Enhanced oil dehalogenation during catalytic pyrolysis of WEEE-derived plastics over Fe- and Ca-modified zeolites

Pyrolysis affords the conversion of plastics from Waste of Electrical and Electronic Equipment (WEEE) into oils with potential applications in the production of valuable chemicals and the formulation of liquid fuels. However, the presence of significant concentrations of halogens (Cl and Br) in these wastes represents an important limitation as it can lead to the generation of hazardous species that negatively affect the environment. In this work, the catalytic pyrolysis of a real WEEE plastic has been investigated using a reaction system that operates with continuous feeding of the raw material. The catalysts assayed include bulk metal oxides (Fe2O3 and CaO) and zeolites (ZSM-5 and USY), as well as hybrid solids obtained by supporting those metal oxides on the zeolites. Pre-treatment of the raw WEEE plastics by water washing allows the Cl concentration to be significantly reduced, but it does not affect the Br content. Thermal pyrolysis produces an oil fraction with a high yield (> 70 wt%) and a large concentration of halogens (700 ppm), even though the char produced effectively retains more than 90% of Br and Cl contained in the feedstock. During catalytic pyrolysis, the halogen content of the oil is further reduced obtaining the best dehalogenation results with the metal-modified zeolites. This fact evidences a synergetic effect derived from the high metal dispersion achieved over the zeolitic supports. Fe/ZSM-5 is the most promising catalyst, showing an almost constant dehalogenation activity along the time-on-stream and producing an oil enriched in monoaromatic hydrocarbons (mainly styrene).