Catalytic Hydrothermal Liquefaction of Polyethylene With Pt/C to Tune Product Selectivity

ABSTRACT Hydrothermal liquefaction (HTL) represents a promising thermochemical pathway for recycling recalcitrant plastic waste, such as polyethylene (PE), offering high conversion efficiency under relatively mild operating conditions. However, oils produced by non‐catalytic HTL typically consist of heterogeneous hydrocarbons, including paraffins, olefins, cyclic hydrocarbons, and aromatics, which complicates downstream refining. This study investigates the catalytic HTL of low‐molecular‐weight polyethylene (LWPE) over a Pt/C catalyst. Experiments were conducted in supercritical water at 425°C, with reaction times varied between 0.5 and 2.5 h to evaluate effects on product distribution and the composition of the GC‐MS‐detectable oil fraction. Within the experimental uncertainty, Pt/C did not significantly change the bulk product‐yield distribution relative to non‐catalytic HTL under the conditions examined. However, the GC‐MS‐detectable oil fraction from Pt/C‐catalyzed HTL showed pronounced enrichment of paraffinic hydrocarbons at shorter reaction times, indicating that Pt/C can influence product composition even when bulk yields remain comparable. By integrating oil, gas, and aqueous‐phase compositional analyses with product yield distributions, plausible reaction pathways for catalytic HTL of PE over Pt/C are proposed. These results provide insight into tuning product composition during HTL of PE and support the rational design of catalytic chemical recycling strategies for recalcitrant polyolefin waste.