Pretreatment of lodgepole pine killed by mountain pine beetle using the ethanol organosolv process: Fractionation and process optimization

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 degrees C, 60 min, 1.1% H2SO4 and 65% ethanol) were close to the optimum for the recovery of glucose and ethanol organosolv lignin. At the center-point conditions, similar to 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 similar to 83% glucose, similar to 46% mannose, similar to 53% xylose, similar to 78% galactose, and similar to 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 similar to 93% and similar to 97% were achieved within 24 and 48 h, respectively, with 20 FPU of cellulase/g of cellulose.