I should point out that the kinetic parameters that I am using in this process simulation example are based on the work by Lylykangas (2004), but the catalyst activity and other parameters for the CSTR and fixed bed reactor were selected by me. Thus, the process being simulated might not be feasible if the catalysts can not be made accordingly. This series of blog posts is purely an example of process development and simulation.
Completion of reaction
The figure below shows that the conditions assumed resulted in nearly complete reaction of the pentenes. As you may recall, that was the goal for this fixed bed reactor.
The plot below shows the minor temperature rise through the bed. The particle temperatures are only slightly higher than the fluid temperatures near the inlet.
Concentration difference across film
The plot below shows the concentration difference as a percent of the local concentration at the particle. In other words, it shows the percent error in reactant (TMP1) concentration that would occur if the model had not included a particle mass balance and intraphase mass transfer.
Pressure drop check
Using the assumed reactor size and flow rate (see post 11/11/2014), the pressure drop was minor (< 1 psi). The main criterion for pressure drop is the crush strength of the catalyst. Other considerations might involve downstream process requirements.
The fixed bed model assumed that the fluid remained as a liquid throughout the reactor. The Prode Properties Program confirmed that assumption for the inlet and outlet streams. The reduction in hydrogen was sufficient to counteract the increase in temperature.
What is meant by "complete reaction"?
For a reaction with a positive reaction order for the limiting reactant, there will always be some of that reactant left in the product. The effluent stream from the fixed bed reactor, as simulated, contains about 0.0001 mole fraction of TMP1 and of TMP2. These reactants will end up with the isooctane product. Thus, the specification for isooctane quality will be the constraint that determines the meaning of complete reaction. Since the isooctane product is likely to be included in the gasoline pool, it's quality will likely depend upon the allowance for olefins in gasoline and the composition of the rest of the gasoline pool at a particular refinery.
The use of theoretical catalyst activity is not just a convenience for demonstration and education. A conceptual design using theoretical parameters can be useful in setting a commercially feasible target for the catalyst and process development team. Setting such a goal while still in the bench scale phase can avoid the cost of building a pilot plant until the process has a chance of commercial success. The goal might also work the other way: it might avoid unneeded catalyst development aimed at making a more active catalyst. In addition to preventing unnecessary catalyst work, the resulting catalyst might make less byproduct and last longer than a more active catalyst.
Lylykangas (2004) ISBN 951-22-6912-0 (print), 951-22-6913-9 (pdf, available at http://lib.hut.fi/Diss/)