L. Cardozo Filho

Biosorption of binary mixtures of Cr(III) and Cu(II) ions by Sargassum sp

The adsorption of two metal ions, Cr(III) and Cu(II), in single-component and binary systems by Sargassum sp., a brown alga, was studied. Equilibrium batch sorption studies were carried out at 30oC and pH 3.5. Kinetic tests were done for a binary mixture (chromium + copper) for a contact time of 72 hours to guarantee that equilibrium was reached. The monocomponent equilibrium data obtained were analyzed using the Langmuir and Freundlich isotherms. The binary equilibrium data obtained were described using four Langmuir-type and Freundlich isotherms. The F-test showed a statistically significant fit for all binary isotherm models. The parameters for isotherms of the Langmuir-type were used to determine the affinity of one metal for the biosorbent in the presence of another metal. The chromium ion showed a greater affinity for Sargassum sp. than the copper ion.

Phase stability analysis of liquid-liquid equilibrium with stochastic methods

Minimization of Gibbs free energy using activity coefficient models and nonlinear equation solution techniques is commonly applied to phase stability problems. However, when conventional techniques, such as the Newton-Raphson method, are employed, serious convergence problems may arise. Due to the existence of multiple solutions, several problems can be found in modeling liquid-liquid equilibrium of multicomponent systems, which are highly dependent on the initial guess. In this work phase stability analysis of liquid-liquid equilibrium is investigated using the NRTL model. For this purpose, two distinct stochastic numerical algorithms are employed to minimize the tangent plane distance of Gibbs free energy: a subdivision algorithm that can find all roots of nonlinear equations for liquid-liquid stability analysis and the Simulated Annealing method. Results obtained in this work for the two stochastic algorithms are compared with those of the Interval Newton method from the literature. Several different binary and multicomponent systems from the literature were successfully investigated.

Modeling and simulation of rapid expansion of supercritical solutions

Rapid expansion of supercritical solution (RESS) is a promising technique for microparticle production. The literature points out that the RESS technique can be applied to process a wide range of materials including ceramics, polymers, biopolymers, pharmaceutics, and organic compounds. In order to achieve an adequate understanding of the RESS process, it is necessary to conduct more comprehensive studies involving the hydrodynamic modeling of the fluid flow through the capillary, the phase behavior of a expanding mixture, and also with regard to the microparticle formation mechanism. In this context, this work is focused on the analysis of process hydrodynamic modeling and on phase equilibrium modeling (thermodynamic modeling of supersaturation), with a phase stability test coupled. The Gibbs tangent plane distance for the phase stability test was minimized using the simulated annealing algorithm. The results showed that the thermodynamic variables exert a remarkable effect simulated variables (temperature, velocity, density and degree of supersaturation) for the profile.

Poly(3-hydroxybutyrate-co-3- hydroxyvalerate) nanoparticles prepared by a miniemulsion/solvent evaporation technique: effect of phbv molar mass and concentration

Miniemulsification and emulsion/solvent evaporation techniques were combined to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanoparticles. Those nanoparticles were prepared with different PHBV molar masses and PHBV concentrations to verify their effect on the final particle size. Nanoparticles with an average diameter of 133 nm were obtained when a low molar mass (Mw = 44,350 g/mol) polymer was used. On the other hand, when high molar mass PHBV (Mw = 369,900 g/mol) was used under the same operational conditions, nanoparticles with a 300 nm average diameter and a broader particle size distribution were formed. Results also showed that increasing the PHBV concentration led to an increase of the particle size and, when the polymer/costabilizer (PHBV/hexadecane) weight ratio was close to 1, nanocapsules (hexadecane core surrounded by a PHBV shell) were formed.

A subdivision algorithm for phase equilibrium calculations at high pressures

Phase equilibrium calculations at high pressures have been a continuous challenge for scientists and engineers. Traditionally, this task has been performed by solving a system of nonlinear algebraic equations originating from isofugacity equations. The reliability and accuracy of the solutions are strongly dependent on the initial guess, especially due to the fact that the phase equilibrium problems frequently have multiple roots. This work is focused on the application of a subdivision algorithm for thermodynamic calculations at high pressures. The subdivision algorithm consists in the application of successive subdivisions at a given initial interval (rectangle) of variables and a systematic test to verify the existence of roots in each subinterval. If the interval checked passes in the test, then it is retained; otherwise it is discharged. The algorithm was applied for vapor-liquid, solid-fluid and solid-vapor-liquid equilibrium as well as for phase stability calculations for binary and multicomponent systems. The results show that the proposed algorithm was capable of finding all roots of all high-pressure thermodynamic problems investigated, independent of the initial guess used.

Determination of liquid-liquid equilibrium data for biodiesel containing ternary systems using near infrared technique

Abstract - 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.