Pyrolysis of mixed plastic waste: Predicting the product yields

Area of Science:

• Chemical Engineering
• Materials Science
• Waste Management

Background:

• Predicting pyrolysis product yields from mixed plastic waste is crucial for efficient recycling and resource recovery.
• Understanding the behavior of individual polymers and their interactions during pyrolysis is essential for developing accurate predictive models.

Purpose of the Study:

• To evaluate the predictability of pyrolysis yields and product composition for mixed plastic waste streams using a superposition model.
• To investigate the influence of specific plastic types, particularly polyethylene terephthalate (PET), on pyrolysis outcomes.

Main Methods:

• Pyrolysis of virgin polymers (HDPE, LDPE, PP, PS, PET) and real waste streams at 500°C in a batch reactor.
• Development and application of a linear superposition model using individual feedstock data to predict mixed stream pyrolysis.
• Analysis of oil/wax product composition using 13C NMR spectroscopy to quantify carbon types (aliphatic, aromatic, carbonyl).

Main Results:

• The superposition model reasonably predicted oil/wax yields for mixed plastic streams, with a maximum deviation of 8%.
• High PET content (above 33 wt%) negatively impacted condensable product formation and increased solid product yield beyond predictions.
• Aliphatic carbon yield in oil/wax was accurately predicted (max difference of 6%), but aromatic carbon yield was not predictable, likely due to PET interactions.

Conclusions:

• A linear superposition model offers a viable approach for predicting mixed plastic pyrolysis yields, particularly for aliphatic carbon content.
• The presence of PET in mixed plastic waste poses a challenge to accurate yield prediction due to its interaction with other polymers and promotion of solid formation.