Phase behaviour and thermodynamic modelling of carbon dioxide + (1-octanol or 1-decanol) + large n-alkanes

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dc.contributor.advisorSchwarz, Cara Elsbeth
dc.contributor.authorMomoh, Chris Favour Ojonugua
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Process Engineering.en_ZA
dc.date.accessioned2023-03-03T12:33:58Z
dc.date.accessioned2023-05-18T07:03:27Z
dc.date.available2023-03-03T12:33:58Z
dc.date.available2023-05-18T07:03:27Z
dc.date.issued2023-03
dc.descriptionThesis (MEng)--Stellenbosch University, 2023.en_ZA
dc.description.abstractENGLISH ABSTRACT: Large alcohols are useful in the synthesis of detergents, surfactants and plasticisers. However, the product stream of these processes often contains an impurity of large n-alkanes. Azeotropic distillation has been the mainly used process to separate the 1-alcohol product from the n-alkanes. However, due to the process requirements, health and safety risks and extreme operating conditions, investigations have been carried out into utilising an alternative process for this separation. Supercritical CO2 fractionation has been proven to be a feasible method for the separation of detergent range n-alkanes and alcohols because it serves as a cheaper, less toxic method to azeotropic distillation. However, there are notable solute-solute interactions exhibited by ternary systems containing CO2, n-alkanes, and 1-alcohol. The main aim of this work was to experimentally identify and analyse the solute-solute interactions that occur in ternary systems containing supercritical CO2 as a solvent and a solute mixture of 1-alcohols (C8 or C10) and n-alkanes (C10 – C20). The secondary aim of the study was to evaluate the capability of the RK-Aspen thermodynamic model to predict the phase transition data. The solute-solute interactions exhibited in these systems were identified and characterised by analysing their high-pressure bubble- and dew-point (HPBDP) data. Literature revealed that there is, however, a lack of data for the systems relevant to this study. HPBDP data for the ternary systems containing CO2 + 1-alcohols + n-alkanes were thus measured at temperatures ranging from 308 K to 358 K. The phase behaviour data were measured at solute mass fractions ranging from 0.015 to 0.65, with pressures up to 30 MPa, using the synthetic visual phase detection method. The experimental HPBDP data revealed that co-solvency was present in all the ternary systems measured. The systems exhibiting the most significant co-solvency effects were CO2 + 1-octanol + n-hexadecane and CO2 + 1-decanol + n-octadecane. The measured data highlighted that the influence of the n-alkanes on the solute mixtures decreased with an increase in molecular mass. The experimental data revealed that co-solvency occurs in alkane-rich mixtures for systems containing C10 – C14 alkanes while the co-solvency effects for systems containing larger alkanes are more prominent for alcohol-richer mixtures. The range of solute mixture compositions and temperatures investigated did not reveal the effects of other complex phase behaviour phenomena such as miscibility windows and l-l-g holes; these may be present at other conditions for these systems. The evaluation of the RK-Aspen model revealed that the model correlated well with the HPBDP data at higher temperatures (T > 328 K). Furthermore, the addition of experimentally determined solute-solute binary interaction parameters improved the ability of the RK- Aspen model to predict the data. The %AADP for the ternary systems investigated improved from a range of 3.95 % - 17.41 % to a range of 1.65 % - 5.99 % when the solute-solute BIPs were included. The RK-Aspen method also struggled to predict the phase behaviour for systems containing larger n-alkanes as these systems exhibited significant temperature inversions. en_ZA
dc.description.abstractAFRIKAANS OPSOMMING: Groot alkohole is behulpsaam in die sintese van reinigingsmiddels, surfaktante en plastiseerders. Die produkstroom van hierdie prosesse bevat egter gereeld ’n onsuiwerheid van groot n-alkane. Aseotropiese distillasie is die hoofgebruikte proses om die 1-alkoholproduk van die n-alkane te skei. As gevolg van die prosesvereistes, gesondheid- en veiligheidsrisiko’s en uiterse bedryfstoestande is ondersoeke egter uitgevoer om ’n alternatiewe proses vir hierdie skeiding te gebruik. Superkritiese CO2-fraksionering is bewys as ’n uitvoerbare metode vir die skeiding van reinigingsmiddel-bestek n-alkane en alkohole omdat dit as ’n goedkoper, minder toksiese metode dien in vergelyking met aseotropiese distillasie. Daar is egter merkwaardige opgeloste stof-opgeloste stof interaksies vertoon deur ternêre stelsels wat CO2, n-alkane, en 1-alkohol bevat. Die hoofdoel van hierdie werk was om die opgeloste stof-opgeloste stof interaksies wat voorkom in ternêre stelsels met superkritiese CO2 as ’n oplosmiddel en ’n opgeloste stof-mengsel van 1-alkohole (C8 of C10) en n-alkane (C10 – C20), eksperimenteel te identifiseer en analiseer. Die sekondêre doel van die studie was om die vermoë van die RK-Aspen termodinamiese model wat die fase-oorgangsdata voorspel, te evalueer. Die opgeloste stof-opgeloste stof-interaksies in hierdie stelsels is geïdentifiseer en gekarakteriseer deur hul hoë-druk borrel- en doupunt (HPBDP) data te analiseer. Literatuur het getoon dat daar wel ’n gebrek is aan data vir die stelsels relevant tot hierdie studie. HPBDP-data vir die ternêre stelsels wat CO2 + 1-alkohole + n-alkane bevat is dus by temperature in bestek van 308 K tot 358 K gemeet. Die fasegedragdata is gemeet by opgeloste stof massafraksie in bestek van 0.015 tot 0.65, met druk tot en met 30 MPa, deur die gebruik van die sintetiese visuele fase opsporingsmetode. Die eksperimentele HPBDP-data het gewys dat saamoplosbaarheid teenwoordig was in al die ternêre stelsels wat gemeet is. Die stelsels wat die mees beduidende saamoplosbaarheideffek getoon het, was CO2 + 1-dekanol + n-oktadekaan. Die gemete data het beklemtoon dat die invloed van die n-alkane op die opgeloste stof mengsels afgeneem het met ’n verhoging in molekulêre massa. Die eksperimentele data het bekend gemaak dat saamoplosbaarheid voorkom in alkaanryke mengsels vir stelsels wat C10 – C14-alkane bevat terwyl die saamoplosbaarheideffek vir stelsels wat groter alkane bevat meer prominent vir alkoholryker mengsels is. Die bestek van opgeloste stof mengselkomposisies en temperature ondersoek, het nie die effek van ander komplekse fasegedragfenomene soos mengbaarheidsvensters en l-l-g-gate bekend gemaak nie; hierdie mag dalk teenwoordig wees by ander kondisies vir hierdie stelsels. Die evaluasie van die RK-Aspen-model het getoon dat die model goed gekorreleer het met die HPBDP-data by hoër temperature (T > 328 K). Verder, die byvoeging van eksperimenteel bepaalde opgeloste stof-opgeloste stof binêre interaksieparameters het die vermoë van die RK-Aspen-model om die data te voorspel, verbeter. Die %AADP vir die ternêre stelsels ondersoek het van ’n bestek van 3.95% - 17.41% tot ’n bestek van 1.65% - 5.99% verbeter toe die opgeloste stof-opgeloste stof BIPs ingesluit het. Die RK-Aspen-metode het ook gesukkel om die fasegedrag vir stelsels wat groter n-alkane bevat te voorspel, omdat hierdie stelsels beduidende temperatuurinversies getoon het.af_ZA
dc.description.versionMastersen_ZA
dc.format.extentiii, 225 pages : illustrations.en_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/127083
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshTemperature inversions en_ZA
dc.subject.lcshAzeotropic distillation en_ZA
dc.subject.lcshDistillation, Fractional en_ZA
dc.titlePhase behaviour and thermodynamic modelling of carbon dioxide + (1-octanol or 1-decanol) + large n-alkanesen_ZA
dc.typeThesisen_ZA
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