Impact of hygrothermal aging on gas release behavior and multi-stage pyrolysis kinetics of biomass: Insights from TG-FTIR and DAEM analysis

Biomass pyrolysis plays a vital role in renewable energy conversion. However, improving its efficiency and reducing the emission of harmful gases remain pressing challenges. Hygrothermal aging is an eco-friendly pretreatment that potentially optimizes biomass structure and pyrolytic behavior. This study systematically investigates the effects of controlled hygrothermal aging on the pyrolysis characteristics of cypress wood (CW) using thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy (TG-FTIR) and the distributed activation energy model (DAEM). The results reveal that hygrothermal aging significantly altered the pyrolysis characteristics of cypress wood, notably elevating the initial pyrolysis temperature and decreasing the peak emission concentrations of key pyrolytic gases. Specifically, after 120 days of aging, the maximum emission concentrations of CO2, phenol, CH4, and H2O decreased by approximately 25.2 %, 47.5 %, 33.6 %, and 39.6 %, respectively. Kinetic modeling with DAEM results indicated that aging reduced the hemicellulose content from 0.27 to 0.18, while cellulose content increased from 0.50 to 0.58. The lignin content remains relatively stable throughout the aging period. Moreover, the inversion results of the reconstructed kinetic model were highly consistent with the experimental data, with R2 > 0.99. Overall, these findings confirm hygrothermal aging as an effective and environmentally friendly pretreatment to reduce the proportion of unstable hemicellulose components and reduce harmful gas emissions.