Hydrothermal Liquefaction of Post-Consumer Recycled\nLinear Low-Density Polyethylene with Different Molar Masses in Supercritical\nWater

Hydrothermal\nliquefaction (HTL), which uses subcritical and supercritical\nwater as reaction media, was used to chemically deconstruct post-consumer\nrecycled linear low-density polyethylene (PCR-LLDPE) with different\nmolar masses (from 7.20 × 10<sup>3</sup> to 1.29 × 10<sup>5</sup> g/mol) into oil at 425 °C for 2 h. When the molar mass\nwas within the range of 7.20 × 10<sup>3</sup>–1.36 ×\n10<sup>4</sup> (g/mol), a comparable oil yield (86–90%) was\nobtained. However, the oil yield was reduced to 66% when the molar\nmass increased to 1.20 × 10<sup>5</sup> (g/mol). The chemical\ncompositions of the oil converted from PCR-LLDPE with varying molar\nmasses were mainly composed of paraffins, olefins, cyclics, and aromatics.\nAdditionally, it was found that PCR-LLDPE and the post-HTL solid residues\ncontained metallic impurities that may participate in HTL of LLDPE.\nThe density functional theory was also used to elucidate the role\nof supercritical water under HTL in aiding deconstruction of LLDPE.\nThe calculated electronic and thermodynamic parameters suggested that\nalkanes with smaller molar mass require lower energy to be deconstructed\nin HTL.