Kraft lignin depolymerization to added-value building blocks by electrooxidation over Ni and Cu electrocatalysts

Lignin is a natural by-product coming from lignocellulosic biomass. Due to its polymeric aromatic structure, it is becoming an attractive source of aromatic building blocks, but the complexity and the heterogeneity of this material makes its depolymerization challenging. Among the possible depolymerization treatments, electrocatalysis has been adopted in this work to depolymerize lignin in mild conditions, applying renewable electricity, by means of a metal electrocatalyst. The electrocatalytic reaction has been conducted into a three-electrode cell, connected to a potentiostat, and registered by chronoamperometry experiment. Four types of catalysts have been tested: Ni bare, Cu bare, calcined Ni and calcined Cu. All of them have been characterized chemical-physically by SEM, XRD and Raman and electrochemically by cyclic voltammetry. Their activities have been evaluated by comparing obtained yield of vanillin, acetovanillone and guaiacol, the most recurrent products. Ni bare displayed the highest total yield. The effects of applied potential and reaction time on total products yields were evaluated. The best operating conditions were found to be 0.7 V applied potential and 10 minutes reaction time. 0.5 w/w% of vanillin yield was reached by applying 0.8 V.