CO2-assisted gasification of polyethylene terephthalate with focus on syngas evolution and solid yield

Abstract

Polyethylene terephthalate (PET) contributes to majority of the global plastics wastes generated and its lack of sustainable recycling calls for the development of pathways for this waste transformation to energy and chemicals extraction that will help avoid landfilling of this waste. In this paper, CO2 assisted gasification of PET was investigated at 800 °C to 950 °C using a fixed bed reactor to understand the feasibility of this pathway for PET waste management. Evolutionary behavior of the yields of H2, CO, CH4, total C2-C3 gases and total syngas from fixed bed reactor were investigated to understand the influence of temperature on isothermal conversion. Gasification composition and total accumulative syngas rate were also calculated and compared. Solid residues from gasification were analyzed for morphological characteristics and CO2 consumption. Evolution rate and yield of H2, CO, CH4 and total syngas from fixed bed reactor changed with increase in reaction time and temperature. CO yields increased from 0.5 to 0.9 g/g (gas mass yield per unit mass of PET), which accounted for 89.9 to 95.2 wt% of the total syngas yield with increase in temperature from 800 °C to 950 °C. The CO mole fraction accounted for about 73.3 to 79.4 vol% of their total syngas at the different temperatures examined. Brunauer-Emmett-Teller (BET) surface area of solid resides from CO2 gasification increased from 434 to 936 m2/g with increase in temperature. These results showed thermal decomposition behavior under CO2 gasification influenced the char structure and the effect became more pronounced with increase in temperature. CO2 gasification of each mass unit of PET provided with the capability to convert about 0.1 to 0.7 mass unit of CO2 into valuable syngas (a precursor for various value-added products) which reveals the synergistic possibility of PET waste management along with CO2 utilization in this process of energy and value-added product recovery.