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

Abstract

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 degrees C resulted in C8-46 aliphatic HCs, while two-step pyrolysis converted the long-chain HCs into C7-8 aromatic compounds in line with H-2 production. During catalytic pyrolysis over Co and Ni catalysts, the dehydrogenation of HCs led to rapid H-2 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 H-2/CO ratios (>15 to 0.7) of output gas also was achieved, controlling the N-2/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.