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Brazilian Journal of Chemical Engineering, Volume: 16, Número: 1, Publicado: 1999
  • PREPARATION OF TANTALUM CARBIDE FROM AN ORGANOMETALLIC PRECURSOR

    SOUZA, C. P.; FAVOTTO, C.; SATRE, P.; L' HONORÉ, A.; ROUBIN, M.

    Resumo em Inglês:

    In this work we have synthesized an organometallic oxalic precursor from tantalum oxide. This oxide was solubilized by heating with potassium hydrogen sulfate. In order to precipitate Ta2O5.nH2O, the fused mass obtained was dissolved in a sulfuric acid solution and neutralized with ammonia. The hydrated tantalum oxide precipitated was dissolved in an equimolar solution of oxalic acid/ammonium oxalate. The synthesis and the characterization of the tantalum oxalic precursor are described. Pyrolysis of the complex in a mixture of hydrogen and methane at atmospheric pressure was studied. The gas-solid reaction made it possible to obtain tantalum carbide, TaC, in the powder form at 1000oC. The natural sintering of TaC powder in an inert atmosphere at 1400°C during 10 hours, under inert atmosphere made it possible to densify the carbide to 96% of the theoretical value.
  • HIGH-PRESSURE VAPOR-LIQUID EQUILIBRIUM DATA FOR BINARY AND TERNARY SYSTEMS FORMED BY SUPERCRITICAL CO2, LIMONENE AND LINALOOL

    MELO, S. A. B. VIEIRA DE; PALLADO, P.; GUARISE, G. B.; BERTUCCO, A.

    Resumo em Inglês:

    The feasibility of deterpenating orange peel oil with supercritical CO2 depends on relevant vapor-liquid equilibrium data because the selectivity of this solvent for limonene and linalool (the two key components of the oil) is of crucial importance. The vapor-liquid equilibrium data of the CO2-limonene binary system was measured at 50, 60 and 70oC and pressures up to 10 MPa, and of the CO2-linalool binary system at 50oC and pressures up to 85 bar. These results were compared with published data when available in the literature. The unpublished ternary phase equilibrium of CO2-limonene-linalool was studied at 50oC and up to 9 MPa. Selectivities obtained using these ternary data were compared with those calculated using binary data and indicate that a selective separation of limonene and linalool can be achieved.
  • A PUBLISHED KINETIC MODEL EXPLAINS THE VARIATION IN NITROGEN CONTENT OF Pichia guilliermondii DURING ITS BATCH CULTIVATION ON DIESEL OIL

    BORZANI, W.

    Resumo em Inglês:

    Variation in nitrogen content of Pichia guilliermondii during its batch cultivation on media containing diesel oil as the main carbon source may be explained by means of a kinetic model proposed earlier to interpret the kinetics of nitrogen consumption during the process.
  • AUTOMATIC EVOLUTION OF HEAT EXCHANGER NETWORKS WITH SIMULTANEOUS HEAT EXCHANGER DESIGN

    LIPORACE, F.S.; PESSOA, F.L.P.; QUEIROZ, E.M.

    Resumo em Inglês:

    Recently, a new software (AtHENS) that automatically synthesizes a heat exchanger network with minima consumption of utilities was developed. This work deals with the next step, which represents the evolution of the initial network. Hence, new procedures to identify and break loops are incorporated, for which a new algorithm is proposed. Also, a heat exchanger design procedure which uses the available pressure drop to determine the film coefficient on the tube side and shell side is added, providing the utilization of more realistic heat exchangers in the network during its optimization. Results obtained from a case study point to the possibility of equipment design having a strong influence on the network synthesis.
  • STATE ESTIMATION AND PARAMETER IDENTIFICATION IN A FED-BATCH PENICILLIN PRODUCTION PROCESS

    RODRIGUES, J.A.D.; ZAIAT, M.; MACIEL FILHO, R.

    Resumo em Inglês:

    This work presents an application of a recursive estimator of states and parameters in a fed-batch penicillin production process based on the use of the extended Kalman filter. The estimated state variables were the cell, substrate, product and dissolved oxygen concentrations, the fermenter volume and the oxygen transfer coefficient. A simplified model of this process was used for the filter, and the actual values for product amount and concentration of dissolved oxygen with independent random Gaussian white noise were obtained using a deterministic and nonstructured mathematical model. The influence of the filter parameters, initial deviations and presence of noise on the observed variables was analyzed. In addition, estimator performance was verified when the parameters and the structure of the process model were changed. The extended Kalman filter implemented was found to be suitable to predict the states of the system and the model parameters. Therefore, it can be used for optimization and control purposes in a fermentative process which requires some state variables that are measured with a long delay time or unmeasured parameters.
  • A HYBRID NEURAL MODEL FOR THE OPTIMIZATION OF FED-BATCH FERMENTATIONS

    COSTA, A.C.; HENRIQUES, A.S.W.; ALVES, T.L.M.; MACIEL FILHO, R.; LIMA, E.L.

    Resumo em Inglês:

    In this work a hybrid neural modelling methodology, which combines mass balance equations with functional link networks (FLNs), used to represent kinetic rates, is developed for bioprocesses. The simple structure of the FLNs allows the easy and rapid estimation of network weights and, consequently, the use of the hybrid model in an adaptive form. As the proposed model is able to adjust to kinetic and environmental changes, it is suitable for use in the development of optimization strategies for fed-batch bioreactors. The proposed methodology is used to model the processes for penicillin and ethanol production, and the development of an adaptive optimal control scheme is discussed using ethanol fermentation as an example.
  • MODELLING AND PARAMETER ESTIMATION IN REACTIVE CONTINUOUS MIXTURES: THE CATALYTIC CRACKING OF ALKANES. PART I

    PEIXOTO, F. C.; MEDEIROS, J.L. de

    Resumo em Inglês:

    Fragmentation kinetics is employed to model a continuous reactive mixture. An explicit solution is found and experimental data on the catalytic cracking of a mixture of alkanes are used for deactivation and kinetic parameter estimation.
  • NONLINEAR MODEL PREDICTIVE CONTROL OF CHEMICAL PROCESSES

    SILVA, R. G.; KWONG, W. H.

    Resumo em Inglês:

    A new algorithm for model predictive control is presented. The algorithm utilizes a simultaneous solution and optimization strategy to solve the model's differential equations. The equations are discretized by equidistant collocation, and along with the algebraic model equations are included as constraints in a nonlinear programming (NLP) problem. This algorithm is compared with the algorithm that uses orthogonal collocation on finite elements. The equidistant collocation algorithm results in simpler equations, providing a decrease in computation time for the control moves. Simulation results are presented and show a satisfactory performance of this algorithm.
  • A SIMPLE METHOD TO CONTROL THE MOISTURE CONTENT OF THE FERMENTING MEDIUM DURING LABORATORY-SCALE SOLID-STATE FERMENTATION EXPERIMENTS

    BORZANI, W.; SALOMÃO, G. L.; MARTINS, J. C.; ALONSO, V.

    Resumo em Inglês:

    When the moisture content of the fermenting medium significantly decreases during laboratory-scale solid-state fermentation tests, the quantity of water to be periodically added to the medium in order to control its moisture content may be evaluated from the water evaporation rate of the non-inoculated medium.
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