Navegando por Autor "Fontes, Maria do Socorro Braga"
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Artigo Catalytic upgrading of Elephant grass (Pennisetum purpureum Schum) pyrolysis vapor using WO3 supported on RHA and RHA-MCM-41(Elsevier, 2017-01-01) Melo, Marcus Antônio de Freitas; Braga, Renata Martins; Melo, Dulce Maria de Araújo; Vitor Sobrinho, Eledir; Barros, Joana Maria de Farias; Carvalho, Alexandre Fontes Melo de; Fontes, Maria do Socorro Braga; Freitas, Júlio César de OliveiraRecently, zeolites have been widely applied in catalytic pyrolysis to improve physical and chemical properties of bio-oil to produce energy or to selectively produce chemicals for industry. This study aims to analyze the catalytic pyrolysis products of Elephant Grass (EG) using WO3 catalysts supported on rice husk ash (RHA) silica and RHA-MCM-41, being low cost materials derived from agro industrial waste, and evaluate the catalysts activity in the formation of deoxygenated compounds. Elephant Grass has been shown as a potential energy crop that has fast growth and is easy to cultivate in different countries, including Brazil. Its energetic characterization was evaluated by proximate and ultimate analysis, High Heat Value (HHV), cellulose, hemicellulose and lignin content, chemical ash composition by FRX and bulk density. Pyrolysis analysis was performed at 500 ◦C in a Py-5200 HP-R connected to a GC–MS, and pyrolysis vapors were carried by N2 to a catalytic bed at 400 and 600 ◦C. It was noticed that increasing catalyst temperature promotes cracking reactions leading to increased aromatic content. The main oxygenated pyrolysis products of EG such as phenols, furans, ketones and acetic acid were converted at 600 ◦C using WO3/RHA catalyst into aromatics (benzene, toluene, xylene, styrene), being of high added value for chemical industry. The main influence on aromatics yields could be related to catalytic activity of WO3 promoted by its redox ability and the rise in temperature which favors cracking reactionsArtigo Comparison of kinetic study of CTMA+ removal of molecular sieve Ti-MCM-41 synthesized with natural and commercial silica(ABM, ABC, ABPol, 2015) Melo, Marcus Antônio de Freitas; Fontes, Maria do Socorro Braga; Melo, Dulce Maria de Araújo; Costa, Cintia de Castro; Braga, Renata Martins; Alves, José Antônio Barros Leal ReisThis work aimed to determine and compare the apparent activation energy, involved in thermal decomposition of CTMA+ from the pores of Ti-MCM-41 synthesized by two different source of silica in order to evaluate their influence in the template removal. The molecular sieves Ti-MCM-41 were synthesized using rice husk ash (RHA), as alternative low cost source of silica, and commercial silica gel, obtaining two mesoporous material by hydrothermal synthesis of gel molar composition of: 1.0 CTMABr: 4.0 SiO2 : X TiO2 : 1.0 Na2 O: 200.0 H2 O. The samples were characterized to compare its properties by X-ray diffraction, IR spectroscopy, BET method and thermogravimetric analysis (TGA). The kinetic study using the model proposed by Flynn and Wall to determine the apparent activation energy for CTMA+ removal was performed using TGA data. The thermogravimetric analysis results of the material obtained from RHA confirmed intrinsic properties of mesoporous MCM-41 as the synthesized with commercial silica gel, such as high specific area, mesoporous range of pore diameter and hexagonal structure. According to the kinetics results the RHA showed similar chemical interaction to commercial silica gel, which makes it an interesting material, since it is a low cost source of natural silica from agricultural wasteArtigo Kinetic study of CTMA+ removal from the pores of the Ti-MCM-41 molecular sieve(Journal of Thermal Analysis and Calorimetry, 2014) Melo, Marcus Antonio de Freitas; Fontes, Maria do Socorro Braga; Melo, Dulce Maria de Araújo; Barros, Joana Maria de Farias; Braga, Renata Martins; Fontes, Vilsinéia dos AnjosThermogravimetry analysis was used to study the thermal decomposition of Ti-MCM-41 to determine the best calcination conditions. Ti-MCM-41 molecular sieve was synthesized using a hydrothermal route in which Ti ions were incorporated into the pore channels of MCM-41 starting from a hydrogel method according to the following molar composition: 1.00 CTMABr:4.00 SiO2:X TiO2:1.00 Na2O:200.00 H2O. Physicochemical properties of samples were investigated using XRD, FTIR, and N2 adsorption– desorption to confirm the incorporation of TiO2 nanoparticles inside of MCM-41 mesoporous without destroying its structure. The high temperatures facilitate the rapid removal of the surfactant; however, it caused destruction of the MCM-41 structure by breaking the bonds of the silica tetrahedral structure. The procedures to obtain the apparent activation energies of CTMABr decomposition were based on the kinetic model proposed by Flynn-Wall using thermal analysis of data performed with heating rates 5, 10, and 20 C min-1Artigo Kinetic study of the removal of pure and mixed TTMA+, CTMA+ and DTMA+ templates from MCM-41(Springer Verlag, 2015-07-02) Martinelli, Antonio Eduardo; Costa, Cíntia de Castro; Melo, Dulce Maria de Araújo; Fontes, Maria do Socorro Braga; Barros, Joana Maria de Farias; Melo, Marcus Antônio de FreitasThis work assessed the thermal degradation of surfactants, i.e., tetradecyltrimethylammonium bromide (TTMA?—C17H38NBr), cetyltrimethylammonium bromide (CTMA?—C19H42NBr) and trimethyloctadecylammonium bromide (DTMA?—C21H46NBr), used to obtain MCM-41-type mesoporous materials using Flynn–Wall kinetic model. The cationic surfactants and their mixture at ratios of 1:1 and 1:1:1 resulting materials were labeled C17, C19, C21, C17C19, C19C21, C17C21 and C17C19C21. Before the kinetic study, the materials obtained by the hydrothermal method were characterized by physical, chemical and microstructural analyses such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetric and nitrogen adsorption–desorption plots (BET). The mesoporous materials showed a well-defined hexagonal arrangement from the calcination process and significant structural differences. The kinetic model was used to determine the apparent activation energy for the removal of pure surfactant and associated with pores of the MCM-41-type molecular sieve. From the kinetic study results, a decrease in activation energy was observed when using the mixture of surfactants, especially C17C19. Combining these results with XRD and BET analyses, it was observed that C17C19 showed the largest surface area and pore volume along with hexagonal arrangement. The mixture of cationic surfactants of hydrophobic chains of different sizes used in the preparation of MCM-41 reduced the activation energy and surfactant removalTese Preparação e caracterização de catalisadores à base de titânio suportado em MCM-41 para produção de compostos oxigenados através da pirólise catalítica do capim elefante(Universidade Federal do Rio Grande do Norte, 2013-05-17) Fontes, Maria do Socorro Braga; Melo, Dulce Maria de Araújo; ; http://lattes.cnpq.br/3318871716111536; ; Vitor Sobrinho, Eledir; ; http://lattes.cnpq.br/8488499388852606; Barros, Joana Maria de Farias; ; http://lattes.cnpq.br/1016070459137884; Ricardo, Nágila Maria Pontes Silva; ; Braga, Renata Martins; ; http://lattes.cnpq.br/4603529162393328; Pergher, Sibele Berenice Castella; ; http://lattes.cnpq.br/5249001430287414Nos últimos anos, a área de materiais tem avançado consideravelmente, principalmente, quando se trata de materiais para uso industrial, como é o caso de catalisadores estruturados com porosidade adequada para os processos catalíticos. O uso de catalisadores combinados ao processo de pirólise rápida é uma alternativa para a produção de compostos oxigenados de alto valor agregado, pois, além de elevar o rendimento e qualidade dos produtos, permite manipular a seletividade para um produto de interesse e, portanto, permite um maior controle sobre as características do produto final. Com base nesses argumentos, neste trabalho foram preparados catalisadores de titânio suportados em MCM-41 para uso em pirólise catalítica da biomassa, denominada de capim elefante. As reações de pirólise da biomassa foram realizadas em um micro pirolisador, Py-5200, acoplado ao GC/MS, da empresa CDS Corporation, sediada nos Estados Unidos. Os catalisadores Ti-MCM-41, em diferentes razões molares, foram caracterizados por DRX, TG/DTG, FT-IR, MEV, FRX, UV-Visível, adsorção de nitrogênio, distribuição de diâmetro de partículas e medidas de área específica pelo método BET. A partir dos testes catalíticos foi possível observar que os catalisadores sintetizados apresentaram bons resultados para a reação de pirólise. Entre os catalisadores Ti-MCM-41 (razões molares Si/Ti = 25 e 50), o de razão Si/Ti=25 (temperatura de 400°C e 600°C) favoreceu o craqueamento de compostos oxigenados, tais como, ácidos, aldeídos, cetonas, furanos e ésteres. Já a amostra de razão Si/Ti = 50 apresentou maior rendimento de aromáticos oxigenados