Carbon dioxide-mediated thermochemical conversion of banner waste using cobalt oxide catalyst as a strategy for...

In this study, the effects of CO₂ thermochemical agent and a metal oxide catalyst (Co₃O₄) on thermochemical banner waste conversion were explored. The results revealed that compared to the non-catalytic conversion of banner waste under N₂ environment, the conversion under CO₂ yielded more non-condensable gases owing to an enhanced thermal cracking of volatiles. In addition, the CO and CH₄ yields at >700 °C in CO₂ increased considerably owing to the reverse water-gas shift reaction and CO₂ methanation. The CO₂ agent reduced the yields of condensables (e.g., benzoic acids, phthalic acids, esters, biphenyls, fluorenes) and decomposition residue (e.g., char and wax), which could be attributed to the enhancement of the thermal cracking of volatiles evolved during the banner waste conversion by CO₂ and the C-H and O-H bonds present in the feedstock. In addition, the Co₃O₄ catalyst promoted the decarboxylation reaction under N₂ environment, whereas it promoted the methanation and reverse water-gas shift reaction under CO₂. This indicates that compared to the non-catalytic CO₂-assisted banner waste conversion, the use of CO₂ for the conversion of banner waste in the presence of Co₃O₄ significantly increased the yields of CH₄ and CO. Furthermore, Co₃O₄ promoted the thermal cracking of polyester bond, thus decreasing the yields of long-chain chemical compounds. In addition, the simultaneous use of Co₃O₄ catalyst and CO₂ agent minimized the formation of char and wax. For all cases (N₂ versus CO₂, non-catalytic versus catalytic), an increase in temperature enhanced the total permanent gas yield and decreased the yields of condensables, char, and wax. The findings of this study revealed the importance of the synergistic use of Co₃O₄ catalyst and CO₂ agent for the plastic waste upcycling, such as banner waste.