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Development of economically viable waste tyre pyrolysis technologies that yield liquid fractions meeting commercial fuel standards
Khosa, M. 2025. Development of economically viable waste tyre pyrolysis technologies that yield liquid fractions meeting commercial fuel standards. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/4e7c63fa-45a7-47de-b0f8-29cb85ee6...
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613875046711296 |
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| access_status_str | Open Access |
| author | Khosa, Matimu |
| author2 | Schwarz, Cara E. |
| author_browse | Khosa, Matimu Schwarz, Cara E. |
| author_facet | Schwarz, Cara E. Khosa, Matimu |
| author_sort | Khosa, Matimu |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Khosa, M. 2025. Development of economically viable waste tyre pyrolysis
technologies that yield liquid fractions meeting commercial fuel standards. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/4e7c63fa-45a7-47de-b0f8-29cb85ee6701 |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/132579 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:43:05.531Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/132579 Development of economically viable waste tyre pyrolysis technologies that yield liquid fractions meeting commercial fuel standards Khosa, Matimu Schwarz, Cara E. Gorgens, Johann F. Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Pyrolysis Waste tires as fuel Tires -- Recycling Biochemical engineering UCTD Khosa, M. 2025. Development of economically viable waste tyre pyrolysis technologies that yield liquid fractions meeting commercial fuel standards. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/4e7c63fa-45a7-47de-b0f8-29cb85ee6701 Thesis (MEng)--Stellenbosch University, 2025. ENGLISH ABSTRACT: Waste tyre pyrolysis involves heating waste tyres in the absence of oxygen to produce non-condensable gases, volatiles, and char. The volatiles can be further processed into liquid fuel fractions with properties similar to commercial fuels. This study optimises the process using Aspen Plus® simulations and techno-economic analyses to produce low-sulphur fuel fractions that meet commercial standards while remaining economically viable. Four process scenarios were evaluated: (1) lumped tyre-derived oil (TDO) from simple condensation, (2) fractional condensation for liquid fractionation, (3) fractional distillation as an alternative to condensation, and (4) fractional distillation with extractive oxidative desulphurisation (OEDS) for sulphur removal. Experimental data from GC-MS and GC-VUV analyses were incorporated into the simulations, with GC-VUV providing a broader carbon range (C3–C36) than GC-MS (C7–C15). The Peng-Robinson Boston-Mathias (PR-BM) thermodynamic model was used for Scenarios 1–3, while Scenario 4 employed both PR-BM and NRTL/UNIFAC models. In Scenario 1, Aspen Plus® simulations of lumped TDO produced mass yields, boiling points, and densities comparable to experimental data and diesel fuel standards. However, the sulphur content was 0.7 wt%, exceeding the SANS342 limit of <0.005 wt%, and the kinematic viscosity was 1.39 mm²/s, below the required range of 2–5.3 mm²/s, necessitating additional treatment. Fractional condensation (Scenario 2) used three condensers to separate heavy (26.77 wt%), medium (39.90 wt%), and light (33.33 wt%) fractions, closely matching experimental values. The estimated densities (1.03, 0.910, and 0.832 kg/L) were comparable to experimental data. The viscosities of the medium and light fractions (2.02 and 0.7 mm²/s) matched experimental results, but the heavy fraction was significantly underestimated (4.1 vs. 37.73 mm²/s). The light fraction’s initial boiling point (57.33°C) was improved to 134°C by adjusting the third condenser temperature, making it kerosene-like. A fourth condenser was added to separate the remaining components from non-condensable gases, yielding a gasoline-like fraction. The medium fraction met diesel standards, while the heavy fraction aligned with marine bunker oil (MBO); however, both exceeded sulphur limits. Scenario 4 incorporated OEDS, with UNIFAC more accurately predicting sulphur removal compared to NRTL. Acetonitrile achieved 67% sulphur removal at 1:2 and 2:1 solvent-to-fuel ratios, closely matching experimental results (62% and 61%), while DMF achieved 65% removal at 1:2, compared to 61% experimentally. Economic analysis used kerosene’s market price (R12.87/L) to estimate the minimum selling price (MSP). Fractional condensation was the most cost-effective (MSP: R5.38/L) due to lower energy costs (R29 million/year). Fractional distillation had a higher MSP of R6.02/L. Heat recovery for preheating rubber crumbs resulted in an MSP of R6.29/L, which was more economical than electricity generation (MSP: R7.47/L). Treating only the heavy fraction via OEDS was technically and economically viable (MSP: R11.05/L), as it met fuel standards. Sensitivity analysis varied discount rate, tax rate, char price, fixed capital investment, and solvent price by ±25%, yearly wages by 65–129%, and plant operation years by a 33–56% reduction. Discount rate, yearly wages, and fixed capital investment were the most significant MSP drivers. All scenarios were economically feasible, except one requiring only experienced chemical engineers. Future work will focus on improving organo-sulphur compound measurements in TDO, studying the liquid–liquid and vapour–liquid equilibria of sulphones, and refining OEDS sulphur removal predictions. AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. Masters 2025-06-11T09:43:34Z 2025-06-11T09:43:34Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/132579 Stellenbosch University xiii, 140 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Pyrolysis Waste tires as fuel Tires -- Recycling Biochemical engineering UCTD Khosa, Matimu Development of economically viable waste tyre pyrolysis technologies that yield liquid fractions meeting commercial fuel standards |
| title | Development of economically viable waste tyre pyrolysis technologies that yield liquid fractions meeting commercial fuel standards |
| title_full | Development of economically viable waste tyre pyrolysis technologies that yield liquid fractions meeting commercial fuel standards |
| title_fullStr | Development of economically viable waste tyre pyrolysis technologies that yield liquid fractions meeting commercial fuel standards |
| title_full_unstemmed | Development of economically viable waste tyre pyrolysis technologies that yield liquid fractions meeting commercial fuel standards |
| title_short | Development of economically viable waste tyre pyrolysis technologies that yield liquid fractions meeting commercial fuel standards |
| title_sort | development of economically viable waste tyre pyrolysis technologies that yield liquid fractions meeting commercial fuel standards |
| topic | Pyrolysis Waste tires as fuel Tires -- Recycling Biochemical engineering UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/132579 |
| work_keys_str_mv | AT khosamatimu developmentofeconomicallyviablewastetyrepyrolysistechnologiesthatyieldliquidfractionsmeetingcommercialfuelstandards |