Existing viscosity prediction methods and relevant literature are reviewed. An exhaustive review of group contribution, corresponding states, and interpolative prediction methods finds that even the best of these models produces large prediction errors and often require significant experimental data. Molecular dynamics simulation techniques for viscosity prediction are evaluated and compared to one another to determine the best choice for this work. A thorough investigation finds that Equilibrium Molecular Dynamics (EMD) simulations are the best option for reproducible and reliable liquid viscosity predictions. The many tuning parameters available in molecular dynamics simulations are investigated for their effects on prediction uncertainty and accuracy. Challenges associated with molecular dynamics predictions are discussed and a rigorous simulation and data analysis methodology is developed which addresses these issues. The TLVMie force field is developed to describe linear alkanes, branched alkanes, alkylbenzenes, and cycloalkanes. The method is developed with a "training set" of compounds and the transferability is evaluated with a completely different "test set" of compounds. Predictive capability with mixture viscosities is evaluated next without any re-fitting of the parameters determined from pure-component data. The TLVMie potential is shown to be significantly more accurate for both pure-components and mixtures, more reliable for compounds that differ greatly from the training set, and predictions are made without the experimental data requirements of other methods.

Determining intake of feeds in horses is an important factor in incorporating supplements in their diets. Fecal recoveries (R), fecal output (FO), dry matter digestibility (DMD) and dry matter intake (DMI) were estimated using alkanes as markers in 8 thoroughbred geldings. The experiment compared two diets in a 2 X 2 latin square experiment. The diets were mixed grass hay only (H) and the same hay plus a cereal by-product (H + CBP). The cereal by-product (CBP) was the high fat component added to feeds at Virginia Tech's Middleburg Agricultural Research and Extension Center. The apparent digestibility of ether extract (EE) and other nutrients in the H and H + CBP, as well as the partial digestibility of CBP were also determined. The periods were 21 d each with a dietary accommodation period followed by eight days of dosing the even chain alkanes dotriacontaine (C32) and hexatriacontane (C36) as external markers. Total collection (TC) was performed the last 4 d of dosing. The results show that mean recoveries of alkanes were close to 100%, but the range for individual alkanes was wide, and the pattern of recoveries for alkanes of different chain length was inconsistent from feed to feed. The results also indicate that mean estimates of the DMI, DMD and FO of a feed, such as H or H + CBP, are determined with reasonable accuracy by means of alkane markers. In contrast, alkane estimates of DMI and DMD in an individual horse fail to predict corresponding TC estimates. The alkane estimate of FO in an individual horse predicts a TC value with error of 16.4%. The CBP was found to be an excellent source of EE, CP and fiber but a poor source of Ca. / Master of Science

The synthesis of pure tris(6-hydroxymethyl-2-pyridylmethyl)amine (H₃L₁₁) is reported for the first time. New complexes of H₃L₁₁ with copper(II), manganese(II) and iron(III) have been characterised by X-ray crystallography. Linear [Fe₃(L₁₁)₂](ClO₄)₃ reveals the tightest Fe-O-Fe angle (87.6°) and shortest Fe...Fe distance (2.834 Å) presently found for a weakly antiferromagnetically-coupled high spin alkoxide-bridged polyiron(III) system. H₃L₁₁ provides a route to various hydrophobic peralkylated TPA ligand derivatives for creating a hydrophobic pocket for the assembly of iron catalysts for the novel 1-hydroxylation of n-alkanes. New 6-py substituted TPA ligands containing methyl (L₁₅) and n-octyl (L₁₆) ether linkages were synthesised via alkylation. Two further novel 6-py substituted ligands were synthesized incorporating n-hexyl substituents on one (L₂₁) and two (L₂₂) of the py moieties. Here a urea spacer group was used to promote hydrogen–bond assisted heterolytic O-O cleavage (generation of the potent FeV=O oxidant) within the hydroxoperoxoiron(III) precursor. High spin [FeII(L)(CH₃CN)[subscript(x)]](CF₃SO₃)₂ complexes (x = 0–2, L = L₁₅,₁₆,₂₁,₂₂) were characterised in solution by ¹H NMR. The structure of [Fe(L₂₂)](CF₃SO₃)₂ reveals a distorted iron(II) centre bound to four N atoms and two urea carbonyls. Iron(II) complexes of H₃L₁₁, L₁₅,₁₆,₂₁,₂₂ and tris(6-Br)-TPA (L₂₄), were investigated for catalysis of the oxygenation of cyclohexane by H₂O₂. Reaction of the iron(II) complexes with H₂O₂ and [superscript(t)]BuOOH was followed by time-resolved EPR and UV-VIS spectrophotometry. A correlation between the observed catalytic activity and the nature of the FeIII(L)-OOR intermediates generated is apparent. A convenient ‘one-pot’ synthesis of benzene-1,3,5-triamido-tris(l-histidine methyl ester) is reported along with attempts at preparing N,N’-bis(pyridylmethyl)-1,3- diaminopropane-2-carboxylic acid (L₂₅), a new water soluble pyridine-amine ligand. The final demetallation step resulted in ligand hydrolysis to the novel amino acid; 1,3-diaminopropane- 2-carboxylic acid which was characterised as its HCl salt by X-ray crystallography.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Alkanes can be used as an inexpensive feedstock to produce more valuable alcohols. The biotransformation of alkanes to alcohols provides an alternative to conventional chemical procedures. The scope of this research was to develop a process utilising a biocatalyst to catalyse the oxidation of an alkane to its corresponding alcohol on a larger scale than had been reported on in previous research. The research utilised a recombinant E. coli BL21(DE3) cell, containing the CYP153A6 operon in pET 28 vector, as the biocatalyst. The CYP153A6 enzyme catalyses the oxidation of octane to 1-octanol. The principle objective of the research was to determine the amount of 1-octanol that can be produced by a system utilising this strain of recombinant E. coli as a biocatalyst on a three orders of magnitude larger scale than what had previously been reported on for this reaction system. An additional objective was to model the 1-octanol production performance in the bioreactor. Bioconversion batch reactions, with excess octane used as a substrate, were conducted in 30ml McCartney bottles and in a 7.5L BioFlo 110 Modular Benchtop Fermentor (New Brunswick). The McCartney bottles were not equipped to actively control process conditions.The bioreactor was equipped to control process conditions such as temperature, pH and dissolved oxygen concentration. Experiments in the bioreactor were therefore described as being performed under controlled conditions. The procedures used to grow, maintain and harvest the biocatalyst cells were based on those developed by the Department of Microbial, Biochemical and Food Biotechnology at the University of the Free State. The product and substrate concentrations were determined through gas chromatography (GC) analysis. The McCartney bottle bioconversion reactions, with a 1.33ml reaction volume, produced 1.88 mg 1-octanol per gram of dry cell weight per hour. The bioreactor under controlled conditions, with a 2L reaction volume, produced 14.89 mg 1-octanol per gram of dry cell weight per hour. The formation of a secondary product, octanoic acid, was observed for the bioreactor under controlled conditions experiment at a production of 1.12 mg per gram of dry cell weight per hour. The McCartney bottle experiments did not produce any by-products. The 1-octanol production performance in the bioreactor experiments was empirically modelled. The empirical rate law was based on the form of the Monod equation, with the addition of a product inhibition term. The model achieved an average Root Mean Square Error of less than 5% when compared to experimental data, and was therefore concluded to be accurate within the range of experimental data and conditions tested for. The principal finding of the research is that the cells produced an order of magnitude more product in the bioreactor than in the McCartney bottles. The literature on this reaction system, however, reports only on smaller scale research than that performed in the bioreactor. The improved production results in the bioreactor therefore give the first insight into the potential that this technology has for being scaled up. Of equal significance is the finding that a secondary product developed during the biotransformations performed in the bioreactor. This refutes the assumption that the biocatalyst cells are unable to catalyse any secondary reactions. This aspect of the cells’ performance must be addressed before the biocatalyst cell strain can be considered to be a viable option for utilisation in large-scale processes. / AFRIKAANSE OPSOMMING: Alkane kan gebruik word as ‘n bekostigbare bron om meer waardevolle alkohol te produseer. Die biotransformasie van alkane na alkohol bied dus ‘n alternatief vir konvensionele chemiese prosedure. Die oogmerk en omvang van hierdie navorsing was om ‘n proses te ontwikkel waarin ‘n biokatalisator gebruik word om die oksidasie van ‘n alkaan tot sy ooreenstemmende alkohol te kataliseer, en om vas te stel hoeveel 1-oktanol vervaardig kan word deur ‘n herverenigde E. coli as katalisator gebruik. ‘n Rekombinante E. coli BL21(DE3) sel, wat die CYP153A6 operon in pET 28 vector bevat, is as biokatalisator gebruik. Die CYP153A6 ensiem kataliseer die oksidasie van oktaan na 1-oktanol. Biokonversie lot-reaksies, met oormatige oktaan wat as substraat gebruik word, is in 30ml McCartney bottels en in 7.5L BioFlo 110 Modular Benchtop Fermentor (New Brunswick) uitgevoer. Die bioreaktor was toegerus om kondisies van die proses soos temperatuur, pH and opgeloste suurstof-konsentrasie te kontroleer. Die prosedures wat gebruik is om die groei, onderhoud en oes van die biokatalisator selle te bewerkstellig, is gebaseer op prosedures wat ontwikkel is deur the Department van Microbiese, Biochemiese and Voedsel Biotegnologie van die Universiteit van die Vrystaat. Die produk- en substraat-konsentrasies is vasgestel deur gaschromatografie (GC) ontleding. Die McCartney bottel biokonversie-reaksie met ‘n 1.33ml reaksie-volume het 1.88 mg 1-oktanol per gram droeë-sel gewig opgelewer. Die bioreaktor, wat onder beheerde toestande ‘n 2L reaksie-volume het, het 14.89 mg 1-octanol per gram droeë-sel gewig gelewer. Onder beheerde eksperimentele kondisies is die vorming van ‘n sekondere produk, oktanol-suur, by die bioreaktor waargeneem teen 1.23 mg per gram droeë-sel gewig per uur. Die McCartney bottel eksperimente egter het geen newe-produkte opgelewer nie. Die ontwikkeling van die 1-oktanol in die bioreaktor-ekperimente is empiries gemodelleer. Die empiriese ‘rate law’ is gebaseer op ‘n vorm van die Monod- vergelyking, met byvoeging van ‘n produk-inhiberingsterm. Die model het ‘n gemiddelde vierkantswortel foutvariansie van minder as 5% opgelewer, vergeleke met die eksperimentele data, en word dus binne die rykwydte van die eksperimentele data, en die kondisies waarvoor getoets is, as akkuraat beskou. Die belangrikste bevinding is dat die selle in die bioreaktor ‘n orde van grootte meer produk gelewer het as die selle in die McCartney bottels. Die literatuur oor hierdie reaksie-sisteem berig egter slegs oor kleiner skaalse navorsing as wat in die bioreaktor gedoen is. Die verbeterde opbrengsresultate van die bioreaktor dui daarop dat laasgenoemde tegnologie die potensiaal inhou om opgegradeer te word. Die bevinding dat ‘n sekondere produk in die biotransformasie in die bioreaktor gevorm het, is beduidend. Dit weerspreek die aanname dat die biokatalisator-selle nie sekondere reaksies kataliseer nie. Hierdie aspek moet aangespreek word alvorens die biokataliseer-selle oorweeg kan word as ‘n lewensvatbare alternatief vir gebruik in grootskaalse prosesse.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2009. / The abundance of alkane by-products formed in South Africa presents a feedstock opportunity for the production of a wide range of commercially important products, such as long-chain dioic acids and alcohols. These compounds are formed as intermediates through the biological conversion of alkanes, a route which is particularly attractive when compared with chemical conversion due to its operation under milder process conditions. Furthermore, advances in genetic manipulation, which enable the accumulation of a range of metabolic intermediates, make the biological route remarkably flexible. From the literature review Yarrowia lipolytica was identified as a promising organism for use in studying alkane bioconversion because of its ability to produce large quantities of fatty acids when grown on n-paraffins as a sole carbon source. The bioconversion of alkanes will not only depend on the genetic modification but also on the process conditions to maximise growth and bioconversion. The overall objective of this project was therefore to investigate the potential of Y. lipolytica for alkane bioconversion by defining the conditions that maximise both cell growth and bioconversion. The Y. lipolytica strains supplied (TVN348, TVN493 and WT), however, were not yet modified to the extent that accumulation of metabolic intermediates was possible. Use was therefore made of a model system in which the alkane substrate was substituted with an even chain alkylbenzene. Since Y. lipolytica is unable to metabolise the benzene ring, the alkylbenzene is converted to the metabolic intermediate, phenyl acetic acid (PAA), and the potential for bioconversion assessed through measuring the accumulation of PAA. The specific objectives of the project were therefore 1) to define and quantify the parameters for the establishment of an effective model system in shake flasks with respect to trace elements, buffering, added nitrogen, oxygen supply, glucose concentration, alkylbenzene substrate and inducer requirements 2) to use the defined model system to identify the most promising strain of Y. lipolytica TVN348, TVN493 and WT 3) to use the defined model system and selected strain for evaluation of the influence of time of substrate addition and glucose concentration on cell growth and bioconversion of Y. lipolytica under controlled conditions in an instrumented bioreactor Furthermore, since poor reproducibility in cell growth and bioconversion had been prevalent in previous studies, it was also aimed to identify and statistically quantify the reproducibility between duplicate or triplicate samples in each experiment and between sets of different experiments with respect to PAA formation and cell concentrations. Studies were conducted in shake flask cultures to define and quantify the parameters for the model system. The parameters assessed included trace elements, buffering, nitrogen concentration, oxygen supply, glucose concentration, alkylbenzene substrate type and possible inducer requirements. Trace elements, phosphate buffering and added nitrogen did not significantly affect the cell growth of Y. lipolytica TVN348. The cell concentration of Y. lipolytica TVN348 and TVN493 was increased by 65% and 43% respectively for an increase in oxygen supply by decreasing the working volume from 150ml to 50ml, while the cell concentration of Y. lipolytica WT was increased by 41% when oxygen supply was increased by switching from non-baffled to baffled flasks in 50ml cultures. Bioconversion was also increased for an increase in oxygen supply: 2.4mM to 29.0mM PAA (Y. lipolytica TVN348) and 1.2mM to 21.7mM PAA (Y. lipolytica TVN493) for a decrease in working volume; 10.5mM to 46.6mM PAA (Y. lipolytica WT) when switching from non-baffled to baffled flasks. These results indicated that adequate oxygen supply is crucial to both growth and bioconversion, and that further study should be conducted in 50ml working volumes. Cell concentrations obtained in 1.6% (wt/v) and 3.2% (wt/v) glucose cultures (3.95x108cells/ml and 4.03x108cells/ml respectively) indicated that cell growth was neither enhanced nor inhibited by 3.2% (wt/v) glucose. Of the range of substrates examined (propylbenzene, butylbenzene, sec-butylbenzene, hexylbenzene, ethyltoluene and tert-butyltoluene for Y. lipolytica TVN348 and TVN493; octylbenzene and decylbenzene for Y. lipolytica WT), hexylbenzene was regarded as the best substrate for bioconversion (14.7mM and 14.1mM PAA for TVN348 and TVN493 respectively; 42.6mM PAA for WT). Lastly, the absence of a requirement for an additional inducer such as ethanol or oleic acid was confirmed when PAA was formed from hexylbenzene in the culture containing additional glucose (25.0mM). This suggested that when using hexylbenzene as substrate, bioconversion was induced provided sufficient glucose was available for cell maintenance. Results from duplicate or triplicate flasks in each individual shake flask experiment were reproducible and conclusions were based solely on results which showed 95% confidence intervals. However, reproducibility problems were experienced with results between different sets of experiments carried out under the same conditions. The model system was therefore defined by: 1) no addition of trace elements, additional buffering or added nitrogen, 2) cultures grown in 50ml volumes to supply an adequate amount of oxygen crucial for growth and bioconversion, 3) 3.2% (wt/v) glucose and 4) addition of 1% (v/v) hexylbenzene at 24h with no inducer requirements. Use of the model system in shake flask cultures to identify the most promising of the three strains of Y. lipolytica supplied demonstrated that there was no significant difference in cell growth or bioconversion between these strains. Y. lipolytica WT (which has no genetic modifications) was therefore used for further investigation until an appropriate strain could be substituted when it became available. The growth and bioconversion of Y. lipolytica WT was further investigated under controlled conditions in a bioreactor. The influence of time of substrate addition (11h, 24h, 48h) and glucose concentration (3.2% and 6.4% (wt/v)) on growth and bioconversion was examined. When hexylbenzene was added at 48h, cell growth was increased (8.90x108cells/ml) when compared to two of the triplicate cultures with hexylbenzene addition at 24h (4.74x108cells/ml and 3.92x108cells/ml) and the culture with hexylbenzene addition at 11h (2.82x108cells/ml). The third of the triplicate cultures with hexylbenzene addition at 24h, on the other hand, exhibited the strongest growth (2.23x109cells/ml). The poor reproducibility between the triplicate cultures with hexylbenzene addition as 24h made it difficult to determine whether hexylbenzene addition at 24h or 48h maximised cell growth. Furthermore, the cell growth was not significantly improved when the glucose concentration was increased from 3.2% (wt/v) to 6.4% (wt/v) (7.47x108cells/ml for 6.4% glucose culture), however it was also not inhibited. The highest amount of specific PAA formed by Y. lipolytica WT was found when hexylbenzene was added at 11h (7.4x10-11mmol PAA/cell), however the highest accumulated PAA was produced in the culture that exhibited the strongest growth with hexylbenzene addition at 24h (41.4mM). This suggested that the bioconversion of hexylbenzene was maximised when it was added during the active growth phase. It is therefore recommended to conduct fed-batch experiments in future to maintain the active growth phase. Accumulated PAA was increased in 6.4% (wt/v) glucose culture (15.2mM PAA) when compared with two of the 3.2% (wt/v) glucose cultures (5.4mM and 4.3mM PAA). These results indicated that the increased glucose concentration did not inhibit the bioconversion. Furthermore, PAA was formed when 5% (wt/v) residual glucose was observed in the culture, suggesting that the bioconversion of hexylbenzene was not inhibited at glucose concentrations as high as 5.0% (wt/v). If future work were to be conducted in bioreactor culture where glucose is added in fed-batch operation, glucose concentrations in cultures of up to 5% (wt/v) could be considered for initial studies. During bioconversion by Y. lipolytica, the PAA measured after hexylbenzene exhaustion did not, however, correspond to 100% conversion. Further, poor reproducibility was found in the bioreactor cultures. The disappearance of hexylbenzene without a corresponding accumulation of PAA and poor reproducibility was investigated by determining whether PAA was further degraded or alternatively, whether other metabolic intermediates were being formed and accumulated from the hexylbenzene. However, substitution of the hexylbenzene with PAA as substrate confirmed that PAA could not be metabolised. Further, NMR analyses of both the aqueous and organic phases of the culture did not identify any additional metabolic intermediates. It is recommended that additional analyses be conducted on the aqueous and organic phases to further assess the possible accumulation of intermediates. The development of the model system in shake flask cultures demonstrated the importance of adequate oxygen supply for both cell growth and bioconversion. It was also shown that no inducer was needed because hexylbenzene acted as its own substrate inducer. Furthermore, comparison of Y. lipolytica strains TVN348, TVN493 and WT under the defined conditions of the model system revealed that the genetically modified strains (TVN348, TVN493) did not exhibit enhanced bioconversion. Bioreactor cultures using the model system under controlled conditions further showed that bioconversion was not inhibited at a 5% (wt/v) residual glucose concentration and suggested that bioconversion was maximised when hexylbenzene was added during active growth phase. This informs on future work, suggesting fed-batch operation in order to extend the active growth phase, where glucose concentrations in the bioreactor of up to 5% (wt/v) can be considered.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2001. / Current methods for wax fractionation result in products with large polydispersity, and due to the high temperatures required, thermal degradation of the wax is often incurred. The need for an alternative process thus exists. The purpose of this project is to investigate the technical viability of supercritical fluid processing as an alternative wax fractionation technology. The main aims of this project are to select a suitable supercritical solvent, to conduct binary phase equilibrium experiments, to determine if the process is technically viable and to investigate the ability of various equations of state to correlate the phase equilibrium data. Based on limited data from the literature, propane and a propane rich LPG (Liquefied Petroleum Gas) were selected as suitable solvents. Literature data for propane and high molecular weight alkanes is scares and incomplete, thus necessitating experimental measurements. A phase equilibrium cell was designed, constructed and commissioned. The cell was designed for pressures up to 500 bar and temperatures to 200 oC, and with the aid of an endoscope, the phase transitions were detected visually. The measurements correspond well to literature values from reliable research groups. Phase equilibrium data sets for propane with nC32, nC36, nC38, nC40, nC44, nC46, nC54 and nC60 as well as LP Gas with nC36 were measured. At temperatures just above the melting point of the alkanes, the phase transition pressures can be considered to be moderate, which will positively impact the economics of the process. The phase transition pressure increases with increasing carbon number, the relationship being found to be linear when the pressure is plotted as a function of carbon number at constant mass fractions and temperature. The increase in phase transition pressure with increasing carbon number indicates that the solvent will be able to selectively fractionate the wax. At higher temperatures the gradient of the line is larger and may thus lead to improved selectivity. The higher temperatures will also lead to better mass transfer. The linear relationship indicates that limited extrapolation to higher carbon numbers may be possible. However, this needs to be verified experimentally. The inability to measure the critical point and vapour pressure curves of the higher molecular weight normal alkanes, as well as the inability of cubic equations of state to predict liquid volumes and to capture the chain specific effects such as internal rotations, results in cubic equations of state requiring large interaction parameters to fit the data. The alternative, statistical mechanical equations of state, have difficulty in predicting the critical point of the solvent correctly and thus overpredicts the mixture critical point, yet require smaller interaction parameters to fit the data. Further work is required to improve the predictability of these non-cubic equations of state. This project has proven that wax fractionation by supercritical extraction with propane is technically feasible.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2007. / Adequate provision of oxygen to aerobic bioprocesses is essential for the optimisation of process kinetics. In bioprocesses in which the feedstock is an alkane, the supply of sufficient oxygen is of particular concern because the alkane molecular structure is deficient in oxygen. As a result, the oxygen demand has to be met solely by transfer of oxygen to the culture, necessitating a proportionately higher requirement for oxygen transfer. Maximisation of the rate of oxygen transfer is therefore of key importance in optimising the potential for alkane bioconversion, with respect to both operation and scale up. Nevertheless, the oxygen transfer rate (OTR), and its dependence on the overall volumetric mass transfer coefficient (KLa) in alkane-aqueous dispersions is not yet well understood. In view of the importance of an adequate OTR in the optimisation of alkane bioconversion, this study has focused on the identification and elucidation of the factors which underpin the behaviour of KLa in an alkane-aqueous dispersion. KLa behaviour was quantified in terms of the pressures imposed by turbulence and alkane fluid properties, through their influence on the Sauter mean diameter (D32), gas hold up, gas-liquid interface rigidity and gas-liquid interfacial area per unit volume. These properties were correlated with KLa over a wide range of agitation rates and alkane concentrations in alkane-aqueous dispersions. Experiments were conducted in a 5 litre aerated and agitated bioreactor at agitation rates of 600, 800, 1000 and 1200 rpm and alkane (n-C10-C13 cut) concentrations of 0, 2.5, 5, 10, and 20% (v/v). KLa determination was executed using both the gassing out and pressure step methods. The accuracy and reliability of these methods were compared under the full range of agitation rates and alkane concentrations. The pressure step method was conclusively shown to be superior provided that probe response was taken into account, and was therefore used in the correlations. The interfacial areas corresponding to the KLa values were calculated from the combined effects of D32 and gas hold up. D32 was determined from the measurement of the dispersed air bubble diameters by means of a photographic technique and image analysis. Image analysis was performed by a program that was developed in Matlab® using image acquisition and image processing techniques. This program used these techniques to extract information of the gas bubbles in the image. The gas hold up was determined using the dispersion height technique. The behaviour of KLa was shown to be dependent on both agitation and alkane concentration. Increasing agitation from 600 to 1200 rpm increased KLa for each of the alkane concentrations. The influence of agitation on the interfacial area was evaluated over the same range of agitation rates and the relationship between the corresponding KLa values and interfacial areas assessed. Increasing agitation rate similarly enhanced the interfacial area available for transfer for each of the alkane concentrations, resulting in the concomitant increase in KLa. This increase in interfacial area was related directly to a shear-induced decease in D32 and indirectly to an increased gas holdup as a result of the lower rise velocity of the smaller bubbles. In addition to the agitation, the presence of alkane markedly influenced KLa behaviour, but in different ways, depending on the alkane concentration. Alkane concentration between 2.5 and 5% (v/v) reduced D32 at constant agitation of 800, 1000 and 1200 rpm, a likely consequence of decreased surface tension and retarded coalescence conferred by the alkane. The smaller D32 and the consequential enhanced gas hold up served to amplify KLa through increased interfacial area. However, as alkane concentration was increased above 5% (v/v), the gas hold up decreased despite a continued decrease in D32, resulting in a corresponding decrease in both the interfacial area and KLa. This suggests that at the higher alkane concentrations, the influence of viscosity predominated, exerting multiple negative influences on the interfacial area and oxygen transfer coefficient. The trends were however, not observed at the low agitation of 600 rpm, where turbulence was significantly reduced and KLa was repressed for all alkane concentrations. The pressures imposed by turbulence and alkane properties on the interfacial area defined locales of KLa behaviour and three distinct KLa behavioural trends were identified, depending on the agitation rate and alkane concentration. Regime 1 was constrained between 2.5 and 5% (v/v) for agitation rates of 800 rpm and above. Here KLa enhancement was directly associated with increased interfacial area which was the major factor defining KLa in this regime. Regime 2 was constrained by alkane concentrations higher than 5% (v/v) for agitation rates of 800 rpm and above. In this regime, the KLa depression was observed with increasing alkane concentration suggesting a predominant influence of viscosity which would be likely to exert multiple negative influences on KLa, through both the interfacial area and KL. The interfacial area in this regime decreased mainly due to the negative effect of viscosity on gas holdup. Regime 3, characterised by a decline in KLa irrespective of the alkane concentration, occurred at agitation rates smaller than 800 rpm. It is likely that at low agitation rates, the contribution of turbulence was insufficient to exert a positive influence on the interfacial area In this regime, the interfacial decreased through the combined negative effect of increased D32 and decreased gas holdup. The resultant variation in OTR depended directly on the relative magnitudes of the KLa and oxygen solubility and indirectly on the process conditions which defined these magnitudes. Under conditions of enhanced KLa, OTR benefited from the combined increases in KLa and oxygen solubility. However, under conditions of KLa depression, the elevated oxygen solubility did not invariably outweigh the influence of KLa depression on OTR. Consequently, despite the considerably increased solubility of oxygen in alkane-based bioprocesses a potential decrease in OTR through depressed KLa underlines the critical importance of the quantification of this parameter in alkane-aqueous dispersions and the necessity for a definition of the locales of optimal KLa. Through the identification of the parameters which underpin the behaviour of KLa in alkane-aqueous dispersions and the quantification of the effect of process conditions on these parameters, a fundamental understanding of the KLa and OTR in alkane-aqueous dispersions has been developed. This provides a knowledge base for the prediction of optimal KLa in these systems and has wide application across all alkane-based bioprocesses.

No description available.

A Series of fluorophores of the general formular P(CF2)nP and P(CF2)n-1CF3 has been synthesized. Copper catalyzed coupling of 1-bromopyrene and the corresponding mono and di-iodoperfluoroalkanes were used in most cases. For the n=3 dimer, a novel 1,w-perfluoroalkylation of pyrene via bis-decarboxylation of hexafluorogultaric acid was utilized. These compounds, along with suitable hydrocarbon analogs, are being used to study the flexibility of fluorocarbon chains using emission. We have found that the excimer formation for the fluorinated pyrene monomers is highly dependent on concentration and is less efficient than for pyene. Excimer formation for the fluorinated pyrene dimers is much more efficient than for the fluorocarbon monomers and is only slightly concentraion dependent. Steady-state emission spectra indicate hydrocarbon dimers-models form excimers more efficiently than the fluorinated dimers suggesting the fluorinated chains are stiffer than the hydrocarbons. We conducted the temperature-dependent studies and quantified the conformational difference.

Ce travail décrit l'étude de différents paramètres qui influent sur les propriétés d'adsorption de composés poreux organométalliques (MOFs). Nous avons utilisé les techniques de volumétrie et de gravimétrie d'adsorption et les systèmes adsorbables sont la série des alcanes linéaires (du n-pentane au n-nonane). Les solides étudiés sont les MIL-47(V), MIL-53(Cr, Al, Fe), les MIL-53(Fe)-X modifiés et la série MIL-88(Fe)-A, B, C. Parmi les nombreuses conclusions de cette étude, nous pouvons en détailler plusieurs : (i) la flexibilité des MIL-53(Cr, Al, Fe), rendue possible par la présence de µ2-OH coordinés aux centres métalliques, dépend de l'identité des centres métalliques et de celle de l'adsorbable. (ii) la modification chimique, par substitution d'un atome d'hydrogène porté par les noyaux aromatiques des ligands, induit une variation dans le degré de flexibilité des structures et dans la stabilité des différentes phases. (iii) la nature des ligands, dans la série des MIL-88(Fe), en termes de nombre de noyaux aromatiques constituent les ligands, modifie les interactions physiques au sein des réseaux organométalliques ce qui a un effet sur leur stabilité et leur flexibilité.(iv) la facilité de la diffusion des alcanes linéaires, de longueur différente, dans les pores des solides dépend notamment des points développés ci-dessus. / This study describes a study of the adsorptive properties of several flexible porous organometallic frameworks (MOFs) using the volumetric and gravimetric methods and apolar normal alkanes (n-pentane to n-nonane) as adsorbate molecules. The materials studied are MIL-47(V), MIL-53(Cr, Al, Fe), the modified MIL-53(Fe)-X and the MIL-88(Fe)-A, B, C.This allows the study of different parameters on the behaviour of the solids during the adsorption process. Amongst the findings of this study, several can be emphasized :(i) the flexibility of the MIL-53(Cr, Al, Fe), made possible by the presence of µ2-OH coordinated to the metal centres, depends on the identity of the metal centres and that of the adsorbate.(ii) the chemical modification by the substitution of a hydrogen atom on the aromatic ligands of the MIL-53(Fe) induces a change in the degree of flexibility of the framework and the stability of the various phases.(iii) the nature of the ligands in the MIL-88(Fe) series, in terms of the number of the aromatic rings comprising the linker, changes the physical interactions within the framework and thus its stability and flexibility.(iv) the ease of diffusion into the pores of the alkanes of various alkyl chain length depends on the three points mentioned above.