Thermal pyrolysis of LDPE/PP multilayer and metalized BOPP plastic packaging to optimize oil/wax yield for use as a fuel source

Thesis (MEng)--Stellenbosch University, 2022.ENGLISH SUMMARY: The pollution caused by plastic waste does not only pose a threat to the environment but leads to the loss of valuable hydrocarbon-based materials. The growing volumes of plastic waste in South African landfills and lack of recycling initiatives multilayer and flexible plastic packaging, leads to the consideration of alterative recycling methods apart from primary and secondary recycling. Pyrolysis has been identified as a promising technology to curb waste plastics that are regarded as “non-recyclable” because of their complex composition caused by the presence of multiple material within the plastics. Various plastic materials have been pyrolyzed with the focus on single layer plastics or manually mixed plastic types in co-pyrolysis with limited report on the pyrolysis of multilayer and metalized flexible plastics. Also, the transition from bench scale to pilot scale has not been investigated for these plastics which could result in complications for the pyrolysis process if the process was considered for production of oil/wax at a commercial level. The aim of the study was to convert two waste packaging plastic types through pyrolysis into oil/wax product for fuel applications through determining the suitability of the plastics as a feedstock using characterization. An optimisation of the oil/wax yield and quality was performed in a semi-batch induction reactor at bench scale and the results were used in a semi-continuous rotary kiln reactor to scale-up the process to a pilot scale. The characterization showed that the plastics were suitable for use as a fuel because a high carbon and hydrogen content >99wt%, a volatile matter >97wt%, and heating rates between 42-45MJ/kg, implying the production of a commercially comparable fuel. A maximum oil/wax yield of 73% was obtained in the pyrolysis of LDPE/PP multilayer and 77% for met BOPP during bench scale tests at 450℃ with an HHV of 42.49MJ/kg and 45.55MJ/kg, respectively. The scale up process resulted in a lower oil/wax yield for both plastics with a maximum yield of 49% obtained for LDPE/PP at 550℃ and 46% obtained for met BOPP at 500℃ having an HHV of 44.24MJ/kg and 43.77MJ/kg, respectively. The temperature at which the maximum oil/wax yield was obtained shifted to higher temperatures with a significant decrease in the oil/wax yields for both plastics. A comparison of oil/wax yield at 460℃ for pure PP and met BOPP pellets showed no significant difference. However, the fuel characterisation showed that the oil/wax for LDPE/PP and met BOPP had similar qualities to diesel which would need further upgrading for use as a commercial fuel."Geen opsomming beskikbaar"Master