Interaction effects of feedstock and temperature on biogas production during torrefaction-coupled catalytic stepwise pyrolysis of phytoremediation biomass

Torrefaction-coupled catalytic stepwise pyrolysis demonstrates significant efficiency and potential for transforming phytoremediation biomass into valuable fuels. This study investigated the bio-oil and biogas formation mechanisms during Pfaffia glomerata (PG) pyrolysis by integrating torrefaction with HZSM-5 and H-BETA catalysts. A thermogravimetry-Fourier transform infrared spectroscopy and a two-dimensional correlation spectroscopy were used to analyze the dynamics and evolution of the main pyrolytic biogases. A pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and a GC/MS were employed to analyze the formation, transformation, and yield of pyrolytic products. CH4 and CO emissions consistently exhibited the highest temperature sensitivity during the stepwise pyrolysis. Torrefaction reduced the oxygen content of PG, diminishing oxygenated organic compounds in pyrolytic biogas and bio-oil while enhancing aromatic hydrocarbon yields and selectivity. Coupling torrefied samples with HZSM-5 resulted in superior catalytic deoxygenation compared with H-BETA, significantly increasing the yield of aromatic hydrocarbons in both biogas and bio-oil. A comprehensive evaluation of torrefaction-pyrolysis-catalysis parameters showed that torrefaction decreased solid and energy yields but increased energy density. Catalytic performance metrics (catalytic effective area, catalytic index, and aromatic enhancement index) were markedly higher for HZSM-5 (ZP@300) than H-BETA, underscoring its efficacy in aromatic hydrocarbon synthesis. This study establishes a systematic framework for optimizing torrefaction-catalysis synergies in phytoremediation biomass valorization.