Enhanced Enzymatic Hydrolysis of Waste Wood by Steam Explosion and Alkaline Peroxide Delignification

Abstract

Ethanol production from various agricultural and forest residues has been widely researched, but there is limited information availableon the use of mixed hardwood for ethanol production. The main objective of this study is to assess the impact of time on the steamexplosion pretreatment of waste wood (mixed hardwood) and to determine the convenience of a delignification step with respect tothe susceptibility to enzymatic hydrolysis of the cellulose residue and the recoveries of both cellulose and hemicellulosic sugars. Delignification did enhance enzymatic hydrolysis yields of steam exploded waste wood. For steam explosion pretreatment times of 3and 5 min, the recovery yield of hemicellulosic-derived sugars decreased. The effective hemicellulose solubilization does not alwaysresult in high recoveries of hemicellulose-derived sugars in the liquid fractions due to sugar degradation. In the steam explosion pretreatmenttimes of 3 and 5 min, where hemicellulose solubilization exceeded 95%, but sugar recoveries in the liquid fraction remained below30%. Cellulose to glucose yield losses were less significant than hemicellulosic-sugar losses, with a maximum loss of 24% at 5 min. Up to 80% of the lignin in the original wood was solubilized, leaving a cellulose-rich residue that led to a concentrated cellulose toglucose yield solution (about 50 g/L after 72 h enzymatic hydrolysis in the best case). The maximum overall process yield, taking intoaccount both sugars present in the liquid from steam explosion pretreatment and cellulose to glucose yield from the steam exploded,delignified and hydrolyzed solid was obtained at the lowest steam explosion pretreatment time assayed.