Research on the thermochemical conversion utilization of nitrogen-rich microalgae: Two-step catalytic pyrolysis of Nannochloropsis sp over ZSM-5

To explore an effective method of utilizing nitrogen-rich microalgae, the two-step pyrolysis (TSP) characteristic of Nannochloropsis sp (NCS) over ZSM-5 were studied by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetric analyzer (TG). The results showed that the TG process of NCS was classified into three stages. ZSM-5 increased the final weight loss and the pyrolysis temperature of NCS. The kinetic analysis was conducted by Flynn-Wall-Ozawa method, and showed that the pyrolysis of NCS conformed to one-dimensional shrinking core model. ZSM-5 did not affect the kinetic model, but decreased the activation en-ergy. Compared with one-step pyrolysis, TSP improved the selectivity of N-heterocyclic compounds in the first step. Catalytic TSP further reduced the complexity of products significantly, and increased the selectivity of olefins in the first step, nitriles and aromatic hydrocarbons in the second step. The possible catalytic TSP reaction pathways of NCS were proposed.

Automated summary

This study investigated the two-step pyrolysis characteristics of Nannochloropsis sp (NCS) over ZSM-5. The results showed that ZSM-5 increased the weight loss and pyrolysis temperature of NCS. Kinetic analysis revealed that NCS pyrolysis followed a one-dimensional shrinking core model, and ZSM-5 decreased the activation energy. Compared to one-step pyrolysis, two-step pyrolysis improved the selectivity of N-heterocyclic compounds, and catalytic two-step pyrolysis reduced product complexity and increased selectivity of olefins, nitriles, and aromatic hydrocarbons.