Research on separation sulfides from fuel oil using sulfolane: Liquid-liquid equilibrium and mechanism exploration

Abstract

Separation of sulfides from fuel oil is of great significance for environmental protection. In this paper, the organic solvent (sulfolane) was selected to separate sulfides (thiophene and 2-methylthiophene) from model fuel oil (n-heptane). The liquid–liquid equilibrium data of the mixtures (n-heptane + thiophene/2-methylthiophene + sulfolane) were measured at 303.15, 313.15 and 323.15 K under 101.3 kPa. The mass conservation of the experimental data were checked, and the reliability of the tie-lie data were evaluated by the Bachman, Hand and Othmer-Tobias equations. The extraction performance of sulfolane was assessed through the separation factor and partition coefficient, and compared with those for other reported solvents, indicating that sulfolane has better extraction performance for thiophene compared with 2-methylthiophene. Then, the quantum chemical calculation was applied to found the separation mechanism of sulfolane. The analysis of electrostatic potential, interaction energies, and reduced density gradient showed that the main interactions between sulfolane and thiophene (or 2-methylthiophene) were van der Waals and weak hydrogen bond forces. Finally, the non-random two-liquid theory (NRTL) and universal quasi-chemical theory (UNIQUAC) models were applied to fit the tie-line data of the investigated mixtures with the root-mean-square deviation (RMSD) lower than 0.01. The mixed surface analysis method based on Gibbs energy topology is used to verify the binary interaction parameters, which provides basic data for simulating the separation process of sulfide in fuel oil.