Experimental investigations on reactor scale-up and optimisation of product quality in pyrolysis of shredder waste

Shredder waste is the light fraction separated from automotive shredder scrap by air classifiers and contains mainly plastics. The present work focuses on pyrolysis of shredder waste as a possible way for chemical recycling of plastic wastes and deals with the technical requirements for an industrial application. Pyrolysis experiments have been conducted in two different laboratory reactors at high and low heating rates in order to determine product yields. The investigations lead to a more detailed understanding of the primary and secondary chemical reactions involved and the influence of the main process parameters. The results indicate clearly that appropriate conditions for secondary reactions are decisive criteria to attain the desired optimum product quality, e.g. a more homogeneous product spectrum with enhanced yields of light aromatics. Catalysts can improve cracking and isomerisation as well as chlorine removal. The derived criteria for reactor design and process development have shown heating rate, residence time, and temperature to be decisive parameters in scale-up considerations and in extrapolation of laboratory-scale experimental results. It can be concluded that reactors with extended residence time like, for example, a rotary kiln in combination with a subsequent solid catalyst bed for refining of the volatiles can provide promising process solutions in a pyrolytic recycling concept for plastic wastes like automotive shredder waste. (C) 2002 Elsevier Science B.V All rights reserved.