A Comparative Study on Waste Plastics Pyrolysis Liquid Products Quantity and Energy Recovery Potential

Plastics thermal processing is an important application for both energy recovery and feedstock recycling. In this study effects of type of plastic (HDPE, LDPE, PET, PP, PS), pyrolysis process temperature and plastic waste prewashing on pyrolysis liquid product (oil) fraction, its hydrocarbon (HC) contents and heat values were investigated. Caustic washing and batch-pyrolysis were applied by keeping pyrolysis heating rate and other conditions constant. Oil yields, C10-C40 HCs, heat values were measured and compared. HDPE type plastic wastes produced the highest oil yield while PET and PP produced the lowest yields. C10-C40 HC contents of pyrolysis oils were strongly affected from the pyrolysis temperatures and pre-washing process under identical pyrolysis conditions. The highest C10-C40 HCs were produced by HDPE pyrolysis. Statistical analysis indicated that the effect of pre-washing process on the pyrolysis oil heat value is significant for HDPE and PP type plastics. Pyrolysis temperature had almost no effects on oil heat values for washed PET and unwashed PS wastes, whereas for other plastic samples, as pyrolysis temperature increased oil heat values increased. HDPE, LDPE, PP and PS pyrolysis oils have higher calorific values than wood and some coal types. These refer to energy recovery from those types of plastics.