Transport fuel from waste plastics pyrolysis - A review on technologies, challenges and opportunities

Despite extensive research in recent years and great potential to help with energy and waste management issues, thermochemical conversion technologies of mixed waste plastics (MWP) into transport engine fuel have not yet been developed in industrial and commercial settings. This study reviewed, discussed, and summarised research findings of over 280 up to date publications, emphasising pyrolysis technologies and their product yields, qualities, challenges and opportunities. The study investigated the suitability of pyrolysis oil for automobile engine application and summarised the experimental findings of diesel engine performance and emission characteristics. Furthermore, techno-economic assessment and key challenges for commercial fuel production from plastic pyrolysis are discussed. The review found that the pyrolysis of MWP produces oil yields of up to 90% by weight, and excellent fuel properties in the pyrolysis temperature range of 500 degrees C-550 degrees C. Polystyrene individually yields the highest oil yield of 97%, followed by low-density polyethylene, high-density polyethylene and polypropylene. However, polyethylene terephthalate and polyvinyl chloride plastics are not suitable for pyrolysis because they produce harmful chlorine gas and HCl that corrode the metallic parts of the pyrolysis reactor and condenser. Engine testing with MWP oil showed delayed combustion, high heat release rate and high cylinder pressure with similar power output and brake thermal efficiency. In contrast, NOx, UHC, CO and CO2 emissions were much higher. The study found that the pyrolysis plants must process at least 50 kT/year to earn an ROI of 25%. Additional research is required to resolve the remaining issues and challenges for industrial and commercial applications.

Automated summary

This study reviewed the research findings of thermochemical conversion technologies of mixed waste plastics (MWP) into transport engine fuel. The study found that pyrolysis of MWP produces high oil yields and good fuel properties. However, certain types of plastics, such as polyethylene terephthalate and polyvinyl chloride, are not suitable for pyrolysis due to the production of harmful gases. Engine testing with MWP oil showed delayed combustion and higher emissions. Further research is needed to address the challenges and issues for industrial and commercial applications.