Towards effective lignin conversion: HZSM-5 catalyzed one-pot solvolytic depolymerization/hydrodeoxygenation of lignin into value added compounds

Abstract

A one-pot greener approach towards lignin depolymerization/hydrodeoxygenation is presented. Water was used as a reaction medium with methanol as a source of reductive equivalents of hydrogen in inert atmosphere. Zeolite HZSM-5 and Ni-doped HZSM-5 were synthesized at low temperature (95 °C), characterized and used as a hydrodeoxygenation catalyst at 220 °C. Lignin conversion up to 96.8–98.5% was observed with highly reduced char formation (<1%). IR, GC-MS and ESI-MS spectroscopy were used to characterize the conversion products. The products were mainly comprised of alkyl substituted phenols (15.4 wt%) found as water soluble products. The water insoluble products showed mostly formation of oligomers with acyclic (4.1 wt%) and cyclic (1.5 wt%) compounds. Acyclic compounds included up to 2.8 wt% of open chain C₁₂–C₁₉ hydrocarbons. ESI-MS showed that the molecular weight of the products formed during solvolytic depolymerization/hydrodeoxygenation of lignin were in the range of m/z ca. 60 to ca. 1000. A mechanistic hypothesis on formation of monomeric products is also presented.