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

In this study, the effects of CO thermochemical agent and a metal oxide catalyst (CoO) on thermochemical banner waste conversion were explored. The results revealed that compared to the non-catalytic conversion of banner waste under N environment, the conversion under CO yielded more non-condensable gases owing to an enhanced thermal cracking of volatiles. In addition, the CO and CH yields at >700 °C in CO increased considerably owing to the reverse water-gas shift reaction and CO methanation. The CO 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 CO and the C-H and O-H bonds present in the feedstock. In addition, the CoO catalyst promoted the decarboxylation reaction under N environment, whereas it promoted the methanation and reverse water-gas shift reaction under CO. This indicates that compared to the non-catalytic CO-assisted banner waste conversion, the use of CO for the conversion of banner waste in the presence of CoO significantly increased the yields of CH and CO. Furthermore, CoO promoted the thermal cracking of polyester bond, thus decreasing the yields of long-chain chemical compounds. In addition, the simultaneous use of CoO catalyst and CO agent minimized the formation of char and wax. For all cases (N versus CO, 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 CoO catalyst and CO agent for the plastic waste upcycling, such as banner waste.