Self-Hydrogen Supplied Catalytic Fractionation of Raw Biomass into Lignin-Derived Phenolic Monomers and Cellulose-Rich Pulps

Abstract

Lignocellulosic biomass is one of the most well-studied and promising green carbon sources. The fullest utilization of lignocellulosic biomass in hydrogen-free and mild conditions to produce phenolic monomers while preserving cellulose-rich pulps is challenging and has far-reaching significance. Here, we report an innovative strategy to convert lignocellulosic biomass into lignin oils and cellulose-rich pulps without exogenous hydrogen under mild conditions over a Pt/NiAl 2 O 4 catalyst. In this process, the structural hydrogens in hemicellulose acted as a hydrogen source to realize the fractionation and depolymerization of lignin into phenolic monomers while keeping the cellulose intact, which is named self-hydrogen supplied catalytic fractionation (SCF). By using water as a solvent, the theoretical yield of phenolic monomers (46.6 wt %, with propyl(ethyl) end-chained syringol and guaiacol as main products) is achieved at 140 °C for 24 h, with 90% cellulose intact in birch sawdust. This H 2 -free process can be extended to other biomass (hardwood, softwood, and grass) and can be scaled up. The Pt/NiAl 2 O 4 catalyst also shows good stability in recycling as well as regeneration treatment. This work provides a new strategy to achieve high utilization of lignocellulosic biomass for sustainable biorefinery by using water as a solvent without exogenous hydrogen under mild conditions.

Selective Production of 4-Propylphenol from Lignin Oil without Exogenous Hydrogen over a RuNi/NiAl2O4 Catalyst

“…Very recently, we developed a new process, i.e., selfhydrogen supplied catalytic fractionation (SCF) of lignocellulosic biomass without exogenous hydrogen sources under mild conditions, in which hemicellulose and water (solvent) were used as hydrogen sources and nearly theoretical yield of lignin phenolic monomers (lignin oil, with propyl(ethyl) end-chained syringol and guaiacol as main products) was realized. 22 thoxylation was difficult on our previous catalysts (Pt(Ru/Pd)/ NiAl 2 O 4 ) and the whole process was challenging. Therefore, we introduced Ni(Fe/Co) as the second metal doped in the Ru/NiAl 2 O 4 catalyst (with good demethoxylation ability based on our previous work), and a hint of hydrogen could be generated by the splitting of water on the Ni(Fe/Co) surface to provide initial hydrogen, followed by demethoxylation to generate methanol and aqueous phase reforming of methanol to supply subsequent hydrogen to drive the whole reaction (Scheme 1).…”

“…Very recently, we developed a new process, i.e., self-hydrogen supplied catalytic fractionation (SCF) of lignocellulosic biomass without exogenous hydrogen sources under mild conditions, in which hemicellulose and water (solvent) were used as hydrogen sources and nearly theoretical yield of lignin phenolic monomers (lignin oil, with propyl­(ethyl) end-chained syringol and guaiacol as main products) was realized . Herein, we attempt to convert the thus-obtained lignin oil without hydroxypropyl groups to 4-propylphenol.…”

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Recently, the depolymerization of lignocellulosic biomass without exogenous hydrogen sources (named self-hydrogen supplied catalytic fractionation, SCF) was realized under mild conditions, with nearly theoretical yield of lignin phenolic monomers (lignin oil) achieved (Zhou et al, JACS Au, 2023, 3, 1911−1917. Herein, we further developed a new process for the demethoxylation of thus-prepared lignin oil to get 4-propylphenol in the absence of exogenous hydrogen over the RuNi/ NiAl 2 O 4 catalyst.

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Hydrogen‐transfer strategy in lignin refinery: Towards sustainable and versatile value‐added biochemicals

“…Notably, hemicellulose from lignocellulosic biomass has been explored for its dual role in lignin depolymerization and as a hydrogen donor through reactions like aqueous-phase reforming (APR) and water-gas shift (WGS). [30][31][32] Additionally, the native chemical groups in lignin -specifically the α,γ-hydroxy and methoxy groups -provide internal hydrogen sources that facilitate the polymer's depolymerization and transformation. [33][34][35] Water electrolysis is another avenue through which hydrogen is produced for refining lignin and creating high-value ligninderived chemicals.…”

Plasma-Enabled Selective Synthesis of Biobased Phenolics from Lignin-Derived Feedstock

“…Phenolics are the building blocks of phenol resins, and phenol is used for the production of bisphenols. As phenolics are currently produced mainly from petroleum-derived or coal-derived feedstocks (e.g., coal tar), the valorization of biomass-derived feedstocks for sustainable synthesis of value-added platform chemicals such as phenolics provides a promising route to support the transition to the zero-carbon circular economy. − Nevertheless, most of the existing synthetic routes require rigorous reaction conditions (i.e., high temperature and/or high pressure) and high-cost hydrogen (Table S1), while still facing significant challenges including waste disposal, corrosion, and catalyst deactivation by coking and sintering. − Therefore, developing innovative and sustainable technologies for the selective synthesis of phenolic bioproducts from lignin-derived feedstocks under mild conditions has attracted increasing attention.…”