Said, Beshir Elias George; (1991) Active transport catalytic reactor. Doctoral thesis (Ph.D.), University College London.

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Abstract

Heterogeneous catalytic reactors can be designed in a wide variety of configurations; usually the catalyst is in the form of pellets or particles to be placed in packed or fluidised beds. In all situations where intrinsic reaction kinetics are fast there is the possibility that actual reaction rates are mass transfer, or diffusion, limited. The objectives of this research are to present the catalyst in a highly accessible geometry and actively to transport the reactants to the catalyst surface; hence the name "Active Transport Catalytic Reactor". This can be accomplished by placing a novel type of static mixing element within a catalyst coated tube. The intention is that these elements will promote high rates of radial transport whilst simultaneously resulting in little axial mixing. This idea is general but is applied specifically to the catalytic treatment of synthetic car exhaust gases. The performance of our novel static mixer design (UCL) has been compared with the performance of those commercially available from Sulzer and Kenics. Initial experiments were conducted to determine the goodness of mixing and the pressure drop in the 3 types of static mixers. This was achieved by blending hot and cold water streams and measuring the point temperature at the mixer outlet. Not much information could be extracted from this type of experiment regarding the effectiveness of the mixers since at number of elements (n) > 2, an essentially homogeneous mixture was produced. However, the pressure drop across the UCL mixer was the highest. Mixing characteristics in the 3 mixers have also been expressed in terms of Residence Time Distribution (RTD) recovered from two-station tracer tests. The one parameter tanks-in-series model was used to characterize non-ideal flow within each of the 3 static mixer systems. The RTD experiments have shown the performance of the 3 types of mixers to be comparable at Re range (200-400), while at Re > 400 the Sulzer and Kenics mixers outperformed the UCL mixer. Chemical reaction within a tubular wall-coated reactor into which the static mixing devices were introduced was studied. The model reaction used was the oxidation of carbon monoxide, on a platinum/rhodium catalyst. Enhanced conversion with the static mixers in place relative to that from the empty tube was observed. Finally the FLUENT computational fluid dynamics package has been used to simulate flow, pressure drop, heat transfer, and by analogy mass transfer, in the novel tubular reactor. An attempt was made to optimise the geometry of the mixing elements, but further optimisation is necessary.

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