Liquid–liquid extraction of sulfur compounds from heptane with tricyanomethanide based ionic liquids

Abstract

Liquid–liquid phase equilibrium (LLE) data for the {tricyanomethanide-based ionic liquid (1) + tiophene, or benzothiophene (2) + heptane (3)} ternary systems were experimentally determined at T = 308.15 K and at pressure p = 0.1 MPa. In this work three ILs, that is: 1-butyl-1-methylmorpholinium tricyanomethanide, [BMMOR][TCM], 1-butyl-1-methylpyrrolidinium tricyanomethanide, [BMPYR][TCM] and 1-hexyl-1-methylmorpholinium tricyanomethanide, [HMMOR][TCM] have been investigated. The high solubility of sulfur compounds and practically complete immiscibility of heptane with the tested ionic liquids have been observed. The selectivity, S12 and solute distribution ratio, k12 derived from the experimental equilibrium data, were calculated and used to determine the efficiency of these ionic liquids as solvents for the extraction of sulfur compounds from model fuels. The experimental results have been compared to literature data for other tricyanomethanide-based ILs and were discussed in terms of the selectivity and solute distribution ratio of separation of related systems. The NRTL equation was successfully used to correlate the experimental tie-lines. The average root mean square (RMSD) of the phase composition was less than 0.8%. Additionally, the oxidative-extractive desulfurization of model fuels has been studied using tricyanomethanide-based ionic liquid (IL): [BMMOR][TCM] and [BMPYR][TCM] and deep eutectic solvent (DES): ([BMMOR] [Br] + diethylene glycol). Model liquid fuel was prepared by dissolving benzothiophene in octane, 500 ppm of sulfur. Oxidation was achieved by adding hydrogen peroxide and acetic acid to the mixture. Different parameters such as a type of extractant, extraction time, and oxidant to sulfur molar ratio and temperature were optimized. The addition of oxidizing agent improves the efficiency of sulfur extraction and the highest extraction efficiency, equal to 69.1%, was obtained for [BMMOR][TCM] at T = 318.15 K.