Leveraging carbon dioxide to control the H₂/CO ratio in catalytic pyrolysis of fishing net waste

The global presence of plastic debris has become an indisputable environmental issue. While it is useful to recycle used plastic materials, contaminated plastics require a series of pretreatments prior to the process. Here, we offer a viable thermochemical conversion (pyrolysis) platform to directly valorize fishing net waste (FNW). Prior to the pyrolysis of FNW that was collected at a Korean seaport, its chemical composition (polyethylene) was examined using thermogravimetric analysis, ultimate analysis, and Fourier-transform infrared spectroscopy measurements. Pyrolysis of FNW was conducted to produce value-added syngas and C_1-2 hydrocarbons (HCs) in both CO₂ and N₂ environments with a variety of pyrolysis setups. The pyrolysis temperature significantly contributed to the thermal cracking of long-chain liquid HCs into H₂ and C_1-2 HCs under the N₂ and CO₂ conditions. In the presence of cobalt-based catalysts, an additional improvement of the reaction kinetics for producing H₂ and C_1-2 HCs was shown in the N₂ environment. However, the synergistic effectiveness of Co-based catalysts and CO₂ resulted in CO formation, because CO₂ provided additional C and O sources over the Co-based catalysts. Thus, it allowed control of the H₂/CO ratio in the CO₂ and N₂ atmospheres. The compositional matrix of the liquid HCs after pyrolysis also confirmed that CO₂ controlled their aromaticity. Thus, the CO₂-cofeeding pyrolysis of FNW can be considered a viable platform for the direct treatment of plastic wastes by harvesting energy as a form of syngas.