Dissertations / Theses on the topic 'Chemical engineering, n.e.c'
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1
McAvoy, Camille Z. "Palladium-catalyzed C-N cross-coupling reactions toward the synthesis of drug-like molecules." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/73388.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Chemistry; and, (S.B.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. ).
The development of methodologies for C-N bond formation reactions is an important scientific challenge because of many academic and industrial applications. This work will focus particularly on palladium-catalyzed cross-couplings of amine-containing compounds with aryl halides. The scope of the BrettPhos precatalyst for the cross-coupling of ortho-substituted aryl iodides with amides is studied using substrates with a variety of functional groups. Due to potential metal-chelating issues with some of the substrates used in this study, a proposed ligand synthesis is discussed in which one of the methoxy groups of BrettPhos is replaced with a morpholine capable of occupying palladium's open coordination site during its catalytic cycle. A final C-N bond formation study focuses on the cross-coupling of aryl halides with amidine salts. For this cross-coupling, a methodology has been developed that can be applied to various electron-rich, electron-poor, and electron-neutral substrates. Furthermore, the products of this cross-coupling can be used for a subsequent electrocyclization through a reaction with aldehyde, demonstrating that a relatively simple two-pot methodology can be used to make relatively complex substrates with pharmaceutical applications. Both amides and amidines are common moieties in drug-like molecules because of the various biological activities of these functional groups. Potential medicinal applications of the developed cross-coupling of amidine salts with aryl halides methodology are described. Thus, methodologies for various palladium-catalyzed, C-N cross-couplings as well as a potential ligand synthesis to be used for palladium catalysis are herein discussed.
by Camille Z. McAvoy.
S.B.
2
Bejarano, Roberto Villa. "An Investigation Into| I) Active Flow Control for Cold-Start Performance Enhancement of a Pump-Assisted, Capillary-Driven, Two-Phase Cooling Loop II) Surface Tension of n-Pentanol + Water, a Self-Rewetting Working Fluid, From 25 ?C to 85 ?C." Thesis, University of Nevada, Reno, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1565813.
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Cold-start performance enhancement of a pump-assisted, capillary-driven, two-phase cooling loop was attained using proportional integral and fuzzy logic controls to manage the boiling condition inside the evaporator. The surface tension of aqueous solutions of n-Pentanol, a self-rewetting fluid, was also investigated for enhancing heat transfer performance of capillary driven (passive) thermal devices was also studied. A proportional-integral control algorithm was used to regulate the boiling condition (from pool boiling to thin-film boiling) and backpressure in the evaporator during cold-start and low heat input conditions. Active flow control improved the thermal resistance at low heat inputs by 50% compared to the baseline (constant flow rate) case, while realizing a total pumping power savings of 56%. Temperature overshoot at start-up was mitigated combining fuzzy-logic with a proportional-integral controller. A constant evaporator surface temperature of 60°C with a variation of ±8°C during start-up was attained with evaporator thermal resistances as low as 0.10 cm2–K/W. The surface tension of aqueous solutions of n-Pentanol, a self-rewetting working fluid, as a function of concentration and temperature were also investigated. Self-rewetting working fluids are promising in two-phase heat transfer applications because they have the ability to passively drive additional working fluid towards the heated surface; thereby increasing the dryout limitations of the thermal device. Very little data is available in literature regarding the surface tension of these fluids due to the complexity involved in fluid handling, heating, and experimentation. Careful experiments were performed to investigate the surface tension of n-Pentanol + water. The concentration and temperature range investigated were from 0.25%wt. to1.8%wt and 25°C to 85°C, respectively.
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Kanuru, Vijaykumar. "Understanding surface mediated C-C and C-N bond forming reactions." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608956.
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Porada, O. K., A. O. Kozak, V. I. Ivashchenko, S. M. Dub, Олександр Дмитрович Погребняк, Александр Дмитриевич Погребняк, and Oleksandr Dmytrovych Pohrebniak. "Hard Si-C-N Chemical Vapor Deposited Films." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42711.
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Si-C-N thin films were deposited on silicon substrates by plasma-enhanced chemical vapor deposition (PECVD) using hexamethyldisilazane as the main precursor. An influence of substrate temperature (TS) on film properties was analyzed. It was established that the deposited films were x-ray amorphous. The growth of the films slows down with increasing substrate temperature. The distribution of Si–C, Si–N and
C–N bonds were almost independent of TS, whereas the number of С–Н, Si–H and N–H bonds essentially decreased when substrate temperature increased. The nanohardness and elastic modulus increased with TS due to a reduction of the weak hydrogen bonds.
5
Qian, Xin. "Cobalt-Catalyzed C-C and C-N Coupling reactions." Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00943479.
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Ce travail de these a permis le déveloippement de nouvelles reactions de couplage catalysées par des sels de cobalt(II) Le premier chapitre décrit l'allylation cobalta catalysée d'halogénures d'alkyles. La méthode est facile à mettre en œuvre, efficace avec une grande variété d'halogénures d'alkyes et des acétates ou carbonates d'allyle substitués. Les rendements vont de bons à excellents et la tolérance fonctionnelle élevée. Dans le cas d'acétates d'allyle substitués le produit linéaire est obtenu majoritairement ou exclusivement. Quelques expériences ont permis de mettre en lumière la formation d'espèce radicalaire lors du cycle catalytique. Les premiers essais pour étendre cette méthodologie aux couplages allyle-allyle et alkyle-alkyle sont également décrits. Le deuxième chapitre porte sur l'amination catalysée au cobalt d'organozinciques fonctionnalisés en utilisant des N-chloroamines. La procédure est simple et générale et demande des conditions plus douces que celles précédemment décrite, tout en tolérant un très large éventail de substrats, avec une bonne tolérance à de nombreux groupes fonctionnels. Les premiers essais pour étendre la méthodologie à la réaction entre un organozincique et une source électrophile de soufre en vue de former des liaisons C-S sont également exposés. Enfin le dernier chapitre décrit la réaction d'organozinciques engendrés par catalyse au cobalt avec une source " verte " de cyanure électrophile, N-cyano-N-phenyl-p-methyl-benzenesulfonamide (NCTS), pour conduire avec de bons rendements aux arylnitriles correspondants. Des sources analogues de CN+ ont également été testées.
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Smith, Gordon Christopher. "Catalytic cracking of n-alkanes and n-alkylbenzenes over H-ZSM-5 zeolite." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12550.
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Gunnarsson, Sophie. "Optimisation of N release : influence of plant material chemical composition on C and N mineralisation /." Uppsala : Dept. of Soil Sciences, Swedish Univ. of Agricultural Sciences, 2003. http://epsilon.slu.se/a381.pdf.
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Gooseman, Natalie. "The influence of the C-N⁺------F-C charge dipole interaction in fluoro organic chemistry /." St Andrews, 2008. http://hdl.handle.net/10023/695.
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Lin, Xufeng. "Density functional theory studies of selected transition metals catalyzed C-C and C-N bond formation reactions." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B39359645.
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Wang, Luo. "Excess enthalpies and excess volumes for n-butyl methyl ether + n-alkane systems at 298.15 K." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5686.
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Research on excess properties plays an important role in solution thermodynamics. The experimental excess properties of liquid mixtures provide essential information for testing and developing solution theories. They also provide the data required for process design in chemical and petroleum industries. In addition excess properties are useful for testing thermodynamic consistency for vapor-liquid equilibrium data. Both excess enthalpies $H\sp{E}$ and excess volume $V\sp{E}$ were determined in this study for six binary systems consisting of n-butyl methyl ether and an n-alkane at 208.15 K. Flory theory with an interaction parameter, which was found to be a quadratic function of the carbon number of the n-alkane molecules, was used to correlate the experimental $H\sp{E}$ data and then to predict $V\sp{E}$ values which were subsequently compared with the experimental $V\sp{E}$ data.
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Lin, Xufeng, and 林旭鋒. "Density functional theory studies of selected transition metals catalyzed C-C and C-N bond formation reactions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39359645.
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Ivashchenko, V. I., P. L. Scrynskyy, A. I. Kuzmichev, L. A. Ivashchenko, O. Yu Khyzhun, I. I. Timofejeva, O. O. Butenko, and V. M. Granko. "Characterization of Ti-B-C-N Nanocomposite Coatings." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35053.
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Nanocomposite Ti-B-N-C coatings were deposited by magnetron sputtering of TiN and B4C targets in the argon-nitrogen atmosphere at different nitrogen flow rates (FN2). The structure, chemical bonding and mechanical properties were investigated. The results of the investigations of the nanocomposite, TiN and BCN coatings show that the Ti-B-C-N coatings consist of the TiNC nanocrystals (3.4 – 6.5 nm) embedded into the amorphous matrix that consists of amorphous boron nitrogen (a-BN) and amorphous carbon (a-C). The coatings contain a small admixture of titanium oxides that are aggregated at the grain boundaries. The coatings deposited at high nitrogen flow rates were textured. An introduction of nitrogen prompts the formation of the nanocrystallites of the TiN-TiC solid solutions and the a-BN amorphous tissue, which, in turn, causes the improvement of the mechanical properties of the Ti-B-C-N coatings. The best samples ex-hibited nanohardnes above 39 GPa.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35053
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Pope, Christopher James. "A chemical mechanism for fullerenes C₆₀ and C₇₀ formation with kinetic modeling of their synthesis in flames." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12663.
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Cowley, Michele. "Conversion of n-pentenes over H-ZSM-5." Master's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/5370.
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Bibliography: leaves 89-93.The skeletal isomerisation of I-pentene provides the feed stock 2-methyl-2-butene and 2-methyl-I-butene for the production of tertiary amyl methyl ether (TAME), an octane booster for petrol. Benzene, toluene, xylenes and ethylbenzene (BTX+EB) are good or even better octane boosters, although the use of benzene is limited due to its carcinogenic nature. From an industrial point of view, these compounds are therefore of importance. The conversion of I-pentene over H-ZSM-5 zeolite catalyst was studied in a fixed-bed micro reactor.
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Al-Damkhi, Ali M. "Separation of n-paraffins by selective adsorption." Thesis, Aston University, 1986. http://publications.aston.ac.uk/10192/.
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A study has been undertaken of the vapor-phase adsorptive separation of n-alkanes from Kuwait kerosene (Kuwait National Petroleum Company, heavy kerosene) using zeolite molecular sieves. Due to the shortage of information on the adsorption of multicomponent systems in the open literature, the present investigation was initiated to study the effect of feed flowrate, temperature, and zeolite particle size on the height of mass transfer zone (MTZ) and the dynamic capacity of the adsorbent for multicomponent n-alkanes adsorption on a fixed-bed of zeolite type-5A. The optimum operating conditions for separation of the n-alkanes has been identified so that the effluent would also be of marketable quality. The effect of multicycle adsorption-desorption stages on the dynamic behaviour of zeolite using steam as a desorbing agent has been studied and compared with n-pentane and n-hexane as desorbing agents. The separation process comprised one cycle of adsorption using a fixed-bed of zeolite type-5A. The bed was fed with vaporized kerosene until saturation had been achieved whereby the n-alkanes were adsorbed and the denormalized material eluted. The process of adsorption-desorption was carried out isobarically at one atmosphere. A mathematical model has been developed to predict the breakthrough time using the method of characteristics. The results were in a reasonable agreement with the experimental values. This model has also been utilized to develop the equilibrium isotherm. Optimum operating conditions were achieved at a feed flowrate of 33.33 x 10-9 m3/s, a temperature of 643 K, and a particle size of (1.0 - 2.0) x 10-3 m. This yielded an HMTZ value and a dynamic capacity of 0.206 m and 9.6S3 x 10-2 kg n-alkanes/kg of zeolite respectively. These data will serve as a basis for design of a commercial plant. The purity of liquid-paraffin product desorbed using steam was 83.24 wt%. The dynamic capacity was noticed to decrease sharply with the cycle number, without intermediate reactivation of zeolite, while it was kept unchanged by intermediate reactivation. Normal hexane was found to be the best desorbing agent, the efficiency of which was mounted to 88.2%.
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Safoniuk, Michael. "A thermogravimetric study of the Si-O-N system /." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61045.
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A thermogravimetric analyzer was used to study the Si-O-N system. Pure, polished single crystal silicon wafers were heated in the analyzer in an atmosphere of flowing high purity nitrogen or argon. The sample weight was measured continuously over specified temperature ranges. The high affinity of silicon for oxygen made it extremely difficult to form silicon nitride. Zirconium metal strips were placed near the sample to further reduce the local oxygen concentration. Silicon nitride was formed at 1250$ sp circ$C with a nitrogen gas with a bulk oxygen concentration of less than 5 ppm. Two distinct modes of formation of silica (SiO$ sb2$) were observed. These were active and passive oxidation. Active oxidation involved the evolution of SiO and resulted in a weight loss while passive oxidation resulted in a weight increase. Due to the formation of silicon dioxide, weight measurements were not useful in determining silicon nitride kinetics.
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Modak, Viraj Prakash. "Surface Freezing in n-Alkanes: Experimental and Molecular Dynamics Studies." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1449013699.
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Koen, Matthew Anthony. "Hydrocracking of long chain n-Paraffins under Fischer-Tropsch conditions." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13260.
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Includes bibliographical references.A number of various iron-palladium loaded H-MFI zeolites used for the hydrocracking of n- hexadecane under Fischer-Tropsch conditions were tested to address the inherent low CO tolerance of the pure palladium noble metal hydrocracking catalysts. The hydrocracking mechanism consists of two functions, namely the metal de-/hydrogenation (HD/DHD) and the acidic -scission function. The addition of CO to reactions involving monometallic palladium hydrocracking catalysts has led to an imbalance between these functions due to the migration of the noble metal resulting in significant and undesirable secondary cracking. However, the inclusion of iron to the hydrocracking catalyst may allow for chemical anchoring of the noble metal (Wen et al., 2002) reducing the effect of the migration and thus retaining the bifunctional balance. The consequent palladium-iron alloy (Garten, 1976) also has the potential for an improved rate of de-/hydrogenation (Fukuoka et al., 1990) resulting in a greater rate of intermediary carbenium ions which in turn could lower any undesired secondary cracking reactions already present. The Fe/H-MFI precursor was prepared using a solid-state ion exchange after which incipient wetness impregnation was used to add the palladium. Different loadings of palladium and iron were used to prepare the PdFe/H-MFI catalysts in order to determine an optimum ratio loading. All experiments were conducted at standard low temperature Fischer-Tropsch conditions in a plug-flow fixed trickle-bed reactor equipped with a homogeneously operating evaporator and on-line GC-FID analysis. It was found that none of the bimetallic catalysts produced showed any greater tolerance to carbon monoxide when compared to the monometallic catalyst. The results indicated that the behaviour of the bimetallic catalyst was near identical to that of the monometallic catalyst in the presence of CO. It was thus concluded that the preparation method used, in particular the Fe/H- MFI precursor through solid state ion-exchange, was unsuitable for the production of an alloyed PdFe/H-MFI catalyst. An effect of iron was noted in the low palladium high iron loaded catalyst i.e. PdFe/H-MFI (16,12). In the absence of CO, this catalyst showed a significantly improved selectivity when com- pared to the low palladium low iron catalyst, PdFe/H-MFI (16,24). This effect of iron was attributed to the blockage of the H-MFI pores due to the large amount of iron present. As a consequence of this, access to the internal acid sites is severely limited and therefore are essentially removed from the hydrocracking reaction. As such the PdFe/H-MFI (16,12) has an improved metal:acid site balance. Poisoning by water (a Fisher-Tropsch product) was found to significantly reduce secondary cracking due to deactivation of the acid sites (lowering of total acidity) resulting in improved selectivity through intermediary olefin product promotion. From this, almost pure primary cracking was possible allowing the noble metal catalysts to retain its ideal hydrocracking properties at very high conversions (as evident by the high isomerization selectivity). This indicates that if the total acid strength of the H-MFI zeolite could be reduced (e.g. dealumination), the overall catalyst selectivity could be improved. Testing into whether the effect of water in reducing secondary cracking could be used to offset the effect of an increase in secondary cracking by CO addition, proved ineffective. It is therefore thought that CO not only causes palladium migration and clustering on the external zeolite but also poisons the active metal sites still available. As a result the balance between the metal and acid function could not be restored. It is thus recommended that for future work a zeolite with a lower total acid strength be used in conjunction with a alternate method for iron addition. Furthermore, testing into higher loadings of palladium may prove fruitful in balancing its migratory nature in the presence of carbon monoxide.
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Drouillard, Ken G. "Physico-chemical property determinations of chlorinated n-alkanes, C¦10 to C¦12, parameters for estimation of the environmental fate of chlorinated n-paraffins." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq23287.pdf.
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Binneman, Jacqueline. "The hydrocracking of long chain n-paraffins under Fischer-Tropsch conditions." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/14415.
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Includes bibliographical references.Interest in the area of hydrocracking has grown rapidly over the years. In the early 1960's companies such as Chevron and Universal Oil Products (UOP) introduced new hydrocracking processes to manufacture high octane gasoline. The demand for transportation fuels such as diesel and jet fuel has increased significantly which results in the continuous development of hydrocracking techniques and catalysts. The conversion of normal long chain paraffins from the Fischer-Tropsch synthesis to clean distillate fuels is a particular area of interest. The objective of this project is to investigate the hydrocracking of long chain paraffins under F-T conditions. The aim is to achieve in situ, the hydrocracking of low temperature Cobalt-based F-T wax by combining F-T synthesis and hydrocracking in a single reactor. For the purpose of this thesis, it involves subjecting the hydrocracking catalyst to F-T conditions. Synthesis gas (carbon monoxide and hydrogen), the paraffin n-C16 and water were co-currently fed to a fixed-bed reactor containing only the hydrocracking catalyst. Therefore care was taken to match the experimental conditions of the hydrocracking experiments to those that prevail in the Fischer-Tropsch synthesis. Practically this means the hydrocracking of n-hexadecane was studied at the space velocity, the reaction temperature and pressure and under partial pressure of H2, CO and water, at which n-hexadecane is produced in F-T process assuming that n-hexadecane is the only hydrocarbon product and that n-hexadecane is a model compound for the low temperature F-T process. The results of this investigation show that the hydrocracking reaction over a Pd catalyst supported on H-MFI Zeolite under F-T conditions is non-ideal. At low feed (n-C16) conversions, product distributions are strongly dominated by secondary reactions. The ability of the metal site is significantly inhibited by the presence of CO and water. The product distributions show exactly this due to the increase in unsaturated and more branched species. Feed conversion in the presence of water and CO increase with increasing reaction temperature. The absence of methane in the product spectrum is an indication that the hydrogenolysis reaction is an unfavorable pathway for the catalyst used. The data obtained from this investigation suggests that the combination of low temperature Fischer-Tropsch and hydrocracking into a single reaction step is feasible.
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Hop, Marina. "Dehydrogenation of N-Propanol to Propionaldehyde over a copper chromite catalyst." Master's thesis, University of Cape Town, 1998. http://hdl.handle.net/11427/18796.
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Methyl methacrylate (MMA) is widely used for a range of polymer products. MMA can be produced from propionaldehyde via the BASF process. n-Propanol is readily available 'in South Africa as a byproduct of Fischer-Tropsch synthesis. This prompted an investigation into the production of propionaldehyde by the dehydrogenation of n-propanol. There is presently no established technology for the dehydrogenation of n-propanol to propionaldehyde and there has been very little work carried out on the effect of process variables on propionaldehyde yield. The emphasis of the current work was optimising propionaldehyde production. A commercial copper-chromite catalyst (G-13), for the dehydrogenation of ethanol to acetaldehyde, was used for the purposes of this study.
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Koffas, Mattheos A. G. "Metabolic engineering of C. glutamicum for amino acid production improvement." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8745.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2001.Includes bibliographical references (leaves 183-210).
A central goal in metabolic engineering is the design of more productive biological systems by genetically modifying metabolic pathways. In this thesis we report such an optimization in the bacterial strain Corynebacterium glutamicum that is employed for the fermentative production of various amino acids such as lysine. The main goal of the research presented here was the application of metabolic and genetic engineering tools in order to investigate the role of the pyruvate node in cellular physiology. This was achieved by integrating the tools of bioinformatics, recombinant DNA technology, enzymology and classical bioengineering in the context of control and genetically engineered strains of C. glutamicum. First, the main anaplerotic pathway responsible for replenishing oxaloacetate, namely pyruvate carboxylase was targeted. After fruitless attempts to establish an in vitro enzymatic activity for this enzyme, our efforts were directed towards its gene identification. This was achieved by designing PCR primers corresponding to homologous regions among pyruvate carboxylases from other organisms. Utilizing these primers, a PCR fragment was isolated corresponding to part of the gene of the C. glutamicum pyruvate carboxylase. The sequence of the complete gene was finally obtained by screening a C. glutamicum cosmid library. In order to investigate the physiological effect that this enzyme has on lysine production, recombinant strains and deletion mutants were generated. The presence of the gene of pyruvate carboxylase in a multicopy plasmid is not sufficient to yield a significant overexpresssion of this enzyme in C. glutamicum. Contrary to our expectations, overexpression of pyruvate carboxylase has a negative effect on lysine production but improves significantly the growth properties of C. glutamicum. A metabolic model was developed according to which pyruvate carboxylase overexpression increases the carbon flux that enters the TCA cycle, thus the higher growth. However due to the presence of a rate-limiting step in the lysine biosynthesis pathway this increased carbon flux does not translate into higher lysine production. The role of aspartokinase, the first step in lysine biosynthesis, was explored as such a potential bottleneck. Its overexpression proves to increase the amount of lysine produced, however it leads to a lower growth and finally a lower productivity. Since pyruvate carboxylase and aspartokinase have opposite effects on cell physiology, the combination of the overexpression of these two enzymes was finally studied. By this simultaneous overexpression, we achieved to create a C. glutamicum recombinant strain with similar growth as that of the control but higher lysine production and productivity. In the context of exploring the physiological role of pyruvate carboxylase, a biotinylated enzyme, two other enzyme that utilize biotin were also investigated namely acetyl-CoA-carboxylase and biotin ligase. The first enzyme was purified to completion and its N-terminal as well internal amino acid sequences were obtained. A cosmid from the C. glutamicum cosmid library was identified that most likely contains the gene of the latter enzyme. In summary, in the present work we have achieved to prove unequivocally the presence of pyruvate carboxylase in C. glutamicum. We have also achieved to characterize the second biotinylated enzyme in this organism, namely acetyl-CoAcarboxylase. The physiological effect of both pyruvate carboxylase and aspartokinase was established and a metabolic model was developed based on these experimental results. This model finally led us to the construction of a new recombinant strain with improved lysine productivity. As such, this work stands as one of the few examples of a primary metabolite production improvement using metabolic engineering techniques.
by Mattheos A.G. Kofas.
Ph.D.
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Chen, Tianyi. "Production of n-Butanol by Clostridium Carboxidivorans." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1556309785594048.
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Wasylenko, Thomas M. (Thomas Michael). "¹³C-metabolic flux analysis of recombinant yeasts for biofuels applications." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98717.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references.
Fossil fuels have powered the transportation industry since the Industrial Revolution. However, rising transportation energy demand and new knowledge about the environmental impact of burning fossil fuels have motivated the development of technologies for sustainable production of renewable, carbon-neutral liquid fuels. To that end, biological systems may be leveraged to fix carbon dioxide and to catalyze the conversion of renewable feed stocks to fuel molecules. Today, the gasoline additive ethanol and biodiesel are produced by yeast fermentation of sugars derived from cornstarch and sucrose and transesterification of vegetable oils, respectively. However ethanol has many drawbacks as a fuel additive, and both biofuels are currently produced from edible feed stocks. For biofuels to contribute significantly to meeting total transportation energy demand, processes for production of fuel molecules from non-food feed stocks must be engineered. Two promising solutions are fermentation of sugars derived from "woody," lignocellulosic biomass and production of fuels from volatile fatty acids (VFAs) such as acetate, which can be produced by fermentation of organics in municipal solid waste and sewage or syngas. The production of biofuels from lignocellulosic material or VFAs will require metabolic engineering of biocatalysts to improve yields, productivities, and final titers. These metabolic engineering efforts can be facilitated by ¹³C-Metabolic Flux Analysis (MFA), a method for elucidating the otherwise unobservable intracellular metabolic fluxes in biological systems. We first developed protocols for extraction and LC-MS/MS analysis of intracellular metabolites, which provides data that may be used for metabolic flux estimation. We then performed an analysis of both the measurement and modeling errors associated with using these data for flux determination. Finally, we applied ¹³C-MFA to two industrially relevant systems: 1) Fermentation of xylose, a sugar present in lignocellulosic biomass, to ethanol in Saccharomyces cerevisiae, and 2) overproduction of fatty acids that may be transesterified to biodiesel from either glucose or acetate in the oleaginous yeast Yarrowia lipolytica. These experiments identified a potential bottleneck in xylose fermentation in S. cerevisiae and the primary source of NADPH for fatty acid biosynthesis in Y. lipolytica, and also suggested potential strategies for improving lipid yields in Y. lipolytica.
by Thomas M. Wasylenko.
Ph. D.
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Piallat, Fabien. "Plasma assisted chemical deposition (CVD/ALD) and integration of Ti(Al)N and Ta(Al)N for sub-20 nm metal gate." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENT015/document.
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L'intégration du métal dans les nœuds technologiques sub-20 nm requiert une conformité supérieure à celle permise par la PVD. Les techniques de CVD, plus spécifiquement la MOCVD et l'ALD, ont été identifiées comme les meilleures solutions pour le dépôt de métal. Pour une application de métal de grille, les alliages carbo-nitrurés de titane et tantale sont considérés comme les plus prometteurs. Dans ce travail une revue détaillée des mécanismes de dépôt par MOCVD et ALD, ainsi que sur l'influence du plasma sur les matériaux déposés est réalisée. Dans un premier temps, les fenêtres de procédés possibles pour un ajustement des propriétés des métaux sont inspectées attentivement. L'accent est mis sur l'impact du plasma sur le métal et sur les mécanismes réactionnels inhérents grâce à une caractérisation poussée du plasma. Par la suite, l'intégration de ces métaux est étudiée avec une analyse précise des interactions se déroulant aux interfaces. La corrélation entre les propriétés physico-chimiques et le comportement électrique des empilements métal/diélectrique à forte permittivité est soutenue par une analyse XPS. Finalement, le dopage aluminium de dépôts de TiN et TaN MOCVD est étudié pour l'obtention de grilles n-mos et p-mos. Par comparaison des propriétés et comportements du dopage aluminium de métaux déposés par PVD et MOCVD, des mécanismes de diffusion sont proposés afin d'expliquer le rôle de l'aluminium sur les variations observéesFor the sub-20 nm technological nodes metal conformity requirements are beyond the possibilities of the currently used PVD deposition technique. CVD techniques, more specifically MOCVD and ALD, are identified as the best techniques for metal deposition. For metal-gate application, titanium and tantalum carbo-nitrides alloys are considered as the most promising. In this work, a detailed review of MOCVD and ALD deposition mechanisms and plasma influence on the deposited material is carried out. First, process windows for successful tuning of the metal properties are examined. Plasma impact on the metal and the inherent reaction mechanisms are also highlighted with the help of plasma characterisation. Then great importance is given to the integration of these metals, by careful study of the interactions taking place at the interfaces. Correlations between physico-chemical properties and electrical behavior of the metal/high-k dielectric stack are introduced thanks to XPS characterisation. Finally, aluminium doping of MOCVD TiN and TaN is considered for n-mos and p-mos gate characteristics achievement. By comparison of the properties and behaviours of Al doped metals deposited by PVD and MOCVD, diffusion mechanisms are proposed to explain the role of Al in the observed changes
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Kukard, Ross S. "The effect of zeolite type on the hydrocracking of long n-paraffins." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/5301.
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Includes synopsis.Includes bibliographical references (leaves 141-144).
Although it is debatable as to the lifetime of the planet’s crude oil reserves, it is indisputable that they are finite and will, eventually, become exhausted. As such it is desired to devise methods whereby currently available non-crude oil derived hydrocarbon feedstocks may be utilised for the production of clean, high quality liquid fuels (particularly middle distillate fuels such as diesel and jet fuel), aiding in alleviating the demand on crude oil reserves. One technique whereby this may be achieved involves the conversion of the non-crude oil derived hydrocarbon feedstock (for example stranded gas, remote natural gas, coal or biomass) to syngas (a mixture of CO and H2). This syngas is subsequently converted to paraffinic wax by Fischer-Tropsch Synthesis, and this wax selectively hydrocracked down to the desired distillate fuels fraction. This hydrocracking may be conducted utilising either monofunctional or bifunctional catalysts. Monofunctional catalysts, such as the supported sulphided base metals or metal oxides utilised in many crude oil refineries, yield a product with minimal additional branching, as desired, though would contaminate the otherwise clean Fischer-Tropsch wax with sulphur. Bifunctional catalysts, utilising a metal on an acidic support, yield a product with significant branching, yet do not contaminate the product. Furthermore, the acid supports utilised in oil refinery applications are limited to either amorphous silica-alumina, or H-USY (a thermally treated large pore zeolite) due to the presence of large, bulky polycyclic and highly branched molecules in the feedstock. Fischer-Tropsch wax exhibits only minimal branching, and it was hence the aim of this investigation to determine whether zeolites with pores smaller than those utilised in the hydrocracking of crude oil derived feedstocks, specifically medium pore zeolites such as H-MFI, may be utilised in the bifunctional hydrocracking of this wax to impart shape selectivity upon the reaction, thereby limiting the extent to which branching may occur. In this regard, four different zeolites (H-MFI, H-BEA, H-USY and H-MOR) were tested under the same, industrially relevant conditions, and the results collated so as to quantify the effects of the each zeolite’s unique properties, in particular their pore geometries (in terms of pore size, shape and channel inter-connectivity), the performance of each catalyst in terms of its activity (the overall conversion of the feedstock) and selectivity (with regards to both carbon number distribution and the degree of branching). Furthermore, it was desired to determine the extent to which the anticipated transition state shape selectivity of some of the zeolites affected the stability (on-stream lifetime) of the catalyst through a reduction in coke formation. The results of this investigation indicated that medium pore zeolites show significant potential for use in the selective hydrocracking of a Fischer-Tropsch wax feedstock. It was found that those zeolites possessing medium sized pores (specifically H-MFI and H-BEA) exhibited a significantly higher activity than did those with only larger pores (H-USY and H-MOR), a phenomenon theorised to be due to the more orderly and efficient configuration of the adsorbed molecules within the medium pores promoting contact with active acid sites. Furthermore, it was found that H-MFI, with a porous network comprised entirely of medium pores, showed an improved selectivity towards the desired linear products, whilst zeolites with only wide pores (H-USY and H-MOR) and those with intersecting wide and medium pores (H-BEA) showed branched product selectivities roughly equivalent to one another, all greatly favouring the production of mono-methyl branched species. Unfortunately, due primarily to the large variations in the observed activity between the zeolites tested, the results of the deactivation analysis were inconclusive.
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Fiaz, Mohammed. "Dipole moments and Kerr effect of poly(n-vinylcarbazole) and its complexes with trinitrofluorenone." Thesis, Aston University, 1994. http://publications.aston.ac.uk/9697/.
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N-vinylcarbazole was polymerised using the free radical catalyst (azo-bisisobutyronitrile) and cationic catalysts (boron-trifluoride etherate and aluminium chloride). The polymers produced were characterised by molecular weight measurements and powder x-ray diffraction. The tacticity of the polymer samples was determined using proton and carbon-13 nuclear magnetic resonance spectroscopy. Mesurements of their static dielectric permittivity and electro-optical birefringence (Kerr effect) in solution in 1,4-dioxane were carried out over a range of temperatures. The magnitudes of the dipole moments and Kerr constants were found to vary with changes in the tacticity of poly(N-vinylcarbazole). The results of these measurements support the view that the stereostructure of poly(N-vinylcarbazole) is sensitive to the mechanism of polymerisation. These results, together with proton and carbon-13 N.M.R. data, are discussed in terms of the possible conformations of the polymer chains and the relative orientation of the bulky carbazole side groups. The dielectric and molecular Kerr effect studies have also been carried out on complexes formed between 2,4,7-trinitro-9-fluorenone (TNF) and different stereoregular forms of poly(N-vinylcarbazole) in solution in 1,4-dioxane. The differences in the molar Kerr constants between pure (uncomplexed) and complexed poly(N-vinylcarbazole) samples were attributed to changes in optical anisotropy and dipole moments. A molecular modelling computer program Desktop Molecular Modeller was used to examine the 3/1 helical isotactic and 2/1 helical syndiotactic forms of poly(N-vinylcarbazole). These models were used to calculate the pitch distances of helices and the results were interpreted in terms of van der Waal's radii on TNF. This study indicated that the pitch distance in 3/1 isotactic helices was large enough to accommodate the bulky TNF molecules to form sandwich type charge transfer complexes whereas the pitch distance in syndiotactic poly(N-vinylcarbazole) was smaller and would not allow a similar type of complex formation.
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Kotsiopoulos, Athanasios. "The hydrocracking of Fischer-Tropsch wax : using n-tetradecane as a model compound." Master's thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/8662.
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Includes bibliographical references (p. 99-102).Increasingly stringent legislation has been applied to transportation fuels to minimise or eliminate aromatics and sulphur compounds in diesel fuel. This has led to manufacturers determining alternative production methods to comply to legislation. Part of the current diesel fuel is being produced by hydrocracking heavier fractions derived from crude oil. These hydrocracking processes utilise bi-functional catalysts which have a metal (hydrogenating/dehydrogenating) function and an acid (cracking) function. The most common of these hydrocracking catalysts are combinations of either noble metals and acid zeolites, such as Pt/ HY, or combined sulphides of group VIA and VIIIA metals on amorphous acidic supports, such as CoMo/SiO2-Al2O3. For good quality diesel, the fuel should have a high cetane number and the aromatics and sulphur content should also be kept to a. minimum (e.g. EU legislation: sulphur content must be below 10 ppm (wt) by 2008). Fischer-Tropsch wax is made up predominantly of long-chain linear paraffins with exceptionally low aromatics and heteroatom content (sulphur and nitrogen-containing compounds) and therefore a good source for very 'clean', good quality diesel. The objective of this study was therefore to investigate the suitability of a conventional bi-functional hydrocracking catalyst namely, CoMo/SiO2-Al2O3 in unsulphided form for the hydrocracking of Fischer-Tropsch wax using n-tetradecane as a model compound. The purpose of using the catalyst in unsulphided form was not to introduce any sulphur to the already sulphur-free feedstock.
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Noorani, Khalid. "Comparative chemical kinetic and experimental study of methanol, ethanol, n-propanol and n-butanol auto-ignition delay times." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106391.
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Much work has been done to model and understand alcohol oxidation individually. Comparative studies of ignition delay times of alcohols, however, are limited. The thesis presents a comparative study of their ignition delay times. Mixtures of methanol, ethanol, n-propanol and n-butanol and synthetic air are ignited behind reflected shock waves at high temperatures (1070K-1760K). The ignition delay times are measured in a shock tube as equivalence ratio, argon to oxygen ratio (dilution) and pressure are changed to highlight trends and similarities between the fuels. Experimental results have indicated that these fuels have comparable ignition delay times, which may indicate similarities of the oxidation pathways of the alcohols. The results are compared against simulations of chemical kinetic models from the literature. The Marinov model is found to be the most accurate of the models. However, the simulations fail to show the similarity of the delay times at fixed equivalence ratio phi, argon to oxygen ratio (dilution), D and pressure, p. Reaction rate dependency analysis of kinetic models indicate dominance of radical chemistry among the fuels and the presence of H abstraction reactions in methanol as opposed to uni-molecular fuel decompositions of larger alcohols like n-butanol.Dans cette these, des melanges de methanol, ethanol, n-propanol et n-butanol avec de l'air synthetique sont exploses derriere une onde de choc reflechie a haute temperature (1070K-1760K) ou les temps de retard a l'allumage sont mesures a differents taux d'equivalences, dilutions, pressions et temperatures pour etablir les points de similitaritees et differences entre alcools. Beaucoup d'etudes ont ete fait pour modeliser et comprendre l'oxydation de ces derniersmais les etudes n'ont pas ete realise de maniere comparative. Ainsi, ce travail presente une etude comparative des temps de retard d'allumage des alcools simples (C1 a C4). Les resultats ont indique que ces combustibles ont des temps de retard d'allumage comparables, ce qui indique une similitaritee des voies d'oxydation des differents alcools.Des modeles cinetiques trouves dans la litterature sont compares aux resultats experimentaux. Il se trouve que celui de Marinov (1998) est le plus proches des valeurs mesurees. De plus, des analyses de dependance des taux de reactions sur les delais d'allumage sur ces modeles indiquent la dominance des reactions a base de radicaux.
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Nelson, Peter Jonathan. "Boiling the immiscible water/n - nonane system from a tube bundle." Thesis, Heriot-Watt University, 1986. http://hdl.handle.net/10399/1060.
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Ewing, Helen Clifford. "The nucleation and growth mechanisms of amorphous Si-N-O fibres." Thesis, University of Strathclyde, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366923.
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Kelly, Mark. "Laser diagnosis and computer modelling of C/H/O and C/H/N plasmas used in diamond chemical vapour deposition." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.653079.
Full textAbstract:
Laser and optical emission spectroscopies have been employed to study the gas phase chemistry in the growth environment for diamond chemical vapour deposition (CVO) in a microwave (MW) reactor. Computational investigations have also been used to explore the energetics of elementary reactions on a diamond surface, to give insight into which species are likely to incorporate into a growing diamond film. The focus of this thesis is on 0 and N containing CIH plasmas.
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Glaves, L. R. "The recovery of precious metals from aqueous solutions using heterocyclic N-oxides." Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356757.
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Esalah, Jamaleddin. "Removal of heavy metals from aqueous solutions by precipitation with sodium di-(n-octyl) phosphinate." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37715.
Full textAbstract:
Two organophosphorus compounds: sodium di-(n-octyl) phosphinate and sodium di-(n-dodecyl) phosphinate, were synthesized and purified. Sodium di-(n-octyl) phosphinate was used both as a surfactant to form reverse micelles and as a precipitating agent to remove heavy metals from aqueous nitrate and chloride solutions.The heavy metals lead, cadmium, and zinc were precipitated from aqueous solutions with sodium di-(n-octyl) phosphinate (NaL) in the form of PbL 2(s), CdL2(s), and ZnL2(s). The mole ratio of NaL to lead in the feed was varied from 0.1 to 6.5, depending on the acidity of the feed. The effects of the feed pH, concentration of chloride, concentration of calcium, and of the chain length of the precipitating agent on the removal of lead, were investigated. Adding acid to the feed solution reduced the removal of lead as some of the phosphinate precipitated in the acid form as HL(s). The presence of chloride or calcium in the feed solution, up to mole ratios to lead of 250 and 2.75, respectively, had no effect on the removal of lead. The solubility of the precipitate PbL 2(s) was reduced by increasing the length of the alkyl group of the phosphinate. The removal of cadmium, zinc, and a mixture of lead, cadmium and zinc was investigated. Behavior similar to that of lead was observed. The selectivity of the precipitating agent for the three metals was in the order Zn > Pb > Cd.
The precipitating agent was completely regenerated by adding NaOH to the precipitate, and then contacted with diethyl ether to extract the reagent. The lead was completely recovered from the PbL2(s). Pure lead-free precipitating agent, and an aqueous solution of lead at a concentration 100 times its concentration in the feed, were obtained.
Using measured solubility products of the precipitates and literature values of the stability constants for the other expected reactions, the removal of metal, the loss of precipitating agent, and the equilibrium pH were predicted.
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Chede, Sneha A. "Fouling Control Using Temperature Responsive Membranes composed of N-isopropylacrylamide (NIPAAm) and Iron Oxide Nanoparticles." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1449426051.
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Du, Yinming. "High-Yield and High-Titer n-Butanol Production from Lignocellulosic Feedstocks by Metabolically Engineered Clostridium tyrobutyricum." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374193011.
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Quan, Congling Soroush Masoud Grady Michael. "High-temperature free-radical polymerization of n-butyl acrylate /." Philadelphia, Pa. : Drexel University, 2005. http://dspace.library.drexel.edu/handle/1860/553.
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Marshall, Brian A. "Immediate C-terminal Extein Effects on the Cleaving Kinetics of the ¿I-CM Mini-Intein." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1532363837193988.
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He, Jiliang. "Silyhydrazines : chemistry and pyrolytic conversion to Si-N-C ceramic materials." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29044.
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A new synthetic route to silylhydrazine molecules and polymers has been developed by the heterodehydrocoupling of organosilanes with hydrazines. A dimethyltitanocene catalyst has been employed to facilitate the dehydrocoupling reaction. The dehydrocoupling was shown to proceed by stepwise replacement of Si-H with hydrazino groups. The controlled hydrolysis of Ph$ sb2$Si(NHNHMe)$ sb2$ formed a hydrazinodisiloxane. Cyclizations of Ph$ sb2$Si(NHNHMe)$ sb2$ to form cyclic silylhydrazines were achieved by the reaction with n-BuLi/Ph$ sb2$SiCl$ sb2,$ or MeI (or HCl or Ph$ sb2$SiCl$ sb2),$ or thermolysis. Crystal structures of Ph$ sb2$Si(NHNR)(NRNH)SiPh$ sb2$ (R = H, Me) reveal chair (R = H) and twist-boat (R = Me) conformations of the Si$ sb2$N$ sb4$ ring, respectively. Planar and pyramidal nitrogen geometries were found to coexist in a hydrazino unit. A preceramic polymer, synthesized by the polymerization of MeHSiCl$ sb2$ with hydrazine in an appropriate ratio, was pyrolyzed to Si$ sb3$N$ sb4$/SiC$ rm sb{x}$N$ rm sb{y}$ in 67-80% ceramic yields. It is proposed that the structural unit of this polymer is a tetraazadisilacyclohexane bridged by MeHSi groups. This assignment is based on $ sp{1}$H and $ sp{29}$Si NMR measurements, as well as by comparison with the well-defined reaction product of Me$ sb2$Si(NHNH) $ sb2$SiMe$ sb2$ with MeHSiCl$ sb2.$ The pyrolysis was carried out from room temperature to 1500$ sp circ$C under argon and studied by using thermogravimetric analysis, solid-state $ sp{29}$Si NMR spectroscopy, infrared spectroscopy, x-ray powder diffraction, and elemental analysis. Serial structural changes were characterized in the pyrolyzed solid products. The ceramic product of this polymer at 1100$ sp circ$C was found to possess a quasi-metallic electrical conductivity ($ sigma$ = 10$ sp3$ ($ Omega$cm)$ sp{{-}1}),$ and was evaluated as an electrode material.
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Ali, J. A. M. "Liquid-phase adsorption of n-paraffins on type 5A molecular sieves." Thesis, Aston University, 1987. http://publications.aston.ac.uk/9700/.
Full textAbstract:
As a basis for the commercial separation of normal paraffins a detailed study has been made of factors affecting the adsorption of binary liquid mixtures of high molecular weight normal paraffins (C12, C16, and C20) from isooctane on type 5A molecular sieves. The literature relating to molecular sieve properties and applications, and to liquid-phase adsorption of high molecular weight normal paraffin compounds by zeolites, was reviewed. Equilibrium isotherms were determined experimentally for the normal paraffins under investigation at temperatures of 303oK, 323oK and 343oK and showed a non-linear, favourable- type of isotherm. A higher equilibrium amount was adsorbed with lower molecular weight normal paraffins. An increase in adsorption temperature resulted in a decrease in the adsorption value. Kinetics of adsorption were investigated for the three normal paraffins at different temperatures. The effective diffusivity and the rate of adsorption of each normal paraffin increased with an increase in temperature in the range 303 to 343oK. The value of activation energy was between 2 and 4 kcal/mole. The dynamic properties of the three systems were investigated over a range of operating conditions (i.e. temperature, flow rate, feed concentration, and molecular sieve size in the range 0.032 x 10-3 to 2 x 10-3m) with a packed column. The heights of adsorption zones calculated by two independent equations (one based on a constant width, constant velocity and adsorption zone and the second on a solute material balance within the adsorption zone) agreed within 3% which confirmed the validity of using the mass transfer zone concept to provide a simple design procedure for the systems under study. The dynamic capacity of type 5A sieves for n-eicosane was lower than for n-hexadecane and n-dodecane corresponding to a lower equilibrium loading capacity and lower overall mass transfer coefficient. The values of individual external, internal, theoretical and experimental overall mass transfer coefficient were determined. The internal resistance was in all cases rate-controlling. A mathematical model for the prediction of dynamic breakthrough curves was developed analytically and solved from the equilibrium isotherm and the mass transfer rate equation. The experimental breakthrough curves were tested against both the proposed model and a graphical method developed by Treybal. The model produced the best fit with mean relative percent deviations of 26, 22, and 13% for the n-dodecane, n-hexadecane, and n-eicosane systems respectively.
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Bao, Teng. "Metabolic engineering of Clostridium cellulovorans for selective n-butanol production from cellulose." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1574686346943506.
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De, Vries Christian. "Adding ammonia during Fischer-Tropsch Synthesis: Pathways to the formation of N-containing compounds." Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25269.
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The Fischer-Tropsch synthesis (FTS) process, better known for its ability to produce synthetic fuel via the hydrogenation of CO, has shown potential to produce valuable chemicals when ammonia is added to the feed. In this work certain aspects of the pathway to the formation of N-containing compounds that form when NH₃ is added during FTS, using mostly iron based catalysts is investigated. In addition, the effect this has on the FTS reaction itself is evaluated. To achieve this goal, both theoretical and experimental techniques are used in this study. The CO adsorption and dissociation reactions are assumed to be important elementary reactions for many proposed FTS pathways. In the theoretical part of this thesis, spin-polarized periodic density functional theory (DFT) calculations are employed to study aspects of the initial stage of the pathway on a model Fe(100) surface. Considering the formation of N-containing hydro- carbons, one would assume that NH₃ initially adsorbs and dissociates on the catalyst surface, which could take place in the presence of CO. The surface chemistry of these adsorbates is well studied both experimentally and theoretically, but their co-existence has not yet been evaluated on model Fe surfaces. Initially a platform is generated by calculating the individual potential energy surfaces (PES) for the decomposition of CO and NH₃ on Fe(100) at a coverage of ϴ = 0.25 ML. These calculations provided the basis for comparing the adsorption and dissoci- ation profiles of CO and NH₃ on the Fe(100) surface via the use of the same computational methodology, and importantly making use of the same exchange correlation functional (RPBE) for both adsorbates. Furthermore, it was desired to evaluate the kinetics and thermodynamics of the NH₃ decomposition on the Fe(100) surface at relevant temperatures and pressures (by combining the DFT results with statistical thermodynamics) to better understand the role of NHₓ surface species involved in the pathway to the formation of the N-containing compounds on a model catalyst surface. The DFT results that are reported for the individual decomposi- tion PES for CO and NH₃ were generally found to be in close agreement with what has been reported in previous DFT studies and deduced experimentally for the relevant adsorption and decomposition pathways. The resulting Gibbs free energies for the PES suggests that NH₂ may be kinetically trapped on the Fe(100) surface at a coverage of ϴ = 0.25 ML and the reaction conditions (T = 523 K and p*NH₃ = 0.2 bar) where NH₃ is co-fed with synthesis gas during FTS. The individual adsorptions of CO and NHₓ (with x = 3, 2, 1, 0) were compared to their coadsorbed states, by calculating the heat of mixing (ΔEmix) and the activation barriers (Eₐ) for CO dissociation in the presence and absence of the NHₓ surface species on the Fe(100) sur- face. Similar to the individual adsorption of NH₃, the 0 K regime inherent to DFT calculations is bridged by calculating the Gibbs free energy of mixing for CO + NH₃ on Fe(100) at higher temperatures. Both repulsive and attractive interaction energies were calculated for the various coadsorbed states (CO + NHₓ on Fe(100)) and similarly some configurations resulted in an energetically favored or unfavored heat of mixing. The activation barrier for CO dissociation was lowered when coadsorbed with NH₃ and NH₂, and raised when coadsorbed with NH and N. With all the coadsorbed structures the CO dissociation reaction became more endothermic. Previous experimental studies have shown a concomitant reduction in oxygenate selectivity with an increase in the selectivity for N-containing compounds, when NH₃ is added during FTS. It is well-known that oxygenates undergo secondary reactions when using iron-based catalysts in FTS. In addition, the catalyst used in aforementioned studies (precipitated Fe/K) are active for the amination reactions of oxygenates. It is therefore hypothesized that some oxygenates pro- duced via the primary FTS pathway are converted to N-containing compounds via a secondary reaction. The experimental part of this thesis is therefore aimed at testing this hypothesis. A base case study included a comparison between a Fe-catalyzed slurry phase FTS reaction and a FTS reaction with all parameters remaining unchanged, except for the addition of 1 vol % NH₃ to the syngas (CO + H₂) feed. The activity (CO and H₂ conversion) data collected did not reveal any appreciable loss in the rate of the FTS reaction when 1 vol % NH₃ was added and steady state was reached (, that is after 48 hours time on stream (TOS)). A slower carburization period was however observed when comparing the CO conversion during the first 24 hours TOS, and further supported by the slow increase in CO₂ selectivity during the same period. The use of two-dimensional gas chromatography (GC × GC-TOF/FID) allowed for the discovery of a formation of a range of secondary and tertiary amines, not reported in previous studies. The expected loss in oxygenate selectivity was observed and further probed by co-feeding 1-octanol with the feed (CO + 2H₂ + 1 vol % NH₃) via a saturator. These results clearly indicated a significant loss in oxygenate formation as a result of secondary conversion to N-containing compounds. Questions regarding the stability of aliphatic nitriles prompted the co-feeding of nonanitrile under similar conditions. The results obtained after co-feeding nonanitrile, sug- gests that nonanitrile is readily converted to secondary and tertiary amines and that the ratios of aliphatic alcohols and nitriles are close to equilibrium. The use of CO₂ as carbon source, the investigation of the product spectrum at higher space velocities and the use of Rh-based catalysts, when NH₃ is added during FTS were included in shorter studies. The combination of these results, adds to the knowledge pool for the case where NH₃ is present in the FTS regime, as a poison or reactant. Additional information regarding the path to the formation of N-containing compounds was obtained via the detailed analysis of the product spectra with two-dimensional gas chromatography and the subsequent co-feeding reactions. The results ob- tained via co-feeding reactions, can be used to devise strategies to increase the selectivity of the desired N-containing compounds.
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Fournier, Martin. "Reactivity of C₃N and C₂H at low temperature : applications for the Interstellar Medium and Titan." Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S100/document.
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Le milieu interstellaire ainsi que certaines atmosphères de corps planétaires, en particulier Titan, un des plus grands satellites du système solaire, présentent une grande diversité d'espèces chimiques. Cette chimie complexe est très différente de celle que nous connaissons sur Terre. Pour comprendre les phénomènes globaux qui s'y déroulent, une connaissance des réactions chimiques, de leur vitesse et de leurs produits est requise. A l'aide de la technique CRESU, nous sommes capables de reproduire certaines conditions des milieux les plus froids de l'espace et d'étudier ces réactionsThe interstellar medium and some atmospheres of planetary bodies, in particular Titan, one of the largest satellites of Saturn, present a large variety of chemical species. This complex chemistry is very different from the one we know on Earth. To understand the global phenomenon that happen in these environments, we need to understand the chemical reactions, their reaction rate and their products. With the CRESU technique, we are able to reproduce partially the coldest environments of space to study these reactions
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Jackson, Colleen. "SiC and B₄C as electrocatalyst support materials for low temperature fuel cells." Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27313.
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Supported nano-catalyst technologies are key for increasing the catalyst utilisation and achieving economically feasible platinum metal loadings in hydrogen polymer electrolyte fuel cells (PEFCs). High surface area carbons are commonly utilised as support materials for platinum due to low cost, large surface areas and high conductivity. However, PEFCs using this technology undergo oxidation of carbon supports, significantly reducing the lifetime of the fuel cell. In this work, silicon carbide and boron carbide are investigated as alternative catalyst support materials to carbon, for the oxygen reduction reaction for low temperature fuel cells. Electrochemical testing, accelerated degradation studies as well as advanced characterisation techniques were used to clarify the structure-property relationships between catalyst morphology, metal-support interaction, ORR activity and surface adsorption onto the Pt nanoparticles. Extended X-ray Absorption Fine Structure (EXAFS) analysis gave insights into the shape of the clustered nanoparticles while X-ray Photoelectron Spectroscopy (XPS) and in-situ X-ray Absorption Near-Edge Spectroscopy (XANES) analysis provided information into how the metal-support interaction influences surface adsorption of intermediate species. Electronic metal-support interactions between platinum and the carbide supports were observed which influenced the electrochemical characteristics of the catalyst, in some cases increasing the oxygen reduction reaction activity, hydrogen oxidation reaction activity and Pt stability on the surface of the support.
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Jackson, Colleen. "Preparation and characterisation of Pt-Ru/C catalysts for direct methanol fuel cells." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/24322.
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The direct methanol fuel cell (DMFC) is identified as a promising fuel cell for portable and micro fuel cell applications. One of the major benefits is that methanol is an energy dense, inexpensively manufactured, easily stored and transported, liquid fuel (Hamann et al., 2007). However, the DMFC's current efficiency and power density is much lower than theoretically possible. This inefficiency is predominantly due to the crossover of methanol from the anode to the cathode, Ru dissolution and Ru crossover from the anode to the cathode. In addition, the DMFC has a high manufacturing cost due to expensive catalyst costs and other materials. Catalyst expenses are further increased by catalyst loading due to low activity at the anode of the DMFC (Zhang, 2008). Hence, with increasing activity and stability of the Pt-Ru/C catalyst, catalyst expenditure will decrease due to a decrease in catalyst loading. In addition, performance will increase due to a reduction in ruthenium dissolution and crossover. Therefore, increasing the activity and stability of the Pt-Ru/C catalyst is paramount to improving the current DMFC performance and viability as an alternative energy conversion device. Pt-Ru/C catalyst synthesis method, precursors, reduction time and temperature play a role in the activity for methanol electro-oxidation and stability since these conditions affect structure, morphology and dispersivity of the catalyst (Wang et al., 2005). Metal organic chemical deposition methods have shown promise in improving performance of electro-catalysts (Garcia & Goto, 2003). However, it is necessary to optimise deposition conditions such as deposition time and temperature for Pt(acac)₂ and Ru(acac)₃ precursors. This study focuses on a methodical approach to optimizing the chemical deposition synthesis method for Pt-Ru/C produced from Pt(acac)₂ and Ru(acac)₃ precursors. Organo-metallic chemical vapour deposition (OMCVD) involved the precursor's vapourisation before deposition and a newly developed method which involved the precursors melting before deposition. An investigation was conducted on the effects of precursor's phase before deposition. The second investigation was that of the furnace operating temperature, followed by an exploration of the furnace operating time influence on methanol electro-oxidation, CO tolerance and catalyst stability. Lastly, the exploration of the Pt:Ru metal ratio influence was completed. It was found that the catalyst produced via the liquid phase precursor displayed traits of a high oxide content. This led to an increased activity for methanol electro-oxidation, CO tolerance and catalyst stability despite the OMCVD catalyst producing smaller particles with a higher electrochemically active surface area (ECSA).
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Maalouf, Manale W. "Structure and Dynamics Influencing Proton Transport in Materials for High Temperature (120 °C) PEM Fuel Cells." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1311010188.
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Yuan, Hongyu. "Optimization of an Innovative Npu-N Resin Production." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555591103161637.
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Van, der Walt Franschua Johan. "Factors influencing the catalytic activity of Fe-ZSM-5 during the catalytic conversion of N₂O." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/24323.
Full textAbstract:
Zeolites have found widespread applications as acid catalysts for decades. By introducing transition metal ions in the cation position, the zeolite is transformed into a redox catalyst. The nature of the trivalent heteroatom influences the properties of the zeolite. Contrary to Al-zeolites, Fe-containing zeolites show redox properties, since Fe can easily change its oxidation state (Fe²⁺, Fe³⁺, or Fe⁴⁺). Catalytic function of isolated redox sites within zeolite cavities (or channels) may result in a material with specific redox properties (Kiwi-Minsker et al., 2003). The properties of transition metal exchanged zeolites have been studied from the 1960's onwards and the conversion of N₂O over Fe-Y zeolites has been studied by Fu et al. (1981) in late 1970's. In this study, the preparation of iron ZSM-5 zeolite catalysts by mechanochemical means and thermally induced solid-state ion exchange was studied. After grinding the NH4-Zeolite and ferrous chloride, no x-ray reflections characteristic of ferrous chloride are detected. After heating the sample to 120 and 200 °C reflections characteristic of ferrous chloride are visible but disappear upon further heating to 300 °C. No porosity is observed after grinding and heating up to 200 °C as a result of pore mouth blocking. Moreover, upon heating up to 500 °C porosity starts to develop with pore volumes and pore sizes slightly lower than those of the parent zeolite. From the thermogravimetric analysis it is evident that the ion exchange takes place during calcination from 150 and 420 °C in agreement with the literature. In the second part of the study commercial Fe-ZSM-5 catalyst samples with different N₂O conversion activities (in the presence of H₂O and NO at 425 °C), ranging between 70 and 90 % (high, mid and low activity) are studied and characterised. The effect of temperature during calcination of the plant produced and laboratory calcined extrudate catalyst material was investigated. Panov et al. (1996) reported in the literature that the Fe²⁺ is oxidised to Fe³⁺ in the presence of N₂O forming what they called the α-oxygen, a form of active surface oxygen, with the evolution of molecular nitrogen. During the conversion, two surface α-oxygen atoms migrate, combine and desorbs as molecular oxygen from the surface. The α-oxygen forms between 200 and 350 °C and desorbs as molecular oxygen above 350 °C (Taboada et al., 2005). In this study, no correlation to N₂O conversion activity could be found for the α-oxygen content and correspondingly the concentrations of the respective iron oxides and iron hydroxides in the Fe-ZSM-5 samples.
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Bertrand-Caumont, Karine. "Conception et synthèse de N. C. E. (New Chemical Entities), ligands des récepteurs NK1 de la substance P." Lille 1, 1996. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/1996/50376-1996-262-1.pdf.
Full textAbstract:
Depuis quelques années, d'importants efforts ont été réalisés pour élaborer des antagonistes des récepteurs nk1 de la substance p (sp). Nous détaillons ici la mise en évidence de ligands de ces macromolécules. Une étude s'appuyant sur les mécanismes de reconnaissance moléculaire d'antagonistes connus et sur la confrontation de relations structure-affinité établies pour des molécules structuralement voisines révèle l'existence de deux types de pharmacophores. Ils se distinguent par la substitution du groupement benzylique qu'ils portent : le pharmacophore de type i possède un groupement benzylique monosubstitué en ortho par un méthoxy, voire non substitué le pharmacophore de type ii est caracterisé par un groupement benzylique disubstitué en méta par des trifluorométhyles. Des modifications structurales de leads peptidiques, identifies pour les deux classes de ligands, permettent d'élaborer des n. C. E. (new chemical entities) ligands des récepteurs de la sp. Possédant les pharmacons de type i, trois squelettes révèlent une liaison modeste pour la protéine nk1. Ils s'articulent autour d'un noyau indole pour le premier. D'un noyau 1,2,3,4-tétrahydroquinoxaline pour le deuxième. D'une pipérazine pour le dernier. Une autre structure originale fondée sur le noyau 1-amino-1,2,3,4-tétrahydronaphtalène contient les pharmacogroupements de type ii et révèle une affinité intéressante pour les récepteurs de la sp
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Hlabangana, Ntandoyenkosi. "Influence of particle size and morphology of Pt₃Co/C on the oxygen reduction reaction." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/24324.
Full textAbstract:
Polymer electrolyte fuel cells have shown great potential in providing clean energy with no emissions. The kinetics of the cathode reaction, i.e. the oxygen reduction reaction (ORR) are sluggish necessitating high loadings of the catalyst metal, i.e. platinum. Platinum is a limited resource and expensive. Its price has been one of the major drawbacks in wide scale commercialisation of fuel cells. In an effort to improve the activity of the catalyst and therefore reduce Pt loadings on the catalyst, Pt can be alloyed with transition metal elements (e.g. Ni, Co and Fe) to form bimetallic catalysts. Alloying has been known to improve the activity and stability of a catalyst for the ORR. The enhanced activity of the alloys originates from the modified electronic structures of the Pt in these alloy catalysts which reduces the adsorption of spectator species therefore increasing the number of active sites for the ORR (Wang et al., 2012 (2)). The aim of this study was to gain a better understanding of the influence of Pt alloy particle size and active surface morphology on the ORR activity. The Pt alloy that was investigated was Pt₃Co/C. The surface morphology was modified by varying the Pt/Pt₃Co loading on a carbon support. The catalysts were prepared using thermally induced chemical deposition. The support used was Vulcan-XC-72R. The effects of varying the metal loadings on the ORR was investigated. The loadings that were investigated were 20, 40, 60 and 80 wt. % Pt and Pt₃Co. The alloy catalysts were subjected to annealing at 900 °C and acid leaching. The catalysts were analysed using electrochemical characterisation techniques such as cyclic voltammetry, CO stripping voltammetry, rotating disk electrode and rotating ring disk electrode. Physical characterisation of the catalysts was also implemented. The techniques used were x-ray diffraction, thermogravimetric analysis and transmission electron microscopy. The Pt particles on the carbon support were found not to agglomerate significantly despite the loading being increased. This trend was also observed for the Pt₃Co/C catalysts even after heat treatment and leaching. The lack of agglomeration was credited to a new reactor system developed in this work. The particle growth increased from low loadings to high loadings for both the Pt/C and Pt₃Co/C catalysts. Particle growth was more significant for the Pt₃Co/C catalysts at high loadings. At lower loadings (20 and 40 wt. %) the particle sizes between the Pt/C and Pt₃Co/C catalysts were comparable despite the Pt₃Co/C catalysts undergoing annealing and leaching. The mass specific activity of the Pt/C catalysts was not improved by alloying with the exception of the 20 wt. % catalyst which saw an enhancement factor of 1.66. The surface specific activity of the Pt/C catalysts was improved significantly with factors of 2.40 and 3.11 being recorded for the 20 and 80 wt. % Pt₃Co/C catalysts respectively. The enhancement factors of the intermediate loadings (40 and 60 wt. %) were lower and fairly similar at 1.30 and 1.35 respectively.