Why I selected the CSTR for the first reactor
The CSTR reactor accomplished a major fraction of the hydrogenation with a fairly inexpensive heat removal system and reactor. The other alternative would have been a tubular fixed bed system with external cooling. The reactor tubes containing catalyst would operate with a gas/liquid stream. Such systems are more difficult to scale than the CSTR. Catalyst loading and unloading are more difficult with the multiple tubes needed. The only negative aspect of the CSTR is the need for maintenance of the catalyst filter on the effluent stream. Proper design of the filter and the effluent location, along with attention to catalyst particle size can minimize the need for maintenance and operator attention.
The CSTR converted about 90% of the pentenes to isooctane. This is actually fairly high conversion for a single CSTR. At this point in the development, there is no point in studying the variables that effect the conversion because the conversion affects the rest of the process design and economics. Thus, I will continue to develop the process.
Options going forward
There are three options for the process at this point.
A qualitative comparison of the options
At some point in the process we have to separate the product and from the reactants and the solvent. The difficulty of this separation will affect the process capital and operating cost. Unreacted pentenes may be recycled with the solvent without separation.
With options 1 and 2, the distillation column will need to make a separation between the C8 reactants (TMP1 and TMP2) and the C8 product, isooctane. [I am assuming that option 1 still has a significant amount of unreacted pentenes, probably about 1% of the original feed.] I expect this will require a large number of trays and a high reflux ratio.
Option 3 offers the possibility of reacting essentially all of the pentenes. Thus, the distillation column would separate the C5 solvent from the C8 product. This is an easy separation so the distillation column capital and operating cost should be lower than for options 1 and 2.
My guess for probable choice
I don't think option 1 offers any advantage over option 2, so the choice is between 2 & 3. Unless the distillation cost comparison is very dramatic, option 2 would probably be chosen just to simplify the process. The fixed bed reactor in option 3 should be simple to operate, but it does require a different catalyst size and possibly a different catalyst support. It also requires an occasional shutdown to replace catalyst.
My choice at this point
Both options 2 & 3 need to be evaluated. I am going to model option 3 first. This will allow me to introduce the fixed bed reactor model.