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Dive into the research topics where P. A. Pessôa Filho is active.

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Featured researches published by P. A. Pessôa Filho.


Fluid Phase Equilibria | 2004

Phase equilibrium and insulin partitioning in aqueous two-phase systems containing block copolymers and potassium phosphate

L.H. Haraguchi; R.S. Mohamed; Watson Loh; P. A. Pessôa Filho

Abstract In this work, phase diagrams of aqueous two-phase systems (ATPS) containing PEO–PPO–PEO block copolymers and potassium phosphate as well as the partitioning behavior of insulin in these systems are presented. Experiments aimed at the identification of the effects of copolymer structure (by varying the number of EO units per polymer molecule), temperature (283.15 and 298.15xa0K) and pH (5.0 and 7.0) on the phase behavior of these systems were carried out. The results indicated the enlargement of the two-phase region upon increasing the temperature, pH and copolymer hydrophobicity (expressed as the PO/EO ratio in the copolymer molecule). Experimental measurements of the partitioning of human insulin in these ATPS also indicated the dependency of the partition coefficients on temperature, pH, and copolymer hydrophobicity, with the latter being the most influential factor. Finally, experimental data on the phase behavior and insulin partitioning were correlated using an excess Gibbs energy virial-type model modified in order to account for coulombic interactions and ionization equilibrium between the various forms of the phosphate ion.


Brazilian Journal of Chemical Engineering | 2010

Water activity of aqueous solutions of ethylene oxide-propylene oxide block copolymers and maltodextrins

Natália D.D. Carareto; E. S. Monteiro Filho; P. A. Pessôa Filho; Antonio J. A. Meirelles

Abstract - The water activity of aqueous solutions of EO-PO block copolymers of six different molar masses and EO/PO ratios and of maltodextrins of three different molar masses was determined at 298.15 K. The results showed that these aqueous solutions present a negative deviation from Raoults law. The Flory-Huggins and UNIFAC excess Gibbs energy models were employed to model the experimental data. While a good agreement was obtained with the Flory-Huggins equation, discrepancies were observed when predicting the experimental behavior with the UNIFAC model. The water activities of ternary systems formed by a synthetic polymer, maltodextrin and water were also measured and used to test the predictive capability of both models. Keywords : Water activity; Excess Gibbs energy; Phase equilibrium; Flory-Huggins; UNIFAC. INTRODUCTION The water activity (a w ) of an aqueous solution is the ratio between the fugacity of water in this solution and the fugacity of pure liquid water at the same temperature and pressure. This property is the most directly accessible measure of liquid-phase non-ideality of aqueous solutions of non-volatile solutes, since there are either well documented techniques or electronic devices to accomplish it. Besides its scientific importance, water activity is also related to the stability of foodstuffs, for it represents the amount of water available to microbial or chemical spoilage. In other words, high a


Brazilian Journal of Chemical Engineering | 2005

A modified UNIQUAC equation for mixtures containing self-associating compounds

P. A. Pessôa Filho; R.S. Mohamed; Gerd Maurer

The UNIQUAC model for the excess Gibbs energy is modified using chemical theory to account for chain-like association occurring in self-associating compounds such as alcohols. The equation considers the alcohol to be a mixture of clusters in chemical equilibrium. The UNIQUAC equation is used to model the behavior of the mixture of clusters, with size and surface parameters related to the number of alcohol molecules involved in their formation. The values of association enthalpy and entropy were obtained through fitting vapor pressure data. The model is used to correlate phase behavior of alcohol-hydrocarbon mixtures at low pressures, presenting excellent results in bubble point calculations. A further extension was made to allow for cross-association, the formation of a hydrogen bond between the molecules of an alcohol and an active solute. This extension was used to model alcohol-aromatic mixtures with equally good results.


Thermochimica Acta | 1999

A chemical theory based equation of state for self-associating compounds

P. A. Pessôa Filho; R.S. Mohamed

Abstract The Redlich–Kwong–Soave equation of state commonly used to describe the volumetric behavior of pure fluids and mixtures is modified using chemical theory to account for chain-like association occurring in self-associating compounds such as alcohols. The equation treats the pure fluid as a mixture of clusters, with parameters a and b related to the number of molecules involved in their formation and obtained by regression of vapor pressure data using hydrocarbons as homomorphs. The model is extended to mixtures of a self-associating compound and inert ones, and used to correlate the phase behavior of alcohol–hydrocarbon mixtures. The model resulted in excellent correlation of bubble point pressure experimental data and good predictions of vapor phase composition, especially at low temperatures, situation in which equations of state are usually inaccurate.


Brazilian Journal of Chemical Engineering | 2001

A SOLVATION-BASED THERMODYNAMIC MODEL FOR AQUEOUS TWO-PHASE SYSTEMS

P. A. Pessôa Filho; R.S. Mohamed

Aqueous two-phase systems (ATPSs) have found wide application in the separation of biological molecules such as amino acids, peptides and proteins. Most of the research in this area has been dedicated to experimental determination and less effort has been devoted to the proper thermodynamic modeling of these systems. This work presents a new model for ATPS that accounts for solvation effects between polymer and water molecules, which are commonly reported to be responsible for phase separation. The model uses the Flory-Huggins equation as a starting point and modifies the combinatorial term by considering the presence of a hydration shell. The modified equation parameters were fit to a number of isotherms of poly(ethylene glycol) - dextran systems, and the results obtained are reported herein. These results show that the adopted modification leads to remarkable improvements in the performance of the model.


Computer-aided chemical engineering | 2012

Application of Computer Aided Mixture Design in Paints and Coatings

Emerson B. Venceslau; P. A. Pessôa Filho; Galo A.C. Le Roux

Abstract In this study we present an application of Computer-Aided Mixture Design in paint and coatings, which is one of the most solvent demanding markets. In recent years, reformulation of solvent systems has gained strength for three main reasons: cost reduction maintaining performance, performance improvement, and the search for solvents which are less aggressive to human and environment, either voluntarily or driven by legislation. Among the several properties required for these solvents, evaporation rate and Hansen solubility parameters are the most important ones. Adjustments and replacements of solvents in formulation are mostly performed by trial and error methods, which are expensive and time consuming. While the solubility parameter theory and evaporation models are well known, there is still room for methodologies that predict solvent and mixture evaporation rates. The object of this study is to propose a methodology to obtain cost-optimized mixtures that meet evaporation and solubility constraints. As a first step, available models for calculating the evaporation rate (based on the Evaporometer method determined by ASTM D3539) of solvents and their mixtures were evaluated. The impact of some assumptions, as activity coefficient model and relative humidity are validated with experimental evaporation rates. Finally, based on Computer-Aided Mixture/Blend Design, optimization models were generated. Due to the non-linearity of the constraints corresponding to the evaporation rate and solubility models these problems are highly non-linear. One solvent substitution problem was studied, and the results showed good agreement with experiments. The approach is a useful tool in solvent system formulation.


Brazilian Journal of Chemical Engineering | 2010

An assessment on the use of the debye-hückel equation for the thermodynamic modeling of aqueous systems containing polymers and salts

K. C.Nascimento Alves; P. A. Pessôa Filho

In this work, a study on the role of the long-range term of excess Gibbs energy models in the modeling of aqueous systems containing polymers and salts is presented. Four different approaches on how to account for the presence of polymer in the long-range term were considered, and simulations were conducted considering aqueous solutions of three different salts. The analysis of water activity curves showed that, in all cases, a liquid-phase separation may be introduced by the sole presence of the polymer in the long-range term, regardless of how it is taken into account. The results lead to the conclusion that there is no single exact solution for this problem, and that any kind of approach may introduce inconsistencies.


Brazilian Journal of Chemical Engineering | 2004

Calculation of liquid-liquid equilibrium of aqueous two-phase systems using a chemical-theory-based excess Gibbs energy model

P. A. Pessôa Filho; R.S. Mohamed

Abstract - Mixtures containing compounds that undergo hydrogen bonding show large deviations from ideal behavior. These deviations can be accounted for through chemical theory, according to which the formation of a hydrogen bond can be treated as a chemical reaction. This chemical equilibrium needs to be taken into account when applying stability criteria and carrying out phase equilibrium calculations. In this work, we illustrate the application of the stability criteria to establish the conditions under which a liquid-phase split may occur and the subsequent calculation of liquid-liquid equilibrium using a chemical-theory-modified Flory-Huggins equation to describe the non ideality of aqueous two -phase systems composed of poly(ethylene glycol) and dextran. The model was found to be able to correlate ternary liquid-liquid diagrams reasonably well by simple adjustment of the polymer -polymer binary interaction parameter. Keywords : Aqueous two -phase systems, thermodynamic modeling, Gibbs energy, liquid-liquid equilibrium .


Fluid Phase Equilibria | 2004

Phase equilibrium for the system rice bran

Christianne E.C. Rodrigues; P. A. Pessôa Filho; Antonio J. A. Meirelles


Fluid Phase Equilibria | 2005

Equilibrium data for systems composed by cottonseed oil + commercial linoleic acid + ethanol + water + tocopherols at 298.2 K

Christianne E.C. Rodrigues; Érika C.D. Reipert; Ana Flávia de Souza; P. A. Pessôa Filho; Antonio J. A. Meirelles

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R.S. Mohamed

State University of Campinas

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Gerd Maurer

Kaiserslautern University of Technology

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Silke Lammertz

Kaiserslautern University of Technology

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Ana Flávia de Souza

State University of Campinas

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