Power input and rheology measurements during sugarcane bagasse enzymatic hydrolysis

The performance of two dual-impeller configurations (DIC) during enzymatic hydrolysis of sugarcane bagasse was investigated. The systems consist: DIC1 - turbine elephant ear down-pumping and up-pumping; and DIC2 - Rushton turbine and elephant ear up-pumping. Experiments were carried out in a conventional bench-scale baffled stirred-tank (3 L) using 10% WIS of steam exploded sugarcane bagasse (17 kg_f, 205 ^oC, 20 min.) in 0.05 M sodium citrate buffer (pH 4.8, 50^oC, 470 rpm) during 96 h. A commercial cellulolytic enzyme preparation with 10 FPU/g of dry biomass was used. The power consumption of each impeller configuration was experimentally measured by digital dynamometer connected to the motor which was freely mounted on a bearing in the cover of the vessel. Throughout the experiments samples were periodically withdrawn for glucose analysis (HPLC) and rheology assessment (digital rheometer). Measurements were made at 50^oC as a function of shear rate (3.4-85.0 s^-1). The slurry presents a pseudoplastic behavior. After 24 h the viscosity decrease becomes less abrupt in both experiments (shear rate > 20.4 s^-1). During the first half hour a sharp power consumption decrease was observed for both configurations. Then these values reached a plateau. Although the initial power consumption of the DIC1 configuration (11.8 W) is higher than DIC2 (8.9 W) the energy consumed during the whole experiment (96 h) was 22% lower. DIC1 configuration produced 39.7 g/L of glucose (82.3% cellulose conversion) while the DIC2 produced 24.0 g/L of glucose (49.8% cellulose conversion).

Acknowledgments: CAPES, CNPq and FAPESP for financial support.