Kinetics, mechanisms and release of nitrogen-containing components during pyrolysis of Chlorella with potassium hydroxide addition

Abstract

Pyrolysis integrated with KOH activation is the most frequently used and efficient method for microalgae to produce N-doped porous biochar. However, the effects of KOH to the pyrolysis process of microalgae are still unclear. Thus, the pyrolysis behavior, kinetics and the release of volatiles especially the nitrogen-containing components during Chlorella pyrolysis with KOH addition were investigated in this study. Results showed that KOH significantly changed the pyrolysis behavior by lowering the initial decomposition temperature and reducing the weight mean activation energy. KOH reacted with the solid matrix even at room temperature. CO₂ was the dominant gas product, the release of which was postponed by KOH addition. KOH inspired the release of NH₃ to lower temperatures (< 400 °C) while the reverse for HNCO. With the increase of KOH, the formation of hydrocarbons in volatiles shifted to higher temperatures while the yield of acids dramatically reduced and even vanished. The release of nitrogen-containing components was greatly inhibited at 600 °C by converting nitrogen in the feedstock to harmless N₂. This study provided insights into the pyrolysis mechanisms of microalgae over KOH for biochar production and the essential environmental impact during the process.