Application of selected ionic liquids for different separation problems : liquid-liquid equilibria and activity coefficients at infinite dilution

Abstract

This work focusses on the application and pre-screening of selected ILs for different industrial separation problems based on limiting activity coefficients at infinite dilution, and liquid-liquid equilibrium data at different temperatures. The selected ionic liquids for pre-screening based on activity coefficients at infinite dilution data include (1,3- dimethyimidazolium dimethylphosphate, trioctylmethylammonium chloride, trihexyltetradecylphosphonium dicyanamide, 2,3-dihydroxypropyl-N-methyl-2- oxopyrrolidinium chloride, 2,3-epoxypropyl methyl-2-oxopyrrolidinium chloride) and deep eutectic solvent (1-butyl-3-methylimidazolium chloride + glycerol) at 1:2 molar ratio. These ionic liquids were tested in 33 solutes (alkanes, alkenes, alkynes, alcohols, tetrahydrofuran, ketones, aromatic hydrocarbons, thiophene, acetonitrile) and water at T = (313 – 343) K and at p = 101 kPa. The use of ionic liquid as a stationary phase on the column loading ranged between (30 – 36) % by mass. Thermodynamic functions at infinite dilution such as (Gibbs free energy, , entropy term, Tref and partial molar enthalpy, ) were also computed to further elucidate the types of intermolecular interactions existing between solutes and the investigated ionic liquids. The separation potential of the ionic liquids was determined from the selectivity ( ), and capacity ( ), values. Different ionic liquids (1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolim dicyanamide, 1,3-dimethylimidazolium dimethylphosphate) were also tested in the separation of azeotropic mixture (ethyl acetate/hexane) and in the desulfurization (thiophene/hexadecane or octane) process. The extraction process was conducted at varying temperatures, T = (308 and 298) K and at p = 101 kPa. The results were compared to previously published ionic liquids involving thermodynamic data found in the literature. The separation capacity was based on the calculated values of selectivities (S) and distribution ratio (β). The data was successfully correlated using the thermodynamic non-random two liquids (NRTL). From this study, it was found that the investigated ionic liquids showed some possible application for selected industrial separation problems.