Nonideal Flow Behavior in Catalytic Column Internals

3 Nonideal Flow Behavior in Catalytic Column Internals 

The mass balances (Eqs. (10.3) and (10.4)) assume plug-flow behavior for both the vapor and the liquid phase. However, real flow behavior is much more complex and constitutes a fundamental issue in multiphase reactor design. It has a strong influence on the column performance, for example via backmixing of both phases, which is responsible for significant effects on the reaction rates and product selectivity. Possible development of stagnant zones results in secondary undesired reactions. To ensure an optimum model development for catalytic distillation processes, we performed experimental studies on the nonideal flow behavior in the catalytic packing MULTIPAK [77]. 

Regarding the reactive tray hydrodynamics, the concentration distribution on a crossflow tray is also not even. The vapor concentration changes gradually when it rises through the liquid on the tray. The liquid concentration also changes 

The situation becomes even more complicated if a reaction takes place on the plates, and there have been only very few attempts to tackle this issue. Among those, Alejski [78] presented a mixed pool model for RD. However, in his model, the mass-transfer modeling applied to the individual pools was based on the traditional equilibrium-stage model and efficiency concept. 

Recently, Higler et al. [79] suggested a nonequilibrium cell model for RD tray columns. In this work, a single distillation tray is represented by a series of cells along the vapor and liquid fiow paths, whereas each cell is described by the film model. Using different number of cells in both flow paths allows various fiow patterns to be described. However, a consistent experimental determination of necessary model parameters (e.g. cell film thickness) appears difficult, whereas the complex iterative character of the calculation procedure in the dynamic case limits the applicability of the nonequilibrium cell model. 

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A.3. Nonideal Flow Behavior in Catalytic Column Internals... 

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