Butanol production from an industrial sugary material (sugarcane and sweet sorghum juices) in an integrated fermentation–gas stripping process

Butanol is an attractive alternative to ethanol biofuel due to its better performance in engines, can be produced by fermentation in the same industrial plant, using common raw materials and equipment. Biobutanol can be produced by acetone–butanol–ethanol (ABE) fermentation. ABE cultivation presents butanol toxicity and substrate inhibition. In this work, the butanol production from a mixture of industrial juices of sugarcane (75%) and sweet sorghum (25%) was evaluated. A fed-batch strategy with integrated product recovery by gas stripping was studied using Clostridium acetobutylicum DSM 792. Tests were conducted in a 2.5 L bioreactor. Tests in batch mode were also done for comparison. The batch fermentation with an initial sugar concentration of 73 g/L ceased after 100 h, when the butanol concentration was 10.5 g/L (17.6 g/L total ABE), showing that the culture was unable to utilize all sugars (78% sugar conversion) because of the toxic effect of butanol. In the integrated process, the sugar and butanol concentration during fermentation did not exceed 60 g/L and 8 g/L, respectively. A sugar conversion of 99.5% and 18.6 g/L butanol (31.8 g/L total ABE) were observed after 142 h of fermentation. The butanol concentration in the condensate was high enough for effective phase separation, generating an organic phase containing up to 450 g/L butanol. The strategy used alleviated both butanol and substrate inhibition and allowed to recuperate a condensate containing high butanol concentration, which could reduce energy consumption in the final product recovery.