Thesis (PhD (Process Engineering))--University of Stellenbosch, 2006. / Existing thermoplastic polyurethanes (TPUs), used in the manufacturing of cardiovascular devices, still have unproven long-term biostability and may be prone to excessive plastic deformation when subjected to cyclic loading. These negative aspects can be attributed to, among other factors, the weak nature of virtual crosslinking through microphase separation. The modification and covalent crosslinking of existing medical grade polyurethanes with unsaturated acyl chlorides are thus proposed to improve these properties. A model compound study was used to find a suitable acyl chloride (4-pentenoyl chloride), confirm the intended carbamate nitrogen as successful reaction site and to optimize the chemistry of the reaction. Two medical grade polyurethanes, Pellethane® 2363- 80AE (Pellethane) and PurSil 35-80A (PurSil), were subsequently successfully modified with 4-pentenoyl chloride. The degree of modification could be accurately controlled (R2 = 0.99) to between 4.5% to 20.0% and between 11.5% to 18.5% for the respective polyurethanes. The degree of modification and method of crosslinking were then optimized to obtain the required mechanical properties (i.e. minimum hysteresis). The hysteresis and creep of the modified and crosslinked Pellethane were reduced by 42.5% and 44.0%, respectively, while the hysteresis of the modified and crosslinked PurSil was reduced by 12.9%. The chemical stability of Pellethane (control) modified Pellethane (15% modification) and crosslinked Pellethane (Pell15.0) was evaluated in an in vitro degradation study. The hysteresis of the crosslinked polymer was at least 27.5% better when compared to Pellethane, and showed a significant resistance to surface degradation (as studied with scanning electron microscopy). Although the soft phases in both polyurethanes are vulnerable toward degradation, it was not as pronounced in Pell15.0, mainly due to the restriction of chain movement resulting from the crosslinking. Small-diameter tubular constructs, with similar fiber and wall thicknesses, were electrospun from Pellethane and the 15% modified Pellethane. A standard electrospinning technique was used in the case of the former while in the case of the latter a novel “reactive” electrospinning technique was used for the in situ crosslinking of the novel material, while simultaneously forming the tubular constructs. It is suggested that the manufacturing of Pell15.0 be scaled up to produce adequate amounts of material to enable the extrusion and in vivo evaluation of e.g. pacemaker leads. A circulatory animal model, e.g. a senescent baboon model, could be used to evaluate and further optimize the electrospun tubular constructs.

Dissertation (PhD)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: QUANTITATIVE YEAST PHYSIOLOGY AND NITROGEN METABOLISM DURING HETEROLOGOUS PROTEIN PRODUCTION By Johann F. Görgens The physiology and nitrogen metabolism of the yeast, Saccharomyces cerevisiae, during heterologous xylanase production in a defined medium was quantified by the comparison of isogenic yeast strains, whereby several potential limitations in the production of the heterologous xylanase could be identified. The presence of global sensing and regulatory mechanisms, by which the yeast is able to actively regulate both heterologous gene expression and the physiological response to the process, was also investigated. The deleterious effects of heterologous xylanase production on the physiology of the recombinant host were disproportionately large with respect to the amount of foreign protein produced. The cellular processes involved in this response were identified by the transcriptional profiling of isogenic recombinant strains, in a novel analytical approach to investigating foreign protein production by S. cerevisiae. Heterologous gene expression affected a combination of cellular processes and induced the yeast stringent stress response. The corresponding loss of metabolic functionality resulted in the disproportionate physiological effects of foreign protein production, similar to previous observations in recombinant Escherichia coli, and a possible reduction in attainable production levels. Reducing the propensity of recombinant gene expression to introduce metabolic stress may therefore increase production levels of foreign proteins by yeast. The metabolic vitality of transformed strains was also reduced by the presence of multiple copies of active, plasmid-based PGK1-promoters in the cell without expression of the heterologous gene. The negative effect was caused by an increase in the biosynthetic and glycolytic capacity of the strain at the expense of other processes. Production levels of heterologous xylanase were influenced by expression vector selection and the presence of auxotrophic mutations in transformed strains of S. cerevisiae. The increased transcription levels obtained with the multicopy plasmidbased YEp-type expression system, compared to the integrative YIp-type expression system, resulted in higher levels of xylanase production. Heterologous xylanase production thus did not saturate the secretory capacity of the host strain. The genetic stability of the autoselective YEp-type expression system in long-term chemostat culture was also demonstrated. High levels of heterologous xylanase production by transformed S. cerevisiae strains containing auxotrophic markers required the stabilisation of nitrogen metabolism via saturation of yeast cells with an excess of imported amino acids. By the removal of excessive auxotrophic markers, high levels of xylanase production by a prototrophic transformant in defined medium without amino acid addition could be obtained. Heterologous xylanase production by the prototrophic transformant was further enhanced by increasing the availability of preferred amino acids or succinate in the defined medium, indicating an additional requirement for metabolic precursors and building blocks for foreign protein synthesis. Comparable levels of heterologous xylanase production were obtained in high cell density cultures of the alternative yeast, Pichia stipitis, by the proper induction of the native ADH2-promoter, the control of oxygenation, and addition of an amino acid mixture to the defined medium, indicating the presence of generic limitations in transcription, nutrient availability and the yeast biosynthetic capacity for foreign protein production by various yeasts. The presence of global sensing and regulatory mechanisms was confirmed by the physiological response of S. cerevisiae to heterologous protein production, which included the downregulation of biosynthesis and growth, and the induction of various processes involved in the stringent stress response. Additionally, heterologous xylanase production was actively regulated on a posttranscriptional level by the auxotrophic transformants in response to the level of amino acid availability. The biosynthetic capacity for foreign protein production by both recombinant S. cerevisiae and P. stiptis was also regulated in response to the physiological state of the yeast and the availability of nutrients. The presence of these regulatory mechanisms complicated the manipulation of cellular biosynthesis at will. / AFRIKAANSE OPSOMMING: KWANTITATIEWE GIS-FISIOLOGIE EN -STIKSTOF METABOLISME GEDURENDE HETEROLOË PROTEÏEN PRODUKSIE Deur Johann Ferdinand Görgens Die fisiologie en stikstof-metabolisme van die gis, Saccharomyces cerevisiae, gedurende heteroloë xilanase produksie in ‘n gedefiniëerde medium is gekarakteriseer deur isogeniese gis-rasse te vergelyk, waardeur verskeie moontlike beperkings in die produksie van die heteroloë xilanase uitgewys kon word. Die teenwoordigheid van globale sensoriese- en beheer-meganismes, wat die gis in staat stel om beide heteroloë geen uitdrukking en die fisiologiese respons op die proses aktief te reguleer, is ook ondersoek. Die nadelige effekte van heteroloë xilanase produksie op die fisiologie van die rekombinante gasheer-organisme was uitermatig groot in vergelyking met die hoeveelheid vreemde proteïen wat geproduseer is. Die sellulêre prosesse verantwoordelik vir hierdie respons is identifiseer deur die transkripsionele profiele van isogeniese rekombinante rasse te vergelyk, in ‘n nuwe analitiese benadering tot die bestudering van vreemde proteïen produksie deur S. cerevisiae. Heteroloë geen uitdrukking het ‘n kombinasie van sellulêre prosesse geaffekteer en die gis se algemene voedingstres-respons geaktiveer. Die gepaardgaande verlies aan metaboliese funksie het die uitermatige fisiologiese effek van vreemde proteïen produksie veroorsaak, soortgelyk aan vorige waarnemings met rekombinante Escherichia coli. Die haalbare produksie-vlakke is moontlik ook verlaag deur hierdie respons. ‘n Verlaging van die geneigdheid van rekombinante geen uitdrukking om metaboliese stres te veroorsaak, mag dus die produksievlakke van vreemde proteïene in gis verbeter. Die metaboliese groei-potensiaal van die getransformeerde rasse is ook verlaag deur die teenwoordigheid van etlike aktiewe kopieë van plasmied-gebaseerde PGK1-promotors in die sel, sonder uitdrukking van die heteroloë geen, deur ‘n toename in die biosintetiese en glikolitiese kapasiteit ten koste van die ander sellulêre prosesse. Die produksievlakke van heteroloë xilanase is deur die keuse van uitdrukkings-sisteem en die teenwoordigheid van autotrofiese mutasies in die getransformeerde rasse van S.cerevisiae beïnvloed. Die verhoogde transkripsie vlakke wat met die multi-kopie, plasmied-gebaseerde YEp-tipe uitdrukkingsisteem, eerder as die geïntegreerde YIp-tipe sisteem, verkry is, het tot verhoogde xilanase produksie gelei. Heteroloë xilanase produksie het dus nie die uitskeidingskapasiteit van die gasheer versadig nie. Die genetiese stabiliteit van die autoselektiewe, YEp-tipe uitdrukkingsisteem in langtermyn chemostaat-kulture is ook gedemonstreer. Hoë vlakke van xilanase produksie deur getransformeerde S. cerevisiae rasse met autotrofiese merkers het die stabilisering van die stikstof metabolisme, deur die versadiging van die sel met ingevoerde aminosure, vereis. Die verwydering van oormatige autotrofiese merkers het tot hoë vlakke van xilanase produksie deur die prototrofiese transformant in gedefinieerde medium sonder aminosuur byvoeging gelei. Heteroloë xilanase produksie deur die prototrofiese transformant kon verder verbeter word deur die byvoeging van voorkeur-aminosure of suksinaat tot die gedefinieerde medium, en ‘n addisionele behoefte aan metaboliese voorloper-molekules en bou-blokke vir vreemde proteïensintese het dus bestaan. Vergelykbare vlakke van heteroloë xilanase produksie is in kulture met hoë sel-digthede van die alternatiewe gis, Pichia stipitis, verkry deur die doeltreffende induksie van die eiesoortige ADH2-promotor en die byvoeging van ‘n aminosuur-mengsel tot die gedefinieerde medium, wat die teenwoordigheid van generiese beperkinge in transkripsie, voedingstof-beskikbaarheid en biosintetiese kapasiteit van die gis vir vreemde proteïen produksie deur verskeie giste uitgewys het. Die teenwoordigheid van globale sensoriese- en beheer-meganismes is bevestig deur die fisiologiese respons van S. cerevisiae tot heteroloë proteïen produksie, wat die afwaartse regulering van biosintese en groei, en die induksie van verskeie prosesse betrokke by die algemene voedingstres-respons, ingesluit het. Heteroloë xilanase produksie is ook op ‘n na-transkripsionele vlak aktief gereguleer deur die autotrofiese transformante in reaksie tot die vlak van aminosuur beskikbaarheid. Die biosintetiese kapasiteit vir vreemde proteïen-produksie van beide rekombinante S. cerevisiae en P. stipitis is ook in reaksie tot die fisiologiese toestand van die gis en die beskikbaarheid van voedingstowwe gereguleer. Die teenwoordigheid van hierdie regulatoriese meganismes het die willekeurige manipulasie van sellulêre proteïen-biosintese bemoeilik.

Thesis (PhD)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The main proposition of this study is that the notion of a single set of universal success factors (enablers) of innovation is naïve. Rather, the importances of different enablers are contextually based and dependent upon different kinds of projects and their attributes. By investigating the roles of project radicalness and maturity in governing the importance of enablers of innovation in the process industries, two major conclusions were made, viz. (1) the importance of enablers are significantly moderated by project attributes, and (2) the mutual interactions between moderators of enabler importance prevent the formulation of middle-range theories of innovation radicalness or maturity, which propose normative relationships between innovation attributes and enabler importance. Although a number of previous studies have posited such outcomes, this study provides empirical evidence thereof for a set of generic enablers of innovation. These findings have suggested that the modelling of innovation at the project level should follow a contingent approach. While contingency theory has widely been applied to correlate structural and environmental attributes when the unit of analysis is the organisation, the literature on project management has largely ignored the importance of project contingencies, assuming that all projects share a universal set of managerial characteristics. This void is addressed through the development of a contingency model of the influence of secondary contingencies (project radicalness and maturity) on the importance of enablers. It represents an integrative perspective of the contextual importance of a number of enablers (and constructs thereof) that have previously been investigated and reported independently. Given that theory development in project management is still in its early years, it may therefore be concluded that the study contributes to the validity of classical contingency theory arguments in the context of the project. Although it does not consider an exhaustive list of all possible contingencies, and findings thereof strictly pertain only to process innovation, it does represent a considerable step in the evolving process of theory development on the modelling of innovation at the project level. / AFRIKAANSE OPSOMMING: Die studie poneer in hoofsaak dat die idee van ‘n enkele stel universele suksesfaktore (drywers) vir innovasie, eng is. Dit word eerder voorgestel dat die belangrikheid van verskillende drywers kontekstueel is en bepaal word deur verskillende tipes projekte en hul eienskappe. Na gelang van ‘n ondersoek na die rolle van projek radikaalheid en stadium van ontwikkeling in die bepaling van die belangrikheid van drywers van innovasie, is twee hoofgevolgtrekkings gemaak, naamlik dat (1) projekeienskappe ‘n beduidende invloed op die relatiewe belangrikheid van drywers het, en (2) die onderlinge interaksies tussen moderators van die belangrikheid van drywers dit verhoed om middelomvang teorieë van innovasie radikaalheid of stadium van ontwikkeling te formuleer, wat normatiewe verhoudings tussen die eienskappe van innovasies en hul drywers voorstel. Alhoewel sulke resultate deur ‘n aantal vorige studies gepostuleer is, verskaf hierdie studie empiriese bewyse daarvan in terme van ‘n generiese stel drywers van innovasie. Bevindinge in hierdie verband het getoon dat innovasie op die projek-vlak deur ‘n voorwaardelikheidsmodel gemodelleer moet word. Alhoewel voorwaardelikheidsteorie algemeen gebruik word om strukturele en omgewingseienskappe op organisatoriese vlak te korrelleer, het die projekbestuur-literatuur tot dusver grootliks die belangrikheid van projekvoorwaardelikhede geïgnoreer deur aan te neem dat alle projekte ‘n universele stel bestuurseienskappe deel. Hierdie leemte word geadresseer deur die ontwikkeling van ‘n voorwaardelikheidsmodel vir die invloed van sekondêre voorwaardelikhede (projek radikaalheid en stadium van ontwikkeling) op die belangrikheid van drywers. Dit verteenwoordig ‘n geïntegreerde perspektief van die kontekstuele belangrikheid van ‘n aantal drywers (en konstrukte daarvan) wat voorheen onafhanklik nagevors en gepubliseer is. Aangesien teorie ontwikkeling in projekbestuur steeds jonk is, word die gevolgtrekking gemaak dat die studie bydra tot die geldigheid van klassieke voorwaardelikheidsteorieargumente in die konteks van die projek. Alhoewel dit nie ‘n veelomvattende lys van alle moontlike voorwaardelikhede beskou nie, en die bevindinge daarvan streng gesproke slegs betrekking het op proses-innovasie, verteenwoordig die studie ‘n beduidende stap vorentoe vir teorie-ontwikkeling in die modellering van innovasie op die projek-vlak.

Thesis (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The importance of waste management is growing rapidly for several reasons. These reasons include the escalating cost of wastewater treatment and cleaning chemicals, an emerging trend of onerous regulatory regime regarding e uent disposal from governments, rising public awareness on the adverse e ects of industrial waste as well as drastic reduc- tion in water resources in the winegrowing regions. In addition, owing to the large energy demand for refrigeration purposes for high quality wine production and rapidly increasing energy costs, the challenges of energy management in the wine industry were also inves- tigated. In order to address these challenges adequately, the solutions were derived via the integration of two disciplines: environmental science (waste and energy management) and computer science (applications of arti cial intelligence). Therefore, the ndings re- ported from this study seek to advance knowledge through the construction of decision support systems for waste and energy management in circumstances where conventional mathematical formalisms are inadequate. In that sense, the dissertation constitutes in- terdisciplinary research on the application of integrated arti cial intelligence technologies (expert systems and fuzzy logic) in designing and developing decision tools for waste and energy management in the wine industry. The dissertation rst presents the domain of interest, where the scope and breadth of the problems it addresses are clearly de ned. Critical examination of the domain data- bases revealed that data, information, and knowledge for waste and energy management in the wine industry are generally incomplete and lack structure overall. Owing to these characteristics, a hybrid system approach was proposed for the development of decision support systems based on fuzzy logic. The integrated decision support systems were de- veloped based on an object-oriented architecture. This approach facilitated the exible design required for waste and energy management-related complex problem-solving. To illustrate the applicability of the o -line decision tools developed, several case stud- ies mirroring on actual industrial practices were considered. These systems were found to be robust and yielded results that were in accordance with actual industrial practices inthe wine industry. Furthermore, they provided intelligent suggestions in scenarios where there was minimal information, and under certain instances they o ered feasible sugges- tions in circumstances where a human novice could have problems in making the right decisions. / AFRIKAANSE OPSOMMING: Die belangrikheid van afvalbestuur neem om verskeie redes vinnig toe. Die redes sluit in die eskalerende koste van afvalwaterbehandeling en skoonmaakmiddels, streng regula- toriese vereistes van regeringskant met betrekking tot die verwydering van uitvloeisels, toenemende openbare bewustheid van die nadelinge e ekte van nywerheidsafval, sowel as die drastiese afname in waterbronne in wynproduserende omgewings. Daarby, a.g.v. die groot energieverbruik wat deur die verkoeling van hokwaliteitwyn vereis word en die snelgroeiende energiekoste, is die uitdagings van energiebestuur in die wynbedryf ook on- dersoek. Ten einde die uitdagings die hoof te kon bied, is oplossings gevind deur die integrasie van twee disciplines: omgewingswetenskap (afval- en energiebestuur) en rekenaarweten- skap (toepassings van kunsmatige intelligensie). Gevolglik is daar deur die bevindinge van die studie gepoog om kennis te bevorder deur die konstruksie van besluitnemingson- dersteuningstelsels vir afval- en energiebestuur onder omstandighede waar konvensionele wiskundige algoritmes ontoereikend sou wees. In die opsig verteenwoordig die proefskrif interdissiplinre navorsing in die toepassing van gentegreerde kunsmatige intelligensieteg- nologie (kundige stelsels en wasige logika) in die ontwerp en ontwikkeling van besluitne- mingshulpmiddels vir afval- en energiebestuur in die wynindustrie. Die proefskrif baken eers die probleemgebied af, waarna die bestek en omvang van die probleme waarop die werk gemik is duidelik gede nieer word. Kritiese ondersoek van die databasisse in die domein het getoon dat die data, informasie en kennis oor afval- en energiebestuur in die wynbedryf in die algemeen onvolledig en gebrekkig gestruktureer is. A.g.v. di eienskappe, is 'n hibriede stelselbeandering voorgestel vir die ontwikkeling van besluitnemingstelsels gegrond op wasige logika. Die gentegreerde besluitnemingsonders- teuningstelsels is ontwikkel op 'n objek-georinteerde argitektuur. Die benadering het die daarstelling van 'n buigsame ontwerp wat benodig word vir komplekse probleemoplossing in afval- en energiebestuur vergemaklik. Om die toepaslikheid van die a ynige besluitnemingshulpmiddels wat ontwerp is, te illustreer, is verskeie gevallestudies wat werklike industrile praktyk uitbeeld beskou. Diestelsels was robuust en het resultate gelewer wat in ooreenstemming was met werklike industrile praktyke in die wynnywerheid. Die kundige stelsels het verder intelligente voorstelle gemaak in scenarios waar daar minimale informasie beskikbaar was, en onder sekere omstandighede het hulle realistiese oplossings voorgestel waar 'n onkundige persoon probleme sou gehad he tom die regte besluite te kon neem.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: See item for full text / AFRIKAANSE OPSOMMING: Sien item vir volteks

Thesis (PhD (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Previous work has shown that microwave heating of mineral ores induces fractures around grain boundaries due to the differences in absorption of microwaves and the resulting differential thermal expansion among the various mineral phases in the ore particles. As a consequence, this reduces the energy required in subsequent grinding and enhances liberation of valuable minerals. In this study, first, the influences of different variables on bulk strength reduction of microwave treated ores have been investigated. Nine different binary ore models were constructed by randomly disseminating 10 vol.% microwave absorbing minerals in transparent matrices. Computational simulations of heating, thermal damage and unconfined compressive strength (UCS) tests on the conceptual binary ores have been undertaken by using finite-difference modelling techniques. The influence of thermo-mechanical properties of minerals on strength reduction of microwave treated ores was examined. It was shown that in general the thermal properties of the microwave absorbing mineral and the mechanical properties of the transparent matrix have the most significant effect on the strength reduction. Binary ores containing a microwave absorbing mineral that has a high thermal expansion coefficient in a strong transparent matrix achieved higher reductions in strength. The influence of absorbent phase grain size on strength reduction of ores was also quantified. It was shown that for the same energy inputs and mineral types, the reductions in strength were much higher in coarse-grained ores. It has also been shown that for the same mineralogy and treatment condition, ores with poorly disseminated heated phase achieved much higher strength reduction. The effect of microwave treatment on the mechanical state of an ore sample was also examined. It was demonstrated that unconfined compressive strength is less sensitive to microwave-induced micro-fractures and found to be a poor descriptor of liberation behaviour. A new method of characterizing damage in microwave treated ore using a continuum approach was developed. The method measures the damage around the grain boundary regions during the heating process. Using the method, it was possible to elucidate in detail the influences of power density, mineralogy, ore texture on microwave treatment of ore. It was shown that the amount of grain boundary damage incurred at a specific power density and energy input is dependent both on the ore mineralogy and its texture. The energy inputs that were required for significant (> 10%) grain boundary damage in the ores range from 0.09 to 7.06 kWh/t depending on the power density applied, the ore mineralogy and its texture. It was also shown that for a given mineralogy and ore texture there is a power density level below which no further increase in grain boundary damage is possible by increasing exposure time. The effect of pulse repetition frequency on grain boundary damage was also elucidated using the method. It was found that high pulse repetition frequencies (³ 50 Hz) resulted in an amount of grain boundary damage that was indistinguishable from that caused by continuous wave operation for a fixed energy input. It has also been shown that for a fixed microwave energy input the best result would be obtained by using the lowest possible pulse repetition frequency and highest peak pulse power. The effect of microwave treatment of ores at different treatment conditions on the extent of damage and crack pattern was also investigated in detail using bondedparticle model (BPM). It has been shown that the amount of micro-cracks and also the cracks pattern in an ore sample after microwave treatment significantly depend on its mineralogy, microwave treatment condition (power density) and absorbent phase grain size. It has also been shown that a minimum power density is required to localize damage around the grain boundary in an ore sample. This minimum power density was found to strongly depend on the ore mineralogy and its texture. Initial simulation test work concerning the effect of microwave treatment on liberation of minerals is also presented. It has been shown that microwave irradiation considerably changed the fracture pattern of an ore in simulated single particle crushing. The fracture pattern of the ore treated at high power density (Pd = 0.1 kW /mm3abs for 1 ms) was along the grain boundary and the absorbent mineral was intact. In the ore treated at lower power density for the same energy input (Pd = 1 W/mm3abs for 0.1 s) both intergranular and transgranular fractures were observed. However, in all cases the fracture patterns were preferentially localized around the grain boundary compared to that of the untreated ore. / AFRIKAANSE OPSOMMING: Vorige studies het getoon dat mikrogolfverhitting van mineraalertse tot breuke om die ertskorrelgrense aanleiding gee, omdat die verskillende mineraalfases in die ertsdeeltjies die mikrogolwe verskillend absorbeer, en dus ook verskillend uitsit. Korrelgrensbreuke verminder die vereiste energie vir latere slypwerk, en verhoog die vrystelling van waardevolle minerale. Hierdie studie het eerstens die uitwerking van verskillende veranderlikes op die algehele sterktevermindering van mikrogolfbehandelde ertse ondersoek. Hiervoor is nege verskillende binêre ertsmodelle vervaardig deur mikrogolfabsorberende minerale met ʼn volumepersentasie van 10% lukraak in deursigtige matrikse te versprei. Met behulp van eindigeverskilmodelleringstegnieke is berekeningsimulasies van verhitting, warmteskade en onbegrensde druksterkte (“unconfined compressive strength”) op die konseptuele binêre ertse uitgevoer. Die invloed van termomeganiese mineraaleienskappe op die sterktevermindering van mikrogolfbehandelde ertse is eerste onder die loep geneem. Daar is bevind dat die warmte-eienskappe van die mikrogolfabsorberende mineraal, en die meganiese eienskappe van die deursigtige matriks, die beduidendste uitwerking op sterktevermindering het. Binêre ertse wat ʼn mikrogolfabsorberende mineraal bevat met ʼn hoë warmte-uitsettingskoëffisiënt in ʼn sterk deursigtige matriks, het groter sterkteverminderings getoon. Die invloed van korrelgrootte in die absorbeerfase op die sterktevermindering van ertse is volgende versyfer. Die studie het getoon dat, op grond van dieselfde energie-insette en mineraalsoorte, grofkorrelrige ertse groter sterktevermindering ondergaan het. Eweneens is bewys dat, met dieselfde mineralogie en behandelingsomstandighede, ertse met ʼn swak verspreide verhittingsfase ook groter sterktevermindering ervaar. Die uitwerking van mikrogolfbehandeling op die meganiese toestand van ʼn ertsmonster is boonop ondersoek. Die studie het getoon dat onbegrensde druksterkte minder gevoelig vir mikrogolfgeïnduseerde mikrobreuke is, en as ʼn swak aanwyser van vrystellingsgedrag beskou word. ʼn Nuwe metode om skade by mikrogolfbehandelde ertse te tipeer is gevolglik met behulp van ʼn kontinuumbenadering ontwikkel. Dié metode meet die skade rondom die korrelgrens gedurende die verhittingsproses. Deur middel van voormelde metode was dit dus moontlik om die invloed van kragdigtheid, mineralogie en ertstekstuur op die mikrogolfbehandeling van erts deeglik te ondersoek. Daar is bevind dat die mate van korrelgrensskade by ʼn bepaalde kragdigtheid en energie-inset, van sowel die ertsmineralogie as ertstekstuur afhang. Na gelang van die toegepaste kragdigtheid, die ertsmineralogie en ertstekstuur, het die vereiste energie-insette vir beduidende (>10%) korrelgrensskade van 0,09 tot 7,06 kWh/t gewissel. Dit het voorts geblyk dat enige bepaalde mineralogie en ertstekstuur oor ʼn minimum kragdigtheidsvlak beskik, onder welke vlak geen verlenging in blootstellingstyd enige verdere korrelgrensskade kan veroorsaak nie. Die uitwerking van pulsherhaalfrekwensie op korrelgrensskade is ook met behulp van bogenoemde metode verklaar. Die studie het getoon dat, op grond van ʼn vaste energie-inset, hoë pulsherhaalfrekwensies (≥50 Hz) en gelykgolfwerking presies dieselfde hoeveelheid korrelgrensskade tot gevolg het. Volgende is daar met behulp van ʼn gebondedeeltjiemodel (“bonded-particle model”) noukeurig ondersoek ingestel na die uitwerking van verskillende mikrogolfbehandelingsomstandighede op die hoeveelheid skade en die kraakpatroon by ertse. Die studie het getoon dat die hoeveelheid mikrokrake sowel as die kraakpatroon in ʼn mikrogolfbehandelde ertsmonster in ʼn groot mate van die betrokke erts se mineralogie, mikrogolfbehandelingsomstandighede (kragdigtheid) en korrelgrootte in die absorbeerfase afhang. Daar is ook bevind dat ʼn minimum kragdigtheid nodig is om skade tot die gebied om die korrelgrens te beperk, welke minimum kragdigtheid oënskynlik grotendeels deur die ertsmineralogie en -tekstuur bepaal word. Die studie bevat ook die resultate van aanvangsimulasietoetse oor die uitwerking van mikrogolfbehandeling op mineraalvrystelling. Die toetse het getoon dat mikrogolfbestraling ʼn beduidende verandering tot gevolg het in die ertsbreekpatroon met gesimuleerde enkeldeeltjievergruising. Die breekpatroon van die erts wat by hoë kragdigtheid (Pd = 0,1 kW/mm3abs vir 1 ms) behandel is, het ál langs die korrelgrens gestrek, terwyl die absorberende mineraal nog ongeskonde was. In die erts wat by laer kragdigtheid dog dieselfde energie-inset behandel is (Pd = 1 W/mm3abs vir 0,1 s), is sowel tussenkorrel- as oorkorrelbreuke opgemerk. In teenstelling met die onbehandelde erts, was die breekpatrone by die behandelde erts egter in alle gevalle steeds merendeels rondom die korrelgrens geleë.

Thesis (PhD (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Biological agents offer several opportunities to address the many challenges faced in intensive reticulated aquaculture. We therefore isolated and selected Bacillus spp. as potential biological agents, because this group has demonstrated an array of biological activities of possible benefit to aquaculture. They also display advantages in terms of robustness during bioprocessing and end product application. Natural isolates obtained from Cyprinus carpio, selected as a model high-value ornamental fish species, and associated culture environments, were purified and assessed for in vitro efficacy based on the inhibition of growth of pathogenic Aeromonas hydrophila and the decrease in concentrations of ammonium, nitrite, nitrate and phosphate ions, typically found as waste products in aquaculture systems. Based on suitability for aquaculture application, isolates B001, B002 and B003 were selected and further evaluated in vitro and in an in vivo trial with C. carpio. Inhibition of Aer. hydrophila growth and a decrease in concentrations of waste ions were demonstrated in these studies. Based on 16S RNA sequence homology, the isolates were identified as Bacillus subtilis, B. cereus and B. licheniformis, respectively. High sequence homology between B. subtilis and B. anthracis necessitated further safety studies on the best isolate, B. cereus NRRL100132 (B002). The isolate was shown not to contain the anthrax virulence genes pOX1, pOX2 or the B. cereus enterotoxin. Elucidation of the potential modes of action of a biological agent facilitates an understanding of functionality and encourages technology uptake by end users. Competitive exclusion through growth rate and competitive uptake of glucose and iron, the latter facilitated by siderophore production, were shown to be key mechanisms at play in inhibition of Aer. hydrophila by the B. cereus isolate. As production cost is an important consideration in development of commercially relevant biological products, we examined the optimization of nutrient supplementation, which has an impact on high-density production of spores by fermentation. Corn steep liquor (CSL) was identified as a lower cost and more effective nutrient source in comparison to conventional nutrient substrates, in particular yeast extract and nutrient broth. The improved sporulation performance of B. cereus could be related to the increased availability of free amino acids, carbohydrates, and minerals in CSL, which had a positive effect on organism growth and sporulation efficiency. The impact of nutrient concentration on spore yield and productivity was modelled to develop a tool for selection of optimal conditions. Excellent correlation with actual laboratory fermentation data was demonstrated. A cost analysis revealed that production using liquid phytase treated and ultra-filtered CSL was less expensive than spray dried CSL and supported cultivation of B. cereus spores at densities higher than 1×1010 CFU ml 1. Adoption of biological agents in commercial applications is lacking, due to limitations in process and product development that address key end user product requirements such as cost, efficacy, shelf life and convenience. The development of suitable spore recovery, drying, formulation and tablet production process steps was thus performed. Key criteria used for downstream process unit evaluation included spore viability, recovery, spore balance closure, spore re-germination, product intermediate stability, end product stability and efficacy. A process flow sheet comprising vertical tube centrifugation, fluidised bed agglomeration and tablet pressing yielded an attractive product. The formulation included corn steep liquor and glucose to enhance subsequent spore re-germination. Viable spore recovery and spore balance closure across each of the process units was high (>70% and >99% respectively), with improvement in recovery possible by adoption of continuous processing at large scale. Spore re-germination was 97%, whilst a product half-life in excess of 5 years was estimated based on thermal resistance curves. The process resulted in a commercially attractive product and affordable variable cost of production. Functionality of the product, incorporating the B. cereus isolate, was investigated across a range of physiological conditions, including salinity, pH and temperature, based on rearing of C. carpio. Temperature had a significant influence on germination, specific growth rate and increase in cell number of B. cereus, whilst salinity and pH did not have any measurable effect on growth. Controlled studies in bioreactors and modelling of the data to the Arrhenius function indicated the existence of high and low growth temperature domains. The rates of pathogenic Aer. hydrophila suppression and decrease in waste ion concentrations (ammonium, nitrite, nitrate and phosphate) were translated into a linear predictive indicator of efficacy of the B. cereus isolate at different temperatures. This study has resulted in development of an upstream and downstream process for production of a new B. cereus isolate (NRRL 100132) which was shown to be safe, stable, functional, robust and cost effective for application in aquaculture. / AFRIKAANSE OPSOMMING: Biologiese middels bied verskeie maniere om die veelvoudige uitdagings van intensiewe netsgewyse akwakultuur aan te spreek. Gevolglik het ons uitgesoekte Bacillus spesies as potensiële biologiese middels geïsoleer, omdat hierdie groep verskeie biologiese aktiwiteite demonstreer wat van potensiële waarde kan wees in akwakultuur. Die groep toon ook voordele in terme van robuustheid gedurende bioprosessering en eind-toepassings. Natuurlike bakteriële isolate vanuit Cyprinus carpio geassosieerde kultuur omgewings, geselekteer as 'n hoë-waarde model ornamentele spesie, is gesuiwer. Die in vitro doeltreffendheid van die isolate is bepaal gebasseerd op die groei inhibisie van patogeniese Aeromons hydrophila asook die afname in konsentrasies van ammonium, nitriete, nitrate en fosfaat ione wat as tipiese afval produkte gevind word in akwakultuur sisteme. Isolate B001, B002 en B003 is geselekteer op grond van geskiktheid en verder evalueer in in vitro en in vivo proewe met C. carpio. Groei inhibisie van Aer. hydrophila asook 'n afname in konsentrasies van afval ione was tydens die studies gedemonstreer is. Die isolate is identifiseer as Bacillus subtilis, B. cereus en B. licheniformis, respektiewelik, op grond van 16S RNS volgorde homologie. Die hoë volgorde homologie tussen B. subtilis en B. anthracis het verdere veiligheidstudies op die beste isolaat, B. cereus NRRL100132 (B002) genoodsaak. Die isolaat het nie die antraks virulensie plasmied pOX1, pOX2 of die B. cereus enterotoksien getoon nie. Uitklaring van die potensiële meganismes van aksie van biologiese middels fasiliteer 'n begrip van funksionaliteit en moedig tegnologie aanvaarding deur eind-gebruikers aan. Mededingende uitsluiting deur groeitempo en mededingende opname van glukose asook die produksie van siderofore is bewys as sleutel meganismes betrokke in die inhibisie van Aer. hydrophila deur die B. cereus isolaat. Aangesien koste 'n belangrike oorweging is in die ontwikkeling van kommersiële toepaslike biologiese produkte, is die optimisering van voedingstof aanvullings wat 'n impak het op hoëdigtheid produksie van spore deur fermentasie ondersoek. Week-vloeistof van mielie prosessering (CSL) is identifiseer as 'n lae koste en effektiewe voedingsbron in vergelyking met konvensionele voeding substrate, veral gisekstrak en voedingsboeljon. Die verbeterde sporulering prestasie van B. cereus kon toegeskryf word aan die verhoogde beskikbaarheid van vrye aminosure, koolhidrate en minerale in CSL, wat 'n postitewe effek op organisme groei en sporulerings effektiwiteit getoon het. Die impak van voedingstof konsentrasie op spoor opbrengs en produktiwiteit is gemodelleer om 'n werktuig vir die selektering van optimale kondisies te ontwikkel. Uitstekende korrelasie met werklike laboratorium data is gedemonstreer. Koste analises het getoon dat produksie deur middel van vloeibare fitase-behandelde en ultra-filtreerde CSL goedkoper is as sproei-gedroogde CSL en ondersteun verder die kultivering van B. cereus spore teen digthede hoër as 1 x 1010 kolonie vormende eenhede.ml-1. Die opname van biologiese middels in kommersiële toepassings skiet tekort as gevolg van beperkinge in proses en produk ontwikkeling wat belangrike eind-gebruiker vereistes soos koste, doeltreffendheid, rak leeftyd en gerieflikheid aanspreek. Die ontwikkeling van toepaslike prosesse vir spoor herwinning, droging, formulering en tablet produksie is gevolglik uitgevoer. Belangrike maatstawwe wat gebruik is vir stroomaf proseseenheid-ontwikkeling het lewensvatbaarheid, herwinning, spoor balans sluiting, spoor her-ontkieming, intermediêre produk stabiliteit, eindproduk stabiliteit en doeltreffendheid ingesluit. 'n Proses vloeidiagram bestaande uit vertikale buis sentrifugasie, vloeibare bed agglomerasie en tablet persing het 'n aantreklike produk voortgebring. Die formulering het ook CSL en glukose ingesluit om gevolglike spoor herontkieming te verbeter. Lewensvatbare spoor herwinning en spoor balans sluiting oor elke proses eenheid was hoog (>70% en 99% respektiewelik) met verbetering in herwinning wat moontlik gemaak is deur die gebruik van aaneenlopende prosessering op groot skaal. Spoor her-ontkieming was 97%, terwyl produk halfleeftyd langer as 5 jaar beraam is, gebasseer op termiese weerstand grafieke. Die proses het gelei tot 'n kommersiële aantreklike produk asook bekostigbare veranderbare produksie koste. Die funksionaliteit van die tablet-produk met die ingeslote B. cereus isolaat is ondersoek oor 'n reeks fisiologiese kondisies insluitend soutgehalte, pH en temperatuur, gebasseer op die kultivering van C. carpio. Temperatuur het 'n betreklike invloed op ontkieming, spesifieke groeitempo en toename in sel hoeveelheid van B. cereus gehad, terwyl soutgehalte en pH nie enige meetbare effek op groei gehad het nie. Gekontrolleerde studies in bioreaktors en modellering van die data op die Arrhenius funksie het hoë en lae groei temperatuur domeins gewys. Die tempo van patogeniese Aer. hydrophila onderdrukking en afname in konsentrasies van afval-ione (ammonium, nitriete, nitrate en fosfaat) is herlei na 'n liniêre voorspellende aanwysing van effektiwiteit van B. cereus isolate by verskillende temperature. Die studie het gelei tot die ontwikkeling van stroomop- en stroomaf-prosesse vir die produksie van 'n nuwe B. cereus isolaat (NRRL 100132) wat bewys is as veilig, stabiel, funksioneel, robuust en koste effektiewe vir toepassing in akwakultuur.

Thesis (PhD (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Future chemical production is faced with a challenge of limited material and energy resources. However, process intensification might play a significant role to alleviating this problem. Vision of process intensification through multifunctional reactors has stimulated research on membrane-based reactive separation processes, in which membrane separation and catalytic reaction occur simultaneously in one unit. These processes are rather attractive applications because they are potentially compact, less capital intensive, and have lower processing costs than traditional processes. Moreover, they often enhance the selectivity and yield of the target product. For about three decades, there has been a great evolution in p-Xylene production technology, with many equipment improvements being instituted in the industry. Typically, these improvements bring economic as well as processing advantages to the producers. Such developments are vital, as the capital costs for process equipment to produce and separate p-Xylene from xylene isomers, especially into high purity p-Xylene, still remain very high. However, with numerous advantages of membrane-based reactive separation processes compared to the conventional processes, the research focus has been channelled toward application of MFI-type zeolite membranes for in situ separation and isomerization of xylene in extractor-type catalytic membrane reactors. To contribute to this research line, this study has focused on characterization and optimization of an extractor-type catalytic membrane reactor (e-CMR) equipped with a nanocomposite MFI-alumina membrane as separation unit for m-Xylene isomerization over Pt-HZSM-5 catalyst. Nanocomposite MFI-alumina zeolite membranes (tubes and hollow fibres) used in this study were prepared via a so-called “hydrothermal pore-plugging synthesis technique” developed by Dalmon and his group more than a decade ago. In this concept, MFI material is grown by 'pore-plugging' direct hydrothermal synthesis in a porous matrix rather than forming thin films on top of the support. The advantages of this type of architecture over conventional film-like zeolite membranes include: (i) minimization of the effect of thermal expansion mismatch between the support and the zeolite, (ii) easy to scale-up, and (iii) easy module assembly, because the separative layer (zeolite crystals) are embedded within the pores of the ceramic support, reducing the effects of abrasion and thermal shocks. After membrane synthesis, the membrane quality and separation performance of these membranes were evaluated through single gas permeation (H2), binary gas separation (n-butane/H2) and ternary vapour mixture of xylene isomers using the vapour permeation (VP) method with p-Xylene as the target product. After evaluating the xylene isomer separation performance of the membranes, the membranes were used in extractor-type catalytic membrane reactors to carry out m-Xylene isomerization over Pt-HZSM-5 catalyst with p-Xylene as the target product. This dissertation has shown that nanocomposite MFI-alumina membrane tubes and hollow fibre membranes were selective to p-Xylene from xylene isomers. The dissertation also reports for the first time in open literature the excellent xylene separation performance of nanocomposite MFI-alumina membrane tubes at higher xylene loading (or vapour pressure). Unlike their film-like counterparts, the membranes still maintain increased selectivity to p- Xylene at higher xylene vapour pressures without showing a drastic decrease in selectivity. This outstanding property makes it a promising choice for pervaporation applications where concentration profile is usually a major problem at higher loading of xylene. With the use of nanocomposite MFI-alumina hollow fibre membranes, this research has demonstrated that membrane configuration and effective membrane wall thickness play a prominent role in enhancing cross membrane flux. Results presented in the study show, for the first time in open literature, that nanocomposite MFI-alumina hollow fibre membrane could enhance p-Xylene fluxes during the separation of ternary vapour mixture of xylene due to the smaller effective wall thickness of the membrane (membrane thickness <1 μm) when compared to conventional randomly oriented MFI zeolite films (membrane thickness >3 μm). During xylene isomers separation with nanocomposite hollow fibre membrane, about 30% increase in p-Xylene flux was obtained compared to the membrane tubes, operated under the same conditions. Additionally, hollow fibres offer the added advantage of membrane surfaceto- volume ratios as high as 3000 m2/m3 compared to conventional membrane tubes. Using this type of system could be instrumental in reducing both the size and cost of permeating modules for future xylene separation processes. However, obtaining high quality nanocomposite MFI-alumina membrane fibres is subject to the availability of high quality fibre supports. Regarding the application of nanocomposite MFI-alumina membrane tubes as extractor-type catalytic membrane reactors (referred to as extractor-type zeolite catalytic membrane reactor (e-ZCMR) in this study) for m-Xylene isomerization over Pt-HZSM-5, the results presented in this study further substantiate and confirm the potentials of e-ZCMRs over conventional fixed-bed reactors (FBRs). In the combined mode (products in the permeate plus products in the retentate), the e-ZCMR displayed 16-18% increase in p-Xylene yield compared to an equivalent fixed-bed reactor operated at the same operating conditions. On the basis of the high p-Xylene-to-o-Xylene (p/o) and p-Xylene-to-m-Xylene (p/m) separation factors offered by the membranes, p-Xylene compositions in the permeate-only mode (products in the permeate stream) in the range 95%-100% were obtained in the e-ZCMR. When a defect-free nanocomposite MFI-alumina membrane tube with p-Xylene-too- Xylene (p/o) separation factor >400 was used, ultra pure p-Xylene with p-Xylene purity approaching 100% in the permeate-only mode was obtained. Moreover, the e-ZCMR displayed 100% para-selectivity in the permeate-only mode throughout the temperatures tested. This is not possible with conventional film-like MFI-type zeolite membranes. Therefore, the application of nanocomposite MFI-alumina membranes in extractor-type catalytic membrane reactors could catalyse the development of energy-efficient membrane-based process for the production of high purity p-Xylene. Furthermore, in this dissertation, a report on modelling and sensitivity analysis of an e-ZCMR equipped with a nanocomposite MFI-alumina membrane tube as separation unit for m-Xylene isomerization over Pt-HZSM-5 catalyst is presented. The model output is in fair agreement with the experimental results with percentage errors (absolute) of 17%, 29%, 0.05% and 19.5% for p-Xylene yield in combined mode, p-Xylene selectivity in combined mode, p-Xylene selectivity in permeate-only mode and m-Xylene conversion, respectively. Therefore, the model is adequate to explain the behaviour of e-ZCMR during m-Xylene isomerization over Pt-HZSM-5 catalyst. The model is also adaptable to e-ZCMRs of different configurations such as hollow fibre MFI-alumina membrane-based e-ZCMRs. To gain more insight into the behaviour of the model to small changes in certain design parameters, sensitivity analysis was performed on the model. As expected, the sensitivity analysis revealed that intrinsic property of membrane (porosity, tortuosity), membrane effective thickness and reactor size (indicated with reactor internal diameter) play a significant role on the performance of e-ZCMR during p-Xylene production from the mixed xylenes. MFI-alumina zeolite membranes with optimized parameters such as membrane porosity, membrane tortuosity, and membrane effective wall thickness might enhance transport of p-Xylene through the membrane and thus resulting in higher p-Xylene flux through the membrane. This eventually would translate into an increase in p-Xylene yield in permeate-only mode. As far as it could be ascertained, this is the first report in open literature on modelling study with sensitivity analysis of e-ZCMR equipped with nanocomposite MFI-alumina membrane tubes as separation unit for m-Xylene isomerization over Pt-HZSM- 5 catalyst. In addition, the results of this study have confirmed previous research efforts reported on the application of extractor-type catalytic membrane reactors, having MFI-type membranes as separation units, for p-Xylene production via m-Xylene isomerization over a suitable catalyst. Also, new ideas were developed, tested and proposed that now provide a solid basis for further scale-up and techno-economical studies. Such studies are necessary to evaluate the competitiveness of the technology with the traditional processes for the production of high purity p-Xylene from mixed xylene. In summary, the encouraging results, as documented in this dissertation and also communicated to researchers in the area of membrane-based reactive separation (in the form of four peer-reviewed international scientific publications and four conference proceedings), could provide a platform for developing a scaled-up membrane-based energy-efficient industrial process for producing high purity p-Xylene through isomerization. / AFRIKAANSE OPSOMMING: Die produksie van chemiese stowwe word belemmer deur die uitdaging van beperkte materiaal- en energiebronne. Prosesuitbreiding kan egter ‘n noemenswaardige rol in die verligting van hierdie probleem speel. Die moontlike gebruik van multi-funksionele reaktore in prosesuitbreiding het navorsing in membraan-gebaseerde reaktiewe skeidingsprosesse (waar membraanskeiding en die katalitiese reaksie gelyktydig in ‘n enkele eenheid plaasvind) aangemoedig. Hierdie prosesse is aantreklik omdat hulle potensieel kompak en minder kapitaal-intensief is en ook teen laer koste as tradisionele prosesse bedryf kan word. Dit is ook dikwels die geval dat die multi-funksionele reaktor die selektiwiteit en opbrengs van die gewenste produk verhoog. In die afgelope drie dekades was daar ’n sterk verandering in die tegnologie wat gebruik word in die produksie van p-Xileen, met vele verbeterings aan nuwe toerusting wat in die nywerheid in bedryf gestel is. Hierdie verbeteringe hou gewoonlik ekonomiese-, sowel as bedryfsvoordele vir die produsente in. Ontwikkelings in hierdie veld is noodsaaklik aangesien die kapitale uitgawes vir die toerusting om p-Xileen, veral baie suiwer p-Xileen, van xileenpolimere te produseer en te skei, steeds baie hoog is. Met talle voordele gekoppel aan membraangebaseerde reaktiewe skeidingsprosesse in vergelyking met normale prosesse, is die navorsing egter gekanaliseer na die gebruik van MFI-tipe zeolietmembrane vir die in-situ skeiding en isomerisasie van xileen in ekstraksie-tipe katalitiese membraanreaktore. As bydrae tot hierdie navorsingsveld het hierdie studie op die karakterisering en optimering van ‘n ekstraksie-tipe katalitiese membraanreaktor (e-KMR), toegerus met ’n nanosaamgestelde MFI-alumina membraan as skeidingseenheid vir m-Xileen isomerisasie in die teenwoordigheid van ‘n Pt-HZSM-5 katalis, gefokus. Nanosaamgestelde MFI-alumina zeolietmembrane (buise en hol vesels) wat in hierdie studie gebruik is, is voorberei deur die sogenaamde “hidrotermiese porie-sperring sintese tegniek” wat meer as ‘n dekade gelede ontwikkel is deur Dalmon en sy groep. In hierdie tegniek word MFI-materiaal gekweek deur direkte hidrotermiese sintese in ‘n poreuse matriks, eerder as die vorming van dun films bo-op die ondersteuningsbasis. Die voordele van hierdie ontwerp bo dié van die konvensionele filmagtige zeolietmembrane sluit in: (i) minimering van die effek van termiese uitsetting op die gaping tussen die ondersteuningsbasis en die zeoliet, (ii) die gemak van opskalering, en (iii) die gemak waarmee die modules aanmekaar gesit kan word, omdat die skeidingslaag (zeolietkristalle) binne die porieë van die keramiek-ondersteuningsbasis geleë is, wat die effek van erodering en termiese skok verminder. Ná die membraansintese is die membraankwaliteit en skeidingsvermoë geevalueer deur enkel-gas-deurdringing (H2), binêre-gas-skeiding (n-butaan/H2), en ternêre dampmengsel van xileen-isomere deur die gebruik van die damp-deurdringingsmetode met p-Xileen as die teikenproduk. Hierdie tesis het gewys dat nanosaamgestelde MFI-alumina membraanbuise en hol vesel membrane selektief was ten opsigte van p-Xileen vanuit xileen-isomere. Die tesis doen ook, vir die eerste keer in die oop literatuur verslag, oor die uitstekende p-Xileen skeidingsvermoë van nanosaamgestelde MFI-alumina buise by hoër xileenladings (of dampdrukke). Anders as hulle filmagtige eweknieë het die membrane steeds hul verhoogde selektiwiteit vir p-Xileen by hoër dampdrukke behou, sonder ‘n merkbare verlaging in die selektiwiteit. Hierdie merkwaardige eienskap maak dit ‘n belowende keuse vir pervaporasie toepassings, waar die konsentrasieprofiel (as gevolg van hoër xileenladings) gewoonlik ’n noemenswaardige probleem is. Met die gebruik van nanosaamgestelde MFI-alumina membrane het hierdie navorsing gewys dat membraankonfigurasie en –wanddikte ‘n prominente rol speel in die verbetering van vloei oor die membraan. Resultate wat in die studie voorgelê word, wys, vir die eerste keer in oop literatuur, dat hol vesel nanosaamgestelde MFI-alumina membrane die deurvloei van p-Xileen kan verbeter gedurende die skeiding van ternêre dampmengsels van xileen, as gevolg van die kleiner effektiewe wanddikte van die membraan (<1 μm) wanneer dit vergelyk word met konvensionele kansgewys-geörienteerde MFI-zeoliet films met ‘n membraandikte van >3 μm. Tydens die skeiding van xileen-isomere met nanosaamgestelde hol vesel membrane is ‘n verbetering van ongeveer 30 % in die deurvloei van p-xileen verkry, vergeleke met membraanbuise, by identiese bedryfstoestande. Hol vesels bied ook die verdere voordeel van oppervlak-tot-volume verhoudings van so hoog as 3000 m2/m3 vergeleke met konvensionele membraanbuise. Die gebruik van hierdie tipe sisteem kan deurslaggewend wees in die vermindering van die grootte en koste van deurlatingseenhede in toekomstige xileen-skeidingsprosesse. Die vervaardiging van hoë-kwaliteit nanosaamgestelde MFIalumina membraanvesels is egter onderworpe aan die beskikbaarheid van hoë-kwaliteit vessel-ondersteuningsbasisse. Wat die gebruik van nanosaamgestelde MFI-alumina membraanbuise as ekstraksietipe katalitiese membraanreaktore betref (ekstraksie-tipe zeoliet katalitiese membraanreaktor, of e-ZKMR in hierdie studie) vir m-Xileen isomerisasie in die teenwoordigheid Pt-HZSM-5, bevestig die resultate die potensiaal van e-ZKM reaktore bo konvensionele vaste-bed reaktore (VBR). In die gekombineerde verstelling (met produkte in die permeaat sowel as die retentaat) toon die e-ZKMR ‘n 16 – 18% verbetering in die opbrengs van p-Xileen vergeleke met ‘n ekwivalente VBR by dieselfde bedryfskondisies. Gegrond op die hoë p-Xileen-tot-o- Xileen (p/o) en p-Xileen-tot-m-Xileen (p/m) skeidingsfaktore wat deur die membraan gebied word, is p-Xileen-samestellings in die slegs-permeaat verstelling (produkte in die permeaatstroom) van tussen 95 en 100% in die e-ZKMR verkry. Toe ‘n defek-vrye nanosaamgestelde MFI-alumina membraanbuis met ‘n (p/o) skeidingsfaktor van >400 gebruik is, is p-Xileen met ‘n suiwerheid na aan 100% in die slegs-permeaat verstelling verkry. Die e-ZKMR het ook 100% para-selektiwiteit in die slegs-permeaat verstelling getoon by alle toets-temperature, iets wat onmoontlik is met gewone filmagtige MFI-tipe zeolietmembrane. Om hierdie rede is dit moontlik dat die gebruik van MFI-alumina membrane in ekstraksie-tipe katalitiese membraanreaktore die ontwikkeling van energie-doeltreffende membraangebaseerde prosesse vir die produksie van suiwer p-Xileen kan bevorder. Verder word daar in hierdie tesis verslag gedoen oor die modelering en sensitiwiteitsanalise van ‘n e-ZKMR wat toegerus is met ‘n nanosaamgestelde MFI-alumina membraanbuis as skeidingseenheid vir m-Xileen isomerisasie in die teenwoordigheid van ‘n Pt-HZSM-5 katalis. Die model-uitsette is redelik in ooreenstemming met eksperimentele resultate met absolute fout-persentasies van 17, 27, 0.05 en 19.5 % vir die p-Xileen opbrengs in die gekombineerde verstelling, p-Xileen selektiwiteit in die gekombineerde verstelling, p-Xileen selektiwiteit in die slegs-permeaat verstelling en m-Xileen omsetting, onderskeidelik. Om hierdie rede kan die model die gedrag van ‘n e-ZKMR verduidelik tydens die m-Xileen isomerisasie in die teenwoordigheid van ‘n Pt-HZSM-5 katalis. Die model kan ook aangepas word na e-ZKM reaktore met verskillende konfigurasies, soos hol vesel MFIalumina membraan-gebaseerde e-ZKMRe. Om meer insig te kry in die gedrag van die model op klein veranderinge in sekere ontwerpparameters, is ‘n sensitiwiteitsanalise op die model uitgevoer. Soos verwag, het die sensitiwiteitsanalise gewys dat die intrinsieke eienskappe van die membraan (porositeit, tortuositeit), die effektiewe van membraandikte en die reaktorgrootte (gemeet as die interne deursnit van die reaktor) ‘n noemenswaardige rol speel in die gedrag van die e-ZKMR gedurende p-Xileen produksie vanuit gemengde xilene. MFI-alumina zeolietmembrane met geoptimeerde parameters soos membraanporositeit, -tortuositeit, en –wanddikte mag dalk die oordrag van p-Xileen deur die membraan bevorder en sodoende ‘n hoër vloei van p-Xileen oor die membraan bewerkstellig. Dit sal uiteindelik lei tot ‘n verhoging in die opbrengs van p-Xileen in die slegs-permeaat verstelling. So ver dit vasgestel kon word, is hierdie die eerste verslag in die oop literatuur wat die modelering en sensitiwiteitsanalise van ‘n e-ZKMR, toegerus met nanosaamgestelde MFIalumina membraanbuise as skeidingseenheid vir m-Xileen isomerisasie in die teenwoordigheid van ‘n Pt-HZSM katalis, aanspreek. Verder ondersteun die resultate van hierdie studie vorige navorsingspogings op die gebruik van e-KMRe, met MFI-tipe membrane as skeidingseenhede, vir die produksie van p-Xileen deur middel van m-Xileen isomerisasie in die teenwoordigheid van ‘n geskikte katalis. Verder is nuwe idees ontwikkel, getoets en voorgestel wat dien as ’n stewige basis vir verdere opskalering- en tegno-ekonomiese studies. Sodanige studies is nodig om die vatbaarheid van die tegnologie relatief tot die tradisionele prosesse te bepaal. Ter opsomming, die bemoedigende resultate, soos in die tesis gedokumenteer (en ook gepubliseer in vier ewe-knie beoordeelde internasionale wetenskaplike joernale en vier konferensiestukke), kan as ‘n platform dien vir die ontwikkeling van ’n opgeskaleerde membraan-gebaseerde energie-doeltreffende nywerheidsproses vir die produksie van suiwer p-Xileen deur middel van isomerisasie.

Thesis (PhD (Process Engineering))--University of Stellenbosch, 2010. / Dissertation presented for the Degree of DOCTOR OF PHILOSOPHY (Extractive Metallurgical Engineering) in the Department of Process Engineering at the University of Stellenbosch / ENGLISH ABSTRACT: Fault diagnosis is an important component of process monitoring, relevant in the greater context of developing safer, cleaner and more cost efficient processes. Data-driven unsupervised (or feature extractive) approaches to fault diagnosis exploit the many measurements available on modern plants. Certain current unsupervised approaches are hampered by their linearity assumptions, motivating the investigation of nonlinear methods. The diversity of data structures also motivates the investigation of novel feature extraction methodologies in process monitoring. Random forests are recently proposed statistical inference tools, deriving their predictive accuracy from the nonlinear nature of their constituent decision tree members and the power of ensembles. Random forest committees provide more than just predictions; model information on data proximities can be exploited to provide random forest features. Variable importance measures show which variables are closely associated with a chosen response variable, while partial dependencies indicate the relation of important variables to said response variable. The purpose of this study was therefore to investigate the feasibility of a new unsupervised method based on random forests as a potentially viable contender in the process monitoring statistical tool family. The hypothesis investigated was that unsupervised process monitoring and fault diagnosis can be improved by using features extracted from data with random forests, with further interpretation of fault conditions aided by random forest tools. The experimental results presented in this work support this hypothesis. An initial study was performed to assess the quality of random forest features. Random forest features were shown to be generally difficult to interpret in terms of geometry present in the original variable space. Random forest mapping and demapping models were shown to be very accurate on training data, and to extrapolate weakly to unseen data that do not fall within regions populated by training data. Random forest feature extraction was applied to unsupervised fault diagnosis for process data, and compared to linear and nonlinear methods. Random forest results were comparable to existing techniques, with the majority of random forest detections due to variable reconstruction errors. Further investigation revealed that the residual detection success of random forests originates from the constrained responses and poor generalization artifacts of decision trees. Random forest variable importance measures and partial dependencies were incorporated in a visualization tool to allow for the interpretation of fault conditions. A dynamic change point detection application with random forests proved more successful than an existing principal component analysis-based approach, with the success of the random forest method again residing in reconstruction errors. The addition of random forest fault diagnosis and change point detection algorithms to a suite of abnormal event detection techniques is recommended. The distance-to-model diagnostic based on random forest mapping and demapping proved successful in this work, and the theoretical understanding gained supports the application of this method to further data sets. / AFRIKAANSE OPSOMMING: Foutdiagnose is ’n belangrike komponent van prosesmonitering, en is relevant binne die groter konteks van die ontwikkeling van veiliger, skoner en meer koste-effektiewe prosesse. Data-gedrewe toesigvrye of kenmerkekstraksie-benaderings tot foutdiagnose benut die vele metings wat op moderne prosesaanlegte beskikbaar is. Party van die huidige toesigvrye benaderings word deur aannames rakende liniariteit belemmer, wat as motivering dien om nie-liniêre metodes te ondersoek. Die diversiteit van datastrukture is ook verdere motivering vir ondersoek na nuwe kenmerkekstraksiemetodes in prosesmonitering. Lukrake-woude is ’n nuwe statistiese inferensie-tegniek, waarvan die akkuraatheid toegeskryf kan word aan die nie-liniêre aard van besluitnemingsboomlede en die bekwaamheid van ensembles. Lukrake-woudkomitees verskaf meer as net voorspellings; modelinligting oor datapuntnabyheid kan benut word om lukrakewoudkenmerke te verskaf. Metingbelangrikheidsaanduiers wys watter metings in ’n noue verhouding met ’n gekose uitsetveranderlike verkeer, terwyl parsiële afhanklikhede aandui wat die verhouding van ’n belangrike meting tot die gekose uitsetveranderlike is. Die doel van hierdie studie was dus om die uitvoerbaarheid van ’n nuwe toesigvrye metode vir prosesmonitering gebaseer op lukrake-woude te ondersoek. Die ondersoekte hipotese lui: toesigvrye prosesmonitering en foutdiagnose kan verbeter word deur kenmerke te gebruik wat met lukrake-woude geëkstraheer is, waar die verdere interpretasie van foutkondisies deur addisionele lukrake-woude-tegnieke bygestaan word. Eksperimentele resultate wat in hierdie werkstuk voorgelê is, ondersteun hierdie hipotese. ’n Intreestudie is gedoen om die gehalte van lukrake-woudkenmerke te assesseer. Daar is bevind dat dit moeilik is om lukrake-woudkenmerke in terme van die geometrie van die oorspronklike metingspasie te interpreteer. Verder is daar bevind dat lukrake-woudkartering en -dekartering baie akkuraat is vir opleidingsdata, maar dat dit swak ekstrapolasie-eienskappe toon vir ongesiene data wat in gebiede buite dié van die opleidingsdata val. Lukrake-woudkenmerkekstraksie is in toesigvrye-foutdiagnose vir gestadigde-toestandprosesse toegepas, en is met liniêre en nie-liniêre metodes vergelyk. Resultate met lukrake-woude is vergelykbaar met dié van bestaande metodes, en die meerderheid lukrake-woudopsporings is aan metingrekonstruksiefoute toe te skryf. Verdere ondersoek het getoon dat die sukses van res-opsporing op die beperkte uitsetwaardes en swak veralgemenende eienskappe van besluitnemingsbome berus. Lukrake-woude-metingbelangrikheidsaanduiers en parsiële afhanklikhede is ingelyf in ’n visualiseringstegniek wat vir die interpretasie van foutkondisies voorsiening maak. ’n Dinamiese aanwending van veranderingspuntopsporing met lukrake-woude is as meer suksesvol bewys as ’n bestaande metode gebaseer op hoofkomponentanalise. Die sukses van die lukrake-woudmetode is weereens aan rekonstruksie-reswaardes toe te skryf. ’n Voorstel wat na aanleiding van hierde studie gemaak is, is dat die lukrake-woudveranderingspunt- en foutopsporingsmetodes by ’n soortgelyke stel metodes gevoeg kan word. Daar is in hierdie werk bevind dat die afstand-vanaf-modeldiagnostiek gebaseer op lukrake-woudkartering en -dekartering suksesvol is vir foutopsporing. Die teoretiese begrippe wat ontsluier is, ondersteun die toepassing van hierdie metodes op verdere datastelle.

Thesis (PhD (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The ongoing trend in papermaking industries is to lower production costs by increasing the low cost filler content in the sheets. However, the disruption of inter-fibre bonding is accompanied by a deterioration of paper stiffness and mechanical properties if filler content exceeds 18 wt%. Polysaccharide solutions, such as starch, are often used as a low cost biodegradable additive to improve internal sheet strength when added to the wet-end of production. The amount of starch that can be added is however limited as only a small percentage will be retained in the paper web. A dual additive multifunctional polysaccharide system was developed to allow higher filler loading levels without detrimental deterioration in paper properties. In order to achieve a larger surface area for fibre/filler interaction and to reduce drainage losses, at least one of these additives was in particulate form. Anionic, cationic, and unsaturated derivatives were prepared using sodium monochloroacetate, 3-chloro-2-hydroxypropyltrimethylammonium chloride, and allyl bromide, respectively. The degree of substitution was determined by 1H-NMR spectroscopy and back titration methods and the interaction of the ionic modified derivatives with paper components was determined using fluorescence microscopy. Anionic modified polysaccharide particles were prepared using techniques such as macrogel ultrasonification, water-in-water emulsification, and in-situ cross-linking and carboxymethylation of granular starch. A process of adding sequential layers of oppositely charged polyelectrolyte layers onto the filler particles was also investigated. A novel approach of preparing modified particles with tailored size and distribution using microfluidics was studied and modelled using response surface methodology. Hand sheets were prepared using the dual additive system and improvements in stiffness, tear resistance, breaking length, and folding endurance were observed. The modified granular maize starch particles had a pre-eminent effect on improving stiffness at higher filler loadings (14% improvement at 30 wt% filler loading), while bulky particles prepared using microfluidics showed a more consistent improvement (between 6% and 10%) across the loading range. Overall improvements gained by the introduction of multi-layered soluble polymers onto fillers suggest that the introduction of nanotechnology to the papermaking process should be of potential benefit to the industry. Furthermore, the dual additive system developed during the course of this study should also be tested on a continuous pilot plant papermaking process. / AFRIKAANSE OPSOMMING: Die papierindustrie neig voortdurend daarna om produksiekostes te verlaag deur die persentasie lae koste vulstof wat gebruik word te verhoog. Aangesien die vulstof vesel kontak belemmer, gaan hoër vlakke (> 18 wt%) egter gepaard met ’n verlaging in papier styfheid en meganiese eienskappe. Polisakkaried oplossings, soos byvoorbeeld stysel, word dikwels gebruik as lae koste vergaanbare bymiddel om papier intern te versterk wanneer dit voor die vormingsproses bygevoeg word. Slegs ’n beperkte hoeveelheid stysel word egter behou in die papier matriks en oormatige oplossings ontsnap tydens dreinering in die afvalwater. ’n Dubbele multi-funksionele polisakkaried bymiddelsisteem was ontwikkel wat ongewensde verwakking in papiereienskappe verminder tydens vulstof verhogings. Ten minste een van die bymiddels was in partikelvorm om sodoende ’n groter oppervlak te bied vir vesel/vulstof interaksie en om dreineringsverliese te verminder. Anioniese, kationiese, sowel as onversadigde derivate was berei deur onderskeidelik gebruik te maak van natrium monochloroasetaat, 3-chloro-2-hidroksiepropieltrimetielammonium chloried, en alliel bromied. Die graad van substitutiese was bepaal met behulp van 1H-KMR spektroskopie sowel as titrasie tegnieke terwyl die ioniese interaksie van die gemodifiseerde stysels met die papierkomponente ondersoek was met behulp van fluoressensie mikroskopie. Anioniese polisakkaried partikels was berei met tegnieke soos makro-jel ultrasonifikasie, water-in-water emulsifikasie, en in-situ kruisbinding en karboksiemetielasie van stysel granulate. ’n Proses was ook ondersoek waar vulstof partikels omhul was in verskeie lae poliëlektroliet oplossings. ’n Nuwe benadering was toegepas waar gemodifiseerde partikels met voorafbepaalde grootte en verspreiding berei is deur gebruik te maak van mikrofluïdika en gemodelleer met behulp van oppervlakte ontwerp metodeleer. Papier toetse was uitgevoer met die bymiddelsisteem en algehele verbetering in styfheid, skeurweerstand, breeklengte, en voulydsaamheid is waargeneem. Die gemodifiseerde stysel granulate het die grootste verbetering in styfheid by hoë vulstofladings getoon (14% verbetering by 30 wt% vulstoflading) terwyl die groter mikrofluïdika-bereide partikels algehele verbetering (tussen 6% en 10%) getoon het oor die hele vulstoflading reeks. Die verbeteringe in styfheid sowel as meganiese eienskappe van papier voorberei met poliëlektroliet omhulde vulstof toon dat aanwending van nanotegnologie in hierdie bedryf potensieel voordelig kan wees. Opskalering van die polisakkaried bymiddels ontwikkel gedurende hierdie studie behoort uitgevoer te word vir verdere toetse op ’n kontinue papier loodsaanleg.