Purification of 1-butanol from rich and lean aqueous heteroazeotropic mixture by sponge-like ionic liquid process

The Acetone-Butanol-Ethanol (ABE) fermentation process is a promising approach for sustainable biobutanol production. However, separation and purification of butanol following membrane-based or distillation separation processes remain challenging due to the formation of a water-butanol heteroazeotropic mixture (55.5 wt% 1-butanol), requiring multiple distillation columns and generating both lean and rich aqueous phases. In this study, a novel sponge-like ionic liquid extraction process was employed to recover 1-butanol from these aqueous mixtures using 1-Methyl-3-octadecylimidazolium bis(trifluoromethyl sulfonyl)imide (C₁₈MIM[Tf₂N]). The liquid C₁₈MIM[Tf₂N] was contacted with a rich and lean butanol aqueous phases at temperatures above IL´s melting point (60 °C to 90 °C) and an IL/aqueous ratio of 1:1. After phase separation, the IL solidified at room temperature, allowing the extraction of the dissolved component via centrifugation.

The results indicated that optimal recovery from the lean phase occurred at 80 °C, achieving enhanced solubility of 1-butanol in the IL while minimizing losses. Under these conditions, the remaining aqueous phase contained only 1 wt% 1-butanol, and over 95 % of the butanol was recovered from the IL. For the rich phase, high butanol concentrations altered the hydrophobicity of C₁₈MIM[Tf₂N], causing water retention and resulting in an aqueous phase with a higher butanol content. These findings highlight the potential of sponge-like IL extraction for efficient butanol purification, reducing energy-intensive distillation steps.