Browsing by Author "Van der Westhuizen, Salomie"
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- ItemPyrolysis of contaminated PS single-layer and LDPE/PET multi-layer waste plastic packaging to optimise the production of oil for fuel applications(Stellenbosch : Stellenbosch University., 2020-03) Van der Westhuizen, Salomie; Gorgens, Johann F.; Collard, Francois-Xavier; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: It has been predicted that by 2050 there will be more plastic in the ocean than fish by weight. Besides the obvious environmental threat, plastic waste also poses a loss of valuable hydrocarbon-based materials. Pyrolysis has been identified as a promising technology for the recycling of waste plastics that cannot be recycled by conventional means due to their mixed and/or contaminated nature.Two such waste plastics are black PS punnets and LDPE/PET multi-layer films used to package raw meat and dry dog food respectively. However, little has been reported on the conversion of multi-layers, the influence of contamination, or the scale-up of the process to larger scale.The pyrolysis process performance has been found to be highly dependent on the composition of the feedstock and process parameters. Additionally, large-scale processing can present added difficulties. Therefore, to make pyrolysis a viable option for processing of these particular waste plastics at a large scale, it is necessary to study its optimisation and scale-up to pilot scale.The aim of this study was to convert these two waste plastics into fuel (oil/wax) products by pyrolysis. To meet this aim, the waste plastics were characterised to determine their suitability as fuel precursors and estimate the amount of contamination.The pyrolysis process was optimised in a bench scale semi-batch reactor for the yield and quality of the oil/wax. Based on optimised conversion, the process was scaled-up in a pilot semi-continuous rotary kiln reactor. Feedstock characterisation proved that the waste plastics were suitable as oil/wax fuel precursors. Contamination in PS negatively affected the characterisation. However, both volatile matter and the sum of carbon and hydrogen contents still represented more than 95wt.%. Contamination in the LDPE/PET multi-layer resulted in insignificant characterisation differences. Oil yield of 89.8-93.2wt.% was achieved during bench scale testing of the clean PS. Heavy meat juice contamination (about 16 wt.%, dry basis) decreased the oil yield by 7.3 wt.% but did not affectthe HHV. Conversion of post-consumer densified PS resulted in similar oil yield and HHV to the clean PS. Scale up to the pilot reactor resulted in lower oil yield of 82.5±1.4wt.% with HHV similar to oils obtained at bench scale in the range of 41.9-42.5 MJ/kg (comparable to gasoline). The gross energy recovered from the oil was 88±3%. Fuel characterisation indicated the oils similarity to gasoline. However, with aromatic content greater than 68 wt.%, blending with conventional fuel will be necessary to make it commercially suitable. Maximum oil/wax yield of 75.37±0.04 wt.% was achieved during bench scale testing of the clean multi-layer. Contamination decreased the oil/wax yield to 71.45±0.03wt.%, potentially due to a catalytic effect,but did not affect the HHV. Scaling up to pilot scale resulted in lower oil/wax yield of 62±12 wt.% and unaffected HHV in the range of 43.5-44.13MJ/kg (similar to diesel). This represented a gross energy recovery of 66±12%. Fuel characterisation indicated the flowable oils similarity to diesel. However, further upgrading will be necessary to make it suitable as commercial diesel.