Browsing by Author "Henry, Kirsty Louise"

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    Upgrading pyrolytic tyre char through acid-alkali demineralisation
    (Stellenbosch : Stellenbosch University, 2015-12) Henry, Kirsty Louise; Schwarz, C. E.; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Waste tyres are proving to be a critical environmental and social problem not only in South Africa, but worldwide; with significant hazards associated with illegal dumping, stockpiling and burning. Efforts are currently directed towards the management of waste tyres, and pyrolysis is proving to be a promising form of waste tyre recycling, with the production of potentially valuable products. Pyrolytic tyre char, in particular, is a carbonaceous solid product originating from the carbon black filler within tyres, and constituting 40% of the total product mass produced by pyrolysis. Pyrolytic tyre char, however, has an undesirable structure and is plagued by contaminants, thus considerably decreasing it value and market potential. Currently, South African waste tyre pyrolysis plants are stockpiling great quantities of char, which reduces revenue and decreases investments. The problem statement was thus that the current char produced by waste tyre pyrolysis is crude and has minimal market value or use which, in turn, reduces waste tyre pyrolysis sustainability and waste tyre recycling efforts. A systematic approach was utilised, with a combination of literature research, experimentation, engineering design and economic evaluation methods employed to (i) investigate pyrolytic tyre char upgrading methods and product opportunities; (ii) develop and propose a process for crude pyrolytic tyre char upgrading; (iii) analyse the economic viability and appeal of the proposed crude pyrolytic tyre char upgrading process. A thorough literature review revealed that, utilising an acid-alkali leaching process, crude pyrolytic tyre char could potentially be upgraded to a carbon black product. Industrial char and carbon black N330 were thus characterised to establish benchmark targets and process requirements, including ash content reduction from 16.24 to 1.95wt.%; BET surface area increase from 58.9m².g-¹ to 80.22m².g-¹; and average particle size reduction from 153.2 to 38.5μm. Furthermore, a mineralogical study revealed the ash contained approximately half silicon/silicon dioxide and half metallic components; thus substantiating the use of both an acid and an alkali. Acids and alkalis mentioned in literature, with regards to pyrolytic tyre char demineralisation, were screened as per demineralisation ability and raw material costs. Hydrochloric acid and sodium hydroxide proved to be superior. Subsequently, significant process factors, including extraction time, extraction temperature and lixiviant concentration, were analysed through kinetic trials and sequential extractions. A final acid-alkali demineralisation process was thus established; and pyrolytic tyre char was upgraded to a carbon black product using 3x 5.0M NaOH washes at 88°C for 60minutes followed by 1x 1.0M hydrochloric wash at 80°C for 20minutes, including water washes prior to each lixiviant wash. Additionally, 100g lixiviant was utilised per wash; with the char: lixiviant ratio decreasing from an initial 20:100 (g/g). The upgraded pyrolytic tyre char was comparable to commercial carbon black N330 in terms of ash content (1.83wt.%) and BET surface area (84.7m².g-¹); however, it had much coarser particles (130.6μm). Finally, using the proposed acid-alkali process, economic analyses were applied to an industrial process design. An industrial upgrading project cannot be eliminated as unprofitable; however project investment is not highly appealing, since the upgraded pyrolytic tyre char has to sell for a high price for the process to be economically feasible, and may not be able to compete in the relevant markets. Two key recommendations for further research include (i) acid-alkali process optimisation aiming to reduce raw material and utility expenditures; (ii) analysing the influence of the upgraded carbon black product on tyre characteristics with the aim of suitability assessment and the requirement of a particle size reduction process.