Molecular-Level Consequences of Biomass Pretreatment by Dilute Sulfuric Acid at Various Temperatures

Abstract

Ex situ room-temperature 13C nuclear magnetic resonance (NMR) measurements are reported on powdered poplar wood that has been pretreated with dilute sulfuric acid (concentrations up to 1 wt %) for times ranging up to 20 min and at temperatures of 120, 130, 140, and 150 °C. There are significant, albeit not dramatic, changes in the measured NMR spectra of the biomass as result of dilute sulfuric acid treatment. Values of T1 for 13C and 1H, as well as TCH and T1ρH, were measured for lignin peaks and cellulose peaks in the 13C NMR spectra, as potential indicators of the degree of atomic-level motion. For lignin components, one finds a trend to larger TCH values as the treatment time or H2SO4 concentration is increased for treatment temperatures of 120 and 130 °C; however, for treatment temperatures of 140 and 150 °C, TCH apparently decreases as the treatment time is increased. This higher temperature TCH behavior implies that the lignin may actually become more rigid at later stages of treatment at temperatu...