Characterization of gas stripping and its integration with acetone–butanol–ethanol fermentation for high-efficient butanol production and recovery

• High-titer n-butanol was produced by C. acetobutylicum in a fibrous bed bioreactor.
• In situ gas stripping for butanol separation alleviated butanol toxicity in the fermentation.
• Two-stage gas stripping produced butanol at a high titer of >500 g/L (600 g/L ABE).
• This process can produce n-butanol with greatly reduced energy consumption.

Two-stage gas stripping coupled with acetone–butanol–ethanol fermentation in a fibrous bed bioreactor was established for energy-efficient butanol recovery. The impacts of process parameters including butanol concentration, temperature and cell density with feed, gas flow rate, and cooling temperature on the efficiency of the gas stripping system were studied. High butanol concentration, low cell density and cooling temperature increased butanol titer in the condensate. The butanol titer in the condensate increased when stripping temperature increased from 25 to 55 °C, and decreased when temperature was above 55 °C. The optimal gas flow rate was 1.6 L/min, above which more water was stripped off and the condensate was diluted. After process optimization, 48.5 g/L butanol (73.3 g/L ABE) was produced in the fed-batch fermentation with in situ gas stripping due to the reduced butanol inhibition on cells. The condensate containing 147.2 g/L butanol (199.0 g/L ABE) was produced by the first-stage gas stripping, while a highly concentrated condensate containing 515.3 g/L butanol (671.1 g/L ABE) was obtained from the second-stage gas stripping. This process can significantly reduce energy consumption in the final product recovery.