Recently, approaches for tandem extraction and quenching of reactive lignin species<i> via</i> heterogeneous catalysis, known as reductive catalytic fractionation (RCF), successfully demonstrated the production of “lignin oils” containing discreet phenolics at high individual yields. However, depending on the conditions of the RCF process, a heavy fraction (apparent weight average molecular weight of about 3-15 kDa) may constitute up to 40% of the lignin stream. Surprisingly, the chemical nature of the heavy fraction remains poorly understood. In this communication, we introduce a solvent fractionation method for facile isolation of the heavy fraction from the low molar mass products in the lignin oil. A detailed characterization demonstrates the heavy fraction of the lignin oil to contain a substantial amount of carbohydrates along with lignin oligomers. We also show the hydrodeoxygenation of the β-O-4 bonding motifs at the Cα<sub> </sub>position to represent a signature of the action of the hydrogenation catalyst on the lignin oligomers. In the broader context of the lignin-first biorefining, the current findings reveal an even more impacting facet of RCF, that is, its ability to obtain stabilized lignin-carbohydrate complexes with controllable structural features.

Chemical insights into the heavy fractions of lignin oil obtained from reductive catalytic fractionation of poplar via catalytic hydrogen transfer reactions

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.