CO2/CH4 Gas Separation by Polyoxometalate Ionic Liquid Confined in Carbon Nanotubes Using Molecular Dynamics Simulation

In this study, we have performed molecular dynamics (MD) simulations to investigate the separation of a CO2/CH4 gas mixture using 1-ethyl-3-methylimidazolium tungstophosphate ([Emim](3)[PW12O40]) or ([Emim](3)[Keggin]) ionic liquid confined into a carbon nanotube (CNT) at several external pressures at 300 K. We have also compared the results with the different ionic liquids (ILs), including imidazolium tetrafluoroborate ([Emim][BF4]), imidazolium hexafluorophosphate ([Emim][PF6]), and imidazolium tetrachloroaluminate ([Emim][AlCl4]). In another model, the membrane was constructed by four similar CNTs (with the confined ILs), which are almost spaced equally from each other (4ILs-4CNTs). Our results indicated the importance of polyoxometalate IL-CNT nanocomposites in the gas separation process. CNTs with [Emim](3)[PW12O40] IL exhibit the highest sorption of CO2 owing to the high electric charge of this particular IL. It is also totally observed that AlCl4- exhibits smaller sorption than the other ILs, especially for the 4ILs-4CNTs system for CO2 sorption. The [Emim](3)[PW12O40] IL in the 4ILs-4CNTs configuration exhibits more than 2 times rejection rate than the 4CNTs without IL. The diffusion coefficients of confined gas molecules in the CNT are also smallest for the [Keggin][Emim] IL, which are in agreement with the sorption and rejection results.