Biobutanol is an attractive renewable transportation biofuel owing to its higher energy density, lower vapor pressure, and higher hydrophobicity compared to ethanol. It is produced by anaerobic microorganisms in the acteone–butanol–ethanol (ABE) fermentation. Key problems here are the high substrate cost, low yield, and high recovery cost for downstream processing. To decrease product recovery costs, various methods, such as gas stripping, vacuum fermentation, and liquid-liquid extraction have been tested to enhance recovery performance. The salting-out extraction (SOE) separates hydrophilic targets from aqueous solution with an organic solvent as extractant and salt as salting-out reagent.

Zhilong Xiu and colleagues, Dalian University of Technology, China, investigated the influences of different SOE systems using a synthetic ABE solution. The best system to extract butanol was composed of acetone and dipotassium hydrogen phosphate. Subsequently, the concentration of acetone and dipotassium hydrogen phosphate was optimized to achieve a high partition coefficient. In a last step the recovery from a real fermentation broth was analyzed under these optimized conditions. The partition coefficient, extraction yield, and concentration fold of butanol reached up to 63.13, 98.10 %, and 1.53, respectively. Simultaneously, cells and proteins are removed. Therefore, the SOE system seems to be an attractive alternative for the downstream processing of butanol from fermentation broth.

• Selection and optimization of a salting-out extraction system for recovery of biobutanol from fermentation broth,
  Yaqin Sun, Ling Yan, Hongxin Fu, Zhilong Xiu,
  Eng. Life Sci. 2013.
  DOI: 10.1002/elsc.201300033