Optimization of extraction solvent-to-feed ratio: Aqueous ethanol mixture separation using [TDTHP][NTf2] ionic liquid

Separation of ethanol from its diluted aqueous solution by liquid-liquid extraction is modelled using ionic liquid tetradecyltrihexylphosphonium bis(trifluoromethylsulfonyl)imide as the extraction solvent. Based on the ternary phase equilibrium data, composition of the extract phase in counter-current separation equipment was computed showing a maximum in the ethanol-to-water mole ratio while the solvent-to-feed mole ratio was changing. Ethanol pre-concentration was further enhanced during the extraction solvent regeneration by ethanol (and water) stripping into inert gas. Final step of the proposed separation process was freeze-drying of the inert gas used for the extraction solvent regeneration. Temperature in the stripper was optimized for the minimum overall heat duty in the stripper and cooler/freezer. A simplified economic balance showed that operational expenditures connected with the proposed separation procedure attain only approximately 40% of those required for the ethanol separation by distillation.