Results from the Microwave Pyrolysis of Plastics

Heat transfer limitations are important restrictions for pyrolytic processes because of the low thermal conductivity of plastics. In general the heat flow from the surface of a plastic particle to its core (internal heat flux) is rather slow compared with the heat flow 

As an approximation, the apparent reaction rate constant was calculated, assuming that the temperature was constant once the polymer started to degrade. From the correlated data the apparent reaction rate constant was calculated for the three materials at 550°C. Table 21.1 shows the values obtained and compared with values calculated at 550°C, from kinetic data in the literature. 

The results shown in Table 21.1 do not imply that microwave pyrolysis is slower than conventional pyrolysis, but confirm the need to consider heat and/or mass transfer limitations because of the particle and size samples used in the experiments [26]. 

It is known [90, 91], that the final yield and hence product composition of pyrolysis products are determined mainly by the secondary and tertiary reactions that occur after 

In terms of the individual compounds found in the condensable products, as with conventional pyrolysis, a-alkenes alkanes and dialkenes were the most abundant compounds. A large number of other aliphatic and aromatic compounds ranging from C3 to approximately 55 were also found, including methylcyclopentene, benzene, cyclohexene, toluene, ethylbenzene, xylene, propylbenzene and methyl-ethylbenzene. The analysis also showed that the condensables obtained at 500 and 700°C, although possessing similar levels of cleavage, showed important differences in the individual compounds present [85], 

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