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 essentia l reaction step in waste incineration, pyrolysis and chemical recycling of polymers. For designing pyrolysis procedures, controlled combustion process es and to control the emissions from incinerators, the behaviour of polymer s in thermal decomposition with regard to decomposition products and the ki netics of decomposition must be known. The kinetic data,for thermal decompo sition of commodity plastics, confirms that in mixtures of different plasti cs the dehydrochlorination of, e.g, poly (vinyl chloride) (PVC) can be cond ucted at moderate temperatures and prior to the thermal degradation of the polymer skeleton. In stepwise low temperature pyrolysis mixtures of, e.g. P VC, polystyrene and polyethylene have been separated into hydrogen chloride , the monomer of polystyrene and aliphatic compounds from polyethylene deco mposition, The degree of conversion of chlorine from PVC into hydrogen chlo ride in the low temperature (330 degrees C) first step is about 99.6%. A si milar behaviour for dehydrochlorination is obtained during the thermal degr adation of electronic scrap. The hydrogen chloride evolution from PVC occur s 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. Al l rights reserved.