Abstract
As green and effective depolymerization processes, CrCl3 and CrCl3-catalyzed ethanol pretreatment were comprehensively investigated to improve cellulose conversion from pretreated residues in poplar in the present study. The influence of pretreatment temperature on delignification, structural characteristics of lignin, and the yield of glucose and ethanol was comparatively analyzed to emphasize the synergy effect of CrCl3 and ethanol solvent. Particularly, CrCl3-catalyzed ethanol pretreatment at 200 °C resulted in the pretreated substrates with >94% removal of hemicellulose and lignin, consequently reaching 88.88% and 56.11% yields of glucose and ethanol, respectively. Lignin's structural change was observed by Gel permeation chromatography and 2D nuclear magnetic resonance spectroscopy and its relationship with the efficiency of enzymatic hydrolysis and fermentation was determined. Results indicated that the increased pretreatment temperature enhanced the lignin depolymerization with smaller molecular weight, fewer β-O-4 linkages, and higher S/G ratio, especially in CrCl3-catalyzed ethanol pretreatment, which was positively associated with poplar cellulose conversion. In addition to offering a comprehensive illustration of the sugar/ethanol generation during CrCl3-catalyzed organosolv pretreatment, this work also provided theoretical support for biofuel and biochemical production from poplar.
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