Energy Demand for Pyrolysis of Mixed Thermoplastics and Waste Plastics in Chemical Recycling: Model Prediction and Pilot-Scale Validation

Pyrolysis of plastic waste is a key technology for
closing the anthropogenic carbon cycle. The energy demand (ED)
of this endothermic process is a crucial factor to evaluate its
benefits compared to established recycling pathways. The pyrolysis
ED can be determined experimentally. However, this is elaborate
and limited in transferability. Existing models cover virgin plastics
or hydrocarbon thermoplastic mixtures on a laboratory scale. Here,
a model for calculating the ED of thermoplastic mixtures based on
the superposition of virgin polymer data is developed. The material
data, such as heat capacity, phase transition enthalpy, and reaction
enthalpy, are determined using differential scanning calorimetry.
Pilot-scale experiments are performed in a 1 kg/h screw reactor.
These experimental data are compared to model calculations. The
feedstock-specific ED for pyrolysis is plastic-type independent. It amounts to approximately 4−6% of the feedstocks’ net calorific
value. The validation shows excellent accordance for virgin plastics and hydrocarbon plastics mixtures. The modeled ED of mixtures
including heteroatoms is systematically underestimated, which indicates changes in the degradation mechanism. ... mehrThe model allows
for resolving several phenomena contributing to the pyrolysis ED. The simple calculation of the ED with in-depth information on
occurring phenomena enables more reliable process design, optimization, and evaluation.