Browsing by Author "Edwards, Devon William"

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    Comparison of the technical and economic feasibility of devulcanisation processes for recycling waste tyres in South Africa
    (Stellenbosch : Stellenbosch University, 2016-03) Edwards, Devon William; Van der Gryp, Percy; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: The problem of the accumulation of waste tyres is receiving increased attention in the 21st century as a result of environmental concerns as well as the economic undesirability of discarding the valuable materials still present in tyres at the end of their useful life. The difficulty associated with recycling waste tyres is linked to the stable thermoset network structure of the vulcanised rubber comprising the majority of a waste tyre’s mass. The recovery of value from tyres via incineration for their relatively high calorific value has been a popular method of diverting tyres from landfills and stockpiles in the past, although newer methods such as pyrolysis and devulcanisation aim to recover more value than merely the energy content of tyres. Pyrolysis processes aim to recover and purify valuable chemicals generated by the thermal decomposition of the rubber compounds in tyres. Devulcanisation processes aim for the controlled breakdown of the vulcanised rubber network in such a way that the rubber regains its thermoplastic properties and can be moulded and revulcanised into new products, without a significant loss of the important mechanical properties associated with vulcanised rubber products. The shortcomings identified in the literature include the lack of comparable technical data between devulcanisation technologies, and the near absence of any form of energy consumption and economic data associated with devulcanisation processes. This study aimed to identify promising devulcanisation technologies and address the shortcomings identified in the literature by generating comparable technical and economic data for the selected devulcanisation technologies. The devulcanisation technologies identified for further analysis included the extrusion-based mechanical and mechanochemical devulcanisation processes. The experimental work showed that increasing extrusion temperature has a strong effect on increasing the extent of devulcanisation in both devulcanisation processes. Varying screw speed in the mechanical devulcanisation process showed a very weak effect on the extent of the devulcanisation reaction. Increasing concentration of the devulcanisation chemical in the mechanochemical devulcanisation process caused an increase in the extent of the reaction, although the effect was rather weak. Overall, the mechanochemical devulcanisation process resulted in a substantially higher selectivity for crosslink scission and therefore higher product quality in comparison to the mechanical devulcanisation process. Economic analysis of the processes was conducted assuming various scales of operation from approximately 400 tons/year to 7000 tons/year, using scaled-up power consumption data generated during the experimental work. The mechanical devulcanisation process was found to be likely to outperform the mechanochemical devulcanisation process from an economic perspective due to the high costs of the extra chemicals required for the mechanochemical devulcanisation process. It should be noted, however, that the economic analysis did not take into account the potentially higher market value of the reclaimed rubber produced by the mechanochemical devulcanisation process. Therefore, further market research will be required in order to come to a firm conclusion as to which process will be more economically viable. A sensitivity analysis also showed that the economics of both processes are very sensitive to the power consumption, which could be a major problem for devulcanisation processes in South Africa.