Solubility and Diffusivity of CO₂ in the Ionic Liquid 1‑Butyl-3-methylimidazolium Tricyanomethanide within a Large Pressure Range (0.01 MPa to 10 MPa)

Ionic liquids (ILs) are promising solvents for carbon capture because of their high sorption capacity and low regeneration energy compared to conventional amine-based solvents. Previously, tetracyanoborate-based ILs have shown enhanced carbon dioxide (CO₂) absorption capacity and absorption kinetics due to their low viscosity. In this work, the related IL 1-butyl-3-methylimidazolium tricyanomethanide ([bmim]­[tcm]) is studied for the first time as a solvent for CO₂ capture. The physicochemical properties (e.g., density, viscosity, electrical conductivity, surface tension, thermal decomposition temperature, glass transition point) of pure [bmim]­[tcm] were experimentally determined and successfully described using appropriate correlations. [Bmim]­[tcm] was found to be a low-viscous IL with a relatively high thermal stability (<i>T</i>_decomp = 473.15 K). The solubilities of CO₂ in [bmim]­[tcm] were measured at temperatures ranging from (288.15 to 363.15) K and a pressure range of (0.01 to 10) MPa using two different methods (volumetric vs gravimetric), which show good agreement with each other. [Bmim]­[tcm] shows higher solubilities and therefore, higher sorption capacity compared to other nonfluorous ILs. The Peng–Robinson equation of state was applied to correlate the experimental data. Henry’s law constants (4 MPa to 13 MPa) and partial molar enthalpies of absorption (−14 kJ·mol^–1) at different temperatures were also calculated from the measured solubility data. The diffusion coefficients of CO₂ in [bmim]­[tcm] were determined at temperatures ranging from (308.15 to 353.15) K using the gravimetric method only. The diffusivity data of CO₂ in [bmim]­[tcm] (∼5·10^–10 m²·s^–1) are comparable to those in other low-viscous ILs, and show that high rates of absorption are possible. Therefore, it can be concluded that [bmim]­[tcm] is a promising candidate for carbon capture