Development of a reactor model for the scale-up of a polyolefin recycling process

The modern economy is heavily reliant on plastics due to their unique properties, including cost-effective production, lightweight nature, and versatility, which are unmatched by any other material. However, a significant drawback is the persistence of plastic waste, which degrades slowly through natural processes and requires substantial effort for recycling. To enhance recycling rates, alternative methods to traditional mechanical recycling and thermal utilization are being explored. One such method is the ReOil® process, which employs pyrolytic reactions in a continuous tubular reactor to decompose the organic molecules in plastics into smaller molecules. These smaller molecules can then be reused to produce high-quality virgin plastics. This process demands less stringent sorting and purity of input materials compared to mechanical recycling and offers greater sustainability than thermal utilization.
In this thesis, a reactor model for a continuously operated pyrolysis tubular reactor is developed. The model includes a physical part that resolves the reactor’s heat balance, accounting for sensible heat, reaction enthalpy, melting enthalpy, and internal heat transfer resistance. Additionally, the physical model calculates the reactor’s pressure loss, incorporating frictional losses and losses due to valves and fittings. To simulate the chemical processes, a lumped kinetic modelling approach was employed, resulting in a novel sequential eight-lump kinetic model. After fitting of the kinetic parameters, the model showed a prediction accuracy of ± 5 wt.% per lump, with a sensitivity analysis confirming the optimality of the kinetic parameters. The model was developed, and the kinetic parameters were fitted using experimental data from a laboratory-scale reactor with a throughput of 2 kg/h of plastic. The model was validated for scale-up using data from a pilot-scale plant with the ability of processing 100 kg/h of plastic.