Catalytic pyrolysis of alkaline lignin: A systematic kinetic study

Lignin being the second most abundant natural polymer gaining interest as a source for production of biobased chemical, fuel and materials. The presence of phenyl, guaiacyl and syringal derivatives in its structure proves it as a prominent candidate for valorization into various aromatics. Though lignin degradation chemistry is very complicated to understand due to its varying nature from source to source, thermochemical routes like pyrolysis found promising for its valorization. In this study, kinetics of catalytic pyrolysis alkaline lignin was investigated with different catalysts (HZSM-5 and Cu modified HZSM-5) using thermogravimetric technique at three different heating rates (10, 40, and 70 °C/min) from room temperature to 900 °C. Cu modified ZSM-5 catalysts are analyzed using XRD and FESEM-EDS analytical techniques to determine the metallic impregnation in its structure. The average apparent activation energies of alkaline lignin, alkaline lignin + HZSM-5 and alkaline lignin + Cu/HZSM-5 pyrolysis from Friedman (FM), Kissinger-Akahira-Sunose (KAS) and Ozawa-Flynn-Wall (OFW) models are observed to be 116.837, 109.911 and 190.719; 299.346, 191.828 and 218.860; 346.597, 244.754 and 346.339 kJ mol−1 respectively. From Criado's master plots a multistep reaction mechanism was detected for all the pyrolysis processes.