Resumo em Inglês:

The modified UNIFAC-Dortmund group contribution model is used for the correlation and prediction of salt effects in binary solvent-salt and ternary mixed solvent-salt systems. The long-range electrostatic interaction contribution, usually represented by a Debye-Hückel term, was empirically dropped. Previously published parameters for interactions between solvent groups (CH2, OH, CH3OH, H2O and CH3CO) were used, and group interactions between ions (Li+, Na+, K+, Ca+2, Cl-, Br-, NO3- and ACE-) and between ions and solvent groups have been estimated. The data base includes 29 binary and 56 ternary systems, used in part for the calculation of group interactions and in part for the testing of predictions.

Resumo em Inglês:

The concentrations of heavy metals in two kinds of Brazilian coals at 100° C (acid digestion) and at 850° C were studied (ashes the obtained in muffle furnace with and without addition of limestone). Data were analyzed by flame atomic absorption, using the air acetylene flame. For Pb, Zn, Ni, Mn and Cu the metal concentration obtained the acid digestion were higher than metal concentration were obtained in tests in the muffle furnace. This behavior observed in the muffle furnace occurs because these metals are fixed in stable sulfated compounds in the ashes, which are difficult to dissociate at flame temperature, and also due to the volatile character of the metals, mainly Pb and Zn. There was a constant concentration in the ashes in of Cr the acid digestion and muffle furnace tests. Results from tests using an XRD apparatus indicated, he formation of sulfated compounds in the ashes for both. coals. The analysis using microprobe electronic showed retention of metals like Ni, Mn, Cu, Fe, Ti and Ca. For both coals, the low mobility of most of the metals studied occured due to the alkaline pH of sulfated ashes. These metals in the ash from coal combustion in fluidized bed reactor were also studied and showed similar results, enabling a scale-up to pilot scale.

Resumo em Inglês:

Molecular simulation data were used to study the performance of equations of state (EoS) and combining rules usually employed in thermodynamic property calculations. The Monte Carlo method and the Gibbs ensemble technique were used for determining composition and densities of vapor and liquid phases in equilibrium for binary mixtures of Lennard-Jones fluids. Simulation results are compared to data in the literature and to those calculated by the t-PR-LJ EoS. The use of adequate combining rules has been shown to be very important for the satisfactory representation of molecular simulation data.

Resumo em Inglês:

A dynamic kinetic-diffusive model for the extraction of metallic ions from aqueous liquors using liquid surfactant membranes is proposed. The model incorporates undesirable intrinsic phenomena such as swelling and breakage of the emulsion globules that have to be controlled during process operation. These phenomena change the spatial location of the chemical reaction during the course of extraction, resulting in a transient moving boundary problem. The orthogonal collocation method was used to transform the partial differential equations into an ordinary differential equation set that was solved by an implicit numerical routine. The model was found to be numerically stable and reliable in predicting the behaviour of zinc extraction with acidic extractant for long residence times.

Resumo em Inglês:

With the aim of producing polyhydroxyalkanoates, a study of the influence of culture conditions (nitrogen and carbon sources and temperature) on the growth of Ralstonia eutropha in stirred flasks was carried out and the use of some low-cost sources (hydrolyzed lactose, inverted sugar and corn steep liquor) as evaluated. The best specific growth rate was obtained when inverted sugar was utilized as the substrate (mumax = 0.26 h-1). Two different phases in the assimilation of the carbon source were observed when hydrolyzed lactose was present, suggesting the assimilation first of glucose and then of galactose. To confirm the growth of Ralstonia eutropha using galactose as the only carbon source, experiments were carried out and the results showed that this bacterium is able to grow in the presence of this sugar at a growth rate of 0.13 h-1. The use of galactose by Ralstonia eutropha for its growth has not been reported in the literature until now. Corn steep liquor was found to be a viable alternative nitrogen source to ammonium sulfate. The results of experiments carried out at 30°C and 34°C were similar.

Resumo em Inglês:

Equilibrium constant and mass transfer parameters are needed for the study of amino acid separation in any process involving adsorption in fixed beds. The adsorption constants, effective diffusion coefficients, and axial dispersion coefficients for two amino acids, L-phenylalanine (Phe) and L-tyrosine (Tyr), are determined from a series of pulse tests in a fixed bed packed with PVP (poly-4-vinylpyridine) resin. Total bed voidage at different flow rates is estimated from NaCl pulse test data. The effective pore diffusivities of Phe, Tyr, and NaCl are estimated from moment analysis of pulse data. A detailed rate model is then solved numerically and adsorption constants, effective diffusion coefficients, axial dispersion coefficients are determined by moment analysis and compared with the pulse data. The advantage of this method is that the effective intraparticle diffusivities can be determined without the influence of extracolumn dispersion or intracolumn axial dispersion effects.

Resumo em Inglês:

Cost optimization in the synthesis decision tree often leads to a reduced degree of freedom which degrades the process’s ability to reject disturbances as a consequence of low controllability. In fact, Heat Exchanger Networks (HENs) obtained by traditional synthesis procedures that ignore controllability aspects must be evaluated in this context a posteriori. The aim of this work was to develop a procedure that includes RGA and SVD measures of controllability, which are solely based on steady state information, thereby freeing the synthesis procedure of the cumbersome dynamic analysis. When a structure is defined during a traditional HEN synthesis procedure, a degree of freedom analysis is approached as a simulation problem. Next, an optimization is performed, since new variables are usually added to increase the degree of freedom of the HEN in order to render it controllable. A key point in the proposed procedure is the inference of controllability based on the proposed controllability measures, which also provide a control scheme by pairing controlled and manipulated variables during the process design. A HEN reported in the literature is used to illustrate the proposed procedure. The steady state simulator Aspen Plus and the dynamic simulator Aspen Dynamics (Aspentech, Inc.) were employed.

Resumo em Inglês:

The galvanic stripping technique for metal recovery uses commercial organic extractants containing a metal to be recovered. The organic phase is placed in contact with a solid metal reducer that allows electrochemical reactions to occur. One product of these reactions is a metal layer deposited on the surface of the reducer consisting of reduced species desorbed from the organic phase. Another product is metal ions from the reducer adsorbed onto the organic phase. This work presents results for gold recovery by galvanic stripping of strong-base anionic extractants of a quaternary amine salt, ALIQUAT336®, in xylene using solid zinc as the metal reducer. The parameters studied were contact time for the organic phase containing gold and the samples of the reducing zinc metal, temperature of the system, gold concentration in the organic phase and type of stirring used in the galvanic stripping system. Experiments showed results higher than 28% of gold recovery and an adherent film of gold on the zinc surface. The Arrhenius plot for gold recovery from the organic extractant suggests a change in the rate- controlling step from mixed control to diffusion control with increasing temperature in the range of 20 to 50ºC.

Resumo em Inglês:

Peracetic acid is a powerful sanitizer that has only recently been introduced in the Brazilian food industry. The main disadvantage of this sanitizer is its decomposition rate. The main purpose of this paper is to present results obtained in experiments carried out to study the decomposition kinetics of peracetic acid in aqueous solutions at 25, 35, 40 and 45 °C. The decompositon of peracetic acid is a first-order reaction. The decomposition rate constants are between 1.71x10-3 h -1 for 25 °C and 9.64x10-3 h-1 for 45 °C. The decomposition rate constant is affected by temperature according to the Arrhenius equation, and the activation energy for the decomposition of peracetic acid in aqueous solutions prepared from the commercial formulation used in this work is 66.20 kJ/mol.