The disposal of mixed waste poses a serious problem, because plastics are usually not bio-degradable. Dumping of plastic is therefore not an acceptable option, due to environmental considerations. Incineration of plastic waste is a better and reasonably cheap option, but there are a few major problems: the energy recovery is low, possible formation of dioxines and furans, emission of heavy metals and HCl. Due to these problems alternative methods for plastic waste recycling are currently being developed. High temperature pyrolysis of plastic waste is one of the most promising alternatives.
At the University of Twente a research program has started investigating the pyrolysis of mixed plastic waste, containing PE, PP, PS and PVC. The pyrolysis reaction will take place at temperatures between 873 and 1173 K. Main products of these pyrolysis reactions may include hydrogen, methane, acetylene, ethene, ethane, propene, propane, butene and butane. In the essay secondary reactions of these primary products are investigated.
It can be concluded that with most of the secondary gas phase reactions radicals are involved. Therefore dehydrogenation and dealkylation are very important reactions. The allyl radical can form C5-rings when reacting with an olefine. Diels-Alder reactions can lead to C6-ring formation.