Oil extraction desulfurization based on ionic liquid: Back-extractant screening, experiment and process simulation

A comprehensive back-extractant screening method was first developed for regenerating ionic liquids (ILs) after oil extraction desulfurization (EDS). Statistical analysis was performed using the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) with the Entropy Weighting Method (EWM) on screening indices obtained based on the COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS) and the Quantitative Structure Activity Relationship (QSAR) models. CCl4 was selected as the optimal back-extractant among 196 candidates for regenerating the IL, 1-butyl-3-methylpyridinium dicyanamide ([BMPy][DCA]), targeting the simultaneous removal of thiophene (TS), benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The experimentally measured hexary liquid-liquid equilibrium (LLE) confirmed the satisfactory selectivities and distribution coefficients of CCl4. Based on the NRTL parameters correlated from the LLE data, a complete EDS process including IL-extraction and IL-regeneration was established and evaluated economically based on the total annual cost (TAC). The results demonstrated that this process significantly decreased the sulfur content from 500 ppm to less than 10 ppm. The study results verified the feasibility and effectiveness of the proposed method and showed the excellent industrial performance of the selected IL and back-extractant.