Optimization of butanol production from tropical maize stalk juice by fermentation with Clostridium beijerinckii NCIMB 8052

► Optimization for butanol yield was conducted using response surface methodology. ► Optimum conditions were predicted, and maximum butanol yield was estimated. ► Individual and interactive effects of parameters on butanol yield were evaluated. ► Agitation greatly influenced the butanol/acetone ratio in total ABE mix. ► Tropical maize is a promising biofuel crop. Mixed sugars from tropical maize stalk juice were used to carry out butanol fermentation with Clostridium beijerinckii NCIMB 8052. Batch experiments employing central composite design (CCD) and response surface methodology (RSM) optimization were performed to evaluate effects of three factors, i.e. pH, initial total sugar concentration, and agitation rate on butanol production. Optimum conditions of pH 6.7, sugar concentration 42.2g/L and agitation rate 48rpm were predicted, under which a maximum butanol yield of 0.27g/g-sugar was estimated. Further experiments demonstrated that higher agitation facilitated acetone production, leading to lower butanol selectivity in total acetone–butanol–ethanol (ABE). While glucose and fructose are more preferable by C. beijerinckii, sucrose can also be easily degraded by the microorganism. This study indicated that RSM is a useful approach for optimizing operational conditions for butanol production, and demonstrated that tropical maize, with high yield of biomass and stalk sugars, is a promising biofuel crop.