Influence of Expansion Pretreatment on the Structure Evolution and Reaction Chemistry during Oxidative Pyrolysis of Tobacco Biomass

This study aimed to investigate the effects of expansion pretreatment on the chemical structure and reaction characteristics of tobacco pyrolysis. Systematic characterization of the pretreated feedstock was conducted to analyze changes in the physicochemical properties of the feedstock. The thermal conductivity and specific heat capacity of the tobacco decreased significantly after expansion pretreatment. Furthermore, the average pore diameter and pore volume of the feedstock increased, leading to a significant enlargement of the specific surface area from 0.18 to 0.46 m²/g, which consequently resulted in higher reaction rates. The pyrolysis characteristics and products of the pretreated feedstock were further investigated using thermogravimetric analysis (TGA), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and pyrolysis-gas chromatography/mass spectrometry (py-GC/MS). The results showed that the presence of oxygen significantly altered the pyrolysis mechanism, resulting in increased mass loss at high temperatures and triggering the decomposition of high molecular weight polymers in the feedstock. The expansion process disrupted the inherent structure of the lignocellulosic fibers, leading to enhanced interactions between aromatic compounds and nitrogen-containing functional groups, which increased the yield of nitrogen-containing compounds.