Lignin is an abundant, cheap, and underutilized carbon source for producing bio-based chemicals and fuels. Despite its enormous potential, practical valorization is still lacking because of its intrinsic heterogeneity and recalcitrant nature. Thermal deconstruction techniques such as fast pyrolysis have demonstrated promise to break down lignin into monomeric phenols, but they produce a high amount of pyrolytic char (35 – 60 C%). Pretreatment or partial deconstruction of lignin prior to pyrolysis has been shown to improve the yield and quality of volatile products generated while simultaneously decreasing char formation. In this study, we investigated the effect of various lignin pretreatments using Pd/C, Ru/C, Pd/Al2O3, Ru/Al2O3, and Y zeolite as catalysts in sub- and super-critical ethanol. By combining GPC, GC-MS, elemental analysis, NMR, and TGA, we first gained insights into these pretreatments and identified the parameters that govern the size distribution of the lignin fragments and chemical changes relative to raw lignin. The deconstructed lignin was further upgraded to hydrocarbons through low-pressure ‘ex-situ’ catalytic hydrodeoxygenation reactions using MoO3. The pretreatment step successfully reduced the char formation from 58.4 C% to 8.8 C% for the sample deconstructed at 250 °C using Pd/C. The relationships between the yield of aromatic and aliphatic products generated during catalytic upgrading and the pretreatment conditions were investigated in detail. This approach provides opportunities to convert lignin into value-added chemicals selectively and, thereby enhance carbon recovery.

Pretreatment of lignin for production of platform chemicals via. hydrodeoxygenation

ACS Spring Meeting 2021

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