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Modelling and uncertainty propagation of measured phase equilibrium data for the 1-nonanol, n-hexadecane, and supercritical carbon dioxide system
Thesis (MEng)--Stellenbosch University, 2025.
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867614073132154880 |
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| access_status_str | Open Access |
| author | Mouton, Corine |
| author2 | Schwarz, Cara Elsbeth |
| author_browse | Mouton, Corine Schwarz, Cara Elsbeth |
| author_facet | Schwarz, Cara Elsbeth Mouton, Corine |
| author_sort | Mouton, Corine |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MEng)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/134720 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:46:13.197Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/134720 Modelling and uncertainty propagation of measured phase equilibrium data for the 1-nonanol, n-hexadecane, and supercritical carbon dioxide system Mouton, Corine Schwarz, Cara Elsbeth Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Phase rule and equilibrium Supercritical fluids Thermodynamics -- Mathematical models Thesis (MEng)--Stellenbosch University, 2025. Mouton, C. 2025. Modelling and uncertainty propagation of measured phase equilibrium data for the 1-nonanol, n-hexadecane, and supercritical carbon dioxide system. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/d022e82b-092c-4a4d-a975-e6f215e0f2a1 ENGLISH ABSTRACT: Detergent-range 1-alcohols are essential to the detergent and pharmaceutical industries and are typically recovered from mixtures with inert n-alkanes that have similar boiling points. Supercritical CO₂ fractionation offers a lower-temperature alternative to azeotropic distillation, although the phase behaviour of these systems is challenging to model, and the uncertainties remain poorly quantified. This study quantifies the impact of measurement uncertainties on the performance of a thermodynamic model by measuring, modelling, and propagating uncertainties in phase equilibrium data for the 1-nonanol (solute) + n-hexadecane (solute) + CO₂ (solvent) system. Data were obtained for the 1-nonanol and/or n-hexadecane + CO₂ systems with solvent-free 1-nonanol fractions of w₁ʳᵉᵈ ∈ {0; 0.2; 0.4; 0.6; 0.8; 1} g·g⁻¹ to improve the understanding of solute–solute interactions. Experiments were conducted over 308.2–358.2 K and 7–26 MPa using the static synthetic method. The high-pressure phase transition measurements showed that the ternary system exhibits temperature inversions, where phase transition pressures decrease with increasing temperature, and cosolvency, where mixtures of 1-nonanol and n-hexadecane display greater solubility in CO₂ than either pure component. These effects arise from solute–solute interactions, are generally more pronounced at lower temperatures, and affect phase boundaries and separation feasibility. A modified Soave–Redlich–Kwong (SRK) equation of state, implemented in Aspen Plus® V14.0 as RK-Aspen, has been the most successful framework for describing the phase behaviour of 1-alcohol and/or n-alkane mixtures + CO₂. The formulation employs van der Waals mixing rules for the energy and co-volume parameters, together with a polar parameter in the alpha function. The measured and literature data were used to parameterise RK-Aspen with the aim of overcoming limitations reported in earlier studies. Despite these efforts, modelling the deterministic (base case) scenario remained challenging near the solvent’s critical temperature and within the mixture critical regions. It is postulated that the mathematical formulation of RK-Aspen is unable to describe behaviour close to the solvent critical point, while the numerical methods implemented in Aspen Plus® V14.0 struggle to capture the mixture critical region. Furthermore, the model overpredicted phase transition pressures for the w₁ʳᵉᵈ = 0.2 g·g⁻¹ mixture. Addressing these limitations may require more advanced computational algorithms. The experimental findings and base case modelling results from this study have been published in Fluid Phase Equilibria (DOI: https://doi.org/10.1016/j.fluid.2025.114587). The measured data were also used to propagate estimated measurement uncertainties to the model correlations and predictions through a Monte Carlo simulation approach – an aspect that, to the best of the author’s knowledge, has not yet been considered in high-pressure phase behaviour studies. The uncertainty quantification of the model showed that experimental uncertainties have a negligible influence on polar and solute-solvent parameters, and only a minor influence on ternary predictions when the model is already capable of representing the phase behaviour (away from lower temperatures and mixture critical regions). While still marginal, uncertainties in the binary measurements produced the largest uncertainties in ternary predictions. Overall, the developed uncertainty propagation method provides a framework for quantifying confidence in high-pressure phase equilibrium descriptions and demonstrates that the RK-Aspen model is robust against measurement uncertainties. AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. Masters 2026-01-05T09:36:42Z 2026-01-05T09:36:42Z 2025-12 Thesis https://scholar.sun.ac.za/handle/10019.1/134720 Stellenbosch University 303 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Phase rule and equilibrium Supercritical fluids Thermodynamics -- Mathematical models Mouton, Corine Modelling and uncertainty propagation of measured phase equilibrium data for the 1-nonanol, n-hexadecane, and supercritical carbon dioxide system |
| title | Modelling and uncertainty propagation of measured phase equilibrium data for the 1-nonanol, n-hexadecane, and supercritical carbon dioxide system |
| title_full | Modelling and uncertainty propagation of measured phase equilibrium data for the 1-nonanol, n-hexadecane, and supercritical carbon dioxide system |
| title_fullStr | Modelling and uncertainty propagation of measured phase equilibrium data for the 1-nonanol, n-hexadecane, and supercritical carbon dioxide system |
| title_full_unstemmed | Modelling and uncertainty propagation of measured phase equilibrium data for the 1-nonanol, n-hexadecane, and supercritical carbon dioxide system |
| title_short | Modelling and uncertainty propagation of measured phase equilibrium data for the 1-nonanol, n-hexadecane, and supercritical carbon dioxide system |
| title_sort | modelling and uncertainty propagation of measured phase equilibrium data for the 1 nonanol n hexadecane and supercritical carbon dioxide system |
| topic | Phase rule and equilibrium Supercritical fluids Thermodynamics -- Mathematical models |
| url | https://scholar.sun.ac.za/handle/10019.1/134720 |
| work_keys_str_mv | AT moutoncorine modellinganduncertaintypropagationofmeasuredphaseequilibriumdataforthe1nonanolnhexadecaneandsupercriticalcarbondioxidesystem |