Influence of biomass type and metallurgical coal properties on functional-group evolution and evolved-gas profiles during co-pyrolysis

The partial substitution of metallurgical coal with renewable biomass may reduce fossil carbon input during cokemaking, but its effects on coke oven gas (COG)-relevant volatile evolution remain insufficiently understood. This study investigated the influence of Chlorella vulgaris (MA) and torrefied Bambusa balcooa (TB) on the thermal decomposition behaviour, IR-active functional-group evolution, and evolved-gas profiles of two Australian metallurgical coals of differing rank. Blends comprising 80 wt.% coal and 20 wt.% biomass were analysed using in situ diffuse reflectance infrared Fourier-transform spectroscopy and thermogravimetric analysis coupled with mass spectrometry. MA-containing blends exhibited higher relative aliphatic C-H and hydroxyl-associated band intensities at low temperatures and earlier, broader evolution of CH 4 -, CO-, and H 2 O-associated signals, particularly in the mid-rank blend. TB produced a more coal-like gas evolution profile with smaller changes in functional-group intensity, consistent with the stabilising effect of torrefaction. However, its effect depended strongly on coal rank. In the high-rank blend, TB was associated with accelerated mass loss during coal devolatilisation and lower-than-calculated light hydrocarbon-associated signals, whereas the mid-rank blend showed a reduced mass-loss rate and non-additive enhancement of propene- and butane-associated signals. These contrasting behaviours demonstrate rank-dependent non-additivity in the TB blends, although the respective contributions of TB ash chemistry, residual organic structure, and physical effects could not be isolated. The results demonstrate that biomass selection and coal rank jointly influence COG-relevant gas evolution during coal-biomass co-pyrolysis.