Jian Li,Wen Fu,Xiaowei Bai,Xiangrui Lin,Heping Yang,Mengfei Wang,Guangxuan Liu,Zhenghua Dai
Oxidative pyrolysis of biomass, which introduces controlled oxygen into the reaction, enables autothermal processes and addresses heat transfer challenges in large reactors. Oxygen promotes exothermic reactions and changes product composition. Given the unique chemistry of cellulose, hemicellulose, and lignin, their pyrolytic behaviors vary with oxygen levels. This study examines these variations. The results indicate that when 10 vol% of oxygen is introduced, for cellulose, the main impact is on the third (310–410 °C) and fourth (410–700 °C) stages of pyrolysis, where O 2 reacts with the produced sugars (reducing by 6.6 %) and biochar to generate CO, a small amount of CO 2 , and water; for hemicellulose, the main impact is on the fourth stage (340–850 °C), where O 2 reacts with the produced biochar to generate CO, a small amount of CO 2 , and water; for lignin, the main impact is on the second (190–410 °C) and third (410–850 °C) stages, where O 2 reacts with the produced phenolic monomers (reducing by 2.2 %) and biochar to generate CO 2 , a small amount of CO, and water. Cellulose and hemicellulose generate more CO in oxidative pyrolysis, whereas lignin produces more CO 2 , due to varying oxygen content. Furthermore, after the introduction of 10 vol% of oxygen, the pyrolysis process of both lignin and cellulose is advanced, with lignin reaching an exothermic peak value of 18.6 mW/mg, which is 5.3 mW/mg higher than that of cellulose and 11.2 mW/mg higher than that of hemicellulose, indicating that lignin releases the most heat, while hemicellulose releases the least.
Converting plastic wastes into value-added products through energy-efficient pyrolysis is essential, and it requires lower pyrolysis temperatures and shorter processing times than that of other processes. An exothermic phenomenon was observed during the process high-pressure polyethylene pyrolysis. It was proven for the first time that the exotherm is caused by a pressure-induced phase transition, in which colossal heat release can be driven by relatively small pressures. A large temperature change (> 100 °C) leads to the deep cracking of polyethylene, although the set temperature is far lower than the required temperature for thermal cracking. Importantly, the heat input stops immediately when the set temperature is reached; thus, the external heating time is short. Polyethylene can be completely converted into liquid products in ~90 wt% yield and with a small number of gases. The self-exothermic phase transition only occurs within a certain range of material thickness, which is related to the corresponding phase behavior. In the self-exothermic pyrolysis process, with an increase in the thickness of polyethylene, the proportion of low-value olefins in oil products decreases gradually, while alkanes, isoalkanes and aromatics show an increasing trend, making the product composition closer to the fuel standard. This work provides a viable approach for plastic recycling at low pyrolysis temperatures and short external heating times with the help of a self-exothermic phase transition in the absence of a catalyst.
危险品化学品经营许可证（带存储）