Co-Valorization of Waste Cooking Oil and Expanded Polystyrene Pyrolysis Fractions as Potential Fuel Blendstocks

The energy demand, depletion of fossil fuels, generation of plastic waste, and final disposal of waste cooking oil (WCO) have become major concerns due to industrialization and population growth, creating significant environmental challenges. These challenges have encouraged the development of sustainable alternatives for the valorization of residual feedstocks. On the one hand, global energy consumption continues to increase, promoting the search for alternative fuel sources; on the other hand, the improper disposal of plastic waste has motivated the development of recycling technologies for plastic residues that are difficult to recycle through conventional routes. Moreover, WCO is commonly discharged into drainage systems, contributing to water contamination. Therefore, this study evaluates the alkaline-assisted co-processing of waste cooking oil with crude and distilled expanded polystyrene (EPS) pyrolysis fractions to obtain liquid products with potential application as fuel blendstock components. Specifically, the work explores the co-valorization of WCO with two aromatic hydrocarbon fractions derived from EPS pyrolysis: crude EPS pyrolysis oil and its distillate fraction. These EPS-derived streams are evaluated as residual hydrocarbon co-feeds for the alkaline-assisted processing of WCO into liquid fuel-like products. The influence of the catalyst loading, WCO-to-EPS-derived fraction mass ratio, and EPS-derived fraction type was analyzed based on the liquid product yield. Furthermore, first-generation vegetable oils were tested under selected conditions to compare their behavior with WCO and assess the applicability of the process to different lipid feedstocks. Finally, the fuel-related properties of the obtained liquid products were evaluated through the density, kinematic viscosity, and heating value, and compared with commercial fuel specifications. The results showed liquid product yields up to 92%, kinematic viscosity values within the range of international fuel specifications under selected conditions, and heating values above 40 MJ/kg. However, the density values indicated limitations for direct use as standalone fuels; therefore, the obtained products should be considered as potential fuel blendstock components requiring further blending and chemical characterization studies.