Heterogeneous Component Degradation Controls Molecular Evolution and Reactivity of Volatile Organic Compounds during Distiller’s Grains Pyrolysis

Biomass pyrolysis is a crucial method of resource utilization, but resulting volatiles may pose environmental concerns due to their impacts on air quality and secondary pollution. However, the mechanisms governing thermal degradation and volatile evolution remain unclear. Herein, we integrate online thermogravimetry–Fourier transform infrared spectroscopy–gas chromatography/mass spectrometry, Gaussian deconvolution, and two-dimensional correlation spectroscopy to elucidate the degradation characteristics and sequential temperature-dependent volatile evolution of distiller’s grains (DG), a protein-rich agro-industrial residue. DG pyrolysis exhibited distinct multistage degradation characteristics governed by coupled decomposition and synergistic interactions of lignocellulosic and protein-derived components. The major volatiles included alcohols/ethers, phenols/esters, hydrocarbons, and aromatics, with pronounced temperature-dependent variations. Volatile and intermediate-volatility organic compounds accounted for 47–60% and 35–52% of total detected organic volatile emissions released during pyrolysis, respectively. Most DG-derived volatiles exhibited reducing characteristics, with average carbon oxidation states below zero, while broad saturation mass concentration distributions reflected substantial chemical heterogeneity. The temperature-dependent evolution sequence of DG-derived volatiles followed alcohols/phenols → aromatics/hydrocarbons → aldehydes/ketones/acids → esters → CO2/CH4/NH3. A DG mechanistic framework was proposed, demonstrating that heterogeneous component degradation regulated dynamic volatile generation and variation. These findings provide mechanistic insight into DG pyrolysis and contribute to sustainable biomass valorization and environmental impact assessment.