Sustainable valorization of styrofoam and CO₂ into syngas

Plastic is a versatile material broadly used in a variety of industries. However, the current disposal practices for plastic wastes (incineration/landfilling) add the hazardous materials into the environment. To offer a sustainable valorization platform for plastic waste, this study adopted the catalytic pyrolysis process using CO₂ as a co-feedstock. A model plastic waste collected from a seaport was waste buoy (WB), which has been widely used in fishing industry. Prior to the pyrolysis tests, the exact type of plastic in WB and the thermolytic characteristics of WB were examined. Since the WB was made of polystyrene, it was mainly converted into styrene monomer (styrene), dimer (diphenyl-1-butene), and trimer (2,4,6-triphenyl-1-hexene) from pyrolysis of WB. To further valorize/detoxify styrene derivatives into value-added syngas, catalytic pyrolysis of WB was practiced using the Ni-based catalysts (2/5/10 wt% Ni/SiO₂). The yield of H₂ from the catalytic pyrolysis process of WB was more than one magnitude higher comparing to that from the non-catalytic one. H₂ formation also increased as catalyst loading increased. When flow gas was switched from inert gas to CO₂, CO gas formation was enhanced due to the chemical reactions between CO₂ and styrene derivatives over Ni catalysts. Syngas (H₂/CO) formation under the CO₂ condition was 5 times higher in comparison to the N₂ condition in catalytic pyrolyses of WB with 10 wt% Ni/SiO₂. CO₂ also effectively suppressed coke deposition on a Ni catalyst. This study proposes a sustainable valorization and disposal platform for used plastic waste and greenhouse gas (CO₂), converting them into value-added fuel.