Co-pyrolysis of Chlorella pyrenoidosa and polystyrene: kinetics and product distributions

Co-pyrolysis of algae with polystyrene (PS) offers a promising and efficient approach to enhancing the quality of algae-derived bio-oil. This study investigated the thermal decomposition behavior, activation energy, and product distribution during the co-pyrolysis of Chlorella pyrenoidosa (CP) and PS. Thermal decomposition behavior was analyzed using non-isothermal thermogravimetric analysis (TGA) at heating rates of 10–40 °C/min. The activation energies were calculated using the OFW, KAS, and STK methods. Product distributions were examined using Py-GC/MS at 600 °C. TGA results revealed that the co-pyrolysis of CP and PS proceeded through four stages. Increasing CP proportions shifted pyrolysis temperatures toward higher values. The addition of PS significantly reduced the apparent activation energy, with the strongest positive synergistic effect at a CP5PS5 ratio. The average apparent activation energies for CP5PS5 were 180, 179, and 179 kJ/mol, as determined by the OFW, KAS, and STK methods, respectively. Py-GC/MS analysis revealed significant changes in the bio-oil composition with increasing PS content. The yields of MAHs and PAHs increased, while aliphatic hydrocarbons, oxygen-containing compounds, and nitrogen-containing compounds decreased. At a CP5PS5 ratio, MAHs increased to 67.09 %, PAHs increased to 30.22 %, oxygen-containing compounds dropped to 2.05 %, and nitrogen-containing compounds became undetectable. Co-pyrolysis of algae with PS provides a simple, effective, and scalable approach for upgrading bio-oil quality while simultaneously contributing to the management of plastic waste.