This problem was taken from a Professional Engineer's Exam.

1. Problem Statement: A homogeneous liquid phase second-order irreversible reaction

is to be carried out in a tubular (plug-flow) reactor. The PFR has a volume of 5.33 ft³. It is proposed that to increase conversion, a stirred reactor (CSTR) of 100-gal capacity be installed in series with, and immediately upstream of, the PFR. Calculate the new conversion.

2. Real Problem:

Will a CSTR upstream of a PFR improve conversion?

Which variables have the same values for both of the systems?

Which variables need to be found in the PFR system in order to have enough data to work on the CSTR & PFR system? 

3. Sketch:

Figure 1. Schematic of the original design with PFR.

Figure 2. Schematic of the CSTR and PFR system

It is necessary to break the problem into 2 parts:

1. Original design with PFR-determine the problem parameters (e.g. k) from the  data given

2. New design with CSTR upstream of PFR - use the parameters for the new design

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