Rectifying and Stripping Profiles for the Reactive Cascade
Stripping and rectifying profiles for the reactive cascade are similar to stripping and rectifying sections of a continuous reactive distillation column, but without vapor or liquid recycles, respectively. This Demonstration computes the stripping and rectifying profiles for the reactive cascade for various values of the Damköhler number . The stripping profile is represented by the orange dots while the rectifying profile is given by the blue dots. The reaction equilibrium curve is cyan. At large Damköhler numbers (), the stripping profile (the orange dots) merges with the reaction equilibrium curve, indicating that the system has reached chemical equilibrium. The fixed point (the point to which the blue dots converge) for the rectifying cascade is pure . At =0 (no reaction is occurring) the fixed point (the point to which the orange dots converge) for the stripping profile is pure .
The generalized cascade model must be used in order to compute stripping and rectifying profiles for the reactive cascade in the case of the following nonequimolar equilibrium-limited chemical reaction: .
For the stripping cascade:
For the rectifying cascade, one has to use:
where is the average molecular weight, the mass fraction of the feed that is vaporized is and is the Damköhler number, which is the ratio of the residence time relative to the reaction time. Short reaction times and long residence times result in large Damköhler numbers; indicates that no reaction is occurring and means that the reaction rate is fast and that the system will rapidly approach chemical equilibrium.
The molecular weights of species , , and for this hypothetical ternary chemical system are 86.18, 100.21 and 186.39 g/mol, respectively.
The relative volatilities have the values: , , and .
The vapor mole fractions are determined by , where is the volatility of species .
The equilibrium-limited chemical reaction taking place between species , , and is with equilibrium constant
A feed with the following composition is assumed: 40% , 40% , and 20% .
Reference: M. F. Doherty and M. F. Malone, Conceptual Design of Distillation Systems, New York: McGraw-Hill, 2001.