Highly selective reductive catalytic fractionation at atmospheric pressure without hydrogen

Reductive catalytic fractionation (RCF) is an efficient and selective way to produce phenolic monomers from lignin. However, this strategy is difficult to scale up due to its high operating pressure. In this work, we investigated RCF reaction at or near atmospheric pressure and without the use of hydrogen. The atmospheric RCF (ARCF) was conducted in acidified ethylene glycol in glass vessels at 185–195 °C catalyzed by 5% Ru/C. The products mainly include propylguaiacol and propylsyringyl (up to 95.6% among the lignin monomers) and do not contain propanolguaiacol, propanolsyringyl, or H monomers. Although the total yield of lignin monomers in ARCF is about one-quarter less than that of RCF, the operation of ARCF is much easier, milder, safer, and cheaper due to the atmospheric condition and the feasibility of the semi-continuous operation.