Efficient Separation of Isoamyl Alcohol from Fusel Oil Using Non-Polar Solvent and Hybrid Decanter–Distillation Process

Fusel oil is a fermentation by-product composed of a complex mixture of alcohols (ethanol, isoamyl, propanol, and butanol isomers) and water. The primary challenges lie in water separation and the recovery of the valuable component, isoamyl alcohol. In this work, we demonstrate an efficient separation process using a non-polar, non-toxic, water-immiscible solvent, namely hexane, to reduce the water content of fusel oil from an initial 14 wt.% to 1.46 wt.% at a solvent to fusel oil ratio of 1:1 and to 0.55 wt.% at a 4:1 ratio. The proposed separation process was designed with a 1:1 ratio to minimize equipment size. In the first step, a decanter vessel enabled phase separation, followed by two distillation columns. The bottom product from the second column achieved a purity of 99.29 wt.% isoamyl alcohol (97.91 wt.% isomers and 1.38 wt.% hexanol) with a recovery rate of 97.33%. The distillate flows were directed to the second decanter vessel, recovering 99.665% of hexane. This study confirms the effectiveness of the proposed process in separation of highly valuable isoamyl alcohol from fusel oil via a hybrid decanter–distillation scheme. The proposed process attains a specific energy consumption in the reboilers of 0.65 kWh per kilogram of product (equivalent to 1.21 kg of steam per kilogram of product). This represents a notable improvement compared to the configuration reported by other authors for the separation of isoamyl alcohol using divided-wall columns (DWC), which requires 2785 kJ per kilogram of product (i.e., 0.774 kWh per kilogram of product). An economic analysis was performed to compare the process of separating isoamyl alcohol from fusel oil using the minimum hexane ratio (1:1) and the maximum ratio (4:1). All cost values increased significantly with higher solvent ratio. Remaining challenges include the purification of waste aqueous streams and future valorization of the hexane–alcoholic mixture.