CH4 Adsorption Research Articles

Effect of binder on CO2, CH4, and N2 adsorption behavior, structural properties, and diffusion coefficients on extruded zeolite 13X

The effect of inorganic binder-based extrusion (Silica sol, Bentonite, Attapulgite, and SB1) in the selective adsorption of CO2, CH4, and N2 on zeolite 13X in the context of flue gas carbon capture and natural gas purification has been studied to reduce CO2 emissions. The effect of extrusion with binders was examined by adding 20 wt% of the mentioned binders to pristine zeolite and the results were analyzed by four approaches; (i) the effect on structural properties was analyzed by XRD patterns followed by Williamson–Hall (W–H) plot, FESEM images, and BET surface area. In addition, the mechanical strength of the shaped zeolites was measured by crush resistance testing; (ii) the effect on the adsorption capacity for CO2, CH4, and N2 were measured by volumetric apparatus up to 100 kPa; (iii) the impact on binary separation (CO2/CH4 and CO2/N2) were investigated; (iv) the influence on diffusion coefficients were estimated by micropore and macropore kinetic model. The results showed that the presence of a binder can cause reductions in BET surface area and pore volume, indicating partial pore blockage. It was found that the Sips model had the best adaptability to the experimental isotherms data. The trend of CO2 adsorption was 13X > pseudo-boehmite > bentonite > attapulgite > silica, in which the adsorption capacity reached 6.02, 5.60, 5.24, 5.00, and 4.71 mmol/g, respectively. Among all samples, silica was found the most suitable binder for CO2 capture in terms of selectivity, mechanical stability, and diffusion coefficients.

Quantum mechanical analysis of adsorption for CH4 and CO2 onto graphene oxides

Graphene oxide (GO) surfaces with rich and diverse oxygen-containing functional groups might endow GOs with unique chemical adsorption activity. Exploring the adsorption behavior of gas molecules on GOs with different degrees of oxidation can help design highly efficient adsorbents and catalysts. Herein, the interaction energies between two kinds of gas molecules, CH4 and CO2, and the GO surfaces with varied oxidization degrees were simulated by density functional theory. It is numerically demonstrated that CO2 has a stronger interaction strength than CH4. More specifically, the interaction energies for the gases on GO surfaces do not show monotonous variation with the degree of oxidization. The results suggest that there exists an appropriate range of oxidized degrees on GOs, which can impose higher adsorption interaction. The AIM (atom in molecule) and NOCV (natural orbital for chemical valence) analyses were applied to reveal the interaction mechanisms between the gas molecules and GO surfaces. The adsorption free energy and adsorption coverage of CH4 and CO2 on GO surfaces were calculated. Generally, the gas adsorption on GO is thermodynamically unfavorable under standard conditions. The computational results provide an improved understanding of the adsorption mechanism, which might be valuable for the application of high-performance GO-based adsorbents and catalysts.

Tuning the Trade-Off between Ethane/Ethylene Selectivity and Adsorption Capacity within Isoreticular Microporous Metal-Organic Frameworks by Linker Fine-Fluorination.

The pore dimension and surface property directly dictate the transport of guests, endowing diverse gas selective adsorptions to porous materials. It is highly relevant to construct metal-organic frameworks (MOFs) with designable functional groups that can achieve feasible pore regulation to improve their separation performances. However, the role of functionalization in different positions or degrees within framework on the separation of light hydrocarbon has rarely been emphasized. In this context, four isoreticular MOFs (TKL-104-107) bearing dissimilar fluorination are rationally screened out and afforded intriguing differences in the adsorption behavior of C2 H6 and C2 H4 . Ortho-fluoridation of carboxyl allows TKL-105-107 to exhibit enhanced structural stabilities, impressive C2 H6 adsorption capacities (>125 cm3 g-1 ) and desirable inverse selectivities (C2 H6 over C2 H4 ). The more modified ortho-fluorine group and meta-fluorine group of carboxyl have improved the C2 H6 /C2 H4 selectivity and adsorption capacity, respectively, and the C2 H6 /C2 H4 separation potential can be well optimized via linker fine-fluorination. Meanwhile, dynamic breakthrough experiments proved that TKL-105-107 can be used as highly efficient C2 H6 -selective adsorbents for C2 H4 purification. This work highlights that the purposeful functionalization of pore surfaces facilitates the assembly of highly efficient MOF adsorbents for specific gas separation.

Time-Resolved MIR Reflection–Absorption Spectroscopy of N2O, CO, and CH4 Adsorption on Graphene

The time- and temperature-dependent adsorption of N2O, CO, and CH4 on CVD-grown graphene has been investigated by MIR reflection–absorption spectroscopy to gain information about the adsorption kinetics, notably the rate constants k and activation energies Ea of the adsorption step. The gas adsorption is followed by determining the change of the reflected beam intensity with time by taking difference spectra, i.e., subtracting the baseline signal (reflectivity of graphene at the respective gas excitation line) from the measurement with added gas. The experiments yield adsorption activation energies Ea of −19.6 ± 1.1 (N2O), −12.1 ± 0.2 (CO), and −9.5 ± 1.7 kJ/mol (CH4). The obtained Ea values are in excellent agreement with the literature results from theory, thereby confirming these studies. The Ea values indicate physisorption, i.e., no strong bonding of the gas molecules to graphene. The analyzed adsorption rate constants k are reported for the first time and are on the order of 1011 to 1012 molecules·s–1·cm–2 with N2O showing the highest value and CH4 the lowest value. The adsorption rate constants follow the series N2O > CO > CH4, in line with the charge transfer abilities of the molecules. This work can be easily extended to kinetic studies of other gases hazardous to the environment and adsorption studies with other 2D materials using versatile MIR reflection–absorption spectroscopy.

EXPERIMENTAL STUDY ON PRESSURIZED ADSORPTION OF CARBON DIOXIDE AND METHANE FROM COMPLEX GAS MIXTURE OF BIOGAS IN ZEOLITE 13X

The majority of research on biogas adsorption does not use biogas gas but by mixing CO2 and CH4 gas or (binary gas) or with additional other gases, such as N2 or H2S. In real application, the adsorption method of biogas purification is conducted by using its complex mixture of biogas to obtain the purer methane gas. Accordingly, in case of biogas purification, adsorption capacity of the adsorbent towards both CH4 and CO2 gases from a complex gas mixture of biogas is indispensable to be studied thoroughly for improving the existing purification method, such as the pressure swing adsorption (PSA) method. The objective of this experiment is to compare the adsorption of carbon-dioxide and methane from complex mixture of biogas by Zeolite 13X under pressurized condition using experimental data. The experiment was conducted using a specially designed experimental setup, and the data obtained was evaluated and analyzed using the Freundlich Isotherm Model. The results show that experimental study on the adsorption of CO2 and CH4 gas from complex mixture of biogas in Zeolite 13X was distinguishable by their values of Freundlich coefficient. CO2 and CH4 gas adsorption in zeolite vary directly with pressure raised to the power 1/n, where its value for CH4 adsorption was higher than CO2. However, within the range of applicable pressure, the equilibrium adsorption of CO2 in Zeolite 13X was still higher than that of CH4.

Design of Olefin-Phobic Zeolites for Efficient Ethane and Ethylene Separation

Selective adsorption of ethane from a mixture of ethane (C2H6) and ethylene (C2H4) has emerged as an energy-efficient process for obtaining high-purity ethylene. Recently, it has been reported that some novel microporous organometallic and organic adsorbents can preferentially adsorb C2H6 over C2H4. Conversely, zeolite adsorbents, which are widely used in industry due to their high stability and low material cost, generally prefer C2H4 adsorption (“olefin-philic”). In this study, we carefully investigated the effects of chemical composition (Si/Al ratio), silanol defect, and pore topology (BEA, CHA, and MFI) of zeolites to develop efficient “olefin-phobic” adsorbents. The results showed that the Si–O–(Na+)–Al (weak Lewis acid) and isolated Si–OH (weak Brønsted acid) groups in the zeolite frameworks undesirably increased the affinity for C2H4 (Lewis base). Consequently, defect-free pure silica zeolites exhibited promising C2H6/C2H4 selectivities (1.98–2.25), which were superior to those of Al-containing zeolites (0.26) and pure silica zeolites with abundant silanols (1.50), at 298 K and 1 bar. In particular, defect-free pure silica BEA exhibited the highest C2H6/C2H4 selectivity (2.25), large C2H6 uptake (2.27 mmol g–1), and facile regeneration at 298 K. The adsorbent enabled the efficient separation of high-purity C2H4 (>99.95%) from a mixture of C2H6/C2H4 with high productivity (22.98 L L–1). The productivity was comparable or even superior to that of recently reported C2H6-selective adsorbents. The present results provide hope for the development of efficient, stable, and scalable inorganic adsorbents for the selective C2H6 adsorption.

High Efficient CO2 Separation at High Pressure by Grain-Boundary-Controlled CHA Zeolite Membrane Investigated by Non-Equilibrium Molecular Dynamics

The CO2 permeability and selectivity of CHA-type zeolite membranes in the separation of a CO2/CH4 mixture gas at high pressure were evaluated using non-equilibrium molecular dynamics (NEMD). It was found that in a perfectly crystalline, defect-free CHA membrane, the adsorption of CH4, which diffuses slowly in the pores, hinders CO2 permeation. Therefore, an increase in the amount of CH4 adsorbed at high pressure decreases the CO2 permeability and significantly reduces the CO2 selectivity of the CHA membrane. CHA membranes with grain boundaries parallel to the permeation direction were found to show higher CO2 selectivity than perfectly crystalline CHA membranes at high pressure, as the blocking effect of CH4 on CO2 permeation occurring within the grain boundary is not significant. This paper is the first to show that the CO2 permeability of CHA membranes with controlled grain boundaries can exceed the intrinsic performance of fully crystalline zeolite membranes at high pressure.

Contributions of CH4-amine interactions by primary, secondary, and tertiary amines on CO2/CH4 separation efficiency

In designing amine-incorporated adsorbents for CO2/CH4 separation, it is essential to understand the individual effects amine moieties have on the separation of CO2/CH4 mixtures. In this work, primary, secondary, and tertiary amines are moderately grafted on SBA-15 to examine factors affecting adsorption of CO2 and CH4. Materials were characterised by thermogravimetric and elemental analysis, and their performance was measured by volumetric and gravimetric gas adsorption. An amine density of 1.6–1.7 mmol/g in secondary and tertiary amines showed an equivalent CH4 uptake of <0.04 mmol/g at 25 °C, while primary amines adsorbed 0.05 mmol/g, indicating stronger interaction forces with CH4. In terms of selectivity, primary and secondary amines grafted at 1.3–1.4 mmol/g had similar values, unaffected by amine type. Adsorption results cross analysed with DFT simulations indicate similar binding energies for CH4 by both amine moieties, concluding the facilitated access of gas molecules to primary amine moieties is the primary factor dictating degree of adsorption. At an amine density of ∼ 1.7 mmol/g for both primary and secondary amines, an increase in temperature from 25 to 40 °C at a CO2 partial pressure of 40 kPa showed a decrease in CO2/CH4 selectivity of only primary amines. Secondary amines are thus more selective amine moieties at these conditions. Furthermore, in isothermal adsorption–desorption conditions, moderately grafted secondary amines have an equal working capacity to primary amines. Both these qualities support secondary amines at moderate densities as candidates for adsorbent development in CO2/CH4 separations.

A Series of Metal–Organic Frameworks with 2,2′-Bipyridyl Derivatives: Synthesis vs. Structure Relationships, Adsorption, and Magnetic Studies

Five new metal-organic frameworks based on Mn(II) and 2,2'-bithiophen-5,5'-dicarboxylate (btdc2-) with various chelating N-donor ligands (2,2'-bipyridyl = bpy; 5,5'-dimethyl-2,2'-bipyridyl = 5,5'-dmbpy; 4,4'-dimethyl-2,2'-bipyridyl = 4,4'-dmbpy) [Mn3(btdc)3(bpy)2]·4DMF, 1; [Mn3(btdc)3(5,5'-dmbpy)2]·5DMF, 2; [Mn(btdc)(4,4;-dmbpy)], 3; [Mn2(btdc)2(bpy)(dmf)]·0.5DMF, 4; [Mn2(btdc)2(5,5'-dmbpy)(dmf)]·DMF, 5 (dmf, DMF = N,N-dimethylformamide) have been synthesized, and their crystal structure has been established using single-crystal X-ray diffraction analysis (XRD). The chemical and phase purities of Compounds 1-3 have been confirmed via powder X-ray diffraction, thermogravimetric, and chemical analyses as well as IR spectroscopy. The influence of the bulkiness of the chelating N-donor ligand on the dimensionality and structure of the coordination polymer has been analyzed, and the decrease in the framework dimensionality, as well as the secondary building unit's nuclearity and connectivity, has been observed for bulkier ligands. For three-dimensional (3D) coordination polymer 1, the textural and gas adsorption properties have been studied, revealing noticeable ideal adsorbed solution theory (IAST) CO2/N2 and CO2/CO selectivity factors (31.0 at 273 K and 19.1 at 298 K and 25.7 at 273 K and 17.0 at 298 K, respectively, for the equimolar composition and the total pressure of 1 bar). Moreover, significant adsorption selectivity for binary C2-C1 hydrocarbons mixtures (33.4 and 24.9 for C2H6/CH4, 24.8 and 17.7 for C2H4/CH4, 29.3 and 19.1 for C2H2/CH4 at 273 K and 298 K, respectively, for the equimolar composition and the total pressure of 1 bar) has been observed, making it possible to separate on 1 natural, shale, and associated petroleum gas into valuable individual components. The ability of Compound 1 to separate benzene and cyclohexane in a vapor phase has also been analyzed based on the adsorption isotherms of individual components measured at 298 K. The preferable adsorption of C6H6 over C6H12 by 1 at high vapor pressures (VB/VCH = 1.36) can be explained by the existence of multiple van der Waals interactions between guest benzene molecules and the metal-organic host revealed by the XRD analysis of 1 immersed in pure benzene for several days (1≅2C6H6). Interestingly, at low vapor pressures, an inversed behavior of 1 with preferable adsorption of C6H12 over C6H6 (KCH/KB = 6.33) was observed; this is a very rare phenomenon. Moreover, magnetic properties (the temperature-dependent molar magnetic susceptibility, χp(T) and effective magnetic moments, μeff(T), as well as the field-dependent magnetization, M(H)) have been studied for Compounds 1-3, revealing paramagnetic behavior consistent with their crystal structure.

Enhanced performance of Pd-[DBU][Cl]/AC mercury-free catalysts in acetylene hydrochlorination

Compared with the rapid deactivation of the Pd/AC catalyst, an eco-friendly Pd-[DBU][Cl]/AC ([DBU][Cl], 1,8-diazabicyclo[5.4.0]undec-7-ene hydrochloride) catalyst with enhanced stability was synthesized and applied in the hydrochlorination of acetylene. The Pd-20[DBU][Cl]/AC catalyst exhibits 96.7% acetylene conversion and 98.9% selectivity of vinyl chloride within the 24 h evaluation under the conditions of T = 180 °C, GHSV(C2H2) = 360 h–1 and V(HCl)/V(C2H2) = 1.2. The enhanced stability of the Pd-[DBU][Cl]/AC catalyst is attributed to the prevention of the reduction of Pd(II) to Pd(0), the inhibition of the formation of coke deposition on the catalyst surface, and the reduction of the loss of Pd species during the reaction. TPD characterization and DFT theoretical simulations confirmed that the PdCl2-[DBU][Cl] complex has stronger adsorption of HCl and weaker adsorption of C2H2 and C2H3Cl compared to PdCl2. Furthermore, the catalytic mechanism of acetylene hydrochlorination over the PdCl2 and PdCl2-[DBU][Cl] site was put forward based on theoretical simulations. The good activity and stability of Pd-20[DBU][Cl]/AC in the 60 h lifetime test indicates that it is likely to be a promising alternative to HgCl2 catalysts.

Selective Photocatalytic Conversion of Methane Induced by Lewis Acid–Base Pair on the Surface of In2O3/TiO2 Heterojunction Photocatalyst

The efficient catalytic conversion of light-driven methane (CH4) is still very challenging. Here, the surface-reconstructed In2O3/TiO2 heterojunction photocatalyst is successfully prepared by a two-step operation of ion exchange and calcination, and the efficient selective photocatalytic conversion of CH4 is achieved. In the absence of O2, the formation rates of ethane (C2H6) and hydrogen (H2) are 68.9 and 78.6 μmol h–1 g–1, respectively, which corresponds to the stoichiometric ratio. However, in the presence of O2 or water (H2O) as the oxidant, CH4 is converted to CO, and the CO formation rates are 113.2 and 94.4 μmol h–1 g–1, respectively. Our results show that the In3–O2– Lewis acid–base pair on the In2O3/TiO2 surface can realize the adsorption and activation of CH4. Moreover, the photogenerated hole-induced reactive oxygen centers (Ti4+O·–Ti4+OH– and Ti4+O2–Ti4+O·–) on the surface of In2O3/TiO2 are identified as the active species for inducing the dissociation of CH4 into ·CH3 radicals, which in turn are coupled into C2H6 by ·CH3. In contrast, in the presence of O2, the surface superoxide anion (O2–), surface ·O– radicals, and O22– anions are identified as the active species for inducing the oxidation of CH4 into CO.

Thermodynamic characteristics of methane adsorption on coals from China with selected metamorphism degrees: Considering the influence of temperature, moisture content, and in situ modification

A better understanding of the thermodynamic characteristics of methane (CH4) adsorption on coal surfaces is needed for the high-efficiency coalbed methane (CBM) preextraction or prevention of coal and gas outbursts. In this study, atomistic representations of selected coal samples with different degrees of metamorphism, such as long flame coal, coking coal, and anthracite coal obtained from China were created; CH4 adsorption isotherms considering the temperature, moisture content, and microwave in situ modification for CBM preextraction were simulated and analysed. The coal molecular structural results showed that as the degree of coal metamorphism increased from long flame coal to coking coal and anthracite coal, the functional groups in the molecular structure of the coal reduced, while the degree of graphite increased. In situ modification of coal facilitated this process. The saturation adsorption capacity of CH4 decreased and then increased with increasing coal metamorphism degree and decreased linearly with increasing temperature. When water molecules were present, the adsorbed CH4 showed different degrees of decreasing trends with increasing moisture content. The isosteric heat of CH4 adsorption followed the order of coking coal > anthracite coal > long flame coal. The isosteric heat gradually decreased with increasing methane adsorption, and the presence of water molecules had a limited effect on the isosteric heat. In situ modification disrupted the self-conjugated hydrogen bonds, reduced the oxygen-containing functional groups, and decomposed some associated minerals in the coal samples. After in situ modification, the amount of methane adsorption decreased due to a greater contribution from the functional group change than that from the pore volume change, and the modification effect was more evident for the low-rank coal samples than for the middle and high metamorphism degree coal samples. In situ modification applied in the coal seams could contributed to designs for CBM exploration, and the results of this experiment and simulation could provide a novel theoretical basis for in situ modification technology.

Thermal-Hydraulic-Mechanical Coupling Simulation of CO2 Enhanced Coalbed Methane Recovery with Regards to Low-Rank but Relatively Shallow Coal Seams

CO2 injection technology into coal seams to enhance CH4 recovery (CO2-ECBM), therefore presenting the dual benefit of greenhouse gas emission reduction and clean fossil energy development. In order to gaze into the features of CO2 injection’s influence on reservoir pressure and permeability, the Thermal-Hydraulic-Mechanical coupling mechanism of CO2 injection into the coal seam is considered for investigation. The competitive adsorption, diffusion, and seepage flowing of CO2 and CH4 as well as the dynamic evolution of fracture porosity of coal seams are considered. Fluid physical parameters are obtained by the fitting equation using MATLAB to call EOS software Refprop. Based on the Canadian CO2-ECBM project CSEMP, the numerical simulation targeting shallow low-rank coal is carried out, and the finite element method is used in the software COMSOL Multiphysics. Firstly, the direct recovery (CBM) and CO2-ECBM are compared, and it is confirmed that the injection of CO2 has a significant improvement effect on methane production. Secondly, the influence of injection pressure and temperature is discussed. Increasing the injection pressure can increase the pressure difference in the reservoir in a short time, so as to improve the CH4 production and CO2 storage. However, the increase in gas injection pressure will also lead to the rapid attenuation of near-well reservoir permeability, resulting in the weakening of injection capacity. Also, when the injection temperature increases, the CO2 concentration is relatively reduced, and the replacement effect on CH4 is weakened, resulting in a slight decrease in CBM production and CO2 storage.

Influence of ligands within Al-based metal-organic frameworks for selective separation of methane from unconventional natural gas

Efficient CH4/N2 separation from unconventional natural gas is vital for both energy recycling and climate change control. Figuring out the reason for the disparity between ligands in the framework and CH4 is the crucial problem for developing adsorbents in PSA progress. In this study, a series of eco-friendly Al-based MOFs, including Al-CDC, Al-BDC, CAU-10, and MIL-160, were synthesized to investigate the influence of ligands on CH4 separation through experimental and theoretical analyses. The hydrothermal stability and water affinity of synthetic MOFs were explored through experimental characterization. The active adsorption sites and adsorption mechanisms were investigated via quantum calculation. The results manifested that the interactions between CH4 and MOFs materials were affected by the synergetic effects of pore structure and ligand polarities, and the disparities of ligands within MOFs determined the separation efficiency of CH4. Especially, the CH4 separation performance of Al-CDC with high sorbent selection (68.56), moderate isosteric adsorption heat for CH4 (26.3 kJ/mol), and low water affinity (0.1 g/g at 40% RH) was superior to most porous adsorbents, which was attributed to its nanosheet structure, proper polarity, reduced local steric hindrance, and extra functional groups. The analysis of active adsorption sites indicated that hydrophilic carboxyl groups and hydrophobic aromatic ring were the dominant CH4 adsorption sites for liner ligands and bent ligands, respectively. The methylene groups with saturated C–H bonds enhanced the wdV interaction between ligands and CH4, resulting in the highest binding energy of CH4 for Al-CDC. The results provided valuable guidance for the design and optimization of high-performance adsorbents for CH4 separation from unconventional natural gas.

Efficient adsorption of carbon dioxide and methane on activated carbon prepared from glycerol with potassium acetate

In the context of global warming and the energy crisis, emissions to the atmosphere of greenhouse gases such as carbon dioxide (CO2) and methane (CH4) should be reduced, and biomethane from landfill biogas should be recycled. For this, there is a need for affordable technologies to capture carbon dioxide, such as adsorption of biogas on activated carbon produced from industrial wastes. Here we converted glycerol, a largely available by-product from biodiesel production, into activated carbon with the first use of potassium acetate as an activating agent. We studied adsorption of CO2 and CH4 on activated carbon. The results show that activated carbon adsorb CO2 up to 20% activated carbon weight at 250 kPa, and 9% at atmospheric pressure. This is explained by high specific surface areas up to 1115 m2g−1. Moreover, selectivity values up to 10.6 are observed for the separation of CO2/CH4. We also found that the equivalent CO2 emissions from activated carbon synthesis are easily neutralized by their use, even in a small biogas production unit.

A comparative ab initio study of acetylene activation over Au9 cluster and Au9 supported over ZnO monolayer

A plane wave density functional theory has been employed to investigate acetylene activation over Au9 cluster and the same supported over single layer ZnO. Adsorption of C2H2 over gold clusters adopts the π mode and σ mode. The σ mode of adsorption is preferable as two C atoms bind to least coordinated Au atoms in Aun cluster. Adsorption energy of C2H2 over Au9 is increases from 0.47 eV to 0.87 eV when Au9 is supported on the ZnO single layer.Significantly lower activation energy barrier for acetylene activation (0.08 eV) has been found for Au9/ZnO in comparison to the same over Au9 cluster (2.14 eV). The lowering in the activation energy barrier is attributable to the reduction of Au9: The underlying ZnO monolayer transfers electronic charge to Au9 and thereby reduces it. It is supported by upshift in the Fermi level of the ZnO single layer by 0.47 eV towards higher energies upon hosting Au9. These results provide useful pointers in optimizing the catalytic processes via an appropriate choice of support for metal clusters serving as catalysts.

Synthesis of grape-seed derived carbon with high specific surface area for CO2 selective adsorption

Nitrogen-doped porous carbons with BET surface area of 1068.2–3314.5 m2/g and nitrogen contents of 3.2–6.5% were prepared with solid waste grape-seed as raw material, NaNH2 as activator and nitrogen source at low activation temperature. Super The activation mechanism of NaNH2 on hydrothermal carbon precursors was first explored by thermodynamic analysis and TG-IR, which provided theoretical support for pore forming of carbon materials. Maximum CO2 and CH4 adsorption capacity at 273 K and pressure of 101 kPa was 5.42 and 1.76 mmol g−1 respectively, which are higher than those of majority of carbon derived from most solid wastes reported in literature. IAST selectivities of GS-3-450 with the largest BET surface area for CO2/CH4 (40v/60v), CO2/N2 (15v/85v), CH4/N2 (50v/50v) were found to be 20.3, 71.4, 6.0 under 101 kPa and 298 K respectively. The competitive adsorption of GS-3-450 for CO2/CH4 (40v/60v), CO2/N2 (15v/85v), CH4/N2 (50v/50v) gases mixture were examined through breakthrough experiments, and the results showed that the breakthrough time of CO2 was longer than that of CH4 and N2, which was beneficial to the separation of CO2 from gases mixture. Eight cycles of CH4 adsorption–desorption studies revealed that the material exhibited excellent recycling stability. Low temperature preparation method, excellent BET specific surface area and total pore volume, as well as excellent adsorption ability of CO2 and CH4 make it have a very great potential for the capture of CO2 and CH4.

Thermodynamic analysis of the difference in adsorption characteristics of CH4 and CO2 on continental shale

In order to explain the difference in adsorption characteristics of CH4 and CO2 on continental shale from the perspective of thermodynamics, the isothermal adsorption experiments of CH4 and CO2 adsorbed by shale in Yanchang Formation in Ordos Basin were carried out, and the excess adsorption capacity was corrected to absolute adsorption capacity. Then the Clausius-Clapeyron equation was used to analyze the isosteric heat of adsorption of CH4 and CO2 on shale. The results show that, for calculating the absolute adsorption capacity, Ozawa empirical formula or Van der Waals approximation method should be used to calculate the adsorption phase density. The absolute adsorption capacity should be selected as the basic data for calculating the isosteric heat of adsorption. The reason is that the excess isosteric heat of adsorption has a negative value in the low adsorption capacity stage, which is contradictory to the fact that the adsorption process is exothermic, and is significantly higher than the absolute isosteric heat of adsorption. There is a good linear positive correlation between the isosteric heat of adsorption and the adsorption amount of CH4 and CO2 adsorbed by continental shale, and the isosteric heat of adsorption of CH4 is greater than that of CO2. The absolute initial isosteric heat of adsorption of CH4 and CO2 adsorbed by shale is 52.04 kJ/mol and 27.71 kJ/mol, indicating that the adsorption force of CH4 on Yanchang Formation shale is stronger than that of CO2.

Effect of Different Placement Sequences of Water on the Methane Adsorption Properties of Coal.

After the coal seam is injected with water, the moisture content in the coal body increases, which affects the output capacity of coalbed methane (CBM). In order to improve the effect of CBM mining, the classical anthracite molecular model has been selected. To analyze the influence of different placement orders of water and methane on the characteristics of coal-adsorbing methane from the micro point of view, a molecular simulation method is used for comprehensive consideration in the study. The results show that H2O does not change the mechanism of CH4 adsorption by anthracite, but it inhibits the adsorption of methane by anthracite. When water enters the system afterward, there arises an equilibrium pressure point where water plays the most significant role in inhibiting methane adsorption by anthracite coals, which increases with increasing moisture content. When water enters the system first, no equilibrium pressure point occurs. The excess adsorption of methane by anthracite when water enters second is higher. The reason is that H2O can replace CH4 at the higher energy adsorption sites of the anthracite structure, while CH4 can only be adsorbed at the lower energy sites, and some of CH4 is not adsorbed. For the coal samples with a low-moisture content system, the equivalent heat of adsorption of CH4 increases first rapidly and then slowly with the increase of pressure. However, it decreases with pressure in the high-moisture content system. The variation of the equivalent heat of adsorption further explains the variation of the magnitude of methane adsorption under different conditions.

High-Pressure Adsorption of CO2 and CH4 on Biochar-A Cost-Effective Sorbent for In Situ Applications.

The search for an effective, cost-efficient, and selective sorbent for CO2 capture technologies has been a focus of research in recent years. Many technologies allow efficient separation of CO2 from industrial gases; however, most of them (particularly amine absorption) are very energy-intensive processes not only from the point of view of operation but also solvent production. The aim of this study was to determine CO2 and CH4 sorption capacity of pyrolyzed spruce wood under a wide range of pressures for application as an effective adsorbent for gas separation technology such as Pressure Swing Adsorption (PSA) or Temperature Swing Adsorption (TSA). The idea behind this study was to reduce the carbon footprint related to the transport and manufacturing of sorbent for the separation unit by replacing it with a material that is the direct product of pyrolysis. The results show that pyrolyzed spruce wood has a considerable sorption capacity and selectivity towards CO2 and CH4. Excess sorption capacity reached 1.4 mmol·g-1 for methane and 2.4 mmol·g-1 for carbon dioxide. The calculated absolute sorption capacity was 1.75 mmol·g-1 at 12.6 MPa for methane and 2.7 mmol·g-1 at 4.7 MPa for carbon dioxide. The isotherms follow I type isotherm which is typical for microporous adsorbents.