Fractional pyrolysis and one-step pyrolysis of natural algae Cyanobacteria from Taihu Lake were comparatively studied from 200 to 500°C.One-step pyrolysis produced bio-oil with complex composition and low high heating value(HHV 30.9 MJ/kg). Fractional pyrolysis separated the degradation of different components in Cyanobacteria and improved the selectivity to products in bio-oil. That is, acids at 200°C, amides and acids at 300°C, phenols and nitriles at 400°C, and phenols at 500°C, were got as main products, respectively. HZSM-5 could promote the dehydration, cracking and aromatization of pyrolytic intermediates in fractional pyrolysis. At optimal HZSM-5 catalyst dosage of 1.0 g, the selectivity to products and the quality of bio-oil were improved obviously. The main products in bio-oil changed to nitriles(47.2%) at 300°C,indoles(51.3%) and phenols(36.3%) at 400°C. The oxygen content was reduced to 7.2 wt% and 9.4 wt%, and the HHV was raised to 38.1and 37.3 MJ/kg at 300 and 400°C, respectively. Fractional catalytic pyrolysis was proposed to be an efficient method not only to provide a potential solution for alleviating environmental pressure from water blooms, but also to improve the selectivity to products and obtain high quality bio-oil.
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