Studies on co-pyrolysis of microalgae and polymeric waste (plastic/rubber): Thermal behavior, kinetics, and product characteristics

Abstract

Frequent global health crises pose the challenge of effectively recycling the vast amounts of waste polymers generated by pandemics. The co-pyrolysis of polymers and microalgae to produce high value-added chemicals and fuels presents a promising solution for waste management. The present work aims to comprehensively study the thermal degradation properties, synergistic effects, kinetic parameters, product distribution, and pyrolytic oil composition of Chlorella vulgaris (CV), polystyrene (PS), and nitrile butadiene gloves (NBG) co-pyrolysis. The results show that the interaction during co-pyrolysis promotes CV decomposition. The kinetic analysis indicated that CV:PS:NBG reduced the activation energy at all phases. The master plot method shows that CV, PS, and NBG correspond to the order reaction model (F8), nucleation model (A2), and diffusional model (D3), respectively. Meanwhile, the 1D diffusion model (D1), second-order model (F2), and first-order model (F1) are more suitable for the pyrolysis processes of CV:PS, CV:NBG and CV:PS:NBG. The thermodynamic characteristics suggest that all components require external energy to form activated complexes, and the presence of polymers promotes this process. Co-pyrolysis greatly enhanced the pyrolysis oil yield, from 45.58 wt% for the CV alone pyrolysis to 67.36 wt% for CV:PS, 50.59 wt% for CV:NBG, and 61.43 wt% for CV:PS:NBG. Compared to the theoretical values, the pyrolysis oil derived from the ternary blend exhibited increases of 17.74 % and 7.04 % in aromatic hydrocarbons and hydrocarbons, while the contents of N and O elements were reduced by 2.96 % and 2.54 %, respectively. The interaction mechanism and potential reaction pathways of CV with PS and NBG co-pyrolysis was proposed based on the reaction process. This study implies that CV co-pyrolyzed with PS and NBG could optimize energy output, providing theoretical and practical support for efficiently utilizing waste resources.