Phase behaviour of 1-butyl-1-methylpyrrolidinium thiocyanate ionic liquid

The phase diagrams for the binary systems of {1-butyl-1-methylpyrrolidinium thiocyanate [BMPYR][SCN] + an alcohol (1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-undecanol, 1-dodecanol), or + water, or + aliphatic hydrocarbons (n-hexane, n-heptane, n-octane), or + cyclohexane, or + cycloheptane, or + aromatic hydrocarbons (benzene, toluene, ethylbenzene)} have been determined at atmospheric pressure using a dynamic method. The basic thermal properties of pure ILs, i.e. melting temperature and the enthalpy of fusion, the solid–solid phase transition temperature and enthalpy have been measured using a differential scanning microcalorimetry technique. The decomposition of [BMPYR][SCN] was detected. The density and viscosity of the IL at 298.15 K were measured. (Solid + liquid) phase equilibrium diagrams with complete miscibility in the liquid phase region were observed for the systems involving alcohols and water. A decrease in the solubility of [BMPYR][SCN] in alcohols was observed with an increase of the alkyl chain length of an alcohol. (Solid + liquid) phase equilibrium diagrams with immiscibility in the liquid phase region were observed for the systems involving hydrocarbons. As for all ionic liquids (ILs) solubility decreases with an increase of number of carbon atoms in n-alkanes, cyclohydrocarbons, or of substituents at the benzene ring. The correlation of the experimental data has been carried out using the NRTL equation. The data presented here have been compared to the systems published earlier for the thiocyanate based ILs and for ILs with 1-butyl-1-methylpyrrolidinium cation. The influence of the cation and anion on the phase behaviour has been discussed.

► We synthesized new ionic liquid [BMPYR][SCN].
► We found low enthalpy of melting and high enthalpy of solid–solid phase transition.
► We examined phase equilibrium changes, SLE and LLE with alcohols, water and hydrocarbons.
► [BMPYR][SCN] may be proposed as a new entrained for the separation processes.