In-situ 13C CM-MAS NMR study of dilute acid biomass pretreatment on 13C enriched poplar wood
Date
2011
Authors
Kohn, Benjamin D., author
Maciel, Gary, advisor
Bernstein, Elliot, committee member
Watson, A. Ted, committee member
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Abstract
In situ 13C NMR measurements are reported on 13C-enriched powdered poplar wood that is subjected to pretreatment with water and 0.5 M sulfuric acid as a function of time at 150 °C. 13C MAS (magic-angle spinning) spectra were obtained in both the CP (cross polarization) and DP (direct polarization) modes, the contrasts in this combination yielding valuable qualitative information on the effect of pretreatment on local molecular mobilities. In addition, spin-lattice relaxation values for 13C and for 1H, as well as cross polarization time constants TCH-1 and T1pH-1, were measured on dry wood, and on wood 10 % in 0.5 M sulfuric acid before, during and after treatment for lignin peaks and for holocellulose peaks in the 13C NMR spectra, as indicators of the degree of molecular motion for those two structural entities. The results show that a substantial fraction of the solid/semi-solid biomass in 0.5 M sulfuric acid is converted at elevated temperatures to a) chemically different and more mobile structures and/or b) locally similar structures with enhanced atomic-level mobilities, and that some fraction of this 'mobilized' biomass does not return to the original level of immobility upon cooling the acid-treated biomass back to room temperature.
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Subject
in situ NMR
biomass
dilute acid pretreatment
nuclear magnetic resonance
poplar pretreatment
solid state NMR