Extraction of Aromatic Hydrocarbons from Aromatic/Aliphatic Mixtures Using Chloroaluminate Room-Temperature Ionic Liquids as Extractants

摘要

The extraction of aromatic hydrocarbons from aromatic/aliphatic mixtures was investigated using chloroaluminate ionic liquids as extractants. Three types of chloroaluminate ionic liquids, i.e., 1-butyl-3-methylimidazolium chloride—aluminum chloride (BMIC/AlCl_3), trimethylamine hydrochloride— aluminum chloride (Me_3NHCl/AlCl_3), and triethylamine hydrochloride—aluminum chloride (Et_3NHCl/AlCl_3), were prepared and used to extract aromatic hydrocarbons. Chloroaluminate ionic liquids have strong aromatic hydrocarbon solvent capacities, small solvent capacities for n-heptane, and good extractive performances. BMIC-2.0AlCl_3 exhibits better extractive performance than Me_3NHCl-2.0AlCl_3 and Et_3NHCl-2.0AlCl_3. Both the benzene distribution coefficient and aromatic-heptane selectivity increase with an increasing ratio of AlCl_3/organic salt (Et_3NHCl) in ionic liquids. The steric effect of substituent groups on the benzene ring lowers the aromatic extractive performance. The π complextion between aromatic molecules with highly delocalized π electron and Lewis acid species (Al_2Cl_7~- or AlCl_3) facilitates the aromatic absorption of chloroaluminate ionic liquids. A lower temperature is favorable for aromatic extraction of the ionic liquids. The regeneration tests show that the used ionic liquids can be recovered through vacuum distillation effectively.