Thermal upgrading techniques such as fast pyrolysis can break down lignin into bio-oil but they simultaneously produce a high amount of pyrolytic char (35 – 60 C%). This char formation currently sets an upper limit to the carbon yields that can be achieved for the overall process, from lignin to final value-added products. We explored various lignin pretreatments to mitigate this challenge. We show that solvolysis using supercritical methanol or ethanol in the presence of a catalyst is effective to deconstruct lignin and enhance the volatilization of its building blocks during fast pyrolysis. The gains are significant as char formation dropped from 58 C% to 9 C% when using organosolv corn stover lignin. Next, the same approach was directly applied to raw biomass (corn stover, switchgrass, red oak) to generate lignin oil along with highly amenable cellulose. The lignin oil was subsequently upgraded using catalytic fast pyrolysis (CFP) and hydrodeoxygenation (HDO). Excellent product yields were achieved using HDO, specifically 38 C% of mono-aromatic hydrocarbons (benzene, toluene, xylenes) relative to the sample’s lignin fraction. Additional gains were achieved when performing the pretreatment in a flow-through reactor instead of a conventional batch reactor. Rapid extraction of the lignin building blocks from the hot zone of the reactor was found to be effective to stabilize these compounds. The hydrogenation catalyst and high-pressure hydrogen that are commonly used to stabilize the most reactive functionalities and overcome recondensation reactions were unnecessary in this case.

Solvolytic fractionation of biomass to enhance the upgrading of lignin to platform chemicals

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ACS Fall 2022

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