Insights for Designing the Hydrocarbon Recovery from Ionic Liquids by Distillation in the Aliphatic/aromatic Separation by Liquid-liquid Extraction

Abstract

Nowadays the aliphatic/aromatic separation by liquid-liquid extraction using ionic liquids (ILs) is an interesting topic in the search of a new class of separation processes for the oil industry. The wide majority of papers published until now has focused in maximizing the IL extractive properties as can be found in a recent review by Canales and Brennecke (2016); in addition, in the recent past, this search was also oriented to find a commitment election between IL extractive and physical properties, with especial focus on reducing the viscosity to limit its impact on mass transfer and pumping (Larriba et al., 2013a). However, the challenge in the development of this new liquid-liquid extraction technology based on ILs is the selective recovery of aromatics from the solvent. Although IL non-volatile character is suggested as a clear advantage for separation purposes, this is truly a limitation in the vapor-liquid separation as was reported in last papers dealing with the vapor-liquid equilibria involving aliphatics, aromatics, and ILs due to the pretty low equilibrium pressures (Navarro et al., 2015). In addition, the thermal stability of ILs is another drawback since scarce species could be used at industrial scale over 473 K (Navarro et al., 2013). Finally, extracted aromatics have not commercial purity and further purification is mandatory before the aromatic/IL separation (Larriba et al., 2013a). In this work, the simulation of three different recovery sections based on vapor-liquid separations was performed to give some remarks that can help to design distillation processes involving large amounts of ionic liquids. Seven ionic liquids among the most promising species proved so far were selected to completely cover the transferability between liquid-liquid and vapor-liquid equilibria (LLE and VLE, respectively). Aspen Plus commercial simulator was used implementing the Non-Random Two Liquids (NRTL) models from the experimental data regressions for the corresponding n-heptane + toluene + ionic liquid ternary systems. Aromatic recoveries and purities for three different process configurations were analysed in order to stablish the impact of the ionic liquid extractive and thermal properties on the design of a suitable recovery section from an industrial point of view.