ABSTRACT
Ionic Liquids (ILs) are a unique class of designer compounds which are salts constituted of cations and anions having a melting point below 100°C. Their properties like negligible vapor pressure, lower melting point, higher ionic conductivity, higher thermal and chemical stability, and tunable physical and chemical properties have made them useful solvents in refineries and the petrochemical sector. This paper precisely reviews the properties and selection of suitable ionic liquids as solvents for greener and efficient separation of various aromatic/aliphatic component systems by liquid–liquid extraction. The conventional sulfolane process employed in the petrochemical industry for the extraction of the aromatics Benzene, Toluene, Ethyl benzene, Xylene (BTEX) from aromatic rich streams of naphtha cracker and reformer, uses the molecular solvent sulfolane which has few physical and chemical limitations when used as an extracting solvent. Replacing it with ionic liquids, which can be tailor-made to achieve desirable solvent characteristics, results in higher selectivity, distribution ratio, purer products, efficient solvent recovery and lower process cost. This paper reports some of the many experimental Liquid–Liquid Extraction (LLE) data collected from the literature regarding IL selectivity and aromatic distribution ratio at particular raffinate compositions, for separation of (aromatic BTEX/aliphatic mixture + IL) systems at various temperatures and atmospheric pressures along with the important conclusions analyzed. This paper focuses mainly on the limitations of sulfolane and highlights the efficiency and greenness of ILs as solvents for aromatic/aliphatic separations. Structural dependency of IL is also reviewed which would help selecting suitable ILs for particular aromatic/aliphatic separations.
