Effect of cryogenic pretreatment on product characteristics of lignocellulosic biomass pyrolysis using liquid nitrogen

Pyrolysis serves as the bedrock of thermochemical conversion of lignocellulosic biomass and constitutes one of the techniques towards high-value utilization of bioenergy, but it encounters core issues such as low bio-oil yield and inferior quality. To address these challenges, a novel pyrolysis method that combines cryogenic pretreatment and fast pyrolysis was adopted and investigated. The freezing pretreatment method was utilized for rice and wheat straws to explore the evolution mechanism of the product distribution and composition of biomass pyrolysis under cryogenic pretreatment. The experiments revealed that, in comparison with conventional pyrolysis, the pyrolysis bio-oil yield of after cryogenic pretreatment increased by 3.2–24.4 wt%, and the cryogenic pretreatment temperature exhibited a positive correlation with the bio-oil yield. The highest bio-oil yield was obtained at −90 °C (22.3–24 wt%). Cryogenic pretreatment exerted a significant transformative impact on the composition of bio-oil, with the content of benzene, toluene, ethylbenzene, and xylenes (BTEX) in bio-oil increasing significantly, with the maximum increment reaching 251.3 wt%. In addition, cryogenic pretreatment inhibited the release of CO 2 and CO during biomass pyrolysis, while promoting the formation of CH 4 and H 2 . Furthermore, cryogenic pretreatment increased the C content and calorific value of bio-char.