Life cycle assessment of the co-combustion system of single-use plastic waste and lignite coal to promote circular economy

Abstract

Single-use plastics waste is a thermosetting-thermoplastic polymer generated specifically from packaging industries. Incineration, landfilling, combustion, open discharge in liquids fail its effective disposal. Co-combustion via co-processing is a novel technique for disposal. In this study, investigative thermogravimetric analysis of the co-combustion of lignite coal (AL) and single-use plastic waste (PW) in the blend ratios of 50:50, 60:40, 70:30 was carried out under non-isothermal conditions to promote co-combustion via co-processing technique for environment-friendly disposal. Thermal degradation behavioral study was carried out at higher blending ratios of 30–50%. The effect of the mass ratio of PW to AL on co-combustion characteristics was analyzed. The Freeman-Carroll, Sharp-Wentworth methods derived energy of activation for the process of co-combustion in the limits of 65–155 kJ/mol, 44–75 kJ/mol. Volume Contracting and Diffusional Reaction 2D solid-state reaction mechanisms were followed by the co-combustion system as derived by Coats-Redfern and Kennedy-Clark methods. Master plot method validated the same results. The co-combustion performance was evaluated using co-combustion (CSI), ignition (IG), burnout (IB) indices. The highest CSI value was reported for the 60:40 blend. Burnout temperature (Tb) decreased with an increase in blending ratio and suggested an effective co-combustion process. Blend (70:30) reported the highest interaction in blends and confirmed the synergistic effect. The principal component analysis described the co-combustion process as three stages (100–200, 265–425, 425–700) oC with specific materials. The co-combustion process was optimized using the methodology of surface response and validated using neural network models (NNM 4,5) for the effect of temperature and blend ratio on mass loss. The characterization study confirmed the presence of minerals alumino-silicates, dimorphs pyrite, marcasite, gypsum, barite, hydrated sulfates, calcite, siderite, and functional groups –OH, -CH2, -Si-O responsible for autocatalytic reactions. Life cycle assessment confirmed the sustainability of the co-combustion process of lignite and plastic waste. The present study benefits for scale-up, optimization, waste to energy conversion, pollution reduction, and environmentally friendly disposal via the co-combustion process.