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We investigated eight representative metal–organic frameworks for methane storage using molecular simulation. Validated force fields were used to calculate the amount adsorbed for pure methane and its mixtures with CO2 and H2O at 5.8 and 65 bar at 298 K within the composition limits specified for natural gas. Within the analyzed concentrations, the MOFs without open metal sites were minimally influenced by the presence of CO2 and H2O. However, for the MOFs with open metal sites, the presence of these species proved to be harmful. We found that concentrations as low as 25 ppm of water can reduce the delivered volume of methane by more than 20%. A detailed analysis of the adsorption mechanisms leading to this poisoning is presented. These results highlight the possible limitations of MOFs with open metal sites for use in natural gas storage. [ABSTRACT FROM AUTHOR]

Adsorption hysteresis is a phenomenon related to phase transitions that can impact applications such as gas storage and separations in porous materials. Computational approaches can greatly facilitate the understanding of phase transitions and phase equilibria in porous materials. In this work, adsorption isotherms for methane, ethane, propane, and n-hexane were calculated from atomistic grand canonical Monte Carlo (GCMC) simulations in a metal-organic framework having both micropores and mesopores to better understand hysteresis and phase equilibria between connected pores of different size and the external bulk fluid. At low temperatures, the calculated isotherms exhibit sharp steps accompanied by hysteresis. As a complementary simulation method, canonical (NVT) ensemble simulations with Widom test particle insertions are demonstrated to provide additional information about these systems. The NVT+Widom simulations provide the full van der Waals loop associated with the sharp steps and hysteresis, including the locations of the spinodal points and points within the metastable and unstable regions that are inaccessible to GCMC simulations. The simulations provide molecular-level insight into pore filling and equilibria between high- and low-density states within individual pores. The effect of framework flexibility on adsorption hysteresis is also investigated for methane in IRMOF-1. Developing computational tools to study the phase behaviour of adsorbate molecules in complex pore architectures can greatly facilitate our understanding of phase transitions and phase equilibria in porous materials. Here, molecular simulations are used to study the hysteresis and phase equilibria of n-alkane adsorbate molecules in a metal–organic framework with both micropores and mesopores, and simulations in the canonical ensemble with Widom insertions are shown to be a powerful complementary approach to grand canonical Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Nanoporous solids are ubiquitous in chemical, energy, and environmental processes, where controlled transport of molecules through the pores plays a crucial role. They are used as sorbents, chromatographic or membrane materials for separations, and as catalysts and catalyst supports. Defined as materials where confinement effects lead to substantial deviations from bulk diffusion, nanoporous materials include crystalline microporous zeotypes and metal–organic frameworks (MOFs), and a number of semi-crystalline and amorphous mesoporous solids, as well as hierarchically structured materials, containing both nanopores and wider meso- or macropores to facilitate transport over macroscopic distances. The ranges of pore sizes, shapes, and topologies spanned by these materials represent a considerable challenge for predicting molecular diffusivities, but fundamental understanding also provides an opportunity to guide the design of new nanoporous materials to increase the performance of transport limited processes. Remarkable progress in synthesis increasingly allows these designs to be put into practice. Molecular simulation techniques have been used in conjunction with experimental measurements to examine in detail the fundamental diffusion processes within nanoporous solids, to provide insight into the free energy landscape navigated by adsorbates, and to better understand nano-confinement effects. Pore network models, discrete particle models and synthesis-mimicking atomistic models allow to tackle diffusion in mesoporous and hierarchically structured porous materials, where multiscale approaches benefit from ever cheaper parallel computing and higher resolution imaging. Here, we discuss synergistic combinations of simulation and experiment to showcase theoretical progress and computational techniques that have been successful in predicting guest diffusion and providing insights. We also outline where new fundamental developments and experimental techniques are needed to enable more accurate predictions for complex systems. [ABSTRACT FROM AUTHOR]

Damping systems using granular particles as the damping medium are promising for application in extreme temperature conditions. In particle-based damping systems, mechanical energy is dissipated through inelastic collisions and friction between particles. In this work, we use particle dynamics simulations to investigate and compare the damping mechanisms of a piston-type thrust damper and a box-type oscillation damper. The mechanisms of energy transfer and energy dissipation are investigated. The roles of friction and inelastic collisions, as well as the wall effects in energy dissipation, are examined. The simulation results provide better understanding of the particle damping mechanisms, which may help in the design of next generation particle damping devices. [ABSTRACT FROM AUTHOR]