Relationship of thermal degradation behavior and chemical structure of lignin isolated from palm kernel shell under different process severities

Lignin has been considered to be a potential feedstock to produce phenols chemicals by fast pyrolysis technology because of its aromaticity. In this work, four types of lignin were isolated from palm kernel shell with different severities: milled wood lignin (MWL), alkali lignin (AL), Klason lignin (KL), and organosolv ethanol lignin (OEL). A deep investigation of the relevance of the pyrolysis behaviors and chemical structure was carried out by FTIR, GPC, 2D-HSQC-NMR, TGA-FTIR and Py-GC/MS. AL contained highest content of β-O-4 aryl ether bond (53.9/100 Ar) and highest value of S/G ratio (1.68). MWL showed the widest temperature range (126–536 °C) of thermal degradation because of its inhomogeneous distribution of molecular weight. Highest content of oxygen-containing non-condensable gas components (H2O, CO2, CO) was observed in AL. The dominant organic components from lignin pyrolysis were S-type phenols, G-type phenols, P-type phenols, and C-type phenols. G-type (9.74–26.01%) was the dominant phenols products in AL, while P-type (44.23–56.01%) for KL, P-type (29.38–56.07%) for OEL, and G-type (9.08–25.81%) and P-type (22.60–29.04%) in MWL. Higher pyrolysis temperature promoted the formation of aromatics. As the conversion rate increased from 0.1 to 0.8, the activation energy estimated from DAEM model of four types of lignin, all gradually increased.