Influence of inherent hierarchical porous char with alkali and alkaline earth metallic species on lignin pyrolysis

Abstract

This study aimed to explore the influence of inherent hierarchical porous char with alkali and alkaline earth metallic species (AAEMs) during pyrolysis of lignin derived from agricultural crop residues in a laboratory fixed-bed at 550 °C. A catalytic strategy was implemented to investigate volatile-char interactions based on ex situ lignin pyrolysis. The physico-chemical properties of the AAEMs-loaded char were characterized by FTIR, XRD, SEM-EDX and N2 nitrogen adsorption analyses. Results indicated that AAEMs-loaded char had a large specific surface area, hierarchical porosity, amorphous carbon structure, surface-active functional groups and highly dispersed metal species. Specifically, the specific surface area of AAEMs-loaded char was significantly reduced owing to coke deposition after interaction with pyrolysis vapours. Bio-oil composition revealed substantial increases in phenol, o-cresol, p-cresol and catechol. These increases were mainly attributed to demethylation, demethoxylation, or alkyl substitution reaction. The experimental results confirmed the occurrence of significant volatile-char interactions during lignin pyrolysis.