Optimization of Process Conditions for Subcritical Water Hydrolysis of Sugarcane Bagasse

Optimization of operation conditions (temperature, time, solvent: solid proportion) of subcritical water hydrolysis (SWH) is needed so that it can be considered an effective process for second generation bioethanol manufacturing. The objective of this study was to optimize operation conditions using a semi-batch SWH system equipped with a 50 mL reaction vessel. Initially, the process was carried out at constant temperature (200 °C), pressure (20 MPa) and amount of raw material (2 g), using different flow rates (11, 22, 33, 44 and 55 mL/min) during 30 min. Reducing sugars recovery rate increased with flow rate increase. In the second part of the work, the flow rate was kept constant at 33 mL/min, the amount of raw material was increased by a factor of 5.5 (i.e. 11 g) and the SWH was performed at different temperatures (213, 251 and 290 °C) while maintaining pressure constant (20 MPa). Reducing sugars recovery rate increased up to a maximum and then decreased for the three temperatures. The hydrolysis process finished earlier for higher temperatures; however, the reducing sugars recovery decreased with temperature increase, possibly due to degradation of glucose. Therefore, the less aggressive condition, of 210 °C, was selected for sugarcane bagasse hydrolysis.