Catalytic pyrolysis of plastics derived from end‐of‐life‐vehicles (ELVs) under the CO2 environment

Summary As the global vehicle demand increases, the significance of waste materials generated from end‐of‐life‐vehicles (ELVs) becomes more severe. However, the heterogeneity of most components of vehicles made them difficult to be recycled. In this study, a sustainable valorization platform for the vehicle wastes was suggested via pyrolysis process. As a case study, bumper waste was used as a feedstock material. Prior to the thermo‐chemical process of bumper waste, multiple analytical tools were employed to identify and quantify the chemical constituents of the bumper waste. Because the bumper consists of mainly polypropylene (PP), pyrolysis of bumper produced hydrogen and different types of hydrocarbons (HCs), and the product distribution was highly contingent on pyrolysis setups and operating conditions. One‐step pyrolysis of PP at 600°C resulted in C8‐46 aliphatic HCs, while two‐step pyrolysis converted the long‐chain HCs into C7‐8 aromatic compounds in line with H2 production. During catalytic pyrolysis over Co and Ni catalysts, the dehydrogenation of HCs led to rapid H2 generation with coke formation on the catalysts. When CO2 was used as a reactive gas medium, additional CO production and suppression of coke formation were shown through gas‐phase reactions between CO2 and volatile HCs evolved from thermolysis of PP. The alteration of H2/CO ratios (>15 to 0.7) of output gas also was achieved, controlling the N2/CO purge gas ratios during catalytic pyrolysis. Therefore, CO2‐assisted pyrolysis can be a considerable valorization platform of vehicle waste materials and CO2 by converting them into energy‐intensive products. This study valorized plastic waste derived from end‐of‐life vehicles into syngas and hydrocarbons that can be used as useful platform chemicals and fuels through CO2‐assisted pyrolysis. The greenhouse gas, CO2, was used as an oxidant to promote the conversion of plastic into syngas, and the reaction mechanism was elucidated. The gas‐phase reactions between CO2 and plastic‐derived hydrocarbons resulted in additional syngas formation at ≤600°C, where no gasification reaction occurs. CO2‐assisted pyrolysis also showed superior capability for syngas formation in the presence of metal catalysts (Ni and Co) with suppression of catalyst deactivation.