Thèses sur le sujet « Long-chain alkanes »

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.

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.

The main focus of this thesis is the investigation of structure and motion of different materials by applying different solid-state NMR techniques. In the first section (1) some of the bases of NMR are described both in a Classical (1.1) and Quantum Mechanical (1.2) approach, while the next two sections deal with the experimental part of the work. In section 2 solid-state NMR studies of CsC60 are described and an unambiguous assignment of the 13C NMR spectrum of the polymer phase of CsC60, which is based solely on our experimental data, is presented. In contrast to previous work, the assignment does not rely on the knowledge of the electronic structure of this material and our results support a fully three-dimensional electronic structure as opposed to a quasi one-dimensional one. This is achieved using a two-dimensional 13C MAS NMR correlation experiment, which identifies nuclei coupled via a through-bond scalar interaction, the Refocused INADEQUATE. In section 3 solid-state NMR experiments performed on polyethylene and long-chain n-alkanes corresponding to the formula C246H494 are described. Particular attention is given to some specific issues such as chain folding and a detailed study of the saturation-recovery curves (T1) obtained is carried out for different materials. The model elaborated is able to simulate all the data recorded and the presence of an interphase between the crystalline and the amorphous parts of the samples is proposed. To help the understanding of the structure and the motion of long-chain n-alkanes in section 3 some deuterated samples such as C216H434-d24 and C12H25(CH2)192CHDC11D23+C162H326 ("the mixture") are also studied. Deuterium NMR is widely used and we fit all the experimental line shape of the different samples at different temperatures. Diverse models for the structure and motion of such materials are given, which take into account all the experimental results obtained.

Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第9180号
農博第1213号
新制||農||834(附属図書館)
学位論文||H13||N3592(農学部図書室)
UT51-2001-N226
京都大学大学院農学研究科応用生命科学専攻
(主査)教授 加藤 暢夫, 教授 清水 昌, 教授 江崎 信芳
学位規則第4条第1項該当

Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第8664号
農博第1160号
新制||農||816(附属図書館)
学位論文||H13||N3490(農学部図書室)
UT51-2001-A752
京都大学大学院農学研究科応用生命科学専攻
(主査)教授 加藤 暢夫, 教授 清水 昌, 教授 熊谷 英彦
学位規則第4条第1項該当

Wetting and phase transitions play a very important role our daily life. Molecularly thin films of long-chain alkanes at solid/vapour interfaces (e.g. C30H62 on silicon wafers) are very good model systems for studying the relation between wetting behaviour and (bulk) phase transitions. Immediately above the bulk melting temperature the alkanes wet partially the surface (drops). In this temperature range the substrate surface is covered with a molecularly thin ordered, solid-like alkane film ("surface freezing"). Thus, the alkane melt wets its own solid only partially which is a quite rare phenomenon in nature. The thesis treats about how the alkane melt wets its own solid surface above and below the bulk melting temperature and about the corresponding melting and solidification processes.
Liquid alkane drops can be undercooled to few degrees below the bulk melting temperature without immediate solidification. This undercooling behaviour is quite frequent and theoretical quite well understood. In some cases, slightly undercooled drops start to build two-dimensional solid terraces without bulk solidification. The terraces grow radially from the liquid drops on the substrate surface. They consist of few molecular layers with the thickness multiple of all-trans length of the molecule. By analyzing the terrace growth process one can find that, both below and above the melting point, the entire substrate surface is covered with a thin film of mobile alkane molecules. The presence of this film explains how the solid terrace growth is feeded: the alkane molecules flow through it from the undercooled drops to the periphery of the terrace.
The study shows for the first time the coexistence of a molecularly thin film ("precursor") with partially wetting bulk phase. The formation and growth of the terraces is observed only in a small temperature interval in which the 2D nucleation of terraces is more likely than the bulk solidification. The nucleation mechanisms for 2D solidification are also analyzed in this work. More surprising is the terrace behaviour above bulk the melting temperature. The terraces can be slightly overheated before they melt. The melting does not occur all over the surface as a single event; instead small drops form at the terrace edge. Subsequently these drops move on the surface "eating" the solid terraces on their way. By this they grow in size leaving behind paths from were the material was collected. Both overheating and droplet movement can be explained by the fact that the alkane melt wets only partially its own solid. For the first time, these results explicitly confirm the supposed connection between the absence of overheating in solid and "surface melting": the solids usually start to melt without an energetic barrier from the surface at temperatures below the bulk melting point. Accordingly, the surface freezing of alkanes give rise of an energetic barrier which leads to overheating.
Sowohl Benetzung als auch Phasenübergänge spielen eine sehr wichtige Rolle im täglichen Leben. Molekular dünne Filme langkettiger Alkane an Festkörper/Gas-Grenzflächen (z. B. C30H62 an Silizium-Waferoberflächen) sind sehr gute Modellsysteme um die Wechselbeziehung zwischen Benetzungsverhalten und (Volumen-)Phasenübergängen zu untersuchen. In einem Temperaturbereich knapp oberhalb der Volumenschmelztemperatur benetzt die Alkanschmelze die Substratoberfläche nur partiell (Alkantropfen). In diesem Temperaturbereich ist die Substratoberfläche mit einer molekular dünnen, festkörperartig geordneten Alkanschicht bedeckt ("Oberflächengefrieren" ). Die Alkanschmelze benetzt also die eigene Festkörperoberfläche nur partiell, ein in der Natur ziemlich seltenes Phänomen. Die Dissertation beschäftigt sich damit wie die Alkanschmelze ihre eigene Festkörperoberfläche über und unter dem Volumenschmelzpunkt benetzt und mit den entsprechenden Vorgängen beim Schmelzen bzw. Erstarren. Flüssige Alkantropfen lassen sich einige Grad unter ihren Schmelzpunkt unterkühlen ohne sich sofort zu verfestigen. Dieses "Unterkühlungsverhalten" ist üblich und es ist theoretisch qualitativ gut verstanden. Allerdings beobachtet man bei den Alkanen bei leichter Unterkühlung statt einer eventuellen Volumenverfestigung oft die Ausbildung von zweidimensionalen Terrassen aus erstarrtem Alkanen. Die Terrassen wachsen auf der Substratoberfläche radial aus den flüssigen Tropfen. Sie bestehen aus wenigen Alkanlagen mit jeweils der Dicke einer Moleküllänge. Die Analyse der Terrassen-Wachstumsprozesse zeigt, dass die gesamte Substratoberfläche einschliesslich der Terrassen sowohl oberhalb als auch unterhalb der Volumenschmelztemperatur mit einer dünnen Schicht mobiler Alkanmoleküle bedeckt ist. Durch diese Schicht fliessen bei Unterkühlung die Alkane vom unterkühlten Tropfen zur Terrassenkante und liefern den Nachschub für deren Wachstum. Die Untersuchungen zeigen damit erstmalig die Koexistenz eines molekular dünnen Films ("Precursor") mit einer partiell benetzenden Volumenphase. Die Entstehung und das Wachstum der Terrassen wird nur in einem engen Temperaturfenster beobachtet in dem die Keimbildung zweidimensionaler Terrassen wahrscheinlicher ist als die dreidimensionale Volumenverfestigung. Auch dieses Keimbildungsverhalten wird in der Dissertation genauer analysiert. Noch erstaunlicher als das Terrassenwachstum, d. h. das Verfestigungsverhalten ist das Schmelzverhalten der Terrassen. Sie lassen sich bis zu einer gewissen Temperatur überhitzen bevor sie schmelzen! Weiterhin findet bei genügender Überhitzung das Schmelzen nicht gleichzeitig überall statt sondern es entstehen zuerst kleine Alkantropfen an den Terrassenrändern. Diese bewegen sich dann über die Substratoberfläche und "fressen" sich durch die festen Terrassen. Dabei wachsen sie weil sie das geschmolzene Material aufnehmen und hinterlassen eine alkanfreie Spur. Sowohl die Überhitzung als auch die Tropfenbewegung lassen sich damit erklären dass die flüssige Alkanschmelze ihren eigenen Festkörper nur partiell benetzt. Die Ergebnisse bestätigen erstmals explizit den seit vielen Jahrzehnten vermuteten Zusammenhang zwischen der üblicherweise nicht beobachtbaren Überhitzung von Festkörpern und Oberflächenschmelzen: Festkörper beginnen normalerweise ohne Energiebarriere von der Oberfläche an zu schmelzen. Entsprechend bildet das Oberflächengefrieren der Alkane eine Energiebarriere und erlaubt damit deren Überhitzen.

O número diminuto de estudos sobre a técnica dos n-alcanos para porcos Alentejanos motivou o interesse em realizar um ensaio que simulasse as ingestões reais dos animais em Montanheira, no sentido de se compreender melhor o comportamento alimentar destes animais em condições extensivas. Para validar a técnica dos n-alcanos com altos níveis de ingestão em porcos Alentejanos, realizou-se um ensaio in vivo, em caixas metabólicas, com nove machos castrados da raça suína Alentejana com peso médio de 97,64 kg. O delineamento do ensaio experimental foi efectuado segundo o quadrado latino e os suínos foram alimentados três vezes por dia com bolota e luzerna desidratada foi também fornecido a cada animal diariamente, dois bolinhos contendo alcanos sintéticos (C32 e C36). No período experimental foram realizadas colheitas de fezes, refugos e alimento, para se estimar pelo método in vivo a digestibilidade e a ingestão. Calcularam-se as taxas de recuperação fecal para os n-alcanos e para os álcoois de cadeia longa, com o intuito de se identificar aqueles que apresentaram valores mais elevados e semelhantes entre si. O alcano que mostrou apresentar uma taxa de recuperação mais elevada e semelhante aos alcanos sintéticos foi o C29. Em relação aos álcoois de cadeia longa o que mostrou a taxa de recuperação fecal mais alta foi o C280H. Os n-alcanos naturais que melhor forneceram uma estimativa da digestibilidade foram o C25 e o C27. Na estimativa da ingestão os pares de alcanos que mais se aproximaram do valor real foram o C 29: C32 e o C29:C36· ABSTRACT; The miniature number of studies of the n-alkanes for Alentejano pigs motivated the interest in carrying 1hrough an essay that it simulated the real intake of the animal in "Montanheira”, the direction of to better understand the alimentary behavior of these animals in extensive conditions. To validate the technique of the n-alkanes with high levels of intake in Alentejano pigs, an in vivo essay was become fulfilled, in metabolic cages, with nine castred males of Alentejana swine race with average weight of97,64 kg. The delineation of the experimental essay was effected according to latin square and the swines had been fed 1hree times per day with acorn and deshydrated lucerne (Medicago sativa). Also it was supplied to each animal daily, two cookies contend synthetic alkanes (C32 e C36). ln experimental period had been carried through harvests of faeces, rubbishes and foods, to estimate digestibility and intake. The fecal recoveries for the n-alkanes and the long chain alcohols had been calculated, with the intention to identifying those that had presented higher and similar values. The alkane that showed to present a tax of higher and similar fecal recovery to synthetic alkanes was the C29. The long chain alcohol that it showed the higher fecal recovery was the C28OH. The natural alkanes that had better supplied an estimate of digestibility had been the C25 and C27. ln the estimate of intake the pairs of alkanes that been more come close to the real value had been the pair C29:C32 and the C29:C36.

This thesis describes the searching, preparation, characterization and catalytic evaluation of active catalysts for the terminal selectivity of long chain linear alkanes. The focus of the thesis is the study of shape selective materials, including the organic material cyclodextrins, and the inorganic material, zeolite and zeolitic membranes. Prepared catalysts were performed with n-decane or n-hexane as models to produce the terminal oxidation products 1-decanol, 1-hexanol, decanoic acid and hexanoic acid. Studies with the Andrews glass reactor showed a stable terminal selectivity of 5%-9% in the autoxidation of n-hexane in short time reactions. A comparison between the Andrews glass reactor and Parr stainless steel reactor showed that the autoxidation reactions can get higher conversion but lower terminal selectivity in the stainless steel reactor than the glass reactor. Most of the metal/support catalysts showed very low conversion and very poor terminal selectivity. Increasing the temperature leads to higher conversion but results in more cracked products and less selectivity for oxygenated C10 products. The most active catalyst was 5 w.t.% Au/TiO2. However, these catalysts did not show good terminal alcohol selectivity (<3%); whereas the cracked acid selectivity was high (32.0%). Cyclodextrin covered Au/SiO2 catalysts showed limited changes in terminal selectivities (1-2%). Zeolite 4A, silicalite-1, ZSM-5, zeolite X/Y coated catalysts were successfully synthesized with alumina and silica sphere supports. The most attractive oxidation results were performed by zeolite X/Y and zeolite 4A coated silica catalysts in n-hexane liquid phase oxidation, iv especially for with short reaction time. With zeolite X/Y membrane, in a 30 min reaction, the terminal selectivity was 16%, while the terminal selectivity for the blank reactions was 0-9%. With longer reaction time, the terminal selectivity decreased to 6-7%. Zeolite 4A membrane can produce a terminal selectivity of 13% in 4 h reactions.

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.

博士
國立臺灣科技大學
化學工程系
98
Abstract In this study, an isothermal titration type calorimeter was installed to measure excess enthalpies(HE) for eighteen pairs of binary systems. The operating condition was fixed at 298.15 K (25℃) / 1.013 bar (1 atm). The binary systems contain 2-octanone, 3-octanone, 2-decanone, valeric anhydride, hexanoic anhydride or dipentyl ether + n-alkanes, where the alkanes include one of following three long chain paraffins: n-dodecane, n-tetradecane and n-hexadecane. The excess enthalpies are all positive, indicating that the mixing processes are all endothermic. The excess enthalpies vary symmetrically with the mole fraction of constituent components. The experimental values of the systems containing dipentyl ether are apparently greater than those of other systems. The correlated results of the modified Redlich-Kister equation are satisfactorily well with the average deviation to be about within the experimental uncertainty. In addition to the modified Redlich-Kister equation, three equations of state: Peng-Robinson (PR), Patel-Teja (PT) and Cubic Chain-of-Rotators (CCOR), and two solution theory models: Wilson and NRTL models were used to correlate excess enthalpy data. The correlated results from the PR and the PT equations of state are not adequate, except for the dipentyl ether-containing systems. The CCOR2, which adopted two binary interaction parameters in the mixing rules, improved the correlated results from the CCOR1. The Wilson model has an inherent upper limit, 800 (J．mol-1), for HE. It can only be applicable to the systems containing dipentyl ether whose values of HE are sufficient small . Among all the studied models, the NRTL gave the best results, except for the anhydride-containing systems; where the correlated results were better than other equations of state and solution theory models.

The study of adsorption of n-alkanes in zeolite pores represents both a fundamental problem in molecular thermodynamics and also a problem with substantial industrial importance. Until mid 19th century, adsorption was mainly used for purification processes such as removal of H2S and mercaptans from natural gas and organic matter from water. However, with the emergence of molecular sieves, especially zeolites, adsorption processes have become an attractive alter- native to distillation in large scale separation of mixtures that have low relative volatility into streams each enriched in one of the components. The pore di- ameters of molecular sieves are of the order of molecular diameters and hence selective adsorption can be achieved by both a difference in adsorbate-adsorbent interactions of various species and obstruction by the pore walls to some of the species in the mixture. The existing adsorption theories such as Henry’s law, Langmuir adsorption model and BET isotherm are incapable of predicting the adsorption isotherms of n-alkanes in zeolite pores. The reason is that in microporous adsorbents, the sorbate molecular mechanisms are influenced by geometrical constraints also. This limitation in the use of theory can be overcome by developing a molecular model and using computers to mimic the real system. This nature of simulation is called molecular simulations. With the development of advanced algorithms, improved force-field parameters and very high computational power of present day computers, molecular simulations have become an important tool in studying adsorption on micro-porous materials. Adsorption experiments of mixtures of long chain alkanes into silicalite under liquid phase conditions show selectivity inversion and azeotrope formation. These effects are due to the subtle interplay between the size of the adsorbed molecules and pore topology of the adsorbent. The underlying molecular mechanisms responsible for selective uptake of one of the components cannot be obtained from experiments but can be realized through simulations. Therefore, in this study, the selective uptake of lighter component during liquid phase adsorption of C14/C15 and C15/C16 n-alkane binary mixtures in the zeolite silicalite is understood through configurational bias grand canonical Monte Carlo (CB- GCMC) molecular simulation technique and a course-grained siting analysis. The simulations are conducted under conditions of low and high loading. The siting pattern of the adsorbates inside the zeolite pores is used to explain the selectivity as seen in experiments.

Knowledge on the grazing/browsing behaviour, especially diet selection, of the different domestic herbivorous species under diverse vegetation communities is of particular importance for the development and application of appropriate grazing management strategies that increase the efficiency of the utilization of the existing vegetation and, consequently, the sustainability of the animal production system. Plant-wax components, namely alkanes and long-chain alcohols (LCOH), have been suggested as faecal markers to estimate diet selection of different ruminant and non-ruminant species. By combining these two marker types, it is possible to obtain a more specific “fingerprint” for each particular plant species, making it possible to obtain more accurate estimates of diet composition. The main objective of this master thesis was to assess the combination of n-alkanes and LCOH to estimate diet composition of the domestic herbivorous species in a field study. Additionally, effect of using different calculation approaches (using all individual plant species or grouping plant species with similar marker profiles) and faecal recovery data on diet composition estimates was also assessed. To study these hypothesis, thirty-thee ewes and thirty-five does were managed in a plot established on a natural shrubland of heather-gorse with an adjacent area of improved pasture. Samples from all the plant species identified in the grazing area and faecal samples of twelve ewes and fourteen does were collected and analysed for their n-alkanes and LCOH patterns. Two different approaches were applied to determine the diet composition: A1 (using all the plant species available as possible diet components) and A2 (grouping plant species according to the results obtained from the cluster analysis). The approach used significantly affected the diet composition obtained in sheep. When using the A1 approach, the proportion of U. galli in sheep diet was higher than the values reported previously for sheep grazing the same vegetation conditions, whereas the proportion of L. perenne was lower than expected. The A2 approach decreased the proportion of U. galli significantly to values closer to the ones reported in previous studies, whilst the proportion of grass species increased to levels closer to the ones expected. The approaches used did not have an effect on the diet composition estimates of goats. The proportion of U. galli was higher than the values reported previously for goats grazing the same vegetation communities, whereas the values for herbaceous species were lower. The faecal recovery values used had no effect on the diet composition estimates of sheep whereas for goats there was a significant effect. Overall, the results show that the combine use of n-alkanes and LCOH as faecal markers produced accurate estimates of the diet composition of sheep when the A2 approach was used. For goats, it was not possible to obtain accurate diet composition estimates for both approaches. The utilizations of more information (direct observation, application of microhistological procedures) on the grazing behaviour of the individuals and increasing the number of markers used in the calculations are two possible solutions that can be used to improve the accuracy of diet composition estimates.
O conhecimento do comportamento alimentar de herbívoros domésticos, particularmente a dieta por eles selecionada nos diferentes tipos de comunidades vegetais, é fundamental no sentido de se desenvolverem estratégias apropriadas de gestão de pastoreio que permitam otimizar a eficiência da sua utilização e, consequentemente, a sustentabilidade dos sistemas de produção. Algumas das substâncias presentes nas ceras epicuticulares das plantas, designadamente os n-alcanos e álcoois de cadeia longa (LCOH), podem ser utilizadas como marcadores fecais para avaliar a composição da dieta de herbívoros ruminantes e não-ruminantes. A utilização simultânea destes dois tipos de marcadores permite obter uma “impressão digital” mais específica para cada espécie vegetal e, deste modo, aumentar a precisão das estimativas obtidas da composição da dieta selecionada pelos animais em pastoreio. O principal objetivo desta dissertação de mestrado foi o de avaliar a utilização simultânea de n-alcanos e LCOH para obter estimativas da composição da dieta de herbívoros, num estudo de campo. Adicionalmente, avaliámos o efeito da utilização de diferentes metodologias de cálculo (utilizando todas as espécies vegetais disponíveis com possíveis componentes da dieta ou agrupando as espécies vegetais com perfil similar em marcadores com base nos resultados obtidos na análise de cluster, A1 e A2, respectivamente) e valores de recuperações fecais nas estimativas da composição das dietas. A metodologia de cálculo utilizada afetou significativamente as estimativas da composição da dieta dos ovinos. Os resultados obtidos com A1 indicaram que as proporções de U. gallii e de L. perenne na dieta dos ovinos foram superiores e inferiores, respectivamente, aos valores observados em estudos conduzidos nas mesmas comunidades vegetais. Com a utilização da metodologia de cálculo A2, a proporção na dieta de U. gallii diminuiu significativamente e, simultaneamente, a proporção das herbáceas aumentou para valores próximos do esperado. As metodologias de cálculo utilizadas não tiveram um efeito significativo nas estimativas da composição da dieta dos caprinos. A proporção de U. gallii na dieta destes animais foi superior aos valores observadas em estudos anteriormente conduzidos nas mesmas comunidades vegetais, enquanto a proporção das herbáceas foi inferior. Os valores de recuperações fecais utilizados não tiveram efeito na composição das dietas estimadas para os ovinos enquanto nas cabras observou-se um efeito significativo. Em geral, os resultados indicam que a utilização, em simultâneo, de n-alcanos e LCOH como marcadores fecais permitiu obter estimativas precisas da composição da dieta dos ovinos quando a metodologia A2 foi utilizada. No entanto, não foi possível obter estimativas precisas da composição da dieta dos caprinos utilizando ambas as metodologias. A utilização de informação complementar (observação direta dos animais, utilização de procedimentos microhistológicos) sobre o comportamento alimentar dos animais nestas comunidades vegetais e o aumento do número de marcadores fecais utilizados são duas soluções que poderão ser utilizadas para aumentar a precisão das estimativas da composição das dietas destes animais.

This thesis is about conversion of the waste lipids into added-value products. In the first chapter, a comprehensive review explains the strength and weak points of the state-ot-the-art on the field and proposes various catalysts and effective parameters to improve the process. The next chapter explains the materials and method for the experimental parts. Subsequently, the following chapter includes the experimental steps and the results. The last chapter models a biodiesel plant based on the experimental results. Finally, the last chapter focuses on the conclusion of the entire study.