Cellulose upgradation by torrefaction pretreatment and effect of torrefaction severity on the quality of pyrolysis products
Xi Ni, Kehui Cen, Xiaoran Li, Dongxu Cui, Mian Liu, Lingzhi Zhu, Dengyu Chen
Abstract
Torrefaction serves as a promising technique for upgrading biomass. In this study, the torrefaction of cellulose, which is the main component of biomass, between 200 and 300°C for 15–45 min was systematically investigated to analyze the impact of torrefaction conditions on properties and pyrolysis polygeneration of cellulose. Results of the study showed that with an increase in torrefaction severity, the yield of torrefied solid products from cellulose decreased, alongside reductions in volatiles and oxygen content, while fixed carbon content and higher heating value (HHV) increased. These changes suggest that torrefaction accelerated the carbonization process of cellulose. Additionally, pyrolysis results revealed that higher torrefaction temperatures and longer residence times increased the yield of biochar. This was accompanied by reducing oxygen-containing functional groups, which facilitated the graphitization of biochar. The yield of syngas increased slightly, with a notable decrease in CO 2 yield and rise in CO and H 2 yields. Moreover, the HHV of syngas increased. Conversely, the bio-oil yield decreased markedly, characterized by a reduction in the relative contents of anhydrosugars and acids, and an increase in the relative contents of furans and ketones, demonstrating that torrefaction modified the compositional distribution of bio-oil. Overall, torrefaction pretreatment improved the pyrolysis performance of cellulose. This work provides valuable data and a foundation for the high-value utilization of biomass pyrolysis polygeneration. • Effects of torrefaction on pyrolysis polygeneration of cellulose are investigated. • Torrefaction reduces oxygen content and optimizes pyrolysis performance. • Torrefaction increases the yield of biochar and promotes its graphitization. • The CO+H 2 content of syngas are enhanced by torrefaction. • The composition and quality of bio-oil is improved by torrefaction.