Extraction of benzothiazole and thiophene from their mixtures with n-heptane using tetrahexylammonium bromide-based deep eutectic solvents as extractive denitrogenation and desulfurization agents

Abstract

The liquid-liquid extraction of a sulfur-nitrogen compound using deep eutectic solvents (DESs) was studied for the first time in this work. Benzothiazole (which contains both nitrogen and sulfur) and thiophene (which only contains sulfur) were separated from n-heptane using two tetrahexylammonium bromide-based DESs. Solubility data for benzothiazole and thiophene in the DESs and the DESs' constituents were determined at 298 K and atmospheric pressure. Subsequently, pseudo-ternary LLE data for the four systems {n-heptane + benzothiazole/thiophene + DES 1/DES 2} were determined at atmospheric pressure and a temperature of 298 K. The consideration of a pseudo-ternary system was validated showing that none of the DES′ constituents appears in the raffinate phase’ in the abstract. Both benzothiazole and thiophene were selectively extracted from their mixtures with n-heptane, but benzothiazole showed even higher affinity towards both DESs than thiophene due to the presence of nitrogen in benzothiazole. From the results derived from the experimental data, the selectivities and distribution ratios of benzothiazole and thiophene were calculated. These calculated values were able to show the potency of the DESs for both desulfurization and denitrogenation. In order to validate the experimental data, the equilibrium data were correlated with the NRTL model using ASPEN Plus. The modeled results showed a strong correlation with the experimental results.