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.