| Summary: | Ethyl cellulose was grafted with ionic liquids in optimal yields (62.5−64.1%) and grafting degrees (5.93−7.90%) by the esterification of the hydroxyl groups in ethyl cellulose with the carboxyl groups in ionic liquids. In IR spectra of the ethyl cellulose derivatives exhibited C=O bond stretching vibration peaks at 1760 or 1740 cm<sup>−1</sup>, confirming the formation of the ester groups and furnishing the evidence of the successful grafting of ethyl cellulose with ionic liquids. The ethyl cellulose grafted with ionic liquids could be formed into membranes by using the casting solution method. The resulting membranes exhibited good membrane forming ability and mechanical properties. The EC grafted with ionic liquids-based membranes demonstrated <i>P</i>CO<sub>2</sub>/<i>P</i>CH<sub>4</sub> separation factors of up to 18.8, whereas the <i>P</i>CO<sub>2</sub>/<i>P</i>CH<sub>4</sub> separation factor of 9.0 was obtained for pure EC membrane (both for CO<sub>2</sub>/CH<sub>4</sub> mixture gas). The membranes also demonstrated an excellent gas permeability coefficient <i>P</i>CO<sub>2</sub>, up to 199 Barrer, which was higher than pure EC (<i>P</i>CO<sub>2</sub> = 46.8 Barrer). Therefore, it can be concluded that the ionic liquids with imidazole groups are immensely useful for improving the gas separation performances of EC membranes.
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