Abstract
Municipal plastic wastes (MPW), formed by degradable and non-degradable components, have become an environmental hurdle. With a production of 380 million tons per year, the accumulated MPW would be around 12,000 million tons by 2050. Subsequently, MPW recycling has become a present obligation to future generations. Thermochemical technologies (e.g., pyrolysis) have shown great potential for MPW recycling into new materials or value-added products (e.g., hydrocarbon compounds). This study proposes a multi-criteria decision-making method to investigate the economic feasibility and environmental benefits of recycling MPW through a portable pyrolysis process unit near landfills. The proposed method consists of techno-economic analysis and life cycle assessment on a real case study in southeast Idaho, USA. The techno-economic analysis estimates the total cost of MPW to pyrolysis oil (p-oil). The life cycle assessment evaluates the environmental impacts of MPW-to-p-oil, including the global warming potential for a 100-year time horizon. The results indicate that the p-oil production cost per metric ton is $228, while the total emission is 22.6 kg CO2 per ton of MPW. It is evident that on-site operation can reduce MPW management and carbon footprint. It is concluded that MPW conversion to hydrocarbon products using the portable refinery unit near the collection sites can be a better practice in comparison to landfilling, as the main used method for solid waste disposal and one of the key sources of environmental pollution to the air, soil, and groundwater. Additionally, this study evaluates the potential of recycling polystyrene (PS) plastic wastes via a fixed bed (batch) slow pyrolysis reactor. The novelty lies in examining the reactor design, conversion parameters, and reaction kinetics to improve the process yield, activation energy, and chemical composition. Particularly, PS samples were pyrolyzed at 475-575°C for 30 min under 69-103 kPa, and process yield, and product attributes were evaluated, using different methods to provide a better understanding of PS thermal degradation characteristics. The results show that PS decomposition started within 2 min from all temperatures, and the total decomposition point of 97% at 475 °C at approximately 5 min. Also, analytical results indicate that the average necessary activation energy is 191 kJ/mol. Pyrolysis oil from PS was characterized by gas chromatography- mass spectrometry, and the results show that styrene was produced 57-60% from all leading oil compounds (i.e., 2,4-diphenyl-1-butene, 2,4,6-triphenyl-1-hexene, and toluene), and 475 °C has the major average of conversion effectiveness of 91.3%. The results show that the reactor temperature remains the main conversion parameter to achieve the high process yield for oil production from PS. It is concluded that pyrolysis provides a sustainable pathway for PS waste recycling and conversion to value-added products. The proposed method and analytical results are compared with earlier studies to identify the directions for future studies.