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