A critical review of developments in the pyrolysis of automotive shredder residue

Worldwide, automotive shredder residue (ASR) is considered an increasingly problematic mixture of materials that needs the development of a processing solution. Pyrolysis is a process that has many advantages to offer, but despite many studies and developments in recent years at various levels of commercialisation, it is still generally considered unproven for this purpose. This paper critically considers developmental work published in the field, presents new results, and suggests that a major reason for the lack of development is the complexity of the landscape created by strong, competing, economic, legislative, environmental and commercial drivers, which in turn make it unclear which products and processes are optimal. This is made doubly complex by the natural variation in the material composition of ASR, with contaminants that can critically affect its potential fate to anywhere in the range from hazardous waste, to energy source, to useful raw material for major cement or steel industries. New data on critical factors such as levels of chlorine and metals in raw and pyrolysed ASR are presented, alongside a much-needed summary of previously published values from references that are often difficult to source. The summaries emphasise the variation in the material, but also indicate rough boundaries for values, which are needed for the design of any potentially successful process. It is suggested that the heterogeneity seen across ASR types implies that specialised processing of SR on its own is unlikely. It is pointed out that small-scale processes that could be suitable for local requirements should be considered for development as they could be able to optimise a process sufficiently to make it viable, e.g. specialised local waste streams of paper pulp and a particular fraction of SR