Insight into effects of torrefaction on biomass: Chemical composition, pyrolysis behavior and products distribution

Torrefaction technology plays a role in biomass pretreatment and upgrading of pyrolysis products, significantly contributing to the sustainable development of bioenergy and carbon-based materials. In this study, a large-scale continuous torrefaction equipment with programmable logic controller was employed to torrefy corn stover (CS) and rice straw (RS) at a temperature of 260 ℃. The chemical composition, pyrolytic behavior, and product distribution of the biomass before and after torrefaction were systematically investigated using Fourier-transform infrared spectroscopy, thermogravimetric analysis, and pyrolysis-gas chromatography/mass spectrometry. The results showed that torrefaction led to a significant reduction in moisture and volatiles content, while the ash and fixed carbon content increased correspondingly. Furthermore, the H/C and O/C ratios declined, and the high heating value increased significantly (15.0% for CS and 21.9% for RS). A reduction in the absorbance of oxygen-containing functional groups such as -OH, CO, and C-O was also observed. indicating chemical modifications in the biomass structure. During pyrolysis, torrefied biomass exhibited a slower mass loss rate, the disappearance of the shoulder peak in the thermogravimetric curve, and a significant higher residual yield compared to untreated biomass, suggesting that torrefaction had a profound effect on its thermal degradation behavior. Additionally, the increased yields of phenols, esters, and alcohols in the pyrolysis products further confirmed the substantial influence of torrefaction on both the chemical structure of the biomass and the distribution of its pyrolysis products. These findings provide valuable scientific insights for improving the efficiency of biomass energy utilization in large-scale.