Solvents evaluation for extraction of polycyclic aromatics from FCC diesel: Experimental and computational thermodynamics

Abstract

The high content of aromatics in fluid catalytic cracking (FCC) diesel, especially bicyclic aromatics, seriously hindered the quality upgrading of FCC diesel. Liquid-Liquid extraction is an effectively method to reduce the content of aromatics in FCC diesel and improve oil quality. In this work, [EMIM][NTF2] (1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfony)imide) was selected as the most appropriate extractant from 44 ILs candidates, the common organic solvents (i.e., sulfolane (SUF), 1-Methyl-2-pyrrolidinone (NMP)) and [EMIM][NTF2] were used to separate 1-Methylnaphthalene from the model oil of 1-Tetradecene + n-Hexadecane + 1-Methylnaphthalene mixtures. The quaternary liquid–liquid equilibrium experiment was carried out at 303.15 K, and the results indicate that IL [EMIM][NTF2] show the higher selectivity than the common solvents. After recycling for 6 times, the extraction efficiency of [EMIM][NTF2] has hardly decreased. Quantum chemical (QC) calculation were performed to study the interaction mechanism between three different extractants and mixtures at the molecular level. Molecular polarity index (MPI) analysis indicated that 1-Methylnaphthalene was more soluble in extractants because its MPI values was closer to that of the extractants. The common results of energy decomposed, independent gradient model and atoms in molecules analysis showed that the interaction energy between 1-Methylnaphthalene and extractants is dominated by weak hydrogen bond and dispersion (e.g., van der Waals). Compared to aliphatic hydrocarbons (i.e. 1-Hetradecene and n-Texadecane), the interaction energy between extractants and 1-Methylnaphthalene systems are larger because of the existence of C-H⋅⋅⋅π and hydrogen bond interaction.