In this work, the capacity of the IRMOF-1 was evaluated, for separation of H2S from gas mixture with the objective of gas sweetening. The grand canonical Monte Carlo simulation (GCMC) was performed in order to simulate adsorption of pure methane, pure H2S and their binary mixtures. The simulations were performed in the conditions close to the real natural gas composition at temperature of 298 K at different pressures to clarify how operating conditions govern the loading behavior. For the adsorption of pure H2S in the IRMOF-1, three force fields were examined and the candidate force-field was selected. Furthermore, effect of temperature on the adsorption of pure H2S was examined by GCMC with conducting simulation at 320 K and 298 K. We have validated simulation results for pure gaseous states against experimental values and good agreements between experimental values and simulated values were observed. For the mixture simulation, further validations were performed by comparing the results with previously published studies, confirming physical consistency in the adsorption isotherms and selectivity trends. Structural investigation by analysis of Radial Distribution Functions (RDFs) and coordination numbers shows that ZnO nodes in IRMOF-1 are preferred sites for H2S adsorption both in pure and mixture states. For the gaseous mixtures of H2S and CH4, the results indicated that IRMOF-1 has high capacity for adsorption and separation of H2S. It was observed that IRMOF-1 has an excellent selectivity of H2S over CH4. This behavior originates from strong electrostatic and van der Waals interactions between H2S molecules and the framework, which dominate over the weaker interactions with CH4. Additionally, a brief evaluation of the heat of adsorptions indicates the thermodynamic driving force for H2S uptake.
This paper reports the results of an international interlaboratory study sponsored by the Versailles Project on Advanced Materials and Standards (VAMAS) and led by the National Institute of Standards and Technology (NIST) on the measurement of low-pressure CO2 adsorption isotherms at 25 degrees C on zeolite 13X (NIST research grade test material 10257). Eighteen laboratories participated in the study and contributed 21 datasets. From these data, a consensus reference isotherm, along with the 95% uncertainty interval (U k=2), were determined and reported. Results indicate the material is suitable for development into NIST reference material, which will become the first zeolitic reference material in beaded form at NIST.
Krypton is scarce, costly, and periodically experiences supply shortages, motivating the search for alternative probe molecules. Methane, which shares many physicochemical properties with krypton—such as kinetic diameter, polarizability, boiling point, and a lack of quadrupole moment—presents itself as a promising and more accessible surrogate. This study addresses whether methane can be used as a substitute for krypton for adsorption studies. Here, we demonstrate that across several representative adsorbents—including activated carbon, a zeolite, and flexible as well as rigid metal-organic frameworks—the adsorption-desorption isotherms of methane and krypton are remarkably similar in both shape and magnitude over a wide range of conditions. Comparative analysis reveals that differences in maximum adsorption capacities and affinity parameters between methane and krypton are minor, generally within experimental uncertainty, and that the qualitative adsorption mechanisms—including phase transitions in flexible MOFs—are consistently captured by both probes. To the best of our knowledge at the exception of H2 isotopes, we show for the first time that same adsorption capacity data can be obtained with two different adsorbates.
The confining pressure of overlying strata can seriously affect the adsorption behavior of shale on CH4 and CO2. To address this issue, the Isothermal adsorption experiments of CH4 and CO2 on shale were conducted under unstressed (powdered sample, 0 MPa) and stressed (cylindrical sample, 21 MPa) conditions, and the micropore structure was characterized using scanning electron microscopy (SEM), low-temperature CO2/N2 adsorption, and nuclear magnetic resonance (NMR). Results indicate that the adsorption capacity of shale to CH4 and CO2 under stress is significantly lower than that under non-stress conditions, while the adsorption equilibrium time of shale to gas is longer than that under non-stress. In addition, the Dubinin-Radushkevich-Langmuir (DR-L) model was employed to describe the adsorption behavior of CH4 and CO2 in nanopores of different scales, and the fitting results reveal that the stress can lead to the existence of gas molecules in shale more inclined to exist in the form of micropore filling. Especially, the adsorption capacity difference between powdered and cylindrical shales a non-monotonic trend with a peak near the critical pressure, attributed to the progressive reopening of compressed adsorption sites as effective stress diminishes and to enhanced supercritical gas diffusivity. This study provides theoretical support for efficient shale gas extraction and CO2 geological storage.
The separation of an adsorption azeotropic binary gas mixture (CO2 and C3H8 on H-mordenite) by pressure swing adsorption (PSA) was studied via simulation using the dynamic adsorption process simulator (DAPS), with the perfect negative dual process Langmuir (PN-DPL) model describing the mixed gas adsorption equilibria. Numerous PSA simulations, carried out to the periodic state using a 4-bed 4-step Skarstrom cycle at five feed flow rates (6 to 10 SLPM) and nine feed compositions (20 and 80 vol s_12^P for a PSA process operating at this achorismic point is defined as s_12^P=y_2^*(dn_1^*/dP)/y_1^*(dn_2^*/dP)=1.0 . In this study, the corresponding y_1^* was determined serendipitously during simulation with DAPS ( y_C3H8^* = 0.300) and analytically from the PN-DPL model using chord (0.308) and differential (0.302) approaches, thereby confirming the existence of this achorismic composition. Achorismic behavior shifts to adsorption azeotropic behavior only in the special (unrealistic) limiting case when the low pressure in the PSA process is set equal to zero.
