(691c) Decoding the Polyethylene Pyrolysis Mechanism: A Multidimensional GC and Design-of-Experiments Approach Toward Sustainable Plastic Recycling

Accurate characterization of plastic pyrolysis products is essential for developing reliable kinetic models and optimizing chemical recycling strategies. Conventional one-dimensional gas chromatography (1D-GC) often falls short when analyzing the complex product mixtures generated from plastic pyrolysis, due to overlapping peaks and limited compound identification—particularly in the presence of olefins, paraffins, and aromatic hydrocarbons. In contrast, comprehensive two-dimensional gas chromatography (GC×GC) offers enhanced resolution via orthogonal separation, identifying significantly more chemical species and structural classes. Prior studies from our group have demonstrated GC×GC's ability to detect 2.8 to 5.3 times more compounds than 1D-GC during the pyrolysis of polymers like polypropylene (PP), high-density polyethylene (HDPE), polystyrene (PS), and their co-pyrolysis products.

This study integrates GC×GC into a micropyrolysis system to investigate HDPE pyrolysis under isothermal, reaction-controlled conditions. A Box–Behnken Design (BBD) was used to systematically evaluate the effects of temperature, particle size, sample size, and carrier gas flow rate on product distribution. Pyrolysis experiments were conducted using a micropyrolyzer coupled with GC×GC–FID and TOF–MS detection (Py–GC×GC–FID/TOF–MS). The analysis confirmed that experiments conducted within the BBD space remained in the isothermal, reaction-controlled regime. Principal Component Analysis (PCA) demonstrated statistically significant differences with varying pyrolysis temperatures (480–600 °C), while changes in particle size (53–125 to >300 μm), sample size (50–150 μg), and carrier gas flow rate (100–300 mL min⁻¹) showed no significant impact. Furthermore, increasing the sample size from 50 μg to 1000 μg and decreasing the carrier gas flow rate from 100 to 50 mL/min led to notable increases in the formation of cyclodiolefins (355%), cycloolefins (67%), and aromatics (62%).

These results underscore the critical role of multidimensional chromatography in resolving complex pyrolysis product mixtures and illustrate the value of statistical design and analysis in identifying intrinsic kinetic regimes. This integrated approach provides the experimental foundation needed to develop microkinetic models that support the advancement of sustainable and circular plastic recycling technologies.