DEPETRO - Artigos publicados em periódicos
URI Permanente para esta coleçãohttps://repositorio.ufrn.br/handle/123456789/32665
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Artigo Kinetic study of template removal of MCM-41 derived from rice husk ash(Journal of Thermal Analysis and Calorimetry, 2013) Melo, Marcus Antonio de Freitas; Braga, Renata Martins Braga; Barros, Joana Maria de Farias Barros; Melo, Dulce Maria de Araújo; Aquino, Flávia de Medeiros; Freitas, Júlio Cézar de Oliveira; Santiago, Rodrigo CésarMolecular sieves MCM-41 were synthesized from rice husk ash (RHA) as alternative sources of silica, called RHA MCM-41. The material was synthesized by a hydrothermal method from a gel with the molar composition 1.00 CTMABr:4.00 SiO2:1.00 Na2O:200.00 H2O at 100 C for 120 h with pH correction. The cetyltrimethyl- ammonium bromide (CTMABr) was used as a structure template. The material was characterized by X-ray powder diffraction, FTIR, TG/DTG, and surface area determination by the BET method. The kinetics models proposed by Ozawa, Flynn–Wall, and Vyazovkin were used to determine the apparent activation energy for CTMA? species decomposition from the pores of MCM-41 material. The results were compared with those obtained from the MCM-41 synthesized with silica gel. The synthesized material had specific surface area, size, and pore volume as specified by mesoporous materials developed from conventional sources of silica.Artigo Rheological properties of a new surfactant-based fracturing gel(Elsevier, 2003-09-15) Dantas, Tereza Neuma de Castro; Santanna, Vanessa Cristina; Dantas Neto, Afonso Avelino; Barros Neto, Eduardo Lins de; Moura, Maria Carlenise Paiva de AlencarSurfactant-based fracturing gels are considered as clean gels due to the absence of insoluble residues in their composition. This kind of fluid has been developed to minimize or eliminate damages to fractures. Therefore, new studies about gel rheological properties become more and more important, namely viscosity, the most important property of fracturing gels. This research was accomplished with the purpose of evaluating a new anionic surfactant based gel. Steady and oscillatory shear experiments were carried out in order to evaluate the inner structure of the developed gel with variable composition, within the gel region in a pseudoternary diagram. It could be observed that small variations in gel composition resulted in changes in micellar structureArtigo Modification of bentonite clay by a cationic surfactant to be used as a viscosity enhancer in vegetable-oil-based drilling fluid(Elsevier, 2017-01) Ratkievicius, Luciana Avelino; Cunha Filho, Fernando José Vieira da; Barros Neto, Eduardo Lins de; Santanna, Vanessa CristinaBentonite clays may be used as additives in drilling fluids aiming at viscosity correction. A surface modification procedure with the purpose of dispersing the clay in the organic phase of a vegetable-oil-based drilling fluid was performed. The fluids were prepared using soybean oil, lauryl alcohol triethoxylate, brine, bentonite modified by hexadecyl trimethylammonium bromide (CTABr), and barite. The clay modification step was performed using three different concentrations of cationic surfactant. To evaluate the surface modification of the clays, surface tension measurements and determination of contact angles on soybean oil with the capillary rise method were performed. A factorial design 23 with triplicate center point was conducted to evaluate the influence of the concentration of CTABr in claymodification, viscosity enhancer concentration in the composition of the drilling fluid and temperature on the rheological properties of the fluid: plastic viscosity, apparent viscosity, thixotropy and yield strength. As higher amounts of quaternary ammonium cations were adsorbed on clay surface, a decrease of the contact angle was observed, suggesting an increasing affinity for soybean oil. The study of the effect of independent variables showed that temperature is the most influential factor in the rheological properties of the prepared fluid