New methods, based on tracer gas measurements and isotopicanalysis can be used to evaluate the moisture properties ofbuilding materials and provide the means for forensic analysisof the origins and history of excessive water in buildings, theimmediate practical consequences of which will be the abilityto improve the moisture performance of constructions. It is shown, in theory and through measurements how thewater vapour permeability of porous building materials can witha good degree of accuracy be estimated with tracer gasmeasurements that provide an efficient alternative to the cupmethod. Complementary measurements may be carried out in orderto evaluate the contribution of surface diffusion and theeventual enhancing effects of moisture content on the diffusioncoefficient. The Random Hopping Model is used to illustrate howthe surface diffusion coefficient depends on the amountadsorbed and the activation energy of migration that can beevaluated from the sorption isotherms. It is explained how the abundance ratios of two of the mostordinary isotopes of hydrogen and oxygen in water can be usedto determine its history. These isotopes are stable and givethe water a distinct signature that can be used to reveal itssource as shown in a case study. In a contrary manner themeasured isotopic separation can be used to determine therelevance of different transport processes and reactions. It isof central importance that not only does the magnitude ofisotopic separation for the reactions vary for deuterium andoxygen-18 but even the ratio thereof. One of the challenges hasbeen to construct an experimental method for retrieving samplesof water for comparison. Furthermore this thesis includes an evaluation of a new typeof a light weight construction with loose-fill cellulose fibre,in which the conventional polyethylene vapour barrier has beenreplaced with polypropylene fabric. With a verified model ithas been investigated how the construction would perform fordifferent internal moisture loads and reference climate fromthe literature. The results suggest that this type ofconstruction is not to be recommended. KEYWORDS:tracer gas, water vapour permeability,diffusion, surface diffusion, isotopic analysis, deuterium,oxygen-18, fractionation, vapour barrier, transient numericalmodelling of diffusion. / QC 20100611

Deux expériences ont été menées sur la plate-forme expérimentale "SCERES" afin d'évaluer les concentrations et les flux de vapeurs de TCE dans SCERES en présence de deux dalles de béton fissurées installées, l'une après l'autre, à la surface de SCERES. Cet aquifère poreux est un milieu hétérogène de grande échelle (25 x 12 x 3 m3). Les résultats ont montré que le panache de vapeur de TCE couvre la plupart du bassin au bout de 3 semaines depuis la création de la zone source de TCE dans le sous sol. L'hétérogénéité du site SCERES a engendrée une distribution verticale non uniforme de la concentration de vapeurs de TCE. La simulation du panache de vapeur dans SCERES a été effectuée au moyen du code de calcul multiphasique "SIMUSCOPP". La présence sur SCERES de la dalle de béton, un milieu peu perméable et peu diffusif, a constitué une "barrière" en vue du transfert de vapeurs de TCE vers l'interface dalle/atmosphère. Afin de mieux quantifier le flux de vapeurs à travers la dalle de béton, une étude de coefficient de diffusion et de perméabilité des deux dalles a été réalisée. Un mouvement vertical ascendant du toit de la nappe a généré un fort gradient de pression motrice de l'air du sol. Ceci a engendré une forte augmentation des flux de vapeurs à l'interface sol/atmosphère. La quantification de ces flux de vapeurs a été effectuée à l'aide d'une solution semi analytique basée sur la loi de Fick et la loi de Darcy en tenant compte à la fois de l'effet de gradient de pression motrice et l'effet de densité de vapeurs sur le transfert de vapeurs vers la surface du sol. L'intrusion de vapeurs de TCE dans le bâtiment modèle, installé sur la dalle de béton, a été générée par une mise en dépression dans ce dernier. Ce qui a fait augmenter la concentration de vapeurs de TCE sous la dalle ainsi dans le bâtiment. La simulation de l'intrusion de vapeurs dans l'air intérieur de bâtiment a été réalisée par l'intermédiaire du code de calcul multiphysics "COMSOL", avec lequel nous avons démontré l'évolution de la concentration de vapeurs obtenues expérimentalement dans le bâtiment et qui dépend directement de la variation spatio-temporelle du flux massique à travers la dalle. / Two experiments were conducted on the experimental platform "SCERES" to assess the TCE vapour concentrations and fluxes in SCERES with two concrete slabs installed, one after the other, on the ground surface. This artificial aquifer is a large scale (25 x 12 x 3 m3) heterogeneous porous medium. The results showed that the TCE vapour plume covers most of the basin 3 weeks after the creation of the TCE source area in unsaturated zone. The heterogeneity of SCERES has generated a non uniform vertical distribution of the TCE vapour concentration. Simulation of vapour plume in SCERES was carried out by the multiphase code "SIMUSCOPP".The presence in SCERES of a low permeability and low diffusive medium compared to the sand in the basin,as a concrete slab, constituted a "barrier" for the transfer of TCE vapour to the interface concrete slab / atmosphere. To better quantify the TOE fluxes through the concrete slab, a study of diffusion coefficient and permeability of both concrete slabs was done. An upward vertical movement of the water table has generated a strong soil air pressure driving gradient, which led to a strong increase in the TCE vapour concentrations near the surface which has increased the vapour fluxes at the interface soil / atmosphere. Quantification of vapour fluxes at the interfaces soil / atmosphere and concrete slab / atmosphere was performed using a semi analytical approach based onFick's and Darcy's laws by taking into account both the effect of the driving pressure gradient and the effect of density vapour on the vapour transfer towards the soil surface.The intrusion of TCE vapours into the model building installed on the concrete slab was generated by creating a vacuum. The results showed that, during the TCE vapour suction from the model building, the concentration of TCE vapours under the concrete slab and in the building increases. Simulation of vapour intrusion into indoor air was done by the computational Multiphysics code "COMSOL", allowing simulation of the evolution of the vapour concentration obtained experimentally in the building. Il was shown that they depend directly on the spatial-temporal variation of the mass flux through the slab.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Long-chain hydrocarbons are of value to numerous lucrative industries. Due to the low volatility and close melting and boiling points of these solutes, traditional fractionation methods lack the required selectivity for separation and cause thermal degradation of the product. This project investigates the feasibility of Supercritical Fluid Extraction (SFE) for processing these systems, with the primary objective of modelling the high-pressure vapour-liquid equilibrium (VLE) properties of hydrocarbon solutes with a light-weight solvent using a semiempirical equation of state (EOS). Pure component vapour pressures and saturated liquid volumes are also investigated. A thorough investigation into the phase behaviour of the n-alkanes, 1-alcohols, carboxylic acids and esters in light weight supercritical solvents CO2, ethane and propane revealed that the solute structure and temperature largely influence the solute solubility and process feasibility. Good selectivity amongst the various solutes was observed for all three solvents, but very high pressures were required for complete miscibility using CO2 (exceeding 30 MPa). The quadrapole moment of CO2 further leads to complexities in phase behaviour such as temperature and density inversions (CO2/alkanes and CO2/alcohols) and 3-phase regions within the operating range. Simple linear trends in pressure vs. carbon number and temperature were observed for all the considered series using ethane and propane and these solvents were thus selected for conducting the modelling for this study. A thorough review of semi-emperical EOS models from literature revealed that the simple cubic equations of state (CEOSs) provide a promising modelling approach for SFE applications due to their simplicity, flexibility and reliability. The simple Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) EOSs provide good correlation of vapour pressure (%AAD below 5 %) for all the series over a large carbon number range (up to nC20), provided a two parameter alpha function is used. A 3rd parameter in the volume dependence for Patel-Teja (PT) EOS provides considerable improvement over the PR and SRK EOSs for satureate liquid volume correlations of the non-polar solutes (alkanes and esters), but offers virtually no advantage for the more polar alcohols and acids. The CEOSs therefore suffer clear limitations in simultaneous representation of these saturation properties (vapour pressure and liquid molar volume) for the systems of interest. Good correlations of high pressure binary VLE data were obtained using CEOSs available in the Aspen Plus ® simulator (% AAD in P, T and X2 generally below 1 % and ranging from 4 to 12 % for Y2 for all series) provided that two binary interaction parameters (BIPs) are used in the model mixing rules, irrespective of the model used. Aspen Plus ® was further validated as a reliable thermodynamic tool by comparing model fits using the RK-ASPEN model with parameters obtained from the Aspen Plus ® data regression routine and computational methods used in self-developed MATLAB software. Very similar results were obtained for both computational methods, which encourages the use of Aspen Plus ® for process modelling in SFE applications. A statistical sensitivity analysis into the relative effect and interactions between 6 modelling factors in applying the CEOSs revealed that the mixing rules, temperature and solute structure had the largest effect on the correlation of the high pressure VLE, with the pure component limit having negligible effect once BIPs are fitted to data. A significant interaction was, however, observed between the pure component model and the solute structure and temperature, which suggest that accurate correlation of mixture VLE does not solely rely on appropriate mixing rule selection, but also the pure model. Binary interaction parameters (BIPs) in model mixing rules were found to become intercorrelated when more than one are used, greatly impeding the development of generalized correlations. BIPs were also found to be sensitive to the pure component limit (alpha function and pure constants used), the temperature, the combining rules used and possibly the fluid density. These factors should all be taken into account systematically for developing generalized correlations which therefore fell outside the scope of this study. Recommendations were, however, made on how the MATLAB software developed in this study can be used to both expand the size of the statistical analysis already conducted into relevant modelling factors and to develop new generalized correlations for BIPs and new mixing rules. / AFRIKAANSE OPSOMMING: Lang-ketting koolwaterstowwe is van waarde in talle winsgewende industriële toepassings. Vanweë die lae vlugbaarheiden ooreenstemmende kook- en smeltpunte van hierdie molekules, toon tradisionele fraktioneringsmetodes nie die nodige selektiwiteit vir ekstraksie nie en veroorsaak bonop termiese degradering van die produk. Hierdie projek ondersoek dus die lewensvatbaarheid van superkritiese ekstraksie vir die prosesering van hierdie sisteme, met primêre fokus op die modellering van die hoë-druk damp-vloeistof ewewig eienskappe van koolwaterstowwe opgelos in ‘n lae-massa oplosmiddel met gebruik van ‘n semi-empiriese toestandsvergelyking. Suiwer-komponent dampdrukke en versadigde vloeistof volumes word ook ondersoek. ‘n Deeglike ondersoek na die fasegedrag van die n-alkane, 1-alkohole, korboksiel-sure asook esters in lae-massa superkritiese oplosmidds CO2, etaan en propaan toon dat die struktuur van die opgeloste stof en die temperatuur ‘n groot invloed het op die oplosbaarheid en proses lewensvatbaarheid. Goeie selektiwiteit tussen die verskillende koolwaterstowwe was waargeneem vir al drie oplosmiddels, alhoewel baie hoë drukke nodig was vir totale vermenging van die fases in CO2 (hoër as 30 MPa). Die quadrupool moment van CO2 veroorsaak verder ongewenste kompleksiteite in fase gedrag soos temperatuuren digtheid inversies (CO2/alkane en CO2/alkohole) en 3-fase-gebiede in die bedryfs-kondisies. Eenvoudige lineêre tendense in druk tenoor die koolstofnommer van die opgeloste stof asook die temperatuur was waargeneem vir al die ondersoekte koolwaterstof reekse in etaan en propaan en hierdie oplosmiddels was dus gekies vir die modellering vir hierdie studie. 'n Deeglike oorsig van semi-empiriese toestandsvergelykings uit die literatuur het getoon dat die eenvoudige kubiese toestandsvergelykings ‘n belowende modelleringsbenadering bied vir superkritiese ekstraksie toepassings vanweë hul eenvoudigeid, buigsaamheid enbetroubaarheid. Die eenvoudige Peng-Robinson (PR) en Soave-Redlich-Kwong (SRK) toestandsvergelykings bied goeie korrelasie van suiwer dampdruk (foute laer as 5 %) vir alle koolwaterstowwe oor ‘n groot koolstofnommer gebied (tot by nC20), met die voorwaarde dat ‘n 2 parameter alpha funksie gebruik word. ‘n 3rde parameter in die volume afhanklikheid van die Patel-Teja (PT) toestandsvergelyking bied ‘n beduidende verbetering in die passing van die versadigde vloeistof volume vir die nie-polêre koolwaterstowwe (n-alkane en die esters), maar bied geen voordeel vir die meer polêre alkohole en karkoksiel sure nie. Die kubiese modelle toon dus duidelike beperkings vir die gelyktydige voorstelling van hierdie versadigingde eienskappe (dampdruk en vloeistof volume) vir die sisteme van belang. Goeie korrelasie van hoë druk binêre damp-vloeistof ewewig data was verkry deur gebruik van die kubiese toestandsvergelykings beskikbaar inAspen Plus ® (fout in P, T en X2 tipies laer as 1 % en van 4 tot 12 % vir Y2 vir alle sisteme), met die voorwaarde dat 2 binêre interaksie parameters gebuik word in die model mengreëls, onafhanklik van die model. Aspen Plus ® was verder bekraktig as ‘n betroubare termodinamiese hulpmiddel deur model passings te vergelyk met die RK-ASPEN model tussen gevalle waar parameters verkry is deur die beskikbare regressie metode in Aspen Plus ® en metodes gebruik in self-ontwikkelde MATLAB sagteware. Eenderse resultate was verkry vir beide berekeningsmetodes, wat die gebruik van Aspen Plus ® vir prosesmodellering in superkritiese ekstrasie toepassings aanmoedig. ‘n Satistiese sensitiwiteits analise op die relatiewe effek en interaksies tussen 6 modelleringsfaktore in die toepassing van die kubiese toestandsvergelykings het gevind dat die mengreëls, temperatuur en die stuktuur van die opgeloste stof die grootste effek op die korrelasie van hoë druk binêre damp-vloeistof ewewig het, met ‘n weglaatbare effek vandie suiwerkomponent limiet waargeneem sodra binêre interaksie parameters gepas is aan data. ‘n Beduidende interaksie was wel waargeneem tussen die suiwerkomponent model en die struktuur van die opgeloste stof asook die temperatuur, wat daarop dui dat akurate korrelasie van mengsel damp-vloeistof ewewig nie slegs afhanklink is van ‘n gepaste keuse van mengreëls nie, maar ook die suiwer-komponent model. Binêre interaksie parameters in die model mengreëls ondergaan inter-korrelasie wanneer meer as een interaksie parameter gebruik word, wat die ontwikkeling van algemeen toepaslike korrelasies grotendeels belemmer. Binêre interaksie parameters was ook bevind om sensitief te wees tot die suiwer component limiet (alpha funksie en suiwer konstantes wat gebruik is), die temperatuur, die kombineringsreëls en moontlik die vloeistof digtheid. Hierdie faktore moet dus almal sistematies in ag geneem word wanneer algemeen toepaslike korrelasies ontwikkel word, wat dus buite die omvang van die huidge studie val. Aanbevelings was wel gemaak vir hoe die MATLAB sagteware ontwikkel vir hierdie studie gebruik kan word om beide die betaande statistiese analise uit te brei, asook nuwe korrelasies vir binêre interaksies parameters en nuwe mengreëls te ontwikkel.

The Physical Vapour Deposition (PVD) magnetron sputtering process is one of the widely used techniques for depositing thin film coatings on substrates for various applications such as integrated circuit fabrication, decorative coatings, and hard coatings for tooling. In the area of coatings on cutting tools, tool life can be improved drastically with the application of hard coatings. Application of coatings on cutting tools for various machining techniques, such as continuous and interrupted cutting, requires different coating characteristics, these being highly dependent on the process parameters under which they were formed. To efficiently optimise and customise the deposited coating characteristics, PVD process modelling using RSM methodology was proposed. The aim of this research is to develop a PVD magnetron sputtering process model which can predict the relationship between the process input parameters and resultant coating characteristics and performance. Response Surface Methodology (RSM) was used, this being one of the most practical and cost effective techniques to develop a process model. Even though RSM has been used for the optimisation of the sputtering process, published RSM modelling work on the application of hard coating process on cutting tool is lacking. This research investigated the deposition of TiAlN coatings onto tungsten carbide cutting tool inserts using PVD magnetron sputtering process. The input parameters evaluated were substrate temperature, substrate bias voltage, and sputtering power; the out put responses being coating hardness, coating roughness, and flank wear (coating performance). In addition to that, coating microstructures were investigated to explain the behaviour of the developed model. Coating microstructural phenomena assessed were; crystallite grain size, XRD peak intensity ratio I111/I200 and atomic number percentage ratio of Al/Ti. Design Expert 7.0.3 software was used for the RSM analysis. Three process models (hardness, roughness, performance) were successfully developed and validated. The modelling validation runs were within the 90% prediction interval of the developed models and their residual errors compared to the predicted values were less than 10%. The models were also qualitatively validated by justifying the behaviour of the output responses (hardness, roughness, and flank wear) and microstructures (Al/Ti ratio, crystallographic peak ratio I111/1200, and grain size) with respect to the variation of the input variables based on the published work by researchers and practitioners in this field. The significant parameters that influenced the coating hardness, roughness, and performance (flank wear) were also identified. Coating hardness was influenced by the substrate bias voltage, sputtering power, and substrate temperature; coating roughness was influenced by sputtering power and substrate bias; and coating performance was influenced by substrate bias. The analysis also discovered that there was a significant interaction between the substrate temperature and the sputtering power which significantly influenced coating hardness, roughness, and performance; this interaction phenomenon has not been reported in previously published literature. The correlation study between coating characteristics, microstructures and the coating performance (flank wear) suggested that the coating performance correlated most significantly to the coating hardness with Pearson coefficient of determination value (R2) of 0.7311. The study also suggested some correlation between coating performance with atomic percentage ratio of Al/Ti and grain size with R2 value of 0.4762 and 0.4109 respectively.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Distillation is the most widely used separation technique in the chemical process industry and typically accounts for approximately one-third of the total capital cost and more than half of the total energy consumption of a typical petrochemical-chemical plant. Therefore, the design and optimization of the distillation sequence are of critical importance to the economics of the entire process. Azeotropic mixtures cannot be separated into their pure components via normal distillation. Enhanced distillation techniques such as heterogeneous azeotropic distillation should be considered for these mixtures. Isobaric vapour-liquid-liquid equilibrium (VLLE) data are highly important for the design and analysis of heterogeneous distillation columns. However, limited VLLE data are available in literature due to the difficulties involved with measuring such data. The objective of this work was to systematically evaluate and compare the performance of selected entrainers (including benzene, DIPE and cyclohexane) for the dehydration of C2 and C3 alcohols. To meet this objective, phase equilibrium data had to be measured. Isobaric VLLE at standard atmospheric conditions were measured with a dynamic Guillespie unit equipped with an ultrasonic homogenizer, which prevented liquid-liquid separation. Vapour-liquid equilibrium (VLE) and VLLE data were measured for ethanol/water/di-isopropyl ether (DIPE), n-propanol/water/DIPE and n-propanol/water/isooctane. The VLE data were found to be thermodynamically consistent according to the L-W (Wisniak 1993) and McDermott-Ellis consistency tests. No thermodynamic consistency test, specifically for VLLE data, could be found in literature, but the LLE part of the data followed a regular profile according to the Othmer-Tobias correlation. The binary DIPE/water and isooctane/water azeotropes, as well as ternary ethanol/DIPE/water and n-propanol/isooctane/water azeotropes, as measured in this work, agree well with those found in literature. Regressed parameters for the NRTL, UNIQUAC, and UNIFAC models, generally improved the model predictions compared with built-in Aspen parameters. This confirmed the importance of having actual measured VLLE data available for evaluation and improvement of estimations by thermodynamic models. NRTL predicted the ethanol/DIPE/water and n-propanol/DIPE/water VLLE most accurately. Despite the improved regressed parameters for n-propanol/isooctane/water predictions, the models are still considered unsuitable for accurate prediction of the VLLE behaviour of this system. Separation sequences were simulated in Aspen with built-in and regressed parameters, respectively, to illustrate the significant effect such inaccurate parameters have on these simulations. Phase diagram (VLLE data) evaluation of ethanol and isopropanol (IPA) with various entrainers, as found in literature, indicated that DIPE might be a good entrainer for the dehydration of these alcohols. Benzene and cyclohexane are generally used as entrainers in industry for these processes. Benzene is however carcinogenic and therefore an alternative has to be found (United States Department of Labour - Occupational Safety & Health Administration 2011). Separation sequences were simulated for ethanol dehydration with benzene and DIPE as entrainers, respectively. Taking cost and safety into account, DIPE can be considered an acceptable replacement for benzene as entrainer for ethanol dehydration. A separation sequence was also simulated for the dehydration of IPA with DIPE as entrainer and compared to a simulation with cyclohexane (Arifin, Chien 2007) as entrainer. DIPE was found to be a reasonable alternative to cyclohexane as entrainer for IPA dehydration. Two other separation sequences were simulated as practical examples where DIPE could be used as entrainer for the recovery of ethanol or n-propanol from aqueous Fischer Tropsch waste streams. DIPE is therefore found to be a feasible alternative entrainer to benzene and cyclohexane for the dehydration of ethanol and IPA via heterogeneous azeotropic distillation, based on pre-liminary cost considerations, separation ability and safety. Better entrainers than DIPE may exist, but from the data available in literature and the measurements made in this work DIPE appears to be superior to benzene, cyclohexane and isooctane. / AFRIKAANSE OPSOMMING: Distillasie is die mees algemeen-gebruikte skeidingstegniek in die chemiese proses-industrie. Dit is tipies verantwoordelik vir ʼn derde van die totale kapitaalkoste en meer as die helfte van die totale energie verbruik op ʼn tipiese petrochemiese chemiese aanleg. Daarom is die ontwerp en optimering van ʼn distillasie trein van kardinale belang vir die winsgewendheid van die proses. Azeotropiese mengsels kan nie slegs deur normale distillasie in suiwer komponente geskei word nie. Gevorderde distillasie tegnieke soos heterogene azeotropiese distillasie moet dus oorweeg word vir sulke mengsels. Isobariese damp-vloeistof-vloeistof ewewigsdata is een van die belangrikste fisiese eienskappe vir die ontwerp van heterogene distillasie kolomme. Die hoeveelheid damp-vloeistof-vloeistof ewewigsdata wat beskikbaar is in die literatuur is egter baie beperk omdat dit moeilik is om die data te meet. In hierdie werk is isobariese damp-vloeistof-vloeistof ewewigsdata met ʼn dinamiese Guillespie eenheid, by standaard atmosferiese druk gemeet. Die eenheid is toegerus met ʼn ultrasoniese homogeniseerder om vloeistof-vloeistof skeiding te voorkom. Temperatuur is gemeet met ʼn akkuraatheid van 0.03oC by 0oC. Die sisteem se druk is konstant gehou op 101.3 kPa met ʼn akkuraatheid van 0.35 % VSU (Vol Skaal Uitset). Die ewewigsamestellings is met ʼn relatiewe akkuraatheid van 2 % gemeet. Daar is damp-vloeistof en damp-vloeistof-vloeistof ewewigsdata van etanol/water/di-isopropiel eter (DIPE), npropanol/ water/ DIPE en n-propanol/water/iso-oktaan gemeet. Die damp-vloeistof ewewigsdata is deur die LW (Wisniak 1993) en McDermott-Ellis termodinamiese konsistensie toetse getoets en konsistent bevind. Geen termodinamiese konsistensie toets spesifiek vir damp-vloeistof-vloeistof ewewigsdata kon gevind word nie. Die Othmer-Tobias korrelasie dui egter aan dat die vloeistof-vloeistof ewewig gedeelte van die data ʼn reëlmatige gang volg. Die binêre DIPE/water en iso-oktaan/water azeotrope en ternêre etanol/DIPE/water en n-propanol/iso-oktaan/water fase-ewewigte wat in hierdie werk gemeet is, stem ooreen met die wat in die literatuur te vind is. Die parameters vir die modelle (NRTL, UNIQUAC en UNIFAC) wat in hierdie werk bestudeer is, is in die algemeen verbeter deur regressie van die eksperimentele data. Dit dui daarop dat dit belangrik is om eksperimentele damp-vloeistof-vloeistof ewewigsdata te hê om die voorspellings van termodinamiese modelle mee te evalueer en te verbeter. Die etanol/water/ DIPE en n-propanol/water/DIPE damp-vloeistof-vloeistof ewewigsdata is die akkuraatste deur NRTL voorspel. Ten spyte van die verbeteringe wat deur regressie behaal is met die NRTL en UNIQUAC parameters vir n-propanol/water/isooktaan, word hierdie modelle steeds nie as gepas vir die voorspelling van hierdie datastel beskou nie. Skeidingsreekse is gesimuleer met die ingeboude Aspen parameters en regressie parameters, onderskeidelik, om te illustreer dat onakkurate parameters ʼn beduidende effek op sulke simulasies het. Die evaluasie van fase diagramme van etanol en IPA met verskeie skeidingsagente, wat in die literatuur te vind is, dui aan dat DIPE ʼn goeie skeidingsagent kan wees vir die dehidrasie van hierdie alkohole. Skeidingsreekse vir die dehidrasie van etanol met benseen en DIPE, onderskeidelik, is gesimuleer. Met koste en veiligheid in ag geneem, is daar gevind dat DIPE ʼn aanvaarbare plaasvervanger vir benseen as skeidingsagent vir etanol dehidrasie kan wees. Daar is ook ʼn skeidingsreeks vir die dehidrasie van IPA met DIPE as skeidingsagent gesimuleer en met ʼn simulasie (Arifin, Chien 2007) wat sikloheksaan as skeidingsagent gebruik, vergelyk. Daar is bevind dat DIPE ʼn redelike alternatief vir sikloheksaan kan wees as skeidingsagent vir IPA dehidrasie. Nog twee skeidingsreekse is gesimuleer om as praktiese voorbeelde te dien van die gebruik van DIPE as skeidingsagent om etanol of n-propanol vanaf waterige Fischer-Tropsch afvalstrome te herwin. Daarom is daar bevind dat DIPE ʼn geldige alternatiewe skeidingsagent vir benseen en sikloheksaan is, gebaseer op koste, skeidingsvermoë en veiligheid. Daar kan beter skeidingsagente as DIPE bestaan, maar vanuit die data beskikbaar in literatuur en die metings geneem in hierdie werk, is DIPE die beste.

Phase equilibrium data is vital for designing chemical separation equipment. Traditionally, such data is obtained through laboratory experiments by sampling and analysing each phase of an equilibrated chemical mixture. An alternative means of generating such data is via molecular simulations, which also gives insight into the microscopic structure of the phases. This project was undertaken due to the lack of work on molecular simulations in predicting vapour-liquid-liquid equilibrium (VLLE). Gibbs Ensemble Monte Carlo molecular simulations were performed in the isochoricisothermal (NVT) and isobaric-isothermal (NVT) ensembles to determine the ability and limitations of the Transferable Potentials for Phase Equilibria (United-Atom) and Extended Simple Point Charge (SPC-E) force fields in predicting three-phase fluid equilibrium for two binary and three ternary industrially relevant mixtures: n-hexane/water (1), ethane/ethanol (2), methane/n-heptane/water (3), n-butane/1-butene/water (4) and nhexane/ ethanol/water (5). The NPT ensemble proved inadequate for predicting VLLE for binary mixtures, as for both binary mixtures (1 and 2), the simulations reverted to two phases. This was due in part to the unlike-pair interactions between pseudoatoms in different molecules not being accurately predicted at the specified simulation conditions to reproduce experimental mixture densities and vapour pressures. It was also due to the sensitivity of the NPT ensemble to perturbations which probably removed the system from its three-phase trajectory in Gibbs phase space, since specifying even the correct pressure corresponding to the potential models was unsuccessful in obtaining stable VLLE. Furthermore, ternary VLLE could not be obtained for a mixture exhibiting an extremely narrow three-phase region (4) and simulations for a miscible, non-ideal mixture (5) gave mole fractions that were in poor agreement with experiment. Good results were obtained for mixture 3 which exhibits limited mutual solubilities and a large three phase region. The NVT ensemble overcame the shortcomings of the NPT ensemble by producing three stable phases for the binary mixtures, revealing that the three-phase pressures were shifted by as much as 12%. Also, the narrow three-phase region of mixture 4 was overcome by adjusting the total system volume, producing three stable phases. These were also the first successful binary VLLE simulations involving complex polyatomic molecules. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.

Due to the ever increasing need for sustainable development, the chemical and allied industries have been at the focus of much change. Decreasing tolerances on pollution via waste streams has resulted in a re-examination of many chemical processes. This has ushered in the era of 'green chemistry' which incorporates the synthesis of a process in both a sustainable and economically viable manner. In the petroleum and chemical industries, this has led to the search for alternatives to volatile organic compounds. Ionic liquids provide one such alternative. With a wide liquid phase and no measurable vapour pressure, ionic liquids have been found to be successful as a medium for reactions. Ionic liquids differ from high-temperature molten salts in that they have a significantly lower melting point. This work investigates the use of ionic liquids as solvents in separations. The work focuses on the separation of alpha-olefins from complex mixtures. The ionic liquids used in this study were: • l-methyl-3-octyl-imidazolium chloride • 4-methyl-N-butyl-pyridinium tetrafluoroborate • trihexyl-tetradecyl-phosphonium chloride Three experimental techniques used to evaluate ionic liquids were: • gas-liquid chromatography • liquid-liquid equilibria measurements • vapour-liquid equilibria measurements l-Methyl-3-octyl-imidazolium chloride ((MOIM)C1) was used as a stationary phase in gas-liquid chromatography. The solutes used were: • Alkanes: n-Pentane; n-Hexane; n-Heptane; n-Octane • Alkenes: 1-Hexene; 1-Heptene; l-Octene • Alkynes: l-Hexyne; l-Heptyne; 1-0ctyne • Cycloalkanes: Cyclopentane; Cyclohexane; Cycloheptane • Aromatics: Benzene; Toluene Activity coefficients at infinite dilution were measured at temperatures (298.15, 308.15 and 318.15) K. Values at 298.15 K ranged from 1.99 for benzene to 26.1 for n-octane. From the temperature dependence of the activity coefficients, the partial excess molar enthalpies at infinite dilution were calculated. These range from 2.0 kJ.mol'l for l-octyne to 7.3 kJ.mol·1 for n-pentane. (MOIM)C1 shows reasonable ability to separate 1-hexene from the longer n-alkanes and aromatics. 4-Methyl-N-butyl-pyridinium tetrafluoroborate (BuMePyBF) was used as a solvent in liquid-liquid equilibria measurements. The following systems were measured at 298.2 K: • LLE System 1: BuMePyBF4 + 1-Hexene + Toluene • LLE System 2: BuMePyBF4 + 1-Hexene + Ethanol • LLE System 3: BuMePyBF4 + 1-Hexene + 2-Butanone • LLE System 4: BuMePyBF4 + 1-0ctene + Ethanol LLE System 1 is a type 11 system and the other systems being type I. All systems exhibit a large two-phase region. LLE System 1 shows low distribution. LLE System 3 show almost equal distribution between phases resulting in a distribution ratio of close to 1. LLE Systems 2 and 4 show high distribution ratios at low concentrations of solute. LLE Systems 1 and 3 show low to moderate selectivity of the solvent towards the solute. LLE Systems 2 and 4 show high to moderate selectivity, but decrease exponentially with increasing solute concentration in the organic phase. For all systems investigated, the solvent shows no miscibility with feed solutions of low to medium solute concentration. The binodial curves were correlated to the Hlavaty equation, the beta function and the log gamma function. The correlations yielded acceptable results for LLE Systems 2, 3 and 4. The tie-lines were correlated to the NRTL model, with LLE systems 2 and 4 giving acceptable results and LLE systems 1 and 3 give excellent results. The following binary vapour-liquid equilibrium systems were measured: • Acetone + Methanol at 99,4 kPa • l-Hexene + 2-Butanone at 74.8 kPa The acetone + methanol system exhibits a minimum boiling azeotrope at 0.78 mole fraction acetone. The l-hexene + 2-butanone system exhibits a minimum boiling azeotrope at 0.83 mole fraction l-hexene. Trihexyl-tetradecyl-phosphonium chloride (CJ3C1PhCl was then added to the above systems in order to evaluate it as a solvent in extractive distillation. (CJ3C1PhCI shifts the azeotrope of the acetone + methanol system to a higher acetone concentration, but does not remove it altogether. (CJ3C1PhCI has a negative effect on the relative volatility of the l-hexene + 2-butanone, thus rendering it ineffective as an extractive distillation solvent for this system. Another aspect that was considered in this work was the production of an ionic liquid. Synthesis steps and experimental considerations were discussed. A major factor in the use of ionic liquids is the cost of the ionic liquid itself. The major problem associated with ionic liquids is the general lack of available information that is necessary for them to be implemented in a process. Ionic liquids show potential as solvents in liquid-liquid extraction for a number of systems. Their potential as solvents in extractive distillation is probably limited, due to their miscibility/immiscibility properties, to systems involving slightly polar to highly polar compounds. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.

No abstract available. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2004.

The measurement of vapour-liquid equilibrium data is extremely important as such data are crucial for the accurate design, simulation and optimization of the majority of separation processes, including distillation, extraction and absorption. This study involved the measurement of vapour-liquid equilibrium data, using a modified version of the static total pressure apparatus designed within the Thermodynamics Research Unit by J.D. Raal and commissioned by Motchelaho, (Motchelaho, 2006 and Raal et al., 2011). This apparatus provides a very simple and accurate means of obtaining P-x data using only isothermal total pressure and overall composition (z) measurements. Phase sampling is not required. Phase equilibrium measurement procedures using this type of apparatus are often tedious, protracted and repetitive. It is therefore useful and realizable in the rapidly advancing digital age, to incorporate computer-aided operation, to decrease the man hours required to perform such measurements. The central objective of this work was to develop and implement a control scheme, to fully automate the original static total pressure apparatus of Raal et al. (2011). The scheme incorporates several pressure feedback closed loops, to execute process step re-initialization, valve positioning and motion control in a stepwise fashion. High resolution stepper motors were used to engage the dispensers, as they provided a very accurate method of regulating the introduction of precise desired volumes of components into the cell. Once executed, the control scheme requires approximately two days to produce a single forty data points (P-x) isotherm, and minimizes human intervention to two to three hours. In addition to automation, the apparatus was modified to perform moderate pressure measurements up to 1.5 MPa. Vapour-liquid equilibrium test measurements were performed using both the manual and automated operating modes to validate the operability and reproducibility of the apparatus. The test systems measured include the water (1) + propan-1-ol (2) system at 313.15 K and the n-hexane (1) + butan- 2-ol system at 329.15 K. Phase equilibrium data of binary systems, containing the solvent morpholine-4-carbaldehyde (NFM) was then measured. The availability of vapour-liquid equilibrium data for binary systems containing NFM is limited in the literature. The new systems measured include: n-hexane (1) + NFM (2) at 343.15, 363.15 and 393.15 K, as well as n-heptane (1) + NFM (2) at 343.15, 363.15 and 393.15 K. The modified apparatus is quite efficient as combinations of the slightly volatile NFM with highly volatile alkane constituents were easily and accurately measured. The apparatus also allows for accurate vapour-liquid equilibrium measurements in the dilute composition regions. A standard uncertainty in the equilibrium pressure reading, within the 0 to 100 kPa range was calculated to be 0.106 kPa, and 1.06 kPa for the 100 to 1000 kPa pressure range. A standard uncertainty in the equilibrium temperature of 0.05 K was calculated. The isothermal data obtained were modelled using the combined (-) method described by Barker (1953). This involved the calculation of binary interaction parameters, by fitting the data to various thermodynamic models. The virial equation of state with the Hayden-O’Connell (1975) and modified Tsonopoulos (Long et al., 2004) second virial coefficient correlations were used in this work to account for vapour phase non-ideality. The Wilson (1964), NRTL (Renon and Prausnitz, 1968), Tsuboka-Katayama-Wilson (1975) and modified Universal Quasi-Chemical (Anderson and Prausnitz, 1978) activity coefficient models were used to account for the liquid phase non-ideality. A stability analysis was carried out on all the new systems measured to ensure that two-liquid phase formation did not occur in the measured temperature range. A model-free method based on the numerical integration of the coexistence equation was also used to determine the vapour phase compositions and activity coefficients from the measured P-z data. These results compare well with the results obtained by the model-dependent method. The infinite dilution activity coefficients for the systems under consideration were determined by the method of Maher and Smith (1979b), and by suitable extrapolation methods. Excess enthalpy and excess entropy data were calculated for the systems measured, using the Gibbs-Helmholtz equation in conjunction with the fundamental excess property relation. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

Accurate and reliable vapour-liquid equilibrium (VLE) and liquid-liquid equilibrium (LLE) data are the key to a successful design and simulation of most important industrial separation processes (traditional distillation, extractive and azeotropic distillation). This work focuses on measurement of new phase equilibrium data for systems comprising of propan-1-ol, water and diisopropyl ether which are of important use in the petrochemical industry. In addition, an investigation of phase equilibrium behavior for systems of interest constituted by solvents and high added-value oxygenated compounds deriving from lignocelluloses biomasses (bio-fuels) was conducted at the Ecole des Mines de Paris CEP/TEP laboratories (France).Various data bases such as Science Direct, ACS publications and Dortmund Data Bank (DDB, 2009) were used to confirm that no literature data is available for these systems. The VLE data measurements for the system of propan-1ol + water and propan-1ol + diisopropyl ether (DIPE) ( 333.15, 353.15 and 373.15 K ) were carried out using a dynamic still of Lilwanth (2011), with a test system (ethanol + cyclohexane at 40 kPa) undertaken prior measurements to confirm the accuracy of the method and apparatus.The phase equilibrium (VLE and LLE) behaviours for furan + n-hexane and furan + Methylbenzene, furfural + n-hexane and furan + water were determined at 101.3 kPa. The atmospheric dynamic ebulliometry was used to measure VLE systems at 101.3 kPa. A set of LLE data for furfural + n-hexane and furan + water systems were obtained using a static analytical method, with a newly commissioned LLE apparatus. Furfural + n-hexane system was compared used as test system, to verify the reliability of the new equipment. The NRTL model was used to correlate the LLE data, with Cox- Herington model used to predict the entire LLE curve for furfural+ n-hexane system. The experimental VLE data were correlated using the combined y − y method. The vapour phase non idealities were described using the methods from Nothnagel et al. (1973), Hayden and O’Connell (1975) and the Peng-Robinson (1976) model. The activity coefficients were correlated using the NRTL model of Renon and Prausnitz (1968) and the modified UNIQUAC model of Abrams and Prausnitz (1976). A propan-1-ol dehydration process was simulated using Aspen to illustrate the use and importance of thermodynamic models in industrial process design and simulation. The model used in the simulation was validated with measured VLE and literature LLE data. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.