Influence of solvent structure on the extraction of aromatics from FCC diesel and computational thermodynamics study

The separation of aromatics from fluid catalytic cracking (FCC) diesel is of great significance for environmental protection. The extraction ability of 1-methyl-2-pyrrolidinone (NMP), sulfolane (SUL), and 4-formylmorpholine (NFM) were studied by the liquid-liquid equilibrium (LLE) experimental, and the corresponding LLE data of NMP/SUL/NFM + 1-methylnaphthalene + dodecane systems were obtained. The calculated distribution coefficients and separation factors showed that the solubility of 1-methylnaphthalene was the highest in NMP and the selectivity of SUL to 1-methylnaphthalene was the strongest. The effects of solvent structures were investigated by a combination of experiments and quantum chemical calculations. The 1-methylnaphthalene is more soluble in solvents with planar molecular structure because the steric hindrance between the two molecules is smaller, and the group with more electronegative has higher selectivity for 1-methylnaphthalene. Moreover, the reduced density gradient (RDG) and atoms in molecules (AIM) analyzed found that the main extraction mechanism of the three solvents was van der Waals (VDW) and weak hydrogen bond, in which VDW was dominant. Finally, the binary interaction parameters of NRTL and UNIQUAC models were obtained, which make up for the blank in Aspen simulation for the separation of FCC diesel by organic solvents.