Pyrolysis chemically recycles mixed or contaminated plastic that mechanical recycling can't handle — shredded feedstock is heated in an oxygen-free rotary kiln until the long polymer chains crack into shorter hydrocarbons. This model treats decomposition as a first-order thermal reaction driven by the Arrhenius equation:
k(T) = A · exp(−Eₐ / R·T) dm/dt = −k · m X(t) = 1 − exp(−k·t)
where A is the pre-exponential (attempt) factor, Eₐ the apparent activation energy, R = 8.314 J/(mol·K), and T the absolute kiln temperature. Small changes in T swing k by orders of magnitude — the hallmark "threshold" behaviour of Arrhenius kinetics you'll see below 400 °C. The polymer-chain sketches tumbling in the drum below shrink into shorter fragments as they approach their turn to convert — a direct read of the computed conversion X(t), not a canned animation.
- Feedstock — PE, PP and PS each carry their own (Eₐ, A), tuned so the qualitative ranking matches TGA studies: PS backbone unzips to styrene monomer at the lowest temperatures, PP's tertiary carbons make it next-easiest to crack, and PE's simple saturated chain is the most thermally stable of the three.
- Temperature — sets k(T) and shifts the product split: higher temperatures crack more of the condensable vapour into permanent gas via secondary reactions, so the oil fraction falls as the gas fraction rises. Char stays a small, roughly constant residue for these polyolefins/polystyrene.
- Process speed — a clock multiplier (and kiln RPM) so a multi-minute batch is watchable; it does not change the physics, only how fast simulated time passes.
- At every instant, decomposed mass is split into oil/gas/char at that instant's temperature-dependent ratio and accumulated — so solid + oil + gas + char always sums to the original feed mass.
Kinetic constants here are illustrative, tuned for a watchable timescale, but the functional form and the relative ordering of the three polymers are consistent with published single-step decomposition studies — and are identical to the 3D version of this reactor, so switching views never changes the numbers.