Synergistic effect study of Chlorella vulgaris and polyethylene in co-pyrolysis process based on kinetic and thermodynamic analysis

Abstract

The co-pyrolysis of algae and plastics shows great potential for bio-oil production. In this study, thermogravimetric analyzer was used to investigate the pyrolysis behavior of Chlorella vulgaris (CV) and polyethylene (PE) at different mixed ratios and heating rates. Their synergistic effects were discussed through kinetic and thermodynamic analyses. According to the thermogravimetric (TG) and Derivative thermogravimetric (DTG) curves, the co-pyrolysis process can be divided into five stages, corresponding to the decomposition of moisture, carbohydrates, proteins, lipids, and biochar, respectively. In the fifth stage, a clear synergistic effect is observed, with the highest ∆TG reaching about 4%. During the co-pyrolysis process, the average activation energy of the mixtures is much lower than expected, indicating the presence of a synergistic effect in co-pyrolysis. Among them, 3CV1PE is the optimal mixing ratio, with the average activation energy of 3CV1PE being 6% lower than that of CV pyrolysis alone. The master plots revealed that the power law reaction models (P3 and P4) are suitable for describing the experimental behavior of mixtures with higher CV content, while the third-order (F3) and eighth-order model (F8) are more appropriate for the decomposition reaction with higher PE content. The calculation of thermodynamic parameters further show that the co-pyrolysis of CV and PE is beneficial to the decomposition process, and the mixed ratio of 3:1 is the most favorable for the reaction. Results obtained in this work are valuable for guiding research on the co-pyrolysis of biomass and plastics.