Lignin valorization: Status, challenges and opportunities

As an abundant aromatic biopolymer, lignin has the potential to produce various chemicals, biofuels of interest through biorefinery activities and is expected to benefit the future circular economy. However, lignin valorization is hindered by a series of constraints such as heterogeneous polymeric nature, intrinsic recalcitrance, strong smell, dark colour, challenges in lignocelluloses fractionation and the presence of high bond dissociation enthalpies in its functional groups etc. Nowadays, industrial lignin is mostly combusted for electricity production and the recycling of inorganic compounds involved in the pulping process. Given the research and development on lignin valorization in recent years, important applications such as lignin-based hydrogels, surfactants, threedimensional printing materials, electrodes and production of fine chemicals have been systematically reviewed. Finally, this review highlights the main constraints affecting industrial lignin valorization, possible solutions and future perspectives, in the light of its abundance and its potential applications reported in the scientific literature.

Automated summary

As an abundant aromatic biopolymer, lignin holds great potential for producing various chemicals and biofuels through biorefinery activities, contributing to a sustainable circular economy. However, lignin valorization faces challenges such as its heterogeneous nature, intrinsic recalcitrance, strong smell, dark color, difficulties in lignocellulosic fractionation, and high bond dissociation enthalpies in its functional groups. Despite these constraints, recent research and development have shown promising applications of lignin-based hydrogels, surfactants, 3D printing materials, electrodes, and fine chemicals production. This review summarizes the main limitations and possible solutions for industrial lignin valorization, and provides future perspectives based on its abundance and potential applications reported in scientific literature.