Toluene/n-Heptane Separation by Extractive Distillation with Tricyanomethanide-Based Ionic Liquids: Experimental and CPA EoS Modeling

Abstract

This work covers the phase equilibrium characterization of systems containing n-heptane, toluene, and two tricyanomethanide-based ionic liquids (ILs), 1-ethyl-3-methylimidazolium tricyanomethanide ([C2C1im]­[TCM]) and 1-butyl-4-methylpyridinium tricyanomethanide ([4-C4C1py]­[TCM]). Aiming at evaluating these ILs for the n-heptane/toluene extractive distillation, the vapor–liquid–liquid equilibria (VLLE) and vapor–liquid equilibria (VLE) were determined by headspace-gas chromatography (HS-GC) in the whole composition range at temperatures from 323.2 to 423.2 K and solvent to feed (S/F) ratios of 1, 5, and 10. Experimental results were modeled with the Cubic Plus Association (CPA) Equation of State (EoS). ILs’ molecular parameters were regressed through density and heat capacity data and further used to describe the binary and ternary mixtures phase equilibria. Extractive distillation with ILs stands as a powerful approach for the dearomatization of liquid fuels, whereas the combination of HS-GC methodology and CPA EoS has been revealed as an ideal strategy to further exploring this new technology.

Extending the UNIFAC model for ionic liquid–solute systems by combining experimental and computational databases

“…For the theoretical selection of ILs as separation solvents, the modeling of thermodynamic properties of IL and IL‐involved mixtures is of central importance. Ab initio methods (e.g., quantum chemical calculations and molecular dynamics), classical activity coefficient models (e.g., NRTL and UNIQUAC), and equation of state methods (e.g., PC‐SAFT and PSRK) have been successfully applied for this purpose. However, these methods require either high computational cost or a number of molecule‐specific parameters fitted from experimental data, making them inapplicable for extensive IL screening.…”

Simplified COSMO‐SAC‐based phase equilibria predictions for extractive distillation of toluene–heptane mixtures using ionic liquids

“…Of these processes, de-aromatization of refinery streams by extractive distillation using novel solvents is one of the recent developments. [1][2][3][4] In extractive distillation, ILs act as the mass-separating agent or entrainer for aliphatic-aromatic separation. The choice of IL mainly depends on its extractive properties (capacity, selectivity, and relative volatility) and thermophysical properties (viscosity, thermal stability, etc.).…”

“…Recent studies on phase equilibria of alkane/aromatic/IL ternary mixtures indicate the establishment of vapor-liquid-liquid equilibria (VLLE) at certain conditions. 2,3 These reported mixtures consist of a two-phase liquid having an ILrich bottom phase (dominant IL concentration) and a lighter top phase that is almost entirely free from IL. 2,3,5 The vapor-phase exclusively consists of the aliphatic-aromatic components, because typically ILs have negligible vapor pressures.…”

“…The reference data used in this work have been obtained from the previous VLLE experiments by Navarro and coworkers involving the separation of toluene/1-heptane mixture using ILs. [1][2][3][4]24,25 Normalized experimental mole-fraction data for various systems at their corresponding temperature, pressure, and IL to feed (S/F) ratio have been depicted in Table S1. Except for sys-tem6 and system7, IL to feed (S/F) ratio varies from S/F = 1 to S/F = 10 for experimental data at 323 K. VLLE data for system6 and system7 have been obtained only at S/F = 10 because the LLE region becomes unstable for lower IL to feed ratios for these systems.…”

Stripping Columns to Regenerate Ionic Liquids and Selectively Recover Hydrocarbons Avoiding Vacuum Conditions

“…Non-Random Two Liquids (NRTL) has been the most extended thermodynamic model used to fit the VLE experimental data due to the easy and accurate fitting of the required parameters 27,41,49 . However, binary interaction parameters were not transferable from binary to ternary or more complex systems when ILs are presented, limiting their use in a process simulator as advised in a recent effort on modelling the complete phase equilibria for this separation and two IL solvents with CPA EoS 50 . Therefore, only approximate methods based on the hydrocarbon K-values, taking them independent from composition, have been developed and used in the literature [19][20][21][22][35][36][37] .…”