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 [NH2emim][BF4] and conventional imidazolium‐based ILs [bmim][BF4]), as absorbents for CO2 capture, possesses some unique advantages, they have a number of disadvantages when independently used for CO2 capture. This study examined a series of binary liquid mixtures of [NH2emim][BF4] and [bmim][BF4] for CO2 capture, exploiting the advantages and reducing the disadvantages of each of the components. The CO2 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 [NH2e‐mim][BF4] (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 [NH2e‐mim][BF4] 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 CO2 absorption and desorption. The above laws were consistent with those of the CO2 capture performances of the IL mixtures basically. An IL mixture containing 0.4 mol/mol [NH2e‐mim][BF4] and 0.6 mol/mol [bmim][BF4] would be an optimal CO2‐capturing absorbent. The findings in this study may enrich the database and provide a theoretical support for CO2 capture with IL mixtures. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.