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Brazilian Journal of Chemical Engineering, Volume: 24, Número: 1, Publicado: 2007
  • Determination of the liquid pool surfactant and protein concentration for semi-batch foam fractionation columns Bioprocess Engineering

    Rosa, P. T. V.; Santana, C. C.; Carbonell, R. G.

    Resumo em Inglês:

    A model is derived for the change with time of the concentration of a surface-active component in the liquid pool of a semi-batch foam fractionation process. The transport of surface-active material to the gas-liquid interface was assumed to be limited by the mass transfer rates, and the concentration of the adsorbed material at the interface was assumed to be in equilibrium with the concentration of liquid adjacent to the bubble gas surface. This model was compared to experimental data obtained for semi-batch foam fractionation of aqueous solutions of bovine serum albumin and cetyltrimetylammonium bromide.
  • Development of a fluidized bed system for adsorption of phenol from aqueous solutions with commercial macroporous resins Bioprocess Engineering

    Corrêa, R. A.; Calçada, L. A.; Peçanha, R. P.

    Resumo em Inglês:

    This work is related to removal of phenol from wastewaters by adsorption onto polymeric resins, a current alternative to activated carbon. A closed circuit, bench-scale liquid fluidized bed system was developed for this purpose. Phenol aqueous solutions with initial concentrations in the range of 0.084 to 0.451 kg/m³ were used to fluidize small permeable capsules of stainless steel screen containing a commercial resin at 308 K. Experiments were carried out using a fluidizing velocity 20% above that of the minimum fluidization of the capsules. Typically, 30 passages of the liquid volume circulating through the bed were required to reach a quasi-equilibrium concentration of phenol in the treated effluent. A simple batch adsorption model using the Freundlich isotherm successfully predicted final phenol concentrations. Suspended solids, often present in residual waters and a common cause of fixed bed clogging, were simulated with wood sawdust.
  • A study of process variables for the photocatalytic degradation of rhodamine B Bioprocess Engineering

    Soares, E. T.; Lansarin, M. A.; Moro, C. C.

    Resumo em Inglês:

    The photoactivated degradation reaction of rhodamine B (RB) was studied using P-25 TiO2 (Degussa) as catalyst. Three process variables - temperature, initial pH, and catalyst concentration - were evaluated. Temperature had a slight effect on reaction rate; however, the combined effect of pH and catalyst concentration was greater. pH affected the catalyst particle's adsorption of RB, altering the reaction rate. The concentration of the catalyst was significant only up to 0,65 g L-1. The effect of temperature was studied at optimum pH and 50ºC was found to be the optimum operational temperature. The effect of the presence of a surfactant (sodium dodecylsulfate, SDS) and ionic contaminants (Cl- and SO4-) in the reaction system was also studied. The surfactant improved the catalyst's adsorption of RB by more than 80%, increasing the degradation reaction rate as well. The ionic contaminants reduced the reaction rate.
  • A turbulent bed contactor: energetic efficiency for particle collection Fluid Dynamics, Heat And Mass Transfer And Other Topics

    Gimenes, M. L.; Handley, D.; Silva, M. G. C.

    Resumo em Inglês:

    Particle collection experiments were conducted in a fluidizing irrigated bed to evaluate the performance of mobile packings: 38 x 50 mm plain oblate spheroids 38 mm ID plain spheres and alternative perforated spheres with a 38 mm ID and 10% and 25% free areas were used as fluidizing media in a 0.264 m diameter and 1.20 m high turbulent bed contactor (TBC). Particle collection experiments were carried out above the minimum fluidization velocity, using as particulate test powder polysized alumina (size 1.5 to 5.5 mm). Experimental results demonstrated that the perforated spheres performed better in collecting particles than the other packings tested. The efficiency of particle collection was analysed based on energy consumption in the TBC, using the energetic efficiency concept. It was verified that not much more energy was consumed per unit of gas flow in fluidized beds of perforated packings than in those of conventional plain sphere packings, since the perforated spheres were more energetically efficient for particle collection than plain spheres and oblate spheroid packings.
  • Prediction of effective diffusivity tensors for bulk diffusion with chemical reactions in porous media Fluid Dynamics, Heat And Mass Transfer And Other Topics

    Silva, E. A. Borges da; Souza, D. P.; Souza, A. A. Ulson de; Souza, S. M. A. Guelli U. de

    Resumo em Inglês:

    In this paper, the volume averaging transport equations of two reactive processes in porous media are presented. The porous media are characterized by different length scales and the information describing the mass transfer mechanisms is transferred hierarchically between scales by applying the volume averaging method. This development provides the theoretical definition of effective transport coefficients, which can be predicted through solution of the closure problems. The theoretical calculation of effective diffusion tensors of the species in the particle pores is presented. Two closure problems are deduced through mathematical formulation of two different scales: microporous (process 1) and macroporous (process 2). In order to solve these closure problems, the volume finite method is used as the numerical methodology. Good agreement is verified between the numerical solutions obtained in this study and the data found in the literature for the closure problems considered.
  • The impact of kappa number composition on eucalyptus kraft pulp bleachability Fluid Dynamics, Heat And Mass Transfer And Other Topics

    Costa, M. M.; Colodette, J. L.

    Resumo em Inglês:

    Consumption of chemicals during ECF bleaching of kraft pulp correlates reasonably well with kappa number, which measures with KMnO4 the total amount of oxidizable material in the pulp. However, the method does not distinguish between the oxidizable material in residual lignin and other structures susceptible to oxidation, such as hexenuronic acids (HexAs), extractives and carbonyl groups in the pulp. In this study an attempt is made to separate the main contributors to the kappa number in oxygen - delignified eucalyptus Kraft pulps and evaluate how these fractions behave during ECF bleaching using chlorine dioxide as the sole oxidant (DEDD sequence). Residual lignin and HexAs proved to be the main fractions contributing to the kappa number and chlorine dioxide consumption in ECF bleaching. Pulp bleachability with chlorine dioxide increases with increasing HexAs content of the pulp but chlorine dioxide per se does not react with HexAs. Reduction of pulp with sodium borohydride under conditions for removing carbonyl groups has no impact on bleachability. No correlation was found between the pulp of the extractive content and pulp bleachability. The removal of HexAs prior to ECF bleaching significantly decreases the formation of chlorinated organics in the pulp (OX) and filtrates (AOX) as well as of oxalic acids in the filtrates.
  • Modeling heat and mass transfer in the heat treatment step of yerba maté processing Fluid Dynamics, Heat And Mass Transfer And Other Topics

    Peralta, J. M.; Schmalko, M. E.

    Resumo em Inglês:

    The aim of this research was to estimate the leaf and twig temperature and moisture content of yerba maté branches (Ilex paraguariensis Saint Hilaire) during heat treatment, carried out in a rotary kiln dryer. These variables had to be estimated (modeling the heat and mass transfer) due to the difficulty of experimental measurement in the dryer. For modeling, the equipment was divided into two zones: the flame or heat treatment zone and the drying zone. The model developed fit well with the experimental data when water loss took place only in leaves. In the first zone, leaf temperature increased until it reached 135°C and then it slowly decreased to 88°C at the exit, despite the gas temperature, which varied in this zone from 460°C to 120°C. Twig temperature increased in the two zones from its inlet temperature (25°C) up to 75°C. A model error of about 3% was estimated based on theoretical and experimental data on leaf moisture content.
  • Evaluation of cyclone geometry and its influence on performance parameters by computational fluid dynamics (CFD) Fluid Dynamics, Heat And Mass Transfer And Other Topics

    Martignoni, W. P.; Bernardo, S.; Quintani, C. L.

    Resumo em Inglês:

    Cyclone models have been used without relevant modifications for more than a century. Most of the attention has been focused on finding new methods to improve performance parameters. Recently, some studies were conducted to improve equipment performance by evaluating geometric effects on projects. In this work, the effect of cyclone geometry was studied through the creation of a symmetrical inlet and a volute scroll outlet section in an experimental cyclone and comparison to an ordinary single tangential inlet. The study was performed for gas-solid flow, based on an experimental study available in the literature, where a conventional cyclone model was used. Numerical experiments were performed by using CFX 5.7.1. The axial and tangential velocity components were evaluated using RSM and LES turbulence models. Results showed that these new designs can improve the cyclone performance parameters significantly and very interesting details were found on cyclone fluid dynamics properties using RSM and LES.
  • Drying in the rotating-pulsed fluidized bed Fluid Dynamics, Heat And Mass Transfer And Other Topics

    Ambrosio-Ugri, M. C. B.; Taranto, O. P.

    Resumo em Inglês:

    There are particulate materials that are cohesive when wet. Although they are Geldart's group A dry powders, they show difficulties in fluidizing in a conventional fluidized bed, which could be diminished by modifying the fluidization equipment. Therefore, the objective of this work was to study the drying of cohesive particulate material using a rotating-pulsed fluidized bed. The material used in the drying study was 2-hydroxybenzoic acid because its cohesive forces are stronger when wet. The drying experiments were carried out according to the following parameters: frequency of disk (5 and 15 Hz), initial moisture content of the material (high and low) and gas temperature at 85°C. From the drying kinetic curves and visual observations during the experiments, it could be concluded that the rotating-pulsed fluidized bed is an alternative for the processing of cohesive solids that preserves the final quality of the dry solids.
  • Recent achievements in facilitated transport membranes for separation processes Kinetic And Catalysis, Reaction Engineering And Materials Science

    Ferraz, H. C.; Duarte, L. T.; Di Luccio, M.; Alves, T. L. M.; Habert, A. C.; Borges, C. P.

    Resumo em Inglês:

    Membrane separation processes have been extensively used for some important industrial separations, substituting traditional methods. However, some applications require the development of new membranes. In this work, we discuss recent progress achieved in this field, focusing on gas and liquid separation using facilitated transport membranes. The advantages of using a carrier species either in a liquid membrane or fixed in a polymer matrix to enhance both the flux and the selectivity of the transport are summarized. The most probable transport mechanisms in these membranes are presented and the improvements needed to spread this technology are also discussed. As examples, we discuss our very successful experiences in air fractioning, olefin/paraffin separation and sugar recovery using liquid and fixed carrier membranes.
  • A kinetic model for the first stage of pygas upgrading Kinetic And Catalysis, Reaction Engineering And Materials Science

    Medeiros, J. L. de; Araújo, O. Q. F.; Gaspar, A. B.; Silva, M. A. P.; Britto, J. M.

    Resumo em Inglês:

    Pyrolysis gasoline - PYGAS - is an intermediate boiling product of naphtha steam cracking with a high octane number and high aromatic/unsaturated contents. Due to stabilization concerns, PYGAS must be hydrotreated in two stages. The first stage uses a mild trickle-bed conversion for removing extremely reactive species (styrene, dienes and olefins) prior to the more severe second stage where sulfured and remaining olefins are hydrogenated in gas phase. This work addresses the reaction network and two-phase kinetic model for the first stage of PYGAS upgrading. Nonlinear estimation was used for model tuning with kinetic data obtained in bench-scale trickle-bed hydrogenation with a commercial Pd/Al2O3 catalyst. On-line sampling experiments were designed to study the influence of variables - temperature and spatial velocity - on the conversion of styrene, dienes and olefins.
  • Synthesis and characterization of Al- and Ti-MCM-41 materials: application to oxidation of anthracene Kinetic And Catalysis, Reaction Engineering And Materials Science

    Araújo, R. S.; Costa, F. S.; Maia, D. A. S.; Sant'Ana, H. B.; Cavalcante Jr., C. L.

    Resumo em Inglês:

    The synthesis and characterization of new molecular sieves of the MCM-41 type are presented in this study. Samples were obtained from the alkoxides of Si, Ti and Al and different long-chain amine and alkylammonium salts surfactants, by the sol-gel method, through moderate agitation at room temperature. The reactions were conducted in two steps, acid hydrolysis (pH=2) and alkaline condensation (pH=10), both taking about 90min. The synthesized crystals were characterized using infrared spectroscopy, thermogravimetry and X-Ray diffraction. Pore diameters and surface areas were measured by N2 adsorption at 77K. Catalytic tests were conducted for anthracene oxidation using different oxidants (H2O2, alkylhydroperoxide) and organic solvents (benzene, tetrahydrofuran).
  • Correlation of (liquid + liquid) equilibrium of systems including ionic liquids Thermodynamics And Separation Processes

    Aznar, M.

    Resumo em Inglês:

    Ionic liquids are neoteric, environmentally friendly solvents (since they do not produce emissions) composed of large organic cations and relatively small inorganic anions. They have favorable physical properties, such as negligible volatility and wide range of liquid existence. Moreover, many different cations and anions can be used to synthesize ionic liquid, so the properties can be designed by the use of selected combinations of anions and cations. (Liquid + liquid) equilibrium (LLE) data for systems including ionic liquids, although essential for the design and operation of separation processes, are still scarce. However, some recent studies have presented ternary LLE data involving several ionic liquids and such organic compounds as alkanes, alkenes, alkanols, water, ethers and aromatics. In this work, LLE data for 24 ternary systems including ionic liquids from the literature are correlated by using the NRTL model for the activity coefficient. The results are very satisfactory, with rms deviations of about 1.4%.
  • The performance of simulated annealing in parameter estimation for vapor-liquid equilibrium modeling Thermodynamics And Separation Processes

    Bonilla-Petriciolet, A.; Bravo-Sánchez, U. I.; Castillo-Borja, F.; Zapiain-Salinas, J. G.; Soto-Bernal, J. J.

    Resumo em Inglês:

    In this paper we report the application and evaluation of the simulated annealing (SA) optimization method in parameter estimation for vapor-liquid equilibrium (VLE) modeling. We tested this optimization method using the classical least squares and error-in-variable approaches. The reliability and efficiency of the data-fitting procedure are also considered using different values for algorithm parameters of the SA method. Our results indicate that this method, when properly implemented, is a robust procedure for nonlinear parameter estimation in thermodynamic models. However, in difficult problems it still can converge to local optimums of the objective function.
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