Effects of sulfuric acid loading and residence time on the composition of sugarcane bagasse hydrolysate and its use as a source of xylose for xylitol bioproduction

A 2(2) full factorial design was employed to evaluate the effects of sulfuric acid loading and residence time on the composition of sugarcane bagasse hydrolysate obtained in a 250-L reactor. The acid loading and the residence time were varied from 70 to 130 mg acid per gram of dry bagasse and from 10 to 30 min, respectively, while the temperature (121 degrees C) and the bagasse loading (10%) were kept constant. Both the sulfuric acid loading and the residence time influenced the concentrations of xylose and inhibitors in the hydrolysate. The highest xylose concentration (22.71 g/L) was achieved when using an acid loading of 130 mg/g and a residence time of 30 min. These conditions also led to increased concentrations of inhibiting byproducts in the hydrolysate. All of the hydrolysates were vacuum-concentrated to increase the xylose concentration, detoxified by pH alteration and adsorption into activated charcoal, and used for xylitol bioproduction in a stirred tank reactor. Neither the least (70 mg/g, 10 min) nor the most severe (130 mg/g, 30 min) hydrolysis conditions led to the best xylitol production (37.5 g/L), productivity (0.85 g/L h), and yield (0.78 g/g).