In-depth into the mechanism of aromatic production from catalytic pyrolysis of wet-torrefied microalgae with HZSM-5 coated biochar

Abstract

Bio-oil from pyrolysis of microalgal biomass tends to exhibit high oxygen and nitrogen content, which is challenging for the commercial application of algae-based fuels. This study started with wet torrefaction of Chlorella to improve its fuel properties, and then Zeolite Socony Mobile-5 (HZSM-5) was used to synthesize HZSM-5 coated biochar (HZSM-5@biochar) catalyst for catalytic pyrolysis. During the process, up to 96.06% of aromatics with benzene, toluene and xylene (BTX) selectivity of 83.24% and a yield of 94.64 mg g⁻¹ was obtained under specific conditions (wet torrefaction at 200 °C, pyrolysis at 500 °C, catalyst-to-feedstock ratio of 20:1). Meanwhile, the content of oxygenates and nitrogenates was reduced from 82.14% under non-catalytic condition to 3.26%. The catalytic conversion pathway was hypothesized by catalytic experiments with model compounds. The transformation process of oxygen- and nitrogen-containing functional groups was probed by XPS and in situ DRIFTS to help elucidate the deoxygenation and denitrogenation mechanism during the catalytic pyrolysis of Chlorella. Besides, the excellent stability of HZSM-5@biochar was demonstrated by six-cycle experiments. The composite catalyst also showed lower yield of coke (0.33%) with less aromaticity after a single use compared to HZSM-5, whose coke yield was 1.87%. Scanning electron microscopy analysis revealed that compared to HZSM-5@biochar, the used HZSM-5 formed more amorphous components suspected to be coke.

Graphical Abstract

Keywords

HZSM-5@biochar / Aromatic hydrocarbons / Deoxygenation and denitrogenation / Biomass catalytic pyrolysis / Catalyst stability

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Funding

National Natural Science Foundation of China(No. 52566015)

Young Talents (academic) of the Ganpo Juncai Support Program of Jiangxi Province(20243BCE51078)

Natural Science Foundation of Jiangxi Province(No. 20242BAB20105)

RIGHTS & PERMISSIONS

The Author(s)