Effect of metal triflates on the microwave-assisted catalytic hydrogenolysis of birch wood lignin to monophenolic compounds

The lignin-first biorefinery strategy could produce bio-based phenols from the extraction and depolymerization of native lignin in lignocellulosic biomass. Herein, we report an effective Lewis acid-promoted delignification and production of monophenolic compounds in birch sawdust assisted by microwave heating without external hydrogen for the first time. The screening of different metal triflates revealed that Fe(OTf)3 was best for the delignification and depolymerization of birch sawdust. Without the addition of a Lewis acid, the yield of monophenolic compounds was 10.5 wt% (based on the lignin content in birch sawdust), while it increased significantly to 32.9 wt% with the addition of Fe(OTf)3 (0.0276 g) under the identical conditions (190 °C, 1 h), which demonstrated the catalytic C[sbnd]O[sbnd]C bond scission promoted by Fe(OTf)3. Simultaneously, the delignification degree also rose sharply from 32.6 wt% to 47.5 wt%. This work demonstrated the efficient Fe(OTf)3-induced delignification and depolymerization of lignin in birch sawdust to obtain a high yield of monophenolic compounds without external hydrogen assisted by microwave heating, representing a novel advance in the “lignin-first” biorefinery field.