The co-pyrolysis of biomass–coal blends improves
energy
utilization efficiency; however, the synergistic mechanisms behind
thermal degradation and volatile formation remain unclear. We combined
online thermogravimetry–Fourier transform infrared spectrometry–gas
chromatography/mass spectrometry (TG–FTIR–GC/MS), Gaussian
deconvolution, and two-dimensional correlation spectrometry (2D-COS)
to reveal the component degradation, sequential response, and evolution
mechanism of volatiles during co-pyrolysis of rice straw (RS) and
semi-bituminous coal (SBC), which were mixed in three proportions
of 1:3, 1:1, and 3:1. The activation energies (24.70–53.43
kJ mol–1) and preexponential factors (44.67–7663.43
min–1) for decomposition and average emission intensity
coefficient (EIC) (0.06–0.12) of volatiles exhibited significant
heterogeneity and were highly dependent on pyrolysis temperature and
blend proportion. The EIC values of phenols/esters, alcohols/ethers,
ketones, aldehydes, and acids increased with increasing RS proportion.
The volatile distribution of blends with high SBC proportions was
mainly located in the decarbonylation/dehydration reaction region.
Moreover, the volatile organic compound (VOC) and intermediate VOC
percentages were 59–83 and 17–39%, respectively, with
N-containing species contributing the most to the intermediate VOC
fraction. Most of the volatiles mainly exhibited reducing character,
with average carbon oxidation state below zero. An increase in the
proportion of RS and SBC contributed to high unsaturation and small
carbon skeletons of volatiles, respectively. Notably, the primary
sequential temperature response of volatiles was hydrocarbons, alcohols/phenols/ethers/esters,
and (aldehydes/ketones/acids, aromatics), in that order. Furthermore,
we proposed a novel synergistic mechanism to demonstrate that the
heterogeneous degradation of RS/SBC components contributed significantly
to the dynamic formation of volatiles during the co-pyrolysis process.
These novel insights into the mechanisms of biomass–coal co-pyrolysis
are useful for energy optimization and pollution control.