Gas Adsorption Characteristics Research Articles

Effect of gas adsorption characteristics of SiC on porosity defects in SiCP/A359 composites

This study systematically investigates the gas adsorption characteristics of silicon carbide (SiC) as a potential contributor to defects, including shrinkage and porosity, in SiC particle reinforced Aluminum (SiCp/Al) composites. Key factors affecting these composite materials defects such as SiC particle size, gas atmosphere, and gas pressure, are comprehensively explored. The research begins by elucidating the mechanism through which the melt absorbs gas during the processing flow. Additionally, mathematical models correlating [O] growth with temperature and [N] peak contentwith gas pressure are established. The paper concludes by proposing effective strategies to diminish defects and enhance the purity of composite materials. These strategies include reducing melting time, decreasing melting temperature, increasing the vacuum during melting, and implementing high-temperature degassing.

Adsorption and Diffusion Properties of Gas in Nanopores of Kerogen: Insights from Grand Canonical Monte Carlo and Molecular Dynamics Simulations

Investigating the adsorption and diffusion processes of shale gas within the nanopores of kerogen is essential for comprehending the presence of shale gas in organic matter of shale. In this study, an organic nanoporous structure was constructed based on the unit structure of Longmaxi shale kerogen. Grand canonical Monte Carlo and molecular dynamics simulation methods were employed to explore the adsorption and diffusion mechanisms of pure CH4, CO2, and N2, as well as their binary mixtures with varying mole fractions. The results revealed that the physical adsorption characteristics of CH4, CO2, and N2 gases on kerogen adhered to the Langmuir adsorption law. The quantity of adsorbed gas molecules increased with rising pressure but decreased with increasing temperature. The variation in the heat of adsorption was also analyzed. Under identical temperature and pressure conditions, the adsorption of CH4 increased with higher mole fractions of CH4, whereas it decreased with greater mole fractions of CO2 and N2. Notably, CO2 molecules exhibited a robust interaction with kerogen molecules compared to the adsorption properties of CH4 and N2. Furthermore, the self-diffusion coefficient of gas within kerogen nanopores gradually decreased with increasing pressure or decreasing temperature. The diffusion capacity of gas molecules followed the descending order N2 > CH4 > CO2 under the same pressure and temperature conditions.

The role of water bridge on gas adsorption and transportation mechanisms in organic shale

This work introduces and discusses the impacts of the water bridge on gas adsorption and diffusion behaviors in a shale gas-bearing formation. The density distribution of the water bridge has been analyzed in micropores and meso-slit by molecular dynamics. Na+ and Cl− have been introduced into the system to mimic a practical encroachment environment and compared with pure water to probe the deviation in water bridge distribution. Additionally, practical subsurface scenarios, including pressure and temperature, are examined to reveal the effects on gas adsorption and diffusion properties, determining the shale gas transportation in realistic shale formation. The outcomes suggest carbon dioxide (CO2) usually has higher adsorption than methane (CH4) with a water bridge. Increasing temperature hinders gas adsorption, density distribution decreases in all directions. Increasing pressure facilitates gas adsorption, particularly as a bulk phase in the meso-slit, whereas it restricts gas diffusion by enhancing the interaction strength between gas and shale. Furthermore, ions make the water bridge distributes more unity and shifts to the slit center, impeding gas adsorption onto shale while encouraging gas diffusion. This study provides updated guidelines for gas adsorption and transportation characteristics and supports the fundamental understanding of industrial shale gas exploration and transportation.

Industrial zone-based harmful gas sensor using pure WS2 via doping transition metals (Co, Ni) - a DFT approach

Tungsten disulphide (WS2) has received a lot of interest for its usage in a variety of fields due to its acceptable bandgap and various traits/characteristics. Presently, density functional theory (DFT) has been deployed to thoroughly study the adsorption characteristics of gases (NO, NO2, NH3, BCl3, & SO2) on Y-WS2 (Y = Co, Ni) by determining the adsorption distance, adsorption energy, electron difference density, charge transfer, electron localisation function, recovery time, & work function, also by comparing the band structure, the density of states and the projected density of states. Our results show that Y-WS2 has better conductivity and enormous charge transfer than pure WS2. Additionally, the Y-WS2 exhibits stronger adsorption of more than −0.5 eV for the harmful gases NO2, BCl3, and SO2. Subsequently, for Y-WS2, there is electron localisation overlap only for the BCl3 gas adsorbed system, which highlights the chemisorption character of the gases. Due to the high adsorption energy, Y-WS2 takes a longer time to recover NO2, BCl3, and SO2 gases at ambient temperature. However, by raising the temperature to 673 K, we can quickly recover these molecules from Y-WS2 in a few microseconds. We came to the conclusion that Y-WS2 is the right approach for NO2, BCl3, and SO2 gas-sensing applications.

Analysis of the influence of temperature on the adsorption characteristics of coal: Insights into low-temperature outburst prevention

To investigate the impact of temperature reduction on the adsorption characteristics of coal gas, isothermal adsorption experiments were conducted with environmental temperature and moisture content as variables. The changing patterns of coal gas adsorption characteristics, adsorption theories, and the temperature response of gas expansion were analyzed. Furthermore, engineering measures for preventing gas outbursts in low-temperature frozen coal seams were discussed. The research findings indicate that the gas adsorption capacity of coal samples increases with decreasing temperature. When the temperature decreases from 20 to −20 °C, the gas adsorption capacity decreases from 34.48 to 19.90 cm3/g. At the same pressure, the adsorption capacity of coal is negatively correlated with temperature. The Langmuir theoretical model better reflects the adsorption law of coal gas under different environmental temperature conditions, wherein the adsorption constant “a” gradually decreases with the increase in environmental temperature. In a closed space, the gas pressure decreases with the decrease in coal sample temperature. Under the new adsorption equilibrium, the gas pressure in the coal sample tank decreases linearly with temperature. Coal samples with different moisture contents exhibit varying degrees of decrease in gas pressure at the same temperature, with higher moisture content resulting in a smaller decrease in gas pressure. Gas expansion energy decreases linearly with the decrease in coal temperature, indicating a proportional relationship between gas expansion energy and coal gas release pressure. As the temperature decreases, the gas pressure decreases. Based on the experimental results, a synergistic approach for preventing gas outbursts through low-temperature freezing is proposed.

Gas adsorption and fluorescence studies of Cd2+ and Zn2+ metal organic frameworks based on the same fluorinated ligand

Two new metal organic frameworks (MOFs) were synthesized by solvent-thermal synthesis with fluorinated 4,4′-(pyridine-3, 5-diyl) bis (3-fluorobenzoic acid) ligands (L1), namely {[Cd(L1)H2O]·DMF}n (MOF 1) and {[Zn(L1)]·3H2O}n (MOF 2). Single crystal X-ray diffraction analysis shows that MOF 1 is a two-dimensional structure with binuclear unit of [Cd2(COO)4N2O2]. MOF 2 displays a three-dimensional structure based on binuclear unit of Zn2(COO)2. The PXRD determination demonstrates the purity of the synthesized MOF 1 and MOF 2 samples, while the TGA shows the thermal stability of the structures. The gas adsorption studies show that MOF 1 and MOF 2 exhibit good gas adsorption characteristics, and MOF 2 has high selectivity for C2H2/CH4. Moreover, both MOF 1 and MOF 2 can selectively and sensitively detect Fe3+ in water.

Study of the Methane Adsorption Characteristics in a Deep Coal Reservoir Using Adsorption Potential Theory

The gas adsorption characteristics in deep coal reservoirs are the focus of deep coalbed methane geology research. In order to reveal the adsorption characteristics in deep coal reservoirs and quantitatively characterize the amount of adsorbed methane in the deep coal seams, four coals were collected from the Permian Longtan Formation in southern Sichuan Province. Methane isothermal adsorption tests were carried out on the collected coal samples at 30 °C. The adsorption characteristic curve was established based on the data of the isothermal adsorption. The adsorption potential theory was used to predict the isothermal adsorption curves under different temperatures and the evolutionary relationship between the methane adsorption capacity and the coal seam burial depth in the C17 and C25 coal seams of the Permian in southern Sichuan Province, China. The results showed that the methane isothermal adsorption curve at 30 °C belonged to the Type I isotherm adsorption curve. The methane isothermal adsorption curves for various samples at 45 °C, 60 °C, and 75 °C were predicted based on the uniqueness of the methane adsorption characteristic curve. The amount of adsorbed gas in deep coal reservoirs was comprehensively controlled by pressure and temperature. The pressure showed a positive effect on the amount of methane adsorbed, while the temperature showed a negative effect on the adsorption of methane. The negative effect of temperature became more significant with the increase in pressure. The results of the study are beneficial for further promoting the exploration and development of deep coalbed methane in the southern Sichuan Province of China.

Effect of disturbed coal pore structure on gas adsorption characteristics: mercury intrusion porosimetry

Studying pore structures of disturbed coal and their influences on adsorption characteristics is conducive to in-depth understanding of occurrence and migration of gas in reservoirs in areas prone to coal and gas outbursts. A mercury porosimeter and a high-pressure gas adsorption instrument were separately used to investigate pore structures and measure adsorption characteristics of disturbed coal and undisturbed coal in Ningtiaota Coal Mine and Xigu Coal Mine (Shaanxi Province, China). In addition, pore structures and gas adsorption characteristics of coal samples were studied. The Menger’s sponge model was adopted to calculate fractal dimensions of coal samples, to estimate influences of pore structures and fractal features on the gas adsorption characteristics of disturbed and undisturbed coal. Results show that the pore volume of undisturbed coal is mainly contributed by micropores and transitional pores, while that of disturbed coal arises mainly from macropores and mesopores. Micropores and transitional pores account for large proportions of the specific surface area of pores in both disturbed and undisturbed coal. The adsorption isotherms of disturbed and undisturbed coal conform to the Langmuir equation and tectonism increases the limiting adsorption quantity of coal. The fractal dimensions D1 of the four types of coal samples in the experiments are in the range of 2.7617–2.9961, while the fractal dimensions D1 and D2 of disturbed coal are both larger than those of undisturbed coal, indicating that disturbed coal is more likely to collapse under high pressure. The total pore volume, total specific surface area of pores, and fractal dimensions are positively correlated with the adsorption constant a, while they have U-shaped correlations with the adsorption constant b of coal samples. The adsorption constant a of disturbed coal is always greater than that of undisturbed coal, while no obvious trend is observed between the adsorption constant b and tectonism. The research results can provide theoretical basis for further study of gas occurrence in disturbed coal seams.

Comparative Analysis of Gas Adsorption and Diffusion Characteristics of the Coal Matrix under Constant Pressure and Constant Volume Conditions

Comparative Analysis of Gas Adsorption and Diffusion Characteristics of the Coal Matrix under Constant Pressure and Constant Volume Conditions

Exploring the adsorption characteristics of toxic CO gas on pristine, defective, and transition metal-doped I-AsP monolayer

Utilizing first-principles calculations based on density functional theory, the adsorption characteristics of toxic carbon monoxide (CO) gas adsorbed on pristine, defective, and transition metal (TM) atoms (Sc, Mn, Fe, Ni, Cu, and Zn)-doped blue arsenic-phosphorene (I-AsP) are investigated to design potential sensing platforms. The pristine and defective monolayers exhibited weak CO gas sensing performance due to weak adsorption and unaltered electronic properties. In contrast, TM-doped monolayers exhibited strong interactions and enhanced the adsorption sensitivity due to their chemisorption behavior towards CO molecule. Furthermore, electronic properties obtained through the spin density of states analysis show significant changes in the adsorption of CO molecules on the doped I-AsP monolayer, influencing electrical conductivity. The significant change in the work function of system monolayers after CO adsorption confirmed that the TM-doped I-AsP monolayer is sensitive to CO gas. Therefore, the TM-doped I-AsP monolayer possesses strong sensitivity to CO gas, among which the Sc and Cu-doped monolayers emerge as promising candidates for toxic CO gas detection.

Research on coal matrix pore structure evolution and adsorption behavior characteristics under different thermal stimulation

The technique of thermal stimulation for coalbed methane extraction is considered an important approach for increasing coalbed methane production capacity in the future. This study focuses on the impact of the thermal evolution of pore structure in coal on gas adsorption characteristics. The low-pressure CO2 and N2 physical adsorption data were analyzed using classical thermodynamic methods and density functional theory. The results showed a decrease in pore volume and an increase in average pore size. The fractal dimensions obtained from the Frenkel-Halsey-Hill and Sierpinski fractal models indicate that the micro-scale spatial structure of coal becomes simpler, and the surface becomes smoother. The high-pressure volumetric method was employed to determine the gas adsorption parameters of the coal, and a comparison was made between the calculated gas adsorption parameters based on the micro-pore structure parameters of the coal samples. It was found that the variation pattern of micro-pores in the coal samples correlated highly with the methane adsorption capacity. The decrease in adsorption capacity increases the proportion of free-phase methane, which helps enhance the early-stage methane extraction rate. Improving gas migration pathways avoids the limitation imposed by diffusion in the later stages of coalbed methane extraction.

Pore structure and gas adsorption characteristics in stress-loaded shale on molecular simulation

Since stress from overlying strata is one of the primary factors influencing pore structure and gas content in shale reservoirs, understanding its role is crucial for developing shale gas fields. In this study, Molecular Mechanics and Molecular Dynamics methods were employed to investigate the intrinsic relationship between pore structure, energy, and adsorption performance of the organic matter matrix under different stress conditions. The results show that the pore structure of the organic matrix can be categorized into three stages with the variation of external stress, with 0.2 and 0.8 GPa as the boundaries. The effect of external stress significantly impacts the methane adsorption capacity in the organic matrix. Changes in stress not only result in a reduction of adsorption space but also an increase in adsorption sites. These two factors have opposite effects on CH4 adsorption in the model. That is, the negative impact of the reduction in adsorption space outweighs the positive impact of the increase in adsorption sites, resulting in a decrease in the adsorption capacity. At 0.8 and 1 GPa, the maximum CH4 adsorption capacity was reduced by 70 % and 58 %, respectively. This study provides an important reference for understanding the pore structure of the organic matrix and the adsorption characteristics of CH4 in shale gas reservoirs.

Highly sensitive chemoresistor based on Ag/TiO2/FTO sandwich structure for evaluation of component concentration in mixed ambient

The performance of membrane electrode assemblies (MEAs) in direct methanol fuel cells (DMFCs) can be greatly affected by ethanol as an impurity in methanol fuels. It is thus necessary to explore an effective method for accurately detecting the ethanol concentration in a mixed atmosphere of methanol and ethanol. Herein, we developed a chemoresistor based on Ag/TiO2/FTO sandwich structure and achieved accurate prediction for the concentration of each component in methanol-ethanol mixed atmosphere. First principles calculations were first performed to reveal the gas adsorption characteristics of TiO2 sensitive layer in different resistive state. It was indicated that methanol and ethanol molecules could be clearly distinguished by TiO2-based device in the high resistive state. In the gas-sensing test, the response value of Ag/TiO2/FTO chemoresistor in the high resistive state to 1 ppm methanol was 2.55, 14.8, 13.19, 15.04 and 17.34 times higher than that of the same concentration of ethanol, acetone, isopropanol, acetic acid and methyl formate, respectively. Meanwhile, when the device was in direct current mode after the response, an ultra-fast recovery characteristic (0.7 s) was observed due to the resistive switching function. Finally, the prediction of the component gas concentration in the methanol-ethanol mixed atmosphere was achieved by combining the optimized neural network algorithm. The present work brings new inspiration for future research on gas sensors.

Adsorption and desorption characteristics of coal seam gas under infrared radiation

Adsorption and desorption characteristics of coal seam gas under infrared radiation

Study on Molecular Model Construction and Gas Adsorption Simulation of Anthracite in the Qinshui Basin.

Uncovering gas adsorption characteristics of coal at the molecular scale is of great theoretical significance for the study of gas occurrence, coalbed methane exploitation, and carbon dioxide sequestration. In this study, based on proximate analysis, ultimate analysis, 13C nuclear magnetic resonance, and Fourier-transform infrared spectroscopy experiments, the existence forms and relative contents of elements of anthracite in the Qinshui Basin were tested and analyzed, and a macromolecular structure model was constructed. Besides, three types of acidic oxygen-containing functional groups, namely, carboxyl groups, phenolic hydroxyl groups, and lactone groups, were added to the molecular model. Furthermore, CH4 adsorption simulation was conducted on the original molecular model of anthracite and models with three types of acidic functional groups added. The following research results were obtained. The molecular formula of the constructed macromolecular model of anthracite in the Qinshui Basin is C193H138N2O7. The molecular structure of coal becomes more compact and curved after structural optimization and annealing optimization. For the four models, the CH4 adsorption characteristics of coal molecules all conform to the Langmuir equation under the same simulation conditions. Among them, the original model has the largest CH4 adsorption capacity, while the addition of oxygen-containing functional groups reduces the CH4 adsorption capacity to varying extents. The reduction of CH4 adsorption capacity follows the order: adding carboxyl groups > adding phenolic hydroxyl groups > adding lactone groups, which is mainly attributed to the different adsorption heats and adsorptive potential wells triggered by the addition of acidic functional groups in molecules.

Temperature evolution in abandoned mines and the effect on gas adsorption properties of residual coal

ABSTRACT Abandoned mines contain a large amount of residual coal and gas resources for development and utilization. In order to accurately establish the calculation model of gas reserves and lay a foundation for the exploitation of gas resources in abandoned mines, based on the analysis of temperature evolution of abandoned mines, gas adsorption experiments and molecular simulations were carried out at temperatures of 30, 60, 90, 120, 150 °C and five different adsorption equilibrium pressures (0.5∼2.5 MPa). The test results show that the attenuation rates of gas adsorption at 30∼60 °C, 60∼90 °C, 90∼120 °C, and 120∼150 °C are 8.53%, 7.89%, 5.55%, and 1.55%, respectively. High temperature inhibits the increase of gas adsorption by residual coal, but its inhibition has a certain limit. At high adsorption equilibrium pressure, the initial adsorption rate increases with the rise of temperature. When the pressure is 2.5 MPa, the initial adsorption rates at 30, 60, and 90 °C is 1.25, 2.22, and 2.32 ml▪g−1▪min−1, respectively. Temperature affects the gas adsorption characteristics of residual coal. Therefore, the influence of temperature should be considered when establishing the gas reserves model of abandoned mines.

Low-Regioregularity Polythiophene for a Highly Sensitive and Stretchable Gas Sensor

In this study, we examined how the regioregularity of poly(3-hexylthiophene) (P3HT) affects molecular packing, free volume, charge transport, and gas sensing properties. Our results showed that the presence of regular alkyl side chains on the polymer backbone promoted a high degree of structural order in regioregular P3HT molecules, leading to a compact packing density and reduced free volume. Consequently, it was more challenging for NO2 molecules to interact with the hole charge carriers in the conductive channel. On the other hand, the regiorandom P3HT films displayed a larger free volume, attributed to the irregular side chains, which facilitated the gas-analyte interaction while impeding efficient charge transport. Thus, these films exhibited greater sensitivity to analyte gas molecules. The molecular order, packing density, and hardness of P3HT films were confirmed through the use of multiple techniques, including UV-vis spectroscopy, atomic force microscopy, and grazing-incidence X-ray diffraction. Additionally, the regiorandom P3HT films showed enhanced mechanical flexibility compared to the regioregular films. In conclusion, our findings emphasize that the regularity of polymer molecules plays a significant role in determining the charge carrier transport and gas adsorption characteristics.

Research on Pore-Fracture Characteristics and Adsorption Performance of Main Coal Seams in Lvjiatuo Coal Mine

Gas prevention and control have always been the focus of coal mine safety. The pore structure characteristics and gas adsorption characteristics of coal seams are the key factors affecting gas adsorption and diffusion in coal seams. Lvjiatuo Mine has the characteristics of a high gas content when it enters deep mining. In order to clarify the influence of the pore-fracture structure characteristics of main coal seams in the research area on coal seam gas adsorption and diffusion, and to study the differences in gas adsorption and diffusion ability in different coal seams, low-temperature nitrogen adsorption (LT-N2GA), high-pressure mercury intrusion (MIP) and computerized tomography (μ-CT) were used as characterization methods, and methane isothermal adsorption experiments were carried out to systematically study the pore structure characteristics of five groups of coal samples, and the pore-fracture structure characteristics and gas adsorption characteristics of each main coal seam were obtained. The results show that: (1) in the LT-N2GA experiment, the adsorption–desorption curves of all coal samples are of type III, and mainly develop cone-shaped pores or wedge-shaped semi-closed pores, with an average pore size of 1.84~4.84 nm, a total pore volume of 0.0010~0.0023 mL/g, a total specific surface area of 0.16~0.24 m2/g, and a fractal dimension D1 of 1.39~1.87 and D2 of 2.44~2.60. The micropores of L12 are more developed, and the mesopores and macropores of L9 are more developed. (2) In the MIP experiment, the porosity of coal samples is 3.79~6.94%. The porosity of L9 is the highest, the macropore ratio is the highest, and the gas diffusion ability is also the strongest. (3) In the μ-CT experiment, the porosity of L8-2 and L12 is 12.12% and 10.41%, the connectivity is 51.22% and 61.59%, and the Df is 2.39 and 2.30, respectively. The fracture of L12 is more developed, the connectivity is better, and the heterogeneity of the pore of L8-2 is higher. (4) In the isothermal adsorption experiment of methane, the gas adsorption capacity basically increases with the increase in the buried depth of the coal seam, and the gas adsorption capacity of the No.12 coal seam is the highest. Based on the pore-fracture structure characteristics and gas adsorption characteristics of the main coal seams in the research area, the gas outburst risk of each coal seam is ranked as follows: No.12 coal seam > No.8 coal seam > No.7 coal seam > No.9 coal seam. The experimental results provide important help for researching the structural characteristics of coal seam pore fractures and preventing gas outbursts during deep coal seam mining.

Adsorption characteristics of shale gas in organic–inorganic slit pores

With the gradual advancement of shale gas exploration and development technology, shale gas has replaced conventional oil and gas as the primary energy source. As the main occurrence form of natural gas in shale reservoirs, the adsorption state is always an important research topic for evaluating the gas-bearing property of shale reservoirs and improving shale gas recovery. However, at present, there are few studies on control factors and control mechanisms of adsorbed gas in organic–inorganic slit pores, with several unexplained control factors and mechanisms. Taking Songliao Basin shale as an example, molecular simulations are employed to investigate shale gas adsorption in organic–inorganic slit pores, the graphene and kaolinite rock matrix model is employed, and molecular dynamics simulations, particularly the grand canonical Monte Carlo simulation is studied for pore sizes of 2, 4, and 6 nm, The adsorption behavior of methane on heterogeneous shale surfaces at temperatures of 298, 323, 348, 373, and 398 K and pressures of 0.1, 5, 10, 15, and 20 MPa reveals the microscopic mechanism of shale gas adsorption in organic–inorganic slit pores at a molecular scale. The results show that as temperature and pressure increase simultaneously, methane is more strongly adsorbed on the surface of graphene than kaolinite, the number of methane molecules also gradually decreases, the root mean square of the displacement of methane and different surface forces between atoms exhibit certain regularity, and the adsorption capacity of the system is proportional to the changes in diameter within the system. Van der Waals energy and electrostatic energy in the system also increase gradually with changes in temperature and pressure, and electrostatic energy has a greater influence on the adsorption of the system than van der Waal energy. These findings provide ideas for the adsorption capacity of shale gas in organic–inorganic slit pores and are critical for the accurate evaluation of shale reservoir gas content and improvement of shale gas recovery.

Study on gas adsorption and desorption characteristics on water injection coal

To study the desorption mechanism of methane in coal by H2O injection and establish the Wiser molecular structure model of bituminous coal, the Grand Canonical Monte Carlo method was used to study the desorption behavior of CH4 in coal with different amounts of H2O injection at molecular scale. The results showed that at 293 K, the maximum adsorption capacity of H2O was about 16 mmol/g, and that of CH4 was about 8 mmol/g, which was about twice that of CH4. This indicates that H2O has a stronger adsorption capacity than CH4. For methane-bearing coal, when the amount of water injected is 100, the average relative concentration of CH4 is 0.5446, and the average relative concentration of CH4 decreases by 33.77% compared to the water content of 20. Under the same time conditions, the root mean square displacement and diffusion coefficient of CH4 decrease with the increase of H2O injection quantity. With the increase of H2O injection, the motion velocity of CH4 in vacuum layer decreased. When water was injected, methane was trapped in the coal by water. The more H2O injected, the more methane trapped in the coal, and the less methane desorption. This research lays a theoretical foundation for further research involving coal-water interaction.