Solubility of carbon dioxide in the low-viscosity ionic liquid 1-hexyl-3-methylimidazolium tetracyanoborate

The solubility of carbon dioxide (CO2) in a new low-viscosity and non-fluorinated ionic liquid, 1-hexyl-3-methylimidazolium tetracyanoborate ([hmim][TCB]), has been studied experimentally using a synthetic method. Bubble point pressures (up to 12.34 MPa) of the system CO2 + [hmim][TCB] are reported for CO2 concentrations ranging from 10.09 to 70.16 mol% and within a temperature range of 283.56–364.04 K. The experimental values of the density, the viscosity and the surface tension of [hmim][TCB] are also reported. The results obtained are compared to available CO2 solubility data and physicochemical properties of other 1-hexyl-3-methylimidazolium based ionic liquids in order to study the effect of the type of anion. It is found that [hmim][TCB] shows higher CO2 absorptive capacity (higher solubility) as well as faster CO2 mass transfer kinetics (lower viscosity), which makes this ionic liquid an attractive solvent for gas separation processes.