Mechanistic Insight into Lignin Slow Pyrolysis by Linking Pyrolysis Chemistry and Carbon Material Properties

As a highly abundant renewable carbon source, lignin can be converted to a variety of advanced carbon materials with tailorable properties through slow pyrolysis. In this study, slow pyrolysis of kraft lignin, for the first time, was investigated with a commercial pyrolysis–gas chromatography−mass spectrometry (Py-GC-MS) system through evolved gas analysis-MS (EGA-MS) and heart-cutting-GC-MS (HC-GC-MS) analyses. These analyses allow recovery and examination of the multi-phased gas products generated from thermal decomposition of lignin during slow pyrolysis over long time course thus making it possible to link pyrolysis chemistry and carbon material properties. The overall product distributions, including volatiles and solid product were quantitatively tracked at different heating rates (2, 20, 40 ℃/min) and different temperature regions (100-200, 200-300 and 300-600 ℃). Solid residues were further characterized using a suite of analytical tools, in correlation with the investigation of formation mechanisms of volatiles to reveal the reaction chemistry of lignin during slow pyrolysis, and to determine the morphology, pore structure, and interfacial chemical properties. This study provides critical insights into the slow pyrolysis chemistry of lignin and the properties of the resulting carbon material. These results will facilitate a better design and control of the lignin slow pyrolysis process for synthesizing functional carbon materials.