Towards high-yield lignin monomer production
Depolymerizing lignin into lignin monomers has been extensively studied as a pathway to valorize lignin biopolymer. However, low monomer yields and selectivities pose a significant disadvantage in process economics when technical lignins (referring to lignin separated or extracted from biomass pretreatment or fractionation) are used as feedstocks. While it is widely recognized that low monomer yields are the result of lignin condensation occurring during biomass fractionation, research efforts to minimize such condensation to improve the monomer yield is limited. In this article, we analyze the causes of the low monomer yield and present a perspective of achieving high-yield monomer production using methods compatible with the conventional biorefinery concept—biomass fractionation followed by lignin hydrogenolysis. After a mechanistic analysis of lignin condensation and a comparative analysis of the state-of-the-art of avoiding lignin condensation, a lignin stabilization stragegy is suggested for minimizing lignin condensation during biomass fractionation and seperating uncondensed lignin stream for mild-temperature continuous upgrading.