Green Chemistry Benchmarking of Lignin Biorefining: A Perspective

Lignin biorefining technologies support the circular bioeconomy by transforming biogenic carbon within lignin into value-added aromatic compounds. While valorizing renewable feedstocks aligns with green chemistry principles, the inherent “greenness” of biorefining technologies is often overlooked. Thus, the goal of this perspective is to critically benchmark prominent lignin biorefining technologies, including organosolv, reductive catalytic fractionation (RCF), pyrolysis, and oxidation, by evaluating process performance and greenness using mass-based green chemistry metrics. Using aromatic monomer yields as a product benchmark, we compare the relative energy and material footprints of competing biorefining technologies to deconstruct lignin into small aromatics. Among biorefining technologies, the material footprints of liquid-phase processes are exacerbated by high solvent consumption, highlighting the need for integrated solvent recycling steps. Conventional thermal processes, such as pyrolysis, mitigate solvent consumption and can operate with relatively short process times, thus demonstrating lower material footprints and favorable energy economies compared to emerging technologies. Promoting solvent recycling alongside separation steps designed for material efficiency will further reduce the resource demands of lignin biorefining. Overall, we present insights into competing trade-offs between process productivity and the sustainability of biorefining technologies and identify challenges impeding sustainable biorefining through a quantitative, mass-based assessment.