Study on the Staged and Direct Fast Pyrolysis Behavior of Waste Pine Sawdust Using High Heating Rate TG-FTIR and Py-GC/MS

To understand the fast pyrolysis kinetics and product evolution of waste pine sawdust, high heating rate thermogravimetry-Fourier transform infrared (TG-FTIR) was used to obtain the kinetic parameters and the chemical groups formed during the pyrolysis process, while pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was used to investigate the detailed compositions of products under the staged (seven stages from 300 to 600 °C) and direct fast pyrolysis process. Spectral bands were identified for acids, alcohols, aldehydes, aromatics, esters, ethers, hydrocarbons, ketones, phenols, and sugars. Research found that the apparent activation energy for fast pyrolysis is much higher than that of slow pyrolysis. The evolution of CO₂ is the major deoxygenation route. Cracking mainly occurred at the 450 °C stage with phenols, ketones, aldehydes, and sugars as the main products. The product distributions for different stages are significantly different; the selectivity of aldehydes decreased, while phenols showed an upward trend with an increase in pyrolysis temperature. Ketones and sugars reached their peak values at 450 °C. The changes in the molecular composition of each stage helped to understand the pyrolysis process. Compared with the staged pyrolysis, the direct pyrolysis process had higher selectivity of acids, aldehydes, esters, and sugars and lower selectivity of phenols, ketones, and alcohols.