Enzymatic hydrolysis of steam-exploded hardwood using short processing times.

Woody materials are generally resistant to enzymatic saccharification unless they undergo harsh fiber disrupting pre-treatments such as steam explosion. In this study, enzymatic hydrolysis of steam-exploded hardwood was investigated using various conditions and commercial cellulase preparations. Hydrolysis times were kept below 24 h in order to approach industrially realistic conditions. The optimal conditions for enzymatic hydrolysis were found to be 55 degrees C and a pH of about 4.5. During enzymatic hydrolysis, acetate was released from the hemicellulose fraction. Increasing the dry matter concentration had a negative effect on glucose yields. Using fermentors with pH control, 66% of the cellulose in steam-exploded hardwood could be hydrolyzed to glucose within 12 h using an enzyme dose of 25 filter paper units (FPU)/g of dry matter. For 24 h hydrolysis maximum cellulose saccharification (71%) was observed at 25 FPU/g, and increasing the enzyme dose further did not increase the sugar yield.