Effects of Two-Stage Dilute Acid Pretreatment on the Structure and Composition of Lignin and Cellulose in Loblolly Pine
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A standard two-step dilute sulfuric acid pretreatment was performed on Loblolly pine to enhance the overall efficiency of enzymatic deconstruction of woody biomass to monomeric sugars. The structure of milled wood lignin and cellulose isolated from the untreated and acid-treated biomass was studied in detail. Solid-state 13C NMR spectroscopy coupled with line shape analyses has been employed to elucidate cellulose crystallinity and ultrastructure. The results indicate an increase in the degree of crystallinity and reduced relative proportion of less ordered cellulose allomorphs following the acid pretreatment. This increase was attributed to a preferential degradation of amorphous cellulose and less ordered crystalline forms during the high temperature pretreatment. Milled wood lignin structural elucidation by quantitative 13C and 31P NMR reveals an increase in the degree of condensation of lignin due to the pretreatment. The increase in degree of condensation is accompanied by a decrease in β-O-4 linkages which were fragmented and recondensed during the high temperature acid-catalyzed reactions.
KeywordsBioethanol Loblolly pine Milled wood lignin Cellulose structure 13C and 31P NMR spectroscopy Acid pretreatment
Cross polarization/ Magic angle spinning
Milled wood lignin
Nuclear magnetic resonance
Scanning electron microscope
The authors wish to acknowledge financial support from Chevron Technology Ventures for these studies.
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