Pyrolysis behaviors and product distribution of Shengli Lignite at different heating rate and final temperature by TG-FTIR and Py-GC-MS

Abstract

ABSTRACT The slow pyrolysis characteristics of Shengli lignite (SL) from ambient temperature to 800°C at heating rates of 20°C/min and 100°C/min were investigated by thermogravimetric analysis coupled with Fourier transform infrared spectrometry (TG-FTIR) and by pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC-MS). The final temperatures had larger effect on the pyrolysis products. The pyrolysis at 800°C of 20°C/min and 100°C/min (from the Py-GC-MS) obtained a variety of aliphatic compounds and monocyclic aromatic compounds, including short-chain olefins, alcohols, and ketones. But at 400°C, almost no short-chain aliphatic compounds were obtained, and a faster heating rate (100°C/min) was beneficial for obtaining long-chain aliphatic alkanes, alcohols, and acids (n-Hexadecanoic acid and Octadecanoic acid). It provides evidence that the aliphatic chains in lignite structure were long-chain, and the short-chain aliphatic compounds were from the secondary decomposition. The bicyclic compounds, monocyclic aromatic compounds were always important products. The real-time FTIR showed obvious differences in the pyrolysis at different heating rates. In the slower pyrolysis process (20°C/min), the absorbance of CO2 was much higher than that in the other processes, but in the faster pyrolysis process (100°C/min), the diversity of the pyrolysis products was substantially improved by the -OH, C = O, -COOH, C-CH3 and aromatic C-H functional groups, so maybe more valuable gas/liquid products could be produced at larger heating rate. The products at some specific temperatures (from the DTG peaks) were also provided for the reaction analysis.