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Improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide
Du Plessis, S. H. 2025. Improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/a32aac46-3928-483...
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613985542504448 |
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| access_status_str | Open Access |
| author | Du Plessis, Susanna Hendrina |
| author2 | Schwarz, C. E. |
| author_browse | Du Plessis, Susanna Hendrina Schwarz, C. E. |
| author_facet | Schwarz, C. E. Du Plessis, Susanna Hendrina |
| author_sort | Du Plessis, Susanna Hendrina |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Du Plessis, S. H. 2025. Improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/a32aac46-3928-4831-9b55-e8c9365e92be
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| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/132188 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:44:50.018Z |
| 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:10019.1/132188 Improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide Du Plessis, Susanna Hendrina Schwarz, C. E. Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Phase rule and equilibrium Supercritical fluids Thermodynamics Solution (Chemistry) UCTD Du Plessis, S. H. 2025. Improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/a32aac46-3928-4831-9b55-e8c9365e92be Thesis (PhD)--Stellenbosch University, 2025. ENGLISH ABSTRACT: The investigation of phase behaviour at low and high pressures have long been a topic of investigation, and phase equilibrium data are vital to process design, thermodynamic model evaluation and development and process simulation. Since high-pressure phase equilibrium data are significantly more complex than its low-pressure counterpart (with respect to the interpretation and analysis, measurement and modelling thereof), the wide-scale implementation of most high-pressure processes, such as supercritical fluid extraction or fractionation is stifled. To date, most investigations regarding high-pressure phase equilibrium have been system-specific, and although a systematic investigation of the carbon dioxide + 1-alcohol + n-alkane system has been conducted, which revealed complex solute + solute interactions that lead to complex mixture phase behaviour, other systems have not been as well investigated. In particular, knowledge of mixtures containing solutes from other homologous series are limited, although co-solvency has been identified in CO2 + n-alkane + n-carboxylic acid systems and island systems have been identified in CO2 + 1-alcohol + n-carboxylic acid systems. The primary aim of this study was to investigate and characterise the solute + solute interactions occurring in mixtures of CO2 + solute + solute systems, where the solutes include 1-alcohols, n-alkanes, n-carboxylic acids and methyl esters. Secondarily, the ability of the RK-Aspen model to predict or correlate the ternary mixtures was investigated. In order to achieve the primary aim, three objectives were achieved. Firstly, new high-pressure bubble- and dew-point (HPBDP) data were measured using a static- synthetic high-pressure view cell, for twenty mixtures. These mixtures were chosen to consider five different solute + solute groups including n-alkane + n-carboxylic acid, n-alkane + methyl ester, 1-alcohol + n-carboxylic acid, 1-alcohol + methyl ester and n-carboxylic acid + methyl ester. Secondly, new high-pressure vapour-liquid equilibrium (HPVLE) data were measured using a static-analytical high-pressure view cell to investigate the effect of the solute + solute interactions on the relative solubility of the mixture at different temperatures and pressures. The third objective was considered with analysing the newly measured data to identify the prevailing solute + solute interactions and further the understanding of the complex phase behaviour. Thus, the newly measured mixture data were evaluated along with binary CO2 + solute data for each homologous series, and mixture data for CO2 + solute + solute data where the solutes were from the same homologous series (n-alkane + n-alkane, 1-alcohol + 1-alcohol and n-carboxylic acid + n-carboxylic acid). It was concluded that enhanced mixture solubility was identified in the n-alkane + n-carboxylic acid, n-alkane + methyl ester, 1-alcohol + n-carboxylic acid and 1-alcohol + methyl ester systems. The extent of the solubility enhancement was a function of temperature. Both enhanced and decreased mixture solubility was observed for the 1-alcohol + n-carboxylic acid system; the former being prevalent at lower temperatures, and the latter being prevalent at higher temperatures. Systems that displayed co-solvency included CO2 + n-tetradecane + n-octanoic acid, CO2 + n-tetradecane + methyl tetradecanoate, CO2 + 1-octanol + methyl tetradecanoate, CO2 + 1-octanol + methyl hexadecanoate and CO2 + 1-decanol + methyl hexadecanoate. Contrastly island systems were identified as CO2 + 1-octanol + n-decanoic acid and CO2 + 1-decanol + n-dodecanoic acid. Thus, for the n-alkane containing systems, association was postulated to likely occur due to the favourable like-like interactions based on the non-polar n-alkane and polar methyl ester or n-carboxylic acid. For 1-alcohol containing systems, in which both association and solvation effects are likely to occur (as both the n-carboxylic acid and methyl ester can participate in cross association), the dominating interaction likely gives rise to the resultant phase behaviour phenomenon. The secondary aim was to investigate the ability of the RK-Aspen to model these systems. This was achieved by first evaluating the model performance when only including solvent + solute binary interaction parameters (BIPs) and then evaluating the effect of the source data on the resultant solute + solute BIPs and subsequently the model performance. The model performed well with only solvent + solute BIPs for the two n-alkane-containing and the n-carboxylic acid + methyl ester groups, while performance was poorer for the 1-alcohol-containing systems, likely due to more complex and significant solute + solute interactions. The inclusion of solute + solute BIPs, as investigated for the CO2 + 1-octanol/n-tetradecane + methyl tetradecanoate systems, improved the model performance, albeit only marginally, but no superior parameter set between the different source data (HPBDP vs HPVLE) could be identified. This indicates that HPBDP data provides sufficient information for thermodynamic model improvement and evaluations, and that the more intensive and time-consuming HPVLE data measurement is not always necessary. AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. Doctoral 2025-05-29T08:23:46Z 2025-05-29T08:23:46Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/132188 Stellenbosch University xiii, 519 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Phase rule and equilibrium Supercritical fluids Thermodynamics Solution (Chemistry) UCTD Du Plessis, Susanna Hendrina Improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide |
| title | Improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide |
| title_full | Improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide |
| title_fullStr | Improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide |
| title_full_unstemmed | Improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide |
| title_short | Improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide |
| title_sort | improving the understanding of the complex phase behaviour of mixtures containing various organics and supercritical carbon dioxide |
| topic | Phase rule and equilibrium Supercritical fluids Thermodynamics Solution (Chemistry) UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/132188 |
| work_keys_str_mv | AT duplessissusannahendrina improvingtheunderstandingofthecomplexphasebehaviourofmixturescontainingvariousorganicsandsupercriticalcarbondioxide |