Properties of ionic liquid mixtures of [NH₂e‐mim][BF₄] and [bmim][BF₄] as absorbents for CO₂ capture

Although the use of ‘task‐specific’ amine‐functionalized imidazolium‐based ionic liquids (ILs) such as [NH 2 emim][BF 4 ] and conventional imidazolium‐based ILs [bmim][BF 4 ]), as absorbents for CO 2 capture, possesses some unique advantages, they have a number of disadvantages when independently used for CO 2 capture. This study examined a series of binary liquid mixtures of [NH 2 emim][BF 4 ] and [bmim][BF 4 ] for CO 2 capture, exploiting the advantages and reducing the disadvantages of each of the components. The CO 2 absorption performances of the mixtures were investigated as well as their physicochemical properties. Densities, viscosities, and surface tensions of the mixtures of varying molar fractions of [NH 2 e‐mim][BF 4 ] (from 0.2–0.5 mol/mol) were experimentally measured over a temperature range of 298.0–343.0 K at a fixed pressure of 0.1 MPa. Thermal expansion coefficients, excess logarithmic viscosities, surface entropies, and surface enthalpies were calculated based on the experimental data. All the estimated physicochemical properties in a mixture with a mole fraction of [NH 2 e‐mim][BF 4 ] of 0.4 had variation characteristics significantly different from those in mixtures with other mole fractions, which might be attributed to the large interaction between the two kinds of IL components and showed a positive effect on CO 2 absorption and desorption. The above laws were consistent with those of the CO 2 capture performances of the IL mixtures basically. An IL mixture containing 0.4 mol/mol [NH 2 e‐mim][BF 4 ] and 0.6 mol/mol [bmim][BF 4 ] would be an optimal CO 2 ‐capturing absorbent. The findings in this study may enrich the database and provide a theoretical support for CO 2 capture with IL mixtures.