Production of cellulosic ethanol from steam-exploded Eucalyptus urograndis and sugarcane bagasse at high total solids and low enzyme loadings

Abstract

Cellulosic ethanol is one of the most important biotechnological products to mitigate the consumption of fossil fuels and to increase the use of renewable resources for fuels and chemicals. By performing this process at high total solids (TS) and low enzyme loadings (EL), one can achieve significant improvements in the overall cellulosic ethanol production process. In this work, steam-exploded materials were obtained from Eucalyptus urograndis chips and sugarcane bagasse to be subsequently used for enzymatic hydrolysis at high TS (20 wt%) and relatively low EL (13.3 FPU g−1 TS of Cellic CTec3 from Novozymes). Also, the fermentability of their corresponding hydrolysates was tested using an industrial strain of Saccharomyces cerevisiae (Thermosacc Dry from Lallemand). Enzymatic hydrolysis of steam-treated E. urograndis reached 125 g L−1 of glucose in 72 h, while steam-treated bagasse gave yields 25 % lower. Both substrate hydrolysates were easily converted to ethanol, giving yields above 25 g L−1 and productivities of 2.3 g L−1 h−1 for eucalypt and 2.2 g L−1 h−1 for bagasse after only 12 h of fermentation. Under the conditions used in this study, sugarcane bagasse glucans showed the potential to boost the ethanol production from sugarcane culms by 31 %, from the 80 L t−1 of first generation to a total production of 105 L t−1. On the other hand, E. urograndis plantations are able to achieve cellulosic ethanol productivities of 2832.2 L ha−1 year−1, which was 57.8 % higher than the projected value of 1794.5 L ha−1 year−1 that was obtained for sugarcane bagasse.