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Catalisadores contendo espécies V2O5 ou VO2+ : atividade e seletividade na redução de NO com amônia
(Universidade Federal de São Carlos, 2009-08-03) Lima Neto, Antonio Vieira; Urquieta-González, Ernesto Antonio; https://lattes.cnpq.br/8488215444152608; http://lattes.cnpq.br/2389975677904655
The selective catalytic reduction of NOx with ammonia is the best technology available today to carry out the abatement of nitrogen oxide emissions in industrial gas effluents. Currently, vanadia-titania catalysts promoted with WO3 or MoO3 are the most active catalysts for the mentioned reaction. They show a very good catalytic stability for a long time. However, vanadia is also active in the oxidation of SO2 (a compound commonly found in industrial effluents) to SO3 this reaction is highly undesirable since SO3 reacts with water present at effluent gas and ammonia, producing sulfuric acid and ammonium sulfates, NH4HSO4 and (NH4)2SO4. The ammonium sulfates can deposit and accumulate themselves on the catalyst surface besides causing pressure drop problems or equipment corrosion. Apart from this, vanadia-titania catalysts are partially sulfated in SO2 presence, they have specific surface area relatively low (in the order of 40 m2/g) and they can show difficulties when they are discarded because vanadia (as well as WO3 and MoO3) is poisonous to the soil and water. Thus, the optimization or search for new catalytic systems for the selective reduction of NOx with ammonia acquires a significative importance. For this reason, the present work was set in the context of technological route of the selective catalytic reduction of NOx with ammonia and it has the objective of investigate the performance of some catalysts and/or supports (zeolites, mesoporous molecular sieves and transition metal oxides) in the reaction in focus. The studied catalysts were prepared through incipient wet impregnation method or by ionic exchange between a support and a VOSO4 solution. Afterwards, the solids were analyzed by a number of characterization techniques and they were tested in the selective catalytic reduction of NOx with ammonia in the presence of oxygen, in a temperature range of 200°C to 500°C. The materials that have shown the best performances in this first test were subjected to stability tests with water and SO2. The results demonstrated that the Si/Al ratio and the molecular sieve structure, as well as the original cation nature to be exchanged, had influence on the catalyst behavior in the face of the reaction in focus. Finally, accordingly to the test battery accomplished in this investigation, one can say that zeolite H-ZSM-5 exchanged with VO2+ ion was the best catalyst to the selective catalytic reduction of NOx with ammonia, in the temperature range of 350°C to 500°C. It was better, in the test conditions, than the V2O5-WO3/TiO2 (similar to a commercial type).
Avaliação da tendência à formação de fase vítrea nas ligas à base de alumínio do sistema Al-Y-Fe
(Universidade Federal de São Carlos, 2009-08-03) Benavides Filho, Marcos Antonio; Botta Filho, Walter José; https://lattes.cnpq.br/8956458007749112; https://lattes.cnpq.br/5427230809487223
The present work aimed to study the glass-forming ability of the aluminum-itrium-iron (Al-Y-Fe) alloys. The work included the preparation of samples through the melt-spinning technique and varying the composition of the samples. The structural characterization of the samples was made by x-ray diffraction technique (DRX) and differential scanning calorimetry (DSC). Some complementary characterizations included the Scanning Electron Microscopy (MEV) together with the Energy Dispersion Spectroscopy (EDS). Also were determinated the sample's characteristics temperatures liquidus temperature (Tliq), crystallization temperature (Tx) and glass-transition temperature (Tg). The glass-forming ability of the alloys was discussed based on different approaches from the literature . A discussion about the present glass-forming ability concept is put forward.
Estudo da dispersão de pigmentos orgânicos em resina de polipropileno para aplicação em fibras e filamentos
(Universidade Federal de São Carlos, 2009-08-03) Dutra, Regiane Defacio; Bretas, Rosario Elida Suman; https://lattes.cnpq.br/2805349172281345; https://lattes.cnpq.br/3954788812913703
Polypropylene has become widely used in fiber and filament applications; most part of these applications use colorful pigments to satisfy aesthetic necessities, communication, identification and others. To achieve the effect of the needed color it is necessary that the pigment has been well dispersed and distribute in the polymer. The appropriate dispersion is usually achieve with the combination of several mechanisms, that can occur at the same time during the mixture operation, such as: initial wetting, size reduction of the pigments, amount of aggregates and agglomerates, intimate wetting, particle uniform distribution in the medium and stabilization of the particles to avoid re-agglomeration. In this work the dispersion of two different organic pigments based on cupper phthalocianine (Pigment Blue 15) and betaoxynaphthoic acid (Pigment Red 48) in polypropylene resin with different humectants systems was studied. The characteristics of each formulation component, the determination of maximum pigment loading in polymer melts based on the CPVC (Critical Pigment Volume Concentration) concept, the ideal conditions of processing in static mixer and co-rotating twin screw extruder and the dispersion were evaluated by tint strength, filter pressure value and scanning electron microscopy. The results showed that there is an optimum humectant for each kind of pigment. The best results were obtained with the red pigment and the oxidized polyethylene wax, in which the filter pressure value was below 2 bar/g. The results for the blue pigment were not satisfactory.