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.