Pyrolysis behaviors of four lignin polymers isolated from the same pine wood

• Isolation process greatly influences lignin structure and pyrolysis behavior.
• AL and MWL have poor thermal stability due to well-preserved weak ether linkages.
• Weights of two reactions in DG-DAEM vary among the four lignins pyrolysis.
• Higher phenols yield in the pyrolysis of AL and MWL via breaking of weak ether bonds.

Four lignin polymers, alkali lignin (AL), klason lignin (KL), organosolv lignin (OL), and milled wood lignin (MWL), were isolated from the same pine wood. Structural characterization by FTIR and 13C NMR indicated that the four lignins have different structural features. Their pyrolysis behaviors were analyzed by TG-FTIR and Py-GC/MS. Thermally unstable ether bonds and side branches were well-preserved in AL and MWL, but were broken in OL and KL. Pyrolysis of AL and KL produce more phenols at low temperature by the breakage of ether bonds. AL and KL show lower activation energies in the main degradation stage, quantified by a distribution activation energy model with two linearly combined Gaussian functions. The evolution behaviors of typical gaseous products, CH4, CO2, and CO, were analyzed, and insights about the correlation between chemical structure and pyrolysis behavior were obtained.

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