Pyrolysis as a value added method for plastic waste management: A review on converting LDPE and HDPE waste into fuel

The global demand for plastic is increasing year by year due to its indispensable uses and excellent properties. Plastic wastes persist for many years due to their slow deterioration and cause severe environmental problems. Therefore, there is a growing focus worldwide on plastic waste disposal methods to overcome adverse environmental impacts. As plastics are petroleum-based materials, the pyrolysis of plastics to fuel oil, gases, and char, has more concern than the other plastic waste management methods of recycling and landfilling. A yield of 70-80 wt.% of liquid fuel from pyrolysis waste has been reported elsewhere, emerging the importance and aptness of this method in plastic waste management. The common reactor types for the pyrolysis process are batch reactor, semi-batch reactor, spouted bed reactor, and fluidized bed reactor.  The common catalysts employed in plastic pyrolysis were zeolites, including ZSM-5, HUSY, Zeolite X, and Y. The pore structure and the catalyst’s acidity are the most influencing parameters in increasing the liquid yield and the quality of the oil produced in the pyrolysis process. This paper reviews the existing literature on pyrolysis processes developed for HDPE and LDPE wastes globally and their governing factors. Furthermore, emissions in the pyrolysis process and engine combustion of the fuel oil, performance, and emission characteristics were discussed. Although plastic waste separation prior to its management is a challenging process, this review highlights the conversion of waste plastic into energy as a smart way to meet the rising demands.