Phosphonium based ionic liquids: Potential green solvents for separation of butanol from aqueous media

Depleting conventional resources leads to the development of alternate energy sources as a result of rising energy demand. As a result of its high energy content, bio-butanol is an appealing fuel. Yet, a fermentation method of butanol generation by acetone *butanol*ethanol using solventogenic Clostridium has significant limitations. In addition to repressing microbial movement (normally greater than 10 g/L), it also affects their production. In order to separate butanol from aging broth, various separation techniques can be used. As an alternative to traditional solvents, ionic liquids can be used as novel extractants to counter these problems. In the present paper, separation of butanol (simulated) from aqueous media utilizing typical hydrophobic ionic liquids was studied at 298±1 K. Various parameters, such as distribution coefficent (Kd), extraction efficiency (%η), diffusion coefficient, solvent-to-feed ratio diffusion coefficient, and number of stages necessary for butanol separation, have been studied. Separation of butanol from aqueous solutions (0.25–2.5 wt%)Trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) amide-CYPHOS IL 109 THTDP [NTF2] ionic liquid, (purity ≥95.0%), Trihexyltetradecylphosphonium chloride-CYPHOS IL 101 THTDP[Cl] (purity ≥95.0%), at ambient conditions (298.15±1 K) was carried out. The average separation efficiency of butanol was observed highest (%E 80.43) with hydrophobic THTDP [NTF2] ionic liquid. The maximum average distribution coefficient (Kd) 11.055 was found for RTIL ionic liquid THTDP [NTF2] compared to THTDP [Cl] ionic liquid. Minimum solvent-to-feed ratio was observed for ionic liquid, THTDP [NTF2], (S/Fmin, 0.3829) and for THTDP [Cl], (S/Fmin, 0.201). Due to excellent/better mixing blending properties with gasoline and diesel fuels, recovery of this prospective butanol by ionic liquid could be utilized in gasoline-driven combustion systems. It would be a more promising alternative to ethanol and gasoline for large-scale applications. Thus, after evaluating the above parameters, it has been determined that butanol would be the most effective renewable biofuel for commercialization using ionic liquids as an extractant.