Selective chemical separation of carbondioxide by ether functionalized imidazolium cation based ionic liquids

A series [C2Omim][X] of imidazolium cation-based ILs, with ether functional group on the alkyl side-chain were synthesized, characterized by various techniques such as 1H, 13C NMR, MS-ESI, FTIR and EA and investigated as potential absorbents for CO2 capture. More specifically, the influence of changing the anion with same cation is carried out. The absorption capacity of CO2 for ILs was investigated at 30 and 50 °C at ambient pressure (0–1.6 bar). Ether functionalized ILs show significantly high absorption capacity for CO2. The CO2 absorption capacity of ILs increased with a rise in pressure and decreased when temperature was raised. Results showed that absorption capacity reached about 0.9 mol CO2 per mol of IL at 30 °C. The most probable mechanism of interaction of CO2 with ILs was investigated using FTIR and 13C NMR, and the result shows that the absorption of CO2 in ether functionalized ILs is a chemical process. The CO2 absorption results and detailed study indicate the predominance of 1:1 mechanism, where the CO2 reacts with one IL to form a carbamic acid. The CO2 absorption capacity of ILs for different anions follows the trend: BF4 < DCA ∼ PF6 ∼ TfO < Tf2N. Moreover, the as-synthesized ILs are selective, thermally stable, long life operational and can be recycled at a temperature of 70 °C or under vacuum and can be used repeatedly.

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► Synthesis of ether functionalized imidazolium cation-based [C2Omim][X] ILs.
► Investigation of CO2 absorption capacity at 30 and 50 °C at ambient pressure (0–1.6 bar).
► Absorption capacity reaches about 0.9 mol CO2 per mol of ILs at 30 °C at 1.6 bar pressure.
► Trend of CO2 absorption capacity for different anions follows BF4 < DCA ∼ PF6 ∼ TfO < Tf2N.
► Mechanism shows 1 mol CO2 reacts with one mole of ILs via chemical interaction.