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Publication Type: search.filters.UBSTyp.ZeitschriftenartikelAuthor: search.filters.author.Eigenberger, Gerhart

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Now showing 1 - 10 of 28
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    Dynamic modelling of multitubular catalytic reactors
    (1991) Stankiewicz, Andrzej; Eigenberger, Gerhart
    This paper presents a study on modelling and simulation of transient operational characteristics in multitubular fixed-bed reactors. The dynamic model of the reactor is based on a porous body approach which regards the intertubular space as a pseudo-homogeneous environment. Such an approach permits to take into account most factors in the geometrical design of the unit and thus to study the influence of various shell-side geometrical and operational parameters on the reactor behaviour. Based on the model, the dynamic responses of the two most common industrial reactor designs, i.e. the parallel flow unit with distributing plates and the crossflow reactor with disk-and-doughnut baffles have been investigated and compared. In addition, some problems of correct space discretization and use of time-dependent regridding procedures, are discussed.
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    Catalyst poisoning and fixed bed reactor dynamics
    (1975) Weng, Hung Shan; Eigenberger, Gerhart; Butt, John B.
    The poisoning kinetics of thiophene on Ni-kieselguhr catalysts and the deactivation behavior of nonisothermal fixed bed reactors have been studied experimentally using benzene hydrogenation as a model exothermic reaction. The time dependent axial temperature profiles in the reactors were measured and compared with values evaluated from a dispersion model, the parameters of which have been determined in separate experimentation. Poisoning kinetics were measured in a series of differential reactor experiments at atmospheric total pressure, thiophene partial pressures of 0·037-0·19 torr, hydrogen to benzene molar ratios >8/1 and temperatures from 60-180°C. Excellent agreement was found with a power law equation for the rate of change of activity with time, first order in catalyst activity and in thiophene concentration, with an experimental activation energy of 1080 kcal/kmole. This correlation of poisoning kinetics, however, was not able to predict the propagation of the zone of activity (hot-spot) on poisoning of an integral fixed bed reactor. Initial (steady state) temperature profiles were modeled satisfactorally, but the rate of migration of the hot spot was found experimentally to be more rapid than that predicted from the correlation of poisoning kinetics. A semi-empirical two site deactivation model is shown to resolve the discrepancy.
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    Acid-base flow battery, based on reverse electrodialysis with bi-polar membranes : stack experiments
    (2020) Xia, Jiabing; Eigenberger, Gerhart; Strathmann, Heinrich; Nieken, Ulrich
    Neutralization of acid and base to produce electricity in the process of reverse electrodialysis with bipolar membranes (REDBP) presents an interesting but until now fairly overlooked flow battery concept. Previously, we presented single-cell experiments, which explain the principle and discuss the potential of this process. In this contribution, we discuss experiments with REDBP stacks at lab scale, consisting of 5 to 20 repeating cell units. They demonstrate that the single-cell results can be extrapolated to respective stacks, although additional losses have to be considered. As in other flow battery stacks, losses by shunt currents through the parallel electrolyte feed/exit lines increases with the number of connected cell units, whereas the relative importance of electrode losses decreases with increasing cell number. Experimental results are presented with 1 mole L^-1 acid (HCl) and base (NaOH) for open circuit as well as for charge and discharge with up to 18 mA/cm2 current density. Measures to further increase the effciency of this novel flow battery concept are discussed.
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    Numerical methods for the simulation of chemical engineering processes
    (1994) Dieterich, Erwin; Sorescu, Gheorge; Eigenberger, Gerhart
    Fundamental aspects and the current state of the art in simulating the dynamic and steady-state behavior of chemical engineering processes are discussed. The discretization of the spatial derivatives in the equations of change leads to a system of differential algebraic equations (DAE), consisting of ordinary differential equations in the time domain, and algebraic equations. The present paper discusses the necessary steps to solve the DAE, and mentions proven standard software for these steps as well as for the solution of the differential algebraic equations as a whole.
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    Problems of mathematical modelling of industrial fixed-bed reactors
    (1986) Eigenberger, Gerhart; Ruppel, Wilhelm
    Modelling and computer simulation for the purpose of design and operation of industrial fixed-bed reactors are discussed with the aid of examples. Emphasis is laid upon difficulties and problems arising from aiming at an adequate model formulation. The following aspects are discussed in some detail: 1) The influence of heat and mass transport in the catalyst pellet, especially with complex reactions. 2) Relationships between radial heat transfer and radial flow profile and its influence upon the temperature profile in packed tubes with or without heat generation by reaction. 3) Problems of adequate modelling of catalyst activity changes during the course of operation. 4) Scale-up problem of multitubular fixed-bed reactors, i.e. the problem of achieving and maintaining the same operating conditions in and around all the tubes of the bundle.
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    Analyse von Stoffwechselprozessen mit der Fermentationskalorimetrie
    (1993) Meier-Schneiders, Martin; Grosshans, Ulrich; Busch, Claudia; Eigenberger, Gerhart
    Biologische Aktivität ist mit der Freisetzung von Wärmeenergie verbunden. Die Wärmeproduktion ist dabei proportional zur gesamten Stoffwechselaktivität. Da Wärme kontinuierlich entsteht, eignet sie sich zur Nutzung als On-Iine-Signal. Kalorimetrische Methoden werden in den Biowissenschaften bereits seit Jahrzehnten verwendet. Fermentationskalorimetrie ist eine neu entwickelte Meßtechnik, die insbesondere für die kalorimetrische Vermessung biotechnisch relevanter Fermentationen im Labormaßstab gedacht ist.
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    Kinetic instabilities in heterogeneously catalyzed reactions. Pt. 1, Rate multiplicity with Langmuir-type kinetics
    (1978) Eigenberger, Gerhart
    This paper is concerned with the occurrence of rate multiplicities (ignition-extinction phenomena). It is shown that rate multiplicity can be caused by the competing chemisorption of A and B upon the same active sites of the catalyst. Rate multiplicity can occur if at least one of the chemisorption or reaction steps is of second order. No rate multiplicity can be expected, if either A or B reacts via an Eley-Rideal type mechanism.
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    Modellierung und numerische Simulation von G/L-Blasen-Strömungen
    (1994) Sokolichin, Alexander; Becker, Stefan; Eigenberger, Gerhart
    In den letzten Jahren zeigt sich ein Trend zu einer detaillierteren modellmäßigen Beschreibung der Hydrodynamik von Gas(G)/Liquid(L)-Reaktoren, wie z. B. Blasensäulen. Die genauere Erfassung der Hydrodynamik wird dabei als Voraussetzung für eine bessere Reaktorauslegung betrachtet. Wegen der Komplexität der Vorgänge scheint eine enge Kopplung von Experiment und Simulation erforderlich. Über erste Ergebnisse aus einem entsprechenden Forschungsprojekt wird nachstehend berichtet.
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    Elektrodialytische Regenerierung von Ionenaustauscher-Harzen
    (1993) Johann, Jürgen; Eigenberger, Gerhart
    Ionenaustauscher-Harze werden überwiegend zur Abtrennung unenwünschter Ionen aus wäßrigen Lösungen eingesetzt. Die Arbeitskapazität der Harze ist jedoch beschränkt. Deswegen müssen die Harze von Zeit zu Zeit regeneriert werden. Die Regenerierung wird meist im Gegenstrom, bei der Wasservollentsalzung mit Säure und Lauge, bei der Enthärtung mit einer NaCl-Lösung, durchgeführt. Nachteilig ist dabei vor allem der überstochiometrische Bedarf an Regenerierchemikalien, insbesondere bei stark sauren Kationenaustauscher-Harzen. Des weiteren ist im Falle schwermetallionenhaltiger Regenerate eine zusäzliche Aufbereitung derselben z. B. durch Fällung notwendig. Ein neueres Verfahren ist die elektrodialytische Regenerierung der Harze.Die nachstehend beschriebenen experimentellen Ergebnisse am Beispiel der Cu-Ionenabtrennung zeigen die Vorteile im Vergleich zu den herkömmlichen Regenerierverfahren.
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    On the dynamic behavior of the catalytic fixed-bed reactor in the region of multiple steady states. Pt. 1, The influence of heat conduction in two phase models
    (1972) Eigenberger, Gerhart
    Die Benutzung des Zweiphasenmodells für den katalytischen Festbettreaktor führte im Bereich mehrfacher stationärer Zustände bisher stets zu Schwierigkeiten, da sich ein Kontinuum von mehrfachen stationären Lösungen ergab. Dabei war es gleichgültig, ob die von Liu und Amundson aufgestellten kontinuierlichen Zweiphasenmodelle oder die von Amundson und Mitarbeitern entwickelten Zellenmodelle zugrunde gelegt wurden. In der vorliegenden Arbeit wird gezeigt, daß sich die unendliche Mannigfaltigkeit stationärer Lösungen auf wenige Lösungen reduziert, wenn man annimmt, daß Wärmeleitung in der Katalysatorphase stattfindet. Unterschiede zwischen den bisher benutzten Modellen und dem vorgeschlagenen Modell werden am Beispiel der Zündung und des Verlöschens der Reaktion dargelegt.