Pyrolysis of waste polypropylene plastics for energy recovery: Influence of heating rate and vacuum conditions on composition of fuel product

This study compared the pyrolysis of waste polypropylene (PP) into fuel products under atmospheric and vacuum pressure conditions at different temperatures and heating rates. Four different temperatures (450, 488, 525 and 600 degrees C) at slow (15 degrees C/min) and fast (about 180 degrees C/min) heating rates were examined on a bench scale reactor. Pyrolysis vapours were recovered as heavy and light fractions by fractional condensation and characterised using GC/MS. Among all temperatures, 488 and 525 degrees C generated promising yields of condensable products under both atmospheric and vacuum conditions, with total yields in the range of 81-93 wt%. Heating rate effects on product composition distribution were more pronounced under vacuum pyrolysis. Gasoline range compounds predominated in light condensable products recovered under both atmospheric and vacuum pyrolysis. Vacuum suction limited the condensation of gasoline range compounds in the heavy fraction, resulting in Diesel/Gasoline ratio higher than 30. Higher Heating Values (HHVs) of all condensable products recovered under both atmospheric and vacuum conditions ranged between 41 and 46 MJ/kg, with higher values being obtained under milder conditions. Increased production of aromatics explained the lower HHVs obtained at higher temperatures.