Doctoral Degrees (Chemical Engineering)

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Browsing Doctoral Degrees (Chemical Engineering) by browse.metadata.advisor "Danon, Bart"

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    Pyrolysis process optimisation to maximise limonene production from waste tyres
    (Stellenbosch : Stellenbosch University, 2018-03) Mkhize, Ntandoyenkosi Malusi; Gorgens, Johann F.; Van der Gryp, Percy; Danon, Bart; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: Globally, increasing waste tyre generation is a major economic and environmental challenge. Economic challenges include depleting natural resources and rising crude oil prices from which synthetic rubbers are derived. Environmental problems are mainly associated with large piles of the waste tyres. Waste tyres are characterised by resistance to degradation under typical environmental conditions, high pollution emissions from fires, soil and water pollutants leakage, breeding grounds for venomous insects, such as, snakes and spiders. Among conventional methods used to reduce waste tyre stock piles include: i) blending the tyre crumb with asphalt for civil works, such as, road construction, ii) combustion for generation of the electricity and/or steam, iii) and reuse in manufacturing of plastic and rubber products, such as, filler. However, the rate of waste tyre generation surpasses consumption capacity by these techniques. Moreover, these techniques are yet to be commercialised as they are fraught with economic and environmental challenges. These challenges include capital and operating costs of the production facilities and toxic compound emissions elimination requirements. One of the promising processing methods for waste tyres valorisation is to produce valuable chemicals (mainly DL-limonene) through increasing their content in the tyre derived oil (TDO) and then use remaining TDO for energy recovery. In the current study modification of the existing waste tyre pyrolysis processes, and development of the novel methods critical to maximising the DL-limonene yield in the pyrolysis oil, was achieved. Additionally, improvement in the total TDO yield and quality [high quality characterised by high DL-limonene content but less heteroatom compounds (nitrogen-, oxygen- and sulphur-compounds, mainly benzothiazole)] was observed. DL-limonene is a natural occurring compound and its composition is high in citrus fruit peels derived-oil at more than 80 wt.%. The market price of the DL-limonene ranges between 2.5 and 30 US$/kg depending on the purity. DL-limonene is an important component in the industrial formulations of solvents, resins, and adhesives. While benzothiazole is a main component in the processing additives used in the manufacturing of the tyres. The approach of the current study entails investigating i) various means to maximise DL-limonene yield in the pyrolysis reactor, ii) improving the DL-limonene yield from condensation of the hot pyrolysis volatiles, and iii) substantially reducing the production of most of the heteroatom compounds (nitrogenous, oxygenous and sulphurous containing compounds) to obtain TDO consisting high amounts of DL-limonene. This approached allowed study of the effect of i) temperature, ii) heating rate, iii) residence time of the hot volatiles in the hot reaction zones, and iv) condensation type and cooling rate of the hot volatiles. These operating conditions parameters were varied by interchanging slow, and flash pyrolysis reactor as well as tube-and-shell condenser and quenching condenser.