Browsing by Author "Chomba, Evans Mwila"
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- ItemPyrolysis of waste plastics into chemicals as an alternative to landfilling or incineration(Stellenbosch : Stellenbosch University, 2018-03) Chomba, Evans Mwila; Gorgens, Johann F.; Collard, Francois-Xavier; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH SUMMARY: World population growth has brought about high production and consumption trends on the petroleum resources. One aspect contributing to this trend is plastic manufacture accounting for considerable petroleum resource consumption. Plastic production is increasing because of its versatile usage in many industries culminating into significant waste plastics generation. Plastic waste management is a large financial burden to local authorities aside from littering communities, blocking sewerage systems and drainages among other negative impacts on the environment and public health. Plastic waste recycling into chemicals through pyrolysis technology is a promising alternative to incineration or landfilling in providing an environmentally sustainable route to plastic waste management. This method can supplement the already established mechanical recycling of plastics in South Africa in diverting significant plastic wastes from landfill and achieve an industrial initiative of zero waste to landfill by 2030. The aim of this study was to determine the major plastic components in South Africa’s plastic stream and to establish if valuable chemicals can be recovered from polystyrene as well as polyethylene terephthalate through pyrolysis. Literature survey of the South African plastic stream revealed that there are six main plastics contained in the stream namely: high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). Before pyrolysis could be performed, physical and thermal characterisation was done to determine the suitability of the plastics to thermal conversion. It was established that the waste samples isolated from a commingled sample were pure enough and possessed significant volatile matter required for conversion to chemicals. In the order of increasing thermal stability PS, PET, PP, LDPE and HDPE plastics were all found to degrade in a single step over about 130 °C temperature change, before completion around 500 °C for heating rates between 10 – 20 °C/min. PVC plastic could not be considered for the study because of its corrosiveness and low content in the landfill stream at Kraaifontein waste management facility. Optimisation of slow and vacuum pyrolysis work conducted on PS and PET revealed that valuable styrene and terephthalic as well as benzoic acids could be recovered from the plastics respectively and quantified. It was concluded that slow pyrolysis was a better technology of converting PS to styrene as it gave about 41 wt% styrene yield at slightly over 58 wt% concentration against 36 wt% produced in vacuum pyrolysis at 56 wt% concentration. Both slow and vacuum pyrolysis of PET gave similar TPA and BA yield range of 4 – 5 wt% and 5 – 8 wt% respectively. The concentration of TPA was better in vacuum process, while BA concentration was significantly improved in slow pyrolysis.