Optimization of liquid ammonia pretreatment variables for maximum enzymatic hydrolysis yield of energy cane bagasse

This study aimed at optimizing a liquid ammonium hydroxide pretreatment for energy cane bagasse for maximum sugar yields (glucose and xylose) via response surface methodology. Optimized pretreatment parameters included temperature (160-220 °C), ammonium hydroxide to biomass ratio (0-0.5:1) and residence time (30-60 min). Temperature was found to be the dominant pretreatment parameter followed by ammonium hydroxide to biomass ratio. High temperatures and long residence times had a negative effect on sugar yields. Sugar yields had the highest correlation with lignin removal. Based on our quadratic models fitted on the experimental results, optimum pretreatment conditions for maximum glucose yield were 208 °C, for 36 min and at an ammonium hydroxide to biomass ratio of 0.4:1. A glucose yield of 30.77 g glucose/100 g (dry weight) untreated biomass and a xylose yield of 3.99 g xylose/100 g (dry weight) untreated biomass were predicted by the model. Optimum pretreatment conditions for maximum xylose yield were 160 °C, for 60 min and at an ammonium hydroxide to biomass ratio of 0.31:1. These conditions resulted in a predicted xylose yield of 9.10 g xylose/100 g (dry weight) untreated biomass and a glucose yield of 23.34 g glucose/100 g (dry weight) untreated biomass. The low xylose yields observed were attributed to the high amounts of xylan lost due to solubilization. The quadratic models were found to be reliable for the prediction of sugar yields within the design space. All predicted values were experimentally confirmed with 95% confidence of the predicted values.