Desulfurization and Denitrogenation Using Betaine-Based Deep Eutectic Solvents

Abstract

Two betaine-based deep eutectic solvents (DESs), betaine/glycerol [1:2] and betaine/ethylene glycol [1:3], were used in separation processes encountered in the petroleum industry. Liquid–liquid equilibrium of six ternary systems {thiophene + betaine/glycerol [1:2] or betaine/ethylene glycol [1:3] + n-heptane}, {pyridine + betaine/glycerol [1:2] or betaine/ethylene glycol [1:3] + n-heptane}, and {toluene + betaine/glycerol [1:2] or betaine/ethylene glycol [1:3] + n-heptane} were measured at 298.15 K under atmospheric pressure. Phase diagrams of the ternary systems were represented by using the COnductor-like Screening MOdel for Real Solvents (COSMO-RS) and Non Random Two-Liquids equation (NRTL) models. In terms of selectivity and capacity values, betaine/ethylene glycol seems to be the most efficient deep eutectic solvent (DES) in this study. Optimal conditions for the separation process of thiophene, pyridine, or toluene from n-heptane were determined using synthetic fluids composed of n-heptane and 5% of thiophene, pyridine, or toluene. In all cases, the optimal conditions for the extraction were observed with a mass ratio m_DES/m_sample = 2 and a temperature fixed at 293.15 K. A fourth stage extraction using betaine/ethylene glycol [1:3] allows to remove 99.7% of pyridine and 57.5% of thiophene.