Pyrolysis of plastic waste into diesel engine-grade oil

Abstract

The pyrolysis of plastic waste to fuel will lead to greener waste management, ensure sustainability and serve as an alternative energy source. This study seeks to convert plastic waste into diesel engine-grade oil as an alternative energy source for various applications. A mixture of plastic waste of 58% PET, 20% HDPE, 12% LDPE, 7% PP, and 3% PS were used for the study. Catalytic and thermal pyrolysis was conducted in a batch reactor at a temperature of 450 °C for 2 h using Nitrogen gas. The plastic fuel produced was then analyzed using the Fourier Transform Infrared (FT-IR) spectroscopy and Gas Chromatography-Mass Spectrometry (GC–MS). The various characteristics of the oil, such as the kinematic viscosity, calorific value, density, and pour point, were determined. The results indicated that thermal pyrolysis produced 13% liquid, 59% gas and 27% solid residue, and on the other hand, catalytic pyrolysis yielded 15.16% liquid, 69.16% of gas, and 14.8% of solid residue. The FT-IR also showed the presence of aliphatic and aromatic compounds with a predominance of the aliphatic group. From the GC–MS analysis, the plastic fuel contains 30 compounds in the C8- C40 range. The calorific value of plastic fuel after analysis was 43.175 MJ/kg in catalytic pyrolysis and 34.132 MJ/kg in thermal pyrolysis. Also, the kinematic viscosity was 4.344 cSt in catalytic pyrolysis and 2.750 cSt in thermal pyrolysis, while the density and pour point were 0.856 g/cm3 and −17 °C respectively. These results show that catalytic pyrolysis yielded more gas and liquid with high calorific value than the thermal pyrolysis. This is an indication of the use of catalysts to improve the conversion of plastic into energy. The conversion of plastic waste into diesel oil will not only address environmental challenges but help achieve the SDGs 7 & 13 as well as Goal 7 of Agenda 2063.