Decomposition Mechanism of PET

In contrast to polymerisates, polycondensates can not be depolymerized under inert conditions. Decomposition usually leads to the destruction of the chemical structure and the monomers. The thermal decomposition of PET starts at about 300°C in an inert atmosphere [25]. Between 320 and 380°C the main products are acetaldehyde, terephthalic acid, and carbon oxides under liquefaction conditions. The amounts of benzene, benzoic acid, acetophenone, C1-C4 hydrocarbons, and carbon oxides increase with the temperature. This led to the conclusion that a P-CH hydrogen transfer takes place as shown in Eigure 25.8 [26]. Today the P-CH-hydrogen transfer is replaced as a main reaction in PET degradation by several analytic methods to be described in the following sections. The most important are thermogravimetry (TG) and differential scanning calorimetry (DSC) coupled with mass spectroscopy and infrared spectroscopy. 

1 Analysis by Negative Chemical Ionization (NCI) Mass Spectrometry 

2 Analysis by Collision-induced Dissociation Tandem Mass Spectrometry (CID-MS/MS) 

Montaudo et al. [28] used CID-MS/MS to obtain information on the original molecular structure from the cleavage pattern of the molecular ion. In this procedure the ion with 

Pyrolysis can be performed for many different reactors. The prodnct distribntion varies markedly between the different reactor types and the reaction conditions, snch as temper-atnre, bed materials or catalyst. The aim of the pyrolysis is the redaction of wastes for landfilling and the prodnction of fnels. Especially fuel oil with a high calorific value is an interesting product. Char can be used as a fuel, but is also seen as a precursor for other carboneous materials such as activated carbon. The best way to obtain these products is decarboxylation of the polymer. In this way carbon oxide-rich gas is produced. 

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