A comparative analysis of slow, fast and oxidative pyrolysis of banana tree waste: a comprehensive study on process performance and product quality

This work investigates the pyrolytic conversion of mixed waste banana tree residues through three thermochemical routes: slow, fast, and oxidative pyrolysis during continuous operation. Feedstock was characterized via proximate and ultimate analysis, followed by thermogravimetric screening and batch pyrolysis to determine the effective temperature window for continuous operation. The maximum gravimetric bio-oil yield of 36.1 wt% occurred at 475 °C, whereas the highest volumetric condensable yield (35.9 wt%) was recorded at 500 °C. Continuous trials revealed that slow pyrolysis facilitated secondary polymerization, repolymerization, and aromatization, generating the highest char fraction (38.4 wt%) with a carbon-rich structure. Fast pyrolysis, enabled by rapid heating rates, favored liquid formation (36.8 wt%) through accelerated depolymerization of cellulose into levoglucosan and acetic acid. Oxidative pyrolysis, under limited oxygen, promoted partial combustion of volatiles, intensifying secondary cracking and yielding the highest gas fraction (54.8 wt%). Product distribution and composition varied significantly across regimes. Fast pyrolysis bio-oil was enriched in phenolics and furans, while oxidative pyrolysis oils contained higher proportions of acids, ketones, and aldehydes. Gas analysis indicated that slow pyrolysis promoted decarbonylation with steady CO evolution; fast pyrolysis suppressed CO₂ while producing appreciable CH₄ and CO; oxidative pyrolysis shifted products toward H₂ and CO₂ via autothermal oxidation. Char analysis showed fast pyrolysis yielded the highest carbon content (52.4 wt%), slow pyrolysis produced 46.5 wt% C, and oxidative pyrolysis resulted in mineral-rich chars (44.7 wt% C).