Preparation of low-nitrogen and high-quality bio-oil from microalgae catalytic pyrolysis with zeolites and activated carbon

Abstract

To reduce the N content and prepare low-nitrogen and high-quality bio-oil from microalgae, the catalytic effects of different zeolite catalysts (HZSM-5, Hβ, HY) and activated carbon (AC) were studied. Zeolite catalysts and AC could effectively remove nitrogen from bio-oil and prepare the bio-oil enriched BTX. Zeolite catalysts promoted hydrodeoxygenation and hydrodenitrogenation of volatiles from microalgae pyrolysis and generated a mass of water, particularly HY, which had the most abundant acid sites. The bio-oil with HY catalyst had the lowest N content (1.25 wt%) and the highest mono-aromatics selectivity. Compared with zeolites, AC had more abundant microcellular structure, andaccelerated the deoxygenation of volatiles to form CO2 rather than H2O. The denitrification strengths on volatiles was as follows: HY > AC>HZSM-5>Hβ. Besides, the production of oil reduced and gas yields increased with temperature increasing, the outputs of aromatics reached maximum value at 500°C. And the N content of bio-oil reduced with temperature increasing, the N content of bio-oil from Nannochloropsis sp. (NS) and Spirulina platensis (SP) catalytic pyrolysis decreased to 0.82 and 1.82 wt% at 700°C. Compared with NS, the BTX from SP catalytic pyrolysis were more stable at higher temperature (700°C).