Breaking Biofuel-Based Isobutanol-Water Azeotropes by Salting-out Effect

Isobutanol is a promising biofuel that can be produced via fermentation. However, its separation from water is challenging due to the formation of an azeotrope during distillation. This study investigates the effects of K₃PO₄ concentration and temperature on the phase separation of isobutanol–water azeotropes. Results show that increasing salt concentration significantly enhances isobutanol recovery and dehydration efficiency, while temperature has a relatively minor effect. Isobutanol recovery exceeded 99.9% and dehydration ratios surpassed 90% at higher salt concentrations, with minimal influence from temperature. The water content in the isobutanol-rich phase decreases sharply with salt addition, and the solubility of isobutanol in the aqueous phase shows a strong logarithmic decline. A good linear fit (R² > 0.997) confirms the reliability of the correlation. These findings demonstrate that salting-out using K₃PO₄ is a highly effective strategy for improving the separation of fermentation-based isobutanol.