The Fate of Chlorine and Heavy Metals During Pyrolysis of Automobile Shredder Residue
One of the major sources of chlorine in automobiles is polyvinyl chloride (PVC). When old discarded automobiles enter the recycling loop by far the largest percent of this material finds its way into the solid waste fraction known as automobile shredder residue (ASR). While the majority of this waste is currently disposed of in landfills new processes are currently being evaluated to recycle and recover the valuable resources contained in this solid waste. Pyrolysis, the thermal cracking of the polymeric materials present in ASR, to recover the petrochemical hydrocarbons is one such technology which is receiving attention. However, like combustion with energy recovery, the pyrolysis process is receiving close scrutiny in terms of its environmental impact. These concerns have centered around the fate of the chlorine and the heavy metals present in the ASR.
The National Research Council of Canada has conducted a series of controlled pyrolysis experiments using well characterized ASR in a laboratory screw kiln pyrolysis unit. The fate of the chlorine and the heavy metals during the pyrolysis process has been evaluated using detailed chemical analysis of the pyrolysis products. The results of the investigate suggest that the presence of chlorine and heavy metals in ASR should not have any negative environmental effects when pyrolysis is used as resource recovery option.