Catalytic depolymerization of lignin macromolecule to alkylated phenols over various metal catalysts in supercritical tert-butanol

Three technical lignins (Asian lignin (AL), Organosolv lignin (OL), and Inbicon lignin (IL)) were selectively degraded to alkylated phenols (AP) over Pt/C, Pd/C, Ru/C, and Ni/C in supercritical t-BuOH. AP and other phenolics present in the lignin depolymerized oil fraction (lignin oil) were subjected to several chemical analyses. GC/MS analysis showed AL yielded a maximum of 1.40 wt% of 4-ethylphenol and 4-ethylguaiacol, while OL produced 1.89, 1.11, and 1.43 wt% of syringol, 4-methylsyringol and 4-propylsyringol, respectively under Pt/C condition. Relatively small amounts of AP were obtained from IL because it contained not only lignin moiety but also carbohydrate, ash, and other components. Meanwhile, the average molecular weights (M-w) of the lignin-oils were significantly lower than those of the lignins, clear evidence of lignin depolymerization. Moreover, elemental analysis indicated hydrodeoxygenation mainly occurred during lignin depolymerization. With increasing catalyst amount (Pt/C), total monomeric phenol yields decreased due to side reaction, but some kind of AP such as 4-ethylphenol and 4-ethylguaiacol showed increase trend with increasing catalyst amount. (C) 2014 Elsevier B.V. All rights reserved.