The increasing accumulation of plastic waste has intensified the need for effective strategies to enable the circular valorization of end-of-life plastics. Polyolefins, particularly polyethylene and polypropylene, account for nearly 50 % of global plastic production by mass and are predominantly used in short-lived packaging applications. As a result, they constitute more than 60 % of post-consumer plastic waste, highlighting the urgent need for efficient recycling pathways for these chemically inert materials. In this context, hydroconversion has emerged as a promising approach for the conversion of polyolefin waste into valuable chemical fractions under relatively mild conditions, with tolerance toward heteroatoms and contaminants.
However, the development of this process remains limited by feedstock diversity, variability and availability, which currently hinder large-scale implementation. One potential strategy to overcome these limitations is the co-processing of polymers with Vacuum Residue, which serves to homogenize the feedstock and allow larger process scales.
The main objective of the present work is to review the state of the art in chemical recycling of polyolefins via hydroconversion, with a particular focus on co-processing strategies and mechanistic hypotheses. This study also investigates the reaction mechanisms of hexadecane as a model solvent using an isotopic tracing method, providing preliminary results from this PhD project.
This pathway elucidation approach is based on the pluri-atomical isotopic tracing of 13C and 2H and was validated using NMR and GC–MS analyses. Hydroconversion experiments were conducted under typical vacuum residue processing conditions using an industrial proprietary CoMoNi catalyst.
Once the methodology is fully established, future work will extend this approach to increasingly complex reaction matrices, including Hexadecane/LDPE and, in the final stage of the PhD, Vacuum Residue/LDPE systems. The ultimate objective is the development of an analytical methodology aimed at advancing mechanistic understanding, with applicability to other complex reaction matrices. This approach seeks to elucidate the intrinsic reactivity of plastics and to assess the influence of the solvent on this reactivity.
