Nonprecious Metal/Bimetallic Catalytic Hydrogenolysis of Lignin in a Mixed-Solvent System

Abstract

Lignin containing numerous phenylpropane units is considered to be a renewable and abundant resource for the production of value-added aromatic chemicals. A series of nonprecious metal/bimetallic catalysts were prepared for the catalytic hydrogenolysis of organosolv poplar lignin (OPL) in ethanol/isopropanol solvent in this work. Effects of Ni/C, Cu/C, NiCu/C, and NiW/C catalysts on OPL depolymerization were investigated, where the NiCu/C catalyst was found to be optimal for the conversion of OPL to phenolic monomers at a yield of 63.4 wt % at 270 °C for 4 h without external H2. The synergistic effect of mixed solvent was remarkable during the catalytic hydrogenolysis process, leading to the increased yield of monomer products. The catalytic process of OPL conversion and possible reaction route of ethanol/isopropanol solvent were proposed with regard to the analysis of products and fresh/spent catalysts. The effects of reaction temperature, reaction time, catalyst recyclability, solvent recyclability, and feedstock adaptability were investigated in view of bio-oil and monomer yields. This work provides an economical and sustainable method for the efficient conversion of lignin to high-value chemicals.

Depolymerization of Technical Lignins in Supercritical Ethanol: Effects of Lignin Structure and Catalyst

“…46 . The conversion of ethanol under similar conditions has been studied in more details by other authors 50,66 . It is well known that metallic catalysts enhance the key role of ethanol to stabilize the radical fragments by ethanol alkylation reactions and therefore to promote monomer yields.…”

Carbon-Based Nanocatalysts (CnCs) for Biomass Valorization and Hazardous Organics Remediation

“…A variety of catalysts based on precious (Pd, Pt, Ru, Rh) and transition metal (Ni, Mo, Cu, Fe, Co) have been widely used in lignin depolymerization. Noble metal catalysts proved to be very active catalysts for lignin depolymerization reactions, but the high cost and the deep hydrogenation ability, led to their replacement by transition metals [ 188 ]. Well-defined molecular catalysts were first used for the selective cleavage of lignin-derived aryl ether linkages.…”

“…Both monometallic and bimetallic catalysts exhibited mesoporous properties which facilitate the mass transfer of the reactants. However, tungsten addition did not improve Ni/AC activity, which resulted in lower bio-oil yield (61.9 wt.%), while none phenolic monomers were detected [ 188 ]. Probably, tungsten nanoparticles promoted the adsorption of reaction solvents (EtOH and IPA), blocking the access of lignin to the catalyst.…”

Advances in Versatile Nanoscale Catalyst for the Reductive Catalytic Fractionation of Lignin

“…[72] Zn II activates facilitates removal of the C γ À OH group through the formation of a six-membered ring complex of Zn II coordinated to the oxygen atoms at C α and C γ . Cheng et al [74] carried out the hydrogenolysis of organosolv poplar lignin (OPL) over Ni/C, Cu/ C, NiCu/C, and NiW/C catalysts in EtOH/iPrOH solvent. The NiCu/C catalyst exhibited the best catalytic hydrogenolysis activity, yielding a maximum monomer yield of 63.4 wt %.…”