Adsorption Equilibria Of Methane Research Articles

Adsorption equilibrium of methane on activated carbon and typical metal organic frameworks

To develop adsorbents suitable for the storage of natural gas by adsorption, activated carbon SAC-02, HKUST-1 and MIL-101(Cr) were synthesized and characterized in terms of structural morphology observation, nitrogen physisorption at 77.15 K, and methane adsorption at 293.15–313.15 K and 0–4 MPa. The methane adsorption isotherms were comparatively correlated with the Toth, D-A and Ono-Kondo equations and the performances of the adsorbent samples were evaluated in terms of the isosteric adsorption heat and the adsorbed phase density. The results indicate that, in comparison with the D-A and Ono-Kondo equations, the Toth equation displays much smaller relative errors in correlating the methane adsorption data and is more suitable for the adsorption equilibrium analysis on the adsorbed natural gas (ANG) system. MIL-101(Cr) exhibits the largest mean isosteric heat for methane adsorption and the density of the adsorbed phase of methane is smaller than that of the liquid methane but increases with the equilibrium pressure; overall, MIL-101(Cr) with the highest adsorption capacity is more suitable for methane adsorption than activated carbon and HKUST-1.

Prediction of Carbon Dioxide and Methane Adsorption on UiO-66 Metal–Organic Framework via Molecular Simulation

The adsorption equilibrium of methane (CH4) and carbon dioxide (CO2) on the metal–organic framework (MOF) UiO-66 is studied via molecular simulation. UiO-66 is a versatile MOF with vast potential for various adsorption processes, such as biogas upgrading, CO2 capture, and natural gas storage. The molecular simulations employ the grand canonical Monte Carlo (GCMC) method, covering a temperature range of 298–343 K and pressures up to 70 bar for CH4 and 30 bar for CO2. The accuracy of different forcefields in describing the adsorption equilibria is evaluated. Two modelling approaches are explored: (i) lumping each hydrogen atom in the MOF framework to the heavy atom it is bonded to (united atom approximation) and (ii) considering explicit hydrogen atoms. Additionally, the influence of electrical charges on CO2 adsorption is also evaluated. The findings indicate that the most effective forcefield to describe the adsorption equilibrium is a united atom forcefield based on the TraPPE parametrization. This approach also yields an accurate calculation of the isosteric heat of adsorption. In the case of CO2, it is observed that the use of electrical charges enhances the prediction of the heat of adsorption, especially in the low-coverage region.

Development of HKUST-1 composites for methane storage by adsorption through incorporation and carbonization

Measuresbeneficial to enhancing the hydro-stability of the HKUST-1 and improving its adsorptive performance for methane are crucial to the further application. In this research, incorporation of graphene oxide (GO) and carbonization were employed to achieve these objectives. Incorporation of the HKUST-1 was solvothermally prepared by mixing the GO with different mass ratios, and carbonization of the HKUST-1 sample was conducted at different temperatures. Structural characterization, structural morphology observation and adsorption equilibrium measurement of methane were then performed on the samples. Analysis of adsorption equilibrium of methane on the composite was finally carried out within temperature-pressure range respectively about 303.15 K–323.15 K and 0–3.6 MPa. It shows that the sample incorporated by 5 wt% GO has the largest increment about 11.7% and 13.3% in specific surface area and specific micropore volume, and the carbonization conducted at a temperature higher than 300 °C had negative effect on the structure stability of the sample. Results also reveal that the mean relative error between the experimental data and those predicted by Toth equation is about 0.54%. It suggests that the temperature for carbonizing should be carefully selected to avoid the collapse of the structure, and the balance measures should be taken to safeguard the benefit from incorporating.

Effect of Methane Adsorption on Mechanical Performance of Coal

Understanding the influence of methane adsorption on coal mechanical properties is an important prerequisite for preventing coal mining and gas mining disasters. In the present research, meager coal and gas coal samples were obtained from Huaneng Yunnan Diandong Energy Co., Ltd. The triaxial compression tests were carried out under different methane adsorption equilibrium pressures and confining pressures. The influence laws of different factors on the mechanical properties of coal were analyzed. The results show that the triaxial stress-strain curve of adsorbed methane coal has similar morphology with that of non-adsorbed coal. Under the same confining pressure, the stress-strain curve morphology of coal before and after adsorbing methane is basically the same but the compressive strength of coal after adsorbing methane decreases. The greater the adsorption equilibrium pressure of methane, the smaller the compressive strength of coal. The change in the mechanical properties (compressive strength and elastic modulus) of coal caused by methane adsorption can be described by the Langmuir curve and the correlation coefficient is more than 0.99. Under any stress environment, high-rank coal shows greater strength and lower elastic modulus than low-rank coal, which is mainly due to the existence of a developed cleat system in high-rank coal that provides more conditions for methane adsorption. The research results provide important data-based support for the prevention of coal and gas outbursts.

The effect of water vapor on methane adsorption in the nanopores of shale

Water plays an essential role in shale gas migration and adsorption, and most studies on the influence of water on shale gas adsorption refer only to moisture-equilibrated shales. To investigate the impact of water vapor on methane adsorption in shales, three experiments were conducted and compared: (1) pure methane adsorption onto dry shale (PMD), (2) pure methane adsorption onto moisture-equilibrated shale (PMMS), and (3) simultaneous adsorption of water vapor and methane (SAWM) onto shale. The experimental results reveal that the detrimental impact of water vapor on methane adsorption is inferior to that of preadsorbed water. Two mechanisms, water blocking and adsorption competition, are responsible for the reduction and difference in the methane adsorption capacity and adsorption rate between PMMS and SAWM. Compared to PMD, the methane adsorption capacity decreases by 81–96% in PMMS and by 20–49% in SAWM. Methane adsorption equilibrium is achieved the fastest in PMD. Before the equilibration degree reaches 95%, methane adsorption during SAWM progresses more rapidly, while the reverse occurs when the equilibration degree exceeds 95%. Water vapor can impact micropores more easily during the premoistening process, which obviously lowers methane adsorption. The adverse effect of water vapor on micro-to mesopores is inhibited by high methane partial pressure in SAWM. In PMMS, adsorbed water mainly occupies micropores (0.3–1.5 nm), and methane is adsorbed in pores larger than 1.5 nm. In SAWM, methane preferentially occupies micropores; the competition between methane and water vapor is mainly concentrated in mesopores (1.5–20 nm).

Experimental study on methane diffusion kinetics in three typical metamorphic coals

During coalbed methane (CBM) depletion, the diffusion property of methane is one of the key factors affecting the production of CBM recovery. In this work, the pore structure of three typical coals with different metamorphic degrees are tested by scanning electron microscopy and low field nuclear magnetic resonance. The high precision diffusion experiment system is developed to study the diffusion property of methane under different pore structure, gas adsorption pressure and coal sample size. The effects of tortuosity and pore length on methane diffusion is quantitatively analyzed, and the multistage clustering effect of coal particle microscopic composition is discussed. The results show that the pore structure leads to different diffusion resistance, which affects the initial diffusion rate of methane. Coals with high metamorphic degree correspond to complex pore structure and low diffusion rate of methane, while coals with low metamorphic degree correspond to simple pore structure and high diffusion rate of methane. With the increase of methane adsorption equilibrium pressure, the maximum diffusion ratio increases gradually, but the growth rate decreases gradually. The diffusion behavior of methane is closely related to the size of coal particles, and this change has an obvious size effect. As the particle size gradually increases, the effective diffusion coefficient of coal samples changes inversely, but when the coal particle reaches the critical size range, the change of diffusion coefficient begins to stop. The structure model of multistage clustering of coal particles is established and the causes of coal particle size effect are revealed. The research results can effectively guide the development of CBM, gas migration during CO2 enhanced coalbed methane and CO2 geological storage.

Experimental investigation of the functional mechanism of methane displacement by water in the coal

During hydraulic fracturing in a high-methane coal seam, there is a water-displacing-methane effect. A pseudo triaxle experimental system, which is opposite to the name of true triaxial system, for the water-displacing-methane effect was created. First, cylindrical coal samples in a methane adsorption equilibrium state, spontaneously desorbed. And then water was injected into the coal samples. The following was shown: (1) The displacement methane volume gradually rises with an increase of injected water, while the displacement methane rate tends to rise at first before declining later. Simultaneously, the water-displacing-methane process is characterised by a time effect. The methane displacement lags behind water injection. (2) Competitive adsorption and displacement desorption between the water and methane will promote adsorption methane into free methane, while the pore pressure increase caused by water injection will turn free methane into adsorption methane. The net free methane of the combination action provides a methane source for the water-displacing-methane effect. (3) A pore pressure gradient, which provides a power source for the water-displacing-methane effect, is formed and reduces gradually at the front of the water seepage along the seepage direction. The increase in water pressure can rapidly improve the pore pressure gradient and boost the displacement methane volume as well as improve displacement methane efficiency. (4) A starting porosity pressure gradient and limit pore pressure exist in the process of water-displacing-methane. When the pore pressure gradient is less than the starting pore pressure gradient, there is free methane in the coal rock, but it cannot be displaced. When the pore pressure is between the starting pore pressure and the limit pore pressure, the free methane can be displaced. When the pore pressure is greater than the limit pore pressure, the methane is almost completely adsorption methane, and water cannot be used to displace the free methane.

Comparing the permeability of dry and moisturized crushed shales determined by the dynamic process data of methane adsorption

Permeability is an important physical characteristic of shales. A lot of researches have been made by scholars to study permeability of shales, but the study of permeability for moisturized shales are insufficient. Water exist in natural shales, therefore, the difference of permeability for dry and moisturized shales and the reasons causing the difference need to be studied carefully. The permeability of dry and wet crushed carboniferous shale samples from the eastern Qaidam Basin, China were calculated by the dynamic process data of methane adsorption equilibrium. To obtain moisturized samples under different water saturation, a portion of the samples was moisturized at relative humidity (RH) values of 65%, 85% and 95%. In addition, the thickness of water in pores of the samples of different RH were calculated. The permeability was reduced by almost one order of magnitude after samples were wetted, and the relationship between permeability and water saturation (S) fit the exponential equation well. By calculating the porosity of dry and moisturized samples, the porosity reduction and connectivity loss accounted for the permeability reduction. Clay minerals and specific surface areas were considered to have a positive effect on permeability reduction. The permeability of moisturized samples were not declined with the water saturation as expectation. The permeability values for each moisturized sample under different RH only fluctuated in a small range. Correspondingly, the biggest water film thickness of moisturized samples under different RH was also almost the same. The difference of the water film thickness between RH = 65% and RH = 95% for each sample is only about 1.8 nm. The small difference in water film thickness under different RH is regarded as the reason for the low permeability difference of moisturized samples.

Experimental verification of the water-methane displacement effect in gassy coal

To verify that water-methane displacement effect in gassy coal exists objectively, a pseudo-triaxial experimental system of water-methane displacement was independently developed and tested. First, methane was injected into the standard cylindrical coal sample until the methane adsorption equilibrium state was reached. Then, the methane in the coal sample spontaneously desorbed. Finally, water was injected into the coal sample. It is shown that: 1) water-methane displacement effect exists objectively; 2) water-methane displacement effect includes the process of free methane generated by competitive adsorption and displacement desorption effect, the consumption caused by methane pressure increase, and water driving methane; 3) competitive adsorption and displacement desorption between methane and water can generate free methane. Due to water injection, the increase of methane pressure leads to consumption of free methane. The net free methane of the combined action provides methane source for the water-methane displacement effect. [Received: August 19, 2017; Accepted: February 2, 2018]

Experimental verification of the water-methane displacement effect in gassy coal

To verify that water-methane displacement effect in gassy coal exists objectively, a pseudo-triaxial experimental system of water-methane displacement was independently developed and tested. First, methane was injected into the standard cylindrical coal sample until the methane adsorption equilibrium state was reached. Then, the methane in the coal sample spontaneously desorbed. Finally, water was injected into the coal sample. It is shown that: 1) water-methane displacement effect exists objectively; 2) water-methane displacement effect includes the process of free methane generated by competitive adsorption and displacement desorption effect, the consumption caused by methane pressure increase, and water driving methane; 3) competitive adsorption and displacement desorption between methane and water can generate free methane. Due to water injection, the increase of methane pressure leads to consumption of free methane. The net free methane of the combined action provides methane source for the water-methane displacement effect. [Received: August 19, 2017; Accepted: February 2, 2018]

A method to determine the permeability of shales by using the dynamic process data of methane adsorption

Permeability is a critical parameter to evaluate the gas migration and development of shales, however, very difficult to get at the laboratory. Methane adsorption in shales is also an important factor of shales in natural state. A method of permeability that considers methane adsorption is described in this study. Permeability is derived from the dynamic data of the methane adsorption equilibrium process. The carboniferous shale samples, C01, C02, C03 and C04, were extracted from the eastern Qaidam Basin in China. The properties of the shales including organic/inorganic matter contents and pore size distribution were obtained by several techniques. Methane adsorption experiments were conducted on crushed shale samples over a pressure range up to 10 MPa and at a temperature of 313.15 K. Additionally, the permeability was calculated using the dynamic data at the adsorption equilibrium. Correlations between the permeability and methane adsorption and sample properties were discussed. The parameters of the calculation process were also analyzed.A parameter called the methane adsorption rate is defined as θ, which represents the variation in methane adsorption amount with pressure. The permeability is found to have the same variation trend with θ at experimental pressures before the inflection point. The pressure relative to the inflection point decreases with the micropore volume percentage, and the permeability increases with the methane adsorption affinity for the sample, nmax. We found that the permeability before the inflection point is considered to represent the micropores permeation property. The methane adsorption rate decreases to an infinitesimal value until the adsorption reaches a saturated state. The permeability values are assumed will stop fluctuating and become a fixed value, which we call kf. The parameter kf is regarded as the true permeability of the sample. The assumption gives a novel idea of permeability calculation. In addition, the permeability of the samples increases with the macropore volume, and the methane adsorption capacity nmax also increases with the total porosity.

Adsorption equilibrium of methane and carbon dioxide on zeolite 13X: Experimental and thermodynamic modeling

A static, volumetric method has been used to determine the adsorption equilibrium of CH4 and CO2 and their binary mixtures on 13X molecular sieves at various temperatures between 273 and 343K. Pressures for the pure component data extend up to 10bar, while all binary data were obtained at 4bar and 6bar. The measured pure isotherms were regressed using different isotherm equations and the regressed parameters were applied to different thermodynamic models such as ideal adsorbed solution theory (IAST), vacancy solution theory (VST) and real adsorbed solution theory (RAST). CH4/CO2 system that deviate from ideality is not well represented by IAST and VST, whereas RAST which include activity coefficient in the adsorbed phase as characterizing parameter for non-ideality, show a much better representation of the binary equilibria. Experimental selectivities CO2/CH4 range from 26 to 2 at different pressure and temperatures. It is concluded that zeolite 13X suitable for natural gas industrial separation with yCO2<0.2 at 303K and 4bar. For landfill gas upgrading, where yCO2<0.45, zeolite 13X can be successfully applied at 303K, 4bar and 303K, 6bar and 323K, 4bar.

Development of composite adsorbents and storage vessels for domestically used adsorbed natural gas

Experiments were designed to develop an adsorbed natural gas (ANG) technique suitable for household environment. The composite adsorbent was synthesized based on four key factors in terms of the maximization of thermal conductivity. The Toth equation was used to analyze adsorption equilibrium of methane on the composite. Charge/discharge cycles of methane on a cylindrical tank and a conformable tank were assessed for evaluation of the structure of tank and the partition plates, the composition of adsorbent, and the dynamic behaviors of storage system. The results show that the maximum thermal conductivity of the composite occurs where the composite adsorbent was consisted of the equal amount of activated carbon and expanded graphite (ENG), heated at the temperature of 600 °C for the duration of 30 seconds, and consolidated under pressure 9 MPa. It also indicates that thermal effect on the conformable tank is much weaker in comparison to that of cylindrical tank. As a consequence, in the case where the composite adsorbent is used, the insertion of partition plates into a conformable ANG vessel does not significantly improve heat conductivity. It suggests that the use of the composite adsorbent in a conformable tank provides a promising method to store natural gas for domestic purposes.

Enhancing Sustainable Recycle Solid Waste to Porous Activated Carbon for Methane Uptake

Potential agro wastes (i.e palm kernel shell and coconut shell) for producing low cost activated carbon (AC) was investigated. In this study, the activated carbon was produced by carbonization, chemical impregnation with KOH and microwave irradiation. The pyrolysis was carried out at 700 °C in an inert environment for 2 h. Microwave activation was carried out at 400W for 6 minutes. Characteristics of the material were investigated using Fourier transform infrared spectroscopy (FT-IR) analysis and scanning electrode microscopy (SEM). Methane adsorption equilibrium data on the activated carbons produced were obtained using static volumetric method. Microwave palm shell activated carbon (MPAC) and microwave coconut shell activated carbon (MCAC) recorded highest methane uptake of 2.489 and 1.929 mmol/g at 3 bar, 30°C. The adsorption data were correlated with Langmuir and Freundlich isotherms. The results shows that microwave activated carbon from palm shell and coconut shell have good methane adsorption characteristics.

Synthesis of Zinc-Organic Frameworks Nano Adsorbent and their Application for Methane Adsorption

In the present work, MOF-5 consisting of Zn4O inorganic vertices was hydrothermally synthesized. Three-step activation treatment including preservation in initial solvent, solvent exchange and drying under evacuated condition was performed and it was found that activation is efficient by increasing the methane adsorption capacity of samples. The final product was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and pore size distribution (PSD). The corresponding pore size of MOF-5/DEF (sample A) and MOF-5/DMF (sample B) which was determined by nitrogen adsorption at 77 K, were equal to 31.27 A and 42.65 A‡Âo and also BET surface area of samples were 2157 and 1532 m2/g, respectively. Methane adsorption equilibrium for both samples was measured in a volumetric adsorption unit and it was found that the adsorbent (A) and (B) in this work have methane adsorption capacity of 18.15 and 11.36 mmol/g at temperature of 298 K and pressure of 36 bar, respectively. Four different models (Langmuir, Unilan, Toth and Sips) were used to correlate the experimental equilibrium data. The root mean square error values demonstrated that the Toth and Sips equation provide better models for correlating adsorption isotherms.

Adsorption equilibrium of methane and carbon dioxide on microwave-activated carbon

The adsorption of methane and carbon dioxide on two microwave-activated carbon samples at different temperatures from 298K to 323K, and the thermodynamics of adsorption have been investigated using a vacuum adsorption apparatus. Henry’s law constant and adsorption equilibrium selectivity of CO2 and CH4 on the two samples were calculated via Virial equation. The results showed that the activated carbon modified by potassium carbonate sample has the higher equilibrium selectivity for CO2 over CH4. The adsorption equilibrium data of CO2 and CH4 at various temperatures were fitted to Langmuir and Langmuir–Freundlich isotherm models. It was found the Langmuir model was better for fitting the adsorption of CH4 than CO2 and the Langmuir–Freundlich model was more suitable for description of the two gases adsorption process than Langmuir model through calculating average absolute relative error. The fitted results showed that the adsorption of CH4 was monolayer and CO2 was multilayer adsorption on the surface of two adsorbents. The isosteric enthalpies of adsorption for both adsorbates on microwave-activated carbon (MAC) and microwave-activated carbon modified with potassium carbonate (K2CO3/MAC) were calculated using the Clausius–Clapeyron equations. The isosteric heat of adsorption decreased with an increase of the surface loading on adsorbents, which means that both of MAC and K2CO3/MAC had an energetically heterogeneous surface.

Unusual Adsorption Site Behavior in PCN-14 Metal–Organic Framework Predicted from Monte Carlo Simulation

The adsorption equilibrium of methane in PCN-14 was simulated by the Monte Carlo technique in the grand canonical ensemble. A new force field was proposed for the methane/PCN-14 system, and the temperature dependence of the molecular siting was investigated. A detailed study of the statistics of the center of mass and potential energy showed a surprising site behavior with no energy barriers between weak and strong sites, allowing open metal sites to guide methane molecules to other neighboring sites. Moreover, this study showed that a model assuming weakly adsorbing open metal clusters in PCN-14, densely populated only at low temperatures (below 150 K), can explain published experimental data. These results also explain previously observed discrepancies between neutron diffraction experiments and Monte Carlo simulations.

Performance of CaX Zeolite for Separation of C2H6, C2H4, and CH4 by Adsorption Process; Capacity, Selectivity, and Dynamic Adsorption Measurements

Adsorption-based process for removal of ethane and ethylene, as the main products of oxidative coupling methane reaction from unreacted methane is discussed. The adsorption equilibrium of methane, ethane, and ethylene was determined experimentally on CaX, the calcium cation exchanged NaX zeolite, by the volumetric measurements in a high pressure setup at three different temperatures. The adsorption isotherms were well modeled by the extended Langmuir-Freundlich isotherm and the adsorbed capacity, adsorption constants, and surface heterogeneity parameter were determined by regression of the model to the isothermal experiments. The results indicated that CaX zeolite would be a selective adsorbent for the separation of ethane, ethylene, and methane from each other at moderate temperatures and pressures. The breakthrough curves of gases were determined in a dynamic adsorption experiment of the gaseous mixture in a fixed bed of CaX zeolites for a feed with similar molar composition of OCM hydrocarbon product. Significant difference of breakthrough times was observed for methane, ethane, and ethylene. It is concluded that construction of an adsorption unit from CaX zeolites at the OCM reactor downstream would be economic and useful for the separation of methane from the C2 products.

Effects of SO2 and pH Concentration on CO2 Adsorption Capacity in Coal Seams for CO2 Sequestration With Considerations for Flue Gas From Coal-Fired Power Plants

Abstract Coal-fired power plants produce flue gas consisting mainly of nitrogen (around 79%), followed by CO2 (around 10 - 15%), and small amounts of other gases such as H2, NOx and SO2. One of the promising methods for reducing CO2 emission is CO2 sequestration into deep, unminable coal seams. At present, flue gases exhausted from coal-fired plant must be separated to extract pure CO2 before injecting it into coal seams. In order to enhance the efficiency of carbon capture and storage (CCS) from a coal-fired power plant, oxy-fuel combustion technology has been employed. This technology uses pure oxygen to burn the coal, and consequently CO2 concentration in the flue gas is theoretically increased up to 95%. This study aims to simulate the CH4 replacement mechanism in coal by using pure CO2 and a synthesized flue gas (99% CO2 and 1% SO2) that is similar to the emission gas from the coal-fired power plants. A measurement procedure for gas adsorption is employed which, after establishing methane adsorption equilibrium of the coal samples, injects pure CO2 or the synthesized flue gas into an adsorption cell in order to investigate CH4 replacement properties. Coal samples used for the present experiments were taken from the coal seams of Vietnam, Japan, Australia, China and Indonesia. The samples were crushed to particle sizes ranging from 250 µm to 5 mm. The concentration of gases was taken from the adsorption cell and analyzed by using a gas chromatograph. Adsorption isotherms of CH4, CO2 and SO2 were measured by using the volumetric method apparatus. This paper discusses the characteristics of methane replacement by using pure CO2, the synthesized flue gas and the effect of SO2 on adsorption properties of coal. Introduction Global warming and climate change due to the greenhouse effect continue to be a serious problem. In particular, CO2 emission into the atmosphere from coal-fired power plants needs to be reduced. One of the most promising methods of reducing CO2 emissions is CO2 sequestration in deep, unminable coal seams. The CO2 adsorption capacities of coals were investigated by Huy et al.(1). The results showed that CO2 adsorption was double that of CH4.

Charge and discharge of methane on phenol-based carbon monolith

Methane adsorptions on various synthesized and commercial activated carbons were assessed in a volumetric apparatus for the design of an efficient adsorbed natural gas storage system. Based on the methane adsorption equilibrium results from different carbon based materials, a monolith was also produced from RP-20. Dynamic studies were also performed for the prepared monolith and the pelletized commercial Norit-B4 activated carbon. The temperature variation in RP-20 monolith was analyzed and compared with those of Norit-B4 and a blank test, which consisted of a run without a sample. The temperature variation in RP-20 monolith was quite high compared to that observed with Norit-B4 and the blank test because of a higher isosteric heat of adsorption and a high packing density.