Combined Experimental and Computational Study on the Structure–Property Relationships of Mono- and Dicationic Imidazolium Ionic Liquids for CO 2 Capture

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Abstract
The present study investigates the potential of dicationic ionic liquids (DILs) and monocationic ionic liquids (MoIL), with and without metal in the anion, for CO2 capture applications. The structures of the samples were confirmed by FTIR, 1H NMR spectroscopy, and Raman spectroscopy, while their physicochemical properties, density, viscosity, and thermal stability were evaluated. A series of computational simulations were conducted by using density functional theory (M11/def2-TZVP) to ascertain the multiplicity of the ground state of the magnetic anion [FeCl4]-. These simulations determined the multiplicity to be a sextet and furthermore identified the trans conformation as the most energetically favorable for cation [E(MIM)2]2+. This finding demonstrates a correlation between the structural conformations and the experimental Raman spectra. The findings of CO2 sorption and kinetic tests, conducted under postcombustion conditions (40 °C, 4 bar), indicated that DILs exhibited superior performance in comparison to MoILs. The DIL [E(MIM)2][2Cl] exhibited the highest sorption capacity (110.20 μmol/g), which is almost three times higher than that of the best MoIL (BMIM FeCl4). These enhancements can be ascribed to reduced viscosities and an augmented number of active interaction sites in the dicationic structures. Furthermore, [E(MIM)2][2Cl] exhibited a high degree of selectivity for CO2 over N2 and demonstrated stability over five recycling cycles, suggesting the potential of DILs as candidates for the development of CO2 capture technologies.
Funding Information
  • Conselho Nacional de Desenvolvimento Científico e Tecnológico
  • Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (001)

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