Sugaring-out plus salting-out: A novel separation and purification technique for biofuel

Abstract

Using fermentation-based alcohol fuel as a substitute for fossil fuels is one of the means to alleviate the oil crisis and exhaust emissions. However, the low fermentation titer and the formation of azeotropes pose challenges to the separation process. In this paper, sugaring-out was proposed to separate a biofuel, namely isobutanol, as sugars are milder than salts and can be used as the fermentation media. The decrease in the water content is a linear function of the initial sugar concentration so that the isobutanol + water azeotrope was broken. The recovery of isobutanol in the 60 wt% isobutanol system using sucrose, glucose, and fructose reached 96.57 %, 97.01 %, and 97.98 %, respectively. After a two-step surgating-out + salting-out process, the isobutanol was purified to 99.82 wt%. The sugaring-out effects of different sugars were quantized by fitting the natural logarithm of isobutanol solubility with sugar molality in the aqueous phase. Due to the different number of hydroxyl groups in the sugar's structure, the order of the sugaring-out effect is glucose ≈ fructose > sucrose. This article provides detailed data on the sugaring-out separation of the concentrated biobutanol systems, which has a guiding role for the use of sugaring-out effect to separate other biofuels from fermentation broth.