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Brazilian Journal of Chemical Engineering, Volume: 18, Número: 1, Publicado: 2001
  • Determination of the enzyme reaction rate in a differential fixed-bed reactor: a case study

    Baruque Filho, E.A.; Baruque, M.G.A.; Sant’Anna Jr., G.L.

    Resumo em Inglês:

    The reaction rate of starch hydrolysis catalyzed by a glucoamylase covalently bound to chitin particles was measured in a Differential Fixed-Bed Reactor (DFBR). Under selected test conditions the initial reaction rate may represent biocatalyst activity. Some aspects which influence measurement of the initial reaction rate of an immobilized enzyme were studied: the amount of desorbed enzyme and its hydrolytic activity, the extent of pore blockage of the biocatalyst caused by substrate solution impurities and the internal and external diffusional mass transfer effects. The results showed that the enzyme glucoamylase was firmly bound to the support, as indicated by the very low amount of desorbed protein found in the recirculating liquid. Although this protein was very active, its contribution to the overall reaction rate was negligible. It was observed that the biocatalyst pores were susceptible to being blocked by the impurities of the starch solution. This latter effect was accumulative, increasing with the number of sequential experiments carried out. When the substrate solution was filtered before use, very reliable determinations of immobilized enzyme reaction rates could be performed in the DFBR. External and internal diffusional resistences usually play a significant role in fixed-bed reactors. However, for the experimental system studied, internal mass transfer effects were not significant, and it was possible to select an operational condition (recirculation flow rate value) that minimized the external diffusional limitations.
  • Analysis of the surface quality of sulphur-coated urea particles in a two-dimensional spouted bed

    Ayub, G.S.E.; Rocha, S.C.S.; Perrucci, A.L.I.

    Resumo em Inglês:

    In this work the quality of sulphur-coated urea was determined by the urea dissolution rate and analysed by electron microscopy. Particles of urea were coated in a two-dimensional spouted bed, having a 60° slanted base angle and an atomization nozzle installed at the base. Elementary sulphur was liquefied and atomized on the particles. The experiments were planned with the objective of verifying the influences of flowrates of sulphur and atomized air and the temperature of the air used in the spouted bed on the quality of the coated particle surface. The temperature of the spout air and the flowrate of the atomized air showed a significant influence on the quality of the coating.
  • The effects of aging temperature and aging time on the oxygen storage capacity of Pt-Rh/CeZrO2 catalysts

    Hori, C.E.; Ng, K.Y. Simon; Brenner, A.; Rahmoeller, K.M.; Belton, D.

    Resumo em Inglês:

    The effects of aging temperature and time on the oxygen storage capacity (OSC) of Pt-Rh-promoted Ce0.75Zr0.25O2 solid solutions were measured and correlated with the BET surface area and noble metal (NM) surface area in the catalysts. The NM surface area is better correlated with OSC than is with the BET surface area. On a practical level, our results demonstrated that, even when operating at 900°C with alternating oxidizing and reducing conditions, these materials deactivate slowly with a near t-1 time dependence. Deactivation rates for these catalysts are dependent on the NM loading with the highest loaded catalysts deactivating roughly half as fast as the lowest loaded catalysts. As the aging temperature is increased from 900°C to 1000°C, the deactivation rate becomes two to four2-4 times higher for all three properties (BET surface area, NM surface area and OSC). The lowest NM loaded samples are more sensitive to aging temperature than the highest loaded ones.
  • Comparison of biomass estimation techniques for a Bacillus thuringiensis fed-batch culture

    Cunha, C.C.F.; Souza Júnior, M.B.

    Resumo em Inglês:

    In this work, the ability of artificial neural nets was investigated for the on-line biomass prediction of the simulated growth of a strain of Bacillus thuringiensis in fed-batch mode. For this purpose, multilayered backpropagation nets with sigmoid nodes were trained. The patterns were composed of input data on current values of biomass concentration, limiting substrate concentration and dilution rate, and output data on prediction of biomass concentration for the following step. The dilution rate was disturbed by a PRBS input, and simulations were conducted using a phenomenological experimentally validated model. The nets were able to predict the biomass concentration for different feeding techniques, and they were also compared with the variable estimation technique using the extended Kalman filter.
  • In-vitro corrosion resistance study of hot worked Ti-6Al-7Nb alloy in a isotonic medium

    Rosa, S.; Barbosa, P.F.; Button, S.T.; Bertazzoli, R.

    Resumo em Inglês:

    This investigation reports the results of linear polarization of hot upset Ti-6Al-7Nb bar samples. Current-potential curves recorded in Hank’s solution were analyzed by correlating characteristics of passivation and microstructures obtained after processing. Results have shown that it is important to select temperature process and deformation rate as parameters when more noble potential values are required. Low deformation rate facilitates the formation of beta phase that is retained in the structure at room temperature shifting the corrosion potential to more positive values. However, samples hot compressed from 750°C to 1030 °C showed passive layer stability over a wide range of potentials extending from -0.15 V to 1.75 V vs SCE . Furthermore, passive films grown onto the Ti-6Al-7Nb samples surfaces have shown no sign of rupture for the processing conditions selected for this study.
  • Non-newtonian carriers in a batch electrophoretic cell with joule heating: hydrodynamic considerations and mathematical aspects

    Bosse, M.A.; Arce, P.; Vasquez, A.

    Resumo em Inglês:

    The Joule heating effects on hydrodynamics are examined for the case of a non-Newtonian fluid flowing in a batch electrophoretic cell. The potential benefits of using non-Newtonian fluids in electrophoretic separations could lead, for example, to an increase in the efficiency of separations and to a better scale-up of the operation for the processing of large quantities on a pilot or even an industrial scale. The analysis conducted in this research is based on the formulation of simplified mathematical models that can capture the most relevant aspects of the physics of the free convection that takes place in a batch electrophoretic cell. The first aspect is associated with the carrier fluid when no solute sample (of particles or macromolecules) is added to the device. This is, indeed, a carrier fluid completely free of solute problem. This aspect of the research is referred to as the carrier fluid problem. The second aspect involved in the investigation is the analysis of the mass transport (i.e., convective-diffusive) process associated with the motion of a solute sample added to the carrier fluid. This particular aspect of the research is referred to as the solute problem of the free-convection electrophoretic cell. The two problems are sequentially coupled and the solution of the carrier fluid problem must be performed first in order to have the velocity profile to study the solute problem. Details about hydrodynamic considerations and the solution approach are discussed in this contribution.
  • The role of the rheological properties of non-newtonian fluids in controlling dispersive mixing in a batch electrophoretic cell with Joule heating

    Bosse, M.A.; Arce, P.; Troncoso, S.A.; Vasquez, A.

    Resumo em Inglês:

    The problem of the effect of Joule heating generation on the hydrodynamic profile and the solute transport found in electrophoretic devices is addressed in this article. The research is focused on the following two problems: The first one is centered around the effect of Joule heating on the hydrodynamic velocity profile and it is referred to as "the carrier fluid problem." The other one is related to the effect of Joule heating on the solute transport inside electrophoretic cells and it is referred to as "the solute problem". The hydrodynamic aspects were studied first to yield the velocity profiles required for analysis of the solute transport problem. The velocity profile obtained in this study is analytical and the results are valid for non-Newtonian fluids carriers. To this end, the power-law model was used to study the effect of the rheology of the material in conjunction with the effect of Joule heating generation inside batch electrophoretic devices. This aspect of the research was then effectively used to study the effect of Joule heating generation on the motion of solutes (such as macromolecules) under the influence of non-Newtonian carriers. This aspect of the study was performed using an area-averaging approach that yielded analytical results for the effective diffusivity of the device.
  • A simulation benchmark to evaluate the performance of advanced control techniques in biological wastewater treatment plants

    Sotomayor, O.A.Z.; Park, S.W.; Garcia, C.

    Resumo em Inglês:

    Wastewater treatment plants (WWTP) are complex systems that incorporate a large number of biological, physicochemical and biochemical processes. They are large and nonlinear systems subject to great disturbances in incoming loads. The primary goal of a WWTP is to reduce pollutants and the second goal is disturbance rejection, in order to obtain good effluent quality. Modeling and computer simulations are key tools in the achievement of these two goals. They are essential to describe, predict and control the complicated interactions of the processes. Numerous control techniques (algorithms) and control strategies (structures) have been suggested to regulate WWTP; however, it is difficult to make a discerning performance evaluation due to the nonuniformity of the simulated plants used. The main objective of this paper is to present a benchmark of an entire biological wastewater treatment plant in order to evaluate, through simulations, different control techniques. This benchmark plays the role of an activated sludge process used for removal of organic matter and nitrogen from domestic effluents. The development of this simulator is based on models widely accepted by the international community and is implemented in Matlab/Simulink (The MathWorks, Inc.) platform. The benchmark considers plant layout and the effects of influent characteristics. It also includes a test protocol for analyzing the open and closed-loop responses of the plant. Examples of control applications in the benchmark are implemented employing conventional PI controllers. The following common control strategies are tested: dissolved oxygen (DO) concentration-based control, respirometry-based control and nitrate concentration-based control.
  • The study of protozoa population in wastewater treatment plants by image analysis

    Motta, M.da; Pons, M.N.; Vivier, H.; Amaral, A.L.; Ferreira, E.C.; Roche, N.; Mota, M.

    Resumo em Inglês:

    Protozoa are important microorganisms for the ecosystem balance in wastewater treatment plants. A procedure for their semi-automated identification and counting based on image analysis is proposed. The main difficulty is segmentation of the protozoa as most of them are in contact with the sludge. The protozoa are characterized by the size of their silhouette (area and length) and three shape factors (elongation, circularity and eccentricity). They are identified after projecting the resulting 5D space into a 3D space of principal components. The rate of automated identification is actually higher than 50% for some of the species commonly found in activated sludge.
  • Adaptive control using a hybrid-neural model: application to a polymerisation reactor

    Cubillos, F.; Callejas, H.; Lima, E.L.; Vega, M.P.

    Resumo em Inglês:

    This work presents the use of a hybrid-neural model for predictive control of a plug flow polymerisation reactor. The hybrid-neural model (HNM) is based on fundamental conservation laws associated with a neural network (NN) used to model the uncertain parameters. By simulations, the performance of this approach was studied for a peroxide-initiated styrene tubular reactor. The HNM was synthesised for a CSTR reactor with a radial basis function neural net (RBFN) used to estimate the reaction rates recursively. The adaptive HNM was incorporated in two model predictive control strategies, a direct synthesis scheme and an optimum steady state scheme. Tests for servo and regulator control showed excellent behaviour following different setpoint variations, and rejecting perturbations. The good generalisation and training capacities of hybrid models, associated with the simplicity and robustness characteristics of the MPC formulations, make an attractive combination for the control of a polymerisation reactor.
  • Single - and multi-component liquid phase adsorption measurements by headspace chromatography Short Communication

    Torres, A.E.B.; Neves, S.B.; Abreu, J.C.N.; Cavalcante Jr., C.L.; Ruthven, D.M.

    Resumo em Inglês:

    This short communication presents a new technique for evaluation of adsorption equilibrium in the liquid phase using headspace chromatography. The technique may be used in two different modes: single-component equilibrium (the "finite bath" mode) and the multicomponent selectivity mode. Illustrative experimental results are presented for xylenes adsorption on Y zeolite pellets.
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