Extractive fermentation with non-ionic surfactants to enhance butanol production

One of the major limitations in butanol fermentation is the end product toxicity which limits the butanol yield and increases the downstream processing costs. In this work, a range of non-ionic surfactants (Triton X 114, L64, L62LF, L61, and L62) was tested to enhance the acetone butanol (AB) production, and to extract and separate butanol from the fermentation broth. In biocompatibility tests, a volume fraction of 3% L62, L62LF, and L61 did not show inhibition to AB production in 72-h fermentation using Clostridium pasteurianum. Three-percent L64 reduced the AB yield whereas Triton X 114 (3%) inhibited the AB production. Further optimization with L62 at 6% resulted in a butanol yield of 225% higher than the control. The partition coefficient of butanol in L62-water two phase systems in cloud point extraction ranged from 3 to 4. A considerable enrichment of butanol (6 times) was achieved in the surfactant-rich phase over the control. In addition, the downstream process volume was reduced by 4-6 times. Butanol was separated from the surfactant-rich phase (obtained from model system) by evaporation between 120 and 130 degrees C. The butanol was enriched in the condensate reaching a concentration of 106.8 g l(-1) under which butanol automatically separated into two phases. The L62 was recovered by evaporation and reused for 3 times without affecting the partition coefficient, volume reduction, and butanol recovery in the surfactant-rich phase. The results demonstrated that the L62 not only significantly enhanced the butanol production but also functioned as a good extractant for separating butanol from the fermentation broth. (C) 2012 Elsevier Ltd. All rights reserved.