Single-step conversion of lignin monomers to phenol: Bridging the gap between lignin and high-value chemicals

Abstract

Transformation of lignin into high-value chemicals is hampered by the complexity of monomers obtained from lignin depolymerization. Here we report a strategy, composed of hydro-demethoxylation and de-alkylation reactions, that is able to chemically converge various lignin-derived phenolic monomers into phenol in a single-step. Using 2-methoxy-4-propylphenol as a model compound, Pt/C exhibited the best performance in hydro-demethoxylation reaction affording >80% 4-propylphenol from 2-methoxy-4-propylphenol, while H-ZSM-5 was identified as the most suitable catalyst for de-alkylation, achieving 83% yield of phenol from 4-propylphenol. Since the two catalysts operate under compatible conditions, combining the two catalysts to simultaneously promote both hydro-demethoxylation and de-alkylation reactions was achieved. Configuration of how to organize the catalysts is a critical parameter, where the physical mixture of the two was most effective, providing over 60% phenol from 2-methoxy-4-propylphenol in a single-step.

Chemicals from Lignin: A Review of Catalytic Conversion Involving Hydrogen

“…In addition, the presence of water is beneficial for ZSM‐5 stability as the competitive adsorption of water and phenol enables to sweep phenol from the catalyst . Recently, Yan and co‐workers reported the single‐step conversion of lignin monomers into phenol through combining the two catalysts, namely Pt/C and H‐ZSM‐5 together to simultaneously break the C−O bond of the methoxy groups and the C−C bond of the alkyl group, but the deactivation of the dealkylation catalyst limits its application . The development of efficient and stable multifunctional catalysts to integrate demethoxylation and dealkylation in a single step is therefore required to avoid multistep processes and complex separations.…”

Catalytic Scissoring of Lignin into Aryl Monomers

“…Poplar lignin was converted into phenol in a 13 wt% yield in a CuCl 2 aqueous solution combined with a Ru/CeO 2 hydrogenation catalyst in a H 2 atmosphere. C ary C α bond cleavage via acid‐catalyzed dealkylation was demonstrated to be effective for monoalkylphenols but showed reduced success for the lignin dimers …”

Product‐oriented Direct Cleavage of Chemical Linkages in Lignin

“…Recently, Yan and co‐workers achieved the selective conversion of lignin monomers into phenol in a single‐step composed of hydrodemethoxylation and dealkylation reactions over Pt/C and HZSM‐5 catalysts together. Notably, the intimate contact between the Pt/C demethoxylation catalyst and the HZSM‐5 transalkylation catalyst is essential for obtaining high yield of phenol.…”