Adsorption Branch Research Articles

Investigation of Ultramicroporous Structure of One-Dimensional Lepidocrocite Titanates Using Carbon Dioxide and Nitrogen Gases.

The novel material, one-dimensional lepidocrocite (1DL) titanate, is attracting industrial and scientific interest because of its applicability to a wide range of practical applications and its ease of synthesis and scale up of production. In this study, we investigated the CO2 adsorption capability and pore structures of 1DL freeze-dried and lithium chloride washed air-dried powders. The synthesized 1DL was characterized by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Using the constant-volume method, CO2 gas adsorption revealed that the 1DL exhibits type IV adsorption-desorption isotherms. The heats of adsorption obtained from the adsorption branches are lower than those obtained from the desorption branches. Brunauer-Emmett-Teller (BET) analysis, using N2 gas adsorption isotherms at 77 K showed that 1DL possesses 80.2 m2/g of BET specific surface area. Nonlocal density functional theory analysis indicated that two types of pores, meso-pores and ultramicro pores, exist in the 1DL freeze-dried powders. This work provides deep insights into the pore structures and CO2 adsorption mechanisms of 1DL powders.

From abandoned mines to carbon sinks: Assessing the CO2 storage capacity of Austrian low-rank coal deposits

This study represents the first assessment of CO2 storage potential in Austrian coal seams. Coal samples were taken from Fohnsdorf and Leoben abandoned coal mines, with particular emphasis on the Fohnsdorf coal since Leoben coal reserves were largely mined during previous coal production. Several methods were used to compare coal characteristics, including Rock-Eval pyrolysis (RE), organic petrography, and low-pressure N2 and CO2 sorption measurements. Both Fohnsdorf and Leoben coal samples show low sulfur and ash yields, as well as correspondingly high total organic carbon (TOC) contents. The pyrolysis Tmax and vitrinite reflectance values agree with a low coal rank for both sites. According to the N2 adsorption measurements at 77 K, low-lying mire coals from Fohnsdorf show a higher BET-specific surface area (BET-SSA) and BJH pore volume compared to raised-mire coals from Leoben. However, sapropelic shales and high-ash coals from Leoben show the highest BET-SSA and BJH pore volumes of all investigated samples and considerably exceed the N2 adsorption volumes of pure coals from both locations (N2 uptake up to 16 cm3/g; avg. for all samples 5.4 cm3/g). In contrast, the mean adsorbed CO2 uptake measured at 273 K and ∼ 1 bar followed the order of Fohnsdorf low-lying mire coals > Leoben raised-mire coals > Leoben sapropelic coals and shales, ranging at ∼0.8 mmol/g, ∼0.7 mmol/g, and ∼ 0.2 mmol/g, respectively. This shows that BET-SSA and BJH equations did not allow for adequate estimation of CO2 adsorption capacity trends in the investigated sample set. Furthermore, based on the existence of a hysteresis loop between CO2 adsorption and desorption branches for all investigated samples, the occurrence of weak chemisorption phenomena during CO2 adsorption is indicated. This effect helps to increase CO2 uptake and storage safety since the chemisorption process is not fully reversible upon pressure decrease. Ultimately, the theoretical CO2 sequestration potential of the remaining unmined Fohnsdorf coal reserves was estimated at 4.65 million tons, with an additional potential for enhanced coal bed methane production due to the gas-rich nature of Fohnsdorf coals with an estimated 1.2 billion m3 of CH4 in place.

Monodispersed, Micron-Sized Supermicroporous Silica Particles by Cetyltrimethylammonium Bromide-Mediated Preparation.

In this study, we present a novel modified Stöber method utilizing cetyltrimethylammonium bromide (CTAB) as a mediator for the preparation of monodispersed, micron-sized supermicroporous silica particles. Observed results show prepared silica particles ranging in size from 0.64 to 1.36 μm with an increase in CTAB concentration from 1.0 to 5.0 mM. The particles exhibited low polydispersity (<5%), a high Brunauer-Emmett-Teller surface area (570 to 1064 m2/g), and pore volumes ranging from 0.22 to 0.39 cm3/g. The pore size, determined using the Barrett-Joyner-Halenda method from the adsorption branches of the isotherms, was approximately 1.9 nm, specifically 1.83, 1.85, and 1.90 nm, as the CTAB concentration increased from 1.0 to 2.5 and 5.0 mM, respectively. The resulting particles displayed a narrow distribution of pore diameters. In addition, to obtain an in-depth understanding of the role of CTAB on the preparation of silica particles, a possible mechanism is also investigated using conductivity, dynamic light scattering (DLS), zeta potential, FT-IR spectra, and transmission electron microscopy. Our findings demonstrate that CTAB plays multiple roles in the hydrolysis/condensation of TEOS (tetraethyl orthosilicate) and subsequent nucleation and growth of silica particles. CTAB acts as a template for superporosity, a stabilizer for colloids, and an accelerator for nucleation and growth, leading to formation of monodispersed micrometer silica particles. Further characterization through FT-IR and 29Si solid NMR spectra revealed that the micron silica particles were obtained with inhomogeneity in the condensation degree, allowing for selective etching through hot incubation to form micron-sized hollow silica spheres.

Physico-chemical properties of Russian natural aluminosilicates for purification of aqueous environment

The paper analyses and compares the physico-chemical properties of aluminosilicate green clay and bentonite and diatomite from the Russian deposits. The research determines specific surface area and the morphological features of aluminosilicates, their pore sizes, and pore distribution by volume. The surface of the green clay includes silicon and aluminum oxides, montmorillonite, kaolinite, impurities of pyrite, saponite, micas, and hydrosludes. It also contains a lot of rounded particles with a diameter of 1-2 μm. According to the research, adsorption isotherms for mesoporous green clay samples belong to type IV; the samples of bentonite and diatomite (Middle Volga regions of Russia) belong to type II. They characterize the monolayer-multilayer concentration of solution components on macroporous bodies. Also the research revealed a sufficiently high amount of adsorbate (31 ml • g-1) to cover the surface of diatomite (Ulyanovsk region, Russia) with a monomolecular layer. The source minerals of diatomite are montmorillonite and muscovite. The study of adsorption and desorption branches for a bentonite sample (Samara region, Russia) indicates the processes asymmetry. Hence, we compared the ability to adsorb iron (II) and lead ions from aqueous systems using green clay extracted in different years (2017 and 2023).

A New Statistical Theory for Constructing Sorption Isotherms in Mesoporous Structures Represented by Bethe Lattices.

In the present work, a new statistical theory is developed to describe adsorption and desorption in mesoporous materials (pore sizes ranging from 2 to 50 nm) represented by pore networks in the form of Bethe lattices. The new theory is an extension of a previous theory applied for Statistically Disordered Chain Model (SDCM) structures and incorporates the cooperative effects emerging during phase transitions in pore networks. The theory is validated against simulations and algorithmic models that describe sorption of lattice and real fluids in Bethe lattices. It is seen that the pore network coordination number, or pore connectivity, z, has a significant impact on two important processes observed in pore networks: pore assisting condensation during adsorption and evaporation by percolation during desorption. The inclusion of pore connectivity in the earlier developed framework accounting for cooperativity effects is an important step, rendering the existing models to mimic fluid behavior in real materials more accurately. Hence, the new theory inherently contains all essential elements that may offer the extraction of more reliable pore size distributions utilizing both the adsorption and desorption branches of the isotherm.

High-Temperature-Induced Pore System Evolution of Immature Shale with Different Total Organic Carbon Contents.

The pyrolysis process of source rock, especially organic-rich immature shale, is required for oil and gas extraction, during which the evolution of the pore structure system in the immature shale determines the heat conduction and fluid flow under the heating treatment. Although some sound achievements have been made regarding the pyrolysis of immature shale, the effect of the total organic carbon (TOC) content on the pore structure evolution of immature shale remains unclear. With respect to this issue, in this work, a series of N2 adsorption/desorption and nuclear magnetic resonance (NMR) experiments were conducted, and fractal dimension theory was also introduced to analyze the pore structure evolution of immature shale subjected to heating treatment in a quantitative manner. The results indicate that the adsorption branch of the nitrogen adsorption-desorption isotherm can be divided into three stages. The pore structure of different TOC immature shales does not change significantly, and they are all slit-shaped. In addition, immature shale with a higher organic content has a higher hydrocarbon expulsion strength and a higher pore volume growth rate, which indicate that the pyrolysis of organic matter greatly affects the pore structure of immature shale during heating. This phenomenon shows that the pyrolysis of organic matter greatly influences the pore structure of immature shale during the heating process. The pores of immature shale in the study area have significant fractal characteristics, the fractal dimension is between 2.397 and 2.636, the pore space of the sample is extremely small, the pore structure is extremely complex, and the heterogeneity is strong.

Effect of Vacuum Heat Treatment on Larch Earlywood and Latewood Cell Wall Properties

The aim of this study was to evaluate the hygroscopicity and nanomechanics of earlywood (EW) and latewood (LW) larch after thermal modification under vacuum conditions. Wood samples were heat-treated in a vacuum atmosphere at 180–220 °C for 6 h, then their cell wall properties were observed using dynamic water vapor sorption (DVS), imaging Fourier-transform infrared (FTIR) microscopy, and nanoindentation. The results showed that the vacuum heat treatment reduced the hygroscopicity of EW and LW and increased hysteresis between the adsorption and desorption branches of the isotherm. Compared with EW, the treatment temperature had a more pronounced influence on the hygroscopicity of LW. The Hailwood-Horrobin model was found to accurately fit the experimental data. Imaging FTIR microscopy revealed degradation of hemicellulose, cross-linking, condensation reactions, and redistribution of lignin in the cell wall. The elastic modulus for the heat-treated EW and LW cell walls increased at first and then decreased as the treatment temperature increased; the increase in LW was more intense than that in EW. Cell wall hardness also markedly increased after heat treatment. Our analysis suggests that vacuum heat treatment decreases hygroscopicity and alters the chemical composition distribution of cell walls, thus improving wood cell wall mechanics.

(Invited) Impact of Pore Morphology and Surface Hydrophobicity of the Carbon Matrix on the Macrokinetics of the Oxygen Reduction Reaction Performance for Atomically Dispersed Fe-N-C Catalysts

Atomically dispersed transition metal catalysts are an important family of non-precious metal electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. The iron-nitrogen-carbon (Fe-N-C) catalyst, wherein the iron metal centers are coordinated by nitrogen atoms (FeNx) on carbonaceous supports, exhibits outstanding ORR activity in both rotating disk electrode (RDE) and membrane electrode assembly (MEA) configurations.[1] The pore structure[2] and surface hydrophobicity[3] of the carbon matrix are of particular significance to the MEA performance, where the high current throughput requires good mass transport capability and controlled water flooding on the electrodes. In this work, we employed two widely used Fe-N-C catalysts – one pyrolyzed from metal organic framework (MOF-derived)[4] and the other produced by using the sacrificial support method (sacrificial templated)[1]. Specifically, nitrogen physisorption and water vapor physisorption were used to study the pore morphology and the specific surface hydrophobicity, respectively. As shown in Figure 1, the sacrificial templated Fe-N-C catalyst showed a significant mesoporosity as compared to the MOF-derived counterpart, while its surface was much more hydrophobic, as indicated by the less water uptake through whole pressure range (Figure 1f). Such difference of carbon morphology was further correlated to their macrokinetic performance in a MEA configuration, to reveal the impact of the morphological and hydrophilic/hydrophobic balance on these two types of Fe-N-C catalysts. Reference [1] T. Asset and P. Atanassov, Joule, 2020, 4, 33.[2] Y. Huang, Y. Chen, M. Xu, T. Asset, P. Tieu, A. Gili, D. Kulkarni, V. de Andrade, F. de Carlo, H. S. Barnard, A. Doran, D. Y. Parkinson, X. Pan, P. Atanassov, and I. Zenyuk, Materials Today, 2021, 47, 53.[3] L. Liu, S. J. Tan, T. Horikawa, D. D. Do, D. Nicholson and J. Liu, Adv Colloid Interface Sci, 2017, 250, 64.[4] K. Kumar, T. Asset, X. Li, Y. Liu, X. Yan, Y. Chen, M. Mermoux, X. Pan, P. Atanassov, F. Maillard and L. Dubau, ACS Catalysis, 11, 484. Figure 1. XRD (a) and AC-STEM (b-d) images of the Fe-N-C catalyst produced by the sacrificial support method. Nitrogen (e) and water vapor (f) physisorption isotherms of MOF-derived and sacrificial templated Fe-N-C catalysts. (g) Pore size distribution of the two catalysts by the BJH method based on the N2 adsorption branch. Figure 1

Effects of functional groups on supercritical CH4 adsorption and desorption characteristics of tectonically deformed coals

With the expansion of coalbed methane exploration and development to deep-buried reservoirs, supercritical CH4 adsorption/desorption on coals have become a key scientific issue. The evolution of functional groups of tectonically deformed coals are bound to affect supercritical CH4 adsorption/desorption characteristics of the coal. In this paper, five coal samples of three deformation series were selected. Supercritical CH4 adsorption/desorption characteristics, i.e. excess/absolute adsorption/desorption isotherms, adsorption model, maximum adsorption capacity and desorption hysteresis, were investigated. Evolution models and dynamic mechanisms of functional groups with coal deformation were discussed based on Fourier Transform Infrared Spectroscopy and 13C Nuclear Magnetic Resonance analyses. Finally, the controlling mechanisms of functional groups evolution on adsorption capacity of tectonically deformed coals were analyzed. Results show that supercritical CH4 excess adsorption and desorption isotherms of tectonically deformed coals exhibit the “single peak” change trend with a maximum value. The maximum value tends to move towards the high pressure zone with increasing adsorption capacity. The absolute adsorption and desorption branches increase monotonically with increasing pressure. Supercritical CH4 desorption hysteresis decreases with increasing adsorption capacity. Oxygen-containing functional groups (CO, COOH, OH and oxygen-bonded aliphatic/aromatic carbons) and aliphatic carbons (methyl, methylene, submethyl and quaternary carbons) are highly sensitive to stress, while aromatic CC and other aromatic carbons are difficult to change. Only some oxygen-containing functional groups and aliphatic structures of brittle deformed coals are reduced due to cataclasis and grallization, and thus adsorption capacity shows the unobvious increase. Strong ductile shear deformation results in widely competitive evolution of functional groups and increased degree of coal aromatization, which thereby induces obviously increased adsorption capacity and decreased desorption hysteresis.

Pore Size Distribution Analysis Using Developing Hysteresis of Nitrogen in the Cylindrical Pores of Silica.

A new method of mesopore size analysis was developed for the cylindrical pores of silica using a developing hysteresis of nitrogen measured at liquid nitrogen temperature. The method is based on the semimacroscopic approach of a modified Bonnet-Wolf model that deals with the grand potential of a vapor bubble in the cylindrical pore. It is capable of assessing correctly the pore structures of mesoporous materials with cylindrical pores using the narrow hysteresis loop of the developing hysteresis. When the mesoporous materials possess cylindrical pores of minor imperfections, two pore size distributions (PSDs) from the adsorption and desorption branches overlap. On the other hand, for cylindrical pores with an enhanced amplitude of pore corrugations and/or constrictions, PSD from the desorption branch is shifted to smaller pore sizes compared to the one from the adsorption branch, and at the same time, both the PSDs evaluated are shifted to lower pore sizes compared to the actual ones. The actual PSD can be assessed from the reversible isotherm measured at a hysteresis critical temperature. In principle, the present method may enable the determination of the PSDs from the adsorption hysteresis measured at any given temperature for mesoporous materials with cylindrical pores.

PRECIPITATION OF NICKEL-CONTAINING PARTICLES FROM NICKEL NITRATE SOLUTIONS UNDER THE ACTION OF A DIRECT CURRENT GLOW DISCHARGE

In this paper we present the results on the synthesis of nickel-containing particles from solutions of nickel nitrate under the action of a DC glow discharge at atmospheric pressure in air. The interaction of the plasma with the solution leads to the formation of a colloidal suspension in the anode part of the cell, followed by the formation of agglomerates and precipitation to the bottom of the cell. The composition and surface structure of the resulting powders were studied using scanning electron microscopy, Brunauer–Emmett–Teller analysis, X-ray diffraction analysis, X-ray energy-dispersive spectroscopy, and thermogravimetric analysis. According to the results of dynamic light scattering, particles in solution have two characteristic sizes of the order of 73.5 nm and 1.2 μm. Images obtained on a scanning electron microscope showed that the resulting powders have a well-developed granular structure. X-ray phase analysis of the obtained samples showed the presence of clearly defined reflections, which indicate the crystallinity of the structure of the synthesized powder. Decoding showed that it is β-type nickel hydroxide. The elemental composition of the surface obtained using X-ray energy-dispersive spectroscopy showed the presence of nitrogen in the sample. Therefore, the powders have a complex composition and are a mixture of hydroxide and hydroxonitrate with a ratio of 0.8 Ni(OH)2 : 0.2 Ni(OH)NO3. Thermogravimetric analysis confirms the data obtained using X-ray energy dispersive spectroscopy. High-temperature treatment of the obtained powders leads to the formation of β-type nickel oxide. The specific surface area (Ssp) was calculated using the Brunauer–Emmett–Teller method from the adsorption branch in the range of relative pressures of 0.05–0.20; the total pore volume (Vp) and pore size distribution were calculated from the desorption branch in the range of 0.40–0.99.

Adsorption Hysteresis in Open Slit-like Micropores.

Adsorption hysteresis in the low-pressure range is only rarely described in the literature. To optimise, for example, heat storage technologies, a deeper understanding of the low-pressure hysteresis (LPH) process is necessary. Here, two thermodynamically based approaches are further developed for analysing the LPH within the framework of thermodynamically irreversible processes and fractal geometry. With both methods developed, it is possible to obtain the description of the adsorption and desorption branches with high accuracy. Within the framework of the two thermodynamic models of the hysteresis loop, generalised equations are obtained with the control parameter in the form of the degree of irreversibility. This is done by taking the adsorption of water on alumina as an example. It is shown that the fractal dimension of the adsorption process is larger than the fractal dimension of the desorption branch, meaning that the phase state of the adsorbate is more symmetric during the adsorption step than in the desorption process.

Pore Structure and Fractal Character of Lacustrine Oil-Bearing Shale from the Dongying Sag, Bohai Bay Basin, China

To better understand the pore structure and fractal character of lacustrine shales and their influence on liquid hydrocarbon occurrences, in this study, a total of 29 lacustrine oil-bearing shale samples collected from the Shahejie Formation in the Dongying Sag, Bohai Bay Basin, were investigated based on nitrogen adsorption (NGA) analysis combined with TOC, Rock-Eval pyrolysis, X-ray diffraction (XRD), and field emission-scanning electron microscopy (FE-SEM) experiments. The relationships among the compositions (TOC, minerals, and oil content), pore structures, and fractal dimensions of the lacustrine shale samples were discussed. The results showed that the adsorption and fractal characteristics of lacustrine oil-bearing shales differ at relative pressures of 0-0.1 and 0.5-1. Two corresponding fractal dimensions D 1 and D 2 were determined by the FHH model according to the nitrogen adsorption branches. Specifically, D 1 varies from 2.4292 to 2.6109 (mean 2.5245), and D 2 varies between 2.4680 and 2.8535 (mean 2.6889). The specific surface area (SSA) ranges from 1.512 m2/g to 34.002 m2/g, with an average of 13.656 m2/g, the total pore volume is between 6.0 × 10-3 cm3/g and 48.4 × 10-3 cm3/g (mean 24.5 × 10-3 cm3/g), and the average pore diameter is in the range of 4.22 nm to 19.57 nm (mean 9.35 nm). Both D 1 and D 2 increase with increasing SSA and increase with decreasing average pore diameters but have no correlation with pore volume. Moreover, D 1 and D 2 exhibit positive relationships with clay minerals and negative correlations with carbonate minerals (calcite and dolomite). The relationship between fractal dimensions ( D 1 and D 2 ) and TOC contents is expressed as a U-shaped curve, characterized by the minimum D values at approximately 3% TOC. The shale oil content is controlled by the pore structures and fractal dimensions, and lacustrine shales with lower SSAs and smaller fractal dimensions would have more free oil. Therefore, lacustrine shales in the oil window with TOC contents ranging from 2% to 4% are probably the preferred shale oil exploration target in the Shahejie Formation, Dongying Sag, Bohai Bay Basin. The results indicate that fractal analysis can provide insight into the pore structure characteristics and oil storage capacity of lacustrine shales.

Revisiting the Nature of Adsorption and Desorption Branches: Temperature Dependence of Adsorption Hysteresis in Ordered Mesoporous Silica.

To gain a deeper understanding as to the nature of the adsorption hysteresis due to capillary condensation of nitrogen in ordered mesoporous silicas, we calculated the temperature dependences of the activated condensation, equilibrium transition, and activated desorption pressures for nitrogen in spherical and cylindrical silica pores with several different pore sizes on the basis of semimacroscopic continuum models. The results clearly indicate that the models capture the exact nature of capillary condensation and evaporation phenomena of a fluid in cagelike and cylindrical mesopores. The temperature dependences of the adsorption hysteresis of nitrogen measured confirm previous theoretical predictions for cylindrical pores: for the ordered mesoporous silicas with cylindrical mesopores at least greater than ∼7 nm in diameter, the capillary condensation takes place via a nucleation process followed by a growth process of a bridging meniscus at pressures higher than the equilibrium transition, while the capillary evaporation takes place via a receding meniscus from pore ends at the equilibrium. For SBA-15 and MCM-41 with smaller mesopore sizes, on the other hand, the capillary condensation takes place close to the equilibrium transition pressures, while the capillary evaporation takes place at pressures lower than the equilibrium, owing to single pore blocking due to corrugation of the cylindrical pores. We discuss the effect of curvature on surface tension in capillary condensation, as well as the relation between a change in the mechanisms of adsorption and desorption and the pore corrugation in the cylindrical pores.

Characterization of an Isostructural MOF Series of Imidazolate Frameworks Potsdam by Means of Sorption Experiments with Water Vapor.

Sorption measurements of water vapor on an isoreticular series of Imidazolate Frameworks Potsdam (IFP), based on penta-coordinated metal centers with secondary building units (SBUs) connected by multidentate amido-imidate-imidazolate linkers, have been carried out at 303.15 K. The isotherm shapes were analyzed in order to gain insight into material properties and compared to sorption experiments with nitrogen at 77.4 K and carbon dioxide at 273.15 K. Results show that water vapor sorption measurements are strongly influenced by the pore size distribution while having a distinct hysteresis loop between the adsorption and desorption branch in common. Thus, IFP-4 and -8, which solely contain micropores, exhibit H4 (type I) isotherm shapes, while those of IFP-1, -2 and -5, which also contain mesopores, are of H3 (type IV) shape with three inflection points. The choice of the used linker substituents and transition metals employed in the framework has a tremendous effect on the material properties and functionality. The water uptake capacities of the examined IFPs are ranging 0.48 mmol g−1 (IFP-4) to 6.99 mmol g−1 (IFP-5) and comparable to those documented for ZIFs. The water vapor stability of IFPs is high, with the exception of IFP-8.

A dual shape pore model to analyze the gas adsorption data of hierarchical micro-mesoporous carbons

Hierarchical micro/mesoporous carbons obtained by template carbonization were investigated by nitrogen adsorption/desorption and gave a type IV isotherm with a H1 hysteresis loop closing perfectly near P/P0 = 0.6. When using the 2D-NLDFT theory to calculate the pore size distribution (PSD) from the adsorption branch of the isotherms, while assuming slit pores with a heterogeneous rough surface (2D–HS–SLIT model), an unexpected artifact was observed ca. 3.5 nm. Recognizing that the H1 hysteresis loop is usually related to the adsorption in materials with cylindrical pores, where in general it is recommended to use the desorption branch for the pore size analysis, we have applied the 2D–HS–SLIT model to the adsorption isotherm up to P/P0 = 0.2 and a cylindrical pore model to the desorption isotherm down to P/P0 = 0.2. Interestingly, the application of this dual shape pore model to hierarchical micro/mesoporous carbons of various mesopore sizes and oxygenated surface functionalities shows an excellent fit with the experimental isotherms, while the mesopore peak in the PSDs is narrower, and the previously labeled artifact is eliminated. It is noteworthy that the cumulative surface area values are significantly larger than when applying the 2D–HS–SLIT model, what is due to the larger surface area of cylindrical than slit-shaped mesopores.

Geochemical Properties and Pore Structure Control on Oil Extraction of Shale

Abstract Despite geochemical properties and pore structures for shale oil extraction, the interplay among shale chemistry, pore network, and hydrocarbon movability still is an open question. Here, by using hybrid experimental methods, including backscatter scanning electron microscopy, X-ray diffraction, adsorption/desorption isotherm, and nuclear magnetic resonance, we provide a general characteristic of geochemistry and pore structures of Chang 7 (C7) shale in Ordos basin and figure out how these properties impact the shale oil extraction. Our results confirmed that the C7 shale in Ordos basin could be divided into three types based on the mineral components with various pore structures, and the proportion of the pores that radius below 4.8 nm (from adsorption branch) or 3.8 nm (from desorption branch) play a dominant role in the determination of pore size distributions. The kerogen index that is derived from maceral types was the most significant geochemical indicator; high kerogen index was corresponding to large pore volumes and surface areas, but low pore diameters. We identify the pore structure mechanism—mesopores predominantly or micropores abundantly (increase free fluid index) and absence of inorganic or organic pores (decrease free fluid index)—responsible for the oil extraction capability and show that the unmovable fluid stained in the voids would lead to the slow rate decay of the curves, which caused the nonsignal disturbance. Our results demonstrate the powerful control of maceral components and pore diameters on shale oil extraction and show the markedly different flow behavior of various types of shale.

Pore structure and adsorption hysteresis of the middle Jurassic Xishanyao shale formation in the Southern Junggar Basin, northwest China

In order to understand the pore structures of the Middle Jurassic Xishanyao Formation in the Junggar Basin, 11 shale samples from a single well were picked and were subjected to several analyses including mineralogy, (programmed) Rock-Eval pyrolysis for geochemical and N2 adsorption for pore structure analysis. The results showed that the mean value of total organic carbon (TOC) content of these samples is around 1.54% while Tmax varies between 429 to 443°C, indicating they are in the oil window. Mineral assemblages of the samples is mainly quartz and clay (illite, chlorite and kaolinite). Moreover, negative correlations between the K-feldspar/plagioclase and micro-mesopore volume was found, depicting that few of such pore sizes exist in these two abundant minerals. In contrast, micro, meso and macro pores all were detected in clay minerals. Particularly, the pores with radii of around 5.35 nm were abundant in clay minerals and there was not a robust relationship between the organic matter, surface area and pore volume. Finally, fractal analysis was performed to better delineate heterogenous characteristics of pore structures which showed that D2 (representing the larger pores) is greater than D1 (smaller pores). In addition, the differences between the fractal dimensions of the adsorption and desorption (D2d–D2a) branches to better interpret the hysteresis, was defined. The positive correlation between the (D2d–D2a) and the meso-macro pore volume, pointed out that the meso-macro condensation is the main reason for hysteresis that was observed in N2 adsorption experiments in the Xishanyao Shale samples.

Effects of composition and temperature on water sorption in overmature Wufeng-Longmaxi shales

Water sorption provides a great approach to understand water-shale interaction. In this research, water sorption isotherms of fourteen Wufeng-Longmaxi shale samples collected from the eastern Sichuan Basin of China were generated and then interpreted by classical sorption models. The sorption behavior of water and its relationship with pore structure, organic/inorganic composition, and temperature (278–333 K) were explored using organic geochemistry, mineralogy, and gas physical sorption. Brunauer-Emmett-Teller theory functions well for these isotherms but generates ambiguous model parameters, suggesting that multilayer sorption concept is not suitable for water sorption. Dent model distinguishes between primary and secondary sorption, and the resulting specific surface area (ADent(H2O)) is not comparable to the nitrogen-determined specific surface area (ABET(N2)). However, ADent(H2O)/ABET(N2) linearly decreases with increasing ABET(N2), and water saturation is negatively correlated with total pore volume. These observations collectively support the surface-chemistry-controlled clustering mechanism for water sorption. Clay minerals dominate water sorption at low relative pressure because they provide more hydrophilic sorption sites for water cluster formation and growth. Nevertheless, organic matter becomes increasingly important with increasing relative pressure, primarily because a specific-sized organic pore has higher filling pressure than the same-sized clay pore resulting in more pronounced condensation in organic pores at high relative pressure. The water desorption branch shifts to higher relative pressure with increasing temperature and thus, the hysteresis loop shrinks, indicating a mechanism of capillary evaporation similar to wetting fluid nitrogen. The water adsorption branch is insensitive to temperature change, reflecting a temperature-independent clustering mechanism between 278 K and 333 K. The enthalpy of adsorption of collected shale samples is smaller than that of lower-maturity shales but close to that of condensation of bulk water. Based on this finding, we argue that higher-maturity shales have weaker interaction with water, which gives rise to lower temperature sensitivity of water sorption. Therefore, in the future, detailed investigations should revolve around water sorption behavior and its response to temperature in shales with different thermal maturities.

Flexible Adsorbents at High Pressure: Observations and Correlation of ZIF-7 Stepped Sorption Isotherms for Nitrogen, Argon, and Other Gases.

Stepped adsorption isotherms with desorption hysteresis were measured for nitrogen, argon, ethane, carbon dioxide, and methane at pressures up to 17 MPa on zeolitic imidazolate framework-7 (ZIF-7) using a gravimetric sorption analyzer. Such stepped sorption isotherms have not been previously reported for nitrogen or argon on ZIF-7, and required the application of pressures as high as 15 MPa to trigger the ZIF-7 structural phase transition at temperatures around 360 K. The stepped hysteretic sorption isotherms measured for carbon dioxide, methane, and ethane were consistent with previous observations reported in the literature. To correlate these stepped hysteretic sorption isotherms, a semi-empirical model was developed by combining a three-parameter Langmuir equation to describe the Type I aspect of the isotherm, with a model designed to describe the temperature-dependent ZIF-7 structural phase transition. Excellent fits of the combined adsorption and desorption branches were achieved by adjusting nine parameters in the temperature-dependent model, with root-mean-square deviations within 2.5 % of the highest measured adsorption capacity. Each parameter of the new semi-empirical model has a physical basis, allowing them to be estimated or compared independently.