Investigation on the low-temperature pyrolysis of automotive shredder residue (ASR) for energy recovery and metal recycling

The automotive shredder residue (ASR) or shredder light fraction (SLF) is the remaining fraction from the metal recovery of end-of-life vehicles (ELVs). While processes for metal recovery from ELVs are well developed, the similar process for ASR remains a challenge. In this work, low-temperature pyrolysis of the ASR fraction was investigated under the assumption that a low temperature and inert environment would enhance the metal recovery, i.e. the metals would not be further oxidised from their original state and the organic material could be separated from the metals in the form of volatiles and char. Pyrolysis experiments were performed in a tube reactor operating at 300, 400 and 500 °C. The gas and oil obtained by pyrolysis were analysed by micro-GC (micro-Gas Chromatography) and GC/MS (Gas Chromatography/Mass Spectrometry), respectively. It was found that the gas produced contained a high amount of CO2, limiting the energy recovery from this fraction. The oil consisted of a high concentration of phenolic and aromatic compounds. The solid residue was crushed and fractionated into different particle sizes for further characterization. The pyrolysis temperature of 300 °C was found to be insufficient for metal liberation, while the char was easier to crush at tested temperature of 400 and 500 °C. The intermediate temperature of 400 °C is then suggested for the process to keep the energy consumption low.