Valorization of Lignin under Mild Conditions: Biorefining Flavonoids and Lignin Nanoparticles

Lignin is the largest store of renewable aromatics. Due to its refractory nature, however, its chemical potential is not fully realized. Here, we propose a biorefinery where the treatment of wastewater by a microbial electrolysis cell (MEC) produces "clean" water and a caustic catholyte that can depolymerize lignin under mild conditions into two high-value product streams. We determine the MEC operating conditions to produce a depolymerization solvent and quantify solution and colloidal phase products using an array of analytical techniques. In contrast to previous reports of limited high-value product yields, we obtain discrete aromatics (monomers and flavonoids) at 17% of initial lignin mass with bulk chemical analyses (11% for identified compounds using LC–MSn). In part, our higher product yield is due to selective repolymerization to form flavonoids. We simultaneously produce lignin nanoparticles and close mass balance. Both flavonoids and lignin nanoparticles have potential applications in the pharmaceutical, nutraceutical, personal care, and agricultural industries.