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

Abstract

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.