Catalytic Pyrolysis of Polystyrene over Steel Slag under CO₂ Environment

As the consumption of plastic materials has been dramatically increased, the abundant presence of their debris has become a significant problem worldwide. Thus, this study proposes a sustainable plastic conversion platform for energy recovery. In detail, polystyrene pyrolysis was examined as a case study under CO₂ atmosphere in reference to N₂ condition. The major gaseous and liquid products from polystyrene pyrolysis include permanent gases (syngas and C_1-2 hydrocarbons) and condensable aromatic compounds. Under CO₂ environment, the reduction of polycyclic aromatic hydrocarbons (PAHs) was achieved during polystyrene pyrolysis, in comparison with N₂ condition. Since its slow reaction kinetics, conversion of condensable hydrocarbons into permanent gases was not fully activated. Therefore, a cheap industrial waste, steel slag (SS), was employed as a catalyst to increase reaction kinetics. The synergistic effects of SS and CO₂ contributed to doubling H₂ production, while CO formation increased more than 300 times, in reference to non-catalytic pyrolysis. Because CO₂ acted as an oxidant for CO production, control of H₂/CO ratio was achieved in different conditions. Thus, the utilization of CO₂ would suggest a promising way to reduce the formation of PAHs, adopting the reliable platform to produce syngas from plastic waste.