Methane Gas Adsorption Research Articles

Improved chemiresistor gas sensing response by optimizing the applied electric field and interdigitated electrode geometry

Improving the sensing performance of chemiresistive gas sensors is largely material-centric, but further studies are needed to optimize the performance of electrode interfaces and interdigitated electrode structures (IDEs) geometry. Hence, we systematically optimize IDEs geometry (spacing between fingers (Sf), finger width (Wf) and number of fingers (Nf)) using methane (100 ppm) selective nanomaterial. This study provides some fascinating findings: Changing the dimensions of Sf/Wf to 50–300 μm/20–75 μm in a constant device area increased sensing response by 1.2/1.54 times, possibly due to increased grain-to-grain contacts in sensing material/potential barrier between electrode and sensing material. Moreover, changing Nf from 2 to 44 and from 44 to 74 resulted in a 2.42-fold improvement and a 3.91-fold decrease in the sensing response, respectively. It can attribute to changes in the base charge density because it affects the contribution of charge carriers due to methane gas adsorption. This research opens the door for fabricating low-power highly sensitive gas sensors that can also be integrated into the Internet of Things.

Interfacial Adsorption Kinetics of Methane in Microporous Kerogen.

Rapid declines in unconventional shale production arise from the poorly understood interplay between gas transport and adsorption processes in microporous organic rock. Here, we use high-fidelity molecular dynamics (MD) simulations to resolve the time-varying adsorption of methane gas in realistic organic rock samples, known as kerogen. The kerogen samples derive from various geological shale fields with porosities ranging between 20% and 50%. We propose a kinetics sorption model based on a generalized solution of diffusive transport inside a nanopore to describe the adsorption kinetics in kerogen, which gives excellent fits with all our MD results, and we demonstrate it scales with the square of the length of kerogen. The MD adsorption time constants for all samples are compared with a simplified theoretical model, which we derive from the Langmuir isotherm for adsorption capacitance and the free-volume theory for steady, highly confined bulk transport. While the agreement with the MD results is qualitatively very good, it reveals that, in the limit of low porosity, the diffusive transport term dominates the characteristic time scale of adsorption, while the adsorption capacitance becomes important for higher pressures. This work provides the first data set for adsorption kinetics of methane in kerogen, a validated model to accurately describe this process, and a qualitative model that links adsorption capacitance and transport with the adsorption kinetics. Furthermore, this work paves the way to upscale interfacial adsorption processes to the next scale of gas transport simulations in mesopores and macropores of shale reservoirs.

Molecular dynamics and energy distribution of methane gas adsorption in shales

This study uses simulations to explore the energy distributions involved in the adsorption of methane gas in shales. Molecular mechanics calculations were carried out using the Forcite module in BIOVIA material studio software. The critical challenge in molecular-scale simulations remains the need to improve the description of the gas adsorption prior to up-scaling to a realistic scenario. Resolving this challenge requires the implementation of multi-scale techniques that employ atomistic/molecular-level results as input. Thus, it is pertinent that the appropriate molecular data on CH4 gas interaction with shale is obtained. This study provides empirical data on CH4 sorption/adsorption in shale at the molecular level to confirm the CH4 storage potential of shales. The effect of pressure on the CH4 sorption/adsorption was also investigated. A vital aspect of this study is elucidating the energy distribution and dominant energy that controls CH4 sorption/adsorption to serve as a basis for the exploitation of CH4 in productive shales. Following the intensive simulation exercise, the average total energy of CH4 sorption varied from approximately −30 to −120 kcal/mol with increase in pressure from 500 to 2500 psi, suggesting increasing thermodynamic stability. The results indicated that van der Waals energy is the major sorption energy with values ranging from 60 to −250 kcal/mol as the sorption pressure increased, while electrostatic energy recorded the least contribution. The total adsorption energy increased from −5 to −16 kcal/mol for reservoir pressure range of 1–15 MPa. This energy distribution data confirmed the possibility of CH4 adsorption on shale under reservoir pressure conditions.

First-Principles Study of Adsorption of Methane on Defective Silicene

Considering the significance of natural gas, such as methane, and the difficulties in storing it, research is increasingly focusing on developing materials for solid-state methane storage. Two-dimensional materials have a large number of possible adsorption sites for gas molecules due to their high surface-to-volume ratio. However, the two-dimensional structure is chemically inactive and attracts nonpolar gases rather weakly. We investigated the methane gas adsorption capabilities of silicene by activating it with different defects. According to our density functional theory calculations, the mono-vacancy (MV) defect is advantageous in increasing the binding strength of energy-carrying gases such as methane. In MV defective silicene, methane adsorption energy is detected in the order of the internationally specified energy regime.

Gas content prediction model of water-sensitive shale based on gas–water miscible competitive adsorption

The evaluation of gas content plays a key role in determining the efficient development of shale reservoirs. To better understand the gas–water miscible competitive adsorption mechanism in the pore-fracture system of water-bearing shale, the water vapor adsorption experiment of dry shale and the methane gas adsorption experiment of water-bearing shale were carried out to compare and analyze the competitive adsorption laws of formation water and methane gas on the shale surface under different temperatures, pressures, and water saturation conditions. Moreover, based on the molecular layer adsorption theory, the gas–liquid–solid interface competitive adsorption model considering the coupling of temperature, pressure, and water saturation was established to predict the actual gas content of water-bearing shale reservoirs. The results show that the main controlling factors affecting the adsorbed gas content of water-bearing shale are specific surface area, temperature, and water content in turn according to weight coefficients; Compared with the gas–solid adsorption model, the gas–liquid–solid competitive adsorption model has higher accuracy in calculation results, which are much closer to the desorption data of shale cores in Jiaoshiba area, Fuling, China. Hence, the competitive adsorption model provides a theoretical foundation for reasonably evaluating the exploitation potential of shale gas reservoirs.

Adsorption Isotherm and Kinetic Study of Methane on Palm Kernel Shell-Derived Activated Carbon

Activated carbon (AC) was synthesized from palm kernel shell (PKS) using different activating agents, i.e., steam, carbon dioxide (CO2), and CO2-steam, in order to analyze the impact of activating agents on the pore opening of AC. In this study, AC produced from PKS was found to have great potential as an adsorbent for methane storage. The different molecular diffusivity and reactivity of the combination of CO2 and steam succeeded in producing AC with the highest burn-off of 78.57%, a surface area of 869.82 m2/g, a total pore volume of 0.47 cm3/g, and leading to maximum methane gas adsorption capacity of 4.500 mol/kg. All types of ACs exhibited the best fit with the Freundlich isotherm model, with the correlation coefficient (R2) ranging from 0.997 to 0.999, indicating the formation of multilayer adsorption. In addition, the adsorption kinetic data for all ACs followed the pseudo-first-order model showing that the rate of adsorption was dependent on both the adsorbent and the adsorbate and was governed primarily by physical adsorption between the pore surface and methane gas. The results of intraparticle diffusion model indicated that the adsorption of methane was affected by both pore diffusion and exterior layer diffusion due to the different adsorption rates.

Belt-like In2O3 based sensor for methane detection: Influence of morphological, surface defects and textural behavior

Herein, gas sensors based on mesoporous belt-like In2O3 products derived from a single-step electrospinning method were produced, and the influence of the annealing temperature on their sensing performance was evaluated. A detailed comparison of the morphology, surface defects and textural behavior of the belt-like In2O3 products was carried out to understand the observed gas sensing trends. The In2O3 sensor produced at an annealing temperature of 550 ℃ displayed improved sensing capabilities with a response of 1.1 to 90 ppm of methane at a lower operating temperature of 100 ℃. The response and recovery times of this sensor were only 36 and 44 s, respectively, and it displayed good stability and selectivity as well as a lower detection limit of 0.18 ppm. Experimental characterization revealed that this enhanced sensing behavior originate from the mesoporous nature of belt-like In2O3 products composed of small-sized particles which offered a large number of active sites for methane gas molecules as a result of the high surface area and high concentration of oxygen vacancies, which enabled greater channels for methane gas adsorption and desorption capacity.

Methane gas adsorption and detection using the metal-decorated blue phosphorene

Previous studies showed that the performances of two-dimensional materials as gas sensor can be effectively improved through the assistance of metal atoms. We study the adsorption energies, charge transfers and electronic structures of the blue phosphorene (BP) adsorbing metal atoms (Au, Ag, Cu, Co, Fe and Mn) and then adsorbing methane (CH4) gas molecule. The metal-decorated BP can be used as an excellent CH4 gas adsorption material, and the adsorption capacity is not easily disturbed by the magnetic field. The transfer charges between metal atoms and BP will induce the new energy bands to modulate the band structure of BP effectively. In the absence of a magnetic field, CH4 adsorption hardly change the band structures of BP decorated by six metal atoms. However, the CH4 adsorption can modulate the spin-polarizedbandgaps and magnetic moments of Co, Fe and Mn decorated BP obviously in the present of a magnetic field. In particular, the spin-down band gap of Fe-decorated BP would be reduced by two-third and the corresponding magnetic moment of Fe-decorated BP also decreases from 2.455 µB to 2.229 µB after CH4 adsorption. So, Fe-decorated BP is expected to be used as a material for high sensitivity CH4 gas detection.

Experimental study on the isothermal adsorption of methane gas in natural gas hydrate argillaceous silt reservoir

Gas hydrate occurs in hydrate reservoirs in a solid form. At present, the conventional exploitation method is to decompose solid hydrate and then extract the resulting gaseous gas. Therefore, the occurrence law of gas in a reservoir is of great significance for the study of gas hydrate seepage and productivity. Adsorption, as an important occurrence mode, has been widely concerned in the research on shale reservoirs. However, the adsorption problem in hydrate reservoirs has not received enough attention. In this paper, the existence of adsorption in a hydrate reservoir has been experimentally confirmed for the first time. Based on the argillaceous silt of a natural gas hydrate reservoir in the South China Sea, the pore structure and adsorption characteristics of argillaceous silt were experimentally studied, and the results were compared with those of typical shale reservoirs. The modified Langmuir and Dubinin-Radushevich equations were used to fit the adsorption data, and the suitable adsorption model of argillaceous silt was established and optimized. The results showed that the inhomogeneous slit pores are dominant in argillaceous silt, and they are formed by the accumulation of lamellar particles. Compared with shale, the adsorption capacity of argillaceous silt is weak under the same conditions. However, adsorption is a spontaneous exothermic reaction, and the ambient temperature of argillaceous silt is much lower than that of shale. Therefore, it is possible for argillaceous silt to achieve an adsorption capacity comparable to that of shale. The modified Langmuir model can be used to simulate argillaceous silt adsorption at low pressure, while under medium and high pressures, the modified Dubinin-Radushevich model performs better. The adsorption capacity of argillaceous silt is affected by moisture. When the water content is 20%, the Langmuir adsorption capacity and the Dubinin-Radushevich maximum adsorption capacity decreases by 21.88% and 13.67%, respectively, which is far less than the influence of moisture on shale adsorption, as reported in the literature. Cited as: Qi, R., Qin, X., Lu, C., Ma, C., Mao, W., Zhang, W. Experimental study on the isothermal adsorption of methane gas in natural gas hydrate argillaceous silt reservoir. Advances in Geo-Energy Research, 2022, 6(2): 143-156. https://doi.org/10.46690/ager.2022.02.06

Methane Gas Adsorption and Detection Using the Metal-Decorated Blue Phosphorene

Methane Gas Adsorption and Detection Using the Metal-Decorated Blue Phosphorene

Methane adsorption on the surface of metal (Fe, Ni, Pd) decorated SWCNT: A density functional theory (DFT) study

Adsorption of methane gas on the catalytic systems comprising (8, 0) single walled carbon nanotube (SWCNT) decorated with transition metals (Fe, Ni, Pd) were investigated using plane-wave density functional theory. SWCNT was modified by adding these transition metals to both inside and outside the nanotube and replacing carbon atoms with them. All structures were relaxed and their structural and electronic properties were investigated before and after CH4 adsorption. The obtained results indicate that metal modified nanotubes exhibit good sensitivity and selectivity to methane. Adsorption energy results show that modifying nanotubes with Ni on the surface are more effective at adsorbing CH4 as compared to systems containing Fe and Pd atoms on the surfaces. CH4 adsorption on the surface of CNT decorated with transition metals changed both electronic and magnetic properties which show that these nanotubes are good candidate for detecting methane from the environment.

Insight into the Adsorption of Methane on Gas Shales and the Induced Shale Swelling.

Shale gas resources are highly abundant in the world. They can provide sustainable energy supply and have the potential to reduce energy prices. Therefore, shale gas has become one of the most important resources for oil and gas exploration and production, especially in North America today. Adsorption and desorption of methane gas are some of the important physical and chemical processes involved in the accumulation, transport, and production of shale gas. The shale matrix will shrink or swell due to the desorption or adsorption of methane gas, which will impact the recovery of shale gas reservoirs. The main purpose of this investigation is to quantitatively ascertain how the adsorption of methane gas affects the volumetric changes of the shale matrix. Based on the adsorption potential theory, a modified Dubinin–Astakhov (D–A) equation was employed to describe the adsorption of supercritical methane gas on shale. Then, a coupled adsorption–strain model was established to investigate the volumetric strain of shale induced by the combined effects of methane gas adsorption and stress compression. The methane adsorption and the induced shale swelling were measured on a black shale sample from the Sichuan Basin at 303.15 K and pressure up to 10 MPa, and the proposed models were employed to interpret the experimental data. The results demonstrate that the proposed models show good applicability and provide a reliable prediction. The swelling moduli of shale samples were obtained by fitting the experimental data using the coupled adsorption–strain model. The results indicate that the swelling modulus of shale in this study is generally greater than that of coal. The calculated ratios of Young’s modulus to the swelling modulus do not show great variation from shale to shale in this study, which is similar to coal. This study can be incorporated into the numerical simulation of the production process of shale gas reservoirs.

Effect of Kerogen Thermal Maturity on Methane Adsorption Capacity: A Molecular Modeling Approach.

The presence of kerogen in source rocks gives rise to a plethora of potential gas storage mechanisms. Proper estimation of the gas reserve requires knowledge of the quantities of free and adsorbed gas in rock pores and kerogen. Traditional methods of reserve estimation such as the volumetric and material balance approaches are insufficient because they do not consider both the free and adsorbed gas compartments present in kerogens. Modified versions of these equations are based on adding terms to account for hydrocarbons stored in kerogen. None of the existing models considered the effect of kerogen maturing on methane gas adsorption. In this work, a molecular modeling was employed to explore how thermal maturity impacts gas adsorption in kerogen. Four different macromolecules of kerogen were included to mimic kerogens of different maturity levels; these were folded to more closely resemble the nanoporous kerogen structures of source rocks. These structures form the basis of the modeling necessary to assess the adsorption capacity as a function of the structure. The number of double bonds plus the number and type of heteroatoms (O, S, and N) were found to influence the final configuration of the kerogen structures, and hence their capacity to host methane molecules. The degree of aromaticity increased with the maturity level within the same kerogen type. The fraction of aromaticity gives rise to the polarity. We present an empirical mathematical relationship that makes possible the estimation of the adsorption capacity of kerogen based on the degree of polarity. Variations in kerogen adsorption capacity have significant implications on the reservoir scale. The general trend obtained from the molecular modeling was found to be consistent with experimental measurements done on actual kerogen samples. Shale samples with different kerogen content and with different maturity showed that shales with immature kerogen have small methane adsorption capacity compared to shales with mature kerogen. In this study, it is shown for the first time that the key factor to control natural gas adsorption is the kerogen maturity not the kerogen content.

The Role of Coal Facies to Adsorption of Methane Gas: Case Study on Warukin and Tanjung Formation Binuang Area, South Kalimantan Province

Adsorption of methane gas is affected by coal facies, as a consideration when exploring Coal Bed Methane (CBM). The Binuang area located in South Kalimantan is an area where coal carrier formations, namely the Warukin Formation and the Tanjung Formation, are well exposed. Sampling of coal was carried out using a channel sampling method from the youngest coal in the Warukin Formation to the oldest coal in the Tanjung Formation. The methodology applied in this research uses mineral analysis and adsorption of methane gas to find out the coal facies using a diagram conducted by previous researchers. There are two types of coal facies in the Warukin Formation, namely coal facies delta plain wet forest swamp and delta plain fen. In Tanjung formation, the coal facies that develops is delta plain wet forest swamp and delta plain fen. Changes in coal facies will cause the different ability of methane gas adsorption. Coal with a depositional environment (facies) of Delta wet plain swamp has more excellent adsorption of methane compared to adsorption of methane gas in delta plain fen facies.

Reverse biased nanocrystalline graphite (NCG)/p-Si schottky junction for methane gas sensor

An investigation on the effect of the reverse biased operation of NCG/p-Si Schottky contact during methane gas exposure at room temperature has been presented. The experimental results show the larger current shift at the reverse bias operation, compared to the forward bias by exposing to methane gas. This can be attributed to the adsorption of methane gas into the metal surface layer and produces a negative charge at the junction, thus reduces the barrier height of the device. The reverse barrier height was calculated under the reverse bias condition, demonstrated the value decreased from 0.58-0.53eV towards a higher concentration of methane gas. The Schottky junction also affected by the increase in a free carrier when exposure to the reducing gas such as methane. Raman spectra are reported to be detected at G, D and 2D band with the grain size 1.88nm to exhibit single crystallite graphite properties. The results correlate well with the 3D AFM scans reveal the RMS surface roughness of 1.1 to 2.8nm.

Effects of doping Mg2+ on the pore structure of MIL-101 and its adsorption selectivity for CH4/N2 gas mixtures

In this paper, one kind of porous materials had been prepared by doping Mg2+ on MIL-101 materials using hydrothermal method. Based on the low-pressure nitrogen adsorption (LPNA), X-Ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and High-pressure methane adsorption (HPMA) analyzer, the characteristics of new materials and its adsorption selectivity had been measured and analyzed systematically. Results show that doped Mg2+ would greatly increase the specific surface areas of MIL-101 by 58.2% at the most. Moreover, the pore structure of MIL-101 @ Mg2+ materials tend to be uniform. Compared with MIL-101 parental material, the single crystal size would be decreased by 100–200 nm. From XRD and TEM results, it can be concluded that the chemical skeleton structure of MIL-101 @ Mg2+ series materials are greatly similar with that of parental MIL-101 and not be destroyed by doping Mg2+. Doping Mg2+ increases the adsorption capacity of CH4 and N2 at different level because doping proper amount of Mg2+ restrains the generation of H bond, which has a positive effect on methane gas adsorption. Based on the maximum adsorption capacity and the hysteresis of adsorption and desorption curves, it can be concluded that the optimal Mg2+ doping amount is determined of 12.8%. And, according to the theory of Ideal Adsorbed Solution Theory (IAST), the separation coefficient of CH4/N2 selective adsorption also indicates that MIL-101@12.8% Mg2+ presents the largest adsorption separation coefficient and highest separation potentials.

The effect of coal petrology on the capacity of gas methane absorption in coal formation Tanjung Barito in Binuang Region, South Kalimantan

Tanjung Formation is an Eocene - Oligocene coal carrier formation. This formation is stratigraphically situated above the bedrock of Pratersier age. The location of this formation is in Binuang area, South Kalimantan approximately 20 km northwest of Banjarbaru city. The method of research by taking the coal sampling from the bottom seam to the top. Laboratory analysis is done in the form of coal petrography analysis and adsorption test. Coal seam of Tanjung Formation is found with thickness 50 to 600 cm. Megascopy, this coal seam is black, bright (bright-bright banded), black scratch, concoidal shards, and lightweight. Results of developing meceral analysis were vitrinite 22. 6% - 46.4%, inertinite 0.6% - 19.4%. and liptinite 0.4%, mineral matter 0.4% - 0.6%. Based on the reflectance reflection of vitrine (Rv) shows the range between 0.53 - 0.58. The rank of the entire coal is subbituminous B, based on the ASTM classification. Based on the analysis of gas adsorption shows from the lower coal seam to upper with the range 412.94 – 675.27 SCF / Ton. The upper coal seam of the small gas adsorption while at the bottom of coal seam is large gas adsorption. This change in gas adsorption is caused because the lower coal seam contains pyrite minerals, while the top is rarely found in pyrite minerals. The size of pyrite mineral content will affect the adsorption of methane gas.

Temperature effect on gas adsorption capacity in different sized pores of coal: Experiment and numerical modeling

Accurate methane gas adsorption capacity estimation is key for the coalbed methane (CBM) reservoir gas-in-place assessment. As in situ, the reservoir pressure and temperature vary from one location to another. The temperature induced gas sorption capacity evaluation is important for the CBM and mining industry. In this study, grand canonical Monte Carlo (GCMC) simulation was used to investigate temperature effect on methane adsorption capacity and adsorbed methane density for different sized pores. Methane adsorption experiments were performed to show realistic temperature effect on methane adsorption capacity and the experimental data were used directly to validate the numerical model. The pore structure of coal was characterized by high-pressure mercury injection, low-pressure N2 gas adsorption, low-pressure CO2 gas adsorption. The simulation results revealed that, first, temperature influence on methane adsorption was more obvious in smaller pores than that in larger pores. Based on the characteristics of the temperature influence on methane adsorption, pores can be divided into three categories: 0.7–0.9 nm pores, 1.0–1.3 nm pores and pores larger than 1.4 nm. In the 0.7–0.9 nm group, methane adsorption capacity decreased by approximately 19% at 3 MPa from 20 °C to 100 °C. In contrast, in the 1.0–1.3 nm pores and pores larger than 1.4 nm, methane adsorption capacity decreased by approximately 32% and 45%. Second, in 0.7 nm and 1.0 nm pores, methane adsorption capacity decreased linearly with an increase in temperature. In 4.0 nm pores methane adsorption capacity exhibited a negative exponential decrease with increasing temperature at low pressure (<3 MPa). Third, when the pore size was the same, the temperature effect was more obvious at a lower pressure than that at a higher pressure. The experimental results indicated that methane adsorption capacity in the coal sample decreased linearly with temperature increasing, and temperature effect on reducing methane adsorption capacity was greater at low pressure. These experimental results were consistent with the simulation results. Based on simulation and experimental data, it was obvious that temperature-induced gas adsorption capacity variation was both pore size dependent and pressure dependent.

Pore Size Effect on Methane Adsorption in Mesoporous Silica Materials Studied by Small-Angle Neutron Scattering.

Methane adsorption in model mesoporous silica materials with the size range characteristic of shale is studied by small-angle neutron scattering (SANS). Size effect on the temperature-dependent gas adsorption at methane pressure about 100 kPa is investigated by SANS using MCM-41 and SBA-15 as adsorbents. Above the gas-liquid condensation temperature, the thickness of the adsorption layer is found to be roughly constant as a function of the temperature. Moreover, the gas adsorption properties, such as the adsorbed layer thickness and the specific amount of adsorbed gas, have little dependence on the pore size being studied, i.e., pore radius of 16.5 and 34.1 Å, but are mainly affected by the roughness of the pore surfaces. Hence, the surface properties of the pore wall are more dominant than the pore size in determining the methane gas adsorption of pores at the nanometer size range. Not surprisingly, the gas-liquid condensation temperature is observed to be sensitive to pore size and shifts to higher temperature when the pore size is smaller. Below the gas-liquid condensation temperature, even though the majority of gas adsorption experiments/simulations have assumed the density of confined liquid to be the same as the bulk density, the measured methane mass density in our samples is found to be appreciably smaller than the bulk methane density regardless of the pore sizes studied here. The mass density of liquid/solid methane in pores with different sizes shows different temperature dependence below the condensation temperature. With decreasing temperature, the methane density in larger pores (SBA-15) abruptly increases at approximately 65 K and then plateaus. In contrast, the density in smaller pores (MCM-41) monotonically increases with decreasing temperature before reaching a plateau at approximately 30 K.

Evaluation of Methane Adsorption on the Modified Zeolite 13X

In this study nano structured zeolite 13X as adsorbent for methane gas was used. Ni and Al ions were used to modify the pores of the zeolite and the methane gas adsorption capacity was measured at room temperature and pressure between 1 to 12 bars. The textural properties and structure order of the zeolite were studied by XRD and nitrogen adsorption-desorption analysis. Inductive coupled plasma (ICP) technique was used to determine the amounts of metals loaded on the zeolite.