Insights into reductive depolymerization of Kraft lignin to produce aromatics in the presence of Pt/HZSM-23 catalyst

Abstract

Lignin is one of the primary residues obtained after the processing of lignocellulosic biomass. However, most residual lignin is burnt directly to get rid of it, albeit one of the few biorenewable waste resources that can yield aromatics. Therefore, the present study investigates reductive depolymerization of Kraft lignin into aromatics in the presence of Pt/HZSM-23 catalyst. In this regard, the lignin conversion experiments were performed under mild reaction conditions at a temperature range of 100 °C to 200 °C for 1 h to 12 h in a high-pressure batch reactor. Besides, a comparative study was done on the effect of the supply of external hydrogen and in-situ hydrogenation. Eventually, 87.3% lignin conversion was measured yielding 65.1% bio-oil, primarily aromatics at optimized experimental conditions. It was observed that the mesopores in the Pt/HZSM-23 catalyst facilitate the transfer of larger molecules derived from the Kraft lignin, thus causing an overall improvement in the catalytic activity. A mechanistic study based on experimental conditions and products detected using GC-MS revealed that the in-situ hydrogen transfer route is more favorable for lignin depolymerization than externally supplied hydrogen.