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Estágio realizado na Portucel Viana e orientado pelo Eng.º Mário António Pinto dos Santos Amaral / Tese de mestrado integrado. Engenharia Química. Faculdade de Engenharia. Universidade do Porto. 2009

Two liquid-solid reactions, in which the morphology of the solid changes as the reactions proceeds, were examined. One is the NA conversion in oil by decarboxylation on metal oxides and carbonates, and the other is the Kraft pulping in which lignin removal by delignification reaction. In the study of the NA conversion, CaO was chosen as the catalyst for the kinetic study from the tested catalysts based on NA conversion. Two reaction mixtures, carrier oil plus commercial naphthenic acids and heavy vacuum gas oil (HVGO) from Athabasca bitumen, were applied in the kinetic study. The influence of TAN, temperature, and catalyst loading on the NA conversion and decarboxylation were studied systematically. The results showed that the removal rate of TAN and the decarboxylation of NA were both independent of the concentration of NA over the range studied, and significantly dependent on reaction temperature. The data from analyzing the spent catalyst demonstrated that calcium naphthenate was an intermediate of the decarboxylation reaction of NA, and the decomposition of calcium naphthenate was a rate-determining step. In the study on the delignification of the Kraft pulping, a new mechanism was proposed for the heterogeneous delignification reaction during the Kraft pulping process. In particular, the chemical reaction mechanism took into account the heterogeneous nature of Kraft pulping. Lignin reacted in parallel with sodium hydroxide and sodium sulfide. The mechanism consists of three key kinetic steps: (1) adsorption of hydroxide and hydrosulfide ions on lignin; (2) surface reaction on the solid surface to produce degraded lignin products; and (3) desorption of degradation products from the solid surface. The most important step for the delignification process is the surface reaction, rather than the reactions occurring in the liquid phase. A kinetic model has, thus, been developed based on the proposed mechanism. The derived kinetic model showed that the mechanism could be employed to predict the pulping behavior under a variety of conditions with good accuracy. / Chemical Engineering

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Zugl.: Potsdam, Univ., Diss., 2009

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In a kraft recovery dissolving tank, high temperature molten smelt droplets fall into an aqueous solution and dissolve. The rapid heat transfer between molten smelt and water can lead to violent dissolving tank operation, and in severe cases, a dissolving tank explosion. In this study, an experimental apparatus was built to investigate the interaction between a molten synthetic smelt droplet and water. Smelt-water interaction was documented, and the effects of water and smelt temperatures on droplet explosion probability, explosion delay time, and explosion intensity were examined. The results show that explosions always occur below a lower critical water temperature, which is a function of smelt temperature, and never explodes above an upper critical water temperature. Up to the upper critical water temperature, as the water temperature increases, the explosion probability decreases, and the explosion delay time and the explosion intensity increases. A Smelt-Water Interaction Temperature (SWIT) diagram was constructed to describe the explosion probability at different smelt and water temperatures.

In a kraft recovery dissolving tank, high temperature molten smelt droplets fall into an aqueous solution and dissolve. The rapid heat transfer between molten smelt and water can lead to violent dissolving tank operation, and in severe cases, a dissolving tank explosion. In this study, an experimental apparatus was built to investigate the interaction between a molten synthetic smelt droplet and water. Smelt-water interaction was documented, and the effects of water and smelt temperatures on droplet explosion probability, explosion delay time, and explosion intensity were examined. The results show that explosions always occur below a lower critical water temperature, which is a function of smelt temperature, and never explodes above an upper critical water temperature. Up to the upper critical water temperature, as the water temperature increases, the explosion probability decreases, and the explosion delay time and the explosion intensity increases. A Smelt-Water Interaction Temperature (SWIT) diagram was constructed to describe the explosion probability at different smelt and water temperatures.