Innovative Protocol for Catalytic Hydrodehalogenation of Chlorobenzene and Bromobenzene for WEEE Cycle Closure

Pyrolysis of plastic from waste electrical and electronic equipment (WEEE) is a promising method for producing value-added chemicals. However, flame retardants in WEEE can cause halogen contamination in pyrolysis oil, reducing its value. This work aims to develop an innovative catalytic hydrodehalogenation (CHD) protocol for the removal of chlorobenzene and bromobenzene. Iron sulphate heptahydrate (FeSO4·7H2O) and nickel ammonium sulphate hexahydrate ((NH4)2Ni(SO4)2·6H2O) were used as catalysts, while sodium borohydride (NaBH4) acted as a hydrogen donor for iron reduction. The novelty of the process lies in the generation of nano zero-valent iron (nZVI) that takes place within the CHD reactor (in situ) without the addition of strong acids. Various experimental set-ups were investigated to optimise the key process parameters (e.g., reagent concentrations). The optimal conditions—obtained in the autoclave at 30 °C with a 1:1 molar ratio of chlorobenzene to catalyst, omission of nickel salt, and 5 mmol of NaBH4—resulted in a 75% reduction in chlorobenzene and complete removal of bromobenzene. The results confirm the effectiveness of the proposed protocol for the dehalogenation of chlorobenzene and bromobenzene, which can facilitate the valorization of pyrolysis oils derived from plastic waste, contributing to the closure of the WEEE cycle (the widest and fastest-growing source of global waste with significant environmental, social and economic impacts).