http://hdl.handle.net/1956/1062 Search the Channel search http://bora.uib.no/simple-search http://hdl.handle.net/1956/2357 Title: Crude oil components with affinity for gas hydrates in petroleum production <br/> <br/>Authors: Borgund, Anna Elisabet <br/> <br/>Abstract: Some crude oils are believed to contain natural inhibiting components that can prevent hydrate plugging of oil pipelines in petroleum production. A method for classification of the oils that form hydrate plugs, as opposed to those that are not problematical, can change the hydrate inhibiting strategies for oil companies, and result in both economical savings and environmental improvements. Furthermore, an identification of natural hydrate plug inhibiting components can eventually give rise to development of more economical and environmentally friendly inhibitors that can be added to crude oil in pipelines. This thesis addresses the issues of chemical characterisation of crude oil with respect to identification of natural plug inhibiting components. Natural plug inhibiting components are probably hydrate surface active, e.g. an acid fraction has previously been shown to be able to convert a plugging oil into a non-plugging oil when added in a low concentration. In this work, methods for extraction of surface active compounds in crude oil have been established; two methods for acid extraction have been tested (liquid-liquid and ion exchange), and in addition components with affinity for freon hydrate and ice surfaces have been extracted. The extracts have been characterised with chromatographic and spectroscopic methods, e.g. an HPLC method for separation of extracts into four groups have been developed; non-polar compounds, saturated carboxylic acids, phenolic compounds and polyfunctional compounds. The results show that the ion exchange is more effective than the liquidliquid method for extraction of acids from crude oil. Freon hydrates are found to extract a specific fraction with polar compounds from crude oil, while ice does not seem to be a good surface for extraction of components. Compounds which absorb to hydrate surfaces are found to be dominated by saturated carboxylic acids, and to contain lower amounts of phenols and polyfunctional compounds. In general, crude oil extracts primarily contain components of intermediate molecular weights. This means that neither high-molecular compounds such as asphaltenes, nor simple low-molecular petroleum acids and bases are present to a large extent in these extracts. FTIR analysis can to some degree differentiate between freon hydrate extracts from plugging and non-plugging crude oils. GC-MS is not suited for the extracts used in this thesis due to limitations regarding molecular weights and low volatility. LC-MS analysis with Ion Trap MS has been tested at the University of Newcastle, but was not optimal for our samples. The freon hydrate extracts have been analysed for compounds similar to a biosurfactant structure, but no such compounds could be found. No structural identification of the natural inhibiting components have been obtained. However, new methods for extraction of components with affinity for freon hydrate and ice surfaces have been developed and acid extraction methods from the literature have been tested. In addition, a set of analytical methods that can characterise the fractions have been established. One reason for the difficulty of identifying the natural inhibiting components can be that they are present in very low amounts, but it may also be that the distribution of compounds in the fractions is as important as the presence of specific molecules. Wed, 27 Jun 2007 22:58:59 GMT http://hdl.handle.net/1956/2355 Title: Effects of initial anaerobic biodegradation on crude oil and formation water composition <br/> <br/>Authors: Skaare, Bent Barman <br/> <br/>Abstract: The e ect of initial biodegradation on oil and formation water was studied using both laboratory degradation schemes and biodegraded oils from the reservoir comprising Troll C. The e ects of biodegradation on the molecular level of oil may be heteroge- neous even in systems that ought to have the same starting point. This is true for both laboratory incubations and for biodegradation processes inside model reservoirs. Simultaneous depletion in di erent oil constituents and compound groups occurs at di erent relative rates, as a result of di erences in the bacterial activity. The dependence of the molecular e ects on the active microbial com- munity is also valid in reservoirs. This makes assessing biodegradation di cult on a molecular level because the e ects may vary according to the prevailing bacterial community in each reservoir. As a result of these di erences using multivariate analysis, e.g. principal component analysis, may provide valuable information that would not have been apparent using univariate ratios. The composition of organic acids in the water phase of the model reservoirs studied are highly dependent on the biodegradation processes it has encoun- tered, as it oods through the system. The identi cation of metabolites speci c for anaerobic biodegradation of naphthalene, 2-methylnaphthalene and tetralin in the formation water from Troll C indicates that the composition of such wa- ter might be dependent on the ongoing biodegradation in the reservoirs as well as in the model reservoirs. The water solubility of such metabolites, along with the assumption that biodegradation occurs at or near the oil water contact, can make identi cation of the metabolites easier in formation water than in the corresponding oils. Hence, the composition of formation waters may contribute information which is not available from the water composition. This was thecase in the samples from Troll C. Tue, 03 Apr 2007 22:58:59 GMT http://hdl.handle.net/1956/2331 Title: Isolation, identification and properties of pyranoanthocyanins and anthocyanin forms <br/> <br/>Authors: Jordheim, Monica <br/> <br/>Abstract: This dissertation focuses on isolation and structural elucidation of anthocyanins, and their chemical properties. The characterization of anthocyanins from castor (Ricinus communis), fourteen cultivars of European gooseberry (Ribes grosssularia), three other Ribes spp., two cultivars of Jostaberry (R. × nidigrolaria), seven Hippeastrum (Amaryllis) hybridum cultivars, and nineteen species belonging to Caprifoliaceae (genera Sambucus, Lonicera and Viburnum) are described. New anthocyanins include: Cyanidin 3-O-β-xylopyranoside-5-O-β- glucopyranoside (11), cyanidin 3-O-β-xylopyranoside-5-O-β-(6'''-malonylglucopyranoside) (19) and the methyl esterified product (18), cyanidin 3-O-β-(6''-E-caffeoylglucopyranoside) (15), and cyanidin 3-O-β-(6''-α-arabinopyranosylglucopyranoside) (6), which is the first complete identification of the disaccharide vicianose. Pigment 15 together with cyanidin 3-O- β-(6''-E-caffeoylglucopyranoside) (17) constitute the major anthocyanin content in the cultivars; ‘Samsø’, ‘Hinnomäki Red’, ‘Taastrup’, ‘Lofthus’ and ‘Glendal’. These cultivars may thus be good candidates for consumption, colorant and breeding programmes, because no other commercial available berries have been reported to contain as high proportions of aromatic acylated anthocyanins. Anthocyanins from black beans (Phaseolus vulgaris) are for the first time hemisynthesized directly from a partly purified anthocyanin extract. The three mother anthocyanins (delphinidin 3-O-β-glucopyranoside (22), petunidin 3-O-β-glucopyranoside (26), malvidin 3-O-β-glucopyranoside (27)) and their hemisynthesis products, 5- carboxypyranoanthocyanins (32-34), were isolated in a preparative scale using Sephadex LH- 20 column chromatography. The individual pigments (22, 26, 27, 32–34) were characterized by NMR; the structures of 32 and 33 have previously only been tentatively identified. The 3-O-β-glucopyranosides of delphinidin, petunidin and malvidin (Phaseolus vulgaris) (22, 26, 27) and cyanidin 3-O-β-galactopyranoside (from Aronia melanocarpa) (4) have been dissolved in deuterated methanolic solutions without and with acid (5%, CF3COOD). Their hemiacetal (hemiketal) forms were characterized by NMR as two epimeric 2-hydroxy-hemiacetals. This is the first report of 13C NMR assignments regarding two epimeric anthocyanin hemiacetal forms. Displacement of nuclear hydrogen by deuterium at various sites on the aglycone part of delphinidin 3-O-β-glucopyranoside (22), petunidin 3-O-β-glucopyranoside (26), and malvidin 3-O-β-glucopyranoside (27) in their flavylium cationic and hemiketal forms were examined based on integration data obtained by 1H NMR spectroscopy. Similar measurements were performed on the three corresponding pyranoanthocyanins (32–34), and the flavonol rutin (quercetin 3-O-β-(6''-α-rhamnopyranosylglucopyranoside), 35. H→D exchanges were observed for the nuclear protons of the A-rings (H-6 and H-8) of 22, 26, 27 and 35. No similar H→D exchanges were observed for 32–34. This is explained with a generalized mechanism including a positively charged σ–complex. Since the oxygen (6-O) included in the pyrano-ring of 32–34, has not the same electron donating effect as the 5-OH group of 22, 26 and 27, the positively charged σ–complexes of 32–34 can not stabilize themselves to the same level as the corresponding complexes of 22, 26 and 27. The H→D exchange reactions appeared to be independent upon the concentration of the substrates and concentration of D+, in accordance with a first order reaction. Most antioxidant measurements are concentration dependent, and purity determination of examined compounds are crucial. To improve correctness in determination of anthocyanin purity, 1H and 13C NMR spectroscopy have been combined with HPLC-DAD and UV-Vis spectroscopy in analysis of anthocyanidin 3-glycosides and 5-carboxypyranoanthocyanidin 3- glycosides. The molar absorptivity (ε) values were found to be relatively similar, in contrast to previously reported literature values. The ε-values for both anthocyanidin 3- monoglycosides and 5-carboxypyranoanthocyanidin 3-glycosides were proposed to be 21800 and 22700 in acidified aqueous and methanolic solutions respectively. To assess the influence of structure on the potential antioxidant capacity of anthocyanins, the 3-glucosides of pelargonidin (1), cyanidin (5), peonidin (24), delphinidin (22), petunidin (26), malvidin (27), 5-carboxypyranopelargonidin (28), 5-carboxypyranocyanidin (30), 5- carboxypyranodelphinidin (32), 5-carboxypyranopetunidin (33), and 5- carboxypyranomalvidin (34) were examined by ferric ion reducing antioxidant power assay, FRAP. The reducing capacities of the individual anthocyanins were in the range of 0.9 to 5.2 Trolox equivalents. The two 5-carboxypyranoanthocyanins 30 and 32, possessing pyrogallolor catechol-type of B-rings, showed the highest potential antioxidant capacity measured by FRAP for any anthocyanin. The relative order of the reducing capacity of the various 5- carboxypyranoanthocyanidin 3-glucosides and anthocyanidin 3-glucosides were nearly alike whether determined by coulometric array detection or FRAP. The inclusion of the 5-hydroxyl in the D-ring and just one oxygen substituent on the B-ring as in 28, diminished the reducing capacity considerably. Thu, 21 Jun 2007 22:58:59 GMT http://hdl.handle.net/1956/2046 Title: A Theoretical Study of Cr/oxide Catalysts for Dehydrogenation of Short Alkanes <br/> <br/>Authors: Lillehaug, Sindre <br/> <br/>Abstract: Natural gas reserves are being produced at increasing rates world wide, thus providing an abundance of short-alkane feedstock for the petrochemical industry. Effective routes to selective activation of short alkanes may represent a bottleneck of this development. In this respect, processes of catalytic dehydrogenation have significant economic potential. Several catalysts have been investigated and some are implemented industrially. At the core of one such catalyst are species of chromium oxide supported on the surface of amorphous alumina. Since the original report by Frey and Huppke in 1933, this system has been under study, the literature expanding with the development of experimental methods. However, due to the heterogeneity of the Cr/alumina surfaces a structure-activity relationship has not been determined to date. Opinions are converging regarding the oxidation state of active chromium, but little is known about the nano-range surroundings of the active site. The involvement of oxygen ligands is a popular issue related to the mechanism of catalysis. Other remaining questions concern the chromium nuclearity of the active surface site and the role of the oxide support. With the development of quantum chemical tools and powerful hardware, computational modelling emerges as a manageable complement to experiment. The combination may lead to novel insight into the structure-activity relationship on Cr/oxide surfaces. Ultimately this may contribute to more effective catalysts by rational design. For this thesis, model catalysts have been investigated computationally with respect to (i) mechanisms of catalytic dehydrogenation, and (ii) surface reactions of chromium precursor species leading to the active catalyst. The work includes simulated annealing to generate realistic surface models, and reactivity studies based on cluster and embeddedcluster approaches. Based on these computations, two mechanisms of catalytic dehydrogenation appear viable depending on the nano range surrounding the active site. One mechanism is found to involve cleavage and reformation of a Cr–O bond. However, the activation energy of this mechanism is found prohibitively high unless the Cr–O bond is weakened by structural strain. Alternatively, a pre-catalytic step of C–H activation in alkane involving irreversible cleavage of a Cr–O bond is found leading to formation of a hydridochromium moiety, which appears highly active according to a second mechanism of catalytic dehydrogenation. Regarding the role of the support, this is proposed one of providing precursor species and sustaining the reactive sites. Moreover, it appears that polynuclear sites of the active chromium species are formed in the typical steps of catalyst preparation. These results form the basis for a hypothesis on which novel experiments are suggested. Thu, 26 Oct 2006 22:58:59 GMT http://hdl.handle.net/1956/2025 Title: Static and dynamic studies of foam and foam-oil interactions <br/> <br/>Authors: Vikingstad, Anne Kari Thu, 02 Nov 2006 22:58:59 GMT http://hdl.handle.net/1956/2017 Title: Interpretation of chromatographic and mass spectrometric data from analyses of fatty acid methyl esters : application of multivariate methods <br/> <br/>Authors: Mjøs, Svein Are <br/> <br/>Abstract: The purpose of this work has been to develop tools for fatty acid identification, with special emphasis on poly-unsaturated fatty acids and trans fatty acids. The work is based on application of gas chromatography with mass spectrometric detection and the fatty acids are analysed as fatty acid methyl esters (FAME). Various multivariate analytical techniques are applied as tools for interpretation of both chromatographic and spectral information. The ten papers are divided into five subsections with the following topics: Identification of FAME from shifts in retention indices: Papers I and II describe methods for partial identification of fatty acid structure from shifts in retention indices. These methods will basically provide information on the polarity (number of double bonds) and the chain lengths of the fatty acids. The procedure is not restricted to any particular class of fatty acids and may also be used to exclude compounds that are not fatty acids. Two-dimensional fatty acid retention indices (2D-FARI) are introduced in Paper II. Application to trans isomers: Papers III and IV are about trans isomers of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Paper III provides data about chromatographic properties of the trans isomers of EPA and DHA, which can be applied both for identification purposes and for optimisation of chromatographic parameters. A practical application of the data is shown in Paper IV. Prediction of equivalent chain lengths: Papers V and VI describe methods for prediction of equivalent chain lengths (ECL), which is the retention indices commonly applied for fatty acids. Paper V is restricted to polyunsaturated fatty acids with methylene-interrupted double bond systems. Paper VI is not restricted to a particular class of fatty acids, but 2D-FARI data must be available. Thus, the two procedures are complementary methods for ECL predictions. Identification of FAME from mass spectra: Paper VII and VIII are about multivariate analysis of mass spectra of FAME. In Paper VII it is shown that trans isomerism in certain positions has significant influence on the mass spectra of polyunsaturated fatty acids. In Paper VIIi it is shown that the number of double bonds in polyunsaturated fatty acids can be determined from selected ions in the mass spectra. Deconvolution of overlapping chromatographic peaks: Papers IX and X are about techniques for deconvolution of overlapping FAME peaks. Transformations for reduction of noise in the mass spectra were introduced in Paper IX. The transformations and the information from Paper VII about differences in the mass spectra caused by trans geometry were utilised for deconcvolution of overlapping chromatographic peaks of trans isomers in Paper X. Although the focus in this paper is basically on the quantification of the isomers, deconvolution of overlapping peaks has relevance also for the identification of the analytes because spectra and accurate retention times of the compounds are also provided. Thu, 09 Nov 2006 22:58:59 GMT http://hdl.handle.net/1956/2016 Title: Lineshape Models in Inner-shell Photoelectron Spectra of Free Molecules and Clusters <br/> <br/>Authors: Abu-samha, Mahmoud <br/> <br/>Abstract: Investigating the nature of molecules and clusters is of paramount importance for our understanding of the composition and the properties of matter. X-ray photoelectron spectroscopy is one of the most powerful techniques for obtaining information at the fundamental level about molecules and clusters. Our interest in this particular kind of spectroscopy derives from its ability to probe individual atoms in a molecule and their chemical surrounding. Experimental core-level photoelectron spectra show great complexity, even for simple molecules. Hence, developing theoretical lineshapes to model and interpret experimental spectra is necessary. This thesis is devoted to the development of novel theoretical methods for modeling x-ray photoelectron spectra of molecules and clusters. It also demonstrates how these models can be used as means of extracting chemical information from experimental spectra. In this thesis, the carbon 1s photoelectron spectrum of gas-phase ethanol has been investigated by calculations, and found to be significantly influenced by the presence of a conformational equilibrium. Furthermore, theoretical models have been used to analyze inner-shell photoelectron spectra of clusters made up of either argon, methane, or methanol molecules. With the help of these models we have been able to interpret the experimental spectra in terms of chemical shifts, vibrations, and the chemical surrounding of atoms (molecules) in the cluster. The results are very interesting and will, hopefully, contribute to the development of the current understanding of the structures and properties of clusters. Thu, 21 Sep 2006 22:58:59 GMT http://hdl.handle.net/1956/1764 Title: Partial molar properties of aqueous monosaccharide solutions at elevated pressure <br/> <br/>Authors: Aarflot, Asbjørn Sun, 29 Oct 2000 22:58:59 GMT