Improved co-production of ethanol and xylitol from low-temperature aqueous ammonia pretreated sugarcane bagasse using two-stage high solids enzymatic hydrolysis and Candida tropicalis

Abstract

Process economics of cellulosic ethanol production can be improved by co-production of high value products. Xylitol is a high value nutraceutical and attracted attention as a co-product in cellulosic ethanol process. Here, the production of ethanol and xylitol from sugarcane bagasse pretreated by low-temperature aqueous ammonia soaking was improved by two-stage high solids enzymatic hydrolysis and separate fermentation of glucose and xylose using Candida tropicalis. First-stage high solids fed-batch enzymatic hydrolysis of pretreated bagasse in 3 L bioreactor resulted in 42.6 g/l xylose. The residual solids rich in cellulose were efficiently hydrolyzed by cellulase in the second-stage to glucose. The second stage hydrolysis at 20% solids loading in bioreactor showed 81% efficiency with a glucose concentration of 115.8 g/l. The separate fermentation of the xylose with C. tropicalis in two-stage aeration resulted in 34.5 g/l of xylitol. Fermentation of the glucose by C. tropicalis produced 55.64 g/l of ethanol. Simultaneous saccharification and fermentation of cellulose rich solids from first stage hydrolysis produced 57.2 g/l of ethanol. These results showed that two-stage enzymatic hydrolysis of low-temperature aqueous ammonia pretreated biomass facilitated higher yields and efficiency of production of ethanol and xylitol.