Method for producing butanol using extractive fermentation with electrolyte addition

A method for recovering butanol from a fermentation medium, the method comprising:

• a) providing a fermentation medium comprising butanol, water, at least one electrolyte at a concentration at least sufficient to increase the butanol partition coefficient relative to that in the presence of the salt concentration of the basal fermentation medium, and a genetically modified microorganism that produces butanol from least one fermentable carbon source;
• b) contacting the fermentation medium with i) a first water-immiscible organic extractant selected from the group consisting of C12 to C22 fatty alcohols, C12 to C22 fatty acids, esters of C12 to C22 fatty acids, C12 to C22 fatty aldehydes, C12 to C22 fatty amides, and mixtures thereof, and optionally ii) a second water-immiscible organic extractant selected from the group consisting of C7 to C22 fatty alcohols, C7 to C22 fatty acids, esters of C7 to C22 fatty acids, C7 to C22 fatty aldehydes, C7 to C22 fatty amides, and mixtures thereof to form a two-phase mixture comprising an aqueous phase and a butanol-containing organic phase;
• and
• c) recovering the butanol from the butanol-containing organic phase to produce recovered butanol.