Kinetic model for the continuous pyrolysis of two types of polyethylene in a fluidized bed reactor

The pyrolysis of two types of polyethylenes, with different degrees of branching, was performed in a continuous fluidized bed reactor with an inert sand bed and in a pyroprobe 1000, where secondary wax and tar cracking is small. A kinetic model has been applied to the data, which considers that the secondary reaction takes place via the same scheme suggested for the batch pyrolysis. The temperature of the primary pyrolysis is a function of the heat transfer and there is a temperature gradient between the reaction zone for volatiles production and the walls of the reactor, where the temperature was measured. Bearing in mind these aspects, the kinetic parameters of the reactions are the same as those obtained in batch pyrolysis. The reaction scheme of the primary reaction was determined previously in a thermobalance. The results indicate that the experimental results obtained in the continuous reactor can be explained by considering a low primary decomposition temperature and a resistance to heat transfer in the secondary decomposition that takes place at the upper part of the reactor. (C) 1997 Elsevier Science B.V.