Pyrolysis of FeCl₃-pretreated spent coffee grounds using CO₂ as a reaction medium

Pyrolysis of spent coffee grounds (SCG) was performed to achieve the multiple purposes of waste disposal and energy recovery. This study placed great emphasis on pretreatment of SCG with FeCl₃ (Fe-SCG) and utilizing carbon dioxide (CO₂) as a reaction medium to enhance the generation of syngas while reducing condensable hydrocarbons (e.g., tar). For example, the principal effect of CO₂ was the enhanced generation of syngas via the CO₂-induced thermal cracking of volatile organic compounds (VOCs) and the reaction between CO₂ and VOCs, which resulted in subsequent reduction of tar. These identified effects on pyrolysis of SCG were more pronounced in pyrolysis of Fe-SCG, which could be attributable to the catalytic effect of the Fe mineral formed from phase transition of FeCl₃ during pyrolysis. The generation of CO in pyrolysis of Fe-SCG in the presence of CO₂ increased up to 8000% as compared to pyrolysis of SCG in N₂.