Argilas especiais: argilas quimicamente modificadas - uma revisão

The simultaneous use of the specific values of some structural and chemical properties of clay minerals, such as kaolinite, montmorillonite and talc, allows the development of new properties for these materials, especially in relation to the external and internal microcrystal surfaces. These developments are very diversified for montmorillonite, due to the high specific surface area, expansible basal spacings, easy intercalation inside the 2:1 structural layers and a reversible and high cation exchance capacity. The review presents examples of chemical modifications on kaolins, montmorillonites (bentonites) and talcs.

Desenvolvimento e validação de metodologia de análise de misturas biodiesel: diesel utilizando cromatografia gasosa-espectrometria de massas

The aim of this work was to develop and validate a method of analysis of biodiesel:diesel blends using HRGC-MS in SIM mode. The proposed method is applicable to biodiesel from linoleic oils, such as soybean oil. The following results were obtained: linearity over the methyl linoleate concentration range of 250-2500 mg L-1 (R² > 0.999); limits of detection and quantification of 2 and 5 mg L-1, respectively; recovery from 82 to 96% of biodiesel in diesel and repeatability < 2% (RSD). Comparison between two operators showed that it is not necessary the same operator to do the analysis.

Determinação de misturas de sulfametoxazol e trimetoprima por espectroscopia eletrônica multivariada

In this work a multivariate spectroscopic methodology is proposed for quantitative determination of sulfamethoxazole and trimethoprim in pharmaceutical associations. The multivariate model was developed by partial least-squares regression, using twenty synthetic mixtures and the spectral region between 190 and 350 nm. In the validation stage, which involved the analysis of five synthetic mixtures, prediction errors lower that 3% were observed. The predictive capacity of the multivariate models is seriously affected by spectral changes induced by pH variations, a fact that acquires a great significance in the analysis of real samples (pharmaceuticals) that contain chemical additives.

Efeito de microondas na estrutura cristalina e na atividade catalítica de argilas

The effect of microwave (MW) irradiation on the crystalline structure of two natural clays and one commercial clay, Montmorillonite K10, was analyzed comparing the X-ray diffraction, N2 isotherms, NMR-MAS of 27Al and 29Si spectra of the clays before and after MW irradiation. The preparation of dioxolane ketals of isatin was used to analyze the MW effect on the catalyst activation. The yields achieved using catalysts activated by MW irradiation were lower (2 to 5%) than the yields achieved using catalysts activated by heat in a conventional oven.

Efeito antagônico do ferro e do zinco em uma formulação de alimentação enteral utilizando planejamento de misturas da metodologia de superfície de resposta

Nutritional therapy with enteral diets became substantially specialized over the last years. This work's aim was to study the effect of the components of a formulation: fiber, calcium and medium-chain triglycerides for dialysability of minerals. Analysis of multiple variables was carried out using response surface methodology. The level curve showed an antagonic effect of interaction between iron and zinc. TCM was the variable responsible for characterizing competition between the two minerals in the formulation. More studies on foods are needed for knowing the effecs of minerals in formulations.

Um novo procedimento de síntese da zeólita A empregando argilas naturais

This work proposes the synthesis of zeolite A by IZA standard proceedures starting from a natural clay. The clay was used in its natural form and after calcination at 900ºC. The resulting materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and porosity analysis by nitrogen adsorption. Results showed low surface area for Na-A zeolite in sodium form, but a higher one in CaA based on the nitrogen accessibility. The presence of cubic crystals for the A phase was observed in the SEM micrographies. The new procedure starting from natural clay favors the formation of sodalite while that using the calcinated clay gives A.

Modificação química de argilas: desafios científicos e tecnológicos para obtenção de novos produtos com maior valor agregado

Chemical modification of clays is possible due to their ion-exchange and adsorption capacities, which allows the adjustment of the physicochemical properties of the surfaces of their layers. This modification makes possible the use of clays to produce a great number of new materials, which range from coarse applications such as oil based drilling fluids to refined applications such as pharmaceutical products. This article intends to expose where there is still space for research and investment aiming at the performance improvement of clay-based materials.

Caracterização de argilas bentonitas e diatomitas e sua aplicação como adsorventes

Five samples of natural clays denominated: diatomite, CN-20, CN-29, CN-40 and CN-45 from Aliança Latina LTDA were characterized by differents supplementary techniques such as: XRD, chemical analysis, adsorption N2 measurements, infrared spectroscopy analysis, thermogravimetric analysis. Clays were tested in adsorption of blue methylene. All of isotherms adjust in a model of physics adsorption with formation of multilayers, however in the case of diatomite was a favorable adsorption (type II) and the CNs were a not favorable adsorption (type III). In the case of CNs had flocculation of clay in high concentration of coloring.

Argilas como catalisadores verdes na esterificação do colesterol: caracterização espectroscópica e identificação de polimorfos por métodos de análise térmica. Uma proposta laboratorial interdisciplinar para o 1º ciclo universitário

A laboratory experiment that enables the professor to introduce the problematic of sustainable development in pharmaceutical chemistry to undergraduate students is proposed, using a simple synthetic procedure. Cholesteryl acetate is prepared by the esterification of cholesterol using Montmorillonite K10 as heterogeneous catalyst. Cholesterol and cholesteryl acetate are characterized by spectroscopic (¹H RMN, 13C RMN, FTIR) and thermal analysis techniques. The thermal methods are used to introduce the concepts of polymorphism and the nature of mesophases.

Argilas bentoníticas da península de Santa Elena, Equador: pilarização, ativação ácida e seu uso como descolorante de óleo de soja

Two samples of calcic bentonite of the Santa Elena Peninsula, Ecuador, were pillared with Al13 ions in the ratio of 10, 15 and 20 meq of Al g-1 of clay, calcinated at 573, 723 and 873 ºK and acid activated with 4, 6 and 8 mol L-1 H2SO4. Analyses by X-ray diffraction, X-ray fluorescence, differential and gravimetric thermal, density, surface area and porosity, were applied in order to study the modifications occurred in the crystalline structure of the montmorillonite. The 8 mol L-1 H2SO4 acid-activated 15 meq of Al g-1 of clay at 573 ºK Al-pillared samples indicated the best results in the bleaching of the soybean oil measured by UV-visible spectrophotometer.

Adsorção e propriedades de volume de misturas binárias água álcool: um experimento didático com base em medidas de tensão superficial

An undergraduate physical chemistry experiment based on the drop counting method for surface tension measurements is proposed to demonstrate adsorption isotherms of binary aqueous solutions of ethanol, n-propanol, and n-butanol. Excess surface is obtained by the derivative of surface tension taken with respect to alcohol activity, after this activity calculation using van Laar equation. Laboratory class contents are surface tension, excess surface, percolation of hydrogen bonds, micelle, activity, and ideal solution.

Utilização de argilas para purificação de biodiesel

This work describes the results of the purification of methyl biodiesel, obtained by oxidized soybean oil, using different methods. After the ester separation from the glycerin by decanting, the ester was purified each time with distillation, washing with water and adsorption with bauxite, bentonite and attapulgite. The removal of total contamination, unsaponifiable material, concentrations of free glycerin and soap were analyzed in the purified ester phase. The best result of purification was observed with the use of bentonite and bauxite, in the removal of soap and free glycerin respectively.

Autoassociação de misturas dos Surfactantes Dodecanoato de Sódio (SDoD) e Decanoato de Sódio (SDeC) com o Polímero Hidrofobicamente Modificado Etil(Hidroxietil)Celulose (EHEC)

In this work, the interactions between the non-ionic polymer of ethyl(hydroxyethyl)cellulose (EHEC) and mixed anionic surfactant sodium dodecanoate (SDoD)-sodium decanoate (SDeC) in aqueous media, at pH 9.2 (20 mM borate/NaOH buffer) were investigated by electric conductivity and light transmittance measurements at 25 ºC. The parameters of the surfactant to polymer association processes such as the critical aggregation concentration and saturation of the polymer by surfactants were determined from plots of specific conductivity vs total surfactant concentration, [surfactant]tot = [SDoD] + [SDeC]. Through the results was not observed a specific link of polymer with the surfactant, implying therefore a phenomenon only cooperative association.

Síntese e caracterização de argilas organofílicas contendo diferentes teores do surfactante catiônico brometo de hexadeciltrimetilamônio

The major applications of organoclays are in adsorption of organic polluents. The objective of this work was the synthesis and characterization of organoclays using differents amounts of cationic surfactant hexadecyltrimethylammonium bromide. The clays were characterized by low angle x-ray diffraction (XRD), scanning electron microscope (SEM), infrared with Fourier tranformation (FTIR), BET surface area, elemental analysis (CHN), Foster swell and adsorption of methylene blue. The surfactant can adsorb in differents forms in the interlamelar region changed the basal spacing. The presence of the surfactant adsorbed can be favorable or not in adsorption of the methylene blue due the different interactions dye-organoclays.

Uso da cromatografia gasosa bidimensional abrangente (GC×GC) na caracterização de misturas biodiesel/diesel: aplicação ao biodiesel de sebo bovino

The growth of biodiesel market and the implementation of regulations related to biodiesel production and biodiesel/diesel blending has encouraged the development of appropriate analytical methods to control the composition of this type of mixture. In this study, an evaluation of the potential of GC×GC for the characterization of samples of beef tallow biodiesel and the composition of blends of biodiesel/diesel is presented. The methodology was applied to beef tallow biodiesel and its mixtures with petrodiesel, ranging from B2 to B50. Results allowed not only the identification and quantification of the biodiesel esters, but also the biodiesel percentage in biodiesel/diesel blends.