Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Thermodynamic models have been investigated extensively since Johannes van der Waals first devised a mathematical relation capable of predicting both vapour and liquid phases for a mixture at equilibrium. With the advent of modern computing power, these equations of state have gone from their humble empirical beginnings to the comprehensive and fundamentally derived models we have today. One such physically sound model is the Statistical Associating Fluid Theory (SAFT) family of equations, derived from the molecular perturbation theories of the 1980’s. The relative youth of this thermodynamic framework has meant that much work has gone into modification and optimisation of the model recently. The variants of particular interest to this work are the simplified perturbed chain SAFT equations with the Jog & Chapman (sPC-SAFTJC) and Gross & Vrabec (sPC-SAFTGV) polar terms. Each of the polar terms supports one adjustable polar parameter that relates to the quantity of polar segments in the reference fluid but not necessarily its position in the carbon chain. The strength of polar interactions is known to decrease as the functional group moves away from the terminal methyl group and the effects of steric hindrance increase. Thus, in question here is whether the models can account for the change in polar interactions associated with the changing position of the polar group, by only adjusting the values of the existing pure component parameters; that is, in lieu of a position specific parameter. The carbonyl group in ketone molecules is one such polar group, and it is this homologous series that is the focus of this study. The decrease in polar interactions as the carbonyl group in a ketone molecule shifts centrally is apparent from the lower boiling points of the isomers where the polar group is central as compared to those where the functional group is nearer the terminal methyl group. The effect of this functional group shift on binary phase behaviour has not previously been assessed for any system however, as the lack of experimental data attests. Thus, experiments had to be conducted to generate phase equilibrium data for systems comprising each structural isomer of a mid-length ketone with a common second component with no functionality. This limitation was imposed to isolate the cause of experimentally observed phenomena to the shifting polar group alone. The generated data could then be appropriately modelled using the polar sPC-SAFT variants and the capabilities of each model, as outlined above, assessed. To this end, isobaric binary vapour-liquid equilibrium data were measured for 2-, 3- & 4-heptanone with three separate normal alkanes of similar length (n-octane, n-nonane & n-decane) at 40kPa. The apparatus used was a dynamic Gillespie VLE still with temperature and pressure accuracies of 0.03°C and 1.6mbar respectively. Equipment verification was achieved through the reproduction of experimental data for the ethanol/1-butanol system at 1.013bar. The vapour and liquid samples for all nine systems were analysed by gas chromatography with a maximum compositional error of ±0.022 mole fraction. All reported data were found to be thermodynamically consistent using both the L/W and McDermott-Ellis consistency tests. When paired with a common n-alkane, all three structural heptanone isomers displayed similar qualitative trends in phase behaviour. Minimum boiling azeotropes were measured in all nine systems; in the high alkane region for n-octane systems (~98 mole%), the equal concentration region for n-nonane systems (34 mole% to 53 mole%) and in the very dilute n-alkane region for n-decane systems (~3 mole%). The n-nonane systems in particular highlighted the effect of shifting functional group, with completely separate phase envelopes away from the pure alkane composition space evident in a particularly small temperature range. Modelling was performed using in-house developed software, with pure component parameters generated for each system using five different regression procedures. The first was traditional fitting of the segment diameter (σ), segment number (m), segment energy (є/k) and the respective polar parameter (xp, np) to DIPPR correlations of pure component saturated vapour pressure, liquid density and the heat of vaporisation. The latter four procedures included the fixing of the polar parameter according to functional group correlations and the three instances of including the binary VLE data set for each of the three alkanes considered in this work. When applied to the nine binary ketone-alkane systems measured in this work, excellent predictions of the experimental data were in evidence in most cases and only small binary interaction parameters were necessary to correlate the data where pure predictions were poor. The performance of the parameter sets based on the fixing of the polar parameter and the inclusion of VLE data were consistent and of a high quality for both models, with near identical parameters generated in all four cases for each of the nine systems. The parameter sets generated in this fashion were shown to be applicable not only to the systems measured in this work, but also successfully predicted the independently measured experimental data of the n-hexane/4-heptanone system. It was thus concluded that either of these regression alternatives are viable for the generation of accurate component parameters, and the choice of VLE data set included is trivial. The pure predictions of the sPC-SAFTGV model were generally better than its sPC-SAFTJC counterpart, particularly in the case of the traditionally regressed parameter sets. sPC-SAFTGV displayed constant qualitative agreement with the experimental data for each of the heptanone isomers with a given n-alkane. The quality of the predictions of sPC-SAFTJC, however, worsened significantly as the polar interactions diminished from 2- to 4-heptanone, with no predictions even possible for the least polar isomer. This was attributed to the different perturbation theories used in the development of these terms, but a more detailed study would be necessary to confirm this. This work thus shows an apparent inability of the sPC-SAFTJC equation of state to account for the decreasing polar interactions associated with the carbonyl group in a ketone molecule shifting centrally, while sPC-SAFTGV produces qualitatively good fits for all three isomers. These flaws can be overcome through the incorporation of VLE data in the regression procedure if such data is available, or otherwise through the use of group specific correlations for fixing the polar parameter value. / AFRIKAANSE OPSOMMING: Sedert Johannes van der Waals die eerste wiskundige verhouding ontwikkel het wat beide die damp- en vloeibare fases van 'n mengsel by ewewig kon voorspel, is die veld van termodinamiese modellering al deeglik ondersoek. Na die koms van die moderne rekenaars het hierdie vergelykings van hul nederige empiriese wortels gegroei tot die omvattende, fundamentele modelle wat ons vandag het. Een so 'n fundamenteel gebaseerde familie van vergelykings is die ‘Statistical Associating Fluid Theory’ (SAFT) modelle, wat afgelei is vanaf molekulêre versteuringsteorieë, ontwikkel in die 1980s. Hierdie relatiewe jong modelle het in die afgelope ruk aansienlike aanpassing en optimering ondervind. Modelvariante van besondere belang tot hierdie werk, is die vereenvoudigde versteurde ketting of ‘simplified perturbed chain’ SAFT vergelykings, met Jog & Chapman (sPC- SAFTJC) en Gross & Vrabec (sPC- SAFTGV) polêre terme. In die sPC-SAFT toestandsvergelyking word elkeen van die polêre terme ondersteun deur een polêre veranderlike. Hierdie veranderlike is afhanklik van die aantal polêre segmente in die verwysingsvloeistof, maar nie noodwendig hul posisie in die koolstofketting nie. Daarteen is dit bekend dat die polêre interaksies tussen molekules swakker word soos die polêre groep wegbeweeg van die terminale metielgroep, en steriese hindernis ʼn groter rol begin speel. Dus is die vraag of die model die verandering in die polêre interaksie, as gevolg van veranderende posisie van die polêre groep, kan voorspel deur in plek van ʼn posisie afhanklike parameter, slegs ʼn aanpassing van die polêre waardes van die suiwer komponente te maak. Die karbonielgroep in ketoon molekules is een so 'n polêre groep, en ʼn homoloë reeks ketone word in hierdie studie ondersoek. Die afname in die polêre interaksie soos wat die karbonielgroep in 'n ketoon molekule weg skuif vanaf die terminale metiel groep is sigbaar deur die afname in kookpunt van die verskillende isomere. Hierdie effek van die funksionele groepsposisie op binêre fasegedrag is nog nie voorheen vir enige stelsels geëvalueer nie en geen eksperimentele data is vrylik beskikbaar nie. Om hierdie tekortkoming in die literatuur aan te spreek, is eksperimentele fase ewewig data gemeet. ʼn Reeks stelsels is ondersoek wat elk bestaan uit ʼn struktuurisomeer van ʼn mid-lengte ketoon en ʼn tweede komponent met geen funksionele bydrae. Eksperimente is so opgestel om die effek van die skuiwende polêre groep op die fasegedrag te isoleer en kwalitatief te ondersoek. Die gegenereerde data is dan gemodelleer met behulp van die polêre sPC- SAFT variante, soos hierbo gespesifiseer, en die vermoëns van elke model is beoordeel. Isobariese binêre fase ewewig data is by 40kPa gemeet vir damp-vloeistof stelsels bestaande uit 2, 3 & 4 heptanoon, gemeng met drie verskillende normaal alkane van vergelykbare kettinglengte (n-oktaan, n-nonaan & n-dekaan). Die apparaat wat gebruik was is 'n dinamiese Gillespie VLE eenheid met temperatuur- en drukakkuraatheid van 0,03°C en 1.6mbar, onderskeidelik. Die akkuraatheid van die toerusting is bevestig deur eksperimentele data vir ʼn etanol/1-butanol stelsel by 1.013bar te reproduseer. Die damp en vloeibare monsters vir al nege stelsels is ontleed deur gaschromatografie met 'n maksimum komposisionele fout van ± 0,022 (molfraksie). Alle data is as termodinamies konsekwent gevind deur van beide die L/W en McDermott-Ellis konsekwentheidstoetse gebruik te maak. Mengsels van die drie strukturele isomere van heptanoon met ʼn gemene n-alkaan het tydens eksperimente soortgelyke kwalitatiewe tendense in fasegedrag getoon. Gedurende eksperimente is die lae kookpunt asiotrope gemeet vir al nege stelsels. Die asiotrope verskyn in die hoë alkaan konsentrasies (~98 mol%) vir n-oktaan stelsels, medium konsentrasies (34 mol% tot 53 mol%) vir n-nonaan stelsels en baie verdunde konsentrasies (~ 3 mol%) vir n-dekaan stelsels. Die n-nonaan stelsels beeld veral die effek van die verskuiwing van die funksionele groep uit, met diskrete fasegrense wat duidelik apart staan van die suiwer alkaan ruimte, binne ʼn klein temperatuurverskil. Modellering van die stelsels is uitgevoer met behulp van sagteware wat in-huis ontwikkel is. Suiwer komponent data is gegenereer vir elke stelsel deur van vyf verskillende regressie prosedures gebruik te maak. Die eerste is die tradisionele passing van die segment deursnee (σ), segment nommer (m), segment energie (є/k) en die onderskeie polêre parameters (xp, np) op DIPPR korrelasies van die suiwer komponent versadigde dampdruk, vloeistof digtheid en die hitte van verdamping. Die oorblywende vier prosedures sluit in die bepaling van die polêre parameter deur funksionelegroep korrelasies, en drie gevalle waar die binêre VLE data vir elk van die drie alkane ingesluit is. Deur hierdie prosedures op die modellering van die nege binêre ketoon/alkaan stelsels toe te pas, is uitstekende passings van die eksperimentele data verkry met slegs baie klein binêre interaksie parameters nodig waar voorspellings minder akkuraat was. Die prestasie van die parameter stelle, gebaseer op die bepaling van die polêre parameter en die insluiting van VLE data, is konsekwent en van 'n hoë gehalte vir albei modelle, met 'n byna identiese parameters gegenereer in al vier gevalle vir elk van die nege stelsels. Die parameter stelle wat op hierdie metode gegenereer is, is nie net toepaslik gevind op eksperimentele data gemeet in hierdie werk nie, maar ook op onafhanklike data vir die n-heksaan/4-heptanoon stelsel. Daar is tot die gevolgtrekking gekom dat beide van die regressie alternatiewe lewensvatbaar is vir die generasie van akkurate suiwer komponent parameters, en dat die insluiting van die VLE data triviaal is. Die suiwer sPC - SAFTGV voorspelling was oor die algemeen beter as die suiwer sPC- SAFTJC model met die voorspelling van data, veral in die geval van passings gedoen met parameters verkry vanaf tradisionele regressie metodes. sPC- SAFTGV het ʼn voortdurende, kwalitatiewe ooreenkoms met eksperimentele data getoon vir elk van die nege stelsels. Daarteen het voorspellings deur sPC- SAFTJC beduidend verswak soos die polêre interaksies afgeneem het vanaf 2- na 4- heptanoon, met geen akkurate voorspelling moontlik vir die minste polêre isomeer nie. Die verskynsel kan toegeskryf word aan die verskil in versteuringsteorieë wat gebruik word in die ontwikkeling van die onderskeie toestandsvergelykings, maar ʼn meer in-diepte ondersoek is nodig om hierdie teorie te bevestig. Hierdie werk toon dus 'n skynbare onvermoë van die sPC - SAFTJC toestandsvergelyking om die verandering in polêre interaksie, as gevolg van die veranderende posisie van die polêre groep, vir die karbonielgroep in ʼn ketoon te voorspel, terwyl die sPC-SAFTGV toestandsvergelyking goeie kwalitatiewe passings vir al drie isomere bied. Hierdie tekortkominge kan oorkom word deur VLE data, indien beskikbaar, in die regressie prosedure in te sluit, of deur die gebruik van groep spesifieke korrelasies vir die aanpassing van die polêre parameter.

Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Efficient process design commonly relies on equation-of-state (EOS) models to provide reliable estimates of thermodynamic properties. The accuracy of EOS models, in turn, depends on the extent to which they account for intermolecular forces. The aim of this project was to improve the simplified Perturbed Chain - Statistical Associating Fluid Theory (sPC-SAFT), enabling it to account more accurately for complex molecular interactions. The more simple SAFT-based Cubic-Plus-Association (CPA) model was evaluated along similar lines for comparative purposes. A literature review showed that both sPC-SAFT and CPA have been widely applied in phase equilibria problems, but not extensively for the prediction of other thermodynamic properties. Consequently, an initial evaluation was performed on the ability of sPC-SAFT and CPA to predict first- and second-order thermodynamic properties. The properties of non-polar, polar and hydrogen bonding fluids were considered, showing that: a) sPC-SAFT and CPA generally predict first-order properties with the same accuracy, but sPC-SAFT provides improved predictions of second-order properties. Significant errors are, however, still observed with sPC-SAFT. b) A parameter regression study with sPC-SAFT, using model parameters obtained by including second-order properties in the regression function, results in poor predictions of the saturated vapour pressure and liquid density. c) Treating strong polar and dispersive forces together as Van der Waals forces results in many properties being poorly predicted by both sPC-SAFT and CPA. d) The major limitation of the association term in both CPA and sPC-SAFT is its inability to account for the influence of bond co-operativity, especially in alcohol/water mixtures. Based on these findings, the following improvements could be made: a) The development of a new association scheme for 1-alcohols, denoted the 2C association scheme. b) The extension of sPC-SAFT with the polar theories of Jog & Chapman (JC) and Gross & Vrabec (GV) to obtain sPC-SAFT-JC and sPC-SAFT-GV. c) The extension of CPA with modified versions of the aforementioned polar theories to obtain CPA-JC and CPA-GV. d) The development of a new ‘universal’ cross-association approach. The new 2C association scheme consists of one bipolar association site and one negative electron donor site and is a combination of the 1A and 2B/3B association schemes. Modelling 1-alcohols with the 2C scheme in sPC-SAFT results in improved VLE predictions of alcohol/water and alcohol/alcohol mixtures, but alcohol/alkane VLE is predicted less accurately compared to the 2B and 3B association schemes. sPC-SAFT-JC and sPC-SAFT-GV provide improved VLE predictions of mixtures with non-associating polar components compared to sPC-SAFT. VLE of polar/alkane and polar/polar systems can be represented accurately with no or only very small binary interaction parameters (BIPs). CPA-JC and CPA-GV also enable improved VLE predictions of the polar/alkane and polar/polar mixtures compared to CPA. sPC-SAFT-GV and sPC-SAFT-JC were also applied to several mixtures of associating components including alcohol/alkane, alcohol/alcohol and alcohol/water systems. New alcohol model parameters for both sPC-SAFT-GV and sPC-SAFT-JC based on the 2C, 2B and 3B association schemes were determined. The predictions of both sPC-SAFT-GV and sPC-SAFT-JC, based on any of the three association schemes, provide similar alcohol/alkane and alcohol/alcohol VLE representations, but the best phase equilibria predictions of water/alcohol systems are obtained when alcohols are modelled with the newly proposed 2C association scheme. The usefulness of a new ‘universal’ cross-association approach was demonstrated with both sPC-SAFT-GV and sPC-SAFT-JC. The philosophy behind the new approach is to set the association volume value of the solvating component equal to the cross-associating volume value of the 1-alcohol of the same molecular size and to determine an association energy value from binary VLE data. This approach aims to characterize the solvating behaviour of the cross-associating component. Preliminary results are demonstrated with systems containing acetone, propyl formate and ethyl acetate. Other thermodynamic properties, such as excess enthalpy and excess volume can be described with the new polar sPC-SAFT and CPA models. In the majority of cases, improvements are observed compared to the normal sPC-SAFT and CPA models, but BIPs are still required to obtain accurate correlations. However, these BIPs cannot be used in phase equilibria calculations and are generally property-specific. To summarise: Through the development of the 2C scheme, and the incorporation of polar terms into the sPC-SAFT model structure, notable improvement in the VLE predictions of polar (nonhydrogen bonding)/alkane, alcohol/alkane, alcohol/water and polar/alcohol systems could be obtained if compared to the original sPC-SAFT EOS. As such, the research pesented in this thesis encapsulates some significant novel contributions, viz.: a) A systematic evaluation of sPC-SAFT and CPA, providing better insight into their ability to predict thermodynamic properties. b) The development of the new 2C association scheme for 1-alcohols, as published in Ind. Eng. Chem. Res. 2011, 50, 8711–8725. c) The extension of sPC-SAFT with the polar theories of JC and GV, with application to non-associating components, as published in Fluid Phase Equilib. 2011, 305, 174–184. d) The extension of CPA with the JC and GV polar theories, as published in Fluid Phase Equilib. 2011, 312, 66–78. e) The application of sPC-SAFT-GV and sPC-SAFT-JC to associating components, including results with the new 2C association scheme. f) The development of the new ‘universal’ cross-association approach. / AFRIKAANSE OPSOMMING: Doeltreffende prosesontwerp steun grotendeels op toestandvergelykings (EOS) om goeie skattings van vloeistofeienskappe te voorspel. Die akkuraatheid van hierdie modelle word bepaal deur hoe goed hulle die invloed van molekulêre kragte kan naboots. Die doel van hierdie projek was dus om die ‘simplified Perturbed Chain-Statistical Associating Fluid Theory’ (sPC-SAFT) te verbeter, sodat dit komplekse molekulêre kragte beter kan beskryf. Die meer vereenvoudigte SAFT-gebaseerde ‘Cubic-Plus-Association’ (CPA) model was ook geëvalueer vir vergelykende doeleindes. 'n Literatuurstudie het getoon dat beide sPC-SAFT en CPA reeds wyd toegepas is in fase ewewig probleme, maar nie vir ander termodinamiese eienskappe nie. Gevolglik, is 'n aanvanklike ondersoek uitgevoer waarin die vermoë van sPC-SAFT en CPA om eerste- en tweede-orde termodinamiese eienskappe te voorspel, geëvalueer is. Die eienskappe van nie-polêre, polêre en waterstof-bindinde komponente is oorweeg en die hoof bevindinge uit hierdie ondersoek is: a) sPC-SAFT en CPA voorspel oor die algemeen eerste-orde eienskappe met dieselfde akkuraatheid, maar sPC-SAFT bied verbeterde voorspellings van tweede-orde eienskappe. Beduidende foute is egter steeds teenwoordig in die voorspellings van sPC-SAFT. b) 'n Model parameter regressie studie met sPC-SAFT het getoon dat deur tweede-orde eienskappe ook in die regressie-funksie in te sluit, swak skattings van die eienskappe wat nodig is vir 'n goeie fase-ewewig voorspellings, verkry word. c) Die gesamentlike behandeling van sterk polêre en dispersie kragte as Van der Waals kragte, lei tot swak voorspellings van baie eienskappe deur sPC-SAFT en CPA. d) Die hoof beperking van die assosiasie term wat gebruik word deur beide CPA en sPC-SAFT, is die term se onbekwaamheid om die invloed van verbinding-samewerkings te beskryf, veral in mengsels van alkohole met water. Hierdie bevindings het as basis gedien om die volgende verbeterings aan te bring: a) Die ontwikkeling van 'n nuwe assosiasie skema vir 1-alkohole: die 2C-assosiasie skema. b) Die uitbreiding van sPC-SAFT met die polêre teorieë van Jog & Chapman (JC) en Gross & Vrabec (GV) om sPC-SAFT-JC en sPC-SAFT-GV onderskeidelik te kry. c) Die uitbreiding van CPA met gewysigde weergawes van die polêre teorieë om CPA-JC en CPA-GV te kry. d) Die ontwikkeling van ʼn nuwe ‘universele’ kruis-assosiasie benadering. Die nuut-voorgestelde 2C assosiasie skema bestaan uit een bipolêre assosiasie sone en een negatiewe elektron skenker sone en is ʼn kombinasie van die 1A en 2B/3B assosiasie skemas. Die modellering van 1-alkohole met die 2C skema in sPC-SAFT lei tot 'n verbetering in damp-vloeistof ewewig (VLE) voorspellings van alkohol/water en alkohol/alkohol sisteme, maar vir alkohol/alkaan sisteme is minder akkurate voorspellings verkry in vergelyking met die 2B en 3B assosiasie skemas. sPC-SAFT-JC en sPC-SAFT-GV lewer beter VLE voorspellings van mengsels met nie-assosiërende polêre komponente in vergelyking met sPC-SAFT. Die VLE van polêre/alkaan en polêre/polêre stelsels kan akkuraat beskryf word deur beide modelle wanneer geen of baie klein binêre interaksie parameters (BIPs) gebruik word. CPA-JC en CPA-GV lewer ook verbeterde VLE voorspellings van polêre/alkaan en polêre/polêre mengsels in vergelyking met CPA. sPC-SAFT-GV en sPC-SAFT-JC is ook toegepas op verskeie assosiërende mengsels, insluitend: alkohol/alkaan, alkohol/alkohol en alkohol/water stelsels. Nuwe alkohol parameters is vir beide sPC-SAFT-GV en sPC-SAFT-JC bepaal gebaseer op die 2C, 2B en 3B assosiasie skemas. Die voorspellings van sPCSAFT- GV en sPC-SAFT-JC, gebaseer op enigeen van die drie assosiasie skemas, lewer soortgelyke alkohol/alkaan en alkohol/alkohol VLE voorspellings, maar die beste fase-ewewig voorspellings vir water/alkohol sisteme is verkry wanneer alkohole gemodelleer word met die 2C assosiasie skema. Die nuwe ‘universele’ kruis-assosiasie benadering is gedemonstreer met beide sPC-SAFT-GV en sPC-SAFT-JC. Die filosofie agter die nuwe benadering is om die assosiasie volume waarde van die solverende komponent gelyk te stel aan die kruis-assosiasie volume waarde van die 1-alkohol met dieselfde molekulêre massa. Die assosiasie energie waarde word dan bepaal vanaf binêre VLE data. Hierdie benadering poog om die solverende gedrag van die kruis-assosiërende komponent meer akkuraat te karakteriseer. Voorlopige resultate met mengsels van asetoon, propiel formaat en etiel asetaat dui aan dat merkwaardige verbeterings in VLE voorspellings gekry word. Ander termodinamiese eienskappe, soos oortollige entalpie en oortollige volume, is ook ondersoek met die nuwe polêre sPC-SAFT en CPA-modelle. In meeste gevalle word verbeterde resultate gekry in vergelyking met die oorspronklike sPC-SAFT en CPA modelle, maar groot BIPs word steeds benodig om aanvaarbare korrelasies te kry. Hierdie BIPs kan egter nie gebruik word vir fase-ewewig voorspellings nie en is eienskap-spesifiek. Om op te som: deur die ontwikkeling van die 2C skema, en insluiting van die polêre terme in die sPC-SAFT model struktuur, is merkwaardige verbeterings in die VLE voorspellings van polêre/alkaan, alkohol/alkaan, alkohol/water en polêre/alkohol sisteme gekry in vergelyking met die oorspronklike sPC-SAFT EOS. Die navorsing voorgelê in hierdie tesis het dus gelei tot die volgende nuwe bydraes: a) Die sistematiese evaluering van die vermoë van sPC-SAFT en CPA om termodinamiese eienskappe te voorspel. b) Die ontwikkeling van die nuwe 2C assosiasie skema vir 1-alkohole soos gepubliseer in Ind. Eng. Chem. Res. 2011, 50, 8711–8725. c) Die uitbreiding van sPC-SAFT met die polêre teorieë van JC en GV soos gepubliseer in Fluid Phase Equilib. 2011, 305, 174–184. d) Die uitbreiding van CPA met die polêre teorieë van JC en GV soos gepubliseer in Fluid Phase Equilib. 2011, 312, 66–78. e) Die toepassing van hierdie nuwe modelle op assosiërende komponente, insluitend resultate met die nuwe 2C skema. f) Die ontwikkeling van ʼn nuwe kruis-assosiasie benadering.

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The simplified Perturbed-Chain Statistical Associating Fluid Theory (sPC-SAFT) is characterised by the dual advantages of decreased computational intensity, while remaining accurate for a variety of systems. Vapour-liquid equilibrium data are used to generate equation of state parameters. However, incorporating monomer fraction data into the parameter regression has long been advocated as a good, or even preferred, practice. Therefore, the monomer fraction data of dilute alcohol-acetone systems were analysed in this study. A small stainless steel sample vessel was constructed with temperature control, manual pressure control and a mechanism for liquid phase analysis via infrared spectroscopy. The performance of the spectrometer was verified by comparison with the ethanol – n-hexane data of von Solms et al. (2007), after which new monomer fraction data were obtained for dilute solutions (between 0.01 and 1.5 mol%) of methanol, ethanol, 1-propanol and 2-propanol in acetone near 23 °C. For dilute alcohol-acetone systems it was found that the propanols had the highest monomer fractions, and methanol the lowest. With increasing alcohol concentration, the monomer fractions decreased exponentially to values of 0.4 and 0.1 for methanol and the other alcohols respectively. The excess availability of hydrogen bond acceptors in the mixtures explains the equivalency observed for ethanol, 1-propanol and 2-propanol. For dilute acetone-alcohol systems it was found that, especially for methanol and ethanol, there was a pronounced trend towards acetone monomer fractions of 1 at infinite dilution. For the acetone – 2-propanol system, a previously unrecorded monomer peak was observed and quantified. Acetone monomer fractions tended to decrease as alcohol chain-length increased, showing that acetone could more easily penetrate the hydrogen bond network of the solvent when the solvent-solvent bonds were weaker. Monomer fraction data were compared to predictions for the sPC-SAFT scheme and parameters combinations published in the literature. The experimental data were accurately modelled using modified association parameters such that the solute associates strongly (εAB≈103 κ≈1), while the solvent parameters were decreased (εAB≈102 κ≈10˗3) to give a weakened solvent association effect. The difficulty for the dilute solute in penetrating the solvent bonding network appeared to be similar to the hydrophobic effect. Two new association schemes were proposed for acetone, assigning a single (N) or two (2N) negative association sites to represent the oxygen valence electron pairs. These schemes showed relative success in modelling acetone as the solvent in the mixture, while not being able to predict acetone monomer fractions when acetone was the solute. For dilute acetone-alcohol systems, the data were best described using the 2B model for acetone, while the best choice of scheme for the alcohol varied from system to system. For dilute alcohol-acetone mixtures it was generally found that a 2B-N model (with modified association parameters) provided the best fit to those experimental data. Accurate modelling below 0.1 mol% was difficult to attain with average errors decreasing to the order of 10% when this area was excluded. In this highly dilute region, not one of the models could describe the rapid change in (monomer fraction) gradient sufficiently while simultaneously offering accurate predictions over the entire experimental range. / AFRIKAANSE OPSOMMING: Die sPC-SAFT of simplified Perturbed-Chain Statistical Associating Fluid Theory toestandsvergelykings word wyd gebruik as gevolg van sy goeie akkuraatheid vir ‘n wye reeks sisteme, ten spyte van verminderde berekeningsintensiteit. Die parameters vir dié toestandsvergelyk word afgelei van faseewewig data, maar monomeer fraksie data word voorgestel vir die verbetering van (veral) die assosiasie parameters. Ten opsigte hiervan, was alkohol-asetoon sisteme bestudeer en hul monomeer fraksies gemeet. ‘n Staal reaktor was ontwerp (met ‘n temperatuurbeheerstelsel sowel as drukbeheer) om vloeistof monsters voor te berei vir analise d.m.v. infrarooi-spektroskopie. Die akkuraatheid van die eksperimentele apparaat is bewys deur nabootsing van etanol – n-heksaan data van von Solms et al. (2007), waarna nuwe monomeer fraksie data gegenereer is vir verdunde mengsels (0.01 tot 1.5 mol%) van metanol, etanol, 1- en 2-propanol met asetoon by 23 °C. Metanol monomeer fraksies het eksponensieël afgeneem na 0.4, terwyl etanol en propanol fraksies afgeneem het na ‘n gemene waarde van ongeveer 0.1. Hierdie tendens word toegeskryf aan ‘n oormaat van toeganklike waterstofbindingontvangers in hierdie mengsels. Vir verdunde asetoon-alkohol sisteme is daar ‘n tendens, (veral vir verdunnings met metanol en etanol) vir die monomer fraksies om te neig na 1 by oneindige verdunning. ‘n Monomeer piek is ook waargeneem vir die asetoon – 2-propanol sisteem. Hierdie piek is nie voorheen gesien in ander studies nie en dit is ook die eerste keer wat sulke data gekwantifiseer is. Daar is bevind dat asetoon monomeer fraksies afneem soos alkohol kettinglengte toeneem. Die gegenereerde monomeer fraksie data word vergelyk met verskeie sPC-SAFT parameterstelle vanuit die literatuur. Oor die algemeen, is die beraamde fraksie veel hoër as die eksperimentele data wanneer die 2B/3B/2C skemas met ‘n nie-assosiërende asetoon molekuul gemodelleer word. Wanneer die 2B parameters van von Solms et al. (2004) gebruik word, toon die beraming ‘n drastiese onderskatting van die data. Om ‘n akkurate beraming van die monomeer fraksie data te kry, moet die assosiasie parameters van die opgeloste stof vermeerder word (met εAB≈103 κ≈1) terwyl die oplosmiddel s’n drasties verswak moet word (met εAB≈102 κ≈10-3). Hierdie patroon kan vergelyk word met die hidrofobiese effek waar die kragte binne die oplosmiddel ‘n netwerk vorm wat die opgeloste stof uitstoot. Twee nuwe assosiasie skemas word ook voorgestel vir asetoon waar onderskeidelik een (N) en twee (2N) negatiewe sones, wat die valenselektroonpare op die suurstofatoom voorstel, aan asetoon geheg word. Hierdie twee skemas het relatiewe sukses getoon in die modellering van verdunde alkohol-asetoon sisteme terwyl dit ‘n swak beskrywing van die verdunde asetoon-alkohol mengsels voorspel het. ‘n Gewysigde 2B asetoon skema gee ‘n goeie beskrywing van die eksperimentele data. In hierdie geval, is die keuse van alkohol skema minder belangrik, terwyl die waardes van die assosiasie parameters verminder moet word. Vir verdunde alkohol-asetoon mengels word daar bevind dat ‘n 2B-N model met nuwe assosiasie parameters die beste passing van die eksperimentele data gee. Daar was ook bevind dat die modelle se akkuraatheid drasties afneem (met fout vermeerdering in die orde van 10%) wanneer die konsentrasie van die opgeloste stof minder as 0.1 mol% is.