Impact of renewable biomass addition on carbon structure evolution during metallurgical cokemaking assessed by multi-scale spectroscopy

Partial substitution of metallurgical coal with renewable biomass may reduce fossil carbon input in cokemaking, but its influence on carbon ordering during pyrolysis remains unclear. Fixed 10 wt-% additions of microalgae (MA) and torrefied bamboo (TB) were blended with two Australian metallurgical coals and examined using thermal-gradient pyrolysis, Raman spectroscopy, solid-state 13 C CP/MAS NMR and HRTEM. Raman analysis revealed non-monotonic carbon ordering, with enhanced defect-related scattering at intermediate temperatures followed by high-temperature structural consolidation. NMR and HRTEM showed complementary changes in aromatic-cluster development, network connectivity and lamellar coherence. C1-based blends were less strongly perturbed than C2-based blends, although coal rank was not independently isolated. MA suppressed aromatic-cluster growth while permitting continued connectivity development, whereas TB promoted stronger intermediate-temperature aromatisation and connectivity, particularly in C2. Overall, biomass addition altered the magnitude, timing and persistence of multiscale carbon-structure evolution without establishing generalised coal-rank or biomass-type effects.