Catalytic pyrolysis of polymers with brominated flame-retardants originating in waste electric and electronic equipment (WEEE) using various catalysts

Abstract

The increasing volume of plastics in waste electric and electronic equipment (WEEE) together with the existence of potentially hazardous compounds make it of paramount importance to explore advanced recycling techniques for controlling the formation of undesirable products while enhancing the formation of the desirable ones. Harmful compounds could be formed during their recycling by pyrolysis because of the brominated flame-retardants usually incorporated into the plastics originating in WEEE. This paper examines catalytic pyrolysis of polymeric blends that consist of acrylonitrile-butadiene-styrene (ABS), high-impact polystyrene (HIPS), polycarbonate (PC) and polypropylene (PP), in the absence and presence of a brominated additive: tetrabromobisphenol A (TBBPA), with a view to reducing the bromo-compounds formed during their pyrolysis, while favouring the production of valuable compounds, such as phenols. Five catalysts: Al2O3, Fe/Al2O3, MgO, Fe/MgO and ZSM-5 with different textural properties were evaluated for their performance during pyrolysis of the mentioned blends at 440 °C (peak degradation temperature). It was found that all catalysts promoted the production of phenolic compounds, which are valuable products that can be further used in chemical industries. Among all catalysts tested, the best one was considered to be Fe/Al2O3, since it led to larger amounts of phenols for all blends examined. As for their debromination efficiency, attention was given on the reduction of dibromophenol formed, due to the presence of TBBPA in the polymeric blends. Results showed that Fe/Al2O3 was the optimal catalyst since it led to bromine reduction greater than ∼75%. Fe/MgO was the second one leading to reduction greater than 60% and MgO led to an important reduction (greater than ∼55%).