Mechanical and Thermal Pretreatment Processes for Increasing Sugar Production from Woody Biomass Via Enzymatic Hydrolysis

Abstract

This work investigated fermentable sugar production by modifying the traditional classical mechanical system used by Pulp & Paper Mills as a potential biorefinery step regarding energy consumption and sugar yield. The study explored the effectiveness of thermal pretreatment, with and without the addition of NaOH, followed by a disk refining pretreatment using various gap and consistency operating conditions through a pilot-scale disk refining system. The chemical components and sugar streams obtained from woody biomass using thermal and/or chemical refining pretreatments were characterized and analyzed. The energy consumption of the disk refining system was also analyzed. The results show that the effects of biomasses on chemical components are mainly caused by the removal of lignin content in the thermochemical pretreatment with the addition of NaOH (5% w/w dry biomass). The combination of thermochemical and disk refining pretreatments could significantly reduce the energy consumption. Moreover, decreasing the refining consistency from 15 to 5% (w/w) and increasing the refining gap from 0.15 to 1.00 mm further decreased refining energy consumption up to 90%. At the same time, the thermochemical and disk refining pretreatment significantly increased the sugar yield. This yield, however, decreases as larger gaps are used in the refining process. Therefore, when using existing mechanical refining equipment, a modified thermochemical disk refining pretreatment can produce a higher sugar yield (an increase 35%), and lower the energy consumption (a decrease 62%), when compared to a typical mechanical refining process.