Toward a facile depolymerization of alkaline lignin into high-value platform chemicals via the synergetic combination of mechanocatalysis with photocatalysis or Fenton process
Dominic Aboagye, Francesc Medina, Sandra Contreras
Abstract
Even though lignin is very rich in aromatic compounds, it remains the least exploited fraction of biomass due to its recalcitrant nature. Consequently, prevailing efforts to fully unlock its potential are still far from reaching due to the use of harsh conditions and energy-intensive processes which are not environmentally friendly. Herein, a facile approach for coupling acid-catalyzed mechanocatalysis (MC) via ball milling with TiO2 photocatalysis (PC)/Fenton for depolymerization of alkaline lignin was investigated. Mechanocatalysis (MC) involved prior acid impregnation (AI) followed by ball milling. A direct comparison of pretreatments (AI, BM, MC) coupled with oxidation processes was preliminarily undertaken. The untreated lignin (UL) served as the control. MC/PC showed the highest yield of major aromatic products. Vanillin, homovanillic acid, acetovanillone, guaiacol, and vanillic acid were major aromatic building blocks identified and quantified. Further optimization revealed a total monomer yield of 22.77 wt%. SEM and FTIR analysis were done with the latter revealing the existence of pre-oxidation reaction in the BM and MC lignin prior to PC. The proposed synergetic process could offer an advantage over prevailing robust systems used for lignin depolymerization.