Catalyst addition in polyethylene pyrolysis

Abstract The effect of catalyst addition on the thermal decomposition of low-density polyethylene has been studied. The pyrolysis has been studied in a thermobalance, using polyethylene mixed with different catalysts, such as MCM41, USY and ZSM-5. The study comprises the analysis of various effects, including the amount of catalyst added and the type of catalyst. It has been observed that almost all the catalytic effect is obtained for a given amount of added catalyst, and a further increase in the catalyst added does not produce a further reduction in the decomposition temperature. A kinetic model has been applied which allows a very good correlation of all the runs performed using the same catalyst. The model involves two different ways for the decomposition, one catalysed and the other non-catalysed. The order of the non-catalysed reaction has been allowed to vary, yielding reaction orders close to zero (i.e. very similar to that found in several thermogravimetric studies of polyethylene decomposition). On the other hand, the catalysed reaction has a rate constant with a saturating dependence with the concentration of the catalyst.