CO2 capture and viscosity of metal chelate-based ionic liquids: Influence of the structure and substitution of the azole-based anion

In this work, the effect of the structure and substitution of azole-based anion on the CO 2 capture and viscosity ( η ) of metal chelate-based dual functional ionic liquids (DFILs) with [K(DGA) 2 ] + cation was investigated. The CO 2 absorption capacity of DFILs at 0.1 MPa and 333.2 K shows that methyl and nitro groups on the azole-based anion, such as pyrazolide ([Pyr] − ) and imidazolide ([Im] − ), attenuate their reactivity with CO 2 through the steric hindrance and electron-withdrawing effects, respectively. Furthermore, the CO 2 absorption capacity of [K(DGA) 2 ][Pyr] is larger than that of [K(DGA) 2 ][Im], which is due to the interaction of the two adjacent N atoms in the [Pyr] − anion with CO 2 , as confirmed by DFT calculations. The CO 2 absorption mechanism shows that both [Pyr] − anion and [K(DGA) 2 ] + cation of [K(DGA) 2 ][Pyr] can chemically interact with CO 2 , making its saturated uptake at 333.2 K as high as 1.47 mol CO 2 per mole IL. Moreover, CO 2 interacts preferentially with [Pyr] − , and the [K(DGA) 2 ] + –CO 2 interaction is enhanced when the CO 2 uptake is greater than 0.5 mol CO 2 per mole IL. η of pure [K(DGA) 2 ][Pyr] is lower than that of pure [K(DGA) 2 ][Im]. η of [K(DGA) 2 ][Pyr] increases with the increase of CO 2 absorption, and the rapid increase in η after CO 2 uptake greater than 0.5 is attributed to the formation of [K(DGA) 2 ] + –CO 2 interactions.