The Evolution Mechanism and N/O Conversion Paths of Microalgae Catalytic Pyrolysis with Activated Carbon

Catalytic pyrolysis is an effective approach to enhance the quality of microalgal pyrolytic oil, and activated carbon (AC) catalysts have garnered extensive attention. However, the evolution mechanism of products with AC catalysis remains unclear, which is crucial for the subsequent utilization of this technology. In this study, the evolution mechanism and N, O conversion pathways of microalgae catalytic pyrolysis with AC were explored through model compounds (lipids, protein, and carbohydrate), and the formation mechanism of aromatics (especially BTEX) was also discussed. It was found that AC catalysis might effectively promote water-gas reaction and reduce the water yield, and obviously accelerate decarboxylation of acid from lipid as well as dehydroxylation, decarbonylation and ring-opening of furfural from carbohydrates. For N-compounds, AC catalysis might facilitate the deamination of amides/amines and the ring-opening reaction and denitrification of unstable N-heterocycles. Moreover, nitrogen-containing groups underwent oxidation to form N_xO_y with AC catalysis. Consequently, the contents of oxygen and nitrogen in the oil decreased under AC catalysis, and the high calorific value gas products rich in C₂₊ and CO were obtained. Besides, AC catalysis increased the yield of aromatics, the BTEX from microalgae primarily derived from lipid and protein.