Recovery of biofuel additives isopropyl alcohol and diisopropyl ether using ionic liquids with intermolecular interactions and process design

Isopropyl alcohol (IPA) and diisopropyl ether (DIPE) are widely used as biofuel additives in fuel processing. When IPA is produced by propylene hydration, a by-product IPA and DIPE is made. Since the existence of azeotropic point formed between IPA and DIPE, the separation of the azeotrope is achieved using special distillation technologies in industry, which requires high energy consumption. Liquid-liquid extraction was used to separate the mixture due to its energy saving in this work. Three imidazolium-based ionic liquids (ILs) 1-butyl-3-methylimidazolium thiocyanate ([BMIM]SCN), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([BMIM]NTf2) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) were synthesized as the extractants. The influence of extraction time, extraction temperature, mass ratio of mixture (IPA + DIPE) to ILs and the initial content of IPA in the mixture (IPA + DIPE) on the extraction performance of ILs were studied. The optimal extraction conditions were determined using the response surface method (RSM). The results showed that the IL [BMIM]SCN had better extraction capacity for separation of the mixture (IPA + DIPE). The in-teractions between molecules were investigated by quantum chemical calculations. Finally, a conceptual sepa-ration process is designed to separate the mixture, which can provide a helpful technology to purify the biofuel additives.