Pyrolysis\nof Polyolefin-Enriched Mixed Plastic Waste\nStreams: Effects of Pretreatments and Presence of Hydrogen during\nPyrolysis

Pyrolysis is considered a promising method for the chemical\nrecycling\nof mixed plastic waste streams, yet systematic experimental evaluations\nof these mixed streams remain limited. Herein, the pyrolysis of a\npolyolefin-enriched (PO-enriched) waste stream derived from a DKR-350\nmixed plastic waste is investigated. Particularly, the influence of\nan additional dry-washing step and the presence of hydrogen during\npyrolysis on product yield and quality is studied. Dry-washing to\nreduce surface contamination in mixed plastic waste is an application\nof a loop dryer to improve the quality of mixed plastic waste. Batch\npyrolysis in an autoclave reactor at 420 °C for 1 h under nitrogen\nresulted in up to 78% oil yield (on material intake) for dry-washed\nDKR-350. Product oil composition was characterized by using elemental\nanalysis and GC × GC-TOFMS, revealing a high aliphatic hydrocarbon\ncontent (up to 94%). Moreover, pyrolysis oils from PO-enriched DKR-350\ncontained significant amounts of linear and branched aliphatic components\n(up to 80%). Dry-washing reduced inorganic feedstock contamination\n(e.g., pigments, salts) to below 4%, enhancing oil yield by 10% as\nwell as increasing the overall hydrogen and carbon to oil yields.\nRemarkably, unwashed DKR-350-derived pyrolysis oil had low chlorine\nlevels (as low as 17 ppm) compared to 32 ppm for oils from dry-washed\nstreams. Experiments in the presence of hydrogen instead of nitrogen\nresulted in product oils with a higher H/C ratio, indicating hydrogen\nincorporation in the product during pyrolysis. For example, the level\nof unsaturated hydrocarbons reduced from 25% to 20%, and the heteroatom\ncontent was reduced by up to 31%. Overall, high liquid and carbon\nyields are obtained for pyrolysis oils from contaminated plastic waste,\nwhich to the best of our knowledge have not been reported before.\nThe pretreatments and processing methods outlined in this work positively\naffect product properties, reducing the need for post-treatment processing.