Theoretical studies of cyclic operation of chemical reaction systems

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1972

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The application of cyclic operation to chemical reaction systems is studied. Four different chemical reaction systems are investigated to examine the effect of cyclic operation on the product distribution (i.e. selectivity) of the reactors. In this work, cyclic operation of the hydrogenation of acetylene in a continuous-stirred tank catalytic reactor is investigated theoretically. Simulation studies show that cyclic operation is superior to steady-state operation for this system. The improvement of reactor performance, i.e. the ethylene selectivity in this case, is found to be as much as 45% for certain operating conditions. Cyclic operation of the hydrogenation of acetylene in a catalyst pellet with only internal mass transfer resistance or with both interanl and external mass transfer resistance is also studied. Several lumping techniques are employed to approximate the performance of a catalyst. The numerical results show that cyclic operation is superior to steady-state operation for a catalyst. An analytical study of the effect of cyclic operation on the selectivities for a complex heterogeneously catalyzed reaction has been performed. Assumption of small reaction rate relative to mass transfer rate (i.e. small Thiele modulus) permits an analytical investigation through the use of a perturbation procedure for this kind of problem. Periodic boundary control is proved to improve the selectivity of a catalyst. Also in this work, a rather simple model for an imperfectly mixed CSTR is proposed. The effect of mixing on a steady-state or cyclic polymerization reactor is examined and demonstrated by employing a linear polycondensation reaction as an example. Periodic monomer inlet control is found to be advantageous in the sense that it can produce a narrower or wider MWD in polymers even when the reactor is imperfectly mixed. The possibility of extending this modeling technique to more complicated polymerization reactions, e.g. Ziegler-catalyzed polymerization of olefins, is also discussed.

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