Sistema aquoso bifásico: uma alternativa eficiente para extração de íons

Solvent extraction has been successfully applied to metal ion preconcentration and often meant the use of toxic organic diluents. However, regulatory pressure is increasingly focusing on the use and disposal of organic solvents, and thus the development of nonhazardous alternatives is important. In this review, we examine the application of aqueous biphasic systems (ABS) to extraction of ions, analyzing their potential and limitations and suggest that ABSs could be an efficient substitute for oil/water biphasic systems. ABSs are formed by mixing certain inorganic salts and water-soluble polymers, or by mixing two water-soluble polymers.

Pilhas a combustível de óxido sólido: materiais, componentes e configurações

In this paper the current status of fuel cells is described with particular emphasis on high (T > 800 ºC) and intermediate (T < 800 ºC) temperature solid oxide fuel cells. Also the importance of the fuel cell technology is shown. Reviewed are the fundamental features, the basic principles, types of fuel cell, fabrication methods, cell configurations and the development of components (cathodes, anodes, electrolytes, interconnect) and materials.

Anéis aromáticos condensados e relação E4/E6: estudo de ácidos húmicos de gleissolos por RMN de 13C no estado sólido utilizando a técnica CP/MAS desacoplamento defasado

In this work, seven samples of humic acids extracted from gleysoils were investigated. These studies, using NMR CP/MAS 13C techniques, did not show significant correlation between the E4/E6 ratio and the degree of aromaticity. However, dipolar dephasing (DD) measurements of condensed aromatic or substituted carbons showed a negative correlation of 0.94. Also, there was a good correlation between the amount of semiquinone free radicals measured by the EPR technique and condensed aromatic rings measured by NMR CP/MAS 13C with the DD technique. The content of semiquinone free radicals was quantified by EPR spectroscopy and was correlated with the humification (degree of aromaticity) of the humic substances. The results indicated that the E4/E6 ratio identifies the degree of aromatic rings condensation. It was also found that the degree of aromaticity, measured by NMR, as frequently presented in the literature (by conventional CP/MAS), underestimates aromatic rings in condensed structures.

Influência do método de extração nos teores de metilxantinas em erva-mate (Ilex paraguariensis a. St.-Hil., aquifoliaceae)

Ilex paraguariensis A. St. -Hil. is a native species of southern South America. The caffeine content in Ilex paraguariensis leaves has been considered an important quality parameter for maté-derived products. In this work different extraction methods for the determination of these methylxantines are compared. The influence of the extraction conditions on the methylxanthine yields was evaluated. Extraction by decoction with acidic aqueous solution (H2SO4 4N) presented the higher efficiency in the theobromine extraction. The extraction in a Soxhlet with acidic aqueous solution and decoction with acidic aqueous solution showed the highest caffeine yield. For the concomitant theobromine and caffeine quantification, the decoction with acidic aqueous solution is suggested.

Utilização da extração em fase sólida (SPE) na determinação de hidrocarbonetos policíclicos aromáticos em matrizes aquosas ambientais

Polycyclic aromatic hydrocarbons (PAHs) are a great environmental concern mainly because of their toxic, mutagenic and carcinogenic potential. This paper reports utilization of the solid-phase extraction (SPE) technique to determine PAHs in environmental aqueous matrices. The recovery from environmental aqueous matrices fortified with PAHs varied from 63.7 to 93.1% for atmospheric liquid precipitation, from 38.3 to 95.1% for superficial river water, and from 71.0 to 95.5% for marine water. No negative matrix effect was observed for the recovery of PAHs from atmospheric liquid precipitation and marine water, but was observed for superficial river water, particularly for PAHs possessing 5 and 6 aromatic rings.

Síntese de copolímeros em bloco com propriedades líquido cristalinas

The principal techniques for the synthesis of liquid crystalline block copolymers are reviewed. The syntheses are done by living/controlled free radical chain polymerization. The copolymers display an amorphous continuous phase and a discontinuous liquid crystalline phase (LC). The presence of oxypropylenic segments disturbs the range of mesophase transitions at lower temperatures. This behavior is not observed when styrenic segments are employed and suggests that the liquid crystalline behavior can be modified in block copolymers to show mesophases at higher and lower temperatures according to the flexibility of the chain segment that is present.

Extração, estruturas e propriedades de alfa- e beta-quitina

The fact that alpha- and beta-chitin adopt different arrays in the solid state is explored to emphasize their different properties and distinct spectral characteristics and X ray diffraction patterns. The methods for their extraction from the biomass in view of the preservation of their native structures and aiming to fulfill the claims of purity and uniformity for potential applications are discussed. The different arrays adopted by alpha- and beta-chitin also result in distinct reactivities toward the deacetylation reaction. Thus, the deacetylation of beta-chitin is more efficient owing to the better accessibility to amide groups due to the lower crystallinity of this polymorph.

Recuperação de cádmio de baterias níquel-cádmio via extração seletiva com tributilfosfato (TBP)

This work describes a recovery process of cadmium from spent nickel-cadmium batteries by a new hydrometallurgical route based on the selective extraction in hydrochloric acid medium with tributylphosphate (TBP), alone or dissolved in kerosene. The best results were obtained when TBP concentration was at least 75 vol%. Nickel extraction was negligible under these conditions. It was isolated after processing the rafinate through an anionic ion-exchange column. Final wastes generated are basically sodium chloride solutions, with no turbidity, color or heavy metals present in significant amounts.

Determinação do coeficiente de atividade na diluição infinita (g¥) através da micro-extração em fase sólida (SPME)

In this study a new approach, solid phase micro extraction (SPME), is used in the evaluation of the infinite dilution activity coefficient of the solute in a given solvent. It is the purpose of the current work to demonstrate a different approach to obtain the data needed for studying the solution thermodynamics of binary liquid mixtures as well as for designing multi-component separations. The solutes investigated at the temperature 298.15 K were toluene, ethyl benzene and xylene in the solvent methanol.

Métodos de extração para quantificação de manganês disponível em fertilizantes

The solubility of Mn in different fertilizers (MnSO4.H2O-p.a., MnO2-p.a.+MnO-Ind., MnO2-Ind.+MnO-Ind., MnO2-p.a., MnO2-Ind. and MnO-Ind.) was determined using different methodologies: total content and soluble contents in water, 10% H2SO4, citric acid at 20 g L-1, diluted neutral ammonium citrate, (1+9) and DTPA at 0.005 mol L-1. The Mn solubilities in the latter three extractors were assessed after agitation of the sample for one hour and after boiling for 5 minutes. The extraction procedure using neutral ammonium citrate (1+9), at 1:100, with agitation for one hour, was shown to be the most adequate to assess the availability of Mn in fertilizers.

Emprego de planejamento fatorial no desenvolvimento de uma metodologia para extração de zinco de resíduos galvânicos

The plating process generates solid waste rich in heavy metals and aiming to reduce environmental impact of such waste, this work suggests a methodology for zinc reduction, through a 2(4) factorial planning, studying the influence of the following variables: acid concentration (15, 20 or 30% v/v), acid type (sulfuric or hydrochloric), acid volume (15, 20 or 25 mL) and extraction time (12, 24 or 36 h). Through this methodology it is possible to establish the optimal conditions (15 mL of a 30% hydrochloric acid concentration during 12 h) to get a 100% efficiency in zinc extraction.

Estudo da decomposição térmica de propelente sólido compósito de baixa emissão de fumaça

The thermal decomposition of hydroxyl-terminated polybutadiene (HTPB)/ammonium nitrate (AN) based propellants, so called smokeless formulations, and raw materials were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). The thermoanalytical profile of different components and of propellant were evaluated and the Arrhenius parameters for the thermal decomposition of the propellant sample were determined by the Ozawa method. The kinetic parameters of the thermal decomposition of propellant samples were determined by DSC measurements. The values obtained for activation energy (Ea) and pre-exponential factor were 163 kJ mol-1 and 1.94x10(6) min-1.

Ondas ultrassônicas e pérolas de vidro: um novo método de extração de beta-galactosidase para uso em laboratório

The optimization of a traditional technique of cellular disruption by abrasion was carried out and a process using ultrasonic waves associated with glass pearls to extract beta-galactosidase from Kluyveromyces marxianus proposed. In the first case, the effects of the diameter and weight of the pearls in relation to the volume of cellular suspension and amount of time for cellular disruption were evaluated. The efficiency of the new process of cellular disruption was evaluated by varying the length of time of sonification and comparing with the method of abrasion under the same conditions. The proposed method can be efficiently applied to obtain beta-galactosidase at laboratory scale.

Extração de β-caroteno de cenouras: uma proposta para disciplinas experimentais de química

This paper reports on the development of a simple and fast procedure for β-carotene extraction from carrots and its quantification by UV/Vis spectroscopy. Carotenoids extracted from carrots may also be used as alternative reagents for TLC (thin layer chromatography) detection of natural compounds with antioxidant properties, replacing the commercial p.a. grade β-carotene. Although this reagent had around 10% b-carotene, it proved to be as efficient for TLC analysis as the commercial p.a. grade β-carotene. This practice is a useful alternative for teaching undergraduate organic chemistry laboratory classes.

Caracterização e classificação de resíduo sólido "pó de rocha granítica" gerado na indústria de rochas ornamentais

The ornamental rock industry generates huge amounts of wastes during the process of extraction and sawing of rock blocks. The ornamental rock powder waste is a non-biodegradable material, which represents the increase in environmental problem. The waste was collected from a granitic rock sawing plant located in Santo Antônio de Pádua, Rio de Janeiro. The chemical-environmental characterization and classification of the waste were done according to ABNT standards. The results showed that the granitic rock powder waste should be classified as Class II A - "No Inert", because of its high concentrations of lead, chrome, iron and manganese.