Thermodynamics and Kinetics of Gas Storage in Porous Liquids

Abstract

The recent synthesis of organic molecular liquids with permanent porosity (Giri et al., Nature, 2015, 527, 216) opens up exciting new avenues for gas capture, storage, and separation. Using molecular dynamics simulations, we study the thermodynamics and kinetics for the storage of CH4, CO2, and N2 molecules in porous liquids consisting of crown-ether substituted cage molecules in a 15-crown-5 solvent. It is found that the gas storage capacity per cage molecule follows the order of CH4>CO2>N2, which does not correlate simply with the size of gas molecules. Different gas molecules are stored inside the cage differently, e.g., CO2 molecules prefer the cage’s core while CH4 molecules favor both the core and the branch regions. All gas molecules considered can enter the cage essentially without energy barriers, and their dynamics inside the cage are only slightly hindered by the nanoscale confinement. Additionally, all gas molecules can leave the cage on nanosecond time scale by overcoming a modest energy penalty. The molecular mechanisms of these observations are clarified.