Methane Adsorbs Research Articles

Modelling of physical and chemical properties of activated carbons which affect methane adsorption mechanisms

Effect of important physical and chemical properties of activated carbons which affect the way methane adsorbs were studied. The Grand Canonical Monte Carlo (GCMC) simulations were used to study how the curvature and size of the platelets affect the mechanisms of methane adsorption process; and which role is played by the amount of oxygen present in activated carbons. Furthermore, Molecular dynamic (MD) simulations were carried out to study the effect of those properties on motion behavior of methane molecules during adsorption. The two simulations are very vital because they were able to exploit mechanisms which are difficult to obtain by using experiments alone. It was found that oxygen content, degree of curvature of platelets and size of basic structural units affected the availability of suitable methane binding sites in activated carbons and hence total methane adsorbed amount. Furthermore, the studied parameters were found to have impacts to the energy of interaction between activated carbons and methane, methane diffusion characteristics and amount of heat generated during adsorption process. It is concluded that the studied activated carbon properties hugely affect the way methane adsorbs and should be given attention during designing of the optimal adsorbent for methane adsorption.

Clarifying the Effect of Clay Minerals on Methane Adsorption Capacity of Marine Shales in Sichuan Basin, China

The effect of clay minerals on the methane adsorption capacity of shales is a basic issue that needs to be clarified and is of great significance for understanding the adsorption characteristics and mechanisms of shale gas. In this study, a variety of experimental methods, including XRD, LTNA, HPMA experiments, were conducted on 82 marine shale samples from the Wufeng–Longmaxi Formation of 10 evaluation wells in the southern Sichuan Basin of China. The controlling factors of adsorption capacities were determined through a correlation analysis with pore characteristics and mineral composition. In terms of mineral composition, organic matter (OM) is the most key methane adsorbent in marine shale, and clay minerals have little effect on methane adsorption. The ultra-low adsorption capacity of illite and chlorite and the hydrophilicity and water absorption ability of clay minerals are the main reasons for their limited effect on gas adsorption in marine shales. From the perspective of the pore structure, the micropore and mesopore specific surface areas (SSAs) control the methane adsorption capacity of marine shales, which are mainly provided by OM. Clay minerals have no relationship with SSAs, regardless of mesopores or micropores. In the competitive adsorption process of OM and clay minerals, OM has an absolute advantage. Clay minerals become carriers for water absorption, due to their interlayer polarity and water wettability. Based on the analysis of a large number of experimental datasets, this study clarified the key problem of whether clay minerals in marine shales control methane adsorption.

Removal of hydrogen sulfide from a binary mixture with methane gas, using IRMOF-1: a theoretical investigation.

The natural gas is mainly composed by methane, ethane, propane, and contaminants. Among these contaminants, the H2S gas has some specific characteristics such as its toxicity and corrosion, besides reducing the combustion power efficiency of natural gas. In this context, metal-organic frameworks appear as promising materials for purification of natural gas by adsorption, due to their large surface area and pore volume. In this work, Grand Canonical Monte Carlo method was used to study the adsorption and separation of CH4:H2S mixture by IRMOF-1. The adsorption isotherms were computed for the pure components, and at different compositions of binary mixture (90:10, 75:25, 50:50, 25:75, and 10:90). Interaction energy obtained with the semiempirical method confirmed that the inorganic unit is the preferred site for CH4 and H2S adsorption. Moreover, in a gas mixture with 50:50 proportion of CH4:H2S mixture, methane adsorbs preferentially in the inorganic unit only at pressures close to 20bar. Non-covalent interaction (NCI) analyses indicated that the interactions involving H2S are more effective than that for CH4, due to an electrostatic character in the H2S interaction. The simulations also showed that the separation of gases occurs in all compositions and pressures studied, suggesting that IRMOF-1 has a promising potential for this application.

Green synthesis of poly(pyrrole methane) for enhanced adsorption of anionic and cationic dyes from aqueous solution

The presence and accumulation of dyestuff in the environment is posing great harm to human beings. In this study, a novel poly(pyrrole methane) (PPm) adsorbent with abundant OH was greenly synthesized via a facile polymerization method. Its physicochemical properties were characterized in detail. Furthermore, the adsorption performance of PPm for anionic dye (acid red G, ARG) and cationic dye (methylene blue, MB) was comparatively studied with a typical dye adsorbent (polyprrrole, PPy). The results revealed that the adsorption of ARG or MB onto PPm followed pseudo-second-order model and Langmuir mode. The adsorption processes were endothermic and spontaneous. The maximum capacities of PPm to adsorb ARG and MB were 555.56 mg/g and 99.11 mg/g, which were about 10 and 2 times higher than that of PPy, respectively. PPm could be reused for 5 cycles without a significant decrease of its adsorption rate. The adsorption of ARG and MB is mainly attributed to electrostatic interaction and hydrogen bonding between ARG or MB and OH in PPm. Additionally, ARG could be adsorbed by ion exchange with the doped Cl− in PPm. Therefore, this study provides a new strategy to synthesis efficient adsorbent for the removal of both anionic and cationic dyes.

A novel composite derived from a metal organic framework immobilized within electrospun nanofibrous polymers: An efficient methane adsorbent

AbstractIn this study, tantalum(V) metal organic framework (Ta‐MOF) nanostructure was incorporated within polyvinyl alcohol (PVA) nanofibers to prepare an electrospun porous composite as a novel CH4 adsorbent. The crystallinity, thermodynamic behavior, and textural properties of the products were investigated using instrumental analyses techniques. The results confirmed that the developed PVA/Ta‐MOF electrospun nanofibrous composite exhibits higher thermal stability, considerable porosity, and larger surface area compared to the parent Ta‐MOF. A 2k factorial design was used for systematic study of the adsorption process. The results of response surface methodology (RSM) optimization indicated that the highest methane adsorption can be achieved at 24.40 °C and 3.70 bar in 23.60 min. These nano pore sorbents showed a significant potential for CH4 adsorption due to the presence of Ta‐MOF at the surface of nanofibrous composite compared to many other conventional sorbents that have been already used. This study introduces a novel biocompatible/biodegradable nanofibrous composite material with high methane adsorption performance and potentials for other applications.

Synthesis of a microporous copper carboxylate metal organic framework as a new high capacity methane adsorbent

Copper (II) carboxylate, (Cu-BDC), with metal-organic-framework (MOF) has been synthesized under the solvothermal condition and used as an adsorbent for the methane. The adsorbent was characterized by means of X-ray diffraction (XRD), Fourier transforms infrared (FT-IR), Scanning electron microscope (SEM) image, Thermogravimetric analysis (TGA) and Brunauer-Emmet-Teller (BET) method. The Sorption capacity of the methane on Cu-BDC at range pressure of 1–20 bar and 298 K was investigated by volumetric measurement. The results show that Cu-BDC has a high sorption capacity for CH4. The high sorption capacity of this adsorbent may be attributed to the appropriate pore diameter of the framework.

Adsorption and Activation of Methane on the (110) Surface of Rutile-type Metal Dioxides

Methane strongly adsorbs on the (110) surface of IrO2, a rutile-type metal dioxide. Its C–H bond is facilely dissociated even below room temperature, as predicted in a few theoretical works and actually observed in a recent experimental study. Thence, three questions are posed and answered in this paper: First, why does methane adsorb on the IrO2 surface so strongly? Second, why is the surface so active for the C–H bond breaking reaction? Third, is there any other rutile-type metal dioxide that is more active than IrO2? A second-order perturbation theoretic approach is successfully applied to the analysis of the electronic structure of methane, which is found to be significantly distorted on the surface. Regarding the first point, it is clarified that an attractive orbital interaction between the surface Ir 5dz2 orbital and the distorted methane’s highest occupied molecular orbital leads to the strong adsorption. As for the second point, the bond strength between the surface metal atom and the CH3 fragmen...

In situ spectroscopic studies of methane catalytic combustion over Co, Ce, and Pd mixed oxides deposited on a steel surface

This study is an approach to resolve the mechanism of methane catalytic combustion over a series of palladium and cobalt palladium and ceria-doped catalysts supported on γ-Al2O3. The first and most important question addressed is whether methane adsorbs on the surface of the catalyst. Another task was to determine the stable intermediate products of methane oxidation. The main method used for both was in situ Diffuse Reflectance Infrared Spectroscopy (DRIFT) aided with Raman and X-ray Fluorescence spectroscopies. The main conclusions drawn from the results are that methane adsorbs only on the catalyst surface with pre-adsorbed oxygen, forming methoxy species on catalysts containing Pd, which has been confirmed by pulse in situ DRIFT experiments. During methane oxidation traced down by DRIFT, formates and carbonates (mono and free carbonates) are the stable intermediate products on catalysts containing Pd. Based on the in situ results and the literature data, the mechanism of methane catalytic combustion has been proposed, assuming one type of active centre.

High-Pressure Methane Adsorption in Two Isoreticular Zr-Based Metal–Organic Frameworks Constructed from C3-Symmetrical Tricarboxylates

Development of porous metal–organic frameworks (MOFs) with enhanced stability and high methane working capacity is of paramount importance to facilitate the use of natural gas as a transportation fuel. In this work, we used C3-symmetrical tricarboxylates to construct two isoreticular Zr-based MOFs (ZJNU-30 and ZJNU-31) featuring the coexistence of a one-dimensional channel and two different types of cages in the overall structures. High-pressure methane adsorption studies show that the two compounds have good methane adsorption capacities. In particular, the methane working capacity of ZJNU-30a is among the highest reported for Zr-based MOFs. More importantly, the two compounds display exceptional hydrostability, making them attractive for use as a methane adsorbent.

Methane and carbon dioxide adsorption and diffusion in amorphous, metal-decorated nanoporous silica

The adsorptive and diffusive behaviour of methane and carbon dioxide in amorphous nanoporous adsorbents composed of spherosilicate building blocks, in which isolated metal sites have been distributed, is examined. The adsorbent contains cubic silicate building blocks (spherosilicate units: Si8O20), which are cross linked by SiCl2O2 bridges and decorated with either –OTiCl3 or –OSiMe3 groups of the other cube corners. The model structures were generated to correspond to experimentally synthesised materials, matching physical properties including density, surface area and accessible volume. It is shown that both methane and carbon dioxide adsorb via physisorption only in the modelled materials. Adsorption isotherms and energies at 300 K for pressures up to 100 bar were generated via molecular simulation. The maximum gravimetric capacity of CH4 is 16.9 wt%, occurring at 300 K and 97 bar. The maximum gravimetric capacity of CO2 is 50.3 wt%, occurring at 300 K and 51.6 bar. The best performing adsorbent was a low-density (high accessible volume) material with no –OTiCl3 groups. The presence of –OTiCl3 did not enhance physisorption even on a volumetric basis, and the high molecular weight of –OTiCl3 groups is a significant penalty on a gravimetric basis. Based on the pair correlation functions, the most favourable adsorption sites for both adsorbates are located in front of the faces of spherosilicate cubes. The self-diffusivity and activation energy for diffusion are also reported.

Effect of Support Structure and Composition on the Catalytic Activity of Pt Nanoclusters for Methane Dehydrogenation

Methane adsorption and dehydrogenation on nanometer-sized Pt clusters, supported by reduced ceria (110), was investigated using density functional theory with Hubbard corrections. Two Pt nanocluster shapes, hemispherical and tetrahedral, are considered. Both stoichiometric and reduced ceria do facilitate methane adsorption and dehydrogenation on the supported clusters, as compared to unsupported clusters; an analogous β-silica support does not significantly enhance methane adsorption. The energy barrier to activation decreases by approximately 0.06 eV for hemispherical Pt/CeO2-x and 0.12 eV for tetrahedral Pt/CeO2-x, compared to the unsupported clusters. Methane adsorbs preferentially atop the Pt atoms at the metal-support interface; upon dehydrogenation, H migrates to the oxygen vacancy site on the ceria surface while CH3 remains on the Pt cluster. We propose that the increased electron density and compressive strain at the low-coordinated Pt sites and oxygen vacancies at the metal–support interface cont...

Production, characterization and methane storage potential of KOH-activated carbon from sugarcane molasses

Activated carbons (ACs) were prepared in the presence of KOH at 400–800°C by carbonization of sugarcane molasses, a low-cost by-product of the vegetable sugar industry. All the ACs obtained were microporous materials. The AC that had the highest surface area (2202m2/g) was tested as a methane adsorbent at temperatures between 20 and 100°C. The adsorption data were modeled by Langmuir, Freundlich, and Temkin isotherm equations, and the Langmuir model was found to have the best fit. The results suggest that ACs prepared from sugarcane molasses using a one-step carbonization and KOH chemical activation process has high potential for natural gas storage applications. The highest methane adsorption capacity was equal to 197.23mg/g (12.33mmolg−1) at 50bar and 20°C.

Molecular simulation of methane adsorption in micro- and mesoporous carbons with applications to coal and gas shale systems

Methane adsorption in porous carbon systems such as coal and the organic matrix of gas shales is an important factor in determining the feasibility of CO2 injection for enhanced natural gas recovery and possible sequestration of CO2. Methane and CO2 adsorb competitively on carbon surfaces and an understanding of each gas individually is important for determining a model to predict the feasibility of this approach for permanent CO2 storage. Coal and gas shales have a very heterogeneous pore system, ranging from the micro, meso, and macro-scales, with the pore size strongly affecting the adsorption behavior. In micropores, the force fields of opposing pore walls are close enough that they will overlap and significantly influence the adsorption behavior, which affects adsorbate packing and density. To determine the size at which these effects become non-negligible and to determine the magnitude of this impact, grand canonical Monte Carlo simulations have been carried out to estimate the adsorption isotherms of methane across a range of pore sizes and at various temperature and pressure conditions characteristic of subsurface conditions. These isotherms have been calculated on graphitic surfaces as an initial model of coal and kerogen of gas shales. The general trend within pore sizes is that larger pores exhibit lower excess density compared to smaller pores. However, at pressure above 1MPa, the adsorption capacities of 0.6-nm pores drop below those of the wider pores, ultimately decreasing below that of the 1.2-nm pore at 18MPa. The density of adsorbed methane changes non-monotonically with increasing pore width, and drops to a minimum in 1.2-nm pores at 12MPa. The isotherms have been compared with experimental data to gauge their accuracy, and the behavior of the adsorbed layer has been examined in detail. At pressures less than 2.5MPa, the molecular simulation estimates underpredict the excess adsorption, while at pressures greater than 2.5MPa up to 20MPa, the simulation estimates overpredict the excess adsorption. This discrepancy is likely due to the limitation of the experimental-based model that was used to generate the pore size distribution and the surface functionalities of the porous media that were ignored in the molecular simulation investigations, but likely play an important role in determining accurate capacities under confinement at the nanoscale.

Sodium Promoter Inducing a Phase Change in a Palladium Catalyst

Alkali metals act as promoters for the catalytic activity of transition metals, but it is unclear whether they only donate electrons or induce the formation of different sodium-containing phases. In the present work, calculations based on density functional theory and ab initio thermodynamics show that, under oxygen-rich conditions, addition of only 6 wt % of sodium to a palladium-based oxidation catalyst can induce a phase change in the catalyst. In presence of sodium, a cubic NaPd3O4 is more stable than tetragonal PdO, which is the stable phase in the absence of sodium. Moreover, the region of stability of the oxides is extended by ∼100 K with respect to the sodium-free case. Wulff construction predicts that (111), (100), and (110) facets should be present at the surface of NaPd3O4 particles at equilibrium. Carbon monoxide and methane adsorb strongest on NaPd3O4(100) and NaPd3O4(110), respectively, with adsorption energies of 3.75 and 3.03 eV, higher than on PdO. In all cases, there is a marked preferen...

Methane Activation and Oxygen Vacancy Formation over CeO2 and Zr, Pd Substituted CeO2 Surfaces

The catalytic properties of CeO2 for hydrocarbon oxidation reactions have implications for a variety of applications. Surface reduction and methane activation are key processes in the overall oxidation reaction, and are examined herein for pure CeO2 (111), (110) and (100) surfaces and surfaces with Zr or Pd substituted in Ce lattice positions. Density functional theory, with the inclusion of an on-site Coulombic interaction (DFT+U), was used to calculate the energetics of oxygen vacancy formation and methane activation. Oxygen vacancy formation is more exothermic for Zr and Pd substituted ceria surfaces than for pure ceria, with Pd-substituted surfaces being significantly more reducible. Methane adsorbs dissociatively as *H and *CH3, and the thermodynamics of dissociative methane adsorption correlate with those of oxygen vacancy formation over the pure and substituted surfaces. The lowest energy pathway for dissociative adsorption on the (111) surface proceeds through H abstraction and the formation of a methyl radical, and subsequent chemisorption of the radical species. Sensitivity of the reported results to the choice of U value within the DFT+U method is discussed.

Gas Storages in Microporous Metal‐Organic Framework at Ambient Temperature

Abstract[Co2(bdc)2(ted)]·2DMF·3H2O (2), (DMF = N,N′‐dimethylformamide, bdc = 1,4‐benzenedicarboxylate dianion, ted = triethylenediamine) was prepared and characterized by IR, elemental analysis, TGA, powder X‐ray analysis and single‐crystal X‐ray determination. At ambient temperature the material [Co2(bdc)2(ted)] (1) was found to be high adsorbent of methane but poor adsorbent of hydrogen.

Laboratory studies of methane and ethane adsorption and nucleation onto organic particles: Application to Titan's clouds

Titan, Saturn's largest moon, has a thick nitrogen/methane atmosphere. The temperature and pressure conditions in Titan's atmosphere are such that the methane vapor should condense near the tropopause to form clouds. Several ground-based measurements have observed sparse cloud-like features in Titan's atmosphere, while the Cassini mission to Saturn has provided large scale images of the clouds. However, Titan's cloud formation conditions remain poorly constrained. Heterogeneous nucleation (from the vapor phase onto a solid or liquid aerosol surface) greatly enhances cloud formation relative to homogeneous nucleation. In order to elucidate the cloud formation mechanism near the tropopause, we have performed laboratory measurements of the adsorption of methane and ethane onto solid organic particles (tholins) representative of Titan's photochemical haze. We find that monolayers of methane adsorb onto tholin particles at saturation ratios less than unity. We also find that solid methane nucleates onto the adsorbed methane at a saturation ratio of S = 1.07 ± 0.008 . This implies that Titan's methane clouds should form easily. This is consistent with recent measurements of the column of methane ruling out excessive methane supersaturation. In addition, we find ethane adsorbs onto tholin particles in a metastable phase prior to nucleation. However, ethane nucleation onto the adsorbed ethane occurs at a relatively high saturation ratio of S = 1.36 ± 0.08 . These findings are consistent with the recent report of polar ethane clouds in Titan's lower stratosphere.

Role of acidity of catalysts on methane combustion over Pd/ZSM-5

Abstract Palladium-based catalysts were prepared by the impregnation (I) and ion-exchange method (E) with ZSM-5 and γ-Al2O3 as support respectively. The high activity of Pd/ZSM-5(I) and Pd-ZSM-5(E) catalysts for methane combustion was observed. The order of activity is consistent with Bronsted acidity of catalysts: Pd/ZSM-5(I) > Pd-ZSM-5(E) > Pd/Al2O3. It is shown by FT-IR that methane adsorbs on acidic bridging hydroxyl groups of ZSM-5-supported Pd catalysts. Symmetric v1 C–H stretching vibrations of methane shift to low frequency due to the interaction between methane molecules and Bronsted acid sites or Pd2+, indicating that methane molecules can be activated.

Catalytic Dry Reforming of Methane in a CREC Riser Simulator Kinetic Modeling and Model Discrimination

The present study deals with catalytic dry methane reforming in a fluidized Chemical Reactor Engineering Centre (CREC) riser simulator and with the modeling of the obtained results using several kinetic rate equations. Experiments were designed and developed using a statistical criterion that optimizes the effort expended for model discrimination. From the eight models originally considered, six of them were initially found to fit the data. However, only one of them was later on retained using model discrimination. Results of the study show that both the adsorption of methane and the adsorption of carbon dioxide play an important role in determining the observed rate of the methane dry reforming reaction and suggest that methane and carbon dioxide adsorb on different sites of the catalyst. The study is also valuable in providing a sound rate equation applicable in the context of a Catforming process under current development at the CREC of the University of Western Ontario.

Temperature Dependent Adsorption Dynamics of CH4 on Alkane-Covered Pt (111)

Supersonic molecular beam experiments were used to probe the temperature dependence of adsorption of methane and ethane into adsorbed layers of methane, ethane, propane, and n-butane on Pt(111). Because adsorption must proceed via a transient state from which either desorption or conversion to a bound state may occur, the adsorption probability is, in general, temperature dependent. As the surface temperature is lowered below 75 K increasing amounts of methane adsorbs into an alkane-covered surface to form a mixed adlayer. Methane forms multilayers on methane, ethane, propane, and butane adsorbates below 35 K; ethane forms multilayers on the same adsorbates below 63 K. The condensation temperature of methane and ethane into multilayers is independent of the type of preadsorbed alkane and occurs well below the normal boiling or melting point of each species. At a given temperature between 75 K and 35 K the steady-state uptake of methane (or ethane between 63 K to 120 K) into the first layer decreases with ...