Solvent Reuse and Environmental Burdens in Dissolution-Assisted Recycling of Mixed Polyolefin Waste: A Life Cycle Comparison with Pyrolysis

Mixed polyolefin waste can be treated by dissolution-assisted recycling or pyrolysis, yet comparisons are often confounded by different feedstocks, pretreatment, system boundaries, and product functions. This study presents a harmonised process-level life cycle assessment of dissolution-assisted recycling and pyrolysis of a 50:50 post-consumer high-density polyethylene/polypropylene blend. Both routes receive 1 kg of clean, dry polymer after identical transport and pretreatment. The dissolution route circulates xylene and yields recycled pellets; pyrolysis yields oil, char, and non-condensable gas. Seventeen selected ReCiPe 2016 midpoint (H) indicators were evaluated. Within this treatment-based boundary, pyrolysis had lower impacts in all 17 categories. Climate change impacts were 1.643 and 0.663 kg CO2-eq per functional unit for dissolution-assisted recycling and pyrolysis, respectively, a 59.6% lower result for pyrolysis. Electricity, fresh-xylene production, and solvent-residue treatment were key dissolution burdens, and pyrolysis was predominantly electricity-driven. Extending xylene reuse to seven cycles while reducing route-specific electricity by 10% lowered dissolution’s climate change impact to 1.293 kg CO2-eq per functional unit, 21.3% below its base case, without changing the ranking. Reducing polymer recovery to 98% and 95% increased the base-case climate change impact of dissolution-assisted recycling by 1.1% and 2.8%, respectively. Separate sensitivity analyses examined pyrolysis process energy, off-gas utilisation, electricity sources, geographical assumptions, and routine solvent deficit and distillation recovery, varied independently. The comparison is limited to treatment of the same plastic-waste input and, therefore, excludes avoided-product credits and downstream conversion of pyrolysis products into new polymers. The fate of routine xylene losses was not measured, which limits interpretation of the toxicity and photochemical-ozone indicators. These results identify solvent containment, reuse, and electricity efficiency as priorities for dissolution-assisted recycling, and process-energy efficiency for pyrolysis, while underscoring the need for harmonised downstream comparisons to assess circularity.