Biobutanol and n-propanol recovery using a low density phosphonium based ionic liquid at T = 298.15 K and p = 1 atm

• Low density IL was used for recovery of butanol and propanol from aqueous solution.
• Raffinate phase contains mainly water due to less solubility of IL in water.
• Selectivity for extraction of 1-butanol ranges from 50 to 250.
• Tie line data correlated with NRTL and UNIQUAC model with RMSD <1%.

In this work, a phosphonium based ionic liquid (IL) trihexyl(tetradecyl) phosphonium bis(2,4,4-trimethylpentyl) phosphinate ([TDTHP] [Phosph]) has been used for the recovery of 1-propanol and 1-butanol. The hydrophobic IL having density (0.895 gm/cm3) lower than water has been specially chosen to recover alcohol from water. A type II ternary diagram with a large immiscible region was observed at T = 298.15 K and p = 1 atm. High values of selectivity ranging from 53 to 252 and 80 to 305 were observed for 1-propanol and 1-butanol, respectively. The distribution coefficient is greater than unity which indicates easier diffusion of solute from aqueous phase to extract phase. Hence less solvent (IL) is required for separation of specific amount of alcohol from water. The NMR spectra pointed out to the fact that the aqueous rich phase was free of IL and contains high percentage (∼92% mol) water. NRTL and UNIQUAC models show deviation (RMSD) in the range of 0.1–0.5% for both the systems.