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Ionic liquids (ILs) are eco-friendly solvents due to their low vapor pressure. Properties such as density should be known as it affects the mass transfer rates. Due to its limitless combinations, it is impractical to measure densities experimentally. For the first time, the cohesion factor in the cubic equations of state (CEOS) is used to predict the densities of six commercial ILs, namely, 1-ethyl-3-methylimidazolium methane sulfonateTris(2-hydroxyethyl)-methylammonium methyl sulfate [TEMA][MeSO 4 ], and trihexyl(tetradecyl) phosphonium bis(2,4,4-trimethylpentyl) phosphinate [TDTHP] [Phosph]. CEOS models such as predictive Soave−Redlich−Kwong (PSRK) coupled with cohesion factor gave better results when compared to the correlations such as Reid et al. (RR), Mchaweh et al. (MH), and the linear generalized model (LGM). In this work the PSRK equation of state (EOS) with the derived NSM1 alpha function and PSRK with original SRK alpha function were used for the prediction. PSRK EOS model with NSM1 alpha function and PSRK EOS with original SRK alpha function proved very accurate with average minimum deviation of 0.02 % to 0.44 % and 0.29 % to 0.66 % from experimental values for six ILs, respectively.

Biobutanol obtained via an acetone–butanol–ethanol (ABE) fermentation process is now considered a potential biofuel. In recent times low density phosphonium cations were found to remove butanol from aqueous solutions. In this regard, low density phosphonium-based ionic liquids (ILs) trihexyl­(tetradecyl)­phosphonium dicyanamide [TDTHP]­[DCA] and trihexyl­(tetradecyl)­phosphonium decanoate [TDTHP]­[DEC] have been used for the separation of 1-butanol from aqueous solution. Ternary liquid–liquid equilibrium data for IL(1)–1-butanol­(2)–water­(3) are measured at T = 298.15 K and p = 1 atm. Butanol partition coefficients are obtained in the range of 25–85 and 20–290 for [TDTHP]­[DCA] and [TDTHP]­[DEC], respectively. 1H NMR spectra indicates the absence of IL and water in the raffinate and extract phase, respectively. This experimentally confirms that there will be negligible cross-contamination of water and IL in either phase. The separation factor of butanol over water approaches infinity for both systems. A wider spread of binodal curve indicated a higher recovery of butanol at different feed concentrations. The experimental data were compared with excess Gibb’s free energy models, namely the nonrandom two liquid (NRTL) and the universal quasichemical (UNIQUAC) models. NRTL and UNIQUAC gave root mean square deviation (RMSD) values in the range of 0.12–0.14% and 0.48–0.55%, respectively, for both ILs. Further the predictive ability of a statistical mechanical framework was also performed using the well-known COSMO-RS model. The COSMO-RS model gave RMSD values of 18.67% and 16.21% for the systems containing the ILs respectively, [TDTHP]­[DCA] and [TDTHP]­[DEC].