Shuai Guo,Yu Wang,Jianwen Yi,Deng Zhao,Deyong Che,Hongpeng Liu,Baizhong Sun
Co-pyrolysis of sludge and waste plastics is a long-term strategic approach for producing valuable fuels. However, sludge is characterized by a high protein content, which serves as a significant source of nitrogenous components in bio-oil. To improve the quality of pyrolysis products, the present study investigated the effect of low-density polyethylene (LDPE) on nitrogen transformation during the pyrolysis of sludge protein (SP). The study findings indicated that LDPE addition reduced the amount of solid residue owing to the interaction between SP and H radicals generated by LDPE pyrolysis. The thermal weight loss difference consistently remained below 0 when the SP-to-LDPE mixing ratio was 7:3, indicating that LDPE promotes the pyrolysis of SP. For the analysis of nitrogen-containing products during pyrolysis, LDPE addition significantly reduced the levels of nitrogen-containing compounds in the bio-oils of glutamate (Glu), histidine (His), and tyrosine (Tyr). Specifically, at 600°C, Glu, His, and Tyr in the bio-oils decreased by 31.4%, 33.3%, and 34.38%, respectively. No significant changes were observed in the nitrogen content within the pyrolysis char of Glu and His. However, all three amino acids exhibited a significant increase in the formation of NO x precursors due to the attack on the nitrogen positions of the heterocyclic nitrogen species by the H radicals generated by LDPE. This study contributes to research on the impact of LDPE on nitrogen migration and conversion during the pyrolysis of SP, laying the foundation for subsequent studies on pollutant removal reactions.
Shuai Guo,Tiecheng Liu,Jicheng Hui,Deyong Che,Xingcan Li,Baizhong Sun,Shaohua Li
The addition of CaO has been used to reduce the harmful NO x precursors (NH 3 and HCN) generated by the pyrolysis of municipal sewage sludge . However, the underlying reduction mechanism remains unclear. To address this issue, we systematically investigated the effects of temperature and CaO addition on the generation of NH 3 and HCN during the pyrolysis of sludge protein and a model protein. With increasing temperature from 300 to 900 °C, the inhibitory effect of CaO on NH 3 emission was observed to fluctuate, maximizing at 400 °C. The inhibition was attributed to the reaction of CaO with nitrogen in the produced char to form CaC x N y , resulting in enhanced fixation of the char pyridines and nitriles. The nitriles exhibited high thermal stability and inertness to CaO. The increased nitrile content at high temperatures was attributed to the formation of the species from amines and N-containing heterocycles . The CaC x produced by the thermal decomposition of CaC x N y above 700 °C was found to increase P–N fixation and decrease NH 3 formation. The observed poor inhibitory effect of CaO on NO x precursor formation at 650 °C was attributed to the production of NH 3 via HCN hydrolysis. Because HCN directly reacted with CaO, the inhibition of HCN formation was highest at 650–900 °C, preventing the conversion of char nitriles into HCN.
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