Assessment of energy efficiency in enzymatic hydrolysis of cellulosic substrates

Enzymatic hydrolysis experiments were carried out using three different substrates: steam exploded sugarcane bagasse (EX-SCB: 17 kg_f, 205^oC, 20min), hydrothermal sugarcane bagasse (HT-SCB: 195°C, 10min, 200 rpm), and hydrothermal sugarcane straw (HT-SCS: 195°C, 10min, 200 rpm). The objective was assessing the energy efficiency in terms of mass of glucose produced according to the energy consumed. Also, the rheological behavior of these slurries was evaluated. Experiments were conducted in a conventional stirred-tank (using a volume of 3 L). A motor was connected to a shaft fitted with a set of two Elephant ear impellers, one operated in “down-pumping” and the other in “up-pumping” mode. Experiments were carried out for 96 h using 10% (m/v) of pretreated substrates and an enzyme load of 10 FPU/g_substrate (Cellic CTEC-2), in sodium citrate buffer (pH 4.8, 50^oC, 470 rpm). The power consumption was experimentally measured by digital dynamometer connected to the motor that was supported on a bearing located in the reactor lid. Torque was measured through a mechanical coupling. Samples were periodically withdrawn throughout the experiments for glucose analysis (HPLC). Rheology measurements were made using a digital rheometer at 50°C. The values of cellulose to glucose conversion (%) obtained were: 78.7 (EXP-SCB), 66.9 (HT-SCB), and 76.2 (HT-SCS). The energy efficiencies (kg_glucose∙kWh^-1) obtained were: 0.402 (EX-SCB), 0.275 (HT-SCB), and 0.285 (HT-SCS). The apparent viscosity (mPa.s) ranging between: 3.15 (4h) to 1.02 (96h) (EX-SCB); 7.71 (4h) to 1.35 (96h) (HT-SCB); and 9.31 to 1.12 (HT-SCS).

Acknowledgments: CAPES, CNPq and FAPESP for the financial support.