Extraction of Butylbenzene from Dodecane Using Hexafluorophosphate-Based Ionic Liquids: Effect of Cation Change

Abstract

Three ternary liquid systems, {dodecane + butylbenzene + [bmim]PF 6 , [hmim]PF 6 , or [omim]PF 6 }, were studied at 313 K and 333 K and atmospheric pressure. Equilibrium tie-line data were measured and plotted for all systems. The effects of the alkyl group in 1-alkyl-3-methylimidazolium hexafluorophosphate, temperature, and solvent-to-feed ratio upon solubility, selectivity (S), and distribution coefficient (K) were investigated. The liquid− liquid equilibrium (LLE) data were correlated sufficiently with both universal quasichemical activity coefficient (UNIQUAC) and nonrandom two-liquid (NRTL) models, and the interaction parameters between each of the three pairs of components for the UNIQUAC and the NRTL models were estimated as a function of temperature. The root-mean-square deviations between the correlated results and experimental data were calculated and found to be satisfactory. ■ INTRODUCTIONLiquid−liquid extraction has been widely used to separate aromatics from aliphatic hydrocarbons. It has proven to be more feasible than distillation for hydrocarbons containing 20 wt % to 65 wt % aromatic content, as it does not require hydrogen and is carried out at atmospheric pressure and comparatively low temperatures. 1 This process aims to enhance middle distillate properties such as the smoke point of kerosene, the cetane number of diesel, or the viscosity index of mineral oil.Appreciable research has been devoted to examine the properties of ionic liquids (ILs). They are considered "green solvents" because of their negligible vapor pressure which implies no significant contamination to the atmosphere. On the other hand, ILs demonstrate high thermal/chemical stability, and they are not flammable nor explosive. They also exhibit a wide liquid temperature range. Another key feature of ILs is tailorability of their physicochemical properties by designing different cation−anion combinations to meet specific needs. 2−5 Recent research has shown that a large number of ionic liquids have better selectivity and capacity in the extraction of aromatics from aromatic/aliphatic mixtures than typical solvents such as sulfolane 6,7 and NMP. 8 Meindersma et al. 9 found that [bmim]BF 4 , [mebupy]BF 4 , [mebupy]CH 3 SO 4 , and [emim]C 7 H 7 SO 3 gave higher distribution coefficients of toluene and toluene/heptane selectivities than with sulfolane. They also studied the effect of alkyl chain length in the cation of [emim]BF 4 and [bmim]BF 4 ionic solvents.Arce et al. 10 investigated the effect of alkyl-chain length in the cation of the 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)-sulfonyl}amide on the extraction of benzene from hexane. Poole and Poole 11 reviewed several systems and stated that the cation plays a dominant role in establishing selectivity. This work is a continuation of our research on the extraction of aromatic compounds from alkane/aromatic mixtures in the middle distillate range using ILs as solvents. 12−14 Dodecane and butylbenzene were selected as representatives of the aliphatic and aromatic groups ...

Effect of Solvent Cation Alkyl-Chain Length on the Separation of Butylbenzene from n-Tetradecane Using Hexafluorophosphate-Based Ionic Liquids at (313.15 and 333.15) K and 101.3 kPa

“…Figure indicates that increasing the temperature from 313.15 to 333.15 K has slight effect on solvent selectivity, and values remain higher than unity. This also agrees with the results obtained by Al-Rashed et al…”

“…Figures and compare our results to data of the extraction of butylbenzene from n -decane, n -undecane, and n -tetradecane using sulfolane (obtained by Kao et al) and from n -dodecane using [bmim]­[PF 6 ], [hmim]­[PF 6 ] and [omim]­[PF 6 ] (obtained by Al-Rashed et al). The distribution coefficients in Figure reveal that ionic liquids can be used to extract butylbenzene from n -tetradecane with efficiencies superior to those obtained using the conventional solvent, sulfolane, even at higher temperatures (348.15 and 373.15 K).…”

“…Measured distribution coefficient ( K ) against butylbenzene mole fraction in the solvent-rich phase ( x 2 ) for the system: paraffin (1) + butylbenzene (2) + solvent (3): •, at 313.15 K and n -tetradecane (1) + butylbenzene (2) + [omim]­[PF 6 ] (3); ○, at 313.15 K and n -dodecane (1) + butylbenzene (2) + [omim]­[PF 6 ]; ■, at 323.15 K and n -tetradecane (1) + butylbenzene (2) + sulfolane (3); □, at 348.15 K and n -tetradecane (1) + butylbenzene (2) + sulfolane (3); ⧫, at 373.15 K and n -tetradecane (1) + butylbenzene (2) + sulfolane (3); △, at 348.15 K and n -undecane (1) + butylbenzene (2) + sulfolane (3); and ▼, at 348.15 K and n -decane (1) + butylbenzene (2) + sulfolane (3) …”

“…The experimental data were correlated to the UNIQUAC thermodynamic model of Abrams and Prausnitz. , The model gave an accurate representation of experimental LLE data in systems containing ionic liquids. − ,− …”

“…Ionic liquids and paraffins have very low mutual solubility, and most ionic liquids are insoluble in paraffin-rich phases with paraffins > C 10 , producing a ready raffinate product without wasting any solvent. − The solubility of paraffin in the ionic-rich phase is also very low, reducing the cost of solvent regeneration by simple flash distillation or stripping . Ionic liquids are nonvolatile, which makes them environmentally attractive alternatives to conventional solvents that contaminate the atmosphere. − They also can be produced in a variety of anion–cation combinations, which allows optimization of the separation process. − …”