Extraction of aromatic and polyaromatic compounds with NMP: experimental and model description

•NMR analysis allows determining the composition of the samples with 0.3% accuracy•Oil and NMP mixtures present LLE in NMP/oil ratio ranging 0.4 to 4 mol/mol•Selectivity range 1-15 for aromatics and even higher for polyaromatics•Mod. UNIFAC (Dortmund) obtained the best predictions for compositions and selectivities Optimization of the extraction process for reducing aromatic and/or polyaromatic compounds is of primary interest in crude oil refining. Several solvents are described for carrying out such operations (furfural, N-methyl-pyrrolidone -NMP-, dimethyl-sulfoxide -DMSO-, …) and experimental data and model description are required for the correct design of the separation operations and the optimization of the conditions. In this work, liquid-liquid equilibria (LLE) data were determined for oil multicomponent mixtures formed by n-dodecane + mono-aromatic + poly-aromatic with NMP at ambient temperature (298.15 K) and pressure and covering a wide range of the solvent/oil ratios. A new analytical method based on NMR was developed, calibrated, and tested to fully determine the composition of equilibrium phases despite the high number of compounds. Obtained values for distribution constants and selectivities are higher than one and ranging 1-15, respectively, for aromatic compounds and even higher for polyaromatic components. Thus NMP appears as a suitable solvent for carrying both separations. The experimental data were predicted by several versions of the UNIFAC model, including the UNIFAC, modified UNIFAC (Dortmund), modified UNIFAC (NIST), and UNIFAC, including fitting parameters. Overall, modified UNIFAC (Dortmund) yields the best results, even when deviations obtained for some of the compositions are around 40% of the value, and simulations carried out with such models should be considered cautiously