La cristallisation en solution est une opération unitaire essentielle du génie chimique. Les conditions opératoires dans lesquelles cette opération est menée déterminent sa productivité et la qualité des cristaux produits, par le biais de l’influence qu’elles ont sur les cinétiques de germination et de croissance. De nombreuses études ont mis en évidence que les conditions d’écoulement influencent significativement ces deux cinétiques. Néanmoins, une compréhension profonde de la nature de cette influence n’a, à l’heure actuelle, pas encore été atteinte. Ceci cause bien souvent des problèmes tant au niveau du procédé que du produit et a également pour conséquence que l’effet des conditions d’écoulement sur les cinétiques de cristallisation est rarement exploité de manière à en tirer le meilleur avantage.La première partie de ce travail a été consacrée à l’étude de l’effet des conditions d’écoulement sur les cinétiques de cristallisation en solution (germination et croissance), avec pour cas pratique la cristallisation d’hydrates de dioxyde de carbone (CO2), une solution émergeante pour la capture et la séquestration du CO2 (gaz à effet de serre majeur).De manière à étudier l’impact des conditions d’écoulement sur le taux de formation des hydrates de CO2, des expériences de formation d’hydrates de CO2 ont été réalisées dans un réacteur de type cuve agitée de 20 L mis en œuvre de manière semi-continue dans des conditions d’écoulement variées, produites à l’aide de trois mobiles d’agitations différents (une turbine à pales inclinées, un MaxblendTM et un DispersimaxTM) opérés à différentes vitesses de rotations. Un modèle mathématique original de l'ensemble du processus de formation des hydrates de CO2 attribuant une résistance à chacune de ses étapes constitutives a été établi. Pour chaque condition expérimentale, le taux de formation est mesuré et l’étape limitante est déterminée sur base de la valeur des différentes résistances. Les trois mobiles d’agitations étudiés sont comparés relativement à leur efficacité et, pour chaque mobile, l’influence de la vitesse de rotation sur l’étape limitante est discutée. En l’occurrence, il est montré que des limitations dues aux transferts de chaleur peuvent se produire à l'échelle relativement petite utilisée dans cette étude.L’étude de l’impact des conditions d’écoulement sur la cinétique de germination des hydrates de CO2 s’est concentrée sur la caractérisation de l’effet du taux de cisaillement sur le temps d’induction associé à cette formation (proportionnel à cette cinétique). Cette étude a été basée sur la réalisation de mesure de temps d’induction au cours d’expériences de formation d’hydrates de gaz, utilisant le système CO2-H2O-tetrahydrofuran comme système modèle, réalisées dans un réacteur de type Couette-Taylor. L’application, à la phase liquide dans laquelle prend place la formation des hydrates de gaz, de différents taux de cisaillement (entre 50 et 300 s-1), maintenus constants tout au long de l’expérience de formation, a révélé que le temps d’induction moyen diminuait significativement lorsque le taux de cisaillement appliqué à la phase liquide augmentait. Il a été montré que cette diminution peut être principalement attribuée à une diminution du temps nécessaire à l’apparition de germes stables d’hydrates et à leurs croissances jusqu’à une taille macroscopiquement détectable. Il a également été montré que le temps d’induction moyen peut également être significativement réduit par l’application, à la phase liquide, d’un haut taux de cisaillement (900 s-1) durant une période relativement courte et définie.La seconde partie de ce travail a été dédiée au développement d’une stratégie permettant d’améliorer le contrôle des procédés de cristallisation de substances pouvant cristalliser sous plusieurs formes cristallines, et ce, relativement à la forme cristalline générée au cours et à l’issue de ces procédés. Le cas pratique de cette partie du travail est le développement d’un procédé de cristallisation en solution par refroidissement en mode batch d’un principe actif, récemment développé par la société pharmaceutique UCB, présentant deux formes cristallines connues. La robustesse et la reproductibilité de ce procédé vis-à-vis de la production de la forme cristalline d’intérêt et de la prévention de l’occurrence d’un phénomène de prise en masse, dû à une formation massive de cristaux de la forme cristalline indésirable, sont deux impératifs ayant guidés son développement.Le procédé qui a été envisagé dans le cadre de la deuxième partie de ce travail est basé sur la production de semences cristallines de forme I (la forme d’intérêt) par germination primaire au sein d’un réacteur tubulaire suivie d’une croissance de ces semences en milieu agité contrôlé en température. Les propriétés particulières de l’écoulement mis en œuvre au sein du réacteur tubulaire permettent d’y contrôler finement l’allure des champs de température et de concentration (et donc de sursaturation) et, de manière inédite, de circonscrire l’apparition de cristaux à la partie centrale de l’écoulement (afin de prévenir tout risque d’incrustation de la paroi interne du réacteur). Les expériences réalisées dans ce travail montrent que, associé aux conditions expérimentales utilisées, ce dispositif permet de produire des semences cristallines de forme I de manière reproductible. Elles montrent également qu’un contrôle adéquat des conditions initiales dans lesquelles les semences cristallines de forme I sont amenées à croitre ainsi que du taux de refroidissement utilisé pour entretenir cette croissance permet de garantir que celle-ci se déroule sans que le phénomène de prise en masse ne prenne place. Il est mis en évidence que ce contrôle repose sur la prévention de toute formation indésirable de cristaux de forme II par un maintient, en tout temps, d’un niveau de sursaturation ne dépassant pas une valeur critique donnée. Enfin, ces expériences montrent aussi que le type d’agitation utilisée dans ce travail n’a pas d’influence sur l’occurrence de la prise en masse mais a une influence majeure sur l’état de surface, la taille moyenne et la distribution en taille des cristaux produits. / Solution crystallization is an essential unit operation in the chemical engineering field. Through their effect on the nucleation and growth kinetics, the operating conditions of such an operation determine its productivity and the quality of the produced crystals. An important number of studies have shown that the flow conditions have a significant influence on these two kinetics. Nonetheless, a deep understanding of the nature of this effect is still lacking, which often leads to severe difficulties in the development and operation of crystallization processes and impedes the emergence of positive applications of this effect.The first part of this work has been dedicated to the study of the effect of the flow conditions on the solution crystallization kinetics (nucleation and growth). Carbon dioxide (CO2) hydrate crystallization, an emerging method for the separation and capture of CO2, was used as a practical case.CO2 hydrate formation experiments have been performed in a 20 L semi-batch stirred tank reactor using three different impellers (a down-pumping pitched blade turbine, a Maxblend™, and a Dispersimax™) at various rotational speeds to examine the impact of the flow conditions on the CO2 hydrate formation rate. An original mathematical model of the CO2 hydrate formation process that assigns a resistance to each of its constitutive steps has been established. For each experimental condition, the formation rate is measured and the rate-limiting step is determined on the basis of the respective values of the resistances. The efficiencies of the three considered impellers are compared and, for each impeller, the influence of the rotational speed on the rate-limiting step is discussed. For instance, it is shown that a formation rate limitation due to heat transfer can occur at the relatively small scale used to perform our experiments.The investigation of the impact of the flow conditions on the nucleation kinetics of CO2 hydrates was focused on the characterization of the effect of the fluid shear rate on the induction time of gas hydrate formation (proportional to this kinetics). This study was based on induction time measurements during gas hydrate formation experiments, using the CO2-H2O-tetrahydrofuran system as model system, realized in a Couette-Taylor reactor. The investigation of the effect of the application of a constant shear rate (50 to 300 s-1) to the liquid phase from which the hydrates are formed revealed that the mean induction time decreases significantly as the applied shear rate increases. This could primarily be attributed to a decrease in the time required for stable gas hydrate nuclei to be generated and to grow to a macroscopically detectable size. The induction time could also be significantly reduced by the application of a high shear rate (900 s-1) to the liquid phase for a relatively short, defined period of time.The second part of this work has been dedicated to the development of a strategy for the improvement of the control of crystallization processes involving compounds able to crystallize under several crystalline forms, relatively to the crystalline form generated during and at the end of these processes. The strategy examined in this work was applied to the development of a batch cooling solution crystallization process of an active pharmaceutical ingredient, recently developed by the pharmaceutical company UCB, exhibiting two known crystalline forms. The robustness and the reproducibility of this process relatively to production of the desired crystalline form produced and the prevention of caking, due to the massive formation of crystals of the undesired crystalline form, were the two main priorities that have driven its development.The process considered in the second part of this work is based on the production of form I (the desired form) crystalline seeds through nucleation in a tubular reactor followed by the growth of these seeds in an agitated medium controlled in temperature. The particular properties of the flow conditions in the tubular reactor enable the temperature and the concentration fields, and therefore the supersaturation field, to be finely tuned and, in an original manner, to confine the emergence of new crystals in the center part of the flow (to prevent any fouling of the inner surface of the reactor). The experiments performed in this work showed that, coupled to the experimental conditions used, this device enables to reproducibly generate form I crystalline seeds. The experiments also revealed that a proper control of the initial conditions in which these seeds are brought to grow and of the cooling rate used to sustain this growth allows ensuring that this growth takes place without caking. It is shown that such a control lies on the inhibition of the formation of undesired form II crystals by keeping, at all times, the supersaturation level under a defined critical value. Finally, the experiments showed that the type of agitation used in this work does not influence the occurrence of caking but has a significant impact on the crystals surface quality, mean size, and size distribution. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

The effect of impurities on crystal morphology is a challenging problem, since even at low concentrations they can have drastic effects on the final habit. Industrially this causes problems with downstream processes such as filtration, processability and even storage. Conversely, structurally related additive molecules may be introduced to a system in order to mimic the effect of an impurity resulting in a beneficial effect on problematic crystal morphologies. The work presented here considers the design and use of tailor made additives on a nonhydrogen bonded crystal, benzophenone. This compound is typical of many agrochemical materials in that the major intermolecular interactions are of the nondirectional van der Waals type. Using crystal packing analysis a selection of additives has been chosen with the intent of specifically hindering certain directions of crystal growth. From an initial group of nine molecules two additives, 4ABP and 4MBP were found tobe particularly effective, both strongly hindering growth. Measured kinetic data suggests that these additives bind to steps in the growth spirals, drastically slowing growth of specific crystal faces altering the crystal morphology to a needle shape. Through nucleation experiments and product analysis the additives were shown to effect only crystal growth becoming incorporated into the crystal structure. Computational modelling of the binding of additives to the crystal surfaces of benzophenone has been used in an attempt to rationalise the experimental effects. In many cases calculated binding energies were in agreement with experimental observation. However, modified attachment energies did not match well with experimental observations.

The objective of this work is to enhance the understanding of the delay observed in the early stages of E-coat deposition. E-coat deposition has been widely used by industries such as the automotive industry to form the primary protective coating against corrosion. Currently, models that are used to find the best conditions under which the desired coating coverage for the entire auto body can be achieved do not accurately predict the coating coverage in recessed areas. The accuracy of large-scale models can be improved by enhancing our understanding of the mechanisms responsible for the observed delay. To accomplish this, experiments are performed to define the processes that control deposition initiation and then a model is developed to describe those processes. Simulation results are compared with experimental measurements for a range of conditions to assess the validity of the results. The delay before the onset of deposition is influenced by the type of substrate and properties of the E-coat solution. The impact of the substrate type on the onset of deposition was experimentally investigated. The results of experiments indicated that surface characteristics such as adhesion of bubbles to the surface and the formation of an initial coating increase the local current density on the surface. Investigations of the morphology of the initial coating on different types of substrates indicated that deposition began at areas where the local current density was higher. Increasing the local current density due to the adhesion of bubbles to the surface resulted in a 40% reduction in the time required for the onset of deposition on galvanized steel compared to bare steel. The processes in the solution adjacent to the surface were also investigated to understand the mechanisms responsible for the onset of deposition. Convection was used as a tool to determine the impact of the accumulation of hydroxide ions on the onset of deposition. The results of rotating disk electrode (RDE) experiments showed that the observed delay before deposition was not due to the time required for accumulation of hydroxide ions at the surface. The results of additional experiments showed that the accumulation of micelles was critical to the deposit initiation. The impact of micelle accumulation on the deposit initiation was further explored by developing a mathematical model of the physical processes in the solution adjacent to the surface. The model was evaluated at different conditions and was found to agree with experimental results at different current densities and bulk micelle concentrations. The model and the experimental results from this study help to explain the observed delay in the early stages of E-coat deposition and provide a basis for improving large-scale simulation of E-coat deposition.

Rechargeable lithium ion batteries have been widely used in portable consumer electronic devices, hybrid and full electric vehicles, and emergency power supply systems, because of their high energy density and long lifespan. The lithium ion battery market was approximately $11.8 billion in 2010 and is expected to grow to $53.7 billion in 2020. However, there is an intrinsic safety issue in these batteries because electrolyte contains a flammable organic solvent which may cause fire and/or even explosion. All solid-state lithium ion battery is recognized as next-generation technology for rechargeable power sources due to improved safety, high energy density, and long cycle life. Inorganic solid electrolyte replace liquid one to eliminate flammable components. The major challenge for all solid-state lithium ion batteries is to develop solid electrolytes with high ionic conductivity and good stability against both electrodes. Amorphous lithium lanthanum titanium oxide (LLTO) is very promising as solid electrolyte owing to its high ionic conductivity, good stability, and wide electrochemical stability window. In this work, amorphous LLTO thin films (or powders) were successfully prepared by sol-gel process. The thin films are smooth and crack-free. The microstructure evolution from dried gel film to fired film to annealed film was examined. The microstructure of the annealed film, either amorphous or crystalline, depends on the annealing temperature and time. Theoretical analysis was conducted to understand the microstructure evolution. Induction time determines the longest annealing time without transformation from amorphous to crystalline state. The induction time decreases with annealing temperature until the time approaches a minimum, and after that, the time increases with the temperature. Ion transport properties were investigated by Electrochemical Impedance Spectroscopy (EIS). The plateau at low frequencies results from lithium ion long-range diffusion which contributes to dc conductivity, while the observed frequency dispersion at high frequencies is attributed to short-range forward¨Cbackward hopping motion of lithium ions. The relaxation processes are non-Debye in nature. Amorphous LLTO is compatible with Li metal due to its disordered atomic configuration. Finally, a 3D structure of electrode with amorphous LLTO was successfully prepared. This electrode displays promising electrochemical performance.

La cristallisation assistée par ultrasons permet de diminuer le temps d'induction et la largeur de la zone métastable, de modifier la distribution de tailles, de modifier le faciès des cristaux et d'augmenter le nombre des cristaux formés. L'origine microscopique de cet effet reste à ce jour non élucidée. Les ultrasons de puissance engendrent dans un liquide la naissance et l'oscillation très violente de milliards de petites bulles de gaz, phénomène appelé cavitation. Le cycle d'une de ces bulles sur une période acoustique consiste en une phase explosive suivie d'une implosion violente. A la fin de l'implosion, la pression peut atteindre 1 GPa. Plusieurs hypothèses sur les mécanismes mis en jeu sont proposées dans la littérature : refroidissement de la solution et augmentation de la pression au voisinage de l'interface, évaporation du solvant dans la bulle, et ségrégation des molécules ou des ions du soluté au voisinage de la bulle lors de la phase implosive. Afin d'examiner l'influence de la pression, des expériences de cristallisation du sulfate de zinc heptahydraté ont été menées (mesure de temps d'induction). Ce sel présente une solubilité indépendante de la pression entre 0 et 10 000 bars. Nos expériences ont montré que le temps d'induction est fortement diminué en présence d'ultrasons. Ce résultat nous permet d'affirmer que la pression au voisinage de la bulle n'entre pas en jeu dans le mécanisme de la nucléation primaire du ZnSO4,7H2O en présence d'ultrasons. Après l'étude de l'effet de la sursaturation, nous avons essayé d'exploré l'effet de la puissance ultrasonore, du gaz dissous et de la hauteur du liquide dans la cuve sur le temps d'induction. Il a été constaté que les ultrasons permettent de diminuer le temps d'induction. Il a été observé que la courbe du temps d'induction en fonction de la hauteur de la solution présente un minimum. Un autre volet de cette thèse réservé à la modélisation et la simulation. Dans un premier temps, la concentration en clusters ou agrégats moléculaires au voisinage de la bulle été calculée dans le cas du ZnSO4,7H2O grâce à la théorie de la ségrégation en fonction de la pression acoustique. La simulation montre qu'il y a une sur-concentration des clusters (jusqu'à 25 fois supérieure à la concentration stationnaire) augmentant ainsi la probabilité de contact des clusters, durant un temps très court, pouvant ainsi modifier le processus global de nucléation. Dans un deuxième temps, la modélisation/simulation de l'acoustique par COMSOL est réalisée en vue de déterminer les résonances de notre système (liquide + parois de la cuve). Les résonances observées sont cohérentes avec les mesures de temps d'induction. / Power ultrasound is known to enhance crystals nucleation, and nucleation times can be reduced by oneup to three orders of magnitude for several organic or inorganic crystals. The precise physics involved in this phenomenon still remains unclear, and various mechanisms involving the action of inertial cavitation bubbles have been proposed. In this paper, two of these mechanisms, pressure and ségrégation effects, are examined. The first one concerns the variations of supersaturation induced by the high pressures appearing in the neighbourhood of a collapsing bubble, and the second one results from the modification of clusters distribution in the vicinity of bubble. Crystallisation experiments were performed on zinc sulphate heptahydrate ZnSO4. 7H2O, which has been chosen for its pressure-independent solubility, so that pressure variations have no effect on supersaturation. As observed in past studies on other species, induction times were found lower under insonification than under silent conditions at low supersaturations, which casts some doubts on a pure pressure effect. The interfacial energy between the solid and the solution was estimated from induction times obtained in silent conditions, and, using classical nucléation theory, the steady-state distribution of the clusters was calculated. Segregation theory was then applied to calculate the over-concentrations of n-sized clusters at the end of the collapse of a 4 lmbubble driven at 20 kHz by different acoustic pressures. The over-concentration of clusters close to the critical size near a collapsing bubble was found to reach more than one order of magnitude, which may favour the direct attachment process between such clusters, and enhance the global nucleation kinetics. The effects of acoustic cavitation on crystallization of ZnSO4. 7H2O was observed in a sono-reactor build-up from a large emitting area transducer located at the bottom of the vessel. The experimental results have shown that the dissipated acoustic power passes through a maximum at about 15±1 cm, and that the induction-time passes through a minimum for the same liquid-level. The dissipated-power and the induction-time are found to be well correlated as the liquid height was varied. The acoustics of the sono-reactor was studied with linear acoustics, accounting for the wall vibrations by using the COMSOL software. Theoretical dissipated acoustic powers were compared to the experimental ones.

Made available in DSpace on 2014-12-17T15:41:43Z (GMT). No. of bitstreams: 1 LuziaPFCG.pdf: 2749949 bytes, checksum: 3f79f78a7f602972e60d8e39c6c0e5d4 (MD5) Previous issue date: 2007-11-19 / The biodiesel is defined as the mono-alkyl ester derived from long-chain fatty acids, from renewable sources such as vegetable oils or animal fat, whose use is associated with the replacement of fossil fuels in diesel engine cycle. The biodiesel is susceptible to oxidation when exposed to air and this process of oxidation affects the quality of fuel, mainly due to long periods of storage. Because of this, the oxidation stability has been the focus of numerous researches since it directly affects the producers, distributors and users of fuel. One of the possibilities to increase the resistance of biodiesel is the autoxidation treatment with inhibitors of oxidation. The antioxidants can be used as potential inhibitors of the effects of oxidation on the kinematic viscosity and the index of acidity of biodiesel, thereby increasing oxidative stability. This work aims to examine the efficiency of antioxidants, α-tocopherol and butylated hydroxy-toluene (BHT), added the biodiesel content of remembrance through Pressurized-Differential Scanning Calorimetry (P-DSC), Thermogravimetry (TG) and Petrology. The results showed that the use of antioxidant BHT, at the concentration of 2000ppm, increased resistance to oxidation of the biodiesel and oxidative induction time (OIT), which is a better result as antioxidant than the α-tocopherol. With the thermogravimetric analysis, it was observed that the biodiesel presented an initial decomposition temperature of lower tendency than that of oil, demonstrating to be more volatile, bearing great similarity to the diesel and being characterized as an alternative fuel. The rheological analysis indicated that each sample of biodiesel behaved as a Newtonian fluid / O biodiesel ? definido como o derivado mono-alquil ?ster de ?cidos graxos de cadeia longa, proveniente de fontes renov?veis como ?leos vegetais ou gordura animal, cuja utiliza??o est? associada ? substitui??o de combust?veis f?sseis em motores ciclo diesel. O biodiesel ? suscept?vel ? oxida??o quando exposto ao ar e este processo de oxida??o afeta a qualidade do combust?vel, principalmente em decorr?ncia de longos per?odos de armazenamento. Em fun??o disso, a estabilidade ? oxida??o tem sido foco de in?meras pesquisas, pois afeta diretamente os produtores de combust?veis, distribuidores e usu?rios. Um das possibilidades de aumentar a resist?ncia do biodiesel ? autoxida??o ? o tratamento com inibidores de oxida??o. Os antioxidantes podem ser utilizados como poss?veis inibidores dos efeitos da oxida??o sobre a viscosidade cinem?tica e o ?ndice de acidez do biodiesel, aumentando assim estabilidade oxidativa. Este trabalho teve objetivo de examinar a efici?ncia dos antioxidantes, α-tocoferol e o hidr?xi-tolueno butilado (BHT), adicionado no biodiesel met?lico de mamona, atrav?s da Calorimetria Explorat?ria Diferencial sob Press?o (P-DSC), Termogravimetria (TG) e PetroOXY. Os resultados obtidos mostraram que o uso do antioxidante BHT, na concentra??o de 2000ppm, aumentou a resist?ncia ? oxida??o do biodiesel e tempo de indu??o oxidativa (OIT), revelando-se um melhor resultado como antioxidante do que o α-tocoferol. Na analise termogravim?trica, observou-se que o biodiesel apresentou uma temperatura de decomposi??o inicial menor que a do ?leo, demonstrando ser mais vol?til, aproximando-se do diesel e se caracterizando com combust?vel alternativo. As an?lises reol?gicas indicaram que cada amostra do biodiesel comportou-se como fluido newtoniano

The long-term performance of stabilized polyolefins in different environments was studied with focus on antioxidant consumption and migration. Plaques of linear polyethylene (LPE) and branched polyethylene (BPE) were stabilized with Santonox® R (4,4'-Thiobis(6-tert-butyl-3-methylphenol)), Irganox® 1081 (2,2’-Thiobis(4-methyl-6-tertbutylphenol)), or Lowinox® 22M46 (2,2’-Methylenebis(6-tert-butyl-4-methylphenol)). The samples were aged in water and nitrogen at 75, 90 and 95°C. Antioxidant concentration profiles were obtained by oxidation induction time (OIT) measurements using differential scanning calorimetry (DSC). The very flat antioxidant concentration profiles of the plaques exposed to non-aqueous media indicated that the migration of antioxidant to the surrounding medium was controlled by the low evaporation rate at the sample boundary. The samples of BPE and Santonox R were also exposed to air and water saturated with air. The similarity of the antioxidant concentration profiles of Santonox R obtained after ageing in air and nitrogen suggested that the fraction of antioxidant oxidized is negligible in comparison with the loss of antioxidant by migration to the surrounding media. The loss of Santonox R in samples exposed to water saturated with air was faster than for the samples exposed to oxygen-free water. This was due to increased mass transport of the antioxidant from the polymer phase boundary to the water phase when oxygen was present. An unexpected higher migration rate from LPE than from BPE was proposed to be due to the low boundary loss rate in BPE, caused by the presence of a thin liquid-like (oligomeric) surface layer developed during ageing. A quantitative relationship was found between the boundary loss rate to water and the polarity of antioxidants. The antioxidant diffusivities were approximately equal in LPE and BPE, indicating that the constraining effect of the crystals on the non-crystalline fraction did not affect the antioxidant molecules. Results obtained by liquid chromatography of extracts confirmed that the gradual decrease in OIT with increasing ageing time was due to migration of antioxidant to the surrounding medium. Pipes of high-density polyethylene stabilized with hindered phenols and phosphites were exposed to chlorinated water at elevated temperatures. OIT showed that the stabilizing system was rapidly chemically consumed by the action of chlorinated water. Size exclusion chromatography and DSC showed extensive polymer degradation strictly confined to the immediate surface of the unprotected inner wall material and to the amorphous phase of the semicrystalline polymer. The rate of growth of the layer of highly degraded polymer was constant. Pipes of isotactic polybutene-1 were pressure-tested in chlorinated water at a controlled pH, and the lifetime was assessed as a function of temperature and chlorine content. The lifetime shortening in chlorinated water was significant even at relatively low chlorine contents, 0.5 ppm. A further increase of chlorine content led to only a moderate shortening of the lifetime. The temperature dependence of the lifetime data obeyed the Arrhenius law. The decrease of the antioxidant concentration was independent of the chlorine concentration in the range of 0.5-1.5 ppm. The time to reach depletion of the antioxidant system could be predicted by linear extrapolation. / QC 20101020

The major objectives of this study were to investigate the antioxidant properties of flaxseed lignans secoisolariciresinol (SECO 2) and secoisolariciresinol diglycoside (SDG 1) and their major oxidative compounds using 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH 47) in an in vitro model of lipid peroxidation. This investigation was facilitated by the structural elucidation of the major oxidative compounds and the ability of flaxseed lignans to delay the onset of oxidation in two model systems. <p>This study showed that SECO 2 oxidation occurs at the aromatic (4-OH) and aliphatic (9-OH) hydroxyl groups. Conversely for SDG 1, only compounds derived from the oxidation of aromatic hydroxyl groups were obtained because the 9-OH position is glucosylated. <p>SECO 2 oxidation with AAPH 47 showed that the intermediate 2a is most likely involved in the generation of early-forming (48 and 52) and 2c for the formation of late-forming (49, 50 and 51) oxidation compounds. Compound 48 is formed from dimerization of 2a that is converted to 52 and then to 51. Compound 50 was formed by the addition of a carbon-centre free radical of AAPH (AP radical) to 2c. Compounds 50 and 51 trap carbon-centered AP radicals supporting SECO 2 as a chain-breaking antioxidant and AAPH 47 as a proper model for study of SECO 2 oxidation in vitro. <p>SDG 1 oxidation with AAPH 47 indicated that intermediates 1b and 1c are most likely involved for the formation of early forming compounds (55 and 58) and 1a leads to the late forming compounds (56 and 57). Compound 55 is a result of dimerization. Compound 56 may be directly formed via intermediate radical 1a by adding AP free radicals. Compound 56 was a stable non-radical compound that could trap AP free radicals, thereby supporting SDG 1 as a chain-breaking antioxidant. Hydrogen abstraction from 4-hydroxyl yielded the radical 1a and hydroxyl radical addition to 1a yielded 57. Compound 58 formed from the addition of OH or H2O to 1c. <p>This study demonstrated that AAPH 47 produces carbon-centred AP radicals upon thermal decomposition and mimics the formation of lipid peroxyl radicals. Interaction of carbon-centred AP radicals with SECO 2 and SDG 1 provides a good model to study the antioxidant reactions of SECO 2 in vitro. p*The relative antioxidant capacity of the flaxseed lignans versus BHT 17, in two model systems, was determined. The stoichiometric ratio for SECO 2 and SDG 1 were 1.5 and 1.1-1.2, respectively, compared to BHT 17 (2.0). The induction time by Rancimat analyzer measured inhibition of autoxidation mediated by flaxseed lignans SECO, SDG and SDG polymer in comparison with BHT 17. The induction time data demonstrated that SECO 2 protected canola oil better than either SDG 1 or SDG polymer 3. <p>These results are important for better understanding about the chemistry behind flaxseed lignan antioxidant activities. This study provided useful evidence that flaxseed lignans can be used as natural antioxidants.

The major objectives of this study were to investigate the antioxidant properties of flaxseed lignans secoisolariciresinol (SECO 2) and secoisolariciresinol diglycoside (SDG 1) and their major oxidative compounds using 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH 47) in an in vitro model of lipid peroxidation. This investigation was facilitated by the structural elucidation of the major oxidative compounds and the ability of flaxseed lignans to delay the onset of oxidation in two model systems. <p>This study showed that SECO 2 oxidation occurs at the aromatic (4-OH) and aliphatic (9-OH) hydroxyl groups. Conversely for SDG 1, only compounds derived from the oxidation of aromatic hydroxyl groups were obtained because the 9-OH position is glucosylated. <p>SECO 2 oxidation with AAPH 47 showed that the intermediate 2a is most likely involved in the generation of early-forming (48 and 52) and 2c for the formation of late-forming (49, 50 and 51) oxidation compounds. Compound 48 is formed from dimerization of 2a that is converted to 52 and then to 51. Compound 50 was formed by the addition of a carbon-centre free radical of AAPH (AP radical) to 2c. Compounds 50 and 51 trap carbon-centered AP radicals supporting SECO 2 as a chain-breaking antioxidant and AAPH 47 as a proper model for study of SECO 2 oxidation in vitro. <p>SDG 1 oxidation with AAPH 47 indicated that intermediates 1b and 1c are most likely involved for the formation of early forming compounds (55 and 58) and 1a leads to the late forming compounds (56 and 57). Compound 55 is a result of dimerization. Compound 56 may be directly formed via intermediate radical 1a by adding AP free radicals. Compound 56 was a stable non-radical compound that could trap AP free radicals, thereby supporting SDG 1 as a chain-breaking antioxidant. Hydrogen abstraction from 4-hydroxyl yielded the radical 1a and hydroxyl radical addition to 1a yielded 57. Compound 58 formed from the addition of OH or H2O to 1c. <p>This study demonstrated that AAPH 47 produces carbon-centred AP radicals upon thermal decomposition and mimics the formation of lipid peroxyl radicals. Interaction of carbon-centred AP radicals with SECO 2 and SDG 1 provides a good model to study the antioxidant reactions of SECO 2 in vitro. p*The relative antioxidant capacity of the flaxseed lignans versus BHT 17, in two model systems, was determined. The stoichiometric ratio for SECO 2 and SDG 1 were 1.5 and 1.1-1.2, respectively, compared to BHT 17 (2.0). The induction time by Rancimat analyzer measured inhibition of autoxidation mediated by flaxseed lignans SECO, SDG and SDG polymer in comparison with BHT 17. The induction time data demonstrated that SECO 2 protected canola oil better than either SDG 1 or SDG polymer 3. <p>These results are important for better understanding about the chemistry behind flaxseed lignan antioxidant activities. This study provided useful evidence that flaxseed lignans can be used as natural antioxidants.

Studying clathrate hydrates is, ideally, a simple task: one just have to keep water under a gas pressure. However, when trying to collect measurements in an accurate and repeatable way, things mess up. When, in particular, kinetic characterizations are required, not only pressure and temperature have to be measured: also particular parameters such as gas evolved/trapped during time, heat released/adsorbed during time, critical phenomena related to additive addition, etc, should be collected in a finer way. In the last years a growing interest has been devoted to investigations on the effects of a wide range of compounds capable to affect the thermodynamics and, in particular, kinetics of clathrate hydrate formation. The study of the effects of these compounds, called conditioners, requires an improvement of the performances of usual lab facilities by introducing a new strategy for the measurement of further characterizing parameters. Presently no standardization of the apparatus designed for clathrate hydrate studies exists, nor any commercial instrumentations are available. Generally, apparatus used are custom-made by the same research team according with the peculiar research requirements To do this we have designed, built, calibrated and tested a novel apparatus that, in addition to the ability of measuring usually unexplored parameters, is based on the idea of obtaining as many parameters as possible in a single formation batch. This in order to solve the problem of collecting a dataset that can be processed homogeneously, thus minimizing errors due stochastic behaviours. Using such an apparatus, several kinds of measurement are presented here, which are related directly to the clathrate hydrate investigation fields, but also more generally related to the study of equilibrium phases involving gaseous components.