Methane Capacity Research Articles

Competitive Adsorption of Methane and Carbon Dioxide on Different Activated Carbons

Adsorbed natural gas (ANG) is one of natural gas storage technologies, in which natural gas is adsorbed by a high porosity adsorbent material at relatively low pressure and room temperature with high methane capacity and low cost. Carbon-based materials, like activated carbons, are promising as an ANG storage adsorbent because of high surface area, high porosity, and high volumetric storage capacity. In this research, the adsorption capacity of single and binary component of CH4 and CO2 was investigated by using activated carbons including coconut shell activated carbon (CSAC), palm shell activated carbon (PSAC), and coal-based activated carbon (CBAC) in a packed bed column at room temperature. The composition ratio of single component of CH4 and CO2 was fixed at 20 vol% of the total feed gas, and the composition ratios of binary component of CH4 and CO2 were fixed at 14.6 : 5.4, 10.0 : 10.0, and 5.0 : 15.0 vol% of the total feed gases, respectively. The result of single component adsorption showed that all activated carbons exhibited preferential adsorption for CO2 in relation to CH4. It can be seen from binary component adsorption that the adsorbed amount increased with increased CO2 composition, while the amount of CH4 adsorbed decreased, indicating competition for adsorption sites and preferential adsorption of CO2 over CH4. In terms of the adsorption capacity of binary component, the methane selectivity was CSAC > PSAC > CBAC for the whole composition ratios of CH4 and CO2.

Gas storage and controlling factors in an over-mature marine shale: A case study of the Lower Cambrian Lujiaping shale in the Dabashan arc-like thrust–fold belt, southwestern China

Lower Cambrian units in the upper Yangtze area of China are important strata for shale gas exploration. The Lower Cambrian Lujiaping shale in the Dabashan arc-like thrust–fold belt of the upper Yangtze area is thermally over-mature and has been transformed to slate by epimetamorphism. The Lujiaping shale has also experienced strong structural deformation; its current stratigraphic dip is 35°–80°. Over-maturity and strong deformation are considered unfavorable conditions for gas storage. However, desorption tests using canisters indicate that gas contents in the Lujiaping shale range from 0.05 to 3.39 m3/t (average, 1.12 m3/t); this level of gas presents challenges for conventional theories of shale gas enrichment. To analyze the controls on gas enrichment, we performed petrological, geochemical, and petrophysical experiments on shale samples from the Lujiaping Formation. Results show that the TOC contents are between 1.17% and 6.91%. The porosities of the shales are very low, in the range of 0.68%–3.93%, possibly related to over-maturity. The correlations between petrophysical parameters and the total organic carbon (TOC) content indicate that the organic fraction contribution to micropores and mesopores is highly significant. The Langmuir volumes for the studied shale samples are in the range of 1.07–5.87 m3/t. The gas content and methane adsorption capacity are strongly dependent on the TOC content. Because the studied shales have low porosities and are from shallow depths, their capacity for free gas storage is extremely limited, and the gas is stored mainly in an adsorbed state. The studied shales occur at temperatures of 20–37 °C. The maximum sorption methane capacity occurs at depths of 500–1500 m. Well-developed micropores, high surface area, and strong gas adsorption capacity are important controls on gas enrichment in the Lujiaping shales. The three controls may be related to the inter-particle pores between the organic matter and clay minerals.

An investigation into the thermodynamic characteristics of methane adsorption on different clay minerals

In this work, we investigate the methane adsorption characteristics of common clay minerals using experimental and theoretical analyses. Models for the isosteric heat of adsorption and variation of the surface free energy were established using thermodynamic theory and an improved D-A model, respectively. The models were used to investigate changes of the isosteric heat of adsorption and variation of the surface free energy of the different clay minerals. Then, the adsorption thermodynamics and adsorption capacity characteristics of the different clay minerals were investigated. An improved D-A model was developed by combining the D-A equation and adsorption characteristic curve and was used to fit the methane adsorption isotherms of the clay minerals. The model fitting results replicated the experimental results. The variation of the surface free energy is a function of pressure and temperature, which increased rapidly with the pressure increase at low pressures, while the free energy increased more slowly at higher pressure and decreased with increasing temperature. The order of the variation of the surface free energy from largest to smallest is illite, chlorite, kaolinite and montmorillonite, which is in disagreement with the order of the methane adsorption capacity, indicating that the specific surface area is a major factor that affects the methane adsorption capacity of the clay minerals. The isosteric heat of adsorption decreased with increasing methane capacity. The initial isosteric heats of adsorption of the clay minerals were 26.088 kJ/mol, 25.543 kJ/mol, 20.503 kJ/mol and 24.229 kJ/mol for montmorillonite, kaolinite, illite and chlorite, respectively. This indicates that the intermolecular forces between the methane molecules and the clay minerals decreases in the following order: montmorillonite, kaolinite, chlorite and illite.

Preparation and methane adsorption of two-dimensional carbide Ti2C

Here a novel material for methane adsorption was synthesized and studied, which is a graphene-like two-dimensional (2D) carbide (Ti2C, a member of MXenes), formed by exfoliating Ti2AlC powders in a solution of lithium fluoride (LiF) and hydrochloric acid (HCl) at 40 °C for 48 h. Based on first-principles calculation, theoretically perfect Ti2C with O termination has a specific surface area (SSA) of 671 m2 g−1 and methane storage capacity is 22.9 wt%. Experimentally, 2.85 % exfoliated Ti2C with mesopores shown methane capacity of 11.58 cm3 (STP: 0 °C, 1 bar) g−1 (0.82 wt%) under 5 MPa and the SSA was 19.1 m2 g−1. For Ti2C sample intercalated with NH3·H2O, the adsorbed amount was increased to 16.81 cm3 (STP) g−1 at same temperature. At the temperature of 323 K, the adsorbed amount of as-prepared Ti2C was increased to 52.76 cm3 (STP) g−1. For fully exfoliated Ti2C, the methane capacity was supposed to be 28.8 wt% or 1148 V (STP)v−1. Ti2C theoretically has much larger volume methane capacity than current methane storage materials, though its SSA is not very high.

Physics of coal methane: decisive role of iron compounds

The role of iron in formation of the coal methane is clarified based on the studies performed on the coal samples taken from different mines in Donetsk coal basin. Using Mossbauer spectroscopy, a correlation is found between the iron content and methane capacity of coal seams. By means of electron paramagnetic resonance, it is found that iron increases the concentration of non-compensated electron spins, i.e. dangled bonds at the carbon atoms. These bonds can be occupied by hydrogen atoms as a prerequisite of methane formation. The two-valence iron is shown to be the most effective in the increase of spin concentration. By using the ion mass spectrometry, the modelling of methane formation is carried out on the mechanical mixture of the iron-free reactor graphite, iron compounds and diluted sulphuric acid as a source of hydrogen atoms. The proposed mechanism is also confirmed by methane formation in the mixture of iron compounds and the coal from the mine where the iron and methane are practically absent.

The terrestrial biosphere as a net source of greenhouse gases to the atmosphere.

The terrestrial biosphere can release or absorb the greenhouse gases, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), and therefore has an important role in regulating atmospheric composition and climate. Anthropogenic activities such as land-use change, agriculture and waste management have altered terrestrial biogenic greenhouse gas fluxes, and the resulting increases in methane and nitrous oxide emissions in particular can contribute to climate change. The terrestrial biogenic fluxes of individual greenhouse gases have been studied extensively, but the net biogenic greenhouse gas balance resulting from anthropogenic activities and its effect on the climate system remains uncertain. Here we use bottom-up (inventory, statistical extrapolation of local flux measurements, and process-based modelling) and top-down (atmospheric inversions) approaches to quantify the global net biogenic greenhouse gas balance between 1981 and 2010 resulting from anthropogenic activities and its effect on the climate system. We find that the cumulative warming capacity of concurrent biogenic methane and nitrous oxide emissions is a factor of about two larger than the cooling effect resulting from the global land carbon dioxide uptake from 2001 to 2010. This results in a net positive cumulative impact of the three greenhouse gases on the planetary energy budget, with a best estimate (in petagrams of CO2 equivalent per year) of 3.9 ± 3.8 (top down) and 5.4 ± 4.8 (bottom up) based on the GWP100 metric (global warming potential on a 100-year time horizon). Our findings suggest that a reduction in agricultural methane and nitrous oxide emissions, particularly in Southern Asia, may help mitigate climate change.

Hybrid molecular simulation of methane storage inside pillared graphene.

In this study, a hybrid molecular dynamics--grand canonical Monte Carlo simulation is carried out to investigate the storage capacity of methane in a new nanostructure adsorbent called pillared graphene. This new nanostructure is composed of graphene sheets in parallel with vertical carbon nanotubes (CNTs), which act as their holders. The adsorption ability of this new structure is compared to graphene sheets to evaluate its potential for methane storage. The results show that in a specific adsorbent volume, applying pillared graphene increases the number of adsorbed methane up to 22% in comparison to graphene sheets. Given the application of various isotherm models such as Langmuir, Freundlich, Sips, and Toth and calculation of their parameters, it is predicted that methane adsorption on pillared graphene displays a heterogeneous behavior. Furthermore, the effects of geometry parameters such as CNTs diameter, the number of CNTs, and graphene sheets layer spacing on the methane uptake are investigated. The results show that the pillared graphene containing 1 CNT per 30 nm(2) graphene sheet areas provides the best configuration for methane adsorption. This optimum structure is characterized by a small diameter of about 0.938 nm and an optimal layer spacing of about 1.2 nm. Finally, our results show that this kind of pillared structure can be suitable for methane storage.

Influence of acid and heavy metal cation exchange treatments on methane adsorption properties of mordenite

In this study, the adsorption of methane (CH 4) capacities onto natural mordenite obtained from _ Izmir, Turkey, and its cationic forms (CuM, AgM, FeM, and HM samples) were investigated at the temperatures of 0 and 25 ◦ C up to 100 kPa. Natural and modied samples were characterized by X-ray diffraction (XRD), X-ray uorescence (XRF), Fourier transform infrared (FT-IR), thermogravimetry (TG-DTG), differential thermal analysis (DTA), scanning electron microscopy (SEM) coupled with energy dispersion spectroscopy (EDS), and N 2 adsorption methods. Quantitative XRD analysis showed that the major component of the natural zeolite was mordenite, together with minor amounts of quartz, feldspar, and clay mineral. The specic surface area and microporosity of the mordenite sample decreased notably after Ag cation exchange treatment. It was found that the adsorption capacity and the affinity of CH 4 with mordenite samples

Permeability Changes of Coal Cores and Briquettes under Tri-Axial Stress Conditions

Abstract The paper is dealing with the permeability of coal in triaxial state of stress. The permeability of coal, besides coal’s methane capacity, is the main parameter determining the quantity of methane inflow into underground excavations. The stress in a coal seam is one of the most important factors influencing coal permeability therefore the permeability measurements were performed in tri-axial state of stress. The hydrostatic three-axial state of stress was gradually increased from 5 MPa with steps of 5 MPa up to a maximum of 30 MPa. Nitrogen was applied as a gas medium in all experiments. The results of the permeability measurements of coal cores from the “Zofiówka” mine, Poland, and three mines from the Czech Republic are presented in this paper. As a “reference”, permeability measurements were also taken for coal briquettes prepared from coal dust with defined porosity. It was confirmed that the decreasing porosity of coal briquettes affects the decreasing permeability. The advantage of experimentation on coal briquettes is its good repeatability. From the experimental results, an empirical relation between gas permeability and confining pressure has also been identified. The empirical relation for coal briquettes is in good correspondence with published results. However, for coal cores, the character of change differs. The influence of confining pressure has a different character and the decrease in permeability is stronger due to the increasing confining pressure

The Outburst Risk as a Function of the Methane Capacity and Firmness of a Coal Seam

Abstract In most coal basins that are currently being exploited, gas and rock outbursts pose a considerable safety threat. The risk of their occurrence is frequently assessed by means of a parameter known as the methane capacity of coal. In a lot of countries, the evaluation of the mechanical properties of coal is conducted by means of another parameter: the firmness of coal. Due to the laboratory investigations and in situ observations carried out by the authors of this paper, it was possible to determine a function space in which the outburst risk can be described as a function of the methane capacity and firmness of a coal seam. This, in turn, made it possible to link the „gas factor” to the „mechanical factor”, and thus provide a more comprehensive risk analysis.

Methane Adsorption on Chemically Modified Microwave Irradiated Palm Shell Porous Carbon

Low-cost palm shell was used as a precursor for preparation of porous carbons via chemical impregnation with K2CO3 and microwave heating. Volumetric adsorption setup was used to measure the adsorption capacity of methane at 303.15 K under pressure up to 4 bars. The methane adsorption data was modelled by Langmuir, Freundlich, and Dubinin–Radushkevich (DR) isotherm equations. Langmuir and Freundlich models were found to have the best fit than DR isotherm. The kinetics of methane adsorption on the microwave porous carbon followed pseudosecond-order model equation. The highest methane adsorption capacity obtained was 3.533 mmol/g at 4 bar and 303.15 K. It was noticed that there is increase in adsorption with increased in initial pressure. The porous carbon displayed good adsorption characteristics for methane.

ANALISA PEMANFAATAN KOMPOS SEBAGAI MEDIA BIOCOVER DI TEMPAT PEMROSESAN AKHIR SAMPAH: Studi Kasus Kota Depok, Jawa Barat

High percentage of organic waste in urban areas makes composting as good alternative in waste processing. However, composting has not been effectively used and the result is not optimal. Previous studies found compost can be used as biocover media to reduce methane emission landfill. The objective of the study is to identify the characteristic of produced at temporary waste unit Depok, West Java and the effect of compaction toward the amount of methane removal in the landfill. Before applied as biocover media, compost was characterized followed by maturation process. Study on methane removal efficiency was conducted as batches in four reactors for 35 days with compaction rate varying from 750, 800, 850 dan 900 kg/m3. Composting media used in the research had 80 cm thickness with artificial gas consisting of 50% CH4 dan 50% CO2. Initially, compost did not meet criteria as mature compost based on SNI 19-7030-2004, and as media biocover hence a pre-treatment was needed to improve the quality compost to meet the requirements. Compaction rate of 900 kg/m3has highest elimination capacity of methane i.e. 98,31%±3,6% and 13,98±4,32 g/m3/hour.

Molecular simulation of natural gas storage in Cu-BTC metal–organic framework

We tested the MOF framework Cu-BTC for natural gas (NG) storage. Adsorption isotherms of C1–C4 alkanes were simulated applying the Grand Canonical ensemble and the Monte Carlo algorithm in a classical molecular mechanics approach. Experimental monocomponent isotherm of the alkanes was used to validate the force field. We performed multicomponent adsorptions calculations for three different quaternary mixtures of C1–C4 alkanes, matching typical NG streams composition, and predicted theoretical storage capacities, efficiency and accumulation of the NG within that composition. Despite being one of the frameworks with greatest storage capacity of methane, we found that Cu-BTC presented great sensitivity to the variation of the heavier alkanes in NG composition. When we increase the percentage of butane from 0.1% to 0.7% in the mixture, the mass of components retained in the discharge pressure (1bar) increases from 35 to 60%. We also perform siting and interaction energy investigations and compare the NG storage performance of the Cu-BTC with that of activated carbons. To our knowledge, this is the first study regarding the efficiency of the NG storage in Cu-BTC.

The Structubent: A Nanocomposite Solution to Compressed Natural Gas Storage

Compressed natural gas (CNG) is an attractive energy storage and transportation platform over liquefaction as it conserves the heat of vaporization of the fuel. However, the high pressure compression between 200 and 250 bar creates challenges in material design. Adequate reinforcement of the compression vessel at high pressure must yield a minimal hydrocarbon capacity to vessel weight ratio, which is unfavorable for those that are exclusively steel lined. Adsorption beds have been proposed for adsorbed natural gas (ANG) storage, but they are not ideal at present due to unfavorable weight to capacity ratios for common adsorbents and kinetic limitations upon discharge. In this work, we develop a model of a structural adsorbent, or structubent, as a reinforcing nanocomposite of the pressure vessel that offset their added volume using hydrocarbon adsorption capacity. Equations are presented that evaluate the stored methane capacity per vessel mass and volume in terms of nanocomposite properties under isothermal conditions. Furthermore, the ratios of mass‐ and volume‐specific capacities of the structubent versus CNG and ANG systems are derived which act as criteria for feasibility. An analysis of common adsorbents and matrix materials are performed, showing the structubent concept to be favorable in intermediate pressure regimes around 10 MPa.

Adsorption of methane and carbon dioxide on gas shale and pure mineral samples

We have measured methane and carbon dioxide adsorption isotherms at 40°C on gas shale samples from the Barnett, Eagle Ford, Marcellus and Montney reservoirs. Carbon dioxide isotherms were included to assess its potential for preferential adsorption, with implications for its use as a fracturing fluid and/or storage in depleted shale reservoirs. To better understand how the individual mineral constituents that comprise shales contribute to adsorption, measurements were made on samples of pure carbon, illite and kaolinite as well. We were able to successfully fit all adsorption data for both gases in accordance with a Langmuir isotherm model. Our results show carbon dioxide to have approximately 2–3 times the adsorptive capacity of methane in both the pure mineral constituents and actual shale samples. In addition to obvious microstructural and compositional differences between real rocks and pure minerals, we hypothesize that water adsorption plays an important role in regulating surface area availability for other molecules to adsorb. The resultant volumetric swelling strain was also measured as a function of pressure/adsorption. We observe both clay and pure carbon to swell an amount that is approximately linearly proportional to the amount of adsorption.

Study of high-pressure sorption of methane on Chinese coals of different rank

To investigate the sorption and diffusion behavior of deep coals, high-pressure sorption experiments of methane on coals were performed by the volumetric method. The experimental sorption isotherms fit the Langmuir model over the experimental pressure and temperature ranges. The sorption volumes of all coals tested exhibit a typical temperature behavior with a negative exponent decreasing as temperature increases. An approximately linear correlation for the methane Langmuir volume with coal rank was observed. The effect of coal rank on adsorption volume decreases with increasing temperature. The Langmuir pressure decreases initially with coal rank, reaches a minimum pressure corresponding to the maximum vitrinite reflectance at ∼2.2 % and then increases. Studies on the diffusion of methane in coal using a unipore diffusion model showed that the effective diffusion coefficients for the seven coals studied varied from 2.98 to 68.3 × 10−5 s−1. The effective diffusion coefficients of coal at the first pressure step generally increased linearly with increasing temperature, and a complex nonlinear relationship for methane sorption rate with coal rank was observed. Finally, an empirical equation was developed to estimate the sorption capacity of methane on coal of a given rank as a function of the coal burial depth in a time-invariant pressure and temperature field. The sorption capacity of the moisture-equilibrated coal was found to increase with burial depth until it reaches a maximum of 24 cm3/g at ∼1,500 m, followed by a slow decline to 20.5 cm3/g at approximately 3,000 m.

Design of an annular microchannel reactor (AMR) for hydrogen and/or syngas production via methane steam reforming

A bench-scale annular microchannel reactor (AMR) prototype with microchannel width of 0.3 mm and total catalyst length of 9.53 × 10−2 m active for the endothermic steam reforming of methane is presented. Experimental results at a steam to methane feed molar ratio of 3.3:1, reactor temperature of 1023 K, and pressure of 11 bar confirm catalyst power densities upwards of 1380 W per cm3 of catalyst at hydrogen yields >98% of thermodynamic equilibrium. A two-dimensional steady-state computational fluid dynamic model of the AMR prototype was validated using experimental data and subsequently employed to identify suitable operating conditions for an envisioned mass-production AMR design with 0.3 mm annular channel width and a single catalyst length of 254 mm. Thermal efficiencies, defined based upon methane and product hydrogen higher heating values (HHVs), of 72.7–57.7% were obtained from simulations for methane capacities of 0.5–2S LPM (space velocities of 195,000–782,000 h−1) at hydrogen yields corresponding to 99%–75% of equilibrium values. Under these conditions, analysis of local composition, temperature and pressure indicated that catalyst deactivation via coke formation or Nickel oxidation is not thermodynamically favorable. Lastly, initial analysis of an envisioned 10 kW autothermal reformer combining 19 parallel AMRs within a single methane-air combustion chamber, based upon existing manufacturing capabilities within Power & Energy, Inc., is presented.

Partial coal pyrolysis and its implication to enhance coalbed methane recovery, Part I: An experimental investigation

This paper examines the feasibility of combining a process known as enhanced methane recovery with partial coal pyrolysis to improve the petrophysics of coal seams and ultimately extract higher methane yields with accompanying pyrolysis gases. Partial pyrolysis for coal gas generation changes the pore and fracture structure, which in turn affect the permeability. A series of laboratory experiments on three coal rank samples monitored the changes in pore structure and permeability accompanying coal pyrolysis. Thermogravimetry–mass spectrometry (TG–MS) analysis evaluated mass loss and product composition. The pore and fracture structure evolution was determined by a combination of mercury intrusion porosimetry (MIP), scanning electron microscope (SEM) and methane adsorption capacity measurements on heat-treated coal blocks of ∼100g. The pore volume and methane adsorption capacity of LRC specimen (0.56% Ro,m) with 10°C/min and a hold time of 30min experienced slight changes during the heating process from 25°C to 400°C, but when heated from 400°C to 800°C, the pore volume in the LRC specimen greatly increased and the mercury-determined total porosity went from 36% at 400°C to 43% at 800°C. The permeability of the specimens at the temperature range of 300–400°C increased exponentially with temperature due to the generated pore–fracture system. The sample LRC (800°C) with the highest mercury-determined pore volume possessed the lowest methane capacity (19.45cm3/g) due to the maximum adsorption volume of pyrolyzed coal obtained from the Langmuir model was related not only to the pore structure but also to the extent of graphitization. Therefore, they may have significant implications for enhanced coalbed methane (CBM) recovery.

Methane Storage in Metal-Substituted Metal–Organic Frameworks: Thermodynamics, Usable Capacity, and the Impact of Enhanced Binding Sites

van der Waals density functional theory (vdW-DFT) and semiempirical grand canonical Monte Carlo (GCMC) calculations are used to predict the thermodynamics and methane storage capacity of 18 metal-substituted variants of the metal–organic framework (MOF) M-DOBDC (DOBDC = 2,5-oxidobenzene-1,4-dicarboxylate). Methane adsorption enthalpies (ΔH) on the benchmark Mg- and Ni-DOBDC systems were calculated using several vdW-DFT methods. The vdW-DF2 scheme was found to yield the best agreement with experiments, with a mean absolute deviation (MAD) of 2.7 kJ/mol. Applying this functional across the entire M-DOBDC series, it is observed that ΔH varies from −16 to −34 kJ/mol. These enthalpies are 10–20 kJ/mol less exothermic than that for CO2 adsorption in M-DOBDC, consistent with a weaker, dispersion-based CH4–MOF interaction. In parallel with these thermodynamic analyses, methane adsorption isotherms for five benchmark M–DOBDC MOFs were evaluated using several established interatomic potentials. An uncharged, single-site model for CH4 yielded the best agreement with experiments, with a MAD of 16 cm3/cm3. This potential was subsequently employed to predict methane capacities across the remainder of the M–DOBDC series, with additional comparisons to other prominent MOFs such as MOF-5, PCN-11, PCN-14, and HKUST-1. Finally, the amount of usable stored methane was examined for two operating scenarios: isothermal pressure swing (PS) and a combined temperature/pressure swing (TPS). Under these conditions, PCN-11 and Be-DOBDC yield the best combination of gravimetric and volumetric methane densities at pressures below ∼50 bar, while MOF-5 is best at higher pressures. We conclude that enhanced binding sites, such as coordinatively unsaturated metal sites, can be detrimental for PS operation at higher pressures due to their tendency to retain adsorbed methane at low (desorption) pressures.

Comparative Study of Textural Characteristics on Methane Adsorption for Carbon Spheres Produced by CO2Activation

Resorcinol-formaldehyde resin polymer was used as raw material for preparation of carbon spheres. Samples were treated with CO2flow at 850°C by varying activation times. The CO2activation granted better pore development of pore structure. The experimental data of CH4adsorption as a function of equilibrium pressure was fitted by Langmuir and Dubinin-Astakhov (D-A) models. It was concluded that the high surface area and micropore volume of carbon spheres did unequivocally determine methane capacities. In addition, a thermodynamic study of the heat of adsorption of CH4on the carbon spheres was carried out. Adsorption of CH4on carbon spheres showed a decrease in the adsorption heat with CH4occupancy, and the heat of adsorption fell from 20.51 to 12.50 kJ/mol at 298 K and then increased to a little higher values at a very high loading (>0.70), indicating that CH4/CH4interactions within the adsorption layer became significant.