Lignocellulosic biomass is gathering tremendous attention because of its abundance and potential for conversion to a wide range of chemicals and fuels. Thermal upgrading techniques such as fast pyrolysis have demonstrated promise to break down lignin into bio-oil, but they simultaneously produce a high amount of pyrolytic char (&gt; 50 C%). Thus, the low yield of value-added products obtained after catalytic upgrading is limited by the efficiency of bio-oil formation from fast pyrolysis itself. Pretreatment or partial deconstruction of lignin prior to pyrolysis has been shown to improve the yield and quality of the volatile products generated. However, the exact effect of this additional step remains poorly understood, and the key parameters that would unlock the selective upgrading of lignin to chemicals remain to be identified. Here, we thoroughly studied the effect of solvolytic and catalytic pretreatments on lignin depolymerization and the subsequent upgrading of the collected fractions to hydrocarbons. The independent contributions of sub- and supercritical solvents and of the catalyst (Pd/C, Ru/C, Pd/Al2O3, Ru/Al2O3, and Y zeolite) were elucidated by combining GPC, GC-MS, elemental analysis, NMR, and TGA. We show that deoxygenation is carried out mainly through solvolysis, while the transition metal catalysts are primarily involved in the hydrogenation of the intermediates. Careful selection of the reaction conditions and metal catalyst allows to find a balance between deoxygenation and hydrogenation, and significantly curb char formation during fast pyrolysis from 58.4 to 8.8 C%. This pretreatment selectively transforms the most reactive functionalities that are responsible for secondary reactions during pyrolysis. We extend this approach to the one-pot fractionation and pretreatment of lignin from biomass (corn stover, switchgrass, and red oak) for low-carbon-footprint chemical production. The pretreated lignin stream was funneled to produce platform hydrocarbons at very high yields (90% increase), while the residual pulp rich in sugars was amenable to bioethanol production.

Catalytic fractionation of lignin to curb char formation and boost product yields

ACS Spring 2022

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