Volumetric and viscometric behaviour of the binary systems of N-methyldiethanolamine and diethanolamine with 1-butyl-3-methylimidazolium acetate at various temperatures

• Density and viscosity of two binary mixtures of MDEA + [bmim][acetate] and DEA + [bmim][acetate] are measured.
• Excess molar volumes (VE) and coefficients of thermal expansions (α) of these two binary mixtures are calculated.
• Using the viscosity data the molar activation entropy, enthalpy and Gibbs free energy of mixtures are obtained.
• The trend of density and viscosity of pure components are as follows: DEA > [bmim][acetate] > MDEA.
• For the DEA + [bmim][acetate] mixtures there is a minimum viscosity point in the DEA-rich region.

In the present work, density and viscosity of two binary mixtures of N-methyldiethanolamine (MDEA) and diethanolamine (DEA) with 1-butyl-3-methylimidazolium acetate ([bmim][acetate]) are measured. The experiments were carried out at atmospheric pressure and at T = (293.15 to 343.15) K for density and from 293.15 K to 353.15 K for viscosity over the whole range of mole fraction. Using the density and viscosity results, several physical and thermodynamic properties such as excess molar volumes (VE), coefficients of thermal expansions (α), viscosity deviation (Δη),molar activation entropy (ΔS), molar activation enthalpy (ΔH) and molar activation Gibbs free energy (ΔG) for these binary mixtures are calculated.The experimental results of the density and viscosity for the pure systems as well as the binary systems show a decrease with increasing temperature as expected. The results of density measurements show that over all ranges of temperatures investigated the density of the pure components show the following trend: DEA > [bmim][acetate] > MDEA. Therefore, in the binary mixtures of the (MDEA + [bmim][acetate]), the density of the mixture reduces with decreasing concentration of the ionic liquid and for the (DEA + [bmim][acetate]) mixture the density of the blend enhances to reduce the concentration of the ionic liquid. Moreover, the calculated excess molar volumes show a positive deviation from ideality for the two binary mixtures. The behaviour of change of viscosity against concentration for the (MDEA + [bmim][acetate]) system is different from the (DEA + [bmim][acetate]) mixture so that for the first system the value of the viscosity rises with increasing [bmim][acetate] mole fraction, but in the second system there is a minimum viscosity point in the DEA-rich region.