Investigations of CO₂ Capture from Gas Mixtures Using Porous Liquids

Porous liquids, a new porous material with fluidity, can be applied in numerous fields, such as gas storage and/or separation. In this work, the separation of binary gas mixtures CO₂/N₂ and CO₂/CH₄ with porous liquids was examined by molecular dynamics (MD) simulations. The pure gas adsorption capacity was analyzed with different concentrations of porous liquids. The dependence of the separation effect of a gas mixture on the total pressure and temperature was investigated. Meanwhile, for both CO₂/N₂ and CO₂/CH₄ systems, the adsorption and separation effects of porous liquids with a cage:solvent ratio of 1:12 are better than those of 1:91 and 1:170. The results of the spatial distribution function and/or trajectories indicated that porous liquids prefer CO₂, leading to the location of CO₂ in the channels formed in porous liquids. However, N₂ and CH₄ are hardly adsorbed into the bulk. The diffusion of gas molecules follows the order of CO₂ > N₂ (for CO₂/N₂) and CH₄ > CO₂ (for CO₂/CH₄) in the bulk and N₂ > CO₂ (for CO₂/N₂) and CH₄ > CO₂ (for CO₂/CH₄) at the interface of porous liquids. Upon increasing the concentrations of porous liquids, the working capacities of CO₂ show small decreases in CO₂/N₂ and CO₂/CH₄ systems, but the sorbent selection parameters are higher in pressure- and temperature-swing adsorption processes. The porous liquid with a cage:solvent ratio of 1:12 is more suitable for the separation of CO₂/N₂ and CO₂/CH₄ systems than ratios of 1:91 and 1:170.