Long-term lime pretreatment has proven to increase digestibility of many herbaceous lignocellulose sources; but until this work, its effects had not been evaluated on wood, whose lignin content is higher, and therefore, more recalcitrant to enzymatic hydrolysis. In this study, the mild conditions of long-term lime pretreatment (1-atm pressure, temperatures ranging from 25 to 75°C, and reaction times between 1 and 12 weeks, with and without air) were systematically applied to poplar wood available in two batches with different lignin contents. These batches were designated as low-lignin biomass (LLB) with lignin content of 21.4% and high-lignin biomass (HLB) with lignin content of 29.1%. Full factorial designs resulted in 79 samples of pretreated poplar that were analyzed for lignin and carbohydrates pretreatment yields, and enzymatic digestibility (15 FPU/g glucan in raw biomass cellulose loading). After aerated lime pretreatment at 65°C for 4 weeks, and subsequent enzymatic hydrolysis, an overall yield of 0.76 g glucan + xylan recovered per gram glucan + xylan in raw biomass was obtained. This is equivalent to an increased poplar wood digestibility of 7.5-fold compared with untreated biomass. Different batches of the feedstock resulted in different lignin and carbohydrates pretreatment yields; however, overall yields of carbohydrates (combining pretreatment and enzymatic hydrolysis) were similar. © 2010 American Institute of Chemical Engineers AIChE J, 2011
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