Comparison of Dilute Acid and Sulfite Pretreatment for Enzymatic Saccharification of Earlywood and Latewood of Douglas f
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Comparison of Dilute Acid and Sulfite Pretreatment for Enzymatic Saccharification of Earlywood and Latewood of Douglas fir Chao Zhang . Xiaochun Lei . C. Tim Scott . J. Y. Zhu . Kecheng Li
Published online: 29 September 2013 © Springer Science+Business Media New York (outside the USA) 2013
Abstract This study applied dilute acid (DA) and sulfite pretreatment to overcome the recalcitrance of lignocelluloses (SPORL) to deconstruct earlywood and latewood cell walls of Douglas fir for fermentable sugars production through subsequent enzymatic hydrolysis. DA pretreatment removed almost all the hemicelluloses, while SPORL at initial pH = 4.5 (SP-B) removed significant amount of lignin between 20 and 25 %. But both are not sufficient for effective enzymatic saccharification. SPORL at low initial pH = 2 (SP-AB) combines the advantage of both DA and SPORL-B to achieve approximately 90 % hemicellulose removal and delignification of 10–20 %. As a result, SP-AB effectively removed recalcitrance and thereby significantly improved enzymatic saccharification compared with DA and SP-B. Results also showed that earlywood with significantly lower density produced less saccharification after DA pretreatment, suggesting that wood density does not contribute to recalcitrance. The thick cell wall of latewood did not limit chemical penetration in pretreatments. The high lignin content of earlywood limited the effectiveness of DA pretreatThis work was conducted while Zhang was a visiting student at the USDA Forest Products Laboratory and on official government time of Zhu and Scott. C. Zhang School of Chemical Engineering and Technology, Tianjin University, Tianjin, China C. Zhang • C. T. Scott • J. Y. Zhu (*) USDA Forest Service, Forest Products Laboratory, Madison, WI, USA e-mail: [email protected] X. Lei • K. Li Dept. of Chemical Engineering, University of New Brunswick, Fredericton, NB, Canada
ment for enzymatic saccharification, while hemicellulose limits the effectiveness of high pH pretreatment of SP-B. The higher hemicellulose content in the earlywood and latewood of heartwood reduced saccharification relative to the corresponding earlywood and latewood in the sapwood using DA and SP-AB. Keywords Cell walls • Pretreatment • Enzymatic hydrolysis, earlywood and latewood • Recalcitrance
Introduction Various types of biomass such as woody plants, herbaceous plants, grasses and agricultural residues have been studied as potential feedstocks for biofuel production. Woody biomass is an important feedstock that can be sustainably produced in large quantities—approximately 300 million tons annually in the US [1]. Woody biomass has several logistical advantages for transportation and storage [2]. However, woody biomass is very recalcitrant to biochemical conversion to sugars partially due to its strong physical structure and high lignin content. Unlike annual plant biomass, woody biomass has heartwood (juvenile) and sapwood (mature) cells with different chemical compositions [3]. Moreover, each growth ring contains wood cells that have pr
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