Non-Newtonian shear-thinning viscosity of carbon monoxide-selective ionic liquid 1-hexyl-3-methylimidazolium chloride doped with CuCl

• Study of rheological properties of CO-selective IL [Hmim][Cl]-CuCl.
• Shear-thinning non-Newtonian flow was found regardless of CuCl concentration.
• Viscosity decreases with increasing CuCl concentration in the range 0–2 M.
• Cross model describes apparent viscosity as a function of shear rate.
• Results will help mass transfer rate characterization and separation process design.

The rheological properties of the ionic liquid 1-hexyl-3-methylimidazolium chloride ([hmim][Cl]) along with that of its mixtures with CuCl, which form the corresponding chlorocuprate(I)-based ionic liquids ([hmim][Cu(Cl)x]) are reported. In addition, the flow behaviour of these ionic liquids is thoroughly described for the first time. In previous works we have reported that these Lewis-acid-based ionic liquids exhibit high chemisorption capacity towards carbon monoxide which can be employed to design novel ionic liquid-based CO separation processes. Therefore, accurate knowledge of the transport properties is of utmost importance given the considerable influence of viscosity on mass transfer. Results showed that both [hmim][Cl] and [hmim][Cu(Cl)x] ionic liquids exhibited shear-thinning non-Newtonian behaviour associated to the presence of a hydrogen-bonding network. However, the onset of shear-thinning progressively shifted to higher frequencies upon increasing temperature for all measured samples. Moreover, a drastic [hmim][Cl] viscosity decrease from 14.2 to 3.98 Pa s was observed after addition of 2 mol CuCl L−1 at 293 K. In addition, the parameters of Cross model that describes shear-dependant viscosity have also been obtained.