Microwave catalytic co-pyrolysis of Chlorella vulgaris and polystyrene: Characteristics, pyrolysis oil component and mechanism analysis

Microwave catalytic co-pyrolysis can transform microalgae and waste plastics into high-value pyrolysis oil, yet its quality requires further enhancement. This paper studied the co-pyrolysis characteristics and product yields of Chlorella vulgaris (CV) and polystyrene (PS) under different mixing ratios (10:0, 8:2, 6:4, 5:5, 4:6, 2:8 and 0:10). The effects of modified biochar catalyst (Fe/BC) with different additions on the co-pyrolysis of CV and PS were investigated. Then, the pyrolysis oil components were analyzed by GCMS. Finally, specific amino acids and fatty acids rich in CV were used as model compounds to explore the formation mechanism of main products in pyrolysis oil by density functional theory (DFT). The results showed that CV:PS = 8:2 (C8P2) exhibited optimal interaction. Adding PS and Fe/BC significantly improved the CV pyrolysis performance and promoted the removal of nitrogen and oxygen. The pyrolysis oil yield (21.50 %) and aromatic hydrocarbons content (73.13 %) under 30 % Fe/BC were the maximum. Concurrently, the minimum content of nitrogen-containing compounds (12.56 %) and oxygen-containing compounds (5.61 %) was observed at 30 % Fe/BC. DFT calculation results showed that the decarboxylation reaction of amino acids and fatty acids exhibited a low potential barrier and was more readily converted to amines. The reaction activity of nitrogen and oxygen containing groups in each reaction was higher than carbon containing groups.