M. A. F. Melo

Preparation and characterization of terbium palygorskite clay as acid catalyst

Abstract Palygorskite clays containing 5% and 10% terbium (W/W) were prepared by ion exchange from acid-leached natural clay. Samples were calcined at 523, 573, 623 and 673 K to verify the effect of the temperature over the physical–chemical properties. Characterization was using X-ray diffraction, infrared spectroscopy ( n -butylamine adsorption), UV–visible diffuse reflectance spectroscopy and N 2 adsorption. Isopropyl alcohol (IPA) transformation was also performed in order to improve the acid behavior. TB 3+ introduction does not change the palygorskite structure, albeit leading to an increase in the surface area and generation of Lewis acid sites. Results from the DRS spectra along with a decrease in the catalytic activity suggested the formation of terbium oxide for relatively high TB 3+ contents.

Characterization and comparative study of pyrolysis kinetics of the rice husk and the elephant grass

A comparative evaluation of different biomasses allows the choice that presents the best potential as fuel for energy production. The knowledge of the thermal and kinetics parameters of the biomass in the process of thermal conversion is fundamental as their chemical and physical characterization. Various methodologies have been developed for the determination of kinetic parameters as apparent activation energy and reaction order from the thermogravimetric analysis. In this work, the apparent activation energy needed to break the bonds of hemicelluloses and cellulose of rice husk and elephant grass during the thermal conversion was evaluated according to the kinetics models of Flynn and Wall and Model Free Kinetics developed by Vyazovkin. The biomass elephant grass and rice husk were characterized for moisture, ash and volatile matter by ASTM E871, ASTM E1755, ASTM E872, respectively, and fixed carbon by difference. The percentage of carbon, hydrogen, nitrogen, and oxygen were determined by ultimate analysis. The elephant grass showed to be more suitable for production of bio-oil through pyrolysis due to the higher percentage of volatile, less ash content and less energy required to break the bonds of hemicellulose and cellulose than rice husk in the thermal conversion process.

Adsorption of crude oil on anhydrous and hydrophobized vermiculite.

This publication reports the adsorption of crude oil on vermiculite samples, expanded and hydrophobized with carnauba (Copernicia Cerifera) wax. The adsorption studies were performed by using columns filled with the vermiculite matrices and by dispersion of the vermiculite samples in an oil-water (50 ppm of oil) emulsion. The hydrate vermiculite exhibits a very low adsorption capacity against crude oil. On the other hand, anhydrous (expanded) and hydrophobized matrices show a high adsorption capacity. The 10% hydrophobized matrix show a 50% increased adsorption capacity, in comparison with the expanded one. For adsorption performed in the water-oil emulsion, saturation of the solid hydrophobized matrix is achieved after 60 min. The hydrophobized samples exhibit adsorption factors in the 0.7-1.0 range.

Synthesis of high value-added zeolitic materials using glass powder residue as a silica source

In this work, zeolite A was obtained using alkaline fusion followed by a hydrothermal treatment of glass powder residue derived from the manufacturing of glass. The following parameters were evaluated: leaching of the stock material (silica source), mineralizing agent, alumina source, and the alkaline fusion and crystallization temperatures. The synthesized materials were characterized by chemical analysis using energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD and SEM results showed that zeolite A was obtained under almost all of the evaluated parameters. The use of pseudoboehmite as an aluminum source led to the formation of zeolite X as a secondary phase and a change in the temperature of fusion, which at 500 °C, there was formation of zeolite A, hydrated sodalite and zeolite X.

Determination of relative acid strength of La/paligorskyte by n-butylamine

The relative acid strength of lanthanum catalysts supported on paligorskyte was determined by thermodesorption of n-butylamine and infrared absorption spectroscopy. The results indicated that the desorption reaction took place in four temperature ranges. The catalyst containing 2% lanthanum particularly showed a considerable number of acid sites probably as a result of the relatively high specific area of the material.

The strength retrogression of special class Portland oilwell cement

Temperatures in excess of 110 oC result in phase transformations of cement, significantly decreasing its compressive strength. This effect is referred to as strength retrogression. It is frequently observed in cement sheaths of heavy oil wells submitted to steam injection. The present study evaluated the mechanical behavior of Special Class Portland Oilwell Cement (SCPOC) slurries containing silica flour to prevent retrogression. A factorial statistical planning was used to assess the effect of the main variables on the mechanical behavior of cement slurries, i.e., mechanical testing temperature (30, 100, 120, 180 and 230 oC); contents of silica flour replacing cement (0-18 and 36%) and curing time for rupture (12 h and 7 days). The results revealed that slurries containing 18% of silica flour tested at 230 oC depicted an increase in compressive strength up to 30% after curing for 12 h and 10% after curing for 7 days, indicating retrogression. On the other hand, testing slurries containing silica flour at temperatures up to 180 oC revealed strength increase of just 10%, suggesting the mechanical stability of the SCPOC, which prevents retrogression. Such behavior was probably related to the relatively low content of C3A and low specific area of the material. Therefore, strength retrogression at typical bottom hole temperatures of up to 180 oC can be controlled by small additions of silica flour, economically contributing to the use of SCPOC cementing.

A correlation between Bogue's equations and Taylor's procedure for the evaluation of crystalline phases in special class Portland oilwell cement clinker

A composicao cristalina das fases do clinquer de cimento Portland e comumente avaliada pelas equacoes de Bogue, que se baseiam em alguns principios que podem ser aplicados aos cimentos para cimentacao de pocos de petroleo. Isto se deve provavelmente a presenca de diversos oxidos e reconversoes de fase durante o resfriamento do clinquer levado a altas temperaturas. Entretanto, diferencas importantes sao observadas entre os valores numericos obtidos nas equacoes e a quantificacao de fases por imagem. Neste estudo, a quantidade das fases cristalinas do clinquer de um cimento especial para poco de petroleo foi determinada empregando o procedimento de Taylor, que consiste na resolucao de um sistema de equacoes lineares correspondente a cada uma das quatro principais fases do clinquer. Os resultados revelam uma adequada inter-relacao entre este metodo e a quantificacao das fases por microscopia otica, principalmente no que se refere a determinacao dos teores de aluminio e ferro.The crystalline composition of Portland cement clinker is commonly established by Bogues equations, which are based on a series of assumptions that seldom apply to oilwell cements. This is probably due to the presence of additional oxides and phase reconversion upon cooling of the clinker from the calcination temperature. Important differences are therefore observed between the numerical values yielded by the mathematical equations and image analysis quantification. In this study, the concentration of crystalline phases in oilwell cement was determined using Taylors procedure, which consists in a system of linear equations corresponding to each one of the four main clinker phases. The results revealed an adequate relationship between this method and phase quantification by optical micrography, especially concerning the contents of aluminate and ferrite.

Effect of the Acid Treatment of Montmorillonite Clay in the Oleic Acid Esterification Reaction

, several solid catalysts have been studied for the production of biodiesel. In this scenario there are the clays, especially those of the smectite group, because it is a natural raw material, abundant in nature, easy operation and excellent physicochemical properties. These clays in their natural form do not have the appropriate properties acidic esterification process and, therefore, have not been studied for this purpose. However, suitable acid treatments can make these solid potential catalysts for biodiesel production by esterification route. Thus, in the present work, montmorillonite clay was treated with sulfuric acid at different concentrations to obtain a material with higher acidity and applied in the oleic acid esterification reaction. The treatment process with sulfuric acid was used because it is a relatively cheap and simple process.

Síntese de MgAl2O4 por combustão assistida por micro-ondas: influência dos parâmetros de síntese na formação e na estrutura cristalina

In recent years, microwave combustion has received special attention because it is a quick, low cost and easy method that produces materials with good chemical homogeneity. Magnesium aluminate (MgAl2O4) is one of the most well-known ceramic materials because of their excellent properties, such as high melting point, high mechanical strength at high temperatures, good resistance to thermal shock, and resistance to acids and bases. The purpose of this study was to evaluate the influence of three parameters on the formation and crystal structure of MgAl2O4: (1) fuel/oxidizer ratio (Rco), (2) calcination temperature (Tcal), and (3) microwave power (Pmic). To carry out the combustion reaction, three different power levels (450, 675 and 900 W) and three fuel/oxidant ratio (0.8:1, 1:1 and 1.2:1) were used. The materials were calcined at three different temperatures (700, 800 and 900 °C) and characterized by X-ray diffraction and scanning electron microscopy. A factorial design 23 was used to evaluate the influence of the three parameters on the crystallinity and crystallite size of the MgAl2O4 powders obtained. The results show that for MgAl2O4 synthesized with Rco larger than 1:1 and Pmic lower than 675 W small crystallite sizes between 10 and 20 nm were obtained when calcined at 700 and 800 oC. Regarding the degree of crystallinity, only the Tcal has significant influence.

Kinetic study of the removal of pure and mixed TTMA+, CTMA+ and DTMA+ templates from MCM-41

This 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 removal.