Molecular insights into the heavy components of bio-oil derived from microwave-assisted co-pyrolysis of microalgae and polyethylene

Microwave-assisted co-pyrolysis of microalgae and polyethylene is a promising approach for sustainable bio-oil production. However, the limited understanding of the heavy components in co-pyrolysis bio-oil significantly restricts its upgrading. In this work, the characteristics and formation mechanisms of heavy components in bio-oil derived from microwave-assisted co-pyrolysis of microalgae and polyethylene were investigated at the molecular level using Fourier transform ion cyclotron resonance mass spectrometry. The results indicated that co-pyrolysis with polyethylene made the heavy components lighter and more saturated. Additionally, there was a significant increase in the content of CHO and CHOS components, which were enhanced by up to 5.00 and 6.65 times compared to the microalgae bio-oil. N 2−3 compounds accounted for 60.47 % in the microalgae bio-oil, while over 58.63 % of the heavy components in the co-pyrolysis bio-oils were nitrogen-free. Moreover, most of the heavy components in the co-pyrolysis bio-oils contained two or more oxygen atoms. The interactions between lipids and polyethylene resulted in the production of fatty acids and long-chain esters, which were the predominant O 2 species and served as precursors for O 3 and O 4 species. The O 5 species consisted of thiopyranosides generated from the reaction of glycosides derived from carbohydrates and sulfur-containing compounds provided by proteins. Additionally, amino acids contributed to the formation of cyclic N 2 O 3 species through fusion. The proposed mechanisms were verified through thermodynamic calculations and monomer experiments. These findings can guide the high-value and eco-friendly utilization of microalgae, as well as other nitrogen-rich biomass and polyethylene.