Recent advances in copyrolysis of algal biomass with waste plastics for the production of upgraded oil

Co-pyrolysis of algae with common plastics (PET, HDPE, LDPE, PVC, PP, and PS) has emerged as a promising thermochemical pathway for simultaneously valorizing renewable biomass and polymeric wastes. This review synthesizes recent advances in mechanistic interactions, kinetic behavior, and liquid-phase product evolution in algae–plastic systems. Across polymers, co-pyrolysis consistently lowers activation energy, enhances devolatilization, increases oil yields beyond theoretical predictions, and suppresses oxygenated and nitrogenated compounds compared with algae alone. Polyolefins act as hydrogen donors that promote deoxygenation and denitrogenation; PET enhances decarboxylation and increases aromatic hydrocarbons; PVC accelerates volatilization through early HCl release with efficient chlorine capture; and PS contributes aromatic fragments that dilute heteroatom-rich vapors. These synergistic pathways generate hydrocarbon-rich oils with fuel-range heating values (∼42–47 MJ/kg) and improved physicochemical properties after catalytic upgrading or hydrotreatment. Key operational variables—including blending ratio, temperature, heating rate, reactor design, and catalyst formulation—strongly influence oil composition and fuel applicability. By integrating mechanistic insights with process-level outcomes, this review clarifies the potential of algae–plastic co-pyrolysis as a viable route for producing energy-dense liquids within circular waste-to-fuel strategies.