Resumo em Inglês:

Currently, the most successful predictive models for activity coefficients are those based on functional groups such as UNIFAC. In contrast, these models require a large amount of experimental data for the determination of their parameter matrix. A more recent alternative is the models based on COSMO, for which only a small set of universal parameters must be calibrated. In this work, a recalibrated COSMO-SAC model was compared with the UNIFAC (Do) model employing experimental infinite dilution activity coefficient data for 2236 non-hydrogen-bonding binary mixtures at different temperatures. As expected, UNIFAC (Do) presented better overall performance, with a mean absolute error of 0.12 ln-units against 0.22 for our COSMO-SAC implementation. However, in cases involving molecules with several functional groups or when functional groups appear in an unusual way, the deviation for UNIFAC was 0.44 as opposed to 0.20 for COSMO-SAC. These results show that COSMO-SAC provides more reliable predictions for multi-functional or more complex molecules, reaffirming its future prospects.

Resumo em Inglês:

The equilibrium and thermodynamics of azo dye (tartrazine and allura red) biosorption onto Spirulina platensis biomass were investigated. The equilibrium curves were obtained at 298, 308, 318 and 328 K, and four isotherm models were fitted the experimental data. Biosorption thermodynamic parameters (ΔG, ΔH and ΔS) were estimated. The results showed that the biosorption was favored by a temperature decrease. For both dyes, the Sips model was the best to represent the equilibrium experimental data (R²>0.99 and ARE<5.0%) and the maximum biosorption capacities were 363.2 and 468.7 mg g-1 for tartrazine and allura red, respectively, obtained at 298 K. The negative values of ΔG and ΔH showed that the biosorption of both dyes was spontaneous, favorable and exothermic. The positive values of ΔS suggested that the system disorder increases during the biosorption process.

Resumo em Inglês:

This work is focused on the determination of liquid-liquid equilibrium data for systems containing methyl and ethyl fatty acid esters, water, glycerol and ethanol at temperatures of 303.15 K and 318.15 K using a near-infrared spectroscopy technique (NIR). The NIR method used in this investigation provided quite satisfactory results when compared to conventional analytical techniques and hence can be used as an advantageous tool to quantify the compounds involved in the liquid-liquid equilibrium systems: i) without previous preparation of the samples; ii) with less waste generation; iii) at low cost; and iv) via a non-destructive technique, as sample analyses are made directly, showing good reproducibility and reliability of the data. The NIR method was effective in the use of different temperatures for calibration and validation of the systems under study. Besides, it is shown that extrapolation with the technique may be possible, making LLE predictions feasible for other conditions not used in the calibration procedure.

Resumo em Inglês:

Triacylglycerols and fatty alcohols are used in the formulation of cosmetic, pharmaceutical and food products. Although information about the phase transitions of these compounds and their mixtures is frequently required for design and optimization of processes and product formulation involving these substances, these data are still scarce in the literature. In the present study, the solid-liquid phase diagrams of two binary systems composed of triolein + 1-hexadecanol and triolein + 1-octadecanol were evaluated by differential scanning calorimetry (DSC) and optical microscopy. The experimental data were compared with predicted data by solving the phase equilibrium equations using an algorithm implemented in MATLAB. The liquid-phase activity coefficients were calculated using the Margules equation (two- and three-suffix) and the UNIFAC model (original and modified Dortmund model). The approaches used for calculating system equilibrium allowed an accurate prediction of the liquidus line with low deviations from the experimental data.

Resumo em Inglês:

The enzymatic synthesis of amoxicillin is catalyzed by Penicillin G Acylase (PGA). As byproducts, hydroxyphenylglycine and alcohol are also formed from hydrolytic reactions and antibiotic synthesis, respectively. The design of this process should be directed to promote the synthesis reaction. At the same time, it is necessary to reduce the hydrolytic reaction of amoxicillin through its crystallization or separation from the reaction medium. This work presents measurements of solid-liquid equilibrium data for amoxicillin and hydroxyphenylglycine in water at different temperatures (283.15 - 298.15 K), pH (5.5 - 7.5) and ethanol composition (0 - 70 wt.%). This information is relevant to determine the conditions that offer the lowest solubility for the antibiotic, favoring its separation and purification. All solubility data were obtained using an analytical method with indirect determination by UV spectroscopy. Ideal thermodynamic modeling was applied to describe the experimental solubility data sets.

Resumo em Inglês:

Specific ion effects - also known as Hofmeister effects - are ubiquitous in several areas of chemistry, chemical engineering and biology. The interfacial tension corresponds to the energy per unit of area at the interface. Thus, the presence of different salts in different concentrations changes the interfacial tension of a system containing an aqueous phase. This effect can be explained based on the concentration profile of different ions in the vicinity of the interface. In order to study this effect we measured the surface tension of aqueous electrolyte solutions and the interfacial tension of various systems containing hydrocarbons and different aqueous electrolyte solutions as a function of the ionic strength of the aqueous phase. We classify the tested ions for their ability to alter the interfacial tension of each system. These data provide valuable information that can be related to the stability of the corresponding emulsions, since the ions with higher capability of increasing the interfacial tension tend to be more effective in destabilizing the corresponding emulsion.

Resumo em Inglês:

Ionic liquids (IL) have been described as novel environmentally benign solvents because of their remarkable characteristics. Numerous applications of these solvents continue to grow at an exponential rate. In this work, high pressure vapor liquid equilibria for 17 different IL + gas binary systems were modeled at different temperatures with Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) equations of state, combined with the van der Waals mixing rule with two binary interaction parameters (vdW-2). The experimental data were taken from the literature. The optimum binary interaction parameters were estimated by minimization of an objective function based on the average absolute relative deviation of liquid and vapor phases, using the modified Simplex algorithm. The solubilities of all gases studied in this work decrease as the temperature increases and increase with increasing pressure. The correlated results were highly satisfactory, with average absolute relative deviations of 2.10% and 2.25% for PR-vdW-2 and SRK-vdW-2, respectively.

Resumo em Inglês:

Cubic equations of state combined with excess Gibbs energy predictive models (like UNIFAC) and equations of state based on applied statistical mechanics are among the main alternatives for phase equilibria prediction involving polar substances in wide temperature and pressure ranges. In this work, the predictive performances of the PC-SAFT with association contribution and Peng-Robinson (PR) combined with UNIFAC (Do) through mixing rules are compared. Binary and multi-component systems involving polar and non-polar substances were analyzed. Results were also compared to experimental data available in the literature. Results show a similar predictive performance for PC-SAFT with association and cubic equations combined with UNIFAC (Do) through mixing rules. Although PC-SAFT with association requires less parameters, it is more complex and requires more computation time.

Resumo em Inglês:

The objective of this study was to estimate thermodynamic data, such as standard enthalpy, entropy and Gibbs free energy changes of reaction and, consequently, chemical equilibrium constants, for a reaction system describing the hydrogen production from Liquefied Petroleum Gas (LPG). The acquisition of those properties was made using computational chemistry methods and the results were compared with experimental data reported in the literature. The reaction system of steam reforming of LPG was reported as a set of seven independent reactions involving the chemical species n-C4H10, C3H8, C2H6, C2H4, CH4, CO2, CO, H2O, H2 and solid carbon. Six computational approaches were used: Density Functional Theory (DFT) employing Becke's three parameter hybrid exchange functional, and the Lee-Yang-Parr correlation functional (B3LYP) using the 6-31G++(d,p) basis set and the composite methods CBS-QB3, Gaussian-1 (G1), Gaussian-2 (G2), Gaussian-3 (G3) and Gaussian-4 (G4). Mole fractions of the system components were also determined between 873.15 and 1173.15 K, at 1 atm and a feed with a stoichiometric amount of water. Results showed that the hybrid functional B3LYP/6-31G++(d,p), G3 and G4 theories were the most appropriated methods to predict the properties of interest. Gaussian-3 and Gaussian-4 theories are expected to be good thermodynamic data predictors and the known efficient prediction of vibrational frequencies by B3LYP is probably the source of the good agreement found in this study. This last methodology is of special interest since it presents low computational cost, which is important when more complex molecular systems are considered.

Resumo em Inglês:

A relationship between the osmotic second virial coefficient of proteins in aqueous salt solutions, the solubility of proteins in these solutions and the salt concentration is presented. The model developed considers that the solid-liquid equilibrium is established with neutral protein molecules and that the relationship between the protein solubility and the salt concentration follows Cohn's equation. The validity of the model is restricted to the salting-out region of the phase diagrams, which is the situation of greater practical importance. The resulting equations were successfully applied to systems containing lysozyme and ovalbumin.

Resumo em Inglês:

This work investigates the use of artificial neural networks in modeling an industrial fermentation process of Pleuromutilin produced by Pleurotus mutilus in a fed-batch mode. Three feed-forward neural network models characterized by a similar structure (five neurons in the input layer, one hidden layer and one neuron in the output layer) are constructed and optimized with the aim to predict the evolution of three main bioprocess variables: biomass, substrate and product. Results show a good fit between the predicted and experimental values for each model (the root mean squared errors were 0.4624% - 0.1234 g/L and 0.0016 mg/g respectively). Furthermore, the comparison between the optimized models and the unstructured kinetic models in terms of simulation results shows that neural network models gave more significant results. These results encourage further studies to integrate the mathematical formulae extracted from these models into an industrial control loop of the process.

Resumo em Inglês:

Production of cellulases under solid-state fermentation (SSF) is a promising technique that can help to reduce costs. Besides optimizing the production process, it is also important to consider enzyme recovery during the extraction step. Here, an experimental design methodology was used to investigate the effects of the operational parameters solid to liquid ratio (1:3, 1:6 and 1:9), stirring rate (80, 120 and 160 rpm), and temperature (10, 22 and 35 °C) on the recovery of endoglucanases produced by Aspergillus niger cultivated under SSF. Statistical analysis revealed that only the solid to liquid ratio had a significant influence on endoglucanase extraction. The highest endoglucanase recovery (35.7 U/g) was achieved using 0.2 mol/L acetate buffer at pH 4.8, together with a solid to liquid ratio of 1:9 and an agitation time of 10 minutes. In sequential extraction experiments, it was shown that most of the enzyme was recovered during the first extraction. The procedure adopted increased the efficiency of endoglucanase extraction by 70%, emphasizing the importance of selection of suitable operational conditions during SSF processes.

Resumo em Inglês:

The present work describes the study of the growth and the cytotoxic and antitumor activities of the extracts of the marine microorganisms Streptomyces acrymicini and Streptomyces cebimarensis, the latter a new strain. Both microorganisms were collected from coastal marine sediments of the north coast of São Paulo state. Growth was performed in a shaker and in a bioreactor using Gym medium and the broths of both microorganisms were extracted with ethyl acetate and n-butanol. Three extracts, two organic and one aqueous, from each microorganism were obtained and tested for cytotoxic and antitumor activity using the SF-295 (Central Nervous System), HCT-8 (Colon) cell lines, and the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) method. The growth methods were compared and show that, although the shaker presented reasonable results, the bioreactor represents the best choice for growth of these microorganisms. The biological activity of the different extracts was evaluated and it was demonstrated that the growth methodology may influence the secondary metabolite production and the biological activity.

Resumo em Inglês:

Anaerobic digestion is an important alternative for domestic wastewater treatment, especially in warm climate regions. Two full-scale anaerobic schemes were investigated: septic tank combined with anaerobic filter (S T A NF) and conventional UASB reactors. Treated effluents from these systems were subjected to disinfection by chlorination. The operational performance of 56 full-scale plants (36 S T A NF and 20 UASB) provided a realistic view. Findings showed that the plants operated with low OLR (< 2.0 kg COD/m³.day). Despite this, the removal of organic material was below values suggested by the literature (around 60% for COD). A removal of 4.0 Log10 units of total coliform and E. coli can be reached with residual chlorine (R CL) of at least 2.0 Cl-Cl2/l. Although UASB plants have performed better, improvement of maintenance is needed in both treatment configurations.

Resumo em Inglês:

In this study the viability of utilising ashes with high chromium oxide content, obtained by thermal treatment of footwear leather waste, in the production of low-carbon ferrochromium alloy (Fe-Cr-LC) by aluminothermic reduction was investigated. The following key-factors were selected for process modelling: the quantity of aluminium (Al) employed in the reaction, the iron amount added, the iron compound (Fe and/or Fe2O3) used, and the chromic acid addition. The process was investigated using a 2(4) full factorial design where the percentage of Cr2O3 reduced was used as the response. Variance analysis was employed to determine the significant effects and to validate the obtained model. The model was useful for finding the optimal operating conditions, including the maximisation of chromium conversion and the gross margin. Both resulted in similar process conditions, with 76.8±12.3% of chromium being reduced to the metallic phase, and 1.65±0.52 USD (kg ash)-1 as the gross margin. The qualities of some alloys obtained were investigated by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy analysis (SEM/EDS). The results showed that the main problem for these alloys in a standard specification was the P and S content, suggesting that a pre-treatment is required.

Resumo em Inglês:

A ZnO film was electrodeposited onto a gold substrate obtained from a recordable compact disc and tested as photocatalyst in degradation of dye in aqueous solution. X-ray diffractometry and atomic force microscopic analysis showed a pure ZnO phase with particle sizes in the nanometric scale. The results showed that the photocatalytic activity of the film is significant, with more than 90 % degradation of the dye in under 6 h sunlight irradiation. The photocatalytic process in sunlight follows first-order kinetics.

Resumo em Inglês:

Mathematical modeling of supercritical fluid extraction of oil from canola and sesame seeds with a two-phase model was performed in this work. A model based on differential mass balance was used to correlate the experimental data. Different adsorption isotherm models (Henry, Freundlich and Brunauer, Emmet and Teller (BET)) were used to describe the equilibrium state. Three model parameters such as effective diffusivity (Deff), mass transfer coefficient (Kf) and axial dispersion coefficient (Dax) of the bed were used as fitting parameters. The experimental data for yields were obtained at pressures of 10-20 MPa, temperatures of 313-333 K and solvent flow rates of 2-4 g/min. From the results, a nonlinear adsorption isotherm exhibited better agreement with experimental data of yield than a linear model in the range of studied conditions.

Resumo em Inglês:

A mathematical model using classical cake-filtration theory and the surface-renewal concept is formulated for describing cross-flow microfiltration under dynamic and steady-state conditions. The model can predict the permeate flux and cake buildup in the filter. The three basic parameters of the model are the membrane resistance, specific cake resistance and rate of surface renewal. The model is able to correlate experimental permeate flow rate data in the microfiltration of fermentation broths in laboratory- and pilot-scale units with an average root-mean-square (RMS) error of 4.6%. The experimental data are also compared against the critical-flux model of cross-flow microfiltration, which has average RMS errors of 6.3, 5.5 and 6.1% for the cases of cake filtration, intermediate blocking and complete blocking mechanisms, respectively.

Resumo em Inglês:

Effect of mass transfer in the magnetohydrodynamic flow of a Casson fluid over a porous stretching sheet is addressed in the presence of a chemical reaction. A series solution for the resulting nonlinear flow is computed. The skin friction coefficient and local Sherwood number are analyzed through numerical values for various parameters of interest. The velocity and concentration fields are illustrated for several pertinent flow parameters. We observed that the Casson parameter and Hartman number have similar effects on the velocity in a qualitative sense. We further analyzed that the concentration profile decreases rapidly in comparison to the fluid velocity when we increased the values of the suction parameter.