Sistema automático para determinação seqüencial de cianeto livre e total empregando eletrodo tubular íon-seletivo de membrana homogênea

This study presents an automated system for potentiometric determination of free and total cyanide which employs a homogeneous membrane tubular ion-selective electrode. After the electrode is assembled, it is connected to a system composed of 3 three-way solenoid valves, sample line, carrier line, acid stream, and gas diffusion chamber. A Turbo Pascal® computer program, developed specifically for this task, automatically performs all the steps involved in data acquisition and processing. The proposed analytical procedure offers operational simplicity, since detection is performed by a tubular electrode, whose assembly is fast and easy. The system has shown reproducibility (r.s.d. < 0.5%, n=6) and high speed (30 readings/hour); it is efficient for determination of free and total cyanide in waste waters of starch processing plants. The detection limit was 1.2x10-5 and 1.5x10-5 mol L-1, for determination of free and total cyanide, respectively. The linear response range was between 1.2x10-5 and 1.0x10-2 mol L-1 for free cyanide and between 1.5x10-5 and 1.0x10-2 for total cyanide.

Extração e pré-concentração de compostos orgânicos voláteis por permeação em membrana para análise cromatográfica

This work discusses sample preparation processes for gas chromatography (GC) based on the technique of extraction through membrane permeation (MPE). The MPE technique may be easily coupled to GC via a relatively simple device, which is a module that holds the membrane and is directly connected to the GC column. The possibility of operational errors due to sample handling is substantially reduced in an MPE-GC system because the sample preparation and the chemical analysis are accomplished as a one-step process. The MPE technique is of relatively wide application as it can be used for aqueous samples, solid samples and gaseous samples. Depending on the type of sample the extraction is performed with the membrane in direct contact with the sample or in contact with its headspace. The MPE-GC technique is very useful in trace analysis, due to the time-dependent enrichment of the analyte. A typical application of MPE-GC is the analysis of VOCs present in water that may be accomplished with detection limits at the low ppb (mugL-1) level.

Redução de poluentes de efluentes das indústrias de papel e celulose pela floculação/coagulação e degradação fotoquímica

The abatement of recalcitrant lignin macromolecules from effluents of pulp and paper industry was investigated by combined process. Flocculation and coagulation with aluminum sulfate and natural polyelectrolytes extracted from cactus Cereus peruvianus were used in the first step. After separation of solid residues by filtration, the photochemical methods using TiO2 as catalyst were employed for photocatalytic degradation of lignin compounds from solution. The abatement of lignin compounds after flocculation and coagulation was 46%, and after the overall process, the pollutants reduction observed were 66%. The remaining organic compounds may be removed by any biological treatment.

Métodos de preparação de nanopartículas metálicas suportadas em carbono de alta área superficial, como eletrocatalisadores em células a combustível com membrana trocadora de prótons

Fuel cells are attracting much interest as efficient and clean energy conversion devices. The main components of low temperature fuel cells are the electrocatalysts used to promote the anodic and cathodic reactions, which are based on platinum and platinum alloys. These electrocatalysts are normally prepared in the form of metal nanoparticles supported on a conductive material, usually high surface area carbon, to improve catalyst utilization and reduce cost. This work presents and comments some methods used presently to produce these electrocatalysts. The performances of the produced electrocatalysts are compared to that of state-of-the-art commercial E-TEK electrocatalysts.

Fotoquímica de alfa,alfa-dimetilvalerofenona adsorvida em celulose microcristalina

Irradiation of a,a-dimethylvalerophenone (1) adsorbed on microcrystalline cellulose employing methanol as the solvent shows a Norrish Type II/Type I ratio of 1.0±0.1. In solution, values of 2.3±0.3 in benzene and 8.7±2.0 in terc-butanol were obtained. The cyclization/elimination ratio for the Norrish Type II reaction of 1 shows values of 1.2±0.3 in cellulose, 17.9±2.7 in benzene and 3.2±03 in terc-butanol. When samples of 1/microcrystalline cellulose were prepared employing n-hexane, the Type II/Type I (29.5±2.9) and the cycl/elim (113.3±12.1) ratios were dramatically modified. These results demonstrate the difference in the behavior of 1 when entrapped in the cellulose chains or adsorbed on the cellulose surface.

Azul de metileno imobilizado na celulose/TiO2 e SiO2/TiO2: propriedades eletroquímicas e planejamento fatorial

The electrochemical properties of methylene blue immobilized on cellulose/TiO2 and mixed oxide SiO2/TiO2 matrices were investigated by means of cyclic voltammetry. The electron mediator property of the methylene blue was optimized using a factorial design, consisting of four factors in two levels. The experimental observations and data analyses on the system indicate that the lowest peak separation occurs for Sil/TiOAM, 1.0 mol L-1 KCl solution and 20 mV s-1 scan rate, while values of current ratio closest to unity were found for Cel/TiOAM independent of electrolyte concentration, 0.2 or 1.0 mol L-1, and scan rate, 20 mV s-1 or 60 mV s-1.

Caracterização química do "pitch" em indústria de celulose e papel de Eucalyptus

The chemical analysis of the acetone, chloroform, toluene and methanol extracts of a pitch sample was carried out by IR and GC-MS, leading to the identification of sixty nine compounds, including fatty acids, alcohols and hydrocarbons. Analysis of the acetone extractive of a eucalyptus wood used in Brazil for pulp production was also carried out, resulting in identification of fifty nine compounds, including mainly fatty acids, phenolic compounds, beta-sitosterol and other steroids. This analysis showed that pitch formation had a contribution from wood extractives and other sources of contamination. The results obtained and the methodology applied can be used by the pulp industry to develop new methods of pitch control.

Adsorção de íons dicromato nos compósitos celulose/ZrO2.nH2O preparados pelos métodos da precipitação convencional e em solução homogênea

This article describes the preparation and characterization of the cellulose/ hydrated zirconium oxide composites prepared by conventional precipitation (PC) and homogeneous solution precipitation (PSH) methods. The composite obtained by the PC method was prepared by using an ammonia solution as the precipitating agent, while the composite obtained by the PSH method was prepared by using urea as the precipitating agent. The adsorption of dichromate ions on the composites was studied using factorial design 2³. The variables were: initial concentration, agitation time and mass of the composite. The data obtained agree better for the composite obtained by the PC method.

Reator de membrana enzimático e fluidos supercríticos: associação de processos

The aim of this work is to present the new applications of membrane technology in fat and oil processing, with emphasis on development and applications of the enzymatic membrane reactor and its association with extraction and purification technology by supercritical fluids (SCF). Combining the extraction by SCFs and the separation by membranes allows the integration of extractions reactions with selective separation by membranes through filtration of the supercritical mixture (SCF + extracted solutes). This association provides important energy savings regarding the SCF recompression costs.

Composição química de um resíduo alcalino da indústria de papel e celulose (DREGS)

Dregs is an alkaline solid by-product generated in the cellulose manufacturing industry that could be used to correct soil acidity. The present study aimed to evaluate the chemical composition of this product and some of its properties. The dregs presented 354 g kg-1 of calcium, neutralization capacity of 80.3%, and pH 10.7, besides low concentration of sodium (10.2 g kg-1), lead (62.9 mg kg-1) and cadmium (5.6 mg kg-1). Thus, it is a product that can safely be used to increase the soil pH.

Efeito dos dióxidos de enxofre e de nitrogênio no desempenho de uma célula a combustível de membrana de intercâmbio de prótons

There is presently much interest in the clean and efficient generation of energy by proton exchange membrane fuel cells (PEMFC), using hydrogen as fuel. The generation of hydrogen by the reforming of other fuels, anaerobic fermentation of residual waters and other methods, often produce contaminants that affect the performance of the cell. In this work, the effect of gaseous SO2 and NO2 on the performance of a H2/O2 single PEMFC is studied. The results show that SO2 decreases irreversibly the performance of the cell under operating conditions, while NO2 has a milder effect that allows the recovery of the system.

Auto-associação do dodecilsulfato de sódio (SDS) com o polímero hidrofobicamente modificado etil(hidroxietil) celulose (EHEC)

Mixtures of ethyl(hydroxyethyl)cellulose (EHEC) and Sodium Dodecyl Sulfate (SDS) were investigated using surface tension, conductivity and viscosity measurements in aqueous solutions. The parameters of the surfactant to polymer association processes such as the critical aggregation concentration (cac) and saturation of the polymer by SDS (psp) were determined from the plots of surface tension and specific conductivity versus surfactant concentration. Through the final results we see that there was no specific link of polymer with the surfactant, implying therefore a phenomenon of only cooperative association.

Preparação de membranas de acetato de celulose organomodificadas para adsorção dos íons Cu(II), Cd(II), Mn(II) e Ni(II)

Cellulose acetate polymeric membranes had been prepared by a procedure of two steps, combining the method of phase inversion and the technique of hydrolysis-deposition. The first step was the preparation of the membrane, and together was organomodified with tetraethylortosilicate and 3-aminopropyltrietoxysilane. Parameters that exert influence in the complexation of the metallic ion, as pH, time of complexation, metal concentration, had been studied in laboratory using tests of metal removal. The membranes had presented resistance mechanics and reactivity to cations, being able to be an alternative for the removal, daily pay-concentration or in the study of the lability of metals complexed.

Desenvolvimento de conjunto membrana-eletrodos para célula a combustível de metanol direto passiva

Direct methanol fuel cells (DMFCs) without external pumps or other ancillary devices for fuel and oxidant supply are known as passive DMFCs and are potential candidates to replace lithium-ion batteries in powering portable electronic devices. This paper presents the results obtained from a membrane electrode assembly (MEA) specifically designed for passive DMFCs. Appropriated electrocatalysts were prepared and the effect of their loadings was investigated. Two types of gas diffusion layers (GDL) were also tested. The influence of the methanol concentration was analyzed in each case. The best MEA performance presented a maximum power density of 11.94 mW cm-2.

Filmes ultrafinos de ésteres de celulose: preparo, caracterização e imobilização de proteínas

In this study cellulose acetate butyrate (CAB) and carboxymehtylcellulose acetate butyrate (CMCAB) films adsorbed onto silicon wafers were characterized by means of ellipsometry, atomic force microscopy (AFM), sum frequency generation spectroscopy (SFG) and contact angle measurements. The adsorption behavior of lysozyme (LIS) or bovine serum albumin (BSA) onto CAB and CMCAB films was investigated. The amounts of adsorbed LIS or BSA onto CMCAB films were more pronounced than those onto CAB films due to the presence of carboxymethyl group in the CMCAB structure. Besides, the adsorption of BSA molecules on CMCAB films was more favored than that of LIS molecules. Antimicrobial effect of LIS bound to CAB or CMCAB layers was evaluated using Micrococcus luteus as substrate.