Energy-efficient thermal waste treatment process with no CO2 emission: A case study of waste tea bag

Everyday waste is a serious matter of concern because of its disruptive impact on the environment. Although disposal and reclaim of such material represent the first lines of intervention to solve this problem, upcycling strategies should eventually be necessary to reconvert huge amounts of the waste. In addition to waste, climate change caused by greenhouse gas emissions (e.g., carbon dioxide (CO2)) is other global environmental problem. Here, we employed a thermal treatment process conducted in CO2 environment to upcycle waste tea bag (a surrogate feedstock for everyday waste) and utilize CO2 simultaneously. Through lab-scale experiments, 6 wt% caprolactam (a value-added nylon monomer), 12.7 wt% combustible gases (higher heating value (HHV): 24.8 MJ kg−1), and 13.8 wt% char (HHV: 28.1 MJ kg−1) were obtained at 500 °C. Based on the experimental results, a large-scale energy analysis of the process was conducted by developing a simulation model of an integrated process to produce caprolactam-rich liquid product. For the integrated process, CO2 in gaseous product mixture is separated, and the separated CO2 is recirculated to the thermal treatment step. The combustible gases and char are used to supply energy to thermal treatment and separation steps. The proposed process has a significant feature that there is no need for external energy with no CO2 emission (i.e., CO2 is fully recirculated in the waste treatment process).