This thesis discusses the field of asymmetric synthesis of oxiranes. An introduction highlighting the most successful methods for the synthesis of chiral epoxides including the latest advances in these areas, with particular attention paid to the organocatalytic techniques is presented in chapter one. The second chapter begins by summarizing the group's previous efforts in the initial stage of this project and sets the motif for this work. These include: the synthesis of enantiopure dihyroisoquinolinium salts with a chiral residue attached to the exocyclic carbon-nitrogen bond as catalysts for asymmetric epoxidation; utilizing systems such as camphor and natural amino acids as starting points for these syntheses; developing other catalyst families in order to delve into the possibility of eliminating the structural weaknesses leading to loss of enantioselectivity in the oxygen transfer process; attempts to probe the reactive intermediates responsible for the asymmetric induction by analytical techniques; checking for catalyst applicability with different alkene and sulphide substrates; the development of anhydrous reaction conditions and their testing with the successful catalysts prepared. Enantiomeric excesses of up to 70% have been obtained. An attempt at exploring the synthesis of chiral reagents for the asymmetric epoxidation via a Payne/peroxyacid route is also described. This chapter concludes with a comparison of the catalyst families generated, and presents a few suggestions for future research in this area. The third chapter is dedicated to, the experimental section and includes the methods of synthesis and characterization of the compounds in the results and discussion chapter. There are three appendices at the. end of the thesis; Appendix A contains a summary the X-ray reports regarding the crystallographic data of the compound structures presented in chapter two. Appendix B contains samples of the analytical spectra of the enantiomeric excess determination for epoxides. Appendix C includes a copy of both publications I was involved in during my research in this topic.

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Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Bioconversion of hydrocarbons to value-added intermediates and products has significant industrial potential using both prokaryotic and eukaryotic organisms. In particular, alkanes can be converted to an expansive range of commercially important products using aerobic bioprocesses under mild process conditions. Coupled with the relative abundance of alkanes derived from gas to liquid (GTL) technologies, such as those employed by SASOL, South Africa, the commercial potential for bioconverison of alkanes is large. However, unlike carbohydrate substrates, alkane feedstocks are devoid of oxygen in their molecular structure. This means that the entire oxygen demand needs to be met by oxygen transfer. Furthermore, a decline in oxygen transfer in aqueous-hydrocarbon dispersions with increasing alkane concentration has been observed to result from depression of the overall volumetric oxygen transfer coefficient (KLa). Therefore, understanding KLa and the fundamental parameters underpinning its behaviour is critical to ensuring the bioprocess is kinetically, rather than transport, limited in terms of both operation and scale-up. Previous studies have examined KLa in aerated-alkane-aqueous systems. In light of the importance of oxygen transfer in bioprocesses, this study expands on the KLa understanding in 3-phase studies by including a fourth solid phase, thus more closely representing a hydrocarbonbased bioprocess. The project aimed to determine the impact of agitation, alkane concentration and solid loading on the Sauter mean bubble diameter (DSM), gas hold-up and specific interfacial area (a) and correlate these parameters to KLa. This ultimately determined which parameter was dominant over a range of process conditions. Furthermore, concurrent measurement of the KLa and interfacial area meant the behaviour of the liquid side oxygen transfer coefficient (KL) could be defined, providing further insight into how changes in the process conditions impact on KLa. Experiments were conducted in a 5 litre stirred tank bioreactor containing n-C14-20 straight chain alkane, sparged with air at 0.8 vvm. In line with process conditions typical of a hydrocarbonbased bioprocess, KLa and a were measured for agitation rates from 450 to 1000 RPM, alkane concentrations from 2 to 20% v/v and yeast solids from 1 to 10 g/l. KLa was measured using the gassing out procedure using a dissolved oxygen (DO) probe which measured the response of the system to a step change in the sparge gas oxygen pressure. The probe response lag ( P), equal to the time taken for the probe to reach 63.2% of the saturation DO concentration, was determined for every set of process conditions. The inverse of P, KP was taken into account when calculating KLa from the DO probe response. The area was calculated from DSM and gas hold-up. DSM was quantified using high speed photography and image analysis was performed in Matlab® using bespoke routines. Elimination of optical distortion and the development of an adequate light source was key to acquiring clear images. Both KLa and interfacial area were found to be affected by changes in agitation, alkane concentration and yeast loading. An increase in agitation increased the KLa over the entire range of alkane concentration and yeast loading. Similarly, an increase in agitation resulted in an increase in interfacial area, underpinned by a decrease in the DSM. It is therefore likely that the interfacial area plays a dominant role in defining KLa when considering an increase in agitation. Increases in alkane concentration resulted in a peak in KLa between 2.5 and 5% alkane concentration while further increases in alkane concentration depressed KLa. This peak was not observed in interfacial area, where an increase in alkane concentration resulted only in a decrease in interfacial area, thus indicating a positive influence of KL on KLa at low alkane concentrations. Further increases in alkane concentration beyond those creating the peak KLa resulted in KLa depression, suggesting that the increasing viscosity imparted by the alkane decreases both KL and interfacial area. Increased yeast loading had opposing effects at low and high agitation rates. At low agitation rates, increased loadings were observed to increase KLa, while increased loadings at high agitation rates caused a decrease in KLa. This behaviour was also evident in interfacial area, suggesting that in this regime KLa was defined by interfacial area behaviour. Increased yeast loading was observed to depress the KLa for all alkane concentrations when examined at a constant midpoint agitation rate. This trend was not evident in interfacial area, which increased with increasing yeast loading at the same agitation rate. The positive influence of yeast on interfacial area was likely caused by adhesion of the yeast particles to the bubble surface, lowering the DSM by preventing coalescence. The disagreement between the KLa and interfacial area results suggested that yeast loading impacted negatively on KL, which had an over-riding negative impact on KLa. The use of reliable methods for the determination of both interfacial area and KLa were demonstrated for application in model hydrocarbon-based bioprocesses. The combined results offer a unique insight into how changes in the process conditions impact independently on KL and interfacial area, which when combined ultimately defined the KLa behaviour. Quantification of the relative magnitude of the impact each parameter had on KLa contributed toward a fundamental understanding of oxygen transfer in model hydrocarbon-based bioprocesses. / AFRIKAANSE OPSOMMING: Biologiese omsetting van koolwaterstowwe na produkte met finansiële waarde het beduidende industriële potensiaal met behulp van beide prokariotiese en eukariotiese organismes. In die besonder, kan alkane omgeskakel word na ’n uitgebreide reeks van kommersieel belangrike produkte met behulp van aerobiese bioprosesse onder ligte proses voorwaardes. Tesame met die relatiewe oorvloed van alkane afgelei van GTL tegnologie, soos dié van Sasol, Suid-Afrika, die kommersiële potensiaal vir bioconverison van alkane is groot. Maar, in teenstelling koolhidrate substrate, alkaan voerstowwe is beroof van suurstof in hul molekulêre struktuur. Dit beteken dat die hele suurstof vereiste moet nagekom word deur suurstof oordrag. Verder het ’n afname in suurstof oordrag in waterige-koolwaterstof dispersies met toenemende alkaan konsentrasie waargeneem te lei van depressie van die algehele volumetriese suurstofoordragkoëffisiënt (KLa). Daarom verstaan KLa en die fundamentele parameters onderliggend sy gedrag is van kritieke belang om te verseker dat die bioprocess is kineties, eerder as vervoer, beperk in terme van beide werking en skaal-up van bioprosesse. Vorige studies het KLa in deurlug-alkaan-waterige stelsels ondersoek. In die lig van die belangrikheid van suurstof oordrag in bioprosesse hierdie studie brei uit op die KLa begrip in driefase studies deur die insluiting van ’n vierde soliede fase, dus meer nou wat ’n koolwaterstofgebaseerde bioprocess. Die doel van die projek is om die impak van vermengingstempo, alkaan konsentrasie en soliede inhout op die Sauter gemiddelde borrel deursnee (DSM), gas-vasvanging en spesifieke gas-vloistof oppervlakarea (a) te kwantifiseer en korreleer met KLa gedrag. Dit sou defineer die dominante parameter oor ’n verskeidenheid van proses voorwaardes. Verder, gelyktydige meting van die KLa en oppervlakarea kan die gedrag van die vloeistof-kant suurstofoordragkoëffisiënt (KL) gedefinieer. Dit sal verskaf verdere insig in hoe die veranderinge in die proses voorwaardes impak op KLa. Eksperimente was uitgevoer in ’n 5 liter belugte geroerde tenk bioreaktor bevat n - C14-20 reguitketting alkane, met lug met lug deurgeborrel by 0.8 VVM. In lyn met die proses voorwaardes tipies van ’n koolwaterstof-gebaseerde bioprocess, KLa en a was gemeet vir vermengignstempos van 450-1000 RPM, alkaan konsentrasies van 2-20 % v/v en gis vastestowwe van 1 tot 10 g / l. KLa is gemeet deur die vergassinguit prosedure met behulp van ’n suurstofmeter wat die reaksie van die stelsel na ’n stap verandering in die voer gas suurstof druk gemeet het. Die suurstofmeter reaksie vertraging ( P), gelyk aan die tyd wat dit neem vir die suurstofmeter 63.2 % van die versadiging DO konsentrasie te bereik, is bepaal vir elke procesopset. Die inverse van P, KP is in ag geneem by die berekening van KLa uit die suurstofmeter reaksie. Die gas-vloistof oppervlak is bereken vanaf DSM en gas hold-up. DSM is gekwantifiseer met behulp van hoë spoed fotografie en beeld analise is uitgevoer in Matlab ® roetines. Uitskakeling van optiese vervorming en die ontwikkeling van ’n voldoende ligbron was die sleutel tot die verkryging van helder beelde. Beide KLa en grens oppervlakarea gevind geraak word deur veranderinge in vermengignstempo, alkaan konsentrasie en gis laai. ’N toename in geroer het die KLa verbeter oor die hele reeks van alkaan konsentrasie en gis laai. Net so, ’n toename in geroer het gelei tot ’n toename in grens oppervlak, ondersteun deur ’n afname in die DSM. Dit is dus waarskynlik dat die grens oppervlak speel ’n dominante rol in die definisie van KLa by die oorweging van ’n toename in roering. Stygings in alkaan konsentrasie gelei tot ’n hoogtepunt in KLa tussen 2.5 en 5 % alkaan konsentrasie terwyl verdere verhogings in alkaan konsentrasie druk die KLa af. Die piek was nie in oppervlakarea duidelik, waar ’n toename in alkaan konsentrasie gelei net tot ’n afname in oppervlakarea, dus dui op ’n positiewe invloed van KL op KLa teen lae alkaan konsentrasies waargeneem. Verdere stygings in alkaan konsentrasie verder as die skep van die piek KLa gelei tot KLa depressie, wat daarop dui dat die toenemende viskositeit meegedeel deur die alkaan verminder beide KL en grens oppervlak. Verhoogde gis laai het opponerende effekte teen ’n lae en hoë vermengingstempo. By lae vermengingstempo, ’n verhoging in gis laai waargeneem KLa te verhoog, terwyl ’n verhoging in gis laai op ’n hoë vermengingstempo veroorsaak ’n afname in KLa . Hierdie gedrag was ook duidelik in grens oppervlak, wat daarop dui dat daar in hierdie regime KLa gedefinieer deur grens oppervlak gedrag. Verhoogde gis laai waargeneem die KLa te onderdruk vir alle alkaan konsentrasies wanneer ondersoek teen ’n konstante middelpunt vermengingstempo. Hierdie tendens was nie duidelik in tussenvlak gebied, wat verhoog met toenemende gis laai op dieselfde geroer koers. Die positiewe invloed van gis op grens oppervlak is waarskynlik veroorsaak deur adhesie van die gis deeltjies aan die borrel oppervlak, die verlaging van die DSM deur die voorkoming van die saamsmelting van gasborrels. Die meningsverskil tussen die KLa en grens oppervlakarea resultate voorgestel dat gis laai negatiewe uitwerking op KL, met ’n dominante negatiewe impak op KLa. Die gebruik van ’n betroubare metodes vir die bepaling van beide oppervlakarea en KLa gedemonstreer vir toepassing in model koolwaterstof-gebaseerde bioprosesse. Die gekombineerde resultate bied ’n unieke insig in hoe die veranderinge in die proses voorwaardes impak onafhanklik op KL en oppervlakarea, wat wanneer gekombineer gedefinieer die KLa gedrag. Kwantifisering van die relatiewe grootte van die impak elke parameter het op KLa bygedra tot ’n fundamentele begrip van suurstof oordrag in model koolwaterstof-gebaseerde bioprosesse.

No description available.

The objective of this research was to characterize the performance of a downflow bubblecontact (DBCA) hypolimnetic aerator — Speece Cone-. The effect of two key design factors, inlet water velocity and the ratio of gas flow rate to water flow rate on four standard units of measure was examined: (a) the Oxygen Transfer Coefficient, KLa, corrected to 20°C, KLa₂₀ (hr­-¹), (b) the Standard Oxygen Transfer Rate, SOTR (g0₂.hr­-¹) (c) the Standard Aeration Efficiency, SAE (gO₂kWhr­-¹), and (d) the Standard Oxygen Transfer Efficiency, SOTE (%). Two sources of oxygen, Pressure Swing Adsorption (PSA) oxygen (87% purity) and air, were compared. KLa₂₀, SOTR, and SAE increased with an increase in the ratio of gas flow rate to water flow rate for both air and oxygen, over a range of 0.5% to 5.0%; while SAE deceased. An increase in inlet water velocity resulted in a decrease in KLa, corrected to 20°C, SOTR, and SAE, but an increase in the SOTE. Treatments on air showed similar, but much less dramatic effect of the gas flow rate to water flow rate ratio and water inlet velocity on KLa₂₀, SOTE, SAE, and SOTE, when compared to treatments on PSA oxygen. The best performance was achieved with an inlet water velocity of 6.9-7.6 ms­-¹ and oxygen flow rate to water flow rate ratio of about 2.5%. At this combination, the SOTE was about 66-72%.

Aeration of wastewater is performed in many wastewater treatment plants to supply oxygen to microorganisms. To evaluate the performance of a single aerator or an aeration system, there is a standard method for oxygen transfer measurements in clean water used today. The method includes a model that describes the aeration process and the model parameters could be estimated using nonlinear regression. The model is a simplified description of the oxygen transfer which could possibly result in performance results that are not accurate. That is why many have tried to describe the aeration at other ways and with other parameters. The focus of this Master Thesis has been to develop alternative models which better describe the aeration that could result in more accurate performance results. Data for model evaluations have been measured in two different tanks with various numbers of aerators. Five alternative methods containing new models for oxygen transfer evaluation have been studied in this thesis. The model in method nr 1 assumes that the oxygen transfer is different depending on where in a tank the dissolved oxygen concentration is measured. It is assumed to be faster in a water volume containing air bubbles. The size of the water volumes and the mixing between them can be described as model parameters and also estimated. The model was evaluated with measured data from the two different aeration systems where the water mixing was relatively big which resulted in that the model assumed that the whole water volume contained air bubbles. After evaluating the results, the model was considered to maybe be useful for aeration systems where the mixing of the water volumes was relatively small in comparison to the total water volume. However, the method should be further studied to evaluate its usability. Method nr 2 contained a model with two separate model parameter, one for the oxygen transfer for the air bubbles and one for the oxygen transfer at the water surface. The model appeared to be sensitive for which initial guesses that was used for the estimated parameters and it was assumed to reduce the model’s usability. Model nr 3 considered that the dissolved oxygen equilibrium concentration in water is depth dependent and was assumed to increase with increasing water depth. Also this model assumed that the oxygen was transferred from both the air bubbles and at the water surface. The model was considered to be useful but further investigations about whether the saturation concentrations should be constant or vary with water depth should be performed. The other two methods contained models that were combinations of the previous mentioned model approaches but was considered to not be useful.

The objective of this research was to characterize the performance of a downflow bubblecontact (DBCA) hypolimnetic aerator — Speece Cone-. The effect of two key design factors, inlet water velocity and the ratio of gas flow rate to water flow rate on four standard units of measure was examined: (a) the Oxygen Transfer Coefficient, KLa, corrected to 20°C, KLa₂₀ (hr­-¹), (b) the Standard Oxygen Transfer Rate, SOTR (g0₂.hr­-¹) (c) the Standard Aeration Efficiency, SAE (gO₂kWhr­-¹), and (d) the Standard Oxygen Transfer Efficiency, SOTE (%). Two sources of oxygen, Pressure Swing Adsorption (PSA) oxygen (87% purity) and air, were compared. KLa₂₀, SOTR, and SAE increased with an increase in the ratio of gas flow rate to water flow rate for both air and oxygen, over a range of 0.5% to 5.0%; while SAE deceased. An increase in inlet water velocity resulted in a decrease in KLa, corrected to 20°C, SOTR, and SAE, but an increase in the SOTE. Treatments on air showed similar, but much less dramatic effect of the gas flow rate to water flow rate ratio and water inlet velocity on KLa₂₀, SOTE, SAE, and SOTE, when compared to treatments on PSA oxygen. The best performance was achieved with an inlet water velocity of 6.9-7.6 ms­-¹ and oxygen flow rate to water flow rate ratio of about 2.5%. At this combination, the SOTE was about 66-72%.

The objective of this research was to characterize the performance of a downflow bubblecontact (DBCA) hypolimnetic aerator — Speece Cone-. The effect of two key design factors, inlet water velocity and the ratio of gas flow rate to water flow rate on four standard units of measure was examined: (a) the Oxygen Transfer Coefficient, KLa, corrected to 20°C, KLa₂₀ (hr­-¹), (b) the Standard Oxygen Transfer Rate, SOTR (g0₂.hr­-¹) (c) the Standard Aeration Efficiency, SAE (gO₂kWhr­-¹), and (d) the Standard Oxygen Transfer Efficiency, SOTE (%). Two sources of oxygen, Pressure Swing Adsorption (PSA) oxygen (87% purity) and air, were compared. KLa₂₀, SOTR, and SAE increased with an increase in the ratio of gas flow rate to water flow rate for both air and oxygen, over a range of 0.5% to 5.0%; while SAE deceased. An increase in inlet water velocity resulted in a decrease in KLa, corrected to 20°C, SOTR, and SAE, but an increase in the SOTE. Treatments on air showed similar, but much less dramatic effect of the gas flow rate to water flow rate ratio and water inlet velocity on KLa₂₀, SOTE, SAE, and SOTE, when compared to treatments on PSA oxygen. The best performance was achieved with an inlet water velocity of 6.9-7.6 ms­-¹ and oxygen flow rate to water flow rate ratio of about 2.5%. At this combination, the SOTE was about 66-72%. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

A 5. 0 em. diameter column was used for gas absorption. The column contained internal baffling and was operated in a countercurrent mode. Oxygen comprised the gaseous phase and tap water the liquid phase. The column was operated both with and without pulsations. The injection and exhaustion of compressed air to the system provided the pulsation mechanism. The mixing as well as the mass transfer characteristics were examined. A Set of experiments independent of the mass transfer work was carried out in order to study mixing in the column. A refluxing mechanism is uncovered in the mixing experiments. Values for the axial dispersion coefficient, volumetric mass transfer coefficient and reflux ratio are reported over the range of the operating parameters. / Thesis / Master of Engineering (MEngr)

The purpose of this research was to apply a discrete-bubble model to predict the performance of several hypolimnetic oxygenators. The model is used to predict the oxygen transfer rate in a hypolimnetic oxygenator based on the initial bubble size formed at the diffuser. The discrete-bubble model is based on fundamental principles, and therefore could also be applied to other mass transfer applications involving the injection of bubbles into a fluid. The discrete-bubble model has been applied to a linear bubble-plume diffuser, a full-lift hypolimnetic aerator and the Speece Cone with promising results. The first step in this research was to investigate the principals of bubble formation at a submerged orifice, bubble rise velocity and bubble mass transfer. The discrete-bubble model is then presented. The model traces a single bubble rising through a fluid, accounting for changes in bubble size due to mass transfer, temperature and hydrostatic pressure. The bubble rise velocity and mass transfer coefficients are given by empirical correlations that depend on the bubble size. Bubble size is therefore recalculated at every increment and the values for the bubble rise velocity and mass transfer coefficients are continually updated. The discrete-bubble model is verified by comparison to experimental data collected in large-scale oxygen transfer tests. Finally, the discrete-bubble model is applied to the three most common hypolimnetic oxygenation systems: the Speece Cone, the bubble-plume diffuser, and the full-lift hypolimnetic oxygenation systems. The latter being presented by Vickie Burris in her thesis, <i>Hypolimnetic Aerators: Predicting Oxygen Transfer and Water Flow Rate</i>. / Master of Science