In situ Study of Dilute H2SO4 Pretreatment of C-13-Enriched Poplar Wood, Using C-13 NMR

Benjamin Kohn, Mark Davis, Gary E. Maciel

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10 Scopus Citations


In situ 13C NMR measurements are reported on 13C-enriched powdered poplar wood that is subjected to pretreatment with 0.5Msulfuric acid as a function of time and at two temperatures. 13C MAS (magic-angle spinning) spectra were obtained in both the DP (direct polarization) and CP (cross-polarization) modes, the contrasts in this combination yielding valuable qualitative information on the effect of pretreatment on local molecular mobilities. T1 values for 13C and for 1H, as well as TCH and T 1ρH, were measured at various stages of treatment with 0.5 M H2SO4 for lignin peaks and for cellulose peaks in the 13C NMR spectra, as quantitative indicators of the degree of molecular motion for those two structural entities. The results show that a substantial fraction of the solid/semisolid biomass is converted at elevated temperatures to (a) chemically different and more mobile structures and (b) locally similar structures with enhanced atomic-levelmobilities and that some fraction of this "mobilized" biomass does not return to the original level of immobility upon cooling the biomass back to room temperature. Analysis of the T1 results by a rather simple model indicates that, for poplar wood in 0.5% H2SO4, the estimated ("global") motional correlation time (at the multiatom level), τc, is in the range of about 0.7-1.5 ns at various stages and temperatures of the treatment.

Original languageAmerican English
Pages (from-to)2301-2313
Number of pages13
JournalEnergy and Fuels
Issue number5
StatePublished - 19 May 2011

NREL Publication Number

  • NREL/JA-5100-52142


  • biomass
  • dilute H2SO4
  • ethanol
  • poplar wood
  • pretreatment


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