From plastics waste to chemical feedstocks: Hydrothermal liquefaction of low-density polyethylene-rich streams

Low recycling rates for plastics, particularly LDPE, hinder circular resource management due to challenges in collection and processing. This study explores hydrothermal liquefaction (HTL) of two LDPE-rich wastes, C-LDPE (∼90 wt% LDPE) and solid recovered fuel (SRF, ∼53 wt% LDPE), at 430–450 °C for 30–60 min, with water-to-feedstock ratios of 1.43–5.72. Higher reaction temperatures and extended residence times promote cracking, yielding less oil but lighter, more aromatic oil. Increasing the water-to-feedstock ratio enhances alkene selectivity and notably raises SRF oil yields from 15 to 24 wt% by mitigating antagonistic effects associated with the biogenic fraction in SRF. Conversely, the yield of C-LDPE oil decreases from 36 to 32 wt% at higher water ratios. While SRF’s heterogeneous nature causes high solid residue yields and experimental uncertainty, its plastic fraction is effectively converted. Overall, this study highlights HTL’s capacity to upcycle real plastic waste into valuable hydrocarbons, advancing circular polyolefin recycling.