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1
Khalil, Enam A. S. A. "A thermodynamic study of binary and ternary mixtures of some alkanes and alkanols." Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328889.
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Løften, Thomas. "Catalytic isomerization of light alkanes." Doctoral thesis, Norwegian University of Science and Technology, Department of Chemical Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1909.
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<p>In recent years the levels of sulfur and benzene in the gasoline pool have been reduced, and in the future there may also be new regulations on vapor pressure and the level of aromatics and olefins as well. The limitations on vapor pressure and aromatics will lead to reduced use of C<sub>4</sub> and reformate respectively. The branched isomers of C<sub>5</sub> and C<sub>6</sub> alkanes have high octane numbers compared to the straight chain isomers, and are consequently valuable additives to the gasoline pool. To maintain the octane rating, it is predicted that an increased share of isomerate will be added to the gasoline pool.</p><p>Today there is a well established isomerization technology with platinum on chlorided alumina as the commercial catalyst for both isomerization of n-butane and of the C<sub>5</sub>/C<sub>6</sub> fraction. This catalyst is very sensitive to catalyst poisons like water and sulfur, and strict feed pretreatment is required. Zeolites promoted by platinum are alternatives as isomerization catalysts, and has replaced Pt/alumina catalysts to some extent. The Pt/zeolite catalyst is more resistant to water and sulfur compounds in the feed, but it is less active than platinum on chlorided alumina. It does therefore require a higher reaction temperature, which is unfortunate since the formation of the branched isomers of the alkanes is thermodynamically favored by a low temperature.</p><p>Because of the limitations of the two types of isomerization catalysts, there is a search for a new catalyst that is resistant to sulfur and water in the feed and is highly active so it can be operated at low temperature. A new type of catalyst that seems to be promising in that respect is sulfated zirconia.</p><p>The first part of this study focuses on a series of iron and manganese promoted SZ catalysts. The catalysts were characterized by various techniques such as XRD, TGA, N<sub>2 </sub>adsorption and IR spectroscopy of adsorbed pyridine. The catalytic activity in n-butane isomerization at 250°C and atmospheric pressure was compared to the physical and chemical properties of the samples. No promoting effect of iron and manganese was found when n-butane was diluted in nitrogen. When nitrogen was replaced by hydrogen as the diluting gas the activity of the unpromoted SZ sample was dramatically lowered, while the activity of the promoted catalyst was not significantly changed.</p><p>If we only consider the promoted samples, the catalytic activity increases with increasing iron/manganese ratio. We also observe that the activity of the samples is clearly correlated with the number of strong Brønsted acid sites. The total number of strong acid sites (i.e. the sum of Brønsted and Lewis sites) does not change significantly when the promoter content is changing, hence no correlation between catalytic activity and the total number of acid sites is found. This underlines the importance of discrimination between Lewis and Brønsted acidity when characterizing the acidity of the samples.</p><p>The second part of this study is focused on a series of noble metal promoted sulfated zirconia. Their catalytic activity in n-hexane isomerization at high pressures was compared to a commercial Pt/zeolite catalyst. Among the noble metal promoted samples the catalyst promoted with platinum was the most active. The samples promoted with rhodium, ruthenium and iridium showed equal activity.</p><p>Common for all the noble metal promoted catalysts is the large increase in activity when catalysts are reduced with hydrogen compared to when they are pretreated in helium. The increase in activity is most likely connected to the reduction of the metal oxides of the promoters to ensure that the promoters are in the metallic state. Reduction at too high temperatures does however give lower activity. This is probably due to the reduction of surface sulfate groups leading to a loss in acid sites.</p><p>The commercial sample was considerably less active than the sample of platinum promoted sulfated zirconia. The commercial catalyst was however more stable than the PtSZ catalyst. All the sulfated zirconia catalysts deactivated, but the initial activity could be regenerated by reoxidation at 450°C followed by reduction at 300°C. The promotion with noble metals appears to inhibit coke formation on the catalyst. But, the main cause of deactivation of the platinum promoted sample is most likely the reduction of sulfate species leading to a loss of acid sites.</p><p>The kinetic study of the catalysts indicates that the n-hexane isomerization proceeds via a classical bifunctional mechanism where the role of the promoting metal is to produce alkenes, which are subsequently protonated on the acid sites. The reaction orders of hydrogen, n-hexane and total pressure are all in accordance with this mechanism. The activation energies of the catalysts are within the typical range of bifunctional catalysts.</p><p>All catalysts, except the unpromoted SZ sample, showed close to 100% selectivity to branched hexane isomers and a similar distribution of these isomers. The isomer distribution being the same for both the noble metal promoted catalyst and the Pt/zeolite is another indication that the isomerization proceeds via the bifunctional mechanism over the promoted samples. The different selectivity of the unpromoted SZ catalyst indicates that the isomerization proceeds via a different pathway over this catalyst; this is probably a pure acidic mechanism</p><p>The acidity characterization can not explain the differences in isomerization activity. It is however likely that the activity of the promoting metals in the dehydrogenation of alkanes is important since the classical bifunctional mechanism is prevailing.</p>
3
Pongtavornpinyo, Ruti. "Indium Carbenes Alkenes and Alkanes." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508494.
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Marozzelli, Filippo. "Alkanes activation over oxide catalysts." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/60089/.
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The basics of the oxidation mechanism of different alkanes within zeolites and over molybdenum oxide surfaces were studied employing state of the art computational modelling. It was shown that the constrained environment inside MFI, MFS and MOR induces terminal selectivity on the reaction of 6-, 8- and 10- term linear alkanes, i.e. hexane, octane and decane, respectively. The Monte Carlo (MC) random alkane configuration sampling showed that the oxidation reactivity is driven by the fact that the terminal C atoms of the substrate are more likely to be closer to the zeolites internal walls than the methylene (–CH2–) C atoms. As a confirmation of this, the calculation of kprim/ksec for all the host/guest (alkane/zeolite) systems estimated that the pore effect exerted by the zeolites in the reaction favors terminal products (terminal selectivity). The alkane oxidation over MoO3(010), Fe2(MoO4)3(001) and (110) surfaces involved the activation of a C–H bond of the substrate. The surface calculations were carried out using DFT+U to localize the electrons at a terminal point of the surface. Energy comparison with hybrid DFT (B3LYP) calculations for cluster models of the MoO3(010) surface showed consistency with the DFT+U results. The propane terminal C–H bond activation generated a propyl radical. Transition state structures were found for the adsorption of radical species on MoO3(010) and Fe2(MoO4)3(001) surface and the corresponding energy barriers showed that the adsorption on the former system is favored, which indicates that the Fe2(MoO4)3 surface alone is not a good catalyst for the reaction studied.
5
ZHENG, TAO. "MOLECULAR SIMULATION OF DIFFUSION AND SORPTION OF ALKANES AND ALKANE MIXTURES IN POLY[1-(TRIMETHYLSILYL)-1-PROPYNE]." University of Cincinnati / OhioLINK, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=ucin973701057.
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Xu, Xiangrong. "Uranyl ion sensitised photooxidation of alkanes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq27436.pdf.
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Gomes, Ana Catarina Costa. "Photocatalysis : Carbonylation of arenas and alkanes." Thesis, University of York, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.516370.
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Smith, Paul Andrew. "Simulation studies of alkanes and surfactants." Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314225.
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Shiimi, Annatolia. "Modeling Diiron enzymes for alkanes activation." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/10669.
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Includes abstract.<br>Includes bibliographical references.<br>The synthesis and characterization of a series of ruthenium 'sawhorse' complexes of the type [RU2(IJ-02CRh(CO)4(Lh]' has been successfully carried out. The complexes have been characterized by IR, 1H and 13C NMR spectroscopy, elemental analysis as well as by mass spectrometry.
10
Correia, Leslie Daniel Camara. "Oxygen transfer in hydrocarbon-aqueous dispersions and its applicability to alkane-based bioprocesses." Thesis, Link to the online version, 2007. http://hdl.handle.net/10019/999.
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Perry, Jason Kendrick Goddard William A. "Alkane activation by first, second, and third row transition metal ions organometallic chemistry in the gas plate /." Diss., Pasadena, Calif. : California Institute of Technology, 1994. http://resolver.caltech.edu/CaltechTHESIS:11122009-152204878.
Texte intégralRésumé :
Thesis (Ph. D.)--California Institute of Technology, 1994. UM #94-27,313.<br>Advisor names found in the Acknowledgements pages of the thesis. Title from home page. Viewed 01/14/2010. Includes bibliographical references.
12
Ramakrishnan, Ayyappan. "Visible light induced catalytic sulfoxidation of alkanes." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981136915.
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Putra, Edy Giri Rachman. "Solution crystallization of long chain n-alkanes." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401188.
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Gallagher, P. "The reductive decomposition of bis-diazo-alkanes." Thesis, University of Liverpool, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381343.
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Su, Yee San 1977. "The heterogeneous partial oxidation of light alkanes." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28306.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2004.<br>Includes bibliographical references.<br>(cont.) With this approach, an upper bound on the yield for OCM was computed. Results showed that even with optimal surface chemistry, strict limits existed on the attainable yield. Surface energetics necessary for superior OCM performance were identified and the origins of these requirements elucidated. The resulting upper bound on OCM yield under conventional, packed-bed, continuous-feed operation was found to be 28%. The catalytic properties of LiCl/sulfated ZrO₂-based catalysts were explored for ODHE. LiCl was shown to strongly interact with the acid sites on sulfated ZrO₂ (SZ), influencing its catalytic behavior. Two approaches were taken to modify the nature/strength of the LiCl-support interaction. Firstly, LiCl/Nd₂O₃-impregnated MoO/ZrO₂ and WOx/ZrO₂ were examined. Unlike SZ, these supports allowed for the tailoring of MoO[sub]x and WO[sub]x surface densities, which in turn drastically altered their ODHE performance. The poor stability of these supports, however, rendered them inferior to SZ. Secondly, the effects of dopant incorporation on the catalytic behavior of LiCI/MO,/SZ were studied. Si-doped ZrO₂-based catalysts synthesized via the sol-gel method were found to exhibit superior activity, selectivity and stability for ODHE. Sulfate decomposition experiments related the ODHE activity of these materials to the influence of the Si dopant on the sulfate binding strength. The sol-gel synthesis conditions were optimized with respect to sol pH, water:alkoxide ratio and silicon precursor, achieving improved catalyst homogeneity and enhanced ODHE performance ...<br>Within the petrochemical industry, a sizeable economic incentive exists for the upgrading of low-value, light alkanes. For instance, the dehydrogenation of ethane to ethene is of considerable interest due to ethene's use as a polymeric and chemical precursor. Partial oxidation provides an attractive alternative to standard pyrolysis methods for alkane-to-alkene conversion. Unlike pyrolysis, partial oxidative routes are largely unaffected by coke formation and have the added benefit of exothermicity. With the inclusion of oxygen as a reactant, however, numerous additional reaction pathways result. Among these, the presence of parallel and consecutive reaction channels to CO[sub]x products is of major concern. For this reason, previous efforts to create selective partial oxidation catalysts with high activity have typically fallen below economic feasibility requirements. This thesis focuses on the following alkane-to-alkene transformation reactions: Oxidative Coupling of Methane (OCM): 2CH₄ + O₂ <--> C₂H₄ + 2 H₂O Oxidative Dehydrogenation of Ethane (ODHE): C₂H₆ + 1/2 O₂ <--> C₂H₄ + H₂O Oxidative Dehydrogenation of Propane (ODHP): C₃H₈ + 1/2 O₂ <--> C₃H₆ + H₂O. Regarding OCM, an approach was presented for determining an upper bound on the yield of a catalytic process, which allowed for variations in the catalytic chemistry. Scaling and thermodynamic arguments were used to set parameters of an elementary step surface mechanism at values resulting in optimal yields, subjected only to physical constraints. Remaining unknowns were treated as independent variables and varied over a broad range. The result was a set of thermodynamically consistent mechanisms with optimal kinetics that could be incorporated into reactor-transport models.<br>by Yee San Su.<br>Ph.D.
16
Grant, C. R. "Evaluation of the bio-oxidation of alkanes." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1367613/.
Texte intégralRésumé :
This thesis documents the progress made in utilising the alkane hydroxylase complex of P.putida GPo1 expressed in E.coli as a whole-cell biocatalyst for the oxidation of n-dodecane to 1-dodecanol. The process is of considerable interest due to the difficulty in performing the reaction using conventional chemistry and the large global market for fatty alcohols. The first results chapter compares the fermentative bio-oxidations using E.coli pGEc47ΔJ on n-octane and n-dodecane in a stirred tank reactor. The first reported conversion of n-dodecane in-vivo using this enzyme system in a recombinant host is reported. A number of bottlenecks were identified in this chapter; in particular, (i) poor induction of the alkS expression system with ndodecane, which controls the expression of the alk enzymes (ii) a suspected mass transport limitation (iii) substantial over-oxidation of the desired 1- dodecanol product to dodecanoic acid. The second results chapter firstly describes the development of a microwell platform in order to characterise the system more efficiently. Phase mixing limitations and organic phase spillage/evaporation were overcome in order to develop the microwell platform for the fermentative bio-oxidation which is the first reported microwell scale-down which matches the volumetric and specific rates achieved in a bioreactor for a substrate of such low solubility. Secondly, the microwell platform was used with design of experiments (DoE) methodology to rapidly and systematically characterise the overoxidation issue and identify appropriate solutions. Using this approach, substrate solubility was identified as the most critical factor affecting the tendency for overoxidation; the use of cosolvents to improve n-dodecane solubility in the aqueous phase was found to improve the 1-dodecanol yields and reduce dodecanoic acid yields. Oxygen availability and carbon source availability also proved important factors in the extent of overoxidation. Despite the improvements made the problem was only partially overcome and it was decided, based on the results, that biological engineering of the strain was necessary to remove the downstream aldehyde dehydrogenase alkH which was likely to be exacerbating overoxidation. The process of designing and constructing 3 new plasmids is described in results chapters four and five. These plasmids were designed with the aim of identifying the role of various alk proteins and ultimately identifying ways of improving substrate access to the enzyme and reducing overoxidation. It was found as a result of this work that overoxidation was reduced by removal of alkH but that the alkane-1-monooxygenase alkB was still capable of direct overoxidation to the dodecanoic acid even in the absence of alkH. More significantly, the function of an outer membrane protein of unknown function was also confirmed by this work. It was found to be essential for conversion of n-dodecane in-vivo but was also found to be toxic to the host organism when overexpressed. Finally, it was found that the alkane-1-monooxygenase enzyme system was also capable of C14 and C16 alkane oxidation; this has not previously been reported in literature in-vivo.
17
Waldstein, Nathaniel A. "Analysis of pump oil and alkanes evaporation." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002786.
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Criswell, Leah. "Neutron diffraction and quasielastic neutron scattering studies of films of N-alkanes and a branched alkane absorbed on graphite." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/6010.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2007.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 11, 2008) Includes bibliographical references.
19
Peter, Sebastian. "Oxyfunctionalization of alkanes, alkenes and alkynes by unspecific peroxygenase (EC 1.11.2.1)." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-113321.
Texte intégralRésumé :
Unspecific peroxygenase (EC 1.11.2.1) represents a group of secreted hemethiolate proteins that are capable of catalyzing the selective mono-oxygenation of diverse organic compounds using only H2O2 as a cosubstrate. In this study, the peroxygenase from Agrocybe aegerita (AaeUPO) was found to catalyze the hydroxylation of various linear (e.g n-hexane), branched (e.g. 2,3-dimethylbutane) and cyclic alkanes (e.g. cyclohexane). The size of n-alkane substrates converted by AaeUPO ranged from gaseous propane (C3) to n-hexadecane (C16). They were mono-hydroxylated mainly at the C2 and C3 position, rather than at the terminal carbon, and the corresponding ketones were formed as a result of overoxidation. In addition, a number of alkenes were epoxidized by AaeUPO, including linear terminal (e.g. 1-heptene), branched (2-methyl-2-butene) and cyclic alkenes (e.g. cyclopentene), as well as linear and cyclic dienes (buta-1,3-diene, cyclohexa-1,4-diene). Furthermore, the conversion of terminal alkynes (e.g. 1- octyne) gave the corresponding 1-alkyn-3-ol in low yield. Some of the reactions proceeded with complete regioselectivity and - in the case of linear alkanes, terminal linear alkenes and alkynes - with moderate to high stereoselectivity. The conversion of n-octane gave (R)-3-octanol with 99% enantiomeric excess (ee) and the preponderance of the (S)-enantiomer reached up to 72% ee of the epoxide product for the conversion of 1-heptene. Catalytic efficiencies (kcat/ Km) determined for the hydroxylation and respectively epoxidation of the model compounds cyclohexane and 2-methyl-2-butene were 2.0 × 103 M-1 s-1 and 2.5 × 105 M−1 s−1. The results obtained in the deuterium isotope effect experiment with semideuterated n-hexane and the radical clock experiment with norcarane clearly demonstrated that the hydroxylation of alkanes proceeds via hydrogen abstraction, the formation of a substrate radical and a subsequent oxygen rebound mechanism. Moreover, stopped-flow experiments and substrate kinetics proved the involvement of a porphyrin radical cation species (compound I; AaeUPO-I) as reactive intermediate in the catalytic cycle of AaeUPO, similar to other hemethiolate enzymes (e.g. cytochrome P450 monooxygenases, P450s)<br>Die Gruppe der Unspezifischen Peroxygenasen (EC 1.11.2.1) umfasst extrazelluläre Häm-Thiolat-Enzyme, die mittels H2O2 als Cosubstrat die selektive Monooxygenierung unterschiedlicher organischer Verbindungen katalysieren. In der vorliegenden Arbeit konnte gezeigt werden, dass die von Agrocybe aegerita sekretierte Peroxygenase (AaeUPO) verschiedene lineare (z. B. n-Hexan), verzweigte (z. B. 2,3-Dimethylbutan) und zyklische Alkane (z. B. Cyclohexan) hydroxyliert. Die Größe der von der AaeUPO umgesetzten Substrate reichte vom gasförmigen Propan (C3) bis hin zu n-Hexadekan (C16). Die Alkane wurden bevorzugt am zweiten und dritten Kohlenstoffatom (C2 und C3) hydroxyliert; eine Hydroxylierung am terminalen Kohlenstoff konnte nur vereinzelt und in geringem Umfang beobachtet werden. Die Überoxidationen der primär gebildeten, sekundären Alkohole führte außerdem zur Entstehung der entsprechenden Ketonderivate. Darüber hinaus wurde eine Vielzahl linearer terminaler (z. B. 1-Hepten), verzweigter (z. B. 2-Methyl-2-Buten) und zyklischer Alkene (z. B. Cyclopenten) sowie linearer und zyklischer Diene (1,3-Butadien, 1,4-Cyclohexadien) durch die AaeUPO epoxidiert. Die Umsetzung terminaler Alkine (z. B. 1-Octin) führte zur Entstehung der jeweiligen 1-Alkin-3-ole. Manche dieser Reaktionen verliefen ausgeprägt regioselektiv und, im Falle der linearen Alkane sowie der linearen terminalen Alkene und Alkine, mit mittlerer bis hoher Stereoselektivität. So ergab beispielsweise die Umsetzung von n-Octan einen Enantiomerenüberschuss größer 99% für (R)-3-Octanol; die Epoxidierung von 1-Hepten lieferte einen Enatiomeerenüberschuss (ee) von bis zu 72% für das (S)-Enantiomer. Die katalytischen Effizienzen, die für die Hydroxylierung bzw. Epoxidierung der Modellverbindungen Cyclohexan und 2-Methyl-2-Buten ermittelt wurden, betragen 2.0 × 103 M-1 s-1 und 2.5 × 105 M−1 s−1. Der ausgeprägte Deuterium-Isotopen-Effekt, der im Zuge der Umsetzung von semideuteriertem n-Hexan beobachtet wurde sowie die Ergebnisse des Radical-Clock-Experiments mit Norcarane als Substrat bestätigten, dass die Hydroxylierung von Alkanen über Wasserstoffabstraktion, die Bildung eines Substratradikals und anschließende direkte Sauerstoffrückbindung verläuft. Die Stopped-Flow-Experimente belegen zudem das Auftreten eines Porphyrin-Kationradikal-Intermediates (Compound I; AaeUPO-I) im katalytischen Zyklus der AaeUPO (vergleichbar mit dem reaktiven Intermediat der P450-Monooxygenasen)
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Grootboom, Natasha Denise. "Alkane oxidation using metallophthalocyanine as homogeneous catalysts." Thesis, Rhodes University, 2002. http://hdl.handle.net/10962/d1007794.
Texte intégralRésumé :
Iron polychlorophthalocyanine (FePc(Cl)₁₆) and tetrasulfophthalocyanine ([M¹¹TSPc]⁴) complexes of iron, cobalt and manganese are employed as catalysts for the oxidation of cyclohexane using tert-butyl hydroperoxide (TBHP), chloroperoxybenzoic acid (CPBA) and hydrogen peroxide as oxidants. Catalysis using the FePc(Cl)₁₆ was performed in a dimethylformamide:dichloromethane (3 :7) solvent mixture. For the [Fe¹¹TSPc]⁴⁻, [Co¹¹TSPc]⁻ and [Mn¹¹TSPc]⁴⁻catalysts, a water:methanol (1:9) mixture was employed. The products of the catalysis are cyclohexanone, cyclohexanol and cyclohexanediol. The relative percentage yields, percentage selectivity and overall percentage conversion of the products depended on types of oxidant, or catalyst, concentrations of substrate or catalysts and temperature. TBHP was found to be the best oxidant since minimal destruction of the catalyst and higher selectivity in the products were observed when this oxidant was employed. Of the four catalysts investigated [Fe¹¹TSPc]⁴⁻ yielded the highest overall percentage conversion of 20%.The mechanism of the oxidation of cyclohexane in the presence of the FePc(Cl)₁₆ and [M¹¹TSPc]⁴⁻ involves the oxidation of these catalysts, forming an Fe(IlI) phthalocyanine species as an intermediate. Electrocatalysis using [Co¹¹TSPc]⁴⁻ as catalyst, employed an aqueous pH 7 buffer medium for electro-oxidation of 4-pentenoic acid. An enone is suggested as the only oxidation product of 4-pentenoic acid. No degradation of [Co¹¹TSPc]⁴⁻ was observed during the electrocatalytic process. In this process water was used as a source of oxygen therefore eliminating the production of by products from oxidant as in the case of TBHP and CPBA. This system was studied In an attempt to set up conditions for alkane electrocatalytic oxidation.
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Stevenson, Julie-Anne. "Selective oxidation of simple alkanes by cytochrome P450cam." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302491.
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El, Nikheli A. H. D. "Phase equilibria in mixtures containing alkanes and alcohols." Thesis, Loughborough University, 1987. https://dspace.lboro.ac.uk/2134/10419.
Texte intégralRésumé :
Vapor-liquid equilibria (VLE) in alkanes and alcohols was measured and a contribution Patel-Teja (GPT) equation proposed in this work. systems of nmodified Group of state was Isothermal vapor-liquid equilibria at temperatures between 298.7K and 333. 7K have been measured for the binary systems n-pentane + n-hexane. n-pentane + noctane. n-pentane + n-decane. and n-pentane + l-propanol. The data were found to be consistent according to a point-to-point consistency test and were correlated using the Wilson. NRTL. and UNIQUAC activity coefficient models. The parameters of the models were estimated using the maximum likelihood principle. A new version of the Group contribution Patel-Teja equation of state was proposed in which a new temperature dependent group interaction expression was introduced. Group interaction parameters for four constituent groups of the alcohols and n-alkanes (viz. CH 2• CH 3 • CH and OH) were determined. These parameters were then used for the prediction of VLE in mixtures of n-alkane + n-alkane. n-alkane + n-alcohol. and n-alcohol + n-alcohol. VLE predictions with the new GPT equation of state were found to be superior to predictions with the original group contributions with molecular equations. The modified equation can be used in systems of nalkanes and alcohols where data for molecular parameters are lacking. The proposed temperature dependence of the group interaction parameters improved predictions over a wide range of temperature and pressure.
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Hall, Christopher. "The coordination of alkanes to transition metal fragments." Thesis, University of York, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.331939.
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Bourdin, Vincent, Stefano Brandani, Alfeno Gunadi, Hervé Jobic, Cordula Krause, Jörg Kärger, and Wolfgang Schmidt. "Diffusion of n-alkanes in MFI-type zeolites." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196416.
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Moses, Alvira. "Synthesis of surface active alkanes for cellulose modification." Thesis, Stellenbosch : University of Stellenbosch, 2006. http://hdl.handle.net/10019.1/4874.
Texte intégralRésumé :
119 leaves single sided printed, preliminary pages and numbered pages 1-101. Includes bibliography and a list of tables, figures, schemes and abbreviations. Digitized at 300 dpi (OCR), used Bizhub 250.<br>Thesis (MSc (Polymer Science))--University of Stellenbosch, 2006.<br>ENGLISH ABSTRACT: The properties and interactions of cellulose surfaces are of a great technical interest
during papermaking and recycling. Sizing, the modification of fiber surfaces, e.g. with
the purpose to reduce water penetration into the paper structure, plays an important role
in obtaining paper with good printability and water resistance. Water resistance is the key
end-property of paper being investigated in this study.
Firstly a comparison was made between the degree of surface modification of cellulose
by means of anionic, nonionic and reactive surfactants. The amount of surfactant
adsorbed by the paperboard was determined and the paper surface evaluated via scanning
electron microscopy (SEM). The sizing efficiency of the three industrial surfactants was
evaluated in order to establish the surfactant structure best suited for sizing recycled
paperboard. This was done via the Cobb test, an industrial method to measure water
uptake by paper, and contact angle measurements. The reactive surfactant was found to
have the best sizing efficiency and focus shifted to synthesizing selected copolymer
surfactants via free radical copolymerization.
Two copolymers were synthesized, with maleic anhydride as the polar part in both. Butyl
methacrylate and lauryl methacrylate were selected as the hydrophobic parts in the
respective copolymer systems. The unavailability of reactivity ratios for the respective
copolymer systems led to the use of in situ proton nuclear magnetic resonance
spectroscopy CH NMR) for the determination of the co-monomer incorporation in both
copolymer systems. Quantitative 13C NMR spectroscopy was also employed in order to
establish the co-monomer content of the isolated copolymers obtained during bench-scale
(laboratory) experiments.
Lastly, a comparison of the degree of surface modification of cellulose was made
between that which was achieved with the industrial reactive surfactant and that with the
two synthesized polymeric reactive surfactants. The two synthesized polymeric
surfactants were found to have a better sizing efficiency than the industrial reactive
surfactant, and the maleic anhydride-lauryl methacrylate copolymer system gave the best
results.<br>AFRIKAANSE OPSOMMING: Die eienskappe en interaksies van sellulose-oppervlaktes is van groot tegniese belang
gedurende die vervaardiging en hergebruik van papier. Oppervlakte behandeling, die
modifikasie van vesel-oppervlaktes bv. met die doel om water indringing in die
papierstruktuur te verminder, speel 'n belangrike rol in die daarstel van papier met goeie
drukkwaliteit en waterweerstand. Waterweerstand is die sleuteleienskap van papier wat in
hierdie werkstuk ondersoek word.
Eerstens is daar 'n vergelyking getref tussen die verandering van sellulose-oppervlaktes
deur middel van anioniese, nie-ioniese en reaktiewe sepe. Die hoeveelheid seep
geabsorbeer deur die papierbord is bepaal en die papier-oppervlak ondersoek deur middel
van skandeer-elektronmikroskopie (SEM). Die behandelingsdoeltreffendheid van die drie
industriele sepe is ondersoek om vas te stel watter seep die beste struktuur het om
hergebruikte papierbord effektief te behandel. Dit is gedoen deur middel van die Cobbtoets,
'n industriele metode om wateropname van papier te meet, asook
kontakhoekmetings. Daar is gevind dat die reaktiewe seep die beste
behandelingsdoeltreffendheid het en daar is vervolgens gekonsentreer op die bereiding
van geselekteerde reaktiewe kopolimeersepe deur middel van vryeradikaalkopolimerisasie.
Twee kopolimere is berei, met maleienanhidried as die polere gedeeite van albei.
Butielmetakrilaat en laurielmetakrilaat is gekies vir die nie-polere gedeeltes van die
onderskeie kopolimeersisteme. Die onbeskikbaarheid van reaktiwiteitsverhoudings vir
die onderskeie kopolimeersisteme het gelei tot die gebruik van in situ proton kern
magnetiese resonansie spektroskopie eH KMR) vir die bepaling van die ko-monomeer
insluiting in beide kopolimeersisteme. Kwantitatiewe koolstofdertienkemmagnetieseresonansie
spektroskopie (13C KMR) is ook gebruik om die ko-monomeerinhoud van die
geisoleerde kopolimere, verkry tydens laboratoriumeksperimente, te bepaal.
Laastens is 'n vergelyking getref tussen die graad van modifikasie van selluloseoppervlaktes
deur middel van die industriele reaktiewe seep in vergelyking met die twee
bereide polimeriese reaktiewe sepe. Daar is gevind dat die twee gesintetiseerde
polimeriese sepe beter behandelingsdoeltreffendheid as die industriele reaktiewe seep het,
met die maleienanhidried-laurielmetakrilaat-kopolimeersisteem wat die beste resultaat
lewer.
26
Schwarz, Cara Elsbeth. "The phase equilibrium of alkanes and supercritical fluids." Thesis, Stellenbosch : University of Stellenbosch, 2001. http://hdl.handle.net/10019.1/2532.
Texte intégralRésumé :
Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2001.<br>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.
27
Du, Xian. "Catalysis for CO2 activation reactions with light alkanes." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:924c17f7-5b71-4e70-b304-e0686d0413ea.
Texte intégralRésumé :
CO<sub>2</sub>, without question, the most famous greenhouse gas, is known to have an increasing concentration in both the atmosphere and oceans. To slow down the pace not only of global warming but also the ocean acidification, several routes are proposed to effectively reduce the net emission of CO<sub>2</sub>. Compared to Carbon Capture and Sequestration/Storage (CCS), Carbon Capture and Utilisation (CCU) has much more potential because of the lower costs of scale up and higher profitability to potentially attract capital investment. Different from the conventional CCU route which is to reduce CO<sub>2</sub> to fuels with hydrogen generated via renewable-energy-driving electricity, two processes are investigated in this thesis; that of Dry Methane Reforming (DMR) and the DeHydrogenation of Propane by CO<sub>2</sub> (DHP by CO<sub>2</sub>). The projects on these two processes not only develop catalysts which would be suitable for the reaction performance, but also the ultimate aim is to link the processes with a renewable energy source (in the thesis we chose Solar Thermal Heating).Thermodynamic calculations and process simulations were also evaluated. The results of DMR unfortunately did not indicate a promising future to link with Solar Thermal Heating due to the very high temperature required during the process. However, the results of thermodynamic calculations and process simulations in DMR project illustrate a good opportunity to utilise flue gas in industry through the so-called Tri- Methane Reforming (TMR). In the DHP by CO<sub>2</sub> process, the catalysts developed were less promising than the ones in DMR due to the severe side-reactions occurred which significantly decreased the selectivity for the desired product. However - and importantly - through our thermodynamic calculations and process simulations, the DHP by CO<sub>2</sub> process has a bright future if the Solar Thermal Heating can be applied with the relative lower temperature requirement, making the CO<sub>2</sub> utilisation process much easier to be fulfilled than DMR.
28
Wickramarachchi, P. A. S. R. "Vibrational spectroscopy of linear and branched long alkanes." Thesis, Sheffield Hallam University, 2006. http://shura.shu.ac.uk/20531/.
Texte intégralRésumé :
In this work we studied monodisperse long chain alkanes as model compounds for semi crystalline polymers, using vibrational spectroscopy. The interest in vibrational spectroscopy is due to its sensitivity to both the crystalline structure and conformational disorder. We used the following vibrational techniques: Fourier transform infrared transmission, Fourier transform infrared - attenuated total reflection (FTIR-ATR), Raman spectroscopy and Inelastic neutron scattering (INS) spectroscopy. In addition, small angle X-ray scattering (SAXS) was used where necessary. In this study FTIR-ATR and INS techniques were not successful in the characterisation of long chain alkanes. A Raman spectroscopic method, based on conformationally sensitive vibrations, was established using a short chain n-alkane to identify solid-solid phase transitions and was applied to long chain alkanes. Using this method a transition to a non-integer form (NIF) form was identified in two 'Y-shaped' long chain alkane samples at similar temperatures as SAXS. One of these samples is partially deuterated (with deuterium end caps) while the other one is its hydrogenated analogue. However, the end-deuterated sample is not 100% end-deuterated due to a fault in the synthesis. Therefore, here we developed a FTIR-transmission method to determine the isotopic ratio in these partially deuterated alkane samples. Our calculations based on this method showed that the end deuterated 'Y-shaped' alkane only consists of 79.9% of the expected deuterium(D)/hydrogen(H) ratio. A SAXS study on a linear end-deuterated alkane showed that the chains achieve a maximum tilt of 35°, which is the most common tilt angle also for polyethylene. Combining these results with those from previous studies on the same sample, a relationship between chain perfecting and the chain tilt was established. It was found that the ordering of the crystal structure induces chain tilting in order to accommodate the incoming chain ends to the crystalline layer. The increase in the domain size during this process was found to be from 16 to more than 50 chains per domain. The attempt to explain the observed shift of the SAXS spacings in the tilting experiment, away from the positions predicted by Bragg's equation by using a paracrystalline model failed. Hence, we suggest a model with an asymmetric thickness distribution will be more appropriate in this regard. The simulated CD[2] bending vibration mode splitting of the infrared spectrum of the random fold model of this end-deuterated alkane is 9.0 cm[-1] whereas a maximum splitting of 9.1 cm[-1] is expected for this mode for a regular fold model of the same alkane. Therefore a vibrational spectroscopic differentiation between these two models based on the experimental CD[2] bending splitting is highly unlikely.
29
Galassi, Giulio Roberto. "Monte Carlo simulations of diatomics, polymers and alkanes." Thesis, University of Southampton, 1993. https://eprints.soton.ac.uk/421719/.
Texte intégral
30
Xu, Wenjian. "Fluorination Effect on the Conformational Properties of Alkanes." Thesis, University of North Texas, 2002. https://digital.library.unt.edu/ark:/67531/metadc3103/.
Texte intégralRésumé :
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.
31
Abudawood, Raed Hasan. "Hydroisomerization of alkanes over metal-loaded zeolite catalysts." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/hydroisomerization-of-alkanes-over-metalloaded-zeolite-catalysts(4511d50c-ff42-49e6-9a8a-d7ad88576bb1).html.
Texte intégralRésumé :
Zeolite catalysis plays an important role in many industrial applications due to their unique properties and has become widely used in the area of oil refining. Of particular interest is Zeolite Y, which can be hydrothermally treated into its ultrastable form, USY. USY offers a superior practicality, especially when dealuminated and metal-loaded. The importance of alkanes hydroisomerization arises from the continuingly stricter regulations imposed on the utilization of gasoline as an automotive fuel. The requirements to reduce the aromatics content in gasoline present a need to find an alternative way to maintain its research octane number (RON). An alternative to gasoline's high-octane aromatic content is to increase the RON for the paraffinic content of gasoline, which can be accomplished through hydroisomerization. Commercially, bifunctional metal-loaded zeolites are used to hydroisomerize the light naphtha stream produced at overheads of atmospheric distillation towers. However, no such process exists for the low-value heavy naphtha cut. This targeted process would, if successful, greatly improve refiner's profitability.In this work, bifunctional USY zeolite catalysts are studied in the hydroisomerization of a normal alkane (nC7, RON = 0). This nC7, found in heavy naphtha, has been used as the 'model' compound. The impact of different reaction conditions and catalyst properties on catalyst activity and stability, in addition to the catalyst selectivity to high octane isomers is one step towards determining optimum conditions and preferential catalyst formulations that favour octane maximization. Six platinum-loaded USY zeolite catalysts, four in-house and two commercial, were tested in an atmospheric glass fixed-bed reactor and a stainless steel reactor purpose-built during the course of this thesis. Reaction temperatures ranged from 170 to 250oC at pressures between 1 and 15 bar. The hydrogen to hydrocarbon molar ratio was fixed at 9, with feed space time ranging from 35.14 to 140.6 kg.s/mol. In-house catalysts were hydrothermally treated at different severities, while commercial ones were originally dealuminated through acid-leaching treatments.Results have shown commercial catalyst CBV-712 gave the best performance and highest octane values for product isomers (>30). In addition, there was no coke generation. The next best catalyst was the most severely steamed in-house catalyst (USY-D) that has shown a remarkable performance at high pressures, almost eclipsing the performance of CBV-712, yet produced higher levels of coke. Other USY catalysts tested were less robust during reactions, probably due to imbalance in their acidic to metallic functions, or diffusion limitations arising from their pore structures. The best catalysts were, nonetheless, highly sensitive to sulfur presence in the feed, which severely impacted their activity, especially their metallic functions, and thus require sulfur-free feeds in order to demonstrate their full capacities. Simple kinetic modelling of experimental data was performed using the initial rates method and estimation of kinetic parameters, whose values were in good agreement with previous literature.
32
Maeda, Nobuo, and nobuo@engineering ucsb edu. "Phase Transitions of Long-Chain N-Alkanes at Interfaces." The Australian National University. Research School of Physical Sciences and Engineering, 2001. http://thesis.anu.edu.au./public/adt-ANU20011203.151921.
Texte intégralRésumé :
An experimental study of phase transitions of long-chain n-alkanes induced by the effect of interfaces is described.
¶
The phase behaviour of long-chain n-alkanes (carbon number 14, 16, 17, 18) adsorbed at isolated mica surfaces and confined between two mica surfaces has been studied in the vicinity of and down to several degrees below the bulk melting points, Tm. Using the Surface Force Apparatus we have measured the thickness of alkane films adsorbed from vapour (0.97 [equal to or greater-than] p/p[subscript o] [equal to or greater-than] 0.997), studied capillary condensation transition, subsequent growth of capillary condensates between two surfaces, and phase transitions in both the adsorbed films and the condensates. By measuring the growth rate of the capillary condensates we have identified a transition in the lateral mobility of molecules in the adsorbed films on isolated mica surfaces. This transition to greater mobility occurs slightly above Tm for n-hexadecane, n-heptadecane and n-octadecane but several degrees below Tm for n-tetradecane, and is accompanied by a change in wetting behaviour and a measurable decrease in adsorbed film thickness for n-heptadecane and n-octadecane. Capillary condensates that form below Tm remain liquid, but may freeze if the degree of confinement is reduced by separation of the mica surfaces. An increase in the area of the liquid-vapour interface relative to that of the liquid-mica interface facilitates freezing in the case of the long-chain alkanes, which show surface freezing at the liquid-vapour interface.
¶
Although thermodynamic properties of the surface freezing transition have been rather well documented, the kinetics involved in formation of such ordered monolayers has so far received very little attention. We studied the surface tension of n-octadecane as a function of temperature in the vicinity of Tm, using the static Wilhelmy plate and the dynamic maximum bubble pressure methods. The two methods give different results on cooling paths, where nucleation of the surface ordered phase is involved, but agree on heating paths, where both methods measure properties of the equilibrium surface phase. On cooling paths, the surface of bubbles may supercool below the equilibrium surface freezing temperature. The onset of surface freezing is marked by a sharp drop in the surface tension. The transition is accompanied by an increased stability of the films resulting in longer bubble lifetimes at the liquid surface, which suggests that the mechanical properties of the surfaces change from liquid-like to solid-like. Our results suggest occurrence of supercooling of the monolayer itself.
33
Paunovic, Irena. "Solid-liquid phase behavior of mixtures of n-alkanes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0021/MQ48067.pdf.
Texte intégral
34
De, Silva D. S. M. "Crystallization and molecular conformation of long chain N alkanes." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246907.
Texte intégral
35
Hobbs, Paul Michael. "Computational sorption studies of alkanes and alkenes in zeolites." Thesis, University of Reading, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320085.
Texte intégral
36
Huguet, Edouard. "Terminal oxidation of long linear alkanes in liquid phase." Thesis, Cardiff University, 2009. http://orca.cf.ac.uk/54952/.
Texte intégralRésumé :
The aim of this project is to investigate the terminal activation of long chain linear alkanes in the liquid phase using the selective oxidation of w-decane to 1-decanol as a model reaction. Firstly the autoxidation of -decane with oxygen was studied. The product distribution is a mixture of Cio ketones and alcohols with shorter chain carboxylic acids. The radical autoxidation mechanism promotes oxidation in the internal position and a very low terminal selectivity is found in the product profile. A range of VMgO catalysts were tested for the oxidation of w-decane with oxygen. Leached vanadium from VMgO leads to an improvement to the conversion over the autoxidation while the same terminal selectivity was observed. Cobalt substituted zeolites catalysts were also investigated. The porous structure of the different zeolites did not improve the terminal selectivity. No cobalt leaching was observed. The silanation of the external surface of the zeolites before ion exchange with cobalt reduces the conversion compared to the same cobalt zeolites without silanation, but does not improve the terminal selectivity. Finally, a comparison of the best results published in the literature for the oxidation of n-hexane in the liquid phase has been carried out. Higher terminal selectivities for the autoxidation were observed than those reported. Autoxidation terminal selectivities match with the best catalysts reported in the literature.
37
Leroy, Frederic H. R., Hervé Jobic, Bernard Rousseau, and Alain H. Fuchs. "Self-diffusion of n-alkanes in MFI-type zeolites." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194594.
Texte intégral
38
Gorce, Jean-Philippe. "Crystallisation and chain conformation of long chain n-alkanes." Thesis, Sheffield Hallam University, 2000. http://shura.shu.ac.uk/19705/.
Texte intégralRésumé :
Hydrocarbon chains are a basic component in a number of systems as diverse as biological membranes, phospholipids and polymers. A better understanding of the physical properties of n-alkane chains should provide a better understanding of these more complex systems. With this aim, vibrational spectroscopy has been extensively used. This technique, sensitive to molecular details, is the only one able to both identify and quantify conformational disorder present in paraffinic systems. To achieve this, methyl deformations have been widely used as "internal standards" for the normalisation of peak areas. However, in the case of n-alkanes with short chain length, such as n-C[44]H[90] for example, the infrared spectra recorded at liquid nitrogen temperature and reported here show the sensitivity of these latter peaks to the various crystal structures formed. Indeed, the main frequencies of the symmetric methyl bending mode were found between 1384 cm[-1] and 1368 cm[-1] as a function of the crystal form. Changes in the frequency of the first order of the L.A.M. present in the Raman spectra were also observed. At higher temperatures, non all-trans conformers, inferred from different infrared bands present in the wagging mode region, were found to be essentially placed at the end of the n-alkane chains. At the monoclinic phase transition, the concentration of end-gauche conformers, proportional to the area of the infrared band at 1342 cm[-1], increases abruptly. On the contrary, in the spectra recorded at liquid nitrogen temperature no such band is observed. We also studied the degree of disorder in two purely monodisperse long chain n-alkanes, namely n-C[198]H[398] and n-C[246]H[494]. The chain conformation as well as the tilt angle of the chains from the crystal surfaces were determined by means of low frequency Raman spectroscopy and S.A.X.S. measurements on solution-crystallised samples. The increase in the number of end-gauche conformers which was expected to occur with the increase of the tilt angle as a function of the temperature was not detected due to a perfecting of the crystals. Indeed, due to successive heating and cooling to -173°C, the concentration of non all-trans conformers was found to decrease within the crystals. Their numbers were found to be up to six times higher in n-C[198]H[398] crystallised in once folded form than when crystallised in extended form. The C-C stretching mode region of the spectra was used to identify the chain conformation and to estimate the length of the all-trans stem passing through the crystal layers at -173°C. The transition between once folded and extended form crystals was indicated by the presence of additional bands in this region at 1089 cm[-1], 1078 cm[-1] and 1064 cm[-1]. Some of those bands may be related to the fold itself. At the same time, a strong decrease of the intensity of the infrared bands present in the wagging mode region was observed. Finally, the triple layered structure proposed on the basis of X-ray measurements obtained from the crystals of a binary mixture of long chain n-alkanes, namely n-C[162]H[326] and n-C[246]H[494], was confirmed from the study of the C-C stretching mode region of the infrared spectra.
39
Ordakowski, Amy L. "Alkanes as Internal Markers to Estimate Digestibility in Horses." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/46511.
Texte intégralRésumé :
Fecal recoveries of n-alkanes were determined in three digestion balance experiments consisting of two periods each. Each experiment compared two diets in a switch-back design using eight mature Thoroughbred geldings. Horses were randomly assigned to two groups of four and offered one of two mixed grass/legume hays (Diets 1 and 2) in Exp. 1, mixed grass/legume hay and one of two concentrates (Diets 3 and 4) in Exp. 2, and mixed grass/legume pasture (Diets 5 and 6) in Exp. 3. In Exp. 1 and 2, horses were housed in stalls and in Exp. 3, two horses from each diet were housed in stalls and two horses remained on pasture. Balance periods lasted 11 days with d 1 to d 7 consisting of a dietary accommodation period, followed by 4 days of total collection. Results indicated that fecal recoveries of odd-chain alkanes (C25 to C33) were less than 100 % and similar between chain lengths. Estimates of DMD (DE) were similar to the total collection DMD (DTC) for Diet 1 in Exp. 1, but underestimated DTC for Diet 2 in Exp. 1 (P < .05) and Diets 3 and 4 in Exp. 2 (P < .05). For Diet 5 in Exp. 3, the DE for stall-fed horses using C25 and C33 was similar to DTC, whereas C27, C29, and C31 underestimated DTC (P < .05). For pastured horses, the DE using C29 and C31 were similar to DTC, whereas C25, C27, and C33 underestimated DTC (P < .05). For Diet 6 in Exp. 3, the DE for stalled horses calculated using C25 was similar to the DTC, whereas use of C27, C29, C31, and C33 underestimated DTC (P < .05). For pastured horses, the DE using C29 was similar to DTC, whereas all other alkanes underestimated DTC (P < .05). When DE was adjusted (DA1) using the mean recovery of each odd-chain alkane, DA1 was similar to DTC for Diet 2 in Exp. 1, Diets 3 and 4 in Exp. 2, and stalled horses offered Diets 5 and 6 in Exp. 3. The DA1 using C25 underestimated DTC for Diet 1 in Exp. 1 (P < .05). For pastured horses offered Diet 5, DA1 for C33 was not different from the DTC estimate, whereas all other DA1 for n-alkanes overestimated DTC (P < .05). For pastured horses offered Diet 6, DA1 for C29 and C31 overestimated, but were similar to the DTC, whereas the DA1 for C33 underestimated DTC and was similar to the DTC. The DA1 for C25 and C27 overestimated DTC (P < .05). When DE was adjusted for the mean recovery of all n-alkanes (DA2), all DA2 estimates for stalled horses in Exp. 1, 2, and 3 were similar. In pastured horses offered Diets 5 and 6 in Exp. 3, the DA2 overestimated DTC (P < .05). These results suggest that accurate mean estimates of DMD can be obtained by adjusting for mean recovery of each odd-chain alkane in a specific diet.<br>Master of Science
40
Maeda, Nobuo. "Phase transitions of long-chain n-alkanes at interfaces." View thesis entry in Australian Digital Theses Program, 2001. http://thesis.anu.edu.au/public/adt-ANU20011203.151921/index.html.
Texte intégral
41
Stothard, Nigel David. "The oxidation of trans-2-butene and propene between 400 and 520 degree C." Thesis, University of Hull, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333710.
Texte intégral
42
Smart, Sharon Patricia. "Structural and dynamic properties of alpha, omega-dibromoalkanes and other guest molecules in their urea inclusion compounds." Thesis, University of St Andrews, 1993. http://hdl.handle.net/10023/14930.
Texte intégralRésumé :
The work described in this thesis focuses on the urea inclusion compounds of α, ω-dibromo-n-alkanes: Br(CH2)[sub]nBr/urea, where n=7-10. The structural and dynamic properties of the host and guest have been studied using complementary techniques. Photographic single crystal x-ray diffraction shows that, in the regions of three- dimensional guest molecular ordering, there is a well-defined offset, Δg, along the channel axis, c, between guest molecules in adjacent channels. Δg is exactly one-third of the periodic repeat distance along c of the basic guest structure: this represents a new mode of interchannel guest ordering in urea inclusion compounds. Raman spectroscopy shows that the 'bulk' conformation of the guest molecules is the linear, trans, extended form, but that there is a small, but measurable, proportion of Br end-groups in the gauche conformation. Incoherent quasielastic neutron scattering indicates that the guest molecules undergo two motions on the picosecond time-scale, at sufficiently high temperature: translations along the channel axis and reorientations about the channel axis. These motions are successfully modelled as, respectively, continuous linear diffusion between two impermeable boundaries and uniaxial rotational diffusion in a one-fold cosine potential. Deuterium nuclear magnetic resonance spectra are shown, via simulations, to be consistent with a 180° flipping motion of the urea molecules about their C=O axes, occurring on the microsecond time-scale at room temperature. This technique also provides confirmation of guest molecular motion. The structure of 1,6-dibromohexane/urea is found to differ from that of the other a,w-dibromoalkane/urea inclusion compounds studied: crystal structure determination shows that it is monoclinic, and that the host and guest structures are commensurate with one another. Raman spectroscopy confirms that the Br end-groups are exclusively in the gauche conformation. The urea inclusion compounds of various other guest molecules have also been investigated briefly. The complementary nature of the techniques used is crucial in establishing a complete picture of the structure and dynamics of all these compounds.
43
Sorigue, Damien. "Biosynthèse d'hydrocarbures dérivés des acides gras chez les microalgues." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4084.
Texte intégralRésumé :
Les alcanes et les alcènes sont des hydrocarbures non cycliques important dans l’industrie. Ils sont synthétisés à partir d'acides gras par une grande variété d’organismes mais les connaissances à ce sujet sont très limitées chez les microalgues. Le but de ces travaux était donc de rechercher la présence d’alcanes ou d’alcènes dans diverses microalgues modèles, et d’essayer d’identifier la ou les enzymes responsables de la synthèse de ces composés. Nous avons mis en évidence la présence d’hydrocarbures linéaires en C15-C17 chez les microalgues Chlorella et Chlamydomonas. Ces composés étaient synthétisés uniquement en présence de lumière. L’absence dans le génome de ces microalgues d’homologues de gènes codant pour des enzymes connues de synthèse d’alcanes/alcènes a permis de conclure à la présence d’un nouveau système de synthèse d’hydrocarbures. Des purifications enzymatique et des analyses protéomique ont permis d’identifier une enzyme candidate qui exprimée chezE. coli est suffisante à la synthèse d’hydrocarbures. L'étude de cette enzyme révella qu'il s'agissait d'une photoenzyme utilisant l'énergie des photons bleue pour décarboxyler les acides grass en alca(e)ne. La structure de cette photoenzyme montre la présence un tunnel hydrophobe contenant l’acide gras et le cofacteur FAD. Cette nouvelle enzyme nommée « alcane photosynthase » amène de nombreuses question: qu'elle est la fonction des hydrocarbures chez ces microorganismes? Quel est le mécanisme catalytique de l’alcane photosynthase? Enfin, elle offre de nouvelles possibilités pour la production de biocarburants utilisant directement l’énergie solaire<br>Alkanes and alkenes are important in industry. Alkanes and alkenes are synthesized from fatty acids by a variety of organisms, such as plants and insects. However, the presence in microalgae of enzymes converting fatty acids into hydrocarbons has been poorly studied. The aim of this work was to investigate the presence of alkanes and alkenes in various microalgae models, and try to identify the enzymes responsible for the synthesis of these compounds.We have first demonstrated the presence of linear hydrocarbons C15-C17 in microalgae Chlorella and Chlamydomonas. Then we have shown that the main hydrocarbon formed in Chlorella and Chlamydomonas was derived from cis-vaccenic acid and was synthesized only in the presence of light. Absence of homologues of genes coding for known alkane/alkene biosynthetic enzymes in the genome of Chlorella and Chlamydomonas indicate the presence of an unknown pathway. Enzymatic purification and proteomic analysis allowed to identify a candidate enzyme which, expressed in E. coli lead to the formation of hydrocarbons with variable chain lengths, thus demonstrating that it was really an synthase alkane. Characterization showed that the enzyme was a photoenzyme, which used blue light to catalyse the decarboxylation of fatty acid to an alka(e)ne. The three-dimensional structure of this enzyme revealed a hydrophobic tunnel containing the fatty acid and the FAD cofactor
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Fisk, Aaron T. "Dietary accumulation, sediment bioavailability and toxicity of polychlorinated n-alkanes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0028/NQ31980.pdf.
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Arnold, Thomas. "The adsorption of alkanes from their liquids and binary mixtures." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249654.
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Thompson, Richard Lewis. "Surfactant properties of semifluorinated alkanes in hydrocarbon and fluorocarbon solvents." Thesis, University of Hull, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363228.
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Adams, Melissa Marie. "The anaerobic oxidation of short-chain alkanes in hydrothermal vents." Thesis, Harvard University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3626342.
Texte intégralRésumé :
<p> Microorganisms are central to the cycling of methane on Earth. The anaerobic oxidation of methane (AOM) is a globally important process in anoxic marine sediments, which is often coupled to the reduction of sulfate by anaerobic methanotroph (ANME) archaea and sulfate reducing bacteria (SRB). However, the environmental and geochemical conditions that constrain these microbial communities remain largely uncharacterized. In this dissertation, I present evidence that methane and C<sub>2</sub>-C<sub>4</sub> alkanes are substantial sources of metabolic energy in sedimented hydrothermal vent systems. Furthermore, these studies demonstrate that AOM and C<sub>2</sub>-C<sub>4</sub> alkane oxidation linked to sulfate reduction (SR) are governed by temperature and substrate availability. </p><p> Using continuous-flow sediment bioreactors and batch incubations, rate measurements revealed a striking uncoupling of AOM from SR across the thermal gradient characteristic of hydrothermal vent sediments, with AOM occurring at the highest temperature (90°C) in the absence of SR. I discovered that ANMEs were present in sediments at all temperatures investigated, including a unique thermophilic ANME clade, while SRB were only detected in cooler regimes. Next, I present data from batch incubations demonstrating for the first time that substantial C<sub>2</sub>-C<sub>4</sub> alkane oxidation occurs over a broad temperature range (25 - 75°C) in hydrothermal vent sediments and is coupled to SR up to 75°C with maximum rates at 55°C. Furthermore, there was preferential degradation of C<sub>2</sub>-C<sub>4</sub> alkanes at 55°C, indicating that the active alkane oxidizers are thermophilic. At the rate maxima, 16S rRNA pyrotag sequence data revealed that a novel SRB lineage was the likely phylotype mediating the anaerobic oxidation of C<sub> 2</sub>-C<sub>4</sub> alkanes. </p><p> Finally, I present a comparative study of methane- and sulfur-cycling ecotypes in geographically separated hydrothermal vent and hydrocarbon seep sediments. By employing high throughput sequencing of 16S rRNA genes coupled to geochemical data, I was able to establish the environmental constraints that determine ANME and SRB ecotype diversity and distribution in these biogeochemically distinct deep sea habitats. In summary, this dissertation sheds light on the pervasive effects of temperature, substrate availability, and habitat type on these metabolic processes that are critical for the cycling of carbon and sulfur in deep sea hydrothermal vent sediments.</p>
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Garba, Mustapha Danlami. "Valorisation of alkanes and alkynes by transhydrogenation in petrochemical processes." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8719/.
Texte intégralRésumé :
The production of high premium fuel is an issue of priority to every refinery. The trans-hydrogenation process was devised to convert two low value refinery cracked products to premium products; the conversion processes involve the combination of dehydrogenation and hydrogenation reactions as a single step process. The low value refinery products (i.e. alkanes and alkynes or alkadienes) have been converted to alkenes (olefins) by trans-hydrogenation using catalysts system based on VOx, CrOx and Pt all supported on alumina. Although trans-hydrogenation has been disclosed in many patents over decades, only little academic literature is available. The success of the process over various catalysts has been claimed in many of these patents. However, further studies are still required to ascertain the actual reaction mechanism, mitigating carbon deposition and catalyst deactivation, and the role of different catalysts to optimize the reaction desired products. The current research work evaluates the potential of CrOx/Al2O3, K-CrOx/Al2O3, Pt/Al2O3 and K-Pt/Al2O3 to investigate the trans-hydrogenation of the pentane (P)/1-hexyne (1HY) system, the pentane (P)/1,5-hexadiene (1,5-HD) system and the pentane (P)/2,4-Hexadiene (2,4-HD) system over a range temperatures (523-773 K). The fresh catalysts were first characterised by N2 adsorption using the BET method, X-ray diffraction, Raman spectroscopy, Thermogravimetric analysis, Temperature programme oxidation (TPO), Temperature programmed reduction (TPR), Electron paramagnetic resonance (EPR), Atomic absorption spectroscopy (AAS) and colorimetric analysis. The Free energy (ΔG) for the reaction of pentane with 1-hexyne, 1,5-hexadiene and 2,4-hexadiene shows that trans-hydrogenation is thermodynamically favoured at most temperatures for the reaction of pentane with 1-hexyne, however this is not always the case when hexadienes are the hydrogen acceptors. When 2,4-HD is the acceptor, ΔG is +ve at all the reaction temperatures tested. When pentane or hexyne/hexadiene or a 5:1 mixture was passed over the catalyst, in the temperature range of 523K -773 K, it was found that trans-hydrogenation process had taken place but many of the products are alkylated olefinic and alkylated hydrocarbons. Regarding all systems previously mentioned above, the ratio of olefin to alkylated olefin products was ~50:50 at 773K, however, this ratio was found to vary at other temperatures. The lowest ratio of ~10:90 was obtained at 523K. Dissociation of the hydrocarbon reactant was also observed leading to production of cracked products such as CH4, C2H4 and subsequent formation of a carbonaceous overlayer on the catalyst surface. This was not the case with the 2,4-hexadiene reactant, the trans-hydrogenation is poor, as expected from the free energies. The trans-hydrogenation process was shown to improve the conversion of pentane when co-fed with the hexyne to ~26% and to ~90% when co-fed with 1,5HD using the chromia catalyst at 773K, both values are much higher than the equilibrium conversion of the pentane dehydrogenation. Higher conversions of the pentane were subsequently obtained with other catalysts, but the chromia/alumina and K-CrOx/Al2O3 catalyst exhibits greater trans-hydrogenation activity. With the 2,4HD acceptor, very low conversions of pentane were obtained with all the catalysts: in general conversions lower than when the pentane was run alone were obtained. The products observed were unique for each catalyst. However, it was observed that for each catalyst, only the distribution of the products changed with temperature. This also accounted for changes in both the cracking products and the carbon laydown on the catalyst. The deactivation regeneration cycles shows very similar conversion of both reactants. There is a small deactivation observed for the longer time run; however these were not very significant. It was observed that some of the major products were consumed with time, but are used for the formation of other major products. However, this is more prominent with pentane/hexyne run using the CrOx/Al2O3 catalyst.
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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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Han, Kyung-Eun. "Transport of n-alkanes through graphene nanoporous atomically thin membrane." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/123294.
Texte intégralRésumé :
Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 67-68).<br>Accurately characterizing molecular transport through a nanoporous atomically thin graphene membrane is important in determining potential for graphene's application as a filter. Amongst many factors that affect the transport, the effect of size of molecules is analyzed in this paper. Diffusion of n-alkanes between C10 and C18 was analyzed to isolate the effect of molecule size in transport trends. The n-alkanes are chosen as the solutes for their similar long-chains but differing lengths. Differently branched structures cause variable interactions with graphene between molecules. Thus, this structural consistency in n-alkanes make them optimal solutes. Additionally, these molecules are comprised of only carbon and hydrogen, allowing the same functional groups and polarities. However, their distinct boiling points allow detection in the gas chromatography-mass spectrometry (GCMS).<br>A diffusion cell with feed and permeate chambers, separated by a semipermeable membrane, was used to induce diffusion with difference in solute concentration between the chambers. Diffusion concentration and rates were calculated using GCMS analysis of samples taken over 6-hour period during the diffusion. The calculations were done for diffusion with and without graphene membrane for comparison. When integrating the GCMS peaks, two types of integration methods - wide-peak and narrow-peak integrations - were used to estimate the error due to difficulties in identifying peak boundaries. These results were further compared to the inherent diffusivity coefficients of the molecules, in order to quantify the selectivity imparted by graphene for diffusion. The diffusion trends from each data set were compared to the diffusion trend from inherent diffusivity coefficients, which shows that diffusiyity should decrease with larger and heavier n-alkanes.<br>The experimentally obtained data shows that smaller molecules diffused at faster rates, and there was a noticeable drop in the diffusion transport between C 12 and C 14. This is consistent with the expected trend. Studies that minimize sources of errors are recommended to further understand the transport of alkanes through graphene.<br>by Kyung-Eun Han.<br>S.B.<br>S.B. Massachusetts Institute of Technology, Department of Mechanical Engineering