Browsing by Author "Butt, John B."

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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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    A modified Crank-Nicolson technique with non-equidistant space steps
    (1976) Eigenberger, Gerhart; Butt, John B.
    A finite difference method with non-equidistant space steps, based upon the Crank-Nicolson technique is presented. Its prime feature is the automatic positioning of axial grid points at required positions. Thus reducing considerably the total number of grid points and hence the amount of computer time. The method is demonstrated for a number of examples of tubular reactor calculations. It proves to be well suited for the solution of all kinds of diffusion type models, especially if steep gradients or moving profiles occur, and can be used even on moderate size process computers.