Enhanced Aromatic Yield from WEEE via Ex Situ Catalytic Pyrolysis: A Comparative Study of HZSM-5, Fe/HZSM-5, and CaO Catalysts in Single and Dual Modes

This study investigated an efficient catalyst configuration to enhance the recycling of waste electrical and electronic equipment (WEEE) fractions into aromatic hydrocarbons. Two engineered WEEE fractions, low-grade (LGEW) and medium-grade (MGEW), were used as feedstock in an ex situ catalytic pyrolysis process conducted in a two-stage lab-scale reactor. The first stage involved a batch pyrolyzer, followed by a fixed-bed catalytic reactor. The interaction between catalyst active sites and pyrolysis vapors played a key role in determining the chemical functionality of the surface intermediates. Five catalytic modes were tested: CaO, HZSM-5, Fe/HZSM-5, and a combination of CaO and HZSM-5 in mixed and separate bed configurations, with a catalyst-to-feedstock ratio of 0.15 w/w. The iron-loaded zeolite favored gas production, while CaO effectively converted acids into ketones. The dual-catalyst mixed bed of CaO and HZSM-5 exhibited the best catalytic synergy, enhancing the production of aromatic hydrocarbons and decarbonizing the process. However, metal doping increased catalyst coke formation due to more Lewis acid sites and the production of polycyclic aromatic hydrocarbons. Overall, this study provides a comparative analysis of catalyst activity during the thermochemical conversion of WEEE.