Performance and reusability assessment of ZSM-5 for the production of lighter aromatics via pyrolysis of waste polystyrene

Abstract

The plastic waste poly styrene (PS) has been selected for the conversion to value added useful products using pyrolysis. The thermal and catalytic pyrolysis of polystyrene (PS) are investigated at reaction temperature ranging from 500°C to
800°C for 30 min, as an effective way to recycle polystyrene and produce valuable aromatic hydrocarbons benzene, toluene, ethyl benzene and xylene (BTEX). The catalytic pyrolysis is performed using commercial catalyst ZSM-5 which is reused repeatedly twice and further regenerated to evaluate the stability of ZSM-5 for PS pyrolysis with reference to BTEX formation. The maximum liquid yield of 96 wt. % and 86.2 wt. % are obtained at a temperature of 700°C for thermal pyrolysis and catalytic pyrolysis (fresh catalyst/1st run), respectively. The product analyses show that liquid yield contains substantial amount of BTEX with the increase in temperature for fresh ZSM-5. The BTEX yield is significantly increased for catalytic pyrolysis (fresh catalyst/1st run) i.e., about 75 wt. % for fresh ZSM-5 in comparison to thermal pyrolysis at a temperature of 700°C. There is very minute change in BTEX yield for the 2nd and 3rd run of catalytic pyrolysis using spent catalyst ZSM-5. The maximum aromatic (BTEX) of 23.71 wt. % for fresh ZSM-5 is obtained at the temperature of 700°C. However, spent ZSM-5(3rd run) produced 20.45 wt. % BTEX at the same temperature. The regenerated ZSM-5 produced only 2 wt. % less BTEX yield in comparison to fresh ZSM-5 at the optimum temperature of 700°C. The gas chromatography and other fuel test have been performed for liquid yield characterisation. The characteristics of product prove that the liquid hydrocarbon has potential to use it as fuel.