Review on production of liquid fuel from plastic wastes through thermal and catalytic degradation

The demand for plastic is increasing in many sectors, leading to a need for effective end-of-life solutions that can make it more environmentally friendly. Several valorization and recycling techniques are being commercialized for waste plastic globally. Among them, pyrolysis attracts researchers’ attention as it converts the waste plastic into energy, in the form of solid, liquid, and gaseous fuels. This process still has several limitations such as inconsistent quality of pyrolytic oil compared to gasoline and diesel range fuel, poor quality of feedstock, costly and inefficient shorting techniques for feedstock selection, absence of markets citing for standardized products, and unclear regulations around plastic waste management. This review focuses on the recent research on liquid fuel from waste plastic through thermal pyrolysis, catalytic pyrolysis, and hydrocracking and a detailed discussion on feedstocks selection, advantages of thermal and catalytic pyrolysis, properties of pyrolytic oil, mechanism of pyrolysis, challenges of pyrolysis, and the future perspective of the utilization of waste plastic. Catalytic pyrolysis produces better-quality oil that can be upgraded into transportation fuels; however, it suffers from catalyst deactivation and regeneration. The efficiency of different heterogeneous catalysts to produce pyrolytic fuel is compared. Zeolite and clay-based catalysts demonstrate remarkable efficiency in pyrolysis of plastics. The effects of process parameters on pyrolysis of plastics are discussed. The pyrolytic oils of HDPE, LDPE, PP, PS, PVC, and PET have similar characteristics to conventional gasoline and diesel fuels. Use of plastic pyrolytic oil in internal combustion engine shows a poor performance but when it is blended with additive or commercial oil, it shows a better performance.