Resumo em Inglês:

Abstract - This work concerns the study of the digestion step in the production process of phosphoric acid. Some qualitative experiments indicate that the difference between the pH at the surface of the phosphate and that in the bulk of the solution is negligible and that the dissolution is controlled by diffusion of products away from the phosphate particle. In further experiments, to isolate the dissolution phenomenon from the formation of calcium sulfate, the sulfuric acid normally used industrially is replaced by hydrochloric acid. The phosphate material used in our experiments is a model apatitic material: synthetic hydroxyapatite (HAP). The dissolution of calcium hydroxyapatite was studied with increasing amounts of calcium and phosphate at different temperatures. A simple method was developed for this observation based on the time required for complete dissolution of the HAP powder. The results confirm that the dissolution is controlled by a diffusional process through an interface of calcium and phosphate ions released from the solid surface. A kinetic model for the dissolution of apatitic materials is proposed which assumes a shrinking particle behaviour controlled by diffusion of calcium ions. The experimental results are fitted to this model to determine the mass transfer constant for HAP dissolution in acid solutions. The activation energy of the reaction is about 14kJ/mol. This study was carried on in conditions similar to the industrial ones for the production of phosphoric acid by the dihydrate-process

Resumo em Inglês:

Abstract - Samples of high purity grade and commercial purity grade type AISI 304L and AISI 316L steels were studied by the potentiodynamic and potentiostatic techniques in a naturally aerated 3.5% NaCl aqueous solution at a controlled temperature of (23±2)°C. The anodic polarization curves of the potentiodynamic technique showed that not always is it possible to determine pitting potential: most of the curves of commercial purity grade steels displayed a smooth curvature in the region where the current density should increase sharply. The density current versus time potentiostatic curves also showed different shapes according to the purity grade steels: for the commercial purity grade steels, the current density showed large oscillations with time (related to unstable pits), whereas for the high purity grade steels, a regular behavior of current density as a function of time was found (related to stable pits)

Resumo em Inglês:

Abstract - The gas balance technique applied to batch cultures of the aerobic microorganism Aspergillus awamori NRRL3112 results in respiratory coefficient,RQ, values as high as 1.4 for glucose concentrations around 50g/L and no nutrients or oxygen concentration limitation. RQ decreases during the culture to values around 1.0 for glucose concentrations lower than 10g/L. Besides of an indication of drastic metabolic changes, these data suggest the need for some care when utilizing the RQ value for process control purposes. This RQ variability also has influence on the determination mode of the specific oxygen uptake rate, qO2 (mmol/gh). If the RQ value is constant, qO2 can be determined through a carbon dioxide (CO2) gas balance. This determination mode gives more reliable results than the one based on the oxygen gas balance since CO2 determination via a spectrophotometer of infrared gives accurate results and is a fast response relative to fluctuations in the CO2. In the case of this process however, reliable values of specific oxygen uptake rate, qO2, can be obtained only through the oxygen gas balance

Resumo em Inglês:

Abstract - The recovery of Bacillus sphaericus strain 2362 spores from fermented medium by batch flotation was tested under different conditions. Flotation kinetic studies were performed at 800 rpm and 3 l air/min. The pH values were adjusted at the following set of values: 5.0, 7.0 and 9.0. The results showed that the spore removal rate is influenced by the pH value. At pH equal to 5.0 we observe an adverse effect on the spore concentrate obtention. In this situation the maximum value of the concentration factor was 1.4 when the recuperation percentage was 99%. At pH equal to 7.0 the concentration factor reached the highest value, 7.0, but the recuperation percentage stayed around 96%. Field experiments with the floated material demonstrated that its larvicide activity was sufficient to keep a Culex quinquefasciatus larvae population under control at in a breeding site, during 3 months with 2 applications

Resumo em Inglês:

ABSTRACTbstract - This work presents a new predictive method for the estimation of properties of pure organic substances. Each compound is assigned a molecular graph or an adjacency matrix representing its chemical structure, from which properties are then obtained as a summation of all contributions associated with functional groups and chemically bonded pairs of groups. The proposed technique is applied to the estimation of critical temperature, critical pressure, critical volume and normal boiling point of 325 organic compounds from different chemical species. Accurate predictions based solely on chemical structure are obtained

Resumo em Inglês:

Abstract - A pilot-scale catalytic incineration system was used to investigate the effectiveness of catalytic incineration as a means of reducing volatile organic compound (VOC) air pollutants. The objectives of the study were: 1) to investigate the effects of operating and design variables on the reduction efficiency of VOCs; and 2) to evaluate reduction efficiencies for specific compounds in different chemical classes. The study results verified that the following factors affect the catalyst performance: inlet temperature, space velocity, compound type, and compound inlet concentration. Tests showed that reduction efficiencies exceeding 98% were possible, given sufficiently high inlet gas temperatures for the following classes of compounds: alcohols, acetates, ketones, hydrocarbons, and aromatics

Resumo em Inglês:

Abstract - An Aerated Submerged Biological Filter was used to promote biological nitrification of a synthetic saline wastewater. Black PVC corrugated plates were used to make the structured packing of the 6 liter reactor. Nitrate, nitrite, and ammonia concentrations, pH and DO were periodically measured, according to APHA (1985). In spite of the deleterious effect of salinity, it was possible to obtain nitrogen removal efficiencies as high as 95% for a 25 g/L salt concentration after a three-day reaction in the batch reactor. Continuous operation using a NaCl concentration of 25 g/L was tested using three different hydraulic retention times: 7, 15, and 25 hours. An increase in ammonia removal was observed when the retention time was increased from 7 to 15 hours. However, no further notable increase was obtained for a 25 hour retention time, showing that nitrogen removal tends towards a maximum limit of about 80%.

Resumo em Inglês:

Abstract - In this work, we applied an experimental planning methodology in order to correlate the necessary amounts with the description of the a tungsten extraction process by microemulsions. The result is a mathematical modelling carried out using the Sheffe Net method, where the mixtures concentration values are represented inside an equilateral triangle. The tungsten concentration process occurs in two stages: extraction and reextraction. The extraction stage was determined by monitoring: phase relative volume (Vr), extraction percentage (%E) and tungsten concentration in the microemulsion phase (Ct<FONT FACE="Symbol">m</font> e). The reextraction phase was determined by monitoring: reextraction percentage (%Re) and tungsten concentration in the aqueous phase (Ctaq). Finally, we obtained equations that relate the extraction / reextraction properties to the composition of specific points inside the extraction region, obeying the error limits specified for the acceptance of each parameter. The results were evaluated through the construction of isoresponse diagrams and correlation graphics between experimental values and those obtained through use of equations.

Resumo em Inglês:

Abstract - The start-up of continuous bioreactors is solved as an optimal control problem. The choice of the dilution rate as the control variable reduces the dimension of the system by making the use of the global balance equation unnecessary for the solution of the optimization problem. Therefore, for systems described by four or less mass balance equations, it is always possible to obtain an analytical expression for the singular arc as a function of only the state variables. The steady state conditions are shown to satisfy the singular arc expression and, based on this knowledge, a feeding strategy is proposed which leads the reactor from an initial state to the steady state of maximum productivity

Resumo em Inglês:

Abstract - The interaction of an Fe-Mn-Al-Si-C alloy with the environment was evaluated. The alloy showed good resistance to air and oxygen oxidation, especially at temperatures of 600 and 700º C for air oxidation and at 600ºC in oxygen atmosphere. Oxidation rates for pure oxygen were lower than those measured for air. Due to autocorrelation identified in the results, it was impossible to employ the usual procedures of Regression Analysis. Kinetic data were then analyzed by the statistical method of Cochrane and Orcutt. A parabolic kinetic behavior was observed for the Fe-Mn-Al-Si-C alloy oxidation process in the air at temperatures of 600, 700 and 800ºC and in an oxygen atmosphere at 900ºC. On the other hand, the TGA results for oxygen oxidation at 600 and 700ºC and for air oxidation at 900ºC adjusted well to the linear kinetic curve. Finally, the cubic kinetic curve was selected to represent the oxidation of the alloy in oxygen at 800ºC.

Resumo em Inglês:

Abstract - A cultivation strategy based on some previous knowledge of the metabolism of Escherichia coli BL21 (DE3) pLysS containing the troponin C gene cloned into plasmid pET was developed and applied through the use of simple fermentation equipment and a feed-forward control strategy in order to achieve a high cell concentration <FONT FACE="Symbol">¾</font> 92 g l-1 dry cell weight <FONT FACE="Symbol">¾</font> and a high cell productivity <FONT FACE="Symbol">¾</font> 3.7 g l-1 h-1.