Investigations of CO₂Capture from Gas Mixtures Using Porous Liquids

Abstract

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.

Porous liquids – the future is looking emptier

“…Gas storage and separation are among the leading applications for porous liquids; computations ranging in scale are used to assess porous liquid performance by confirming gas preferentially occupies cavities, 44 supporting solubility measurements, 26 and identifying specific adsorption sites, 35 among other utilities. 72 MD simulations demonstrate the impact of gas separation via RDFs, and spatial distribution functions have revealed energetics and structure are the driving forces behind transferring gas from the ionic liquid to the MOF in a type III porous liquid. 44 Spatial distribution functions have also been used to probe the topology–geometry relationship between gas and POCs within a type II porous liquid, revealing which gases are preferentially bound to the cage cavity.…”

“… 44 Spatial distribution functions have also been used to probe the topology–geometry relationship between gas and POCs within a type II porous liquid, revealing which gases are preferentially bound to the cage cavity. 72 In a similar approach, the isosurface of gas occupancy within the cavities of POC-based porous liquids were calculated from MD trajectories to examine gas entrance kinetics. 73 The energy barrier of gas entrance/exit from cage cavities was calculated using potential of mean force (PMF) of gas molecules near and inside the cavities; the existence of an energy penalty for leaving the cage suggests the cage can trap gas.…”

Practical considerations in the design and use of porous liquids

“…In both cases, PLs' working capacity can be decreased with increasing concentrations of cage molecules, while the separation can be enhanced. 98…”

Shining Light on Porous Liquids: From Fundamentals to Syntheses, Applications and Future Challenges

“…However, the gas separation was not investigated. Thus, very recently, Yang et al [68] investigated the effect of separation performance toward some gas pairs using molecular dynamics simulation (Figure 16f). Two adsorption processes including pressure-swing adsorption (PSA) and temperature-swing adsorption (TSA) were adopted to get closer to the practical condition.…”