Dehydrochlorination of plastic mixtures

Dehydrochlorination of plastic mixtures from domestic waste as well as from other chlorine containing mixtures such as electronic scrap is an essential reaction step in waste incineration, pyrolysis and chemical recycling of polymers. For designing pyrolysis procedures, controlled combustion processes and to control the emissions from incinerators, the behaviour of polymers in thermal decomposition with regard to decomposition products and the kinetics of decomposition must be known. The kinetic data,for thermal decomposition of commodity plastics, confirms that in mixtures of different plastics the dehydrochlorination of, e.g, poly (vinyl chloride) (PVC) can be conducted at moderate temperatures and prior to the thermal degradation of the polymer skeleton. In stepwise low temperature pyrolysis mixtures of, e.g. PVC, polystyrene and polyethylene have been separated into hydrogen chloride, the monomer of polystyrene and aliphatic compounds from polyethylene decomposition, The degree of conversion of chlorine from PVC into hydrogen chloride in the low temperature (330 degrees C) first step is about 99.6%. A similar behaviour for dehydrochlorination is obtained during the thermal degradation of electronic scrap. The hydrogen chloride evolution from PVC occurs in the same way as in mixtures of commodity plastics with a maximum rate of HCl loss at 280 degrees C, when heated at 2 K min(-1). Brominated flame retardants are decomposed or evolved at higher temperatures(> 300 degrees C). A possibility to fix bromine in the residue is to add calcium carbonate to the electronic scrap before pyrolysis. (C) 1999 Elsevier Science B.V. All rights reserved.