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.

Biomass conversion processes have become increasingly important to mitigate fossil fuel consumption and to increase the contribution of renewable fuels into the world energy matrix. In this study, Eucalyptus urograndis wood chips were pretreated by autocatalytic steam explosion to produce cellulosic ethanol after enzymatic hydrolysis and fermentation. These experiments were organized in a central composite rotatable design using temperatures and reaction times ranging from 174 to 216 °C and from 4 to 11 min, respectively. Mass yields, cellulose degree of polymerization, and glucose yields after enzymatic hydrolysis showed a linear correlation with pretreatment severity. The best condition was set at 210 °C for 5 min due to its higher glucose yield after pretreatment and enzymatic hydrolysis. Pectins were almost completely solubilized after pretreatment while galactoglucomannans were more resistant to acid hydrolysis than arabinoglucuronoxylans. Alkaline delignification led to 90.3% lignin removal from steam-exploded materials, but its effect on enzymatic hydrolysis was almost negligible. For the best pretreatment condition, analyses by confocal laser scanning microscopy and solid-state nuclear magnetic resonance revealed important changes in fiber morphology and chemical composition, respectively. Enzymatic hydrolysis at 4 wt % total solids with Cellic CTec2 and Cellic CTec3 (Novozymes) led to 22.4 and 27.8 g L–1 glucose equivalents in 96 h, respectively, whose fermentation with a commercial strain of Saccharomyces cerevisiae led to ethanol productivities greater than 3.5 g L–1 h–1 in 6 h.

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.