received extensive attention in the fields of biomimetic and smart materials. The gradient transition law is mathematically related to the driving force of isomerization reaction and component phase separation. In this study, a dissipative particle dynamics simulation is used to introduce photoisomerization reactions into the system. Lambert's law is used to construct a reaction model for the variation of light intensity with irradiation depth, and a gradient structure with a spatial transition law is obtained. The effects of the extinction coefficient ε, the initial reaction probability Pr0, and the interactions α(A,B) between the isomerized molecules as well as the viscosity on the formation of the gradient structure are investigated in detail. Furthermore, the mathematical proportionality between the size of the phase region and interfacial energy of the two phases is elucidated. This study provides preliminary computational insights into the factors affecting the photoinduced phase separation process of polymeric gradient materials. It may help to develop effective strategies to improve the phase separation and properties of polymer gradient materials in subsequent studies.

Characterization of soil pores in strip-tilled and conventionally-tilled soil using X-ray computed tomography

Changes in soil pore size distribution and connectivity can affect contaminant transport. Climate, soil type, and agricultural management practices can influence these characteristics. Conservation tillage practices, such as strip tillage, have been promoted as agricultural management practices that can help reduce soil erosion and nutrient loss in runoff. However, limited information exists in the literature on the effect of strip tillage on soil pore characteristics. Thus, the objective of this research study was to assess the effects of different tillage practices i.e., conventional tillage (CT) vs. strip tillage (ST), on soil pore properties and quantify change in soil pore characteristics as a function of season. Undisturbed cylindrical soil columns (150 mm diameter and 640 mm length) were collected from a field in Alabama, USA planted with cotton (Gossypium hirsutum L.) under ST and CT treatments during two seasons i.e., fall 2021 and spring 2022. Soil cores were collected from CT and ST portions of the field, in the fall, following cotton harvest and before planting a cover crop (season 1), and in the spring, after the cover crop had matured (season 2). X-ray computed tomography was used to scan the soil cores and quantify soil pore characteristics. Results show that the ST treatment had significantly (p < 0.05) greater macroporosity values, network density, macropore length density, and interconnectivity compared to the CT in season 1. This was attributed to ST being a minimally disturbed treatment: thereby, it has a better chance of preserving cracks and biological activity as compared to CT, which is more prone to destruction of large macropores. The pore properties also showed a drastic decrease in values during season 2, especially for the top 200 mm of the soil profile in response to rainfall induced soil reconsolidation in both the tillage systems. Overall, this study showed that pore morphology can be affected by tillage and seasonal aspects associated with them.

Liming leads to changes in the physical properties of acidified forest soils

AbstractBackgroundForest liming is a common practice in many German forests, which aims primarily at improving soil chemical properties that have been negatively impacted by acid rain. Effects on physical functions have not yet been studied widely.AimsThe hypothesis of this study is that chemical changes after liming lead to changes in the physical properties of the humus layer and mineral soil.MethodsWe studied soil physical characteristics (water retention characteristics, air and water permeabilities, and conductivities) of limed and adjacent control plots of sandy to loamy, acidified soils under spruce and beech‐dominated stands.ResultsWe found differences between limed and control plots, especially in the humus layer and mineral top soil. Here, air capacity values (representing air‐filled macropores at −6 kPa) have experienced an increase, while available water capacities (representing the sum of dewatered mesopores between −6 and −1500 kPa) were reduced to a variable extent. These changes in pore size distributions affected gas diffusion as well as gas permeability positively. Unsaturated hydraulic conductivity was not affected. Below the top mineral soil, a tendency to a reduced macroporosity and gas permeability was observed, but no clear changes were detected.ConclusionsSmall but significant changes of soil physical properties and functions in the humus layer and top mineral soil are discussed to be an indirect effect of forest liming. Liming improves pH and nutrient availability, which in turn should have stimulated activity and abundance of soil fauna, especially earthworms. Where observed, their activity could explain the observed changes in soil physical properties. We believe that effects below the top soil might be due to mobilization and translocation of soil particles and a clogging of pores, but these depths were only studied at three plots. Compared to common liming practices, however, the investigated sites are characterized by significantly higher lime applications. The effects on practice liming areas in forestry praxis are therefore likely to be smaller than in this study.

Design of a Tension Infiltrometer with Automated Data Collection Using a Supervisory Control and Data Acquisition System

This study highlights the importance of water infiltration in hydrological basin management, emphasizing its role in water services, water quality regulation, and temporal patterns. To measure this crucial function, this study introduces a portable and user-friendly tension infiltrometer designed for easy assembly and data collection. The tension infiltrometer, based on the 2009 design by Spongrová and Kechavarzi, offers a comprehensive characterization of the soil properties related to water flow. It eliminates the influence of preferential flow, providing accurate data. Additionally, it accommodates changes in pore size distribution within the soil, which is crucial for understanding water movement. This study discusses the challenges associated with traditional infiltration measurement tools, like double-ring infiltrometers and single rings, which are not easily transported and can lead to inaccuracies. In response, the proposed infiltrometer simplifies data collection, making it accessible to a broader range of users. This study also explores the use of the VL53L0X distance sensor in the infiltrometer, providing an innovative solution for measuring the water column height. The system’s user interface allows real-time data collection and analysis, significantly reducing the processing time compared to that of the manual methods. Overall, this work demonstrates the potential for advancement in hydrological basin management using user-friendly instrumentation and automated data collection, paving the way for improved research and decision making in environmental services, conservation, and restoration efforts within these ecosystems.

Effects of one-sided thermal shock and hold on alumina-based oxide/oxide ceramic matrix composites for temperatures in excess of 1200 °C

Nextel™720/alumina based ceramic matrix composite plates were subjected to one-sided thermal shock and 30-minute hold at 1100 °C, 1250 °C, 1400 °C and 1550 °C. Post exposure, the plates were evaluated for physical, structural, and microstructural changes using state-of-the art characterization techniques as well as standard mechanical testing procedures. Physically, no significant mass or dimensional changes were noted, while the surface roughness decreased on the exposed side for all the cases. Structurally, both the tensile and flexural strengths decreased for the 1550 °C case, but not for the other temperatures. In addition, short-beam strength tests showed no effect on interlaminar strength as a result of the elevated temperature exposures for the 30-minute duration considered. Microstructurally, SEM/EDS evaluations showed no significant change in the microstructure or element composition on the exposed and back sides. However, mercury intrusion porosity measurements did show a change in pore size distribution due to the combined effect of matrix shrinkage and further matrix microcracking. Combined results show that the operational limit of the composite can be pushed significantly beyond 1200 °C for shorter (in minutes) durations provided it is structurally viable for the application sought.

Experimental study of high temperature on the shear properties of early-age concrete

Fire accidents happen randomly which may occur in the construction of concrete buildings. In this study, the effects of high temperature and curing ages on shear properties of early-age concrete were experimentally studied. The pore structure of early-age concrete before heating, after heating, and re-curing after heating were examined through nuclear magnetic resonance and scanning electron microscope tests. Experimental results reveal that high temperature treatment of early-age concrete multiplies the number of pores but has little influence on the change of pore size distribution, while the re-curing treatment reduces pore size but has little influence on the change of pore numbers. Under the same exposed temperature, the shear strength of concretes before heating, after heating, and re-curing after heating increases gradually with curing ages. For concretes with certain curing ages, the shear strength increases first and then decreases with the exposed high temperature. While the cohesion and internal friction angle show a negative relationship with elevated temperature. The research can provide base data for buildings encountering fire accidents.

Pore Characteristics, Oil Contents and Factors Influencing Laminated Shale in the First Member of the Qingshankou Formation in the Gulong Sag, Northern Songliao Basin

To clarify the reservoir characteristics of laminated shale, the occurrence mechanism of shale oil and its influencing factors in the Gulong Sag, northern Songliao Basin, are studied to better guide the exploration and development of shale oil there. First, X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) are used to characterize the pore types, pore geneses and factors influencing the pore volume in the study area. Second, the organic matter of the samples is extracted with a mixture of dichloromethane and methanol. Total organic carbon (TOC), nitrogen adsorption and Rock-Eval tests are performed on the samples before and after extraction to reveal the pore size distribution after extraction. The factors influencing free and adsorbed shale oil and the lower limit of pore size are discussed in detail. The results show that interparticle pores (interP pores), intraparticle pores (intraP pores), organic matter pores (OM pores) and microfractures can be found in the laminated shale (Q1) in the Gulong Sag, Songliao Basin, and that the interP pores and intercrystalline pores in clay minerals are the main pores. The FE-SEM results show that the diameters of interP pores vary from several hundred nanometers to several microns, and their morphologies are mainly triangular, strip-shaped or irregular. The morphology of the intercrystalline pores in the clay minerals is generally irregular, depending on the crystal type and arrangement of clay minerals. According to the characteristics of the nitrogen adsorption and desorption curves, the pore morphologies are mainly slit-shaped pores, parallel-plate-shaped pores and ink-bottle-shaped pores. The pore size distribution is mostly bimodal, and the pore volume contribution is the greatest in the pore size range of 10~20 nm. Before and after extraction, the overall characteristics of the pore size distribution change only slightly, but the number of micropores increases significantly. Different minerals have different degrees of influence on the proportions of micropores, mesopores and macropores. Quartz mainly inhibits the formation of micropores, while the overall effect on mesopores and macropores is positive depending on the diagenetic period. Feldspar has a strong positive correlation with the micropore and mesopore proportions but is not highly correlated with the macropore proportions. The influence of the carbonate mineral content on the pore volume is not obvious because of its complex composition. The TOC content and vitrinite reflectance (Ro) are the two most important factors controlling free oil and adsorbed oil, and the contents of mineral components, such as felsic minerals, carbonate minerals and clay minerals, have no obvious correlation with shale oil content. With increasing pore volume, the contents of free oil and adsorbed oil increase, but the proportion of adsorbed oil decreases gradually. The correlation between the specific surface area and adsorbed oil content is poor. At normal temperatures and pressures, the lower limit of the pore diameters that can contain free oil is 4 nm, and the lower limit of the pore diameters that can contain movable oil is 10 nm.

Semi-Automated Rock Classification for Permeability Estimation Using High-Resolution Computed Tomography Scan Images, Core Photos, and Well Logs

Summary Reliable estimation of petrophysical properties can be challenging, especially in geological formations with rapid variation in the spatial distribution of rock components. The spatial distribution of rock components, also known as rock fabric, is often not captured by conventional well logs that are typically used for the estimation of petrophysical properties. The aforementioned challenge is rooted in the limited vertical resolution of conventional well logging tools. Alternatively, specialized tools and techniques, such as nuclear magnetic resonance (NMR) and computed tomography (CT) scan images, can provide information on the variation in the rock fabric of geological formations. The objectives of this paper are (a) to use 2D CT scan images and core photos, conventional well logs, NMR logs, and core-measured properties for semi-automated rock classification, (b) to develop class-based rock physics models for enhanced petrophysical properties estimation, and (c) to provide a method to expedite the detection of quantitative image-based rock classes in cored wells. First, we conducted conventional formation evaluation (CFE) for the initial assessment of petrophysical properties. Then, we implemented three different rock classification techniques for class-based estimation of petrophysical properties. The first of the rock classification techniques uses routine core analysis (RCA) data to define hydraulic units. The second rock classification technique uses NMR data to characterize the changes in pore-size distribution of the evaluated formation. The last rock classification technique integrates quantitative image-based features from CT scan images and core photos with NMR data. Finally, the obtained rock classes from the abovementioned rock classification techniques are used to derive class-based permeability models. We applied the proposed workflow to a pilot well drilled in a saline water aquifer formation that will be used for CO2 injection and storage in the Northern Lights carbon capture and storage (CCS) project. The extracted image-based rock fabric features were in agreement with the visual aspect of the evaluated depth intervals. The detected rock classes captured the fluid-flow behavior using a permeability-based cost function in two of the implemented rock classification techniques, the variation in petrophysical and compositional properties through well logs, and quantitative rock fabric of the evaluated depth interval through the core image data. Finally, the use of class-based rock physics models improved permeability estimates, decreasing the mean relative error by up to 37% compared with formation-based permeability estimates from a conventional method (formation-based porosity-permeability correlations). One of the key contributions of the proposed workflow is that it integrates conventional well logs, core-measured properties, NMR logs, and high-resolution image data. As a result, the obtained integrated rock classes capture key petrophysical and geological parameters of the evaluated depth intervals that are typically not included in rock classification efforts. The obtained integrated rock classes can potentially improve the development of accurate geological models, which are used in simulation efforts as a screening tool for the selection of geological formations for CO2 storage as well as for storage capacity, selection of CO2 injection intervals, and containment forecasting.

Changes in Pore-Size Distribution and Hydraulic Conductivity of Compacted Soils by Grass-Derived Hydrochar

Changes in Pore-Size Distribution and Hydraulic Conductivity of Compacted Soils by Grass-Derived Hydrochar

Impact of Polymer Chain Rearrangements in the PA Structure of RO Membranes on Water Permeability and N-Nitrosamine Rejection.

The use of solvents is overall recognized as an efficient method to improve the water permeability of polyamide thin film composite membranes (PA-TFC). The objective of this work was to test the performance of the membranes after exposing them to n-propanol (n-PrOH) to improve the permeability of the membranes while maintaining the rejection factor for small uncharged organic molecules, namely N-nitrosamines (NTRs). After the membranes were exposed to n-PrOH, the water permeability of the UTC73AC membrane increased by 98%, with minimal change in rejection. N-nitrosodiethylamine (NDEA) rejection decreased (3.4%), while N-nitrosodi-n-propylamine (NDPA) and N-nitrosodi-n-butylamine (NDBA) rejection increased by 0.9% and 2.8%, respectively. In contrast, for the BW30LE membrane, water permeability decreased (by 38.7%), while rejection factors increased by 14.5% for NDEA, 6.2% for NDPA, and 15.0% for NDBA. In addition, the morphology of the membrane surface before and after exposure to n-PrOH was analyzed. This result and the pore size distribution (PSD) curves obtained indicate that the rearrangement of polymer chains affects the network or aggregate pores in the PA layer, implying that a change in pore size or a change in pore size distribution could improve the permeability of water molecules, while the rejection factor for NTRs is not significantly affected.

Impact of Silicon Content and Particle Size in Lithium-Ion Battery Anodes on Particulate Properties and Electrochemical Performance

Silicon (Si) is considered a promising anode active material to enhance energy density of lithium-ion batteries. Many studies have focused on new structures and the electrochemical performance, but only a few investigated the particulate properties in detail. Therefore, a comprehensive study on the impact of Si content (5, 10, 15 wt.%) and particle size (120, 160, 250 nm) of core–shell structured Si@Gr composites on particulate and electrode properties was conducted. It was shown that both parameters had significant impact on the specific surface area (SSA) of particles, which was later correlated to the initial capacities and coulombic efficiencies (ICEs). Furthermore, changes in pore size distribution and electrical conductivity were found. The built full cells showed high initial capacities (&gt;150 mAh g−1), good rate capability (75% at 1 C, 50% at 2 C) and ICEs (&gt;80%). The energy density was found to increase by 32% at 15 wt.% Si compared to graphite (Gr), indicating the future potential of Si. In addition, the impact of a carbon coating was investigated (Si@Gr/C), which led to a reduction in SSA, improved particle stability and higher capacity retention. Consequently, this study emphasizes the importance of also investigating the particulate properties of Si anodes.

Effect of heating–water cooling cycle treatment on the pore structure and shear fracture characteristics of granite

In hot dry rock (HDR) geothermal energy extraction systems, jointed rock masses are often subjected to heating–water cooling (H-WC) cycles. In this process, HDR is at risk of failure and instability due to the change in pore structure and fracture characteristics. To identify the shear fracture characteristics of rocks after H-WC cycle treatment. First, shear fracture mechanical tests were carried out on granite specimens treated with H-WC cycles by using the short core compression (SCC) test method. The experimental results show that cyclic H-WC treatment leads to a decrease in fracture toughness values. It is especially noteworthy that the weakening effect of fracture toughness decreases with increasing cycles. Second, the NMR analysis results show that the porosity of granite samples increases with the number of H-WC cycles. At 400℃ and 600℃, the pore size distribution changes under H-WC. The slope of the fitting curve between fracture toughness and porosity indicates that the higher the temperature is, the lower the sensitivity of fracture toughness to porosity. Then, acoustic emission characteristics in the mechanical experimental process were analysed by using the b-value analysis method. The results indicated that the b-value of acoustic emission decreased with increasing cycles at 200 °C, so the crack size and energy release increased; however, at T = 400 °C and 600 °C, the b-value increased with an increasing number of cycles, so the crack size and energy release decreased. Finally, the fracture plane morphology of the failure specimens was obtained by a 3D optical scanner. The calculation results of the fractal dimension DF indicate that the cyclic H-WC treatment enhanced the fracture plane roughness, and the average increase in fractal dimension DF increases with increasing temperature, also indicating that the increasing effect of fracture plane roughness with increasing temperature becomes increasingly significant. At the same time, the fracture toughness under cyclic H-WC action was negatively correlated with the fracture plane roughness of granite.

Microstructure evolution of a compacted lateritic silt upon drying–wetting and loading

Lateritic soil usually contains a large amount of iron and aluminium, which promotes the formation of large-size aggregations and further affects soil fabric. It has been demonstrated that the microstructure of soil influences the hydraulic and mechanical behaviour significantly. As a commonly used filling material with special mineral composition, the microstructure change of lateritic soil under common environment actions, such as wetting and loading, is thus of great importance. In this study, the microstructure properties of a lateritic silt under drying–wetting and one-dimensional compression were investigated using mercury intrusion porosimetry and scanning electron microscopy. Test results show that large-sized aggregates are formed in the compacted lateritic silt with 10% of hematite. These aggregates induce a bi-modal pore size distribution (PSD) which includes both micropore and macropore peaks. The different macropore distributions under various dry densities lead to scattered soil–water characteristic curves in a suction range less than 20 MPa. Changes in volume and pore structure mainly occur in the suction path within the “transition zone” where the dominant capillarity affects only the macropore. Drying causes an increase in macropores due to the decreased volume of aggregates, while has limited effect on micropores, whereas wetting weakens the bonding between aggregates, and induces a reduction in macropores. The compacted lateritic silt shows obvious collapse upon soaking, in which the collapse grows up to a peak and then turns to decrease with increasing stress level. Both loading and soaking lead to the collapse of macropores, whereas soaking tends to affect a broader range of pore sizes. It is inferred that, the strong particle cementation produced by hematite leads to a strong micropore structure, which is almost unaffected by the suction change under both confined and unconfined conditions. The PSD change due to the variation in suction is different from that observed on other compacted fine-grained soils, which verifies the effects of special mineral composition (iron and aluminium) on microstructure and further the hydro-mechanical behaviour of lateritic soil.

A dual-geometry pore-size-resolved model to predict deep-bed loading in a wall-flow filter

A gasoline particulate filter (GPF) is an effective wall-flow technology for gasoline engine particulate matter (PM) emission control via deep-bed filtration through porous ceramic walls within a honeycomb channel structure. An analytical filter model is desired to understand its efficiency and pressure drop under engine operating conditions and, thereby, reduce the development costs for meeting emission regulations and engine performance targets. Most existing models either oversimplify the filter geometry or do not offer good predictions in the soot loading regime. The present work treats the deep bed regime as two co-existing filters with different geometries based on their natural morphologies, one that describes the porous wall and the other for the fiber structure created by soot deposition. Both models are dynamic to account for changes in pore size distribution and soot dendrite growth during loading. Model validation by 12 sets of experimental filter loading data shows that it provides reasonable predictions of both filter efficiency and pressure drop during deep-bed loading for different GPF wall-flow filters under various operating conditions. Scanning electron microscopy (SEM) confirms model predictions for the unit collector size of the dendritic filter formed by soot deposition. Numerical simulation using GeoDict was also carried out to validate the model predictions on particle deposition location. The model is used to investigate the evolution of pore-size-resolved aerosol flow, filtration efficiency, mass loading, and particle packing density during loading. The impact of porosity, mean pore size, and pore size distribution on filter loading performance is studied. The results suggest that increasing porosity, narrowing pore size distribution, and increasing mean pore size can improve filter performance, offering pathways for future filter optimization.

Modeling Gas Adsorption–Desorption Hysteresis in Energetically Heterogeneous Coal and Shale

Adsorption of gases in porous adsorbents such as coal and shale generally exhibits the phenomenon of hysteresis. Most of the previous studies on desorption hysteresis were conducted via experimental tests. However, few theoretical models that represent adsorption–desorption hysteresis of gases in porous sorbents are available. To address this issue, this work develops a new adsorption–desorption model for describing adsorption and desorption isotherms of gases with hysteresis. Particularly, the energetically heterogeneous surfaces of an adsorbent are considered via the patchwise model. Based on the change in site energy distribution, a logarithmically pressure-dependent hysteresis index, which is used to measure the degree of hysteresis, is derived for quantitative assessment of the degree of hysteresis. Besides, the correlation between the desorption isotherm and initialized pressure for desorption is established. The accuracy of the proposed model to adequately describe the adsorption–desorption hysteresis of gas in coal and shale is demonstrated by validating the model against laboratory experiments obtained from the literature. The results indicate that the adsorption isotherm depends significantly on site energy distribution. By comparing the site energy distributions for adsorption and desorption isotherms, it is found that the desorption hysteresis can be attributed to the change in pore size distribution caused by adsorption-induced deformation. The analyses support that the proposed model can be used as an effective tool to quantitatively predict the amount of released gas during desorption, which is significant for designing coalbed methane or shale gas production and assessing long-term CO2 storage behavior.

Determination of intrinsic kinetic of corncob char gasification with CO2 and steam using multipore diffusion model

Abstract The intrinsic heterogeneous reactivity of biochar in CO2 and steam gasification plays an important role in thermochemical reactor design, adjusting operating conditions, and predicting the quality of biomass gasification products, especially when the combined valorization of syngas and biochar with important textural properties is required. In the present work, the intrinsic heterogeneous kinetics of CO2 and steam gasification of corn biochar is estimated by fitting a multimodal pore size distribution (PSD) with random capillary model evolution with respect to the experimental results by thermogravimetric analysis (TGA). As novelty the independence of the initial biochar textural properties was considered, using two samples with different initial pore size distributions (PSDs): A1 sample with an initial surface area of 54.09 m2/g and A2 sample with 22.14 m2/g. The experimental intraparticle gradient effect is considered by using samples with a particle size of 149 µm conventionally larger than those reported to guarantee chemical kinetic control at 60 µm. The apparent kinetics obtained by TGA revealed a difference of 70 kJ/mol for CO2 gasification and 30 kJ/mol for steam gasification in contrast to initial PSD change. The average activation energies and pre-exponential factor obtained by parametric fitting of the model with respect to the evolution of the conversion for CO2 gasification were E = 210.2 kJ/mol and A0 = 1.13*106 g/m2s, while steam revealed E = 136.64 kJ/mol and 7.1*102 g/m2s. Furthermore, the model reduced the activation energy differences with respect to different PSDs by 5 kJ/mol for CO2 and 18 kJ/mol for steam biochar gasification.

Chemically enhanced pretreatment (CEPT) to reduce irreversible fouling during the clean-in-place process for membranes operating under constant flux and constant pressure filtration

The goal of this study was to evaluate membrane degradation after 10 clean-in-place (CIP) cycles for polyvinylidene fluoride (PVDF) membranes exposed to chemically enhanced pretreated (CEPT) feed water under constant flux (CF) and constant pressure (CP) filtration modes. Cycles of filtration (20 min) and backwashing (3 min) were employed for both filtration modes for a period of 10 h, followed by the CIP process. The changes in the membrane pore size distribution, membrane symmetry, and bond structure were analyzed using the Brunauer-Emmett-Teller method, scanning electron microscopy, and Fourier-transform infrared radiation, respectively. Severe damage to the membrane pores and significant structural variation were observed with the use of untreated feed water, particularly under CF mode, due to the defluorination and oxidation of the membrane arising from the action of the residual inorganic foulants and cleaning chemicals. Membranes exposed to CEPT feed water exhibited a recovery of 79 % and 83 % of the initial membrane flux under CF and CP modes, respectively at end of study. Interestingly, a decrease in irreversible fouling of 16.7 % was observed for CEPT feed water, with fewer inorganic foulants (Al and Mn) on the membrane surface. The fouling propensity was 14.54 % and 14.78 % lower when using CEPT feed water under CP and CF modes.

Changes in microstructure and mechanical properties of shales exposed to supercritical CO2 and brine

Shale is a source rock for hydrocarbon recovery that can be stimulated by CO 2 -based fluids, as well as a caprock for CO 2 geological sequestration due to its extremely low permeability. To examine the changes in microstructure and mechanical properties of shale exposed to supercritical CO 2 , the marine LMX gas shale and terrestrial Chang 7 oil shale from China, were treated with supercritical CO 2 with temperature of 110 °C and pressure of 30 MPa for 30 days. The microstructural alterations were characterized by scanning electron microscopy (SEM) method and the pore size distribution changes were quantified by the low-field nuclear magnetic resonance (NMR) method. Finally, the cylindrical samples were loaded uniaxially to failure to measure the crack initiation stress and strength. The results show that new surface morphologies are created by microstructural changes due to the dissolution of calcite , precipitation of minerals and induced cracks. The reactions between supercritical CO 2 and organic matter (OM) are much more significant in relatively low-mature Chang 7 shale in which massive oil in organic pores is extracted. Due to the cracks induced by the combined effects of brine and supercritical CO 2 , the macropores increase in the shale sample. Compared to the brine-saturated cases, the peak stress reduces 1.3% and 7.87%, Young's modulus decreases 30.80% and 18.31%, but the crack initiation stress increases 15.97% and 12.54% respectively, for the LMX and Chang 7 shales treated by supercritical CO 2 -brine. Overall, the mechanical properties are significantly altered by the microstructural variations in shale induced by the strong interactions between CO 2 -rich fluid and rock minerals.