Catalytic and Non-catalytic Thermolysis of Waste Polystyrene for Recovery of Fuel Grade Products and Their Characterization

Abstract

One of the important types of plastic extensively used in packing industry is polystyrene (PS). Having the lowest recycling rate among other categories of plastic waste, and not been included in the roadside recycling program, polystyrene is an attractive polymer waste for recovery of energy. PS mostly contains a large volume due to high air content in its products such as styrofoam. Being produced from petroleum product, it contains a large amount of energy which can be recovered by pyrolysis process which produces fuels like pyrolytic oil, combustible gases and char (carbon). In this study, zeolite (ZSM-5) catalyst was used during the catalytic pyrolysis process. Initially, TG analysis was performed to analyze the minimum degradation temperature of PS at four different heating rates and also to determine the effect of heating rate on its degradation. From the analysis, optimum temperature was selected based on time and temperature and was used as final temperature (500 °C) for batch pyrolysis. Ten percent of the catalyst is used with 200 gm of PS waste crushed in small size of 1–2 cm and then pyrolyzed. The main product from catalytic thermolysis was non-condensable gases 52%, pyrolytic oil 42% and remaining residue as char whereas non-catalytic process produces 78% pyrolytic oil, 14% gases and remaining 8% char. The products obtained from cracking in presence and absence of catalyst mainly constitutes aromatic, branched and cyclic hydrocarbons in the liquid phase, a high amount of hydrogen and C1–C4 hydrocarbons and some amount of CO and CO2 due to the presence of oxygen in the raw material. The presence of catalyst during degradation increases the cracking forming a high amount of gaseous product whereas produces low range hydrocarbons (C8–C16) in oil phase as compared to non-catalytic pyrolytic oil which contains a high range of hydrocarbons (C8–C25).