Thesis (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Structured packing is a popular column internal for both distillation and absorption unit operations. This is due to the excellent mass transfer characteristics and low pressure drop that it offers compared to random packing or trays. The main disadvantage is the lack in reliable models to describe the mass transfer characteristics of this type of packing. The recent development of the non-equilibrium model or rate based modelling approach has also emphasized the need for accurate hydraulic and efficiency models for sheet metal structured packing. The main focus of this study was to develop an accurate model for the mass transfer efficiency of Flexipac 350Y using a number of experimental and modelling techniques. Efficiency is however closely related to hydraulic capacity. Before attempting to measure and model the efficiency of Flexipac 350Y, the ability of existing published models to accurately describe the hydraulic capacity of this packing was tested. Holdup and pressure drop were measured using air/water and air/heavy paraffin as test systems. All experiments were performed on pilot plant scale 200mm ID glass columns. Satisfactory results were obtained with most of the models for determining the loading point and pressure drop for the air/water test system. All of the models tested predicted a conservative dependency of capacity on liquid viscosity for the air/paraffin test system. Efficiency and pressure drop were measured using the chlorobenzene/ethylbenzene test systems under conditions of total reflux in a 200mm ID glass column. Widely differing results were however obtained with the different models for the efficiency of Flexipac 350Y. Experiments were subsequently designed and performed to measure and correlate the vapour phase mass transfer coefficient and the effective surface area of Flexipac 350Y independently. The vapour phase mass transfer coefficient was measured and correlated by subliming naphthalene into air from coatings applied to specially fabricated 350Y gauze structured packing. The use of computational fluid dynamics (CFD) to model the vapour phase mass transfer coefficient is also demonstrated. The effective surface area for vapour phase mass transfer was measured with the chemical technique. The specific absorption rate of CO2 into monoethanolamine (MEA) using n-propanol as solvent was determined in a wetted-wall column and used to determine the effective surface area of Flexipac 350Y on pilot plant scale (200mm ID glass column). The efficiency of Flexipac 350Y could be modelled within an accuracy of 9% when using the correlations developed in this study and ignoringliquid phase resistance to mass transfer for the chlorobenzene/ethylbenzene test system under conditions of total reflux. The capacity and efficiency of the new generation high capacity packing Flexipac 350Y HC was also measured and compared with that of the normal capacity packing Flexipac 350Y. An increase in capacity of 20% was observed for the HC packing for the air/water system and 4% for the air/heavy paraffin system compared with the normal packing. For the binary total reflux distillation the increase in capacity varied between 8% and 15% depending on the column pressure. The gain in capacity was at the expense of a loss in efficiency of around 3% in the preloading region. / AFRIKAANSE OPSOMMING: Gestruktureerde pakking is 'n populêre pakkingsmateriaal en word algemeen gebruik in distillasie en absorpsie kolomme. Dit is hoofsaaklik as gevolg van die goeie massa-oordragseienskappe en lae drukval wat dit bied in vergelyking met 'random' pakking en plate. The hoof nadeel is egter die tekort aan akkurate modelle om die massa-oordrags eienskappe te bepaal. Om modelle te kan gebruik waar die massaoordragstempo direk gebruik word om gepakte hoogte te bepaal, word akkurate kapasiteits- en effektiwiteitsmodelle vir gestruktureerde plaatmetaalpakking benodig. Die hoof doelwit van hierdie studie was om 'n akkurate model te ontwikkel vir die massa-oordragseffektiwiteit van die plaat metaal pakking Flexipac 350Y deur gebruik te maak van verskillende eksperimentele- en modelleringstegnieke. Effektiwiteit is egter direk gekoppel aan hidroliese kapasiteit. Bestaande modelle in die literatuur is eers getoets om te bepaal of hulle die hidroliese kapasitiet van Flexipac 350Y akkuraat kan voorspel. Vir die doel is vloeistofterughou en drukval gemeet deur gebruik te maak van die sisteme lug/water en lug/swaar parafien. Alle eksperimente is in loodsaanlegskaal 200mm ID glaskolomme uitgevoer. Meeste van die modelle was relatief akkuraat in hulle berekening van die ladingspunt en die drukval vir die lug/water toets sisteem, maar was konsertief in voorspellings van die groothede vir die lug/swaar parafien sisteem. Effektiwiteit en drukval was gemeet deur gebruik te maak van die binêre toetssisteem chlorobenseen/etielbenseen onder totale terugvloei kondisies in 'n 200mm ID glaskolom. Daar is 'n groot verskil in die effektiwiteitsvoorspelling deur die verskillende modelle. Vervolgens is eksperimente ontwerp en uitgevoer om die dampfase massaoordragskoeffisiënt en die effektiewe oppervlakarea vir Flexipac 350Y onafhanklik te meet en te korreleer. Die dampfase massaoordragskoeffisient is gemeet en gekorreleer deur naftaleen te sublimeer vanaf spesiaal vervaardigde 350Y gestruktureerde pakking van metaalgaas. Die gebruik van numeriese vloeimeganika (CFD) om die dampfase massaoordragskoeffisient te bereken word gedemonstreer. Die effektiewe oppervlakarea vir dampfase massaoordrag is bepaal deur van 'n chemiese metode gebruik te maak. Die spesifieke absorpsietempo van CO2 in monoetanolamien (MEA) met n-propanol as oplosmiddel is gemeet in a benatte wand kolom en gebruik om die effektiewe oppervlakarea van Flexipac 350Y te bepaal op loodsaanlegskaal (200mm ID). Die effektiwiteit van Flexipac 350Y kon met 'n akkuraatheid van binne 9%gemodelleer word deur vloeistoffaseweerstand te ignoreer en van die korrelasies gebruik te maak wat in hierdie studie ontwikkel is. Die effektiwiteit en kapasiteit van die nuwe generasie hoë kapasiteit pakking Flexipac 350Y HC is ook gemeet en vergelyk met die normale kapasiteit pakking Flexipac 350Y. 'n Verhoging in kapsiteit van 20% is gemeet vir die HC pakking in vergelyking met die normale kapasiteit pakking vir die lug/water sisteem en 'n 4% verhoging in kapasiteit vir die lug/swaar parafien sisteem. Die verhoging in kapasiteit het gevarieër tussen 8% en 14% in die binêre totale terugvloei distillasie toetse en was afhanklik van die kolom druk. Die verhoging in kapasiteit was ten koste van 'n verlaging in effektiwiteit van ongeveer 3% onderkant die ladingspunt.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Structured packing is often the preferred choice for column internals because of its low pressure drop and high efficiencies compared to that of trays and random packing. However, the mass transfer phenomena in these gas-liquid contacting devices is still not well understood, even though it is widely used in industry. A contributing factor to this is the lack of understanding and availability of experimental data in the open literature. These shortcomings complicate the design of a distillation column and make practical experience essential. There is thus a need for more experimental data, especially for packings where only limited information is available. The focus of this study was to establish a testing facility that can be used to measure the efficiency of structured packing under total reflux, and not to measure vast quantities of experimental data; the latter will be done in future. The facilities available at Stellenbosch University limited the internal diameter of the column to 0.2 m, which is sufficient to test higher surface area structured packings (≥350 m2/m3). The column is used with a thermosyphon reboiler that uses steam as the heating source and is equipped with a total condenser. Two sections are used for the packed bed that allow for a total packed height of 3.78 m (2x1.89 m). The column is set up to operate under total reflux and was designed to operate at pressures ranging from 0.3 to 1 bar abs, vapour flow rates of 0.73 – 3.65 (m/s) (kg/m3)0.5 and liquid flow rates of 5 – 25 m3/(m2.h). It was found that the 2-butanol/iso-butanol and the p-xylene/o-xylene systems are suitable test mixtures for this pilot plant setup. The VLE data from Kutsarov et al. (1993) and Zong et al. (1983) for p-xylene/o-xylene and 2-butanol/iso-butanol are thermodynamic consistent and was validated by VLE experiments done in this study. It was found that the experimentally obtained efficiency (HETP) and pressure drop data for Mellapak 350Y compared well with published results of Spiegel and Meier (1987). With regard to the predictive models, it was found that i) the SRP model predicted the HETP of Mellapak 350Y structured packing accurately in the pre-loading region and slightly over predicted the HETP in the loading region, whereas ii) the Delft model over predicted HETP and iii) the Billet and Schultes model under-predicted HETP under the entire tested range (i.e. over-predict efficiency). With regard to the pressure drop data i) the Billet model iv accurately predicted the pressure drop over the entire tested range, whereas ii) the SRP model accurately predicted the pressure drop in the pre-loading region and slightly over predicted the pressure drop in the loading region and iii) the Delft model over predicted the pressure drop over the entire range and followed an almost parallel trend to the results from the SRP model. It was also found that information in the field of mass transfer in a packed column is far from saturated, and there is a need for more experimental data and better understanding of the mass transfer phenomena in packed columns. / AFRIKAANSE OPSOMMING: Gestruktureerde pakking het ʼn laer drukval en ʼn hoër effektiwiteit in vergelyking met willekeurige pakkings en plate, en is daarom dikwels die voorkeur keuse vir pakkings materiaal in ʼn distilleer kolom. Die massa-oordrags verskynsels in hierdie gas-vloeistof kontaktors word egter nog nie goed verstaan nie, ten spyte van die grootskaalse aanwending in die nywerheid. ʼn Bydraende faktor is die tekort aan eksperimentele data in die ope literatuur. Die tekortkomings bemoeilik die ontwerp van distilleerkolomme en maak praktiese ervaring ʼn noodsaaklike vereiste. Daar is dus ʼn behoefte aan meer eksperimentele data veral vir pakkings waar daar min of geen data beskikbaar is nie. Die fokus van die studie was om ʼn toetsfasiliteit op te rig wat gebruik kan word om die effektiwiteit van gestruktureerde pakking onder totale terugvloei kondisies te bepaal, en dus nie om ‘n groot hoeveelheid data te genereer nie; laasgenoemde sal wel deel uitmaak van toekomstige studies. Die fasiliteite beskikbaar by die Universiteit van Stellenbosch het die binne diameter van die kolom beperk tot 0.2 m. Die diameter is voldoende om gestruktureerde pakkings met ʼn hoë oppervlakarea te toets byvoorbeeld pakkings met areas 350 m2/m3 en hoër. Die kolom gebruik ‘n verdamper (met stoom as energie bron) om die vloeistof te verdamp en ‘n totale kondensator (verkoel met verkoelingswater) om die damp te laat kondenseer. Twee seksies van 1.89 m elk word gebruik vir die gepakte bed en die kolom het dus ‘n totale pakkingshoogte van 3.78 m. Die kolom is opgestel vir totale terugvloei en is ontwerp om bedryf te word by drukke tussen 0.3 en 1 bar abs, damp snelhede van 0.73 tot 3.65 (m/s) (kg/m3)0.5 en vloeistof vloeitempo’s tussen 5 en 25 m3/(m2.h). 2-butanol/iso-butanol en p-xylene/o-xylene is gevind om geskik te wees as mengsels vir die toetsopstelling. Die damp-vloeistof fase-ewewig data van Kutsarov et al. (1993) en Zong et al. (1983) vir p-xylene/o-xylene and 2-butanol/iso-butanol is termodinamies konsistent en is gevalideer deur damp-vloeistof fase ewewig toetse in die studie. Daar is gevind dat die eksperimenteel bepaalde effektiwiteit en drukval data vir Mellapak 350Y pakking goed vergelyk met gepubliseerde data van Spiegel and Meier (1987). Die eksperimenteel bepaalde effektiwiteit data is met waardes van beskikbare modelle model vergelyk en daar is gevind dat: i) die SRP voorspel die effektiwiteit van Mellapak 350Y pakking akkuraat in die ‘pre-loading’ gebied maar toon afwykings van die eksperimentele data in die ‘loading’ gebied, ii) die Delft model voorspel ‘n hoër hoogte ekwivalent aan ‘n teoreties plaat (HETP) oor die hele gebied terwyl iii) die Billet en Schultes model weer ‘n laer HETP voorspel oor die hele gebied. Met betrekking toe die drukval data i) voorspel die Billet model die drukval akkuraat oor die hele gebied, ii) die SRP model voorspel die drukval korrek in die ‘pre-loading’ gebied maar begin afwyk van die eksperimentele data in die ‘loading’ gebied en iii) die Delft model voorspel groter waardes vir drukval oor die hele gebied en volg amper ʼn parallelle tendens met die SRP model. In die studie is daar gevind dat daarin die gebied van massa-oordrag nog ʼn tekort is aan eksperimentele data en daar baie navorsings geleenthede is.

Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: As result of the increasingly competitive performance in today’s industrial environment, it has become necessary for production facilities to increase their efficiency. An essential step towards increasing the efficiency of these production facilities is through tighter processes control. Process control is a monitoring and modelling problem, and improvements in these areas will also lead to better process control. Given the difficulties of obtaining theoretical process models, it has become important to identify models from process data. The irregular behaviour of many chemical processes, which do not seem to be inherently stochastic, can be explained by analysing time series data from these systems in terms of their nonlinear dynamics. Since the discovery of time delay embedding for state space analysis of time series, a lot of time has been devoted to the development of techniques to extract information through analysis of the geometrical structure of the attractor underlying the time series. Nearly all of these techniques assume that the dynamical process under question is stationary, i.e. the dynamics of the process did not change during the observation period. The ability to detect dynamic changes in processes, from process data, is crucial to the reliability of these state space techniques. Detecting dynamic changes in processes is also important when using advanced control systems. Process characteristics are always changing, so that model parameters have to be recalibrated, models have to be updated and control settings have to be maintained. More reliable detection of changes in processes will improve the performance and adaptability of process models used in these control systems. This will lead to better automation and enormous cost savings. This work investigates and assesses techniques for detecting dynamical changes in processes, from process data. These measures include the use of multilayer perceptron (MLP) neural networks, nonlinear cross predictions and the correlation dimension statistic.The change detection techniques are evaluated by applying them to three case studies that exhibit (possible) nonstationary behaviour. From the research, it is evident that the performance of process models suffers when there are nonstationarities in the data. This can serve as an indication of changes in the process parameters. The nonlinear cross prediction algorithm gives a better indication of possible nonstationarities in the process data; except for instances where the data series is very short. Exploiting the correlation dimension statistic proved to be the most accurate method of detecting dynamic changes. Apart from positively identifying nonstationary in each of the case studies, it was also able to detect the parameter changes sooner than any other method tested. The way in which this technique is applied, also makes it ideal for online detection of dynamic changes in chemical processes. / AFRIKAANSE OPSOMMING: Dit is belangrik om produksie aanlegte so effektief moontlik te bedryf. Indien nie, staar hulle die moontlikheid van finansiële ondergang in die gesig – veral as gevolg van toenemende mededinging die industrie. Die effektiwiteit van produksie aanlegte kan verhoog word deur verbeterde prosesbeheer. Prosesbeheer is ‘n moniterings en modellerings probleem, en vooruitgang in hierdie areas sal noodwendig ook lei tot beter prosesbeheer. Omdat dit moeilik is om teoretiese proses modelle af te lei, word dit al hoe belangriker om modelle vanuit proses data te identifiseer. Die ongewone optrede van baie chemiese prosesse, wat nie inherent stogasties blyk te wees nie, kan meestal verklaar word deur tydreeks data vanaf hierdie prosesse te analiseer in terme van hul nie-liniêre dinamika. Sedert die ontdekking van tydreeksontvouing vir toestandveranderlike stelsels, is baie tyd daaraan spandeer om tegnieke te ontwikkel wat inligting uit tydreekse kan onttrek deur die onderliggende geometriese struktuur van die attraktor te bestudeer. Byna al hierdie tegnieke aanvaar dat die dinamiese proses stationêr is, m.a.w dat die dinamika van die proses nie verander het tydens die observasie periode nie. Die vermoë om hierdie dinamiese proses veranderinge te kan identifiseer, is daarom baie belangrik. Ook in gevorderde beheerstelsels is vroegtydige identifisering van dinamiese veranderinge in prosesse belangrik. Proses karakteristieke is altyd besig om te verander, sodat model parameters herkalibreer moet word, modelle opgedateer moet word en beheer setpunte onderhou moet word. Meer betroubare tegnieke om veranderinge in prosesse te identifiseer sal die aanpasbaarheid van proses modelle in hierdie beheerstelsels verbeter. Dit sal lei tot beter outomatisering en sodoende lei tot enorme kostebesparings. Hierdie werk ondersoek tegnieke om dinamiese veranderinge in prosesse te identifiseer, deur die analise van proses data. Die tegnieke wat gebruik word sluit die volgende in:multilaag-perseptron neurale netwerke, nie-liniêre kruisvoorspelling statistieke en die korrelasie dimensie statistiek. Die tegnieke is op drie gevallestudies toegepas om te sien of hulle die dinamiese veranderinge in die data kan identifiseer. Vanuit die navorsing is dit duidelik dat proses modelle nadelig beinvloed word deur niestationêre data. Dit kan dien as ‘n indikasie van veranderinge in die proses parameters. Die nie-liniêre kruisvoorspellings algoritme gee ‘n beter indikasie van dinamiese veranderinge in die proses data, behalwe waar die tydreeks baie kort is. Toepassings van die korrelasie dimensie statistiek gee die beste resultate. Hierdie tegniek kon dinamiese veranderinge vinniger as enige ander tegniek identifiseer, en die manier waarop dit gebruik word maak dit ideaal vir die identifisering van dinamiese veranderinge in chemiese prosesse.

Thesis (MScIng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Titanium dioxide (TiO2) is extensively used as pigment in paint formulations, but due to the high cost associated with it, along with its’ depleting natural resources, paint manufacturers are seeking substitutes that can at least partially replace this pigment. Vesiculated beads have been successfully used in the past as a replacement for the TiO2-pigment. These beads are spherical polymer particles that contain a multitude of aerated micro voids within the polymer shell. The aerated voids cause effective scattering of light inside the particles, presenting the beads with a white appearance. It was found that low levels of TiO2 could be encapsulated in the particles as a means of increasing the whiteness and hiding power of the beads in the wet- and dry state. Because the beads are about two-thirds air by volume and contain only small amounts of TiO2, it also presents a method of reducing the formula cost. The beads are produced with an emulsification process where by an organic phase containing unsaturated polyester resin and styrene monomer is emulsified within an aqueous phase. This phase consists mainly of de-ionised water and stabilisers that assist in forming a stable emulsion of organic droplets in the continuous aqueous phase. A polyamine is also added to the system to achieve the uptake of water droplets inside the organic phase. It is this water that is replaced with air when it evaporates from the beads upon drying, and leaves the particles with air-filled vesicles. Emulsification is currently achieved locally with the use of a Cowles disperser system or an emulsion reactor set-up with the application of a specified stirring speed for a specific period of time. These stirring specifications are manipulated so that the organic globules are subjected to a specific shear rate and consequently are broken down to the required particle size. The polymeric reaction is initiated with the addition of a free-radical initiator and redox activator and the product is left overnight to allow completion of the reaction and subsequent formation of slurry containing solid polymer particles. In this study, homogenisation was investigated as a means of emulsifying and producing vesiculated beads in a continuous process. Homogenisation is defined as the act of breaking down globules into smaller particles under pressure and produces a product with evenly dispersed (homogeneous) fine particles. This process could therefore also be used to produce particles with a smaller average particle size than those obtained by the existing Cowles- and emulsion reactor manufacturing processes. These batch processes produce vesiculated beads with an average particle size between 3 and 10 micron on industrial scale. With the incorporation of the homogeniser in a continuous process it would be possible, not only to produce particles in the order of 1 micron required for the addition to gloss paint, but it would also have the added advantages of easy cleaning, higher production rates and the use of smaller equipment. The most important operating parameters when using a homogenisation system were determined using a laboratory scale homogeniser set-up. These parameters included the geometry of the internals of the homogeniser, the number of passes and the flow rate. From the information and results obtained from the batch experiments a semicontinuous bench-scale homogeniser set-up was designed. This experimental set-up consisted of a homogeniser, high-pressure pump, continuous feed section for the initiator and a loop-reactor equipped with a heating mantle to facilitate continuous curing of the product. Vesiculated beads with properties similar to those obtained by the existing batch processes, but with an average particle size in the order of 1 micron, were produced successfully with this semi-continuous set-up. Although the beads were not entirely cured after leaving the loop-reactor it is believed that with increased heating and an increase in the length of the reactor, this problem can be addressed. The results obtained with the semi-continuous process could be used in future in the design and construction of a continuous pilot plant for the production of vesiculated beads. / AFRIKAANSE OPSOMMING: Titaandioksied (TiO2) word in groot hoeveelhede as pigment in verf gebruik, maar as gevolg van die hoë koste van hierdie pigment en die uitputting van die natuurlike bronne, is verfvervaardigers op soek na alternatiewe. Polimeerpartikels met lugholtes daarin vasgevang, is in die verlede suksesvol as plaasvervanger vir die pigment gebruik. Hierdie partikels is sferiese polimeerpartikels met ‘n menigte klein lugholtes wat effektiewe verstrooiing van lig binne die partikels veroorsaak. Dit verskaf aan die partikels ‘n wit voorkoms en daar is gevind dat klein hoeveelhede TiO2 binne die partikels vasgevang kan word om die witheid in die nat- en droë fase te verhoog. Omdat die partikels uit ongeveer twee derdes lug bestaan en slegs klein hoeveelhede TiO2 bevat, word ‘n vermindering in produksiekoste verkry as dit in verf gebruik word. Die polimeerpartikels word geproduseer met ‘n emulsifiseringsproses waarby ‘n organiese fase, bestaande uit onversadigde poliëster en stireen monomeer, in ‘n waterfase geëmulsifiseer word. Laasgenoemde bestaan hoofsaaklik uit gedeïoniseerde water en stabiliseerders wat die vorming van ‘n stabiele emulsie van organiese druppels in die kontinue waterfase bewerkstellig. ‘n Poli-amien word ook by die sisteem gevoeg om die organiese fase in staat te stel om water op te neem. As hierdie water dan van die partikels verdamp wanneer dit droog word, word dit deur lug verplaas en laat dit die partikels met ‘n menigte lugholtes agter. In Suid-Afrika, word emulsifisering tans bewerkstellig deur die gebruik van ‘n “Cowles” menger of ‘n emulsiereaktorsisteem waar ‘n spesifieke roerspoed vir ‘n vasgestelde tydperk aangewend word. Hierdie roerspesifikasies word so gekies dat ‘n bepaalde skuifkrag op die organiese druppels uitgeoefen word en dit dus tot die verlangde partikelgrootte opgebreek word. As die bepaalde partikelgrootte bereik is, word die reaksie geïnisieer deur die byvoeging van ‘n vry-radikaal inisieerder en ‘n redoksaktiveerder. Die produk word dan oornag gelaat sodat die reaksie voltooi kan word en die soliede polimeerpartikels binne die kontinue waterfase gevorm kan word. Tydens hierdie studie is homogenisering ondersoek as ‘n moontlike metode om emulisifisering te bewerkstellig en sodoende die polimeerpartikels te produseer. Homogenisering word gedefinieer as ‘n proses waartydens partikels afgebreek word onder hoë druk en gevolglik lei dit tot die vorming van ‘n produk bestaande uit klein partikels uniform versprei deur die produk. Die moontlikheid bestaan dus dat homogenisering in ‘n proses gebruik kan word om kleiner partikels te produseer as wat moontlik is met die bestaande Cowles- of emulsiereaktor prosesse. Hierdie enkelladingsprosesse word gebruik om polimeerpartikels met ‘n gemiddelde partikelgrootte tussen 3 en 10 mikron op industriële skaal te produseer. Deur die homogeniseerder in ‘n kontinue proses te gebruik sal so ‘n proses gebruik kan word nie net om partikels met ‘n grootte van ongeveer 1 mikron (noodsaaklik vir glansverf) te produseer nie, maar hou dit ook verdere voordele in soos hoër produksie, kleiner toerusting en die gemak waarmee so ‘n sisteem skoongemaak kan word. ‘n Laboratorium-skaal enkelladings homogeniseerder is gebruik om die belangrikste bedryfsparameters van ‘n homogeniseringsisteem te bepaal. Hierdie parameters sluit in die geometrie van die interne dele van die homogeniseerder, asook die vloeitempo en die aantal deurgange deur die homogeniseeder. Die resultate van die enkelladings eksperimente is gebruik om ‘n semi-kontinue loodsaanleg skaal opstelling met ‘n hoë druk pomp, homogeniseerder, kontinue toevoer seksie vir die inisieërder en ‘n kontinue buisreaktor om die volledige verloop van die reaksie te verseker, te ontwikkel. Polimeerpartikels gevul met lugholtes is geproduseer met bogenoemde proses en produkeienskappe vergelykbaar met die van die bestaande enkelladingsprosesse is verkry. Die enigste verskil tussen die produkeienskappe van die verskillende prosesses was die gemiddelde partikelgrootte met die partikels geproduseer met die homogeniseerderproses in die order van 1 mikron en die van die ander prosesse veel groter. Die resultate verkry met die semi-kontinueproses sal in die toekoms gebruik word vir die ontwerp en bou van ‘n ten volle kontinue loodsaanleg.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2005. / Catalytic Distillation (CD) is a hybrid technology that utilizes the dynamics of si- multaneous reaction and separation in a single process unit to achieve a more compact, economical, efficient and optimized process design when compared to the traditional multi-unit designs. The project goal (and key question) is (how) to design a cost-effective, simple and accurate laboratory-scale continuous CD system that will sufficiently and accurately supply useful data for model validation. The system to be investigated is the continuous hydrogenation of an a-olefin C6 (1-hexene) feed stream to the corresponding alkane (n-hexane) product with simultaneous reactant/product separation. Hypothetically, a system can be constructured to determine whether hydrogenation will benefit from the heat and mass transfer integration observed under CD conditions in terms of energy usage, temperature control and the catalyst's surface hydrogen concentration. System convergence with commercial distillation simulation packages ...

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2005. / An increased demand for hydrogen in recent years has led to a revival of interest in methods for hydrogen separation and purification. Palladium (Pd) and palladium composite membranes have therefore received growing attention largely due to their unique permselectivity for hydrogen and good mechanical and thermal stability. Previous research on Pd composite membranes by Keuler (2000) in the Department of Process Engineering at the University of Stellenbosch has shown that some assumptions which he made during characterisation procedures needed further investigation, such as the assumptions about the influence of support membranes on preparation of Pd composite membranes, method of precleaning before pretreatment, vacuum applied during electroless plating, and heat treatment after electroless plating. In this study, Pd composite membranes (with Pd film thickness of 1.7 μm ~ 4 μm) were prepared on the inside layer (claimed pore diameter of 200 nm) of α-alumina ceramic support membrane tubes, consisting of three layers with varying pore diameters from inside to the outside layer, via a modified electroless plating technique (with a gauge vacuum of 20 kPa applied on the shell side of the plating reactor). Bubble point tests and bubble point screening tests were performed on the support membranes before the electroless plating to investigate the influence of the substrates characteristics on the preparation of the Pd composite membranes. It was found that Pd composite membranes with a better permselectivity can be prepared on a support membrane that contains smaller pore sizes and a smoother surface. The surface pretreatment step was modified to provide a uniform Pd surface for Pd electroless plating. The membrane was first rinsed in PdCl2 solution for 15 min using a stirrer at a stirring speed of 1300 rpm, and was then dipped into distilled water 10 times (1-2 second each). Subsequently, the membrane was rinsed in SnCl2 solution for 15 min, and was then dipped into distilled water 10 times. These procedures were repeated 4 times. In addition, by using a new method of assessment for heat treatment (i.e. cutting the Pd composite membranes into two pieces and then exposing them to two different heating methods), the most effective heat treatment method could be identified without the influences of the substrates or the plating technique. The preferable procedures was to anneal the Pd composite membrane in N2 for 5 h from 20°C to 320°C, and then oxidize it in air for 2 h at 320°C, followed by annealing it in N2 for 130 min from 320°C to 450°C and then in H2 for 3 h at 450°C. Finally the membrane was cooled down in N2 to 350°C and held at this temperature for 30 min. Additional oxidation in air for more than 10 hours changes the structure of the Pd films. PdO then forms and decreases the H2 permeation through the Pd composite membrane. More detailed characterisations of the Pd composite membranes were performed by membrane permselectivity tests (from 350°C to 550 ◦C) using either H2 or N2 in single gas test, membrane morphology and structure analysis using scanning electron microscopy (SEM), energy dispersive detectors (EDS), atomic force microscopy (AFM), Brunauer-Emmett- Teller (BET) and X-ray diffraction (XRD) analysis. Hydrogen permeability between 4.5-12 μmol/(m2.Pa.s) and an average hydrogen/nitrogen permselectivity of ≥ 150 were achieved in this study. The permselectivities of the heat treated membranes were superior to Keuler’s membranes, which had an average permselectivity of ≥ 100. AFM and BET analysis showed that dense and smooth Pd films with smaller Pd crystals sizes and compact Pd layers were obtained.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2007. / Lactic acid bacteria (LAB) are producers of bacteriocins, ribosomally synthesized antimicrobial peptides. Bacteriocins are secreted into the surrounding environment where they inhibit growth of other bacteria competing for the same nutrients in a particular environment, usually closely related strains. Some of the bacteriocin-sensitive bacteria include food spoilers and - pathogens, which makes bacteriocins potential natural food preservatives. The need for more natural preservation techniques in the food industry is high: Consumers prefer ready-toeat, minimally processed foods containing no chemical preservatives, but at the same time food spoilage and food-related illnesses are areas of big concern. The antibacterial and antiviral properties of some bacteriocins have also made them suitable for controlling bacterial infections, e.g. as part of pharmaceutical ointments. The increasing rate of resistance against antibiotics by micro-organisms has created a market for alternative treatments for infections. Commercial bacteriocin manufacturing proceeds in controlled fermentations or by extraction from plant material. Enterococcus mundtii ST4SA produces a bacteriocin, bacST4SA, with properties giving it potential for use as a food preservative or as part of a pharmaceutical product. In this study, production of bacST4SA by fermentation of low-cost food-grade growth media, sugarcane molasses, corn steep liquor (CSL) and cheese whey, was considered to increase the economic viability of production for food application. Furthermore, individual de Man Rogosa and Sharpe (MRS) medium components, pH and fed-batch fermentation were evaluated to improve bacST4SA activity...

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2006. / The study presented in this thesis symbolises one of the first ever efforts to better understand and describe the durability of geopolymers used in large scale commercial applications. In terms of the construction industry, geopolymers can be seen as a value-added approach to substitute the Ordinary Portland Cement (OPC) monopoly. It is particularly the fly ash-based geopolymers that are the main attraction, due to their economic and environmental advantages, over and above the large quantities of this material that are commonly available. Despite the fact that geopolymers have been around for thousands of years, it is only now that the accumulation of research across the globe has pooled their knowledge to broadly define this material in terms of its physical and chemical composition. The development of geopolymers for construction applications remains quite new, therefore requiring insight into the durability that can be expected from these materials, consequently leading to this work. Concrete technology and -science is one of many techniques which can offer considerable insight into effective durability studies, in addition to acting as a reference for firm material comparisons. Thus, this work is based on a collection of concrete durability studies and recommendations which resulted from a broad range of investigations. Principally, this work aims to confirm the superiority of geopolymers in terms of corrosion resistance. Chloride induced corrosion has been identified as being the main cause for deterioration of OPC structures and subsequently the origin of very costly, and frequent, reconstructive requirements. Geopolymers now have the opportunity to be introduced into this monopoly due to its advanced, yet credible, chloride penetration resistance. This thesis reports the development of the experimental design, as well as the associated analyses to describe the diffusive properties exhibited by fly ash-based geopolymers. Ultimately, two independent methods showed that Chloride Diffusion Coefficients (CDC) for all of the geopolymeric formulations are significantly lower (typically 1.43 x 10-15 cm2/s) than for cement (typically 0.5 x 10-8 cm2/s) or any other concrete mixture. Furthermore, the work presented here will consider the diffusive behaviour of the geopolymer formulations in an acidic sulphate environment, presenting this material’s superior resistance not only to the sulphate ion, but more so to the acid attack. Probable geopolymer applications are now further expanded to industrial applications, due to its acid resistance along with reduced Sulphate Diffusion Coefficients (SDC). In addition, the development of a time-to-corrosion software-tool is discussed. This tool may prove to be a valuable instrument for future geopolymer durability research, as well as iv commercial users in which extended material comparisons can be made. It may even assist the formulation-tailoring process where the relevant CDC/SDC can be chosen for a specific life-expectancy, reaching far beyond the limited scope of recipes covered in this work. Finally, this thesis provides the stepping-stone in proving geopolymer durability superiority. The formulations which proved to show the best results in terms of durability and acid resistance are highlighted and valuable recommendations are made towards the selection of suitable starting materials for optimum material robustness. The findings of this work, however, can be fortified by future research and exposure.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: A project was initially commenced for optimising the production output at a specific high-carbon ferromanganese furnace. Since operational difficulties were experienced in this furnace and with a lack of reliable data for the year 2007, it was decided that data from a more stable high-carbon ferromanganese furnace should be analysed instead. Three key performance indicators (KPI’s) were selected to give an indication of overall process performance. These were: (1) the total tonnes of high-carbon ferromanganese produced per tonne of feed material, (2) the percentage recovery of manganese to the alloy product, and (3) the alloy:slag ratio. Maximisation of each of these would contribute to the overall improvement of the process. To achieve the objectives of the project, a hybrid model was developed to characterise the production behaviour of the furnace and to optimise the proposed KPI’s. The hybrid model consisted of two modelling branches, viz. equilibrium and dynamic modelling. An equilibrium sub-model was created and the output results were then used as inputs into a dynamic sub-model, which not only considered the effects of thermo-equilibrium interactions, but also the faster-changing electrical dynamics of furnace control. The final modelling step involved genetic optimisation, whereby model variables were manipulated to optimise the proposed KPI’s. In other words, operating conditions were established to improve furnace performance. It was determined that significant improvement in the values of the KPI’s may be expected if the optimised setpoints are implemented on-site. The existing setpoints for electrical operation should be maintained while the power expended per tonne of alloy should be altered (by tapping more regularly). Specific adjustments to the proportions of the feed recipe should also be made. / AFRIKAANSE OPSOMMING: ‘n Projek is aanvanklik begin om die produksieproses by ‘n spesifieke hoëkoolstof ferromangaanoond te optimiseer. Sedert operasionele probleme ondervind is in die oond en daar ‘n tekort is aan vertroubare data vir die jaar 2007, is daar besluit om data van ‘n meer stabiele hoëkoolstof ferromangaanoond te annaliseer. Drie sleutelverrigtingsaanwysers (SVA’s) is geselekteer om die algehele prosesverrigting aan te dui. Hulle is: (1) Die totale tonnemaat hoëkoolstof ferromangaan geproduseer per tonnemaat van voermateriaal, (2) die persentasie herwinning van mangaan tot die allooiproduk, en (3) die allooi:slak verhouding. Die verhoging van elk van die bogenoemde sal bydra tot die algehele bevordering van die proses. Om die doelwitte van die projek na te kom, is ‘n Kombinasiemodel ontwikkel om die produksie gedrag van die oond te karakteriseer en om die voorgestelde SVA’s te optimiseer. Die Kombinasiemodel het bestaan uit twee modelleringsvertakkings, nl. termodinamiese ewewig en dinamiese modellering. ‘n Termodinamiese ewewig submodel is geskep en die uitset resultate is gevolglik gebruik as invoerdata na ‘n dinamiese sub-model, wat nie slegs die uitwerking van termo-ewewiginteraksies in ag neem nie, maar ook die vinnigveranderende elektriese dinamika van die oond. Die finale modelleringstap het genetiese optimisering behels, waarby model veranderlikes gemanipuleer is om die voorgestelde SVA’s te optimiseer. Met ander woorde, operasionele kondisies is vasgestel om oond produksie te bevorder. Dit is bepaal dat kenmerkende verbetering in die waardes van die SVA’s verwag kan word as die ge-optimiseerde setpunte toegepas is op die oond. Die oorspronklike setpunte vir elektriese beheer hoort gehandhaaf te word terwyl die krag verbruik per ton allooi verander moet word (deur om meer gereeld te tap). Spesifieke verstellings op die proporsies van die voerresep moet ook gemaak word.

Thesis (MScEng)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: During the production of pure Ti02 for the pigment industry, ilmenite, containing 35 - 60 % Ti02, is reduced to high titania slag, containing 85 - 95 % Ti02 and pig iron. These ilmenite smelters are operated in very tight operating windows. Over reducing the slag may lead to the formation of TiC and reducing much of the Ti02 to Th03. According to Namakwa Sands furnace operators, this does not only affect the grade of the product, but it can cause slag foaming and furnace eruptions. In under reducing conditions, the liquid slag is fluxed by the FeO and may corrode the furnace lining and consequently lead to run-outs. The reducing conditions in the furnace are not only controlled by carbon addition, but also by temperature. Standard practise in industrial ilmenite smelters is to operate the furnace with a slag freeze lining to protect the refractory lining from chemical and physical attack by the slag. It is therefore clear that it is of great importance to be able to predict the slag liquidus temperature at different compositions. This can help the operator to avoid dangerous operating conditions. Over the past few decades, a number of solution models have been developed to describe non-ideal solutions. With the rapid increase in computer power, these models became more valuable and practical to use in advanced control and decisionsupport. In this study, some of the better-known models are discussed and evaluated for the Ti02 - Th03 - FeO system, based on a critical review of properties and measurements published in literature. Two of these models, the "modified quasi-chemical" model and the "cell" model were chosen to be applied to the high-titania slag system. Both these models are based on statistical thermodynamics with some differences in the initial assumptions. In this study, the model parameters for the cell model were regressed from experimental data. The high-titania slag produced, consists mainly of titanium in different oxidation states and FeO, placing its composition inside the Ti02 - Th03 - FeO ternary system. Reliable experimental data for this system are very limited. All three binary systems contained in the Ti02 - ThO) - FeO system were considered, namely FeO - Ti02, Ti02 - ThO) and FeO - ThO). Only liquidus data for these three binaries were used to regress the model parameters. Accuracy of the models was determined by calculating the root mean square (RMS) error between the experimental data point and the value calculated using the model and the newly determined model parameters. These errors corresponded weil with the reported experimental error of the datasets for both the models and all the binary systems. Due to the fact that this study focussed on the liquidus surface of the system, the results were also plotted in the form of binary phase diagrams and ternary liquidus isotherms. The cell model uses only binary interaction parameters to describe the ternary system. These parameters are not expanded to higher order polynomials, which makes this model more robust, but also less accurate than other models such as the modified quasi-chemical model. / AFRIKAANSE OPSOMMING: Tydens die produksie van suiwer Ti02 vir die pigmentbedryf, word ilmeniet, wat 35 tot 60 % Ti02 bevat, gereduseer tot 'n hoë titaan slak, met 'n Ti02 inhoud van 85 tot 95 % Ti02, en potyster. Hierdie ilmeniet smeltoonde word binne baie nou bedryfskondisies beheer. Oor-redusering van die slak kan lei tot the formasie van TiC en die redusering van Ti02 tot Th03. Dit affekteer nie net die produk se kwaliteit nie, maar kan volgens Namakwa Sands oond operateurs ook slak skuiming en ontploffings tot gevolg hê. Gedurende onder-reduserende omstandighede in die oond, word die vloeibaarheid van die slak verhoog deur die hoër FeO inhoud in die slak. Dit maak die slak meer korrosief en kan lei tot faling van die vuurvaste stene. Die mate van redusering in die oond word nie net bepaal deur die toevoeging van koolstof nie, maar ook deur die temperatuur van die slak. Dit is 'n standaard praktyk van die industrie om die oond te bedryf met 'n gevriesde slak laag om sodoende die vuurvaste stene te beskerm teen chemiese en fisiese aanval van die slak. Dit is dus duidelik dat dit baie belangrik is om die slak se smeltpunt by verskillende samestellings te kan voorspel. Dit kan die operateur help om die oond binne veilige bedryfskondisies te hou. 'n Hele aantaloplossingsmodelle is oor die afgelope paar dekades ontwikkel vir die beskrywing van nie-ideale oplossings. Hierdie modelle het oor die afgelope paar jaar baie toegeneem in praktiese waarde as gevolg van die snelle toename in rekenaarkapasiteit en -spoed. Dit het veral groot waarde in gevorderde beheerstelsels en besluitneming steun. Sommige van die meer bekende modelle word in hierdie studie bespreek en ge-evalueer vir die Ti02 - Th03 - FeO stelsel, gebaseer op 'n kritiese evaluasie van eienskappe en eksperimentele data gepubliseer in die literatuur. Twee van hierdie modelle, die "gemodifiseerde kwasi-chemiese" model en die "sel" model, is gebruik om die hoë titaan slak stelsel te beskryf. Beide hierdie modelle is gebaseer op statistiese termodinamika en het klein verskille m.b.t. die aanvanklike aannames. Die model veranderlikes vir die sel model is in hierdie studie afgelei vanaf die eksperimentele data. Die hoë titaan slak wat tydens hierdie proses geproduseer word, bestaan hoofsaaklik uit FeO en titaan in sy verskillende oksidasie toestande. Dit plaas die samestelling van die slak reg binne die Ti02 - Th03 - FeO temêre stelsel. Betroubare eksperimentele data vir hierdie stelsel is baie beperk. In hierdie studie word daar gekyk al drie binêre stelsels binne die Ti02 - Th03 - FeO temêre stelsel, naamlik: FeO - Ti02, Ti02 - Th03 en FeO - Th03. Slegs die smeltpunt temperatuur data vir hierdie twee binêre is gebruik in die afskatting van die model veranderlikes. Die akkuraatheid van die modelle is bepaal deur die wortel van die gemiddelde kwadraat van die fout tussen die eksperimentele waardes en die berekende waardes te bepaal. Albei die modelle het 'n relatiewe klein fout in vergelyking met die geraporteerde eksprimentele fout gehad vir al die binêre stelsels. Hierdie studie het gefokus op die smeltpunt temperatuur van die slak en die resultate is daarom ook in die vorm van binêre fasediagramme en isoterme projeksies op die temêre fasediagramme gestip. Die "sel" model gebruik slegs binêre interaksie parameters om die temêre stelsel te beskryf Hierdie parameters word vir die "sel" model nie uitgebrei tot hoër order polinome en dit maak die "sel" model meer robuust, maar minder akkuraat as ander modelle soos byvoorbeeld die "kwasi-chemiese" model.