Enhancing styrene monomer recovery from polystyrene pyrolysis: insights from density functional theory

Area of Science:

• Chemical Engineering
• Materials Science
• Environmental Science

Background:

• Plastic waste, particularly polystyrene, poses significant environmental challenges.
• Pyrolysis offers a method for plastic waste management and resource recovery.
• Efficient monomer recovery from pyrolysis is key to mitigating plastic pollution.

Purpose of the Study:

• To enhance styrene yield from polystyrene pyrolysis.
• To investigate the thermal and kinetic aspects of polystyrene degradation.
• To identify optimal conditions for maximizing styrene recovery.

Main Methods:

• Density Functional Theory (DFT) calculations using B3LYP/6-31G(d) level of theory.
• Geometry optimization, frequency calculations, and transition state optimization (TS Berny, QST3).
• Reaction path validation using the Intrinsic Reaction Coordinate (IRC) method.

Main Results:

• Identified energetically favorable pathways involving non-terminal C-C bond cleavage.
• Proposed four distinct pyrolysis pathways with determined thermodynamic and kinetic parameters.
• Identified major products including styrene, alpha-methylstyrene, and methane.
• Demonstrated that optimizing reactor temperature profiles enhances styrene recovery.

Conclusions:

• Polystyrene waste pyrolysis can be optimized for high styrene monomer yield.
• Understanding thermal degradation pathways is crucial for effective waste management.
• Controlling pyrolysis conditions, especially temperature, is vital for efficient resource recovery from plastic waste.