Dilute Acid Pretreatment of Short Rotation Woody and Herbaceous Crops

Large-scale production of ethanol or other transportation fuels by biological conversion of lignocellulosic biomass will eventually require integration with large-scale production of biomass substrates. The most promising candidates for efficient production of biomass in the US are short rotation hardwoods and herbaceous crops. The following samples of short rotation hardwoods were provided by the Biomass Production Program managed for the Department of Energy Biofuels and Municipal Waste Technology Division by the Oak Ridge National Laboratory: Poplar hybrid NE388 (Populus, maximowiczii x P. trichocarpa), Poplar hybrid Nil (Populus. trichocarpa x P. deltoides), and Sweetgum (Liquidambar styraciflua). Samples of two short rotation grasses (weeping lovegrass and switchgrass) and one herbaceous legume (sericea lespedeza) were also obtained from the same source. Milled and debarked hardwoods and herbaceous samples were subjected to prehydrolysis with dilute sulfuric acid at 140 and 160 °C for reaction times ranging from 5 to 60 min. The dilute sulfuric acid hydrolyzed all hemicelluloses at longer reaction times (30-60 min at 140 °C and 5-10 min at 160 °C), but solubilized very small amounts (< 15%) of lignin and cellulose. Cellulose in all three pretreated hardwoods became highly digestible by cellulase enzyme from Trichoderma reesei. The two grasses also responded to dilute acid pretreatment very well.