Biomass Fractionation for the Biorefinery: Heteronuclear Multiple Quantum Coherence-Nuclear Magnetic Resonance Investigation of Lignin Isolated from Solvent Fractionation of Switchgrass

Two-dimensional heteronuclear multiple quantum coherence and quantitative C-13 nuclear magnetic resonance spectroscopy are used to identify the structural features of lignin isolated from solvent fractionation of switchgrass at several different severities. The spectra are consistent with a progressive deconstruction of the lignin as the fractionation severity increases, with structural units involved in cross-linking and capping of the bulk lignin polymer removed first, followed by increasing levels of acid-catalyzed, solvolytic cleavage of the bulk lignin. The results show that solvent fractionation conditions between about 120 degrees C and 0.1 M H2SO4 and 160 degrees C and 0.025 M H2SO4 are optimal for separating biomass in the biorefinery to give process streams most suitable for biobased fuel and chemical production.