Improved CO2/CH4 separation using a nanocomposite ionic liquid gel membrane

This work evaluates carbon dioxide (CO2) and methane (CH4) gases permeations through polyether block amide (Pebax1074) based membranes synthesized using 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) ionic liquid (IL) and silica (SiO2) nanoparticles. Ionic liquid gel membranes (ILGMs) were prepared by incorporating [BMIM][PF6] into Pebax1074 matrix at four levels of 20 -80 wt. %. The gas permeation results indicated that for the ILGMs, as the IL content increases in the Pebax matrix, both gases permeability values increase significantly (CO2 and CH4 permeabilities increase from 58.6 to 2.9 Barrer to 104.3 and 5.6 Barrer, respectively) while ideal CO2/CH4 selectivity decreases slightly (ideal CO2/CH4 selectivity changes from 20.2 to 18.5). However, the ILGMs performance moves closer to the Robeson upper bound with increasing the IL content and accordingly, the ILGM with 80 wt. % of [BMIM][PF6] can be considered as the best ILGM. To prepare nanocomposite ionic liquid gel membranes (NCILGMs), SiO2 nanoparticles were added into the ILGM casting solution containing 80 wt. % of [BMIM][PF6] at different levels (2, 4, 6, and 8 wt. % based on the polymer weight). The results showed that incorporation of the SiO2 content increases CO2 and CH4 permeability values from 104.3.6 to 5.6 Barrer to 153.6 and 8.1 Barrer, respectively and ideal CO2/CH4 selectivity from 18.5 to 19.1. Thus, the NCILGM with 8 wt. % of SiO2 nanoparticles was introduced as the membrane with the best performance. The characterization of the prepared membranes was examined by XRD, ATR-FTIR and FESEM analyses. (C) 2017 Elsevier B.V. All rights reserved.