Electrocatalytic Upgrading of Phenolic Compounds Observed after Lignin Pyrolysis

Abstract

Lignin valorization is increasingly important as biomass fractionation approaches achieve higher technology readiness levels. One approach to upgrade lignin first involves its deconstruction by fast pyrolysis to create a lignin-derived bio-oil. The phenolics-rich liquid product is a promising feedstock for electrocatalytic hydrogenation, as aromatics can be deoxygenated and saturated by hydrogen chemisorbed on catalytic cathodes, mitigating the product’s corrosivity and raising its energy content. By integrating biomass fractionation with pyrolytic deconstruction and electrocatalytic upgrading, lignin can be valorized to fuels and chemicals that significantly enhance the profitability of biorefineries. In this study, model compounds representing lignin bio-oil components were subjected to electrocatalytic hydrogenation (ECH) at mild temperatures using ruthenium on activated carbon cloth. Phenol, guaiacol, syringol, and several related alkyl phenols and aryl methyl ethers were studied. In addition to hydrogenation, C–O and C–C hydrogenolysis were observed. Conversion of the alkyl phenols decreased with increasing alkyl chain length. Similarly, for alkyl-substituted guaiacols, conversion decreased as alkyl chain length increased, and selectivity shifted away from demethoxylation, favoring alkyl-substituted 2-methoxycyclohexanol. Increasing substrate concentration improved the Faradaic efficiency up to a plateau at higher concentrations. By mapping out electrocatalytic conditions and reactivities of lignin-relevant substrates, this work further opens the door to the promise of biomass upgrading to fuels and chemicals via the pyrolysis–electrocatalysis pathway.

Greener Routes to Biomass Waste Valorization: Lignin Transformation Through Electrocatalysis for Renewable Chemicals and Fuels Production

“…Overcoming these challenges will requirer esearch and development in new areas,l eading to solutionst hat propele lectrochemical lignin valorization forward.T he integration of the use of ionic liquids, deep eutectic solvents, and redox mediators are all examples of thev arious tools that are . [191,192] Figure 7. Simultaneous upgrading of organic substrates (fractionated lignin compounds) in aSPE reactor.…”

Electrochemical Lignin Conversion

“…ment, pyrolysis, and electrocatalysis to valorize lignin to fuels and chemicals, significantly enhancing the profitability of biorefineries. [176] Using this pyrolysis-electrocatalytic hydrogenation sequence, guaiacol showed improved stability to bio-oil compounds compared to electrocatalytic hydrogenation alone. The reaction rates of electrocatalytic hydrogenation at potentials above 0.7 V vs Ag/AgCl were higher than thermal catalytic hydrogenation to functionalized aromatic molecules.…”

“…[174] Figure 25 depicts an electrocatalytic hydrogenation cell for upgrading lignin-oil compounds, highlighting the electrode material, electrolyte, and catalyst. The anode material, individually depicted in Figure 25 (top left), can include cobaltphosphate, [175] platinum wire, [143,169,171,176] platinum sheet, [142] and platinum mesh, [148,177,178] of which the platinum electrode is mostly used. Meanwhile, carbon is electrocatalytically inactive and serves only as a mechanical support.…”

“…Meanwhile, carbon is electrocatalytically inactive and serves only as a mechanical support. Therefore, carbonsupported electrocatalysts, such as Ru/ACC, [172,176] Pt/ graphite, [142] Pt/carbon, [148,173,177,178] Pd/carbon, [177,178] Rh/ carbon, [143,177,178] and Ni/carbon [178] are generally used as cathodes in the electrocatalytic hydrogenation process. In addition, various electrolytes (anolyte/catholyte) including BK 3 O 3 buffer/ BK 3 O 3 buffer, [175] phosphate buffer/HCl solution, [176] acetate buffer/acetate buffer, [143,177,178] H 2 SO 4 /HClO 4, [173] LiCl/LiCl, [169] and H 3 PO 4 /SiW 12 [148] were utilized, as shown in Figure 25 (bottom left).…”

Extraction and Modification of Lignin from Red Pine Using Ionic Liquid

“…Lignocellulose biomass is a renewable resource with the potential for conversion into liquid transport fuel and high value-added products. Many value-added products have been obtained from cellulose and hemicellulose, but relatively few studies have focused on the utilization of lignin 1), 2) . Lignin is a complex biopolymer that accounts for 25-35 % of potentially renewable carbon resources and is a potentially valuable source of aromatic compounds 3) , which form an important component in bio-oils.…”