Two-stage pyrolysis of polystyrene: Pyrolysis oil as a source of fuels or benzene, toluene, ethylbenzene, and xylenes

Abstract

The recycling rate of plastic waste needs to be improved worldwide. In that context, pyrolysis, through which petrochemical feedstock and alternative fuel can be obtained, has received significant attention. In this study, pyrolysis of polystyrene was conducted in a continuous two-stage process that has an auger reactor and a fluidized bed reactor connected in series. The main objective was to produce oils rich in benzene, toluene, ethylbenzene, and xylenes instead of typical polystyrene pyrolysis oils, which contain high amounts of styrene monomers with low thermal-oxidative stability. The effects of different reaction temperatures (in both reactors) and the type of fluidizing medium on the product distribution and composition were investigated. The maximum yield of benzene, toluene, ethylbenzene, and xylenes (26.3 wt%) was obtained at a temperature of 780 °C in the fluidized bed reactor. The oil and styrene yields at 780 °C were 86 and 26 wt%, respectively. To evaluate the fuel properties of the pyrolysis oil, its calorific value, API gravity, viscosity, density, ash content, pour point, flash point, and pH were examined. The results indicate that the pyrolysis oil can be both a good source of benzene, toluene, ethylbenzene, and xylenes and can potentially be used as a substitute source to gasoline or diesel fuels when it is mixed with oils with a low aromatic content.