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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 (13)C 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 °C and 0.1 M H(2)SO(4) and 160 °C and 0.025 M H(2)SO(4) are optimal for separating biomass in the biorefinery to give process streams most suitable for biobased fuel and chemical production.