Kinetic data obtained from micro thermogravimetry and gradient free reactor
experiments confirm that different molecular structures of commodity plast
ics bring about different reaction mechanisms of thermal decomposition, dif
ferent reaction rates, and different temperature dependencies of the decomp
osition rates. From that, stepwise pyrolysis of mixtures of plastics seems
to be reasonable where the different components of the mixture are pyrolyse
d at different temperatures.
To perform a stepwise pyrolysis in laboratory scale a cascade of well stirr
ed reactors has been developed where mixing of the reactor contents occurs
by circulating of stainless steel spheres. Examples for the separation of s
ingle plastics by stepwise thermal decomposition of mixtures of poly(vinyl
chloride), polystyrene and polyethylene are presented. In the first step hy
drogen chloride from poly(vinyl chloride)is released, in the second step st
yrene from polysytrene is formed and in the third step aliphatic compounds
from polyethylene decompositon are trapped.
Differences in the thermal degradation of single polymers and mixtures of p
olymers, e.g. in the apparent activation energies and preexponential factor
s, are investigated using mixtures and blends of polyethylene and polystyre
ne. (C) 1999 Elsevier Science Ltd. All rights reserved.