Recovery of Multicomponent Shale Gas from Single Nanopores

The adsorption of multicomponent gas mixtures in shale formations and their recovery are of great interest to the shale gas industry. Here we report molecular dynamics simulations of the adsorption of methane/ethane mixtures in 2 and 4 nm-wide nanopores and their recovery from these nanopores. Surface adsorption contributes significantly to the storage of methane and ethane inside the pores, and ethane is enriched inside the nanopores in equilibrium with bulk methane–ethane mixtures. The enrichment of ethane is enhanced as the pore is narrowed but is weakened as the pressure increases due to entropic effects. These effects are captured by the ideal adsorbed solution (IAS) theory, but the theory overestimates the adsorption of both gases. Upon opening the mouth of the nanopores to gas baths with lower pressure, both gases enter the bath. The production rates of both gases show only weak deviation from the square root scaling law before the gas diffusion front reaches the dead end of the pores. The ratio of the production rate of ethane and methane is close to their initial mole ratio inside the nanopore despite the fact that the mobility of pure ethane is smaller than that of pure methane inside the pores. Scale analysis and calculation of the Onsager coefficients for the transport of binary mixtures of methane and ethane inside the nanopores suggest that the strong coupling between methane and ethane transport is responsible for the effective recovery of ethane from the nanopores

Multicomponent Gas Storage in Organic Cage Molecules

Porous liquids are a promising new class of materials featuring nanoscale cavity units dispersed in liquids that are suitable for applications such as gas storage and separation. In this work, we use molecular dynamics simulations to examine the multicomponent gas storage in a porous liquid consisting of crown-ether-substituted cage molecules dissolved in a 15-crown-5 solvent. We compute the storage of three prototypical small molecules including CO₂, CH₄, and N₂ and their binary mixtures in individual cage molecules. For porous liquids in equilibrium with a binary 1:1 gas mixture bath with partial gas pressure of 27.5 bar, a cage molecule shows a selectivity of 4.3 and 13.1 for the CO₂/CH₄ and CO₂/N₂ pairs, respectively. We provide a molecular perspective of how gas molecules are stored in the cage molecule and how the storage of one type of gas molecule is affected by other types of gas molecules. Our results clarify the molecular mechanisms behind the selectivity of such cage molecules toward different gases

Dynamic Charge Storage in Ionic Liquids-Filled Nanopores: Insight from a Computational Cyclic Voltammetry Study

Understanding the dynamic charge storage in nanoporous electrodes with room-temperature ionic liquid electrolytes is essential for optimizing them to achieve supercapacitors with high energy and power densities. Herein, we report coarse-grained molecular dynamics simulations of the cyclic voltammetry of supercapacitors featuring subnanometer pores and model ionic liquids. We show that the cyclic charging and discharging of nanopores are governed by the interplay between the external field-driven ion transport and the sloshing dynamics of ions inside of the pore. The ion occupancy along the pore length depends strongly on the scan rate and varies cyclically during charging/discharging. Unlike that at equilibrium conditions or low scan rates, charge storage at high scan rates is dominated by counterions while the contribution by co-ions is marginal or negative. These observations help explain the perm-selective charge storage observed experimentally. We clarify the mechanisms underlying these dynamic phenomena and quantify their effects on the efficiency of the dynamic charge storage in nanopores

Simultaneous Enhancements in Toughness and Electrical Conductivity of Polypropylene/Carbon Nanotube Nanocomposites by Incorporation of Electrically Inert Calcium Carbonate Nanoparticles

Although the presence of carbon nanotubes (CNTs) makes polypropylene (PP) electrically conductive, the resulting PP/CNT binary nanocomposites become brittle limiting their practical applications. To toughen PP/CNT nanocomposites, calcium carbonate (CaCO₃) inorganic nanoparticles are melt-compounded with PP and CNTs components to fabricate electrically conductive and tough PP/CNT/CaCO₃ ternary nanocomposites. The PP/CNT nanocomposites have a relatively large percolation threshold of 6.2 wt %, which reduces to 5.6 wt % by the addition of 30 wt % of pristine CaCO₃, and further to 3.6 wt % in the presence of 30 wt % of modified CaCO₃. Simultaneously, the electrically conductive PP/CNT nanocomposites are efficiently toughened by the CaCO₃ nanoparticles, and the notched impact strength increases from 16.0 to 33.1 KJ/m² by compounding 30 wt % of modified CaCO₃ with PP/9 wt % CNT components. The dual roles of CaCO₃ in volume-exclusion and toughening are well demonstrated

Importance of Ion Packing on the Dynamics of Ionic Liquids during Micropore Charging

Molecular simulations of the diffusion of EMIM⁺ and TFSI^– ions in slit-shaped micropores under conditions similar to those during charging show that in pores that accommodate only a single layer of ions, ions diffuse increasingly faster as the pore becomes charged (with diffusion coefficients even reaching ∼5 × 10^–9 m²/s), unless the pore becomes very highly charged. In pores wide enough to fit more than one layer of ions, ion diffusion is slower than in the bulk and changes modestly as the pore becomes charged. Analysis of these results revealed that the fast (or slow) diffusion of ions inside a micropore during charging is correlated most strongly with the dense (or loose) ion packing inside the pore. The molecular details of the ions and the precise width of the pores modify these trends weakly, except when the pore is so narrow that the ion conformation relaxation is strongly constrained by the pore walls