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PRODUÇÃO DE ETENO A PARTIR DE ETANOL UTILIZANDO ALUMINAS / ETHYLENE PRODUCTION FROM ETHANOL USING ALUMINASRos, Simoní da 24 September 2012 (has links)
Conselho Nacional de Desenvolvimento Científico e Tecnológico / Calcination variables, temperature, time and heating rate, used in obtaining different
transition aluminas were simultaneously investigated using statistical experimental design.
Empirical models correlating catalyst final properties and calcination conditions were
employed. It was found that all calcination variables play fundamental roles on acidity of
alumina catalyst. Furthermore, interaction effects among these variables and non-linear
effects also are of fundamental importance for the final properties catalyst. Therefore, the use
of simultaneous variation of calcination conditions through experimental design is of great
importance in detecting such interactions. It was observed that the use of high heating rates
favor the formation of pore with larger diameters and with high pore volume and, for short
calcination time, high heating rate also contributes to the formation of higher concentration of
acid sites. The acid sites characterization of transition aluminas were performed by
temperature programmed desorption of ammonia (NH3-DTP), which showed that there are
two distinct acid sites on the surface these materials. The desorption dates were adjusted by a
model in which the catalyst bed was considered as single continuously stirred tank reactor and
the intrinsic kinetic was chosen to be of first order for adsorption and desorption. The ethanol
conversion was higher for the alumina with higher acid sites concentration, suggesting a
relationship between the activity of the alumina for the ethanol conversion and its acidity. The
selectivity for the ethylene formation also was higher for the more acid aluminas, while the
selectivity to ether presented opposite behavior. Therefore, a successful control of all
calcination conditions can be an effective method to adjust the final physical and chemical
properties of transition alumina catalyst, aiming the highest yield of ethylene from ethanol
dehydration. / Foram preparadas aluminas de transição investigando-se simultaneamente o efeito das
variáveis de calcinação: temperatura, tempo e taxa de aquecimento, usando planejamento
estatístico de experimentos. Modelos empíricos foram empregados para correlacionar as
propriedades finais dos catalisadores às variáveis de calcinação. Foi observado que todas as
variáveis de calcinação influenciam a concentração de sítios ácidos das aluminas. Além disso,
efeitos de interação entre estas variáveis, bem como efeitos não lineares também são de
fundamental importância para as propriedades finais deste catalisador. Estes efeitos só podem
ser identificados com a variação simultânea das condições de calcinação através do uso do
planejamento de experimentos. Foi observado que o uso de elevada taxa de aquecimento
favorece a formação de aluminas com maior volume e tamanho de poros e, para curtos
períodos de tempo de calcinação, elevada taxa de aquecimento também contribui para a
formação de maior concentração de sítios ácidos. A caracterização dos sítios ácidos das
aluminas foi realizada pela técnica de dessorção de amônia à temperatura programada (DTPNH3).
Esta caracterização indicou a presença de dois tipos de sítios ácidos na superfície destes
materiais. Os dados de dessorção foram ajustados por um modelo que considera a cinética de
dessorção e readsorção como reações de primeira ordem em um modelo de reator de mistura
perfeita. A conversão de etanol foi maior para as aluminas com maior concentração de sítios
ácidos, indicando uma relação entre a atividade das aluminas para a conversão de etanol e sua
acidez. A seletividade para a formação de eteno também foi maior para as aluminas mais
ácidas, enquanto que a seletividade para éter exibiu comportamento inverso. Portanto, o
controle adequado de todas as condições de calcinação pode ser um método eficiente para
ajustar as propriedades físicas e químicas finais de aluminas de transição, visando obter maior
rendimento na produção de eteno a partir da desidratação de etanol.
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Réhydratation des protéines laitières dans un milieu complexe : influence de l'état d'hydratation sur les propriétés texturales des gels acides / Dairy proteins powders rehydration into a complex media : effects of rehydration state on textural properties of acid milk gelsKaram, Marie-Céleste 13 September 2013 (has links)
L'objectif de la thèse a été d'élucider le processus de réhydratation des caséines micellaires et des protéines solubles dans un milieu complexe et opaque : le lait. L'influence de l'état d'hydratation de ces ingrédients laitiers en fonction du temps (5, 120, 180, 240, 300, 480, 900 et 1440 min de réhydratation) sur les propriétés rhéologiques, texturales, physiques ainsi que la microstructure des gels laitiers acides a également été étudiée. Il en résulte que le processus de réhydratation des caséines micellaires diffère de celui des protéines solubles, et est extrêmement long avec trois étapes : une étape de mouillage des particules, suivie d'une étape de gonflement caractérisée par une augmentation de la taille des particules et enfin une étape de dispersion marquée par la diminution de la taille des particules. La réhydratation des protéines solubles est caractérisée par une grande rapidité, avec deux phases : le mouillage et la phase de dispersion (superposée). D'autre part, l'allongement de la durée de réhydratation des caséines micellaires est associé à une augmentation du point de gélification ainsi qu'à une nette amélioration des propriétés physiques, texturales et rhéologiques des gels : augmentation de leur fermeté et de leur force, diminution de la synérèse et de la formation de grumeaux. La durée de réhydratation des protéines solubles n'a pas d'influence sur ces paramètres. En revanche, leur dénaturation (par chauffage à sec) est associée à une dégradation des propriétés texturales des gels acides. Finalement, il s'avère que les gels acides formulés à partir des protéines solubles sont de meilleure qualité texturale (à l'exception de la formation de grumeaux) que ceux préparés à partir des caséines micellaires / The main objectives of this work were to elucidate the rehydration mechanism of the two major milk proteins (micellar casein and whey protein) into a complex and opaque medium such as milk and to assess the influence of hydration state (defined as a function of rehydration length after 5,120,180,240,300, 480, 900 and 1440 minutes of rehydration) on the rheological, textural, physical properties and microstructure of the obtained acid milk gels. Whereas, micellar casein presented a long rehydration process into milk characterized by three stages: a wetting, swelling and dispersion phase, whey protein displayed a quick rehydration process characterized by an overlapping of wetting and dispersion phase. Furthermore, an extended rehydration time of micellar casein powder into the milk base was associated with a postponed onset of gelation and enhanced physical, textural as well as rheological properties of the obtained acid milk gels characterized by increases in gel firmness, strength, and decreases in syneresis susceptibility and grains formation. In contrast, acid milk gels prepared with whey protein powder exhibited comparable overall textural properties regardless the different rehydration times. Nevertheless, denaturation of whey protein powder (by dry heating) was associated with a deterioration of the textural properties of the acid milk gels. Finally, acid gels prepared with whey proteins displayed better overall textural quality than those prepared with micellar casein (except for grains formation)
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