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

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.

Effect of microstructure and chemical composition of coal on methane adsorption

High-pressure adsorption of methane, carbon dioxide, and nitrogen on zeolite 13X was measured in the pressure range (0 to 5) MPa at (298, 308, and 323) K and fitted with the Toth and multisite Langmuir models. Isosteric heats of adsorption were (12.8, 15.3, and 37.2) kJ/mol for nitrogen, methane, and carbon dioxide respectively, which indicate a very strong adsorption of carbon dioxide. The preferential adsorption capacity of CO2 on zeolite 13X was much higher than for the other gases, indicating that zeolite 13X can be used for methane purification from natural gas or for carbon dioxide sequestration from flue gas.

Parameters from single-component isotherm models were used in multicomponent isotherm models to predict the aqueous phase sorption of trichloroethylene (TCE) in the presence of tetrachloroethylene (PCE) in four zeolites, Tenax, and three natural solids. The Langmuir, the Polanyi-Dubinin, and the Freundlich or the Langmuir-Freundlich isotherm models were used to simulate single-component sorption in zeolites. The Langmuir two-site, the Polanyi-Dubinin two-site, and the Freundlich or the Langmuir-Freundlich isotherm models were used to simulate single-component sorption in Tenax and natural solids. Two-site models have been used previously to model sorption in soils and sediments, and they combine an adsorption component (e.g., Langmuir) with a linear partitioning component. By using parameters from the different single-component isotherm models, the multicomponent Langmuir, the ideal adsorbed solution theory, and the Polanyi theory were each used to predict multicomponent sorption. In general, the ability to predict TCE sorption in the presence of PCE depended more on the choice of the single-component model than the multicomponent model, and better results were obtained when the Freundlich or the Langmuir-Freundlich isotherm was used for single-component sorption. This suggests that the more mechanistically based Langmuir and Polanyi-type models may not adequately describe the distribution of adsorption sites in some model and natural solids. The Freundlich or the Langmuir-Freundlich model, although empirical, has greater flexibility in characterizing sorbent heterogeneity and results in better multicomponent model predictions. However, this last statement is tenuous, because more solids must be tested against various model combinations.

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

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).

Herein, we report carbon dioxide (CO2) and methane (CH4) adsorption behavior in MeMOFs, methylated analogues of FMOFs with -CF3 groups replaced with -CH3, utilizing grand canonical Monte Carlo (GCMC) simulations at 288, 298, and 308 K and P ≤ 40 bar and density functional theory (DFT) computations of adsorption energies. Isosteric heats of adsorption (Qst), Henry's constants (KH) and interaction energies were used to analyze the adsorbate-adsorbent interaction strengths and gas uptake of guest molecules. The Qst of CO2 was found to be 1.29-1.73 times higher in MeMOF-1 than in FMOF-1, vs. 1.30-1.47 times for CH4, hence demonstrating higher guest affinity to MeMOF-1 than to the FMOF-1 polymorph. Simulated isotherms were further fitted with Langmuir, Langmuir-Freundlich, and Tóth models to calculate the isosteric heat of adsorption at infinite dilution (Qst0) using the Clausius-Clapeyron equation. The data were then compared with those obtained from force-field-based Monte Carlo (MC) simulations to determine the consistency. The Tóth model presented excellent characterization of CO2 and CH4 adsorption, implying both FMOF-1 and MeMOF-1 materials have inhomogeneous surfaces. The order of the Qst0 values obtained using the Clausius-Clapeyron equation was consistent with that obtained from MC simulations and confirmed the higher uptake of CO2 and CH4 in MeMOF-1 as predicted by GCMC. The presence of H2O vapor, up to 80% relative humidity, did not affect the CO2 and CH4 adsorption in MeMOF-1 structures, as was observed in the analogous FMOF-1 parent structure. The larger pore size and surface area upon substituting -CF3 groups with -CH3 groups allow for significantly greater CO2 and CH4 uptake in MeMOFs compared to FMOFs with no water uptake even at high humidity. These simulations were applied upon MeMOF analogues of multiple FMOF-1 polymorphs known to date and are thus expected to hold for MeMOF analogues of other FMOF and MOFF structures reported by the Omary and Miljanić teams, respectively. Experimental data have validated the superhydrophobic nature of the MeMOF-1 composition via a polymorphic form with a different topology, MeMOF-2, attaining an ∼100° increase in water-drop contact angles, from ∼74° for a control plastic substrate to ∼172° upon dry-coating it with MeMOF-2. Experimentally synthesized MeMOF-2 possesses the same {Ag(3,5-(CH3)2-1,2,4-triazolate)} empirical formula as that of simulated MeMOF-1 structures, albeit with a different crystal structure and lower porosity.

In this paper, two types of adsorption materials SA-C-Fe and SA-C-Fe(C) were prepared using bagasse biochar produced by one-step microwave pyrolysis and activation for Cr(VI) removal of wastewater. The adsorption materials were characterized, and Cr(VI) adsorption performance, kinetics and thermodynamics on adsorption materials were studied. Results show that microwave pyrolysis/activation contributes to developed pore structure and abundant active functional groups, resulting in high Cr(VI) adsorption capacities. The optimal preparation conditions for biochar is: microwave power 500 W, ZnCl2/bagasse ratio 2.5:1 and pyrolysis/activation time 15 min, and the specific surface area of biochar is 1,787.64 m2/g. The Cr(VI) adsorption of the two materials is more in line with the pseudo-second-order kinetic model, and the adsorption process is dominated by chemical adsorption. The static removal experiment of Cr(VI) using SA-C-Fe and SA-C-Fe(C) has the best removal effect at pH = 2, and the whole adsorption process is more in line with the Langmuir-Freundlich isotherm model. Calculated by the pseudo-two-order kinetic model and the Langmuir-Freundlich isothermal model, the maximum adsorption rate for Cr(VI) of SA-C-Fe and SA-C-Fe(C) are 211.87 mg/g and 388.92 mg/g, respectively. The removal process is mainly dominated by three mechanisms: electrostatic adsorption, ion exchange and redox reactions. The improvement of Cr(VI) adsorption capacity is attributed to more developed pore structure. The results offer beneficial reference for the application of low-cost carbon-based adsorption materials for pollutants separation, and effectively realize the utilization of bagasse pyrolysis by-products.

Equilibrium and kinetics studies of 2,4,5-trichlorophenol adsorption onto organophilic-bentonite

Adsorption separation of N 2, O 2, CO 2 and CH 4 gases by β-zeolite

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

Thermodynamic adsorption data of CH4, C2H6, C2H4 as the OCM process hydrocarbons on SAPO-34 molecular sieve

This work investigated the adsorption of autoantibodies such as anti-SS-A/Ro, anti-SS-B/La, anti-Sm, and anti-dsDNA on protein L-agarose gel. In order to determine better conditions for IgG adsorption on this matrix, some buffer systems were tested. Adsorption data were analyzed using the Langmuir and Langmuir-Freundlich isotherm models. The experimental isotherms were best described by the Langmuir-Freundlich model, which indicated negative and positive cooperativities for binding in the presence of PBS and HEPES buffers, respectively. The K(d) values for phosphate buffered saline solution (PBS) and hydroxyethylpiperazine ethanesulfonic acid (HEPES) were 2.8 x 10(-7) M and 3.2 x 10(-7) M, respectively, which indicate a high affinity between IgG and the immobilized protein L. The amount of protein adsorbed per amount of protein loaded was high for anti-Sm (44%) and anti-dsDNA (46%), but low for anti-SS-B/La (9%). The amount of albumin adsorbed was lower than 0.06 mg/mL, which may remove the need for a plasma replacement solution in clinical apheresis.

Design and optimization of Immobilized Metal Affinity Chromatography (IMAC) processes require deep knowledge of driving factors responsible for interaction between immobilized metal and biomolecules. Based on this requirement, interactions between lactoferrin from cheese whey and IDA-Cu2+-cryogel system was investigated. Data from adsorption of lactoferrin in the system at pH 6, 7 and 8, as well as NaCl concentration from 200 to 1000 mmol L−1 were adjusted Langmuir, Freundlich, Temkin and Langmuir-Freundlich isotherm models. Although all models were able to explain the interaction lactoferrin-cryogel system, the Langmuir-Freundlich model was the most accurate one. In addition, it could explain quantitatively the cooperativity and heterogeneity of the bounds between protein and matrix. The methods used in this project are useful for both better understanding of the protein-immobilized metal interactions and developing preparative scale IMAC.

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