DCA]-based ionic liquids for the extraction of sulfur and nitrogen compounds from fuels: Activity coefficients at infinite dilution

Abstract

Some petroleum processes need the removal of low level aromatic-sulfur and nitrogen compounds for many products, which are extremely important according to the new strict environmental regulations to reduce sulfur and nitrogen content compounds in liquid fuels. Thus the new, alternative solvents such as ionic liquids (ILs) have been proposed. ILs reveal a high selectivity and capacity of extraction of sulfur- and nitrogen-compounds from alkanes with little solvent loss during the process. The measurements of activity coefficients γ13∞ at infinite dilution of different solutes in the IL shows the effect of interactions between organic solutes, or water on the interfacial and bulk properties of the IL. The new (3-cyanopropyl)pyridinium dicyanamide, [N–C3CNPy][DCA] and (3-cyanopropyl)methylpyrrolidinium dicyanamide, [N–C3CNMPyr][DCA] were investigated in this work. The data were obtained using the gas-liquid chromatography technique. Measurements were undertaken at six temperatures, in 10 K intervals, in the range of (318.15–368.15) K. The solutes studied included both non-polar and polar compounds, as alkanes, alkenes, alkynes, as well as aromatic hydrocarbons, alcohols, water, ethers, ketones, and esters. The most important solutes used were thiophene, pyridine, and 1-nitropropane. Densities, ρ, measurements for a range of temperatures, T (298.15–368.15) K for the chosen ILs were undertaken at pressure, p = 101 kPa. The gas-liquid partition coefficients, KL at infinite dilution were calculated. The fundamental thermodynamic functions such as partial molar excess Gibbs energy, enthalpy and entropy at infinite dilution were calculated from the experimental data measurements to discuss the interaction between solutes and the ILs. The values of selectivity and capacity for three separation cases, viz. heptane/thiophene, heptane/pyridine, and heptane/1-nitropropane were calculated from γ13∞ values and compared to literature data for dicyanamide-based ILs. The Abraham solvation parameter model was presented for all solutes. The obtained results indicated that [N–C3CNPy][DCA] has large selectivity and capacity values for all three of the separation cases studied.