Upgrading of lignin-derived bio-oils by catalytic hydrodeoxygenation

TLDR

Renewable resources are being explored to replace fossil fuels, and lignin‑derived bio‑oils from cellulosic biomass are a promising feedstock that requires depolymerization and oxygen removal, typically via catalytic hydrodeoxygenation to produce hydrocarbons and water. The review aims to critically introduce HDO chemistry for lignin‑derived compounds, summarizing reactions, accompanying processes, and comparing catalysts for activity, selectivity, and stability. The review evaluates HDO reaction pathways for lignin‑derived bio‑oil components such as anisole, guaiacol, and phenol, discussing depolymerization by pyrolysis followed by catalytic upgrading with hydrogen. The review recommends further research and contextualizes HDO among renewable fuel options, though it does not provide an economic assessment.

Abstract

The incentive for use of renewable resources to replace fossil sources is motivating extensive research on new and alternative fuels derived from biomass. Bio-oils derived from cellulosic biomass offer the prospect of becoming a major feedstock for production of fuels and chemicals, and lignin is a plentiful, underutilized component of cellulosic biomass. Lignin conversion requires depolymerization and removal of oxygen. Likely processes for lignin conversion involve depolymerization (e.g., by pyrolysis) and catalytic upgrading of the resultant bio-oils. A major goal of the upgrading is catalytic hydrodeoxygenation (HDO), which involves reactions with hydrogen that produce hydrocarbons and water. The aim of this review is to present a critical introduction to HDO chemistry focused on compounds derived from lignin, including a summary of HDO reactions and those that accompany them, with a comparison of catalysts addressing their activities, selectivities, and stabilities. The reactions are evaluated in terms of reaction pathways of compounds representative of lignin-derived bio-oils, including anisole, guaiacol, and phenol. The review includes recommendations for further research and an attempt to place HDO in a context of options for renewable fuels and chemicals, but it does not provide an economic assessment.