Pretreatment of Lodgepole Pine Killed by Mountain Pine Beetle Using the Ethanol Organosolv Process: Fractionation and Process Optimization

Abstract

Lodgepole pine ( Pinus contorta ) killed by mountain pine beetle ( Dendroctonus ponderosae ) (MPB-LPP) was evaluated for bioconversion to ethanol using the ethanol organosolv process. The pretreatment was optimized using an experimental matrix designed with response surface methodology. It was found that MPB-LPP was easy to pretreat and delignify, but gave low yields of substrate and carbohydrate as a result of excessive hydrolysis and subsequent decomposition of cellulose and hemicellulose during the pretreatment. The center-point conditions (170 °C, 60 min, 1.1% H 2 SO 4 and 65% ethanol) were close to the optimum for the recovery of glucose and ethanol organosolv lignin. At the center-point conditions, ∼75% of the cellulose present in the untreated wood was recovered in the substrate fraction, and approximately 79% of the lignin in the wood was recovered as ethanol organosolv lignin (EOL). The combined recovery of carbohydrate in the substrate and water-soluble fractions was ∼83% glucose, ∼46% mannose, ∼53% xylose, ∼78% galactose, and ∼55% arabinose. The lost carbohydrate was decomposed to furfural, hydroxymethylfurfural, and levulinic and formic acids. The substrate generated at center-point conditions from MPB-LPP was readily digestible. Cellulose-to-glucose conversion yields of ∼93% and ∼97% were achieved within 24 and 48 h, respectively, with 20 FPU of cellulase/g of cellulose.