Low-cost N-methylpyrrolidone-based coordinated ionic liquids as extractants for separating aromatics from aliphatics

Abstract

The separation of aromatic and aliphatic hydrocarbons is one of the most challenging and energy-consuming operations in the petrochemical industry. In this study, a number of N-methylpyrrolidone (NMP)-based coordinated ionic liquids (ILs) with various metal salts were prepared and their separation performances were investigated. Among these coordinated ILs, NMP-0.1Fe(NO3)3·9H2O showed high selectivity and was used to separate toluene from n-heptane or cyclohexane. Fourier-transform infrared spectroscopy was used to verify that the synthesis of NMP-0.1Fe(NO3)3·9H2O was achieved. The toluene distribution coefficient and selectivity were 0.20 and greater than 70, respectively, for a 10 mol% toluene/n-heptane system, and 0.20 and 23.5, respectively, for a 20 mol% toluene/cyclohexane system. Changing the extraction temperature had little effect on the separation performance. The effects of the solvent dosage, initial concentrations of system components, and regeneration times were also investigated. Experimental liquid–liquid equilibrium data for the studied ternary systems were correlated with the non-random two-liquid model. The results show that NMP-0.1Fe(NO3)3·9H2O has potential industrial applications.